Level Sensor and Its Application in Thermal Power Plant
I. Introduction Level Measurement Level Measurement is a branch. Level refers to industrial production equipment, storage containers or in liquid, powder granular solid, the interface between the location of gas, according to the specific uses are divided into liquid, level and community spaces Sensor .
Present, mainly coal for power generation fuel, most of the coal power plant boilers are used to feed the boiler. Direct blow to feed the boilers, coal bunker level related to the boiler feed-bit and even power generation systems can function properly. Bunker Level been full of overflow, causing the accident risk coal; coal bunker material level is too low or empty cause instability or even burning down a large fire incidents. For the storage type boiler feed both coal bunker, another bunker, coal bunker powder-bit control is particularly important. Pulverized Coal is a fuel transfer station, coal is air transport, and heat the gas to pulverized coal into the bunker will have a certain "base temperature", typically around 70 ° C, its role is to make coal certain discrete. However, this temperature is so rapid evaporation of pulverized coal in the water was discharged to absorb moisture management positions, the coal will become increasingly dry, this coal is highly collector, collector of the end result is burning. Increased burning around the collector as well as warehouse, cycle, vicious circle, so as not timely and effective control, the outcome would be a lot of coal burned in vain. According to the information reported, the total coal spontaneous combustion of coal power generation capacity of about 0.5%. In addition, coal bunker explosion damage more years, coal bunker explosion often occurs, causing huge losses to the thermal power plant. At present, the most economical, most suitable method is through reliable material level Sensor Position on the coal bunker and coal powder position monitoring, it is always in the best transfer appropriate control state, which is fire Generator Priority to ensure safe operation.
2, principle and characteristics of Power Plant Level sensors currently used mainly hammer type, type of nuclear radiation, ultrasonic and capacitive.
1. Hammer-type material level sensor Hammer material level sensor from the servo motors, steel wire rope hanging a heavy hammer, level writing devices and instruments with a computer display is composed. Start after the computer send the signal drop hammer, drop hammer rotating servo motor, when the hammer hit material surface, sent a signal to the computer device to stop the hammer down and issued rose hammer signal, servo motors reverse to re- hammer up, and issued material digital signal value to the display instrument. Rose to the top position after the hammer motor stall, and then repeat after a delay action. Shows there is still material level meter, the lower limit alarm devices such letters. Hammer-type material level sensor addresses within a certain range of measurement problems, the typical measurement range up to 60m, and this measurement with the steam, dust has nothing to do with high accuracy.
2. Nuclear radiation material level sensor
Sources Co-60 (half-life of 5.26 years) and Cs-137 (half-life of 32.2 years) of the g-ray emission can penetrate the container wall and the container materials. In the silo with g-rays under the receiver side, with the expected changes in height, g-ray intensity after passing through material layers are also different, the receiver detects the incoming g-ray intensity and by showing the material level meter shows a high degree of .
This is a non-contact measurement, no perforation of the container damaged containers, are applicable to hazardous materials and high-temperature High pressure Measured under such adverse circumstances. g-ray is certainly harmful effects on the human body, but for a limited dose, under the proper protection is not dangerous.
3. Ultrasonic material level sensor
Facing material in the silo at the top surface with ultrasonic generator and receiver. Issued by the ultrasonic generator shoot through the air layer to the material surface after being reflected, in part reflected by the receiver received from the ultrasonic emission to reception time multiplied by the speed of sound experienced by the bed level can be calculated. As the air temperature will affect the level of sound speed, it needs to measure the air temperature to correct the speed of sound.
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