Pressure change and control of the solid circulation rate of Geldart A particles in a small diameter L-valve

In a circulating fluidized bed (CFB) with a riser 2.6 m in height and 0.009 m in ID, the solid circulation rate and pressure drop of Geldart A and B particles in an L-valve 0.016 m-ID × 0.22 m-horizontal length were investigated as a function of the change in aeration rate through the L-valve. The gas velocity in the riser was maintained at 2.1 m/s to circulate particles transported from the L-valve. The bubbling bed was maintained above the minimum fluidizing velocity, Umf. As a result, it was found that the solid circulation rate of KR40 (dp = 70 μm, ρp = 1730 kg/m3), located in the middle region of Geldart A, increased gradually with increasing aeration rate up to Umf in the L-valve and then increased sharply with increasing aeration rate. Therefore, the solid circulation rate of KR40 could not be controlled at velocities greater than Umf. On the other hand, in the case of FCC (dp = 85 μm, ρp = 1880 kg/m3), another set of Geldart A particles that are similar in size and density to KR40 is located at the boundary of Geldart A and B particles. These particles allowed the solid circulation rate to be controlled normally until the aeration rate in the L-valve reached the value of 3.5 Umf. The bubbling bed of KR40 exhibited a sharp increase in solid circulation rate at Umf and expanded by a factor of 1.05 as soon as the aeration rate reached the value of Umf. This phenomenon was not observed for the other particles in this study. At the moment of the sharp increase in the solid circulation rate of KR40, the pressure in the L-valve and standpipe drastically changed, indicating that the solid circulation rate was intimately related to the pressure drop in the L-valve. The correlation equation between the solid circulation rate and gas aeration in the L-valve was derived for Geldart A particles ranging from 70 ≤ dp ≤ 148 μm in particle size and 1,350 ≤ ρp ≤ 1880 kg/m3 in particle density.