U.S. patent application number 16/023885 was filed with the patent office on 2019-02-21 for refrigerant and nitrogen recovery.
The applicant listed for this patent is GE Oil & Gas, LLC. Invention is credited to Karl Erhard Beck, Jay C. Schleicher, Christopher Scott Yount.
Application Number | 20190056175 16/023885 |
Document ID | / |
Family ID | 65359969 |
Filed Date | 2019-02-21 |
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United States Patent
Application |
20190056175 |
Kind Code |
A1 |
Schleicher; Jay C. ; et
al. |
February 21, 2019 |
REFRIGERANT AND NITROGEN RECOVERY
Abstract
Systems, devices, and methods for recovering mixed refrigerant
and/or nitrogen within liquefaction systems are provided. The
systems, devices, and methods facilitate recovering mixed
refrigerant (MR) and/or nitrogen vapor that can leak from a
compressor, separating the MR from the nitrogen, and reusing the MR
and/or the nitrogen within the liquefaction system. Recovering and
reusing MR and/or nitrogen can minimize loss of MR and nitrogen
which can lower the total operating cost of a liquefaction system.
Additionally, recovering the MR, rather than burning it, can reduce
environmental emissions by reducing the amount of MR that is
burned.
Inventors: |
Schleicher; Jay C.; (New
Braunfels, TX) ; Yount; Christopher Scott; (Schertz,
TX) ; Beck; Karl Erhard; (Schertz, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GE Oil & Gas, LLC |
Schertz |
TX |
US |
|
|
Family ID: |
65359969 |
Appl. No.: |
16/023885 |
Filed: |
June 29, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62548163 |
Aug 21, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 2205/02 20130101;
F25J 2270/904 20130101; F25J 2260/20 20130101; F25J 1/025 20130101;
F25J 1/0292 20130101; F25J 3/066 20130101; F25J 1/0052 20130101;
F25J 2230/42 20130101; F25J 1/0022 20130101; F25J 3/061 20130101;
F25J 2205/60 20130101; F25J 1/0212 20130101; F25J 1/0236 20130101;
F25J 2210/62 20130101; F25J 2205/40 20130101; F25J 2230/60
20130101; F25J 1/0045 20130101; F25J 3/0635 20130101; F25J 2270/90
20130101 |
International
Class: |
F25J 1/02 20060101
F25J001/02; F25J 1/00 20060101 F25J001/00 |
Claims
1. A liquefaction system, the system comprising: a first
compressor; a recovery system in fluid communication with the first
compressor, the recovery system comprising a first heat exchanger
configured to receive a first vapor comprising mixed refrigerant
and nitrogen from the first compressor and to convert the first
vapor to a mixture of nitrogen rich vapor and a hydrocarbon rich
liquid, the first heat exchanger having at least one cooling
element configured to receive a cold fluid that provides
refrigeration to the first vapor, and a separator configured to
receive the mixture of hydrocarbon rich liquid and nitrogen rich
vapor from the first heat exchanger, and to separate the
hydrocarbon rich liquid and the nitrogen rich vapor.
2. The liquefaction system of claim 1, further comprising a
nitrogen removal assembly positioned upstream of the first heat
exchanger, the nitrogen removal assembly being configured to
produce the first vapor from a second vapor comprising mixed
refrigerant and nitrogen, wherein the first vapor possesses less
nitrogen than the second vapor.
3. The liquefaction system of claim 2, wherein the nitrogen removal
assembly includes an adsorption bed.
4. The liquefaction system of claim 1, further comprising a
nitrogen removal assembly positioned downstream of the separator,
the nitrogen removal assembly being configured to receive the
nitrogen rich vapor from the separator and to remove a portion of
the nitrogen from the nitrogen rich vapor.
5. The liquefaction system of claim 1, wherein the first compressor
includes a seal assembly that is configured to receive at least a
portion of the nitrogen rich vapor from the separator.
6. The liquefaction system of claim 5, further comprising a second
compressor in fluid communication with the separator, the second
compressor being configured to receive the at least a portion of
the nitrogen rich vapor from the separator and to urge the at least
a portion of the nitrogen rich vapor to the seal assembly.
7. The liquefaction system of claim 1, further comprising a second
heat exchanger in fluid communication with the compressor, the
second heat exchanger being configured to receive a
methane-containing vapor and to convert the methane-containing
vapor to a methane-containing liquid.
8. The liquefaction system of claim 7, wherein the cold fluid
comprises at least a portion of the methane-containing liquid.
9. The liquefaction system of claim 1, further comprising a pump
configured to receive the hydrocarbon rich liquid from the
separator and to pump the hydrocarbon rich liquid to a storage
vessel.
10. A method of operating a liquefaction system, the method
comprising: receiving a seal gas including hydrocarbons at a seal
assembly of a first compressor; receiving a nitrogen vapor at the
seal assembly of the first compressor; receiving, at a first heat
exchanger, a first vapor including at least a portion of the seal
gas and at least a portion of the nitrogen vapor; transferring a
cold fluid to a cooling element of the first heat exchanger;
transferring heat from the first vapor to the cold fluid, thereby
creating a mixture of nitrogen rich vapor and a hydrocarbon rich
liquid; and separating the hydrocarbon rich liquid from the
nitrogen rich vapor at a separator positioned downstream of the
first heat exchanger.
11. The method of claim 10, further comprising: receiving the
nitrogen rich vapor at a second compressor; compressing the
nitrogen rich vapor using the second compressor; and delivering at
least a portion of the nitrogen rich vapor to the seal assembly of
the first compressor.
