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1975

Reprinted

edition I979

Second

with

Reprinted

1982, 1987, I99 I

corrections

1994

edition

Reprinted 2001, 2003,2005,2006,

2007

J. F. Richardson, J. R.
0 1991,J. M. Coulson,
Ltd. All rights reserved

Copyright

Backhurst

and J. H.

Harker.

by Elsevier

Published

The

MA


1971

First edition

Third

is an imprint of Elsevier
Hill, Oxford OX2 8DP,UK

of J. M . Coulson,

right

J.

as the author of this
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identified

F . Richardson,
J. R . Backhurst
and J.
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CONTENTS

vi

1.8 Continuous
1.8.1

1.8 .2

1.8.3

1.9

Autothermal

1.8.5

Kinetic

operation

Reactor output

continuous
tubular and

44

47
49
50

stirred-tank reactors

from

data
of

Comparison

43

reactors

methods

Graphical

1.8.4

batch,

and

Batch

1.9.2


Continuous stirred-tank

reactor

1.9.3 Comparison

of

stirred-tank

reactors

for a

single reaction.

plug-flow reactor

tubular

1.9 .1

1.10 Comparison

43

reactors

stirred-tank


of ideal mixing.
Residence
time
Assumption
Design equations for continuous stirred-tank

reactor

52

reactors

54

of batch,
tubular and
Reactor yield
Types of multiple reactions

stirred-tank

reactors

for multiple

reactions.

55


1.10.1

56

1.10.2Yield

and

57

selectivity

1.10.3 Reactor type
1.10.4 Reactions in
in
1.10.5 Reactions
1.10.6 Reactions in
in
1.10.7 Reactions

and

57

backmixing

58

parallel


reactants

parallel-two
series
series-two

reactants

61
63
67

1.11

Further

I.12

References

68

1.13 Nomenclature

68

68

reading


2. Flow Characteristics

2.1

Non-ideal

2.1.1
2.1.2
2.1 .3
2.1.4

2.2

of Reactors-FlowModelling

and mixing in chemical reactors
of non-ideal
flow patterns
Types
tracer
methods
Experimental
of a stream leaving a vessel-E
-curves
Age distribution
of tracer information
to reactors
Application
flow


Tanks-in-series model

2.3 Dispersedplug-flow

2.4

2.5

2.6 References

2.7

Nomenclature

Gas-Solid

3.1
3.2

3.3

and Reactors

Reactions

Mass transfer within
solids
porous
The effective diffusivity
3.2.1

in porous catalyst
Chemical
reaction
in porous
3.3.1 Isothermal
reactions
diffusion

3.3.3 Non-isothermal reactions

in

3.3.4 Criteria for

diffusion

71

71
71
73
75
78

control'

80

83


84

88

93

96

98
102
104
105
105
106
108
108

Introduction

3.3.2 Effect of intraparticle

71

80

model

Axial dispersion and model development
Basic differential
equation

2.3.3
of tracer
Response to an ideal pulse input
2.3.4
of dispersion
coefficient from a pulseinput
Experimental determination
2.3.5
Further
of tracer injection
development
theory
2.3.6
Values of dispersion coefficients
from
and experiment
theory
2.3.7 Dispersed plug-flow
model
with first-order
chemical reaction
2.3.8 Applications
and
limitations
of the dispersed plug-flow
model
Models
involving combinations of the basic flow elements
Further reading
2.3.1

2.3.2

3.

51
52

111

112

pellets
catalyst pellets

on experimental
parameters
Dorous
catalvst<. Dellets

115

116
122
124

I28


CONTENTS


3.3.5

3.3.6

Mass transfer

3.5

Chemical

3.5.1

Adsorption

Surface reaction as the

3.5.4

Rate determining
of rate
Examples

Desorptionof

Packed tubular

3.6 .2

Thermal


3.6.3

Fluidised

3.8

Further

References

determining

transfer

129

143
144
146
148
148
148
150

step
step

determining

steps for other mechanisms

equations for industrially

important

reactions

151

151

reactors

packedreactors

172

180

181

reactors

design of gas-solid reactors
unreacted
core models

and

particle
of equipment


3.9

and heat

139

as the rate

characteristics of
bed reactors

3.7 Gas-solid non-catalytic
3.7.1 Modelling
Types

mass

poisoning

rate

a product

calculations

Design
3.6 .1

Single


by

stream to a solid surface
of heterogeneous catalytic reactions
of a reactant
as the rate determining
step

3.5.2
3.5.3

3.7.2
3.7.3

influenced

a fluid

from

kinetics

3.5.5

3.6

and

de-activation


Catalyst

3.4

reactions

in catalytic

Selectivity
effects

vii

and contacting

182

183

186

patterns

190
190
192

reading


3.10 Nomenclature
4.

4.1

4.1.2
4.1.3

4. I .4
4.1.5

4.1.6
4.1.7
4.1.8

4.1.9

4.2

4.2.2

4.2 .3
4.2 .4

5.

Equations for mass

with
chemical

reaction
reactor
Information
for gas-liquid
reactor design
required
of gas-liquid
reactors
Examples
bubble columns and multiple-impeller agitated
High
aspect-ratio
Axial dispersion in bubble
columns
the kinetics
of gas-liquid
Laboratory reactors for investigating

Choiceof

transfer

a suitable

reactors
reactions

Gas-liquid-solid

4.4


References

4.5

Nomenclature

reading

Engineering

5.1 .2

The

Biologicalproducts

Scalesof

and

diversity

and

the

Prokaryotic organisms

230


231

235

248

Tolerance

of

living

257

259
262

physical properties

of cells

environmental

conditions

to

systems


256

260

organisms

Eukaryotic

General

systems

production

classification

5.2.2

5.2.5

229

255

ecology

operation

Classification


5.2.4

223

254

world and

biological

5.2.1

5.2.3

218

reactions

252

Cellsas reactors

Cellular

216

252

Introduction


5.1.4

tanks

249

5. I.1

5.I .3

204

205

248

Reaction

Biochemical

202

229

Mass transfer and reaction
steps
Gas-liquid-solid reactor types: choosinga reactor
Combination
of mass transfer
and

reaction
steps

Further

5.2

reactors

of

Types

4.3

5.1

reactions

Gas-liquid

Gas-liquid-solid

4.2.I

196
196
196
196
197


reactors

Gas-liquid

4.1 .1

Reactors

and Gas-Liquid-Solid

Gas-Liquid

265

269

270


CONTENTS

viti

5.3

Chemical

Elemental


5.3.2

Proteins

5.3.3
5.3.4
5.3.5
5.3.6

5.3.9
5.4

Protein

purification
of proteins

Stability

277

277

Nucleic acids

278

278

membranes


278

Carbohydrates

Biological versus chemical reaction
of

Properties

processes

Enzyme kinetics

5.4 .9

5.4.10

285

286

Michaelis-Menten

the

Enzyme inhibition
The kinetics of two-substrate
reactions
The effects of temperature and pH on


de-activation.

5.4.11 Enzyme
5.5

5.5 .2

Types of

5.5.3

Energetic

5.5.4

Energy

level

Photosynthesis

5.8
5.9

and

phosphorylation

309


315

316

mutagenesis

Genetic recombination
Genetic engineering
DNA

in

318

bacteria

320

320

technology

engineered products

Genetically

304
315


and

325

their manipulation

326

326

activity

5.7 .2

327

5.7.3

334

The control of metabolic pathways
The control of protein
synthesis
Stoichiometric
aspects of biological processes

