developments in vacuum drying and press drying of timber · not suitable for timber with high...

COST E 15 - Drying Seminar Limerick, Eire / 21-11-2003 29-10-2003 / JBR / 1

Centre for Forest ProductsMechanical Wood Processing

Prof. Dr. J. B. ResselUniversity of Hamburg

Developments in Vacuum Drying and Press Drying of Timber

Fundamentals Process TechnologyPlant ManufacturersPress Drying

��

Center for Forest Products

Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Objectives of Timber Drying

Optimisation ... meeting target moisture con-tent of the kiln load as soon as possible with reasonable or best possible drying quality

→Short drying time→Low Energy con-

sumption

→Reasonable drying cost

→Appropriate drying quality

Compromise ...required due to opposing effects of individual measu-res to meet the overall target

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Fundamentals of Timber Drying

Drying → removal of water from green wood requires energy to ...

→ Initiate driving forces for water (vapour) movement within wood pieces

→ Evaporate water (liquid water → water vapour) → Remove bound water from internal wood surface (mc < fiber

saturation)

Real drying processes / drying plants require additional energy(electricity and heat) in particular for .... → heating up the material being dried→ heating up the drying plant→ covering energy losses of the drying plant→ circulating the drying medium (movement of humid air in con-

vective drying by fans)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Fundamentals of Timber Drying

Heat transfer to wood finally leads to mass transfer (water vapourtransition from the wood surface to the surronding atmosphere)

Within wood heat conduction initiates water and / or vapourmovement, removal of bound water and evaporation of water

...inside the wood

Heat con-duction

Mass transfer

Water / vapour

movement

Heat transfer

Coupled processes• Interfering each

other, partially with opposing effects

• None may be con-sidered alone

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Fundamentals of Vacuum Drying of Timber

Principles and limits of heat transfer and heat conduction

Convection Forced movement of drying medium (humid air, steam)

Conduction Direct contact between wood and heating elementsRadiation Energy transmission by electromagnetic waves (IR)

Dielectric field Internal heat generation by stimulated oscillation of dipole molecules, i.e. water

• Continuous / discontinuous heat transfer (depending on process control)

Add

ition

al c

ondi

tions

• Velocity of drying medium (humid air, steam)• Absolute pressure of surrounding atmosphere• Partial vapour pressure of surrounding atmosphere• Accessibility of the material to be dried to heat transfer

• Physical material properties (→ wood, water, vapour)

Environ-mental conditions}

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Fundamentals of Vacuum Drying of Timber

0 200 400 600 800 10000

10

20

30

40

50

60

70

80

90

100

Absolute pressure p [mbar]

0,25 0,5 0,75 1,0Relative vapour pressure [-]

Fog (satura-ted steam)

VAK-013 / JBR

Working range

Superheatedsteam

Saturation line

Closed system (air tight sealed vessel; batch drying processes)

• Decreasing absolute pres-sure → decreasing boiling temperature of water

• Absolute pressure difference between inner and outer lay-ers of the material being dried → accelerated mois-ture movement in the mate-rial (steam flow) → improved surface mass transfer

→ Suitable pressure level→ Economic limits in

practice ?

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying – Heat-and-Vent Drying

• Increased drying rate short drying time

• Suitable for drying of larger timber dimensions

• Less risk of discolouration ( O2-free atmosphere, low temperature)

• Easy and fast set-up and installa-tion of prefabricated vacuum-plant

• Reasonable energy efficiency due to suitable recovery systems heat exchanger, tandem operation of two kilns

• Small plant units small batches, different wood species

• Short response on specific custo-mer demand delivery just in time

• .......

• Individual technologies not suitable for timber with high initial mc

• Less benefits from dry-ing small timber dimensions and soft-wood species

• Increasing risk of drying defects when choosing unsuitable pro-cess parameters ( temperature, pressure ... due to fast drying ra-te, no visual control of the load during the process closed batch system)

• Substantial operational experien-ce required for successful drying

• Relative high investment cost• .......

