US20170038139A1

US20170038139A1 - Method for the production of liquefied natural gas

Info

Publication number: US20170038139A1
Application number: US15/230,034
Authority: US
Inventors: Michael A. Turney; Alain Guillard
Original assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2015-08-06
Filing date: 2016-08-05
Publication date: 2017-02-09
Also published as: CN108027199A; US20170038138A1; RU2018106658A3; RU2018106658A; EP3332198A1

Abstract

A method for the production of liquefied natural gas (LNG) without the use of externally provided electricity is provided The method may include the steps of: providing a transportable apparatus, wherein the transportable apparatus comprises a housing, a heat exchanger, a phase separator, a first refrigeration supply, and a second refrigeration supply, wherein the first refrigeration supply and the second refrigeration supply are configured to provide refrigeration within the heat exchanger; introducing a natural gas stream into the transportable apparatus at a first pressure under conditions effective for producing an LNG stream; withdrawing the LNG stream from the transportable apparatus; and withdrawing a warm natural gas stream from the transportable apparatus, wherein the warm natural gas stream is at a second pressure, wherein the second pressure is lower than the first pressure.

Description

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 62/201,947, filed on Aug. 6, 2015, U.S. Provisional Patent Application No. 62/305,381, filed on Mar. 8, 2016, and U.S. Provisional Application Ser. No. 62/370,953 filed on Aug. 4, 2016, all of which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to a method and apparatus for producing liquefied natural gas (LNG) in a packaged unit without any rotating machinery.

