Mixing of liquids, solids and high viscosity materials

Mixing of Liquids, Solids and
High Viscosity Materials
A Practical Course on
Industrial Mixing Technology & Equipment
22-23 February, 2013
Mumbai
CII Naoroji Godrej Centre of Excellence

Introduction
• Jayesh R. Tekchandaney
• Director Technical – Unique Mixers
• Founder of Mixing Expert
• Author – “Process Plant Equipment
Operation, Reliability and Control”
Chapter 12 – “Mixers”
John Wiley Publication

Objectives
• Share knowledge and experience on Industrial
Mixing
• Discuss best practices in mixing
• R&D, Process Engineers, Project Engineers, Plant
Managers, Chemical Engineering Professionals and
Students
• Industries – Chemical, Food, Pharmaceutical,
Ceramics
• Creating better products at lower costs through
improvements in mixing system performance
“No matter how good you are, You can always get
better.
And that’s the exciting part” - Tiger Woods

Contents
• Fundamentals of liquid mixing, solid
mixing and high viscosity mixing
• Mixing theory and concepts
• Mixing equipment selection, design
and operation
• Advances in mixing technology
• Mechanical components of mixing
equipment
• Solve any mixing problem framework

Mixing
• Process of thoroughly combining
different materials to produce a
homogenous mix
• Mixing is a critical process
• Quality of the final product, attributes
are depend on the mixing performance

Poor Mixing
• Non homogenous product lacking
consistency in chemical composition,
color, flavor, reactivity
• Failed batches
• Loss of high value product
• Cost of poor mixing estimated as
US$ 100 million per year

Reasons for
Poor Mixing
• Lack of understanding of material
characteristics
• Inadequate, inaccurate definition of
mixing objectives
• Incorrect selection of mixer
• Wrong scale-up techniques
• Limited knowledge on mixing
equipment design, parameters

Polymer Company
• Product purity – 90%, US$ 45,000/ton
• Required purity – 95%, US$ 50,000/ton
• Change in agitator operating
parameters – 92 to 93 %
• Change in agitator design – 95 %
• Production capacity ~ 55,000 tons/yr
• Profitability !!!
• “Mixing Expert”

Challenges
• Ever increasing customer expectation
• Need for higher product purity, higher
product value
• Scale-up from laboratory to production
• Need to lower production costs
• Equipment operation and maintenance
issues
• Lower lead times

Challenges
• Increase in costs of machines,
materials, power and people
• Intense competition
• Operational Safety
• Environmental Issues
• Statutory obligations
• Similar challenges, different
environment

Challenges
20-20
◊ Development of New Products
◊ Frequent Product Change Overs
◊ Minimum time from new product conception
to implementation
◊ Little time for lab trials - pilot scale -
production
◊ Multi-purpose equipment – Coating,
granulation, heat transfer, drying
◊ Mixer is no longer a generic production tool.
It is a critical and decisive business tool.

Explosive Company
• Manufacture of explosive materials
• Production size unit – 8 liters only
• Equipment specifications detailed
• Factory visit
• The empty room
• The real mixer

Explosive Company
• Process engineers, plant personnel,
engineering and maintenance team
• Collaborative customization –
Equipment specifications precisely
defined
• QAP
• HAZOP
• Trouble free mixer operation

Module 1 – Mixing Concepts
Fluid Mixing Mixing of Solids

All raw materials charged
together or in a predefined
sequence
Mixed until homogeneity
Output is measured in
kg/batch
Batch Mixing

Batch Mixing
Batch mixing is preferred for applications where:
• Production quantities are small
• Strict control of mix composition is required
• Many formulations are produced on the same
production line
• Ingredient properties change over time and
compensation must be on a batch-by-batch basis
• It is required to identify a batch for further follow
up, example - pharmaceutical formulations, food
products.

Continuous Mixing
Material flows steadily from
an upstream process into
the mixer
Material is mixed as it moves
from the charging point to
the discharge point
The time that material is
retained in the mixer is
known as the retention time
Weighing, loading, mixing
and discharge steps occur
continuously and
simultaneously
Output is measured in kg/hr

Continuous Mixing
Continuous mixing is preferred for applications
where:
 Large quantities of a single product are to be mixed
 In a continuous process line requiring high
production rate
 Strict batch integrity is not critical
 Smoothing out batch product variations is required

Selection of Mixing Equipment
Material
Characteristics
Process
Set-Up
Mixer Operating
Parameters
Mixing
Accuracy
Mixer
Cleanability
Equipment
Costs

Design of Mixing Equipment
Process
Design
Mixer
Characteristics
Mechanical
Design

Scale-Up of Mixing Equipment
Geometric
Similarity
Kinematic
Similarity
Dynamic
Similarity

Module 2 – Fluid Mixing
Fluid mixing includes mixing of liquid with liquid, gas with liquid, or solids with
liquid.
Mixing - Mixing refers to any operation used to change a non-uniform system
into a uniform one (i.e. the random distribution into and through one another,
of two or more initially separated phases). Mixing therefore requires a
definition of degree and/or purpose to clearly define the desired state of the
system [Ludwig, 1995].

Agitation - Agitation implies forcing a fluid by mechanical means to generate
flow. Agitation does not necessarily imply any significant amount of actual
intimate and homogeneous distribution of the fluid [Ludwig, 1995].
Fluid Mixing Processes
- Mechanical Agitation
- Jet Mixing
- Gas Sparging
- In-line Mixing

Fluid Mixing Applications
Blending of
miscible liquids
Blending of
immiscible liquids
Liquid gas
mixing
Liquid solid
mixing
Fluid
motion

Blending of
Miscible Liquids
 Blending of two or more homogeneous liquids
 Liquid blending operation may be purely physical in
nature or may involve chemical reaction
 Low to medium viscosity liquid mixing involves
macro-scale and micro-scale mixing concepts
 Liquid blending can be achieved using top entering
agitators, side entering mixers or jet mixers
 Blending of miscible, mutually soluble liquids with
viscosities upto 10,000 centipoise is carried out
using axial and radial impellers
 Viscous liquids are blended using close clearance
impellers

Blending of
Immiscible Liquids
 Blending of mutually insoluble, immiscible liquids
may be required to produce stable or unstable
emulsions.
 Stable emulsions - Shampoos, polishes and other
specialty chemicals.
 Liquid extractions employ an unstable emulsion to
boost the rate of mass transfer and reaction -
applications in petroleum, chemical, food and
pharmaceutical industries.

Blending of
Immiscible Liquids
 Turbine impellers are used for the purpose of
creating large enhancements in interfacial area;
thereby increasing the rate of mass transfer and
reaction.
 Low shear hydrofoil design impellers can be used
for coarse dispersions.
 Axial and radial flow impellers are effective for fine
emulsions.
 High-shear impellers are required for preparing
stable emulsions

Liquid-Gas Mixing
 Type 1- Involves physical distribution and dispersion of the
gas in the liquid. Application of this type is limited only if foam
or froth is desired.
 Type 2 - Involves mass transfer process such as absorption,
stripping, chlorination, oxidation all of which require transfer
of gas into liquid.
 Radial flow impellers are preferred over axial flow impellers.
Disk turbine impellers are most suited
 Fermentation equipment - High solidity ratio hydrofoil
impellers - produce large flows in biological operations to
ensure adequate distribution of oxygen.
 Special type of gas mixing systems are used for hazardous,
expensive and critical applications like hydrogen which
necessitate the need for recycling the gas of the vapor space
above the liquid in to the vessel.

Liquid-Solid Mixing
 Wide range of industrial applications like catalyst
polymer systems, paper pulp industry, washing of
solids, crystallization processes
 Type 1- Suspension of solids into the liquid, a
physical process
 Type 2 - Dissolving of solids in the liquid phase, a
mass transfer process
 Axial Flow Impellers with high pumping efficiencies
are best suited for majority of solid suspensions.

Fluid Motion
 Some applications require a combination of liquid-
solid-gas mixing
 Physical processes such as heat transfer may be
required
 Description of mixing is provided in terms of the
fluid motion produced by the impeller
 Defining the magnitude of the required fluid motion,
the system description can be provided for the
desired process objective

Power Consumption
in Agitated Vessels
Impeller
Type
Impeller
Diameter
Speed of
Rotation
Fluid
Density
Fluid
Viscosity
Vessel Design,
Attachments

Dimensionless Numbers
• Reynolds Number
• Froude Number
• Power Number
ρ- Density of the fluid in Kg/m3
n – Rotational speed in revolution / sec
Da – Impeller diameter in meters
µ – Fluid viscosity, Pa-s
g – Acceleration due to gravity, 9.8m/s2

Flow Regimes
 Laminar Flow - Reynolds number < 10
 Turbulent Flow - > 103
to 105
 Flow is considered transitional between these two
regimes
 Impeller power numbers are compared in the
turbulent regime, which for common use is taken as
Re > 105
 In laminar flow, the liquid moves with the impeller.
At a distance away from the impeller, the fluid
remains stagnant. In such cases, the Froude
number accounts for the force of gravity which
determines the fluid motion.

The power number Np depends
on the impeller geometry and the
location of the impeller in the
vessel.
In the laminar regime, Power
number is inversely proportional
to the Reynolds Number. The
power depends largely on the
fluid viscosity.
In the transitional regime, the
power number changes slightly.
In the turbulent regime, the
power number is constant and
independent of the fluid viscosity.
Power Number
Plot of the Power number versus the impeller Reynolds
number for different types of impellers, vessel
geometrics.

Power Consumption
in Agitated Vessels
.
Using the power number
equation, the power
consumed by an impeller for
specified system geometry
can be determined.
The connected motor power
should be higher since it has
to account for the electrical
and mechanical losses of the
agitator drive system.

Flow Number
 The flow number (pumping number) is
defined as
NQ = QP / nDa
3
QP – effective pumping capacity m3
/s
 For most impellers operating in the turbulent
regime, the flow number varies in the range
of 0.4 – 0.8
 The pumping number is used to define the
pumping rate of an impeller.

Flow Characteristics
 Depends on the vessel size and geometry, the
internal attachments like baffles, and the fluid
properties.
 The velocity of the fluid has three components –
• Radial velocity component - Acts perpendicular to
the agitator shaft
• Axial velocity component - Acts parallel to the shaft
• Tangential or rotational component - Acts in a
tangential direction to a circular path around the
shaft. Tangential flow is detrimental – creates
vortex.

Shear
 Relative motion of the liquid layers within the mixing vessel
results in shearing forces that are related to flow velocities.
 The fluid shear stress is the multiplication of fluid shear rate
and fluid viscosity
 These forces, represented by shear stress carry out the
mixing process
 Pumping capacity is important in establishing shear rate due
to the flow of the fluid from the impeller.
 Understanding the location and magnitude of shear generated
by an impeller in an agitated vessel has significant
implications for design.
 Most axial flow impellers are low-shear and have high pumping
efficiencies.
 Radial flow impellers provide high shear but are low pumping.

Liquid Agitation
Equipment
 Top Entering Mixers
 Side Entering Mixers
 Portable Mixers
 Jet Mixers
 Motionless Mixers

Vessel
 Vertical cylindrical vessel with a liquid height which is
equal to the tank diameter
 The vessel top and bottom may be provided with flat or
dished ends
 Dished bottom heads can be 2:1 ellipsoidal,
torispherical, hemispherical or conical
 Nozzles - Agitator mounting, feeding, measurement
instruments, manhole, material discharge
 Design for the operating temperature and pressure
conditions.
 The thickness of the vessel shell and dished ends should
be calculated using the relevant pressure vessel design
codes.

Baffles are installed on agitator
vessels to produce a flow
pattern conducive to good
mixing and to prevent vortex
formation.
In standard agitation equipment
configurations, 4 vertical baffles
are provided each of which has
a width of 1/10th
or 1/12th
of the
tank diameter.
Baffles are generally offset from
the vessel wall by a distance
equal to1/3rd
to 1/6th
width of the
baffle.
Baffles increase the power
consumption of the mixer but in
turn improve the process
performance.
Baffles

Draft tube is a cylindrical duct
slightly larger than the impeller
diameter and is positioned
around the impeller.
Used with axial impellers to
direct the suction and discharge
flows.
The impeller draft tube system
acts as a low efficiency axial
flow pump.
The top to bottom circulation
flow is of significance for flow
controlled process, suspension
of solids and for dispersion of
gases.
They are particularly useful in
tall vessels having high ratio of
height to diameter.
.
Draft Tubes

Heat transfer surfaces are
provided for applications which
require heating or cooling of
process.
Heat transfer for an agitated
vessel is dependent on the
following:
• Overall heat transfer
coefficient
• Surface area for heat transfer
• Temperature difference
between the heat transfer fluid
and the process fluid.
The heat transfer co-efficiencies
can be estimated using
established corrections
The turbulence created by the
action of the impeller improves
the heat transfer coefficient.

Heat Transfer
Surfaces

Impellers
• Based on the liquid viscosity,
impellers can be classified as
turbines for low viscosity fluids
and close clearance impellers
for high viscosity fluids.
• Depending on the flow patterns
developed by the mixing
impellers, they are classified as
axial flow impellers and radial
flow impellers.
• Impeller designs may also be
classified based on the amount
of shear that they produce.
Axial flow impellers
• Marine propellers
• Pitched bade turbines
• Hydrofoil impellers
Radial flow impellers
• Rushton turbine
• Smith Impeller
• Open blade turbine
• Coil or spring impellers

Low clearance impellers
• High shear impellers

Axial Flow Impellers
The impeller blade makes an angle of
less than 90° with the plane of
impeller rotation.
The locus of the flow occurs along
with axis of the impeller, parallel to
the impeller shaft.
Axial flow impellers are used for
blending, solid suspensions, solid
incorporation or draw down, gas
inducement and heat transfer
applications.
Commonly used axial flow impellers
for transitional and turbulent flow
applications include, marine
propellers, pitched blade turbines
and hydrofoil impellers.

Fluid flow pattern of axial flow marine propeller.
Impeller is mounted at the centre of a baffled vessel

Marine Propellers
Speed range – 400 to 1800 rpm
Top Entering – Diameter < 450 mm
Side Entering – Diameter 250 mm to 850 mm
In a theoretical environment, one full revolution
would move the liquid longitudinally a fixed
distance depending upon the of inclination of
propeller blades. The ratio of this distance to
the diameter of the propeller is known as the
pitch of the propeller. Propellers are available
with 1.0 pitch ratio; these are often referred to
as square pitch.
Variations include four bladed propellers,
propellers with saw tooth edges for tearing
action, perforated blades for shredding and
breaking of lumps.
Marine propellers are also used on side
entering mixers. They are mounted with the
impeller shaft inclined at an angle with respect
to the vessel centerline, for improving process
results.
Three blade marine propeller

Pitched Blade Turbine
Impeller Diameter - 450 mm to 3000 mm
Hub with even number of blades are
mounted at an angle of 10° to 90° with
respect to the horizontal
The most commonly used impeller of this
type is the four bladed 45° pitched blade
turbine
Mixed flow impeller as fluid discharge has
both axial and radial components
Generally down-pumping
Up-pumping in applications such as gas
dispersions and floating solids mixing
Used in flow control applications
45° pitched blade turbine impeller

