Computational Fluid Dynamics (CFD) and Thermal Analysis for Kettle Reboiler

Abstract

Kettle reboilers play a vital role in refinery processes, where the operation has a direct impact on overall system performance. To enhance reliability and minimize operational issues such as liquid carryover, a comprehensive approach involving mechanical optimization and continuous monitoring is essential. This optimization process requires careful evaluation of several critical design and operational parameters, including the entrainment ratio to ensure proper vapor-liquid separation, optimal positioning of inlet and outlet nozzles to maintain flow efficiency, appropriate shell sizing to facilitate effective heat transfer, and assessment of current operating conditions to identify potential improvements. By systematically addressing these factors, refineries can significantly reduce liquid carryover, improve thermal efficiency, and extend the operational lifespan of kettle reboilers, ultimately leading to more stable and cost-effective refinery operations. ANSYS Fluent software is used for geometric modeling, meshing, thermal simulation, and post-processing. Simulations have been done by varying the shell side diameters of the Kettle Reboiler, with the given boundary conditions as per the problem. The physics of the problem employs a steady-state approach and utilizes a viscous model, specifically the Realizable k-ε turbulence model, and the Eulerian phase change model. Three simulation trials have been conducted in ANSYS Fluent to analyze the effect of reducing the kettle diameter. The baseline model has a diameter of 1790 mm. And second trial was done with a diameter of 1750 mm, and the third trial was done with a diameter of 1690 mm. The results from the first two trials were approximately the same, both achieving a vapor quality (dryness fraction) of about 0.997. This indicates that a reduction of 40 mm is feasible without compromising performance. This size reduction would save approximately 0.412 feet of sheet metal used in the kettle's fabrication. However, the third trial was conducted on a 1690 mm diameter, resulting in a lower vapor quality of 0.97, which is not acceptable for the application. Therefore, we conclude that the diameter cannot be reduced further than 1750 mm. Keywords: CFD; Heat Transfer; Kettle Reboiler; Shell and Tube Heat Exchanger; Entrainment Ratio