US20190086147A1

US20190086147A1 - Methods and apparatus for generating a mixed refrigerant for use in natural gas processing and production of high purity liquefied natural gas

Info

Publication number: US20190086147A1
Application number: US15/711,482
Authority: US
Inventors: William George Brown, III; Billy Roger Minton
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-09-21
Filing date: 2017-09-21
Publication date: 2019-03-21

Abstract

A novel method and system for liquefying and distilling raw natural gas into NGL and liquid methane (LNG) product streams, with at least one novel feature including the use of a mixed refrigerant comprising naturally occurring natural gas liquids that were recovered from the inlet gas stream being processed. Heat exchangers and distillation towers are configured to produce high purity liquefied natural gas (LNG) and NGL product streams, utilizing liquid NGL as the process refrigerant for both systems.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates to methods and apparatus for natural gas processing. In another aspect, the present invention relates to a mixed refrigerant for use in natural gas processing, and the generation of such mixed refrigerant, in which the mixed refrigerant comprises natural gas liquids recovered from the inlet gas stream of the processing. In even another aspect, the present invention relates to refrigerants, methods and apparatus for generation and/or recovery of high purity natural gas. In yet another aspect, the present invention relates to the processing of raw natural gas, for the purpose of recovering ethane and heavier hydrocarbons in liquid form, and for the liquefaction of the natural gas residue; more particularly, to a system for providing a pipeline quality Natural Gas Liquid (NGL) product and high purity Liquefied Natural Gas (LNG), utilizing a mixed refrigerant system that is more cost effective, energy efficient, robust, and operationally flexible to changing conditions.

