HANDBOOK OF SOLID FERTILISER BLENDING - Code of Good Practice for Quality 1 EUROPEAN FERTILIZER BLENDERS ASSOCIATION HANDBOOK OF SOLID FERTILISER BLENDING Code of Good Practice for Quality Third Edition Edited by Jo Gilbertson and Estelle Vallin 2016 www.european-blenders.org 89 rue Magenta 53000 LAVAL, France This handbook is also available in French or German
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Fertiliser production, marketing and use - HANDBOOK OF SOLID … · 2019. 11. 25. · This Handbook of Solid Fertiliser Blending has been prepared by the European Fertilizer Blenders
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Blendedfertilisershavethreemainadvantagesovercomplexfertilisers. Thefirstisthatofversatility,thesecondisasimplematterofeconomicsandthethirdisabetterprotectionoftheenvironment.Usingalimitednumberofbasematerials,analmostinfiniterangeofcompoundscanbeproduced.These can be specificallymatched to local soil conditions and plant needs, thus avoiding excessnutrientswhichmayentertheenvironment.Multiplehandlingof thebasicrawmaterialssuchasphosphaterock, isavoidedbymaintaining theprimaryproductionprocessesat thesourceof thenutrients. Thematerialswhichthenneedtobetransportedtotheagriculturalareascontainthehighestpossibleamountsofnutrients,thusreducingoverallcosts.
Themaindisadvantageofblended fertilisers, incomparisonwithcomplex fertilisers, is theriskofsegregationofthecomponentsduringhandlingorspreading. However,thisbookshowshowtoavoidsegregation.
There isacleareconomicbenefit tosuppliersandusersalike in improvingthequalityofblendedfertilisers. Poorqualityproductscanhaveseriousconsequences,bothlegalandfinancial.
Blending can be considered to be a complete system provided for the farmer, startingwith soilsampling,analysingitsnutrientrequirements,andfinishingwiththeaccuratespreadingofthecorrectblendofnutrients.
Throughoutthishandbookthegeneraltermsblendandblendingareusedtodenotetheproductandtheprocessofmixinggranularmaterials. Blendedfertilisersmaybesuppliedtofarmersinbagsorin bulk. The term bulk-blend is reserved for situations where the blend is handled (stored,transported)inbulkratherthaninbags.
Note: Some of these materials are not the basic source materials which provide the nitrogen,phosphateandpotash. Inthesecases,theyareoftenknownasintermediatesorpre-mix.
Straight fertiliser: Qualification generally given to a nitrogenous, phosphatic or potassic fertiliserhavingadeclarablecontentofonlyoneoftheplantnutrientsnitrogen,phosphorusorpotassium.
Note: It is possible for a straight fertiliser to be a blend. For example a mixture of granularammoniumnitrateandgranularammoniumsulphatewouldbeastraightnitrogenfertiliser.
Every rawmaterial should be bought to as tight a specification as possible. Deliveriesmust becheckedregularly,preferablybyindependentinspectors,toensureconsistentquality.Allsamplingandtestingshouldbecarriedoutusingmethodsagreedbetweensupplierandpurchaser,basedeitheronNationalorEuropeanlegislationoronacceptedInternationalStandards(CEN,ISOetc.). Moreinformationaboutsamplingwillbefoundinsection8.
Whilstmany fertiliser rawmaterialsmaybeconsideredtobecommodities, rather thanspecialitychemicals, theopportunisticpurchaseof spotconsignmentsofdoubtfuloriginandquality isNOTRECOMMENDED.Norawmaterialshouldbepurchasedwithoutanagreedcontractualspecificationcovering,asaminimum,theregistrationtoREACH,thechemicalanalysisandtheparticlesizedetails.
3.1 CHEMICALPROPERTIES
Thenutrientcontentofeachrawmaterialusedmustbeknowninordertoprepareformulationsfor the different compounds required. Raw material suppliers should be asked to supplycertificatesofanalysisforeachlargeconsignment. Whereconsignmentsdiffermarkedlytheyshouldbestoredseparatelyandtheformulationsadjustedtotakeaccountofthetrueanalysisfigures(seeChapter9)
In all cases it is advisable tomakeoccasional randomchecksby arranging for representativesamplestobetakenbyindependentinspectors. Thesesamplesshouldbeanalysedassoonaspossibleandbeforetheconsignmentisused.
