Enhancing peak shaving capability by optimizing reheat-steam temperature control of a double-reheat boiler

Double-reheat coal-fired power plants elicit much research attention due to their high efficiency and low emissions. However, steam temperatures fluctuate heavily, especially in transient processes, thereby compromising the load cycling capacity of these power plants and even threatening their stable operation. To overcome these challenges and optimize the operations of double-reheat boilers, a dynamic boiler model was established and validated with values measured from a real power plant. A revised reheat steam control logic was proposed that considers the heat storage variation in boiler metals and the deviation of steam temperatures during peak shaving transient processes. The performance of the original and revised reheat steam control logics in terms of temperature control and energy delivery characteristics was compared and discussed. Calculation results show that the revised control logic performs better than the original logic in large-range load cycling processes. The steam temperature fluctuations are alleviated, and the overshoots are reduced substantially. The revised reheat steam control logic ensures that the accessible maximum load variation rate is 4.0% BMCR min−1, which cannot be safely guaranteed by the original logic. These improvements are beneficial to increasing the threshold of the load variation rate and improve the flexibility of the power plant. The average thermal (ηI) and exergetic (ηII) efficiencies of the original and revised control logics in load cycling are compared. For loading up processes, ηI and ηII decrease by 1.04% and 0.28% at the most, respectively. For the loading down processes, the maximum increments in ηI and ηII are 1.44% and 0.77%, respectively.