Particle Drying Ressel Komp

Prof. Dr. Joerg B. Resselwww.biologie.uni hamburg.de/zentrum holzwirtschaft.html

Center for Wood Sciences

CAS Wood Based Panels

Module 1: Process Technology

Particle drying

Prof. Dr. Joerg B. Ressel

September 7 12, 2015 – Biel, CH

Prof. Dr. Joerg B. Resselwww.biologie.uni hamburg.de/zentrum holzwirtschaft.html 2015 08 05

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ContentWood Based Panels

ContentParticle drying - fundamentalsParticle drying – dryer typesDrying plant components

Flash tube pre-dryerDrum dryerSingle pass drum dryerDrum dryer for OSB strandsIndirect heated tube bundle dryerIndirect heated rotary tube bundle dryerFibre dryerSuperheated steam dryer for wood fibres

Additional InformationMOLLIER-h,x-Diagram for humid airemc of wood – KEYLWERTH-Diagram


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Particle dryingWood Based Panels

Particle drying process - fundamentals• Continuous drying process • Combined heat transfer to particles by convection

(fluid = hot gas / air, steam) and conduction (contact …)• Drying phases (simplified)

1. Particle mc FSP evaporation of free water, fast increase of particle temperature up to constant level (cooling limit temp.) below the boiling point of water

2. Particle mc < FSP desorption and evaporation of capillary and bound water, increasing particle tempe-rature up to gas temperature; fire hazard ! (self ignitionat approx. 240ºC)!

• Drying parameters (… process parameters)• Material related …: wood species, density, particle di-

mensions (thickness, width, length), mc (initial, final) ...• Process related …: gas/air/steam temperature, partial

pressure of water vapour, gas velocity, retention time …

t

FSP

mc

mcfin

mcinDrying curve

const. evaporation( free water)

decreas. evaporation( bound water)

FSP … fibre saturation (point); upper limit of hygroscopic mc-range (0 emc approx. 28% mc … FSP)

dmc/dt

t

Drying rate

2. Phase1.


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Particle drying process - fundamentalsEnergy required for … heating up wood particles ( wood substance & water!)(heat and electricity) evaporation and desorption of free and bound water from wood

covering exhaust heat lossescovering transmission heat losses (drying plant)electric power for fans, drum drive, servo-motors …

Specific energy consumption is related to 1 kg water removed from wood particles

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

0 5 10 15 20 25

Spec

. ene

rgy

cons

umpt

. [M

J/kg

wat

er]

Initial moisture content [%]

2,50

2,55

2,60

2,65

2,70

25 50 75 100 125

Spec

. ene

rgy

cons

umpt

. [M

J/kg

wat

er]

Initial moisture content [%]

Heat ofevaporationhv = 2,5 MJ/kg

Heat of adsorption(hv+hb)max = 3,6 MJ/kg

Left:Heat of evaporation and heat of adsorp-tion for flake drying depending on mc (May 1979)

Right:Average specific ener-gy consumption of fla-ke drying depending on initial mc (May 1979)


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Ressel J B Energieanalyse der Holzindustrie der Bundesrepublik Deutschland. BMFT-PS T 86-184. 1986. 161 pages

(http://sankeymatic.com/build/ 26.08.2015)

all figures in % of the total energy consumption

Particle drying process - fundamentalsTotal energy consumption

o PB production 140.000 m³/a

o PB coating 40.0000 m³/a

Heat 2,69 GJ/m³ 84,6 %

Electricity 0,49 GJ/m³ 15,4 %


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Particle drying process - fundamentalsEnergy consumption

entire PB production

Heat 2,95 GJ/m³ 82 %

Electricity 0,65 GJ/m³ 18 %

FAO Energy conservation in the mechanical forest industries. FORESTRY PAPER 93. Rome, 1990

(http://sankeymatic.com/build/ 26.08.2015)

all figures in % of the total energy consumtion


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Particle drying process - basic dryer types

acc.

