U.S. patent application number 11/817379 was filed with the patent office on 2009-08-20 for method for liquefaction of a stream rich in hydrocarbons.
This patent application is currently assigned to Linde Aktiengesellschaft. Invention is credited to Hans Schmidt.
Application Number | 20090205366 11/817379 |
Document ID | / |
Family ID | 36508129 |
Filed Date | 2009-08-20 |
United States Patent
Application |
20090205366 |
Kind Code |
A1 |
Schmidt; Hans |
August 20, 2009 |
METHOD FOR LIQUEFACTION OF A STREAM RICH IN HYDROCARBONS
Abstract
A method for liquefying a hydrocarbon-rich stream is disclosed.
In an embodiment, the hydrocarbon-rich stream is liquefied in a
heat exchanger countercurrent to a three component refrigerant
mixture. The refrigerant mixture is compressed in a two stage
compressor. The refrigerant mixture is separated into a higher
boiling fraction and a lower boiling fraction. A fluid fraction is
recovered from a partial stream of the lower boiling fraction. The
fluid fraction is supercooled and expanded to a pressure of the
higher boiling fraction and the fluid fraction is provided to a
compressor stage to which the higher boiling fraction is taken.
Inventors: |
Schmidt; Hans;
(Wolfratshausen, DE) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
Linde Aktiengesellschaft
Wiesbaden
DE
|
Family ID: |
36508129 |
Appl. No.: |
11/817379 |
Filed: |
February 28, 2006 |
PCT Filed: |
February 28, 2006 |
PCT NO: |
PCT/EP2006/001804 |
371 Date: |
October 16, 2008 |
Current U.S.
Class: |
62/612 ;
62/614 |
Current CPC
Class: |
F25J 1/0055 20130101;
F25J 1/0092 20130101; F25J 1/0212 20130101; F25J 1/0022
20130101 |
Class at
Publication: |
62/612 ;
62/614 |
International
Class: |
F25J 1/02 20060101
F25J001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2005 |
DE |
10 2005 010 055.4 |
Claims
1-7. (canceled)
8. A process for liquefying a hydrocarbon-rich stream, specifically
a natural gas stream, wherein: liquefaction of the hydrocarbon-rich
stream takes place in heat exchange countercurrent to a three or
more component refrigerant mixture; one of the components is a part
of the hydrocarbon-rich stream to be liquefied; one of the
components is propane, propylene or a C.sub.4 hydrocarbon; one of
the components is C.sub.2H.sub.4 or C.sub.2H.sub.6; compression of
the refrigerant mixture is carried out by means of an at least
two-stage compression; before cooling and expansion of the
refrigerant mixture to provide refrigeration, separation of the
refrigerant mixture into a higher boiling and a lower boiling
refrigerant fraction takes place; the higher boiling and the lower
boiling refrigerant fractions following their expansion to provide
refrigeration are taken at a hot end of the heat exchange at
different pressures for compression; and at least one partial
stream of the lower boiling refrigerant fraction is partially
condensed and a fluid fraction recovered is supercooled and
expanded; wherein the fluid fraction recovered is expanded to a
pressure of the higher boiling fraction and taken to a compressor
stage to which the higher boiling fraction is also taken.
9. The process according to claim 8, wherein the refrigerant
mixture is a three-component refrigerant mixture.
10. The process according to claim 8, wherein the refrigerant
fractions are cooled separately, expanded separately to provide
refrigeration and heated separately countercurrent to the
hydrocarbon-rich stream to be liquefied.
11. The process according to claim 8, wherein a further component
of the refrigerant mixture is nitrogen.
12. The process according to claim 8, wherein at least one C.sub.4
to C.sub.6 hydrocarbon is used as an additional component of the
refrigerant mixture.
13. The process according to claim 8, wherein a second fluid
fraction is recovered and supercooled, is expanded to a pressure of
the lower boiling fraction and taken to a compressor stage to which
the lower boiling fraction is also taken.
14. The process according to claim 8, wherein the liquefaction of
the hydrocarbon-rich stream takes place countercurrent to the
refrigerant mixture in a plate heat exchanger.
15. The process according to claim 14, wherein the plate heat
exchanger is a single plate heat exchanger.
16. A method for liquefying a hydrocarbon-rich stream, comprising
the steps of: liquefying the hydrocarbon-rich stream in a heat
exchanger countercurrent to a three component refrigerant mixture;
compressing the refrigerant mixture in a two stage compressor;
separating the refrigerant mixture into a higher boiling fraction
and a lower boiling fraction; recovering a fluid fraction from a
partial stream of the lower boiling fraction; supercooling and
expanding the fluid fraction to a pressure of the higher boiling
fraction; and providing the fluid fraction to a compressor stage to
which the higher boiling fraction is taken.
17. The method according to claim 16, wherein the lower boiling
fraction is taken to a first stage of the compressor.
18. The method according to claim 17, wherein the higher boiling
fraction is taken to a second stage of the compressor.
19. The method according to claim 16, wherein the fluid fraction is
supercooled in the heat exchanger.
20. The method according to claim 16, wherein the fluid fraction is
expanded in an expansion valve external to the heat exchanger.
21. The method according to claim 16, wherein the fluid fraction is
recovered in a separator.
22. The method according to claim 16, wherein the partial stream of
the lower boiling fraction is taken from the lower boiling fraction
in the heat exchanger.
23. The method according to claim 16, wherein after the step of
expanding the fluid fraction, the fluid fraction is provided to the
heat exchanger.
24. The method according to claim 21, wherein the fluid fraction is
drawn off from a bottom of the separator.
25. The method according to claim 24, wherein a gaseous fraction of
the partial stream of the lower boiling fraction is drawn off at a
head of the separator.
26. The method according to claim 24, wherein the gaseous fraction
is provided to the heat exchanger.
27. The method according to claim 26, wherein the gaseous fraction
is provided to the lower boiling fraction.
Description
[0001] This application claims the priority of International
Application No. PCT/EP2006/001804, filed Feb. 28, 2006, and German
Patent Document No. 10 2005 010 055.4, filed Mar. 4, 2005, the
disclosures of which are expressly incorporated by reference
herein.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] The invention relates to a process for liquefying a
hydrocarbon-rich stream, specifically a natural gas stream.
[0003] Natural gas liquefaction plants are laid out either as what
are known as LNG baseload plants--plants for liquefying natural gas
to provide natural gas as primary energy--or as what are known as
peak shaving plants--plants for liquefying natural gas to meet peak
demands.
[0004] Larger LNG plants are usually operated with refrigeration
circuits which consist of hydrocarbon mixtures. These mixture
circuits are more energy-efficient than expander circuits and allow
relatively low specific energy consumption.
[0005] From German Patent Document No. DE-A 102 09 799 a process
for liquefying a hydrocarbon-rich stream, specifically a natural
gas stream, is known in accordance with which the liquefaction of
the hydrocarbon-rich stream takes place in the heat exchange
countercurrent to a two-component refrigerant mixture stream; the
one component is a part of the hydrocarbon-rich stream to be
liquefied, while the other component is a heavy hydrocarbon,
preferably propane or propylene. Before the cooling and the
expansion to provide refrigeration of these components, the
refrigerant mixture is separated into a higher boiling and a lower
boiling refrigerant fraction.
[0006] A disadvantage of the procedure described in DE-A 102 09 799
is that providing two refrigerant components can result in
relatively large temperature differences in the heat exchangers.
These temperature differences in turn require correspondingly high
compressor performance.
[0007] A similar process for liquefying a hydrocarbon-rich stream
is known from U.S. Pat. No. 6,347,531. In this process, the
low-pressure refrigerant is inducted cold through the circulating
compressor. These cold-inducting compressors have the disadvantage
that in operation, in particular during start-up and shut-down,
they are more complicated to operate than compressors not inducting
cold. Furthermore, in the liquefaction process described in U.S.
Pat. No. 6,347,531 it is disadvantageous that the refrigerant is
partially liquefied at an intermediate pressure, which results in
greater expense for equipment.
[0008] The object of the present invention is to specify a generic
process for liquefying a hydrocarbon-rich stream, specifically of a
natural gas stream, which avoids the disadvantages of the known
processes and in addition allows a lower specific energy
requirement to be realized.
[0009] To achieve this object, a generic process for liquefying a
hydrocarbon-rich stream is proposed, wherein:
[0010] the liquefaction of the hydrocarbon-rich stream takes place
in the heat exchange countercurrent to a three- or multi-component
refrigerant mixture,
[0011] one of the components is a part of the hydrocarbon-rich
stream to be liquefied,
[0012] one of the components is propane, propylene or a C.sub.4
hydrocarbon,
[0013] one of the components is C.sub.2H.sub.4 or
C.sub.2H.sub.6,
[0014] the compression of the refrigerant mixture stream takes
place by means of an at least two-stage compression,
[0015] before the cooling and the expansion of the refrigerant
mixture to provide refrigeration, the refrigerant mixture is
separated into a higher boiling and a lower boiling refrigerant
fraction, and
[0016] the higher boiling and the lower boiling refrigerant
fractions, after their expansion to provide refrigeration are taken
at different pressures to compression.
[0017] Surprisingly, it has been shown that the specific
expenditure of energy for liquefaction by means of the process in
accordance with the invention can be reduced by approximately 30%.
Furthermore, the temperature differences within the heat exchanger
or heat exchangers can be reduced significantly. The result is that
transient operation is easier to control.
[0018] Additional advantageous embodiments of the process in
accordance with the invention for liquefying a hydrocarbon-rich
stream are:
[0019] the refrigerant mixture is a three-component refrigerant
mixture,
[0020] the refrigerant fractions are cooled separately, expanded
separately to provide refrigeration and heated separately
countercurrent to the hydrocarbon-rich stream to be liquefied,
[0021] a further component of the refrigerant mixture is
nitrogen,
[0022] compression of the refrigerant mixture stream takes place by
means of an at least two-stage compression and the higher boiling
refrigerant fraction is admixed to the lower boiling refrigerant
fraction at an intermediate pressure level,
[0023] at least one C.sub.4 to C.sub.6 hydrocarbon is used as
further component(s) of the refrigerant mixture; the use of
additional refrigerant components makes sense in particular at
greater liquefaction outputs above 10 t/h, and
[0024] at least one partial stream of the lower boiling refrigerant
fractions is partially condensed and the liquid fraction obtained
thereby is supercooled and expanded.
[0025] The process in accordance with the invention and additional
embodiments of the invention are to be explained in what follows
using the embodiment shown in the drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0026] The FIGURE illustrates an embodiment of the invention for
liquefying a hydrocarbon-rich stream.
DETAILED DESCRIPTION OF THE DRAWING
[0027] In accordance with the procedure shown in the drawing, a
dry, pre-treated hydrocarbon-rich stream, for example natural gas,
is taken to the liquefaction process in accordance with the
invention through line X and liquefied in heat exchanger E and
supercooled if required. The hydrocarbon-rich stream is, as an
example, at a pressure of between 10 and 60 bar. The liquefied and,
if necessary supercooled, hydrocarbon-rich stream is then taken
through line X' for further use. Not shown in the drawing is a
separation, which may have to be provided, of undesirable
components, for example higher hydrocarbons. For this, reference is
made to the appropriate explanations in the aforementioned DE-A 102
09 799.
[0028] The cooling and liquefaction of the hydrocarbon-rich stream
X, X' takes place in accordance with the invention in the heat
exchange countercurrent to a three or more component refrigerant
mixture stream where one of the components is part of the
hydrocarbon-rich stream to be liquefied--preferably methane--one of
the components is propane, propylene or a C.sub.4 hydrocarbon and
one of the components is C.sub.2H.sub.4 or C.sub.2H.sub.6.
