Developments in vacuum drying and press drying of
Developments in vacuum drying and press drying of
Developments in vacuum drying and press drying of
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University <strong>of</strong> Hamburg<br />
<strong>Developments</strong> <strong>in</strong><br />
Vacuum Dry<strong>in</strong>g<br />
<strong>and</strong> Press Dry<strong>in</strong>g<br />
<strong>of</strong> Timber<br />
� Fundamentals<br />
� Process Technology<br />
� Plant Manufacturers<br />
� Press Dry<strong>in</strong>g<br />
Centre for Forest Products<br />
Mechanical Wood Process<strong>in</strong>g<br />
Pr<strong>of</strong>. Dr. J. B. Ressel<br />
COST E 15 - Dry<strong>in</strong>g Sem<strong>in</strong>ar Limerick, Eire / 21-11-2003 29-10-2003 / JBR / 1
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Objectives <strong>of</strong> Timber Dry<strong>in</strong>g<br />
→ Short dry<strong>in</strong>g time<br />
→ Low Energy consumption<br />
→ Reasonable dry<strong>in</strong>g<br />
cost<br />
→ Appropriate dry<strong>in</strong>g<br />
quality<br />
Optimisation ...<br />
meet<strong>in</strong>g target moisture content<br />
<strong>of</strong> the kiln load as soon<br />
as possible with reasonable or<br />
best possible dry<strong>in</strong>g quality<br />
Compromise ...<br />
required due to oppos<strong>in</strong>g<br />
effects <strong>of</strong> <strong>in</strong>dividual measures<br />
to meet the overall target
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Fundamentals <strong>of</strong> Timber Dry<strong>in</strong>g<br />
Dry<strong>in</strong>g → removal <strong>of</strong> water from green wood requires energy to ...<br />
→ Initiate driv<strong>in</strong>g forces for water (vapour) movement with<strong>in</strong><br />
wood pieces<br />
→ Evaporate water (liquid water → water vapour)<br />
→ Remove bound water from <strong>in</strong>ternal wood surface (mc < fiber<br />
saturation)<br />
Real dry<strong>in</strong>g processes / dry<strong>in</strong>g plants require additional energy<br />
(electricity <strong>and</strong> heat) <strong>in</strong> particular for ....<br />
→ heat<strong>in</strong>g up the material be<strong>in</strong>g dried<br />
→ heat<strong>in</strong>g up the dry<strong>in</strong>g plant<br />
→ cover<strong>in</strong>g energy losses <strong>of</strong> the dry<strong>in</strong>g plant<br />
→ circulat<strong>in</strong>g the dry<strong>in</strong>g medium (movement <strong>of</strong> humid air <strong>in</strong> convective<br />
dry<strong>in</strong>g by fans)
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Fundamentals <strong>of</strong> Timber Dry<strong>in</strong>g<br />
Heat transfer to wood f<strong>in</strong>ally leads to mass transfer (water vapour<br />
transition from the wood surface to the surrond<strong>in</strong>g atmosphere)<br />
With<strong>in</strong> wood heat conduction <strong>in</strong>itiates water <strong>and</strong> / or vapour<br />
movement, removal <strong>of</strong> bound water <strong>and</strong> evaporation <strong>of</strong> water<br />
Heat<br />
transfer<br />
Heat conduction<br />
...<strong>in</strong>side the wood<br />
Mass<br />
transfer<br />
Water /<br />
vapour<br />
movement<br />
Coupled processes<br />
• Interfer<strong>in</strong>g each<br />
other, partially<br />
with oppos<strong>in</strong>g<br />
effects<br />
• None may be considered<br />
alone
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Fundamentals <strong>of</strong> Vacuum Dry<strong>in</strong>g <strong>of</strong> Timber<br />
Pr<strong>in</strong>ciples <strong>and</strong> limits <strong>of</strong> heat transfer <strong>and</strong> heat conduction<br />
� Convection Forced movement <strong>of</strong> dry<strong>in</strong>g medium (humid air,<br />
steam)<br />
� Conduction Direct contact between wood <strong>and</strong> heat<strong>in</strong>g elements<br />
