WO2003037107A2

WO2003037107A2 - Heat treatment of wood by electricity

Info

Publication number: WO2003037107A2
Application number: PCT/IL2002/000868
Authority: WO
Inventors: David Reznik
Original assignee: David Reznik
Priority date: 2001-11-01
Filing date: 2002-10-29
Publication date: 2003-05-08
Also published as: WO2003037107A3

Abstract

A method and apparatus for treating wood (12), which includes arranging at least first and second electrodes (20, 22) in electrical contact with wood (12) to be treated via an electrically conductive material (28) and applying a voltage across the at least first and second electrodes (20, 22). The wood (12) is typically heated, under pressure, up to temperatures as high as 200°C. Typical applications of the wood treatment include wood sterilization, coloration and debarking.

Description

HEAT TREATMENT OF WOOD BY ELECTRICITY

REFERENCE TO CO-PENDING APPLICATIONS

Applicant hereby claims priority of U.S. Provisional Patent Application Serial No. 60/335,399, filed on November 1, 2001, entitled "Wood Electro-Heating" and U.S Provisional Patent Application Serial No. 60/375,737, filed on April 26, 2002, entitled "Electrical Heat Treatment of Wood".

FIELD OF THE INVENTION

The present invention relates to wood treatment generally and more particularly to heat treatment of wood.

BACKGROUND OF THE INVENTION

Heat treatment of wood is known in the art typically for drying wood, for sterilization of wood and also for darkening the color of the wood. The conventional methods used for these applications are based on hot air or steam flow over wood.

Although steam heating is an efficient method of wood sterilization, the conventional methods are time consuming and costly due to the slow heat penetration especially for large diameter logs.

Methods of dielectric heating of wood produce unacceptable temperature gradients in the wood. Although the electric field can supply heat at a uniform rate, the heat is conducted away from the surface at a faster rate than the interior. Thus, these methods are inefficient.

Microwave methods are also known in the art but these methods encounter the same problems as found with dielectric heating.

The following U.S. Patents are believed to represent the current state of the arf 3,971, 139; 3,986,268; 4,472,245; 4,992,307; 5,188,707; 5,245,154; 5,480,679; 5,5 13,444 and 6,090,452.

The following U.S. Patents of the present inventor may possibly be considered to be relevant: 4,739,140; 5,583,960; 5,609,900; 5,636,317; 5,768,472; 5,863,580 and 6,304,718. SUMMARY OF THE INVENTION

The present invention seeks to provide a novel methodology and system for heat treatment of wood.

The wood is typically heated, under pressure, up to temperatures as high as 200°C. Typical applications of the wood treatment include wood sterilization, coloration and debarking. A typical minimum temperature for sterilization of the wood is approximately 120°C and a typical temperature for achieving wood coloration could be as high as 160°C.

Additionally, the heat treatment disclosed by the present invention also allows for controlling the pH of wood for preservation and coloration purposes.

The present invention discloses a method and apparatus for heating the wood by passing an electrical current through the wood.

There is thus provided in accordance with a preferred embodiment of the present invention a method for treating wood, which includes arranging at least first and second electrodes in electrical contact with wood to be treated via an electrically conductive material and applying a voltage across the first and second electrodes.

There is also provided in accordance with a preferred embodiment of the present invention an apparatus for treating wood. The apparatus includes a conductive electrode assembly operative for establishing electrical contact of at least first and second electrodes with wood to be treated via an electrically conductive material and an electrical voltage source applying a voltage across the first and second electrodes.

Further in accordance with a preferred embodiment of the present invention the step of applying the voltage includes applying an AC voltage across the first and second electrodes.

Still further in accordance with a preferred embodiment of the present invention the step of arranging the at least first and second electrodes includes locating the wood to be treated within a pressure chamber.

Additionally in accordance with a preferred embodiment of the present invention the pressure chamber contains an electrically conductive liquid. Typically, the electrically conductive liquid includes de-ionized water. Further in accordance with a preferred embodiment of the present invention the voltage is applied across the first and second electrodes while the wood to be treated is maintained under positive pressure within the pressure chamber.

Additionally, the wood to be treated is more electrically conductive than the electrically conductive liquid.

Still further in accordance with a preferred embodiment of the present invention the wood to be treated includes at least one elongate wood element. The first and second electrodes are arranged adjacent the ends of the elongate wood element.

Preferably, the voltage includes an AC voltage, at line frequency and the voltage typically exceeds 400 volts.

Additionally in accordance with a preferred embodiment of the present invention the first and second electrodes are not in direct contact with the wood to be treated.

Preferably, a conductive pad is placed between the first and second electrodes and the wood to be treated. Typically, the conductive pad is constructed from an electrically conductive material. Preferably, the electrically conductive material is steel wool.

Additionally or alternatively, a conductive paste is applied between the electrodes and the wood to be treated. Preferably, the conductive paste is an agar-agar gel. Preferably, the agar-agar gel includes at least 3% KCl. Additionally, the agar-agar gel includes an electrically conductive material. The electrically conductive material may be selected from a group consisting of iron powder and carbon powder.

Further in accordance with a preferred embodiment of the present invention the first and second electrodes are non-metallic.

Still further in accordance with a preferred embodiment of the present invention the step of applying the voltage includes applying a sufficiently high voltage for a sufficiently long time for sterilizing the wood to be treated.

Additionally or alternatively, the step of applying the voltage includes applying a sufficiently high voltage for a sufficiently long time in order to provide enzymatic inactivation and biological stability of the wood to be treated. Additionally or alternatively, the step of applying the voltage includes applying a sufficiently high voltage for a sufficiently long time in order to provide desired coloration of the wood to be treated.

Further in accordance with a preferred embodiment of the present invention the wood to be treated includes bark. Additionally, the step of applying the voltage includes applying a sufficiently high voltage for a sufficiently long time in order to facilitate separation of the bark from the remainder of the wood to be treated.

Additionally or alternatively, the step of applying the voltage includes applying a sufficiently high voltage for a sufficiently long time in order to heat the wood to be treated to at least a desired temperature within a pressure chamber, which contains the conductive material. The method also includes the step of, following heating of the wood to be treated to at least the desired temperature, gradually reducing the pressure within the pressure chamber to a desired sub-atmospheric pressure, thereby providing desired removal of moisture from the wood to be treated.

Typically, the desired temperature is 200°C.

Still further in accordance with a preferred embodiment of the present invention the method for treating wood also includes removing the conductive liquid from the pressure chamber prior to gradually reducing the pressure within the pressure chamber.

There is further provided in accordance with a preferred embodiment of the present invention a method for treating wood, which includes impregnating wood to be treated with a liquid having a pH higher than the pH of the wood to be treated, thereby providing at least one of wood preservation and wood coloration.

There is also provided in accordance with yet another preferred embodiment of the present invention an apparatus for treating wood. The apparatus includes an impregnator operating to impregnate wood to be treated with a liquid having a pH higher than the pH of the wood to be treated, thereby providing at least one of wood preservation and wood coloration.

Further in accordance with a preferred embodiment of the present invention the method for treating wood also includes, following the step of impregnating, applying a voltage across the wood to be treated, for desired heating thereof. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description, taken together with the drawings in which:

Figs. 1A and IB are schematic illustrations of an apparatus for treating wood by applying a voltage thereacross and in which the wood treatment apparatus contains a liquid having an electrical conductivity less than wood, in accordance with a first preferred embodiment of the present invention;

Figs. 1C and ID are schematic illustrations of an apparatus for treating wood by applying a voltage thereacross, in accordance with another preferred embodiment of the present invention;

Figs. 2A - 2P are illustrations of various embodiments of apparatus for treating wood by applying a voltage thereacross, in accordance with yet further preferred embodiments of the present invention;

Fig. 3 is an illustration of one embodiment of apparatus for treating wood by applying a voltage thereacross in accordance with another preferred embodiment of the present invention;

Fig. 4 is an illustration of a preferred system for treating wood in accordance with a preferred embodiment of the present invention;

Fig. 5 is a simplified flow chart of a preferred methodology for wood treatment, in which the wood treatment apparatus contains a liquid having an electrical conductivity less than wood, in accordance with a preferred embodiment of the present invention; and

Fig. 6 is a simplified flow chart of a preferred methodology for wood drying, in accordance with another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to Figs. 1 A and IB, which are illustrations of one embodiment of apparatus for treating wood by applying a voltage thereacross in accordance with a preferred embodiment of the present invention. As seen in Fig. 1A and I B, there is preferably provided a bath 10, preferably formed of an electrically insulative material, such as wood with a high temperature resistant insulating coating. The bath 10 may have an insulative coating formed of a suitable high voltage, high temperature resistant material, such as rubber or any other suitable insulating coating. In such a case, the bath 10 may be formed of a metal.

Preferably wood to be treated, such as a log 12, illustrated in Figs. 1A and I B, is supported within bath 10 by a pair of electrically insulative supports 14. The entire bath may be static or movable, as shown in Fig. 1 A.

Disposed in spaced relationship with ends of log 12 and preferably adequately insulated from the end walls 16 and 18 of bath 10, are first and second electrodes 20 and 22. Electrodes 20 and 22 are preferably formed of graphite. Alternatively, but not preferably, the electrodes 20 and 22 may be formed of metal.

An AC voltage source 24 is connected to electrodes 20 and 22 by suitable conductors 26. Preferably, AC voltage source 24 comprises a step-up transformer receiving an electrical input from a mains power source or from a conventional generator and providing an output across electrodes 20 and 22 which is preferably within the range of 400 to 20,000 volts at mains frequency.

A liquid 28, having an electrical conductivity less than wood, such as de- ionized water, preferably fills the bath 10 and surrounds log 12.

In accordance with a preferred embodiment of the present invention the apparatus of Figs. 1 A and IB is operative to apply a voltage via the liquid 28, having an electrical conductivity less than wood, across the ends of the log 12, thereby causing electrical current to pass along the length of the log 12, preferably throughout the entire cross section thereof.

Preferably, a sufficiently high voltage is applied to the log 12 for a sufficiently long time in order to raise the temperature of the wood to above 120°C in order to sterilize the log 12. The wood need not remain at this temperature for more than approximately one minute.

