| With the shortage of water resources,China's water supply industry faces the dual pressures of deteriorating water quality of drinking water sources and continuous improvement of effluent water quality standards.Therefore,it is particularly urgent to study the new theory and technology of water treatment to improve the efficiency of various processes in the water treatment process and to ensure the safety of drinking water for the majority of residents.The micro vortex flocculation process with intellectual property right is superior to the traditional flocculation process in water production rate and treatment effect in engineering application,but the study on its flow field characteristics and mechanism is still immature,and there is also blindness and randomness in the selection of process parameters in engineering application.Therefore,on the basis of previous research on micro vortex flocculation technology,the flow field in the process of flocculation was simulated and analyzed by using Fluent numerical simulation software,and the velocity and energy vector diagram and cloud diagram were obtained.The turbulent kinetic energy,energy dissipation and vortex scale were analyzed and studied,and the flocculation mechanism was revealed.At the same time,the floc performance parameters such as floc number,equivalent diameter and fractal dimension were obtained by computer image processing technology.The relationship between floc performance parameters and flocculation effect was further studied,and the operation parameters of micro-vortex current process were optimized.The concrete research results are as follows:1.Numerical simulation of flow field in micro-vortex flocculation reaction zone The hydraulic conditions and temperature affecting the flocculation effect in the micro vortex flocculation reaction zone were numerically simulated.The relationship?=2.743L11/32 A21/32[1-f?n?]3/4?v/Q?21/32 was obtained and verified in another circular clarifier.The experimental results can provide theoretical and practical guidance for engineering design.1)The average turbulent kinetic energy k,the average effective energy consumption ? and its changing rate increase with the increase of flow rate,and the vortex scale ? and its changing rate decrease with the increase of flow rate under 41 different working conditions at 20? and flow rate range from 2.0 m3.h-1 to 6.0m3.h-1?corresponding hydraulic load is 32 m3.m-2h-1 to 96 m3.m-2h-1??interval 0.1 m3.h-1?.The power function relation between vortex scale and flow rate is? = 96.896?v/Q?21/32,R2=0.9997.2)The vortex reactor dosage ratio 1?HJTM-1 type vortex reactors with opening diameter of 25mm and opening ratio of 45%are placed in grids 1#-5#,and HJTM-2 type vortex reactors with opening diameter of 35mm and opening ratio of 60%are placed in grids 6#-9#,without vortex reactors in the 10#-12#grids?,dosage ratio 2?1#-12#grids are equipped with HJTM-1 vortex reactors?,dosage ratio 3?no vortex reactor in the reaction chamber?were simulated.The correlations between vortex scale and flow rate can be obtained under different dosage ratios which are ?=95.666?v/Q?21/32,?=90.539?v/Q?21/32 and ?=115.883?v/Q?21/32,the correlation coefficients are R2 = 0.9956,R2 = 0.9937 and R2 = 0.9994 respectively;? With the addition of the vortex reactor,the vortex scale was gradually decreased;? By analyzing the reactor influence ratio,the vortex reactor can reduce the vortex scale value,wherein HJTM-1 vortex reactor can better reduce the vortex scale due to its smaller opening diameter and smaller opening ratio,but the influence of the vortex reactor with different opening ratio on the vortex scale will decrease with the increase of the flow rate.3)The flow field was simulated at 4.5m3.h-1?hydraulic load q = 72 m3.m-2h-1?and the temperatures were O?,5?,10?,15?,20?,25?,30?.The results show that the average turbulent kinetic energy k,the average effective energy consumption? and the vortex scale will be decreased with the increase of temperature;when the temperature is too low or too high,the vortex scale and the particle size of the squid were quite different,and the flocculation effect is poor,which explains the effect of temperature on the flocculation effect;the power function relationship between the 21 vortex scale ? and temperature?kinematic viscosity v?is ? = 95.666?v/Q?21/32,R2 =0.9964,which further demonstrates the relationship of ?