Hydrogen cryogenic recovery

Ahuja V, Green R. Application of matrix heat exchangers to thermomechanical energy recovery from liquid hydrogen. Cryogenics 1998 38(9) 857-867. 

In common with other processes, the overall efficiency can be improved by recovery of hydrogen from the purge gas instead of using it as fuel. Either of the two general types of hydrogen recovery unit may be used cryogenic recovery " or membrane separation. ... 

Cryogenic processes using turboexpanders facilitate high levels of ethylene recovery from refinery gas while producing byproducts of hydrogen- and methane-rich gas. In a cryogenic process, most of the ethylene and almost all of the heavier components are liquified and ethylene is separated from this liquid. 

After the recovery of natural gas liquids, sweet dry natural gas may be liquefied for transportation through cryogenic tankers. Further treatment may be required to reduce the water vapor below 10 ppm and carbon dioxide and hydrogen sulfide to less than 100 and 50 ppm, respectively. 

HARP [Hybrid argon recovery process] A process for extracting argon from the hydrogen recycle stream in ammonia synthesis. Both PSA and a cryogenic process are used. Krishnamurthy, R., Lemer, S. L., and MacLean, D. M., Gas Sep. Purif, 1987,1, 16. 

PSA hydrogen recovery will also compete more favorably with cryogenic alternatives In the future Streams of 50 to 100 thousand cubic meters per hour will be processed at pressures up to about 70 atmospheres In addition, as hydrogen becomes more valuable In chemical processes, hlgh-purlty hydrogen via PSA will be used more frequently to minimize vent-stream losses Conversely Impure hydrogen In other vent streams will be a candidate for recovery and cleanup via PSA ... 

Due to increased feedstock costs, some new ammonia plant designs use fuel more efficiently but their capital cost may be higher. The recovery of the hydrogen and ammonia from the synthesis purge gas by a cryogenic unit or a membrane system results in an ammonia capacity increase of about 5%57. 

HARP [Hybrid Argon Recovery Process] A process for extracting argon from the hydrogen recycle stream in ammonia synthesis. Both PSA and a cryogenic process are used. 

Figure 97. Simplified flow diagram of cryogenic hydrogen recovery unit...

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