Proposal, exergy analysis and optimization of a new biomass-based cogeneration system

•Energy and exergy assessments are reported of a novel cogeneration system.•The influences of the S-CO2 and gas turbine pressure ratios are investigated.•Exergy efficiency of 40.11% is obtained for a biomass fed cogeneration system.•The highest exergy destruction occurs in the combustion chamber. A new cogeneration system consisting of a biomass gasifier, a gas turbine, a S-CO2 cycle and a domestic water heater is proposed and analyzed in detail. Applying the conservation of mass and energy as well as the exergy balance for each system component and using the engineering equation solver (EES), the system performance is simulated. The combustion chamber and the gasifier are observed to be two major sources of irreversibility in the system. Through a parametric study it is observed that the gas turbine and the S-CO2 turbine pressure ratios play key roles in the system performance. In addition, considering the system as a combination of three subsystems, i.e. the standalone gas turbine, the whole system without the domestic water heater (power generation system) and the cogeneration system, an environmental impact assessment in terms of CO2 emission is carried out. Wood and paper are examined as biomasses and it is observed that using wood leads to a maximum exergy efficiency of 40.11% with a CO2 emission of 4.99×10−2t/MWh for the cogeneration system. The values of these parameters are 39.12% and 4.95×10−2 t/MWh when paper is used as biomass.