(339ac) Rotating Fluidized Bed in a Static Geometry (RFB-SG) : Determination of a Range of Stable Operating Conditions

In a Rotating Fluidized Bed with a Static Geometry (RFB-SG) type of reactor, the centrifugal force is balanced by the radial drag force [1]. This leads to an axisymmetric rotation of solid particles which are fluidized. RFB reactors offer several advantages over conventional gravitational fluidized bed reactors (FBR): more uniform fluidization and temperature, higher slip velocity and, hence, higher heat and mass transfer at the particle scale [2, 3]. The present contribution reports on experimental results obtained in a versatile cold-flow experimental set-up [4].

A schematic representation of the set-up and a snapshot of a stable operation are shown in Figures 1 and 2. The rotational motion of the solid particles in a RFB-SG is realized  by the tangential feeding of gas, in this case air, under a given angle at the reactor periphery, via regularly positioned inlet slots. The width of the latter, I_O, is varied from 2 mm to 6 mm.  They define a circle with a diameter, D_R, of 0.54 m. Polyethylene particles with average an diameter, ranging from 0.3 mm to 3 mm are used. The amount of solids in the reactor is varied in the range of 0.5 kg to 7 kg. The air mass flow rate is varied from 0.4 to 1.2 kg/s. The reactor is operated with a horizontal axis of rotation. A stable rotating bed is obtained over the investigated operating range.

Dependent variables, such as, pressure drop, maximum solids capacity of the reactor, solid particles velocity, both radial and tangential, and solids volume fraction are measured as a function of the above mentioned independent variables. The maximum solids capacity of the reactor, increases with increasing air mass flow rate. The former is determined at the condition at which the solid particles start to be entrained via the reactor exhaust, D_E, from the uppermost position of the reactor. At this condition, the centrifugal force acting on the solid particles is balanced by the gravitational force. As the air mass flow rate is increased, the centrifugal force acting on the solid particles increases. This allows an increased capacity of solids in the reactor, until a new equilibrium of centrifugal and gravitational force acting on solid particles is established. These observations and explanations can be quantified. The corresponding equations allow to design a RFB-SG for industrial operations.

Figure 1: Schematic of the RFB-SG reactor with tangential feed inlets, reactor diameter (D_R), exhaust diameter (D_E), axial length of the reactor (L_R) and inlet opening thickness (I_O).         (a) Front view (b) Side view

Figure 2: Snapshot of a stable rotating solid particles bed

References:

[1] J. De Wilde, A. Habibi, G. B. Marin, G. J. Heynderickx, R. P. Ekatpure and A. de Broqueville, Experimental Investigation of Rotating Fluidized Bed in a Static Geometry, AIChE  Annual Meeting, Salt Lake City, Utah, November 4-9, 2007

[2] J. De Wilde and A. de Broqueville, ?Rotating Fluidized Beds in a Static Geometry: Experimental Proof of Concept?, AIChE Journal, Vol. 53, 793-810, 2007

[3] A. de Broqueville and J. De Wilde, ?Numerical investigation of gas-solid heat transfer in rotating fluidized beds in a static geometry?, Chemical Engineering Science, Vol. 64, 6, 1232-1248, 2009

[4] R. P. Ekatpure, G. J. Heynderickx, A. de Broqueville and G.B. Marin, ?Experimental Investigation of a Rotating fluidized Bed in a Static Geometry?, 2^nd European Process Intensification Conference, Venice, Italy, June 14-17, 2009