Fouling at post desalter and preflash drum heat exchangers of CDU preheat train

• Severe fouling at PDPF exchangers experienced at EORC and 4 major industrial cases.
• Data over 2 shutdowns revealed +50% wt foulant content were inorganics: CaCO3 and FeS.
• A 6-step mechanism based on Lambourn–Durrieu's proposed for PDPF exchangers fouling.
• At PDPF exchangers contrary to other preheaters, shell-side fouling is significant.

Following an 8-year field study at EORC refinery including visual inspection, operational data and fouling resistance analysis, as well as foulant chemical characterization, it became clear that post desalter and preflash drum (PDPF) exchangers experience irregular severe fouling. To find effective factors for examination in future pilot tests, literature was studied and four industrial cases with the same problem were identified. Notably in this type of fouling, more than 50% of the foulant contents sampled in two shutdowns at EORC were inorganics, and similar to Yanbu and Chevron cases consisted of iron compounds and calcium carbonate. Considering EORC results and reported causes and remedies employed in the cases, a 6-step mechanism based on that of Lambourn and Durrieu is proposed in which asphaltene interactions with water, salts and iron sulfides (i.e. collaboration of physical and chemical processes) lead to deposition of severe, tenacious and stable foulant on the tube surfaces of PDPF exchangers. Desalting performance and water injection, brine chloride hydrolysis and caustic injection, asphaltenes solubility dependence on temperature variation, and its molecular structure as a surfactant agent as well as non-negligible shell-side fouling deposited off the vacuum gas oil have been identified as the effective factors discussed here in detail.