US 2025/0101329 A1Published application

Methane Purification System and Method

OwnerJames Podolski, Joseph M. Schwartzinventors

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Abstract

A process for producing high-purity methane is disclosed wherein a mixture containing predominantly methane, and at least one higher hydrocarbon, such as ethane or propane, and nitrogen is liquefied and fed to a first fractionation column that removes nitrogen and other light gases from the mixture through the top of the first fractionation column as a vapor. The remainder of the mixture is fed to a second fractionation column that removes the higher hydrocarbons and other heavier components through the bottom of the second fractionation column as a liquid producing high-purity methane out the top of the second fractionation column as a vapor. The high-purity methane vapor is warmed, compressed, and liquefied by heat exchange. The liquid leaving the second fractionation column can be further purified in a stripping column to remove non-hydrocarbon components such as carbon dioxide.

A system for purifying a natural gas stream to produce a methane stream comprising:

a. A natural gas inlet line configured to receive a liquid natural gas stream;
b. a first heat exchanger having a first heat exchanger warming passage in downstream fluid communication with the natural gas inlet line, said first heat exchanger having a first heat exchanger warming passage outlet;
c. a first expansion device in downstream fluid communication with the natural gas inlet line, said first expansion device having a first expansion device outlet;
d. a nitrogen removal column having a nitrogen removal column inlet in downstream fluid communication with the first heat exchanger warming passage outlet and the first expansion device outlet, said nitrogen removal column having a nitrogen removal column first vapor outlet, a nitrogen removal column liquid outlet and a nitrogen removal column reflux fluid inlet;
e. a second heat exchanger having a nitrogen reflux vapor cooling passage in downstream fluid communication with the nitrogen removal column first vapor outlet and a nitrogen reflux vapor cooling passage outlet in fluid communication with the nitrogen removal column reflux fluid inlet;
f. a first hydrocarbon product control valve in downstream fluid communication with the nitrogen removal column liquid outlet, said first hydrocarbon product control valve having a first hydrocarbon product control valve outlet;
g. a demethanizer having a demethanizer fluid inlet, a demethanizer first vapor outlet through which a methane-enriched vapor stream flows, a demethanizer reflux fluid inlet and a demethanizer liquid outlet;
h. a third heat exchanger having a third heat exchanger warming passage and a third heat exchanger cooling passage, said third heat exchanger warming passage in downstream fluid communication with the demethanizer first vapor outlet;
i. a compressor in downstream fluid communication with the third heat exchanger warming passage, said compressor having a compressor outlet;
j. an aftercooler in downstream fluid communication with the compressor outlet, said aftercooling having an aftercooler outlet;
k. said third heat exchanger cooling passage in downstream fluid communication with the aftercooler outlet so that a methane-enriched fluid passing through the cooling passage is cooled by a methane-enriched fluid passing through the third heat exchanger warming passage;
l. a hydrocarbon product stream warming passage configured to receive a fluid stream from the first hydrocarbon product control valve outlet, further cool a methane-enriched fluid stream downstream of the aftercooler and direct warmed fluid from the hydrocarbon product stream warming passage to the demethanizer fluid inlet;
and
m. a supplemental cooling circuit configured to cool the second heat exchanger.

11 more elements

Abstract

Claims30