Patent Application
20170016668
The invention relates to the liquefaction of natural gas to form liquefied natural gas (LNG), and more specifically, to the production of LNG in remote or sensitive areas where the construction and/or maintenance of capital facilities, and/or the environmental impact of a conventional LNG plant may be detrimental.
LNG production is a rapidly growing means to supply natural gas from locations with an abundant supply of natural gas to distant locations with a strong demand of natural gas. The conventional LNG cycle includes: a) initial treatments of the natural gas resource to remove contaminants such as water, sulfur compounds and carbon dioxide; b) the separation of some heavier hydrocarbon gases, such as propane, butane, pentane, etc. by a variety of possible methods including self-refrigeration, external refrigeration, lean oil, etc.; c) refrigeration of the natural gas substantially by external refrigeration to form LNG at near atmospheric pressure and about −160° C.; d) transport of the LNG product in ships or tankers designed for this purpose to a market location; e) re-pressurization and re-gasification of the LNG to a pressurized natural gas that may distributed to natural gas consumers. Step (c) of the conventional LNG cycle usually requires the use of large refrigeration compressors often powered by large gas turbine drivers that emit substantial carbon and other emissions. Large capital investments in the billions of US dollars and extensive infrastructure are required as part of the liquefaction plant. Step (e) of the conventional LNG cycle generally includes re-pressurizing the LNG to the required pressure using cryogenic pumps and then re-gasifying the LNG to pressurized natural gas by exchanging heat through an intermediate fluid but ultimately with seawater or by combusting a portion of the natural gas to heat and vaporize the LNG. Generally, the available exergy of the cryogenic LNG is not utilized.
A cold refrigerant produced at a different location, such as liquefied nitrogen gas (“LIN”), can be used to liquefy natural gas. A process known as the LNG-LIN concept relates to a non-conventional LNG cycle in which at least Step (c) above is replaced by a natural gas liquefaction process that substantially uses liquid nitrogen (LIN) as an open loop source of refrigeration and in which Step (e) above is modified to utilize the exergy of the cryogenic LNG to facilitate the liquefaction of nitrogen gas to form LIN that may then be transported to the resource location and used as a source of refrigeration for the production of LNG. U.S. Pat. No. 3,400,547 describes shipping liquid nitrogen or liquid air from a market place to a field site where it is used to liquefy natural gas. U.S. Pat. No. 3,878,689 describes a process to use LIN as the source of refrigeration to produce LNG. U.S. Pat. No. 5,139,547 describes the use of LNG as a refrigerant to produce LIN.
The LNG-LIN concept further includes the transport of LNG in a ship or tanker from the resource location to the market location and the reverse transport of LIN from the market location to the resource location. The use of the same ship or tanker, and perhaps the use of common onshore tankage, are expected to minimize costs and required infrastructure. As a result, some contamination of the LNG with LIN and some contamination of the LIN with LNG may be expected. Contamination of the LNG with LIN is likely not to be a major concern as natural gas specifications (such as those promulgated by the United States Federal Energy Regulatory Commission) for pipelines and similar distribution means allow for some inert gas to be present. However, since the LIN at the resource location will ultimately be vented to the atmosphere, contamination of the LIN with LNG (a greenhouse gas more than 20 times as impactful as Carbon Dioxide) must be reduced to levels acceptable for such venting. Techniques to remove the residual contents of tanks are well known but it may not be economic or environmentally acceptable to achieve the needed low level of contamination to avoid treatment of the LIN or vaporized nitrogen at the resource location prior to venting the gaseous nitrogen (GAN).
United States Patent Application Publication No. 2010/0251763 describes a variation of the LNG liquefaction process using both LIN and liquefied carbon dioxide (CO2) as refrigerants. While CO2 is itself a greenhouse gas, it is less likely that liquefied CO2 will share storage or transport facilities with LNG or other greenhouse gases and so contamination is unlikely. However, the LIN may be similarly contaminated as described above and should be decontaminated prior to venting of the resulting GAN streams. In addition, the LNG liquefaction system may be supplemented by pre-chilling of the natural gas with a propane, mixed component or other closed refrigeration cycle in addition to the once-through refrigeration provided by vaporization of the LIN. In these cases, decontamination of the gaseous nitrogen may still be required prior to venting the GAN. What is needed is a method of using LIN as a coolant to produce LNG, where if the LIN and the LNG use common storage to facilities, any greenhouse gas present in the LIN can be efficiently removed.