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Superheated Steam Vacuum Drying - Plant Facilities

Cooling water

Vapour exhaust

to vacuum pump

Condensate pipe

Insulated pres-sure vessel

Heating medium

Insulated front door

Fan

Vacuum pump

Coolingwater

Condensate bin(6 volume mea-surement)

internal conden-sation device

Circulationpump

Motor valve

ControllingComputer

Sen-sors

VAK-09 e/ JBR

Circu-lationpump

Control panel(connected tomeasuring sen-sors, regulationunits, pumpsand controllingcomputer)

Coolingdevice

• Pressure vessel, loading door and carriage• Heating system• Vapour circulation system (fans)• Dehumidification system (condenser)• Vacuum pump(s)• Sensors, regulating units and process

control (computer)

± similar facilities and components for all vaccum dry kilns

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Innovations in Vacuum Drying

…no remarkable changes happened in process technology and drying facilities in the last years – exept minor improvements with individual kiln manufacturers …

→ Advantageous improvements for kiln manufacturers, e.g., ...• reduction of manufacturing costs, e.g., construction by modules, use

of prefabricated components (wall segments from aluminium-profiles for variable pressure vessel size, rectangular pressure vessels)

• improvements in measuring systems and controlling units (sensor technology: temperature, pressure, gas humidity, wood moisture con-tent, computerized process control …)

→ Advantageous improvements for kiln users, e.g., ...• improved durability of the drying plant / lesser maintenance of all

plant facilities (exclusive use of stainless steel and/or aluminium →lesser break down time)

• improved handling, process control, maintenance and repair (online support with fault detection, drying schedule development ...)

• lesser energy consumption, integrated condensation equipment• lesser or no cooling water required (air cooling system)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying - Process Technologies

• Convective 1. Intermittent heating periods under normal pressureheat transfer Drying during intermittent vacuum phases = Discon-

tinuous Vacuum Drying Process2. Continuous heat transfer in low pressure atmosphere

(= Superheated Steam / Vacuum; pAbs = 100…250 mbar), sufficient gas density for convective heat trans-

2. Microwave generator (Magnetrons) integrated in vacu-um vessel; continuous heating, pressure level as low as possible / suitable = Continuous Vacuum Drying Process

fer with high gas flow (vsteam ≥ 20 m/s) = Continuous Vacuum Drying Process

Today the most common pro-cess technology

Superheated Steam/Vacuum

• Conductive Direct contact to wood - heating plates (sticker re-heat transfer placement); pressure level as low as possible / sui-

table = Continuous Vacuum Drying Process

• Dielectric 1. Hot / cold electrodes integrated in vacuum vessel; field continuous heating, pressure level as low as possible

/ suitable = Continuous Vacuum Drying Process

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Continuous Vacuum Drying Process

Continuous vacuum drying at constant pressure level

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70

60

50

40

30

20

10

00 1 2 3 4 5 6 7 8 9

R ela tive d rying tim e t [h]

P la te tem peratu re h Pl

W ood tem peratu re hH Evapora tion tem pera tu re atp ressure leve l in the k iln

M o istu re conten t u

VAK -011 / J BR

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Continuous Vacuum Drying Process

�

Pressure difference (envi-ronment ↔ kiln chamber) ensures compression of platen stacked timber layers

Platen vacuum press drying kiln (WDE Maspell / I)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Discontinuous Vacuum Drying Process

Discontinuous vacuum drying at different pressure levels

�

70

60

50

40

30

20

10

00 1 2 3 4 5 6 7 8 9

Relative drying time t [h]

Circulating air temperature hL

VAK-012 / JBR

Wood temperature hH

Evaporation temperature at pressure level duringvacuum phase

One cycle

10 11 12

Heating phase(Normal pressure)

Drying phase (Vacuum)

Moisture content u

Two different pressure levels (→ alternating heating phase at normal pressure and drying phase at reduced pressure level)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Discontinuous Vacuum Drying Process

3.800 mm

15.000 mm

12.500 mm

1.250 mm 1.250 mm

Gleisbahn

Maspell Trockner GOLIATH 50

Platen-less vacuum kilns (Type GOLIATH, WDE Maspell / I; two kilns in tandem operation, horizontal air circulation during heating phases ( l o-la ⇒ l ongitudinal-lateral))

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Superheated Steam / Vacuum Drying

Continuous vacuum drying in superheated steam atmosphere

7 0

6 0

5 0

4 0

3 0

2 0

1 0

00 1 2 3 4 5 6 7 8 9

R ela tive dry ing tim e t [ ...]

