A method for precooling CO2 cargo holds using supercooled liquid CO2

Abstract

This invention discloses a method for pre-cooling a CO2 cargo tank using subcooled liquid CO2. Pre-cooling a CO2 cargo tank with liquid CO2 requires that the liquid CO2 entering the cargo tank cools the CO2 cargo tank to its minimum design temperature, provided that the minimum temperature after vaporization is not lower than the minimum design temperature of the CO2 cargo tank. Therefore, firstly, it is necessary to utilize the latent heat of vaporization of liquid CO2 to absorb heat from the CO2 cargo tank and lower its temperature; secondly, it is necessary to ensure that the final temperature of the liquid CO2 after vaporization is close to, but not lower than, the minimum design temperature of the CO2 cargo tank. This invention obtains subcooled liquid CO2 by changing the pressure of saturated liquid CO2. The subcooled liquid CO2 serves as a cold source, is transported in a subcooled state, and undergoes saturated vaporization at the pressure of the CO2 cargo tank upon entering, thus achieving the goal of pre-cooling the CO2 cargo tank using the latent heat of vaporization of liquid CO2, provided that the temperature is not lower than the minimum design temperature of the CO2 cargo tank.

Description

Technical Field

[0001] This invention relates to the field of innovative applications of liquid CO2, specifically a method for pre-cooling CO2 cargo holds using supercooled liquid CO2. Background Technology

[0002] With economic development, the variety and number of gas carriers, liquid cargo ships, and chemical carriers are constantly increasing. Against this backdrop, the world's first liquid CO2 carrier has been successfully delivered and put into operation, and it is expected that the market demand for liquid CO2 carriers will continue to increase in the future.

[0003] The core equipment of a liquid CO2 carrier is the CO2 cargo tank, which is usually made of low-temperature carbon steel and is generally designed to be no lower than -40°C. This type of ship can only be delivered after the gas test and refueling are completed at the shipyard. Before refueling, liquid CO2 is used to pressurize and pre-cool the CO2 cargo tank on board.

[0004] Based on the minimum design temperature of the CO2 cargo hold and the CO2 liquid saturated vapor pressure gauge, before precooling the CO2 cargo hold, the pressure of the CO2 cargo hold must first be increased to the set pressure. For example, for a CO2 cargo hold with a minimum design temperature of -35°C, in order to ensure that the minimum temperature during precooling is not lower than the minimum design temperature, the pressure of the CO2 cargo hold needs to be increased to about 12 barg before precooling can begin.

[0005] Pre-cooling a CO2 cargo tank with liquid CO2 requires that the liquid CO2 entering the cargo tank, after vaporization, reaches a minimum temperature no lower than the minimum design temperature of the CO2 cargo tank, thus cooling the cargo tank to the minimum design temperature. Therefore, this can only be achieved by utilizing the latent heat of vaporization of liquid CO2 to absorb heat from the CO2 cargo tank, based on the principle that temperature remains essentially constant during phase transitions. Simultaneously, the final vaporization temperature of the liquid CO2 entering the cargo tank must be close to, but not lower than, the minimum design temperature of the CO2 cargo tank to achieve the goal of cooling the CO2 cargo tank to near its minimum design temperature.

[0006] If saturated liquid CO2 is used as a cold source to pre-cool the CO2 cargo tank, as the pressure of the liquid CO2 gradually decreases during transportation and absorbs external heat, the liquid CO2 will be in a superheated state of about 12 barg when it enters the CO2 cargo tank. Although it can release latent heat and absorb heat to lower the temperature of the CO2 cargo tank when it vaporizes in the CO2 cargo tank, the final temperature after vaporization will be higher than the minimum design temperature of the CO2 cargo tank. That is, even if the amount of liquid CO2 used is increased, the goal of cooling the CO2 cargo tank to the minimum design temperature cannot be achieved. Summary of the Invention

