Patent ID: 12247007

DETAILED DESCRIPTION

Embodiments of the present disclosure will now be described in detail with reference to the accompanying Figures. Like elements in the various figures may be denoted by like reference numerals for consistency. Further, in the following detailed description of embodiments of the present disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the claimed subject matter. However, it will be apparent to one of ordinary skill in the art that the embodiments disclosed herein may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description. Additionally, it will be apparent to one of ordinary skill in the art that the scale of the elements presented in the accompanying Figures may vary without departing from the scope of the present disclosure.

As used herein, the term “coupled” or “coupled to” or “connected” or “connected to” or “attached” or “attached to” may indicate establishing either a direct or indirect connection, and is not limited to either unless expressly referenced as such. Wherever possible, like or identical reference numerals are used in the figures to identify common or the same elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale for purposes of clarification.

Typically, NGL processing systems comprise multiple cooling stages. For example, the NGL feed stream is processed by a first chilling system to condense the feed stream prior to introduction into the distillation column. The captured overhead vapor from the distillation column is then processed by a second chilling system to condense the overhead vapor into a reflux stream that can be re-introduced to the distillation column as another stream, distinct from the feed stream. As a result of the multiple cooling stages, typical NGL processing systems have respective equipment necessities for each of the feed stream and the reflux stream. Further, each cooling stage of the conventional systems require a respective condenser, reservoir drum, pump, and/or piping circuits. As the equipment requirements of a NGL processing system increase; so too does the cost of the system, the maintenance requirements of the system, and/or the system's likelihood of failure.

Embodiments in accordance with the present disclosure generally relate to reflux arrangements for distillation columns that minimize the equipment count of a NGL processing system by utilizing a cooling stage that incorporates captured overhead vapor directly into the feed stream prior to introduction into the distillation column, rendering a pseudo reflux stream. One or more embodiments described herein include a piping circuit that routes overhead vapor from a distillation column back to a cooling stage that directly chills the NGL feed stream. Thereby, the captured overhead vapor is comingled with the NGL feed stream. In various embodiments, the feed stream is directed to the top of the distillation column, such that the captured overhead vapor component in the feed stream can provide internal reflux process for top trays positioned in the distillation column.

FIG.1illustrates a diagram of a non-limiting example NGL processing system100that can employ a pseudo reflux feed stream in accordance with one or more embodiments described herein. As shown inFIG.1, the NGL processing system100can include one or more piping circuits101to carry and/or route fluids between various features of the system100. For example,FIG.1depicts the one or more piping circuits101via solid arrows, where the direction of the arrows can indicated the direction of flow within the piping circuit101. In various embodiments, the one or more fluid streams (e.g., gas streams and/or liquid streams) can be housed, carried, and/or routed within the piping circuit101. For instance, respective sections of the piping circuit101can route respective fluid streams between components of the system100in accordance with various embodiments described herein.

In various embodiments, the NGL processing system100can separate one or more desired NGL products from an NGL offgas stream102. In one or more embodiments, the NGL offgas stream102can be the product from one or more separators at an oil terminal and/or the overhead fraction from a crude distillation column in a refinery. For example, raw natural gas can be treated to remove acid gasses (e.g., hydrogen sulfide and/or carbon dioxide), mercury, nitrogen, and/or methane to achieve the NGL offgas stream102. For each respective NGL product, the NGL processing system100can include a processing module103. WhileFIG.1depicts an example embodiment of the NGL processing system100comprising a single processing module103, the architecture of the NGL processing system100is not so limited. For example, embodiments in which the NGL processing system100includes multiple processing modules103are also envisaged. For instance, the NGL processing system100can include, but is not limited to: an ethane separation processing module103, a propane separation processing module, and/or a butane separation processing module103. In one or more embodiments, the equipment features of the one or more processing modules103can be the same, or nearly the same, but configured to operate at different temperatures and/or pressures per processing module103to facilitate separation of the respective NGL product. Further, in some embodiments multiple processing modules103can be connected in series such that the residual NGL stream104of one processing module103can be fed to another processing module103to facilitate the extraction of another desired NGL product.