12. The method of claim 11, further comprising: receiving, at the
second compressor, a portion of the nitrogen vapor from the first
compressor; and combining the portion of the nitrogen vapor
received at the seal assembly with the nitrogen rich vapor.
13. The method of claim 10, wherein the seal gas is a mixed
refrigerant.
14. The method of claim 10, further comprising: receiving a
methane-containing vapor at a second heat exchanger; and removing
heat from the methane-containing vapor within the second heat
exchanger, thereby creating the cold fluid.
15. The method of claim 10, further comprising: receiving a second
vapor at a nitrogen removal assembly positioned upstream of the
first heat exchanger, the second vapor comprising at least a
portion of the seal gas and at least a portion of the nitrogen
vapor; and removing a portion of the nitrogen vapor from the second
vapor, thereby generating the first vapor.
16. The method of claim 10, further comprising: receiving the
nitrogen rich vapor at a nitrogen removal assembly positioned
downstream of the separator; and remove a portion of the nitrogen
from the nitrogen rich vapor.
17. The method of claim 10, further comprising: receiving the
hydrocarbon rich liquid at a pump; and pumping the hydrocarbon rich
liquid to a storage vessel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application No. 62/548,163 entitled "Refrigerant and Nitrogen
Recovery," filed on Aug. 21, 2017, which is hereby incorporated by
reference in its entirety.
FIELD
[0002] Systems and methods are provided for reducing loss of
refrigerant and/or nitrogen in liquefaction systems that liquefy
gases, e.g., natural gas.
BACKGROUND
[0003] Liquefied natural gas ("LNG") is natural gas which has been
cooled to a temperature of approximately -162 degrees Celsius
(.about.-260 degrees Fahrenheit) with a pressure of up to
approximately 25 kPa (4 psig) and has thereby taken on a liquid
state. Natural gas (NG) is primarily composed of methane, and can
include ethane, propane, and heavy hydrocarbon components such as
butanes, pentanes, hexanes, benzene, toluene, ethylbenzene, and
xylenes. Many natural gas sources are located a significant
distance away from the end-consumers. One cost-effective method of
transporting NG over long distances is to liquefy the natural gas,
converting it to liquefied natural gas (LNG), and to transport it
in tanker ships, also known as LNG-tankers. The LNG is transformed
back into gaseous natural gas at the destination.
[0004] In a typical NG liquefaction process, a compressor
compresses a mixed refrigerant MR to an elevated pressure, forming
a pressurized MR. The pressurized MR is delivered to a cold box,
which in turn is used to cool an NG feedstock to form LNG. During
normal operation, and in certain shutdown scenarios, MR and
nitrogen can leak from the compressor. The nitrogen can employed as
part of a dry gas seal employed for containment of MR within the
compressor and mixes with the MR. Often, the leaked MR and nitrogen
are captured and delivered to a flare to be burned. Over time this
lost, flared MR and nitrogen must be replaced for the liquefaction
process to continue, which is costly.
SUMMARY
[0005] Systems, devices, and methods are provided for reducing loss
of refrigerant and nitrogen in liquefaction systems. In one aspect,
a liquefaction system is provided that includes a first compressor
and a recovery system in fluid communication with the first
compressor. The recovery system can include a first heat exchanger
configured to receive a first vapor from the first compressor. The
first vapor can be, for example, a mixed refrigerant and nitrogen.
The first heat exchanger can be configured to convert the first
vapor to a mixture of nitrogen rich vapor and a hydrocarbon rich
liquid. In certain embodiments, the first heat exchanger can have
at least one cooling element configured to receive a cold fluid
that provides refrigeration to the first vapor, and a separator
configured to receive the mixture of hydrocarbon rich liquid and
nitrogen rich vapor from the first heat exchanger, and to separate
the hydrocarbon rich liquid and the nitrogen rich vapor.
[0006] In one embodiment, a method of operating a liquefaction
system is provided. The method can include receiving a seal gas
including hydrocarbons at a seal assembly of a first compressor.
The method can also include receiving a nitrogen vapor a the seal
assembly of the first compressor. The method can additionally
include receiving, at a first heat exchanger, a first vapor
including at least a portion of the seal gas and at least a portion
of the nitrogen vapor. The method can also include transferring a
cold fluid to a cooling element of the first heat exchanger. The
method can further include transferring heat from the first vapor
to the cold fluid, thereby creating a mixture of nitrogen rich
vapor and a hydrocarbon rich liquid. The method can also include
separating the hydrocarbon rich liquid from the nitrogen rich vapor
at a separator positioned downstream of the first heat
exchanger.
DESCRIPTION OF DRAWINGS
[0007] FIG. 1 is a diagram of one exemplary embodiment of a
liquefaction system;
[0008] FIG. 2 shows a cross-sectional view of a sealing assembly of
a compressor;
[0009] FIG. 3 is a schematic of one exemplary embodiment of a mixed
refrigerant (MR) recovery system;
[0010] FIG. 4 is a schematic of one exemplary embodiment of a
nitrogen recovery system; and
[0011] FIG. 5 is a flow diagram illustrating one exemplary
embodiment of operating a liquefaction system.
DETAILED DESCRIPTION
[0012] One method of addressing refrigerant leakage from a
compressor of a compression system involves utilizing a recovery
system that allows the refrigerant to be captured and injected
directly back into the compressor or into circulation elsewhere
within the refrigeration process, thereby eliminating, or
mitigating, loss of refrigerant from the refrigeration system.
However, for certain liquefaction systems that use a mixed
refrigerant (MR), direct recovery and reintroduction of MR into the
compressor, or into circulation within the refrigeration process,
may not be feasible. As an example, the MR that leaks from the
compressor does so through the seals of the compressor. Such
compressor seal can include dry seals that employ nitrogen gas as a
buffer gas and this nitrogen can contaminate the MR. As a result, a
mixture of MR and nitrogen can leak from the compressor. Over time,
direct reintroduction of the MR and nitrogen mixture into the
compressor can result in performance degradation, since the
composition of the MR within the liquefaction system will be
altered, becoming enriched with nitrogen.
[0013] In order to address these issues, MR and nitrogen recovery
systems can be employed to capture leaked mixtures of MR and
nitrogen from a compressor of a liquefaction system. The MR and
nitrogen recovery systems are each configured to separate the MR
from the nitrogen (e.g., by condensing the MR hydrocarbons),
allowing recovery of the MR and nitrogen. Recovered MR can safely
be reintroduction back into the compressor, and/or into circulation
within the refrigeration process. Recovered nitrogen can be used as
a component of the buffer gas of the compressor seals, and/or for
use elsewhere.
[0014] FIG. 1 illustrates one embodiment of a new LNG liquefaction
system 100. The liquefaction system 100 includes a refrigerant
supply system 102 containing a mixed refrigerant MR 102v in a vapor
state, a compression system 106, one or more condensers 108, a heat
exchanger 112, and a natural gas (NG) supply system 114 containing
natural gas (NG) feedstock 114v in a vapor state. The refrigerant
supply system 102 is in fluid communication with the compression
system 106, and a valve 104 is interposed therebetween for
regulating a flow rate of the supply MR 102v to the compression
system 106. The condensers 108 are in fluid communication with, and
downstream from, the compression system 106. The heat exchanger 112
is in fluid communication with, and downstream from, the condensers
108. An expansion valve 110 is interposed between the condensers
108 and the heat exchanger 112. The heat exchanger 112 is in
further configured to receive the NG feedstock 114v from the NG
supply system 114. The heat exchanger 112 is also in fluid
communication with the valve 104.
[0015] Operation of the liquefaction system 100 is discussed with
further reference to FIG. 1. The valve 104 regulates a flow of
mixed refrigerant, supply MR 102v in a vapor state at a first
temperature T1 and a first pressure P1 from the refrigerant supply
system 102 to the compression system 106. The compression system
106 can be, e.g., a multistage compression system including a
compressor 105.
[0016] Embodiments of the compressors 105 can adopt a variety of
forms. Examples of the compressor 105 can include a single-casing
compressors, multi-stage compressors, and trains of multiple
compressors, each with one or more compression stages. The
compressors 105 are driven by a mover, which can be, e.g., a gas
turbine, a steam turbine, an expander, or an electric motor that
receives electric power 107 from an external power source (not
shown).
[0017] The compression system 106 increases the temperature and
pressure of the supply MR 102v from the first temperature T1 and
the first pressure P1, yielding a high-temperature, high-pressure
mixed refrigerant MR 102v' in the vapor state that possesses a
second temperature T2 greater than the first temperature T1 and
second pressure P2 greater than the first pressure P1.
[0018] The high-pressure, high-temperature MR 102v' can
subsequently flow to one or more condensers 108 that are downstream
of the compression system 106. The condensers 108 can be any device
(e.g., condensers, intercoolers, air coolers, etc.) configured to
facilitate a phase change of the high-temperature, high-pressure MR
102v' from vapor, or mostly vapor, to a predominantly liquid state,
liquid MR 1021, by removing excess heat generated during the
compression process. Thus, the liquid MR 1021 can possess a third
temperature T3 that is less than the first and second temperatures
T1, T2. For clarity of discussion, it is assumed that the pressure
of the liquid MR 1021 remains constant at the second pressure P2.
However, in alternative embodiments, the pressure of the liquid MR
can be less than the second pressure P2.
[0019] FIG. 1 illustrates the condensers 108 as being downstream
from the compression system 106. However, in alternative
embodiments, the condensers can be located between stages of the
compressors of the compression system 106. Condensers integrated
with the compressors of the compression system can be provided in
lieu of, or in addition to, condensers downstream from the
compression system.
[0020] The liquid MR 1021 output by the condensers 108 travels
through the expansion valve 110. The expansion valve 110 creates a
pressure drop that puts at least a portion of the liquid MR 1021 in
a low-pressure, low-temperature, liquid state, MR 1021'. The
low-pressure, low-temperature liquid MR 1021' can possess a third
pressure P3 that is lower than the first and second pressures P1,
P2. It is assumed for clarity of discussion that the temperature of
the low-temperature, low-pressure liquid MR 1021' remains constant
at T3. However, in alternative embodiments, the temperature of this
liquid MR can be less than the second temperature P2.
[0021] The low pressure, low-temperature, low-pressure liquid MR
1021' output from expansion valve 110 flows inside conduits (or
channels) of heat exchange surface(s) of a heat exchanger 112. As
shown, the heat exchanger 112 also receives the natural gas (NG)
feedstock 114v and the low-temperature, low-pressure liquid MR
1021' cools the NG feedstock 114v that contacts the heat exchange
surface(s). As the NG feedstock 114v and the low-temperature,
low-pressure liquid MR 1021' travel through the heat exchanger 112,
heat is transferred from the warmer NG feedstock 114v to the cooler
low-temperature, low-pressure liquid MR 1021' such that the NG
feedstock 114v cools and begins to condense, forming LNG 124.
