pelleting handbook

74

PelletingHandbook

A Guide for Production Staff in the Compound FeedIndustry

John Payne, Wolter Rattink, Ted Smith and Tom Winowiski

The

Pelleting Handbook ny 11.05.01 15:02 Side 74

2

SECTION Page No.

1 INTRODUCTION1.1 Why do we Condition and Pellet? 51.2 Terminology 61.2.1 Definitions of animal feedstuffs 61.3 History and Principles of Pelleting 8

2 OBJECTIVES IN PELLETING2.1 Pellet Quality 112.2 Pelleting Efficiency 11

3 PELLETING ADVICE 3.1 Meal Conditioning (short term) 133.1.1 Horizontal barrel type conditioner 133.2 Meal Conditioning (long term) 143.2.1 Double pelleting 153.2.2 Expander systems 153.3 Pellet Press 173.3.1 Pre-start-up procedure 173.3.2 Start-up procedure (conventional barrel type) 173.3.3 To stop pelleting operations 183.3.4 Greasing of bearings 193.3.5 Die selection 193.3.6 Starting new dies 193.3.7 Die care 203.3.8 Die changing 203.3.9 Roll design 213.3.10 Roller setting (manual) 213.3.11 Roller adjustment (remote) 223.3.12 Knife setting 223.3.13 Fat application 233.4 Pellet Cooler 253.4.1 Vertical coolers 253.4.2 Horizontal belt coolers 263.4.3 Counterflow-bunker coolers 273.5 Crumblers 283.6 Sifters 29

4 MEAL CONDITIONING4.1 Grist Spectrum 304.2 Steam Conditioning 304.3 Pipe Sizes and Steam Velocity 30

5 PRODUCTION GUIDELINES5.1 Ruminant Feeds 335.2 Concentrates 34

3

This Handbook is dedicated to everyone who is involved inmanaging or operating a plant for the manufacture of pelletedfeeds, anywhere in the world. It is no substitute for your ownexperience and knowledge, and those of your colleagues, butit can perhaps add to it.

The material contained in the Pelleting Handbook is based onthe experience of the authors and their colleagues atBorregaard LignoTech. This is a team which has many years’experience of pelleting many different kinds of feeds in manydifferent kinds of feedmills – both old and new – in manydifferent countries. The Handbook is therefore part ofBorregaard LignoTech’s strategy of helping their customersthrough "expertise, service and partnership".

This Handbook was first published under the Borregaardname in 1991. The aim of this new edition is to help feedproducers in all five continents. This is an ambitiousobjective, because of the wide variation in processingconditions and raw materials which might be encountered,but we feel the task is fulfilled in a systematic and practicalway. We therefore believe this Handbook will succeed infilling a real need, and prove itself to be of immense valueworldwide.

The authors wish to acknowledge the help of colleagues,associates and friends in the industry, whose advice andassistance have proved invaluable in the preparation of thishandbook, in particular Mr. Ian Buick for illustrations.

Acknowledgement

ContentsForeword


4 5

World production of pelleted compound feeds continues toexpand in order to satisfy an industry of great and growingimportance, supplying balanced rations so essential for theproduction of meat, milk, fish and eggs.

The need for efficient and hygienic feed production demandsthe vast majority of compound feed to be pelleted.Conditioning of the mixed meal prior to pelleting is anessential part of the process.

1.1 Why do we Condition and Pellet?Reasons for conditioning and pelleting are many; the chartbelow shows the most generally recognised advantages.

5.3 Pig Feeds 345.4 Poultry Feeds 35

6 RAW MATERIAL CHARACTERISTICS6.1 Why Raw Materials Affect Pelleting 376.2 Raw Materials – Physical and Nutritional Factors 37

7 BORREGAARD’S LIGNIN PELLETING PERFORMANCE ENHANCERS7.1 Advantages of Borregaard’s Lignin PPEs 437.2 Pelleting Trial Procedures 437.3 Problem Solving from Trial Format 487.3.1 Broken steam regulator 487.3.2 Incorrect set-up of steam system 487.3.3 Overtaxed boiler 497.3.4 Mill supplied by surge bin 497.3.5 Oversized feeder screws 497.4 Borregaard Lignin PPEs 507.4.1 Packaging 507.4.2 Mill intake and storage 507.4.3 Application in the mill 507.4.4 Accidental spillages at the mill 51

8 TROUBLE SHOOTING8.1 Production 528.1.1 Conditioning 528.1.2 Pellet press 538.1.3 Dies 558.1.4 Cooling 558.2 Problem Pellets 568.2.1 Cracks at one end or down one side 568.2.2 Horizontal cracks 568.2.3 Vertical cracks while cooling 578.2.4 Cracks from a single point 588.2.5 Mis-shapen pellets 588.2.6 Short ends 598.2.7 Whiskery pellets 59

9 QUALITY CONTROL METHODS9.1 Durability (Pneumatic) Pellet Testers 609.1.1 The Borregaard LT 609.1.2 The Borregaard LTA 609.1.3 The Borregaard LTOL 619.2 Durability (Mechanical) Pellet Testers 629.2.1 Tumbling can (ASAE) method 629.3 Hardness 629.4 Evenness of Length 639.5 Percentage of Dust 639.6 Guideline Recommendations 63

10 CONVERSION TABLES10.1 General Conversion Factors 6410.2 Steam Pressures 6510.3 Temperatures 66

Effects of conditoning

Effects of pelleting

Benefits for compounder and farmer

Increased bulk density

Prevents'de-mixing' of ingredients

Increased feed intake

Improved digestibility

Improved nutritional quality of ration and increased profitability for farmer

More cost efficient food production therefore increased profitability for compounder

Improved efficiency of food production

Reduces waste on farm

Easier formulation changes without rejection

Stock cannot 'select' ingredients

Allows drug additions without risk of inaccurate dosage

Improved flow and metering characteristics

Reduces transport costs

Facilitates bulk transport and storage

Kills bacteriae.g. salmonella

Introduction 1SECTION Page No.


76

1.2 TerminologyFor the purposes of this Handbook you will see that we haveused the term pellets for all compressed compound feeds ofwhatever size. Compound feed producers use a variety ofnames, including pellets, cubes, pencils, cake, cobs, shilfers,nuts, slabs and rolls.

1.2.1 Definitions of Animal Feedstuffs(Courtesy HGM Publications, "Digest of Feed Facts and Figures")

The following are not intended to be legal definitions butsimply an indication as to what is meant by various terms inthe compound feed industry.

Roughages. Fibrous ingredients suitable for ruminants,generally produced on the farm, eg. silage, hay, grass.

Compound Feeds. A number of different ingredients (including major minerals, trace elements, vitamins and otheradditives) mixed and blended in appropriate proportions, toprovide properly balanced diets for all types of stock at everystage of growth and development.

In some cases, eg. ruminants, compound feeds are technicallydesigned, when fed without further mixing with cereals, tosupplement natural foods (eg. grass or roughages) available on thefarm. In such cases the compound feed is frequently given a namedefining its purpose, such as for balancing straw, grass, kale,silage, etc.

Protein Concentrates. Products specially designed forfurther mixing before feeding, at an inclusion rate of 5% ormore, with planned proportions of cereals and other feedingstuffs either on the farm or by a feeding stuffs compounder.

Since the aim is that the final diet mixed in this way shouldbe balanced for a particular feeding purpose, proteinconcentrates contain blended protein rich ingredients fortifiedwith such essential nutrients as the major and trace minerals,vitamins, etc.

Where the rate at which protein concentrates are designed tobe used in the mix is high, eg. 50%, they will contain somecereal or cereal by-products.

Some protein concentrates are specially designed so that, afterfurther mixing with the appropriate quantities of cereals, theresultant product is then suitable for balancing farm roughages.

Coarse Mixes. A number of different ingredients of differentphysical form, eg. rolled, flaked and cracked, mixed togetherwith protein concentrate pellets.

Straights. Single feeding stuffs of animal or vegetableorigin, which may or may not have undergone some form of processing before purchase.

Straights rarely provide, in their own right, the completenutritional requirements of livestock. Some examples ofstraights are wheat, barley, flaked maize, field beans,groundnut cake and meal, soybean meal and fish meal, etc.

Straights form the basis of all forms of technically formulatedfeeds whether mixed on the farm or manufactured.

Additives. Substances added to a compound or a proteinconcentrate in the course of manufacture for some specificpurpose other than as a direct source of nutrient.

These substances include coccidiostats and anti-blackheaddrugs for mass prophylaxis or treatment on veterinaryprescription, anti-oxidants, colouring agents, binders,flavourings, lignin pelleting performance enhancers etc.

Supplements. Technical products for use at less than 5% ofthe total ration in which they are included, and designed tosupply planned proportions of vitamins, trace minerals, one ormore non-nutrient additives and other special ingredients.

RoughagesSilage, Hay, By-Products

Cereal By-productsBran, Midds, Corn Gluten Feed, Hulls

Cereal / StarchesCorn, Wheat, Triticale, Barley, Oats, Manioc

Vegetable proteinsSoybean, Cottonseed and Sunflower Meals,Distillers and Brewer's Grains, Corn Gluten Meal

Trace MineralsVitamins

AdditivesAntibiotics, Probiotics, Mould Inhibitors, Flavours, Colourants, Lignin Pelleting Performance Enhancers

Macro MineralsSalt, Magnesium, Dicalcium Phosphate, Limestone, Potassium

Animal ProteinsFish meal

Examples of Ingredient

use in Feeds

See alsoPhysical Factors

Page 38

Vitam

in Mineral Supp

Premix

Total M

ixed R

ation

/Co

mp

lete Feed R

um

inan

t

Co

mp

ou

nd

Feed

Protein

Co

ncen

trate


was pressed before being cutoff by the stationary knivesinside each wheel.

More popular than the"Scheuler" presses were theflat-die machines currentlyused in many European feedmills and grass-drying plants.Here there are horizontal rollswhich revolve around avertical axis while forcingmeal down through astationary horizontal die.

However the ring dieprinciple of 1920 continu-ed, in various forms, todominate the industry.Either the die or the rollerassembly could rotate, anddie or rollers (or both) were driven. Theprocess depends initiallyon friction between the rol-ler and the layer of mealbetween roller and die.

High-tech single/twinextruders entered thecompound feed productionindustry with convictionduring the late 1970’s. Initiallythey were used to producefeeds mainly for pets but soonprogressed into production ofpelleted feed for fish and otherspecialised feeds.

The energy/output ratio of these extruders can be as much asfour times that required by a conventional pellet press.

However, following the introduction of double-pelleting inthe early 1980’s a further method of pre-compression i.e,Expanders (see 3.2.2) was introduced prior to the pellet pressin an effort to improve pellet quality and make better use ofnutritionally good but difficult to pellet raw materials.

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To facilitate adequate mixing into the total ration, planned levelsof the active materials are normally present in supplements in anappropriate diluent carrier. Most supplements are available to thefarmer as well as to the feeding stuffs manufacturer.

1.3 History and Principles of PelletingThe forerunner of the modern pelleting press was based noton extrusion, but on a moulding process. It consisted of twoindented rollers which rotated in opposite directions, the mealwas forced into the indentations and moulded into a variety ofshapes. These included triangles, diamonds, ovals or buttons.

