CN113418135A

CN113418135A - Novel marine LNG fuel self-pressurization gas supply system and control method thereof

Info

Publication number: CN113418135A
Application number: CN202110828963.0A
Authority: CN
Inventors: 郑健; 叶爱君
Original assignee: 708th Research Institute of CSIC
Current assignee: 708th Research Institute of CSIC
Priority date: 2021-07-22
Filing date: 2021-07-22
Publication date: 2021-09-21

Abstract

The invention provides a novel self-pressurization gas supply system for marine LNG fuel. The invention further provides a control method of the novel marine LNG fuel self-pressurization gas supply system. The invention optimizes the LNG fuel gas supply system by adopting two key technologies: firstly, adopt a novel low resistance, efficient from booster and from turbocharging system, reduce from turbocharging system's resistance, improve from turbocharging system's pressure boost effect from turbocharging system from improving from the angle of booster inner structure form, increase from turbocharging system valve flow area and optimize LNG fuel gas supply system. And secondly, the precision control of the gas supply pressure and the safety protection cut-off are realized from the perspective of improving the system design and the control method thereof, and the practical problem of natural gas emission escape is solved.

Description

Novel marine LNG fuel self-pressurization gas supply system and control method thereof

Technical Field

The invention relates to a novel gas supply system for ship LNG fuel and a control method thereof.

Background

With the increasingly strict environmental requirements of ships, the use of clean energy Liquefied Natural Gas (LNG) instead of conventional fuel oil has become one of the main directions of ship fuel. LNG is stored in liquid form on board the ship, but is very volatile to produce boil-off gas after being heated on board, creating a flammable and explosive hazardous environment. To avoid the diffusion of volatile gases from such alternative fuels, the international maritime organization allows the use of type C fuel tanks (pressure vessel type) for storing such low flash point fuels.

In an LNG liquid tank which is in a vacuum heat insulation form and is coated with a heat insulation material for storing LNG liquid, when fuel needs to be supplied to a ship engine or other gas consumption equipment, the pressure of the tank is insufficient, an LNG vaporizer called a self-booster is usually adopted to raise the pressure of the low-temperature LNG liquid tank to a required value, and then the LNG liquid is heated to be normal-temperature gas fuel, so that the pressure, temperature and flow rate of the gas fuel are ensured to meet the technical requirements of the ship engine or other similar gas consumption equipment.

For a self-pressurization system form and principle introduction of a typical LNG tank, see published papers: the design optimization of the self-pressurization device of the liquefied natural gas cylinder for the vehicle is an article of No. 9 of volume 43 of the journal of Low temperature and superconduction in 2015 by Gaoyun. The working principle of the self-pressurization system and the pressurization regulating valve of the key components thereof is described in detail. In the paper, the basic principle of the LNG tank self-pressurization system is shown in figure 1, and the structural form of the mechanical spring self-operated pressurization regulating valve is shown in figure 2.

When the mechanical spring self-operated pressure increasing valve shown in fig. 2 is adopted conventionally, the tightness of the spring changes correspondingly along with the pressure change of the LNG tank, so that the opening degree of the valve is automatically adjusted, the opening degree of the pressure increasing valve is larger when the pressure of the LNG tank is lower, the opening degree of the pressure increasing valve is smaller when the pressure of the LNG tank is higher, and the pressure increasing valve is completely closed when the set pressure of the pressure increasing is reached. However, when the opening degree of the valve is small, the resistance of the valve is greatly increased, and the liquid inflow of the LNG booster (gasifier) is influenced; when the spring fails or the spring force fails to close the valve completely, liquid can continuously flow into the LNG booster (vaporizer), resulting in continuous pressurization of the LNG tank, causing the risk of overpressure in the LNG tank.

The marine LNG gasifier mainly uses hot water, hot oil, steam and other media as heat sources, and a typical marine LNG gasifier scheme is disclosed in published papers: the comparison of the scheme of the marine pipe-wound LNG vaporizer in volume 69 of the journal of the chemical industry, No. S2 of Tianya Jie and Linwensheng, of the research institute of refrigeration and cryogenic engineering of Shanghai university of transportation. The form of the structure of the around-tube LNG vaporizer is shown in figure 3.

The conventional marine LNG self-pressurizer usually adopts a shell-and-tube heat exchanger using various media such as hot water, hot oil, steam and the like as heat sources, and a coil in the heat exchanger is usually manufactured by spirally winding a thin tube. LNG is from booster belongs to the big classification of LNG vaporizer, nevertheless because the particularity of its use occasion, the actual effect of LNG is directly influenced from the booster to the resistance size of LNG heat exchange tube, and the LNG that adopts the tradition to wind tubular LNG vaporizer form design and manufacturing often can appear from the unobvious problem of pressure boost effect when in-service use, especially when LNG booster resistance is too big, can influence the work efficiency of LNG self-booster greatly.

The technical scheme of traditional boats and ships LNG fluid reservoir pressure boost is shown in figure 4, wherein, 1 is the LNG fluid reservoir, 2 is mechanical spring formula pressure boost valve of relying on oneself, and 3 is spiral wound tube formula LNG self-pressurizing ware.

The LNG flows into the spiral-wound tube type LNG self-pressurizing device 3 by its own weight through the height difference between the LNG tank 1 and the spiral-wound tube type LNG self-pressurizing device 3, and therefore the liquid inflow amount of the LNG self-pressurizing device and the pressurizing efficiency of the LNG self-pressurizing device are directly determined by the internal resistance of the spiral-wound tube type LNG self-pressurizing device 3.

Traditional LNG is from booster for in limited space increase heat transfer area as far as possible, improve heat exchange efficiency, consider simultaneously that compensation LNG is from the cold and hot expansion deflection of pipeline that the huge difference in temperature of booster import and export arouses, often adopt one set of or multiunit small-bore pipeline to design with spiral winding coil form.

