Separation of gases

Abstract

A process for separating sour shifted synthesis gas feedstock into liquid carbon dioxide, a gaseous hydrogen-containing gas and separated sulphur-containing components includes the steps of a. scrubbing the sour shifted gas elevated pressure with an alcohol solvent in a first scrubber and separately recovering an alcohol stream containing the sulphur-containing components and a sweet shifted gas; b. thereafter cooling the sweet shifted gas to a temperature and elevated pressure at which the carbon dioxide contained therein condenses and a two-phase gas-liquid mixture is formed; c. separating the two-phase mixture of stage (b) into separate liquid carbon dioxide and gaseous hydrogen-containing fractions in a fractionation unit; d. extracting residual carbon dioxide from the separated gaseous hydrogen-containing fraction by scrubbing the gaseous hydrogen-containing fraction at elevated pressure with an alcohol solvent in a second scrubber and recovering an alcohol stream containing carbon dioxide; e. feeding the alcohol stream containing carbon dioxide produced in step (d) to the first scrubber and f. warming and expanding the scrubber gaseous hydrogen-containing fraction using at least one heat exchanger to exchange heat with the mixture of step (b) and at least one turbo-expander capable of recovering mechanical work. The process described may be used in for example Integrated Gasification Combined Cycles (IGCC) where the source of fuel is coal or low grade carbon sources such as lignite, tar sands and shale oil.