This type of press is no longer seen in feed mills, but similarbriquetting presses, as they usually are known, are still to befound in use in some other industries.

The first press to work on theextrusion process and pro-duce a cylindrical pellet wasdeveloped in 1910. It wasalso the first to use what wewould call a die: in this casethe die was vertical, flat andstationary. Meal was forcedthrough holes in the die by aworm, and the pellets cut offby revolving knives fixed tothe worm shaft.

1920 saw the development of the first press to work on thering die principle most widely used nowadays. Meal is forcedoutward through holes in a cylindrical die by the action of asingle roller. Later versions had either one, two or threerollers.

A more short-livedvariation on theextrusion process wasalso developed in the1920’s. The "Scheuler"press consisted of twospur-toothed gearwheels which ran inopposite directions.The rims of bothwheels had holes atthe roots of the teeth,through which meal

Scheuler Press

Flat Die Press

Ring Die Press

Early Press

Meal in

Pellets out

Die Rotatingknife

Material In

Pellets Out

Meal Flow

Knife

KnivesMaterial Flow

Material Flow

Die Rotation

Roller Rotation

First Extrusion Press

Rotation


The objectives to be followed when running a press manuallyor by computer are second nature to the experienced operator.However, it might still be helpful to re-state what we consideras the two main objectives, both of which should beachieved.

• To produce saleable pellets i.e. to achieve and maintaingood Pellet Quality.

• To achieve desired tonnage of product, at minimumenergy cost, and to maximise Pelleting Efficiency.

2.1 Pellet Quality (physical)Pellets must present the following characteristics.• Good appearance• Dust free• Without cracks• Uniform length• Hard – sufficient only to withstand pressures during storage.• Durable – the most important characteristic of all. It must be

durable enough to withstand the handling it will receivebetween manufacture and feeding to stock.

See Section 9 (Quality control methods) for details of how tomeasure hardness and durability.

2.2 Pelleting EfficiencyEfficiency of pelleting means producing pellets of goodphysical quality at the optimum ratio of output to energy consumption by the press. This does not necessarily meanrunning the press at the lowest possible amps or at the maxi-mum possible output, but achieving the most economicalcombination of the two factors while still maintaining pelletquality.

Pelleting efficiency is defined as the amount of energy (kWh)used to produce one tonne of pellets (kWh/T).

Overleaf we show how you can calculate the pelletingefficiency of your pellet press.

1110

Expander

Extruder

Objectives in pelleting 2Steam

Steam and Molasses

Meal In

Meal In

Meal Out

Meal Out

DieRotating

Knife

Steam

Adjustable Gap


13

Information given in this section is intended to supplementthe instructions available from your equipment supplier.Observe recognised safety procedures.

3.1 Meal Conditioning (short term)

3.1.1 Horizontal barrel type conditionerGenerally single or dual barrel arrangements. Each barrelcontains paddles revolving at speed, blending steam, molassesor other additives into the meal. Duration time varies between10 and 60seconds. It cansometimes becontrolled by theangle of thepaddles, whichshould bechecked frequent-ly for wear.

Best results can be obtained if the conditioner runs as full asis practical. In this way the paddles rub and blend steam,liquid additives and meal together, persuading rather thanbeating them into a mixture. The resulting meal texture willbe more conducive to efficient production of good qualitypellets and reduced likelihood of die blockage. The angle atwhich the paddles are set in relation to r.p.m. determines thevolume of meal in the conditioner during production.

Steam can be injected into this conditioner either independently or with molasses. Generally a combination isused, in which case you should direct steam at 4 bar into themolasses pipe just before entry into the conditioner. Thesteam injection raises the temperature of the molasses, thushelping to disperse it more evenly.

Ensure that the steam entry ports into the conditioner remainclear of meal build-up. Check frequently that meal has notbuilt up on the shaft, paddles, barrel and outlet, by removinginspection doors. Clean if required, as meal build-up canseriously affect efficiency of conditioning. Cleaning is madeeasier by first steaming the inside of the barrel, thus softeningthe deposits. Check also the outlet end of the meal feeder

12

The efficiency of your pellet press can be calculated asfollows:• Determine pelleting production rate (T/h).

• Determine average press motor amperage.

• Determine plant voltage.

• Apply the following formulas to find the press power inkW and the pelleting efficiency.

• Power (kW) = A x voltage x √ 3 x power factorT/h 1000

(Assume a power factor of 0.93 unless known)

• Pelleting efficiency (kWh/T) = kWT/h

Practical exampleA pellet press took 1.25 hrs to convert 10 tonnes of meal intopellets. The average amperage was recorded at 128.3 and thevoltage was 415. The power factor is 0.9. What was thepelleting efficiency?

• Power = 128.3 x 415 x 1.73 x 0.9 = 82.9 kW1000

• Pellet press production rate = 10 = 82 T/h1.25

• Pelleting efficiency = 82.9 = 10.4 kWh/T8

Note. When double pelleting or expanding, the combinedamperage of both presses/pre-densifier must be used.

It is acknowledged that total pelleting plant efficiency willincorporate ancillary plant, electric motors and steamgeneration.

Pelleting advice 3

Steam and MolassesMeal in

PaddlesMeal Out

Short Term Conditioner


optimised at the bottom. A ripener full of over wet mealpresents a difficult disposal problem!

Addition of steam (4 bar pressure) at the bottom conditioneris strongly recommended in order to provide meal particleswith surface moisture, which aids extrusion through the dieand reduces the electrical energy consumption of the pressmotor.

3.2.1 Double pelletingConditioned meal enters the top press, where it isprecompressed through a "thin" die. The pre-formed pelletsthen pass to the bottom press fitted with a die of specificationrequired for the finished product.

However, some feeds do not require double pelleting andtherefore pass only through the bottom press.

If an excessive amount of short ends are found in finishedpelleted product when double pelleting, then it is possiblethat the die specification of the top press is too severe.

For efficient production when double pelleting, it is importantto use optimum die specifications. Consultation with yourdie/press supplier is recommended in order to select a diecompatible with your formulations and the physicalcharacteristics of your pellet presses.

3.2.2 Expander systemsMeal is first conditioned, using a horizontal type barrelconditioner, prior to entry into a high compression chamberthat creates a high meal temperature just before it is extrudedthrough an adjustable annular gap. The expanded material is passed through a "Breaker" then pelleted by means of aconventional press.

There are several types of Expander in use. All are designedto create shear, which ruptures the cell structure of feedingredients, resulting in increased temperature andgelatinisation of starch.

Expanders lend themselves best to long production runsbecause of the time required to optimise conditions. Whenpelleting expanded material, die specification is critical.Too much compression and the soft expandate squeezes outbetween rollers and die face, causing a blockage.Insufficient compression results in poor pellet quality. Notethat with some feed types, mainly low oil/high fibre, the

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above the conditioner as steam rising from the conditionercan cause meal to build up here.

Barrel conditioners are fitted with a meal temperature gauge,the probe of which is generally located in the outlet. (See section 5 for recommended temperatures).

Note. If you are raising meal to a certain temperature,either by manual or automatic control, be sure that theend of the probe is clean. If heavily coated with meal,gauges will read around 10 ºC low. Conversely, the gaugewill read too high if too much uncondensed steam ispassing over a clean probe. Automatic self-cleaningtemperature probes are recommended.

3.2 Meal Conditioning (long term)Long term conditioningsystems comprisevarious configurations,but generally combinetwo horizontal barreltype conditioners. Onefeeds into a holdingvessel, generally calleda ripener. The othertakes meal from theripener and delivers it to the press.

The ripener generallyhas a holding time 20 – 30 minutes. Noneuse steam (other thanfor jacket heat) andnone provide for theaddition of liquidadditives, which are added at the top barrel conditioner.However, these restrictions do not apply to pasteurising con-ditioners which operate as continuous flow heat exchangers.

Long term conditioning permits higher levels of liquidingredients to be added. Time in the ripener is the importantelement. However, some ripeners are fitted with stirring armsto aid dispersion.

Difficulty can be experienced with blocked dies if the meal isallowed to become too wet at the entry to the ripener. Hencesteam addition is generally limited at the top conditioner and

Long Term Conditioner

Meal in:

Feeder Worm

Conditioner

Steam outfrom Jacket

Feeder Worm

Conditioner

Steam in to Jacket

Steam andMolasses

Steam andMolasses


X

Pencil

X

Re: Pencil

expandate can cause the amperage of the pellet press motorto fluctuate excessively making it difficult to control theprocess.

3.3 Pellet PressPellet presses are controlled manually or by computer. Eitherway, it is essential to understand the requirements foreffective operation and control, in order to optimiseproduction rate and pellet quality.

A computer continually monitors press conditions andoptimises output, whilst safeguarding against die blockage.However, as and when required, the plant operator must beable to run the press manually.

The following points outline start-up, running and stoppingprocedures for a conventional pelleting press.

3.3.1 Pre-start-up procedureIt’s more than just pressing the start button• Ensure pelleting system is empty of meal and pellets from

previous production run, particularly if starting a newformulation i.e. to prevent cross contamination.

• Ensure die chamber, feed chutes and magnets are clean andthat temperature probes and other monitoring equipment arealso clean.

• The roller setting should be adjusted if necessary (see 3.3.10).

• Ensure transport elements are running and that the route forproduct flow has been selected.

3.3.2 Start-up procedure(conventional barrel type conditioner)• Ensure meal is in the pre press bin.

• Start press motor and conditioning plant.

• It is recommended to circulate initial production of pellets backto the pre press bin until optimum conditions are satisfied.

• Start meal feeder and slowly increase speed allowing asmall flow of meal into the die. Watch amperage meter ofpress motor until it indicates about 50% of maximum.

• Check to ensure that the die is pelleting.

1716

Meal In

Bottom Press

Conditioner

Top Press

To Cooler

Steam And Molasses

Feeder Worm

Steam And Molasses

Pre-PressBin

Dump Chute and By-Pass

Dump Chuteand By-Pass

Double Pelleting

Press

Conditioner

To Cooler

AdjustableGap

Pre-PressBin

DumpChute andBy-Pass

Pre-Compression ExpansionEquipment


2)Ensure that meal is not allowed to build up in the feed chute,a build-up which then breaks away can block the die. Also,ensure that the feed cone (if there is one) ploughs, rollers,dies and knives are in good condition. If badly worn,pelleting efficiency and pellet quality will suffer. Be alert forvibrations or changes in sound, as these can be indicationsof a badly adjusted machine or imminent breakdown.

3.3.4 Greasing of bearingsIt is vitally important that mainshaft and roller bearings areregularly and adequately greased. Fully automatic systemsare recommended.

3.3.5 Die selectionSelecting the right die is clearly one of the most importantdecisions in pelleting. Depending on the formulation and theraw materials, there is a wide range available from lowcompression (thin dies with counter-bored parallel holes) up tohigh compression (thick dies with well or taper bored holes).A comprehensive treatment of this subject would fill anotherbook, so we suggest that you should consult your die/presssupplier to find the exact specification to meet your needs.

3.3.6 Starting new dies• Check bores and track for scoring, burring and poor

machining before fitting die to press.

• Some dies are supplied "pre run-in" and the holes are thusplugged with an oily material. This is removed by handfeeding the press with whole cereal (i.e. maize) after thedie has been fitted and while the press is running.