2. Description of the Related Art

Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
The continued desire to switch to cleaner fuels and the coincident relative low cost in natural gas has prompted the power and transportation industries, in particular, to give more emphasis to switching from fuels such as coal, gasoline and diesel to compressed and liquefied natural gas. At the same time, Producers and Processors of raw natural gas streams from oil and gas production facilities, continue striving to process the gas streams in the most economic manner, while looking to expand the markets for their finished products. Thus, with the abundance of natural gas supply and the increasing demand for low-cost, clean energy, there is great incentive to find the most cost and energy efficient way to liquefy and transport the liquid gas to markets worldwide.
The processing of raw natural gas to remove contaminants, recover a NGL Product stream and provide a Liquefied Natural Gas (LNG) product requires a multitude of different systems to treat and process the inlet gas stream. The Inlet Gas may be treated using an amine facility and molecular sieves to remove excess sulfur, CO₂and water. The Treated Gas is then typically processed in a Gas Processing Plant, using any number of gas processing technologies available, to recover whatever heavy-end hydrocarbons (Ethane and heavier components) are desired into a liquid NGL Product and a Residue Gas stream; each meeting specific quality requirements set by the transportation pipelines. Depending on the pressure of the Inlet Gas into the Gas Processing Plant, the hydrocarbon liquid content in the Inlet Gas and the degree of product recovery desired, an external mechanical refrigeration system may be employed to assist in the proper operation and performance of the processing plant. Generally, the mechanical refrigeration used in such instances is Propane which utilizes compression, heat rejection, expansion, vaporization of the refrigerants, etc. in a closed loop design.
Most LNG Facilities utilize a feed gas stream, fed from pipelines, which requires some type of pretreatment, such as CO₂removal, water removal and heavy hydrocarbon removal, in order for the LNG Liquefaction Plant to work properly. If the feed gas is instead taken from the tailgate of a Gas Processing Plant, these pretreatment facilities can be eliminated. Conventional LNG facilities can be constructed using various technologies but generally all utilize a mechanical refrigerant system that requires compression, heat rejection, expansion, vaporization of the refrigerants, etc. Because of the extremely low cryogenic temperatures involved in the liquefaction of the natural gas, Propane refrigeration is inadequate for this process, so a Mixed Refrigerant (MR) or a Nitrogen Cycle (N₂) refrigerant is typically used. Thus, if both a Gas Processing Plant and LNG Liquefaction Plant are to be installed at the same facility, two separate refrigeration systems are typically required. More importantly, if a mixed refrigerant is to be used for LNG liquefaction, it typically must be kept within tight compositional specifications in order for the overall process to work properly. For these reasons, there will generally be significantly more equipment required, along with a significant amount of storage for the various refrigerant components needed to keep the refrigerant composition at specified levels.
There is a need to process raw natural gas, to recover the Natural Gas Liquids (NGL product) and produce high quality Liquefied Natural Gas (LNG) at a single facility, in an environmentally friendly way, to take advantage of common markets and to reduce the capital and operating expenditures associated with having two separate facilities. There is a further need to integrate the two processes together in order to improve overall plant efficiency, allow for changing conditions and minimize equipment and the environmental footprint.
A system and method is needed that provides a single mixed refrigerant system that can be utilized for both gas processing for NGL recovery and for natural gas liquefaction, while improving overall efficiency and cost effectiveness for both processes.
U.S. Pat. No. 6,250,105, issued Jun. 26, 2001 to Kimble, discloses Dual multi-component refrigeration cycles for liquefaction of natural gas. The process for liquefying natural gas produces a pressurized liquid product having a temperature above −112° C. using two mixed refrigerants in two closed cycles, a low-level refrigerant to cool and liquefy the natural gas and a high-level refrigerant to cool the low-level refrigerant. After being used to liquefy the natural gas, the low-level refrigerant is (a) warmed by heat exchange in countercurrent relationship with another stream of the low-level refrigerant and by heat exchange against a first stream of the high-level refrigerant, (b) compressed to an elevated pressure, and (c) aftercooled against an external cooling fluid. The low-level refrigerant is then cooled by heat exchange against a second stream of the high-level mixed refrigerant and by exchange against the low-level refrigerant. The high-level refrigerant is warmed by the heat exchange with the low-level refrigerant, compressed to an elevated pressure, and aftercooled against an external cooling fluid.
U.S. Patent Publication 20060260355, published Nov. 23, 2006 by Mark Roberts et al., discloses an integrated NGL recovery and liquefied natural gas production system, in which the separation of methane from an admixture (110) with ethane and higher hydrocarbons, especially natural gas, using a scrub column (114), in which the admixture is separated into a methane-rich overhead (116) that is partially condensed (122) to provide reflux to the column (114) and liquid methane-depleted bottoms liquid (126), is improved by providing additional reflux (136) derived from an ethane enriched stream (130) from fractionation (128) of the bottoms liquid. Preferably, absorber liquid (140) from the fractionation (128) also is introduced into the scrub column. The vapor fraction (120) remaining after partial condensation can be liquefied (122) to provide LNG product (124).
U.S. Patent Publication No. 20120137726, published Jun. 7, 2012 by Kevin L. Currence et al., discloses NGL Recovery from Natural Gas Using a Mixed Refrigerant, in which an NGL recovery facility utilizes a single, closed-loop mixed refrigerant cycle for recovering a substantial portion of the C2 and heavier or C3 and heavier NGL components from the incoming gas stream. Less severe operating conditions, including a warmer refrigerant temperature and a lower feed gas pressure, contribute to a more economical and efficient NGL recovery system.
U.S. Patent Publication No. 20120304690, published Dec. 6, 2012 by Michael Malsam et al., discloses iso-pressure open refrigeration NGL recovery, an improved process for recovery of natural gas liquids from a natural gas feed stream. The process runs at a constant pressure with no intentional reduction in pressure. An open loop mixed refrigerant is used to provide process cooling and to provide a reflux stream for the distillation column used to recover the natural gas liquids. The processes may be used to recover C3+ hydrocarbons from natural gas, or to recover C2+ hydrocarbons from natural gas.
U.S. Pat. No. 8,505,312, issued Aug. 13, 2013 to Mak et al., discloses a liquid natural gas fractionation and regasification plant, in which LNG vapor from an LNG storage vessel is absorbed using C 3 and heavier components provided by a fractionator that receives a mixture of LNG vapors and the C3 and heavier components as fractionator feed. In such configurations, refrigeration content of the LNG liquid from the LNG storage vessel is advantageously used to condense the LNG vapor after separation. Where desired, a portion of the LNG liquid may also be used as fractionator feed to produce LPG as a bottom product.
Oil & Gas Journal (will get complete citation). IPOR (IsoPressure Open Refrigeration) has been developed by Randall Gas Technologies, a division of Lummus Technology, a CB&I company. The advanced refrigeration process can economically achieve essentially total C3+ recovery from most natural gas streams. Using conventional closed-loop mechanical refrigeration combined with an open-loop mixed refrigeration cycle, the new technology can achieve NGL recovery efficiencies comparable to that of advanced turboexpander cycles but for lower capital and operating expenditures. Using an ethane-rich cycle, the advanced refrigeration NGL extraction process can economically achieve deep NGL extraction from most natural gas streams. Using conventional closed-loop mechanical refrigeration combined with an open-loop mixed refrigeration cycle, this process can provide performance comparable to that of advanced turboexpander technologies but with much lower CAPEX and OPEX. Unique about the IPOR process is its open-loop ethane-rich mixed refrigeration cycle. This refrigerant, extracted from the feed gas itself, is a mixture of predominantly ethane with lower concentrations of methane, propane, and other feed-gas constituents. The cooled and partially condensed gas stream flows to the de-ethanizer overhead separator. The liquid from this separation, a mixture of methane, ethane, and propane, is used as the refrigerant for the open-loop mixed refrigerant cycle. The de-ethanizer overhead separator therefore has a twofold function: It acts as a conventional two-phase gas-liquid separator, and it provides surge capacity for the liquid mixed refrigerant system. From a thermal efficiency perspective, the IPOR process requires about 15-40% less compression power than a comparable turboexpander design. As a result, plants using the IPOR technology will also have lower emissions and a smaller carbon footprint.
Chemical and Engineering Processing (will get complete citation) discloses a novel process configuration for recovery of hydrocarbon liquids from natural gas is proposed. The required refrigeration in this configuration is obtained by a self-refrigeration system (open-closed cycle). High performance of the multi-stream heat exchangers, high recovery levels of the hydrocarbon liquids and low required compression power (in the internal refrigeration section) are three of most important characteristic of the proposed configuration. The effects of the mixed self-refrigerant flow rate and pressure on the performance of the process are discussed. Various values for feed composition are tested and the results show that the process can work efficiently with different feeds. In order to analyze the need of external refrigeration by a close or open cycle that is related to the composition of the inlet gas, a configuration with external refrigeration is designed the manner that it is similar with the purposed configuration in the separation section
U.S. Publication No. 20150260451, published Oct. 15, 2015 by Haberberger et al., discloses a liquefied natural gas facility employing an optimized mixed refrigerant in processes and systems for producing liquefied natural gas (LNG) with a single mixed refrigerant, closed-loop refrigeration cycle are provided. Liquefied natural gas facilities configured according to embodiments of the present invention include refrigeration cycles optimized to provide increased efficiency and enhanced operability, with minimal additional equipment or expense.

