EP2668457B1 - Method and device for the heat treatment of wood using dust-free dehydrated gases - Google Patents

Description

The invention relates to a method of heat treatment of wood, the principle of which is based on the generation of hot gases from the combustion of biomass, said gases feeding an oven. Heat treatment of wood can improve its biological resistance to insects and xylophagous fungi, or increase its dimensional stability through a modification of the material and without the introduction of chemical.

Processes on the market, which allow the heat treatment of wood, use electricity or gas. In this second case, the systems involved in these processes, are grouped under the name of "hot air generators", and operate on the principle of forced air. Fans allow the introduction of air for combustion into the fireplace, the flow rates can be modulated through the addition of a dimmer. The flue gases from the furnace are sucked by means of a smoke extractor at the outlet of chimneys, and pass outside of a heat exchanger of variable geometry, which may for example be tubular or square. They then transmit their heat to fresh air pulsed by another fan in the exchanger. The product resulting from these hot air generators, is therefore an air with 20% oxygen, and whose temperature does not generally exceed 150 ° C because of the shape of the exchanger.

Thermal treatment processes based on gases resulting from the combustion of biomass, as they are for example described in the patent application WO2007147961 , and FR2907884 involve gases with 10% oxygen, and whose temperature is above 300 ° C, low oxygen is particularly sought to reduce the risk of fire. The processes currently used on the market therefore do not meet these two specifications.

However, the use of biomass creates additional constraints related to the production of fumes, heavily loaded with water and dust, and must therefore be treated, otherwise it will cause significant pollution of the environment, otherwise the quality of the thermal treatment of wood could be affected.

The methods of heat treatment of the wood according to the invention, and using the biomass for the generation of hot gases, include not only a specific step of dehydration and flue cleaning, specially designed to allow the cleaning of fumes, to achieve the heat treatment of the wood with clean and non-polluting gases, but also additional means for trapping the residual pollutant particles remaining in said fumes. In this way, the wood heat treatment processes according to the invention, implement two cleaning steps to increase the quality of gas cleanliness.

The subject of the invention is a method for heat treatment of wood, comprising in order a step of producing hot gases and fumes by means of a gas generator using biomass, a fume treatment stage consisting of dehydrate and dust off the fumes by the implementation of specific means. a step of conveying the gases to an oven, a step of heating the wood in the oven by means of said gases, and a step of extracting the vapors, said step of treating the fumes being effected by means of a device comprising a gas cooling chamber for dehydrating said gases, said cooling chamber being extended by a first condensate collection chamber resulting from the dehydration of the fumes, said collection chamber being located below the cooling chamber, characterized in that the first collection chamber is surmounted by at least one outlet tube, the diameter of which is sized to slow down the gases, and to allow the sedimentation of the dust. In other words, the method of heat treatment of the wood according to the invention, based on the generation of hot gases by means of a biomass boiler, devotes a full and complete step to the cleaning and dehydration of the harmful fumes resulting from the heat treatment. wood. Indeed, the use of biomass to generate gases, leads almost systematically, the emission of fumes heavily loaded with water and in dust, which has the effect of polluting the atmosphere and increasing the risks of adversely affecting the quality of the heat treatment of the wood. However, usually, the treatment of these vapors could be carried out indirectly and partially, by playing, for example, on certain parameters of the wood treatment process, at the risk of affecting the quality of this treatment. By instituting a specific step of dehydration and dedusting of fumes with means specially designed to fulfill these two functions, the designers of the wood heat treatment process according to the invention, attach great importance to the realization of heat treatment of wood at truly clean gas means, for an optimized and reliable result, without negative effects on the environment in terms of pollution. The method according to the invention is carried out continuously, in an isolated installation, without loss of gas, between the gas generator and the extraction of vapors, and operates at a low pressure. This process also relies on a final stage of extraction of the vapors, by means for example of pumps, which will influence the geometry, dimensioning and the functional characteristics of the device, developed to ensure this phase of dusting and dehydration of the fumes . By the presence of outlet tubes, the solid particles, which are deposited on the inner wall of each of said outlet tubes, tend to migrate by inertia to the first collection chamber located below. This first collection chamber serves both as a receptacle for condensates from the cooling chamber, and for solid particles that have deposited in each outlet tube. Preferably, the gases in each outlet tube are significantly slowed down. The condensates, which are deposited on the walls of the cooling chamber, and which migrate inertia to the first collection chamber, will also serve to trap the solid particles and dust fumes, retaining them in their passage. The collection chamber thus has a gas inlet from the cooling chamber and a gas outlet via each of the outlet tubes.
advantageously, the step of producing the gases by means of the gas generator is separated from the flue gas treatment step by a cooling step, making it possible to change the temperature of the gases from 900 ° C. to a temperature of less than 200 ° C. ° C. Indeed, dehydration and dust removal operations, are better controlled, and therefore easier to perform on cooled gases, rather than gas raised to very high temperatures, close to 1000 ° C. Preferentially, the gases are cooled to a temperature of between 120 ° C. and 200 ° C. If this cooling step is included in the method of heat treatment of the wood according to the invention, a step of reheating of the cooled gases will have to be added in said process, in order to carry out the step of heat treatment of the wood in the oven with sufficiently hot gases.

