14.03.2003 - Modern hydrogen plants are normally operated with Pressure Swing Adsorption (PSA) units for purification of hydrogen. The advantage offered by the PSA procedure, compared to former purification methods, is the high purity of the hydrogen up to 99.9%. In addition to pressure swing absorbers, feed-gas and waste-gas compressors are often required.

The feed-gas compressor is needed to feed the absorber with the hydrogen rich gas. Typical feed gases are syngas, coke oven gas and styrene monomer gas. Waste gas is produced during the regeneration of the absorbers. Sometimes this waste gas (also called tail gas), can be used as fuel gas or at refinery service returned to the refinery process. Often this requires a compressor as well.

As a positive displacement compressor, the screw compressor is ideal for handling the relatively light hydrogen rich gas. Compared to a centrifugal compressor, higher pressure ratios can be reached in one single stage. If the feed gas comes out of a styrene monomer unit or a coke oven plant, the screw compressor can easily be equipped with liquid injection. Offering a reliability which is similar to that of turbocompressors, process-gas screw compressors have availability figures of up to 99% over a large number of operating years.

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