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F21/1755/2011 Page i
UNIVERSITY OF NAIROBI SCHOOL OF ENGINEERING
DEPARTMENT OF ENVIRONMENTAL AND BIOSYSTEMS ENGINEERING
DESIGN OF A MICRO-HYDROPOWER FOR DRYING
TEA AT KINORO
CANDIDATE NAME: KISA DUNCAN KIPROTICH
CANDIDATE No.: F21/1755/2011
DATE: ……………. SIGN: ……………….
SUPERVISOR’S NAME: ENG. DANIEL MUTULI
DATE: ……………. SIGN: ……………….
A Report Submitted in Partial Fulfilment for the Requirements of the Degree of Bachelor of Science in Environmental and Biosystems Engineering, of the University of Nairobi
4th APRIL, 2016
FEB 540: ENGINEERING DESIGN PROJECT REPORT
2015/2016 ACADEMIC YEAR
F21/1755/2011 Page ii
DECLARATION
I declare that this is my original work and has not yet been submitted for degree award
in any university.
DUNCAN KIPROTICH KISA SIGNATURE…………………………………
F21/1755/2011 Date …………………………………..
This report has been submitted for examination with my approval as a university
supervisor.
ENG. DANIEL A. MUTULI SIGNATURE …………………
(SUPERVISOR) DATE…………………..
F21/1755/2011 Page iii
DEDICATION
I dedicate this project to my loving parents, my two brothers, sister and my fellow
classmates for their support and prayers throughout this period in school.
F21/1755/2011 Page iv
ACKNOWLEDGEMENT
First I would like to acknowledge great assistance offered by my supervisor Eng. Daniel
.A Mutuli. This project would not have been accomplished without his invaluable input,
guidance and support.
I would also like to acknowledge my lecturers and the technical staff who offered me
extremely helpful suggestions during the design of this project.
I would also like to acknowledge my loving family for their patience, understanding and
financial support during the project writing process. I would also like to thank my
grandmother in Meru Edivije Matia for hosting me when I was collecting data at Kinoro
Tea Factory.
I would also like to acknowledge the Unit Manager ,Kinoro Tea Factory, Mr.Njue for
allowing me to collect data and interacting with the factory technicians who helped me
expound my knowledge on this project.
Lastly, but not least, I would like to acknowledge The University of Nairobi for providing
me with an excellent education for five years and enabling me achieve my dreams.
F21/1755/2011 Page v
KISA DUNCAN KIPROTICH
F21/1755/2011
DESIGN OF A MICRO-HYDROPOWER FOR DRYING TEA AT KINORO
ABSTRACT
Kenya’s tea sector provides livelihood for more than 500,000 farmers and among
Kenya’s top foreign exchange earner. Energy costs make up around 30% of the
production cost of the processing cost of tea, with significant increases in the price of
wood that is used in the weathering and drying process. Deforestation is a major issue
in Kenya with firewood as the main source of energy at the national level.
This project is focused in designing a Micro-Hydropower for drying tea at Kinoro, which
is clean, affordable and would increase farmers’ profits. The key parameters for drying
tea to required quality were obtained by a visit to Kinoro Tea Factory and interviewing
the Factory Unit Manager. The energy required to dry tea was then determined by use
of thermodynamic analysis of these parameters. Google Earth software was used to
find an optimum hydraulic head, while the design water discharge was used to size the
micro-hydropower components. The final power delivered to the factory was obtained
by finding the difference of the power generated at the power house and the power
transmission losses.
F21/1755/2011 Page vi
TABLE OF CONTENTS
1 INTRODUCTION ............................................................................................................................... 1
1.1 PROBLEM STATEMENT AND ANALYSIS ..................................................................................... 2
1.2 PROJECT JUSTIFICATION ........................................................................................................... 3
1.3 SITE ANALYSIS AND INVENTORYS ............................................................................................. 3
1.3.1 CLIMATIC CONDITIONS. .................................................................................................... 6
1.4 OBJECTIVES .............................................................................................................................. 7
1.4.1 OVERALL OBJECTIVE ......................................................................................................... 7
1.4.2 SPECIFIC OBJECTIVES ........................................................................................................ 7
1.5 STATEMENT OF SCOPE. ............................................................................................................ 8
2 LITERATURE REVIEW. ....................................................................................................................... 9
2.1 DRYING .................................................................................................................................... 9
2.1.1 FACTORS AFFECTING THE RATE OF DRYING ...................................................................... 9
2.2 Water Activity .......................................................................................................................... 9
2.3 AIR PROPERTIES ..................................................................................................................... 10
2.4 METHODS OF DRYING TEA ..................................................................................................... 10
2.4.1 Superheated steam drying- ......................................................................................... 11
2.4.2 Air drying- ..................................................................................................................... 11
2.5 TEA DRYERS............................................................................................................................ 12
2.5.1 MAJOR COMPONENTS OF A TEA DRYING SYSTEM .......................................................... 12
2.5.2 TYPE OF TEA DRYERS ...................................................................................................... 12
2.6 MICRO HYDROPOWER SYSTEM .............................................................................................. 14
2.6.1 RIVER MUTONGA ........................................................................................................... 14
2.6.2 HYDRAULIC HEADS OF RIVERS. ....................................................................................... 15
2.6.3 MICRO HYDROPOWER SYSTEM COMPONENTS. .............................................................. 15
2.7 TRANSFORMERS ..................................................................................................................... 19
2.7.1 History of Transformers .................................................................................................. 19
2.7.2 Use of Power Transformer .............................................................................................. 19
2.7.3 Transmission Losses ....................................................................................................... 20
2.8 CASE STUDY; RWANDA MOUNTAIN TEA GICIYE HYDRO POWER ............................................. 20
2.9 ADVANTAGES OF MICRO HYDROPOWER ................................................................................ 21
2.10 DISADVANTAGES OF MICRO-HYDROPOWER ........................................................................... 22
F21/1755/2011 Page vii
3 THEORETICAL CONSIDERATIONS .................................................................................................... 23
3.1 Determining electrical power required to dry tea in peak and normal seasons ....................... 23
3.1.1 DRYING RATE .................................................................................................................. 23
3.1.2 THIN LAYER DRYING OF TEA............................................................................................ 25
3.1.3 Theoretical models ......................................................................................................... 25
3.1.4 Semi-theoretical models ................................................................................................. 25
3.1.5 Emperical Models ........................................................................................................... 27
3.1.6 HEAT TRANSFER IN FLUIDIZED BED DRYERS .................................................................... 29
3.1.7 The quantity of heat required to evaporate the water .................................................... 30
3.1.8 PSYCHROMETRY ............................................................................................................. 30
3.1.9 LAWS OF THERMODYNAMICS ......................................................................................... 32
3.1.10 Zeroth Law ..................................................................................................................... 33
3.1.11 The First Law of Thermodynamics for open system:........................................................ 33
3.1.12 MASS BALANCE EQUATION............................................................................................. 34
3.2 DETERMINING THE HYDRAULIC HEAD OF RIVERS ................................................................... 35
3.2.1 USE OF GPS TECHNIQUES FOR RIVER SLOPE CALCULATION (case study; upper biebrza
basin, Poland) ................................................................................................................................ 35
3.2.2 GENERATING ELEVATION PROFILE USING GOOGLE EARTH. ............................................. 36
3.3 Designing the micro hydropower components ....................................................................... 38
3.3.1 Designing the weir .......................................................................................................... 38
3.3.2 Design of the intake ........................................................................................................ 39
3.3.3 Headrace Canal Design (Trapezoidal) .............................................................................. 39
3.3.4 Spillway Design Parameters ............................................................................................ 41
3.3.5 Design of the Settling Basin ............................................................................................ 42
3.3.6 Design of fore bay tank ................................................................................................... 43
3.3.7 Designing the penstock................................................................................................... 44
3.3.8 Design of the saddles ...................................................................................................... 46
3.3.9 POWER HOUSE COMPONENTS ....................................................................................... 47
3.3.10 Tailrace channel ............................................................................................................. 48
3.3.11 TRANSFORMERS ............................................................................................................. 48
3.4 Power transmission losses and the final power delivered to the factory ................................. 50
4 METHODOLOGY ............................................................................................................................. 51
F21/1755/2011 Page viii
4.1 Data Acquisition ..................................................................................................................... 51
4.2 Determination of electrical power required to dry tea in peak and normal seasons. ............... 51
4.3 Determination of a site along River Mutonga with the highest hydraulic head. ...................... 51
4.4 Designing Micro Hydropower components ............................................................................. 52
4.4.1 Design of the weir .......................................................................................................... 52
4.4.2 Design of the intake ........................................................................................................ 52
4.4.3 Design of the head race canal ......................................................................................... 52
4.4.4 Design of spillayway ....................................................................................................... 52
4.4.5 Design of settling basin ................................................................................................... 52
4.4.6 Design of the penstock ................................................................................................... 53
4.4.7 Design of the fore bay .................................................................................................... 53
4.4.8 Powerhouse ................................................................................................................... 53
