Note: Descriptions are shown in the official language in which they were submitted.
322807-5
REFRIGERANT AND NITROGEN RECOVERY
100011 [BLANK1
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 (-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.
1
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SUMMARY
[00051 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, fot 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,
[00061 In one embodiment, a method of operating a liquefaction system is
provided. The
method can include receiving a seal gas including hydrocarbons ata 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
100071 FlG I is.a diagram of one exemplary embodiment of a liquefaction
system;
100081 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;
10010J F1G. 4 is a Schematic of one exemplary embodiment ofa nitrogen
recovery
system; and
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100111 FIG. 5 is a flow .diagram illustrating one exemplary embodiment of
operating a
liquefaction system.
DETAILED DESCRIPTION
100121 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 he 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. call result in
performance degradation, since the composition of the MR within the
liquefaction system
will be altered, becoming enriched with nitrogen,
[00131 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,
[00141 FIG. 1 illustrates one embodiment of a new LNG liquefaction system
IOU. 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
(NC) feedstock I 14v in a vapor state. The refrigerant supply system 102 is in
fluid
communication with the compression system 1.06, and a valve 104 is interposed
therebetween
for regulating a flow rate of the supply MR IO2v to the compression system
106. The
condensers 108 are in fluid communication with, and downstream from, the
compression
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system 106. The heat exchanger 112 is in fluid communication with, and
downstream from,
the condensers 108. An expansion .valve II is interposed between the
condensers 108 and
the heat exchanger 112. The heat exchanger 112 is in further configured to
receive the NO
feedstock 114v from the NO supply system 114, The heat exchanger 112 is also
in fluid
communication with the valve 104,
100151 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 PI from the refrigerant supply
system 102 to the
compression system 106. The compression system 106 can be, e.g;õ a multistage.
compression system including a compressor 105.
100161 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 he, 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).
100171 The compression system 106 increases the temperature and pressure of
the supply
MR 102v from the first temperature Ti and the first pressure PI, yielding a
high-
temperature, high-pressure mixed refrigerant MR 102y in the vapor state that
possesses a
second temperature T2 greater than the first temperature TI and second
pressure P2 greater
than the first pressure PI,
100181 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
13 that is less than the first and second temperatures TI, 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.
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1001.91 FIG. I illustrates the condensers 108 as being downstream from the
compression
system 106. However, in alternative embodiments, the condensers can he 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.
100201 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 Pl, 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.
100211 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 11.4v cools and begins to condense,
forming LNG
124.
[00221 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.
100231 The NG feedstock 114v can contain both NG- vapor 120 and heavy
hydrocarbon
components (H.H.Cs) such as butanes, pentanes, hexanes, benzene, toluene,
ethylbenzene, and
xylem's. It can be desirable to remove HHCs during production of the LNG 124
to prevent
them front freezing. As illustrated in FIG. 1, the heat exchanger 112 can
include a Ill-IC
separation system 116 configured to remove .HHCs from the NG feedstock 114v.
As the NG
feedstock 114v is cooled within the heat exchanger 112, HHes condense at
higher
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temperatures than lighter molecules, e.g., methane. Therefore, a liquid 118
containing
primarily H.EICs can be separated front NO feedstock 1.14v, yielding a.
purified NG vapor 120
by the 111-1C separation system 116. The purified NO vapor 120 flows through
the heat
exchanger 112 and condenses to form the LNG 124. The LNG 124 an be
subsequently let
down in pressure and stored in a storage vessel (not shown).
100241 The liquid 118 can be handled in a variety always. In one
embodiment, as
shown, the liquid 118 exits the heat exchanger 112 and is stored in a HI-IC
storage vessel 122.
In alternative embodiments, not shown, the Hi-IC 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 neat from
the NO
feedstock. 114v, the purified NO 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
Ti and the
first pressure PI 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.
1002(1 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 tecOvery,
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
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is further configured to reintroduce recovered MR as a component of the buffer
gas of the
compressor seals, and/or for use elsewhere.
100271 Leakage of M.R. and, nitrogen is discussed with reference to FIG. 2.
FIG. 2
illustrates a cosS-seetional vieW of a compressor 200 including a seal
assembly 201 that can
be used within a compression system, such as the compressio.n System 106 shown
in FIG. I,
to contain MR (e.g., supply MR I 02v and(or high-temperature, high-pressure MR
102V),
The seal assembly 201 is positioned adjacent to an intake port and/or a
diseharge 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.
