Exergy-energy-environ evaluation of combined cooling heating and power system based on a double stage compression regenerative gas turbine in large scales

Abstract

In the present paper a combined cooling heating and power cycle is proposed to recover exhaust and compression heat of a 35.5MW industrial gas turbine rated in summer operation. The cogeneration cycle comprises of double stage compressor, a regenerative gas turbine, absorption chiller, pumps and heat recovery units. The thermodynamical and environmental mathematical model of the cycle is developed using the Engineering Equation Solver software. The epsilon-number of transfer unit method is used to analyze the heat recovery system. A fitness function is proposed to aggregate five thermodynamical and environmental criteria and genetic algorithm is used for optimization. The results of the gas turbine and absorption chiller models are validated with the available data in the references and good agreement is achieved. Four design parameters of combustion temperature, compression ratio, pinch point temperature difference, and evaporator temperature are used for optimization. In the optimum state, the overall energy and exergy efficiencies are about 56% and 69%. Electricity production is 42.8MW and 6.6% and 9.4% of the fuel energy can be recovered from the compression heat and exhaust gases. This heat recovery corresponds to producing 24.5tons/h of superheated steam at 134.8°C and 167.4kPa. The chiller produces 7.8MW of cooling and its coefficient of performance is 0.68. The carbon monoxide, carbon dioxide and nitrogen oxides reduction are more than 87%, 17%, and 13% respectively.