7 th International Scientific Conference on “Energy and Climate Change”

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 Turbines, Condensers and Generators Separator 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)

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