Patent Application
20150300731
The present invention relates to a method and apparatus for treating a hydrocarbon stream comprising methane.
Hydrocarbon streams comprising methane can be derived from a number of sources, such as natural gas or petroleum reservoirs, or from a synthetic source such as a Fischer-Tropsch process. In the present invention, the hydrocarbon stream preferably comprises, or essentially consists of, natural gas. It is useful to treat and cool such streams for a number of reasons. It is particularly useful to liquefy the hydrocarbon stream.
Natural gas is a useful fuel source, as well as a source of various hydrocarbon compounds. It is often desirable to liquefy natural gas in a liquefied natural gas (LNG) plant at or near the source of a natural gas stream for a number of reasons. As an example, natural gas can be stored and transported over long distances more readily as a liquid than in gaseous form because it occupies a smaller volume and does not need to be stored at high pressure.
WO2012/000998 discloses a method and apparatus for treating a methane-containing hydrocarbon stream, wherein a wet hydrocarbon stream, before it is de-hydrated in a water removal device, is cooled by indirect heat exchanging against an effluent stream from the water removal device and by indirect heat exchange against an auxiliary refrigerant stream. After the indirect heat exchanging against the wet hydrocarbon stream, the effluent stream is passed to a further heat exchanger where it is cooled against an evaporating refrigerant fraction which is obtained from a part of a source refrigerant stream. The auxiliary stream and the part of the source refrigerant stream are obtained by splitting a source refrigerant stream, obtained from a refrigerant compressor and an ambient heat exchanger, into the auxiliary refrigerant stream and said part of the source refrigerant stream. Spent refrigerant discharged from the further heat exchanger is conveyed back to the refrigerant compressor, optionally via a suction drum, and a discharged auxiliary refrigerant stream, resulting from the auxiliary refrigerant stream after cooling the wet hydrocarbon stream, is passed to a second suction inlet in the same refrigerant compressor, optionally via another suction drum.
The present invention provides a method of treating a hydrocarbon stream comprising methane, the method comprising:
In another aspect, the present invention provides an apparatus for treating a hydrocarbon stream comprising methane, the apparatus comprising:
The invention will be further illustrated hereinafter, using examples and with reference to the drawing in which;
In these figures, same reference numbers will be used to refer to same or similar parts. Furthermore, a single reference number will be used to identify a conduit or line as well as the stream conveyed by that line. While the invention is illustrated making reference to one or more a specific combinations of features and measures, many of those features and measures are functionally independent from other features and measures such that they can be equally or similarly applied independently in other embodiments or combinations.
The present description concerns removal of a wet disposal stream from a wet hydrocarbon stream in a water removal device, yielding an effluent stream comprising the wet hydrocarbon stream from which the wet disposal stream has been removed.
The effluent stream is intended to be cooled in a further heat exchanger against an evaporating refrigerant stream obtained from a source refrigerant stream. After evaporating, the evaporating refrigerant stream is discharged from the further heat exchanger as a spent refrigerant stream and passed to a refrigerant compressor. An auxiliary refrigerant stream, split-off from the same source refrigerant stream in the same refrigerant circuit as used to further the effluent stream, is used to cool the wet hydrocarbon stream before the wet hydrocarbon stream enters the water removal device. A discharged auxiliary refrigerant stream is obtained from the auxiliary refrigerant stream following said cooling of the wet hydrocarbon stream with the auxiliary refrigerant stream.
The source refrigerant stream is formed from a refrigerant stream in compressed condition. The refrigerant stream in compressed condition is formed by compressing the spent refrigerant and the discharged auxiliary refrigerant stream whereby the auxiliary refrigerant is brought in direct heat exchanging contact with the spent refrigerant as it is being passed to the refrigerant compressor.
An advantage of said direct heat exchanging before the compressing is that any liquid phase that may be present in the auxiliary refrigerant stream is evaporated by the direct heat exchanging against the spent refrigerant stream.