[0022] The heat exchanger 112 can be any type of heat exchanger.
Examples of the heat exchanger 112 can include core plate and fin,
etched plate, diffusion bonded, wound coil, shell and tube,
plate-and-frame, and the like.
[0023] The NG feedstock 114v can contain both NG vapor 120 and
heavy hydrocarbon components (HHCs) such as butanes, pentanes,
hexanes, benzene, toluene, ethylbenzene, and xylenes. It can be
desirable to remove HHCs during production of the LNG 124 to
prevent them from freezing. As illustrated in FIG. 1, the heat
exchanger 112 can include a HHC separation system 116 configured to
remove HHCs from the NG feedstock 114v. As the NG feedstock 114v is
cooled within the heat exchanger 112, HHCs condense at higher
temperatures than lighter molecules, e.g., methane. Therefore, a
liquid 118 containing primarily HHCs can be separated from NG
feedstock 114v, yielding a purified NG vapor 120 by the HHC
separation system 116. The purified NG vapor 120 flows through the
heat exchanger 112 and condenses to form the LNG 124. The LNG 124
can be subsequently let down in pressure and stored in a storage
vessel (not shown).
[0024] The liquid 118 can be handled in a variety of ways. In one
embodiment, as shown, the liquid 118 exits the heat exchanger 112
and is stored in a HHC storage vessel 122. In alternative
embodiments, not shown, the HHC liquid can be put through a
multistage distillation process to separate it into its constituent
components. The separated constituents can be stored in respective
storage vessels.
[0025] The low-temperature, low-pressure liquid MR 1021' absorbs
heat from the NG feedstock 114v, the purified NG vapor 120, and/or
the LNG 124 within the heat exchanger 112. The absorbed heat is
sufficient to result in vaporization of the low-temperature,
low-pressure liquid MR 1021'. Thus, at least a portion of the MR
that leaves the heat exchanger 112 undergoes a phase change to a
vapor. This vapor can be recovered in the form of recycled MR
102v'' that flows to the valve 104 to the compression system 106.
In certain embodiments, the recycled MR 102v'' can be conditioned
to the first temperature T1 and the first pressure P1 prior to
delivery at the valve 104 by one or more conditioning systems (not
shown). By recovering and reusing the recycled MR 102v'', rather
than burning it, environmental emissions associated with burning
can be avoided.
[0026] During normal operation of the liquefaction system 100, the
compressors 105 can leak MR (e.g., supply MR 102v and/or
high-temperature, high-pressure MR 102v') and nitrogen due to
imperfect sealing at various locations. The liquefaction system 100
can also include at least one of an MR recovery system 300 and a
nitrogen recovery system 400 in fluid communication with the
compressor 105 of the compression system 106. As discussed in
detail below, the MR recovery system 300 and the nitrogen recovery
system 400 are each configured to separate the leaked MR from the
nitrogen (e.g., by condensing the MR hydrocarbons), allowing
recovery of the MR and nitrogen. The MR recovery system 300 is
further configured to reintroduce recovered MR back into the
compressor 105 of compression system 106, and/or into circulation
within other portions of the liquefaction system 100 (e.g., between
the condensers 108 and the expansion valve 110. The nitrogen
recovery system 400 is further configured to reintroduce recovered
MR as a component of the buffer gas of the compressor seals, and/or
for use elsewhere.
[0027] Leakage of MR and nitrogen is discussed with reference to
FIG. 2. FIG. 2 illustrates a cross-sectional view of a compressor
200 including a seal assembly 201 that can be used within a
compression system, such as the compression system 106 shown in
FIG. 1, to contain MR (e.g., supply MR 102v and/or
high-temperature, high-pressure MR 102v'). The seal assembly 201 is
positioned adjacent to an intake port and/or a discharge port of
the compressor 200 to prevent leakage of fluids from the
compressor. The seal assembly 201 includes a primary seal 202, a
secondary seal 204, and a tertiary seal 206 positioned along a
length of a shaft 203 of the compressor 200, between a compressor
side 209 and a bearing side 211 of the compressor 200, to separate
fluids that are within the compressor 200. The primary and
secondary seals 202, 204 can be, e.g., dry gas seals, and the
tertiary seal 206 can be, e.g., a type of carbon ring seal. The
compression side 209 can include a compression chamber (not shown)
used to compress MR (e.g., supply MR 102v), and the bearing side
211 can include one or more bearings (not shown) positioned about
the shaft 203 of the compressor to allow the shaft 203 to
rotate.
[0028] While the seal assembly 201 of FIG. 2 is illustrated in the
form of a tandem type dry gas sealing system, other sealing systems
can be used. Examples can include single dry gas seals, double dry
gas seals, multi-arranged dry gas seals, labyrinth type seals,
carbon ring type seals, any combination of the aforementioned
seals, or any other type of seal known in the art.
[0029] A person skilled in the art will have a basic understanding
of how compressors and sealing assemblies work. A brief description
is provided below.
[0030] During normal operation, supply MR 102v, high-temperature,
high-pressure MR 102v', and combinations thereof in the form of
unfiltered MR 209, is present at a compressor side pressure. As
discussed above, the supply MR 102v possesses the first temperature
T1 and first pressure P1 and the high-temperature, high-pressure MR
102v' possess the second temperature T2 and the second pressure P2.
Thus, the unfiltered MR 209 can possess a temperature ranging from
approximately the first temperature T1 to the second temperature T2
and a pressure ranging from approximately the first pressure P1 and
the second pressure P2. Solely for clarity, it is assumed in the
discussion below that the unfiltered MR 209 possesses the second
pressure P2.
