SETTING CRITICAL OPERATIONAL TAN AND SULFUR LEVEL FOR CRUDE DISTILLATION UNITS

摘要

Refiners are continuously challenged with processing crudes that have increased concentrations of sulfur and naphthenic acid. Very often the original equipment metallurgy was not designed for such corrosive conditions, and therefore substantial upgrades are required in the high temperature areas (greater than 428 °F (220 °C)) where this type of corrosion will show up. This paper will present new concepts for the evaluation of critical TAN (Total Acid Number) and sulfur level based on the comprehensive evaluation of high temperature corrosion risk. A model consisting of public and proprietary data has been developed for this assessment. The primary factors evaluated include TAN / sulfur content, materials of construction, and temperature. Utilization of this model enhances the predictability of corrosion due to TAN and sulfur. Historical data of corrosion monitoring is used to validate the accuracy of the model. Minimum wall thickness required for pressure vessels and piping is also calculated. Then, high risk parts of distillation units are identified. Critical operational TAN and sulfur level of a crude distillation unit is determined by the identified maximum allowable TAN and sulfur concentration of any one circuit. This advanced knowledge will allow for increased reliability of crude distillation units where this is implemented.