TW201213692A - Integrated liquid storage - Google Patents

Abstract

A system and process for liquefying a gas, comprising introducing a feed stream into a liquefier comprising at least a warm expander and a cold expander; compressing the feed stream in the liquefier to a pressure greater than its critical pressure and cooling the compressed feed stream to a temperature below its critical temperature to form a high pressure dense-phase stream; removing the high pressure dense-phase stream from the liquefier, reducing the pressure of the high pressure dense-phase stream in an expansion device to form a resultant two-phase stream and then directly introducing the resultant two-phase stream into a storage tank; and combining a flash portion of the resultant two-phase stream with a boil-off vapor from a liquid in the storage tank to form a combined vapor stream, wherein the temperature of the high pressure dense-phase stream is lower than the temperature of a discharge stream of the cold expander.

Description

201213692 VI. Description of the Invention: [Technical Field of the Invention] The present invention relates to a system and method for liquefying a gas. [Prior Art] Nitrogen liquefiers are well known in the art and are typically coupled to a nitrogen generator, for example, or an air separation unit (ASU). The liquefier can be used to liquefy low pressure gaseous nitrogen from the ASU, for example. The liquefier can also withdraw at least a portion of its feed from the ASU at a higher pressure and/or at a freezing temperature for liquefaction purposes. In a conventional liquefaction process, high pressure nitrogen is cooled to a freezing temperature to form a uniform dense phase fluid (ie, a fluid below its critical temperature and above its critical pressure) and then reduced in dust force, normally through a valve or dense The fluid applicator is such that most of it forms a liquid with some vane vapor. This biphasic mixture is then fed to a separator. Cold expanders also often discharge a vapor or microliquefied stream into the separator. The base gas from the separator is rewarmed to ambient temperature and then recirculated at the same time, while the liquid is overcooled prior to feeding to the insulating liquid reservoir, for example. This over-production cooling can be carried out by boiling the liquid at a lower pressure or indirectly in the hopper by decompression at a lower pressure or by boiling the liquid at a lower temperature. The use of a subcooler allows the helium liquid to maintain sufficient pressure to 苴 for example. L is sent for storage without the use of millet. The liquid portion produced in the liquefier can be stored, for example, in an insulated liquid storage tank for application in the step or by the tank truck, 201213692 and Other portions of the liquid can be returned to the ASU for freezing, for example. If a second separator is used, the first separator must be raised above the height of the tank if the application with the pump is to be avoided. However, storing the liquid in an insulated liquid reservoir is not a simple solution. Due to imperfect insulation, heat eventually leaks from the surrounding into the insulating liquid reservoir, for example. Moreover, some of the liquid stored in the insulating liquid reservoirs will vaporize and additional liquid needs to be generated to compensate for such losses. Conventionally, the cold vapor formed by the vaporization of the liquid in the insulating liquid storage tank is discharged to the atmosphere to prevent the pressure of the insulating liquid storage tank from rising, but the cooling loss in the process is caused. Like the role. The previously disclosed nitrogen liquefier connected to the ASU equipment, therefore, due to

Application of cold-end liquid nitrogen separator to process addition

For such large pre-insulated loads (i.e., because the separators must be sealed in the insulation box, it is difficult to handle according to the scheduled route, ie, the cold box load) may be difficult or even impossible to reach certain 201213692 destination. Third, the liquefaction process often includes a package, and a subcooler is included to reduce the emulsion formed in the tank. This is too cold and complex & Also - the money process adds undesired success, even though the early liquefiers Γ $ -Γ ffi, Μ ΛΑ (that is, the liquefiers used in today's conventional liquefiers) use single expansion, 彳日曰^ H « 胀^' and use only a single separator device. Some of the early liquefiers of Renqi Ting have phase needles, Λ ^ ^ 邳 pairs, and efficiency. In order to improve the efficiency of the liquefied thief, the later liquefied tongue Μ ^ ^ ^ ° and the application of multiple expanders and multiple knife separator to recover the sudden boiling distillation at intermediate pressure. Salt believes that these quenching base gases must be recovered under intermediate pressure... Rolling has been for many years and until now, because the sudden vapors formed by the liquid product entering the liquid storage tank are not desirable and therefore It is obtained in the large rolling to control the U of the storage tank. The read emissions will, inevitably, result in a valuable loss of refrigeration for the surge vapor. Therefore, there is a need in the industrial gas industry for the benefits of tanked steam and vaporized vapor recovery without the need for a cold blower, a cold end separator or a simplification of a simple and low cost liquefaction process. 'Comprehensive' [Description of the Invention] The specific embodiment provides a simplified and efficient liquefier that uses a liquid storage tank as a sudden boiling separator and recovers the ablation through the liquefied 1 仉 storage tank And vaporizing the vapor to meet the needs of this technology. Separators and subcoolers can be excluded from the liquefier design and process. Because the two liquids: the cold part of the device is basically only the heat exchanger and the pipe, so the J Μ is added with 201213692 to isolate and exclude the independent cold box. The particular embodiment described utilizes materials and fabrications relative to conventional thinking for the construction of efficient liquefier settings and processes. The production of liquids in a stand-alone liquefier rather than in an ASU unit has operational advantages, such as ease of switching on demand' but has significant disadvantages associated with high capital costs and lower efficiency associated with stand-alone process units. In general, increasing process efficiency will increase investment costs, and investment costs will increase to improve efficiency. The described method and system reduce investment costs while improving efficiency. In a specific embodiment, a method for liquefying a gas is disclosed, the method comprising introducing a feed stream to a liquefier comprising at least one warm expander and a cold expander; compressing the feed stream in the liquefier Up to a pressure above its critical pressure and cooling the compressed feed stream to a temperature below its critical temperature to form a high pressure dense phase flow; removing the high pressure dense phase flow from the liquefier and in an expansion device Reducing the pressure of the high pressure dense phase flow to form a final two phase flow and then introducing the final two phase flow to a storage tank; and the boiling portion of the final two phase flow and the vaporized vapor of the liquid in the storage tank A combined vapor stream is formed, wherein the temperature of the high pressure dense phase stream is lower than the temperature of the discharge stream of the cold expander. In another embodiment, a system for liquefying atmospheric gas is disclosed, comprising: a first conduit for receiving a feed stream; a fluid coupled to the first conduit for compressing and cooling the feed stream a liquefier for forming a high pressure dense phase fluid, wherein the liquefier comprises at least one warm expander, a cold expander, a pressure 201213692 for compressing the feed stream to a pressure above its critical pressure, and a heat exchanger for compressing the feed stream to a temperature below its critical temperature, the fluid being connected to the liquefier for receiving a second conduit from the liquefier for compacting the dense phase flow; the fluid is connected to the first a second conduit for reducing the pressure of the still-pressure dense phase flow to form a first two-phase flow of the first expansion device 'fluid connected to the first expansion device for receiving the second-phase expansion flow; and the fluid a storage tank connected to the third conduit for receiving and storing the two-phase expansion stream, the tank system being designed to operate at or below 1 · 5 bar absolute, and wherein the heat exchanger system is designed The high pressure dense phase The temperature of the stream is lower than the discharge stream temperature of the cold expander. [Embodiment] FIG. 1 illustrates an exemplary system and method for recovering the ablation and vaporization vapor from the liquid storage tank 1 70 using the liquid storage tank 170 as