It is appreciated that the bath 10 and its associated equipment may be placed in a pressure chamber, as described hereinbelow with respect to Fig. 4.

In accordance with a preferred embodiment of the present invention, a sufficiently high voltage is applied for a sufficiently long time in order to provide enzymatic inactivation and biological stability of the wood in the log 12. These effects may occur at temperatures as low as 100°C. The wood need not remain at this temperature for more than approximately one minute.

Additionally in accordance with a preferred embodiment of the present invention, a sufficiently high voltage is applied for a sufficiently long time in order to provide desired darkening of the wood. These effects may occur at temperatures even below 100°C and increase with temperature and time of heat treatment.

Preferably a sufficiently high voltage is applied for a sufficiently long time in order to facilitate separation of bark from the wood of the log 12. This may occur at temperatures as low as 100°C. The wood need not remain at this temperature for more than approximately one minute. This bark removal facilitation treatment is preferably carried out under elevated pressure, such as at least 2 atmospheres.

Reference is now made to Figs. 1C and ID, which are schematic illustrations of the apparatus for treating wood by applying a voltage thereacross and in which the bath 10 does not contain the liquid 28, in accordance with another preferred embodiment of the present invention. As described hereinbelow with respect to Fig. 4, the bath 10 and its associated equipment are located within a pressure chamber.

Figs. 1C and ID show that the electrodes 20 and 22 are tightly abutted against the end of the log 12. In order to ensure good electrical conduction between the electrodes 20 and 22 and log 12, pads 30 and 32, which are constructed of electrically conductive material, are placed between the electrodes 20 and 22 and the log 12. It is appreciated that the pads 30 and 32 are contoured so as to conform to the contours of the ends of the log 12, thus ensuring good electrical conduction between the electrodes 20 and 22 and the log 12.

The pads 30 and 32 may be constructed from any suitable material, such as steel wool. Additionally or alternatively, a conductive gel is applied to the electrodes 20 and 22 prior to the electrodes 20 and 22 being placed in contact with the log 12. Typical conductive gels may be an agar-agar gel comprising about 3% KCl, or an agar- agar gel comprising iron powder and/or carbon powder.

It is appreciated that using the bath 10 without the liquid conductor 28, allows the wood treatment process, as described hereinbelow with respect to Fig. 6, to proceed without a water supplying step and a wood drying step. Thus, time and costs for wood treatment are typically reduced. Reference is now made to Figs. 2A - 2P, which are illustrations of various embodiments of apparatus for treating wood by applying a voltage thereacross in accordance with a preferred embodiment of the present invention.

Turning to Figs. 2A and 2B, there are shown a three-electrode arrangement, suitable for simultaneous heat treatment of two logs 50 and 52. As in the embodiment of Figs. 1A and IB, there is preferably provided a bath 54, preferably formed of an electrically insulative material, such as wood or high temperature resistant plastic.

The bath 54 may have an insulative coating formed of a suitable high temperature resistant plastic, rubber or any other suitable organic coating. In such a case, the bath 54 may be formed of a metal.

Preferably two logs of wood to be treated, such as a logs 50 and 52, are supported within bath 54 by electrically insulative supports 56. The entire bath may be static or movable.

Disposed in spaced relationship between adjacent ends of logs 50 and 52 there is preferably provided a live electrode 58, while disposed in spaced relationship with the respective outwardly facing ends of logs 50 and 52 and adequately insulated from the end walls 60 and 62, there are preferably provided first and second ground electrodes 64 and 66. Electrodes 58, 64 and 66 are preferably formed of graphite. Alternatively, but not preferably, the electrodes 58, 64 and 66 may be formed of metal.

An AC voltage source 68 is connected between live electrode 58 and respective ground electrodes 64 and 66 by suitable conductors 69. Preferably, the AC voltage source 68 comprises a step-up transformer receiving an electrical input from a mains power source or from a conventional generator and providing an output between electrode 58 and respective electrodes 64 and 66, which is preferably within the range of 400 to 20,000 volts at mains frequency.

A liquid 70, having an electrical conductivity less than wood, such as de- ionized water, preferably fills the bath 54 and surrounds logs 50 and 52.

In accordance with a preferred embodiment of the present invention the apparatus of Figs. 2 A and 2B is operative to apply a voltage via the liquid 70, having an electrical conductivity less than wood, across the ends of the logs 50 and 52, thereby causing electrical current to pass along the length of the logs, preferably throughout the entire cross section thereof

The functionality of the apparatus of Figs. 2 A and 2B may be identical to that of Figs. l A and IB and applies both to logs and to wood in other forms and configurations.

Reference is now made to Figs. 2C and 2D, which show the bath 54 and its associated equipment, in a configuration in which the bath 54 does not contain the liquid 70

In the assembly illustrated in Figs. 2C and 2D, the electrodes 58 and 64 and the electrodes 58 and 66 are tightly abutted against the logs 50 and 52, respectively. In order to ensure good electrical conduction between the electrode 58 and 64 and the log 50, pads 72 and 74, constructed of electrically conductive material, are placed between the electrodes 58 and 64 and the log 50. Similarly, pads 76 and 78, which are also constructed of electrically conductive material, are placed between the electrodes 58 and 66 and the log 52.

