Inert gas upper-liquid lower-liquid fire extinguishing system and fire extinguishing method for oil storage tank

Abstract

The invention relates to the field of oil storage tank fire extinguishing, in particular to an oil storage tank inert gas upper-liquid lower fire extinguishing system and method. The fire extinguishing system comprises a carbon dioxide fire extinguishing device, a nitrogen fire extinguishing device, a flame detector and a control module, the carbon dioxide fire extinguishing device comprises a carbon dioxide supply assembly and a carbon dioxide injection assembly, the carbon dioxide supply assembly is connected with the carbon dioxide injection assembly, and the carbon dioxide injection assembly is installed in the oil storage tank and located below the floating disc; the nozzle is used for spraying carbon dioxide below liquid from bottom to top; the nitrogen fire extinguishing device comprises a nitrogen supply assembly and a nitrogen injection assembly, the nitrogen supply assembly is connected with the nitrogen injection assembly, and the nitrogen injection assembly is installed in the oil storage tank, located above the floating disc and used for injecting nitrogen to the liquid from top to bottom; the control module is connected with the flame detector, the carbon dioxide supply assembly and the nitrogen supply assembly. High coverage is achieved through liquid-down and liquid-up synergistic fire extinguishing, and efficient and accurate fire extinguishing of the oil storage tank is achieved.

Description

Technical Field

[0001] The invention relates to the field of fire extinguishing of oil storage tanks, and in particular to an inert gas upper liquid lower liquid fire extinguishing system and a fire extinguishing method for oil storage tanks. Background Art

[0002] As the core storage facility of the petrochemical industry, fire prevention and control of storage tanks is the focus of industrial safety. Storage tank fires are characterized by long duration, difficulty in extinguishing, and great destructiveness. Commonly used fire extinguishing technologies such as foam and dry powder have problems such as low efficiency and heavy pollution. In addition, in oil storage tank fires, such as the sinking of the floating plate and the failure of the sealing ring, the oil surface fire or the smoldering fire at the bottom of the tank is difficult to extinguish successfully through traditional liquid fire extinguishing technology.

[0003] Gas fire extinguishing technology has gradually become the focus of fire protection research due to its advantages such as rapid response and environmental protection. Gas fire extinguishing technology achieves rapid fire extinguishing through the effects of materials such as suffocation and cooling. While ensuring the fire extinguishing effect, it can also reduce the degree of pollution to the materials in the storage tank. Commonly used gas fire extinguishing technologies include carbon dioxide fire extinguishing technology and nitrogen fire extinguishing technology. Carbon dioxide fire extinguishing technology injects gas from the top of the storage tank, which is easily affected by wind and has low diffusion efficiency. Nitrogen fire extinguishing technology simply dilutes oxygen, and the density of nitrogen is close to that of air, with low coverage efficiency and requires continuous gas supply.

[0004] Therefore, it is urgent to design a fire extinguishing system that can achieve high coverage and efficient fire extinguishing. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide an inert gas above-liquid and below-liquid fire extinguishing system for oil storage tanks, which achieves high coverage through the coordinated fire extinguishing of below-liquid and above-liquid, thereby realizing efficient and accurate fire extinguishing of oil storage tanks.

[0006] In order to solve the above technical problems, the technical solution of the present invention is: an inert gas liquid upper liquid lower fire extinguishing system for oil storage tanks, wherein the oil storage tank has a floating plate, comprising:

[0007] A carbon dioxide fire extinguishing device, comprising a carbon dioxide supply assembly and a carbon dioxide injection assembly, wherein the carbon dioxide supply assembly is connected to the carbon dioxide injection assembly to supply carbon dioxide, and the carbon dioxide injection assembly is installed in the oil storage tank and located below the floating plate, and is used to inject carbon dioxide from bottom to top into the liquid;

[0008] A nitrogen fire extinguishing device, comprising a nitrogen supply assembly and a nitrogen injection assembly, wherein the nitrogen supply assembly is connected to the nitrogen injection assembly to supply nitrogen, and the nitrogen injection assembly is installed in the oil storage tank and located above the floating plate, and is used to spray nitrogen from top to bottom onto the liquid;

[0009] A flame detector, used to detect whether there is a flame in the oil storage tank;

[0010] The control module is connected to the flame detector, the carbon dioxide supply assembly and the nitrogen supply assembly respectively, and is used to control the carbon dioxide supply assembly and the nitrogen supply assembly to work when the flame detector detects a fire.