SUMMARY OF THE INVENTION

According to one non-limiting embodiment of the present invention, there is provided a method of using a NGL product as a mixed refrigerant for liquefying an inlet hydrocarbon gas and distilling the hydrocarbon liquid into a natural gas liquid (NGL) and for liquefying methane rich natural gas (LNG). The method may include introducing a pretreated hydrocarbon gas to a first heat exchange unit. The method may also include flowing the cooled hydrocarbon gas from the first heat exchange unit to a separator and separating a liquid portion from a vapor portion. The method may also include flowing the liquid and vapor portions from the separator through a process to a first pressurized distillation tower. The method may also include flowing a vapor product of hydrocarbons from the first pressurized distillation tower. The method may also include flowing a liquid NGL product from the first pressurized distillation tower. The method may also include flowing a portion of NGL product that is mixed refrigerant to at least the first heat exchange unit to aid in cooling of the hydrocarbon gas. Other embodiments include any apparatus (i.e. system, equipment, or machine) that performs any part of or all of the methods as described herein.
According to another non-limiting embodiment of the present invention, there is provided a method of using a mixed refrigerant for liquefying methane rich natural gas (LNG). The method may include introducing a mixed refrigerant to a first heat exchange unit and partially condensing the refrigerant. The method may also include flowing the partially condensed mixed refrigerant from the first heat exchange unit to a first separator and separating a liquid portion from a vapor portion. The method may also include flowing the liquid portion from the first separator to the second heat exchange unit at an intermediate pressure to act as a refrigerant stream to cool both the inlet methane rich stream and the vapor portion of the mixed refrigerant from the separator. The method may also include flowing the vapor portion from the first separator through the second heat exchange unit and at least partially condensing the stream. The method may also include reducing the pressure of the at least partially condensed vapor portion and routing back to the second heat exchange unit to act as refrigerant and assist in condensing the inlet methane rich stream into LNG and the vapor portion of the mixed refrigerant. Other embodiments include any apparatus (i.e. system, equipment, or machine) that performs any part of or all of the methods as described herein.
These and other embodiments of the present invention will become apparent to those of skill in the art upon review of this patent specification, including its claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are provided merely to illustrate a few non-limiting embodiments of the present invention, and are not meant to limit the scope of the claims of the invention.

For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and description and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale, some areas or elements may be expanded to help improve understanding of embodiments of the invention.

FIG. 1 (Cryo Plant PFD) is a schematic showing a non-limiting embodiment for the condensation, distilling and fractionation of raw natural gas to produce a pipeline quality Y-Grade NGL product, using the NGL Product as a refrigerant in accordance with the present invention.

FIG. 1A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 1.

FIG. 2 (NGL Prod Condensation PFD) is a schematic showing a non-limiting embodiment for the condensation, of the NGL Product back into liquid form in accordance with the present invention.

FIG. 2A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 2.

FIG. 3 (Cryo Plant PFD) is a schematic showing a non-limiting embodiment for the condensation, distilling and fractionation of raw natural gas to produce a NGL product, having a higher concentration of the Methane component and using the NGL Product as a refrigerant for both the Gas Processing Plant and for the LNG Plant in accordance with the present invention.

FIG. 3A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 3.

FIG. 4 (NGL Prod Condensation PFD) is a schematic showing a non-limiting embodiment for the separating the vapor and liquid phases of the mixed refrigerant, to provide a quality NGL Product back into liquid form and a resulting mixed refrigerant vapor stream that can be used as the LNG Plant mixed refrigerant stream in accordance with the present invention.

FIG. 4A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 4.

