In the petrochemical industry, the safety of storage tanks is of vital importance. The vapor space of flammable material storage tanks may contain explosive gases, which, when mixed with air, can lead to catastrophic explosions. To ensure safety and prevent such accidents, the nitrogen seal device has been developed. By using an inert gas sealing method, this device maintains an oxygen-deficient environment in the vapor space, effectively eliminating the risk of explosions. This article will provide a detailed introduction to the working principles, design specifications, and applications of nitrogen seal devices in petrochemical storage tank areas, helping everyone gain a better understanding of this crucial safety technology.
Nitrogen seal devices are primarily used at the top of storage tanks, with the core function of maintaining a slight positive pressure inside the tank. This slight positive pressure effectively isolates the material from external contact, reduces the evaporation and waste of the material, and protects the safety of the storage tank. The nitrogen control valve is a key component of the nitrogen seal device. It operates without external energy sources, using the energy of the controlled medium itself as the power source to automatically control the flow of the valve medium, keeping the pressure after the valve constant.
Specifically, the nitrogen sealing system injects nitrogen into the storage tank to maintain a certain pressure in the vapor space inside the tank. When the pressure inside the tank exceeds the set value, the nitrogen control valve will automatically close, stopping the supply of nitrogen; when the pressure falls below the set value, the valve will open to replenish nitrogen, ensuring that the pressure inside the tank remains within a safe range. For example, if the vapor space pressure of the storage tank is set at around 1.2 KPa, the nitrogen control valve will close if the pressure exceeds 1.4 KPa; if the pressure drops below 0.8 KPa, the valve will open to replenish nitrogen. This automated pressure control mechanism not only enhances the safety of the storage tank but also reduces the need for manual intervention.
The design specifications of nitrogen seal devices are crucial to ensuring their safe and efficient operation. Here are several key points:
One of the main functions of nitrogen seal devices is to reduce the evaporation of volatile materials and minimize losses due to breathing. In the petrochemical industry, many materials are highly volatile, toxic, and prone to oxidation. By maintaining a slight positive pressure inside the storage tank, nitrogen seal devices can effectively prevent the material inside the tank from coming into contact with external gases, thereby reducing evaporation and waste. Additionally, nitrogen seal devices can lower the static electricity inside the tank, reducing safety hazards caused by static electricity.
For materials that are prone to oxidation, such as styrene, hydrogenation feedstocks, and acrylonitrile, nitrogen seal devices can prevent material degradation. These materials are susceptible to oxidation reactions when exposed to air, which can lead to a decline in material quality and even the production of harmful substances. By setting up a nitrogen sealing system, air can be effectively isolated, protecting the quality of the material.
Pressure control is a key aspect of the design of nitrogen seal devices. Generally, the pressure control range of nitrogen seal devices is around ±800 Pa. When the pressure inside the tank exceeds the set value, the nitrogen control valve will automatically stop the supply of nitrogen; when the pressure falls below the set value, the valve will automatically open to replenish nitrogen. This automated pressure control mechanism not only enhances the safety of the storage tank but also reduces the need for manual intervention.
Nitrogen seal devices also have important safety protection functions. In some cases, nitrogen seal devices can replace traditional safety valves. For example, when the pressure inside the tank is too high, the nitrogen control valve can maintain pressure by venting gas, preventing overpressure in the tank. When the pressure inside the tank is too low, the valve will automatically replenish nitrogen to prevent the formation of a vacuum inside the tank, avoiding the risk of the tank being sucked in.
The application of nitrogen seal devices in petrochemical storage and transportation tank areas is extremely widespread. By maintaining a slight positive pressure inside the storage tank, these devices effectively isolate the material from external air, reduce evaporation and waste, and protect the safety of the storage tank. Here are the specific applications of nitrogen seal devices in different types of storage tanks.
For internal floating roof tanks with a single-tank capacity of less than or equal to 5000 m³, if the floating roof is made of fusible materials, nitrogen protection and other safety measures should be provided. This design can effectively prevent the material inside the tank from coming into contact with external gases, reduce evaporation and waste, and protect the safety of the storage tank.
For special-grade A and B liquid materials, such as styrene, hydrogenation feedstocks, and acrylonitrile, which are prone to polymerization, oxidation, or toxicity, using fixed roof tanks or horizontal tanks with nitrogen sealing for storage is also feasible. This design can effectively prevent material degradation while reducing evaporation and waste.
Heavy oil fixed roof tanks with a storage temperature exceeding 120°C should be equipped with nitrogen protection. This design can effectively prevent the material inside the tank from coming into contact with external gases, reduce evaporation and waste, and protect the safety of the storage tank.
