1. CHE315 3.1 Flow in Packed Beds v’ v  The packed bed (or packed column) is found in a number of  chemical processes including a fixed bed catalytic reactor, filter bed, absorption and adsorption. Examples: http://www.envitechinc.com/NOx_scrubber_packed_bed_absorber/ http://www.mon-env.com/PDF/ME_Packed_Bed_Scrubbers.pdf Introduction

2. CHE315 Flow in Packed Beds Pressure Drop in Packed Bed Laminar Flow: Turbulent Flow: v’ =  v Blake-Kozeny Eq. Burke-Plummer Eq.

3. CHE315 General Equation Ergun Eq.

4. CHE315 Flow in Fluidized Beds  Minimum velocity and porosity At a certain velocity, when the pressure drop force (i.e. ∆P*A) equalizes the gravitational force on the mass of particle (mg), the particles begin to move (fluidize). At very low velocity, packed bed remains stationary When fluid velocity is increased, the pressure drop increases, according to Ergun (Eqn. 3.1-20). L min v’ min

5. CHE315 This velocity is called the minimum fluidization velocity (v’ mf m/s) (based on the superficial velocity). At the minimum velocity, the porosity is called the minimum porosity of fluidization, ε mf (See Table 3.1-2 for ε for some materials ) Similarly, the new height of the bed is called the minimum height of fluidization L mf in m.

6. CHE315 The total volume of the solid particles is constant for a bed having a uniform cross-sectional area A and is: Flow in Fluidized Beds  Relation between bed height L and porosity  Therefore:

7. CHE315  Pressure drop and minimum fluidizing velocity At the onset of fluidization, the following is approximately true:

8. CHE315 Flow in Fluidized Beds Modifying the general equation of Ergun (substitute D p with D p  s ) to correct for non-spherical particles, this yield to: This equation with the previous one can be combined to calculate the minimum fluidization velocity: