KR20160038030A - System and integrated process for liquid natural gas production - Google Patents

Abstract

A system and method for producing liquefied natural gas (LNG) from a natural gas stream is provided. The system includes a moisture removal device and a compressor to remove moisture from the natural gas stream and compress it. To release the cooled compressed discharge stream, a low moisture compressed natural gas stream is cooled in the heat exchanger. The polyphase turboexpander provides additional cooling and expansion of the cooled compressed discharge stream to produce an expanded discharge stream comprising a mixture of LNG / ice / solid CO ₂ slurry substantially consisting of CH ₄ . The expanded effluent stream is separated to produce a vapor stream consisting essentially of CH ₄ and a liquefied natural gas / ice / solid CO ₂ slurry stream. Additional separation of the liquefied natural gas / ice / solid CO ₂ slurry stream produces an output stream consisting of a liquefied natural gas output stream and substantially ice / solid CO ₂ .

Description

[0001] SYSTEM AND INTEGRATED PROCESS FOR LIQUID NATURAL GAS PRODUCTION [0002]

The present invention relates to systems and processes for the production of liquefied natural gas (LNG). More particularly, the present invention relates to a system and process for liquefied natural gas, which integrates natural gas purification and refrigeration steps into a single process.

Conventional liquefied natural gas production from pipeline-quality natural gas is typically used to remove moisture and CO ₂ first in the first treatment step, i.e., the purge step, and to use liquefaction in subsequent second processing steps , A two-step process. In order to integrate these multiple process steps, attempts have previously been made to integrate natural gas purification and refrigeration processes in the production of liquefied natural gas. Typically, these attempts were based on an external refrigeration system in which slurry composed of liquefied natural gas, ice, and solid CO ₂ is initially provided with the energy required for liquefaction and a process that occurs during the expansion of the nozzle. In general, minimal equipment integration is provided, thus requiring substantial equipment footprint. This results in costly systems and processes for the production of liquefied natural gas. appear.

Also, these LNG production processes, for example known as the two-step process described above, can be energy intensive as well as capital intensive.

Accordingly, there is a desire to provide an improved system and method for the production of liquefied natural gas.

These and other disadvantages of the prior art are overcome by the present invention which provides an improved system and method for the production of liquefied natural gas.

One aspect of the present invention is directed to a system for producing liquefied natural gas (LNG) from a natural gas stream comprising a water removal device, a compressor, a heat exchanger, a multi-phase turboexpander, a separator, One additional separator. The moisture removal device and compressor remove moisture from the natural gas stream and compress it to produce a low-moisture compressed natural gas stream. The heat exchanger cools the low moisture compressed natural gas stream to produce a cooled compressed discharge stream. Multi-phase turboexpander generates, the expanded exhaust stream consisting of a mixture of vapor and liquid natural gas / ice / solid CO ₂ to the slurry consisting of the expansion cooling the compressed effluent stream, substantially as CH _4. The separator is to separate the expanded effluent stream, thereby generating a substantially vapor stream and a liquid natural gas / ice / solid CO ₂ to the slurry stream consisting of CH _4. The at least one additional separator separates the liquefied natural gas / ice / solid CO ₂ slurry stream to produce an output stream consisting of a liquefied natural gas output stream and substantially ice / solid CO ₂ .

Another aspect of the invention relates to a system for producing liquefied natural gas (LNG) from a natural gas stream, said system comprising at least one compression stage, at least one cooling stage, and at least one expansion stage. The at least one compression stage and the at least one cooling stage are configured to compress and cool the natural gas stream to produce a cooled compressed effluent stream. The at least one expansion stage is configured to expand the cooled compressed discharge stream to produce an expanded discharge stream. The at least one expansion stage includes at least one multiphase turboexpander in fluid communication with the cooling stage and the compression stage. The multi-phase turboexpander housing, is arranged on at least one rotatable element, a housing disposed in the housing is disposed at least one inlet, and a housing configured to receive the cooled compressed discharge stream consists substantially CH ₄ And at least one outlet configured to discharge an expanded exhaust stream comprising a mixture of steam and liquefied natural gas / ice / solid CO ₂ slurry.

Another aspect of the present invention is directed to a method for producing liquefied natural gas (LNG) from a natural gas stream, said method comprising: providing an input natural gas stream; Removing moisture, compressing and cooling the natural gas stream to produce a cooled compressed discharge stream; By the step of expanding the compressed discharge stream from the cooling multi-phase turboexpander, generating an expanded exhaust stream that substantially comprises a mixture of vapor and liquid natural gas / ice / solid CO ₂ slurry consisting of CH _4; Separating the expanded effluent stream in at least one separator to produce a vapor stream and a liquefied natural gas / ice / solid CO ₂ slurry stream substantially consisting of CH ₄ ; And separating the liquefied natural gas / ice / solid CO ₂ slurry stream from at least one additional separator to produce an output stream and a liquefied natural gas (LNG) output stream substantially consisting of ice / solid CO ₂ do.