The phenomenon of insufficient supercharging capacity or slow supercharging often occurs in the actual engineering application of the ship by the LNG self-supercharging device, and the reason is as follows:

firstly, the liquid of the LNG tank 1 flows into the spiral wound tube type LNG self-pressurizing device 3 only by the self weight generated by the liquid level height difference, particularly when the liquid level of the LNG tank is low, the inlet net pressure head generated by the height difference is small, and the power of the LNG flowing into the spiral wound tube type LNG self-pressurizing device 3 is very small;

secondly, in the process of changing liquid into gas, the volume is greatly expanded, so that the flow velocity is rapidly increased, and the pipeline resistance is also greatly increased. The frozen liquid is gasified after entering the spiral wound tube type LNG self-pressurizer 3, and due to the design of the spiral tube form, gas-liquid separation is not timely, so that the mixed flow resistance of the gas and the liquid is large, even gas is reversed to flow back to blow the liquid out of an inlet, and the LNG is difficult to continuously flow into the spiral wound tube type LNG self-pressurizer 3;

finally, the resistance of the small-caliber spiral coil pipe in the spiral winding pipe type LNG self-pressurizing device 3 is too large, and when the resistance of the small-caliber spiral coil pipe and the resistance of the spiral winding pipe type LNG self-pressurizing device are offset by a net pressure head generated by the liquid level height difference at the inlet of the spiral winding pipe type LNG self-pressurizing device 3, the LNG self-pressurizing device can obviously cause insufficient liquid inlet, so that the pressurizing effect is poor, and the phenomenon of insufficient pressurizing capacity or very slow pressurizing process is caused.

Typical LNG fuel supply systems with an auto-supercharged LNG vaporizer on a ship as a main device have been patented as follows (not limited thereto):

authorization notice number: CN 110886670A

The date of authorized announcement: 2020.03.17

The patent name: marine low-pressure gas supply system capable of self-pressurizing gas supply and self-pressurizing gas supply method thereof

In the patent, a front-stage LNG vaporizer in a two-stage heating heat exchanger for LNG vaporization and heating is used as a self-pressurizing device for pressurization, and a BOG self-operated pressure regulating valve is used for pressure reduction. Wherein, the heat exchanger adopts the form of back and forth folding pipe type or winding pipe, and the air supply system realizes the function of adjusting the air supply pressure through a self-operated pressure adjusting valve, which is shown in detail in figure 5.

Authorization notice number: CN 213065523U

The date of authorized announcement: 2021.04.27

The patent name: marine liquefied natural gas low pressure fuel supply system

In the patent, a front-stage LNG vaporizer in a two-stage heating heat exchanger for vaporizing and heating LNG is used as a self-pressurizer for pressurization, a rear-stage NG heater is used as a heater for BOG utilization decompression, and a BOG self-operated pressure regulating valve is used for decompression. See figure 6 for details.

Authorization notice number: CN 111550675A

The date of authorized announcement: 2020.08.18

The patent name: automatic-pressurization low-temperature liquid delivery method and device

The patent controls the opening degree remotely controlled valve automatically by the pressure signal of the tank, and controls the pressurizing process by automatically adjusting the size of the valve. See figure 7 for details.

Authorization notice number: CN 104791602B

The date of authorized announcement: 2018.06.05

The patent name: LNG (liquefied Natural gas) fuel gas supply method and device with BOG (boil off gas) preferentially utilized

This patent uses a self-pressurizer directly serving as the main gasifier, and the BOG generated by the self-pressurizer is used for pressurizing the tank and also for external delivery as fuel. See figure 8 for details.

In the LNG-fueled gas supply system of the above patent application, various optimization schemes for the existing gas supply system are proposed only from the viewpoint of the system principle. However, when the actual gas supply system is used, the LNG self-pressurizing device has too large resistance and the pressure regulating valve has a large structural form to form a large valve resistance, so that the self-pressurizing effect is not obvious and the gas supply pressure is unstable, and the problems of non-ideal self-pressurizing effect and inaccurate gas supply pressure regulation cannot be solved in principle and source. This patent is from improving the through-flow area of supercharger inner structure form, increase self-pressurization system valve and realizing a novel self-pressurization system who is used for boats and ships LNG fluid reservoir pressure boost through accurate pressure regulation control method to with the LNG self-pressurization of LNG fluid reservoir pressure boost and the LNG vaporizer design formula heat exchanger as an organic whole of air feed, also further optimize the improvement to air feed system's scheme.

Authorization notice number: CN 108716441A

The date of authorized announcement: 2018.10.30

The patent name: LNG gas supply system and natural gas power ship

Meanwhile, referring to the above patent, when a Gas fuel is used by a Gas engine or other Gas consuming equipment on a ship, a set of Gas pipeline with a double-wall pipe structure and a set of Gas Valve Unit (GVU) including a fuel valve and a vent valve forming an interlocking function and a closed container accommodating the interlocking valve are also required to be disposed in a cabin in which the Gas engine is disposed. Thereby avoid the leakage of gas pipeline and valve to lead to the gas to enter the cabin that holds gas engine, nevertheless set up one set of gas valves unit and can improve the manufacturing degree of difficulty and cost greatly for holding above-mentioned interlocking valves in the cabin, the operation maintenance of the valve of also being convenient for overhauls.

Authorization notice number: CN 205048157U

The date of authorized announcement: 2015.09.08

The patent name: liquefied natural gas storage tank

When LNG liquid filling gets into the LNG fluid reservoir, for preventing that the LNG fluid reservoir from excessively filling, the full valve is surveyed to the biggest filling liquid level department setting of jar usually, and whether the LNG fluid reservoir is full is judged to the LNG liquid or gaseous the come out when opening through surveying full valve, but this kind of measuring method can lead to LNG liquid or gaseous evacuation to atmosphere, uneconomic environmental protection.

It can be seen from the papers published and the patents applied, that in this kind of system using the self-pressurizing device as the core device of the LNG fuel gas supply system, the operation efficiency of the self-pressurizing device and the self-pressurizing system is directly related to the merits of the whole LNG fuel gas supply system, and it can be seen from the papers that the actual effect of the self-pressurizing system, which is directly influenced by the resistance of the self-pressurizing system as a key factor, has attracted attention and developed research from all parties, but the solution proposed in the above documents mainly proposes an optimization scheme for the existing self-pressurizing system from the aspects of the trend arrangement of the liquid introduction pipeline, the installation arrangement angle of the valve, etc., and the LNG fuel gas supply system applied for patent also mainly implements the difference of the gas supply systems through the mutual function multiplexing change between one or more LNG heat exchangers.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the prior art scheme does not solve the practical use problems of non-ideal self-pressurizer effect, inaccurate pressure regulation and natural gas emission escape in principle and source.

