Internal floating roof storage tank capable of recycling nitrogen

Abstract

The utility model discloses an internal floating roof storage tank capable of recycling nitrogen, which is used for storing organic liquid and at least comprises a tank body, a floating disc capable of moving up and down is arranged in the tank body, a liquid phase space is arranged below the floating disc, and a gas phase space is arranged above the floating disc; the air bag is cylindrical and is fixed on the upper surface of the floating disc; the upper end of the air bag is necked and is provided with a vent hole; the gas-phase space outside the air bag is an oil-gas space; the double-membrane gas holder is arranged outside the tank body and selectively communicated with the gas bag, and a space in an inner-layer membrane of the double-membrane gas holder is used for exhausting or inflating the gas bag. According to the utility model, through the arrangement of the double-membrane gas holder, low-concentration waste gas of which the main component is nitrogen can be recycled and used for inflating the gas bag, so that more effective energy conservation and emission reduction are realized.

Description

Technical Field

[0001] The utility model relates to the technical field of environmental protection and energy conservation, and particularly relates to an internal floating roof storage tank with nitrogen recycling. Background Art

[0002] Organic liquids such as oil products and organic chemicals are generally stored in storage tanks. When the organic liquid in the tank evaporates, volatile organic compounds (VOCs) will be generated and enter the gas space above the tank. These VOC-containing gases will be discharged into the atmosphere due to the "inhalation" and "exhaust" of the storage tank, causing environmental pollution and resource loss. Usually, for storage tanks of oil products and organic chemicals with relatively high vapor pressure, a floating roof needs to be installed in the tank, or an external floating roof storage tank or an internal floating roof storage tank needs to be built to control the emission of VOCs. However, by installing a floating roof, the exhaust gas concentration can only be reduced to a certain extent, far from meeting the emission standard requirements. In addition to adding a floating roof, in order to prevent the storage tank from introducing too much oxygen during inhalation, which may cause potential safety hazards and oxidation of oil products, a nitrogen seal is generally set in the storage tank. Nitrogen is supplemented into the tank body when the storage tank inhales to isolate the air. The consumption of nitrogen greatly increases the cost during the maintenance and use of the storage tank. In addition, the external floating roof or internal floating roof tank needs to be subjected to closed air extraction treatment, and the extracted gas needs to be subjected to VOC recovery or high-temperature oxidation treatment to achieve near-zero emission of exhaust gas.

[0003] Chinese Patent Application CN114435780A discloses an energy-saving and emission-reducing storage tank. The storage tank includes a shell, an internal airbag located inside the shell, an airbag support, and a U-shaped oil and gas conduit; the internal airbag includes an outer airbag and an inner airbag. The outer airbag and the inner airbag share an airbag top, and a ventilation hole is provided on the airbag top; the outer airbag has no airbag bottom, and the outer airbag is fixed on the airbag support and can move up and down along the support; the lower part of the outer airbag extends below the upper surface of the oil product; one pipe orifice of the U-shaped oil and gas conduit is located in the space surrounded by the outer airbag and the shell, and the other pipe orifice is located in the space surrounded by the outer airbag, the inner airbag and the oil product. This solution realizes the volume pressure balance and automatic volume adjustment of the oil and gas gas phase space in the inner and outer airbags of the storage tank through the setting of the inner and outer airbags and the U-shaped oil and gas conduit in the storage tank, and no volatile oil and gas is discharged into the atmosphere from the storage tank, thereby realizing zero emission of the exhaust gas of the storage tank.

[0004] This type of solution uses the pressure balance of the oil and gas gas phase space in the inner and outer airbags of the storage tank to recover and treat the escaped oil and gas. However, low-concentration exhaust gas and high-concentration oil and gas will be continuously output to the subsequent exhaust gas treatment device, and the subsequent exhaust gas treatment device will be frequently started, which is not conducive to energy conservation.

[0005] Therefore, there is an urgent need for an internal floating roof storage tank with nitrogen recycling, which can recycle the low-concentration exhaust gas mainly composed of nitrogen for inflating the airbag to achieve more effective energy conservation and emission reduction.

[0006] The information disclosed in this background section is only intended to enhance the overall understanding of the background of the present utility model and should not be regarded as an admission or any form of implication that this information constitutes prior art already known to those of ordinary skill in the art. Summary of the Utility Model

[0007] An object of the present utility model is to provide an internal floating roof storage tank with nitrogen recycling. Through the setting of a double - membrane gas holder, low - concentration waste gas mainly composed of nitrogen can be recycled and reused for inflating the airbag, achieving more effective energy conservation and emission reduction.

[0008] To achieve the above object, the present utility model provides an internal floating roof storage tank with nitrogen recycling for storing organic liquids, which at least includes: a tank body, inside which there is a floating disc that can move up and down. Below the floating disc is a liquid - phase space, and above the floating disc is a gas - phase space; an airbag, which is cylindrical and fixed on the upper surface of the floating disc; the upper end of the airbag is provided with a necking and has a ventilation hole; the inside of the airbag is a nitrogen space, and the gas - phase space outside the airbag is an oil - gas space; a double - membrane gas holder, which is arranged outside the tank and is selectively connected to the airbag, and the space in the inner membrane of the double - membrane gas holder is used to exhaust or inflate the airbag.

[0009] Further, in the above - mentioned technical solution, when the airbag is filled with nitrogen and in a fully stretched state, the volume ratio of the nitrogen space inside the airbag to the oil - gas space outside the airbag is preferably 9:1.

[0010] Further, in the above - mentioned technical solution, four connection points fixed to the top wall of the tank body can be provided at the top of the airbag, and the four connection points can be arranged axially symmetrically.

[0011] Further, in the above - mentioned technical solution, the double - membrane gas holder can be hemispherical and fixed on a base, and includes: an inner membrane, which is a flexible membrane and is used to store low - concentration waste gas mainly composed of nitrogen; an outer membrane, which is a flexible membrane and is used for protecting and heat - insulating the low - concentration waste gas.

[0012] Further, in the above - mentioned technical solution, the nitrogen space and the oil - gas space can be selectively connected to independently controlled nitrogen supply pipelines.

[0013] Further, in the above - mentioned technical solution, the nitrogen space can also be selectively connected to a low - concentration waste gas discharge pipeline. The low - concentration waste gas discharge pipeline can be provided with two branches connected to the double - membrane gas holder; a first centrifugal pump is provided on the first branch for pumping the low - concentration waste gas in the airbag to the double - membrane gas holder; a second centrifugal pump is provided on the second branch for filling the low - concentration waste gas in the double - membrane gas holder into the airbag.

[0014] Further, in the above - mentioned technical solution, the oil - gas space can also be selectively connected to a high - concentration oil - gas discharge pipeline.

[0015] Further, in the above technical solution, a pressure gauge for monitoring the oil and gas pressure is provided at the top of the tank body.

[0016] Further, in the above technical solution, flow meters and valves can be correspondingly provided on the nitrogen replenishing pipeline, the low-concentration waste gas discharge pipeline, and the high-concentration oil and gas discharge pipeline.

[0017] Compared with the prior art, the utility model has the following beneficial effects:

[0018] 1) By arranging a double-membrane gas holder and selectively connecting it with the airbag, the utility model can receive the exhaust gas from the airbag when the storage tank is refueled, and inflate the airbag when the storage tank is discharged, so as to realize the cyclic recovery and utilization of nitrogen in the airbag; in addition, since the volume of the nitrogen space B in the airbag is relatively larger than that of the oil and gas space A, most of the discharged gas can be nitrogen in the airbag on the premise of keeping the tank top pressure stable during refueling, thus reducing the waste gas emission of the internal floating roof storage tank.

