Thermo-economic assessment of a hybrid tri-generation system making simultaneous use of biomass and solar energy

Abstract

In this work, a tri-generation system is proposed that relies on a biomass-gasification-based externally fired gas turbine (EFGT) generator and an array of solar flat-plate collectors. A LiBr-water-based absorption cooling (VAR) system utilizes the waste heat of a 100-kW power generator as well as solar thermal energy of a 200 sq. m. solar collector to run a vegetable cold store of 200 metric ton capacity. A domestic water-heating system is also integrated with the unit that recovers low-temperature thermal energy to produce 150 tons of hot water daily. The power generator shows its maximum electrical efficiency of 27.5% at 1100 °C turbine inlet temperature and 10 pressure ratio. The maximum efficiency of solar collector is found to be 48%. The overall energetic efficiency of the tri-generation system varies in the range of 59 to 76%, while the overall exergetic efficiency varies in the range of 19 to 26.5%. The components of EFGT generator show high exergetic efficiencies, about 93% for air compressor and about 90% for GT, whereas the solar thermal system shows the poor exergetic performance of about 17%. Based on economic analysis of the proposed plant, the effective price of electricity is estimated as 0.068 USD/kWh without any subsidy, but considering 50% capital subsidy the price is estimated as 0.04 USD/kWh. The discounted payback period is found to be 10.8 years without any capital subsidy, but when 50% subsidy is considered, the payback period is reduced to 5 years.