How to Measure the Liquid Level of the Medium in the Storage Tank in the Petrochemical Industry

In the petrochemical industry, accurate measurement of the liquid level used for storing chemical media is crucial because it ensures the stability and safety of the production process. Accurate liquid level measurement is essential in the petrochemical industry. An excessively high level can lead to oil spills or fire hazards, while a low level can result in pump cavitation or air ingress into the system, affecting equipment operation. Therefore, choosing high-precision liquid level measurement equipment is crucial. Here is a brief analysis of some commonly used level gauges and their advantages and disadvantages.

How to Measure the Liquid Level of the Medium in the Storage Tank in the Petrochemical Industry

Float Level Gauge

The float level gauge is designed based on Archimedes’ buoyancy principle. As the liquid level in the container changes, the float moves up and down accordingly. Due to magnetic effects, the reed switch of the float level gauge is magnetically attracted, causing the resistance inside the sensor to change linearly. This resistance change is then converted into a standard DC signal output of 4mA to 20mA by the converter, enabling remote detection and control of the liquid level. Depending on the chemical properties of the liquid, different materials can be chosen to adapt to it. Likewise, different floats can be selected to match the density of the liquid, ensuring optimal measurement accuracy.

Magnetic float level transmitter

Advantages

  1. Simple structure, easy operation, suitable for most liquid media.
  2. Relatively low cost, suitable for general process requirements.
  3. Applicable in harsh environments such as high temperature and high pressure.

Disadvantages

  1. Not suitable for viscous liquids or media containing solid particles.
  2. Regular maintenance and calibration, affected by changes in float density.

Differential Pressure Level Gauge

Differential pressure liquid level transmitters are sensors used to measure the difference in pressure between two liquids. They are typically employed to measure the pressure difference between the front and rear ends of a particular device or component. These transmitters can be utilized to measure the level, flow, and pressure of liquids, gases, or steam, converting them into a 4-20 mA DC signal output. The working principle of a differential pressure liquid level transmitter is based on Poisson’s law, which states that the pressure of a gas or liquid is directly proportional to its density in a static state. Therefore, when there is a differential pressure between two pressure points, the fluid’s flow rate, level, density, and other parameters can be calculated by measuring the differential pressure.

Differential Pressure Transmitter with Remote Diaphragm Seal

Advantages

  1. Suitable for various media, including corrosive and high temperature and pressure media.
  2. Capable of long-distance transmission of level signals.
  3. High precision level measurement is achievable.

Disadvantages

  1. Requires additional differential pressure transmitters and pressure sensors, resulting in higher costs.
  2. Installation and maintenance are complex, requiring regular calibration.

Guided Wave Radar Level Gauge

Guided wave radar level transmitter is a type of liquid level measuring instrument commonly used in the chemical industry. It is based on the time-domain reflectometry (TDR) principle, a radar level transmitter. The electromagnetic pulses of the radar level transmitter propagate along a steel cable or probe at the speed of light. When they encounter the surface of the measured medium, some of the pulses are reflected, forming echoes that travel back along the same path to the pulse transmission device. The distance between the transmission device and the surface of the measured medium is directly proportional to the propagation time of the pulse between them. The liquid level height is calculated based on this information.

Radar-level-meter

Advantages

  1. Suitable for various liquid media, including corrosive and high temperature and pressure media.
  2. Non-contact measurement, suitable for volatile or scaling-prone media.
  3. Capable of high-precision level measurement, suitable for applications requiring high precision control.

Disadvantages

  1. Sensitive to the dielectric constant and temperature of the medium, requiring calibration for different media.
  2. Relatively higher price, suitable for applications less sensitive to cost.

Ultrasonic Level Gauge

Ultrasonic level transmitters are digital level meters controlled by a microprocessor. During measurement, ultrasonic pulses are emitted by the sensor (transducer). And the sound waves are reflected by the liquid surface and received by the same sensor. These are then converted into electrical signals by piezoelectric crystals. The time between the emission and reception of the sound waves is used to calculate the distance from the sensor to the liquid surface. Since it is a non-contact measurement, the measured medium is almost unlimited and is suitable for measuring the height of various liquid and solid materials.

Ultrasonic-Level-meter

Advantages

  1. Suitable for various liquid media, regardless of corrosiveness, high temperature, high pressure, or scaling.
  2. Non-contact measurement, suitable for volatile or scaling-prone media.
  3. Capable of high-precision level measurement, unaffected by the medium.

Disadvantages

  1. Requires a high reflectivity of the liquid surface, needing to avoid surface foam or uneven liquid levels.
  2. May experience decreased measurement accuracy in multiphase flow or fluctuating liquid levels.

Conclusion

In summary, selecting the appropriate level gauge requires considering multiple factors. For applications with general process requirements, a float level gauge is an economically practical choice; whereas, for environments with high temperature and pressure demanding precision, a differential pressure level gauge or guided wave radar level gauge might be more suitable. Ultrasonic level gauges are suitable for applications requiring non-contact measurement and high precision. In practical applications, the most suitable level gauge should be chosen based on specific circumstances to ensure accurate and reliable level measurement.

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