Hydrofoil Impellers
High efficiency impellers designed to maximize
fluid flow and minimize shear rate.
3 or 4 tapering twisted blades, cambered and
sometimes provided with rounded leading
edges.
The blade angle at the tip is lower than that at
the hub. Resultant flow is streamlined. Vertices
around the impeller are lower. Lower power
number than PBT.
The solidity ratio is the ratio of the total blade
area to a circle circumscribing the impeller.
Low solidity ratio - Liquid blending and solid
suspensions.
Higher solidity ratio - Axial flow patterns as the
viscosity increases. In gas-liquid dispersions
wide blades provide an effective area of
preventing bypass of gas through the impeller
hub.
Myths about Hydrofoil Impellers
Hydrofoil Impeller
Hydrofoil impeller with different solidity ratios

Radial Flow
Impellers
The impeller blade is parallel to
the axis of the impeller.
Radial flow impeller discharges
flow along the impeller radius
Radial flow impellers are used
for single and multi-phase
mixing applications.
Effective for gas-liquid and
liquid-liquid dispersions.
Commonly used radial flow
impellers include, the Rushton
turbine, bar turbine, open blade
turbine.
Radial flow pattern produced by flat blade turbine

Rushton Turbine,
Smith Impeller
The Rushton turbine is a disk type (six blade
turbine) radial flow impeller.
The diameter of the disk ranges from 66 to 75
percent of the internal vessel diameter.
Impeller design is best suited for gas liquid
contacting because of the circular disk.
Gas is introduced through a sparger below the
impeller; the disk directs the gas along a path
of maximum liquid contact and prevents the
gas from taking the direct vertical route along
the mixer shaft
Variant of the Rushton turbine is the Smith
impeller in which the impeller blades are semi -
circular or parabolic, instead of flat.
For gas dispersion, the impeller shape allows
for much higher power levels to be obtained in
the process as compared to the Rushton
turbine.
.
Six blade Rushton turbine impeller
Smith impeller

Open Blade Turbine,
Coil Impeller
In open blade turbine, the blades are
directly mounted on the hub. The number
of blades may be two, four, six or eight.
Two-blade paddle is generally used for
solid suspension or blending applications
requiring high flow and low shear.
Paddles are normally operated at low
speeds
Coil impellers were developed for
applications where solids frequently settle
at the bottom of the vessel
Spring design ensures that the impeller has
adequate mechanical rigidity, strength to
overcome the resistance offered by stiff
solids during mixing operation
Flat blade turbine impeller
Coil impeller

Low Clearance Impellers
The anchor impeller and the helical impeller are
the two commonly used close clearance impellers.
The diameter of the close clearance impellers is
typically 90 – 95 percent of the inside diameter of
the vessel.
The shear near the vessel wall reduces the build
up of stagnant material and promotes treat
transfer.
The anchor impeller is a radial flow impeller
Helical impeller provides axial discharge of
material by producing strong top to bottom motion
Anchor blades may be used in combination with
other types of impellers
Anchor impeller
Helical impeller

High Shear Impellers
Used for application such as grinding,
dispersing pigments and making emulsions
High shear impellers are operated at high
speeds and are generally used for addition of
the second phase
Saw tooth impeller generates heavy
turbulence in the area around the impeller.
Star shaped impeller having tapered blades
provides intermediate shear levels.
Start shape impeller is used in polymerization
reactor.
High shear impellers may be used in
combination with other types of impellers
such as anchor.
Saw tooth impeller
Helical impeller

Impeller Selection
• Application
• Process function
• Material properties
• Viscosity
• Equipment SizeImpeller selection (Source: Penny, W.R., "Guide to
trouble free mixers", Chem. Eng.,Vol.77, No.12,
1970, p.171)

Side Entering Mixers
Side entering mixers are mounted at an angle of
7-10 degree to the tank centre line.
Power levels for side entering mixers are low to
the order of 0.01 KW/m3
Usually operate at an output speed of 400 rpm
Low installation cost, easy to install
The mixing efficiency of side entering mixers is
low as compared to the top entering mixers
Side entering mixers do not require baffles, but
correct positioning of the impeller is absolutely
necessary
Used for very large tanks used in storing
petroleum, crude oil and gasoline and in vessels
which are used for long term storage.

Portable Mixers
Small size mixers easy to mount on
vessels or drums that may not require
agitation at all times
The propeller impeller with small diameter
and high speed results in low torque is
best suited
Mounted using a clamp from the rim of the
tank, with an adjustment that allows the
mixer shaft to be set at an angle of 10-15
degree from the vertical
Can be swiveled to locate the mixer shaft
off centre
Baffles are not required with portable
mixers.

Jet Mixers
Mechanical energy required for
mixing of fluids is imparted through
high velocity jets
Jet mixers are driven by external
pumps located outside the tank
The liquid jet entrains and mixes the
surrounding fluid using the
mechanical energy supplied from the
pump.
Single or multiple jets may be
provided depending on the
application, size of the vessel.
Jet Mixers are used in large storage
tanks to maintain homogeneity of the
liquid stored.

Motionless Mixers
Motionless or static mixers use
stationary elements of various profiles,
geometries that are placed inside pipes
or conduits.
The material to be mixed is pumped
through this pipe where mixing occurs
through successive diversions and
recombination of the process fluid.
For ‘n’ elements, there are 2n division
and recombination. For a mixer with 20
elements, the number of combinations
would be over 1 million.
Applications – Liquid blending, mixing
gases, dispersion of gases into liquids,
Chemical reaction, dispersion of dyes
and for mixing solids in viscous liquids,
heat transfer.

Module 3
Solid Blending
 Chemical process industries involve solid mixing of
chemicals, ceramics, fertilizers, powdered detergents.
 In pharmaceutical industry small amounts of a powdered
active ingredient are precisely blended with excipients
such as sugar, starch, cellulose, lactose or lubricants.
 Most powdered food products like soft-drink premixes,
food flavors and instant foods are produced from custom
mixed batches.
 Worldwide production annually accounts for over a
trillion kilograms of granular and powdered products
that must be uniformly blended to meet quality and
performance goals

Material Properties
Affecting Blending
• Angle of Repose
• Flowability
• Bulk Density
• Particle Size,
Distribution
• Particle Shape
• Cohesiveness
• Adhesiveness
• Agglomeration
• Friability
• Abrasiveness
• Explosiveness
• Material Composition
• Surface
Characteristics
• Moisture Content of
Solids
• Density, Viscosity,
Surface Tension of
Liquids Added
• Temperature
Limitations of
Ingredients

Material Properties
Affecting Blending

 Angle of Repose - The angle of repose of a bulk material is the angle formed
between the horizontal and sloping surface of a piled material, which has been
allowed to form naturally without any conditioning.

 Flowability - Flowability is the ease with which a bulk material flows under the
influence of gravity only. The “Coefficient of Friction” of a powder is the
tangent of the angle of repose and is the measure for its flowability. Flowability
of bulk solids depends upon factors such as particle size and size distribution,
particle shape, bulk density, cohesiveness, all of which affect blending.

Material Properties
Affecting Blending

 Bulk Density - Bulk density is defined as the mass of a material that occupies a
specific volume. It includes not only particle mass but also the air entrained in the
void spaces between the particles. It is generally measured in kg/m3 or lb/ft3.
 Particle Size, Distribution - Particle size and size distribution in powders have a
considerable impact on the flow properties of powders. As a result, the dynamics of
blending is affected by the size of particles and their distribution in the bulk solids.
Particle size is generally quantified in microns or as mesh size.
 Particle Shape - Particle shape affects inter-particle powder friction and thereby
the flow, blending properties of the powder.

