Safety control system for volatile liquid normal-pressure and low-pressure storage tank

Abstract

The utility model provides a volatile liquid normal pressure and low pressure storage tank safety control system which comprises a tank body, a fire retardant system, a pressure control system, a liquid level system, a cut-off system and a nitrogen sealing system, the fire retardant system comprises a fire barrier, the pressure control system comprises a breather valve and a pressure release valve, and the nitrogen sealing system comprises a nitrogen sealing valve and a nitrogen supply pipe. The connecting pipe position of a nitrogen supply pipe connected with the nitrogen seal valve is arranged at the position away from the connector of the breather valve and is inserted into the tank body, the cut-off system comprises an evaporation gas recovery valve and a cut-off valve, and the liquid level system comprises a liquid level meter, a liquid level transmitter and a liquid level control valve. According to the utility model, a fire-retardant explosion-proof system, a nitrogen sealing system, a pressure control system, a cut-off system and a temperature, pressure and liquid level monitoring system are integrated on the top of a normal-pressure or low-pressure storage tank, so that the safe operation of the storage tank is greatly improved, and safety and environmental protection accidents can be effectively prevented.

Description

Technical Field

[0001] The utility model relates to the technical field of oil product and chemical storage and transportation and oil and gas management, and in particular to a safety control system for normal pressure and low pressure storage tanks of volatile liquids. Background Art

[0002] With the development of petrochemical equipment capacity towards large-scale development and the expansion trend of refining and chemical integration, the capacity of liquid oil and chemical tank areas is getting larger and larger, and the number and variety of tank groups are becoming more and more diverse, posing new challenges to the overall safety of tank areas. The serious dangers of oil and chemical liquid storage tanks themselves and the serious consequences of accidents have made tank areas a focus of safety in the petrochemical field. How to ensure the safety of oil and chemical liquid storage tanks has become a technical problem in the storage and transportation of oil and chemicals.

[0003] The significance of intrinsic safety and explosion protection in tank areas is to eliminate or reduce the probability of accidents, improve the level of intrinsic safety in the storage and transportation of liquid oil and chemicals, and provide safety technical guarantees for capacity expansion. The main factors affecting the safety of liquid storage tanks are: fire and explosion, nitrogen sealing system, pressure control, etc.

[0004] The storage tanks in the petroleum refining and chemical industry mostly store flammable, explosive, and volatile media. In order to prevent leakage or the storage media from coming into contact with air, which poses a safety hazard and environmental pollution, nitrogen is usually filled into the gas phase space of the storage tank to isolate it from the air. This measure of using nitrogen as the protective gas for the storage tank is called a storage tank nitrogen sealing system. The pressure of the storage tank nitrogen sealing system is generally maintained at 0.5-1.5kPa. The main functions of nitrogen sealing are as follows: maintaining a slight positive pressure in the tank, preventing air or dust from entering the tank, ensuring the quality of the medium product, ensuring that the medium does not come into contact with the air, and preventing the medium from absorbing moisture or being oxidized; after nitrogen sealing, the gas space in the tank is a mixture of the medium and nitrogen, which can reduce the probability of forming a mixed explosive gas.

[0005] The tail gas single-call valve on the top of the atmospheric storage tank is connected to the recovery. If the pressure control design is not well considered, the following problems will occur: the breathing exhaust gas during the tank feeding is discharged through the single-call valve to the tail gas collection pipe and then to the recovery device. The discharge is not smooth. While the single-call valve is discharging, the breathing valve is also discharging to the atmosphere; if the exhaust fan is added to the collection pipe, the negative pressure value is not well controlled, which will cause nitrogen to be replenished while exhausting, and in severe cases, the storage tank will be deflated. The reasons that affect the deflation of the storage tank are generally the following: breathing valve obstruction, self-operated regulating valve failure, sudden weather changes, and insufficient nitrogen replenishment in the nitrogen sealing system.

