CA2005419A1 - Method and apparatus for the heating of wood or other materials sensitive to dehydration and heat - Google Patents
Method and apparatus for the heating of wood or other materials sensitive to dehydration and heatInfo
- Publication number
- CA2005419A1 CA2005419A1 CA 2005419 CA2005419A CA2005419A1 CA 2005419 A1 CA2005419 A1 CA 2005419A1 CA 2005419 CA2005419 CA 2005419 CA 2005419 A CA2005419 A CA 2005419A CA 2005419 A1 CA2005419 A1 CA 2005419A1
- Authority
- CA
- Canada
- Prior art keywords
- wood
- chamber
- heating
- temperature
- steam
- 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.)
- Abandoned
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
- B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
- B27K3/02—Processes; Apparatus
- B27K3/0278—Processes; Apparatus involving an additional treatment during or after impregnation
- B27K3/0292—Processes; Apparatus involving an additional treatment during or after impregnation for improving fixation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
- B27K1/00—Damping wood
- B27K1/02—Apparatus
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
- B27K5/00—Treating of wood not provided for in groups B27K1/00, B27K3/00
- B27K5/001—Heating
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Forests & Forestry (AREA)
- Drying Of Solid Materials (AREA)
Abstract
A B S T R A C T
The invention relates to a method for the quick and care-ful heating of wood or other materials which are sensitive to dehydration and heat damage. The heating is effected by placing the material in a chamber from which the air is completely evacuated prior to the heating phase. The chamber is then filled with saturated water vapours at a temperature which does not significantly exceed the temperature of the material which is required to be heat-ed. The heating takes place by the saturated water vapours penetrating the spaces between the individual material parts. Here, the vapours condense on the surface of the material, whereby the material is heated. Among other things, the method can be used with advantage for the fixation of a number of impregnation agents in wood and for the drying of wood.
There is also revealed an apparatus for use in the execution of the invention.
(Fig. 1)
The invention relates to a method for the quick and care-ful heating of wood or other materials which are sensitive to dehydration and heat damage. The heating is effected by placing the material in a chamber from which the air is completely evacuated prior to the heating phase. The chamber is then filled with saturated water vapours at a temperature which does not significantly exceed the temperature of the material which is required to be heat-ed. The heating takes place by the saturated water vapours penetrating the spaces between the individual material parts. Here, the vapours condense on the surface of the material, whereby the material is heated. Among other things, the method can be used with advantage for the fixation of a number of impregnation agents in wood and for the drying of wood.
There is also revealed an apparatus for use in the execution of the invention.
(Fig. 1)
Description
~ . \
~oos~
METHOD AND APPARATUS FOR THIE HEATING OF WOOD OR OTHER
~ATERIALS SENSITIVE TO DEHYDRATION AND HEAT.
', :
The inventlon relates to a method and apparatus for the heating of wood or other materials which are sensitive to dehydration and ovarheating. `~
In 1988, on a world basis more than 15 million m3 of wood were impregnated with agents consisting of copper and hexavalent chromium, and with arsenic, boron, fluorine or -. ~
phosphorous as possible third/fourth component. ; `
..
These agents are characteristic in that the hexavalent 15 chromium reacts with the organic components of the wood, `~
and is hereby converted to trivalent chromium. During this process, the main part of the chromium, copper, arsenic and phosphate forming part of the agents is preclpitated as salts which are difficult to dissolve, and which only with difficulty can be washed out of the wood. This process i~ called fixation.
The speed at which the fixation takes place depends on a ;~
number of factors such as, for example, the precise chemical composition of the agents, the concentration of the impregnation agent, the kind of wood etc. However, the speed of fixation depends first and foremost on the , temperature of the wood.
Until the conclusion of fixation, the salts can be washed out of the wood and hereby give rise to environmental problems and problems connected with health. With the increasing environmental demands, there is considerable interest in being able to accelerate the fixation process 2~ 9 ':
by heating the newly-impregnated wood in a quick and lenient manner. Also within other areas in the wood lndustry there are need~ for a quick and lenient heating of wood, for example in the drying of wood.
It has long been known that wood can ba dried by alternat-ing between a heating phase and a vacuum phase, see for example U5 patent publications no. 3,921,309, no.
~oos~
METHOD AND APPARATUS FOR THIE HEATING OF WOOD OR OTHER
~ATERIALS SENSITIVE TO DEHYDRATION AND HEAT.
', :
The inventlon relates to a method and apparatus for the heating of wood or other materials which are sensitive to dehydration and ovarheating. `~
In 1988, on a world basis more than 15 million m3 of wood were impregnated with agents consisting of copper and hexavalent chromium, and with arsenic, boron, fluorine or -. ~
phosphorous as possible third/fourth component. ; `
..
These agents are characteristic in that the hexavalent 15 chromium reacts with the organic components of the wood, `~
and is hereby converted to trivalent chromium. During this process, the main part of the chromium, copper, arsenic and phosphate forming part of the agents is preclpitated as salts which are difficult to dissolve, and which only with difficulty can be washed out of the wood. This process i~ called fixation.
