Patent Description:
This section is intended to introduce various aspects of the art, which can be associated with exemplary examples of the present techniques. This description is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

Numerous applications such as <CIT>, <CIT> and <CIT>, within the upstream and downstream oil and gas industry use absorption and fractionation columns for a variety of processes including, for example, dehydration for water removal from hydrocarbon gas, amine treating for acid gas removal from hydrocarbon gas and fractionation of hydrocarbons. One application of hydrocarbons fractionation is the fractionation column - also known as a scrub column - in a typical LNG process. <FIG> illustrates a known scrub column <NUM> that may be used in such an LNG process. According to known LNG processes, gas fed to the scrub column is first pre-treated and cooled. The scrub column typically operates at high pressure. The main objective of the scrub column is to remove most of the heavy hydrocarbons, such as pentane, from the natural gas stream. The traditional scrub column <NUM> includes a bottom section, also known as a stripping section <NUM>, and a top section, also known as a rectification section <NUM>. A gas stream <NUM> enters the scrub column <NUM> at high pressure and at a position adjacent both the stripping section <NUM> and the rectification section <NUM>. The vapor and liquid in the gas stream separate from each other, with the vapor moving upward into the rectification section <NUM> and the liquid moving downward into the stripping section <NUM>. The stripping section <NUM> uses trays <NUM> to separate and direct liquid downward. Trays <NUM> are typically used instead of packing because of anticipated high liquid flux, which is defined as a volumetric flow per unit area.

A liquid stream <NUM> is extracted near the bottom of the scrub column <NUM> and is re-heated in a reboiler <NUM>. The reheated stream <NUM> is returned to the stripping section <NUM>, where vapors in the reheated stream can rise through the stripping section and enter the rectification section <NUM>. Liquids in the reheated stream <NUM> combine with other liquids at the bottom of the scrub column <NUM>. A scrub column liquid bottoms stream <NUM> may be taken from the bottom of the scrub column.

Vapors from the gas stream <NUM> combine with vapors rising from the stripping section <NUM> and pass into the rectification section <NUM>, where they contact liquid descending the column. In the rectification section <NUM>, packing <NUM> is typically used instead of trays because of the low liquid circulation rate. The rectification section <NUM> includes several theoretical separation stages (typically two to four) where, based on the different boiling points of the components in the stream going to that separation stage, the fractionation/separation of hydrocarbons takes place. The packing in each section promotes intimate contact and mass transfer between the liquid and vapor. A vapor stream <NUM> exits the top of the scrub column <NUM> and is cooled in a reflux cooler system <NUM>, which may include one or more heat exchangers or other coolers. The cooled vapor stream <NUM> is sent to a reflux drum <NUM> where liquids and vapor are separated from each other. A reflux liquid stream <NUM> is returned to a top portion of the scrub column, while the reflux vapor stream <NUM> exiting the reflux drum <NUM> is sent for further processing, which may include the remainder of a natural gas liquefaction process. Vapor rising in the scrub column <NUM> gets richer in the lighter hydrocarbons components and the liquid descending the column gets richer in the heavier hydrocarbons components. Therefore, the scrub column liquid bottoms stream <NUM> is proportionally higher in heavier hydrocarbons components than in lighter hydrocarbons components, and the reflux vapor stream <NUM> is proportionally higher in lighter hydrocarbons components than in heavier hydrocarbons components.

Typically, the diameter of the rectification section <NUM> of the scrub column <NUM> is much larger than the diameter of the stripping section <NUM> because of the high gas flow rate through the rectification section. Therefore, due to its size, pressure, and material selection due to cold temperatures, the rectification section controls the cost and weight of the scrub column, which in some applications may be substantial. The size and weight of the fractionation column may limit its application in populated areas where height must be minimized for visual population reasons. Additionally, applications where size and weight are critical design factors, such as offshore LNG processing, can be limited by the size and weight of such a large fractionation column. What is needed is a method and apparatus for removing heavy hydrocarbons from a natural gas stream that eliminates the large, heavy, and costly rectification section of a fractionation column.

Besides height and weight considerations, the theory of operation of a typical fractionation column may itself be a limiting design factor. The fractionation process requires a certain amount of liquid to interact with the incoming gas stream, and in the process shown in <FIG> this liquid is designed to come from the fractionation process itself. This can pose difficulties for applications when relatively small amounts of heavy hydrocarbons are present in a natural gas stream to be liquefied. Additionally, it may not be economically feasible to install an additional fractionation column in a pre-existing facility, such as an LNG facility, for de-bottlenecking purposes. What is needed is a method and apparatus for removing heavy hydrocarbons from a natural gas stream that can be used in applications having low liquid circulation rates. What is also needed is a method and apparatus for removing heavy hydrocarbons from a natural gas stream that can be economically used in debottlenecking applications.

The disclosed aspects include the use of a fractionation system for removing heavy hydrocarbons in a gas stream. A feed gas stream is introduced through a feed gas stream inlet. A stripping section receives a predominantly liquid phase of the feed gas stream. First and second co-current contacting systems are located in-line within a pipe. The first co-current contacting system receives a predominantly vapor phase of the feed gas stream. Each of the first and second co-current contacting systems includes a co-current contactor and a separation system. Each co-current contactor includes a droplet generator and a mass transfer section. The droplet generator generates droplets from a liquid and disperses the droplets into a gas stream. The mass transfer section provides a mixed, two-phase flow having a vapor phase and a liquid phase. The separation system separates the vapor phase from the liquid phase. The vapor phase of the co-current contactor in the first co-current contacting system comprises the gas stream for the co-current contactor in the second co-current contacting system. The liquid phase of the co-current contactor in the second co-current contacting system comprises the liquid from which droplets are generated in the co-current contactor of the first co-current contacting system.

