Effect of fluid field on the eco-friendly utilization and recycling of CO2 and dyes in the waterless dyeing

Abstract

Abstract During the supercritical waterless dyeing, ineffectual separation of dye powders from carbon dioxide often occurs with the gas random motion in the separator, which easily causes gas recontamination in the final separation and recycling period. In this work, a novel separator structure was designed, which greatly helps to enhance the separation efficiency. The flow field characteristics of carbon dioxide in the improved separator were investigated using numerical simulation. Numerical results showed that the regular rotating airflow, quasi-forced vortex and quasi-free vortex of carbon dioxide appear in the separator vessel. The total pressure loss at 200 L/h is 0.98 Pa, which is much smaller than the prototype separator. Furthermore, the enhanced separation efficiency of 9.96 %, 8.82 %, 13.24 % and 13.24 % is obtained for the dye particle sizes from 0.5 µm to 2 μm in the improved separator, which displays a better separation performance. The minimum cycle number which exists at the gas exit is 15654. Separation mechanism of carbon dioxide and dyes in the the supercritical dyeing was also proposed.