Study on the Impact of Waste Heat Recovery on Ammonium Bisulfate Deposition in Tail Heating Surfaces of Coal-Fired Power Units During Transient Processes

When coal-fired power plants are tasked with deep peak-shaving and frequency regulation, the concentration of pollutants in the flue gas at the boiler's tail section exhibits significant fluctuations. The ammonia slip from the Selective Catalytic Reduction(SCR) denitration system reacts with SO₃ in the flue gas to form ammonium bisulfate (ABS,NH4HSO4), which poses serious operational hazards to the tail heating surfaces of the boiler. To mitigate this issue, a waste heat recovery system was proposed for integration into the tail flue. This system is designed to transfer waste heat from the flue gas to the feedwater and condensate through a series of heat exchangers (including the low-pressure economizer, the high-pressure economizer, and the air heater), thereby regulating the flue gas temperature and inhibiting ABS deposition in the air preheater. A thermal model of the tail-flue system incorporating the waste heat recovery system was developed. The impact of the waste heat recovery system on flue gas temperature at the boiler's tail heating surfaces and ABS deposition patterns were investigated during the load variation process between 75% and 50% Turbine Heat Acceptance (THA) load. The results demonstrate that integrating the waste heat recovery system significantly improves the temperature distribution across the tail heating surfaces and markedly reduces ABS deposition in the air preheater. During the load reduction process from 75% to 50% THA, the ABS deposition rate (referred to as the Radian number) decreased by 32.53%, 32.27%, 32.24%, and 31.89% at load variation rates of 0.5%, 1.0%, 1.5%, and 2.0% of the plant's nominal capacity (PN) per minute, respectively. A similar reduction was observed during the load increase process. This research provides valuable technical support for coal-fired power plants to achieve synergistic energy conservation and enhanced pollutant control during transient processes.