It is appreciated that the conductive pads 72, 74, 76 and 78 are contoured so as to conform to the contours of the ends of the logs 50 and 52. The contouring ensures good electrical conduction between the electrodes 58 and 64 and the log 50 and between the electrodes 58 and 66 and the log 52.

The pads 72, 74, 76 and 78 may be constructed from any suitable material, such as steel wool. Additionally or alternatively, a conductive gel is applied to the electrodes 58, 64 and 66 prior to the electrodes 58 and 64 being placed in contact with the log 50 and the electrodes 58 and 66 being placed in contact with the log 52. Typical conductive gels may be an agar-agar gel comprising about 3% KCl, or an agar- agar gel comprising iron powder and/or carbon powder.

The functionality of the apparatus of Figs. 2A and 2B may be identical to that of Figs. 1 C and I D and applies both to logs and to wood in other forms and configurations

Turning to Figs. 2E and 2F, there is shown another three-electrode arrangement, suitable for simultaneous heat treatment of one or more logs 80. As in the embodiment of Fig. 1, there is preferably provided a bath 82, preferably formed of an electrically insulative material, such as wood or high temperature resistant plastic. The bath 82 may have an insulative coating formed of a suitable high temperature resistant plastic, rubber or any other suitable organic coating. In such a case, the bath 82 may be formed of a metal.

Preferably wood to be treated, such one or more logs 80, is supported within bath 82 by electrically insulative supports 84. The entire bath may be static or movable.

Disposed in spaced relationship around a middle portion of a log or collection of logs 80 there is preferably provided a live electrode 86 in the form of a ring, while disposed in spaced relationship with the respective outwardly facing ends of log 80 and adequately insulated from the end walls 88 and 90, there are preferably provided first and second ground electrodes 92 and 94, preferably in the form of a disk. Electrodes 86, 92 and 94 are preferably formed of graphite. Alternatively, but not preferably, the electrodes 86, 92 and 94 may be formed of metal.

An AC voltage source 96 is connected between live electrode 86 and respective ground electrodes 92 and 94 by suitable conductors 98. Preferably, the AC voltage source 96 comprises a step-up transformer receiving an electrical input from a mains power source or from a conventional generator and providing an output between electrode 86 and respective electrodes 92 and 94, which is preferably within the range of 400 to 20,000 volts at mains frequency.

A liquid 99, having an electrical conductivity less than wood, such as de- ionized water, preferably fills the bath 82 and surrounds the log 80.

In accordance with a preferred embodiment of the present invention, the apparatus of Fig. 2E is operative to apply a voltage via the liquid 99, having an electrical conductivity less than wood, across the ends of the log or logs 80, thereby causing electrical current to pass along the length and preferably throughout the entire cross section thereof.

The functionality of the apparatus of Figs. 2E and 2F may be identical to that of Figs. 1 A and IB and applies both to logs and to wood in other forms and configurations.

Reference is now made to Figs. 2G and 2H, which show the bath 82 and its associated equipment, in a configuration in which the bath 82 does not contain the liquid 99. In the assembly illustrated in Figs. 2G and 2H, the electrodes 92 and 94 are tightly abutted against the log 80. Similarly, the electrode 86, which is typically in the form of a ring, is also tightly abutted against a middle portion of the log 80.

In order to ensure good electrical conduction between the electrodes 86, 92 and 94 and the log 80, pads 100, 102 and 104, which are constructed of electrically conductive material, are placed between the electrodes 86, 92 and 94 and the log 80, as shown in Figs. 2G and 2H.

It is appreciated that the pad 100 is contoured so as to conform to the contour of the middle portion of the log 80. Additionally, the pads 102 and 104 are contoured so as to conform to the contours of the ends of the log 80. The contouring of the pads 100, 102 and 104 ensures good electrical conduction between the electrodes 86, 92 and 94 and the log 80.

The pads 100, 120 and 104 may be constructed from any suitable material, such as steel wool. Additionally or alternatively, a conductive gel is applied to the electrodes 86, 92 and 94 prior to the electrodes 86, 92 and 94 being placed in contact with the log 80. Typical conductive gels may be an agar-agar gel comprising about 3% KCl, or an agar-agar gel comprising iron powder and/or carbon powder.

The functionality of the apparatus of Figs. 2G and 2H may be identical to that of Figs. 1 C and ID and applies both to logs and to wood in other forms and configurations.

Turning to Figs. 21 and 2J, there is shown a multiple ring electrode arrangement, suitable for simultaneous heat treatment of one or more logs 120. As in the embodiment of Figs. 1A and IB, there is preferably provided a bath 124, preferably formed of an electrically insulative material, such as wood or high temperature resistant plastic.

The bath 124 may have an insulative coating formed of a suitable high temperature resistant plastic, rubber or any other suitable organic coating. In such a case, the bath 124 may be formed of a metal.

Preferably wood to be treated, such one or more logs 120, is supported within bath 124 by electrically insulative supports 126. The entire bath may be static or movable. Disposed in spaced relationship around a log or collection of logs 120 there are preferably provided a plurality of ring electrodes 128, while disposed in spaced relationship with the respective outwardly facing ends of log 120 and adequately insulated from the end walls 130 and 132, there are preferably provided first and second ground electrodes 134 and 136, preferably in the form of a disk. Electrodes 128, 134 and 136 are preferably formed of graphite. Alternatively, but not preferably, the electrodes 128, 134 and 136 may be formed of metal.

Preferably ring electrodes 128 preferably include three live electrodes 138, 140 and 142, separated by grounded electrodes 144 and 146 as shown in Fig. 2J.

A three phase AC voltage source 148 provides single phase AC voltage on lines 150, 152 and 154. The AC lines 150, 152 and 154 are connected to respective live electrodes 138, 140 and 142, and between respective pairs of ground electrodes 134 and 144, 144 and 146 and 146 and 136 by suitable conductors 156. Preferably, the three phase AC voltage source 148 comprises a step-up transformer receiving an electrical input from a mains power source or from a conventional generator and providing an output across a live electrode and a grounded electrode which is preferably within the range of 400 to 20,000 volts at mains frequency.

A liquid 158, having an electrical conductivity less than wood, such as de-ionized water, preferably fills the bath 124 and surrounds log or logs 120.

In accordance with a preferred embodiment of the present invention the apparatus of Figs. 21 and 2J is operative to apply a voltage via the liquid 158, having an electrical conductivity less than wood, across the ends of the log or logs 120, thereby causing electrical current to pass along the length and preferably throughout the entire cross section thereof.

The functionality of the apparatus of Figs. 21 and 2J may be identical to that of Figs. 1 A and IB and applies both to logs and to wood in other forms and configurations.

Reference is now made to Figs. 2K and 2L, which show the bath 124 and its associated equipment, in a configuration in which the bath 124 does not contain the liquid 158. In the bath assembly illustrated in Figs. 2K and 2L, the electrodes 134 and 136 are tightly abutted against the log or logs 120. Similarly, the electrodes 128, which are typically ring-shaped, are also tightly abutted against the log or logs 120.

In order to ensure good electrical conduction between the electrodes 134 and 136 and the log or logs 120, pads 160 and 162, which are constructed from electrically conductive material, are placed between the electrodes 134 and 136 and the log or logs 120, as shown in Figs. 2K and 2L. Similarly, in order to ensure good electrical conduction between the electrodes 128 and the log or logs 120, pads 164, 165, 166, 167 and 168, which are typically ring-shaped and constructed from electrically conductive material, are placed between the electrodes 138, 140, 142, 144 and 146, and the log or logs 120.

Tt is appreciated that the pads 164, 165, 166, 167 and 168 are contoured in order to conform to the contours of the portions of the log or logs 120, which they are in physical contact therewith. Additionally, the pads, 160 and 162, are also contoured so as to conform to the contours of the ends of the log or logs 120. The contouring of the pads 160, 162, 164, 165, 166, 167 and 168 ensures good electrical conduction between the electrodes 128, 134 and 136 and the log or logs 120.

The pads 160, 162, 164, 165, 166, 167 and 168 may be constructed from any suitable material, such as steel wool. Additionally or alternatively, a conductive gel is applied to the electrodes 128, 134 and 136 prior to the electrodes 128, 134 and 136 being placed in contact with the log 120. Typical conductive gels may be an agar-agar gel comprising about 3% KCl, or an agar-agar gel comprising iron powder and/or carbon powder.

The functionality of the apparatus of Figs. 2K and 2L may be identical to that of Figs. 1 C and ID and applies both to logs and to wood in other forms and configurations.

Turning to Figs. 2M and 2N, there are shown another two-electrode arrangement, in a top view and a side view, respectively, suitable for simultaneous heat treatment of a uniform stack of wood 170. As in the embodiment of Figs. 1A and IB, there is preferably provided a bath 172, preferably formed of an electrically insulative material, such as wood or high temperature resistant plastic. The bath 172 may have an insulative coating formed of a suitable high temperature resistant plastic, rubber or any other suitable organic coating. In such a case, the bath 172 may be formed of a metal.

Preferably the uniform stack of wood 170 to be treated is supported within bath 172 by electrically insulative supports 174. The entire bath 172 may be static or movable.

Disposed in spaced relationship adjacent stack 170 and preferably alongside the longer two sides thereof there are preferably provided a pair of electrodes 176 which are adequately insulated from the side walls 177 and 178. Electrodes 176 are preferably formed of graphite. Alternatively, but not preferably, the electrodes 176 may be formed of metal.

An AC voltage source 180 is preferably connected across electrodes 176 by suitable conductors 182. Preferably, the AC voltage source 180 comprises a step-up transformer receiving an electrical input from a mains power source or from a conventional generator and providing an output across electrodes 176, which is preferably within the range of 400 to 20,000 volts at mains frequency.

A liquid 184, having an electrical conductivity less than wood, such as de-ionized water, preferably fills the bath 172 and surrounds stack 170.

