FR2857291A1 - Thermal processing method for wood, involves recovering mixture containing heat transfer fluid and gas produced from heating of wood through outlet opening and extracting resin part and water vapor contained in gas - Google Patents

Abstract

The method involves reheating a heat transfer fluid in a heating chamber (60) and transferring the fluid in injection chambers (30,31). The fluid is injected in a processing enclosure (2) through an inlet opening (2a) to process a wood (100). A mixture containing the fluid and a gas produced from the heating of the wood is recovered via an outlet opening (2b). A resin part and water vapor contained in the gas are extracted. An independent claim is also included for a device for thermal processing of wood.

Description

2857291 1

  METHOD AND DEVICE FOR HIGH TEMPERATURE THERMAL TREATMENT OF WOODY MATERIAL

  The present invention relates to a high temperature heat treatment process of ligneous material during which the ligneous material is placed in a treatment chamber filled with a heat transfer fluid which is circulated continuously in the treatment chamber.

  It also relates to a device for implementing this method. Woody materials such as wood are widely used materials because they have many advantages both in terms of aesthetics and their mechanical, acoustic and insulating properties. However, in order for them to retain all their characteristics and dimensional stability in the presence of moisture or immersed in water, woody materials must be treated in order to eliminate all media that generate germs and molds. This treatment can be done by impregnation with chemicals that are toxic products harmful to the environment, or thermally by a process consisting in a chemical bridging between the macromolecular chains of the constituents of these ligneous materials. This chemical bridging is obtained thermally in a controlled atmosphere and at a minimum temperature of 230 C. This second solution is clearly preferable because chemical treatments can have adverse consequences on the environment and health. However, to ensure the reliability of the results obtained by the heat treatment, the homogeneity and the reproducibility of the treatment are of course essential.

  To obtain such results in industrial application, it is important and indispensable to have appropriate industrial technical means to achieve a good homogeneity of treatment of the wood material to be treated.

  There are different processes and equipment arranged for this type of high temperature treatment. One of these methods described by the French patent FR-2 604 942 requires expensive equipment because of the creation of an indispensable neutral atmosphere, that is to say the filling of the volume of the treatment chamber to using a neutral gas such as nitrogen, and heating equipment using an outdoor heat exchanger.

  The high temperature heat treatment of woody material requires the use of devices to bring the ligneous material to high temperature without igniting. This can only be done by reducing the oxygen content of the volume of air contained in the treatment chamber. Such devices are described in French patents FR 2 591 611 and FR-2 609 927 which propose furnaces provided with one or more burners which, by heating the volume of air contained in the heating chamber, reduce the content. in oxygen of this volume of air.

  These known devices have successfully obtained, in the laboratory, good results as to the homogeneity and quality of the treatment in small wood pieces packaged in small volumes. However, during the transition to the industrial phase, these devices do not provide acceptable reproducibility or good homogeneity of treatment and there are differences in quality between similar woody materials.

  To overcome these disadvantages, French patent FR-2,790,698 proposes a high temperature treatment device comprising a treatment chamber provided with burners for heating the volume of air in the treatment chamber and reducing the oxygen content thereof. This device also comprises means for regulating the temperature and humidity in the treatment chamber to humidify the treatment chamber during its rise in temperature, stabilize its temperature during the treatment of the load of ligneous material and allow its successive step cooling after treatment. The use of this device is nevertheless very risky because the direct heating in the treatment chamber causes the rise in temperature of the gases from the heating of the ligneous material. These gases can then reach stoichiometric conditions generating significant risks of explosion. These risks are accentuated by the presence of the burners directly in the treatment chamber and therefore in direct contact with the gases resulting from the heating of the ligneous material. In addition, the gases being discharged without specific precautions to the outside of the treatment chamber, this device has a negative impact on the environment. Finally, the direct heating in the treatment chamber does not allow to quickly obtain a good homogeneity of the temperature throughout this treatment chamber.

  Existing devices and processes are therefore not satisfactory.

  The present invention aims to overcome the disadvantages encountered in the operation of currently proposed devices by providing a method and a high temperature wood material treatment device, reliable, effective, simple, ecological, limiting the risk of explosion and allowing to obtain a homogeneous qualitative treatment of the ligneous material.

