Thermodynamic and economic evaluation of a CCHP system with biomass gasifier, Stirling engine, internal combustion engine and absorption chiller

Abstract

This work proposes a combined cooling, heating and power (CCHP) system based on biomass gasification with an internal combustion engine (ICE), a Stirling engine and an absorption chiller. The energy and exergy efficiencies and economic performance of the CCHP are evaluated under different working conditions by thermodynamic model and net present value method. The Stirling engine recovers the high temperature potential of syngas during cooling process and improves the CCHP output power by 14 % along with ICE, while the thermal efficiency of ICE reaches 39 % at 5000 rpm. In this work, about half of the total exergy destruction comes from ICE rather than gasifier due to the utilization of Stirling engine as an additional mover to produce electricity. The recycling of weak solution in absorber is adopted in order to increase the COP (Coefficient of performance) of single-effect absorption chiller. The COP could be increased by 7 % and reach 76 % as half of the weak solution recycling to absorber. The electric efficiency and total CCHP efficiency of this system reach 37 % and more than 60 %, respectively. The payback period is estimated to be less than 6 years at an ICE rotational speed of over 4000 rpm and an operation time of more than 4000 h/year.