In accordance with a preferred embodiment of the present invention the apparatus of Figs. 2M and 2N is operative to apply a voltage via the liquid 184, having an electrical conductivity less than wood, across the shortest extent of stack 170, thereby causing electrical current to pass therealong and preferably throughout the entire cross section thereof.

The functionality of the apparatus of Figs. 2M and 2N may be identical to that of Figs. 1A and IB and applies to wood in other suitable forms and configurations.

Reference is now made to Figs. 2O and 2P, which show the bath 172 and its associated equipment, in a configuration in which the bath 172 does not contain the liquid 184.

In the bath assembly illustrated in Figs. 2O and 2P, the electrodes 176 are tightly abutted against the stack of wood 170. In order to ensure good electrical conduction between the electrodes 176 and the stack of wood 170, pads 186 and 188, which are constructed of electrically conductive material, are placed between the electrodes 176 and the stack of wood 170, as shown in Figs. 2O and 2P.

It is appreciated that the pads 186 and 188 are contoured in order to conform to the contours of outer surfaces 190 and 192 of the stack of wood 170. This contouring of the pads 186 and 188 ensures good electrical conduction between the electrodes 176 and the stack of wood 170.

The pads 186 and 188 may be constructed from any suitable material, such as a steel wool. Additionally or alternatively, a conductive gel is applied to the electrodes 176 prior to the electrodes 176 being placed in contact with the wood stack 170. Typical conductive gels may be an agar-agar gel comprising about 3% KCl, or an agar-agar gel comprising iron powder and/or carbon powder.

The functionality of the apparatus of Figs. 2O and 2P may be identical to that of Figs. 1 C and ID and applies both to logs and to wood in other forms and configurations.

Reference is now made to Fig. 3, which is an illustration of another embodiment of apparatus for treating wood by applying a voltage thereacross in accordance with a preferred embodiment of the present invention. As seen in Fig. 3, there is preferably provided an enclosure 210, preferably formed of an electrically insulative material, such as wood or high temperature resistant plastic.

The enclosure 210 may have an insulative coating formed of a suitable high temperature resistant plastic, rubber or any other suitable organic coating. In such a case, the enclosure 210 may be formed of a metal.

Preferably wood to be treated, such as a log 212, illustrated in Fig. 3, is supported within enclosure 210 by a pair of electrically insulative supports 214. The entire enclosure may be static or movable, as shown in Fig. 3.

Disposed in spaced relationship with ends of log 212 and adequately insulated from the end walls 216 and 218 of enclosure 210, are first and second waterfall generation and electrode assemblies 220 and 222. Each assembly preferably comprises a container 224 of de-ionized water, salt water or any other suitable liquid, having a perforated side wall defining an electrode 226, spaced from and facing an end of log 212. A pump 228 forces water into container 224 and out through perforations in electrode 226 producing a generally water filled volume 230 between electrode 226 and an end of log 212. The water falls by gravity into a collection basin 232 and is recycled by pump 228.

Electrodes 226 are preferably formed of graphite. Alternatively, but not preferably, the electrodes 226 may be formed of metal.

An AC voltage source 234 is connected to electrodes 226 on either end of log 212 by suitable conductors 236. Preferably AC voltage source 234 comprises a step-up transformer receiving an electrical input from a mains power source or from a conventional generator and providing an output across electrodes 226, which is preferably within the range of 400 to 20,000 volts at mains frequency.

It is seen that the embodiment of Fig. 3 provides the electrical conductive arrangement of Figs. 1 A and IB without requiring that the entire log be in a bath.

It is appreciated that the embodiments described hereinabove with reference to Figs. 1 A - 3 may operate at atmospheric pressure, at an elevated pressure or at a sub-atmospheric pressure.

It is also appreciated that the embodiment described hereinabove with respect to Fig. 3, may be preferably used for wood drying, when the apparatus of Fig. 3 is enclosed in a vacuum chamber. In the case of Fig. 3, the electrical current flowing through the log 212 provides the heat of evaporation of the water or moisture in the log 212.

Reference is now made to Fig. 4, which is an illustration of a preferred system for treating wood in accordance with a preferred embodiment of the present invention. The system of Fig. 4 shows a typical batch processing system where there are three groups of pressure and/or vacuum chambers 300, each associated with a bath 302. At any given time, one group of pressure chambers 300 is being loaded with baths 302 containing logs 304, as shown for example in Figs. 1A - 3 and as designated by reference numeral 3 10, while at the same time, another group of logs 304 are being electrically treated as described hereinabove within pressure and/or vacuum chambers 300, as designated by reference numeral 312 and yet another group of baths 302 are being removed from pressure and/or vacuum chambers 300, as designated by reference numeral 314. The arrangement shown in Fig. 4 provides efficient utilization of available electrical power capacity.

Reference is now made to Fig. 5, which is a simplified flow chart of a preferred methodology for wood treatment, in which the bath contains a liquid, having an electrical conductivity less than wood, such as water, in accordance with a preferred embodiment of the present invention. For simplicity, unless indicated otherwise, reference is made to apparatus of the type shown in any of Figs. 1 A and IB, 2A and 2B, 2E and 2F, 21 and 2J, 2M and 2N, and 3 in a system, such as that shown in Fig. 4 and described hereinabove.