Various improvements of the foregoing features exist in connection with various aspects of the present invention. Additional features may also be incorporated in various aspects. These improvements and additional features may be present individually or in any combination. For example, various features described below in connection with one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the invention, alone or in any combination. Furthermore, the foregoing summary is intended merely to enable a reader to be familiar with certain aspects and contents of the present invention without being limited by the claimed subject matter.

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein like reference numerals refer to like parts throughout the drawings.

1 is a block diagram of a system for liquefied natural gas production in accordance with one or more embodiments shown or described herein.
2 is a block diagram of a system for liquefied natural gas production according to one or more embodiments shown or described herein.
3 is a schematic diagram of a polyphase turboexpander for solid, liquid, and gas separation, according to one or more embodiments shown or described herein.
4 is a schematic cross-sectional view of a polyphase turboexpander for solid, liquid, and gas separation, in accordance with one or more embodiments shown or described herein.
Figure 5 is a flow chart illustrating the steps involved in an exemplary process for the production of liquefied natural gas, in accordance with one or more embodiments shown or described herein.
6 is a comparison of liquefied natural gas yields as a function of compression, in accordance with one or more embodiments shown or described herein.

It is to be understood that while the invention will be described in connection with certain embodiments only for purposes of illustration, other objects and advantages of the invention will be apparent from the following description of the drawings according to the invention. While preferred embodiments have been described, they are not intended to be limiting. Rather, the generic principles set forth herein should be considered as illustrative only of the scope of the invention, and it is further to be understood that numerous changes may be made without departing from the scope of the invention.

As described in detail below, embodiments of the present invention provide systems and processes suitable for the production of liquefied natural gas. As described in detail below, embodiments of the present invention include a system comprising one or more integrated polyphase turbo expanders and refrigeration means capable of operating in a multiphase flow (gas, liquid, and solid). The system includes cooling the gas stream to form liquefied natural gas and natural gas impurities comprising CO ₂ gas, solid CO _2, and / or liquid CO ₂ . Embodiments of the present invention further include a method suitable for producing liquefied natural gas using said integrated polyphase turboexpander and refrigeration means.

The terms "first", "second", and the like in this specification do not denote any order, amount, or importance, but rather distinguish one element from another and also specify the reader as a particular element of the device ≪ / RTI > As used herein throughout the specification and claims, "approximating languages" are applied to modify any quantitative expression that may change acceptably without causing a change in its associated underlying functionality . The vertical word "about" used in connection with the quantity includes the stated value and also has context-dependent meaning (e.g., including the degree of error associated with a particular amount of measurement). Accordingly, the term " about "or the value modulated by the term is not limited to the exact value specified. In some cases, such approximate terms may correspond to the accuracy of the instrument for measuring the value.

In the following specification and claims, the singular forms " a " include plural referents unless the context clearly dictates otherwise. As used herein, the term "or" is not meant to be exhaustive and refers to at least one of the recited parts, and also unless the context clearly dictates otherwise, And may be present. Also, in this specification, the suffix "(s)" is generally intended to include both the singular and the plural of that defining term, and thus includes one or more of the terms (e.g., Quot; may include one or more jets unless otherwise specified). Throughout the specification, references to "one embodiment", "another embodiment", "an embodiment", and the like refer to the specific elements (eg, features, structures, and / Quot; is included in at least one embodiment described herein, and may or may not be present in other embodiments. Likewise, the criteria for a "special configuration" may be included in at least one configuration described herein with respect to the configuration and / or the particular element (e.g., feature, structure, and / ≪ / RTI > can be present or can not be present. It should also be appreciated that the described inventive features can be combined in any suitable manner in various embodiments and configurations.

As used herein, the term " may ", "may be" may refer to the possibility of occurrence within a set of circumstances; May indicate one or more of the related capabilities, talents, or possibilities associated with a verb that represents a particular feature, feature, or possession of the feature, and / or the verb is vertically modified. The use of the terms "can" and "can" can thus take into account some cases in which the modified term is sometimes inappropriate, unlikely, or unlikely, It appears to be appropriate, feasible, or appropriate for the ability, function, or use to appear. For example, in some cases, an event or capability may be expected, but in other situations the event or capability may not occur and the difference may be captured by the terms "can" and "can" .

Turning now to the drawings, FIG. 1 illustrates an exemplary liquefied natural gas (LNG) production system 10 in accordance with one or more embodiments shown or described herein. The LNG production system 10 includes at least one cooling stage 200 configured to receive a natural gas stream 16. The system 10 further includes at least one compression stage 100 in fluid communication with the at least one cooling stage 200. The combination of the at least one compression stage 100 and the at least one cooling stage 200 allows the expansion of the natural gas stream 16 (FIG. 1) prior to expansion and further cooling of the low moisture compressed natural gas stream 21 in the expansion stage 300, ) And partially cool it. In the expansion stage 400 (described below), separation stage 400 that is multi-phase turboexpander in flow communication with the low-temperature CH ₄ vapor and LNG / ice / solid CO separation of the _second slurry, and the solid to the slurry LNG CO Providing additional separation into _two components.