This works best if the temperature of the spent refrigerant is higher than the temperature of the auxiliary refrigerant immediately after the indirectly heat exchanging of the auxiliary refrigerant against the wet hydrocarbon stream and the if the auxiliary refrigerant stream flow rate is less than 10% of the spent refrigerant stream flow rate.
A benefit of this proposed method and apparatus is that the liquid loading on the suction drums is lower due to the direct heat exchanging. Furthermore, that no separate suction drum is needed for the auxiliary refrigerant. By omitting the separate suction drum for the auxiliary refrigerant associated capital expenditure may be avoided.
The water removal device 525 is arranged to receive the wet hydrocarbon stream 510 downstream of the auxiliary heat exchanging arrangement 575. Typically the water removal device comprises a first water removal device inlet 551 to receive the wet hydrocarbon stream 510 through. The water removal device 525 further comprises a wet disposal stream outlet 589 for discharging a wet disposal stream 590 comprising water from the wet hydrocarbon stream 510, and a vapour outlet 559 for discharging an effluent stream 590 comprising the wet hydrocarbon stream from which the wet disposal stream 590 has been removed.
A further heat exchanger 535 is provided, arranged with a first tube bundle inlet 531 for receiving the effluent stream 560 from the water removal device 525. The further heat exchanger 535 is also provided with a first tube bundle outlet 539 for discharging a cooled hydrocarbon stream 540. The first tube bundle outlet 539 is within the further heat exchanger internally connected with the first tube bundle inlet 531 via a first tube bundle 532. The first tube bundle 532 is arranged in a cooling zone within the further heat exchanger 535 in a heat exchanging relationship with an evaporating refrigerant fraction inside the further heat exchanger 535.
The vapour outlet 559 of the water removal device 525 is connected with the first tube bundle inlet 531 of the further heat exchanger 535 via first connecting means 565. The first connecting means 565 passes through the wet feed heat exchanger 545 in indirect heat exchanging interaction with the wet hydrocarbon stream 510.
A refrigerant circuit 200 provides cooling to the further heat exchanger 535. The refrigerant circuit 200 is arranged to cycle a refrigerant in repetitive cycles. When being considered following the flow of the refrigerant during one single pass through the refrigerant circuit 200 starting from a discharge outlet 279 of a refrigerant compressor 270, the refrigerant encounters: a condenser 285, a splitter 245, a first expansion device 225, and the cooling zone in the further heat exchanger 535.
The condenser 285 is arranged to receive a refrigerant stream in a compressed condition and to extract heat from the refrigerant stream in said compressed condition, thereby forming a source refrigerant stream 280 comprising a refrigerant stream in a compressed condition and comprising a liquid phase. The first expansion device 225 is arranged to receive and expand at least a part 220 of a part 210 of the source refrigerant stream 280, thereby obtaining the evaporating refrigerant fraction.
The further heat exchanger 535 is arranged to receive the evaporating refrigerant fraction from the first expansion device 225. The evaporating refrigerant fraction is arranged in indirect heat exchanging contact with at least the effluent stream in the first tube bundle 532 in the cooling zone within the further heat exchanger 535, whereby the evaporating refrigerant fraction is transformed into spent refrigerant. The further heat exchanger comprises a shell outlet 239 to discharge the spent refrigerant from the cooling zone. A spent refrigerant line 240 connects the shell outlet 239 to the refrigerant compressor 270.
The refrigerant compressor 270 comprises at least a first suction inlet 271, and a discharge outlet 279. Optionally, more suction inlets may be available to allow feeding into another stage of compression.
The splitter 245 is provided to split the source refrigerant stream 280 into the auxiliary refrigerant stream 250 and the part 210 of the source refrigerant stream 280. The auxiliary refrigerant stream 250 comprises at least a part of the liquid phase from the source refrigerant stream 280.