  This object is achieved by the method according to the invention as defined in the preamble and characterized in that the following successive steps are carried out: a) the heat transfer fluid is heated in at least one heating chamber; heat transfer fluid heated in at least one injection chamber, c) the coolant is injected into the treatment chamber through at least one inlet for treating the ligneous material, d) is recovered by at least one outlet orifice. at least part of the mixture containing the coolant and the gases from the heating of the ligneous material, e) extracting at least a portion of the resins and the water vapor contained in the gases, and f) transfer the coolant into the heating chamber, and g) steps a) to f) are repeated for a predetermined period.

  The heating chamber is preferably distinct and remote from the treatment chamber by a distance of between 1 meter and 10 meters and preferably greater than 1.5 meters.

  The temperature and the hygrometry rate of the coolant contained in the treatment chamber are advantageously regulated and its temperature is notably varied according to the following six successive phases: Phase n 1 of rise in temperature starting from the ambient temperature TO for to reach a temperature T 1 of about 140 C in a time t 1 of about 8 hours, Phase n 2 of raising the temperature starting from a temperature Ti of about 140 C to reach a temperature T2 of about 160 C in a time t2 of about 4 hours, Phase n 3 of raising the temperature starting from a temperature T2. about 160 ° C. to reach a temperature T3 of about 180 ° C. in a time t3 of about 2 hours. Step 4 of raising the temperature starting from a temperature T 3 of about 180 ° C. to reach a temperature T4 of about 200 C in a time t4 of about 1 hour, Phase 5 of stabilization of the temperature T4 at a temperature of about 200 C for a time t5 of about 3 hours, Phase n 6 cooling of the temperature up to room temperature TO in a time t6 of about 2 hours.

  Preferably, during step f), the resins contained in the gases are at least partially burned and the steam is evacuated.

  During the cooling phase n 6, cold water and / or a neutral gas are advantageously injected into the treatment chamber so as to compensate for the reduction in the volume of heat transfer fluid and maintain a predetermined pressure.

  This object is also achieved by the device according to the invention as defined in the preamble and characterized in that it comprises at least: separate heating means and remote from the heat transfer fluid treatment chamber, injection means of the heat transfer fluid in the treatment chamber through an inlet port provided in the treatment chamber.

  means for continuously circulating the coolant in the treatment chamber between the inlet orifice and an outlet orifice and, outside the treatment chamber between the outlet orifice and the orifice inlet, the circulation means being arranged to allow recovery at the outlet orifice of at least a portion of the mixture containing the coolant and the gases from the heating of the ligneous material, - extraction means at least a part of the resins and the water vapor contained in the gases.

  The injection means advantageously comprise at least one injection chamber of the heat transfer fluid heated in the treatment chamber, the injection chamber being connected to the inlet port.

  The circulation means preferably comprise at least a first duct connecting the treatment chamber to the heating chamber, a second duct connecting the heating chamber to the injection chamber and at least one fan arranged in the heating chamber or in the injection chamber.

  The extraction means may comprise at least one condenser provided on the first conduit between the treatment chamber and the heating chamber and connected to a combustion chamber comprising at least one burner and an exhaust stack.

  The heating means preferably comprise at least one heating chamber provided with at least one burner and the distance of separation between the treatment chamber and the heating chamber is advantageously between 1 meter and 10 meters and preferably greater at 1.5 meters.

  The device may comprise means for regulating the temperature and the degree of hygrometry of the coolant in the treatment chamber, the control means comprising at least one of the equipment selected from the group comprising programmable electronic management means. , a water spray ramp, a flap for reversing the direction of circulation of the coolant.

  According to a preferred embodiment, the heating means are arranged to vary the temperature of the heat transfer fluid in the treatment chamber according to the following six successive phases: Phase n 1 of rise in temperature from the ambient temperature TO to reach a temperature Ti of about 140 ° C. in a time of about 8 hours; phase No. 2 of raising the temperature starting from a temperature T 1 of about 140 ° C. to reach a temperature T2 of about 160 ° C. C in a time t2 of about 4 hours, - Phase n 3 of raising the temperature starting from a temperature T2 of about 160 C to reach a temperature T3 of about 180 C in a time t3 of about 2 hours. Phase n 4 of raising the temperature starting from a temperature T3 of approximately 180 ° C. to reach a temperature T4 of approximately 200 ° C. in a time t4 of approximately 1 hour. Phase n. stabilization of the temperature T4 at a temperature of about 2 00 C for a time t5 of about 3 hours, Phase n 6 cooling the temperature to room temperature TO in a time t6 of about 2 hours.

