• Energy Research

In advanced combined-cycle power plants, significant improvements in the thermodynamic performance are mainly achieved by the development of more efficient gas-turbine systems. This paper evaluates the effect of selected decision variables in the steam system for optimization of Thermal Combined Cycle Gas Turbine (TCCGT) power plant using an iterative exergoeconomic. The design variables were the thermodynamic parameters that establish the configuration both of the steam and gas systems. The design data of an existing plant (Damavand power plant in Tehran-Iran) is used. Two different objective functions are proposed: one minimizes the total cost of production per unit of output, and the other maximizes the total exergetic efficiency. The analysis shows that the total cost of production per unit of output is 2% lower and exergy efficiency is 4% higher with respect to the base case. It demonstrates that selected decision variables have suitable results for the exergy analysis and cost effectiveness. Since, environmental pollution and energy shortage are the two factors limiting the development of the society; nevertheless, this analysis tends to optimally find the design parameters which result in a decrease in the fuel mass flow rate. Also, this reduction (about 5%) in the mass flow rate and increasing exergetic efficiency can decrease the environmental impacts.

Abstract A multi-generation system has been considered to meet different purposes in recent years. Two main purposes of this system are producing various products, as well as the improved performance of this system, simultaneously. In this paper, a new cogeneration hybrid cycle is introduced to provide electricity and urea production. This system includes gas cycle, steam cycle, carbon capture system, proton exchange membrane, electrolyzer, cryogenic air separation unit, and urea and ammonia synthesis reactors. The energy, economic, exergy, exergoenvironmental, and environmental analyses of this proposed system have been investigated. The results of this study demonstrate that this system produces 689 GW h electrical energy and 1.323 million tons of urea annually. The energy and exergy efficiencies of these hybrid systems are equal to 31. 8% and 53.3%, respectively. The highest and lowest rate of exergy distribution is related to the urea synthesis reactor and cryogenic air separation unit, respectively. In the economic evaluation, the social cost of carbon dioxide is considered. The four main economic factors: net present value, payback period and simple payback period, and internal rate of return are examined and calculated. By considering the social cost of the carbon dioxide separation unit, the economic factors are improved considerably. The exergoenvironment and environmental damage effectiveness and exergy stability factors for this system are equal to 1.64, 3.1, and 0.76, respectively.

This paper shows a new possible way with particle swarm optimisation (PSO) to achieve an exergoeconomic optimisation of combined-cycle power plants. The optimisation has been done using a classic exergoeconomic and genetic algorithm, and the effects of using three methods are investigated and compared. The design data of an existing plant is used for the present analysis. Two different objective functions are proposed: one minimises the total cost of production per unit of output, and maximises the total exergetic efficiency. The analysis shows that the total cost of production per unit of output is 2%, 3% and 5% lower and exergy efficiency is 4%, 8% and 6% higher with respect to the base case for the classic, PSO and GA procedures, respectively. Finally, a sensitivity analysis to assess the effects of change in the decision variables of the plant on the objective functions performed, and the results are reported.