Energy-saving process and device for recovering C2 from refinery dry gas

Patent metadata

Field	Value
Publication number	US-12247173-B2
Application number	US-202018014442-A
Country	US
Kind code	B2
Filing date	Oct 15, 2020
Priority date	Oct 15, 2020
Publication date	Mar 11, 2025
Grant date	Mar 11, 2025

Abstract

The preset invention provides an energy-saving process and device for recovering C2 from refinery dry gas. The process is as follows: dry gas is cooled and then sent to a multi-stage absorption tower for treatment; the gas phase from the multi-stage absorption tower is sent to a fuel gas pipeline network or PSA unit, and the liquid phase is sent to a high-pressure flash zone for treatment; the gas phase from the high-pressure flash zone is returned to a compression section of a dry gas pretreatment system; the gas phase from the low-pressure flash zone is sent to a C2 concentrated gas compressor system; and the gas phase from the desorption tower is mixed with the gas phase obtained from the low-pressure flash zone and sent to an ethylene cracking furnace as a C2 concentrated gas product, most of the liquid phase is returned to the multi-stage absorption tower.

First claim

The invention claimed is:

1. An energy-saving process for recovering C2 from refinery dry gas, wherein the process flow is as follows:
(1) sending refinery dry gas treated through deacidification, drying, compression and cooling by a dry gas pretreatment system to a multi-stage absorption tower, sending the gas phase at the top of the tower obtained from the multi-stage absorption tower to a fuel gas pipeline network or PSA unit, and sending the liquid phase at the bottom of the tower obtained from the multi-stage absorption tower to a high-pressure flash zone;
(2) arranging multiple stages of high-pressure zone flash tanks in the high-pressure flash zone, and returning the gas phase obtained by flash to the compression section of the dry gas pretreatment system; and recycling one part of the obtained liquid phase back to the multi-stage absorption tower as a semi-lean solvent, and sending the other part to a low-pressure flash zone for treatment; and the multiple stages of high-pressure zone flash tanks are successively depressurized and connected in series, and the pressure of the last flash tank is 0.1˜0.3 MpaG;
(3) arranging multiple stages of low-pressure zone flash tanks in the low-pressure flash zone, sending the gas phase, C2 concentrated gas to a C2 concentrated gas compressor system, recycling one part of the obtained liquid phase back to the multi-stage absorption tower as a secondary lean solvent, and sending the other part to a desorption tower; and the multiple stages of low-pressure zone flash tanks are successively depressurized and connected in series, and the pressure of the last flash tank is 0˜0.1 MpaG;
(4) mixing the gas phase obtained from the desorption tower with the gas phase from the low-pressure flash zone and sending to an ethylene cracking furnace as C2 concentrated gas, returning part of the liquid phase obtained from the desorption tower to the multi-stage absorption tower as a lean solvent, sending the other part out of the battery limit as C4, and supplementing the C4 from the battery limit as fresh adsorbent.

2. The energy-saving process for recovering C2 from refinery dry gas according to claim 1 , wherein the treatment method of the multi-stage absorption tower is as follows: the cooled refinery dry gas is supplied to the multi-stage absorption tower to be in contact with the mixed C4 adsorbent, the number of theoretical plates of the multi-stage absorption tower is 30˜60, the operating pressure is 3˜5 MpaG, the tower top temperature is −15° C. ˜−35° C., and the tower bottom temperature is −10° C. ˜−30° C.

3. The energy-saving process for recovering C 2 from refinery dry gas according to claim 1 , wherein in the liquid phase obtained from the high-pressure flashzone: the liquid phase entering the low-pressure flash zone is the liquid phase of the last flash tank, the semi-lean solvent is the liquid phase of each flash tank, the feed plate of the semi-lean solvent is 20˜45, and the temperature of the semi-lean solvent is −10° C. ˜−40° C.

4. The energy-saving process for recovering C2 from refinery dry gas according to claim 1 , wherein in the liquid phase obtained from the low-pressure flash zone: the liquid phase sent to the desorption tower is the liquid phase of the last flash tank, the secondary lean solvent is the liquid phase of each flash tank, the feed plate of the secondary lean solvent is 5˜25, and the temperature of the secondary lean solvent is −30° C. ˜−70° C.

