Effects of Height to Diameter Ratio and Aeration rate on Liquid Mixing and Hydrodynamic Properties in a Bubble Column
Experimental measurements of overall gas holdup (eg), residence time distribution (RTD) and liquid mixing time (tm) have been carried out in an air-water system in a 17 lit bubble column with an 11 cm diameter, over a wide range of superficial gas velocity (0.14-1.46 ms -1 ) and height to diameter ratio (1.36-8.84). The bed expansion method was used to obtain holdup values and the change of slope related to eg versus superficial gas velocity (Usg) indicated the transition point from homogeneous to heterogeneous regime at Usg= 0.7-0.9 ms -1 . Besides, the experiments illustrated that H/D ratio had no effect on holdup values. The axial dispersion model was used with semi-closed boundary conditions for prediction of RTD, and hence, the axial dispersion coefficients (Dax). Moreover, fitting results of the model and experimental RTD curves achieved from tracer injection method attained the model parameter, Dax , in three H/D ratios of 4.73, 6.36 and 8.84. Results showed that an elevation in H/D ratio, caused a rise in Dax. On the other hand, the mixing time data declined with an increase in Usg; however enhancement of H/D ratio caused an increase in tm.
EFFECT OF SPARGER DESIGN AND HEIGHT TO DIAMETER RATIO ON FRACTIONAL GAS HOLD-UP IN BUBBLE COLUMNS
The combined effect of sparger design and dispersion height on fractional gas hold-up (−ɛG) was investigated in a 0.385 m i.d. bubble column. Perforated plates were used as -spargers. Free areas of sparger plates (F. A.) and hole diameters were varied in the range of 0.13% to 5.0% and 0.8 mm to 87 mm, respectively. The height to diameter ratio (HD/D) was varied in the range of 1–8. In all the cases, the superficial gas velocity was covered in the range of 30-300 mm s−1. In order to investigate the combined effects of sparger design and the HD/D ratio together with the coalescing nature of the liquid phase, three liquid systems were considered, namely, water, an aqueous solution of an electrolyte and an aqueous solution of carboxymethyl cellulose (CMC). The comparative behaviour of these systems has been presented. The effects of sparger design, HD/D ratio and the gas- liquid system have also been analysed on the basis of drift flux model. A predictive procedure has been given for the drift flux constants by simulating the flow pattern in bubble columns using Computational Fluid Dynamics (CFD).
Thermodynamics on the Carbochlorination of Titanium-bearing Ores
The equilibrium compositions of the multi-component, multi-phase and multi-reaction system of carbochlorination of titanium-bearing ores are calculated with HSC, a computational chemistry software. The thermodynamic equilibrium calculation of the reaction system shows that a complete conversion of titanium-bearing ores is feasible at a temperature near 200oC. At temperatures ranging from 800 to 1600oC, the products of the reaction system are all in gaseous phase. Thermodynamic analysis accords with the industrial practice. The simulated results provide reasonable scientific basis for improving suitable technological conditions of the carbochlorination reduction.