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Production of Puree & Potato Product
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PRODUCTION OF POTATO PUREE, CHIPS AND EXTRACTION OF
POTATO STARCH
A Design Project Presented to the
DEPARTMENT OF CHEMICAL AND PROCESS ENGINEERING
SCHOOL OF ENGINEERING
MOI UNIVERSITY
Presented in Partial Fulfillment of the Requirements for the Award of a Bachelor
of Engineering Degree in Chemical and Process Engineering
PRESENTED BY:
LIMO K. RICHARD CPE/12/08 .................................................
EDWIN MUTUA CPE/17/08 .................................................
EVANS M. AKAKA CPE/1005/08 .................................................
SUPERVISOR:
DR. S. NAMANGO ………………………………
21st May, 2013
ii
ABSTRACT
Potatoes (Solanum tuberosum) are second in importance after maize in Kenya as food crop. It is grown
mainly by small scale farmers in more than 100,000 ha country wide producing more than 1 million
tonnes annually. The marketing value chain has been described as ineffective, with farmers getting far
much lesser compared with other players e.g. maize, wheat farmers. The major reasons for this, is the
presence of cartels, lack of storage facilities and information about the potato production costs and
prevailing market prices at any given time. The design project for the processing potato purees, potato
chips and extraction of potato starch has been formulated and the task was to carry out mass and
enthalpy balances for the entire process.
iii
DECLARATION
We, the following fifth year students of the academic year 2012/2013 do declare that this report is an
original work and to the best of our knowledge, it has not been submitted for any degree award in any
University or Institution.
LIMO K. RICHARD,
CPE/12/08
Signed______________________________________________ Date ____________
EDWIN J. MUTUA,
CPE/17/08
Signed______________________________________________ Date ____________
EVANS M. AKAKA,
CPE/1005/08
Signed______________________________________________ Date ____________
iv
TABLE OF CONTENTS
ABSTRACT ......................................................................................................... ii
DECLARATION ................................................................................................ iii
TABLE OF CONTENTS ................................................................................... iv
LIST OF TABLES ........................................................................................... viii
LIST OF FIGURES ........................................................................................... ix
Chapter 1: INTRODUCTION ........................................................................... 1
1.1:STATEMENT OF THE PROBLEM ------------------------------------------------------------------------------------ 1
1.2:OBJECTIVES ------------------------------------------------------------------------------------------------------------- 1
1.3: LITERATURE REVIEW ------------------------------------------------------------------------------------------------- 1
1.3.1: POTATO -------------------------------------------------------------------------------------------------------------- 1
1.3.2: INTERESTED POTATO PRODUCTS ------------------------------------------------------------------------------ 4
1.4: JUSTIFICATION -------------------------------------------------------------------------------------------------------- 7
Chapter 2: PROCESS DESCRIPTION .......................................................... 10
2.1 PROCESS FLOW CHART OF POTATO STARCH, POTATO CHIPS AND POTATO PUREE2.2 POTATO
STARCH EXTRACTION ---------------------------------------------------------------------------------------------------- 10
2.2 POTATO STARCH EXTRACTION ------------------------------------------------------------------------------------ 11
2.3 POTATO CHIPS -------------------------------------------------------------------------------------------------------- 12
2.4 POTATO PUREE ------------------------------------------------------------------------------------------------------- 14
Chapter 3: MASS AND ENERGY BALANCE .............................................. 18
3.1 MASS BALANCE ------------------------------------------------------------------------------------------------------- 18
3.2 ENERGY BALANCE ---------------------------------------------------------------------------------------------------- 27
Chapter 4: EQUIPMENT SIZING AND SPECIFICATION ....................... 31
4.1 EQUIPMENT SPECIFICATION: STARCH PLANT. ---------------------------------------------------------------- 31
4.2 EQUIPMENT SPECIFICATION: CHIPS PLANT. ------------------------------------------------------------------- 33
4.3 EQUIPMENT SPECIFICATION: PUREE PLANT. ------------------------------------------------------------------ 35
Chapter 5: EQUIPMENT DESIGN ................................................................ 36
5.0 ROTARY DRUM VACUUM FILTER BY: LIMO KIPTALAM R. (CPE /12/08)
............................................................................................................................. 36
5.0.1 INTRODUCTION ---------------------------------------------------------------------------------------------------- 36
5.0.2 FILTER SELECTION ------------------------------------------------------------------------------------------------- 39
5.0.3 ROTARY DRUM FILTER -------------------------------------------------------------------------------------------- 39
v
5.0.4 DESIGN EQUATIONS----------------------------------------------------------------------------------------------- 40
5.0.5 CHEMICAL DESIGN OF THE ROTARY DRUM FILTER -------------------------------------------------------- 43
5.0.6 MECHANICAL DESIGN--------------------------------------------------------------------------------------------- 49
5.0.7 SUMMARY OF ROTARY DRUM FILTER DESIGN ------------------------------------------------------------- 52
5.1 DESIGN OF A PNEUMATIC DRYER/FLASH DRYER BY EVANS AKAKA -
CPE/1005/08 ...................................................................................................... 54
5.1.1 INTRODUCTION ---------------------------------------------------------------------------------------------------- 54
5.1.2 PNEUMATIC / FLASH DRYING ----------------------------------------------------------------------------------- 54
5.1.3 DESIGN PROCEDURE ---------------------------------------------------------------------------------------------- 55
5.1.4 DESIGN METHODS ------------------------------------------------------------------------------------------------- 56
5.1.5 DESIGN EQUATIONS USED. -------------------------------------------------------------------------------------- 56
5.5.1.1. DRYING UNIT ---------------------------------------------------------------------------------------------------- 56
5.5.1.2 SIZING DRYING-GAS PREPARATION UNIT ----------------------------------------------------------------- 63
5.5.1.3 DRYER SIZING ----------------------------------------------------------------------------------------------------- 63
5.5.1.4 SIZING EXHAUST GAS UNIT. ---------------------------------------------------------------------------------- 64
5.5.1.5 CYCLONE ----------------------------------------------------------------------------------------------------------- 64
5.1.5 MECHANICAL DESIGN--------------------------------------------------------------------------------------------- 65
5.1.6 SUMMARY OF THE VARIOUS PARAMETERS CAN BE WRITTEN AS BELOW: ------------------------- 67
5.2 DESIGN OF SPRAY DRYER BY EDWIN MUTUA - CPE/17/08 . ...... 68
5.2.1 INTRODUCTION ---------------------------------------------------------------------------------------------------- 68
5.2.2 GENERAL DESCRIPTION ------------------------------------------------------------------------------------------ 68
5.2.3 DESIGN PROCEDURES. -------------------------------------------------------------------------------------------- 69
5.2.4 ATOMIZER SELECTION AND DESIGN -------------------------------------------------------------------------- 69
5.2.5 CHEMICAL DESIGN------------------------------------------------------------------------------------------------- 71
5.2.6 MECHANICAL DESIGN--------------------------------------------------------------------------------------------- 73
5.2.7 SUMMARY OF DESIGN DATA------------------------------------------------------------------------------------ 76
Chapter 6: PROCESS CONTROL AND INSTRUMENTATION ............... 77
6.0 INTRODUCTION ------------------------------------------------------------------------------------------------------- 77
6.1 OBJECTIVES OF PROCESS CONTROL ----------------------------------------------------------------------------- 77
6.2 PROCESS CONTROLS ------------------------------------------------------------------------------------------------- 78
Figure 1: Flow Control from the blancher to the holding tank ------------------------------------------------- 78
Figure 2: temperature control used to control the temperature of the fryer ------------------------------ 79
Figure 3: Level controller used to control the level of mashed potato -------------------------------------- 79
CHAPTER 7: ECONOMIC AND PROFITABILITY ANALYSIS ............. 80
vi
7.0 INTRODUCTION ------------------------------------------------------------------------------------------------------- 80
Table 28: Production rate of the plant ------------------------------------------------------------------------------- 80
7.1 ESTIMATION OF CAPITAL COSTS---------------------------------------------------------------------------------- 81
Table 30: Fixed capital cost estimates ------------------------------------------------------------------------------- 87
Table 30: Total capital cost estimates -------------------------------------------------------------------------------- 88
Table 31: Annual raw materials cost estimates -------------------------------------------------------------------- 89
Table 32: Utilities cost estimates (annual) -------------------------------------------------------------------------- 89
Table 34: Annual Operating labour cost estimates --------------------------------------------------------------- 91
Table 9.9: Total product cost estimates ----------------------------------------------------------------------------- 92
7.3 ANNUAL CASH FLOW ANALYSIS ---------------------------------------------------------------------------------- 94
Table 35: Annual sales from products ------------------------------------------------------------------------------- 94
7.4 CUMULATIVE CASH FLOW ANALYSIS ---------------------------------------------------------------------------- 96
7.5 PROFITABILITY ANALYSIS ------------------------------------------------------------------------------------------- 97
7.6 BREAK-EVEN POINT (BEP) ANALYSIS --------------------------------------------------------------------------- 100
Figure 9.2: Break-even point analysis chart ---------------------------------------------------------------------- 100
Chapter 8: SAFETY, HEALTH AND ENVIRONMENTAL IMPACT ASSESSMENT
........................................................................................................................... 101
8.0 INTRODUCTION ----------------------------------------------------------------------------------------------------- 101
8.1 SAFETY ---------------------------------------------------------------------------------------------------------------- 101
8.2 ENVIRONMENTAL IMPACT ASSESSMENT -------------------------------------------------------------------- 105
Chapter 9: HAZARD AND OPERABILITY ANALYSIS (HAZOP) ........ 108
9.0 INTRODUCTION ----------------------------------------------------------------------------------------------------- 108
9.1 PURPOSE OF HAZOP ----------------------------------------------------------------------------------------------- 108
9.2 HAZOP PROCESS ---------------------------------------------------------------------------------------------------- 109
9.3 HAZOP CONCEPTS -------------------------------------------------------------------------------------------------- 109
Chapter 10: PLANT LOCATION AND LAYOUT ..................................... 112
10.1 PLANT LOCATION ------------------------------------------------------------------------------------------------- 112
10.2 PLANT LAYOUT ---------------------------------------------------------------------------------------------------- 114
Chapter 11: REFERENCES .......................................................................... 118
APPENDICES ................................................................................................. 119
APPENDIX A: DATA ------------------------------------------------------------------------------------------------------ 119
TABLE A-1: SPECIFIC HEAT CAPACITIES OF VARIOUS COMPOUNDS AND ELEMENTS ------------------ 119
TABLE A-2: DENSITIES OF VARIOUS COMPOUNDS AND ELEMENTS ---------------------------------------- 119
TABLE A-3: NATURAL GAS DATA------------------------------------------------------------------------------------- 119
vii
APPENDIX B: DETAILED SAMPLE MASS BALANCE CALCULATIONS 120
i.Extractor ----------------------------------------------------------------------------------------------------------------- 120
ii. Hydro cyclone --------------------------------------------------------------------------------------------------------- 122
APPENDIX C: DETAILED SAMPLE ENERGY BALANCE CALCULATIONS 123
i. Flash drier--------------------------------------------------------------------------------------------------------------- 123
APPENDIX D: EQUIPMENT SIZING CALCULATIONS ....................... 125
1. ROTARY WASHER ---------------------------------------------------------------------------------------------------- 125
2. VIBRATORY MESH ---------------------------------------------------------------------------------------------------- 126
APPENDIX E: FIGURES .............................................................................. 127
Figure 4: Structure of cellulose (www.wikipedia.com) -------------------------------------------------------- 127
Figure 5: structure of starch (www.wikipedia.com) ------------------------------------------------------------ 127
Figure 6: Flash drying system (Perry's handbook) -------------------------------------------------------------- 127
Figure 7: Rotary vacuum filter (www.wikipedia.com) --------------------------------------------------------- 128
viii
LIST OF TABLES
Table 1: Typical chemical composition of potato tuber (http://en.www.wikipedia.org/wiki/ potato tuber) ---- 3
Table 2: : Potato wholesale market price information in Kenya(http://en.www.wikipedia.org/wiki/ potato
production in Kenya) ------------------------------------------------------------------------------------------------------------------- 8
Table 3: mass balance around the 1st washer ---------------------------------------------------------------------------------- 19
Table 4: mass balance around the separator ------------------------------------------------------------------------------------ 20
Table 5: mass balance around the Rasper ---------------------------------------------------------------------------------------- 20
Table 6: mass balance around the extractor ------------------------------------------------------------------------------------ 21
Table 7: mass balance around the hydro cyclone ------------------------------------------------------------------------------ 21
Table 8: mass balance around the rotary vacuum filter ---------------------------------------------------------------------- 22
Table 9: mass balance around the flash dryer ---------------------------------------------------------------------------------- 22
Table 10: mass balance around the steam peeler ------------------------------------------------------------------------------- 23
Table 11: mass balance around the chipper ------------------------------------------------------------------------------------ 23
Table 12 mass balance around the blancher ------------------------------------------------------------------------------------- 26
Table 13: energy balance around the flash dryer ------------------------------------------------------------------------------- 27
Table 14: energy balance around the steam peeler ---------------------------------------------------------------------------- 28
Table 15: energy balance around the dryer -------------------------------------------------------------------------------------- 28
Table 16: energy balance around the fryer --------------------------------------------------------------------------------------- 30
ix
LIST OF FIGURES
Figure 1: Flow Control from the blancher to the holding tank --------------------------------------------------------------- 78
Figure 2: temperature control used to control the temperature of the fryer -------------------------------------------- 79
Figure 3: Level controller used to control the level of mashed potato ----------------------------------------------------- 79
Figure 4: Structure of cellulose (www.wikipedia.com) ----------------------------------------------------------------------- 127
Figure 5: structure of starch (www.wikipedia.com) --------------------------------------------------------------------------- 127
Figure 6: Flash drying system (Perry's handbook) ----------------------------------------------------------------------------- 127
Figure 7: Rotary vacuum filter (www.wikipedia.com) ------------------------------------------------------------------------ 128
1
Chapter 1: INTRODUCTION
Potato (Solanum tuberosum) is the second most important food crop in Kenya after maize both in
production and consumption. The crop is grown under rain-fed conditions in two main seasons,
April-June and October-December by small-holder farmers for home consumption as well as a source
of family income. While the Kenyan population has been increasing, the potato production per
person in Kenya has been declining (FAOSTAT, 2008), which is in contrast to the increasing demand
of the commodity. Most often at harvesting, there is glut of supply and farmer’s income is reduced
ostensibly due to low prices offered in the market. The lack of storage facilities reduces the ability of
farmers to negotiate prices as potatoes are perishable and farmers will dispose them off sooner before
they deteriorate. Another contribution to low income gained by farmers is the role of the market
cartels which dictates commodity prices; Poor road infrastructure is known to increase the
transportation expenses while lack of market intelligence information at farmer level contributes to
exploitation of farmers by traders.
1.1:STATEMENT OF THE PROBLEM
During different harvesting season which occurs at different times of the year across the country e.g.
Burnt forest-August, Kinangop-July, Nakuru-July e.t.c there is a lot of potato wastage due to lack of
proper storage facilities and their perishability, therefore there is need to produce potato products
which have longer shelf life, hence creating market for wasted potatoes. This includes frozen puree,
chips and potato starch.
1.2:OBJECTIVES
To produce potato starch.
To produce potato puree.
To produce potato chips.
1.3: LITERATURE REVIEW
1.3.1: POTATO
Potato is an edible starchy tuber. It is produced by certain plants of a genus of the nightshade family,
especially the common white potato. The name is also applied to the plants themselves. The tuber of
the white potato is a staple food in most countries of the temperate regions of the world. The plant is
2
grown as an annual herb. The stem attains a length up to almost 1 m (3 ft), erect or prostrate, with
pointed leaves and white to purple flowers. The fruit is a many-seeded berry about the size of a
cherry. Like the stems and the foliage, the fruit contains significant amounts of solanin, a poisonous
alkaloid characteristic of the genus. Three to six tubers form on the underground stem, although in
some varieties there may be as many as 10 to 20. The tuber skin varies from brownish-white to
purple.
The plant, native to the Peruvian Andes, was probably first taken to Europe in the mid-16th century
by Spanish explorers and was probably introduced to Britain by English explorers sailing from the
New World only a few years later. The cultivation of the potato spread rapidly, especially in the
temperate regions, and early in the 18th century the plant was introduced into North America.
In ordinary cultivation, propagation is accomplished by planting the tuber or a section of the tuber
containing an eye, which is an undeveloped bud. New varieties are developed from seed produced
after controlled pollination. Improved varieties may be propagated rapidly by using cuttings from the
sprouts.
There are hundreds of varieties of potatoes. Rich, sandy loams are most suitable for producing the
light, mealy types favored by British and American tastes; heavy, moist soils produce the firm type
preferred by other Europeans. Scientific classification: Potatoes are produced by plants of the genus
Solanum, of the family Solanaceae. The common white potato is classified as Solanum tuberosum.
Potatoes require cold storage. 3-4 oC is the optimum storage temperature for seed potatoes. The low
temperature prevents sprouting. After harvesting the potatoes is kept for two to three weeks at 15 oC
(a wound healing period) and first then, they are over a one month period gradually cooled down to
their storage temperature and they will keep well for a year or so. In spring the seed potatoes are
during minimum a fortnight gradually heated to 10 to 15 oC before planting. It may be done by
shutting of the cooling system mid March and starting air heating early April for the potatoes to be
ready for planting end of April.
Potatoes for chips and other food products have to be stored at a higher temperature not below 6-7
oC. That temperature is to prevent sprouting and sprout depressing gas has to be used. At 8
oC and
below sugars are formed - the colder the more - and the sugar forms a brown color by a Maillard
reaction not acceptable in food products. The sugar formation is however not a quantity problem and
does not affect starch yield from potatoes used for starch manufacturing and the Maillard reaction is
easy to control during starch extraction and refining.
3
Potatoes are sensible to dehydration during storage. They need a near 100% relative humidity or they
will dehydrate and shrink. Prolonged storage may take place in layers up to four meters with humid
temperate air circulating through the bed. The optimum storage temperatures may depend on variety
this bringing a difficulty to many farmers around the world.