Material Properties
Affecting Blending

 Cohesiveness - Cohesiveness describes the tendency of a material to adhere
to itself.
 Adhesiveness - Adhesiveness is described as "external cohesiveness" which
is the ability of material to adhere to other surfaces.
 Agglomeration - Adherence of particles due to moisture, static charge or
chemical or mechanical binding results in agglomeration.
 Friability - Friability describes a bulk material where particles are easily
crumbled or pulverized.
 Abrasiveness - The abrasiveness of a material is determined by its hardness
factor and the shape of its particles. The hardness of materials is quantified by
Moh's hardness factor.
 Explosiveness - In certain conditions, some bulk materials can form potentially
explosive mixtures when combined with air.
 Material Composition - Composition of unit particle is its quantitative and
qualitative makeup. Individual units of pure substances have their unique
molecular composition and arrangement that dictates their behavior and
distinguishes them from other substances. The chemical composition is
important because chemical reactivity shall be a major factor in choice of a
particular substance for the application.

Material Properties
Affecting Blending

 Surface Characteristics - Surface characterizes include surface area and
electrostatic charge on the particle surface. Smaller particle have a larger
surface area which lead to formation of weak polarizing electrical forces
termed as “Van Der Walls” forces. When electrostatic charge is generated due
to friction between two surfaces, the electric charge generated is referred to
as “Triboelectric” charge.
 Moisture of Liquid Content of Solids - Increased surface exposure of fine
particles to the atmosphere may result in moisture adsorption, absorption.
Materials that naturally contain bound moisture or tend to adsorb, absorb
moisture are termed as hygroscopic.
 Density, Viscosity, Surface Tension of Liquids Added - Some blending
operations require addition of liquids into the solids for a specific purpose. In
such cases, it is essential to know the properties of the liquids to be added
during blending and its purpose.
 Temperature Limitations of Ingredients - An unwanted rise in the temperature
of materials during the blending operation beyond product limits can lead to
product degradation, melting or even be a source for ignition.
Effects of each property must be considered individually, their combined
effect as a set of group of co-related variables must be accounted.

Structured and Random
Blend Structures
 In structured blends, the different blend components interact
with one another by physical, chemical, molecular means or a
combination of these resulting in agglomeration. The
agglomerates formed thus comprise of a uniform blend of
smaller particles.
 Fine materials in particular have a tendency to adhere only to
themselves, without adhering to the dissimilar components.
e.g. carbon black, fumed silica. For blending of these
materials, shear blending mechanisms are adopted.
 When the different blending components do not adhere or
bind to each other within the blender, the result is a random
blend structure.
 Dissimilar particles readily segregate under the influence of
external forces like gravity, vibration and get collected in
zones of similar particles. e.g. a blend of salt and pepper.
 Completely random blends are rarely encountered in
industrial applications.

Mechanisms of Solid Blending
• Diffusion Blending
• Convection Blending
• Shear Blending
These three mechanisms occur to varying
extents depending on the type of mixers,
blenders and the characteristics of the
solids to be blended.

Mechanisms of
Solid Blending
Primary Mechanisms of
Solid Blending
◊ Diffusion Blending
◊ Convection Blending
◊ Shear Blending

Diffusion Blending
• Diffusion blending is characterized by small scale
random motion of solid particles.
• Blender movements increase the mobility of the
individual particles and promote diffusive blending.
• Diffusion blending occurs where the particles are
distributed over a freshly developed interface.
• In the absence of segregating effects, the diffusive
blending will in time lead to a high degree of
homogeneity.
• Tumbler blenders like the double cone blenders, v-
blenders function by diffusion mixing.

Convection Blending
• Convection blending is characterized by
large scale random motion of solid particles.
• In convection blending, groups of particles
are rapidly moved from one position to
another due to the action of a mixing agitator
or cascading of material within a tumbler
blender.
• The blending of solids in ribbon blenders,
paddle blenders, plow mixers is mainly a
result of convection mixing.

Shear Blending
• Shear blending is the high intensity impact
or splitting of the bed of material to
disintegrate agglomerates or overcome
cohesion.
• Shear blending is very effective at producing
small-scale uniformity generally on a
localized basis.
• Blenders with a high speed chopper blades,
intensifiers are an examples of shear
blending.

Segregation
(De-mixing)
• Occurs during blending, transport, storage or
discharge.
• Greater with free-flowing powders since they
can separate easily (based on size, shape, and
density)
Overcome by
• Minimizing physical differences
• Increasing cohesiveness of formulation
• Optimizing blending conditions

Segregation Mechanisms
• Blending and segregation (de-mixing) are
competing processes.
• Segregation is defined as the separation of
particles into distinct zones due to particle size,
shape, density, resiliency, or other physical
attributes like static charge.
• Common particle segregation mechanisms
include
- Sifting segregation
- Fluidization segregation(air entrainment)
- Dusting segregation (particle entrainment)

Sifting Segregation
• Sifting - smaller particles slipping between larger
ones.
– Particle size differences > 3:1
– Mean Particle size > 300 mμ
– Free flowing pile formed through funnel
– Major component is > 3 times minor one.
• Sifting segregation occurs when fine particles
concentrate in the center of a bin during filling,
while more coarse particles roll to the pile’s
periphery.
• Smaller particles move through a matrix of larger
ones.
• During discharge, the fine particles shall flow out
first followed by the coarse material.

Fluidization segregation
• Fluidization segregation occurs when the finer,
lighter particles (generally smaller than 100
microns) rise to the upper surface of a fluidized
blend of powder, while the larger, heavier
particles concentrate at the bottom of the bed.
• The fluidizing air entrains the lower
permeability fines and carries them to the top
surface.
• Fluidization segregation generally occurs when
fine materials are pneumatically conveyed,
when they are filled or discharged at high rates,
if gas counter-flow occurs

Dusting segregation
• Dusting segregation is commonly encountered
with fine pharmaceutical and food powders
being discharged from blenders into drums,
tableting press hoppers and packaging
equipment surge hoppers.
• In dusting segregation the fine particles get
concentrated near the container walls or at
points furthest from the incoming stream of
material.

Minimizing Segregation
Segregation of materials can be minimized
or eliminated using one of the following
approaches
• Changing the properties of the process
material
• Changing the process
• Changing the equipment design

Design Practices for
Minimizing segregation
•Solid blending should be located as far downstream in the process as
possible.
•Post-blend handling of the material should be minimized.
•Surge and storage bins should be designed for mass flow (no stagnant
regions in hopper)
•Velocity gradients within bins should be minimized
•A mass-flow bin with a tall, narrow cylinder is preferred as compared to
short, wide bin. Keeping the material level in the bin high is preferred.
•Use venting to avoid air counter-flow (inducing fluidization segregation).
•Minimize the generation of dust

Scale Up of
Solid Mixers
Maintaining constant tip speed (also known as peripheral speed)
Tip speed = πD n
D – Agitator diameter (m)
n – Rotational speed of the mixer (revolutions per second)
Maintaining the Froude number constant.
Froude Number (Fr) for solid mixing equipment can be defined as:
• v – Tip speed of mixing (m/s)
• R – mixer radius (m)
• - angular velocity (rad/s)ω

Scale Up of
Solid Mixers
Pilot Scale Development
• Evaluate and determine blending times
• Start at 10 minutes, further samples based on observations
• Sampling methods, sizes and locations are developed
Qualify Production Blender
• Verify blending time, speed of rotation, power drawn
Production Blending Instruction
• Blender speed and blending time to be specified
• Consistency of operation and performance batch after batch

Solid Blending
Equipment
• Tumbler blenders
Double Cone Blender, V- Blender, Octagonal
• Convective blenders
Ribbon Blender, Cone Screw Blender, Paddle Blender, Plow Mixer,
Twin Shaft Paddle
• Silo blenders
Gravity Silo Blender, Mechanical Silo Blender
• Pneumatic blenders

Tumbler Blenders
Function mainly by diffusion mixing.
Rely upon the action of gravity to cause the
powder to cascade within the rotating
vessel.
Mixing homogeneity of upto 98 percent and
higher can be achieved using tumbler
blenders.
Blending efficiency is affected by the
volume of the material loaded into the
blender and speed of the blender rotation
Can be provided with high speed intensifier
bars for disintegration of agglomerates.
Preferred for precise blend compositions
Best suited for free-flowing, non-
segregating powders.