5.8.1

Microbial


Yield

growth
Phases of

5.9.3

Product

Immobilised

growth

a microbial

culture

354
diffusion
diffusion

limitation
limitation

5.11.3 Continuous
Estimation

of kinetic

5.12 .1 Use

5.12.2 Use

of batch
of continuous

360
364

of micro-organisms
culture
of micro-organisms

parameters
culture

356
364

configurations
Enzyme reactors
growth

342

352

formation

biocatalysts


5.11.2 Batch

339
345

kinetics

5.10.1 Effect of external
5.10.2 Effect of internal

5.1 1 Reactor
5.1 I.1

337
342

of

5.9.2 Microbialgrowth

5.12

oxidative

and

methods

improvement
Mutation


302

304

phosphorylation

Cellularcontrol
mechanisms
5.7. I The control
of enzyme

5.9.1

5.10

294

298

of biological processes

respiration

5.6.4 Recombinant
5.7

and enzyme

298

metabolism

generation

Aerobic

5.6.5

kinetics

295

reactionsin

5.5.7

5.6.3

29I
enzyme

metabolism

5.5.5
5.5 .6

5.6.2

289


298

of

aspects

Substrate

287

equation

de-activation

Metabolism
5.5.1
The roles

5.6 Strain
5.6.1

282

equation

The Haldane relationship

5.4.7 Transformationsof
5.4.8


279
281

enzymes

5.4.4 Derivationof the Michaelis-Menten
5.4.5 The significanceof kinetic
constants
5.4.6

278
279
279

Cell walls

5.4.1
5.4.3

275

of proteins
and separation

properties

Physical

Enzymes


5.4.2

271
273

composition

5.3.7 Lipidsand
5.3 .8

27I

cells

composition of

5.3.1

experiments
culture
experiments

365

367

386

386


393


ix

CONTENTS

5.13

5.14

state microbial

Non-steady

5.13.I

Predator-prey

5.13 .2

Structured

Further

396

398

models


402

considerations

design

5.14.1

396

systems

relationships

405

Aseptic operation

405

5.14.2 Aeration
5.14.3

aspects of biological reactors

Special

5.15 Appendices
5.1


Appendix

410

410

Proteins

Appendix

5.2 Nucleic acids

Appendix

5.3

416

of Michaelis-Menten
rapid-equilibrium
assumption
Derivation

Appendix 5.4 The Haldane

equation

using


the

418

419

relationship

421

inhibition

Appendix

5.5

Enzyme

Appendix

5.6

Information

5.16 Further

409

storage and


retrieval

in

the cell

425

431

reading

References

431

5.18 Nomenclature

433

5.17

for Measurement and Control

6. Sensors

6.1

Introduction


6.2

The

6.3

6.5

6.6

6.2 .1

Methods

6.2 .2

Further

6.2 .3

The measurement

6.2.4
6.2.5

The measurement
Open channel

438


flow

on

dependent

methods of

between

relationship

volumetric

measuring

pressure
flow

Classification

6.3.2

Elastic elements

of

Differential

6.4 .1


Thermoelectric

6.4.2

Thermal

463

466

468

sensors

473

detection

of level

Simple

6.5 .4

Radioactive

6.5 .5

Other methods of level


float

The measurement
6.6.I Liquids

465

temperature

Techniques using
Capacitive sensing

478

479

systems
hydrostatic
elements

methods
of

density

480

head


481

(nucleonic

level sensing)

measurement

measurement

6.7.2

Off-line
Continuous

(specific gravity)

484

of viscosity
measurement
of viscosity
on-line
measurement
of

6.8.2

Electrometric


6.8 .3

The chromatograph

The mass

Thermal

484

488

6.8 The measurement
of composition
6.8 .1 Photometric analysers
6.8 .4

482
484

Gases

I

6.8 .5

454

cells
devices


6.5 .2
6.5 .3

The

452

454

6.5.1

6.7.

452
sensors

pressure

radiation

The measurement

439

449

pressure

6.3 .5 Vacuum

sensing
The measurement of

438

448

transducers for pressure measurement

Electric

flowrate

448

flow

6.3.1

drop and

445

mass flow
of low flowrates
of

6.2.6
Flow profile distortion
The measurement

of pressure

6.6 .2

6.7

437
of

measurement

6.3.3
6.3.4
6.4

437

analysers

489

489
viscosity

495
497

503

as


an

on-line

process

spectrometer
conductivity

493

sensors

for gases

analyser

511

515

516


CONTENTS

X

The detection of water

Other methods of gas composition

6.8 .6
6.8 .7

6.9

6.10

6.I1

Process sampling
6.9 .1 The sampling

systems
of

523
523

523

systems

single-phase

6.9.2 The sampling
of multiphase
systems (isokinetic sampling)
The static characteristics of sensors


528

535

6.11 .I

Bridge circuits

6.11.3

Signals and

6. 11 .5

Converters

Signal

539

539
(telemetry)

6.12 .2
6.12 .3

Serial digital
The transmission


6.12.4

Non-electrical

6.12 .5

Smart

6.14

References

542
546
547
547

effects

6.12. I Multiplexers

Further

537

noise

transmission

6.13


536
536

6.11.6Loading

(time

division

multiplexing)

signals
of

transmitters

549

analog
signals
transmission

signal

associated

and

549

hardware

protocols-intelligent

553
555

Control

Process

7.I

Introduction

7.2

Feedback

7.2.1

560

560

control

The

560


block

562

diagram

7.3

Fixed parameterfeedback
control
action
Characteristics of different
control
modes-offset
Qualitative approaches to simple feedbackcontrol
system
7.3 .1 The heuristic
approach
of freedom approach
7.3 .2 The degrees

7.4

The

7.2 .2
7.2.3

transfer


564

566
design

function

Linear systems
7.4.2 Blockdiagram
The polesand
7.4 .3

7.5 Transfer functions
7.5 .1 Order of a
7.5 .2 First-order

the

and

of superposition

principle
a transfer
systems

of

capacity

system

579

579

7.5 .4

Second-order systems

series

583

589

(dead time)
fixed parameter

592

controllers

593

593

Industrial three term controllers
Responseof control loop components to
7.8. I

Common types of forcing
function
7.8 .2
Response to step function

594

7.7 .2

7.8

7.9

and

7.8.3

Initial

7.8 .4

Response to

7.8 .5
7.8 .6

Response
Response

final


576

579
in

systems
lag

573

579

function

systems

First-order

Transfer functions
of
7.7.1 Ideal controllers

571

577

algebra
zeros
of


7.5.3

Distance-velocity

570
575

7.4 .1

7.7

552
552

reading

6.15 Nomenclature

7.6

528

conditioning

Signal

6.11.4 Filters

7.