FIG. 5 (LNG Liquefaction Plant) is a schematic showing a non-limiting embodiment for a LNG Liquefaction Plant using the mixed refrigerant generated from the NGL Product, as well as a method for improving the efficiency of the refrigerant system operation in accordance with the present invention. It should be noted that a closed loop refrigeration system is shown for the purpose of providing enough refrigeration duty for liquefying the entire residue gas stream; should the amount of LNG to be produced be reduced, it is possible for the refrigeration system to become an open loop.

FIG. 5A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

The innovative teachings of the present invention will be described with particular reference to few non-limiting embodiments (by way of example, and not of limitation). The present invention describes several embodiments, and none of the statements below should be taken as limiting the claims generally.
The present invention discloses new approaches, both methods and apparatus, to take advantage of the produced Natural Gas Liquids (NGL) from gas processing plants and use these liquids as a refrigerant for both the Gas Processing Plant and a natural gas liquefaction plant (LNG Plant). The present invention takes advantage of the naturally occurring elements contained in the raw natural gas stream entering the Gas Processing Plant facility, without need of importing or storing components that are outside of the naturally occurring components, such as ethylene, propylene, nitrogen, butylene, etc. The new invention method also demonstrates ways in which to improve the overall efficiency and performance of the LNG Plant mixed refrigeration system.
The methodology for the non-limiting system described herein is based upon processing of raw natural gas streams and utilizing the recovered hydrocarbon liquids (NGL Product) from the Gas Processing Plant as the refrigerant for both the Gas Processing Plant and, if present, the LNG Plant. This methodology may be utilized with any of the common Gas Processing technologies in use today. Simply stated, rather than operating the Gas Processing Plant in the conventional manner, to deliver a NGL Product from the plant fractionation tower to pipeline for sale, a portion of the NGL Product may be recycled, in an open loop, back through the plant heat exchange loop providing refrigeration duty for the process. A portion of the exiting refrigerant from the heat exchange loop may be vapor; if the refrigerant is comprised of two phases, the vapor and liquid portions are separated, with the liquid being pumped to required sales pressure and the vapor portion being compressed and condensed for comingling with the liquid portion for product sales. The system allows for fully integrated heat exchange using Process Heat Exchangers and a minimal number of other pieces of process equipment, thus maintaining a minimal Plot Area. And since the refrigerant (NGL Product) is already a liquid when it exits the fractionation tower, there is no need for a closed loop Refrigerant Compressor System to be installed in the Gas Processing Plant.
The NGL Product from the Gas Processing Plant may also be utilized to generate the mixed refrigerant to be used in the LNG Plant refrigeration process and is much more robust and flexible than other mixed refrigerant systems which commonly use components that are not naturally occurring in gas feed streams and must be stored on site.
The system does not require use of any turbo expander machinery, though these items may be used to improve overall system efficiency. The Gas Processing Plant and LNG Liquefaction Plants utilize any commonly used technology; however, the refrigeration requirement is provided via the mixed refrigerant which is the NGL Product. As the refrigerant is generated as liquid from the fractionation tower within the Gas Processing Plant, there is no need for a closed loop refrigerant compression within the Gas Processing Plant design. Vaporized refrigerant from the Gas Processing Plant may be captured for further fractionation, used as make-up to the LNG Plant mixed refrigerant, used as fuel gas or condensed and routed to pipeline. The open loop mixed refrigerant system is significantly more efficient than a single component, closed loop refrigerant system, thus minimizing energy input and reducing overall atmospheric emissions by eliminating equipment and storage requirements. This invention may be a standalone system as a mixed refrigerant for natural gas processing and recovery of Natural Gas Liquids (NGL) as well as being used as a mixed refrigerant in the process of recovering methane (LNG) as a liquid.
As will be recognized by those skilled in the art, the innovative concepts described in the present invention may be modified and varied over a tremendous range of applications, and accordingly the scope of patented subject matter is not limited by any of the specific exemplary teachings given. It is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
This method and system will meet all of the necessary refrigeration functions required of a typical Gas Processing Plant and LNG facility, of any size or Inlet Gas composition, but in a much more efficient and cost effective manner. This method and system allows for combining Gas Processing for NGL recovery and LNG liquefaction into one plant location while it eliminates the need for separate refrigeration systems, reduces compression requirements, eliminates use of special refrigerants and the storage required for them, and thereby requires less equipment, thus minimizing the overall plant footprint, reducing emissions and lowering capital and operating costs.
In one embodiment, a system for liquefying and distilling raw natural gas in a NGL processing facility to recover natural gas components as liquid products (NGL) that meets all Y-Grade product specifications and then using the NGL Product as a mixed refrigerant.
In one embodiment, a system for liquefying and distilling high quality methane gas in a LNG Liquefaction Plant using a system generated mixed refrigerant from the NGL Product.
Because the NGL is a finished product coming out of the Gas Processing Plant, the system may operate under an “open loop” design, and the need for a closed loop refrigerant system within the Gas Processing Plant design may therefore be eliminated. Additionally, the Gas Processing Plant may be operated in a slightly different mode to generate a mixed refrigerant that may not only provide the refrigerant service for the Gas Processing Plant, but also be used as the feedstock for the mixed refrigerant system used in a LNG Liquefaction Plant.
