| This paper describes flow field in the air separator and kinematic behaviors of gas/solid flow. It is suggested that the flow field in the decentralized fractionation-zone is a three-dimensional turbulence rotational flow field, in which there are three velocity components, namely, tangential velocity V_t, axial velocity Vz and radial velocity Vr. The flow field is dominated by V_t and Vr. Driven by V_t, the particles are in a state of high speed rotation and activated by centrifugal force they are thrown toward the outer wall and separated apart. Vz is mainly determined by recirculating air, and increase in Vz can promote centralization of coarse fines, thus favorable for fractionation. As a result, relation between cut size of particles and recirculating air output of the air separator, rotating speed of separating impeller and radius of separating impeller is expressed as follows:With increase of the separating impeller's speed, cut size of particles becomes smaller;and with increase of recirculating air, cut size of particles becomes larger. As a matter of fact, separating impeller's speed should match well with recirculating air depending on actual situations in production practices. In this paper, on the basis of production of V-slag in the Panzhihua Iron and Steel Company, the above formula is used for theoretical calculation. The results derived basically coincide with experimental data and can be applied to production practices.In addition, in the case of rotation speed of the separating impeller and recirculating air remaining unchanged, the concentration of fine material shows significant effects on fractionation performance of the air separator. The smaller concentration, the stronger impact. Experimental results suggest that in the case of V-slag, the impact on fractionationperformance is unnoticeable when the concentration is in the range of 0.8-1.68 kg / m3.The existing air separator in the V2O3 workshop is used equipment imported in 1998. There are no spare parts, technical documentation and some components becomes heavily worn. Based on theoretical computation results, modification has been made to major parameters and structures of the impeller, feeding system, whcei ■ .i , supporting roller gas seal and cooling system. The modification adopts a coaxial structure in which the separating impeller(driven by solid shaft) and air recirculating impeller(driven by hollow shaft) are well integrated. The solid shaft sleeve is mounted inside the hollow shaft, featuring a compact structure and smaller occupying space. To achieve better reliability, standstill of the feeding plate is equipped with monitoring system while efficiency of rotation of the feeding plate is ensured. The abrasive layer is provided with home-made ceramic tile and binding agent instead of imported ones. To prevent against peeling off, special consideration is given to linear expansion coefficient of ceramics, binder and shell besides strength and abrasion resistance of ceramics and binder at room temperature.The paper gives particular details to the design of the air recirculating impeller, including its structure and operating parameters. The air recirculating impeller serves as the main impeller of the air separator and consumes the largest portion of power. The backward bent blade is adopted, which results in higher efficiency. Major parameters include blade inner diameter D|, blade outer diameter D2 , inlet blade angle Pia, outlet blade angle P:a, number of blades Z, blade arc radius R, arc pitch circle radius Ro and blade arc length L. The parameters are determined based on requirements of recirculating air output of the separator and outlet gas flow speed and efficiency.The working frequency of the motor for the separating impeller is adjusted to regulate rotational speed of the separating impeller. Separation size changes with working frequency. Off-line tests suggests optimum working frequency of 17.5Hz—25Hz, productivity of 10-12 t / h and size of 80um -125 urn. And finer V-slag can be obtained when required.Through technical modification, remarkable improvement of the separator performance has been achieved. With the same power input and V-slag of 125um over 75%, productivity reaches 12t/h, which can meet requirements of workshop expansion. |
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