[0029] The corresponding refrigeration circuit preferably has a
two-stage compressor unit, consisting of the compressor stages C1
and C2. An air or water cooler--not shown in the drawing--is
located in series with each compressor stage. The refrigeration
circuit further has a high-pressure extractor D. Providing only one
high-pressure separator D reduces the operating cost of the process
in accordance with the invention substantially--compared with the
known refrigerant mixture circuits.
[0030] In the separator D, the refrigerant mixture is separated
into a lower boiling and a higher boiling fraction. The lower
boiling fraction is removed from the separator D through line 2,
cooled in the heat exchanger E, condensed and supercooled and then
expanded at the cold end of the heat exchanger E in expansion valve
b, providing refrigeration. The expanded fraction is again taken to
the heat exchanger E through line 3, evaporated and superheated
therein countercurrent to process streams to be cooled and then
taken to the first compressor stage C1 through line 4.
[0031] Following compression and cooling not shown in the drawing,
the compressed lower boiling fraction is taken to the second
compressor stage C2 through line 8--the admixture of the higher
boiling fraction will be discussed in more detail in what
follows--and compressed to the desired circulation pressure which
is, for example, between 20 and 60 bar. A heat exchanger as cooler
not shown in the drawing is also located in series with the second
compressor stage C2. The refrigerant mixture cooled and partially
condensed in the cooler is taken back to the separator D through
line 1.
[0032] A higher boiling liquid fraction is drawn off from the
bottom of the separator D through line 5, cooled in the heat
exchanger E and then expanded in expansion valve a to the desired
intermediate pressure, providing refrigeration. Then this fraction
is taken back to the heat exchanger E through line 6, evaporated
and superheated therein countercurrent to process streams to be
cooled and then taken through line 7 to the compressor unit ahead
of its second compressor stage C2.
[0033] In accordance with an advantageous embodiment of the
liquefaction process in accordance with the invention, at least one
partial stream 9 of the lower boiling refrigerant fraction 2 can be
drawn off from the heat exchanger following cooling and partial
condensation through the broken line 9, and taken to ("cold")
separator D' indicated by broken lines. The gaseous fraction drawn
off at the head of the separator D' through line 10 indicated by
broken lines, is again returned to the heat exchanger E,
supercooled and expanded for the purpose of providing the peak cold
in valve b required for the liquefaction process.
[0034] The liquid fraction drawn off from the bottom of the
separator D' through the broken line 11 is supercooled in the heat
exchanger E, expanded in valve c providing refrigeration, taken to
the heat exchanger E through line 12 and admixed to the refrigerant
fraction in line 3.
[0035] Additional "cold separators" can be provided in addition to
this separator D'. They result in an improvement of the specific
energy requirement of the liquefaction process in accordance with
the invention, but they make sense only in larger liquefaction
plants because of the additional expense required for
equipment.
[0036] The higher boiling fractions recovered in the separator D'
and any additional "cold separators" are preferably supercooled,
expanded to the pressure of the (first) higher boiling fraction and
taken to the compressor stage to which the (first) higher boiling
fraction is also taken. This embodiment of the process in
accordance with the invention is indicated in the drawing by the
dotted line 13. Depending on the temperature profile in the heat
exchanger E, admixture to the low-pressure refrigerant stream in
line sections 3 and 4 also makes sense.
[0037] In accordance with an advantageous embodiment of the
inventive process, the liquefaction of the hydrocarbon-rich stream
takes place countercurrent to the refrigerant mixture in plate heat
exchangers. Because of the process management in accordance with
the invention, process management can be realized in a single plate
heat exchanger in liquefaction plants having a liquefaction
capacity of up to 10 to 15 t/h.
[0038] The process in accordance with the invention to liquefy a
hydrocarbon-rich stream, specifically a natural gas stream, avoids
all the disadvantages of the prior art cited at the beginning.
* * * * *