Processing Foundation Module 2: Powder mixing & Granulation

Purpose of MixingPowder HandlingWhich mixer do I choose?Mixing MechanismsPowder mixing: technologiesTumbler Mixers (Diffusive)Convective MixersFluidized MixersCombinations of convective & diffusiveVertical axis or horizontal axisBatch or ContinuousMixer Selection - A Step-wise ApproachSegregation can happen in all process steps and equipmentProcessing Of PowdersGranulationSpray DryingExtrusionHigh Shear GranulationLow Shear GranulationProcess model for Savoury mixingCombination of high and low shearMixing – key parameter & challenges

Processing Foundation

Module 2: Powder mixing & Granulation

Powder Processing & Mixing

Filling & Packing

The purpose of a mixing operation is that the

process as a whole leads to an internal

structure of acceptable quality Thus the

feeding of material to the mixer, the behaviour

of the mixer itself plus that of the equipment

downstream of the mixer need to be

understood

Purpose of Mixing

• Question 1: What is the mixer meant to do?

•Answer: Produce a good mix

•Question 2: So what do you mean by “good”?

Purpose of Mixing

Ideal Mixing

Even Ingredient Distribution

Even dosing into pack

Reproducible Product

Why Mixing?

Degrees of Mixing

Ideal Mix Good Random Mix

M = Mixing Index

CT = Concentration in Top 1/4 of bed

Poor Random Mix

Concentration Average

CT

M =

Powder Handling

Scales of Scrutiny

• Must be appropriate for the system

• In most cases is the anticipated minimum dosage size

• No benefit in trying to achieve good mixing below this

• minimum scale of scrutiny

Powder Handling

Good Random Mix

Powder Handling

Scales of Scrutiny

Sample size = 100 50% black

50% white

Sample size = 100 50% black

50% white

Powder Handling

Unit Operations – Module 2

Which mixer do I choose?

•

Mixing Mechanisms

Powder mixing: technologies

• Tumbler Mixers (Diffusive)

• Convective Mixers

• Fluidized Mixers

• Combinations of convective & diffusive

• Vertical axis or horizontal axis

• Batch or Continuous

Which mixer do I choose?

Tumbler Mixers

• Powders need to be free flowing

• Ingredients in the mix need to be non

segregating – similar sizes and densities

• Discharge from such mixers needs to be well designed to prevent segregation on emptying

• Suitable for fragile ingredients

Ploughshare – Convection

Convective Mixers

• Good for mixing segregation prone blends

• Some have high shear mixing elements and so mix cohesive powders well When run at high speeds the energy input in convective mixers can fluidize the materials and the temperature can rise appreciably

• Can be difficult to clean

• Not suitable for fragile ingredients prone to

breakage

Convective Mixers High Shear Elements

Which Mixer?

• Sample A – Corn flour & Gravy Powder

• Sample B – Cereal Flakes & Fruit Flakes

• Sample C – Sand & glass ballatini

• Sample D – Soup powder &

vegetable/pasta pieces

• Sample E – Corn flour, gravy powder & croutons

Nature of mix?

Cohesive Free Flowing

Segregation problems?

Tumbler Mixer Shear Impact

Mixer Selection - A Step-wise Approach

Screw Mixer Ribbon Blender Artofex Mixer

Bowl Chopper Grater/Mill

Combination of high and low

shear

• For complex multi

component blends it may

be better to combine

different mixing

technologies

• Eg Use a highshear

mixer for the cohesive

components followed by

a low shear mixer to add

the friable materials

Amixon HM2000

Mixing – Real Life – The Problems

Mixing Problems:

• Ingredient cohesiveness (stickiness)…… fats, hygroscopic materials

• Ingredient fragility (sensitivity to shear)… (large) particulates, especially FD

• Ingredient sensitivity (eg to heat)… sugars, flavour compounds

• Ingredient size/quantity distributions… pieces vs powders; bulk vs trace

De-Mixing (segregation) Problems

“dry”/dusty mixes tend to de-mix due to very high flowability

• Transportation… acceleration rates - large particles

move faster than small

Segregation can happen in all process steps and equipment

Intermediate Storage

e.g Bins Mixers

Mixing

e.g Tableting Presses

Shaping / Forming Dosing / Filling

Break!

