477306S Introduction Non-ideal Reactors

8/16/2019 477306S Introduction Non-ideal Reactors

http://slidepdf.com/reader/full/477306s-introduction-non-ideal-reactors 1/13

15.05.2008

Non-ideal Reactors(477306S - 5 op)

Course period (10 Nov-12 Dec 2014)

Contact: Prof. Riitta Keiski, E-mail: [email protected]. Prem Kumar Seelam, E-mail: [email protected]

Environmental and Chemical Engineering

Faculty of TechnologyUniversity of Oulu

1

10.11.2014



15.05.2008

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 ???,)

2

10.11.2014



15.05.2008

Outline

L1a. Introduction – Ideal Vs. Non-ideal reactors

– Measurement and/or Diagnosing ofNon-ideality

3

10.11.2014



15.05.2008

4

CSTR Batch

A A r

dV

dX F

0

PFR design equationsdV

X C t

AA0

A X

A

A A

r

dX C t

00 )(

A

A

F

F A

A

r

dF V

0

A X

A

A

A

r

r

dX

F

V

00 )(

)(0

A

A

A

r

r

X

F

V

Ideal Reactor Types

13.11.2012

10.11.2014



15.05.2008

CSTR: well stirred and uniform throughout

Three ideal reactors: (a) batch reactor, or BR; (b) plug flow reactor, or PFR; and (c) mixed flowreactor, or MFR.

Ideal Reactor Types

1. It has neither inflow nor outflow of reactants orproducts 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)

5



15.05.2008

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 inconcentration• 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 temperaturedevelopment of a chemicalprocess

Non- ideal……….Deviation of real reactors from ideal reactors

6

10.11.2014



15.05.2008

1. Dead Zone2. Short Circuit3. ideal mixing

4. ideal plug flowbehaviour in

correspondingreactors.

(1). The ideal plugflow Radial

concentration& temperature

differences occur,depending on the

particular flowconditions

(e.g. (2) Turbulent(3) Laminar

Non-ideal7



15.05.2008

8

Non-ideal flow patterns which may exist in process equipment.10.11.2014



15.05.2008

9

Two extremes of aggregation of fluid

Examples of macro- and micro fluid behavior.

10.11.2014



15.05.2008

Measurement of Non-ideality

Three concepts used to describe non-idealreactors:

• The residence times distribution (RTD) inthe system

• The quality of mixing

• The model used to describe the system

10

13.11.201210.11.2014



15.05.2008

Generally, the performance of non-ideal flow systemscan 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 microor macroscopic level.

10.11.2014



15.05.2008

• When the fluid in a reactor is neither well mixed nor

approximates plug flow ( i.e., non-ideal ), one can use RTD dataand 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

10.11.2014



15.05.2008

SummaryNon-ideal reactors – PFR and CSTR

TR with bypassingSTR with incomplete mixingLFTR

– 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

13

10.11.2014

Documents

477306S Introduction Non-ideal Reactors