KR102391748B1 - Refrigerant and nitrogen recovery - Google Patents

Abstract

Systems, apparatus, and methods are provided for recovering mixed refrigerant and/or nitrogen in a liquefaction system. The system, apparatus, and method include recovering mixed refrigerant (MR) and/or nitrogen vapor that may leak from a compressor, separating the MR from nitrogen, and reusing the MR and/or nitrogen within a liquefaction system. make it easy By recovering and reusing MR and/or nitrogen, the loss of MR and nitrogen can be minimized, which can lower the total operating cost of the liquefaction system. Additionally, by recovering MR rather than burning it, the amount of MR burned can be reduced, thereby reducing environmental emissions.

Description

Refrigerant and nitrogen recovery

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed on August 21, 2017, and is entitled "Refrigerant and Nitrogen Recovery," U.S. Provisional Application No. 62/548,163, and filed on June 29, 2018, which is incorporated herein by reference in its entirety. Priority is claimed to U.S. Patent Application Serial No. 16/023,885, filed and entitled "Refrigerant and Nitrogen Recovery."

technical field

Systems and methods are provided for reducing the loss of refrigerant and/or nitrogen in a liquefaction system for liquefying a gas, such as natural gas.

Liquefied natural gas (“LNG”) is natural gas that has been cooled to a temperature of approximately -162°C (approximately -260°F) to a pressure of up to approximately 25 kPa (4 psig) and taken in the liquid state. Natural gas (NG) consists primarily of methane and may include ethane, propane, and heavy hydrocarbon components such as butane, pentane, hexane, benzene, toluene, ethylbenzene, and xylene. Many natural gas sources are located at considerable distances from the end consumer. One cost-effective way to transport NG over long distances is to liquefy natural gas, convert it to liquefied natural gas (LNG), and transport it on a tanker ship, also known as an LNG-tanker. LNG is converted back to gaseous natural gas at the destination.

In a typical NG liquefaction process, a compressor compresses the mixed refrigerant MR to an elevated pressure, forming pressurized MR. The pressurized MR is delivered to a cold box, which is again used to cool the NG feedstock to form LNG. During normal operation, and in certain shutdown scenarios, MR and nitrogen may leak from the compressor. Nitrogen can be used as part of a dry gas seal used for containment of the MR in the compressor and is mixed with the MR. Often, the leaked MR and nitrogen are captured and delivered to a flare for combustion. Over time, these lost, flared MR and nitrogen must be replaced in order to continue the liquefaction process, which is costly.

A system, apparatus, and method are provided for reducing the loss of refrigerant and nitrogen in a liquefaction system. 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 may include a first heat exchanger configured to receive first vapor from the first compressor. The first vapor may be, for example, a mixed refrigerant and nitrogen. The first heat exchanger may be configured to convert the first vapor to a mixture of a nitrogen-rich vapor and a hydrocarbon-rich liquid. In certain embodiments, the first heat exchanger may have at least one cooling element configured to receive a cryogenic fluid that provides refrigeration to the first vapor, wherein the separator comprises a hydrocarbon rich liquid and a nitrogen rich liquid from the first heat exchanger. and receiving a mixture of vapors and configured to separate a hydrocarbon-rich liquid and a nitrogen-rich vapor.

In one embodiment, a method of operating a liquefaction system is provided. The method may include receiving a seal gas comprising a hydrocarbon in a seal assembly of a first compressor. The method may also include receiving nitrogen vapor in the seal assembly of the first compressor. The method may further include receiving, in a first heat exchanger, a first vapor comprising at least a portion of the seal gas and at least a portion of the nitrogen vapor. The method may also include delivering a cryogenic fluid to a cooling element of the first heat exchanger. The method may further comprise transferring heat from the first vapor to the cryogenic fluid to produce a mixture of a nitrogen-rich vapor and a hydrocarbon-rich liquid. The method may also include separating the hydrocarbon-rich liquid from the nitrogen-rich vapor in a separator located downstream of the first heat exchanger.

1 is a diagram of an exemplary embodiment of a liquefaction system.
2 is a cross-sectional view of the sealing assembly of the compressor;
3 is a schematic diagram of an exemplary embodiment of a mixed refrigerant (MR) recovery system.
4 is a schematic diagram of an exemplary embodiment of a nitrogen recovery system.
5 is a flow diagram illustrating an exemplary embodiment for operating a liquefaction system.

One method of dealing with refrigerant leaks from the compressor of a compression system involves the use of a recovery system in which the refrigerant is captured and injected directly back into the compressor or into circulation elsewhere in the refrigeration process. Thus, it is possible to eliminate or mitigate the loss of refrigerant from the refrigeration system. However, for certain liquefaction systems using mixed refrigerant (MR), direct recovery of MR and direct re-introduction into the compressor or into circulation within the refrigeration process may not be feasible. As an example, the MR leaking from the compressor is doing so through the compressor's seal. Such compressor seals may include dry seals using nitrogen gas as the buffer gas, which may contaminate the MR. As a result, a mixture of MR and nitrogen may leak from the compressor. Over time, the direct re-introduction of the MR and nitrogen mixture into the compressor can lead to performance degradation, since the composition of the MR in the liquefaction system will change, resulting in nitrogen enrichment.

