高水分稻谷的分段干燥策略(澳籍专家)

PaddyDryingSystemsBy:MGummertJRickmanAgriculturalEngineeringUnitIRRI,LosBaños,PhilippinesContent•Whydrying•Dryingandquality•Dryingmethods•Mechanicaldryingsystems•DryingstrategiesWhyDrying?•Riceisharvestedathighmoisturecontents20%•Qualitydeteriorationstartsimmediatelyafterharvest•Thewetterthegrainthefasterthelossofquality•DifferentMCfordifferentpurposes(seeTable)PurposeRequiredMCPotentialproblems2-3weeksstorage14-18%Molds,discoloration,respirationloss8-12monthsstorage=13%Insectdamage1yearstorage=9%LossofviabilityMilling14%Damagedgrains,crackingImproperdrying,1•Heatbuild-up–fromnaturalrespiration–excellentgrowthconditionsformoldsandinsects•Molddevelopment–propagatediseasesinthegrain–mayreleasetoxinsintothegrain–properdryingandstoragecanreducepropagationofmolds•Insectinfestation–insectsarealwaysaprobleminstoredgrain–atlowermoisturecontentinsectactivitiesarelower–properdryinghelpskeepinginsectsatacceptablelevel(4insectsperkg)Improperdrying,2•Discoloration/Yellowing–heatbuild-upinthepaddygrainbeforedrying–drasticallyreducesthemarketvalueofrice•Lossofgerminationandvigor–activerespirationdepletesthenutritionreserves–moldsanddiseasescanreducetheabilityoftheseedtogerminate–thelowertheMCatthebeginningofstorage,thelongertheseedremainsviableImproperdrying,3•Lossoffreshness/odordevelopment–Heatbuildup-mustyodorinrice.–Reducesthemarketvalueofrice.–Iffrommycotoxin-producingfungiricemightbecomeunusable.•Reducedheadriceyield–moistureadsorptionofindividualdrygrainswithmoisturecontentsbelow16%-fissuringmixingdrywithwetgrainsExposingdrygrainstohumidair–Fissurescausecrackinginmillingprocess-reducedtheheadricerecovery.Equilibriummoisturecontent(EMC)•Riceishygroscopic•Equilibriummoisturecontent(EMC)–IfgrainisexposedtoairforalongertimeitwillreachEMC–Drygrainwilladsorbwaterfromhumidair–Wetgrainwilldry•Grainproperties–MoistureContent,MC–Temperature•Airproperties–RelativeHumidity,RH–TemperaturePurposeRequiredMCPotentialproblems2-3weeksstorage14-18%Molds,discoloration,respirationloss8-12monthsstorage=13%Insectdamage1yearstorage=9%LossofviabilityMilling14%Damagedgrains,crackingDryingmethodsDryingTraditionalMethods(Sundrying)MechanicaldryingFieldDryingPanicledryingMatdryingHeated-AirDryingLow-TemperatureDryingBatchdryerRe-circulatingBatchDryerContinuousFlowDryerFlashDryingAerationIn/storedryingPavementdryingFielddrying•Whyfielddrying?–Waitingforthethresher–Manualthreshing•How?–Spreadingthecropinthefield–Stacking/piling•Advantages–CanreduceMCby1%perday•Disadvantages–Rapidqualitydeterioration–Shattering–Lossestobirdandrodentswhenspreadinthefield–Heatbuildupandrapidqualitydeteriorationinpiles–Re-wettingfromstrawinpilesItisimpossibletoproducegoodqualitygrainswithfielddryingpractices.Fielddryingshouldthereforebeavoided.Panicledrying•Traditionalmethod–harvestedwithasmallknife(aniani)–paddygrainsthatarestillattachedtothepanicles–fordryingsmallamountsofpaddy.–storedinfarmers’houses,e.g.undertheroofforprotectionfromrodents.•Problems–lowcapacity–grainsinsidethepanicledryslowerthanthegrainsthatareexposeddirectlytothesun.•Tips–turningofthepaniclesimprovesthedryingprocessMatdrying•Paddycanbeplacedonnets,matsorplasticsheets(canvas).•Advantages–Mosthygienicmethod.–lesscontaminationwithstonesandotherdirt–Easycollectionincaseofsuddenrainfalls.–Easymixing•Disadvantagesofnets–dangerofre-wettingofthebottomgrainsfromsoilmoisturePavementdrying•Better-offfarmers,graincollectors,tradersandmillersusedryingpavements–specificallyconstructedfordrying–multipurposes(basketballcourt)•Advantages–highcapacity/economicsofscale–canbepartiallymechanized–toolsformixingandgraincollection–largermillsoftenusetwoorfourwheeltractors•Disadvantages–capitalrequirementsforthepavement–pollutionwithstonesanddirtSundryingandqualityLayerthickness•Spreadthegrainsinthinlayers,ideally2-4cm.•Toothinlayers-heatupveryquickly•ToothickresultinalargemoisturegradientMixinginterval•mixingthegrainisthemostimportantactivityformaintaininggoodquality•Turnorstirthegrainatleastonceperhour,betterevery30minutestoachieveuniformMC.6065707580859001234567Mixinginterval,hRecovery,%55.255.55.7566.256.5DryingTime,hHeadriceMilledriceDryingtimeSource:IRRI,(Gayanilo)Location:PhilippinesIntitalM.C.=24%FinalM.C.=14%74767880828486889001234567Layerthickness,cmRecovery,%33.544.555.566.577.58DryingTime,hHeadriceMilledriceDryingtimeSource:IRRI,(Gayanilo)Location:PhilippinesIntitalM.C.=24%FinalM.C.=14%Tipsforbettersundrying•Management–Layerdepthof4cm–Mixingevery30minutes–Monitormoisturecontent–Monitortemperature•Protection–Coverthegrainwhentemperatureriseabove50-60ºC–Coverduringrain.–Preventcontamination–keepanimalsoffthegrainUsetoolstoimprovesundryingHeatedairdryingComponentsofadryer•Maincomponents–Dryingbin–Airdistributionsystem–Fan–Airheater•Optional–Conveyors•Accessories–Moisturemeter–DustseparatorOptionsforheatedairdryingFixedbedbatchdryerRe-circulatingbatchdryerContinuousflowdryingplantTemperingSectionDryingSectionDryerTemperingbinsInOutAirGrainFixedbedbatchdryer(1)Flatbeddryer•Keyfeatures–BatchCapacity: