Method of cooling a system in the range 120k to 200k

Abstract

A system and method are provided for cooling a user of a liquid cryogenic fluid using an inert, unpressurized liquid refrigerant in a temperature range of 120K to 200K. This includes: maintaining a first liquid cryogenic fluid within a first predetermined temperature range using a subcooler and / or a recirculation pump; maintaining a second liquid cryogenic fluid within a second predetermined temperature range using a heat exchanger; and recondensing the second liquid cryogenic fluid using pressurized first liquid cryogenic fluid.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 027,819, filed May 20, 2020, pursuant to 35 U.SC §119(a) and (b), the entire contents of which are incorporated herein by reference. Background Technology

[0003] In industrial applications, isothermal cooling is required within a temperature range of 120K to 200K. This isothermal cooling must be inert, low-pressure, and cost-effective. Within this temperature range, the molecules that can be used (nitrogen, oxygen, argon, krypton, xenon, carbon dioxide, methane, ethane, etc.) are subject to certain limitations. These limitations may include price, flammability, high saturation pressure, or combinations thereof, making them unsuitable for user applications.

[0004] A typical example of existing technology for this application is the use of an inert refrigerant (such as nitrogen) that indirectly transfers heat to the user in a single loop. However, the user's demand for low-pressure cooling results in temperatures lower than required. For example, N2 refrigerant at 1 bara (absolute bar) produces an evaporation temperature of approximately 80 K. This results in wasted cooling energy input in the range of 80 K to 120 K (or worse, up to 200 K). Summary of the Invention

[0005] A system is provided that uses an inert, unpressurized liquid refrigerant in a temperature range of 120K to 200K to cool a user of a cryogenic liquid fluid. The system includes a primary cooling circuit having at least a main cryogenic tank, a subcooler, and a recirculation pump, and is designed to operate using a first cryogenic liquid fluid under pressure. The primary cooling circuit is connected to a secondary cooling circuit consisting of a liquid phase separator connected to the cryogenic liquid fluid user. This liquid phase separator houses a heat exchanger and is designed to operate using a second cryogenic liquid fluid at very low pressures. The secondary cooling circuit is connected to a gas buffer tank, allowing the addition or removal of the second cryogenic liquid fluid from the secondary cooling circuit during cooling and / or heating phases. The system is configured to condense the second cryogenic liquid fluid using a pressurized first cryogenic liquid fluid.

[0006] A method is provided for cooling a user of a liquid cryogenic fluid using an inert, unpressurized liquid refrigerant in a temperature range of 120K to 200K. The method includes: maintaining a first liquid cryogenic fluid within a first predetermined temperature range using a subcooler and / or a recirculation pump; maintaining a second liquid cryogenic fluid within a second predetermined temperature range using a heat exchanger; and recondensing the second liquid cryogenic fluid using pressurized first liquid cryogenic fluid. Attached Figure Description

[0007] To further understand the nature and purpose of the invention, reference should be made to the following detailed description in conjunction with the accompanying drawings, in which similar elements are given the same or similar reference numerals, and in the drawings:

[0008] - Figure 1 This is a schematic diagram of one embodiment of the present invention.

[0009] Figure Labels

[0010] 101 = Primary Circuit Main Cryogenic Tank

[0011] 102 = Secondary loop main cryogenic tank / liquid phase separator

[0012] 103 = Liquid cryogenic fluid flow

[0013] 104 = Cryogenic fluid flow undergoing vaporization

[0014] 105 = Exhaust valve

[0015] 106 = Supercooler

[0016] 107 = Warm Recirculating Flow

[0017] 108 = Supercooled recirculation flow

[0018] 109 = Recirculation control valve

[0019] 110 = Recirculation pump

[0020] 111 = Liquid Buffer Tank

[0021] 112 = Buffer tank transport flow

[0022] 113 = Buffer tank transfer control valve

[0023] 114 = Liquid cryogenic fluid (in the main cryogenic tank)

[0024] 115 = Cryogenic fluid vapor (in the main cryogenic tank)

[0025] 116 = Cryogenic Liquid Fluid User

[0026] 117 = External liquid cryogenic fluid source

[0027] 118 = Supercooler bypass line

[0028] 119 = First pressure transmitter (in the primary circuit main cryogenic tank)

[0029] 120 = First Peripheral Interface Controller

[0030] 121 = Second Peripheral Interface Controller

[0031] 122 = Second pressure transmitter (in the supercooler bypass line)