528

6.10.1Definitions
6.11.2Amplifiers

6.12

519
measurement

value

functions

594

594

597

theorems

600

function

600

sinusoidal


to pulse
of more

forcing

603

function

complexsystems

to

forcing

Transfer functions
of feedback
control systems
C and
7.9.1 Closed-loop
transfer
function
between

functions

605
608


R

608


CONTENTS

7.9.2

Closed-loop

7.9 .3

Calculation

7.9.4

The

7.10.1

characteristic

The

7.10 .2 The Routh-Hurwitz
7.10 .3 Destablising
7.10.5
7.10.6


The Nyquist stability
The log modulus

7.12
.2
7.13

Cascade

613
614

a feedback

loop

criterion

feedback
methods

setting

parameters

635

638

638


Dead time compensation

638

640

compensation

control

645

646

control

ratio

control

Feed-forward

646

651
and

systems-interaction


7.15 .3

and
the

Estimating

7.16Non-linear
systems
7.16.1Linearisation
7.16.2
7.17

653

design
degree of interaction between

654

control loops

The describing

661

series
Taylor\342\200\231s

function


664

technique

time control systems
7.17 .1 Sampled data (discrete time)
systems
7.17 .2 Block diagram algebra for sampled data systems
7.17 .3 Sampled data feedback control systems
7.17 .4 Hold elements (filters)
7.17.5 The stability
of sampled
data systems
7.17.6 Discretetime (digital)
fixed parameter
feedback controllers

7.18 .1

7.18.2

controllers

7.18.3 The self-tuning
regulator
Computer control of a simple
7.19.1 Directdigital
control
Real


7.19.3

System

7.19 .4

7.20 Distributed
7.20.1

7.21 .2

677

679

681

684

686

time

computer

689

690


691

(STR)
operator

plant-the

(DDC)

interface

and supervisory

control

control

692

692
694

696

interrupts

The operator/controller interface
control
computer
systems (DCCS)


696

Hierarchical

698

systems

7.20 .2 Design of distributed
control
computer
systems
7.20.3 DCCS hierarchy
7.20.4
Data highway (DH) configurations
7.20 .5 The DCCS operator station
7.20 .6 System integrity
and security
7.20 .7 SCADA
(Supervisory control and data acquisition)
The programmable
controller

7.21.1

672

675


688

(programmed) adaptive control
reference
control (MRAC)
adaptive

Scheduled

7.19.2

672

686

algorithms

control
Model

658

660
using

Discrete

7.18 Adaptive

7.2 1


loops

their

7.17.7 Tuning
discrete
time
7.17.8 Responsespecification

7.19

653

decoupling

7.15.1 Interaction between control

7.15.2Decouplers

632

634

7.14.2 Ratio control

7.15 MIMO

619
632


controller

compensation

Series

617
625

(Nichols) plot

methods

search

7.14 Feed-forwardand
7.14 .1

612

reaction curve methods

7.1I.3 Direct

609

611

criterion


response

7.1 1.2 Process

7.12.1

609

function

system
equation

a stable processwith

The Bodestability

System

C and V
transfer

criterion

7.11 Common proceduresfor

7.12

closed-loop


equation

7.10.4

7.11.1 Frequency

the

unity feedback
the characteristic

equivalent
and
stability

7.10 System

between

function

transfer

of offset from

xi

Programmable


controller

Programming the PLC

design

698

698

700
703

703

708

708

709

709

711


CONTENTS

xii


7.22

Regulators and actuators (controllersand
7.22 .1 Electronic controllers

7.22.2 Pneumatic

Appendix

7.1

Appendix

7.2

712

715

719

724

valves

726

Table of Laplace and z-transforms
Determination
of the step responseof

from
its transfer
function

726
a second-order

system
726

7.24 Further reading

729

Nomenclature

731

7.25 References
7.26

Conversion

729

737

Problems

Index


712

valves)

controllers

7.22 .3 The control valve
7.22 .4 Intelligent
control

7.23 Appendices

control

Factors

for Some CommonSI Units

750
753



PREFACE

xiv
various

in-line


the essential

updated
concludes
January

of

for measurement

techniques

inputs to the controlsystem

treatment

with

TO THIRD EDITION

of

the

a discussion

principles

of


and

of computer

the

the

constitute

which

variables

process

chapter gives an
of process control and

The last

plant.

applications

control of processplant.

RICHARDSON


J F

1994

Department of Chemical Engineering
University

of

Wales

Swansea

Swansea

SA2 8PP

UK

D G PEACOCK
School

London

of Pharmacy

WClN

1AX


UK




PREFACE TO

in
the subject of a chapter. Parallelwith
the
growth
plants has developedthe need for much closer control of
and a chapter
on process control is therefore
included.
in the particular field, and
of Volume 3 is the work
of a specialist

problems

complexity

of chemical

operation,

Each

chapter


xvii

forms

engineering
their

THE FIRST EDITION

or past members of the staff of the Chemical Engineering
present
of
the
of Swansea. W.J. Thomas is now
at the Bath
Department
University
College
is
Technische
of
and
J.
M.Smith
at
the
University
Technology
Hogeschool. Delft.

