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Published byGladys Quinn Modified over 3 years ago

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**Fixed Bed Reactor Quak Foo Lee Chemical and Biological Engineering**

The University of British Columbia

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Fixed Bed Reactor Solids take part in reaction unsteady state or semi-batch mode Over some time, solids either replaced or regenerated 1 2 CA,in CA,out Regeneration Breakthrough curve CA,out/CA,in t

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**Isothermal Reaction: Plug Flow Reactor**

Plug flow of fluid – no radial gradients, and no axial dispersion Constant density with position Superficial velocity remains constant

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**Plug Flow Model z + dz CA,f + dCA,f z CA,f**

U0 (m/s) superficial velocity

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**Input – Output – Reaction = Accumulation**

Mass Balance Input – Output – Reaction = Accumulation Divide by ∂z and take the limits as ∂z 0 ε is void fraction in bed

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**For first order reaction, fluid only:**

Void fraction For first order reaction, fluid only: For steady state: Volume of reactor Therefore,

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**Conversion as a function of Height**

Integrating with CA,f = CA,f,in at z = 0 Note 1: Same equation as for catalytic reactor with 1st order reaction Note 2: Can be used in pseudo-homogeneous reaction

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**Balance on Solid aA (fluid) + S (solid) Products**

Input – Output – Reaction = Accumulation Over increment of dz: input = 0, output =0 Volume fraction of solid = m3 of solid m3 of reactor volume mol m3 of solid · s

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Balance on Solid

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**Solve These Equations = 0 (In quasi steady state, we ignore the**

accumulation of A in gas) Substitute rAv

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**Non-Isothermal Packed Bed Reactor**

For mass continuity did balance on fluid and on solid For energy balance, we do balance on each phase

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**Non-Isothermal Packed Bed Reactor**

Assumptions: Adiabatic reaction – no heat lost through shell to surroundings (no radial temperature gradients) q = 0 Biλ is small – uniform T within particle (an exothermic reaction Tp > Tg) Plug flow of gas and use Tref =0 for enthalpy calculations Assume an average density can be used (ρg = constant)

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Modeling q =0 Tf + dTf z + dz Tf z Tf,0 U0

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**Governing Equations Fluid Solid Solve all these equations together.**

Quasi Steady State

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**For Heat Transfer Z=0 all t Tf = Tf,0; Ts = Ts,0**

T = 0 all z Ts = Ts,0; Tf = Tf,0 Generally, require a numerical solution for the solution of the set of equations.

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