[0032] 123 = Third Peripheral Interface Controller

[0033] 124 = Fourth Peripheral Interface Controller

[0034] 125 = Bypass control valve

[0035] 126 = Secondary circuit gas buffer tank

[0036] 127 = Secondary circuit heater

[0037] 128 = Secondary circuit compressor

[0038] 129 = Secondary circuit main cryogenic tank coil / heat exchanger

[0039] 130 = Cold secondary flow

[0040] 131 = Warm secondary flow

[0041] 201 = Primary Cooling Circuit

[0042] 202 = Secondary cooling circuit Detailed Implementation

[0043] The following describes illustrative embodiments of the invention. While the invention is susceptible to various modifications and alternatives, specific embodiments thereof have been shown by way of example in the accompanying drawings and described in detail herein. However, it should be understood that the description of specific embodiments herein is not intended to limit the invention to the specific forms disclosed, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0044] Of course, it will be understood that in the development of any such practical embodiment, many implementation-specific decisions must be made to achieve the developer’s specific goals (e.g., compliance with system-related and business-related constraints), which will vary depending on the implementation. Furthermore, it will be understood that such development work can be complex and time-consuming, but remains a common assurance to those skilled in the art who will obtain the benefits of this disclosure.

[0045] The following system describes the use of liquid nitrogen, but those skilled in the art will recognize that any suitable cryogenic fluid (oxygen, methane, etc.) can be used with the same concept, depending on the temperature level required to cool the target system.

[0046] The only accompanying drawing schematically illustrates one embodiment of the invention. The reliquefaction system includes a primary cooling circuit 201, which comprises a primary circuit main cryogenic tank 101, a liquid nitrogen stream 103, a vaporized nitrogen stream 104, and an exhaust valve 105 fluidly attached to the vaporized nitrogen stream 104. The primary cooling circuit also includes a supercooler 106, a warm recirculation stream 107, a subcooled recirculation stream 108, a recirculation control valve 109, and a recirculation pump 110. The primary cooling circuit also includes a liquid buffer tank 111, a buffer tank transfer stream 112, and a buffer tank transfer control valve 113. The liquid buffer tank 111 can be refilled as needed from an external liquid nitrogen source 117 (such as a liquid nitrogen truck trailer (not shown)).

[0047] The reliquefaction system includes a secondary cooling circuit 202, which includes a secondary circuit main cryogenic tank 102, a secondary circuit gas buffer tank 126, a secondary circuit heater 127, a secondary circuit compressor 128, and a secondary circuit main cryogenic tank coil 129.

[0048] Liquid nitrogen 114 is stored at saturation conditions (pressure P1) in the primary loop main cryogenic tank 101. Nitrogen vapor 115 occupies the headspace of the primary loop main cryogenic tank 101. During normal operation, a portion of the liquid nitrogen 114 is extracted from the primary loop main cryogenic tank 101 and sent to the secondary loop main cryogenic tank 102. Within the secondary loop main cryogenic tank coil 129, liquid nitrogen stream 103 exchanges heat with liquid nitrogen stream 103, thereby providing internal cooling for the secondary loop main cryogenic tank 102. As the liquid nitrogen stream 103 passes through the secondary loop main cryogenic tank coil 129, at least partially vaporized stream 131 is at least partially condensed. The secondary loop main cryogenic tank 102 serves as a vapor / liquid phase separator. Therefore, the liquid nitrogen stream 103 will be vaporized, and the vaporized nitrogen stream 104 will be recycled back to the primary loop main cryogenic tank 101.

[0049] Simultaneously, a portion of liquid nitrogen 114 is extracted as a warm recirculation stream 107 from the primary loop main cryogenic tank 101 and sent to the recirculation pump 110. The pressurized liquid nitrogen then enters the supercooler 106. The supercooler 106 cools the liquid nitrogen by at least a few degrees Celsius. This can be accomplished by any refrigeration unit known in the art capable of achieving the desired temperature level. The subcooled recirculation stream 108 is then sent back to the primary loop main cryogenic tank 101, where it is introduced as a spray into the vapor phase 115. Upon contact with the subcooled liquid, the vaporized nitrogen stream 104 returning from the secondary loop main cryogenic tank 102 is cooled and condensed back into saturated liquid 114.

