Study On Oil-Water-Sand Separation Performance Of Three-Phase Decanter Centrifuge With Adjustable Overflow Structures

Oily sludge is one of the main solid waste produced in the process of petroleum exploration,mining,refining,processing,storage,and transportation.It is generally a very stable suspension emulsion system composed of three phases of water,oil and sand.The recovery of crude oil in oily sludge will produce considerable economic and environmental benefits.Oil-water-sand three-phase mechanical centrifugal separation technology has the advantages of low energy consumption,low pollution,simple operation,etc.,and is suitable for industrial applications in the treatment of oil sludge resources.The oil-water-sand three-phase separation process such as oily sludge treatment has the characteristics of complex material and liquid properties and large differences in concentration.During the use of traditional three-phase decanter centrifuges,the oil-water separation phase interface cannot be accurately adjusted according to the properties and concentration of the feed liquid and the needs of the separation product,which makes the separation effect unsatisfactory,and the separated products cannot meet the environmental protection and recycling requirements.Therefore,a new type of adjustable overflow weir plate three-phase decanter centrifuge structure model is proposed.Starting from the theoretical analysis of centrifugal separation,the analysis of the flow field and separation performance of the three-phase decanter centrifuge,and the experimental research on the three-phase separation of oil,water and sand,the optimized operating and structural parameters of the three-phase decanter centrifuge were obtained.Provide a strong basis for the industrial application of oily sludge treatment.First,the structural model and separation characteristics of the traditional three-phase decanter centrifuge were analyzed.And on this basis,a new type of adjustable overflow weir plate three-phase decanter centrifuge structural model was proposed,which was equipped with radial oil drain channel and overflow weir plates with adjustable position and size.The large-end flange structure was analyzed.The reason and characteristics of radial oil drainage were explained.The three-dimensional system assembly drawings of the new three-phase decanter centrifuge with adjustable overflow weir plates were established,and the structural parameters of the three-phase decanter centrifuge were optimized and analyzed to provide theoretical basis for subsequent numerical simulation and experimental research.In order to further deepen the understanding of the oil-water-sand three-phase separation process and mechanism in the drum of the three-phase decanter centrifuge,the centrifugal acceleration,oil-water-sand action mechanism and hydraulic balance in the three-phase separation process were studied and analyzed,and the separation effect was also evaluated,which provided a reference basis for the experimental measurement and result analysis of oil-water-sand three-phase separation.Next,a dynamic process model of the three-phase decanter centrifuge with interconnected compartments was proposed.The fluid separation process and the sediment accumulation and transport mechanism in the countercurrent three-phase decanter centrifuge were explained.Obtain the solid-phase mass dynamic balance equation and the dynamic change relationship equation of sediment transport and accumulation in the centrifuge compartment fluid regions.This dynamic process method can simulate the particle filling process at different times,and can determine the critical state during the operation of the centrifuge,providing opportunity for model-based separation process control.Secondly,based on the Euler-Euler model,the flow field and separation performance of the three-phase decanter centrifuge were numerically simulated,and the Euler-Euler multiphase flow theory and turbulence model were explained and analyzed.Established three-dimensional watershed model of the three-phase decanter centrifuge,and carried out grid division,boundary conditions and numerical setting.Through CFD numerical calculation,the oil concentration of the oil outlet was compared and analyzed for the traditional three-phase decanter centrifuge and the new three-phase decanter centrifuge with adjustable overflow weir plates.It is found that the former has a low oil volume concentration of about60% of oil outlet on average,and the separation effect of the oil phase and solid phase is not good,while the latter has an oil volume concentration of about 90% of oil outlet and solid phase volume concentration of 70% of sludge outlet.The recovery rate of the oil phase is high,and the solid phase of the residue is relatively dry.It is suitable for the three-phase separation of oil,water and sand,and is used as the three-phase decanter centrifuge model for the final experiment.Through structural model and numerical simulation comparative analysis,the traditional three-phase decanter centrifuge cannot accurately adjust the position of the oil-water interface,and cannot change the structure according to the difference of the feed liquid concentration to further improve the separation efficiency.The new type of adjustable overflow weir plate type of water drainage and oil discharge method,the overflow oil baffle and water baffle are adjustable.By adjusting the overflow weir,changing its height and position,the depth of the liquid pool can be controlled and therefore achieve the goals of controlling the dryness of the discharged solid residue and the clarity of the filtrate and oil phase.In addition,the oil-water two-phase separation interface can be controlled by adjusting the overflow weir,and the crude oil recovery or the clarification of the filtrate can be realized according to the required separation product,thereby improving the separation efficiency.Finally,through the oil-water-sand separation experiment of the three-phase decanter centrifuge with adjustable overflow weir plates,the influence of operating parameters,physical parameters and structural parameters on the separation performance was studied,and the numerical simulation research was compared and analyzed to verify the reliability of the numerical calculation.The optimized operating parameters of the three-phase decanter centrifuge and the structural parameters suitable for different materials were obtained,which laid a good foundation for the efficient and stable operation of the three-phase decanter centrifuge in the industrial production process.First,established the three-phase decanter centrifuge experimental system scheme based on the basic principles of economy and feasibility,and then built an oil-water-sand separation experimental system platform for the three-phase decanter centrifuge.The experimental process flow chart was determined to establish the oil-water-sand three-phase separation experiment system equipment,and detailed experimental procedures were formulated,so that the experimental research and measurement work were conducted.Starting from the rotating drum speed,processing capacity,sand concentration in the feed,oil concentration in the feed,and structural parameters,the respective effect laws on the solid phase recovery rate,oil phase recovery rate,oil loss in the filter cake and filtrate were studied.The suitable operating parameters,physical property parameters and adjustment methods of the overflow oil baffle and the inner oil baffle of the water outlet used in different material systems were obtained.By adjusting the overflow oil baffle and the water baffle,the position of the oil-water phase interface can be changed,thereby affecting the water content of the oil outlet and the oil content of the water outlet,so that changing the clarification efficiency and the oil phase recovery rate.In addition,when the required product is more focused on the clarification of the filtrate(water phase),or the main purpose is to recover crude oil and the purity requirement of the oil phase is higher,or it is beneficial to the drying of the solid phase or to the solid phase removal,the three-phase separation can be changed into different drainage methods such as water and oil-sand,oil and water-sand,or oil-water and sand.The new three-phase decanter centrifuge with adjustable overflow weir plates proposed in this paper can accurately adjust the overflow baffle according to the property and concentration of the feed liquid and the requirements of the separated product,thereby changing the phase interface of oil-water separation,so that the separated product basically reaches environmental protection and recycling requirements.Different liquid discharging methods can also be chose for separation according to the purpose and use of the separated product.The research on the separation performance of oil,water and sand by the three-phase decanter centrifuge will provide important theoretical and practical support for the application of high-efficiency complete sets of equipment including oily sludge treatment.