S u pe rhe a te d va p ou r tem p era tu re h Va p

E va p ora t io n te m pe ra tu re a tp re ssu re le ve l in th e k iln h S

A vg . m o is tu re co nte n t u m

� � � ��

W oo d su rfa ce tem p .

W oo d co re te m p .

P re ssure d eve lop -m en t in th e k iln p Va p

H ea tin gu p

1 st D ry in gp h as e

C on d i-tio nin g

5 0

1 00

1 50

2 00

2 n d D ry in gp h as e

3 rd D ry in gp h as e

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying


Integrated heat-pump as main heating system

Electricity

Compressor

Warm water

Cold water

Expansion valve

Evapora-tor (cold)

Warm hu-mid air from stack

Warm dry air to the stack

Additio-nal water circuit

Condenser (hot)

Mode of action of heat-pump (dehumidification unit)(see plants from Eberl and Kronseder) Details

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying


Superheated steam flow in convectively heated vacuum kilns

Crosswise steam flow

• heat pipes and fan at the side of the stack side; vertical flow back into the stack at opposite kiln wall. One or two fan / heat pipe lines (e.g., Brunner, Mühlböck, IWT, Kron-seder)

• Heat pipes and fans on top of the stack (IWT, Mühlböck - former kiln types)

• Heat pipes and fans in front of the stack (at both sides), horizontal steam flow reversal (longitudinal -lateral with WDE / Maspell and Eberl)

Lengthwise steam flow

• Heat pipes and fans in front of stack, horizontal steam flow rever-sal (small kilns, special corrugated stickers required, e.g. Mühlböck)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Radio Frequency / Vacuum Drying

Radio Frequency-Vacuum dry kiln (RF/V-drying)

Cold electrode

Cold electrode

Hot electrode

Steam-conden-ser

Vacuum-pump

Radiofre-quency-generator

“Hot” electrode

“Cold” electrodeGround

Scheme of a RF/V-dry kiln (Wolf)P = 0,556 f E2 ε´´ 10-12 [W/cm³]

• Dielectric Heating of wet wood in a dielectric field

• Wet Wood as dielectric material

• Power absorption of the material

P [W/cm³] Power per unit volumef [Hz] FrequencyE [V/cm] Field strengthε” [-] Loss factor of wood

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Radio Frequency / Vacuum Drying

Radio Frequency-Vacuum dry kiln (RF/V-drying)

Up to now only one success-ful kiln manufacturer on the American market : → HeatWave Technologies / CAN

Advantages• Very short drying time• Wide thickness range of

timber to be dried• Very good drying quality• Stacking without stickers Disadvantages

• Limited to highly permeable species

• High investment costs• High energy costs (electricity!) • Low efficiency of RF-generator

(η = 0,55..0,65)• Limited life time RF-tube

(approx. 4000 - 8000 h)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - Brunner

Superheated steam vacuum dry kilns Brunner Trockentechnik BR U NN E R

• Rectangular pressure vessel

• Fans and heat-ing coils on one side of the timber stack

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying


��

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' !�#�$� �!�

'��(�) ��

*�� !"��

'�!$� �!�� "� � ��+��*&,

Superheated steam vacuum dry kilns Brunner Trockentechnik BR U NN E R (1) Heating coil, separately

adjustable(2) Intermediate heating

coils (on demand)(3) Integrated steam

generator(4) Fans, reversible rotation,

separately adjustable(5) Vacuum pump(6) Controlled fresh air

supply (7) Drain-pipe, continuously

condensate extractionduring the process

(8) Controlled heat supply,separately adjustable foreach sections

(9) Kiln load / stacks(10) Evaporated steam from

timber(11) Condensed water from

timber(12) Two temperature probes

sides of the stack(13) Wood-moisture content

probes (12 x), for dryinggradient control (sur-face - 1/3-depth and 1/2-depth)

