A method for pressurizing and precooling CO2 cargo holds using superheated liquid CO2

Abstract

This invention discloses a method for pressurizing and precooling a CO2 cargo hold using superheated liquid CO2. The method relies on a system that utilizes superheated liquid CO2 for pressurization and precooling of the CO2 cargo hold. The system includes an inlet regulating valve, a vaporizer, temperature and pressure sensors, an outlet coarse regulating valve, and a fine regulating valve, connected in series to the CO2 cargo hold. The method first establishes a three-dimensional dynamic parameter table consisting of the CO2 cargo hold pressure, the vaporizer outlet temperature and pressure of the pressurization and precooling system, and so on. Based on the CO2 cargo hold pressure in the three-dimensional dynamic parameter table, the temperature and pressure at the vaporizer outlet of the pressurization and precooling system are adjusted. While ensuring that the temperature does not fall below the minimum design temperature of the CO2 cargo hold, the latent heat of vaporization of liquid CO2 is used to precool the CO2 cargo hold simultaneously with pressurization. This invention utilizes part of the cooling capacity of the liquid CO2 during pressurization, reducing the amount of liquid CO2 used in the precooling process.

Description

Technical Field

[0001] This invention belongs to the field of innovative carbon dioxide application technology, specifically a technology that uses superheated liquid CO2 to simultaneously pre-cool the CO2 cargo hold during pressurization. Background Technology

[0002] 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 needed to pre-cool the CO2 cargo tank on board.

[0003] To precool the CO2 cargo tanks on a ship using liquid CO2, which has three phases and whose temperature varies with pressure, it is necessary to first establish a certain pressure in the CO2 cargo tanks before proceeding with the next step of precooling. Otherwise, not only will the cooling rate and temperature be difficult to control, but dry ice may also form in severe cases.

[0004] Establishing pressure in a CO2 cargo hold typically involves using vaporized CO2 gas. However, this method completely wastes the latent heat of vaporization of the liquid CO2 used during the pressure build-up phase. Therefore, the problem this invention aims to solve is how to utilize the latent heat of vaporization of liquid CO2 from the initial pressure build-up stage, absorbing heat from the CO2 cargo hold without falling below its minimum design temperature, thus reducing the amount of liquid CO2 used in subsequent pre-cooling processes.

[0005] The CO2 cargo hold (cooled container) involved in this invention refers to a carbon steel CO2 cargo hold (such as 16MnDR) with a design temperature of not lower than -40°C. The method of utilizing the cooling capacity during the pressurization process here refers to making full (or better) use of the latent heat of vaporization of CO2. For the cooled container that needs to be pre-cooled after pressurization, pre-cooling is carried out simultaneously during the pressurization process. The purpose is to save the amount of carbon dioxide used in the pre-cooling process.

[0006] To better achieve simultaneous precooling during pressurization, liquid CO2 should be used instead of gaseous CO2 as much as possible. However, if liquid CO2 in a normal saturated state is used, the temperature will be lower than the minimum design temperature of the CO2 cargo tank when it enters the CO2 cargo tank with a pressure of less than 1 MPa, or even below -40°C. Summary of the Invention

[0007] To address the aforementioned issues, this invention utilizes the latent heat of vaporization of liquid CO2 from the CO2 cargo hold pressure establishment stage. Under the premise of not falling below the minimum design temperature of the CO2 cargo hold, it absorbs heat from the CO2 cargo hold, reducing the amount of liquid CO2 used in the subsequent pre-cooling process, thereby saving the amount of carbon dioxide used in the pre-cooling process.

[0008] This invention addresses the aforementioned problems by providing a pressurized precooling system that generates superheated liquid CO2 by altering the temperature of saturated liquid CO2. The system utilizes the latent heat of vaporization of liquid CO2 to determine the CO2 cargo tank pressure changes, vaporizer outlet temperature, and pressure based on the physical properties of CO2 and computer simulations. This invention enables precooling during the CO2 cargo tank pressurization process, starting from the pressure build-up stage, while ensuring the temperature does not fall below the minimum design temperature of the CO2 cargo tank. This maximizes the utilization of the latent heat of vaporization of liquid CO2, reducing the amount of liquid CO2 used in subsequent precooling processes.

