7th International Scientific Conference on “Energy and Climate
Change”
Kostis Palamas Building, Athens, GreeceOctober 8-10 , 2014
Proudly Kenyan
WR
Energy and Exergy Analysis Concepts: Modeling of Olkaria II Geothermal Power Plant in Kenya.
Authors Mr. Nyambane NDr. Gatari M. JDr. Githiri J. G
Dr. Mariita N. O
Outline Introduction/Background Description of Olkaria II geothermal power plant Thermodynamic Analysis Methodology Results and Discussions Conclusions Recommendations Questions and Comments
Introduction Energy is an essential component for economic
development of any country.• Improves the economy
For the case of Kenya• Demand is higher than supply
To bridge this gap• Invest in energy generating projects• Improve the efficiency of existing ones
Introduction
Kenya is endowed with huge potentials of geothermal energy
• Over 7000 MW• Only 5 % is being exploited for electricity generation
The efficiency of conversion of the exploited geothermal energy is demanding due to
• Huge exergy losses in plant subsystems• Turbine(s) and Condenser(s)
Introduction Studies have shown huge exergy losses occur in the
turbine(s) and condenser(s).• Aligan (2001)• Kwambai (2005)
Minimal efforts have been made to curb this menace.• For turbine, improve the steam condensation process• Translates to higher vacuum pressure in condenser• Higher exergy drop across turbine• Increase exergy efficiency and power output
Introduction
Steam condensation efficiency is influenced by cooling water temperature.
• The lower the cooling water temperature the efficient the steam condensation process
Kenya being in tropical region experiences high ambient temperature which leads to
• High cooling water temperature• High condenser pressure
The big question is, “how do we minimize the effect of ambient temperature on cooling efficiency of geothermal power plant?”
Absorption Chiller
In this study an absorption chiller system has been adopted for Olkaria II geothermal Power plant in Kenya.
• Incorporated into the cooling system.• Cool water out of the cooling tower.
Study by Tesha (2009), have shown a 131 kW power increase for a geothermal power plant that adopts an absorption chiller as an integrated condenser unit.
Description of Olkaria II Geothermal Power Plant, Kenya
Cooling TowersTurbines, Condensers and Generators
Separator
Transmission line
Power Distribution Station
Thermodynamic Analysis
Thermodynamic Analysis Exergy flow diagram
Absorption Chiller Cycle
QdQd
1122
QabsQabs
2626
1515
cold
1414
QshxQshxhot
SHX
2525
2323
2424
cold
QevQevhot
cold
1212 1313
QrhxQrhxhot
RHXcoldcold
3232
3131
3030
2929
2828
QcondQcondhot
Condcold
2727
1717
1616
2222
2121
Absorption Chiller Model
Methodology
Parameters considered during data collection were • Pressure(s)• Mass flow rate(s)• Temperature(s)
The measured parameters served as inputs to the modelled system for simulation on Engineering Equation Solver (EES).
Methodology
Absorption chiller Model• Based on simple steady state• Uses mass and energy balance principles• Formulated on the basis of UA and LMTD
EES codes are developed and simulated using EES software to compute the output parameters.
Iterations for the evaporator temperature were run.
Results and DiscussionsTable 1: Comparison of efficiencies between the current geothermal power plant (GPP) and the geothermal power plant with hybridized cooling system (HCS)
Subsystem Desired Exergy for each
subsystem (MW)
Exergy wasted in each subsystem
(MW)
Exergy destroyed in each subsystem
(MW)
Exergetic efficiency of each
subsystem (%)
Current GPP
GPP with HCS
Current GPP
GPP with HCS
Current GPP
GPP with HCS
Current GPP
GPP with HCS
Turbine 37.5 39.13 8.04 6.8 7.7 7.3 83.0 84.3Condenser 5.0 4.9 0.15 0.14 2.89
2.3 63.4 65.9
Energy Efficiency of turbine 19.4 20.2Overall Exergetic efficiency of Plant as a function of steam into transmission lines
52.4 65
Overall Exergetic efficiency of Plant as a function of geo-fluid 46.6 55.6
Results and Discussions
Adoption of the hybrid cooling system showed some positive results.
• Increase in power output from 35.6 MW to 37.2 MW• Decrease in exergy loss in the turbine(s) and condenser(s)• Net annual gain of 819,542 US $
Results and Discussions
Figure 1:Relationship between condenser pressure and changes in cooling water temperature.
Figure 2: Relationship between turbine power
output and changes in condenser pressure
10 11 12 13 14 15 16 17 18 19 20 21 224
4.254.5
4.755
5.255.5
5.756
6.256.5
6.757
7.257.5
7.758
8.258.5
Cooling water temperature [oC]
Con
den
ser
pre
ssu
re [
kP
a]
4 4.5 5 5.5 6 6.5 7 7.5 8 8.536
36.5
37
37.5
38
38.5
39
39.5
40
40.5
41
41.5
42
Condenser pressure [kPa]
Tu
rbin
e ou
tpu
t p
ower
[M
W]
Results and Discussions
Figure 3: Condenser heat transfer rate due to cooling water temperature and flow rate changes at constant condenser pressure of 5 kPa.
10 12 14 16 18 20 22140000
160000
180000
200000
220000
240000
260000
Cooling water temperature [oC]
Cond
enser
heat
trans
fer ra
te [K
W]
Cooling water flow rate [kgs-1]
2194
2000
1800
1500
Conclusions
By lowering cooling water temperature from 25 0C to 16 0C• Condenser pressure reduced from 6.9 kPa to 5.9 kPa• Output power increased by 1.5 MW• Exergy loss in condenser reduced by 0.59 MW• Exergy loss in turbine reduced by 0.4 MW• Overall exergy efficiency improved by 12.6 %
Recommendations
There is need to carry out an economic analysis to ascertain the cost of investing in the absorption chiller
Evaluate the payback period which will help the investors to evaluate if the investment is economically feasible.
Thank You
Questions & Comments