Dynamics of hot zones on top of packed-bed reactors

Abstract

The evolution and dynamics of hot zones on the top of a shallow packed-bed reactor (10 cm diameter), packed with spherical catalyst pellets ( Pd / Al 2 O 3 ) were studied using infrared thermography. The test reaction, the atmospheric oxidation of carbon monoxide, was run under conditions for which steady-state multiplicity existed. Slow cooling of the reactor close to its extinction temperature shifted the fully ignited state to one with a hot region, separated by a sharp temperature front from the adjacent colder region ( Δ T = 75 ∘ C ) . The size of the hot zone was much larger than that of individual particles and it usually exhibited some rather intricate motion. Three qualitatively different types of motions sequentially evolved on cooling: breathing (contraction and expansion of hot zone), antiphase (standing wave) and rotation motion. The angular velocity of the rotating hot zone and its size changed with angular position. In some experiments the rotation occurred in several steps, i.e., the hot zone halted at one or more locations before completing one cycle of rotation. Several types of this hopping motion were observed. Global coupling between the non-converted reactant and the catalyst on the top of the bed had a strong impact on the dynamic motion of the hot zone.