MXPA99011424A - Improved multi-component refrigeration process for liquefaction of natural gas - Google Patents

Abstract

This invention relates to a process for liquefying a pressurized gas stream (10) rich in methane in which the liquefication of the gas stream occurs in a heat exchanger (33) being cooled by a closed-loop multi-component refrigeration system (45) to produce a methane-rich liquid product having a temperature above about -112°C (-170°F) and a pressure sufficient for the liquid product to be at or below its bubble point. The liquefied gas product is then introduced to a storage means (50) at a temperature above about -112°C (-170°F).

Description

COOLING PROCESS OF IMPROVED MULTIPLE COMPONENT FOR LIQUIDATION OF NATURAL GAS 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). 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 dollars, including field development costs. The plant's cooling systems can add up to 30 percent of the cost. In the design of an LNG plant, three of the most important considerations are (1) the selection of the liquefaction cycle, (2) the materials used in the containers, pipe and other equipment, and (3) the process steps to convert the natural gas feed stream in LNG. 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 approximately 4,830 kPa (700 psia) to approximately 7,600 kPa (1,100 psia) and temperatures of approximately 20 ° C (68 ° F), ~ to approximately ~ 40 ° C (104 ° F). 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 (-116.5 ° F). 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 (-121 ° F) and -62 ° C (-80 ° F). Typically, natural gas compositions at atmospheric pressure will liquefy in the temperature range of between about -165 ° C (-265 ° F) and -155 ° C (-247 ° F). Since refrigeration equipment represents a significant part of the cost of LNG installation, considerable effort has been made to reduce cooling costs. 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" which uses multiple individual component refrigerants in heat exchangers progressively arranged to reduce the gas temperature to a liquefaction temperature, (2) "expander cycle" that expands the gas from a very high pressure up to a low pressure with a corresponding reduction in temperature and (3) "multi-component cooling cycle" which uses a multi-component refrigerant in specially designed exchangers. Most natural gas liquefaction cycles use variations or combinations of these three types.

A mixed refrigerant system involves the circulation of a multiple component refrigeration stream, usually from pre-cooling to approximately -35 ° C (-31 ° F) with propane. A typical multiple component system will comprise methane, ethane, propane and optionally other light components. Without prior propane cooling, the heavier components such as butane and pentanes can be included in the multiple component refrigerant. The nature of the mixed refrigerant cycle is such that the heat exchangers in the process must routinely handle the flow of a two-phase refrigerant. This requires the use of specialized large heat exchangers. Mixed refrigerants exhibit the desirable property of condensation over a wide range of temperatures, allowing the design of heat exchange systems: which can be thermodynamically more efficient than pure component refrigerant systems. Examples of multiple component cooling process are described in U.S. Patent Nos. 5,502,972; 5,497,626; 3,763, 638; and 4,586,942. The materials used in conventional LNG plants also contribute to the cost of the plant. The containers, tubing and other equipment used in the LNG plants are normally constructed, at least in part from aluminum, stainless steel or high nickel steel to provide the required strength and fracture toughness at low temperature. 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 of parts per million levels (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 still a need in the industry for an improved process for liquefying natural gas which minimizes the amount of refrigeration equipment and process of "power required." This invention relates to an improved process for liquefying a methane-rich feed gas stream. The feed gas stream has a pressure above about 3,100 kPa (450 psia) .If the pressure is too low, the gas can be compressed first.The gas is liquified by a multi-component cooling system to produce a product liquid having a temperature of about -112 ° C (-170 ° F) and a sufficient pressure for the liquid product that is at or below its bubble point temperature, a product referred to herein as liquid natural gas Pressurized ("PLNG") Pre-liquefaction by cooling multiple components, the gas is preferably cooled by recycled vapors which pass through the expansion means without being liquefied. The PLNG is introduced to storage means to store at a temperature of about -112 ° C (-170 ° F). In another embodiment of the invention, if the gas contains components heavier than pentane, the predominant portion of the heavier hydrocarbons are removed by a fractionation process prior to liquification by cooling of multiple components. In yet another embodiment of the invention, an evaporated portion gas resulting from the evaporation of the liquefied natural gas can be added to the feed gas for liquefaction by expanding the pressure to produce pressurized liquid natural gas (PLNG). The process of the present invention can be used for the initial liquefaction of a natural gas in the source of supply for storage or transportation and for re-liquefying natural gas vapor arising during storage and loading. Accordingly, an object of this invention is to provide an improved liquification system for the liquefaction or re-liquefaction of natural gas. Another object of the invention is to provide an improved liquefaction system wherein substantially less compression power is required than in prior art systems. A further object of the present invention is to provide an improved liquefaction process that is economical and efficient for the operation. The very low temperature cooling 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. Fig. 1 is a schematic flow diagram of