• If the holes of the new die are empty, then it is preferableto plug them prior to commencing production by handfeeding whole pellets.

• Care should be taken when starting production not to "over feed" the die i.e. run the die in gently.

• After running for approximately one hour, stop the pressand inspect the die track and rollers to ensure all holes arerunning.

• Some dies can be troublesome to start because patches ofthe track initially remain blocked. The recommendedprocedure is to remove the die and punch out all holesbefore refitting. If, after carrying out this procedure threetimes, there is still a problem, consult the die supplier.

1918

• Open steam valve and add liquid additives that may berequired. This action will cause a reduction in the pressmotor amperage.

• Increase feeder screw speed and then increase opening ofsteam valve. This procedure should continue until eitherthe required meal temperature is reached (see section 5) orthe point where the addition of steam does not reduce theamperage any more, when operating close to maximumproduction rate.

• Now check pellet quality (see section 9). If it is not up torequirement, adjust feeder screw speed and/or adjust steamaddition according to feed type (see section 5).

• If the press has been started from cold, then afterapproximately 15 to 20 minutes, the die will be hot. Re-adjust meal feeder speed and steam in order to find newoptimum operating conditions.

• For optimum pelleting performance see Borregaard’sApplied Lignin Technology and Pelleting Techniqueconcept in section 7.

3.3.3 To stop pelleting operations• On signal from low-level sensor in the pre press bin,

prepare to stop pelleting.

• Reduce speed of feeder screw and addition of liquidadditives, together with a reduction in steam.

• Close steam valve and stop liquid additives. Allow pressto continue pelleting until the pre press bin is completelyempty i.e. that fines returns have also stopped, thus allo-wing the plant to be clear of all materials, thereby nega-ting any possibility of cross contamination with follo-wing production.

• If production is not to continue, then the die should befilled with a non-corrosive oily meal before stopping thepress (see 3.3.7 Die care).

General notes1)When starting a die from cold or if it has been idle for a

while, then the first pellets produced will be either oilyfrom meal used to flush out the die, or very hard anddark, resulting from meal cooking in the hot die. Thesepellets must not be allowed into the finished product.


This flushing procedure also removes harmful fats or acidswhich may be present. Some raw materials are corrosiveunder pelleting conditions, thus eats into the surface of thedie holes, reducing efficiency, pellet quality and die life.

• Ideally, once a die and set of rollers have been "mated" andformed the same wear pattern, they should only operatetogether. Many mills don’t stick to this because it takes solong to change both die and rolls. However, it is importantto ensure that new rolls are not used with a badly worn die,or vice versa. Otherwise poor pellet quality will result,together with excessive wear. Some mills machine worndies before fitting new rollers.

3.3.9 Roll design• Fluted rolls tend to wear more at the corners where meal

can be squeezed out rather than be forced through the holesin the die.

• Dimpled rolls tend to have greater grip and form a moreeven wear pattern.

• Textured rolls have a harder surface and generally have alonger life, but care should be taken with roller adjustmenti.e. avoid metal to metal contact.

Some feed producers use a combination of roller design.

3.3.10 Roller setting (manual)Correct roller setting is essential for optimum pellet quality,press capacity and die/roller life.

• If the rolls are set too tight, the die will flex excessivelyand may finally crack. It also increases the possibility ofmetal-to-metalcontact, thus rollingover the ends of theholes on the die andcreating excessivewear and splitting ofroller shells. Closefitting rolls generallymaximise presscapacity.

• Under-adjusted rollscreate excessive rollerslip, heat and possible

2120

3.3.7 Die care• Avoid "face to face" roller/die contact.

• If blocked solid: soak in oil, then try to re-start. Ifunsuccessful, punch out. Drilling out should be a last resort(see also section 8.1.3).

• Never strike a die with a steel tool.

• Protect die from metal objects by fitting magnets.

• Punch out any tramp metal which manages to enter the die.

• Log the use of your die.

• Check that die holes are not rolled over by feeling edgewith wire or fine screw driver. Holes only slightly rolledover will drastically reduce press production rate. Arecognised practice to overcome this is to remove the dieand machine the track face.

3.3.8 Die changingThe exact procedure will be given in the press manualissued by the manufacturer. We list below somesupplementary tips:• Cover entry to cooler. This stops dirty meal – and

maintenance tools etc. – getting into the system.

• Always fill die with non-corrosive oily meal beforestopping press for die removal or other stoppages.Otherwise, heat of the die can sometimes bake hard themeal remaining in the holes. This can mean -

• Re-starting impossible.• Die experiences excessive stress during start up,

which weakens it.• All holes may not "go", thus reducing output and

efficiency of press.

Photograph from Felleskjøpet ØV, Norway.

Manual Roller Setting


The latter can result in a high percentage of very long pelletsentering the cooler. However, further processing, i.e. sifting,elevating, conveying etc., usually breaks pellets to anacceptable length.

The shearing or tearing action of the knives on the softpellets as they leave the die creates fines. Generally, thesharper the knife, the less fines. Rations containing a ligninPPE will also produce less fines at the die.

3.3.13 Fat applicationLiquid fat added to the meal before pelleting isdeterimental to physical pellet quality. It coats the mealparticles which prevents binding during pelleting. Fatlubricates the die which reduces compression required toform the pellet.

For these reasons it is recommended to add no more than 1%fat prior to pelleting. Additional amounts should be added afterthe pellet has formed i.e. at the die and/or after the cooler.

Fatspray at the dieFat or oil is more readily absorbed into hot pellets. Thisovercomes the "greasy pellet" syndrome, i.e.

• Reduces palatability problems.

• Improves pellethandling andstorage andfacilitates theuse of all typesof fats and oils.

OperationFat or oil isatomized by the spray headwhich isdesigned to caterfor maximum andminimum flowrate according to pelleting production rate. The spraynozzles are designed to provide the correct angle of sprayaccording to the width of the die and the distance from itsouter face. It is important that fat/oil does not spray beyondthe die surface as this can cause a build up of fatty meal oninternal surfaces of the press door and cooler entry.

2322

consequent die blockage, thus seriously affectingproduction output. However, pellet durability generallyimproves as rolls are moved away from the die face, butpress capacity is sacrificed and pellet length is more varied.

To manually adjust rolls refer to pellet press manufacturersoperating manual.

3.3.11 Roller adjustment (remote)Pellet presses can be supplied with, or can be modified toinclude, remote roller adjustment. By this means rollers canbe positioned at the touch of a button or completelyautomatically by computer. Rollers can be adjusted while thepress is running during production, or when stationary.

• At start-up, in order to reduce load on the press motor andunnecessary wear and tear on the die, rollers should first bemoved completely away from the die face. The press isthen started and, on reaching full die speed, the rolls areadjusted to their required working position.

• With press controlcomputers thisprocedure takes placeautomatically, as doesovercoming problemssuch as blockagescaused by scrap metalor other extraneousmatter entering the die.

In combination with aBorregaard online pellettester and press controlcomputer, auto rolleradjustment can be used to facilitate automatic control of pelletquality within required preset limits.

3.3.12 Knife settingKnives are used to control the length of pellets as they leavethe die. The setting position will depend on the requiredpellet length.

Generally, for pellets smaller in diameter than 6mm, oneknife per roll should be used. Some 6 mm or larger pelletsmay require the action of only one knife or may dispensewith the knives completely – the pellets simply knocked fromthe die by a breaker bar or, naturally, by centrifugal force.

Fatspraying at the Die

Door ofPress

SprayHead

Roller

Die

Knife

Remote controlled roller gap adjustmentessembly. Photograph courtesyCalifornia Pellet Mill Europe Limited.


flow indication signals from the fat/oil flow meter. Theaccuracy of this method is dependent on knowing mealdensity, thus it is important to make regular checks toupdate the controller, as changes in formulation occur.

• Do not allow air to be drawn into the cooler via the feedspout from the press as this can cause fat to build up insidethe cooler, air ducting and cyclone.

• Fat coated fines entering the cooler can also be “picked up”by the cooling air inside the cooler, again causing build ups inair ducting and cyclone. In many situations, the only remedyis to ensure fines produced at the die are at an absolute mini-mum. This can be achieved by correct grist spectrum, properconditioning, correct die specification and the use of aBorregaard Lignin Pelleting Performance Enhancer.Alternatively, a routine cleaning operation must be carried out.

3.4 Pellet CoolerCoolers are designed to extract heat and surplus moisturecreated during pelleting, thereby increasing the strength of the pellet.

The temperature of pellets leaving a cooler should be nomore than 4 to 5 ºC above ambient.

Almost all coolers are based on either crossflow orcounterflow principles or a combination of both. Verticalcoolers are of the crossflow type. Most horizontal andcarousel coolers are a combination of the crossflow andcounterflow types. Bunker or bin type coolers are usuallybased on counterflow principles.

3.4.1 Vertical coolersWith this type of cooler itis important to set the rateof discharge so as toobtain long and evendischarge periods, i.e. tosuit the production rate ofthe press and the pelletsize. A smooth dischargehelps prevent "hang ups"in the cooler by keepingthe pellets on the move italso provides better con-trol if you are crumbing(see also section 3.5).

2524

Atomised fat/oil from the spray head coats pellets in three ways.• It coats the ends of pellets emerging from the die.

• Fat/oil which lands on the die face is drawn into pellets bycapillary action as they emerge from holes in the die

• Pellets are cut/broken from the die and tumble through thespray.

Up to 6% fat/oil addition can be achieved with some rations.Between 2% and 4% has been found to be the norm.

Fat coating after coolerFat applied to cooled pellets tends to remain on the surfaceand the affect of this is to reduce dust. Palatability, however,may be adversely affected.

High levels of fat/oil applied to cold pellets may create flowproblems from storage silos, particularly when fines arepresent. Heating of associated equipment prevents build up offat. Other liquids can be added to cold pellets, e.g. enzymes,probiotics and flavours.

Operational hints• Ensure clean fat/oil lines – always incorporate a filter to

prevent nozzle blockage.

• Ensure pipe lines are heated and insulated to prevent fatsolidifying.

• It is preferable to incorporate automatic steam purging ofthe spray head, i.e. steam purge before start and after aproduction run. Ensure that on/off valves and non-returnvalves are located such that fat/oil is prevented fromgetting to the steam boiler.

• Fines are always produced at the die and these too aresprayed with fat/oil which are returned for pelleting. It isrecommended that these fines should be directed to thefeeder screw above the press. On production runs of 20tonnes and over, the build up of "fatty fines" in the mealentering the press can cause pellet quality to deteriorate. Iffaced with this situation, it is advisable to allow the prepress bin to completely empty and then continue using"fresh meal".

• Most control systems are based on volumetricproportioning of the press feeder screw speed in relation to

Vertical (cascade) cooler. Photograph courtesy Sprout-Matador.


Ensure that the bed of the cooler is completely covered withan even depth of pellets, in this way cooling air is evenlydispersed and drying/cooling is uniform.

Air curtains (usually plastic sheet) must also be regularlychecked in order to ensure cooling air is drawn through the bedof pellets. Damaged curtains seriously affect the efficiency ofthe cooler, particularly when spraying fat at the die.

Regular inspection of cooler tray perforations should be made.

3.4.3 Counterflow-bunker coolersIn the counterflow type of cooler, the pellets and cooling airflow in opposite directions. The coolest pellets contact thecoldest air and the hottest pellets contact the warmest air.This design principle is "more kind" to pellets, because iteliminates thermal shock and brings about gradual cooling ofthe pellets.

