A gas, at =120 degrees C, requiring purificn. and to which can be added an oxidising agent, e.g. H2O2 or potassium permanganate, is passed through a series of tubes where it is mixed with an adsorption agent, e.g. slake lime, calcium carbonate, iron oxide, amorphous silica, porous perlite or filter carbon, having a granulometry pref. 50 mu. Each mixing tube is followed by a separator which removes the absorbant from the gas stream and recycles it counter-currently to the gas flow. Absorbant is introduced into each mixing tube through =1 nozzle pointing downstream, each nozzle followed by a conical flow obstacle with its pointed end facing the nozzle, then a truncated converging section of the mixing tube reducing the flow area for the gas. Absorbant recycled counter-currently is removed from the separator after the first stage mixing tube, par of the absorbant is rejected and the rest is sent back to enter the final stage mixing tube, fresh make-up absorbant being added before it enters the mixing tube. Alternatively the recycled part of the absorbant is introduced into the penultimate mixing tube, with the fresh make-up absorbant being fed into the final mixing tube and the absorbant recovered from the separators after these stages is mixed before passing to the next mixing tube upstream. Rejected absorbant can be rid of harmful prods. by converting them to calcium sulphate using air and lime wash or by heating it in a Claus furnace after which it can be re-used. Process is used for purificn. of flue gases contg. SO2 and NOx. The absorbant need not be expensive and can be re-used several times with the process still giving a very high purificn. effect. The reaction is very rapid so that the installation is small and there is low energy usage.
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