Dry ice and liquid CO2 combined transportation ship and method

Abstract

The invention belongs to the technical field of ships, and discloses a dry ice and liquid CO2 combined transportation ship and method. The device comprises a small two-phase tank, a large two-phase tank, a storage tank, a circulating pump, a flow control valve, a check valve, a stop valve and a heat exchange coil. The dry ice and the liquid CO2 are mainly combined for transportation, and the liquid CO2 is kept at a lower temperature by utilizing the cold energy of the dry ice, so that BOG is prevented from being generated in the transportation process of the liquid CO2. Meanwhile, a high-energy-consumption refrigerating device is omitted, and the equipment investment cost, the operation cost and the personnel management cost are reduced. Besides, according to the method, the length of the route of the CO2 transport ship is flexibly coped with, and different transport scene requirements are met by dynamically adjusting the carrying quantity of the dry ice, so that the refrigeration requirement of the liquid CO2 is met, BOG (boil off gas) generated by the liquid CO2 is avoided, and the carrying quantity of the dry ice is reduced to the greatest extent.

Description

Technical Field

[0001] The invention belongs to the technical field of ships and relates to a ship and a method for combined transportation of dry ice and liquid CO2. Background Art

[0002] In response to climate change, many countries and regions around the world have set carbon reduction targets, requiring a significant reduction in greenhouse gas emissions. Carbon capture and storage (CCS) is one of the key technologies to achieve the "dual carbon" goal. With the continuous increase in the amount of CO2 captured on land, the captured CO2 needs to be safely transported to the seabed or Iceland for storage. This process requires CO2 transport ships to transport it from the port to the destination. Therefore, the maritime transportation process of CO2 transport ships is a very important link in achieving carbon storage.

[0003] During the ship transportation process, CO2 is usually stored in a liquid form in a storage tank under semi-cold and semi-pressure conditions (temperature is about -50℃~-20℃, pressure is about 7bar~15bar). Even if the storage tank is equipped with a thicker insulation layer, the liquid CO2 will still exchange heat with the external environment through the tank wall and insulation layer, and it is inevitable to produce CO2 boil-off gas (BOG for short). Especially when the CO2 transport ship transports CO2 on a long route, a large amount of BOG will be produced during the transportation process. Therefore, in order to avoid the generation of BOG, CO2 transport ships are usually equipped with refrigeration devices to maintain the low temperature state of the liquid CO2 storage environment, thereby avoiding the generation of BOG. ​​However, the operation of the refrigeration device will generate a large amount of power consumption, and the installation of a refrigeration device will correspondingly generate a large equipment investment cost, operating cost and management personnel cost.

[0004] In addition to being transported in liquid form, CO2 can also be transported in solid form (dry ice). The storage temperature of dry ice (-78.5℃) is relatively low, and it will still exchange heat with the external environment during transportation to produce gaseous CO2. Therefore, refrigeration equipment is also required when transporting CO2 in the form of dry ice. However, the ambient temperature required for dry ice storage is lower, and the refrigeration equipment requires higher power consumption, which will also increase equipment investment costs, operating costs, and personnel management costs. Therefore, whether CO2 is transported in liquid form or in the form of dry ice, it needs to be equipped with a refrigeration device, and the refrigeration device needs to be managed by the ship's personnel on the ship, which undoubtedly increases the workload and management costs.

[0005] Based on this, in order to solve the problems of large amounts of BOG generated by CO2 transport ships during the transportation of liquid CO2, as well as high energy consumption of refrigeration devices, the present invention proposes a ship and method for combined transportation of dry ice and liquid CO2. The scheme combines CO2 in liquid and solid (dry ice) states, fully utilizes the cold energy of dry ice, and realizes autonomous refrigeration during transportation, thereby effectively avoiding the generation of BOG by liquid CO2, and eliminating the need to equip refrigeration devices, saving equipment investment costs, operating costs, and personnel management costs. The present invention can flexibly respond to market demand and dynamically adjust the amount of dry ice according to the length of the CO2 transport ship's sailing time and the changes in the operating season, thereby meeting the refrigeration needs of liquid CO2 and minimizing the use of dry ice. Summary of the invention

[0006] The present invention substantially solves the above problems and proposes a ship and method for combined transportation of dry ice and liquid CO2. The first object of the present invention is to propose a ship for combined transportation of dry ice and liquid CO2, which is mainly composed of a small two-phase tank, a large two-phase tank, a storage tank, a circulation pump, a flow control valve, a check valve, a stop valve, and a heat exchange coil.

[0007] The small two-phase tank and the large two-phase tank both adopt C-type tanks with a cylindrical middle and hemispherical ends, which can store both liquid CO2 and dry ice; the storage tank adopts a C-type double-ear tank to store liquid CO2.

[0008] The small two-phase tank, the large two-phase tank and the storage tank are all placed in the cargo hold of the CO2 transport ship. In the present invention, two small two-phase tanks, one large two-phase tank and a plurality of storage tanks are provided, wherein the volume of the storage tank is twice that of the large two-phase tank, and the volume of the large two-phase tank is twice that of the small two-phase tank. The two small two-phase tanks are placed in the same cargo hold as the large two-phase tank, wherein the two small two-phase tanks are placed in sequence from the bow to the stern and are parallel to the large two-phase tank. The storage tanks are placed in the remaining cargo holds of the CO2 transport ship.

[0009] A circulation pump is placed in each of the small two-phase tank, the large two-phase tank and the storage tank; the heat exchange coil is placed at the bottom of the small two-phase tank and the large two-phase tank. The circulation pump is used to pump out the liquid CO2; the heat exchange coil is used for heat exchange of liquid CO2.

[0010] The circulation pump is connected to the left end of the check valve through a pipeline, the right end of the check valve is connected through various branch pipelines and collected into the same pipeline, connected to the left end of the heat exchange coil through a pipeline via a stop valve, the right end of the heat exchange coil is re-collected into the same pipeline through a branch pipeline, and then connected to the left end of the flow control valve through a pipeline, and the right end of the flow control valve enters a small two-phase tank, a large two-phase tank or a storage tank for storing liquid CO2 through a pipeline.

