Agglomeration

Agglomeration

The formation of larger particles form smaller particles

Opposite process of agglomeration

Milling, making smaller particles from larger ones

Why agglomeration/pelleting?

Improve palatibility

Provision of definite quanity units for metering, dispensing and administration

Reduction of (potential) allergenic dust, reduciton of handling hazards

Destroy pathogens/microorganisms

Creation of non-segregating blends of particles

Improved product-appearance and flow-properties

Control of heat transfer and moisture diffusion by, for example, control of porosity and surface-to-volume ration (particle size in grinding)

Control over the release of acive substances in certain parts of the digestive tract by applyging coatings with different solubility’s.

Increase formulation flexibility (allowing for alternative ingredients)

Affects (improves) nutritional value

Heat and moisture diffusion

Diffusion coefficents

Heat diffusion is quick

Particles in a hot environment (e.g. conditioner) are typically heated to the core in 1 about 1 sec.

Water diffusin is lower than heat diffusion, this is due to

Amount of available moisture (from steam or added liquid)

Amount of mechanical energy (agitation)Mo

Moisture, conditoning and starch transformation

Transformation on particle level

State phase diagrams

Tell you somethign about the state of a raw material or one of its components as a function of (at least) moisture and temperature

All sorts of chagnes of state can be graphed

• melt stage: (e.g. native starch to gelatinized starch; melting of fats)

• tg: glass transition (for amorphous polymers the cahgne from hard/brittle to soft/rubbery/elastic)

• tr: thermo setting temperature, above which polymers (proteins) set

also: bioactives (e.g. vitamins, enzymes, yeats, proteinaceous ANF’s( are transformed and may become inactive (tdenaturation)

note: a state phase diagram tells you only something where a transofmration may take place. It does not say anything about the time involved

Compactuin agglomeration - e.g. pelleting

re-arrangement, collapse of cohesive arches

elastic and plastic deformation

materail aproaching true density

Bond types - how to hold pellets together

Types of steam

Issues in steam supply

Defective steam regulator

Blocked conditioner steam jets

Worn conditioner paddles

Faulty insulation

Excessive boiler blow-down

Variations in piping size

Step-down/undersized steam regulators

Low total dissolved solids (boiler)

Pellet cooler malfunction

Low boiler pressure

Steam tram line leaks

In summary: steam supply

We can’t alter heat diffusivity (particles heat up very quickly)

We can affect the amount of moisture that is added or taken away from the feed

Conditioning quality depend on

• Starting moisture content and temprature of the raw materials

• Conditoining installation (Type and steam supply)

• Formulation type

• 80% of problems with pellet quality are associated with steam and team supply

Conditioning types

Standard barrel type conditioner - work horse in feed manufacturing

Ripening vessel - process principle very good; not economic in current feed manufacture operations

Long term conditioners - started of as sterilisation equipment

Double pelleting - if one press is good, two must be better

Boa compactor - pressure conditioner

Expander - pressure conditoner

Standard barrel type condtioner

Workhorse to improve capacity and quality in feed manufacturing

Homogenous mixing of gas (steam) and powder

One of the most important piece of equipment in feed manufacture

Thin layer mixer

Hot start version (alwasy hot feed msash at start up)

Ripening vessel

Large vessel which can hold sufficient conditioned feed mash to hold-up for 15-20 minutes

Absorption of large amouts of liquids

Advantages

• conditioning quality

• Large liquid inclusion level, 12%

Disadvantages

• Long residence time 15-20 min

• Construction height

• Contamination with moulds and bacteria (cold spots)

Mainly due to rapid changes required in formulations, the ripening vessel is no longer installed in compound feed factories

In terms of pelletability,it’s a good system

Long term conditioners

Archimedes screw which controls feed mash flow (FIFO)

residence time can be adjusted up till 4 minutes

Advantages

• conditioning quality

• large luquid inclusion levels, 5%

• construction size (<1 m requiremnt)

• low energy consumption

• good controllability of time/temperature for sterilisation purposes

disadvantages

• static feed mash (no relative movement of particles to help moisutre diffusion)

  • can’t go higher than 95C

Double pelleting

Two pelletizers on top of one another

• the first pre-densifying

• the second shaping the feed mash into granules

advantages

• high density, and hence low pellet porositiy

• short residence time, short strat-up/slow down sequence

disadvantages

• extra pelletizer required

• construction height required for extra pelletizer and condtioner

  • for bio-actives, extra shear → breakage of particles

Expander

Advantes

• good pre-conditong (shear enhances water diffusion)

• high liquid levels, 15%

• modern expanders L/D<5

disadvantages

• energy consumption

  • may be consider difficult by operators

boa compactor - PTN

advantages

• conditioning and pre-compaction in one installation (construction height)

disadvantages

• extra pelletizer required

  • less broad processing parameter spectrum as compared to expander (but larger processing soectrym as for most other installations)

In summary: conditioning

Large variety in pre-conditioning system

Which one to choose is often a matter of taste/preference/history of the feed plant

Selection of equipment is preferably based on

• formulation types that require producing

• raw materials and quality of rm available

• level and/or availabilit of liquids that can be used

• desired production capacity

arguably the most imporant unit-operation in making good quality pellets

pelletizer - shaping the feed

large particles are shattered (large number of small fragments) or are deformed

pelletizer - specific power consumption

Tcritical

Phase separation and slip layer development

The lubrication layer forms a direct coupling between (net) mechanical energy use (SME) and temperature gain over the die

Pellet temperature and PDI

mimimum temperature Tcritical for pellet formation

close to tcritical high quality pelelts cannot be produced at high capacity

high above tcritical pellet quality is too good (emisions and energy use)

monitorign of lubrication layer and subsequent actions (steam, water) can decrease energy use whilst maintaining pellet quality

Pelletizer surplus energy into reactions

O

optimizing total energy use

Futur

future developments in pelleting

optimisation and understanding the effects of

• slip layer development in the pelleting die

  • surplus energy and the connection with pellet quality and change in feed components

purpose of cooling

remove moisture and heat included and/or generated during the conditioning and pelleting process

transform the liquid type of bond into a solid type of bond (stronger pellets)

Cooler design

co-flow

• hot and old air flow jointly together

cross-flow

• hot and cold air cross onea nother (belt-cooler)

counter-flow

• hot and cold air flow in counter current

Counter=flow cooler

features

• minimal floor space required

• moderate to high capacities available

• low air requirement

• lower capital costs as opposed to belt cooler

• mechanically simple

limitations

• doesn’t work well for small particles of mashes

  • difficult to add heat if drying is required

Measuremtn of physical pellet quality

hardness and durabiltiya re correlated

• particle size distribution

• elasticity of particles making up the pellet

• porosityu

  • binder mechanism in the pellet

Strenght of one granule

expressed as force (kgf or N) to break a certain agglomerate

or stress (force per surface unit N/m2 kgf/mm2)

kahl hardness tester

tablet strenght measuremnt device

durability testers

measuremetn of the amount of fines

• expresses as percentage fines

  • or, durability, percentage prudcti (100%-fines%)

In summary: physical pellet quality

pellet quality measurements should folllow feed back obtained from feed users

durability, from a practical point of view, is more relevant than hardness