Experimental investigation of a biomass-fired ORC-based micro-CHP for domestic applications

The ever-increasing global energy demand and the mounting environmental concerns caused by the increasing consumption of fossil fuels call for more and more utilisation of sustainable energy sources such as biomass. Many medium- and large-scale biomass-fired combined heat and power (CHP) plants have been demonstrated and commercialised in many parts of the world, such as several European countries and China. However, few biomass-fuelled micro-scale CHP (1–10 kWe) systems suitable for domestic applications have been demonstrated or commercialised. This paper presents the preliminary results of an experimental investigation on the biomass-fired organic Rankine cycle (ORC)-based micro-CHP system currently developed by the authors. The biomass-fired ORC-based micro-CHP system mainly consists of a biomass boiler, an evaporator, an ORC expander, an alternator, a heat recuperator and a condenser. The heat of biomass combustion in the boiler is used to generate hot water, which is then used to heat and vaporise the organic working fluid through the evaporator. The organic fluid vapour drives the expander to rotate an alternator, producing power. The expanded organic fluid vapour leaving the expander first passes through the heat recuperator and then is condensed in the condenser. The cooling water leaving the condenser can be heated to a temperature (∼46 °C) suitable for domestic washing and under-floor heating etc. Testing results of the micro-CHP system with a 50 kWth biomass-pellet boiler are analysed and presented in this paper. The current micro-CHP generated 861 W electricity and 47.26 kWth heat, corresponding to electricity generation efficiency of 1.41% and CHP efficiency of 78.69%. Further improvements on the performance of the expander and the alternator assembly as well as the design of the biomass boiler’s heat exchanger need to be addressed in the future.