Ethane recovery methods and configurations for high carbon dioxide content feed gases

• US 8,567,213 B2
• Filed: 06/19/2007
• Issued: 10/29/2013
• Est. Priority Date: 06/20/2006
• Status: Expired due to Fees

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Primary Examiner(s): Jules, Frantz
• Assistant Examiner(s): CRENSHAW, HENRY T
• Application Number:
  US12/300,031
• Publication Number:
  US 20090301133A1
• Time in Patent Office: 2,324 Days
• Field of Search: 62617-621, 626/28, 626/57, 626/40, 626/43, 626/56
• US Class Current: 62/657
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• CPC Class Codes: F25J 2240/02 Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2280/02 Control in general, load changes, different modes ("runs"), measurements
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more

Abstract

Ethane is separated from a carbon dioxide-containing feed gas in a demethanizer that receives a rich subcooled reflux stream at very low temperature. Freezing of carbon dioxide is prevented by feeding a temperature-controlled vapor portion of the feed gas to the column, wherein the temperature of the vapor portion is adjusted by routing a portion of the expander discharge through a heat exchanger in response to the tray temperature in the demethanizer. Thus, high separation efficiency is achieved at reduced, or even eliminated carbon dioxide freezing.

Claims

1. A processing plant for ethane recovery from a carbon dioxide-containing feed gas comprising:

a control circuit that is operationally coupled to (1) a thermal sensor that is thermally coupled to a refluxed demethanizer and (2) a flow control element;

an expander that is coupled to the refluxed demethanizer and a heat exchanger such that (a) the expander provides a first portion of an expander discharge stream to the heat exchanger to thereby form a heated expander discharge stream, (b) the expander provides a second portion of the expander discharge stream to the heated expander discharge stream to thereby form a temperature-controlled expander discharge, and (c) the temperature-controlled expander discharge is provided to the refluxed demethanizer;

wherein the control circuit is configured such that the flow control element controls a flow ratio between the first and second portions of the expander discharge stream in response to a temperature sensed by the thermal sensor in the demethanizer such that the flow ratio is effective to increase a temperature in an upper section of the refluxed demethanizer while providing cooling to a portion of the carbon dioxide-containing feed gas; and

wherein the heat exchanger is configured to form a subcooled stream from the portion of the carbon dioxide-containing feed gas for delivery to the demethanizer using refrigeration content of the first portion of an expander discharge.

2. The processing plant of claim 1 wherein the thermal sensor is located within the upper section of the demethanizer.

3. The processing plant of claim 1 further comprising a separator that is fluidly coupled between the expander and the demethanizer such that the expander discharge stream is a vapor portion of an expander discharge.

4. The processing plant of claim 3 wherein the separator is further configured to provide a liquid stream to the demethanizer.

5. The processing plant of claim 1 wherein the heat exchanger is further configured to use refrigeration content from an absorber overhead product to cool the portion of the carbon dioxide-containing feed gas.

6. The processing plant of claim 5 wherein the heat exchanger is configured to allow cooling of the portion of the carbon dioxide-containing feed gas from a temperature of between −

20°

F. and 50°

F. to a temperature of −

100°

F.

7. The gas processing plant of claim 5 further comprising a pressure reduction device that further reduces temperature of the cooled portion of the carbon dioxide-containing feed gas to thereby form a subcooled reflux stream to the refluxed demethanizer.

8. The processing plant of claim 1 further comprising a primary exchanger that is configured to chill the carbon dioxide-containing feed gas to a temperature of between −

20°

F. and 50°

F.

9. A method of recovering ethane from a carbon dioxide-containing feed gas comprising:

providing a control circuit and operationally coupling the control circuit to a thermal sensor that is thermally coupled to a refluxed demethanizer and to a flow control element;

feeding a temperature-controlled expander discharge to the refluxed demethanizer;

wherein the temperature-controlled expander discharge is formed from a combination of first and second portions of an expander discharge stream, and wherein the first portion of the expander discharge stream is heated in a heat exchanger prior to forming the combination;

configuring the control circuit such that the flow control element controls a flow ratio between the first and second portions of the expander discharge stream in response to a temperature sensed by the thermal sensor in the demethanizer such that the flow ratio is effective to increase a temperature in an upper section of the refluxed demethanizer while providing cooling to a portion of the carbon dioxide-containing feed gas; and

configuring the heat exchanger to form a subcooled stream for the refluxed demethanizer using refrigeration content of the first portion of the expander discharge stream, wherein the subcooled stream is a portion of the carbon dioxide-containing feed gas.

10. The method of claim 9 wherein the thermal sensor is located within an upper section of the demethanizer.

11. The method of claim 9 further comprising a step of fluidly coupling a separator between an expander and the demethanizer such that the expander discharge stream is a vapor portion of an expander discharge.

12. The method of claim 11 wherein the separator further provides a liquid stream to the demethanizer.

13. The method of claim 9 wherein the heat exchanger cools the portion of the carbon dioxide-containing feed gas from a temperature of between −

20°

F. and 50°

F. to a temperature of −

100°

F.

14. The method of claim 9 wherein a pressure reduction device reduces temperature of the cooled portion of the carbon dioxide-containing feed gas to thereby form a subcooled reflux stream to the refluxed demethanizer.

15. The method of claim 9 wherein a primary exchanger chills the carbon dioxide-containing feed gas to a temperature of between −

20°

F. and 50°

F.