BACKGROUND OF THE INVENTION

There are numerous reasons for the liquefaction of gases, including naturally occurring gases such as methane. Perhaps the chief reason is that liquefaction greatly reduces the volume of a gas, making it feasible to store and transport the liquefied gas in containers of improved economy and design. Liquid gases can be stored in suitably designed cryogenic containers and dispensed into vehicle tanks using techniques that have been in use for many years in the industrial cryogenic gas industries.
Many industrial gases such as propane, butane and carbon dioxide can be liquefied by placing them under very high pressure. However, producing liquid from methane may not be achieved with high pressure alone. To this extent, methane, a cryogenic gas, is different from other industrial gases. To liquefy methane it is typically necessary to reduce the temperature of the gaseous phase to below about −160° C., depending upon the pressure at which the process is operated.
Numerous systems exist in the prior art for the production of liquefied natural gas (“LNG”). Conventional processes known in the art require substantial refrigeration to reduce the gas to liquid. Among the most common of these refrigeration processes are: (1) the cascade process; (2) the single mixed refrigerant process; and (3) the propane pre-cooled mixed refrigerant process.
The cascade process produces liquefied gases by employing several closed-loop cooling circuits, each utilizing a single pure refrigerant and collectively configured in order of progressively lower temperatures. The first cooling circuit commonly utilizes propane or propylene as the refrigerant; the second circuit may utilize ethane or ethylene, while the third circuit generally utilizes methane as the refrigerant.
The single mixed refrigerant process produces LNG by employing a single closed-loop cooling circuit utilizing a multi-component refrigerant consisting of components such as nitrogen, methane, ethane, propane, butanes and pentanes. The mixed refrigerant undergoes the steps of condensation, expansion and recompression to reduce the temperature of natural gas by employing a unitary collection of heat exchangers known as a “cold box.”
The propane pre-cooled mixed refrigerant process produces LNG by employing an initial series of propane-cooled heat exchangers in addition to a single closed-loop cooling circuit, which utilizes a multi-component refrigerant consisting of components such as nitrogen, methane, ethane and propane. Natural gas initially passes through one or more propane-cooled heat exchangers, proceeds to a main exchanger cooled by the multi-component refrigerant, and is thereafter expanded to produce LNG.
Most liquefaction plants utilize one of these gas liquefaction processes. Unfortunately, the cost and maintenance of such plants is expensive because of the cost of constructing, operating and maintaining one or more external, single or mixed refrigerant, closed-loop cooling circuits. Such circuits typically require the use and storage of multiple highly explosive refrigerants that can present safety concerns. Refrigerants such as propane, ethylene and propylene are explosive, while propane and propylene, in particular, are heavier than air, further complicating dispersion of these gases in the event of a leak or other equipment failure. It would therefore be beneficial to eliminate the external refrigeration circuit(s) in a liquefaction plant.
One of the distinguishing features of a conventional liquefaction plant in the prior art is the large capital investment required. The equipment used to liquefy cryogenic gases in high volumes is large, complex and very expensive. The plant is typically made up of several basic systems, including a gas treatment system (to remove impurities from the initial feed stream), and liquefaction, refrigeration, power, storage and loading facilities. Materials required in conventional liquefaction plants also contribute greatly to the plants' cost. Containers, long runs of piping, and multiple-level tiers of other equipment are principally constructed from aluminum, stainless steel or high nickel content steel to provide the necessary strength and fracture toughness at low temperatures. It would therefore be beneficial to decrease the initial amount of capital investment needed to form a liquefaction plant.
Another distinguishing feature of a conventional liquefaction plant in the prior art is that as a result of its complexity and size, the plant, by necessity, is typically a fixed installation that cannot be easily relocated. Even if a conventional plant can be physically relocated, such a move is very costly and requires the plant to be out of service for many months while plant systems, components and structures are disassembled, moved and then reassembled on a newly prepared site. It would therefore be beneficial to provide a liquefaction plant that is small and simple in design so that it can be easily relocated without significant operational down time.
There exists a multitude of current prior art methods for the liquefaction of natural gas. For example, U.S. Pat. No. 5,755,114 to Foglietta discloses a hybrid liquefaction cycle for the production of LNG. The Foglietta process passes a pressurized natural gas feed stream into heat exchange contact with a closed-loop propane or propylene refrigeration cycle prior to directing the natural gas feed stream through a turboexpander cycle to provide auxiliary refrigeration. The Foglietta process requires at least one external closed-loop refrigeration cycle comprising propane or propylene, both of which are explosive.
The system of U.S. Pat. No. 6,085,545 to Johnston first compresses the natural gas feed (typically methane) which then passes through an after-cooler to remove the heat of compression. At this point the natural gas flow is split into two flow portions, the first of which is cooled in at least one heat exchanger and then throttled into a collector, and the second of which enters a turboexpander wherein the temperature and pressure are lowered and the work of expansion is extracted. The second flow portion is then used in at least one heat exchanger as the heat exchange cooling medium.
U.S. Pat. No. 3,616,652 to Engel discloses a process for producing LNG in a single stage by compressing a natural gas feed stream, cooling the compressed natural gas feed stream to form a liquefied stream, dramatically expanding the liquefied stream to an intermediate-pressure liquid, and then flashing and separating the intermediate-pressure liquid in a single separation step to produce LNG and a low-pressure flash gas. The low-pressure flash gas is recirculated, substantially compressed and reintroduced into the intermediate pressure liquid. While the Engel process produces LNG without the use of external refrigerants, the process yields a small volume of LNG compared to the amount of work required for its production, thus limiting the economic viability of the process.
While these prior art inventions may be sufficient for the particular problems that they solve, it would be beneficial in the industry to provide an improved process for the cryogenic refrigeration and liquefaction of gases. It would also be beneficial to eliminate the external refrigeration circuit(s) in a liquefaction plant. It would be likewise be advantageous to decrease the initial amount of capital investment needed to form a liquefaction plant. It would also be advantageous to provide a liquefaction plant that is small and simple in design so that it can be easily relocated without significant operational down time.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus that satisfies at least one of these needs. In certain embodiments, the invention can provide a lower cost, more efficient and flexible method to produce LNG using a transportable apparatus. For example, in certain embodiments, the invention utilizes a natural gas letdown to produce LNG in a packaged unit, without the need for electrically powered compressors or the use of rotating machinery.
In one embodiment, a transportable apparatus for the production of liquefied natural gas (“LNG”) is provided. In this embodiment, the apparatus can include a housing, a natural gas feed inlet, a heat exchanger, a phase separator, a liquid outlet disposed on the cold end of the heat exchanger, an LNG product outlet disposed on the cold end of the heat exchanger, a first refrigeration supply, a second refrigeration supply, and wherein the heat exchanger, the phase separator, the first expansion valve, the first refrigeration supply, and the second refrigeration supply are all disposed within the housing.
In one embodiment, the natural gas feed inlet configured to accept a stream of pressurized natural gas originating from outside the housing. In another embodiment, the heat exchanger is in fluid communication with the natural gas feed inlet, such that the heat exchanger is configured to receive the stream of pressurized natural gas from the natural gas feed inlet, wherein the heat exchanger has a warm end, a cold end, and an intermediate section. In another embodiment, the phase separator has a fluid inlet, a gaseous outlet, and a liquid outlet, wherein the fluid inlet is in fluid communication with a first intermediate fluid outlet located in the intermediate section of the heat exchanger, such that the phase separator is configured to receive a partially cooled fluid from the heat exchanger, wherein the liquid outlet of the phase separator is in fluid communication with a first intermediate fluid inlet of the intermediate section of the heat exchanger, wherein the gaseous outlet of the phase separator is in fluid communication with a second intermediate fluid inlet of the intermediate section of the heat exchanger, such that the second intermediate fluid inlet of the intermediate section of the heat exchanger is configured to receive at least a first portion of gas coming from the phase separator. In another embodiment, the liquid outlet is disposed on the cold end of the heat exchanger and in fluid communication with the second intermediate fluid inlet of the intermediate section of the heat exchanger. In another embodiment, the LNG product outlet is in fluid communication with the liquid outlet disposed on the cold end of the heat exchanger. In another embodiment, the first refrigeration supply comprises a first expansion valve, a first LNG inlet disposed on the cold end of the heat exchanger, and a first natural gas outlet disposed on the warm end of the heat exchanger, wherein the first refrigeration supply is in fluid communication with the liquid outlet disposed on the cold end of the heat exchanger, wherein the heat exchanger is configured to indirectly exchange heat between a first LNG stream and a natural gas stream when the first LNG stream flows from the first LNG inlet to first natural gas outlet.
In another embodiment, the second refrigeration supply is configured to provide refrigeration within the heat exchanger. In one embodiment, the flow of first and second LNG stream combined can account for less than 10% of the flow of the natural gas flowing through the natural gas feed inlet. In another embodiment, the expanded second portion of top gas can constitute a third refrigeration supply. In another embodiment, the expanded heavy hydrocarbons can constitute a fourth refrigeration supply.
In optional embodiments of the transportable apparatus:

- the second refrigeration supply comprises a liquid nitrogen inlet disposed on the cold end of the heat exchanger and a nitrogen outlet disposed on the warm end of the heat exchanger, and wherein the heat exchanger is configured to indirectly exchange heat between a liquid nitrogen fluid and the natural gas stream when the liquid nitrogen flows from the liquid nitrogen inlet to the nitrogen outlet;
- the second refrigeration supply further comprises a liquid nitrogen storage tank in fluid communication with the liquid nitrogen inlet, such that the liquid storage tank is configured to deliver liquid nitrogen to the heat exchanger via the liquid nitrogen inlet;
- the second refrigeration supply comprises a second expansion valve, a second LNG inlet disposed on the cold end of the heat exchanger, and a second natural gas outlet disposed on the warm end of the heat exchanger, and wherein the heat exchanger is configured to indirectly exchange heat between a second LNG stream and the natural gas stream when the second LNG stream flows from the second LNG inlet to second natural gas outlet;
- the first expansion valve is configured to expand the first LNG stream to a first pressure, wherein the second expansion valve is configured to expand the second LNG stream to a second pressure, wherein the first pressure is higher than the second pressure;
- the first pressure is between 4 and 10 bara, wherein the second pressure is between 1 to 2 bara;
- the transportable apparatus may also include a third intermediate fluid inlet of the intermediate section of the heat exchanger that is configured to receive a second portion of gas coming from the phase separator;
- the transportable apparatus may also include a third expansion valve in fluid communication with, and disposed inline between, the gaseous outlet of the phase separator and a second intermediate fluid inlet of the intermediate section of the heat exchanger;
- the transportable apparatus may also include a lower pressure natural gas outlet in fluid communication with the first natural gas outlet of the heat exchanger, wherein the lower pressure natural gas outlet is configured to send a stream warm natural gas received from the first natural gas outlet to outside of the housing;
- the transportable apparatus may also include a liquid expansion valve in fluid communication with, and disposed inline between, the liquid outlet of the phase separator and the first intermediate fluid inlet of the intermediate section of the heat exchanger;
- the heat exchanger is split into a first portion and a second portion, wherein the warm end of the heat exchanger is disposed in the first portion, wherein the cold end of the heat exchanger is disposed in the second portion, wherein the intermediate section is disposed in both the first portion and the second portion;
- the transportable apparatus may also include an absence of compression means;
- the transportable apparatus may also include an absence of a rotating compressor;
- the transportable apparatus may also include an absence of rotating machinery;
- the transportable apparatus may also include an absence of electrically powered compression or expansion devices;
- the transportable apparatus is configured to liquefy natural gas without the use of externally provided electricity; and/or
- the housing is configured to fit within a shipping container such that the transportable apparatus is configured to be transported via a truck and/or a barge.

In another aspect of the invention, a method for the production of liquefied natural gas (“LNG”) using a transportable apparatus is provided. In this embodiment, the method can include the steps of: providing a transportable apparatus, wherein the transportable apparatus comprises a housing, a heat exchanger, a phase separator, a first refrigeration supply, and a second refrigeration supply, wherein the first refrigeration supply and the second refrigeration supply are configured to provide refrigeration within the heat exchanger; introducing a natural gas stream into the transportable apparatus at a first pressure under conditions effective for producing an LNG stream; withdrawing the LNG stream from the transportable apparatus; and withdrawing a warm natural gas stream from the transportable apparatus, wherein the warm natural gas stream is at a second pressure, wherein the second pressure is lower than the first pressure.
In optional embodiments of the method for the production of LNG:

