| The nozzle is widely used in industry, agriculture, transportation and daily life, etc. The used of nozzle in powder gasification and combustion equipment is particularly important. The characteristics of the dry coal powder dispersion were studied through simulation and experiment on the basis of pulverized coal gasification. The influences of different parameters on the dry pulverzied coal dispersion characteristics were investigated. The dispersion characteristics of the pulverized coal nozzle are significant to the puvlerzied coal gasification technology and industrial application. The rasearch can provide theoretical guidance and data support for design, control and operation of the gasifier and the nozzle.According to structure and parameter of industrial nozzle, the experiment nozzle and the dispersion experiment system were designed using the theory of cold model. In design process, the single-valued condition and the equality of gas-solid momentum ratio were kept to the same. The flow characteristics with the actual industrial production conditions were simulated with different operation parameters, powder properties and the nozzle structure parameters, etc.The powder properties of the dry pulverized coal were analyzed. Results showed that total moisture contents of these two kinds of coal powder were below 3%, which were very dry. Two different particle sizes of pulverized coal showed similar apparent morphology. The particle was irregular, rough and compact structure, which adhered a little small particles. Two kinds of pulverized coal had different volume fractions and particle size distributions. The distribution of particle size was concentrated and highly reprentative. Two kinds of pulverized coal were sticky and easy-flow. The larger size particles had better flowability.By establishing the geometric model, meshing the model, setting the control condition and determining parameters of calculation model, the pulverized coal dispersion process was simulated by using Fluent software. The simulation results indicated that improving the center air velocity, reducing the solid mass flow rate, improving the gas-solid flow velocity and introducting of cyclone can promote mixed gas-solid two-phase flow, which improved the quality of dispersion and the particle size distribution uniformity. As the angle of internal rotational flow increased from 30°to 60°, the average particle size almost maintained constant in downstream section. The dispersion characteristics were improved as particle reverse flow entered into the spiral flow area. The property of powders have great influence on dispersion effect. Large diameter particle had poor dispersion quality.Through the dry pulverized coal dispersion experiment mastered the influence of different parameters on dispersion characteristics. Experimental results showed that increasement of center air velocity from 175 m/s to 275 m/s can significantly improve the quality of dispersion. As solid mass flow rate increased from 30 kg/h to 70 kg/h, dispersion quality gradually deteriorated in the downstream. When the velocity of outer ring gas-solid two phase flow increased from 6 m/s to 10 m/s, the downstream dispersion quanlity almost maintained stability. Compared to different size pulverized coal, dispersion ability of large size particle was much poorer. Internal spiral flow promoted the distribution of the particles. When diameter of nozzle outlet increased from 4.8 mm to 5.2 mm, dispersion quality improved slightly.The simulation results agreed well with experimental results. The flow mechanism and regularity were analyzed and studied deeply. Results indicated that the average velocity of particles decreased gradually on cross section with the increasement of axial distance. At the same time, the average diameter of particles decreased firstly and then increased. The larger size particle can move much further in axial direction. |
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