Nitrogen filling inerting and exhaust liquid nitrogen subzero treatment system of external floating roof tank

Abstract

The utility model relates to a nitrogen filling inerting and exhaust liquid nitrogen subzero treatment system of an external floating roof tank, which comprises the external floating roof tank (1), an external floating roof (2), a primary seal (3), a sealed space (4), a secondary seal (5), a pressure transmitter (6), a frequency conversion fan (7), a sampling pump (8), a gas sensor, a subzero condenser (11), a liquid nitrogen tank (12), a nitrogen injection valve (15) and a nitrogen buffer tank (16). The sealed space (4) is connected with the cryogenic condenser (11) through the pressure transmitter (6) and the frequency conversion fan (7), the sampling pump (8) is connected with the sealed space (4) and the cryogenic condenser (11), the gas sensor is arranged between the sampling pump (8) and the cryogenic condenser (11), and the cryogenic condenser (11) is connected with the liquid nitrogen tank (12) and the nitrogen buffer tank (16). The problems of nitrogen source of active safe nitrogen charging and oil gas recycling and up-to-standard emission of exhausted gas during nitrogen charging are solved.

Description

Technical Field

[0001] The utility model belongs to the technical field of oil storage and transportation, and relates to a system for actively and safely filling nitrogen and recovering and treating exhaust gas generated during the storage and transportation of oil products, and in particular to a system for actively and safely filling nitrogen and cryogenically treating exhaust gas containing VOCs in an external floating roof tank of an oil product. Background Art

[0002] Crude oil is a flammable and explosive hazardous material. While there are various ways to store crude oil, external floating roof oil storage tanks are currently the most commonly used. Because of the primary and secondary seals between the edge of the floating roof and the inner wall of an external floating roof oil storage tank, a mixture of explosive gas and oxygen can persist between the primary and secondary seals, creating an explosion-hazardous zone. Besides human factors, factors such as lightning, static electricity generated by the tank itself, and sparks can easily trigger oil and gas explosions within this sealed space. Numerous fires and explosions have occurred in large floating roof oil storage tanks around the world, resulting in significant casualties, property damage, and widespread environmental pollution.

[0003] At present, the fire-fighting methods for large oil storage tanks mainly use foam and water to rescue fire accidents, and active safety systems have also been developed.

[0004] For example, Chinese invention patent CN113003028B discloses a full-process operation safety protection system and method for external floating roof storage tanks. The system comprises a floating roof gas collection system on a floating plate. The floating roof gas collection system connects several automatic vent valves and edge breathing valves on the floating plate to form a closed gas collection environment. The floating roof gas collection system is provided with a nitrogen injection port and an air extraction port. The safety protection system also includes a pressure detection unit. The nitrogen injection port is connected to a nitrogen recovery supply system via a nitrogen pipeline, and the air extraction port is connected to the nitrogen recovery supply system via an adaptive telescopic vent network. The floating roof gas collection system is connected to a protective device via a nitrogen injection and extraction network and a sampling network, respectively, and the protective device is connected to the nitrogen recovery supply system. This invention addresses the safety hazards that exist in the full-process operation of the floating plate of an external floating roof storage tank. It controls the VOCs leakage points of the floating plate at the source, reduces the unorganized emission of VOCs, and realizes intelligent nitrogen sealing and orderly collection of VOCs during the full operation of the external floating roof storage tank. However, this invention requires a separate nitrogen generator to meet the demand for nitrogen, and also requires a separate oil and gas processing device to pressurize, condense, adsorb and purify the oil and gas. The system has many moving equipment, a long process, high investment and a high operating failure rate.