In various embodiments, the NGL offgas stream102can be a product of one or more stages of natural gas processing, including, but not limited to: gas-oil separation, condensate separation, contaminant removal, and/or methane separation. For example, the NGL offgas stream102can comprise various NGL components, such as: ethane, propane, i-butane, b-butane, i-pentane, n-pentane, n-hexane, and/or C7+ hydrocarbons. The NGL processing system100can control the supply of the NGL offgas stream102to a dehydration system105via a control valve106. Example types of valves that can be employed herein include, but are not limited to: globe valves, butterfly valves, needle valves, a combination thereof, and/or the like. In various embodiments, the control valve106can regulate the pressure of the NGL offgas stream102such that the pressure of the NGL offgas stream102ranges from, for example, less than or equal to 31 barg.

In one or more embodiments, the water content of the NGL offgas stream102can be reduced in dehydration system105to mitigate the formation of hydrates (e.g., decrease the amount and/or size of hydrate particles) that may otherwise accumulate and/or plug the equipment of the NGL processing system100. The dehydration system105can employ a variety of suitable methods to perform the water removal, such as using an ethylene glycol (glycol injection) system as an absorption mechanism to remove water and/or other solids from the NGL offgas stream102. Alternatively, the dehydration system105can utilize a dry-bed dehydration tower (e.g., containing desiccants, such as silica gel and/or activated alumina) to perform the water extraction.

For example, the dehydration system105can be a triethylene glycol (“TEG”) dehydration system, where the NGL offgas stream102can contact lean TEG in one or more columns using structured packing. For instance, the dehydration system105can be a TEG dehydration system configured based on: the lean TEG water content; the temperature of the NGL offgas stream102at the inlet of the TEG absorber (not shown) of the TEG dehydration system; the number of stages of the TEG absorber; and/or the packing efficiency of the TEG absorber (e.g., a function of packing type, bed height, and/or the quality of liquid and gas distributors). In one or more embodiments: the TEG water content can range from, for example, greater than or equal to 0.1 weight percent (wt. %) and less than or equal to 0.2 wt. %; the temperature of the NGL offgas stream102can range from, for example, greater than or equal to 24° C. and less than or equal to 34° C.; and/or the number of stages of the TEG absorber can range from, for example, greater than or equal to 3 stages and less than or equal to 4 stages. Thereby, the one or more dehydration systems105can dehydrate the NGL offgas stream102into a dry feed stream108. For instance, the dry feed stream108can have a water content that is less than 0.02 wt. %.

In various embodiments, the dry feed stream108can be a non-cooled stream. For instance, a temperature of the dry feed stream108can range from, for example, greater than or equal to 50° C. The NGL processing system100can further route the dry feed stream108to a cooling unit110, which can cool the dry feed stream108. For example, one or more piping circuits101can be coupled to the dehydration system100and one or more chillers112and/or condensers of the cooling unit110. In one or more embodiments, the cooling unit110can utilize one or more chillers/condensers112coupled to one or more refrigerant systems114to cool the dry feed stream108. For example, the cooling unit110can utilize one or more refrigerant loops, where a cool refrigerant stream116can be supplied to the one or more chillers112from the refrigerant system114. The cool refrigerant stream116can cycle through the one or more chillers112adjacent to the dry feed stream108to facilitate a heat exchange. Thereby, the cool refrigerant stream116can be heated to form a warm refrigerant stream118, which can be returned to the refrigerant system114to be re-cooled. In some embodiments, the gas used as the refrigerant can be a propane refrigerant. As a result of the cooling, a cold feed stream120can be supplied from the one or more chillers112and routed to one or more feed drums122. For example, one or more piping circuits101can be coupled between the one or more chillers112and the one or more feed drums122. In some embodiments, the cold stream120can be partially condensed by the cooling unit110.

In one or more embodiments, the cooling unit110can cool the dry feed stream108below the hydrocarbon dew point such that the cold feed stream120is a mixture of gas and liquid components. In various embodiments, the cooling unit110can cool the cold feed stream120to an operating temperature depending on, for example, the operating pressure of one or more distillation columns described herein (e.g., deethanizers, depropanizers, and/or debutanizers). For instance, where the processing module103is configured to extract ethane from the NGL offgas stream102, the cooling unit110can reduce the temperature of the dry feed stream108such that the temperature of the cold feed stream120is, for example, less than or equal to 35° C. In another instance, where the processing module103is configured to extract propane from the NGL offgas stream102, the cooling unit110can reduce the temperature of the dry feed stream108such that the temperature of the cold feed stream120is, for example, less than or equal to 57° C. In a further instance, where the processing module103is configured to separate butane from the NGL offgas stream102, the cooling unit110can reduce the temperature of the dry feed stream108such that the temperature of the cold feed stream120is, for example, less than or equal to 57° C. (e.g., at a low operating pressure).