The present system may provide the necessary refrigeration duty for essentially any Gas Processing Plant technology currently used within the Oil & Gas Industry, as well as be used to generate and provide the mixed refrigerant necessary for LNG liquefaction, while minimizing capital and operating costs, reducing energy input and reducing overall atmospheric emissions.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and the claims, if any, may be used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover non-exclusive inclusions, such that a process, method, article, apparatus, or composition that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, apparatus, or composition.
The necessary materials and facilities for gas feeding and gas pipes, heat exchange material, controlling valves are known arts in the field. Other enabling descriptions may be found in the US Patent Application Publication US 2011/0259044 A1 the entirety of which is hereby incorporated by reference.
Referring now to FIG. 1, there is shown a non-limiting example of a typical natural gas processing plant system 100 that includes a pretreatment and molecular sieve system 102, process heat exchanger system 103A and 103B, cold separator 105, expander 107A and compressor 107B, and fractionation tower 109. FIG. 1 illustrates a typical natural gas processing plant system known as the Gas Subcooled Process (GSP), though the present invention will apply to any gas processing plant technology commonly used throughout the gas processing industry. Process conditions shown are non-limiting for this non-limiting embodiment only, and certainly, other process conditions may be utilized as desired or necessary depending upon the inlet gas stream 2 and the resulting product desired.
The pretreatment and molecular sieve system 102 is well known in gas processing and is designed to remove water and carbon dioxide (CO2) from the inlet gas in order to prevent freezing in the gas processing plant and is a typical system for essentially all cryogenic gas processing plants. It is believed that any suitable commercially available pretreatment and molecular sieve system may be utilized in the practice of the present invention.
The inlet stream 1 is separated in vessel VSSL-100 into liquid stream 16 and inlet gas stream 1 which is feed to molecular sieve system 102, exiting as treated inlet gas 2 that then flows to the cryogenic gas processing plant for recovery of the ethane and heavier hydrocarbon components from the treated gas stream.
The treated inlet gas 2 from pretreatment is chilled and partially condensed in the first process heat exchanger system 103A, exchanging heat with several product and process streams (6D, 7 and 9), exiting as chilled and partially condensed stream 13, passing through valve VLVE-100 as stream 13A before being fed to the cold separator 105. The vapor portion stream 4 off the cold separator 105 is split with a portion 4A flowing to the second process heat exchanger 103B where the stream is condensed and sub-cooled, exiting as stream 4L which is then fed to the top of the fractionation tower 109 and the remaining portion 4B is fed to the expander 107A where the gas is work expanded exiting as stream 4M and fed to the fractionation tower 109. Please note, that while tower 109 is illustrated as having 10 stages, any suitable number of stages could be utilized, and streams 4L, 4M, 3M, Q5, and 18 may enter tower 109 at any suitable stage as desired not just at the stages as shown. Cold liquids stream 3 from the cold separator is flashed, via level control, through valve VLVE-101 and are routed as stream 3M to an intermediate point of fractionation tower 109.
Fractionation tower 109 is a distillation tower with multiple sections that may operate over a wide range of conditions as necessary to generate the desired Natural Gas Liquid (NGL) product from the bottom of the tower stream 5. The vapor overhead from the fractionation tower 109 stream 6 is that remaining portion of the treated inlet gas stream 2 not recovered as liquid stream 5 from the bottom of the fractionation tower 109. This residue gas stream 6 is then typically used to provide a portion of the gas processing plant 100 heat exchange cooling duty in process heat exchangers 103B (as stream 6C) and 103A (as stream 6D) before exiting as stream 6H and being compressed in compressor 107B. Please note that VLVE-103 may or may not be present in each embodiment. Exiting as stream 24, it is then passed through heat exchanger XCHG-100 exiting as stream 6S and routed to sales or fed to a LNG liquefaction plant 130.
The above described gas processing system is one example of many different processing technologies currently in use. No matter the technology used, there has been and still remains a long standing need in many cases to include additional refrigeration within the system to attain the desired recovery levels of heavy hydrocarbons into a liquid NGL product or to provide a specific quality of residue gas for feed to a pipeline or LNG liquefaction plant. Additionally, if a LNG liquefaction plant is present, a refrigerant capable of supplying the necessary level of cryogenic refrigeration must be provided the entirety of which is hereby incorporated within the embodiments of the invention.
FIG. 1 presents a non-limiting embodiment of the invention wherein a portion of the mixed refrigerant that is the quality NGL product stream 5 passes through splitter SPLT-101 exiting as stream 11 and through valve VLVE-104 and acts as the refrigerant stream 7 for the gas processing plant 100 passing through the first process heat exchanger 103A and providing cooling duty to assist in the partial condensation of the treated inlet gas stream 2. The refrigerant exiting the process heat exchanger 103A stream 8 may be one or two phases and is routed to FIG. 2 for condensing of any vapor portion of stream 8. The portion of NGL product stream 5 not used for refrigeration in the process heat exchanger 103A stream 9, that is, stream 15 from splitter SPLT-101 may be routed for other process heat exchange, such as is shown in FIG. 1.
FIG. 1A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 1. The invention is not to be limited to the values in this table, as certainly, any of the stream summary may be different depending upon the inlet feed and the desired product.
