A field study of fouling in CDU preheaters at Esfahan refinery

In a field study at a CDU in Esfahan Oil Refinery, the influences of preheat exchangers fouling on the performances of downstream equipments were investigated. Relevant process flow diagrams were updated to incorporate the latest alterations made in the 30 years-old plant. Scattered preheaters mechanical data was compiled, diagrams were produced for several exchangers indicating the changing trends for a number of fouling related process variables and fouling resistances against time, using a specific spreadsheet developed for this purpose. Results indicate that Rf generally increased with time, reduced operating pressure and increased crude temperature, but anomalies were observed for re-tubed exchangers. The most severe fouling was observed at post-desalter, pre-flash drum exchangers, E-155A-B, with tube deposits having 80% inorganic content including CaSO4, indicative of desalter inefficiency and possible 2-phase fluid formation at the tube-side. Installation of E-251A-B aiming to reduce ISO.F. temperature in shells of E-155A-B, had little effect on the fouling extent of these exchangers, but improved the inlet temperature to the furnace by about 5 °C. With regards to the extra cost of fuel required to compensate the inlet temperature decline to the furnace at EORC, this was estimated to be around US$170 million p.a. (US$5.0/MMBtu-2010 gas price).