US 4,662,919 AGranted

Nitrogen rejection fractionation system for variable nitrogen content natural gas

AssigneeAir Products and Chemicals, Inc.

InventorRuth A. Davis

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Abstract

The present invention is directed to a gas separation system for separating or rejecting nitrogen from a natural gas feed containing nitrogen, over a wide range of nitrogen concentrations, under elevated pressure using a single distillation column with two intermediate side condensers and a closed loop heat pump which reboils and partially refluxes the column. The lower of the intermediate condensers is cooled by heat exchange with the heat pump fluid and the overhead nitrogen fraction of the column. The upper of the intermediate condensers is cooled by heat exchange with the overhead nitrogen fraction of the column. The process can handle feeds with increasing nitrogen composition and more than 100 vppm carbon dioxide. The process provides a high methane recovery over the entire feed range, and provides a nitrogen product having an elevated pressure suitable for recycling and reinjection into an oil or gas well to maintain well head pressure.

Claims13

Dependent claims

A process for separating nitrogen from a pressurized feed containing natural gas and nitrogen over a wide concentration range of 5 to 85 volume percent nitrogen in a single distillation column with two side intermediate condensers to form pressurized product streams of nitrogen and natural gas comprising:

(a) cooling and separating the pressurized feed into separate multiple feeds to the column and distilling the cooled feeds in the distillation column to form a pressurized overhead vapor rich in nitrogen and a pressurized bottoms liquid rich in natural gas hydrocarbons;
(b) condensing an overhead vapor of an upper section of the column by heat exchange with a first closed loop refrigerant to provide reflux to the column;
(c) condensing in the upper of two side condensers an intermediate vapor from an intermediate section of the column between the overhead vapor condenser and the lower of the two side condensers by heat exchange with the overhead vapor without expansion to provide an intermediate reflux to the column, wherein the intermediate section vapor condensing with the overhead product stream increases with increasing nitrogen concentration in the feed;
and
(d) condensing in the lower of two side condensers an intermediate vapor from an intermediate section of the column between the upper of the two side condensers and the highest feed point by heat exchange with a second closed loop refrigerant and by heat exchange with the overhead vapor without expansion to provide reflux to the column, wherein the intermediate section vapor condensing with the overhead product stream increases with increasing nitrogen concentration in the feed.

2 more elements

In a process for separating nitrogen from a pressurized feed containing natural gas and nitrogen consisting of cooling said pressurized feed and distilling the cooled feed in a single distillation column to form a pressurized overhead vapor rich in nitrogen and a pressurized bottoms liquid rich in natural gas hydrocarbons, the improvement for accommodating a wide concentration range of nitrogen in the feed and forming a pressurized product stream of nitrogen suitable for reinjection to maintain a well head pressure for enhanced oil or gas recovery comprising:

(a) cooling and separating the pressurized feed into separate multiple feeds to the column;
(b) condensing an overhead vapor of an upper section of the column by heat exchange with a first closed loop refrigerant to provide reflux to the column;
(c) condensing in the upper of two side condensers an intermediate vapor from an intermediate section of the column between the overhead vapor condenser and the lower of the two side condensers by heat exchange with the overhead vapor without expansion to provide an intermediate reflux to the column, wherein the intermediate section vapor condensing with the overhead product stream increases with increasing nitrogen concentraton in the feed;
and
(d) condensing in the lower of two side condensers an intermediate vapor from an intermediate section of the column between the upper of the two side condensers and the highest feed point by heat exchange with a second closed loop refrigerant and by heat exchange with the overhead vapor without expansion to provide reflux to the column, wherein the intermediate section vapor condensing with the overhead product stream increases with increasing nitrogen concentration in the feed.

2 more elements

Dependencies are inferred from the claim text.