In general, thesecoolers use lesselectrical energy, arephysically smaller,low in maintenanceand are ideal forcontrol by computer.They provideconstant retentionand an even flowover the entiredischarge surfacearea. They can alsoprovide a very

2726

When there is a formulation change, the cooler must beemptied and this is time consuming, particularly when thereare frequent changes. Some coolers, however, are fitted withdoors so that the top half of the cooler can be filled while thebottom half is discharging. If you use this method, it is essen-tial that the fines returning from the pellets in the bottom ofthe cooler are not mixed with the batch being pelleted.

This procedure also reduces problems of pellets "hanging up"in the cooler – a common feature, particularly with verymoist, heavy molassed or urea-containing pellets. If a "hangup" in a cooler is not spotted in time (and remember, theautomatic control system may not prevent this happening),the cooler will continue to fill and pellets may back-up intothe pellet press causing considerable damage.

3.4.2 Horizontal belt coolersThis type gives much more flexibility to help achieve correctcooling and drying by controlling the speed at which thepellets travel through the cooler, i.e. the retention or "dwell"time. Bed depth and air flow can be controlled manually orautomatically. Details of bed depth and retention time forvarious pellet sizes can be provided by your cooler supplier.

Counterflow cooler

1

1

1

1

2

2

2

2

3

3

3

3

4

4

4

4

5

5

5 5

Crossflow cooler

Horizontal cooler

AirflowA

irflow

Carousel cooler

Combinations of crossflow and counterflow coolers

Prod

uct flo

w

Prod

uct flo

wProduct flow

Diagrams courtesy Van Aarsen.

Horizontal cooler. Photograph courtesy Sprout-Matador.

Counterflow cooler.Photograph courtesy Geelen.


28

effective means of trapping fat droplets which would otherwi-se be drawn into the aspiration system when fat-spraying atthe die.

The formation of product peaking towards the centre of thecooler produces a detrimental effect with regard to coolingefficiency. By incorporating a well designed productdistributor, this problem is eliminated.

3.5 CrumblersFor very young poultry, even small pellets may be too large,thus intake is reduced. Crumbs overcome this problem andstill provide a nutritionally balanced diet. However, thecrumbs must be of good quality, i.e. dust free, and goodquality pellets will make the best crumbs. The use of a ligninPPE will improve pellet quality before crumbing.

4 mm pellets are generally used and a constant and even feedinto the crumbler is essential. Discharge from a horizontal orcarousel cooler tends to be in surges, making crumbingdifficult, therefore some form of control should be fittedbetween the cooler exit and the inlet to the crumbler in orderto smooth the flow.

Setting the rolls too close results in mashing the pellets ratherthan breaking them. The meal created is then returned for re-pelleting, consequently production efficiency is reduced.

It is also important that the rolls are well maintained,ensuring that the flutes are sharp.

29

3.6 SiftersFines produced during the manufacture of pelleted feed mustbe removed in order to provide your customer with a meal-free product. Sifters are generally located immediately afterthe cooler and before discharge into bulk road tanker. Thescreens in the sifter should be checked periodically to see thatthe perforations are not blind, worn or damaged.

Crumbler.Photograph courtesy Sprout-Matador.


The tables overleaf enable you to check whether your pipe-work can cope with the quantity of steam you require. Werecommend that the steam velocity after the pressurereducing valve should be around 20 m/sec. Knowing that nomore than 45 kg of steam are generally required per hourper tonne of pellets produced, you can check the size ofpipe being used in your mill, by referring to the loweststeam pressure you will need. (See our pressurerecommendations, section 5).

For example, if your press can produce a maximum of 8 tonnes per hour of pellets, then it could be demanding up to360 kg per hour of steam, and the table shows that when usingat, say, 1 bar downstream of the reducing valve (ourrecommended pressure for high starch rations), then a pipe boreof 80 mm will be required. This bore will be more than adequatefor the higher pressure steam needed for less starchy rations.

Note• All steam pipes must be lagged.

• Ensure all steam traps are working (a sight glass after thetrap shows if condensate is returning). Remember there willalways be condensate which must be returned to the boiler.

• Be prepared to change steam pressure to suit rations.

• Consult your steam plant supplier if experiencingdifficulties achieving the desired amount of steam.

3130

Efficient pelleting depends upon adequate conditioning ofraw materials and the first pre-requisite is a good distributionof particle size.

4.1. Grist SpectrumOur general recommendation is as follows:On 3 mm – up to 1% on 500µ – around 30%On 2 mm – up to 5% on 250µ – around 24%On 1 mm – around 20% "throughs" – not less than 20%

4.2 Steam ConditioningAlthough water conditioning can be used, particularly onsmall units, it is not recommended. Steam is much moreefficient and avoids creation of wet spots in the pelletedproduct. We therefore concentrate on this method, as it is usedby virtually all commercial feed mills. When using aconventional barrel conditioner the "quality" of steam must beas dry as possible. For high temperature/steralizingconditioners, a certain amount of super-heated steam may berequired.

Steam pressure must remain constant and this is achievedby a pressure reducing valve (see diagram). It allows forpressure fluctuations upstream (caused by the firing of theboiler) but keeps pressure constant downstream. This valve,which you can use to change pressure according to theration being processed, should be located approximately 20 ft (6 metres) upstream from the conditioner and in aposition where it can easily be adjusted. It is considered thatthis distance is necessary so that the steam can stabiliseafter pressure reduction. In some cases, where the reducingvalve is too close to the conditioner, The result is a mixtureof superheated and wet steam, with the superheated steambeing carried through (particularly in the barrel type)without giving up its heat and moisture.

4.3 Pipe Sizes and Steam VelocityVelocity of steam entering the conditioner can also affect theefficiency of mixing with the meal. Steam velocity andquantity determine the pipe bore size which should be used.However, we have noticed in a number of plants that fullbenefit is not obtained from the steam (particularly lowpressure steam) because the bore of the steam pipe after thereducing valve is too small.

Meal conditioning 4

General note (for barrel conditioners).

To get hot moist meal – use low pressure steam

To get hot dry meal – use high pressure steam

Steam Installation prior to Conditioner

HighPressureSteam

PressureReducing

ValveReducedPressureSteam

SafetyValve

By-Pass Valve

Sight Glass

Valve

StrainerSteam Trap

Separator


Pip

e b

ore

(m

m)

Suggested operating conditions for pelleting various feed types.

Note: These are guidelines only. Raw material variationsmight make it necessary to vary operating conditions (see section 6). Steam pressure relates only to barrel typeconditioner.

Re Meal Temperature: Ensure that your operatingtemperature complies with your Companies requirement forhygiene and nutrition.

Re Energy Input: This is an indication of the amountneeded to produce pellets of durability around 95 Holmen (1 min. test, 4 – 5 mm pellets. 0.5 min test, 3 mm pellets)when pelleting a feed formulation with a FPQF equal to 4.7.

5.1 Ruminant Feeds

Notes on Ruminant Feeds• These feeds tend to be fibrous and bulky. The more fibrous

a feed, the more difficult it is to add steam. Too muchsteam causes the pellets to expand and crack, particularlyon large diameter pellets.

• High fibre materials will tend to help pellet quality butreduce production rate.

• Processed starch by-products (e.g. maize gluten feed) willtend not to absorb moisture, therefore you may havedifficulty applying steam when using these materials – a lignin PPE helps tremendously.

• With some combinations of raw materials, which tend notto accept steam, benefit may be gained by adding up to 1%water at the blending mixer. However, this can cause wetspots, which lead to vitamin degradation.

• If using a barrel type conditioner inject part, if not all, thesteam with the molasses.

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Capacity of pipes passing dry saturated steam

IMPERIAL Gauge steam pressures (lb/sq. in)

15 20 30 45 50 65Capacity in lb/hr at 60 ft/sec.

1 85 98 125 164 176 2141 1/4 133 153 195 256 276 3351 1/2 191 221 281 368 397 4822 340 393 499 655 706 8572 1/2 531 613 780 1023 1102 13393 764 883 1123 1473 1587 19274 1359 1571 1996 2619 2822 34275 2123 2454 3119 4091 4408 5354

METRIC Gauge steam pressures (bar)

1 1.5 2 3 4 5

Capacity in kg/hr at 20 m/sec

20 25 31 37 48 60 7125 39 49 58 76 93 11132 65 80 95 125 153 18340 102 125 149 195 240 28650 159 196 233 305 375 44780 408 503 597 782 961 1146

100 638 786 933 1222 1502 1790150 1435 1769 2099 2751 3380 4029

Production guidelines 5

Pip

e b

ore

(in

.)

Steam Meal Energy Input Borregaard Pressure Temperature pellet press PPE

at exit of motor inclusion atconditioner guideline

2.5 – 4 bar 75 – 85 ºC 20 – 24 kWh/T 1 – 2%


that the pellet press rollers are set correctly in order tominimise rollers slip, thus reducing heat generated byfriction. This type of feed cuts press output and dieblockages can be frequent. However, adding 1% of aBorregaard Lignin PPE will increase traction betweenrollers, meal and die thereby helping you to increaseproduction rate.

Correct die specification is very important for this type offeed – consult your die supplier.

• Pig feeds generally contain a relatively high level ofcereals. Best operating procedure depends on theproportions of wheat, barley, maize etc., but in general,high temperature high moisture meal using low pressuresteam produces the best pellets.

• Sow rolls (10 – 12 mm pellets), particularly when fedoutdoors, must be very durable. They must also be largeenough i.e., no "short ends" to prevent birds from carryingthem away. They are best produced using a slow-revolvingdie at relatively low production rate, in order to maximisedwell time in the die. If meal passes through the holes in thedie without forming, the practice of plugging the holesshould be tried. This is done by hand feeding hard pelletsinto the die chamber. Molasses, if well dispersed, will helpformation.

Excess use of steam can cause vertical cracking in the pelletson leaving the die.

5.4 Poultry feeds

Notes on poultry Feeds• Poultry feeds generally contain high levels of cereals,

mainly wheat or maize, and fibre is relatively low.Therefore pellet structure and strength depend on goodconditioning, i.e. heat and moisture to soften the mealparticles so they can mould easily together. There is somegelatinisation of the starches, which then act as a naturalbinder.

3534

• With some formulations, in order to maintain pellet quality, it may be found necessary to run the press under capacity inorder to increase meal dwell time in the die. If you need to dothis it may indicate that you need a higher compression die.

• With a multi-speed gearbox, a slow speed is generallyfound to provide best results.

• Some dairy feeds are produced using high cereal, low fibreraw materials. In this case, refer to Poultry Feedconditioning, section 5.4.

5.2 Concentrates

Notes on concentrates• To produce good pellets from high protein feeds heat is

required to plasticise the protein, which in turn acts as anatural binder. Moreover, the meal particles will soften andmould easily together during formation of pellets in the die.

• Heat is more important than moisture in the production ofconcentrates. The amount of moisture added at the conditi-oner should be sufficient for lubrication through the die.

• It is particulary important that holes in the die are flushedout if you have to stop production or remove the die.

• For feed containing urea ensure the steam is very dry.

