Proposal and thermo-economic optimization of using LNG cold exergy for compressor inlet cooling in an integrated biomass fueled triple combined power cycle

Abstract

Utilization of renewable energy resources and efficiency improvement of energy conversion systems are of great importance due to energy crisis and environmental issues. Renewable energy driven Triple Combined Cycle (TCC) is a relatively new idea in this respect. In this paper, a biomass gasification-fueled TCC is presented in which the conventional gas turbine, as the topping cycle, is combined with a Closed Brayton Cycle (CBC) and an Organic Rankine Cycle (ORC). The proposed TCC is integrated with LNG regasification process to exploit its cold exergy for compressor inlet cooling of the CBC. For the CBC three working fluids (namely: helium, nitrogen and carbon dioxide) are considered. There is a good thermal match between the LNG and these fluids in heat rejection process and they can be cooled down to temperatures of below 0°C at the compressor inlet for net power augmentation. Thermoeconomic method is applied to evaluate the TCC performance and optimization using genetic algorithm is employed to minimize the Levelized Cost of Electricity (LCOE). In the economic analysis the cost rate of environmental impacts due to pollutant emissions is also considered. The results indicated the superiority of helium over the other investigated working fluids from the economic perspective for which the LCOE is found to be 51.38 $/MWh. However, as an interesting outcome it is found that, from thermodynamic standpoint using CO2 as the working fluid yields higher exergy efficiency by 6.7% than the helium.