To solve these problems, an MR and nitrogen recovery system can be used to capture the mixture of MR and nitrogen leaking from the compressor of the liquefaction system. The MR recovery system and the nitrogen recovery system are each configured to separate MR from nitrogen (eg, by condensing MR hydrocarbons), thereby enabling recovery of MR and nitrogen. The recovered MR can be safely reintroduced back into the compressor and/or into circulation within the refrigeration process. The recovered nitrogen may be used as a component of the buffer gas of the compressor seal and/or for use elsewhere.

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 vapor state, a compression system 106, one or more condensers 108, a heat exchanger 112, and natural gas in vapor state. and a natural gas (NG) supply system 114 containing (NG) feedstock 114v. The refrigerant supply system 102 is in fluid communication with the compression system 106 with a valve 104 interposed therebetween for regulating the flow rate of the supply MR 102v to the compression system 106 . Condenser 108 is in fluid communication with and downstream from compression system 106 . Heat exchanger 112 is in fluid communication with and downstream from condenser 108 . An expansion valve 110 is interposed between the condenser 108 and the heat exchanger 112 . Heat exchanger 112 is further configured to receive NG feedstock 114v from NG supply system 114 . Heat exchanger 112 is also in fluid communication with valve 104 .

The operation of the liquefaction system 100 is discussed with further reference to FIG. 1 . The valve 104 regulates the flow rate of the mixed refrigerant and applies a first pressure P1 from the refrigerant supply system 102 and MR 102v in vapor state at a first temperature T1 to the compression system 106 . supply Compression system 106 may be, for example, a multistage compression system including compressor 105 .

Embodiments of the compressor 105 may take various forms. Examples of compressors 105 may include single-casing compressors, multistage compressors, and trains of multiple compressors each having one or more compression stages. Compressor 105 is driven by a prime mover, which may be, for example, a gas turbine, steam turbine, expander, or electric motor that receives power 107 from an external power source (not shown).

The compression system 106 increases the temperature and pressure of the supply MR 102v from the first temperature T1 and the first pressure P1, so that the second temperature T2 and the first temperature T2 higher than the first temperature T1 A high-temperature, high-pressure mixed refrigerant MR 102v' in a vapor state having a second pressure P2 higher than the pressure P1 is calculated.

Subsequently, the high pressure hot MR 102v ′ may flow to one or more condensers 108 downstream of the compression system 106 . Condenser 108 is any configured to facilitate the phase change of hot high pressure MR 102v' from vapor or predominantly vapor to a predominantly liquid state, liquid MR 102l, by removing excess heat generated during the compression process. device (eg, condenser, intercooler, air cooler, etc.). Accordingly, the liquid MR 102l may have a third temperature T3 that is less than the first temperature and the second temperature T1 and T2. For clarity of discussion, it is assumed that the pressure of the liquid MR 102l is kept constant at the second pressure P2. However, in an alternative embodiment, the pressure of the liquid MR may be less than the second pressure P2.

1 illustrates the condenser 108 as being downstream from the compression system 106 . However, in an alternative embodiment, the condenser may be located between stages of the compressors of the compression system 106 . A condenser integrated with the compressor of the compression system may be provided in lieu of or in addition to a condenser downstream of the compression system.

The liquid MR 102l output by the condenser 108 moves through the expansion valve 110 . Expansion valve 110 causes a pressure drop that places at least a portion of liquid MR 102l in low pressure cold liquid state MR 102l'. The low-pressure low-temperature liquid MR 102l ′ may have a third pressure P3 lower than the first pressure and the second pressure P1 and P2 . For clarity of discussion, it is assumed that the temperature of the low-temperature low-pressure liquid MR 102l' is kept constant at T3. However, in an alternative embodiment, the temperature of this liquid MR may be lower than the second temperature P2.

The low-temperature low-pressure liquid MR 102l' output from the expansion valve 110 flows into the conduit (or channel) of the heat exchange surface(s) of the heat exchanger 112 . As shown, heat exchanger 112 also receives natural gas (NG) feedstock 114v, and low temperature low pressure liquid MR 102l' receives NG feedstock 114v in contact with the heat exchange surface(s). Cool down. As the NG feedstock 114v and cold low pressure liquid MR 102l' move through the heat exchanger 112, heat is transferred from the warmer NG feedstock 114v to the cooler cold low pressure liquid MR 102l'. As a result, the NG feedstock 114v is cooled and begins to condense to form the LNG 124 .

Heat exchanger 112 may be any type of heat exchanger. Examples of heat exchanger 112 include core plate and fin, etched plate, bonded and wound diffusion coil, shell and tube, plate-and-frame. ) may be included.

