Thermoeconomic optimization of the pinch point and gas-side velocity in heat recovery steam generators

Abstract

In the present article, thermodynamic and thermoeconomic analysis are applied to find the optimum values of design parameters for water-tube heat recovery steam generators (HRSGs) in combined cycle power plants. Design variables optimized in this article are pinch point and gas-side velocity. Optimization is carried out based on two different objective functions. The first one is thermodynamic, which is the summation of exergy loss due to an outflow of hot gas escaping from the HRSG through stack, and exergy destruction due to internal irreversibility inside the HRSG. The second one is a thermoeconomic objective function, which is the summation of exergy loss and destruction in terms of expenses including the cost of fuel and electricity, and the capital cost of HRSG in terms of the future value of money according to the interest rate. The capital cost of HRSG includes procurement and erection of piping and insulation, electrical panels and wiring, control and instrumentation equipment, insurance, tax, engineering, and supervision. The effects of pinch point and gas-side velocity on the components of objective functions are investigated in details. The pinch point and gas-side velocity that make these objective functions minimum are called optimum values.