A Control Method for Marine Liquefied CO2 Solid Transportation

Abstract

The present invention discloses a control method for the solid-state transportation of marine liquefied CO2. A ship is provided with a storage tank and an emergency overflow tank that are interconnected; the storage tank is equipped with heat exchange equipment with a cooling mode and a heating mode. The transportation method includes: S1: When the ship is loading goods, liquefied CO2 is filled into the storage tank through a pipeline; S2: When the liquefied CO2 in the storage tank is full and starts to overflow, the cooling mode is turned on to solidify the liquefied CO2; when the single storage tank is loaded until the overflow tank is full, the loading of liquefied CO2 is stopped; S4: During the ship's voyage at sea, the solid CO2 in the storage tank is maintained without a phase change; S5: When it is necessary to unload the goods, the storage tank starts the heating mode to liquefy and convert the solid CO2; when all the goods in the storage tank are unloaded, the unloading work of the storage tank is ended. The present invention can increase the single-voyage cargo capacity of a ship with a fixed total cargo hold volume by up to 25%; it can improve the degree of intelligent management of the ship, increase the ship's unloading capacity, reduce unloading energy consumption, and improve the operation efficiency.

Description

Technical Field

[0001] The present invention relates to the field of liquid cargo ships, and more specifically, to a control method for marine liquefied CO2 solid transportation. Background Art

[0002] With the increasing annual requirements for carbon emission restrictions, liquefied CO2 carriers, as new stars in the shipping industry, have currently attracted great attention from shipowners in the shipping market, and have brought many new technological challenges and opportunities to ship design and manufacturing. For example, there is an increasing demand for the enlargement of marine liquefied CO2 storage tanks that can carry more cargo.

[0003] Currently, all existing liquefied CO2 carriers on the market use the transportation method of fully loading liquefied CO2 in the storage tank throughout the process, and the volume of the storage tank is relatively small; and when encountering the ship demand for transporting more cargo in a single voyage, all of them solve it by increasing the volume of the on-board storage tank. Due to the limited space of marine transportation ships, the engineering difficulty and cost increase rapidly after the enlargement of a single storage tank; when the ship is at sea, it will generate large-amplitude swaying due to the influence of dynamic loads such as waves in the natural environment. When the storage tank is enlarged, it will lead to an increase in the free surface of the liquid cargo. And the large free surface of the liquid is prone to cause damage to the storage tank and other problems and poor ship stability when swaying. Currently, this type of problem is solved by adding anti-rolling steel structures inside the storage tank to divide the free surface, but the cryogenic steel is expensive and difficult to build.

[0004] Currently, the density of liquefied CO2 transported by ships is about 1.1 tons per cubic meter, while the density of solid CO2 is about 1.5 tons per cubic meter. Theoretically, transporting the same volume of solid CO2 in a single voyage can carry nearly 30% more mass of cargo than liquefied CO2; currently, there are mainly three methods for converting liquefied CO2 to solid CO2 (the latter two methods can be used in combination). The first is to depressurize and vaporize and evaporate to cool liquefied CO2 to solidify it. The second is to cool liquefied CO2 to solidify it by means of a heat exchange device. The third is to add ultra-high pressure to solidify it (basically all require more than 10 MPa). Currently, when converting liquefied CO2 transported by ships to solid CO2, liquefied CO2 can be solidified by cooling it by no more than 15 degrees Celsius. After research and comparison, using the second method of cooling and solidifying by a heat exchange device, the process is easy to control and has the most engineering practical value; with the continuous development of scientific and technological means, by using some functions of the improved on-board monitoring system combined with the added intelligent program autonomous adjustment means, a series of operations can be completely realized in which liquefied CO2 remains solid during ship transportation, liquefied CO2 enters and exits the storage tank during ship loading and unloading, and then liquefied CO2 is quickly solidified in the storage tank.

[0005] Therefore, for large-scale marine liquefied CO2 storage tanks, there is an urgent need to invent a marine liquefied CO2 solid transportation control method for increasing the loading capacity of storage tanks with the same tank volume. By converting the cargo inside the CO2 storage tank from liquid to solid during the actual marine transportation process of the ship, the purpose of increasing the loading capacity per voyage can be achieved, thereby improving the transportation efficiency of the CO2 carrier and enhancing the ship's profitability. Summary of the Invention

[0006] The present invention provides a marine liquefied CO2 solid transportation control method to achieve the purpose of increasing the quality of the cargo transported by the ship in a single journey.

