Intergrated Ngl Recovery and Lng Liquefaction

• US 20080271480A1
• Filed: 03/14/2006
• Published: 11/06/2008
• Est. Priority Date: 04/20/2005
• Status: Abandoned Application

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Application Number:
  US10/574,671
• Publication Number:
  US 20080271480A1
• Time in Patent Office: Days
• US Class Current: 62/626
• 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 1/0239 Purification or treatment step being integrated between two refrigeration cycles of a refrigeration cascade, i.e. first cycle providing feed gas cooling and second cycle providing 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 2200/04 in a dual 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 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2230/08 Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• 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 2260/20 Integration in an installation for liquefying or solidifying a fluid stream
• 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 2280/02 Control in general, load changes, different modes ("runs"), measurements
• CPC Class Codes: F25J 2290/10 Mathematical formulae, modeling, plot or curves; Design methods
• 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

Contemplated plants include a refluxed absorber and a distillation column, wherein the absorber is operated at a higher pressure than the distillation column to thereby produce a cryogenic pressurized lean gas. The lean gas is further compressed to a pressure suitable for liquefaction using energy from feed gas vapor expansion. Desired separation of C2 products is ensured by temperature control of the absorber and distillation column using flow ratios of various streams within the plant, and by dividing the separation process into two portions at different pressures.

Claims

1. A plant for natural gas liquids recovery in which the plant is coupled with an LNG liquefaction plant, comprising

an absorber configured to receive an absorber feed stream and a first and a second reflux stream, and further configured to provide a bottom product stream;

a distillation column configured to receive a first portion of the bottom product stream and a second portion of the bottom product stream at different points, and wherein the distillation column is further configured to operate a pressure that is lower than an operating pressure in the absorber; and

a control unit that is configured to control a flow ratio of (a) the feed stream to the second reflux stream and (b) the first portion of the bottom product stream to the second portion of the bottom product stream, wherein the flow ratio is a function of desired ethane recovery in the distillation column bottom product stream.

2. The plant of claim 1 further comprising at least one of a heat exchanger and a reflux condenser that are configured to heat the first portion of the bottom product stream, and still further comprising an expansion device configured to cool the second portion of the bottom product stream.

3. The plant of claim 1 wherein the distillation column is configured to produce a distillation column overhead, and wherein the plant further comprises a compressor that compresses the distillation column overhead to at least absorber pressure.

4. The plant of claim 3 further comprising a cooling device thermally coupled to the distillation column overhead and configured to cool the compressed distillation column overhead.

5. The plant of claim 4 wherein the cooled compressed distillation column overhead is the first reflux.

6. The plant of claim 1 wherein the absorber is configured to produce an absorber overhead product that has a temperature of equal or lower than −

90°

F. and a pressure of between 500 psig and 700 psig.

7. The plant of claim 6 further comprising a compressor that is configured to receive the absorber overhead product and to compress the absorber overhead product to a pressure of at least 800 psig.

8. The plant of claim 7 wherein the compressor is operationally coupled to an expander that expands the absorber feed stream.

9. A method of processing a gas for delivery to an LNG liquefaction plant, comprising:

providing an absorber that receives an absorber feed stream and a first and a second reflux stream, and that produces a bottom product stream;

fluidly coupling the absorber to a distillation column such that a first portion of the bottom product stream and a second portion of the bottom product stream are fed to the distillation column at different points;

operating the distillation column at a pressure that is lower than an operating pressure of the absorber; and

controlling a flow ratio of (a) the feed stream to the second reflux stream and (b) the first portion of the bottom product stream to the second portion of the bottom product stream as a function of desired ethane recovery in the distillation column bottom product stream.

10. The method of claim 9 further comprising a step of feeding a distillation column overhead product to the absorber.

11. The method of claim 10 wherein the distillation column overhead product is compressed, cooled, and fed to the absorber as the first reflux stream.

12. The method of claim 9 wherein the distillation column is operated at a pressure between 300 psig and 500 psig, and wherein the absorber is operated at a pressure of between 500 psig and 800 psig.

13. The method of claim 9 further comprising a step of separating a cooled feed gas into a liquid portion and a vapor portion, and feeding the liquid portion after at least partial depressurization and warming into the distillation column.

14. The method of claim 13 wherein the vapor portion is split into a first and second stream to thereby form the second reflux stream and the absorber feed stream.

15. The method of claim 9 wherein the absorber produces a cryogenic absorber overhead stream, and further comprising a step of compressing the cryogenic absorber overhead stream to a pressure suitable for liquefaction.

16. The method of claim 15 wherein the step of compressing is driven by expansion of the absorber feed stream.

17. A method of variably recovering C2 from a feed gas to a LNG liquefaction plant comprising:

feeding an expanded and heated liquid portion of a feed gas to a distillation column and feeding a vapor portion of the feed gas to an absorber;

adjusting a flow ratio of an absorber feed to a second reflux to the absorber, and using a first reflux that is provided by a distillation column overhead-product to thereby control an absorber overhead temperature;

adjusting a temperature of an absorber bottom product that is fed to the distillation column to thereby control a distillation column overhead temperature; and

operating the absorber at a higher pressure than the distillation column.

18. The method of claim 17 wherein the step of adjusting the absorber bottom product temperature is performed by heating at least one portion of the absorber bottom product in a heat exchanger.

19. The method of claim 17 wherein the step of adjusting the absorber bottom product temperature is performed by cooling at least another portion of the absorber bottom product using a JT valve.

20. The method of claim 17 wherein the step of adjusting the flow ratio of the absorber feed to the second reflux to the absorber is a function of desired C2 recovery.