Double Cone
Blenders
Consists of two conical sections
separated by a central cylindrical
section.
The blender is mounted at the centre
of the container between two trunions
that allow the blender to tumble end
over end.

Charging of material into the double
cone blender is through one of the
conical ends whereas the discharge is
through the opposite end.
The recommended fill-up volume is 50
to 60 percent of the total blender
volume.
Blending time is generally 10 to 15
minutes.

V Blender
Two hollow cylindrical shells joined at
an angle of 75 degrees to 90 degrees.
Material continuously splits and
recombines.
Repetitive converging and diverging
motion, combined with increased
frictional contact between the
material and the vessel’s long,
straight sides result in gentle yet
homogenous blending.

The recommended fill-up volume is 50
to 60 percent of the total blender
volume.
The blend time ranges from about 5 to
15 minutes.

Advantages
The following are distinct advantages of tumbler blenders:
• Ease of product charging, operation and discharging of material.
• The shape of the blender shell ensures complete discharge of product
material.
• Particle size reduction is minimized due to the absence of moving blades,
agitators.
•The absence of shaft projection, seals in the working area of the blender
eliminate the possibility of product contamination.
•Cleaning of tumbler blenders is easy.
•Tumbler blenders require minimal maintenance

Disadvantages
The disadvantages of the tumbler blender are as follows:

• Tumbler blenders need high head room for installation.
• Segregation problems occur with mixtures having a wide
particle size distribution or large differences in particle
densities.
• Highly cohesive materials cannot be handled in tumbler
blenders since they tend to form a bridge over the blender
outlet.

Convective Blenders
•Blending occurs because of the random movement of particles
through out the mixing vessel caused by the action of the mixing
elements.
•Depending on the rotational speed and the geometry of the mixing
elements, solid particles are thrown randomly and the product is
sheared or fluidized.
•Combination of the mixing mechanisms results in effective and
efficient mixing.
•Can be designed for operation in both batch as well as continuous
modes.
•For materials that tend to form agglomerates during mixing, high
speed choppers can be provided for disintegration of the
agglomerates.

Convective Blenders
• Horizontal ribbon blender
• Vertical ribbon blender
• Vertical cone screw blender
• Paddle blender
• Plow mixer
• Twin shaft paddle mixer

Horizontal Ribbon,
Paddle Blender
•U-shaped horizontal trough
containing a rotating double helical
ribbon or paddle agitator.
•Clearance of 3 - 6 mm is maintained
•Charging material is through top
nozzles. Discharge through bottom
valve.
•- Working capacity ranges from 40 –
70 % of total volumetric capacity.
•Blending time - 15 to 20 minutes,
•90 to 95 percent or better
homogeneity.
•Specific power - 5 to 12 kW/m3
•Ribbons are Best suited for free
flowing and cohesive products.
•Paddles are suitable for wet and
heavy materials

Vertical
Ribbon Blender
Blender container is cylindrical, with a
conical bottom
Flexibility to operate at capacities
from low volumes to 90 % volumetric
capacity
The material at the walls is lifted
vertically upwards. After reaching the
top, material travels down along
centre of the blender.
100 percent material discharge
Can handle friable products such as
cereals, plastics
Are more expensive than the
horizontal blender configurations.

Vertical Cone
Screw Blender
Consists of a conical shape vessel
with a screw agitator that rotates
about its own axis while orbiting
around the vessel’s periphery
Drive system generally consists of two
motors; one for rotation of the main
drive, the other for the rotation of the
screw
Blender can operate efficiently with
batch sizes from 10-100 % of total
working capacity
100 percent material discharge
Mixing time ~ 10 to 15 minutes

Plow Mixer
Operate on the principle of a
mechanically generated fluid bed with
three dimensional movement of the
product.
Cylindrical drum containing plow
shaped mixing elements mounted on a
horizontal shaft
May be fitted with high speed chopper
units for applications which require
break down of lumps or when the
mixer is to be used for wet granulation
Tulip shaped choppers and the X-
mass tree chopper

Plow Mixer
Working volume ranges from 30
percent to 70 percent of the total
drum volume.
Plow tip speed of more than 200
metres per minute to effect fluidizing
action
Mix ratios of as high as 1:20,000
Mixing time is 5 minutes with 95 to 98
percent homogeneity.
Capable of handling viscosities of up
to 600,000 centipoises.
Specific power for the mixer drive
generally ranges from 30 to 40 kW/m3

Twin Shaft
Paddle Blender
Paddles mounted on twin shafts in a ‘w’
shaped trough
Normal filling level of material in the
mixer is slightly above the shafts
Overlapping motion and paddle design
facilitates rapid fluidization and ensures
excellent movement of particles
Surplus space in the mixer trough to
provide air around the particles so that
they can move freely
Twin shaft, counter-rotating paddles lift
the particles in the centre of the mixer
trough, in the fluidized zone, where
mixing takes place in a weightless state.

Twin Shaft
Paddle Blender
Normal working volume is about 25
percent of the total volume of the trough
Range of operation of the mixer is 40 to
140 percent of the rated capacity
Peripheral speed ~100 metres per
minute
Mixing time can be as low as 1 minute.
Mixing homogeneity of 98 – 99 percent.
Choice of discharge valves including
half bomb bay doors, spherical disc
valves are available.
High speed choppers can be provided
Rotating twin shaft paddle mixers are
the most recent development.

Silo Blenders
• Several industrial applications where the methods
of production, the properties of material or the
nature of process may lead to variations in the
quality of the solid powders as a function of time
• Instances where material blended in small batches,
are required to be homogenized to produce a single
bulk lot
• Homogenization of material is carried out in large
silos, using either gravity blending techniques or
using mechanical silo blenders

Gravity Silo Blender
Convenient and economical method of
blending large volumes of free flowing
powders
Use multi-tube construction on inserts
to create velocity gradients within the
silo
Material is simultaneously drawn off
by a system of tubes positioned at
different heights and radial locations,
brought together and mixed.
Capacities ranging from 5m3
to 200 m3
Low energy, less than 1 kW-hr per ton
of product being blended

Mechanical
Silo Blender
Provided with a screw housed in a
cylindrical shell, isolating the bulk
material in the silo from the material
inside the shell
Material from the bottom section of
vessel is lifted by the screw and
spread over the upper sections
Principle of blending is based on the
differential travel speeds of product
particles in the conical section of the
vessel, and the velocity of material in
the screw region.
Power required - 1.5 to 2 kW-hr per
ton

Pneumatic
Blender
Air or gas is injected intermittently at high velocities at the bottom or
the sides of the silos, to blend powder materials that exhibit expansion
characteristics when aerated.
The solid particles rise due to the drag force of the injected air.
Increase in air velocity causes agitation in the bed, resulting in
formation of bubbles, which cause blending to take place.
The blending action can be optimized by adjusting the air pressure,
pulse frequency, or on/off duration.
Specific power input ranges from 1 to 2 kW-hr per ton of product.
The largest pneumatic blenders are used in cement industry with
blender capacities of upto 10,000 m3
.