[0011] During the voyage of the CO2 transport ship, the circulating pumps in the small two-phase tank, the large two-phase tank and the storage tank pump out the liquid CO2, and the liquid CO2 in each pipeline is collected into the same pipeline through the check valve, flows through the stop valve, and enters the heat exchange coil in the small two-phase tank or large two-phase tank storing dry ice through the pipeline. The liquid CO2 flows through the heat exchange coil through the pipeline, where the cold energy of the dry ice is used for efficient heat exchange, thereby maintaining the low temperature environment of the liquid CO2. Then the liquid CO2 in each branch pipeline is collected into the same pipeline again, and then through the flow control valve, it is finally transported to the small two-phase tank, large two-phase tank or storage tank storing liquid CO2.

[0012] The second object of the present invention is to propose a method for combined transportation of dry ice and liquid CO2. In order to solve the problem that a large amount of BOG is generated in the process of transporting liquid CO2 by CO2 transport ships and the high energy consumption of refrigeration equipment, a method for combined transportation of dry ice and liquid CO2 is adopted. According to the length of the ship's voyage time and the different operating seasons, the number of small two-phase tanks and large two-phase tanks for storing dry ice can be dynamically adjusted, and the cold energy of dry ice is used for efficient heat exchange to replace the refrigeration equipment, thereby maintaining the low temperature environment of liquid CO2 and avoiding the generation of BOG.

[0013] Before the ship sails, the sailing time T0 required for the CO2 transport ship to travel from the departure port to the destination is calculated. Based on the fact that the cold released by the final conversion of dry ice into liquid CO2 is always greater than the heat exchange between dry ice and liquid CO2 and the external environment during the T days of sailing, the number of small two-phase tanks and large two-phase tanks for storing dry ice is dynamically adjusted according to the length of the ship's sailing time and the different operating seasons. There are four schemes in total, and the maximum number of sailing days T1, T2, T3, and T4 under the combination of the number of small two-phase tanks and large two-phase tanks for storing dry ice in each scheme is obtained. Then, the sailing time T0 required for the CO2 transport ship is compared with the calculated maximum number of sailing days T1, T2, T3, and T4, and a scheme is selected from T0≤T1, T0≤T2, T0≤T3, and T0≤T4.

[0014] Solution 1: Use a small two-phase tank to store dry ice, and another small two-phase tank, a large two-phase tank and n storage tanks to store liquid CO2. According to formulas (1) and (2), the maximum number of sailing days T1 during which liquid CO2 does not produce BOG when dry ice is stored in the small two-phase tank is calculated.

[0015] 86.4V 101 ρ 冰 q≥[(A 102 +A2+nA3)Δt1+A 101 Δt2]μT1k (1)

[0016]

[0017] Among them, V 101—The volume of solid CO2 (dry ice) stored in the small two-phase tank, m 3 ;

[0018] ρ 冰 —Density of solid CO2 (dry ice), kg / m 3 ;

[0019] q—the amount of cold released when each kilogram of dry ice turns into liquid CO2, kJ / kg;

[0020] A 102 —Surface area of ​​small two-phase tank, m 2 ;

[0021] A 101 —Surface area of ​​small two-phase tank, m 2

[0022] A2—Surface area of ​​the large two-phase tank, m 2 ;

[0023] n—the number of storage tanks;

[0024] A3—Surface area of ​​the tank, m 2 ;

[0025] μ—Seasonal correction factor, which is the correction factor for different seasons on the ship route;

[0026] T1—maximum number of sailing days for plan 1, day;

[0027] k—heat transfer coefficient of the tank, W / m 2 K, different tank materials have different heat transfer coefficients;

[0028] Δt1—temperature difference between liquid CO2 and the external environment, K;

[0029] Δt2—Temperature difference between solid CO2 (dry ice) and the external environment, K.

[0030] The constant 86.4 in the formula is the result of unit conversion. According to the unit conversion 1J=1W·s, 0.001kJ=1W×(1 / 86400)day is obtained, that is, 86.4kJ=1W·day. In the present invention, a seasonal correction coefficient is calculated according to the proportion of spring, summer, autumn and winter when the ship passes through different seasons on the route. The coefficient is used to correct Δt1 and Δt2 to ensure the accuracy of calculating the heat transfer of the small two-phase tank, the large two-phase tank and the storage tank; the small two-phase tank, the large two-phase tank and the storage tank are made of the same material, and the heat transfer coefficient k of the tank body is the same.

[0031] Solution 2: Use a large two-phase tank to store dry ice, and the remaining two small two-phase tanks and n storage tanks to store liquid CO2. According to formulas (3) and (4), the maximum number of sailing days T2 during which liquid CO2 does not produce BOG when dry ice is stored in the large two-phase tank is calculated.

[0032] 86.4V2ρ 冰 q≥[(A 101 +A 102 +nA3)Δt1+A2Δt2]μT2k (3)

[0033]

[0034] Where, V2 is the volume of solid CO2 (dry ice) stored in the large two-phase tank, m 3 ;

[0035] T2—maximum sailing days for option 2, day;

[0036] Solution 3: Use one small two-phase tank and one large two-phase tank to store dry ice, and the remaining small two-phase tank and n storage tanks to store liquid CO2. According to formulas (5) and (6), the maximum number of sailing days T3 when liquid CO2 does not produce BOG when dry ice is stored in one small two-phase tank and one large two-phase tank is calculated.

[0037] 86.4(V 101 +V2)ρ 冰 q≥[(A 102 +nA3)Δt1+(A 101 +A2)Δt2]μT3k (5)

[0038]

[0039] Among them, T3—maximum sailing days for plan three, day;

[0040] Solution 4: Use two small two-phase tanks and one large two-phase tank to store dry ice, and the remaining n tanks to store liquid CO2. According to formulas (7) and (8), the maximum number of sailing days T4 during which liquid CO2 does not produce BOG when dry ice is stored in two small two-phase tanks and one large two-phase tank is calculated.