  Advantageously, the device comprises means for introducing a neutral gas into the treatment chamber, sealing means arranged to ensure gastightness and thermal sealing of the treatment chamber, means for adjusting the pressure in the treatment chamber, said adjustment means being arranged to maintain it at an overpressure at a predetermined value, and a remote control unit arranged to control at least one of the parameters chosen in the group comprising the hygrometry rate, the temperature, the pressure, the heating rate, the circulation velocity of the heat transfer fluid.

  The present invention and its advantages will appear better in the following description of an exemplary embodiment given by way of non-limiting example, in which: FIG. 1 represents a schematic sectional view of the device according to the invention, and the FIG. 2 represents the curve of the temperature at which the ligneous material is subjected during the process according to the invention.

  With reference to FIG. 1, the device 1 for high-temperature heat treatment of ligneous material 100, for example wood, comprises according to the invention: a treatment chamber 2 filled with a coolant, injection means 3 heat transfer fluid in the treatment chamber 2 through inlet openings 2a provided in the upper part of the treatment chamber 2, circulation means 4 continuously heat transfer fluid inside the treatment chamber 2 between the inlet orifices 2a and the outlet orifices 2b also provided in the upper part of the treatment enclosure 2 and, outside the treatment enclosure 2, between the outlet orifices 2b through which one recovers the coolant mixed with the gases from the heating of the ligneous material and the inlet orifices 2a, means 5 for extracting at least part of the resins and the water vapor contained in the gases, means for heating 6 d u coolant remaining after extraction of resins and water vapor, and control means (not shown) of the temperature and the hygrometric degree of the coolant in the treatment chamber 2.

  The treatment chamber 2 is in the general form of a parallelepiped with a rectangular base comprising four substantially vertical walls connected by one. bottom and a ceiling. The walls, the bottom and the ceiling consist of a sandwich formed of two metal plates between which is placed a thermally insulating material. In order to avoid corrosion, the inner faces of the treatment chamber 2 are preferably made of stainless steel sheets. The front wall of the treatment chamber 2 is provided with a door (not shown) for loading and unloading the ligneous material 100 into the treatment chamber 2.

  The treatment chamber 2 comprises sealing means (not shown) ensuring its gastightness and its thermal seal. This is for example seals including provided around the door and at the inlet ports 2a, outlet ports 2b and connections. The treatment chamber 2 may be provided with several watering ramps (not shown) intended to be activated in the event of accidental ignition of the ligneous material 100 or involuntary overheating. When the irrigation ramps are used, discharge holes (not shown), provided at the bottom of the treatment chamber 2, allow the flow of recovered liquids in recovery bins (not shown). These recovery tanks are also intended to receive runoff water due to the condensation occurring during the treatment of the ligneous material 100.

  The circulation means 4 comprise in particular a first duct 40 connecting the treatment chamber 2 to the heating means 6 via the extraction means 5. This first duct 40 is connected to a collector 41 provided for example in the upper part. of the treatment chamber 2. This manifold 41 has outlet orifices 2b for the outgoing heat transfer fluid mixed with the gases resulting from the heating of the ligneous material 100.

  The extraction means 5 comprise in particular a condenser 50 of conventional type intended to separate the gases from the coolant. Once separated, the gases are conveyed via an additional duct 51 to a combustion chamber 52 comprising at least one burner 53 intended to burn the resins contained in the gases and an evacuation chimney 54 intended for the evacuation of the steam. 'water. These extraction means 5 thus allow the device 1 not to pollute the environment. The coolant is, after extraction of the gases, conveyed by the first conduit 40 to the heating means 6.

