To produce substitute natural gas (SNG) from purified synthesis gas produced by coal gasification, using shift and methanation reactions.
The synthesis gas is fed to a sulfur guard vessel (1) to remove residual catalyst poisons, and it is then split into two parts. Part of the feed is mixed with the recycle gas and passed to the first bulk methanator (2) where shift and methanation reactions take place to produce a methane-rich product in an exothermic reaction. Product from the first bulk methanator is cooled by producing high-pressure (HP) steam (3) and is then mixed with the remaining feed gas. The gas mixture is passed to the second bulk methanator (4). After cooling to raise additional HP steam, the product stream from the reactor (4) is split, part providing recycle gas to the first bulk methanator and the remainder passing to the trim methanation stages (5) and (6). The number of trim-methanation stages required depends on the final product specifications. Generally, two trim-methanation stages are sufficient to produce a high-methane, pipeline-quality gas.
Licensor: Davy Process Technology, UK