[0031] The unfiltered MR 209 can leak through a sealing element 230
which can be, e.g., a labyrinth seal, and into the seal assembly
201, which can damage the primary, secondary, and tertiary seals
202, 204, 206. In order to prevent the unfiltered MR 209 from
leaking through the sealing element 230, filtered, high-pressure MR
208, or another seal gas, can be delivered to a region 205 of the
seal assembly 201 positioned adjacent the compressor side 209. The
filtered, high-pressure MR 208 can pressurize a cavity 207 located
adjacent the sealing element 230 to a fourth pressure P4 that is
higher than that of the second pressure P2 on the compressor side
209, thereby preventing the unfiltered MR 209 from leaking into the
seal assembly 201.
[0032] A portion of the filtered MR 208 can leak through the
primary seal 202 and travel to a primary vent 212. To ensure that
approximately all of the MR that leaks through the primary seal 202
(e.g., unfiltered MR 209, filtered MR 208) is directed toward the
primary vent 212, a buffer gas such as, e.g., nitrogen 214 (e.g.,
nitrogen vapor), can be delivered to a primary buffer region 216
adjacent to the primary vent 212. The nitrogen 214 can be at a
fifth pressure P5 that is high pressure than the fourth pressure P4
observed at the primary vent 212. A portion of the nitrogen 214 can
leak through a sealing element 232 which can be, e.g., a labyrinth
seal that prevents MR leakage, into the primary buffer region 216.
The nitrogen 214 that leaks through the sealing element 232 can
combine with the MR that leaks through the primary seal 202 (e.g.,
unfiltered MR 209, filtered MR 208) to create a mixture 218 of MR
leakage and the nitrogen 214 at the primary vent 212. Another
portion of the nitrogen 214 can leak through the secondary seal 204
and travel to a secondary vent 220. The mixture 218 of MR leakage
and nitrogen 214 can be delivered from the primary vent 212 to a
flare to be burned.
[0033] To prevent bearing oil mist from migrating from the bearing
side of the tertiary seal 206, nitrogen 222 can also be injected
into a secondary buffer region 224 between the secondary vent 220
and the bearing side 211 of the seal assembly 201. A portion of the
nitrogen 222 that is delivered to the secondary buffer region 224
can leak beyond the tertiary seal 206 and travel to the secondary
vent 220. Nitrogen 226 from the secondary vent 220 can be captured
and reintroduced to the seal assembly 201 as buffer gas.
[0034] As discussed in detail below, rather than flaring the
mixture 218 of leaked MR and nitrogen 214 from the primary vent
212, as commonly done, embodiments of the present disclosure
illustrate systems and corresponding methods that facilitate
recovery of the MR (e.g., unfiltered MR 209, filtered MR 208) that
leaks from a compressor of a liquefaction system (e.g., compressor
105 of liquefaction system 100) can be recovered and returned to
circulation. This significantly reduces the need to stock, purchase
and reintroduce "lost" MR into the liquefaction system 100.
[0035] FIG. 3 is a schematic diagram illustrating one exemplary
embodiment of a new MR recovery system n for recovering all or a
portion of either (or both) MR leakage (e.g., unfiltered MR 209,
filtered MR 208) and/or nitrogen 214 that leaks from a compressor
(e.g., compressor 105 of compression system 106).
[0036] The MR recovery system 300 includes a heat exchanger 302 and
a two-phase separator 308. The heat exchanger 302 is configured to
receive a cold fluid 304 and a nitrogen rich vapor 305 having MR
components and nitrogen (e.g., mixture 218) from a compressor of a
compression system, such as compressor 105 of the compression
system 106 shown in FIG. 1. The heat exchanger 302 can include at
least one cooling element configured to receive the cold fluid 304
and provide refrigeration to the nitrogen rich vapor 305. The
two-phase separator 308 is configured to separate an input fluid
into two or more different phases.
[0037] The cold fluid 304 can be a liquefied product created by the
liquefaction system 100. For example, the cold fluid 304 can be
LNG, such as the LNG 124 that exits the heat exchanger 112 shown in
FIG. 1. Accordingly, the cold fluid 304' that leaves the heat
exchanger 302 is delivered to a storage vessel 320, via valve 311,
to be stored and/or distributed as desired. Alternatively, the cold
fluid 304 can be a refrigerant from another refrigeration system
configured for the described purpose. Therefore, the cold fluid
404' that leaves the heat exchanger 302 can continue within a
refrigeration cycle to provide refrigeration to the nitrogen rich
vapor 305
[0038] The heat exchanger 302 can take a variety of forms. In
certain embodiments, the heat exchanger 302 can be, e.g., a shell
and tube heat exchanger, or it can be a condensing coil heat
exchanger. Alternatively, other heat exchangers such as core, core
plate-and-fin, etched plate, diffusion bonded, wound coil, shell
and tube, plate-and-frame, etc. can be used. As shown, valves 309,
311 are positioned on either side of the heat exchanger 302 control
a flow rate of the cold fluid 304 through the heat exchanger
302.
[0039] In some embodiments, prior to being delivered to the heat
exchanger 302, the nitrogen rich vapor 305 is delivered to a
nitrogen removal assembly 303 positioned upstream of the heat
exchanger 302. As discussed above, the nitrogen rich vapor 305 can
be the mixture 218 of leaked MR and nitrogen. The nitrogen removal
assembly 303 is configured to removes a portion of the nitrogen
from the nitrogen rich vapor 305 and outputs a nitrogen poor vapor
307 that contains less nitrogen than the nitrogen rich vapor 305.