This apparatus can be operated in accordance with a method wherein a wet hydrocarbon stream 510 comprising at least methane and water is provided at a temperature equal to a first temperature. The wet hydrocarbon stream 510 is cooled, thereby lowering the temperature from the first temperature to a second temperature. The cooling of the wet hydrocarbon stream 510 comprises indirectly heat exchanging against the effluent stream 560, followed by indirectly heat exchanging in the auxiliary heat exchanging arrangement against the auxiliary refrigerant stream 250. A discharged auxiliary refrigerant stream 265 consisting of the auxiliary refrigerant containing heat from the wet hydrocarbon stream 510 is discharged from the auxiliary heat exchanging arrangement 575.
The cooled wet hydrocarbon stream is then fed to the water removal device 525 though the first water removal device inlet 551. In the water removal device 525 a wet disposal stream 590 comprising water, and optionally comprising mercury, is removed from the wet hydrocarbon stream 510 at the second temperature, resulting in the effluent stream 560, which comprises the wet hydrocarbon stream from which the wet disposal stream 590 has been removed. The wet disposal stream 590 is discharged from the water removal device 525 via wet disposal stream outlet 589, for further treatment (not shown) and disposal (not shown).
The effluent stream 560, containing the wet hydrocarbon stream from which components including water and optionally mercury have been removed, is discharged from the water removal device 525 through the vapour outlet 559, and passed to the further heat exchanger 535 via the first connecting means 565. While passing the effluent stream to the further heat exchanger 535, the effluent stream is heated in the wet feed heat exchanger 545, by indirect heat exchange between the effluent stream 560 and the wet hydrocarbon stream 510 prior to admission of the wet hydrocarbon stream 510 into the water removal device 525. Subsequently, the effluent stream 560 is cooled in the further heat exchanger 535 by indirect heat exchanging against the evaporating refrigerant fraction.
To provide this cooling in the further heat exchanger 535, a refrigerant is cycled in repetitive cycles, wherein a single pass of the refrigerant through the cycle comprises the following consecutive steps: providing a refrigerant stream in a compressed condition; and passing the refrigerant stream in said compressed condition through the condenser 285, whereby at least partially condensing the refrigerant stream in said compressed condition, thereby forming the source refrigerant stream 280. The source refrigerant stream 280 comprises a liquid phase at a refrigerant temperature and a refrigerant pressure.
In addition to the effluent stream 560, a part 210 of the source refrigerant stream 280 is passed to the further heat exchanger 535 as well. The evaporating refrigerant fraction is obtained by at least expanding at least a part 220 of the part 210 of the source refrigerant stream 280, to a pressure lower than the refrigerant pressure. The evaporating refrigerant fraction then is passed to the further heat exchanger 535, where the spent refrigerant is formed from the evaporating refrigerant fraction by absorbing heat from at least the effluent stream in the further heat exchanger 535. The spent refrigerant is discharged from the further heat exchanger 535 and passed to the refrigerant compressor 270. The refrigerant compressor 270 discharges said refrigerant stream in compressed condition from the discharge outlet 279 of the refrigerant compressor 270.
In each said single pass of the refrigerant through the refrigerant circuit 200, the cycle further comprises the following consecutive steps: splitting the source refrigerant stream 280 into said auxiliary refrigerant stream 250 and said part 210 of the source refrigerant stream 280; and indirectly heat exchanging the auxiliary refrigerant stream 250 against the wet hydrocarbon stream 510 in the auxiliary heat exchanger arrangement 575.
The splitting is such that the auxiliary refrigerant stream 250 comprises at least a part of the liquid phase from the source refrigerant stream 280. During the indirectly heat exchanging of the auxiliary refrigerant stream 250 against the wet hydrocarbon stream 510 heat passes from the wet hydrocarbon stream 510 to the auxiliary refrigerant stream 250. A discharged auxiliary refrigerant stream 265, which contains heat from the wet hydrocarbon stream 510, is discharged from the auxiliary heat exchanger arrangement 575.
