DEVICE FOR HEAT TREATMENT OF LOGS

Description

[0001] The present invention relates to the field of phytosanitary treatment of logs, in particular hardwoods and softwoods. It relates more particularly to a device for heat treatment under the bark of logs.

[0002] Log transport contributes to the spread of plant pests, including fungi and insects. It is therefore necessary to treat the logs to limit this phenomenon. Such phytosanitary treatment is even mandatory for the export of logs to certain countries. According to current standards, it consists of maintaining all the logs under the bark (subcortical) at a temperature above 71.1°C for at least 75 minutes. Heat treatment is usually carried out, consisting of injecting a stream of hot air or steam into a container of logs at a temperature between 80 and 150°C. The injection is carried out from the rear of the container, after opening the doors. Since the heat comes from the rear of the container, this process does not allow for even heat distribution in the container and results in significant energy consumption.The heat treatment cycle is also long due to the significant temperature rise time under the bark of the logs furthest from the heat source.

[0003] Document US5447686 discloses a method for heat treating pieces of wood with steam to eliminate various parasites. The pieces of wood are loaded into the hold of a boat equipped for steam production. Said pieces are brought into contact with steam, injected through the bottom of the hold, to raise the temperature and maintain it at a level sufficient for a long time to eliminate the various parasites that may be present. However, to apply this method, the wood cannot remain in a container but must be unloaded into the hold of the boat.

[0004] Document US20122147067 discloses a device for heating a liquid load in a container, but the solution is not suitable for the treatment of solid parts.

[0005] The object of the present invention is to at least partially overcome these drawbacks by proposing a device for processing logs located in a container without having to remove said logs from said container. The operation can take place in the container remaining on the semi-trailer coupled to its tractor, without any handling of the logs. The device according to the invention also allows a rapid rise in temperature of the logs at any point in the container.

[0006] To this end, the present invention proposes a heat treatment device comprising a container loaded with logs, and a pressurized steam inlet pipe. Said heat treatment device is particular in that it comprises at least one, preferably two, tubes provided with a plurality of openings distributed along its length and around its circumference, said at least one tube being intended to be introduced from the rear into said container loaded with logs, and to be supplied with said pressurized steam so that the steam comes into contact with the logs, said at least one tube being substantially rectilinear in the sense that it has a certain elasticity, allowing it to go around a log to find its way to the front of the container.

[0007] Thanks to these arrangements, the heat injection being distributed over the entire length of the container, the heat treatment of the logs is rapid and optimal in terms of energy consumption. The device also allows heat treatment to be easily implemented in a standard container such as used for transport by truck or ship.

[0008] According to other characteristics: said openings of said tubes are of increasing size and / or number starting from the side of the water vapor supply, improving the distribution of the steam in the container so that the logs located at the end of the container opposite the steam supply of the tubes, and therefore conveying more cooled or already condensed steam, can rise in temperature as quickly as the logs located close to the supply, said at least one tube may have an external diameter of less than 25 mm, which makes it easy to insert it into the container in the free spaces between the logs, said device may further comprise a gutter for recovering condensed water, allowing the evacuation and recovery of the water produced during the heat treatment by the condensation of the steam for another use, said device may further comprise a pipe for discharging the water recovered in the gutter,said pipe being provided with a filter, making it possible to recover the water from the gutter for another use, for example the production of water vapor to supply the pipe, said device may further comprise a sealing device, consisting in particular of at least one foam strip, intended to be arranged at the rear opening of said container in order to reduce the escape of water vapor and heat, making it possible to reduce the energy consumption of the device according to the invention; in particular, the left door can be closed after the device has been put in place, and said foam strip can be arranged at the opening of the right door, said foam strip can be provided with a magnetic strip for its attachment to the container, which constitutes a simple and easy to implement embodiment, even repeatedly, of the invention.

[0009] The present invention also relates to a method for heat treatment of logs loaded into a container, characterized in that it comprises the following steps: opening the container from the rear, introducing at least one tube from the rear into said container loaded with logs, said tube being provided with a plurality of openings distributed along its length and around its circumference, so that it extends over at least three-quarters of the length of the container, said at least one tube being substantially rectilinear in the sense that it has a certain elasticity, allowing it to go around a log to find its way to the front of the container, connecting said tube to a steam supply pipe, pressurizing the pipe.

[0010] Before pressurizing the pipe, you can close the left door of the container, then lock the right door half-open.

[0011] Thanks to these arrangements, the heat injection being distributed over the entire length of the container, the heat treatment of the logs is rapid, optimal in terms of energy consumption. Such a heat treatment process is easy to implement in a standard container such as used for transport by truck or ship.

[0012] According to other characteristics: said method may further comprise a step of sealing the door openings with a sealing device before pressurizing the pipe, making it possible to reduce the energy consumption of the method according to the invention.