[0011] Further provided is a specific structure of a carbon dioxide supply assembly capable of providing a stable gas-liquid two-phase flow of carbon dioxide, wherein the carbon dioxide supply assembly comprises a liquid carbon dioxide storage tank, a cryogenic pump and a carbon dioxide delivery pipeline; wherein,

[0012] The liquid carbon dioxide storage tank is connected to the carbon dioxide injection assembly through the carbon dioxide delivery pipeline, and the cryogenic pump is arranged on the carbon dioxide delivery pipeline;

[0013] A first-stage throttle valve and a second-stage throttle valve are sequentially arranged along the flow direction of carbon dioxide at a position of the carbon dioxide delivery pipeline between the cryogenic pump and the carbon dioxide injection assembly.

[0014] In order to further reduce the risk of cavitation and avoid gas accumulation, the distance between the cryopump and the outlet of the liquid carbon dioxide storage tank does not exceed 2m, and the inlet pipe of the cryopump is inclined downward toward the cryopump with a slope exceeding 1%.

[0015] A specific structure of a carbon dioxide injection assembly with stable injection pressure and wide coverage is further provided, the carbon dioxide injection assembly comprising:

[0016] A carbon dioxide annular pipeline connected to the carbon dioxide delivery pipeline;

[0017] A plurality of swirl injectors are installed at an upper end of the carbon dioxide annular pipeline at intervals along the circumference of the carbon dioxide annular pipeline;

[0018] A plurality of third-stage throttle valves are provided, each of which is installed between the carbon dioxide annular pipe and the swirl ejector.

[0019] In order to further cope with the impact of the sinking plate, the carbon dioxide annular pipeline is installed in the oil storage tank through a bellows compensator.

[0020] In order to prevent the oil surface from being violently disturbed, the apertures of the first-stage throttle valve, the second-stage throttle valve and the third-stage throttle valve are successively reduced; the swirl injector is configured to inject carbon dioxide into the liquid at a driving pressure of 1.5MPa-2.2MPa, and the flow rate is controlled at 2-3m 3 / min.

[0021] Furthermore, the inner diameter of the carbon dioxide annular pipe is larger than the outer diameter of the floating plate.

[0022] Furthermore, the nitrogen supply assembly includes a nitrogen preparation machine, a nitrogen delivery pipeline and a cooling device; wherein,

[0023] The nitrogen preparation machine is connected to the nitrogen injection assembly via a nitrogen delivery pipeline;

[0024] The cooling device is connected in series to the nitrogen delivery pipeline and is used for cooling the nitrogen.

[0025] Furthermore, the nitrogen injection assembly includes a nitrogen annular pipe, which is installed on the top of the oil storage tank and connected to the nitrogen delivery pipe. The lower surface of the nitrogen annular pipe is circumferentially provided with multiple injection holes.

[0026] The present invention also relates to a fire extinguishing method based on an inert gas upper liquid and lower liquid fire extinguishing system for a petroleum storage tank, comprising:

[0027] Step S1, using a flame detector to monitor the fire condition in the oil storage tank;

[0028] Step S2, when the flame detector detects a fire, the control module controls the carbon dioxide supply component and the nitrogen supply component to operate;

[0029] Step S3, the carbon dioxide injection assembly injects carbon dioxide in a gas-liquid two-phase flow from bottom to top below the liquid, and the nitrogen injection assembly injects nitrogen from top to bottom above the liquid, and the carbon dioxide in the gas-liquid two-phase flow and the nitrogen cooperate to extinguish the fire;

[0030] Step S4, after the fire is extinguished, continuously inject carbon dioxide and nitrogen in a gas-liquid two-phase flow to prevent re-ignition.

[0031] After adopting the above technical scheme, this patent starts from the injection position and the injection medium, sprays carbon dioxide in a gas-liquid two-phase flow under the liquid to achieve asphyxiation cooling fire extinguishing, sprays nitrogen above the liquid, and cooperates with liquid carbon dioxide for efficient fire extinguishing, thereby expanding the coverage range. In addition, the upper and lower spraying can avoid the disturbance of the flame caused by the spraying under the liquid surface and prevent the disturbance of the oil surface. The present invention can achieve efficient and accurate fire extinguishing of storage tank fires, and is very effective for oil tank sinking plate fires. In addition, the present invention adopts liquid carbon dioxide and nitrogen as fire extinguishing media, which reduces the degree of pollution to the storage tank materials, and improves the fire extinguishing effect of the storage tank while ensuring environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of the inert gas upper liquid and lower liquid fire extinguishing system for petroleum storage tanks of the present invention;

[0033] Figure 2It is a structural schematic diagram of the inert gas upper liquid and lower liquid fire extinguishing system of the petroleum storage tank of the present invention when in operation;

[0034] Figure 3 It is a structural schematic diagram of the carbon dioxide injection assembly of the present invention;

[0035] Figure 4 It is a schematic structural diagram of the nitrogen injection assembly of the present invention;

[0036] In the figure:

[0037] 1. Oil storage tanks;

[0038] 2. Carbon dioxide supply assembly; 21. Liquid carbon dioxide storage tank; 22. Cryogenic pump; 23. Carbon dioxide delivery pipeline; 24. First-stage throttle valve; 25. Second-stage throttle valve; 26. Stop valve; 27. Check valve; 28. Carbon dioxide pressure relief valve;

[0039] 3. Carbon dioxide injection assembly; 31. Carbon dioxide annular pipeline; 32. Swirl injector; 33. Third-stage throttle valve;

[0040] 4. Nitrogen supply assembly; 41. Nitrogen preparation machine; 42. Nitrogen delivery pipeline; 43. Cooling device; 44. Valve; 45. Mass flow controller; 46. Nitrogen pressure relief valve;

[0041] 5. nitrogen injection assembly; 51. nitrogen annular pipeline; 52. injection hole;

[0042] 6. Flame detector;

[0043] 7. Control module. DETAILED DESCRIPTION

[0044] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0045] like Figures 1 to 4 As shown, an inert gas liquid upper and liquid lower fire extinguishing system for oil storage tanks, the oil storage tank 1 has a floating plate, including:

[0046] The carbon dioxide fire extinguishing device comprises a carbon dioxide supply assembly 2 and a carbon dioxide injection assembly 3. The carbon dioxide supply assembly 2 is connected to the carbon dioxide injection assembly 3 to supply carbon dioxide. The carbon dioxide injection assembly 3 is installed in the oil storage tank 1 and is located below the floating plate, and is used to inject carbon dioxide from bottom to top into the liquid.

[0047] The nitrogen fire extinguishing device comprises a nitrogen supply assembly 4 and a nitrogen injection assembly 5. The nitrogen supply assembly 4 is connected to the nitrogen injection assembly 5 to supply nitrogen. The nitrogen injection assembly 5 is installed in the oil storage tank 1 and located above the floating plate, and is used to spray nitrogen from top to bottom onto the liquid.

[0048] The flame detector 6 is used to detect whether there is a flame in the oil storage tank 1;

[0049] The control module 7 is connected to the flame detector 6, the carbon dioxide supply assembly 2 and the nitrogen supply assembly 4 respectively, and is used to control the carbon dioxide supply assembly 2 and the nitrogen supply assembly 4 to work when the flame detector 6 detects a fire.

[0050] Among them, the fire extinguishing method of this oil tank inert gas liquid above liquid below fire extinguishing system is:

[0051] Step S1, using the flame detector 6 to monitor the fire condition in the oil storage tank 1;

[0052] Step S2, when the flame detector 6 detects a fire, the control module 7 controls the carbon dioxide supply component 2 and the nitrogen supply component 4 to operate;

[0053] Step S3, the carbon dioxide injection assembly 3 injects carbon dioxide in a gas-liquid two-phase flow from bottom to top below the liquid, and the nitrogen injection assembly 5 injects nitrogen from top to bottom above the liquid, and the carbon dioxide in the gas-liquid two-phase flow and the nitrogen cooperate to extinguish the fire;

[0054] Step S4, after the fire is extinguished, continuously inject carbon dioxide and nitrogen in a gas-liquid two-phase flow to prevent re-ignition.