[0009] To achieve the above objectives, this invention provides a method for pressurizing and precooling a CO2 cargo tank using superheated liquid CO2. This method relies on a system that uses superheated liquid CO2 to pressurize and precool the CO2 cargo tank. The system includes a precooling pipeline connected to the CO2 cargo tank, which comprises an inlet regulating valve, a vaporizer, a temperature sensor, a pressure sensor, an outlet coarse regulating valve, and an outlet fine regulating valve connected in series. The pipeline upstream of the inlet regulating valve is connected to a liquid CO2 supply end.

[0010] During the pressurization process, as the pressure RP inside the CO2 cargo tank increases, the pressure QP and temperature QT of the liquid CO2 before entering the CO2 cargo tank are adjusted so that the transmitted liquid CO2 is in a superheated state under the corresponding pressure; and the temperature of the liquid CO2 after vaporization entering the CO2 cargo tank is higher than the minimum design temperature of the CO2 cargo tank.

[0011] Under the optimal selection method, for 7500M 3 The CO2 cargo hold, with a minimum design temperature of -35°C to -40°C, is pressurized and pre-cooled; the pre-cooling pipeline uses DN32 304 stainless steel pipe; adjustments are made according to the following table:

[0012]

[0013] 3D dynamic parameter table

[0014] In the table, the unit for pressure is barg, and the unit for temperature is °C.

[0015] The optimal solution of the above-mentioned selection method specifically includes the following process:

[0016] Preparation: Shut down the supply of all liquid CO2 to the CO2 cargo tank; open the outlet coarse regulating valve and fully open the outlet fine regulating valve in the precooling pipeline, and close the inlet regulating valve;

[0017] Step 1: Open the inlet regulating valve. When the vaporizer outlet temperature sensor shows a temperature of -14°C, repeatedly adjust the opening of the outlet coarse regulating valve and the inlet regulating valve to make the vaporizer outlet temperature -16°C and pressure 11 barg. Then gradually reduce the opening of the outlet fine regulating valve until the vaporizer outlet temperature is -12°C and pressure is 13 barg. After that, as the CO2 cargo tank pressure gradually increases, gradually increase the opening of the vaporizer outlet fine regulating valve to make the vaporizer outlet temperature and pressure reach -14°C and 12 barg, and enter the next adjustment cycle.

[0018] Step 2: After the outlet fine-tuning valve is fully open, increase the opening of the inlet regulating valve. When the vaporizer outlet temperature sensor shows that the temperature has dropped to -16°C, adjust the opening of the outlet coarse regulating valve and the inlet regulating valve to stabilize the vaporizer outlet temperature and pressure at -17°C and 11 barg. Then gradually decrease the opening of the outlet fine-tuning valve until the vaporizer outlet temperature and pressure stabilize at -14°C and 13 barg. After that, gradually increase the opening of the vaporizer outlet fine-tuning valve to make the vaporizer outlet temperature and pressure reach -16°C and 12 barg, and enter the next adjustment cycle.

[0019] Step 3: After the outlet fine-tuning valve is fully open, increase the opening of the inlet regulating valve. When the vaporizer outlet temperature drops to -17°C, repeatedly adjust the opening of the outlet coarse regulating valve and the inlet regulating valve to stabilize the vaporizer outlet temperature and pressure at -19°C and 11 barg. Then gradually decrease the opening of the outlet fine-tuning valve to stabilize the vaporizer outlet temperature and pressure at -16°C and 13 barg. After that, gradually increase the opening of the vaporizer outlet fine-tuning valve to reach -17°C and 12 barg, and enter the next adjustment cycle.

[0020] Step 4: Following the valve adjustment method in Step 2 or Step 3 above, control the parameters according to the three-dimensional dynamic parameter table until the CO2 cargo compartment pressure increases to 11.5 barg.

[0021] The above process ensures that the CO2 temperature entering the CO2 cargo hold is maintained above -35°C.

[0022] Furthermore, in a preferred embodiment, the CO2 cargo compartment of the present invention is connected to a pipeline for injecting liquid CO2 or a cargo compartment pressurization pipeline; the precooling pipeline is arranged in parallel with the pipeline for injecting liquid CO2 or the cargo compartment pressurization pipeline.

[0023] In the preferred embodiment, the inlet regulating valve A1, the outlet coarse regulating valve A5, and the outlet fine regulating valve A6 are selected from DANFOSS REG-SA and REG-SB series, all with a diameter of DN32.