[0007] To achieve the above object, the present invention provides a marine liquefied CO2 solid transportation control method. First, the ship is provided with a single storage tank with a volume of A1 and an emergency liquefied CO2 overflow tank with a tank volume of A2; the storage tank is a sealed space resistant to fluctuating low temperature T1 and fluctuating pressure P1, and is equipped with a heat exchange device with a cooling mode and a heating mode; the storage tank and the emergency overflow tank are connected to each other through a valve, and after the storage tank is filled with liquid cargo, it will overflow into the emergency overflow tank;

[0008] The A1, A2, T1, P1 and related parameters below satisfy the following settings:

[0009] Parameter symbol Unit Lower limit Upper limit A1 Cubic meter 1000 12000 T1 Degree Celsius Minus 70 Minus 40 P1 Megapascal 0.5 20 A2 Cubic meter 0 2500 H1 One percent 50 98 T2 Degree Celsius Minus 70 Minus 57 P2 Megapascal 0.1 20 V1 Cubic meter per hour 500 1500

[0010] Table 1

[0011] The transportation method of the present invention includes the following steps:

[0012] S1: When the ship is loading cargo, liquefied CO2 is filled into the storage tank through a pipeline; during loading, the storage tank and the emergency overflow tank are kept connected to each other;

[0013] S2: When the liquefied CO2 in the storage tank is full and starts to overflow, the cooling mode is turned on to solidify the liquefied CO2; when the single storage tank is loaded until the overflow tank is full, the loading of liquefied CO2 is stopped;

[0014] When the solid CO2 in the storage tank is filled to the fullness H1, the cooling mode is stopped;

[0015] Thereafter, the temperature in the storage tank is kept at T2 and the pressure is kept at P2;

[0016] S3: If there are multiple such storage tanks on the ship, each storage tank is loaded in the manner of S2 in sequence;

[0017] S4: During the ship's voyage at sea, the temperature in the storage tank is kept at T2 and the pressure is kept at P2 to keep the solid CO2 in the storage tank from undergoing a phase change;

[0018] S5: When it is necessary to unload the goods, the storage tank starts the heating mode for the liquefaction conversion of solid CO2; the unloading flow rate V1 of the solid CO2 after liquefaction can be determined by the solid-to-liquid conversion rate. When liquid appears in the overflow tank, the normal unloading operation of the storage tank is carried out at the flow rate V1. When all the goods in the storage tank are unloaded, the unloading operation of the storage tank ends;

[0019] S8: Unload each of the storage tanks in the manner of S5 in sequence.

[0020] In the optimal mode, the volume A2 of the emergency overflow tank is 15% of A1.

[0021] In the preferred mode, the emergency overflow tank is used as a liquefied CO2 cargo carrier tank.

[0022] In the preferred mode, in step S2, a liquefied CO2 injection port is provided in the emergency overflow tank. The solidification operation of the storage tank is for the supplementary injection of liquefied CO2 until the solid CO2 in the storage tank is filled to the specified fullness degree H1.

[0023] In addition, the heat exchange equipment of the storage tank includes heat exchange pipelines, a compressor-driven heat exchange device, and a heat exchange medium. The heat exchange medium is R23, CO2, or liquid nitrogen.

[0024] In the preferred mode, in step S5, when the temperature of the storage tank rises to T3, the heating mode is turned off; T3 satisfies -56.5 °C to -40 °C.

[0025] The method of the present invention mainly includes three stages and their corresponding sub-operation methods. The main advantages of each sub-operation method are briefly described as follows:

[0026]

[0027] The beneficial effects of the present invention are as follows: By applying the method of the present invention, the single voyage cargo capacity of a ship with a fixed total cargo hold capacity can be increased by up to 25%; the degree of intelligent management of the ship can be improved, the unloading capacity of the ship can be increased, the unloading energy consumption can be reduced, and the operation efficiency can be improved; the adverse situations such as the uncertain liquid sloshing load in the large cargo hold when the ship carries liquid cargo on the storage tank structure and stability can be avoided, and the operation safety of the ship can be improved; the technical part of the large-scale limitation of the liquefied CO2 marine storage tank can be broken through, the structure design of the storage tank can be simplified, and the use of cryogenic-resistant steel can be reduced; the economy in the whole life cycle of the liquefied CO2 transport ship can be improved, which is beneficial for the shipowner to quickly recover the cost. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the solid transportation mode of liquefied CO2 for ships of the present invention;

[0029] Figure 2 It is a schematic diagram of the existing marine liquefied CO2 transportation mode;

[0030] Figure 3 The flow chart of the loading stage of the present invention;

[0031] Figure 4 The flow chart of the transportation stage of the present invention;

