Investigation On Fluid Mechanics And Technology Of Air-Blow Feeding For Sintering Of Iron Ores

The iron and steel industry is one of the greatest energy-consumers.The share of sintering procedure in the total energy consumption of ironand steel industry accounts for about 10%, of which about 75%～80% isfor solid fuel. Recently, the aggravated competition in the steel marketand the tension of the mineral resources have lead to the deterioration ofthe material condition and the increase in energy consumption of thesintering procedure. So the energy saving has become an importantdesign and production subject in sintering field. Segregated feeding as aneffective measure plays an important part to realize the high-yeild andlow energy consumption of the sintering procedure. Although the presentsegregated feeding techniques have a certain effect, they are not verysatisfying. So developing an advanced segregated feeding technology toreduce the solid fuel consumption in the precondition of ensuring thesinter yield and quality is of profound significance for either theenhancement in competitive power or the continuable development of theenterprise. The air-blow feeding has been reported to be applied in a fewforeign countries, but there hasn't been successful application domesticlyso far. So the deep investigations on the new feeding technology are ofgreat therical and actual values to promote the technical development ofsegregation feeding and its application in our country.The air-blow feeding was systematically investigated from thefoundation, the device development, to the technical parameters and thesintering confirmatory tests in this paper.The investigation on the fluid mechanics principle of air-blow feedingshowed that the differences in the density, the size and the shape factor ofthe particles of the sintering blend make the particles' falling speed,falling time and motion locus different. So the way of blowing air couldmake the sintering blend gain sized distribution along thealtitude-direction of the sinter bed by changing the falling speed and themoving locus of the particles. That means that, for granularity, the finegrain materials could be charged on the upper part, while coarse grains atthe bottom; for the solid fuels such as the coke powder, they could be more easily affected by the air-blow because of their small size and lowdensity, and their distribution is prone to decrease from top to bottom ofthe sintering bed. The bottom-blowing method was a way to make thesintering blend pass the air-blow field firstly after they fall down from thefeed plate, and utilize the air-blow to make the materials of differentphysicochemical properties generate effective segregation. While thetwo-feed-plate method was a way to realize the segregation effect bymaking the fine-grained materials got across the front plate and branchedto the back plate, than fell from the back plate to the pallet.Based on the simulation to sintering field, the rationality of thetechnology and structure, the reliability of the equipment operation, themanipuility of the equipment and the service to the experimental research,the laboratory air-blow feeding device was designed. The device weremade up of the charging car, the hopper, the feeding roller, the feedingplate, the pallet and the air-injection system including the nozzle, the aircompressor and the flowmeter.The influence on the segregation of the feeding way was investigated.It was shown that the bottom-blowing method was a good air-blowfeeding way that could make the materials generated obvious segregatedeffect at the proper airspeeds. While the two-feed-plate method couldn'tgenerate effective influence on the materials' size segregation even athigh airspeed, and there was obvious loss of the fine-grained materialsespecially of the coke powder. Meanwhile the effectiveness of thetwo-feed-plate method on the solid fuel segregation wasn't as notable asthat of the bottom-blowing method. In the bottom-blowing method, theproper location of the nozzle was found between the bottom edge of thefeeding roller and the pallet.It is found that there was a proper range of the airspeed, in the rangethe materials' segregated effect was enhanced gradually with theincrement of the airspeed. If slower, the air flow couldn't generateeffective segregation on the minerals; and if faster, it would lead to theloss of the fine-grained minerals especially of the coke powder. For thematerials and moving gaseous medium in this investigation, the properrange was from 42m/s to 50m/s and the best segregated effect was obtained at the airspeed of 50m/s.The influence on the materials' segregation of the air-blow form wasinvestigated. It was shown that in the condition of the same airspeed andair flux, the segregated effect of the slit air-blow was much better thanthat of the hole air-blow. The reason was that the slit air-blow wascontinuous in the whole feeding area, so the influence on the materialswas homogeneous; while for the hole air-blow, there would be the vacantareas and recession areas which would affect the continuity of theair-blow, and then affect the segregated effect furtherly.The influence on the materials' segregation of the blowing angle wasinvestigated. It was shown that for the materials and moving gaseousmedium in this investigation, the best segregated effect was obtained atthe angle of 10°.The sintering test with the segregated feeding simulating air-blowfeeding was conducted. It was shown that, with the conventional feeding,the best coke powder content was 4.6% and the best water content was8.5%, and under the best condition, the vertical sintering speed was20.08mm/min; the tumble index was 61.05%; and the productivity was1.401t/ (m~2·h). After the adoption of the segregated feeding, the bestaverage coke powder content was 4.4%, and under the condition thetumble index was 61.05%; the vertical sintering speed was 21.51mm/min;and the productivity was 1.558t/(m~2·h). The results showed that thevertical sintering speed and the productivity with segregated feeding wereincreased obviously by 7.1% and 11.2% individually when the tumbleindexes were equivalent to that with conventional feeding, but the solidfuel consumption was reduced 4.105kg/t. Compared to the conventionalfeeding, the air-blow feeding could not only notably reduce the solid fuelconsumption, but increase the productivity obviously under theprecondition of ensuring the sinter quality.