one embodiment of this invention showing a closed loop multiple component cooling system for producing PLNG. Figure 2 is a schematic flow chart of a third embodiment of this invention in which the natural gas of feed is fractioned before liquefaction to PLNG. Figure 3 is a schematic flow chart of a third embodiment of this invention in which a closed-loop individual component cooling system is used for pre-cooling the natural gas stream prior to liquefaction to PLNG. Figure 4 is a schematic flow chart of a fourth embodiment of this invention in which a closed cycle multiple component refrigeration system previously cools a natural gas feed stream prior to fractionation and the cooling system also liquefies. the natural gas feed stream to produce PLNG. Figure 5 is a schematic flow chart of a fifth embodiment of this invention in which the natural gas is fractionated and then liquified in a heat exchanger that is cooled by a second closed-cycle cooling system using the multiple component liquid and multiple component vapor as refrigerants. The vapor from the evaporated part is liquefied "only with the vapor-from the multiple component cooling system. ~ Figure 6 is a schematic flow chart of a sixth embodiment of this invention in which the evaporated part steam and a feed of natural gas are mixed before liquefaction using a multiple component cooling system to produce PLNG.; j? n schematic flow chart of a seventh embodiment of this invention in which natural gas is "fractionated and then liquified in a heat exchanger that is cooled by a second closed cycle refrigeration system using multiple component liquid and the multiple component vapor as refrigerants Figure 8 is a schematic flow diagram of an expanding process used in the modes illustrated in Figures 2, 5, 6 and 7. Figure 9 is a schematic flow diagram of a system Preferred multiple component cooling system used in the embodiments illustrated in Figures 1, 2, 3, 4 and 6. Figure 10 is a schematic flow chart of a preferred multiple component cooling system used in the modes illustrated in Figures 5 and 7. The flow charts illustrated in the Figures show various modalities of the practice. of the process of this invention. The Figures are not intended to exclude from the scope of the invention other modalities that are the result of the normal and expected modifications of those specific modalities. Various required subsystems such as pumps, valves, flow stream mixers, control systems and sensors have been eliminated from the Figures for the purposes of simplicity and clarity of presentation. The present invention utilizes a multiple component cooling system for liquefying natural gas to produce a liquid product rich in methane having a temperature above about -112 ° C (-170 ° F) and a sufficient pressure for the Liquid product is at or below its bubble point. Methane-rich product is sometimes referred to in this description as liquid and pressurized natural gas (PLNG). The term "bubble point" is the temperature and pressure at which the liquid begins to turn into gas. For example, if a certain volume of PLNG is maintained at a constant pressure, even if its temperature is increased, the temperature at which the gas bubbles begin to form in the PLNG is the bubble point. Similarly, if a certain volume of PNLG is maintained at a constant temperature even if the pressure is reduced, the pressure at which the gas begins to form defines the bubble point. At the bubble point, the mixture is saturated liquid. Using a multiple component cooling system according to the present invention requires less energy to liquefy natural gas than the multiple component processes used in the past and the equipment used in the process of the invention can be made from materials less expensive By comparison, the processes of the prior art that produce LNG at atmospheric pressure having temperatures as low as -160 ° C. (-256 ° F) require that at least part of the process equipment be made of costly materials for safe operation.

The energy needed to liquefy natural gas in the practice of this invention is greatly reduced over the energy requirements of a conventional LNG plant. 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, greatly increasing the economy of gas production liquefied natural "At the operating pressures and temperatures of the present invention, steel with about 3.5 weight percent nickel may be used in the pipes and installations in the colder operating areas" of the liquefaction process, considering that the Percent by weight or aluminum are generally 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. A "The first consideration in the cryogenic processing of natural gas is pollution, The natural gas feed stocks suitable for the process of this invention may comprise natural gas obtained from crude oil wells (associated gas) or - Gas wells (without associated gas) The composition of natural gas can vary significantly As used herein, a natural gas stream contains methane (Ci) as a main component Natural gas usually contains ethane ( C2), higher hydrocarbons (C3 +), and smaller amounts of contaminants such as water, carbon dioxide, hydrogen sulfide, nitrogen, butane, hydrocarbons of six or more carbon atoms, dust, iron sulfide, wax, and crude oil. The solubilities of these pollutants vary with temperature, pressure and composition. C02 cryogenic temperatures, carbon dioxide, water and other pollutants can form solids, which can clog the flow passages in cryonic heat exchangers. These potential difficulties can be avoided by removing such contaminants and conditions within their pure component, and the solid phase pressure-temperature phase limits are anticipated. In the following description of the invention it is assumed that the natural gas stream has been suitably treated to remove the sulfides "and the carbon dioxide and dried to remove the water using conventional and well-known processes to produce a gas stream. If the natural gas stream contains heavy hydrocarbons that could freeze during liquefaction or if the heavy hydrocarbons are not desired in the PLNG, the heavy hydrocarbon can be removed by fractionation process before producing the PLNG as it is described in more detail below. 