As an example, the nitrogen removal assembly 303 can be an
absorption bed. The nitrogen poor vapor 307 exiting the nitrogen
removal assembly 303 is delivered to the heat exchanger 302.
[0040] As the nitrogen poor vapor 307 and the cold fluid 304 travel
through the heat exchanger 302, heat is transferred from the
nitrogen poor vapor 307 to the cold fluid 304 such that the
nitrogen poor vapor 307 begins to cool and condense. While the
nitrogen poor vapor 307 is cooled within the heat exchanger 302,
hydrocarbon components that make up MR condense at higher
temperatures than lighter components such as nitrogen. Therefore, a
mixture 306 of a nitrogen rich vapor 310, and a hydrocarbon rich
liquid 312 can be formed. The mixture 306 can be cooled
sufficiently to achieve the nitrogen rich vapor 310 with high
purity due to preferential condensation of hydrocarbon components.
In some cases, the mixture 306 is cooled sufficiently to produce
the nitrogen rich vapor 310 with approximately 95% purity. As an
example temperature of the mixture 306 that exits the heat
exchanger 302 can be at a temperature in the range of approximately
-51 to -160 degrees Celsius (-60 to -257 degrees Fahrenheit).
[0041] The mixture 306 exiting the heat exchanger 302 flows to the
two-phase separator 308. The two-phase separator 308 is configured
to receive the mixture 306 of the nitrogen rich vapor 310 and
hydrocarbon rich liquid 312 from the heat exchanger 302 and to
separate the nitrogen rich vapor 310 and the hydrocarbon rich
liquid 312. As shown, the hydrocarbon rich liquid 312 is delivered
to a pump 316 that pumps the hydrocarbon rich liquid 312 to a
refrigerant supply system, such as refrigerant supply system 102
shown in FIG. 1, and the nitrogen rich vapor 310 is delivered to a
flare 322.
[0042] However, in alternative embodiments, the hydrocarbon rich
liquid 312 and/or the nitrogen rich vapor 330 output from the
two-phase separator 308 can be handled differently than discussed
above.
[0043] In one aspect, the hydrocarbon rich liquid can be directly
reintroduced to circulation within the liquefaction system (e.g.,
between the condenser and the expansion valve), or it can be
vaporized and reintroduced within the compressor as the filtered MR
208 described above with regard to FIG. 2. In some cases, the
hydrocarbon rich liquid is heated before reintroduction into
circulation within the liquefaction system, and/or prior to
reintroduction within the compressor of the compression system, to
prevent low-temperature embrittlement of components of the
liquefaction system and/or the compressor.
[0044] In a further aspect, the hydrocarbon rich liquid can be
distilled to separate various hydrocarbon components such as, e.g.,
methane, ethylene, and propane, and pentanes such that they can be
stored separately within the refrigerant supply system.
[0045] In alternative embodiments the nitrogen rich vapor output
from the two-phase separator can be handled differently than
flaring. In one aspect, the nitrogen rich vapor can be distilled to
further purify the nitrogen. The purified nitrogen vapor can be
delivered back to the compressor as a buffer gas of a dry seal of
the compressor, it can be stored in a storage vessel, or it can be
delivered to other components within a liquefaction system.
[0046] In alternative embodiments, not shown, a distillation system
can be used to separate components of the nitrogen poor vapor into
nitrogen rich vapor and hydrocarbon rich liquid, rather than the
heat exchanger and two-phase separator. In either case, each of the
components of the nitrogen poor vapor 307 can be separated,
reintroduced to the liquefaction system 100, stored, and/or
distributed as desired.
[0047] As described above, nitrogen and MR that leak from a
compressor of a compressor system are recovered, separated, stored,
and/or reintroduced back into a liquefaction system. FIG. 4 shows
one example of a nitrogen recovery system 400 for recovering
nitrogen and MR that leaks from a compressor 429 of a compressor
system 430. In certain embodiments, the compressor system 430 can
be compression system 106 of liquefaction system 100. Nitrogen
buffer gas that leaks from the compressor (e.g., compressor 105,
compressor 200), without mixing with MR, can also be recovered and
reintroduced to the compressor as a buffer gas (e.g., nitrogen 214
of seal assembly 201).
[0048] As shown, the nitrogen recovery system 400 includes a heat
exchanger 402 and a two-phase separator 408, The heat exchanger 402
is configured to receive a cold fluid 404 and a vapor 405 having MR
components and nitrogen from a compressor (e.g., compressor 105,
compressor 200) of a compression system, such as the compression
system 106 shown in FIG. 1. The heat exchanger 402 can generally be
similar to heat exchanger 302. Valves 409, 411 are positioned on
either side of the heat exchanger 402 for control a flow rate of
the cold fluid 404 through the heat exchanger 402. The two-phase
separator 408 can be generally similar to the two-phase separator
308 and is configured to separate an input fluid into two or more
different phases.
[0049] In some embodiments, the cold fluid 404 is a liquefied
product created by the liquefaction system 100. For example, the
cold fluid 404 can be LNG, such as the LNG 124 that exits the heat
exchanger 112 shown in FIG. 1. Alternatively, the cold fluid 404
can be, e.g. propane, R-134A, propylene, etc. As another example,
the cold fluid 404 can be liquid nitrogen or ethylene stored at the
liquefaction system 100. Accordingly, the cold fluid 404' that
leaves the heat exchanger 402, via valve 411, is delivered to a
storage vessel 420 to be stored, and/or distributed as desired.