[0055] In this embodiment, the flame detector 6 may be an infrared flame detector, and a plurality of them may be provided and installed at the top of the oil storage tank 1 along the circumference of the oil storage tank 1 . The control module 7 may be a PLC.

[0056] Specifically, general gas fire extinguishing is sprayed from the liquid, but due to the wind speed, flame plume and other factors affecting the coverage rate, it is not possible to quickly achieve suffocation extinguishing. In order to solve the problems existing in extinguishing fire above the liquid, the inventor of this patent tried to use underwater fire extinguishing, but underwater fire extinguishing will cause disturbances in the oil surface, which will cause the oil to surge and boil to a certain extent, increasing the fire. Therefore, the inventor of this patent started with the injection position and the injection medium, considering that liquid carbon dioxide is more stable than liquid nitrogen in underwater fire extinguishing, and the suffocation cooling effect is better than liquid nitrogen. Therefore, carbon dioxide in a gas-liquid two-phase flow is sprayed under the liquid to achieve suffocation cooling extinguishing, and nitrogen is sprayed on the liquid to cooperate with liquid carbon dioxide for efficient fire extinguishing, which expands the coverage range. In addition, the upper and lower spraying can avoid the disturbance of the flame caused by the spraying under the liquid surface and prevent the disturbance of the oil surface. Therefore, this embodiment can achieve efficient and accurate fire extinguishing of storage tank fires, and is very effective for oil tank sinking plate fires.

[0057] Among them, the reason why this embodiment is very effective against oil tank sinking fire is that: the tank sinking fire refers to the disaster accident in which the floating plate of the external floating roof or internal floating roof tank is completely sunk below the oil liquid level, resulting in the oil storage tank 1 being exposed and burning on the entire surface. Because the sinking fire is a fire on the entire liquid surface, it is necessary to consider whether the coverage of the fire extinguishing medium is wide. Therefore, the liquid and the liquid are coordinated, and the liquid fire extinguishing avoids the influence of wind and flame plume, which can achieve a wide coverage effect, and directly contact the bottom of the fire source, eliminating the contact between fuel and oxygen, and also reducing the liquid level rise and flowing fire formation caused by the gasification and expansion of oil products.

[0058] In one embodiment, Figure 1 and Figure 2 As shown, the carbon dioxide supply assembly 2 includes a liquid carbon dioxide storage tank 21, a cryogenic pump 22 and a carbon dioxide delivery pipeline 23; wherein,

[0059] The liquid carbon dioxide storage tank 21 is connected to the carbon dioxide injection assembly 3 through a carbon dioxide delivery pipeline 23, and the cryogenic pump 22 is arranged on the carbon dioxide delivery pipeline 23;

[0060] A first-stage throttle valve 24 and a second-stage throttle valve 25 are sequentially arranged along the flow direction of carbon dioxide at a position of the carbon dioxide delivery pipeline 23 between the cryopump 22 and the carbon dioxide injection assembly 3 .

[0061] The carbon dioxide delivery pipeline 23 is also provided with a stop valve 26, a check valve 27 and a carbon dioxide pressure relief valve 28. The cryogenic pump 22, the stop valve 26, the check valve 27, the first-stage throttle valve 24, the carbon dioxide pressure relief valve 28 and the second-stage throttle valve 25 are arranged in sequence along the flow direction of carbon dioxide.

[0062] Preferably, the stop valve 26 has a pressure rating of ≥1.5 times the maximum output pressure of the cryogenic pump and is of full-bore design. The check valve 27 is a lift or swing check valve with a pressure drop of ≤0.2MPa. The first-stage throttle valve 24 and the second-stage throttle valve 25 are fixed-aperture throttle orifices or adjustable throttle valves.

