DRYING and DRYERS

Objectives , Applications, Mechanism, and Rate of DRYING.
Types of dryers.
Principle, Construction, Working, Pharmaceutical Uses, Advantages and Disadvantages of Tray dryer, Drum Dryer, Spray Dryer, Fluidized bed Dryer, Vaccum Dryer, Freeze Dryer.

1. Drying
University Institute Of Pharmacy
ORIENTAL UNIVERSITY INDORE
Prepared by: -
MANOJ VERMA
3
RD
SEMESTER
Guided by: -
Mr. Rahul Sisodiya SIR
Assistant Professor

2. Highlights
Objectives
Applications
Mechanism of drying process
Measurement and Applications of
Equilibrium moisture content
Rate of Drying Curve
Tray Dryer
Drum Dryer
Spray Dryer
Fluidized bed Dryer
Vaccum Dryer
Freeze Dryer

3. Introduction
Dryingisamasstransfeprocessconsistingoftheremovalofwater
oranothersolventbyevaporationfromasolid,semisolidorliquid.
Thisprocessisoftenusedasafinalproductionstepbeforesellingor
packagingproducts.
Asourceofheatandanagenttoremovethevaporproducedbythe
processareofteninvolved.
Inbioproductslikefood,grains,andpharmaceuticalslikevaccines,
thesolventtoberemovedisalmostinvariablywater.
Dessicationmaybesynonymouswithdryingorconsideredan
extremeformofdrying.

4. DRYING
Thermaldrying
Dryingcommonlydescribestheprocessofthermallyremoving
volatilesubstances(moisture)toyieldasolidproduct.
Non-thermaldrying
1.AsSqueezingwettedsponge
2.Adsorptionbydesiccant(desiccation)
3.Extraction.

5. Objectives
Infoodtechnology,dryingiscarriedoutforoneormorofthefollowing
reasons:
1.Toavoidoreliminatemoisturewhichmayleadtocorrosionand
decreasetheproductstability.
2.Toimproveorkeepthegoodpropertiesofamaterial,e.g.flow
ability,compressibility.
3.Toreducethecostoftransportationoflargevolumematerials
(liquids)
4.Tomakethematerialeasyormoresuitableforhandling.
5.Preservative.
6.Thefinalstepin:Evaporation,Filtration,Crystallization

6. Applications
Food:-
Foodsaredriedtoinhibitmicrobialdevelopmentandqualitydecay.However,
theextentofdryingdependsonproductend-use.Cerealsandoilseedsare
driedafterharvesttothemoisturecontentthatallowsmicrobialstability
duringstorage.
NonfoodProducts:-
Amongnon-foodproducts,someofthosethatrequireconsiderabledrying
arewood(aspartoftimberprocessing),paper,flax,andwashingpowder.The
firsttwo,owingtotheirorganicorigins,maydevelopmoldifinsufficiently
dried.Anotherbenefitofdryingisareductioninvolumeandweight.

7. Applications
Sludgesandfecalmaterialsfromsanitationprocesses:-
Intheareaofsanitation,dryingofsewagesludgefromsewage
treatmentplants,fecalsludgeorfecescollectedinurinedivertingdry
toilets(UDDT)isacommonmethodtoachievepathogenkill,as
pathogenscanonlytolerateacertaindrynesslevel.

8. MECHANISM OF DRYING
Liquiddiffusion:ifthewetsolidisatatemperaturebelowthe
boilingpointoftheliquid
Vapordiffusion:iftheliquidvaporizeswithinmaterial
Condensationdiffusion:ifdryingtakesplaceatverylow
temperaturesandpressures,e.g.,infreezedrying
Surfacediffusion(possiblealthoughnotproven)
Hydrostaticpressuredifferences:wheninternalvaporizationrates
exceedtherateofvaportransportthroughthesolidtothe
surroundings
Combinationsoftheabovemechanisms

9. Measurement and Applications
of Equilibrium moisture
Expressedeitherinwetbasisi.e.massofwaterperunitmassofwetmaterial
ordrybasisi.e.massofwaterperunitmassofdrysolids
EquilibriumMoisturecontent-moisturecontentafterequilibrationwith
specifiedconditionsoftemperatureandhumidity
Waterwithinfoodwillbeeitherboundorunboundtosolids,thisinfluences
thedryingprocessandstabilioy
Boundwaterexertsvapourpressurelessthanthatofliquidwateratthesame
temperature.
Unboundwaterismoistureinexcessofboundmoisture,alsocalledfree
moisture.Heldprimarilyinvoidsofthesolid.