[0006] When the oil is stored in a normal pressure tank, even if the tank is insulated, the temperature of the gas space and the oil surface in the tank will rise as the atmospheric temperature rises and the intensity of solar radiation increases, the volume of the mixed gas in the gas space expands, and the oil evaporates more rapidly, increasing the pressure of the mixed gas. When the pressure in the tank increases to the set value, VOCs will be exhaled out of the tank. When the normal pressure tank is collecting oil, the oil will flash into the tank and produce some VOCs. As the oil level rises, the mixed gas in the gas space is compressed, and the pressure in the tank continues to rise. When the pressure in the tank increases to the set value, VOCs will be exhaled out of the tank. Summary of the invention

[0007] In order to solve the problem in the above-mentioned prior art that the breathing exhaust gas during the storage tank feeding is discharged into the tail gas collection pipe and then into the recovery device through the single exhalation valve, the breathing valve is discharged to the atmosphere at the same time as the single exhalation valve is discharged; an exhaust fan is added to the collection pipe, and poor control of the negative pressure value will cause nitrogen to be replenished and exhaust gas to be discharged at the same time, and in severe cases, the storage tank will be deflated. When the atmospheric pressure storage tank is stationary to store oil, as the pressure in the tank increases to the set value, VOCs will be exhaled out of the tank.

[0008] The utility model proposes a safety control system for normal pressure and low pressure storage tanks of volatile liquids. The utility model is realized through the following technical solutions:

[0009] The utility model comprises a tank body, a fire-blocking system, a pressure control system, a liquid level system, a cut-off system and a nitrogen sealing system, wherein the fire-blocking system, the nitrogen sealing system, the cut-off system and the pressure control system are all arranged on the top of the tank body; a part of the liquid level system is arranged on the side wall of the tank body near the bottom, and the other part is arranged inside the tank body.

[0010] The fire arresting system includes a flame arrester, the pressure control system includes a breathing valve and a pressure relief valve, the nitrogen sealing system includes a nitrogen sealing valve and a nitrogen supply pipe, the flame arrester, the breathing valve, the nitrogen sealing valve and the pressure relief valve are all arranged on the top of the tank body, and the connecting pipe position of the nitrogen supply pipe connected to the nitrogen sealing valve is arranged at an interface far away from the breathing valve and inserted into the tank body,

[0011] The cut-off system includes an evaporation gas recovery valve and a cut-off valve. The evaporation gas recovery valve is arranged between the flame arrester and the tank body. The cut-off valve is arranged on the connecting pipeline between the tank body and the oil and gas recovery device. It also includes a second pressure transmitter and a first pressure transmitter arranged on the collecting main pipe.

[0012] The liquid level system comprises a liquid level meter, a liquid level transmitter and a liquid level control valve. The liquid level control valve is arranged on the liquid feed and discharge pipes, and the liquid level meter and the liquid level transmitter are arranged on the side of the tank body.

[0013] Furthermore, the nitrogen sealing valve is a self-operated nitrogen sealing valve.

[0014] Furthermore, the nitrogen supply pipe is inserted into the tank body by a distance of 200 mm.

[0015] Furthermore, the opening pressure of the pressure relief valve is ≤ the designed positive pressure of the storage tank; the pressure at which the breathing valve reaches the maximum suction volume is ≤ the designed negative pressure of the storage tank; the opening pressure of the relief valve is ≥ the opening pressure of the breathing valve ≥ the opening pressure of the nitrogen sealing valve.

[0016] Furthermore, the control system also includes a thermometer and a temperature transmitter, and the temperature transmitter is arranged near the thermometer.

[0017] Furthermore, the thermometer is arranged on the floating roof tank and the internal floating roof tank, 700mm-1000mm above the tank bottom.

[0018] Furthermore, the thermometer is arranged in a manner of being fixed on the top tank and arranged 700mm-1500mm above the tank bottom.

[0019] Compared with the prior art, the beneficial effects of the utility model are:

[0020] 1. The fire-proof and explosion-proof system, nitrogen sealing system, pressure control system, cut-off system, temperature, pressure and liquid level monitoring system are integrated on the top of a normal pressure or low pressure storage tank, which greatly improves the safe operation of the storage tank. Control measures are pre-set for problems such as overpressure, overtemperature, combustion, explosion, environmental pollution, etc. that may exist during the storage of oil and chemicals, which can effectively prevent the occurrence of safety and environmental accidents.

[0021] Advantages and features of the present invention will be illustrated and explained by the following non-limiting description of preferred embodiments, which are given as examples only with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of the utility model system.

[0023] Indicated in the figure:

[0024] 1. Tank body; 2. Nitrogen sealing valve; 3. Breathing valve; 4. Pressure relief valve; 5. Evaporative gas recovery valve; 6. Flame arrester; 7. First pressure transmitter; 8. Second pressure transmitter; 9. Temperature transmitter; 10. Thermometer; 11. Liquid level gauge; 12. Liquid level transmitter; 13. Liquid level control valve. DETAILED DESCRIPTION

[0025] The present application is further described below in conjunction with the accompanying drawings and embodiments.