a sudden boiling separator and passing through the liquefier 101. Figure 1 discloses combining a low pressure nitrogen feed stream with a quenching and vaporizing vapor stream 1 〇2 of a warming tank to form a combined stream. The low pressure feed stream 1 may be nitrogen or it may be another gas or gas mixture such as air, oxygen, argon, carbon monoxide, helium, ethylene, helium or hydrogen, for example. The combined stream 104 is then compressed in the feed compressor 106 to about 6 bar absolute to form a compressed stream 1 〇8. The compressed stream 1 〇 8 is then cooled in the aftercooler II 以 to form a cooling stream 112. Cooling stream 112 is then combined with recycle stream 4 to form stream 116. Stream 116 is then compressed to about 32 bar absolute in recycle compressor 118 to cause compressed stream 120. Stream 120 is then cooled in aftercooler 122 to form stream 124. Stream 124 is then separated into streams 126 and 128. 201213692 Stream 126 (optional) is cooled in heat exchanger 13A to form stream 1 32. Stream 132 is then expanded in warm expander crucible 34 to about 6 absolute cells to form a warm expanded stream 136. Stream 128 is further compressed in the warm compression compressor 138 to form stream 140. Stream 140 is then cooled in the warm-pressed aftercooler crucible 42 to form a cooling stream 144. Cooling stream 144 is then compressed in compression compressor 146 to about 65 bar absolute to form compressed stream 148. The compressed stream ι48 is then cooled in the cold press compressor aftercooler 丨5〇 to form a high pressure stream 152. This high pressure stream 152 is cooled in the heat exchanger 丨3〇 to an intermediate temperature of about 18 2 K to produce streams 丨 5 4 and 156. Stream 1 54 expands in cold expander crucible 58 to form a discharge stream 16 . The effluent stream 160 is returned to the cold end of the heat exchanger ,3〇 where it is warmed and mixed with the exhaust stream from the warm expander 丨 34 to form a stream 162. Stream 162 is warmed in heat exchanger 13() to form recirculating stream 114. The recirculation stream 114 is then mixed with the compressed feed stream i 12 and fed to the suction portion of the recirculation compressor 118. Stream 1 54 is further cooled in the heat exchanger 丨3〇 to form a high pressure dense phase stream 1 64. The south pressure dense phase flow 164 is withdrawn from the cold end of the heat exchanger 丨3〇 at a temperature of about 96 K, reducing the pressure across one or more expansion devices 166 to form a stream 168 where the stream 丨 68 is fed directly In the liquid reservoir 170. As used herein, the phrase "direct feed," means the designated machine, after exiting the one or more expansion devices 66, is supplied to the liquid reservoir 170 via a conduit without encountering any other changes that may change. The specified flow, ', temperature, or pressure device. Again, as used herein, "direct connection" 8 201213692 means connecting the first device or part of the device to the second device or part of the device without any The equipment intermediate or part that passes, for example, the composition, temperature, or pressure of the first set of streams to the second unit may be altered. Stream 168 is streamed into the liquid reservoir 170 to produce a majority Liquid and some vapor. The liquid from stream 16 8 is added to the liquid already present in the liquid reservoir 170 while the boiling vapor is combined with the vaporized vapor already present in the liquid reservoir 170. From the liquid The reservoir [7] draws a combined vapor stream 172 consisting of a surge of vapor and vaporized vapor and, during normal operation, is fed to the heat exchanger 丨3 of the liquefier 1〇1 in a stream 174. The stream 174 is warmed in the exchanger 130 to form a warmed boiling and vaporizing vapor stream 1 〇2 and mixed with the low pressure feed weir to form a combined stream 104 and fed into the liquefier 1 〇1 for recompression compression 1 〇 6. If the liquefier 101 is not operating, the vapor reservoir 710 vaporized vapor may be removed from the liquid reservoir 170 as a combined vapor stream 172, 176, reducing one or more expansions. The pressure of the device forms a stream 180 and is vented to the atmosphere to control the pressure of the liquid reservoir 。