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 (-256 ° F) the C02 should be below about 50 ppm to avoid freezing problems. By comparison, by keeping process temperatures above about -112 ° C (-170 ° F), natural gas can contain C02 at levels as high as about 1.4% by mole of C02 at temperatures of -112 ° C (-170 ° F) and about 4.2% at -95 ° C (-139 ° F) 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. to reduce, or in some cases omit, the equipment required for gas treatment and the ejection of nitrogen provides significant technical and economic advantages These and other advantages of the invention will be better understood by reference in the Figures. 1, the pressurized natural gas feed stream 10 preferably enters the liquefaction process at a pressure of about 1,724 kPa (250 psia) and more preferably about 700 psi (about 4,727 kPa) and preferably at temperatures below about 40 psi. ° C (104 ° F), however, different pressures and temperatures can be used If desired, the system can be appropriately modified accordingly by those skilled in the art taking into account the teachings of the invention. If the gas stream 10 is below approximately 1,724 kPa (250 psia) it can be pressurized by suitable compression means (not shown), which may comprise one or more compressors. The natural gas feed stream 10 is passed to a feed cooler 26, which can be any conventional cooling system that cools the natural gas stream to a temperature of below about 30 ° C (86 ° F). The cooling is preferably effected by thermal exchange with air or water. The cooled stream 11 exiting the feed cooler 26 is conveyed to a first cooling zone 33a of a conventional multiple component heat exchanger 33 that is commercially available and is familiar to those of ordinary skill in the art. This invention is not limited to any type of heat exchanger, although due to the economy, the heat exchangers of the cooling box and the coiled spiral of the plate-fin are preferred. Preferably, all streams containing vapor and liquid phases that are sent to the heat exchangers have the vapor and liquid phases equally distributed through the cross-sectional area of the passages they enter. To achieve this, it is preferred to provide distribution apparatuses for individual vapor and liquid streams. The separators can be added to the multiple phase flow stream as required to divide the streams into liquid and vapor. For example, the separators could be added to the currents 18 to 24 of Figure 1 (such spacers are not shown in Figure 1), before the currents 18 and 24 enter the cooling zones 33a and 33b, respectively. The heat exchanger 33 may have one or more cooling zones, preferably at least two. The heat exchanger 33 illustrated in Figure 1 has two cooling zones 33a and 33b. The natural gas in stream 11 is liquified in cooling zone 33a by a heat exchange with the refrigerant from a multiple component cooling system 45, which is referred to in the description as MCR system 45. The preferred embodiment of an MCR system 45 is illustrated in Figure 9, which is described in more detail below. The refrigerant in the MRC system is comprised of a mixture of hydrocarbons, which may include for example methane, ethane, propane, butanes and pentanes. A preferred coolant has the following composition on a molar percentage basis: methane (25.8%), ethane (50.6%), propane (1.1%), i-butane (8.6%), n-butane (3.7%), i-pentane (9.0%), and n-pentane (1.2%). The concentration of the MCR components can be adjusted to match the cooling and condensing characteristics of the feed gas that is cooled and the cryogenic temperature requirements of the liquefaction process. As an example of the proper temperature and pressure for the closed-loop MCR refrigeration system, the in-line multiple component refrigerant 27a 345 kPa (50 psia) and 10 ° C (50 ° F) is aimed at conventional understanding and cooling in the MCR system 45 to produce a multiple component fluid stream 18 having a pressure of 1.207 kPa (175 psia) and a temperature of 13.3 ° C (56 ° F). The stream 18 is cooled in the cooling zone 33a and further cooled in the cooling zone 33b to produce a cooling stream 23 that leaves the cooling zone 33b at a temperature of -99 ° C (-146 ° F) . Current 23 is expanded through a Joule-Thomson valve 46 to produce the current 24 to 414 kPa (60 psia) and -108 ° C (-162 ° F). The stream 24 is then heated in the cooling zone 33b and then heated in the cooling zone 33a to produce the stream 27 at 10 ° C (50 ° F) and 345 kPa (50 psia). The multi-component refrigerant is circulated again in the closed-cycle cooling system. In the liquefaction process illustrated in Figure 1, the MCR 45 system is the only closed-cycle cooling system used to produce PLNG. The liquefied natural gas stream _19 is _ PLNG at a temperature above about -112 ° C (-170 ° F) and a temperature sufficient for the liquid product to be at or below its bubble point. If the pressure of the stream 19 is greater than the pressure necessary to maintain the stream 10 in the liquid phase, the stream 19 may optionally be passed through one or more expansion means, such as a hydraulic turbine 34, to produce a PLNG product at a lower pressure but still having the temperature above about -112 ° C (-170 ° F) and a sufficient pressure so that the liquid product is at or below its bubble point. The PNLG is sent via lines 20 and 29 to an appropriate storage or transportation means 50 such as a pipeline."stationary storage tank" or a conveyor such as a PLNG vessel, truck or rail car In the storage, transportation and handling of liquefied natural gas, there may be a considerable amount of "evaporated portion", the vapor resulting from of the evaporation of a liquefied natural gas. This invention is particularly suitable for liquefying the evaporated part vapor produced by PLNG. The process of this invention can optionally liquefy such vapors of evaporated part. Referring to Figure 1, the evaporated part vapor is introduced to the process of the invention through the line 22. Optionally, a portion of the stream 