The non-condensed vapor component of the cold feed stream120can be exported from the feed drum122as a product stream124to one or more downstream gas plants by ether gravity or using an offgas compressor126. For instance, where the processing module103is configured to perform an ethane separation process, the product stream124can be ethane vapor. As shown inFIG.1, the product stream124can be regulated via a second control valve128. The condensed liquid component of the cold feed stream120can be exported from the feed drum122as a liquid hydrocarbon feed stream130to a distillation column132via one or more feed pumps134. For example, one or more piping circuits101can be coupled between the one or more feed drums122and the one or more feed pumps134. Additionally, the one or more piping circuits101can be further coupled between the one or more feed pumps134and the distillation column132. In various embodiments, the liquid hydrocarbon feed stream130can be supplied to a top of the distillation column132, in some cases at the top third of the column132, in other cases the top forth of the column132, and in still other cases above the first tray of the column132.

In various embodiments, the distillation column132can be utilized to separate an additional portion of the desired NGL product from the liquid hydrocarbon feed stream130. For example, the distillation column132can be configured to perform a separation process that is based on the relative volatility of the components of the liquid hydrocarbon feed stream130. In some embodiments, the distillation column132can be configured to perform one or more separation operations, including, but not limited to: absorption, rectification, striping, re-boiled stripping, re-boiled absorption, extractive distillation, and/or zeotropic distillation. For instance, the distillation column132can comprise a plurality of stages that facilitate one or more equilibrium or non-equilibrium separation processes. Additionally, the plurality of stages can be defined by one or more trays133(e.g., represented by dotted lines inFIG.1) comprised within the distillation column132. In one or more embodiments, the distillation column132can comprise N number of trays133, where N is an integer less than or equal to 60.

In one or more embodiments, the distillation column132can be a deethanizer, configured to have: a top temperature that is, for example, less than or equal to 35° C.; a top pressure being, for example, greater less than or equal to 31 barg; a bottom temperature that is, for example, greater than or equal to 115° C.; and/or a bottom pressure that is, for example, less than or equal to 32 barg. In one or more embodiments, the distillation column132can be a depropanizer, configured to have: a top temperature that is, for example, less than or equal to 57° C.; a top pressure that is, for example, less than or equal to 22 barg; a bottom temperature that is, for example, greater than or equal to 138° C.; and/or a bottom pressure that is, for example, less than or equal to 23 barg. In one or more embodiments, the distillation column132can be a debutanizer, configured to have: a top temperature that is, for example, less than or equal to 57° C.; a top pressure that is, for example, less than or equal to 7 barg; a bottom temperature that is, for example, greater than or equal to 121° C.; and/or a bottom pressure that is, for example, less than or equal to 8 barg.

In one or more embodiments, heat can be supplied to the distillation column132via a re-boiler136. For example, the liquid hydrocarbon feed stream130can travel down the distillation column132and exit as an export stream135that is supplied to the re-boiler136, where the fluid is partially vaporized. For instance, the re-boiler136can heat the export stream135, thereby creating a boil-up vapor stream138that is returned to the distillation column132(e.g., via the one or more piping circuits101) and a residual liquid that is drawn from the re-boiler136as a bottom product stream140(e.g., via the one or more piping circuits101). As the liquid hydrocarbon feed stream130travels down the distillation column132, it can contact the vapor of the boil-up vapor138at various stages. Further, the re-boiler136can be a heat exchanger that utilizes a steam loop to heat the export stream135in which a hot steam stream142is supplied to the re-boiler136from a steam system146and a condensate stream144is returned to the steam system146for re-heating. In some embodiments, the given processing module103can utilize a direct-fire heater to perform the re-boiling. Additionally, one or more re-boiler circulation pumps (not shown) can be utilized to feed the re-boiler136and/or the direct-fire heater. In one or more embodiments, the bottom product stream140can be further supplied to one or more coolers148to render the residual NGL stream104.