4.5 To determine the power transmission losses and the final electric power reaching the factory.
53
5 DATA ANALYSIS AND RESULTS ....................................................................................................... 54
5.1 DATA COLLECTED ................................................................................................................... 54
5.1.1 Air Properties ................................................................................................................. 54
5.1.2 Dryer Properties ............................................................................................................. 54
5.1.3 DATA ON THE RIVER (collected from WARMA officer in Meru Region) ............................ 54
5.2 Determining the power requried to dry tea by doing thermal analysis. ................................... 55
5.3 Determination of the highest Hydraulic Head along R.Mutonga by creating a Digital Elevation
Model using Google Earth Software. .................................................................................................. 60
5.4 Design of Micro-Hydropower components ............................................................................. 60
5.4.1 Design of weir and the intake ......................................................................................... 60
5.4.2 Design of the Intake........................................................................................................ 64
5.4.3 Design of Headrace Canal ............................................................................................... 64
5.4.4 Design of spillway ........................................................................................................... 68
5.4.5 Design of the settling basin ............................................................................................. 69
5.4.6 Design of the penstock ................................................................................................... 71
5.4.7 Design of the saddles ...................................................................................................... 73
5.4.8 Design of the fore bay .................................................................................................... 75
5.4.9 Determining the dimensions of the power house; .......................................................... 77
F21/1755/2011 Page ix
5.4.10 Design of the tail race ..................................................................................................... 78
5.5 Determining the total power losses and the final power reaching the factory. ....................... 79
5.5.1 Calculating the power losses........................................................................................... 79
5.5.2 Determining the final power reaching the factory in any single hour; ............................. 80
5.6 COST ESTIMATION.................................................................................................................. 83
5.6.1 BILL OF QUANTITIES ....................................................................................................... 83
6 DISCUSSION ................................................................................................................................... 85
7 CONCLUSION ................................................................................................................................. 86
8 RECOMMENDATION ...................................................................................................................... 87
9 WORKS CITED ................................................................................................................................ 88
10 APPENDICIES .............................................................................................................................. 92
10.1 Appendix 1 ............................................................................................................................. 92
10.2 Appendix 2 ............................................................................................................................. 93
10.3 Appendix 3 ............................................................................................................................. 94
10.4 Appendix 4 ............................................................................................................................. 95
10.5 APPENDIX 5 ............................................................................................................................ 96
10.6 WEIR ...................................................................................................................................... 97
10.6.1 APPENDIX 6 A ................................................................................................................. 97
10.6.2 APPENDIX 6 B ................................................................................................................. 98
10.7 APPENDIX 7 ............................................................................................................................ 99
10.8 SPILLWAY ............................................................................................................................. 100
10.8.1 APPENDIX 8 A ............................................................................................................... 100
10.8.2 APPENDIX 8 B ............................................................................................................... 101
10.9 APPENDIX 9 .......................................................................................................................... 102
10.10 APPENDIX 10 .................................................................................................................... 103
10.11 PENSTOCK ........................................................................................................................ 104
10.11.1 APPENDIX 11 A ......................................................................................................... 104
10.11.2 APPENDIX 11 B ......................................................................................................... 105
10.11.3 APPENDIX 11 C ......................................................................................................... 106
10.12 APPENDIX 12 .................................................................................................................... 107
10.13 APPENDIX 13 .................................................................................................................... 108
10.14 APPENDIX 14 .................................................................................................................... 109
F21/1755/2011 Page x
LIST OF TABLES
Table 3.1: Results of non-linear regression analysis for empirical constants of the Lewis model ............. 28
Table 3.2: Results of non-linear regression analysis for empirical constants of the Arrhenius and Power
equations. ............................................................................................................................................. 29
Table 3.3: Notation ................................................................................................................................ 29
Table 3.4: Statics of the results and measurements and their accuracy .................................................. 36
Table 3.5: Table showing the side slope ................................................................................................. 39
Table 3.6: Table showing Roughness Coefficients for Masonry Canal : ................................................... 40
Table 3.7: The difference in Penstock Material. ..................................................................................... 45
Table 3.8: Hydraulic measurements that determine the selection of a suitable turbine ......................... 47
Table 3.9: Table showing powerhouse dimensions ................................................................................ 47
5.1: Average monthly rainfall ................................................................................................................. 54
Table 5.2: Reasons of concrete gravity weir ........................................................................................... 60
Table 5.3: side slope of different materials ............................................................................................ 65
Table 5.4: Roughness coefficients for masonry canals ............................................................................ 65
Table 5.5: Summarised Results .............................................................................................................. 81
LIST OF FIGURES
Figure 1.1: satellite image showing the location of the Kinoro Tea Factory. ............................................. 4
Figure 1.2: Map of Kenya ......................................................................................................................... 5
Figure 1.3: Map of Meru County .............................................................................................................. 5
Figure 1.4: Map showing the location of Kinoro Tea Factory .................................................................... 5
Figure 1.5: Rainfall forecast, adopted for Kenya issued in September, 2008 ............................................. 6
Figure 1.6: Showing rainfall distribution in Meru County: http://en.climate-
data.org/location/781051/#climate-graph ........................................................................................... 7
Figure 2.1: General arrangement and assemble of Kilburn Vibro Fluid Bed Dryer .................................. 13
Figure 2.2: Micro Hydro Power components .......................................................................................... 15
Figure 2.3: impulse turbine and how it operates .................................................................................... 17
Figure 2.4: reaction turbine and how it operates ................................................................................... 18
Figure 2.5: Generator and Turbine source (USGS, 2015) ........................................................................ 18
Figure 2.6: gravity concrete dam ........................................................................................................... 21
Figure 2.7: interior of a power house ..................................................................................................... 21
Figure 2.8: power house ........................................................................................................................ 21
Figure 3.1: The research area................................................................................................................. 36
Figure 3.2: Elavation Profile, source (Google Earth, 2015) ...................................................................... 36
Figure 3.3: Broad Crested Weir .............................................................................................................. 38
Figure 3.4: Step-Up Transformer............................................................................................................ 48
F21/1755/2011 Page xi
Figure 3.5: Step-Down Transformer ....................................................................................................... 49
Figure 5.1: Broad crested weir ............................................................................................................... 62
LIST OF ABBREVIATIONS
UNEP = United Nation Environment Programme
FAO = Food and Agriculture Organization
BC =Before Christ
USDA = United States Department of Agriculture
UNDP =United Nations Development Programme
ISRN = International Scholarly Research Notices
CTC = Crush, Tear and Curl
UPASI = United Planter’s Association of Southern India
ESHA = European Small Hydropower Association
ASAE = American Society of Agricultural Engineers
GPS = Global Positioning System
3D = three dimensional space
HDPE = High Density Polyethylene
UPVC = unplasticized polyvinyl chloride
WARMA = Water Resource Management Authourity
MT = metric tonnes
JICA = Japan International Cooperation Agency
F21/1755/2011 Page xii
MW =megawatt
KW = kilowatt
KV = kilovolt
F21/1755/2011 Page 1
1 INTRODUCTION
Tea (Camellia sinensis) is the second most consumed beverage in the world, after
water, with approximately 18 to 20 billion cups of tea consumed daily (UNEP, 2015). It
is one of the oldest beverages in the world, discovered about 2700BC (FAO, 2015).
About 84% of consumed tea was Black Tea, 15% was Green Tea and the remaining
amount was Oolong, Dark and White Tea. The expected strong growth in the industry
will be driven by interest in the health benefits associated with tea and innovation in
discovering new unique flavours (Inc, 2014)
China is the largest tea producing country in the world, with an output of 1.9 million
tonnes, representing more than 38% of the world’s total. India comes in the second
place with an output of 1.2 million tonnes. Output from the two largest exporting
countries increased reaching 436,300 tonnes in Kenya and 343,100 in Sri Lanka.
Despite a fall of 7.5% in Vietnam to 185,000 tonnes (FAO, 2015).
Kenya is the world’s leading best quality and exporter of black tea by weight contributing
10% of the total global tea production and commands a remarkable 21% of the world
tea exports outside producing countries. In 2012 tea exports earned the country $1.45
billion, a 4% increase from 2011 earning it then the top foreign exchange earner.
Exports stood at 429.6 million kilograms (kgs) in 2012 from a cultivated area of about
180,000 hectares. It provides employment and income to 600,000 smallholder
households and 150,000 workers at tea estates (USDA, 2013)
Tea processing is energy intensive with its costs contributing to 30% of the total
processing cost. Most tea factories in Kenya depend heavily on biomass to meet their thermal
energy requirements. Energy audit data indicates that 0.5 KWh of electrical energy and 1.5 kg
of firewood are consumed to produce 1 kg of made tea. This translates into an annual
consumption of approximately 435 million units of electricity and 1.3 million tons of
‘firewood. Energy audit also suggests that it is possible to save 20% of each of electrical
and thermal energy. These energy efficient interventions in the tea sector have the
potential to conserve 87 million units of electricity and 0.26 million tons of firewood
yearly (UNDP, 2008).
F21/1755/2011 Page 2
In Kinoro Tea Factory, wood is used as the source of thermal energy. The factory buys
wood from the tea farmers. These pauses two challenges; the factory incurs heavy
financial costs to buy this wood from farmers which leads to the second problem;
deforestation causing environmental degradation, which in turn compromises the life
support systems in Kinoro region.
Meru region has good potential for micro-hydropower generation schemes because it is
located in mountainous terrains and hilly regions. Ravines and streams are available to
provide sources of water. Energy from water is not only economical but also non-polluting to
the environment. Depending on the head of water available, mini hydro can produce 100-
500kW. Research should therefore be done to determine how these rivers can be used
as a source of energy.
1.1 PROBLEM STATEMENT AND ANALYSIS
The tea industry is challenged with the lack of clean and renewable sources of fuel to
provide thermal energy for drying tea leaves. The continued use of wood fuel to produce
thermal energy for drying tea causes extensive deforestation, destroying biodiversity in
natural habitats and global warming.
In India, the second largest producer tea producer with a production of 1,197.18 million
kg in 2014-15, consumed 780,000 tons of firewood (CSIR, 2012). Sri Lanka 85% of the
thermal energy used in the tea industry comes from wood fuel to produce 5331TJ
annually (Melbourne, 2015)
In Kenya, wood is used as the main source of thermal energy in nearly all tea factories.
One large tree can absorb as much as 48 pounds of carbon dioxide per year as well as
it can provide a day’s supply of oxygen for up to four people .With these figures in mind
it is easy to visualize how continued use of wood as the main source of thermal energy
leads to global warming and adverse problems to our forests.
In developed countries in the Middle East such as China and Sri Lanka, natural gas,
coal and oil are commonly used in place of wood fuel. In developing countries such as
Kenya, most of the tea factories lack the financial muscle to purchase these resources.
F21/1755/2011 Page 3
Large scale hydropower electricity development can result in environmental damage and social
conflict. Dams emit methane (CH4) and carbon (iv) oxide (CO2). Displacement of human
settlement and competition for water usage between power generation station owners and
surrounding communities in the dam catchment area are some of the main social
challenges associated with this large scale hydropower stations. The main electricity
supply effort in Kenya has been on meeting electricity demand by expanding large scale
hydropower generation plants. As result, other renewable energy technologies which
may be viable sustainable power supply options such as small-scale hydropower have
been neglected (ISRN, 2012)
In Kinoro Meru region Kinoro Tea Factory tried to initiate small hydropower generation
project to reduce the cost of production associated with its tea processing. However the
project met stiff resistance from farmers who insisted they would not allow penstock
which connects the fore bay and the power house containing the turbine to pass
through their farms.
As a result, this project aims to investigate the prospect of constructing the fore bay
tank, penstock and the powerhouse containing turbine along the river line. This will
reduce social conflicts with the farmers and hasten the implementation plan which in the end
will result to cheap, clean and renewable energy for Kinoro Tea Factory to supplement
the conventional wood fuel either partially or fully in tea drying processes.
1.2 PROJECT JUSTIFICATION
Micro-hydropower generation aims at producing cheap, clean and renewable energy
from freely available rivers resources present in Meru and converting it to thermal
energy for tea drying process.
1.3 SITE ANALYSIS AND INVENTORYS
Kinoro Tea Factory is situated in South Imenti in Eastern Kenya, Meru County, 204km
North east of the city of Nairobi.Its altitude is 1618 m above sea level and is
characterised by temperatures ranging from a low of 80C to a high of 320C during the
cold and hot seasons respectively. It lies within latitude -0.179923 S and longitude
F21/1755/2011 Page 4
37.630668 E. As of 2009 the population was 179,604 and its residents rely mostly on
tea farming.
Figure 1.1: satellite image showing the location of the Kinoro Tea Factory.
(http://www.google.com/earth/download)
F21/1755/2011 Page 5
Figure 1.2: Map of Kenya
Figure 1.3: Map of Meru County
Figure 1.4: Map showing the location of Kinoro Tea Factory
F21/1755/2011 Page 6
1.3.1 CLIMATIC CONDITIONS.
Hydropower generation is heavily dependent on the climatic conditions of the area
particularly in the rainfall patterns. Rainfall pattern change can generate changes in river
flow that are related to precipitation, it may also increase the likelihood of extreme
events such as droughts or floods that increase costs and risks for hydropower projects.
Finally any climate change may cause changes in sedimentation as a result of the first
two effects. Sediment can result in blockages caused by fallen logs, turbine abrasions
reducing the efficiency of the whole system (Birmingham, 2014).
