Patent Description:
Natural gas streams, or other methane-rich gas streams, are often liquefied for ease of transport and use. <CIT> discloses a system for removing heavy hydrocarbon components from a feed gas stream comprising:a. a heavies removal heat exchanger having a main feed stream cooling passage, a reflux stream cooling passage and a return vapor stream warming passage;b. said main feed stream cooling passage of the heavies removal heat exchanger configured to receive and cool at least a portion of the feed gas stream so as to produce a cooled main feed stream;c. a scrubbing section including a main feed inlet, a liquid outlet, a return vapor outlet and a reflux inlet, wherein said main feed inlet is configured to receive the cooled main feed stream;d. a stripping section having a first fluid inlet, a second fluid inlet, a liquid outlet and a vapor outlet, said first fluid inlet configured to receive a fluid stream from the liquid outlet of the scrubbing section;e. a stripping gas feed expansion device having an inlet configured to receive a portion of the feed gas stream, said stripping gas feed expansion device having an outlet in fluid communication with the second fluid inlet of the stripping section;f. a side draw vapor line configured to receive a vapor stream from the vapor outlet of the stripping section, said side draw vapor line in fluid communication with the reflux stream cooling passage of the heavies removal heat exchanger;g. a reflux separation device configured to receive fluid from the reflux cooling stream passage of the heavies removal heat exchanger, said reflux separation device including a liquid outlet and a vapor outlet, wherein the liquid outlet of the reflux separation device is in fluid communication with the reflux inlet of the scrubbing section;h. a return expansion device having an inlet configured to receive a stream from the return vapor outlet of the scrubbing section and an outlet configured to direct a cooled vapor stream to the return vapor stream warming passage of the heavies removal heat exchanger;i. said reflux separation device vapor outlet configured so that fluid passing therethrough joins with fluid that has exited the return expansion device after the fluid that has exited the return expansion device flows through the return vapor stream warming passage of the heavies removal heat exchanger.

It is often desirable to process such feed gas streams to remove heavier hydrocarbons (hydrocarbons that are heavier than propane) so as to provide a higher methane purity in the resulting liquid natural gas product and a co-product liquid (natural gas liquids) that contains the heavy hydrocarbons. Such purified liquid natural gas products burn cleaner in LNG-powered vehicles so that less air pollution results. In addition, purifying the feed stream prior to liquefaction prevents freeze-up of the liquefying heat exchanger that would otherwise occur due to presence of heavy hydrocarbon components. The co-product liquid stream, rich in heavy hydrocarbons such as ethane, propane, butane and heavier hydrocarbons, have several valuable industrial uses. It is further desirable that such processing minimizes energy consumption given the volume of gas that must be purified.

The current invention is defined solely by the appended claims.

In one aspect of the current invention, the current invention provides an apparatus according to claim <NUM>.

In another aspect of the current invention, the current invention provides a method according to claim <NUM>.

<FIG> show embodiments of the present invention as defined by the appended claims.

Embodiments of a heavy hydrocarbon removal system in accordance with the disclosure are illustrated in <FIG>. It should be noted that while the embodiments are illustrated and described below in terms of removing heavy hydrocarbons components from a natural gas feed stream prior to being liquefied, the technology of the disclosure may be used to remove other components from alternative gas feed streams prior to alternative types of downstream processing.

It should also be noted that in the descriptions presented below, the lines or passages and streams are sometimes both referred to by the same reference numbers set out in the figures.

With reference to <FIG>, a first embodiment of the system of the disclosure is indicated in general at <NUM>. A hydrocarbon feed gas stream <NUM> (such as a natural gas stream) enters a feed gas expander turbine <NUM> and the resulting expanded gas stream is split into a main feed stream <NUM> and a stripping gas feed stream <NUM>.

The main feed stream <NUM>, which contains the bulk of the feed gas stream <NUM>, passes through a heavies removal heat exchanger <NUM> and is cooled and partially condensed. The resulting mixed phase stream <NUM> is then routed to a scrubbing section <NUM> of a heavies removal column, indicated in general at <NUM>, where liquids are separated from the main feed vapor. The resulting liquid stream <NUM>, which contains a large portion of the feed gas heavy hydrocarbon/freezing components is directed to an optional expansion device <NUM> (such as a Joule-Thomson or JT valve) with the resulting mixed phase stream <NUM> traveling to the upper portion of the column stripping section <NUM>. As used herein, the term "expansion device" includes, but is not limited to, a JT valve, rotating expander, turbine, orifice plate and any other expansion device known in the art. Stream <NUM> is separated into a vapor portion and a liquid portion upon entering the column stripping section <NUM>.