[0013] The present invention will be better understood upon reading the detailed description which follows, with reference to the appended figures in which: There figure 1 is a schematic view of the heat treatment device according to the invention.

[0014] The heat treatment device according to the invention, illustrated in fig. 1 , comprises a pipe 1 for supplying pressurized water vapor, feeding a tube 2 intended to be introduced into a container 3 of logs from the rear.

[0015] This device is intended to be introduced into a container 3, it is therefore separable from said container 3, and can be used to treat several separate containers 3 one after the other.

[0016] The tube 2 is substantially rectilinear, and it is provided with a plurality of openings distributed along its length and around its circumference. These openings may consist of notches sawn into the tube 2. The tube 2 has a length which may be for example approximately 10 meters, so that once introduced into the container 3, the water vapor escaping through its openings can quickly reach all the logs in the container 3 and along their entire length. The heat treatment can thus be homogeneous throughout the container 3. In order to obtain an optimal result, the tube 2 may be inserted halfway up the container 3.

[0017] In the preferred embodiment of the invention illustrated in fig. 1 , the heat treatment device according to the invention comprises two tubes 2, in order to further improve the distribution of water vapor in the container 3. The two tubes 2 can for example both be placed halfway up the container 3 and distributed across its width.

[0018] The openings of the tube 2 may be of increasing size and / or number from the end supplied by the pipe 1. This ensures that sufficient water vapor reaches the end of the tube 2 furthest from the water vapor supply to obtain a uniform thermal environment within the container 3.

[0019] The tube 2 may have an outside diameter of less than 25 mm, so that it can be easily inserted among the logs in the container 3. However, this outside diameter must be large enough to carry the desired amount of water vapor. The thickness of the tube 2 may be at least 2 mm, so that the tube 2 is sufficiently strong and does not deform too much when inserted between the logs of the container 3, while resisting the pressure exerted within it by the water vapor. The tube 2 may have a certain elasticity, allowing it for example to go around a log to find its way to the front of the container. Such elasticity will cause the tube to be slightly deformed, but for the purposes of the present invention it must nevertheless be considered to be “substantially straight”.

[0020] Partial condensation of the steam takes place in tube 2, thus releasing most of the latent heat without damaging the logs. The rest of the steam condenses on contact with the bark of the logs, ensuring an optimal rise in temperature of the latter.

[0021] The device according to the invention may further comprise a sealing device, consisting for example of one or more foam strips. The sealing device may comprise magnetic strips for its attachment to the container, and it may be arranged at the rear opening of the container, in particular at the opening of the right door through which the end of the pipe 1 and the tube 2 are inserted. This makes it possible to reduce the escape of water vapor and heat from the container 3 during the heat treatment, and therefore to reduce the energy consumption of the heat treatment device.

[0022] In the embodiment of the fig. 1 , the heat treatment device comprises a water recovery gutter 4, in the form of a tray placed at the rear of the container 3. The container 3 can then be inclined, for example at an angle of the order of 5 to 10 degrees, so that the condensed water and any tannins produced during the heat treatment flow towards the gutter 4.

[0023] The water collected in the gutter 4 can then be directed to a discharge pipe 5 which can include a filter 6. The filter 6 can include one or more filter tanks 7, each tank comprising one or more layers of filter material such as filter foam, activated carbon and fine filter wadding. The discharged water can be sent, for example using a diaphragm pump 8, from the gutter 4 to the filter 6 and successively pass through the different layers of the tanks 7. The filtered water can then be recovered for any use, for example to the boiler producing the water vapor from the pipe 1. This boiler can be a boiler burning waste, thus allowing very low consumption of natural resources.

[0024] A pipe 14 can be placed at the right door in the corner of the upper hinge of the container to draw a vacuum from the container enclosure. This allows cold air to be extracted at the start of treatment and circulation to be created on demand.

[0025] Such a vacuum (under slight atmospheric pressure) can be provided by a vacuum pump or a steam air ejector 15. It can be operated by a demand valve.

[0026] To reduce the temperature rise time, and / or to reduce steam consumption, insulation, for example glass wool, can be placed inside the container walls, and / or a cover can be placed on top of the logs, for example a vapour barrier film such as those used as roof insulation.

[0027] A tube 2 can also be added on top of the logs, if necessary under the said cover, to optimize access to the steam logs.

[0028] The heat treatment process according to the request is a treatment of logs directly in the container in which they are loaded. It involves the following steps: opening the container 3 from the rear, for example one of the doors of the container 3 can be ajar. introduction of at least one tube 2 from the rear into said container loaded with logs, said tube 2 being provided with a plurality of openings distributed over its length and over its circumference, so that it extends over at least three-quarters of the length of the container, preferably substantially over the entire length of the container 3, said at least one tube 2 being substantially rectilinear in the sense that it has a certain elasticity, allowing it to go around a log to find its way to the front of the container; for example if the container is 12 m long, a 10 m tube can be used, connection of said tube 2 to a steam supply pipe 1, pressurizing the pipe 1, for example a pressure at least equal to 5 bar.