Dep

pe, E

rnst

200

0 / F

ig. 3

.2-5

40 t/h20 - 30 minup to450ºC

Single-pass drum dryer

10 … 18 t/hn.a.up to160ºC

Tube bundle dryer( spinning drum)

1 … 9 t/h20 minup to200ºC

Rotary bundle dryer( spinning tubes)

10 t/h 0,5 - 3 minapprox.500ºCJet tube dryer

2 … 14 t/h 20 sup to500ºC

Flash tube pre-dryer

25 t/h5 - 7 minup to400ºC

Triple-pass drum dryer

CapacityDrying timeTemp. rangeSchemeDryer type


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Basic drying plant componentsHeating system for drying medium (fluid = flue gas, hot air, superheated steam) boilerDryer - one or two stages – pre-dryer optionalMaterial infeed systems – material sluice/airlock … cellular wheelMaterial separators – cyclonesHeating gas re-circulating system and fan(s) – feed-back of flue gas etc.Exhaust gas cleaning system – filter systems reduction of VOC emissions !Chimney stack

Heating systems – direct heating indirect heating

Burner for natural gas, oil, dust Flue gas from energy system (e.g., grate firing systems)Turbine exhaust gasCombination of heating systems mentioned above

Particle movement / particle transport through the dryerPneumatic transport, particles carried by fluid (gas velocity approx. 5…25 m/s)Mechanical transport by built-in devices (“paddles”), e.g., rotating with the drumCombined transport (fines pneumatic transport, coarse particles mechanical transport)


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Flash tube pre-dryer Type VT (Buettner 2015)Used for material with high initial moisture content

Separate pre-dryer or combined a downstream drum dryerIncrease capacity of existing dryerWater evaporation from 1…15 t/hMaterial throughput: 1…70 t/h (dry) resp. 1…85 t/h (wet material)Fresh air or re-circulating air operationHeating systems

Direct heating flue gases from gas, dust, oil burner or grate firing, exhaust gas from turbineIndirect heating heat exchangers with steam, thermal oil

Infeed of material with different moisture content and bulk densities at the same timePower and control switch plant including PLC and visualization Flash tube pre-dryer (Buettner 2015)


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Flash tube pre-dryer Type VT (Buettner 2013)

Stack / to exhaust gas cleaning system

Fan

Dry material to production

Emergency material

discharge

Oversized material

Rotary valveRotary valve

(Buettner 2013)

Heating system

• Direct heating flue gases

• Indirekt heating heat exchanger

Cyclone / separator

Optional re-circulation gasapprox. 25% of thermal

energy savingWet material


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Particle / Flake dryingWood Based Panels

Drum dryer Type NH (Buettner 2013)Water evaporation from 5…50 t/hMaterial throughput: 5…70 t/h (dry) resp.

10…120 t/h (wet material)Fresh air or re-circulating air operationHeating systems:

Burner for natural gas, oil, dust ( heat exchanger)Flue gas from energy plant (e.g., grate firing systems)Turbine exhaust gas ( heat exchanger)Combination of above mentioned heating systems

Possible combination with flash tube pre-dryer and discharge of coarse particlesDrum diameter 3000…6200 mmMaterial discharge via cyclonesIndividual exhaust gas cleaning system (e.g., high efficiency cyclones, filter systems (EFB, WESP, RTO)Power and control switch plant including PLC and visualization, also for conveyors in front and behind the dryer

Drum dryer Type NH with material discharge box (Buettner 2013)Drum dryer Type NH without material discharge box (Buettner 2013)


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(http://www.wbpionline.com/uploads/newsarticle/853739/images/210594/large/vanachai1.jpg / 24.08.2015)


(Flash-Dryer) Pre-dryer and Drum dryer


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(http://www.instalmec.it/images/stories/settori/orig/01.jpg / 24.08.2015)


(Flash-Dryer) Pre-dryer and Drum dryer


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Wet material

Pre-dried material

Oversized materialDry material to production

Emergency material

discharge

Material separators or high efficiency cyclones

FanRecirculation duct

Swivel damper

Pre-dryer

Drum dryerHeating system

Drum dryer Type NH … without discharge box (Buettner 2013)• Material discharge directly via cyclone

(Buettner 2013)


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Wet material

Pre-dried material

Oversized material


Emergency material

discharge

High efficiency cyclones

Fan

Recirculation duct

Swivel damper

Pre-dryer

Drum dryer

Heating system


Emergency material

discharge

Reversible srew feeder

Discharge box

Mixing chamber

Drum dryer Type K (Buettner 2013)• Material discharge via outlet box• Fine material discharge via cyclone

(Buettner 2013)


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Flash tube pre-dryer and single pass drum dryer (Ø 5200 mm, length 28 m, 30 t h-1; Buettner 2005)

Pre-dryer and single pass drum dryer (SPE 2005)


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Single pass drum dryer (SPE – Dieffenbacher Group 2007)Standard installation

Options• Direct discharge to

cyclons• Discharge via drop-

out box


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Bison ( o. J.)

Pre-dryer and single pass drum dryer (Binos 2011)Single-pass drum dryers are either direct or indirect heated. The dimen-sions of the dryer drum are similar to the three-pass drum dryer; gas inlet temperature is lower (< 500°C).The moisture is removed more gent-ly, retention time is longer (> 20 min).The system is suitable for drying ma-terial with various mc and dimen-sions.

Combustionchamber

Mixing chamber

Pre-dryer

Wet material inlet

Drum dryerDischargebox

Cyclone battery

Dry mat. discharge

Stack

Emergency stack


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Drum dryer datails (SPE 2007)

Single pass drum dryer (SPE 2007)Particle discharge

Dust se-paration

Sand / ash separation

Particles

Dischargebox

Dust se-paration

Particles


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Single pass drum dryer (SPE 2007)Design details for the flake dryer

Drum (Ø 2…7 m, thick drum shell, rigid concept) Trunnion assemblyVariable speed drive with friction, chain or rack ring

Drum dryer datails (SPE 2007)


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Flake / Strand dryingWood Based Panels

Single pass drum dryer (SPE 2007)Specific drum internals for PB (left) and OSB (right)

Omega supports

Support discs

Cross internals

Drum dryer datails(SPE 2007)


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Strand dryingWood Based Panels

Drum dryer Type NH for OSB strandsParticularly developed for strand drying requirements

Water evaporation from 5…40 t/hMaterial throughput: 5…40 t/h (dry) resp.

10…80 t/h (wet material)Fresh air or re-circulating air operationHeating systems:

Burner for natural gas, oil, dust ( heat exchanger)Flue gas from energy plant (e.g., grate firing systems)Turbine exhaust gas ( heat exchanger)Combination of above mentioned heating systems

Drum diameter 4000…6200 mmParticularly designed internal strand transport system inside the drumMaterial discharge via cyclonesIndividual exhaust gas cleaning system (e.g., high efficiency cyclones, filter systems (EFB, WESP, RTO)Power and control switch plant including PLC and visua-lization, also for conveyors in front and behind the dryer

Drum dryer for OSB strands (Buettner 2013)

Single-pass drum dryer for OSB strands (Metso panelboard 2004)


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(Buettner 2013)

Wet material


Emergency material

discharge

Material separator


Swivel damper

Drum dryer

Heating system

Mixing chamber

Grate firing system

Drum dryer Type NH for OSB strands (Buettner 2013)



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Wet

material


Emergency material discharge

Material separator


Drum dryerDirect heating system

Drum dryer Type LS (Buettner 2013)


(Buettner 2013)


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Triple pass drum dryer for flakes (Binos 2011)Pre-drying in the centre tube of the dryer drumFinal drying during the second and third pass of the drum after turning back of flow direction with decreasing temperature and flake mc

(Binos 2011)