7. One of the significant benefits of this system configuration is a simplified design. Heat exchanger 13〇, expander 134, 15δ and The relevant conduit can be isolated, for example, by a margin material such as mineral wool, polyurethane foam, foamed glass, pyrogel or suitable substitutes, or stand alone In a small close-up cold box connected by an insulated official track. Reducing the size requirements of the cold box when handling and orchestrating routes is particularly important because larger pre-insulated loads (i.e., cold box loads) may be difficult or impossible to reach certain 201213692 destinations. Furthermore, 'relative to the conventional belief, the design of recovering the vaporized vapor from the liquid storage tank i 7〇 is surprisingly improved by the design of the vaporizer gas and the storage system. The overall efficiency of the liquefier 101 and the storage system is about 0 5 to 1.0. % (depending on the relative size of the liquid reservoir 170 and the liquefier 101 and the insulation of the tank) 'because its cold is used to partially cool the product and reduce the power required by the liquefier 101 rather than being directly It is wasted to the atmosphere. In addition, the reduced nitrogen feed flow required (because the recovery of previously drained nitrogen) may result in the use of smaller ASUs. If the low pressure nitrogen feed stream 1 entering the liquefier 1 〇1 is at a pressure high enough for the low pressure gas feed stream 1 to directly enter the suction portion of the recycle compressor 118, then the The material compressor 1〇6 can also be eliminated, and in this case 'the warmed tank ablation and vaporization vapor stream 1〇2 can be vented through the valve to the atmosphere to simply control the pressure of the liquid reservoir 170. Due to the surprising and unexpected results, Applicants have discovered that if the high pressure dense phase stream 164 is cooled by indirect heat exchange against the combined vapor stream 174 recovered in the heat exchanger 13 crucible to a temperature below the discharge stream 16 Torr, the high pressure dense phase The pressure of stream 164 is reduced to a pressure of 16 Torr. The pressure of the stream 16 will not cause a significant amount of sulphur gas to be produced. Therefore, the efficiency of the liquefier 1 不会 will not be excluded by the exclusion of the additional separator and its associated components. reduce. In fact, it will be apparent to those skilled in the art that this exemplary embodiment eliminates the need for separators and subcoolers (e.g., separator 304 and subcooler 3 10 of Figure 3) while maintaining high efficiency. For example, although conventional systems and methods can use two or more separators to recover such ablation vapors under reduced pressure, the disclosed system and method 10 201213692 can achieve and subtract substantial capital costs and substantial delivery meters. Draw the same results while achieving the same or better efficiency. In another embodiment, and as illustrated in Figure 2, a similar system and method similar to that of Figure 1 is disclosed; however, this particular embodiment includes different expander arrangements. In this system/method, stream 124 from the recycle compressor aftercooler 122 is split into two streams 226 and 228 which are fed to the parallel arrangement of warm and cold pressers 238 and 246. The end of the compressor. The separate exhaust streams 240 and 248 of the warm and cold compressors 238 and 246 are combined into a stream 249 and cooled in the aftercooler 250 prior to being fed to the heat exchanger 130 in stream 252. Stream 252 is cooled to a first intermediate temperature in heat exchanger 130 prior to being separated into streams 232 and 253. Stream 232 is expanded in warm expander 234 to form stream 236 and combined with warmed discharge stream 160 to form stream 162 at an intermediate location of heat exchanger 13A. Stream 253 is further cooled to a second intermediate temperature and subdivided into streams 256,254. Stream 256 is expanded in cold expander 258 to form a discharge stream 160. The discharge stream 16 0 is then warmed in the heat exchanger 13A. Further, the stream 2 5 4 is cooled in the heat exchanger 130 to form the high pressure dense phase stream 16 4 ' to the high pressure dense phase stream 164 via the expansion device 16 6 to the liquid reservoir i 7 . Figure 3 is a flow diagram of a prior art method previously disclosed with the same expander configuration as shown in Figure 1, but which does not involve aspirating vapor or vaporization recovery from the tank. Figure 3 is for illustrative purposes and is used to compare with the system and method of Figure 1. 