Parametric optimization of supercritical power plants using gradient methods

Gradient nonlinear optimization methods are among the most effective approaches to determine the optimal parameters of thermal power plants. These methods allow us to consistently optimize a large number of thermodynamic and design parameters and mass flow rates of actuation fluids and of heat-transfer fluids. This paper proposes an original gradient method to optimize the parameters of a 660 MW supercritical coal-fired power unit. The specific feature of the method is that it can start from a point where there is no solution of the combined equation defining the plant. The exact solution of the nonlinear combined equation is achieved only at the optimal point, consequently the calculation time is reduced. The method provides better convergence and greater accuracy of solving the nonlinear combined equation defining the processes in the power unit. Optimization is carried out according to the criterion of maximum efficiency, minimum specific plant investments and minimum cost of electricity at different fuel prices. The austenitic and nickel alloys are considered for superheater and reheater tubes of a steam generator. Co-optimization of the thermodynamic and design parameters of the power unit by the criterion of the minimum cost of electricity allowed us to get original solutions that combine the high temperature (615–622 °C) and low pressure (16.7–18.1 MPa) of live steam.