[0007] To address the aforementioned problems, this invention solves them by establishing a subcooled state for liquid CO2. Specifically, it transforms saturated (equilibrium) liquid CO2 into a subcooled (intermediate) cold source with a certain degree of subcooling. This cold source is subcooled liquid CO2 in an intermediate (or unstable) state. Following Le Chatelier's Principle, which states that equilibrium shifts towards a less subcooled state, the subcooled liquid CO2 will gradually slow its subcooling process towards saturation during transport. Upon entering the CO2 cargo hold, it reaches a new saturated state of approximately 12 barg. When it vaporizes during the phase change in the CO2 cargo hold, it releases latent heat and absorbs heat, lowering the CO2 cargo hold temperature. Furthermore, the final temperature after vaporization approaches or reaches the minimum design temperature of the CO2 cargo hold, thus achieving the goal of cooling the CO2 cargo hold to its minimum design temperature.

[0008] The supercooling involved in this invention is the same as the physical concept of supercooling. For example, if the temperature of saturated liquid CO2 at 1.97 MPa is -20°C, and the actual temperature of liquid CO2 at that pressure is -25°C, then it is called supercooled liquid CO2 at that pressure.

[0009] This invention changes the pressure of saturated (equilibrium) liquid CO2 to transform it into subcooled (intermediate) liquid CO2 with a certain degree of subcooling. During the transportation process, the subcooled liquid CO2 gradually transforms into a new saturated state, reaching a new saturated state at the corresponding pressure of the CO2 cargo tank when it enters the CO2 cargo tank. This ensures that the final vaporization temperature of the CO2 cargo tank is close to or reaches the minimum design temperature of the CO2 cargo tank. During the phase change vaporization process, latent heat is released and heat is absorbed, thereby achieving the goal of cooling the CO2 cargo tank to the minimum design temperature.

[0010] It should be emphasized that the present invention is a pre-cooling operation performed after the CO2 cargo hold has a certain pressure (after pressurization).

[0011] To achieve the above objectives, the present invention provides a method for pre-cooling a CO2 cargo hold using supercooled liquid CO2. This method relies on a system that utilizes supercooled liquid CO2 to pre-cool the CO2 cargo hold, the system comprising:

[0012] The liquid CO2 tank truck, tank truck hose, cryogenic liquid pump skid module, multi-layer thermal insulation composite hose, throttling and pressure reducing module, shore flange, CO2 cargo hold inlet valve, and CO2 cargo hold are connected in series.

[0013] A cryogenic liquid pump skid module consists of two identical cryogenic liquid pump systems connected in parallel, typically one as a backup, but can also be used with inlet branching and outlet branching in parallel. The module comprises a system inlet valve, a cryogenic pump inlet valve, a dual-head cryogenic liquid pump, a cryogenic pump motor, a damper, a check valve, temperature and pressure sensors, and a safety vent valve connected in series. Control of the cryogenic liquid pump skid module is achieved by a PLC control cabinet mounted on the skid. Its main components are a programmable logic controller (PLC) that interlocks with the pressure parameters in the throttling and pressure-reducing module to control the frequency converter frequency of the cryogenic pump motor, thus achieving constant pressure output from the throttling and pressure-reducing module.

[0014] The throttling and pressure-reducing module consists of a flow meter, a pressure sensor, a temperature sensor, and a throttling valve connected in series. The throttling valve of the module is adjusted to control the pressure of the liquid CO2 during pipeline transport, generating the subcooled liquid CO2 required by the CO2 cargo hold precooling system.

[0015] Based on the above system, the present invention provides a method for pre-cooling a CO2 cargo hold using subcooled liquid CO2. The subcooled liquid CO2 is saturated liquid CO2 at a set temperature and pressure, which is pressurized and transported through the cryogenic liquid pump skid module. Based on the principle of fluid continuity, the degree of subcooling of the subcooled liquid CO2 is controlled by adjusting the opening of the throttle valve of the throttling and pressure reducing module during the transportation process. By transporting the CO2 in a subcooled state, it is saturated and vaporized under the pressure of the CO2 cargo hold. The latent heat of vaporization of the liquid CO2 is used to complete the pre-cooling of the CO2 cargo hold under the condition that it is not lower than the minimum design temperature of the CO2 cargo hold.