In various embodiments, the overhead vapor from the distillation column132can be captured as a vapor stream152that is controlled by a third control valve154and routed back to the dry feed stream108. For example, the one or more piping circuits101can be coupled to a top section of the distillation column132and/or can introduce the vapor stream152back into the dry feed stream108. In various embodiments, the vapor stream152can be supplied to the dry feed stream108at a pressure that is, for example, less than or equal to 31 barg. For example, the vapor stream152can be comingled with the dry feed stream108prior to the cooling unit110. Thereby, reflux functionality stemming from the vapor stream152can be combined with the distillation column132feed network. As such, the cold feed stream120, and thereby the liquid hydrocarbon feed stream130can serve as pseudo reflux streams. For example, re-introduction of the vapor stream152into the dry feed stream108can result in the liquid hydrocarbon feed stream130providing an internal reflux process for the top trays133of the distillation column132. For instance, by comingling the vapor stream152with the dry feed stream108, the cooling unit110will also partially condense the captured overhead vapor from the distillation column132; which in turn can enable a reflux process incorporated into the cold feed stream120and the liquid hydrocarbon feed stream130. The incorporation of the reflux process into the liquid hydrocarbon feed stream130can provide a down-flowing liquid throughout a rectification stage at the top section of the distillation column132to make contact with upward flowing vapor (e.g., supplied from boil-up vapor stream138) in the distillation column132; thereby achieving a stage-by-stage equilibrium heat and mass transfer, and a purification of the top product.

Advantageously, the processing module103eliminates the need for a separate cooling stage to condense just the captured overhead vapor and render the reflux process; rather cooling unit110can simultaneously cool the dry feed stream108and the overhead vapor (e.g., supplied by the vapor stream152) to separate out the desired NGL product and render a reflux process that is incorporated into the liquid hydrocarbon feed stream130. Further, the processing module103can minimize capital expenditures and/or operational expenditures by reducing the equipment requirements to implement the given NGL product separation.

FIG.2illustrates a non-limiting example method200that can be implemented by one or more NGL processing systems100(e.g., via one or more processing modules103) in accordance with one or more embodiments described herein. In accordance with one or more embodiments described herein, the method200can facilitate separation of one or more desired NGL products from a NGL offgas stream102.

At202, the method200can comprise suppling a dry feed stream108to a cooling unit110. In accordance with one or more embodiments described herein, the dry feed stream108can be a pre-processed stream of NGLs. For example, the dry feed stream108can comprise a gaseous dehydrated stream of NGL components such as, but not limited to: ethane, propane, butane, pentane and/or C5+ hydrocarbons. As exemplified inFIG.1, the dry feed stream108can be supplied to the cooling stage110via one or more pipe circuits.

At204, the method200can comprise cooling the dry feed stream108into a partially condensed cold feed stream120. In accordance with one or more embodiments described herein, the cooling unit110can comprise one or more chillers112and/or condensers that can reduce the temperature of the dry feed stream108below a hydrocarbon dew point. For example, the cooling unit110can utilizing one or more propane refrigeration loops (e.g., comprising a cool refrigerant stream116cycled to the one or more chillers112and/or a warm refrigerant stream118cycled to a refrigeration system114). For instance, the method200can be employed to separate ethane from the dry feed stream108, where the cooling at204can cool the temperature of the dry feed stream108to a temperature that is, for example, less than or equal to 35° C.

In one or more embodiments, the partially condensed cold feed stream204can be stored in a feed drum122and the method can progress to206and208. At206, the method200can comprise exporting a non-condensed portion of the cold feed stream120as a product stream124. In accordance with one or more embodiments described herein, the non-condensed portion can comprise vapor of the desired NGL product. At208, the method200can comprise supplying the condensed portion of the cold feed stream120to a distillation column132as a liquid hydrocarbon feed stream130. In accordance with one or more embodiments described herein, a residual portion of the desired NGL product can remain trapped within the liquid hydrocarbon stream130. Thus, the method200can further process the liquid hydrocarbon stream130to separate additional portions of the desired NGL product.

At210, the method200can comprise performing a separation process via the distillation column132. In accordance with one or more embodiments, the distillation column132can be, but is not limited to: a deethanizer, a depropanizer, and/or a debutanizer. Further, the distillation column132can comprise a plurality of trays133to facilitate a stage-wise separation process. For instance, the separation process can be fractional distillation process based on the volatility of the hydrocarbon components comprised within the liquid hydrocarbon stream130. In one or more embodiments, the liquid hydrocarbon stream130can flow down the distillation column132; thereby traversing through multiple zones of contact with one or more heated vapors rising up the distillation column132. As such, the separation process can result in separating the liquid hydrocarbon feed stream130into a gaseous phase and a liquid phase.

