Developing an operating instruction to attenuate pressure stress during fuel shortage events of a power boiler based on dynamic modelling

Abstract

Stress control of boilers is a major concern in the aged power plants. The studied forced circulation boiler suffers from a malfunction of the combustion control system. In order to reduce cyclic stress on boiler equipment and prevent undesirable shutdowns of power unit during fuel shortage events, an operating instruction is proposed. In order to predict dynamic behavior of the boiler, a nonlinear state space model is developed using mathematical modelling approach. A gray box identification procedure is introduced using only steady state measurements of plant. The dynamic model is verified compared to actual plant data and accuracy of model parameters is evaluated by sigma-normalized sensitivity analysis. Considering aim of steam pressure regulation, a three-step optimization approach is proposed based on golden section search, parabolic interpolation and interior-point methods to optimize arbitrary parameters of the proposed manual control scheme. Simulation results for different loads and various fuel limitation scenarios show that proposed instruction improves the cyclic stress in superheater tubes at least 84.5%. In addition, Monte Carlo experiments illustrate despite a 10% operators’ error in implement of the instruction, the stress is still reduced by an average of 78.1% for a given case.