Recovery purge gas

A. J. Finn, "Cryogenic Purge Gas Recovery Boosts Ammonia Plan Productivity and Efficiency," Nitrogen (175), 25—32 (Sept.—Oct. 1988). 

If the make-up gas contains inerts, purge gas is drawn from the loop after the second cold exchanger just before addition of the make-up gas. At this point the gas has the maximum content of inerts. The purge gas is usually transferred to a purge gas recovery unit for recovery of hydrogen. Recovered hydrogen is recycled to the process and introduced at a relevant stage of the synthesis gas compressor. 

Several types of processes have been developed for purge gas recovery. The most important are discussed in the following. Reviews and comparisons may be found in [648-650]. 

A very rapid development has taken place in the use of membranes for gas separation. Reviews are given in [664-666]. The most popular process for purge gas recovery using membranes is based on the use of hollow fibres, although other types such as spiral wound membranes and stacks of flat elements have also been used. 

Ammonia recovery by absorption in water and distillation. Cryogenic purge gas recovery. The energy consumption is claimed to be 6.7 Gcal/MT of ammonia [123]. 

---