� Radiation Energy transmission by electromagnetic waves (IR)<br />
� Dielectric field Internal heat generation by stimulated oscillation <strong>of</strong><br />
dipole molecules, i.e. water<br />
Additional conditions<br />
• Physical material properties (→ wood, water, vapour)<br />
• Cont<strong>in</strong>uous / discont<strong>in</strong>uous heat transfer (depend<strong>in</strong>g on process<br />
control)<br />
}<br />
• Velocity <strong>of</strong> dry<strong>in</strong>g medium (humid air, steam)<br />
• Absolute <strong>press</strong>ure <strong>of</strong> surround<strong>in</strong>g atmosphere<br />
• Partial vapour <strong>press</strong>ure <strong>of</strong> surround<strong>in</strong>g atmosphere<br />
• Accessibility <strong>of</strong> the material to be dried to heat transfer<br />
Environmental<br />
conditions
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Fundamentals <strong>of</strong> Vacuum Dry<strong>in</strong>g <strong>of</strong> Timber<br />
Closed system (air tight sealed<br />
vessel; batch dry<strong>in</strong>g processes)<br />
• Decreas<strong>in</strong>g absolute <strong>press</strong>ure<br />
→ decreas<strong>in</strong>g boil<strong>in</strong>g<br />
temperature <strong>of</strong> water<br />
• Absolute <strong>press</strong>ure difference<br />
between <strong>in</strong>ner <strong>and</strong> outer layers<br />
<strong>of</strong> the material be<strong>in</strong>g<br />
dried → accelerated moisture<br />
movement <strong>in</strong> the material<br />
(steam flow) → improved<br />
surface mass transfer<br />
→ Suitable <strong>press</strong>ure level<br />
?<br />
→ Economic limits <strong>in</strong><br />
practice<br />
VAK-013 / JBR<br />
100<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
Relative vapour <strong>press</strong>ure [-]<br />
0,25 0,5 0,75 1,0<br />
Superheated<br />
steam<br />
Saturation l<strong>in</strong>e<br />
Fog (saturated<br />
steam)<br />
10<br />
0<br />
Work<strong>in</strong>g<br />
range<br />
0 200 400 600 800 1000<br />
Absolute <strong>press</strong>ure p [mbar]
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g – Heat-<strong>and</strong>-Vent Dry<strong>in</strong>g<br />
• Increased dry<strong>in</strong>g rate<br />
�<br />
� short dry<strong>in</strong>g time<br />
• Suitable for dry<strong>in</strong>g <strong>of</strong><br />
larger timber dimensions<br />
• Less risk <strong>of</strong> discolouration (� O2- free atmosphere, low temperature)<br />
• Easy <strong>and</strong> fast set-up <strong>and</strong> <strong>in</strong>stallation<br />
<strong>of</strong> prefabricated <strong>vacuum</strong>-plant<br />
• Reasonable energy efficiency due<br />
to suitable recovery systems �<br />
heat exchanger, t<strong>and</strong>em operation<br />
<strong>of</strong> two kilns<br />
• Small plant units � small batches,<br />
different wood species<br />
• Short response on specific customer<br />
dem<strong>and</strong> � delivery just <strong>in</strong><br />
time<br />
• .......<br />
• Individual technologies<br />
�<br />
not suitable for timber<br />
with high <strong>in</strong>itial mc<br />
• Less benefits from dry<strong>in</strong>g<br />
small timber dimensions <strong>and</strong><br />
s<strong>of</strong>t-wood species<br />
• Increas<strong>in</strong>g risk <strong>of</strong> dry<strong>in</strong>g defects<br />
when choos<strong>in</strong>g unsuitable process<br />
parameters (� temperature,<br />
<strong>press</strong>ure ... due to fast dry<strong>in</strong>g rate,<br />
no visual control <strong>of</strong> the load<br />
dur<strong>in</strong>g the process � closed<br />
batch system)<br />
• Substantial operational experience<br />
required for successful dry<strong>in</strong>g<br />
• Relative high <strong>in</strong>vestment cost<br />
• .......
