Study On Non-intrusive Level Gauging Method

Real-time accurate level gauging for high pressure close reactor like fluidized-bed and close tank with dangerous liquid is necessary for chemical process to optimize operation parameters, to prolong producing cycle, to ensure process safety and to increase output. The wild used level gauging systems are not essentially safe, because their detecting principles need intrusive probes. So, a novel non-intrusive level gauging method is needed. This dissertation use ultrasonic wave as medium to study the relationship between particle level and the ultrasonic signal received by the probe on the out-surface of the close tank base on ultrasonic radiation damping. And a liquid level gauging model is setup by using ultrasonic radiation damping, impulse transmission and ultrasonic resonance. The innovative results can be summarized as follow:(1) The relationship of particle level and the ultrasonic signal attenuation which go through the surface from bottom to top of the close tank damped by radiation damping and material damping is revealed. And a novel static particle level gauging model is setup base on this relationship.(2) Non-intrusive accurate level gauging of close storage bin is achieved by using PE particles as an example base on static particle level gauging model. Four factors of this model are reviewed. Generally, ultrasonic signal decreases when level increases, and more energy loss in high particle level than low level. Output power of emitting probe is important to the accuracy of level gauging result that higher output power leads to more accurate. The ultrasonic signal also decreases with the stacking density. The receiving probe can receive more energy when receiving probe and emitting probe at the same side of the storage bin.(3) Dynamic particle level gauging is achieved in the fluidized bed when static level gauging model is revised to dynamic level gauging model. The ultrasonic signal attenuate in the wall of fluidized bed the same as it appears in the wall of storagebin. The attenuation of the signal is not influenced by gas velocity in the fluidized bed.(4) Non-intrusive level gauging for close tank with dangerous liquid is achieved by emitting ultrasonic signal on the surface of close tank base on ultrasonic radiation damping, impulse transmission and ultrasonic resonance. The ultrasonic signal is divide into three parts after transmit through the wall of close tank. The energy of main peak fluctuates with liquid level. The integral energy of the signal increase acutely when liquid level rises over the receiving probe. The detecting results never change wherever the emitting probe is when receiving probe is below the liquid level. But when receiving probe is over the liquid level, it received more energy when emitting probe is on the top of the tank. And the energy of ultrasonic signal is stronger in the stainless steel wall than in the Perspex wall because of the difference of acoustic resistance.