GB741900A - Improvements in or relating to method for treating material - Google Patents

Abstract

<PICT:0741900/III/1> <PICT:0741900/III/2> In a method of drying, baking or similarly treating materials by contact with a stream of heated gases in the course of which treatment oxidizable fumes are given off into the gas stream and the effluent gases containing such fumes are conducted to a zone where they are contacted with an oxidation catalyst under conditions permitting substantially complete oxidation of the fumes before recirculation of the gas (Group XIII) catalysts are prepared by dipping catalytically active alumina in solutions of salts of copper, chromium, vanadium manganese, molybdenum, silver, nickel, cobalt iron, magnesium, platinum, palladium, ruthenium or combinations of these metals followed by thermal or chemical decomposition of the metal salts Catalytically active magnesia, beryllia or thoria may be substituted for the alumina. The unit supporting the catalyst consists of end plates 24 having a plurality of apertures for receiving rods 25 to support them in spaced relation, one end being freely supported to allow expansion and the plates being fastened together by a single central post surrounded by the rods. To ensure a minimum pressure drop through the unit the rods 25 are streamlined in contour having a rounded leading edge 26 and a tapered trailing edge 27. The unit is composed of high quality porcelain with the catalyst disposed thereon in a thin tightly adherent film such as a thin coat of active alumina to which platinum is added by dipping in a solution of the metal salt with subsequent thermal or chemical decomposition. The catalyst bed is made up of a number of units stacked one upon the other in rows and layers. In order to bring the catalyst up to operating temperature (a minimum of 500 DEG F with platinum-onalumina) a gas burner is provided and is turned off when the concentration of combustible vapour reaches a level sufficient to retain the bed at the required temperature. To keep below the maximum permissible operating temperature (2100 DEG F with platinum-on-alumina) the vapour concentration and temperature is controlled by a heat-exchanger and by recirculating large volumes of gas. Cooling may be necessary when large quantities of combustible vapour are evolved.