It is presently proposed to bring the discharged auxiliary refrigerant stream 265 and the spent refrigerant stream 240 into direct heat exchanging contact by injecting the discharged auxiliary refrigerant stream 265 into the spent refrigerant stream 240 that is being passed from the further heat exchanger 535 to the refrigerant compressor 270. A combiner 266 may be provided, to bring the spent refrigerant 240 and the discharged auxiliary refrigerant 265 together in direct heat exchanging contact, such that the auxiliary heat exchanging arrangement 575 is arranged in the auxiliary refrigerant stream 250 between the splitter 245 and the combiner 266. The combiner 266 is arranged between the auxiliary heat exchanger arrangement 575 and the refrigerant compressor 270. This allows for directly heat exchanging the discharged auxiliary refrigerant stream 265 with the spent refrigerant 240 being passed to the refrigerant compressor 270, and forming of the refrigerant stream in compressed condition by compressing the spent refrigerant 240 and the discharged auxiliary refrigerant stream 265.
Said directly heat exchanging is allowed before said compressing in each single pass of the refrigerant through the refrigerant circuit 200. Thus, the refrigerant stream in compressed condition is formed by compressing both the (discharged) auxiliary refrigerant stream 250 (265) and the spent refrigerant stream 240.
Direct heat exchanging, as opposed to indirect heat exchanging, involves bringing the two stream in physical contact with each other whereby the two streams are mixed to form a single combined stream.
Preferably, the wet hydrocarbon stream 510 is also passed through a wet feed ambient heat exchanger 585, before being fed to the wet feed heat exchanger 545. The wet feed ambient heat exchanger 585 is suitably provided in the supply conduit. In the wet feed ambient heat exchanger 585, wet hydrocarbon stream 510 may be heat exchanged against ambient. If the optional wet feed ambient heat exchanger 585 is employed, the first temperature is controlled by heat exchanging against an ambient stream, such as for instance an air stream or a water stream. The first temperature may be within 10° C. from ambient temperature. For the purpose of the present disclosure, ambient temperature is the temperature of the air stream or the water stream against which the wet hydrocarbon stream 510 is heat exchanged. Ambient temperature may for instance lie in the range of from 0 to 50° C.
There is essentially no separate other heat exchanger present between the optional wet feed ambient heat exchanger 585 and the wet feed heat exchanger 545, such that the wet hydrocarbon stream 510 can be provided at the temperature equal to the first temperature. No heat exchanging with another medium will be taking place between the optional wet feed ambient heat exchanger 585 and the wet feed heat exchanger 545, other than de-minimis unavoidable heat exchanging with the environment via the piping used for the supply conduit 510 downstream of the wet feed ambient heat exchanger 585. The temperature of the wet hydrocarbon stream as it passes into the wet feed heat exchanger 545 is therefore essentially equal to the first temperature, which is the temperature of the wet hydrocarbon stream as it is discharged from the wet feed heat exchanger 585. In practice this may mean that the temperature of the wet hydrocarbon stream as it passes into the wet feed heat exchanger 545 is less than 5° C. different, preferably less than 2° C. different, from the first temperature.
Preferably, the refrigerant condenser 285 is provided in the form of an ambient heat exchanger. This allows for condensing of the refrigerant stream in compressed condition by heat exchanging the refrigerant stream in compressed condition that is discharged from the refrigerant compressor 270 against ambient. Thus, the source refrigerant stream 280 is conveniently provided at a refrigerant temperature equal to a third temperature, which is within 10° C. from the first temperature.
Optionally, further heat exchanger 535 is further provided with at least one second tube bundle inlet 211, for receiving the part 210 of the source refrigerant stream 280, and at least one second tube bundle outlet 219. The optional at least one second tube bundle outlet 219 is internally in the further heat exchanger 535 connected with the second tube bundle inlet 211 via a second tube bundle 212 arranged in and passing through the cooling zone. This way the second tube bundle 212 is arranged in a heat exchanging relationship with the evaporating refrigerant fraction inside the further heat exchanger 535 in a similar way as the first tube bundle 532. At least one cooled refrigerant stream 220 can thus be discharged from the at least one second tube bundle outlet 219.
With such an optional second tube bundle 212 present, second connecting means may be provided connecting the condenser 285 with the second tube bundle inlet 211. Preferably, the second connecting means is essentially free from any separate heat exchanger. In such embodiments, both the effluent stream 560 and the part 210 of the source refrigerant stream 280 can be cooled in the further heat exchanger 535 by indirect heat exchanging against the evaporating refrigerant fraction 230.
With the indirectly heat exchanging in the wet feed heat exchanger 545 between the effluent stream 560 and the wet hydrocarbon stream 510 it is achieved that the temperature of the effluent stream 560 is restored, within the limits of the approach temperature of the wet feed heat exchanger 545, to better match the temperature of the wet hydrocarbon stream 510. Thus, the heating of the effluent stream 560 by indirectly heat exchanging against the wet hydrocarbon stream 510 in the wet feed heat exchanger 545 during passing of the effluent stream 560 to the further heat exchanger 535, the temperature of the effluent stream 560 is matched to the first temperature as close as the warm end approach temperature of the wet feed heat exchanger 545.
This way, the temperature difference between the effluent stream, suitably in the form of “dried hydrocarbon feed gas”, and the refrigerant stream is substantially the same, such as the same within the approach temperature of the wet feed heat exchanger 545—for instance within 10° C. or preferably within 5° C.—as the temperature difference between the original wet hydrocarbon stream and the source refrigerant stream 280, regardless of the temperature conditions in the water removal device 525.
As a result, any pinching and thermal stress that may be induced in the further heat exchanger 535 when the effluent stream and the refrigerant streams are fed into such further heat exchanger 535 would not be significantly worse than would be the case if the wet hydrocarbon stream would be passed to the further heat exchanger without having passed through the water removal device 525.
Preferably, the wet hydrocarbon stream 510 and the source refrigerant stream 280 may have substantially the same temperature, for instance within 10° C. from each other, preferably within 5° C. from each other. This can for instance be achieved by heat exchanging both the wet hydrocarbon stream and the refrigerant stream against ambient.
However, in addition to the indirect heat exchanging between the effluent stream 560 from the water removal device 525 and the wet hydrocarbon stream 510, the resulting cooled wet hydrocarbon stream is indirectly heat exchanged against the auxiliary refrigerant stream 250 in the auxiliary heat exchanging arrangement 575. Since the temperature of the wet hydrocarbon stream entering the auxiliary heat exchanging arrangement 575 is lower than the first temperature, due to the heat exchanging in the wet feed heat exchanger 545, the temperature of the auxiliary refrigerant stream as it is discharged from the auxiliary heat exchanging arrangement 575 will also be lower than the first temperature. As the auxiliary refrigerant passes from the splitter 245 to the auxiliary heat exchanging arrangement 575 in each single pass the auxiliary refrigerant stream 250 may be expanded in a second expansion device 255. Herewith, it is achieved that, during each single pass of the refrigerant through the refrigerant circuit 200, the auxiliary refrigerant stream 250 is expanded after the splitting in splitter 245 and before the indirectly heat exchanging of the auxiliary refrigerant stream 250 against the wet hydrocarbon stream in the auxiliary heat exchanging arrangement 575.
More heat may be extracted from at least one of:
The wet hydrocarbon stream 510, as well as the dried effluent stream 560, contains methane. The wet hydrocarbon stream 510 may be obtained from natural gas or petroleum reservoirs or coal beds. As an alternative the hydrocarbon stream may also be obtained from another source, including as an example a synthetic source such as a Fischer-Tropsch process. Preferably the hydrocarbon stream comprises at least 50 mol % methane, more preferably at least 80 mol % methane.