[0063] Specifically, the liquid carbon dioxide storage tank 21 is used to store liquid carbon dioxide; the cryogenic pump 22 is installed at the outlet of the liquid carbon dioxide storage tank 21 to ensure that the liquid carbon dioxide maintains a low temperature during transportation to avoid gasification and cause two-phase flow instability; the stop valve 26 is installed at the outlet of the cryogenic pump 22 to urgently cut off the supply of liquid carbon dioxide for isolation maintenance; the check valve 27 is installed downstream of the stop valve 26 to prevent high-pressure liquid carbon dioxide from flowing back and impacting the cryogenic pump 22 to protect the safety of the equipment; the first-stage throttle valve 24 is installed downstream of the check valve 27 to reduce the pressure of the transported high-pressure liquid carbon dioxide and reduce erosion damage; the carbon dioxide pressure relief valve 28 is used to release the residual pressure in the carbon dioxide delivery pipeline 23; the second-stage throttle valve 25 is installed on the carbon dioxide delivery pipeline 23 near the carbon dioxide injection assembly 3 to finely adjust the flow and pressure of the liquid carbon dioxide to ensure that the liquid carbon dioxide is evenly and stably delivered to the carbon dioxide injection assembly 3.

[0064] Preferably, the distance between the cryopump 22 and the outlet of the liquid carbon dioxide storage tank 21 is no more than 2 m to reduce the risk of cavitation, and the inlet pipe of the cryopump 22 is inclined downward toward the cryopump 22 with a slope exceeding 1% to avoid gas accumulation.

[0065] In one embodiment, Figure 1 , Figure 2 and Figure 3 As shown, the carbon dioxide injection assembly 3 includes:

[0066] The carbon dioxide annular pipeline 31 is connected to the carbon dioxide delivery pipeline 23;

[0067] A plurality of swirl injectors 32 are installed at an upper end of the carbon dioxide annular pipe 31 at intervals along the circumference of the carbon dioxide annular pipe 31;

[0068] A plurality of third-stage throttle valves 33 are provided, each of which is installed between the carbon dioxide annular pipe 31 and the swirl injector 32, to ensure that the carbon dioxide enters the swirl injector 32 in a stable gas-liquid two-phase flow with precise driving pressure and flow rate. The number of swirl injectors 32 can be adjusted according to the fire extinguishing requirements.

[0069] Preferably, the distance between the third-stage throttle valve 33 and the corresponding swirl injector 32 is ≤ 1 m to reduce pressure fluctuations.

[0070] Preferably, the swirl injector 32 has a built-in spiral guide vane with a diffusion cone angle of 45°, which can greatly improve the coverage range.

[0071] Preferably, the apertures of the first-stage throttle valve 24, the second-stage throttle valve 25 and the third-stage throttle valve 33 are successively reduced. Thus, through the step-by-step control of the three-stage throttle valve, the swirl injector 32 can inject carbon dioxide into the liquid at a driving pressure of 1.5MPa-2.2MPa, and the flow rate of carbon dioxide injected by the carbon dioxide injection assembly 3 is controlled at 2-3m 3 / min. This pressure can break through the hydrostatic pressure and effectively prevent the oil surface from being violently disturbed. This pressure will not cause displacement impact on the float.

[0072] In a specific example, the apertures of the first-stage throttle valve 24 , the second-stage throttle valve 25 , and the third-stage throttle valve 33 are 8 mm, 5 mm, and 3 mm, respectively, but are not limited thereto.

[0073] Preferably, the carbon dioxide annular pipe 31 is installed in the oil storage tank 1 through a bellows compensator. In this way, the displacement stress of the sinker can be absorbed.

[0074] In this embodiment, the carbon dioxide annular pipe 31 can be made of seamless steel pipe, which is resistant to high pressure and low temperature. In addition, the carbon dioxide annular pipe 31 can also adopt a segmented structure, so that even if a part is damaged due to the impact of the sinking plate, it will not affect the normal operation of other areas.

