Experimental And Simulation Study On The Stirring Mechanism Of Sludge Anaerobic Reactor

With the continuous deepening of the sewage treatment process in China,the problem of sludge treatment as a by-product of sewage treatment has drawn increasing attention.Anaerobic digestion is the main method for sludge treatment and disposal,and sludge is stirred in anaerobic digestion reactors.The influence of the mass transfer process on anaerobic digestion efficiency has begun to be studied in recent years.In this paper,the 95%moisture content of sludge as the object,using the tracer method to study the mixing characteristics in the stirred tank reactor found that:By monitoring the change of tracer concentration at three different height sampling ports,it can be seen that the mixing time is exactly 31 minutes when the rotation speed is 140 rpm.At this point,the tracer concentrations at the three sampling points were 70%,80%,and 98%of the final concentration,respectively,but they showed a rapid upward trend,that is,the sludge was evenly stirred in a theoretical calculation at a stirring speed of 140 rpm.When the effect is achieved,the relevant mixing area has not been well mixed or evenly mixed.It cannot meet the optimal mixing and mixing time.When the rotation speed is 180 rpm,the mixing time is 19.5 minutes.At this time,the three sampling points are Tracer concentrations were 65%,81%,and 98%of the final concentration,respectively,but showed a rapid upward trend,that is,at the stirring speed of 180 rpm,when the sludge reached the theoretically calculated stirring uniformity effect,the relevant stirring area was It is evenly mixed and can meet the best mixing and mixing time.When the rotation speed is 220 rpm,the uniform mixing time is 8.5 minutes.At this time,the tracer concentrations at the three sampling points are 81%,78%,and 99%of the final concentration,and they show a stable state,that is,at a stirring speed of 220 rpm.When the sludge reaches the theoretically calculated uniform mixing effect,the relevant mixing zone has been mixed uniformly and is more able to meet the optimal mixing and mixing time.In other words,the rotation speed of 220 rpm stirs the sludge with 95%moisture content.However,through the energy analysis,it was found that the energy efficiency at a rotational speed of 220 rpm is higher than that at 180 rpm,and it has an unsustainable behavior.Through CFD technology,the non-turbulent model of the flow field in the agitating tank was numerically simulated in the mixing process at 180 rpm,and the tracer at the surface first flowed with the liquid flow to the agitator shaft under the reflux action generated by the upper blade,and then passed through.The axial pumping action of the upper blade entrains the flow to the upper blade and is then pushed to the wall with the liquid jet under the radial action of the upper blade or to the lower blade zone diagonally.Participate in the axial flow and radial flow motion of the lower blade to achieve the overall cycle process including the flow of the tracer,and realize the diffusion and mass transfer of the tracer through continuous shearing and tearing to achieve the most total mixing.Uniform.Based on the similarity principle and the Reynolds criterion and the Fondsworth criterion in the basic theory of model tests,the feasibility of 15 g·L^-1 KCl-XGKT solution as a similar solution for 95%water content sludge was proved theoretically.The test verified the theoretical analysis.After adding KCl,when the shear rate is in the range of?0-180?s^-1,the correlation exponents of the rheological characteristics of the two fluids are R2=0.9953 and R²=0.8935,respectively,showing the highest similarity,indicating the density Under similar conditions,the 15 g·L^-1 KCl-XGKT solution has similar rheological properties with 95%water content sludge.The mixed tracer experiment and significance analysis showed that the15 g·L^-1KCl-XGKT solution not only has 95%water content sludge without significant difference rheological properties,conforms to the similarity criterion of the same fluid movement,but also satisfies the actual flow field mixing.experiment.Therefore,the 15g·L^-1KCl-XGKT solution can be used as a transparent similar solution for sludge,providing a feasible method for the subsequent visualization of the anaerobic digestion flow field of the sludge.