Treatment plant for hydrocarbon gas having variable contaminant levels

Patent metadata

Field	Value
Publication number	US-11255603-B2
Application number	US-201615245965-A
Country	US
Kind code	B2
Filing date	Aug 24, 2016
Priority date	Sep 24, 2015
Publication date	Feb 22, 2022
Grant date	Feb 22, 2022

Abstract

A method of designing, constructing, and operating a hydrocarbon gas treatment plant is disclosed. A target hydrocarbon production range for a hydrocarbon gas meeting a required product specification is established. A cryogenic distillation column is designed and constructed with a vapor capacity to meet the target hydrocarbon production range. A variable feed refrigeration system is incorporated to cool an inlet feed of the hydrocarbon gas. The variable feed refrigeration system is designed to handle the target hydrocarbon production range and a wide range of contaminant concentrations in the inlet feed. A variable bottoms heating system is incorporated to handle heating duties associated with the wide range of contaminant concentrations in the inlet feed. A variable bottoms pumping system is incorporated to handle liquid flows associated with the wide range of contaminant concentrations in the inlet feed.

First claim

What is claimed is:

1. A method of treating, in a gas treatment plant, a feed gas stream comprising hydrocarbon gas and acid gas, the method comprising:
(a) measuring an acid gas concentration in the feed gas stream at a first time to determine a first acid gas fraction, wherein the first acid gas fraction is less than a threshold value;
(b) cooling and liquefying the feed gas stream in at least one first feed refrigeration unit to produce a liquefied acid gas;
(c) separating the liquefied acid gas from the feed gas stream in a feed separator to create a first vapor stream;
(d) passing the first vapor stream through an expander device located between the feed separator and a cryogenic distillation column to produce an expanded first vapor stream;
(e) introducing the expanded first vapor stream into the distillation column via a first inlet:
(f) introducing the liquefied acid gas separated from the feed gas stream into the distillation column via a second inlet;
(g) in the cryogenic distillation column, separating, by freezing, from the expanded first vapor stream acid gas remaining in the first vapor stream to create frozen acid gas and a hydrocarbon gas stream;
(h) melting the frozen acid gas to create melted acid gas;
(i) removing, from the cryogenic distillation column, the melted acid gas and the liquefied acid gas separated from the feed gas stream, which combine together to form a first bottoms stream, and pumping the first bottoms stream using at least one first bottoms stream pump;
(j) removing the hydrocarbon gas stream from the cryogenic distillation column;
(k) measuring the acid gas concentration in the feed gas stream at a second time to determine a second acid gas fraction, wherein the second acid gas fraction is greater than the threshold value and the feed gas stream is treated by:
separating the feed gas stream into a first portion and a second portion so that in step (b) the at least one first feed refrigerant unit cools and liquefies the first portion of the feed gas stream;
cooling and liquefying the second portion of the feed gas stream using at least one additional feed refrigeration unit to produce an additional liquefied acid gas;
combining the cooled first portion and the cooled second portion of the feed gas stream to produce a combined cooled feed gas stream;
separating the liquefied acid gas from the combined cooled feed gas stream to create a second vapor stream;
passing the second vapor stream through the expander device located between the feed separator and the cryogenic distillation column to produce an expanded second vapor stream;
introducing the expanded second vapor stream into the distillation column via the first inlet;
introducing the liquefied acid gas separated from the combined cooled feed gas stream into the distillation column via the second inlet;
in the cryogenic distillation column, separating, by freezing, from the expanded second vapor stream acid gas remaining in the second vapor stream to create additional frozen acid gas and an additional hydrocarbon gas stream;
melting the additional frozen acid gas to create additional melted acid gas;
removing, from the cryogenic distillation column, the additional melted acid gas and the liquefied acid gas separated from the combined cooled feed gas stream, which combine together to form a second bottoms stream, and pumping the second bottoms stream using the at least one first bottoms stream pump; and
removing the additional hydrocarbon gas stream from the cryogenic distillation column; wherein the threshold value is 40 mole % of the acid gas in the feed gas stream.