The speed at which the fixation takes place depends on a ;~
number of factors such as, for example, the precise chemical composition of the agents, the concentration of the impregnation agent, the kind of wood etc. However, the speed of fixation depends first and foremost on the , temperature of the wood.
Until the conclusion of fixation, the salts can be washed out of the wood and hereby give rise to environmental problems and problems connected with health. With the increasing environmental demands, there is considerable interest in being able to accelerate the fixation process 2~ 9 ':
by heating the newly-impregnated wood in a quick and lenient manner. Also within other areas in the wood lndustry there are need~ for a quick and lenient heating of wood, for example in the drying of wood.
It has long been known that wood can ba dried by alternat-ing between a heating phase and a vacuum phase, see for example U5 patent publications no. 3,921,309, no.
3.986,268, no. 4,176,466, no. 4,194,296 and no. 4,198,763.
This process is called vacuum drying.
With the hitherto-known vacuum drying processes, the heat-ing has, however, been carried out by the traditional heating methods, of which can be mentioned:
1. Heating by means of steam with a temperature of 100-120C, and 2. Heating by means of hot air.
With the vacuum drying proaess from the above-ment$oned US
patent publication no. 3,921,309, the heating is effected ' by the first method of heating with steam at a temperature of 100C, and with the vacuum drying processes which are known from the similarly above-mentioned US patent publications no. 4,176,466, no. 4,19~,296 and no.
This process is called vacuum drying.
With the hitherto-known vacuum drying processes, the heat-ing has, however, been carried out by the traditional heating methods, of which can be mentioned:
1. Heating by means of steam with a temperature of 100-120C, and 2. Heating by means of hot air.
With the vacuum drying proaess from the above-ment$oned US
patent publication no. 3,921,309, the heating is effected ' by the first method of heating with steam at a temperature of 100C, and with the vacuum drying processes which are known from the similarly above-mentioned US patent publications no. 4,176,466, no. 4,19~,296 and no.
4,198,763, the heating is effected following the second of ~the two methods of heating, i.e. with hot air. ~-~
Among other known methods for the heating of wood can be mentioned heat radiation, submersion in hot liquid or by means of high-frequency energy, as in the above-mentioned US patsnt publication no. 3,986,268. However, these last-mentioned methods of heating are not as common as the ",'' .~'.' ',''''' ~ ,' Z00~ 9 3 `
aforementioned f~rst and second heating methods.
For the abova-mentioned methods of heating, it applles that the heated materials are strongly exposed to drying out during the heating. When using heat radiation, the application of steam and high frequency there is also a great risk of heat damage to the wood in the form of di-minished strength, discoloration and resin secretion. `
. .. ~ .
With the first method of heating, the heating is effectedby the steam penatrating the wood pack, where it condenses on the surface of the wood and hareby heats the wood. The penetration of steam into the wood takes place either by diffusion or as a consequence of the dynamic pressure which the vapours achieve in connection with ths reduction in pressure which ariseR when the vapours are introduced into the heating chamber. Actually, the greater the re~
duction in pressure, the greater will be the dynamic pressure. However, the use of steam at high prcssure in-volves the risk of overheating of the wood and of a strongdrying out of the surface of the wood.
. . .
The dynamic pressure disappears rapidly. Therefore, in or-der to utlllze the dynamic pressure as well as possible, it is important that the supply of steam takes place at many points evenly distributed in the chamber, and there should be ample air spaces between the itams of wood in the wood pack, hereby enabling the steam to penetrate the pack unhindered. The latter requires that the indlvidual items of wood are mutually separated by placlng lists between them, wh~ch results ln considerable extra costs.
As a consequence of the limited ability of the water vapours to penetrate into the wood pack, the heating often becomes irregular. Moreover, because of the great difference ln temperature between tha vapour~ and the wood, the vapours could have a strong drying-out effect on the wood surface.
With the second mathod of heating, the heating is effected by hot air being circulated through the wood pack by natural or forced circulation. A circulation of air through the wood pack presupposes that the wood has been carefully stacked with lists between the individual layers of wood.
In order to prevent the surface of the wood drying out during the heating in accordance with the second method of heating, it is important for the relative humidity of the air to be Icept constantly relatively high. This is done by introduclng water to the air durlng the heating, and by ensuring that the temperature of the air does not slgni-ficantly axceed the temperature of the wood. With a small temperature difference, the transfer of heat from the air to the surace of the wood will, however, take place very slowly, and the circulation of viery large amounts of air is required.
With both the first and the second methods of heating, 25 there are often great problems with corrosion of the `
materials forming part of the heating chambers, and there~
fore the chamber~ should preferably be executed in corrosion-proof materials, which considerably increases the cost of construction. ` -The obJect of the present invention is therefore to pro-vide a method for the heating of wood and other materials which are sensitive to de~ydration and overheating, by which method the necessary heating and drying of the rele-' ~"' ''.'', 2 ~
',: 'vant materlals i9 effacted in the quickest possible and therewith the most economical manner, and also that the said method shall be devoid of the disadvantages described, and this obJect i~; achieved by a method which according to the invention is characteristic in that the wood or the materlal dllring heating is placed in an air-tlght, thermally-insulated chamber whlch, during the heating phase, is completely evacuated of air and instead filled with aturated steam at a temperature which is only slightly higher than the surface temperature of the material or the wood.
