METHOD TO PRODUCE PLNG AND CCNG AT STRADDLE PLANTS

• US 20160238314A1
• Filed: 02/11/2016
• Published: 08/18/2016
• Est. Priority Date: 02/12/2015
• Status: Active Application

• Current Assignee: 1304338 Alberta, Ltd., 1304342 Alberta, Ltd.
• Original Assignee: 1304338 Alberta, Ltd., 1304342 Alberta, Ltd.
• Inventors: Millar, MacKenzie, Lourenco, Jose
• Application Number:
  US15/041,884
• Publication Number:
  US 20160238314A1
• Time in Patent Office: Days
• US Class Current: 1/1
• 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 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2215/04 Recovery of liquid products
• 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 2240/30 Dynamic liquid or hydraulic expansion with extraction of work, e.g. single phase or two-phase turbine
• 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 3/0209 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

There is provided a method to produce PLNG and CCNG at Straddle Plants. In contrast to present practice at Straddle Plants, there is added a slipstream of high pressure, pre-treated, pre-cooled natural gas stream to feed a new PLNG and or CCNG production section. This slipstream is further cooled in a heat exchanger by a counter-current vapour fraction of the expanded gas before entering an expander apparatus. The cooled gas is expanded into a separator. The cold vapour fraction from the separator is routed and expanded to the Straddle Plant fractionator. The produced PLNG is routed to storage.

Claims

1. A method to produce pressurized liquid natural gas (PLNG) and cold compressed natural gas (CCNG), comprising the steps of:

passing a dewatered natural gas stream at pressures of between 450 psig and 1200 psig through one or more heat exchangers to pre-cool the natural gas stream;

passing the pre-cooled natural gas stream through a gas column where natural gas liquid fractions and natural gas fractions are separated;

passing the pre-cooled natural gas fractions at pressures of between 450 psig and 1200 psig through one or more heat exchangers to further cool the natural gas fractions;

passing the further cooled natural gas fractions at pressures of between 450 psig and 1200 psig through a gas expansion apparatus where pressure of the natural gas fractions is lowered to a pressure of less than 300 psig; and

passing the natural gas fractions at a pressure of less than 300 psig through a separator where they are separated into a PLNG stream and a CCNG stream at a pressure of less than 300 psig.

2. The method of claim 1, further comprising the step of modifying an existing straddle plant to perform the steps.

3. A method to produce pressurized liquid natural gas (PLNG) where a high pressure, pre-treated, pre-cooled natural gas stream from a straddle plant is routed to a gas expansion apparatus, comprising the steps of:

providing heat exchangers on a high pressure, pre-treated, pre-cooled natural gas PLNG feed line to a gas expansion apparatus;

providing a gas liquid separator downstream of the expansion apparatus; and

providing a pressure reducing device for a separated gaseous stream into a straddle plant fractionator.

4. The method of claim 3, wherein the gas expansion apparatus is a Joule-Thompson (JT) valve or a gas expander turbine.

5. The method of claim 3, wherein cooling is provided by a vapour fraction of the expanded gas.

6. The method of claim 3, wherein the gaseous stream from the gas liquid separator is returned to the straddle plant fractionator.

7. The method of claim 3, wherein the gas to be liquefied is PLNG.

8. A method to produce cold compressed natural gas (CCNG) where a high pressure, pre-treated, pre-cooled natural gas stream from a straddle plant is routed to a gas expansion apparatus.

9. A cold compressed natural gas (CCNG) section of a straddle plant, the CCNG section comprising:

a gas expansion apparatus;

a feed line feeding gas to the gas expansion apparatus;

a CCNG receiver to separate vapour and liquid fractions; and

a liquids return line to a straddle plant fractionator.

10. The CCNG section of claim 9, further comprising a pressurized liquid natural gas line to storage.

11. The CCNG section of claim 9, wherein the CCNG liquid fraction is routed to the straddle plant fractionator for NGL'"'"'s recovery.

12. A method to produce Pressurized Liquid Natural Gas (PLNG), the method comprising the steps of:

passing a dewatered natural gas stream at pressures of between 450 psig and 1200 psig through a first phase separator to obtain a natural gas liquid fraction and a natural gas fraction, the separated natural gas fractions being at a pressure of between 450 psig and 1200 psig;

passing at least a portion of the natural gas fraction through a gas expansion apparatus to reduce the pressure of the natural gas fraction to less than 300 psig; and

passing the pressure-reduced natural gas fraction through a second phase separator to obtain at least one of a PLNG stream and a CCNG stream at a pressure of less than 300 psig.

13. The method of claim 12, wherein the dewatered natural gas stream is a natural gas stream in a straddle plant.

14. The method of claim 12, further comprising the step of passing a natural gas stream through a dewaterer and a heat exchanger to cool the natural gas stream to obtain the dewatered natural gas stream.

15. The method of claim 12, further comprising the step of cooling at least a portion of the separated natural gas fraction in one or more heat exchangers.

16. The method of claim 12, further comprising the step of collecting each of the at least one of the PLNG stream and the CCNG stream separately in a storage vessel.

17. The method of claim 12, wherein the gas expansion apparatus comprises a Joule-Thompson valve or a gas expander turbine.

18. The method of claim 12, wherein at least a portion of an output of the first or the second phase separator is used to cool the natural gas stream.

19. The method of claim 12, wherein at least a portion of the output of the second phase separator is used to cool a fractionator of the saddle plant.