This study has been carried out for the LOW-BIN (Efficient Low Temperature Geothermal Binary Power) project, which is supported by the European Commission FP6 program. Its aim is to study and recommend optimal Rankine cycles using Isobutane (R600a) and R134a as working fluids for two geothermal binary power machines. The first one (ORC machine A) should be able to generate electricity from low temperature geothermal resources, with profitable operation down to 65°C. The second one (ORC machine B) should be able to cogenerate both heat and power by heat recovery from the cooling water circuit, corresponding to geothermal fluids of 120-150ºC and cooling water supplying a district heating system at 60/80ºC. The main Rankine Cycle parameters and components are modelled, such as the shell and tube condenser and the geothermal plate heat exchanger. The objectives of the optimization are maximizing overall conversion efficiency and minimizing the cost of the plant, which is represented as minimizing of the exchangers’ surface. Through this study, a set of optimal solutions for ORC machines A and B are obtained, that combine maximum plant’s efficiency (6.7-7.4 %) and minimum cost. Each optimal solution corresponds to an optimal Rankine Cycle and every parameter of the cycle is defined.

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ENGINE - FP6