Methanation of carbon dioxide over a ruthenium catalyst for AGR gas circuit composition control

Some of the methane added to the carbon dioxide AGR coolant to inhibit graphite oxidation is decomposed in the reactor circuit so a continuous supply of 'make' gas is required. This is generated on-site by reacting pure hydrogen from an electrolysis plant with carbon dioxide, from bulk storage tanks, over a ruthenium-on-alumina catalyst. This methane is compressed and added to the circuit gas. Laboratory experiments to establish the performance characteristics of methanation units are described in this paper. The two designs of converter installed on AGR stations both comprise tubes packed with ruthenium-on-alumina catalyst with external cooling to control the strongly exothermic reaction. Methanation is achieved in two stages - the water vapour produced in the first stage is removed to perturb the equilibrium and to thereby enhance the conversion efficiency. The laboratory experiments reported were designed to yield reaction kinetic data relevant to conditions obtained in power station control plant. (author)