Exergo-economic analysis of a 1-MW biomass-based combined cycle plant with externally fired gas turbine cycle and supercritical organic Rankine cycle

This paper deals with exergo-economic modeling and analysis of a 1-MW biomass integrated gasification combined cycle plant that couples an indirectly heated gas turbine (GT) cycle with a supercritical organic Rankine cycle (ORC). The GT produces a fixed net output of 500 kWe, and the organic vapor turbine produces the rest. Saw dust is considered as biomass feed for the gasifier, and toluene acts as ORC working fluid. GT cycle working fluid is heated through a combined combustor-heat exchanger (CHX) unit. Effects of plant parameters, viz. compressor pressure ratio (r (p)), gas turbine inlet temperature (TIT) and cold end temperature difference (CETD) of the CHX unit on the thermodynamic and economic performance of the plant are reported. Energy efficiency is maximized at a fixed value of r (p) (=6), for all TITs. Higher TIT yields in higher efficiency of the plant. Although increase in CETD lowers the plant efficiency but decreases the size of CHX unit, resulting in the lower capital cost of the unit. Exergo-economic analysis reveals that unit product cost (UPC) is lower at higher TITs and higher r (p) values. Levelized unit cost of electricity (LUCE) is also minimized at r (p) = 6 for all TITs. Higher TIT also yields lower UPC and LUCE values. Both UPC and LUCE decrease with increase in CETD. For r (p) = 6, TIT = 1100 A degrees C and CETD = 300 A degrees C, the plant offers minimum UPC and LUCE values.