FIG. 2 presents a non-limiting embodiment of the invention wherein that portion of the mixed refrigerant exiting the first process heat exchanger 103A stream 8 from FIG. 1 is separated into vapor stream 10 and liquid stream 11 in scrubber 113. The liquid portion stream 11 is pumped, via pump 117, to sufficient pressure to be sent to sales or storage. Exiting pump 117 as 11P this stream is combined with other streams 6P, 13P and 16 in mixer MIX-101 to form liquid product stream 18 for sales or storage. The vapor portion from scrubber 113 stream 10 is fed to the first stage compressor 121 where it is compressed to an intermediate pressure stream 1IP, cooled in interstage cooler 122 and fed as stream 2C to the second stage compressor suction scrubber 115. After acting as a refrigerant for additional process cooling, stream 9W (from FIG. 1) may be single or two-phase so may be separated in scrubber 111 into the vapor portion stream 12 and liquid portion stream 13. The liquid stream 13 is pumped via pump 127. Exiting as stream 6P at sufficient pressure to be combined in mixer MIX-101 with streams 11P, 13P and 16, and sent to sales or storage. The vapor portion stream 12 leaving scrubber 111 is routed to the compressor suction scrubber 115 and combined with the compressed and cooled stream 2C. The combined stream may be single or two-phase with the liquid portion stream 14 and vapor portion stream 15 being separated in compressor suction scrubber 115. The vapor portion stream 15 is routed to the product recompressor 123 where the vapor is compressed into compressed stream 4 to such pressure that it may be condensed in product condenser 125 exiting as a bubble-point liquid stream 16. The liquid portion stream 14 is pumped, via pump 119, as stream 13P to sufficient pressure and commingled with stream 16, stream 6P and stream 11P to form stream 18 which matches the quality NGL product stream 5. Utilizing the NGL product as the refrigerant for the gas processing plant requires substantially less energy input while providing significantly more control and flexibility in the overall operation of the gas processing plant 100.
FIG. 2A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 2. The invention is not to be limited to the values in this table, as certainly, any of the stream summary may be different depending upon the inlet feed and the desired product.
FIG. 3 presents a non-limiting embodiment of the same invention as shown in FIG. 1 with the exception that the mixed refrigerant stream 5 will now contain a greater portion of the methane component such that the exiting refrigerant stream 8 may now be utilized as the basis of the mixed refrigerant to be used in a LNG liquefaction plant 130. As in FIG. 1, a portion of the mixed refrigerant stream 5 passes through splitter SPLT-101 exiting as stream 11 and through valve VLVE-104 and acts as the refrigerant stream 7 for the gas processing plant 100 passing through the first process heat exchanger 103A and providing cooling duty to assist in the partial condensation of the treated inlet gas stream 2. However, due to the increased content of methane in stream 5, the process operates colder than when making a high quality NGL product as depicted in FIG. 1. In FIG. 3, the refrigerant exiting the process heat exchanger 103A stream 8 may be one or two phases and is routed to FIG. 4 for separation of the vapor and liquid portions of stream 8. The portion of NGL product stream 5 not used for refrigeration in the process heat exchanger 103A stream 9 may be utilized as a refrigerant for other process cooling, such as cooling of the LNG Feed Gas stream.
FIG. 3A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 3. The invention is not to be limited to the values in this table, as certainly, any of the stream summary may be different depending upon the inlet feed and the desired product.
FIG. 4 presents a non-limiting embodiment of the invention wherein that portion of the mixed refrigerant exiting the first process heat exchanger 103A stream 8 from FIG. 3 is separated into its vapor stream 10 and liquid stream 11 in scrubber 113. The liquid portion stream 11 is pumped, via pump 117, to sufficient pressure to be sent to sales or storage. Exiting pump 117 as 11P this stream is combined with other streams 6P and 13P in mixer MIX-101 to form liquid product stream 18 for sales or storage. The vapor portion from scrubber 113 stream 10 is fed to the first stage compressor 121 where it is compressed to an intermediate pressure stream 1IP, cooled in interstage cooler 122 and fed as stream 2C to the second stage compressor suction scrubber 115. After acting as a refrigerant for additional process cooling, stream 9W (from FIG. 3) may be single or two-phase so may be separated in scrubber 111 into the vapor portion stream 3 and liquid portion stream 5. The liquid stream 5 is pumped, via pump 127. Exiting as stream 6P at sufficient pressure to be combined in mixer MIX-101 with streams 11P and 13P and sent to sales or storage. The vapor portion stream 3 leaving scrubber 111 is routed to the compressor suction scrubber 115 and combined with the compressed and cooled stream 2C. The combined stream may be single or two-phase with the liquid portion stream 13 and vapor portion stream 12 being separated in compressor suction scrubber 115. The vapor portion stream 12 is routed to the product recompressor 123 where the vapor is compressed into compressed stream 4 and then partially condensed in condenser 125 exiting as stream 16. The exiting mixed refrigerant stream 16 may now be utilized as the refrigerant for the LNG liquefaction plant 130 and requires substantially less energy input while providing significantly more control and flexibility in the overall operation of the LNG liquefaction plant 130. The liquid portion stream 13 is pumped, via pump 119 as stream 13P, to sufficient pressure and commingled with stream 6P and stream 11P to form stream 18 which meets the quality specifications for NGL product streams.
FIG. 4A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 4. The invention is not to be limited to the values in this table, as certainly, any of the stream summary may be different depending upon the inlet feed and the desired product.
FIG. 5 presents a non-limiting embodiment of the invention wherein the mixed refrigerant, from recompressor 123 stream 16 in FIG. 4, is the basis of the mixed refrigerant system 132 for the LNG liquefaction plant 130. Depending on the amount of LNG to be liquefied, the mixed refrigerant system may be an open or closed loop system. In the case where a closed loop system is required, the mixed refrigerant stream 16 is generated only at times when make-up into the mixed refrigerant system 132 is required. As a feature of some embodiments of the invention, some embodiments of the invention allow for the supplementing of the refrigeration on-line, with no need to formulate the composition or shut down any portion of the plant operation. If refrigerant make-up is required, simply lower the Demethanizer Bottoms temperature in the Gas Processing Plant and then feed stream 16 straight into the refrigerant system.