The invention provides a liquefied natural gas production system. A natural gas stream is supplied from a supply of natural gas. A refrigerant stream is supplied from a refrigerant supply. At least one heat exchanger exchanges heat between the refrigerant stream and the natural gas stream to at least partially vaporize the refrigerant stream and at least partially condense the natural gas stream. A natural gas compressor compresses the natural gas stream to a pressure of at least 135 bara to form a compressed natural gas stream. A natural gas cooler cools the compressed natural gas stream after being compressed by the natural gas compressor. A natural gas expander expands the compressed natural gas to a pressure less than 200 bara, but no greater than the pressure to which the natural gas compressor compresses the natural gas stream, after being cooled by the natural gas cooler. The natural gas expander is connected to the at least one heat exchanger to supply natural gas thereto.
The invention also provides a method of producing liquefied natural gas (LNG). A natural gas stream is supplied from a supply of natural gas. A refrigerant stream is provided from a refrigerant supply. The natural gas stream and the liquefied nitrogen stream are passed through a first heat exchanger that exchanges heat between the refrigerant stream and the natural gas stream to at least partially vaporize the refrigerant stream and at least partially condense the natural gas stream. The natural gas stream is compressed in a natural gas compressor to a pressure of at least 135 bara to form a compressed natural gas stream. The compressed natural gas stream is cooled in a natural gas cooler after being compressed by the natural gas compressor. After being cooled by the natural gas cooler, the compressed natural gas stream is expanded, in a natural gas expander, to a pressure less than 200 bara, but no greater than the pressure to which the natural gas compressor compresses the natural gas stream. Natural gas is supplied from the natural gas cooler to the at least one heat exchanger to be at least partially condensed therein.
The invention further provides a method of removing greenhouse gas contaminants in a liquid nitrogen stream used to liquefy a natural gas stream. The natural gas stream is compressed in a natural gas compressor to a pressure of at least 135 bara to form a compressed natural gas stream. The compressed natural gas stream is cooled in a natural gas cooler after being compressed by the natural gas compressor. After being cooled by the natural gas cooler, the compressed natural gas stream is expanded in a natural gas expander to a pressure less than 200 bara, but no greater than the pressure to which the natural gas compressor compresses the natural gas stream. The natural gas stream and the liquefied nitrogen stream are passed through a first heat exchanger that exchanges heat between the liquefied nitrogen stream and the natural gas stream to at least partially vaporize the liquefied nitrogen stream and at least partially condense the natural gas stream. The liquefied nitrogen stream is circulated through the first heat exchanger at least three times. A pressure of the at least partially vaporized nitrogen stream is reduced using at least one expander service. A greenhouse gas removal unit is provided that includes a distillation column and heat pump condenser and reboiler system. The pressure and condensing temperature of an overhead stream of the distillation column is increased. The overhead stream of the distillation column overhead stream and a bottoms stream of the distillation column are cross-exchanged to affect both an overhead condenser duty and a bottom reboiler duty of the distillation column. The pressure of the distillation column overhead stream after the cross-exchanging step to produce a reduced-pressure distillation column overhead stream is reduced. The reduced-pressure distillation column overhead stream is separated to produce a first separator overhead stream. The first separator overhead stream is gaseous nitrogen that exits the greenhouse gas removal unit having greenhouse gases removed therefrom. The first separator overhead stream is vented to atmosphere.
Various specific embodiments and versions of the present invention will now be described, including preferred embodiments and definitions that are adopted herein. While the following detailed description gives specific preferred embodiments, those skilled in the art will appreciate that these embodiments are exemplary only, and that the present invention can be practiced in other ways. Any reference to the “invention” may refer to one or more, but not necessarily all, of the embodiments defined by the claims. The use of headings is for purposes of convenience only and does not limit the scope of the present invention. For purposes of clarity and brevity, similar reference numbers in the several Figures represent similar items, steps, or structures and may not be described in detail in every Figure.
All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.
As used herein, the term “compressor” means a machine that increases the pressure of a gas by the application of work. A “compressor” or “refrigerant compressor” includes any unit, device, or apparatus able to increase the pressure of a gas stream. This includes compressors having a single compression process or step, or compressors having multi-stage compressions or steps, or more particularly multi-stage compressors within a single casing or shell. Evaporated streams to be compressed can be provided to a compressor at different pressures. Some stages or steps of a cooling process may involve two or more compressors in parallel, series, or both. The present invention is not limited by the type or arrangement or layout of the compressor or compressors, particularly in any refrigerant circuit.
As used herein, “cooling” broadly refers to lowering and/or dropping a temperature and/or internal energy of a substance by any suitable, desired, or required amount. Cooling may include a temperature drop of at least about 1° C., at least about 5° C., at least about 10° C., at least about 15° C., at least about 25° C., at least about 35° C., or least about 50° C., or at least about 75° C., or at least about 85° C., or at least about 95° C., or at least about 100° C. The cooling may use any suitable heat sink, such as steam generation, hot water heating, cooling water, air, refrigerant, other process streams (integration), and combinations thereof. One or more sources of cooling may be combined and/or cascaded to reach a desired outlet temperature. The cooling step may use a cooling unit with any suitable device and/or equipment. According to some embodiments, cooling may include indirect heat exchange, such as with one or more heat exchangers. In the alternative, the cooling may use evaporative (heat of vaporization) cooling and/or direct heat exchange, such as a liquid sprayed directly into a process stream.
As used herein, the term “expansion device” refers to one or more devices suitable for reducing the pressure of a fluid in a line (for example, a liquid stream, a vapor stream, or a multiphase stream containing both liquid and vapor). Unless a particular type of expansion device is specifically stated, the expansion device may be (1) at least partially by isenthalpic means, or (2) may be at least partially by isentropic means, or (3) may be a combination of both isentropic means and isenthalpic means. Suitable devices for isenthalpic expansion of natural gas are known in the art and generally include, but are not limited to, manually or automatically, actuated throttling devices such as, for example, valves, control valves, Joule-Thomson (J-T) valves, or venturi devices. Suitable devices for isentropic expansion of natural gas are known in the art and generally include equipment such as expanders or turbo expanders that extract or derive work from such expansion. Suitable devices for isentropic expansion of liquid streams are known in the art and generally include equipment such as expanders, hydraulic expanders, liquid turbines, or turbo expanders that extract or derive work from such expansion. An example of a combination of both isentropic means and isenthalpic means may be a Joule-Thomson valve and a turbo expander in parallel, which provides the capability of using either alone or using both the J-T valve and the turbo expander simultaneously. Isenthalpic or isentropic expansion can be conducted in the all-liquid phase, all-vapor phase, or mixed phases, and can be conducted to facilitate a phase change from a vapor stream or liquid stream to a multiphase stream (a stream having both vapor and liquid phases) or to a single-phase stream different from its initial phase. In the description of the drawings herein, the reference to more than one expansion device in any drawing does not necessarily mean that each expansion device is the same type or size.
The term “gas” is used interchangeably with “vapor,” and is defined as a substance or mixture of substances in the gaseous state as distinguished from the liquid or solid state. Likewise, the term “liquid” means a substance or mixture of substances in the liquid state as distinguished from the gas or solid state.
A “heat exchanger” broadly means any device capable of transferring heat energy or cold energy from one medium to another medium, such as between at least two distinct fluids. Heat exchangers include “direct heat exchangers” and “indirect heat exchangers.” Thus, a heat exchanger may be of any suitable design, such as a co-current or counter-current heat exchanger, an indirect heat exchanger (e.g. a spiral wound heat exchanger or a plate-fin heat exchanger such as a brazed aluminum plate fin type), direct contact heat exchanger, shell-and-tube heat exchanger, spiral, hairpin, core, core-and-kettle, printed-circuit, double-pipe or any other type of known heat exchanger. “Heat exchanger” may also refer to any column, tower, unit or other arrangement adapted to allow the passage of one or more streams therethrough, and to affect direct or indirect heat exchange between one or more lines of refrigerant, and one or more feed streams.
As used herein, the term “indirect heat exchange” means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other. Core-in-kettle heat exchangers and brazed aluminum plate-fin heat exchangers are examples of equipment that facilitate indirect heat exchange.
As used herein, the term “natural gas” refers to a multi-component gas obtained from a crude oil well (associated gas) or from a subterranean gas-bearing formation (non-associated gas). The composition and pressure of natural gas can vary significantly. A typical natural gas stream contains methane (C1) as a significant component. The natural gas stream may also contain ethane (C2), higher molecular weight hydrocarbons, and one or more acid gases. The natural gas may also contain minor amounts of contaminants such as water, nitrogen, iron sulfide, wax, and crude oil.
Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are contemplated unless otherwise indicated. All numerical values are “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.
All patents, test procedures, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted.
Described herein are systems and processes relating to the natural gas liquefaction process using once-through LIN as a primary refrigerant to remove a substantial portion of residual LNG contamination of the LIN prior to venting of the gaseous hydrogen. Specific embodiments of the invention include those set forth in the following paragraphs as described with reference to the Figures. While some features are described with particular reference to only one Figure (such as
After the LIN passes through the first heat exchanger 22 and the second heat exchanger 26, it is expected that the LIN and any greenhouse gas contaminants will be fully vaporized to form a contaminated gaseous nitrogen (cGAN) stream 27. As the gaseous nitrogen is processed as further described, it may not be fully vaporized even though it is described herein as gaseous nitrogen or cGAN. For the sake of simplicity any mixture of gaseous and partially condensed nitrogen is still noted as cGAN or gaseous nitrogen.
The cGAN stream 27 is directed to a first expander 28. The output stream of the first expander 28, which is an expanded cGAN stream 29, is directed a greenhouse gas removal unit 30. The pressure of the expanded cGAN stream 29 may range from 5 bara to 30 bara based largely upon the phase envelope of the cGAN mixture, which typically is a mixture of nitrogen, methane, ethane, propane and other potential greenhouse gases. In one aspect, the pressure of the expanded cGAN stream 29 is between 19 and 20 bara and the temperature of the expanded cGAN stream 29 is about −153 degrees Celsius. However, the pressure of the expanded cGAN stream may be as low as 1 bara if alternative removal technologies, such as adsorption, absorption, or catalytic processes are used.
The greenhouse gas removal unit 30 may be required to produce a GAN stream with greenhouse gas content of less than 500 ppm, or less than 200 ppm, or less than 100 ppm, or less than 50 ppm, or less than 20 ppm. The greenhouse gas removal unit 30 may be required to produce a greenhouse gas product stream with a nitrogen content of less than 80%, or less than 50%, or less than 20%, or less than 10%, or less than 5%.
The greenhouse gas removal unit 30 may include a partially refluxed and partially re-boiled distillation column 32. The distillation column 32 separates the gaseous nitrogen from the greenhouse gas contaminants based on the differences in vaporization temperatures of nitrogen and the greenhouse gases. The outputs of the distillation column are an overhead stream 34, which is a decontaminated gaseous nitrogen stream, and a bottoms product, which is a greenhouse gas product stream 36. Side-re-boilers, side condensers and intermediate draws (not shown) may be included to remove products at other locations in the distillation column 32.
The greenhouse gas removal unit 30 may include an overhead condenser associated with the distillation column 32 and having a cooling duty supplied by heat exchange with LIN, GAN, cGAN, natural gas or LNG sources from other parts of the LNG Production System, or even from a supplemental refrigeration system. Similarly, the greenhouse gas removal unit may include a bottoms reboiler associated with the distillation column 32 and having a heating duty supplied by heat exchange with LIN, GAN, cGAN, natural gas or LNG from other parts of the LNG Production System or another process external to the LNG Production System. The disadvantage of these types of arrangements is the adverse impact of the largely condensing and largely boiling-type heating requirements of the distillation column condenser and reboiler on the overall heating and cooling curves to condense the natural gas to LNG. These impacts may result in temperature pinches in the heat exchangers that diminish the effectiveness of the available LIN supply. According to the invention, the condenser and reboiler cooling and heating duties are cross-exchanged such that the cold duty available from the reboiler is used to meet the hot duty required of the condenser. To accomplish this, a heat pump condenser and reboiler system is used to increase the pressure of the distillation column overhead stream 34 such that the temperature of the compressed overhead stream is higher than the temperature of the greenhouse gas product stream 36. Specifically, the heat pump condenser and reboiler system comprises an overhead compressor 38 that compresses and warms the overhead stream 34, a heat pump heat exchanger 40 that cools the overhead stream and warms the greenhouse gas product stream, and a pressure reduction device 42 that reduces the pressure of the cooled overhead stream and reduces its pressure. The pressure reduction device 42 may be a Joule-Thomson valve or a turbo-expander. At this point the overhead stream has become a partially condensed overhead stream 43. If desired, a first separator 44 may be used to separate the partially condensed overhead stream 43 to form an overhead product stream 45 and a column reflux stream 46. The overhead product stream 45, being the overhead product of both the distillation column 32 and the first separator 44, is comprised of GAN substantially decontaminated of greenhouse gases such as methane, ethane, etc., and exits the greenhouse gas removal unit 30 for further heat exchange operations and venting as will be described herein. Because the column reflux stream 46 may include some greenhouse gases, the column reflux stream is sent back to the distillation column 32 for further separation steps.
