A novel flue gas waste heat recovery system for coal-fired ultra-supercritical power plants

Abstract

Recovering flue gas waste heat is important in improving power plant efficiency. The most widely method is installing a low-temperature economizer (LTE) after the electrostatic precipitator (ESP) to heat the condensed water, thereby saving the extraction steam from the steam turbine and achieving extra work. The inlet flue gas temperature of the LTE is relatively low, so it can only heat condensed water from low-grade regenerative heaters, resulting in comparatively minor energy savings. After conducting an in-depth analysis of the conventional waste heat recovery system (WHRS), this paper proposes a novel WHRS, in which the air preheater is divided into high-temperature (HT) and low-temperature (LT) air preheaters, and the LTE can be situated between the ESP and the LT air preheater. Through system integration, higher-grade extraction steam can be saved, resulting in greater economic benefits. Results show that the net additional power output can reach 9.00 MWe and using the proposed WHRS can yield net benefits up to USD 2.60 million per year, which is much greater than those of conventional WHRS. Exergy destruction is also reduced from 34.1 MWth in the conventional WHRS to 28.5 MWth in the proposed WHRS.