Experimental Study on Characteristics of Pyrolysis, Ignition and Combustion of Blends of Petroleum Coke and Coal in CFB

It is a common understanding that co-firing of petroleum coke and coal in circulating fluidized bed (CFB) is an efficient, economical and environment-friendly way to utilize petroleum coke with medium or high sulfur content. Experimental investigations on characteristics of pyrolysis, ignition and combustion of petroleum coke, coal and their blends with different mixing ratios were conducted on a thermogravimetric analyzer and a pilot CFB combustor systematically. Ignition temperature and burnout temperature were also acquired. The effects of several parameters in terms of the fuel category, the heating rate, the coal/coke mass flow ratio, the CO₂ partial pressure, and the Ca/S molar ratio on the ignition and burnout characteristics of the petroleum coke and the blends of the petroleum coke and coal were verified. The results show that the ignition temperature and the burnout temperature of the petroleum coke are between those of bituminous coal and anthracite, which implies that its combustion characteristic is between bituminous coal and anthracite, but is more closer to the bituminous. The pyrolysis process of blends of petroleum coke and coal accords with mechanism model (1−α)^1.5 well, and the combustion process accords with mechanism model w^1.5 well. Although the ignition temperature of the blended fuels keeps the same when the heating rate, or the CO₂ partial pressure or the Ca/S molar ratio increases, the burnout temperature decreases gradually. With decrease in the coal/coke mass flow ratio, the ignition temperature and the burnout temperature of the blends rise.