Cryogenic liquid storage tank

Description

[0001] The utility model relates to cryogenic technology, in particular to cryogenic tank equipment for storing cryogenic liquids.

[0002] Cryogenic liquid storage tanks are known that contain an inner vessel with thermal insulation and an outer shell, a liquid drain / fill pipe from the inner vessel, a gas discharge pipe from the inner vessel, shut-off and safety valves (see A.M. Arkharov and A.I. Smorodin, “Cryogenic Systems,” Vol. 2, Moscow, 1999, p. 643, Fig. 5.72, Bulavin A.B., Filin N.V., “Liquid Cryogenic Systems,” Leningrad, 1985, pp. 192-194, Fig. 6.13).

[0003] One of the problems when storing cryogenic liquids in double-walled tanks with vacuum insulation types (e.g. vacuum-powder, vacuum-multilayer) is the possible loss of tightness of the inner vessel or pipelines in the interwall space, the flow of cryogenic liquid into the interwall space, boiling of the liquid with the formation of a vapor phase and an increase in pressure in the interwall space, and if the pressure in the interwall space exceeds the pressure in the inner vessel, destruction (crumpling) of the inner vessel is possible due to the loss of stability of the vessel shell.

[0004] Known devices for limiting the increase in pressure in the inter-wall space provide for connecting the said space to the atmosphere through a safety rupture membrane, which opens if the pressure in the inter-wall space exceeds the atmospheric value, and liquid vapor from the inter-wall space is discharged into the atmosphere.

[0005] However, since the vessel maintains a pressure above atmospheric pressure, if liquid leaks through a leak, the interwall space may overflow and spill. While the spill of cryogenic liquids such as oxygen, nitrogen, and argon is an incident, the spill of liquefied natural gas poses an increased fire and explosion hazard.

[0006] Tanks for storing and transporting cryogenic liquid are known, including an inner vessel and an outer shell made of materials resistant to the effects of cryogenic liquids, a vacuum-insulated cavity between the inner vessel and the shell, a pipe for draining and filling liquid from the inner vessel, passing through the vacuum-insulated cavity and the shell wall, and a membrane safety device located on the outer wall of the shell and connected by an outlet to a gas discharge pipeline, wherein the membrane safety device and the volume of the interwall space are selected with parameters at which, in the event of destruction of the inner vessel, the pressure in the interwall space will not exceed 0.05 MPa, regardless of the pressure in the inner vessel (RU 203053, 2021).

[0007] However, the description of the known solution does not contain information on the calculation method and optimization of the above parameters for different liquids.

[0008] Also known are tanks for storing cryogenic liquid, consisting of an inner vessel, a casing and an evacuated insulating cavity between them, a pipe for draining and filling liquid from the inner vessel and a gas discharge pipe from the inner vessel, passing through the insulating cavity and the wall of the casing, and a membrane safety device installed on the casing, and in one version, the latter can be connected to the gas discharge pipe or the inner vessel by means of a bypass device (S.P. Gorbachev et al. "Technological schemes of cryogenic double-shell tanks for LNG", Chemical and Oil and Gas Engineering Journal, No. 7, 2021).

[0009] By selecting rational values ​​for the flow sections of the bypass device and the safety valve, the destruction of the internal vessel is excluded.

[0010] However, the said solution does not provide the criteria for selecting the said parameters.

[0011] Of the known technical solutions, the closest to the proposed one in terms of technical essence and the achieved result is a reservoir for storing cryogenic liquid, consisting of an inner vessel, a casing and an evacuated insulating cavity between them, and also including a pipe for draining and filling liquid from the inner vessel and a gas discharge pipe from the inner vessel, passing through the insulating cavity and the wall of the casing, and a membrane safety device installed on the casing, the outlet of which is connected by a pipeline to the gas discharge pipe, while the casing is made of a material that is operational at the temperature of the cryogenic liquid, and the thickness of the casing wall is determined from the strength condition at a pressure not lower than the value of the working pressure of the inner vessel (RU 2653611, 2018).

[0012] When the inner vessel is not sealed and the pressure in the interwall space increases, the interwall space membrane opens, and the pressure in the inner vessel and in the interwall space are equalized, thereby preventing overflow of the interwall space and destruction of the inner vessel due to loss of stability of the shell.

[0013] However, if the liquid is stored at high pressure (0.8-1.6 MPa), then it is necessary to increase the thickness of the wall of the outer casing to eliminate the possibility of destruction when liquid spills into the inter-wall space.

[0014] Furthermore, the pressure relief device only activates when the pressure has already reached the emergency threshold. Its activation means complete depressurization of the tank and the release of its entire contents into the atmosphere, leading to significant financial losses and a potential fire and explosion hazard.

[0015] After a membrane trip, it fails to recover. The tank loses its seal, and restoring operation requires replacing the membrane, inspecting the system, and re-chilling the tank, which can be a lengthy and expensive process.

[0016] The technical problem solved by this utility model is to increase the reliability and safety of operation of a cryogenic liquid storage tank, prevent the release of cryogenic liquid to the outside, and reduce the risk of fire and explosion.

[0017] The stated problem is solved in that a reservoir for storing cryogenic liquid contains an internal vessel with a casing and with an isolated cavity between them, a pipe for draining and filling liquid from the internal vessel with a shut-off valve installed on it, a rupture safety membrane of the inter-wall space installed on the casing and safety and drain valves installed on the gas discharge pipe from the internal vessel, characterized in that it is equipped with an additional adjustable drain valve with a drive installed on the gas discharge pipe from the internal vessel, a pressure-vacuum gauge placed in an insulating cavity between the internal vessel and the casing, and a control unit, wherein the pressure-vacuum gauge is connected to the input of the control unit, the output of which is connected to the drive of the additional adjustable drain valve.