5.3 Pig feeds

Notes on pig Feeds. • Pig weaner feeds containing milk powder and sugar are

heat sensitive due to caramelization that occurs atrelatively low temperature. Therefore, it is imperative



4 – 5 bar 75 – 85 ºC 20 – 24 kWh/T 1 – 2%



1 – 3 bar 75 – 85 ºC 15 – 17 kWh/T 1 – 2%(3% in rolls for sows)



1 – 1.5 bar 85 – 95 ºC 10 – 12 kWh/T 1 – 1.5%(enzymes permitting)


37

In section 5 we have suggested operating conditions for arange of basic feed types. However, we have also stressedthat these are only guidelines. It is well known thatdifferent raw materials behave differently in their effectboth on pellet quality and output, and thus changes informulations might dictate changes in these guidelinerecommendations.

6.1 Why Raw Materials Affect PelletingThere are many characteristics of raw materials which affectproduction, but the main factors are:

The relationship between these factors and pellet quality isnot straightforward, but we hope the chart overleaf will help.

Most feed raw materials are variable in character. All thefactors listed above affect pellet production, so when any orall of them change, pelleting is affected. These variations arethe main reason why pellet quality can suddenly alter withoutany change in formulation or production method.

Ideally, it should be possible to devise a mathematicalrelationship between the factors listed above and theproduction characteristics of a raw material, so that simplechemical analysis could give a pellet quality prediction.

6.2 Raw Materials – physical and Nutritional Factors

Clearly it is important to try and anticipate problems due to the use of certain raw materials, or to a change in thecharacter of those raw materials. We have therefore preparedthe chart overleaf, which we hope may be of assistance.

In addition to the usual chemical or nutritional values,which are in every compounder’s computer matrix, we havealso given figures for three important physical values, on a scale from 0-10.

36

• When using a barrel type conditioner low pressure steammust be used. This type of steam starts to give up its heat andmoisture more rapidly.

• The addition of a Borregaard lignin PPE will allow you touse more steam, while improving pellet quality. It alsomaintains "traction" between roller, meal and die – this isvery important with high moisture meals.

• Too much fat added at the mixer causes mealy pellets. Fatcoating helps solve this problem, but it is still useful to addthe first 0.5 to 1% fat at the mixer. This will aid presscapacity and extend die life.

• The requirement to produce poultry feed free of allpathogens, in particular Salmonella, puts great importanceon effective heat conditioning. Temperature and dwell timeare the most important factors, but because of the manyother parameters which can influence this, it is difficult togive hard and fast guidelines in this handbook. Mostexisting pelleting plants, if using a barrel type conditionerand pellet press, will be required to extend their presenttemperature and dwell time.

Depending on production capacity requirements, it may benecessary to use a pasteurisation process of conditioning,whereby a specially designed steam unit and mixing/-holding vessel is used. Whatever process is adopted, it isabsolutely essential that the plant is equipped with a meansof monitoring production such that any meal which has notbeen subjected to the required temperature and time, is cir-culated for reprocessing.

Raw materials characteristics 6

• Natural or processed• Starch content• Protein content• Moisture content• Particle size, distribution

and shape

• Oil content• Fibre content• Mineral matter content• Moisture absorbency• Abrasiveness


38

Physical Factors

• Pellet QualityThe raw material’scontribution tophysical quality. (Thehigher the number, thebetter the quality).

• Press capacityIts effect upon output.(The higher thenumber, the higher theproduction rate).

• AbrasivenessA key to die life (The higher thenumber, the moreabrasive the rawmaterial).

These values are basedon our experience andpractical observations,supported by those ofcustomers and friends inthe industry. We hopethe chart will be ofassistance to you.

Notes on the Chart• The three "physical

factors" are designedso that virtually all rawmaterials fall between0 and 10.

• The exceptions are fat and Borregaard’srange of ligninPelleting PerformanceEnhancers. As theseaffect pellet qualitysignificantly at verylow inclusion rates,they have "pelletquality factors" outsidethe normal scale.

RAW MATERIAL Pellet Press Abrasive- Protein 0II Fibre Ash Bulk Bulkquality capacity ness per cent per cent per cent content density densityfactor factor factor per cent Ib/ft3 kg/m3

0 – 10 0 – 10 0 – 10Mill by-productBarley meal 5.0 6.0 5.0 10.5 2.0 4.5 2.2 30 480Maize meal 5.0 7.0 6.0 9.0 3.5 1.9 1.2 38 610Milo meal 4.0 6.0 7.0 10.0 3.0 2.5 5.0 34 540Oat meal 2.0 3.0 7.0 10.5 4.5 10.5 3.2 32 520Rice (rough) 5.0 5.0 4.0 8.0 1.5 9.0 12.0 30 480Screenings (grain) 2.0 2.0 8.0 12.0 4.0 12.0 8.0 27 480Wheat meal 8.0 6.0 3.0 11.0 1.5 2.5 ---- 34 540Wheatfeed 6.0 5.0 4.0 15.0 3.5 8.0 4.7 23 370Wheat pollards 5.0 5.0 4.0 14.0 4.0 9.0 ---- 30 400

Oilseeds and derivativesCoconut cake 5.0 8.0 6.0 21.0 8.0 11.5 6.5 30 480Cotton dec. 7.0 8.0 6.0 40.0 6.0 11.5 6.0 40 640Cotton meal ext. 8.0 6.0 7.0 39.0 1.0 12.0 6.0 38 610Groundnut cake dec. 7.0 8.0 4.0 47.0 5.5 6.0 6.0 39 620Groundnut meal ext. 8.0 6.0 5.0 54.0 1.0 9.5 6.0 42 670Guar meal 7.0 7.0 5.0 42.0 4.0 11.0 5.5 35 560Linseed meal ext. 7.0 6.0 5.0 35.0 1.5 9.0 5.5 30 400Linseed cake 6.0 7.0 4.0 32.0 6.5 8.5 5.0 34 540Palm kernel cake exp. 6.0 7.0 4.0 19.0 6.5 12.0 3.8 28 480Palm kernel meal ext. 6.0 5.0 5.0 20.0 1.0 15.0 3.7 47 700Palm kernel (whole) 3.0 8.0 3.0 13.9 49.0 7.3 1.8 47 750Rapeseed meal ext. 6.0 6.0 6.0 36.0 1.0 11.0 ---- 32 510Sesame meal exp. 7.0 7.0 4.0 45.0 10.0 6.0 11.5 35 560Soyabean meal HIPRO 4.0 5.0 4.0 48.0 1.6 3.1 6.5 36 500SoyPass 5.0 5.0 4.0 45.0 1.5 3.1 ---- 36 500Soya full fat 4.0 8.0 3.0 35.0 18.0 4.5 5.8 30 480Sunflower cake exp. 6.0 6.0 4.0 39.0 8.0 16.2 7.0 35 560Sunflower meal ext. 6.0 5.0 5.0 39.0 1.0 18.0 7.0 33 530

By-productsVegetable oil (added before die) -40.0 50.0 0.0 ---- 100.0 ---- 0.0 56 900Vegetable oil (added after die) -5.0 0.0 0.0 ---- 100.0 ---- 0.0 56 900Fish meal white 4.0 7.0 5.0 67.0 8.3 ---- 20.0 40 640Fish meal Peruvian 4.0 7.0 5.0 65.0 10.3 ---- 15.0 40 640Herring meal 4.0 7.0 5.0 72.0 9.0 1.0 10.5 37 590

LegumesField beans 7.0 5.0 5.0 27.4 1.3 6.2 3.4 43 690Peas 6.0 5.0 5.0 23.0 1.2 6.3 2.9 45 720Lentils 4.0 4.0 5.0 25.5 1.3 4.5 3.0 50 800Locust beans 4.0 4.0 6.0 4.0 ---- 6.9 3.0 25 400

OthersBiscuit meal 2.0 8.0 3.0 8.0 10.0 1.0 ---- 30 480Brewers grains 3.0 4.0 5.0 13.8 8.0 14.0 ---- 20 320Cereal replacer pellets 3.5 4.0 7.0 8.0 1.5 8.0 ---- 35 560Chinese leaf meal 7.0 2.0 8.0 16.0 4.0 15.0 ---- 20 320Citrus pulp 7.0 3.0 6.0 6.0 3.0 12.5 6.0 21 330Coffee residue 2.0 8.0 3.0 10.0 25.0 36.0 1.9 25 400Distillers' grains - barley 4.0 5.0 5.0 22.0 4.0 17.0 ---- 20 320Distillers' grains - maize 3.0 4.0 5.0 27.0 8.0 13.0 ---- 20 320Distillers' grains + solubles 5.0 6.0 5.0 27.0 7.5 8.5 ---- 30 480Distillers' solubles (maize) 7.0 6.0 0.0 27.0 9.0 5.0 ---- 38 600Grass meal 7.0 2.0 8.0 15.0 3.0 20.0 9.0 20 320Maize germ meal 5.0 8.0 3.0 11.0 10.0 3.5 3.0 30 480Maize gluten feed 3.0 4.0 6.0 23.0 2.0 8.0 6.3 34 540Maize gluten meal 4.0 5.0 5.0 60.0 2.0 1.3 6.3 30 480Malt culms 6.0 2.0 7.0 22.0 1.5 14.0 6.0 15 240Manioc 5.0 3.0 7.0 2.5 ---- 4.0 4.0 40 640Minerals 2.0 4.0 10.0 ---- ---- ---- 95.0 61 1000Molasses 7.0 6.0 0.0 3.6 ---- ---- 11.0 77 1230Nutritionally improved straw 4.0 4.0 6.0 3.5 1.0 38.5 11.0 8 130Olive pulp 7.0 3.0 6.0 10.0 3.0 29.0 7.4 45 720Rice bran 2.0 3.0 9.0 13.0 14.0 12.0 ---- 20 320Skim milk powder 9.0 2.0 5.0 34.0 0.5 ---- 8.5 40 640Sugar beat pulp (molassed) 7.0 3.0 6.0 9.0 0.5 16.0 7.1 15 240Borregaard Lignin PPE 50.0 30.0 0.0 ---- ---- ---- 14.0 31 500


Experience and practical trials have shown that when combiningthe expertise of a Feed Company’s Production and Nutrition personnel with Borregaard’s Lignin Technology and AppliedPelleting Technique, massive improvements in overall pelletingperformance can be achieved.

4140

• Raw materials in combination can behave unpredictably (the"synergy effect"). This is why pellet quality may sometimesdiffer from the value calculated from our figures, which arebased on experience of raw materials within the range ofinclusion levels common in European compound feeds.

• Our table refers to average samples. Feed raw materials,being natural products, may vary from batch to batch. Ifyou see a change in your production without a formulationchange, it may be that the specification of one of your rawmaterials has changed.

• We won’t be surprised if you disagree with some figures.Results depend on plant factors as well as raw materialfactors. There is no such thing as a standard feed mill, sothe same raw material will behave differently in differentmills. Remember, these are average figures; this subject isbeset with many variations and complications.

• The "physical factors" in the chart may help you toanticipate any problems before they occur. We also hopethat this handbook in general will help you to make perfectpellets from any formulation.

Please remember that formulations are devised to provide therequired nutrients in the most economical combination of theraw materials available, not to cause headaches for production!

Raw material cost accounts for 85% of the feed’s sellingprice, and this exceeds production cost by a factor of between15:1 and 20:1. That’s why a formulation change forproduction purposes, which might well increase overall costssignificantly, is generally viewed as a last resort.

However, with the advent of computer control of the entire feedmill and the production data which can be generated, actualproduction costs for each feed formulation can be determined,thus enabling an "optimum" cost ration to be produced.

FPQF (Feed Pellet Quality Factor)Calculation of the FPQF indicates how well a particular feedformulation will pellet (see following examples). The level ofacceptability is your decision depending on factors such asmarket area, production constraints and feed type. As aguideline we take 4.7 as the minimum. Values below thissuggest pellet quality problems unless a higher than normalamount of electrical energy is used in pelleting. Higher valuesindicate that production rate can be maximised.

CALCULATION OF FEED PELLET QUALITY FACTORTypical Examples

Table No. 1, Dairy Feed

% PQF FPQFGluten 13.0 3.00 0.39Citrus 22.5 7.00 1.57Distillers 6.0 3.50 0.21Barley 20.0 5.00 1.00Palm kernal 10.0 6.00 0.60oo-Rape 6.0 6.00 0.36Veg. oil -40.00Minerals 2.5 2.00 0.05Wheat 20.0 8.00 1.60Beet Pulp 7.00

Total FPQF 5.78

Table No. 2, Pig Feed

% PQF FPQFBarley 23.0 5.00 1.15Oat Meal 37.2 2.00 0.74Wheat Meal 13.0 8.00 1.04Veg. oil 2.0 -40.00 -0.80Fish Meal 3.0 4.00 0.12Protein Meal 6.0 4.00 0.24Grass Meal 1.6 7.00 0.11Mins on carrier 7.0 2.00 0.14Vitamins 2.2 3.00 0.07Returns 5.0 5.00 0.25

Total FPQF 3.06

PQF = Pellet Quality FactorFPQF = Feed Pellet Quality Factor


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7.1 Advantages of Borregaard’s Lignin PPEsA lignin PPE is an important production tool that enablespelleting plant operators to:

Increase• Pellet quality (Durability Holmen value)• Pelleting production rate (T/h)• Pelleting efficiency (kWh/T)• Die and roller life• The ability to add more steam and fat

Decrease• Production costs• Fines returns• Power consumption• Roller slip• Die blockages• Feed rejections!

The effects are best illustrated by practical example of apelleting trial carried out in a commercial feed mill, which isoutlined in the following pages.

7.2 Pelleting Trial ProceduresThese trials are based on a procedure we have developedduring several year’s experience and can easily be adopted byyou. Basically a trial consists of pelleting three consecutiveproduction runs.

Under trial conditions it is necessary to explore the fullbenefits, beyond that of improvements to physical quality,that can be achieved by the incorporation of a PPE. Thesemay be improvements in productivity (pelleting throughput),pelleting efficiency and power consumption. All leading toimproved profitability for the business.

With this in mind the following protocol is used:• A suitable formulation is selected. Preferably one that is

not currently meeting your pelleting performance/qualitycriteria. Its FPQF (see page 38 – 39) is first calculated.This is done initially to provide an indication of pelletquality and later in relation to energy input (kWh/T).

Table No. 4, Talapia Feed

% PQF FPQFProtein Meal 3.00 4.00 0.12Fish Meal 2.00 4.00 0.08Distillers grain 1.90 3.00 0.06Veg. oil 1.15 -40.00 -0.46Minerals 2.51 2.00 0.05Rape Meal 5.00 6.00 0.30Wheat Pollard 15.00 5.00 0.75Wheat 27.00 8.00 2.16Soya 25.60 4.00 1.02Sunflower Meal 16.80 6.00 1.00

100 %Total FPQF 5.08

PQF = Pellet Quality FactorFPQF = Feed Pellet Quality Factor

Borregaard’s lignin pelletingperformance enhancers 7

Table No. 3, Duck Feed

% PQF FPQFMaize Meal 16.0 5.00 0.80Rice Broken 35.0 5.00 1.75Soya 30.0 4.00 1.20Veg. oil 0.5 -40.00 -0.20Fish Meal 5.0 4.00 0.20Mins + Vits 3.5 2.00 0.07Rice Bran 10.0 2.00 0.20Wheat 8.00

100 %Total FPQF 4.02


45

is also taken from the cooler exit approximately 20 minuteslater i.e., a time period equal to the dwell time of pellets inthe cooler. Period of sampling is every 15 minutes.

The pellet samples are used for durability measurementusing the Borregaard LT portable pellet tester (successor tothe Holmen Tester) and also your own method if different.Pellet hardness is also measured if required. Both hardnessand durability tests are completed in the same time framefor each production run.

The option of average pellet weight may be determinedby taking a random quantity from the composite sample,weighing and then counting their number. Adding aBorregaard PPE such as LignoBond DD, can bedemonstrated to increase pellet density and lengthresulting from a more positive pelleting action andincreased production rate.

A composite of the samples taken from each productionrun is retained for chemical analysis. This will check thatthe ingredients and their proportions are similar for theformulations used in each production run.

• A fully documented report should always be preparedimmediately following the trial. This is standard procedurefor a Borregaard Feed Production Technologist.

7.2.1 Typical pelleting trialThe following data was obtained when monitoring production ofa dairy feed that contained 1.6% LignoBond. By increasingLignoBond to 2% and using Applied Lignin Technology andPelleting Technique, production rate was increased in steps untilmaximum power of the pellet press motor was reached.

Production rate was normally around 8 T/h corresponding to apower consumption of 17 kWh/T and pellet durability (ex-plantcooler) of 91 Holmen, although a level of 92 to 95 was sought.As can be seen, it was possible to increase production rate34.6% to 10.7 T/h, reduce power consumption 10.5% to 15.4kWh/T, whilst increasing pellet durability to around 94/95.

At 10.7 T/h the pellet press had very positive pelleting actionwith little amperage fluctuation. Had more steam been availableproduction rate could have increased further. Modifications tosteam supply were later made whereupon it was found possibleto run the plant with confidence at 12 T/h (50% increase) whistmaintaining power consumption and pellet durability around 15kWh/T and 92/93 Holmen respectively.

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• The quantity of feed required for a single production run,of a minimum one-hour duration under normal operatingconditions, is established.

• Production Run 1. The "control". Consisting of aroundone hours pelleting production of the standard formulation.

• Production Run 2. As per the "control" but with theaddition of 1 – 2% of the PPE.

• Production Run 3. As per Production Run 2, but using theproperties of the PPE to increased meal temperature (if required) and production rate whilst maintaining therequired level of pellet quality.

• During each production run use data loggers or yourplant equipment to monitor and record: production runduration, press motor voltage (measured between twophases), pellet press motor amperage (one phase only),meal feeder speed (r.p.m) and meal temperature at exit ofthe conditioner.

The pellet press voltage, amperage and production rate(T/h) data is used to calculate energy input (kWh/T) foreach production run. The conditioned meal temperature datais used to confirm that the meal conditioning is the same forRun 1 and Run 2, and that changes made during Run 3 aredocumented. Meal feeder speed data is used to calculateproduction rate per revolution. By doing so, any step-up inproduction rate during Run 3 can be calculated precisely.

The collated information should provide a comparison ofthe following and in so doing provide a means of assessingthe Pelleting Performance of any pelleting line:• Production rate (T/h)• Energy Input (kWh/T)• Conditioned meal temperature• Pellet durability (Holmen)

Moreover, the character of amperage, meal feederspeed and temperature traces, if using dedicated dataloggers, provides an insight to the mechanical operation of the pellet press and effectiveness of control systems.

• A sample of pellets is taken direct from the die at aprecise time so that the event can be marked on theloggers and/or readings taken from your plant displaymonitors, gauges and meters. This enables the exactproduction conditions to be related to the sample. A sample


46 47

Energy InputPellet Press MotorkWh/T Energy Input reduced 10.5%

Substantial improvement in pellet quality

20

19

18

17

16

15

14

9695949392

9091

8988

8687

9.45 10.00 10.15 10.30 10.45 11.45 11.30 11.45 12.00 12.15

9.45 10.00 10.15 10.30 10.45 11.45 11.30 11.45 12.00 12.15

Production RateTonnes/hr

Time when taking sample

12

11

10

9

8

7

69.45 10.00 10.15 10.30 10.45 11.45 11.30 11.45 12.00 12.15

Production Rate increased 34.6%

Pellet DurabilityHolmen

Pellet durability ex-die

Pellet durability ex-plant cooler

Feed Formulation: Dairy Rich FPQF = 4.51 Trial: Using applied Lignin Technology & PelletingMonitoring present production with 1.6% LignoBond Technique to increase production rate & pellet quality

Time 9.45 10.00 10.15 10.30 10.45 11.45 11.30 11.45 12.00 12.15Feeder speed (actual R.P.M from logger) 42,2 42,2 42,2 42,2 42,2 42,2 46,8 51,3 54 56,8Tonnes/hr (Actual) 7,92 7,92 7,92 7,92 7,92 7,92 8,78 9,63 10,13 10,66Meal temperature. C (actual from logger) 79,5 79,5 78 77,5 78 85,5 85,2 85,5 87,5 83,5Press motor amps (actual from logger) 218 222 218 222 225 222 235 258 260 265Voltage (actual from logger) 395 395 397 393 393 393 396 388 398 398kW press motor 134,07 136,53 134,75 135,84 137,68 135,84 144,89 155,86 161,12 164,22kWh/T 16,93 17,24 17,01 17,15 17,38 17,15 16,5 16,19 15,9 15,4Holmen (from die & cooled) 1min.test 89,7 88,8 90,1 89,8 89,1 93,8 94,1 93,8Holmen. (pellets ex-cooler) 91 90 91 91 91 95 95 94 95 95%'Dosage (from control room monitor) 60 60 60 60 60 60 67 74 78 82Actual roller gap mm 4,2 4,2 4,2 4,2 4,2 4,2 4,2 4,2 4,2 4,2

Plant details: 160 kW motor (max amps 300) Buhler pellet press

6 mm x 120 mm die. Matador barrel conditioner. Boiler pressure: 9 bar reduced to 3.5 bar.Auto Roller Adjustment

Trial: with feed formulation containing 2% LignoBondFPQF = 4.68

Test result from Sweden


7.3.3 Overtaxed boilerFeed type: Soybean meal pelletProblem:Two pellet mills and a steam flaker were drawing somuch steam that the boiler pressure fell below the level set forthe pressure reducing valve.Effect: Blowdown of steam traps caused sudden pressurereduction and drops in temperature.

7.3.4 Mill supplied by surge binFeed type: Rabbit pelletProblem:As the bin emptied, a low level switch started asupply screw which refilled the bin. Bulk density varieddepending on fill, causing the amount of feed delivered to theconditioner to vary.Effect: Temperature, amperage and pellet quality varied.

7.3.5 Oversized feeder screwsFeed type: Poultry pelletProblem:The large sized feeder screw required it to be run at a low rate of 15 rpm.Effect: The feeder screw dumped 5 kg of feed into theconditioner at 4 second intervals. The conditioner was not ableto evenly distribute the flow before the feed reached the die.This erratic supply caused the press load to fluctuate between130 amps and 170 amps every 4 seconds.

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7.3 Problem Solving from Trial FormatLignoTech’s plant trial format often identifies equipmentproblems that can prevent optimisation of production, as thefollowing instances show.

