Configurations and methods of heating value control in LNG liquefaction plant

• US 8,635,885 B2
• Filed: 10/12/2011
• Issued: 01/28/2014
• Est. Priority Date: 10/15/2010
• Status: Active Grant

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Primary Examiner(s): Pettitt, John
• Assistant Examiner(s): Alosh, Tareq M
• Application Number:
  US13/271,959
• Publication Number:
  US 20120090350A1
• Time in Patent Office: 839 Days
• Field of Search: 626/18, 626/19, 626/20, 626/22, 626/30, 626/31
• US Class Current: 62/622
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0087 Propane; Propylene
• CPC Class Codes: F25J 1/0238 Purification or treatment step is integrated within one refrigeration cycle only, i.e. the same or single refrigeration cycle provides feed gas cooling (if present) and overhead gas cooling
• CPC Class Codes: F25J 1/0255 controlling the composition of the feed or liquefied gas, e.g. to achieve a particular heating value of natural gas
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2215/64 Propane or propylene
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/04 Internal refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/60 Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• 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 3/0242 separation of CnHm with 3 carbon atoms or more
• CPC Class Codes: F25J 3/0247 separation of CnHm with 4 carbon atoms or more

Abstract

NGL recovery from natural gas is achieved by processing the natural gas in a scrub column that operates at high pressure. A C3+ depleted vapor stream is generated from the vapor portion of partially condensed scrub column overhead and expanded to provide refrigeration for the vapor portion to so form a second reflux stream and the C3+ depleted vapor stream. The C3+ depleted vapor stream is then combined with another vapor portion of partially condensed column overhead to produce a lean liquefaction feed stream.

Claims

1. A method of recovering NGL from a natural gas comprising:

cooling and separating an overhead product of a scrub column to produce a C5+ depleted vapor fraction and a first reflux for the scrub column;

cooling and separating a first portion of the C5+ depleted vapor fraction to produce a second reflux for the scrub column and a C3+ depleted vapor stream.

expanding the C3+ depleted vapor stream in an expansion device to generate refrigeration for the first portion of the C5+ depleted vapor fraction;

compressing and combining the expanded C3+ depleted vapor stream with a second portion of the C5+ depleted vapor fraction to thereby form a liquefaction feed stream; and

using a ratio between the first and second portions of the C5+ depleted vapor fraction and/or a discharge pressure of the expansion device to control C3 recovery in a bottom product of the scrub column.

2. The method of claim 1 wherein the C3 recovery in the bottom product of the scrub column is controlled by using a ratio between the first and second portions of the C5+ depleted vapor fraction.

3. The method of claim 1 wherein the C3 recovery in the bottom product of the scrub column is controlled by controlling the discharge pressure of the expansion device.

4. The method of claim 1 further comprising a step of processing the C3+ enriched bottoms product in an NGL fractionation unit.

5. The method of claim 1 further comprising a step of liquefying the liquefaction feed stream in a downstream liquefaction unit.

6. The method of claim 1 wherein the scrub column is operated at a pressure of at least 700 psi.

7. The method of claim 1 wherein the expansion device is a turboexpander that is operably coupled to a compressor that compresses the expanded C3+ depleted vapor stream.

8. The method of claim 1 wherein the ratio between the first and the second portions of the C5+ depleted vapor fraction is between 1:

1 and 9;

1.