Module 4 – Mixing of High Viscosity
Materials and Pastes
“ The viscosities of materials to be processed are constantly
on the rise, as there is an urgent need to cut levels of
volatile organic compounds in most parts of the process
industry ”
MATERIAL APPROXIMATE
VISCOSITY
(in centipoise)
Water @ 70 F 1 to 5
Honey 10,000
Chocolate Syrup 10,000 to 25,000
Ketchup or French Mustard 50,000 to 70,000
Plastisol
50,000 (2 - 2.5 million cps
during mixing process)
Tomato Paste or Peanut Butter 150,000 to 250,000
Silicone Sealant 6 to 7 million
Solid Propellant 10 to 15 million
Dental whitening gels, polyester compounds, epoxies,
transdermal drugs, dental composites, butyl sealants,
automotive sound absorbing compounds, color pigment
compounding pastes, and chewing gum formulations.

High Viscosity Mixing
“ Mixing in viscous systems can be achieved only by
mechanical action or by the forced shear or by elongation
flow of the matrix ”

Mixing Mechanisms
Dispersive mixing : Dispersive mixing is defined as the breakup of agglomerates or lumps
to the desired ultimate grain size of the solid particulates or the domain size (drops) of
other immiscible fluids.

Distributive mixing : Distributive mixing is defined as providing spatial uniformity of all the
components and is determined by the history of deformation imparted to the material.

Convective mixing : Convective mixing in the laminar regime is effected by shear,
kneading and stretching of material and results in reorientation of the dispersed
elements.

Mixing Challenges
Equipment Design, Scale-Up : Because of the viscosity and temperature changes that occur
during the mixing process, it is difficult to model the system. Mixer drive systems should
provide constant torque throughout the speed range, even at very low rotational speeds.
Power Requirement : Mixing requires large amounts of mechanical energy for shearing,
folding over, dividing and recombining.
Heat Transfer : Heat transfer is generally poor in viscous materials. Mixers for high viscosity
materials therefore need to be designed for promoting efficient heat transfer.

BATCH
Dual Shaft Mixer
Triple Shaft Mixer
Planetary / HSD Hybrid
Double Planetary Mixer
Kneaders
Kneader Extruder
Intensive Mixer
Banbury Mixer
High Intensity Mixer
Roll Mill
Pan Muller Mixer
CONTINUOUS
Single Screw Extruder
Twin Screw Extruder
Pug Mill
Viscous Mixing
Equipment

Mixing element operates within all parts of the mixing
vessel.
Low clearances between the mixing element and the
mixing container (1 to 2 mm).
The mixing elements may comprise of intermeshing
blades that prevent the material from cylindering
along with the rotating mixing element.
Most mixers are provided with close-clearance
blades and / or scraper devices to move stagnant
material away from heat-transfer surfaces.
High connected power per unit volume.
(upto 6 kW / kg of product)
High viscosity mixers operate at low speeds, require
high power and therefore need high torque.
Discharge of materials after mixing may be difficult
and may require special arrangements.
As the forces generated during mixing process are
high, mixers are rigid in construction.
Mixer Design

Change Can Mixers
•Like most liquid agitators are vertical configuration equipment with a vertical cylindrical
vessel
•Provided with an arrangement for lifting of the agitator head, mixing element out of the
mixing vessel once the mixing is completed, thus enabling the movement of the mixing vessel
•Some change can mixers have mixing vessels that can be lifted and lowered with the agitator
head stationary.
•Change can mixers may be provided with one or more mixing blades.

Change Can Mixers
The removal of the mixing vessel provides the following advantages:
•Weighing of material can be accurately done.
•Cleaning of the mixing vessel is easier thereby resulting in less batch
to batch contamination.
•The packing glands, seals do not come in contact with the material,
thereby eliminating product contamination.
•Multiple cans can be used to enhance the productivity without any
down time during material charging, discharge.
•Because of the vertical configuration, these mixers can be operated at
as low as 10 percent of their designed working capacity.
•Discharge of highly viscous materials from the mixing vessel can be
achieved by locating the vessel on a separate hydraulically operated
automatic discharge system.

Single
Planetary Mixer
Mixing element (commonly known as
the beater) rotates in a planetary
motion inside the mixer bowl
The most commonly used beaters are
the batter, wire whip and hook type.
The discharge of material from the
mixer bowl can be by hand scooping
when the material is pasty and does
not flow or through a bottom
discharge valve when the material is
flowable.
The single planetary mixer is used for
mixing of dry and wet powders, light
pastes, gels and dough.

Double
Planetary Mixer
The double planetary mixer includes two blades that rotate on their own axes, while they
orbit the mix vessel (also known as bowl) on a common axis.
The mixer bowl may be jacketed for circulation of heating or cooling media.
The mixer can be designed for operation under pressure or vacuum.
Material is generally discharged by manual scooping of the material from the bowl.
For extremely viscous materials, hydraulically operated automatic discharge systems
are available that push the material out through the discharge valve.

Planetary Mixer, HSD
•Specific power - 30 to 50 kW/m3
•Fill levels - 20 to 85 % of bowl
volume
•Viscosity Range -1 to 8 million
cps
•Can be equipped with additional
mixer shafts that are provided
with other types of mixing
impellers.
•A high shear impeller can be
used to incorporate powdered
material or create a stable
emulsion resulting in the
formation of viscous paste

Double Arm
Kneader Mixer
Two mixing blades placed in a ‘w’
shaped horizontal trough
Commonly used blade types are the
sigma blade, masticator blade, spiral
blade, shredder and naben blade
Rotation of the blades is either
tangential to each other or the blades
may overlap within the trough.
Blades pass the container walls and
each other at close clearances
generally (1-2 mm)
The mixer bowl may be jacketed for
circulation of heating or cooling media.

Double Arm
Kneader Mixer
Viscosity range upto 10 million cps
Viscous mass of material is pulled,
sheared, compressed, kneaded and
folded by the action of the blades
against the walls of the mixer trough.
Fill Up is 40 – 65 % of bowl volume
Mixing homogeneity upto 99 percent
Specific power - 45 to 75 kW/ m3
Discharge of the material from the
mixer
- By tilting of the mixer container
- Bottom discharge valve
- Through an extruder, screw

High Intensity Mixer
Combines a high shear zone with
fluidized vortex for mixing of pastes
and powders
Mixing blades placed at the bottom of
the vessel scoop the material upwards
at very high rotation speeds
High blade impact disintegrates
product agglomerates thereby
resulting in an intimate dispersion of
powders and liquids
Scale up based on constant
peripheral speed of the blade which is
about 40 m/s
Specific power - 200 kW/m3

Roll Mill
Pair of smooth metal rolls set in the same
horizontal plane, mounted on a heavy
structure
Provided with an arrangement for adjusting
the distance between the rolls and
regulating the pressure
To increase the shearing action, the rolls
are usually operated at different speeds
Two roll mills are used primarily for
preparing color pastes for inks, paints, and
coatings.
Rubber products and pastes are
compounded in batch roll mills as they
provide extremely high localized shear.
Continuous mills for mixing pastes contain
three to five horizontal rolls.

Pan Muller Mixer
Industrial equivalents of the traditional
mortar and pestles.
Consist of two broad wheels mounted
on an axle located inside a circular
pan
Mixers are available in the following
designs:
- Pan is stationary and the mixer
rotates
-Pan is rotating and the axis of the
wheels is held stationary
-Both the pan and wheels are rotating.
Wheels are offset
Muller mixers are used for mixing of
heavy solids and pastes which are not
too pasty or sticky

Single screw extruders consist of stationary
barrel which houses a rotating screw having
close clearance with the internal wall of the
barrel.
The material to be mixed is continuously fed
in the feed throat area using a feed hopper.
The design of the screw is such that the root
diameter of the screw increases gradually
from the feed point to the point of discharge.
External jacket may be provided for heating or
cooling of the product material.
A discharge dye is fitted at the outlet to
extruder the material in the required form,
shape, profile.
The specific energy required for polymer
mixing application ranges from 0.15 – 0.3 kW-
hr /kg.