The stripping gas feed stream <NUM> travels to an expansion device <NUM> (such as a Joule-Thomson or JT valve) with the resulting mixed phase stream <NUM> traveling to the lower portion of the column stripping section <NUM>. The vapor portion of stream <NUM> is separated from the liquid portion upon entering the stripping column section <NUM> and rises to provide heating action to the liquids from stream <NUM> coming down through the stripping section internals thereby revaporizing a portion of the lighter components in said liquids. The liquid portion of stream <NUM> exits the stripping section <NUM> as a portion of natural gas liquids (NGL) condensate stream <NUM> as does the remaining liquid portion of the stream <NUM>. Condensate stream <NUM> contains a majority of the heavy hydrocarbon/freezing components that were present in the feed gas stream <NUM>.

A vapor side draw stream <NUM> exits the stripping section <NUM> of the heavies removal column and is cooled and partially condensed in the heavies removal exchanger <NUM>. A resulting mixed phase stream <NUM> travels to a separation device, such as a heavies removal reflux drum <NUM>, and is separated into vapor and liquid portions. The liquid stream <NUM> from the separation device <NUM> is routed via pump <NUM> (optional) to the top of the heavies removal column scrubbing section <NUM> as reflux stream <NUM> after passing through optional control valve <NUM>.

The vapor stream <NUM> from the separation device <NUM> is routed across an expansion device <NUM> (such as a JT valve) where it is cooled to form cooled stream <NUM>, a portion (or all) of which passes through the heavies removal exchanger <NUM> and is warmed and thereby provides cooling to other streams in the exchanger. Vapor stream <NUM> is provided as a result.

The vapor portion of the main feed stream <NUM> in the heavies removal column scrubbing section undergoes mass transfer with the reflux provided by reflux stream <NUM> within the column scrubbing section internals, which may be trays. random packing, or structured packing. This removes freezing components/heavy hydrocarbons from the vapor portion of the main feed stream <NUM>. The scrubbed return vapor stream <NUM> exits the top of the column <NUM> and is then routed across an expansion device <NUM> (such as a JT valve) to produce cooling. The cooled return vapor stream <NUM> is then routed to the heavies removal exchanger <NUM> where it is warmed in one or more passages and thereby, along with stream <NUM>, provides cooling to other streams in the exchanger. After warming and combination with stream <NUM>, the return vapor stream <NUM> is compressed by feed gas compressor <NUM> and sent to a liquefaction process so that a liquefied stream (such a liquid natural gas/LNG) is produced.

The feed gas compressor <NUM> is preferably powered by the feed gas expander turbine <NUM>, while a booster compressor <NUM> (which may or may not be powered by the gas expander turbine <NUM>) may optionally also be provided. By expanding the feed gas stream <NUM> prior to cooling, greater power is developed by the turbine <NUM>, which results in greater power being available to run the compressor <NUM> (and any booster compressors). This decreases net power usage of the system and thus increases system efficiency in some applications. Furthermore, expanding the feed gas stream <NUM> prior to cooling lowers equipment cost as, in some applications, carbon steel may be used to construct the feed gas turbine <NUM> (as opposed to stainless steel, which is required for expanding at colder fluid temperatures).

As examples only, the systems described herein may provide purified gas to the liquefaction processes and systems described in commamly owned <CIT>, <CIT> or <CIT>, the contents of each of which are hereby incorporated by reference.

It should be noted that, in alternative embodiments, streams <NUM> and <NUM> may be combined prior to introduction into the heat exchanger <NUM>, as illustrated in <FIG>. Furthermore, the vessel head <NUM> (<FIG>) separating the scrubbing and stripping sections of column <NUM> may optionally be removed so that the functions are combined into a single column with trap-out trays or other devices used to capture liquid. In other alternative embodiments, the scrubbing and stripping sections may be provided as entirely separate individual columns.

Advantages of the embodiment of <FIG> include the expander <NUM> both extracting power and providing cooling to the feed gas stream. In addition the side draw reflux stream provides high recovery of heavy hydrocarbons, including captures of Benzene, Toluene, Ethylbenzene, Xylenes (BTEX).

In a second embodiment of the system of the disclosme, indicated in general at <NUM> in <FIG>, a reboiler service has been added to the system of <FIG> whereby the liquid stream <NUM> from the scrubbing section <NUM>, after being expanded and cooled in optional reboiler expansion device <NUM>, such as a JT valve, is warmed in the heavies removal exchanger <NUM> to provide cooling therein. In an alternative embodiment, a portion of stream <NUM> may go directly to the stripping section either before or after passing through expansion device <NUM>. An expansion device <NUM> has also been added to vapor side draw stream <NUM> to cool the vapor from the stripping section prior to travel to the heavies removal exchanger <NUM>. In addition, optional streams <NUM> and <NUM> from the exchanger may be used to optimize the temperatures of the stripping gas stream <NUM> and reboiler return stream <NUM>, respectively. Furthermore, line <NUM> may optianally be provided (either with or without control valve <NUM>) to provide injection of side draw reflux to the stripping section <NUM>. In an alternative embodiment, a branch <NUM> may direct a portion of the scrubbed return vapor stream <NUM> to the separation device (reflux drum) <NUM>. The remaining components of the system of <FIG> may generally be the same and provide the same functionality as those illustrated in <FIG>.

