Modification of working fluid in geothermal organic Rankine cycle engines

The organic Rankine cycle engines for geothermal water are in general fitted with full admission reaction turbines. Thus the rated power cannot be varied by altering the number of active nozzle. The power however has to be varied to match the grid requirements and the water temperature variation. To substitute the working fluid is an alternative to the power reduction by lamination of the vapour at the turbine inlet. The influence of fluid substitution vs throttling is discussed with reference to a 100 kW engine. Experiments were made on a 4 kW engine, using perchloro-ethylene-trichloro-ethylene mixtures to investigate if operational difficulties could arise due to erratic fluid composition at the interface. Mixtures seem promising, psrticularly if the variable change-of-state temperatures are properly exploited.