[0019] 2) The inventor has found through research that the larger the proportion of the nitrogen space B, the greater the flexibility of the storage tank pressure regulation. When the volume ratio of the two is about 9:1, especially during the large breathing process of the storage tank, inflating and deflating the nitrogen space B in the airbag can basically balance the tank top pressure. Even when the pressure cannot be effectively regulated, only a small amount of high-concentration oil and gas in the oil and gas space A needs to be discharged, which can better achieve low oil and gas emissions at the source of the storage tank.

[0020] 3) The utility model fixes the bottom of the airbag on the upper surface of the floating roof and connects it to the top wall of the tank body through four fixing points at the top, which can better fix the position of the airbag, so that when the floating roof moves up and down to squeeze or release the airbag, the airbag will not shift, thus ensuring the stability of the upper end necking position of the airbag.

[0021] 4) Through the double-layer membrane setting of the double-membrane gas holder, the utility model can not only use the space inside the inner membrane to store low-concentration waste gas (that is, a mixture including a very small amount of waste gas and mainly nitrogen), but also use the outer membrane to insulate and protect the gas.

[0022] 5) The utility model can be applied in the large breathing and / or small breathing process of the storage tank. Under normal conditions, the contraction of the nitrogen space B in the airbag can be used to meet the requirement of basically stable tank top pressure. When the tank top pressure still cannot be adjusted to the required stable pressure in this case, a small amount of oil and gas can be appropriately discharged for pressure regulation to achieve the effect of energy conservation and emission reduction.

[0023] 6) For the storage tank adopting the present utility model, the oil product is hermetically separated from the air, which can ensure that the oil gas generated by the volatilization of the oil product is pure oil gas (excluding air), the gas itself has no explosiveness, and the volatilized oil gas can be safely controlled; the storage tank can be used in the storage process of oil products or organic chemicals, and has the characteristics of energy conservation, environmental protection, simple process and safe operation.

[0024] The above description is only an overview of the technical solution of the present utility model. In order to be able to more clearly understand the technical means of the present utility model and implement it according to the content of the specification, and at the same time to make the above and other purposes, technical features and advantages of the present utility model more understandable, one or more preferred embodiments are listed below and described in detail with the accompanying drawings as follows. Description of the Drawings

[0025] Figure 1 It is a schematic connection structure diagram of the internal floating roof storage tank for nitrogen recycling of the present utility model.

[0026] Main reference numerals description:

[0027] 1 - Tank body, 10 - Floating disc, 11 - Tank top pressure gauge, 2 - Airbag, 21 - Vent hole, 3 - Double - membrane gas holder, 30 - Base, 31 - First centrifugal pump, 32 - Second centrifugal pump, 4 - Nitrogen make - up gas pipeline, 40 - Nitrogen flowmeter, 41 - First make - up gas branch, 411 - First nitrogen valve, 42 - Second make - up gas branch, 421 - Second nitrogen valve, 5 - Low - concentration waste gas discharge pipeline, 50 - Waste gas flowmeter, 51 - Waste gas valve, 52 - First waste gas branch, 53 - Second waste gas branch, 6 - High - concentration oil gas discharge pipeline, 60 - Oil gas flowmeter, 61 - Oil gas valve;

[0028] A - Oil gas space, B - Nitrogen space. Detailed Embodiments

[0029] The following combines the accompanying drawings to describe the detailed embodiments of the present utility model in detail, but it should be understood that the protection scope of the present utility model is not limited by the detailed embodiments.

[0030] Unless otherwise clearly stated, in the whole specification and claims, the term "comprising" or its variations such as "including" or "having" etc. will be understood to include the stated elements or components, without excluding other elements or other components.

