Setting Critical Operational Tan and Sulfur Level for Crude Distillation Units

Naphthenic acid corrosion and sulfidation corrosion are the major safety concerns for high temperature parts (>220°C) of crude distillation units. Processing lower quality crude oil with confidence is increasely a challenging task for refineries since contents of inherently present corrosive naphthenic acids and sulfur containing coumponds in crude oil are far beyond the designer of distillation units could forcast before construction started. In the life cycle of distillation units, critical components of distillation units might be changed or upgraded by better material in line with expectations of severe high temperature corrosion attack or failure. Walls of unchaneged components thin after years of corrosion. Therefore, different components of distillation units are at different stages with different remaining life. New concepts of critical operational TAN (Total Acid Number) and Sulfur level are suggested based on the comprehensive evaluation of high temperature corrosion risk. A computer model constructed by using public and proprietary data is the tool for evaluating risk of high temperature corrosion of all components. The factors evaluated include TAN, sulfur, materials, temperature, pressure, wall thickness, corrosion monitoring methods, anti-corrosion mothods and so on. Critical operational TAN and sulfur level of whole units, determined by the bearable TAN and sulfur concentration of worst location, help refineries balance risks and benefits, and make the best use of crude distillation units.