22 can be withdrawn and directed through the cooling zone 33a to heat the Evaporated part gas withdrawn for later use as a fuel and to provide additional cooling to the cooling zone 33a. The remaining portion of the stream 22 is passed into the cooling zone 33b, where the evaporated part gas is liquefied again. The liquefied natural gas leaving the cooling zone 33b (stream 28) is pumped by the pump 36 to the pressure of the PLNG that leaves the hydraulic turbine 34 and is then combined with the stream 20 and sent to an appropriate storage medium 50. The fluid streams leaving the turbine Hydraulic 34 and pump 36 are preferably passed to one or more phase separators (such separators are not shown in the Figures) which separate the liquefied natural gas from any gas that has not been liquified in the process. The operation of such spacers is well known to those skilled in the art. The liquefied gas is then passed to the PLNG 50 storage medium and the "gas phase of a phase separator can be used as a fuel or recycled" to the process for liquefaction. Figure 2 illustrates another embodiment of the process of this invention and the others Figures in this description with parts having similar numbers that are the same process functions Those skilled in the art will recognize, however, that the process equipment from one mode to the other may vary in size and capacity to handle different speeds of operation. flow of fluid, temperatures and compositions Referring to Figure 2, a stream of natural gas feed enters the system through line 10 and passes through a conventional feed cooler 26. Natural gas is passed from the cooler of supply 26 to an expanding process 30 which cools the natural gas stream to a temperature sufficient to condense at least a major portion of the heavier hydrocarbon components of natural gas, which are called natural gas liquids (NGL). NGL includes ethane, propane, butane, pentane, isopentane, and the like. At pressures ranging from 4,137 kPa (600 psia) to 7,585 kPa (1,100 psia), the temperatures required to effect the condensation scale from about 0 ° C (32 ° F) to about -60 ° C (-76 ° F) ). A preferred embodiment of an expanding process 30 is illustrated in Figure 8, which is described in more detail below. The bottom stream 12 of the expanding process 30 is passed to a conventional fractionation plant 35, the general operation of which is known to those skilled in the art. The fractionation technique can comprise one or more fractionation columns (not shown in Figure 2) that separate the stream from the liquid bottom 12 in predetermined amounts of ethane, propane, butane, pentane and hexane. The plant of. The fractionation comprises preferably multiple fractionation columns (not shown) such as a deethanizer column that produces ethane, a column of. propane-producing depropanizer; and a butan-producing debutanizer column, all of which can be used as forming coolants for the multiple component cooling system 45 or any other suitable cooling system. The refrigerant forming streams are collectively illustrated in Figure 2 by line 15. If the feed stream 10 contains high concentrations of C02, one or more of the coolant forming streams 15 may need to be treated to remove C02 to avoid problems of potential clogging in the refrigerant equipment. The fractionation plant 35 will preferably include a CO 2 removal process, if the CO 2 concentration in the coolant stream would otherwise exceed approximately 3 mole percent. The liquids are removed from the fractionation plant 35 as condensed products, which are collectively illustrated in Figure 2 as the stream 14. The top streams from the fractionation columns of the fractionation plant 35 are rich in ethane and others light hydrocarbons, which are shown collectively in Figure 2 as stream 13. A methane-rich stream 16 from demethanizer 30 is combined with the methane-rich stream 13 and passes as stream 17 to the coolant cooling zone mixed 33a to liquefy natural gas. The cooling to the cooling zone 33a is provided by a "multiple component" cooling system., described in more detail above with respect to the description of the MCR system in Figure 1. Although the MCR refrigerants circulate in a closed cycle system, if the refrigerants are lost from the system through spills, the forming refrigerants may obtained from the fractionation plant 35 (line 15). In the illustrated liquefaction process _ in Figure 2, the multiple component cooling system 45 is the only closed loop refrigeration system used to liquefy the natural gas feed gas stream 10. page 12 The liquefied natural gas stream 19 which leaves the mixed refrigerant cooling zone 33a is passed through the hydraulic turbine 34 to reduce the fluid pressure to produce PLNG at a temperature above about -112 ° C (-170 ° F) and at a pressure enough for the PLNG to be at or below its bubble point. "The main advantage of this mode is that the removal of heavy hydrocarbon is possible in the expanded plant and the refrigerants that can accumulate in the fractionation plant 35. Figure 3 illustrates another embodiment of the present invention in which a system of Closed loop individual component cooling is used to precool the natural gas stream 10 prior to liquefaction to PLNG. The process shown in Figure 3 is similar to the process shown in Figure 2, except that a closed-cycle cooling system 40 is used to provide at least part of the cooling for the supply chiller 26 and to provide cooling in the heat exchanger 60. The stream 11 exiting the feed cooler 26 is passed directly to a conventional demethanizer 80 without the need for an expanding process 30 which is used in the process of Figure 2. The cooling system 40 can be a system Conventional closed-cycle refrigeration that has propellant, propylene, ethane, carbon dioxide, or any other liquid suitable as a refrigerant. In Figure 3, the liquid refrigerant in the line 18a of the MCR system 45 can optionally be cooled in the heat exchanger 70 by the coolant in the stream 27 which is returned to the MCR system 45 from the heat exchanger 33. The stream 18a can be further cooled in the heat exchanger 60 by the starting