| In recent years,with,the continuous promotion of China's economic constriction,coal,as the main energy in China,has always maintained at a high position in China's primary energy production and consumption.With the mining of coal,a large number of mine water will be discharged.The direct discharge the water will not only pollute the environment,but also cause a huge waste of water resources.At the same time,due to the continuous improvement of the manufacturing level of high-end equipment in China,the comprehensive mechanized coal mining rate and coal output of underground mining also continue to improve,resulting in some new characteristics of the discharged mine water,the main performances are as follows:?the phenomenon of "running,emitting,dripping and leaking" of large-scale comprehensive mining equipment and hydraulic support increases the content of emulsified oil in mine water.?the increase of mining speed makes the concentration of suspended matter in mine water and special pollutants related to hydrogeological conditions increase.These new characteristics cause many problems in the operation of traditional,mine water treatment process.In addition,the central and western regions are the main coal producing areas in China,and the mine water is a kind of supplement of ecological water.It is generally required that the external drainage of coal mining enterprises should meet the requirements of class III water body in?the environmental quality standard for surface water?(GB3838-2002).The limits of petroleum and special pollutants(such as selenium,arsenic,mercury,etc.)in water are set.In other areas,the external drainage is required to meet((the requirements for suspended solids and petroleum in emission standard for pollutants from coal industry?(GB20426-2006).The new characteristics of mine water and the increasingly strict water quality standards in the future put forward higher requirements for the treatment effect and integration degree of water treatment equipment.Therefore,it is of great significance to develop an integrated equipment which can adapt to the new characteristics of mine water,meet the requirements of different water quality in different areas,and has the advantages of short process flow,small floor area,strong impact load resistance and quite intelligent.In this paper,a coal mine water in Ziyang County of Shaanxi Province is taken as the research object,and the contents of emulsified oil,suspended matter and selenium in the water were determined to exceed the standard through water quality analysis.Through process comparison and selection,to meet the relevant discharge standards,the floatation-ballasted flocculation-zero valent iron filtration process was adopted to treat the mine water.In the floatation unit,a new type of dissolved air release device was designed,which had the advantages of simple structure,adjustable bubble particle size and efficient operation.The mechanisms of bubble generation and change were explored.In addition,the design method of the release device was summarized,and the optimal demulsifier was screened through small-scale test.The removal efficiency of emulsified oil was compared with traditional TV type release device.The ballasted flocculation unit was used to remove the high concentration suspended solids in the water.The optimal range of the reaction conditions affecting the water quality were determined by the single factor test method.The factors that have significant influence on the water quality were screened out from the reaction conditions by Plackett Burman experiment.The interactions between the factors were determined by the steepest climbing experiment and response surface analysis experiment,and the optimal reaction condition was obtained.Under this condition,the flocs in the sludge bucket of the sedimentation tank were obtained.The fractal dimension,radius of gyration,porosity and characteristic length of the flocs were observed by stereomicroscope,and compared with the morphological characteristics of the ballasted flocs generated by the improved DLA model.The difference in settlement rate between the ballasted flocs and the ordinary flocs was calculated by the improved DLA model.According to the inclined tube sedimentation model,the difference between the general flocculation and ballasted flocculation in the total efficiency of sedimentation was compared,and the effect of ballasted flocculation to alleviate the blockage of inclined tube was verified by the experiment.For the special pollutant selenium contained in the water sample,the zero valent iron filtration method was used to remove it.The effects on the removal rate of selenium were investigated from four aspects:filtration speed,filtration layer height,residence time and filtration time.The changes in the properties of zero valent iron before and after selenium removal were characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD).At last,according to the conclusion of floatation unit,ballasted flocculation unit and zero valent iron filtration unit,the pilot plant was used to carry out the confirmatory operation.The data obtained in the operation process were fitted by the back propagation artificial neural network(BPNN),the generalized regression artificial neural network(GRNN)and the radial basis function neural network(RBFNN),respectively,and the optimal intelligence control method was determined.The main conclusions are as follows:(1)The size and quantity of bubbles in the hose of the release device are the result of the interaction of water cavitation,gas-liquid mass transfer and coalescence among bubbles,and the conditions such as the pore diameter,pipe diameter and dissolved gas pressure of the releaser will affect the above factors,thus changing the treatment effect of the release device;by comparing the numerical calculation of the particle size with the actual particle size released at the outlet,it is considered that the adopted calculation method has a considerable accuracy,which can be used to guide the engineering practice application.Through the small-scale test,the optimal formula of demulsifier is determined as AR:PFS:PAM=10mg:40mg:0mg.By the way of continuous test,it is considered that the emulsion oil removal performance of the new type release device is better than that of the traditional TV type release device.(2)In many conditions that affect the quality of the effluent from ballasted flocculation and common flocculation,the dosage of coagulant,the dosage of flocculant,the mixing intensity of the curing tank and the mixing intensity of the injection tank all have significant effects on the quality of the effluent.Under the optimal reaction conditions,the flocs generated by the improved DLA model are in good agreement with the actual flocs in terms of morphological characteristics.Through the settlement rate experiment,it is observed that the difference between the theoretical and measured settling rate fitting curves of ballasted flocs and common flocs are small,which shows that the theoretical calculation method can effectively represent the actual settlement process of flocs;through theoretical analysis and experimental results show that the total efficiency of ballasted flocculation are higher than that of common flocculation,and ballasted flocculation can effectively alleviate the sludge accumulation and blockage in inclined pipe of sedimentation tank.(3)in the process of selenium removal by zero valent iron,the backflow of the filter material has an important influence on the homogeneity of the filter material and the separation of selenium in the filter layer;the filter speed,the height of the filter layer and the residence time have an important influence on the removal rate of selenium,and the increase of the filter speed will significantly reduce the removal rate of selenium;in a certain range,the increase of the filter layer height will increase the removal rate of selenium in the selenium mine water,but when it exceeds a certain range,the removal rate of selenium will decrease with the increase of filter height;for the contact time,the removal rate of selenium in water will increase with the time.When the filter material is flow back,the selenium removal rate of the filter keeps stable with the prolongation of the filtration time;when the filter material is not flow back,the selenium removal rate tends to decrease with the prolongation of the filtration time,but compared with the traditional iron and manganese removal filter,the decrease is smaller,which shows that the filter material has the characteristics of high selenium removal capacity and long service life.(4)BPNN,GRNN and RBFNN are used to fit the parameter relationships of the pilot plant.From R2 and RMSE,RBFNN performs better than the other two artificial neural networks.Through the comparison of the optimal reaction conditions between the artificial neural network control and the small-scale experiment,the reason for the difference in the results is the difference in the treatment scale.A smaller treatment scale is more conducive to the mixing of the liquid medicine solution and the raw water,the mixing time is shorter,and the reaction is more sufficient.The larger treatment scale means that the greater mixing strength is needed,and the greater hydraulic shear force will be available near the mixing blade,which is not conducive to the formation and continuous growth of flocs. |
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