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• THERMAL• VACUUM• FREEZING
http://www.grecobrothers.com/centrifugal-dryers/K94.jpg
http://www.arrowhead-dryers.com/steam-tube-dryers.html
VACUUM DRYERS
• SHELF ROTARY CONICAL
• TRAY/BATCH CONTINUOUS BATCH• SEE SECTION 11 IN PERRY’S
http://www.mcgillairpressure.com/index.html
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– Chemicals– Pharmaceuticals– Foods
http://www.bocedwards.com/index.cfm?ProcessVacuum/pharmaceutical-upgrades.cfm~content
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
WIPED FILM DRYER
FINISH DRYER
FEED
http://www.atlascoffee.com/imgz/1br/1br07.jpg
FREEZE DRYERS
• USED FOR BIOLOGICALS
• USE SUBLIMATION
http://www.pharmaceutical-technology.com/contractors/process_automation/telstar/telstar1.html
http://www.niroinc.com/html/chemical/freezedryers.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– MAY BE INCLUDED ON TALL
TOWER (PRILLING) OPERATION
http://www.oc-sd.co.jp/english/exampleusage/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.html
FLUID BED DRYER EXAMPLE
http://www.barr-rosin.com/english/products/fluid-bed-dryer.htm
PSYCHROMETRIC RELATIONSHIPS
• HUMIDITY
• SATURATION HUMIDITY
• PERCENT RELATIVE HUMIDTY
• PERCENT HUMIDITY
)13.9()(
AsysB
AA
pPM
pMH
)23.9()(
ASsysB
ASA
pPM
pMH
)43.9(100 AS
AR p
pH
)33.9(100 S
P H
HH
PSYCHROMETRIC RELATIONSHIPS
• MOLE FRACTION
• HUMID HEAT
• HUMID VOLUME– (IG Conditions)
– vsat at Ĥsat
)143.9(1
AB
A
MH
M
MH
y
)63.9( PAPBS cHcc
ABH
ABmH
M
H
MKT
kg
mv
M
H
MRT
lb
ftv
1)(
2.273
41.22
)73.9(1
)(492
359
3
3
PSYCHROMETRIC RELATIONSHIPS
• TOTAL ENTHALPY– REFERENCED TO T0
– USING (9.3-6)
– FOR AIR WATER @ IG CONDITIONS• ENGLISH (9.3-8)• SI (9.3-9)
)()( 000 TTcHTTcH PAPBy
00 )( HTTcH Sy
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
• RESULT IS ADIABATIC SATURATION LINE
)103.9()( SSSSS HHTTc
)113.9(
S
PAPB
S
S
S
S Hccc
TT
HH
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
• EQUATING AROUND q YIELDS WET BULB RELATIONSHIP
)173.9()()(
)173.9()()(
)133.9()()(
)123.9()('
ATThkWq
AHHkMkWq
yykyyx
kN
ANMkWq
W
WWyB
WyWBM
yA
WAA
)183.9(
W
yB
W
WkMh
TT
HH
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