Petroleum coke has become an increasingly important feedstock for circulating fluidized bed (CFB) combustors since it can be effectively utilized in an environmentally sound matter. Despite its relatively high sulfur content, petroleum coke can be fired along with sorbent material which yields acceptable sulfur capture. However, vanadium in a petroleum coke can cause potential agglomeration problems in the combustor or loop seal of a circulating fluidized bed due to the formation of molten ash compounds. In addition, other constituents in the coke ash and calcium-based sorbents can react with vanadium to form complexes with low melting temperatures. Simple laboratory techniques were developed for assessing the agglomeration potential from petroleum coke firing. The results of these tests showed that combustor temperature has a strong effect on the formation of low melting vanadium eutectics and the rate of agglomeration. Also, defluidization of ash in the loop seal can lead to sintering at relatively low temperatures since packing promotes particle-to-particle bonding. Magnesium-based solid additives were found to reduce vanadium related agglomeration in laboratory tests by increasing the melting point of vanadium compounds.