In order to solve the technical problems, one technical scheme of the invention is to provide a novel self-pressurization gas supply system for marine LNG fuel, which is characterized by comprising a low-temperature frozen liquid storage tank, wherein the low-temperature frozen liquid storage tank is communicated with a J set of gas supply systems positioned inside a joint, J is more than or equal to 1, each set of gas supply system supplies gas for K sets of gas consumption equipment, K is more than or equal to 1, and the gas consumption equipment is positioned in a machine place, wherein:

collecting a pressure signal of the low-temperature frozen liquid storage tank by a pressure signal collecting unit, and sending the collected pressure signal to a controller outside a joint; the low-temperature frozen liquid storage tank is provided with a liquid fuel outlet, a self-pressurization liquid outlet and a gas phase port;

each set of gas supply system comprises an integrated heat exchanger and a gas buffer tank, wherein the integrated heat exchanger integrates a self-pressurizing device and a gasifier; the integrated self-pressurizing device in the integrated heat exchanger is provided with a low-temperature freezing liquid inlet and a steam outlet after the low-temperature freezing liquid is heated and gasified; the integrated gasifier in the integrated heat exchanger is provided with a low-temperature fuel inlet and a normal-temperature gas fuel outlet; the integrated heat exchanger is also provided with a heat source medium inlet and a heat source medium outlet; a low-temperature freezing liquid inlet of the integrated heat exchanger is communicated with a self-pressurization liquid outlet of the low-temperature freezing liquid storage tank through a low-temperature freezing liquid conveying pipe, and a switch control remote control self-pressurization valve is arranged on the low-temperature freezing liquid conveying pipe; a steam outlet of the integrated heat exchanger is communicated with a gas phase port of the low-temperature frozen liquid storage tank through a steam conveying pipe; one end of the bypass pipe is communicated with the steam delivery pipe, the other end of the bypass pipe is communicated with the low-temperature fuel delivery pipe, and a switch control remote control gas fuel valve is arranged on the bypass pipe; the low-temperature fuel conveying pipe is communicated with a low-temperature fuel inlet of the integrated heat exchanger, and meanwhile, the low-temperature fuel conveying pipe is also communicated with a liquid fuel outlet of the low-temperature freezing liquid storage tank through the liquid fuel conveying pipe; the liquid fuel conveying pipe is provided with a switch control remote control liquid fuel valve; a normal-temperature gas fuel outlet of the integrated heat exchanger is communicated with the gas buffer tank through a normal-temperature fuel conveying pipe, and a temperature signal acquisition unit II acquires a temperature signal of gas in the normal-temperature fuel conveying pipe and sends the temperature signal to the controller; a heat source medium inlet and a heat source medium outlet of the integrated heat exchanger are respectively communicated with a heat source medium inlet interface and a heat source medium outlet interface which are positioned outside the joint; the gas buffer tank is communicated with K gas consumption devices outside the joint through a gas supply pipe.

Preferably, an overflow liquid outlet is provided at the maximum filling level of the cryogenic freezing liquid storage tank, and the cryogenic freezing liquid storage tank is further provided with an overflow air return port;

each set of gas supply system also comprises an overflow cylinder;

an overflow liquid outlet of the low-temperature freezing liquid storage tank is communicated with an overflow cylinder through an overflow liquid outlet pipe, and the overflow cylinder is communicated with an overflow air return port of the low-temperature freezing liquid storage tank through an overflow air return pipe; and a first temperature signal acquisition unit acquires a temperature signal of the overflow cylinder and sends the acquired temperature signal to the controller.

Preferably, the integrated heat exchanger comprises a shell and N straight tube type heat exchange tubes I arranged in the shell, wherein N is more than or equal to 1;

the shell is provided with the heat source medium inlet and the heat source medium outlet;

m groups of spiral tube type heat exchange tubes are wound on the outer part of one of the N straight tube type heat exchange tubes, M is more than or equal to 1, and the heat exchange tubes are provided with the low-temperature fuel inlet and the normal-temperature gas fuel outlet which independently enter and exit the shell; or M groups of straight tube type heat exchange tubes II which are arranged in parallel with the N straight tube type heat exchange tubes I are provided with the low-temperature fuel inlet and the normal-temperature gas fuel outlet which are independently arranged in and out of the shell;

the low-temperature freezing liquid enters the first straight tube type heat exchange tube through the low-temperature freezing liquid inlet, and the natural gas gasified by heating the low-temperature freezing liquid flows out of the first straight tube type heat exchange tube and then flows out of the integrated heat exchanger from the steam outlet; and a bent pipe used for compensating the deformation expansion amount caused by expansion with heat and contraction with cold is arranged between the low-temperature freezing liquid inlet and the first straight pipe type heat exchange pipe and/or between the first straight pipe type heat exchange pipe and the steam outlet.

Preferably, the shell and the straight tube type heat exchange tube are arranged in a small-angle inclined manner with the horizontal direction, so that the heat source medium outlet is located at a low position, the heat source medium inlet is located at a high position, the low-temperature freezing liquid inlet is located at a low position, the steam outlet is located at a high position, low-temperature freezing liquid from the bottom of the low-temperature freezing liquid tank enters from the bottom of the integrated heat exchanger through the low-temperature freezing liquid inlet, and gasified steam passes through the top of the integrated heat exchanger through the steam outlet, so that the problem that the resistance of the supercharger is overlarge due to gas-liquid mixed flow is avoided.

Preferably, the diameter of the low-temperature freezing liquid inlet is smaller than the inner diameter of the first straight-tube heat exchange tube; an expanding joint is arranged between the low-temperature freezing liquid inlet and the straight-tube heat exchange tube I, the inner diameter of the expanding joint is larger than that of the low-temperature freezing liquid inlet, and the low-temperature freezing liquid entering from the low-temperature freezing liquid inlet flows through the expanding joint and then enters the straight-tube heat exchange tube I.

Another technical solution of the present invention is to provide a control method for the above-mentioned novel marine LNG-fueled self-pressurization gas supply system, which is characterized by comprising the following steps:

when the pressure of the low-temperature freezing liquid storage tank needs to be increased for air supply, the pressure is increased, and the method comprises the following steps:

the controller collects a pressure signal of the low-temperature frozen liquid storage tank through a pressure signal collecting unit; the controller compares the pressure value acquired in real time with a target boosting set value preset in the controller, and controls the switch of the remote control self-boosting valve through the switch to realize the target of boosting starting and boosting stopping; when the self-pressurization is carried out, the switch controls the remote control self-pressurization valve to be in a full-open flow state, and the flow area is maximum; the pressure of the low-temperature frozen liquid storage tank can freely modify a target pressure-boosting set value in a controller according to needs to achieve the purpose of boosting pressure in different degrees;

when the pressure of the low-temperature freezing liquid storage tank needs to be reduced to prevent the overpressure of the liquid tank, the pressure is reduced, and the method comprises the following steps:

the controller collects a pressure signal of the low-temperature frozen liquid storage tank through a pressure signal collecting unit; the controller compares the pressure value acquired in real time with a target depressurization set value preset in the controller, controls the switch of a remote control gas fuel valve through the switch, and reduces the pressure of the low-temperature refrigeration liquid storage tank in a mode of conveying the evaporated gas to gas consumption equipment as fuel so as to realize the purposes of depressurization starting and depressurization stopping; the pressure of the low-temperature frozen liquid storage tank can freely modify a target pressure reduction set value in a controller according to requirements to achieve the purpose of reducing the pressure in different degrees;

when various accidents and emergencies occur, the controller forcibly stops the normal operation of pressurization or decompression by controlling the remote control self-pressurization valve or controlling the remote control gas fuel valve by a forced cut-off switch or a method of controlling the remote control gas fuel valve by a switch, thereby realizing the safety protection function of the gas supply system and avoiding the problem of natural gas escape caused by overpressure of the cryogenic liquid storage tank and the pipeline.

Preferably, before the cryogenic liquid storage tank needs to be refilled with cryogenic liquid, the pressure of the cryogenic liquid storage tank is reduced as much as possible by a pressure reduction method by reducing the target pressure reduction set value of the controller, so that the cryogenic liquid can be more easily filled.

Preferably, the controller collects the operation signal of the gas consumption equipment through the operation signal collection unit, collects the temperature signal of the gas in the normal-temperature fuel conveying pipe through the temperature signal collection unit II, and controls the switch to control the remote control self-pressurization valve based on the operation signal and the temperature signal collected in real time: when the gas consumption equipment is judged not to be operated based on the operation signal or the outlet temperature of the gasifier is judged to be too low based on the temperature signal, the forced cut-off switch controls the remote control self-pressurization valve, and the self-pressurization system is automatically forbidden to work to avoid the risk of frost cracking of the gasifier.

Preferably, the gas supply pipe in the joint is communicated with the ventilation pipe; along the transmission direction of the gas fuel, a switch control remote control gas main fuel valve, a switch control remote control fuel valve and a pressure regulating valve are sequentially arranged on the gas supply pipe; the vent pipe and the gas supply pipe are connected with the part between the switch control remote control gas main fuel valve and the switch control remote control fuel valve, and the vent pipe is provided with a switch control remote control fuel vent valve and a check valve; the switch control remote control gas main fuel valve, the switch control remote control fuel ventilation valve, the check valve and the pressure regulating valve are all positioned in the joint; the switch control remote control gas main fuel valve, the switch control remote control fuel valve and the switch control remote control fuel ventilation valve form an interlocking valve group: when the switch-controlled remote-control gas main fuel valve and the switch-controlled remote-control fuel valve are closed, the switch-controlled remote-control fuel ventilation valve is automatically opened; when the switch-controlled remote-control gas main fuel valve and the switch-controlled remote-control fuel valve are opened, the switch-controlled remote-control fuel ventilation valve is automatically closed; when the interlocking control switch controls the remote control gas main fuel valve, the switch control remote control fuel valve and the switch control remote control fuel vent valve, a mode of immediately closing the valve and opening the valve in a delayed mode is arranged in the controller, the overlapping time of opening an interlocking valve group consisting of the switch control remote control gas main fuel valve, the switch control remote control fuel valve and the switch control remote control fuel vent valve is avoided, and the phenomenon of gas escape is avoided.

Preferably, the controller collects a temperature signal in the overflow cylinder through the first temperature signal collecting unit, and compares the collected real-time temperature with a target temperature set value preset in the controller: when the overflow does not occur, the overflow cylinder is in a normal temperature state in contact with the environment; when overflow occurs, the temperature of the overflow cylinder is too low, and the controller generates low-temperature overflow alarm, so that whether the low-temperature freezing liquid storage tank is excessively filled or not is judged.

The invention optimizes the LNG fuel gas supply system by adopting two key technologies: firstly, adopt a novel low resistance, efficient from booster and from turbocharging system, reduce from turbocharging system's resistance, improve from turbocharging system's pressure boost effect from turbocharging system from improving from the angle of booster inner structure form, increase from turbocharging system valve flow area and optimize LNG fuel gas supply system. And secondly, the precision control of the gas supply pressure and the safety protection cut-off are realized from the perspective of improving the system design and the control method thereof, and the practical problem of natural gas emission escape is solved.

Specifically, the novel marine LNG fuel self-pressurization gas supply system and the control method thereof provided by the invention achieve the beneficial gas supply effect through the following modes:

(1) the novel efficient integrated heat exchanger is adopted to realize the functions of the self-pressurizer and the gasifier, wherein the arrangement form of the self-pressurizer is inclined, and the inclination angle is generally within 30 degrees. The heat exchange tube in the self-pressurizer adopts a straight tube design method. This design form is in time realizing gas-liquid separation from the booster is inside, the problem of the unable gas-liquid separation gas-liquid mixed flow resistance of spiral wound tube formula is big or even gaseous anti-scurrying backward flow blows off liquid from the entry has been solved, the pipe diameter of straight tube formula also is far greater than the spiral wound tube formula coil pipe of the same type, the pipeline velocity of flow is low, the resistance is little, the feed liquor is continuous, the pressure boost efficiency from the booster is improved by a wide margin, the design form of integral type will realize the function integration of two LNG gasifiers, the quantity of gasifier has been reduced, heat exchange efficiency is improved.

(2) The switch-controlled remote-control pressure-increasing valve is adopted to replace the traditional mechanical spring self-operated pressure-increasing valve. The controller is through gathering the pressure signal of LNG fluid reservoir, and the target pressure setting value of controller inside setting carries out the comparison, reaches the switch of automatic control pressure increasing valve in order to realize the pressure boost target, and pressure increasing valve is in the full open flow state during from the pressure boost, and the through-flow area is the biggest, and the pipeline and the valve resistance of greatly reduced self-pressurization system improve feed liquor volume and from pressure boost efficiency.

(3) The switch-controlled remote-control gas fuel valve is adopted to replace a traditional mechanical spring self-operated pressure reducing valve, the controller acquires a pressure signal of the LNG liquid tank and compares the pressure signal with a target pressure set value arranged in the controller to achieve the purpose of automatically controlling the on-off state of the gas fuel valve and reducing the pressure of the LNG liquid tank in a mode of conveying evaporated gas to an engine to serve as fuel. The pressure of the LNG tank can be freely modified in the controller 400 according to the requirement to achieve the purpose of depressurization of different degrees.

(4) Before the LNG tank needs to be refilled with the LNG liquid, the pressure of the LNG tank needs to be reduced as much as possible, so that the LNG liquid can be injected more easily. According to the method of the point (3), the beneficial effect of reducing the pressure of the LNG tank and facilitating the filling can be achieved by reducing the set value of the pressure reduction pressure of the controller.

(5) The heat source required by the integrated heat exchanger comes from external hot water, but when the hot water is insufficient, the LNG liquid flows into the integrated heat exchanger, so that the LNG liquid is easily frozen and cracked, and the low-temperature damage to an engine is caused due to the low outlet temperature of the gasifier. The controller controls the self-pressurization valve by acquiring the running signal of the engine and the temperature signal of the gasifier outlet, and when the engine does not run or the gasifier temperature outlet is too low, the self-pressurization valve is forcibly cut off even if the LNG liquid tank needs pressurization to increase the pressure, and the self-pressurization system is automatically forbidden to work to avoid the risk of frost cracking of the gasifier.

(6) Traditional interlocking valves 3 are arranged in the cabin, are arranged near the machine, and according to the ship specification requirement, for avoiding the valve leakage to lead to gas fuel to enter the cabin, the interlocking valves need to be installed in a closed container to form a complete gas valve group unit GCU, wherein the gas pipeline of the gas valve group unit is communicated with the inner pipe of the double-wall pipe, and the inner space of the pressure container is communicated with the outer pipe of the double-wall pipe. The interlocking valve banks are arranged inside the joints of the LNG tank in a centralized manner and are arranged in a centralized manner together with pipeline valves of other gas supply systems, so that operation, maintenance and centralized monitoring of gas leakage are facilitated, and a gas valve bank unit GCU with high cost and high requirements in an engine room is also eliminated.

(7) By providing a check valve downstream of the remote fuel vent valve of one of the interlock valves, the formation of a dangerous source of air-gas mixture is avoided after venting has been opened by the backflow of air into the gas conduit.

(8) When the traditional interlocking valve group is switched, the valve is simultaneously opened and closed, and due to the fact that the valve is opened and closed for a time period, three interlocking valves are simultaneously in an overlapped opening state, gas fuel (such as a gas buffer tank) in an equipment pipeline on the upstream and the downstream of the interlocking valves in the overlapped time period can escape out through a remote control fuel ventilation valve. In order to solve the hidden trouble, when the controller controls the interlocking valve group in an interlocking manner, the controller is provided with a mode of immediately closing the valve and opening the valve in a delayed manner, so that the interlocking valve group is avoided, the overlapping time is opened, and the gas escape phenomenon is avoided.

(9) The biggest filling liquid level department that fills at the LNG fluid reservoir sets up the overflow liquid outlet, and liquid flows into in the overflow section of thick bamboo from the liquid outlet when the liquid level is too high, and an overflow section of thick bamboo position is less than the overflow liquid outlet, returns to in the LNG fluid reservoir through the overflow gas return port after the liquid gasification in the overflow section of thick bamboo to suppress gas pressure accumulation and lead to liquid unable inflow in having avoided an overflow section of thick bamboo, also avoided LNG liquid or gaseous emission to atmospheric problem. The temperature signal in the overflow cylinder is collected to the controller and compared with a target temperature set value arranged in the controller, when overflow does not occur, the overflow cylinder is in a normal temperature state in contact with the environment, when overflow occurs, the temperature of the overflow cylinder is too low, and the controller generates low-temperature overflow alarm.

Drawings

FIG. 1 is a diagram of a LNG tank self-pressurization system;

FIG. 2 is a schematic view of a mechanical spring self-operated booster regulator valve;

FIG. 3 is a schematic diagram of a wound tube LNG vaporizer;

FIG. 4 is a schematic diagram of a conventional marine LNG tank self-pressurization;

FIG. 5 is a schematic view of a system disclosed in CN 110886670A;

FIG. 6 is a schematic diagram of a system disclosed in CN 213065523U;

FIG. 7 is a schematic view of a system disclosed in CN 111550675A;

FIG. 8 is a schematic view of a system disclosed in CN 104791602B;

FIG. 9 is a schematic diagram of a novel marine LNG fueled self-pressurizing gas supply system as disclosed in the examples;

FIG. 10 is a side view of an integrated heat exchanger used in the embodiments;

fig. 11 is a top view of an integrated heat exchanger used in the embodiment.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

The embodiment discloses a novel self-pressurization gas supply system for marine LNG fuel, as shown in fig. 9, which includes an LNG tank 100 having a liquid fuel outlet 110, a self-pressurization liquid outlet 111, a gas phase port 112, an overflow gas return port 113, and an overflow liquid outlet 114. The joint 101 is welded to the LNG tank 100 casing and is a sealed structure to accommodate leakage of the joint of the LNG tank 100. The material of the joint 101 is equivalent to the material of the LNG tank 100 that can withstand LNG liquid. Inside the junction 101 are an integrated heat exchanger 102, which integrates the self-pressurizer and the gasifier, a gas buffer tank 103, and an overflow cylinder 104.

The pressure signal of the LNG tank 100 is collected by the pressure signal collecting unit 402 and the collected pressure signal is transmitted to the controller 400 located outside the joint location 101.

The overflow outlet 114 of the LNG tank 100 is communicated with the overflow cylinder 104 via an overflow outlet pipe, and the overflow cylinder 104 is communicated with the overflow return port 113 of the LNG tank 100 via an overflow return pipe. The temperature signal of the overflow cylinder 104 is collected by the first temperature signal collecting unit 403, and the collected temperature signal is sent to the controller 400 located outside the joint location 101.

The integrated heat exchanger 102 comprises a group of straight-tube heat exchange tubes 6 for realizing the self-pressurization function of the self-pressurizer and a group of wound coils 10 wound on the straight-tube heat exchange tubes 6, wherein the wound coils 10 are used for realizing the function of heating low-temperature fuel of the gasifier into normal-temperature fuel. Meanwhile, the integrated heat exchanger 102 is provided with an LNG liquid inlet 120 communicated with the straight-tube heat exchange tube 6 and a steam outlet 121 after the LNG liquid is heated and gasified; the integrated heat exchanger 102 is also provided with a low-temperature fuel inlet 122 and a normal-temperature gas fuel outlet 123 which are communicated with the wound coil 10; the integrated heat exchanger 102 also has a hot water or other heat source medium inlet 2 and a hot water or other heat source medium outlet 3.

The LNG liquid inlet 120 of the integrated heat exchanger 102 is communicated with the self-pressurizing liquid outlet 111 of the LNG tank 100 via an LNG liquid transfer pipe, and the LNG liquid transfer pipe is provided with a switch-controlled remote self-pressurizing valve 300. The vapor outlet 121 of the integrated heat exchanger 102 is communicated with the gas phase port 112 of the LNG tank 100 via a vapor transport pipe. One end of the bypass pipe is communicated with the steam delivery pipe, the other end is communicated with the low-temperature fuel delivery pipe, and a switch-controlled remote-control gas fuel valve 302 is arranged on the bypass pipe. The cryogenic fuel transfer line is in communication with the cryogenic fuel inlet 122 of the integrated heat exchanger 102, while the cryogenic fuel transfer line is also in communication with the liquid fuel outlet 110 of the LNG tank 100 via a liquid fuel transfer line. The liquid fuel delivery pipe is provided with a remote liquid fuel valve 301 controlled by an on-off switch. The normal temperature gas fuel outlet 123 of the integrated heat exchanger 102 is communicated with the gas buffer tank 103 through a normal temperature fuel delivery pipe, and a temperature signal of the gas in the normal temperature fuel delivery pipe is collected by a second temperature signal collecting unit 404 and sent to the controller 400 located outside the joint 101.

The hot water or other heat source medium inlet 2 and the hot water or other heat source medium outlet 3 of the integrated heat exchanger 102 are respectively communicated with a heat source medium inlet interface 124 and a heat source medium outlet interface 125 which are positioned outside the joint 101.

The gas buffer tank 103 communicates with a gas engine 201 using gas fuel located outside the joint place 101 via a gas supply pipe. The gas supply pipe in the joint 101 communicates with the gas permeable pipe. An on-off control remote-controlled gas main fuel valve 303, an on-off control remote-controlled fuel valve 304, and a pressure regulating valve 307 are provided in this order along the direction of transportation of the gas fuel in the gas supply pipe. The gas permeable pipe and the gas supply pipe are connected with the part between the switch control remote control gas main fuel valve 303 and the switch control remote control fuel valve 304, and the switch control remote control fuel gas permeable valve 305 and the check valve 306 are arranged on the gas permeable pipe. An on-off controlled remote controlled gas main fuel valve 303, an on-off controlled remote controlled fuel valve 304, an on-off controlled remote controlled fuel vent valve 305, a check valve 306 and a pressure regulating valve 307 are all located within the junction 101. The switch control remote control gas main fuel valve 303, the switch control remote control fuel valve 304 and the switch control remote control fuel ventilation valve 305 form an interlocking valve group: when the switch-controlled remote-controlled gas main fuel valve 303 and the switch-controlled remote-controlled fuel valve 304 are closed, the switch-controlled remote-controlled fuel ventilation valve 305 is automatically opened; switch-controlled remote-controlled gas main-fuel valve 303 and switch-controlled remote-controlled fuel valve 304 are opened, and switch-controlled remote-controlled fuel vent valve 305 is automatically closed.

The gas engine 201 is located in the machine room 200, and the machine room 200 has a double-walled gas piping 203 therein, and the aforementioned gas supply pipe communicates with the gas engine 201 via an inner pipe 202 of the double-walled gas piping 203. The gas engines 201 each have an operation signal acquisition unit 401, and the operation signal acquisition unit 401 transmits the acquired operation signal of the gas engine 201 to the controller 400 located outside the joint site 101.

In this embodiment, the structure of the integrated heat exchanger 102 is as shown in fig. 10 and 11, and includes a housing 1, and the front end and the rear end of the housing 1 are respectively provided with a hot water or other heat source medium inlet 2 and a hot water or other heat source medium outlet 3. A straight tube type heat exchange tube 6 is arranged in the shell 1. The shell 1 and the straight tube type heat exchange tube 6 therein are all arranged in a manner of inclining at a small angle with the horizontal direction, so that the hot water or other heat source medium outlet 3 is positioned at a low position and the hot water or other heat source medium inlet 2 is positioned at a high position, and the LNG liquid inlet 120 communicated with the straight tube type heat exchange tube 6 is positioned at a low position and the steam outlet 121 communicated with the straight tube type heat exchange tube 6 is positioned at a high position. The included angle theta between the axis of the shell 11 and the axis of the straight-tube heat exchange tube 6 and the horizontal plane is generally within 30 degrees.

The LNG liquid entering through the LNG liquid inlet 120 is connected with the straight-tube heat exchange tube 6 through the expanding joint 5 and the elbow 7-1 in sequence. The gasified steam out of the straight heat exchange tube 6 is discharged out of the integrated heat exchanger 102 from the steam outlet 121 through the elbow 7-2. Assuming that the diameter of the LNG liquid inlet 120 is R1, the inner diameter of the expanding joint 5 is R2, the inner diameter of the straight-tube type heat exchange tube 6 is R3, the inner diameters of the elbow 7-1 and the elbow 7-2 are R4, and the diameter of the steam outlet 121 is R5, the LNG liquid inlet has the following advantages: r1< R2, R2 ═ R3 ═ R4 ≦ R5, and the inner diameter R5 of the gasification steam outlet pipe 121 can be further expanded according to actual needs to reduce drag. The thermal expansion and the cold contraction are compensated by the bent pipe 7-1 and the bent pipe 7-2. The connection between the expanding joint 5 and the elbow 7-1, the connection between the elbow 7-1 and the straight-tube heat exchange tube 6, and the connection between the straight-tube heat exchange tube 6 and the elbow 7-2 are all in a butt welding mode.

A group of winding type coil pipes 10 are sleeved outside the straight pipe type heat exchange pipe 6. The coiled tubing 10 has a separate cryogenic fuel inlet 122 and a normal temperature gaseous fuel outlet 123. It should be noted that: other configurations and arrangements of the coiled tubing 10 are possible, such as: the wound coil 10 may be of a straight pipe structure, and arranged side by side with the straight pipe heat exchange pipe 6, and so on, which are not described herein again.

In this embodiment, the self-pressurization device integrated in the integrated heat exchanger 102 realizes the self-pressurization work with low resistance and high pressurization efficiency by greatly reducing the resistance of the self-pressurization system, timely separating gas from liquid without mixing flow, and improving the liquid inlet efficiency of the self-pressurization device. Meanwhile, the integrated heat exchanger 102 integrates the self-pressurizing device and the gasifier, so that the internal space of the heat exchanger is utilized to the maximum extent, the number of the heat exchangers is reduced, and the heat exchange efficiency of the heat exchanger is improved.

The control method of the novel marine LNG fuel self-pressurization gas supply system comprises the following steps:

when the pressure of the LNG tank 100 needs to be raised for gas supply, the pressure is raised, and the method comprises the following steps:

the controller 400 collects a pressure signal of the LNG tank 100 through the pressure signal collecting unit 402. The controller 400 compares the pressure value acquired in real time with a target pressure-increasing set value preset in the controller 400, and controls the opening and closing of the remote-control self-pressure-increasing valve 300 through the switch to achieve the target of pressure-increasing starting and pressure-increasing stopping. During self-pressurization, the switch-controlled remote-control self-pressurization valve 300 is in a full-open circulation state, the circulation area is the largest, the resistance of a pipeline and a valve of a self-pressurization system is greatly reduced, and the liquid inlet amount and the self-pressurization efficiency are improved. The pressure of the LNG tank 100 may be freely modified at the controller 400 as desired to achieve various levels of boost.

When the LNG tank 100 needs to be depressurized to prevent overpressure, the depressurization is performed, which includes the following steps:

the controller 400 collects a pressure signal of the LNG tank 100 through the pressure signal collecting unit 402. The controller 400 compares the pressure value acquired in real time with a target pressure reduction set value preset in the controller 400, controls the opening and closing of the remote control gas fuel valve 302 through a switch, and reduces the pressure of the LNG tank 100 by conveying the vaporized gas to the engine 201 to serve as fuel, so as to achieve the purposes of pressure reduction starting and pressure reduction stopping. The LNG tank 100 pressure can be freely modified at the controller 400 as desired to achieve various levels of depressurization.

Before the LNG tank 100 needs to be refilled with LNG liquid, the pressure of the LNG tank 100 needs to be reduced as much as possible, so that the LNG liquid can be more easily filled. The pressure of the LNG tank 100 can be reduced by adjusting the target pressure reduction set value of the controller 400 by using the pressure reduction method described above, so as to facilitate the LNG liquid filling.

When various accidents and emergencies such as but not limited to fire, gas leakage, abnormal hot water supply, low gasifier outlet temperature and the like occur, the controller 400 forcibly stops the pressurization or depressurization function of normal operation and stops conveying low-temperature fuel outwards by a method of forcibly cutting off the switch to control the remote-control self-pressurization valve 300 or the switch to control the remote-control gas fuel valve 302 or the switch to control the remote-control liquid fuel valve 301, thereby realizing the safety protection function of the gas supply system and avoiding the natural gas escape problem caused by overpressure of the LNG tank 100 and the pipeline.

The heat source required for the integrated heat exchanger 102 is external hot water, but when the hot water is insufficient, the LNG liquid flows into the integrated heat exchanger 102, which is likely to cause frost cracking, and the temperature of the normal temperature gaseous fuel outlet 123 of the vaporizer integrated in the integrated heat exchanger 102 is too low, which causes low temperature damage to the engine 201. In order to solve the problem, in the technical solution disclosed in this embodiment, the controller 400 collects the operation signal of the engine 201 through the operation signal collection unit 401, and collects the temperature signal of the gas in the normal temperature fuel conveying pipe through the second temperature signal collection unit 404. The remote-control self-pressurization valve 300 is controlled to be switched and controlled based on the real-time collected operation signal and temperature signal, and specifically: when it is judged that the engine 201 is not operated based on the operation signal or that the outlet temperature of the vaporizer is excessively low based on the temperature signal, even if the LNG tank 100 needs to boost the boost pressure, the remote-controlled self-pressurization valve 300 is forcibly turned off and the self-pressurization system is automatically prohibited from operating to avoid the risk of frost crack of the vaporizer.

When the traditional interlocking valve group is switched, the valve is simultaneously switched, and due to the fact that the valve action has the switching travel time, the time period that three interlocking valves are simultaneously in the overlapped opening state exists in the switching period of the interlocking valves, gas fuel (such as a gas buffer tank 103) in an equipment pipeline on and downstream of the interlocking valves in the overlapped time period can escape through the remote control gas fuel valve 302 controlled by the switch. In order to solve the above hidden danger, in this embodiment, when the interlocking control switch control remote control main gas fuel valve 303, the switch control remote control fuel valve 304, and the switch control remote control fuel vent valve 305 are implemented by the controller 400, the controller 400 sets a mode of immediately closing the valve and opening the valve in a delayed manner, so as to avoid the overlapping time of opening the interlocking valve set composed of the switch control remote control main gas fuel valve 303, the switch control remote control fuel valve 304, and the switch control remote control fuel vent valve 305, and avoid the gas escape phenomenon.

An overflow liquid outlet 114 is provided at the maximum filling level of the LNG tank 101, and when the liquid level is too high, the liquid flows from the overflow liquid outlet 114 into the overflow cylinder 104 at a position lower than the overflow liquid outlet 114 by its own weight. The top of the overflow cylinder 104 is provided with an overflow air return opening communicated with an overflow air return opening 113 at the top of the LNG tank 101, and liquid in the overflow cylinder 104 is gasified and then returns to the LNG tank 101 through the overflow air return opening 113, so that the phenomenon that the liquid cannot flow into the overflow cylinder 104 due to the fact that the pressure is held back and the pressure is accumulated is avoided, and the problem that the LNG liquid or the gas is discharged to the atmosphere when the overflow cylinder is full is also avoided. The controller 400 collects a temperature signal in the overflow cylinder 104 through a first temperature signal collecting unit 403, and compares the collected real-time temperature with a target temperature set value preset in the controller 400. When the overflow does not occur, the overflow cylinder 104 is in a normal temperature state in contact with the environment. When the temperature of the overflow cylinder 104 is too low when the overflow occurs, the controller 400 generates a low-temperature overflow alarm, thereby determining whether the LNG tank 101 is overfilled.

