MXPA99011351A - Process for liquefying a natural gas stream containing at least one freezable component - Google Patents

Abstract

This invention is a process for producing pressurized liquid (19) rich in methane from a multi-component feed stream (10) containing methane and a freezable component having a relative volatility less than that of methane. The multi-component feed stream (10) is introduced into a separation system (31) having a freezing section operating at a pressure above about 1,380 kPa (200 psia) and under solids forming conditions for the freezable component and a distillation section positioned below the freezing section. The separation system (31) produces a vapor stream (14) rich in methane and a liquid stream (12) rich in the freezable component. At least a portion of the vapor stream is cooled to produce a liquefied stream rich in methane having a temperature above about -112°C (-170°F) and a pressure sufficient for the liquid to be at or below its bubble point to produce a product (20) and a stream (21) to provide refrigeration to the separation system.

Description

PROCESS P7ARA LICUATION OF A NATURAL GAS CURRENT CONTAINING AT LEAST A FROZEN COMPONENT DESCRIPTION OF THE INVENTION This invention relates to a natural gas liquefaction process, and more particularly it relates to a process for producing pressurized liquid natural gas (PLNG) of a stream of natural gas containing at least one freeze component. Due to its clean burning qualities and convenience, natural gas has been widely used in recent years. Many sources of natural gas are located in remote areas, at great distances from any of the commercial markets for gas. Sometimes the pipeline is available to transport the produced natural gas to a commercial market. When pipeline transportation is not feasible, the natural gas produced is often processed into liquefied natural gas (which is called "LNG") to transport to the market. One of the hallmarks of an LNG plant is the large capital investment required for the plant. The equipment used to liquefy natural gas is usually very expensive. The liquified plant is made up of several basic systems, including gas treatment to remove impurities, liquefaction, refrigeration, energy facilities and storage and loading facilities. While the cost of an LNG plant can vary widely depending on the location of the plant, a conventional LNG project can cost from $ 5 thousand to $ 10 billion, including field development costs. The plant's cooling systems can add up to 30 percent of the cost. LNG refrigeration systems are costly because much refrigeration is required to liquefy natural gas. A typical natural gas stream enters an LNG plant at pressures from about 4,830 kPa (700 psia) to about 7,600 kPa (1,100 psia) and temperatures of about 20 ° C, at about 40 ° C. Natural gas, which is predominantly methane, can not be liquefied by simply increasing the pressure, as is the case with the heavier hydrocarbons used for energy purposes. The critical temperature of methane is -82.5 ° C. This means that methane can only liquefy below that temperature despite the applied pressure. Since natural gas is a mixture of gases, it liquefies over a wide range of temperatures. The critical temperature of natural gas is between -85 ° C and -62 ° C. Typically, natural gas compositions at atmospheric pressure will liquefy in the temperature range of between about -165 ° C and -155 ° C. Since refrigeration equipment represents a significant part of the cost of LNG installation, considerable effort has been made to reduce cooling costs. Many systems exist in the prior art for the liquefaction of a natural gas by the sequential passage of the gas at an elevated pressure through a plurality of cooling stages whereby the gas is cooled to successively lower temperatures until the gas is liquefied. gas. Conventional liquefaction cools the gas to a temperature of about -160 ° C or near atmospheric pressure. Cooling is generally achieved by thermal exchange with one or more refrigerants such as propane, propylene, ethane, ethylene and methane. Although many refrigeration cycles have been used to liquefy natural gas, the three types most commonly used in LNG plants today are: (1) "cascade cycle" using multiple individual component refrigerants in placed heat exchangers progressively to reduce the gas temperature to a liquefaction temperature, (2) "expander cycle" which expands the gas from a high pressure to a low pressure with a corresponding reduction in temperature, and (3) "refrigeration cycle Multiple component "using a multi-component refrigerant in specially designed exchangers. Most natural gas liquefaction cycles use variations or combinations of these three basic types. In conventional LNG plants, water, carbon dioxide, sulfur-containing compounds, such as hydrogen sulfide and other acid gases, n-pentane and heavy hydrocarbons, including benzene, must be substantially removed from natural gas processing, below levels of parts by million (ppm). Some of these compounds will freeze, causing clogging problems in the process equipment. Other compounds, such as those containing sulfur, are typically removed to meet sales specifications. In a conventional LNG plant, gas treatment equipment is required to remove carbon dioxide and acid gases. The gas treatment equipment normally uses a regenerative process of chemical and / or physical solvent and requires a significant capital investment. Likewise, operating costs are high. Dry-bed dehydrates, such as molecular sieves, are required to remove water vapor. A washing column and fractionation equipment are normally used to remove hydrocarbons that tend to cause clogging problems. The mercury is also removed in a conventional LNG plant, since it can cause faults in the equipment built with aluminum. In addition, a large portion of the nitrogen that may be present in natural gas is removed after processing, since nitrogen does not remain in the liquid phase during conventional LNG transport and has nitrogen vapor in LNG containers at the point of supply what is undesirable. There is a continuing need in the industry for an improved process to liquefy natural gas that contains C02 in concentrations that freeze during the liquefaction process and at the same time have power requirements that are economical. The invention relates generally to a process for producing liquefied and pressurized natural gas (PLNG) in which the natural gas feed stream contains a freezing component. The freezing component, although typically C02, H2S or other acid gas, can be any component that has the potential to form solids in the separation system. In the process of that invention, a multiple component feed stream containing methane and a freeze component having a relative volatility less than that of methane is introduced into a separation system having a freezing section operating at a pressure of above about 1,380 kPa (200 psia) and under conditions of solid formation for the freezing component and a distillation section placed below the freezing section. The separation system containing a controlled freezing zone ("CFZ") produces a