CHE 354 Chemical Reactor Design
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Transcript of CHE 354 Chemical Reactor Design
CHE 354 CHE 354 Chemical Reactor Chemical Reactor
DesignDesignThe General Mole The General Mole
BalanceBalance&&
Ideal ReactorsIdeal Reactors
Example of Reactor Example of Reactor DesignDesign
In – Out + Generation = Accumulation
FA0 FA
dtdNGFF A
AAA 0
What do we do with this term?
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:
The General Mole The General Mole BalanceBalance
dtdNdVrFF A
A
V
AA 0
Let’s apply it to the three ideal reactors!
Batch ReactorBatch Reactor
Perfectly mixedNo flow in or out
dtdNdVrFF A
A
V
AA 0
Batch ReactorBatch Reactor
No flow in
No flow out
Perfectly mixedVrdVrdVr A
V
AA
V
Batch ReactorBatch Reactor
VrdtdN
AA
And if the volume is not a function of time (constant)
AAA r
dtdC
dtVNd
)/(
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?
Continuous Stirred Tank Continuous Stirred Tank ReactorReactorCSTRCSTR
Perfectly mixedSteady state
dtdNdVrFF A
A
V
AA 0
CSTRCSTR
Perfectly mixed
VrdVrdVr A
V
AA
V
Steady state
CSTRCSTR
00 VrFF AAA
What would the design equation look like at
startup and with some spatial variations?
dtdNdVrFF A
A
V
AA 0
Plug Flow ReactorPlug Flow ReactorPFRPFR
No radial gradients – only axialSteady state
PFRPFR
dtdNdVrFF A
A
V
AA 0
Steady stateThis is the integral form. Often the differential form is more useful. Take the derivative with respect to volume of each term.
PFRPFR
00
dVdVrd
dVdF
dVdF A
V
AA
Derivative of a constant is
just 0 rA
PFRPFR
AA r
dVdF
)],,([)( PTCfTkrdVdF
AAAA
Here is where some complication sets in:
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?