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Superheated Steam Vacuum Dry<strong>in</strong>g - Plant Facilities<br />
Heat<strong>in</strong>g<br />
medium<br />
Controll<strong>in</strong>g<br />
Computer<br />
Control panel<br />
(connected to<br />
measur<strong>in</strong>g sensors,<br />
regulation<br />
units, pumps<br />
<strong>and</strong> controll<strong>in</strong>g<br />
computer)<br />
Motor valve<br />
Sensors<br />
Circulation<br />
pump<br />
• Pressure vessel, load<strong>in</strong>g door <strong>and</strong> carriage<br />
• Heat<strong>in</strong>g system Insulated<br />
front door<br />
• Vapour circulation system (fans)<br />
VAK-09 e/ JBR<br />
• Dehumidification system (condenser)<br />
• Vacuum pump(s)<br />
• Sensors, regulat<strong>in</strong>g units <strong>and</strong> process<br />
control (computer)<br />
Fan<br />
Vapour exhaust<br />
to <strong>vacuum</strong> pump<br />
Insulated <strong>press</strong>ure<br />
vessel<br />
Condensate pipe<br />
Cool<strong>in</strong>g water<br />
Circulation<br />
pump<br />
Cool<strong>in</strong>g<br />
device<br />
<strong>in</strong>ternal condensation<br />
device<br />
± similar facilities<br />
<strong>and</strong> components for<br />
all vaccum dry kilns<br />
Cool<strong>in</strong>g<br />
water<br />
Vacuum pump<br />
Condensate b<strong>in</strong><br />
(6 volume measurement)
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Innovations <strong>in</strong> Vacuum Dry<strong>in</strong>g<br />
…no remarkable changes happened <strong>in</strong> process technology <strong>and</strong><br />
dry<strong>in</strong>g facilities <strong>in</strong> the last years – exept m<strong>in</strong>or improvements<br />
with <strong>in</strong>dividual kiln manufacturers …<br />
→ Advantageous improvements for kiln manufacturers, e.g., ...<br />
• reduction <strong>of</strong> manufactur<strong>in</strong>g costs, e.g., construction by modules, use<br />
<strong>of</strong> prefabricated components (wall segments from alum<strong>in</strong>ium-pr<strong>of</strong>iles<br />
for variable <strong>press</strong>ure vessel size, rectangular <strong>press</strong>ure vessels)<br />
• improvements <strong>in</strong> measur<strong>in</strong>g systems <strong>and</strong> controll<strong>in</strong>g units (sensor<br />
technology: temperature, <strong>press</strong>ure, gas humidity, wood moisture content,<br />
computerized process control …)<br />
→ Advantageous improvements for kiln users, e.g., ...<br />
• improved durability <strong>of</strong> the dry<strong>in</strong>g plant / lesser ma<strong>in</strong>tenance <strong>of</strong> all<br />
plant facilities (exclusive use <strong>of</strong> sta<strong>in</strong>less steel <strong>and</strong>/or alum<strong>in</strong>ium →<br />
lesser break down time)<br />
• improved h<strong>and</strong>l<strong>in</strong>g, process control, ma<strong>in</strong>tenance <strong>and</strong> repair (onl<strong>in</strong>e<br />
support with fault detection, dry<strong>in</strong>g schedule development ...)<br />
• lesser energy consumption, <strong>in</strong>tegrated condensation equipment<br />
• lesser or no cool<strong>in</strong>g water required (air cool<strong>in</strong>g system)
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g - Process Technologies<br />
• Convective 1. Intermittent heat<strong>in</strong>g periods under normal <strong>press</strong>ure<br />
heat transfer Dry<strong>in</strong>g dur<strong>in</strong>g <strong>in</strong>termittent <strong>vacuum</strong> phases = Discont<strong>in</strong>uous<br />
Vacuum Dry<strong>in</strong>g Process<br />
Today the most 2. Cont<strong>in</strong>uous heat transfer <strong>in</strong> low <strong>press</strong>ure atmosphere<br />
common pro- (= Superheated Steam Steam/Vacuum / Vacuum; pAbs = 100…250<br />
cess technology mbar), sufficient gas density for convective heat transfer<br />
with high gas flow (vsteam ≥ 20 m/s) = Cont<strong>in</strong>uous<br />
Vacuum Dry<strong>in</strong>g Process<br />
• Conductive Direct contact to wood - heat<strong>in</strong>g plates (sticker reheat<br />
transfer placement); <strong>press</strong>ure level as low as possible / suitable<br />
= Cont<strong>in</strong>uous Vacuum Dry<strong>in</strong>g Process<br />
• Dielectric 1. Hot / cold electrodes <strong>in</strong>tegrated <strong>in</strong> <strong>vacuum</strong> vessel;<br />
field cont<strong>in</strong>uous heat<strong>in</strong>g, <strong>press</strong>ure level as low as possible<br />
/ suitable = Cont<strong>in</strong>uous Vacuum Dry<strong>in</strong>g Process<br />
