Research On Fluid Atomization Characteristics By Centrifugal Granulator

Blast furnace slag is the main solid by-products in ironmaking process, with hightemperature (1450℃) and large displacement. Water quenching is widely used slagtreatment process at home and abroad currently. However, this process causes lots ofwater consumption, releases sewage and H2S and SO2. At the same time, large amountsof slag waste heat can’t be recycled. Therefore, slag drying quenching technology isurgently to await development. Centrifugal granulation and air quenching method isone of the research hotspot today, due to its low energy consumption, particle sizecontrol preferably and operation simply. In this method, how to quickly pyrolysismolten slag as fine slag particles is very important for slag waste heat recovery rate.The research about centrifugal atomization is one of the vital theoretical basis forslag waste heat high-efficiency recovery system. Accordingly, though theoreticalanalysis and centrifugal atomization experiments, the mechanism of liquid filmformation and film disintegrated intodroplets has been analyzed in this thesis.Experimental investigation of film thickness and velocity, liquid ligament number anddiameter, droplets diameter distribution and average diameter has been done.Meanwhile, experimentswith different test mediawere also conducted, which wasfocused on the effect of viscosity and surface tension on the filmformationcharacteristic. Besides, the effect of cup structure on granulation has beeninvestigated experimentally, and the optimized atomizers structure has been proposed.Moreover, though the analysis of granulating mechanism in cold and hot experiments,the correlation formulas related to granulation were obtained. The research results areas following:As the fluid flows onto the rotating disc, liquid film will be formed immediatelyby centrifugal force. Though using boundary layer theory, the simplified N-S functionof liquid film motion was established.and film thickness and radical velocity wascalculated. The results revealed that, when increasingrotation speed or radial distance,or decreasing liquid flowrate, the film thickness decreased. In addition, the radicalvelocity increased due to increasing rotation speed or decreasing liquid flowrate.Under the effect of surface tension, many bugles generated at the rim of therotary disc. Then the bugles kept growing into ligaments, and the ligaments finallybroke up into droplets. As rotating speed increased, film thickness, length and diameter of ligament, break-up time of ligament, as well as diameter ofdropletsdecreased. Inversely, ligament number increased. Increasing flowrate wouldlead to increasing liquid film thickness and ligament number. The droplets diameterwas affected by film thickness and Weber number.The force on the film is changed by changing rotary cup structure, as aresult,film thickness isdecreased. The best inner face angle and depth of cupwereaffected by specific rotating speed and working medium flowrate. In currentexperiment,30°inner angle and15mm depth cup got the best atomization result.Increasing rotary cup outer edge angle could retard liquid film separation, and as aresult, the bugle formation positions were changed and liquid droplets diameters weredecreased.Experiments with different working media were carried out anddifferentgranulation phenomena were observed. At the rim of atomizer, film wouldbreach the constraint of surface tension and then continue to spread out of the cup, asa result, film formed outside the atomizer. As film velocity and thickness increased, itsinertia increased. Also, surface energy of the film decreased when the thicknessincreased.