Numerical Calculation Of Fluid Flow Characteristics In A Fixed-bed Frame Stirred Tank

The stirred tank has good mass and heat transfer rates,and can be used in gas-liquid,liquid-liquid,liquid-solid,gas-liquid-solid and other multi-phase reaction systems.Fixed-bed frame stirred tank as a liquid-solid or gas-liquid-solid heterogeneous reactor,and the fixed catalyst bed is filled with a frame to make up for the inconvenience of replacing the catalyst in the fixed-bed reactor,and the catalyst is not easy to wear,which can use for a long time and is suitable for intermittent production.However,for the fixed bed frame stirred tank,both the experimental research of the cold model and the theoretical study of the simulation are relatively lacking.Therefore,the numerical simulation method is used to study the fluid flow in the fixed bed frame stirred tank,and the univariate factor is used.Our research investigates the effects of stirring speed,height from the bottom of the agitator,blade layer spacing,blade combination type,and catalyst bed size on the radial velocity and distribution of the fluid on the catalyst bed,which can be used to optimize the performance of the reactor.Based on this,we can provide a theoretical basis to optimize the reactor.We established a 3 m3 fixed-bed frame stirred tank physical model,used commercial computational fluid dynamics software Fluent to simulate the fluid flow on the catalyst bed,and simulated the rotation of the blades by using the multiple reference frame method(MRF).We simplify the fluid flow in the catalyst bed by using the porous media model.The performance of the reactor is evaluated by the average value and variance of the radial velocity of the fluid on the inner wall of the catalyst.The simulation of the stirred tank under the actual structural conditions and operating parameters of the reactor shows that the high-speed zone in the tank is concentrated at the tip of the blade,the low-speed zone is concentrated at the top,bottom and wall of the stirring shaft.The radial velocity of the catalyst bed is fast near the height of the first and second blades,but the radial velocity in other areas of the bed is slow.The research work on parameter optimization of the fixed-bed frame stirred tank shows that after considering the resistance of the fixed bed,the radial velocity of the fluid on the bed decreases sharply and the flow pattern changes greatly from the flow without the interaction resistance.The performance of the reactor can be optimized by adjusting the stirring speed,the height of the stirrer from the bottom,the distance between the blade layers,the combination of blades and the size of the catalyst bed,and the optimal stirring speed in several sets of conditions is determined to be 220 rpm.The optimal height from the bottom is 450 mm.The best combined type of the impeller is four-layer combined stirring paddle.The stirring paddle is made of A four-layer combined agitator composed of one-layer straight-blade oblique-blade disc turbine,two-layer curved-blade oblique-blade disc turbine and four-blade propeller.The optimal catalyst bed type is the catalyst bed when the distance from the inner wall of the catalyst bed to the center of the stirring shaft is 300 mm,and the bed thickness is 133 mm.