[0075] In this embodiment, a certain distance is left between the floating plate and the inner wall of the oil storage tank 1, and this distance is mainly used for the setting of the sealing ring. Therefore, a certain gap can be set between the carbon dioxide annular pipeline 31 and the edge of the floating plate, that is, the inner diameter of the carbon dioxide annular pipeline 31 is larger than the outer diameter of the floating plate. In this way, even if the plate sinks, the floating plate will not cause too much shielding to the carbon dioxide annular pipeline 31.

[0076] In one embodiment, the nitrogen supply assembly 4 includes a nitrogen preparation machine 41, a nitrogen delivery pipeline 42 and a cooling device 43; wherein,

[0077] The nitrogen preparation machine 41 is connected to the nitrogen injection assembly 5 through the nitrogen delivery pipeline 42;

[0078] The cooling device 43 is connected in series to the nitrogen delivery pipeline 42 for cooling the nitrogen.

[0079] The cooling device 43 is provided so that the nitrogen injection assembly 5 can inject low-temperature nitrogen, which can reduce the oxygen concentration more quickly, achieve a faster fire extinguishing effect, realize a high coverage of the liquid surface of the storage tank, greatly reduce the fire extinguishing blind spots in the storage tank, and further improve the fire extinguishing effect.

[0080] A valve 44 is installed at the outlet of the cooling device 43 , and a mass flow controller 45 and a nitrogen pressure relief valve 46 are sequentially installed on the nitrogen delivery pipeline 42 along the nitrogen flow direction.

[0081] The nitrogen preparation machine 41 is used to quickly prepare nitrogen; the cooling device 43 is installed at the outlet of the nitrogen preparation machine 41 to cool the nitrogen; the valve 44 is installed at the outlet of the cooling device 43 to control the delivery of low-temperature nitrogen; the mass flow controller 45 is installed downstream of the valve 44 to control the delivery rate of low-temperature nitrogen; the nitrogen pressure relief valve 46 is installed on the nitrogen delivery pipeline 42 to release the residual pressure in the nitrogen delivery pipeline 42. After the nitrogen preparation machine 41 extracts air from the air and compresses it, it can use a membrane separation method to deoxygenate and filter out high-purity nitrogen with nitrogen as the main component. The nitrogen delivery pipeline 42 can use a hose that is easy to fold and disassemble.

[0082] In one embodiment, Figure 4 As shown, the nitrogen injection assembly 5 includes a nitrogen annular pipe 51, which is installed at the top of the oil storage tank 1 and connected to the nitrogen delivery pipe 42. The lower surface of the nitrogen annular pipe 51 is circumferentially provided with multiple injection holes 52.

[0083] The diameter of the injection hole 52 is preferably 3-5 mm, and the hole center spacing is 30-80 mm, but it is not limited thereto.

[0084] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. An inert gas liquid-on-liquid-off-liquid fire extinguishing system for a petroleum storage tank, wherein the petroleum storage tank (1) has a floating plate inside, characterized in that: include: A carbon dioxide fire extinguishing device comprises a carbon dioxide supply component (2) and a carbon dioxide injection component (3), wherein the carbon dioxide supply component (2) is connected to the carbon dioxide injection component (3) to supply carbon dioxide, and the carbon dioxide injection component (3) is installed in the oil storage tank (1) and located below the floating plate, and is used to inject carbon dioxide from bottom to top into the liquid; A nitrogen fire extinguishing device, comprising a nitrogen supply assembly (4) and a nitrogen injection assembly (5), wherein the nitrogen supply assembly (4) is connected to the nitrogen injection assembly (5) to supply nitrogen, and the nitrogen injection assembly (5) is installed in the oil storage tank (1) and located above the floating plate, and is used to inject nitrogen from top to bottom onto the liquid; A flame detector (6) for detecting whether there is a flame in the oil storage tank (1); A control module (7) is respectively connected to the flame detector (6), the carbon dioxide supply assembly (2) and the nitrogen supply assembly (4), and is used to control the carbon dioxide supply assembly (2) and the nitrogen supply assembly (4) to operate when the flame detector (6) detects a fire.