2. Microwave generator (Magnetrons) <strong>in</strong>tegrated <strong>in</strong> <strong>vacuum</strong><br />
vessel; cont<strong>in</strong>uous heat<strong>in</strong>g, <strong>press</strong>ure level as low<br />
as possible / suitable = Cont<strong>in</strong>uous Vacuum Dry<strong>in</strong>g<br />
Process
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Cont<strong>in</strong>uous Vacuum Dry<strong>in</strong>g Process<br />
Cont<strong>in</strong>uous <strong>vacuum</strong> dry<strong>in</strong>g at constant <strong>press</strong>ure level<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
VAK -011 / JBR<br />
Plate temperature h Pl<br />
Wood temperature h H<br />
Evaporation temperature at<br />
<strong>press</strong>ure level <strong>in</strong> the kiln<br />
0<br />
0 1 2 3 4 5 6 7 8 9<br />
Relative dry<strong>in</strong>g tim e t [h]<br />
��<br />
Moisture content u
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Cont<strong>in</strong>uous Vacuum Dry<strong>in</strong>g Process<br />
Platen <strong>vacuum</strong><br />
<strong>press</strong> dry<strong>in</strong>g kiln<br />
(WDE Maspell / I)<br />
�<br />
Pressure difference (environment<br />
↔ kiln chamber)<br />
ensures com<strong>press</strong>ion <strong>of</strong><br />
platen stacked timber<br />
layers
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Discont<strong>in</strong>uous Vacuum Dry<strong>in</strong>g Process<br />
Discont<strong>in</strong>uous <strong>vacuum</strong> dry<strong>in</strong>g at different <strong>press</strong>ure levels<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
VAK-012 / JBR<br />
Heat<strong>in</strong>g<br />
phase<br />
(Normal<br />
<strong>press</strong>ure)<br />
One cycle<br />
Dry<strong>in</strong>g phase<br />
(Vacuum)<br />
0<br />
0 1 2 3 4 5 6 7 8 9<br />
Relative dry<strong>in</strong>g time t [h]<br />
�<br />
Circulat<strong>in</strong>g air temperature h L<br />
Wood temperature hH Evaporation temperature<br />
at <strong>press</strong>ure level dur<strong>in</strong>g<br />
<strong>vacuum</strong> phase<br />
Moisture content u<br />
10 11 12<br />
Two different <strong>press</strong>ure levels (→ alternat<strong>in</strong>g heat<strong>in</strong>g phase at<br />
normal <strong>press</strong>ure <strong>and</strong> dry<strong>in</strong>g phase at reduced <strong>press</strong>ure level)
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Discont<strong>in</strong>uous Vacuum Dry<strong>in</strong>g Process<br />
Maspell Trockner GOLIATH 50<br />
Gleisbahn<br />
3.800 mm<br />
15.000 mm<br />
12.500 mm<br />
1.250 mm 1.250 mm<br />
Platen-less <strong>vacuum</strong> kilns (Type GOLIATH, WDE Maspell / I; two kilns <strong>in</strong> t<strong>and</strong>em<br />
operation, horizontal air circulation dur<strong>in</strong>g heat<strong>in</strong>g phases (� lo-la ⇒ longitud<strong>in</strong>allateral))
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Superheated Steam / Vacuum Dry<strong>in</strong>g<br />
Cont<strong>in</strong>uous <strong>vacuum</strong> dry<strong>in</strong>g <strong>in</strong> superheated steam atmosphere<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
����� ������� � �<br />
Heat<strong>in</strong>g<br />
up<br />
1 st Dry<strong>in</strong>g<br />
phase<br />
Superheated vapour temperature h Vap<br />
Evaporation temperature at<br />
<strong>press</strong>ure level <strong>in</strong> the kiln h S<br />
Pressure development<br />
<strong>in</strong> the kiln p Vap<br />
2 nd Dry<strong>in</strong>g<br />
phase<br />
3 rd Dry<strong>in</strong>g<br />
phase<br />
Condition<strong>in</strong>g<br />
Wood surface temp.<br />
W ood core temp.<br />
200<br />
Avg. moisture content u m<br />
0 1 2 3 4 5 6 7 8 9<br />
R elative dry<strong>in</strong>g tim e t [...]<br />
150<br />
100<br />
50
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Superheated Steam / Vacuum Dry<strong>in</strong>g<br />
Warm humid<br />
air<br />
from stack<br />
Integrated heat-pump as ma<strong>in</strong> heat<strong>in</strong>g system<br />
Evaporator<br />
(cold)<br />
Electricity<br />
Expansion valve<br />
Com<strong>press</strong>or<br />
Condenser<br />
(hot)<br />
Additional<br />
water<br />
circuit<br />
Warm<br />
water<br />
Cold<br />
water<br />
Warm dry<br />
air to the<br />
stack<br />
Mode <strong>of</strong> action <strong>of</strong> heat-pump (dehumidification unit)<br />
(see plants from Eberl <strong>and</strong> Kronseder) Details
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Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Superheated Steam / Vacuum Dry<strong>in</strong>g<br />
