PowderTechnologyDivisionBarr-RosinRotaryDryersCoolersandCalciners2RotaryDryersBarr-RosinAsamemberoftheGEAGroup,Barr-Rosinisoneoftheforemostcompaniesinthefieldofindustrialdryingandcooling.Extensiveexperiencehasbeengainedwithawiderangeofthermalprocessingequipmentdesignedtomeetthedemandsofmoderndayprocessindustriesworldwide.WithengineeringandsalesofficesinMaidenhead(nearLondon)andMontreal(Canada),aswellasGEAofficesaroundtheworld,acompleteserviceisavailable-frominitialdesignthroughtofinalcommissioning.EachRotaryDryerinstallationiscustomengineeredtosuittheclientsspecificrequirementsandcomplementsthewellknownrangeofBarr-Rosinfluidbed,ring,flash,columnandRosinairepaddledryers.TheCascadeDryerDespitetheintroductionofnewtechnology,thelongestablishedRotaryCascadeDryerisstillwidelyregardedastheworkhorseofmanyprocessindustries.Therobustyetsimpleconstructioncombinesflexibilitywithreliability,enablingthistypeofdryertohandleavastrangeofmaterialsandtooperatecontinuouslyunderthemostarduousconditions.Thedesignalsopermitstheuseofthehighestpossibledryingtemperaturesandincontrasttootherdryersisnotsensitivetowidevariationsinmaterialsize,moisturecontentorthroughput.PrinciplesofOperationInitssimplestform,thecascadedryerconsistsofaslightlyinclinedrotatingcylinder,fittedwithaseriesofperipheralflightsarrangedtolift,distributeandtransportthematerial.Theflightsaredesignedtosuittheparticularhandlingcharacteristicsofthematerial,whichmayvarywithincreasingdryness.Theprincipleofoperationisbasedonshowering,orcascadingthewetmaterialthroughahotgasstream,flowingeitherco-currentorcounter-currenttothesolids.Thehotgasinducestheevaporationofthemoisture.Theheatlosttothematerialandevaporationofwatervapourreducesthegastemperaturerapidly,suchthatitleavesthedryeratacomparativelylowtemperature.Theefficiencyofthedryerislargelydependantonthedifferentialbetweentheinletandexhaustgastemperatures,althoughtheheattransferrateisalsoinfluencedbytherelationshipbetweenthedesignofflightsandthespeedofrotation.However,irrespectiveofthegasandmaterialtemperaturesthedrying(orresidence)timemaybecritical,asthisisgovernedbytherateofdiffusionofwaterfromthecoretothesurfaceofthematerial.Forspecialapplications,therotarycascadedesignisadaptedtoprovideashortfall,orCruciform,lifterconfiguration.Similarly,RotaryCascadeCoolersandCombinedDryer/Coolersareavailableasrequired.FeedAirHeaterSupportRollersTypicalCo-CurrentDryerInstallation3Thechoiceofdustcollectionequipmentwillvaryaccordingtotheapplication,butinadditiontotherangeofhighefficiencyandhighcapacitycyclones,abagfilter,wetscrubberorscrubber/condensercanbesuppliedasrequired.ToAtmosphereDustCollectionDustDischargeDriveUnitProductDischarge4Co-CurrentPrincipleCo-Currentdryersarethemostwidelyusedandareparticularlysuitablefordryingmaterialscontainingahighmoisturecontent,whichareheatsensitiveorhaveatendencytostickorcake.Thewetmaterialisincontactwiththegasatitshighesttemperature,whichrapidlyevaporatessurfacemoisture.Theinitialheattransferrateishigh,causinganimmediateandconsiderabledropingastemperature,whichpreventsoverheatingofthematerialandthedryershell.Thefinalproductisincontactwiththegasatitslowesttemperature,enablingthemoisturecontenttobereadilycontrolled,usuallybymaintainingthedryerexhaustgastemperatureatapre-setvalue.Counter-CurrentPrincipleCounterCurrentdryersaremoresuitableformaterialsthatmustbedriedtoverylowlevelsofmoisture,wherethelasttracesofmoisturearedifficulttoremove,orwhereanelevatedproducttemperatureisdesirable.Theyarealsousedeffectivelyascombineddryer/preheaters.However,sincethefinalproductisincontactwiththegasatitshighesttemperaturethecounter-currentdryerisoftenunsuitableforheatsensitivematerials.Althoughthissystemcanbemoreefficient,moisturewhichistoremainintheproduct,isnotsoreadilycontrolled.HeatingSystemInbothco-currentandcounter-currentsystems,thematerialisindirectcontactwiththehotdryinggases,whicharenormallysuppliedasproductsofcombustionfromanoil,gasorsolidfuelfiredfurnaceinthetemperaturerange250Cto1000C,asrequired.However,forlowtemperatureandheatsensitiveapplications,orwherecontaminationmustbeavoided,indirectlyheatedaircanbesuppliedviaanelectricorsteamtubetypeexchanger.Thedryernormallyoperatesonatwofan,balanceddraughtsystem,wherebythegasinletismaintainedunderslightlynegativepressuretominimiseairin-leakage.Whendrying(and/orpreheating)materialswhichareunaffectedbyheatorexposuretoaflame,anoilorgasburnercanbearrangedtofiredirectlyintothedrum.Thecombinedeffectsoftheveryhightemperature(800C-1300C)andtheradiationfromtheflame,ensuresmaximumthermalefficiencywhiler