2. The oil storage tank inert gas upper and lower liquid fire extinguishing system according to claim 1 is characterized in that: The carbon dioxide supply assembly (2) comprises a liquid carbon dioxide storage tank (21), a cryogenic pump (22) and a carbon dioxide delivery pipeline (23); wherein: The liquid carbon dioxide storage tank (21) is connected to the carbon dioxide injection assembly (3) via the carbon dioxide delivery pipeline (23), and the cryogenic pump (22) is arranged on the carbon dioxide delivery pipeline (23); A first-stage throttle valve (24) and a second-stage throttle valve (25) are sequentially arranged along the flow direction of the carbon dioxide at a position between the cryogenic pump (22) and the carbon dioxide injection assembly (3) of the carbon dioxide delivery pipeline (23).

3. The inert gas upper and lower liquid fire extinguishing system for petroleum storage tanks according to claim 2 is characterized in that: The distance between the cryopump (22) and the outlet of the liquid carbon dioxide storage tank (21) does not exceed 2 m, and the inlet pipe of the cryopump (22) is inclined downward toward the cryopump (22) with a slope exceeding 1%.

4. The oil storage tank inert gas upper and lower liquid fire extinguishing system according to claim 2 is characterized in that: The carbon dioxide injection assembly (3) comprises: A carbon dioxide annular pipeline (31) connected to the carbon dioxide delivery pipeline (23); A plurality of swirl injectors (32) are installed at intervals along the circumference of the carbon dioxide annular pipeline (31) at the upper end of the carbon dioxide annular pipeline (31); A plurality of third-stage throttle valves (33), each of which is installed between the carbon dioxide annular pipeline (31) and the swirl ejector (32).

5. The oil storage tank inert gas upper and lower liquid fire extinguishing system according to claim 4 is characterized in that: The carbon dioxide annular pipeline (31) is installed in the petroleum storage tank (1) via a bellows compensator.

6. The inert gas upper and lower liquid fire extinguishing system for petroleum storage tanks according to claim 4 is characterized in that: The apertures of the first-stage throttle valve (24), the second-stage throttle valve (25) and the third-stage throttle valve (33) decrease in sequence; The swirl injector (32) is configured to inject carbon dioxide into the liquid at a driving pressure of 1.5 MPa-2.2 MPa, and the flow rate is controlled at 2-3 m 3 / min.

7. The inert gas upper and lower liquid fire extinguishing system for petroleum storage tanks according to claim 4 is characterized in that: The inner diameter of the carbon dioxide annular pipe (31) is larger than the outer diameter of the floating plate.

8. The inert gas upper and lower liquid fire extinguishing system for petroleum storage tanks according to claim 1 is characterized in that: The nitrogen supply assembly (4) comprises a nitrogen preparation machine (41), a nitrogen delivery pipeline (42) and a cooling device (43); wherein: The nitrogen preparation machine (41) is connected to the nitrogen injection assembly (5) via a nitrogen delivery pipeline (42); The cooling device (43) is connected in series to the nitrogen delivery pipeline (42) and is used to cool the nitrogen.

9. The inert gas upper and lower liquid fire extinguishing system for petroleum storage tanks according to claim 8, characterized in that: The nitrogen injection assembly (5) comprises a nitrogen annular pipe (51), which is installed at the top of the petroleum storage tank (1) and connected to the nitrogen delivery pipe (42). The lower surface of the nitrogen annular pipe (51) is provided with a plurality of injection holes (52) along the circumferential direction.

10. A fire extinguishing method based on the inert gas upper and lower liquid fire extinguishing system for petroleum storage tanks according to any one of claims 1 to 9, characterized in that: include: Step S1, using a flame detector (6) to monitor the fire condition in the oil storage tank (1); Step S2, when the flame detector (6) detects a fire, the control module (7) controls the carbon dioxide supply component (2) and the nitrogen supply component (4) to operate; Step S3, the carbon dioxide injection assembly (3) injects carbon dioxide in a gas-liquid two-phase flow from bottom to top below the liquid, and the nitrogen injection assembly (5) injects nitrogen from top to bottom above the liquid, and the carbon dioxide in the gas-liquid two-phase flow and the nitrogen cooperate to extinguish the fire; Step S4, after the fire is extinguished, continuously inject carbon dioxide and nitrogen in a gas-liquid two-phase flow to prevent re-ignition.

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