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8. REMOVAL OF CO2 FROM GASES
The removal of carbon dioxide from the gas is usually performed, if not a part of the alkazid process, in the final step of the synthesis gas preparation, after it is under pressure. Carbon dioxide is readily soluble in water at elevated pressure and the gas is absorbed by passing the CO2 containing gas in direct countercurrent contact with water in absorption columns. The absorbed CO2 is released in a discharge system by passing the outlet water at about 200 to 300 lbs. per square inch (the usual absorption pressure) into a Pelton water turbine whose outlet is at atmospheric temperature and pressure. The jet action of the water impinging on the pelton wheel breaks the stream into a fine spray for quick release of the absorbed CO2 and at the same time produces power to assist in driving a centrifugal pump which recycles the cold water back into the spray tower. About half of the power required to drive the centrifugal pump can be obtained from the pelton water turbine. This water absorption system also removes the last traces of any ammonia that may be present. However, the CO2 thus produced is usually substantially pure and in Germany is recovered, compresses and sold as commercially pure CO2.