(14) Wood-temperature pro-be for process control

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying


Superheated steam vacuum dry kilns Brunner Trockentechnik BR U NN E R

1992 1997 20000

100

200

300

400

500Investment costs [1000 Euro]

Vacuum dry kilns (high-low)Conventional dry kilns (high-low)(gross capacity 95...140 m³)

Decline of investment costs superheated steam vacuum - heat-and-vent kiln drying during the past decade (Brunner, 1999) Total drying time [d]

0 10 20 30 40 50 60 70 80 90 10020

30

40

50

60

70

80

90

European White Oak Total drying time down to mcfinal = 8 %

High VAC® - Superheated Steam -VacuumHeat-and-Vent (Conventional kiln Drying)

Heat-and-Vent

SH / V

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - IWT

Superheated steam vacuum dry kilnsInnovative Wood Technology IWT

(1) Heating pipes (6) Temperature probe (2) Fans (7) EMC-Sensor(3) Carriage (8) Pressure Sensor(4) Top Baffle (9) Hydraulic closing (5) Wood- MC-probes system (11) Stainless steel vessel (10) Hydraulic pump

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - Mühlböck

�• Cylindrical pressure vessel• Crosswise steam flow in two di-

rections• Fans / heating coils on one side of the stack (bisectional)

Superheated steam vacuum dry kilnsMÜHLBÖCK Holztrocknungsanlagen

• Cylindrical pressure vessel• Lengthwise steam flow• Fans at the backside of the vessel

• Special corrugated stickersrequired

Stickers

EMC-Probe

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - Kronseder

Superheated steam vacuum dry kiln (on demand with heat-pump)EUROVAC / ��!��$-�!��$�! -

Kiln loading

Outdoor installation on prefabri-cated foundations

Switch board, heat-pump and vacuum pump

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - Eberl

Superheated steam vacuum dry kiln with heat-pump systemEBERL Trocknungsanlagen

Top view - horizontal steam flow across the stack

Details

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - Opel

Platen-vacuum dry kiln (Press-drying kiln). /01 ��*2��3

1� ��$��1� ��$��

Compression applied by inflated rubber tube

Rigid structure in right angle pressure vessel

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - Opel

Platen-vacuum dry kiln (Press-drying kiln). /01 ��*2��3

Awkward handling of heating plates

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - HeatWave

Radio-frequency vacuum dry kiln �� 4 5� ��$�!��" ��+!$&��*�6

4

57

8

9

1 Power amplifier and matching network

2 Vacuum pump3 Vacuum condenser4 hydraulic compression

system (total pressure approx. 1,1 MN)

5 RF-electrode6 Condensate drain7 Control unit8 Drier chamber9 Material handling system

HeatWave type 5.20• Capacity 5 m³ (net timber volume)• RF power output 20 kW (air cooled RF-tube)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying Plants - HeatWave

Radio-frequency vacuum dry kiln �� 4 5� ��$�!��" ��+!$&��*�6

HeatWave type 50.150• Capacity 50 m³

(net timber volume)• RF power output 150 kW

(water cooled RF-tube)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Press Drying - Fundamentals

Conductive heat transfer → no ... moderate compression of tim-ber (or timber surface) to be dried

→ Compression strength depending on wood species, moisture content and (process) temperature (0...140°C → 30...35% strength reduction)

→ Initiated internal pressure (water evaporation) increases rapidly with temperature (100°C → 0,1 MPa; 120°C → 0,2 MPa; 140°C → 0,38 MPa)

→ Compression forces < compression strength of wood perpendicular to grain (softwood species approx. 2...10 MPa; hardwood species approx. 5...20 MPa)

Lim

itatio

ns

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Press Drying - Process Technology

Pressure

Pressure

Heating plate

Tray

TimberFeeding

Scheme of a press drying plant - multi-day-light press (batch process) with feeding trays