NG feedstock 114v may contain both NG vapor 120 and heavy hydrocarbon components (HHC) such as butane, pentane, hexane, benzene, toluene, ethylbenzene, and xylene. It may be desirable to remove HHCs during the production of LNG 124 to prevent them from freezing. As illustrated in FIG. 1 , the heat exchanger 112 may include an HHC separation system 116 configured to remove HHC from the NG feedstock 114v. As the NG feedstock 114v cools in the heat exchanger 112, the HHC condenses at a higher temperature than lighter molecules, eg, methane. Accordingly, HHC-containing liquid 118 may be separated from NG feedstock 114v by HHC separation system 116 to yield purified NG vapor 120 . The purified NG vapor 120 flows through the heat exchanger 112 and condenses to form LNG 124 . Subsequently, LNG 124 may be depressurized and stored in a storage vessel (not shown).

Liquid 118 may be handled in a variety of ways. In one embodiment, as shown, liquid 118 exits heat exchanger 112 and is stored in HHC storage vessel 122 . In an alternative embodiment (not shown), the HHC liquid may be subjected to a multi-stage distillation process to separate it into its constituents. Separated components may be stored in respective storage vessels.

Low temperature low pressure liquid MR 102l' absorbs heat from NG feedstock 114v, purified NG vapor 120, and/or LNG 124 in heat exchanger 112. The absorbed heat is sufficient to cause evaporation of the low temperature low pressure liquid MR 102l'. Accordingly, at least a portion of the MR leaving the heat exchanger 112 undergoes a phase change to become steam. This vapor may be withdrawn in the form of recycled MR 102v″ and flow to valve 104 to flow to compression system 106. In certain embodiments, recycled MR 102v″ may include one or more conditioning systems. (not shown) may be conditioned to a first temperature T1 and a first pressure P1 prior to delivery at the valve 104 . By recovering and reusing the recycled MR 102v" rather than burning it, environmental emissions associated with combustion can be avoided.

During normal operation of liquefaction system 100, compressor 105 may leak MR (eg, feed MR 102v and/or hot high pressure MR 102v') and nitrogen due to incomplete sealing at various locations. can Liquefaction system 100 may also include at least one of MR recovery system 300 and nitrogen recovery system 400 in fluid communication with compressor 105 of compression system 106 . As discussed in detail below, MR recovery system 300 and nitrogen recovery system 400 are each configured to separate leaked MR from nitrogen (eg, by condensing MR hydrocarbons) to recover MR and nitrogen, respectively. makes it possible The MR recovery system 300 reintroduces recovered MR back into the compressor 105 of the compression system 106 and/or in other parts of the liquefaction system 100 (eg, with the condenser 108 and and to reintroduce into circulation (between the expansion valves 110 ). The nitrogen recovery system 400 is further configured to reintroduce the recovered MR as a component of the buffer gas of the compressor seal and/or for use elsewhere.

MR and leakage of nitrogen are discussed with reference to FIG. 2 . FIG. 2 is a seal assembly that may be used to receive an MR (eg, feed MR 102v and/or hot high pressure MR 102v') within a compression system, such as compression system 106 shown in FIG. 1 . A cross-sectional view of the compressor 200 including 201 is illustrated. A seal assembly 201 is positioned adjacent the suction port and/or discharge port of the compressor 200 to prevent leakage of fluid from the compressor. The seal assembly 201 is positioned along the length of the shaft 203 of the compressor 200 between the bearing side 211 and the compressor side 209 of the compressor 200 to separate fluids within the compressor 200 . a primary seal 202 , a secondary seal 204 , and a tertiary seal 206 . The primary and secondary seals 202 and 204 may be, for example, dry gas seals, and the tertiary seal 206 may be, for example, a type of carbon ring seal. The compression side 209 may include a compression chamber (not shown) used to compress the MR (eg, the supply MR 102v), and the bearing side 211 may include a compression chamber (not shown) in which the shaft 203 is to be rotated. one or more bearings (not shown) positioned around the shaft 203 of the compressor.

The seal assembly 201 of FIG. 2 is illustrated in the form of a tandem type dry gas sealing system, other sealing systems may be used. Examples include a single dry gas seal, a double dry gas seal, a multi-arranged dry gas seal, a labyrinth type seal, a carbon ring type seal, any combination of the aforementioned seals, or any other type of seal known in the art. may be included.

Those skilled in the art will have a basic understanding of how a compressor and sealing assembly works. A brief description is provided below.

During normal operation, feed MR 102v in the form of unfiltered MR 209, hot high pressure MR 102v', and combinations thereof are present at compressor side pressure. As discussed above, the supply MR 102v has a first temperature T1 and a first pressure P1, and the hot high pressure MR 102v' has a second temperature T2 and a second pressure P2. has Accordingly, the unfiltered MR 209 may have a temperature in the range of about the first temperature (T1) to the second temperature (T2) and a pressure in the range of about the first pressure (P1) and the second pressure (P2). For the sake of clarity, it is assumed in the discussion that follows that the unfiltered MR 209 has a second pressure P2.