10. Rate of Drying Curve
Thedryingratedependsuponthefollowingfactors-
Vapourpressureofwateratdryingtemperature
Vapourpressureofwaterinexternalenvironment
Equilibriumvapourpressureofwaterinthefood
Moisturecontentoffood

11. Drying rate curve

12. FACTORS THAT INFLUENCE DRYING
1.DryingTemperature-Thisvarieswithfoodandthemethodof
drying,greaterthetemperaturedifferencebetweenheatingmedium
andfood,greatertherateofheattransfer
2.RelativeHumidityofair-Sorptioncharacteristicoffoodtobe
driedshouldbeknown,asEMCisthelowestmoisturecontentthat
canbeachievedundergivensetoftemperatureandhumidity
conditions.
3.Velocityofair-Higherthevelocityofair,moreefficientthe
processofdrying
4.DryingTime-Dryingtimedependsuponthetypeoffoodandits
moisturecontentandtemperature

13. Difference between drying
&evaporation

14. Tray Dryer
AboutTrayDryer
Traydryeristhedevicewhichisusedfordryingofthewetproducts
ofthecrudedrugs,chemicals,powdersorthegranulesetc.
Thematerialwhichneedstoagitate,arenotdriedintraydryer.
Traydrierisusedindustriallyinlargeaswellasinsmalloperations
fordryingthedesiredfeedmaterialforfulfillingouraspects.

15. Tray dryer
CONSTRUCTION
1.Itconsistofrectangular
chamberofsheetmetal
containingtwotrucksthat
supportracksH.
2.Eachrackcarriesanumber
ofshallowtrays,perhaps750
mm2and50to150mmdeep,
thatareloadedwithmaterialto
bedried.

16. Tray dryer
3.Heatedairiscirculatedat2to5m/s
b/wthetraysbyfanCandmotorDand
passesoverheatersE.
4.BafflesGdistributetheairuniformly
overthestackoftrays.
5.Somemoistairiscontinuously
ventedthroughexhaustductB;makeup
freshairentersthroughinletA.
6.Theracksaremountedontruck
wheelI,sothattheendofthedrying
cyclethetruckcanbepulledoutofthe
chamberandtakentoatray-dumping
station.

17. Tray dryer
WorkingOfTrayDryer
1.WetsolidisloadedintothetraysandTraysareplacedinthechamber.
2.Freshairisintroducedthroughinlet,whichpassesthroughtheheaters
andgetsheatedup.
3.Thehotairiscirculatedbymeansoffansandthenwaterispickedupby
theair.
4.Theseeventsoccurinasinglepassofair.Thetimeofcontactisshort
andamountofwaterpickedupinasinglepassissmall.
5.Attheendofthedryingtraysortrucksarepulledoutofthechamber
andtakentoatraydumpingstation.

18. Tray dryer
Advantages
1.Traydryerareveryusefulwhenthe
productionrateissmall.
2.Theyfindmostfrequentapplicationfor
valuableproductslikedyesand
pharmaceuticals.
3.Inthetraydryersthehandlingofthe
materials,loadingandunloadingofthe
materialscanbedonewithoutlosses.
4.Energysavingissignificant.
Disadvantages
1.Traydryersrequiresmore
labourtoloadandunload,hence
increasesinthecost.
2.Theyareexpensivetooperate.
3.Dryingbycirculationofair
acrossstationarylayerofsolidis
slow,anddryingcyclesarelong:
3to48hourperbatch

19. Drum Dryer
Principal:
•Materialondrum&dried.
Construction:
•HollowsteelDrum
•Feedpan
•Spreader
•Doctor’sknife
•Storagebin(Aconveyor)

20. Drum dryer
Working:
•Steamindrum-drumisrotated–throughfeedpan.
•Materialadheretopan-thinlayerform.
•Materialdryduringrotation.
•Doctor’sknife-Drymaterialisscrap–fallinstoragebin.
Application:
•Fordrying-solutions,slurries,Suspensions,
milkproducts,starchproducts,antibiotics,
varioussubstancesetc,.

21. Drum dryer
Advantages:
•Suitableforheatsensitivematerials.
•Compactsize.
•Completedrying.
Disadvantages:
•Highmaintenancecost.
•Skilledoperatorrequired.
•Notsuitableforlesssolublesaltssolutions.

