Study On Adhesion And Removal Fine Coal Characteristics Of Coal And Associated Minerals And Pneumatic Removal Fine Coal From Thermal Coal

In the cost structure of the coal preparation plant,the treatment of coal slurry water can account for more than 40%of the capital construction cost of the coal preparation plant,accounting for more than 30%of the operating cost.Therefore,reducing the amount of powdered coal entering the coal preparation plant and realizing the pre-selection of removed powdered coal to reduce the load of the slime water system and the amount of wet coal mud is one of the best ways to reduce the cost of the coal preparation plant.However,most of the domestic thermal coal preparation plants are restricted by the current screening technology in the depth screening of wet fine-grain coal.The domestic coal-fired coal preparation plant can only be sorted by about 13mm for pre-removal powdered coal.However,the content of powdered coal in the underground is increasing with the improvement of mechanization of coal mining,the final coal content of less than 13mm can reach 70-80%.If such a large amount of coal is not selected,the overall washing rate of raw coal is very low,and it is difficult to produce good economic and environmental benefits.The Pneumatic grading technology can achieve a dry-grained classification of any size between 0.5-13mm of damp coal.It not only expands the proportion of washing and selection,optimizes the product structure,but also simplifies the slime water treatment system,reduces the investment in construction and production costs,and maximizes economic benefits.Therefore,this paper begins with the study of the agglomeration and depolymerization characteristics between wet and viscous coal powders,combined with laboratory research and half industrial field test provides theoretical basis and technical application basis for its application,based on the commercial application of air classification technology and the improvement of the efficiency of ensuring the classification of moist coal gas stream.The bond characteristics of the coal and associated minerals were studied by studying the shear strength coefficient.The results show that:(1)The liquid bridge force between coal and mineral particles increases with the increase of particle size,the liquid bridge force increases gradually,and the adsorption amount of small particle coal samples increases,which aggravates the agglomeration effect between coal particles;If it is increased,the liquid bridge bond will be broken,the liquid bridge force will disappear,and the coal sample agglomeration effect will be weakened;However,as the coal particle spacing increases,the liquid bridge bond will be broken,the liquid bridge force will disappear,and the coal sample agglomeration effect will be weakened;(2)The increase of water content,the volume of the liquid bridge also increases,resulting in an increase in the coal bridge force of the coal sample,and the coal sample agglomeration effect is intensified.However,when the moisture exceeds 25-30%,the liquid bridge force can change from attractive force to repulsive force,from agglomeration to deagglomeration and dispersion;(3)The shear strength coefficient of coal and minerals is kaolin>bentonite>calcite>coal>quartz.The higher the mineral content,the smaller the contact angle.The larger the liquid bridge force,the easier the coal is agglomerated;The actual shear strength coefficient of the mixture is not a linear superposition,which reflects the synergistic strengthening between coal and associated minerals to increase the cohesiveness;(4)When the mixing ratio of different types of associated minerals is equivalent,the synergistic enhanced bonding effect increases the shear resistance coefficient significantly;(5)When the coal is mixed with the associated minerals,the sphericity of the shape of the mineral becomes better and the adhesion becomes weaker as the particle size decreases.(6)The greater the fractal dimension of coal and associated minerals,the weaker the agglomeration ability.As the moisture increases,the fractal dimension in each fraction decreases,and the coal is more likely to agglomerate,increasing the coal's bonding characteristics.Through laboratory and field actual removal of powdered coal tests,the results show that:(1)A given air volume has different total grading efficiencies corresponding to different grading granularities;Conversely,corresponding to a hierarchical granularity,different air volumes will have different overall classification efficiencies.With the increase of air volume,the classification granularity increases gradually,and the depolymerization effect increases with the increase of air volume,the upper limit rate increases gradually,the limit rate decreases gradually,and the classification efficiency increases.(2)The relationship between the graded particle size x and the required air volume Y is fitted according to the test data:Y=185.91x~3-11737.x~2+25527.x+646.23;(3)With the increase of feed rate,the dispersion depolymerization effect is worse,the limit rate is gradually increased,and the overall classification efficiency is gradually reduced,almost linearly decreasing;(4)The classification efficiency decreases as the moisture increases;(5)Applying Air classification technology to the Yitai Group Xizhao and Kaida wet raw coal for on-site dry-removing powdered coal,it is completely feasible to achieve the reduction of slime.For the coal of the West Call coal preparation plant,Air classification technology can carry out the classification of removable powdered coal of any size of 3-6mm for raw coal with up to 25%moisture.When the classification efficiency is about 17%,the classification efficiency can reach nearly 90%.When the moisture is as high as 25%,the screening efficiency can still reach more than 75%.For the raw coal of Kaida easy to be muddy and easy to be knotted,when the moisture content is 18.3%,the limit rate and the upper limit rate of the graded products are as low as 8.85%,and the total classification efficiency is 76%,and the effect is good.The pneumatic classification model is established based on the neural network,and the data set is randomly disrupted and then divided into a training set and a test set.The three factors of initial moisture content,presence or absence of vibration and drying time in the Pneumatic classification test were selected as the input of the neural network,and the two large-grain grades of the coarse-grained and fine-grained grades were respectively>6 mm,3-6 mm,and<3 mm.The content is used as an output to find the optimal parameters of the neural network by means of cross-validation.Two networks NN1 and NN2 are trained.The paper has 80pictures,72 tables,and 219references.