1. 7th International Scientific Conference on “Energy and Climate Change”
Kostis Palamas Building, Athens, Greece
October 8-10 , 2014

2. Proudly Kenyan WR

3. Energy and Exergy Analysis Concepts: Modeling of Olkaria II Geothermal Power Plant in Kenya.
Authors Mr. Nyambane N
Dr. Gatari M. J
Dr. Githiri J. G
Dr. Mariita N. O

4. Outline Introduction/Background
Description of Olkaria II geothermal power plant
Thermodynamic Analysis
Methodology
Results and Discussions
Conclusions
Recommendations
Questions and Comments

5. 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

6. 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)

7. 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

8. 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

9. The big question is, “how do we minimize the effect of ambient temperature on cooling efficiency of geothermal power plant?”

10. 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.

11. Description of Olkaria II Geothermal Power Plant, Kenya
Cooling Towers
Separator
Turbines, Condensers and Generators
Power Distribution Station
Transmission line

12. Thermodynamic Analysis

13. Thermodynamic Analysis
Exergy flow diagram

14. Absorption Chiller Cycle

15. Absorption Chiller Model

16. 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).

17. 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.

18. Results and Discussions
Table 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
Turbine
37.5
39.13
8.04
6.8
7.7
7.3
83.0
84.3
Condenser
5.0
4.9
0.15
0.14
2.89
2.3
63.4
65.9
Energy Efficiency of turbine
19.4
20.2
Overall 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

19. 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 $

20. 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

21. 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.

22. 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 %

23. 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.

24. Thank You

25. Questions & Comments