Twin Screw Extruder
Twin screw extruders comprise of two
screws that are housed in figure-‘8’ shaped
barrels connected to each other.
The mixing and the shearing action takes
place due to the interaction between the
screw and the barrel, and also due to the
interaction between the two screws.
The most common type of twin screw
extruders is the counter rotating
intermeshing type.
The screw shafts are fitted with slip-on
kneading or conveying elements that
provide a wide range of mixing effects
combined with compression, expansion,
shearing and elongation of material.
At the point of discharge, a plate with a well
defined opening size is provided to control
the amount of pressure developed and the
quantity of discharge.
Twin Screw Extruder

Pug Mills
Pug mills consist of single or twin shaft
fitted with short heavy paddles rotating
within an open trough or a closed cylinder..
Paddles may position tangentially or may
overlap each other.
Solids are continuously fed into the mixing
chamber from one end and discharged from
the opposite end. Liquids may be added
depending on process requirements.
The product may be discharged through the
open ports, or may be extruded through
nozzles in the desired shape and cross
section.
The extruded material can be cut into
pellets, blocks of required size. Pug mills
are used to blend and homogenize clays,
mix liquids with solids to form thick, heavy
slurries.

Module 5 – Mechanical Components
in Mixing Equipment
• Motor
• Gear reducer
• Couplings
• Mixer seals
• Bearings
• Variable speed operation devices

Motors
Electrical Motors
• While specifying electrical motors the following essential information should be provided:
• Single phase / three phase AC or DC motors
• Supply voltage (volts)
• Frequency (Hz)
• Power (hp)
• Speed in revolutions per minute (rpm)
• Motor frame size
• Insulation class; A,B,F,H. This establishes the maximum safe operating temperature
• Temperature classification
• Amperage (full load motor current)
• Duty
• Type classification
• Explosion proof motor
• Other parameters like motor efficiency and so on may also be defined.
- Motors should preferably not to be loaded beyond 90 percent of their maximum rated current.
- While deciding the motor horsepower, besides the power requirement for mixing, the drive transmission
losses should be considered
Pneumatic Motors
Hydraulic Motors

Gear Reducer
Provides speed reduction and increasing
allowable torque.
The speed reduction ratios may vary from
as low as 5:1 to as high as 100:1.
Selection of Speed Reducers
•Details of the prime mover
•Details of the Mixer
•Details of gear box design
•Shaft connection
The selection of gear box involves:
•Selection of gear box for mechanical
capacity.
•Determining the service horse power for
the gear box.
•Selection of gear box based on thermal
rating
•Selection based on overhung loads, axial
thrust loads

Gear Reducer
Helical gears are used in parallel shaft
gear reducers.
Spiral bevel gears are used when the
input and output shaft of the gear
reducers are required to be at right
angles.
Worm gears are the most economical
speed reducers capable of providing
large speed reduction with a single
gear set.
Planetary gears consist of internal
gear with small pinion known as sun
gear, surrounded by multiple
planetary gears.

Couplings
A coupling is a mechanical device used to connect
the mixer shaft to the shaft of the drive system for
the purpose of transmitting power.
Rigid Coupling - Rigid couplings are used when
precise shaft alignment is required. Rigid
couplings can be of the following types:
Sleeve or muff coupling
•Clamp of split-muff or compression coupling
•Flange Coupling
Flexible Coupling - Flexible couplings are
designed to transmit torque while permitting some
radial, axial, and angular misalignment.
•Elastomer couplings - Bushed pin coupling, Tyre,
Spider or jaw coupling
•Resilient coupling
•Disc coupling
•Diaphragm coupling
•Gear coupling
•Roller chain and sprocket coupling
•Fluid coupling (Selection of Fluid Coupling)

Bearings
The type and the magnitude of axial and radial
loads transmitted by the mixer shaft depend upon
the configuration of the agitator, vertical or
horizontal, the forces caused by mixing operation.
Different types of bearings used in mixers
Ball bearings - Used for radial loads and
moderate thrust loads. Ball bearings are generally
used for high speed drive shafts and portable
mixers.
Tapered roller bearings - They are used for
heavy radial and thrust loads.
Spherical roller bearings - Spherical roller
bearings are popular in side entering mixers,
horizontal mixers where fluctuating loads can
occur. Excellent for heavy radial loads and
moderate thrust. Self aligning.
Pillow block bearings - Pillow block bearings
are commonly used in side entering, horizontal
mixers
Mixer bearings should be selected for a L-10 life of
at least 10,000 hours.

Shaft Seals
Mixers are provided with seals that are used to
ensure that the mixer vessel contents are not
exposed to the surrounding environment. Seals
may be required when the operating pressure
within the mixer is different from the atmospheric
pressure or when the material being mixed is toxic,
inflammable or can vaporize.
Most common shaft seals are as follows:
Stuffing boxes : A stuffing box consists of a
housing located around the mixer shaft and is filled
with a compression packing material to minimize
the leakage
Mechanical seals: Mechanical seals are most
advanced type of seals used in the mixers.. With
proper installation, they can handle high pressure,
ensure nearly leak free operation.
Hydraulic seals: Hydraulic seals are generally
used for vapor retention and are limited to very low
pressure applications.
Lip seals: A lip seal is manufactured using
elastomer material and is positioned in the gap
between the rotating mixer shaft and stationary
seal housing. These seals are not suitable for
pressure applications and exhibit high leakage
rates even at low pressures.

Variable Speed
Operation Devices
• Least expensive mechanical means for achieving variable speed
operation is through the use of v-belts and sheaves with variable
pitch diameters. These are however rarely used in modern day.
• Two speed electrical motors are available and can offer variable
speed operation of mixers at two defined speeds.
• Variable frequency drives as the most preferred electronic device for
changing the speed of the mixers. The variable frequency drive
provides stepless speed variation where in the speeds can be
infinitely adjusted and varied within the specified electrical
frequency limits.
• Variable speed operation can also be achieved using hydraulic
motors, pneumatic motors or hydraulic couplings.

Mixer Installation
• Mixer installation, start-up and maintenance should be carried out by trained
technical personnel as per the directives of the mixer manufacturer.
• Some equipment would require civil foundation. Consult the mixer
manufacturer for such requirements.
• The equipment should be positioned at the desired location taking into
consideration the utility requirements/ availability.
• It should be ensured that adequate space is provided around the equipment
for operation and maintenance.
• The alignment / level of the mixer assembly should be checked
• It is recommended that the moving / rotating parts should be checked with
manual operation of the drive winch assembly.
• Complete all the electrical connections between the mains and electrical
control panel.
• Ensure that the mixer is connected in proper electrical phase sequence. The
mixer shaft should rotate in the direction as recommended by the equipment
manufacturer.
• Earthing connection should be provided to the mixer body and its electrical
control panel by using suitable size / type of cable as per country norms.

Mixer Start Up
Follow up check-list before mixer start-up:
• Check oil level of the gear reducer. In most cases, the grade of Oil is ISO VG
220 mineral oil. For details refer manufacturer’s literature.
• Connect and check the electrical supply to the electrical control panel for
mixer operation..
• Check the tightness of the bolts of the gearbox, motor, and other important
drive components for proper bolting torques.
• Check that the mixing vessel is thoroughly cleaned and there are no foreign
particles inside. This exercise should be done prior to “switching on” of the
mixer motor.
• Ensure that the mixer bottom valve is in closed position.
• Ensure that the safety guards for all rotating components are in position.
• Check the connections of utilities to the mixer.
• Understand the use of operating push buttons and digital instruments
provided on the control panel thoroughly including that of emergency stop. If
possible, check the operation of each push button, instruments individually
and collectively before actual use of mixer.

Mixer Start Up
The mixer should be first started at “no load” condition.
• Start the mixer and check the direction of rotation of agitator shaft. The shaft
should rotate in the direction recommended by the equipment manufacturer.
• Check the power / current drawn by the mixer motor when assembled to the
mixer. This current should be only marginally higher when compared to the
current drawn by the motor under no load conditions. It should however be
much lower than the maximum rated current of the motor.
• Incase of excessive power drawn; check the electrical / mechanical features.
• If the power drawn is in the range specified, allow the motor to run for 2-3
minutes and minutely observe the working of the mixer drive components.
• Incase of any abnormality of the functions, try to analyze and rectify the defect
by following the instructions provided in the equipment manufacturer’s
manual. If the same can not be solved, contact the manufacturer for guidance.
• If all the functions operate satisfactorily, test – run the mixer motor for longer
period; for half an hour followed with 1 to 2 hours idle run.
• Check the operation of the other features, instruments provided on the mixer.

Mixer Start Up
• Load limited quantity of the process material in the mixer and observe its functions in
terms of mechanical and electrical operations. Do not use the mixer for any process
material, or operating conditions other than that for which it has been designed by the
equipment manufacturer.
• If the “no load” functions of the mixer are within the permissible limits, increase the
material charge quantity gradually, following the specified limits of 50 percent material
charge, 75 percent material charge and 100 percent material charge (“full load”). When
the material is loaded to it full capacity the maximum current drawn by the mixer motor
should not exceed 90 percent of the maximum rated motor current.
• Check the temperature of the geared reducer, bearing housings, stuffing box area and
so on. These should be within the permissible limits as specified by the mixer
manufacturer. Incase of any abnormality or excess heating observed, contact the
manufacturer.
• Continue monitoring the power supply, load drawn at different percentage of loadings of
the product mass and maintain records to check and confirm the performance of the
mixer on full load condition. If the results are satisfactory the second batch trial can be
conducted. Monitor the performance continuously for first few trials and maintain the
records before the mixer is handed over for regular production.
• In the case of continuous mixers, the process of mixer start-up would require several
other considerations. In such cases, the equipment manufacturer’s guidelines should be
strictly adhered to.

Mixer Maintenance
• A sound preventive maintenance program is necessary to ensure trouble free
operation of the mixer, increase equipment life and minimize downtime.
• Equipment records, maintenance drawings, repairs and maintenance history
should be well documented and easily accessible to the operational team.
• The requirement of critical equipment spares should be clearly identified and
available.
• A preventive maintenance schedule, electrical and mechanical maintenance
program, detailed lubrication program should be defined and strictly adhered
to.
• Lubrication is of the most critical aspects of equipment maintenance.
• It is recommended that the first fill of the oil in the gearbox to be replaced after
about 10,000 working hours of running or after two years whichever earlier.
• Lubrication, greasing of the bearings should be carried out at least once a
week.
• The total de-greasing, re-greasing of the bearings should to be carried out
based on operational usage.

Module 7 – Advances in
Mixing Technology
◊ CFM – Computation fluid mixing
◊ DPIV – Digital particle image velocimetry
◊ LDA – Laser doppler anemometry
◊ LIF – Laser induced fluorescence
◊ Mixing simulation programs
◊ Advances in manufacturing technology
◊ Scientists, Engineers, Managers need to
abreast with new technologies
◊ Need for development of expertise

Advances in Mixing
Technology
◊ Using DPIV technology, it is possible to
measure the fluid velocity field in the mixing
vessel at all points almost instantaneously
◊ LDA is probably the best method of non-
intrusively determining mean velocity and
turbulence data to high level of accuracy.
◊ LIF is a measurement technique, which
provides both qualitative and quantitative
assessment of mixing.

Advances in Mixing
Technology
◊ The effects of vessel geometry and internals
such as baffles can be factored into the
system design.
◊ Mixing problems, such as low-velocity areas,
circulation zones, staging and anomalies in
the fluid flow and other potential problems
can be identified using mixing simulation
programs such as VisiMix and quickly
resolved, instead of adopting the
conventional and time consuming trial and
error process.

Solve Any Mixing
Problem Framework
◊ Precise definition of the mixing objectives
◊ Accurate description of the mixing problems
◊ Answer Questions
What in the mixing process does not work to
your satisfaction ?
Is the problem repeatable in nature or
occurs occasionally ?
Does the problem occur only with some
products or processes ?
What are the characteristics and properties
of the material ?

Solution Framework
Is there a difference in the process,
equipment, product quality in lab and plant ?
What is the basis of equipment selection,
design ? Were these communicated to the
equipment manufacturer ?
What are the mixer capabilities ? What
functions are performed by the mixer ?
Is there any other mixer which has been
tried for the same application?
Can the mixing conditions be changed ?

Solution Framework
◊ Answer the questions to form the basis of
corrective action plan
◊ Detail implementation plan
◊ Step 1 - Change of material addition
sequence, mixer operating speed, batch
cycle time – quick & easy
◊ Step 2 – Change of equipment design,
equipment, process. Revalidate process and
equipment – expensive and time consuming
◊ Seek Mixing Expert advise

Education, Consultation,
Manufacturing
◊ Mixing process review
◊ Mixing equipment review
◊ Laboratory and pilot scale trials
◊ Scale-up
◊ Mixing Simulation
◊ Mixer troubleshooting
◊ Short courses, seminars
◊ Mixing equipment specification
◊ Purchasing assistance
◊ Proposal evaluation
◊ Mixer inspection
◊ Engineering services
◊ Ask the Mixing Expert

References
• Holloway M., Nwaoha C., and Onyewueni (Editors), Tekchandaney J.R. (2012). “Mixers” Process Plant
Equipment, John Wiley.
• Oldshue, J. Y. (1983). Fluid Mixing Technology, McGraw-Hill, New York.
• Perry, R. H., and D. Green (eds.) (1984). The Chemical Engineers’ Handbook, 6th ed.,
• Mcgraw-Hill, New York.
• McCabe, W.L., and Smith, J.C., (1993), Unit Operations of Chemical Engineering, McGraw Hill, New York.
• Ludwig E.E., (1995), Applied Process Design in Chemical and Petrochemical Plants Vol- I, Gulf
Publishing Company
• Walas, Stanley M., (1998), Chemical Process Equipment - Selection and Design,
(Butterworth-Heinemann Series in Chemical Engineering). Boston, MA: Butterworth-Heinemann, a
division of Reed Publishing (USA) Inc.
• Paul, E. L., Atiemo-Obeng, V. A., and Kresta, S. M. (Editors), (2004), Handbook of Industrial Mixing,
Wiley.
• Maynard, E., (2008), “Blender selection and avoidance of post-blender segregation”, Chemical
Engineering, May 2008. -
• Clement, S. and Prescott, J. (2005), "Blending, Segregation, and Sampling", Encapsulated and
Powdered Foods, C. Onwulata, Ed. (Taylor & Francis Group, N.Y.), Food Sciences and Technology
Series Vol. 146, 2005. (www.crcpress.com)
• Jenike, A, (1994), "Storage and Flow of Solids", Rev. 1980. University of Utah, Salt Lake City, 16th
Printing, July 1994.

Acknowledgments
Equipment photos and videos
• Unique Mixers & Furnaces Pvt. Ltd.
www.uniquemixer.com
• Unimix Equipment Pvt. Ltd.
www.uni-mix.com

THANK YOU
◊ Visit us – www.mixing-expert.com
◊ Email – info@mixing-expert.com
◊ Phone – (+91)-(22)-2580 1214
“Whatever you vividly imagine,
ardently desire, sincerely believe, and
enthusiastically act up on
must inevitably come to pass”
Paul Meyer

Mixing of liquids, solids and high viscosity materials

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