As seen in Fig. 5, wood, in the form of logs or cut wood is loaded into a bath and the bath is placed inside a vacuum/pressure chamber. A vacuum is applied and air is removed from the vacuum/pressure chamber. The bath is filled with tap water to which is added a conductive basic solution, such as sodium hydroxide or calcium hydroxide, for wood impregnation. It is appreciated that impregnating the logs with the base solution increases the electrical conductivity of the logs. Typical salt concentrations are 0.1 % to 0.5 %.

An elevated pressure, typically 5 - 10 atmospheres, is applied to the chamber, causing impregnation of the wood by the water/base solution in the bath. The wood impregnation enhances the electrical conductivity and the pH of the wood and enables the use of lower voltages.

The water solution is then drained from the bath, which may then be filled with de-ionized water.

A sufficiently high voltage is applied across the electrodes adjacent the wood for a sufficiently long time in order to heat the wood to a desired temperature. The wood is typically heated, under pressure, up to temperatures as high as 200°C. Typical applications of the wood treatment include wood sterilization, coloration and debarking. A typical minimum temperature for sterilization of the wood is approximately 120°C and a typical temperature for achieving wood coloration is approximately 160°C.

Following application of the high voltage and on reaching the predetermined temperature, the electrical current is then turned off and the water is drained from the chamber. The pressure in the chamber is gradually reduced, first to atmospheric pressure and then to a vacuum, typically 27 - 29 inches of mercury, for a few minutes, to provide quick cooling of the wood. As the pressure is reduced, the boiling point of the water is reduced and the water within the wood evaporates. The vacuum is then broken.

The wood and the bath are then unloaded from the pressure vessel. At this stage, bark on the wood may be readily physically separated from wood.

Reference is now made to Fig. 6, which is a simplified flow chart of a preferred methodology for wood drying, in which the bath is not filled with a liquid, in accordance with another preferred embodiment of the present invention. For simplicity, unless indicated otherwise, reference is made to apparatus of the type shown in any of Figs. 1 C and ID, 2C and 2D, 2G and 2H, 2K and 2L, 20 and 2P, such as that shown in Fig. 4 and described hereinabove.

As seen in Fig. 6, wood, in the form of logs or cut wood is loaded into a bath and the bath is placed inside a vacuum/pressure chamber and pressure is applied to the chamber.

Following application of the high voltage and on reaching the predetermined temperature, the pressure in the chamber is gradually reduced, first to atmospheric pressure and then to a vacuum, typically 27 - 29 inches of mercury, for a few minutes, to provide quick cooling of the wood. As the pressure is reduced, the boiling point of any liquid, which may be contained within the wood, is reached and the liquid evaporates. The electrical power is then turned-off and the vacuum is then broken.

The wood and the bath are then unloaded from the pressure vessel. At this stage, bark on the wood may be readily physically separated from wood. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove as well as variations and modifications which would occur to persons skilled in the art upon reading the specification and which are not in the prior art.

Claims

C L A I M S

1 . A method for treating wood comprising: arranging at least first and second electrodes in electrical contact with wood to be treated via an electrically conductive material; and applying a voltage across the at least first and second electrodes.

2. A method for treating wood according to claim 1 and wherein said applying said voltage comprises applying an AC voltage across said at least first and second electrodes.

3. A method for treating wood according to claim 1 and wherein arranging said at least first and second electrodes comprises locating said wood to be treated within a pressure chamber.

4. A method for treating wood according to claim 3 and wherein said pressure chamber contains an electrically conductive liquid.

5. A method for treating wood according to claim 3 and wherein said voltage is applied across said at least first and second electrodes while said wood to be treated is maintained under positive pressure within said pressure chamber.

6. A method for treating wood according to claim 1 and wherein said wood to be treated comprises at least one elongate wood element and said at least first and second electrodes are arranged adjacent ends of said at least one elongate wood element.

7. A method for treating wood according to claim 4 and wherein said electrically conductive liquid comprises water.

8. A method for treating wood according to claim 7 and wherein said wood to be treated is more electrically conductive than said electrically conductive liquid.

9. A method for treating wood according to claim 1 and wherein said voltage comprises an AC voltage at line frequency.

10. A method for treating wood according to claim 1 and wherein said voltage exceeds approximately 400 volts.

1 1. A method for treating wood according to claim 1 and wherein said at least first and second electrodes are not in direct contact with said wood to be treated.

12. A method for treating wood according to claim 11 and wherein a conductive pad is placed between said at least first and second electrodes and said wood to be treated.

13. A method for treating wood according to claim 12 and wherein said conductive pad comprises steel wool.

14. A method for treating wood according to claim 12 and wherein a conductive paste is applied between said conductive pad and said at least first and second electrodes.

15. A method for treating wood according to claim 14 and wherein said conductive paste comprises an agar-agar gel comprising at least 3% KCl.

16. A method for treating wood according to claim 14 said conductive paste comprises an agar-agar gel and wherein said agar-agar gel comprises an electrically conductive material selected from a group consisting of iron powder and carbon powder.