coolant. of the refrigeration system 40 having a refrigerant flow stream 51 circulating between the refrigeration system 40 and the heat exchanger 60. In this embodiment, a significant portion of the cooling requirements move towards a closed-cycle cooling system. , of conventional pure component 40, such as the propane system. Although additional heat exchangers are required, the size and cost of the heat exchanger 33 will be reduced. Figure 4 illustrates another embodiment of the process of this invention in which a closed loop multiple component cooling system 33 previously cools a natural gas feed stream prior to fractionation and the cooling system also liquefies the natural gas stream to produce PLNG. A natural gas feed stream enters the system through line 10 and is passed through the feed cooler 26 which cools and can partially liquefy the natural gas. The natural gas then passes through line 11 to a first cooling zone 33a of the multiple component heat exchanger 33. The heat exchanger 33 in this mode has three cooling zones (33a, 33b, 33c). The second cooling zone 33b is located between the first cooling zone 33a and the third cooling zone 33c and operates at a lower temperature than the first cooling zones and at a temperature higher than the third cooling zone. liquefied which leaves the first cooling zone 33a and passes through the line lia to a demethanizer 80. The demetallizer 80 fractionates the natural gas to produce a methane-rich top stream 16 and a bottom stream 12. The bottom stream 12 is passed to a fractionation plant 35 which is similar to that of the previous description for Figure 2. The methane-enriched stream 16 from the demethanizer 30 and the top product stream 13 from the fractionation plant 35 combine and pass as stream 17. to a second cooling zone 33b of the heat exchanger 33. The stream 19 leaving the second cooling zone at 33b is passed through one or more expansion means such as a hydraulic turbine 34. The hydraulic turbine 34 produces a cold expanded stream 20 (PLNG) which is passed to a storage medium 50 at a temperature above about - 112 ° C (-170 ° F) and a sufficient pressure so that the liquid product is at or below its bubble point. The evaporated part gas resulting from the evaporation of liquefied natural gas within a storage receptacle during transportation or loading operations can optionally be introduced via line 22 into the third cooling zone 33c, in which the evaporated part gas is liquefied again. Optionally, a portion of the evaporated part gas can be passed through the second cooling zone 33b to heat the evaporated part gas before use as a fuel (stream 38). The liquefied natural gas leaving the cooling zone 33c is pumped by the pump 36 to the pressure of the PLNG in the stream 20A and then sent to the storage medium 50. The embodiment of Figure 4 allows the removal of the heavy hydrocarbons and the conformation of the refrigerant without significant pressure drop, as required in the embodiment of Figure 2, or an additional refrigeration system such as the embodiment of Figure 3. Figure 5 illustrates yet another embodiment of this invention in which the natural feed gas is cooled by a feed cooler 26 and the natural gas is liquefied in a heat exchanger 33 which is cooled by a closed cycle cooling system 45 which uses multiple component liquid and multiple component vapor as a refrigerant. This allows the liquefaction of. vapors of evaporated part of the tank only with multi-component vapor. This modality is "similar to the modality described in Figure 2, except for the operation of the multiple component heat exchanger system 33. A preferred embodiment of an MCR system 45 using the vapor and liquid refrigerants is illustrated in Figure 10, which is described in more detail below.

Referring to Figure 5, "a natural gas feed stream enters the system, through line 10 and is passed through a feed cooler 26 comprising one or more heat exchangers that partially liquefy natural gas. In this embodiment, the cooling is preferably effected by heat exchange with air or water.The feed cooler 26 is optionally cooled by a conventional "closed cycle refrigeration system" wherein the cooling refrigerant is propane, propylene, ethane, dioxide carbon, or any other suitable refrigerant. As an example of the temperature and pressure suitable for the closed cycle MCR system 45 illustrated in Figure 5, the in-line multiple refrigerant 27 to 345 kPa (50 psia) and 10 ° C (50 ° F) is directed towards the compression and cooling in the MCR system 45 to produce a multiple component liquid stream 18 and a multiple component vapor stream 21, each of which has a pressure of 1207"kPa (175 psia) and a temperature" of 13.3 ° C (56 ° F). The steam stream 21 is further cooled in the cooling zone 33a and is further cooled in the cooling zone 33b to produce a cold stream 23 leaving the cooling zone 33b at a temperature of -99 ° C (-146 °). F). The stream 23 is then expanded through a conventional Joule-Thomson 46 valve to produce the current 24 to 414 kPa (60 psia) and -108 ° C (-162 ° F). The stream 24 is then heated in the cooling zone 33b and then further heated in the cooling zone 33a to produce the current 27 at 10 ° C (50 ° F) and 345 kPa (50 psia). The stream 18 is cooled in the cooling zone 33a and is expanded through a conventional Joule Thomson valve 47. The expanded fluid exiting the expansion valve 47 is combined with the stream 25 and recirculated. This mode has the advantage that the evaporated part vapor is liquefied again using only the MCR vapor. Figure 6 illustrates another embodiment of the invention which is similar to the embodiment of Figure 2 except that the multiple component heat exchanger 33 has only one cooling zone (33a) and the evaporated part steam is mixed with the stream of natural gas 16 and 13 instead of being liquefied by a cooling zone separated from the heat exchanger 33. The evaporated part vapor 22 ^ is first passed through the cooling zone 33a to provide cooling for hotter streams 17 and 18 which pass through the heat exchanger 33a. After leaving the cooling zone 33a, part of the stream 22 may optionally be