Method for realizing CO2 cargo hold precooling by using supercooled liquid CO2

Abstract

The invention discloses a method for realizing CO2 cargo hold precooling by using supercooled liquid CO2. The liquid CO2 is used for precooling the CO2 cargo hold, and the liquid CO2 entering the CO2 cargo hold is required to cool the CO2 cargo hold to the lowest design temperature under the condition that the lowest temperature of the liquid CO2 entering the CO2 cargo hold after vaporization is not lower than the lowest design temperature of the CO2 cargo hold. Therefore, firstly, latent heat of vaporization of liquid CO2 needs to be utilized to absorb heat of the CO2 cargo hold so as to reduce the temperature of the CO2 cargo hold; and secondly, the final temperature after the liquid CO2 is vaporized is close to but not lower than the lowest design temperature of the CO2 cargo hold. The supercooled liquid CO2 is obtained by changing the pressure of the saturated liquid CO2, the supercooled liquid CO2 serves as a cold source, is conveyed in a supercooled state and is saturated and vaporized under the pressure of the CO2 cargo hold when entering the CO2 cargo hold, and the aim of precooling the CO2 cargo hold by utilizing latent heat of vaporization of the liquid CO2 under the condition that the temperature is not lower than the lowest design temperature of the CO2 cargo hold is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of innovative application of liquid CO2, and particularly to a method for realizing precooling of a CO2 cargo tank by using supercooled liquid CO2. BACKGROUND

[0002] With the development of economy and the technical requirements of energy saving and emission reduction, the types and quantities of gas transport ships, liquid cargo ships and chemical transport ships are increasing. Under this background, the first liquid CO2 transport ship in the world has been successfully delivered and put into operation, and it is expected that the market demand for liquid CO2 transport ships will continue to increase in the future.

[0003] The core equipment of the liquid CO2 transport ship is the CO2 cargo tank, which usually adopts low-temperature carbon steel materials, and the general design temperature is not lower than -40°C. This type of ship needs to be completed in the shipyard after gas test and filling, and before filling, liquid CO2 needs to be used to pressurize and precool the CO2 cargo tank on the ship.

[0004] According to the CO2 cargo tank minimum design temperature and CO2 liquid saturation vapor pressure table, before precooling the CO2 cargo tank, the pressure of the CO2 cargo tank needs to be increased to the set pressure, for example: for the CO2 cargo tank with a minimum design temperature of -35°C, in order to make the minimum temperature during precooling not lower than the minimum design temperature, the pressure of the CO2 cargo tank needs to be increased to about 12 barg before precooling can be started.

[0005] Using liquid CO2 to precool the CO2 cargo tank requires that the liquid CO2 entering the CO2 cargo tank during the precooling process is cooled to the minimum design temperature of the CO2 cargo tank under the condition that the minimum temperature of the liquid CO2 after vaporization is not lower than the minimum design temperature of the CO2 cargo tank. Therefore, only according to the principle that the temperature basically remains unchanged during the phase change process of the material, the latent heat of vaporization of the liquid CO2 is used to absorb the heat of the CO2 cargo tank to reduce its temperature, and at the same time, the final temperature of the liquid CO2 entering the CO2 cargo tank after vaporization needs to be close to but not lower than the minimum design temperature of the CO2 cargo tank, so as to achieve the goal of cooling the CO2 cargo tank to close to the minimum design temperature.

[0006] If saturated liquid CO2 is used as a cold source to precool the CO2 cargo tank, with the gradual decrease of the pressure of the liquid CO2 during transportation and the absorption of external heat, the liquid CO2 will be in a superheated state of about 12 barg when it enters the CO2 cargo tank. Although the latent heat can be released and heat can be absorbed when the liquid CO2 vaporizes in the CO2 cargo tank to reduce the temperature of the CO2 cargo tank, the final temperature after vaporization will be higher than the minimum design temperature of the CO2 cargo tank, that is, the use amount of the liquid CO2 is increased, and the goal of cooling the CO2 cargo tank to the minimum design temperature cannot be achieved. SUMMARY

[0007] To solve the above problems, the application is to establish the supercooling state of liquid CO2, i.e. to transform the liquid CO2 in the saturated state (equilibrium state) into the supercooling state (intermediate state) with a certain degree of supercooling. The cold source is the supercooling liquid CO2 in the intermediate state (or unstable state), which will continuously reduce the degree of supercooling and develop to the saturated state in the delivery process according to the principle that the balance will move to the direction of reducing the supercooling state. When it enters the CO2 cargo tank, it reaches the new saturated state of about 12 barg, and when it vaporizes in the CO2 cargo tank, it releases latent heat and absorbs heat to reduce the temperature of the CO2 cargo tank, and the final temperature after vaporization is close to or reaches the minimum design temperature of the CO2 cargo tank, so that the CO2 cargo tank can be cooled to the minimum design temperature.

