New heat integration system with bypass flue based on the rational utilization of low-grade extraction steam in a coal-fired power plant

Recovering waste heat is an effective way to save energy in coal-fired power plants. The bypass flue waste heat recovery system (bypass flue WHRS) has considerable energy-saving effects. After conducting an in-depth analysis of the bypass flue WHRS, a new heat integration system is proposed in this report. Compared with the bypass flue WHRS, a steam-air heater (SAH) is added between the air preheater (AP) and the pre-positioned air preheater in the proposed system. In the SAH of the proposed system, low-grade extraction steam is used to further preheat the air before the AP, thus resulting in more flue gas sent into the bypass flue to save extraction steam and better energy-saving effects. The results indicate that for a typical 1000 MWe coal-fired power plant, the proposed system could produce 13.51 MWe of additional net power output with a 4.00 g/kW h decrease in the standard coal consumption, and the net annual economic benefit is 2.74 million USD, which are significantly greater than those of the bypass flue WHRS. The exergy decrease of the air preheating process is reduced from 25.5 MWth in the bypass flue WHRS to 19.5 MWth in the proposed system.