Depending on the source, the wet hydrocarbon stream may contain varying amounts of other components, including one or more non-hydrocarbon components other than water, such as N2, CO2, Hg, H2S and other sulphur compounds; and one or more hydrocarbons heavier than methane such as in particular ethane, propane and butanes, and, possibly lesser amounts of pentanes and aromatic hydrocarbons. Hydrocarbons with a molecular mass of at least that of propane may herein be referred to as C3+ hydrocarbons, and hydrocarbons with a molecular mass of at least that of ethane may herein be referred to as C2+ hydrocarbons.
If desired, the wet hydrocarbon stream 510 may have been pre-treated to reduce and/or remove one or more of undesired components such as CO2 and H2S, or have undergone other steps such as pre-pressurizing or the like. Such steps are well known to the person skilled in the art, and their mechanisms are not further discussed here. The composition of the wet hydrocarbon stream thus varies depending upon the type and location of the gas and the applied pre-treatment(s).
The wet feed heat exchanger 545 may be provided in the form of a tube in shell type heat exchanger or pipe in pipe heat exchanger, but preferred is a plate-type heat exchanger such as a plate-fin heat exchanger and/or a printed circuit heat exchanger, optionally in a cold box. Preferably, the wet feed heat exchanger 545 may be installed in a counter current operating mode. In particular, the second outlet 569 may be located on the same heat exchanging side of the wet feed heat exchanger 545 as the first inlet 541 while the second inlet 561 may be located on the same heat exchanging side of the wet feed heat exchanger 545 as the first outlet 549. The second outlet discharges to the first inlet 531 of the further heat exchanger 535. The further heat exchanger 535 is preferably embodied in the form of a coil-wound heat exchanger.
Additionally, the further heat exchanger 535 is provided with a shell inlet 231 to provide access to the cooling zone. The second tube bundle outlet 219 may be connected to the shell inlet 231 via lines 220 and 230 which are connected to each other via the first expansion device 225, which is here shown in the form of a Joule-Thomson valve.
The refrigerant may be a single-component refrigerant such as propane, but is preferably a multicomponent refrigerant. For example, the multicomponent refrigerant may contain a mixture of hydrocarbon components including one or more of pentanes, butanes, propane, propylene, ethane, and ethylene.
The refrigerant condenser 285 may for example be provided in the form of an air cooler or a water cooler. The wet feed ambient heat exchanger 585 is preferably provided in the same form as the refrigerant condenser 285. The refrigerant compressor 270 together with the refrigerant condenser 285 provides the refrigerant source stream 280 in the form of a compressed and ambient cooled refrigerant stream in line 280. The temperature of the source refrigerant stream 280 is equal to a third temperature, preferably at a value within 10° C. from the first temperature, which is the temperature at which the wet hydrocarbon stream 510 is discharged from the wet feed ambient heat exchanger 585.
Spent refrigerant in line 240 is preferably conveyed back to the refrigerant compressor 270 via a suction drum 263. The suction drum 263 may be provided in the form of a phase separator to remove any remaining liquids 269 from the refrigerant compressor feed stream 268 which is fully vaporous.
The wet feed heat exchanger 545 may comprise:
The water removal device 525 may be of any suitable known type. It may typically comprise a separator vessel for separating precipitated components from the wet hydrocarbon stream 510, and downstream thereof a water sorbing device for absorbing or adsorbing remaining water components from the residue vapour from which the precipitated components have been removed. Common in the field are solid bed dehydration units, also referred to as dry desiccant dehydration units. Typically, multiple beds are in use in a cyclic mode of operation involving drying (absorbing or adsorbing) and regeneration (desorbing). Preferably, the water sorbing device is also capable of removing mercury from the wet hydrocarbon stream, which can be facilitated by an appropriate selection of the sorbent employed in the solid bed.
