DRY SORPTIONThe process of dry sorption is characterized by the use of an adsorbent — usually referred to as an additive — that is dispersed in the exhaust gas stream in the from of a fine dispersible solid. The air pollutants found in the exhaust gas are separated out on the inner and outer interphase of the additive by chemisorption or physisorption. The resulting reaction products are then separated from the gas stream by a downstream dedusting device, preferably a fabric filter.
The process of contaminant removal begins immediately after adding the additive, under the provision that the additive has been homogenously dispersed in the exhaust gas stream. In order to make possible the convective and diffuse mass transport of the contaminants to or through the phase boundary of the additive particles, adequate retention times — at least 1 – 2 seconds — must be provided for in the so-called “in stream” phase of the process.
The additive, which is partially loaded with contaminants, is then separated out in the subsequent process step, along with fly ash particles found in the exhaust gas, in a fabric filter located downstream from the “in stream” process phase. Because of the existing hydrodynamic flow relationships, i.e., a high relative velocity between the additive particles and the exhaust gas, the filter cake that accumulates on the surface of the filter bags makes possible an additional and effective separation of acid-building noxious gases, as well as organic and inorganic trace pollutants.