Establlshing of a high vacuum in the vacuum chamber makes the steam pressure of the water in the wood exceed the pressure o~ the surroundings, and the water will thereby start to boil out into the wood. By evaporation of the water the thermal onergy in the wood is consumed, and the temperature of the wood will drop until the steam pressure of the water present in the wood corresponds to the ;
pressure of the ~urroundings, whereby the further drying ceases. By repeating the mentioned heating and evacuation ~ ;
phase several times, the main part of the water in the wood will gradually be removed from the wood. 3 If the air is evacuated from the vacuum chamber, the transfer of heat will then take place very ~uickly, sven with a small difference in temperature, and thus the heat transfer can take place with steam if the temperature is only slightly higher than the surface temperature of the material in the vacuum chamber, and as already mentioned it is a prerequisite to be able to ensure that the water vapours in the vacuum chamber can be held saturated.
Since the temperature for the saturated steam is only in---` 2~05~
significantly higher than the temperature of tha material or the wood, no slgnificant increase in the temperature of these takes place, and therefore no heat damage is caused to the wood or the materlal.
It is advantageous to produce the steam in tha manner reveale~ in claim 2, as the least possible heat loss and pressure drop in the steam is hereby achieved.
It is herewith expedient to generate the steam as described in claim 3.
In order to reduce the corrosion in the chamber, it ls advantageous to introduce neutralizing amlnes as revealed ln claim 4.
.~:
Furthermore, it is expedient to heat the wall~ of the chamber, a~ revealed in claim 5, whereby the condensation of the vapours is countered.
For use in the execution of the method according to the - `
invention, there ls provided an apparatus as revealed and characterized in claim 6.
..,, ~:, '', 25 The method and the apparatus according to the invention ; ~ `
will now be described in more detail with reference to the drawing, where ~
, ~ , ' ; "' :. ' . .' ';"
Fig. 1 shows schematically an embodiment of the -apparatus according to the invention, Fig. 2a and 2b show schematically two different embodi~
ments of a steam generator in a condensate tank in the apparatus shown in fig. 1, and ' . ,' :~ -... ,' `
2~4~
. ' ' '-,, Fig. 3 shows the rela-tionship between the surface temperature of material in the apparatus shown in fig.1 and the pressure in this apparatuq.
, .
The heating takes place in an apparatus of the k~nd shown in fig. 1. The apparatus consists o~ a vacuum chamber 1 with one or two covers 2 which can be opened. The vacuum chamber must be completely airtight and must ba able to withstand full vacuum.
' ~
The walls 3 of the vacuum chamber should be thermally insulated :Ln order for better control to be effected over the climate in the chamber. In order to limit the condens-ation of the water vapour on the inner walls of the chamber, it is an advantage to provide the walls 3 of the vacuum chamber with heating elements 4 which can maintain the walls of the chamber at a temperature which i~ higher than thé dewpoint temperature of the water vapours present in the vacuum chamber 1, but at the same time so low that the water vapours are not heated further by the walls 3.
The vacuum chamber 1 is filled batchwise with the material 5 which is desired to be heated. Tha material 5 i8 intro-duced into the vacuum chamber 1 through the covers 2 in the chamber. After the f$11ing of the chamber with mate-rial, the covers 2 are closed and air is evacuated from the chamber 1 by means of a vacuum pump 6, an extractor or a similar alement. With this evacuation, as much air as ~-possible iR removed from the vacuum chamber 1.
After the a:Lr has been evacuated from the vacuum chamber 1, saturatedl water vapour 8 is introduced into the chamber at a temperature which is slightly higher than that of the material in the chamber. The steam is easiest to produce 2~ 19 by heating water placed in the vacuum chamber 1 itself or in a steam generator 7 which stands in direct connection with the vacuum chamber 1 (see fig. 2). In order to ensure that the water vapour produced is saturated and has the same temperature as the surface temperature of the mate-rial 5 ln the vacuum chamber 1, lt is important that there is no pressure regulating valve, cut-off or the like between the steam generator 7 and the vacuum chamber 1.
The pressure and the temperature in the vacuum chamber and the steam generator must be the same.
In order to control the surface temperature ~of the material 5 in the vacuum chamber 1, and also the temperature of the saturated vapours, in the vacuum chamber there is arranged a measuring element 14 which, in a commonly-known manner, is in connection with a not-shown control unit for the automatic control of the drying process.
Use can also be made of steam produced at high pres~ure in a separate steam generator. In this case the steam must be cooled and have molsture added before it comes lnto con~
tact with the material 5 in the vacuum chamber 1. This moisturi~ing is effected most expediently by leading the steam through a water bath, which is placed in the same manner as the water in the steam generator 7 described in the above. The steam 8 will hereby be automatically !~ saturated and assume approximately the same temperature as the surface temperature of the material 5 in the vacuum chamber 1.
In the vacuum chamber 1, the steam 8 produced in the steam generator 7 will condense on the surface of the material 5, whereby this is heated. Under gravitation, the condens-- ~ :
,-'~ ~,'', -` 2013~9 ed steam will seek towards; the bottom of the vacuum chamber 1. The condensata is collected ~rom the bottom of the vacuum chamber by means oP gravitation or by a condensate pump in a condensate tank 9. It can be advantageous to connact the condensate tank directly to the steam generator 7.
In order to ensure a rapid transfer of heat rom the vapours 8 to the material 5, it is important that in principle the vacuum chamber 1 is completely evacuated of air. The reason ~or this is that if there is air in the system, a considerable difference in temperature will be necessary between the water vapours 8 and the material 5 in order to ensure a sufficiently rapid transfer of heat.
This difference in temperature will have the effect that the vapours around the material 5 will not remain saturated, and there will hereby arise a risk o~ a ~trong drying out of the material. ~here is also a rlsk of heat damage to the material in the form of reduced strength in the material, resin secretion and discoloration.
The faat that the transfer of heat is very effective, and the fact that there is a direct connection between the vacuum chamber 1 and the steam generator 7, results auto-matically ln the vapours produced in the steam generator 7becoming saturated and that they assume approximately the same temperature a~ the surface temperature of the material 5 present in the vacuum chamber 1, and this is a precondition for the prssent system to be able in a simple manner to avoid the drying out of the matsrial 5 in the vacuum chamber 1 and heat damage to the material.
Providing that the vacuum chamber 1 is evacuated of air, the pressure in the vacuum chamber 1 will depend on the .
~`` 200~ 9 surface temperature of the material 5 in the vacuum chamber in tha relationship as shown in fig. 3, namely that the higher the temperature of the material 5, the yreater will also be the pre~ssure in the vacuum chamber.
In the event of possible pressure differences, the steam pressure wlll be lowest in those areas of the vacuum chamber 1 which are the coldest. The vapours 8 wlll there-by automatically seek towards the coldest parts of the va-cuum chamber 1, and possible temperature differences in the vacuum chamber 1 will thus be equali~ed rapidly and effectively. Since the movement of the water vapours 8 is due to pressure differences in the vacuum chamber 1, the vapour~ can penetrate deeply even into materials 5 which are packed tightly, and hereby the system dlstinguishes itself fundamentally from the earlier described systems of heating.
"
With the method accordlng to the invention, the problems of corrosion can be held on a relatively low level, for the reason that the system i~ devoid of air. By adding neutralizing amines such as, for example, morpholine to the water vapours 8 produced in the steam generator 7, the risk of corrosion can be held on a very low level. ~he neutralizing am~nes will remove the acids which emanate from the material 5 during the heating, and without oxygen and acids in the system the corrosion will be extremely limited. The addition of amines is regulated most expe~
diently by measuring the pH of the water collected in the condsnsate tank 9, and the amine is added in a manner so that the condensate water does not become ac~d at any time. In order to further reduce the r~s~ of corrosion, the walls 3 of th0 vacùum chamber 1 are provided with heating elements 4 which prevent the condensation of water .. ~: . , vapours 8 on the inside walls of the vacuum chamber 1 by '',, '~',:~
holding the temperature of the wall~ 3 at a slightly higher temperature than the dewpoint temparature of the vapours present in the chamber.
The condensate collected in the condensate tank 9 is re used with advantage for the production of new steam, in that the condensate collected in the condensate tank is particularly suitable for steam production. As a con-sequence of the process taking place in an air-free atmosphere, the condensate is totally devoid of oxygen. In the cases where neutralizlng amines are added *o the steam, the condensate is also completely devoid of corrosive acids.
A considerable amount of the water present in the material 5 can be removed from the material 5 by concluding the heatlng phase with the vacuum. This concluding vacuum is established most easily by condensing the water vapours in the vacuum chamber 1 by means of not~shown aooling ele-ments disposed in the vacuum chamber 1 or in an al50 not-shown saparate cooling tank. This condensation is effected relatively easily in the present system, as th0 system is completely evacuated of alr prior to the concluding vacuum phase. -~
`
Out of regard for the condensation of the water vapours in the above-mentioned cooling system, it is important that tha vacuum chamber 1 is completely airtight and that it is completaly evacuated of air prior to *he conaluding vacuu~
phase.
If there is air in the system, a vacuum pump 6, an extractor or a similar element is required for the removal of the air, and the demands on the condenser used for the ~- 2~110~
.~
condensation of the water vapours are considerable.
With air in the system, as with the known mathods of heat-ing as discussed by way of introduct~on, the condenser must have a far greater cooling area and lower cooling temperature than required in the condensation o water vapours in an air-free atmosphere. As a consequence here-of, the system's economy is considerably diminished.
Moreover, these known methods of heating give rise to great problems with strong drying out of the surface of the wood and other heat damage, and as a consequence of this and other things, vacuum drying has hitherto never found partlcularly broad application. However, by using the method of heating as revealed with this invention, it is possible to heat the wood in both a quick and careful manner. At the same time, since the process takes place in a completely air-free atmosphere, one avoids the problems in the form of long heating times, difficulties surround~
ing the establishing of complete vacuum, corrosion problems and discoloration of the wood, which arise in those systems where the drying chamber is filled with air during the heating phase.