[0024] During pressurization, RP, QT, and QP adjust their control parameters according to a three-dimensional dynamic parameter table to complete pre-cooling and pressurization. This process ensures that the liquid CO2 entering the CO2 cargo tank is superheated liquid CO2 with a vaporization temperature higher than the minimum design temperature of the CO2 cargo tank at the corresponding CO2 cargo tank pressure RP. Specific adjustments are achieved through regulating valves. Specifically: the pressurization pre-cooling system is equipped with an inlet regulating valve, which controls the temperature of the superheated liquid CO2 entering the CO2 cargo tank by adjusting its opening; the pressurization pre-cooling system is also equipped with an outlet coarse regulating valve and an outlet fine regulating valve, which control the pressure of the superheated liquid CO2 entering the CO2 cargo tank by adjusting their openings.

[0025] To further explain, the adjustment process of the system of the present invention includes the following steps:

[0026] Close the inlet valve of the pressurized pipeline in the CO2 cargo compartment, so that the liquid CO2 supplied from the supply end enters the CO2 cargo compartment through the pressurized precooling system;

[0027] After fully opening the outlet micro-adjustment valve of the CO2 cargo hold pressurization and precooling system, control the opening of the inlet adjustment valve and the outlet coarse adjustment valve of the CO2 cargo hold pressurization and precooling system to obtain the liquid CO2 pressure QP and liquid CO2 temperature QT before entering the CO2 cargo hold corresponding to the CO2 cargo hold pressure RP in the three-dimensional dynamic parameter table;

[0028] By adjusting the opening of the outlet fine-tuning valve of the CO2 cargo hold pressurization and precooling system, the pressure of the liquid CO2 entering the CO2 cargo hold can be finely adjusted within the step size of the CO2 cargo hold pressure change in the three-dimensional dynamic parameter table.

[0029] Based on the above system, the present invention also provides a method for pressurizing and precooling a CO2 cargo tank using superheated liquid CO2. First, a pressurizing and precooling pipeline for the CO2 cargo tank is set up. During the pressurization stage, as the pressure RP inside the CO2 cargo tank increases, the relationship between the pressure QP and temperature QT of the liquid CO2 entering the CO2 cargo tank through the pressurizing and precooling system is adjusted so that the CO2 entering the CO2 cargo tank is superheated liquid CO2 with a vaporization temperature higher than the minimum design temperature of the CO2 cargo tank. The latent heat of phase change during the vaporization of the superheated liquid CO2 inside the CO2 cargo tank is used to absorb heat from the CO2 cargo tank, thereby achieving precooling of the CO2 cargo tank.

[0030] The present invention provides a pressurized precooling method that establishes a three-dimensional dynamic parameter table of the pressure RP of the CO2 cargo tank, the liquid CO2 pressure QP and liquid CO2 temperature QT before the pressurized precooling system enters the CO2 cargo tank, and during the pressurization process, the liquid CO2 pressure QP and liquid CO2 temperature QT at the CO2 cargo tank inlet are adjusted according to the parameters in the three-dimensional dynamic parameter table to achieve precooling of the CO2 cargo tank at a temperature not exceeding its minimum design temperature during the pressurization process.

[0031] The beneficial effects of this invention are as follows: Based on the principle that the latent heat of vaporization of liquid CO2 during phase change is much greater than its sensible heat, by converting fully vaporized liquid CO2 into superheated liquid CO2, the latent heat of vaporization of liquid CO2 during the pressurization process of the CO2 cargo tank is utilized. Under the premise of not falling below the minimum design temperature of the CO2 cargo tank, pre-cooling is achieved simultaneously during the pressurization process of the CO2 cargo tank, saving a significant amount of liquid CO2 for the next pre-cooling process. For example: one 7500M... 3 By incorporating precooling during the pressurization process, the storage tank can essentially combine the original pressurization and precooling processes into one, saving approximately 200 tons of liquid CO2 used in the next precooling step. Specifically, the precooling step previously used approximately 200 tons of liquid CO2; now, with the process combined, only 240 tons are needed to achieve the same effect as the original 400 tons of CO2 (200 tons of pressurization + 200 tons of precooling), saving approximately 160 tons of CO2. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the pressurization and precooling system for the CO2 cargo compartment of the present invention.

[0033] In the diagram, valve 1 is the first valve, valve 2 is the second valve, heat exchanger (vaporizer) 3 is the third valve, valve 4 is the fourth valve, valve 5 is the pressure gauge in the CO2 cargo compartment 6 is the CO2 cargo compartment 7;

[0034] The system includes an inlet regulating valve A1, a vaporizer A2, a temperature sensor A3, a pressure sensor A4, an outlet coarse regulating valve A5, and an outlet fine regulating valve A6. Detailed Implementation

[0035] Combination Figure 1 This document describes the operation methods and principles of a pressurized precooling system. The CO2 cargo hold pressurized precooling system consists of an inlet regulating valve A1, a vaporizer A2, a temperature sensor A3, a pressure sensor A4, an outlet coarse regulating valve A5, and an outlet fine regulating valve A6. The CO2 cargo hold pressurized precooling system can be connected in parallel to a CO2 cargo hold pressurized gas supply system or connected to the inlet of the CO2 cargo hold. The inlet of the CO2 cargo hold pressurized gas supply system or the pressurized precooling system is connected to the liquid CO2 supply end.

[0036] Pressurized gas supply system, such as Figure 1 As shown, it includes valve 1, valve 2, heat exchanger (vaporizer) 3, valve 4, and valve 5; it is the pressurized gas supply system for the original CO2 cargo compartment 7. Label 6 in the figure is the pressure gauge for the CO2 cargo compartment.

[0037] This invention uses liquid CO2 to pre-cool a CO2 cargo tank. First, a pressure of approximately 12 barg must be established in the CO2 cargo tank. Establishing this pressure in a large CO2 cargo tank requires a large amount of liquid CO2 (e.g., one 7500M...). 3 A storage tank, requiring approximately 200 tons of liquid CO2 to establish a pressure of around 12 barg, will require more liquid CO2, with larger containers requiring even more. If this partially vaporized liquid CO2 is converted into superheated liquid CO2, and the latent heat of vaporization during its entry into the CO2 cargo hold is used to absorb heat from the cargo hold, pre-cooling can be achieved simultaneously with pressurization, reducing the amount of liquid CO2 used in the subsequent pre-cooling process. To achieve this objective, this invention provides a system for simultaneously pre-cooling a CO2 cargo hold during pressurization using superheated liquid CO2, namely, a CO2 cargo hold pressurization and pre-cooling system.

[0038] The CO2 cargo hold pressurization and precooling system consists of an inlet regulating valve A1, a vaporizer A2, a temperature sensor A3, a pressure sensor A4, an outlet coarse regulating valve A5, and an outlet fine regulating valve A6 connected in series, or connected in parallel to the CO2 cargo hold pressurization supply system, or connected to the inlet of the CO2 cargo hold. The inlet of the CO2 cargo hold pressurization supply system or the pressurization and precooling system is connected to the liquid CO2 supply end. The schematic diagram of the CO2 cargo hold pressurization and precooling principle is shown below. Figure 1 As shown.

[0039] The interchange of the positions of temperature and pressure sensors, and the presence of other pipeline accessories and auxiliary valves before and after the vaporizer, the inlet regulating valve, the outlet coarse regulating valve, and the fine regulating valve, are all considered equivalent.

[0040]

[0041] 3D dynamic parameter table

[0042] Reference Figure 1 Methods and principles for operating a pressurized precooling system:

[0043] 1. The temperature displayed by the temperature sensor A3 is controlled by adjusting the opening of the inlet regulating valve A1 and the flow rate of the vaporizer A2.

[0044] 2. The outlet coarse regulating valve A5 and the outlet fine regulating valve A6 are mainly used to regulate the pressure detected by the vaporizer outlet pressure sensor A4.

[0045] 3. As the CO2 cargo tank pressure gradually increases, the temperature of the superheated liquid CO2 at the outlet of vaporizer A2 should be gradually reduced according to the three-dimensional dynamic parameter table.

[0046] Operational preparation: Close the first inlet valve 1 of the CO2 cargo hold pressurized gas supply system, so that liquid CO2 at the gas supply end can only enter the CO2 cargo hold through the CO2 cargo hold pressurized precooling system; open the coarse regulating valve A5 at the outlet of the CO2 cargo hold pressurized precooling system and fully open the fine regulating valve A6 at the outlet, while keeping the inlet regulating valve A1 closed.

