What is tank gauging?
Tank gauging system is used to measure the level of large tank in order to quantify the product quantity and mass in the tanks.
There are various methods to measure the liquid level and other liquid characteristics. The technique of measurement relies on the type of tank, the liquid type and how the tank is used.
Modern tank measuring devices digitize tank measurements and communicate tank information digitally to a control room where liquid volume and mass information are distributed to inventory data consumers.
Usually storage tanks come in four basic designs: Cylindrical fixed roof tanks, cylindrical floating roof tanks and either spherical or horizontal cylinder design pressurized tanks. For all these kinds of tanks, tank gages are accessible.
Where is tank gauging used?
• Refineries
• Petrochemical industry
• Distribution terminals
• Pipeline terminals
• Fuel depots
• Air fueling storage at airports
• Chemical storage
Functions of tank gauging:
Fluid/Oil movement and operations:
It is essential to understand precisely what is going on inside the tanks to run the tank farm securely and effectively. In that case, a tank gauging system should provide these information about the gauge:
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How much liquid is in the tank?
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How much available room is left in the tank?
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At what level rate the tank is being filled/discharged?
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When the tank will reach a dangerously high level?
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When the tank will become empty at a given pump rate?
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How long a given batch transfer will take?
Control:
The tank gauge system should be able to provide inventory reports of elevated precision at certain intervals or immediately if necessary. The system should be capable of calculating net quantities and mass in accordance with the guidelines established by industry standards organizations such as API and others.
Loss control and mass balance:
The technique by which losses are estimated is to achieve a refinery’s high-quality mass balance. Distinguishing between actual losses and apparent losses arising from measurement errors is important. In that case, it is important to measure the Loss, Loss calculation equation:
Loss = inputs - outputs - current inventory + previous inventory - fuel
Overfill prevention:
A overfilling of tanks can have catastrophic effects. A spill can cause explosions and fire to spread throughout the tank farm and the surrounding region to all tanks. Since these tanks holds huge amount of oil the impact will be high.
Tank gauge systems provide the tank farm’s fundamental process control layer. The next layer of security is independent high-level indicators or level switches.
For this reason, the reliability of the tank gauge system and the high-level alarm system must fulfill the criteria of the Functional Safety standards.
Leak detection:
If the tank gauging system is sufficiently precise and stable, it can be used to detect tank leakage. The tank gauge system can be set to detect tiny liquid motions when a tank is established and closed.
Leak detection is suggested based on Net Standard Volume (NSV) rather than mere level. By tracking the NSV, it is possible to cancel the level motions induced by temperature modifications.