The growing energy demand, depleting fossil fuel reserves, and global warming concerns call for a further increase in biomass energy utilization. At present, biomass is mostly used in small-scale applications where the production of electricity is technically and economically disadvantageous. On the other hand, district or communityscale CHP applications with higher efficiencies and lower specific investment costs are a better alternative. Biomass combined heat and power (BCHP) systems can reduce GHG emissions and also have the potential for higher overall energy efficiencies than conventional home heating methods. In this research, an organic Rankine cycle (ORC)-based BCHP for community-scale applications is investigated concerning technical and economic aspects. MDM (Octamethyltrisiloxane) is selected as the ORC working fluid, taking into account the cycle efficiency and system design. The heat of biomass combustion in the boiler is used to vaporize the organic working fluid in the evaporator. The working fluid vapor drives the turbine that spins an alternator. A mathematical model for the community-scale ORC BCHP system is developed to predict its operational performance. Various costs for the BCHP plant are analyzed and the cost of electricity (COE) is calculated. The community-scale or district BCHP plant generates 520.9 kWe electricity with the electrical efficiency reaching 17.24 % at a turbine inlet temperature of 250 °C, and provides hot water with a heating load of 2365.7kWth at a temperature of 79.2 °C. The COE of the BCHP plant is 98.2 $/MWh when not including CO2 credit.
Keywords Biomass, organic Rankine cycle, BCHP, model, working fluid