Particularly suitable are catalysts containing nickel which contain aluminum oxide, aluminum silicate or magnesium silicate as support material. Many of the suitable catalysts are commercially available. The reaction heat from the methanation can be removed by passing the reaction mixture emerging from each catalyst layer, prior to the admixture of the gas rich in CO and CO2,<a href="http://www.sellercrusher.com/solutions/palm-kernel-crushing-machine.html">palm kernel crushing machine</a> through a heat exchanger where it is cooled by the evaporation of water boiling under pressure. Another method of cooling consists in performing the methanation in tubular reactors containing the catalyst in tubes surrounded by a coolant, especially water, boiling under pressure. A contribution is made to the cooling of the reaction mixture by mixing the hydrogen-rich partial stream or the reaction mixture, as the case may be, with the portions of the partial stream that is rich in CO and CO2 while the latter are cold, say, at the ambient temperature or even lower. On the other hand, the reaction conditions, especially the hydrogen content and the temperature of the entering reaction mixture, can be influenced by placing a layer of a catalyst which brings about the conversion of carbon monoxide with steam to carbon dioxide and hydrogen ahead of one, several or all of the catalyst beds. The conversion reaction will increase the hydrogen content and raise the temperature, on the one hand, and on the other hand it will reduce the carbon monoxide and water vapor contents.
Referring now to the drawing, the complete plant of FIG. 1 consists of the pressure gasification apparatus, A, the carbon monoxide conversion apparatus B, the two gas purification stages C and D with their common regeneration system E,<a href="http://www.sellercrusher.com/solutions/rock-crushing-equipment-for-sale.html">rock crushing equipment for sale</a> a first methanation stage F, a compression stage G, and a final methanation stage H. The pressure gasification apparatus A includes the actual pressure gasifier and the immediately adjoining system for direct cooling in a washing condenser, followed by indirect condensers in the form, for example, of waste-heat boilers. The converter system B is advantageously constructed in the form of a raw gas converting system as described in U.S. Pat. Nos. 3,069,249 and 3,069,250 for which the raw gas is cooled only down to the vicinity of the dewpoint and is separated from the condensate so that the excess water vapor still present after the pressure gasification will be utilized.
The two gas purifying systems C and D include gas condensers in which the gas, still containing the medium oils and light oils of the tar, is cooled down to the ambient temperature, the oils and water vapor being removed as condensate. The actual purification of the gas is performed in both of the partial streams of the gas by washing with methanol at temperatures of about -30°C. using a procedure known as the "Rectisol Process" and described in U.S. Pat. No. 2,863,527. The two gas purification systems C and D are of a two-stage construction, so that a selective desulfurization can be carried out in the first stage with only a slight absorption of CO2. The absorption stages C and D have a common regeneration system E.