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15.05.2008
Non-ideal Reactors
(477306S - 5 op)
Course period (10 Nov-12 Dec 2014)
Contact: Prof. Riitta Keiski, E-mail: [email protected]
Dr. Prem Kumar Seelam, E-mail: [email protected]
Environmental and Chemical Engineering
Faculty of Technology
University of Oulu
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Course contents: Non-ideal Reactors
• Theory of residence time distribution (RTD)
• Mixing models
• Dispersion and Tank-in-series models
• Microreactor technology
• Bioreactors
• Heterogeneous catalysis: Mechanism and Kinetics
• Gas-Liquid reactions: reactor modelling, mechanism and
reactor design
• Exercises, home assignments and exam
(Contact: Prem and ???,)
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Outline
L1a. Introduction
– Ideal Vs. Non-ideal reactors
– Measurement and/or Diagnosing of
Non-ideality
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CSTR Batch
AA rdV
dXF 0
PFR design equations
dV
XCt
AA0
AX
A
AA
r
dXCt
0
0)(
A
A
F
FA
A
r
dFV
0
AX
A
A
A
r
r
dX
F
V
00 )(
)(0 A
A
A
r
r
X
F
V
Ideal Reactor Types
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15.05.2008CSTR: well stirred and uniform throughout
Three ideal reactors: (a) batch reactor, or BR; (b) plug flow reactor, or PFR; and (c) mixed flow
reactor, or MFR.
Ideal Reactor Types
1. It has neither inflow nor outflow of reactants or products which the reaction is being carried out.
2. Perfectly mixed.
3. No variation in the rate of reaction throughout the reactor volume.
4. Normally run at steady state.
5. Generally modelled as having no spatial variations in concentration, temperature, or reaction ratethroughout the vessel.
100% Backmixing (CSTR)
0% Backmixing (PFR)
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Ideal Vs. Non-ideal reactors
Ideal Reactors
• Uniform flow distribution
• Uniform mixing
• Ideal mixing
• Ideal design equations
• No flow effects
• No bypass
• No radial variation in
concentration
• No hot spots
Non-ideal Reactors
• Non-uniform flow
• In-efficient mixing, unmixed
• Design equations changes
• Different flow effects can
occur: Laminar & turbulent
• Bypass
• Affect the reactor design,
the yield or temperature
development of a chemical
processNon-ideal……….Deviation of real reactors from ideal reactors
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1. Dead Zone
2. Short Circuit
3. ideal mixing
4. ideal plug flow behaviour in
corresponding reactors.
(1). The ideal plug flow Radial
concentration
& temperature differences occur, depending on the
particular flow
conditions (e.g. (2) Turbulent
(3) Laminar
Non-ideal7
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Non-ideal flow patterns which may exist in process equipment.
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Two extremes of aggregation of fluid
Examples of macro- and micro fluid behavior.
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Measurement of Non-ideality
Three concepts used to describe non-ideal
reactors:
• The residence times distribution (RTD) in
the system
• The quality of mixing
• The model used to describe the system
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Generally, the performance of non-ideal flow systems
can be determined from known parameters, such as:
• The kinetics of the system
• The RTD of fluid in the system
• State of aggregation
• The earliness or lateness of fluid mixing in the system
• The nature of the fluid (i.e., whether a micro or macro
fluid) in the system, whether the mixing occurs in micro
or macroscopic level.
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• When the fluid in a reactor is neither well mixed nor
approximates plug flow (i.e., non-ideal), one can use RTD data
and some model to predict conversion in the reactor.
• Frequently used models include:
– Zero adjustable parameters
• segregation model
• maximum mixedness model
– One parameter model
• tanks-in-series model
• dispersion model
– Two adjustable parameters
• real reactor modeled as combinations of ideal reactors
Reactor modeling with the RTD
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Summary
Non-ideal reactors – PFR and CSTR
TR with bypassing
STR with incomplete mixing
LFTR
– Tracer response techniques and
– Curves for ideal and non-ideal reactors
RTD
- E(t) – E(Θ), F(t), I(t)
- Estimating reactor performance using E(t)
- Predicting reactor behaviour
- The macro fluid model
- Moments of RTD
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