Entrained Bed Reactor Quak Foo Lee Department of
Entrained Bed Reactor Quak Foo Lee Department of Chemical and Biological Engineering
Entrained Bed Reactor n Entrained bed, pneumatic transport reactor n Riser reactor, raining bed reactor n Dilute suspension of solids and usually reactors have large L/D ratio n Near plug flow n If feed particles are all of the same size, them all have same residence time
Entrained Bed Reactor n Advantage is one can control the residence time n Small particle and co-current flow n Simplified analysis n Flat velocity profile for gas n Plug flow of solids n Isothermal n Constant fluid properties
Reactor Configurations Gas + Solid Down flow D Up flow L Gas + Solid
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
Terminal Velocity
Reynolds Number Region Strokes Region
For Higher Solid Concentrations
Example n If we considered U 0 ~Up, and we have 1 mol of gas reacting with 1 mol of solid of Mwt = 100 g/mol and p = 2 g/cm 3
n n For uniform gas composition Plug flow of solids Where, = time for complete reaction
For Strokes Region and SCM n With no Mass Transfer (MT) of Product Layer Diffusion (PLD) Resistance:
Critical Point Goes through a maximum at some critical R Hcrit Hmax HXs=1 Rcrit R
Find Hcrit and Rcrit n Differentiate HXs=1
Find Hcrit and Rcrit n Substitute Rcrit into HXs=1 to get Hcrit Note: To transport largest particles through the system:
Within the Strokes Region Substitute U 0 into Hcrit to get Up flow
Notes n Comparison indicates Rcrit ~ 0. 77 Rmax n One would do a similar calculation for any expression for τ and also can use more general equation for CD. n 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).
Down Flow – Raining Bed Gas + Solid For some simplified case: At For chemical reaction controlling: Down flow
Recall Up flow Down flow Ratio
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