11 201213692 As illustrated in Fig. 3, the cold end separator 304 and the subcooler 3 10 are added to the liquefier 30, and the ablation and vaporization vapor are not recovered from the liquid storage tank. The high pressure dense phase flow 164 from the cold end of the heat exchanger crucible 30 is depressurized in one or more expansion devices 3, and then the final two phase flow 302 is coupled to a cold expander discharge stream that may contain some liquid 160 — fed to a separator 304. The vapor stream 306 from the separator 304 is warmed to an intermediate temperature in the heat exchanger 130, where it is combined with the warm expander effluent stream 136 to form stream 16 2 . The liquid stream 308 from separator 304 is overcooled to about 78 κ in subcooler 310 to form stream 3 12 . A portion 3 16 of the supercooled liquid stream 3 12 is depressurized in one or more expansion devices 318 and then vaporized in a subcooler 31 crucible to form a vapor stream 320 and reheated in the heat exchanger crucible 3〇 Forming stream 102 ^ feeds the remaining portion 3 14 of subcooled liquid stream 312 to the liquid reservoir port 7 via one or more expansion devices 166 to form stream 168, wherein stream 168 is fed to the liquid reservoir 17〇. The ablation and vaporization vapor from the liquid storage tank 17 is discharged through a stream 176 through an expansion device 178 to form a stream 180 (discharged into the atmosphere) to control the tank pressure. 4 is a flow chart illustrating exemplary options for several integrated liquefier systems and methods and ASU or nitrogen generators. For example, the low pressure nitrogen feed stream from the warm end of the ASU can be completely or partially replaced by one or more of the alternative feed streams 400, 404 or 408. The high pressure nitrogen stream 4 from the warm end or nitrogen generator of the ASU can also be mixed with stream 112 from the feed compressor post cold a 110 to form stream 402, which can be mixed with stream 114 to form a Feed to the recycle 11 201213692 Compressor 11 8 stream 11 6 . Alternatively, stream 4 〇 may be mixed downstream of where stream 114 is mixed with stream 112, or mixed into the intermediate stage of the feed compressor _ 1 〇 6 or recirculation compressor 117. A low pressure nitrogen stream 404 from a low pressure column or subcooler at the cold end of the ASU can be mixed with a return low pressure stream 74 from the liquid storage tank 7 to form a stream 406 'the stream 406 followed by the heat exchange The device is heated in 3〇. A single column of cold high pressure nitrogen stream 408 from the ASU or nitrogen generator high pressure column or single column nitrogen generator can be combined with the discharge stream 160 from the cold expander crucible 58 to form stream 4 10, which is followed by It is heated in the heat exchanger 130. Additionally, a separate partial stream 412 from the cold end of the liquefier may be fed directly to the a SU or gas generator to provide a cold bead effect while the remaining portion 414 may be fed to the liquid. Storage tank 170. As used herein, the term "separate portion" means a portion having the same chemical composition as the stream, the portion being taken from the stream, and the separated portion stream 412 can be fed to, for example, a high pressure (HP) tower. , Low Pressure (Lp) Tower, Subcooler or ASU Heat Exchanger. Examples Tables 1 and 2 provide exemplary flow rates, temperatures, and pressures for the configuration/method of Figures 1 and 3. The configuration disclosed in Figure 1 The method results in the data of Table 1, wherein 300 tons of liquid nitrogen per day is produced in the liquid storage tank 170. The configuration/method consumes approximately 5,950 kW of electricity. 13 201213692 Table 1 Logistics 100 102 114 132 152 156 160 164 174 Flow rate (kmol/hr) 446 122 2386 978 1977 1409 1409 569 122 446 Temperature (K) 299 299 299 267 303 182 97 96 78 78 Pressure (absolute bar) 1.03 1.03 6.00 31.84 64.80 64.60 6.20 64.60 1.10 1.10 As shown in Figure 3 The configuration/method results in the data of Table 2, which produces 300 tons of liquid nitrogen per day in the liquid storage tank 170. This configuration/method consumes approximately 6000 kW of electricity. Table 2 Logistics 100 102 114 132 152 156 160 164 176 312 314 Slots Middle stream Amount (kmol/hr) 460 97 2552 1238 1871 1369 1369 502 13 557 460 446 (K) 299 299 299 254 303 174 97 99 78 79 79 78 Pressure (absolute bar) 1.03 1.03 6.00 30.05 64.80 64.60 6.20 64.60 1.10 6.00 6.00 1.10 Importantly, the exemplary method of Figure 1/Table 1 produces the same net amount (446 kmol/hr) of liquid nitrogen in the liquid reservoir, but uses less than the previously disclosed method of Figure 3/Table 2. 