Abstract: A purifying system is disclosed for the removal of small particles of impurities from a gaseous mixture flowing in a conduit, including a venturi connected in series in the conduit, a liquid injection device for introducing jets of liquid to produce a liquid mist pattern extending transversely within the venturi to moisturize the small particles of impurities, and a regulator operable in response to the pressure differential across the venturi for adjusting the effective cross-section of the venturi and/or the operation of the injection device, thereby to maintain the pressure differential across the venturi at a predetermined value.