Economic, environmental and multi objective optimization of a clean tri-generation system based co-firing of natural gas and biomass: An emergy evaluation

There is a recognized need for developing the novel clean systems to solve the environmental and energy issues. In this regard, a novel tri-generation system of power, cooling and freshwater triggered by was developed. Emergy analysis was utilized for simultaneously evaluation of system from economic and environmental view-points. The effects of gasification temperature, combustion temperature and natural gas contribution in the input fuel to the supercritical carbon dioxide Brayton cycle were studied on system performance. Environmental loading ratio, Emergy sustainability index, Emergy investment ratio, Renewability scale, Emergy yield ratio and energy efficiency were considered as system performance indicators. Response surface methodology was utilized for four-objective optimization of the system performance. The results showed that natural gas contribution in the input fuel was the most effective parameter on system energy efficiency and increasing natural gas contri-bution in the input fuel resulted in improving the system energy efficiency. Maximization of Emergy sustain -ability index, minimization of Environmental loading ratio, minimization of Emergy investment ratio and maximization of energy efficiency were considered as the targets of the multi-objection optimization. The findings revealed that natural gas contribution in the input fuel of 1, gasification temperature of 1000 degrees C and combustion temperature of 1403 degrees C were the optimum conditions. Response surface methodology efficiently predicted the optimum outputs with errors smaller than 5%.