[0018] The technical result achieved consists of preventing the overfilling of the inter-wall space of the tank with cryogenic liquid (including liquefied natural gas) in the event of a breach in the tightness of the inner vessel and an increase in pressure in the inter-wall space by equalizing the pressures between the inner vessel and the inter-wall space and establishing a quasi-stationary regime with evaporation of liquid in the inter-wall space and in the vessel at a pressure close to the atmospheric value.

[0019] The achievement of the specified technical result is ensured by integrating continuous monitoring of the pressure in the inter-wall space using a pressure-vacuum gauge integrated into the pressure control system, and the use of membrane safety devices (rupture membrane) in case of an emergency.

[0020] The essence of the utility model is explained by a drawing, which depicts the proposed reservoir for storing cryogenic liquid.

[0021] The cryogenic tank comprises an inner vessel 1 and an outer shell 2 (casing) made of materials resistant to the effects of cryogenic liquids, an interwall space 3 (a vacuum-insulated cavity between the inner vessel and the shell), a liquid drain / fill pipe 4 from the inner vessel 1 with a shut-off valve 5 installed on it. A drain valve 7 and a safety valve of the inner vessel 8 are installed on the gas discharge pipe 6 from the inner vessel 1. A membrane safety device of the interwall space 9, connected to the atmosphere, is installed on the outer wall of the shell 2.

[0022] The membrane safety device 9 is a device consisting of a rupture safety membrane (one or more) and its fastening unit (clamping elements) assembled with other elements, ensuring the required discharge of the mass of the steam-gas mixture at a given response pressure.

[0023] An additional adjustable drain valve 10 with a drive 11 is installed on the gas discharge pipe 6, and a pressure-vacuum gauge 12 is installed in an isolated cavity (inter-wall space 3) between the inner vessel 1 and the casing 2, which is placed in a branch pipe with a valve (not shown in the figure) on the cylindrical part of the shell 2 of the tank, without violating the integrity of the housing during the normal operation of the tank.

[0024] The output of the pressure gauge 12 is connected to the input of the control unit 13, the output of which is connected to the drive 11 of the additional adjustable drain valve 10.

[0025] The letter "A" in the drawing indicates a possible leak in the inner vessel.

[0026] The cryogenic liquid storage tank operates as follows.

[0027] During normal tank operation, the liquid pressure in inner vessel 1 does not exceed 1.6 MPa. Liquid from inner vessel 1, under a pressure of 1.6 MPa, is discharged through valve 5 to the consumer.

[0028] From the inner vessel 1 and from the inter-wall space 3, vapors are discharged through the gas discharge pipe 6. The maximum permissible pressure is maintained in the inter-wall space 3.

[0029] If the pressure in the inner vessel 1 rises above the working value, the safety valve 8 installed on the branch pipe that is connected to the gas discharge pipe 6 from the inner vessel 1 opens, and the vapors from the inner vessel 1 are discharged into the atmosphere.

[0030] If the wall of the inner vessel 1 or the fluid lines passing through the interwall space 3 become leaky during draining, fluid from the vessel enters the interwall space 3 through the leak, where it accumulates and partially evaporates. This causes the pressure in the interwall space 3 to increase.

[0031] During operation of the tank, the pressure gauge 12, connected to the control unit 13, monitors the change in pressure in the inter-wall space 3 in real time.

[0032] Based on the information about the dynamics of pressure changes in the inner vessel 1 and in the interwall space 3, as well as the degree of filling of the interwall space with liquid, the control unit 13 generates a signal to open and close the drain valve 11.

[0033] When the pressure in the inter-wall space 3 reaches a value higher than the permissible value, the drive 11 opens the additional drainage valve 10 upon a signal from the control unit 13.

[0034] After the valve 10 is opened, the cryogenic liquid vapor from the inner vessel is released into the atmosphere, the pressure in the inner vessel 1 decreases and becomes equal to the pressure in the interwall space 3, the value of which on the shell 2 does not exceed the atmospheric pressure.

[0035] A quasi-stationary mode is established with evaporation of liquid in the inter-wall space 3 and in the inner vessel 1.

[0036] Burst disc 9 is provided in the device in case the control system (including the pressure gauge and maintenance personnel) fails and the pressure reaches critical values.

[0037] Thus, the emergency mode is completely analogous to the emergency mode in tanks with low liquid pressure and there is no need to increase the thickness of the vessel wall.

[0038] In the proposed cryogenic tank, these devices are not opposed, but complement each other: pressure gauge + safety valve + rupture disc in case of an emergency.

[0039] The proposed device, through the integrated use of a pressure gauge, a pressure control circuit on the outlet line from the internal tank and a rupture disc (diaphragm safety device) in case of an emergency, increases the reliability of the cryogenic tank and allows for the prediction of the tank's condition.

[0040] The proposed solution makes it possible to integrate a pressure gauge into a control system (SCADA, controllers) for automatic pressure maintenance (e.g. opening / closing of electro-pneumatic valves).

Claims

A reservoir for storing a cryogenic liquid, comprising an internal vessel with a casing and with an insulated cavity between them, a pipe for draining and filling liquid from the internal vessel with a shut-off valve installed thereon, a rupture safety membrane of the inter-wall space installed on the casing, and safety and drain valves installed on a gas discharge pipe from the internal vessel, characterized in that it is equipped with an additional adjustable drain valve with a drive installed on the gas discharge pipe from the internal vessel, a pressure-vacuum gauge placed in an insulating cavity between the internal vessel and the casing, and a control unit, wherein the pressure-vacuum gauge is connected to the input of the control unit, the output of which is connected to the drive of the additional adjustable drain valve.

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