[0041] 86.4(V 101 +V 102 +V2)ρ 冰 q≥[nA3Δt1+(A 101 +A 102 +A2)Δt2]μT4k (7)

[0042]

[0043] Among them, V 102—The volume of solid CO2 (dry ice) stored in the small two-phase tank, m 3 ;

[0044] T4—maximum sailing days for scheme 4, day;

[0045] When a CO2 transport ship determines its sailing route, the volumes of its small two-phase tank and large two-phase tank for storing dry ice are fixed.

[0046] The sailing time required for a CO2 transport ship to transport liquid CO2 from the departure port to the destination can be calculated as T0 days before the ship sets sail. First, implement plan 1. The volume V of a small two-phase tank storing dry ice, the seasonal correction factor μ, and the density ρ of dry ice are respectively 冰 Substitute the parameters into formula (2) first and calculate T1. If T0≤T1, select plan 1; if T0>T1, implement plan 2.

[0047] The volume V of a large two-phase tank storing dry ice, the seasonal correction factor μ and the density ρ of dry ice are respectively 冰 Substitute the parameters into formula (4) to calculate T2. If T0≤T2, then select plan 2; if T0>T2, then implement plan 3.

[0048] The volume V of a small two-phase tank and a large two-phase tank storing dry ice, the seasonal correction factor μ and the density ρ of dry ice are respectively 冰 Substitute the parameters into formula (6) to calculate T3. If T0≤T3, then select option 3; if T0>T3, then select option 4.

[0049] Beneficial effects of the present invention:

[0050] 1. The present invention designs a combined transportation of dry ice and liquid CO2, and uses the cold energy of dry ice to maintain the liquid CO2 at a lower temperature, thereby avoiding the generation of BOG by liquid CO2 during transportation. At the same time, it eliminates the need for high-energy refrigeration equipment, reduces equipment investment, operating costs and personnel management costs, and has good economic efficiency.

[0051] 2. The combined transportation method of dry ice and liquid CO2 of the present invention can flexibly cope with the route length of the CO2 transport ship and meet the needs of different transportation scenarios by dynamically adjusting the amount of dry ice. It not only realizes the refrigeration demand of liquid CO2 and avoids the generation of BOG by liquid CO2, but also minimizes the amount of dry ice carried. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A top view of the CO2 transport ship of the present invention;

[0053] Figure 2 This is a schematic diagram of the distribution of the small two-phase tank, the large two-phase tank and the storage tank on a ship according to the present invention;

[0054] Figure 3 It is a system diagram of the present invention;

[0055] Figure 4 This is a schematic diagram of a small two-phase tank storing dry ice to maintain the temperature of liquid CO2 in the present invention;

[0056] Figure 5 This is a schematic diagram of a large two-phase tank storing dry ice to maintain the temperature of liquid CO2 in the present invention;

[0057] Figure 6 A schematic diagram of a small two-phase tank and a large two-phase tank storing dry ice to maintain the temperature of liquid CO2 in the present invention;

[0058] Figure 7 This is a schematic diagram of two small two-phase tanks and one large two-phase tank storing dry ice to maintain the temperature of liquid CO2 in the present invention;

[0059] In the attached figure: 1. Small two-phase tank; 2. Large two-phase tank; 3. Storage tank; 4. Circulation pump; 5. Flow control valve; 6. Check valve; 7. Shut-off valve; 8. Heat exchange coil. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0061] The first object of the present invention is to propose a ship for combined transportation of dry ice and liquid CO2 based on the above problems. Figure 1 , Figure 2 , Figure 3 As shown, the present invention includes a small two-phase tank 1, a large two-phase tank 2, a storage tank 3, a circulation pump 4, a flow control valve 5, a check valve 6, a stop valve 7, and a heat exchange coil 8.

[0062] like Figure 1 , Figure 2 As shown, the small two-phase tank 1 and the large two-phase tank 2 both adopt C-type tanks with a cylindrical middle and hemispherical ends, which can store both liquid CO2 and dry ice; the storage tank 3 adopts a C-type double-ear tank to store liquid CO2.

[0063] like Figure 1 , Figure 2As shown, the small two-phase tank 1, the large two-phase tank 2 and the storage tank 3 are all placed in the cargo hold of the CO2 transport ship. In the present invention, two small two-phase tanks 1 are provided, namely a small two-phase tank 101, a small two-phase tank 102, a large two-phase tank 2 and n storage tanks 3, wherein the volume of the storage tank 3 is twice the volume of the large two-phase tank 2, and the volume of the large two-phase tank 2 is twice the volume of the small two-phase tank 1. The small two-phase tank 101 and the small two-phase tank 102 are placed in the same cargo hold as the large two-phase tank 2, wherein the small two-phase tank 101 and the small two-phase tank 102 are placed in sequence from the bow to the stern of the ship and are parallel to the large two-phase tank 2. The storage tank 3 is placed in the remaining cargo holds of the CO2 transport ship.

[0064] like Figure 3 As shown, a circulation pump 4 is placed in each of the small two-phase tank 101, the small two-phase tank 102, the large two-phase tank 2 and the storage tank 3; the heat exchange coil 8 is placed at the bottom of the small two-phase tank 101, the small two-phase tank 102 and the large two-phase tank 2. The circulation pump 4 is used to pump out the liquid CO2; the heat exchange coil 8 is used for heat exchange of the liquid CO2.

[0065] like Figure 3 As shown, the circulation pump 4 is connected to the left end of the check valve 6 through a pipeline, the right end of the check valve 6 is connected through various branch pipelines and collected into the same pipeline, connected to the left end of the heat exchange coil 8 through the stop valve 7 through a pipeline, the right end of the heat exchange coil 8 is re-collected into the same pipeline through the branch pipeline, and then connected to the left end of the flow control valve 5 through a pipeline, and the right end of the flow control valve 5 enters the small two-phase tank 1, the large two-phase tank 2 and the storage tank 3 storing liquid CO2 through a pipeline.