The auxiliary heat exchanging arrangement 575 functions to further lower the temperature of the wet hydrocarbon stream 510 to facilitate the drying. In
Preferably the part 210 of the source refrigerant stream 280 is passed to the further heat exchanger 535 while maintaining its temperature essentially equal to the third temperature. To this end, it will not be passed through a deliberate heat exchanger and no heat exchanging with another medium will be taking place other than de-minimis unavoidable heat exchanging with the environment via the piping used for line 210. In practice this may mean that the temperature of the part 210 of the source refrigerant stream 280 that passes through the second tube bundle inlet 211 is less than 5° C. different, preferably less than 2° C. different, from the temperature of the source refrigerant stream 280 as it is discharged from the refrigerant condenser 285.
Preferably, the temperature of the part 210 of the source refrigerant stream, as it passes through the second tube bundle inlet 211 in the further heat exchanger 535, is within 10° C. from the first temperature. One way of achieving this is by passing the refrigerant through the refrigerant condenser 285 and heat exchanging it against the same type of ambient stream as the wet hydrocarbon stream 510. While it is possible to install a further heat exchanger in the effluent stream 560 between the wet feed heat exchanger 545 and the further heat exchanger 535 in order to even better approach the first temperature and/or the third temperature, for reasons of capital expenditure control and operational simplicity it is preferred that the temperature of the effluent stream 560 in the first tube bundle inlet 531 is essentially the same as the temperature of the effluent stream 560 that was reached by the indirectly heat exchanging against the wet hydrocarbon stream 510 in the wet feed heat exchanger 545. To this end, the first connecting means is preferably essentially free from any separate heat exchanger between the wet feed heat exchanger 545 and the first tube bundle inlet 531 of the further heat exchanger 535. The effluent stream 560 that is discharged from the wet feed heat exchanger 545 is thus preferably not passed through any deliberate heat exchanger, and no heat exchanging with another medium will be taking place other than de-minimis unavoidable heat exchanging with the environment via the piping used for the connection between the wet feed heat exchanger 545 and the first tube bundle inlet 531 of the further heat exchanger 535. In practice this may mean that the temperature of the effluent stream 560 that passes through the first tube bundle inlet 531 is less than 5° C. different, preferably less than 2° C. different, from the temperature of the effluent stream 560 as it is discharged from the wet feed heat exchanger 545.
Both the effluent stream 560 and the part 210 of the source refrigerant stream 280 that is passed to the further heat exchanger 535 are cooled in the further heat exchanger 535, by indirect heat exchanging against an evaporating refrigerant fraction 230. The evaporating refrigerant fraction is passed into the shell side of the further heat exchanger 535 via the shell inlet 231. The evaporating refrigerant may be a separate refrigerant from the part of the source refrigerant in line 210 that is being cooled. However, as shown in
Preferably the temperature of the effluent stream 560 as admitted into the further heat exchanger 535 via the first tube bundle inlet 531 is within less than 10° C., preferably within less than 5° C., different from the temperature of the part 210 of the source refrigerant stream 280 as it is admitted into the further heat exchanger 535 via the second tube bundle inlet 211.
The expanded auxiliary refrigerant stream 260 is passed into the auxiliary heat exchanging arrangement 575 and discharged from the same after it has extracted heat from the wet hydrocarbon stream 510. The discharged auxiliary refrigerant 265 is recompressed.
The spent refrigerant 240 may be discharged from the further heat exchanger at a fourth temperature. The discharged auxiliary refrigerant stream 265 immediately after indirectly heat exchanging the discharged auxiliary refrigerant stream 265 against the wet hydrocarbon stream may be at a fifth temperature. The fifth temperature may be lower than the forth temperature. The direct heat exchanging of the discharged auxiliary refrigerant stream 265 will then cause vaporization of remaining liquid that might be present in the discharged auxiliary refrigerant stream 265 before the discharged auxiliary refrigerant stream 265 reaches the refrigerant compressor 270 for the first time after having been discharged from the auxiliary heat exchanging arrangement 575.
