Study On The Properties Of Settling Dehydration Of Weaking Caking Coal Slime From Pingshuo

Slurry treatment is one of the key steps in the production of coal preparation, the technological treatment of slurry is very important to improving the economic benefits of coal products and the social benefits of society. The feeding metamorphic degree is an important prerequisite in determining the effect of slurry treatment, at present, especially the slime water treatment of low metamorphic degree coal becoming an outstanding problem. While exploring the inherent laws of settlement and dehydration characteristics in slime water system will provide a theoretical basis for solving this focus, thus have a great practical significance. In this paper, we use the weakly caking coal in Pingshuo withing a low metamorphic grade for research, studying the impact of all the factors, including slime size composition, mineral composition and content, the slime oxidation degree on the effect of slime settlement and dehydration; using particle image velocimetry (PIV) technique to obtain slime settlement characteristics under the effect of different feeding nature, and different pharmacy system, At the same time, studying the surface-active functional groups in sample surface, wettability, mineral composition, size distribution, and thermal gravimetric analysis and so on, combining the dewatering discipline of coal cake in dehydration process, exploring the settlement and dehydration characteristics as well as the coupling effect of the two. And under the guidance of this theory, we have completed the settlement and dehydration industrial test of II wells in air weathered and oxidized coal in NO.2 coal preparation plant, the main conclusions of this paper are as following:1、The calculation method of critical size is proposed and established based on Stocks formula. The sedimentation rate of solid particles were determined by PIV technology when the suspension is in stable condition, and the critical diameter of solid particles were calculated in suspension according to the settling final velocity formula in retention area which the critical size for weekly caking coal of Pingshuo is 0.026mm. When the number of particles less than the critical size is increasing, particles will show a uniform distribution in suspension, with the improved suspension stability and the worsen dehydration sedimentation effects. When the number of particles larger than the critical size is increase, solids can achieve settling. It will provide accurate date support for the scientifically modulate of coal slurry management.2、Study the influence of different evenness of coal slurry feed on dewatering effect, the results show that:in coal slurry containing a lot of particles less than the critical size, the greater of evenness, the worse of dehydration effect; In feed with little different evenness, the finer the particles size, the worse filtration and dehydration effects. This is because the smaller of evenness, the greater of porosity in filter cake formed by particles packing, the higher of permeability, which is beneficial to moisture removal; With a greater evenness, the drilling and blocking effect of fine particles will make themselves filling in pores, thus preventing dehydration in filter cake. Through the deposition kinetics study of filter cake, we find that,the relation of filter cake quality and filtration time is y=0.0002x3-0.0308x2+1.3565x+5.904, with the correlation index of 0.96.3、Study the influence of type and quantity of clay minerals on slime settlement and dehydration. There are many associated minerals in coal, with complex structure. Under the same broking conditions, minerals with sheet structure,like montmorillonite and kaolinite will have a smaller size composition, and quartz sands which belongs to parallelepiped structure will have a larger size composition. Under the influence of particles size and shape, the sedimentation effects of different minerals are quite different; With the decreasing content of minerals, organic components in coal will plays a dominant role in settlement and dehydration effect:the higher of vitrinite content in coal, the better of dehydration effect, as well as the decreasing quantity of hydrophilic groups, the increasing wetting heat and water absorption.4> Reveal the influence of the oxidation degree of weakly caking coal on settlement and dehydration effect. With the increasing oxidation degree, the law of settling velocity and filtration rate can be depicted as y=-5E-05x+0.0091 y=-0.0006x+0.0587, The supernatant turbidity and filter cake moisture can be depicted respectively as y=42.162e0.0222x、y=-0.0004x2+0.0688x+21.952, with correlation indexes higher than 0.9. This is because inorganic minerals and organic substance in oxidized slime have been separated, and clay minerals will disintegrate into micron-sized particles, thus coal water system will stay in stable suspension, due to its structure and surface properties and some other reasons. The organic composition of coal samples will react with H2O2, generating a lot of oxygen-containing groups after oxidation (-COOH、R-OH etc), making the Zeta potential increasing, in this way,the coal slurry system becomes more stable.5、Explore the coupling effect law of polymer flocculant on slime settlement and dehydration, the slime water system will produce closed vortex, making the instantaneous velocity gradient of local area increasing in vortex, causing the particles collide with each other, then producing floccules, showing three levels of settlement:single particle sedimentation, flocculation sedimentation and flocculation net settlement.And because of the different extent of bridging netting caused by flocculant, floccule size will have a big difference, resulting in a larger change of instantaneous sedimentation rate; when using flocculant alone, with the increasing amount of reagent, dehydration effect will gradually become better, but an excess of flocculants will lead to porous floccules, coercing more free water, adding the viscosity of slurry water system, causing sedimentation rate slowing down, worsen the permeability of filter cake, at last, affecting the final results of settlement and dehydration. When using coagulant and flocculant together, floccules will be dense and homogeneous, without the phenomenon of larger floccule hinding dehydration, However, the large number of positively charged ions released after flocculant hydrolysis will cause the particle surface charge reversing, presenting electropositivity, inhibiting flocculation and sedimentation in slime water.6、Based on the coupling effect of dehydration and settlement, we have determined the appropriate agents in dehydration system suiting for Pingshuo weakly caking coal, combined with sedimentation and dehydration strategy in reconstruction particles slime water, successfully resolved the dehydration and settlement problem of slime water in Pingshuo No.2 coal preparation plant which containing weathered and oxidized coal. Industrial test results show that, with the introduction of new reagents system and theoretical methods guidance, the selected raw coal increase from 15,000 t/d to 35,000 t/d, the pressure filter handling capacity increase from 1,500 t/d to 4,000 t/d, the reagents cost fells 60 percentage points, the overall economic efficiency improves significantly.