Research On Frictional Resistance Of Pipeline Transportation Based On Sludge Rheological Properties

At present,the national sludge disposal requirements for urban sewage treatment plants are increasingly strict,and the rapid development of sewage treatment processes has caused the diversity and complexity of sludge types.At the same time,sludge is a complex non-Newtonian fluid with complex and diverse rheology.The characteristics directly affect the flow characteristics of the sludge during pipeline transportation and pumping.However,there is still a lack of systematic and in-depth research on the effect of the rheological properties of the sludge on sludge transport and pumping at home and abroad.In this dissertation,we will conduct research on the characteristics of sludge rheological characteristics,combine it with the transport characteristics of sludge pipeline transportation and pumping,and use numerical simulation of computational fluid dynamics to analyze the rheological characteristics of sludge.The influence of the parameters on the sludge pipeline transportation system is expected to provide a data foundation for sludge pipeline transportation system design and provide a scientific basis for the sludge disposal of the urban wastewater treatment plant and achieving the goals of economical efficiency,energy conservation and emission reduction.In this study,the rheological properties of sewage sludge from surrounding wastewater treatment plants in Beijing were tested,and the effects of TS,temperature,and treatment processes on the rheological properties of the sludge were investigated.The relationship between TS and temperature and rheological parameters was also fitted.Based on the rheological parameters,the CFD numerical simulation of the sludge transport in the pipeline was conducted.The influences of the diameter,flow velocity,TS,and inclination angle on the sludge transport in the pipeline were examined.The rheological parameters and transport friction were analyzed.Friction coefficient and transitional flow rate relationship.Now draw the following conclusions:(1)With the increasing of the shear rate,it exhibits the characteristics of the expanding plastic fluid.The variable characteristics can be fitted using the Herschel-Bulkley model;the yield stress is a power law relationship with TS;the limiting viscosity and the thixotropy ring area are exponentially related to TS;TS greater than 6.77%,the yield stress is significantly higher,and the viscosity of the sludge occurs Significant changes;when the TS of the sludge reached 6.22%,the area of the thixotropic ring was 1388.80 Pa·s-1,showing a strong thixotropy.The limit viscosity,yield stress,k value and the area of thixotropic ring of sludge showed a decreasing trend with the increase of temperature,and the viscosity was more obvious at low shear rate,and the change rate of high shear rate was not significant.(2)The flow velocity at the tube wall is the lowest,the maximum flow rate appears at the center of the tube,and the pressure decreases radially from the wall toward the axis.As the flow rate increases,the pressure drop of the pipeline increases linearly.At the same flow velocity V,with the increase of pipe diameter,the pipeline pressure drop gradually decreases,and the decreasing trend gradually increases.When TS is greater than 6.77%,the velocity and pressure are not evenly distributed,and the maximum velocity is located at the lower right of the axis.With the increase of TS,this trend is more and more significant;the pressure difference of pipeline increases with the increase of TS.The relationship between pipeline pressure difference and TS accords with the index relationship;when TS is greater than 6.77%,it is not suitable for long-distance transportation.(3)When the pipeline has an inclination angle,the velocity distribution is similar to that of the horizontal pipeline,and the pressure difference of the pipeline at different inclination angles is fitted by the formula,which is consistent with the polynomial relationship.When the inclination angle is about 60°,the differential pressure peaks.After the sludge flows through the 90° elbow,a high velocity zone is formed at the inside of the vertical pipe and a vortex is generated at the corner,causing energy loss.When the pipe section is suddenly expanded,vortices will form at the shoulders,and the energy exchange will occur between the vortex area and the flowing mainstream area,resulting in a reduction of the mainstream energy and an increase in transportation friction.(4)The greater the sludge viscosity,the yield stress,and k,the greater the pressure drop of the sludge transported in the pipeline,and the increasing trend gradually increases.The pressure drop of transport increases with n.And falling.The relationship between the limiting viscosity,yield stress,k,and n and the pressure drop of the pipeline was fitted.The friction coefficient f decreases with increasing flow rate.When the flow velocity is greater than 2.0 m/s,f tends to a stable value;the relationship between f and flow velocity can be described by an exponential function;f increases with the increase of TS,and The change in the low flow rate zone is more significant: f decreases with increasing pipe diameter.The transition velocity increases first and then decreases with the increase of TS,and increases with the increase of temperature,and this trend is more significant when TS is higher.