[0005] Chinese utility model patent CN206032280U discloses an active safety protection and oil and gas recovery device for an external floating roof tank. The device comprises a sampling and analysis system, an inerting system, and an oil and gas recovery system. The sampling and analysis system includes a sampling probe, a gas analyzer, and a negative pressure buffer tank, with multiple sampling probes positioned within the secondary containment space of the external floating roof tank. The inerting system includes an inerting gas filling head and an inerting gas storage tank, with multiple inerting gas filling heads positioned within the secondary containment space of the external floating roof tank. This utility model uses the sampling and analysis system to analyze the oil and gas composition within the secondary containment space of the external floating roof tank, comprehensively calculate the oil and gas explosion limits, and determine whether the oil and gas have reached the explosion range based on oxygen content to perform gas inerting, achieving active inerting. The oil and gas recovery system simultaneously recovers the oil and gas using molecular sieve adsorption followed by refrigeration and deliquification, achieving zero emissions and preventing atmospheric pollution from oil and gas emissions. However, this utility model requires an inerting gas storage tank but does not address the source of the inerting gas. Furthermore, the oil and gas recovery system is complex and costly.

[0006] Therefore, it is necessary to develop a solution with convenient nitrogen source, low oil and gas condensation temperature, and sufficient liquefaction and recovery of VOCs. Utility Model Content

[0007] The purpose of the utility model is to overcome the shortcomings of the prior art and provide a nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank. The system takes liquid nitrogen cryogenic oil and gas recovery technology as its core, and solves the nitrogen source of the active safety nitrogen filling system and the oil and gas recovery and standard emission problems of the exhaust during nitrogen filling, thereby having significant safety benefits, environmental and social benefits and economic benefits.

[0008] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0009] A nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank, comprising an external floating roof tank, an external floating roof, a primary seal, a sealed space and a secondary seal, wherein the external floating roof is installed in the external floating roof tank and the primary seal and the secondary seal are installed between the external floating roof and the external floating roof tank, and the sealed space is formed between the primary seal and the secondary seal. The invention is characterized in that it also includes a pressure transmitter, a variable frequency fan, a sampling pump, a gas sensor, a cryogenic condenser, a liquid nitrogen tank, a nitrogen injection valve and a nitrogen buffer tank, wherein the sealed space is connected to the pressure transmitter and the pressure transmitter is connected to the variable frequency fan, the variable frequency fan is connected to the cryogenic condenser, one end of the sampling pump is connected to the sealed space and the other end is connected to the cryogenic condenser, and the gas sensor is installed between the sampling pump and the cryogenic condenser, the cryogenic condenser is connected to the liquid nitrogen tank and the nitrogen buffer tank, and the nitrogen buffer tank is connected to the sealed space through the nitrogen injection valve.

[0010] Preferably, the gas sensor includes an oxygen sensor and a VOCs concentration sensor.

[0011] Preferably, the nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank further comprises a condensate tank, and the condensate tank is connected to the cryogenic condenser.

[0012] Preferably, the nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank further comprises a condensate pump, and the condensate tank is connected to the external floating roof tank via the condensate pump.

[0013] Preferably, the nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank further comprises an exhaust pipe, and the exhaust pipe is connected to the cryogenic condenser.

[0014] Compared with the prior art, the nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for the external floating roof tank of the present invention has one or more of the following beneficial technical effects:

[0015] 1. The utility model uses liquid nitrogen as the cooling source and nitrogen source, which comprehensively solves the nitrogen source problem during active safety protection nitrogen injection in sealed spaces and the VOCs oil and gas condensation recovery problem during nitrogen injection exhaust, without the need to set up a separate nitrogen generator and oil and gas recovery and processing equipment.

[0016] 2. Since the liquid nitrogen produced by large-scale air separation units is easily accessible and inexpensive, and the oil and gas condensation temperature is as low as -120~-160℃, it has a higher recovery rate for crude oil and gas with a high light component content than mechanical refrigeration (generally the oil and gas condensation temperature is -50~-70℃), meeting the relevant national environmental protection emission standards. In addition, the nitrogen purity after liquid nitrogen absorbs heat and vaporizes is high, generally reaching 99.9%, and has better performance when used for nitrogen injection inerting.

[0017] 3. Compared with the existing active safety protection nitrogen injection technology and oil and gas processing technology, the solution provided by this utility model has low cost and simple operation, which significantly reduces the owner's comprehensive operating costs and has significant safety benefits, environmental and social benefits and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The utility model is a schematic diagram of the structure of the nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank.

[0019] In the figure: 1. External floating roof tank; 2. External floating roof; 3. Primary seal; 4. Sealed space; 5. Secondary seal; 6. Pressure transmitter; 7. Variable frequency fan; 8. Sampling pump; 9. Oxygen sensor; 10. VOCs concentration sensor; 11. Cryogenic condenser; 12. Liquid nitrogen tank; 13. Condensate tank; 14. Condensate pump; 15. Nitrogen injection valve; 16. Nitrogen buffer tank; 17. Exhaust pipe. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more apparent, the technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of the present invention. It should be understood that the described embodiments are only a portion of the embodiments of the present invention, not all of them. Generally, the components of the embodiments of the present invention described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations.

[0021] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0022] The utility model relates to a nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank. In order to deal with explosive oil and gas in the sealed space of an oil product external floating roof tank, the system detects the oil and gas concentration and oxygen content. When the oil and gas concentration and oxygen content are in an explosion risk state, nitrogen is injected for inerting, thereby reducing the oil and gas concentration and oxygen content to a safe range. After nitrogen injection, the pressure of the sealed space increases, and the VOCs oil and gas in the sealed space are extracted through a pressure transmitter interlocked with a variable frequency fan. The extracted oil and gas are sent to a liquid nitrogen cryogenic condenser for condensation treatment. The VOCs are cooled and condensed into liquid. The exhaust gas after cryogenic treatment meets the emission standards. The condensate returns to the condensate tank, and the liquid nitrogen absorbs the latent heat of liquefaction of the VOCs. The vaporized nitrogen is used as an inerting air supply source. With liquid nitrogen cryogenic oil and gas recovery technology as its core, the system solves the nitrogen source of the active safety nitrogen filling system and the oil and gas recovery and emission standards of the exhaust gas during nitrogen filling. It has significant safety benefits, environmental and social benefits, and economic benefits.

[0023] Figure 1 The figure shows the structure of the nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank of the present invention. Figure 1 As shown, similar to the prior art, the nitrogen filling, inerting, and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank of the present invention includes an external floating roof tank 1, an external floating roof 2, a primary seal 3, a sealed space 4, and a secondary seal 5. The external floating roof 2 is installed within the external floating roof tank 1, and the primary seal 3 and secondary seal 5 are installed between the external floating roof 2 and the external floating roof tank 1. The sealed space 4 is formed between the primary seal 3 and the secondary seal 5.

[0024] Different from the prior art, the nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank of the utility model also includes a pressure transmitter 6, a variable frequency fan 7, a sampling pump 8, a gas sensor, a cryogenic condenser 11, a liquid nitrogen tank 12, a nitrogen injection valve 15 and a nitrogen buffer tank 16.

[0025] The sealed space 4 is connected to the pressure transmitter 6, which is in turn connected to the variable frequency blower 7. The variable frequency blower 7 is connected to the cryogenic condenser 11. Thus, the pressure transmitter 6 can sense pressure changes within the sealed space 4 and drive the variable frequency blower 7 to increase its frequency when the pressure rises, allowing the variable frequency blower 7 to extract oil and gas from the sealed space 4 and pump the oil and gas into the cryogenic condenser 11 for condensation and recovery.

[0026] The sampling pump 8 is connected to the sealed space 4 at one end and to the cryogenic condenser 11 at the other end. The gas sensor is installed between the sampling pump 8 and the cryogenic condenser 11. Thus, the sampling pump 8 can pump oil and gas from the sealed space 4, which is then detected by the gas sensor to determine if it is safe. Furthermore, the pumped oil and gas can be sent to the cryogenic condenser 11 for condensation and recovery.