In a third embodiment of the system of the disclosure, indicated in general at <NUM>, in <FIG>. an expansion device <NUM>, such as a JT valve, is substituted for the feed gas expander turbine <NUM> of the systems of <FIG>. System <NUM> of <FIG> also substitutes a return vapor expander turbine <NUM> for the JT valve <NUM> of systems <NUM> and <NUM> of <FIG> that receives the return vapor stream <NUM> from the heavies removal column <NUM>. This return vapor expander turbine <NUM> preferably powers the feed gas compressor <NUM>. The remaining components of the system of <FIG> may generally be the same and provide the same functionality as those illustrated in <FIG>. In an alternative version of the system of the disclosure, as illustrated in <FIG>, a portion <NUM> of the scrubber liquid stream goes through the scrubber liquid reheat passage of the heavies removal heat exchanger <NUM> and a remaining portion <NUM> of the scrubber liquid stream goes directly to the stripping section.

In a fourth embodiment of the system of the disclosure, indicated in general at <NUM> in <FIG>, a cascade side draw reflux arrangement has been added to the system of <FIG>. More specifically, a vapor side draw stream <NUM> exits the stripping section <NUM> of the heavies removal column and is cooled and partially condensed in the heavies removal exchanger <NUM>. A resulting mixed phase stream <NUM> travels to a first reflux separation device, such as a warm reflux drum <NUM>, and is separated into vapor and liquid portions. The liquid stream <NUM> from the warm reflux drum <NUM> is routed via pump <NUM> (optional) to the top of the stripping section <NUM> of the heavies removal column as reflux stream <NUM> after passing through optional expansion device <NUM>.

With continued reference to <FIG>, the vapor stream <NUM> from the warm reflux drum <NUM> travels to heavies removal exchanger <NUM> and is cooled and partially condensed. A resulting mixed phase stream <NUM> travels to a second reflux separation device, such as cold reflux drum <NUM>, and is separated into vapor and liquid portions. The liquid stream <NUM> from the separation device <NUM> is routed via pump <NUM> (optional) to the top of the heavies removal column scrubbing section <NUM> as reflux stream <NUM> after passing through optional control valve <NUM>. Vapor stream <NUM> exits the top of cold reflux drum <NUM> and joins return vapor stream <NUM> after passing through expansion device <NUM>. While a single packing section for the scrubbing section <NUM> is illustrated in <FIG>, the scrubbing section may optionally be provided with two (or more) packing sections based on design considerations.

The remaining components of the system of <FIG> may generally be the same and provide the same functionality as those illustrated in <FIG>.

The cascade reflux arrangement of <FIG> lowers the level of heavy hydrocarbon components present in the reflux streams (as compared to the systems of <FIG>) in some applications.

In a fifth embodiment of the system of the disclosure, indicated in general at <NUM> in <FIG>, a split feed reflux arrangement has been added to the system <NUM> of <FIG>. More specifically, the system <NUM> includes a branch off of the hydrocarbon feed gas stream <NUM> before the feed gas expander <NUM>. A small portion of the feed gas stream splits off at the branch and flows through line <NUM> as a split feed reflux gas stream that is cooled in the heavies removal exchanger <NUM> and at least partially condensed to form mixed phase stream <NUM>. This stream is then expanded via a split feed reflux expansion device <NUM>, such as a JT valve, with the resulting cooled stream <NUM> directed to the scrubbing section <NUM> of the heavies removal column as reflux to aid in the removal of heavy hydrocarbons from the column main feed. Such a system provides improved efficiency for some high pressure feed gas applications. The scrub section can be single or double packed and the stream <NUM> may enter the scrub section above the packing or at a mid-point between the two packing sections.

In an alternative embodiment, the expansion device <NUM> of <FIG> may be omitted. In a further alternative embodiment, line <NUM> may optionally be provided (either with or without control valve <NUM>) to provide injection of side draw reflux to the stripping section <NUM>.