[0031] In this text, for the convenience of description, spatial relative terms such as "below", "beneath", "under", "above", "over", "on" etc. may be used to describe the relationship between one element or feature and another element or feature in the accompanying drawings. It should be understood that spatial relative terms are intended to encompass different directions of an object in use or operation in addition to the directions depicted in the figures. For example, if the object in the figure is flipped, an element described as "below" or "under" another element or feature will be oriented "above" that element or feature. Thus, the exemplary term "below" can encompass both the lower and upper directions. The object can also have other orientations (rotated 90 degrees or other orientations) and the spatial relative terms used herein should be interpreted accordingly.

[0032] In this text, the terms "first", "second", etc. are used to distinguish two different elements or parts, and are not used to define a specific position or relative relationship. In other words, in some embodiments, the terms "first", "second", etc. can also be interchanged with each other.

[0033] As Figure 1 shown, the present utility model provides an internal floating roof storage tank for nitrogen recycling, which is used for storing organic liquids such as oil products and organic chemicals, and at least includes a tank body 1, an airbag 2 and a double-membrane gas holder 3. Among them, a floating tray 10 (i.e., the internal floating roof storage tank) that can move up and down is arranged in the tank body 1. Below the floating tray 10 is a liquid phase space, and above the floating tray is a gas phase space. The airbag 2 is cylindrical and fixed on the upper surface of the floating tray 10; the upper end of the airbag 2 is provided with a necking and has a vent hole 21; the inside of the airbag is a nitrogen space B, and the gas phase space outside the airbag is an oil and gas space A. The double-membrane gas holder 3 is arranged outside the tank body 1 and is selectively communicated with the airbag 2. The space in the inner membrane of the double-membrane gas holder 3 is used to exhaust or inflate the airbag.

[0034] Through the above technical solution of the present utility model, by arranging a double-membrane gas holder and selectively communicating it with the airbag, the exhaust gas from the airbag can be received when the storage tank is refueled, and the airbag can be inflated when the storage tank is drained, so as to realize the cyclic recovery and utilization of nitrogen in the airbag; in addition, since the volume of the nitrogen space B in the airbag is relatively larger than that of the oil and gas space A, most of the discharged gas can be nitrogen in the airbag under the premise of keeping the tank top pressure stable during refueling, thereby reducing the waste gas emission of the internal floating roof storage tank. It should be noted here that: the airbag material used in the present utility model is an organic polymer membrane material, and this kind of membrane material generally absorbs molecules that are similar and compatible with it. The gas phase space outside the airbag (i.e., the oil and gas space A) contains high-concentration oil and gas. Under the condition of relatively high pressure, a very small amount of oil and gas will penetrate into the nitrogen space B in the airbag. Therefore, after a period of time, there may be a mixture of nitrogen + a small amount of waste gas in the nitrogen space B, that is, nitrogen containing a low VOCs concentration ( Figure 1 the low-concentration waste gas in

[0035] Further, preferably but not limited to, when the airbag 2 is filled with nitrogen and in a fully expanded state, the volume ratio of the nitrogen space B in the airbag 2 to the oil-gas space A outside the airbag is 9:1. The inventor has found through research that the larger the proportion of the nitrogen space B, the greater the flexibility of the storage tank pressure regulation. When the volume ratio of the two is about 9:1, especially during the large breathing process of the storage tank, inflating and deflating the nitrogen space B in the airbag can basically balance the tank top pressure. Even when the pressure cannot be effectively regulated, only a small amount of high-concentration oil and gas in the oil-gas space A needs to be discharged, which can better achieve low emissions of oil and gas at the source of the storage tank.

[0036] Further, four connection points (not shown in the figure) fixed to the top wall of the tank body 1 can be provided at the top of the airbag 2, and the four connection points are preferably arranged axially symmetrically. By fixing the bottom of the airbag 2 on the upper surface of the floating roof 10 and connecting it to the top wall of the tank body 1 through the four fixing points at the top, the position of the airbag 2 can be better fixed, so that when the floating roof moves up and down to squeeze or release the airbag, the airbag 2 will not shift, thereby ensuring the stability of the upper end necking position of the airbag.

