Simplifying assumptions Unit 4 Batch Reactorsdechema-dfi.de/kwi_media/slides_4-p-374.pdf · Unit 4 Batch Reactors Simplifying assumptions ... the reactor Specific heat ... Aspen Plus

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Unit 4 Batch Reactors

Simplifying assumptions- Perfectly mixed (no spatial gradients)

- No continuous feed and product

A

AA R A A0 A

A0 AA R

AA0 A R

XA

A0A R0

dn r V with : n n (1 X )dt

d[n (1 X )] r Vdt

dXn r Vdt

dXt nr V

= − = −

−= −

− = −

= ∫

RAVr1

AX0

Area = t/nA0

Material Balance (Reactant A)- single phase- single reaction

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Unit 4 Batch Reactors

Adiabatic Operation (no heating/cooling)

Enthalpy Balance

W R pW R R j j

j

d[(C m c ) T]ha(T T) V ( H ) r

dt+ ⋅

= − + −∆∑

Heat capacity of the reactor

Specific heat capacityof the reaction mixture

W R pR R j j

j

d[(C m c ) T]V ( H ) r

dt+ ⋅

= −∆∑

A0 R0 A

W R p

n ( H )T T X(C m c )

−∆= + ⋅

+ Adiabatic Temperature Change

For single irreversible reaction (constant heat capacity, density and heat of reaction):

If cooling is insufficient, i.e. ha(T-TW) is small compared to the heat release by the reaction(-∆HR)r, reactor stability becomes a critical issue(rate depends on T)

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Unit 4 RBatch

Continuous feed

Vent

Semibatch Reactor

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Unit 4 RBatch Flowsheet Integration

Aspen Plus Flowsheet calculations refer to steady state, but batch operations are unsteady

→→→→ RBatch assumes storage tanks and uses a cycle time

Flowsheet Stream for Continuous Feed

(optional)

Flowsheet Stream for Batch Charge

Flowsheet Stream for Vent Product

Flowsheet Stream for Reactor Product

Feed Holding

Tank

Vent Accu-

mulator

VentHolding

Tank

ProductHolding Tank

Vent Product transferred once each cycleBatch Charge transferred

once each cycle

Reactor Product transferred once each cycle

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Unit 4 RBatch Batch Charge and Operation Times

If specified „Batch Feed Time“ and calculated „Cycle Time“ differ, inlet and outlet streams will not be in mass balance !

Continuous Feed Stream

„Feed Stream“ mFeed

Vent Product Stream

„Product Stream“

Batch Charge:mFeed × tFeed or:mFeed × tCycle

Vent = f(t)

Vent Product

Reactor Product

RBATCHSystem Boundary

Reaction Mixture = f(t)

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Unit 4 RBatch Forms

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Unit 4 RBatch Setup

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Unit 4 RBatch Specifications

Reactor Operating Specification

• Constant Temperature• Temperature Profile• Constant Heat Duty• Heat Duty Profile• Constant Coolant Temperature• Heat Transfer User Subroutine

Pressure Specification

• Specify Reactor Pressure• Specify Reactor Pressure Profile• Calculate Reactor Pressure

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Unit 4 RBatch Temperature and Pressure Specifications

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Unit 4 Rbatch Reactions

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Unit 4 RBatch Stop Criteria

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Unit 4 RBatch Operation Times I

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Unit 4 RBatch Operation Times II

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Unit 4 RBatch Continuous Feeds

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Unit 4 RBatch Controller