[0016] At 7500M 3 Taking a liquid CO2 transport ship as an example, the parameter settings, equipment selection, and operation methods of the subcooled liquid CO2 precooling system include:

[0017] The pressure of the liquid CO2 tanker was set to 15 barg, and liquid CO2 with a saturation temperature of -28°C was obtained at this pressure.

[0018] The cryogenic liquid pump skid module is designed for a maximum flow rate of 6m³ / h. 3 The equipment selection was based on the following conditions: / h, liquid carbon dioxide pressure at the through-shore flange delivery point of 25 barg, and temperature ≤-18°C (the saturation temperature at this pressure is -12°C, i.e., the subcooling exceeds -6°C). The cryogenic liquid pump motor power is 18KW, the inlet pressure of the cryogenic liquid pump skid module is 1.3-2.3MPa, and the outlet pressure is 2.0-4.0MPa.

[0019] The frequency of the frequency converter of the cryogenic liquid pump motor is gradually increased by a programmable logic controller (PLC) to achieve a flow rate of 6 m³ / h for the cryogenic liquid pump. 3 / h;

[0020] The multi-layer thermal insulation composite hose is made of stainless steel corrugated pipe with metal braided mesh, with a diameter of DN32 and a pressure rating of PN4.0MPa. The insulation material is rubber and plastic cotton, and the insulation layer thickness is 100mm.

[0021] Adjusting the operation of the throttling and pressure reducing module: When the flow rate of its flow meter reaches 6m³ / s. 3 At / h, manually adjust the opening of the throttle valve until the pressure of the pressure sensor reaches 25 barg and the temperature of the temperature sensor is ≤-18°C. After that, the programmable controller of the PLC control cabinet and the pressure sensor of the throttle pressure reduction module interlock to control the frequency of the frequency converter of the cryogenic liquid pump motor, so as to achieve a constant pressure output of 25 barg of pressure sensor under the given throttle conditions.

[0022] The above describes the use of subcooled liquid CO2 with a volume of 7500M³. 3 This document describes the specific application process of precooling a CO2 cargo hold with a design pressure of 19 barg and a design temperature of -36°C. When the volume, design pressure, and design temperature of the cooled container change, the required flow rate (flow meter), pressure at the junction point (pressure sensor), and subcooling degree (temperature sensor) parameters for precooling will change accordingly. This necessitates adjustments to the saturation state (pressure and temperature) of the liquid CO2 tanker, the selection of the cryogenic liquid pump skid module, the diameter and pressure rating of the multi-layer insulated composite hose, the design and selection of the throttling and pressure-reducing module, and the opening of the throttling valve. However, the typical configuration, parameter settings, node locations, and operation process of the subcooled liquid carbon dioxide precooling system can be found within the specific application scenarios described above.

[0023] The minimum design temperature involved in this invention refers to the lowest temperature at which a container can operate or be used safely under design conditions. It is usually marked on the equipment nameplate as the lower limit of the temperature for safe operation of the equipment.

[0024] In a preferred embodiment, the volume of the cryogenic container (CO2 cargo hold) to be pre-cooled is 7500M³. 3 The minimum design temperature is -36°C, and the injection port diameter is DN32 (mm). To achieve pre-cooling, the parameters of the liquid CO2 before injection must be 25 barg and the temperature ≤ -18°C (this temperature is sufficient for subsequent operations; temperatures significantly lower than this will not occur). The flow rate is 4 m³ / s. 3 / h injection.

[0025] Precooling the container is a lengthy process. During the injection start-up, by gradually adjusting relevant valves, pumps, and other components, the injection parameters before the injection port valve can be determined, such as 25 barg, temperature ≤ -18°C, and flow rate 4 m³ / s. 3 / h. This completes the pre-cooling process.