The LNG production system 10 includes a bulk moisture removal device 12 in fluid communication with a natural gas inlet 14 through which a natural gas (NG) stream 16 . The moisture removal device 12 provides for a preliminary moisture removal from the NG stream 16 to generate a low moisture NG stream 20 at the outlet of the moisture removal device 12. In an embodiment, the moisture removal device 18 may be configured as a molecular sieve bed. Other absorber and absorber-based systems known in the art may also be used.

At least one cooling stage 200 includes one or more heat exchangers disposed downstream of and in fluid communication with the moisture removal device 12 (described below). During operation of the LNG production system 10, the moisture in the NG stream 16 must be reduced in the moisture removal device 12 to avoid freezing of the downstream heat exchanger (s). In contrast to the LNG production system 10 described herein, in a typical LNG liquefaction plant, a heat exchanger, typically operating at -100 DEG C or below, is used to reduce the moisture content of the input NG stream to <0.5 ppm . In the present invention, the temperature of the NG stream 16 in the heat exchanger is typically -40 DEG C or higher, requiring that the moisture content of the input NG stream 16 be reduced to < 180 ppm.

The compression stage 100 of the LNG production system 10 includes a first compressor 22 disposed between the water removal means 12 and the at least one heat exchanger 24. More specifically, the first compressor 22 is disposed downstream of the moisture removal device 12 and upstream of the one or more heat exchangers 24. The first compressor 22 provides compression of the low moisture NG stream 20 to release the compressed NG stream 28. More specifically, in an embodiment, the first compressor 22 discharges the compressed NG stream 21 of low moisture to a pressure sufficient to provide a reduction in temperature in the final cooling step.

In an alternative embodiment, and as best shown in FIG. 2, the LNG production system may provide moisture removal from the NG stream 16 following compression at the first compressor 22. More specifically, in an embodiment, the compression stage 100 of the LNG production system includes a first compressor 22 disposed upstream of the water removal means 12, and one or more heat exchangers 24. More specifically, in contrast to the embodiment of FIG. 1, the moisture removal device 12 is disposed downstream of the first compressor 22 and upstream of the one or more heat exchangers 24. In this particular embodiment, the first compressor 22 provides compression of the NG stream 16 to release the compressed NG stream 28. The subsequent removal of moisture from the compressed NG stream 28 releases a low moisture NG stream 28, and more particularly a low moisture compressed gas stream 21.

The temperature of the gas is usually increased as a result of compression work. In an embodiment, the first compressor 22 includes a multi-stage compressor 26 with internal stage cooling and also provides for the compression of a low moisture NG stream 20. In an alternative embodiment, the first compressor 22 may include a plurality of compressors (not shown) having one or more air coolers disposed therebetween. The first compressor (22) generates a compressed NG air stream (28) at the outlet of the first compressor (22). After the final compression stage of multi-stage compressor 26, NG cooling is achieved by air cooler 29.

Referring again to Figure 1, as shown, the cooling stage 200 includes one or more heat exchangers 24 (only one of which is shown) configured to remove heat from the low moisture compressed NG stream 21, . The heat exchanger (24) is disposed downstream of the compression stage (100), and more particularly the first compressor (22). In an embodiment, the low moisture compressed NG stream 21 is precooled to about -40 占 폚 by low temperature methane vapor in one or more heat exchangers 24 and is further cooled to release the cooled compressed effluent stream 32 . As shown, in some embodiments, the cooling stage 200 may include a plurality of heat exchangers. It should be appreciated that in Figures 1 and 2 a single heat exchanger 24 is shown as an exemplary embodiment only and that the actual number of heat exchangers and their individual configurations may vary depending on the desired end result. In some embodiments, the one or more heat exchangers 24 may be cooled using a cooling medium. In some embodiments, the one or more heat exchangers 24 may be cooled using cooling air, cooling water, or both. In some embodiments, the cooling stage 200 may additionally include one or more intercoolers (not shown) to cool the low-pressure compressed NG stream 21 without substantially affecting the pressure. have.

The LNG production system 10, and more particularly the expansion stage 300, comprises a multiphase turboexpander (not shown) configured to receive a compressed discharge stream 32 from a heat exchanger 24 to produce an expanded discharge stream 34 30). As described above, at least one cooling stage 200 is in fluid communication with at least one expansion stage 300 that includes a multiphase turboexpander 30 as described herein. As shown by the dashed lines, the first compressor 22 and the multiphase turboexpander 30 are typically mechanically coupled, such as are coupled through a common axis 36. Alternatively, the multiphase turboexpander 30 may be mechanically coupled to the compressor 46. The temperature of the natural gas stream, and more particularly the cooled compressed discharge stream 32, is controlled by a localized drop of the static temperature in the high velocity flow, and by a polyphase turboexpander 30 &Lt; / RTI &gt; during the expansion process. In operation, the energy recovered in the polyphase turboexpander 30 is used to partially offset the energy requirements for the compression stage 100. As the natural gas stream cools, the stream is partially converted to LNG, and moisture and natural gas impurities such as CO ₂ form a solid phase. More specifically, the expansion process is substantially cooled to generate the expanded exhaust stream 34 is natural gas comprising a mixture of a vapor stream and LNG / ice / solid CO ₂ slurry consisting of CH ₄ compression discharge stream ( 32) is further cooled.

