High efficiency nitrogen rejection unit

A process for separating nitrogen and hydrocarbon from a mixture thereof and flowing the separated nitrogen to a nitrogen discharge and flowing the separated hydrocarbon to a hydrocarbon discharge, comprising the steps of:

• adjusting the pressure of said mixture to provide a relatively high pressure feed gas respective to the nitrogen and hydrocarbon discharge pressure;
• splitting the feed gas into a plurality of separate streams and throttling the flow of each of said separate streams to achieve a selected variable flow rate therebetween;
• connecting the secondary of a plurality of heat exchangers to exchange heat with a nitrogen rejection column;
• cooling said plurality of separate streams by exchanging heat with respective ones of the primary of said plurality of heat exchangers;
• expanding one cooled split stream to the internal pressure of said nitrogen rejection column and thereby reducing the temperature of the fluid flowing through said nitrogen rejection column;
• recombining the other cooled split streams and thereafter expanding the recombined cooled split streams into said nitrogen rejection column to further lower the temperature thereof;
• whereby the lighter fractions including nitrogen ascend in the nitrogen rejection column while the heavier fractions, including hydrocarbon, descend in the nitrogen rejection column and flow through a reboiler thereof;
• said reboiler includes one of said heat exchangers;
• cooling the hydrocarbon from the nitrogen rejection column bottom by flowing the cooled hydrocarbons through one of said heat exchangers, and expanding the cooled hydrocarbons into an internal reflux condenser located within said nitrogen rejection column, thereby cooling the internal reflux condenser, and then through the secondary side of one of said plurality of heat exchangers, and then to the hydrocarbon discharge;
• and,
• passing separated nitrogen from the nitrogen rejection column, through the secondary of one of the recited heat exchangers, and to the nitrogen discharge.

A method of improving the quality of a mixture of high pressure feed gas that includes nitrogen and hydrocarbon by separating the nitrogen and hydrocarbon from said mixture;

• and flowing the separated nitrogen to a nitrogen discharge outlet means and flowing the separated hydrocarbon to a hydrocarbon discharge means, comprising the steps
• splitting said feed gas into a plurality of streams that include a first split stream and three other split streams;
• and, throttling the flow of each of said split streams to achieve a selected variable flow rate therebetween;
• cooling each of the split streams by passing the first split stream through the primary of a first heat exchanger, and passing the three other split streams, respectively, through the primary of a second, third, and fourth heat exchanger, respectively;
• arranging the primaries of said heat exchangers in parallel relationship respective to one another;
• recombining the cooled three split streams and thereafter expanding the recombined split streams into a nitrogen rejection column to remove heat therefrom;
• where the lighter fractions, including nitrogen, ascend the nitrogen rejection column while the heavier fractions, including hydrocarbon, descend the nitrogen rejection column and flow through a reboiler thereof;
• placing a reflux condenser at the top of said nitrogen rejection column;
• cooling the separated hydrocarbon flowing from the nitrogen rejection column by expanding the hydrocarbon into the reflux condenser;
• passing the separated nitrogen flowing from the nitrogen rejection column through a second of said heat exchangers and then to said nitrogen discharge, and flowing the separated hydrocarbon from the reflux condenser through a secondary of one of the heat exchangers and then to the hydrocarbon discharge.

A method of separating nitrogen and hydrocarbon from a feed gas containing a mixture thereof and flowing the separated nitrogen and the separated hydrocarbon to separate collection means, comprising the steps of:

• splitting a stream of relatively high pressure feed gas into a first split stream and a plurality of split streams to achieve a selected variable flow rate therebetween;
• cooling the first split stream by passing the first split stream through a heat exchanger in which heat is exchanged with a downstream process stream, then expanding the cooled first split stream into a nitrogen rejection column to further reduce the temperature thereof;
• cooling each of the plurality of split streams by passing each of the plurality of split streams through a respective one of a plurality of heat exchangers in which heat is exchanged with a downstream process stream, combining the plurality of cooled split streams, further cooling the combined split streams by expanding the cooled combined streams into the nitrogen rejection column to further reduce the temperature thereof to effect separation of the nitrogen and hydrocarbon which then exit in separate streams therefrom;
• expanding one of the separate streams exiting from the separation column to reduce the temperature thereof and using the expanded stream for cooling an internal reflux condenser located in the nitrogen rejection column;
• and flowing the expanded stream from the condenser and using the expanded stream for the recited step of cooling one of the split streams, and flowing the expanded stream to one of said separate collection means;
• flowing another of the separate streams exiting from the separation column for the recited step of cooling another one of the split streams by flowing the another of the separate streams through the secondary of a heat exchanger having a primary through which one of the split streams flows in heat transfer relationship therewith;
• and then flowing the stream to another one of said separate collection means;
• carrying out the step of cooling one of the split streams by connecting the secondary of the heat exchanger thereof as the reboiler for the nitrogen rejection column.