The Importance of Gas Sealing Systems in Storage Tanks

 
Storage tanks play a crucial role in industrial production and storage, especially in sectors such as petrochemicals, food processing, and pharmaceuticals. The safety and reliability of these tanks not only impact the continuity of production but also relate to environmental protection and personnel safety. To prevent contamination or adverse reactions of the materials inside the storage tanks due to contact with external gases (like air), storage tanks are typically equipped with gas sealing systems. These systems maintain a certain positive pressure within the tank, ensuring that the contents are isolated from external gases, thus avoiding undesirable reactions.

Basic Principles of the Gas Sealing System

 
The working principle of a gas sealing system primarily includes the following aspects.

1. Maintaining Positive Pressure

 
The gas sealing system maintains positive pressure inside the tank by introducing sealing gases (such as nitrogen, fuel gas, or natural gas). This positive pressure effectively prevents the intrusion of external gases, ensuring the purity and stability of the stored materials. Additionally, maintaining positive pressure helps prevent the volatilization and oxidation of materials, especially when storing volatile or oxidizable substances.

2. Automatic Gas Compensation

 
When materials are withdrawn from the tank, or when the temperature drops, causing condensation or contraction of the gas inside the tank, the gas sealing system automatically replenishes the sealing gas to maintain the set pressure level. This function ensures a stable internal environment, preventing material degradation or damage due to pressure fluctuations.

3. Pressure Relief Mechanism

 
If the external temperature rises, causing the liquid inside the tank to vaporize, or when filling the tank causes the internal pressure to exceed the sealing pressure, the gas sealing system will release excess gas to the atmosphere through a pressure relief valve. This prevents excessive pressure from damaging the tank. The design of the pressure relief valve must respond quickly to pressure changes, ensuring effective release before reaching dangerous pressure levels.

Selection of Sealing Gases

 
There are various types of sealing gases, with commonly used options including nitrogen, fuel gas, and natural gas. When choosing the appropriate sealing gas, the following factors should be considered.

1. Nature of the Stored Material

 
Different materials react differently to gases; for example, some chemicals may react with oxygen, while nitrogen is an inert gas suitable for protecting sensitive materials. It is essential to select a suitable sealing gas to avoid chemical reactions and ensure the safety of the materials.

2. Availability of the Gas

 
The ease of obtaining sealing gas can impact the system's cost-effectiveness and operability. In some regions, certain gases may be difficult to source, requiring consideration of local resources and supply chains when selecting sealing gases.

3. Economic Factors

 
The cost of sealing gases is also an important consideration to ensure the system's economic viability. For instance, nitrogen is relatively common but can be more expensive, while some industrial waste gases may be used as sealing gases, offering a cost-effective solution that also reduces emissions.

Components of the Gas Sealing Device

 
A gas sealing device typically consists of the following four main components.

1. Sealing Valve (Main Valve)

 
This valve controls the inflow and outflow of the sealing gas, maintaining the gas pressure inside the tank. The opening and closing of the sealing valve are crucial for achieving the sealing function, and it is usually driven by electric or pneumatic means for quick response to pressure changes.

2. Signal Valve (Control Valve)

 
This valve monitors the gas pressure within the tank. When the pressure falls below the set value, the signal valve automatically opens, prompting the sealing valve to operate. The sensitivity and response speed of the signal valve directly affect the safety of the gas sealing system.

3. Pressure Reducing Valve

 
This valve reduces the pressure of the high-pressure sealing gas to ensure that the gas entering the tank is at a moderate pressure. The pressure reducing valve must have good control precision to avoid damage to the tank due to excessive pressure.

4. Needle Valve

 
This valve is used for fine-tuning the gas flow, ensuring system stability. Adjustments via the needle valve allow for precise control of gas flow rates to meet the requirements under different working conditions.

Pressure Control Mechanism

 
The pressure control mechanism of the gas sealing system operates as follows.

1. Low Pressure Operation

 
When the pressure inside the tank drops below the set value, the signal valve opens, causing the sealing valve to open as well. High-pressure sealing gas flows through the pressure reducing valve into the tank, gradually restoring the pressure to the set level. Once the set level is reached, both the signal valve and sealing valve close. This process requires the gas sealing system to respond quickly to ensure the safety and stability of the tank.

2. High Pressure Operation

 
If the pressure inside the tank exceeds the set value, the pressure relief valve equipped with a flame arrestor will automatically open, releasing excess gas and restoring the pressure to normal levels. The design of the pressure relief valve must effectively prevent fire and explosion risks, particularly when handling flammable or explosive materials.

Dual Protection Mechanism

 
To enhance tank safety and prevent overpressure or negative pressure conditions due to failure of the pressure relief valve or gas sealing device, a liquid seal device is often used in conjunction. The functions of the liquid seal include:

1. Backup for Pressure Relief

 
In the event of a pressure relief valve failure, the liquid seal can serve as an additional pathway for gas release, ensuring the safe discharge of gases from the tank. This dual protection mechanism is crucial in practical applications, especially when dealing with high-pressure and high-temperature materials.

2. Negative Pressure Protection

 
If the gas sealing device fails, causing the tank pressure to exceed the set value, the liquid seal can automatically relieve pressure, alleviating the load on the pressure relief valve. Moreover, in extreme situations where both the pressure relief valve and gas sealing device fail simultaneously, leading to negative pressure in the tank, the liquid seal can draw in air, preventing deformation or damage to the tank.

Conclusion

 
Gas sealing systems play a vital role in the safe operation of storage tanks. By maintaining positive pressure, providing automatic gas compensation, implementing effective pressure relief mechanisms, and employing dual protection systems, gas sealing systems ensure the purity and safety of stored materials, preventing various potential risks caused by external factors. The design and implementation of this system not only enhance tank safety but also provide crucial support for the sustainable development of modern industry. Therefore, when designing and selecting gas sealing systems for storage tanks, it is essential to comprehensively consider the characteristics of the sealing gas, the selection of system components, economic factors, and safety measures to achieve optimal protection for the tanks.