Natural gas enrichment process
First Claim
1. A method for purifying a gas stream containing primarily hydrocarbon gases and nitrogen by flowing said gas stream through a plurality of adsorbent beds each containing an adsorbent which selectively adsorbs said hydrocarbon gases with said nitrogen gas substantially passing therethrough, cycling each of said adsorbent beds sequentially through a series of phases comprising an adsorption phase, a recycle phase, a depressurization phase, an evacuation phase, a nitrogen pressurization phase and a recycle feed pressurization phase, said adsorption phase comprising passing said gas stream into a first adsorbent bed at an elevated pressure for a first part of a first period of time with said hydrocarbon gases being adsorbed therein and collecting a portion of said nitrogen gas substantially passing therethrough for use in pressurizing an adsorbent bed that is to enter said adsorption phase, while said first adsorbent bed is in said adsorption phase depressurizing a third adsorbent bed in said depressurization phase to a first lower pressure to produce a depressurization gas and passing said depressurization gas through a fourth adsorbent bed in said recycle phase and collecting a recycle feed gas therefrom for use at least in further pressurizing an adsorbent bed that is to enter said adsorption phase, and evacuating a second adsorbent bed in said evacuation phase to a lowest pressure and recovering a hydrocarbon gas product containing substantially hydrocarbon gases, said first adsorbent bed prior to undergoing said adsorption phase being repressurized with a portion of said nitrogen gas in said nitrogen pressurization phase and then with a portion of said recycle feed gas in said recycle feed pressurization phase.
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Accused Products
Abstract
A natural gas feed stream containing significant quantities of nitrogen can be increased to a content of greater than 95 percent by volume of natural gas, and preferably greater than about 98 percent, by passing the natural gas feed stream sequentially through at least four adsorbent beds which are cycled through six phases comprising an adsorption phase to adsorb natural gas, a recycle phase to remove feed gas from the voids in the adsorbent bed and nitrogen from the adsorbent by the passage of a depressurization gas therethrough to produce a recycle gas, a depressurization phase to reduce the adsorbent bed pressure to about ambient and to produce the depressurization gas, an evacuation phase where the pressure in the adsorbent is further reduced and an enriched natural gas product stream recovered, a pressurization phase where the pressure in the adsorbent bed is increased using nitrogen gas from a bed in an adsorption phase, and further pressurizing the adsorbent bed in a recycle feed pressurization phase by the flow of the recycle gas therein.
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Citations
20 Claims
- 1. A method for purifying a gas stream containing primarily hydrocarbon gases and nitrogen by flowing said gas stream through a plurality of adsorbent beds each containing an adsorbent which selectively adsorbs said hydrocarbon gases with said nitrogen gas substantially passing therethrough, cycling each of said adsorbent beds sequentially through a series of phases comprising an adsorption phase, a recycle phase, a depressurization phase, an evacuation phase, a nitrogen pressurization phase and a recycle feed pressurization phase, said adsorption phase comprising passing said gas stream into a first adsorbent bed at an elevated pressure for a first part of a first period of time with said hydrocarbon gases being adsorbed therein and collecting a portion of said nitrogen gas substantially passing therethrough for use in pressurizing an adsorbent bed that is to enter said adsorption phase, while said first adsorbent bed is in said adsorption phase depressurizing a third adsorbent bed in said depressurization phase to a first lower pressure to produce a depressurization gas and passing said depressurization gas through a fourth adsorbent bed in said recycle phase and collecting a recycle feed gas therefrom for use at least in further pressurizing an adsorbent bed that is to enter said adsorption phase, and evacuating a second adsorbent bed in said evacuation phase to a lowest pressure and recovering a hydrocarbon gas product containing substantially hydrocarbon gases, said first adsorbent bed prior to undergoing said adsorption phase being repressurized with a portion of said nitrogen gas in said nitrogen pressurization phase and then with a portion of said recycle feed gas in said recycle feed pressurization phase.
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11. A method for purifying a gas stream containing primarily hydrocarbon gases and nitrogen by flowing said gas stream at an elevated pressure through a plurality of adsorbent beds each containing an adsorbent which selectively adsorbs said hydrocarbon gases with said nitrogen gas substantially passing therethrough, cycling each of said adsorbent beds sequentially through a series of phases comprising an adsorption phase, a recycle phase, a depressurization phase, an evacuation phase, a nitrogen pressurization phase and a recycle feed pressurization phase, said adsorption phase comprising flowing said gas stream at an elevated pressure into an adsorbent bed undergoing said adsorption phase with said hydrocarbon gases being adsorbed in said adsorbent bed and said nitrogen gas substantially passing therethrough;
- said recycle phase comprising compressing an effluent depressurization gas from an adsorbent bed undergoing said depressurization phase and flowing said depressurization gas into an adsorbent bed which has completed said adsorption phase and is in said recycle phase with a recycle feed gas flowing therefrom, flowing a portion of said recycle feed gas to an adsorbent bed that is to undergo said adsorption phase to at least partially pressurize said adsorbent bed;
said evacuation phase comprising reducing the pressure in an adsorbent bed that has completed said depressurization phase to less than about ambient pressure and recovering a product gas that contains adsorbed hydrocarbon gases;
said pressurization phase comprising flowing a portion of said nitrogen gas from an adsorbent bed on said adsorption phase into an adsorbent bed on said nitrogen pressurization phase to at least partially pressurize said adsorbent bed, and said recycle feed pressurization phase comprising flowing said recycle feed gas into an adsorbent bed which has completed said nitrogen pressurization phase to additionally pressurize said adsorbent bed. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
- said recycle phase comprising compressing an effluent depressurization gas from an adsorbent bed undergoing said depressurization phase and flowing said depressurization gas into an adsorbent bed which has completed said adsorption phase and is in said recycle phase with a recycle feed gas flowing therefrom, flowing a portion of said recycle feed gas to an adsorbent bed that is to undergo said adsorption phase to at least partially pressurize said adsorbent bed;
Specification