In the chemical industry, liquid storage tanks are indispensable and vital facilities. They are responsible for storing liquid and gaseous raw materials, products, and intermediate products. However, the safe operation of storage tanks has always been a key focus of safety management in petrochemical enterprises. Since the quantity of materials stored in tanks is far greater than the critical amount of major hazards, the potential risks are significant. Any mistake could lead to catastrophic accidents. Statistics show that the accident rate of storage tanks is much higher than that of high-temperature, high-pressure, and continuous reaction equipment in petrochemical enterprises. Therefore, ensuring the stable and safe operation of storage tanks and related equipment is of utmost importance.
During the process of process system design, setting up tank level alarms and indicators is a key measure to ensure the safe operation of storage tanks. For tanks that need to be closely monitored or protected in the equipment, it is not only necessary to set up conventional high-level and low-level alarms, but also to set up low-low level and high-high level alarms, along with corresponding interlock devices. These alarms and interlock devices can promptly issue warnings and take measures when the liquid level is abnormal, preventing safety issues caused by excessively high or low liquid levels.
For example, when the liquid level in a storage tank is too high, it may lead to liquid overflow and cause leakage accidents. On the other hand, if the liquid level is too low, it may result in insufficient supply of materials in the tank, affecting the normal progress of the production process. By setting reasonable level alarm values, these problems can be effectively avoided. Moreover, the setting of high alarm values should fully take into account the specific requirements of the production process and the parameters of the container itself to ensure the accuracy and reliability of the alarm system.
In chemical production, the safe operation of storage tanks is crucial, and the level alarm system is the key line of defense to ensure tank safety. As mentioned earlier, the tank level alarm system can promptly issue warnings and take measures when the liquid level is abnormal, effectively preventing safety issues caused by excessively high or low liquid levels. So, how can we ensure that the level alarm system is set up in a scientific and standardized manner? Next, we will delve into the setting standards of the tank level alarm system to ensure its efficient and reliable operation.
The setting height of the high-level alarm for a storage tank should not exceed the tank's design storage high level; the setting height of the low-level alarm should not be lower than the tank's design storage low level. This is the basic requirement to ensure the safe operation of the storage tank. Different tanks have different design storage levels according to the production process and tank structure, so the alarm height must strictly follow the tank's design parameters when setting.
For tanks with a capacity greater than 100 cubic meters, a continuous level measurement remote instrument should be installed, and high and low-level alarms should be set in the automatic control system. For tanks storing Class I and II toxic liquids, tanks with a capacity of 3,000 cubic meters or more for Class A and B flammable liquids, and tanks with a capacity of 10,000 cubic meters or more for other liquids, high-high level alarms and interlocks should also be installed. The high-high level alarm should interlock to close the emergency shut-off valve of the tank's inlet pipeline. These measures can effectively prevent leakage accidents caused by excessively high liquid levels, protecting the safety of personnel and the environment.
The alarm method for storage tanks can be chosen according to their capacity and application scenarios. For small-capacity tanks, it is advisable to set alarm values in terms of capacity percentage, which should meet the reaction time of operators and interlock valves. This method can more intuitively reflect the changes in liquid level, facilitating operators to take timely measures. For large-capacity tanks with a height-to-diameter ratio close to 1:1, the liquid level changes relatively smoothly, and continuous level measurement instruments can be used for precise measurement and alarms.
Liquefied hydrocarbon spherical tanks should be equipped with local and remote level gauges, but glass plate level gauges should not be selected. The level gauges used should be safe and reliable and minimize the number of openings on the liquefied hydrocarbon spherical tanks. This is because glass plate level gauges may pose safety hazards such as rupture due to changes in pressure and temperature when used on liquefied hydrocarbon spherical tanks. Using other types of level gauges, such as ultrasonic or radar level gauges, can not only improve measurement accuracy but also reduce damage to the tank structure.
Interlock devices are an important part of the tank level alarm system. When the liquid level reaches the set alarm value, the interlock device can automatically take measures, such as closing the emergency shut-off valve of the tank's inlet pipeline or stopping the material transfer pump. This is crucial for preventing accidents caused by abnormal liquid levels.
For example, raw material storage tanks in the equipment should be equipped with low-low level alarms, which should preferably interlock to stop the pump. This can prevent pump cavitation due to excessively low liquid levels, thereby avoiding equipment damage and production accidents. For liquefied hydrocarbon spherical storage tanks, a high-high level automatic interlock emergency shut-off feed device should be installed. When the liquid level reaches the high-high level, the feed is automatically cut off to prevent liquid overflow and ensure the safe operation of the storage tank.
After understanding the setting standards of the tank level alarm system, we also need to pay attention to its installation and maintenance. No matter how perfect the system is, if it is not installed properly or lacks effective maintenance, it will be difficult to play its due role. Therefore, next, we will discuss in detail the key points of installation and maintenance of the tank level alarm system to ensure that the system can operate stably in the long term and provide continuous protection for the safe operation of the storage tank.
When installing the tank level alarm system, appropriate level gauges and alarm devices should be selected according to the type of storage tank and its application scenario. For example, various liquid carbon steel storage tanks without lining and dirt layers on the inner wall can use externally mounted ultrasonic level switches. This type of level switch is easy to install, does not require complex installation operations inside the tank, and will not pollute the materials inside the tank.
For floating roof tanks or heavy oil storage tanks, externally mounted ultrasonic level switches are recommended. Liquefied hydrocarbon spherical tanks should also use externally mounted ultrasonic level switches. When installing ultrasonic sensors, it should be ensured that there are no obstacles such as pipelines and components inside the tank in the sensor's measurement direction, and the tank wall welds should be avoided. This can ensure that the sensor can accurately measure the liquid level and avoid false alarms caused by the reflection of obstacles or welds.
The maintenance of the tank level alarm system is equally important. Regularly check the operating conditions of the level gauges and alarm devices to ensure their normal operation. For continuous level measurement instruments, regular calibration should be carried out to ensure the accuracy of the measurements. At the same time, the reliability of the interlock devices should be checked to ensure that they can automatically take measures when needed.
For the retrofitting of old tanks, sensors that can be installed without cleaning the tank should be prioritized. This can reduce the workload and risks during the retrofitting process. Moreover, according to the actual situation, interlock automatic control equipment for the tank's temperature, liquid level, pressure, and ambient temperature parameters can be set up, including automatic cutoff or transfer of materials and sprinkler cooling equipment. These measures can further improve the safety and reliability of the storage tank.
The level alarm system for storage tanks is an important part of the safety management of chemical enterprises. By setting reasonable level alarm values, selecting appropriate alarm methods and interlock devices, and doing a good job of system installation and maintenance, the stable and safe operation of storage tanks and related equipment can be effectively ensured. With the continuous development of technology, the level alarm system for storage tanks will become more intelligent and efficient, providing more reliable protection for the safe production of chemical enterprises.
In summary, the importance of the level alarm system for chemical storage tanks goes without saying. Every link needs to be carefully designed and strictly managed to ensure the safe operation of the storage tanks. Only in this way can accidents caused by abnormal tank levels be avoided in the chemical production process, protecting the safety of personnel and the environment and achieving sustainable development of the enterprise.
