Part
1 Introduction
Part 2 The classification
and selection of solvent extraction equipment
Part 3 Mathematical
methods for liquid-liquid extractors
Part 4 Scale-up
of liquid-liquid extraction equipment
Part 5 Design of
column contactors for liquid-liquid extraction
Part 6 Integral
box mixer-settlers for solvent extraction processes
Part 7 The design
of pump-mix mixer-settlers
Part 8 Design of
simple gravity settlers for the coalescence of
liquid-liquid dispersions
Part 9 Design of
tank reactors for the processing of dispersed
liquid systems
Part 10 In-line mixers
and their scale-up
Volume
SE VI Part 1 Introduction.
This part gives an overview
of the volume and how to use it to best effect.
Volume
SE VI Part 2 The classification and selection of
solvent extraction equipment.
The wide
diversity of types of contactor which have been described
in the literature presents a bewildering choice to the
design engineer not familiar with the subject. Various
ways of classifying contactors are described. Most classifications
first divide contactors into discrete-stage contactors
and continuous differential contactors. These two broad
categories can be divided further into sub-groupings.
All types of contactor are listed and a brief description
of each is given. Contactors used industrially are described
in greater detail. The many criteria which need to be
considered when selecting a contactor are discussed.
Most appertain to a wide range of applications but some
are applicable to specific processes. Not all can be
satisfied simultaneously and most require value judgements
to be made. A comprehensive contactor selection procedure
using a point score method is used. The various items
of ancillary equipment required for contactor operation
are discussed. These include interface control, phase
disentrainment, pulsing and sampling equipment.
Examples
are given of the point score method of contactor selection
for typical process applications.
Volume
SE VI Part 3 Mathematical methods for liquid-liquid
extractors.
This report is concerned
with the use of models for developing realistic and
useful design equations for column contactors. The purpose
of these models is to provide more realistic representation
of column performance, particularly with regard to residence
time distribution characteristics, than is obtained
from calculations based on the plug-flow assumption.
Plug-flow calculations do however, provide a simple
introduction to considerations of equilibrium, mass
transfer and mass balances used in the formulation of
design equations. More realistic models which take account
of the non-plug-flow behaviour are needed in mass transfer
calculations for the design and scale-up of industrial
columns, and for the interpretation of data from pilot-plant
or laboratory columns. The residence time distribution
characteristics of column contactors, often termed "axial
mixing", are usually described by one of two types
of model; differential and stage-wise. The concepts
of differential or stage wise contact used in the formulation
of these models have the same basis as those used in
simple calculations of mass transfer, and the characteristics
of the models and their relationship to one another
are described. The analysis of concentration profiles
and procedures for multicomponent systems are reviewed
and an assessment given of the practical considerations
which influence the success or otherwise of design procedures.
Volume
SE VI Part 4 Scale-up of liquid-liquid extraction
equipment.
Methods for classifying
industrial-type contactors are given and the factors
which determine the performance of column contactors
and mixer-settlers are discussed. The need to exercise
caution in applying empirical correlations, determined
with small-scale apparatus and pure solutions, to the
design of large-scale equipment is stressed. The performance
characteristics, in terms of mass transfer and hydrodynamics
of unagitated, pulsed and mechanically-agitated columns
are discussed. Dispersed phase hold-up, flooding, mass
transfer, capacity and axial mixing are taken into account.
A short description of the few centrifugal-type contactors
available is given. Scale-up of mixer-settlers is described
and the major design parameters, power input, drop size,
rate of mass transfer, settler area and settler shape,
are discussed. The importance of entrainment from the
mixer and the settler in mixer-settler design is also
discussed.
Volume
SE VI Part 5 Design of column contactors for
liquid-liquid extraction.
This part sets out a general
method for the design of liquid-liquid extraction column
contactors, but with particular emphasis on randomly
packed columns, pulsed sieve plate rotating disc and
Kuhni columns. The design method is largely based upon
experimental data obtained from the SPS liquid-liquid
extraction research programme. The design method begins
with the measurement of physical properties and the
calculation of the number of transfer units. This is
followed by hydrodynamic calculations in which the flooding
point and hence required diameter of the column is derived
from considerations of drop size and the velocity/dispersed
phase hold-up relationship. The rate of mass transfer
under plug flow conditions is corrected by axial mixing
calculations to give a realistic column height. Other
items included are the mechanical design of end sections,
feed distributors, agitation equipment and safety aspects.
Volume
SE VI Part 6 Integral box mixer-settlers for
solvent extraction processes.
Mixer-settlers
find frequent application in liquid-liquid extraction
processes for the separation and purification of materials,
particularly metals, because they provide good contacting
between the phases. They are usually simple to construct,
low in capital cost and generally require little maintenance.
The integral box design is particularly reliable, being
compact without inter-stage piping and is ideally suited
to small and medium-scale operation. This report gives
a systematic procedure for the design of the integral
box mixer-settler. An overall design guide is described
together with a design decision diagram.