Preferably, the fumes treatment step is performed by means of a device comprising a gas cooling chamber, for dehydrating said gases. Indeed, since the wood heat treatment process is based on the aspiration of the fumes, one of the constraints to be respected for said method is to keep a low pressure at any point and at any time, in the installation provided for unfold this wood treatment process. An increase in the pressure drop at the passage of the flue gas treatment elements, results in a loss of suction flow and thus power of the boiler. In the same way, a functioning in depression and high overpressure of the system, also means an increase of the electrical consumption which penalizes the energy balance of the treatment. For all these reasons, the dehydration of the fumes is therefore achieved by a cooling of the fumes. Advantageously, the fumes are cooled to 30 ° C in this cooling chamber or dehydration.

Advantageously, the cooling chamber is extended by a first condensate collection chamber resulting from the dehydration of the fumes, said collection chamber being located below the cooling chamber. Indeed, the condensates that have been deposited on the walls of the cooling chamber, will tend to flow by inertia, along these walls, to go to the first collection chamber. It is important to be able to concentrate these condensates in a very specific and unique place, not risking to foul the device of dehydration and dedusting.

Preferably, the first collection chamber is equipped with first condensate discharge means. Indeed, once the condensates have accumulated in the first collection chamber, and to limit the risk of total or partial closure of the gas circulation circuit, it is desirable to be able to empty this first collection chamber, at easy and fast handling, not requiring the interruption of the wood heat treatment process. These first evacuation means can be activated manually, or trigger automatically once a threshold filling rate reached in the collection chamber. These first evacuation means could also be triggered automatically by preprogrammed time cycle.

Preferably, each outlet tube is provided with at least one electrostatic filter for fixing the dust. These filters are arranged transversely in each tube, and are intended to retain any solid particles or dust transported by the gas passing through said tubes. Said particles or dust agglutinate against the underside of each filter, and tend to fall into the first collection chamber. These filters allow the fixing of dust on each outlet tube, for a loss of almost zero load.

Advantageously, the first collection chamber is equipped with second means for discharging the solid particles. Indeed, for the same reasons as those invoked for condensates, it is desirable to be able to rid the first collection chamber, solid particles or dust that have accumulated in it, without having to interrupt the treatment method according to the invention. These second evacuation means can be activated manually, or trigger automatically once a threshold filling rate reached in the collection chamber. They could also be triggered automatically by preprogrammed time cycle. Preferably, each outlet tube of the first collection chamber, opens into a second collection chamber located above the first collection chamber, and provided with an outlet pipe connected to a gas suction system. These suction means make it possible to ensure the continuous circulation of the gases in the treatment device.

Advantageously, each outlet tube (20,21) has a diameter greater than or equal to 200 mm.

Preferably, each outlet tube (20,21) is dimensioned to reduce the speed of the gas to a value less than or equal to 3m / s.

The invention also relates to a device for carrying out the fumes treatment step of a method according to the invention. The main characteristic of a device according to the invention is that it comprises a cooling chamber having an orifice for the arrival of the gases from the gas generator, said cooling chamber opening into a first collection chamber, equipped with first means for discharging the condensates and second means for discharging the solid particles, said first chamber being extended by two outlet tubes opening into a second collection chamber provided with an outlet pipe connected to a suction system; diameter of said tubes being dimensioned to reduce the speed of the gases.

Advantageously, the cooling chamber is vertical, and the two collection chambers are horizontal, the second chamber being located above the first chamber, and the two outlet tubes connecting said collection chambers, are vertical and are each provided with an electrostatic dust filter.

Preferably, the device constitutes an insulated gas circuit, having a hot gas inlet orifice, and a treated gas outlet orifice. In this way it can be inserted easily, in a hot gas duct, for supplying a wood heat treatment furnace.

The treatment processes according to the invention have the advantage of implementing a step of dehydration and dedusting fumes by means of a compact device, compact and efficient. In addition, the device is designed to perform these two operations almost simultaneously, allowing time savings in the treatment method according to the invention. Finally, the treatment device has the advantage of being equipped with condensate removal systems and / or solid particles recovered from the fumes, avoiding total or partial fouling, which can lead to an interruption of the treatment process according to the invention. invention.

• La figure 1 est une vue schématisée des différents blocs matérialisant les différentes étapes d'un procédé de traitement selon l'invention,
• La figure 2, est une vue en perspective d'un dispositif de traitement des fumées selon l'invention.