Superheated steam flow <strong>in</strong> convectively heated <strong>vacuum</strong> kilns<br />
Crosswise steam flow<br />
• heat pipes <strong>and</strong> fan at the side <strong>of</strong><br />
the stack side; vertical flow back<br />
<strong>in</strong>to the stack at opposite kiln wall.<br />
One or two fan / heat pipe l<strong>in</strong>es<br />
(e.g., Brunner, Mühlböck, IWT, Kronseder)<br />
• Heat pipes <strong>and</strong> fans on top <strong>of</strong> the<br />
stack (IWT, Mühlböck - former kiln<br />
types)<br />
• Heat pipes <strong>and</strong> fans <strong>in</strong> front <strong>of</strong> the<br />
stack (at both sides), horizontal<br />
steam flow reversal (longitud<strong>in</strong>al -<br />
lateral with WDE / Maspell <strong>and</strong> Eberl)<br />
Lengthwise steam flow<br />
• Heat pipes <strong>and</strong> fans <strong>in</strong> front <strong>of</strong><br />
stack, horizontal steam flow reversal<br />
(small kilns, special corrugated<br />
stickers required, e.g. Mühlböck)
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Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Radio Frequency / Vacuum Dry<strong>in</strong>g<br />
Radio Frequency-Vacuum dry kiln (RF/V-dry<strong>in</strong>g)<br />
Steamcondenser<br />
Vacuum<br />
-pump<br />
“Hot” electrode<br />
“Cold” electrode<br />
Scheme <strong>of</strong> a RF/V-dry kiln (Wolf)<br />
• Dielectric Heat<strong>in</strong>g <strong>of</strong> wet wood <strong>in</strong><br />
a dielectric field<br />
• Wet Wood as dielectric material<br />
• Power absorption <strong>of</strong> the material<br />
Radi<strong>of</strong>requencygenerator<br />
Ground<br />
Cold electrode<br />
Hot electrode<br />
Cold electrode<br />
P = 0,556 � f � E 2 � ε´´ � 10 -12 [W/cm³]<br />
P [W/cm³] Power per unit volume<br />
f [Hz] Frequency<br />
E [V/cm] Field strength<br />
ε” [-] Loss factor <strong>of</strong> wood
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Eberl<br />
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HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Radio Frequency / Vacuum Dry<strong>in</strong>g<br />
Radio Frequency-Vacuum dry kiln (RF/V-dry<strong>in</strong>g)<br />
Advantages<br />
• Very short dry<strong>in</strong>g time<br />
• Wide thickness range <strong>of</strong><br />
timber to be dried<br />
• Very good dry<strong>in</strong>g quality<br />
• Stack<strong>in</strong>g without stickers<br />
Up to now only one successful<br />
kiln manufacturer on the<br />
American market :<br />
→ HeatWave Technologies /<br />
CAN<br />
Disadvantages<br />
• Limited to highly permeable<br />
species<br />
• High <strong>in</strong>vestment costs<br />
• High energy costs (electricity!)<br />
• Low efficiency <strong>of</strong> RF-generator<br />
(η = 0,55..0,65)<br />
• Limited life time RF-tube<br />
(approx. 4000 - 8000 h)
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Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Brunner<br />
Superheated steam <strong>vacuum</strong> dry kilns<br />
BRUNNER<br />
Brunner Trockentechnik<br />
• Rectangular<br />
<strong>press</strong>ure vessel<br />
• Fans <strong>and</strong> heat<strong>in</strong>g<br />
coils on one<br />
side <strong>of</strong> the<br />
timber stack
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Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Brunner<br />
Superheated steam <strong>vacuum</strong> dry kilns<br />
BRUNNER<br />
Brunner Trockentechnik<br />
����<br />
���������������� ������������ ��<br />
����������������� ����������������� ����������������� ��������������������<br />
�����������<br />
����������������<br />
������������<br />
���� �<br />
�����<br />
(1) Heat<strong>in</strong>g coil, separately<br />
adjustable<br />
(2) Intermediate heat<strong>in</strong>g<br />
coils (on dem<strong>and</strong>)<br />
(3) Integrated steam<br />
generator<br />
(4) Fans, reversible rotation,<br />
separately adjustable<br />
(5) Vacuum pump<br />
(6) Controlled fresh air<br />
supply<br />
(7) Dra<strong>in</strong>-pipe, cont<strong>in</strong>uously<br />
condensate extraction<br />
dur<strong>in</strong>g the process<br />
(8) Controlled heat supply,<br />
separately adjustable for<br />
each sections<br />
(9) Kiln load / stacks<br />
(10) Evaporated steam from<br />
timber<br />
(11) Condensed water from<br />
timber<br />
(12) Two temperature probes<br />
sides <strong>of</strong> the stack<br />
(13) Wood-moisture content<br />
probes (12 x), for dry<strong>in</strong>g<br />
gradient control (surface<br />
- 1/3-depth <strong>and</strong> 1/2depth)<br />
(14) Wood-temperature probe<br />
for process control