The other portion of the heat pump condenser and reboiler system may include a bottoms pump 48 to deliver the greenhouse gas product stream 36 to the heat pump heat exchanger 40 at an increased pressure. After being heated in the heat pump heat exchanger 40, the greenhouse gas product stream 36 is now partially vaporized and may be sent to a second separator 50, which separates the partially vaporized greenhouse gas product stream to form a separated greenhouse gas product stream 54 and a column reboiler vapor stream 56. A greenhouse gas pump 58 may be used to deliver the separated greenhouse gas product stream 54 to another location in system 10 at a required pressure. In the embodiment shown in
The overhead product stream 45, which is substantially decontaminated GAN, exits the greenhouse gas removal unit 30 and passes iteratively through the second heat exchanger 26 and second and third expanders 60, 62 to further cool the natural gas stream 24. In
After passing through the third expander 62 and the second heat exchanger 26 for the final time, the overhead product stream 45 passes through a third heat exchanger 64 that cools the natural gas stream 24 an additional time. The overhead product stream, which as previously stated is GAN, is vented to the atmosphere at GAN vent 66 or is otherwise disposed of. If the GAN is vented, the GAN plume should be sufficiently buoyant to be widely distributed and diluted by the atmosphere prior to any significant part of the plume returning to near ground level, which may cause a potentially hazardous oxygen deficiency. Since the GAN is likely to have essentially zero relative humidity and a specific gravity only slightly less than the ambient air, embodiments should ensure GAN vent temperatures greater than the local ambient temperature to improve buoyancy and promote dispersal of the GAN plume. Those skilled in the art of vent and vent stack design are aware of alternatives to temperature to improve plume dispersal, including modifying stack height and providing a higher velocity stack exit that, as an example, may be provided by a venturi feature as part of the stack design.
The path of natural gas through system 10 will now be described. The natural gas supply 20 is received at pressure, or is compressed to a desired pressure, and then flows through various heat exchangers in series, parallel or a combination of series and parallel to be cooled by the refrigerant or refrigerants. The natural gas pressure supplied to the system 10 is typically between 20 bara and 100 bara with the upper pressure generally limited by the economic selection of heat exchange equipment. With future advances in heat exchanger design, supply pressure of 200 bara or more may be feasible. In a preferred embodiment, the natural gas supply pressure is selected at about 90 bara. Those skilled in the art are aware that increasing the natural gas supply pressure generally improves the heat transfer effectiveness within an LNG liquefaction process. As shown in
After exiting the first heat exchanger, the natural gas stream 24 is chilled and condensed at pressure in the second heat exchanger 26, where the natural gas stream is cooled by several passes of the GAN in the overhead product stream 45. The natural gas stream 24 is merged with the separated greenhouse gas product stream 54, which as previously described is greenhouse gases with substantially all GAN removed therefrom. The natural gas stream 24 then passes through the first heat exchanger 22, which uses LIN from the LIN supply system 14 to cool the natural gas stream 24. The first heat exchanger 22 may be eliminated from system 10 if desired. At this point the natural gas in the natural gas stream 24 has been substantially completely liquefied to form LNG. The condensed high pressure LNG is reduced to near ambient pressure through a pressure reduction device 68 that may comprise a single-phase or multi-phase hydraulic turbine, Joule-Thomson valve or a similar pressure reduction device.