The disclosed aspects also include a method of removing heavy hydrocarbons in a gas stream. According to the method, a feed gas stream is introduced into a feed gas inlet. A predominantly liquid phase of the feed gas stream is received into a stripping section. A predominantly vapor phase of the feed gas stream is received into a first co-current contacting system located in-line within a pipe with a second co-current contacting system. Each of the first and second co-current contacting systems includes a co-current contactor including a droplet generator and a mass transfer section, and a separation system. Using each droplet generator, droplets are generated from a liquid and the droplets are dispersed into a gas stream. In each mass transfer section a mixed, two-phase flow is provided having a vapor phase and a liquid phase. In each separation system, the vapor phase is separated from the liquid phase. The vapor phase of the co-current contactor in the first co-current contacting system comprises the gas stream for the co-current contactor in the second co-current contacting system. The liquid phase of the co-current contactor in the second co-current contacting system comprises the liquid from which droplets are generated in the co-current contactor of the first co-current contacting system.

The disclosed aspects further include the use of a fractionation system for removing heavy hydrocarbons in a gas stream. A feed gas stream, comprising a natural gas stream, is introduced through a feed gas inlet. A stripping section receives a predominantly liquid phase of the feed gas stream. First and second co-current contacting systems are located in-line within a pipe. The first co-current contacting system receives a predominantly vapor phase of the feed gas stream. Each of the first and second co-current contacting systems include a co-current contactor and a separation system. Each co-current contactor includes a droplet generator and a mass transfer section. Each droplet generator generates droplets from a liquid and disperses the droplets into a gas stream. The mass transfer section provides a mixed, two-phase flow having a vapor phase and a liquid phase. Each droplet generator includes an annular support ring securing the droplet generator in-line within the pipe, a plurality of spokes extending from the annular support ring, the annular support ring having a plurality of liquid channels configured to allow a liquid stream to flow through the plurality of spokes and out of injection orifices disposed on the plurality of spokes. Each droplet generator also includes a gas entry cone supported by the plurality of spokes and configured to allow a first portion of a gas stream to flow through a hollow section of the gas entry cone and through gas exit slots included in the plurality of spokes, and a second portion of the gas stream to flow around the gas entry cone and between the plurality of spokes, wherein the second portion of the gas stream is separate from the first portion of the gas stream. The separation system separates the vapor phase from the liquid phase of the respective co-current contactor. The vapor phase of the co-current contactor in the first co-current contacting system comprises the gas stream for the co-current contactor in the second co-current contacting system. The liquid phase of the co-current contactor in the second co-current contacting system comprises the liquid from which droplets are generated in the co-current contactor of the first co-current contacting system. An in-line flash separator receives the predominantly vapor phase of the feed gas stream prior to said predominantly vapor phase being sent through the first co-current contacting system. The in-line flash separator separates liquids from the predominantly vapor phase. A flash reflux line is connected to the in-line flash separator and to the stripping section, the flash reflux line conveying liquids separated from the predominantly vapor phase in the in-line flash separator to the stripping section.

The advantages of the present techniques are better understood by referring to the following detailed description and the attached drawings, in which:.

At the outset, for ease of reference, certain terms used in this application and their meanings as used in this context are set forth. Further, the present techniques are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments, and terms or techniques that serve the same or a similar purpose are considered to be within the scope of the present claims.

"Acid gas" refers to any gas that produces an acidic solution when dissolved in water. Non-limiting examples of acid gases include hydrogen sulfide (H<NUM>S), carbon dioxide (CO<NUM>), sulfur dioxide (SO<NUM>), carbon disulfide (CS<NUM>), carbonyl sulfide (COS), mercaptans, or mixtures thereof.

"Co-current contactor" refers to a vessel that receives a gas stream and a separate solvent stream in such a manner that the gas stream and the solvent stream contact one another while flowing in generally the same direction.

The term "co-currently" refers to the internal arrangement of process streams within a unit operation that can be divided into several sub-sections by which the process streams flow in the same direction.

As used herein, a "column" is a separation vessel in which a counter-current flow is used to isolate materials on the basis of differing properties.

As used herein, the term "dehydration" refers to the pre-treatment of a raw feed gas stream to partially or completely remove water and, optionally, some heavy hydrocarbons.

The term "fractionation" refers to the process of physically separating components of a fluid stream into a vapor phase and a liquid phase based on differences in the components' boiling points and vapor pressures at specified temperatures and pressures. Fractionation is typically performed in a "fractionation column," which includes a series of vertically spaced plates. In a typical process, a feed stream enters the fractionation column at a mid-point, dividing the fractionation column into two sections. The top section can be referred to as the rectification section, and the bottom section can be referred to as the stripping section. Condensation and vaporization occur on each plate, causing lower boiling point components to rise to the top of the fractionation column and higher boiling point components to fall to the bottom. A reboiler is located at the base of the fractionation column to add thermal energy. The "bottoms" product is removed from the base of the fractionation column. A condenser is located at the top of the fractionation column to condense the product emanating from the top of the fractionation column, which is called the distillate. A reflux pump is used to maintain flow in the rectification section of the fractionation column by pumping a portion of the distillate back into the distillation column.

As used herein, the term "facility" is used as a general term to encompass oil and gas field gathering systems, processing platform systems, and well platform systems.

The term "gas" is used interchangeably with "vapor," and is defined as a substance or mixture of substances in the gaseous state as distinguished from the liquid or solid state. Likewise, the term "liquid" means a substance or mixture of substances in the liquid state as distinguished from the gas or solid state.

A "hydrocarbon" is an organic compound that primarily includes the elements hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or any number of other elements can be present in small amounts. As used herein, hydrocarbons generally refer to components found in natural gas, oil, or chemical processing facilities.

A "heavy" hydrocarbon is a hydrocarbon with three or more carbon atoms in each molecule. The precise number of carbon atoms comprising a heavy hydrocarbon molecule may depend on the feed gas and the desired product gas. For example, if methane gas (having one carbon atom per molecule) is the desired product gas, then heavy hydrocarbons may include propane (having three carbon atoms). Examples of heavy hydrocarbons include pentane, hexane, heptane, and the like.

With respect to fluid processing equipment, the term "in series" means that two or more devices are placed along a flow line such that a fluid stream undergoing fluid separation moves from one item of equipment to the next while maintaining flow in a substantially constant downstream direction. Similarly, the term "in line" means that two or more components of a fluid mixing and separating device are connected sequentially or, more preferably, are integrated into a single tubular device. Similarly, the term "in parallel" means that a stream is divided among two or more devices, with a portion of the stream flowing through each of the devices.

The term "stream" indicates a material that is flowing from a first point, such as a source, to a second point, such as a device processing the stream. The stream may include any phase or material, but is generally a gas or liquid. The stream may be conveyed in a line or pipe, and used here, reference to the line or pipe also refers to the stream the line is carrying, and vice versa.

"Natural gas" refers to a multi-component gas obtained from a crude oil well or from a subterranean gas-bearing formation. The composition and pressure of natural gas can vary significantly. A typical natural gas stream contains methane (CH<NUM>) as a maj or component, i.e., greater than <NUM> mol % of the natural gas stream is methane. The natural gas stream can also contain ethane (C<NUM>H<NUM>), heavy hydrocarbons (e.g., C<NUM>-C<NUM> hydrocarbons), one or more acid gases (e.g., CO<NUM> or H<NUM>S), or any combinations thereof. The natural gas can also contain minor amounts of contaminants such as water, nitrogen, iron sulfide, wax, crude oil, or any combinations thereof. The natural gas stream can be substantially purified, so as to remove compounds that may act as poisons.

"Solvent" refers to a substance capable at least in part of dissolving or dispersing one or more other substances, such as to provide or form a solution. The solvent can be polar, nonpolar, neutral, protic, aprotic, or the like. The solvent may include any suitable element, molecule, or compound, such as methanol, ethanol, propanol, glycols, ethers, ketones, other alcohols, amines, salt solutions, ionic liquids, or the like. The solvent may include physical solvents, chemical solvents, or the like. The solvent may operate by any suitable mechanism, such as physical absorption, chemical absorption, or the like.

"Substantial" when used in reference to a quantity or amount of a material, or a specific characteristic thereof, refers to an amount that is sufficient to provide an effect that the material or characteristic was intended to provide. The exact degree of deviation allowable may depend, in some cases, on the specific context.

The present techniques provide for the fractionation of substances from a gas stream, for example removing heavy hydrocarbons from a natural gas stream, using co-current contacting systems. Alternatively, the present techniques provide for the separation of at least a portion of heavy hydrocarbons from a hydrocarbons stream that includes heavy hydrocarbons and light hydrocarbons. The co-current contacting systems disclosed herein include stages composed primarily of in-line devices, or of bundles of parallel in-line devices, in either case the devices and/or the bundles having smaller diameters than a conventional tower.

Known counter-current flow schemes, such as the known scrub column <NUM> of <FIG>, require comparatively low velocities to avoid entrainment of the down-flowing liquid in the natural gas stream. Further, relatively long distances are useful for disengagement of the liquid droplets from the raw natural gas stream. Depending on the flow rate of the natural gas stream, the scrub column <NUM> may be greater than four meters in diameter and more than <NUM> meters tall. For high-pressure applications, the vessel has thick, metal walls. Consequently, counter-current contactor vessels can be large and very heavy. This is generally undesirable, particularly for offshore liquefaction applications, and may not be feasible for other applications.

The present technological advancement can use a co-current flow scheme as an alternative to the counter-current flow scheme demonstrated in the scrub column <NUM> of <FIG>. The co-current flow scheme utilizes one or more co-current contacting systems connected in series within a pipe. A natural gas stream and a liquid reflux stream may move together, i.e., co-currently, within each co-current contacting system. In general, co-current contactors can operate at much higher fluid velocities than counter-current contacting systems. As a result, co-current contacting systems tend to be smaller than counter-current contactors that utilize standard towers with packing or trays. Further, the co-current contacting systems are smaller than conventional pressure vessels of equivalent processing capacity, and are thus more suited to modular design/construction, offshore deployment, de-bottlenecking applications, and applications where visual pollution may be a factor. In natural gas liquefaction application, two to three co-current contacting systems in series can be used to separate heavy hydrocarbons from a natural gas stream.

<FIG> is a schematic of a co-current contacting system (CCCS) <NUM>. to used in the invention. The co-current contacting system <NUM> can provide for the separation of components within a gas stream. The co-current contacting system <NUM> can include a co-current contactor <NUM> that is positioned in-line within a pipe <NUM>. The co-current contactor <NUM> may include a number of components that provide for the efficient contacting of a liquid droplet stream with a flowing gas stream <NUM>. The liquid droplet stream may be used for the separation of impurities, such as heavy hydrocarbons, from a gas stream <NUM>.