The following is a detailed description of a preferred embodiment of a method for heat treatment of wood according to the invention, as well as a smoke treatment device according to the invention, with reference to the Figures 1 to 2 .

• The figure 1 is a schematic view of the different blocks embodying the different steps of a treatment method according to the invention,
• The figure 2 , is a perspective view of a smoke treatment device according to the invention.

Referring to the figure 1 , A method of heat treatment of wood according to the invention comprises various steps carried out continuously, the first step 1 of producing hot gases, whose temperature is close to 900 ° C, by the use of biomass. In this configuration, the emission of hot gases is accompanied by fumes also brought to temperatures close to 900 ° C, and which are charged with water vapor and dust, the diffusion of said vapors in the atmosphere being not wanted for pollution reasons. The second step 2 of a process according to the invention is to cool the gases emitted by means of a cooling exchanger to bring them to temperatures below 200 ° C, and more specifically at temperatures between 120 ° C and 200 ° C. These cooled gases, however, remain at temperatures well above ambient temperature, are then conveyed to a treatment device 10, to undergo a third step 3 dehydration and dedusting, so as to make them clean vis-à-vis the atmosphere. These two operations of dedusting and dehydration are almost simultaneous, and are carried out by the same processing device 10. Once the gases have been treated, they are only at 40 ° C at the output of said device 10, and must therefore be subjected to a fourth heating step 4 to be heated to temperatures of the order of 600 ° C to ensure the heat treatment of wood. These very hot and clean gases are then fed to an oven to provide the fifth stage of heat treatment of the wood itself. The last step 6 consists in recovering the gas vapors resulting from combustion in the furnace by means of a pump system.

Referring to the figure 2 , a gas treatment device 10 according to the invention comprises a base 11 multi-tubular feet, surmounted by a holding structure 12 also tubular. The device 10 comprises an inlet port 13 for receiving the gases from a gas generator using the biomass, and having already undergone a cooling phase by means of a cooling exchanger. In this way, the gases and fumes emitted at temperatures in the region of 900 ° C. are cooled to temperatures between 120 ° C. and 200 ° C. before entering the treatment device 10, said device 10 remaining fully effective for gas whose temperature is below 200 ° C. The inlet port is located at the top of the device 10, and is formed at the upper end 14 of a cylindrical cooling chamber 15, the axis of revolution is oriented vertically. This chamber 15 is constituted by a heat exchanger for cooling the fumes, allowing their temperature to be raised from 200 ° C. to 30 ° C. This cooling phase leading to the dehydration of fumes. Advantageously, the diameter of this cooling chamber 15 is substantially equal to 25 mm. The lower end 16 of this cooling chamber 15 opens into a first cylindrical collection chamber 17 whose axis of revolution is oriented horizontally. The junction between the cooling chamber 15 and the first collection chamber 17 is effected at the central portion of the wall 18 of said first collection chamber 17. This first collection chamber 17, which is placed under the chamber cooling 15 and which preferably has a diameter of the order of 700 mm, is intended in particular to recover the condensates deposited on the wall 19 of the cooling chamber 15, and which tend to flow by inertia, along said wall 19 to said first chamber 17. This first collection chamber 17 is surmounted by two cylindrical outlet tubes 20,21, originating at the wall 18 of this chamber 17 and ending in the wall 22 of a second collection chamber 23, whose axis of revolution is horizontal, and which is placed above the first collection chamber 17. This second collection chamber 23 has, preferably, a diameter of the order of 700 mm and is parallel to the first collection chamber 17. The two tubes 20,21 connecting the two collection chambers 17,23, are found in a vertical position and each have a diameter of the order of 300mm. They are therefore parallel to the vertical cylindrical cooling chamber, and are placed on either side of said chamber 15. They are thus implanted in the wall 18 of the first collection chamber 17, framing the cooling chamber 15. These two tubes 20,21, which are sized to slow down the gases at a speed of the order of 3m / s, each have, at their lower end 24,25, a horizontal electrostatic filter 26,27, crossing each of said 20,21 tubes, and for the purpose of trapping the dust or solid particles of the gases located in the first collection chamber 17, and which have a tendency to go up through the two tubes 20,21 to move towards the second collection chamber 23 superior. The first lower collection chamber 17, besides recovering the condensates from the vertical cooling chamber, also collects the dusts. which have agglutinated at the bottom wall of each electrostatic filter 26,27 placed in each of the tubes 20,21. These two tubes 20,21 thus serve as a place of sedimentation of dust. The first collection chamber 17 is equipped with first condensate discharge means, in the form of a drawer system 28, placed under said first chamber 17, the operation of which has no influence on the pressure prevailing in the device. 10 of treatment. This first collection chamber is also provided with second means of evacuation of dust, in the form of a screw 29 without end, driven by a motor, said screw 29 being also placed under said first chamber 17. The second collection chamber 23 has a horizontal outlet pipe, for routing the clean gas from the processing device 10 to a suction system, said outlet pipe 30 having a diameter of 100mm. At the input of device 10, the gases have a temperature of between 120 ° C. and 200 ° C., and at the output of device 10, their temperature is only 40 ° C. The treatment device 10 constitutes an insulated gas circuit, provided with an inlet 13 and an outlet 30, and makes it possible both to dehydrate the gases by cooling, and to clean them, by ridding them of their dust.