- the first refrigeration supply comprises a first expansion valve, a first LNG inlet disposed on a cold end of the heat exchanger, and a first natural gas outlet disposed on a warm end of the heat exchanger, wherein the first refrigeration supply is in fluid communication with a liquid outlet disposed on the cold end of the heat exchanger, wherein the heat exchanger is configured to indirectly exchange heat between a first LNG stream and the natural gas stream when the first LNG stream flows from the first LNG inlet to first natural gas outlet;
- the second refrigeration supply comprises a liquid nitrogen inlet disposed on the cold end of the heat exchanger and a nitrogen outlet disposed on the warm end of the heat exchanger, and wherein the heat exchanger is configured to indirectly exchange heat between a liquid nitrogen fluid and the natural gas stream when the liquid nitrogen flows from the liquid nitrogen inlet to the nitrogen outlet;
- the second refrigeration supply further comprises a liquid nitrogen storage tank in fluid communication with the liquid nitrogen inlet, such that the liquid storage tank is configured to deliver liquid nitrogen to the heat exchanger via the liquid nitrogen inlet;
- the second refrigeration supply comprises a second expansion valve, a second LNG inlet disposed on the cold end of the heat exchanger, and a second natural gas outlet disposed on the warm end of the heat exchanger, and wherein the heat exchanger is configured to indirectly exchange heat between a second LNG stream and the natural gas stream when the second LNG stream flows from the second LNG inlet to second natural gas outlet;
- the first expansion valve is configured to expand the first LNG stream to a first LNG pressure, wherein the second expansion valve is configured to expand the second LNG stream to a second LNG pressure, wherein the first LNG pressure is higher than the second LNG pressure;
- the first LNG pressure is between 4 and 10 bara, wherein the second LNG pressure is between 1 to 2 bara;
- the transportable apparatus further comprises a natural gas feed inlet configured to accept a stream of pressurized natural gas originating from outside the housing, wherein the heat exchanger is in fluid communication with the natural gas feed inlet, such that the heat exchanger is configured to receive the stream of pressurized natural gas from the natural gas feed inlet, wherein the heat exchanger has a warm end, a cold end, and an intermediate section, wherein phase separator has a fluid inlet, a gaseous outlet, and a liquid outlet, wherein the fluid inlet is in fluid communication with a first intermediate fluid outlet located in the intermediate section of the heat exchanger, such that the phase separator is configured to receive a partially cooled fluid from the heat exchanger, wherein the liquid outlet of the phase separator is in fluid communication with a first intermediate fluid inlet of the intermediate section of the heat exchanger, wherein the gaseous outlet of the phase separator is in fluid communication with a second intermediate fluid inlet of the intermediate section of the heat exchanger, such that the second intermediate fluid inlet of the intermediate section of the heat exchanger is configured to receive at least a first portion of gas coming from the phase separator, wherein the transportable apparatus further comprises a third intermediate fluid inlet of the intermediate section of the heat exchanger that is configured to receive a second portion of gas coming from the phase separator;
- a third expansion valve is in fluid communication with, and disposed inline between, the gaseous outlet of the phase separator and a second intermediate fluid inlet of the intermediate section of the heat exchanger;
- a lower pressure natural gas outlet is in fluid communication with the first natural gas outlet of the heat exchanger, wherein the lower pressure natural gas outlet is configured to send a stream warm natural gas received from the first natural gas outlet to outside of the housing;
- a liquid expansion valve is in fluid communication with, and disposed inline between, the liquid outlet of the phase separator and the first intermediate fluid inlet of the intermediate section of the heat exchanger;
- the heat exchanger is split into a first portion and a second portion, wherein the warm end of the heat exchanger is disposed in the first portion, wherein the cold end of the heat exchanger is disposed in the second portion, wherein the intermediate section is disposed in both the first portion and the second portion;
- the method may include an absence of compressing the natural gas stream within the transportable apparatus;
- the transportable apparatus comprises an absence of a rotating compressor;
- the transportable apparatus comprises an absence of rotating machinery;
- the transportable apparatus comprises an absence of electrically powered compression or expansion devices;
- the method may include an absence of a step of providing external electric power to the transportable apparatus;
- the step of providing the transportable apparatus comprises loading the transportable apparatus on a truck or barge and transporting the transportable apparatus from a first location to a second location; and/or
- the heat exchanger, the phase separator, the first refrigeration supply, and the second refrigeration supply are all disposed within the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

FIG. 1 provides an embodiment of the present invention.

FIG. 2 provides an embodiment of the present invention, wherein the second refrigeration supply includes expanding a portion of the liquefied natural gas.

FIG. 3 provides an embodiment of the present invention, wherein the second refrigeration supply includes liquid nitrogen.

FIG. 4 provides another embodiment of the present invention having an expansion turbine.

FIG. 5 provides an embodiment of the present invention having an expansion turbine driving a gas booster.

DETAILED DESCRIPTION

While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims.
There is a demand for low cost localized nano-scale (e.g., <10 mtd) LNG production. Typical current systems on the market for nano-scale LNG production utilize forms of closed loop cycles with a refrigeration compressor that requires electrical consumption.
In one embodiment, the present invention proposes a solution for liquefaction of natural gas (LNG) which can be packaged (within size of truck trailer, barge, etc. . . . ) and preferably requires “zero energy” consumption and contains no rotating machinery equipment. This saves on setup of electrical equipment and operating maintenance.
In one embodiment, the apparatus can effectively achieve the goal of liquefaction of LNG with no rotating machinery by utilizing the letdown energy of available letdown stations. For example, one potential location that could benefit from an embodiment of the present invention would include city gates where high pressure natural gas from transmission lines are letdown to low pressure distribution lines. This available letdown energy can be converted to refrigeration energy with a combination of pressure letdown valves described herein.
“Warm split”
Purified natural gas from a high pressure transmission pipeline (typically >20 bara) can be fed to a main exchanger (such as brazed aluminum), where it can be cooled to an intermediate temperature (e.g., to between −40° C. to −70° C.) where heavy hydrocarbons (HHCs) are liquefied and separated in a separator. The HHCs can be re-warmed in the exchanger and sent to a medium pressure tail gas header or distribution pipeline (e.g., typically between 4 to 10 bara). Vapor from the separator can be split into two streams. The first can be reduced in pressure through a control valve, re-warmed in the main exchanger and also sent to the medium pressure natural gas header (distribution header). In one embodiment, this expanded stream can provide a majority source of refrigeration for the system. The second vapor stream from the separator can be further cooled and liquefied in the main exchanger to form the LNG product at the cold end.
In this embodiment, the separation of the vapor stream (first being sent to MP header and second being liquefied as product LNG) occurs at the same temperature as the HHC separator. This removes headers and distributors on the main exchanger thus simplifying its design compared to having different temperatures for the vapor split and the HHC removal. The impact is a small (<5%) loss in thermal efficiency, which is justified by the small scale and simplified design.
In other embodiments, this HHC stream at the separator outlet can be processed as NGLs, or sent to the LNG production (depending on product constraints of HHC freezing). In one embodiment, the re-warmed medium pressure vapor from the separator can be used as a regenerating stream to remove impurities such as water and CO₂from the adsorption unit. In another embodiment, the re-warmed low pressure vapor is mixed with the vaporized HHC stream.