The co-current contactor <NUM> may include a droplet generator <NUM> and a mass transfer section <NUM>. As shown in <FIG>, the gas stream <NUM> may be flowed through the pipe <NUM> and into the droplet generator <NUM>. A liquid stream <NUM> may also be flowed into the droplet generator <NUM>, for example, through a hollow space <NUM> coupled to flow channels <NUM> in the droplet generator <NUM>.

From the flow channels <NUM>, the liquid stream <NUM> is released into the gas stream <NUM> as fine droplets through injection orifices <NUM>, and is then flowed into the mass transfer section <NUM>. This can result in the generation of a treated gas stream <NUM> within the mass transfer section <NUM>. The treated gas stream <NUM> may include small liquid droplets dispersed in a gas phase. For fractionation associated with a natural gas liquefaction process, the liquid droplets may include heavy hydrocarbons from the gas stream <NUM> that were absorbed or dissolved into the liquid stream <NUM>.

The treated gas stream <NUM> may be flowed from the mass transfer section <NUM> to a separation system <NUM>, which includes a cyclonic separator <NUM> and a collector <NUM>. Alternatively the separation system may include a mesh screen, or a settling vessel. Preferably, in-line cyclonic separators may be used to realize the benefits of compactness and reduced diameter. The cyclonic separator <NUM> removes the liquid droplets from the gas phase. The liquid droplets, which as previously stated may include heavy hydrocarbons <NUM> absorbed or dissolved into the liquid stream <NUM>, are diverted into collector <NUM>, which directs the collected liquids stream <NUM> through a valve <NUM> and pump <NUM> to other portions of the disclosed aspects as will be further described herein. A gas purge line <NUM> extends from the collector <NUM> and operates to re-inject gas present in the collector into the separation system <NUM>. In an aspect, this gas is re-injected using a nozzle <NUM> or eductor situated inside the separation system <NUM>. A gas stream <NUM>, from which the heavy hydrocarbons-rich liquid has been separated, exits the separation system <NUM> in an in-line orientation with the pipe <NUM>. The proportion of light hydrocarbons to heavy hydrocarbons is higher in gas stream <NUM> than in gas stream <NUM>.

<FIG> is a front view of a contacting device <NUM>. The contacting device <NUM> may be implemented within a co-current contactor, for example, in the co-current contactor <NUM> described with respect to the co-current contacting system <NUM> of <FIG>. The contacting device <NUM> can be an axial, in-line co-current contactor located within a pipe. The front view of the contacting device <NUM> represents an upstream view of the contacting device <NUM>.

The contacting device <NUM> may include an outer annular support ring <NUM>, a number of spokes <NUM> extending from the annular support ring <NUM>, and a gas entry cone <NUM>. The annular support ring <NUM> may secure the contacting device <NUM> in-line within the pipe. In addition, the spokes <NUM> may provide support for the gas entry cone <NUM>.

The annular support ring <NUM> may be designed as a flanged connection, or as a removable or fixed sleeve inside the pipe. In addition, the annular support ring <NUM> may include a liquid feed system and a hollow channel described further with respect to <FIG>. A liquid stream may be fed to the contacting device <NUM> via the hollow channel in the annular support ring <NUM>. The hollow channel may allow equal distribution of the liquid stream along the perimeter of the contacting device <NUM>.

Small liquid channels within the annular support ring <NUM> may provide a flow path for the liquid stream to flow through liquid injection orifices <NUM> within the spokes <NUM>. The liquid injection orifices <NUM> may be located on or near the leading edge of each spoke <NUM>. Placement of the liquid injection orifices <NUM> on the spokes <NUM> may allow the liquid stream to be uniformly distributed in a gas stream that is directed between the spokes <NUM>. Specifically, the liquid stream may be contacted by the gas stream flowing through the gaps between the spokes <NUM>, and can be sheared into small droplets and entrained in the gas phase.

A portion of the feed gas stream flows between the spokes to the mass transfer section while the remainder of the gas stream flows into the gas entry cone <NUM> through a gas inlet <NUM>. The gas entry cone <NUM> may block a cross-sectional portion of the pipe. The spokes <NUM> include gas exit slots <NUM> that allow the gas stream to be flowed out of the gas entry cone <NUM>. This may increase the velocity of the gas stream as it flows through the pipe. The gas entry cone <NUM> may direct a predetermined amount of the gas stream to the gas exit slots <NUM> on the spokes <NUM>.

Some of the liquid stream injected through the spokes <NUM> may be deposited on the surface of the spokes <NUM> as a liquid film. As the gas stream flows through the gas entry cone <NUM> and is directed out of the gas exit slots <NUM> on the spokes <NUM>, the gas stream may sweep, or blow, much of the liquid film off the spokes <NUM>. This may enhance the dispersion of the liquid stream into the gas phase. Further, the obstruction to the flow of the gas stream and the shearing effect created by the exit of the gas through the gas exit slots may provide a zone with an increased turbulent dissipation rate. The may result in the generation of smaller droplets that enhance the mass transfer rate of the liquid stream and the gas stream.