Process parametersPressure• Without compression

Softwoods p < 1,5 MPaHardwoods p < 2,5 MPa

• Slight compression p < 5...12 MPa, depending on wood species

• short intermittent decom-pression periods

Temperature• 100...140°C, depending on

wood speciesTime• 12...24 hours, depending

on final mc and accepta-ble discoloration of wood

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying


Process characteristics and advantages(according to Arboreo Technologies Ltd. / FIN)

• Rapid drying process• Less cracks, warping and cupping• Due to pressing the timber stays / becomes straight • Hardness increases by 11 ... 18 %• Strength properties improve by 15 ... 33 %• More resistant towards rotting• Moisture expansion reduced up to 2,7 times (Spruce)• Net material savings 15 ... 20 % due to higher net

recovery and minimized drying defects

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying


1.Pre-Drying

Time [h]

95 °C105 °C

130 ... 200 °C

80 °C

Total process duration ~ 12 ... 24 h

2. Main Drying

3.FinalDrying

4. CoolDown

4...10 h 3...16 h 2...4 h 2...8 h

3 MPa

12 MPa

a r b o r e o technologies

TECHNICAL DATA- cell size length 6200 mm- cell size width 2200 mm- timber thickness 15 … 55 mm- kiln capacity 10 … 25 m³ - initial mc predried … green - final mc 6 … 8 %- drying time 6…24 hours, de-

pending on the treatment in-tention

- energy consumption approx.250 … 300 kWh / m³

Process phases and temperatures(Arboreo Technologies Ltd. - Compression dryers /FIN)

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying


TECHNICAL FEATURES- timber stacked crosswise bet-

ween hollow, perforated metal profiles (press plates)

- convective heat transfer to press plates / layers

- air velocity through platesapprox. 5…6 m/s (initiated by 4 fans á 25.000 m³/h)

- conductive heat transfer bet-ween press plates and timber

- continuous process control(temperature probes inside wood, temperature control drying condi-tions, humidity control by dampers …)


��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Press Drying Plant


Press dry kiln

Stack carriage

Stacking frame

Stacking and loading/unloading from both sides of the kiln

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Press Drying Plant


View into the Press Drying Plant

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Compression Dryer – diagram of cross section (former HitWood Plant RSA)

Com-pression

External frame

Fan-motor

Removable rails

Press Drying Plant

FansHeatingcoils

Com-pression

Circulating hot air

External frame

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Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Press Drying Plant – HitWood

Stacking frame

Stack carriage

Heating panels → hollow metal profiles (convec-tive heating !)

Stacking frame in loading po-sition (open)

Compression Dryer – diagram of cross section (former HitWood Plant in RSA)

COST E 15 - Drying Seminar Limerick, Eire / 21-11-2003 29-10-2003 / JBR / 40

Center for Forest ProductsMechanical Wood Processing

Prof. Dr. J. B. ResselUniversity of Hamburg

Thank you for your attention !Vacuum and press drying ….have been presented by

J. B. ResselUniversity of Hamburg Center for Forest ProductsLeuschnerstr. 91D-21031 [email protected]

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Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying



Sucking canal, heat-pump or dehumidification system and fans behind end wallLoading the kiln built up on the timber yard

��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying


Dehumidifica-tion system and fans behind the back wall in the pressure vessel

Integrated operation room with condensate tank at the back of the kiln

Compressor

Condensate collector

Evaporator

Radial fans

Expansion valve

Condenser


��


Prof. Dr. Ressel

Plant Examples

Innovations

Plant Facilities

Process Technology

Fundamentals

Introduction

Brunner

IWT

Mühlböck

Opel

Kronseder

HeatWave

Eberl

Press Drying

Vacuum Drying – Process Technologies

Integrated heat-pump as main heating system

Mode of action of heat-pump (dehumidifi-cation system) and EBERL dry kiln

Steam into stack

Steam from stack

Compressor

Condensate to drain

Condenser

Expansion valve

Evaporator

Radial fans

Auxiliary electrical heating

Refrigerant circuit

developments in vacuum drying and press drying of timber · not suitable for timber with high...

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