Abstract
In this study an attempt was made to use internally circulating fluidized bed reactor (ICFBR) as a flue gas desulfurization reactor. The height of the bed was 2.5 m, and the inner diameter was 9 cm. The bed materials were calcium sorbent and silica sand. One of the special features of the ICFBR is high attrition of the particles in the bed, which would remove the product layer of sulfation and increase the utilization of the calcium sorbent. The other features are easy control of the solids circulation rate and gas residence time in the bed by individually adjusting the gas velocity in the annulus and the draft tube, which would increase the efficiency of the desulfurization process. The effects of the operating parameters including relative humidity, particle size of the calcium sorbent, inlet concentration of SO2, difference superficial gas velocity in the draft tube and the annulus and superficial gas velocity in the draft tube on attrition rate, calcium sorbent conversion, solids circulation rate and SO2 removal efficiency in the ICFBR were investigated. It was found that a higher relative humidity had a higher calcium sorbent conversion, but had a lower attrition rate and solids circulation rate. The removal efficiency of SO2 had a maximum value at steady state when the relative humidity was from 40 to 80%. When RH = 50、60 and 70% RE decreased initially and then increased. After that RE decreased again until a steady state was reached. A smaller particle size of calcium sorbent had a higher attrition rate, a higher solids circulation rate and a higher removal efficiency of SO2. In addition, the effect of the inlet concentration of SO2 on calcium sorbent conversion, attrition rate and solids circulation rate was negligible from 200 ppm to 500 ppm, but the removal efficiency of SO2 was decreased with increasing the inlet SO2 concentrations. Moreover, a higher total superficial gas velocity and a higher difference superficial gas velocity in the draft tube and the annulus had a higher attrition rate, but had a lower calcium sorbent conversion. However, the solids circulation rate might have a maximum value with respect to the difference superficial gas velocity in the draft tube and the annulus at the same total superficial gas velocity in the bed. A higher difference superficial gas velocity in the draft tube and the annulus had a higher removal efficiency of SO2 that was resulted by a higher reactivity of calcium sorbent due to a higher attrition rate. Futhermore, a higher attrition rate had a higher total volume of the flue gas treated. Finally, an attrition rate model proposed in this study could predict the attrition rate satisfactorily. A model to predict the removal efficiency of SO2 at steady state in ICFBR was also proposed. It assumed that the draft tube section was a bubbling fluidized bed while the annulus section was a moving bed. In addition, the effects of the calcium sorbent conversion, attrition rate and gas-bypassing fractions on the removal efficiency of SO2 at steady state were also taken into account in this model. It was found that the values of the removal efficiency of SO2 at steady state predicted by this model agreed with the experimental results.