Alternatively, the cold fluid 404 can be a refrigerant from another
refrigeration system configured for the described purpose.
Therefore, the cold fluid 404' that leaves the heat exchanger 402
can continue within a refrigeration cycle to provide refrigeration
to the vapor 405.
[0050] As the vapor 405 and the cold fluid 404 travel through the
heat exchanger 402, heat is transferred from the vapor 405 to the
cold fluid 404 such that the vapor 405 begins to cool and condense.
As the vapor 405 is cooled within the heat exchanger 402,
hydrocarbon components that make up MR condense at higher
temperatures than lighter components such as nitrogen. Therefore, a
mixture 406 of a nitrogen rich vapor 410 and a hydrocarbon rich
liquid 412 can exit the heat exchanger 402. The mixture 406 can be
cooled sufficiently such that the nitrogen rich vapor 410 is of
high purity due to preferential condensation of hydrocarbon
components. In some cases, the mixture 406 is cooled sufficiently
to produce the nitrogen rich vapor 410 with approximately 95%
purity. For example, the mixture 406 can exit the heat exchanger
402 at a temperature in a range of approximately -118 to -160
degrees Celsius (-180 to -257 degrees Fahrenheit).
[0051] The mixture 406 exiting the heat exchanger 402 is flow to
the two-phase separator 408 and is separated into the nitrogen rich
vapor 410 and the hydrocarbon rich liquid 412. The nitrogen rich
vapor 410 is combined with nitrogen vapor 431 from the compressor
429 of the compressor system 430 (e.g., a first compressor), and is
delivered to a second compressor 425. The nitrogen vapor 431 can be
nitrogen that leaks from a compressor, such as nitrogen 226
described above with regard to FIG. 2.
[0052] Nitrogen vapor 424 exiting the second compressor 425 is
urged into combination with nitrogen vapor 426 from a nitrogen
source 428 such that it is delivered back to the compressor 429 of
the compressor system 430 to be used as a buffer gas (e.g.,
nitrogen 214 of seal assembly 201), as described above with regard
to FIG. 2. In some cases, the nitrogen vapor 424 can be heated
prior to being combined with the nitrogen vapor 426 from the
nitrogen source 428, and/or prior to reintroduction into the
compressor system 430, to prevent low temperature embrittlement of
components of the compressor system 430.
[0053] In some embodiments, prior to combination with the nitrogen
vapor 431 from the compressor of the compressor system 430 and
input to the second compressor 425, the nitrogen rich vapor 410 is
delivered to a nitrogen removal system 417. The nitrogen removal
system 417 is positioned downstream from the two-phase separator
408 and configured to remove at least a portion of nitrogen within
the nitrogen rich vapor 410. As an example, the nitrogen removal
system 417 can be an adsorption bed that removes a portion of
adsorbed nitrogen. The adsorbed nitrogen is released as a result of
a desorption process, and the released nitrogen is delivered to the
second compressor 425, and combined with the nitrogen vapor 426, as
described above.
[0054] In alternative embodiments, the nitrogen vapor 424 output by
the second compressor 425 can be handled differently than being
combined with the nitrogen vapor 426. In one aspect, rather than
delivering the nitrogen vapor back to the compressor system, the
nitrogen vapor can be compressed, condensed, and stored in a
storage vessel (not shown). In another aspect, the nitrogen vapor
can be stored as a vapor, or delivered to another component of a
liquefaction system for use elsewhere.
[0055] As shown, in FIG. 4, the hydrocarbon rich liquid 412 that
exits the two-phase separator 408 is delivered to a pump 416 that
pumps the hydrocarbon rich liquid 412 to a flare 422. However, in
alternative embodiments, the hydrocarbon rich liquid 412 can be
handled differently. In one aspect, rather than flaring the
hydrocarbon rich liquid 412, a portion of the hydrocarbon rich
liquid 412 can be distilled to remove excess nitrogen. The
distillation process separates the hydrocarbon rich liquid 412 into
various hydrocarbon components such as methane, ethylene, and
propane, and pentanes such that they can be stored separately
within a refrigerant supply system. As another example, rather than
using the heat exchanger 402 and two-phase separator 408, a
distillation system can be used to separate components of the vapor
405. Accordingly, each of the components of the vapor can be
separated, reintroduced to a liquefaction system, stored, and/or
distributed as desired.
[0056] FIG. 5 is a flow diagram illustrating one exemplary
embodiment of a method 500 for operating a liquefaction system.
Embodiments of the method include operations 502-512. It can be
understood that, in alternative embodiments, the method can include
greater or fewer operations and the operations can be performed in
an order different than illustrated in FIG. 5.
[0057] In operation 502, a seal gas is received at a seal assembly
of a first compressor (e.g., compressor 105). In certain
embodiments, the seal gas is a mixed refrigerant (MR), such as
supply MR 102v, high-temperature, high-pressure MR 102v', and
combinations thereof.
[0058] In operation 504, a nitrogen vapor is received at the seal
assembly of the first compressor. In certain embodiments, the
nitrogen vapor is the nitrogen 214 employed as a buffer gas in the
seal assembly 201.
[0059] In operation 506, a first vapor is received at the first
heat exchanger. In certain embodiments, the first vapor includes at
least a portion of the sea gas and at least a portion of the
nitrogen vapor.
