Dynamic Modeling And Control Of A Natural Gas Combined Cycle Power Plant For Load-Following Operation

Abstract With the increasing penetration of intermittent renewable sources into the electric grid, conventional thermal power plants are being forced to cycle their load and operate under low-load conditions much more frequently. A high-fidelity dynamic model of a natural gas combined cycle power plant with rigorous models of key equipment items is developed. A model of the gas turbine, a thermo-hydraulic model for the heat recovery steam generator, and a model of the steam turbine with moisture detection and model adaptation capability are also developed. The model is used to study the issue of ‘spraying to saturation’ or overspraying in the attemperators during load transients and low-load operation. Performances of a two-stage attemperation system versus a one-stage attemperation system are evaluated using coordinated control strategies when the plant load is decreased from 100% to 45% at a ramp rate of 5% load change per min. It was observed that the two-stage attemperation strategy can not only avoid ‘spraying to saturation’ but leads to a superior control of the main steam temperature.