The distillation column 32 of the greenhouse gas removal unit 30 may be controlled to meet required specifications for greenhouse gas content of the overhead product stream 45 and the nitrogen content of the greenhouse gas product stream 36 and/or the separated greenhouse gas product stream 54. Generally, the temperature and fraction vaporized of the expanded cGAN stream 29 will affect the relative condenser and reboiler duties, with higher fraction vaporized or higher temperatures of the expanded cGAN stream 29 increasing the condenser duty while decreasing the reboiler duty at the same product specifications. Lower fraction vaporized or lower temperatures of the expanded cGAN stream 29 have the opposite effects. In addition, an increase (or decrease) of the heat transfer rate within the heat pump heat exchanger 40 tends to increase (or decrease) both the condenser and reboiler duties that affect the product specifications. A controller 72 to adjust both the temperature and/or fraction vaporized of the expanded cGAN stream 29 and the heat pump heat exchanger 40 heat transfer rate may be used to both balance the condenser and reboiler duties (with adjustments for the extra energy added by the overhead compressor 38) and the product specifications of the distillation column 32. In practice, these controls may be realized by adjusting the inlet temperature of the first turbo-expander 28 and by controlling the pressure increase of the column overhead compressor 38. Alternatively, other components of the system 10 may be controlled to achieve the same outcome.
Having described an embodiment of the invention, additional aspects will now be described.
The included figures each depict a greenhouse gas removal unit 30 as part of an LNG production system 10, 200, 300, 400, 500, 600, 700, 800, where the greenhouse gas removal unit is depicted as based on distillation technologies and methodologies. Alternative systems and methods may be used to remove the greenhouse gas contaminants of the LIN supply 14. These alternative methods are not shown in detail but may include: adsorption processes including pressure-swing, temperature-swing or a combination of pressure and temperature-swing adsorption; bulk adsorption or absorption such as by an activated carbon bed; or catalytic processes.
The heat exchangers in the disclosed embodiments have been described as being cooled by solely by LIN, GAN, or a combination thereof, sourced from the LIN supply 14. However, it is possible to increase the cooling capability of any of the disclosed heat exchangers by employing a supplemental refrigeration system having no fluid connection with the natural gas or nitrogen in the LNG production system 10. The refrigerant used by the supplemental refrigeration system may comprise any suitable hydrocarbon gas (e.g., alkenes or alkanes such as methane, ethane, ethylene, propane, etc.), inert gases (e.g., nitrogen, helium, argon, etc.), or other refrigerants known to those skilled in the art.
A supplemental refrigeration system similar to supplemental refrigeration system 900 may be used to increase the cooling effectiveness of other heat exchangers disclosed herein, such as the first heat exchanger 22, second heat exchanger 26, third heat exchanger 64, and/or the feed-effluent heat exchanger 606. Further, while the refrigerant of the supplemental refrigeration system 900 is not fluidly connected to the LNG production system 10, in some embodiments the refrigerant may be sourced from natural gas streams and/or nitrogen streams of the LNG production system. Further, the supplemental heat exchanger 904 may exchange heat (or cold) with gaseous streams and/or liquid streams of the LNG production system 10, such as the LIN stream 12, natural gas stream 24, cGAN stream 27, or the greenhouse gas product stream 36.
The embodiments and aspects provide an effective method of removing greenhouse gas contaminants from an LIN stream used to liquefy natural gas. An advantage of the invention is that the heat pump system in the greenhouse gas removal unit 30 removes the necessity of external heating or cooling sources to separate the greenhouse gases from the nitrogen.
Another advantage of the efficient removal of greenhouse gases from LIN is that LIN storage facilities can more economically be used as LNG storage facilities, thereby reducing the areal footprint of natural gas processing facilities.
Still another advantage is that the gaseous nitrogen may be vented without the unwanted release of greenhouse gases into the atmosphere.
