SEPARATION OF CARBON DIOXIDE AND HYDROGEN

摘要

A process is described for removing carbon dioxide from a synthesis gas feed stream in a cryogenic separation plant. In an example described the synthesis gas feed stream comprises 40 to 65 mole % hydrogen and is fed to a single stage or a first stage of a series of separation stages at a pressure in the range of 46 to 90 bar absolute. The single stage or a stage of the series is operated at a temperature in the range of -53 to -48 °C and a pressure in the range of 44 to 90 bar absolute. In some examples, the single stage or the combined stages of the series remove 70 to 80 % of the total moles of carbon dioxide in the synthesis gas feed stream. Liquefied CO2 product stream(s) discharged from the stage(s) of the cryogenic separation plant may be sequestrated and/or used in a chemical process. Also described is a process for separating a synthesis gas stream into a hydrogen rich vapour stream and a carbon dioxide rich stream. In an example, the process includes the steps of cooling a synthesis gas stream to a temperature at which at which a two-phase mixture is formed, passing the cooled stream formed in step (a) either directly or indirectly to a gas-liquid separator vessel, the feed to the gas-liquid separator vessel having a pressure of less than 150 bar, withdrawing a hydrogen rich vapour stream from the separator vessel and a liquid CO2 stream from separator vessel; and feeding a separated hydrogen rich vapour stream to an expansion system including a plurality of expanders arranged in series, wherein the hydrogen rich vapour stream is subjected to expansion in each of the expanders of the series such that an expanded hydrogen rich vapour stream is withdrawn from each of the expanders at reduced temperature and at successively reduced pressures; and using at least one expanded hydrogen-rich vapour stream as a coolant.