  In the illustrated example, the heating means 6 comprise a heating chamber 60 provided with at least one burner 61. It is understood that the heating means 6 may comprise several heating chambers 60, each being equipped with a or several burners 61. The burners 61 are preferably gas and adjustable power to effectively heat the coolant and reduce its oxygen content. Each burner 61 is preferably disposed at the bottom of the heating chamber 60 so that its flame extends vertically between the bottom and the ceiling of the heating chamber 60. This heating chamber 60 may be provided with inlet valves and output (not shown) allowing, if necessary, to regulate the flow of heat transfer fluid in the heating chamber 60 allowing for example the exit of a portion of this fluid by a chimney 62 in case of overpressure in the chamber heating 60.

  To avoid any risk of explosion, the heating chamber 60 is separate from the treatment chamber 2 and preferably a distance of between 1 meter and 10 meters and preferably greater than 1.5 meters. Thus, the flame of the burner 61 is not in direct contact with the gases resulting from the heating of the ligneous material 100, these gases being previously extracted and treated by the extraction means 5.

  The circulation means 4 include in particular a fan 41 provided in the heating chamber 60 for circulating the heat transfer fluid to a second conduit 42 connecting the heating chamber 60 to the injection means 3.

  The injection means 3 comprise at least one injection chamber and in the example shown two injection chambers 30, 31 disposed above the treatment chamber 2. The second conduit 42 forms a Y, each branch of which is connected an injection chamber 30, 31 each comprising a fan 43, 44.

  The control means (not shown) comprise for example programmable electronic management means and / or water spray ramps and / or inversion flaps of the coolant circulation direction. The water spray ramp is for example disposed horizontally in the upper part of the treatment chamber 2. This water spray bar is provided with a sufficient number of nozzles for spraying a fog with a high flow rate. It is supplied with cold water, or possibly refrigerated, by known means not shown. It is intended to humidify the heat transfer fluid contained in the treatment chamber 2 during the rise in temperature, to stabilize the temperature during the treatment of the ligneous material 100 and to allow its gradual cooling after the treatment.

  The device 1 comprises adjustment means (not shown) of the pressure in the treatment chamber 2 to maintain a predetermined overpressure. The device 1 also comprises a remote control unit (not shown) controlling the degree of hygrometry, the temperature and the pressure of the coolant as well as the heating rate and the circulation velocity of the coolant.

  The operating principle of this device 1 is based on a continuous circulation of the heat transfer fluid formed by the air freed of its oxygen and mixed. flue gases to provide a neutral atmosphere. It allows the implementation of the high temperature heat treatment process of ligneous material 100 as described below.

  To implement this method, a piece of ligneous material 100 or a batch of pieces is placed in the form of board, beam, etc. in the treatment chamber 2 and the following successive steps are carried out: a) the heat transfer fluid is heated in said heating chamber; b) the heated heat transfer fluid is transferred to the injection chambers 30, 31, c) by means of fans 43, 44, the coolant is injected into the treatment chamber 2 which is filled by the inlet ports 2a. The heat transfer fluid is circulated continuously between the inlet orifices 2a and the outlet orifices 2b in order to treat the ligneous material 100, d) after the passage of the heat transfer fluid in the treatment chamber 2, it is recovered through the orifices. 2b at least a portion of the mixture containing the coolant and the gases from the heating of the wood material 100, e) by means of the condenser 50, is extracted at least a portion of the resins and the water vapor contained in said gases are burned in the combustion chamber 52 a portion of the resins by means of the burner 53 and the water vapor is discharged through the chimney 54, f) transfer the coolant remaining in the heating chamber 60 where it is Heated, and g) steps a) to f) are repeated for a predetermined period.

  In order to treat the ligneous material 100, the temperature of the coolant contained in the treatment chamber 2 is varied according to the following successive phases (see FIG. 2): Phase n 1 of rise in temperature starting from the ambient temperature TO to reach a temperature T 1 of about 140 C in a time t 1 of about 8 hours, Phase n 2 of raising the temperature starting from a temperature T i of about 140 C to reach a temperature T2 about 160 C in a time t2 of about 4 hours, Phase n 3 of raising the temperature starting from a temperature T2 of about 160 C to reach a temperature T3 of about 180 C in a time t3 approximately 2 hours, Phase n 4 of temperature rise starting from a temperature T3 of about 180 C to reach a temperature T4 of about 200 C in a time t4 of about 1 hour, Phase n 5 stabilizing temperature T4 at a temperature of about 5 200 C for a time t About 3 hours, Step 6 cooling the temperature to room temperature TO in a time t6 of about 2 hours.