Freshly dug potatoes contain 75 per cent water, 18 per cent starch, 1 per cent fiber, 2.2 per cent
protein, 1 per cent ash (inorganic constituents), and 0.1 per cent fat and a little sugar. Potatoes grown
for starch manufacture may contain as much as 22% starch dry matter. About 75 per cent of the dry
weight is carbohydrate. The potato is an important source of starch for the manufacture of adhesives
and alcohol. Potatoes also contain many vitamins, including riboflavin, niacin, and vitamin C, and a
number of minerals and also proteins.
substance Content (%)
range Mean
dry matter 13.1-36.8 23.7
Starch 8.0-29.4 17.5
reducing sugar 0.0-5.0 0.3
total sugar 0.05-8.0 0.5
crude fibre 0.17-3.48 0.71
pectic substances 0.2-1.5 0
total nitrogen 0.11-0.74 0.32
crude protein (total nitrogen x 6.25) 0.69-4.63 2
protein nitrogen in total nitrogen 27.3-73.4 54.7
amide nitrogen 0.029-0.052 0
amino acid nitrogen 0.065-0.098 0
Nitrates 0.0-0.05 0
Lipids 0.02-0.2 0.12
Ash 0.44-1.87 1.1
organic acids 0.4-1.0 0.6
ascorbic acid and dehydroascorbic
acid 1.0-54.0 10.0-25.0
Glycoalkaloids 0.2-41 3.0-10.0
phenolic compounds 5.0-30.0 0
Table 1: Typical chemical composition of potato tuber (http://en.www.wikipedia.org/wiki/ potato tuber)
4
1.3.2: INTERESTED POTATO PRODUCTS
1. STARCH
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined by
glycosidic bonds. This polysaccharide is produced by all green plants as an energy store. It is
contained in large amounts in such staple foods as potatoes, wheat, maize (corn), rice, and cassava.
Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It
consists of two types of molecules: the linear and helical amylose and the branched amylopectin.
Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by
weight. Glycogen, the glucose store of animals, is a more branched version of amylopectin. Starch
can be hydrolyzed into simpler carbohydrates by acids, various enzymes, or a combination of the
two. The resulting fragments are known as dextrins. The extent of conversion is typically quantified
by dextrose equivalent (DE), which is roughly the fraction of the glycosidic bonds in starch that have
been broken. Starch sugars are by far the most common starch based food ingredient and are used as
sweetener in many drinks and foods. They include:
Maltodextrin, a lightly hydrolyzed (DE 10–20) starch product used as a bland-tasting filler and
thickener.
Various glucose syrups (DE 30–70), also called corn syrups in the US, viscous solutions used as
sweeteners and thickeners in many kinds of processed foods.
Dextrose (DE 100), commercial glucose, prepared by the complete hydrolysis of starch.
High fructose syrup, made by treating dextrose solutions with the enzyme glucose isomerase, until a
substantial fraction of the glucose has been converted to fructose. In the United States, high fructose
corn syrup is the principal sweetener used in sweetened beverages because fructose has better
handling characteristics, such as microbiological stability, and more consistent sweetness/flavor. One
kind of high fructose corn syrup, HFCS-55, is typically sweeter than regular sucrose because it is
made with more fructose, while the sweetness of HFCS-42 is on par with sucrose.
Sugar alcohols, such as maltitol, erythritol, sorbitol, mannitol and hydrogenated starch hydrolysate,
are sweeteners made by reducing sugars.
Being an essential component of food providing a large proportion of the daily calorific intake and is
important in non‐food uses such as in adhesives. However much the world has improved over the last
century it is being surpassed by the high growth in population around the world doubling in countries
5
like China. Thus, production is not much greater than demand. In the world an increasing amount of
the harvested crops are being processed and, therefore, the quality of the raw product becomes an
increasingly important issue. There is, therefore, an increasing need to combine the modern
mathematical modeling tools with modern biochemical tools and the modern science of genomics to
increase starch production.
Potato starch contains one phosphate ester group per 200 to 400 anhydroglucose units which gives a
slight anionic character. GMO potatoes may have starch with a higher number of phosphate groups.
Sources of starch
Major sources of starch include; arrowroot, cassava, corn, potatoes, rice and wheat. But other sources
may include tree crops, cereals, herbs/shrubs, pulses & Also other minor root starches (arrowroot,
pacchyrrhizus, arracacha, Chinese water chestnut, East Indian arrowroot, giant taro, coleus, lotus
root, oca, Queensland arrowroot, shoti, swamp taro, breadfruit, sago, mango, amaranthus, tacca,
plantain, okenia, quinoa, enset, sorghum, tef, bamboo, black pepper, buffalo gourd, chickpea,
cowpea, horse gram, winged bean, baby lima bean, and velvet bean), may give starch in considerable
amounts.
Applications of Starch
1. Starch may be used as food;
Making jellies and gum
Ingredient in making medicines and candies
It is used as food thickener in soups
Carefully selected starches help make yogurts and puddings
Starch is also used as bakery fillings for cream and fruit pies and doughnuts
It is used as dry mixes for cakes and muffins, brownies and cookies
It is used as ingredients for jellies, cookies, glazes, icings and frostings
There are specialty starches used to help create reduced-fat and no-fat products
It improves baked goods rich in fiber
Dextrose is made from starch
2. Starch as raw material in industrial products
Starch is used to make foam for packaging
6
It is used in making sizing for textiles and papers
Hydrolysis of starch glucose can be fermented to biofuel ethanol
As filler in papermaking
Preparing laundry starch
A substitute for talcum powder and other beauty and health products
Produce of dextrin- a gummy substance used primarily in making adhesive
Starch can combine nitric acid to form nitrostarch i.e an explosive
Making biodegradable plastics
Making dry cell batteries
Used printed circuit boards
In leather finishing
2. PUREE
Puree is basically a paste or thick liquid suspension usually made from cooked food ground finely
with constant flow of particles.Vegetable, flesh and fruit purées are important parts of prepared
ready-meals. Further expansion of this food sector will depend among other things on improved and
consistent product quality. Innovative properties in ready-meal components will assist in product
diversification and the growth of market.
Research efforts have demonstrated that potatoes can be made into liquid and semi-solid food
products such as beverages, soups, baby foods, ice cream, baked products, restructured fries,
breakfast cereals, and various snack and dessert items. Puree and dehydrated forms processed from
potatoes are the main ingredients that provide the functionality required in these processed products.
For the food processing industry, the unavailability of puree and dehydrated forms for diverse
functionalities is a limiting factor in the utilization of potatoes in processed foods. with recent
developments in processing technologies to convert potatoes into purees and powders that can be
readily used by the food industry as functional ingredients in processed foods.
3. CHIPS
A potato chip is a thin slice of potato that is deep fried or baked until crunchy. Potato chips are
commonly served as an appetizer, side dish, or snack. The basic chips are cooked and salted;
additional varieties are manufactured using various flavorings and ingredients including seasonings,
herbs, spices, cheeses, and artificial additives.
7
1.4: JUSTIFICATION
Agriculture in Kenya remains the catalyst for sustainable development and has a multi-faceted impact
on poverty, food security i.e “when people have physical, social and economic access to sufficient
safe and nutritious food that meets their dietary needs and food preferences for active and healthy
life.” and the environment. The crop contributes to food security, generates cash income for the
farmers and creates employment opportunities. The annual production of potatoes in Kenya is 0.6 m
to 1.0 m metric tonnes per annum with small quantities exported to neighbouring countries.
The bulk of the crop is used for direct home consumption, with 60% brought to the market and some
used in processing, yet unknown quantities are stored. In 2011, 95 % and 93 % of the households in
Nairobi and Kisumu respectively, utilized potatoes. There has been a worldwide increase in
consumption of potato products, hence a need to pay keen interest on consumer behavior and
innovations in the sector. Three quarters of the urban households consume potatoes regularly, on
average 5 kilograms per adult per month. Apart from households, restaurants, hotels and canteens are
major potato consumers. Largely, Kenya’s population depends on maize as the main food item. The
major area of conflict is that the same maize is over 80% the basis used in animal feed
manufacturing. This places a lot of pressure on maize leading to cyclic food shortages. Potato
development could take off this pressure, as it has higher yields per unit area (7-10 tons per ha)
compared to maize (2-3.5 tons per ha) based on current yields at farm level.
Data collected indicate that market oriented potato farmers who follow technical recommendations
on good agricultural practices and use clean or certified seeds achieve yields of about 50 tons per ha
and season. The effects on income flow are considerable. The farmer enjoys a farm family income of
KES 288,5001 per ha and a return of KES 704 per family labour day which is about 4 times higher
than what a casual labourer can earn. Potato cultivation requires 410 person-days per ha and is
therefore very efficient in employment creation. Usually a farm household cannot supply all the
labour needed and has to employ about 70% of all labour needed as casual labour. Therefore this
enterprise is highly pro-poor: it creates substantial employment and income. PSDA’s labour studies
have also shown that women (49%) and men (51%) are nearly equally involved in the operations.
Some of the operations are of a heavy duty nature and thus require young men.
8
Table 2: : Potato wholesale market price information in Kenya(http://en.www.wikipedia.org/wiki/ potato production in Kenya)
Location Weight unit low High
Nairobi 100 Kg bag 3000 3100
Mombasa 100 Kg bag 2500 2750
Kisumu 100 Kg bag 1500 1800
Eldoret 100 Kg bag 2100 2400
Kitale 100 Kg bag 1800 2300
Advantages of potatoes to other sources of starch production
Low Fat Content - Similar to other vegetables, potatoes are naturally low in fat. Preparing mashed
potatoes with skim milk or vegetable stock can help keep the fat content of this dish low.
Plant-Based Iron Source - As a plant-based source of iron, potatoes have the advantage of providing
iron without unwanted dietary fats. Your body requires iron to produce the oxygen-carrying proteins
found in your muscles and red blood cells.
Rich in Vitamin C - A 1 cup serving of potatoes includes nearly 12 mg of vitamin C, which supports
your immune system, helps maintain your bones and muscles and protects your tissues from chemical
damage.
Digestion - Since potatoes predominantly contain carbohydrates, they are easy to digest and facilitate
digestion. This property makes them a good diet for patients, babies and those who cannot digest
hard food but need energy. But you must remember that eating too much of potatoes regularly may
cause acidity in the long run. Potatoes also contain considerable amount of roughage, more in raw
potatoes and cold ones than boiled or hot ones.
Disease - It is an excellent energy-rich diet for those suffering from diarrhoea, since it is very easy to
digest as well as contains mild roughage. But an over intake may cause diarrhoea due to excess
ingestion of starch.
Potatoes are an important food crop in Kenya, with production volumes only second to maize.
The national production is far below the potential, largely due to limited use of certified
seeds, low application of fertilizers and other organic amendments, and low use of fungicides
and other production chemicals. There is a lot of handling and in the process the producer’s
9
share in the final price of the commodity is minimal. Transport of potatoes to the market is
expensive due to poor road infrastructure in the producing area. Seasonality in production and lack of
on-farm ware potato storage lead to minimal returns to farmers.
10
Chapter 2: PROCESS DESCRIPTION
2.1 PROCESS FLOW CHART OF POTATO STARCH, POTATO CHIPS AND POTATO
PUREE
Dispatch (potato puree)
PACKING &
FREEZING
STORAGE
Potato storage
Raw potato
mash
Dispatch (chips)
Hot
Water
Water
Hot Water H.P. Steam
Size 2 Size 1
Dispatch (starch)
M. C 15%
M. C < 40%
Water
(gas)
Water
(liquid)
Fruit
water
Muddy
Water
Water
1ST WASHING
SEPARATOR
RASPING
EXTRACTOR
HYDRO
CYCLONE
SEPARATOR
ROTARY VACUUM
FILTER
FLASH DRYER
PACKING
STORAGE
STEAM
PEELING
BLANCHING
CHIPPING
2ND WASHING
BLANCHING
DRYING
PAR - FRYING
DRYING (REMOVAL OF EXCESS FAT)
COOLING & FREEZING
PACKING & STORAGE
SURGE TANK
MASHING
SPRAY DRYER
Slurry
storage
11
2.2 POTATO STARCH EXTRACTION
Process description
Potatoes are mainly received from storage within the processing facility or from suppliers and
farmers who deliver truckloads in bags and crates to factory. At this point, green, misshapen,
excessively sprouting and rotten, mechanically damaged and tubers that are infested should be
removed. In continuous plant operations, the tubers are conveyed along an inspection belt where
defective tubers are removed by hand.
Starch extraction
Industrial starch production uses many different extraction techniques. In principle, they are
differentiated by the origin of the raw materials. Our raw material is potato tuber. The processing of
supplied raw materials starts with a cleaning step. After that, the material is crushed and then the
components are separated by various physical means. Then the separated starch passes on to one
more cleaning step and finally it is dehydrated and dried.
Potato starch extraction
Cleaning
After the delivery the potatoes are coarsely cleaned for removal of soil and stones and then stored.
They are transported into the factory by flumes, which are equipped with strow and stone separators.
The main cleaning is conducted in a trough washing machine where the potatoes are spinned around.
Constant abrasion completely removes soil and also most of the skin. The washing water is then
pumped into clarification pools for sand and stone removal and reintroduced into the process.
Rasping
Potato skins are only roughly torn. This is inevitable to avoid that fine skin fragments pass through
the sieves during the following extraction step and remain in the starch, which would lead to poor
starch quality. The purified potatoes are mashed by means of a rotary saw blade rasp. In these rasps
rows of saw blades are closely arranged on a drum which is driven by high rotation speed. Sharp saw
teeth convert the potatoes into a fine mash. This process results in an almost complete disruption of
the potato cells, which therefore release the starch. Also the rasping machine is incorporated with
sieves to eliminate the skin fragments concurrently as they being rasped.
12
Extraction and fruit water separation
Firstly coarse skin and cell fragments, the so called pulp, have to be separated from the rasped
potatoes. This separation step is conducted by means of conical rotating sieves, the so called
centrisieves. For better starch isolation water is applied to the sieves through nozzles. While starch
and fruit water passes through, the fibres are retarded by the sieves. The remaining pulp is drained
off. The pulp can be used as mix feed.
The fruit water is separated in several steps by means of hydro-cyclone plants. Separated fruit water
has a high content of proteins, amino acids, and mineral nutrients. About one half of the soluble
proteins are coagulated by treatment with acid and heat and then separated in decanters.
Dewatering and drying
the refined starch milk has a dry matter content of about 35 % to 40 %. The starch is dewatered by
rotary vacuum filtration to moisture contents below 40 %.Drying is conducted by means of a flash
dryer. Starch must not exceed 15 % of residual moisture to be suitable for storage.
2.3 POTATO CHIPS
Processing procedures
Washing
Inspecting clean potatoes makes detection of defects easier. Dirty potatoes should be washed to
remove soil, insects, sprouts and other foreign matter. Small amounts of soil can be removed during
peeling. Following a wet harvest, the tubers may have high soil content and washing is essential.
Washing is done using high-pressure spray washers wherein water at 250 psi is directly sprayed at
the surface of potatoes as they tumble over rotating brushes.
Peeling and trimming
The yield of chips and crisps is governed mainly by peeling, trimming and cutting methods and the
size and shape of potatoes. Peeling is done by use of high pressure steam. Peeling losses are between
10 and 15% and depend on the efficiency of the equipment, size and shape of potatoes, depth of eyes
and depth of peeling.
Cutting/chipping
13
When cutting potatoes for chips the tubers are cut lengthwise to obtain maximum long sticks with
minimum loss. Strips that are shorter than 30 mm are removed and are taken to the starch extraction
section. They should be 15 x 15 mm, 20 x 20 mm or 120 x 120 mm depending on consumer
preferences. For crisps, the slice thickness may be varied between 12 and 20 mm. Thicker slices
absorb less oil as oil mainly 'sits' at the surface of the crisps (with less surface area) resulting in less
oil on the crisps.
Washing and drying
Surface starch and other materials that come out of cut potato cells cause the products to stick
together and to cook and colour unevenly. They should be removed by washing using water and
drying using mechanical de-watering. It is important to remove as much of the wash water as
possible from the slices or sticks before drying.
Blanching
Hot water blanching at 65-100oc before frying destroys enzyme activity and leaches out, reducing
sugars and other chemical constituents that cause off-colour and off flavour. Chips strips should be
water-blanched before frying in order to:
produce a more uniform colour of fried products
reduce absorption of fat through gelatinisation of the surface layer of starch
reduce frying time since the potato is partially cooked by blanching
improve texture of final product
Blanching of chips inactivates the polyphenoloxidase enzyme, a result of which enzymatic
discoloration in par-fried products is avoided. The non-enzymatic browning through the reaction of
reducing sugars and nitrogen is avoided through blanching. The non-enzymatic grey (after-cooking)
discoloration can be prevented in the blanching process by adding acid-sodium pyrophosphate. The
chemical forms a colourless compound with ferrous ions in the potato thus preventing the formation
of the grey colouration between chlorogenic acid and ferrous ions. It is added to the blanching water
or as a dip after the blanching process. The blanching also influences texture of chips. It contributes
to a firm texture which facilitates further handling. Blanch water is re-used in order to minimise
excessive leaching out of important flavour compounds from the potato. Excess moisture on the
surface of the strips is removed before frying. Potatoes for crisping should not be water-blanched to
prevent excessive loss of flavor.
14
Par-frying
Evaporation of water from cut surfaces before deep-frying gives chips their characteristic crispy
exterior. The temperature of the fat in the fryer should be 135-190°C but higher temperatures fry
faster. Par-frying should be for between 30 seconds and 6 minutes depending on the type of product.
Deep frozen products fry for a shorter time than fresh chips. The inside of chips is cooked when the
exterior becomes crispy. Chips should be deep-fried in fat that is solid at room temperature. As crisps
are eaten at room temperature, the solid fat would give them a granular texture. They are therefore
fried in liquid oil.
Drying
The pre-cooked potato chips are now taken to moving bed drier which is enclosed at the top and has
an exit of a chimney. Basically cold air at around 20 oc is pumped from below and alternately from
below this induces a cooling effect which actually dries and cools the potato chips. Cooling is done
for around 25 to 10 minutes continuously.
Cooling and freezing
After frying and removing superficial fat, the product should be cooled and, where necessary, deep-
frozen within 20 min at -18 to -20°C in order to retain texture and to avoid damage as a result of ice
crystal formation.
2.4 POTATO PUREE
Process description
Over the years, techniques have been developed for puree processing in order to produce purees with
consistent quality, as mentioned above, despite the variations due to cultivar differences and post-
harvest practices. Process operations for pureeing of potatoes involve washing, peeling, hand-
trimming, cutting, steamed blanching or cooking, and grinding into purees which can be subjected to
canning or freezing for preservation.
Washing
Potatoes are stored without removing the dirt for prolonging storability. In the plant, stored potatoes
are passed through the packing line for washing and sizing. The roots are generally unloaded from
the pallet bins into a tank of water, conveyed to high-pressure spray washers wherein water at 250 psi
15
is directly sprayed at the surface of potatoes as they tumble over rotating brushes. The washed roots
are then sorted by size using pitch roller sizers or electronic sensors. The size number 1 roots are
selected and channeled to the starch extraction section. The remaining size number two continues in
the same line.
Peeling and Rewashing
Prior to peeling, the cleaned roots can be preheated in hot water for a short time to provide some
benefits including reduction of peeling time. However, preheating treatment of the unpeeled roots is
not necessary. Potato peel is removed by high pressure steam. The technology is referred as a thermal
blast process in which the potato roots are enclosed for a short time (20 to 90 sec) in a chamber
pressurized with heated steam, followed by an instantaneous release of pressure. As the pressure
suddenly release, the super-heated liquid water beneath the skin surface immediately flashed into
vapor, and blasted the peel off the roots. This process can be automated, result in less peeling loss
than lye peeling, and produce a product with less enzymatic discoloration also avoiding corrosion
caused by lye peeling.
