Screw Type Engine
At present the only useful technologies from a technical and economic point of view for CHP generation based on biomass fuels in the power range between 200 to 1,500 kWel are the screw-type steam engine and the ORC process. The screw-type engine is used for steam applications and is orientated to industry and process heat supply. The screw-type engine cycle is based on the conventional Rankine process. In opposite to the steam turbine process the steam is expanded in a screw-type engine, which is connected to a generator producing electric power. The screw-type engine is derived from the screw compressor and is consequently based on comprehensive engine know-how. Screw-type engines are suitable for biomass CHP plants in the range of 200 to 2,500 kWel, where steam parameters can vary, due to variations of the fuel water content and the kind of biomass fuel used, and where a simple and heavy duty design is needed causing low operating and maintenance costs.