[0027] Preferably, the gas sensor includes an oxygen sensor 9 and a VOCs concentration sensor 10. The oxygen sensor 9 can detect the oxygen concentration in the sealed space 4, and the VOCs concentration sensor 10 can detect the VOCs concentration in the sealed space 4. Thus, whether the oxygen concentration and VOCs concentration exceed the standard can be used to determine whether the environment is in a safe state.

[0028] The cryogenic condenser 11 is connected to the liquid nitrogen tank 12 and the nitrogen buffer tank 16. The nitrogen buffer tank 16 is connected to the sealed space 4 via the nitrogen injection valve 15. Thus, the liquid nitrogen in the liquid nitrogen tank 12 can enter the cryogenic condenser 11, where it cools the oil and gas entering the cryogenic condenser 11, condensing the VOCs in the oil and gas into a condensate. The liquid nitrogen then absorbs heat in the cryogenic condenser 11, vaporizing into nitrogen and entering the nitrogen buffer tank 16. Furthermore, by opening the nitrogen injection valve 15, the nitrogen in the nitrogen buffer tank 16 can be injected into the sealed space 4. This injected nitrogen can reduce the oxygen and VOC concentrations in the sealed space 4 to ensure safety.

[0029] Preferably, the nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank of the present invention further includes a condensate tank 13, and the condensate tank 13 is connected to the cryogenic condenser 11. Thus, VOCs in the oil and gas are condensed into condensate and can be stored in the condensate tank 13.

[0030] More preferably, the nitrogen-charged inertization and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank further comprises a condensate pump 14 and the condensate tank 13 is connected to the external floating roof tank 1 through the condensate pump 14. Thus, when the liquid level in the condensate tank 13 reaches a high level, the condensate pump 14 is started to transport the condensate in the condensate tank 13 back into the external floating roof tank 1, so as to realize recycling.

[0031] Furthermore, the nitrogen-charged inertization and exhaust liquid nitrogen cryogenic treatment system of the external floating roof tank can further comprise an exhaust cylinder 17 connected with the cryogenic condenser 11. Thus, the non-condensable tail gas in the oil gas can be discharged through the exhaust cylinder 17 to achieve standard discharge.

[0032] In use, the oil gas in the sealed space 4 can be extracted through the sampling pump 8, and the oxygen concentration and VOCs concentration in the sealed space 4 are detected through the oxygen sensor 9 and the VOCs concentration sensor 10 to determine whether it is in a safe state.

[0033] When it is in a safe state, that is, the oxygen concentration and VOCs concentration do not exceed the standard, nitrogen injection measures are not needed, the nitrogen injection valve 15 is closed, and the oil gas extracted by the sampling pump 8 is sent to the cryogenic condenser 11. The liquid nitrogen stored in the liquid nitrogen tank 12 is also sent to the cryogenic condenser 11, and the oil gas is cooled by the liquid nitrogen in the cryogenic condenser 11 to condense the VOCs in the oil gas into condensate. The condensate flows into the condensate tank 13, the liquid nitrogen is gasified into nitrogen gas in the cryogenic condenser 11 to enter the nitrogen buffer tank 16, and the non-condensable tail gas in the oil gas after cryogenic treatment is discharged through the exhaust cylinder 17.