(a) (b)
Figure 1.5: Rainfall forecast, adopted for Kenya issued in September, 2008
F21/1755/2011 Page 7
Figure 1.6: Showing rainfall distribution in Meru County: http://en.climate-data.org/location/781051/#climate-graph
Data from the meteorological department based in KeMU University indicated that the
mean annual rainfall is about 52 inches (1,300 mm), ranging from 15 inches (380 mm)
in lowland areas to 98 inches (2,500 mm) on the slopes of Mount Kenya.
From the graph above June is the driest month, with 17 mm. With an average of 576
mm the most precipitation falls in April.
1.4 OBJECTIVES
1.4.1 OVERALL OBJECTIVE
The overall objective of this study is to design a micro-hydropower for drying tea at
Kinoro using water from River Mutonga, which is a clean and renewable energy
resulting to less energy costs and a safer environment.
1.4.2 SPECIFIC OBJECTIVES
1. To determine the electrical power required to dry tea in peak and normal
seasons.
2. To determine a site along River Mutonga with the highest hydraulic head.
3. To design the micro-hydropower components.
4. To determine the power transmission losses and the final power delivered to the
factory.
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1.5 STATEMENT OF SCOPE.
The scope of this project is to design a micro-hydropower, required to reduce the
energy costs associated with tea drying. It will involve the following;
1. Determining the amount of electrical power required to dry tea in a single day
and in doing this I will not consider the energy losses in the drying chamber.
2. Determining the optimum head for my design
3. Design of micro hydro power components. I will not design the turbine and the
generator but choose from the market varieties to suit my design.
4. Determine the transmission losses and the final power reaching the factory. I will
not design the transmission lines.
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2 LITERATURE REVIEW.
2.1 DRYING
Drying commonly describes the process of thermally removing volatile substances
(moisture) to yield a solid product. Moisture held in loose chemical combination, present
as liquid solution within the solid or even trapped in microstructure of the solid, which
exerts a vapour pressure less than that of pure liquid is called bound moisture. Moisture
in excess of bound moisture is called unbound moisture. When a wet solid is
subjected to thermal drying , two process occur simultaneously;
1. Transfer of energy (mostly as heat) from the surrounding environment to
evaporate the surface moisture.
2. Transfer of internal moisture to the surface of the solid and its subsequent
evaporation due to process 1 (Mujumdar, 2015)
2.1.1 FACTORS AFFECTING THE RATE OF DRYING
According to (American Society of Agricultural Engineers, 2005) the general factors
affecting the rate of drying of agricultural products includes;
1. Air temperature
2. Air velocity (drying rate is approximately proportional to u0.8)
3. Size, shape and arrangement of pieces to be dried.
4. Physical and chemical composition, moisture content.
5. Wet-bulb depression (t-twb ), or relative humidity, or partial pressure of water
vapour in the air.
2.2 Water Activity
According to (LB, 1980)Water activity is the ration of the vapour pressure of water in a
material (p) to the vapour pressure of pure water (po) at the same temperature. Relative
humidity of air is the raton of the vapour pressure. When vapour and temperature
equilibrium are obtained, the water activity of the sample is equal to the relative humidity
of air surrounding the sample in a sealed measurement chamber. Multiplication of water
activity by 100 gives the equilibrium relative humidity (ERH) in percent;
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aw = water activity
p = vapour pressure of water in a material
po = vapour pressure of pure water at the same temperature as the material
ERH = equilibrium relative humidity
As described by the above equation, water activity is a ratio of vapour pressures and
thus has no units. It ranges from 0.0aw (bone dry) to 1.0aw (pure water)
2.3 AIR PROPERTIES
Air should be hot, dry and moving for effective drying. These factors are interrelated and
should be applied in the correct way. The psychrometric chart shows clearly the
relationship between temperature, humidity and the rest of the thermodynamic
properties. The relative humidity (RH) of air of the air in contact with the product is an
important air property as gives a ratio of the moisture content of air at the specific
temperature for drying to the moisture content of the air if it were saturated at the same
temperature. Air with low relative humidity (dry air) should be passed over the food as it
has the ability to remove moisture from the product.
2.4 METHODS OF DRYING TEA
A proper drying process and control is necessary not only to preserve and promote
quality but also to minimize energy inputs. A suitable process method can be concluded
by comparing different drying methods in order to find the best way to process food
materials.
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2.4.1 Superheated steam drying-
Involves the use of superheated steam in a direct (convective) drier instead of hot air,
combustion, or flue gases as the drying medium to supply heat for drying and to carry
away the evaporated moisture. Any direct or indirect (combined convection/ conduction)
drier can be in principle, operated as superheated steam drier although in practice, this
conversion may not always be straight forward (Xio Dong Chen, 2008)
2.4.2 Air drying-
Hot air is passed over the products to be dried. Prior to entering the drying chamber the
air is heated by applying thermal energy. This increases the heat content (enthalpy) of
the air and to increase its moisture holding capacity by increasing its subsequent
volume according to Charles’ Law which states that, “ when the pressure on a sample of
dry gas is held constant, its absolute temperature and volume will be directly related/
proportional” (SCIENTIFIC, 1998)
The main objectives of tea drying are;
1. To breakdown complex chemical compounds in the cells to simpler compounds
which along with other simpler molecules then recombine to contribute to quality
attributes of tea like the ‘body’ and ‘flavour’ at a later stage,
2. To reduce the moisture content of the fresh leaf which ranges between 74-83%
The principle involved in conventional drying is that fermented leaf is subjected to a
blast of hot air in such a manner that the hottest air first comes in contact with the tea
having the least moisture content. Fermented leaves fall on a series of moving
perforated trays on which it is passed and re-passed through a moving stream of hot air.
The perforated trays are mounted on an endless chain and arranged in a tier of six or
eight unit which alternate in the direction of motion. The design is such that at each
stage of the drying operation, the leaf is subjected to a different temperature. As the leaf
passes from tray to tray, it progressively comes into contact with higher temperatures.
When the air takes up moisture, the dry bulb temperature falls. A final moisture content
of between 2.5 to 3.0% should be the aim. If the tea is dried below 1%, it loses some
quality. The optimal inlet temperature for CTC processed leaf is 100 50c. The exhaust
temperature should be maintained at 54.4 2.70c (130 50F). If the exhaust
F21/1755/2011 Page 12
temperature is less than 490c (1200F), the post drying process will continue for a
considerable time and will soften the liquor. This condition is referred to as “stewing”. If
the exhaust temperature is greater than 57.2 0c (1350F) the rate moisture removal is too
rapid and results in case hardened tea in which the particles are hard on the outside but
incompletely dried within; such teas yield harsh liquors and do not keep well so it is of
paramount importance to ensure that temperatures are kept under control to the extent
as possible (UPASI, 2015)
2.5 TEA DRYERS
2.5.1 MAJOR COMPONENTS OF A TEA DRYING SYSTEM
The essential components of a tea dryer are:-
1. An air heater which mostly is a furnace in which gas ,oil or wood is burnt.
2. A heat exchanger where the heat of the furnace gases is transferred to clean air.
3. The drying chamber in which the clean hot air is passed through the leaf and
evaporates the moisture in the tea leaves
2.5.2 TYPE OF TEA DRYERS
Presently there exists three main types of commercial tea dryers; Conventional Tea
Driers, Fluidized Bed Dryers and Hybrid Dryers. Fluidized Bed Dryers are currently the
most used systems in tea drying.
2.5.2.1 FLUIDIZED BED DRYING
The fluid bed drier consists of a drying chamber, plenum chamber, dust collectors and
control dampers. The drying chamber consists of three drying zones and one cooling
zone. Fermented leaf is loaded on a grid plate of the drying chamber. The top of the
drying chamber is totally closed and two sets of centrifugal exhaust fans are provided
with cyclones; one is re-firing and the other for dust extraction. Beneath the drying
chamber is a plenum chamber where the air pressure is equalized. The direction of the
hot air entering into a grid plate is controlled by the flow control dampers which can be
operated independently. The flow control dampers have dual purposes- during the
operation their direction determines the residence time of tea particles in the drier and at
the end of manufacture, they serve to evacuate the dryer completely. In each zone, the
required volume and pressure of air is maintained by independent air valves.
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When the fermented leaf enters the drying chamber, it has very high moisture content
which is rapidly reduced in the first zone. At this point, maximum volume of air is
introduced since rapid evaporation is required. As the moisture loss takes place, density
of the materials which contain more moisture and hence have high density. The
movement of the tea particles within the drying chamber is governed by the principle of
displacement. When the material is fully dried, it is expelled into a cooling chamber
wherein ambient air is introduced by a forced draft fan.
The desirable inlet temperature ranges from 1400 c to 1500 c. firing at this temperature
resulted in improved leaf appearance and better bloom. The exhaust temperature has to
be maintained at 71.10 c (1600 F) to 76.70 c (1700 F) in the third section (UPASI, 2015).
Figure 2.1: General arrangement and assemble of Kilburn Vibro Fluid Bed Dryer
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2.6 MICRO HYDROPOWER SYSTEM
Hydropower systems use the energy in flowing water to produce electricity or
mechanical energy. For run-of-the river micro hydropower systems, a portion of a river’s
water is diverted to a water conveyance channel, pipeline, or pressurized pipeline
(penstock), that delivers it to a turbine or waterwheel. The moving water rotates the
wheel or turbine, which spins a shaft. The motion of the shaft can be used for
mechanical processes, such pumping water, or it can be used to power an alternator or
generator to generate electricity. A micro hydropower can be connected to an electric
distribution system (grid-connected), or it can stand alone. A micro-hydro power
produces power ranging from 5kW up to 100kW; usually provided power for a small
community or rural industry in remote areas away from the grid but it also depends with
the country and its own classification.
2.6.1 RIVER MUTONGA
The Mutonga River is a river in Eastern Kenya. The river flows on a southerly direction
through thick equatorial rainforests from a source high on Mount Kenya. It is a tributary
of the Tana River.
2.6.1.1 Geography
The river is formed by the melting glaciers on the peaks of Mount Kenya hence the
reason why its water are cold all seasons, even the piped water from this river is this
distinct in this attribute of being cold. The river follows a meandering course skirting the
small village towns of Kinoro, Kithaku, Katheri, Kaing’inye, Gitumbene and finally cuts
through the heart of the Meru town.
2.6.1.2 Cultural significance
It is the largest rive in the Imenti region of Meru County and the site of Meru People rites
and rituals including the initiation of boys into adulthood. As the river flows through
valleys, hills and mountains, all characterised by indigenous forest, it weaves together a
number of communities, all of whom have their own spiritual connections and
understandings of its significance.
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2.6.2 HYDRAULIC HEADS OF RIVERS.
Schemes are generally classified according to
1. High head: 100-m and above
2. Medium head : 30-100 m
3. Low head : 2-30 m
This ranges are not rigid but are merely means of categorizing sites
Medium and high head schemes use weirs to divert water to the intake, it is then
conveyed to the turbines via a pressure pipe or penstock. Low head schemes are
typically built in river valleys. Two technological options can be selected. Either the
water is diverted to power intake with short penstock as in high head schemes, or the
head is created by a small dam, provided with sector gates and integrated intake,
powerhouse and fish ladder (ESHA, 2004)
2.6.3 MICRO HYDROPOWER SYSTEM COMPONENTS.
Figure 2.2: Micro Hydro Power components
2.6.3.1 Diversion Weir and Intake
The diversion weir- a barrier built across the river used to divert water through an
opening in the riverside (the ‘Intake’ opening) into a settling basin.