[0047] 1. Control the opening of the inlet regulating valve A1 of the CO2 cargo hold pressurization and precooling system to gradually reduce the outlet temperature of vaporizer A2. When the outlet temperature sensor A3 of vaporizer A2 reaches the initial target temperature of -14°C, repeatedly adjust the opening of the outlet coarse regulating valve A5 and the inlet regulating valve A1 until the outlet temperature and pressure of vaporizer A2 are stabilized at the left column of the target outlet temperature and pressure of vaporizer A2, that is, the outlet temperature of vaporizer A2 is -16°C and the pressure is 11 barg, reaching a stable equilibrium state; then gradually reduce the outlet fine regulating valve A6. The opening is adjusted until the temperature and pressure at the outlet of vaporizer A2 stabilize at the right column of the target temperature and pressure at the outlet of vaporizer A2, i.e., the outlet temperature of vaporizer A2 is -12°C and the pressure is 13 barg. Then, as the CO2 cargo tank pressure gradually increases within the step, the opening of the micro-adjustment valve A6 at the outlet of vaporizer A2 is gradually increased. Before entering the next step of increasing CO2 cargo tank pressure, the outlet temperature and pressure of vaporizer A2 are brought to the target values ​​of this adjustment, i.e., the outlet temperature of vaporizer A2 is -14°C and the pressure is 12 barg, and then the next adjustment cycle begins.

[0048] 2. After fully opening the outlet fine-tuning valve A6, increase the opening of the inlet regulating valve A1 of the CO2 cargo hold pressurization and precooling system. When the temperature of the outlet temperature sensor A3 of vaporizer A2 drops to the next long-term target temperature of -16°C, repeatedly adjust the opening of the outlet coarse regulating valve A5 and the inlet regulating valve A1 until the outlet temperature and pressure of vaporizer A2 are stabilized at the left column of the target outlet temperature and pressure of vaporizer A2, that is, the outlet temperature of vaporizer A2 is -17°C and the pressure is 11 barg, in a stable equilibrium state; then gradually reduce the outlet fine-tuning valve A6. The opening of the valve is adjusted until the temperature and pressure at the outlet of vaporizer A2 stabilize at the right column of the target temperature and pressure at the outlet of vaporizer A2, i.e., the outlet temperature of vaporizer A2 is -14°C and the pressure is 13 barg. Then, as the CO2 cargo tank pressure gradually increases within the step, the opening of the micro-adjustment valve A6 at the outlet of vaporizer A2 is gradually increased. Before entering the next step of increasing CO2 cargo tank pressure, the outlet temperature and pressure of vaporizer A2 are made to reach the target values ​​of this adjustment, i.e., the outlet temperature of vaporizer A2 is -16°C and the pressure is 12 barg, and then the next adjustment cycle begins.

[0049] 3. After fully opening the outlet fine-tuning valve A6, increase the opening of the inlet regulating valve A1 of the CO2 cargo hold pressurization and precooling system. When the outlet temperature of vaporizer A2 drops to the next long-term target temperature of -17°C, repeatedly adjust the openings of the outlet coarse regulating valve A5 and the inlet regulating valve A1 until the outlet temperature and pressure of vaporizer A2 are stabilized at the left column of the target outlet temperature and pressure of vaporizer A2, i.e., the outlet temperature of vaporizer A2 is -19°C and the pressure is 11 barg, reaching a stable equilibrium state. Then gradually reduce the opening of the outlet fine-tuning valve A6, so that... The temperature and pressure at the outlet of vaporizer A2 are stabilized at the right column of the target temperature and pressure at the outlet of vaporizer A2, that is, the outlet temperature of vaporizer A2 is -16°C and the pressure is 13 barg. Then, as the CO2 cargo tank pressure gradually increases within the step, the opening of the micro-adjustment valve A6 at the outlet of vaporizer A2 is gradually increased. Before entering the next step of increasing CO2 cargo tank pressure, the outlet temperature and pressure of vaporizer A2 are brought to the target values ​​of this adjustment, that is, the outlet temperature of vaporizer A2 is -17°C and the pressure is 12 barg, and then the next adjustment cycle begins.

[0050] 4. Follow the adjustment method described above. Continue in this manner until the CO2 cargo hold pressure increases to 11.5 barg.