[0029] A step of sealing the container 3 can be added to the previous process just before pressurizing the pipe 1, so that the pressurized steam coming from the pipe 1 and spread into the container 3 via the tube 2 does not escape largely through the opening of the container 3.

[0030] For example, one of the two rear doors is kept closed, the other is ajar to allow the steam pipe 1 and the tubes 2 to pass through. The half-opening of this door creates an opening space, approximately 20 mm wide and the height of the door. This space can then be filled with a strip of polymer foam resistant to the temperature and pressure conditions prevailing in the container. Depending on the arrangement of the door in relation to the ceiling and floor of the container, such a foam strip can also be placed on the top and / or bottom of the half-open door.

[0031] It is possible to arrange a magnetic strip on the foam strip, allowing the foam strip to be fixed to the container and easily removed after treatment, so that it can be reused for another treatment.

[0032] The steam supply line 1 may include a pressure reducer 9. The latter makes it possible to regulate the supply of steam into the container 3 during the heat treatment. The device may then include temperature sensors 10, placed at certain locations in the container 3, and a computer 11, in order to automate the control of the pressure reducer 9 and to temperature-control the supply of steam into the container 3.

[0033] Upstream of the pressure reducer 9, the line 1 may include a safety valve 12. In the event of excess pressure in the line 1 upstream of the pressure reducer, the valve 12 can reduce the pressure to avoid endangering personnel in the surrounding area. The valve 12 may be set to 10 bar, for example.

[0034] The device may also include a safety device 13 of the “mast riser” type controlling the pressure within the container 3 in order to avoid overpressure during the heat treatment. The safety device 13 may also simply consist of an interruption of the foam strip to allow excess steam to escape, this interruption being correctly sized to maintain the desired pressure in the container, without allowing the pressure to rise beyond what is acceptable.

[0035] According to another embodiment, at least one temperature probe is placed in the container enclosure, at a point judiciously chosen to give an indication of the lowest temperature in the logs, which makes it possible to monitor that under the bark all points of the logs are well above the prescribed temperature. The control of the regulator, by increasing the pressure to raise the temperature and decreasing it to lower the temperature, can be done automatically, but also manually, thanks to a simple display of the measured temperature.

[0036] Although the above description is based on particular embodiments, it is in no way limiting of the scope of the invention, and modifications may be made, in particular by substitution of technical equivalents or by different combination of all or part of the characteristics developed above.

Claims

1. Heat treatment device comprising a container (3) loaded with logs, and a pipe (1) for supplying pressurised steam, characterised in that it comprises at least one, preferably two, tubes (2) provided with a plurality of openings distributed along its length and around its circumference, the said at least one tube (2) being intended to be introduced from the rear into the said container (3) loaded with logs, and to be supplied with said steam under pressure so that the steam comes into contact with the logs, said at least one tube (2) being substantially straight in the sense that it has a certain elasticity, enabling it to go around a log to find its way towards the front of the container (3).

2. Device according to the preceding claim, wherein said openings of said tubes (2) are of increasing size and / or number starting from the steam supply side.

3. Device according to one of the preceding claims, wherein said at least one tube (2) has an external diameter of less than 25 mm.

4. Device according to one of the preceding claims, further comprising a gutter (4) for collecting condensed water.

5. Device according to the preceding claim, further comprising a pipe (5) for draining the water recovered in the gutter (4), said pipe (5) being provided with a filter (6).

6. Device according to one of the preceding claims, further comprising a sealing device, consisting in particular of at least one strip of foam, intended to be arranged at the rear opening of the said container (3) with a view to reducing the escape of water vapour and heat.

7. Device according to the preceding claim, in which the said foam strip is provided with a magnetic strip for fixing it to the container (3).

8. Method of using a device according to one of the preceding claims for the heat treatment of logs loaded into a container (3), characterised in that it comprises the following steps: - opening the container (3) from the rear, - introducing at least one tube (2) from the rear into the said container (3) loaded with logs, the said tube (2) being provided with a plurality of openings distributed over its length and circumference, so that it extends over at least three quarters of the length of the container, the said at least one tube (2) being substantially straight in the sense that it has a certain elasticity, enabling it to go around a log to find its way towards the front of the container (3). - connecting the said tube (2) to a steam supply pipe (1), - pressurising the pipe (1).

9. Method according to the preceding claim, further comprising a step of sealing the door openings with a sealing device before pressurising the pipe (1).

10. Method according to claim 8, in which at least one tube (2) is introduced so that it extends along the entire length of the container.