The dimensions of various components of the contacting device <NUM> may be varied such that the gas stream flows at a high velocity. This may be accomplished via either a sudden reduction in the diameter of the annular support ring <NUM> or a gradual reduction in the diameter of the annular support ring <NUM>. The outer wall of the contacting device <NUM> may be slightly converging in shape, terminating at the point where the gas stream and the liquid stream are discharged into the downstream pipe. This can allow for the shearing and re-entrainment of any liquid film that is removed from the contacting device <NUM>. Further, a radial inward ring, grooved surface, or other suitable equipment may be included on the outer diameter of the contacting device <NUM> near the point where the gas stream and the liquid stream are discharged into the downstream pipe. This may enhance the degree of liquid entrainment within the gas phase.

The downstream end of the contacting device <NUM> may discharge into a section of pipe (not shown). The section of pipe can be a straight section of pipe, or a concentric expansion section of pipe. The gas entry cone <NUM> may terminate with a blunt ended cone or a tapered ended cone. In other embodiments, the gas entry cone <NUM> can terminate with a ridged cone, which can include multiple concentric ridges along the cone that provide multiple locations for droplet generation. In addition, any number of gas exit slots <NUM> may be provided on the cone itself to allow for the removal of the liquid film from the contacting device <NUM>.

<FIG> is a side perspective view of the contacting device <NUM>. Like numbered items are as described with respect to <FIG>. As shown in <FIG>, the upstream portion of the gas entry cone <NUM> may extend further into the pipe than the annular support ring <NUM> and the spokes <NUM> in the upstream direction. The downstream portion of the gas entry cone <NUM> can also extend further into the pipe than the annular support ring <NUM> and the spokes <NUM> in the downstream direction. The length of the gas entry cone <NUM> in the downstream direction depends on the type of cone at the end of the gas entry cone <NUM>, as described further with respect to <FIG>.

<FIG> is a cross-sectional side perspective view of the contacting device <NUM> according to a disclosed aspect. Like numbered items are as described with respect to <FIG>. According to <FIG>, the gas entry cone <NUM> of the contacting device <NUM> terminates with a tapered ended cone <NUM>. Terminating the gas entry cone <NUM> with a tapered ended cone <NUM> may reduce the overall pressure drop in the pipe caused by the contacting device <NUM>.

<FIG> is a cross-sectional side perspective view of the contacting device <NUM> according to another disclosed aspect. Like numbered items are as described with respect to <FIG>. According to <FIG>, the gas entry cone <NUM> of the contacting device <NUM> terminates with a blunt ended cone <NUM>. Terminating the gas entry cone <NUM> with a blunt ended cone <NUM> may encourage droplet formation in the center of the pipe.

<FIG> depicts a gas fractionation system <NUM> according to disclosed aspects, which may be used with natural gas liquefaction process. The gas fractionation system <NUM> includes a bottom section, also known as a scrub stripper column <NUM>, and a top section or rectification section <NUM>, which according to disclosed aspects comprises a plurality of co-current contacting systems. The scrub stripper column <NUM> may be a stand-alone column, and performs an equivalent function to the stripping section <NUM> of scrub column <NUM> depicted in <FIG>. As can be seen in <FIG>, the feed gas stream <NUM>, which typically is a two-phase stream, enters the gas fractionation system <NUM> at high pressure and at a position adjacent both the scrub stripper column <NUM> and the rectification section <NUM>. A predominantly vapor phase and a predominantly liquid phase in the feed gas stream <NUM> separate from each other, with the predominantly vapor phase moving upward into the rectification section <NUM> and the predominantly liquid phase moving downward into the scrub stripper column <NUM>. The scrub stripper column <NUM> uses trays <NUM> to separate and direct liquid downward. Trays <NUM> are typically used instead of packing because of anticipated high liquid flux, which is defined as a volumetric flow per unit area.

A liquid stream <NUM> is extracted near the bottom of the scrub stripper column <NUM> and is re-heated in a reboiler <NUM>. The reheated stream <NUM> is returned to the scrub stripper column <NUM>, where vapors in the reheated stream may rise through the scrub stripper column and enter the rectification section <NUM>. Liquids in the reheated stream <NUM> combine with other liquids at the bottom of the scrub stripper column <NUM>. A scrub stripper column liquid bottoms stream <NUM> may be taken from the bottom of the scrub stripper column <NUM>.

The vapor phase of the feed gas stream <NUM> is combined with the vapor rising from the from the scrub stripper column <NUM>. The combined vapor stream <NUM> enters the rectification section <NUM>, which in an aspect includes a separation system <NUM> and one or more scrubbing stages, with each scrubbing stage including an in-line co-current contacting system 421a, 421b, 421c similar to the in-line co-current contacting system <NUM> described in <FIG>. In a preferred aspect the separation system <NUM> includes a cyclonic separator, and in a more preferred embodiment includes an in-line cyclonic separator <NUM> and a collector <NUM> similar to the cyclonic separator <NUM> and collector <NUM> used in separation system <NUM> of <FIG>. The in-line cyclonic separator <NUM> serves as a flash zone to cause some of the liquids entrained in the combined vapor stream <NUM> to be separated therefrom. If the gas fractionation system <NUM> is used where no fouling is expected due to the content of the feed stream, an agglomerator <NUM> may be placed in front of the in-line cyclonic separator <NUM> to increase the size of the liquid droplets entering the in-line cyclonic separator. Agglomerator <NUM> may improve the liquid separation performance of the in-line cyclonic separator <NUM>. The liquid collected from the collector <NUM> is fed through a flash reflux line <NUM> to a top region of the scrub stripper column <NUM> for further separation therein.

