EP0388459A1 - Process for drying wood. - Google Patents
Process for drying wood.Info
- Publication number
- EP0388459A1 EP0388459A1 EP89910628A EP89910628A EP0388459A1 EP 0388459 A1 EP0388459 A1 EP 0388459A1 EP 89910628 A EP89910628 A EP 89910628A EP 89910628 A EP89910628 A EP 89910628A EP 0388459 A1 EP0388459 A1 EP 0388459A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- drying
- wood
- tunnel
- substreams
- section
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/02—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure
Definitions
- the present invention relates to a process for drying wood in a drying tunnel through which the wood is gradually fed and there permeated by drying air which flows in the longi ⁇ tudinal direction of the tunnel.
- the present invention relates to such a process in which the drying tun ⁇ nel is divided into two sections separated by an intervening space and with the drying medium divided into two circulating substreams.
- Sawn wood should be dried to a moisture content of approx. 15-22 %, calculated on the dry weight of the wood, in order that the wood can be stored without biological attack in the form of mould etc.
- two main types of drying kiln are employed, so-called compartment kilns and progressive kilns (tunnel kilns) , whereas timber- yard drying has practically ceased.
- drying schedule is meant how the temperature and moisture content of the drying air and its speed of flow through the wood pile are caused to vary during the drying period. It is therefore possible in this type of kiln to employ what is, by some criterium, the optimum drying schedule. This is the principal advantage of this kiln.
- the disadvantages include a relatively high energy consumption and that these kilns cannot, be made especially large because otherwise the drying climate would vary too much in different parts of the wood load.
- the pro ⁇ gressive kiln has the advantage that the energy consumption is appreciably lower since the air which leaves the kiln is almost saturated and also heat recovery can readily be ob ⁇ tained. Further, the progressive kiln can advantageously be constructed for high capacities, 10,000 - 20,000 m /annum.
- a division of the progressive kiln into two stages has been proposed and has also come into use at some sawmills.
- the drying air is introduced into the tunnel oetween the stages so that part flows in a counter- current direction in the first stage of the kiln and part in a concurrent direction in the second drying stage.
- this two-stage pro ⁇ gressive kiln has advantages primarily in regard to control technology as it has a number of self-regulating properties.
- the final moisture content of the wood after the desired drying time should be that which is aimed for, and on the other hand the quality loss of the wood in drying should be as little as possible or at least acceptable.
- the speed of drying increases as the difference be ⁇ tween the dry-bulb and wet-bulb temperatures of the air in ⁇ creases.
- the magnitude of the change in the quality of the wood is a more complicated function of the drying procedure, but roughly it can be said that the faster drying is carried out the greater are the quality losses.
- the quality loss of the wood in drying can be divided into two main components.
- One is that with high temperature levels and/or long drying times there is a flow of resin at knots etc. together with a darkening of the surface of the wood, the other is the occurrence of cracks in the wood.
- crack formation is, especially with thicker dimen ⁇ sions, clearly the more important...
- the cause of crack forma ⁇ tion can be explained in the following manner. In drying the surface of the timber dries faster than the inner parts of the piece of timber because of the resistance to the movement of moisture within the material. When the fibre saturation point is reached, i.e. when the free water has been removed and only water bound to the wood substance remains, the wood starts to shrink.
- the present invention is accordingly based on the discovery that if the direction of flow of the drying air during the first stage of drying is countercurrent and during the lat ⁇ ter stage is concurrent in relation to the wood, then a low psychrometric difference is obtained during the period which is critical for the quality of the wood with a increasing psychrometic difference on either side of this point.
- Figure 3 is pre ⁇ sented.
- the psychrometric difference here decreases with time, which leads to a rapid drying at in the beginning, so that the fibre saturation point is reached al ⁇ ready after 12 hours, whereas the stress level does not now rise as high as in Figure 2.
- the heating unit for the drying air fans for transport of the air through the timber, and the ventilation unit for maintenance of the desired air humidity.
- Figure 4 shows an example comparable with Figures 2 and 3 and in which the same air (psychrometric difference 9.5°C) is fed into both drying stages and in which the air speeds (3.12 and 2.24 m/s respectively) are matched so that the pressure drops are the same, i.e. a situation which can be obtained using only a single common heating unit and a single fan unit. It is apparent from the figure that the stress peaks are practi ⁇ cally identical with the peaks in Figure 3. Further it is found that the drying air from each of the stages has almost the same condition (psychrometric difference approx. 4°C) .
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Drying Of Solid Materials (AREA)
- Chemical And Physical Treatments For Wood And The Like (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FI884428 | 1988-09-27 | ||
FI884428A FI98092B (en) | 1988-09-27 | 1988-09-27 | Method for drying timber |
PCT/FI1989/000186 WO1990003543A1 (en) | 1988-09-27 | 1989-09-27 | Process for drying wood |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0388459A1 true EP0388459A1 (en) | 1990-09-26 |
EP0388459B1 EP0388459B1 (en) | 1995-11-29 |
Family
ID=8527099
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP89910628A Expired - Lifetime EP0388459B1 (en) | 1988-09-27 | 1989-09-27 | Process for drying wood |
Country Status (8)
Country | Link |
---|---|
EP (1) | EP0388459B1 (en) |
AT (1) | ATE130929T1 (en) |
AU (1) | AU4228389A (en) |
DE (1) | DE68924974T2 (en) |
FI (1) | FI98092B (en) |
LV (1) | LV11064B (en) |
RU (1) | RU2080532C1 (en) |
WO (1) | WO1990003543A1 (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
AT504578B1 (en) * | 2006-11-21 | 2009-11-15 | Muehlboeck Kurt | METHOD FOR DRYING WOOD MATCHED IN STACKS |
AT510007B1 (en) * | 2010-12-07 | 2012-01-15 | Muehlboeck Kurt | PROCESS FOR WOOD DRYING |
CN102321249B (en) | 2011-06-30 | 2013-01-16 | 无锡碧杰生物材料科技有限公司 | Thermoplastic starch (TPS), biodegradable polyester/starch composite material and preparation thereof |
CN102889757A (en) * | 2012-10-24 | 2013-01-23 | 无锡市通和工机有限公司 | Tunnel type drier |
AT515466B1 (en) * | 2014-02-26 | 2016-05-15 | Mühlböck Kurt | Process for drying bulk material |
CN109405445A (en) * | 2018-11-06 | 2019-03-01 | 中山市大涌镇志吉烘干厂 | A kind of timber stoving technique |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
SE368740B (en) * | 1966-08-22 | 1974-07-15 | Svenska Flaektfabriken Ab | |
AT335918B (en) * | 1974-07-11 | 1977-04-12 | Vanicek Viktor | DRYING SYSTEM, IN PARTICULAR DRYING CHANNEL |
-
1988
- 1988-09-27 FI FI884428A patent/FI98092B/en not_active IP Right Cessation
-
1989
- 1989-09-27 DE DE68924974T patent/DE68924974T2/en not_active Expired - Lifetime
- 1989-09-27 AU AU42283/89A patent/AU4228389A/en not_active Abandoned
- 1989-09-27 AT AT89910628T patent/ATE130929T1/en not_active IP Right Cessation
- 1989-09-27 EP EP89910628A patent/EP0388459B1/en not_active Expired - Lifetime
- 1989-09-27 WO PCT/FI1989/000186 patent/WO1990003543A1/en active IP Right Grant
- 1989-09-27 RU SU4830243/06A patent/RU2080532C1/en active
-
1993
- 1993-06-22 LV LVP-93-645A patent/LV11064B/en unknown
Non-Patent Citations (1)
Title |
---|
See references of WO9003543A1 * |
Also Published As
Publication number | Publication date |
---|---|
FI884428A (en) | 1990-03-28 |
WO1990003543A1 (en) | 1990-04-05 |
DE68924974T2 (en) | 1996-05-02 |
FI884428A0 (en) | 1988-09-27 |
FI98092B (en) | 1996-12-31 |
LV11064A (en) | 1996-02-20 |
AU4228389A (en) | 1990-04-18 |
EP0388459B1 (en) | 1995-11-29 |
DE68924974D1 (en) | 1996-01-11 |
RU2080532C1 (en) | 1997-05-27 |
ATE130929T1 (en) | 1995-12-15 |
LV11064B (en) | 1996-04-20 |
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Legal Events
Date | Code | Title | Description |
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PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
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Owner name: VALMET PAPER MACHINERY INC. |
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