LNG production in cryogenic natural gas processing plants

• US 6,889,523 B2
• Filed: 03/07/2003
• Issued: 05/10/2005
• Est. Priority Date: 03/07/2003
• Status: Expired due to Fees

• Current Assignee: Ortloff Enigneers, Ltd.
• Original Assignee: Elkcorp (Standard Industries, Inc.)
• Inventors: Hudson, Hank M., Cuellar, Kyle T., Wilkinson, John D.
• Primary Examiner(s): DOERRLER, WILLIAM CHARLES
• Application Number:
  US10/384,038
• Publication Number:
  US 20040177646A1
• Time in Patent Office: 795 Days
• Field of Search: 626/13, 626/11, 626/20, 626/21, 626/25
• US Class Current: 62/613
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0035 by gas expansion with extraction of work
• CPC Class Codes: F25J 1/004 by flash gas recovery F25J1/0267 takes precedence
• CPC Class Codes: F25J 1/0042 by liquid expansion with extraction of work
• CPC Class Codes: F25J 1/0045 by vaporising a liquid return stream
• CPC Class Codes: F25J 1/0201 using only internal refrigeration means, i.e. without external refrigeration
• CPC Class Codes: F25J 1/0229 Integration with a unit for using hydrocarbons, e.g. consuming hydrocarbons as feed stock
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/04 in a dual 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 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• 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 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• 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 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2245/90 the recycled stream being boil-off gas from storage
• CPC Class Codes: F25J 2260/20 : Integration in an installation for liquefying or solidifying a fluid stream
• CPC Class Codes: F25J 2270/02 : Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/90 : External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• 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
• CPC Class Codes: F25J 3/0242 : separation of CnHm with 3 carbon atoms or more

Abstract

A process for liquefying natural gas in conjunction with processing natural gas to recover natural gas liquids (NGL) is disclosed. In the process, the natural gas stream to be liquefied is taken from one of the streams in the NGL recovery plant and cooled under pressure to condense it. A distillation stream is withdrawn from the NGL recovery plant to provide some of the cooling required to condense the natural gas stream. A portion of the condensed stream is expanded to an intermediate pressure and then used to provide some of the cooling required to condense the natural gas stream, and thereafter routed to the NGL recovery plant so that any heavier hydrocarbons it contains can be recovered in the NGL product. The remaining portion of the condensed stream is expanded to low pressure to form the liquefied natural gas stream.

Claims

1. A process for liquefying a natural gas stream containing methane and heavier hydrocarbon components wherein

(a) said natural gas stream is withdrawn from a cryogenic natural gas processing plant recovering natural gas liquids;

(b) said natural gas stream is cooled under pressure to condense at least a portion of it and form a condensed stream;

(c) a distillation stream is withdrawn from said plant to supply at least a portion of said cooling of said natural gas stream;

(d) a first portion of said condensed stream is withdrawn, expanded to an intermediate pressure, and directed in heat exchange relation with said natural gas stream to supply at least a portion of said cooling, whereupon said first portion is directed to said plant; and

(e) the remaining portion of said condensed stream is expanded to lower pressure to form said liquefied natural gas stream.

2. A process for liquefying a natural gas stream containing methane and heavier hydrocarbon components wherein

(a) said natural gas stream is withdrawn from a cryogenic natural gas processing plant recovering natural gas liquids;

(b) said natural gas stream is cooled under pressure sufficiently to partially condense it;

(c) a distillation stream is withdrawn from said plant to supply at least a portion of said cooling of said natural gas stream;

(d) said partially condensed natural gas stream is separated into a liquid stream and a vapor stream, whereupon said liquid stream is directed to said plant;

(e) said vapor stream is further cooled at pressure to condense at least a portion of it and form a condensed stream;

(f) a first portion of said condensed stream is withdrawn, expanded to an intermediate pressure, and directed in heat exchange relation with said expanded vapor stream to supply at least a portion of said cooling, whereupon said first portion is directed to said plant; and

(g) the remaining portion of said condensed stream is expanded to lower pressure to form said liquefied natural gas stream.

3. A process for liquefying a natural gas stream containing methane and heavier hydrocarbon components wherein

(a) said natural gas stream is withdrawn from a cryogenic natural gas processing plant recovering natural gas liquids;

(b) said natural gas stream is cooled under pressure sufficiently to partially condense it;

(c) a distillation stream is withdrawn from said plant to supply at least a portion of said cooling of said natural gas stream;

(d) said partially condensed natural gas stream is separated into a liquid stream and a vapor stream, whereupon said liquid stream is directed to said plant;

(e) said vapor stream is expanded to an intermediate pressure and further cooled at said intermediate pressure to condense at least a portion of it and form a condensed stream;

(f) a first portion of said condensed stream is withdrawn, expanded to an intermediate pressure, and directed in heat exchange relation with said expanded vapor stream to supply at least a portion of said cooling, whereupon said first portion is directed to said plant; and

(g) the remaining portion of said condensed stream is expanded to lower pressure to form said liquefied natural gas stream.

4. A process for liquefying a natural gas stream containing methane and heavier hydrocarbon components wherein

(a) said natural gas stream is withdrawn from a cryogenic natural gas processing plant recovering natural gas liquids;

(b) said natural gas stream is cooled under pressure;

(c) a distillation stream is withdrawn from said plant to supply at least a portion of said cooling of said natural gas stream;

(d) said cooled natural gas stream is expanded to an intermediate pressure and further cooled at said intermediate pressure to condense at least a portion of it and form a condensed stream;

(e) a first portion of said condensed stream is withdrawn, expanded to an intermediate pressure, and directed in heat exchange relation with said expanded natural gas stream to supply at least a portion of said cooling, whereupon said first portion is directed to said plant; and

(f) the remaining portion of said condensed stream is expanded to lower pressure to form said liquefied natural gas stream.

