The process of polymer devolatilization is a critical step in manufacturing high quality polymers. Polymer devolatilization is a technique that involves removing unwanted substances, such as unreacted monomers, volatile by-products, solvents, or any other unwanted materials, with the use of superheated steam. The polymer mixture considered here, initially consists of polymer and an excess hydrocarbon solvent like cyclohexane. This polymer mixture is referred to as "cement". To remove the cyclohexane, superheated steam is mixed with the cement, and the steam causes the cyclohexane to evaporate, leaving behind a cement mixture with less solvent and a higher concentration of polymer. As the cement dries out and forms into particles, or "crumb", it is carried away and further processed while the steam and solvent vapor are vented out of the contactor. This process is modeled using computational fluid dynamics (CFD), specifically employing the commercial code, ANSYS FLUENT, to gain insights into the complex phenomena occurring and accounts for several aspects of this multiphase flow problem. The model shows the initial breakup of the cement and the heat transfer and phase change as the solvent evaporates, in addition to tracking the droplet’s size, temperature, solvent content, and other important parameters used to monitor the droplet’s evolution within the contactor. After completion of the simulation, the cement particle sizes are compared to average values from the field for the actual final product to verify this model.
This thesis focuses on modeling two separate contactors, referred to as Contactor A and Contactor B, which differ in shape, but involve the same processes. For each contactor, once a final model is constructed, a parametric study is performed to test for several modifications involving lower levels of steam usage, which can in turn potential reduce the manufacturing cost. Contactor A tested the effects of different initial polymer temperature on the final polymer product. Increasing the cement operating temperature reduced the solvent concentration in the cement crumb significantly, and the final cement crumb sizes showed a slight decrease as well, which indicated a better production performance. For Contactor B, several simulations were carried to determine the effects of changing the operating steam pressure and also several geometric parameters. Simulations were carried out using steam as the only phase to test how the flow rate and residence time were affected with the changes in such operating parameters. After determining an improved geometry modification, a full simulation was carried out with steam and cement particles and compared to the original case. The modified case performed better compared to the original case by providing reduced particle sizes, residence times, and cyclohexane content, all indicating better performance.