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Triple pass drum dryer (Binos 2011)Pre-drying in an upstream flash tube dryerFinal drying during the passage of the nested tubes within the drum: Particles are carried through the dryer by the flowing hot gas; temperature and flake mc decrease with transport distance

(Binos 2011)


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(Buettner 2013)


Indirectly heated tube bundle dryer

Water evaporation from 8…25 t/hMaterial throughput: 8…>30 t/h (dry) respectively

16…> 55 t/h (wet material)Heating systems:

Steam - combination with flue gas optionalDrum diameter 3000…5600 mmRotating drum, stationary tube bundlesMaterial discharge via outlet boxExhaust gas cleaning by filter system – no cyclonesPower and control switch plant including PLC and visualization, also for conveyors in front and behind the dryerPreferred in combination with cogeneration ( coupled heat & electricity generation)

Indirect heated tube bundle dryer (Buettner 2013)

Tube bundle (Buettner 2013)


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Indirectly heated tube bundle dryer (Buettner 2013)


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Indirectly heated rotary bundle dryer

Stationary dryer case (drum or trough) – rota-ting tube bundle (designed as single or doub-le rotary bundle dryer), tube bundle size up to 3.600 mmWater evaporation from 2… 10 t/hMaterial throughput: 2 …10 t/h (dry)

respectively 4…20 t/h (wet material)Heating systems:

Steam – thermal oil – hot waterMaterial discharge via outlet boxDust cleaning by cyclonesIndividual exhaust gas cleaning systems, e.g., cyclones, EFB, WESP, RTOPower and control switch plant including PLC and visualization, also for up- and downstream conveyorsPreferred in combination with cogeneration

Indirectly heated rotary bundle dryer (Buettner 2015)

(Buettner 2015)


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http://www.buettner-energy-dryer.com/en/drying-systems/drying-systems-indirectly-heated-tube-bundle-dryers/ / 24.08.2015


Indirectly heated rotary bundle dryer (Buettner 2015)


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Indirectly heated rotary tube bundle dryer (Bison o.J.)

Fully insulated rotary bundle dryer

(Ponndorf 2005)

Heat pipe arran-gement in rotary tube bundle dryers

• type RK (top)

• type RS (bottom) (Ponndorf 2005)


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Indirectly heated rotary tube bundle dryer (Buettner 2013)

(Buettner 2013)

Wet material

Dry mate-rial to pro-duction

Heat exchanger

Fresh air

Combus-tion air

Fuel

Ash

Fresh air

Fan

Pump

Rotary tube bundle dryer

Thermal oil heater

Wet electrosta-tic precipitator

WESPCyc-lone


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Dryer for fibrous materials – heating system (Buettner2013)

Fibre dryingWood Based Panels

Fibre dryer (Buettner 2013)Particularly designed for drying fibrous materials

Water evaporation from 5…> 60 t/hMaterial throughput: 5…> 60 t/h (dry) respectively

10…> 90 t/h (wet material)Fresh air or re-circulating airHeating systems:

Indirect heating via heat exchanger steam, hot water or thermal oilDirect heating burner for natural gas, LPG, oil, dust, flue gas from energy plants (grate firing systems) or turbine exhaust gas

High efficiency radial fansDryer duct diameter 800…> 3.000 mmCyclone (diameter 3.000…6.500 mm) for material discharge and dust removalPower and control switch plant including PLC and visualization, also for subsequent fibre sifter

Dryer for fibrous materials (Buettner 2013)


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Flash dryer types for fibrous material

(Deppe / Ernst 1996)

Fibre inlet

Steam recovery

Fibre inlet

Single stageflash dryer

Fibre inlet

Two stageflash dryer

Single stage flash dryer


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One stage fibre dryer

Simple process solution and controlLow capital costHigh level of temperature and therefore over-drying or fire hazardHigh pre-curing rates of resinsDirect flue gas from energy plantLow electrical energy consumption

(SPE 2005)

Wet material from refiner

Fresh air

dry mate-

rial


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(Buettner 2013) Wet material from refiner

Heating system

Fresh air


High efficiency cyclone Flue gas

Dryer duct


Emergency material discharge

Fan

Dryer for fibrous material (Buettner 2013)


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Two stage fibre dryer

Advanced process controlHigh capital cost (more construction space)Higher electric power consumption

(SPE 2005)

Fresh air

dry material

Lower gas temperature levelGood control of final mc, less overdryinglow pre-curing of resins

1. stage

2. stage

Fibre bin Sifter

Wet material from refiner

Fresh air


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(Metso panelboard 2002)

Wet material from refinerFresh

air

1. stage

2. stage

Return air system (RAS)

Fibre bin Sifter

Two stage fibre dryer Advantages compared to single-stage fibre drying

Increased fibre quality and more uniform final mcReduced resin consumption with blow-line blendingReduced energy consumption; 15 % compared to one-stage drying, 25 % with RASSmaller ducts and cyclones, particularly at high capacities

Advantages of RASlower energy consumptiondecreased emission of par-ticleslower exhaust gas flow and lower investment costs for environmental control tech-nology

(Metso panelboard 2002)

020406080

100120140160180

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

Relative drying time [-]

Tem

pera

ture

[°C

]

020406080

100120140160180

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

Relative drying time [-]

Tem

pera

ture

[°C

]

Two-stage dryer

One-stage dryer

Fresh air


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Superheated steam dryer for wood fibres (SPE – Dieffenbacher 2005)

Superheated steam as drying medium offers considerable advantages compared to humid air in conventional drying processes:

less energy consumption (heat & electric power)heat recovery up to 60…80 %closed loop system no exhaust gas, no dust and other emissions (VOC); all emis-sions removed by condensate waste water treatment requiredalmost oxygen-free gas circulation no fire and explosion hazard reduced drying time due to better heat transfer less mass flow (fluid = steam), less fan powershorter drying duct

(SPE 2005)


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Superheated steam dryer for wood fibres (SPE – Dieffenbacher 2005)Comparison of mass flow

Conventional fibre drying process

Superheated steam fibre drying process

SPE 2005


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Superheated steam dryer for wood fibres (SPE – Dieffenbacher 2005)Comparison of energy consumption

Superheated steam fibre drying process

SPE 2005

Conventional fibre drying process


Overview

emc & humid air



MOLLIER-h,x-Diagramme

... changes of humid air con-ditions, e.g., with convective drying processes. recommended literature

Prof. Dr. Joerg B. Resselwww.biologie.uni hamburg.de/zentrum holzwirtschaft.html (http://public.beuth-hochschule.de/~wseifert/lmr/thermo/BilderThermo/Theorie/HX_Diagramm4.jpg / 27.08.2013)


Keylwerth-DiagrammeWood Based Panels

The KEYLWERTH-Diagram… how to determine emc …

• Psychrometertemperatures TDB

and TWB EMC und r.h.

• Dry bulb Temperature TDB and

relative humidity r.h. EMC und

WBT

Note: use of the psychrometer for determination of r.h. and emc res-pectively requires an air flow of at least vL 2 m/s at the wet bulb thermometer to met the adiabatic evaporation temperature !

TDB = 60 °C EMC = 8,7 %TWB = 50 °C r.h. = 58 %

TDB = 25 °C EMC = 6,1 %r.h. = 30 % TWB = 15 °C

Prof. Dr. Joerg B. Resselwww.biologie.uni hamburg.de/zentrum holzwirtschaft.html07.05.2008 46

EMC-ChartTDB = 25°C

WBD = (TDB-TWB)

= 5°C

EMC 11,1 %

r.h. 63 %

TDB = 60°C

WBD = 10°C

EMC 8,7 %

r.h. 58 %

Wood Based Panels Wood mc-determination EMC-Chart

Prof. Dr. Joerg B. Resselwww.biologie.uni hamburg.de/zentrum holzwirtschaft.html07.05.2008 47


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Overview / Intro

Particle Drying Ressel Komp

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