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