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Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Brunner<br />
Superheated steam <strong>vacuum</strong> dry kilns<br />
BRUNNER<br />
Brunner Trockentechnik<br />
Investment costs [1000 Euro]<br />
500<br />
Vacuum dry kilns (high-low)<br />
Conventional dry kilns (high-low)<br />
400<br />
(gross capacity 95...140 m³)<br />
300<br />
200<br />
100<br />
0<br />
1992 1997 2000<br />
Decl<strong>in</strong>e <strong>of</strong> <strong>in</strong>vestment costs superheated<br />
steam <strong>vacuum</strong> - heat-<strong>and</strong>-vent kiln dry<strong>in</strong>g<br />
dur<strong>in</strong>g the past decade (Brunner, 1999)<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
European White Oak<br />
Total dry<strong>in</strong>g time down to mc f<strong>in</strong>al = 8 %<br />
High VAC ® - Superheated Steam -Vacuum<br />
Heat-<strong>and</strong>-Vent (Conventional kiln Dry<strong>in</strong>g)<br />
SH / V<br />
Heat-<strong>and</strong>-Vent<br />
0 10 20 30 40 50 60 70 80 90 100<br />
Total dry<strong>in</strong>g time [d]
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Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - IWT<br />
(1) Heat<strong>in</strong>g pipes (6) Temperature probe<br />
(2) Fans (7) EMC-Sensor<br />
(3) Carriage (8) Pressure Sensor<br />
(4) Top Baffle (9) Hydraulic clos<strong>in</strong>g<br />
(5) Wood- MC-probes system<br />
(11) Sta<strong>in</strong>less steel vessel (10) Hydraulic pump<br />
Superheated steam <strong>vacuum</strong> dry kilns<br />
Innovative Wood Technology IWT
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Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Mühlböck<br />
EMC-Probe<br />
Stickers<br />
• Cyl<strong>in</strong>drical <strong>press</strong>ure vessel<br />
• Lengthwise steam flow<br />
• Fans at the backside <strong>of</strong> the<br />
vessel<br />
• Special corrugated stickers<br />
required<br />
Superheated steam <strong>vacuum</strong> dry kilns<br />
MÜHLBÖCK Holztrocknungsanlagen<br />
�• Cyl<strong>in</strong>drical <strong>press</strong>ure vessel<br />
• Crosswise steam flow <strong>in</strong> two directions<br />
• Fans / heat<strong>in</strong>g coils on one side<br />
<strong>of</strong> the stack (bisectional)
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Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Kronseder<br />
Superheated steam <strong>vacuum</strong> dry kiln (on dem<strong>and</strong> with heat-pump)<br />
EUROVAC / � �������� � �������������<br />
Kiln load<strong>in</strong>g<br />
Outdoor <strong>in</strong>stallation on prefabricated<br />
foundations<br />
Switch board, heat-pump <strong>and</strong><br />
<strong>vacuum</strong> pump
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Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Eberl<br />
Superheated steam <strong>vacuum</strong> dry kiln with heat-pump system<br />
EBERL Trocknungsanlagen<br />
Top view - horizontal steam flow across the stack<br />
Details
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Brunner<br />
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Mühlböck<br />
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Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Opel<br />
Platen-<strong>vacuum</strong> dry kiln (Press-dry<strong>in</strong>g kiln)<br />
�����������<br />
Com<strong>press</strong>ion applied<br />
by <strong>in</strong>flated rubber tube<br />
���������<br />
���������<br />
Rigid structure <strong>in</strong> right angle <strong>press</strong>ure vessel
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Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Opel<br />
Platen-<strong>vacuum</strong> dry kiln (Press-dry<strong>in</strong>g kiln)<br />
�����������<br />
Awkward h<strong>and</strong>l<strong>in</strong>g <strong>of</strong> heat<strong>in</strong>g plates
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Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - HeatWave<br />
Radio-frequency <strong>vacuum</strong> dry kiln<br />
����� ��� �����������������������<br />
9<br />
HeatWave type 5.20<br />
• Capacity 5 m³ (net timber volume)<br />
• RF power output 20 kW (air cooled RF-tube)<br />
5<br />
4<br />
8<br />
7<br />
1 Power amplifier <strong>and</strong><br />
match<strong>in</strong>g network<br />
2 Vacuum pump<br />
3 Vacuum condenser<br />
4 hydraulic com<strong>press</strong>ion<br />
system (total <strong>press</strong>ure<br />
approx. 1,1 MN)<br />
5 RF-electrode<br />
6 Condensate dra<strong>in</strong><br />
7 Control unit<br />
8 Drier chamber<br />
9 Material h<strong>and</strong>l<strong>in</strong>g system
