Exergetic and exergoeconomic assessment of a novel CHP system integrating biomass partial gasification with ground source heat pump

The renewable energy has drawn increasingly attention for the utilization of energy in the worldwide, especially biomass and geothermal energy. The total biomass gasification usually leads to the higher exergy destruction and lower exergy efficiency of gasification process subsequently, and the flue gas at middle temperature (400 °C) is always used to generate domestic hot water from environment temperature to required temperature e.g. 55 °C, the relative large temperature difference leads to high exergy loss. For adopting ground source heat pump system to generate domestic hot water, relative high target temperature (e.g. 55 °C) always leads to the high compression ratio, which decreases the coefficient of performance (COP) of the ground source heat pump host. Therefore, so as to make a better use of biomass and increase the COP of ground source heat pump systems, a novel CHP system coupling biomass partial gasification and ground source heat pump is presented. It mainly consists of four parts: biomass partial gasification subsystem; gas turbine power generation subsystem; steam turbine power generation subsystem; and ground source heat pump subsystem. The main products of proposed system are electricity and domestic hot water (55 °C). The exergetic and exergoeconomic performance analysis of proposed system are investigated, and in a further way, the effects of several key system integrating parameters on system performance are also studied. The results show that the system exergy efficiency can be reached at about 13.65%. The main exergy destruction exists in gasifier and followed by char boiler, which accounts for 38% and 21.71% of total exergy destruction, respectively. Moreover, the unit cost of hot water, power generated by gas turbine and steam turbine are 92.5 $/GJ, 12.4 $/GJ and 23.9 $/GJ, respectively. The proposed CHP integration system is valuable to other advanced biomass and geothermal based multi-generation systems.