Experimental Study On The Reduction Of Sludge Flowing Resistance In Pipe Flow Based On Water Film Method

As a by-product of urban sewage and wastewater treatment,the output of sludge is increasing day by day.Generally,the sludge treated by the sewage plant still contains a lot of toxic substances.If it is not treated in time,it will cause great harm to people and the environment.In view of the limitation of sewage plant construction in China and the current situation of land resource utilization,it may be impossible to build a similar sludge plant near the sewage plant for on-site disposal of sludge.Therefore,more and more large-scale sludge plants are established in the suburbs,and the sludge from different sewage plants is treated in a unified manner,and the importance of sludge transportation has been highlighted.Compared with trucks,barges,etc.,pipelines have advantages in large-scale transportation.But as a viscous material,wet sludge has poor fluidity and strong adhesion will seriously harm the normal operation of the system.Therefore,exploring the method of reducing viscosity and drag during wet sludge pipeline transportation has great application value for wet sludge pipeline transportation.In view of the mature application of water film viscosity reduction in pipeline transportation of other viscous materials,our research group built a small wet sludge pipeline viscosity reduction device based on a self-made water film generator.Factors such as sludge moisture content,flow rate,water-sludge ratio,water injection temperature and other factors are analyzed and explored.Furthermore,a medium-sized wet sludge pipeline viscosity reduction device was constructed,and the changes in the pipeline specific friction and drag reduction efficiency were analyzed.The overall experimental results provided reference for the practical application of wet sludge water film viscosity reduction and drag reduction.The experiment first carried out the research on the rheological characteristics of wet sludge,which provided a reference for the flow resistance of the wet sludge pipeline.The experimental results show that the stress-time curve of wet sludge has mainly gone through four stages.The dynamic yield stress value will increase significantly as the moisture content of the sludge decreases.The dynamic yield stress of the sludge at 75% moisture content can reach 7961 Pa.In the case of low moisture content,the dynamic yield stress value measured by repeated experiments fluctuates bigger.Next,a self-made water film generator was used to carry out a small-scale wet sludge water film pipeline viscosity reduction and drag reduction experiment.The results found that the water film viscosity reduction efficiency will increase with the increase of the water-soil ratio,but if the water-soil ratio keeps increasing,The efficiency increase will be smaller.Under the condition of82.4% moisture content and 42.4 m L/min,the water-sludge ratio of 0.03 is the best working condition for reducing the viscosity of the wet sludge water film.The increase in the flow of wet sludge in the pipe will result in a decrease in the efficiency of water film viscosity reduction.In addition,increasing the water temperature can also improve the viscosity reduction efficiency of the water film.The lower the water content,the more significant the improvement effect of the viscosity reduction efficiency.On the basis of the above experiments,a medium-sized wet sludge pipeline viscosity reduction device was further designed and built.The device is mainly composed of a pushing part,a cylinder part,a water film injection part,a pipeline part,and a data acquisition part.The device has sufficient driving force to ensure continuous flow of wet dirt in a longer pipeline.At the same time,the water film injection part can achieve precise water addition control.The pipeline pressure data during the experiment can be read in real time by a pressure sensor.After the experimental device was built,the accuracy test was launched.The result shows that the maximum fluctuation error of the measurement result is 5.1%,which meets the requirements of experimental measurement.Finally,further experiments were carried out in the medium-sized wet sludge water film viscosity and drag reduction device.It is found that the specific friction resistance of the pipeline increases with the increase of the wet sludge flow rate.At a sludge flow rate of 0.16 m/s,the pipeline specific friction resistance can reach 371,642 Pa/m.As the water-mud ratio increases,the specific friction of the pipeline decreases.The drag reduction efficiency will increase with the increase of the water-sludge ratio.The 0.03 water-sludge ratio is the best drag reduction point when the flow rate of the wet sludge is 0.06m/s and 0.10m/s.The rheological parameters of the wet sludge pipeline under various experimental conditions are fitted with the Bingham model,and the yield stress value obtained by the fitting is relatively close to the experimental results.But as the water-soil ratio increases to 0.03,the model is no longer applicable.The analysis shows that the flow velocity distribution of the water film flow is the same as that of the ordinary round pipe,and has nothing to do with the core fluid.The theoretical value of the shear stress during water film flow is quite different from the actual value.The water film encapsulation degree increases with the increase of the water-sludge ratio,and decreases with the increase of the sludge flow rate.