Research Of Theory About Dust Prevention By Water-Cloud And Relevant Techniques For Fully-Mechanized Caving Coal Face

In this dissertation,the theories and techniques of dust prevention by water-cloud in fully mechanized and roof caving coal face are researched through the method of combining theoretical analysis,numerical simulation,experimental measuration and application on-spot. Therefore,the systematic knowledge hierarchy of dust prevention by water-cloud for fully mechanized caving face is formed.The atomization model about interaction of cavitation,turbulence and aerodynamic is put forward through the analysis about the control equation of jet disturbance and its solution, according to the conceptual model of spray based on two-phase flow,while the typical mechanism of dust capture by water-cloud is improved,through the active collision theory of droplet to dust particle.Using micro-particle image analyzer and dry powder laser granularity analyzer to measure the granularity,particle size distribution and form of the coal dust, sampling with the filter and manual method,which is produced in each production process in fully mechanized caving face pre and post the water-cloud is started,the qualitative regularities about the influence of spraying to average particle size and dispersity degree of coal dust produced in each production process are obtained.The basic mathematical model of fluid dynamics about the gas-particle two-phase flow is established during the process of dust prevention by water-cloud in fully mechanized and roof caving coal face,based on the combining method of Eulerian-Eulerian model and Eulerian-Lagrangian model,using hybrid difference scheme and SIMPLE algorithm on the basis of collocated grid to derive the numerical solution of the gas-particle two-phase flow,and carrying out the numerical simulation of gas-dust-droplet flow based on the computing platform of FLUENT software when spray is along the cross-section of the coal face.On the condition of utilizing the experimental device which is self-designed and manufactured to simulate the actual wind velocity of fully mechanized caving face,the simulative experiment of dust prevention by water-cloud in three different conditions—fan off, fan on without dust source and fan on with dust source is conducted,to research the coupling relationship between dust field and droplet field.From the experimental data,the droplets distribution regularity in the whole model space under the above three different conditions is obtained;the conception of "three fields" about the atomization effect of spray is put forward; the quantitative function expressions between D_{droplet without dust} andΔD are fitted in three intervals—[40,65]μm,[65,100]μm,[100,160]μm,which are all in the range of particle size 40-160μm that can ensure the droplet of capturing the dust basically,by using the method of numerical analysis.Furthermore,it is put forward that the optimum droplet size to capture respirable dust is 15-75μm;the quantitative mathematical formulae between D_{droplet without dust} and D_{dust not captured},formulae among D50_{droplet without dust},η_{total coal dust} andη_{respirable coal dust} are fitted; several qualitative conclusions about surfactant solution improving the effect of dust prevention by water-cloud are obtained through the coupling experiment of dust-droplet field while the surfactant is added into the water used for spray.According to the measured results of surface tension and contact angle of the single surfactant solution,the conclusions about the coal dust settling Walker experiment and the up-ward seepage experiment of the surfactant combination solution,the optimum surfactant reagent CZYNS-1 used for dedusting is defined; the technique of using volum-fixed pump to add surfactant is researched and developed. Moreover,the dedusting theory of surfactant is improved and extended through measuring and analyzing the critical surface tension of coal-dust test piece,the contact angle of coal-dust test piece in different granularity and coal simple in different porosity.Above-mentioned conclusions of the theoretical and experimental research can provide evidence for optimal selection of atomizing nozzles according to the characteristics of dust granularity in different production process,optimization design for devices used for dust prevention by water-cloud and confirmation of optimum surfactant reagent used for dedusting in fully mechanized and roof caving coal face.Finally,the engineering application about the research achievement is carried out in 1303 fully mechanized caving face of Dongtan mine and 10301 fully mechanized caving face of Xinglongzhuang mine in Yanzhou Mining Group, acquiring fine dedusting effect.