Experimental Research And Mechanism Analysis On High Intensity Conditioning Of Coal Flotation

Slurry conditioning is critical in the coal slime flotation technology. It is believed that the conventional slurry conditioning process can increase the probability of collision and adsorption between collector droplets and coal slime particles, thus improving the flotability of coal slime. However, the shear force is increasing in the high intensity conditioning(HIC) process, which leads to the surface hydrophobic coal slime particles overcome the energy barrier between the particles and form agglomerate. At the same time, not only the cavitation phenomenon will occur but also the shear force have a scrubbing effect on coal slime surface.In this paper, the coal slime with different coal rank floatation test was carried out by taking the bidirectional impinging stream mixing tank which is made and designed by our research group as HIC. First, flow field simulation of the mixing tank was carried out by Fluent software. The results show that there is bidirectional recycle stream between the top impeller and the bottom impeller, and the turbulence intensity is very strong, thus the probability of collision between the coal slime particles is increased and there is enough kinetic energy for coal slime particles to overcome the energy barrier and form agglomerate finally. The introducing cavitation model results show that the gas phase volume number behind the top and bottom impeller blades increase significantly, which indicates that cavitation is existing in the process of HIC. PIV experiment was carried out by taking microbubbles as tracer particles. It was shown that the actual flow field on the HIC almost consistents with the vector flow field simulated by Fluent software.When the coal slime with different rank is in different mixing conditions, the change rule of cleaned coal yield and ash content is different. And compared with the conventional flotation process, the HIC can increase combustible recovery rate conspicuously with the same reagent dosages. For the coal slime which is easy or extremely easy to float, such as Dongqu, Zhangcun and Malan, the HIC can reduce20%～40%of reagent dosages and improve approximately4%of cleaned coal yield when keeping almost the same cleaned coal ash content. For the coal slime of middling floatability, such as Pangpangta and Tunlan, the cleaned coal ash content remain unchanged after HIC, but the cleaned coal yield can increase about6%～9%with the same reagent dosages; For Pingshuo steam coal slime which is difficult to float, there is little change of cleaned coal ash content after HIC, but the cleaned coal yield significantly increase13%-14%.The image-analysis show that ultrafine coal particles form agglomerate after HIC, there are more or less0.02mm-microbubbles, then coal slime particles and agglomerates form "gas-agglomerate" by the connection of those microbubbles eventually except TunLan coal slime. The size and the shape of agglomerate and "gas-agglomerate" are different for each kind of coal slimes. Those agglomerates have an important influence on flotation effect and flotation rate of various coal slime.