methane-rich vapor stream and a liquid stream rich in the freezing component. At least a portion of the vapor stream is cooled to produce a liquefied methane-rich stream having a temperature of about -112 ° C (-170 ° F) and a sufficient pressure for the liquid product to be at or below from its bubble point. A first portion of the liquefied stream is removed from the process as a stream of pressurized liquified product (PLNG). A second portion of the liquefied stream is returned to the separation system to provide the refrigeration cycle for the separation system. In one embodiment, a vapor stream is withdrawn from an upper region of the separation system and is compressed at a higher pressure and cooled. The compressed and cooled stream is then expanded by means of an expansion medium to produce a predominantly liquid stream. A first portion of the liquid stream is fed as reflux current to the separation system, thereby providing cycle-open cooling to the separation system, and a second portion of the liquid stream is withdrawn as a product stream having a temperature above about -112 ° C (-170 ° F) and sufficient pressure for the liquid product to be at or below its bubble point. In another modalitya vapor stream is withdrawn from an upper region of the separation system and cooled by a closed-cycle cooling system to liquefy the methane-rich vapor stream to produce a liquid having a temperature of approximately -112 ° C (-170 ° C) and a sufficient pressure so that the liquid product is at or below its bubble point. The method of the present invention can be used for the initial liquefaction of a natural gas at the source of supply for storage or transportation and for relicing the vapors of natural gas produced during storage and loading. Accordingly, an object of the invention is to provide an integrated and improved C02 liquefaction and removal system for the liquefaction or relicing of natural gas with high C02 concentrations (greater than about 5%). Another object of this invention is to provide an improved liquefaction system where substantially less compression energy is required than in the prior art systems. A further object of the invention is to provide a more efficient liquefaction process that maintains the process temperature for the entire process above about -112 ° C, thus allowing the process equipment to be made from less expensive materials than the process equipment. that would be required in a conventional LNG process that has at least part of the process operating at temperatures below approximately -160 ° C. the very low temperature refrigeration of the conventional LNG process is very expensive compared to the relatively moderate cooling required in the production of PLNG in accordance with the practice of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The present invention and its disadvantages will be better understood by reference to the following detailed description and the appended Figures, which are schematic flow diagrams of representative embodiments of this invention. Figure 1 is a schematic representation of a cryogenic CFZ process that generally illustrates a closed cycle refrigeration cycle for producing the liquefied and pressurized natural gas according to the process of this invention. Figure 2 is a schematic representation of a cryogenic CFZ process that generally illustrates an open cycle refrigeration cycle for producing liquefied and pressurized natural gas according to the process of this invention.

Figure 3 is a schematic representation of another embodiment of the present invention wherein carbon dioxide and methane are separated by means of distillation in a distillation column having a CFZ in which current above product is natural gas liquefied and pressurized and other the top product stream is the product sales gas. The flow diagrams illustrated in the Figures show various embodiments of the practice of the process of this invention. The figures are not intended to exclude the scope of other modalities that are the result of normal and expected modifications of these specific modalities. Various required subsystems such as pumps, valves, flow stream mixers, control systems and detectors have been omitted from the figures for the purpose of simplicity and clarity of presentation. The process of this invention separates distilled way a separation system a feed stream multiple component containing methane and at least one freezable component having a lower relative volatility than that of methane wherein the separation system contains a zone freezing controlled ("CFZ"). The separation system produces a steam stream enriched with methane and a sediment product enriched with the freezing component. At least part of the upper vapor stream is then liquefied to produce the liquefied natural gas product having a temperature at about -112 ° C (-170 ° F) and a sufficient pressure for the liquid product to be in or through below its bubble point. This product is sometimes referred to herein as liquefied and pressurized natural gas ("PLNG"). Another portion of the liquefied top stream is returned to the separation system as a reflux stream. The term "bubble point" is the temperature and pressure at which a liquid begins to turn into gas. For example, if a certain volume of PLNG is maintained at constant pressure even though its temperature increases, the temperature at which the gas bubbles begin to form in the PLNG is the bubble point. Similarly, if a certain volume of PLNG is maintained at a constant temperature although the pressure is reduced, the pressure at which the gas begins to form defines the bubble point. At the bubbling point PLNG is a saturated liquid. It is preferred that PLNG not only condense to its bubble point, but also cool to subcool the liquid. The sub-cooling of PLNG reduces the amount of vapors from the evaporated part during storage, transportation and handling.

Prior to this invention, it was well known to those skilled in the art that CFZ could remove the undesirable C02. It was not appreciated that the CFZ process could be integrated with a liquefaction process to produce PLNG. The process of the present invention is more economical in its use since the process requires less energy for the liquefaction of natural gas than the processes used in the step and the equipment used in the process of this invention can be made from less expensive materials. In contrast, prior art processes that produce LNG at atmospheric pressures having temperatures as low as -160 ° C require process equipment made of expensive materials for safe operation. In the practice of this invention, the energy needed to liquefy natural gas containing significant concentrations of a freezing component such as C02 is greatly reduced over the energy requirements of a conventional process to produce PLNG from said natural gas. The reduction in the necessary cooling energy required for the process of the present invention results in a large reduction in capital costs, proportionally lower operating costs and increased efficiency and reliability, thereby vastly improving the economics of natural gas production smoothie.