Both in the fixation of wood and in the drying of wood, the method according to the invention thus affords a number of advantages in relation to the traditional methods of heating. The method according to the invention is not, however, restricted to these applications, and can be usad ~n almost all cases where there is a need for a quick and careful heating of wood or other materials which are sensitive to dehydration and overheating. The method according to -the invention can also be used with liquids other than water.
~ : .
'"'.~
``:` 2~)~5~9 Furthermore, it lles within the scope of the inventlon for the vacuum chamber 1 to be fi:Lled with hot water instead of with saturated water vapours.
. . . : . - .. , . ., . . :
, ., ~ ! . ' ' ~ ' " ` ~ ' .~' ` . ' : ` `' ~ '; '`: '' ' ` , ,;"'`'. ' ` ' ' ` ' , ' ~. - '~' ", "` '
Among other known methods for the heating of wood can be mentioned heat radiation, submersion in hot liquid or by means of high-frequency energy, as in the above-mentioned US patsnt publication no. 3,986,268. However, these last-mentioned methods of heating are not as common as the ",'' .~'.' ',''''' ~ ,' Z00~ 9 3 `
aforementioned f~rst and second heating methods.
For the abova-mentioned methods of heating, it applles that the heated materials are strongly exposed to drying out during the heating. When using heat radiation, the application of steam and high frequency there is also a great risk of heat damage to the wood in the form of di-minished strength, discoloration and resin secretion. `
. .. ~ .
With the first method of heating, the heating is effectedby the steam penatrating the wood pack, where it condenses on the surface of the wood and hareby heats the wood. The penetration of steam into the wood takes place either by diffusion or as a consequence of the dynamic pressure which the vapours achieve in connection with ths reduction in pressure which ariseR when the vapours are introduced into the heating chamber. Actually, the greater the re~
duction in pressure, the greater will be the dynamic pressure. However, the use of steam at high prcssure in-volves the risk of overheating of the wood and of a strongdrying out of the surface of the wood.
. . .
The dynamic pressure disappears rapidly. Therefore, in or-der to utlllze the dynamic pressure as well as possible, it is important that the supply of steam takes place at many points evenly distributed in the chamber, and there should be ample air spaces between the itams of wood in the wood pack, hereby enabling the steam to penetrate the pack unhindered. The latter requires that the indlvidual items of wood are mutually separated by placlng lists between them, wh~ch results ln considerable extra costs.
As a consequence of the limited ability of the water vapours to penetrate into the wood pack, the heating often becomes irregular. Moreover, because of the great difference ln temperature between tha vapour~ and the wood, the vapours could have a strong drying-out effect on the wood surface.
With the second mathod of heating, the heating is effected by hot air being circulated through the wood pack by natural or forced circulation. A circulation of air through the wood pack presupposes that the wood has been carefully stacked with lists between the individual layers of wood.
In order to prevent the surface of the wood drying out during the heating in accordance with the second method of heating, it is important for the relative humidity of the air to be Icept constantly relatively high. This is done by introduclng water to the air durlng the heating, and by ensuring that the temperature of the air does not slgni-ficantly axceed the temperature of the wood. With a small temperature difference, the transfer of heat from the air to the surace of the wood will, however, take place very slowly, and the circulation of viery large amounts of air is required.
With both the first and the second methods of heating, 25 there are often great problems with corrosion of the `
materials forming part of the heating chambers, and there~
fore the chamber~ should preferably be executed in corrosion-proof materials, which considerably increases the cost of construction. ` -The obJect of the present invention is therefore to pro-vide a method for the heating of wood and other materials which are sensitive to de~ydration and overheating, by which method the necessary heating and drying of the rele-' ~"' ''.'', 2 ~
',: 'vant materlals i9 effacted in the quickest possible and therewith the most economical manner, and also that the said method shall be devoid of the disadvantages described, and this obJect i~; achieved by a method which according to the invention is characteristic in that the wood or the materlal dllring heating is placed in an air-tlght, thermally-insulated chamber whlch, during the heating phase, is completely evacuated of air and instead filled with aturated steam at a temperature which is only slightly higher than the surface temperature of the material or the wood.
Establlshing of a high vacuum in the vacuum chamber makes the steam pressure of the water in the wood exceed the pressure o~ the surroundings, and the water will thereby start to boil out into the wood. By evaporation of the water the thermal onergy in the wood is consumed, and the temperature of the wood will drop until the steam pressure of the water present in the wood corresponds to the ;
pressure of the ~urroundings, whereby the further drying ceases. By repeating the mentioned heating and evacuation ~ ;
phase several times, the main part of the water in the wood will gradually be removed from the wood. 3 If the air is evacuated from the vacuum chamber, the transfer of heat will then take place very ~uickly, sven with a small difference in temperature, and thus the heat transfer can take place with steam if the temperature is only slightly higher than the surface temperature of the material in the vacuum chamber, and as already mentioned it is a prerequisite to be able to ensure that the water vapours in the vacuum chamber can be held saturated.
Since the temperature for the saturated steam is only in---` 2~05~
significantly higher than the temperature of tha material or the wood, no slgnificant increase in the temperature of these takes place, and therefore no heat damage is caused to the wood or the materlal.
It is advantageous to produce the steam in tha manner reveale~ in claim 2, as the least possible heat loss and pressure drop in the steam is hereby achieved.
It is herewith expedient to generate the steam as described in claim 3.
In order to reduce the corrosion in the chamber, it ls advantageous to introduce neutralizing amlnes as revealed ln claim 4.
.~:
Furthermore, it is expedient to heat the wall~ of the chamber, a~ revealed in claim 5, whereby the condensation of the vapours is countered.
For use in the execution of the method according to the - `
invention, there ls provided an apparatus as revealed and characterized in claim 6.
..,, ~:, '', 25 The method and the apparatus according to the invention ; ~ `
will now be described in more detail with reference to the drawing, where ~
, ~ , ' ; "' :. ' . .' ';"
Fig. 1 shows schematically an embodiment of the -apparatus according to the invention, Fig. 2a and 2b show schematically two different embodi~
ments of a steam generator in a condensate tank in the apparatus shown in fig. 1, and ' . ,' :~ -... ,' `
2~4~
. ' ' '-,, Fig. 3 shows the rela-tionship between the surface temperature of material in the apparatus shown in fig.1 and the pressure in this apparatuq.
, .
The heating takes place in an apparatus of the k~nd shown in fig. 1. The apparatus consists o~ a vacuum chamber 1 with one or two covers 2 which can be opened. The vacuum chamber must be completely airtight and must ba able to withstand full vacuum.
' ~
The walls 3 of the vacuum chamber should be thermally insulated :Ln order for better control to be effected over the climate in the chamber. In order to limit the condens-ation of the water vapour on the inner walls of the chamber, it is an advantage to provide the walls 3 of the vacuum chamber with heating elements 4 which can maintain the walls of the chamber at a temperature which i~ higher than thé dewpoint temperature of the water vapours present in the vacuum chamber 1, but at the same time so low that the water vapours are not heated further by the walls 3.
The vacuum chamber 1 is filled batchwise with the material 5 which is desired to be heated. Tha material 5 i8 intro-duced into the vacuum chamber 1 through the covers 2 in the chamber. After the f$11ing of the chamber with mate-rial, the covers 2 are closed and air is evacuated from the chamber 1 by means of a vacuum pump 6, an extractor or a similar alement. With this evacuation, as much air as ~-possible iR removed from the vacuum chamber 1.
After the a:Lr has been evacuated from the vacuum chamber 1, saturatedl water vapour 8 is introduced into the chamber at a temperature which is slightly higher than that of the material in the chamber. The steam is easiest to produce 2~ 19 by heating water placed in the vacuum chamber 1 itself or in a steam generator 7 which stands in direct connection with the vacuum chamber 1 (see fig. 2). In order to ensure that the water vapour produced is saturated and has the same temperature as the surface temperature of the mate-rial 5 ln the vacuum chamber 1, lt is important that there is no pressure regulating valve, cut-off or the like between the steam generator 7 and the vacuum chamber 1.
The pressure and the temperature in the vacuum chamber and the steam generator must be the same.
In order to control the surface temperature ~of the material 5 in the vacuum chamber 1, and also the temperature of the saturated vapours, in the vacuum chamber there is arranged a measuring element 14 which, in a commonly-known manner, is in connection with a not-shown control unit for the automatic control of the drying process.
Use can also be made of steam produced at high pres~ure in a separate steam generator. In this case the steam must be cooled and have molsture added before it comes lnto con~
tact with the material 5 in the vacuum chamber 1. This moisturi~ing is effected most expediently by leading the steam through a water bath, which is placed in the same manner as the water in the steam generator 7 described in the above. The steam 8 will hereby be automatically !~ saturated and assume approximately the same temperature as the surface temperature of the material 5 in the vacuum chamber 1.
In the vacuum chamber 1, the steam 8 produced in the steam generator 7 will condense on the surface of the material 5, whereby this is heated. Under gravitation, the condens-- ~ :
,-'~ ~,'', -` 2013~9 ed steam will seek towards; the bottom of the vacuum chamber 1. The condensata is collected ~rom the bottom of the vacuum chamber by means oP gravitation or by a condensate pump in a condensate tank 9. It can be advantageous to connact the condensate tank directly to the steam generator 7.
In order to ensure a rapid transfer of heat rom the vapours 8 to the material 5, it is important that in principle the vacuum chamber 1 is completely evacuated of air. The reason ~or this is that if there is air in the system, a considerable difference in temperature will be necessary between the water vapours 8 and the material 5 in order to ensure a sufficiently rapid transfer of heat.
This difference in temperature will have the effect that the vapours around the material 5 will not remain saturated, and there will hereby arise a risk o~ a ~trong drying out of the material. ~here is also a rlsk of heat damage to the material in the form of reduced strength in the material, resin secretion and discoloration.
The faat that the transfer of heat is very effective, and the fact that there is a direct connection between the vacuum chamber 1 and the steam generator 7, results auto-matically ln the vapours produced in the steam generator 7becoming saturated and that they assume approximately the same temperature a~ the surface temperature of the material 5 present in the vacuum chamber 1, and this is a precondition for the prssent system to be able in a simple manner to avoid the drying out of the matsrial 5 in the vacuum chamber 1 and heat damage to the material.
