Advanced ORC architecture for geothermal combined heat and power generation

Abstract

Several approaches to enhance the performance of Organic Rankine Cycles (ORC) have been investigated in literature, including architecture, working fluid selection and part-load optimization together with combined heat and power (CHP) generation. To contribute to these developments, the design and the first operation of an advanced ORC-CHP architecture is being presented in this study. This architecture extends the state of the art by a two-stage concept with turbine bleeding and a regenerative direct contact preheater. The aim of this architecture is to increase the heat source utilization, flexibility and part-load efficiency. To evaluate the performance of this concept, a test rig has been constructed. It is heated with a 200 kW electrical heater and a twin-screw expander is being used. The low-GWP fluid R1233zd(E) is applied as working fluid. In order to analyze the system in its full operating range, experiments are conducted with varying heat loads of the district heating network. Furthermore, an operating strategy of the system is being developed. With this first operation, a very high operational range of the novel ORC-CHP architecture down to a minimum load of 15.3% is being demonstrated. Furthermore, is could be proven that thermal efficiency increases during part-load operation.