7.3.1 Broken steam regulatorFeed type: Dairy pellet Problem: A broken steamregulator allowed steam pressuredelivered to the conditioner to varyas the boiler cycled on and off.Effect: Changing pressure causedthe amount of steam delivered tothe conditioner to vary, eventhough the steam valve was notchanged. Pellet quality varieddirectly with steam.

7.3.2 Incorrect set-up of computer controlled steam system

Feed type: Dairy pelletProblem:The controller’s observation/response time betweenadjustments was too short. The controller would open the steamcontrol valve and then check the temperature (conditioner out-let) before the affected feed had reached the temperature probe.Effect: Overshooting of the temperature set-point, followed byovercorrection, with the cycle constantly repeating. Erratictemperature caused variable pellet quality.


From bulkBorregaard lignin PPEs can be delivered pneumaticallyfrom the bulk vehicle into a blending bin and dischargedfrom the blending bin into the batch weigher in exactly thesame way as other raw materials. However, it should not bethe first or the last material to enter the blending system.Lignin PPEs can also be discharged volumetrically via ascrew bin discharger, direct into the batch mixer.

7.4.4 Accidental spillages at the millUnless swept up immediately, lignin PPEs may absorbmoisture from the atmosphere, forming hard leatherypatches on the floor. These can be cleared by using water in conjunction with brushing and scraping. An alternativesuggestion is to sprinkle with urea prills which, after a shorttime, will soften the patches, making removal easier.

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7.4. Borregaard Lignin PPEs

7.4.1 PackagingBorregaard lignin PPEs can be supplied in three ways.

• 25 kg bags on pallets.• 1 tonne bulk bags• By 24 tonne pressure tankers

7.4.2 Mill intake and storage25 kg bagsDryness is maintained by packaging in 25 kg bags with apolythene moisture barrier. For ease of handling, bags aredelivered on non-returnable pallets and are shrink-wrapped.Special storage requirements in the mill are not necessary – although a dry area is best suited.

1 tonne bulk bagsThese bags are non-returnable polypropylene, with apolythene innerbag, and are complete with lifting straps forease of handling by fork lift truck. Bulk bags can be stacked,provided care is exercised.

Delivery by tankerLignin PPEs can be blown direct from the delivery tankerinto a standard blending bin or silo. No special requirementsare necessary.

7.4.3 Application in the mill25 kg bagsLignin PPEs can be added at the "tip" hopper located in theblending/batch weigher area, or direct into the batch mixer.However, PPEs should not be the first or the last material toenter the mixer or conveying system from the blending plant.

1 tonne bulk bagsThese bags are for discharge into a pneumatic intake systemfor storage in a blending bin. Mechanical handling is notrecommended. However, if the conveying system is primedby using talc (one 25 kg bag is sufficient), then mechanicalintake is possible – but not on a continous basis. Afterdelivery, the system should be purged again with talc.


• If using a ripener investigate a means of injecting steaminto meal before entering die (assuming bottom barrelconditioner isn’t installed.)

• Conditioner not full enough – barrel type. Adjust paddlesfor greater meal retention.

8.1.2 Pellet pressWide fluctuation in amps?• Observe meal flow into die (must be even). If erratic, does

it correspond to feeder or conditioner speed (r.p.m.)?

• Check feeder controls.

• Check wear on paddles (if barrel conditioner).

• Check for wear on ploughs.

• Check for correct roller setting.

• Check die for blocked holes.

• Oversize fines returns can cause problems, as caninsufficiently ground pelleted raw materials.

• Ensure raw materials and liquids added at the blendingmixer have had sufficient mixing time.

• Separation of meal particles in conditioner – conditionernot full enough.

• One roll working more than the other(s).

• Check steam traps. Slugs of condensate can cause intermittentroller slip and, sometimes, die blockage, as can wet steam.

Uneven pellet length?• Check knife setting.

• One roll working more than the other? Check ploughs ormeal diverters.

• Check that all holes are working. Punch out if blocked (see section 3.3.6).

• Uneven die compression, i.e. badly worn holes workingless than others.

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This section can be divided neatly into two halves. First, we discuss various production problems, subdivided by themajor items of pelleting plant. Then we illustrate variouscategories of "problem pellets" and suggest possible remedies.

8.1 Production

8.1.1 ConditioningVariable meal temperature at exit of conditioner?• See section 7.3.

• Check steam fittings prior to press, i.e. pressure reducingvalves, traps, separators (see 4.3).

• Ensure steam injection nozzles are not blocked.

• Conditioner not full enough – barrel type.

• Incorrect adjustment of steam controller (see 7.3.2).

• Uneven flow of meal from pre press silo (see 7.3.4).

Can’t get meal hot enough before choking die?• Check to ensure condensate is returning to boiler and not

into the conditioner.

• Try increasing steam pressure into the conditioner.

• Use a lignin PPE from Borregaard.

• Conditioner not full enough – barrel type.Adjust paddles for greater retention.

• Whole or part pellets in meal.

Can get meal hot enough but not sufficiently moist?• Reduce steam pressure. Note: pressure reducing valve must

be approximately 20 ft (6 m) upstream of the conditionerand the connecting pipe must be of sufficient size to carrythe volume of steam at low pressure (section 4).

• If still more moisture is required due to very dry rawmaterials, water can be added at the blending mixer, but onlyif absolutely necessary because water addition can cause wetspots which lead to rapid degradation of vitamins.

Trouble shooting 8


8.1.3 DiesNew die won’t "go"?• Hand feed maize meal, then dry mixed meal. If holes start,

continue with dry meal at slowest die speed and meal feedrate. Gradually introduce steam and feed until optimumproduction is achieved. This could take quite a while withsome dies. Check that over-tight rollers have not rolledover die holes. Try using dimpled roll shells.

Used die won’t "go"?• Hand feed hard pellets to force out existing meal. If this

fails, the holes must be punched out. Soaking the die in abath of penetrating oil may sometimes soften residual mealsufficiently for hand fed pellets to remove it. "Drilling out"is a last resort as it damages the holes (see section 3.3.6).

• Check roller condition and setting. Try using dimpled roll shells.

Rapid die wear?• Check roller setting.

• Do not use old rollers with new die or vice versa (see section 3.3.7).

• Check raw materials for abrasiveness, particularly silicacontent (in section 6).

• If the die is pitted, check raw materials for corrosiveproperties – consult the nutritionist.

• Consult your die supplier.

• Pellet press oversized or production rates not high enoughfor size of press.

8.1.4 Cooling"Hang up" in vertical cooler?• This can be caused by very moist, heavily molassed or

mealy pellets. Try to keep pellets constantly on the moveby adjusting exit feed gates. If too wet, try to get thepellets hotter leaving the press (see section 4.2).

Pellets too warm and moist at cooler exit?• If horizontal cooler, ensure that bed is completely covered to a

depth recommended by manufacturer. Also control dwell timeby adjusting speed. For vertical cooler, check all perforations areclear and air cannot by-pass the column of pellets, and that thereis sufficient dwell time. Mealy pellets might also be the cause.

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• Whole grains or large meal particles in feed. Also brokenor small pellets in fines returns.

Too much meal leaving die with pellets?• Worn die.

• Blunt or incorrectly positioned knives.

• Badly fitting or worn feed cone allowing meal to dribblethrough.

• Not enough compression in the die, allowing productionrate to increase disproportionately with amps. Try "plugging" the die (section 5.3 sow rolls).

• Check grist spectrum (see section 4.1)

• Excessive rate of feed.

Soft blocking?This is a term often used by press operators when, for noapparent reason, the die suddenly blocks, even though thepress is working well under its predicted blocking point.

Check the following.• Boiler and steam plant, in particular, steam traps. Slugs of

condensate may periodically be pushed into the conditioner,causing the rollers to skid and block the die.

• Sometimes pelleted raw materials by-pass the grindereither intentionally or unintentionally and will contributetowards soft blocking. This should be avoided for thereasons given below.

• Check sifters after cooling, to ensure pellets are notpassing through worn screens and returning with the finesto the pre press bin. Pellets can often separate from themeal and fines and enmass to enter the conditioner in largevolume. As pellets do not readily absorb steam, adisproportionate amount is absorbed by the meal, whichbecomes too wet and blocks the die.

After a blockage• Never "jog" the die to restart.

• Always use a low feed rate for at least five minutes, inorder to get rid of pieces of wet meal which break awayfrom the conditioner sides and exit spout.


regrind) and a reduction in therate at which meal passesthrough the die. Dwell time isimportant with this type ofration. Check grist spectrum (see section 4.1).

An exaggerated "fir tree"formation happens when mealis very wet or when there isurea present. It can also occurif meal contains excessivelubricating properties, such thatfriction between particles isless than that between theparticles and the internal surface of the die holes. Also if thefriction on the hole surface is excessive, causing adjacent mealparticles to adhere to it.

8.2.3 Pellets which develop a vertical crack, either part or full length, while cooling.

This usually indicates theprocessing of a light fluffy mealwhich, when compressed, hasthe resilience to spring open.

A ball of cotton wool, afterbeing compressed in the hand,expands equally in alldirections. However, a pellet,being cylinderical and notspherical will, on expansion,split along its line of leastresistance. Palm kernel meal isa classic example.

SolutionFormulation can be changed to increase meal density, butthat may be costly. You will need dry heat duringconditioning. Added moisture should be kept to aminimum. Good compression in the die is essential andyou should hold back throughput so that retention time inthe die is as long as practical. The greater the number of"shear planes" in this case, the better. A thick die withparallel bore holes also seems to reduce this problem.However, a well type die contributes significantly to thecause of the problem. Here, as elsewhere, a Borregaardlignin PPE will help.

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Pellets cool and dry outside, warm and moist inside?• These pellets break down, usually in the customer’s bin!

Usually caused by too much air or insufficient dwell time.

8.2 Problem PelletsThey say that one picture is worth a thousand words. Wehave six pictures!

Many, but not all pellet quality problems fall into thesecategories, or a combination of the effects shown.

8.2.1 Severe cracks at one end and/or hairline cracks down one side.

This usually happens when thepellet leaves the die.

When knives are set away fromthe die, especially when bluntor when a breaker bar is used,pellets are knocked or torn fromthe die, rather than cut. Underthese circumstances the pelletsbend and crack down one side,usually with a severe crack atone end. This later breakes offcreating mealy pellets.

The cracks usually occur across the shear planes of the pellets.A shear plane is the area across the diameter of the pellet, bet-ween each slug of meal pressed into the die by the roller).

SolutionMore compression in the die, a finer grist, improved molasses/fat dispersion and the use of a Borregaard lignin PPE.This will create a harder pellet at exit of the die, which in turnwill snap off rather than be torn away. Reduce the die speed.Consider making a different diameter pellet (smaller).

8.2.2 Horizontal cracks across the whole pellet.These also usually occur across the shear planes, found whenpelleting fibrous bulky rations. These pellets sometimes have a"fir tree" formation, created by each slug of meal entering thehole, and exaggerated by fibres longer than the pellet diameter.

SolutionMore compression in the die, control of fibre length duringgrinding (this does not mean finer grist, but separate and


8.2.6 Excessive amount of short ends

An increase in short ends canresult from double pelleting.