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Brunner<br />
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Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - HeatWave<br />
Radio-frequency <strong>vacuum</strong> dry kiln<br />
����� ��� �����������������������<br />
HeatWave type 50.150<br />
• Capacity 50 m³<br />
(net timber volume)<br />
• RF power output 150 kW<br />
(water cooled RF-tube)
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HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g - Fundamentals<br />
Conductive heat transfer → no ... moderate com<strong>press</strong>ion <strong>of</strong> timber<br />
(or timber surface) to be dried<br />
Limitations<br />
→ Com<strong>press</strong>ion forces < com<strong>press</strong>ion strength <strong>of</strong> wood<br />
perpendicular to gra<strong>in</strong> (s<strong>of</strong>twood species approx. 2...10<br />
MPa; hardwood species approx. 5...20 MPa)<br />
→ Com<strong>press</strong>ion strength depend<strong>in</strong>g on wood species,<br />
moisture content <strong>and</strong> (process) temperature (0...140°C<br />
→ 30...35% strength reduction)<br />
→ Initiated <strong>in</strong>ternal <strong>press</strong>ure (water evaporation) <strong>in</strong>creases<br />
rapidly with temperature (100°C → 0,1 MPa; 120°C → 0,2<br />
MPa; 140°C → 0,38 MPa)
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Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g - Process Technology<br />
Pressure<br />
Process parameters<br />
Pressure<br />
• Without com<strong>press</strong>ion<br />
S<strong>of</strong>twoods p < 1,5 MPa<br />
Hardwoods p < 2,5 MPa<br />
Heat<strong>in</strong>g plate • Slight com<strong>press</strong>ion<br />
p < 5...12 MPa, depend<strong>in</strong>g<br />
Timber on wood species<br />
Feed<strong>in</strong>g•<br />
short <strong>in</strong>termittent decom-<br />
Tray<br />
<strong>press</strong>ion periods<br />
Pressure Temperature<br />
• 100...140°C, depend<strong>in</strong>g on<br />
wood species<br />
Scheme <strong>of</strong> a <strong>press</strong> dry<strong>in</strong>g plant - multi-day- Time<br />
light <strong>press</strong> (batch process) with feed<strong>in</strong>g<br />
trays<br />
• 12...24 hours, depend<strong>in</strong>g<br />
on f<strong>in</strong>al mc <strong>and</strong> acceptable<br />
discoloration <strong>of</strong> wood
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Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g - Process Technology<br />
Process characteristics <strong>and</strong> advantages<br />
(accord<strong>in</strong>g to Arboreo Technologies Ltd. / FIN)<br />
• Rapid dry<strong>in</strong>g process<br />
• Less cracks, warp<strong>in</strong>g <strong>and</strong> cupp<strong>in</strong>g<br />
• Due to <strong>press</strong><strong>in</strong>g the timber stays / becomes straight<br />
• Hardness <strong>in</strong>creases by 11 ... 18 %<br />
• Strength properties improve by 15 ... 33 %<br />
• More resistant towards rott<strong>in</strong>g<br />
• Moisture expansion reduced up to 2,7 times (Spruce)<br />
• Net material sav<strong>in</strong>gs 15 ... 20 % due to higher net<br />
recovery <strong>and</strong> m<strong>in</strong>imized dry<strong>in</strong>g defects
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Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g - Process Technology<br />
1. Pre-<br />
Dry<strong>in</strong>g<br />
105 °C<br />
95 °C<br />
3 MPa<br />
2. Ma<strong>in</strong><br />
Dry<strong>in</strong>g<br />
3. F<strong>in</strong>al<br />
Dry<strong>in</strong>g<br />
130 ... 200 °C<br />
4. Cool<br />
Down<br />
4...10 h 3...16 h 2...4 h 2...8 h<br />
12 MPa<br />
80 °C<br />
Total process duration ~ 12 ... 24 h<br />
Time [h]<br />
Process phases <strong>and</strong> temperatures<br />
(Arboreo Technologies Ltd. - Com<strong>press</strong>ion<br />
dryers /FIN)<br />
a r b o r e o<br />
technologies<br />
TECHNICAL DATA<br />
- cell size length 6200 mm<br />
- cell size width 2200 mm<br />
- timber thickness 15 … 55 mm<br />
- kiln capacity 10 … 25 m³<br />
- <strong>in</strong>itial mc � predried … green<br />
- f<strong>in</strong>al mc � 6 … 8 %<br />
- dry<strong>in</strong>g time 6…24 hours, depend<strong>in</strong>g<br />
on the treatment <strong>in</strong>tention<br />
- energy consumption approx.<br />
250 … 300 kWh / m³
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g - Process Technology<br />
a r b o r e o<br />
technologies<br />
TECHNICAL FEATURES<br />
- timber stacked crosswise between<br />
hollow, perforated metal<br />