Fromthechart,itisclearthatureaandammoniumnitrateshouldneverbeusedtogetherasthemixturewillquicklybecomewetandabsorbmoisture. Blendscontainingureaandsingleortriplesuperphosphatemayalsobecomestickyandcake. Suchblendsshouldneverbebagged. Mixtures of di-ammonium phosphate and superphosphates should be avoided as chemicalreactionsmaytakeplacewhichcanleadtocakingorchangesinthesolubilityofthephosphate.
Themost important physical property - as far as blending is concerned - is the particle sizedistribution.
Theparticlesizedistributionmustbeknowninsomedetailandthespecificationmustincludeafulldescriptionofthisproperty. Attheveryleast,themeanparticlesize(asmeasuredbythed50)mustbespecified. Ideally,thespecificationshouldincludeameasureofthegranulometricspread index (GSI) and shouldalso includemaximumvalues for theamountsofoversize (forexample>5mm)andfines(forexample<1mm).
In all cases it is advisable tomakeoccasional randomchecksby arranging for representativesamples tobe taken and assessedby independent inspectors. It is also recommended thatsamplesbetakenduringthedeliveryandtestedforsizedistributionattheblendingplant.SeeSection5.4)
The official method of test sieving is fully described in European Standard EN 1235 andAmendment A1 [3]. A number of numerical parametersmay be calculated from the sieveanalysis. Theseincludethemeanparticlesize(d50)andgranulometricspreadindex(GSI). Inviewoftheimportanceofsizedistribution,fulldescriptionsoftheseparametersandtheuseofthevarioussystemsaredescribedbelow.
The density of the fertiliser can have an influence on the behaviour of the particles duringspreadingonthefield. Severesegregationmayoccur if thedensitiesareverydifferent (seesection5.3).
Generally,theloosebulkdensityoffertilisersisbetween900and1100kg/m³butextremevaluescan be between 750 and 1350 kg/m³. In practice these extreme values rarely occursimultaneously.
Duringhandlingandspreading,thefertiliserwillbesubmittedtostresseswhichcanbreaktheparticles,forexampletheimpactwiththevanesduringspreading. Thisprocessleadstotheproductionofsmallgrainswhichcausesomeproblems(segregation,caking). Forthisreasonthe particles should be of a sufficient hardness. Unfortunately, the test methods are notstandardised because of the variability of the measurement and the evolution of theseparameterswithtime. Iftheparticlehardnessislow,thefertilisermaycontaintoomanysmallparticlesandthusmaynolongermeetthequalitycriteria(seesection5.4).
Somefertiliserrawmaterialsarehygroscopicwhichmeanstheycanpickupmoisturefromhumidair. Storesholdingthesematerialsshouldbeair-conditionedorthematerialshouldbecoveredwhennotbeingused. Figure2showsthecriticalrelativehumidityforanumberofcommonblendcomponentsandmixtures.Thelowerthecriticalrelativehumidity,themoremoisturewillbetakenfromtheair. Generallythephosphatesincludingtheammoniumphosphateshaveahighcriticalrelativehumidityand thus almost never present hygroscopic problems. The opposite applies to nitrates such ascalciumammoniumnitrate,ammoniumnitrate,andespeciallycalciumnitrate.
Forblendedandcomplexfertilisersthecriticalrelativehumidityinmostcasesisbelowtheaveragederivedfromitscomponents. ThiscanbeseenwhenlookingatthedataforPKandNPKfertilisers. Anextremeexampleforthisisdemonstratedbythecriticalrelativehumidityofablendconsistingofurea and ammoniumnitrate. Such ablendwouldpickupmoisture soquickly that itwouldbeimpossibletohandleitinadrystate,evenifspreadingoccursimmediatelyafterblending.
Goodhousekeepingisvitaltoanyblendingoperation.Allspillagesshouldbesweptupassoonaspossible andall equipment kept clean. Overhead conveyorsmustbe kept in good condition tominimise spillage into other storage areas. Theuse of special chutes to avoid excessive dust isstronglyrecommended.