The flash zone vapor stream <NUM> exiting the in-line cyclonic separator <NUM> is fed to the first co-current contacting system 421a, which includes a droplet generator 428a, a mass transfer section 430a, a cyclonic separator 432a with an optional agglomerator 434a, and a collector 436a. Liquid 438b collected from a subsequent or downstream in-line co-current contacting system (such as in-line co-current contacting system 421b) is injected into the droplet generator 428a and mixed and combined in the mass transfer section, where heavy hydrocarbons in the flash zone vapor stream are transferred to the sprayed liquid, and light hydrocarbons in the liquid stream are transferred to the flash zone vapor stream. The liquid and vapor in the mass transfer section 430a are separated from each other using the cyclonic separator 432a and optional agglomerator 434a, with the liquid being collected in the collector 436a and sent through a liquid collection line 438a to be combined with the flash reflux line <NUM>. The gas stream 440a with heavy hydrocarbons removed therefrom is sent as an input to the second co-current contacting system 421b. The second co-current contacting system 421b is constructed similar to first co-current contacting system 421a and functions in a similar manner, with liquid 438c collected from a subsequent or downstream in-line co-current contacting system (such as in-line co-current contacting system 421c) being mixed with the gas stream 440a. The gas stream 440b with heavy hydrocarbons removed in the second co-current contacting system 421b is sent as an input to the third co-current contacting system 421c. The third co-current contacting system 421c is constructed similar to first and second co-current contacting systems 421a, 421b and functions in a similar manner. The gas stream 440c with heavy hydrocarbons removed therefrom is sent to a reflux cooler <NUM>, which condenses heavy hydrocarbons remaining in the gas stream, which are in turn separated in liquid form from the gas stream in a reflux drum <NUM>. The reflux liquid stream <NUM> is used as the liquid input to the third co-current contacting system 421c, and the gas stream <NUM> exiting the reflux drum is sent for further processing, which may include liquefaction.

The gas fractionation system <NUM> may include any number of co-current contacting systems as desired or required. Further, any number of additional components can be included within the gas fractionation system <NUM>, depending on the details of the specific implementation. Further, the gas fractionation system <NUM> may include any suitable types of heaters, chillers, condensers, liquid pumps, gas compressors, blowers, bypass lines, other types of separation and/or fractionation equipment, valves, switches, controllers, and pressure-measuring devices, temperature-measuring devices, level-measuring devices, or flow-measuring devices, among others.

<FIG> is a schematic diagram of another arrangement of the rectification section <NUM> of the gas fractionation system <NUM>. Shown are the separation system <NUM> and three scrubbing stages which comprise the first, second, and third in-line co-current contacting systems 421a, 421b, 421c. For each of the separation system and the first through third in-line co-current contacting systems, <FIG> also shows the pumps 450a, 450b, 450c, 450d, valves 452a, 452b, 452c, 452d, gas purge lines 454a, 454b, 454c, 454d, and nozzles 456a, 456b, 456c, 456d that were described with respect to <FIG>. <FIG> shows more clearly that the disclosed aspects are operated with an overall countercurrent flow of the liquid from previous scrubbing stages, with co-current contacting in individual scrub stages.