In an embodiment, the water content of the NG stream 16, and more particularly the compressed NG stream 21 of low moisture, is used at the beginning of the process, using a bulk water removal system, more specifically a water removal device 12 May be adjusted prior to expansion in the polyphase turboexpander 30 to optimize the LNG output and CO ₂ particle size. In an embodiment, at least a portion of the solid CO ₂ and ice are separated from the NG stream 16 and are also removed from the polyphase turboexpander 30 by forcing the swirling motion of the stream.

The LNG production system 10 is configured to receive the expanded effluent stream 34 comprised of a mixture of a vapor stream consisting essentially of CH ₄ and a LNG / ice / solid CO ₂ slurry and to convert the components into substantially CH ₄ Further comprising at least one separation stage (400) comprising a separator (38) configured to separate into an output vapor stream (40) and an LNG / ice / solid CO ₂ slurry stream (42) More specifically, the vapor stream 40, which is substantially composed of CH ₄ , is separated from the LNG / ice / CO ₂ slurry in the separator 38 and is also separated from the slurry in the first compressor 22 and the polyphase turboexpander 30 Is recycled to the LNG production system 10 as shown by the arrows for precooling the low moisture NG stream 20 prior to compression and expansion.

More specifically, the system 10 includes at least a portion of the vapor stream 40, which is substantially composed of CH ₄ , as best shown in FIG. 1, as a low-moisture NG stream 20, Further comprises a recycle stage 500 configured to recycle to the low moisture NG stream 20 upstream of the stage 100 and also to the compressor 22 of the recycle path 501. In an alternative embodiment, in the recycle stage 500 is substantially NG stream 28 is compressed at least a portion of vapor stream 40 consisting of CH ₄ as best seen in Figure 2, more specifically To the compressed NG stream 28 downstream of the compression stage 100 and also to the compressor 22 of the recycle path 501. In some embodiments, the recovery (recuperation) of CH ₄ cold vapor stream 40 may appear as an additional cooling of the gas stream 16.

During the recycle process of the vapor stream 40 consisting essentially of CH ₄ , the vapor stream 40 is compressed in the second compressor 44. In one exemplary embodiment, the second compressor 44, CH ₄ mechanically by providing a compression of vapor stream 40 and to produce a compressed vapor stream (48), a drive source (46) or electrically driven .

LNG / ice / solid CO ₂ The slurry stream 42 is liquefied natural gas (LNG) to form an output stream 52 and substantially in the output stream (54) consisting of ice / solid CO _2, the liquid / solid separator (50). In an embodiment, the liquid / solid separator 50 is one of a gravity separator, a cyclone, a sintered metal filter, or any type of filter configured to separate solid contaminants from LNG.

Referring now to Figure 2, an alternative embodiment of the LNG production system of the present invention is shown. More specifically, an LNG production system 60 including an integrated external refrigeration system is shown. It should be noted that like elements have like reference numerals throughout the examples.

The LNG production system 60 includes a first compressor 22 in fluid communication with a natural gas inlet 14 through which a natural gas (NG) stream 16 is supplied. As described for the previous embodiments, the first compressor 22 may include a multi-stage compressor 26 with intermediate stage cooling and also provides compression of the NG stream 16. In an alternative embodiment, the first compressor 22 may include a plurality of compressors (not shown) having one or more air coolers disposed therebetween. The first compressor (22) generates a compressed NG air stream (28) at the outlet of the first compressor (22). The LNG production system 60 further comprises a water removal device 12 disposed between the first compressor 22 and the heat exchanger 24. The water- The heat exchanger (24) is disposed downstream of, and in fluid communication with, the moisture removal device (12). More specifically, the moisture removal device 12 is disposed downstream of the first compressor 22 and upstream of the heat exchanger 24. The heat exchanger (24) is used to remove heat from the low moisture condensed NG stream (21). The heat exchanger 24 is configured to discharge the cooled compression discharge stream 32. The LNG production system 60 is configured to receive the cooled compressed discharge stream 32 from the heat exchanger 24 and to generate an expanded discharge stream 34. The first compressor 22 and the multiphase turboexpander 30 are typically mechanically coupled, such as are typically coupled through a common axis 36. Expansion process by substantially adding the cooled compressed effluent stream 32 of natural gas for generating the expanded exhaust stream 34 comprising a mixture of a vapor stream and LNG / ice / solid CO ₂ slurry consisting of CH ₄ Cool.

LNG production system 60 is substantially accommodate the expanded exhaust stream 34, consisting of a mixture of the vapor stream and LNG / ice / solid CO ₂ slurry consisting of CH _4, and and a substantially CH ₄ The components Further comprising a separator 38 configured to separate the vapor stream 40 and the LNG / ice / CO ₂ slurry stream 42 comprised. As noted earlier, the low-temperature steam CH ₄ is separated from the LNG / ice / CO ₂ slurry separator 38, and in each water-removal device 12, heat exchanger 24, and the multi-phase turboexpander 30 Is recycled to the LNG production system 60 as shown by the arrows for precooling the compressed NG stream 28 prior to moisture removal, cooling, and expansion of the stream.

