simplifying assumptions unit 4 batch...
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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