Setting and selection scheme of liquid level instrument in atmospheric storage tank
The setting and selection of the liquid level instrument of the atmospheric storage tank are selected according to the size of the tank and the characteristics of the medium. Generally, there are the following four setting schemes.
Option 1: The storage tank is equipped with a set of continuous liquid level measuring instruments. This solution is generally used for small storage tanks. Liquid level instruments such as radar level gauges, servo level gauges, and magnetostrictive level gauges can be used, which can be selected according to the characteristics of the medium and the project budget.
Option 2: The storage tank is equipped with a set of continuous liquid level measuring instruments. One set of high-high, low-low liquid level switch, the liquid level switch is used for high-high, low-low alarm and interlocking. This scheme is generally used to store Class I and II toxic liquid level storage tanks, Class A B and Class B A combustible liquid storage tanks with a capacity of more than 3000m³ and other liquid storage tanks with a capacity of 10000m³.
Option 3: Two sets of continuous liquid level measuring instruments are installed in the storage tank. This solution is also applicable to the working conditions mentioned in the second solution, and is also applied to a storage tank with a capacity of 1,000,000m³. Compared with scheme 2, the liquid level switch is limited by the high and low liquid level alarm positions of the storage tank, while the continuous measuring instrument belongs to real-time measurement and is not limited by the installation height. The continuous measuring instrument is more reliable than the liquid level switch, so when the requirements are high In terms of reliability, it is recommended to use a continuous measuring instrument instead of a liquid level switch, but the cost of the liquid level switch is lower than that of a continuous measuring instrument. When two sets of continuous measuring instruments are selected, two sets of continuous liquid level measuring instruments with different measuring principles are preferred. However, when limited by the characteristics of the measuring medium, two sets of liquid level instruments with the same measuring principle can be selected. For example, when the medium viscosity is high and the temperature is high (such as crude oil, wax oil, asphalt and other media), it is not suitable to use servo level gauge and magnetostrictive level gauge. At this time, two sets of radar level gauges can be used.
Option 4: Two sets of continuous liquid level measuring instruments (same type or different types) + one set of liquid level switches (high and high, low and low liquid level switches) are installed in the storage tank. The liquid level switch can choose a tuning fork switch, an external stick switch, a float switch, etc. When the continuous liquid level measuring instrument selects the bus type and participates in the interlock control, the continuous liquid level measuring instrument can output two signals, one 4mA-20mA or one dry contact signal for liquid level interlock control, one bus The signal enters into the DCS system or TGS system for oil measurement, oil movement, liquid level control, etc.
When two sets or three sets of liquid level timers are installed in the storage tank, and there are high-high, low-low liquid level interlocking, the scheme of one-to-one, two-to-one, and three-to-two should be selected according to the actual medium characteristics and materials. Comprehensive consideration of supply, SIL rating, etc.