Substantially of the recycle of the vapor stream (40) consisting of CH ₄ process, the vapor stream 40 is substantially a second compressed in compressor 44 to produce a compressed vapor stream 48 consisting of CH ₄ do. LNG / ice / solid CO ₂ The slurry stream 42 is liquefied natural gas (LNG) to form an output stream 52 and substantially in the output stream (54) consisting of ice / solid CO _2, the liquid / solid separator (50).

In contrast to the embodiment of FIG. 1, the embodiment shown in FIG. 2 further includes an external refrigeration system 62 configured to generate a low temperature vapor stream 64. The external refrigeration system (62) is configured to be in fluid communication with the heat exchanger (24). In operation, the external refrigeration system 62 provides precooling to about -40 &lt; 0 &gt; C in the heat exchanger 24, prior to expansion in the multiphase turboexpander 30. The low temperature vapor stream 64 provides additional cooling of the effluent stream 32 to -60 &lt; 0 &gt; C. As mentioned earlier, the use of this additional refrigeration means provides additional cooling of the compressed NG stream 21 of additional energy and low moisture to the heat exchanger 24, even though the external refrigeration system 62 is not required. In an embodiment, the external refrigeration system 62 is configured as a propane refrigeration system.

In the disclosed embodiment, a multi-phase turboexpander, more specifically a multi-phase turboexpander, is used to expand the cooled compressed discharge stream 32 generated by the heat exchanger 42, (30). Expansion of the cooled compressed discharge stream 32 is to generate a, the expanded exhaust stream 34 comprising a mixture of low-temperature steam and CH ₄ LNG / ice / solid CO ₂ slurry. As used herein, the term "polyphase turboexpander" refers to a radial, axial, or blend turbo-machine through which a gas or gas mixture is expanded to produce work and additional output components .

Referring now to FIG. 3, a polyphase turboexpander 70, similar to the polyphase turboexpander 30 of FIGS. 1 and 2, is shown in simplified block diagram form in accordance with an embodiment of the present invention. 4 shows a cross-sectional view of an embodiment of a polyphase turboexpander 70 in accordance with an embodiment of the present invention. As shown in FIG. 4, the multiphase turbo expander 70 includes a housing 72. As shown in FIG. 3, the multiphase turboexpander 70 further includes at least one rotatable element or rotor 74 configured to extract work from the flow stream. In some embodiments, the polyphase turbo expander 70 further includes at least one stationary element 76. In some embodiments, The stationary element 76 may comprise a stator or nozzle. In some embodiments, the nozzle is equipped with a vane that forces swirling motion of the stream. As shown in FIG. 4, the polyphase turboexpander 70 further includes one or more seals 78 in some embodiments. As shown in FIG. 4, the polyphase turboexpander 70 further includes one or more blades 80/82. In some embodiments, the multiphase turbo expander 70 further includes one or more stationary blades 80 and one or more rotor blades 82, as shown in FIG.

3 and 4, the multiphase turbo expander 70 further includes at least one inlet 84 disposed in the housing 72. As shown in FIG. The inlet 84 is configured to receive the gas stream 86 in some embodiments. The gas stream 86 is compressed in a compressor such as the first compressor 22 of Figures 1 and 2 and cooled in a heat exchanger 24 before being cooled Is substantially similar to the compression discharge stream 32. The polyphase turbo expander (70) further includes at least one outlet (88) disposed in the housing (72). The outlet 88 is configured to discharge the expanded exhaust stream 90 in some embodiments. The expanded exhaust stream 90 is expanded in a polyphase turboexpander 70 such as the polyphase turboexpander 30 of Figures 1 and 2 following the expansion of the polyphase turboexpander 70, Which is generally similar to the effluent stream 34. [ In an embodiment, the multiphase turboexpander 70 may include additional outlet and / or separation means (as described herein).

As mentioned above, the gas stream 86 contains carbon dioxide and also has a certain moisture content. In some embodiments, the gas stream 86 further comprises at least one of nitrogen, heavy hydrocarbons, or water vapor. In some embodiments, the gas stream 86 further includes impurities, examples of which include, but are not limited to, hydrogen sulphide. In some embodiments, the gas stream 86 is substantially free of impurities. In some embodiments, the gas stream 86 comprises nitrogen and carbon dioxide.

In some embodiments, the amount of impurities in the gas stream 86 is less than about 50 mole%. In some embodiments, the amount of impurities in the gas stream 86 is less than about 20 mole percent. In some embodiments, the amount of impurities in the gas stream 86 ranges from about 10 mole percent to about 50 mole percent. In some embodiments, the amount of impurities in the gas stream 86 is less than about 5 mole percent.