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2.6.3.2 Headrace canal
Channel leading water to a fore bay or turbine. The headrace follows the contour of the
hillside so as to preserve the elevation of the diverted water.
2.6.3.3 Spillway
Spillway need to be designed to remove the excess water due to floods, in order to
minimize the adverse effects to other components of the Micro-Hydropower System.
Spillways are often constructed in de-sanding basin and the fore bay, from which the
excess water is safely diverted to the water source (KUNWOR, 2012).
2.6.3.4 Settling basin
Rivers carry large amount of sediments due to erosion in the hilly and mountainous
regions. Sediments affect other components of the micro hydropower negatively and
hence the need to reduce the sediment density.
Sediments are captured by de-sanding basins by allowing particles to settle by reducing
the speed of the water and clearing them out before entering the canal. They are
normally built at the head of the canal. De –sanding basin is capable of settling particle
s above 0.2-0.3 mm of size.
2.6.3.5 Penstock
A close conduit or pressure pipe for supplying water under pressure to a turbine
2.6.3.6 Saddles
Saddles are designed to support the weight of penstock full of water.
2.6.3.7 Fore bay
Acts as a pool at the tail end of the headrace canal connected to the penstock. It mainly
reduces entry of air into the penstock pipe, which could in turn cause the high pressure
of trapped air bubbles to explode in the penstock or the turbine.
2.6.3.8 Powerhouse
This is the stage where the mechanical energy of water is converted into electrical
energy. It basically consists of the electro-mechanical equipment such as the turbines,
generator and the drive systems.
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2.6.3.9 Tailrace
Channel leading the discharge water from the powerhouse back to the river.
2.6.3.10 Turbines
Turbines are commonly used today to power micro hydropower systems. The moving
systems strike the turbine blades, to spin a shaft. They are more compact in relation to
their energy output. They have fewer gears and require less material for construction
(ENERGY, 2015)
2.6.3.10.1 Impulse turbine
In an impulse turbine which has the least complex, are most commonly used for high-
head micro hydro systems (ENERGY, 2015). A fast-moving fluid is fired through a
narrow nozzle at the turbine blades to make them spin around. The blades of an
impulse turbine are usually bucket-shaped so they catch the fluid and direct it off at an
angle or sometimes even back the way it came (because that gives the most efficient
transfer of energy from the fluid to the turbine). In an impulse turbine, the fluid is forced
to hit the turbine at high speed, the types are Pelton wheel, Turgo impulse wheel, Jack
Rabbit turbine (Woodford, 2008)
Figure 2.3: impulse turbine and how it operates
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2.6.3.10.2 Reaction Turbines
Reaction turbines, which are highly efficient, depend on pressure rather than velocity to
produce energy. All blades of the reaction turbine maintain constant contact with the
water. These turbines are often used in large-scale hydropower sites. Because of their
complexity and high cost, they are not usually used for micro hydropower projects.
Figure 2.4: reaction turbine and how it operates
2.6.3.11 Generator
Figure 2.5: Generator and Turbine source (USGS, 2015)
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Although this project is not mainly concerned with the uses and selection of the
generators, it is important to know the basic types of generators. They are two types of
generators;
1. Synchronous-are primarily used in large scale power generation
2. Induction generators- are generally used in low power output (less than 10MW)
and they are preferred type in micro hydropower because they can operate at
variable speeds with constant frequency, are cheaply available and require less
maintenance.
2.7 TRANSFORMERS
According to (elecrical4u, 2015) a transformer is a static machine used for transforming
power from one circuit to another without changing frequency.
2.7.1 History of Transformers
The history of transformer was commenced in the year 1880. In the year 1950, 400kv
electrical power transformer was introduced in high voltage electrical power system. In
the early 1970s, unit rating as large as 1100MVA was produced and 800KV and even
higher KV class transformers were manufactured in 1980.
2.7.2 Use of Power Transformer
Generation of electrical power in low voltage level is very much cost effective. Hence
electrical power is generated in low voltage level. Theoretically, this low voltage level
power can be transmitted to the receiving end. But if the voltage level of a power is
increased, the current of the power is reduced which causes reduction in ohmic or I2R
losses in the system, reduction in cross sectional area of the conductor i.e reduction in
capital cost of the system and it also improves the voltage regulation of the system.
Because of these, low level power must be stepped up for efficient electrical power
transmission. This is done by step up transformer at the sending side of the power
system network. As this high voltage power may not be distributed to the consumers
directly, this must be stepped down to the desired level at the receiving end with the
help of a step down transformer.
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2.7.3 Transmission Losses
According to (Mehta, 2013) electric power can be transmitted or distributed either by
means of underground cables or by overhead lines. The underground cables are rarely
used for power transmission due to two main reasons. Firstly, power is generally
transmitted over long distances to load centres. The installation costs for underground
transmission will be very heavy. Secondly, electric power has to be transmitted at high
voltages for economic reasons. It is very difficult to provide proper insulation to the
cables to withstand such higher pressures. Therefore, as a rule, power transmission
over long distances is carried out by using overhead lines. With the growth in power
demand and consequent rise in voltage levels, power transmission by overhead lines
has assumed considerable importance.
Electricity can be distributed in single phase or 3-phase, but I will focus on the 3-phase
because it is a common method of electric power transmission. It is a type of polyphase
system mainly used to power motors and many other devices. A three-phase system
uses less conductor material to transmit electric power than equivalent single-phase,
two-phase, or direct-current systems at the same voltage (Cableorganizer, 2015)
2.8 CASE STUDY; RWANDA MOUNTAIN TEA GICIYE HYDRO POWER
As energy is a major price factor in the manufacturing process, Rwanda Mountain Tea
was looking for ways to reduce its power bill. Sing the Nyathibu and Rubaya plantations
borders the Gishwati forests,, the source of the Giciye River, and several streams flow
through the plantations, thought was given to tapping this water for producing clean
energy. Development of the Giciye hydropower project was considered a worthwhile
way of achieving both the RMT’s and national objectives. With the following figures;
Water flow: 4 m3/s, Gross Head: 130 m; 350 m long and 1 m welded steel
penstock,Turbines : 2 Pelton turbines (2*2 m3/s),Dam : Gravity concrete dam of height
of 6.5 m,Estimated power generation : 18.3 GWh/y
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Figure 2.6: gravity concrete dam
Figure 2.7: interior of a power house
Figure 2.8: power house
According (ENERGY A. , 2006) to the following are the advantages and disadvantages;
2.9 ADVANTAGES OF MICRO HYDROPOWER
1. Efficient energy source
2. Reliable electricity source
3. No reservoir required
4. Cost effective energy solution
5. Power for developing countries
6. Integrate with the local power grid
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2.10 DISADVANTAGES OF MICRO-HYDROPOWER
1. Energy expansion is not possible
2. Low power in the dry months
3. Environmental impact however on a smaller scale.
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3 THEORETICAL CONSIDERATIONS
3.1 Determining electrical power required to dry tea in peak and normal seasons
According to my research the following is what is used in the industry for analyzing the
tea drying process;
3.1.1 DRYING RATE
Drying occurs in two steps, constant rate drying period and the falling rate period. Free
moisture is the moisture that moves through the product unrestrictedly. For constant
rate drying period, moisture evaporates causing a subsequent drop in moisture content.
In this stage, the product temperature is close to the wet bulb temperature of the drying
air.
According to Fortes and Okos (1980 ) suggested that the drying rate during the constant
rate drying period can be calculate by;
= drying rate
=convective heat transfer coefficient
= surface are of product
= dry bulb temperature of drying air
= wet bulb temperature of air at the surface of the material
L- latent heat of vaporization
According to (Chinenye, 2009) the following equation can be used to describe the
drying rate during the falling rate drying rate period;
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MR= moisture ratio
Mi = initial moisture content
Me = equilibrium moisture content
M = moisture content at time t
K= drying constant
According (ASAE, 2009) to the general equations governing equations for indicating
moisture content are:
M= decimal moisture content wet basis (wb)
M= decimal moisture content dry basis (db)
Md =mass of dry matter in the product
Mw =mass of water in the product
Mt = total mass of the product, water plus dry matter
Percentage moisture content is found by multiplying the decimal moisture content by
100%
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The relationship between wet and dry moisture content on a decimal basis is given by
or
.
3.1.2 THIN LAYER DRYING OF TEA
According to (P.C. Panchariya, 2001) it has been accepted that drying phenomenon of
biological products during the falling rate period is controlled by the mechanism of liquid
and or vapour is diffusion. Thin layer drying models that describe the drying
phenomenon of these materials mainly fall into three categories namely;
1. Theoretical models
2. Semi-theoretical models
3. Empirical models
3.1.3 Theoretical models
Assuming that the resistance to moisture flow is uniformly distributed throughout the
interior of the homogeneous isotropic material, the diffusion coefficient, D is
independent of the local moisture content and if the volume shrinkage is negligible,
Fick’s second law can be derived as follows:
Crank (1975) gave the analytical solutions of equation 1 for various regularly shaped
bodies such as rectangular, cylindrical and spherical. Drying of many food products,
such as rice (Ece & Cihan, 1993), hazelnut (Demirtas, Ayhan, & Kaygusuz, 1998) and
rapeseed (Crisp & Woods, 1994) has been successfully predicted using the Fick’s
second law with Arrhenius-type temperature-dependent diffusivity.
3.1.4 Semi-theoretical models
These models are derived by simplifying general series solutions of Fick’s second law
or modification of simplified models and valid within the temperature, relative humidity,
air flow velocity and moisture content range for which they were developed (Fortos &
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Okos, 1981). These models required small time compared to theoretical thin-layer
models and do not need assumptions of geometry of a typical food, its mass diffusivity
and conductivity (Parry, 1985).
Sharaf-Eldeen, Blaisdell, and Hamdy (1980) presented a two-term model to predict the
drying rate of shelled corn fully exposed to air.. However, it requires constant product
temperature and assumes constant diffusivity. The two-tem exponential model has the
form;
Where
M, Mo, Me are the material, initial and equilibrium moisture contents in dry basis,
respectively and Ao, ko, A1, k1 are the empirical coefficients.
The Henderson and Pabis model is the first term of general series solution of Fick’s
second law.
This model was used successfully to model drying corn, wheat and peanut. The slope of
this model, coefficient ko, is related to effective diffusivity when drying process takes
place only in the falling rate period and liquid diffusion controls the process.
The Lewis model is a special case of the Henderson and Pabis model where intercept is
unity. He described that the moisture transfer from the food products and agricultural
material can be seen as analogous to the flow of heat from a body immersed in a cool
fluid. By comparing this phenomenon with Newton’s law of cooling, the drying rate is
proportional to the difference in moisture content between the materials being dried and
the equilibrium moisture content at the drying air condition as;
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Or after integrating yields
The Page model is a modification of the Lewis model to overcome its shortcomings.
This model has produced good fits in predicting drying of grain, rough rice, white bean
and barley.
The Page model was also modified to describe the drying of soya bean
3.1.5 Emperical Models
The empirical models derive a direct relationship between average moisture content
and drying time. They neglect the fundamentals of the drying process and their
parameters have no physical meaning. Therefore they cannot give a clear accurate
view of the important processes occurring during drying although they may describe the
drying curve.