[0026] like Figure 1As shown, the utility model comprises a tank body 1, a fire-blocking system, a pressure control system, a liquid level system, a cut-off system and a nitrogen sealing system. The fire-blocking system, the nitrogen sealing system, the cut-off system and the pressure control system are all arranged on the top of the tank body 1; the liquid level system is composed of a liquid level detection system arranged on the side of the tank body and a regulating system arranged on the feed and discharge liquid pipelines.

[0027] The fire arresting system includes a flame arrester 6. The flame arrester 6 on the gas phase connecting pipe adopts a pipeline type flame arrester and has a bidirectional fire arresting function. The installation position is close to the tank mouth on the top of the tank body 1. If the storage tank is a connected tank group, then each tank top connected to the tank group needs to be installed with an independent flame arrester 6. When the distance of the potential fire source cannot be determined, a non-steady-state detonation arrester needs to be selected.

[0028] If the tank is equipped with a single call valve, the flame arrester can be installed at the tank mouth or the outlet of the single call valve, and the type should be a non-steady-state detonation flame arrester with a two-way flame arresting function.

[0029] The design pressure of petrochemical atmospheric pressure storage tanks is mostly 2kPa, and the pressure drop of the flame arrester should not be greater than 0.3kPa.

[0030] The pressure control system comprises a breathing valve 3 and a pressure relief valve 4, both of which are arranged on the top of the tank body 1, and has two control systems: a positive pressure control system and a negative pressure control system.

[0031] Positive pressure control system: A pressure control system with safety accessories is used to ensure that the low-pressure storage tank will not be damaged due to overpressure. When the pressure in the storage tank rises due to feeding or temperature rise, the gas is first exhausted through the exhaust regulating valve (self-operated regulating valve); if the pressure continues to rise and reaches the set value of the breathing valve 3, the gas is exhausted to the outside through the breathing valve 3; if the pressure continues to rise and reaches the set value of the pressure relief valve 4, the pressure relief valve 4 opens to release the overpressure gas.

[0032] Negative pressure control system: Use pressure control system plus safety accessories to ensure that low-pressure storage tanks will not be damaged due to excessive negative pressure. When the pressure in the storage tank drops due to discharge or lower temperature, first use the nitrogen-sealed regulating valve (or self-operated regulating valve) to replenish air to maintain the pressure in the tank. If the pressure continues to drop and reaches the set value of the breathing valve 3, then use the breathing valve 3 to replenish air to ensure that the storage tank will not be damaged due to excessive vacuum. However, oxygen will enter the system at this time. If the nitrogen sealing system is reliable and has sufficient capacity, the breathing valve 3 can also be connected to the nitrogen sealing system to ensure that no oxygen enters the system. If the amount of nitrogen cannot be guaranteed and oxygen cannot be completely prevented from entering the system, an online oxygen content analyzer can be set up or the oxygen content of the exhaust can be regularly analyzed to ensure system safety. If the medium is not allowed to contact the air, its breathing valve 3 should be connected to the nitrogen sealing system.

[0033] The nitrogen sealing system includes a nitrogen sealing valve 2 and a nitrogen supply pipe. The working principle of the nitrogen sealing system is that when the pressure in the storage tank drops and is lower than the set value, the nitrogen sealing valve 2 opens to add nitrogen to the tank; when the pressure in the storage tank reaches the set pressure, the nitrogen sealing valve 2 closes and stops adding nitrogen; when the pressure in the storage tank rises and reaches the set value, the gas is discharged to the outside of the tank through the nitrogen sealing valve 2 or the breathing valve 3. Compared with the atmospheric pressure storage tank, the low-pressure storage tank has a relatively high design pressure, so the range of allowable changes in the operating pressure of the storage tank is wider, which is conducive to the selection of the regulation system. At the same time, it can also avoid the frequent operation of the pressure regulating valve or self-operated regulating valve on the gas phase inlet and outlet pipelines, reducing the chance of damage.

[0034] Regarding the installation position of the nitrogen sealing system. The connection position of the nitrogen supply pipe connected to the nitrogen sealing valve 2 should be far away from the interface of the breathing valve 3 and inserted into the tank for about 200mm, so that the nitrogen will not be discharged directly after entering the tank, and the purpose of nitrogen sealing can be better achieved.

[0035] The nitrogen sealing valve 2 may be an on-off type nitrogen sealing valve or a self-operated nitrogen sealing valve, and the self-operated nitrogen sealing valve is preferred.

