Waste to Electricity: Electricity from Used Brine of an Operating Flash Power Plant

The power sector faces two main challenges of high greenhouse gas emissions responsible for global warming and high dependence on fossil fuels. Although geothermal energy is significant and can play a leading role in emission reduction through increased generation, most of the resources are low to medium temperature resources with most of the power being generated by flash power plants. The organic Rankine cycle (ORC) is a promising for waste heat and low to medium temperature heat recovery. This study analysis the feasibility of an Organic Rankine cycle (ORC) for extra power generation from used brim exiting flashing stations of an operating flash technology geothermal power plant. Depending on the thermodynamic conditions, it is possible to install an organic Rankine plant as a bottoming plant to a conventional geothermal power plant, most of which are the flash power plants. In this study, a review of the organic Rankine cycle is done as well as a preliminary design of an organic Rankine plant proposed to recover heat from waste brine for generation of extra electricity. The study targeted Olkaria 1 Power Plant in Kenya, which applied a single stage flash technology for power generation. to utilize waste heat in used geothermal fluid exiting the flash stations for Olkaria IV flash power plant in Kenya. It was demonstrated that used brine exists the flash station at 12 bar exits with heat content of about 2,268,960 MWth/hr (mega-watt thermal/hour) which can be used to generate to 7.39 MWe by development of an Organic Rankine cycle to use the waste energy in brine. The study proposes development of an ORC geothermal power plant to generate electricity from brine leaving flash tanks to reduce energy wastage in brine with on n-pentane as the working fluid. The preliminary design and analysis shows that the investment is technically and economically feasible.