Effect of calcium oxide on pyrolysis of coal in a fluidized bed

The pyrolysis of Shenmu bituminous coal in both the presence and absence of calcium oxide was studied under atmospheric pressure over a temperature range of 450–750°C in a fluidized bed reactor. Calcium oxide significantly increases the gas yield while decreasing the tar yield. Tars produced in both the presence and absence of calcium oxide were analyzed and compared. The results indicated that tar yields reach a maximum at 650°C for coal pyrolysis without calcium oxide, in accordance with Tylerʹs results. When calcium oxide is added, the temperature of tar maximum yield is reduced to 550°C. It is also demonstrated that the ratio of H/C; benzene, toluene, xylene (BTX); phenol, cresol, xylenol (PCX) and other light components in tar increase while the ratio of (O+N+S)/C and oxide compounds in tar decrease in the presence of calcium oxide. It is noted that the maximum composition of alkanes in tar is C14–C20 in the presence of calcium oxide, while it is C8–C15 in the absence of calcium oxide. It results from the fracture of alkanes with long chains to alkanes with short chains when calcium oxide is added.