As mentioned above, the gas stream 86 expands in the polyphase turboexpander 70 and as the work is extracted from the expanding gas stream, the gas stream 86 is cooled (cooled) inside the polyphase turboexpander 70, do. Cooling of the gas stream 86 in the multiphase turboexpander 70 is indicated by the formation of one or both of the CH ₄ vapor, LNG, and solid CO ₂ and liquid CO ₂ in the polyphase turboexpander 70. More specifically, the multi-phase turboexpander 70 has a gas stream 86 is typically 1 and 2 of the stream (40, 42) that are similar, substantially vapor stream consisting of CH _4, and liquefied natural gas / ice / And is configured to cool the gas stream 86 to predominantly form a solid CO ₂ slurry stream. As used herein, the term "predominantly formed " as used herein means that the amount of solid CO ₂ formed in the polyphase turboexpander is less than about 5 wt%. As used herein, the term "predominantly formed " as used herein means that the amount of LNG formed in the polyphase turboexpander is less than about 45 wt%. In one exemplary embodiment, the "mainly formed" term, as used herein, means that the amount of CH ₄ vapor formed in the multi-phase turboexpander is less than about 50% by weight.

In some embodiments, the flow field within the multiphase turboexpander 70 may be used to assist in the separation of the LNG / ice / solid CO ₂ slurry and the CH ₄ vapor. This can be accomplished by employing one or more separation channels (not shown) within the multiphase turboexpander housing 70 and additional outlets. In some embodiments, the separation channel may be designed to allow liquid or solid particles to be introduced due to centrifugal force, and may also exclude re-entry into the polyphase turboexpander flow path by a deflector . An exemplary configuration for the inclusion of certain aspects of the multi-phase turboexpander 70, including a plurality of outlets, separate channel D. Hofer entitled & name of "expander and CO ₂ separation process" in commonly assigned U.S. Patent Publication No. 2013/0125580, which is hereby incorporated by reference in its entirety.

In some embodiments, at least one component of the multiphase turboexpander 70 further comprises a coating configured to preclude attachment of solid CO ₂ to the surface of the multiphase turboexpander component. In some embodiments, at least one of the housing 72, the rotatable element 74, or the stationary element 76 includes a coating configured to preclude attachment of solid CO ₂ to the surface of the multiphase turboexpander component can do. In a particular embodiment, the rotatable element 74 of the multiphase turboexpander 70 includes a coating 92. In some embodiments, the coating 92 is configured to preclude attachment of solid CO ₂ to the surface 94 of the rotatable element 74. In some embodiments, the coating 92 includes a non-tacky material that is capable of excluding the adherence of solid CO ₂ to the surface 94 of the rotatable element 74.

In some embodiments, the multiphase turboexpander 70 further comprises at least one heated component. In some embodiments, the heated part is configured to preclude attachment of solid CO ₂ to the surface of the polyphase turboexpander component. In some embodiments, one or more of the housing 72, the rotatable element 74, or the stationary element 76 may include a heated element (not shown) to exclude the adherence of solid CO ₂ to the surface of the multiphase turboexpander component . In a particular embodiment, the fixed element 76 of the polyphase turboexpander 70 is heated to exclude the adherence of solid CO ₂ to the surface 96 of the stationary element 76.

In some embodiments, one or more stationary blades 80 may be heated by using an electrical heating element. In this embodiment, the blade 80 may include a heated element (not shown) disposed in one or more holes formed in the blade 80. In some embodiments, one or more components of the multiphase turboexpander 70 may be heated by circulating air or gas. In some embodiments, the blade 80 may further include a gas flow channel (not shown), such as, for example, a Z-shaped channel. In some embodiments, the gas flow channel may have any suitable shape, such as, for example, U, E, and the like. As described above, an exemplary configuration for inclusion of certain aspects of the polyphase turboexpander 70, including the use of an electric heating element to heat the blades, the gas flow channels, and circulating air or gas, U.S. Patent Application Publication No. 2013/0125580 entitled " Expander and CO ₂ Separating Method &quot;, the title of D. Hofer et al., Which is incorporated herein by reference in its entirety.

The polyphase turboexpander arrangement in accordance with an embodiment of the present invention may advantageously allow the separation of the CH ₄ vapor stream and the liquefied natural gas / ice / solid CO ₂ slurry stream from the gas stream in the multiphase turboexpander itself, And the need for additional separators such as the separator 38 of FIG.

As illustrated in Figures 3 and 4, the multi-phase turboexpander 70 CH expanded exhaust is comprised of _four vapor stream 90 and the LNG / ice / solid CO, at least one outlet is configured to discharge the _second slurry (88). As shown in Figures 3 and 4, in some embodiments, the at least one outlet 88 is disposed downstream of the rotatable element 74. In some embodiments, the expanded exhaust stream 90 may comprise one or more non-condensable components. In some embodiments, the expanded exhaust stream 90 may comprise one or more liquid components. In some embodiments, the expanded exhaust stream 90 may comprise one or more solid components. The expanded exhaust stream 90 may be further configured to be in fluid communication with one or both of a liquid-gas and a solid-gas separator, such as the separator 38, 50 shown in Figures 1 and 2.

In some embodiments, the multiphase turboexpander 70 for generating LNG from the gas stream 86 may comprise a single stage multiphase turboexpander, as shown in FIGS. In some other embodiments, the multi-phase turboexpander 70 D. Hofer this invention had the name of the "inflator and CO ₂ separation process" in commonly assigned U.S. Patent Publication for generating a gas from the LNG stream 86, the And may include a multi-stage, polyphase turboexpander 70 as described in U.S. Pat. No. 2013/0125580, which is incorporated herein by reference in its entirety.