When storing Class A liquids in fixed roof tanks or low-pressure tanks, to prevent large-scale evaporation of oil and gas and improve the safety conditions of the storage tank, measures should be taken to reduce temperature rise due to sunlight exposure. These measures mainly include fixed cooling water spray (mist) systems, gas venting or gas condensation and solid flow, nitrogen sealing, or applying qualified thermal insulation coatings.
For equipment such as reactors, storage tanks, and filters that produce high-concentration organic waste gas, to avoid the formation of explosive mixtures with oxygen, nitrogen sealing systems should be used for protection and transported to the waste gas main pipeline in a positive pressure manner.
For Class A and B liquid materials with a single-tank capacity of less than 100 m³ or with special requirements such as being prone to oxidation or polymerization, fixed roof tanks with nitrogen or inert gas sealing can be selected. This design can effectively prevent material degradation while reducing evaporation and waste.
When using internal floating roof tanks or fixed roof tanks to store Class B liquids with a boiling point below 45°C or a saturated vapor pressure greater than 88 kPa at 37.8°C, a nitrogen sealing protection system should be installed. This design can effectively prevent the material inside the tank from coming into contact with external gases, reduce evaporation and waste, and protect the safety of the storage tank.
When using fixed roof tanks with a capacity of less than or equal to 10,000 m³, low-pressure tanks, or horizontal tanks with a capacity of no more than 100 m³ to store Class B and A liquid chemical products and light naphtha with a boiling point not lower than 45°C or a saturated vapor pressure not greater than 88 kPa at 37.8°C, a nitrogen sealing protection system should be installed. This design can effectively prevent the material inside the tank from coming into contact with external gases, reduce evaporation and waste, and protect the safety of the storage tank.
To ensure that nitrogen seal devices operate safely and efficiently under different conditions, it is crucial to set the operating pressure reasonably. Here are the operating pressure setting specifications for several common types of storage tanks:
The operating pressure of low-pressure tanks and pressure tanks should be the saturated vapor pressure of the liquid at the highest storage temperature or the highest pressure required for process operations. This design ensures that the storage tank operates within a safe pressure range while meeting the needs of process operations.
For tanks with nitrogen sealing protection, the operating pressure should be between 0.2 kPa and 0.5 kPa. This design can effectively prevent the material inside the tank from coming into contact with external gases, reduce evaporation and waste, and protect the safety of the storage tank.
For other tanks equipped with breather valves, the operating pressure should be between 1 kPa and 1.5 kPa; for other tanks, the operating pressure should be atmospheric pressure. This design allows for the selection of an appropriate operating pressure based on the specific conditions and process requirements of the storage tank, ensuring its safe operation.
The application of nitrogen seal devices in petrochemical storage tanks not only improves operational efficiency but also significantly enhances safety. Here are the main safety advantages:
Nitrogen seal devices can effectively prevent overpressure in storage tanks. When the pressure inside the tank is too high, the nitrogen control valve can maintain pressure by venting gas, preventing overpressure in the tank. This design can effectively avoid safety accidents such as explosions caused by overpressure in the storage tank.
Nitrogen seal devices can also prevent negative pressure in storage tanks. When the pressure inside the tank is too low, the nitrogen control valve will automatically replenish nitrogen to prevent the formation of a vacuum inside the tank, avoiding deformation and other safety accidents caused by negative pressure in the storage tank.
Nitrogen seal devices can effectively reduce the evaporation of materials inside the storage tank. By maintaining a slight positive pressure inside the tank, nitrogen seal devices can prevent the material inside the tank from coming into contact with external gases, thereby reducing evaporation and waste. This design not only saves material costs but also reduces environmental pollution.
Nitrogen seal devices can effectively reduce the static electricity inside the storage tank. When the storage tank is receiving or shipping goods, the gas flow in the vapor space increases, and the static electricity generated by the friction between individual gases is relatively low, which can reduce the negative impact of static electricity. This design can effectively avoid safety hazards caused by static electricity.
In summary, the application of nitrogen seal devices in petrochemical storage and transportation tank areas not only effectively reduces the evaporation and waste of materials but also significantly enhances the safety and reliability of storage tanks. By designing and using nitrogen seal devices properly, the material inside the storage tank can be effectively isolated from external gases, reducing evaporation and waste while protecting the safety of the storage tank. With the continuous advancement of technology and increasing environmental requirements, nitrogen seal devices will play an increasingly important role in the petrochemical industry, providing strong support for the sustainable development of the industry. It is hoped that the introduction in this article will help everyone better understand the importance and application value of nitrogen seal devices, promoting their widespread use in more fields.