=?v/Q?21/32.4)Different from the square tank studied in the experiment,the Fluent simulation of the circular micro vortex clarifier was carried out.The results show that under the condition of the HJTM-2 type vortex reactor being placed in the reaction chamber of the circular micro vortex clarifier,the vortex scale also has a good power function relationship with the flow rate.The correlation formula is ??48.860?v/Q?21/32 R2=0.9842,which fully proves the power function relation of ???v/Q?21/322.The effects of dosage of coagulant,vortex reactor dosage ratio and hydraulic load on flocculation were investigated.The process was optimized by orthogonal experiment.The relationships among floe performance parameters,between floe performance parameters and effluent quality,and between floe performance parameters and vortex scale were explored.The concrete conclusions are as follows:1)Orthogonal test study on hydraulic load,coagulant dosage and vortex reactor dosage ratio as control factors.? The removal rates of turbidity ranged from 62.11%to 96.81%,while the removal rates of CODMn and UV254 ranged from 16.82%to 64.12%and 30.21%to 55.56%respectively.The removal rates of turbidity and organic pollutants by adding vortex reactor was significantly higher than that by ordinary hydraulic clarifier?when the ratio was 3,that is,without adding vortex reactor?.Therefore,a reasonable dosage combination of vortex reactor could improve the flocculation effect.? The analysis of variance showed that the F value of the ratio on the removal of turbidity and UV254 was a highly significant factor.The dosage ratio of the removal of CODMn was a significant factor.The coagulant dosage on the removal of UV254 was a significant factor.The influence of the dosage on the removal of turbidity and CODMn was not significant.Hydraulic load was a significant factor for turbidity removal but not for the removal of CODNn and UV254.The overall contribution of factors for turbidity removal follows a trend in a sequence:dosage ratio>hydraulic load>coagulant dosage,while the primary and secondary relationship of CODMn and UV254 removal was dosage ratio>coagulant dosage>hydraulic load.? The optimum condition was working condition 2,i.e.96 m3.m-2h-1,coagulant dosage 22 mg.L-1,dosage ratio 1?HJTM-1 type vortex reactor is placed in 1#?5#grids,HJTM-2 type vortex reactor is placed in 6#?9#grids,without vortex reactors in the 10#?12#grids?,with a turbidity removal rate of 96.81%,CODMn removal rate of 47.88%and UV254 removal rate of 55.56%.2)The relationships among floc performance parameters,between floc performance parameters and effluent quality,and between floc performance parameters and vortex scale are as follows:? There is a good correlation between the fractal dimension of floc and the equivalent particle size.The relationship between the two was in accordance with the power exponent relationship,the correlation formula is Df = 1.5693·d0.4086,and the correlation coefficient R2 is 0.8935.? There are good relationships among the turbidity of water after settling and the floc performance parameters:the relationship between the turbidity of water after settling and the floc equivalent size is y= 4.06057x2-10.25439x + 7.12712,and the correlation coefficient R2 is 0.9282;the relationship between the turbidity of water after settling and the floc fractal dimension is y= 5.69169x2-20.26185x+18.77868,and the correlation coefficient R2 is 0.9016.? The smaller the difference between the vortex scale and the equivalent particle size,the better the effluent effect.The difference and turbidity removal rate are nearly in line with the linear relationship y =-63.4653 x +105.5974 with the correlation coefficient R2=0.7800.Complicated flow regime during flocculation has been simulated numercially and flow field information,such as turbulent kinetic energy,energy dissipation and eddy scale have been analyzed,which leads to the power function ???v/Q?21/32.the results contribute to reveal the dynamic mechanism about micro vortex flocculation and theoretically provide the basis supporting to optimize the structure of micro vortex reactor and flocculation tank.Meanwhile,flocculation characteristic parameters,such as floc quantity,equivalent diameter and fractal dimension have been obtained during flocculation.Relationships among floc characteristic parameters,floc characteristic parameters and effluent quality,floc characteristic parameters and vortex scale have been expored respectively,which establish the model combining the flow field information parameters,floc characteristic parameters and effluent quality together and further reveal the inherent law of micro vortex flocculation.The research combining analysis of flow field numercial simulation,floc imaging and pilot test plays a large role in optimizing the operation parameters of micro vortex flocculation process and provides theoretical basis and practice reference for the process,which makes far-reaching significance to promote the further development and application of the process. |
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