In a sixth embodiment of the system of the disclosure, indicated in general at <NUM> in <FIG>, a reflux heat exchanger <NUM> has been added to the system of <FIG> to provide additional cooling to the vapor side draw <NUM> from the stripping section <NUM> of the column prior to the reflux drum <NUM>. The cooling in supplemental reflux heat exchanger <NUM> is provided by the cooled (via heavies removal heat exchanger <NUM>) and expanded (via expansion device <NUM>) split feed reflux stream <NUM>. The remaining components of the system of <FIG> may generally be the same and provide the same functionality as those illustrated in <FIG>.

The additional heat exchanger <NUM> allows for cooler reflux and provide more efficient removal of heavy hydrocarbons in some applications. It should be noted that the heat exchangers <NUM> and <NUM> may be combined into a single heat exchanger in alternative embodiments.

In a seventh embodiment of the system of the disclosure, indicated in general at <NUM> in <FIG>, the cascade side draw reflux arrangement of <FIG> may be added to the system of <FIG>. As a result, the system <NUM> of <FIG> includes a first reflux separation device, such as a warm reflux drum <NUM>, which receives and separates a mixed phase stream <NUM> (resulting from cooling of side draw vapor stream <NUM>) into liquid and vapor portions. The vapor portion <NUM> is cooled and the resulting mixed phase stream <NUM> is provided to a second reflux separation device, such as cold reflux drum <NUM>, and is separated into vapor and liquid portions, which are further processed as explained with reference to <FIG>.

In an eighth embodiment of the system of the disclosure, indicated in general at <NUM> in <FIG>, a feed separation device <NUM> has been added to the system of <FIG>. As in previous embodiments, the feed gas stream <NUM> is expanded by feed gas expander <NUM> and then cooled by the heavies removal heat exchanger <NUM>. The resulting mixed phase stream <NUM> is directed to the feed separation device <NUM> where it is separated into a vapor portion and a liquid portion. The liquid portion exits the feed separation device <NUM> as liquid stream <NUM> and, after expansion via separated feed liquid expansion device <NUM> (such as a JT valve) is warmed in the heavies removal heat exchanger to provide refrigeration therein. The resulting mixed phase stream <NUM>, which may pass through optional cooled separated feed liquid expansion device <NUM>, such as a JT valve, is directed to the stripping section <NUM> of the heavies removal column, where it is separated into vapor and liquid portions.

The vapor stream <NUM> from the feed separation device <NUM> is directed through (optional) separated feed vapor expansion device <NUM>, such as a JT valve, where it is cooled and partially condensed so that mixed phase stream <NUM> is formed. Mixed phase stream <NUM> is then directed to the scrubbing section <NUM> of the heavies removal column where it is separated into vapor and liquid portions. Such a system provides improved efficiency at moderate pressure for some applications and may also be beneficial for richer feed gas applications.

The system <NUM> of <FIG> may include an optional branch <NUM> to the stripping section <NUM> from the mixed phase stream <NUM>. Branch <NUM> may optionally include an expansion device <NUM>. such as a JT valve. Such an arrangement may be desirable when additional flow is required at the top of the stripping section to meet wetting criteria. In such an embodiment, the stripping section <NUM> has two layers of internal trays or the like to allow for the additional injection location higher in the stripping section.

The embodiment of <FIG> provides improved efficiency at moderate feed pressures and/or when the feed gas stream <NUM> is rich in some applications.

In a nineth embodiment of the system of the disclosure, indicated in general at <NUM> in <FIG>, a split feed reflux arrangement has been added to the system <NUM> of <FIG>. More specifically, the system <NUM> includes a branch off of the hydrocarbon feed gas stream <NUM> before the feed gas expander <NUM>. A small portion of the feed gas stream splits off at the branch and flows through line <NUM> as a split feed reflux gas stream that is cooled in the heavies removal exchanger <NUM> and at least partially condensed to form mixed phase stream <NUM>. This stream is then expanded via an expansion device <NUM>, such as a JT valve, with the resulting cooled stream <NUM> directed to the scrubbing section <NUM> of the heavies removal column as reflux to aid in the removal of heavy hydrocarbons from the column main feed. In an alternative embodiment, expansion device <NUM> may be omitted. In a further embodiment, a branch <NUM> may be added to the line <NUM> leading from the heavies removal heat exchanger <NUM> so that a portion of the mixed phase stream in line <NUM> may be transferred to line <NUM>, which also enters the stripping section <NUM> of the heavies removal column.

In a tenth embodiment of the system of the disclosure, indicated in general at <NUM> in <FIG>, a cold reflux stream is provided to the stripping section <NUM> of the heavies removal column. More specifically, as described previously for the systems of <FIG> and <FIG>, split reflux line <NUM> may be provided (either with or without control valve <NUM>) after reflux pump <NUM> to provide injection of side draw reflux to the stripping section <NUM>. Such a split of the side draw reflux provides additional efficiency in the removal of heavy hydrocarbons in some applications. The split reflux also lowers BTEX and enhances control of reflux BTEX concentration in the reflux stream and thus lowers BTEX in the clean gas exiting the top of the heavies removal column in some applications. As a result, the system <NUM> is suitable for applications having high BTEX levels in the feed gas stream.