SolutionDepending on the severity ofthe problem, it may be worthconsidering pelleting throughone press only and using alignin PPE from Borregaard.Alternatively, try using athinner die on the top press.

8.2.7 Whiskery pelletsPellets which feel "prickly" can be a result of excess steam,which becomes trapped in the fibres and meal particles. Thisexpands as the pellets leave the die, lifting fibres and otherparticles from the surface of the pellet. The more steam youuse, the worse the problem. Pellets containing barley or oats,for example, are particularly susceptible.

When pelleting high starch rations, a low steam pressure(15/20 psi, 1/1.35 bar) is required to maximise the heat andmoisture given up to the meal. If steam pressure is too high(or if the pressure reducing valve is less than 20 ft (6 m) fromthe conditioner) then condensation can be incomplete. Somesteam becomes trapped in the meal and gives the "whiskery"effect described above. Some steam escapes completely andthus the final temperature (hence starch gelatinisation) willsuffer.

SolutionGood conditioning, with particular attention to correct steampressure and positioning of the reducing valve. Ensure thatyour conditioner, if using a barrel type, is running as full aspossible (see section 3.1.1). This reduces the amount ofsteam which may otherwise be carried into the die with themeal, before condensing.

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8.2.4 Numerous cracks originating from a single point.

This is indicative of a pelletwhich contains large particles(eg. half or whole corns) which,because of their size, are not aswell conditioned as surroundingparticles. On cooling, -"differential shrinkage" occurs,which produces these cracks.Large particles also create anatural breaking point, thusincreasing fines.

SolutionImproved control on grist size during the grinding operationand improved conditioning. Ensure all pelleted raw materialsare passed through the grinder. Grinding of all soya, maizegluten and other cereal by-products is strongly recommended.Ensure there are no pellets returning from the sifters to thepre press silo. Broken pellets and pellet chips should becrumbled or ground before returning to the press.

8.2.5 Mis-shapen pelletsThis pellet is difficult todescribe, but basically is mal-formed, having lumpy sides. Itis usually produced as a resultof whole pellets or large piecesof raw material by-passing thegrinder, or large returns fromthe sifter. Again (as in 8.2.4),large pieces of individual rawmaterials are not conditionedproperly and stresses are set upwhich lead to irregular shapedpellets.

SolutionAgain, improved control of grist spectrum. Also, lack of diecompression can highlight this fault.

Similar effects can be caused by pockets of steam whichbecome trapped during extrusion and explode on exit fromthe die. This can happen with any fibrous ration, so don’t addtoo much steam.


9.1.3 The Borregaard LTOL On-line Pellet TesterThis fully automatic "On-Line" version of the LTA completewith IL50 sampler tests hot pellets directly leaving the pelletpress. This machine is recommended for integration with auto-matic press control systems for optimisation of production rateand pellet quality. When used with a personal computer (PC)pellet durability is displayed graphically with trend line.

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Pellet Quality is hard to define, as it is a combination ofmany factors. Some of these are a matter of personalpreference, but certain quality factors can and should bemeasured. We list below the factors which are oftenassociated with the term pellet quality.

• DURABILITY – Objective • HARDNESS – Objective• APPEARANCE

• Colour – Subjective• Surface texture, sheen, etc. – Subjective• Evenness of length – Objective• Dust level – Objective• Palatability – Subjective

The factors we have described as "subjective" are thosewhich are wholly or partly a matter of personal opinion.True, it is possible to define colour, but what constitutes agood colour for a pelleted product is a matter of opinion,likewise surface texture. The factors which we describe as"objective" can be measured, as described below.

9.1 Durability (Pneumatic)This is possibly the most important aspect of pellet quality.Durability means the ability of pellets to withstand thestresses of handling and delivery without breaking up. It canbe measured in one of two ways, pneumatically ormechanically.

9.1.1 The Borregaard LT Portable Pellet Tester100 grammes of screened pellets are cascaded inside a testchamber by high velocity air. They are screened automatic-ally and then weighed. The percentage of whole pelletsremaining represents the durability value. The LT is acompact, robust, fast, accurate, repeatable and virtually dustfree portable pneumatic pellet tester.

9.1.2 The Borregaard LTA Automatic Pellet TesterBased on the same pneumatic principle as the LT, thisautomatic version is given a volumetric sample. It thenautomatically removes fines, weighs, tests, re-weighs andremoves pellets from tester. Pellet durability expressed as apercentage is instantly displayed on the control panel withoptional printed copy.

Quality control methods 9

Borregaard LT

Borregaard LTABorregaard LTOL


The reason is simple. Durability is essential to avoidbreakdown between manufacture and feeding, but a certaindegree of hardness is also important to avoid breakdown dueto pressure in bulk silos. Contrary to what many peoplebelieve, hard pellets are not always durable, and vice versa.

9.4 Evenness of Length (or Length Distribution)

If the press is set up to produce pellets 20 mm long, then asmany as possible should be very close to this length. If manyof the pellets are shorter, then not only does the appearanceof the product suffer, but also the pellet durability – moreends mean more breakdown.

9.5 Percentage of DustThis is self explanatory. However, there should be minimumdust in a load of pellets leaving the mill, provided they havebeen sifted correctly.

9.6 What Level of Pellet Quality?The majority of livestock producers prefer pellets with aminimum amount of fines. However, circumstances differfrom country to country, even from mill to mill, due to variati-on in processing conditions and raw materials. Pellet testersprovide a tool by which you can measure your pellet qualitybut it is up to each mill to set its standard based on thefollowing:

• The amount of handling pellets get between manufacturing and feeding.

• The demands of the local market.

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9.2 Durability (Mechanical)

9.2.1 Tumbling can (ASAE) method500 grammes of screened pellets are tumbled for 10 minutesat 50 rpm. The sample is then screened again and the wholepellets are weighed. The percentage of whole pelletsremaining is expressed as the durability.

9.3 HardnessNormally measured by the spring hardness tester.

The pellet is held between the jaws of the tester and pressure isexerted by screwing down by hand onto a coil spring. The pointerindicates the load in kilogrammes at which the pellet bursts.

It is advisable to take the average of several readings, as resultsdo vary slightly according to the pellet’s position between thejaws. Also, different operators can record slightly differentresults, depending on the rate at which the load is applied.We recommend that pellet quality testing should include bothdurability and hardness tests.

Spring Hardness Tester

Tumbling can type pelletdurability tester. Photographcourtesy Sprout-Matador.


10.2 Steam Pressures

psi bar kp/cm2

15 1.02 1.0420 1.36 1.3930 2.04 2.0845 3.06 3.1250 3.40 3.4760 4.08 4.1665 4.42 4.51

Note: 1 bar = 1 atmosphere = 14.7 psi

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10.1 General Conversion Factors

Length 1 mile = 1.609 km 1 km = 0.621 mile1 yd = 0.914 m 1 m = 1.09 yd1 ft = 0.305 m 1 m = 3.28 ft1 in = 25.4 mm 1 mm = 0.039 in

Area 1 acre = 0.405 ha 1 ha = 2.47 acre1 ft2 = 0.093 m2 1 m2 = 10.8 ft2

1 in2 = 6.45 cm2 1 cm2 = 0.155 in2

Velocity 1 m/s = 3.60 km/h 1 km/h = 0.278 m/s1 mph = 1.61 km/h 1 km/h = 0.622 mph

Volume 1 ft3 = 0.028 m3 1 m3 = 35.3 ft3

1 in3 = 16.4 cm3 1 cm3 = 0.061 in3

1 gall (UK) = 4.55 l 1 l = 0.220 gall (UK)1 gall (US) = 3.79 l 1 l = 0.264 gall (US)1 pint = 0.568 l 1 l = 1.76 pint

Mass 1 lb = 0.454 kg 1 kg = 2.20 lb1 oz = 28.3 g 1 g = 0.035 oz1 t (long) = 1,016 kg 1 t (metric) = 0.984 t (long)1 t (short) = 907 kg 1 t (metric) = 1.10 t (short)1 cwt = 50.8 kg 100 kg = 1.97 cwt

Force 1 kp = 9.81 N 1 N = 0.102 kp1 lbf = 4.45 N 1 N = 0.225 lbf

Pressure 1 kp/cm2 = 98.1 kPA 1 kPa = 0.010 kp/cm2

1 kg/cm2 = 0.981 bar 1 bar = 1.02 kg/cm2

1 atm = 101.3 kPa 1 kPa = 0.0099 atm1 lbf/in2 = 6.89 kPa 1 kPa = 0.145 lbf/in2

1 bar = 100 kPa 1 kPa = 0.01 bar1 bar = 14.7 psi 1 psi = 0.068 bar

Energy 1 kpm = 9.81 J 1 J = 0.102 kpm1 cal = 4.19 J 1 J = 0.239 cal1 kWh = 3.60 MJ 1 MJ = 0.278 kWh

Power 1 hp = 0.746 kW 1 kW = 1.36 hp

Conversion tables


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10.3 Temperatures NotesºC ºF ºC ºF

ºC ºF ºC ºF

-17.2 1 33.8 10.6 51 123.8-16.7 2 35.6 11.1 52 125.6-16.1 3 37.4 11.7 53 127.4-15.6 4 39.2 12.2 54 129.2-15.0 5 41.0 12.8 55 131.0-14.4 6 42.8 13.3 56 132.8-13.9 7 44.6 13.9 57 134.6-13.3 8 46.4 14.4 58 136.4-12.8 9 48.2 15.0 59 138.2-12.2 10 50.0 15.6 60 140.0-11.7 11 51.8 16.1 61 141.8-11.1 12 53.6 16.6 62 143.6-10.6 13 55.4 17.2 63 145.4-10.0 14 57.2 17.8 64 147.2-9.4 15 59.0 18.3 65 149.0-8.9 16 60.8 18.9 66 150.8-8.3 17 62.6 19.4 67 152.6-7.8 18 64.4 20.0 68 154.4-7.2 19 66.2 20.6 69 156.2-6.7 20 68.0 21.1 70 158.0-6.1 21 69.8 21.7 71 159.8-5.6 22 71.6 22.2 72 161.6-5.0 23 73.4 22.8 73 163.4-4.4 24 75.2 23.3 74 165.2-3.9 25 77.0 23.9 75 167.0-3.3 26 78.8 24.4 76 168.8-2.8 27 80.6 25.0 77 170.6-2.2 28 82.4 25.6 78 172.4-1.7 29 84.2 26.1 79 174.2-1.1 30 86.0 26.7 80 176.0-0.6 31 87.8 27.2 81 177.80.0 32 89.6 27.8 82 179.60.6 33 91.4 28.3 83 181.41.1 34 93.2 28.9 84 183.21.7 35 95.0 29.4 85 185.02.2 36 96.8 30.0 86 186.82.8 37 98.6 30.6 87 188.63.3 38 100.4 31.1 88 190.43.9 39 102.2 31.7 89 192.24.4 40 104.0 32.2 90 194.05.0 41 105.8 32.8 91 195.85.6 42 107.6 33.3 92 197.66.1 43 109.4 33.9 93 199.46.7 44 111.2 34.4 94 201.27.2 45 113.0 35.0 95 203.07.8 46 114.8 35.6 96 204.88.3 47 116.6 36.1 97 206.68.9 48 118.4 36.7 98 208.49.4 49 120.2 37.2 99 210.2

10.0 50 122.0 37.8 100 212.0

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