[0032] Figure 5 The flow chart of the unloading stage of the present invention. Detailed implementation manners

[0033] The following describes the detailed implementation manners of the present invention in conjunction with the attached Figures 1 - 5 A marine liquefied CO2 solid transportation control method of the present invention includes the following steps:

[0034] S1: When the ship is loading goods, liquefied CO2 is filled into a storage tank with a single volume of A1 through a pipeline. This storage tank is a sealed space resistant to a specified fluctuating low temperature T1 and a specified fluctuating pressure P1. It is necessary to set up an emergency liquefied CO2 overflow tank with a volume of A2 (the volume of A2 can refer to not exceeding 15% of A1, preferably 15%, as large as possible, and not zero). (Designed with a conventional cargo hold, it can also be used as a liquefied CO2 cargo carrier). After the conventional loading fills a single storage tank, the subsequent loading work is carried out according to S2;

[0035] S2: The loading control method for the solidified transportation of liquefied CO2. When the liquefied CO2 in the storage tank is full and starts to overflow, S3 (only the cooling mode) is turned on. During loading, the storage tank and the emergency overflow tank are kept connected. The liquefied CO2 in a single storage tank is loaded until the emergency liquefied CO2 overflow tank is full, and then the liquid cargo loading stops. Because solid CO2 has a greater density than liquefied CO2, affected by gravity and the like, the volume of solid CO2 in the storage tank will decrease and sink to the lower part of the storage tank; when the liquefied CO2 solidifies and sinks due to gravity and the volume decreases significantly, the liquefied CO2 in the emergency overflow tank flows to supplement the storage tank where the solidification operation is in progress. If necessary, liquefied CO2 can be directly supplemented into the emergency overflow tank until the solid CO2 in the storage tank is loaded to the specified fullness degree H1, and then S3 is turned off to complete the liquid-solid conversion work of the goods in this storage tank; the temperature in this storage tank is kept at T2, and the pressure in the storage tank is kept at P2 to ensure the maintenance of CO2 in a solid state during transportation;

[0036] S3: The CO2 liquid-solid two-phase conversion device in the storage tank includes two working modes: cooling and heating. It mainly uses heat exchange pipelines (and equivalent devices) arranged in the storage tank (or outside) to drive the heat exchange medium flowing in the heat exchange device by a compressor (liquid or gaseous refrigerants such as R23, CO2, liquid nitrogen, etc.) to take away (or bring) the heat of the goods in the storage tank, realizing the conversion between the solid and liquid states of CO2 after temperature reduction (or increase);

[0037] S4: Method for loading liquefied CO2 into other storage compartments on the ship and solidifying it. After the liquefied CO2 in the emergency overflow compartment of the storage compartment is filled, while performing the liquid-solid conversion operation, load the cargo of other storage compartments (if any) according to the method of S2 above until all the cargo storage compartments on the whole ship are filled and the solidification work is completed;

[0038] S5: During the sea voyage of the ship, through the monitoring of the cargo status in the storage compartment (preferably using an intelligent management system), maintain the transportation of solid CO2 in the storage compartment according to the method described in this step. The method for maintaining the solid state of CO2 during transportation is to monitor the pressure and temperature in the storage compartment (preferably compare the monitored data with the preset parameters and use an intelligent program to automatically judge and execute the preset countermeasures to be taken), keep the temperature in the system storage compartment within the range of T2, and keep the pressure in the storage compartment within the range of P2 to ensure that the solid CO2 in the storage compartment does not undergo a phase change;

[0039] S6: When the ship needs to unload the cargo, first perform the liquefaction conversion of solid CO2 according to S7. Preferably, use the preset program, the port unloading capacity, the solid-liquid conversion rate, etc. to calculate the unloading flow rate V1 after the liquefaction of solid CO2. When liquid appears in the overflow compartment, carry out the regular unloading work of the storage compartment at the flow rate of V1. When all the cargo in the storage compartment is unloaded, end the unloading work of the storage compartment;

[0040] S7: Control method for liquefying and unloading solid CO2 after solidification transportation; turn on S3 (only the heating mode) to heat the solid CO2 to cause liquefaction. The volume of the cargo in the storage compartment expands. Due to the influence of gravity, the liquefied CO2 floats up and overflows to the emergency liquefied CO2 overflow compartment. When all the solid CO2 is converted into liquid, the overflow speed will decrease significantly. When it is judged through the monitored data that the storage compartment (the temperature of the storage compartment rises to T3 or the overflow speed decreases rapidly), turn off S3;

[0041] S8: While performing the regular unloading work on the storage compartment that has completed the liquefaction work of solid CO2, unload the cargo of other storage compartments (if any) according to the method of S7 above until all the storage compartments on the whole ship are unloaded;

[0042] The present invention preferably uses an intelligent management module to collect and process the data of the monitoring system and automatically adjust the operation of relevant equipment according to the corresponding control methods and measures, realizing the function of using liquefied CO2 to enter and exit the storage compartment during ship loading and unloading, and then quickly solidifying the liquefied CO2 in the storage compartment, as well as maintaining the solid state of CO2 during ship transportation.

