Otimização geométrica de hidrociclones convencionais e filtrantes para operar com suspensões não-newtonianas

Abstract

Hydrocyclones are devices that use the principle of centrifugal sedimentation to separate a dispersed phase from a continuous liquid phase. To improve hydrocyclone performance, it is possible to replace the solid material of the cone with a permeable element, creating filtering hydrocyclones. This study evaluated how changes in equipment geometry and suspension's rheology influence the performance of conventional and filtering hydrocyclones. Three suspensions of different rheology were evaluated, which were obtained by varying the mass concentration of carboxymethylcellulose (CMC) from 0.2% to 0.6%. Using a Central Composite Design, the effect of geometric variables: feed and overflow diameter, total length of the hydrocyclone, and angle of the conical section were studied. Based on the results and using the Differential Evolution algorithm, it was possible to propose conventional and filtering hydrocyclones optimized to operate suspensions whose rheology resembled that of the fluids studied. These devices exhibited high separation efficiency (Case 01), or were able to generate highly concentrated underflow streams (Case 02), or showed low energy consumption (Case 03). Regardless of the rheology of the fluid, the filtering hydrocyclone had lower energy consumption than conventional equipment. The rheology of the suspension influenced the performance of both categories of hydrocyclone. By increasing the mass concentration of CMC from 0.2% to 0.6%, the separation efficiencies of the conventional and filter hydrocyclones decreased by around 29% and 16%, respectively. The optimized conventional hydrocyclones, and in brackets, the optimized filtering hydrocyclones of Case 01, operated with suspensions containing a mass concentration of CMC of 0.2%, 0.4% and 0.6%, showed separation efficiencies of 68.54% (72.03%), 60.91% (72.22%) and 57.29% (67.21%), respectively. For Case 02, and operating the suspensions with a mass concentration of CMC of 0.2%, 0.4%, and 0.6%, the optimized conventional hydrocyclones, and in parentheses the optimized filters, achieved liquid ratios of 5.18% (1.01%), 9.42% (13.18%) and 15.06% (14.43%) respectively. For Case 03, the optimized conventional hydrocyclones and, in brackets, the optimized filtering hydrocyclones, when operated with suspensions containing mass concentrations of CMC of 0.2%, 0.4%, and 0.6%, achieved Euler numbers of 896 (722), 756 (836) and 572 (541) respectively. How the filtration operation influences hydrocycloning was evaluated computationally. When the filtering hydrocyclones were simulated with a Newtonian continuous phase, the difference between the simulated and experimental pressure drop was 6%, while the difference regarding the liquid ratio was 7%; these results indicate that the computational approach was satisfactory. In addition, it was simulated how the rheology of the suspension influences the performance of the filtering hydrocyclone. The results showed that increasing the CMC concentration from 0.2% to 0.6% reduces the tangential velocity component of the suspension and increases the volume of the external vortex, reducing the separation efficiency and increasing the liquid ratio.