The unfiltered MR 209 may leak into the seal assembly 201 through a sealing element 230 , which may be, for example, a labyrinth seal, which may leak into the primary, secondary, and tertiary seals 202 , 204 , 206) may be damaged. To prevent the unfiltered MR 209 from leaking through the sealing element 230 , the filtered high pressure MR 208 , or other seal gas, is placed adjacent to the compressor side 209 of the seal assembly 201 . may be transferred to area 205 . The filtered high pressure MR 208 pressurizes the cavity 207 located adjacent to the sealing element 230 to a fourth pressure P4 higher than the second pressure P2 at the compressor side 209, so that the unfiltered It is possible to prevent the MR 209 from leaking into the seal assembly 201 .

A portion of the filtered MR 208 may leak through the primary seal 202 and travel to the primary vent 212 . To ensure that approximately all of the MRs leaking through the primary seal 202 (eg, unfiltered MR 209 , filtered MR 208 ) are directed towards the primary vent 212 , the buffer A gas, such as nitrogen 214 (eg, nitrogen vapor) may be delivered to the primary buffer region 216 adjacent the primary vent 212 . Nitrogen 214 may be at a fifth pressure P5 that is higher than a fourth pressure P4 observed in the primary vent 212 . A portion of nitrogen 214 may leak into primary buffer region 216 through sealing element 232 , which may be, for example, a labyrinth seal that prevents MR leakage. Nitrogen 214 leaking through sealing element 232 is combined with MR leaking through primary seal 202 (eg, unfiltered MR 209 , filtered MR 208 ) to the primary vent. A mixture 218 of MR effluent and nitrogen 214 may be produced at 212 . Another portion of nitrogen 214 may leak through secondary seal 204 and travel to secondary vent 220 . A mixture 218 of the MR effluent and nitrogen 214 may be delivered from the primary vent 212 to the flare and combusted.

To prevent the bearing oil mist from migrating from the bearing side of the tertiary seal 206 , nitrogen 222 is also added to the secondary buffer between the secondary vent 220 of the seal assembly 201 and the bearing side 211 . may be implanted into region 224 . A portion of the nitrogen 222 delivered to the secondary buffer region 224 may leak beyond the tertiary seal 206 and move to the secondary vent 220 . Nitrogen 226 from secondary vent 220 may be captured and reintroduced into seal assembly 201 as a buffer gas.

As discussed in detail below, rather than flaring the mixture 218 of the leaked MR and nitrogen 214 from the primary vent 212 as is commonly done, an embodiment of the present invention is a liquefaction system. Facilitates recovery of leaking MR (eg, unfiltered MR 209, filtered MR 208) from a compressor (eg, compressor 105 of liquefaction system 100) of system and corresponding methods), This significantly reduces the need to stockpile, purchase, and reintroduce “lost” MR into the liquefaction system 100 .

3 shows MR leaks (e.g., unfiltered MR 209, filtered MR 208) and/or nitrogen (e.g., compressor 105 of compression system 106) leaking from a compressor (e.g., compressor 105 of compression system 106). 214) is a schematic diagram illustrating one exemplary embodiment of a novel MR recovery system for recovering all or part of any (or both) of.

The MR recovery system 300 includes a heat exchanger 302 and a two-phase separator 308 . Heat exchanger 302 is a nitrogen rich vapor 305 (eg, having nitrogen and MR components from compressor 105 of compression system 106 shown in FIG. 1 ) with cryogenic fluid 304 and a compressor of the compression system For example, it is configured to receive the mixture 218 ). The heat exchanger 302 may 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 the input fluid into two or more different phases.

The cryogenic fluid 304 may be a liquefied product produced by the liquefaction system 100 . For example, the cryogenic fluid 304 may be LNG, such as LNG 124 exiting the heat exchanger 112 shown in FIG. 1 . Accordingly, the cold fluid 304 ′ leaving the heat exchanger 302 is delivered to the storage vessel 320 via a valve 311 , where it is stored and/or circulated as needed. Alternatively, the cryogenic fluid 304 may be a refrigerant from another refrigeration system configured for the purposes described. Thus, the cold fluid 404 ′ leaving the heat exchanger 302 may continue to provide refrigeration to the nitrogen rich vapor 305 within the refrigeration cycle.

Heat exchanger 302 may take a variety of forms. In certain embodiments, heat exchanger 302 may be, for example, a shell and tube heat exchanger, or it may be a condensing coil heat exchanger. Alternatively, other heat exchangers may be used, such as core, core plate-and-fin, etched plate, bonded and wound diffusion coil, shell-and-tube, plate-and-frame, and the like. As shown, valves 309 , 311 are located on either side of heat exchanger 302 to control the flow rate of cryogenic fluid 304 through heat exchanger 302 .

