Pitch and coke combustion in a circulating fluidized bed

Combustion tests were carried out with two hydrocarbon processing residues: a high-volatile pitch from a hydrotreating process and a green petroleum coke. It was demonstrated that both fuels can be treated successfully by circulating fluidized bed combustion, with sulfur capture by limestone addition. Levels of calcium sulfide in the baghouse ash were acceptable in both cases, and were especially low for the pitch. The presence of vanadium pentoxide in the residues from pitch burning appears to have caused significant conversion of SO₂ to SO₃, Limestone addition led to an increase in NO_x emissions for the pitch, but to a decrease for the coke, probably because of the low volatile matter of the latter, such that limestone catalysis of NO_x reduction by CO predominated over catalysis of N₂O production from fuel volatile nitrogen. N₂O levels were higher for the coke than for the pitch or other fuels investigated.