[0037] Further as Figure 1 shown, the double-membrane gas holder 3 is preferably hemispherical and fixed on the base 30. The double-membrane gas holder 3 includes an inner membrane and an outer membrane (not shown in the figure). Among them, the inner membrane is a flexible membrane and is used to store low-concentration waste gas mainly composed of nitrogen; the outer membrane is also a flexible membrane and is used for the protection and heat insulation of the low-concentration waste gas. Through the setting of the double-layer membrane, not only can the space inside the inner membrane be used to store low-concentration waste gas (that is, a mixture including a very small amount of waste gas and mainly nitrogen), but also the outer membrane can be used to insulate and protect the gas.

[0038] Further as Figure 1 shown, in order to maintain the stability of the tank top pressure during the large breathing and / or small breathing process of the storage tank, the present utility model also designs a nitrogen supply pipeline 4, a low-concentration waste gas discharge pipeline 5, and a high-concentration oil and gas discharge pipeline 6. The nitrogen space B and the oil-gas space A are respectively selectively communicated with the independently controlled nitrogen supply pipeline. Referring to Figure 1 , a nitrogen flowmeter 40 is provided on the nitrogen supply pipeline 4 to facilitate the statistics of the amount of nitrogen entering the A and B spaces of the storage tank. The nitrogen supply pipeline 4 includes a first air supply branch 41 (for supplying nitrogen to the nitrogen space B) and a second air supply branch 42 (for supplying nitrogen to the oil-gas space A). A first nitrogen valve 411 is provided on the first air supply branch 41, and a second nitrogen valve 421 is provided on the second air supply branch 42.

[0039] Further as Figure 1As shown, the low-concentration waste gas discharge pipeline 5 is selectively connected to the nitrogen space B. An exhaust gas flowmeter 50 and an exhaust gas valve 51 are provided on the low-concentration waste gas discharge pipeline 5. The low-concentration waste gas discharge pipeline 5 is provided with two branches connected to the double-membrane gas holder 3; a first centrifugal pump 31 is provided on the first waste gas branch 52 for pumping the low-concentration waste gas in the airbag 2 into the double-membrane gas holder 3 during the oil inlet process of the storage tank; a second centrifugal pump 32 is provided on the second waste gas branch 53 for filling the low-concentration waste gas in the double-membrane gas holder 3 into the airbag 2 during the oil outlet process of the storage tank.

[0040] Further as Figure 1 shown, the high-concentration oil and gas discharge pipeline 6 is selectively connected to the oil and gas space A. An oil and gas flowmeter 60 and an oil and gas valve 61 are provided on the high-concentration oil and gas discharge pipeline 6. When the storage tank is receiving oil and the tank top pressure cannot be adjusted only by the compression of the space inside the airbag, a small amount of oil and gas in the oil and gas space A can be appropriately discharged. This part of the oil and gas can enter the downstream oil and gas recovery and treatment device (not shown in the figure) through the high-concentration oil and gas discharge pipeline 6 for treatment.

[0041] Further as Figure 1 shown, a pressure gauge 11 for monitoring the oil and gas pressure is provided at the top of the tank body 1. Through this pressure gauge 11, the pressure change can be monitored in real time, and the exhaust or inflation of the nitrogen space B of the airbag can be controlled according to the pressure change. When the exhaust and inflation of the airbag cannot stabilize the tank top pressure, the exhaust or nitrogen filling of the aforementioned oil and gas space A can be further carried out.

[0042] The working process of the internal floating roof storage tank for nitrogen recycling of the present utility model will be described in detail below:

[0043] Before the storage tank is put into use, first install the airbag 2 inside the storage tank, and then introduce nitrogen into the space A to complete the air replacement of the storage tank; then, fill nitrogen into the space B inside the airbag. While filling, the exhaust gas volume of the space A is measured by the flowmeter 60 (i.e., FT101). When the exhaust gas volume reaches a certain value, observe that the airbag has fully expanded, and stop filling nitrogen. At this time, the oil receiving can be prepared. The oil receiving is the storage process, and the oil using is the oil outlet process. These two processes are the large breathing processes of the storage tank.

