Experimental investigation of a biomass-fired micro-scale CHP with organic Rankine cycle

The continual increases in global energy demand and greenhouse gas emissions call for more and more utilisation of sustainable energy sources such as biomass. Among the existing biomass conversion technologies such as combustion, gasification and biochemical approaches, combustion is the most mature and widely used conversion technology. Several biomass-fired combined heat and power (CHP) plants) with capacities in the order of 1000kWe have been demonstrated in several European countries. However, biomass-fired micro-scale CHP (1-10kWe) suitable for domestic applications has not been demonstrated. The micro-scale biomass-fired organic Rankine cycle (ORC) CHP system currently developed by the authors mainly consists of a boiler, an ORC fluid evaporator, an ORC turbine, an alternator, a heat recouperator and a condenser. The boiler produces hot water which transfers heat to the organic working fluid via the evaporator. The generated organic fluid vapour drives a turbine to rotate an alternator, producing power. The expanded organic fluid vapour leaving the turbine transfers some of its heat to the recouperator and then is condensed by cooling water which can be heated to around 40°C for domestic washing and under-floor heating etc. The testing of the CHP system has been conducted initially with a 9kW electric boiler and then with a 25kWth biomass boiler. Preliminary testing results of the CHP system are analysed and presented in this paper.