Numerical Simulation Study On Stirring Process Of Pig Manure Straw Vertical Hydrolysis Tank

As a promising new energy source,biogas energy is gradually gaining importance.Biogas fermentation is divided into three stages.When a two-phase fermentation process is used,the three stages are divided into a hydrolysis tank and an anaerobic fermentation tank.In this paper,the hydrolysis tank was used as the research object,and the flow characteristics and mixing process of the fluid in the tank were studied by numerical simulation.This paper has carried out a series of research and analysis,including:(1)Firstly,in order to study and analyze the flow field in a single-layer paddle stirring tank.In this paper,the physical model of the hydrolysis tank is established,and the appropriate meshing is carried out according to the characteristics of the model.The numerical simulation of the flow field in the tank is carried out by using the multiple reference system method and the standard k-? model.The basic flow characteristics of the fluid in the tank are obtained by analyzing the simulation results.(2)Secondly,the influence of different variables on the flow field in the stirred tank was studied.This paper studies the effects of different blade bottom height,blade spacing,material density and viscosity on the flow field in the tank.A small height from the bottom of the blade can result in excessive power consumption.The height of the blade from the bottom is too large,and the bottom of the tank is easy to deposit material.The effect is better when the height of the blade from the bottom is 0.35 m.When the pitch of the blade is small,more kinetic energy loss is caused.When the pitch of the blade is larger,the dead zone between the two blades increases.0.53 m is considered to be a suitable pitch of the blade.The hydrolysis reaction has little effect on the density of the material in the tank.During the hydrolysis reaction,the density has little effect on the flow field in the tank,and the velocity of the material in the tank is slightly reduced.As the hydrolysis reaction occurs,the viscosity of the material in the tank decreases.When the total solid concentration of the initial material is high,the initial viscosity of the hydrolysis is large.As the hydrolysis reaction occurs,the viscosity decreases more,and the viscosity change has a greater influence on the flow characteristics of the fluid in the tank.With the occurrence of the hydrolysis reaction,the range of the speed dead zone in the stirred tank is reduced,and the mixing effect is better.(3)Finally,the mixing process of the fluid in the double-layer paddle tank was studied and analyzed.The axial velocity of the intermediate horizontal surface of the two propellers is close to zero.It is difficult for the tracer to pass from above to the intermediate horizontal surface of the two propellers.The tracer in the double-layer paddle stirring tank is mainly rotated in the form of a mass around the stirring shaft at the beginning of the diffusion.It spreads around the paddle in a wraparound shape on the vertical plane.After the concentration gradient in the tank becomes smaller,the tracer diffusion rate becomes slower.