Preferably, the auxiliary refrigerant stream flow rate with which the auxiliary refrigerant stream 250 flows is less than 10% of the spent refrigerant stream flow rate with which the spent refrigerant stream 240 flows. The excess of the spent refrigerant stream 240 compared to the auxiliary refrigerant stream helps with the evaporation of remaining liquid that might be present in the discharged auxiliary refrigerant stream 265.
In
In the embodiment of
A further optional feature illustrated in
The cooled other refrigerant stream 320 may be partially or fully condensed in the further heat exchanger 535.
The cooled other refrigerant stream 320 may for instance be passed to another heat exchanger (not shown) to perform cooling duty therein. In performing said cooling duty, part of the condensed other refrigerant stream 320 may be evaporated in the other heat exchanger.
In one group of embodiments, as illustrated in
In another group of embodiments, the other refrigerant stream 310 may be circulated in another refrigerant circuit (not shown) that is separate from the discussed refrigerant circuit 200. For example, the refrigerant circuit 200 may be a pre-cooling refrigerant circuit used to produce the cooled hydrocarbon stream 540 and the cooled other refrigerant stream 320 in the form of a pre-cooled main refrigerant stream. The main refrigerant of the main refrigerant stream may be cycled in main refrigerant circuit that is distinct from the pre-cooling refrigerant circuit, such as described in for instance U.S. Pat. No. 6,370,910. In such a case, each of the pre-cooling refrigerant and the main refrigerant may be composed of a mixed refrigerant. A mixed refrigerant or a mixed refrigerant stream as referred to herein comprises at least 5 mol % of two different components. More preferably, any mixed refrigerant comprises two or more of the group consisting of: methane, ethane, ethylene, propane, propylene, butanes and pentanes.
Suitably, the pre-cooling refrigerant has a higher average molecular weight than main refrigerant. More specifically the pre-cooling refrigerant in the pre-cooling refrigerant circuit may be formed of a mixture of two or more components within the following composition: 0-20 mol % methane, 20-80 mol % ethane and/or ethylene, 20-80 mol % propane and/or propylene, <20 mol % butanes, <10 mol % pentanes; having a total of 100%. The main cooling refrigerant in the main refrigerant circuit may be formed of a mixture of two or more components within the following composition: <10 mol % N2, 30-60 mol methane, 30-60 mol % ethane and/or ethylene, <20 mol % propane and/or propylene and <10% butanes; having a total of 100%.
Alternatively, and one embodiment employing this is illustrated in
In the embodiment of
As illustrated in
In any case, the cooled hydrocarbon stream 540 that is discharged from the further heat exchanger 535 may be further treated in a variety of manners. In one group of embodiments, it may be cooled in one or more other heat exchangers against one or both of at least a part of the continuing refrigerant stream 235 being evaporated in another heat exchanger at a lower pressure than the evaporating refrigerant fraction 230 and at least a part of the cooled other refrigerant stream 320. Preferably, at least part of the cooled hydrocarbon stream 540 is cooled to a temperature low enough, such as below −125° C. or preferably below −150° C., to form liquefied natural gas. Such liquefied natural gas be depressurized in an end-flash system or depressurization stage as known in the art, and subsequently stored in a cryogenic liquid storage tank at a pressure of between 1 and 2 bar absolute and a temperature of approximately −162° C. This will not be described in further detail herein.
In another group of embodiments, the cooled hydrocarbon stream 540 may be subjected to one or more extraction steps wherein C2+ hydrocarbons, preferably C3+ hydrocarbons, are extracted from the cooled hydrocarbon stream 540 thereby generating a residue in the form of a methane-enriched hydrocarbon stream. This methane-enriched hydrocarbon stream may be sold as pipe line gas, or subjected to more cooling in the way described in the preceding paragraph, to produce liquefied natural gas. The extracted C2+ hydrocarbons, preferably C3+ hydrocarbons, may be sold and/or further processed, for instance by fractionation into single-component streams including ethane and/or propane and/or butane.
The person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 4866/CHE/2012 | Nov 2012 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/050021 | 1/2/2013 | WO | 00 |