J. M.C.
the

authors

are

J.F.R.

D.G.P.



2

ENGINEERING

CHEMICAL

(b)

to the reactor.
Thus, the
physical condition of the reactants at the inlet
basic processing conditionsin terms of pressure,temperature
and
compositions of the reactants on entry
to the reactor
have to be decided,if not already
as part of the original processdesign.

specified

The

the

Subsequently,

(a)
(b)

the

following

reactor:

overall size of the

and the more
reactor, its general
configuration
dimensionsof
internal
structures.
important
any
The exact composition and physicalconditionof the products
from
emerging

the reactor. The compositionof the products
must
of course lie within
any
limits
set in the original specification of the process.

The

(c) The

for heat

(d) The operating

. Byproducts

Before

up

taking

question

important

the reactor

transfer.


of the

the reactor

within

pressure

flow

the

with

within

prevailing

temperatures

be made

1.1 .1

reach logical conclusions
concerning

is to


aim

principal features of the

reaction mixture.

and any provision

and any pressure

which

must

drop associated

and their EconomicImportance
the design of
of whether any

reactors

us first

consider the

byproducts are formed in the

reaction. Obvious-


in

detail,

let

very

to give unwanted,and perhaps unsaleable,
byproducts
affect the operating costsof the process.
from
Apart
the
nature
of
formed
and
their
amounts
must
be
this, however,
any
byproducts
known so that plant for separating and purifying the products from the reaction
ofunforeseen
on start-up
of
may be correctly designed. The appearance

byproducts
a full-scale plant can be utterly
disastrous.
the
cost
of
the
Economically,
although
reactor may sometimes
not appear
to be great comparedwith
that
of the associated
is
such
as
distillation
it
the
columns,
etc.,
separation equipment
composition of the
mixture of products issuing
from
the reactor
which determines the capital and
costs
of the separation processes.

operating
For example,in producing
with
several other valuable hydroethylene\342\200\230\342\200\235
together
carbons like butadiene from the thermal cracking of naphtha, the design of the
is determined
whole
complex
plant
by the composition of the mixture formed in a
in which the conditions are very
As we shall
tubular
reactor
controlled.
carefully
see later, the design of a reactoritself can affect the amount of byproducts formed
and thereforethe size of the separation equipment required. The designof a reactor
and its mode of operation can thus have
on the remainder
profound
repercussions
ly,
is

consumption
wasteful
and


of reactants
will directly

of the plant.

1.1.2.

In the
principles

of a

Appraisal

Preliminary

we

pages

following

of chemical

shall

Reactor

Project


see that

reactor design

engineering

with

the

addition

involves

of chemical

all

the

basic

kinetics. Mass

fluid
flow are all concerned and complications
arise
these
transfer
case, interaction occursbetween

processes
and the reaction itself. In designing
a reactor
it is essential to weigh up all the

transfer, heat
when,

as

so

transfer

often

and

is the


3

PRINCIPLES

DESIGN-GENERAL

REACTOR

in their

factors involved and, by an exercise
of judgement,
to place them
is
of
Often
the
basic
of
the
reactor
determined
proper
importance.
design
by
is seen to be the most troublesome
what
step. It may be the chemical kinetics; it
between
it may be heat transfer; or it may
even
be
may be mass transfer
phases;
in
the need to ensure safe operation.For example,
or
oxidising
naphthalene

with
the reactor
must be designed so that
air,
o-xylene to phthalic anhydride
which
are not infrequent, may be rendered harmless.The theory
of
ignitions,
is being extended rapidly and more precisemethods
reactor
for
detailed
design
if the final design is to be
and optimisation are being evolved.
However,
design
the
decisions
taken at the outset must
be correct.
a careful
successful,
major
Initially,
is required and at this
of the reactor
appraisal of the basic role and functioning
the

of a little chemical engineering commonsensemay
be
stage
application

various

order

invaluable.

1.2 .

OF REACTORS AND

CLASSIFICATION

1.2 .1.

Homogeneousand HeterogeneousReactors
reactors

Chemical

mixing

is the way

reactors


homogeneous

is present. If morethan
them

reactant

one

to form

together

of starting

into two main categories,homogeneous
and
one
a
or
a
only
phase, usually
gas
liquid,
is involved, provision must of coursebe made

be divided

may


In

heterogeneous.

for

the

off

a homogenouswhole.Often,

reaction,

examplesbeinggas-liquid,
of the

one

reactors

catalytic

ical

is

thus


thus

truly

the

However,

heterogeneous.

to dissolve

the gas in

the

where

liquid

but the

homogeneous

worth

reactor,

greatervariety


reactors. Initially,

of

therefore,

geneous reactors,

little

with

1.2.2.

kind

Another
division

shown
preparative

Reactors

Batch

is

in


the

Fig.

of

liquid.