Trimming and Cutting
Peeled potatoes are next conveyed along a trimming and inspecting line for trimming the surface
blemishes and fibrous ends and removing the diseased roots. The materials are then fed to size
reduction machine for cutting into slices, strips and cubes. Cutting and grinding machines with
capacity up to over 1000 kg/hr are being used for this operation.
Pureeing Processes
The purees can be simply produced by steam cooking of the peeled potato roots which have been cut
into cubes of 15mm or 20mm and passing the cooked materials through a pulp finisher. Next, the
materials are blanched at 65 to 75°C which activates the amylases and gelatinizes the starch for
hydrolysis. For the process with slices, strips and cubes, comminuting the blanched materials into
puree is carried out at this point using the hammer mill. The blanched puree is pumped into a surge
tank and held at 65 - 75°C for further starch hydrolysis depending on the targeted maltose levels.
Raw potato mash as a source of amylases can be optionally added at this stage to increase starch
conversion. Alpha- and ß- amylases hydrolyze the starch producing maltose, maltotriose, glucose and
dextrins. The majority of maltose production is likely completed in the first few minutes of the starch
conversion process. Maltose is the only sugar produced and the majority of maltose is produced in
the first 10 minutes of cooking at temperatures of 70 to 80°C. Rapid heating of raw potato slurries to
16
80ºC may be optimal for starch conversion. However, further decreases in the molecular size of
starch and dextrins occur for up to 60 minutes resulting in the purees with high maltose content and
low apparent viscosity.
In order to control the process to produce a consistent product, the length of conversion time can be
adjusted from a few minutes to 1 hour depending on the starch content and amylase activity in the
raw materials. A final grinding step will be carried out with the use of a pulp finisher to obtain the
smooth puree. The temperature and time program in the described pre-cook process has significant
effects on the puree quality. A very fast heating procedure tended to result in puree with low levels of
maltose and high viscosity, and a temperature and time program that allows sufficient amylase-
hydrolysis on gelatinized starch would produce sweet and more flow able purees.
This potato type has moist texture after cooking, produces purees that are viscous, but flow able, and
can be handled in various processing operations. Potatoes with white, yellow and purple flesh colors
have higher levels of dry matter (25-38%) with potentially different starch properties, which may
present challenges for the commercial production of flow able purees from these materials.
Therefore, the processing hurdle in pureeing these potato types could be overcome by either addition
of water to decrease the solid levels of the material to 18-21%, amylase hydrolysis of starch
components, or a combination of the two treatments.
Canning and Freezing
The finish-cooked puree is packaged in plastic containers for refrigerated or frozen storage. pH
adjustment of potato puree to 1.5, 4.5 and 11.5 prior to filling in jars followed by pasteurizing at 90ºC
could prolong the shelf-life of the product up to 9 months at room temperature. Preservation by
canning for low acid food such as potato purees (pH, 5.8 – 6.3) usually involves excessive thermal
treatment of the product because heat transfer in the puree is mainly by conduction. Excessive
thermal treatment of the product also results in severe degradation of color, flavor, texture, and
nutrients. The slow- rate of heat transfer from the wall to the center of the can to attain commercial
sterilization of the product limits the maximum can size for canned potato purees. This size limitation
is another obstruction for the wider uses of potato purees as a food ingredient in the food industry.
Other issues associated with canning include the difficulty in handling, opening and dispensing of the
product, and disposal of emptied cans. Nevertheless, canning does not have the need for special
storage, lower capital investment and unit of production is less when comparing to refrigerated and
frozen puree.
17
Frozen puree is an established method for preservation which provides the lower degradation on
nutritional and sensory quality as compared to can processing. However, preservation by freezing
requires considerable investment in frozen distribution and storage as well as space, energy, time-
consuming, and poorly controlled defrosting treatment before use.
Microwave-assisted Sterilization and Aseptic Packaging
Aseptic processing is considered as a potential alternative to overcome the stated problems associated
with canning and low temperature preservation. As opposed to conventional canning, the use of high
temperature for a short period of time in aseptic processing can produce a higher quality product with
equal or better level of microbiological safety as that in a conventional canning system.
18
Chapter 3: MASS AND ENERGY BALANCE
3.1 MASS BALANCE
The basis feed 3000Kg/hr was found as follows;
We used the research data that was carried by Kenya Agricultural Institute carried on December
2009.From the data we considered the possible location of four company and it was to be located in
Burnt forest where it will be in the middle of the our major potato producing counties;
Nakuru
Baringo
Uasin gishu
Bomet
The four counties contribute a production of 200 metric tones annually. Looking at consumption in
the service sector i.e hotels and restaurants, domestic consumption i.e used at homes as staple food
and what actually remains at the moment and which most goes to wastage due to perish ability of
potatoes and lack of proper storage devices. In the market the research actually estimated
consumption as follows;
Service sector consumption-60%
Domestic consumption-30%
Remaining-10%
Getting in the market at first will mean utilizing the remaining percentage before stabilizing and
expanding hence it becomes the basis of our calculations.
0.1 x 200=20MT
Having 300 operational days in year factoring servicing, maintenance and general cleanliness;
, for an hour =
Therefore having a basis=3000Kg/hr
Assuming 1 sack weigh 180 Kg then 3000/180=16.667 bag/hour. Apprx; 16bags/hour
19
Basis: 1 hour
Basis Feed= 3000 kg/hr
1. Mass balance around the washer
Table 3: mass balance around the 1st washer
COMPONENT Potato
(kg/hr)
water
(Kg/hr)
Stone,
metallic &
mud
(kg/hr)
TOTAL
Mass
in(kg/hr)
3000 6000 0 9000
Mass
out(kg/hr)
2997 6000 3 9000
Mass balance around the separator
S 5
S 6
S 4
Separator
S 3 S 4
S 2 S 1
1st
Washer
20
Table 4: mass balance around the separator
COMPONENT Water Potato TOTAL
Mass in 60 2997 3057
Mass out 60 2997 3057
Mass balance around the rasping unit
Table 5: mass balance around the Rasper
COMPONENT potato(kg/hr) Water
(Kg/hr)
Skin
fragment
(kg/hr)
TOTAL
Mass
in(kg/hr)
899.1 18 0 917.1
Mass
out(kg/hr)
894.6 18 4.5 917.1
Mass balance around the extractor
S 9
S 10
S 11
S 8
Extractor
S 7
S 8
S 6
Rasper
21
Table 6: mass balance around the extractor
COMPONENT Rasped
potato(kg/hr)
Water
(Kg/hr)
Pulp & fibres
(kg/hr)
Starch
(Kg/hr)
Proteins/
soluble
TOTAL
Mass
in(kg/hr)
894.6 1805.4 0 0 0 2700
Mass
out(kg/hr)
0 1805.4 223.515 178.92 492.03 2700
Mass balance around the hydro cyclone
The efficiency of the hydro cyclone is 95%
Table 7: mass balance around the hydro cyclone
COMPONENT starch(kg/hr) proteins(Kg/hr) water (kg/hr) TOTAL
Mass in(kg/hr) 178.92 492.03 1444.32 2115.27
Mass out(kg/hr) 178.92 492.03 1444.32 2115.27
Mass balance around the dewatering (rotary vacuum)
The efficiency of the rotary vacuum filter is 90%
S 13
S 12
S 11
Hydro
cyclone
S 15
S 14
S 13
Dewatering
22
Table 8: mass balance around the rotary vacuum filter
COMPONENT starch(kg/hr) proteins(Kg/hr) water (kg/hr) TOTAL
Mass in(kg/hr) 169.97 24.60 72.22 266.79
Mass out(kg/hr) 169.97 24.60 72.22 266.79
Mass balance around the flash dryer
The efficiency of the flash dryer is 90%
Table 9: mass balance around the flash dryer
COMPONENT starch(kg/hr) proteins(Kg/hr) water
(kg/hr)
Water
vapor(kg/hr)
TOTAL
Mass in(kg/hr) 169.97 24.60 7.22 0 201.79
Mass
out(kg/hr)
169.97 24.60 0.73 6.49 201.79
Mass balance around the steam peeler
S 17
S 16
S 15
Flash dryer
S 18
S 20
S 19
S 5
Steam
peeler
23
Table 10: mass balance around the steam peeler
COMPONENT
potato(kg/hr) water (Kg/hr) steam (kg/hr) Skin
fragments
(kg/hr)
TOTAL
Mass in(kg/hr) 2097.9 42 2860.65 0 5000.55
Mass
out(kg/hr)
2087.41 2902.65 0.00 10.49 5000.55
Mass balance around the chipping section
Table 11: mass balance around the chipper
COMPONENT
potato(kg/hr) water (Kg/hr) Excess water
(Kg/hr)
TOTAL
Mass in(kg/hr) 2087.41 290.27 250.67 2628.35
Mass out(kg/hr) 2087.41 540.94 0 2628.35
Mass balance around the washer
S 25
S 24 S 23
S 26
2nd
Washer
S 21
S 22
S 20
S 23
Chipping
24
Table 12: mass balance around the 2nd washer
COMPONENT potato(kg/hr) water (Kg/hr) TOTAL
Mass in(kg/hr) 2087.41 4715.76 6803.17
Mass out(kg/hr) 2087.41 4715.76 6803.17
Mass balance around the blanching section
Table 13: mass balance around the blancher
COMPONENT potato(kg/hr) water (Kg/hr) Hot
water(kg/hr)
TOTAL
Mass in(kg/hr) 2087.41 540.94 4174.82 6803.17
Mass out(kg/hr) 2087.41 540.94 4174.82 6803.17
Mass balance around the dryer
The target is to reduce moisture content to 15%
S 28
S 27 S 26
S 29
Blanching
S 31
S 29
S 30
Dryer
25
Table 14: mass balance around the dryer
COMPONENT potato(kg/hr) water(Kg/hr) moisture (kg/hr) TOTAL
Mass in(kg/hr) 2087.41 540.94 0 2628.35
Mass out(kg/hr) 2087.41 368.45 172.49 2628.35
Mass balance around the fryer
Target in frying is to reduce the moisture content to 10%
= 10%; x = 231.99 kg
Table 15: mass balance around the fryer
COMPONENT potato(kg/hr) water
(Kg/hr)
Water
vapor
(kg/hr)
oil
(kg/hr)
absorbed
oil
(kg/hr)
TOTAL
Mass
in(kg/hr)
2087.41 368.45 0 2456.45 0 4912.31
Mass
out(kg/hr)
2087.41 231.99 136.46 2210.81 245.64 4912.31
Mass balance around the dryer (removal of excess fat)
Factor is time to reduce fat by 50%
S 32
S 33
S 30
S 34
Fryer
S 35
S 34
S 36
De-fatting
vibrator
26
Table 16: mass balance around the de-fatting vibrator
COMPONENT potato(kg/hr) water(Kg/hr) Absorbed oil
(kg/hr)
oil (kg/hr) TOTAL
Mass in(kg/hr) 2087.41 231.99 245.64 0 2565.04
Mass
out(kg/hr)
2087.41 231.99 122.82 122.82 2565.04
Mass balance around the steam blanching section
Table 12 mass balance around the blancher
COMPONENT potato(kg/hr) water
(Kg/hr)
Hot water
(kg/hr)
warm
water
(kg/hr)
TOTAL
Mass in(kg/hr) 2087.41 540.94 Excess 0 2628.35
Mass
out(kg/hr)
2087.41 540.94 0 excess 2628.35
S 37
S 38
S 23
S 39
Blanching
27
3.2 ENERGY BALANCE
Energy balance around the flash dryer
Table 13: energy balance around the flash dryer
Compound Input (Kj/hr) Output (Kj/hr)
Semi dried starch 49060 0
Hot air 74176.64 0
Moist air 0 67486.64
Dried starch 0 55750
Totals 123236.64 123236.64
Hot air @ 150oC
74176.64 kJ
Dried starch @ 100oC
55750 kJ
Semi dried starch @
88oC
49060 kJ
Moist air @ 100oC
67486.64 kJ
Flash dryer
28
Energy balance around the steam peeler
Table 14: energy balance around the steam peeler
Compound Input (Kj/hr) Output (Kj/hr)
Potato & water 38682.07 276387.41
Steam 93467.4 0
Skin fragment & condensate 0 -144237.94
Totals 132149.47 132149.47
Energy balance around the Dryer:
Table 15: energy balance around the dryer
Compound Input (Kj/hr) Output (Kj/hr)
Potato & water 249444.55 135766.62
Cold air 0 0
Warm air 0 113677.88
Totals 249444.55 249444.55
Steam @ 164oC & 7
bars
93467.4 kJ
Potato & water @ 93 oC 276387.41 kJ
Potato & water @
20oC
38682.07 kJ
Skin fragment &
condensate @ 93oC
-144237.94 kJ
Steam peeler
Potato & water @
60oC
135766.62kJ
Warm air @ 42.5 oC
113677.88 kJ
Cold air @ 20oC
0kJ
Potato & water @
80OC
249444.55 kJ
Dryer
29
Energy balance around the Heat exchanger:
Steam is available at 300oC (superheated)
540.9464Kg/hr
4.187 Kj/kg
0.0335
+ 0.8374 = 0.8443Kj
We have:
Q = UA = M
Where: (logarithmic temperature)
=
Assume no energy losses:
Energy in = energy out
T2 = 224.2 oC
T4 = 100oC T3 = 70oC
T1 = 280oC
T3 = 70oC
T2 = x oC T4 = 100oC
T1 = 300oC
30
= +
We have:
Energy lost by steam = energy gain by process fluid (mash potato + water)
Steam available at T = 280oC, = 200 kg/hr, P = 1.5 bar, U = 3033 kJ/ kg
Hence =
= 10.83 kJ/kgoC
=
= 120832.6964 kJ
= 120832.6964
200 10.83 (280 – T2) = 120832.6964
T2 = 224.2 OC
This steam passes through an economizer which is used for heating water at the surge tank
Energy balance around the fryer:
Table 16: energy balance around the fryer
Compound Input (Kj/hr) Output (Kj/hr)
Potato 124153.75 0
Sunflower oil 876965.505 0
Warm air 0 57135.80
Fried chips 0 943983.455
Totals 1001119.255 1001119.255
Fried chips @
162.5OC
943983.455 kJ
Warm air
@100OC
57135.80 kJ
Sunflower oil @
162.5OC
876965.505 kJ
Potato @ 60OC
124153.75 kJ
Frying
31
Chapter 4: EQUIPMENT SIZING AND SPECIFICATION
4.1 EQUIPMENT SPECIFICATION: STARCH PLANT.
Unit Specification
rotary
washer
equipment
code: RW
service:
To remove soil, stones and other foreign materials
by washing.
type: Slanted cylindrical drum with inlet chute.
height: 4.5 m
diameter: 1.5 m
capacity: 8.5 m3
material: Stainless steel
number: 1
vibratory
mesh
equipment
code: VM
service:
To separate the potatoes for starch & chips/puree
section.
type:
Slanted, Cubical with single output with mesh at
the bottom surface.
length: 3000 mm
Width: 1500 mm
capacity: 2.14 m3
material: Stainless steel
number: 1
rasping
machine
equipment
code: RM
service:
To completely disrupt potato cells to release
starch
type:
A horizontal cylindrical drum with saw blades on
the drum which is driven by a high speed motor.
height: 1.574 m
diameter: 0.787 m
throughput: 2-3 t/hr
material: Stainless steel
number: 1
Extractor
equipment
code: E
service: For starch isolation
type:
A moving sieve with spraying water at high
pressure at the top of an enclosed cabinet
height: 0.3 m
32
width: 1.2 m
Length: 2.4 m
capacity: 0.85 m3
material: Stainless steel
number: 1
Hydro
cyclone
separator
equipment
code: HC
service:
To remove the soluble and insoluble protein, fine
fibers in starch slurry.
type:
A cylindrical section at the top where liquid is
being fed tangentially, and a conical base.
Height (LC +
ZC): 3.9 M
Diameter
(Dc): 1.3 m
throughput: 1.92 m3/hr
material: Stainless steel
Tapering
angle: (9-12)o
number: 1
Rotary
vacuum
filtration
equipment
code: RVF
service: To remove excess water from the starch.
type:
Consists of a drum rotating in a tube of liquid to
be filtered.
height: 4m
diameter: 2.78m
capacity: 266.73Kg/hr
material: Stainless steel
number: 1
flash dryer
equipment
code: FD
service:
To disperse solid cakey material as fine as
possible, this increases surface area of raw
material and speed up heat transfer process.
type:
A vertical cyclone with a top inlet screw and a
discharge vent.
capacity: 0.1694 m3
material: Stainless steel
number: 1
storage
tank
equipment
code: ST
service: To store starch waiting for packaging.
type:
Vertical, cylindrical closed tank with a screw
conveyor at the bottom.
33
height: 6 m
diameter: 2.4m
capacity: 27.34 m3
material: Stainless steel
number: 2
4.2 EQUIPMENT SPECIFICATION: CHIPS PLANT.
Unit Specification
Steam
peeler
equipment
code: SP
service: To peel the potato skin fragments
type:
Pressure vessel with pneumatically operated
inlet/outlet door and steam basket
throughput: 4.65 m3/hr
material: Stainless steel
number: 1
Chipper
equipment
code: C
service: Potato slicing and shredding
type:
It’s an enclosed cabinet where the product is
carried in water and pumped at high pressure
through a cutting head.
Dimension
of chips
slice: 100 mm * 150 mm * 200 mm
capacity: 2.19 m3/ hr
material: Stainless steel
number: 1
Blancher
equipment
code: B
service:
To destroy enzyme activity and leach out reducing
sugar.
type:
A close cabinet with an elevated feed inlet and
bucket conveyer inside and hot water sprayers at
the top of the moving buckets.
height: 1.44m
Length: 1.92m
width: 0.96m
throughput: 6.46m3/hr
material: Stainless steel
number: 2
Drier
equipment
code: D
service: To remove excess moisture before frying.
34
type:
It is a direct rotary drier made up of cylindrical
shell slightly inclined where the feed enters at the
upper end and leave at the lower end while air
flows counter currently.
length: 2.67 m
diameter: 0.89 m
capacity: 1.71 m3
material: Stainless steel
number: 1
Par –
frying
equipment
code: PF
service: To fry the chips.
type:
Its is an indirectly heated frying pan which is
cuboid closed vessel with a pan inside having a
conveyer moving inside the pan.
height: 0.45m
length: 2.52m
width: 1.26m
Throughput: 2.1m3/hr
material: Stainless steel
number: 1
De-fatting
vibrator
equipment
code: DV
service:
To remove as much as possible surface fat from
the product.
type:
Perforated conveyor which is moving in a cabinet
where ambient air is taken by means of a fan.
length: 3.0 m
Width: 1.5 m
capacity: 2.14 m3
material: Stainless steel
number: 1
Freezer
equipment
code: F
service: To freeze the chips
type:
Perforated conveyor with a high capacity cold
airflow blowing upward through the product.
length: 3.0 m
Width: 1.5 m
capacity: 2.14 m3
material: Stainless steel
number: 1
35
4.3 EQUIPMENT SPECIFICATION: PUREE PLANT.
unit Specification
Steam
blanching
equipment
code: B
service:
To destroy enzyme activity and leach out reducing
sugar.
type:
A close cabinet with an elevated feed inlet and
bucket conveyer inside and steam sprayers at the
top of the moving buckets.
height: 1.02m
length: 1.36m
width: 0.68m
throughput: 2.28m3/hr
number: 1
Surge tank
equipment
code: ST
service:
To further hydrolyse starch and to facilitate its
conversion.
type:
It’s a cylindrical drum with a short conical bottom
outlet.
capacity: 2.28 m3/hr
material: Stainless steel
number: 1
mashing
equipment
code: R.M
service: To mash the blanched potatoes.
type:
throughput: 2.28 m3/hr
material: Stainless steel
number: 1
Spray
drying
equipment
code: S.D
service: To dry the potato puree slurry.
type:
It’s a cylindrical drum with a short conical bottom
outlet.
height: 3.7m
diameter: 3.4m
capacity: 12m3
material: Stainlees steel
number: 1
36
Chapter 5: EQUIPMENT DESIGN
5.0 ROTARY DRUM VACUUM FILTER BY: LIMO KIPTALAM R. (CPE /12/08)
5.0.1 INTRODUCTION
5.0.1.1 Separator Design
There are two major types of separation processes; Component and Phase separation.
In component separation, the components are separated from a single phase by mass transfer. An
example is gas absorption where one or more components are removed from a gas by dissolving in a
solvent.
In phase separation, two or more phases can be separated because a force acting on one phase differs
from a force acting on another phase or because one of the phases impacts on a solid barrier. The
forces are usually gravity, centrifugal, and electromotive.
Examples are removal of a solid from a liquid by impaction (filtration), gravity (settling), centrifugal
force, and the attraction of charged particles in an electrostatic precipitator.
5.0.1.2 Solid-Liquid Separators
The separation of solids from a suspension in a liquid by means of a porous medium or screen which
retains the solids and allows the liquid to pass is termed filtration. The pores of the medium are larger
than the particles which are to be removed, and the filter works efficiently only after an initial deposit
has been trapped in the medium. In the industrial difficulties are encountered in the mechanical
handling of much larger quantities of suspension and solids. A thicker layer of solids has to form and,
in order to achieve a high rate of passage of liquid through the solids, higher pressures are needed,
and a far greater area has to be provided.
5.0.1.3 Factors considered in filtration processes
The main factors to be considered when selecting equipment and operating conditions are:
(a) The properties of the fluid, particularly its viscosity, density and corrosive properties.
(b) The nature of the solid—its particle size and shape, size distribution, and packing characteristics.
37
(c) The concentration of solids in suspension.
(d) The quantity of material to be handled, and its value.
(e) Whether the valuable product is the solid, the fluid, or both.
(f) Whether it is necessary to wash the filtered solids.
(g) Whether very slight contamination caused by contact of the suspension or filtrate with the various
components of the equipment is detrimental to the product.
(h) Whether the feed liquor may be heated.
(i) Whether any form of pre-treatment might be helpful.
The most important factors on which the rate of filtration then depends will be:
The drop in pressure from the feed to the far side of the filter medium.
The area of the filtering surface.
The viscosity of the filtrate.
The resistance of the filter cake.
The resistance of the filter medium and initial layers of cake.
5.0.1.4 Filtration theory
In filtration the bed steadily grows in thickness. It may be noted that there are two quite different
methods of operating a batch filter. If the pressure is kept constant then the rate of flow progressively
diminishes, whereas if the flow rate is kept constant then the pressure must be gradually increased.
Because the particles forming the cake are small and the flow through the bed is slow, streamline
conditions are almost invariably obtained, and, at any instant, the flow rate of the filtrate may be
represented by the following form of equation;
Where; V - volume of filtrate which has passed in time t
A - Total cross-sectional area of the filter cake
Uc -superficial velocity of the filtrate
38
L - Cake thickness
S- Specific surface of the particles
- Voidage
μ- Is the viscosity of the filtrate
P- Is the applied pressure difference
In deriving this equation it is assumed that the cake is uniform and that the voidage is constant
throughout. In the deposition of a filter cake this is unlikely to be the case and the voidage, e will
depend on the nature of the support, including its geometry and surface structure, and on the rate of
deposition. The initial stages in the formation of the cake are therefore of special importance for the
following reasons:
For any filtration pressure, the rate of flow is greatest at the beginning of the process since the
resistance is then a minimum.
High initial rates of filtration may result in plugging of the pores of the filter cloth and cause a very
high resistance to flow.
The orientation of the particle in the initial layers may appreciably influence the structure of the
whole filter cake.
Filter cakes may be divided into two classes—incompressible cakes and compressible cakes.
5.0.1.5 Compressible cake
The increase of the pressure difference or of the rate of flow causes the formation of a denser cake
with a higher resistance. Nearly all filter cakes are compressible to some extend but in many cases
the degree of compressibility is so small that the cake is regarded as incompressible for practical
purpose.
5.0.1.6 Incompressible cake
The resistance to flow of a given volume of cake is not appreciably affected either by the pressure
difference across the cake or by the rate of deposition of material.
39
For incompressible cakes may be taken as constant and the quantity
is then a property of
the particles forming the cake and should be constant for a given material. Therefore equation
reduces, (Richardson et. al., Coulson and Richardson’ Chemical Engineering Vol. 2, 2000 );
Thus:
5.0.2 FILTER SELECTION
The most suitable filter for any given operation is the one which will fulfill the requirements at
minimum overall cost. Since the cost of the equipment is closely related to the filtering area, it is
normally desirable to obtain a high overall rate of filtration.
Although a higher throughput from a given filtering surface is obtained from a continuous filter than
from a batch operated filter, it may sometimes be necessary to use a batch filter, particularly if the
filter cake has a high resistance, since most continuous filters operate under reduced pressure and the
maximum filtration pressure is therefore limited.
Ease of discharge of filter cake, a method of observing the quality of filtrate obtained is another
desirable quality.
5.0.2.1 Considerations in filter selection
Specific resistance of the filter cake
Quantity to be filtered
Solids concentration in the slurry
For free-filtering materials, a rotary drum filter is the most satisfactory.
5.0.3 ROTARY DRUM FILTER
Because of its versatility and simplicity, one of the most widely used vacuum filters is the rotary
drum filter.
Rotary vacuum filters may be divided into two categories:
Those where vacuum is created within compartments formed on the periphery of the drum.
40
Those where vacuum is applied to the whole of the interior of the drum.
The most frequently used continuous drum type filters fall into the first category. These give
maximum versatility, low cost per unit area, and also allow a wide variation of the respective time
periods devoted to filtration.
Essentially, a multi-compartment drum type vacuum filter consists of a drum rotating about a
horizontal axis, arranged so that the drum is partially submerged in the trough into which the material
to be filtered is fed. The periphery of the drum is divided into compartments, each of which is
provided with a number of drain lines. These pass through the inside of the drum and terminate as a
ring of ports covered by a rotary valve, through which vacuum is applied. The surface of the drum is
covered with a filter fabric, and the drum is arranged to rotate at low speed, usually in the range
0.0016–0.004 Hz (0.1–0.25 rpm) or up to 0.05 Hz (3 rpm) for very free filtering materials.
Advantages:
Continuous operation is possible until the filter medium requires changing.
Adaptability to many types of slurries.
Dry cake discharge is achieved (moisture content ranging from 20-70%).
Minimum operating attention and low maintenance.
Provides lowest cost per unit area
5.0.4 DESIGN EQUATIONS
The primary factor in the design of filters is the cake resistance or cake permeability.
The rate of filtrate delivery is inversely proportional to the combined resistance of the cake and
filtering medium, the viscosity of the filtrate, and directly proportional to the available filtering area
and the pressure – difference driving force. This is;
)( FK RR
PA
t
V
---(3)
A variation is also given,
)/(
1
rAwV
P
d
dV
A
--- (4) (Perry, 1987)
Where
V= Volume of filtrate delivered in time t
A= Area of filtering surface
P = Pressure drop across filter
41
RK = Resistance of the cake
RF = Resistance of the filter medium
= viscosity of the filtrate
= the filtration time,
= the cake-specific resistance
w = the weight of cake solids/unit volume of filtrate,
r = the resistance of the filter cloth plus the drainage system.
Cake resistance RK varies indirectly with the thickness of the cake, and the proportionality can be
expressed as:
RK = cL --- (5)
Where c = proportionality constant
L= the cake thickness at time t
RF= cLF --- (6)
The actual cake thickness plus the fictitious cake thickness is:
Lc = L + LF = A
AVVW
c
F
)( --- (7)
Where
W = Mass of dry-cake solids per unit volume of filtrate (kg/m3)
c = cake density expressed as kg of dry cake solids per unit volume of wet filter Cake (kg/m3)
VF = The fictitious volume of filtrate per unit of filtering area necessary to lay
down a cake of thickness LF.
Combining equations (4) and (6) gives:
)(
2
AVFVW
PA
t
V
--- (8)
where = c / c = Specific cake resistance.
Equation (8) can be integrated between the limits of zero and V to give:
V2 + 2AVFV = W
PtA 22 --- (9)
Cake removal
Dead zone
Pick up zone
Dewaterin
g
42
Table22: Fractions of the drum zones
Name of Zone Symbol Angle Ratio = Φ/360
Cake Pick-Up
Zone
Φs 160 0.444
Drying Zone Φd 148 0.411
Cake Removal
Zone
Φc 40 0.111
Dead Zone Φr 12 0.033
Total Φ 360 1.000
(Peters and Timmerhaus)
The design equations is developed in terms of the total area available for filtering service, even
though only a fraction of this area is designated as Ad and the fraction of this area immersed in the
slurry as s .
The effective area of the filtering surface then becomes Ad s , and equation (4) can be expressed in
the following form:
)( FK
sd
RR
PA
t
V
--- (10)
But according to equation (5) and (6)
RK + RF = c (L + LF) --- (11)
With a rotary drum filter, the thickness .This thickness can be expressed by the following equation:
Lleaving filtering zone = dc
r
A
WV
--- (12)
Where Vr = volume of filtrate delivered per revolution
c = the cake density as kg of dry-cake solids per unit volume of wet filter cake leaving
filter zone.
Lavg = dc
r
A
WV
2 --- (13)
L + LF = Lavg + LF = dc
Fsdr
A
VAVW
)2/( --- (14)
Combining equations (10), (11) and (14) with = c / c gives,
)2(
22
sdr
d
AVW
PsA
t
V
--- (15)
Integration of equation (15) between the limits of V=0 and V = Vr, and t = 0 and t =1/Nr, where Nr is
the number of revolutions per unit time, gives;
r
sd
rFsdrNW
PAVVAV
2
2 22 --- (16)
43
Volume of filtrate per unit revolution:
r
s
drNW
PAV
2 --- (17) (Perry, 1987),
5.0.5 CHEMICAL DESIGN OF THE ROTARY DRUM FILTER
Assumptions:
1. The cake is incompressible.
2. The slurry feed is at constant temperature. This ensures constant viscosity of slurry.
3. The efficiency of the filter is 90%.
4. The density of the cake is 1500kg/m3
5. Cake resistance coefficient = 0.0003
6. Pressure drop through the filter = 75kpa
7. Thickness of the cake formed in 1 second = 0.005m
8. N, speed of rotation = 0.3 rev/min
9. Viscosity of air is 0.0000186Pa.s
10. Viscosity of the slurry is 0.00115Pa.s
Concentration of solids in the entering stream,
C1 =
Concentration of solids in the wet cake
C2 =
The rate of wet cake formation, Mc
Rotary Drum
Filter
Filtrate=64.81kg/hr
Cake=201.98/hr
Slurry=266.79kg/hr
44
Mc=
--- (18) (Peters and Timmerhaus)
Where
M = mass flow rate of suspension slurry = 266.79 kg/hr
C1 = Concentrations of solids in suspension = 0.73
C2 = concentration of solid in wet cake = 0.964
Hence
Mc= hrkg /659.201964.0
79.073.266
Volumetric flow rate of liquid in the exit stream
Vf =
Where
W = mass of the cake per m3 of the filtrate (kg/m3)
W = 21 /1/1 CC
c
--- (20)
= 3/03.4511964.0/173.0/1
1500mkg
Vf = hrm /043.003.4511
73.073.266 3
Filtration Media
i) Filtration constant of the filtering media (B1)
B1 = P
Wrm
2
--- (21)
Where,
rm = cake resistance coefficient = 0.0003
Efficiency, = 90%
P = pressure drop through the filter = 75N/m2
45
Hence the filtration constant,
B1 = 31012.8752
03.45110003.090.0 xx
xx
ii) Volume of filtration media passing through to give the desired thickness (V0)
V0 = mWr
0
= 30037.00003.003.4511
005.0m
x
Filtration Area (Ad)
Ad = L
VV jfs
--- (22)
Where,
Vf =Volumetric flow rate of liquid in the exit stream=0.043m3
Vj = 0.035
L = cake thickness formed in 1 second = 0.005
s = Filtration time
The drum is arranged to rotate at low speed, usually in the range 0.0016–0.004 Hz (0.1–0.25
rpm) or up to 0.05 Hz (3 rpm) for very free filtering materials. Slurry flow rate is relatively high;
we take 1.5rev/min as the time for one cycle.
44.44 % of the drum is submerged during filtration, hence filtration time,
rss xN --- (23)
Area required in the cake pick-up zone.
Ad = L
VV jfs
--- (24)
Ad =
=11.92m2
46
Calculating Diameter of filter;
The ratio of Cake Pick-Up Zone Φs to area required in the cake pick-up zone is
0.44 : 11.92
Hence the total surface area of the rotary drum filter,
m2
Taking Drum length of 4m we can calculate the drum diameter using,
A=πDL --- (25)
D=
The drum diameter
D=2.16m
Hence the rotary drum characteristics; Diameter is 2.16and the drum length is 4m.
Drum Submergence(H)
H =
]
2cos[12/ rsD
--- (26) (Peters and Timmerhaus)
s = 160° - drum pick-up zone angle
r = 12 ° - dead zone angle
D = 2.16m
H = m005.1]2
12160cos[12/16.2
Time Duration in Filtration Zones
rr xN --- (27)
Where ω=angular velocity
Nr=revolutions per minute
47
r =angle covered per one complete revolution (6.283 rads/rev)
Thus
rr xN
= 6.283 x 1.5 = 9.4245rads/min
= 0.157rads/sec
Total Filtration Time,
For one complete revolution, the duration of time to complete it gives the filtration time.
Nr = 1.5rev/min from specification
Therefore,
= 1.5 rev/min x 1 rev = 1.5min
= 40 s
Pick-up Zone Time,
Angle subtended in the pick-up zone is 160 degrees = 2.79 rads
Hence s = 2.79rads
/ss
= 2.79 / 0.157 = 17.77 s
Drying Time,
Angle =148°
d = 2.58 rads
d = 2.58 / 0.157 = 16.43 s
Cake Removal Time,
Angle =40°
c = 0.7 rads
48
d = 0.7 / 0.157 = 4.459sec
Dead Region under slurry,
rcds --- (28)
40 = 17.77+16.43+4.459+τr
r = 1.341sec
Air Suction in Rotary Drum Filter (Albright LF, Albright’s Chemical Engineering Handbook,
2008)
Volume of air per hour is given by
w
MV
as
ac
a
2
---(29)
Where
Mc = weight of dry cake per unit time
= viscosity of liquor
a = viscosity of air
a = fraction of total surface available for air suction
s = fraction of total surface submerged into the slurry for material pick-up
W = Mass of dry-cake solids per unit volume of filtrate (kg/m3)
/ = 0.6 (Peter, Timmerhaus)
w = 4511.03 kg/m3 a = 0.0000186Pa.s
Mc = 201.65 kg/hr a= 0.1
=0.0115pa.s s = 0.444
Therefore
49
w
MV
as
ac
a
2
m3/hr
Estimated Horsepower required for the vacuum pump on the filter
A vacuum pump must be supplied for the operation of a rotary vacuum filter. Since air leakage
into the vacuum system may supply a major amount of the air that passes through the pump,
design method for predicting air suction rates are approximation, as they do not account for
air leakage.
Theoretical horsepower for isentropic single-stage compression
1)/
1
1003.3)( /)1(
12
11
5
kkfmPP
K
qkPxhpPower ---(30)
Where;
P1=vacuum pump intake pressure
P2=vacuum pump delivery pressure
qfm1 = volumetric flow rate at vacuum-pump intake conditions (m3/hr)
∆P=10 .9psi
k=1.4
P1= (14.7 – 10.9) x 144 = 547.7 psf
P2==14.7 x 144 = 2116.8 psf
Mc =201.65 kg/hr =444.56/hr
qfm1= min/91.22757.547
8.2116444.56
1
2 ftx
x
P
PM c
Thus,
1)/1
1003.3)( /)1(
12
11
5
kkfmPP
K
qkPxhpPower
Power (hp) = hpxxxx
63.014.1
)1)7.547/8.2116((9.227.5474.11003.3 )4.1/14.1(5
The power requirement is; Hp = 0.63hp = 0.468kw.
5.0.6 MECHANICAL DESIGN
The following assumptions are made during Mechanical Design of the filter;
1. The filter drum and shaft are of homogeneous material.
50
2. Shear stress is constant throughout the drum and shaft.
3. Pulley system has negligible friction and thermal generation.
5.0.6.1 Pulley System The pulley system consists of two pulleys;
Driver pulley
Driven pulley The pulley diameters are set as;
Diameter of driven pulley = 800 mm
Diameter of driver pulley = 200 mm
Consider the pulley mechanical system design;
1) Velocity Ratio transmitted by the pulleys, VR
V.R.= 25.0800
200
2
1
1
2 r
r
n
n
2) Length of belt, L
C
DDCDDL
42
2
2
1212
---(31)
Where C=distance between the pulley centers=1.2m
L= mx
x 0.42.14
)2.08.0()2.12()2.08.0(2/
2
3) Angle of Contact, θ
Larger Pulley:
rad
C
DD 121
---(32)
Smaller Pulley:
rad
C
DD 122
And upon substitution, the following angles of contact are obtained;
51
1 = 2.642 radians
2 = 2.308 radians
4) Peripheral Speed of the Belt, V
V = 11 81.660
6502.0
60
msxxND
5) Maximum Belt Tension, T
1
2
1
e
T
T---(33)
Where,
T1 = tension on the tight side of the belt, N
T2 = tension on the slack side of the belt, N
1 = Angle of contact in radians
= Coefficient of friction (0.2)
7.1642.22.
2
1 xeT
T But,
N
VxhpxT 39.1772
7.1181.6
7.1450026.4
)7.11(
7.1500,41
NT
T 58.10427.1
12
6) Torque acting on shaft, TS
Torque acting on shaft,
Ts = NmV
N58.466
810.6
43.3177
7) Drum Design
i) Drum thickness
Drum diameter, D = 2 .16m
52
Drum length, L = P
At
Where At= total area=27.09 m2
P= drum circumference=6.786 m
Therefore, on substitution;
L=3.99 m
The drum thickness is set at 20 cm (0.2 m).
Do =2.16m
Di = 1.96m
ii) Torque on Drum, TD
T0 = NmdT is 25.457
2
96.158.466
2
8) Cake Discharge System
The cake discharge system will consist of a screw conveyor with a diameter of 25 mm, and a
length of 2.5 m. The cake discharge system will be a Scraper discharge system.
5.0.7 SUMMARY OF ROTARY DRUM FILTER DESIGN
Table23 Summary of rotary drum filter design
Chemical design Value
Rate of cake formation 266.79Kg/s
Filtrate Volumetric Flow 0.043m3/s
Filtration area 27.09m2
Drum submergence H 1.86m
Volume of air sucked into the filter 1.86m3/hr
Total filtration time 40seconds
53
Pick-up zone time 17.77seconds
Drying time 16.43seconds
Cake removal time 4.46seconds
Time in dead region 1.34seconds
Mechanical Design Values
Drum diameter 2.78m
Drum length 4m
Diameter of driven pulley 0.8m
Velocity ratio transmitted by the pulleys 0.25
Diameter of driven pulley 0.2m
Shaft diameter 12mm
Torque acting on drum 457.25
Angle of contact between belt and large pulley
2.642
Angle of contact between belt and small pulley
2.308
Peripheral speed of belt 17.6m/s
Tension acting on the tight side of the belt 1722.39N
Tension acting on the slack side of the belt 1042.58N
54
5.1 DESIGN OF A PNEUMATIC DRYER/FLASH DRYER BY EVANS AKAKA -
CPE/1005/08
5.1.1 INTRODUCTION
Drying is the removal of water, or other volatile liquids, by evaporation. Most solid materials require
drying at some stage in their production. The choice of suitable drying equipment cannot be
separated from the selection of the upstream equipment feeding the drying stage.
Drying is carried out for one or more of the following reasons:
1. To reduce the cost of transport.
2. To make a material more suitable for handling as, for example, with soap powders, dye stuffs and
fertilizers.
3. To provide definite properties, such as, for example, maintaining the free-flowing nature of salt.
4. To remove moisture this may lead to corrosion.
5.1.2 PNEUMATIC / FLASH DRYING
General description
A pneumatic-conveyor dryer consists of a long tube or dryer duct carrying a gas at high velocity, a
fan to propel the gas, a suitable feeder for addition and dispersion of particulate solids in the gas
stream, and a cyclone collector or other separation equipment for final recovery of solids from the
gas.
Feeding system
The solids feeder may be of any type; screw feeders, venturi sections, high-speed grinders, and
dispersion mills may be employed. Selection of the correct feeder to obtain thorough initial
dispersion of solids in the gas is of major importance.
Fan system
Fans may be of the induced-draft or the forced-draft type. Dust and hot gas will not be blown out
through leaks in the equipment.
Dryer duct system
Dryer duct system ensures complete drying after thorough dispersion of lumps and agglomerates. If
disintegration is required to disperse the wet feed, the stages can be reversed, or disintegration can be
employed in both stages e.g. drying synthetic resins, of which low-pressure polyethylene and
polypropylene are examples.
55
Final recovery of solids from gas system
Cyclone separators are preferred for low investment.
If maximum recovery of dust or noxious fumes is required, the cyclone may be followed by a wet
scrubber or bag collector.
In ordinary heating and cooling operations, during which there is no moisture pickup, continuous
recirculation of the conveying gas is frequently employed. Also, solvent-recovery operations
employing continuously re circulated inert gas with inter condensers and gas reheaters are carried out
in pneumatic conveyors.
Salient features of pneumatic drying include:
1. Suitable for materials which are granular and free-flowing when dispersed in the gas stream, so they
do not stick on the walls or agglomerate.
2. Contact times are short, and this limits the size of particle that can be dried (0-5) seconds.
3. The thermal efficiency of this type is generally low.
Pneumatic conveyors may be single-stage or multistage. Single stage is employed for evaporation of
small quantities of surface moisture.
Multistage installations are used for difficult drying processes, e.g., drying heat-sensitive products
containing large quantities of moisture and drying materials initially containing internal as well as
surface moisture.
5.1.3 DESIGN PROCEDURE
1. Determination of
2. Estimation of evaporated water through material balance
3. Determination of enthalpies of the process. I.e. net heat and steady state dryer heat requirement.
4. Obtain the heat transfer area.
5. Estimate the natural gas consumption.
6. Sizing the drying-gas preparation unit
7. Dryer sizing.
8. Sizing exhaust gas unit.
9. Estimation of required residence time
56
10. Design of the cyclone.
5.1.4 DESIGN METHODS
The equation recommended for calculation of the air-outlet temperature is
This approach is adopted in order to be relatively safe. for flash dryers is often chosen to
guarantee a desired product-moisture content; a large exit driving force is often mandatory to obtain
the desired process result in a short time.
A factor of 1.2 allows for the steady-state heat losses for flash/ pneumatic drying.
Assumptions made:
1. The ambient temperature is 10°C.
2. = temperature of feed = 20°C.
3. = exit temperature of the product.
Basic data
Potato starch - 100μm spheres, =1500 kg/m3, =0.15 W/m/K, =1.01504 Kg
-1.K
-1
Air – μ= , W/m/K
Water -feed T=20oC, A1=35% Wt
-Product T=60oC, A2=15% Wt
Ambient air -T=10oC, R.H=60%
5.1.5 DESIGN EQUATIONS USED.
5.5.1.1. DRYING UNIT
Gas flows and gas powder
1. Air flow to the dryer
---(35)
57
1.05 = specific heat of air in Kj.kg-1
.K-1
(mean, 0-60) oC
1.25 = specific mass of air in kg/m3 @10
oC and atmospheric pressure.
2. Air specific mass at atmospheric pressure
3. Power consumption of the fan conveying the air to the dryer
4. Air leaving the dryer
, f= attraction of ingress air.
5. Gas flow removed by exhaust fan
---(39)
6. Specific mass of steam at and atmospheric pressure
---(40)
7. Power consumption of the fan removing the gas from the drying system
---(42)
8. Thermal degree of utilisation of the flash dryer
T1= inlet hot air temperature
58
T2= outlet moist air temperature
Material balance (kg/hr)
Where
= water flow leaving the dryer =
= water flow to the dryer =
Cap= product mass flow = 165.393 kg/hr
A2= Product moisture content = 15%
A1= Feed moisture content = 35%
Sol= dry solids flow =
= dry water evaporation load =
Table 24: mass balance around the flash dryer
Component In out
Solids 165.39 165.39
Water 89.05 29.19
Evaporated water 0 59.86
Total 254.44 254.44
Heat Balance
59
The relationship between and is such that when varies from 100 to 1000oC
The heat transferred in the dryer from the air to the process stream is the net heat. Heat is also
transferred from the air in other directions, but that heat is not taken into account at the moment.
The enthalpy of the process stream changes due to this transfer. This enthalpy change consists of
three parts:
1. The evaporation of the water and the heating of the water vapor
2. The heating of the solid
3. The heating of the water remaining in the product
Expressed quantitatively in the same order, we have
20oC is taken as the reference temperature.
Where - 2500 is the heat of evaporation of water at 20oC in Kj/kg
- 1.9 is the specific heat of steam in Kj.kg-1.K-1
- 4.2 is the specific heat of water in Kj.kg-1.K-1
Net heat
60
Where d = constant steady state heat loss for a flash/pneumatic dryer = 1.2
Heat transfer
Heat transfer is analogous to mass transfer. The results obtained were used to obtain a Nusselt
correlation:
---(45)
If the medium around the sphere is stagnant, Re = 0, and the correlation degrades to Nu = 2. This is
the Nusselt number for the heat transfer due to conduction. The heat transfer coefficient in the
flash dryer will be calculated by the above equation.
Assumptions
The gas surrounding the particles is air
Spherical particles fall through stagnant air with their terminal velocity, .
The Reynolds number falls between (2 to 800) in flash drying
RA=air specific mass = 0.84
V= velocity of gas = 1.0 m/s
=diameter of the particle= m
=
61
---(46)
=air specific heat at constant pressure = 1000
=gas thermal conductivity = 0.0355
Overall heat transfer coefficient estimation, U
Logarithmic mean temperature difference (LMTD)
Heat transfer area
---(47)
Natural gas data
Composition: 85% by volume of methane, 15% by volume of nitrogen
Methane heat of combustion: 804 kJ /mol
0.80 kg/nm3. It is assumed that the dried-product temperature is 30K lower than the gas-exit
temperature. The product is not recycled.
KJ per kg of evaporated water =
62
Due to start up, shut down, and cleaning, for example, the long term consumption figure is probably
a factor of 1.5 higher:
Dew – point exhaust gas (oC)
Amount of heat transferred in the combustion chamber = 306, 596.32 Kj/hr
Required methane flow =
Natural gas consumption =
Secondary air mass flow = 2,085.68-1,661.8
= 423.89 Dry air = 422.304 kg/hr
= 1.696 kg/hr
Ingress air into the dryer amounts to 20% f that amount of gases from the combustion chamber.
Dry air = 415kg/hr
= 2 kg/hr
Table 25: mass balance of air
Process flow Dry Water Total
Combustion 1462.7 199.1 1661.8
Secondary air 422.304 1.696 424
Ingress air 415 2 417
Evaporation 0 59.87 59.87
Total 2300.004 262.666 2562.67
Water content =
Exhaust gases must be cooled from 150oC to 60.5oC
63
5.5.1.2 SIZING DRYING-GAS PREPARATION UNIT
Gas mass flow from combustion chamber = 2,085.68 kg/hr
The gas mass flow to the combustion chamber is approximately equal to this gas mass flow.
5.5.1.3 DRYER SIZING
The gas flow leaving the dryer is considered. The upward gas flow, excluding water vapour is
2,300.004 kg/hr. The composition is approximately equal to the composition of dry air.
Upward water vapour flow: 262.666 kg/hr
The gas velocity in a flash dryer ranges between (10-30) m/s.
Use a gas velocity of 20 m/s.
The ratio of drying height to that of the drying diameter is 25:1
64
5.5.1.4 SIZING EXHAUST GAS UNIT.
Area passed through the dryer per hour
Required residence time in the dryer
5.5.1.5 CYCLONE
Design equations
Calculation of cyclone diameter,
Calculation of friction loss factor,
Where K= 7.5(if neutral inlet is present) & 16(if neutral inlet is absent)
a=0.5 DC
b=0.2 DC
65
Calculation of pressure drop
5.1.5 MECHANICAL DESIGN
The most important characteristics to be considered when selecting a material of construction are:
(Coulson and Richardson’s Chemical Engineering Vol. 6)
1. Mechanical properties:
- Strength-tensile strength.
- Stiffness-elastic modulus (Young’s modulus).
- Toughness-fracture resistance.
- Hardness-wear resistance.
- Fatigue resistance.
- Creep resistance.
2. The effect of high and low temperatures on the mechanical properties.
3. Corrosion resistance.
4. Any special properties required; such as, thermal conductivity, electrical resistance, magnetic
properties.
5. Ease of fabrication forming, welding, casting.
6. Availability in standard sizes plates, sections, tube.
7. Cost
Material of construction chosen for this project will be SA-516 stainless steel on product contact
parts and on the outside parts.
Cylindrical shell part
66
Wall thickness cone part
---(54)
The thickness of the chamber can be given by the following relationship:
Given the following data: (Surface production operations, VOLUME 2, pg 331- pg 336)
We can calculate the thickness of the chamber as follows:
67
5.1.6 SUMMARY OF THE VARIOUS PARAMETERS CAN BE WRITTEN AS BELOW:
Table 26: summary of flash dryer design
Parameter Dimension
Residence time 2 seconds
Dryer duct diameter 0.21 m
Dryer tube length 5.25 m
Diameter of cyclone 1.6 m
Height of cyclone 6.8 m
Thickness of chamber 21 mm
FD power consumption 2.3 KW
ID power consumption 3.6 KW
68
5.2 DESIGN OF SPRAY DRYER BY EDWIN MUTUA - CPE/17/08 .
5.2.1 INTRODUCTION
Drying is the removal of water, or other volatile liquids, by evaporation. Most solid materials require
drying at some stage in their production. The choice of suitable drying equipment cannot be
separated from the selection of the upstream equipment feeding the drying stage.
In a spray drying system the food, powder or particles, is continuously dried in a vertical duct while
being conveyed by the heated air one or more cyclones are used to separate the dried material from
the exhaust air small particle sizes (less than 2 mm) and concurrent operation allow the use of
relatively air temperatures without overheating the product.
If the product separates from the air at the bottom of the conical chamber, it is removed through a
auger .It is common to product to remain entrained in the air stream, so cyclones are used to recover
the product.
Reasons for drying
5. To reduce the transport cost.
6. To make a material more suitable for handling as, for example, with soap powders, dye stuffs and
fertilisers.
7. To provide definite properties,required density etc.
8. Moisture removal which may lead to corrosion.
They are different Airflow patterns: concurrent, counter current, mixed. Recommended of higher
efficiency is concurrent as designed below.
5.2.2 GENERAL DESCRIPTION
A spray dryer consists of an atomizer which spreads and atomizes the slurry from the upper side of
the dryer chamber. While hot air comes from the downward side of the chamber to dry the atomized
slurry.
Fan system
Fans may be of the induced-draft or the forced-draft type. Dust and hot gas will not be blown out
through leaks in the equipment.
Dryer duct system
Dryer duct system ensures complete drying after thorough dispersion of lumps and agglomerates. If
disintegration is required to disperse the wet feed, the stages can be reversed, or disintegration can be
employed in both stages.
69
Final recovery of solids from gas system
Cyclone separators are preferred for low investment.
If maximum recovery of dust or noxious fumes is required, the cyclone may be followed by a wet
scrubber or bag collector.
In ordinary heating and cooling operations, during which there is no moisture pickup, continuous
recirculation of the conveying gas is frequently employed. Also, solvent-recovery operations
employing continuously re circulated inert gas with inter condensers and gas reheaters are carried out
in pneumatic conveyors.
Suitable mostly for;
4. Suitable for materials which are granular and free-flowing when dispersed in the gas stream, so they
do not stick on the walls or agglomerate.
5. Contact times are short, and this limits the size of particle that can be dried.
6. The thermal efficiency of this type is generally low.
Multistage installations are used for difficult drying processes, e.g., drying heat-sensitive products
containing large quantities of moisture and drying materials initially containing
internal as well as surface moisture.
5.2.3 DESIGN PROCEDURES.
Basis of operation;1 hour
Design aspects considered;
Atomizer type and general design
Flow rate of drying air
Solid and air operating velocity in the chamber
Residence time
Chamber dimensions
Parameters considered for the design;
Slurry to be dried from 82% to 15% moisture content.
Temperature of inlet solid=500c
Temperature of outlet solid =650c
Drying air inlet temperature=1500c
Drying air outlet temperature=1200c
Slurry feed rate=2100kg/hr
5.2.4 ATOMIZER SELECTION AND DESIGN
70
Considering the various disk atomizers the following specifications were selected;
Type of disk atomizer:35 cm
Rotational speed:65000 rpm
Peripheral speed:10,000m/min
Mean particle size:100 microns
Design
Assumed mean particle size=100 microns
Feed rate = (1+0.82)*2100=3822Kg/hr ---(56)
Peripheral speed versus Mean particle size with feed rate as constant parameter (Ref Herring and
Marshall Chart, Vol 12).
Having a drop size: 100 microns
Feed rate: 140Ibs/min
Interpolating we get the rpm=750ft/sec or 24600rpm.
Hence the disk type selected;
Disk type =B-1
Diameter=0.59 ft
Vane height=0.406
Vane length =1m
No of vanes=60
(Ref Study of disk atomization, Alder and Marshall).
Getting the power;
P=1.02 * 10-8 *F *(N*D)2
---(57)
Where; N-rotational speed in rpm=24600
D-radious of disk atomizer ft=0.59
F-feed rate in Ib/min=140Ib/min
Calculating we get; Power in Hp=300.82 Hp
71
5.2.5 CHEMICAL DESIGN
SPRAY CHAMBER
Where:
Gs=air flow rate ,
Ls=slurry flow rate
Y1=humidity of entering air
Y2=humidity of outlet air
T1 and T2 =air temperatures
t1 and t2 =solid temperatures
X1 and X2 slurry moisture and powder respectively
Mass balance;
LsX1 +GsY1=LsX2+GsY2 ---(58)
Enthalpy balance;
LsHl1 +GsH1=LsHl2+GsH2 ---(59)
Where
Hl1=enthalpy of entering solid
Hl2=enthalpy of exit solid
H1=enthalpy of entering air
H2=enthalpy of exit solid
Equations for the enthalpies;
Hl1= (Cps+X1Cpw)*t1---(60)
Hl2= (Cps+X2Cpw)*t2 ---(61)
Gs H1 T1 Ls Hl1 t1
Gs H2 T2 Ls Hl2 t2
72
H1= (CPA+Y1Cpv)*T1+Y1ƛ ---(62)
H2= (Cpa+Y2Cpv) +Y2ƛ ---(63)
Where;
Cps =specific heat of potato powder=3.43KJ/KgoC
Cpw=specific heat of water=4.2 KJ/KgoC
Cpv=specific heat of water vapour=1.89 KJ/KgoC
Cpa=specific heat of air =1.0312 KJ/KgoC
ƛ=latent heat of evaporation=2510.7 KJ/Kg
(Ref Engineering Toolbox, Design of chemical equipments; vol 3).
Calculating and getting the values as below;
Hl1=343.7 KJ/Kg, Hl2=227.05 KJ/Kg, H1=1328.2 KJ/Kg,H2= KJ/Kg
Doing the enthalpy and mass balance simultaneously we get;
Gs=200Kg/hr and Y2=0.73.
Evaporation rate of water=(0.82-0.15)*2100=1407Kg/hr.Taking efficiency as 90% then;
Net water evaporation=
Moisture removed=(0.73-0.42)=0.31
Gs=1563/0.31=5041kg/hr
Humid volume(VH)=
Where;
Ma=molecular weight of air=29g/mol
Mw=molecular weight of water=18g/mol
Tg=average temperature of air=135oC
P= Pressure in N/M2
Hence calculating VH=1.9214 m3/Kg
Operating velocity
For non-dusting dryers;
73
Operating velocity= 2*settling velocity
Vs =
In stokes law.
Calculated data:
-density of slurry=1705Kg/m3
-density of water=1000 Kg/m3
-density of potato puree particles=(82*1000 + 18*1705)/100=1126.9 Kg/m3
-density of air at average temperature=0.865 Kg/m3
-viscosity of at an average temperature=23.329 *10-6
N/M
Substituting in the stokes equation we get Vs=0.3078 m/s
Va=2*Vs=0.6156m/s
5.2.6 MECHANICAL DESIGN
The most important characteristics to be considered when selecting a material of construction are:
(Coulson and Richardson’s Chemical Engineering Vol. 6)
8. Mechanical properties:
- Strength-tensile strength.
- Stiffness-elastic modulus (Young’s modulus).
- Toughness-fracture resistance.
- Hardness-wear resistance.
- Fatigue resistance.
- Creep resistance.
9. The effect of high and low temperatures on the mechanical properties.
10. Corrosion resistance.
11. Any special properties required; such as, thermal conductivity, electrical resistance, magnetic
properties.
74
12. Ease of fabrication forming, welding, casting.
13. Availability in standard sizes plates, sections, tube.
14. Cost
Material of construction chosen for this project will be SA-516 stainless steel on product contact
parts and on the outside parts.This due to resistant in corrosion and also a relative high tensile
streghnt.
Getting the column diameter;
Column area=(Gs *Vavg)/Va---(66)
=
=2.67m2
Diameter,Dc=
=3.398 m---(67)
Assuming a 15% safety;
=1.15*3.398=3.907 m approx 4 meters.
Getting chamber dimensions;
Total volume(Vt)=Gs*Vavg*Td
Td=50( ) this getting residence time.(Ref.Brown et al Unit Operations).
=4.5 seconds
Vt= *1.9214*4.5=12.107 m3
Height of cylindrical part=Vs*Ѳp
Ѳp=time required for evaporation
Ѳp=ƛWρX1Dp2/12KfΔTt ---(68)
ΔTt=Tavg-tavg=135-57.5
=77.5oC
Where;
Ρ-density of feed=705 kg/m3
75
ƛ-latent heat of evaporation at normal boiling point=2256Kj/Kg
Kf=thermal conductivity of air at average temperature=0.033925Watt/m/k
(Ref Unit operations in Food processing vol. 2).
Substituting and calculation we get;
Ѳp=3.5 seconds less than (drying time) Td .Therefore design acceptable.
Height of cydrical part=0.6278*3.5=2.19 meters
Height of cyclone part=0.6*Dc=0.6*3.398=2.0388 meters
Height of cone=
---(69)
Getting volume of cone, Vc= t-
Hence, Vc=11.107 m3
Hcone=3*4*11.107/π*3.3982
=3.674 meters
Angle of cone;
Tan( )=3.398/2*3.674
=130
Thickness of chamber;
Stainless steel available has a thickness of 0.25 inch. Head and well are under same stress ,so we can
assume the same thickness for both (Ref Wet milling Industries,V0l 2).
Dust Collector design;
Outlet area of dust collector;-
Ad=Ls/ρVs
=(2100)/(1126*0.3078)=6 m2
Diameter of dust collector;-
Dd= =2.7 meters
Legnht of Dust collector;-
Ld=Dd/8=0.3375 meters
76
Hot air inlet;
Air operating velocity assumed as =10m/s
Minimal crossection area=(Gs*Vavg)/Vair
We know contamination of outlet air with fine particles requires a higher crossectional area for outlet
duct than that of inlet duct, (Ref Engineering Toolbox).
A rectangular duct having length to breadth ratio as =1.2:1(FGRE dryers, Vol 1).Therefore we shall
have the following specifications;
Area of inlet pipe=1.2*(breadth)
Breadth of inlet duct=0.2517 meters
Length of inlet duct=0.3020 meters
5.2.7 SUMMARY OF DESIGN DATA
Table 27: Summary of the spray dryer design
Parameters Dimensions
Power required for atomization 300.81 Hp
Residence time 4.5 seconds
Angle of cone 130
Height of cone 3.674 meters
Diameter of cone 3.398 meters
Height of cylindrical part 2.19 meters
Thickness of chamber 0.25 inches
Air operating velocity 10m/s
Slurry atomization velocity 0.6156m/s
77
Chapter 6: PROCESS CONTROL AND INSTRUMENTATION
6.0 INTRODUCTION
A process can be defined simply as a set or series of orderly physical or chemical transformations in
which a raw material/ reactant is altered into a desired state. It forms a set of production or processing
functions executed in and by means of process hardware such as tanks, pipes, fittings, motors, shafts,
couplings, measuring devices, etc.
The plant's overall objective is to convert certain raw materials (input feedstock) into desired
products using available sources of energy, in the most economic way. During its operation, a
chemical plant must satisfy several requirements imposed by its designers and the general technical,
economic and social conditions in the presence of ever-changing external influences (disturbances).
The conditions governing the operation of the plant are known as process variables, it is these
variables that are monitored and controlled according to predetermined values. These can be further
classified into the following categories:
a) Energy variables
Variables influenced by the energy state of the material. They include temperature, pressure,
electricity, sound and radiation.
b) Quantity and Rate Variables
These depend on the quantity and flow rate relations of process component under scrutiny. They
include volumetric flow rate, mass flow rate, liquid level, mass and speed.
c) Chemical and Physical Variables
These heavily rely on the physical and chemical characteristics of the process materials. They include
density, humidity, moisture content, viscosity, calorific value, colour, chemical absorption, PH.
6.1 OBJECTIVES OF PROCESS CONTROL
Process control is employed to achieve one or more of the following objectives:
1. Maintaining the stability of the process.
2. Optimizing the performance of the plant as designed.
3. Suppressing the interference of external disturbances.
4. Ensure safe plant operation at all times.
5. Maintain the design parameters for optimal plant operation
78
6.2 PROCESS CONTROLS
The control of process variables in the plant is achieved by use of pneumatic valves and other
associated components such as transducers and sensors. The process controllers employed in the
three plants include:
6.2.1 Flow Controllers (FC)
These consist of flow meters (liquid and gas) which measure, report and record fluctuating flow
variables for the necessary counter action to be taken.
E-16
E-18
E-17
FT FC
Figure 1: Flow Control from the blancher to the holding tank
6.2.2 Temperature controller (TC)
Various thermal sensitive instruments are used to regulate this parameter; they may be thermostats,
thermocouples or digital thermometers. These transmit temperature data to controllers which then
regulate the amount of steam or cooling water supplied to the equipment in question.
79
E-26
S-33
TC
TT
S-32
Figure 2: temperature control used to control the temperature of the fryer
6.2.3 Level controller (LC)
These simply detect rising levels of fluids in holding vessels and prevent spillage upon attaining the
maximum capacity.
E-4LT
LC
S-13
Figure 3: Level controller used to control the level of mashed potato
80
CHAPTER 7: ECONOMIC AND PROFITABILITY ANALYSIS
7.0 INTRODUCTION
Profitability is generally defined as the measure of the amount of profit that can be obtained from a
given venture. It is important to determine the profitability of any business venture before fully
establishing it. An acceptable plant design must present a process that is capable of operating under
conditions which will yield a profit.
Before any estimation, the expected plant operation specifications must be set out. Therefore, for this
particular design problem, the basis is set as follows.
7.0.1 Plant Development Timeline
Expected Dates
Commencement of construction : January 2014
Completion of construction: December 2015.
Commencement of operation: January 2016.
7.0.2 Plant Operation Specifications
Daily Operation Time: 24 hrs
Number of shifts: 3
Weekly Operation Time: 6 days with every 7th
day used for equipment cleaning and maintenance.
7.0.3 Plant Rate of Production
From the above operation specifications, the plant output is expected to have a total productive time
of 300 days a year which translates to the following individual product outputs.
Name of Material Annual production(tonnes)
Potato starch 1406.14704
Potato chips 8791.992
Potato puree 7612.0452
Table 28: Production rate of the plant
81
Factors Affecting Investment and Production Costs
Equipment cost
Price fluctuations
Company policies
Rate of production and operating time
Government policies
7.1 ESTIMATION OF CAPITAL COSTS
7.1.1 Capital Investments
Capital Investments can be classified as
7.1.1.1 Fixed Capital Investment (FCI)
It is the capital needed to supply necessary manufacturing and plant facilities. Fixed capital is the
total cost of the plant ready for start-up.
It includes direct cost and indirect cost.
Direct costs
Purchased equipment
Purchased equipment installation
Piping
Electrical equipment and materials
Buildings
Yard improvement
Service facilities: - Utilities e.g. steam, water.
Facilities e.g. electricity
Non-process equipment e.g. office furniture
Distribution and packing
Land
Indirect costs
Engineering and supervision
Construction expenses
Contractor’s fee
82
Contingency
7.1.1.2 Working Capital
This is the capital required for the operation of the plant. It includes:
Start-up.
Raw materials and intermediates in the process.
Finished product inventories.
Funds to cover outstanding accounts from customers.
Working Capital has been taken as 10% of the FCI.
7.1.1.3 Total Capital Investment
This is the sum of the Fixed Capital Investment (FCI) and the Working Capital (WC)
7.1.1.4 Estimation of the cost of purchased equipment
To determine the capital investments, the percentage of delivered equipment cost method was used.
Before the plant is fully operational, all the necessary equipment components must be purchased and
installed.
The costs were obtained from:
Chemical Engineering Design, practice and economics of plant and design.
The base year used is 2006.
The formula is used where:
= purchased equipment cost $
a& b= cost constant
S = size parameter
n = index
Marshall and Swift Equipment Cost Indexes
2006 = 499.6
2011 = 585.7
83
Cost Estimation factor
84
Table 29: Estimation of the cost of purchased equipment
85
Equipment a b S n C
CURRENT
COST
Current Cost
(US $)
No.
Required Total cost (US $)
rotary washer -2500 200 250.00 0.6 2992.80272 3508.575963 3508.57596 1 3508.575963
vibratory mesh 100 120 5.00 2 3100 3634.247398 3634.2474 1 3634.247398
Rasper 3000 390 4000.00 0.5 27665.7657 32433.6249 32433.6249 1 32433.6249
water sprayer -400 230 150.00 0.6 4249.2467 4981.552826 4981.55283 1 4981.552826
moving sieve 23000 575 10.00 1 28750 33704.71377 33704.7138 1 33704.71377
hydro cyclone -10000 600 124200.00 0.6 673320.119 789358.6744 789358.674 1 789358.6744
rotary vacuum filter -45000 56000 180.00 0.3 220931.497 259006.3608 259006.361 1 259006.3608
flash dryer -7400 4350 180.00 0.9 458437.57 537443.7244 537443.724 1 537443.7244
storage tank 53000 2400 100.00 0.6 91037.4366 106726.6346 106726.635 1 106726.6346
steam peeler -15000 560 114000.00 0.6 590802.328 692619.9428 692619.943 1 692619.9428
Chipper -15000 114000 560.00 0.6 5064461.44 5937259.935 5937259.94 1 5937259.935
Blanching bucket
conveyor 14000 1450 100.00 1 159000 186401.7214 186401.721 2 372803.4428
blanching hot water
sprayer -400 230 15.00 0.6 767.83797 900.1655307 900.165531 2 1800.331061
belt dryer -5300 24000 15.00 0.5 87651.6003 102757.2904 102757.29 1 102757.2904
frying pan -5300 24000 15.00 0.5 87651.6003 102757.2904 102757.29 1 102757.2904
frying conveyor 23000 575 10.00 1 28750 33704.71377 33704.7138 1 33704.71377
defatting vibrator -5300 24000 15.00 0.5 87651.6003 102757.2904 102757.29 1 102757.2904
freezing conveyor 23000 575 500.00 1 310500 364010.9087 364010.909 1 364010.9087
freezing fan 4200 27 200.00 0.8 6071.49108 7117.838918 7117.83892 1 7117.838918
bucket elevator 14000 1450 35.00 1 64750 75908.8771 75908.8771 1 75908.8771
surge tank 5700 700 10.00 0.7 9208.31064 10795.25128 10795.2513 1 10795.25128
hammer mill 400 900 20.00 0.5 4424.92236 5187.504055 5187.50406 1 5187.504055
spray dryer -5300 24000 15.00 0.5 87651.6003 102757.2904 102757.29 1 102757.2904
storage silo 5700 700 4000.00 0.7 238262.686 279324.3694 279324.369 1 279324.3694
centrifugal flow fan 4200 27 5000.00 0.8 28777.6167 33737.08992 33737.0899 3 101211.2698
86
axial flow fan 4200 27 5000.00 0.8 28777.6167 33737.08992 33737.0899 1 33737.08992
centrifugal pump 8400 3100 132.00 0.6 66437.1467 77886.78301 77886.783 5 389433.9151
Conveyor 23000 575 10.00 1 28750 33704.71377 33704.7138 3 101114.1413
TOTAL 10587856.8
87
Estimation of Fixed Capital Investment
Direct costs % Purchased
Equipment cost Cost($)
Purchased Equipment cost 100 10,587,857
Equipment Delivery cost 10 1,058,786
Delivered Equipment Cost(ID)
11,646,642
% Delivered
Equipment cost Cost($)
Purchased Equipment Installation 39 4,542,191
Insulation 56 6,522,120
Instrumentation and Control 26 3,028,127
Piping 31 3,610,459
Electrical Installation 10 1,164,664
Yard Improvement 10 1,164,664
Service Facilities Installed 55 6,405,653
Land 6 698,799
Total Direct Costs
50,429,962
Indirect Costs
% of Fixed Capital
Investment Cost($)
Table 30: Fixed capital cost estimates
88
Engineering and Supervision 4 3,955,291
Contractor's cost 15 14,832,342
Contingencies 8 7,910,582
Startup expense 15 14,832,342
Construction cost 7 6,921,759
Total Indirect costs (49%) 49 48,452,316
Total FCI($)
98,882,278
Total Capital Investment estimates
% of TCI Cost($)
Total FCI 90 98,882,278
Working Capital (10 % of TCI) 10 10,986,920
Total Capital Investment($) 109,869,198
9.2.2 Total Product Cost
This is the cost involved in the manufacture of goods and sale of products. It can be
estimated on one of the three bases:
Daily basis
Unit-of-product basis
Annual basis
The annual basis is chosen for the calculation of the total product cost because it
smoothes the effect of seasonal variations.
TPC is divided into:
Direct production costs
Raw material cost
Utilities cost
Operating labour
Direct supervisory and clerical labour
Table 30: Total capital cost estimates
89
Maintenance and repair
Laboratory charges
Fixed charges
These are costs not affected by the level of production and include
Depreciation
Local taxes and insurances
Plant overhead costs
Rent
General expenses
These are costs associated with management and administrative activities not directly
related to the manufacturing process. They include:
Administration cost
Ware housing
Distribution and marketing costs
Research and development
Name of Material Price,
$/kg
Annual
Amount,
million kg/yr
Annual raw
materials cost,
million $/yr
Potato 0.27 20.00 5.4
Total annual cost($) 5.4
Utilities % of FCI Cost($)
Electricity 1.3 1285469.61828
Fuel 0.1 98882.27833
Waste disposal 1.5 1483234.17494
Steam saturated 3 2966468.34988
Raw material storage 0.5 494411.39165
Finished product storage 1 988822.78329
Safety installations 0.4 395529.11332
Total Utilities cost($) 7712817.70970
Table 31: Annual raw materials cost estimates
Table 32: Utilities cost estimates (annual)
90
Depreciation
Depreciation is calculated using the Declining Balance (or fixed percentage method).
Annual depreciation cost is a fixed percentage of the property value at the beginning of
a particular year.
The fixed percentage (or declining balance) factor remains constant throughout the
entire service life, while the annual cost for depreciation is different each year.
If f = fixed percentage factor = 0.1
Dep. Cost for first year = V f .Asset value at the end of n years (service life)
In practice, many times, the fixed percentage factor f is chosen arbitrarily, by
experience.
Depreciation is gotten by;
Va = V (1-f)n
V= total FCI-land, n= 20 years
Table 33: Depreciation estimation
double declining method
F 0.10
V Va D
1 98,183,480 88,365,132 9,818,348 9.818348
2 88,365,132 79,528,619 8,836,513 8.836513
3 79,528,619 71,575,757 7,952,862 7.952862
4 71,575,757 64,418,181 7,157,576 7.157576
5 64,418,181 57,976,363 6,441,818 6.441818
6 57,976,363 52,178,727 5,797,636 5.797636
7 52,178,727 46,960,854 5,217,873 5.217873
8 46,960,854 42,264,769 4,696,085 4.696085
9 42,264,769 38,038,292 4,226,477 4.226477
10 38,038,292 34,234,463 3,803,829 3.803829
11 34,234,463 30,811,016 3,423,446 3.423446
12 30,811,016 27,729,915 3,081,102 3.081102
13 27,729,915 24,956,923 2,772,991 2.772991
14 24,956,923 22,461,231 2,495,692 2.495692
15 22,461,231 20,215,108 2,246,123 2.246123
16 20,215,108 18,193,597 2,021,511 2.021511
17 18,193,597 16,374,237 1,819,360 1.81936
18 16,374,237 14,736,814 1,637,424 1.637424
91
19 14,736,814 13,263,132 1,473,681 1.473681
20 13,263,132 11,936,819 1,326,313 1.326313
Operating labour cost estimates
Department Job description Number Monthly
pay($)
Annual
pay ($)
Administration General Manager 1 3500 42000
Human Resource
Manager
1 2000 24000
Marketing manager 1 2000 24000
Procurement officer 1 1750 21000
Clerk 1 255 3060
Secretary 2 200 4800
Receptionist 2 150 3600
Helper 2 125 3000
Accounting Finance manager 1 2000 24000
0
20000000
40000000
60000000
80000000
100000000
120000000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Ase
ts V
alu
e,V
Life, Years
V
year
DECLINING BALANCE DEPRECIATION
Table 34: Annual Operating labour cost estimates
92
Clerk 1 255 3060
Accountant 1 800 9600
Secretary 1 200 2400
Sales and marketing Sales representative 2 522 12528
Clerk 1 250 3000
Secretary 1 200 2400
Production Production manager 1 2000 24000
Engineers 2 1500 36000
Technicians 4 500 24000
Supervisors 5 652 39120
Operators 15 300 54000
Casual workers 12 200 28800
Quality control Chemists 3 800 28800
Support staff Chief security officer 1 700 8400
Cafeteria staff 2 250 6000
Guards 8 200 19200
Driver/messenger 4 300 14400
Total Operating
Labour costs ($)
465,168
TOTAL PRODUCT COST ESTIMATES
Direct Product Costs Factor
Raw Material
5,420,000
Operating Labour costs
534,943
Utilities
7,712,818
Maintenance(2 % of FCI) 0.020 211,757
Operating Supplies(0.5% of FCI) 0.005 494,411
Total Direct Costs 14,373,929
Fixed Charges
Depreciation( Vs=10 % of FCI) 0 4,342,910
Property Taxes(0.025% of FCI) 0.000250 24,721
Insurance(0.1 % of FCI) 0.0001 9,888
Table 9.9: Total product cost estimates
93
Total Fixed Charge 4,377,518
General Expenses
Plant Overhead Costs(11 % of TPC) 0.11 3,547,137
Administrative Costs(3 % of TPC) 0.030 967,401
Distribution and Marketing(2 % of TPC) 0.020 644,934
Research and Development(2% of TPC) 0.020 644,934
Financing(7% of TCI) 0.070 7,690,844
Total Product Cost($) 32,246,697
94
7.3 ANNUAL CASH FLOW ANALYSIS
7.3.1 Annual Sales
Potato starch, potato puree and potato chips are the major products produced.
The table below shows the annual sales from the three major products.
Name of
Material
Price,
$/tonne
Annual Amount,
tonne/yr
Annual value of
product, $/y
Potato starch 5000 1406.14704000 70,307,352
Potato puree 4500 7612.04520000 34,254,203
Potato chips 4000 8791.99200000 35,167,968
Total annual value of products 76,452,906
Definitions:
The following assumptions are made:
Income tax is charged at 30% of the gross profit
The production capacity in the first year is only 60%
The production capacity in the second year is only 75%
The production capacity from the third year onwards is 100%
All the products are sold.
Table 35: Annual sales from products
95
Year Plant
capacity
Annual sales
USD x 106
Annual TPC Annual dep Gross
income Net income
Annual cash
flow
Cumulative cash
flow
0 0.00 0 0 0 0 0 0 -109,869,198
1 0.60 45,871,744 19,348,018 9,818,348 1,873,036 1,311,125 11,129,473 -98,739,725
2 0.75 57,339,680 24,185,023 8,836,513 24,318,144 17,022,701 25,859,214 -72,880,511
3 1.00 76,452,907 32,246,697 7,952,862 36,253,347 25,377,343 33,330,205 -39,550,306
4 1.00 76,452,907 32,246,697 7,157,576 37,048,634 25,934,044 33,091,619 -6,458,687
5 1.00 76,452,907 32,246,697 6,441,818 37,764,391 26,435,074 32,876,892 26,418,205
6 1.00 76,452,907 32,246,697 5,797,636 38,408,573 26,886,001 32,683,637 59,101,842
7 1.00 76,452,907 32,246,697 5,217,873 38,988,337 27,291,836 32,509,708 91,611,551
8 1.00 76,452,907 32,246,697 4,696,085 39,510,124 27,657,087 32,353,172 123,964,723
9 1.00 76,452,907 32,246,697 4,226,477 39,979,732 27,985,813 32,212,290 156,177,013
10 1.00 76,452,907 32,246,697 3,803,829 40,402,380 28,281,666 32,085,495 188,262,508
11 1.00 76,452,907 32,246,697 3,423,446 40,782,763 28,547,934 31,971,380 220,233,888
12 1.00 76,452,907 32,246,697 3,081,102 41,125,108 28,787,575 31,868,677 252,102,565
13 1.00 76,452,907 32,246,697 2,772,991 41,433,218 29,003,252 31,776,244 283,878,809
14 1.00 76,452,907 32,246,697 2,495,692 41,710,517 29,197,362 31,693,054 315,571,863
15 1.00 76,452,907 32,246,697 2,246,123 41,960,086 29,372,060 31,618,183 347,190,047
16 1.00 76,452,907 32,246,697 2,021,511 42,184,699 29,529,289 31,550,800 378,740,847
17 1.00 76,452,907 32,246,697 1,819,360 42,386,850 29,670,795 31,490,154 410,231,001
18 1.00 76,452,907 32,246,697 1,637,424 42,568,786 29,798,150 31,435,574 441,666,575
19 1.00 76,452,907 32,246,697 1,473,681 42,732,528 29,912,770 31,386,451 473,053,026
20 1.00 76,452,907 32,246,697 1,326,313 42,879,896 30,015,927 31,342,240 504,395,266
Totals 1,479,363,743 462,740,106 86,246,661 754,311,148 528,017,803 614,264,464 3,945,101,301
Average
profit
26,400,890
Average
depreciatio
n 4,312,333
96
7.4 CUMULATIVE CASH FLOW ANALYSIS
A plot illustrating the above cumulative cash flow position against time is as shown
below.
-15
-10
-5
0
5
10
15
20
25
30
35
-4 -2 0 2 4 6 8 10 12 14 16
Cu
mu
lati
ve c
ash
flo
w
Mill
ion
s
WC
+FC
I+La
nd
Cumulative Cash Flow Curve
Year
Pay-out period
Break-even point
97
7.5 PROFITABILITY ANALYSIS
Profitability analysis is a measure of the attractiveness of the project. Absolute profit is
of little significance; instead the rate of return on invested capital is to be looked into.
The methods used to analyze the profitability of this design project are:
Rate of return on investment
Discounted cash flow based on full life performance
Pay out period
7.5.1 Rate of return on investment
Rate of return (ROR), which is the ratio of annual profit to investment, is a simple
index of the performance of the money invested.
7.5.2 Payout period
The payout period is defined as the minimum length of time theoretically necessary to
recover the original capital investment in the form of cash flow to the project based on
total income minus all costs except depreciation.
98
7.5.3 Discounted cash flow rate of return
This method of approach for a profitability takes into account the time value of money
and is based on the amount of the investment that is unreturned at the end of each year
during the estimated life of the project.
A trial-and-error procedure is used to establish a rate of return which can be applied to
yearly cash flow so that the original investment is reduced to zero (or to salvage and
land value plus working capital investment) during the project life.
20
20
1 1
1
1
1
iVWC
iNITCI S
nn
Where:
Using excel, the DCFROR was established to be 25% as shown in the table below. For
a project to be viable, DCFROR should be at least 5 % more than the bank lending
rate. For an Initial investment of $ 109,869,198, the DCFROR is therefore or
Estimating the Bank Lending Rate (BLR) to be approximately 18%, the
difference between the DCFROR and the bank lending rate is an indication that
the venture is profitable.
99
Trial for i=15% Trial for i=10% Trial for i=19% Trial for i=16.1556% Trial for i=25.0 %
1+i 1.150 1+i 1.090 1+i 1.190 1+i 1.1615561 1+i 1.25
YEAR CASH FLOW 1/(1+i)n
P.W 1/(1+i)n
P.W 1/(1+i)n
P.W 1/(1+i)n
P.W 1/(1+i)n
P.W
1 11,129,473 0.869565 9,677,803 0.917431 10,210,526 0.840336 9,352,498 0.860914 9,581,520 0.8 8903578.467
2 25,859,214 0.756144 19,553,281 0.84168 21,765,183 0.706165 18,260,867 0.741173 19,166,152 0.64 16549896.86
3 33,330,205 0.657516 21,915,151 0.772183 25,737,034 0.593416 19,778,671 0.638086 21,267,547 0.512 17065065
4 33,091,619 0.571753 18,920,241 0.708425 23,442,937 0.498669 16,501,756 0.549337 18,178,466 0.4096 13554327.24
5 32,876,892 0.497177 16,345,626 0.649931 21,367,724 0.419049 13,777,041 0.472932 15,548,546 0.32768 10773099.96
6 32,683,637 0.432328 14,130,038 0.596267 19,488,185 0.352142 11,509,292 0.407154 13,307,277 0.262144 8567819.446
7 32,509,708 0.375937 12,221,604 0.547034 17,783,924 0.295918 9,620,205 0.350525 11,395,456 0.209715 6817779.983
8 32,353,172 0.326902 10,576,309 0.501866 16,236,966 0.248671 8,045,280 0.301772 9,763,270 0.167772 5427961.574
9 32,212,290 0.284262 9,156,743 0.460428 14,831,433 0.208967 6,731,300 0.259799 8,368,735 0.134218 4323460.321
10 32,085,495 0.247185 7,931,044 0.422411 13,553,260 0.175602 5,634,289 0.223665 7,176,402 0.107374 3445153.822
11 31,971,380 0.214943 6,872,032 0.387533 12,389,960 0.147565 4,717,857 0.192556 6,156,292 0.085899 2746320.665
12 31,868,677 0.186907 5,956,484 0.355535 11,330,421 0.124004 3,951,850 0.165774 5,283,013 0.068719 2189998.809
13 31,776,244 0.162528 5,164,528 0.326179 10,364,732 0.104205 3,311,251 0.142718 4,535,028 0.054976 1746917.486
14 31,693,054 0.141329 4,479,137 0.299246 9,484,034 0.087567 2,775,279 0.122868 3,894,048 0.04398 1393875.265
15 31,618,183 0.122894 3,885,700 0.274538 8,680,394 0.073586 2,326,658 0.105778 3,344,521 0.035184 1112465.931
16 31,550,800 0.106865 3,371,669 0.25187 7,946,692 0.061837 1,951,008 0.091066 2,873,209 0.028147 888076.0627
17 31,490,154 0.092926 2,926,251 0.231073 7,276,530 0.051964 1,636,351 0.0784 2,468,831 0.022518 709095.2389
18 31,435,574 0.080805 2,540,155 0.211994 6,664,145 0.043667 1,372,701 0.067496 2,121,768 0.018014 566292.951
19 31,386,451 0.070265 2,205,379 0.19449 6,104,340 0.036695 1,151,728 0.058108 1,823,805 0.014412 452326.4279
20 31,342,240 0.0611 1,915,020 0.178431 5,592,424 0.030836 966,475 0.050026 1,567,928 0.011529 361351.4307
20 10,986,920 0.0611 671,304 0.178431 1,960,406 0.030836 338,795 0.050026 549,632 0.011529 126670.5612
180,415,497 272,211,252 143,711,154 168,371,447 107,721,534.749
100
7.6 BREAK-EVEN POINT (BEP) ANALYSIS
This is the point at which the total sales and the total cost of production are equal. It
marks the production rate below which the plant is operating at a loss and must therefore
be exceeded.
The BEP is calculated as:
Where:
The break-even point ( ) is at of the maximum production capacity (
).
101
Chapter 8: SAFETY, HEALTH AND ENVIRONMENTAL IMPACT ASSESSMENT
8.0 INTRODUCTION
The significance of safety and health in chemical industries is a vital issue in achieving
productivity. Industries are faced with the task of producing and using their products in a manner
that is safe for:-
Persons involved with production.
Persons using the products.
Persons living near the process plants.
The environment i.e. land, air, water, plants and animals.
Industrial operations and products must undergo proper hazard assessment and industries
must put in place appropriate standards and procedures to ensure that chemical risks are
kept to a minimum.
Any manufacturing industry has a legal and moral obligation to safeguard the health and
welfare of its employees and the surrounding populace. All manufacturing processes are to
some extent hazardous and the designer should ensure, through the application of sound
engineering practices, that the risks are reduced to acceptable levels.
8.1 SAFETY
Safety is an area of safety engineering and public health that deals with the protection of
workers' health, through control of the work environment to reduce or eliminate hazards.
Chemical process safety refers to the application of technology and management practices;
To prevent accidents in plants
To reduce the potential for accidents.
Work place hazards can generally be grouped into:-
Mechanical hazards
Chemical hazards
Physical hazards
Biological hazards
102
Psycho-Social hazards
Unsafe working conditions and production may lead to industrial accidents and can result
in:
Temporary or permanent injuries.
Fatalities.
Loss of future productivity by training new personnel
Loss of valuable work hours
Cost implications due to compensation, medical fees, insurance etc.
The Occupational Health and Safety Act (OHSA, 2007) stipulates the guidelines for
ensuring favorable and bearable working conditions in Kenya. The Act establishes
occupational, safety and health standards to be adhered to in places of work.
Major provisions of this Act include:
Inspection of work places
Maintenance of accurate records of employees
Maintenance of accurate records of any toxic or harmful material whose levels exceed those
prescribed by an applicable standard.
Provides for the rights of employees to be informed of any violations by employers cited by
inspectors of work places.
The provisions of this Act are enforced by inspection officers who carry out inspections for
work places.
Safety in the entire plant can be grouped into the following:
Safety in the operations and design of the starch extraction plant
Safety in the operations and design of the chipping plant
8.1.1 Safety Management in the starch extraction plant
Potential hazards in the starch extraction include the following:
Electrical components malfunction, electrocution and risk of electrical fires
Failure of instruments and process equipment
Risk of fires
103
Odour
Leakages from equipment causing spills
High pressure steam in the steam peeler
Slips, trips and falls
8.1.2 Safety Management in the chipping plant.
Potential hazards in the chipping plant are:
Leakages causing slips and trips
Fumes
Instruments failure such as valves and relief vents
Risk of fires
These hazards can be avoided by employing preventive and control mechanisms in the
process design and operations of the plant. These include:-
Fire Detection and Evacuation systems
Smoke and fire detectors and sensors will be installed across the plant area. A sensor, on
detecting heat or smoke, should let off an alarm to allow evacuation. The workers must
always be inducted once hired so as to know the procedures of evacuation incase of fire
scares and periodical training should be done as well as fire and evacuation grills.
Proper Housekeeping
This includes:
Marking escape and transport routes
Tidiness and clear marking of areas during plant construction.
All construction equipment to follow safety requirements.
No ignition sources
Marking equipment for identification
Good access to the site should be controlled.
Spillages and wastes
Spillages should be taken note off, contained and collected.
When opening valves, the risk of spillages should be considered.
104
Labeling
All equipment should be classified according to their risk and labeled accordingly.
Spacing
There should be adequate spacing between equipment and pipelines.
Safety Relief Vents, Interlocks and trip systems
For pressure vessels, relief vents should be installed. Interlocks and trip systems should
also be installed in case of failure of the instruments.
Control valves
There should be remote control valves to isolate equipment and areas of the plant in case of
emergency.
Inspection of equipment
Regular inspection of equipment such as storage vessels, heat exchangers, belts, steam
peeler and pipelines helps to avoid explosions and mechanical failure through thermal
vibrations, corrosion and stresses. Frequent testing to confirm compliance to design
parameters should be conducted on the relevant equipment.
Training of workers
Specialized training of workers on personal protection equipment, fire prevention and
protection techniques, accidents prevention and safety management can contribute
significantly to risk management in the plant.
Accident Documentation
All accidents should be reported to the relevant section managers and eventually to the
safety manager for effective investigation.
Employee Requirements
It shall be a requirement for each worker to have the following within the factory premises.
Masks: for protection against dust.
105
Protective clothing: these include overalls and dust coats to be replaced weekly for
cleaning purposes.
Protective shoes: special shoes to prevent any damage due to falling objects and also to
prevent falling or sliding.
Ear plugs: Prevent damage caused by vibration or noise produced by equipment.
Safety helmet: mandatory inside the factory to protect the head from metal objects.
Management and Safety
Management should be at the forefront in enforcing safe engineering practices by:-
Organizing safety trainings and safety promotional campaigns.
Enacting rules and policies to be adhered to concerning safety, for which there are
repercussions for violations committed.
Management should ensure that they get a safety report periodically.
There should be an independent inspector doing regular safety audits.
Ensuring there is proper and regular inspection and maintenance of equipment.
8.2 ENVIRONMENTAL IMPACT ASSESSMENT
An environmental impact assessment is a study of the possible positive and negative
impact that a proposed project may have on the environment. It is the process of
identifying, predicting, evaluating and mitigating the biophysical, social, and other relevant
effects of development proposals prior to major decisions being taken and commitments
being made.
EIA aims to ascertain:-
The degree of impact of a proposed activity on the environment.
Whether impacts could be avoided or mitigated by any means or not.
All process industries have chemical wastes and discharges which could cause extensive
environmental pollution and damage to human health if not controlled.
In Kenya, the government set up the National Environmental Management Authority
(NEMA) under the Environmental Management and Coordination Act (EMCA) No.8 of
106
the 1999, as the principal instrument of government in the implementation of policies
relating to the environment.
NEMA has to collaborate with experts in production industries to come up with standards
for Environmental Impact Assessments and also what is called Environmental Audits.
Other organization which deals with awareness, training and waste reduction audits is
Kenya National Clearer production Center at KIRDI.
8.2.1 Environmental concerns
In the starch extraction plant and the chipping plant being basically a food industry there is
toxic from any chemicals hence generally the source of pollutants are:
Spills and leakages of fluids e.g. wash water.
Waste and sludge from filters in the extractors and peelers.
Effluents from washing operations.
Fumes from the chimney.
8.2.2 Consequences
These pollutants may have the following effects on the health of humans and animals and
the environment:
Impairment of health
Imbalance of the ecosystem
Pollution of water
Pollution of air.
8.2.3 Waste treatment practices
These refer to the control and management of toxic substances by the application of
various treatment technologies, which include pre-treatment, waste minimization and waste
disposal.
8.2.3.1 Minimization of wastes
Leakages
Leakages and spills should be eliminated so that there is reduced effluent leakage to the
soil and water without detection through proper housekeeping.
107
Recycling of Used Water
Recycling of washing water into clarification ponds is required so as to reduce the amount
of waste water effluent generation from the plant. All waste water pipeline systems should
be checked regularly and any fault corrected immediately.
8.2.3.2 Disposal of wastes
Solid wastes
The main solid wastes are:
Infested tubers, rotten tubers
Wastes from washing i.e mud
Stones
These wastes should be properly disposed of by incineration or open dumps.
Liquid wastes
Liquid wastes include:
Washing solvents used to cleaning
Washing water used for cleaning floors
Spillages and leakages
These should be treated prior to disposal into sewerage streams. This is done by use of
clarification pools. Biological treatment methods may also be used.
Gaseous wastes
The main sources of gaseous wastes are:
Fumes from the chimney in the fryer unit
Odor eg. From the slurry storage tank and also the rotten potatoes.
These wastes should be removed from the gaseous streams before discharge into the
atmosphere. Operators should also be provided with masks to prevent exposure to fumes.
108
Chapter 9: HAZARD AND OPERABILITY ANALYSIS (HAZOP)
9.0 INTRODUCTION
Hazard and operability study (Hazop) is a structural and systematic examination of a plant
or existing process or operation in order to identify and evaluate problems that may
represent risk to personnel or equipment or prevent efficient operation.
The Hazop process is based on the principle that a team approach to a hazard analysis will
identify more problems than when individuals working separately combine results.
Hazop is a quantitative technique based on guide words and is carried out by a multi-
disciplinary team (Hazop Team) during a set of meetings.
Hazard - any operation that could possibly cause a catastrophic release of toxic,
flammable or explosive chemicals or any action that could result in injury to personnel.
Operability - any operation inside the design envelope that would cause a shutdown that
could possibly lead to a violation of environmental, health or safety regulations or
negatively impact profitability.
9.1 PURPOSE OF HAZOP
HAZOP is carried out for the following reasons:
• HAZOP identifies potential hazards, failures and operability problems.