To improve the efficiency and performance of the LNG liquefaction Plant 130 and the mixed refrigerant system 132 the present invention utilizes several unique features including partial condensation of the mixed refrigerant stream 50 in the first heat exchange unit 133; separation of stream 50 into its liquid stream 52 and its vapor stream 54 in separator 135 and using each stream as separate refrigerant supply streams to the LNG process heat exchanger 140; use of flashed LNG vapor streams 150 and 154 and a portion of LNG liquid stream 152 as refrigerant streams in the LNG process heat exchanger 140.
FIG. 5A is a table presenting a non-limiting stream summary for the non-limiting embodiment as shown in FIG. 5. The invention is not to be limited to the values in this table, as certainly, any of the stream summary may be different depending upon the inlet feed and the desired product.
Some non-limiting embodiments of the present invention may utilize the finished NGL Product from a Gas Processing Plant as an open loop, single mixed refrigerant, to provide required refrigeration duty to the Gas Processing Plant.
Some prior art designs use an internal heat pump to provide system refrigeration and reboiler heat that is subject to the internal operation of the plant process and results in difficult and inefficient operation. These are also not open-loop designs. Use of the finished NGL Product, in an open loop manner, allows for much more efficient control and easier operation.
It should be noted that the amount of NGL generated should always be sufficient to provide the required refrigeration needs for the Gas Processing Plant.
In the practice of the present invention, the leaner the Inlet Gas stream is in C2+, the less process refrigeration that is required; thus, even though there is less NGL produced, less is required for Plant refrigeration needs. Conversely, the richer the inlet gas, the more refrigeration is required to condense and recover the NGL products; but, the increased NGL production provides the additional refrigeration duty requirements.
In some non-limiting embodiments, only a portion of the NGL Product stream may be used as refrigerant within the Plant, thus minimizing the amount of vaporized refrigerant that must be recompressed and condensed for remixing with rest of NGL Product to sales.
Simulations show that this type of open-loop, mixed refrigerant system will require 15% to 20% less overall refrigerant compression horsepower than a typical closed-loop propane refrigerant system.
Some non-limiting embodiments of the present invention provide a means to generate and utilize a single mixed refrigerant stream for use in both Natural Gas Processing, for the recovery of a NGL Product, and for the liquefying of the methane-rich Residue Gas stream into Liquefied Natural Gas (LNG).
Various non-limiting embodiments of the present invention provide a single mixed refrigerant system to provide cooling duty for both Gas Processing and LNG liquefaction processes.
Various non-limiting embodiments of the present invention provide that the NGL Product from the Gas Processing Plant is utilized to make-up refrigerant into the LNG Plant mixed refrigerant system.
In various non-limiting embodiments of the present invention, and depending on the amount of LNG to be produced, the NGL Product may be used in an open-loop configuration, or made up into a closed-loop system on a batch basis.
In various non-limiting embodiments of the present invention, when making up into a closed-loop, mixed refrigerant system for the LNG Liquefaction Plant, the composition of the NGL Product, from the Gas Processing Plant, may be easily modified to include additional methane and other light-end components into the mixed refrigerant stream.
For some non-limiting embodiments of the present invention, maintaining a specific and constant refrigerant composition is not a requirement for proper operation of this new invention.
For some non-limiting embodiments of the present invention, the refrigerant consists of only those components that are naturally occurring within the natural gas feed stream into the Gas Processing Plant.
For some non-limiting embodiments of the present invention, some changes in the refrigerant composition are acceptable, without effect on the overall system operation.
Some non-limiting embodiments of the present invention have an advantage over prior art design, in that those designs require addition of components that do not naturally occur in natural gas feed streams, such as Propylene, Ethylene and Butylene.
For some non-limiting embodiments of the present invention, due to specific compositional requirements, on-site storage of these components is oftentimes required.
For some non-limiting embodiments of the present invention, if a change in composition is required for process operation, this may be done manually and with a shutdown of the system.
Some non-limiting embodiments of the present invention encourage the combination of Gas Processing and Natural Gas Liquefaction into one facility, whereas this is almost never done currently. By doing both operations at the same time, at the same facility, the following benefits may be realized.
For some non-limiting embodiments of the present invention the Inlet Gas only has to be treated for CO2, H2S and water removal one time, at the inlet to the Gas Processing Plant.
For some non-limiting embodiments of the present invention, the C2+ hydrocarbons from the Inlet Gas may be recovered within the Gas Processing Plant, making the feed gas to the LNG Liquefaction Plant suitable for liquefaction without freezing concerns.
It should be noted that not all gas fed into Sales Gas Pipelines are free of the above contaminants, and that most LNG Liquefaction take their feedstock directly off of pipelines, meaning LNG Feed Gas has to again be treated for removal of CO2, H2S and water; and, LNG Feed Gas may need to be processed for removal of heavy-end hydrocarbons.
For some non-limiting embodiments of the present invention Using a single mixed refrigerant to act in providing cooling duty to both the Gas Processing Plant and LNG Liquefaction Plant reduces the amount of equipment and storage facilities required to perform refrigeration duties for both plants.
None of the description in the present invention should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope: THE SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS. Moreover, none of these claims are intended to invoke paragraph six of 35 USC section 112 unless the exact words “means for” are followed by a participle.
The claims as filed are intended to be as comprehensive as possible, and NO subject matter is intentionally relinquished, dedicated, or abandoned.