22. Spray Dryer
Principal:
•Materialtofinedroplets-moving
streamofhotgas.
Construction:
•Largecylindricaldryingchamber.
•Inletofhotair&atomizer-InRoof.
•Connectedtoacycloneseparator.

23. Spray Dryer
Working:
1.Atomizationoftheliquid:Liquidfeed-intochamberthrough
atomizer.
2.Dryingofliquiddroplets:Duetohotairdrying.
3.Recoveryofdriedproduct:Recoveryinlaststep.
Application:
•Fordryingoflargequantitymaterial.
•Dryingofthermo-labile,hygroscopicmaterial.
•Dryingofmedicinelikechloramphenicol.

24. Spray Dryer
Advantages:
•Veryrapid&continueprocess.
•Lowlaborcost.
•Givesproductofuniformsphereform
&finedroplet.
•Suitableforsterileproducts
Disadvantages:
•Verybulky&expensive.
•Hugeequipment(noteasytooperate)
•Lowthermalefficiency.

25. Fluidized bed Dryer
Principal:
•Hotair-troughbedofgranules.
•Granulesliftedfrombottom&suspendinair(Fluidizedstate).
Construction:
•Fluidizedbeddryer-steelorplastic.
•Detachablebowl-perforatedbottomwithwiremesh-supportmaterial.
•Fan-upperpart-circulateair.
•Freshairinlet/pre-filter/heatexchanger-toheatair.
•Bagfilters-collectfine

26. Fluidized bed Dryer

27. Fluidized bed Dryer
Working:
•Materialload–detachablebowl.
•Freshenter–inlet-heater-hotair-throughbed-withoptimumvelocity.
•Particlesuspend-fluidizedstate-dryingtakesplace.
Application:
•Dryingoftabletgranules.
•Suitableforotherprocesstomixingetc.
•Modifiedform–useforcoatingofgranules.

28. Fluidized bed Dryer
Advantages:
•Fastprocess.
•Availableindifferentcapacity.
•Easyhandling,reducelaborcost.
•Highthermalefficiency.
•Suitableforapplyinghightemp.
•Suitableforthermo-labilesubstances.
Disadvantages:
•Developselectriccharges.
•Attritionmayoccur.

29. Vaccum Dryer
Principal:
•Drying–byapplicationofvacuum.
Construction:
•Ironheavyjacketedvessel.
•Hallowshelves.
•Metaltrays.
•Oventovacuumpump.

30. Vaccum Dryer
Working:
•Materialoftrays-placedonshelves.
•Pressuredecreasedbyvacuumpump.
•Steam/hothair-intojacketofshelves.
•Dryingwilltakesplace.
Application:
•Dryingofheatsensitivematerial,dustyhygroscopicmaterial,
•Drugscontainingtoxicsolvents.

31. Vaccum Dryer
Advantages:
•Easyoperating
•Easyforbatchprocessofdifferentcompounds.
•Variousmodescanbeusedforheating.
Disadvantages:
•Lowheattransferefficiency.
•Limitedcapacity.
•Moreexpensive.

32. Freeze dryer
Principal:
•Dryingbysublimation-triplepoint-temp.&pressurebelowtriplepoint.
Construction:
•Dryingchamberintrays.
•Heatingcoils.
•Vaporcondensingoradsorptionsystemwithrefrigerator.
•Vacuumpump.

33. Freeze dryer

34. Freeze dryer
Working:
1.Preparation&pretreatment:vacuumayvacuumtraydryers
2.Pre-freezingforsolidifyingwater:cold(-50oC)
3.Primarydrying(Sublimationoficeundervacuum):at0.0098oC&
0.533kilopasals.temperatureisincreasedto300Cwithin2hours.
Thentemperaturekeptconstant.around98to99%wateris
removed.
4.Secondarydrying(Removalofmoistureathighvacuum):temp
as50to60oC&lowvacuum.
5.Packing:airreplacewithgasandseal.

35. Freeze dryer
Application:
•Forproductionofdosageformsas
injections,solutions,suspensions.
•FordryingofBloodplasmaandits
fractionatedproducts,Bacterial&
viralcultures,Humantissue,
Antibiotics,Steroids,Fooditems
(Prawnsetc)

36. Freeze dryer
Advantages:
•Suitableforthermo-labilematerial.
•Lossofvolatileisless.
•Nomigrationoccurs.
•Suitableformoisturesensitivematerial.
•Sterilitymaintain
Disadvantages:
•Highcosts.
•Timeconsuming.
•Oxidationmayoccurs.