At the operating pressures and temperatures of the present invention, steel with about 3 1/2 weight percent of nickel may be used in the pipes and installations in the cooler operating areas of the liquefaction process, considering that the nickel 9 percent by weight or aluminum are usually required for the same equipment in a conventional LNG process. This provides another significant cost reduction for the process of this invention compared to the processes of the prior art LNG. The first consideration in the cryogenic processing of natural gas is pollution. The existence of natural gas feed suitable for the process of this invention may comprise natural gas obtained from a crude oil well (associated gas) or from a gas oil well (non-associated gas). The original natural gas frequently contains water, carbon dioxide, hydrogen sulfide, nitrogen, butane, hydrocarbons of 6 or more carbon atoms, dust, iron sulfide, wax and crude oil. The solubilities of these pollutants vary with temperature, pressure and composition. At cryogenic temperatures, C02, water and other contaminants can form solids, which can clog the flow passages in cryogenic heat exchangers. These potential difficulties can be avoided by removing such contaminants and the conditions within their pure component, the solid phase pressure-temperature phase limits are anticipated. In the following description of the invention, it is assumed that the natural gas stream contains C02. If the natural gas stream contains heavy hydrocarbons that could freeze during liquefaction, those heavy hydrocarbons will be removed with C02. An advantage of the present invention is that the higher operating temperatures allow the natural gas to have higher concentration levels of freezeable components than would be possible in a conventional LNG process. For example, in a conventional LNG plant that produces LNG at -160 ° C, the C02 must be below approximately 50 ppm to avoid freezing problems. By comparison, by keeping process temperatures above about -112 ° C, natural gas can contain C02 at levels as high as about 1.4% by mole of C02 at temperatures of -112 ° C and about 4.2% a - 95 ° C without causing problems of freezing in the liquefaction process of this invention. Additionally, moderate amounts of nitrogen in the natural gas do not need to be removed in the process of this invention, because the nitrogen will remain in the liquid phase with the liquefied hydrocarbons at the operating pressures and temperatures of the present invention. The ability to reduce, or in some cases omit, the equipment required for gas treatment and the reextraction of nitrogen provides significant technical and economic advantages. These and other advantages of the invention will be better understood by reference to the liquefaction process illustrated in the Figures. Referring to Figure 1, a stream of natural feed gas 10 enters the system at a pressure above about 3,100 kPa (450 psia) and more preferably about about 4,800 kPa (700 psia) and temperatures preferably between about 0 ° C and 40 ° C; however, different pressures and temperatures can be used, if desired, and the system can be modified accordingly. If the gas stream 10 is below approximately 1,380 kPa (200 psia), it can be pressurized by a suitable compression means (not shown), which may comprise one or more compressors. In this description of the process of this invention, it is assumed that natural gas stream 10 has been adequately treated to remove water using conventional and well-known processes (not shown in Figure 1) to produce a stream of "dry" natural gas . The feed stream 10 is passed through the cooler 30. The cooler 30 may comprise one or more conventional heat exchangers that cool the natural gas stream to cryogenic temperatures, preferably below about -50 ° C to -70 ° C and more preferably up to temperatures just below the solidification temperature of C02. The cooler 30 may comprise one or more heat exchange systems cooled by conventional cooling systems one or more expansion means such as valves or Joule-Thomson turbo expanders, one or more heat exchangers using the liquid from the lower section of the fractionation column 31 as a refrigerant, one or more heat exchangers using the bottom product stream of the column 31 as a refrigerant, or any other suitable source of refrigerant. The preferred cooling system will depend on the availability of cooling cooling, space limitation, if any, and environmental and safety considerations. Those skilled in the art can select an adequate cooling system that takes into account the operating circumstance of the liquefaction process. The cooled stream 11 exiting the feed cooler 30 is conveyed to a fraction column 31 having a controlled freezing zone ("CFZ"), which is a special section for handling the solidification and melting of C02. The CFZ section, which handles the solidification and melting of Co2, does not contain packing or trays like conventional distillation columns instead containing one or more spray nozzles and a melting tray. The solid Co2 is formed in the vapor space in the distillation column and falls into the liquid in the melting tray. Substantially all the solids they form are confined to the CFZ section. The distillation column 31 has a conventional distillation section below the CFZ section and preferably another distillation section on the CFZ section. The design and operation of the fractionation column 31 are known to those skilled in the art. Examples of CFZ designs are illustrated in U.S. Patent Nos. 4,533,372; 4,923,493; 5,062,270; 5,120,338; and 5,265,428. A C02-rich stream 12 leaves the bottom of column 31. The liquid bottom product is heated in a kettle 35 and a portion is returned to the lower section of column 31 as superheated steam. The remaining portion (stream 13) leaves the process as a product rich in C02. A methane-rich stream 14 leaves the top of column 31 and passes through a heat exchanger 32 which is cooled by stream 17 which is connected to a conventional closed cycle refrigeration system 33. A system can be used individual cooling, multiple component or cascade. A cascade cooling system would comprise at least two closed cycle refrigeration cycles. The closed cycle refrigeration system can use methane, ethane, propane, butane, pentane, carbon dioxide, hydrogen sulfide and nitrogen as refrigerants. Preferably, the closed cycle refrigeration system uses propane as the predominant refrigerant. Although Figure 1 shows only one heat exchanger 32, in the practice of the invention, several heat exchangers can be used to cool the vapor stream 14 in multiple stages. The heat exchanger 32 preferably condenses substantially all of the vapor stream 14 to a liquid. The stream 19 leaving the heat exchanger has a temperature of more than about -112 ° C and a sufficient pressure for the liquid product to be at or below its bubble point. A first portion of the liquid stream 19 is passed as stream 20 to suitable storage means 34 such as a stationary storage tank or a conveyor such as a PLNG ship, truck or rail to contain the PLNG at a temperature above about -112. ° C and a sufficient pressure so that the liquid product is at or below its bubble point. A second portion of the liquid stream 19 is returned as stream 21 to the separation column 31 to provide cooling for the separation column 31. The relative proportions of the streams 20 and 21 will depend on the composition of the feed gas 10, the operating conditions of the separation column 31 and the specifications of the desired product. In the storage, transportation and handling of liquefied natural gas, there may be a considerable amount of "evaporated portion", the vapor that results from the evaporation of a liquefied natural gas. The process of this invention can optionally be re-liquified evaporated part vapor which is rich in methane. Referring to Figure 1, the vapor from the evaporated part may optionally be introduced to the vapor stream 14 before being cooled by the exchange 32. The vapor stream from the evaporated part 16 must be at a pressure adjusted by one or more compressors or extenders ( not shown in the Figures) matches the pressure at the vapor point of the evaporated part, enters the liquefaction process. A smaller portion of the vapor stream 14 can optionally be removed from the process as a fuel (stream 15) to supply a portion of the energy needed to drive the compressors and pumps in the liquefaction process. This fuel can optionally be used as a cooling source to assist in the cooling of the feed stream 10.Figure 2 illustrates in schematic form another embodiment of this invention in which open cycle refrigeration is used to provide cooling to the separation column 51 and to produce PLNG. Referring to Figure 2, a multiple component gas stream 50 containing methane and carbon dioxide that has been dehydrated and cooled by any suitable cooling source (not shown in Figure 2) is fed into a CFZ column. which essentially has the same design as the separation column 31 of Figure 1. This embodiment effectively handles the potential for solids formation in the liquefaction process by means of the feed stream 64 directly within the CFZ 51 column. The temperature of the gas fed into the CFZ column 51 is preferably above the solidification temperature of C02. A steam stream enriched with methane 52 leaves the top of the CFZ column 51 and an enriched stream of carbon dioxide 53 flows out of the bottom of the CFZ 51 column. The lower liquid product is heated in a boiler 65 and a portion thereof. it is returned to the lower section of the CFZ 51 column as superheated steam. The remaining portion (stream 54) leaves the process as a liquid product rich in C02.

A first portion of the upper stream 52 is again flowed back to the CFZ column 51 as stream 64 to provide open cycle cooling to the CFZ column 51. A second portion of the upper stream 52 is withdrawn (stream 63) as a current of product PLNG at a pressure that is at or near the operating pressure of the CFZ 51 column and at a temperature above approximately -112 ° C (-170 ° F). A third portion of the upper stream 52 can optionally be removed (stream 59) for use with sale gas or additional process. The main components of the open-cycle refrigeration in this mode comprise compressing by one or more compressors 57 the upper stream 52 that leaves the top of the CFZ column 51, cooling the compressed gas by one or more coolers 58, passing through at least part of the cooled gas (stream 61) to one or more expansion means 62 to decrease the pressure of the gas stream and to cool it, and to feed a portion (stream 64) of the expanded and cooled stream to the CFZ 51 column. Reflowing part of the upper stream 52 by this process provides the open cycle refrigeration to the CFZ 51 column. The stream 60 is preferably cooled by heat exchange 55 which also heats the upper current 52. The pressure of the stream 64 is preferably controlled by regulating the amount of compression produced by the compressor 57 to ensure that the fluid pressures of the streams 60, 61 and 64 are high enough to avoid the formation of solids. By returning at least part of the upper steam stream 52 to the upper portion of the column 51 as liquid condensed by the open cycle refrigeration, reflux is also provided to the column 51. The CFZ 51 column has a conventional distillation section by below the CFZ section and potentially another distillation section above the CFZ section. The CFZ section handles any formation and fusion of C02 solids. During start-up, all current 64 can be diverted directly to the CFZ section. As the stream 64 becomes smaller in the solid formers, more of the stream 64 can be fed to the distillation section of the column before the CFZ section. Figure 3 schematically illustrates another embodiment of this invention in which the process of this invention produces PLNG and sale gas as product streams. In this mode, the upper product streams are 50% PLNG (current 126) and 50% sales gas (stream 110). However, the additional PLNG, up to 100% can be produced by providing additional cooling either from the cooler thermal exchange with fluids or additional pressure drop in the expander through the additional compression installation and subsequent coolers. In the same way, less PLNG can be produced by providing less cooling. Referring to Figure 3, it is assumed that the natural gas feed stream 101 contains more than 5% moles of C02 and is virtually free of water to prevent freezing and hydrate formation occurring in the process. After dehydration, the feed stream is cooled, depressurized and fed to the distillation column 190 which operates at a pressure on the scale from about 1,379 kPa (200 psia) to about (4,482 kPa (650 psia). distillation 190, which has a CFZ section similar to the separation column 31 of Figure 1 separates the feed into an upper steam product enriched with methane and a liquid bottom product enriched with carbon dioxide In the practice of this invention , the distillation column 190 has at least two, and preferably three different sections: a distillation section 193, a controlled freezing zone 192 (CFZ) and the distillation section 193, and optionally a superior distillation section 191. In In this example, the tower feed is introduced into the upper part of the distillation section 193 through the stream 105 where it supports the typical distillation Distillation sections 191 and 193 contain trays and / or pack and provide the necessary contact between the liquids that fall down and the vapors that rise upwards. The lighter vapors leave the distillation section 193 and enter the controlled freezing zone 192. Once in the frozen freezing zone 192, the vapors make contact with the liquid (reflux of liquid from the freezing zone sprayed) that emanates from the nozzles or spray jet assemblies 194. The vapors continue through the upper distillation section 191. For effective separation of the C02 from the natural gas stream in the 190 column cooling is required to provide the liquid traffic in the upper sections of the column 190. In the practice of this embodiment, cooling to the upper portion of the column 190 is provided by the open cycle refrigeration. In the embodiment of Figure 3, the incoming feed gas is divided into two streams. The current 102 and the current 103. The current 102 is cooled in one more heat exchangers. In this example, three heat exchangers 130, 131, 132 are used to cool the cold stream 102 and to serve as superheaters to provide heat to the distillation section 190. The stream 103 is cooled by one or more heat exchangers that are in thermal exchange with one of the bottom product streams of column 190. However, the number of heat exchangers to provide the power supply cooling services will depend on the number of factors including, but not limited to, flow rate of inlet gas, inlet gas composition, feed temperature, and heat exchange requirements. Optionally, although not shown in Figure 3, the feed stream 101 can be cooled by a process stream leaving the top of the column 190. As another option, the feed stream 101 can be cooled by at least partially by cooling systems, such as the individual closed cycle component or multiple component cooling systems. The streams 102 and 103 are recombined and the combined current is passed through appropriate expansion means, such as the Joule-Thomson 150, up to approximately the operating pressure of the separation column 190. Alternatively, a turbo expander can be used in place of the Joule-Thomson 150 valve. Immediate expansion through the valve 150 produces a cold expanded stream 105 which it is directed towards the top of the distillation section 193 at a point where the temperature of preference is high enough to avoid freezing of C02. The upper steam stream 106 from the separation column 190 passes through the heat exchanger 145 which heats the steam stream 106. The heated steam stream (stream 107) is recompressed by single-head compression or multiple-stage compressor train . In this example, stream 107 passes successively through two conventional compressors 160 and 161. After each compression step, stream 107 is cooled by rear coolers 138 and 139, preferably using ambient air or water as the cooling medium. . The compression and cooling of stream 107 produces a gas that can be used for sale to a natural gas pipe or additional processing. The vapor current compression 107 will usually be at least one pressure that meets the requirements of the pipe. A portion of the stream 107 after passing through the compressor 160 may be optionally removed. (stream 128) for use as fuel for the gas processing plant. Another portion of the stream 107 after passing through the rear cooler 139 is removed (stream 110) as a sale gas. The remaining part of stream 107 is passed as stream 108 to heat exchangers 140, 136 and 137. Stream 108 is cooled in heat exchangers 136 and 137 with cooling fluids from stream 124 leaving the bottom of the column 190. The stream 108 is then further cooled in the heat exchanger 145 by thermal exchange with the upper vapor stream 106, which results in heating of the stream 106. The stream 108 is then expanded by pressure then by an appropriate expansion device. , such as the expander 158 to approximately the operating pressure of the column 190. The stream 108 is then divided, a portion is passed as the PLNG product (stream 126) at a temperature about about -112 ° C and at a pressure about about 1.380. kPa (200 psia) for storage or transportation. The other portion (stream 109) enters the separation column 190. The discharge pressure of the compressor 161 is regulated to produce a pressure that is high enough so that the pressure drop across the expander 158 provides sufficient cooling to ensure that the streams 109 and 126 are predominantly liquid enriched with methane. In order to produce additional PLNG (stream 126) the additional compression can be installed after the compressor 160 and before the heat exchanger 136. To start the process, the stream 109 is preferably fed through the stream 109a and sprayed directly into the section 192 through the spray nozzle 194. After the process starts, the stream 109 can be fed (stream 109b) to the upper section 191 of the separation column 190. A stream of liquid product enriched with C02 115 exits the bottom of column 190. Stream 115 is divided into two portions, stream 116 and stream 117. Stream 116 passes through an appropriate expansion device, such as a Joule-Thomson valve 153, at a lower pressure. The stream 124 leaving the valve 153 is then heated in the heat exchanger 136 and the stream 124 passes through another Joule-Thompon valve 154 and through another heat exchanger 137. The resulting stream 125 is then fused with the current of steam 120 from the separator 181. The stream 117 is expanded by an appropriate expansion device such as an expansion valve 151 and passed through the heat exchanger 133 thereby cooling the feed stream 103. The stream 117 is then directed towards the separator 180, a conventional gas-liquid separation device. The steam from the separator 180 (stream 118) passes through one or more compressors and high pressure pumps to drive the pressure. Figure 3 shows a series of two compressors 164 and 165 and one pump 166 with conventional chillers 143 and 144. The product stream 122 leaving the pump 166 in the series has a pressure and temperature suitable for injection into an underground formation . The liquid products leaving the separator 180 through stream 119 are passed through an expansion device such as an expansion valve 152 and then passed through the heat exchanger 141 which is in heat exchange relationship with the current of feed 103, further cooling the feed stream 103. Stream 119 is then directed to separator 181, a conventional gas-liquid separator device. The vapors of the separator 181 are passed (stream 120) to a compressor 163 followed by a subsequent cooler 142. The stream 120 is then fused with the stream 118. Any condenser available in the stream 121 can be recovered by conventional stabilization or evaporation processes. and then they can be sold, incinerated or used as fuels. Although the separation systems illustrated in Figures 1-3 have only one distillation column (column 31 of Figure 1, column 51 of Figure 2 and column 190 of Figure 3), the separation systems of this invention may comprise two or more distillation columns. For example to reduce the height of the column 190 of Figure 3 it may be desirable to divide the column 190 into two or more columns (not shown in the figures). The first column contains 2 sections, a distillation section and a controlled freezing zone over the distillation section and the second column contains a distillation section, which performs the same function as section 191 in Figure 3. A stream of Multiple component feed is fed to the first distillation column. The liquid pellets of the second column are fed to the freezing zone of the first column. The upper part of the vapor of the first column is fed to the lower region of the second column. The second column has the same open cycle refrigeration cycle as that shown in Figure 3 for column 190. A vapor stream from the second distillation column is removed, cooled and a portion thereof is reflowed into the region top of the second separation column. Examples Simulated mass and energy equilibria were created to illustrate the modalities shown in Figures 1 and 3 and the results are shown in Tables 1 and 2 below respectively. For the data presented in Table 1, it is assumed that the top product stream was 100% PLNG (stream 20 of Figure 1) and the cooling system was a cascaded propane-ethylene system. For the data presented in Table 2, it was assumed that the top product streams were 50% PLNG (stream 126 of Figure 3) and 50% sales gas (stream 110 of Figure 3). The data was obtained using a commercially available process simulation program called HYSYS ™ (available from Hyprotech Ltd. of Calgary, Canada); however, other commercially available process simulation programs can be used to develop the data, including, for example, HYSIM ™, PROIT ™, and ASPEN PLUS ™, which are familiar to those with ordinary skill in the art. The data presented in the Tables are offered to provide a better understanding of the modalities shown in Figures 1 and 3, although the invention is not considered in a limited and necessary way to them. Temperatures and flow rates are not considered as limitations on the invention that may have many variations in temperatures and flow rates in view of the teachings herein. An additional process simulation was performed using the basic flow scheme shown in Figure 1 (using the same composition of feed stream and temperature as used to obtain the data in Table 1) to produce conventional LNG near atmospheric pressure and a temperature of -161 ° C (-258 ° C). The conventional CFZ / LNG process requires significantly more cooling than the CFZ / PLNG process illustrated in Figure 1. To obtain the refrigeration required to produce LNG at a temperature of -161 ° C, the cooling system must be expanded from a system propane / ethylene cascade to a propane / ethylene / methane cascade system. Additionally, stream 20 would need to be further cooled using methane and the product pressure would need to be dropped using a liquid expander or Joule-Thomson valve to produce an LNG product at or near atmospheric pressure. Due to the lower temperatures, the C02 in the LNG must be removed to approximately 50 ppm to avoid operational problems associated with the freezing of C02 in the process instead of 2% of C02 as in the CFZ / PLNG process illustrated in Figure 1 Table 3 shows a comparison of the refrigerant compression requirements for the conventional LNG process and the PLNG process described in the simulation example of the previous paragraph. As shown in Table 3, the total required refrigerant compression power was 67% greater to produce the conventional LNG than to produce PLNG in accordance with the practice of this invention. A person skilled in the art, particularly someone who has the benefit of the teachings of this patent, it will recognize many modifications and variations to the specific process described above. For example, a variety of temperatures and pressures are used according to the invention, depending on the general design of the system and the composition of the feed gas. Likewise, the feed gas cooling train can be complemented or reconfigured depending on the overall design requirements to achieve the optimum and efficient thermal exchange requirements. Additionally, certain stages of the process can be achieved by the addition of devices that are interchangeable with the devices shown. For example, separation and cooling can be achieved in a simple device. As described above, the specifically described embodiments and examples should not be used to limit or restrict the scope of the invention, which is determined by the claims and their equivalents.