“Cold Split(s)”

In one embodiment, the LNG leaving the cold end of the main exchanger can be split into three streams. The first stream can be reduced in pressure and sent to the LNG storage tank. The second can be reduced in pressure, vaporized and warmed against the natural gas being liquefied in the main exchanger and sent to the MP header (e.g., 4-10 bara). The third can be reduced to a lower pressure (e.g., 1.1 to 2 bara) (to provide the required final cold end cooling).
The combination of the two described “warm split” and “cold split” concepts yields a particular cooling curve to effectively produce LNG without a turbine.
In one embodiment, the Low Pressure natural gas return stream can be sent to a pretreatment unit where it is burned as fuel to heat a regeneration stream. In one embodiment, the pretreatment unit removes water and CO₂from the natural gas feed for cryogenic processing.
In another embodiment, the final cold end cooling can be provided by vaporizing liquid nitrogen at the cold end of the main exchanger. LIN can be vaporized at approximately 6 bara and can be utilized as a utility or instrument gas or vented to atmosphere. This is an alternative to vaporizing a portion of the low pressure natural gas (e.g., 1.1 to 2 bara) if there is no demand for this fuel gas and if LIN is available.
The product package shown in FIG. 1 describes both the low pressure natural gas stream as well as the LIN injection at the cold end. However, embodiments of the invention may be practiced with only one of the refrigeration sources present. In certain embodiments, the invention can be designed as a standard product to accommodate a site with either resource, such that the apparatus will be enabled to work with either of the refrigeration sources (e.g., LIN or LP NG as fuel).
As shown in FIG. 3, the LIN demand can be on the order of 1 to 1.5 mtd continuous. The source of the liquid nitrogen may be trucked in by batch from external source, stored in a LIN tank inside the insulated cold box package. As such, the typical external expensive double walled vacuumed insulated storage tank is not required.
This cold box package, which can include the main exchanger, separator, valves and LIN tank, can be packaged into the size and shape of a standard shipping container.
In another embodiment, the first vapor stream from the HHC separator described in the “warm split” above can be replaced by a natural gas stream letdown through a turbine. This turbine creates a cold vapor stream which can be warmed by heat exchange with the natural gas stream being liquefied in the main exchanger. This significantly reduces the flow rate of natural gas required to be letdown. While this turbine adds a rotating machinery component, there is still no refrigeration compressor needed, thereby requiring no electrical system and resulting in “zero energy” LNG production.
In one embodiment, this natural gas turbine can be connected to an oil brake, or connected to a booster brake to recover additional refrigeration, or connected to a generator brake.
Referring to FIG. 1, a process flow diagram of an embodiment of the current invention is shown. In FIG. 1, HP natural gas 4 can be withdrawn from high pressure natural gas pipeline 2 and sent to purification unit 10 for purification of impurities such as water and CO₂to form purified natural gas 12. In one embodiment, purification unit 10 can be located within housing 20. Purified natural gas 12 can then be introduced to housing 20 via natural gas feed inlet 13, and then introduced to warm end of heat exchanger 30, where purified natural gas 12 is then partially cooled to a temperature effective for condensing heavy hydrocarbons. Partially cooled natural gas 32 is then removed from an intermediate portion of heat exchanger 30 and fed to phase separator 40 under conditions effective for separating the natural gas from the heavy hydrocarbons. Top gas 42 is then withdrawn from the top of phase separator 40 and preferably split into two portions: first portion of top gas 44 and second portion of top gas 46. First portion of top gas 44 can be then introduced into cold split 30 b (see FIG. 2), and fully cooled and liquefied to form liquefied natural gas 50.
In one embodiment, liquefied natural gas 50 can then be split into two or three streams: LNG product 64, first LNG stream 52 and optionally second LNG stream 54. LNG product 64 can be removed from housing 20 and then expanded across LNG expansion valve 62 and stored in LNG storage tank 60.
One portion of the refrigeration for the apparatus can be provided by expansion of first LNG stream 52 across first expansion valve 51. After expansion, first LNG stream 52 is then warmed in heat exchanger 30 (or in the embodiment shown in other figures cold split 30 b and warm split 30 a), wherein it is withdrawn from the warm end of heat exchanger 30 at first natural gas outlet 55, and then from housing 20 and optionally split into two streams, with first portion of warmed first natural gas stream 82 optionally being used to regenerate purification unit 10, while the remaining portion is expanded across warm expansion valve 84 and combined with first portion of warmed first natural gas stream 82 to form medium pressure natural gas 86, before being introduced to medium pressure natural gas pipeline 90.
In one embodiment, second refrigeration supply can be created by expanding second LNG stream 54 across second expansion valve 53 and warming second LNG stream 54 within heat exchanger 30, wherein it can be withdrawn from heat exchanger 30 at second natural gas outlet 57 as warmed natural gas 76.
In another embodiment, second refrigeration supply is accomplished with warming of liquid nitrogen, and in certain embodiments, vaporizing the liquid nitrogen within heat exchanger 30. In this embodiment, LIN delivery truck 100 can input liquid nitrogen feed 68 to LIN storage tank 70 by connecting to housing 20 via liquid nitrogen feed inlet 67. When refrigeration is needed, the flow of nitrogen is started by opening LIN control valve 71 and flowing liquid nitrogen fluid 72 into cold split 30 b via liquid nitrogen inlet 73. Liquid nitrogen fluid 72 can then be withdrawn from warm split 30 a of heat exchanger 30 via nitrogen outlet 59 as warmed nitrogen 74.
