Study On The Effect Of Rheology On Internal Flow Characteristics And Separation Mechanism Of Drilling Fluid Centrifuge

The working performance of drilling fluid centrifuge is closely related to the properties of separation medium,while the centrifuge is a solid-liquid separation application.And due to the complicated internal structure,the existing theory is inadequate for centrifuges,and quantitative guiding the production and application process of centrifuge.Then,the working principles is the main cause of the contradiction between the "large throughput","high separation efficiency" and "low energy consumption".Considering the above-described issues,a research on the flow field of the drilling fluid centrifuge was carried out,which according to the different rheological fluid.Meanwhile,the flow characteristics and separation mechanism of the Newtonian fluid and non-Newtonian fluid in the centrifuge were discussed based on the numerical simulation and theory research.On one hand,the influence of parameters on the internal flow characteristics was analyzed,and a mathematical model of particle settlement in a drilling fluid centrifuge was presented to develop the calculation methods for the separation efficiency with the different theological fluid.On the other hand,the large throughput,high separation efficiency and low energy consumption were treated as the target to optimize the operation parameters of centrifuge,and analyze the influence of each parameter on the optimization results.The main research contents are as follows:Based on the structural characteristics of the drilling fluid centrifuge,with full consideration of the distributor,the speed difference of the screw propeller and the solid-liquid separation of the multiple-grain size granule,a numerical simulation model of drilling fluid centrifuge was built,and verified by contrast with experimental data.Then the influence of speed difference on the flow field parameters was analyzed to provide an analytical basis for the theoretical study of the centrifuge flow flied while the medium was the Newtonian fluid.Based on the structural characteristics and working principles of a drilling fluid centrifuge,with full consideration of its solid and liquid flow characteristics,a mathematical model of particle settlement in a drilling fluid centrifuge which related to the influence of initial settling position on centrifuge separation effect was presented.During the analysis of the drilling fluid's flow process that from different shapes distributor to the free surface of the drum,a calculation method of the initial settlement position of centrifuge was presented.This paper provided a theoretical foundation for the separating property calculation of different rheological fluids in the centrifuge.The calculation expression of circumferential velocity,axial velocity of fluid and settling velocity of particles were deduced with different flow states.Then the calculation methods for collection efficiency and separation efficiency of drilling fluid centrifuge were proposed,while the separation medium was Newtonian fluid,to reveal the relationship between the separation efficiency,fluid parameters,structure parameters and operating parameters.The numerical simulation model of drilling fluid centrifuge was built for the power-law fluid.Meanwhile,the centrifuge separation experiments was made for verifying the correctness and the accuracy of this model.The flow characteristics of the power-law fluid and the Newton fluid in the centrifuge were comparative studied to analyze the distribution regularities of velocity field,solid volume distribution,shear rate,viscosity and turbulence intensity,et al.Lay a foundation for the theoretical study on the centrifuge drum flow field of the power-law fluid.During the research that the consistency coefficient and the rheological index of the power-law fluid impact on the inner flow characteristics of centrifuge,the results were found that the influences of the power-law fluid's consistency coefficient and the Newton fluid viscosity on the centrifuge's flow characteristics are similar,and the influence of the rheological index on centrifuge's flow field is fully reflection of the shear dilution of the pseudoplastic fluid.The N-S equation which describes the flow of power-law fluid in the drum of the drilling fluid centrifuge was established to present the calculation method for the velocity distribution of power-law fluid in the drum.And the force analysis of a particle in power-law fluid was used to obtain the hindered settling velocity expression of particles with power-law fluid in the centrifugal field.Then,combined with the model of particle settlement,the calculation methods for collection efficiency and separation efficiency with power-law fluid were developed to firstly reveal the relationship between the separation efficiency,power-law fluid parameters,structure parameters and operating parameters.The energy consumption mechanism of drum which caused by the internal fluid was analyzed to deduce the calculation expression of drum energy consumption.Then two software were compiled,one was for predicting the separation performance of drilling fluid centrifuge;another one was for optimizing the operating parameters in goal of large throughput,high separation efficiency and low energy consumption.The above two software combines the theory research with the engineering practice,has a strong practical guiding significance.