[0050] The lower the temperature downstream of subcooler 106, the less pumping flow is required into subcooler 106. Therefore, utilizing the lowest possible downstream temperature will reduce the power consumed by recirculation pump 110, and only reduce the size of recirculation pump 110, as well as the size of the piping in flows 107 and 108 and within exchanger 106. However, approaching such low subcooling temperatures (typically at least 1 or 2 degrees Celsius (possibly at least 3 degrees Celsius) above the freezing point of the cryogenic fluid under internal pressure) presents challenges. For example, extreme care must be taken to ensure minimal impurities in the nitrogen flow (especially argon), which could freeze and disrupt the entire process. To achieve subcooling levels below fourteen degrees Celsius and preferably ten degrees Celsius below the freezing point of nitrogen, the argon content typically needs to be below 2% mol, and preferably below 0.5% mol.

[0051] The primary loop main cryogenic tank 101 may include a first pressure transmitter 119. The first pressure transmitter 119 may interface with one or more peripheral interface controllers (PICs). A first PIC 120 is functionally connected to the first pressure transmitter 119 and the recirculation control valve 109. A second PIC 121 is functionally connected to the first pressure transmitter 119 and the vent valve 105. A subcooler bypass line 118 is fluidly connected to the warm recirculation flow 107 and the subcooled recirculation flow 108, thereby allowing at least a portion of the pressurized recirculation flow exiting the recirculation pump 110 to bypass the subcooler 106. The subcooler bypass line 118 may include a second pressure transmitter 122. The second pressure transmitter 122 may interface with one or more PICs. A third PIC 123 is functionally connected to the second pressure transmitter 122, the bypass control valve 125, and the recirculation pump 110. Alternatively, the pressure at 119 can be controlled by using a variable speed drive on pump 110 without bypassing 118.

[0052] The delivery pressure of the liquid nitrogen flow 103 at the interface with the secondary loop main cryogenic tank 102 can be correlated with the pressure in the primary loop main cryogenic tank 101. The pressure within the primary loop main cryogenic tank 101 is primarily controlled by a recirculation control valve 109 on the subcooled recirculation flow 108 exiting the supercooler 106. If the first pressure transmitter 119 indicates a low pressure in the primary loop main cryogenic tank 101, the first PIC 120 opens the recirculation control valve 109. If the first pressure transmitter 119 indicates a high pressure in the primary loop main cryogenic tank 101, the first PIC 120 closes the recirculation control valve 109. The cooling capacity of the supercooler 106 is adjusted based on the outlet temperature. The outlet temperature of the supercooler 106 is directly affected by the opening position of the downstream recirculation control valve 109. The greater the opening of the recirculation control valve 109 (meaning a higher pressure in the primary loop main cryogenic tank 101), the greater the tendency for the temperature to rise downstream of the supercooler 106. Therefore, the cooling capacity of the supercooler 106 will increase.

[0053] The recirculation pump 110 can be a variable frequency drive (VFD) type pump. The speed of the recirculation pump 110 is controlled by a third PIC 123, which will accelerate the pump if the pressure read by the second pressure transmitter 122 in the subcooling line is low (meaning that the subcooling flow is increasing).

[0054] If the supercooler 106 cannot provide sufficient cooling capacity to compensate for the refrigeration load required by the secondary loop primary cryogenic tank 102, the pressure in the cooling loop will increase. To prevent the pressure from rising above the required or predetermined level (which could affect the secondary loop primary cryogenic tank 102), an exhaust valve 105 is installed on the vaporized nitrogen flow 104 returning from the secondary loop primary cryogenic tank 102 to the primary loop primary cryogenic tank 101. Upon receiving feedback from the first pressure transmitter 119, the second PIC 121 instructs the exhaust valve 105 to open to reduce and / or regulate the pressure in the primary loop primary cryogenic tank 101. The exhaust valve 105 may be installed between two valves (not shown) connected only to the primary loop primary cryogenic tank 101, or only to the vaporized nitrogen flow 104.

[0055] A supercooling system may not fully compensate for the heat load from the user. By design, a supercooling system can be capable of operating below the heat load. The supercooling system may perform poorly or stop due to malfunction or maintenance, or it may be deliberately slowed down if a trade-off between power consumption costs and the availability of liquid nitrogen is a concern.

[0056] When the flow rate of the subcooled recirculation flow 106 or the warm recirculation flow 107 decreases or stops, a liquid cryogenic fluid flow 103 is maintained through the primary loop main cryogenic tank 101 leading to the secondary loop main cryogenic tank 102. Since the cooling load from the user is not compensated by the subcooler 106, the pressure within the liquid cryogenic fluid flow 103 and the vaporized cryogenic fluid flow 104 will tend to increase. The drain valve 105 will open as needed to maintain the required constant tank pressure.

[0057] Liquid buffer tank 111 is used to isolate the cooling circuit (i.e., the subcooled recirculation flow 106 or the warm recirculation flow 107) from interference caused by liquid nitrogen transfer from an external liquid nitrogen source 117 (such as a trailer for the loading circuit). The liquid nitrogen stockpile in liquid buffer tank 111 can also be used to maintain the liquid nitrogen supply in both the subcooled recirculation flow 106 and the warm recirculation flow 107 when the flow through the subcooling system decreases or stops. The pressure in liquid buffer tank 111 is controlled by a booster coil (not shown) while liquid nitrogen is transferred to the primary circuit main cryogenic tank 101.

[0058] In one embodiment of the invention, cooling is provided to the cryogenic liquid user 116 by an inert liquid within the desired temperature range of 120K-200K and at low pressure. This avoids supplying temperatures lower than the desired temperature, thus preventing inefficient cooling. Consequently, overall cooling efficiency is improved.

[0059] The proposed solution consists of two cooling circuits 201 / 202 using thermal integration. The primary cooling circuit 201 can use a cryogenic fluid, which may be flammable and maintained at a high pressure. This allows for the use of relatively inexpensive fluids (e.g., nitrogen or methane). The primary cooling circuit 201 consists of a primary circuit main cryogenic tank and at least one subcooler 106 for subcooling the liquid refrigerant.

[0060] The pressurized subcooled liquid refrigerant 108 generated in the primary cooling circuit is then introduced into the secondary circuit main cryogenic tank coil 129 to exchange heat with the secondary cooling circuit 202. The transfer of the pressurized subcooled liquid refrigerant to the heat exchanger can be carried out using a transfer pump or simply by gravity. The secondary cooling circuit 202 typically consists of a smaller closed loop that includes the secondary circuit main cryogenic tank 102, houses the secondary circuit main cryogenic tank coil 129, and supplies refrigerant to the liquid cryogenic fluid user 116.

[0061] The specific refrigerant used in the secondary loop 202 can be selected from more expensive inert refrigerants that have a saturation temperature in the range of 120K-200K at low pressure. The table below lists the possible refrigerant combinations and process conditions:

[0062]

[0063] As a non-limiting example, consider the following system in which methane is used as the primary cooling loop fluid and xenon is used as the secondary cooling loop fluid.

[0064] As the cooling phase begins, the primary loop main cryogenic tank 101 is filled with a predetermined amount of methane at a pressure slightly greater than 15.5 bara (±5 bar) to maintain the methane in a fully saturated phase. The secondary loop main cryogenic tank 102 is filled with a predetermined amount of xenon at a pressure slightly greater than 1 bara (±1 bar) to maintain the xenon in a fully saturated phase.

[0065] As described above, the first portion of saturated methane exits the primary loop main cryogenic tank 101 as a warm recirculation stream 107, is pressurized in the recirculation pump 110, and, as needed, bypasses or passes through the subcooler 106 via the subcooler bypass line 118 to maintain the desired temperature. Subcooled methane exits the subcooler 106 via a subcooled recirculation stream 108 and is reintroduced into the primary loop main cryogenic tank 101 as it is injected into the cryogenic fluid vapor space 115.

[0066] The second portion of the saturated methane leaves the primary loop main cryogenic tank 101 again as a warm recirculation stream 107, but this portion then enters the secondary loop main cryogenic tank coil 129 via a liquid cryogenic stream 103A. As the liquid cryogenic stream 103A passes through the secondary loop main cryogenic tank coil 129, it cools the xenon contained in the secondary loop main cryogenic tank 102, and the liquid cryogenic stream itself is heated and typically vaporized 104. The vaporized cryogenic fluid stream 104 is then returned to the primary loop main cryogenic tank 101, where, as the vaporized cryogenic fluid stream is injected into the cryogenic fluid vapor space 115, it directly exchanges heat with the subcooled recirculation stream 108.

[0067] As heat is transferred to the liquid cryogenic fluid flow 103A, reaching and / or maintaining the saturation temperature (and therefore saturation pressure) within the secondary loop main cryogenic tank 102, a portion of the cold secondary flow 130 is directed to the liquid cryogenic fluid user 116. The liquid nitrogen user 116 will utilize the cold secondary flow 130 for internal cooling purposes. Therefore, the cold secondary flow 130 will be heated and typically vaporized. The warm secondary flow 131 will be recirculated back to the secondary loop main cryogenic tank 102.