5. An apparatus for liquefying a natural gas stream containing methane and heavier hydrocarbon components comprising

(a) first withdrawing means connected to a cryogenic natural gas processing plant recovering natural gas liquids to withdraw said natural gas stream;

(b) heat exchange means connected to said first withdrawing means to receive said natural gas stream and cool it under pressure to condense at least a portion of it and form a condensed stream;

(c) second withdrawing means connected to said plant to withdraw a distillation stream, said second withdrawing means being further connected to said heat exchange means to heat said distillation stream and thereby supply at least a portion of said cooling of said natural gas stream;

(d) third withdrawing means connected to said heat exchange means to withdraw a first portion of said condensed stream;

(e) first expansion means connected to said third withdrawing means to receive said first portion and expand it to an intermediate pressure, said first expansion means being further connected to supply said expanded first portion to said heat exchange means to heat said expanded first portion and thereby supply at least a portion of said cooling, whereupon said heated expanded first portion is directed to said plant; and

(f) second expansion means connected to said heat exchange means to receive the remaining portion of said condensed stream and expand it to lower pressure to form said liquefied natural gas stream.

6. An apparatus for liquefying a natural gas stream containing methane and heavier hydrocarbon components comprising

(a) first withdrawing means connected to a cryogenic natural gas processing plant recovering natural gas liquids to withdraw said natural gas stream;

(b) heat exchange means connected to said first withdrawing means to receive said natural gas stream and cool it under pressure sufficiently to partially condense it;

(c) second withdrawing means connected to said plant to withdraw a distillation stream, said second withdrawing means being further connected to said heat exchange means to heat said distillation stream and thereby supply at least a portion of said cooling of said natural gas stream;

(d) separation means connected to said heat exchange means to receive said partially condensed natural gas stream and to separate it into a vapor stream and a liquid stream, whereupon said liquid stream is directed to said plant;

(e) said separation means being further connected to supply said vapor stream to said heat exchange means, with said heat exchange means being adapted to further cool said vapor stream at pressure to condense at least a portion of it and form a condensed stream;

(f) third withdrawing means connected to said heat exchange means to withdraw a first portion of said condensed stream;

(g) first expansion means connected to said third withdrawing means to receive said first portion and expand it to an intermediate pressure, said first expansion means being further connected to supply said expanded first portion to said heat exchange means to heat said expanded first portion and thereby supply at least a portion of said cooling, whereupon said heated expanded first portion is directed to said plant; and

(h) second expansion means connected to said heat exchange means to receive the remaining portion of said condensed stream and expand it to lower pressure to form said liquefied natural gas stream.

7. An apparatus for liquefying a natural gas stream containing methane and heavier hydrocarbon components comprising

(a) first withdrawing means connected to a cryogenic natural gas processing plant recovering natural gas liquids to withdraw said natural gas stream;

(b) heat exchange means connected to said first withdrawing means to receive said natural gas stream and cool it under pressure sufficiently to partially condense it;

(c) second withdrawing means connected to said plant to withdraw a distillation stream, said second withdrawing means being further connected to said heat exchange means to heat said distillation stream and thereby supply at least a portion of said cooling of said natural gas stream;

(d) separation means connected to said heat exchange means to receive said partially condensed natural gas stream and to separate it into a vapor stream and a liquid stream, whereupon said liquid stream is directed to said plant;

(e) first expansion means connected to said separation means to receive said vapor stream and expand it to an intermediate pressure, said first expansion means being further connected to supply said expanded vapor stream to said heat exchange means, with said heat exchange means being adapted to further cool said expanded vapor stream at said intermediate pressure to condense at least a portion of it and form a condensed stream;

(f) third withdrawing means connected to said heat exchange means to withdraw a first portion of said condensed stream;

(g) second expansion means connected to said third withdrawing means to receive said first portion and expand it to an intermediate pressure, said second expansion means being further connected to supply said expanded first portion to said heat exchange means to heat said expanded first portion and thereby supply at least a portion of said cooling, whereupon said heated expanded first portion is directed to said plant; and

(h) third expansion means connected to said heat exchange means to receive the remaining portion of said condensed stream and expand it to lower pressure to form said liquefied natural gas stream.

8. An apparatus for liquefying a natural gas stream containing methane and heavier hydrocarbon components comprising

(a) first withdrawing means connected to a cryogenic natural gas processing plant recovering natural gas liquids to withdraw said natural gas stream;

(b) heat exchange means connected to said first withdrawing means to receive said natural gas stream and cool it under pressure;

(c) second withdrawing means connected to said plant to withdraw a distillation stream, said second withdrawing means being further connected to said heat exchange means to heat said distillation stream and thereby supply at least a portion of said cooling of said natural gas stream;

(d) first expansion means connected to said heat exchange means to receive said cooled natural gas stream and expand it to an intermediate pressure, said first expansion means being further connected to supply said expanded natural gas stream to said heat exchange means, with said heat exchange means being adapted to further cool said expanded natural gas stream at said intermediate pressure to condense at least a portion of it and form a condensed stream;

(e) third withdrawing means connected to said heat exchange means to withdraw a first portion of said condensed stream;

(f) second expansion means connected to said third withdrawing means to receive said first portion and expand it to an intermediate pressure, said second expansion means being further connected to supply said expanded first portion to said heat exchange means to heat said expanded first portion and thereby supply at least a portion of said cooling, whereupon said heated expanded first portion is directed to said plant; and

(g) third expansion means connected to said heat exchange means to receive the remaining portion of said condensed stream and expand it to lower pressure to form said liquefied natural gas stream.