[0026] The injection pipeline only requires the necessary valves, pumps, and sensors. Therefore, this invention provides a system for pre-cooling a CO2 cargo hold using subcooled liquid CO2. The CO2 cargo hold pre-cooling system consists of a liquid CO2 tank truck, tank truck hoses, a cryogenic liquid pump skid module, multi-layer insulated composite hoses, a throttling and pressure-reducing module, a shore flange, a CO2 cargo hold inlet valve, and the CO2 cargo hold connected in series. The cryogenic liquid pump skid module consists of a system inlet valve, a cryogenic pump inlet valve, a dual-pump-head cryogenic liquid pump, a cryogenic pump motor, a damper, a check valve, temperature and pressure sensors, and a safety vent valve connected in series. The cryogenic liquid pump skid module consists of two sets of cryogenic liquid pump systems connected in parallel, typically one for standby and one for use, but also with inlet branching and outlet convergence for parallel use. The PLC control cabinet mainly consists of a programmable logic controller (PLC) and a frequency converter for the cryogenic pump motor. The PLC is interlocked with the pressure sensor in the throttling and pressure-reducing module to control the frequency converter of the cryogenic pump motor, thereby achieving constant pressure control of the subcooled liquid CO2 at the outlet of the throttling and pressure-reducing module, achieving the required subcooling degree and flow rate. The throttling and pressure reducing module consists of a flow meter, a pressure sensor, a temperature sensor, and a throttling valve connected in series.

[0027] The beneficial effects of this invention are as follows: By changing the pressure conditions of saturated liquid CO2 to obtain subcooled liquid CO2, and by transporting it in the subcooled state and using it in the new saturated state, the latent heat of vaporization of liquid CO2 is utilized to the maximum extent while ensuring that its final temperature after vaporization is close to or reaches the minimum design temperature of the CO2 cargo hold. This achieves the goal of precooling the CO2 cargo hold by utilizing the latent heat of vaporization of liquid CO2 under the condition of not being lower than the minimum design temperature of the CO2 cargo hold.

[0028] This invention discloses a system and method for pre-cooling a CO2 cargo tank using supercooled liquid CO2. Pre-cooling a CO2 cargo tank with liquid CO2 requires that the minimum temperature of the liquid CO2 entering the cargo tank after vaporization is not lower than the minimum design temperature of the CO2 cargo tank, thus cooling the CO2 cargo tank to the minimum design temperature. Based on the principle that temperature remains essentially constant during a phase transition, the latent heat of vaporization of liquid CO2 is used to absorb heat from the CO2 cargo tank, thereby lowering its temperature while ensuring that the final temperature of the liquid CO2 after vaporization is close to but not lower than the minimum design temperature of the CO2 cargo tank. This achieves the goal of cooling the CO2 cargo tank to near or at the minimum design temperature. To achieve this goal, this invention obtains supercooled liquid CO2 by changing the pressure conditions of saturated liquid CO2. By transporting the supercooled liquid CO2 and using it in the new saturated state, the method of pre-cooling the CO2 cargo tank using the latent heat of vaporization of liquid CO2 is achieved, ensuring that the temperature is not lower than the minimum design temperature of the CO2 cargo tank. Attached Figure Description

[0029] Figure 1This is a schematic diagram of the system principle of the present invention, which uses supercooled liquid CO2 to precool the CO2 cargo hold. Detailed Implementation

[0030] Implementation Case: Specific application of the G7500-1 & G7500-2 liquid CO2 transport sister ships. The ship's liquid cargo system is 7500M... 3 The liquid CO2 cargo tank has a design pressure of 1.9 MPa and a design temperature of -36°C. The required cooling rate is less than 10°C / h, and the maximum temperature difference within the tank during cooling is less than 15°C. Based on these CO2 cargo tank process requirements, the subcooled liquid carbon dioxide parameters at the junction of the through-shore flange 6 are: flow rate 4 m³ / h. 3 / h, 25 barg, temperature ≤ -18°C (supercooling is about -6°).

[0031] Therefore, a system was designed to precool conventional cryogenic containers using supercooled liquid CO2, such as... Figure 1 As shown, the system includes: a liquid CO2 tank truck 1, a tank truck hose 2, a cryogenic liquid pump skid module 3, a multi-layer insulated composite hose 4, a throttling and pressure reducing module 5, a shore flange 6, a CO2 cargo hold inlet valve 7, and a CO2 cargo hold 8 connected in series.

[0032] The cryogenic liquid pump skid module 3 consists of two identical cryogenic liquid pump systems connected in parallel, typically one for standby and one for use, but it can also be used in parallel with inlet branching and outlet branching. The cryogenic liquid pump skid module is composed of a system inlet valve 31, a cryogenic pump inlet valve 32, a dual-pump head cryogenic liquid pump 33, a cryogenic pump motor 34, a damper 35, a check valve 36, a temperature and pressure sensor 37, and a safety vent valve 38 connected in series. The control of the cryogenic liquid pump skid module is achieved by a PLC control cabinet 39 installed on the pump skid, which mainly consists of a programmable logic controller (PLC) and a frequency converter for the cryogenic pump motor 34.

[0033] The throttling and pressure reducing module 5 consists of a flow meter 51, a pressure sensor 52, a temperature sensor 53, and a throttling valve 54 connected in series.

[0034] The programmable logic controller in the PLC control cabinet 39 is interlocked with the pressure sensor 52 in the throttling and pressure reducing module 5 to control the frequency of the frequency converter of the cryogenic liquid pump motor, thereby achieving constant pressure control of the subcooled liquid CO2 at the outlet of the throttling and pressure reducing module 5, and achieving the required subcooling degree and flow rate.

[0035] Figure 1 In the diagram, A1 is the inlet of the cryogenic liquid pump skid module, B1 is the outlet of the cryogenic liquid pump skid module, A2 is the inlet of the throttling and pressure reducing module, and B2 is the outlet of the throttling and pressure reducing module.

[0036] Furthermore, the present invention can be better understood by referring to the CO2 liquid saturated vapor pressure table in the prior art as shown in Table 1. The unit of measurement for saturated vapor pressure in the table is kPa, and the density of the subcooled liquid noted in ① is 1359.51 kg / m³.

[0037]

[0038] Table 1: Saturated Vapor Pressure of Liquid CO2

[0039] The specific operation of the above system is as follows:

[0040] 1. Adjust the pressure of the liquid CO2 tanker: By venting the gas phase pipeline of the liquid CO2 tanker, gradually reduce the pressure inside the liquid CO2 tanker to about 15 barg. When the pressure is stable, it means that the liquid CO2 inside the liquid CO2 tanker is saturated. According to Table 1, its temperature is about -28°C.

[0041] 2. Connect the liquid phase pipeline of the liquid CO2 tanker to the inlet of the cryogenic liquid pump skid module 3. Open all valves between the pump skid outlet and the CO2 cargo compartment. Control the opening of the liquid phase valves of the liquid CO2 tanker to pre-cool the subcooled liquid CO2 system. After the cryogenic liquid pump skid module 3 has completed pre-cooling, turn on the start button of the cryogenic liquid pump skid module control cabinet 39. Its programmable controller will gradually increase the frequency of the cryogenic pump motor 34 according to the set program to load the cryogenic liquid dual-head pump 33. When the frequency reaches about 40Hz and the flow meter 51 of the throttling and pressure reducing module is 6m³ / h, the load will be applied to the cryogenic liquid pump 33. 3 When the pressure reaches approximately 25 barg, gradually reduce the opening of the throttle valve 54 until the pressure reaches 25 barg. Then, the programmable controller in the pump skid PLC control cabinet 39, in conjunction with the pressure sensor 52, controls the frequency of the inverter in the cryogenic pump motor 34 to achieve the set flow rate of 4 m³ / h at the connection point of the through-shore flange 6. 3 A constant pressure output of 25 barg per hour, temperature ≤ -18°C. The specific design and implementation process is as follows:

[0042] Cryogenic liquid pump skid module 3 is designed for a maximum flow rate of 6m³ / h. 3 The equipment selection was based on the following conditions: / h, liquid carbon dioxide pressure at the 6th delivery point of the shore flange 25 barg, temperature ≤ -18°C (the saturation temperature at this pressure is -12°C, i.e., the subcooling exceeds -6°C). The cryogenic liquid pump motor power is 18KW, the inlet pressure of the cryogenic liquid pump skid module 3 is 1.3-2.3MPa, and the outlet pressure is 2.0-4.0MPa.

[0043] The frequency of the frequency converter of the cryogenic liquid pump motor is gradually increased by a programmable logic controller (PLC) to achieve a flow rate of 6 m³ / h for the cryogenic liquid pump 35. 3 / h;

[0044] The multi-layer thermal insulation composite hose 4 is a stainless steel corrugated pipe with an outer metal braided mesh, with a diameter of DN32 and a pressure rating of PN4.0MPa. The insulation material is rubber and plastic cotton, and the insulation layer thickness is 100mm.

[0045] Adjusting the operation of the throttling and pressure reducing module 5: When the flow rate of its flow meter 51 reaches 6m³ / s... 3 At / h, manually adjust the opening of the throttle valve 54 until the pressure of the pressure sensor 52 reaches 25 barg and the temperature of the temperature sensor 53 is ≤-18°C. After that, the programmable controller of the PLC control cabinet 39 and the pressure sensor of the throttle and pressure reduction module 5 are interlocked to control the frequency of the frequency converter of the cryogenic liquid pump motor, so as to achieve a constant pressure output of 25 barg for the pressure sensor 52 under the given throttle conditions.

[0046] The above are specific implementation cases of the G7500-1 & G7500-2 liquid CO2 transport sister ships. The main parameters of their CO2 cargo holds are: volume 7500M³. 3 Design pressure 19 barg, design temperature -35°C.

[0047] When the volume, design pressure, and design temperature of the cooled container change, the cargo tank pressure at which the CO2 cargo tank begins precooling can be found in Table 1 based on the minimum design temperature of the CO2 cargo tank. The required flow rate (flow meter 51), the pressure at the junction point (pressure sensor 52), and the degree of subcooling (temperature sensor 53) will change accordingly. The corresponding settings and adjustments for the pressure and temperature (saturated state) of the liquid CO2 in the liquid CO2 tanker 1, the selection of the cryogenic liquid pump skid module 3, the diameter and pressure rating of the multi-layer insulated composite hose 4, the design and selection of the throttling and pressure-reducing module 5, and the opening of the throttling valve 54 will also be adjusted. These specific parameters can be obtained through a limited number of simulations and experimental verifications. However, the typical configuration, parameter settings, node locations, and operation process of the subcooled liquid carbon dioxide precooling system can be found in the specific application scenarios described above.

[0048] Based on the above description, this invention provides a method for pre-cooling a CO2 cargo hold using subcooled liquid CO2. First, according to Table 1, the liquid CO2 in the liquid CO2 tank truck 1 is brought to a saturated state at the required system temperature. Then, it enters the cryogenic liquid pump skid module 3. The flow rate is adjusted by the frequency converter of the cryogenic pump motor 34 to achieve the set flow rate. Based on the principle of fluid continuity, the temperature and pressure of the liquid CO2 during pipeline transportation are controlled by the throttle valve 54 of the throttling and pressure-reducing module 5. Subcooled (intermediate) liquid CO2 is obtained at the junction of the shore flange 6. The specific process is as follows: First, the pressure of the tank truck is adjusted to bring the liquid CO2 in the tank truck to a saturated state at the set temperature and pressure. Second, the liquid CO2 in the tank truck flows through the cryogenic liquid pump skid to fully pre-cool the system. Then, the cryogenic liquid pump is started, and the system reaches the set flow rate through frequency converter adjustment. Finally, the opening of the throttle valve is adjusted to obtain subcooled liquid CO2 at the junction of the shore flange 6, achieving the specified degree of subcooling (intermediate state).

[0049] There are many ways to achieve this. One method is to first adjust the liquid CO2 to a stable state, store it in a container, and then, before outputting it to the container to be pre-cooled, use a relevant adjustment module to ensure that the parameters of the liquid CO2 before injection meet the necessary conditions (e.g., 25 barg, temperature ≤ -18°C, and flow rate of 4 m³ / s in the example). 3 ( / h injection), which is suitable for pre-cooling.