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

[0009] The application is to change the pressure of the saturated liquid CO2 (equilibrium state) to become supercooling liquid CO2 (intermediate state) with a certain degree of supercooling. The supercooling liquid CO2 gradually changes to the new saturated state in the delivery process, reaches the new saturated state at the corresponding pressure of the CO2 cargo tank when it enters the CO2 cargo tank, and the final temperature of the vaporization in the CO2 cargo tank is close to or reaches the minimum design temperature of the CO2 cargo tank. In the phase change vaporization process, latent heat is released and heat is absorbed, so that the CO2 cargo tank can be cooled to the minimum design temperature.

[0010] It should be emphasized that the precooling operation of the application is carried out after the CO2 cargo tank is pressurized (after pressurization).

[0011] To achieve the above goal, the application provides a method for realizing the precooling of the CO2 cargo tank by using supercooling liquid CO2, which relies on a system for realizing the precooling of the CO2 cargo tank by using supercooling liquid CO2, which comprises: The liquid CO2 tank truck, the tank truck hose, the low-temperature liquid pump sled module, the multi-layer adiabatic composite hose, the throttling pressure reduction module, the shore flange, the CO2 cargo tank inlet valve, and the CO2 cargo tank are connected in series.

[0012] The low-temperature liquid pump pry module is composed of two sets of parallel low-temperature liquid pump systems, usually one standby and one in use, or inlet shunt, outlet confluence parallel use. The low-temperature liquid pump pry module is connected in series by a system inlet valve, a low-temperature pump inlet valve, a double-pump head low-temperature liquid pump, a low-temperature pump motor, a damper, a check valve, a temperature pressure sensor, and a safety relief valve. The control of the low-temperature liquid pump pry module is realized by a PLC control cabinet installed on the pump pry, which mainly includes a programmable controller and a throttling pressure reducing module, and the frequency of the low-temperature pump motor frequency converter is controlled by the pressure parameter to realize the constant pressure output of the throttling pressure reducing module.

[0013] The throttling pressure reducing module is connected in series by a flowmeter, a pressure sensor, a temperature sensor, and a throttling valve. The throttling valve of the throttling pressure reducing module is adjusted to control the pressure of the liquid CO2 in the pipeline during transportation, and supercooled liquid CO2 required by the CO2 cargo hold precooling system is generated.

[0014] Based on the above system, the application provides a method for realizing CO2 cargo hold precooling by using supercooled liquid CO2. The supercooled liquid CO2 is saturated liquid CO2 with a set temperature and pressure, which is pressurized and transported by the low-temperature liquid pump pry module. According to the continuity principle of fluid, the supercooling degree of the supercooled liquid CO2 is controlled by adjusting the opening of the throttling valve of the throttling pressure reducing module during transportation. The CO2 cargo hold precooling is completed by using the latent heat of vaporization of liquid CO2 under the condition that the saturation vaporization is carried out at the pressure of the CO2 cargo hold and the temperature is not lower than the minimum design temperature of the CO2 cargo hold.

[0015] For example, for a 7500M 3 For example, for a 7500M The pressure of the liquid CO2 tank truck is set to 15 barg, and the saturated temperature of the liquid CO2 at this pressure is -28°C.