<FIG> is a side view of a single stage multiple co-current contactor configuration <NUM> that may be used as part or all of a rectification section in a gas fractionation system as previously disclosed. The single stage multiple co-current contactor configuration <NUM> is generally contained within a vessel <NUM> which may form a unitary (single and/or common) pressure boundary for the compact contacting occurring therein. The vessel <NUM> may be configured to withstand in excess of (may have a pressure vessel rating of) about <NUM> psia (about <NUM> bar) of pressure, e.g., from about <NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar), from about <NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar), from about <NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar) from about <NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar), from about <NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar), from about <NUM>,<NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar), from about <NUM>,<NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar), from about <NUM>,<NUM> psia (about <NUM> bar) to about <NUM>,<NUM> psia (about <NUM> bar), or any range there between. The differential pressure across the length of the vessel <NUM>, e.g., between the gas stream <NUM> and natural gas stream <NUM>, may be about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), about <NUM> psia (about <NUM> bar) to about <NUM> psia (about <NUM> bar), or any range therebetween. The vessel <NUM> generally contains a single stage bundle of substantially parallel separation units or compact contactors comprising contacting units <NUM>a-<NUM>n, also referred to herein as separation units. Those of skill in the art will understand that the number of contacting units <NUM>a-<NUM>n in the bundle of compact contactors may be optionally selected based on the desired design characteristics, including desired flow rate, separation unit diameter, etc., and could number from anywhere between one to <NUM> or more units. The use of the letter nomenclature (i.e., 'a', 'b', 'n', etc.) in conjunction with the numerical reference characters is for ease of reference only and is not limiting. For example, those of skill in the art will understand that an illustrated set of contacting units <NUM>a-608n may, in various embodiments, comprise two, four, five, twenty, or several hundred contacting units. The vessel <NUM> comprises an inlet manifold <NUM> having droplet generators <NUM>a-612n in the inlet section <NUM> of the single stage multiple co-current contactor configuration <NUM>. The inlet section <NUM> is configured to receive the natural gas stream <NUM> in a common inlet plenum through which the natural gas stream <NUM> may be distributed substantially equally across the contacting units 608a-608n. While a gas stream <NUM>, gas stream <NUM>, etc. are discussed herein, those of skill in the art will appreciate that generally the same principles may be applied to any fluid stream, including with respect to liquid-liquid contacting. Consequently, use of the phrases "gas stream," "gas inlet," "gas outlet," etc. are to be understood as non-limiting and may optionally be replaced with "fluid stream," "fluid inlet," "fluid outlet," and so forth in various embodiments within the scope of this disclosure. Use of the phrases "gas stream," "gas inlet," "gas outlet," etc. are for the sake of convenience only. The contacting units 608a-608n may be of a suitable size depending on the design requirements. For example, the contacting units 608a-608n may have an individual diameter from about <NUM> inches (in) (about <NUM> centimeters (cm)) to about <NUM> in (about <NUM>), about <NUM> in (about <NUM>) to about <NUM> in (about <NUM>), about <NUM> in (about <NUM>) to about <NUM> in (about <NUM>), about <NUM> in (about <NUM>) to about <NUM> in (about <NUM>), about <NUM> in (about <NUM>) to about <NUM> in (about <NUM>), about <NUM> in (about <NUM>) to about <NUM> in (about <NUM>), about <NUM> in (about <NUM>) to about <NUM> in (about <NUM>), or any range there between. The inlet manifold <NUM> is configured to receive a liquid stream <NUM> and pass the liquid stream <NUM> to the droplet generators 612a-612n, where the liquid stream <NUM> may be atomized. Droplet generators 612a-612n are similar to the droplet generator <NUM> or contacting device <NUM> as previously described. The droplet generators 612a-612n may serve to entrain the atomized liquid stream in the gas stream <NUM>, and the mixed stream of atomized solvent and natural gas may be passed to the mass transfer section <NUM> where absorption occurs. Each contacting unit 608a-608n has a recycle gas inlet 618a-618n supplied by recycle gas collected and returned, e.g., from a common boot <NUM>. The boot <NUM> may be optionally included in low liquid rate applications to improve liquid rate flow control. As depicted, the boot <NUM> may have an internal vortex breaker <NUM> or other appropriate internals. For ease of viewing, the recycle gas supply lines for each of the recycle gas inlets 618a-618n are not depicted, but may be similar to gas purge line <NUM> as previously described. As will be understood by those of skill in the art, the recycle gas inlets 618a-618n are optional, and recycle gas may additionally or alternatively be sent downstream in other aspects. Liquid exiting the contacting units 608a-608n via liquid outlets 624a-624n may drain into a common liquid degassing section or common liquid collection plenum <NUM>. The plenum <NUM> may provide sufficient residence time for desired degasing, may reduce liquid surges coming with the natural gas stream <NUM>, and may provide a liquid seal to a cyclonic separation occurring in a contacting section <NUM> of each contacting unit 608a-608n. The residence time provided by the plenum <NUM> can vary from <NUM> seconds to <NUM> minutes, depending on the operation of the process, or from <NUM> seconds to <NUM> minute in various aspects. The vessel <NUM> contains a mist eliminator <NUM>, e.g., a wire mesh, vane pack plates, baffles, or other internal devices to reduce liquid droplet carry over from degassing gas, leaving the liquid in the plenum <NUM>. The mist eliminator <NUM> may also serve as a momentum breaker for the liquid exiting each contacting unit 608a-608n to minimize aeration of the liquid. In aspects installed in offshore facilities or floating facilities or otherwise subject to motion, the mist eliminator <NUM> may mitigate wave motion effects in the bottom portion of the vessel <NUM>. Each contacting unit 608a-608n has a treated gas outlet 632a-632n and a liquid outlet 624a-624n in a separation section <NUM>. The vessel <NUM> has a vent <NUM> for expelling degassing gas, e.g., gas degassed from liquid collected in the plenum <NUM> that may be fed upstream or downstream of the multiple co-current contacting unit, depending on the process configuration. The treated gas outlets 632a-632n couple to an outlet manifold <NUM>. The vessel <NUM> also contains level control ports 638a and 638b for coupling a level control system (not depicted) and controlling the amount of liquid <NUM> exiting the boot <NUM>. Liquid <NUM> exiting the boot <NUM> may be sent to a rectification section of a fractionation system, as previously described.

<FIG> is a cross-sectional end view of the single stage multiple co-current contactor configuration <NUM> of <FIG> taken at the inlet manifold <NUM>. <FIG> shows an example arrangement of the contacting units in the vessel <NUM>, although for the sake of simplicity only the droplet generators 612a-612n associated with the contacting units are shown. Other acceptable arrangements will be readily apparent to those of skill in the art. <FIG> also shows a location of the mist eliminator <NUM>, the plenum <NUM>, the vent <NUM>, the boot <NUM>, the level control ports 638a and 638b, and the liquid stream <NUM>.

<FIG> depict a single stage multiple co-current contactor configuration. Additional stages may also be included in a multiple co-current contactor, as disclosed in co-owned U. Patent Application Publication No. <CIT> titled "Separating Impurities from a Fluid Stream Using Multiple Co-current Contactors", Additionally, any of the in-line co-current contacting systems 421a, 421b, 421c of the gas fractionation system depicted in <FIG> and <FIG> may be replaced by a single stage or multiple stage multiple co-current contactor as described herein.

<FIG> is a method <NUM> of removing heavy hydrocarbons in a gas stream according to aspects of the disclosure. At block <NUM> a feed gas stream is introduced into a feed gas inlet. At block <NUM> a predominantly liquid phase of the feed gas stream is received into a stripping section. At block <NUM> a predominantly vapor phase of the feed gas stream is received into a first co-current contacting system located in-line within a pipe with a second co-current contacting system. Each of the first and second co-current contacting systems comprise a co-current contactor including a droplet generator and a mass transfer section, and a separation system. At block <NUM>, using each droplet generator, droplets from a liquid are generated and dispersed into a gas stream. At block <NUM>, in each mass transfer section a mixed, two-phase flow is provided having a vapor phase and a liquid phase. At block <NUM>, in each separation system the vapor phase from the liquid phase are separated. The vapor phase of the co-current contactor in the first co-current contacting system comprises the gas stream for the co-current contactor in the second co-current contacting system. The liquid phase of the co-current contactor in the second co-current contacting system comprises the liquid from which droplets are generated in the co-current contactor of the first co-current contacting system.