Providing that the vacuum chamber 1 is evacuated of air, the pressure in the vacuum chamber 1 will depend on the .
~`` 200~ 9 surface temperature of the material 5 in the vacuum chamber in tha relationship as shown in fig. 3, namely that the higher the temperature of the material 5, the yreater will also be the pre~ssure in the vacuum chamber.
In the event of possible pressure differences, the steam pressure wlll be lowest in those areas of the vacuum chamber 1 which are the coldest. The vapours 8 wlll there-by automatically seek towards the coldest parts of the va-cuum chamber 1, and possible temperature differences in the vacuum chamber 1 will thus be equali~ed rapidly and effectively. Since the movement of the water vapours 8 is due to pressure differences in the vacuum chamber 1, the vapour~ can penetrate deeply even into materials 5 which are packed tightly, and hereby the system dlstinguishes itself fundamentally from the earlier described systems of heating.
"
With the method accordlng to the invention, the problems of corrosion can be held on a relatively low level, for the reason that the system i~ devoid of air. By adding neutralizing amines such as, for example, morpholine to the water vapours 8 produced in the steam generator 7, the risk of corrosion can be held on a very low level. ~he neutralizing am~nes will remove the acids which emanate from the material 5 during the heating, and without oxygen and acids in the system the corrosion will be extremely limited. The addition of amines is regulated most expe~
diently by measuring the pH of the water collected in the condsnsate tank 9, and the amine is added in a manner so that the condensate water does not become ac~d at any time. In order to further reduce the r~s~ of corrosion, the walls 3 of th0 vacùum chamber 1 are provided with heating elements 4 which prevent the condensation of water .. ~: . , vapours 8 on the inside walls of the vacuum chamber 1 by '',, '~',:~
holding the temperature of the wall~ 3 at a slightly higher temperature than the dewpoint temparature of the vapours present in the chamber.
The condensate collected in the condensate tank 9 is re used with advantage for the production of new steam, in that the condensate collected in the condensate tank is particularly suitable for steam production. As a con-sequence of the process taking place in an air-free atmosphere, the condensate is totally devoid of oxygen. In the cases where neutralizlng amines are added *o the steam, the condensate is also completely devoid of corrosive acids.
A considerable amount of the water present in the material 5 can be removed from the material 5 by concluding the heatlng phase with the vacuum. This concluding vacuum is established most easily by condensing the water vapours in the vacuum chamber 1 by means of not~shown aooling ele-ments disposed in the vacuum chamber 1 or in an al50 not-shown saparate cooling tank. This condensation is effected relatively easily in the present system, as th0 system is completely evacuated of alr prior to the concluding vacuum phase. -~
`
Out of regard for the condensation of the water vapours in the above-mentioned cooling system, it is important that tha vacuum chamber 1 is completely airtight and that it is completaly evacuated of air prior to *he conaluding vacuu~
phase.
If there is air in the system, a vacuum pump 6, an extractor or a similar element is required for the removal of the air, and the demands on the condenser used for the ~- 2~110~
.~
condensation of the water vapours are considerable.
With air in the system, as with the known mathods of heat-ing as discussed by way of introduct~on, the condenser must have a far greater cooling area and lower cooling temperature than required in the condensation o water vapours in an air-free atmosphere. As a consequence here-of, the system's economy is considerably diminished.
Moreover, these known methods of heating give rise to great problems with strong drying out of the surface of the wood and other heat damage, and as a consequence of this and other things, vacuum drying has hitherto never found partlcularly broad application. However, by using the method of heating as revealed with this invention, it is possible to heat the wood in both a quick and careful manner. At the same time, since the process takes place in a completely air-free atmosphere, one avoids the problems in the form of long heating times, difficulties surround~
ing the establishing of complete vacuum, corrosion problems and discoloration of the wood, which arise in those systems where the drying chamber is filled with air during the heating phase.
Both in the fixation of wood and in the drying of wood, the method according to the invention thus affords a number of advantages in relation to the traditional methods of heating. The method according to the invention is not, however, restricted to these applications, and can be usad ~n almost all cases where there is a need for a quick and careful heating of wood or other materials which are sensitive to dehydration and overheating. The method according to -the invention can also be used with liquids other than water.
~ : .
'"'.~
``:` 2~)~5~9 Furthermore, it lles within the scope of the inventlon for the vacuum chamber 1 to be fi:Lled with hot water instead of with saturated water vapours.
. . . : . - .. , . ., . . :
, ., ~ ! . ' ' ~ ' " ` ~ ' .~' ` . ' : ` `' ~ '; '`: '' ' ` , ,;"'`'. ' ` ' ' ` ' , ' ~. - '~' ", "` '
Claims (6)
1. Method for the heating of wood or other materials which are sensitive to dehydration and overheating, c h a -r a c t e r i z e d in that during the heating the wood or the material is placed in an airtight, thermally in-sulated chamber from which the air is completely evacuated during the heating phase, and instead filled with saturated steam at a temperature which is only slightly higher than the surface temperature of the wood or the material.
2. Method according to claim 1, c h a r a c t e -r i z e d in that the steam used for the heating of the wood or the material is produced by the heating of liquid placed either in the chamber itself or in a separate tank which is in direct connection with the chamber.
3. Method according to claim 1, c h a r a c t e -r i z e d in that the steam used for the heating of the wood or the material is produced by a steam generator which is independent of the chamber, and thereafter con-verted to saturated steam with a temperature which is only slightly higher than the surface temperature of the wood or the material, by being led through a liquid which is placed either in the chamber itself or in a separate tank which is in direct connection with the chamber.
4. Method according to claim 1, c h a r a c t e -r i z e d in that during the heating phase, neutralizing amines, such as morpholine, are introduced into the chamber for the neutralization of the acids emanating from the wood or the material.
5. Method according to claim 1, c h a r a c t e -r i z e d in that the walls in the chamber are heated to a temperature which is slightly higher than the dewpoint temperature of the vapours present in the chamber.
6. Apparatus for use in the execution of the method as revealed in claim 1, in which wood or other materials sen-sitive to dehydration or overheating are heated, c h a -r a c t e r i z e d in that the apparatus comprises a pressure-proof chamber (1) provided with covers (2), in that said chamber (1) can be evacuated by means of a vacuum pump (6) connected with the chamber (1), and a steam generator (7) connected with the chamber (1) via an open channel with large cross-sectional area, and which is arranged for the production of saturated vapours (8), said steam generator (7) being preferably disposed in a con-densation tank (9) connected to the chamber (1), and in that a measuring element (14) is provided for the control of the surface temperature of the wood or material (5) present in the chamber (1), and also the temperature and pressure of the saturated vapours.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DK7019/88 | 1988-12-16 | ||
| DK701988A DK701988D0 (en) | 1988-12-16 | 1988-12-16 | PROCEDURE FOR IMPROVING TREE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2005419A1 true CA2005419A1 (en) | 1990-06-16 |
Family
ID=8149194
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2005419 Abandoned CA2005419A1 (en) | 1988-12-16 | 1989-12-13 | Method and apparatus for the heating of wood or other materials sensitive to dehydration and heat |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU4809490A (en) |
| CA (1) | CA2005419A1 (en) |
| DK (1) | DK701988D0 (en) |
| WO (1) | WO1990006840A1 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NZ241950A (en) * | 1992-03-12 | 1995-04-27 | Nz Secretary Forestry | Heating lignocellulosic material to provide plant growth material and water treatment material |
| CA2162374C (en) * | 1993-05-12 | 2005-09-27 | Pertti Viitaniemi | Method for improving biodegradation resistance and dimensional stability of cellulosic products |
| US5447686A (en) * | 1994-06-17 | 1995-09-05 | Seidner; Marc A. | Method for heat-treating wood and wood products |
| DK200200872A (en) * | 2002-06-07 | 2003-12-08 | Iwotech As | Heat treatment of wood with steam |
| US7963048B2 (en) * | 2005-05-23 | 2011-06-21 | Pollard Levi A | Dual path kiln |
| DE102005047362A1 (en) * | 2005-10-04 | 2007-04-12 | Basf Ag | Preparation of modified lignocellulosic materials |
| DE102005047363A1 (en) | 2005-10-04 | 2007-04-12 | Basf Ag | Low-formaldehyde lignocellulosic material and process for its preparation |
| US8201501B2 (en) | 2009-09-04 | 2012-06-19 | Tinsley Douglas M | Dual path kiln improvement |
| FR3063925B1 (en) * | 2017-03-20 | 2020-02-07 | Thermodynamic Workshop Training - Twt | DEVICE FOR HEAT TREATMENT OF LOGS |
| US10619921B2 (en) | 2018-01-29 | 2020-04-14 | Norev Dpk, Llc | Dual path kiln and method of operating a dual path kiln to continuously dry lumber |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1678559A (en) * | 1927-05-28 | 1928-07-24 | Joseph P Devine | Drying materials |
| US2293453A (en) * | 1939-02-24 | 1942-08-18 | Gen Electric | Dehydrating treatment |
| DE3510364A1 (en) * | 1985-03-22 | 1986-09-25 | Dr. Wolman Gmbh, 7573 Sinzheim | METHOD FOR THE ACCELERATED FIXING OF CHROMATE-CONTAINING WOOD PROTECTING SALTS |
| DE3630743A1 (en) * | 1986-09-10 | 1988-03-24 | Scholz Gmbh Co Kg Maschbau | Process and apparatus for salt-impregnation of wood |
-
1988
- 1988-12-16 DK DK701988A patent/DK701988D0/en not_active Application Discontinuation
-
1989
- 1989-12-13 CA CA 2005419 patent/CA2005419A1/en not_active Abandoned
- 1989-12-14 AU AU48094/90A patent/AU4809490A/en not_active Abandoned
- 1989-12-14 WO PCT/DK1989/000294 patent/WO1990006840A1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DK701988D0 (en) | 1988-12-16 |
| AU4809490A (en) | 1990-07-10 |
| WO1990006840A1 (en) | 1990-06-28 |
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