Experimental Study On Improvement Of Flocculation Efficiency Of Mixing Paddle In Mechanical Stirring Clarifier

Mechanically stirring clarifier has been widely used in tap water and wastewater treatment plants because of their high treatment efficiency,good flocculation effect,and strong adaptability.In the process of urban construction and development,the condition of water resources is constantly changing,and regulations such as tap water have become more and more stringent.These put forward higher requirements on traditional water treatment equipment,causing it to be overloaded frequently,and at the same time the effluent quality also fluctuates greatly.Some scholars have analyzed and studied the mechanical stirring clarifiers under actual engineering,and pointed out that the mechanical stirring clarifiers has great potential for transformation.The hydraulic conditions of the structure directly determine the flocculation effect.Therefore,it is necessary to optimize the design of the mechanical stirring clarifiers from the hydraulic conditions.As the main component of the flocculation and stirring,the structure of the mixing paddle is directly related to the hydraulic dynamics of the equipment.At present,there is a lack of relevant research on the structural parameters of the mixing paddle at home and abroad,and the current standards in our country have not been clearly stipulated.Therefore,this article will use a combination of physical model tests and numerical simulations to study the hydraulic conditions of the clarifier under different outer diameters,shapes and numbers of mixing paddle structures,then clarify the impact of each key structural element on the efficiency of the clarifier water treatment.Give the best mixing paddle structure parameters.The main results are as follows:1.Through physical experiments,it is found that the current water treatment effect under the common mixing paddle structure is not ideal,the turbidity of the effluent is high,and the amount of sedimentation of flocs is small.The main reason for its low efficiency is insufficient disturbance to the water body.After optimizing the outer edge diameter,shape and quantity of the mixing paddle,the water treatment effect has been improved to varying degrees,indicating that the structural parameters of the mixing paddle have an important influence on the efficiency of the clarifier.2.Different factors have different degrees of influence on the water treatment effect of the mechanically stirring clarifiers.The shape of the mixing paddle>the outer diameter of the mixing paddle>the number of the mixing paddle.The shape and outer diameter have a significant influence,and the influence coefficient of the number of the mixing paddle is less than a half of the first two items,so the optimization of the clarifier should first focus on the shape and outer diameter of the mixing paddle.3.In terms of the shape of the mixing paddle,under the condition that the area of the paddle is increased by 25%,the treatment effect of the trapezoidal mixing paddle is better than increasing the width,and the increase of the length has little effect on the water quality;in terms of the outer edge diameter of the mixing paddle,3.6 m outer diameter is better than 3.2m and 4.0 m,the turbulence is insufficient when the outer diameter is too small,and the floc will be destroyed when the outer diameter is too large.4.Comparing the hydraulic conditions and water treatment effects of the mechanically stirring clarifier under different mixing paddle structure parameters,the best structure parameters are given when the nominal water volume is 1330 m³/h:The diameter of the outer edge of the mixing paddle is 3.6 m,the shape of the mixing paddle is trapezoidal,and the number of mixing paddle is 10.The remaining turbidity is 2.16 NTU,the sedimentation ratio is 18.8%,compared with the control group,the remaining turbidity has dropped by 66.4%,the sedimentation ratio has increased by 161.1%,and the flocs have entered a stable state.5.The average turbulent kinetic energy,average turbulent energy dissipation rate,velocity gradient,etc.can characterize the degree of flocculation reaction.When the velocity gradient is around 40.00 s^-1,a good flocculation effect can be achieved.When the disturbance is too low,the turbulence is not sufficient.If it is too high,it will easily cause the risk of floc damage.