In some embodiments, prior to delivery to the heat exchanger 302 , the nitrogen rich vapor 305 is delivered to a nitrogen removal assembly 303 located upstream of the heat exchanger 302 . As discussed above, the nitrogen rich vapor 305 may be a mixture 218 of leaked MR and nitrogen. The nitrogen removal assembly 303 is configured to remove a portion of nitrogen from the nitrogen-rich vapor 305 and output a nitrogen-poor vapor 307 containing less nitrogen than the nitrogen-rich vapor 305 . As an example, the nitrogen removal assembly 303 may be an absorption bed. The nitrogen-poor vapor 307 exiting the nitrogen removal assembly 303 is delivered to a heat exchanger 302 .

As the nitrogen-poor vapor 307 and cryogenic fluid 304 travel through the heat exchanger 302 , heat is transferred from the nitrogen-poor steam 307 to the cryogenic fluid 304 , whereby the nitrogen-poor steam 307 cools. and start to condense. While the nitrogen-poor vapor 307 is cooled in the heat exchanger 302, the hydrocarbon components constituting the MR are condensed at a higher temperature than the lighter components, such as nitrogen. Thus, a mixture 306 of the nitrogen rich vapor 310 and the hydrocarbon rich liquid 312 may be formed. Mixture 306 may be cooled sufficiently to achieve high purity nitrogen rich vapor 310 due to preferential condensation of hydrocarbon components. In some cases, mixture 306 is cooled sufficiently to produce nitrogen rich vapor 310 at approximately 95% purity. As an example, the temperature of the mixture 306 exiting the heat exchanger 302 may be at a temperature in the range of approximately -51 to -160°C (-60 to -257°F).

The mixture 306 exiting the heat exchanger 302 flows to a two-phase separator 308 . Two-phase separator 308 receives mixture 306 of nitrogen-rich vapor 310 and hydrocarbon-rich liquid 312 from heat exchanger 302 and separates nitrogen-rich vapor 310 and hydrocarbon-rich liquid 312 . is configured to As shown, the hydrocarbon-rich liquid 312 is delivered to a pump 316 which pumps the hydrocarbon-rich liquid 312 to a refrigerant supply system, such as the refrigerant supply system 102 shown in FIG. 310 is delivered to flare 322 .

However, in alternative embodiments, the hydrocarbon-rich liquid 312 and/or the nitrogen-rich vapor 330 output from the two-phase separator 308 may be treated differently than discussed above.

In one aspect, the hydrocarbon-rich liquid may be reintroduced directly into circulation within the liquefaction system (eg, between the condenser and the expansion valve), or it may be reintroduced into the compressor as filtered MR 208 described above with respect to FIG. 2 . It can be vaporized and reintroduced. In some cases, the hydrocarbon-rich liquid is heated prior to re-introduction into the circulation within the liquefaction system and/or prior to re-introduction into the compressor of the compression system to prevent low temperature embrittlement of the components of the liquefaction system and/or compressor.

In a further aspect, the hydrocarbon-rich liquid may be distilled to separate various hydrocarbon components, such as methane, ethylene, and propane, and pentane, so that they can be stored separately in a refrigerant supply system.

In an alternative embodiment, the nitrogen rich vapor output from the two-phase separator may be treated differently than flaring. In one aspect, the nitrogen-rich vapor can be distilled to further purify the nitrogen. The purified nitrogen vapor may be delivered back to the compressor as a buffer gas in the dry seal of the compressor, it may be stored in a storage vessel, or it may be delivered to other components in the liquefaction system.

In an alternative embodiment (not shown), rather than a heat exchanger and a two-phase separator, a distillation system may be used to separate the components of the nitrogen-poor vapor into a nitrogen-rich vapor and a hydrocarbon-rich liquid. In either case, each of the components of the nitrogen-poor vapor 307 may be separated and/or reintroduced into the liquefaction system 100 , stored and/or distributed as needed.

As noted above, nitrogen and MR leaking from the compressor of the compressor system are recovered, separated, stored, and/or reintroduced back into the liquefaction system. 4 shows an example of a nitrogen recovery system 400 for recovering nitrogen and MR leaking from the compressor 429 of the compressor system 430 . In certain embodiments, the compressor system 430 may be the compression system 106 of the liquefaction system 100 . A nitrogen buffer gas leaking from the compressor (eg, compressor 105 , compressor 200 ) without mixing with the MR is also recovered, such that the buffer gas (eg, nitrogen 214 in seal assembly 201 )) can be reintroduced into the compressor as

As shown, the nitrogen recovery system 400 includes a heat exchanger 402 and a two-phase separator 408 . Heat exchanger 402 transfers nitrogen and MR components from cryogenic fluid 404 and a compression system, such as a compressor (eg, compressor 105 , compressor 200 ) of compression system 106 shown in FIG. 1 . and is configured to receive vapor 405 with Heat exchanger 402 may be generally similar to heat exchanger 302 . Valves 409 and 411 are located on either side of the heat exchanger 402 to control the flow rate of the cold fluid 404 through the heat exchanger 402 . The two-phase separator 408 may be generally similar to the two-phase separator 308 and is configured to separate an input fluid into two or more different phases.