  The treatment cycle requires several passes of the coolant through the treatment chamber 2. This circulation of the coolant is obtained in particular by the fans 41, 43, 44 provided in the heating chambers 60 and injection 30, 31, and which aspire or propel the coolant.

  The cooling phase n 6 is obtained using a high-pressure cold water spray in the treatment chamber 2 by means of the spray boom (not shown) or the aforementioned irrigation booms. This spraying may also be used to prevent thermal shocks on the ligneous material 100 to be treated during an abnormal rise in the temperature in the treatment chamber 2. During the cooling phase n 6, the pressure of the order of 4mmCE is maintained in the treatment chamber 2 by the injection of a neutral gas via the conduit 7 to compensate for the reduction in the volume of heat transfer fluid.

  The regulation of the temperature and the degree of hygrometry prevailing in the treatment chamber 2 during the treatment is obtained by probes of temperature and hygrometry (not shown) known per se and arranged in the treatment chamber 2 Another probe also housed in the treatment chamber 2 allows a permanent control of the oxygen content of the heat transfer fluid. The method can be controlled by programmable electronic means not shown.

  The treated wood material 100 obtained according to the process of the invention has very good mechanical characteristics and a very good resistance to moisture.

  The description clearly shows that the goals sought are attained, and in particular that the device and the method according to the invention allow the high temperature treatment of all types of woody material in complete safety.

  The present invention is not limited to the embodiment described but extends to any modification and variation obvious to a person skilled in the art while remaining within the scope of the protection defined in the appended claims. In particular, it is possible to change the number and position of burners and fans.

Claims (21)

