The majority of the conversion takes place in the bulk methanation step which, due to the high concentration of reactants, produces a large amount of heat and takes place at high temperature.
The trim methanation step, which takes place at lower temperatures to encourage the methanation equilibrium, is used to convert residual unreacted CO, CO2 and H2 into product.
The resulting dry substitute natural gas (SNG) is high-purity and suitable for use within gas distribution networks.
In the non-stoichiometric flow sheet, the syngas does not pass through a sour shift system. Instead, following sulphur removal, it proceeds directly to the methanation step, where the CRG catalyst facilitates both the shift and methanation reactions. CO2 is then removed from the product gas instead of the feed, which means that a very low CO2 content can be achieved.
As the methanation step in this flow sheet performs all of the shift duty, the catalyst volume is larger than that used in an equivalent capacity stoichiometric route. However, the overall flow sheet is smaller resulting in a reduced plot size and lower net capital expenditure.