[0016] The low-temperature liquid pump pry module is selected according to the maximum flow of 6m 3 / h, the liquid carbon dioxide pressure at the delivery point of the through flange is 25 barg, and the temperature is ≤-18°C (the saturated temperature at this pressure is -12°C, i.e. the supercooling degree exceeds -6°C). The low-temperature liquid pump motor power is 18KW, the low-temperature liquid pump pry module inlet pressure is 1.3-2.3MPa, and the outlet pressure is 2.0-4.0MPa; The frequency of the low-temperature liquid pump motor frequency converter is gradually increased by the programmable controller, so that the flow of the low-temperature liquid pump reaches 6m 3 / h; The multi-layer heat-insulating composite hose is provided with a stainless steel corrugated pipe and a metal woven mesh, has a diameter of DN32, a pressure rating of PN4.0MPa, and is made of rubber-plastic cotton with a thickness of 100mm; The operation of the throttling pressure-reducing module is adjusted as follows: when the flow rate of the flow meter reaches 6m 3 / h, the opening of the throttling valve is manually adjusted until the pressure of the pressure sensor reaches 25barg and the temperature of the temperature sensor is less than or equal to -18°C, and then the programmable controller of the PLC control cabinet is connected to the pressure sensor of the throttling pressure-reducing module to control the frequency of the motor frequency converter of the low-temperature liquid pump, so that the pressure of the pressure sensor is kept at 25barg under the given throttling condition.

[0017] The above is a specific application process of using supercooled liquid CO2 to precool a CO2 cargo tank with a volume of 7500M 3 , a design pressure of 19barg and a design temperature of -36°C. When the volume, design pressure and design temperature of the cold container change, the required flow rate (flow meter), pressure (pressure sensor) and supercooling degree (temperature sensor) parameters will change accordingly. The corresponding settings and adjustments of the saturation state (pressure and temperature) of the liquid CO2 tank car, the selection of the low-temperature liquid pump module equipment, the diameter and pressure rating of the multi-layer heat-insulating composite hose, the design and selection of the throttling pressure-reducing module and the opening of the throttling valve will also be adjusted accordingly, but the typical configuration, parameter setting, node position and operation process of the supercooled liquid CO2 precooling system can be found in the above specific application scenarios.

[0018] The minimum design temperature referred to in the present application refers to the minimum temperature at which the container can be safely operated or used under the design working condition, which is usually marked on the equipment nameplate as the lower limit of the safe operating temperature of the equipment.

[0019] In a preferred embodiment, the low-temperature container (CO2 cargo tank) to be pre-cooled has a volume of 7500M 3 , a minimum design temperature of -36°C, and an injection port with a diameter of DN32 (millimeters). At this time, in order to complete the pre-cooling, the parameters of the liquid CO2 before injection are 25barg and a temperature of less than or equal to -18°C (the temperature reaches this value and the subsequent operation can be performed, and the temperature will not be much lower than this value), and the injection is performed at a flow rate of 4m 3 / h.

[0020] The pre-cooling of the container is a relatively long process, and during the start of the injection process, the injection parameters before the injection port valve, such as 25barg, a temperature of less than or equal to -18°C and a flow rate of 4m 3 / h, can be determined by gradually adjusting related valves, pump bodies and other components. Then the pre-cooling operation is completed.

[0021] And the pipeline for realizing injection, according to the need, set the necessary valve, pump body, and detection sensor can. For this the application provides a kind of using supercooled liquid CO2 realizes CO2 cargo hold precooling system.The CO2 cargo hold precooling system by liquid CO2 tank truck, tank truck hose, low-temperature liquid pump skid module, multilayer adiabatic composite hose, throttling pressure reduction module, shore flange, CO2 cargo hold import valve, CO2 cargo hold in turn are connected in series.Wherein:low-temperature liquid pump skid module by system import valve, low-temperature pump import valve, double pump head low-temperature liquid pump, low-temperature pump motor, damper, check valve, temperature, pressure sensor, safety release valve are connected in series and constitute.Low-temperature liquid pump skid module is connected in parallel by two sets of low-temperature liquid pump system, usually one is used, also can be inlet shunt, outlet converging parallel use.PLC control cabinet is mainly composed of programmable controller and low-temperature pump motor frequency converter, and the pressure sensor in the throttling pressure reduction module is connected by programmable controller to realize the constant pressure control of the supercooled liquid CO2 in the outlet of throttling pressure reduction module, so that the required supercooling degree and flow are achieved.The throttling pressure reduction module is connected in series by flowmeter, pressure sensor, temperature sensor and throttling valve.