withdrawn (stream 38) as fuel to provide power to the PLNG plant. The other portion of the stream 22 is passed to a compressor 39 to pressurize the evaporated part gas to approximately the gas pressure in the stream 17. The evaporated part gas (stream 32) exiting the compressor 39 is then combined with the stream 17. This mode does not require mixing cryogenic liquid and may be a simpler operation than the embodiment illustrated in Figure 2. Figure 7 illustrates another embodiment of "this invention in which the feed gas is cooled by the cooler of feed 26 and the natural gas is liquified in a multiple component heat exchanger 33 which is cooled by a closed cycle cooling system 45 which uses both the multiple component liquid (stream 18) and the multiple component vapor (stream 21) as a refrigerant The processing in this Figure 7 is similar to the operation of the process illustrated in Figure 5 except that at least part of the the evaporated part 22 is compressed by the compressor 39, up to approximately the pressure of the stream 16 and the compressed evaporated part stream 32 is combined with the stream of natural gas 16. The stream 17, which contains vapors from the expanding process 30, the vapors from the fractionating plant 35 and the vapors from the evaporated part from the stream 32, is then passed through the cooling zones 33a and 33b of the heat exchanger 33 to liquefy the stream of water. gas 17 to produce PLNG (stream 19). Referring to Figure 7, a portion of the stream 22 is preferably withdrawn and passed through the cooling zones 33b and 33a and leaves the heat exchanger 33 (stream 38) for use as a fuel. A preferred expander process for use in practice of the embodiments of Figures 2, 5, 6 and 7 is illustrated in Figure 8. Referring to Figure 8, the gas stream 11 is divided into two separate streams. and 101. The gas stream 100 is cooled in the heat exchanger 102 by the cold waste gas in the line 104. The gas stream 101 is cooled by the side boiler heat exchanger "105" through which the liquid flow of the demethanizer from the demethanizer column 130. The cooled streams 100 and 101 are re-combined and the combined stream 103 is passed to a conventional phase separator 106. The separator 106 divides the stream 103 into the liquid stream 107 and the "vapor stream". 108. "Vapor stream 108 is expanded to reduce its pressure such as turboexpander 109. This expansion further cools the gas before it is fed into the upper region of the desmetani column. 80. The condensed liquid stream 107 is passed through a Joule-Thomson valve 110 to further expand and cool the liquid stream 107 before it passes to the demethanizer column 80. The waste gas from the top of the column of demethanizer 80 is transported to the heat exchanger 102 and passed through the compressor 111 which is fed at least in part by the expander 109. The compressed methane-rich stream 16 exiting the expanding process 30 is processed in accordance with the practice of This invention The demethanizer produces a lower liquid stream 12 which is predominantly liquid natural gas (NGL), mainly ethane, propane, butane, pentane, and heavier hydrocarbons. Additional examples of an expander process suitable for the use in practice of this invention are described in U.S. Patent No. 4,698,081 and Gas Conditioning and Processing, Volume 3 of Advanced Techniques and Applications, John M. Campbell and Co. , Tulsa, Oklahoma (1982). Figure 9 illustrates a schematic flow diagram of a preferred MCR system 45 for use in the embodiments illustrated in Figures 1, 2, 3, 4 and 6. Referring to Figure 9 the stream 27 enters a conventional compressor 150 for compress the refrigerant. Starting from the compressor 150, a compressed stream 151 is cooled by passing through a conventional cooler 152, such as an air or water cooler, before the stream 151 enters a conventional phase separator 153. The steam from the separator of phase 153 is passed by stream 154 to a compressor 155. From compressor 155 the compressed refrigerant vapor (stream 156) is cooled by a conventional cooler 157 to produce "the cooled refrigerant stream 18. A stream of liquid 158" from the phase separator 152 is pumped by the pump 159 approximately to the same pressure as the outlet pressure of the compressor 155. The liquid pressurized from the pump 159 (stream 160) is combined with the stream 156 before being cooled by the cooler 157 The "Figure 10 is a schematic flow chart of the preferred MCR system 45 for use in the modes illustrated in Figures 5 and 7. The MCR system illustrated in Figure 10 is s milar to the MCR system 45 of Figure 9 except that after the liquid refrigerant stream 160 and the vapor stream 156 are combined and cooled by the cooler 157, the stream cooled from the cooler 157 is passed to a conventional phase separator 161. The vapor exiting the separator 161 is converted to the vapor stream 21 and the liquid exiting the separator 161 is converted to the liquid stream 18.

Examples A simulated mass and energy equilibrium was carried out to illustrate the embodiments exemplified in the Figures and the results are set forth in Tables 1-7 below. The data presented in the following Tables are offered to provide a better understanding of the modalities shown in Figures 1-7, although the invention is not considered to be unnecessarily limited thereto. The temperatures and flow rates presented in the Tables are not considered as limitations on the invention which may have many variations in temperatures and flow rates in view of the teachings herein. The Tables correspond to the Figures as follows: Table 1 corresponds to Figure 1, Table 2 corresponds to Figure 2 Table 3 corresponds to Figure 3, Table 4 corresponds to Figure 4, Table 5 corresponds to the Figure 5, Table 6 corresponds to Figure 6, Table 7 corresponds to Figure 7. The data was obtained using a commercially available process simulation program called HYSYS ™, although, other commercially available process simulation programs can be use -.to develop the data including for example HYSIM ™, PROII ™ and ASPEN PLUS ™, all of which are common to those with ordinary skill in the art.

