Selection and Application of Level Measurement Sensors for 'Fly Ash/Bottom Slag Island' in Large Thermal Power Plants

Abstract: The selection and application information of 'fly ash/bottom slag island' level measurement sensors in large thermal power plants are provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. 1 Overview With the development of automatic control technology, continuous level measurement sensors have been widely used in industrial fields such as power stations, petrochemicals, and oil fields. Material (liquid) level measurement of solid particles, ash and slurry mixtures, especially non-contact continuous measurement. For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the selection and application details of the level measurement sensors of 'fly ash/bottom slag island' in large thermal power plants. 1 Overview With the development of high-tech automatic control, continuous level measurement sensors are widely used in industrial fields such as power stations, petrochemicals, and oil fields. Material (liquid) level measurement of solid particles, ash powder and slurry mixture, especially non-contact continuous measurement has always been a difficult problem for level measurement technology, which is used in thermal power plants“fly ash/bottom slag island”The problem of material level detection in ash warehouse and dewatering warehouse is more prominent. It always has problems such as high dust viscosity, high temperature, and low dielectric constant. How to reasonably select and design new material level measurement sensors suitable for power plant ash storage and dehydration bins has become the key. Level measurement sensors measure the level potential energy of different media. It has an important position in PLC/DCS system interface. 2 Classification and principle of level measurement sensors Level measurement sensors can be divided into: sensors that measure the continuous change of material level and switch sensors that measure the state as the goal. Continuous measurement sensors are mainly used for continuously controlled silos, ash warehouses, etc., and can also be used in multi-point alarm systems; switch-type level measurement sensors are mainly used for sequence control limit, alarm, etc. The basic principle, PLC/DCS interface and application technology of 3 kinds of continuous level measurement sensors are mainly introduced below. 2.1 Radar measurement principle Radar measurement application“emission—reflection—take over”Measurement principle. The antenna of the radar sensor transmits a minimum 5.8GHz radar signal in the form of a beam, and the reflected echo signal is still received by the antenna; the running time of the radar pulse signal from transmission to reception is proportional to the distance from the measurement sensor to the medium surface and the material level . The transmission time of a beam of radar pulses is 1ns, and the antenna system transmits a beam of pulse signals every 277ns. The frequency of the pulse beam is 3.6MHz, and the antenna system is used as a receiving device during the transmission interval. The sensor analyzes and processes the echo signal of the running time (10-9s) and analyzes and processes the echo image in a very short moment. 2.2 Phase tracking measurement principle The phase tracking principle uses a high-frequency transmission line as a probe. The probe consists of two parallel wires suspended vertically inside the tank. The electronics send a high-frequency sine wave along the measuring sensor, which generates an electromagnetic field. The electromagnetic field moves around both wires simultaneously. This signal moves toward the material surface at a constant speed, and when it reaches the material surface, the signal is reflected and moves back at the same speed. The signal is reflected back from the material surface because the impedance of the measurement sensor changes abruptly at the interface between the air and the material. Because the electromagnetic field extends outside the two wires of the measurement sensor, the impedance of the probe depends on the dielectric constant c of the surrounding medium. 2.3 Ultrasonic measurement principle It is a non-contact level measurement sensor. Its principle is to emit a beam of ultrasonic waves to the liquid surface or powder surface during operation, and after being reflected by it, the measurement sensor then receives the reflected wave. Assuming that the speed of sound is constant, the distance from the measuring sensor to the liquid surface (powder surface) can be calculated according to the round-trip time of the sound wave, that is, the position of the liquid surface (powder surface) is measured. There are two kinds of sensing elements, one is composed of coils, magnets and membranes, and the other is composed of piezoelectric magnetostrictive materials. The former produces ultrasonic waves of 10 kHz, and the latter produces ultrasonic waves of 20 to 40 kHz. The lower the frequency of the ultrasonic wave, the smaller the attenuation of the distance, but the smaller the reflection efficiency. Generally speaking, in air (or vacuum), the dielectric constant is equal to 1, and in all materials, the dielectric constant is always greater than 1. Therefore, at the interface between air and material, an echo will always be generated due to the difference in dielectric constant. The difference between the minimum dielectric constants is about 0.5, that is, the minimum dielectric constant of the material is about 1.5. 3 Functional characteristics of three new continuous level measurement sensors, analysis and comparison of PLC interface technology 3.1 Functional analysis of radar measurement sensors and PLC interface

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