[0022] The beneficial effects of the application are as follows: by changing the pressure conditions of saturated liquid CO2 to obtain supercooled liquid CO2, by transporting in a supercooled state and using in a new saturated state, the latent heat of vaporization of liquid CO2 is maximized while ensuring that the final temperature after vaporization is close to or reaches the minimum design temperature of the CO2 cargo hold, achieving the goal of precooling the CO2 cargo hold using the latent heat of vaporization of liquid CO2 at a temperature not lower than the minimum design temperature of the CO2 cargo hold.

[0023] The application is a system and method for precooling a CO2 cargo hold using supercooled liquid CO2. To precool the CO2 cargo hold using liquid CO2, the minimum temperature of the liquid CO2 entering the CO2 cargo hold after vaporization must not be lower than the minimum design temperature of the CO2 cargo hold. According to the principle that the temperature remains basically unchanged during the phase change of a substance, the latent heat of vaporization of liquid CO2 is used to absorb the heat of the CO2 cargo hold to reduce its temperature while ensuring that the final temperature after vaporization of the liquid CO2 is close to but not lower than the minimum design temperature of the CO2 cargo hold, thereby achieving the goal of cooling the CO2 cargo hold to close to or reach the minimum design temperature. To achieve the above goal, the application changes the pressure conditions of saturated liquid CO2 to obtain supercooled liquid CO2, and uses the method of transporting in a supercooled state and using in a new saturated state, thereby achieving the goal of precooling the CO2 cargo hold using the latent heat of vaporization of liquid CO2 at a temperature not lower than the minimum design temperature of the CO2 cargo hold. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1is a schematic diagram of the system principle of the application for pre-cooling CO2 cargo tank with supercooled liquid CO2. DETAILED DESCRIPTION

[0025] Case: G7500-1 & G7500-2 liquid CO2 transport sister ships. The ship liquid cargo system is 7500M 3 Liquid CO2 cargo tank, design pressure 1.9MPa, design temperature -36°C, cooling rate less than 10°C / h, maximum temperature difference of tank body less than 15°C during cooling process, according to the above CO2 cargo tank process requirements, the supercooled liquid carbon dioxide parameters at the junction of the shore flange 6 are: flow 4m 3 / h, 25 barg, temperature ≤-18°C (supercooling degree about -6° or so).

[0026] Therefore, a system for realizing pre-cooling of conventional low-temperature containers with supercooled liquid CO2 is designed, as shown in Figure 1 Fig. 1, which includes: liquid CO2 tank truck 1, tank truck hose 2, low-temperature liquid pump sled module 3, multi-layer adiabatic composite hose 4, throttling and pressure reducing module 5, shore flange 6, CO2 cargo tank inlet valve 7, CO2 cargo tank 8 connected in series.

[0027] Among them: the low-temperature liquid pump sled module 3 is composed of two identical low-temperature liquid pump systems in parallel, usually one for standby and one for use, or inlet shunt, outlet shunt parallel use. The low-temperature liquid pump sled module 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 is realized by the PLC control cabinet 39 installed on the pump sled, which mainly consists of a programmable controller and a frequency converter of the low-temperature pump motor 34.

[0028] The throttling and pressure reducing module 5 is connected in series by flow meter 51, pressure sensor 52, temperature sensor 53, throttling valve 54.

[0029] The programmable controller in the PLC control cabinet 39 and the pressure sensor 52 in the throttling and pressure reducing module 5 are interlocked to control the frequency of the low-temperature liquid pump motor frequency converter, so as to realize the constant pressure control of the supercooled liquid CO2 at the outlet of the throttling and pressure reducing module 5, and achieve the required supercooling degree and flow.

[0030] Figure 1 A1 is the inlet of the low-temperature liquid pump sled module, B1 is the outlet of the low-temperature liquid pump sled module, A2 is the inlet of the throttling and pressure reducing module, and B2 is the outlet of the throttling and pressure reducing module. Furthermore, the present application can be better understood in conjunction with the CO2 liquid saturation vapor pressure table in the prior art as shown in Table 1. The saturation vapor pressure in the table is measured in kPa, and the subcooled liquid density is 1359.51 kg / m3.