The data presented in Table 3 assumed that the embodiment shown in Figure 3 had a propane cooling system 40 for cooling the feed stream 10. Using the basic process flow scheme shown in Figure 3 and using the same composition of current supply and temperature, the total installed power required to produce conventional LNG (close to atmospheric pressure and a temperature of -160 ° C (-256 ° F) was "more than twice the total installed power requirement for produce PLNG using the modality illustrated in Figure 3: 185,680 kW (249,000 hp) to produce LNG against 89,040 kW (119,400hp) against PLNG.This comparison was performed using the HYSYS ™ process simulator, a person skilled in the art, particularly someone who has the benefit of the teachings of this patent, 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 overall design of the system and the composition of the feed gas. Likewise, the cooling train - of the feed gas can be complemented or reconfigured depending on the general design requirements to reach the optimum and the efficient thermal exchange requirements. 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 Table 1, continued Power ? co Table 2 ? I heard Table 2, continued Power or Table 3 Cp Table 3, continued Ro power Table 4 ? Cp Table 4, continued Power Table 5 Cp cp Table 5, continued Power Table 6 Table 6 CO Cp Table 6, continued Power Table 7 Cp O Cp Table 7, continued Power cp H1

Claims (21)

1. CLAIMS 1. A process for liquefying a methane-rich pressurized gas stream characterized in that it comprises the steps of liquefying the gas stream in a heat exchanger that is cooled by a multiple component "closed cycle refrigeration system to produce a rich liquid product. in methane having a temperature above about -112 ° C (-170 ° F) and a sufficient pressure so that the liquid product is at or below its bubble point, and introducing the liquid product into a medium of storage at a temperature up to about -112 ° C (-170 ° F) 2. The process according to claim 1, characterized in that it further comprises reducing the pressure of the liquid product by means of an expander before introducing the liquid. liquid product to the storage medium, the expanding medium that produces a liquid stream at a temperature above about -112 ° C (-170 ° F) and at a enough for the liquid product to be at or below its bubble point. 3. The process according to claim 1, characterized in that it also comprises passing to the heat exchanger a gas of evaporated part resulting from the evaporation of liquefied natural gas, the evaporated part gas that is at least partially liquified by the heat exchanger, and the pressurization of liquefied evaporated part gas, the pressurized evaporated part gas having a temperature above about -112 ° C (-170 ° F) and a sufficient pressure for the liquid product to be at or below its bubble point. 4. The process in accordance with the claim 3, characterized in that the heat exchanger comprises a first cooling zone and a second cooling zone operating at a lower temperature than the first cooling zone, passing the gas stream of claim 1 to the first cooling zone for liquefaction and passing the evaporated part gas to the second cooling zone for liquefaction. 5. The process in accordance with the claim 4, characterized in that it further comprises removing a portion of the gas from evaporated apart before the evaporated part gas passes to the heat exchanger and passes the removed portion of the evaporated part gas from the first cooling zone to heat the evaporated part gas removed and to cool the gas stream in the heat exchanger and use the removed evaporated part gas heated as fuel. The process according to claim 1, characterized in that it also comprises compressing an evaporated part gas resulting from the evaporation of the liquefaction natural gas for a pressure that approaches the pressure of the gas stream that is fed to the heat exchanger and that combines the compressed evaporated part gas with the gas stream before the gas stream is passed to the heat exchanger. The process according to claim 1, characterized in that it also comprises passing an evaporated part gas resulting from the evaporation of the liquefaction natural gas to the heat exchanger to cool the evaporated part gas, which comprises the evaporated part gas and combining the compressed evaporated part gas with the gas stream, and passing the combined evaporated part gas and the gas stream to the thermal exchanger for liquefaction. The process according to claim 7, characterized in that it also comprises after passing the evaporated part gas through the heat exchanger and before compressing the cooled evaporated part gas, removing a portion of the evaporated part gas and using the portion removed as fuel. 9. The process according to claim 3, characterized in that the heat exchanger comprises a first cooling zone., a second cooling zone and a third cooling zone, the second cooling zone operating at a temperature below the temperature of the first cooling zone and over the temperature of the third cooling zone, further comprising the steps of pass the evaporated part gas to the third cooling zone to liquefy the evaporated part gas, remove a portion of the evaporated part gas before it is passed through the third cooling zone and pass the evaporated part gas withdrawn to through the second cooling zone to heat the evaporated part gas withdrawn and use the evaporated part gas withdrawn and heated as fuel. The process according to claim 1, characterized in that the gas stream contains methane and heavier hydrocarbon components than methane, which further comprises removing a predominant portion of heavier hydrocarbons by fractionation to produce a vapor stream rich in methane and a liquid stream rich in heavier hydrocarbons, the vapor stream that is liquefied by the heat exchanger. 11. The process according to claim 10, characterized in that the liquid stream rich in heavier hydrocarbons is fractionated further producing ethane-rich steam which is combined with the methane-rich stream of claim 7. 12. The process according to claim 10, characterized in that it also comprises cooling the supply current before the fractionation of the feed stream. - 13. The process in accordance with the claim 1, characterized in that the heat exchanger comprises a first cooling zone and a second cooling zone, the first cooling zone which is cooled by the passage of a multiple component liquid refrigerant through the first cooling zone to cool the refrigerant liquid, to pass the liquid refrigerant through a pressure expansion means to further reduce the temperature of the liquid refrigerant and to pass the refrigerant from the expansion means through the first cooling zone, to pass a vapor refrigerant, of multiple component through the first cooling zone and the second cooling zone to reduce its temperature, the cooled vapor refrigerant passing through an expansion medium, passing the expanded refrigerant through the second cooling zone and then through the first cooling zone and liquefying the gas stream passing the corr of gas through the first cooling zone and the second cooling zone to produce a liquid product having a temperature above about -112 ° C (-170 ° F) and a sufficient pressure. is at or below its bubble point. 