CFX Simulation Of Mixing Effect In Oxygen Mixer Of The Vinyl Acetate Synthesizing Plant

An oxygen mixer need to be scaled up during the capability's scale up of vinyl acetate synthesizing plant from 90 kt/a to 270 kt/a. For this purpose, a simulation was taken to analyze the mixed result performed with ANSYS CFX, and the effecting factor of scaling up was also studied. The simulation of the scale-up mixer was taken after those studies. Different methods of mesh generation have been compared, and the mesh generation method considering the size of boundary has been selected. By comparing the laminar model and other four turbulence models, it is discovered that the effect of turbulence model is small to the mixing, but laminar model do have significant difference to the mixing result. Finally, k-e model has been selected to the simulation based on its widely applicable cases. The Study is showing that the mixing effect is stable under the flow ratio variation from 1.5Qrecycle gas:Qoxygen to Qrecycle gas:(1.5Qoxygen).The mixer structure has been optimized based on its original structure by extending the mixing section. When 1m length is added to the mixing section, the maximum oxygen mass fraction can be reduced from 11.23% to 5.951% at the mixer outlet,, and the average oxygen mass fraction reduction is from 3.292% to 3.158%.The influence of inlet angle on mixing effect was researched under the condition of single and double inlet section of the ethylene circulating gas. The mixing result is very good when a is-15°with single inlet. The maximum oxygen mass fraction is 6.113%, and the average oxygen mass fraction is 3.088%. The distribution of flow velocity field is well-proportioned, and the distinction of speed is small. At the condition of double inlets of ethylene gas, when the angle is changed from -45°to 0°, the maximum oxygen mass fraction reduces gradually, the diffusion becomes strong increasingly, the flow field trends to confusion. When the angle changed from 0°to 45°, no significant difference of oxygen mass fraction were found at the outlet of the mixer, and the flow velocity field in the mixing section remain. The mixing result can be improved by changing the structure of oxygen inlets from two-rings to three-rings. When a is -45°, with single inlet, the maximum oxygen mass fraction is 8.816%, and the average oxygen mass fraction is 3.093%. When a is -45°, with double inlets, the maximum oxygen mass fraction is 8.691%, and the average oxygen mass fraction is 3.033%. The maximum oxygen mass fraction are both lower than the oxygen explosion limit. The average oxygen mass fraction are both similar to the theoretical calculation 3.073%. Different principle was studied to the scale-up from 90 kt/a to 270 kt/a. It is found that when keep the velocity of the fluid equally is better to scale up this mixer. The optimized mixer with 270 kt/a capacity still get ideal mixing, the errors of most of data are below 2%.