This is
followed by a description of the measurement of physical
properties, and equilibrium and kinetic data; the need
to use real process fluids is stressed. As part of the
design procedure it may be necessary to carry out continuous
flow tests at either laboratory or pilot scale, and
guidance is given as to how best to undertake these
tests. The operational characteristics of the integral
box mixer-settler are described, and techniques for
improving the performance of existing equipment discussed.
Sample calculations illustrating each part of the design
procedure are given in appendices.
Volume
SE VI Part 7 The
design of pump-mix mixer-settlers.
Stagewise contactors such
as the mixer-settler provide a particularly simple means
of achieving countercurrent liquid-liquid extraction,
since the residence time in the mixing stages, for example,
for slow mass transfer operations, is well characterised.
The pump-mix type is especially suitable for very large-scale
operations such as copper from leach liquors, due to
its reduced pumping costs and depth of the equipment.
The principles of operation of the pump-mix mixer-settler
are explained and the many different types reported
in the literature are described. The important aspects
of impeller performance are discussed; in addition to
providing the mixing and pumping requirements the impeller
determines the drop size distribution and phase inversion
characteristics. Some settler designs are described
and aspects of settler performance together with dispersion
band characteristics discussed. A design summary with
a design decision flow diagram, is provided. Methods
are described for the measurement of basic physical
properties, and equilibrium and kinetic data. Procedures
for pilot plant design and interpretation, leading to
final settler design are recommended. A discussion of
plant operational characteristics is given and a complete
sample calculation is included.
Volume
SE VI Part 8 Design of simple gravity settlers
for the coalescence of liquid-liquid dispersions.
The proper
design of simple settlers in which liquid-liquid dispersions
segregate under the influence of gravity is important
in optimising the dimensions of mixer-settler equipment
and the disengaging zones of column contactors.
Many settlers
are, however, almost certainly oversized for their duty
due to the difficulties inherent in predicting settler
behaviour. This report gives a systematic design procedure
for settlers, based on recent theoretical and experimental
work at ETH Zurich and at AEA Technology, Harwell, whereby
the continuous-flow disengagement performance of a settler
is predicted from batch disengagement data obtained
in the laboratory. The state of the art in the theory
of liquid-liquid coalescence is reviewed; the contributory
mechanisms in liquid-liquid disengagement of settling
(sedimentation), interdrop coalescence and interfacial
coalescence are introduced. A design guide including
a decision flow diagram is given. This is followed by
suggested techniques for the conduct and interpretation
of batch settling tests, leading to an operating settling
velocity. From this the complete design of the settler
is elaborated, including feed and outlet port calculations.
Concluding chapters consider the retrofitting of existing
settlers, operational and safety considerations. Complete
worked examples of settler calculation are given.
Volume
SE VI Part 9 Design of tank reactors for the
processing of dispersed liquid systems.
Liquid-liquid reaction
systems are a class of chemical reaction processes of
significant importance in the chemical, petroleum, mining,
food and pharmaceutical industries. This report develops
a rational design and scale-up procedure for the equipment
needed for these reaction processes. Agitator types
are described and methods given for selecting the most
appropriate one for a particular process. The advantages
and disadvantages of batch and continuous stirred tank
reactors are fully discussed. Correlations are recommended
for estimating the power consumption and the minimum
agitator speed needed to maintain a uniform dispersion.
The factors which determine drop size distribution and
correlations for predicting the mean drop size in agitated
tanks are discussed. Also described are the methods
and parameters which can be applied to characterise
the residence time and residence time distribution in
homogeneous tank reactors. The various tank reactor
configurations which can be used are described together
with requirements for operating at elevated temperatures
and pressures. The different types or flow pattern which
are produced by the wide range of agitators available
are described, including vortex formation and suppression.
To assist the designer a flow chart is given for the
steps to be followed in arriving at a tank reactor design
for a given duty together with a worked example.
Volume
SE VI Part 10 In-line mixers and their scale-up.
In-line
mixers are much used in process engineering solvent
extraction practice. This manual part is concerned with
all types of mixer used in low-residence time in-line
applications, not just strictly static designs, where
the nature of the pipe flow within, upstream and downstream
of the mixing element has a significant bearing on mixing
quality. The emphasis is upon design and scale-up methods,
and comparisons are made with agitated tank mixers.
The manual
part first discusses available types of in-line mixer,
and introduces performance characteristics for the turbulent
mixing of low-viscosity fluids. Subsequent sections
cover the issues of energy requirements, mechanisms
for creating a dispersion, phase stability and ambivalence,
and drop size prediction. Methods for rate calculation
are then described, covering both kinetically slow and
rapid reactions.
Finally,
the rather sparse information on scale-up methods is
reviewed and a recommended scale-up strategy proposed.