[0050] The foregoing has shown and described the basic principles and main features of the invention and the advantages of the invention. Those skilled in the art should understand that the invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope. However, the typical configuration, parameter setting node location, and operation process of the subcooled liquid carbon dioxide precooling system can be found in the above specific application scenarios. These changes and modifications all fall within the scope of the invention as claimed. The scope of protection of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for pre-cooling a CO2 cargo tank using supercooled liquid CO2, characterized by, The method relies on the use of supercooled liquid CO2 to achieve the CO2 cargo tank pre-cooling system, which comprises: liquid CO2 tank truck (1), tank truck hose (2), low-temperature liquid pump sled module (3), multi-layer adiabatic composite hose (4), throttle pressure reduction module (5), shore flange (6), CO2 cargo tank inlet valve (7), CO2 cargo tank (8) are connected in turn; The low-temperature liquid pump sled module (3) is composed of two sets of identical low-temperature liquid pump systems connected in parallel, and each set of low-temperature liquid pump system is connected in series by system inlet valve (31), low-temperature pump inlet valve (32), double-pump-head low-temperature liquid pump (33), low-temperature pump motor (34), damper (35), check valve (36), temperature and pressure sensor (37), safety relief valve (38). The control of the low-temperature liquid pump sled module (3) is realized by the PLC control cabinet (39) installed on the low-temperature liquid pump sled module (3), and the PLC control cabinet (39) is composed of a programmable controller and a pressure parameter interlocking control frequency converter of the low-temperature pump motor (34) in the throttle pressure reduction module (5) to realize constant pressure output; The throttle pressure reduction module (5) is composed of flowmeter (51), pressure sensor (52), temperature sensor (53), throttle valve (54) connected in series; the throttle valve (54) of the throttle pressure reduction module (5) is adjusted to control the pressure of liquid CO2 in the pipeline during transportation, and the required supercooled liquid CO2 of the system is generated; Method for precooling of CO2 cargo hold with supercooled liquid CO2 3 Liquid CO2 cargo hold, comprising the steps of: The supercooled liquid CO2 is saturated liquid CO2 with set temperature and pressure, which is pressurized and transported by the low-temperature liquid pump sled module (3). The supercooling degree of the supercooled liquid CO2 is controlled by adjusting the opening of the throttle valve (54) of the throttle pressure reduction module (5) during transportation. The supercooled liquid CO2 is transported in a supercooled state, saturated vaporization under the pressure of the CO2 cargo tank, and the latent heat of vaporization of liquid CO2 is used to complete the pre-cooling of the CO2 cargo tank under the condition that the lowest design temperature of the CO2 cargo tank is not lower than the lowest design temperature of the CO2 cargo tank; The liquid CO2 tank truck (1) is set to have a pressure of 15 barg, and the saturated temperature of the liquid CO2 at this pressure is -28°C; The cryogenic liquid pump skid module (3) is selected for a maximum flow of 6 m 3 / h, a liquid carbon dioxide pressure of 25 barg, a temperature of -18°C or less at the point of delivery of the land flange (6), the cryogenic liquid pump (33) motor power is 18 KW, the cryogenic liquid pump skid module (3) inlet pressure is 1.3-2.3 MPa, and the outlet pressure is 2.0-4.0 MPa; A programmable controller is arranged to control the frequency of the motor frequency converter of the cryogenic liquid pump to gradually increase the flow rate of the cryogenic liquid pump to 6 m 3 / h. The multi-layer adiabatic composite hose (4) is a stainless steel corrugated pipe plus a metal woven mesh, with a diameter of DN32, a pressure rating of PN4.0MPa, and an insulation material of rubber-plastic cotton, with an insulation layer thickness of 100mm; Adjusting the operation of throttling pressure reducing module (5): when the flow of flowmeter (51) reaches 6 m 3 / h, manually adjust the opening of throttling valve (54) until the pressure of pressure sensor (52) reaches 25 barg, the temperature of temperature sensor (53) is ≤-18°C, after that, the programmable controller of PLC control cabinet (39) is interlocked with the pressure sensor of throttling pressure reducing module (5) to control the frequency of frequency converter of low temperature pump motor (34), so as to realize the constant pressure output of pressure sensor (52) under the given throttling condition.

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