Further, the method200can proceed (e.g., simultaneously and/or concurrently) to212and/or214. At212the method200can comprise capturing the overhead vapor from the distillation column as a vapor stream152. For example, the gaseous phase rendered by the separation process can escape from a top of the distillation column132as the overhead vapor. At216, the method200can comprise comingling the vapor stream152with the dry feed stream108. For example,FIG.1exemplifies routing the vapor stream152back to the dry feed stream108to re-introduce the overhead vapor from the distillation column132into the column's feed network. Additionally, as shown inFIG.2, the method200can proceed back to202and supply the dry feed stream108(now comingled with the vapor stream152) to the cooling unit110.

As a result of the comingling at216, the overhead vapor from the distillation column132is cooled again at the cooling unit110, thereby incorporating reflux functionality into the cold feed stream120. For example, following the comingling at216, the liquid hydrocarbon feed stream130supplied in the subsequent iterations of feature208can provide an internal reflux mechanism for the top trays133of the distillation column132, where a rectification process can be performed as part of the distillation.

At214, the method200can comprise exporting a portion of the liquid hydrocarbon feed stream130from a bottom of the distillation column132as an export stream135. For example, hydrocarbon components having a boiling point lower than the desired NGL product can flow down the distillation column132as a liquid and be exported as the export stream135. At218, the method200can comprise partially vaporizing the export stream135. In accordance with one or more embodiments, the export stream135can be supplied to one or more re-boilers136and/or dire-fire heaters to perform the partial vaporization at216. Further, the method200can proceed (e.g., simultaneously and/or concurrently) to220and/or222.

At220, the method200can comprise re-introducing the vaporized portion of the export stream135back into the distillation column132. In accordance with various embodiments described herein, the vaporized portion of the export stream125can be re-introduced into the distillation column132as the boil-up vapor stream138. For example, once re-introduced into the distillation column132, the boil-up vapor stream138can rise through the distillation column132and contact the liquid hydrocarbon feed stream130that is flowing down the distillation column132.

At222, the method200can comprise capturing the non-vaporized portion of the export stream135as a bottom product stream140. In accordance with various embodiments described herein, the bottom product stream140can comprise NGL components that are heavier than the desired NGL product comprised within the product stream124. Further, the bottom product stream140can be subject to further processing (e.g., cooling by one or more coolers148) and supplied to one or more refinery operations. In one or more embodiments, the bottom product stream140can be supplied to one or more other processing modules103and be subject to one or more other implementations of method200to separate another NGL product.

For example, a first processing module103can execute a first implantation of method200using a deethanizer distillation column132and/or cooling unit110configuration to separate ethane as the product stream124. Further, NGL processing system100can supply the bottom product stream140resulting from the first processing module103to a second processing module103. For instance, the bottom product stream140can serve as the dry feed stream108for the second processing module103. Additionally, the second processing module103can execute a second implementation of method200using a depropanizer distillation column132and/or cooling unit110configuration to separate propane as the product stream124.

In another example, the NGL processing system100can supply the bottom product stream140resulting from the second processing module103to a third processing module103. For instance, the bottom product stream140can serve as the dry feed stream108for the third processing module103. Additionally, the third processing module103can execute a third implementation of method200using a debutanizer distillation column132and/or cooling unit110configuration to separate butane as the product stream124.

It is to be further understood that like or similar numerals in the drawings represent like or similar elements through the several figures, and that not all components or steps described and illustrated with reference to the figures are required for all embodiments or arrangements.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “contains”, “containing”, “includes”, “including,” “comprises”, and/or “comprising,” and variations thereof, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Terms of orientation are used herein merely for purposes of convention and referencing and are not to be construed as limiting. However, it is recognized these terms could be used with reference to an operator or user. Accordingly, no limitations are implied or to be inferred. In addition, the use of ordinal numbers (e.g., first, second, third) is for distinction and not counting. For example, the use of “third” does not imply there is a corresponding “first” or “second.” Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

While the disclosure has described several exemplary embodiments, it will be understood by those skilled in the art that various changes can be made, and equivalents can be substituted for elements thereof, without departing from the spirit and scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation, or material to embodiments of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, or to the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.