In addition, as illustrated in <FIG>, the system <NUM> may include an optional branch <NUM> to the stripping section <NUM> from the reboiler line <NUM> that leads from the heavies removal heat exchanger <NUM>. Such an arrangement may be desirable when additional flow is required at the top of the stripping section to meet wetting criteria. In such an embodiment, the stripping section <NUM> has two layers of internal trays or the like to allow for the additional injection location higher in the stripping section.

As illustrated by system <NUM> of <FIG> at <NUM>, the feed separation device of <FIG> (<NUM> in <FIG>) may be added to the system of <FIG>. The system of <FIG> also illustrates that the system of <NUM> of <FIG> may be modified to omit the expansion device <NUM> present in the liquid line <NUM> leading from the scrubbing section <NUM> of the heavies removal column to the heavies removal heat exchanger <NUM>. In the system <NUM> of <FIG>, expansion devices, such as JT valves <NUM>, <NUM>, <NUM> and <NUM>, have been added to the lines <NUM>, <NUM>, <NUM> and <NUM>. respectively, leading to the scrubbing section <NUM> of the heavies removal column, with the scrubbing section including multiple layers of internal trays of the like to accommodate the multiple injection locations.

As illustrated by system <NUM> of <FIG>, the system of <FIG> may be modified to add a side draw expansion device, such as JT valve <NUM>, to the side draw vapor line <NUM> exiting stripping section <NUM>. Furthermore, as described previously with respect to <FIG>, a branch <NUM> may direct a portion of the scrubbed return vapor stream <NUM> from the heavies removal column <NUM> to the separation device (reflux drum) <NUM> prior to expansion device <NUM>. In an alternative embodiment, the expansion device <NUM> and corresponding line portion <NUM> may be omitted so that all of the scrubbed return vapor stream <NUM> is directed to reflux drum <NUM>. The vapor stream <NUM> from the reflux drum is then directed to through, and warmed within, the heavies removal heat exchanger <NUM> after passing through and being cooled in an expansion device, such as JT valve <NUM>.

In the embodiments of <FIG>, optimization of the stripping gas temperature is obtained in some applications to provide improved control for tighter natural gas liquids (NGL) specifications.

In the system indicated in general at <NUM> in <FIG>, a feed gas heat exchanger <NUM> receives the feed gas stream <NUM>. A cooled feed gas stream <NUM> exits the feed gas heat exchanger and is expanded and cooled within feed gas expander turbine <NUM>. The stream exiting the turbine is split to form main stream <NUM>, which contains the majority of the feed gas stream, and stripping gas stream <NUM>. Stripping gas stream <NUM> travels through the feed gas heat exchanger <NUM> and is warmed so that refrigeration is provided to cool feed gas stream <NUM>. The warmed stripping gas stream <NUM> exits the feed gas heat exchanger <NUM> and is expanded in an optional expansion device, such as JT valve <NUM>, and directed to the stripping section <NUM>. Such an arrangement optimizes the temperature of the stripping gas in some applications to meet some specifications for NGL condensate stream <NUM>. For example, the warmer stripping gas lowers the levels of methane present in the NGL condensate stream <NUM>. Alternative options for warming the stripping gas stream include using heating mediums other than fluids and different types of heat exchangers, including braised aluminum heat exchangers, plate-frame heat exchangers and shell & tube heat exchangers.

As illustrated by system <NUM> in <FIG>. the split feed reflux arrangement of <FIG> may added to the system <NUM> of <FIG>. More specifically, the system <NUM> includes a branch off of the cooled hydrocarbon feed gas stream <NUM> downstream of the feed gas heat exchanger <NUM> before the feed gas expander <NUM>. As in the embodiment of <FIG>, a small portion of the feed gas stream splits off at the branch and flows through line <NUM> as a split feed reflux gas stream that is cooled in the heavies removal exchanger <NUM> and at least partially condensed to form mixed phase stream <NUM>. This stream is then expanded via optional expansion device <NUM>, such as a JT valve, with the resulting cooled stream directed to the scrubbing section <NUM> of the heavies removal column as reflux.

In addition, the cold reflux stream <NUM> of the systems of <FIG>, <FIG> and <FIG> may optionally be added to the system <NUM> of <FIG>.

As illustrated by the system <NUM> of <FIG>, the split feed reflux and side draw reflux heat exchange arrangement of <FIG>, including reflux heat exchanger <NUM>, may be combined with the feed gas heat exchanger <NUM>. which is also employed in the systems of <FIG> and <FIG>.

