Application of liquid level measuring device in thermal power plant

In the production process of thermal power generation enterprises, it is often necessary to control the volume or height of the medium stored in storage tanks, pools and other containers to ensure the safe and stable operation of production. In general production work, usually only need The surface position of the measured medium is recorded and stored to ensure the needs of production and safety. However, with the continuous improvement of the degree of automation, higher requirements are also placed on the liquid level measurement technology: the measurement object is required to be wide , The measurement accuracy should be high, the measurement reliability should be better, and the special environment applicability of the measurement should be strong. The liquid level fluctuation of the measured medium, the existence of air bubbles in the storage tank, whether it is viscous or corrosive, etc. are all related to liquid level measurement. It has caused a great impact. Therefore, the correct selection of the liquid level measuring device according to the actual working conditions in the production process is a guarantee for production. At present, the liquid level gauges commonly used in the production of domestic thermal power generation enterprises have the following five categories. 1 Ultrasonic liquid level measurement generally refers to the sound wave with a sound wave frequency exceeding 20kHz as ultrasonic wave. Ultrasonic wave is a kind of mechanical wave, that is, a propagation process of mechanical vibration in an elastic medium. It is characterized by high frequency, short wavelength, and diffraction. The phenomenon is small, and the directionality is good, and it can become a ray and propagate in a direction. The ultrasonic pulse emitted by the ultrasonic transducer is reflected in the air on the surface of the measured medium and returns to the receiving transducer, through the round-trip time of the ultrasonic pulse. , the distance from the radiation surface of the ultrasonic transducer to the measured surface can be obtained. Then according to the installation height of the ultrasonic transducer, the actual liquid level height can be obtained. The ultrasonic liquid level gauge has no direct contact with the medium and has strong corrosion resistance. , high precision and easy installation. However, its paper model is relatively high, the ultrasonic wave is greatly affected by the gas composition of the transmission medium, and is greatly affected by the geometric structure of the container. .2 Radar level measurement The radar level gauge emits a special form of electromagnetic wave, and its physical properties are similar to visible light. Whether the radar signal is reflected mainly depends on two factors: (1) The conductivity of the measured medium; (2) The dielectric constant of the measured medium. When the radar level gauge emits electromagnetic waves toward a target, the electromagnetic waves are reflected and returned to the emission source. The receiver installed at the emission source captures the reflected wave and combines it with the emission wave. Compare, and finally determine the distance between the target and the emission source. The radar wave is not easily interfered, and has a strong penetrating ability. It can measure the liquid level in the pressure vessel, and the influence of high temperature, high pressure, scaling and condensate can be ignored. The accuracy is high, It has no direct contact with the medium, and has strong corrosion resistance. It can be used in a vacuum environment and an environment with strong vortexes. It is easy to install. However, it is expensive, and is easily affected by electromagnetic interference due to the geometric structure and material characteristics of the container. 3 Capacitance Type liquid level measurement Capacitive liquid level gauge compares the dielectric constant of the liquid to be measured with the dielectric constant of the air above the liquid, and uses the change in the capacitance value between the two polar plates of the capacitor to measure the level of the liquid level. It has a simple structure, a small volume, It is easy to realize remote transmission and adjustment, and is suitable for corrosive and high-pressure media. However, the dielectric constant of the capacitive liquid level gauge medium and the upper part of the liquid surface must be kept constant for accurate measurement. And the conductive medium is easy to produce hanging material, and the error is large. When the liquid level rises and falls, the magnetic float in the body tube of the liquid level gauge also rises and falls, and the permanent magnet in the float is transmitted to the magnetic flip column indicator through magnetic coupling, which drives the red and white flip columns to flip 180°. When the liquid level rises When the turning column changes from white to red, when the liquid level drops, the turning column changes from red to white. The red and white junction of the indicator is the actual height of the liquid level inside the container, so as to achieve a clear indication of the liquid level. The position meter can read quickly and intuitively, and the paper model is relatively low, and it can realize remote transmission and adjustment. However, it has low precision, complicated installation, limited range, and relatively large installation volume. 5 Differential pressure type liquid level transmitter Differential pressure type The level transmitter is installed in The bottom of the liquid container reflects the liquid level height through the gauge pressure signal. When one end of the differential pressure gauge is connected to the liquid phase and the other end is connected to the gas phase, according to the principle of hydrostatics, under normal circumstances, the density and acceleration of gravity of the measured medium are already Therefore, the differential pressure measured by the differential pressure transmitter is proportional to the height H of the liquid, which turns the problem of measuring the height of the liquid into a problem of measuring the differential pressure. The differential pressure liquid level transmitter is stable Good performance, high precision, and commonly used pressure transmitters can be used as measuring equipment.
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