橘皮烘干机的设计设计外文文献翻译Word文档下载推荐.docx
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橘皮烘干机的设计设计外文文献翻译Word文档下载推荐.docx
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556-568.
Abstract:
Citruspeelisanimportantfoodadditivefortheproduction.SouthAfricaistheworld'
sthirdlargestcitrusexportintheworldbutcurrentlynocitruspeelisusedforfurtherprocessing.Incontrast,thestatehadtoimportthesechemicalsfromoverseasdespitethequalityofrawmaterialsourcesintheformofcitruswaste.Becausecitrusfruitsareseasonal,itisnecessarytokeepthesepeelsinuseintheoff-season.Thepurposeofthisstudywastoinvestigatethedrydynamicsoflemonpeelanddisplaydesignstrategiesonindustrialscaledryersbasedonlaboratoryandpilotplanttests.Thelaboratorytestsanddrynessoftheskinwerecrushedintothreedifferentsizes(3,6,and9mm)toprovidedryingtime(15,20,and40minutesat150°
C,and30,35,100and60min°
C)Toachievethedesiredfinalmoisturecontent(10%)peel.Becausetheparticlesareaggregatedandtherelativelylongdryingfluidizedbeddryerhasbeenselected.Afterthesuccessofthepilotplanttesttheinitialdesignofthefluidizedbeddryerrequiredcapacityhasbeendone.©
2007ElsevierAllrightsreserved.
Keywords:
dryfluidizedbeddryer;
foodadditive
1Introduction
SouthAfricaistheworld'
sthirdlargestcitrusexportintheworldbutcurrentlynofoodchemicalsareproducedlocally.Thenewinitiativeisdealingwithlocalandcit-ruswastetoproducevaluablefoodchemicals.Thiscanbeseenasanopportunitytogeneratenewjobsandincomeforlocalcitrusproducers.Becausecitrusfruitsareseasonal,itisnecessarytosavethesepeelsintheoffseason.Thisisdonebyreducingthemoisturecontentofabout85%to10%ofthepeel.Citrusfruitcandiedfruitcanbeusedinbakedgoodsorfastfood.Thedebrisofthepeelisusedforjam.Polysaccharideextractpectincit-russkingellingagentusedinjamandsomecandy.Itisalsotechnicallypossibletoproducesolidwastefromfruitvinegar(fruitwasteuse,2007).
Dryingisanenergy-intensiveprocessthatresultsintheremovalofmoisturefromthebody.Ingeneral,theeffectofthedryingprocessisconsiderabletoexerttheexternalconditionsandtheinternalstructureofthematerialisdry.Thesefactorsaffectthevariousdryingtimesinavarietyof.Therateofheattransferduringmassdryingandthemasstransfermainlydependsonthetransportmechanismoftheboundarylayer,butinthedescendingsectionthecontrolfactorbecomestheadditionalresistancewithinthedrymaterial(strumillowithkudra,1986).
Fluidizedbeddryingtechnologyhasanimportantpositionofthedryingmethod.Thismethodhasbeenwidelyusedingranularmaterials;
butitalsoappliestodrysolutionswherepasteandliquidaresprayedintofluidizedbedinertia.Thefluidizedbeddryerischaracterizedbyaparticleresidencetimedistribution,near-perfectmixing(truewithBaker,1985).Thedryingmethodissupportedbyhotairthroughthemateriallayerlocatedinthegrid(gasdistributor).Ifthespeedofthegasishigherthantheinitialfluidizedbed,thevelocityisgraduallyexpandedtoreachasimilarboilingliquidinacountry.Thisphenomenoniscalledafluidizedbed.Fluidizedbeddryinghasbeenextensivelystudiedintheliterature(offwithJoslinLin,1967;
reduction,1978;
truewithBaker,1985).Kudra,mujum-dar,lata,andkalwar(1992)studiedfluidmechanics,heattransferanddryingcharacteristicsusingatwo-dimensionalspoutedbed.Theyfoundthatdenseparticletransferratesleadtohighheattransferrates,anduniformmoisturecontentandtemperature.Bedtemperature,soitcanbeeasilycontrolled.Itisparticularlyimportantforheatsensitivematerialssuchasinthefoodindustry.However,notonlythethermaldegra-dation(ie,massloss,color,shape,texture,nutrientcontent,etc.)shouldbeconsideredasadryproduct(grain,sugar,fruit,vegetables,etc.)infoodbuttheirsensitivemechanicalstressandProlongeddryingtimeaswell(Grabowskiandmujumdar,1992lewicky;
andReynette,1992;
talburtand,1987).Inthecaseofcitruspeeldrydegradationmayoccurattemperaturesabove150°
Cafter30-40minutesofshort-ratedryingperiod,mostofthedryingprocessattherateofper-iod,bothintermsofgasvelocityanddryareasaffectthepeeldryingrate,Mainlybecausethecontrolmechanismisinternaltothevaportransportintheparticles(ramsunkarandRamdio,2006).Asexpectedtheparticle-to-fluidheattransfercoefficientdependsonthevelocityofthegas,itismoreinthefluidizedbedthaninafixedbed(otheretal.,1985;
supportoriginal,kaguei,andfunazkri,1979).However,inthedryingoffoodproductsthisphenomenonaffectsthedryingrateonlybeforethestartofthedryingprocess,andmasstransitbecomesinternalcontrol.
