System and Method for Separating Wide Variations in Methane and Nitrogen
First Claim
1. A system for removing nitrogen and for producing a high pressure methane product stream from a first feed stream comprising nitrogen, methane, and other components, the system comprising:
- a first splitter wherein the first feed stream is divided into a second feed stream and a third feed stream;
a first fractionating column wherein the second feed stream and the third feed stream are separated into a first overhead stream and a first bottoms stream;
a second fractionating column comprising a condenser and a reboiler, wherein first overhead stream is separated into a second overhead stream and a second bottoms stream;
a first heat exchanger for cooling the first feed stream upstream of the first splitter and for cooling the second feed stream upstream of the first fractionating column through heat exchange with the first bottoms stream and the first overhead stream;
an external reboiler for cooling the third feed stream upstream of the first fractionating column through heat exchange with the first bottoms stream;
wherein the methane product stream comprises the first bottoms stream and second bottoms stream;
wherein the second overhead stream is a nitrogen vent stream; and
wherein a duty for the condenser and a duty for the reboiler for the second fractionating column are independent of each other.
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Abstract
A system and method for removing nitrogen and producing a high pressure methane product stream from natural gas feed streams having wide variations in nitrogen and methane content are disclosed. Optional add-on systems may be incorporated into the nitrogen and methane separation to produce an NGL sales stream to reduce excess hydrocarbons in the nitrogen vent stream, or to recover helium. The system and method of the invention are particularly suitable for use with feed streams in excess of 50 MMSCFD and up to 300 MMSCFD and containing up to 100 ppm carbon dioxide. Typical power requirements for compressing the methane product stream to produce a suitably high pressure stream for sale are reduced according to the systems and methods of the invention.
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Citations
18 Claims
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1. A system for removing nitrogen and for producing a high pressure methane product stream from a first feed stream comprising nitrogen, methane, and other components, the system comprising:
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a first splitter wherein the first feed stream is divided into a second feed stream and a third feed stream; a first fractionating column wherein the second feed stream and the third feed stream are separated into a first overhead stream and a first bottoms stream; a second fractionating column comprising a condenser and a reboiler, wherein first overhead stream is separated into a second overhead stream and a second bottoms stream; a first heat exchanger for cooling the first feed stream upstream of the first splitter and for cooling the second feed stream upstream of the first fractionating column through heat exchange with the first bottoms stream and the first overhead stream; an external reboiler for cooling the third feed stream upstream of the first fractionating column through heat exchange with the first bottoms stream; wherein the methane product stream comprises the first bottoms stream and second bottoms stream; wherein the second overhead stream is a nitrogen vent stream; and wherein a duty for the condenser and a duty for the reboiler for the second fractionating column are independent of each other. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for removing nitrogen and for producing a high pressure methane product stream, the method comprising the steps of:
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providing a first feed stream comprising nitrogen and methane; dividing the first feed stream into a second feed stream and a third feed stream in a first splitter; feeding the second feed stream and third feed stream into a first fractionating column; separating the second feed stream and the third feed stream in the first fractionating column into a first overhead stream and a first bottoms stream; feeding the first overhead stream into a second fractionating column comprising a condenser and a reboiler; separating the first overhead stream in the second fractionating column into a second overhead stream and a second bottoms stream; cooling the first feed stream upstream of the first splitter and cooling the second feed stream upstream of the first fractionating column in a first heat exchanger through heat exchange with the first, bottoms stream and the first overhead stream; cooling the third feed stream upstream of the first fractionating column through heat exchange with the first bottoms stream in an external reboiler; wherein the methane product stream comprises the first bottoms stream and second bottoms stream; wherein the second overhead stream is a nitrogen vent stream; and wherein a duty for the condenser and a duty for the reboiler for the second fractionating column are independent of each other. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification