CA1150497A - Process for drying of wood - Google Patents
Process for drying of woodInfo
- Publication number
- CA1150497A CA1150497A CA000379373A CA379373A CA1150497A CA 1150497 A CA1150497 A CA 1150497A CA 000379373 A CA000379373 A CA 000379373A CA 379373 A CA379373 A CA 379373A CA 1150497 A CA1150497 A CA 1150497A
- Authority
- CA
- Canada
- Prior art keywords
- wood
- drying
- moisture
- drying oil
- reduced pressure
- 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.)
- Expired
Links
Landscapes
- Drying Of Solid Materials (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention deals with a process for drying of wood and the other organic material. The drying is carried out by heating the wood in an oil with an adapted boiling point and under vacuum. The feature of the process is that the heating wholly or partly is carried out by dielectrical energy.
The present invention deals with a process for drying of wood and the other organic material. The drying is carried out by heating the wood in an oil with an adapted boiling point and under vacuum. The feature of the process is that the heating wholly or partly is carried out by dielectrical energy.
Description
Process for Drying of Wood 3 '~ 7 According to my ~we~ish paten-t -3-~3~-G-~ a very fast and mild drying of wood can be carried out in warm oil under vacuum.
The most difficult problem by this process is to avoid that rests of the drying medium - the oil -remain in ~he surface layer of the wood. Too large rests increase the costs, results in fire risks and environment problems and the difficulties in combination with for instance gluing and painting.
In order to solve these problems a drylng medium lS chosen with a specially adjusted boiling point and the process is carried out at suitable vacuum and temperature.
Furthermore the process can be performed in separated operations to facilitate the drying medium to evaporate from the wood surface.
Investigations have made it clear that this oil drying process under vacuum (ODV) with a defini-te advantage can be combined with an electrical drying process (ED~. ~
The most difficult problem by this process is to avoid that rests of the drying medium - the oil -remain in ~he surface layer of the wood. Too large rests increase the costs, results in fire risks and environment problems and the difficulties in combination with for instance gluing and painting.
In order to solve these problems a drylng medium lS chosen with a specially adjusted boiling point and the process is carried out at suitable vacuum and temperature.
Furthermore the process can be performed in separated operations to facilitate the drying medium to evaporate from the wood surface.
Investigations have made it clear that this oil drying process under vacuum (ODV) with a defini-te advantage can be combined with an electrical drying process (ED~. ~
2 ~ '3~
ED has the advantage that the heat can be applied directly within the wood a-t the place where it is needed. Thus the heat does not as by usual convection slowly move from the surface to the inner parts of the wood in order to be utilized there for the evaporation of the mois-ture.
ED-heat can be supplied dielectrically within a large frequency range. From conventional and apparatus technical reasons it is above all two ranges that are of interest. The higher lies in the GHz region (1000 millions waves peF second). The lower frequency range - usually called high-frequency - lies in a region of sorne tens of MHz (million waves per se~ond). The energy producers for the higher frequency generally are called microwave generators. The energy producers within the lower frequency range are called HF- or high-frequency-generators.
Below the notation EDA is used for heating~drying that takes place within the higher frequency range, preferably the GHz region, the notation EDB is used for heating/drying that takes place within the lower frequency range prefera~ly the region of some tens of MHz. The given limi-ts shall not ,~. ' be understood literally, they fluctuate depending on different ways of construction and other circumstances.
The EDA model must have electrically closed rooms (cavities) with wave guides as connections to the microwave-generator while EDB uses capacitive fieldactivators with relatèd electrodes and connecting wires~
EDA seems definitely to be preferrea but EDB has not to be excluded as different ways of procedure and constructions can give different results. The disadvantage with EDB is that the wood must be fixed between electrodes so that the realization of ODV can be more dlfficult or result in a decrease in capacity.
In ODV it is possible to introduce heat wholly or partly by the ED~ The ED-enexgy is, however, rather expensive and when then ODV is suitable from the point of view of capacity and heat technology for the evaporation of the large quantities of water that are present comparatively near the surface, this indicates that a combina-tion of the usual ODV and ED gives the best result. The way will then be that the process is started w~th the usual ODV. In this way the . . 4 main part of the water is evaporated from the wood. It may here be a question oE for instance 80 per cent of the water that totally has to be evaporated from the wood.
When the outer and more voluminous parts of the wood in this way have been essentially dried and when the inner parts still are moistured the ED-drying starts. The problem then is to dry away a smaller part of the water in the wood. When this water is present in the inner parts of the wood the evaporation of it represents decidely tne most difflcult par-t of the drying. The ED heat will, however, be directed just to this moisture region within the wood and represents therefore an excellent way to solve this problem and comple-te the drying.
Another circumstance that also speaks for the here described di~iding of the drying is that the heat that is generated by EDA can be introduced only a short distance in to very wet wood and not to the inner parts depending on the fact that a high moisture content is electrically screening.
~L~5~J~97 From above it is clear that the ED-heating in an effective way can be used in ODV. There exists other interesting circumsta~lces which show how well ODV fits for all ED-heating. The drying medium has for the task suitable electric properties which means that the ED heat in the first hand is introduced not to the drying medium but to the wood.
If a part of the heat should be transferred to the drying medium this part is not wholly lost, but results in that less heat from other sources is needed for the warming of the medium. The wood is enclosed in a metallic cavity which forms a suitable room for the EDA heat. The cavity can be made in different ways. Very often its main ~art is made of iron in form of a cylinder and is further improved by covering the inside of the cylinder with a suitable metal as copper or aluminium. By the vacuum in the cylinder ionization effects and arcs are easier kept under control. l~hen the last part of the dryiny is carried out accordingly with ED the possibiLities to solve the most difficult problem in connection with ODV
is facilitated, that is to remove the rest of -the of the drying medium from the surface of the wood. This means "
~51~
also that the rules for the performance of the ODV can be simplified. Thus there is not necessary to demand the same high quality of the drying mediums. By example mediums with somewhat higher boiling point - up to 30C
higher than given in patent 992.307 (drying oil boiling points from about 150 to about 250C, heat between about 50 and 90C, at reduced pressures of about 15 to about 120 mm Hg) - can be used which next facilities the oper-ation of ODV.
Above it has been described how ED can be in-troduced into the latter part of the ODV. As ODV together with ED has such improving qualities the ED can, as well, be introduced earlier in the ODV. Thus ED can very well be applied from the beginning of the drying. In this case a ED-heated ODV process is obtained where the drying in the beginning occurs comparatively similar to usual ODV - specially when adapting EDA - and without real action on the inner parts of the wood. Gradually the process changes character and the ED heat is more and more concentrated to the inner parts of the wood. The heat would in such a process to begin with be more ex-- pensive than in a normal ODV process corresponding to the above given description. Here ls, however, to remember the important sawing that is gained ..~,..~, 7 ~150497 because no heating unit for a normal ODV process is needed.
When the heating is carried out dielectrically with drying medium left in the cylinder later or sooner a higher temperature is obtained in the inner parts of the wood than in the outer parts and in the drying medium. In this situation it is possible to arrange so that the steam evaporating from the wood is condensed in the dryiny medium which then is heated, i.e.it takes care of the condensing heat of the stam. The condensed water is separated from the drying medium in the bottom region in the drying cylinder.
Usually the condens heat is taken care of in condensors outside ~
the drying cylinder~ ¦
.
ED has the advantage that the heat can be applied directly within the wood a-t the place where it is needed. Thus the heat does not as by usual convection slowly move from the surface to the inner parts of the wood in order to be utilized there for the evaporation of the mois-ture.
ED-heat can be supplied dielectrically within a large frequency range. From conventional and apparatus technical reasons it is above all two ranges that are of interest. The higher lies in the GHz region (1000 millions waves peF second). The lower frequency range - usually called high-frequency - lies in a region of sorne tens of MHz (million waves per se~ond). The energy producers for the higher frequency generally are called microwave generators. The energy producers within the lower frequency range are called HF- or high-frequency-generators.
Below the notation EDA is used for heating~drying that takes place within the higher frequency range, preferably the GHz region, the notation EDB is used for heating/drying that takes place within the lower frequency range prefera~ly the region of some tens of MHz. The given limi-ts shall not ,~. ' be understood literally, they fluctuate depending on different ways of construction and other circumstances.
The EDA model must have electrically closed rooms (cavities) with wave guides as connections to the microwave-generator while EDB uses capacitive fieldactivators with relatèd electrodes and connecting wires~
EDA seems definitely to be preferrea but EDB has not to be excluded as different ways of procedure and constructions can give different results. The disadvantage with EDB is that the wood must be fixed between electrodes so that the realization of ODV can be more dlfficult or result in a decrease in capacity.
In ODV it is possible to introduce heat wholly or partly by the ED~ The ED-enexgy is, however, rather expensive and when then ODV is suitable from the point of view of capacity and heat technology for the evaporation of the large quantities of water that are present comparatively near the surface, this indicates that a combina-tion of the usual ODV and ED gives the best result. The way will then be that the process is started w~th the usual ODV. In this way the . . 4 main part of the water is evaporated from the wood. It may here be a question oE for instance 80 per cent of the water that totally has to be evaporated from the wood.
When the outer and more voluminous parts of the wood in this way have been essentially dried and when the inner parts still are moistured the ED-drying starts. The problem then is to dry away a smaller part of the water in the wood. When this water is present in the inner parts of the wood the evaporation of it represents decidely tne most difflcult par-t of the drying. The ED heat will, however, be directed just to this moisture region within the wood and represents therefore an excellent way to solve this problem and comple-te the drying.
Another circumstance that also speaks for the here described di~iding of the drying is that the heat that is generated by EDA can be introduced only a short distance in to very wet wood and not to the inner parts depending on the fact that a high moisture content is electrically screening.
~L~5~J~97 From above it is clear that the ED-heating in an effective way can be used in ODV. There exists other interesting circumsta~lces which show how well ODV fits for all ED-heating. The drying medium has for the task suitable electric properties which means that the ED heat in the first hand is introduced not to the drying medium but to the wood.
If a part of the heat should be transferred to the drying medium this part is not wholly lost, but results in that less heat from other sources is needed for the warming of the medium. The wood is enclosed in a metallic cavity which forms a suitable room for the EDA heat. The cavity can be made in different ways. Very often its main ~art is made of iron in form of a cylinder and is further improved by covering the inside of the cylinder with a suitable metal as copper or aluminium. By the vacuum in the cylinder ionization effects and arcs are easier kept under control. l~hen the last part of the dryiny is carried out accordingly with ED the possibiLities to solve the most difficult problem in connection with ODV
is facilitated, that is to remove the rest of -the of the drying medium from the surface of the wood. This means "
~51~
also that the rules for the performance of the ODV can be simplified. Thus there is not necessary to demand the same high quality of the drying mediums. By example mediums with somewhat higher boiling point - up to 30C
higher than given in patent 992.307 (drying oil boiling points from about 150 to about 250C, heat between about 50 and 90C, at reduced pressures of about 15 to about 120 mm Hg) - can be used which next facilities the oper-ation of ODV.
Above it has been described how ED can be in-troduced into the latter part of the ODV. As ODV together with ED has such improving qualities the ED can, as well, be introduced earlier in the ODV. Thus ED can very well be applied from the beginning of the drying. In this case a ED-heated ODV process is obtained where the drying in the beginning occurs comparatively similar to usual ODV - specially when adapting EDA - and without real action on the inner parts of the wood. Gradually the process changes character and the ED heat is more and more concentrated to the inner parts of the wood. The heat would in such a process to begin with be more ex-- pensive than in a normal ODV process corresponding to the above given description. Here ls, however, to remember the important sawing that is gained ..~,..~, 7 ~150497 because no heating unit for a normal ODV process is needed.
When the heating is carried out dielectrically with drying medium left in the cylinder later or sooner a higher temperature is obtained in the inner parts of the wood than in the outer parts and in the drying medium. In this situation it is possible to arrange so that the steam evaporating from the wood is condensed in the dryiny medium which then is heated, i.e.it takes care of the condensing heat of the stam. The condensed water is separated from the drying medium in the bottom region in the drying cylinder.
Usually the condens heat is taken care of in condensors outside ~
the drying cylinder~ ¦
.
Claims (18)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the drying of wood, and other organic materials, under vacuum in a heated drying medium, including a drying oil, with a boiling point sufficiently high for effecting the drying but sufficiently low for its evaporation from the wood surface after the termina-tion of the drying, wherein the heating source comprises dielectric energy.
2. A process for the drying of wood, and other organic materials, which comprises heating wood to be dried in a closed container under reduced pressure in a drying oil, said wood being at least partially heated by means of dielectric energy and said pressure being reduced sufficiently to cause moisture present in the wood to be removed therefrom, thereafter removing said drying oil from contact with the wood upon removal of the desired amount of moisture from the wood while maintaining the wood under reduced pressure to permit residual oil and moisture to evaporate therefrom, and recovering said wood.
3. A process for the drying of wood, and other organic materials, which comprises heating wood to be dried in a closed container under reduced pressure in a heated drying oil, said wood being heated and said pressure being reduced sufficiently to cause moisture present in the wood to be removed therefrom, removing the wood having a reduced moisture content from contact with the drying oil while maintaining the wood under reduced pressure, further heating the wood to remove additional moisture therefrom by use of dielectric energy, and thereafter re-covering said wood.
4. The process of claim 1, 2 or 3, wherein said drying oil boils from about 150 to about 250°C.
5. The process of claim 1, wherein said drying medium has a boiling point below about 230°C.
6. The process of claim 1, 2 or 3, wherein said drying oil boils below about 200°C.
7. The process of claim 1, 2 or 3, wherein said drying oil is heated to a temperature of between about 60 to 90°C.
8. The process of claim 2 or 3, wherein said reduced pressure ranges from about 20 to about 120 mm Hg.
9. The process of claim 1, 2 or 3, wherein said dielectric energy is provided by a microwave generator.
10. The process of claim 1, 2 or 3, wherein said dielectric energy is provided by a high-frequency genera-tor.
11. The process of claim 1, 2 or 3, wherein all drying is carried out with the use of dielectric energy.
12. The process of claim 1, 2 or 3, wherein the dielectric energy is only utilized at the latter part of the drying process.
13. The process of claim 1, 2 or 3, wherein the dielectric energy is utilized at about the time when the wood and drying oil are separated.
14. The process of claim 2, wherein said di-electric energy is employed to heat the wood after at least a major portion of the moisture is removed from the wood as a result of contact thereof with said drying oil under reduced pressure.
15. The method of claim 14, wherein said at least major portion comprises at least about 80 percent by weight of said moisture.
16. The method of claim 3, wherein said dielec-tric means is employed to heat the wood after at least a major portion of the moisture is removed from the wood as a result of contact thereof with said heated drying oil under reduced pressure.
17. The method of claim 16, wherein said at least major portion comprises at least about 80 percent by weight of said moisture.
18. Process according to claim 1, 2 or 3, wherein copper or aluminum means is used to facilitate the transfer of the dielectric energy to the wood.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000379373A CA1150497A (en) | 1981-06-09 | 1981-06-09 | Process for drying of wood |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000379373A CA1150497A (en) | 1981-06-09 | 1981-06-09 | Process for drying of wood |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1150497A true CA1150497A (en) | 1983-07-26 |
Family
ID=4120190
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000379373A Expired CA1150497A (en) | 1981-06-09 | 1981-06-09 | Process for drying of wood |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1150497A (en) |
-
1981
- 1981-06-09 CA CA000379373A patent/CA1150497A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |