U.S. patent application number 14/410803 was filed with the patent office on 2015-11-26 for system and method for liquefying natural gas.
The applicant listed for this patent is KOREA INSTITUTE OF ENERGY RESEARCH. Invention is credited to Hee-Tae BEUM, Tae Sung JUNG, Jong-Ho PARK, Jong-kee PARK, Hyung Chul YOON.
Application Number | 20150338161 14/410803 |
Document ID | / |
Family ID | 49783509 |
Filed Date | 2015-11-26 |
United States Patent
Application |
20150338161 |
Kind Code |
A1 |
PARK; Jong-Ho ; et
al. |
November 26, 2015 |
SYSTEM AND METHOD FOR LIQUEFYING NATURAL GAS
Abstract
Provided is a system for liquefying natural gas including: a
pre-cooling means; a gas-liquid separating means; a first heat
exchanging means; a second heat exchanging means; a first expanding
means; a second expanding means; a first mixed refrigerant
converting means; a pre-cooled refrigerant supplying means; a
natural gas supplying means; and a mixer. Provided is also a method
for liquefying natural gas including: a first pre-cooling operation
(S01); a first mixed refrigerant separating operation (S02); a
first introducing operation (S03); a first expanded refrigerant
forming operation (S04); a second introducing operation (S05); a
second expanded refrigerant forming operation (S06); and a second
cooling operation (S07).
Inventors: |
PARK; Jong-Ho; (Daejeon,
KR) ; PARK; Jong-kee; (Daejeon, KR) ; YOON;
Hyung Chul; (Daejeon, KR) ; JUNG; Tae Sung;
(Daejeon, KR) ; BEUM; Hee-Tae; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOREA INSTITUTE OF ENERGY RESEARCH |
Daejeon |
|
KR |
|
|
Family ID: |
49783509 |
Appl. No.: |
14/410803 |
Filed: |
June 27, 2013 |
PCT Filed: |
June 27, 2013 |
PCT NO: |
PCT/KR2013/005678 |
371 Date: |
December 23, 2014 |
Current U.S.
Class: |
62/611 |
Current CPC
Class: |
F25J 1/0055 20130101;
F25J 1/0216 20130101; F25J 1/0052 20130101; F25J 1/0022 20130101;
F25J 1/0262 20130101; F25J 1/0292 20130101; F25J 1/0214
20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2012 |
KR |
10-2012-0071377 |
Claims
1. A system for liquefying natural gas, comprising: a pre-cooling
means; a gas-liquid separating means connected to the pre-cooling
means; a first heat exchanging means connected to the pre-cooling
means and the gas-liquid separating means, respectively; a second
heat exchanging means connected to the first heat exchanging means;
a first expanding means having one end which is connected to the
first heat exchanging means; a second expanding means having both
ends which are each connected to the second heat exchanging means;
a first mixed refrigerant converting means connected to the
pre-cooling means and the first heat exchanging means,
respectively; a pre-cooled refrigerant supplying means connected to
the pre-cooling means; a natural gas supplying means connected to
the pre-cooling means; and a mixing means connecting the other end
of the first expanding means and the first heat exchanging means to
each other and connected to the second heat exchanging means.
2. The system for liquefying natural gas of claim 1, wherein the
first heat exchanging means is a first heat exchanger connected to
the pre-cooling means and the gas-liquid separating means, and the
second heat exchanging means is a third heat exchanger connected to
the first heat exchanger.
3. The system for liquefying natural gas of claim 1, wherein the
first heat exchanging means is a first heat exchanger connected to
the pre-cooling means and the gas-liquid separating means, and a
second heat exchanger connected to the first heat exchanger, and
the second heat exchanging means is a third heat exchanger
connected to the second heat exchanger, and a fourth heat exchanger
connected to the third heat exchanger.
4. The system for liquefying natural gas of claim 3, wherein the
first expanding means has one end connected to the first heat
exchanger and the other end connected to the second heat exchanger,
and the second expanding means has one end connected to the third
heat exchanger and the other end connected to the fourth heat
exchanger.
5. The system for liquefying natural gas of claim 1, wherein the
first mixed refrigerant converting means supplies a first mixed
refrigerant to the pre-cooling means, the pre-cooled refrigerant
supplying means supplies a pre-cooled refrigerant to the
pre-cooling means, the natural gas supplying means supplies natural
gas to the pre-cooling means, the pre-cooling means pre-cools the
first mixed refrigerant and the natural gas which are each supplied
from the pre-cooling means and the natural gas supplying means
using the pre-cooled refrigerant supplied from the first mixed
refrigerant converting means, the gas-liquid separating means
separates the first mixed refrigerant introduced from the
pre-cooling means into a first separated refrigerant of a liquid
state and a second separated refrigerant of a gas state, the first
heat exchanging means introduces the natural gas, the first
separated refrigerant, and the second separated refrigerant from
the pre-cooling means, cools the natural gas, the first separated
refrigerant, and the second refrigerant using a mixed refrigerant,
and forms the first separated refrigerant at high temperature by
cooling less the first separated refrigerant than the natural gas
and the second separated refrigerant, the first expanding means
forms a first expanded refrigerant by expanding the first separated
refrigerant introduced from the first heat exchanging means, the
second heat exchanging means introduces the natural gas and the
second separated refrigerant from the first heat exchanging means,
cools the natural gas and the second separated refrigerant using a
second expanded refrigerant, forms the second separated refrigerant
at high temperature by cooling less the second separating
refrigerant than the natural gas, and forms liquefied natural gas
by over-cooling the natural gas, the second expanding means
supplies the second expanded refrigerant formed by expanding the
second separated refrigerant introduced from the second heat
exchanging means to the second heat exchanging means, and the
mixing means supplies the mixed refrigerant formed by mixing a
portion of the first expanded refrigerant introduced from the first
expanding means and the second expanded refrigerant introduced from
the second heat exchanging means to the first heat exchanging
means.
6. The system for liquefying natural gas of claim 5, wherein the
pre-cooled refrigerant is a single refrigerant or a second mixed
refrigerant.
7. The system for liquefying natural gas of claim 5, wherein the
first mixed refrigerant converting means converts a mixed
refrigerant introduced from the first heat exchanging means into a
first mixed refrigerant by sequentially compressing and cooling the
mixed refrigerant introduced from the first heat exchanging means
and supplies the first mixed refrigerant to the pre-cooling
means.
8. A method for liquefying natural gas, comprising: a first
pre-cooling operation pre-cooling a first mixed refrigerant and
natural gas; a first mixed refrigerant separating operation
separating the first mixed refrigerant into a first separated
refrigerant of a liquid state and a second separated refrigerant of
a gas state, respectively; a first introducing operation
introducing the natural gas, the first separated refrigerant, and
the second separated refrigerant into a first heat exchanging
region without being mixed; a first expanded refrigerant forming
operation forming a first expanded refrigerant by introducing the
first separated refrigerant into a first expanding region and
expanding the first separated refrigerant which is introduced into
the first expanding region; a second introducing operation
introducing the natural gas and the second separated refrigerant
into a second heat exchanging region without being mixed; a second
expanded refrigerant forming operation forming a second expanded
refrigerant by introducing the second separated refrigerant into a
second expanding region and expanding the second separated
refrigerant which is introduced into the second expanding region;
an over-cooling operation cooling the natural gas and the second
separated refrigerant which were introduced into the second heat
exchanging region by supplying the second expanded refrigerant to
the second heat exchanging region, forming the second separated
refrigerant at high temperature by cooling less the second
separated refrigerant than the natural gas, and forming liquefied
natural gas by over-cooling the natural gas; a mixed refrigerant
forming operation forming a mixed refrigerant by mixing the second
expanded refrigerant and the first expanded refrigerant; and a
cooling operation cooling the natural gas, the first separated
refrigerant, and the second separated refrigerant which were
introduced into the first heat exchanging region by supplying the
mixed refrigerant to the first heat exchanging region, and forming
the first separated refrigerant at high temperature by cooling less
the first separated refrigerant than the natural gas and the second
separated refrigerant.
9. The method for liquefying natural gas of claim 8, wherein in the
first pre-cooling operation, the first mixed refrigerant and the
natural gas are pre-cooled using a single refrigerant or a second
mixed refrigerant.
10. The method for liquefying natural gas of claim 8, further
comprising: a converting operation converting the mixed refrigerant
into the first mixed refrigerant by sequentially compressing and
cooling the mixed refrigerant; a second pre-cooling operation
pre-cooling the first mixed refrigerant and the natural gas; and a
repetition cycle operation repeating the first mixed refrigerant
separating operation to the second pre-cooling operation as one
period one or more times.
11. The method for liquefying natural gas of claim 10, wherein in
the second pre-cooling operation, the first mixed refrigerant and
the natural gas are pre-cooled using a single refrigerant or a
second mixed refrigerant.
Description
TECHNICAL FIELD
[0001] The present invention relates to a system and a method for
liquefying natural gas, and more particularly, to a system and a
method for liquefying natural gas using freezing, liquefaction or
coagulation.
BACKGROUND ART
[0002] A thermodynamic process of liquefying natural gas to produce
liquefied natural gas (LNG) has been developed since the 1970s in
order to satisfy various problems including demands for higher
efficiency and larger capacity. In order to satisfy these demands,
that is, increase efficiency and capacity of a liquefying process,
various attempts to liquefy natural gas using different
refrigerants or different cycles have been continuously conducted
up to now. However, currently, the number of liquefaction processes
that are practically used is very small.
[0003] One of the liquefaction processes that are being operated
and have been most widely spread is a `propane pre-cooled mixed
refrigerant process (or a C3/MR process)`.
[0004] FIG. 1 is a flowchart of a C3/MR process.
[0005] As shown in FIG. 1, in the C3/MR process, natural gas is
pre-cooled up to approximately 238 K by a multi-stage of propane
(C3) Joule-Thomson (JT) cycle. The pre-cooled natural gas is
liquefied and sub-cooled up to 123 K by heat exchange with a mixed
refrigerant (MR) in a heat exchanger.
[0006] In this case, in describing a freezing cycle of the mixed
refrigerant in more detail, the mixed refrigerant is compressed at
high pressure, cooled, and then introduced into a gas-liquid
separator 10.
[0007] The mixed refrigerant is separated into a gas state (light
components) and a liquid state (heavy components) by the gas-liquid
separator 10, which are each introduced into a primary heat
exchanger 20, wherein the mixed refrigerant in the liquid state is
expanded once a primary heat exchange is completed in the primary
heat exchanger 20, and is used for cooling a high temperature
stream introduced into the primary heat exchanger 20. The mixed
refrigerant in the gas state is introduced into a secondary heat
exchanger 30 and is cooled therein. The mixed refrigerant in the
gas state is further cooled by expansion and is used for cooling
the secondary heat exchanger 30 and the primary heat exchanger
20.
[0008] The above-mentioned C3/MR process has a disadvantage that
the heat exchangers 20 and 30 have low heat exchanging
efficiency.
[0009] As the related art, U.S. Pat. No. 6,691,531 B1 has been
suggested and various developments of a system for liquefying
natural gas for solving the above-mentioned problem have been
required.
RELATED ART DOCUMENT
[0010] (Patent Document 1) U.S. Pat. No. 6,691,531 B1
(2004.02.17)
DISCLOSURE
Technical Problem
[0011] An object of the present invention is to provide a system
and a method for liquefying natural gas capable of maximizing heat
exchanging efficiency and energy saving efficiency by improving a
configuration of a heat exchanger.
Technical Solution
[0012] In one general aspect, a system for liquefying natural gas
includes: a pre-cooling means 100; a gas-liquid separating means
200 connected to the pre-cooling means 100; a first heat exchanging
means 300 connected to the pre-cooling means 100 and the gas-liquid
separating means 200, respectively; a second heat exchanging means
400 connected to the first heat exchanging means 300; a first
expanding means 510 having one end which is connected to the first
heat exchanging means 300; a second expanding means 520 having both
ends which are each connected to the second heat exchanging means
400; a first mixed refrigerant converting means 600 connected to
the pre-cooling means 100 and the first heat exchanging means 300,
respectively; a pre-cooled refrigerant supplying means 700
connected to the pre-cooling means 100; a natural gas supplying
means 800 connected to the pre-cooling means 100; and a mixing
means 900 connecting the other end of the first expanding means 510
and the first heat exchanging means 300 to each other and connected
to the second heat exchanging means 400.
[0013] The first heat exchanging means 300 may be a first heat
exchanger 310 connected to the pre-cooling means 100 and the
gas-liquid separating means 200, and the second heat exchanging
means 400 may be a third heat exchanger 410 connected to the first
heat exchanger 310.
[0014] The first heat exchanging means 300 may be a first heat
exchanger 310 connected to the pre-cooling means 100 and the
gas-liquid separating means 200 and a second heat exchanger 320
connected to the first heat exchanger 310, and the second heat
exchanging means 400 may be a third heat exchanger 410 connected to
the second heat exchanger 320 and a fourth heat exchanger 420
connected to the third heat exchanger 410.
[0015] The first expanding means 510 may have one end connected to
the first heat exchanger 310 and the other end connected to the
second heat exchanger 320, and the second expanding means 520 may
have one end connected to the third heat exchanger 410 and the
other end connected to the fourth heat exchanger 420.
[0016] The first mixed refrigerant converting means 600 may supply
a first mixed refrigerant to the pre-cooling means 100, the
pre-cooled refrigerant supplying means 700 may supply a pre-cooled
refrigerant to the pre-cooling means 100, the natural gas supplying
means 800 may supply natural gas to the pre-cooling means 100, the
pre-cooling means 100 may pre-cool the first mixed refrigerant and
the natural gas which are each supplied from the pre-cooling means
100 and the natural gas supplying means 800 using the pre-cooled
refrigerant supplied from the first mixed refrigerant converting
means 600, the gas-liquid separating means 200 may separate the
first mixed refrigerant introduced from the pre-cooling means 100
into a first separated refrigerant of a liquid state and a second
separated refrigerant of a gas state, the first heat exchanging
means 300 may introduce the natural gas, the first separated
refrigerant, and the second separated refrigerant from the
pre-cooling means 100, cool the natural gas, the first separated
refrigerant, and the second refrigerant using a mixed refrigerant,
and form the first separated refrigerant at high temperature by
cooling less the first separated refrigerant than the natural gas
and the second separated refrigerant, the first expanding means 510
may form a first expanded refrigerant by expanding the first
separated refrigerant introduced from the first heat exchanging
means 300, the second heat exchanging means 400 may introduce the
natural gas and the second separated refrigerant from the first
heat exchanging means 300, cool the natural gas and the second
separated refrigerant using a second expanded refrigerant, form the
second separated refrigerant at high temperature by cooling less
the second separating refrigerant than the natural gas, and form
liquefied natural gas by over-cooling the natural gas, the second
expanding means 520 may supply the second expanded refrigerant
formed by expanding the second separated refrigerant introduced
from the second heat exchanging means 400 to the second heat
exchanging means 400, and the mixing means 900 may supply the mixed
refrigerant formed by mixing a portion of the first expanded
refrigerant introduced from the first expanding means 510 and the
second expanded refrigerant introduced from the second heat
exchanging means 400 to the first heat exchanging means 300.
[0017] The pre-cooled refrigerant may be a single refrigerant or a
second mixed refrigerant.
[0018] The first mixed refrigerant converting means 600 may convert
a mixed refrigerant introduced from the first heat exchanging means
300 into a first mixed refrigerant by sequentially compressing and
cooling the mixed refrigerant introduced from the first heat
exchanging means 300 and supply the first mixed refrigerant to the
pre-cooling means 100.
[0019] In another general aspect, a method for liquefying natural
gas includes: a first pre-cooling operation S01 pre-cooling a first
mixed refrigerant and natural gas; a first mixed refrigerant
separating operation S02 separating the first mixed refrigerant
into a first separated refrigerant of a liquid state and a second
separated refrigerant of a gas state, respectively; a first
introducing operation S03 introducing the natural gas, the first
separated refrigerant, and the second separated refrigerant into a
first heat exchanging region without being mixed; a first expanded
refrigerant forming operation S04 forming a first expanded
refrigerant by introducing the first separated refrigerant into a
first expanding region and expanding the first separated
refrigerant which is introduced into the first expanding region; a
second introducing operation S05 introducing the natural gas and
the second separated refrigerant into a second heat exchanging
region without being mixed; a second expanded refrigerant forming
operation S06 forming a second expanded refrigerant by introducing
the second separated refrigerant into a second expanding region and
expanding the second separated refrigerant which is introduced into
the second expanding region; an over-cooling operation S07 cooling
the natural gas and the second separated refrigerant which were
introduced into the second heat exchanging region by supplying the
second expanded refrigerant to the second heat exchanging region,
forming the second separated refrigerant at high temperature by
cooling less the second separated refrigerant than the natural gas,
and forming liquefied natural gas by over-cooling the natural gas;
a mixed refrigerant forming operation S08 forming a mixed
refrigerant by mixing the second expanded refrigerant and the first
expanded refrigerant; and a cooling operation S09 cooling the
natural gas, the first separated refrigerant, and the second
separated refrigerant which were introduced into the first heat
exchanging region by supplying the mixed refrigerant to the first
heat exchanging region, and forming the first separated refrigerant
at high temperature by cooling less the first separated refrigerant
than the natural gas and the second separated refrigerant.
[0020] In the first pre-cooling operation S01, the first mixed
refrigerant and the natural gas may be pre-cooled using a single
refrigerant or a second mixed refrigerant.
[0021] The method for liquefying natural gas may further include: a
converting operation S10 converting the mixed refrigerant into the
first mixed refrigerant by sequentially compressing and cooling the
mixed refrigerant; a second pre-cooling operation S11 pre-cooling
the first mixed refrigerant and the natural gas; and a repetition
cycle operation S12 repeating the first mixed refrigerant
separating operation S02 to the second pre-cooling operation S11 as
one period one or more times.
[0022] In the second pre-cooling operation S11, the first mixed
refrigerant and the natural gas may be pre-cooled using a single
refrigerant or a second mixed refrigerant.
Advantageous Effects
[0023] According to the present invention, the temperature
difference between the refrigerant introduced into the first heat
exchanging means and the natural gas is decreased, such that the
energy consumption for liquefying the natural gas may be saved.
DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a flowchart of a conventional C3/MR process.
[0025] FIG. 2 is a system for liquefying natural gas according to a
first exemplary embodiment of the present invention.
[0026] FIG. 3 is a system for liquefying natural gas according to a
second exemplary embodiment of the present invention.
[0027] FIG. 4 is a system for liquefying natural gas according to a
third exemplary embodiment of the present invention.
[0028] FIG. 5 is a system for liquefying natural gas according to a
fourth exemplary embodiment of the present invention.
[0029] FIG. 6 is a method for liquefying natural gas according to
the present invention.
BEST MODE
[0030] Hereinafter, a technical spirit of the present invention
will be described in more detail with reference to the accompanying
drawings.
[0031] The accompanying drawings are only examples shown in order
to describe the technical spirit of the present invention in more
detail. Therefore, the technical spirit of the present invention is
not limited to shapes of the accompanying drawings.
[0032] FIG. 2 is a system for liquefying natural gas according to a
first exemplary embodiment of the present invention.
[0033] As shown in FIG. 2, a system 1000a for liquefying natural
gas according to a first exemplary embodiment of the present
invention is configured to include a pre-cooling means 100, a
gas-liquid separating means 200, a first heat exchanging means 300,
a second heat exchanging means 400, a first expanding means 510, a
second expanding means 520, a first mixed refrigerant converting
means 600, a pre-cooled refrigerant supplying means 700, a natural
gas supplying means 800, and a mixing means 900.
[0034] The components of the system 1000a for liquefying natural
gas according to the first exemplary embodiment of the present
invention are connected to each other by a plurality of pipes. A
detailed description thereof is as follows.
[0035] A first pipe sequentially connects the natural gas supplying
means 800, the pre-cooling means 100, the first heat exchanging
means 300, and the second heat exchanging means 400, and is
connected to the pre-cooling means 100, the first heating
exchanging means 300, and the second heat exchanging means 400,
respectively, so as to penetrate therethrough.
[0036] A second pipe, which has a cycle shape, connects the
pre-cooled refrigerant supplying means 700 and the pre-cooling
means 100 to each other.
[0037] A third pipe sequentially connects the first mixed
refrigerant converting means 600, the pre-cooling means 100, and
the gas-liquid separating means 200, and is connected to the
pre-cooling means 100 so as to penetrate therethrough.
[0038] A fourth pipe sequentially connects the gas-liquid
separating means 200, the first heat exchanging means 300, the
first expanding means 510, the mixing means 900, the first heat
exchanging means 300, and the first mixed refrigerant converting
means 600, and is connected to the first heat exchanging means 300
so as to penetrate therethrough two times.
[0039] Particularly, in connecting the gas-liquid separating means
200, the first heat exchanging means 300, and the first expanding
means by the fourth pipe, the fourth pipe is connected from the
gas-liquid separating means 200 to a central portion of the first
heat exchanging means 300, is led to a lower side or an upper side
of the first heat exchanging means 300, and is then connected to
the first expanding means 510.
[0040] That is, the fourth pipe is formed so as not to straightly
penetrate through the first heat exchanging means 300.
[0041] A fifth pipe sequentially connects the gas-liquid separating
means 200, the first heat exchanging means 300, the second heat
exchanging means 400, the second expanding means 520, the second
heat exchanging means 400, and the mixing means 900, is connected
to the first heat exchanging means 300 so as to penetrate
therethrough, and is connected to the second heat exchanging means
400 so as to penetrate therethrough two times.
[0042] Next, the components of the system for liquefying natural
gas according to the first exemplary embodiment of the present
invention will be described in detail.
[0043] The first mixed refrigerant converting means 600 is
configured to include a first MR compressor 610 and a first MR
cooler 620.
[0044] The first MR compressor 610 is configured by a three-stage
compressor and compresses the first mixed refrigerant.
[0045] The first MR cooler 620 introduces the first mixed
refrigerant which is compressed in the first MR compressor 610
thereinto, cools the first mixed refrigerant and then supplies it
to the pre-cooling means 100.
[0046] That is, the first mixed refrigerant converting means 600
has a configuration for compressing and cooling the first mixed
refrigerant and supplying it to the pre-cooling means 100.
[0047] The pre-cooled refrigerant supplying means 700 is configured
to include a C3 compressor 710, a C3 cooler 720, and a C3 expansion
valve 730.
[0048] In addition, the pre-cooled refrigerant supplying means 700
sequentially compresses, cools, and expands a single refrigerant
using the C3 compressor 710, the C3 cooler 720, and the C3
expansion valve 730, and supplies it to the pre-cooling means
100.
[0049] In this case, as the single refrigerant, propane is used,
the C3 compressor 710 is configured by a four-stage compressor, and
the C3 expansion valve 730 is configured by a four-stage
Joule-Thomson valve.
[0050] The natural gas supplying means 800, which is a tank in
which natural gas is stored, supplies the stored natural gas to the
pre-cooling means 100.
[0051] The pre-cooling means 100 independently introduces the first
mixed refrigerant from the first mixed refrigerant converting means
600, the single refrigerant from the pre-cooled refrigerant
supplying means 700, and the natural gas from the natural gas
supplying means 800, respectively.
[0052] In addition, the pre-cooling means 100 pre-cools the first
mixed refrigerant and the natural gas using the single
refrigerant.
[0053] The gas-liquid separating means 200 introduces the first
mixed refrigerant from the pre-cooling means 100 and separates it
into a first separated refrigerant in a liquid state and a second
separated refrigerant in a gas state, respectively.
[0054] The first heat exchanging means 300 is configured by a first
heat exchanger 310, independently introduces the natural gas from
the pre-cooling means 100, independently introduces the first
separated refrigerant and the second separated refrigerant,
respectively, from the gas-liquid separating means 200, cools the
natural gas, the first separated refrigerant and the second
separated refrigerant using a mixed refrigerant introduced into the
first heat exchanging means 300 through several post-processes, and
forms the first separated refrigerant at high temperature by
cooling less the first separated refrigerant than the natural gas
and the second separated refrigerant.