It is relatively simple to add micronutrients to blended fertilisers either as granular or powdermaterials, but the homogeneity of distribution is particularly important. As a guide, granularmaterialsshouldnotbeusedifthemicronutrientcarrierrepresentslessthan5%ofthetotalweight. Inthesecasesitispreferabletoaddthemicronutrientinpowderformwithabindingagenttoensuregoodadherencetothegranules.Suitablebindingagentsincludeheavyviscosityoils,UANsolutionsandwater. Alternatively,themicronutrientsmaybeaddedasasolutionwhichissprayeddirectlyontotheblendinthemixer. Notehowever,thatoilshouldnotbeusedwhenammoniumnitrateformspartoftheformulation.
Anti-cakingagentsarenotnormallyrequired if theproduct is tobeused immediately. Productswhicharetobestoredorbaggedmayrequiretheadditionofasmallamountofanti-cakingagent. Itisrecommendedthatadust-suppressantisaddedtotheblend.
The choice of design will depend on individual circumstances and is outside the scope of thishandbook. However,oneaspectofmixingwhichisofimportanceisthemixingtime.Mixingtimesarenormallyaroundtwominutesandtimesabove5minutesarenotrecommendedbecauseoftheriskofparticlebreakdownanddeteriorationofthemixingquality.
Segregation is the separation of particles due to differences in physical characteristics. Forsegregationtotakeplacetheremustbemovementbetweentheparticles.
Variouscharacteristicsmaycausesegregationbutthemostcommonareparticlesize,particledensityandparticleshape. Thesize iscertainlyby far themost important factortoexplainsegregationduringflow. Duringspreading,thethreepropertiesplayarole,theshapebeingtheleastimportantandthesizeagainhavingadominatingeffect.
From the above it is seen that segregation may occur during manufacture, bulk transport (andhandling)orduringapplicationtothesoilorcrops. Theeffectsasseenbythecropsmaybethesameinallcasesunlessremixingtakesplaceduringlaterhandlingstages.
“Thetwomainfactorsareavoidanceofsegregationinfillingandemptyingandensuringthehopperwillbe“self-clearing.” Inexaminingthequestionofsegregationinfilling…ifthematerialischargedintothehopperfromasinglepoint,thecoarserparticleswillmigratetotheouteredgesandacentralcoreofmaterialcontaininganexcessoffineswillform. Ifnowfillingisdiscontinuedandthehopperisallowedtodischargeitwilldosoinzones…Ifthezonescontainparticlesofdifferentsizesduetosegregation in filling,nodevice fittedat theconedischargetoremixcanpossiblybeeffective. Ifhowever,thehopperisfilledwithoutsegregation,littlesegregationwilloccurwhenemptying.”
By applying the above to blending, it can be seen that the avoidance of segregation and thesubsequenthandlingoftheproduct,isthemostimportantpartofanyblendingprocess. Thismaybeachievedinthreeways:
1 Thecarefulmatchingoftheblendcomponents
2 Thedesignofhoppers(seeLeonard[19])
3 Theloadingmethodsofthehoppersandvehicles,etc.
The origin of the segregation is always a difference of physical properties leading to a physicalseparationoftheparticleswhichmayormaynotresultinachemicalsegregation. Sizesegregationmayalsooccurwithinrawmaterialsorcomplexfertilisersbutthiswillhaveno(orverylittle)effectonthe chemical content. However, in bulk blends, physical segregation often leads to chemicaldifferences.
5.1 FLOWSEGREGATION
Care must be taken when storing any material to avoid size segregation in the storage heaps. Whenevergranularmaterialfallsfreelytoformaconeorpartcone,thelargerparticleswilltendtorundowntheoutsidewiththesmallerparticlesremainingnearthecentreofthecone. Shouldthishappen,theremaybequitelargevariationsinsizecharacteristicsbetweenvariouspartsofaheapandthiscouldhaveseriouseffectsonallfertilisers(Figure3). Batchestakenfromasegregatedheapcan
Theremaybesomeremixingatlaterhandlingstages. Suchremixingmaybecausedsimplybytippingabagoffertiliseroutintoahopperorevenmoresimplybyturningalooselyfilledbagover. Remixingmay also occur during loading and unloading of bulk fertiliser (Figure 4). However, systematicremixingcanrarelybecountedon.
Itisoftensaidthatblendsaresubjectedtoserioussegregationduringvehicletransportbutthisisnottrue. Thelevelofvibrationintransportvehiclesisnothighenoughtoinduceamovementofthefertiliser. In fact, the segregationoccurswhen filling (andemptying) the container asdescribedabove.
Blenders should have some knowledge of the kinds of spreading equipment available and theadvantagesanddisadvantagesofthesewhenusingblendedfertilisers. Blendersshouldbepreparedand able to advise farmers on the type of equipment to use and the setting up, calibration andmaintenancenecessary. Thismeansthattheyshouldbepreparedtogiveasmuchinformationaspossibleaboutthephysicalqualityoftheirproducts.Suchinformationmayincludethecomposition,bulkdensityandflowcharacteristicsaswellastheparticlesizedistribution. Thisisanotherreasonforkeepingadequaterecordsofrawmaterialsandproductbatches.
Centrifugal, pneumatic, and auger spreaders are available. The segregation inducedbyphysicaldifferencesofthefertiliserparticlesmaybeduetotrickling,asisthecasewithaugerspreaders,ormaybecausedbytheaerodynamicresistanceoftheparticleswhenthrownthroughtheair,aswithcentrifugalandpneumaticspreaders.
0 10 20 30 40 50 60 70 80
Difference between raw materials (absolute sum of difference d16 and d84/d50mel)
Auger spreaders will segregate heavily. Since these spreaders, when correctly adjusted have arectangularlateralmassdistribution,nooverlappingoccursandthusalsonoreductionofsegregationtakesplace. Forthisreason,augerspreadersarenotrecommendedforblendedfertilisers. Furtherinformationmaybefoundinreference[2].
InWestern Europe, themost common devices are centrifugal spreaders with two discs. Theirworkingwidths(widthbetweentractortracks)varybetween12andmorethan36m. Thespreadingwidthcanreachmorethan50m.
Segregationoccursduring spreadingdue tophysical differencesbetween the componentsof theblended fertiliser. The larger,heavierandmore spherical theparticlesare, the further theyarespread. Thesizeanddensityarethemajorfactors(Figure8,Figure9andFigure10).
In practice, the components present differences for more than one physical property and eachdifferencecanaccentuateorreducethefinalsegregation. Forexample,sizedifferencebetweencomponentscancompensateforadensitydifferenceandviceversa. Thelarger,heavierandmoresphericaltheparticlesare,thefurthertheyarespread. Forexample,ureawhichhasalowdensityincomparisonwithother fertilisersshould ideallyhave largesizedparticleswithad50near themaximumtoleranceinordertolimitspreadingsegregation.
The final impact of segregation during spreading can be significantly reduced by appropriateoverlappingbetweenthepasses. Indeed,thesegregationisgenerallymarkedinsuchawaythatonecomponenttendstoaccumulatebehindthespreaderandanothertendstobespreadfurther. Iftheoverlappingbetweenthepassesissufficient,ateachplaceinthefieldthefinalquantityoffertilisercomesfromtwopasses(Figure11,topandcentre). Withagoodspreadercorrectlyadjusted,itisevenpossible forworkingwidthsup to24or28m. However, forbadlyadjusted spreaders thesegregation remains. Practically,acorrectoverlappingmeans that thespreadingwidthmustbeaboutdoubletheworkingwidth. Sowithaworkingwidthof24m,itmeansthatthespreadingwidthmustapproach48m. Figure11,below,showsanexampleofinsufficientoverlapping,resultingfromaworkingwidthwhichismuchgreaterthanhalfthespreadingwidth.
0% 20% 40% 60% 80% 100%
Elongation (shape) difference between raw materials (%)
Toreducesegregationproblems,itisrecommendedtoblendrawmaterialshavingsimilarphysicalproperties, themost importantbeing thesizeof theparticles. TheEuropeanFertilizerBlendersAssociation (EFBA) has defined quality recommendations for the particle sizes (Table 2). Therecommendationsconcentrateonad50around3,25mmwithalimitedgranulometricspreadindex(GSI). Iftherawmaterialscomplywiththeserecommendations,flowsegregationisnotsignificantandspreading segregationonlyoccurs if thereare importantdensityand/or shapedifferences. Thishappensonlywhencertainspecificfertilisersareused.
