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KYAMBOGO UNIVERSITY
FACULTY OF ENGINEERING
DEPARTMENT OF MECHANICAL AND PRODUCTION
PROGRAMME: BACHELOR OF ENGINEERING IN
MECHANICAL AND MANUFACTURING ENGINEERING
TOPIC: INDUSTRIAL TRAINING AT MUKWANO GROUP
NAME: ORTEGA IAN
REG NO: 11/U/11049/EMD/PD
Place of Training: Mukwano Group and
Mukwano Industries (U) Ltd
June 4th
- August 4th
2013
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DECLARATION
I sincerely declare that:
1. I am the sole writer of this report
2. The details of training and experience contain in this report describe my involvement as a
trainee in the field of Mechanical and Manufacturing Engineering at Mukwano Group and
Mukwano Industries (U) Ltd.
3. All the information contains in this report is certain and correct to the knowledge of the
author.
Signature: ___________________________________
Name: ORTEGA IAN
Reg. No: 11/U/11049/EMD/PD
Date: 19th August 2009
For Company Supervisor: ___________________________________
For University Supervisor: __________________________________
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Acknowledgments
First and foremost, I thank the Management and the entire staff of Mukwano Group for
according me the opportunity to train with such a big company. The lifetime skills ingrained in
me will never be forgotten. I thank my university Supervisor, Mr. Sseku Charles for the
guidance and great service offered.
My special thanks go to my parents for the guidance and discipline instilled in me. I can‘t forget
to thank my mentor, Andrew Mwenda for teaching me about life. And to the Almighty God,
nothing beats your love. To everyone I may have missed out, accept my appreciation.
Namaste.
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Report Summary
The report covers the events, skills attained and lessons learned during my Industrial training at
Mukwano Group and Mukwano Industries (U) Ltd. The internship program was undertaken in
the manufacturing division covering a period of two (2) months from 4th June 2013 to 4th
August 2013.
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TABLE OF CONTENTS
Declaration .................................................................................................................................................. 2
Acknowledgements .................................................................................................................................. 3
Report Summary .................................................................................................................................. 4
Table of Contents ......................................................................................................................................... 5
Introduction .............................................................................................................................................. 6
BOILERS ................................................................................................................................................. 9
Soap Plant……………………………………………………………………………………………………………………………………………16
Production of Vegetable Oil………………………………………………………………………………………………………………….20
Beverages……………………………………………………………………………………………………………………………………………..24
Plastics………………………………………………………………………………………………………………………………………………….25
Utilities (Pumps, Heat Exchangers, valves, Chillers)..........................................................................…...38
Challenges………………………………………………………………………………………………………………………………………….60
Recommendations……………………………………………………………………………………………………………………………..60
Conclusion………………………………………………………………………………………………………………………………………...60
References………………………………………………………………………………………………………………………………………...61
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INTRODUCTION
Background
Brief-History of Mukwano
The Mukwano Group of Companies is the leading manufacturer of Fast Moving Consumer
Goods (FMCG) in the Great Lakes region, producing a wide range of market leader brands in
soaps, edible cooking oils and fats, detergents, beverages, personal care products and plastics.
Having pioneered Uganda‘s economic resurgence in the late 1980s and early 1990s, the Group
has proudly attained unparalleled regional reputation for uncompromised quality and
affordability of its products. Today, Mukwano products can be found in almost every household
in Eastern and Central Africa where they have been warmly embraced by loyal customers.
The Mukwano Group continues to steadily diversify into other business interests such as
agriculture, estate development and supply and logistics with commitment towards responsible
investment and national development.
Mukwano Vision Statement – To become the supplier of choice for Fast Moving Consumer
Goods in East and Central Africa
Mukwano Mission – To ensure timely delivery of quality, affordable products to our customers
in East and Central Africa
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The Company Organization Structure is as follows:
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Aims and Objectives For Industrial Training
1. To broaden my knowledge as far as mechanical and manufacturing systems and processes are
concerned.
2. To gain practical hands-on skills in partial fulfillment to my Mechanical and Manufacturing
degree.
3. To acquire insight in project progress from the planning phase to completion.
4. To get exposure to organization policy and culture.
5. To gain an understanding of company structure and hierarchy.
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BOILER SECTION
Design and operation
A boiler is an enclosed vessel that provides a means for combustion heat to be transferred into
water until it becomes heated water or steam. The hot water or steam under pressure is then
usable for transferring the heat for the steam requirements of Mukwano Industries and for power
generation.
Combustion boilers are designed to use the chemical energy in fuel to raise the energy content of
water so that it can be used for heating and power applications. Many fossil and non-fossil fuels
are fired in boilers, but the most common types of fuel include coal, oil and natural gas.
Previously, Mukwano had oil fired boilers but due to the high cost of operation, it has focused on
only wood-husk fired boilers. During the combustion process, oxygen reacts with carbon,
hydrogen and other elements in the fuel to produce a flame and hot combustion gases. As these
gases are drawn through the boiler, they cool as heat is transferred to water. Eventually the gases
flow through a stack and into the atmosphere. As long as fuel and air are both available to
continue the combustion process, heat will be generated.
Boilers are manufactured depending on the characteristics of the fuel, the specified heating
output, and the required emission controls.
Components of a boiler system
The main components in a boiler system are boiler feedwater heaters, deaerators, feed pump,
economiser, superheater, attemperator, steam system, condenser and condensate pump. In
addition, there are sets of controls to monitor water and steam flow, fuel flow, airflow and
chemical treatment additions.
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More broadly speaking, the boiler system comprises a feedwater system, steam system and fuels
system. The feedwater system provides water to the boiler and regulates it automatically to meet
the steam demand. Various valves provide access for maintenance and repair.
The stem system collects and controls the steam produced in the boiler. Steam is directed
through a piping system to the point of use. Throughout the system, steam pressure is regulated
using valves and checked with steam pressure gauges. The fuel system includes all equipment
used to provide fuel to generate the necessary heat. The equipment required in the fuel system
depends on the type of fuel used in the system.
Feedwater system
The water supplied to the boiler, which is converted into steam, is called feedwater. The two
sources of feedwater are condensate or condensed steam returned from the process and makeup
water (treated raw water) which must come from outside the boiler room and plant processes.
Feedwater heater
Boiler efficiency is improved by the extraction of waste heat from spent steam to preheat the
boiler feedwater. Heaters are shell and tube heat exchangers with the feedwater on the tube side
(inside) and steam on the shell side (outside). The heater closest to the boiler receives the hottest
steam. The condensed steam is recovered in the heater drains and pumped forward to the heater
immediately upstream, where its heat value is combined with that of the steam for that heater.
Ultimately the condensate is returned to the condensate storage tank or condenser hotwell.
Deaerators
Feedwater often has oxygen dissolved in it at objectionable levels, which comes from air in-
leakage from the condenser, pump seals, or from the condensate itself. The oxygen is
mechanically removed in a deaerator. Dearators function on the principle that oxygen is
decreasingly soluble as the temperature is raised. This is done by passing a stream of steam
through the feedwater. Deaerators are generally a combination of spray and tray type. One
problem with the control of deaerators is ensuring sufficient temperature difference between the
incoming water temperature and the stripping steam. If the temperature is too close, not enough
steam will be available to strip the oxygen from the make-up water.
Economisers
Economisers are the last stage of the feedwater system. They are designed to extract heat value
from exhaust gases to heat the steam still further and improve the efficiency of the boiler. They
are simple finned tube heat exchangers. Not all boilers have economizers. Usually they are found
only on water tube boilers using fossil fuel as an energy conservation measure.
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A feedwater economiser reduces steam boiler fuel requirements by transferring heat from the
flue gas to incoming feedwater. By recovering waste heat, an economiser can often reduce fuel
requirements by 5 per cent to 10 per cent and pay for itself in less than two years.
A feedwater economiser is appropriate when insufficient heat transfer surface exists within the
boiler to remove combustion heat. Boilers that exceed 100 boiler hp, operating at pressures
exceeding 75 psig or above, and those that are significantly loaded all year long are excellent
candidates for economiser retrofit.
Steam system
Steam and mud drums
A boiler system consists of a steam drum and a mud drum. The steam drum is the upper drum of
a watertube boiler where the separation of water and steam occurs. Feedwater enters the boiler
steam drum from the economizers or from the feedwater heater train if there is no economiser.
The colder feedwater helps create the circulation in the boiler.
The steam outlet line normally takes off from this drum to a lower drum by a set of riser and
downcomer tubes. The lower drum, called the mud drum, is a tank at the bottom of the boiler
that equalizes distribution of water to the generating tubes and collects solids such as salts
formed from hardness and silica or corrosion products carried into the boiler.
In the circulation process, the colder water, which is outside the heat transfer area, sinks and
enters the mud drum. The water is heated in the heat transfer tubes to form steam. The steam-
water mixture is less dense than water and rises in the riser tubes to the steam drum. The steam
drum contains internal elements for feedwater entry, chemical injection, blowdown removal,
level control, and steam-water separation. The steam bubbles disengage from the boiler water in
the riser tubes and steam flows out from the top of the drum through steam separators.
Boiler tubes
Boiler tubes are usually fabricated from high-strength carbon steel. The tubes are welded to form
a continuous sheet or wall of tubes. Often more than one bank of tubes is used, with the bank
closest to the heat sources providing the greatest share of heat transfer. They will also tend to be
the most susceptible to failure due to flow problems or corrosion/ deposition problems.
Superheaters
The purpose of the superheater is to remove all moisture content from the steam by raising the
temperature of the steam above its saturation point. The steam leaving the boiler is saturated, that
is, it is in equilibrium with liquid water at the boiler pressure (temperature).
The superheater adds energy to the exit steam of the boiler. It can be a single bank or multiple
banks or tubes either in a horizontal or vertical arrangement that is suspended in the convective
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or radiation zone of the boiler. The added energy raises the temperature and heat content of the
steam above saturation point.
In the case of turbines, excessive moisture in the steam above saturation point. In the case of
turbines, excessive moisture in the steam can adversely affect the efficiency and integrity of the
turbine. Super-heated steam has a larger specific volume as the amount of superheat increases.
This necessitates larger diameter pipelines to carry the same amount of steam. Due to
temperatures, higher alloy steel is used. It is important that the steam is of high purity and low
moisture content so that non-volatile substances do not build up in the superheater.
Attemperators
Attemperation is the primary means for controlling the degree of superheat in a superheated
boiler.
Attemperation is the process of partially de-superheating steam by the controlled injection of
water into the superheated steam flow. The degree of superheat will depend on the steam load
and the heat available, given the design of the superheater. The degree of superheat of the final
exiting steam is generally not subject to wide variation because of the design of the downstream
processes. In order to achieve the proper control of superheat temperature an attemperator is
used.
A direct contact attempaerator injects a stream of high purity water into the superheated steam. It
is usually located at the exit of the superheater, but may be placed in an intermediate position.
Usually, boiler feedwater is sued for attemperation. The water must be free of non-volatile solids
to prevent objectionable buildup of solids in the main steam tubes and on turbine blades.
Since attemperator water comes from the boiler feedwater, provision for it has to be made in
calculating flows. The calculation is based on heat balance. The total enthalpy (heat content) of
the final superheat steam must be the mass weighted sum of the enthalpies of the initial superheat
steam and the attemperation water.
Condensate systems
Although not a part of the boiler per se, condensate is usually returned to the boiler as part of the
feedwater. Accordingly, one must take into account the amount and quality of the condensate
when calculating boiler treatment parameters. In a complex steam distribution system there will
be several components. These will include heat exchangers, process equipment, flash tanks, and
storage tanks. Heat exchangers are the places in the system where steam is used to heat a process
or air by indirect contact. Shell and tube exchangers are the usual design, with steam usually on
the shell side. The steam enters as superheated or saturated and may leave as superheated,
saturated, or as liquid water, depending on the initial steam conditions and the design load of the
exchanger.
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Process equipment includes turbines whether used for HVAC equipment, air compressors, or
turbine pumps. Condensate tanks and pumps are major points for oxygen to enter the condensate
system and cause corrosion. These points should be monitored closely for pH and oxygen ingress
and proper condensate treatment applied.
Fuel system
Fuel feed systems play a critical role in the performance of boilers. Their primary functions
include transferring the fuel into the boiler and distributing the fuel within the boiler to promote
uniform and complete combustion. The type of fuel influences the operational features of a fuel
system
The fuel feed system forms the most significant component of the boiler system.
Feed system for gaseous fuels
Gaseous fuels are relatively easy to transport and handle. Any pressure difference will cause gas
to flow, and most gaseous fuels mix easily with air. Because on-site storage of gaseous fuel is
typically not feasible, boilers must be connected to a fuel source such as a natural gas pipeline.
Flow of gaseous fuels to a boiler can be precisely controlled using a variety of control systems.
These systems generally include automatic valves that meter gas flow through a burner and into
the boiler based on steam or hot water demand.
The purpose of the burner is to increase the stability of the flame over a wide range of flow rates
by creating a favourable condition for fuel ignition and establishing aerodynamic conditions that
ensure good mixing between the primary combustion air and the fuel. Burners are the central
elements of an effective combustion system.
Other elements of their design and application include equipment for fuel preparation and air-
fuel distribution as well as a comprehensive system of combustion controls. Like gaseous fuels,
liquid fuels are also relatively easy to transport and handle by using pumps and piping networks
that link the boiler to a fuel supply such as a fuel oil storage tank. To promote complete
combustion, liquid fuels must be atomized to allow through mixing with combustion air.
Atomisation by air, steam, or pressure produces tiny droplets that burn more like gas than liquid.
Control of boilers that burns liquid fuels can also be accomplished using a variety of control
systems that meter fuel flow.
Feed system for solid fuels
Solid fuels are much more difficult to handle than gaseous and liquid fuels. Preparing the fuel for
combustion is generally necessary and may involve techniques such as crushing or shredding.
Before combustion can occur, the individual fuels particles must be transported from a storage
area to the boiler.
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Mechanical devices such as conveyors, augers, hoppers, slide gates, vibrators, and blowers are
often used for this purpose. The method selected depends primarily on the size of the individual
fuels particles and the properties and characteristics of the fuel.
Stokers are commonly used to feed solid fuel particles such as crushed coal, TDF, MSW, wood
chips, and other forms of biomass into boilers. Mechanical stokers evolved from the hand-fired
boiler era and now include sophisticated electromechanical components that respond rapidly to
changes in steam demand.
The design of these components provides good turndown and fuel-handling capability. In this
context, turndown is defined as the ratio of maximum fuel flow to minimum fuel flow.
In the case of pulverized coal boilers, which burn very fine particles of coal, the stoker is not
used. Coal in this form can be transported along with the primary combustion air through pipes
that are connected to specially designed burners.
A burner is defined as a devices or group of devices for the introduction of fuel and air into a
furnace at the required velocities, turbulence, and concentration to maintain ignition and
combustion of fuel with in the furnace. Burners for gaseous fuels are less complex than those for
liquid or solid fuels because mixing of gas and combustion air is relatively simple compared to
atomizing liquid fuels or dispersing solid fuel particles.
The ability of a burner to mix combustion air with fuel is a measure of its performance. A good
burner mixes well and liberates a maximum amount of heat from the fuel. The best burners are
engineered to liberate the maximum amount of heat from the fuel and limit the amount of
pollutants such as CO, NOx, and PM that are released. Burners with these capabilities are now
used routinely in boilers that must comply with mandated emission limitations.
Mukwano Industries’ Boilers
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Cocomax is a high-efficiency packaged smoke tube boiler designed to use crushed wood husks
as fuel. It can achieve an unmatched efficiency of 81%.
Product Features
Low cost heating
Bubbling bed combustion to enhance output and efficiency
Wood-husk fired boiler
Provided with unique combustor to prevent fuel from falling below the grate
Specially designed chromium grate bar to protect smoke tubes from abrasion
Fuel feeding can be mechanized as per customer requirement
Operating Range
Capacities: In the range of 2 to 5 TPH
Pressure: In the range of 10.54 to 17.5 kg/cm2 (g)
Firing fuels: Wood husk
Efficiency: Overall efficiency of 81 % (+/-2%)
Boiler System Failures
1. Dearator cracking: This is due to poorly treated water which causes corrosion at welds
and heat-affected zones near the welds.
2. Feedwater Line Erosion: This is due to high velocity water.
3. Economizer tubes
4. Faults due to over-heating
5. Failures due to corrosion.
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SOAP PLANT
In the soap plant, manufacture of soaps at Mukwano Industries takes place. Below is a process
flow diagram of soap-making.
Process Description
The process starts off from the mixing of sodium silicate, china clay and salt. These are then
taken in a mixing tank in the required quantity and mixed thoroughly into a homogenous mass.
The basic raw materials of soap making are thus; oil (containing FFA greater than 10%), caustic
soda, steam, salt and scarp soap.
1. Crutcher
-The crutcher is a vertical mixer used in the semi-boiled batch saponification, for
the neutralization of fatty acids with caustic soda and for the neutral fats
saponification.
-The crutcher is also used to add additives such as caoline, silicate and to color the
laundry soap in the drying plant.
-Another use of the crutcher is the synthetic detergent soaps base production.
-The crutcher can operate either at atmospheric pressure of pressurized.
-The crutcher is provided with a vertical mixing worm placed inside a containing
tube which assures a strong mixing of the material to be processed.
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-The worm directs the fluent ascendant movement of the material to be processed
inside the containing tube and the fluent descendent movement outside the
containing tube.
2. The Dryer
Here, the continuous drying of the laundry soap takes place.
Neat Soap Filtration
The liquid soap is pumped through the soap filter into the service tank.
Neat Soap Heating
The liquid soap is fed by the feeding pump into the heat exchanger where
it is heated at 80 to 90 degrees centigrade.
Drying
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The heated liquid soap is atomized inside of the atomizer. The vapors
liberated inside (ones preformed inside heat exchanger and the ones
flashed off) are sucked away by the vacuum system. Soap that is sprayed
on the wall of the atomizer is, at this point dry, cold and solid. The spray
dryer chamber is at a pressure of 5-6mm of Hg. It is scrapped off the wall
by action of rotary scrappers. Scrapped soap falls on the worms of the
plodder and is extruded out in form of pellets or continuous bar.
Soap Fines Separation and Recovery
The vapors containing the soap dusts formed during spraying, are
conveyed out of the atomizer through the cyclones where they are
separated from the dusts which falls on the bottom of cyclones and is
recovered.
Vapours Condensation
The vapors are condensed inside barometric condenser. The vacuum pump
produces and maintains the vacuum degree inside the plant by removing
all uncondensables.
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Plodding and Extrusion
The dried soap is then forced out by a twin-worm plodder through a
perforated plate. The soap, coming out through the perforated plate is cut
into small pieces by a rotating knife cutter. The pieces are finally extruded
in the form of a bar through the nozzle plate of the specified dimensions.
Packing
Here, stamping, wrapping and packing takesplace which completes the
soap process.
Main Task Carried Out In the Soap Plant
1. Pump diagnosis and repair
2. Valve replacements
3. Replacement of Gaskets
4. Repair of conveyors
5. Preventive Maintenance
6. Breakdown Maintenance
7. Compressor fault-finding and maintenance
8. Repairs done on wrapping and sealing machines
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PRODUCTION OF VEGETABLE OIL
At Mukwano Industries, the main section to do with Production of Vegetable Oil is AK Oils and
Fats (AKOF).
Extraction
Oil is extracted from beans, grains, seeds, nuts, and fruits. The raw materials are received at the
facility and stored before initial processing. The type of storage depends on the raw material,
(e.g. soybeans are stored in grain elevators). The raw materials are prepared using a variety of
processes, including cleaning, drying, crushing, conditioning, and pressing. Beans are processed
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into flakes so that the oil cells are exposed, facilitating oil extraction, and fruits are pressed to
extract oil.
Oil extraction can be performed mechanically (e.g. by boiling fruits and pressing seeds and nuts)
or in combination with the use of solvents. During solvent extraction, hexane is used to wash the
processed raw materials, typically in a countercurrent extractor.
Refinement
The crude oil is refined to remove undesired impurities such as gums, free fatty acids (FFA),
traces of metals, coloring components, and volatile components. During refining, the FFA are
removed to the level of less than 0.1 percent in the refined oil either by chemical or physical
refining. Where appropriate, preference should be given to physical rather than chemical refining
of crude oil as the bleaching earth used in this process has a lower environmental impact.
Conversely, chemical refining results in a better product quality in terms of lower FFA levels,
longer shelf life, and a more reliable process
Chemical Refining
Conventional chemical refining involves degumming for the removal of phospholipids,
neutralization for the removal of FFA, and bleaching for decolorization and deodorization. Water
is added during degumming to hydrate any gums present and the mixture is then centrifuged for
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separation. Non-hydratable gums are removed using phosphoric or citric acid before water is
added and separation takes place in a centrifuge. During degumming, caustic soda is added to the
oil, which has been preheated to between 75oC and 110oC to saponify the FFA. This process
gives rise to two main outputs, namely semirefined oil and soap stock. The soap stock is
removed by precipitation followed by sedimentation or centrifugation and may be further
processed into acid oils by splitting. The soap stock is heated to between 70oC and 100oC and
reacts with sulfuric acid to reform the fatty acids. The resulting by-products can be sold to the
paints and cosmetics sector, as well as to the animal feed industry. The neutralized oil is
bleached to remove coloring matter and other minor constituents.
Physical Refining
Physical refining is a more simple process in which the crude oil is degummed and bleached, and
then steam stripped to remove FFA, odor, and VOCs all in one step. A physical pretreatment can
be used to achieve a low phospholipid content by degumming and using bleaching earth.
Following this, FFA can be stripped from the physically pretreated oil using steam in a vacuum
at temperatures of around 250oC and refined by the oil flowing over a series of trays
countercurrent to the flow of the stripping steam. Previous neutralization stages are not necessary
because the neutralization and deodorization are combined. A scrubber is then used to condense
the greater part of the fat from the vapors as a water-free product.
Other Modifications
1. Hydrogenation
Most installations carry out hydrogenation to produce fats with superior retention
qualities and higher melting points. Hydrogenation is usually carried out by
dispersing hydrogen gas in the oil in the presence of a finely divided nickel
catalyst supported on diatomaceous earth. The resultant hydrogenated fats are
filtered to remove the hydrogenation catalyst, subjected to a light earth bleach,
and deodorized before they can be used for edible purposes. After hardening, the
oil is mixed with an aqueous solution to produce an emulsion. The emulsified
mixture is then pasteurized, cooled, and crystallized to obtain the final product.
2. Interestification
Interestification involves the separation of triglycerides into fatty acids and
glycerol followed by recombination. The reaction is carried out using phosphoric
or citric acid with a catalyst, typically sodium methoxide. Interestification
modifies the functional properties of the treated oil and may be carried out after
neutralization or deodorization.
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Deodorization
During deodorization, the bleached oil is steam-distilled at low pressure to remove volatile
impurities, including undesirable odors and flavors. Volatile components are removed from the
feedstock using steam in a process that may last from 15 minutes to 5 hours. The vapors from the
deodorizer contain air, water vapor, fatty acids, and other variables. Before entering the vessel,
the vapors pass through a scrubber and a scrubbing liquid is sprayed in the vapor stream. Fatty
acids and volatiles partly condense on the scrubbing droplets or alternatively on the packing
material. This process produces the fully refined, edible oils and fats.
Filmatics
This is the final process to the processing of vegetable oil and it simply involves the use of
electro-mechanical machines to fill the ready cooking oil in their respective containers ready for
consumption.
Tasks In This Section
1. Repairing pumps in the physical and chemical refinery
2. Stopping leakages on steam, water and air lines
3. Preventive maintenance of various equipment in the refineries
4. Repairing of filmatic machines during break-down.
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BEVERAGES
This is the section where Aqua Sipi water is made from. Currently, the company uses a fully
automated plant to process its water. From the borehole area, water is stored in water reservoirs
awaiting transportation.
Water is loaded onto trucks and transported to the beverages plant. The water goes through the
filtration stage passing through the sand filter (removing 50 micron particle sizes) to the carbon
filter. The main use of the carbon filter is to remove smell, dechlorinate the water, and absorb
dust.
The water is then sent to the UV system filter before it‘s sent for the ozonation process. This
process is carried out by the ozone generator which has a high electrical discharge. The ozone
reacts with the water and kills bacteria. The advantage of which, is that it never produces any by-
products and has a half-life period of 28 minutes thus helps to preserve the water.
Once the ozonation is done, water is bottled and filled, and shrink sealing tunneling takes place.
The final process involves cartooning, and palletizing the read drinking mineral water.
How The Bottles Get to The Line
The pet-jar bottles are fed onto the bottle feed conveyor. Thereafter, they go through bottle
rinsing. The washed bottles are then made available for filling. Bottle rinsing is done using a
combination of steam and the UV system.
Tasks Handled In the Section
1. Replacement of moulds in the cap making and bottle making machines.
2. Working on faults on the stretch blow moulding machines.
3. Chiller and compressor breakdown maintenance.
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PLASTICS SECTION
The plastics section of the Mukwano Group is at AK Plastics. Plastic products at this section are
formed through a manufacturing process known as Plastic Blow Molding.
Plastic Blow Molding
These processes represent the most popular way of producing hollow products such as bottles,
drums, and other vessels out of thermoplastic materials. This modern industrial technology has
evolved from the ancient art of glass blowing.
Among the many types of resins used are:
• various densities of polyethylene
• polyethylene terephthalate polypropylene
• polyvinyl chloride
• thermoplastic elastomers
• polystyrene
• fluoropolymers, and many others
The principle process is ―extrusion blow molding.‖ Others include injection blow molding,
biaxial stretch blow molding, and co-extrusion blow molding.
All of which utilize elements of either extrusion or injection, or both. All of the processes share
distinct production stages:
• plasticizing or the melting of resin
• Parison production which refers to most blow molding operations; or preform production when
referring to biaxial stretch blow molding
• Inflation and cooling phases in the mold
• Ejection from the mold
A fifth stage required in extrusion blow molding involves trimming the final product.
Process Operation
The same blowing technique is common to all the process variations and is accomplished
through either a blow pin, needle, stuffer, or a core rod.
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The process begins with applications of heat and pressure to create the ―melt.‖ The melt is then
processed through a reciprocating screw and ram assembly that pushes the material through a die
to produce the ―parison.‖ This production of the parison may be continuous or intermittent and is
similar to the injection molding process. The reciprocal screw, which heats and moves the resin,
has feed, compression, and metering zones. Once the proper amount of melt is available, a
ramming action delivers the material to the die and forms the parison. In the case where very
large parisons need to be formed, an accumulator type of machine is used. This is reservoir
system, which allows a melt delivery rate independent of the screw and ramming sequences.
In the continuous extrusion form of blow molding. The screw does not reciprocate, but continues
turning and thus continuously delivers melt to the head and die assemblies, forming a continuous
parison. Most extruder head and die assemblies are known as the ―cross head‖ type which divert
the flow of the resin from horizontal to vertical. Crossheads may either be center-feed or side-
feed. The center-feed design produces a uniform flow downward around the tip of conical core
or mandrel and results in a straight flow all around the mandrel. Side-feed assemblies force the
resin around the perimeter of the mandrel and then extruded through the die as a parison with
varying wall thickness‘. To control the parison‘s temperature and wall thickness, a programmer
is used.
While the intermittent extrusion system is able to produce a wide range of products, the
continuous system uses several process variations that widen the product range even further.
These include the shuttle or reciprocating blow molding system and the rotary wheel blow
molding system.
The shuttle system uses multiple molds and so requires multiple parisons. To accomplish this a
manifold is used to distribute the melt to several dies at once as the parisons arrive at the molds
blow position. A cutting device separates the required portion of the continuous parison, a blow
pin or needle is inserted in the parison and with a jet of air the product is blown into shape. For
high volume production, 20 or more split molds can be mounted on a horizontal turntable or
vertical rotary wheel for continuous molding.
Injection blow molding utilizes elements of conventional thermoplastic injection molding. This
is more economical than the extrusion process and generally is used for large production
quantities of smaller containers of less than liter size. Basically, the systems include an injection
station, a blow station, and a strip or eject station.
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Plastics Formation Explained
Plastics can be subdivided into three main categories, thermoplastics, thermosets and elastomers.
Thermoplastics melt and flow when heated and solidify as they cool. On subsequent re-heating
they regain the ability to flow. This means they can be reprocessed and hence recycled by re-
melting them. Thermoplastics are used to make consumer items such as drinks containers, carrier
bags and buckets. Thermosets materials decompose before they can melt, therefore, they cannot
be reprocessed in the same way as thermoplastics. An Elastomer is ‗a material that, at room
temperature, can be stretched repeatedly to at least twice its original length, and upon immediate
release of the stretch, will return with force to its approximate original length‘. Which means, to
put it in layman‘s terms, it‘s rubbery!
Injection Molding Machinery
The basic parts of an injection molding machine are:
3. Injection Unit
4. Machine Base with Hydraulics
5. Control Unit and Control Cabinet
6. Clamping Unit with Mould
The Injection Unit
The first aim of the plastication stage is to produce a homogeneous melt for the next stage where
the material enters the mould. A second important function of the injection unit is the actual
injection into the mould. Here, it is important that injection speeds are reproducible as slight
changes can cause variations in the end product.
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There are two different injection units available. There is the Piston (plunger) injection unit
which is being phased out. The other one, which is used world-wide and at Mukwano is the
Reciprocating Screw Piston injection unit.
In the screw piston injection unit, the material is plasticized and dosed simultaneously as
previously described. The design of a plasticising screw has several advantages over a piston
type mainly in the ability to produce a homogeneous melt as a result of mixing. The flow of the
material is also improved as shear from the screw lowers the viscosity of the material. The long
residence times present in the piston type machines are eliminated allowing heat sensitive
materials such as PVC to be processed. The screw is also easier to purge and less prone to
degradation or material hang-ups.
Important parameters for these screws are:
1. The diameter of the screw and the ratio of the diameter to the length
2. Shot Capacity: This is the amount of material required to fill a moulding tool.
3. Plasticizing Capacity: This is the maximum rate at which the injection unit can deliver
polymer melt.
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The Feeding Hopper
Material is placed in the hopper prior to plastication. It must be designed to avoid material
bridging in the throat and to let gravity feed the material. Material hold up spots must be
avoided. Additives, especially when they are different weights to the polymer, may tend to
accumulate and be fed inconsistently. This can lead to variations in melt quality. The hopper may
contain magnets to collect metal contamination, which must be prevented from entering the feed
system. It may also contain grids to prevent large particulates from entering and blocking the
feeding system, especially important if using recyclate materials. Keeping the feed system cool is
also important, if material begins to melt in the throat of the feeding system it may stick to the
sides of the throat and in extreme cases block the machine completely.
The Injection Cylinder
Once the material has passed through the hopper, it enters the injection barrel. The barrel will
consist of a number of separately controlled heating zones as can be seen. The heat is generated
from conduction of heat from the cylinder and also the heat generated by the shearing action of
the screw on the material feedstock. Polymers are not particularly good conductors of heat;
therefore the polymer thickness in any section of the screw tends to be kept low. The amount of
shear is material dependent, mainly viscosity related and controlled by the machine screw back
and back pressure.
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Non-Return Valve
Many materials require the use of a valve with a check ring to be fitted to the end of the screw to
prevent backflow. They also help to ensure that a constant cavity pressure is maintained. The
most important design consideration is that they should avoid flow restrictions or hold up of the
melt flow.
Non-return valves are more prone to wear than other components, so it must be ensured that
suitably toughened materials are used in manufacture.
The Nozzle
The nozzle provides the connection between the injection cylinder and the mould tool. Its job is
to convey the material with minimal pressure or heat change. There are two common types of
nozzle.
-Open Nozzle
-Nozzle shut-off Valve
Clamping Units
The clamping units of injection machines are described and rated separately to the injection unit.
The clamping units are required to enable mounting and holding of the two mould halves. They
must also provide sufficient clamping force during injection and cooling to enable effective
moulding. The mould halves must also open and close accurately and smoothly to enable part
injection and begin the next process cycle. Injection machines can be run by hydraulics, a
hydraulic and toggle combination or by electrical power. The clamping units on injection
moulding machines use hydraulic force.
Figure below shows a clamping unit. The stationary platen is attached to the machine with four
tie rods connecting it to the movable platen. The clamp ram moves the moving platen until it
reaches the stationary platen and the pressure begins to build up. The ejectors are fitted onto the
moving platen and can be activated once the tool is opened and the moving platen retracted.
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Differential Piston System
For the opening and closing movements of the mould tool a minimal volume of oil is required.
The oil volume required from the pump results from the differential surface and stroke of the
piston (approx. 7% of the clamping cylinder volume). The rest of the oil flows through the
borings in the main piston as a result of the piston stroke.
When opening with increased opening force (high pressure opening) the control piston closes the
main piston. The main piston and opening piston now open the mould with 50 bar pressure.
When the injection unit is in the vertical position and ‗braking‘ is selected, the borings in the
main piston are closed shortly before the end of the opening motion, This ensures an exact
positioning of the movable platens in their lower-most end position. Sinkage of the movable
platern on an idle machine is also avoided.
Mould Weights
Each machine will have a maximum permitted mould weight for the movable mould halves.
These values should not be exceeded for any reason as production problems and premature wear
would be the result.
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Mould Clamping Force
The mould clamping force must be set high enough to prevent flash. This is caused by the
swelling of the mould under the compound force during initial injection resulting in the
compound coming out of the mould cavity. The mould clamping force required depends on the
size of the moulded component surface projected onto the parting plane, and on the internal
mould pressure.
The type of clamp and the clamping force are the main specifications of a clamping unit.
However, there are other design features which also need consideration. These are:
• Maximum daylight
•Space between tie bars
•Clamp stroke
•Clamp speed
•Knockout stroke.
Injection Mould Tooling Basics
An injection mould tool has two major purposes:
•It is the cavity into which the molten plastic is injected
• The surface of the tool acts as a heat exchanger (as the injected material solidifies with contact)
Injection mould designs differ depending on the type of material and component being moulded.
Mould tool design and component design are equally important considerations for success.
After parts are injection moulded they must be ejected. A variety of mechanisms can be
employed such as ejector pins, sleeves, plates or rings. The design standard for injection mould
tools is the two-plate design.
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The Feed System
The feed system accommodates the molten polymer coming from the barrel and guides it into the
mould cavity. Its configuration, dimensions and connection with the moulding greatly affect the
mould filling process and subsequently, the quality of the product. A design that is based
primarily on economic viewpoints, (rapid solidification and short cycles) is mostly incompatible
with quality demands. The two main areas that need to be considered are the runner system and
the gate.
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Ejection Systems
After a component has solidified and cooled down, it needs to be removed from the mould
cavity. Ideally, this is done by gravity and the part falls to the floor. However, some components
with design features such as undercuts, adhesion or internal stresses may have to be removed
from the mould manually or by robots.
Ejection equipment is usually actuated mechanically by the opening stroke of the moulding
machine. If this simple arrangement is insufficient, ejection can be performed pneumatically or
hydraulically.
The ejector system is normally housed in the movable mould half. Mould opening causes the
mechanically actuated ejector system to move towards the parting line and to eject the moulding.
The result of this procedure is that the moulding stays on or in the movable mould half. This can
be achieved by undercuts or by letting the moulding shrink onto a core. Taper and surface
treatment should prevent too much adhesion.
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Venting
Another design aspect of tooling is the need to provide vents for compressed air and gases to
escape during moulding. Trapped air and gases can cause a variety of moulding defects such as:
1. short shots (incomplete filling of the mould)
2. scorching or burning
3. shrinkage (often seen as ripples or depressions in finished parts)
4. in extreme cases volatile gases may cause etching on the mould surface.
Process Control Systems
The control system is there to ensure repeatability during moulding operation. It monitors both
the hydraulic system and the process parameters such as temperature, injection speed, screw
retraction speed and injection and back pressure. The ability to control the process has a direct
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impact on final part quality, part to part consistency and economy. The nature of the control
system may vary from a simple relay switch to a complex microprocessor system with closed-
loop control.
The major mechanical control components include:
1. The Pump: The hydraulic pump generally draws the hydraulic fluid from the supply
reservoir and delivers it to the pump outlet.
2. The Motor: Hydraulic motors transform the hydraulic energy supplied by the pumps
back into a mechanically- utilized working force with a rotary motion.
3. The Cylinder: The cylinder (located behind the injection unit) is charged with hydraulic
fluid through valves in the base and the head. Through this, a motion is transferred
through the piston surface of the working cylinder to the piston‘s connecting rod.
4. Directional Valves: The function of directional valves is to block different hydraulic
lines from one another or to open them, and to continually create alternating line
connections. In this manner, the effective direction of pressures and volume flows is
influenced, and the starting, stopping and the direction of motion of the consumer
(cylinder or hydraulic) motor are thus controlled.
5. Pressure Valves: Pressure control valves have the primary task of limiting pressure in the
system and thus protecting individual components and lines from rupturing or
overloading. The valve opens when a predetermined pressure is reached and conveys the
pump‘s excess delivery flow back into the tank.
6. Flow Regulator Valves: The task of the flow-regulator valve is to influence volume flow
by changing the diameter of the valve governor, and thus to control the speeds of
cylinders and hydraulic motors.
7. Check Valves: Non-return valves have the task of blocking the volume flow in one
direction and allowing free-flow in the opposite direction. The blockage should provide
completely leakproof sealing. Balls or cones are used primarily as sealing elements.
8. Receivers: Hydropneumatic receivers have the task of collecting and storing hydraulic
energy, and then releasing it on demand. This type of receiver is used in conjunction with
injection moulding machines with very rapid injection (with accumulator). Here, a high
volume flow which can be partially accessed from the receiver is required periodically
for brief intervals. The benefits in the application of a hydropneumatic receiver are in the
use of relatively small pumps, drive motors and oil reservoirs. The working principle of a
receiver is that it is virtually impossible to compress the hydraulic fluid. If it is
nevertheless to be stored under pressure, a gas is utilized, in this case nitrogen. The gas is
compressed in a pressure reservoir by the hydraulic fluid and decompresses as needed
through the release of fluid. In order to ensure that the gas does not mix with the
hydraulic fluid, the pressure reservoir is divided into two chambers by an elastic
separation wall (membrane).
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Tasks Handled At The Plastics Section
1. Mould Replacements
2. Trouble shooting of faults on the injection moulding machines
3. Preventive Maintenance
4. Machining jobs in the Workshop at Plastics
UTILITIES
There is machinery and equipment, that is required for the successful running of a plant and it
includes:
1. Pumps
2. Compressors
3. Chillers
4. Heat Exhangers
5. Valves
PUMPS
A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical
action.
Classification of Pumps
All pumps may be divided into two major categories: (1) dynamic, in which energy is
continuously added to increase the fluid velocities within the machine
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to values greater than those occurring at the discharge so subsequent velocity reduction within or
beyond the pump produces a pressure increase, and (2) displacement, in which energy is
periodically added by application of force to one or more movable boundaries of any desired
number of enclosed, fluid-containing volumes, resulting in a direct increase in pressure up to the
value required to move the fluid through valves or ports into the discharge line.
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Pump Priming
Centrifugal pumps usually are completely filled with the liquid to be pumped before starting.
When so filled with liquid, the pump is said to be primed. Pumps have been developed to start
with air in the casing and then be primed. This procedure is unusual with low-specific-speed
pumps but is sometimes done with propeller pumps. In many installations, the pump is at a lower
elevation than the supply and remains primed at all times. This is customary for pumps of high
specific speed and all pumps requiring a positive suction head to avoid cavitation.
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Pumps operated with a suction lift may be primed in any of several ways. A relatively
inexpensive method is to install a special type of check valve, called a foot valve, on the inlet end
of the suction pipe and prime the pump by filling the system with liquid from any available
source. Foot valves cause undesirable frictional loss and may leak enough to require priming
before each starting of the pump. A better method is to close a valve in the discharge line and
prime by evacuating air from the highest point of the pump casing.
Many types of vacuum pumps are available for this service. A priming chamber is a tank that
holds enough liquid to keep the pump submerged until pumping action can be initiated. Self-
priming pumps usually incorporate some form of priming chamber in the pump casing.
The Commonest Pumps At Mukwano
1. Gear Pump
This is the simplest of rotary positive displacement pumps. It consists of two meshed
gears that rotate in a closely fitted casing. The tooth spaces trap fluid and force it around
the outer boundary. The fluid does not travel back on the meshed part, because the teeth
mesh closely in the centre.
2. Screw Pump
A Screw pump is a more complicated type of rotary pump that uses two or three screws
with opposing thread—e.g., one screw turns clockwise and the other counterclockwise.
The screws are mounted on parallel shafts that have gears that mesh so the shafts turn
together and everything stays in place. The screws turn on the shafts and drive fluid
through the pump. As with other forms of rotary pumps, the clearance between moving
parts and the pump's casing is minimal.
3. Plunger Pump
Plunger pumps are reciprocating positive displacement pumps. These consist of a
cylinder with a reciprocating plunger. The suction and discharge valves are mounted in
the head of the cylinder. In the suction stroke the plunger retracts and the suction valves
open causing suction of fluid into the cylinder. In the forward stroke the plunger pushes
the liquid out of the discharge valve. Efficiency and common problems: With only one
cylinder in plunger pumps, the fluid flow varies between maximum flow when the
plunger moves through the middle positions, and zero flow when the plunger is at the end
positions. A lot of energy is wasted when the fluid is accelerated in the piping system.
Vibration and water hammer may be a serious problem.
4. Centrifugal Pump
A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the
pressure and flow rate of a fluid. Centrifugal pumps are the most common type of pump
used to move liquids through a piping system. The fluid enters the pump impeller along
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or near to the rotating axis and is accelerated by the impeller, flowing radially outward or
axially into a diffuser or volute chamber, from where it exits into the downstream piping
system. Centrifugal pumps are typically used for large discharge through smaller heads.
Centrifugal pumps are most often associated with the radial-flow type.
Centrifugal Pump Packing
Packing is used in the stuffing box of a centrifugal pump to control the leakage of the pumped
liquid out, or the leakage of air in,where the shaft passes through the casing. This basic form of a
seal can be applied in light- to medium-duty services and to those liquids that prove difficult for
mechanical seals.
How To Install A Packing
To install continuous coil packing, perform the following steps:
1. Loosen and remove the gland from the stuffing box.
2. Using a packing puller, begin to remove the old packing rings.
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3. Remove the split lantern ring (if present) and then continue removing the packing with the
puller.
4. After the packing has been removed, check the sleeve for scoring and nicks. If the shaft sleeve
or shaft cannot be cleaned up, it must be replaced. Check the size of the stuffing box bore and the
shaft sleeve or shaft diameter to determine which size packing should be used.
5. After the size of the packing has been determined, wrap the packing tightly around a mandrel,
which should be the same size as the pump shaft or sleeve. The number of coils should be
sufficient to fill the stuffing box. Cut the packing along one side to form the individual rings.
6. Before beginning the assembly of any packing material,be sure to read all the instructions
from the manufacturer. Assemble the split packing rings on the pump. Each ring should be
sealed individually with the split ends staggered 90° and the gland tightened to seal and fully
compress the ring. Be sure the lantern ring is reinstalled correctly at the flush connection. Then
back off the gland and retighten it, but only finger-tight. The exception to this procedure is that
TFE packing should be installed one ring at a time, but not seated because TFE packings have
high thermal expansion.
7. Allow excess leakage during break-in to avoid the possibility of rapid expansion of the
packing, which could score the shaft sleeve or shaft so that leakage could not be controlled.
8. Leakage should be generous upon startup. If the packing begins to overheat at startup, stop the
pump and loosen the packing until leakage is obtained. Restart only if the packing is leaking.
Packing Troubles, Causes and Cures
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45
Water Hammering
Waterhammer is a very destructive force that exists in any pumping installation where the rate of
flow changes abruptly for various reasons.
Diagnostic Chart For Centrifugal pump Troubles
Pump Installation
The following factors are taken into consideration during pump installation:
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1. Pump Location: Working space must be checked to assure adequate accessibility for
maintenance. Pumps should be located as close as practicable to the source of liquid
supply. Whenever possible, the pump centerline should be placed below the level of the
liquid in the suction reservoir.
2. Foundation
3. Alignment
4. Grouting: The purpose of grouting is to prevent lateral shifting of the baseplate, to
increase the mass to reduce vibration, and to fill in irregularities in the foundation.
5. Doweling of Pump and Driver: When the pump handles hot liquids, doweling of both the
pump and its driver should be delayed until the unit has been operated. A final recheck of
alignment with the coupling bolts removed and with the pump and driver at operating
temperature is advisable before doweling.
Large pumps handling hot liquids are usually doweled near the coupling end, allowing
the pump to expand from that end out. Sometimes the other end is provided with a key
and a keyway in the casing foot and the baseplate.
Piping
Suction Piping: The suction piping should be as direct and short as possible. If a long suction
line is required, the pipe size should be increased to reduce frictional losses. (The exception to
this recommendation is in the case of boiler-feed pumps, where difficulties may arise during
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transient conditions of load change if the suction piping volume is excessive. This is a special
and complex subject, and the manufacturer should be consulted.)
Discharge Piping: Generally both a check valve and a gate valve are installed in thdischarge
line. The check valve is placed between the pump and the gate valve and protects the pump from
reverse flow in the event of unexpected driver failure or from reverse flow from another
operating pump. The gate valve is used when priming the pump or when shutting it down for
inspection and repairs. Manually operated valves that are difficult to reach should be fitted with a
sprocket rim wheel and chain. In many cases, discharge gate valves are motorized and can be
operated by remote control.
Pump Operation
Pumps are generally selected for a given capacity and total head when operating at rated speed.
These characteristics are referred to as ―rated conditions of service‖ and, with few exceptions,
represent those conditions at or near which the pump will operate the greatest part of the time.
Positive displacement pumps cannot operate at any greater flows than rated except by increasing
their speed, nor can they operate at lower flows except by reducing their operating speed or
bypassing some of the flow back to the source of supply.
On the other hand, centrifugal pumps can operate over a wide range of capacities, from near zero
flow to well beyond the rated capacity. Because a centrifugal pump will always operate at the
intersection of its head-capacity and system-head curves, the pump operating capacity may be
altered either by throttling the pump discharge (hence altering the system-head curve) or by
varying the pump speed (changing the pump head capacity curve).This makes the centrifugal
pump very flexible in a wide range of service and applications that require the pump to operate at
capacities and heads differing considerably from the rated conditions. There are, however, some
limitations imposed upon such operation by hydraulic, mechanical, or thermodynamic
considerations.
Priming
With very few exceptions, no centrifugal pump should ever be started until it is fully primed; that
is, until it has been filled with the liquid pumped and all the air contained in the pump has been
allowed to escape. The exceptions involve self-priming pumps and some special large-capacity,
low-head, and low-speed installations where it is not practical to prime the pump prior to
starting; the priming takes place almost simultaneously with the starting in these cases.
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Reciprocating pumps of the piston or plunger type are in principle self-priming. However, if
quick starting is required, priming connections should be piped to a supply above the pump.
Positive displacement pumps of the rotating type, such as rotary or screw pumps, have clearances
that allow the liquid in the pump to drain back to the suction. When pumping low-viscosity
liquids, the pump may completely dry out when it is idle. In such cases a foot valve may be used
to help keep the pump primed. Alternately, a vacuum device may be used to prime the pump.
When handling liquids of higher viscosity, foot valves are usually not required because liquid is
retained in the clearances and acts as a seal when the pump is restarted. However, before the
initial start of a rotating positive displacement pump, some of the liquid to be pumped should be
introduced through the discharge side of the pump to wet the rotating element.
How To Start A Pump
Assuming that the pump in question is motor-driven, that its shutoff power does not exceed the
safe motor power, and that it is to be started against a closed gate valve, the starting procedure is
as follows:
1. Prime the pump, opening the suction valve, closing the drains, and so on, to prepare the pump
for operation.
2. Open the valve in the cooling supply to the bearings, where applicable.
3. Open the valve in the cooling supply if the seal chambers are liquid-cooled.
4. Open the valve in the sealing liquid supply if the pump is so fitted.
5. Open the warm-up valve of a pump handling hot liquids if the pump is not normally kept at
operating temperature. When the pump is warmed up, close the valve.
6. Open the valve in the recirculating line if the pump should not be operated against dead
shutoff.
7. Start the motor.
8. Open the discharge valve slowly.
9. For pumps equipped with mechanical seals, check for seal leakage: there should be none.
10. For pump with shelf packing, observe the leakage from the stuffing boxes and adjust the
sealing liquid valve for proper flow to ensure the lubrication of the packing. If the packing is
new, do not tighten up on the gland immediately, but let the packing run in before reducing the
leakage through the stuffing boxes.
11. Check the general mechanical operation of the pump and motor.
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12. Close the valve in the recirculating line when there is sufficient flow through the pump to
prevent overheating.
If the pump is to be started against a closed check valve with the discharge gate valve open, the
steps are the same, except that the discharge gate valve is opened some time before the motor is
started.
In certain cases, cooling to the bearings and flush liquid to the mechanical seals or to the packing
seal cages is provided by the pump. This, of course, eliminates the need for the steps listed for
the cooling and sealing supply.
How To Stop A Pump
Just as in starting a pump, the stopping procedure depends upon the type and service of the
pump. Generally, the steps followed to stop a pump that can operate against a closed gate valve
are
1. Open the valve in the recirculating line.
2. Close the gate valve.
3. Stop the motor.
4. Open the warm-up valve if the pump is to be kept at operating temperature.
5. Close the valve in the cooling supply to the bearings and seal chambers.
6. If the sealing liquid supply is not required while the pump is idle, close the valve in this supply
line.
7. Close the suction valve, open the drain valves, and so on, as required by the particular
installation or if the pump is to be opened up for inspection.
If the pump is of a type that does not permit operation against a closed gate valve, steps 2 and 3
are reversed.
Most of the steps listed for starting and stopping centrifugal pumps are equally applicable to
positive displacement pumps. There are, however, two notable exceptions:
1. Never operate a positive displacement pump against a closed discharge. If the gate valve on
the discharge must be closed, always start the pump with the recirculation bypass valve open.
2. Always open the steam cylinder drain cocks of a steam reciprocating pump before starting, to
allow condensate to escape and to prevent damage to the cylinder heads.
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Maintenance Of Pumps
Because of the wide variation in pump types, sizes, designs, and materials of construction, these
comments on maintenance are restricted to those types of pumps most commonly encountered.
The manufacturer‘s instruction books must be carefully studied before any attempt is made to
service a particular pump.
The following is taken into consideration for maintenance:
1. Daily Observation of Pump Maintenance
When operators are on constant duty, hourly and daily inspections should be made and
any irregularities in the operation of a pump should be recorded and reported
immediately. This applies particularly to changes in sound of a running pump, abrupt
changes in bearing temperatures, and seal chamber leakage. A check of pressure gages
and of flowmeters, if installed, and vibration should be made routinely during the day. If
recording instruments are provided, a daily check should be made to determine whether
the current capacity, pressure, power consumption or vibration level indicates that further
inspection is required. If these readings are taken electronically, trending charts should be
produced to allow observation of changes as a function of time. Certain trends may allow
for scheduled outages to address deterioration of specific performance values.
2. Semiannual Inspection
The following should be done at least every six months:
1. For pumps equipped with shaft packing, the free movement of stuffing box glands
should be checked, gland bolts should be cleaned and lubricated, and the packing should
be inspected to determine whether it requires replacement.
2. The pump and driver alignment should be checked and corrected if necessary.
3. Housings for oil-lubricated bearings should be drained, flushed, and refilled with fresh
oil.
4. Grease-lubricated bearings should be checked to see that they contain the correct
amount of grease and that it is still of suitable consistency.
3. Annual Inspection
A very thorough inspection should be performed once a year. In addition to the
semiannual procedure, the following items should be considered:
1. Vibration trends should be reviewed. If the pump is trending toward unacceptable
vibration levels,
a. The bearings should be removed, cleaned, and examined for flaws and wear.
b. The bearing housings should be carefully cleaned.
c. Rolling element bearings should be examined for scratches and wear.
d. Immediately after cleaning, rolling element bearings that are considered acceptable for
reinstallation should be coated with oil or grease. Note: If there is any sign of damage, or
if the bearings were damaged during removal, they should be replaced with new bearings
of the correct size and type per the manufacturer‘s instruction book.
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e. The assembled rotor—or major rotor components if the rotor is not assembled of
shrink-fit components—should be checked for balance prior to reassembly in the pump.
2. For pumps equipped with shaft packing, the packing should be removed and the shaft
sleeves—or shaft, if no sleeves are used—should be examined for wear.
3. For pumps equipped with mechanical seals, if the seals were indicating signs of
leaking, they should be removed and returned to the seal manufacturer for inspection,
possible bench testing, and refurbishment.
4. When coupling halves are disconnected for an alignment check, the vertical shaft
movement of a pump with sleeve (journal) bearings should be checked at both ends with
packing or seals removed. Any movement exceeding 150% of the original design
clearance should be investigated to determine the cause. Endplay allowed by the bearings
should also be checked. If it exceeds that recommended by the manufacturer, the cause
should be determined and corrected.
5. All auxiliary piping, such as drains, sealing water piping, and cooling water piping,
should be checked and flushed, as necessary. Auxiliary coolers should also be flushed
and cleaned.
6. Pump equipped with stuffing boxes should be repacked, and the pump and driver
should be realigned and reconnected.
7. All instruments and flow-metering devices should be recalibrated, whenever feasible,
and—whenever possible—the pump should be tested to determine whether proper
performance is being obtained. If internal repairs are made, the pump should again be
tested after completion of the repairs.
Complete Overhaul
It is difficult to make general rules about the frequency of complete pump overhauls as it
depends on the pump service, the pump construction and materials, the liquid handled, and the
economic evaluation of overhaul costs versus the cost of power losses resulting from increased
clearances or of unscheduled downtime. Some pumps on very severe service may need a
complete overhaul monthly, whereas other applications require overhauls only every two to four
years or even less frequently.
A pump should not be opened for inspection unless either factual or circumstantial evidence
indicates that overhaul is necessary. Factual evidence implies that the pump performance has
fallen off significantly or that the noise or driver load indicates trouble.
Circumstantial evidence refers to past experience with the pump in question or with similar
equipment on similar service. In order to ensure rapid restoration to service in the event of an
unexpected overhaul, an adequate store of spare parts should be maintained at all times.
Diagnosis Of Pump Problems
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Pump operating problems may be either hydraulic or mechanical. In the first category, a pump
may fail to deliver liquid, it may deliver an insufficient capacity or develop insufficient pressure,
or it may lose its prime after starting. In the second category, it may consume excessive power,
or symptoms of mechanical difficulties may develop at the seal chambers or at the bearings, or
vibration, noise, or breakage of some pump parts may occur.
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Common Pump Problems
1. Suction Problems
1. Insufficient suction pressure
2. Partial loss of prime
3. Cavitation
4. Lift too high
5. Leaking suction at foot valve
6. Acceleration head requirement too high
2. System Problems
7. System shocks
8. Poorly supported piping, abrupt turns in piping, pipe too small, piping misaligned
9. Air in liquid
10. Overpressure or overspeed
11. Dirty liquid
12. Dirty environment
13. Water hammer
3. Mechanical Problems
14. Valves broken or badly worn
15. Packing worn
16. Obstruction under valve
17. Main bearings loose
18. Bearings worn
19. Oil level low
20. Plunger loose
21. Main bearings tight
22. Ventilation inadequate
23. Belts too tight
24. Driver misaligned
25. Condensation
26. Seals worn
27. Oil level too high
28. Pump not level and rigid
29. Packing loose
30. Corrosion
31. Valve binding
32. Valve spring broken
33. Cylinder plug loose
34. O-ring seal damaged
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CHILLERS
Chillers are typical refrigerant equipment that uses heat transfer between two different fluids to
achieve desired temperatures. Chillers are air-cooled or water-cooled, depending on the capacity
of the refrigeration system as well as the operating conditions of the system. The three primary
components of a chiller are condensers, compressors, and evaporators.
How A Chiller Operates:
1. Refrigerant flows over evaporator tube bundle and evaporates, removing heat energy
from the fluid.
2. The refrigerant vapor is drawn out of the evaporator by a compressor that ―pumps‖ the
vapor to the condenser.
3. The refrigerant condenses on the condenser cooling coils giving its heat energy to the
cooling fluid; the condensed refrigerant heads back to the evaporator.
Key Components of A Chiller
Evaporator
Chillers produce chilled water in the evaporator where cold refrigerant flows over the evaporator
tube bundle. The refrigerant evaporates (changes into vapor) as the heat is transferred from the
water to the refrigerant. The chilled water is then pumped, via the chilled-water distribution
system to the manufacturing plant‘s air-handling units.
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The chilled water passes through coils in the air-handler to remove heat from the air used in
various equipment. The warm water (warmed by the heat transferred from the plant machinery)
returns to the evaporator and the cycle starts over.
Compressor
This works on the principle of the refrigeration cycle. Vaporized refrigerant leaves the
evaporator and travels to the compressor where it is mechanically compressed, and changed into
a high-pressure, high-temperature vapor. Upon leaving the compressor, the refrigerant enters the
condenser side of the chiller.
Condenser
Inside the water-cooled condenser, hot refrigerant flows around the tubes containing the
condenser-loop water. The heat transfers to the water, causing the refrigerant to condense into
liquid form. The condenser water is pumped from the condenser bundle to the cooling tower
where heat is transferred from the water to the atmosphere. The liquid refrigerant then travels to
the expansion valve.
Expansion Valve
The refrigerant flows into the evaporator through the expansion valve or metering device. This
valve controls the rate of cooling. Once through the valve, the refrigerant expands to a lower
pressure and a much lower temperature. It flows around the evaporator tubes, absorbing the heat
of the chilled water that‘s been returned from the air handlers, completing the refrigeration cycle.
HEAT EXCHANGERS
The word exchanger really applies to all types of equipment in which heat is exchanged but is
often used specially to denote equipment in which heat is exchanged between two process
streams. Exchangers in which a process fluid is heated or cooled by a plant service stream are
referred to as heatsers and coolers. If the process stream is vaporized the exchanger is called a
vaporizer if the the stream is essentially completely vaporized: called a reboiled if associated
with a distillation column: and evaporator if used to concentrate a solution.
If the process fluid is condensed the exchanger is called a condenser. The term fired exchanger is
used for exchangers heated by combustion gases, such as boiler. In heat exchanger the heat
transfer between the fluid takes place through a separating wall. The wall may a solid wall or
interface.
Heat exchangers are classified basing on the following:
1. Transfer Process (Direct or Indirect)
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2. Surface Compactness
3. Construction (Tubular, Plate)
4. Flow Arrangement
5. Transfer mechanisms
Figure 1: U-tube Heat Exchanger
Figure 2: Plate Heat Exchanger
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The common heat-exchanger at Mukwano is the Gasketed-plate heat exchanger. It consists of
a series of corrugated alloy material channel plates, bounded by elastomeric gaskets are hung off
and guided by longitudinal carrying bars, then compressed by large-diameter tightening bolts
between two pressure retaining frame plates (cover plates). For these heat-exchangers, common
repairs rotate around gasket replacements due to over-heating. They rarely break-down.
VALVES
By definition, valves are mechanical devices specifically designed to direct, start, stop, mix, or
regulate the flow, pressure, or temperature of a process fluid. Valves can be designed to handle
either liquid or gas applications.
Valve Classification According to Function
By the nature of their design and function in handling process fluids, valves can be categorized
into three areas: on–off valves, which handle the function of blocking the flow or allowing it to
pass; nonreturn valves, which only allow flow to travel in one direction; and throttling valves,
which allow for regulation of the flow at any point between fully open to fully closed.
One confusing aspect of defining valves by function is that specific valve-body designs—such as
globe, gate, plug, ball, butterfly, and pinch styles—may fit into one, two, or all three
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classifications. For example, a plug valve may be used for on–off service, or with the addition of
actuation may be used as a throttling control valve.
Another example is the globe-style body, which, depending on its internal design, may be an on–
off, nonreturn, or throttling valve.
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CHALLENGES FACED
1. Difficulty in accessing machine manuals for background information to machinery
2. Some PPEs like overalls were not provided to interns, which limited us during the hands-
on work
3. Machine operators not having detailed information about the machine processes.
RECOMMENDATIONS
1. Maximizing production during off-peak hours (Night-shifts) thus conserve energy
2. Separating metal chips produced in the machine shop (Workshop)
3. Fabricate a cover for the neutralizers in chemical refinery
4. Devise an ultimate disposal method of disposing off malfunctioning machines say selling
off functioning components.
5. Machine guarding so as to minimize accidents.
CONCLUSION
The two months training at Mukwano Group and Mukwano Industries was worth it. To
summarize the gains:
1. Hands-on practical experience as far as mechanical and manufacturing systems are
concerned.
2. Better Time Management skills and on-job etiquette
3. Confidence gained as far as operations are concerned and a wide range of holistic kills
that a mechanical and manufacturing engineer would ever acquire during training.
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References
1. Company Equipment and Machinery Manuals
2. Pump Hand-book by Igor J. Karassik
3. Engineering Maintenance, A Modern Approach by B. Dhillon
4. Maitra, G.M.; and Prasad, L.V. 1985. Handbook of Mechanical Design, pp. 89-108.
McGraw Hill, New Delhi, India.
5. The Art Of Soap Making by Alexander Watt
6. Plastics Machinery and Technology and Ian Willsburg
7. Company Engineers, Machine Operators and Documents