Claims

1. A method of operating a gas processing plant by using an NGL product from the gas processing plant as a mixed refrigerant for liquefying an inlet hydrocarbon gas being introduced to said gas processing plant, wherein said liquefied inlet hydrocarbon gas is further processed into the NGL product and a methane rich residue gas the method comprising:

introducing the inlet hydrocarbon gas to a first heat exchange unit utilizing a mixed refrigerant to produce a cooled hydrocarbon gas having a liquid portion and a vapor portion;

flowing the liquid and vapor portions to a first pressurized distillation tower;

flowing a vapor product of hydrocarbons comprising methane rich residue gas from the first pressurized distillation tower;

flowing NGL product from the first pressurized distillation tower;

flowing said NGL product to at least the first heat exchange unit said NGL product to be used as the mixed refrigerant to aid in cooling of the hydrocarbon gas.

2. The method of claim 1, further comprising vaporizing at least a portion of the mixed refrigerant forming a mixed refrigerant vapor portion and a mixed refrigerant liquid portion, separating the mixed refrigerant vapor portion from the mixed refrigerant liquid portion, recompressing and condensing that vapor portion and recombining with the liquid portion to form a final NGL product.

3. The method of claim 1, wherein the NGL product contains a percentage of ethane and methane, the method further comprising:

flowing the methane rich residue gas to an LNG liquefaction unit utilizing a mixed refrigerant;

providing the NGL product to the LNG liquefaction unit for use as the mixed refrigerant; and,

liquefying the methane rich natural gas in the LNG liquefaction unit using the NGL product as the mixed refrigerant to liquefy the methane rich natural gas into Liquid Natural Gas (LNG).

4. The method of claim 3, further comprising vaporizing at least a portion of the mixed refrigerant forming a mixed refrigerant vapor portion and a mixed refrigerant liquid portion and separating the mixed refrigerant vapor portion from the mixed refrigerant liquid portion.

5. The method of claim 4, wherein the mixed refrigerant vapor portion is utilized as the mixed refrigerant in the process used to liquefy methane rich natural gas (LNG) while the mixed refrigerant liquid portion is delivered as a final NGL product.

6. The method of claim 5, wherein the mixed refrigerant generated for use in the LNG process may be used in an open loop process or as make-up into a closed loop process.

7-16. (canceled)

17-19. (canceled)

20. A method of operating a liquefaction unit to liquefy methane rich natural gas into liquid natural gas (LNG), the method comprising:

introducing methane rich natural gas from a gas processing plant to a liquefaction unit utilizing a mixed refrigerant;

providing NGL product to the liquefaction unit for use as the mixed refrigerant, wherein the NGL product contains methane and ethane, and wherein the NGL product is from said gas processing plant, or another gas processing plant; and,

liquefying the methane rich natural gas in the liquefaction unit using the NGL product as the mixed refrigerant to liquefy the methane rich natural gas into Liquid Natural Gas (LNG).