[0036] When an on-off nitrogen sealing valve is used, when the storage tank is discharged and (or) due to the decrease in external temperature, the pressure of the storage tank will decrease. When the pressure at the pressure source point decreases to the set opening pressure of the nitrogen sealing valve 2 (generally 200Pa), the nitrogen sealing valve 2 will open, and there will be a resistance drop in the pipeline behind the valve. When the pressure at the pressure source point is higher than the set closing pressure of the nitrogen sealing valve 2 (generally 500Pa), the nitrogen sealing valve 2 will close, but at this time, the pressure in the storage tank has not actually reached the set closing pressure of the nitrogen sealing valve 2; after the nitrogen sealing valve 2 is closed, the resistance drop will disappear, and the pressure at the pressure source point will return to below the set opening pressure of the nitrogen sealing valve 2, and the nitrogen sealing valve 2 will open again to replenish nitrogen, and the cycle will be repeated. When the air replenishment speed of the nitrogen sealing valve 2 cannot keep up with the pressure reduction speed of the storage tank, the pressure of the storage tank will continue to decrease, and it may decrease to the set suction pressure of the breathing valve 3 (-300PaG). At this time, the breathing valve 3 inhales air, affecting the nitrogen sealing effect of the storage tank.

[0037] When using a self-operated nitrogen sealing valve, when the tank is exposed to the elements and / or the outside temperature drops, the tank pressure will drop. When the pressure at the pressure source drops to the set pressure of nitrogen sealing valve 2 (generally 300PaG), nitrogen sealing valve 2 will open. The self-operated nitrogen sealing valve will automatically adjust the valve opening to balance the pressure at the pressure source to a value lower than the set pressure of nitrogen sealing valve 2 (generally 300PaG). The reasons for giving priority to self-operated nitrogen sealing valves are summarized as follows: simple, reliable, and safe; pure mechanical structure, more reliable, durable, and easy to maintain; self-operated, no additional gas source and power supply required; extra-large diaphragm senses small pressure difference changes and responds quickly.

[0038] Storage tanks using a nitrogen sealing system must be equipped with a pressure relief valve4.

[0039] Design pressure of nitrogen sealing system valves: the opening pressure of pressure relief valve 4 ≤ the designed positive pressure of the tank; the pressure at which the breathing valve 3 reaches the maximum suction volume shall not exceed the designed negative pressure of the tank; the opening pressure of relief valve 4 ≥ the opening pressure of breathing valve 3 ≥ the opening pressure of nitrogen sealing valve 2.

[0040] When the evaporation gas or volatile gas of the storage tank may pollute the environment, or its evaporation gas has recycling value, it is necessary to recycle or process its evaporation gas. At this time, the storage tank needs to be equipped with a cut-off system. The cut-off system includes an evaporation gas recovery valve 5, a cut-off valve, etc.

[0041] The evaporative gas recovery valve 5 is arranged between the flame arrester 6 and the tank body 1. The working principle of the evaporative gas recovery valve 5 is: when the material is pumped into the storage tank and the temperature rises, the pressure is released to protect the storage tank; when the pressure is higher than the set point, it is opened and the pressure is released; it is usually used for storage media that may generate flammable gases or cause pollution to the environment, and the evaporative gas is discharged to the recovery device or processing equipment through the pipe.

[0042] When the storage tank is equipped with an oil and gas recovery device, a shut-off valve needs to be installed on the connecting pipe between the tank and the oil and gas recovery device. The shut-off valve is installed at the location of the tank group collection main pipe near the oil and gas recovery device. The opening state of the shut-off valve is controlled by the second pressure transmitter 8 on the collection main pipe through 2oo2 interlocking. When the pressure on the gas phase collection main pipe reaches the set upper limit pressure value, the shut-off valve is opened to send the oil and gas to the oil and gas recovery device for recovery; the closing state of the shut-off valve is controlled by the first pressure transmitter 7 on the collection main pipe through 1oo2 interlocking. When the pressure on the gas phase collection main pipe reaches the set minimum pressure value, the shut-off valve is closed to stop oil and gas recovery.

[0043] A single call valve is installed upstream of the anti-detonation flame arrester on the oil and gas collection pipeline of the storage tank. The single call valve is mechanically operated by the pressure in the tank. The exhaust start setting pressure should be lower than the exhalation start pressure of the tank top breathing valve, and the closing setting pressure is higher than the inhalation start pressure of the tank top breathing valve. If the storage tank is equipped with nitrogen protection, this pressure should also be higher than the closing pressure of nitrogen protection.