5. The energy-saving process for recovering C2 from refinery dry gas according to claim 1 , wherein the treatment method of C2 concentrated gas compression is as follows: the pressure of the gas phase obtained from the low-pressure flash zone is increased to 0.5˜2 MPaG.

6. The energy-saving process for recovering C2 from refinery dry gas according to claim 5 , wherein the C2 concentrated gas compression is multi-stage compression.

7. The energy-saving process for recovering C2 from refinery dry gas according to claim 1 , wherein the cooling treatment method is as follows: the treated refinery dry gas is cooled to −15° C. ˜−40° C., and propylene refrigeration is used for cooling; and in combination with the operating temperature of other equipment in the process, the propylene refrigeration adopts primary to tertiary refrigeration.

8. The energy-saving process for recovering C2 from refinery dry gas according to claim 7 , wherein the C4 adsorbent is C4 fraction containing n-butane and isobutane, saturated liquefied gas containing saturated C3 fraction and C4 fraction, or C5 fraction containing n-pentane and isopentane.

9. The energy-saving process for recovering C2 from refinery dry gas according to claim 8 , wherein in the C4 adsorbent: the recycled lean solvent is composed of 80˜95 mol % of C4 and the balance of C3 and C5; and the recycled secondary lean solvent is composed of 50˜80 mol % of C4, and the recycled semi-lean solvent is composed of 30˜70 mol % of C4.

10. The energy-saving process for recovering C2 from refinery dry gas according to claim 1 , wherein the treatment method of the desorption tower is as follows: the liquid phase material obtained from the low-pressure flash zone is supplied to the C2 desorption tower for separation, the number of theoretical plates of the absorption tower is 20˜60, the operating pressure is 0.5˜4 MpaG, the tower top temperature is −35° C.˜40° C., and the tower bottom temperature is 60° C.˜130° C.

11. The energy-saving process for recovering C2 from refinery dry gas according to claim 10 , wherein the lean solvent returned to the multi-stage absorption tower for recycling is cooled to −15° C. ˜−40° C., and returned to the top of the multi-stage absorption tower as lean adsorbent for recycling.

12. An energy-saving device used in the energy-saving process for recovering C2 from refinery dry gas according to claim 1 , wherein the energy-saving device comprises a dry gas pretreatment system, a multi-stage absorption tower, high-pressure zone flash tanks, low-pressure zone flash tanks, a desorption tower, a C2 concentrated gas compressor system and a lean solvent cooling heat exchanger;
the outlet of the dry gas pretreatment system is communicated with a dry gas precooler;
the outlet of the dry gas precooler is communicated with the bottom of the multi-stage absorption tower;
the bottom of the multi-stage absorption tower is communicated with the first-stage high-pressure zone flash tank;
the top of the high-pressure zone flash tank is communicated with the dry gas pretreatment system, and the bottom of each stage of high-pressure zone flash tank is connected with the inlet of the next stage of flash tank, wherein a pipeline at the bottom of one or multiple stages of flash tanks is connected with the lower part of the multi-stage absorption tower, and the bottom of the last stage of flash tank is connected with the inlet of the first-stage low-pressure zone flash tank;
the top of the low-pressure zone flash tank is communicated with the C2 concentrated gas compressor system, and the bottom of each stage of low-pressure zone flash tank is connected with the inlet of the next stage of flash tank, wherein a pipeline at the bottom of one or multiple stages of flash tanks is connected with the middle part of the multi-stage absorption tower, and the bottom of the last stage of flash tank is connected with the inlet of the desorption tower;
the top of the desorption tower is connected with a production pipeline of C2 concentrated gas products, and a pipeline at the bottom of the tower is divided into two branches:
one is communicated with the lean solvent cooling heat exchanger, and the other is an extracted C4 pipeline; and a pipeline for supplement

Assignees

• Univ Dalian Tech

Inventors

• Dong Hongguang
• Chang Wenchang
• Ye Haotian
• Jia Jilong
• Han Zhizhong

Classifications

• C10G2300/4081

  Recycling aspects · CPC title

• C10G2300/4012

  Pressure · CPC title

• C10G2300/4006

  Temperature · CPC title

• Y02P20/50

  Improvements relating to the production of bulk chemicals · CPC title

• Y02P20/10

  Process efficiency · CPC title