che 354 chemical reactor design
DESCRIPTION
CHE 354 Chemical Reactor Design. The General Mole Balance & Ideal Reactors. F A0. F A. What do we do with this term?. Example of Reactor Design. In – Out + Generation = Accumulation. F A0. F A. As D V goes to zero and M goes to infinity:. - PowerPoint PPT PresentationTRANSCRIPT
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CHE 354 CHE 354 Chemical Reactor Chemical Reactor
DesignDesign
The General Mole The General Mole BalanceBalance
&&Ideal ReactorsIdeal Reactors
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Example of Reactor Example of Reactor DesignDesign
In – Out + Generation = Accumulation
FA0 FA
dt
dNGFF AAAA 0
What do we do with this term?
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The Generation TermThe Generation Term
iAi
M
iAi
M
iA VrGG
11
FA0 FA
Divide reactor into little regions, small enough that intensive variables (CA, T, P) do not vary within.
dVrG A
V
A
As V goes to zero and M goes to infinity:
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The General Mole The General Mole BalanceBalance
dt
dNdVrFF AA
V
AA 0
Let’s apply it to the three ideal reactors!
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Batch ReactorBatch Reactor
Perfectly mixed
No flow in or out
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dt
dNdVrFF AA
V
AA 0
Batch ReactorBatch Reactor
No flow in
No flow out
Perfectly mixedVrdVrdVr A
V
AA
V
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Batch ReactorBatch Reactor
Vrdt
dNA
A
And if the volume is not a function of time (constant)
AAA r
dt
dC
dt
VNd
)/(
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Team ExerciseTeam Exercise
What does design equation (mole balance) look like for a semi-batch
reactor - continuous flow of Reactant A, Reactant B, or
Product P?
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Continuous Stirred Tank Continuous Stirred Tank ReactorReactorCSTRCSTR
Perfectly mixed
Steady state
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dt
dNdVrFF AA
V
AA 0
CSTRCSTR
Perfectly mixed
VrdVrdVr A
V
AA
V
Steady state
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CSTRCSTR
00 VrFF AAA
What would the design equation look like at
startup and with some spatial variations?
dt
dNdVrFF AA
V
AA 0
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Plug Flow ReactorPlug Flow ReactorPFRPFR
No radial gradients – only axial
Steady state
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PFRPFR
dt
dNdVrFF AA
V
AA 0
Steady state
This is the integral form. Often the differential form is more useful. Take the derivative with respect to volume of each term.
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PFRPFR
00
dV
dVrd
dV
dF
dV
dF A
V
AA
Derivative of a constant is
just 0 rA
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PFRPFR
AA r
dV
dF
)],,([)( PTCfTkrdV
dFAAA
A
Here is where some complication sets in:
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Example 1-1Example 1-1
Assume isomerization is first order with k
= 0.23 min-1
What volume PFR and CSTR are required for 90% conversion and 10
L/min?