The number of the gas engines 201 may be 1, may be plural, or may be other gas consuming devices. The LNG tank can only comprise one set of joint 101 welded on the LNG tank and an internal gas supply system, and can also comprise a plurality of sets of mutually independent joint 101 adopting the same gas supply principle and an internal gas supply system. The controller 400 may have only one controller, and the controller 400 may have a redundant function or no redundant function, or may be a plurality of independent controllers having process control and safety protection functions, respectively. Each signal source collected by the controller 400 may be provided by one sensor, or may be provided by a plurality of sensors that are redundant or independent of each other. The heat source for LNG vaporization is illustrated as hot water, and may be various types of heat sources such as hot oil, steam, glycol-water, or other antifreeze. The cryogenic medium of the LNG fuel gas supply system is illustrated as LNG, and can be liquid nitrogen, liquefied petroleum gas, liquid hydrogen, liquid ammonia and other various cryogenic freezing liquids. Variations of the above details, using the same or similar LNG fuel supply system design methods, are within the scope of the present invention.

Claims

1. The utility model provides a novel marine LNG fuel's self-pressurization gas supply system, a serial communication port, including cryogenic liquid storage tank, cryogenic liquid storage tank is located the inside gas supply system of joint department with the J cover and is linked together, and J is greater than or equal to 1, and every set of gas supply system consumes the gas equipment air feed for K platform, and K is greater than or equal to 1, consumes the gas equipment to be located the machine department, wherein:

2. A novel marine LNG fueled self pressurizing gas supply system as claimed in claim 1 wherein an overflow liquid outlet is provided at the maximum filling level of the cryogenic liquid storage tank, the cryogenic liquid storage tank further having an overflow return air port;

each set of gas supply system also comprises an overflow cylinder;

3. The novel marine LNG fuel self-pressurization gas supply system as claimed in claim 1, wherein the integrated heat exchanger comprises a shell and N straight-tube heat exchange tubes I arranged in the shell, wherein N is more than or equal to 1;

4. The self-pressurization gas supply system for the novel marine LNG fuel as claimed in claim 3, wherein the arrangement form of the outer shell and the straight tube type heat exchange tube is inclined at a small angle to the horizontal direction, so that the heat source medium outlet is located at a low position and the heat source medium inlet is located at a high position, and the cryogenic liquid inlet is located at a low position and the steam outlet is located at a high position, the cryogenic liquid from the bottom of the cryogenic liquid tank enters from the bottom of the integrated heat exchanger through the cryogenic liquid inlet, and the gasified steam passes through the top of the integrated heat exchanger through the steam outlet, so that the problem of overlarge booster resistance caused by gas-liquid mixed flow is avoided.

5. The self-pressurization gas supply system for the novel marine LNG fuel as claimed in claim 4, wherein the diameter of the cryogenic liquid inlet is smaller than the inner diameter of the first straight heat exchange tube; an expanding joint is arranged between the low-temperature freezing liquid inlet and the straight-tube heat exchange tube I, the inner diameter of the expanding joint is larger than that of the low-temperature freezing liquid inlet, and the low-temperature freezing liquid entering from the low-temperature freezing liquid inlet flows through the expanding joint and then enters the straight-tube heat exchange tube I.

6. A method for controlling a new self-pressurizing gas supply system for marine LNG as set forth in claim 1, comprising the steps of:

7. The method of claim 6, wherein the pressure in the cryogenic liquid storage tank is reduced as much as possible by the depressurization method by lowering the target depressurization set point of the controller before the cryogenic liquid storage tank needs to be refilled with cryogenic liquid, thereby making it easier to fill the cryogenic liquid.

8. The control method of claim 6, wherein the controller collects an operation signal of the gas consumption device through the operation signal collection unit, collects a temperature signal of the gas in the normal temperature fuel conveying pipe through the temperature signal collection unit II, and controls the switch to control the remote-control self-pressurization valve based on the operation signal and the temperature signal collected in real time: when the gas consumption equipment is judged not to be operated based on the operation signal or the outlet temperature of the gasifier is judged to be too low based on the temperature signal, the forced cut-off switch controls the remote control self-pressurization valve, and the self-pressurization system is automatically forbidden to work to avoid the risk of frost cracking of the gasifier.

9. A control method as claimed in claim 6, wherein the gas supply duct in the junction communicates with the gas permeable duct; along the transmission direction of the gas fuel, a switch control remote control gas main fuel valve, a switch control remote control fuel valve and a pressure regulating valve are sequentially arranged on the gas supply pipe; the vent pipe and the gas supply pipe are connected with the part between the switch control remote control gas main fuel valve and the switch control remote control fuel valve, and the vent pipe is provided with a switch control remote control fuel vent valve and a check valve; the switch control remote control gas main fuel valve, the switch control remote control fuel ventilation valve, the check valve and the pressure regulating valve are all positioned in the joint; the switch control remote control gas main fuel valve, the switch control remote control fuel valve and the switch control remote control fuel ventilation valve form an interlocking valve group: when the switch-controlled remote-control gas main fuel valve and the switch-controlled remote-control fuel valve are closed, the switch-controlled remote-control fuel ventilation valve is automatically opened; when the switch-controlled remote-control gas main fuel valve and the switch-controlled remote-control fuel valve are opened, the switch-controlled remote-control fuel ventilation valve is automatically closed; when the interlocking control switch controls the remote control gas main fuel valve, the switch control remote control fuel valve and the switch control remote control fuel vent valve, a mode of immediately closing the valve and opening the valve in a delayed mode is arranged in the controller, the overlapping time of opening an interlocking valve group consisting of the switch control remote control gas main fuel valve, the switch control remote control fuel valve and the switch control remote control fuel vent valve is avoided, and the phenomenon of gas escape is avoided.

10. The control method as claimed in claim 6, wherein the controller collects the temperature signal in the overflow cylinder through a temperature signal collecting unit, and compares the collected real-time temperature with a preset target temperature set value in the controller: when the overflow does not occur, the overflow cylinder is in a normal temperature state in contact with the environment; when overflow occurs, the temperature of the overflow cylinder is too low, and the controller generates low-temperature overflow alarm, so that whether the low-temperature freezing liquid storage tank is excessively filled or not is judged.