[0031] Table 1: CO2 liquid saturation vapor pressure table The specific operation of the above system is as follows: 1. Adjust the pressure of the liquid CO2 tank truck: gradually reduce the pressure in the liquid CO2 tank truck to about 15 barg by exhausting the gas phase pipeline of the liquid CO2 tank truck. When the pressure is stable, it indicates that the liquid CO2 in the liquid CO2 tank truck is in a saturated state, and according to Table 1, the temperature is about -28°C.

[0032] 2. Connect the liquid phase pipeline of the liquid CO2 tank truck to the inlet of the low-temperature liquid pump module 3, open all valves between the outlet of the pump module and the CO2 cargo hold, and control the opening of the liquid CO2 tank truck liquid phase valve to precool the subcooled liquid CO2 system. When the low-temperature liquid pump module 3 is pre-cooled, turn on the start button of the low-temperature liquid pump module control cabinet 39. The programmable controller will follow the set program and load the low-temperature liquid double-head pump 33 by gradually increasing the frequency of the frequency converter of the low-temperature pump motor 34. When the load reaches about 40 Hz and the throttling pressure module flowmeter 51 is about 6 m 3 / h, gradually close the opening of the throttling valve 54 until the pressure is 25 barg. After that, the programmable controller of the pump module PLC control cabinet 39 will be connected with the pressure sensor 52 to control the frequency of the frequency converter of the low-temperature pump motor 34, and the set flow of 4 m 3 / h, temperature ≤ -18°C, pressure 25 barg constant pressure output. The specific design and implementation process is as follows: The low-temperature liquid pump module 3 is designed according to the maximum flow of 6 m 3 / h, the liquid carbon dioxide pressure at the delivery point of the shore flange 6 is 25 barg, and the temperature is ≤ -18°C (the saturation temperature at this pressure is -12°C, i.e. the subcooling degree exceeds -6°C). The low-temperature liquid pump motor power is 18 KW, the low-temperature liquid pump module 3 inlet pressure is 1.3-2.3 MPa, and the outlet pressure is 2.0-4.0 MPa.

[0033] The programmable controller is set to control the frequency of the low-temperature liquid pump motor frequency converter to gradually increase, so that the flow of the low-temperature liquid pump 35 reaches 6 m 3 / h; The multi-layer adiabatic composite hose 4 is made of stainless steel corrugated pipe plus metal woven mesh, with a diameter of DN32 and a pressure rating of PN4.0 MPa. The insulation material is rubber-plastic cotton, and the insulation layer thickness is 100 mm. The operation of the throttling pressure reducing module 5 is adjusted: when the flow of the flow meter 51 reaches 6 m 3 / h, the opening of the throttling valve 54 is manually adjusted until the pressure of the pressure sensor 52 reaches 25 barg and the temperature of the temperature sensor 53 is ≤-18°C, and thereafter, the programmable controller of the PLC control cabinet 39 is connected to the pressure sensor of the throttling pressure reducing module 5 to control the frequency of the low-temperature liquid pump motor frequency converter, so as to realize the constant pressure output of the pressure sensor 52 under the given throttling condition.

[0034] The above is a specific implementation example of the G7500-1 & G7500-2 liquid CO2 transport sister ships, and the main parameters of the CO2 cargo hold are: volume 7500 m 3 , design pressure 19 barg, and design temperature -35°C.

[0035] When the volume, design pressure, and design temperature of the cold container change, the cargo hold pressure at which the CO2 cargo hold starts to precool can be obtained by corresponding inquiry in Table 1 according to the minimum design temperature of the CO2 cargo hold; the required flow (flow meter 51), the pressure of the junction point (the pressure of the pressure sensor 52), and the supercooling degree (the temperature of the temperature sensor 53) will change accordingly; the corresponding pressure and temperature (saturation state) of the liquid CO2 in the liquid CO2 tank truck 1, the equipment selection of the low-temperature liquid pump module 3, the diameter and pressure grade of the multi-layer heat-insulating composite hose 4, the design selection of the throttling pressure reducing module 5, and the opening of the throttling valve 54 will also be adjusted accordingly, and these specific parameters can be obtained through a limited number of simulations and test verifications. However, the typical configuration, parameter setting, node position, and operation process of the supercooled liquid CO2 precooling system can be found in the above specific application scenarios.

