3.2.2 Pinning under different gas superficial velocities
Based on the computation method in the rectangular bed, the pinning thickness is derived in the radial bed, which is listed in theAppendix . However, it is analyzed qualitatively as the coefficients can not be determined accurately in equation (A9) ofAppendix due to the lack of experimental data. The equation is simplified into equation (10) when the pinning thickness variation is a constant. The upward and downward forces can be computed when the baffles are put in different positions, which is seen in Fig.10. The pinning easily appears under small particle gravity and large frictional force. In the centrifugal bed, with the increasing of the position of baffle, the pinning is firstly controlled and then promoted in the inner area; while it is eliminated in the outer area. In the centripetal bed, with the decreasing of the position of baffle, the pinning is controlled in the inner area; while it is firstly eliminated and then improved in the outer area. The original bed CA can be seen as the inner area of the bed B when the baffles put in the (r -r 1)/(r 2-r 1)=1; or the outer area when the baffles put in the (r -r 1)/(r 2-r 1)=0. For instance, in the inner area of the centrifugal bed, the difference of these two terms (downward and upward forces) in equation (10) has greater values in the bed with baffles (where the baffles put in (r -r 1)/(r 2-r 1)<1) than the original bed (where the baffles put in (r -r 1)/(r 2-r 1)=1).The pinning can be controlled with baffles in type CB.
(10)