Microscopy of fouling deposits in bitumen furnaces

This study investigated the deposition of foulants in a delayed coker furna ce. The main components observed in several foulant samples were fine- to v ery coarse-grained mosaic semicoke, pyrolytic carbon, iron sulfide (FeS) an d mineral matter (clays). The optical texture and reflectance tin oil) of t he carbonaceous deposits were in agreement with the variations in temperatu re and residence time in the furnace tube. Semicoke became more prevalent, as the distance from the furnace tube wall increased and indicated areas, w here the temperature was less than 500 degrees C. Pyrolytic carbon was pres ent primarily at the tube wall and indicated areas where temperatures were in excess of 600 degrees C. The concentrations of iron and sulfur in the fo ulant both increased towards the tube wall. A continuous FeS phase was obse rved at the wall and in cracks within the carbonaceous deposits, while, wit hin the bulk foulant, the FeS existed as particulates. This iron sulfide wa s believed to have originated from components of the bitumen feed rather th an process equipment. The ratio of iron to carbon in the deposit was greate r by a factor of 1000 than the ratio found in the bitumen. Bitumen feeds de rived from Alberta oil sands typically contain about 0.5 wt% of toluene ins oluble solids (mineral matter), if recovered by a hot water extraction proc ess. Only a very small proportion of other minerals was deposited within th e furnace tubes. Crown copyright (C) 2000 Published by Elsevier Science Ltd . All rights reserved.