[0044] During the process of oil filling the storage tank, the float 10 rises with the rise of the liquid level. The liquid level continues to rise during the oil filling process, and the float also moves upward, and the air bag is compressed until the oil filling is completed. This process will produce a large amount of oil and gas; monitor the tank top pressure. For example, when the tank top pressure reaches 750Pa, open the exhaust valve 51 (also known as KV-102), start the first centrifugal pump 31, and pump the nitrogen containing low-concentration VOCs in the B space in the storage tank (also known as the space in the air bag) into the double-membrane gas cabinet 3 for storage; when the tank top pressure is less than 700Pa, close the exhaust valve 51 (also known as KV-102), and stop the first centrifugal pump 31. The purpose of this utility model is to minimize the emission of high-concentration VOCs oil and gas from the A space.

[0045] When the tank top pressure is too high and space B has shrunk to its minimum state, it is necessary to discharge high-concentration exhaust gas from space A to ensure the safety of the tank. That is, when the tank top pressure reaches 800Pa, the oil and gas valve 61 (also known as KV-101) is opened and space A begins to exhaust. When the tank top pressure reaches 600Pa, the oil and gas valve 61 is closed.

[0046] The oil level of the storage tank is continuously reduced during the oil discharge process until the oil discharge is completed. During this process, the tank top pressure is continuously reduced. When the tank top pressure is low, it is necessary to replenish nitrogen in the tank in time. That is, when the tank top pressure gauge 11 (i.e. PT-101) reading reaches 300Pa, nitrogen can be replenished to the A space in the tank first, and the tank top pressure is maintained at 600Pa during the nitrogen replenishment process (i.e., nitrogen replenishment is stopped when the pressure reaches 600Pa), and then nitrogen is replenished to the B space. In order to reduce the use of fresh nitrogen, the nitrogen replenished to the B space can be transported by the nitrogen containing low concentration of VOCs stored in the double membrane gas cabinet 3 through the second centrifugal pump 32 (i.e. P-102). During the nitrogen replenishment process, the exhaust valve 51 (i.e. KV-102) is opened, and the second centrifugal pump 32 is started. When the pressure reaches 600Pa, the nitrogen replenishment is stopped, the exhaust valve 51 is closed, and the second centrifugal pump 32 is stopped. During the nitrogen replenishment process, the airbag 2 returns to a cylindrical shape after the B space is replenished with nitrogen. Here, the maximum amount of gas discharged from the B space to the double membrane gas holder 3 and the maximum amount of gas replenished from the double membrane gas holder to the B space are the same.

[0047] During the storage process of the storage tank, "inhalation" and "exhaust" (i.e., the minor breathing process) will occur due to the influence of temperature, environmental changes, etc. At this time, the "inhalation" and "exhaust" of the storage tank will cause slight fluctuations in the liquid level inside the tank. Similar to the oil inlet and outlet processes, the pressure at the top of the storage tank is detected. When the pressure at the top of the tank is higher than 750 Pa, the waste gas valve 51 is opened, and the first centrifugal pump 31 is started. The space B starts to exhaust gas to the double-membrane gas holder 3; when the pressure at the top of the tank is less than 700 Pa, the waste gas valve 51 is closed, and the first centrifugal pump 31 is stopped. When the pressure at the top of the tank is lower than 550 Pa, nitrogen is first supplied to the space A inside the tank, and when the pressure reaches 600 Pa, the nitrogen supply stops; then nitrogen is supplied from the double-membrane gas holder 3 to the space B, the waste gas valve 51 is opened, and the second centrifugal pump 32 is started. When the pressure reaches 600 Pa, the nitrogen supply stops. After the space B is replenished with nitrogen, the airbag will return to a cylindrical shape.

[0048] Therefore, the internal floating roof storage tank with nitrogen recycling of the present utility model can be applied in the major breathing and / or minor breathing processes of the storage tank. Under normal conditions (i.e., when the pressure at the top of the tank is not too high), the contraction of the nitrogen space B inside the airbag can be preferentially used to meet the requirement of basically stable pressure at the top of the tank. In this case, when the pressure at the top of the tank cannot be adjusted to the required stable pressure, a small amount of oil and gas can be appropriately discharged for pressure regulation to achieve the effect of energy conservation and emission reduction.

[0049] The foregoing description of the specific exemplary embodiments of the present utility model is for the purposes of illustration and exemplification. These descriptions are not intended to limit the present utility model to the precise forms disclosed, and obviously, many changes and variations are possible in light of the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present utility model and its practical applications, so that those skilled in the art can implement and utilize various different exemplary embodiments of the present utility model, as well as various different selections and changes. Any simple modifications, equivalent changes, and modifications made to the above exemplary embodiments shall fall within the protection scope of the present utility model.

Claims

1. An internal floating roof storage tank for nitrogen recycling, characterized in that: For storage of organic liquids, including: The tank body is provided with a floating plate that can move up and down, the space below the floating plate is a liquid phase, and the space above the floating plate is a gas phase; The airbag is cylindrical and fixed on the upper surface of the floating plate; the upper end of the airbag is configured as a constricted opening and has a vent hole; the airbag contains a nitrogen space, and the gas phase space outside the airbag is an oil and gas space; A double-membrane gas cabinet is arranged outside the tank body and selectively communicated with the air bag. The space in the inner membrane of the double-membrane gas cabinet is used to exhaust or inflate the air bag.

2. The internal floating roof storage tank for nitrogen recycling according to claim 1, characterized in that: When the airbag is filled with nitrogen and is in a fully expanded state, the volume ratio of the nitrogen space inside the airbag to the oil and gas space outside the airbag is 9:

1.

3. The internal floating roof storage tank for nitrogen recycling according to claim 1, characterized in that: The top of the airbag is provided with four connection points fixed to the top wall of the tank body, and the four connection points are arranged in an axisymmetric manner.

4. The internal floating roof storage tank for nitrogen recycling according to claim 1, characterized in that: The double-membrane gas cabinet is hemispherical and fixed on a base, and comprises: An inner membrane, which is a flexible membrane and is used to store low-concentration exhaust gas whose main component is nitrogen; The outer film is a flexible film and is used for the protection and heat insulation of the low-concentration exhaust gas.

5. The internal floating roof storage tank for nitrogen recycling according to claim 1, characterized in that: The nitrogen space and the oil-gas space are selectively connected to independently controlled nitrogen gas supply pipelines.

6. The internal floating roof storage tank for nitrogen recycling according to claim 5, characterized in that: The nitrogen space is also selectively connected to a low-concentration exhaust gas discharge pipeline.

7. The internal floating roof storage tank for nitrogen recycling according to claim 6, characterized in that: The low-concentration exhaust gas discharge pipeline is provided with two branches connected to the double-membrane gasholder; a first centrifugal pump is provided on the first branch for extracting the low-concentration exhaust gas in the airbag into the double-membrane gasholder; a second centrifugal pump is provided on the second branch for filling the low-concentration exhaust gas in the double-membrane gasholder into the airbag.

8. The internal floating roof storage tank for nitrogen recycling according to claim 7, characterized in that: The oil and gas space is also selectively connected to a high-concentration oil and gas discharge pipeline.

9. The internal floating roof storage tank for nitrogen recycling according to claim 1, characterized in that: A pressure gauge for monitoring oil and gas pressure is provided on the top of the tank.

10. The internal floating roof storage tank for nitrogen recycling according to claim 8, characterized in that: The nitrogen gas supply pipeline, the low-concentration exhaust gas discharge pipeline and the high-concentration oil and gas discharge pipeline are all provided with flow meters and valves accordingly.

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