[0051] The above are the principle operating procedures for the CO2 cargo hold pressurization and precooling system. Following these procedures will ensure that the temperature does not fall below the minimum design temperature of the CO2 cargo hold, while fully utilizing the latent heat of vaporization of liquid CO2 to achieve the goal of precooling during the CO2 cargo hold pressurization process.

[0052] In actual operation, the pressurization process of CO2 cargo tanks takes a long time. Each increase of 1 barg in pressure often requires several hours. The adjustment time for each round is also relatively ample. Under the premise of ensuring that the temperature does not exceed the minimum design temperature of CO2 cargo tanks, operating according to the above principles and methods can reduce the amount of liquid CO2 used in the subsequent pre-cooling process. The more precise the adjustment, the more latent heat of vaporization of liquid CO2 will be utilized. Otherwise, the utilization of the latent heat of vaporization of liquid CO2 will be relatively reduced.

[0053] This process is a dynamic adjustment process that varies with the CO2 cargo tank pressure. The lower the CO2 cargo tank pressure, the greater the expansion coefficient of the liquid CO2 entering the CO2 cargo tank, and the lower the final temperature after expansion. Conversely, the higher the CO2 cargo tank pressure, the smaller the expansion coefficient of the liquid CO2 entering the CO2 cargo tank, and the higher the final temperature after expansion. To avoid the final temperature of the liquid CO2 after vaporization and expansion being lower than the design temperature of the CO2 cargo tank when utilizing the cooling capacity of liquid CO2, the temperature and pressure at the vaporizer outlet should be continuously adjusted according to the CO2 cargo tank pressure changes in the three-dimensional dynamic parameter table. The entire process should follow the three-dimensional dynamic parameter table.

[0054] The pressure build-up in the CO2 cargo tank is a gradual process from approximately 0 to 12 barg. During this process, the lower the CO2 cargo tank pressure, the greater the expansion coefficient of liquid CO2 during vaporization, resulting in more heat absorption and a greater temperature drop. Therefore, it is necessary to dynamically control the temperature of the superheated liquid CO2 entering the CO2 cargo tank to ensure that its final temperature after vaporization and expansion is not lower than the minimum design temperature of the CO2 cargo tank. Based on the physical properties of CO2 and computer simulations, this invention establishes a three-dimensional dynamic parameter table that includes the relationship between the pressure QP and temperature QT of the superheated liquid CO2 at the vaporizer outlet corresponding to the CO2 cargo tank pressure RP. The first column of the table represents the CO2 cargo tank pressure, denoted by RP. The first row of the table represents the pressure of the superheated liquid CO2 at the vaporizer outlet in the pressurized precooling system, denoted by QP. The middle part of the table represents the minimum allowable vaporizer outlet temperature, denoted by QT, under the corresponding CO2 cargo tank pressure RP and vaporizer outlet pressure QP. The temperature QT will be gradually lowered as the CO2 cargo tank pressure increases, so as to better utilize the latent heat of vaporization of liquid CO2 under conditions that are not lower than the minimum design temperature of the CO2 cargo tank.

[0055] In the three-dimensional dynamic parameter table, the pressure RP in the CO2 cargo tank is increased in increments of 0.5 bar. A preferred operating step is 1 barg. The operating step can be adjusted according to specific circumstances, but the pressure QP and temperature QT of the superheated liquid CO2 at the vaporizer outlet should correspond to the CO2 cargo tank pressure RP. If the CO2 cargo tank pressure RP step is not set to 0.5 or an integer such as 1, but is set to 0.3, 0.6, 0.9, 1.2, etc., the corresponding superheated liquid CO2 pressure QP and temperature QT at the vaporizer outlet should be recalculated and simulated based on the physical properties of CO2, and this is considered an equivalent method.

