The semi-dry desulphurisation process is particularly suitable for systems up to 1 million Nm3/h flue gas. To purify the gases from SOx, but also from other acid components like HCl and HF, an aqueous absorbent (e.g. lime slurry) is injected into the spray absorber. The acidic harmful gases react with the absorbent to form salts, while at the same time the water in the suspension evaporates and the flue gas cools down before leaving the absorber.
The reaction product is usually separated in a downstream fabric filter, while a partial flow can be circulated for better utilization. By gas cooling and increasing the gas humidity the process is also positively influenced. The separate control of water and absorbent enables the ideal operating point to be set by adapting the cooling and absorption ratio to the pollutant load of the flue gas.