Effects of Flue Gas Cooler on the Reduction of “Gypsum Rain” in Coal-Fired Power Plants

Abstract

Sulfur dioxide (SO2) derived from the combustion of sulfur in raw coal is one of the major pollutants in coal-fired power plants. Wet flue gas desulfurization (WFGD) is applied to capture SO2 in flue gas, which is usually followed by a gas–gas heater (GGH). The water vapor content is usually saturated in flue gas after WFGD. GGH increases the flue gas temperature to reduce water vapor condensation in flue gas duct/stack, which produces “gypsum rain.” Recently, considering the leakage in GGH leads to higher pollutants emission which is not allowed by the government regulations, lots of power plants in China have removed GGH. As a consequence, the gypsum rain problem is becoming more severe. In this work, a specified flue gas cooler is applied just after WFGD to decrease the flue gas temperature, which further removed 20 % of water vapor content and 70 % of water droplets in flue gas. Computational fluid dynamic (CFD) simulation was used to study the effects of flue gas cooler on the reduction of “gypsum rain” in coal-fired power plants. There is a distinct reduction of droplets discharging both in summer and in winter after adding flue gas cooler. Under the condition of ideal insulation, this reduction percent reaches 57 % in summer, comparing to 52.8 % in winter. If the conductivity resistance of the stack wall is decreased to 1/20, this reduction percent changes to 22.4 % in summer, and 18.9 % in winter.