[0060] In operation 508, a cold fluid is transmitted to a cooling
element of the first heat exchanger. As an example, the cold fluid
can be cold fluid 304. Examples of the cold fluid 304 include a
liquefied product created by the liquefaction system 100 (e.g., LNG
124 that exits the heat exchanger 112), a refrigerant from another
refrigeration system, different from the liquefaction system 100,
and combinations thereof.
[0061] In operation 510, heat is transferred from the first vapor
to the cold fluid, thereby creating a mixture of nitrogen rich
vapor and a hydrocarbon rich liquid. In certain embodiments, the
nitrogen rich vapor is possesses approximately 95% purity or
greater. The heat transfer can be performed by a heat exchanger
(e.g., 302, 402).
[0062] In operation 512, the hydrocarbon rich liquid is separated
from the nitrogen rich vapor at a separator (e.g., 308, 408)
positioned downstream of the first heat exchanger.
[0063] Embodiments of the method 900 can optionally include one or
more of the following operations.
[0064] In another embodiment, the method 500 can include receiving
the nitrogen rich vapor (e.g., 410) at a second compressor. As an
example, the second compressor can be second compressor 425 and the
nitrogen rich vapor 410 can be received from the heat exchanger
402. Following receipt by the second compressor 425, the nitrogen
rich vapor 410 is compressed by the second compressor 425. At least
a portion of the nitrogen rich vapor 410 output by the second
compressor 425 is delivered to the seal assembly of the first
compressor (e.g., 201). Optionally, the nitrogen rich vapor 410 is
combined with the nitrogen 214 prior to delivery to the seal
assembly 201.
[0065] In another embodiment, the method 500 can include receiving
a methane-containing vapor at a second heat exchanger and removing
heat from the methane-containing vapor within the second heat
exchanger to thereby create the cold fluid. In certain embodiments,
the methane-containing vapor can be a natural gas (NG). In further
embodiment, the second heat exchanger can be heat exchanger
302.
[0066] In another embodiment, the method 500 can include receiving
a second vapor at a nitrogen removal assembly positioned upstream
of the first heat exchanger. The second vapor includes at least a
portion of the seal gas and at least a portion of the nitrogen
vapor. In certain embodiments, the second vapor is nitrogen rich
vapor 305 and the nitrogen removal assembly is nitrogen removal
assembly 303. Following receipt of the second vapor, the nitrogen
removal assembly removes a portion of the nitrogen vapor from the
second vapor, thereby generating the first vapor (e.g., nitrogen
poor vapor 307).
[0067] In another embodiment, the method 500 can include receiving
the nitrogen rich vapor at a nitrogen removal assembly positioned
downstream of the separator; and removing a portion of the nitrogen
from the nitrogen rich vapor. As an example, the separator is
two-phase separator 408, the nitrogen removal assembly positioned
downstream of the two-phase separator 408 is nitrogen removal
system 417, and the nitrogen rich vapor is nitrogen rich vapor
410.
[0068] In another embodiment, the method 500 can include receiving
the hydrocarbon rich liquid at a pump (e.g., 316, 416) and pumping
the hydrocarbon rich liquid (e.g., 312, 412) to a storage vessel
(e.g., 322, 422).
[0069] A person skilled in the art will appreciate that the
methods, systems, and devices described herein can be applied
within liquefaction facilities that can produce liquefied products
other than LNG. For example, embodiments of the MR recovery system
300, and/or the nitrogen recovery system 400, can be implemented in
liquefaction system that produces liquefied petroleum gas (LPG),
ethane, propane, helium, ethylene etc.
[0070] Exemplary technical effects of the methods, systems, and
devices described herein include, by way of non-limiting example,
the ability to recover, and separate, and store MR components
and/or nitrogen that leak from a compressor. Other technical
effects of the methods, systems, and devices described herein
include the ability to reintroduce the MR components into
circulation within a liquefaction system, and/or to reuse recovered
nitrogen as a buffer gas within a compressor. Recovering and
reusing MR and nitrogen can minimize loss of MR and nitrogen which
can lower the total operating cost of a liquefaction system.
Additionally, recovering the MR, rather than burning it, can reduce
environmental emissions by reducing the amount of MR that is
burned.
[0071] Certain exemplary embodiments are described to provide an
overall understanding of the principles of the structure, function,
manufacture, and use of the systems, devices, and methods disclosed
herein. One or more examples of these embodiments are illustrated
in the accompanying drawings. Those skilled in the art will
understand that the systems, devices, and methods specifically
described herein and illustrated in the accompanying drawings are
non-limiting exemplary embodiments and that the scope of the
invention is defined solely by the claims. The features illustrated
or described in connection with one exemplary embodiment may be
combined with the features of other embodiments. Such modifications
and variations are intended to be included within the scope of the
present invention. Further, in the present disclosure, like-named
components of the embodiments generally have similar features, and
thus within a particular embodiment each feature of each like-named
component is not necessarily fully elaborated upon.
[0072] In the descriptions above and in the claims, phrases such as
"at least one of" or "one or more of" may occur followed by a
conjunctive list of elements or features. The term "and/or" may
also occur in a list of two or more elements or features. Unless
otherwise implicitly or explicitly contradicted by the context in
which it is used, such a phrase is intended to mean any of the
listed elements or features individually or any of the recited
elements or features in combination with any of the other recited
elements or features.
[0073] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term or terms, such as "about" and
"substantially," are not to be limited to the precise value
specified. In at least some instances, the approximating language
may correspond to the precision of an instrument for measuring the
value. Here and throughout the specification and claims, range
limitations may be combined and/or interchanged, such ranges are
identified and include all the sub-ranges contained therein unless
context or language indicates otherwise.
* * * * *