Recovery of NGL's and rejection of N.sub.2 from natural gas
First Claim
1. A method of separating a super-pressured sub-cooled feed gas, predominating in methane and containing significant amounts of ethane and higher hydrocarbons and nitrogen, said feed gas being at a pressure substantially above atmospheric pressure and a temperature substantially below atmospheric temperature sufficient to form a vapor phase and liquid phase, comprising:
- (a) separating said feed gas, in at least one separation step, to produce a methane- and nitrogen-enriched first vapor phase and an ethane and higher hydrocarbon-enriched first liquid phase;
(b) fractionating said first liquid phase, in a first fractionation zone, under conditions sufficient to produce a product, methane-enriched, second vapor phase and a product, ethane and higher hydrocarbon-enriched, second liquid phase;
(c) fractionating said first vapor phase, in a second fractionation zone, under conditions sufficient to produce a nitrogen-enriched, third vapor phase and a methane-enriched, third liquid phase; and
(d) fractionating said third vapor phase, in a third fractionation zone, under conditions sufficient to produce a product, nitrogen-enriched, fourth vapor phase and a product, methane-enriched fourth liquid phase.
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Abstract
A super-pressured, sub-cooled feed gas, predominating in methane and containing significant amounts of ethane and higher hydrocarbons and nitrogen, is separated by passing the feed gas through at least one separation step to separate a vapor phase and a liquid phase, fractionating the liquid phase to recover ethane and higher hydrocarbons as a liquid and a pipeline gas as a vapor phase product, the vapor phase from the separation step is then sequentially fractionated in second, third and fourth fractionation steps to produce liquid phase from the second fractionation step, which is recycled to the first fractionation step as a reflux, a liquid phase from the third fractionation step which is recovered as a product pipeline gas, a liquid phase from the fourth fractionation step which is recovered as an in-plant fuel and a vapor phase from the fourth fractionation step which is vented to the atmosphere as substantially pure nitrogen. The vapor phase from the first fractionation step and the liquid phases from the third and fourth fractionation step and the vapor from the fourth fractionation step are passed in indirect heat exchange with portions of the feed gas to cool the same and portions of the vapor phase from the separation step, the second fractionation step and the third fractionation step are utilized in reboilers to heat the second, third and fourth fractionation steps.
49 Citations
13 Claims
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1. A method of separating a super-pressured sub-cooled feed gas, predominating in methane and containing significant amounts of ethane and higher hydrocarbons and nitrogen, said feed gas being at a pressure substantially above atmospheric pressure and a temperature substantially below atmospheric temperature sufficient to form a vapor phase and liquid phase, comprising:
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(a) separating said feed gas, in at least one separation step, to produce a methane- and nitrogen-enriched first vapor phase and an ethane and higher hydrocarbon-enriched first liquid phase; (b) fractionating said first liquid phase, in a first fractionation zone, under conditions sufficient to produce a product, methane-enriched, second vapor phase and a product, ethane and higher hydrocarbon-enriched, second liquid phase; (c) fractionating said first vapor phase, in a second fractionation zone, under conditions sufficient to produce a nitrogen-enriched, third vapor phase and a methane-enriched, third liquid phase; and (d) fractionating said third vapor phase, in a third fractionation zone, under conditions sufficient to produce a product, nitrogen-enriched, fourth vapor phase and a product, methane-enriched fourth liquid phase. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification