Modelling and Development of an Automated LDPE Autoclave Reactor in CFD for Revealing Ethylene Hot Spots

Download or read book Modelling and Development of an Automated LDPE Autoclave Reactor in CFD for Revealing Ethylene Hot Spots written by Eric Turman and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational Fluid Dynamics (CFD) was employed to develop a rigorous model of a low-density polyethylene (LDPE) autoclave reactor. Different numerical settings within the solver were evaluated to minimize false diffusion and to reflect the sensitive heat generation taking place during free radical polymerization. The rigorous CFD model employed reaction kinetics, Proportional Integral Derivative (PID) automated thermal management, and a rotating stirrer shaft. Validation was carried out to determine the sensitivity to time-step size, turbulence model, and grid resolution. Data were compared to an industrial scale plant autoclave to guide the development of CFD. Time-step independence was confirmed by comparing the moving time- and spatial-average temperatures across eleven thermocouples. The selected time-step size represents 1/130th of a stirrer revolution per time-step. A mesh refinement study revealed slight variation in the results between the base mesh of 6 million computational elements and the refined mesh consisting of 40 million. Ultimately, the variation between different grid resolutions was not significant enough to justify slowing down the solver speed by 14X by using the refined mesh. In a comparison of turbulence models, the shear stress transport (SST) model was found to predict higher concentrations of turbulent kinetic energy (TKE) resulting in a lower temperature distribution throughout the reactor than the differential Reynolds stress model (DRSM). The less diffusive DRSM was recommended for future studies. Increased rigor improved the model’s ability to match plant data, and CFD thermocouples were within 2.5% of temperatures from plant data. Next, CFD was used to study local decompositions in an LDPE autoclave reactor by identifying, characterizing, and tracking the trajectories 3 of contiguous hot spots (CHS). Local decomposition of ethylene occurs in very short time and spatial scales, potentially leading to thermal runaway and global decompo