[0034] Due to the continuous volatilization of VOCs components contained in crude oil and the infiltration of air, the oxygen concentration and VOCs concentration in the sealed space 4 will continue to increase. When in an unsafe state, that is, when the oxygen concentration or VOCs concentration exceeds the standard, nitrogen injection measures must be taken. The nitrogen injection valve 15 is opened, and the nitrogen in the nitrogen buffer tank 16 is injected into the sealed space 4 to achieve active protection. The injected nitrogen reduces the oxygen concentration and VOCs concentration in the sealed space 4, and at the same time causes the pressure in the sealed space 4 to increase. After the reading of the pressure transmitter 6 increases, the variable frequency blower 7 is controlled to increase its frequency to extract the oil and gas in the sealed space 4 after nitrogen injection, to prevent the oil and gas from escaping unorganizedly through the secondary seal 5. The oil and gas extracted by the variable frequency blower 7 contains VOCs, which are valuable resources. Venting them will waste resources and cause environmental pollution. Therefore, the oil and gas extracted by the variable frequency blower 7 are fed into the cryogenic condenser 11. Liquid nitrogen stored in the liquid nitrogen tank 12 is also fed into the cryogenic condenser 11. In the cryogenic condenser 11, the liquid nitrogen cools the oil and gas, condensing the VOCs in the oil and gas into condensate. The condensate flows into the condensate tank 13. The liquid nitrogen absorbs heat in the cryogenic condenser 11 and vaporizes into nitrogen. It enters the nitrogen buffer tank 16. The non-condensable tail gas in the oil and gas after cryogenic cooling is discharged through the exhaust pipe 17. During this period, the oil and gas extracted by the sampling pump 8 is continuously tested by the oxygen sensor 9 and the VOC concentration sensor 10. The tested oil and gas are then fed into the cryogenic condenser 11, where the VOCs in the oil and gas are condensed and recovered. The non-condensable tail gas is discharged through the exhaust pipe 17, and the condensate enters the condensate tank 13. Furthermore, when the oxygen sensor 9 and the VOCs concentration sensor 10 detect that they are in a safe state, the nitrogen injection valve 15 is closed, and the variable frequency blower 7 is operated at a reduced frequency or turned off.

[0035] When the liquid level in the condensate tank 13 reaches a high liquid level, the condensate pump 14 is started to transport the condensate in the condensate tank 13 back to the external floating roof tank 1 to recycle resources.

[0036] The above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the manner in which the present invention may be implemented. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. This list of all possible embodiments is not exhaustive. Any obvious variations or modifications arising from the technical solution of the present invention remain within the scope of protection of the present invention.

Claims

1. A nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank, comprising an external floating roof tank (1), an external floating roof (2), a primary seal (3), a sealed space (4) and a secondary seal (5), wherein the external floating roof (2) is installed in the external floating roof tank (1) and the primary seal (3) and the secondary seal (5) are installed between the external floating roof (2) and the external floating roof tank (1), and the sealed space (4) is formed between the primary seal (3) and the secondary seal (5), and is characterized in that: The invention also includes a pressure transmitter (6), a variable frequency fan (7), a sampling pump (8), a gas sensor, a cryogenic condenser (11), a liquid nitrogen tank (12), a nitrogen injection valve (15) and a nitrogen buffer tank (16), wherein the sealed space (4) is connected to the pressure transmitter (6) and the pressure transmitter (6) is connected to the variable frequency fan (7), the variable frequency fan (7) is connected to the cryogenic condenser (11), one end of the sampling pump (8) is connected to the sealed space (4) and the other end is connected to the cryogenic condenser (11), and the gas sensor is installed between the sampling pump (8) and the cryogenic condenser (11), the cryogenic condenser (11) is connected to the liquid nitrogen tank (12) and the nitrogen buffer tank (16), and the nitrogen buffer tank (16) is connected to the sealed space (4) through the nitrogen injection valve (15).

2. The nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank according to claim 1 is characterized in that: The gas sensor includes an oxygen sensor (9) and a VOCs concentration sensor (10).

3. The nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank according to claim 2, characterized in that: It further comprises a condensate tank (13), and the condensate tank (13) is connected to the cryogenic condenser (11).

4. The nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank according to claim 3, characterized in that: It further comprises a condensate pump (14), and the condensate tank (13) is connected to the external floating roof tank (1) via the condensate pump (14).

5. The nitrogen filling inerting and exhaust liquid nitrogen cryogenic treatment system for an external floating roof tank according to claim 4, characterized in that: It further comprises an exhaust pipe (17), and the exhaust pipe (17) is connected to the cryogenic condenser (11).

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