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Choosing the right process for a DeSOx plant always depends on the particular case of application. The semidry method is suitable for plants up to 1 million Nm³/h. Here, an aqueous absorbent suspension , usually a calcium hydrate suspension with high reactivity, is injected into the flue gas flow. The acidic pollutant gases react with the absorbent to become salts, while at the same time the water of the lime milk evaporates and the flue gas cools before leaving the absorber. The reaction product is a dry mixture of calcium salts and unreacted lime. The mixture is usually separated in a downstream fabric filter from the flue gas, a partial flow can be recirculated for better efficiencies.
The main design feature of the spray absorber is a cylinder above a conical discharge section. The raw gas distributer is positioned above it, containing the centrally-arranged rotary atomiser. The calcium hydrate suspension is fed to the rotary atomiser. There, an atomised spray with very fine droplets is generated by a rapidly rotating atomiser wheel and distributed evenly into the flue gas flow. The spray absorber is designed to provide a sufficient reaction time between flue gas pollutants and absorbent to bind the SO2 and dry the solid reaction product.
The use of the rotary atomiser as a complete unit, including drive motor, has an economic benefit: In the event of a neccessary maintenance of the atomizer, the complete unit can be replaced in a short time, allowing uninterrupted operations of the boiler plant.
Advantages of the semidry method
Use in plants up to approx. 1 million Nm³/h