In some embodiments, the cryogenic fluid 404 is a liquefied product produced by the liquefaction system 100 . For example, the cryogenic fluid 404 may be LNG, such as LNG 124 exiting the heat exchanger 112 shown in FIG. 1 . Alternatively, the cryogenic fluid 404 may be, for example, propane, R-134A, propylene, or the like. As another example, the cryogenic fluid 404 may be liquid nitrogen or ethylene stored in the liquefaction system 100 . Accordingly, the cold fluid 404 ′ leaving the heat exchanger 402 is delivered to the storage vessel 420 via a valve 411 , where it is stored and/or circulated as needed. Alternatively, the cryogenic fluid 404 may be a refrigerant from another refrigeration system configured for the purposes described. Thus, the cold fluid 404 ′ leaving the heat exchanger 402 may continue to provide refrigeration to the vapor 405 within the refrigeration cycle.

As steam 405 and cold fluid 404 travel through heat exchanger 402 , heat is transferred from steam 405 to cold fluid 404 , causing steam 405 to begin cooling and condensing. . As the vapor 405 cools in the heat exchanger 402, the hydrocarbon components constituting the MR condense at a higher temperature than the lighter components, such as nitrogen. Accordingly, a mixture 406 of nitrogen-rich vapor 410 and hydrocarbon-rich liquid 412 may exit heat exchanger 402 . The mixture 406 can be sufficiently cooled so that the nitrogen rich vapor 410 has a high purity due to preferential condensation of hydrocarbon components. In some cases, mixture 406 is cooled sufficiently to produce nitrogen rich vapor 410 at approximately 95% purity. For example, mixture 406 may exit heat exchanger 402 at a temperature within the range of approximately -118 to -160°C (-180 to -257°F).

The mixture 406 exiting the heat exchanger 402 flows to a two-phase separator 408 , where it is separated into a nitrogen rich vapor 410 and a hydrocarbon rich liquid 412 . Nitrogen rich vapor 410 is combined with nitrogen vapor 431 from compressor 429 (eg, first compressor) of compressor system 430 and delivered to second compressor 425 . Nitrogen vapor 431 may be nitrogen leaking from a compressor, such as nitrogen 226 described above with respect to FIG. 2 .

Nitrogen vapor 424 exiting second compressor 425 is forced to combine with nitrogen vapor 426 from nitrogen source 428, which causes it to combine with a buffer gas (e.g., nitrogen in seal assembly 201) 214)), to the compressor 429 of the compressor system 430, as described above with respect to FIG. In some cases, nitrogen vapor 424 is heated prior to combining with nitrogen vapor 426 from nitrogen source 428 and/or prior to reintroduction into compressor system 430 , such that the components of compressor system 430 are heated. It is possible to prevent low-temperature embrittlement of urea.

In some embodiments, prior to combining with nitrogen vapor 431 from the compressor of compressor system 430 and prior to input to second compressor 425 , nitrogen rich vapor 410 is delivered to nitrogen removal system 417 . A nitrogen removal system 417 is located downstream from the two-phase separator 408 and is configured to remove at least a portion of the nitrogen in the nitrogen rich vapor 410 . As an example, the nitrogen removal system 417 may be an adsorption bed that removes a portion of the adsorbed nitrogen. The adsorbed nitrogen is released as a result of the desorption process, and the released nitrogen is passed to a second compressor 425 and combined with nitrogen vapor 426, as described above.

In an alternative embodiment, the nitrogen vapor 424 output by the second compressor 425 may be treated differently than being combined with the nitrogen vapor 426 . In one aspect, rather than passing the nitrogen vapor back to the compressor system, the nitrogen vapor may be compressed, condensed, and stored in a storage vessel (not shown). In another aspect, the nitrogen vapor may be stored as vapor or delivered to other components of the liquefaction system for use elsewhere.

As shown in FIG. 4 , the hydrocarbon-rich liquid 412 exiting the two-phase separator 408 is delivered to a pump 416 , which pumps the hydrocarbon-rich liquid 412 to a flare 422 . However, in alternative embodiments, the hydrocarbon-rich liquid 412 may be treated differently. In one aspect, rather than flaring the hydrocarbon-rich liquid 412 , a portion of the hydrocarbon-rich liquid 412 may 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 pentane, which can be stored separately in a refrigerant supply system. As another example, rather than using heat exchanger 402 and two-phase separator 408 , a distillation system may be used to separate the components of vapor 405 . Accordingly, each of the components of the vapor may be separated, reintroduced into the liquefaction system, stored and/or distributed as needed.