Processing Of Powders

Granulation Spray Drying Extrusion

Raw materials as delivered

Particle size distribution

Particle attrition,liquids distribution Temperature profile

Phase changes Hydration/drying

Product…

Particle size distribution Physical chemistry

Particle/Domain size Equilibrium position Kinetic barriers Storage temperature Storage humidity

Control of product delivery depends on control of product microstructure

- get it wrong loss of product delivery!

What is Processing?

Processing is a major source of change in physical chemistry and microstructure

• Spray drying

Processing Options

Granulation Microstructure vs Process

route

NTR granule

Fluid bed granule

High Active granule

Increasing intra & inter particle porosity

Increasing shear rate

Spray dried

Spray Drying

 Slurry making is the first crucial step

particle size range

 Co-current required for heat sensitive

materials eg milk powders

Detergent Spray Drying

• Advantages include:

• Lower capital cost

• Scope for inclusion of heat sensitive ingredients

• Greater energy efficiency

Granulation

Extrusion

• Control of Shape

• Regular sized particles

• Low porosity compacted material

• Mixing

– Single screw – poor

– Twin screw, intermeshed – good

• Addition of liquids and solids along extruder possible

Extrusion

Key Learnings

• Mixing

– How to measure & scale of scruitiny

– Equipment choices – based on material type and behaviour

• Powder Processing

– Spraydrying – co-current vs counter current – Granulation – find out more tomorrow!

Q&A

Properties of each raw ingredient:

Amount Particle size Density Heat capacity Melting point & melt status (for fat)

Density Porosity Temperature

% solid fat & crystal form Effect of fat technology Powder flow properties (F.C.C) Particle size distribution Water activity

Heat capacity, including phase change Crystallisation kinetics

MIXING

MATURATION / STORAGE

Key:

Material properties Process parameters we set directly

Liquid dosing method: spray

vs pour (if using liquid fat)

Fat dosing rate

% solid fat Distribution

Process model for Savoury mixing

High shear

1 Z-Blade Mixers

ZZ- / Sigma- Mixer

Z-Blade Mixer (Winkworth)

• High intensity mixer using counter/co-

rotating Z-shaped arms to provide mixing

via “kneading” action

• Blades also have a scraping action which

results in a very powerful mixing effect

• Widely used in polymer industry for

highly viscous materials

• Not really suitable for fragile ingredients

and heating of mix can be a problem due

to high energy input

• Most useful for heavy pastes

(e.g bouillons)

High shear

2 Bowl Chopper

Bowl Chopper (Seydelmann)

• The ultimate high intensity mixer!

• Horizontally rotating bowl combined with

very sharp vertical rotary knives provide a

comminution/mixing action

• Only suitable for mixtures of low sensitivity dry ingredients and fat/other liquids where a finely emulsified paste is required

• Very high intensity mixing = short mixing

times but potentially high temperatures in mix

• Careful control is vital!

High shear

3 Drais Mixer

Drais Mixer (Seydelmann)

• A single central shaft runs through the centre

of the mixer with scraper arms at regular

intervals, the mixer speed is variable and only

minimal heat generation occurs

• The scraper blades direct the product into

the intensifier blades which assist with rapid

homogenization of the batch

• Whole bottom can open for offloading

=> minimal remains on offloading - easy to

clean

• Particles are easily damaged, fat softening

can occur

•High cost

High shear

• High intensity mixer using central rotating

axle fitted with blades to circulate mix

• Can also be fitted with rotating

knives/choppers to increase shear

• Useful for low sensitivity ingredients and for

use where fat/other liquid incorporation is

required

• Dust can be a problem where no liquid

components are present

• Not suitable for fragile ingredients

4 Plough Share Mixer

Pough Share Mixer (Lödige)

