Research On On-line Measurement Of Pulverized Fineness Of Primary Air Using Ultrasonic Method

At present,the pulverized coal furnace is still one of the most common types of boiler used in thermal power plants in China.In the process of pneumatic transmission,the fineness of pulverized coal is one of the kernel parameters in the optimal control of the combustion process.And the accurate measurement of pulverized coal fineness has great reference value for boiler combustion optimization.Ultrasonic wave is widely used in engineering field and has the advantages of non-contact and self-cleaning.It has a good application prospect in the measurement of pulverized coal fineness.In this paper,the purpose of the study is to testify the feasibility of the ultrasonic method for the fineness measurement of pulverized coal.The following research work have been:(1)The particle size distribution of pulverized coal in three power plants was obtained by sieving method.Considering the characteristics of coal dust,irregular shape,easy moisture absorption and long-term accumulation and spontaneous combustion,the same series of glass beads were used instead of pulverized coal in the follow-up study in this paper.(2)The attenuation characteristics of ultrasonic signal under stacking state were studied.The relationship between ultrasonic attenuation coefficient and particle size was studied by using different frequency ultrasonic wave through glass beads layer with different particle size.The results show that the attenuation coefficient difference between the ultrasonic waves of 40kHz and 80kHz passing through the same diameter glass bead layer has a monotone correspondence in the concentrated section of coal particle size of power plant,which can be used to measure the particle size.(3)In order to simulate the pneumatic transport process in the pulverized coal pipeline,it has been done that designing and building the dynamic circulating experiment platform and the measurement system and the debugging work ofthe experimental platform is completed.(4)The attenuation characteristics of ultrasonic signals with different particle sizes are tested on the experimental platform The experimental results are similar to those under the state of particle accumulation.It is found that different particle sizes can be distinguished by two kinds of ultrasonic waves with different frequencies.And this can be used to measure the fineness of pulverized coal in primary air pipe ofpower plant.