Multi-objective optimization of a tri-generation system based on biomass gasification/digestion combined with S-CO2 cycle and absorption chiller

A novel configuration of biomass-based cooling, heating and power (CCHP) system, consisting of Gas Turbine (GT), Supercritical Carbon dioxide cycle (S-CO2) and double effect LiBr-H2O absorption chiller is proposed and its performance is analyzed and compared for two cases: 1) fueling with syngas from the gasification process and 2) fueling with biogas from the digestion process. Thermodynamic models are developed to evaluate the proposed systems' performance from energy, exergy and exergoeconomic viewpoints and an environmental assessment is conducted to evaluate the systems' CO2 emission. Then, a multi-objective optimization is applied for which the exergy efficiency and unit cost of system products are selected as the objective functions. The results revealed that the digestion-based system performs better than the gasification-based one in terms of efficiency, unit product cost and environmental impacts. The former yields a maximum exergy efficiency of 47.8%, while for the latter a maximum efficiency of 42.74% is calculated. For digestion-based system, the values of 47.09% and 5.436 $/GJ are calculated for exergy efficiency and product unit cost at the optimum operating conditions. Also, the results of environmental assessment indicated the values of 2.6x10(-2)t/MWh and 4.21x10(-2)t/MWh for CO2 emissions for digestion- and gasification-based systems, respectively.