Computational Fluid Dynamics analysis of a supercritical CO2 dyeing process of textiles

The present work deals with the CFD modelling of an industrial dyeing process assisted by supercritical carbon dioxide. Supercritical carbon dioxide (scCO2) is a sustainable alternative used in various processes to greatly reduce (or even eliminate) the need of conventional organic solvents. More and more frequently in modern technologies it has been made use of supercritical fluids (SCFs) and the main reason can be found in their low environmental impact. Also textile industry has been influenced by the use of supercritical fluids, being one of the largest water consumers. The wide use of scCO2 is mainly attributed to the fact that it has all the characteristics of a good solvent: it is non-toxic, non-flammable, economical and easy to remove. In the scCO2 dyeing process the conventional solvent (water) is replaced by scCO2 with numerous advantages (e.g., rapid coloration, possibility of reuse of the dye and solvent, low process costs). The only fully operational scCO2 dyeing process on an industrial scale is that one of Dyecoo, a Dutch engineering company. In the present work the scCO2 dyeing system developed by DyeCoo has been modelled using the software Ansys Fluent. In this system textile fabrics are wrapped on a beam and placed inside the dyeing vessel, the dyestuff is placed in a separate cartilage which is connected to the beam before the introduction into the vessel for the dyeing process. Here the dyeing vessel is modelled in order to investigate the flow distribution. The attention is focused on two different types of fabrics, woven and knitted, in order to better understand their behaviour when dyed in scCO2 medium. Since in the present work fabrics are modelled as a porous medium on ANSYS Fluent, the value of permeability is important to figure out the distribution of supercritical CO2 inside the fabric. Indeed, a good and homogeneous distribution of the flow inside the porous medium is necessary to reach the desirable level of dyeing of the fabric itself. To obtain the value of fabric permeability, CFD simulations have been conducted.