5 is a flow diagram illustrating an exemplary embodiment of a method 500 for operating a liquefaction system. Embodiments of the method include operations 502 - 512 . It will be appreciated that in alternative embodiments, the method may include more or fewer acts, which may be performed in a different order than illustrated in FIG. 5 .

In operation 502 , a seal gas is received at a seal assembly of a first compressor (eg, compressor 105 ). In certain embodiments, the seal gas is a mixed refrigerant (MR), such as feed MR 102v, high temperature high pressure MR 102v', and combinations thereof.

In operation 504, nitrogen vapor is received at the seal assembly of the first compressor. In certain embodiments, the nitrogen vapor is nitrogen 214 used as a buffer gas in the seal assembly 201 .

In operation 506 , a first vapor is received in a first heat exchanger. In certain embodiments, the first vapor comprises at least a portion of the seal gas and at least a portion of the nitrogen vapor.

In operation 508, the cold fluid is delivered to the cooling element of the first heat exchanger. As an example, the cryogenic fluid may be the cryogenic fluid 304 . Examples of cryogenic fluid 304 include liquefied products produced by liquefaction system 100 (eg, LNG 124 exiting heat exchanger 112 ), other refrigeration systems, different from liquefaction system 100 . refrigerants from, and combinations thereof.

In operation 510, heat is transferred from the first vapor to the cold fluid to produce a mixture of a nitrogen-rich vapor and a hydrocarbon-rich liquid. In certain embodiments, the nitrogen rich vapor has a purity of greater than or equal to approximately 95%. Heat transfer may be performed by a heat exchanger (eg, 302 , 402 ).

In operation 512, the hydrocarbon-rich liquid is separated from the nitrogen-rich vapor in a separator (eg, 308, 408) located downstream of the first heat exchanger.

Embodiments of method 900 may optionally include one or more of the following operations.

In another embodiment, method 500 may include receiving nitrogen rich vapor (eg, 410 ) in a second compressor. As an example, the second compressor may be the second compressor 425 , and the nitrogen rich vapor 410 may be received from the heat exchanger 402 . After being received 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 a seal assembly (eg, 201 ) of the first compressor. Optionally, nitrogen rich vapor 410 is combined with nitrogen 214 prior to delivery to seal assembly 201 .

In another embodiment, method 500 may include receiving the methane-containing vapor in a second heat exchanger, and removing heat from the methane-containing vapor in the second heat exchanger to produce a cold fluid. . In certain embodiments, the methane-containing vapor may be natural gas (NG). In a further embodiment, the second heat exchanger may be a heat exchanger 302 .

In another embodiment, method 500 may include receiving the second vapor in a nitrogen removal assembly located 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 a nitrogen rich vapor 305 and the nitrogen removal assembly is a nitrogen removal assembly 303 . After receiving the second vapor, the nitrogen removal assembly removes a portion of the nitrogen vapor from the second vapor to produce a first vapor (eg, nitrogen-poor vapor 307 ).

In another embodiment, method 500 includes receiving a nitrogen rich vapor in a nitrogen removal assembly located downstream of a separator; and removing a portion of the nitrogen from the nitrogen rich vapor. As one example, the separator is a two-phase separator 408 , the nitrogen removal assembly located downstream of the two-phase separator 408 is a nitrogen removal system 417 , and the nitrogen-rich vapor is a nitrogen-rich vapor 410 .

In another embodiment, method 500 includes receiving a hydrocarbon-rich liquid (eg, 316, 416) in a pump (eg, 316, 416) and storing the hydrocarbon-rich liquid (eg, 312, 412) in a storage vessel (eg, 322, 422).

Those skilled in the art will recognize that the methods, systems, and apparatus described herein may be applied within liquefaction plants capable of producing liquefied products other than LNG. For example, embodiments of MR recovery system 300 and/or nitrogen recovery system 400 may be implemented in liquefaction systems that produce liquefied petroleum gas (LPG), ethane, propane, helium, ethylene, and the like.

Exemplary technical effects of the methods, systems, and apparatus described herein include, by way of non-limiting example, the ability to recover, separate, and store MR components and/or nitrogen leaking from a compressor. Other technical effects of the methods, systems, and apparatus described herein include the ability to reintroduce the MR component into circulation within the liquefaction system and/or reuse recovered nitrogen as a buffer gas in the compressor. By recovering and reusing MR and nitrogen, the loss of MR and nitrogen can be minimized, which can lower the total operating cost of the liquefaction system. Additionally, by recovering MR rather than burning it, the amount of MR burned can be reduced, thereby reducing environmental emissions.

Certain illustrative embodiments are described in order to provide a general understanding of the principles of 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, apparatus, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments, and that the scope of the invention is limited only by the claims. Features illustrated or described in connection with one exemplary embodiment may be combined with features of another embodiment. Such modifications and variations are intended to be included within the scope of the present invention. Also, in this specification, like-named components of the embodiments have substantially similar characteristics, and thus, within a particular embodiment, each characteristic of each like-named component is not necessarily described in full detail. .