] .la,

Generally,

and contacting

be concerned
the treatment

mainly

that

it is

serve
reaction

required

heterogeneous


just
is

to effect
reactors

pattern than homogeneous
with

that follows

the

simpler

homo-

can be extendedto

modification.

and Continuous Reactors
across the homogeneous-heterogeneous
or continuous.Batchwise
operation,
to
who has carried out small-scale
anybody
There are many
situations,

however,
laboratory.

of classification
which cuts
mode of operation-batchwise

reactions

are mixed

present, common
systems. In cases
catalyst; gas-solid

bubbling a gas through a liquid
may
it then reacts homogeneously; the

and

configuration
we shall
parts

although

reactors
heterogeneous


quite

in
reactor is heterogeneous

contact between two phases-gas

exhibit a

is

three, phases are
and liquid-liquid
often present as a

reactants

the

mixing

the reactants

an important class of heterogeneouschemnoting that, in a heterogeneous reactor, the
but this is not necessarily so.
heterogeneous,
reaction
takes place on the surface of the solid

form


may be

itself

reaction

In a gas-solidcatalytic
and

solid, it

particularly
It is
systems.

reaction

chemical

liquid-solid

gas-solid,

is a

phases

sometimes


although

and then brought
to the required
temperature.
In heterogeneousreactorstwo, or possibly
where

OF

CHOICE

TYPE

REACTOR

is

familiar

in

the


CHEMICALENGINEERING

4

where considerable advantages accrue by caroperation,

reaction
rying
continuously in a flow reactor.
1.1
illustrates
the
two
basic
be employed.
Figure
types of flow reactor which may
In the tubular-flow reactor (b) the aim is to pass the reactants
a
tube so that
along
there is as little intermingling
as possible
between the reactants entering the tube and
the products leaving
at the far end. In the continuous
stirred-tank
reactor
(C.S.T .R .)
introduced
to disperse
the reactants thoroughly into
(c) an agitator is deliberately
the reaction mixture immediately
enter
the tank. The product streamis drawn

they
off
have
the
same
and, in the ideal state of perfect mixing, will
continuously
as the contentsof the tank. In someways,
a C.S.T.R.,
or backmix
composition
using
reactor as it is sometimescalled,seemsa curious
method
of conducting
a reaction
becauseas soonas the reactants
enter
the tank they are mixed and a portion leaves
in the product
stream flowing out. To reducethis effect,
it is often advantageous to
in series as shownin Fig. 1.Id.
of stirred
tanks connected
employ a number
The
The
stirred-tank
reactor

is by its nature well suitedto liquid-phase
reactions.
tubular
is the natural
reactor, although sometimes used for liquid-phase
reactions,
choice for gas-phase
even on a small scale. Usually
the
or
reactions,
temperature
the
rate of reaction
is high, in which case a comparatively
catalyst is chosen so that
small
tubular
reactor
is sufficient to handle a high volumetric
flowrate
of gas. A few
combustion
and
certain
chlorinations,
gas-phase reactions, examplesbeing
partial
are carried out in reactors
which

resemble
the stirred-tank reactor; rapid mixingis
about
for the gases to enterwith a vigorous
usually
brought
by arranging
swirling
motion instead of by mechanicalmeans.
in

especially

out

large-scale

a chemical

chargd II
b.ginning of reaction

Reactants

Products

FIG.1.1.

(a)


Batch

Basic types of chemical reactors

reactor

(b)

Tubular-flow reactor

(c)

Continuous

(d)

stirred-tank

C.S.T .R .sin

reactor

seriesas frequently

(C.S .T.R.)or
used

\342\200\234backmix
reactor\342\200\235



REACTOR

DESIGN-GENERAL

Variations in ContactingPattern-

1.2.3.
Another

should be

which

question

reactor is whether there

pattern. Figure 1.h
vesselhereis essentially

is

any

advantage
the

illustrates


a batch

Semi-batch

Operation

asked in assessingthe
to

semi-batch

most

suitable

be gained by varying
mode of operation.

