| Shale gas is a very important strategic resource of natural gas,and it is being exploited vigorously in our country.The actual exploit process will produce a large amount of shale gas fracturing flowback fluid which contains fine particles such as organic and rock particles.These fine particles makes the shale gas fracturing flowback fluid difficult to deal with.To come up with this problem,this thesis takes shale gas fracturing flowback fluid as the research object,adopts polyaluminum chloride(PAC)and polyacrylamide(PAM)as coagulants and flocculants,and adopts self-developed multi-flow step enhanced flocculation reactor for processing.The flocculation reactor has the advantages of good flocculation performance,short reaction time and low maintenance cost.The performance of flocculation reactor was evaluated by the treatment of shale gas fracturing flowback fluid.By monitoring the flow field inside the flocculation reactor,the mechanism of enhanced flocculation was studied The particle image velocimetry(PIV)was used to test the flow field distribution and enhanced flocculation mechanism in different areas of the flocculation reactor.A focused beam reflectometry(FBRM)was used to test the dynamic changes of particle number and particle size distribution in the samples.The fractal theory was used to analyze the morphology of flocs and evaluate the flocculation performance,so as to provide a technical solution for the flocculation treatment of microfine particles in shale gas fracturing flowback fluid.(1)Analyze of the enhanced flocculation mechanism of micro-fine particle by flow field and bulid the kinetic modeling in the cyclonic flocculation reaction zone.The effect of feed volume,PAC and PAM dosage,sample p H,as well as the structural parameters of the device(tangential inlet angle)on the removal rates of chemical oxygen demand(COD)and turbidity was investigated.The results showed that the removal rates of COD and turbidity reached 70.05%the 93.41%,respectively,when the inlet angle was 45~o,the feed volume was 40 L/h,the PAC dosage was 1 g/L,the PAM dosage was 0.2 mg/L,and the p H was 5.The internal flow field of the cyclonic flocculation reaction zone was tested by PIV,and the effect of fluid flow on the number and size of microfine particles and microflocs in the samples was tested by FBRM.The fractal dimension of flocs at vortex scale was calculated,and the kinetic mathematical model of cyclone flocculation reaction region was established based on vortex scale-fractal dimension.The results showed that the fractal dimension of microflocs reached the maximum when the feed volume was 40 L/h(the minimum vortex scale was about250μm).(2)Analyze of the enhanced flocculation mechanism of micro-fine particle by flow field and bulid the kinetic modeling in the vortex flocculation reaction zone.The effects of the inlet volume,the amount of PAC and PAM and the sample p H on the removal rates of COD and turbidity were investigated.The test results showed that the removal rates of COD and turbidity reached 69.00%and 90.19%,respectively,when the feed volume was 120 L/h,PAC dosage was 0.75 g/L,PAM dosage was 0.6 mg/L and p H was 4.The internal flow field of the vortex flocculation reaction zone was tested using PIV,and the effect of fluid flow on the number and particle size of microfine particles in the samples was tested using FBRM.The fractal dimension of the flocs at different fluid flows was calculated,and the kinetic mathematical model of vortex flocculation reaction region was established based on vortex scale-fractal dimension.The results showed that the fractal dimension of flocs was the largest when the feed rate was 120L/h(the minimum vortex scale was about 500μm).(3)Analyze of the enhanced flocculation mechanism of micro-fine particle by flow field and bulid the kinetic modeling in micro-vortex flocculation reaction zone.The effect of inlet volume,PAC and PAM dosage and sample p H on the removal rates of COD and turbidity were investigated.The results showed that the removal rates of COD and turbidity reached 72.00%and 86.00%,respectively,when the micro-vortex generator was arranged in 4 layers in the micro-vortex flocculation reaction zone,with the feedvolume of 80 L/h,PAC dosage of 0.5 g/L,PAM dosage of 0.4 mg/L and p H=6.The internal flow field of micro-vortex flocculation reaction zone was tested,and the effect of fluid flow on the number and size of microfine particles and microflocs in the samples was tested by FBRM.The fractal dimension of flocs at vortex scale was calculated,and the kinetic mathematical model of micro-vortex flocculation reaction region was established based on vortex scale-fractal dimension.The results showed that the fractal dimension of microflocs reached the maximum when the feed volume was80 L/h(the minimum vortex scale was about 300μm).There are 62 figures,9 tables and 110 references included in this thesis. |
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