[0066] like Figure 3 As shown, during the navigation of the CO2 transport ship, the circulating pump 4 in the small two-phase tank 101, the small two-phase tank 102, the large two-phase tank 2 and the storage tank 3 pumps out the liquid CO2, passes through the check valve 6, and the liquid CO2 in each pipeline is collected into the same pipeline, flows through the stop valve 7, and enters the heat exchange coil 8 in the small two-phase tank 101 or the small two-phase tank 102 storing dry ice through the pipeline. The liquid CO2 flows through the heat exchange coil 8 through the pipeline, where the cold energy of the dry ice is used for efficient heat exchange, thereby maintaining the low temperature environment of the liquid CO2. Then the liquid CO2 in each branch pipeline is collected into the same pipeline again, and then passes through the flow control valve 5, and is finally transported to the small two-phase tank 1, the large two-phase tank 2 or the storage tank 3 storing liquid CO2. During the transportation process, the dry ice absorbs heat and sublimates into gaseous CO2, and finally becomes liquid CO2. The pressure in the small two-phase tank 1 and the large two-phase tank 2 changes continuously, and the range of pressure change is always within the pressure bearing capacity of the small two-phase tank 1 and the large two-phase tank 2.

[0067] like Figure 1As shown, two small two-phase tanks 1 are provided on the ship, and are named 101 and 102 in sequence from the bow to the stern, and n storage tanks 3 are provided on the ship. In this embodiment, two storage tanks 3 are provided on the ship.

[0068] In this embodiment, the volume of the small two-phase tank 101 and the small two-phase tank 102 is Vm 3 , then the volume of the large two-phase tank 2 is 2Vm 3 , the volume of tank 3 is 4Vm 3 .

[0069] like Figure 3 As shown, the circulation pump 4 is placed in the small two-phase tank 101, the small two-phase tank 102, the large two-phase tank 2, and the storage tank 3. Each circulation pump 4 is connected to the check valve 6 through a pipeline, and the liquid CO2 is pumped out through the check valve 6. After the liquid CO2 in each branch pipeline is collected into the same pipeline, it flows through the stop valve 7 and enters the heat exchange coil 8 in the small two-phase tank 101, the small two-phase tank 102, and the large two-phase tank 2 storing dry ice through the pipeline, and uses the cold energy of dry ice for efficient heat exchange, thereby maintaining the temperature of the liquid CO2. Afterwards, it is collected into the same pipeline through each branch pipeline and passed through the flow control valve 5, and finally transported to the small two-phase tank 101, the small two-phase tank 102, the large two-phase tank 2, and the storage tank 3 storing liquid CO2.

[0070] In this embodiment, for a better understanding of the present invention, Figure 3 Based on the system diagram, Figure 4 , Figure 5 , Figure 6 , Figure 7 As shown in the figure, in each scheme, the unused circulating pump 4, flow control valve 5, check valve 6, stop valve 7, heat exchange coil 8 and the related pipelines are Figure 4 , Figure 5 , Figure 6 , Figure 7 However, the circulating pump 4, flow control valve 5, check valve 6, stop valve 7, heat exchange coil 8 and related pipelines that are not used in actual application are present and in a closed state.

[0071] According to the length of the CO2 transport ship's voyage and the change of the operating season, there are four combination schemes for storing dry ice in the small two-phase tank 101, the small two-phase tank 102, and the large two-phase tank 2:

[0072] Option 1: If Figure 4As shown, when the voyage time is short, a small two-phase tank 101 can be used to store dry ice, and the remaining small two-phase tanks 102, large two-phase tanks 2 and two storage tanks 3 can store liquid CO2. The liquid CO2 is pumped out by the circulation pump 4, and after passing through the check valve 6, it is collected into the same pipeline through various branch pipes, and then passes through the stop valve 7, and enters the heat exchange coil 8 in the small two-phase tank 101 storing dry ice through the pipeline. The liquid CO2 flows through the heat exchange coil 8, where the cold energy of the dry ice is used for efficient heat exchange, thereby maintaining the temperature of the liquid CO2. Then the liquid CO2 is collected into the same pipeline again through various branch pipes, and finally passed through the flow control valve 5, and transported back to the small two-phase tank 102, large two-phase tank 2 and two storage tanks 3 storing liquid CO2, respectively, to form a complete circulation cooling system.

[0073] Option 2: If Figure 5 As shown, when the voyage time is longer than that of the first scheme, a large two-phase tank 2 can be used to store dry ice, and the remaining small two-phase tanks 101, small two-phase tanks 102 and two storage tanks 3 can store liquid CO2. The liquid CO2 is pumped out by the circulation pump 4, and after passing through the check valve 6, it is collected into the same main pipeline through various branch pipes, and then passes through the stop valve 7, and enters the heat exchange coil 8 in the large two-phase tank 2 storing dry ice through the pipeline. The liquid CO2 flows through the heat exchange coil 8, where the cold energy of the dry ice is used for efficient heat exchange, thereby maintaining the temperature of the liquid CO2. Then the liquid CO2 is collected into the same pipeline again through various branch pipes, and finally passed through the flow control valve 5, and transported back to the small two-phase tanks 101, small two-phase tanks 102 and two storage tanks 3 storing liquid CO2, respectively, to form a complete circulation cooling system.

