Abstract
There exists a certain amount of SO3 in flue gas discharged from coal-fired power plants. The implementation and “ultra-low emission” retrofitting of SCR in China greatly increased the concentration of SO3 in flue gas, which will lead to fouling, erosion and plugging of the SCR reactor and the air preheater downstream. With the lowered dew point of the flue gas, the ammonia sliped from the SCR reactor together with the SO3 in flue gas will leads to dust accumulation in the Electric Precipitator or in the Bag-house Filter, too. In this study, the main effects and its mechanism of SO3 on the safety, stability and efficiency of units were analyzed, and measures to control SO3 were proposed.
Highlights
In the operation process of coal-fired power plants, a small amount of SO3 exists in most flue gases, which depends on sulfur content in the charge coal, ranging from about 1 μl/L to 30-40 μl/L
As environmental protection standards become increasingly strict, boilers of coal-fired power plant have been equipped with selective catalytic reduction (SCR) flue gas denitrification, dedusting and wet flue gas desulfurization (WFGD) facilities to remove routine pollutants such as NOx, dust and SO2 generated in the process of coal combustion
When temperature ranges from 275 to 350 °C[7], SO3 can react with NH3 and generates ammonium bisulfate or ammonium sulfate in SCR reactor, which mainly depends on SO3 concentration, and the lower temperature is called minimum operating temperature (MOT) of SCR
Summary
In the operation process of coal-fired power plants, a small amount of SO3 exists in most flue gases, which depends on sulfur content in the charge coal, ranging from about 1 μl/L to 30-40 μl/L. As environmental protection standards become increasingly strict, boilers of coal-fired power plant have been equipped with selective catalytic reduction (SCR) flue gas denitrification, dedusting (electrostatic precipitator or bag-house filter) and wet flue gas desulfurization (WFGD) facilities to remove routine pollutants such as NOx, dust and SO2 generated in the process of coal combustion. The emission of SO3 can cause plume opacity which leads to some environmental problems. The SO3 in flue gas can make acid dew point rise, thereby leading to corrosion, fouling, and plugging problems of air preheater and other devices. From the view point of environmental protection, safety, stability and performance, the SO3 in flue gas of coal-fired power plants should be paid more attention
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