CHE 354 Chemical Reactor Design
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CHE 354 CHE 354 Chemical Reactor Chemical Reactor Design Design The General Mole The General Mole Balance Balance & & Ideal Reactors Ideal Reactors
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 Presentation
Transcript of CHE 354 Chemical Reactor Design
CHE 354 CHE 354 Chemical Reactor Chemical Reactor
DesignDesign
The General Mole The General Mole BalanceBalance
&&Ideal ReactorsIdeal Reactors
Example of Reactor Example of Reactor DesignDesign
In – Out + Generation = Accumulation
FA0 FA
dt
dNGFF AAAA 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
dt
dNdVrFF AA
V
AA 0
Let’s apply it to the three ideal reactors!
Batch ReactorBatch Reactor
Perfectly mixed
No flow in or out
dt
dNdVrFF AA
V
AA 0
Batch ReactorBatch Reactor
No flow in
No flow out
Perfectly mixedVrdVrdVr A
V
AA
V
Batch ReactorBatch Reactor
Vrdt
dNA
A
And if the volume is not a function of time (constant)
AAA r
dt
dC
dt
VNd
)/(
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 mixed
Steady state
dt
dNdVrFF AA
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?
dt
dNdVrFF AA
V
AA 0
Plug Flow ReactorPlug Flow ReactorPFRPFR
No radial gradients – only axial
Steady state
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.
PFRPFR
00
dV
dVrd
dV
dF
dV
dF A
V
AA
Derivative of a constant is
just 0 rA
PFRPFR
AA r
dV
dF
)],,([)( PTCfTkrdV
dFAAA
A
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?