[0074] Option 3: If Figure 6 As shown, when the voyage time is longer than that of the second scheme, a large two-phase tank 2 cannot maintain the low temperature of the liquid CO2, so a small two-phase tank 101 and a large two-phase tank 2 are used to store dry ice, and the remaining small two-phase tanks 102 and two storage tanks 3 are used to store liquid CO2. The liquid CO2 is pumped out by the circulation pump 4, and after passing through the check valve 6, it is collected into the same main pipeline through various branch pipes, and then passes through the stop valve 7, and enters the heat exchange coil 8 in the small two-phase tank 101 and the large two-phase tank 2 storing dry ice through the pipeline. The liquid CO2 flows through the heat exchange coil 8, where the cold energy of the dry ice is used for efficient heat exchange, thereby maintaining the temperature of the liquid CO2. Then the liquid CO2 is collected into the same pipeline again through various branch pipes, and finally passed through the flow control valve 5, and transported back to the small two-phase tank 102 and the two storage tanks 3 storing liquid CO2, respectively, to form a complete circulation cooling system.

[0075] Option 4: If Figure 7As shown, when the voyage time is longer than that of the third scheme, a small two-phase tank 101 and a large two-phase tank 2 cannot maintain the low temperature of the liquid CO2, so the small two-phase tank 101, the small two-phase tank 102 and the large two-phase tank 2 are used to store dry ice, and the remaining two storage tanks 3 store liquid CO2. The liquid CO2 is pumped out by the circulation pump 4, and after passing through the check valve 6, it is collected into the same main pipeline through each branch pipeline, and then passes through the stop valve 7, and enters the heat exchange coil 8 in the small two-phase tank 101, the small two-phase tank 102 and the large two-phase tank 2 storing dry ice through the pipeline. The liquid CO2 flows through the heat exchange coil 8, where the cold energy of the dry ice is used for efficient heat exchange, thereby maintaining the temperature of the liquid CO2. Then the liquid CO2 is collected into the same pipeline again through each branch pipeline, and finally passed through the flow control valve 5, and is respectively transported back to the two storage tanks 3 storing liquid CO2, forming a complete circulation cooling system.

[0076] The second object of the present invention is to propose a method for combined transportation of dry ice and liquid CO2 based on the above-mentioned ship. According to the length of the ship's voyage time and the different operating seasons, the combined number of small two-phase tanks 1 and large two-phase tanks 2 for storing dry ice can be dynamically adjusted to obtain the maximum number of sailing days under the storage of dry ice of different qualities.

[0077] In this method, when the CO2 transport ship determines the route, the volume of the small two-phase tank 1 and the large two-phase tank 2 for storing dry ice is a fixed value. The sailing time required for the CO2 transport ship from the departure port to the destination can be calculated as T0 days before the ship sets sail. Based on the fact that the cold released by the dry ice turning into liquid CO2 is always greater than the heat exchange between the dry ice and the liquid CO2 and the external environment during the T days of sailing, the conditions of the route are substituted into the formulas (2), (4), (6), and (8) of each scheme, and four maximum sailing days T1, T2, T3, and T4 can be obtained. And a scheme is selected from T0≤T1, T0≤T2, T0≤T3, and T0≤T4.

[0078] Solution 1: According to formulas (1) and (2), the small two-phase tank 101 stores dry ice, and the small two-phase tank 102, the large two-phase tank 2 and the n storage tanks 3 store liquid CO2. The maximum number of sailing days during which liquid CO2 does not produce BOG is T1. If T0≤T1, this solution is selected.

[0079] 86.4V 101 ρ 冰 q≥[(A 102 +A2+nA3)Δt1+A 101 Δt2]μT1k (1)

[0080]

[0081] Among them, V 101—The volume of solid CO2 (dry ice) stored in the small two-phase tank 101, m 3 ;

[0082] ρ 冰 —Density of solid CO2 (dry ice), kg / m 3 ;

[0083] q—the amount of cold released when each kilogram of dry ice turns into liquid CO2, kJ / kg;

[0084] A 102 —Surface area of ​​small two-phase tank 102, m 2 ;

[0085] A2—Surface area of ​​large two-phase tank 2, m 2 ;

[0086] n—the number of storage tanks 3;

[0087] A3—Surface area of ​​tank 3, m 2 ;

[0088] k—heat transfer coefficient of the tank, W / m 2 K, different tank materials have different heat transfer coefficients;

[0089] Δt1—temperature difference between liquid CO2 and the external environment, K;

[0090] Δt2—temperature difference between solid CO2 (dry ice) and the external environment, K;

[0091] μ—Seasonal correction factor, which is the correction factor for different seasons on the ship route;

[0092] T1—Maximum sailing days for Plan 1, day.

[0093] The constant 86.4 in the formula is the result obtained by unit conversion. According to the unit conversion 1J=1W·s, 0.001kJ=1W×(1 / 86400)day is obtained, that is, 86.4kJ=1W·day. In the calculation of the present invention, Δt1 and Δt2 are calculated according to constant values, but the outside temperature is different in different seasons on the ship route. Therefore, there is a certain error in using the constant values ​​of Δt1 and Δt2. For this reason, a seasonal correction coefficient μ is calculated according to the proportion of spring, summer, autumn and winter on the route of the ship. The coefficient is used to correct Δt1 and Δt2 to ensure the accuracy of the calculation of the heat transfer of the small two-phase tank 1, the large two-phase tank 2 and the storage tank 3. The proportion of winter days is large, and μ is less than 1. The proportion of summer days is large, and μ is greater than 1. The proportion of spring and autumn days is large, and μ is close to 1; the materials of the small two-phase tank 1, the large two-phase tank 2 and the storage tank 3 are the same, and the heat transfer coefficient k of the tank body is the same.

[0094] Solution 2: According to formulas (3) and (4), when the large two-phase tank 2 stores dry ice and the remaining small two-phase tanks 101, 102 and n storage tanks 3 store liquid CO2, the maximum number of sailing days during which liquid CO2 does not produce BOG is T2. If T0≤T2, this solution is selected.

