Techno-economic performance evaluation of a direct biomass-fired combined cycle plant employing air turbine

Techno-economic performance analysis of a biomass-fired combined cycle plant, employing a topping air turbine (AT) cycle and a bottoming steam turbine cycle, is reported in this paper. The net power output is 500 kWe, the AT producing 350 kWe and the ST producing the rest. Biomass (saw dust) is directly fired in a biomass combustor-heat exchanger (BCHX) duplex unit which supplies heat to the topping cycle. Influences of major plant parameters on the thermo-economic performance of the plant are analysed. Overall efficiency is found to maximise at topping cycle pressure ratio of 4. Higher TIT results in better energetic performance, while higher hot end temperature difference of the BCHX unit lowers the plant efficiency. Thermo-economic analysis reveals that the lowest unit cost of electricity (UCOE) of about 0.12 $/kWh could be achieved for the plant, while still giving an overall efficiency of about 48 %. Based on minimum UCOE, the payback period is estimated to be about 6 years with 50 % capital subsidy and about 13 years with no capital subsidy.