The operating mode of this processing device 10 is as follows. The hot gases from the gas generator using the biomass are emitted at about 900 ° C. and are then cooled to a temperature of between 120 ° C. and 200 ° C. by means of a cooling exchanger placed upstream of the cooling device. treatment 10. The concept of "upstream" is to be considered in relation to the direction of propagation of gases. The gases which are cooled, but still remain warm with respect to the ambient temperature, enter the treatment device 10 through the inlet orifice 13. They first pass through the cooling chamber 15, where they are cooled down to a temperature of 30.degree. temperature of the order of 30 ° C, and are therefore dehydrated, the condensate being deposited on the wall 19 of the chamber 15. The cooled gases then arrive in the first collection chamber 17. Under the effect of pressure, they go back to the second collection chamber 23, using the two tubes of output 20,21, whose large diameter will reduce their speed of progression to 3m / s. They then cross the electrostatic filters 26,27, which trap their dust. The clean gases, cooled to about 40 ° C, arrive in the second upper collection chamber 23, where they are then conveyed via the outlet pipe 30 to a suction system. The condensates deposited on the wall 19 of the cooling chamber 15, and the dust trapped by the two electrostatic filters 26,27, migrate to the first collection chamber 17, where they can be discharged with the appropriate means 28,29. .

Claims (9)

1. A method for the heat treatment of wood, comprising, in order:

   - a step for producing (1) hot gases and fumes using a gas generator using biomass,

   - a step for treating (3) fumes consisting of dehydrating and removing dust from the fumes by implementing specific means (10), said step being carried out using a device (10) comprising a cooling chamber (15) for the gases making it possible to dehydrate said gases, said cooling chamber (15) being extended by a first collection chamber (17) for condensates derived from the dehydration of the fumes, said collection chamber (17) being situated below the cooling chamber (15) and being topped by at least one outlet tube (20, 21), the diameter of which is dimensioned to slow the gases, and to allow the sedimentation of the dusts,

   - a step for conveying (40) gases toward a furnace,

   - a step for heating (5) wood in the furnace using said gases,

   - a step for extraction (6) of the vapors,

   characterized in that each outlet tube (20, 21) has a diameter larger than or equal to 200 mm so as to cause the speed of the gases to drop to a value below or equal to 3 m/s.
2. The method according to claim 1, characterized in that the step for producing (1) gases using the gas generator is separated from the step for treating (3) fumes, by a cooling step (2) making it possible to bring the temperature of the gases from 900°C to a temperature below 200°C.
3. The method according to claim 1, characterized in that the first collection chamber (17) is equipped with first means (28) for evacuating condensates.
4. The method according to claim 1, characterized in that each outlet tube (20, 21) is provided with at least one electrostatic filter (26, 27) intended to catch dust.
5. The method according to any one of claims 1 to 4, characterized in that the first collection chamber (17) is equipped with second means (29) for evacuating solid particles.
6. The method according to any one of claims 1 or 4, characterized in that each outlet tube (20, 21) of the first collection chamber (17) emerges in a second collection chamber (23) situated above the first collection chamber (17), and provided with an outlet tubing (30) connected to a gas suction system.
7. A device (10) for carrying out the step for treating fumes of a method according to any one of claims 1 to 6, comprising a cooling chamber (15) having an orifice (13) for the arrival of gases derived from the gas generator, said cooling chamber (15) emerging in a first collection chamber (17), equipped with first means (28) for discharging condensates and second means (29) for discharging solid particles, said first chamber (17) being extended by two outlet tubes (20, 21) emerging in a second collection chamber (23) provided with an outlet tubing (30) connected to a suction system, characterized in that each outlet tube (20, 21) has a diameter larger than or equal to 200 mm so as to cause the speed of the gases to drop to a value below or equal to 3 m/s.
8. The device according to claim 7, characterized in that the cooling chamber (15) is vertical, and the two collection chambers (17, 23) are horizontal, the second chamber (23) being situated above the first chamber (17), and in that the two outlet tubes (20, 21) connecting said collection chambers (17, 23) are vertical and are each provided with an electrostatic filter (26, 27) for dust retention.
9. The device according to any one of claims 7 or 8, characterized in that it constitutes an isolated gas circuit, having a hot gas inlet orifice (13), and a treated gas outlet orifice (30).

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