Thompson model (Eq. 8) was used to describe the shelled corn drying and the Wang
and Sing Model (Eq. 9) was applied to study the intermittent drying of rough rice
2
And
The influence strength of the experimental drying variables is determined by the values
of the model parameters, Ao from the inital conditions and ko in the form of Arrhenius
and Power-type equations in the following way
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In the Arrhenius type
In the Power type
T= Absolute temperature of the air (K),
V = air velocity (m/s),
, , are constants.
Experiments were conducted by the Central Electronic Engineering Research Institute
(India), to determine the effect of process variables on the thin-layer drying
characteristics of black tea. The variables considered were the drying air temperature,
absolute humidity and air velocity. The change in absolute humidity was very low and
later on it was neglected. All the three models were used and from the results obtained,
the Lewis Model gave better predictions as compared to the other two models.
Table 3.1: Results of non-linear regression analysis for empirical constants of the Lewis model
Model T (oC) ko R2 MSE X2(*10-4)
Lewis Model 80 0.0017 0.941 0.0048 1.2143
90 0.0024 0.944 0.0030 1.1630
100 0.0030 0.947 0.0026 0.9479
110 0.0036 0.949 0.0014 0.1499
120 0.0046 0.948 0.0026 1.0011
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Table 3.2: Results of non-linear regression analysis for empirical constants of the Arrhenius and Power equations.
Equation parameters R2 MSE X
2 (*10
-4)
Arrhenius 0.12563 1.15202 209.12341 0.99869 0.02318 1.654
Power 0.64801 * 10
(-7)
2,14815 1.14635 0.9975 0.03154 1.734
Table 3.3: Notation
a, b drying constant R2 correlation coefficient
A, Ao, A1 drying constant R universal gas constant
c, co, c1, drying constant t time (s)
Deff effective diffusivity (m/s) T temperature
Do diffusivity coefficient Subscripts
Ea action energy (KJ/mol) i ith observation
k, ko, k1 drying constant 0 initial
M moisture content e equilibrium
MR moisture ratio
3.1.6 HEAT TRANSFER IN FLUIDIZED BED DRYERS
Heat transfer between a single particle and the gas phase can be defined by
Where;
q= rate of heat transfer (W)
= heat transfer coefficient (W/m2K)
= surface area of a single particle (m2)
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= temperature of the particle (K)
= Temperature of the gas (K)
3.1.7 The quantity of heat required to evaporate the water
The amount of heat required to evaporate water can be calculated using the following
equation;
Where:
E = total heat energy, kJ
Ma = mass flow rate of air, kg/hr
hf and hi = final and initial enthalpy of drying and ambient air, respectively, kJ/kgda (will
be obtained from the psychometric charts)
td= drying time, hrs
From my research I used psychrometry to determine the air properties of the ambient
air and assuming the drying chamber as a thermal system and boundary.
3.1.8 PSYCHROMETRY
Definitions
Psychrometricts – deals with the thermodynamic properties of moist air and uses
these properties to analyze conditions and processes involving moist air, (Bhatia, 2012).
Dry bulb temperature (DBT) - the temperature of air registered by an ordinary
thermometer
Wet bulb temperature- the temperature registered by a thermometer whose bulb is
covered by a wetted wick and exposed to a current of rapidly moving air.
Saturated vapour pressure (psat
)- saturated partial pressure of water vapour at the dry
bulb temperature. It is available in thermodynamic charts and tables.
Relative humidity (RH )- is an expression of the moisture content of a given
atmosphere as a percentage of the saturation humidity at the same temperature
represented in percentage. Using the perfect gas equation then we can show:
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Humidity ratio (W) - can be defined as the mass of water associated with each
kilogram of dry air. By use of perfect gas equation humidity ratio can be calculated
using;
Substituting the values of water vapour and air R and Ra the humidity ratio is;
Dew-point temperature (DPT) - the temperature at which condensation of moisture
begins when the air is cooled.
Degree of saturation (μ): the ratio of the humidity ratio W to the humidity ratio of a
saturated mixture Ws at the same temperature and pressure;
µ = (
) t
Enthalpy: a thermal property indicating the quantity of heat in the air above an arbitrary
datum. For moist air, the enthalpy of dry air is given a zero value at 0o
C, and for water
vapor the enthalpy of saturated water is taken as zero at 0o
C.
The enthalpy of moist air is given by:
cp = specific heat of dry air at constant pressure, kJ/kg.K;
cpw
= specific heat of water vapor, kJ/kg.K
t = Dry-bulb temperature of air-vapor mixture, o
C
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W = Humidity ratio, kg of water vapor/kg of dry air
ha = enthalpy of dry air at temperature t, kJ/kg
hg= enthalpy of water vapor3 at temperature t, kJ/kg
hfg
= latent heat of vaporization at 0o
C, kJ/kg
Properties of moist air
Pressure, volume, density and thermal properties are related by the use ‘perfect gas’
laws. For a mixture of water vapour and dry air, this law can be used with negligible
error at the range of temperatures and pressures.
Where: P = absolute pressure (pa)
M = mass (kg)
R = gas constant ( Kg. C)
T = temperature ( K)
V = volume (m ᵌ)
3.1.9 LAWS OF THERMODYNAMICS
According to (Al-Shemmeri, 2010), thermodynamics is the science relating heat and
work transfers and the related changes in the properties of the working substance. The
working substance is isolated from its surroundings in order to determine its properties.
Thermodynamic system – a collection of matter within prescribed and identifiable
boundaries. A system may either an open one, or a closed one, referring to whether
mass transfer or does not take place the boundary.
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3.1.10 Zeroth Law
If an object with a higher temperature comes in contact with a lower temperature object,
it will transfer heat to the lower temperature object. The objects will approach the same
temperature, and in the absence of loss to other objects, they will maintain a single
constant temperature. Therefore, thermal equilibrium is attained.
The “zeroth law” states that if two systems are at the same time in thermal equilibrium
with a third system, they are in thermal equilibrium with each other.
3.1.11 The First Law of Thermodynamics for open system:
It states that, “For a thermodynamic system, the algebraic sum of heat transfers is
proportional to the sum of work transfer through the system boundary.”
For an open system shown below, ma is the mass flow rate of air at the inlet and outlet
mp is the mass flow rate of the product at inlet and outlet,
Where;
Ma = Air flow rate, kgDA/hr
Mp = Product flow rate, kgDS/hr
Ta1 = inlet temperature of air (oc)
Ta2 = Outlet temperature of air (oC)
Tp1 = outlet temperature of the product (oC)
DRYING CHAMBER
Ma,Ta1, W1
Ma,Ta2, W2
Mp,Tp1, w1
Mp,Tp2, w1
q
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Tp2 =inlet temperature of the product (oC)
W1 = Absolute humidity of air in, kg water/ kg DA
W2 = Absolute humidity of air out, kg water/ kg DA
w1 = Outlet product moisture content, kg water/ kg DS
w2 = Inlet product moisture content, kg water/ kg DS
3.1.12 MASS BALANCE EQUATION
MaW1+ Mp w2 = MaW2 + Mp w1
Energy required is given by;
E= energy required to heat the dried tea leaves(KJ)
H=enthalpy (KJ/kg)
M= mass of tea leaves dried per second(Kg/s)
t = time in seconds
To determine the power required to dry the tea leaves;
P = power
E = energy used to dry the tea leaves
t = time in seconds
Determining a site along River Mutonga with the highest hydraulic head
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3.2 DETERMINING THE HYDRAULIC HEAD OF RIVERS
According to (Wensink, 2005) measuring the geometry and the flow in river channels is
an area of great interest in hydraulic engineering. Data describing these physical
parameters has practical value in predicting hydro-electric power generation potential of
a river, predicting floods and river restoration designs. Traditional survey techniques for
mapping river bathymetry and determining flows are time consuming, and imprecise.
3.2.1 USE OF GPS TECHNIQUES FOR RIVER SLOPE CALCULATION (case study; upper
biebrza basin, Poland)
The GPS measurements of the Biebrza River water stages were performed in total 90
points, located in the few hundred meters interval of the river length between the railway
bridge in Jastrzebna and a Jaglowo village. Since a key for river slope determination is
an altitude, during measurements were not focused on horizontal coordinates. In order
to that Base station was located on moraine scarp with open horizon and precisely
determined altitude. The Rover receiver was installed on motorboat, which flowed from
Jastrzebie to Jaglowo. The water level measurements were performed every few
hundred meters. Next, the coordinates of collected points were transferred. The
transformation of horizontal coordinates from WGS84 coordinate system into local
Polish coordinate system “1965” was based on Helmert transformation, and elevation
transformation based on a geoid model. Both the above-mentioned activities were
processed with the use of Geo- Trans software (GEO-SYSTEMS, 1998)The results of
GPS measurements were used for slopes determination, which were calculated in GIS.
The Biebrza River main stream were digitized in ArcView GIS, and next, divided for
numerous river segments according to location measured by GPS. The slope was
calculated for every river segment. The measurement error was automatically
calculated by GPS receivers serving software for each measurement point.
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Figure 3.1: The research area
Table 3.4: Statics of the results and measurements and their accuracy
3.2.2 GENERATING ELEVATION PROFILE USING GOOGLE EARTH.
You can explore elevations of a particular path through the Elevation Profile. To start,
either draw a path or an existing one. Once the path is chosen from the Places panel,
there are two ways to see its Elevation profile. Either go to Edit>show Elevation Profile.
An Elevation Profile will appear in the lower half of the 3D viewer as shown below:
Figure 3.2: Elavation Profile, source (Google Earth, 2015)
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It is easier to use it, because you do not need to go to the field especially if it is a far or
difficult site to access.To get the head you have to choose the steepest slope and take
the highest point of the slope as elevation 2 and the lowest point of the slope as
elevation 1 the
1. Gross head-vertical distances between the top of the penstock that conveys the
water under the pressure and the point where the water discharges from the
turbine.
2. Net head- available head after subtracting the head loss due to friction in the
penstock from the total (gross head)
H=Gross Head
h1= elevation 1
h2=elevation 2
HN = net head
HG =gross head
F= frictional losses
Head loss due to friction is given by
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Where
f=coeffient of friction of penstock depending on the type of material of penstock
L= total length of the penstock
V=mean flow velocity of water through the penstock
D=is the diameter of penstock
g=acceleration due to gravity
3.3 Designing the micro hydropower components
3.3.1 Designing the weir
Figure 3.3: Broad Crested Weir
For broad crested weirs: on low heights
with a slope ranging from of 0.2679-0.5773 according to (Rickard, 2003).
Converting the slope into an angle that the weir makes with the floor of the river at
the tail end of the weir
H=head of the water above the weir structure
h=height of the weir from the floor of the river
h
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B=breadth of the weir
Head of water flowing over the weir
Q= discharge flowing over the weir
= coefficient of discharge which is usually 1.49
=length across the channel (5 m)
=water head above the weir
3.3.2 Design of the intake
Optimum Velocity through the intake ( 0.5 – 1.0 m3/s)
A= cross-sectional area of the intake
v=velocity of the water in the intake
3.3.3 Headrace Canal Design (Trapezoidal)
According to (Anil, 2012) the dimensioning of the cross section of a canal depend on
volume, velocity of water, side slope, head loss and type of sediment disposition in the
canal and seepage.
Table 3.5: Table showing the side slope
Material used in the canal Side slope (N)
Stone masonry with mud mortar 0.5-1.0
Stone masonry with cement mortar 0-1.5
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Table 3.6: Table showing Roughness Coefficients for Masonry Canal :
Brickwork Roughness coefficient
Masonry canals Normal Masonry with cement
mortar
0.017
Coarse rubble masonry 0.020
Cross-sectional area is given by;
Determining the side slope N; determined from the table
Determining the optimum height of the canal (H);
Determining the optimum width of the canal bed (B);
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Determining the width of the top of the canal (T);
Calculating the wetted perimeter (P);
Calculating the hydraulic radius (R);
Calculating the slope (S) of the headrace canal;
Calculating particle size in diameter that can be transported in the head race canal can
be calculated;
3.3.4 Spillway Design Parameters
Length of the spillway is calculated;
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It is important to calculate the intake during the rainy season, then determine the
maximum height of the water in the canal in the rainy season to provide the dimensions
for the spillway.
3.3.5 Design of the Settling Basin
The first step is to choose a suitable width of the basin (W). Conventionally the width of
the settling basin is taken as 2-5 times larger than that of the headrace canal.
I chose the width of the basin to be
Determining the length of the settling basin;
Q= design flow(m3/s)
Vvertical= fall velocity (for the settling particles of the fall velocity is taken as 0.03 m/s)
The length of the settling basin makes an angle of with the inlet and an angle of
with the outlet.
Determining the silt load;
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Sload=silt load (kg)
Q=discharge (m3/s)
T=silt emptying frequency in seconds. In micro Hydro Power, 12 hrs or 43200 s is used
C=silt concentration of incoming flow (kg/m3)(if there is no silt concentration data,
0.5kg/m3 can be used)
Determining the volume of the silt load;
VOsilt =volume of silt stored in basin
Sdensity =desity of silt (2.6kg/m3 is generally used)
Pfactor =packing factor of sediments submerged in water (50% is generally used)
Determining the depth required for the settling basin;
3.3.6 Design of fore bay tank
Determining the submergence head which is the depth of water above the crown of the
penstock pipe;
Where V=velocity in the penstock
Calculating the storage depth.
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The convention is for it to be 300 mm or same as the penstock pipe diameter. An air
vent is usually designed to prevent vacuum created by rapid closure of valve which
might cause it to collapse.
Since the fore bay is manually cleaned the minimal size of the structure should allow a
normal person to enter and clean the tank. Minimum clear width recommended is 1
meter. A gate valve is often situated at the entrance of the penstock which allows the
water flow in the penstock pipe to close for maintenance work in the turbine.
Dimensioning the air vent;
=internal diameter of air vent (mm)
Q=maximum flow of water through turbine (l/s)
E=Young’s modulus of the penstock (210000N mm2)
to = minimum thickness of the penstock wall (mm)
3.3.7 Designing the penstock
The most important factor to be considered is the material to be used. Mild steel and
HDPE pipes are mostly used in the design of micro hydropower project. Table below
shows the different type of materials that can be used. The higher the number of “stars”
the more favourable the material is under different characteristics.
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Table 3.7: The difference in Penstock Material.
Material Friction
Loss
weight corrosion cost Jointing Pressure
Mild Steel *** *** *** **** **** *****
uPVC ***** ***** **** **** **** ****
Concrete * * ***** *** *** *
Ductile
Iron
**** * **** ** ***** ****
Velocity of water flowing through the penstock should be between 2.5m/s-3.5m/s.
Determining the diameter of the pipe;
Where,
=inside diameter of the pipe (m)
Q= design flow (m3/s)
V=average velocity in the pipe (m/s)
Calculating the minimum thickness of the penstock material;
Where
=minimum thickness of pipe
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P=design water pressure i.e. hydrostatic pressure + water hammer (kgf/cm2), in micro-
hydro scheme P=1.1*hydrostatic pressure. For instance, if the head (Hp) which from the
headtank to turbine is 25m, P=2.5*1.1=2.75kgf/cm2
d=inside diameter (cm)
=admissible stress (kgf/cm2)SS400:1300 kgf/cm2
=welding efficiency (0.85-0.9)
=margin (0.15cm in general)
P=9.6*1.1=10.56 kgf/cm2
=0.87
3.3.8 Design of the saddles
Calculating the verticla weight to be supproted, in KN
Where
Wp=weight og the penstock per meter (KN/m)
Ww=weight of water per meter (KN/m)
Lms=length of the penstock between mid-points of each span (m)
=angle of pipe with the horizontal
Where
=internal diameter of penstock (m)
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=unit weight of the penstock full of water (Kg/m)
3.3.9 POWER HOUSE COMPONENTS
3.3.9.1 Selection of the turbines
Primarily it is the hydraulic head measurements that determine the selection of a
suitable turbine as shown in the table below;
Table 3.8: Hydraulic measurements that determine the selection of a suitable turbine
Head Classification Type of Turbine
Impulse Reaction
High (>10m) Pelton,Turgo
Low (<10m) Cross flow Propeller, Kaplan, Francis
(Open Flume )
3.3.9.2 Generators
Synchronous generators are used in most Micro Hydro Power because it has the ability
to establish its own operating voltage and maintain frequency while operating in a
remote location.
3.3.9.3 Powerhouse dimensions
Table 3.9: Table showing powerhouse dimensions
Capacity (kW) Below 25 Above 25
Floor area (m2) 12 >25
Windows area (m2) 1.2 >2.5
Minimum height between floor and ceiling >2.5m
Calculating the power generated per day (kWH) can be calculated as follow
g=gravitational constant (9.8 m/s2)
=water density (1000kg/m3)
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Hn=net head (m)
=turbine efficiency (80-90%)
=generator efficiency (98-99%)
=gear box efficiency (76-80%)
=transformer efficiency (98-99%)
=number of hours in a day which the specified flow occurs.
3.3.10 Tailrace channel
Average slope of tailrace >5cm per 10m
Dimensions specified for the headrace channel are applicable for the tailrace as well.
3.3.11 TRANSFORMERS
3.3.11.1.1 Step-up transformers
Figure 3.4: Step-Up Transformer
Source; www.physicstutorials.org
This type of transformer used for increase the incident voltage. Number of turns in
secondary coil is larger than the number of turns in primary coil.
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3.3.11.1.2 Step Down Transformer
This type of transformer used for decrease incident voltage. Number of turns in primary
coil is larger than the number of turns in secondary coil (PhysicsTutorials, 2015).
Figure 3.5: Step-Down Transformer
Source; www.physicstutorials.org
Transformer Equations
The following equations are used to find the potential, current or number of turns of any
coil;
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3.4 Power transmission losses and the final power delivered to the factory Calculating the current in 3-phase;
Where
I=current
P=power
V=voltage
=power factor of the load (normally 0.8)
Resistance of the conductor;
=resistivity
a=cross-sectional area
l=length (6670m)
Calculating total power losses
Calculating final power reaching the factory;
Calculating the transmission distance to the factory by use of Google Earth software
Transmision distance={distance from power +{ distance from mainroad to the factory}
House to the main road} eqn (3.62)
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4 METHODOLOGY
4.1 Data Acquisition
I went to Kinoro Tea Factory where I interviewed the Factory Unit Manager on the air
properties of the tea during drying and the dryer properties.
I obtained the river data from Mr. Kimotho a WARMA officer based in Meru through the
phone and also through emails.
4.2 Determination of electrical power required to dry tea in peak and normal
seasons.
I assumed my drying chamber to be a thermodynamic system with a boundary. I
obtained the moisture content wet basis of the tea and the total mass of the moisture in
te dhool using equation (3.5). I used the psychrometric charts to determine the
properties of ambient air before heating, the sensible heating of ambient air before
taking to drying chamber, properties of ambient air during removal of moisture content
from particle.
I obtained the mass of the dried tea leaves per second using equation (3.27) and the
amount of heat required to dry a kilogram of tea from the pyschrometric chart.
I used equation (3.28) to determine the total amount of energy required to dry the tea
leaves.
I used equation (3.29) to determine the total electrical power required to dry the tea
leaves both in normal and peak seasons.
4.3 Determination of a site along River Mutonga with the highest hydraulic head. 1. Upon opening Google Earth Software I clicked on the Add Path Tool which
resulted to a Google Earth-New Path window.
2. I named my path R.Mutonga Elevation Profile.
3. For Style,Color I chose Green for my path.
4. For my Altitutde I set it to be 274 m Relative to ground.
5. For Measurements I set the length to be in meters.
6. I drew the river path from Magutuni upto Kinoro Tea Factory using te Regular
Shape (clicking and releasing. Moving the mouse to a new point and clicking
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to add additional points. In this mode the cursor remains a square drawing
tool).
7. Then I clicked ok to save my river path.
8. On th left side of the Google Earth Window under Places I Right clicked on
R.Mutonga Elavation Profile, from the Right Click Menu I clicked on show
elevation profile, and the elevation profile appeared at the bottom of the 3d
viewer as I moved the cursor through the chart the information displayed was
the distance travelled, elavation above sea level and percentage slope of
the path.
4.4 Designing Micro Hydropower components
4.4.1 Design of the weir
To determine the water head (H) above the weir I used equation (3.34) and for the
breadth (B) of the weir I used equation (3.33) while the angle of the weir makes with the
floor of the river I used 300 as indicated in the theoretical analysis
4.4.2 Design of the intake
To determine the cross-sectional area (A) of the intake I used equation (3.35).
4.4.3 Design of the head race canal
To determine the cross-sectional area (A) I used equation (3.36), to determine the water
depth (H) I used equation (3.38), to determine breadth (B) I used to equation (3.39), to
determine the top width (T) I used equation (3.40), to determine wetted perimeter (P)
used equation (3.41), to determine the hydraulic radius (R) I used equation (3.42), to
determine bed slope (S) I used equation (3.43), to determine size of the largest particle
I used equation (3.44).
4.4.4 Design of spillayway
To determine the length of the spillway I used equation (3.45).
4.4.5 Design of settling basin
To determine the length of the settling basin I used equation (3.46), to determine the silt
load I used equation (3.47), to determine the volume of the silt I used equation (3.48), to
detemine the depth of collection I used equation (3.49).
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4.4.6 Design of the penstock
To determine the internal diameter of the penstock I used equation (3.52), to determine
the minmum thickness of the penstock material I used equaton (3.53), to determine the
vertical weight to be supported by the saddles I used equation (3.54), to determine the
length of the penstock between mid points of each span I used equation (3.55).
4.4.7 Design of the fore bay
To determine the submergence head I used equation (3.50), to determine the diameter
of the air vent I used equation (3.51).
4.4.8 Powerhouse
To determine the amount of power produced in the power house I used equation (3.56),
to determine the voltage and current after stepping down or stepping up I used equation
(3.57)
4.5 To determine the power transmission losses and the final electric power
reaching the factory.
To determine the current in 3-phase I used equation(3.58) , to determine the
transmission distance I used equation (3.62), to determine the resistance of a conductor
I used equation (3.59) , to determine the total power losses I used equation (3.60) , to
determine the final power that reaches the factory I used equation (3.61).
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5 DATA ANALYSIS AND RESULTS
5.1 DATA COLLECTED
I collected the from Kinoro Tea Factory with the permission of the Factory Unit
Manager.
5.1.1 Air Properties
1. Temperature of inlet air = 140 oC – 1450C
2. Temperature of outlet air = 90oC – 95o C
3. Relative humidity of ambient air = 50%
5.1.2 Dryer Properties
1. Throughput through the dryer = (1300kgDS/hr)
2. Inlet product moisture content (wb) = 65% – 67%
3. Outlet product moisture content (wb) = 3.0 – 3.1%
4. Drying time per unit fed into the drier = 30 min
5. Pressure required at the drying chamber = 9 bars
6. Number of hours for drying during peak season=24hours
7. Number of hours for drying during normal season=12hours
8. Wood fuel consumption per kilogram MT produced = 2.68 kgs/m3
9. Amount of fresh leaf processed in peak seasons = 4000 Tonnes
10. Species of wood used =soft wood
5.1.3 DATA ON THE RIVER (collected from WARMA officer in Meru Region)
5.1: Average monthly rainfall
Month Min River discharge (m3/s)
January 1.62
February 1.67
March 1.75
April 3.41
May 1.74
June 1.47
July 1.52
August 1.62
September 1.49
october 3.04
November 3.35
December 2.78
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1.
2.
3.
4.
5. Width of the river= 5 m
5.2 Determining the power requried to dry tea by doing thermal analysis.
The drying chamber was assumed to be a thermodyanmic system with a boundary.
The first law of thermodynamics and continuity was used to find the unknown
values.
Moisture content of the product (tea leaves) dry basis
Mp = 1300kgDs/hr
w2 (wb) = 0.65
moisture content wet basis of the product was calculated as;
DRYING CHAMBER
Ma,Ta1, W1
Ma,Ta2, W2
Mp,Tp1, w1
Mp,Tp2, w2
q
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If Md =1300kgDS the total mass of moisture in the dhool :-
The total mass of the dhool
=3714.23 Kg
Properties of ambient of air before heating were obtained from pyschrometric charts
in Appendix 1 with relative humidity and dry bulb temperature known:
Tdb = 280C
Twb = 20.50C
W = 50%
HR = 12g/Kg DA
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H = 58.5 Kj/kg DA
=0.8700 m3/Kg DA
Sensible heating of ambient air before taking to drying chamber occurs at a constant
humidity ratio, the following properties of air were obtained using the dry bulb
temperature and the humdity ratio;
Tdb = 1400C
Twb = 41.750C
W = 0.533%
H = 173.897KJ/Kg
= 1.1919 m3/kg
HR=12g/Kg DA
Removal of moisture content from particles results into an increase of the moisture
content of the drying air at a constant wet bulb temperature. Using the dry bulb
temperature and the wet bulb temperature the following properties were obtained;
Twb =41.750C
Tdb = 900C
W = 7.2028%
HR = 32.66 g/Kg DA
H =177.4967 KJ/Kg
= 1.0816 m3/Kg
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Properties of inlet air.
Ma = unknown
Ta1 =1400C
W1 = 0.012 Kg water/Kg DA
H1 = 173.896 KJ/Kg DA
Properties of dhool before drying
Mp = 1300KgDS/hr
Tp2 = 280C
w2 = 1.875 Kg water/Kg DS
Properties of outlet air
Ma = unknown
Ta2 = 900C
W2 = 0.0327 Kg/Kg DA
Properties of dried tea
Ma = unknown
Tp1 = 550C
w1 = 0.03Kg water/ KgDS
Ma can be obtained using equation the following equation;
MaW1+ Mp w2 = MaW2 + Mp w1 eqn (5.3)
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The required enthalpy, temperature and mass flow rate of the heated air as determined
from the psychrometric charts in Appendix 1 are as follows;
T = 1400C
H=173.897 KJ/Kg
Ma = 32.16 Kg DA/sec
I assumed that during the peak season the factory operates for 24hrs to obtain the daily
thermal energy requirement for the factory;
Amount of power required by the factory during peak season for 24hours of drying
For design purpose I designed a micro-hyrdropower which provides 6.00MW per day to
cater for the energy power requirements of the factory during peak and normal season
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5.3 Determination of the highest Hydraulic Head along R.Mutonga by creating a
Digital Elevation Model using Google Earth Software.
The were obtained from the Google Earth Software in Appendix 2
Gross Head
5.4 Design of Micro-Hydropower components
5.4.1 Design of weir and the intake
The diversion weir- a barrier built across the river used to divert water through an
opening in the riverside (the ‘Intake’ opening) into a settling basin (JICA, 2009).
In my design I used concrete gravity weir because of the following reasons.
Table 5.2: Reasons of concrete gravity weir
TYPE MATERIAL USED APPLICATION CONDITIONS
Concrete gravity
dam
Concrete is used for the
construction of the entire body
1. Foundations: in principle,
Bedrock
2. River conditions: not affected
by the gradient, discharge or level
of sediment load.
3. Intake conditions; good
interception performance and
intake efficiency.
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Standards for designing a weir.
Maximum height of the weir = should not be more than 2m
Crest width= should not be less than 20 cm for a concrete weir.
Should allow for at least 20% of the river to permanently flow over the weir to sustain
the ecosystem.
My design was going to produce power all year long so I designed using the discharge
rate of the dry season
To cater for the 20% of the water that will sustain the ecosystem I will divert 80% of the
dry season discharge;
For the purpose of design of the spillway it was important to determine how much
the intake can deliver during the rainy season,
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Designing the weir
Figure 5.1: Broad crested weir
For broad crested weirs: on low heights
H=head of the water above the weir structure
h=height of the weir
B=breadth of the weir
Discharge of the river
Discharge of the intake
Discharge over the weir during the dry season
Head of water during the dry season
= coefficient of discharge
=length across the channel (5 m)
=water head above the weir
h
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Calculating the water head during the rainy season;
Discharge flowing over the weir
Head of the water
Calculating the breadth of the weir;
I used the discharge over the weir for the rainy season so that the weir will be strong
enough to survive the rainy season.
I chose the slope of my weir to be
Converting the slope into an angle
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Maximum height of the weir should not be more than 2 m
From my calculations below the length of my intake was 1.084 m so I designed a weir of
height 1.1 m which is less than 2 m recommended height and also less than the 1.2 m
height of the river during the dry season.
A 3 D Auto-card model of the weir has been shown in Appendix 6 A while the front view
is shown in Appendix 6 B.
5.4.2 Design of the Intake
Velocity (approximately 0.5 – 1.0 m/s)
For my design I took the highest velocity (1.0 m/s) to have a small area of the intake.
v=velocity of the water in the intake
A= cross-sectional area of the intake
A 3 D Auto-card model of the intake has been shown in Appendix 6 A while the front
view is shown in Appendix 6 B.
5.4.3 Design of Headrace Canal
I chose the stone masonry with the cement mortar for my canal with the design
discharge Q=1.176m3/s. I chose it because local materials can be used and has strong
resistance to back scouring.
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Table 5.3: side slope of different materials
Material used in the canal Side slope(N)
Stone masonry with mud
mortar
0.5-1.0
Stone masonry wit cement
mortar
0-1.5
In micro-hydro scheme are higher as compared to the small-hydro scheme due to the
low skill on the survey of levelling and construciton by local contractor.
Table 5.4: Roughness coefficients for masonry canals
Masonry canals Brickwork Rougness coefficient (n)
Normal masonry with
cement mortar
0.017
Coarse rubble masonry 0.020
From the table :
For my design side slope (N) I selected =0.5 (mostly used)
Velocity of water allowed in a channel =
For this designl select 2.0 m/s as my velocity.
With this information and given that ,I calculated the cross sectional
area of the headrace canal
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I then calculated the optimum height of the canal (H), width of the canal bed (W) and the
width of the canal top (T). For that, it is necessary to find which is the factor used to
optimize the canal shape and given by;
The water depth in the canal (H) was calculated as follows;
Calculating the bed width of the headrace canal (B) as follows:
To calculate the top width of the design water level (T)
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The wetted perimeter of the headrace canal which was given by;
Calculating the hydraulic radius “R”;
Bed Slope “S” calculations
This slope value indicates that in a 1 m of drop in 167m of horizontal canal length.
Checking the size of the largest particle that can travel through the canal. Any particle
that will be beyond this particle will not be desirable to pass through the canal;
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Any particle larger than 19.21mm will settle in this headrace canal. To avoid deposition
upstream of the settling basin, the gravel trap must be designed to remove all particle
greater than 19.206 mm
The head race canal Auto card side view has been shown in Appendix 7.
5.4.4 Design of spillway
The dimensions of the spillway were given as;
= length of the spillway (m)
=flood flow via intake ( )
=design flow in headrace canal ( )
=height of the flood level in the canal (m)
=height of the spillway crest from canal bed (m)
(by convention)
It was necessary to first consider what would be the length required if the design flow
was
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length of the spillway considering the actual flow that enters through the orifice and the
head race canal,
In order to satisfy both of these conditions it was desirable that the spillway of length
53.91m be constructed.
The spillway Auto card side view has been shown in Appendix 8A and the front view
has been shown in Appendix 8 B.
5.4.5 Design of the settling basin
I first chose an arbitrarily the suitable width of the settling basin. The convention is that it
should be 2-5 times the bed width of the headrace canal, from prior calculations the
width of the headrace canal from calcualtions is 0.719m.
The width of the settling basin was
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Vvertical refers to the fall velocity taken as 0.03 m/s for a particle of the size 0.3 mm. the
same value will be taken in this case
As the design paramater has shown, the length of the settling basin should be 4-10
times of its width.
the design was thus accaptable
Calculating the silt load
T=silt emptying frequency in seconds
C or the silt concentration of the incoming flow was given as 0.5kg/m3
Calculating volume of the silt load
= taken as 2600kg/m3 if no reliable data is available
= packing factor of sediments submerged in water was given as (0.5)
Calculating the average collection depth in the settling basin
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The Auto card design of the settling basin has been shown in Appendix 9.
5.4.6 Design of the penstock
Penstock Material
Currently, the main pipe materials for the penstock are ductile iron, mild steel and
FRPM (fibre reinforced plastic multi-unit). I chose mild steel as it can withstand high
pressure, is cheap to get in case where several joints are needed and they are the
easiest to manage (Kunwor, 2012).
The rule of the thumb principle is that the velocity through the penstock ranges between
, a velocity out of this range will lead to power output loss and would
be expensive in the long run.
Determining the diameter of the pipes;
=inside diameter of the pipe (m)
Q=design flow (m3/s)
V= average velocity in the pipe (m/s)
In my design I chose V=2.6 m/s
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Calculatng the head loss
In order to get a 6.00 MW per day I require a net head of 34.03 m and I chose an
optimum penstock distance of 100 m.
(determined from Moody Chart; provided in the Appendix 3)
L=100m
V=2.6m3/s
d=0.759m
Net head
Calculating the minimum thickness of steel pipe of penstock was determined by the
following formula;
Where
=minimum thickness of pipe
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P=design water pressure i.e. hydrostatic pressure + water hammer (kgf/cm2), in micro-
hydro scheme P=1.1*hydrostatic pressure. For instance, if the ead (Hp) which from the
headtank to turbine is 25m, P=2.5*1.1=2.75kgf/cm2
d=inside diameter (cm)
=admissible stress (kgf/cm2)SS400:1300 kgf/cm2
=welding efficiency (0.85-0.9)
=margin (0.15cm in general)
P=9.6*1.1=10.56 kgf/cm2
=0.87
The Auto card design showing the penstock has been shown in Appendix 11 A and
11 B
5.4.7 Design of the saddles
Calculating the vertical weight to be supproted, in KN
Where
Wp=weight og the penstock per meter (KN/m)
Ww=weight of water per meter (KN/m)
Lms=length of the penstock between mid-points of each span (m)
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=angle of pipe with the horizontal(from google earth)
Where
=internal diameter of penstock (m)
=unit weight of the penstock full of water (Kg/m)
The Auto card design showing the weight acting on the saddle is shown in Appendix 11
C
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5.4.8 Design of the fore bay Calculation of the submergence head (depth of the water a bove the penstock), should
fulfil the criteria
I chose the submergence head of the forebay tank to be 0.517m
I chose my storage depth to be 300mm and my clearing width to be 1.5m
Calculation for the diameter of the air vent
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The Autocard drawing showing the design of the fore bay tank is shown in Appendix 10.
Calculating the power generated from my project at in 24 hours it is operating;
I chose the pelton flow turbine since my design project has a head of more than 10 m
and with an operating efficiency of 80-90%.
g=gravitational constant (9.8 m/s2)
=water density (1000 kg/m3)
Hn=net head (m)
=turbine efficiency (80-90%) - I will use 85%
=generator efficiency (98-99%) – I will use 98%
=gear box efficiency (76-80%) –I will use 78%
=transformer efficiency (98-99%) – I will use 98%
Calculating electrical power energy produced in a single day;
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In a single hour =
5.4.9 Determining the dimensions of the power house;
If the design project produces more than then the floor area should be greater
than .
The height of the powerhouse should be greater than .
I chose the following dimensions for my powerhouse;
Area of the power house,
Length of the power house,
Width of the power house,
Height of the power house,
The Auto card drawing showing the design of the powerhouse is shown in Appendix 12
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5.4.10 Design of the tail race
Dimensions of the tail race were the same as those of the head race canal;
Side slope (N) = 0.5
Cross-sectional area of the tail race (A) = 0.588 m2
Depth of the water (wd) = 0.582 m
Bed width (B) = 0.791 m
Top width (T) = 1.301 m
L (from the powerhouse to the river) = 5 m
The Auto card drawing showing the design of the tail race is shown in Appendix 12.
Total distance from the power house to the factory calculated from the Google Earth
shown in Appendix 4;
Produced at 11kV and transmitted at 11kv because the distance is short 6.67km and it
will be uneconomical to step up.
Calculating the current in 3-phase;
Where
I=current
P=power
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V=voltage
=power factor of the load (normally 0.8)
Resistance of the conductor;
=resistivity
a=cross-sectional area
l=length (6670m)
5.5 Determining the total power losses and the final power reaching the factory.
5.5.1 Calculating the power losses
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5.5.2 Determining the final power reaching the factory in any single hour;
In twenty four hours power delivered to the factory
Stepping down the transmitted voltage to 415 voltage for the factory use;
Where
V1 = transmission voltage (11000V)
V2=stepped down voltage (415V)
I1= transmission current (16.40)
I2=current supplied to the factory after stepping down(unknown)
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Table 5.5: Summarised Results
Components Critical Dimensions
Factory power requirements per During peak season = 5.593MW
Hydraulic Head Gross hydraulic head (HG) = 36.22 m
Net hydraulic head (HN) = 34.03 m
Flow of water Design of water discharge (Q) = 1.176 m3
Weir Length of the weir (L) = 5 m
Height of weir from the floor of the river (h) = 1.1 m
Head of water during the rainy season (HR) = 0.45 m
Head of water during dry season (HD) = 0.12 m
The slope of the weir (S) = 0.5773
Angle of the weir with the floor =300
Breadth of the weir (B) = 0.30 m
Intake (square) Velocity (V) = 1.0 m/s
Cross-sectional area = 1.176 m2
L = 1.084 m
W =1.084 m
Head race canal Slope (N) = 0.5
Velocity (V) = 2.0 m/s
Cross-sectional area (A) = 0.588 m2
Water depth (wd) = 0.582 m
Bed width (B) = 0.719 m
Top width (T) = 1.301 m
Wetted perimeter (P) = 2.02 m
Hydraulic radius = 0.291 m
Bed slope = 0.006
Spillway Length of spillway (Lspillway) = 53.91 m
Hflood = 0.682 m
Hsp =0.582 m
Settling basin Length of settling basin = 27.27 m
Volume of silt load VOsilt = 19.54 m3
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Average collection depth Dcollection =0.249m
Penstock Internal diameter = 0.759 m
External diameter =0.769 m
Length of penstock from the weir to the
powerhouse = 100 m
Saddles Weight, F = 0.5499 KN
Fore bay Submergence depth = 0.517 m
Diameter of the airvent =0.123 m
Storage depth = 0.3 m (300 mm)
Clearance width = 1.5 m
Powerhouse
h=3 m
L =6 m
w =5 m
Power produced at powerhouse in 24 hrs =
5.9995 MW
Voltage =11 kv
Current =16.40 A
Tail race Slope of sides (N) = 0.5
Cross-section area =0.588 m2
Water depth (wd) = 0.582 m
Bed width (B) = 0.791 m
Top width (T) = 1.301 m
Transmission Distance (d) = 6.67 km
Transmission losses = 41828.64 W
Factory power in 24 hours Power delivered =5.96 MW
Current after stepping down = 434.70A
Voltage after stepping down =415 v
Surplus power
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5.6 COST ESTIMATION
5.6.1 BILL OF QUANTITIES
According to (Jica, 2009); the rough cost estimates of a micro-hydropower system are
calculated as follows;
No. Description Formulae remarks
(1) Preparatory Works Transportation, Cleaning, Temporary Works
(2) Civil works 1 to 7
1. Intake facilities Concrete weir
H: height of the weir (m) L: length of the weir (m)
2. Head race and spillway
Q: turbine discharge (m3/s) L: length of the headrace and spillway
3. Settling basin Q: turbine discharge
4. Forebay tank Q:turbine discharge
5. penstock Civile works:
Penstock
:diameter of the penstock (m) L:length of the penstock
6. power house foundation
P: maximum output (kw) (include tailrace)
7. power house building
P:Maximum output
(3) ELECTROMECHANINCAL WORKS
P:maximum output (kw) He: effective head (m)
(4) DISTRIBUTION WORKS d:distance from the power house to factory
Sub total (A)
Indirect Cost
1 Design Fee 5-10% of SUBTOTAL (A)
2 Supervisor Fee 5-10% of SUBTOTAL (A)
3 Management Fee 5-10% of SUBTOTAL (A)
4 Tax 12.5% of SUBTOTAL (A)
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No Description Cost
1 Preparatory Works
2 Civil works
1. Intake facilities .
2. Head race and spillway .
3. Settling basin .
4. Forebay tank .
5. penstock Civil works
.
Penstock .
6. Power house foundation .
7. Power house building
3 ELECTROMECHANICAL WORKS
=5192454.962
4 DISTRIBUTION WORKS
SUBTOTAL A Ksh.25,458,033.12 Indirect Cost
1 Design fee 2 Supervisor fee
3 Management fee
4 tax
SUBTOTAL B =10,819,664.07 Total 36,277,697.19
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6 DISCUSSION
Final power delivered to the factory is 5.96 MW which has a surplus of 0.4065 MW
during the peak season. This power connected to the tea farmers near the factory.
The current produced at the step down transformer is high at 434.70 A. Normal current
at the mains switch of a normal house is 80 A because the circuit current demands are
low at the ring final ranging from 4 A – 32 A. The factory however requires high energy
in order to dry tea leaves. To get this high energy, high current should pass through the
heating coils so as to be converted to heat energy. Other factories which operate at high
currents include Electrochemical Process, Refinery and Plating Operations, Rectifier
By-pass Operations which can use currents ranging from 3000 A -500000 A.
The transmission losses of 41828.64 W are high although the transmission distance
from the power house to the factory is short (6.67 km). When calculating the power
losses the factors involved are current and resistance and an increase in these two
quantities is directly proportional to the power losses.
The net hydraulic head reduced from 36.22 m to 34.03 m. The head loss is directly
proportional to coefficient of friction of the penstock material, velocity of water in the
penstock and the length (100 m) of the penstock from the intake weir to the power
house. When any of these quantities increases it will cause an increase in the head
loss.
The selection of the micro hydropower for drying tea leaves was based on the fact that it
is a renewable energy and environmentally friendly. There is no water loss in power
generation because all the diverted water is returned to the river. The site of major civil
works like the intake weir and the powerhouse are near roads which mean that the site
is accessible.
The use of wood as the main source of energy on the other hand is expensive in the
long term, and will only lead to the deforestation and land degradation which will result
in the climate change affecting the production of tea. If gone unchecked the erratic
production of tea might lead to the factory operating in losses hence closing down. This
can all be avoided by the use of micro hydropower to dry the tea.
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7 CONCLUSION
The goal of this project was to design Micro-Hydro Power for drying tea at Kinoro. This
objective was achieved by determining the factory power requirements, and by using
environmentaly acceptable diversion river discharge to come up with the final design.
Micro-Hydro Power has been proven to reduce the use of thermal energy in the tea
processing industry in Kenya and initiate a process of reducing green house gas
emissions whilst enhancing power reliability. It can be concluded that the use of micro-
hydropower for drying tea is a viable option as a well as an alternative way for
generating extra income by selling the surplus power.
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8 RECOMMENDATION
The following are my recommendations;
1. An extensive Bill of Quantities should be done to determine the exact cost of this
project.
2. An Environmental Impact Assessment should be done to determine the
environmental and social economic impact of this project.
3. Feasibility studies done by KenGen shows that Meru County has the potential of
generating 400MW of wind power. I recommend that a study be carried out on
how to tap into this alternative source of renewable energy.
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10 APPENDICIES
10.1 Appendix 1
Psychrometic Chart for determining the air properties.
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10.2 Appendix 2
1550.78m 1587m
Digial Elevation Model of R. Mutonga using Google Earth Software for determining the
optimum hydraulic head.
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10.3 Appendix 3
Moody chart for determining co-efficient of friction of mild steel
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10.4 Appendix 4
Digital Elevation Model showing the power transmission distance from the powerhouse
to Kinoro Tea Factory
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AUTO-CARD DRAWINGS
10.5 APPENDIX 5
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10.6 WEIR
10.6.1 APPENDIX 6 A
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10.6.2 APPENDIX 6 B
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10.7 APPENDIX 7
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10.8 SPILLWAY
10.8.1 APPENDIX 8 A
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10.8.2 APPENDIX 8 B
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10.9 APPENDIX 9
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10.10 APPENDIX 10
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10.11 PENSTOCK
10.11.1 APPENDIX 11 A
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10.11.2 APPENDIX 11 B
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10.11.3 APPENDIX 11 C
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10.12 APPENDIX 12
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10.13 APPENDIX 13
Photos showing Kinoro Tea Factory
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10.14 APPENDIX 14
Photos showing R.Mutonga.