Returning now to Figure 5, in an embodiment, a method 600 for generating LNG from a gas stream is provided. The method includes processing the input gas stream in a cooling stage, a compression stage, an expansion stage, and a separation stage. More specifically, the method includes inputting a gas stream, more particularly a natural gas stream, in step 602. The method further comprises compressing the input gas stream in a compression stage in step 604. [ The compressed gas stream is then expanded at step 606 in the multiphase turboexpander of the expansion stage. And said expansion stage to produce the expanded effluent stream consisting of a mixture of energy, and the low-temperature steam and CH ₄ LNG / ice / solid CO ₂ slurry. Then, in step 608, the expanded exhaust stream into components in the separator, and more particularly to a low temperature separation CH ₄ vapor output stream and LNG / ice / CO ₂ slurry stream. The CH ₄ vapor stream, in order to pre-cool the gas stream prior to compression and expansion, is recycled to the input gas stream in step 610. In addition, the LNG / ice / solid CO ₂ slurry stream is further separated in a separator to release liquefied natural gas and a solid CO ₂ stream in step 612.

Referring now to FIG. 6, an exemplary graph, generally designated 700, illustrates the relative compression ratios and process energy requirements achieved during the compression stages described above in accordance with an exemplary embodiment. More specifically, the graph 700 illustrates the compression ratio for the LNG output stream of a new liquefied natural gas (LNG) production system according to the embodiment described herein (shown on axis 704) Shown on axis 702). The energy requirement per gallon of the LNG output stream (shown as point / line 706) is reduced by increasing the compression ratio until the energy requirement reaches a stable level near 706 at a compression ratio greater than about 30 psi . More specifically, in FIG. 6, normalizing by the amount of LNG produced shows that process energy requirements are reduced as the compression ratio increases, stabilizing at about 0.8 kWH / gallon at a compression ratio of -30.

To calculate the compression ratio shown in FIG. 6, an initial NG pressure of 10 atm (corresponding to stream 16 of FIGS. 1 and 2) was used. As the initial pressure changes, the shape of the compression curve of Fig. 6 also changes.

Accordingly, a new method and system for the production of liquefied natural gas incorporating a natural gas (NG) purification and refrigeration step to produce LNG in one process step by using a polyphase turboexpander is disclosed. The method and system includes a multi-phase turboexpander to operate the multi-phase flow (gas, liquid, solid), a mixture of low-temperature steam and CH ₄ LNG / ice / solid CO ₂ slurry is discharged. The resulting systems and methods provide lower equipment costs, smaller footprint, increased LNG production, and lower total cost than conventional LNG production processes.

The description set forth describes embodiments of the present invention, including the best mode, and any person skilled in the art may make and use the invention, including the manufacture and use of any device or system and the performance of any integrated method I used the example to make it. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. These other examples, if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that are not significantly different from the literal language of the claims, It is intended to be within the scope of the scope.

Claims (22)

