Study On Wettability Of Coal Dust Based On Its Surface Properties

The wettability of coal dust is a kind of physical and chemical characteristics of coal.In coal mine,the wettability of coal directly affects the success of coal dust injection technology.Wetting coal by changing the physical,chemical and mechanical properties of coal,thereby reduce or inhibit the dust-producing ability of coal mining.Meanwhile,water or aqueous solution can also wet the original coal and wrap the broken surface of coal,which effectively reduces the flying of the coal dust in the mining.Therefore,this paper studies the influence of the surface structure on wettability,introduces the research work of improving the wettability by adding the surfactants with different structures and presents the development effort of the coal dust removal.The specific work includes the following aspects:(1)In this paper,eight kinds of coal dust are selected as research objects.The properties of coal dust are analyzed and their variation law with the degree of metamorphism is studied.This research systematically measures and studies the surface properties of coal dust microscope via EDS spectrum analyzer,AFM atomic force microscope,laser particle size analyzer,high performance specific surface and the aperture analyzer,contact angle measuring instrument,surface tension meter and zeta potentiometer,etc.Different deformation degree of coal dust surface causes the extreme complexity of the surface properties such as chemical composition,pore structure and microscopic morphology and so on,which limits the wetting and agglomeration of coal dust to some extent.(2)After four characterization methods of coal dust wettability were studied,it was found that the concentrations of the four surfactants ranged from 0.1%to 0.6%have a better wetting effect.Through the analysis of four kinds of wetting liquid surface tension value of the minimum,the surface tension of the APG,the surface tension of SDBS,verify the good wetting effect of non-ionic surfactants to anionic surfactant.When the concentration of APG is 0.2%,the minimum surface tension is only 28.261mN·m-1,while when the concentration of SDBS is 0.2%,the maximum surface tension is 34.796mN m-1,The formula of wetting force is derived.The wetting force increases with the increase of surfactant concentration.For eight kinds of coal dust,YA coal dust with the best wettability and TX coal with the worst wettability.To different concentration and surfactant,the wettability of coal dust is also different.(3)Using APAM and CPAM as binder,the agglomeration effect of surfactant on coal dust was measured.The agglomeration effect of APAM is better than that of CPAM.On the one hand,due to the large molecular weight of APAM,more hydrogen bonds are formed on the surface of coal dust.On the other hand,the interaction time with hydrogen bond is relatively long,which is conducive to the formation and growth of agglomerates and the formation of larger agglomerates.However,the electrostatic adsorption time between CPAM and coal dust surface is relatively short and the formation size of agglomerates is relatively small.(4)This study analyses the effect of coal dust properties on the wettability and agglomeration of coal dust with the multi-step regression method.The result shows that the surface free energy,surface roughness and average pore diameter are the main influencing factors of the wettability of coal dust;and the surface potential and average pore diameter are the main influencing factors of the agglomeration of coal dust.In this study,the surface free energy,as a start,is used to derive the equilibrium contact angle equation between the droplets on the smooth surface and the Wenzel and Cassie droplets on the surface of the structure,and then it studies the coal dust wetting mechanism.At the same time,the influencing factors of the wettability and agglomeration of coal dust are analyzed microscopically.The mechanism of roughness on the two models was different.In the Wenzel model,the apparent contact angle is increased by increasing the solid-liquid contact area to increase the adhesion to the liquid.In the Cassie-Bax model,the apparent contact angle is increased by reducing the area fraction of solids in the composite contact to trap the air layer.It turns out that the former has better hydrophily than the latter.(5)The contact angle method was adopted to measure and analyze the wetting effect of surfactant on coal dust.And combining with the structural characteristics of rough surface of coal dust,the surface wetting model and permeability model of coal dust were established,and the applicability of these models were verified by experiments.Besides,this study analyses the agglomeration effect of the binder on coal dust with the transmissivity method,the adsorption behavior and mechanism of surfactants on the surface of coal dust are investigated from the experimental point of view.The effects of different concentrations of surfactants on the wettability of the coal dust with different degrees of metamorphism are analyzed in this study.(6)The optimal dusting agent formula for lignite is obtained through calculation and analysis:the concentration of the reagent with good wetting and agglomeration effect is as follows:alkyl glycoside(APG)0.25%,sodium dodecyl benzene sulfonate(SDBS)0.50%,anionic polyacrylamide(APAM)0.04%.At this concentration ratio,the model predicts a settling time of 20.4848s and a transmittance of 91.4827%.The optimum dusting agent formula for anthracite is:the concentration of the reagent with good wetting and agglomeration effect is as follows:alkyl glycoside(APG)0.15%,sodium dodecyl benzene sulfonate(SDBS)0.43%,cationic polyacrylamide(CPAM)0.03%.At this concentration ratio,the model predicts a settling time of 10.7619 s and a transmission rate of 89.8505%.The optimum dusting agent formula for bituminous coal is:the concentration of the reagent with good wetting and agglomeration effect is as follows:alkyl glycoside(APG)0.17%,sodium dodecyl benzene sulfonate(SDBS)0.49%,anionic polyacrylamide(APAM)0.05%.At this concentration ratio,the model predicts a settling time of 34.9025 s and a transmission rate of 93.7259%.