2.research
Anordinarykitchenequipment(Kenwoodmincer/de-juicer)isfirstremovedwithlemonjuiceandthenpassedthroughthescreenofthreedifferentsizes,namelysmall(3mm),medium(6mm),large(9mm)TheThelaboratoryworkbroughtthetraydryingexperimentfromwhichthedataobtainedwasusedtoproducethedryingratecurve.Alaboratorytraydryer(LabconFSOE-D-8man-ufacturedmarketingservice,throughexperiments,RSA)wasusedtotestattwodifferenttemperatures(150and100°
C).TheskinisevenlydispersedinPetri-monthsandthenplacedinatraydryer.Thenremovethesamplepre-intervalandmoisturecontentfortheinfraredmoisturemeterusingtheinfrared-200(producedbyDenverEquipmentInc.USA).Experimentsindifferentwatercon-tentprovidevalueforthetimeinterval.Thesameprocedurecarriesoutalltheparticlesize.
Seethetestdeviceexperiment(Figure1),indryuseofliquefiedlemonpeelinabatchopenbeddry.Sincecontinuousdryingisimpossibletostayforalongtime,therequiredfigureisusedtotesttheliquefierbeddryer(asopposedtoanindustrialdryer).ThehotairdryerprovidesthecombustionLPG(liquefiedpetro-leumgas)inthecombustionchamber(3),theairvelocityismeasuredbytheairspeedtube(4).Goodfluidizedbedparticlesizeachievesallaveragespeedsof3.5m/s.Allfineparticlesmayescapetrappedinstrongtropicalstorms(7).Theproductcollectstheshotthroughtheexit.22litersupagivensizeisusedforeveryrun.Entertheairtemperatureat150°
Cdryer.Thefinalbedtemperaturereaches110°
C;
adequatesafetytoavoiddamagetotheproduct.Thentakethesampleandholdthecon-tentinthewaterregularlytoevaluateit.Fromtheproductionhistoryexperimentcurve,itisestimatedthateachdevicerunsfor30minutes.
Figure1.Deviceflowchart
-Verygoodcondition,heattransferprocess
-goodmix,thatis,theinformationontheuniformityofthebed
-Bettercontrolofdryingconditionswithintherangeofdryers
-Stayshorter,somoretostrengthenthedry,comparedtootherindustrialdryers
-smaller,comparedtootherindustrialdryers
Inadditiontothegeneraladvantagesthereisalsoagoodexperienceandtheuseofdry-temperaturesensitivematerialsfortheuseoffluidizedbeddryersinthefoodindustryhasaspecificgoal.AllowalongerstaytimeThecontinuousdryershouldbelongenoughtohaveasideofthegranularmaterialforthetravelproduct,asdescribedinFigure4.Theresultsofacomprehensivesizingmachineareamplifiedbythepilotplantdryeraccordingtotheperformanceanalysisofthedesignandpilotplantdryers.Brieflydescribethedesignprocessthroughthefollowingrelationship:
Freshcitruspeeldry(kg/year)=freshskinrequirements(kg/year)*fractionyears(off-season,thatisnotgenerated)
Dryer(kg/h)=freshskinrequirements(kg)/dwelltime(h)
Airflow(m3/s)==fluidizedbedspeed*dryercross-sectionalarea
Enlargementratio=capacityofindustrialdryer(kg/h)/capacityofpilotplantDryer(kg/h)
CrosssectionareaDryer=liquefiedvolumeofbed/0.64
0.64minthepastrelationshipwiththeaverageheightofthebedgeom-etryaccordingtothedryer.SincethecitrusfruitisnotintheyearofApril,thismakestheremainingeightmonths(2/3)ayearneededtodrytheskinthisperiod.Takingadvantageofthisopportunitytobindwiththerequirednumberofannualprocessingrequirements,strippingthedryingduringthisperiodcanbecalculatedtotherequiredcapacitytodeterminetheindustrialdryer.Theabilitytoratetheabilitytoprovideapilotplantdryer---scale.Usethisratiotodeterminethesizeoftheindustrialdryerrequired.
3.Decisionmaking
Traydryingwascarriedoutatdifferenttemperaturesattwodifferenttemperatures(150°
Cand100°
C)inordertodeterminethemoisturecontentoftheskinatdifferenttimesinthedryingprocess.Figure2showsthedrynessofthetrayatadrynessof150°
Cwithaparticlesizeof3mm.TheseconditionsareshowninFig.Thedrycurvesweremeasuredunderdifferentconditionsforthecriticalmoisturecontenttomakedifferentparticlesizesanddifferentdryingtemperatures.Thevaluesobtainedshowthatmostofthedryingprocessoccursduringthedecelerationphase(seeTable1).Thetrialalsoprovidedaconservativeestimateofthetimerequiredtoachievethedesiredwatercontent(about10%),showninTable2.Theheatandmasstransfercoefficientisusuallyhigherinbedthanthetrayisdry.Thesamemassunitdryareaparticlesarenotthesameforthelaboratorytraydryerandthepilotplantbeddryer,butthesedifferencesplaytheroleoftherisingsectionofthedrysectionbutmostofthedryingprocessoccursduringthedecelerationperiod.
Apilotplantwascarriedouttoverifytheresultsofthetraydry.Onlylargepar
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