Improvement of thermal efficiency for combined cycle power plant during load following operation

An optimization method for unit startup and shutdown timing in the load control system is proposed for combined cycle power plants to improve thermal efficiency during load following operation. The optimum timings are derived from regression equations obtained through offline dynamics simulation analysis. The system is applied to a simulation for a plant of a three-pressure staged reheat type (1650 MW rated capacity) which consists of seven units, and the following points are seen: (1) the larger the load change amount is, the earlier the recommended additional startup timing is; (2) the tendency described in (1) is more remarkable when the load change is faster; and (3) thermal efficiency is expected to be increased by 9% compared with the conventional method.