The Comparison Of Downcomer Operating Capacities Between CTST And Valve Plates And The Optimization Of Downcomer Structure

In a transparent plexiglas column with inner diameter of 600mm, the comparison of downcomer capacities between CTST tray and Fl valve tray were studied with the air-water and foaming systems.The residence time of distribution and froth height in the downcomer were measured. The tracer used was 10 wt% sodium chloride solution. The residence time of distribution curves in a downcomer were measured by using the tracer technique. The range of liquid flow-rates is from 1.6m3/h to Ilm3/h, and the range of kinetic energy factors based on perforated plate is from 6.3Pa1/2 to 22.39Pa1/2. The effect of gas rates, liquid flow-rates, downcomer width, weir heightand the addition of surface active agent on the liquid mean residence time, t, effective diffusion coefficient, DE, and froth height, Hf were studied. Results obtained showed that for two systems,the t in the downcomer of CTST plate is 20-50% smaller than that of Fl valve plate, and theDE is 40-70% smaller than that of Fl valve plate. In addition, the Hf in the downcomer of CTST plate is 110~150mm lower than that of Fl valve plate. It was showed that making a comparison of two plates, the downcomer of CTST tray can cope with more operation loads with the same size downcomers. or, if have the same operation loads, the downcomer size of CTST tray can be designed smaller than the Fl valve tray. It was found that CTST plates have bigger operating capabilities than other traditional plates in coping with foaming systems.The dispersion model, with axial dispersion only was used to describe the liquid flow in the downcomer. The model parameters were fitted by the least-squares method. It was found that the curve of dispersion model fitted the experimental RTD curve well.The optimization of segmental downcomer of the CTST tray was also studied. For improving the flow manner on the plate, the downcomer apron was modified from straight shape to trapezoidal shape. The hydrodynamics performance of the modified CTST tray, for example, the pressure-drop of dry tray and wet tray, liquid weeping and vapor entrainment etc were measured. The experimental data showed that the hydrodynamics performance of the modified CTST tray was more preferable.In conclusion, either the comparison of the downcomer capacities between CTST tray and Fl valve tray or the optimization of segmental downcomer of the tray is very important for further studies and improvements.