Study On Technology Of Efficient Coal Dust Prevention And Control By Foam

Coal dust,one of the major hazards in the mining process,seriously threatens the occupational health of underground workers and the safe production of coal mining enterprises.With the advantages of high dust-reducing efficiency,strong wetting,low water consumption and large coverage area,the foam dust-reducing technology has become an important way to efficiently prevent and control coal dust.However,this technology still has problems such as large ratio of dust-reducing agent addition,high consumption as well as considerable pressure loss and poor stability of quantitative addition,which restricts its promotion and application to some extent.The foam dustreducing agent,which is the core material of the foam dust-reducing technology,directly determines the economic cost and comprehensive performance of the dustreducing foam.The performance of the quantitative addition equipment determines the available pressure range of its downstream equipment,further affecting the foaming effect of the foam dust-reducing agent and limiting the foam spray distance.This study is aimed at solving the problems of high cost of the foam dust-reducing technology and large pressure loss induced by quantitative addition.To achieve this aim,in this study,based on the basic theories of surface physics and chemistry and fluid mechanics,the foam dust-reducing technology was investigated from four aspects,i.e.,the characteristics of foam for efficient coal dust control,its mechanism of wetting coal dust,the law of energy loss of quantitative addition equipment,and the low-energy-loss and high-precision quantitative addition technology,through the combination of experimental research,molecular dynamics simulation and fluid mechanics numerical calculation.Furthermore,the new foam dust-reducing agent and the new nonaxisymmetric quantitative addition equipment were tested and applied in the field.The main research results are as follows:A new type of foam dust reduction agent based on the biopolysaccharide stabilization foam was developed through analysis and experimental research on the characteristics of the dust-reducing foam.On the basis of in-depth analysis on the factors influencing the hard water resistance,foaming,wettability and environmental protection of the dust reduction foam,the effects of compound systems with different ratios on the foam volume and foam stability were explored by using the synergistic effect of anionic/nonionic surfactant and nonionic surfactant.The exploration reveals that the foam achieves the best comprehensive performance when the mass ratio is 8:2.The mechanism of biopolysaccharide XG delaying the decay of the foam film and enhancing the foam stability was elucidated.According to the requirements of foam stability in excavation operation,the optimal concentration ranges of foam wetting component and foam stabilizing component are 0.75‰-5‰ and 0.3‰-1‰,respectively.The mechanism of hydrolyzed cations and EO group of anionic surfactants in the foam dust-reducing agent on coal dust wettability was revealed by combining experiments with molecular dynamics simulations and quantum mechanics calculations.The results show that at low concentrations,ammonium dodecyl polyoxyethylene ether sulfate(ALES)and sodium dodecyl polyoxyethylene ether sulfate(SLES)are superior to TD and SDS in terms of wetting ability,and the wetting ability of these four solutions differs insignificantly when the concentration is greater than 3‰.This is because the performance of the solutions in wetting coal dust is not only related to their surface tension and the adsorption density of surfactants on the coal dust surface,but also largely dependent on the hydrophilic and lipophilic equilibrium values of surfactants,the type of hydrolyzed cations and their adsorption configurations on the coal dust surface.Besides,the molecular dynamics simulations show that the hydrolytic ions of TD and SDS have a stronger binding force on the water molecules around them,which is inconducive to the diffusion of water molecules on the coal dust surface.For the four systems,the stability,the distribution width of surfactant molecules along the Zdirection and the active degree of water molecules on the coal dust surface follow the descending order:ALES>SLES>TD>SDS.Compared with Na+ and TEA+,NH4+ is more capable of penetrating into the surfactants and adsorbing to the coal dust surface.According to the surface electrostatic potential analysis,NH4+ makes a certain contribution to improving the wetting properties of coal dust surface.The energy conversion,the law of energy loss and the main causes of energy loss under the cavitation condition of the quantitative addition equipment were investigated by both experiments and numerical simulations,and a new type of non-axisymmetric quantitative addition equipment was developed.The following findings were obtained.The periodic oscillation of the cavitation cloud is caused by the spatial and temporal difference of fluid medium vaporization and liquefaction.The head loss in the c-d section(Hc-d)has a more notable influence on the total head loss.When the cavitation number σ is smaller than the critical cavitation number σcr and the inlet pressure pi and the secondary flow rate Qs are certain,the pressure losses in the c-d and a-d sections(Pc-d and Pa-d)decrease linearly with the increase of σ,and the pressure losses in other sections remain unchanged.When pi and σ(σ<σcr)are constant,Pb-c decreases with the increase of Qs,while Pc-d increases with the increase of Qs.When Qs=0 and σ(σ<σcr)is constant,the pressure losses in all the sections increase with the increase of pi.The energy loss in the quantitative addition process is mainly caused by cavitation and turbulence,and it is basically symmetrically distributed along the central axis of the equipment.Reducing the diffusion angle on the side farther from the suction tube can effectively weaken the turbulence and cavitation intensity on that side.Resultantly,the cavitation cloud only appears in the local area near the suction port of the diffusion tube,which not only shrinks the scope of cavitation damage and energy loss,but also effectively enhances the cavitation performance and suction stability of the quantitative addition equipment under low pressures.The total head loss rate φ1-5 is the smallest when the area ratio f between the diffusion tube inlet and the contraction tube outlet,the diffusion angle β,the characteristic length of throat lt and the contraction angle αare 1.44,6°,2 and 30°,respectively.The#7 equipment has both a high hcr,0(critical pressure ratio in the non-absorbent state)and a large k(slope of the critical pressure ratio-critical flow ratio fitting curve),while the#1 equipment is more suitable for the foam dust-reducing process as its hcr,0 is as high as 0.799.Engineering experiments and field applications were performed on the new foam dust reduction agent and non-axisymmetric quantitative addition equipment,and its effect was compared with that of the common foam dust-reducing agent without a stabilizer.The results demonstrate that the foaming performance of the new foam dustreducing agent is better than that of the common foam dust-reducing agent,especially under a relatively low addition concentration.The new addition equipment fully meets the requirements of stable adding and foam spraying distance under the condition of high multiplier foaming.When the addition concentration of the new foam dustreducing agent is 1‰,the foam achieves a dust-reducing rate of 90.50%and 90.09%for total dust and respirable dust,respectively,which is higher than that of the common foam dust-reducing agent under the addition concentration of 2‰.In its application,the addition concentration of the new foam dust-reducing agent can be reduced to 1/2 of the original one,or even lower,and meanwhile a good dust-reducing effect can still be ensured.In summary,the new foam dust-reducing agent boasts reduced cost and promoted efficiency.This dissertation contains 140 figures,35 tables,and 266 references.