Study On Multi-parameter Measurement Of Coal Particles

Pneumatic conveyance of coal powder plays an important part in power plant, and it can influence the capacity of coal mills, efficiency of boiler combustion and the prevention of material degradation. In order to achieve the maximum efficiency of the power plant, it is necessary to measure the parameters of the flow in an on-line continuous manner, such as flow velocity and particle size distribution. The trajectory imaging based method for measuring the velocity and diameter of coal particles was further studied on the basis of previous research and was applied to wind tunnel test stand subsequently. According to the results of wind tunnel tests, the author proposed the plan for online measurement of coal particle size and velocity distribution by trajectory imaging.First, an image processing program was implemented in VC6.0combined with Open Source Computer Vision Library for image binarization, morphological processing and the calculation of particle diameter and velocity. By using Matcom, the program can realize the real-time display of particle size and velocity distribution.Secondly, fundamental researches on this method with special attention to recording parameters, e.g. magnification factor and exposure time, were carried out. For most of the tested cases, the results agree with those by PIV and shadow imaging method. Measurements with good accuracy can be obtained when the imaging magnification factor and exposure time are set appropriately, making N be larger than3.5, and R between5-7, where N and R are the number of pixels occupied by the average width and the ratio of length to width of particle trajectory on the image.Thirdly, this trajectory imaging method was applied to the wind tunnel test stand of high-temperature gas-solid two-phase flow. The testing process, focused on the influence of two dimensionless parameters N and R on measurement, also was carried out to study the factors that may influence the test, such as the pipeline concentration and velocity of coal particles, hardware parameters such as laser power. The obtained size and velocity distributions were compared with those using shadow image method and PIV respectively, and both particle size distribution and velocity distribution from trajectory imaging agree generally with the results of shadow image method and high speed photography. The work indicates the feasibility and potential application of the present measurement method for on-line measurement of coal powder in pipe in industrial power plants.Finally, a design proposal for online measurement of coal particle diameter and velocity was demonstrated after the market survey.