[0043] The limitation ranges of the relevant technical parameters used in the present invention are shown in the following table.

[0044] Table 1 Limitation Range Table of Technical Parameters

[0045]

[0046]

[0047] For specific reference to the accompanying drawings, in combination with Figures 3 - 5 the following describes an embodiment. A control method for the solid-state transportation of marine liquefied CO2 is a control method that executes corresponding steps in three different stages: the loading stage, the transportation stage, and the unloading stage during the operation of a certain ship. In the loading stage, S1 to S4 are executed, and S3 adopts a cooling mode; in the transportation stage, S5 is executed, and if necessary, S3 in the cooling mode may be executed; in the unloading stage, S6 to S8 and the heating mode of S3 are executed.

[0048] This ship is equipped with 2 storage tanks of equal size and 1 emergency liquefied CO2 overflow tank. Only in the 2 storage tanks, heat exchange pipelines are set near the internal partial transverse frames of the tanks as heat exchange devices. Some relevant technical parameters of this ship are as follows in the table.

[0049] Table 2 Partial relevant technical parameter table of a certain ship

[0050] Parameter symbol Unit Design value A1 Cubic meter 3000 T1 Degree Celsius Minus 45 A2 Cubic meter 450 H1 One percent 90 T2 Degree Celsius Minus 60

[0051] During the loading stage of this ship, according to Figure 4 the process, sub-method 1 is executed. The liquefied CO2 is filled into a storage tank with a single volume of A1 through a pipeline. This ship has an emergency liquefied CO2 overflow tank with a volume of A2. The storage tank and the emergency overflow tank are kept connected to each other during loading. After the conventional liquid cargo is loaded to fill a single storage tank, the liquefied CO2 solidification transportation loading control method S2 is applied. That is, when the liquefied CO2 in the storage tank is filled and starts to overflow, S3 is turned on (only the cooling mode, mainly by arranging heat exchange pipelines in the storage tank and using the relatively low-temperature heat exchange medium flowing in them (such as liquid nitrogen, etc.) to cool and solidify the liquefied CO2 in the storage tank). When the liquefied CO2 solidifies, due to gravity, the solid CO2 will reduce in volume and sink to the lower part of the storage tank. The single storage tank is loaded with liquefied CO2 until the emergency liquefied CO2 overflow tank is filled, and then the loading of liquid cargo into the storage tank stops; when the liquefied CO2 solidifies and sinks due to gravity and the volume significantly decreases, the liquefied CO2 in the emergency overflow tank flows to supplement the storage tank that is undergoing solidification operation (if necessary, liquefied CO2 can be directly supplemented into the emergency overflow tank). When the solid CO2 in the storage tank is loaded to the specified fullness degree H1, S3 is closed, and the liquid-solid conversion work of the goods in this storage tank is completed; the solidification operation method for other storage tanks on the ship is carried out according to the above operation; when all the cargo storage tanks on the ship are filled and the solid cargo in the storage tanks is filled to the specified fullness degree H1, the loading work of this method is completed (the overflow tank can continue the conventional loading operation to load liquid cargo).

[0052] During the sea voyage transportation process of the ship, according toFigure 4 The process execution sub - method 2 ensures that the goods in the storage tank remain stable in a solid state during transportation (maintaining one - way connection from the storage tank to the emergency overflow tank). By regularly monitoring the state of the goods in the storage tank (temperature and pressure), preferably using an intelligent management system to compare the measured and preset data (temperature T2 and pressure), when a response measure is triggered, an alarm is given and response measures (temperature adjustment and / or pressure adjustment) are automatically taken; if no response measure is triggered, the state of the goods is continuously monitored regularly.

