Fundamentals in feed manufacture: particles and grinding

Certainties and uncertainties on a global scale

Changing political corridores

Human population growth

Climate change

Consumers loyality and trust

Food security and scarcity

Shift in markets for feed raw materials → fuel, goods

Whole raw materials to human food; co-products to animal feed

Increased global requiremtn for animal protein

Why milling and mixing

Milling

• making smaller particles, increasing SA (surface area) → better access for digestive enzymes

Mixing

• obtain a uniform mixture, every portion of animal feed has the same composition, smaller particles makes for better homogeneity

Particle size reduction - state of stress

How to make particles smaller - principles

Compression, impact, shear, cutting, abrasion

Milling laws (energy involved in grinding)

Milling laws - when to use what

Mass-balance populations (particle size distribution in grinding)

Mill types

Beater mills

• comminution based on impact, velocity

Friction mills

0 based on shear, rubbing

Milling in the feed industry

hammer mills

• most universally used due to high reduction ratio >50

roller mills

• used to obtain narrow-sized particle size distributions, drawback reduction ratio around 10

multicracker

• new mill type in feed industry, mainly for structuring (course girnding) of feed

Advantages and disadvantages of the hammer mill

Advantages

• Large assortment of raw materials can be ground

• both firbours and brittle material can be ground

• ease of use

• low investment costs compared to roller mill

• relative maintenance free

Drawbacks

• large spread in particle size distribution (compared to rolelr mill)

• production of heat, typical 5 degrees added to feed mash

• noisy

  • dusty (fines produced)

Comparison hammer mill, roller mill and mulicracker

Hammer mill consumes the most specific energy

roller mill and multicracker have comparable energy consumptions

soybeans require more energy for girnding than wheat and maize

in the range of grinding (coarse endproduct), particle size decreases linearly with an increase in energy input

Where to grind int he factory?

Pre-mill

• grinding of all raw materials upon entryin the factory

• storage of both intake raw materials and ground raw materials

• dosing of ground raw mateials in main mixer

• controllability of particle size

post-mill

• dosing of raw materials

• grinding of raw materials per batch

  • transport ot main mixer

• Most common type of grinding process

pre-sieving before grinding

reduces the load on the mill and therefore saves energy

Animal feed

all animal feed starts as ground or milled raw materails,a fter additional processing it is transformed into agglomerates or pellets

Particle size analysis

Properties

• weight, sieve analysis

• volume, light scattering method

• property, e.g. sedimentation in a liquid

in the animal feed indsutry most comon is an analysis based on weigth (sieve) or volume (laser diffractometer)

it follows that for a given sample, when using different methods of analysis, you’ll have different numerical values for the mean or spread of the particle size distribution

Equivalent particle size (concept of)

Distrubution types

Log-normal, popular for grinding purposes of wide and/or fine particle sizes after grinding

Weiball distriution, very flexible can accomodate a whole range of (cumulative) distributions

Rosin-Rammler, used in grinding

Take home points 0 particle fundamentals

Many different evaluation possibilites for particle size and particle size ensembles

Choose a method of evaluaton that is relevant for you application

most particle size characteristics that are menthioned in relation to feed manufacture are based on weight

particle sizes can also be obtained based on counting lenght, diameter or other characteristics