Abstract: An apparatus for conducting an endothermic catalytic reaction wherein closed ended, i.e., double pass, externally heated reformer tubes are employed. The inner return tube are insulated so that there is only a small temperature drop between the reacted gas leaving the catalyst zone and entering the return tubes and the gas leaving the return tubes. The outer, closed end, tubes preferably have fins to increase the surface area, and are surrounded by sheaths through which a heating medium passes. The heating medium is preferably hot gas obtained by subjecting the primary reformed gas to secondary reforming.

Abstract: A process for producing a product gas stream containing hydrogen and carbon oxides by incomplete catalytic reaction of a hydrocarbon feedstock with steam and/or carbon dioxide. The process involves passing a reactants stream containing the feedstock and steam and/or carbon dioxide over a catalyst disposed in an elongated, externally heated, zone and withdrawing the product gas stream through a tube within that zone and countercurrently to the flow of the reactants stream over the catalyst. Heat exchange between the product gas stream and the reactants stream across the wall of the tube is limited so that the temperature of the product gas stream leaving the tube is less than that of the stream leaving the elongated zone by at most 100.degree. C. Apparatus for carrying out the process is also disclosed.