1. Entrained Bed Reactor Quak Foo Lee Department of Chemical and Biological Engineering

2. Entrained Bed Reactor • Entrained bed, pneumatic transport reactor • Riser reactor, raining bed reactor • Dilute suspension of solids and usually reactors have large L/D ratio • Near plug flow • If feed particles are all of the same size, them all have same residence time

3. Entrained Bed Reactor • Advantage is one can control the residence time • Small particle and co-current flow • Simplified analysis • Flat velocity profile for gas • Plug flow of solids • Isothermal • Constant fluid properties

4. Reactor Configurations Gas + Solid Down flow Up flow D L Gas + Solid

5. Riser Reactor Upward particle velocity Superficial gas velocity Settling velocity of particle Gas + Solids Terminal velocity of a single particle in an unbounded fluid Note: Concentration of solids is low

6. Terminal Velocity

7. Reynolds Number Region Strokes Region

8. For Higher Solid Concentrations

9. Example • If we considered U0 ~Up, and we have 1 mol of gas reacting with 1 mol of solid of Mwt = 100 g/mol and p = 2 g/cm3

10. For uniform gas composition • Plug flow of solids Where,  = time for complete reaction

11. For Strokes Region and SCM • With no Mass Transfer (MT) of Product Layer Diffusion (PLD) Resistance:

12. Critical Point Goes through a maximum at some critical R Hcrit Hmax HXs=1 Rcrit R

13. Find Hcrit and Rcrit • Differentiate HXs=1

14. Find Hcrit and Rcrit • Substitute Rcrit into HXs=1 to get Hcrit Note: To transport largest particles through the system:

15. Within the Strokes Region Substitute U0 into Hcrit to get Up flow

16. Notes • Comparison indicates Rcrit ~ 0.77 Rmax • One would do a similar calculation for any expression for τ and also can use more general equation for CD. • Note: for CA,f to be constant, e.g. at some over reactor height, we need small gas conversion (or large molar excess of species A in gas phase).

17. Down Flow – Raining Bed Gas + Solid For some simplified case: At For chemical reaction controlling: Down flow

18. Recall Up flow Down flow Ratio