14. The process according to claim 1, characterized in that the process further comprises: (a) cooling the gas stream to effect partial liquefaction of the gas stream; (b) separating the partially condensed gas into a liquid rich in hydrocarbons heavier than methane and the methane-rich vapor stream; (c) fractionating the liquefaction part in at least one fractionation column to produce a steam stream rich in ethane and a liquid stream rich in hydrocarbons heavier than ethane and remove the liquid stream from the process; (d) combining the methane-rich vapor stream and the ethane-rich vapor stream and passing the combined stream to the heat exchanger of claim 1, whereby the combined stream is liquefied; and (e) before introducing the combined liquid stream to the storage means, expanding at least a portion of the subcooled liquid to produce a liquid product having a temperature above about -112 ° C (-170 ° F) and a sufficient pressure so that the liquid product is at or below its bubble point. 15. The process according to claim 14, characterized in that the cooling of the natural ga7s stream in step (a) is at least partially provided by a closed cycle propane refrigeration system. 16. The process according to claim 14, characterized in that the process further comprises passing to the heat exchanger the vapors of evaporated part resulting from the evaporation of a liquefied natural gas to produce a second liquefied natural gas stream having a temperature of above approximately -112 ° C (-170 ° F) and a sufficient pressure so that the liquid product is "at or below its bubble point, and combining the second stream of liquefied natural gas with the expanded liquified gas of step (e) of claim 14 17. The process according to claim 14, characterized in that the heat exchanger of stage (d) comprises a first cooling zone and a second cooling zone operating at a lower temperature which "the first cooling zone, in where the methane-rich streams of step (b) and step (c) of claim 14 are passed to the first cooling zone and the vapors of the evaporated portion resulting from the evaporation of a liquefied natural gas having a temperature above about -112 ° C (-170CF) are passed to the second cooling zone for liquefaction. 18. The process in accordance with the claim 10, characterized in that the gas stream enters the process at an elevated temperature ranging from about 0 ° C to about 50 ° C and at an elevated pressure ranging from about 2758 kPa (400 psia) to about 8274 kPa (1200 psia) and the liquified product produced by the process is at a pressure greater than about 1724 kPa (250 psia) and at a temperature above about -112 ° C (-170 ° F). The process according to claim 1, characterized in that the multiple cooling system has a refrigerant comprising methane, ethane, propane, butane, pentane, carbon dioxide, hydrogen sulfide, and nitrogen. 20. A process for liquefying a stream of natural gas characterized in that it comprises methane, propane, and the heavier hydrocarbons to produce liquefied natural gas having a top pressure of about 1724 kPa (250 psia) and a temperature of more than about -112 ° C (-170 ° F), which process comprises: (a) passing the natural gas stream to the first cooling zone of a multiple component heat exchanger comprising three cooling zones, with the second cooling zone operating at a temperature below the temperature of the first cooling zone and above the temperature of the third cooling zone; (b) fractionating the cooled natural gas feed stream to separate a methane-rich stream from the heavier hydrocarbon stream; (c) fractionating the flow of heavier hydrocarbons to produce a stream rich in ethane and a stream containing heavier hydrocarbons than ethane and removing heavier hydrocarbons than ethane from the process; (d) combining the methane-rich stream from step (b) _ and the ethane-rich stream from step (c) and passing the combined stream to the second cooling zone of the multi-component cooling system and cooling the stream combined to produce a subcooled condensate; (e) expanding at least a portion of the subcooled condensate to provide a liquefied gas having a higher pressure of about 1724 kPa (250 psia) and a temperature above about -112 ° C (-170 ° F); and (f) moving to the third cooling zone of the multi-component cooling system gas resulting from the evaporation of a natural liquefaction gas contained in a storage vessel to produce a second natural gas stream of liquefaction and combining the second liquefied natural gas stream with the liquefied natural gas produced in stage (e). 21. A process for liquefying a stream of natural gas characterized in that it comprises methane, propane, and heavier hydrocarbons to produce liquefied natural gas having a top pressure of about 1724 kPa (250 psia) and a temperature above about -112 ° C (-170 ° F), whose process comprises: (a) cooling the natural gas stream by means of a propane cooling system; (b) fractionating the chilled natural gas stream to separate a methane-rich stream and a heavy hydrocarbon stream; (c) fractionating the heavier hydrocarbon stream to produce a stream rich in ethane and at least one stream containing heavier hydrocarbons than ethane and removing heavier hydrocarbons than the ethane process; (d) combining the methane-rich stream of step (b) and the ethane-rich stream of step (c) and passing the combined stream to the first cooling zone of a multi-component cooling system having a first cooling zone cooled by a multiple component liquid and a multiple component vapor in heat exchange relationship with the combined methane-rich stream and the methane-rich stream "to produce a condensate subcooling: and (e) expanding at least a portion of the subcooled condensate to provide the liquefied natural gas having a top pressure of about 1724 kPa (250 psia) and a temperature above about -112 ° C (-170 ° F) ). ~~~ (f) passing to the second cooling zone of the multi-component refrigeration system the gas resulting from the evaporation of a liquefied natural gas contained in a storage vessel to produce a second liquefied natural gas stream and combines the second liquefied natural stream with the liquefied natural gas produced in step (e).