In the above description and claims, phrases such as "at least one" or "one or more" may appear following a combinatorial listing of elements or features. The term “and/or” may also appear in a listing of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which such a phrase is used, it means individually any of the listed elements or features, or any of the other recited elements or features. It is intended to mean any of the recited elements or features in combination with that of

As used herein throughout this specification and claims, an approximation expression may be applied to modify any quantitative expression that may vary permissibly without causing a change in the underlying function involved. Accordingly, a term or a value modified by terms such as “about” and “substantially” should not be limited to the precise value specified. In at least some cases, the approximate expression may correspond to the precision of an instrument for measuring a value. Here and throughout the specification and claims, range limits may be combined and/or interchanged, such ranges are identified and include all subranges subsumed therein unless the context or expression indicates otherwise.

Claims (17)

In the liquefaction system,
a first compressor;
a recovery system in fluid communication with the first compressor, the recovery system comprising:
a low temperature configured to receive a first vapor comprising nitrogen and a mixed refrigerant from the first compressor and convert the first vapor to a mixture of a nitrogen-rich vapor and a hydrocarbon-rich liquid, the low temperature providing refrigeration to the first vapor a first heat exchanger having at least one cooling element configured to receive a fluid, and
a separator configured to receive a mixture of the hydrocarbon-rich liquid and the nitrogen-rich vapor from the first heat exchanger and to separate the hydrocarbon-rich liquid and the nitrogen-rich vapor
which comprises, a recovery system; and
a second heat exchanger in fluid communication with the first compressor
wherein the second heat exchanger is configured to receive the methane-containing vapor and convert the methane-containing vapor to a methane-containing liquid. The nitrogen removal assembly of claim 1 , further comprising a nitrogen removal assembly located upstream of the first heat exchanger, the nitrogen removal assembly configured to produce the first vapor from a second vapor comprising a mixed refrigerant and nitrogen; , wherein the first vapor has less nitrogen than the second vapor. 3. The liquefaction system of claim 2, wherein the nitrogen removal assembly comprises an adsorption bed. The nitrogen removal assembly of claim 1 , further comprising a nitrogen removal assembly located downstream of the separator, the nitrogen removal assembly configured to receive the nitrogen-rich vapor from the separator and remove a portion of the nitrogen from the nitrogen-rich vapor. Consisting of a liquefaction system. The liquefaction system of claim 1 , wherein the first compressor includes a seal assembly configured to receive at least a portion of the nitrogen rich vapor from the separator. 6. The apparatus of claim 5, further comprising a second compressor in fluid communication with the separator, the second compressor receiving at least a portion of the nitrogen-rich vapor from the separator and removing at least a portion of the nitrogen-rich vapor from the separator. and a liquefaction system configured to press against the seal assembly. The liquefaction system of claim 1 , wherein the cryogenic fluid comprises at least a portion of the methane-containing liquid. The liquefaction system of claim 1 , further comprising a pump configured to receive the hydrocarbon-rich liquid from the separator and pump the hydrocarbon-rich liquid to a storage vessel. A method of operating a liquefaction system comprising:
receiving a seal gas comprising hydrocarbons in a seal assembly of a first compressor;
receiving nitrogen vapor in the seal assembly of the first compressor;
receiving, in a first heat exchanger, a first vapor comprising at least a portion of the seal gas and at least a portion of the nitrogen vapor;
delivering a cryogenic fluid to a cooling element of the first heat exchanger;
transferring heat from the first vapor to the cryogenic fluid to produce a mixture of a nitrogen-rich vapor and a hydrocarbon-rich liquid;
separating the hydrocarbon-rich liquid from the nitrogen-rich vapor in a separator located downstream of the first heat exchanger;
receiving the methane-containing vapor in a second heat exchanger; and
removing heat from the methane-containing vapor in the second heat exchanger to produce the cryogenic fluid;
A method comprising 10. The method of claim 9,
receiving the nitrogen rich vapor in a second compressor;
compressing the nitrogen rich vapor using the second compressor; and
and passing at least a portion of the nitrogen rich vapor to a seal assembly of the first compressor. 11. The method of claim 10,
receiving, in the second compressor, a portion of the nitrogen vapor from the first compressor; and
and combining a portion of the nitrogen vapor received in the seal assembly with the nitrogen rich vapor. 10. The method of claim 9, wherein the seal gas is a mixed refrigerant. 10. The method of claim 9,
receiving a second vapor in a nitrogen removal assembly located 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
and removing a portion of the nitrogen vapor from the second vapor to produce the first vapor. 10. The method of claim 9,
receiving the nitrogen rich vapor in a nitrogen removal assembly located downstream of the separator; and
and removing a portion of the nitrogen from the nitrogen rich vapor. 10. The method of claim 9,
receiving the hydrocarbon-rich liquid in a pump; and
and pumping the hydrocarbon-rich liquid to a storage vessel. delete delete

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