and at

reactor,

of the reactants A. However,
the
over
the
of
the
continuously
period


5

PRINCIPLES

type

of

the contacting
The reaction

the start of a batch it is charged
B is not all added at once,

with one

second

reactant

but

reaction. This

is

the

natural


and obvious

if a liquid has to be treated with
reactions.
For example,
a
way to carry out many
in
a
chlorination
or
the
is
far
too
reaction,
gas, perhaps
hydrogenation
gas
normally
voluminous
to be charged
all at once to the reactor; instead
it is fed continuously
at the rate at which
it is used up in the reaction. Another caseis wherethe reaction
if
is too violent
both

reactants
are mixed suddenly together. Organicnitration,
for
can be conveniently controlled by regulating
the
rate
of addition of the
example,
The maximum
in such a case
acid.
rate of addition of the second
reactant
nitrating
will be determinedby the rate of heat transfer.
A
characteristic
of semi-batch
is that the concentration C, of the
operation
B in Fig.
1 .2, is low throughout
reactant added slowly,
the
course
of the reaction.
This may be an advantage if more than one reactionis possible,and if the desired
reaction is favoured by a low value
of
the semi-batch method may

be
C,. Thus,
chosen
for a further
that
of improving the yield of the desiredproduct, as
reason,
shown

in

1.10.4 .

Section

Summarising, a
(a)
(b)

to react a
to control

semi-batchreactormay

gas with

be

chosen:


a liquid,

a highly
exothermic
and
reaction,
in suitable
circumstances.
(c) to improve product yield
In semi-batch operation, when the initial
of A has been consumed,the flow
charge
of B is interrupted,
the products discharged, and the cyclebegunagain with
a fresh
If
of
A.
the
of
semi-batch
charge
required, however,
advantages
operation
may be
In
retained but the reactor system
for
continuous

flow
of
both
reactants.
designed

I,

First reactant
Second

dumwd in
A----,

, Tadded

reactant

continuoudy

Products
Roductr

discharged at end

(4
.2. Examples of possiblevariations
(a) Semi-batchoperation

FIG.1


(b)Tubular

reactor

(c) Stirred-tank
(in each casethe

in reactant

with divided feed
divided feed
of B, C,, is

reactors
with
concentration

low

contacting pattern

throughout)


CHEMEAL ENGINEERING

6
flow version


tubular

the

of B is divided

1.2.4. Influenceof Heat
Associated
few

with

reaction often
exothermic

take

will

the enthalpy

unless

place

of

of

heat


and

reaction,

is made

only

in

a

The magnitude of the heat of

on the design of a reactor.With
substantialrise in temperature
of

provision

to

heat

for

a

strongly


the reaction

be transferred

as the

between
heat transferred, and the temperature change of the
is expressed by an enthalpy balance (Section
this
to

the

reaction,

mixture;

there is a
change
be neglected.

for example, a

reaction proceeds. It is important

reaction
1.5).If


the feed

1 .24,

(Fig.

as cross-flowreactors.In

Type

can

it

influence

a major

has

on Reactor

Reaction

of

small that

reaction,


mixture

points.

chemical

every

is this so

cases

stirred-tankversion

These are known

low throughout.

C, is

cases

both

(Fig. 1.2b) and the
several

between

quantitatively


clearly the relation

to appreciate

try

of the reaction
mixture is to remain
constant
(isothermal
equivalent to the heat of reaction at the operating
temperature
If no heat is transferred (adiabatic
transferred to or from
the
reactor.
of the reaction
mixture will rise or fall as the reacoperation),the temperature
In practice,
tion
it may be most convenient to adopt a policy
intermediate
proceeds.
between
these two extremes; in the case of a strongly exothermic reaction, some
heat-transfer
from
the reactor
may be necessary in order to keep the reaction

under
but
a
moderate
control,
temperature rise may be quite acceptable,
especially
if strictly isothermal operation would involve
an
elaborate
and costly control
scheme.
In setting
out
to design a reactor, therefore, two
to ask are:
very
important
questions
the

temperature

the heat

operation),
must be

(a)


What

is

(b)

What

is

the
the

mixture may
The answers
to

of reaction?

heat

range

acceptable
be

over which the temperature of the

reaction


to vary?

permitted

the
may well dominate the whole design.Usually,
limit
roughly specified;often the lower temperature
is determined by the slowing
down
of the reaction, and the upper temperature
limit
of undesirable side reactions.
by the onset

range

temperature

it

is

questions

can only be

Reactors

Adiabatic


If

these

feasible,

adiabatic

is to

operation

Figure 1.3 shows the reactor section

petroleum naphtha;
of gasoline.
operation
reactor
either

The

this

is an

reforming

of


important

reactions

are

a

be preferred
plant

process for
mostly

occur, or the

reaction would

would be too low.The problem
three sections.Heat is supplied

temperaturesareraisedsothat

be

of design.

simplicity
the


improving

endothermic

would fall during the
temperature
were
made as one single unit,
this
temperature
the
at
the
inlet
would
be too high
temperature
the

for

reforming of

for the catalytic

octane

so that


in

number
adiabatic

course of the reaction.If the
fall would be too large, i.e.
and

undesired

because
the temperature
incomplete
is conveniently
solved by dividing
between
the sections, and
externally
each
section
of the reactor will operate

reactions

would

near the outlet
the reactor into
the intermediate

adiabatically.


REACTOR DESIGN-GENERAL PRINCIPLES

7

Reactors

Reactants

LProducts

_o,

U

Intermediate
furnace

Reactor charge
furnace

.3. Reactor system of a petroleum
(The reactor
naphtha
catalytic reforming plant.
is divided into three units each of which operates adiabatically,
the heat required being
furnace)

supplied at intermediate
stages via an external

FIG.1

into sections also has the advantage
that the intermediate
can
be
of
the
inlet
temperature
adjusted
independently
temperature; thus an
In
distribution
can
be
achieved.
this
we can see that
optimum temperature
example
the furnaces where heat is transferred
and
the catalytic
reactors are quite separate
This

each
for the one function.
of function
units,
designed
specifically
separation
easeof
of
and
often
leads
to a good
control,flexibility
generally provides
operation
Dividing

the reactor

overall engineeringdesign.

Reactors

with

If

the


Heat

reactor

Transfer

does not operate

provision
of a batch reactormay be
part of the reactor itself,
for

recirculating

heat

pump.

transfer.

then
its design
must include
adiabatically,
1.4
in
shows
some
of

the
which
the contents
Figure
ways
heated
or cooled. In a and b the jacket and the coils form
in c an external heat exchangeris used with
whereas
a

If one

FIG. 1.4. Batch

of the constituentsof the reactionmixture,

reactors

showing

different

methods of

(a) Jacket

(b)

Internal


(c) External

coils

heat

exchangers

heating

or cooling

possibly

a


solvent,

a

ENGINEERING

CHEMICAL

8

reflux


is volatile at the
condenser,

just

Figure 1.5shows
the

amount

ways

of heat

operating temperature,the
as in
of

the laboratory.
is

large,

heat

may be

exchanger

If

reactors to includeheat transfer.
the ratio of heat transfer surface

tubular

designing

to be transferred

external

then

like a heat
to reactor volume
will
be large,
and the reactor will look very
much
in
If
as
1.56
.
the
reaction
has
to
be
carried

out
at
a
exchanger
Fig.
high temperature
and
is strongly
endothermic
(for example, the production of ethylene
by the thermal
of
or
ethane-see
also
Section
the
reactor will
1.7.1,
1.4),
cracking
naphtha
Example
be directly
fired by the combustion of oil or gas and will look like a pipe furnace
(Fig.

1%).

I


Convection

Radiant

section

section

- Products

FIG. 1.5.

(a) Jacketedpipe

(6) Multitube
(c) Pipefurnace
Autothermal

reactor

Reactor

(pipes

Methods of

heat

transfer


(tubes in parallel)
mainly in series although

to tubular

some

reactors

pipe runs may

be

in

parallel)

Operation

If a reaction requiresa relatively
before
it will proceed at a
high
temperature
reasonable rate, the products
of the reaction
will
leave
the

reactor
at a high
be recovered
from
temperature and, in the interestsof economy,heat will normally
them. Since heat must be supplied
to
the reactants
to raise them to the reaction
is to use the hot products to heat the incoming
temperature,a commonarrangement
in Fig.
feed as shown
1.6~.If
the reaction is sufficiently
heat
exothermic,
enough
in
will be produced in the reactionto overcome
losses
the
and
to
any
system
provide
in the heat exchanger. The term aurorhermal
the necessary
difference

is
temperature
in
used
to describe such a system which
is completely
its
thermal
self-supporting
energyrequirements.
The
essential
feature
of an autothermal reactor systemis the feedback
of reaction
hence
heat to raise the temperature and
the reaction
rate of the incoming reactant
stream. Figure1.6shows a number of ways in which this can occur. With a tubular
reactor
the feedback may be achievedby external
heat
as in the reactor
exchange,
shownin Fig. 1.6u,or by internal
heat
as in Fig. 1.66. Both of these are
exchange
their

thermal
characteristics
are discussed in more detail in
reactors;
catalytic
the reaction
can only take place in that
Chapter3, Section3.6.2.Being catalytic
of the reactor which holds the catalyst, so the temperature
has the form
part
profile


9

PRINCIPLES

DESIGN-GENERAL

REACTOR

AI

T-

---

----T---


Position

in reactor

Position
in

Heat

heat

exchanger

exchanger

Inlet

React_ants

reactents

Outlet

products

.Inlet
sP&?-

Outlet


reactants

Droducts

Cold

reactants

Products

I

1

Position

Conical
flame

front

products

Burner
fuel

fuel

gas


I-

Position

through

front

FIG. 1.6. Autothermal

reactor

operation

flame