DRYING

DRYING



PSYCHROMETRIC REVIEW &

EQUIPMENT

SOLIDS DRYING PROCESSES

• OBJECTIVE - REMOVAL OF SOLVENTS FROM

SOLIDS

• CONTACT SOLIDS WITH FLUID NOT SATURATED

WITH SOLVENT

• ECONOMICS

– RECOVER SOLVENT

– AVOID SHIPPING SOLVENT

– MAY AVOID SPOILAGE (BIO-MATERIALS)

• SEE PERRY’S SECTION 12 – SOLIDS DRYING

FUNDAMENTALS

DRYING EQUIPMENT



• CATEGORIES

– BATCH OR CONTINUOUS

– DRYING MECHANISM

• MECHANICAL http://www.grecobrothers.com/centrifugal-

dryers/K94.jpg

• THERMAL

• VACUUM

• FREEZING



http://www.arrowhead-dryers.com/steam-tube-

dryers.html

VACUUM DRYERS



• SHELF ROTARY CONICAL









http://www.mcgillairpressure.com/index.ht

ml

• TRAY/BATCH CONTINUOUS BATCH

• SEE SECTION 11 IN PERRY’S

SHELF DRYERS

• BATCH UNITS

• CIRCULATE AIR PAST TRAYS OF FLUIDS

– OVER (CROSS-CIRCULATION)

– AND/OR PERPENDICULAR TO (THROUGH-

CIRCULATION)

– SEE (FIG. 9.2-1)

• CAN OPERATE UNDER VACUUM

• LONG BATCH CYCLES (4 - 48 HOURS) ARE COMMON

• PRIMARY USES

– Plastics

– Metals

http://www.bocedwards.com/ind

– Chemicals

ex.cfm?ProcessVacuum/pharmac

– Pharmaceuticals eutical-upgrades.cfm~content

– Foods

TUNNEL DRYERS

• MOVE MATERIAL ON BELT OR CONVEYOR THROUGH DRYING

ZONE

• USED FOR A WIDE RANGE OF FREE-FLOWING PARTICULATES

(GRANULAR, FLAKE OR FIBROUS)

• USED FOR PASTES AND FILTER CAKES WITH EVEN APPLICATION

TO BELT

• DRYING TIMES APPROXIMATELY 5 - 120 MINUTES

• LARGE CAPACITY IS PRACTICAL WITH THESE UNITS









http://www.dryer.com/Columbia%20Flyer%2005%20.pdf

ROTARY DRYERS

• KILNS AND CALCINERS

• DROP SOLIDS THROUGH COUNTERCURRENT FLOWING HOT

GASES

• CAN BE LINED WITH REFRACTORY TO ALLOW VERY HIGH

TEMPERATURE OPERATION

• HIGH VOLUME WITH WIDE STABLE OPERATING RANGE

• RESIDENCE TIMES TYPICALLY MEASURED IN MINUTES









http://www.siko.co.id/images/kiln.jpg

DRUM AND WIPED-FILM DRYERS

• DRUM DRYERS

– THIN FILM DRYERS WITH INDIRECT HEATING

– SLURRY APPLIED TO DRUM AND DRIED SOLID REMOVED (SEE FIG.

9.2-4)

• WIPED FILM DRYERS

– INVERSE OF DRUM DRYER WITH INTERNAL WIPER TO APPLY FILM TO

VERTICAL SURFACE

– MATERIAL LEAVING DRYER MUST BE FREE FLOWING

– HIGH THERMAL EFFICIENCY



FEED

WIPED FILM DRYER









FINISH DRYER





http://www.atlascoffee.com/imgz/1br/1br07.jpg

FREEZE DRYERS

• USED FOR

BIOLOGICALS

• USE SUBLIMATION









http://www.niroinc.com/html/ch http://www.pharmaceutical-

emical/freezedryers.html technology.com/contractors/process_automa

tion/telstar/telstar1.html

FLASH OR SPRAY DRYERS

• CONTACT FLOW WITH COCURRENT

FLOW OF HOT AIR

– SOLIDS MAY BE ENTRAINED

– SOLIDS MAY FALL THROUGH AIR

– MAY INCORPORATE CYCLONE

– MAY INCORPORATE SPRAYER TO

PRODUCE SLURRY DROPLETS http://www.oc-

– MAY BE INCLUDED ON TALL TOWER sd.co.jp/english/exampleusage/

(PRILLING) OPERATION index01.html

FLUID BED DRYERS

• SUSPEND SOLIDS IN HOT AIR STREAM

• GENTLE PROCESSING – NO DEGRADATION

• UNIFORMITY OF PROCESS CONDITIONS

• FED SLURRY FROM A CENTRIFUGE

• RECOVER FINES WITH EITHER CYLCONE, FILTER

OR ESP AND RE-SLURRY









http://www.niroinc.com

/html/drying/fluidbed.h

tml

FLUID BED DRYER EXAMPLE









http://www.barr-rosin.com/english/products/fluid-bed-dryer.htm

PSYCHROMETRIC RELATIONSHIPS



• HUMIDITY H

M A pA

(9.3  1)