[0068] As the heating phase begins, the flow rate of the saturated second portion that has flowed through the secondary loop primary cryogenic tank coil 129 decreases and then stops. Since no heat is transferred from the secondary loop primary cryogenic tank 102, the saturation temperature within the secondary loop primary cryogenic tank 102 is no longer maintained. As a portion of the cold secondary flow 130 continues to be directed to the liquid cryogenic fluid user 116, the warm secondary flow 131 is now redirected to the secondary loop gas buffer tank 126. The warm secondary flow 131 passes through the secondary loop heater 127, where it is fully vaporized and / or superheated, and then through the secondary loop compressor 128, which increases the pressure of the flow and allows it to be introduced into the secondary loop gas buffer tank 126. Thus, the predetermined amount of saturated liquid xenon initially maintained in the secondary loop primary cryogenic tank 102 is depleted and transferred to the secondary loop gas buffer tank 126.

[0069] It should be understood that many additional changes in details, materials, steps, and arrangements of parts that have been described herein to explain the essence of the invention can be made by those skilled in the art within the principles and scope of the invention as set forth in the appended claims. Therefore, the invention is not intended to be limited to the specific embodiments given in the examples above.

Claims

1. A system for cooling a user of a cryogenic liquid fluid using an inert, unpressurized liquid refrigerant in the temperature range of 120 K to 200 K, comprising: The primary cooling circuit comprises at least a main cryogenic tank, a subcooler, and a recirculation pump configured to operate at pressures of 6.5 bara ± 5 bar, 15.5 bara ± 5 bar, 18.5 bara ± 5 bar, or 33 bara ± 5 bar, and is designed to operate using a first liquid cryogenic fluid. in, The primary cooling circuit is connected to a secondary cooling circuit, which consists of a liquid phase separator connected to the cryogenic fluid user. This liquid phase separator houses a heat exchanger and is designed to operate with a second cryogenic fluid at a pressure of 1 bara ± 1 bar. The secondary cooling circuit is connected to a gas buffer tank, thereby allowing the addition or removal of the second cryogenic liquid from the secondary cooling circuit during the cooling and / or heating phases. The system is configured to use a pressurized first liquid cryogenic fluid to condense the second liquid cryogenic fluid.

2. The system as claimed in claim 1, wherein, The first liquid cryogenic fluid is liquid nitrogen.

3. The system as described in claim 1, wherein, The second liquid cryogenic fluid is liquid krypton.

4. The system as claimed in claim 1, wherein, The first cryogenic liquid is methane, and the second cryogenic liquid is tetrafluoride.

5. The system as claimed in claim 1, wherein, The first cryogenic liquid is methane, and the second cryogenic liquid is xenon.

6. The system of claim 1, wherein, The first cryogenic liquid is methane, and the second cryogenic liquid is nitrous oxide.

7. A method for cooling cryogenic liquid users using an inert and unpressurized liquid refrigerant in a temperature range of 120 K to 200 K as a cooling medium, wherein a system comprising: The primary cooling circuit comprises at least a main cryogenic tank, a subcooler, and a first liquid-operated recirculation pump configured to operate at pressures of 6.5 bara ± 5 bar, 15.5 bara ± 5 bar, 18.5 bara ± 5 bar, or 33 bara ± 5 bar using an inert, unpressurized liquid refrigerant in a temperature range of 120 K to 200 K. The secondary cooling loop, consisting of a liquid phase separator connected to the cryogenic liquid user, houses a heat exchanger and is configured to operate a second liquid at a pressure of 1 bara ± 1 bar using an inert, unpressurized liquid refrigerant comprising a temperature range of 120 K to 200 K. The method includes: Using the subcooler and / or the recirculation pump, the first liquid containing an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K is maintained within a first predetermined temperature range. Using this heat exchanger, the second liquid, containing an inert and unpressurized liquid refrigerant in a temperature range of 120 K to 200 K, is maintained within a second predetermined temperature range, and The first liquid, which is pressurized and contains an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K, is used to recondense the second liquid, which also contains an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K.

8. The method of claim 7, wherein, The first liquid containing an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K is liquid nitrogen.

9. The method of claim 7, wherein, The second liquid, which contains an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K, is liquid krypton.

10. The method of claim 7, wherein, The first liquid comprising an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K is methane, and the second liquid comprising an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K is tetrafluoride.

11. The method of claim 7, wherein, The first liquid comprising an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K is methane, and the second liquid comprising an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K is xenon.

12. The method of claim 7, wherein, The first liquid comprising an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K is methane, and the second liquid comprising an inert and unpressurized liquid refrigerant in the temperature range of 120 K to 200 K is nitrous oxide.

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