Blendersmustbeawareofthehazardsassociatedwithrawmaterialsandfertilisers,especiallythosecontaining ammonium nitrate. Recognition of the hazards is made simpler by classificationsystemssuchas thosepreparedby theUnitedNations (UN), InternationalMaritimeOrganisation(IMO)andtheEuropeanCommission(EC). AllproductsmustbelabelledaccordingtoNationalandEuropeanRegulationsandinsomecircumstancesonlypackagedfertilisersmaybesuppliedtotheenduser.
P305+P351+P338 : IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses if present, and easy to do. Continue rinsing.
P310: Immediately call a POISON CENTRE or doctor/physician.
xx kg net Company name, address, phone number
Name, address, phone number of supplier(s)
signal word, hazard and precautionary statements
Nominal quantity of fertiliser in packaging
(except if mentioned elsewhere on the packaging)
Product identifiers
Hazard pictogram (in colour, covering at least 1/15th of the label, minimum size 1 cm²)
Type denomination name Name and identification number of hazardous substances contributing to classification (4 max except if > 4 hazard classes, then à 1 for each hazard)
Asmentioned in section 3.2, theparticle size distribution of the rawmaterials is themostimportantpropertytobecontrolled. RepresentativesamplesofrawmaterialfeedsshouldbetakenandtestedasdetailedinChapter8atregularintervalswithaminimumfrequencyofoncepershift.Afullsieveanalysisshouldbecarriedoutoneachrawmaterial.
7.2 FINISHEDPRODUCTS
AllblendershaveanobligationtomeettherequirementsoftheirNationalFertiliserRegulationsandforthosefertiliserswhicharemarketedasECfertilisers,commonRegulationEC2003/2003[25]applies throughout theCommunity. NationalRegulationswill coverproductswhicharenot declared as EC fertilisers. It should be noted that in caseswhere the farmer does notpurchasea fertiliserwitha specifiednutrient ratio, forexample, ifhepurchaseshisownrawmaterialsandcontracts theblender tomix them forhim,allofficial controls for theblendedfertilisermaynotapply.
The regulations set out the tolerances on the declared chemical analysis for all fertilisers. Fertilisersnotmeetingthesetolerancesmayresultinprosecutionandpenalty. Itisthereforerecommendedthatsomedegreeofqualitycontrolisexercisedbyblenders(auto-control).
The amount of quality control requiredwill depend verymuch on the scale of the blendingoperation. Forsimplesmallscalebatchblendingoperationsitmaybesufficienttorelyontheprinciplethat“whatgoesinmustcomeout”. However,eventheseoperationswillneedsomeregularcontroloftheweighingequipment.
Inbetweenthesetwoextremes,itisrecommendedthatonerepresentativerandomsampleistakenfromoneofthegradesmadeeachday. Iflaboratoryfacilitiesareavailableonsite,thesesamples should be analysed daily. If outside contract laboratory services are used, thefrequencyofanalysis shouldbeat leastone sampleperweek, selectedat random from theweek’scollection.
Representative sampling of any material requires special techniques and equipment. Fulldetails are outside the scope of this handbook but it is recommended that blenders followrecognisedsamplingmethodssuchasthosesetoutinEuropeanStandardEN1482Part1[9].
Itisessentialthatallsamplesarecorrectlytakentoensuretheirrepresentativity. Thereisnopoint in taking and analysing unrepresentative samples. The quality of the measurementsmade on the samples depends on their representativity. This is particularly important forblendedfertiliserswheretheriskofheterogeneityishigher.
AsstipulatedbyCEN,blendedsamplesmustalwaysbetakenfrommaterialinmotion,eitherinfreefalloronconveyorsystems.Itisessentialtosamplethroughthewholestreamratherthanfrom the same part of the stream. Suitable automated equipment is available for mostcircumstancesandistoberecommendedwheneverpossible.
