Potential for Organic Rankine Cycle Plants in Kenya
Nyakundi, Kay Nyaboe
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Binary power plants utilizing Organic Rankine Cycle is a the most preferred way of utilizing geothermal resource that is water dominated or has low to medium enthalpy and a new way that is gaining momentum is the use of separated brine. In Kenya, binary power plants are rarely used and they are currently only used by two IPPs. Most of the geothermal power plants in Kenya are single flash plants. The major challenge that the single flash plants being operated in Kenya face is the inefficiencies due to the energy loss from the geothermal separated brine. Geothermal separated brine is a by-product of geothermal electricity generation which contains substantial amount of energy. In Olkaria, Kenya the geothermal fluid is basically a two phase mixture that consists of significantly of 50-90% brine by mass and 4% by volume while the steam is 10-50% by volume. The separated brine has extractable energy of about 1500t/h which is currently reinjected back into the ground. In addition, wells that are drilled and are more water dominated and have low enthalpy are just disregarded though this are quite a small number. In this study, we shall look the general overview of the potential Organic Rankine cycle plants in Olkaria, Kenya. In order to assess the prefeasibility of binary power plants we access and rank the available geothermal resources of Olkaria. The technical analysis is done by modelling an air cooled binary power plant by use of the EES software for the best ranked geothermal resource while the economic analysis is done by a costing comparison of the main components of the modelled binary power plants. The choice of the cooling medium is air as it is free and air cooled binary power plants are easy to maintain with a better aesthetic value. The working fluid is selected based on their harmful effects and analysis of their thermodynamic properties. The regenerative air cooled model is found to be the most technical and economic option as compared to the basic air cooled model for binary power plants for Kenya.