[0036] Based on the above description, the application provides a method for realizing CO2 cargo hold precooling by using supercooled liquid CO2. First, according to Table 1, the saturation state of liquid CO2 at the required temperature in the liquid CO2 tank truck 1 is established, and then it enters the low-temperature liquid pump module 3, and the set flow is achieved through the frequency converter adjustment of the low-temperature pump motor 34, and the temperature and pressure of the liquid CO2 in the pipeline during transportation are controlled through the throttling valve 54 of the throttling pressure reducing module 5, and the supercooled liquid CO2 in the intermediate state is obtained at the junction point of the shore flange 6. The specific process is as follows: first, the pressure of the tank truck is adjusted to make the liquid CO2 in the tank truck reach the saturation state at the set temperature and pressure, second, the liquid CO2 in the tank truck flows through the low-temperature liquid pump module to make the system fully precool, then the low-temperature liquid pump is started and the system reaches the set flow through frequency adjustment, and finally the opening of the throttling valve is adjusted to obtain the supercooled liquid CO2 in the intermediate state at the junction point of the shore flange 6.

[0037] The method of the related manner can be implemented in many ways. Liquid CO2 can be kept in a certain stable state in a container through prior adjustment, and then output to a container to be pre-cooled. Before injection, the liquid CO2 is adjusted through a related adjustment module to ensure that the parameters of the liquid CO2 meet the necessary conditions (for example, 25 barg, temperature ≤-18°C, and injection flow rate 4 m 3 / h) so as to be suitable for pre-cooling.

[0038] The above shows and describes the basic principles and main features of the variations of the present application and the advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples. The above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application. However, the typical configuration, parameter setting node position, and operation process of the supercooled liquid carbon dioxide pre-cooling system can be found in the above specific application scenarios. These changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application 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 system for realizing the pre-cooling of the CO2 cargo tank by using supercooled liquid CO2, which comprises a liquid CO2 tank truck (1), a tank truck hose (2), a low-temperature liquid pump sled module (3), a multi-layer heat-insulating composite hose (4), a throttling pressure reduction module (5), a shore flange (6), a CO2 cargo tank inlet valve (7), and a CO2 cargo tank (8) connected in series. The low-temperature liquid pump sled module (3) is composed of two sets of identical low-temperature liquid pump systems connected in parallel, each of which is connected in series by a system inlet valve (31), a low-temperature pump inlet valve (32), a double-pump-head low-temperature liquid pump (33), a low-temperature pump motor (34), a damper (35), a check valve (36), a temperature and pressure sensor (37), and a safety relief valve (38). The control of the low-temperature liquid pump sled module is realized by a PLC control cabinet (39) installed on the pump sled. The PLC control cabinet (39) is composed of a programmable controller and a pressure parameter interlocking control variable frequency converter frequency of the low-temperature pump motor (34) to realize constant pressure output. The throttling pressure reduction module (5) is composed of a flowmeter (51), a pressure sensor (52), a temperature sensor (53), and a throttling valve (54) connected in series. The throttling valve (54) of the throttling pressure reduction module (5) is adjusted to control the pressure of the liquid CO2 in the pipeline during transportation, generating the supercooled liquid CO2 required by the CO2 cargo tank pre-cooling system. The method for realizing the pre-cooling of the CO2 cargo tank by using supercooled liquid CO2 comprises the following steps: The supercooled liquid CO2 is saturated liquid CO2 with a set temperature and pressure that 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 throttling valve (54) of the throttling pressure reduction module (5) during transportation. The pre-cooling of the CO2 cargo tank is completed by using the latent heat of vaporization of the liquid CO2 under the conditions of saturation vaporization under the pressure of the CO2 cargo tank and not lower than the minimum design temperature of the CO2 cargo tank.

2. The method of claim 1, wherein the supercooled liquid CO2 is used to pre-cool the CO2 cargo tank. Precool 7500M 3 Liquid CO2 cargo hold, comprising the steps of: The pressure of the liquid CO2 tank truck (1) is set to 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 heat-insulating composite hose (4) is a stainless steel corrugated pipe with a metal woven mesh, with a diameter of DN32 and a pressure rating of PN4.0MPa. The thermal insulation material is rubber-plastic cotton, and the thickness of the thermal insulation layer is 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 low-temperature liquid pump motor frequency converter, so as to realize the constant pressure output of 25 barg of pressure sensor (52) under the given throttling condition.

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