8 % of electricity, with a lower feed rate of 3% due to recovery from liquid storage tanks 201213692 / E and V vapor (stream 17 4) and removal of tank vaporization losses to the atmosphere (stream 1 76) 1 〇〇), and the elimination of the first separator, the second separator or the subcooler and its associated valves, regulators and insulation covers saves considerable investment costs because the cold part of the liquefier contains essentially only heat The exchanger and associated piping 'so directly isolates the liquefier equipment and eliminates the need for a separate cold box structure and associated valves and controls that accommodate and isolate the first separator, the second separator or subcooler, So 'the size of the cold box is reduced considerably many. Reducing the size requirements of the cold box when handling and orchestrating routes is particularly important because larger pre-insulated loads (i.e., cold box loads) may be difficult or even impossible to achieve certain purposes. Although the present invention has been described in connection with the preferred embodiments of the various embodiments of the invention, it is understood that other specific embodiments may be used or modified and supplemented for execution. The same functions of the present invention are not deviated from the present invention. Therefore, the claimed invention should not be limited to any single embodiment, but should be determined in accordance with the breadth and scope of the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing description, as well as the detailed description of the exemplary embodiments described herein, Exemplary embodiments are shown in the drawings for the purpose of illustrating the specific embodiments; however, the invention is not limited to the disclosed methods and mechanisms. In the drawings: Figure 1 is a flow diagram of the use of a liquid storage tank as a sudden boiling separator and 15 201213692 to recover the ablation and vaporization vapor from a storage tank through the liquefier in accordance with the present invention; An alternative exemplary method of incorporating a different liquefier configuration, a prior flow chart of a 1 1 π awkward expander, wherein the Ma Shi i ° Hai method includes a cold end separator and a subcooler containing a vapor from the tank Or vaporization recovery; and FIG. 4 is a routine diagram illustrating that the flow method of the air separation unit can be integrated in a similar manner with a plurality of different manners, wherein the air separation unit according to the present invention is integrated into the method The process of the process is not inclusive. What is the other [main component symbol description] ASU air separation unit LP low pressure tower 101 liquefier 104 combined flow 108 compressed flow 112 cooling flow 116 logistics 120 compressed flow 124 logistics 128 logistics 132 logistics 136 warm Expansion flow HP two pressure column 100 low pressure nitrogen feed stream 102 ablate and vaporize steam I 0 6 feed compressor 110 aftercooler 114 recycle flow II 8 Ring Compressor 122 Aftercooler 126 Stream 130 Heat Exchanger 134 Warm Expander 138 Warm Pressure Extruder 16 201213692 140 Stream 144 Cooling Stream 148 Compressed Stream 152 High Pressure Stream 156 Stream 160 Discharge Stream 164 High Pressure Dense Phase Flow 168 Stream 172 Merger Vapor stream 176 combined vapour stream 180 stream 228 stream 234 warm expander 238 warmer 246 cold press 249 stream 252 stream 254 stream 258 cold expander 301 liquefier 3 04 cold end separator 308 liquid stream 3 1 2 logistics 316 part of the supercooled liquid stream 142 warm pressure extension aftercooler 146 compression and compression compressor 150 cold compression and extension compressor aftercooler 1 5 4 logistics 1 5 8 cold expander 162 logistics 166 expansion device 170 liquid storage tank 174 logistics 178 Expansion unit 226 stream 232 stream 236 stream 240 bleed stream 248 outflow 250 aftercooler 253 stream 256 stream 300 expansion unit 302 final two-phase stream 306 vapor stream 310 subcooler 314 remaining portion of subcooled liquid stream 318 expansion device 17 201213692 320 Vapor Stream 400 Feed Stream 402 Stream 404 Feed Stream 408 Feed Stream 410 Stream 412 Separate Partial Stream 414 Remaining Part 18

Claims (1)