100281 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,
[00291 A person skilled in the art will have a basic understanding of how
compressors
and sealing assemblies work. A brief description is provided below.
100301 During normal operation, supply MR 102v, high-temperature, high-
pressure MR
102v', and combinations thereof in the form of unfiltered M.R 209, is present
at a compressor
side pressure. As discussed above, the supply MR 102v possesses the first
temperature Tl.
and first pressure PI and the high-temperature, high-pressure MR 1021/'
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 TI to the second
temperature
T2 and a pressure ranging from approximately. the first pressure P I and the
second pressure
P2, Solely for clarity, it is assumed in the discussion below that the
unfiltered MR 209
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possesses the second pressure P2.
[0031] The unfiltered MR 209 can leak through a sealing element 230 which
can be, e.gõ
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 clement 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 PS 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.,gõ
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 primacy. vent 21.2. 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.
100331 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,
100341 As discussed in detail below, rather than flaring the mixture 218 of
leaked MR
8
322807-5
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 carried from a second conduit portion
340 of conduit
342 that branches from a first conduit portion 344 at first conduit location
346, 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 the second conduit
portion 340 and
valve 311, so as to rejoin the first conduit portion 344 at a second conduit
location 348,
whereby the cold fluid 304' is able 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
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flow rate of the cold fluid 304 through the heat exchanger 302.
100391 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.
100401 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 he: 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).
[00411 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
fine 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.
I, and the
nitrogen rich vapor 310 is delivered to a flare 322..
100421 However,. in. alternative embodiments, the hydrocarbon rich liquid
312 and/or the
nitrogen rich vapor 310 output from the two-phase separator 308 can be handled
differently
than discussed above.
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100431 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 andior the compressor.
100441 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 stich
that they can be stored separately within the refrigerant supply system.
100451 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.
100461 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.
100471 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
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),
[00481 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
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and a vapor 406 having MR components and nitrogen from a compresscir (e.ga
compressor
105, compressor 200) of a compression system, such as the compression system
106 shown
in FIG. I. 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.
100491 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. I. 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 heatexchanger 402 can continue within a
refrigeration cycle to
provide refrigeration to the vapor 405.
100501 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).
100511 The mixture 406 exiting the heat exchanger 402 is flow to the two-
phase separator
408 and is separated into the nitrogen rich vapor 440 and the hydrocarbon rich
liquid 412.
The nitrogen rich vapor 410 is combined with nitrogen vapor 431 from the
compressor 429 of
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the compressor system 430 (e.gõ a first compressor), and is delivered to a
second compressor
:425. The nitrogen vapor 431 can be nitrogen that leaks from a compresseir,
such as nitrogen
226 described above with regard to FIG. 2.
[0052I 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 case*
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.
100531 In some embodiments, prior to combination with the nitrogen vapor
431 from the
compressor of the compressor system 430 and input to the second compressot
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.
[00541 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.
[00551 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 ona 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
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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.
100561 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.
100571 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 102µ;', and
combinations
thereof
100581 In operation 504, a nitrogen vapor is received at the seal as.sembly
of the first
compressor. In certain embodiments, the nitrogen vapor is the nitrOgen 214
employed as a
buffer gas in the seal assembly 201.
10059] 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
Icasta portion of
the nitrogen vapor.
100601 In operation 508, a cold fluid is transmitted to a coding 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.
100611 In operation 510, heat is transferred from the first vapor to the
cold fluid, thereby
creating a mixture of nitrogen ii0h.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).
100621 In operation 512, the hydrocarbon rich liquid is separated from the
nitrogen rich
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vapor at a separator (e.g., 308, 408) positioned downstream of the first heat
exchanger.
100631 Embodiments of the method 900 can optionally include one or more of
the
following operations,
100641 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,
[006.51 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 (NC). In
further
embodiment, the second heat exchanger can be heat exchanger 302.
100661 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).
100671 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.
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100681 In another embodiment, the method 500 can include receiving the
hydrocarbon
rich liquid at a pump (e.gõ 316, 416) and pumping the hydrocarbon rich liquid
(e.g., 312,
412) to a storage vessel (e.g., 322, 422),
100691 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.
100701 Exemplary technical effects dale 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,
100711 .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
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.
100721 In the descriptions above and in the claims, phrases such as. "at
least one er" or
"one or more of' may occur followed by a conjunctive list of elements or
features. The term
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"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,
[00731 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.
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