Membrane recovery and hierarchical recovery
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For the off-gases from the new 200,000 ton/year ammonia synthesis plant, a membrane recovery unit is used to recover hydrogen. Given that the synthesis pressure is 13.6 MPa, the recovery process is designed in two stages: high-pressure hydrogen (93%) at 6.6 MPa, and low-pressure hydrogen (89%) at 2.95 MPa. It is said that this reduces some of the compression work. Has it been used? What are the results? Let’s discuss it.
My view is as follows: First, with recycling in two stages, the power consumption of the compressor should be lower than that when all the recycled gas is sent to one stage (2.95 MPa), and this can be confirmed； Secondly, due to the recovery in two stages, the volume of gas recovered in the high-pressure stage is generally relatively small. For 200,000 tons of synthetic ammonia as suggested by the original poster, the gas volume is estimated to be around 6,000 cubic meters. To keep the investment cost within acceptable limits, one or two membranes are typically used in the high-pressure stage, with a maximum gas production volume of 800 cubic meters; whereas the gas production volume in the second stage is around 3,000–3,500 cubic meters. Therefore, the savings in energy consumption seem to be limited. These are my views; I wonder if anyone with practical experience could share their thoughts. :D