An embodiment of the system of the disclosure including a heat pump is indicated in general at <NUM> is illustrated in <FIG>. In the system <NUM>, a hydrocarbon feed gas stream <NUM> (such as a natural gas stream) enters a feed gas expander turbine <NUM> and the resulting expanded gas stream is split into a main feed stream <NUM> and a stripping gas feed stream <NUM>.

The main feed stream <NUM>, which contains the bulk of the feed gas stream <NUM>, passes through a heavies removal heat exchanger <NUM> and is cooled and partially condensed. The resulting mixed phase stream <NUM> is then routed to a scrubbing section <NUM> of a heavies removal column, indicated in general at <NUM>, where liquids are separated from the main feed vapor. An NGL condensate stream <NUM> containing heavy hydrocarbons exits the bottom of the stripping section <NUM>. The resulting liquid stream <NUM>, which contains a large portion of the feed gas heavy hydrocarbon/freezing components is directed to an optional expansion device <NUM> (such as a Joule-Thomson or JT valve) with the resulting mixed phase stream <NUM> being warmed in the heavies removal heat exchanger <NUM> and then to a stripping section heat exchanger <NUM> where it is further warmed and directed to stripping section <NUM> of the column <NUM>. The stripping section heat exchanger <NUM> also receives a stream <NUM> after it has passed through a stripping gas feed expansion device <NUM> so that at least a portion of the stripping gas <NUM> is warmed prior to introduction into the stripping section <NUM> of column <NUM>. The remaining portion of the stripping gas <NUM> is expanded via a scrub expansion device, such as JT valve <NUM>. and joined with the mixed phase stream <NUM> that is routed to the scrubbing section <NUM>.

A side draw vapor stream <NUM> exits the stripping section <NUM> of the column <NUM> and is cooled via a side draw expansion device, such as JT valve <NUM>, with the resulting stream traveling to heat pump compressor <NUM>. The compressed gas leaving the compressor <NUM> is cooled in reflux compressor aftercooler <NUM> and then cooled in stripping section heat exchanger <NUM> so that a mixed phase stream <NUM> is formed. Mixed phase stream <NUM> travels to a first reflux separation device, such as a warm reflux drum <NUM>, and is separated into vapor and liquid portions. The liquid stream <NUM> from the warm reflux drum <NUM> is routed to the top portion of the stripping section <NUM> of the heavies removal column as reflux stream <NUM> after passing through an optional expansion device, such as JT valve <NUM>.

With continued reference to <FIG>. the vapor stream <NUM> from the warm reflux drum <NUM> travels to heavies removal exchanger <NUM> and is cooled and at least partially condensed. A resulting stream <NUM> travels through an optional expansion device, such as JT valve <NUM>, to a second reflux separation device, such as cold reflux drum <NUM>, and is separated into vapor and liquid portions. A portion of vapor stream <NUM> from the warm reflux drum <NUM> is split off and travels through an expansion device, such as JT valve <NUM>, with the resulting mixed phase stream joining the mixed phase stream from JT valve <NUM> in traveling to cold reflux drum <NUM>. The liquid stream <NUM> from the cold reflux drum <NUM> is routed to the top portion of the heavies removal column scrubbing section <NUM> as reflux stream <NUM> after passing through an optional control valve <NUM>. Vapor stream <NUM> exits the top of cold reflux drum <NUM> and joins the scrubbed return vapor stream to form stream <NUM> after passing through an optional expansion device, such as JT valve <NUM>.

The scrubbed return vapor stream exits the top of the column <NUM> and is then routed across an expansion device, such as JT valve <NUM>, to produce cooling. The cooled return vapor stream is then combined with the stream from JT valve <NUM> (as noted previously) with the resulting stream <NUM> being routed to the heavies removal exchanger <NUM> where it is warmed and thereby provides cooling to other streams in the heat exchanger. After warming, the return vapor stream <NUM> is compressed by feed gas compressor <NUM> and sent as stream <NUM> to liquefaction so that a liquefied stream (such a liquid natural gas or LNG) is produced.

The feed gas compressor <NUM> is preferably powered by the feed gas expander turbine <NUM>. The reflux compressor <NUM> may also be powered by the feed gas expander turbine <NUM> or alternatively with a dedicated motor <NUM>.

With reference to <FIG>, a seventeenth embodiment of the system of the disclosure is indicated in general at <NUM>. A hydrocarbon feed gas stream <NUM> (such as a natural gas stream) is split to form a stripping gas feed stream <NUM> and a main feed stream <NUM>. As in previous embodiments, stripping gas feed stream <NUM> is expanded in expansion device <NUM> and directed as mixed phase stream <NUM> to a stripping section <NUM>. The stripping section <NUM> may include an upper packing section <NUM>, an added middle packing section <NUM> and lower packing section <NUM>, with the stream <NUM> entering the stripping section below the lower packing section <NUM>. As an example only, the packing sections may include beds of random packing with a distribution tray between each packing bed to red-distribute the liquid evenly over the beds. The beds could also be trays or even structured packing.

Main feed stream <NUM> is expanded in expansion device <NUM> with the resulting stream directed to heavies removal heat exchanger <NUM>. The resulting mixed phase stream <NUM> is directed to a feed separation device <NUM> where it is separated into a vapor portion and a liquid portion. The liquid portion exits the feed separation device <NUM> as liquid stream <NUM> and, after expansion via separated feed liquid expansion device <NUM> is directed to the stripping section <NUM> of the heavies removal column. as mixed phase stream <NUM>. Mixed phased stream <NUM> may enter the stripping section below the added middle packing section <NUM>. With the additional mid-weight hydrocarbons from the reflux drum (via a reflux recycle stream described below), the additional middle packing section provides for improved separation of the freezing components. The additional middle packing section <NUM> is not required.

The vapor stream <NUM> exiting the top of the feed separation device <NUM>, after expansion via expansion device <NUM>, is cooled in the heavies removal heat exchanger <NUM>. The resulting mixed phase stream <NUM> is directed to the scrubbing section <NUM> of the heavies removal column. By decreasing the pressure of the vapor stream <NUM> before the stream enters the heat exchanger <NUM>, the temperature profiles of passages B and A2 of the heat exchanger <NUM> better match, providing better efficiency. This also allows the feed heat exchanger and reflux heat exchanger to be combined into a single unit. It also helps to reduce probability of formation of solids in the A2 heat exchanger passage.

As in the embodiment of <FIG>, the system <NUM> of <FIG> uses a return vapor expander turbine <NUM> that receives the return vapor stream <NUM> from the heavies removal column <NUM>. This return vapor expander turbine <NUM> preferably powers the feed gas compressor <NUM>. In addition, as in the system of <FIG>, the system <NUM> may include an optional branch <NUM> to the stripping section from the reboiler line <NUM> that leads from the heavies removal heat exchanger <NUM>. Such an arrangement may be desirable when additional flow is required at the top of the stripping section to meet wetting criteria.

A reflux recycle line <NUM> includes a control valve <NUM> and receives a portion of the liquid reflux stream exiting the reflux pump <NUM>. The reflux recycle stream in line <NUM> travels to a reflux recycle warming passage E in the heavies removal heat exchanger <NUM>, where it is warmed and vaporized. The resulting stream <NUM> joins the main feed stream <NUM>. In addition, an optional second reflux recycle line <NUM> may direct a portion of the liquid reflux stream exiting reflux pump <NUM> to the top of the stripping section. The remaining aspects of the reflux handling system of <FIG> are the same as <FIG> and <FIG>.

The streams <NUM> and <NUM> provide mid-weight hydrocarbon components, such as propane, butane, etc. to the front of the process. These mid-weight hydrocarbons need to be provided in sufficient quantities so they will form a liquid phase at a temperature wanner than the de-sublimation temperature of the heavier weight freezing components, such as benzene and other similar components that enter the process. Returning the stream <NUM> through the heavies removal heat exchanger helps to balmot the heat exchanger heating and cooling curves which improves the efficiency of the process. By vaporizing the stream <NUM> before mixing with the feed gas stream <NUM>, the mixing process is improved and there is no concern of maldistribution into the feed stream.

In the system of <FIG>, the inlet feed gas <NUM> is cooled to a temperature where a two phase flow <NUM> exiting expansion device <NUM> will exist at the process conditions of the feed separation vessel <NUM>. The food separation vessel <NUM> separates out the liquid phase <NUM>, which contains much of the recycled mid-weight hydrocarbons from the reflux drum as well as most of the heavier freezing componenets. As noted previously, the liquid stream <NUM> is sent to the stripping section <NUM> of the column to separate out the high molecular weight hydrocarbons and freezing components.

In an alternative embodiment, the stream in reflux recycle line <NUM> may be mixed into the feed gas stream <NUM> before the heat exchanger <NUM> without warming the stream, but it may not be optimum. In an alternative embodiment, the recycle stream in line <NUM> can also be mixed at the exit of the passage A1 of the heavies removal heat exchanger <NUM> without warming the recycle stream through the heavies heat exchanger. This may also not be optimal since it risks poor mixing and could create poor separation in the food separation vessel <NUM> due to poor distribution of the liquid/vapor flow regimes.

An additional section of packing is added to the stripping section of the column.

A reboiler <NUM> can be added as an optional item depending on the amount of mid-weight hydrocarbons that need to be recycled along with the amount of heavier freezing components and desire to produce NGL liquids in liquid stream <NUM> exiting the stripping section <NUM>.

The system of <FIG> is best designed for a lean natural gas stream (low quantities of propanes, butanes, pentanes and heavier components) but with freezing contaminants in the incoming stream, such as benzenes or others. When a stream has very low concentrations of mid-weight hydrocarbons, it can be difficult to remove to an acceptable level the freezing components. The freezing components stay in the vapor phase and will tend to desublimate (freeze) directly from the vapor phase to solid before they can be drawn into a liquid phase. This takes place since there are limited amounts of mid-weight hydrocarbons which will only form a liquid phase at temperatures lower than the desublimation temperature of the freezing components.

In an alternative embodiment of the system of the disclosure, indicated in general at <NUM> in <FIG>, an expansion device <NUM> has been added to the line <NUM> leading from the heavies removal heat exchanger <NUM> to the scrubbing section <NUM> of a heavies removal column. As an example only, the expansion device <NUM> may be a valve (such as a JT valve) or a turbine. If the expansion device <NUM> is a turbine, it may be used to power a compressor. In some applications, expansion device <NUM> allows for the heavies removal column to operate at optimal pressure for improved separation. In addition, a stream of a refrigerant <NUM>, such as a mixed refrigerant from a liquefier, travels to passage <NUM> of the heavies removal heat exchanger <NUM> where it is cooled. The cooled stream is expanded via an expansion device <NUM> which may be, as an example only, a JT valve. The resulting stream flows through a supplemental refrigeration passage <NUM> to provide additional cooling in the heavies removal heat exchanger <NUM>. The remaining components of the system of <FIG> may generally be the same and provide the same functionality as those illustrated in <FIG>.

In the system of <FIG>. indicated in general at <NUM>. a separation device <NUM> has been added to the system of <FIG> to receive a stream <NUM> from the heavies removal heat exchanger <NUM>. Stream <NUM> is produced after feed stream <NUM> passes partially through a passage of the heavies removal heat exchanger <NUM>. The vapor stream <NUM> from the separation device <NUM> travels back to another passage of the heat exchanger <NUM> for further cooling before traveling to expansion device <NUM> and then to the scrubbing section <NUM> of the heavies removal column. The liquid stream <NUM> from the separation device <NUM> is directed through expansion device <NUM> and then to the scrubbing section <NUM> of the heavies removal column. Expansion device <NUM> may be, as an example only, a JT valve.

Claim 1:
A system for removing heavy hydrocarbon components from a feed gas stream comprising:
a. a heavies removal heat exchanger (<NUM>) having a main feed stream cooling
passage, a reflux stream cooling passage and a return vapor stream warming passage;
b. said main feed stream cooling passage of the heavies removal heat exchanger configured to receive and cool at least a portion of the feed gas stream (<NUM>) so as to produce a cooled main feed stream;
c. a scrubbing section (<NUM>) including a main feed inlet, a liquid outlet, a return
vapor outlet and a reflux inlet, wherein said main feed inlet is configured to receive the cooled main feed stream;
d. a stripping section (<NUM>) having a first fluid inlet, a second fluid inlet, a liquid
outlet and a vapor outlet, said first fluid inlet configured to receive a fluid stream from the liquid outlet of the scrubbing section;
e. a stripping gas feed expansion device (<NUM>) having an inlet configured to
receive a portion of the feed gas stream, said stripping gas feed expansion device having an outlet in fluid communication with the second fluid inlet of the stripping section;
f. a side draw vapor line (<NUM>) configured to receive a vapor stream from the
vapor outlet of the stripping section, said side draw vapor line in fluid communication with the reflux stream cooling passage of the heavies removal heat exchanger;
g. a reflux separation device (<NUM>) configured to receive fluid from the reflux
cooling stream passage of the heavies removal heat exchanger, said reflux separation device including a liquid outlet and a vapor outlet, wherein the liquid outlet of the reflux separation device is in fluid communication with the reflux inlet of the scrubbing section;
h. a return vapor expansion device (<NUM>) having an inlet configured to receive a
vapor stream from the return vapor outlet of the scrubbing section and an outlet configured to direct a cooled vapor stream to the return vapor stream warming passage of the heavies removal heat exchanger;
i. said reflux separation device vapor outlet configured so that fluid passing therethrough (<NUM>) joins with fluid that has exited the return vapor
expansion device either before or after the fluid that has exited the return vapor expansion device (<NUM>) and flows through the return vapor stream warming passage of the heavies removal heat exchanger.