Application of level gauges in measuring liquid levels in oil tank storage volumes

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Oil tanks are storage devices commonly used in oil depots, oil terminals, oil field refineries, and petrochemical enterprises. For the liquid substances contained within these tanks – namely petrochemical products – it is necessary to measure parameters such as their level, temperature, density, and pressure (in the case of tanks under pressure), in order to calculate the volume and weight of the stored liquid. Oil tanks are generally divided into trading tanks and intermediate tanks. The level, temperature, density, volume, and mass of trading tanks must be monitored and measured frequently, with high precision requirements. Intermediate tanks typically only monitor parameters such as liquid level, temperature, and pressure (for tanks under pressure) in order to prevent accidents like overfilling or emptying of the tank, and no transfer measurement is required. For storage tanks of different sizes and types, the performance characteristics of the level gauges used also vary. Therefore, it is necessary to select the appropriate level gauge based on the user’s actual conditions and investment requirements, in order to achieve the best performance-to-price ratio. In current designs for measuring liquid levels in oil storage tanks, steel belt level gauges, as well as float balls, buoys, and radar level gauges, are commonly used. Level gauges such as floats and buoyants are rather troublesome to install and maintain. However, although radar level gauges offer high precision, they are also expensive. Differential pressure level gauges are widely used in enclosed vessels such as boiler drummers, but the measurement results do not represent the actual liquid level; therefore, they are rarely used in the design of oil tank level measurement systems. Two measurement methods for level gauges in oil tanks: 1. Indirect measurement method: A sensing element is used to detect signals related to the liquid level, and then electrical conversion is employed to determine the measured liquid level. For example, the differential pressure level gauge used in a certain tank area of a oil depot measures the pressure difference generated by the liquid at different heights; thereafter, a computer is used to determine the liquid level by performing density conversion and temperature compensation. Another example is the photoconductive level gauge, which uses optoelectronic principles to read the level coding information from the data strip connected to the float in the float tank, and then converts this information into a level value through an auxiliary meter. This measurement method is relatively complex, costly, and subject to significant systematic errors; however, it can **reduce labor intensity, effectively and promptly prevent safety incidents such as tank overfilling, and facilitate automated management of tank areas. 2. Direct measurement: The manual measurement method involves using measuring instruments to directly determine the liquid level, without any need for intermediate conversions. For example, in petrochemical storage and transportation systems, these include manual dipsticks, float-type steel-band direct-reading level gauges (such as those that read the scale values on a photoconductive gauge), magnetic level gauges, and magnetic flip-board level gauges, among others. This measurement method is intuitive, highly reliable, easy to use, and inexpensive, but it has significant human reading errors. At present, manual gauging remains the primary method for measuring and controlling liquid levels in most petrochemical enterprises, and it is often used as the main reference for calibrating other instruments. In fact, the exact liquid level in oil storage tanks is not that important; what users really need to know is not the level itself, but rather the actual amount of oil in the tank (in terms of tons), so as to prevent overfilling. Based on this analysis, using the differential pressure method to measure liquid level (actually in terms of tons) is also a good option.