Although exemplary embodiments discussed herein in with respect to
Embodiments of the invention may include any combinations of the methods and systems shown in the following numbered paragraphs. This is not to be considered a complete listing of all possible embodiments, as any number of variations can be envisioned from the description above.
a natural gas stream from a supply of natural gas;
a refrigerant stream from a refrigerant supply;
at least one heat exchanger that exchanges heat between the refrigerant stream and the natural gas stream to at least partially vaporize the refrigerant stream and at least partially condense the natural gas stream;
a natural gas compressor that compresses the natural gas stream to a pressure of at least 135 bara to form a compressed natural gas stream;
a natural gas cooler that cools the compressed natural gas stream after being compressed by the natural gas compressor; and
a natural gas expander that expands the compressed natural gas to a pressure less than 200 bara, but no greater than the pressure to which the natural gas compressor compresses the natural gas stream, after being cooled by the natural gas cooler;
wherein the natural gas expander is connected to the at least one heat exchanger to supply natural gas thereto.
providing a natural gas stream from a supply of natural gas;
providing a refrigerant stream from a refrigerant supply;
passing the natural gas stream and the liquefied nitrogen stream through a first heat exchanger that exchanges heat between the refrigerant stream and the natural gas stream to at least partially vaporize the refrigerant stream and at least partially condense the natural gas stream;
compressing the natural gas stream in a natural gas compressor to a pressure of at least 135 bara to form a compressed natural gas stream;
cooling, in a natural gas cooler, the compressed natural gas stream after being compressed by the natural gas compressor; and
expanding, in a natural gas expander, the compressed natural gas to a pressure less than 200 bara, but no greater than the pressure to which the natural gas compressor compresses the natural gas stream, after being cooled by the natural gas cooler; and
supplying natural gas from the natural gas cooler to the at least one heat exchanger to be at least partially condensed therein.
increasing a pressure and condensing temperature of an overhead stream of the distillation column;
cross-exchanging the overhead stream of the distillation column and a bottoms stream of the distillation column to affect both an overhead condenser duty and a bottom reboiler duty of the distillation column;
reducing a pressure of the distillation column overhead stream after the cross-exchanging step to produce a reduced-pressure distillation column overhead stream; and
separating the reduced-pressure distillation column overhead stream to produce a first separator overhead stream, wherein the first separator overhead stream is gaseous nitrogen that exits the greenhouse gas removal unit having greenhouse gases removed therefrom.
compressing the natural gas stream in a natural gas compressor to a pressure of at least 135 bara to form a compressed natural gas stream;
cooling, in a natural gas cooler, the compressed natural gas stream to near ambient temperature after being compressed by the natural gas compressor; and
expanding, in a natural gas expander, the compressed natural gas to a pressure less than 200 bara, but no greater than the pressure to which the natural gas compressor compresses the natural gas stream, after being cooled by the natural gas cooler;
passing the natural gas stream and the liquefied nitrogen stream through a first heat exchanger that exchanges heat between the liquefied nitrogen stream and the natural gas stream to at least partially vaporize the liquefied nitrogen stream and at least partially condense the natural gas stream, wherein the liquefied nitrogen stream is circulated through the first heat exchanger at least three times;
reducing a pressure of the at least partially vaporized nitrogen stream using at least one expander service;
providing a greenhouse gas removal unit that includes a distillation column and heat pump condenser and reboiler system;
increasing a pressure and condensing temperature of an overhead stream of the distillation column;
cross-exchanging the overhead stream of the distillation column overhead stream and a bottoms stream of the distillation column to affect both an overhead condenser duty and a bottom reboiler duty of the distillation column;
reducing a pressure of the distillation column overhead stream after the cross-exchanging step to produce a reduced-pressure distillation column overhead stream;
separating the reduced-pressure distillation column overhead stream to produce a first separator overhead stream, wherein the first separator overhead stream is gaseous nitrogen that exits the greenhouse gas removal unit having greenhouse gases removed therefrom; and
venting the first separator overhead stream to atmosphere.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims the priority benefit of U.S. Patent Application No. 62/192,657 filed Jul. 15, 2015 entitled INCREASING EFFICIENCY IN AN LNG PRODUCTION SYSTEM BY PRE-COOLING A NATURAL GAS FEED STREAM, the entirety of which is incorporated by reference herein. This application is related to the U.S. Provisional Patent Application No. 62/192,654 titled “Liquefied Natural Gas Production System and Method with Greenhouse Gas Removal,” having common inventors and assignee and filed on an even date herewith, the disclosure of which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62192657 | Jul 2015 | US |