[0044] The liquid level system includes a liquid level meter 11, a liquid level transmitter 12 and a liquid level control valve 13. The liquid level control valve 13 is arranged on the feed and discharge pipes of the tank body 1, and is used to control the inlet and outlet rate of the volatile liquid. The liquid level meter 11 and the liquid level transmitter 12 are arranged on the side of the tank body 1, and are used to indicate the liquid level in the tank in real time. When the liquid level is below the maximum liquid level control value, the liquid level control valve 13 is opened, and when the liquid level reaches the maximum liquid level control value, the liquid level control valve 13 is closed and cannot be opened.

[0045] In addition to the above systems, the tank body 1 should also be provided with a thermometer 10 and a temperature transmitter 9. The thermometer on the floating roof tank and the internal floating roof tank should be installed 700mm-1000mm above the tank bottom. The thermometer on the fixed roof tank should be installed 700mm-1500mm above the tank bottom. When there is a heater in the tank, the upper limit should be taken, and when there is no heater, the lower limit should be taken. The temperature transmitter 9 is arranged near the thermometer 10, and is used to send the measured value of the thermometer 10 to the control room in real time.

[0046] In addition to the above embodiments, the present application may also have other implementation modes. Any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present application.

Claims

1. A safety control system for atmospheric and low pressure storage tanks of volatile liquids, characterized in that: The invention comprises a tank body (1), a fire-blocking system, a pressure control system, a liquid level system, a cut-off system and a nitrogen sealing system, wherein the fire-blocking system, the nitrogen sealing system, the cut-off system and the pressure control system are all arranged on the top of the tank body (1); the liquid level system is composed of a liquid level detection system arranged on the side of the tank body and a regulating system arranged on the feed and discharge liquid pipelines. The fire arresting system comprises a flame arrester (6), the pressure control system comprises a breathing valve (3) and a pressure relief valve (4), the nitrogen sealing system comprises a nitrogen sealing valve (2) and a nitrogen supply pipe, the flame arrester (6), the breathing valve (3), the nitrogen sealing valve (2) and the pressure relief valve (4) are all arranged on the top of the tank body (1), the connecting pipe position of the nitrogen supply pipe connected to the nitrogen sealing valve (2) is arranged at an interface far away from the breathing valve (3), and is inserted into the tank body (1), The cut-off system comprises an evaporative gas recovery valve (5) and a cut-off valve, wherein the evaporative gas recovery valve (5) is arranged between the flame arrester (6) and the tank body (1), and the cut-off valve is arranged on a connecting pipe between the tank body (1) and the oil vapor recovery device, and further comprises a second pressure transmitter (8) and a first pressure transmitter (7) arranged on the collecting main pipe. The liquid level system comprises a liquid level meter (11), a liquid level transmitter (12) and a liquid level control valve (13); the liquid level control valve (13) is arranged on the feed and discharge pipes of the tank body (1); and the liquid level meter (11) and the liquid level transmitter (12) are arranged on the side of the tank body (1).

2. A volatile liquid normal pressure and low pressure storage tank safety control system according to claim 1, characterized in that: The nitrogen sealing valve (2) is a self-operated nitrogen sealing valve.

3. A volatile liquid normal pressure and low pressure storage tank safety control system according to claim 1, characterized in that: The nitrogen supply pipe is inserted into the tank body (1) by a distance of 200 mm.

4. A volatile liquid normal pressure and low pressure storage tank safety control system according to claim 1, characterized in that: The opening pressure of the pressure relief valve (4) is ≤ the positive pressure designed for the storage tank; the pressure at which the breathing valve (3) reaches the maximum suction volume is ≤ the negative pressure designed for the storage tank; the opening pressure of the pressure relief valve (4) is ≥ the opening pressure of the breathing valve (3) ≥ the opening pressure of the nitrogen sealing valve (2).

5. A volatile liquid normal pressure and low pressure storage tank safety control system according to claim 1, characterized in that: It also includes a thermometer (10) and a temperature transmitter (9), wherein the temperature transmitter (9) is arranged near the thermometer (10).

6. A volatile liquid normal pressure and low pressure storage tank safety control system according to claim 5, characterized in that: The thermometer (10) is arranged on a floating roof tank and an internal floating roof tank, and is arranged 700 mm to 1000 mm above the tank bottom.

7. A volatile liquid normal pressure and low pressure storage tank safety control system according to claim 5, characterized in that: The thermometer (10) is arranged in a manner of being fixed on the top tank and arranged 700 mm to 1500 mm above the tank bottom.

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