Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D7/00—Forming, maintaining or circulating atmospheres in heating chambers
  • F27D7/06—Forming or maintaining special atmospheres or vacuum within heating chambers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B21/00—Arrangements for supplying or controlling air or other gases for drying solid materials or objects
  • F26B21/30—Controlling, e.g. regulating, parameters of gas supply
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B21/00—Arrangements for supplying or controlling air or other gases for drying solid materials or objects
  • F26B21/40—Arrangements for supplying or controlling air or other gases for drying solid materials or objects using gases other than air
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B25/00—Details of general application not covered by group F26B21/00 or F26B23/00
  • F26B25/005—Treatment of dryer exhaust gases
  • F26B25/006—Separating volatiles, e.g. recovering solvents from dryer exhaust gases
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D7/00—Forming, maintaining or circulating atmospheres in heating chambers
  • F27D7/02—Supplying steam, vapour, gases or liquids
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B2210/00—Drying processes and machines for solid objects characterised by the specific requirements of the drying goods
  • F26B2210/16—Wood, e.g. lumber, timber

Definitions

• 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 a furnace designed to provide this treatment.
• 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.
• Wood heat treatment processes using a gas generator using biomass are generally confronted with two major risks, which are fire and environmental pollution, both of which are related to the production of toxic fumes. . Indeed, wood heated to a temperature above 180 ° C undergoes chemical modifications of its carbon chains. Cellulose, hemicelluloses and wood lignin undergo a gradual degradation producing molecules such as aldehydes, such as furfural or formaldehyde, methanol formic and acetic acids as well as combustible gases such as hydrogen, monoxide of carbon and methane. These gases are likely to self-ignite and thus cause a fire in wood heat treatment furnaces.
• the main drawbacks of these techniques are that they do not systematically allow the capture of products in small quantities and with high vapor pressures, that they can not, moreover, surely avoid the re-aspiration of the fluids in the form of vapors by the pumping system, and finally, that they do not provide a self-cleaning of the condensation system. In addition, they do not guarantee condensation of vapors without lowering the gas flow, and do not guarantee to make the liquid state permanent, including in a low vacuum system.
• the methods of heat treatment of wood according to the invention implement means for limiting the risk of fire, and means for recovering the vapors from the treatment, these means overcoming all the aforementioned drawbacks.
• said method includes an additional step of controlling this oxygen level, in particular to organize an intervention fast at the facility in the event that this control step would detect an abnormally high value of this rate.
• the subject of the invention is a method for heat treatment of wood, comprising a step of heating the wood in an oven placed in an enclosure, by means of hot gases supplied by a generator, a step of recovering the vapors resulting from the treatment and a step of injecting water into the oven so as to create water vapor.
• the main characteristic of a heat treatment process according to the invention is that it implements a step of controlling the oxygen level in the oven, by the presence of at least one oxygen probe implanted in said oven and connected to a reading means of the measurement.
• the enclosure which represents the specific part of the installation in which is implemented the method of heat treatment of wood, corresponding to the space dedicated to the furnace, and the means for recovering the vapors from heat treatment wood, will be filled with water vapor.
• the process of treatment according to the invention implements a simple and perfectly well controlled means, to significantly reduce the risk of fire in the enclosure, and to recover completely or partially, the harmful vapors emanating from the heat treatment of the wood.
• the injection of water into the furnace can be effected either by means of at least one directional jet or by diffusion in the form of droplets, via at least one injection nozzle.
• the orientation of the water inlet in the furnace is flexible, and will be a function of geometric constraints and congestion encountered.
• the water injection step can be continuous throughout the heat treatment of the wood. According to another preferred embodiment of a method according to the invention, it can be carried out intermittently, at predefined time intervals depending on the constraints encountered.
• a method according to the invention can be performed "à la carte” over time ranges random, dictated by the constraints for a real-time adjustment.
• the implantation of an oxygen probe in the furnace makes it possible to continuously inform an operator of the oxygen content present in said furnace during the heat treatment of the wood, and to evaluate the risk of fire. If the flow rate of injected water is constant, that is to say operating all or nothing, an unacceptable rise in the oxygen level will indicate to an operator that it is necessary to activate the injection of water into the furnace. If the flow of water is variable, the operator will adjust its flow punctually, to adapt to the critical situation encountered, and thus reduce the oxygen level.
• the oxygen sensor is connected to a buzzer to inform, in real time, an operator that the oxygen level has reached a value too high. This alarm may be visual, such as a light that comes on, or sound, such as an alarm or a siren.
• the water injection rate is variable. This possibility increases the flexibility of use of the wood heat treatment system, by adjusting the quality of the wood to be treated, and the dimensions and geometry of the oven and the enclosure, the amount of water to be injected . Similarly, if the rate of oxygen were to grow during the same thermal treatment of wood, a temporary increase in the flow of injected water would bring it down to an acceptable level.
• the gas generator uses the biomass.
• the interest of using biomass is no longer to be proven, on the other hand, it generates disadvantages related to the emission of vapors heavily loaded with water and various dusts and varied.
• vapor recovery is therefore a major issue, in particular to avoid environmental pollution.
• the water injected into the oven is preheated to accelerate the vaporization phenomenon.
• the water injected into the oven is hot, and is heated to a temperature of the order of 80 ° C.
• This preheating phenomenon will accelerate the process of formation of water vapor in the chamber containing the furnace, and instantly make operational this water vapor, against the occurrence of a fire, and vis-à-vis the collection of vapors charged with dust, resulting from the heat treatment of wood.
• the hot gases supplied by the gas generator are used to heat the water which is injected into the furnace.
• the energy used to heat the water pre-exists, and therefore does not have to be brought or created from the outside.
• the gases supplied by the generator allowing, in these two cases, to increase the temperature of the water to accelerate the phenomenon of vaporization.
• the temperature of the gases emitted can reach 600 ° C., said gases then being able to heat the water rapidly and significantly.
• the oxygen sensor is connected to a self-regulating system of the flow of water injected into the oven, so as to maintain the oxygen level in the oven below a threshold value, at each instant of the process.
• the device triggering the injection of water is connected to the oxygen sensor, and is programmed to trigger automatically from that the measured value of the oxygen level is found above a threshold value.
• the flow-regulating device is connected to the oxygen probe, and is programmed to adapt the flow of water to be injected, as soon as the measured value of the oxygen level is above a threshold value.
• the threshold value below which the oxygen level must be maintained is 7%. Indeed, this rate guarantees conditions of non-occurrence of fire, and this, so almost safe.
• the step of recovering the vapors resulting from the heat treatment of the wood involves a cooling exchanger, part of the water vapor present in the enclosure condensing at said exchanger.
• a cooling exchanger may already be present in the chamber to recover the vapors from the heat treatment of wood.
• this exchanger will concentrate, in condensed form, a portion of the emitted water vapor. This important condensation will allow:
• the water injected into the furnace comes from a parallel and autonomous circuit.
• the water supply circuit to be injected into the furnace is dissociated from the rest of the plant specially designed for the heat treatment of wood, to avoid accidental interference, between said circuit of water and said installation, which could be detrimental to the smooth running of the treatment method according to the invention.
• an incident that would occur at this water circuit would not require the interruption of the treatment process.
• the wood treatment methods according to the invention have the advantage of using water, which is a simple, inexpensive and well controlled way, both to avoid the occurrence of a fire and to recover the harmful vapors resulting from the heat treatment of the wood. Moreover, this means, which is based on an injection of water into the furnace, can not in any way, including in the event of a malfunction, have any negative influence on the progress of the wood treatment process and on the quality of this treatment.
• FIG. 1 is a schematic view of a water circuit mounted in an installation for the implementation of a wood treatment method according to the invention.
• the methods of heat treatment of the wood according to the invention implement a closed circuit 1 of hot water, parallel to the main circuit of gas, made from biomass for thermally treating the wood.
• the heat treatment processes of the wood according to the invention in fact comprise a step of producing gas at about 600 ° C., a stage of heat treatment of the wood itself. speak, involving an oven 2 in which these particular hot gases arrive, and a terminal stage of recovery of the vapors emitted during said treatment, these vapors being heavily loaded with water and harmful dust.
• the treatment methods according to the invention propose to solve these two problems by implementing a single technique, which is that of injecting hot water into the oven 2, in order firstly to create instantaneously water vapor, the main consequence of which is to contribute to lowering the oxygen content in said furnace 2 to values of less than 7% and, secondly, to promote condensation at the level of the cold elements of the chamber, for trapping the vapors from the furnace 2.
• This hot water injection into the furnace 2 is made possible by the circuit 1 of hot water, implanted parallel and autonomous, in the installation specially dedicated to the heat treatment of wood.
• the production of hot water is carried out by means of a tubular 3 gas / water heat exchanger, fed by hot gases 16 at 600 ° C.
• a temperature probe 9 placed at the outlet of the hot water preparer 5 triggers the tilting of a valve 10 and the deviation of the flow of water towards the cooled circuit 7.
• the temperature of the water in the circuit is measured by a number of temperature probes 11, 12, 13, distributed along the latter, and in particular at the inlet 12 and at the outlet 13 of the gas / water exchanger 3.
• the gases 17 coming out of the 3 gas / water heat exchanger have a temperature of the order of 300 ° C, and are routed to the furnace 2 via a system of valves 18.
• the introduction into the oven 2 of gas 17 at this temperature allows a lower heat input, making it a regulating element for the establishment of bearings in the furnace 2 during processing.
• the gases 17 leaving the exchanger 3 gas / water are used for an optimized supply of heat during the phases of temperature steps in the furnace 2.
• the control of the oxygen level in the chamber is achieved by means of an oxygen sensor.
• this probe can be connected to a visual or audible alarm, which is triggered as soon as the oxygen level is higher than a threshold value.
• this rate is 10%.
• the probe is connected to a regulator of the flow of hot water, which increases said flow rate, if the rate of oxygen tends to increase towards the threshold value.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical And Physical Treatments For Wood And The Like (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=45755372

Family Applications (1)

Country Status (3)

Family Cites Families (3)

• 2011
  • 2011-01-25 FR FR1150558A patent/FR2970771B1/fr not_active Expired - Fee Related
• 2012
  • 2012-01-19 EP EP12705338.7A patent/EP2668458B1/fr not_active Not-in-force
  • 2012-01-19 WO PCT/FR2012/050109 patent/WO2012101358A1/fr not_active Ceased

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