claims   1. A method of high temperature heat treatment of ligneous material (100) during which said ligneous material (100) is placed in at least one treatment chamber (2) filled with a heat transfer fluid which is circulated continuously. in said treatment chamber (2), characterized in that the following successive steps are carried out: h) said heat transfer fluid is heated in at least one heating chamber (60), i) said heated heat transfer fluid is transferred into the at least one injection chamber (30, 31), j) injecting said heat transfer fluid into said treatment chamber (2) by at least one inlet orifice (2a) for treating said ligneous material (100), k) recovering from at least one outlet orifice (2b) of said treatment chamber (2) at least a part of the mixture containing said heat transfer fluid and the gases resulting from the heating of said ligneous material (100), 1) at least one part of the resins and the water vapor contained in said gases, and m) transfer said heat transfer fluid into said heating chamber (60), and n) steps a) to f) are repeated for a predetermined period.   2. Method according to claim 1, characterized in that one uses a heating chamber (60) separate and remote from said treatment chamber (2).   3. Method according to claim 2, characterized in that said distance distance is between 1 meter and 10 meters and preferably greater than 1.5 meters.   4. Method according to claim 1, characterized in that one regulates the temperature and the hygrometry rate of said heat transfer fluid contained in said treatment chamber (2).   5. Method according to claim 1, characterized in that the temperature of said heat transfer fluid contained in said treatment chamber (2) is varied according to the following six successive phases: Phase n 1 of rise in temperature starting from the temperature ambient TO to reach a temperature Tl of about 140 C in a time t1 of about 8 10 hours, Phase n 2 of raising the temperature starting from a temperature T 1 of about 140 C to reach a temperature T2 about 160 C in a time t2 of about 4 hours, Phase n 3 of raising the temperature starting from a temperature T2 of about 160 C to reach a temperature T3 of about 180 C in a time t3 about 2 hours, - Phase n 4 of temperature rise from a temperature T3 of about 180 C to reach a temperature T4 of about 200 C in a time t4 of about 1 hour, Phase No. 5 stabilizing temperature T4 at a temperature of about 20 0 C for a time t5 of about 3 hours, Phase n 6 cooling the temperature to room temperature TO in a time t6 of about 2 hours.   6. Method according to claim 1, characterized in that during said step f), at least partially burns said resins contained in said gas and said water vapor is removed.   7. The method of claim 5, characterized in that at least during said cooling phase n 6 is injected into said treatment chamber (2) of cold water.   8. Method according to claim 5, characterized in that at least during said cooling phase n 6, is injected into said treatment chamber (2) a neutral gas to compensate for the reduction of the volume of heat transfer fluid and maintain a predetermined pressure.   9. Device (1) for high temperature heat treatment of ligneous material (100), said device (1) comprising at least one treatment chamber (2) filled with a heat transfer fluid circulating continuously in said treatment chamber (2). ), characterized in that it comprises at least: heating means (6) separate and remote from said treatment chamber (2) of said coolant, injection means (3) of said coolant in said treatment chamber (2) by an inlet port (2a) provided in said treatment chamber (2).   - means for continuously circulating (4) said heat transfer fluid in said treatment chamber (2) between said inlet orifice (2a) and an outlet orifice (2b) and, outside said treatment chamber ( 2) between said outlet port (2b) and said inlet port (2a), said circulation means (4) being arranged to allow recovery at said outlet port (2b) of at least a portion of the mixture containing said heat transfer fluid and the gases resulting from the heating of said ligneous material (100), - means for extracting (5) at least part of the resins and the water vapor contained in said gases.   10. Device (1) according to claim 9, characterized in that said injection means (3) comprise at least one injection chamber (31, 32) of said heat transfer fluid heated in said treatment chamber (2). said injection chamber (31, 32) being connected to said inlet port (2a).   11. Device (1) according to claim 9, characterized in that said circulation means (4) comprise at least a first conduit (40) connecting said treatment chamber (2) to said heating chamber (60), a second conduit (42) connecting said heating chamber (60) to said injection chamber (30, 31) and at least one fan (41, 43, 44) disposed in said heating chamber (60) or said chamber injection (30, 31).   12. Device (1) according to claim 9, characterized in that said extraction means (5) comprise at least one condenser (50) provided on said first conduit (40) between said treatment chamber (2) and said chamber heating (60).   13. Device (1) according to claim 12, characterized in that said condenser (50) is connected to a combustion chamber (52) having at least one burner (53) 20 and an exhaust stack (54).   14. Device (1) according to claim 9, characterized in that said heating means (6) comprise at least one heating chamber (60) provided with at least one burner (61).   15. Device (1) according to claim 9, characterized in that said distance distance between said treatment chamber (2) and said heating chamber (60) is between 1 meter and 10 meters and preferably greater than 1 , 5 meters.   16. Device (1) according to claim 9, characterized in that it comprises means for regulating the temperature and the degree of hygrometry of said heat transfer fluid in said treatment chamber (2), said regulating means comprising at least one of the equipment chosen from the group comprising programmable electronic management means, a water spray bar, a shutter for reversing the flow direction of said heat transfer fluid.   17. Device (1) according to claim 9, characterized in that said heating means (6) are arranged to vary the temperature of said heat transfer fluid in said treatment chamber (2) according to the following six successive phases: Phase n 1 temperature rise from the ambient temperature TO to reach a temperature Ti of about 140 C in a time t1 of about 8 hours, Phase n 2 of raising the temperature starting from a temperature T 1 15 d approximately 140 ° C. to reach a temperature T2 of approximately 160 ° C. in a time t2 of approximately 4 hours. Phase n ° 3 of temperature rise starting from a temperature T2 of approximately 160 ° C. to reach a temperature T3 about 180 ° C. in a time t3 of about 2 hours, step 4 of raising the temperature starting from a temperature T3 of about 180 ° C. to reach a temperature T4 of about 200 ° C. in a time t4 about 1 hour, Phase 5 stabilization of the temper ature T4 at a temperature of about 200 C for a time t5 of about 3 hours, - Phase n 6 of cooling the temperature to room temperature TO in a time t6 of about 2 hours.   18. Device (1) according to claim 8, characterized in that it comprises means for introducing (7) a neutral gas into said treatment chamber (2).   19. Device (1) according to claim 8, characterized in that it comprises sealing means arranged to seal the gas and thermal sealing of said treatment chamber (2).   20. Device (1) according to claim 8, characterized in that it comprises means for adjusting the pressure in said treatment chamber (2), said adjusting means being arranged to keep it overpressure at a predetermined value .   21. Device (1) according to claim 8, characterized in that it comprises a remote control unit arranged to control at least one of said parameters selected from the group comprising the hygrometry rate, the temperature, the pressure , the heating rate, the circulation velocity of said heat transfer fluid.