Calculation Related to Overhead Corrosion Evaluation of Crude Distillation Unit

The corrosion of the overhead system of crude distillation unit (CDU) is one of the most serious threats to the safe long-term operation of the refinery. However, due to its local occurrence, complicated process and a considerable amount of influencing factors, there were difficulties in measurements in field or simulation experiments in the laboratory. As a result, the monitoring and control of the overhead corrosion have not been solved well so far. In this paper, the corresponding theoretical models were established for two main corrosion mechanisms of the overhead system, i. e., the HCl dew point corrosion and the ammonium chloride fouling. Using these models, parameters such as the aqueous dew point, water injection rate and ammonium chloride formation temperature can be calculated according to the existing refinery data. The calculation results can be used to assess the overhead corrosion risk and to provide guidance for the anti-corrosion operation of the refinery.