2. The method of claim 1 , wherein each of the additional feed refrigeration units has a performance characteristic in common with the first feed refrigeration unit.

3. The method of claim 2 , wherein the performance characteristic is a cooling capacity of the first feed refrigeration unit.

4. The method of claim 2 , wherein the performance characteristic is a power rating of the source of refrigeration.

5. The method of claim 1 , further comprising adding at least one second bottoms stream pump when the acid gas concentration in the feed gas stream increases above the threshold value.

6. The method of claim 5 , wherein each second bottoms stream pump has a performance characteristic in common with the at least one first bottoms stream pump, wherein the performance characteristic is selected from a flow rate of the at least one first bottoms stream pump and a discharge pressure of the at least one first bottoms stream pump.

7. The method of claim 1 , further comprising:
heating the first bottoms stream to remove residual hydrocarbon gas therefrom.

8. The method of claim 7 , wherein the heating of the first bottoms stream is accomplished using a first bottoms stream heat exchanger.

9. The method of claim 8 , further comprising:
heating the second bottoms stream to remove residual hydrocarbon gas therefrom using the first bottoms stream heat exchanger and at least one additional bottoms stream heat exchanger.

10. The method of claim 9 , wherein the at least one additional bottoms stream heat exchanger being utilized has a heating duty that is based on the second acid gas fraction.

11. The method of claim 1 , wherein:
the cryogenic distillation column comprises a stripper section and a freezing section disposed above the stripper section, and
the first inlet and the second inlet introduce both the first vapor stream and the liquefied acid gas separated from the feed gas stream, respectively, into the stripper section or the freezing section such that the first vapor stream and the liquefied acid gas separated from the feed gas stream are introduced into the same section of the cryogenic distillation column.

12. The method of claim 1 , wherein the liquefied acid gas separated from the feed gas stream is passed through a liquid control valve located between the feed separator and the cryogenic distillation column and is introduced into the distillation column via the second inlet.

13. The method of claim 1 , wherein:
the cryogenic distillation column comprises a stripper section and a freezing section disposed above the stripper section, and
the first inlet and the second inlet introduce both the second vapor stream and the liquefied acid gas separated from the combined cooled feed gas stream, respectively, into the stripper section or the freezing section such that the second vapor stream and the liquefied acid gas separated from the combined cooled feed gas stream are introduced into the same section of the cryogenic distillation column.

14. The method of claim 1 , wherein the liquefied acid gas separated from the combined cooled feed gas stream is passed through a liquid control valve located between the feed separator and the cryogenic distillation column and is introduced into the distillation column via the second inlet.

15. The method of claim 1 , wherein the acid gas concentration in each of the first vapor stream and the second vapor stream is substantially the same and in a range of 10 mole % to 30 mole %.

16. The method of claim 1 , wherein:
the cryogenic distillation column comprises a stripper section and a freezing section disposed above the stripper section,
the first inlet and the second inlet introduce both the first vapor stream and the liquefied acid gas separated from the first portion of the feed gas stream, respectively, into the freezing section,
the liquefied acid gas separated from the feed gas stream is passed through a liquid control valve located between the feed separator and the cryog

Assignees

• Valencia Jaime A
• Denton Robert D
• Maher David W
• Exxonmobil Upstream Res Co

Inventors

• Valencia Jaime A
• Denton Robert D
• Maher David W

Classifications

• F25J2290/40

  Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc. · CPC title

• F25J2235/60

  the fluid being (a mixture of) hydrocarbons · CPC title

• F25J2210/06

  Splitting of the feed stream, e.g. for treating or cooling in different ways · CPC title

• F25J3/0209

  Natural gas or substitute natural gas · CPC title

• F25J2290/50

  Arrangement of multiple equipments fulfilling the same process step in parallel · CPC title