[0053] During the ship's unloading stage, according to Figure 5 The process execution sub - method 3 keeps the storage tank and the emergency overflow tank interconnected. Before the regular liquid cargo unloading, the liquefaction of solid CO2 is carried out according to S7 first, that is, S3 is executed (only the heating mode, mainly by arranging heat - exchange pipelines in the storage tank and using the relatively high - temperature heat - exchange medium flowing in them (such as liquefied CO2 at - 40 degrees Celsius) to heat up the solid CO2 in the storage tank to liquefy it). After the solid CO2 is heated up and liquefied, the volume of the goods in the storage tank expands. Due to gravity, the liquefied CO2 floats and overflows into the emergency liquefied CO2 overflow tank. When all the solid CO2 in the storage tank is converted into liquid, the overflow speed will decrease significantly. When it is monitored that the overflow in the storage tank decreases rapidly or the temperature in the storage tank rises to the T3 range, S3 is closed; at the same time, using the preset program, the port unloading capacity, the liquefaction rate, etc., the unloading flow rate V1 after the liquefaction of solid CO2 is calculated. When liquid appears in the overflow tank, the regular unloading of the storage tank is carried out at the flow rate V1. When all the goods in the storage tank are unloaded, the unloading work of the storage tank ends; while carrying out the regular unloading work on the storage tank that has completed the liquefaction of solid CO2, the solid goods in other storage tanks (if any) are unloaded according to the above - mentioned S7 method. When all the storage tanks on the ship have completed the conversion of solid goods to liquid, the unloading work of this method ends, and the regular unloading operation can continue until all the liquid cargo is unloaded.

[0054] After calculating and comparing the loading capacity of this ship and applying the method of the present invention, the cargo - carrying mass of this ship per single voyage can be increased by more than 25%.

[0055] The above - mentioned is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A control method for marine liquefied CO2 solid transportation, characterized in that The ship is provided with a single storage tank with a volume of A1 and an emergency liquefied CO2 overflow tank with a capacity of A2; the storage tank is a closed space resistant to fluctuating low temperature T1 and fluctuating pressure P1, and is equipped with heat exchange equipment with a cooling mode and a heating mode; the storage tank and the emergency overflow tank are connected to each other through valves, and after the storage tank is filled with liquid cargo, it will overflow to the emergency overflow tank; The A1, A2, T1, P1 and related parameters below satisfy the following settings: The transportation method includes the following steps: S1: When the ship is loading goods, liquefied CO2 is injected into the storage tank through a pipeline; when loading, keep the storage tank and the emergency overflow tank connected to each other; S2: When the liquefied CO2 in the storage tank is full and starts to overflow, turn on the cooling mode to solidify the liquefied CO2; When the single storage tank is loaded until the overflow tank is full, stop loading liquefied CO2; When the solid CO2 in the storage tank is loaded to the fullness H1, stop the cooling mode; thereafter, the temperature in the storage tank is maintained at T2 and the pressure is maintained at P2; S3: If there are multiple storage tanks on the ship, load each storage tank in the manner of S2 in sequence; S4: During the ship's sea voyage, the temperature in the storage tank is maintained at T2 and the pressure is maintained at P2 to keep the solid CO2 in the storage tank from undergoing a phase change; S5: When the goods need to be unloaded, the storage tank starts the heating mode to liquefy and convert the solid CO2; the unloading flow rate V1 of the liquefied solid CO2 can be determined through the solid-to-liquid conversion rate. When liquid appears in the overflow tank, carry out the normal unloading work of the storage tank at the flow rate V1. When all the goods in the storage tank are unloaded, end the unloading work of the storage tank; S8: Unload each storage tank in the manner of S5 in sequence.

2. The marine liquefied CO2 solid transportation control method according to claim 1, wherein The volume A2 of the emergency overflow tank is 15% of A1.

3. The marine liquefied CO2 solid transportation control method according to claim 1, characterized in that, The emergency overflow tank is used as a liquefied CO2 cargo carrier tank.

4. The marine liquefied CO2 solid transportation control method according to claim 3, characterized in that, In step S2, a liquefied CO2 injection port is provided in the emergency overflow tank, and the solidification is supplemented with liquefied CO2 until the solid CO2 in the storage tank is loaded to the specified fullness H1.

5. The marine liquefied CO2 solid transportation control method according to claim 3, characterized in that, The heat exchange equipment of the storage tank includes heat exchange pipelines, a compressor-driven heat exchange device, and a heat exchange medium.

6. The marine liquefied CO2 solid transportation control method according to claim 5, characterized in that, The heat exchange medium is R23, CO2, liquid nitrogen.

7. The marine liquefied CO2 solid transportation control method according to any one of claims 1 to 6, characterized in that, In step S5, when the temperature of the storage tank rises to T3, turn off the heating mode; T3 satisfies -56.5 °C to -40 °C.

Images