Table 1 - Integrated CFZ / PLNG Phase Pressure Temperature Total Flow Mol% Current Steam / Liquid kPa psia ° C kg-moles / hr Ib-moles / hr C02 CH4 10 Steam 6,764 981 18.3 65.0 49,805 109,800 71.1 26.6 11 Steam / Liquid 3,103 450 -56.7 -70.0 49,805 109,800 71.1 26.6 12 Liquid 3,103 450 -7.7 18.2 55,656 122,700 95.9 1.4 13 Liquid 3,103 450 -4.9 23.2 36,424 80,300 96.6 0.5 14 Vapor 3,068 445 -92.0 -133.6 30,844 68,000 2.0 97.7 19 Liquid 3,068 445 -94.6 -138.3 30,844 68,000 2.0 97.7 20 Liquid 3,068 445 -94.6 -138.3 13,381 29,500 2.0 97.7 co 21 Liquid 3,068 445 -94.6 -138.3 17,463 38,500 2.0 97.7 Table 2 - CFZ / PLNG Integrated with open cycle refrigeration Phase Pressure Temperature Total Flow Moi% Current Steam / Liquid kPa psia ° C ° F kg-moles / hr Ib-moles / hr C? 2 N CH, H2S C2 + 101 Vapor 6,764 981 18.3 65 49,850 109,900 71.1 0.4 26.6 0.6 1.3 102 Steam 6,764 981 18.3 65 19,731 43,500 71.1 0.4 26.6 0.6 1.3 103 Steam 6,764 981 18.3 65 30,119 66,400 71.1 0.4 26.6 0.6 1.3 104 Steam / Liquid 6,695 971 -7.8 18 5,942 13,100 71.1 0.4 26.6 0.6 1.3 105 Steam / Liquid 2,758 400 -56.7 - 70 49,850 109,900 71.1 0.4 26.6 0.6 1.3 106 Steam 2,758 400 -99.4 -147 31,116 68,600 0.1 1.5 98.4 16 ppm 0.0 107 Steam 2,551 370 -30.6 -23 31,116 68,600 0.1 1.5 98.4 16 ppm 0.0 108 Steam 16,823 2,440 51.7 125 23,723 52,300 0.1 1.5 98.4 16 ppm 0.0 109 Liquid 2,758 400 -101.7 -151 18,008 39,700 0.1 1.5 98.4 16 ppm 0.0 110 Steam 16,823 2,440 51,7 125 5,715 12,600 0.1 1.5 98.4 16 ppm 0.0 115 Liquid 2,758 400 -1 1.1 12 36,741 81,000 96.5 0.0 1.0 0.7 1.8 116 Liquid 2,758 400 -1 1.1 12 6,532 14,400 96.5 0.0 1.0 0.7 1.8 117 Liquid 2,758 400 -1 1.1 12 30,209 66,600 96.5 0.0 1.0 0.7 1.8? 118 Steam 1, 862 270 -21.1 -6 21, 727 47,900 96.8 0.0 1.3 0.7 1.2 119 Liquid 1, 862 270 -21.1 -6 8,482 18,700 95.5 0.0 0.1 0.9 3.5 120 Steam 621 90 -23.3 -10 8,210 18,100 97.8 0.0 0.1 0.9 1.2 121 Liquid 621 90 -23.3 -10 227 500 18.7 0.0 0.0 0.6 80.7 122 Liquid 29,751 4,315 65.6 150 36,514 80,500 97.0 0.0 1.0 0.7 1.3 123 Steam 16,616 2,410 -28.3 -19 23,723 52,300 0.1 1.5 98.4 16 ppm 0.0 124 Va / Liquid Ido 1, 931 280 -22.2 -8 6,532 14,400 96.5 0.0 1.0 0.7 1.8 125 Steam 621 90 -22.2 -8 6,532 14,400 96.5 0.0 1.0 0.7 1.8 126 Liquid 2,758 400 -101.7 -151 5,715 12,600 0.1 1.5 98.4 16 ppm 0.0 128 Vapor 6,895 1, 000 56.1 133 1, 633 3,600 0.1 1.5 98.4 16 ppm 0.0 Table 3 Comparison of Refrigerant Compression Energy Requirements CFZ / PLNG POWER, horsepower POWER, kW CFZ / CFZ / Conventional CFZ / PLNG Conventional Difference CFZ / PLNG Difference Compressors Propane Coolant Compressors 162,210 115,960 46,250 120,962 86,473 34,489 Ethylene Coolant Compressors 86,090 41,490 44,600 64,198 30,940 33,259 Methane Coolant Compressors 14,031 0 14,031 10,463 0 10,463 Compressed Installed Coolant Total 262,331 157,450 104,881 195,623 117,412 78.211% CFZ / PLNG? Total Installed 167% 100% 67% 167% 100% 67% < _p

Claims (30)

1. CLAIMS 1. A process for producing methane-rich pressurized liquid from a multiple component feed stream containing methane and a freezing component having a relative volatility lower than that of methane, characterized in that it comprises: (a) introducing the current of multiple component feed in a separation system having a freezing section operating at a pressure above about 1,380 kPa (200 psia) and under conditions of solid formation for the freezing component and a distillation section placed below the freezing section, the separation system that produces a methane-rich vapor stream and a liquid stream rich in a freezing component; (b) cooling at least a portion of the vapor stream to produce a liquefied methane-rich stream having a temperature of about -112 ° C (-170 ° F) and a sufficient pressure for the liquid product to be in or near its bubbling point; (c) removing a first portion of the liquefied stream from step (b) as a stream of liquefied product rich in methane; and (d) introducing a second portion of the liquefied stream from step (b) to said separation system to provide cooling to said separation system.
2. 2. The process according to claim 1, characterized in that it further comprises introducing the liquefied product stream to storage media for storage at a temperature above -112 ° C (-170 ° F).
3. The process according to claim 1, characterized in that the cooling step (b) further comprises the steps of compressing said vapor stream to a high pressure stream, cooling at least a portion of the compressed stream in the exchanger and expand the compressed and cooled stream to a lower pressure whereby the compressed stream is further cooled to produce a liquefied stream rich in methane having a temperature of about -112 ° C (-170 ° F) and a sufficient pressure to that the liquid product is close to its bubble point.
4. The process according to claim 3, characterized in that the cooling of the compressed stream in the heat exchanger is by indirect thermal exchange with the steam stream of stage (a).
5. The process according to claim 3, characterized in that it further comprises cooling the liquid stream produced by the separation system by pressure expansion and using the cooled and expanded liquid stream to cool the compressed stream by indirect thermal exchange.
6. 6. The process in accordance with the claim 3, characterized in that it also comprises regulating the pressure of the compressed stream and the pressure of the expanded current to prevent the formation of solids in the second portion of the liquefied stream introduced into the separation system.
7. The process according to claim 1, characterized in that the separation system of step (a) comprises a first distillation column and a second distillation column, the first distillation column comprising a distillation section and a zone of freezing on the distillation section, the second distillation column comprising a distillation section, further comprising the steps of introducing the multiple component feed stream of stage (a) into the first distillation column, feeding a stream steam from the freezing zone to a lower region of the second distillation column, withdraw a vapor stream from the second distillation column and cool the vapor stream according to step (b), feed the second portion of the liquefied stream from step (d) to the upper region of the second separation column, withdrawing a lower stream of liquid from the second distillation column, and feeding the lower stream of liquid to the freezing zone of the first distillation column.
8. The process according to claim 1, characterized in that the separation system comprises a first distillation section, a second distillation section of the first distillation section and a freezing zone between the first and second distillation sections. , wherein the second portion of the liquefied stream of step (d) is introduced to the first distillation section.
9. 9. The process according to claim 1, characterized in that the cooling of the steam stream in step (b) is carried out in a heat exchanger cooled by a closed-cycle cooling system.
10. 10. The process according to claim 9, characterized in that the closed cycle refrigeration system has propane as the predominant refrigerant.