17. A method for treating wood according to claim 1 and wherein said at least first and second electrodes are non-metallic.

18. A method for treating wood according to claim 1 and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to sterilize said wood to be treated.

19. A method for treating wood according to claim 1 and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to provide enzymatic inactivation and biological stability of said wood to be treated.

20. A method for treating wood according to claim 1 and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to provide desired coloration of said wood to be treated.

21. A method for treating wood according to claim 1 and wherein said wood to be treated includes bark and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to facilitate separation of said bark from said remainder of said wood to be treated.

22. A method for treating wood according to claim 1 and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to heat said wood to be treated to at least a desired temperature within a pressure chamber which contains said conductive material, said method also comprising said step of: following heating of said wood to be treated to at least said desired temperature, gradually reducing the pressure within said pressure chamber to a desired sub-atmospheric pressure, thereby providing desired removal of moisture from said wood to be treated.

23. A method for treating wood according to claim 22 and also comprising removing said conductive liquid from said pressure chamber prior to gradually reducing said pressure within said pressure chamber.

24 A method for treating wood comprising: impregnating wood to be treated with a liquid having a pH higher than said pH of said wood to be treated, thereby to provide at least one of wood preservation and wood coloration

25 A method for treating wood according to claim 24 and also comprising, following said impregnating, applying a voltage across said wood to be treated, for desired heating thereof

26 Apparatus for treating wood comprising: a conductive electrode assembly operative for establishing electrical contact of at least first and second electrodes with wood to be treated via an electrically conductive material, and an electrical voltage source applying a voltage across said at least first and second electrodes.

27 Apparatus for treating wood according to claim 26 and wherein said electrical voltage source comprises an AC voltage source

28 Apparatus for treating wood according to claim 26 and wherein said conductive electrode assembly comprises a pressure chamber which contains said conductive material

29 Apparatus for treating wood according to claim 28 and wherein said voltage is applied across said at least first and second electrodes while said wood to be treated is maintained under positive pressure within said pressure chamber.

30. Apparatus for treating wood according to claim 26 and wherein said wood to be treated comprises at least one elongate wood element and said at least first and second electrodes are arranged adjacent ends of said at least one elongate wood element

3 1 Apparatus for treating wood according to claim 26 and wherein said electrically conductive material comprises an electrically conductive liquid.

32. Apparatus for treating wood according to claim 31 and wherein said electrically conductive liquid comprises water

33 Apparatus for treating wood according to claim 31 and wherein said wood to be treated is more electrically conductive than said electrically conductive liquid.

34. Apparatus for treating wood according to claim 26 and wherein said voltage comprises an AC voltage at line frequency.

35 Apparatus for treating wood according to claim 26 and wherein said voltage exceeds approximately 400 volts.

36. Apparatus for treating wood according to claim 26 and wherein said at least first and second electrodes are not in direct contact with said wood to be treated.

7 Apparatus treating wood according to claim 26 and wherein a conductive pad is placed between said at least first and second electrodes and said wood to be treated

38 Apparatus for treating wood according to claim 37 and wherein said conductive pad comprises steel wool.

39. Apparatus for treating wood according to claim 26 and wherein a conductive paste is applied between said conductive pad and said at least first and second electrodes.

40. Apparatus for treating wood according to claim 39 and wherein said conductive paste comprises an agar-agar gel comprising at least 3% KCl.

41 Apparatus for treating wood according to claim 39 said conductive paste comprises an agar-agar gel and wherein said agar-agar gel comprises an electrically conductive material selected from a group consisting of iron powder and carbon powder

42 Apparatus for treating wood according to claim 26 and wherein said at least first and second electrodes are non-metallic

43 Apparatus for treating wood according to claim 26 and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to sterilize said wood to be treated.

44 Apparatus for treating wood according to claim 26 and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to provide enzymatic inactivation and biological stability of said wood to be treated

45 Apparatus for treating wood according to claim 26 and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to provide desired coloration of said wood to be treated.

46 Apparatus for treating wood according to claim 26 and wherein said wood to be treated includes bark and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to facilitate separation of said bark from said remainder of said wood to be treated.

47 Apparatus for treating wood according to claim 26 and wherein applying said voltage comprises applying a sufficiently high voltage for a sufficiently long time in order to heat said wood to be treated to at least a desired temperature within a pressure chamber which contains said conductive material, said apparatus also comprising: a vacuum drying subsystem operative, following heating of said wood to be treated to said at least said desired temperature, to gradually reduce the pressure within said pressure chamber to a desired sub-atmospheric pressure, thereby providing desired removal of moisture from said wood to be treated.

48. Apparatus for treating wood according to claim 47 and also comprising a conductive liquid drying subsystem operative for removing said conductive liquid from said pressure chamber prior to gradually reducing said pressure within said pressure chamber.

49. Apparatus for treating wood comprising: an impregnator operative to impregnate wood to be treated with a liquid having a pH higher than said pH of said wood to be treated, thereby to provide at least one of wood preservation and wood coloration.

50. Apparatus for treating wood according to claim 49 and also comprising a wood heater, operative following operation of said impregnator, to apply a voltage across said wood to be treated, for desired heating thereof.