[0095] 86.4V2ρ 冰 q≥[(A 101 +A 102 +nA3)Δt1+A2Δt2]μT2k (3)

[0096]

[0097] Where, V2 is the volume of solid CO2 (dry ice) stored in the large two-phase tank 2, m 3 ;

[0098] A 101 —Surface area of ​​small two-phase tank 101, m 2 ;

[0099] A 102 —Surface area of ​​small two-phase tank 102, m 2

[0100] A2—Surface area of ​​large two-phase tank 2, m 2 ;

[0101] A3—Surface area of ​​tank 3, m 2 ;

[0102] T2—maximum sailing days for option 2, day;

[0103] Solution 3: According to formulas (5) and (6), when one small two-phase tank 101 and one large two-phase tank 2 store dry ice, and the remaining small two-phase tanks 102 and n storage tanks 3 store liquid CO2, the maximum number of sailing days during which liquid CO2 does not produce BOG is T3. If T0≤T3, this solution is selected.

[0104] 86.4(V 101 +V2)ρ 冰 q≥[(A 102 +nA3)Δt1+(A 101 +A2)Δt2]μT3k (5)

[0105]

[0106] Among them, V 101 —The volume of solid CO2 (dry ice) stored in the small two-phase tank 101, m 3 ;

[0107] V2—The volume of solid CO2 (dry ice) stored in the large two-phase tank 2, m 3

[0108] A 102 —Surface area of ​​small two-phase tank 102, m 2 ;

[0109] A3—Surface area of ​​tank 3, m 2 ;

[0110] A 101 —Surface area of ​​small two-phase tank 101, m 2 ;

[0111] A2—Surface area of ​​large two-phase tank 2, m 2 .

[0112] T3—maximum sailing days for plan 3, day;

[0113] Solution 4: According to formulas (7) and (8), when the small two-phase tank 101, the small two-phase tank 102 and the large two-phase tank 2 store dry ice and the remaining n storage tanks 3 store liquid CO2, the maximum number of sailing days during which liquid CO2 does not produce BOG is T4. If T0≤T4, this solution is selected.

[0114] 86.4(V 101 +V 102 +V2)ρ 冰 q≥[nA3Δt1+(A 101 +A 102 +A2)Δt2]μT4k (7)

[0115]

[0116] Among them, V 101 —The volume of solid CO2 (dry ice) stored in the small two-phase tank 101, m 3 ;

[0117] V 102 —The volume of solid CO2 (dry ice) stored in the small two-phase tank 102, m 3 ;

[0118] V2—The volume of solid CO2 (dry ice) stored in the large two-phase tank 2, m 3

[0119] A3—Surface area of ​​tank 3, m 2 ;

[0120] A 101 —Surface area of ​​small two-phase tank 101, m 2 ;

[0121] A102 —Surface area of ​​small two-phase tank 102, m 2 ;

[0122] A2—Surface area of ​​large two-phase tank 2, m 2 .

[0123] T4—maximum sailing days for scheme 4, day;

[0124] like Figure 1 As shown, in order to better understand the above method for calculating the maximum sailing days, in this embodiment, two small two-phase tanks 1 are provided on the ship, namely small two-phase tank 101 and small two-phase tank 102; one large two-phase tank 2 is provided; and two storage tanks 3 are provided. The above four schemes are analyzed:

[0125] Solution 1: Calculate the maximum number of sailing days T1 during which liquid CO2 does not generate BOG when the small two-phase tank 101 stores dry ice and the other small two-phase tanks 102, large two-phase tank 2, and two storage tanks 3 store liquid CO2 according to formula (2). If T0≤T1, this solution is selected.

[0126]

[0127] Among them, V 101 —The volume of solid CO2 (dry ice) stored in the small two-phase tank 101, m 3 ;

[0128] ρ 冰 —Density of solid CO2 (dry ice), kg / m 3 ;

[0129] q—the amount of cold released when each kilogram of dry ice turns into liquid CO2, kJ / kg;

[0130] A 102 —Surface area of ​​small two-phase tank 102, m 2 ;

[0131] A2—Surface area of ​​large two-phase tank 2, m 2 ;

[0132] A3—Surface area of ​​tank 3, m 2 ;

[0133] k—heat transfer coefficient of the tank, W / m 2 K, different tank materials have different heat transfer coefficients;

[0134] Δt1—temperature difference between liquid CO2 and the external environment, K;

[0135] Δt2—temperature difference between solid CO2 (dry ice) and the external environment, K;

[0136] μ—Seasonal correction factor, which is the correction factor for different seasons on the ship route;

[0137] T1—Maximum sailing days for Plan 1, day.

[0138] The constant 86.4 in the formula is the result of unit conversion. According to the unit conversion 1J=1W·s, we get 0.001kJ=1W×(1 / 86400)day, that is, 86.4kJ=1W·day.

[0139] Solution 2: Calculate the maximum number of sailing days T2 during which liquid CO2 does not produce BOG when the large two-phase tank 2 stores dry ice and the remaining small two-phase tanks 101, 102 and two storage tanks 3 store liquid CO2 according to formula (4). If T0≤T2, this solution is selected.

[0140]

[0141] Where, V2 is the volume of solid CO2 (dry ice) stored in the large two-phase tank 2, m 3 ;

[0142] A 101 —Surface area of ​​small two-phase tank 101, m 2 ;

[0143] A 102 —Surface area of ​​small two-phase tank 102, m 2

[0144] A3—Surface area of ​​tank 3, m 2 ;

[0145] A2—Surface area of ​​large two-phase tank 2, m 2 ;

[0146] T2—maximum sailing days for option 2, day;

[0147] Solution 3: Calculate the maximum number of sailing days T3 during which liquid CO2 does not generate BOG when the small two-phase tank 101 and the large two-phase tank 2 store dry ice and the remaining small two-phase tank 102 and the two storage tanks 3 store liquid CO2 according to formula (6). If T0≤T3, this solution is selected.

[0148]

[0149] Among them, V 101 —The volume of solid CO2 (dry ice) stored in the small two-phase tank 101, m 3 ;

[0150] V2—The volume of solid CO2 (dry ice) stored in the large two-phase tank 2, m 3

[0151] A 102 —Surface area of ​​small two-phase tank 102, m 2 ;

[0152] A3—Surface area of ​​tank 3, m 2 ;

[0153] A 101 —Surface area of ​​small two-phase tank 101, m 2 ;

[0154] A2—Surface area of ​​large two-phase tank 2, m 2 .