<FIG> is a method <NUM> of a method of removing heavy hydrocarbons in a gas stream. At block <NUM> a feed gas stream is introduced into a feed gas inlet. At block <NUM> a predominantly liquid phase of the feed gas stream is received into a stripping section. At block <NUM> a predominantly vapor phase of the feed gas stream is received into a first co-current contacting system located in-line within a pipe with a second co-current contacting system. At least one of the first and second co-current contacting systems comprises a compact contacting bundle disposed within a vessel that forms a unitary pressure boundary. The compact contacting bundle includes a plurality of substantially parallel contacting units. Each of the plurality of contacting units has a droplet generator and a mass transfer section, and a separation system. At block <NUM> the liquid is distributed to each droplet generator of the plurality of contacting units. At block <NUM>, using each droplet generator, droplets are generated from a liquid and dispersing the droplets into a gas stream. At block <NUM>, in each mass transfer section, a mixed, two-phase flow is provided having a vapor phase and a liquid phase. At block <NUM>, in each separation system, the vapor phase is separated from the liquid phase. The vapor phase of the first co-current contacting system comprises the gas stream for the second co-current contacting system, and the liquid phase of the second co-current contacting system comprises the liquid from which droplets are generated in the first co-current contacting system.

The disclosed aspects may be varied in many ways. For example, the compact co-current contacting systems have been shown in the Figures as being connected to each other in series, but for additional turndown flexibility one or more of the compact co-current contacting systems may be connected to each other in parallel. The separation systems disclosed herein may also be varied. Instead of the disclosed single cyclonic separator, in-line demisting cyclones may be used. Additional in-line demisting cyclones may be installed after the last scrubbing stage if further liquid separation is desired or required. Other known mist-eliminating devices may replace the cyclonic separator. The methods, processes, and/or functions described herein can be implemented and/or controlled by a computer system appropriately programmed.

Moreover, it is contemplated that features from various examples described herein can be combined together, including some but not necessarily all the features provided for given examples. Furthermore, the features of any particular example are not necessarily required to implement the present technological advancement.

The disclosed aspects replace the large diameter packed rectification section of known LNG scrub columns. An advantage of the disclosed aspects is that the disclosed aspects may be used with many different LNG processes with scrub column schemes. Another advantage is that the compact co-current contacting systems can be horizontally oriented, vertically oriented, or in a mixed orientation as required or desired to best meet the limitations of an existing plot or module space.

Other advantages of the disclosed aspects may be seen through reduced capital costs and potentially enhanced processing capacity in space-limited retrofit and de-bottlenecking opportunities. Due to the operating pressure of conventional LNG Scrub columns (~ <NUM> bar, <NUM> psia) and the low operating processing temperatures of the system (-<NUM> ), the column must be constructed of very expensive stainless steel with a very thick wall. For example, a scrub column where the top/rectification section of a conventional packed stainless steel scrub column has a diameter of <NUM>, approximately <NUM> height (including a flash zone) and <NUM> wall thickness, can be replaced with the disclosed scrubbing system enclosed in a pipe having a <NUM> inch (<NUM>) diameter. This may result in an approximately <NUM>% reduction in capital expenditures, not to mention additional savings in transportation, civil and structural supports, when compared to known scrub columns.

Claim 1:
Use of a fractionation system (<NUM>) for removing heavy hydrocarbons in a gas stream, comprising:
a feed gas inlet configured to introduce a feed gas stream (<NUM>) through it;
a stripping section (<NUM>) configured to receive a predominantly liquid phase of the feed gas stream; and
first and second co-current contacting systems (<NUM>, 421a, 421b, <NUM>) located in-line within a pipe, the first co-current contacting system (<NUM>, 421a, <NUM>) configured to receive a predominantly vapor phase of the feed gas stream, each of the first and second co-current contacting systems (<NUM>, 421a, 421b, <NUM>) comprising:
a co-current contactor (<NUM>) including a droplet generator (<NUM>, 428a, 612a-n) and a mass transfer section (<NUM>, 430a), the droplet generator (<NUM>, 428a, 612a-n) configured to generate droplets from a liquid (<NUM>) and to disperse the droplets into a gas stream (<NUM>), and the mass transfer section (<NUM>, 430a) configured to provide a mixed, two-phase flow having a vapor phase and a liquid phase; and
a separation system (<NUM>, <NUM>) configured to separate the vapor phase from the liquid phase;
wherein the system is configured such that the vapor phase of the co-current contactor (<NUM>) in the first co-current contacting system (<NUM>, 421a, <NUM>) comprises the gas stream (440a) for the co-current contactor in the second co-current contacting system (<NUM>, 421b, <NUM>), and wherein the system is configured such that the liquid phase of the co-current contactor (<NUM>) in the second co-current contacting system (<NUM>, 421b, <NUM>) comprises the liquid (<NUM>, 438b) from which droplets are generated in the co-current contactor (<NUM>) of the first co-current contacting system (<NUM>, 421a, <NUM>).