Category
Applied
Description
Because of the exothermic nature of polyethylene polymerization, process improvements must be performed carefully. Reactor failure can occur due to thermal runaway in which the added heat increases the reaction rates, increasing the temperature further, and so on. This is dangerous, because the pressure increases along with temperature, and it can explode if it exceeds the design conditions of the reactor. This makes experimental work obviously dangerous, so researchers often prefer simulations. Although, a common assumption is that the reaction mixture is perfectly homogeneous, lessening its applicability. Computational Fluid Dynamics (CFD) makes no such assumptions and can resolve internal temperature and chemical species concentration gradients. This work uses CFD to locate local heterogeneity in an industrial-scale Low-Density Polyethylene (LDPE) autoclave reactor and identify areas in which the reactor can be improved. To ensure the CFD simulation was accurate, its results were compared to an industry standard simulation software and a plant LDPE reactor. Across various cases, the CFD model had excellent agreement with the baseline data. It then revealed distinct regions with relatively uniform temperature and chemical species concentrations along the reactor shaft that arose because of the axial flow patterns. Additionally, entrainment by the central agitator caused a significant difference in these quantities inside and outside of the agitator swept volume. These are the regions of the reactor which would benefit most from mixture homogenization, which could be achieved through the addition of baffles or a different agitator design. The simulation could be improved through the inclusion of variable thermophysical properties, hot spot detection, and prediction of the final product’s molecular weight distribution.
Identifying Spatial Inhomogeneity in an Industrial-Scale Autoclave Polymer Reactor Using Computational Fluid Dynamics
Applied
Because of the exothermic nature of polyethylene polymerization, process improvements must be performed carefully. Reactor failure can occur due to thermal runaway in which the added heat increases the reaction rates, increasing the temperature further, and so on. This is dangerous, because the pressure increases along with temperature, and it can explode if it exceeds the design conditions of the reactor. This makes experimental work obviously dangerous, so researchers often prefer simulations. Although, a common assumption is that the reaction mixture is perfectly homogeneous, lessening its applicability. Computational Fluid Dynamics (CFD) makes no such assumptions and can resolve internal temperature and chemical species concentration gradients. This work uses CFD to locate local heterogeneity in an industrial-scale Low-Density Polyethylene (LDPE) autoclave reactor and identify areas in which the reactor can be improved. To ensure the CFD simulation was accurate, its results were compared to an industry standard simulation software and a plant LDPE reactor. Across various cases, the CFD model had excellent agreement with the baseline data. It then revealed distinct regions with relatively uniform temperature and chemical species concentrations along the reactor shaft that arose because of the axial flow patterns. Additionally, entrainment by the central agitator caused a significant difference in these quantities inside and outside of the agitator swept volume. These are the regions of the reactor which would benefit most from mixture homogenization, which could be achieved through the addition of baffles or a different agitator design. The simulation could be improved through the inclusion of variable thermophysical properties, hot spot detection, and prediction of the final product’s molecular weight distribution.