M B ( Psys  p A )



 M A p AS

• SATURATION HUMIDITY H

M B ( Psys  p AS )

(9.3  2)





 pA

• PERCENT RELATIVE HUMIDTY H R  100

p AS

(9.3  4)





 H

• PERCENT HUMIDITY H P  100 

HS

(9.3  3)

PSYCHROMETRIC RELATIONSHIPS



H

• MOLE FRACTION MA

y  (9.3  14)

1 H



MB MA

• HUMID HEAT



cS  cPB  HcPA (9.3  6)



• HUMID VOLUME  ft  359

3

 1 H 



vH  

 492 T ( R)  M  M  (9.3  7)

– (IG Conditions)  lbm   B A

– vsat at Ĥsat 

 m  22.41

3

 1 H 

 kg   273.2 T ( K )  M  M 

vH  

   B A

PSYCHROMETRIC RELATIONSHIPS

• TOTAL ENTHALPY

– REFERENCED TO T0

 

H y  cPB (T  T0 )  H0  cPA (T  T0 )

– USING (9.3-6)

 

H y  cS (T  T0 )  H0



– FOR AIR WATER @ IG CONDITIONS

• ENGLISH (9.3-8)

• SI (9.3-9)

PSYCHROMETRIC CHART









http://www.thermmax.com/psych-chart.jpg

PSYCHROMETRIC CHART PROPERTIES

• FIXED PRESSURE – STEADY STATE

CONDITIONS

• AXES ARE HUMIDITY & TEMPERATURE

• PLOTS CAN INCLUDE

– PERCENT HUMIDITY

– PERCENT RELATIVE HUMIDITY

– ISENTHALPS

– WET BULB TEMPERATURE

– ISOCHORS

OTHER PSYCHROMETRIC CHARTS

• TEXT FIGURE 9.3-2

– SI UNITS

– ISENTHALPIC PLOTS

• PERRY’S SECTION 12

– LOW, MEDIUM & HIGH TEMPERATURES

– TABLES WITH MORE PRECISE VALUES

– EXAMPLES OF APPLICATIONS TO SPECIFIC

PROCESSES

– SYSTEMS OTHER THAN AIR-WATER

ADIABATIC SATURATION PROCESS

• REFERENCING FIGURE 9.3-3 IN

TEXT

• OVERALL ENTHALPY BALANCE

– Ts = ADIABATIC SATURATION

TEMPERATURE

– Ts =S ENTHALPY REFERENCE

TEMPERATURE FOR MODEL

 

cS (T  TS )  HS  H S S (9.3 10)

• RESULT IS ADIABATIC

SATURATION LINE

  

H  HS cS cPB  cPA H

  (9.3  11)

T  TS S S

WET BULB DETERMINATION

• Tw – WET BULB TEMPERATURE

– A DYNAMIC, STEADY STATE, NON-EQUILIBRIUM

MEASUREMENT OF TEMPERATURE

– ACHIEVED BY FORCED EVAPORATION OF LIQUID INTO THE

VAPOR.

– SLING PSYCHROMETER

– HYGROMETER









http://edis.ifas.ufl.edu/CH182

WET BULB EQUATION

• HEAT BALANCE FOR HYGROMETER

q (kW )  M A N AW A (9.3  12)

'

ky

NA  ( yW  y )  k y ( yW  y ) (9.3  13)

xBM

 

q (kW )  M B k y W ( H W  H ) A (9.3  17)

q (kW )  h(T  TW ) A (9.3  17)





• EQUATING AROUND q YIELDS WET BULB

RELATIONSHIP

 

H  HW h M Bky

 (9.3  18)

T  TW W

WET BULB & ADIABATIC SATURATION

• PSYCHROMETRIC RATIO =

h/MBky LEWIS RATIO

• FOR SYSTEM AIR/WATER

– h/MBky=1

– ISETHALPS = WET

BULB LINE

– WET BULB CAN BE

USED TO MEASURE

HUMIDITY

• FOR OTHER SYSTEMS

– h/MBky≠1

– SYSTEM AIR/BENZENE

– PERRY’S SECTION 12

• WET BULB CAN ALSO BE

MEASURED WITH

WEIGHED DESSICANT