Dynamic Simulation and Optimization of a Subcritical Coal-Fired Power Plant During Load- Ramping Operations

Abstract

Abstract With increasing penetration of renewable energy sources, traditional power plants are required to operate more flexibly with higher ramp rates than originally planned for by design. A dynamic model for a subcritical coal-fired power plant was developed in the open-source, equation-oriented IDAES (Institute for the Design of Advanced Energy Systems) modeling framework. PID-based regulatory controllers and a supervisory- level coordinated control system (CCS) were also implemented. The plant-wide dynamic model and controls were used to investigate and optimize flexible operations. Plant-wide dynamic simulations were performed under load-ramping cycles from full load to 50 % load and back to full load at different ramp rates. In addition, dynamic optimizations were performed at ramp rates of 5 % full load per minute. The objective of the dynamic optimization was to maintain a stable main steam temperature (MST) at the boiler exit while maximizing plant efficiency during ramping. Dynamic simulation results show large excursions in MST, which are detrimental to equipment health. The CCS implementation leads to a drop in MST during the ramp down and an overshoot during the ramp up when attemperator water spray capacity is limited. Through dynamic optimization, the maximum MST deviation is reduced from 12 K, at a 5 %/min ramp rate from full load to 70 % load, to within 2 K by changing three manipulated variable profiles: the furnace stoichiometric ratio, the water spray valve opening, and the setpoint for sliding-pressure operation. This improves the average plant efficiency slightly, while the reduced MST excursion benefits the health of the steam turbine.