Rectisol gasification applications

Another application of the Sulfolin process is at the Rheinbraun AG HTW coal gasification plant near Cologne, West Germany (Heisel, 1989). The raw synthesis gas is purified in various steps, and eventually the H2S, and part of the CO2, are removed in a non-selective Rectisol wash. The H2S/CO2 stream from the Rectisol unit is treated using the Sulfolin process. 

Early efforts to employ water as a physical solvent met with limited success (see Chapter 6), but the solubilities of CO2 and H2S in water are too low for water wash to be a practical commercial process. The earliest commercial process based on an organic physical solvent, methanol, was the Rectisol Process, which has been used for synthesis gas applications where the removal of other impurities in addition to CO2 and H2S and the production of treated gas containing only ppm levels of CO2 and H2S is required. This process operates at very low temperatures (to minus 100°F) and is quite complex compared to other physical solvent processes. As a result, the Rectisol process is not considered applicable to most gas treating services, although it continues to find application in purifying synthesis gases derived from the gasification of heavy oil and coal. 

Operation at very low temperatures with very sharp separations results in relatively complex flow schemes. This, combined with the need for low level refrigeration, leads to high plant costs. As a result, most applications of the Rectisol process represent relatively difficult gas treating conditions where other gas treating processes are not suitable for one reason or another. Typical applications are the purification of gas streams in the heavy oil partial oxidation processes of Shell and Texaco and the Lurgi coal gasification process, as used at the Sasol plants in South Africa. 

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