CFD aided Design imperilment and the utilization, modification of exhaust gas treatment plant

OIL AND GAS ENGINEERING

This research focused on a refit project for an Al2O3 calcination exhaust gas treatment line that included the installation of a fabric filter downstream of an existing electrostatic precipitator (ESP). In this scenario, replacing the old exhaust fan with a higher-performing one could have exposed the existing precipitator to suction circumstances outside of the process parameters contemplated when the ESP was developed. In other words, by conducting a detailed safety analysis focused on the interface between new and existing plants, it was discovered that there was a potential risk of implosion that would not have been discovered by using traditional methods such as historical analysis or a HAZOP limited to new equipments. Due to the difficulty (both technically and economically) of modifying such existing equipment, this threat could not have been simply mitigated by installing reinforcements. The selected solution was to handle the problem in the same way that a vessel is protected against overpressure: create a direct action PSV (counterweight triggered) that opens when a given differential pressure (with the opposite sign as the typical PSV design) is reached. The risk was then transformed into a worst-case scenario, on the basis of which safeguards were designed. This situation was chosen because all of the pressure drops are focused upstream of the equipment to be protected, exposing the filter to maximum suction levels. The worst case scenario included the presence of a fabric filter bypass duct that allowed direct communication between the fan and the ESP, the complete blocking of a duct upstream of it, and the fan running at full rotational speed. A computational fluid-dynamics analysis was used to verify and validate design choices, demonstrating that CFD can be a powerful and useful tool for addressing safety design issues, allowing for numerical testing of safeguards and, as a result, evaluating the impact that design choices would have for the purposes of risk reduction and mitigation.

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