[0155] T3—maximum sailing days for plan 3, day;

[0156] Solution 4: Calculate the maximum number of sailing days T4 during which liquid CO2 does not generate BOG when the small two-phase tank 101, the small two-phase tank 102 and the large two-phase tank 2 store dry ice and the other two storage tanks 3 store liquid CO2 according to formula (8). If T0≤T4, this solution is selected.

[0157]

[0158] Among them, V 101 —The volume of solid CO2 (dry ice) stored in the small two-phase tank 101, m 3 ;

[0159] V 102 —The volume of solid CO2 (dry ice) stored in the small two-phase tank 102, m 3 ;

[0160] V2—The volume of solid CO2 (dry ice) stored in the large two-phase tank 2, m 3

[0161] A3—Surface area of ​​tank 3, m 2 ;

[0162] A 101 —Surface area of ​​small two-phase tank 101, m 2 ;

[0163] A 102 —Surface area of ​​small two-phase tank 102, m 2 ;

[0164] A2—Surface area of ​​large two-phase tank 2, m 2 .

[0165] T4—maximum sailing days for scheme 4, day;

[0166] The sailing time required for the CO2 transport ship to travel from the departure port to the destination can be calculated as T0 days before the ship sets sail, and plan 1 is implemented first.

[0167] Solution 1: Set the volume V of the small two-phase tank 101 to 101 , the density of dry ice ρ 冰 , the amount of cold released when each kilogram of dry ice turns into liquid CO2 q, the surface area A of the small two-phase tank 102 102 , the surface area A2 of the large two-phase tank 2 and the surface area A3 of the two storage tanks 3, the seasonal correction coefficient μ, the heat transfer coefficient K, the temperature difference Δt1 between the liquid CO2 and the external environment, and the temperature difference Δt2 between the dry ice and the external environment are preferentially substituted into the formula of Scheme 1 If T0≤T1, then use Solution 1. If T0>T1, then use Solution 2.

[0168] Solution 2: Set the volume V2 of the large two-phase tank 2 and the density ρ of dry ice 冰 , the amount of cold released when each kilogram of dry ice turns into liquid CO2 q, the surface area A of the small two-phase tank 101 101 , small two-phase tank 102 surface area A 102 Substitute the surface area A3 of the two tanks 3, the seasonal correction coefficient μ, the heat transfer coefficient K, the temperature difference Δt1 between the liquid CO2 and the external environment, and the temperature difference Δt2 between the dry ice and the external environment into the formula of Scheme 2 If T0≤T2, the calculated T2 uses solution 2; if T0>T2, solution 3 is used.

[0169] Solution 3: Set the volume V of the small two-phase tank 101 to 101 , the volume of the large two-phase tank 2 V2, the density of dry ice ρ 冰 , the amount of cold released when each kilogram of dry ice turns into liquid CO2 q, the surface area A of the small two-phase tank 102 102 and two storage tanks 3 with a surface area of ​​A3 and small two-phase tank 101 with a surface area of ​​A 101 , the surface area A2 of the large two-phase tank 2, the seasonal correction coefficient μ, the heat transfer coefficient K, the temperature difference Δt1 between the liquid CO2 and the external environment, and the temperature difference Δt2 between the dry ice and the external environment are substituted into the formula of Scheme 3 If T0≤T3, the calculated T3 uses plan 3; if T0>T3, plan 4 is implemented.

[0170] Solution 4: When the ship was initially designed, the ship took into account the extreme operating conditions of the longest route from the departure port to the destination port. The small two-phase tank 101, the small two-phase tank 102 and the large two-phase tank 2 of the present invention all store dry ice. The cold energy released when the dry ice is converted into liquid CO2 can definitely maintain the temperature of the liquid CO2 stored in other storage tanks 3, thereby avoiding the generation of BOG when the liquid CO2 is stored in storage tank 3. Therefore, there is no situation where T0>T4.

[0171] In summary, the CO2 transport ship of the present invention is included in the above four solutions in any case.

[0172] The present invention skillfully combines dry ice and liquid CO2 for transportation, stores dry ice in a small two-phase tank 1 and a large two-phase tank 2, and fully utilizes the cold energy of dry ice. A large amount of cold energy is released in the process of dry ice becoming liquid CO2, which can effectively maintain the low temperature environment of liquid CO2 and avoid the generation of BOG by liquid CO2. Traditional liquid CO2 transportation requires a refrigeration device to maintain low temperature, which results in high energy consumption, and the normal operation of the refrigeration device requires personnel to manage, thereby increasing equipment investment costs, operating costs, and personnel management costs. Through the combined transportation of dry ice and liquid CO2, a circulating pump 4 is used to circulate liquid CO2, fully utilizing the cold energy of dry ice. A large amount of cold energy is released in the process of dry ice becoming liquid CO2, which can effectively maintain the low temperature environment of liquid CO2 and avoid the generation of BOG by liquid CO2, that is, the refrigeration device is omitted, so that the use and management of the circulating pump 4 and various valves are very simple, so the present invention reduces equipment investment costs, operating costs, and personnel management costs.

[0173] During long-haul transportation, more BOG is generated due to the continuous heat exchange between liquid CO2 and the external environment. Through the combined transportation of dry ice and liquid CO2, the storage capacity of dry ice can be dynamically adjusted according to the length of the voyage. The ambient temperature varies greatly in different seasons. High temperatures in summer will increase the risk of evaporation of liquid CO2, while low temperatures in winter may reduce the amount of evaporation. Therefore, the present invention can flexibly adjust the storage capacity of dry ice according to seasonal changes through the combined transportation of dry ice and liquid CO2, thereby coping with the length of the CO2 transport ship's route and meeting the needs of different transportation scenarios by dynamically adjusting the amount of dry ice. It not only meets the refrigeration needs of liquid CO2 and avoids the generation of BOG by liquid CO2, but also minimizes the amount of dry ice carried.

