Since the synthesis gas exiting the partial oxidation process consists mainly of carbon monoxide and hydrogen, usually a sulfur tolerant CO shift (i.e. water-gas shift reaction) is installed in order to convert as much carbon monoxide into hydrogen as possible.
Shifting carbon monoxide and water into hydrogen also produces carbon dioxide, usually this is removed in an acid gas scrubbing process together with other sour gases as e.g. hydrogen sulfide (e.g. in a Rectisol Wash Unit).
[7] This gaseous high pressure nitrogen is partially liquefied in the process and is used as washing agent.
These impurities are dissolved together with a small part of hydrogen and leave the column as the bottom stream.
[5] Since part of the purified gas is reheated in the Rectisol Wash Unit, small fluctuations in flow and temperatures can easily be compensated leading to best operability.