Gas-injected Vortex Flocculation Reactor And Experimental Study On The Treatment Of Fracturing Flowback Fluid From Shale Gas

With the wide application of fracturing technology in oil fields and natural gas development,a large number of fracturing flowback fluids have been produced.Fracturing flowback fluid has the characteristics of complex composition,variety of organic matters,high degree of emulsification and stable system,which make it difficult to treat.The treatment process of conventional fracturing flowback treatment is complex,variety and large amount of chemicals,and easy to cause environmental pollution and large investment in equipment,which is one of the urgent problems to be solved in the development of shale gas and environmental protection.Therefore,it is imperative to high efficiency and low cost fracturing flowback treatment technologies.Flocculation technology is an essential part of fracturing flowback treatment.The development of efficient flocculation equipment has become the important directions of flocculation technology development.In this paper,aiming at the flocculation treatment of the flowback fluid of shale gas fracturing,a novel gas-injected vortex flocculation reactor was developed by strengthening the flocculation of micro-floc in the micro-vortex flow field with micro-bubbles.Computational fluid dynamics?CFD?numerical simulation technology was used to simulate the flow field and optimize the structure of the reactor.Particle image velocimeter?PIV?was used to measure the single-phase flow field in the reactor and verify the simulation results.The enhanced flocculation experiment of shale gas fracturing flowback was carried out in a laboratory-type vortex flocculation reactor,and its flocculation performance was evaluated?1?Numerical simulation and experimental study of gas-injected vortex flocculation reactor.The physical model of gas-injected vortex flocculation reactor construct was desigin by using the three-dimensional modeling software solidworks.The Eulerian multiphase flow model,standard k-?turbulence model,Schiller-Naumann drag coefficient model and Tomiyama lift model were selected to simulate the flow field of the reactor.Simulation results show that the large-vortex zone occupies a large proportion of space and the micro-vortex is not obvious,which is not conducive to formation the micro-vortex flocculation.The field flocculation experiment was carried out in in a pilot-scale gas-injected vortex flocculation reactor to investigate the effect of liquid feeding rate,gas feeding rate,PAC and PAM on the flocculation effect.The experimental results shown that the COD removal rate in the shale gas fracturing flowback fluid reached 23.64%at the condition of liquid feeding rate was 600 L/h,gas feeding rate was 120 L/h,and PAC and PAM consumption of 10mg/L and 1 mg/L,respectively.?2?The structure optimization and numerical simulation of gas-injected vortex flocculation reactor.Based on the separation of the fluid boundary layer and the addition of local blocking flow,the structure of the gas-injected vortex flocculation reactor was optimized,and the inverted cone-cone-inverted cone structure was set,and the vortex generator was added.Through numerical simulation,the distribution of the flow field and its influence on flocculation were analyzed.Under the conditions of inlet velocity of 0.5 m/s,0.7 m/s and 1.0 m/s,the influence of inlet velocity the vortex flow field was analyzed and the inlet velocity was optimized.The turbulent dissipation rate,the vortex velocity gradient G₀ and the vortex scale?at different characteristic sections of the reactor were analyzed.Simulation results shown that the small-vortex flocculation reaction zone become larger and was dominated by radial motion,and the radial velocity range is 0⁰.08 m/s.The radial velocity gradient maked the flocs collide and break up,forming large and loose flocs.In the micro-vortex flocculation reaction zone had the double flocculation of vortex and cyclone,and the contact flocculation is carried out under the participation of micro-bubbles,which was conducive to breaking up the large and loose flocs to regenerate the small and dense floc.The mean vortex velocity gradient in the small-vortex zone was 42.78⁴8.06 s^-1,and that in the micro-vortex flocculation zone and the plug flow zone was 96.44 s^-1 and 7.69 s^-1,respectively.The shear breaking effect was relatively weak,and the collision of particles generated by velocity gradient can form a more effective flocculation effect.The vortex scales at different characteristic sections were all less than 1.0 mm,and the micro-vortex promotes the formation of small and dense floc.?3?Flow field measurement of gas-injected vortex flocculation reactor.Single phase flow measure was carried out for the internal flow field of the improved gas-injected vortex flocculation reactor.The range of Y=-350 mm^Y=-50 mm was selected for measurement.The height of Y=-270 mm and Y=-100 mm were selected as the data reading line,and compare their axial and radial velocity with CFD simulation results.The results shown that the measured values of axial velocity and radial velocity of the characteristic cross sections at Y=-270 mm and Y=-100 mm were consistent with the CFD simulation values,and the trend of velocity distribution was consistent.Measure results proved the reliability and accuracy of the simulation results.?4?Treatment of Fracturing Flowback Fluid from Shale Gas by Improved Gas-injected Vortex Flocculation Reactor.The enhanced flocculation experiment of shale gas fracturing flowback fluid was carried out in a improved gas-injected vortex flocculation reactor.The effects of flocculation sedimentation time,liquid feeding rate,gas feeding rate,rubber breaker?K₂FeO₄?,dosage of coagulant?PAC?,flocculant?PAM?and pH value on COD and TOC removal were investigated.CCD camera was used to take pictures of floc at different characteristic section heights,calculate and the equivalent particle size of floc,and compared with the simulation values of vortex scale.The experimental results shown that the removal rate of COD and TOC was up to 27.40%and 35.45%,respectively,under the conditions of liquid feeding rate and gas feeding rate were 2.0 L/h and 2.0 L/h,K₂FeO₄,PAC and PAM dosage were 120mg/L,15 mg/L and 2.5 mg/L,respectively,and pH=11.The images of flocs under different characteristic sections were photographed by CCD camera,and the floc images were statistically analyzed.The relative deviation between the equivalent particle size of flocs and the simulation value of vortex scale was 0.38 mm at the maximum and 0.01 mm at the minimum,and the vortex scale was close to the floc equivalent particle size,which indicated that the micro-vortex generated in the reactor promotes the mutual collision of colloidal particles,thus forming an efficient flocculation.The paper has 47 pictures,11 tables and 115 references.