Fortheblendproduceritisimportanttoknowthesamplingandmeasurementmethodsandthenecessary equipment. Generally, all of this is described in standards which are regularlyupdated.Blendersarerecommendedtostudythelatestversionsofsamplingandmeasurementstandards.
NumberofbagsMinimalnumberofincrements<5bagsAsamplefromeachbag4<numberofbags<114bags10<numberofbags<401Wholenumberabove thesquare rootof the
numberofbags>400bags20bags
If theweightofabag is less than5kg,a completebag is consideredasa sub-sample. Thenumberofselectedbagscanbehigherifthefinalquantityofthesampleisnotsufficient. Forbagsof50kg,thecontentmustideallybedividedinordertoobtainarepresentativesample(seeparagraph8.1.3). SamplingthecontentsofanIBC(bigbag)isnoteasy. Thebestsolutionistosampleduringemptying,butthisisnotalwayspossible. FurtherinformationisgiveninEN1482Part1.
Appropriate samplingequipment is essential. Thereare various automated systems forusewithconveyorbelts. Thesearecertainlyrecommendediftherearelargeamountsoffertiliserhandled. Forsmallerdeliveries,manualsamplingismoresuitable. Asuitabletypeofsamplingcup is described in EN 1482 Part 1 [9] and is essential for sampling from falling streams ofmaterials(Figure15). Informationaboutthenumberofincrementstobetakenmustbegiventotheoperator(Table6).
Standardreferencetestmethodsformostofthecommonchemicalanalysesusedforfertilisermaterials may be found in EC Directives, National Standards, European and InternationalStandardsandtheAOACMethodsofAnalysisHandbook. Itisnotessentialthatthesemethodsare used for routine process control and simpler, often automated, methods are available. However,allsuchmethodsmustbeevaluatedagainstoneoftherecognisedstandards.
8.3 PHYSICALTESTS
Recognisedstandardtestmethodsexistforseveralphysicalproperties.Theinterestofblendersshould focus on test sieving and bulk density (see section 3.2). Some laboratories have anaccreditation for these special measurements. No Standard methods are available for such
Sumthemassesofthefractionsretainedonthesievesandinthereceiverandcheckthat the total mass is within 2,5g of the original mass. Calculate each fraction mass as a percentage of the sum of the masses and draw up a table showing the cumulative percentagepassingeachsieve.
Placethesampleoffertiliserinthefunnelwiththeapertureclosed. Weightheemptycylinderandplaceitunderthefunnel. Opentheapertureofthefunnelandallowthefertilisertoflowintothecylinder. Whenthecylinderisfull,closethefunnelandremovethe excess fertiliser above the cylinder with a spatula. Weigh the cylinder and itscontentsandcalculatetheweightoffertiliser(minkg).
Thissectiongivessomeexamplesoftheresultsofphysicaltestsonfertilisers. Thedatausedare realistic but the actual physical properties will vary considerably for the same productdependingonitsorigin[14].
With the sieving test data, it is possible to determine the mean particle size (d50) and theGranulometricSpreadIndex(GSI). Thed16isjustunder3,15mm,thed50isbetween3,15mmand3,55mmand thed84 isbetween3,55mmand4,00mm. Theuseof theequation (seeparagraph3.2.1)leadstothefollowingresults:
14 Guillon D. Enquête granulométrique sur lesmatières premières pour les engrais de mélange.RencontresInternationalesdel’AFCOME,Strasbourg,novembre2003.
15 Heege H. Quality of raw materials for fertilizer-blends: defining a standard. RencontresInternationalesdel’AFCOME,Strasbourg,novembre2003.
20 Miserque O. Analyse de l’influence des caractéristiques physiques des particulesd’engraissurlecomportementdesmélanges. PhDthesis–UniversityofLiège,FacultyofAppliedSciences-Belgium–2005.
23 Regulation1272/2008/ECoftheEuropeanParliamentandoftheCouncilonclassification,labellingandpackagingofsubstancesandmixtures,amendingandrepealingDirectives67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006 OJ353/131.12.2008andimplementinglegislation
24 Regulation1907/2006/EC of the European Parliament and of the Council on theRegistration, Evaluation, Authorisation and Restriction of Chemicals (REACH)OJ396/130.12.1996andimplementinglegislation