A combined cycle plant with air and fuel recuperator for captive power application. Part 2: Inverse analysis and parameter estimation

• Inverse analysis of a combined power cycle is presented.
• The inverse problem is solved using a simplex search minimization algorithm.
• Method was found suitable for estimation of unknown operating parameters.
• Multiple combinations of operating parameters exist that satisfies a given objective function.
• The study provides guidelines for selecting feasible combinations of parameters.

An inverse problem is solved for estimating fuel flow rate (FFR), air flow rate (AFR) and steam injection rate (STIR) separately and then simultaneously two and three parameters in a combined gas–steam turbine cycle power plant. Initially, a model developed and discussed in part 1 of this article simulates the combined cycle steady state operation and its performance in terms of net power and efficiency. An inverse problem is then solved for estimating the above parameters using a simplex search minimization algorithm. The two objective functions i.e. the net power and efficiency and the estimation accuracy are studied for the effects of initial guess values of the operating parameters and the number of iterations required for retrieval/estimation of these parameters, choosing one objective function at a time. An objective function is represented by the sum of square of the error between its measured value and value corresponding to initial guessed values of the unknowns, which are then regularized in an iterative manner for solution of the inverse problem. The study reveals that a multiple combinations of parameters (FFR, AFR and STIR) exist for the two inverse strategies that satisfy the same reference net power and the efficiency obtained from the direct method in part 1.