3.1 Pinning, cavity and air lock in rectangular bed
Fig.3 shows the gas superficial velocity when the pinning, cavity and air lock appears in the beds. In the rectangular bed with gas-solid baffles (type RB), the critical gas superficial velocities of pinning, cavity and air lock are improved compared to the original bed (type RA). It denotes that the structural improvements can eliminate these three abnormal phenomena, which is further discussed in the following sections.