Reducing refrigeration and dehydration load for a feed stream entering a cryogenic distillation process

Patent metadata

Field	Value
Publication number	US-10495379-B2
Application number	US-201615534358-A
Country	US
Kind code	B2
Filing date	Jan 13, 2016
Priority date	Feb 27, 2015
Publication date	Dec 3, 2019
Grant date	Dec 3, 2019

Abstract

A system for conditioning a sour gas feed stream for a cryogenic distillation tower. A dehydration unit separates the sour gas feed stream into a first stream including water and a feed stream. A sequential cooling assembly is coupled to both the dehydration unit and the cryogenic distillation tower. The sequential cooling assembly includes: a first stage that separates the feed stream into a partially cooled feed stream and a second stream including acid gas; a second stage that cools the partially cooled feed stream into a cooled feed stream and a third stream including acid gas; and a cooled feed stream header coupled to a cryogenic distillation tower feed inlet. The first stage, the second stage, or both send at least one of the second and third streams to a bottom section of the cryogenic distillation tower.

First claim

What is claimed is:

1. A system for conditioning a sour gas feed stream for a cryogenic distillation tower, comprising:
a dehydration unit configured to separate the sour gas feed stream into a first stream comprising water and a feed stream;
a first chiller configured to cool the feed stream into a partially cooled feed stream;
a scrubber configured to separate the partially cooled feed stream into a cooled feed stream and a liquid stream comprising acid gas;
a line connected to the scrubber or to a sour gas feed stream line for supplying a recycle stream to the scrubber or to the sour gas feed stream line, wherein the recycle stream is an acid-rich gas and comprises
a stream from an outlet of a bottom section of the cryogenic distillation tower, or
a slip stream from an intermediate location in the bottom section of the cryogenic distillation tower,
wherein the recycle stream is received by the scrubber or the sour gas feed stream during an upset event in which ice and/or hydrates have formed upstream of the cryogenic distillation tower;

and
a second chiller configured to further cool the cooled feed stream to form a chilled stream that is directed to a cryogenic distillation tower feed inlet;
wherein the scrubber is configured to send the liquid stream to a bottom section of the cryogenic distillation tower.

2. The system of claim 1 , wherein when the recycle stream is connected to the scrubber, a heat exchanger is disposed along the recycle stream between the cryogenic distillation tower bottom section outlet and the scrubber.

3. The system of claim 1 , wherein the temperature of the partially cooled feed stream is between about +10° C. to about −60° C. and the temperature of the chilled stream is between about −10° C. to about −60° C.

4. The system of claim 1 , wherein the cryogenic distillation tower comprises a controlled freeze zone section.

5. A method of sequentially cooling a sour gas feed stream for a cryogenic distillation tower, comprising:
receiving the sour gas feed stream;
separating the sour gas feed stream into a water stream and a partially dehydrated feed stream;
cooling the partially dehydrated feed stream to a first temperature;
in a scrubber, separating the partially dehydrated feed stream into a partially cooled feed stream comprising vapor and a first stream comprising liquid;
cooling the partially cooled feed stream to a second temperature, thereby forming a cooled feed stream;
feeding the cooled feed stream to the cryogenic distillation tower; and
mixing an acid-gas-rich liquid recycle stream into the scrubber or into the sour gas feed stream, wherein the acid-gas-rich liquid recycle stream originates at least in part from a bottom section of the cryogenic distillation tower or downstream of the cryogenic distillation tower;
wherein the mixing step is part of an upset recovery technique, and further comprising temporarily employing the upset recovery technique to recover from or eliminate an upset condition in which ice and/or hydrates have formed upstream of the cryogenic distillation tower.

6. The method of claim 5 , wherein the first stream comprises carbon dioxide.

7. The method of claim 5 , further comprising cooling the cooled feed stream to a third temperature prior to feeding the cooled feed stream to the cryogenic distillation tower.

8. The method of claim 5 , wherein the acid-gas-rich liquid recycle stream passes through a scrubber before being mixed with the partially cooled feed stream.

9. The method of claim 5 , wherein the first stream is sent to a bottom section of the cryogenic distillation tower.

10. A cryogenic distillation system, comprising:
a progressive conditioning section for a sour gas feed stream, comprising:
a dehydration unit configured to separate the sour gas feed stream into a first stream comprising water and a partially dehydrated feed stream;
a first chiller configured to cool, to a first temperature, the partially dehydrated feed stream, thereby forming a partially cooled feed stream;
a scrubber coupled to the first chiller and configured to separate the partially dehydrated feed stream into a cooled feed stream comprising a hydrocarbon and a liquid stream comprising an acid gas;
a second chiller coupled to the chiller and further configured to cool the cooled feed stream to a second temperature to form a chilled stream, wherein the second temperature is colder than the first temperature;
a cryogenic distillation tower comprising a controlled freeze zone, wherein the cryogenic distillation tower is configured to receive the chilled stream; and
a recycle stream connected to the scrubber or to the sour gas feed stream, wherein the recycle stream is an acid gas and comprises
a stream from an outlet of a bottom section of the cryogenic distillation tower, or
a slip stream from an intermediate location in the bottom section of the cryogenic distillation tower,

wherein the recycle stream is received by the scrubber or the sour gas feed stream during an upset event in which ice and/or hydrates have formed in the progressive conditioning section.

11. The system of claim 10 , wherein the third stage assembly is further configured to split the progressively dehydrated feed stream into a cooled feed stream comprising a hydrocarbon and a third stream comprising an acid gas, and wherein the second stage assembly, the third stage assembly, or both are coupled to a bottom section of the cryogenic distillation tower.

12. The system of claim 10 , further comprising a fourth stage assembly configured to cool the cooled feed stream to a third temperature, wherein the third temperature is colder than the second temperature.

Assignees

• Nagavarapu Ananda K
• Northrop P Scott
• Denton Robert D
• Valencia James A
• Exxonmobil Upstream Res Co

Inventors

• Nagavarapu Ananda K
• Northrop P Scott
• Denton Robert D
• Valencia James A

Classifications

• F25J2200/30

  using a side column in a single pressure column system · CPC title

• F25J2205/30

  using a washing, e.g. "scrubbing" or bubble column for purification purposes · CPC title

• F25J2205/04

  in the feed line, i.e. upstream of the fractionation step · CPC title

• F25J2240/02

  Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream · CPC title

• F25J2220/68

  Separating water or hydrates · CPC title