Countercurrent repressurization

For the Gemini process, the ammonia synthesis gas can be produced as the effluent gas from step (a) by (i) carrying out the final countercurrent repressurization (step f) of the A beds by introducing N2 from an external source, (ii) eliminating... 

Countercurrent repressurization, carried out with hydrogen, at first taken from the bed operated in phase 2 and then coming from a vessel in production. 

The repressurization step returns the adsorber to feed pressure and completes the steps of a PSA cycle. Pressurization is carried out with product and/or feed. Pressurizing with product is done countercurrent to adsorption so that purging of the product end continues indeed it may be merely a continuation of the purge step but with the bed exit valve closed. Pressurizing with feed cocurrent to adsorption in effect begins adsorption without producing any product. 

Fig. 15. Four-bed PSA system cycle sequence chart (64). EQ, equalization C D A, cocurrent depressurization C D T, countercurrent depressurization R, repressurization A, cocurrent flow T, countercurrent flow. Courtesy of American Institute of Chemical Engineers.

Applications PSA cycles are used primarily for purification of wet gases and of hydrogen. One of the earhest applications was the original Skarstrom two-bed cycle (adsorption, countercurrent blowdown, countercurrent purge, and cocurrent repressurization) to diy air stream to less than 1 ppm H9O [Skarstrom, ibid.]. Instrument-air diyers stiU use a PSA cy(de similar to Skarstrom s with activated alumina or sihca gel [Armond, in Townsend, The Propei ties and Applications of Zeolites, The Chemical Society, London, pp. 92-102 (1980)]. 

E = Equalization and cocurrent depressurization PD = Purge and cocurrent depressurization BD = Blowdown and countercurrent depressurization P = Purge R = Repressurization... 

Repressurization of the adsorber to feed pressure completes the steps of a pressure-swing cycle. Pressurization can be done with product and/or i. When piquet is used, it should be applied countercurrent to adsorption to continue put png of the effluent end. Pressurization with feed should be carried out cocurrent to adsorption to prevent contamination of the effluent end. 

EQ—Equalization CD —Cocurrent depressurization CD —Countercurrent depressurization R—Repressurization... 

EQ - equalization CD - cocurrent depressurization CD - countercurrent depressurization R - repressurization... 

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