Fluidized bed combustion of petroleum cokes: kinetics and catalytic effects

In the fluid coking process, large quantities of coke particles are circulated between a burner vessel and the fluid coking reactor, with the coke-to-fresh feed ratio generally about 7 to 8 pounds of coke per pound of residual feed. During each burning cycle, a portion of coke equivalent to about 5% of the charge is burned off, and the hot coke particles are then returned to the coker supplying process heat. As a result of this type of repeated burning and coke deposition cycle, the coke is deposited in multiple, thin onion-skin layers. Product coke is withdrawn from the burner vessel, the temperature of which is maintained between /approximately/ 595/degree/ and 650/degree/C. Because the fluid coking process itself takes place at /approximately/ 510/degree/C, followed by the coke being first steam stripped and then burned at /approximately/ 625/degree/C, an essentially dry coke product is produced, i.e., one which is free of residual oils. Although fluid coking is attractive from the viewpoint of higher liquid yield, the coke tends to be higher in sulfur than delayed coke, which could create SO/sub x/ pollution problems in any subsequent combustion application. In addition to the sulfur question is that of the intrinsic combustibility ofmore » fluid coke vs. delayed coke. Since little information is available in the literature on this point, the present work examined whether process differences have any major impact on the combustion characteristics of the coke products. A second goal of this study was the investigation of the possibility of catalytically enhancing coke burning rates by employing separate particle catalysis.« less