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

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

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

Reactor Configurations D L Gas + Solid Up flow Down flow

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

Terminal Velocity

Reynolds Number Region Strokes Region

For Higher Solid Concentrations

Example If we considered U 0 ~U p, and we have 1 mol of gas reacting with 1 mol of solid of M wt = 100 g/mol and  p = 2 g/cm 3 If we considered U 0 ~U p, and we have 1 mol of gas reacting with 1 mol of solid of M wt = 100 g/mol and  p = 2 g/cm 3

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

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

Critical Point R crit R H Xs =1 H max H crit Goes through a maximum at some critical R

Find H crit and R crit Differentiate H Xs=1 Differentiate H Xs=1

Find H crit and R crit Substitute R crit into H Xs=1 to get H crit Substitute R crit into H Xs=1 to get H crit Note: To transport largest particles through the system:

Within the Strokes Region Substitute U 0 into H crit to get Up flow

Notes Comparison indicates R crit ~ 0.77 R max Comparison indicates R crit ~ 0.77 R max One would do a similar calculation for any expression for τ and also can use more general equation for C D. One would do a similar calculation for any expression for τ and also can use more general equation for C D. Note: for C A,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). Note: for C A,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