11. 11. The process according to claim 9, characterized in that the closed cycle refrigeration system has a refrigerant comprising methane, ethane, propane, butane, pentane, carbon dioxide, hydrogen sulfide and nitrogen.
12. 12. The process according to claim 1, characterized in that it also comprises before step (b), passing to the process the evaporated part gas resulting from the evaporation of liquefied gas rich in methane.
13. 13. The process in accordance with the claim 1, characterized in that the liquefaction of the gas stream is executed using two cycles of closed cycle refrigeration in cascade arrangement.
14. The process according to claim 1, characterized in that the multiple component gas stream of step (b) has a pressure over 3,100 kPa (450 psia).
15. 15. The process according to claim 1, characterized in that the freezing component is carbon dioxide.
16. The process according to claim 1, characterized in that the cooling step (b) further comprises the steps of compressing the vapor stream to a compressed stream, cooling at least a portion of the compressed stream in a heat exchanger, removing a first portion of the compressed and cooled stream as a stream of product gas, and expanding a second portion of the compressed stream and cooled to a lower pressure whereby the compressed stream is further cooled to produce a liquefied stream rich in methane that it has a temperature of about -112 ° C (-170 ° C) and a sufficient pressure for the liquid product to be at or below its bubble point.
17. 17. A process for separating a multiple component feed stream comprising at least methane and at least one freeze component having a relative volatility lower than that of methane to produce a liquid product enriched in methane, comprising: (a) ) introducing the multiple component feed stream into a separation system, the separation system operating under conditions of solid formation for the freezing component; (b) withdrawing a vapor stream from an upper region of the separation system; (c) compressing the vapor stream to a higher pressure stream (d) cooling at least a portion of the compressed stream using the available cooling in the vapor stream of step (b); (e) expanding the cooled compressed stream to further cool the compressed stream, the expanded stream which is predominantly liquid; (f) feeding at least a portion of the expanded stream to an upper region of the separation system to provide cooling to the separation system; and (g) recovering from the current expands a stream of liquid product enriched with methane.
18. The process according to claim 17, characterized in that it further comprises recovering a portion of the compressed vapor stream of step (c) and cooling the remaining portion of the vapor stream according to step (d).
19. 19. The process according to claim 17, characterized in that the vapor stream of stage (b) is heated before compression in step (c).
20. 20. The process in accordance with the claim 17, characterized in that the separation system comprises a first distillation section, a second distillation section below the first distillation section and a freezing zone between the first and second distillation sections, wherein the expanded liquid stream is introduced within the first distillation section.
21. 21. The process according to claim 20, characterized in that the multiple component feed stream is introduced below the first distillation section.
22. 22. The process according to claim 17, characterized in that it also comprises removing the liquid from the separation system, cooling the liquid by means of pressure expansion and at least partially vaporizing said liquid by thermal exchange with the compressed stream of the stage (c) ).
23. 23. The process according to claim 17, characterized in that it further comprises removing the liquid from the separation system enriched with the freezing component, cooling the liquid enriched with the freezing component through pressure expansion means, and cooling the multiple component feed stream before it enters the system. separation by thermal exchange with the liquid enriched with expanded frozen component.
24. 24. The process according to claim 17, characterized in that it further comprises cooling the multiple component stream by expansion means before it enters the separation system.
25. 25. The process in accordance with the claim 17, characterized in that the pressure of the upper pressure current of stage (c) and the expanded current (e) are controlled to prevent the formation of solids in the power supply to the separation system in step (f).
26. 26. The process according to claim 17, characterized in that the liquid product stream recovered from step (g) has a pressure on about 1,380 kPa (200 psia).
27. 27. A process for producing liquefied natural gas at a pressure of about 1,380 kPa (200 psia) from a multiple component feed stream containing methane and a freeze component having a relative volatility lower than that of methane, comprising : (a) introducing the multiple component feed stream into a separation system, the separation system operating under conditions of solid formation for the freezing component; (b) withdrawing a vapor stream from an upper region of the separation system; (c) compressing the vapor stream to a higher pressure stream; (d) cooling at least a portion of the compressed stream using the available cooling in the steam stream of step (b); (e) expanding the compressed and cooled stream to further cool the compressed stream, the expanded stream which is predominantly liquid at a pressure of about 1,380 kPa (200 psia); (f) feeding at least a portion of the expanded stream to an upper portion of the separation system to provide cooling to the separation system; and (g) recovering from the expanded stream a liquid product stream enriched in methane at a pressure of approximately 1,380 kPa (200 psia).
28. 28. A process for liquefying a multiple component stream comprising methane and at least one freezeable component to produce a methane-rich liquid having a temperature of about -112 ° C and a sufficient pressure for the liquid to be in or through below its bubbling point, comprising the steps of: (a) introducing the multiple component feed stream having a pressure over approximately 1,380 kPa (200 psia) in a separation system operating under solid-forming conditions for said freezing component to provide a methane-rich vapor stream and a liquid stream rich in the component that solidifies in the separation system; (b) liquefying the vapor stream by means of a closed cycle refrigeration system to produce a methane-rich liquid having a temperature of about -112 ° C and a sufficient pressure for the liquid to be at or below its point bubbling; and (c) introducing the methane-rich liquid to a storage container for storage at a temperature above -112 ° C.
29. 29. The process according to claim 28, characterized in that the liquefaction of the feed stream is executed with a closed-cycle cooling system.
30. 30. The process according to claim 28, characterized in that before the liquefaction of the feed stream it comprises further combining with the vapor stream from the separation system an evaporated part gas resulting from the evaporation of the liquefied natural gas .