201213692 VII. Patent Application Range: 1. A method for liquefying a gas, comprising: introducing a feed stream into a liquefier comprising at least one warm expander and a cold expander; feeding the feed in the liquefier The stream is compressed to a pressure above its critical pressure and the compressed feed stream is cooled to a temperature below its critical temperature to form a high pressure dense phase stream; the high pressure dense phase stream is removed from the liquefier and is applied to an expansion device Reducing the pressure of the high-pressure dense phase flow to form a final two-phase flow and then introducing the final two-phase flow into a storage tank; and the violent part of the final two-phase flow of π and 5 hai (fiash p〇rti〇n) The vaporized vapor of the liquid in the reservoir forms a combined vapor stream, wherein the temperature of the high pressure dense phase stream is lower than the discharge stream temperature of the cold expander. 2. The method of claim 2, further comprising heating at least a portion of the combined vapor stream to ambient temperature. 3. The method of claim 2, further comprising mixing the warmed combined vapor stream with the feed stream for recycle. 4. As in the scope of claim 2, the combined vapor stream is vented to the atmosphere as a < method, which additionally includes the pressure of the warming to control the tank. Method of item 2 5. If the scope of patent application is the second, the pressure of the tank is low 19 201213692 at 1.5 bar. 6. The method of claim 2, further comprising removing at least a portion of the combined vapor stream from the storage tank, reducing the pressure of the combined vapor stream in one or more expansion devices to form a low pressure combined vapor stream, and The low pressure combined vapor stream is vented to the atmosphere to control the pressure of the reservoir. 7. The method of claim 2, wherein the feed stream is a low pressure nitrogen feed stream from a warm end of the air separation unit. 8. The method of claim 5, further comprising mixing the low pressure nitrogen stream from the low pressure column or subcooler of the air separation unit with the combined vapor stream from the storage tank prior to heating. 9. The method of claim 2, further comprising removing a separate portion of the dense phase-phase fluid from the liquefier, directly feeding the separated portion of the high-pressure dense phase fluid to the gas separation unit or nitrogen Production & stomach reading for freezing. 10. The method of claim 9 wherein the pressure of the separate portion of the high pressure dense phase fluid is reduced and fed to a high pressure (Hp) column low pressure (Lp) column, subcooled The main heat exchanger of the air separation unit. 11. A system for liquefying atmospheric gases, comprising: 20 201213692 a first conduit for receiving a feed stream; a liquefier 'connecting the fluid to The first conduit is for compressing and cooling the feed stream to form a high pressure dense phase fluid, wherein the liquefier includes at least one warm expander, a cold expander, and a pressure for compressing the feed stream above its critical pressure a compressor and a heat exchanger for cooling the compressed feed stream to a temperature below its critical temperature; a second conduit connected to the liquefier for receiving from the liquefier a high pressure dense phase flow; a first expansion device connected to the second conduit to reduce the pressure of the high pressure dense phase flow to form a final two phase flow; a third conduit to which the fluid is connected to the first An expansion device for receiving the two-phase expansion flow; and a reservoir for connecting the fluid to the third conduit for receiving and storing the two-phase expansion flow, wherein the storage tank is designed to be at or below 1.5 Absolute bar operation, and wherein the heat exchanger is designed such that the temperature of the high pressure dense phase flow is lower than the discharge flow temperature of the s-cold expander. 12. The system of claim 11 wherein the storage tank Directly connected to the third conduit and the first expansion device is directly connected to the second conduit. 13. The system of claim 11 further comprising a fluid connected to the storage tank for acceptance a fourth conduit of the vapor stream, the combined vapor stream 21 201213692 comprising a portion of the final vapor phase of the final two-phase expanded stream and a vaporized vapor portion of the liquid in the reservoir. 14. The system of claim 13 wherein The fourth conduit fluid is coupled to the heat exchanger and the first conduit. 1. The system of claim 13 further comprising a second expansion device fluidly coupled to the fourth conduit The pressure of the combined vapor stream is reduced to control the pressure of the reservoir.