• Encourages creativity in design concept evaluation.
• Confirms overall cost effectiveness improvement.
• Provides a necessary management tool and bonus in so far that it demonstrates to insurers
and inspectors evidence of comprehensive thoroughness.
• HAZOP reports are an integral part of plant and safety records and are also applicable to
design changes and plant modifications, thereby containing accountability for equipment
and its associated human interface throughout the operating lifetime.
109
9.2 HAZOP PROCESS
The HAZOP process is undertaken in the following procedure:
1. Divide the system into sections (i.e., extractor, storage)
2. Choose a study node (i.e., line, vessel, pump, operating instruction)
3. Describe the design intent
4. Select a process parameter
5. Apply a guide-word
6. Determine cause(s)
7. Evaluate consequences/problems
8. Recommend action: What? When? Who?
9. Record information
10. Repeat procedure (from step 2)
9.3 HAZOP CONCEPTS
a) Node - A specific location in the process in which (the deviations of) the design/process
intent are evaluated. Examples might be: separators, heat exchangers, and interconnecting
pipes with equipment.
b) Design Intent - A description of how the process is expected to behave at the node; this is
qualitatively described as an activity (e.g., feed, reaction, sedimentation) and/or
quantitatively in the process parameters, like temperature, flow rate, pressure, composition,
etc.
c) Deviation - A deviation is a way in which the process conditions may depart from their
design/process intent.
d) Parameter - The relevant parameter for the condition(s) of the process (e.g. pressure,
temperature, composition).
e) Guideword - A short word to create the imagination of a deviation of the design/process
intent. The most commonly used set of guide-words is: no, more, less, as well as, part of,
other than, and reverse.
110
The guidewords are applied, in turn, to all the parameters, in order to identify unexpected
and yet credible deviations from the design/process intent.
Guide-word + Parameter Deviation
f) Cause - The reason(s) why the deviation could occur. Several causes may be identified for
one deviation. It is often recommended to start with the causes that may result in the worst
possible consequence.
g) Consequence - The results of the deviation, in case it occurs. Consequences may both
comprise process hazards and operability problems, like plant shut-down or reduced
quality of the product.
h) Safeguard - These are facilities that help to reduce the occurrence frequency of the
deviation or to mitigate its consequences.
Vessel: flash dryer
Design intent: To disperse solid cakey material as fine as possible.
Drying chamber
Intention: Continuously contact the hot air and solid particles
Guide word deviation Causes consequences Action
required
Assigned to
Less Temperature Reduced inflow of hot air. Failure of control valve. Large steam leakage.
High moisture
content
Poor thermal
stability
Regular inspection of control valves. Proper maintenance.
Process
engineer
High pressure Failure of venting system. Increase inflow of material.
Strain on the vessel. Explosion of vessel.
Inspection of controls regularly. Maintenance of pump.
Process
engineer
111
Vessel: blancher
Design intent: To destroy enzyme activity and leach out reducing sugar
Hot water blanching
Intention: Continuously intact spraying of hot water and potato chip
Guide word deviation Causes consequences Action required Assigned to
Less Temperature Failure of control valve. Large steam leakage.
Decrease temperature of steam
Low temperature input
Less destroy enzyme activity
High reducing sugar
Regular inspection of control valves.
Proper maintenance.
Process
engineer
High Temperature Increased temperature of steam Decrease inflow of material.
Higher outlet temperature may impact negatively on subsequent processes. High energy consumption.
Repair/replace malfunctioning sensors and valves. Maintenance of alarm systems
Process
engineer
112
Chapter 10: PLANT LOCATION AND LAYOUT
10.1 PLANT LOCATION
Plant location refers to the choice of region and the selection of a particular site for setting
up a business or factory. The location of a business venture plays an important role in
determining its profitability and viability. Primarily, an ideal location should be one that
harnesses minimum production costs with the realization of maximum obtainable profits.
The location depends upon several factors; however some are more critical than others
while choosing the ideal location as not all factors can be satisfied at a time. The principal
factors are:
Raw material availability
Market for the product
Labour availability
Transportation facilities
Availability of utilities such electricity, water
Climate
Site considerations
Environmental impact and effluent disposal
Community factors
Based on the above factors, Timboroa is chosen as the ideal location for the plant. The
choice is determined by the following reasons.
a) Raw material availability
The availability and price of suitable raw material will often determine the site location.
Potato is widely produced in Rift Valley Province and specifically in Timboroa due to the
favorable climatic conditions. The location of the plant in this region will ensure a
considerable reduction in transport and storage costs. In addition, a vast pool of suppliers
in the area ensures that there is steady supply of raw materials avoiding shortages and
hence production downtime. The company could also set up its own potato growing
113
department due to availability of land to reduce on costs of buying them from external
producers.
b) Market
Eldoret and Nakuru and theirs environs provide a huge market for paint. This is because of
the increase in the number of hotels and restaurant in both towns and also the general
increase in population.
c) Utilities
Production of potato products requires large quantities of water for washing and as a
solvent, for cooling and for general process use. Electrical power is another key utility for
any processing industry. The power required in running the plant will be supplied by
Kenya Power.
d) Labour availability
Labour is cheap and readily available with unemployment rates of more than 45%.
Prevailing pay rates stand at Kshs. 300 per 8-hour-working day on unskilled labour, which
is cheap.
e) Transportation costs
Timboroa has a well-developed transport infrastructure in the country. The roads are
tarmacked and passable throughout the year. The roads connecting the proposed potato
plant in Timboroa with the product market in Nakuru, Eldoret and other neighboring towns
are modern, passable and reliable.
f) Climate
Adverse climatic conditions at a site will increase costs. Abnormally high temperatures
will require the provision of additional storage devices as the raw materials requires law
temperature storage. Timboroa is ideal in that it has a moderately lower temperatures
throughout the year.
g) Site Characteristics
114
Sufficient and suitable land should be available for plant location and possible future
expansion. It should be well drained, ideally flat and have good load bearing
characteristics. It should also be easier for movement of modern machinery during
construction and operation and thus low initial cost of investment. There is available and
cheap land in Timboroa as compaired to other viable places in the country.
h) Environmental impact and effluent disposal
All industrial processes produce waste products. Effluent from the plant is not toxic and
can be discharged directly into the sewerage system.
i) Community factors
The location of the plant in the area offers the population a great opportunity in terms of
alleviation of unemployment. The plant provides a vast market to the local thus saving
them from wastage due to lack of storage devices. It has existing facilities such as
recreational centers and social amenities for the employees.
10.2 PLANT LAYOUT
Plant layout is an important decision as it represents long-term commitment. An ideal
plant layout should provide the optimum relationship among output, floor area and
manufacturing process. It facilitates the production process, minimizes material handling,
time and cost, and allows flexibility of operations, easy production flow, makes economic
use of the building, promotes effective utilization of manpower, and provides for
employees’ convenience, safety, comfort at work, maximum exposure to natural light and
ventilation. It is also important because it affects the flow of material and processes,
labour efficiency, supervision and control, use of space and expansion possibilities.
The process units and ancillary buildings should be laid out to give the most economical
flow of materials and personnel around the site. Hazardous processes must be located at a
safe distance from other buildings. Consideration must also be given to the future
expansion of the site. The ancillary buildings and services required on a site, in addition to
the main processing units (buildings), will include:
115
1. Storages for raw materials and products: tank farms and warehouses.
2. Maintenance workshops.
3. Stores, for maintenance and operating supplies.
4. Laboratories for process control.
5. Fire stations and other emergency services.
6. Utilities: steam boilers, compressed air.
7. Effluent disposal plant.
8. Offices for general administration.
9. Canteens and other amenity buildings.
10. Car parks.
The direction of prevailing wing should be considered such the administrative buildings,
car park and utilities are on the upwind side while the processing plant, tank farms and
burning flames on the downwind side.
When roughing out the preliminary site layout, the process units will normally be sited first
and arranged to give a smooth flow of materials through the various processing steps, from
raw material to final product storage. Process units are normally spaced at least 30 m apart;
greater spacing may be needed for hazardous processes.
The location of the principal ancillary buildings should then be decided. They should be
arranged so as to minimize the time spent by personnel in travelling between buildings.
Administration offices and laboratories, in which a relatively large number of people will
be working, should be located well away from potentially hazardous processes. Control
rooms will normally be located adjacent to the processing units, but with potentially
hazardous processes may have to be sited at a safer distance. The location of the main
process units will determine the layout of the plant roads, pipe alleys and drains. Access
roads will be needed to each building for construction, and for operation and maintenance.
Utility buildings should be sited to give the most economical run of pipes to and from the
process units.
Cooling towers should be sited so that under the prevailing wind the plume of condensate
spray drifts away from the plant area and adjacent properties.
116
The main storage areas should be placed between the loading and unloading facilities and
the process units they serve. Storage tanks containing hazardous materials should be sited
at least 70 m (200 ft) from the site boundary. (Chemical Engineering Design, Coulson Vol
6)
The plant layout is shown in the diagram below.
117
PLANT LAYOUT
KEY:
Security check
Road
Wind
Car
Park
Workshop
Administration
Offices
Fire
Assembly
Point
Canteen
Expan
sion
Laboratory Control
Room
Plant area
Tank Farm
Product
Warehouse
Raw material
Reception
Waste
Water
Treatment
Utilities
118
Chapter 11: REFERENCES
Cengel Y. L (1998), Heat Transfer McGraw-Hill Book Co. Princeton Road.
C.M. van ’t Land, DRYING IN THE PROCESS INDUSTRY
Chattopadhyay, P., (1996) Unit Operations of Chemical Engineering 2nd
ed. Khanna
Publishers
Couper, Penney, Fair & Wals, Chemical Process Equipment; Selection and Design
Dale. E. Seborg et al., (2003). Process Dynamics and Control.
GAVIN TOWLER, RAY SINNOTT, Chemical engineeting design principles, practice and economics of plant and process design
Holman (1999), Heat Transfer McGraw-Hill Book Co.
http://en.www.wikipedia.org/wiki/ potato chips
http://en.www.wikipedia.org/wiki/ potato puree
http://en.www.wikipedia.org/wiki/ potato starch
J. F. Richardson and J. H. Harker. (2002). Coulson and Richardson’s Chemical
Engineering,5th
edn.,Vol 2.
James G. Speight, CHEMICAL AND PROCESS DESIGN HANDBOOK Max S. Peters Klaus D. Timmerhaus, PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS 4th ed.
Perry and Green D. (ED.), (1987) Perry’s Chemical Engineer’s Handbook, 6th
ed. McGraw-
Hill
Perry, R.H., Green, D.W. and Maloney, J.O. (1997).Perry’s Chemical Engineer’s
Handbook, 7th
edition.
Peters, M and Timmerhaus. Plant Design and Economics for Chemical Engineers
Robert H. Perry, Don W. Green: Perry’s Chemical Engineering Handbook
Sinnot, R. K (4th
Ed.). Coulson’s & Richardson’s Chemical Engineering Design. Volume 6
Sinnot, R.K. (2005). Coulson and Richardson’s Chemical Engineering: Chemical Engineering
Design, 4th
edn., volume 6.
Smith and Van Ness, (1987) Introduction to Chemical Engineering Thermodynamics, 4th
ed.
McGraw-Hill Book Co. New York.
Stephanopulos. Chemical Process Control and Chemical Modelling.
Towler, G and Sinnot, R. (2006).Chemical Engineering: Design Principles, Plant Design and
Economics. www.answers.com
www.engineeringtools.com
119
APPENDICES
APPENDIX A: DATA
TABLE A-1: SPECIFIC HEAT CAPACITIES OF VARIOUS COMPOUNDS AND ELEMENTS
Compound Cp (Kj/kg.K)
Water 4.187
Sunflower oil 2.197
Potato 0.0335 * %M.C +0.8374
Steam @ 7 bar 2.464
Air 1.25
Moist air 4.187
TABLE A-2: DENSITIES OF VARIOUS COMPOUNDS AND ELEMENTS
Compound/ Element
Water 1000
Starch 1500
Potato 1200
TABLE A-3: NATURAL GAS DATA
Stoichiometric Natural-Gas
Combustion (kg/hr)
In out
Natural gas
120
Methane
Nitrogen
85.7 0.0
26.5 26.5
Dry air
Oxygen
Nitrogen
343.0 0.0
1200.4 1200.4
Water vapour
In air 6.2 6.2
By combustion 0.0 192.9
Carbon dioxide 0.0 235.8
Total 1661.8 1661.8
APPENDIX B: DETAILED SAMPLE MASS BALANCE CALCULATIONS
i.Extractor
The outlet stream from the rasper (S8) is extracted with water (S9) to extract starch.
The composition of the feed into the extractor is given below.
COMPONENT potato(kg/hr) Water
(Kg/hr)
Skin
fragment
(kg/hr)
TOTAL
Mass
in(kg/hr)
899.1 18 0 917.1
Mass
out(kg/hr)
894.6 18 4.5 917.1
S 9
S 10
S 11
S 8
Extractor
121
Assumption:
The extractor operates at 90% efficiency.
25% of pulp and fibres is extracted.
55% of protein/soluble is extracted.
20% of the feed is water.
Washing ratio is potato: water = 1:2.
The equation of conservation of mass with no accumulation is expressed as:
Overall mass balance
Stream 8 (S 8) Stream 9 (S 9)
Rasped potato = 0.995 899.1 = 894.6 kg Ratio of washing = 1:2
Water = 0.9 18 = 16.2 kg Purified water = 2 894.6 = 1789.2
kg
Stream 10 (S 10) Stream 11 (S 11)
Pulp & fibres = 0.25 894.6 = 223.515 kg Starch = 0.2 894.6 = 178.92 kg
Water = 0.2(16.2 + 1789.2) = 361.08 kg Proteins/soluble = 0.55 894.6 =
492.03 kg
Water = 0.8(16.2 + 1789.2) = 1444.32 kg
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COMPONENT Rasped
potato(kg/hr)
Water
(Kg/hr)
Pulp &
fibres
(kg/hr)
Starch
(Kg/hr)
Proteins/
soluble
TOTAL
Mass
in(kg/hr)
894.6 1805.4 0 0 0 2700
Mass
out(kg/hr)
0 1805.4 223.515 178.92 492.03 2700
ii. Hydro cyclone
Assumption:
The hydro cyclone operates at 95% efficiency.
The equation of conservation of mass with no accumulation is expressed as:
Overall mass balance
S 13
S 12
S 11
Hydro
cyclone
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Stream 11 (S 11) Stream 12 (S 12)
Starch = 0.2 894.6 = 178.92 kg Fruit water (proteins) = 0.95
492.03 kg
Proteins & soluble = 0.55 894.6 = 492.03 kg Water = 0.95 1444.32 = 1372.104
kg
Water = 0.8(16.2 + 1789.2) = 1444.32 kg Starch = 0.05 178.92 = 8.946 kg
Stream 13 (S 13)
Fruit water (proteins) = 0.05 492.03 = 24.602 kg
Water = 0.05 1444.32 = 72.216 kg
Starch = 0.95 178.92 = 169.97 kg
Milk starch (fruit water (proteins) + water + starch) = 24.602 + 72. 216 + 169.97 = 266.732
kg
COMPONENT starch(kg/hr) proteins(Kg/hr) water (kg/hr) TOTAL
Mass in(kg/hr) 178.92 492.03 1444.32 2115.27
Mass out(kg/hr) 178.92 492.03 1444.32 2115.27
APPENDIX C: DETAILED SAMPLE ENERGY BALANCE CALCULATIONS
i. Flash drier
Starch coming in = 194.58 kg/hr
Water coming in = 7.2216 kg/hr
Energy requirement:
Amount of water that is vaporized = 6.4944 kg
Let temperature in for starch = 88oC
Temperature rise = 100oC – 88oC = 12oC
124
Amount of starch coming out of the dyer, Assume no starch evaporates = 194.58 kg
Amount of energy required to evaporate 6.494kg =
= 6.494 4.187 12 = 326.3 KJ
Energy absorbed by water = = 7.2216 2502.3 = 18070.61 kJ
Energy absorbed by starch = = 194.58 2.71 12 = 6327.7 kJ
Total energy required = 6327.7 + 18070.81 + 326.3 = 24724.61 kJ
Mass of hot air required assuming no heat loss
=
= 490.1 Kg/hr
Volumetric flow rate of air
; = 1.29 kg/m3
V =
= 379.9 m3/hr
Total amount of energy coming in should be equal to the amount of energy coming out.
= (194.58 2.71 88) + (7.2216 4.187 88) = 49060 kJ
= (194.58 2.71 100) + (7.2216 4.187 100) = 55750 kJ
= (490.1 150 1.009) = 74176.64 kJ
=
+ -
= 49060 + 74176.64– 55750 = 67486.64 kJ
Hot air @ 150oC
74176.64 kJ
Dried starch @ 100oC
55750 kJ
Semi dried starch @
88oC
49060 kJ
Moist air @ 100oC
67486.64 kJ
Flash dryer
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APPENDIX D: EQUIPMENT SIZING CALCULATIONS
1. ROTARY WASHER
The equipment is used for washing to remove soil, stones and other foreign materials
from the potato surface. The design chosen for this equipment is a slanted cylindrical
drum with inlet chute with brushes at the inner circumference.
Mass flow rate of potato = 3000 kg/ hr
Mass flow rate of water = 6000 kg/ hr
Assumption
- No build up of material
- Basis is 1 hour
- Density of potato is 1200 kg/m3
- Mass of stones and foreign materials are negligible
- The ratio of Diameter: Height is 1:3
Volume flow rate of water =
= 6 m3
Volume flow rate of potato =
= 2.5 m3
Total volume flow rate = 8.5 m3
Capacity of equipment = 8.5 m3/hr
Volume of equipment = πr2h = π (
)2h , h = 3D
Volume =
3D = 8.5
Solving gives, D= 1.5 m and h= 4.5 m
126
2. VIBRATORY MESH
The equipment is used for separation of potatoes into two, those for starch extraction
(smaller sizes) and those for chips / puree production section. The design chosen for this
equipment is a slanted, cubical with single output with a mesh at the bottom surface.
Mass flow rate = 2997 kg/hr
Assumptions
- No build up of material
- Aperture size of mesh is 30 mm
- Residence time is 3 minutes
- The equipment should be a quarter full
- The height is 200 mm
- The L:W ratio is 2:1
- Density of potato is 1200 kg/m3
Volume flow rate of potato =
= 2.14 m3 /hr
Volume of the equipment = 2W W 0.05 = 2.13 m3
W2 = 2.13/0.1
Solving for W, W=1.5 m and L= 3 m
127
APPENDIX E: FIGURES
Figure 4: Structure of cellulose (www.wikipedia.com)
Figure 5: structure of starch (www.wikipedia.com)
Figure 6: Flash drying system (Perry's handbook)
128
Figure 7: Rotary vacuum filter (www.wikipedia.com)