In one embodiment, second portion of top gas 46 can be expanded across third expansion valve 47 to produce additional refrigeration (i.e., third refrigeration supply). In one embodiment, third refrigeration supply is configured to provide the predominant portion of cooling within warm split 30 a. As such, second portion of top gas 46 is introduced into intermediate portion of heat exchanger 30, and preferably combined with first LNG stream 52 within heat exchanger 30. While FIG. 1 shows second portion of top gas 46 combining with first LNG stream 52, those of ordinary skill in the art will recognize that the two streams could be within separate flow paths of heat exchanger 30.
In another embodiment, heavy hydrocarbons 48 can be withdrawn from the bottom of phase separator 40, expanded across liquid expansion valve 49 to create additional refrigeration for warm split 30 a (i.e., fourth refrigeration supply). As such, heavy hydrocarbons 48 can be introduced into intermediate section of heat exchanger 30 and warmed within heat exchanger 30, wherein it can be combined with first LNG stream 52 and second portion of top gas 46 prior to exiting housing 20. In one embodiment, heavy hydrocarbons 48, can be combined with first LNG stream 52 and second portion of top gas 46 within heat exchanger 30. In a preferred embodiment, first portion of top gas 44, second portion of top gas 46, and heavy hydrocarbons 48 are all preferably expanded to the substantially same pressure.
In one embodiment, a portion of stream 46 following expansion in third expansion valve 47 can be sent to storage tank 60 without being rewarmed in heat exchanger 30. In another embodiment, the portion of stream 46 can be further cooled in heat exchanger prior to being sent to storage tank 60.
Referring to FIG. 2, a process flow diagram of an embodiment of the current invention is shown, wherein the second refrigeration supply is accomplished using expansion of LNG. In FIG. 2, 156 tpd of high pressure natural gas is withdrawn at 40 bara from the high pressure natural gas pipeline. As shown in FIG. 1, it is cooled and then separated in phase separator. In this embodiment, 9 tpd of heavy hydrocarbons are expanded and warmed in warm split 30 a, while 139 tpd of second portion of top gas 46 are expanded and warmed in warm split 30 a. 8 tpd of first portion of top gas 44 are then cooled in cold split 30 b with 5 tpd of LNG being stored at 3 bara. In this embodiment, approximately 2 tpd of first LNG stream 52 is expanded and warmed in cold split 30 b and warm split 30 a, and approximately 0.8 tpd of second LNG stream 54 is expanded to 1.9 bara and then warmed in cold split 30 b and warm split 30 a, wherein it can be used as fuel gas.
Referring to FIG. 3, a process flow diagram of an embodiment of the current invention is shown, wherein the second refrigeration supply is accomplished using expansion of LIN. In FIG. 3, in order to produce the same amount of LNG (i.e., 5 tpd at 3 bara), only 140 tpd of high pressure gas is needed from the pipeline. In this embodiment, approximately 1.5 tpd of LIN, which can be stored at a temperature −176° C. can be expanded from 6.3 bara to approximately 6 bar, and warmed in cold split 30 b and warm split 30 a before being introduced to a nitrogen pipeline. In another embodiment not shown, it is possible to adjust the pressure of the nitrogen based on the need for nitrogen utility gas.
Referring to FIG. 4, a process flow diagram of an embodiment of the current invention is shown, which includes a supplemental refrigeration supply that includes natural gas expansion turbine 110. In FIG. 4, purified natural gas 12 can be split, outside or within heat exchanger 30 into first portion of purified natural gas 15 and second portion of purified natural gas 16, with first portion of purified natural gas 15 going to form LNG and first/second refrigeration supply. In this embodiment, second portion of purified natural gas 16 is preferably partially cooled in warm split 30 a and then expanded in natural gas expansion turbine 110 to form expanded natural gas 112, which is then fed into cold split 30 b and warmed therein. In another embodiment, a portion of expanded natural gas 112 can be direct either directly to LNG storage tank 60 or cooled in heat exchanger 30 before being sent to LNG storage tank 60.
While the embodiment shown in FIG. 4 does not include second portion of top gas 46 and second expansion valve 53, those of ordinary skill in the art will recognize that second portion of top gas 46 and second expansion valve 53 could be included in this embodiment. While this embodiment includes rotating equipment, the embodiment can still produce LNG without the need for any externally provided electricity for the process equipment. In the embodiment shown, natural gas expansion turbine 110 also can include oil brake B. While not shown, brake B may be replaced by an electrical generator.
Referring to FIG. 5, a process flow diagram of an embodiment of the current invention is shown, which includes a supplemental refrigeration supply that includes natural gas expansion turbine 110 and natural gas booster 120. In FIG. 5, purified natural gas 12 is again split into first portion of purified natural gas 15 and second portion of purified natural gas 16, but instead of second portion of purified natural gas 16 being first expanded, in this embodiment, second portion of purified natural gas 16 can be compressed by natural gas booster 120, cooled in aftercooler, partially cooled in warm split 30 a and then expanded in natural gas expansion turbine 110 to form expanded natural gas 112, which is then fed into cold split 30 b and warmed therein. While the embodiment shown in FIG. 5 does not include second portion of top gas 46 and second expansion valve 53, those of ordinary skill in the art will recognize that second portion of top gas 46 and second expansion valve 53 could be included in this embodiment. While this embodiment includes rotating equipment, including both a compressor and turbine, the embodiment can still produce LNG without the need for any externally provided electricity, since natural gas expansion turbine 110 powers natural gas booster 120 via a common shaft.
The term “ambient temperature” if used herein refers to the temperature of the air surrounding an object. Typically the outdoor ambient temperature is generally between about 0 to 110° F. (−18 to 43° C.).
Efficiency data for the various embodiments described herein can be found in Table I below:

TABLE I

Efficiency Data for Various Embodiments

FIG. 2	FIG. 3	FIG. 4	FIG. 5
(no turbine)	(no turbine with LIN assist)	1 Turbine/oil brake	1 Turbine/booster

INLET	NG FEED	tpd	156.3	139.6	35.5	26.2
		bara	40	40	40	40
OUTLET	LIN ASSIST	tpd	—	1.5	—	—
	NG PRODUCT	tpd	150.4	134.5	29.6	20.3
	(TAIL GAS)	bara	6	6	6	6
	NG PRODUCT	tpd	0.8	0	0.8	0.8
	(E.G., FUEL GAS)	bara	1.9	—	1.9	1.9
	LNG PRODUCT	tpd		5	5	5	5
		bara	3	3	3	3
		° C.	sat	sat	sat	sat
	TURBINE BRAKE	kW	—	—	38	32

The term “cryogenic gas” if used herein refers to a substance which is normally a gas at ambient temperature that can be converted to a liquid by pressure and/or cooling. A cryogenic gas typically has a boiling point of equal to or less than about −130° F. (−90° C.) at atmospheric pressure.
The terms “liquefied natural gas” or “LNG” as used herein refers to natural gas that is reduced to a liquefied state at or near atmospheric pressure.
The term “natural gas” as used herein refers to raw natural gas or treated natural gas. Raw natural gas is primarily comprised of light hydrocarbons such as methane, ethane, propane, butanes, pentanes, hexanes and impurities like benzene, but may also contain small amounts of non-hydrocarbon impurities, such as nitrogen, hydrogen sulfide, carbon dioxide, and traces of helium, carbonyl sulfide, various mercaptans or water. Treated natural gas is primarily comprised of methane and ethane, but may also contain small percentages of heavier hydrocarbons, such as propane, butanes and pentanes, as well as small percentages of nitrogen and carbon dioxide.
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

Claims

I claim:

1. A method for the production of liquefied natural gas (“LNG”) using a transportable apparatus, the method comprising the steps of:

providing a transportable apparatus, wherein the transportable apparatus comprises a housing, a heat exchanger, a phase separator, a first refrigeration supply, and a second refrigeration supply, wherein the first refrigeration supply and the second refrigeration supply are configured to provide refrigeration within the heat exchanger;

introducing a natural gas stream into the transportable apparatus at a first pressure under conditions effective for producing an LNG stream;

withdrawing the LNG stream from the transportable apparatus; and

withdrawing a warm natural gas stream from the transportable apparatus, wherein the warm natural gas stream is at a second pressure, wherein the second pressure is lower than the first pressure.

2. The method as claimed in claim 1, wherein the first refrigeration supply comprises a first expansion valve, a first LNG inlet disposed on a cold end of the heat exchanger, and a first natural gas outlet disposed on a warm end of the heat exchanger, wherein the first refrigeration supply is in fluid communication with a liquid outlet disposed on the cold end of the heat exchanger, wherein the heat exchanger is configured to indirectly exchange heat between a first LNG stream and the natural gas stream when the first LNG stream flows from the first LNG inlet to first natural gas outlet.

3. The method as claimed in claim 2, wherein the second refrigeration supply comprises a liquid nitrogen inlet disposed on the cold end of the heat exchanger and a nitrogen outlet disposed on the warm end of the heat exchanger, and wherein the heat exchanger is configured to indirectly exchange heat between a liquid nitrogen fluid and the natural gas stream when the liquid nitrogen flows from the liquid nitrogen inlet to the nitrogen outlet.

4. The method as claimed in claim 3, wherein the second refrigeration supply further comprises a liquid nitrogen storage tank in fluid communication with the liquid nitrogen inlet, such that the liquid storage tank is configured to deliver liquid nitrogen to the heat exchanger via the liquid nitrogen inlet.

5. The method as claimed in claim 2, wherein the second refrigeration supply comprises a second expansion valve, a second LNG inlet disposed on the cold end of the heat exchanger, and a second natural gas outlet disposed on the warm end of the heat exchanger, and wherein the heat exchanger is configured to indirectly exchange heat between a second LNG stream and the natural gas stream when the second LNG stream flows from the second LNG inlet to second natural gas outlet.

6. The method as claimed in claim 5, wherein the first expansion valve is configured to expand the first LNG stream to a first LNG pressure, wherein the second expansion valve is configured to expand the second LNG stream to a second LNG pressure, wherein the first LNG pressure is higher than the second LNG pressure.

7. The method as claimed in claim 6, wherein the first LNG pressure is between 4 and 10 bara, wherein the second LNG pressure is between 1 to 2 bara.

8. The method as claimed in claim 1, wherein portable apparatus further comprises a natural gas feed inlet configured to accept a stream of pressurized natural gas originating from outside the housing,

wherein the heat exchanger is in fluid communication with the natural gas feed inlet, such that the heat exchanger is configured to receive the stream of pressurized natural gas from the natural gas feed inlet, wherein the heat exchanger has a warm end, a cold end, and an intermediate section,

wherein phase separator has a fluid inlet, a gaseous outlet, and a liquid outlet, wherein the fluid inlet is in fluid communication with a first intermediate fluid outlet located in the intermediate section of the heat exchanger, such that the phase separator is configured to receive a partially cooled fluid from the heat exchanger, wherein the liquid outlet of the phase separator is in fluid communication with a first intermediate fluid inlet of the intermediate section of the heat exchanger, wherein the gaseous outlet of the phase separator is in fluid communication with a second intermediate fluid inlet of the intermediate section of the heat exchanger, such that the second intermediate fluid inlet of the intermediate section of the heat exchanger is configured to receive at least a first portion of gas coming from the phase separator,

wherein the transportable apparatus further comprises a third intermediate fluid inlet of the intermediate section of the heat exchanger that is configured to receive a second portion of gas coming from the phase separator.

9. The method as claimed in claim 8, further comprising a third expansion valve in fluid communication with, and disposed inline between, the gaseous outlet of the phase separator and a second intermediate fluid inlet of the intermediate section of the heat exchanger.

10. The method as claimed in claim 8, further comprising a lower pressure natural gas outlet in fluid communication with the first natural gas outlet of the heat exchanger, wherein the lower pressure natural gas outlet is configured to send a stream warm natural gas received from the first natural gas outlet to outside of the housing.

11. The method as claimed in claim 8, further comprising a liquid expansion valve in fluid communication with, and disposed inline between, the liquid outlet of the phase separator and the first intermediate fluid inlet of the intermediate section of the heat exchanger;

12. The method as claimed in claim 8, wherein the heat exchanger is split into a first portion and a second portion, wherein the warm end of the heat exchanger is disposed in the first portion, wherein the cold end of the heat exchanger is disposed in the second portion, wherein the intermediate section is disposed in both the first portion and the second portion.

13. The method as claimed in claim 1, further comprising an absence of compressing the natural gas stream within the transportable apparatus.

14. The method as claimed in claim 1, wherein the transportable apparatus comprises an absence of a rotating compressor.

15. The method as claimed in claim 1, wherein the transportable apparatus comprises an absence of rotating machinery.

16. The method as claimed in claim 1, wherein the transportable apparatus comprises an absence of electrically powered compression or expansion devices.

17. The method as claimed in claim 1, further comprising an absence of a step of providing external electric power to the transportable apparatus.

18. The method as claimed in claim 1, wherein the step of providing the transportable apparatus comprises loading the transportable apparatus on a truck or barge and transporting the transportable apparatus from a first location to a second location.

19. The method as claimed in claim 1, wherein the heat exchanger, the phase separator, the first refrigeration supply, and the second refrigeration supply are all disposed within the housing.

20. The method as claimed in claim 1, wherein the combined flow rates of refrigerant through the first refrigeration supply and the second refrigeration supply are less than 10% of the flow of the natural gas stream into the transportable apparatus at the first pressure.

21. The method as claimed in claim 1, wherein the warm natural gas stream at the second pressure is burned as fuel in a purification unit.