Study On Velocity And Size Measurement Of Coal Particle Based On Trajectory Imaging

In energy, environment and chemical sectors, on-line monitoring of particle parameters is of great significance for optimal operation in multiphase flow and combustion equipment. Typically, online monitoring of coal particles in power plant in an important prerequisite and means to optimize of mill output, boiler combustion, to achieve energy saving and emission reduction. Although there has developed a variety of advanced particle field measurement instruments, such as PIV, PDA, etc., but real-time industrial site online measurement technology is still relatively lacking, especially in front of pulverized coal particles with complex structures and poor optical properties. To this end, we study the velocity and size measurement of coal particle based on trajectory imaging, with the expectation of applying in monitoring coal particle parameters in power plant.First, by using a cheap industrial CCD camera and a semiconductor laser, images of coal particles at different detection angle and exposure time were investigated. Comparing with the transient images of coal particles, which are normally indistinct and non uniform due to their strong absorption and complicated surfaces, their trajectory images are found to be with much more clear shapes, leading to a possibility that both velocity and size of coal particles may be determined from the length and width of the trajectory. To verify this idea, a large number of trajectory images of coal particles coming out from an electro-vibrating feeder were recorded wih a certain exposure time. The statistical distributions of particle velocities and sizes were obtained by analyzing the widths and lengths of particle trajectories. It is found that the mean values as well as the distribution shapes agree with those from commercial PIV and Malvern sizer, which verify the feasibility of the present measurement method and open a possibility to develop a cheap on-line measurement technique for coal power in pipe.Secondly, key parameters, including image magnification and exposure time, were studied systematically in laboratory table, which have a major impact on measurement results. Coefficient N and R can be obtained, which are very important to the measurement system. Factor N can be used to guide the experiment or commercial products selecting appropriate field of view, while factor R for reasonable exposure time. It is found that good measurement results will occur when N is greater than 6 and R is between 3 and 7. Finally, under the guidance of coefficient N and R, experiments were taken in high-temperature gas-solid two-phase flow wind tunnel in Institute of Thermal Engineering at Zhejiang University, to verify the reliability of the measurement system. Experiments on glass particles were carried out, meeting the coefficient of N and R conditions. The results are also agree well with those from commercial PIV and Malvern sizer, indicating that the measurement system based on trajectory imaging consisting of cheap industrial CCD camera and laser can be applied to on-line monitoring of particles in the tube two-phase flow.