Thermoeconomic optimization of triple pressure heat recovery steam generator operating parameters for combined cycle plants

Abstract

The aim of this work is to develop a method for optimization of operating parameters of a triple pressure heat recovery steam generator. Two types of optimization: (a) thermodynamic and (b) thermoeconomic were performed. The purpose of the thermodynamic optimization is to maximize the efficiency of the plant. The selected objective for this purpose is minimization of the exergy destruction in the heat recovery steam generator. The purpose of the thermoeconomic optimization is to decrease the production cost of electricity. Here, the total annual cost of heat recovery steam generator, defined as a sum of annual values of the capital costs and the cost of the exergy destruction, is selected as the objective function. The optimal values of the most influencing variables are obtained by minimizing the objective function while satisfying a group of constraints. The optimization algorithm is developed and tested on a case of combined cycle gas turbine plant with complex configuration. Six operating parameters were subject of optimization: pressures and pinch point temperatures of every three (high, intermediate, and low pressure) steam stream. The influence of these variables on the objective function and production cost are investigated in detail. The differences between results of thermodynamic and the thermoeconomic optimization are discussed.