초록 ▼

A process for treating natural gas or other methane-rich gas to remove excess nitrogen. The invention relies on membrane separation using methane-selective membranes, but does not require the membranes to be operated at very low temperatures. We have found that, by using a two-step membrane system d

A process for treating natural gas or other methane-rich gas to remove excess nitrogen. The invention relies on membrane separation using methane-selective membranes, but does not require the membranes to be operated at very low temperatures. We have found that, by using a two-step membrane system design, and controlling the operating pressures for the membrane steps within certain ranges, the capital and operating costs of the process can be kept within economically acceptable limits.

대표청구항 ▼

1. A process for removing nitrogen from a gas stream comprising methane and at least about 4% nitrogen, the process comprising the steps of:(a) compressing the gas stream to a first pressure in the range 400-1,500 psia to form a compressed gas stream; (b) providing a first membrane unit containing a

1. A process for removing nitrogen from a gas stream comprising methane and at least about 4% nitrogen, the process comprising the steps of:(a) compressing the gas stream to a first pressure in the range 400-1,500 psia to form a compressed gas stream; (b) providing a first membrane unit containing a first membrane having a first feed side and a first permeate side, the first membrane being more permeable to methane than to nitrogen; (c) providing a second membrane unit containing a second membrane having a second feed side and a second permeate side, the second membrane being more permeable to methane than to nitrogen, the second membrane unit being connected in series with the first membrane unit such that gas leaving the first feed side can enter the second membrane unit on the second feed side; (d) introducing the compressed gas stream at a first temperature higher than about -40.degree. C. into the first membrane unit at a first inlet of the first feed side, and passing the compressed gas stream across the first feed side; (e) withdrawing from a first outlet of the first feed side a first residue stream enriched in nitrogen compared with the gas stream; (f) withdrawing from the first permeate side, at a second pressure lower than the first pressure and above about 25 psia, a first permeate stream depleted in nitrogen compared with the gas stream; (g) introducing the first residue stream into the second membrane unit at a second inlet of the second feed side, and passing the first residue stream across the second feed side; (h) withdrawing from a second outlet of the second feed side a second residue stream enriched in nitrogen compared with the first residue stream; (i) withdrawing from the second permeate side, at a third pressure lower than the first pressure and above about 25 psia, a second permeate stream depleted in nitrogen compared with the first residue stream.