Method to produce natural gas liquids NGLs at gas Pressure Reduction Stations

• US 8,640,494 B2
• Filed: 05/15/2008
• Issued: 02/04/2014
• Est. Priority Date: 05/15/2008
• Status: Active Grant

• Current Assignee: 1304338 Alberta, Ltd., 1304342 Alberta, Ltd.
• Original Assignee: 1304338 Alberta, Ltd.
• Inventors: Lourenco, Jose, Millar, MacKenzie
• Primary Examiner(s): Jules, Frantz
• Assistant Examiner(s): RAYMOND, KEITH MICHAEL
• Application Number:
  US12/121,486
• Publication Number:
  US 20090282863A1
• Time in Patent Office: 2,091 Days
• Field of Search: 626/18, 626/11, 626/21
• US Class Current: 62/618
• CPC Class Codes: C10L 3/10 Working-up natural gas or synthetic natural gas
• 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 2260/02 Integration in an installation for exchanging heat, e.g. for waste heat recovery
• CPC Class Codes: F25J 2260/10 Integration in a gas transmission system at a pressure reduction, e.g. "let down" station
• CPC Class Codes: F25J 3/061 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0635 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/064 separation of CnHm with 2 carbon atoms or more

Abstract

A method to recover NGL'"'"'s at gas Pressure Reducing Stations. A first step involve providing at least one heat exchanger having a flow path for passage of high pressure natural gas with a counter current depressurized lean cold gas. A second step involves passing the high pressure natural gas stream in a counter current flow with the lean cold gas and cooling it before de-pressurization. A third step involves the expansion of the high pressure cooled gas in a gas expander. The expansion of the gas generates shaft work which is converted into electrical power by the power generator and the expanded low pressure and cold gas enters a separator where NGL'"'"'s are recovered. This process results in the recovery NGL'"'"'s, electricity and the displacement of a slipstream of natural that is presently used to pre-heat gas at Pressure Reduction Stations.

Claims

1. A method to recover natural gas liquids (NGLs) at a pressure reduction station, comprising the steps of:

providing at least one heat exchanger, a gas expander, a first separator, and a second separator at the pressure reduction station where gas from a main transmission gas line is reduced in pressure from between 400 to 900 PSIG (pounds per square inch gage) to from 50 to 95 PSIG for distribution through local distribution lines, each separator having a single inlet and only two outlets, namely, a first outlet and a second outlet, each heat exchanger having a flow path for passage of a high pressure natural gas stream and a counter current passage for a depressurised cold lean gas stream;

removing water from the high pressure natural gas stream in order to prevent formation of hydrates by passing the high pressure natural gas stream, that has previously had a majority of the natural gas liquids removed during processing at a straddle plant, along the heat exchanger in order to cool the high pressure natural gas stream through a heat exchange with the depressurized cold lean gas stream before pressure reduction, and through the first separator such that water is condensed out of the high pressure natural gas stream and exits via the first outlet of the first separator;

passing all of the remainder of the high pressure natural gas stream exiting via the second outlet of the first separator, which has had water removed, through the gas expander to reduce pressure of the natural gas stream to a reduced pressure of between 50 and 95 PSIG so it is suitable for consumption by a downstream user;

passing the natural gas stream, which has been reduced in pressure to between 50 and 95 PSIG, through the second separator to produce a first stream of depressurized cold lean natural gas exiting through the first outlet of the second separator and a second stream of NGLs exiting through the second outlet of the second separator; and

communicating the first stream exiting via the first outlet of the second separator at the reduced pressure of between 50 and 95 PSIG to the downstream user.

2. The method of claim 1, including a step of heating a portion of the first stream and then blending selected quantities of the heated portion of the first stream with selected quantities of an unheated portion of the first stream.

3. The method of claim 1, including a step of heating at least a portion of the first stream by passing the portion of the first stream through a heat exchanger.

4. The method of claim 3, including a step of heating at least a portion of the first stream by passing the portion of the first stream through a heat exchanger to effect a heat exchange with ambient outdoor air.

5. The method of claim 3, including a step of heating at least a portion of the first stream by passing the portion of the first stream through a heat exchanger having a counter current waste heat stream.

6. The method of claim 1, including a step of connecting the gas expander to a power generator and using the power generated to run heaters and heating at least a portion of the first stream with the heaters.