Optimization of HRSG Supply Unit and Consideration of Thermal Stress State of Critical Elements of Steam-Water Path at Variable GTU Modes

In accordance with the requirements of power systems to power units of thermal power plants, there are different approaches to variable modes of their operation, duration of start-ups from different thermal states, regulating rates of equipment loading during start-ups and load changes. A considerable role at performance of start-up operations is assigned to supply of heat recovery steam generator (HRSG) circuits that provide the change of HRSG steam capacity corresponding to the loading rate while maintaining all main parameters within the permissible limits. Besides, optimization of duration of CCPP start-up modes should take into account accumulation of damage by the most loaded thick-walled elements of steam path equipment. This occurs due to continuous monitoring of thermal stress state and cyclic strength of CCPP elements under conditions of minimum resource consumption on the basis of finite element mathematical models of critical elements of steam path and calculation studies of thermal stresses arising in them. The influence of HRSG steam capacity on CCPP power change rate under different schemes of high, medium and low-pressure steam circuits supply (HP,MP, LP) has been analyzed. It is shown that the least inertial are deaeratorless schemes with a separate electric feed pump (EFP) of HP, which allows to provide fast, at the pace of the process, change of steam capacity of the HP circuit at any alternating mode, including starts and stops.