[0055] Here, the mixed refrigerant will be described below.
[0056] The first expanding means 510, which is an expansion valve
disposed at the lower side or the upper side of the first heat
exchanger 310, is connected to the central portion of the first
heat exchanger 310 by the fourth pipe to forcedly introduce and
expand the first separated refrigerant from the first heat
exchanger 310, thereby forming a first expanded refrigerant.
[0057] That is, the first expanding means 510 forcedly extracts the
first separated refrigerant introduced into the first heat
exchanger 310 from the central portion of the first exchanger
310.
[0058] The second heat exchanging means 400 is configured by a
third heat exchanger 410, independently introduces the second
separated refrigerant and the natural gas from the first heat
exchanger 310, and cools the natural gas and the second separated
refrigerant using a second expanded refrigerant introduced into the
second heat exchanging means 400 through several post-processes,
wherein the second heat exchanging means 400 forms the second
separated refrigerant at high temperature by cooling less the
second separated refrigerant than the natural gas and forms
liquefied natural gas by over-cooling the natural gas.
[0059] Here, the second expanded refrigerant will be described
below.
[0060] The second expanding means 520, which is an expansion valve,
forms the second expanded refrigerant by introducing and expanding
the second separated refrigerant from the third heat exchanger 410
and supplies the second expanded refrigerant which is formed to the
third heat exchanger 410.
[0061] The mixing means 900 supplies the mixed refrigerant formed
by mixing the first expanded refrigerant introduced from the first
expanding means 510 and the second expanded refrigerant introduced
from the third heat exchanger 410 to the first heat exchanger
310.
[0062] Consequently, according to the present invention, as a final
discharging temperature difference between the mixed refrigerant
introduced from the mixing means 900 to the first heat exchanging
means 300 and the natural gas and the second separated refrigerant
which are cooled in the first heat exchanging means 300 is
decreased, heat exchanging efficiency is increased, thereby making
it possible to reduce energy consumption for liquefying the natural
gas.
[0063] Meanwhile, the first mixed refrigerant converting means 600
sequentially compresses and cools the mixed refrigerant introduced
from the first heat exchanger 310 to again supply it to the
pre-cooling means 100.
[0064] That is, the first mixed refrigerant converting means 600
converts the mixed refrigerant into the first mixed refrigerant and
again supplies it to the pre-cooling means 100.
[0065] Experiment results of a process for liquefying natural gas
using a system 1000a for liquefying natural gas according to the
first exemplary embodiment of the present invention are as
follows.
TABLE-US-00001 TABLE 1 Component Mol % Nitrogen 0.22 Methane 91.33
Ethane 5.36 Propane 2.14 I-butane 0.46 n-butane 0.47 I-pentane 0.01
n-pentane 0.01
TABLE-US-00002 TABLE 2 Pressure(Bar) 53 Temperature(.degree. C.) 45
Flow Rate(kmol/hr) 35065
[0066] The natural gas is composed of compositions illustrated in
Table 1, has pressure and temperature illustrated in Table 2, and
sequentially passes through the pre-cooling means 100, the first
heat exchanging means 300, and the second heat exchanging means
400.
[0067] The single refrigerant (propane) is compressed in four
stages by the C3 compressor 710 of the pre-cooled refrigerant
supplying means 700 to have pressure of 16.4 bar, is expanded in a
four stages by the C3 expander 730 to sequentially have pressure of
7.5 bar, 4.2 bar, 2.5 bar, 1.114 bar, and is supplied to the
pre-cooling means 100.
TABLE-US-00003 TABLE 3 mole fraction (--) N2 0.0827 C1 0.4555 C2
0.3062 C3 0.1555
[0068] The first mixed refrigerant is composed of compositions
illustrated in Table 3, is compressed in three-stages by the first
MR compressor 610 of the first mixed refrigerant converting means
600 to have pressure of 60 bar, is pre-cooled through the
pre-cooling means 100, and is then separated into the first
separated refrigerant of the liquid state and the second separated
refrigerant of the liquid state through the gas-liquid separator
200.
[0069] The first separated refrigerant is introduced into the first
expanding means 510 through the first heat exchanging means 300 and
is expanded therein, is formed to be the first expanded refrigerant
having pressure of 4 bar, and then introduced into the mixer
900.
[0070] The second separated refrigerant is introduced into the
second expanding means 520 through the second heat exchanging means
400 and expanded therein, next formed to be the second expanded
refrigerant, and then introduced into the mixer 900 through the
second heat exchanging means 400 again.
[0071] The mixer 900 introduces the mixed refrigerant formed by
mixing the first expanded refrigerant and the second expanded
refrigerant into the first heat exchanging means 300.
[0072] Meanwhile, the first separated refrigerant, the second
separated refrigerant, and the natural gas which are introduced
into the first heat exchanging means 300 are cooled by the mixed
refrigerant introduced from the mixer 900.