[0174] The above is only a preferred implementation mode of the present invention, but it is not limited to the above embodiments when it is implemented. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A ship for combined transportation of dry ice and liquid CO2, characterized in that: The present invention comprises a small two-phase tank (1), a large two-phase tank (2), a storage tank (3), a circulation pump (4), a flow control valve (5), a check valve (6), a stop valve (7), and a heat exchange coil (8). The small two-phase tank (1), the large two-phase tank (2) and the storage tank (3) are all placed in the cargo hold of the CO2 transport ship. The volume of the storage tank (3) is twice the volume of the large two-phase tank (2), and the volume of the large two-phase tank (2) is twice the volume of the small two-phase tank (1). A circulation pump (4) is placed in each of the small two-phase tank (1), the large two-phase tank (2) and the storage tank (3). The circulation pump (4) is connected to the left end of the check valve (6) through a pipeline. The right end of the check valve (6) is connected to the same pipeline through various branch pipelines. The left end of the heat exchange coil (8) is connected to the same pipeline through a stop valve (7). The right end of the heat exchange coil (8) is re-collected to the same pipeline through a branch pipeline. Then, the left end of the flow control valve (5) is connected to the left end through a pipeline. The right end of the flow control valve (5) enters the small two-phase tank (1), the large two-phase tank (2) and the storage tank (3) storing liquid CO2 through a pipeline.

2. A ship for combined transportation of dry ice and liquid CO2 according to claim 1, characterized in that: The small two-phase tank (1) and the large two-phase tank (2) are both C-type tanks with a cylindrical middle and hemispherical ends, which can store both liquid CO2 and dry ice. The storage tank (3) is in the form of a double-ear tank to store liquid CO2.

3. A ship for combined transportation of dry ice and liquid CO2 according to claim 1, characterized in that: The small two-phase tank (1) is provided with two, namely a small two-phase tank (101) and a small two-phase tank (102), and the large two-phase tank (2) is provided with one. The small two-phase tank (101), the small two-phase tank (102) and the large two-phase tank (2) are placed in the same cargo hold. The small two-phase tank (101) and the small two-phase tank (102) are placed in sequence from the bow to the stern of the ship and are parallel to the large two-phase tank (2). The storage tank (3) is placed in the remaining cargo holds of the CO2 transport ship.

4. A ship for combined transportation of dry ice and liquid CO2 according to claim 1, characterized in that: The heat exchange coil (8) is placed below the small two-phase tank (101), the small two-phase tank (102) and the large two-phase tank (2).

5. A method for combined transportation of dry ice and liquid CO2 based on the ship of claim 1, characterized in that: Before the ship sails, the sailing time T0 required for the CO2 transport ship to travel from the departure port to the destination is calculated. Then, according to the length of the ship's sailing time and the different operating seasons, the combined number of small two-phase tanks (1) and large two-phase tanks (2) for storing dry ice is dynamically adjusted to obtain the maximum sailing days for storing dry ice of different qualities. The sailing time T0 required for the CO2 transport ship is then compared with the calculated maximum sailing days, and a solution is selected.

6. A method for combined transportation of dry ice and liquid CO2 according to claim 5, characterized in that: Solution 1: When using a small two-phase tank (101) to store dry ice, and a small two-phase tank (102), a large two-phase tank (2) and a storage tank (3) to store liquid CO2, according to the formula Calculate the maximum number of sailing days T1 for liquid CO2 without producing BOG. ​​When T0≤T1, select this solution, where V 101 is the volume of the small two-phase tank (101) storing solid CO2, ρ 冰 is the density of dry ice, q is the amount of cold released when each kilogram of dry ice turns into liquid CO2, A 102 is the surface area of ​​the small two-phase tank (102), A2 is the surface area of ​​the large two-phase tank (2), n is the number of storage tanks (3), A3 is the surface area of ​​the storage tank (3), A 101 is the surface area of ​​the small two-phase tank (101), k is the heat transfer coefficient of the tank, Δt1 is the temperature difference between the liquid CO2 and the external environment, Δt2 is the temperature difference between the liquid CO2 and the external environment, μ is the seasonal correction coefficient, and T1 is the maximum number of sailing days of Scheme 1.

7. The method for combined transportation of dry ice and liquid CO2 according to claim 5, characterized in that: Solution 2: When a large two-phase tank (2) is used to store dry ice, and the remaining small two-phase tanks (101), (102) and storage tank (3) are used to store liquid CO2, according to the formula Calculate the maximum number of sailing days T2 for liquid CO2 to not produce BOG. ​​When T0≤T2, select this option. T2 is the maximum number of sailing days for option 2. V2 is the volume of the large two-phase tank (2) storing solid CO2.

8. The method for combined transportation of dry ice and liquid CO2 according to claim 5, characterized in that: Solution 3: When a small two-phase tank (101) and a large two-phase tank (2) are used to store dry ice, and the remaining small two-phase tanks (102) and the storage tank (3) are used to store liquid CO2, according to the formula Calculate the maximum number of sailing days T3 for liquid CO2 without producing BOG. ​​When T0≤T3, select this option. T3 is the maximum sailing day of option 3. V 101 V2 is the volume of the small two-phase tank (101) storing solid CO2, and V3 is the volume of the large two-phase tank (2) storing solid CO2.

9. The method for combined transportation of dry ice and liquid CO2 according to claim 5, characterized in that: Solution 4: When using small two-phase tanks (101), small two-phase tanks (102), and large two-phase tanks (2) to store dry ice, and the remaining tanks (3) to store liquid CO2, according to the formula Calculate the maximum number of sailing days T4 for liquid CO2 without producing BOG. ​​When T0≤T4, select this option. T4 is the maximum number of sailing days for option 4. V 102 The volume of the small two-phase tank (102) storing solid CO2.

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