Design And Performance Of A High-Throughput Tubular Mixer-Reactor For Oily Wastewater Treatment

Measures to improve the efficiency of oil-water separation by adding chemicals to break the stability of oil droplets in emulsified oily wastewater are widely used in oily wastewater treatment processes.With the trend towards compact and piped equipment,the single side injection type tubular coagulator,although simple in structure,suffers from a single hydraulic condition,making the application limited.The complex mixing element structure of a traditional static mixer embedded in a tubular coagulant makes it difficult to clean and clog the pipes with the large amount of floc or sludge generated during the flocculation process.This thesis addresses the problem that the two stages of mixing and flocculation require different hydraulic conditions,and designs a high throughput tube type mixing-reactor with a two-stage structure of mixing and coagulation+flocculation reaction,using a simple thin plate mixing element and setting the chemical injection port at the rear end of the mixing element;the flocculation reactor is arranged with shaped convex blades on the inner wall of the tube to create moderate turbulence.The flocculation reactor is equipped with shaped convex blades on the inner wall of the pipe to create moderately turbulent hydraulic conditions to ensure large flocs.The paper starts with a CFD numerical simulation of the mixing performance of a high flux tubular mixer with four dispersed phase injection methods:single straight tube,single downstream plume,single counterflow plume and double downstream plume.The results show that when the three single tube injection methods are used,the internal and external mass transfer of the stable vortex is difficult and the mixing"dead zone"is easily formed;when the double compliant plume injection is used,the initial secondary flow intensity Se in the mixer is high and decreases quickly,and the rapid change of the secondary flow intensity in the flow field contributes to the rapid mixing of oil and water,and the CoV decreases at L/D=7 to 0.05,reducing the mixing distance by 76.9%compared to single tube injection.In order to establish the required hydraulic environment for the flocculation process,a flocculation mixing tank indoor test rig was built prior to the flocculation reactor structure design,and the influence of different hydraulic environments on the flocculation effect was investigated using numerical simulation+indoor experiments.With the increase of stirring speed,the treatment effect showed a trend of first increasing and then decreasing,and the best treatment effect was achieved at the speed of 800rpm,when the Reynolds number Re₁ in the stirred tank was 33333,and the turbidity removal rate and oil removal rate were 98.89%and 88.06%respectively.According to the optimum hydraulic environment for the flocculation reaction,the design of the shaped convex blades of the flocculation reactor was completed using the equivalent diameter method with the design criterion of maintaining the same Reynolds number Re.The distribution of Reynolds number and velocity in the flocculation reactor was analysed by CFD numerical simulations with different structural parameters of the shaped projecting blade.The structural parameters of the shaped projecting blade were selected according to the distribution of Reynolds number as follows:the height of the support blade L_a is 10 mm and the width of the blade L_b is 6 mm,and its Re₂ is closest to the optimum hydraulic condition Re₁=33333 at the same flow rate.The paper concludes with the design and construction of an indoor test and evaluation platform for the mixing-reactor for oily emulsified wastewater,using the response surface method and the floc characteristics parameters as evaluation indicators to analyse the treatment effect under different working conditions and obtain a quadratic multinomial regression model equation predicting the optimum shaped protruding blade spacing L₁ to be 2.84 D.The coagulation-sedimentation experiments of the emulsified oily wastewater were carried out based on the high flux tubular mixing-reactor.The effect of dosing rate,flow rate and flocculation reactor length on the treatment effect of the high flux tubular mixer-reactor was investigated.As the dosage and flow rate increased,the turbidity removal rate and oil removal rate both showed a trend of increasing and then decreasing.At a flow rate of 1.2 m³/h,a dosing rate of 10mg/L and a flocculation reactor length of 3 m,the turbidity removal rate was 80.27%and the oil removal rate was 89.09%.The theoretical and experimental research results show that the independently designed and developed tubular mixing-reactor can achieve efficient coagulation under low pressure drop conditions and help to improve the oil removal efficiency,which establishes the basis for the subsequent development of the product’s scaled-up design.