[0073] In this case, a temperature difference between the first
separated refrigerant, the second separated refrigerant, and the
natural gas which are introduced into the first heat exchanging
means 300 and the mixed refrigerant which is again introduced into
the first heat exchanging means 300 through several processes was
maintained at 4K, and power consumed in liquefying the natural gas
in the case the above-mentioned temperature difference is
maintained was 203900 KW.
[0074] Power consumed for liquefying the natural gas using a
general C3/MR process is 210700 KW. Therefore, the system for
liquefying natural gas according to the first exemplary embodiment
of the present invention may reduce the power as much as 6800 KW as
compared to the general C3/MR process.
[0075] The present applicant has empirically and experimentally
devised the experiment results as described above.
[0076] FIG. 3 is a system for liquefying natural gas according to a
second exemplary embodiment of the present invention.
[0077] As shown in FIG. 3, a system 1000b for liquefying natural
gas according to the second exemplary embodiment of the present
invention has the same configuration as that of the system 1000a
for liquefying natural gas according to the first exemplary
embodiment of the present invention, but has different
configurations of the first pipe, the fourth pipe, the fifth pipe,
the first heat exchanging means 300, and the second heat exchanging
means 400.
[0078] The first heat exchanging means 300 is configured to include
a first heat exchanger 310 and a second heat exchanger 320, and the
second exchanging means 400 is configured to include a third heat
exchanger 410 and a fourth heat exchanger 420.
[0079] A first pipe sequentially connects the natural gas supplying
means 800, the pre-cooling means 100, the first heat exchanger 310,
the second heat exchanger 320, the third heat exchanger 410, and
the fourth heat exchanger 420, and is connected to the pre-cooling
means 100, the first heat exchanger 310, the second heat exchanger
320, the third heat exchanger 410, and the fourth heat exchanger
420, respectively, so as to penetrate therethrough.
[0080] A fourth pipe sequentially connects the gas-liquid
separating means 200, the first heat exchanger 310, the first
expanding means 510, the mixing means 900, the second heat
exchanger 320, the first heat exchanger 310, and the first mixed
refrigerant converting means 600, and is connected to the second
heat exchanger 320 so as to penetrate therethrough, and connected
to the first heat exchanger 310 so as to penetrate therethrough two
times.
[0081] A fifth pipe sequentially connects the gas-liquid separating
means 200, the first heat exchanger 310, the second heat exchanger
320, the third heat exchanger 410, the second expanding means 520,
the fourth heat exchanger 420, the third heat exchanger 410, and
the mixing means 900, is connected to the first heat exchanger 310,
the second heat exchanger 320, and the fourth heat exchanger 420 so
as to penetrate therethrough, and connected to the third heat
exchanger 410 so as to penetrate therethrough two times.
[0082] According to the system 1000b for liquefying natural gas
according to the second exemplary embodiment of the present
invention, the first heat exchanging means 300 includes the first
heat exchanger 310 and the second heat exchanger 320, such that the
system 1000b for liquefying natural gas according to the second
exemplary embodiment of the present invention may have the same
effect as that of the configuration of the first heat exchanging
means 300 according to the first exemplary embodiment of the
present invention.
[0083] In addition, according to the system 1000b for liquefying
natural gas according to the second exemplary embodiment of the
present invention, the second heat exchanging means 400 includes
the third heat exchanger 410 and the fourth heat exchanger 420,
such that the system 1000b for liquefying natural gas according to
the second exemplary embodiment of the present invention may have
the same effect as that of the configuration of the second heat
exchanging means 400 according to the first exemplary embodiment of
the present invention.
[0084] FIG. 4 is a system for liquefying natural gas according to a
third exemplary embodiment of the present invention.
[0085] As shown in FIG. 4, a system 1000c for liquefying natural
gas according to the third exemplary embodiment of the present
invention has the same configuration as that of the system 1000a
for liquefying natural gas according to the first exemplary
embodiment of the present invention, but has a different
configuration of the pre-cooled refrigerant supplying means
700.
[0086] The pre-cooled refrigerant supplying means 700, which is a
configuration for providing the second mixed refrigerant to the
pre-cooling means 100, is configured to include a second MR
compressor 740, a second MR cooler 750, and a second MR expansion
valve 760.
[0087] That is, the pre-cooled refrigerant supplying means 700
supplies the second mixed refrigerant to the pre-cooling means 100
using the second MR compressor 740, the second MR cooler 750, and
the second MR expansion valve 760.
[0088] Here, the second mixed refrigerant is formed of the same
material as that of the first mixed refrigerant.
[0089] FIG. 5 is a system for liquefying natural gas according to a
fourth exemplary embodiment of the present invention.
[0090] As shown in FIG. 5, a system 1000d for liquefying natural
gas according to the fourth exemplary embodiment of the present
invention has the same configuration as that of the system 1000b
for liquefying natural gas according to the second exemplary
embodiment of the present invention, and has the same configuration
of the pre-cooling refrigerant supplying means as that of the third
exemplary embodiment of the present invention.
[0091] FIG. 6 is a method for liquefying natural gas according to
the present invention.
[0092] As shown in FIG. 6, a method for liquefying natural gas
according to the present invention is configured to include a
pre-cooling operation (S01), a first mixed refrigerant separating
operation (S02), a first introducing operation (S03), a first
expanded refrigerant forming operation (S04), a second introducing
operation (S05), a second expanded refrigerant forming operation
(S06), an over-cooling operation (S07), a mixed refrigerant forming
operation (S08), a cooling operation (S09), a converting operation
(S10), a second pre-cooling operation (S11), and a repetition cycle
operation (S12).
[0093] The method for liquefying natural gas according to the
present invention will be described in detail with reference to
FIG. 6.
[0094] First, the first mixed refrigerant and the natural gas which
are supplied from the outside are pre-cooled using the single
refrigerant or the second mixed refrigerant. This corresponds to
the first pre-cooling operation (S01) shown in FIG. 6.
[0095] Next, the first mixed refrigerant which is pre-cooled is
separated into the first separated refrigerant of the liquid state
and the second separated refrigerant of the gas state,
respectively. This corresponds to the first mixed refrigerant
separating operation (S02) shown in FIG. 6.
[0096] Next, the natural gas, the first separated refrigerant, and
the second refrigerant which are pre-cooled are introduced into a
first heat exchanging region without being mixed. This corresponds
to the first introducing operation (S03) shown in FIG. 6.
Meanwhile, the natural gas, the first separated refrigerant, and
the second separated refrigerant which are introduced into the
first heat exchanging region are cooled by the mixed refrigerant,
which will be described below.
[0097] Next, the first separated refrigerant is introduced into the
first expanded region and is expanded therein, thereby forming the
first expanded refrigerant. This corresponds to the first expanded
refrigerant forming operation (S04) shown in FIG. 6.
[0098] Next, the natural gas and the second separated refrigerant
are introduced into the second heat exchanging region without being
mixed. This corresponds to the second introducing operation (S05)
shown in FIG. 6.
[0099] Next, the second separated refrigerant is introduced into
the second expanded region and is expanded therein, thereby forming
the second expanded refrigerant. This corresponds to the second
expanded refrigerant forming operation (S06) shown in FIG. 6.
[0100] Next, the second expanded refrigerant is supplied to the
second heat exchanging region to cool the natural gas and the
second separated refrigerant which were introduced into the second
heat exchanging region in the second introducing operation (S05),
wherein the second separated refrigerant is formed at high
temperature by cooling less the second separated refrigerant than
the natural gas and the liquefied natural gas is formed by
over-cooling the natural gas. This corresponds to the over-cooling
operation (S07) shown in FIG. 6.
[0101] Next, the mixed refrigerant is formed by mixing the second
expanded refrigerant used in the over-cooling operation (S07) and
the first expanded refrigerant formed in the first expanded
refrigerant forming operation (S04). This corresponds to the mixed
refrigerant forming operation (S08) shown in FIG. 6.
[0102] Next, the mixed refrigerant is supplied to the first heat
exchanging region to cool the natural gas, the first separated
refrigerant, and the second separated refrigerant which were
introduced into the first heat exchanging region in the first
introducing operation (S03), wherein the first separated
refrigerant is formed at high temperature by cooling less the first
separated refrigerant than the natural gas and the second separated
refrigerant. This corresponds to the cooling operation (S09) shown
in FIG. 6.
[0103] Next, the mixed refrigerant which was introduced into the
first heat exchanging region is introduced into a converting
region, and is compressed and cooled therein, thereby converting it
into the first mixed refrigerant. This corresponds to the
converting operation (S10) shown in FIG. 6.
[0104] Next, the first mixed refrigerant generated in the
converting operation (S10) and the natural gas which is supplied
from the outside are pre-cooled using the single refrigerant or the
second mixed refrigerant. This corresponds to the second
pre-cooling operation (S11) shown in FIG. 6.
[0105] Next, the first mixed refrigerant separating operation S02
to the second pre-cooling operation S11 are repeated as one period
one or more times. This corresponds to the repetition cycle
operation (S12) shown in FIG. 6.
[0106] The present invention is not limited to the above-mentioned
exemplary embodiments, and may be variously applied, and may be
variously modified without departing from the gist of the present
invention claimed in the claims.
DETAILED DESCRIPTION OF MAIN ELEMENTS
[0107] 1000a, b, c, d: system for liquefying natural gas according
to the present invention [0108] 100: pre-cooling means [0109] 200:
gas-liquid separating means [0110] 300: first heat exchanging means
[0111] 310: first heat exchanger 320 second heat exchanger [0112]
400: second heat exchanging means [0113] 410: third heat exchanger
420 fourth heat exchanger [0114] 510: first expanding means [0115]
520: second expanding means [0116] 600: first mixed refrigerant
converting means [0117] 700: pre-cooled refrigerant supplying means
[0118] 800: natural gas supplying means [0119] 900: mixing
means
* * * * *