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Share your Experience about Hydrogen Recovery using Prism Set:
we are getting 90% hydrogen in permeate against design value of 92%. What are the possible causes and Please give suggestion to improve it.
What is the expected life of prism membranes?After 30 years with these I believe life can easily be 15 years plus, with some reaching 30 years. but damage is possible and it is important both to keep ammonia in the washed purge gas low (I think <100 ppm) and to avoid liquid water. These skids have a heater to provide a small temperature rise above saturation. We test, from, time to time, the permeate from each shell and have found a substandard unit and replace it at next T/A. Operation of these units is in part, a balance between H2 recovery and H2 purity and in the final modules H2 partial pressure is quite low while N2 and inert partial pressures are quite high so H2 purity is quite sensitive to H/N and fraction Ar and CH4. To me, H2 in non-permeate is more important than H2 purity and provides a better reflection of membrane condition. We did add additional modules as part of a revamp and the PREISM< unit functions well at 14=+% of nameplate. I hope others respoond-this is an interesting topic.
Reduction in H2 efficiency is an indication of damage of the membrane which is very sensitive to ammonia and water. Please do following to sustain the membrane unit efficiency:
1. Keep ammonia and water below 50 ppm;
2. Provide trip of HRU unit on high ammonia slip.
3. Evaluate purge gas recovery unit performance using actual plant data.Ammonia GrowHow can support on evaluation, hazop.
Satyajit
Getting 90 to 92% H2 recovery was quite optimum. The typical life of membrane bundles was about 10-15 yrs. The supplier of the membrane unit would perform the evaluation if you supply the operating data and make recommendations about the replacement. It all depends on your feed gas prices and if they were low, one should be happy even with an 85% recovery.
Some precautions should be followed during shutdown and startup of unit:
– insure NO passing from the unit inlet valve
-keep purging and nitrogen blanket for the unit during the unit shutdown.
-proper heating and loading up for the prisms during startup
-smooth and gradually pressurized and loading (H2 rich gas) during startup
-closely monitored for the unit conditions during operation ( Ammonia inlet content/ temperature/DP/inlet flow).
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