[0056] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. When the minimum design temperature of the refrigerated container changes, the temperature and pressure at the vaporizer outlet will also change accordingly. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

Claims

1. A method for pressurized precooling of a CO2 cargo tank with superheated liquid CO2, characterized in that, The method is realized by using a system of superheated liquid CO2 to realize CO2 cargo hold pressurization and precooling, The system comprises a precooling pipeline connected to the CO2 cargo hold, wherein the precooling pipeline comprises, in series, an inlet regulating valve (A1), a vaporizer (A2), a temperature sensor (A3), a pressure sensor (A4), an outlet coarse regulating valve (A5), and an outlet fine regulating valve (A6); and the liquid CO2 supply end is connected to the front end pipeline of the inlet regulating valve (A1). During the pressurization process, the pressure QP of the liquid CO2 before entering the CO2 cargo hold and the temperature QT of the liquid CO2 are adjusted as the pressure RP in the CO2 cargo hold increases, so that the transmitted liquid CO2 is in a superheated state at the corresponding pressure; and the temperature of the vaporized liquid CO2 entering the CO2 cargo hold is higher than the lowest design temperature of the CO2 cargo hold. For 7500M 3 The minimum design temperature of the volume is -35°C~ -40°C, and the CO2 cargo tank is pressurized and pre-cooled; the pre-cooling pipeline is made of 304 stainless steel pipe with a diameter of DN32; and the following three-dimensional dynamic parameter table is adjusted: In the table, the pressure unit is barg, and the temperature unit is °C. Specifically, the following processes are included: Preparation: all liquid CO2 supplies to the CO2 cargo hold are closed; the outlet coarse regulating valve (A5) in the precooling pipeline is opened, the outlet fine regulating valve (A6) is fully opened, and the inlet regulating valve (A1) is closed; Step 1: the inlet regulating valve (A1) is opened; when the outlet temperature sensor (A3) of the vaporizer (A2) displays a temperature of -14°C, the opening degrees of the outlet coarse regulating valve (A5) and the inlet regulating valve (A1) are repeatedly adjusted, so that the temperature at the outlet of the vaporizer (A2) is -16°C and the pressure is 11 barg; then the opening degree of the outlet fine regulating valve (A6) is gradually reduced until the temperature at the outlet of the vaporizer (A2) is -12°C and the pressure is 13 barg; then, as the pressure of the CO2 cargo hold gradually increases, the opening degree of the outlet fine regulating valve (A6) of the vaporizer (A2) is gradually increased, so that the temperature and pressure at the outlet of the vaporizer (A2) reach -14°C and 12 barg, respectively, and the next adjustment cycle is entered; Step 2: when the outlet fine regulating valve (A6) is fully opened, the opening degree of the inlet regulating valve (A1) is increased; when the outlet temperature sensor (A3) of the vaporizer (A2) displays a temperature of -16°C, the opening degrees of the outlet coarse regulating valve (A5) and the inlet regulating valve (A1) are adjusted, so that the temperature and pressure at the outlet of the vaporizer (A2) are stabilized at -17°C and 11 barg, respectively; then the opening degree of the outlet fine regulating valve (A6) is gradually reduced until the temperature and pressure at the outlet of the vaporizer (A2) are stabilized at -14°C and 13 barg, respectively; then the opening degree of the outlet fine regulating valve (A6) of the vaporizer (A2) is gradually increased, so that the temperature and pressure at the outlet of the vaporizer (A2) reach -16°C and 12 barg, respectively, and the next adjustment cycle is entered; Step 3: After the outlet fine adjustment valve (A6) is fully opened, the opening of the inlet adjustment valve (A1) is increased, and when the outlet temperature of the vaporizer (A2) drops to -17°C, the opening of the outlet coarse adjustment valve (A5) and the inlet adjustment valve (A1) is repeatedly adjusted to stabilize the outlet temperature and pressure of the vaporizer (A2) at -19°C and 11 barg; then the opening of the outlet fine adjustment valve (A6) is gradually reduced to stabilize the outlet temperature and pressure of the vaporizer (A2) at -16°C and 13 barg; and then the opening of the outlet fine adjustment valve (A6) of the vaporizer (A2) is gradually increased to make the outlet temperature and pressure of the vaporizer (A2) reach -17°C and 12 barg, and enter the next adjustment cycle; Step 4: According to the valve adjustment method of step 2 or step 3, the parameters are controlled according to the three-dimensional dynamic parameter table until the CO2 cargo tank pressure increases to 11.5 barg.

2. The method for pressurizing and precooling a CO2 cargo hold using superheated liquid CO2 according to claim 1, characterized in that, The CO2 cargo tank is connected with a liquid CO2 filling pipeline or a cargo tank pressurizing pipeline; the pre-cooling pipeline is arranged in parallel with the liquid CO2 filling pipeline or the cargo tank pressurizing pipeline.

Images