pr<strong>of</strong>iles (<strong>press</strong> plates)<br />
- convective heat transfer to<br />
<strong>press</strong> plates / layers<br />
- air velocity through plates<br />
approx. 5…6 m/s (<strong>in</strong>itiated by<br />
4 fans á 25.000 m³/h)<br />
- conductive heat transfer between<br />
<strong>press</strong> plates <strong>and</strong> timber<br />
- cont<strong>in</strong>uous process control<br />
(temperature probes <strong>in</strong>side wood,<br />
temperature control dry<strong>in</strong>g conditions,<br />
humidity control by dampers<br />
…)
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g Plant<br />
Stack carriage<br />
Stack<strong>in</strong>g frame<br />
a r b o r e o<br />
technologies<br />
Press dry kiln<br />
Stack<strong>in</strong>g <strong>and</strong> load<strong>in</strong>g/unload<strong>in</strong>g from both sides <strong>of</strong> the kiln
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g Plant<br />
View <strong>in</strong>to the Press Dry<strong>in</strong>g Plant<br />
a r b o r e o<br />
technologies
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g Plant<br />
Heat<strong>in</strong>g<br />
coils<br />
Circulat<strong>in</strong>g<br />
hot air<br />
Com<strong>press</strong>ion<br />
Fans<br />
External<br />
frame<br />
Fanmotor<br />
Com<strong>press</strong>ion<br />
Removable<br />
rails<br />
External<br />
frame<br />
Com<strong>press</strong>ion Dryer – diagram <strong>of</strong> cross section (former HitWood Plant RSA)
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Press Dry<strong>in</strong>g Plant – HitWood<br />
Stack<strong>in</strong>g frame<br />
<strong>in</strong> load<strong>in</strong>g position<br />
(open)<br />
Heat<strong>in</strong>g panels<br />
→ hollow metal<br />
pr<strong>of</strong>iles (convective<br />
heat<strong>in</strong>g !)<br />
Stack<strong>in</strong>g frame<br />
Stack carriage<br />
Com<strong>press</strong>ion Dryer – diagram <strong>of</strong> cross section (former HitWood Plant <strong>in</strong> RSA)
University <strong>of</strong> Hamburg<br />
Thank you for<br />
your attention !<br />
Vacuum <strong>and</strong><br />
<strong>press</strong> dry<strong>in</strong>g ….<br />
have been presented by<br />
J. B. Ressel<br />
University <strong>of</strong> Hamburg<br />
Center for Forest Products<br />
Leuschnerstr. 91<br />
D-21031 Hamburg<br />
ressel@holz.uni-hamburg.de<br />
Center for Forest Products<br />
Mechanical Wood Process<strong>in</strong>g<br />
Pr<strong>of</strong>. Dr. J. B. Ressel<br />
COST E 15 - Dry<strong>in</strong>g Sem<strong>in</strong>ar Limerick, Eire / 21-11-2003 29-10-2003 / JBR / 40
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Eberl<br />
Superheated steam <strong>vacuum</strong> dry kiln with heat-pump system<br />
EBERL Trocknungsanlagen<br />
Load<strong>in</strong>g the kiln built up on the timber yard<br />
Suck<strong>in</strong>g canal, heat-pump or<br />
dehumidification system <strong>and</strong><br />
fans beh<strong>in</strong>d end wall
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g Plants - Eberl<br />
Superheated steam <strong>vacuum</strong> dry kiln with heat-pump system<br />
EBERL Trocknungsanlagen<br />
Integrated operation<br />
room with condensate<br />
tank at the back <strong>of</strong> the<br />
kiln<br />
Dehumidification<br />
system <strong>and</strong><br />
fans beh<strong>in</strong>d the<br />
back wall <strong>in</strong> the<br />
<strong>press</strong>ure vessel<br />
Condenser<br />
Condensate<br />
collector<br />
Expansion<br />
valve<br />
Evaporator<br />
Radial fans<br />
Com<strong>press</strong>or
Center for<br />
Forest Products<br />
Pr<strong>of</strong>. Dr. Ressel<br />
Introduction<br />
Fundamentals<br />
Plant Facilities<br />
Innovations<br />
Process<br />
Technology<br />
Plant Examples<br />
Brunner<br />
IWT<br />
Mühlböck<br />
Kronseder<br />
Eberl<br />
Opel<br />
HeatWave<br />
Press Dry<strong>in</strong>g<br />
����������� � �� ����<br />
Vacuum Dry<strong>in</strong>g – Process Technologies<br />
Integrated heat-pump as ma<strong>in</strong> heat<strong>in</strong>g system<br />
Auxiliary<br />
electrical<br />
heat<strong>in</strong>g<br />
Steam<br />
<strong>in</strong>to<br />
stack<br />
Radial<br />
fans<br />
Steam<br />
from<br />
stack<br />
Refrigerant circuit<br />
Mode <strong>of</strong> action <strong>of</strong> heat-pump (dehumidification<br />
system) <strong>and</strong> EBERL dry kiln �<br />
Com<strong>press</strong>or<br />
Condenser<br />
Evaporator<br />
Condensate<br />
to dra<strong>in</strong><br />
Expansion<br />
valve
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