Emission Control of Gaseous Pollutants From Co-Firing of Petroleum Coke and Coal in CFB

Abstract

Petroleum cokes including delayed coke, fluid coke, etc. are byproducts of solid residuals from the crude refining process. Using high sulfur petroleum coke as alternative fuel is feasible owing to its high fixed carbon and low ash content, but petroleum cokes are difficult to ignite due to their low volatile content and containing substantial concentrations of vanadium, nickel, nitrogen and sulfur, which can be sources of pollution emission and fireside fouling or corrosion problem. Co-firing petroleum coke and coal in circulating fluidized bed (CFB) is an ideal solution for those problems. Emission characteristic of gaseous pollutants from co-firing petroleum coke and coal is investigated in the paper. Experiments were carried out in a 0.6 MWt pilot-scale CFB combustor with the total height of 12m from the air distributor to the exit of combustor. The concentrations of SO2, NO, N2O, O2, CO2 and CO were measured on line by the gas analyzer. The effect of several parameters, in term of the primary air percentage, air excess coefficient, bed temperature, Ca/S molar ratio and percentage of petroleum coke in mixed fuel on the emission of SO2, NO, N2O is verified in experiments. Experimental results show that SO2 concentration in flue gas reduces with increase in the primary air percentage, excess air coefficient and Ca/S ratio for all kinds of fuel mixtures, whereas NO, N2O concentration rises with increase in the primary air percentage and excess air. When the bed temperature changes, the NO concentration varying trend is opposite to N2O. There is an optimal temperature for sulfur retention. Co-firing of petroleum coke and coal with different mixing ratio in CFB can be stable, efficient and environment friendly.