A system for producing liquefied natural gas (LNG) from a natural gas stream comprising:
A water removal device and a compressor for removing water from the natural gas stream and compressing the natural gas stream to generate a low-moisture compressed natural gas stream;
A heat exchanger for cooling the low moisture compressed natural gas stream to produce a cooled compressed discharge stream;
By the expansion of the cooled compressed stream release, multi-phase turboexpander for generating the expanded effluent stream consisting of a mixture of vapor and substantially liquefied natural gas / ice / solid CO ₂ slurry consisting of CH _4;
The separating and discharging the expanded stream, a separator to generate a vapor stream and substantially liquefied natural gas / ice / solid CO ₂ to the slurry stream consisting of CH _4; And
The liquefied natural gas / ice / solid slurry to separate the CO ₂ stream, the liquefied natural gas output stream and at least one additional separator for substantially as to produce an output stream that is composed of a ice / solid CO ₂
The liquefied natural gas production system. The liquefied natural gas producing system of claim 1, wherein the moisture removal device comprises a molecular sieve bed. 2. The liquefied natural gas production system of claim 1, wherein said low moisture compressed natural gas stream comprises a natural gas stream having a moisture content of less than 180 ppm. The method of claim 1, wherein the multi-phase turboexpander, the liquefied natural gas / ice / solid CO ₂ slurry to produce a liquefied natural gas is configured such that, to cool further to the cooling the compressed effluent stream from the heat exchanger mainly formed system. The method of claim 1, wherein: a vapor stream consisting of the CH ₄ further comprising a recycle path configured to recycle into the gas stream, the liquid natural gas production system. The method of claim 5, wherein the recirculation path is substantially CH and ₄ compress the vapor stream consisting substantially CH to ₄ to produce a compressed vapor stream consisting further comprising a compressor, liquefied natural gas production system. The liquefied natural gas production system of claim 1, wherein the at least one additional separator is one of a filter, a cyclone, or a gravity separator. 2. The multi-phase turboexpander according to claim 1,
housing;
At least one rotatable element disposed within the housing;
At least one inlet disposed in the housing and configured to receive the cooled compressed discharge stream; And
At least one outlet disposed in the housing and configured to discharge an expanded exhaust stream comprised of a mixture of vapor and a liquefied natural gas / ice / solid CO ₂ slurry substantially consisting of CH ₄
The multi-phase turboexpander comprising: a is substantially CH vapor consisting of ₄ is formed is formed in the liquefied natural gas and from the cooled discharge gas stream, at least a portion of the CO ₂ to form a solid CO ₂ heat exchanger And to further cool the cooled compressed discharge stream from the liquefied natural gas producing system. 9. The method of claim 8 wherein the multi-phase turbo emitter is substantially in order to discharge the slurry stream consisting of a vapor stream and substantially liquefied natural gas / ice / solid CO ₂ consisting of CH _4, which is substantially composed of CH ₄ a liquefied natural gas production system of further configured to separate the vapor and liquid natural gas / ice / solid CO ₂ slurry. The liquefied natural gas production system of claim 1, further comprising an external refrigeration system in fluid communication with the heat exchanger to provide additional cooling to the low moisture compressed natural gas stream. A system for producing liquefied natural gas (LNG) from a natural gas stream comprising:
At least one compression stage and at least one cooling stage configured to compress and cool the natural gas stream to generate a cooled compressed discharge stream;
At least one expansion stage configured to expand the cooled compressed discharge stream to produce an expanded discharge stream and at least one polyphase turbo expander in fluid communication with the compression stage and the cooling stage,
, Wherein the polyphase turbo expander
housing;
At least one rotatable element disposed within the housing;
At least one inlet disposed in the housing and configured to receive the cooled compressed discharge stream; And
At least one outlet disposed in the housing and configured to discharge an expanded exhaust stream comprising a mixture of vapor and substantially liquid CH ₃ / ice / solid CO ₂ slurry,
Wherein the liquefied natural gas production system comprises: 12. The method of claim 11, wherein: a CH a mixture of vapor and liquid natural gas / ice / solid CO ₂ slurry consisting of _four substantially CH ₄ vapor stream and substantially liquefied natural gas consisting / ice / solid CO ₂ Further comprising a separation stage configured to separate into an output stream comprised of slurry. 13. The method of claim 12, substantially in a vapor stream consisting of CH ₄ further comprising a recirculation stage, configured to recycle into the gas stream, the liquid natural gas production system. The method of claim 13 wherein the LNG production system to the recirculation stage substantially comprises a compressor to compress the vapor stream consisting of CH _4, in order to generate a substantially compressed vapor stream that is composed of CH _4. 13. The multiphase turboexpander of claim 11, wherein the polyphase turboexpander is further configured to further cool the cooled compressed discharge stream so that at least a portion of the CO _{2 in} the cooled discharged natural gas stream forms solid CO ₂ Wherein the liquefied natural gas production system comprises: 12. The liquefied natural gas production system of claim 11, wherein the at least one cooling stage further comprises an external refrigeration system configured to provide additional cooling to the low moisture compressed natural gas stream. A method for producing liquefied natural gas (LNG) from a natural gas stream comprising:
Providing an input natural gas stream;
Removing moisture, compressing and cooling the natural gas stream to produce a cooled compressed discharge stream;
By the step of expanding the cooled compressed stream emitted from the multi-phase turboexpander, generating an expanded exhaust stream that substantially comprises a mixture of vapor and liquid natural gas / ice / solid CO ₂ slurry consisting of CH _4;
Separating the expanded effluent stream in at least one separator to produce a vapor stream and a liquefied natural gas / ice / solid CO ₂ slurry stream substantially consisting of CH ₄ ; And
Separating the liquefied natural gas / ice / solid CO ₂ slurry stream from at least one additional separator to produce an output stream and a liquefied natural gas (LNG) output stream consisting essentially of ice / solid CO ₂
&Lt; / RTI &gt; 18. The method of claim 17, wherein: a CH ₄ further comprising, a method of producing liquefied natural gas to the step of recycling the vapor stream as an input stream of natural gas recirculation path consisting of. 18. The method of claim 17, further comprising separating at least a portion of the ice / solid CO ₂ from the cooled compressed natural gas stream in the multiphase turboexpander. 18. The multi-phase turboexpander of claim 17,
housing;
At least one rotatable element disposed within the housing;
At least one inlet disposed in the housing and configured to receive the cooled compressed discharge stream; And
At least one outlet disposed in the housing and configured to discharge an expanded exhaust stream comprising a mixture of vapor and substantially liquid CH ₃ / ice / solid CO ₂ slurry,
Wherein said multiphase turboexpander is configured to cool said cooled multistage turboexpander so that at least a portion of the CO _{2 in} the cooled discharged natural gas stream forms solid CO ₂ , wherein vapor consisting essentially of CH ₄ is formed and liquefied natural gas is formed, And to further cool the compressed discharge stream. 18. The method of claim 17, further comprising the further cooling of the natural gas stream in an external refrigeration system in fluid communication with the cooled compressed discharge stream. 18. The method of claim 17, substantially further comprising the step of separating the slurry stream consisting of liquefied natural gas / ice / solid CO _2, at least in part substantially in a vapor stream consisting of CH ₄ in the multi-phase turboexpander, Liquefied natural gas production method.

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