Combination of high and low shear

Vertical (Double) Screw Mixer – Amixon/Ruberg

Alternative: 2-in-1 equipment, combining both shear rates

• Based on movement of a vertical helical

screw in an upright vessel

• Available in single and double screw

configurations

• As with other screw mixers effectiveness

dependant on screw geometry and

enhanced by baffles/vanes etc

• Helical product motion results in very

effective mixing

• Can be used for solids and pastes

• Sequential mixing in one equipment possible

due to flexible speed and screw geometry:

gentle and efficient (short mixing speed)

Amixon HM2000 –

key design principles

• The benefits of this mixer are the following:

– highly effective mixing resulting in short batch times

– inclusion of high fat levels possible (due to high speed cutting rotors which are positioned deep inside the mixing chamber and are effective in mixing of highly viscous fluids, extracts, essences, solid fats and oils)

– very limited damage to fragile particles (if choppers switched off)

– good hygienic design

– effective emptying of mixer (remaining product ~0.2%)

– easy inspection and cleaning (CIP enabled)

– suitable for a product range from dry powder to high fat level powders and Pasty Cubes mixes

– compact construction; optimal layout, footprint & elevation

– low power consumption base

• A vertical twin-shaft flat-bottomed mixer Mixing is achieved by a

double helical agitator and by two choppers, enabling very

effective mixing in the full low to high shear range

Amixon Design Criteria - ctnd

• Working volume of 2000 liter; fill level

from 200l to 2000l for dry powders, from

1000l to 2000l for powders with liquid/fat

addition (in order to cover choppers)

• HM1000 for small batch size and high

complexity requirements (batch size 100l

to 1000l for dry powders, 500l to 1000l for

liquid/fat addition)

• Two types of mixers defined, a Powders

Mixer (low fat levels) and a Multipurpose

Mixer (Pasty, Pressed, Powders – high fat

level possible)

1 Complexity of recipes

single- or multi-step (sequential) mixing

2 Particle Size and mechanical stability (shear stress)

low- or high shear mixer

3 Mixing time

efficiency vs quality sequential mixing or 2-in-1 equipment

4 Handling of oil/fat, liquids and pastes

format decision (oil, liquidised fat, fat flakes, powdered fat) mixing regime to optimise cleaning

5 Equipment diversity/availability of equipment across SUs

no easy roll-outs possible

6 Capacity & Flexibility in SC

pre-mixes – Chassis – Toolbox (Core Product Designs)

Mixing – key parameter & challenges

Due to the gentle mixing technology the mixing time

is naturally higher compared to high shear mixers

Low shear

1 Simple Batch Mixers

arms moving in both vertical and horizontal planes

moving within a rotating bowl

whisk/blade/hook in static bowl

• Both widely used in bakery industry for dough

preparation Hobart used in many catering mixing

operations

• Highly manual operation and relatively slow but

useful for small batches and able to handle most

product configurations

Artofex

Hobart

Low shear

2 Tumble Mixers

Drum Mixer

V Mixer (Patterson Kelly)

• Based on rotation of closed container

• Effectiveness dependant on geometry

• Effectiveness enhanced by baffles/vanes

and in some cases rotating knives

• Very gentle mixing - low energy input

• Suitable for fragile ingredients

• Can be modified to allow for addition

of liquids (eg fat)

• Not especially effective for mixes with

broad particle size range

Low shear

3a Screw Mixers

Ribbon Blender

• Based on movement of a horizontal

helical screw in a bath shaped container

• Effectiveness dependant on screw

geometry e.g blade pitch & thickness

• Effectiveness enhanced by baffles/vanes

• Fairly gentle mixing - medium energy

input - quite slow

• Can be modified to allow for addition

of liquids (e.g fat)

Ribbon Blender

(Morton)

Low shear

3b Screw Mixers

Rotating Spiral

• Based on movement of an angled

helical screw in a conical

• Product motion results in very

effective mixing from relatively

low energy input

• Often used as a buffer tank for

sachet filling machines

• Care needs to be taken to manage

(Nauta/Vrieco, Vortex )

• A series of internal flights (or

baffles) for maximum blending action

• Widely used to blend fragrance,

colorant, and emotives