Patent Grant
8857074
The present invention relates to a method for stabilizing timbers. It also relates to a system for implementing this method. By timber is meant, in this case, wood intended for use in the secondary timber processing sectors, in particular for industry, building, joinery, or for urban, industrial, public and domestic external and internal construction.
Passing wood through a flame to heat it to its ignition limit in order to render it rot-proof, and even impervious to attack by its natural predators, is an age-old practice. It is in order to homogenize these effects on much larger quantities of wood that research is being carried out into the heating of wood.
The stabilization methods currently being developed all have their characteristics. There can in particular be mentioned the high-temperature wood-treatment method disclosed in the document FR 2757097. This treatment method utilizes a generation of gaseous treatment flows introduced into the kiln for treating the load of wood.
With current methods it is too often difficult to achieve the objective which is to raise the temperature such that it is homogeneous as far as the core of a mass of wood, to the point of making this wood stable and rot-proof without any added chemical agent. This temperature point is approximately 230° C. It is essential that it is reached and maintained with no risk to the load or to the system, given that the timber's self-ignition temperature is approximately 120/160° C.
The purpose of the present invention is to propose a method for stabilizing timber, which provides guarantees of safety and treatment in complete harmony with the environment and ecology.
This objective is achieved with a bio-thermal method for stabilizing a load of wood, in particular timber, comprising:
The independence of the heat generation means with respect to the treatment kiln contributes significantly to making the wood-treatment method according to the invention safe. Moreover, this method can be implemented simultaneously with several treatment kilns while using only a single gaseous treatment flow generation.
The method according to the invention can advantageously comprise a recycling of the loaded gaseous flow in order to recover gas capable of being used in the gaseous treatment flow. The thermal gaseous flow is preferably a flow comprising carbon dioxide CO2. The gas used for the gaseous treatment flow is advantageously obtained from a combustion gas which is output from the heat generation means.
In a particular embodiment, the method according to the invention comprises a preliminary phase of condensing elements contained in the combustion gas, in order to recover a residual gas containing carbon dioxide.
The residual gas can pass through a heat exchanger in order to reach the treatment temperature, and is then reintroduced into the treatment cycle, in order to be used in a wood-drying phase. Moreover compression of the residual gas is provided, in order to condense and recover the carbon dioxide in liquid phase.
The method according to the invention can moreover advantageously comprise, at the end of the treatment phase, a phase of lowering the temperature of the load of wood during which the treatment gas is introduced into the treatment volume at a progressively lower temperature.
According to another aspect of the invention, a bio-thermal system is proposed for stabilizing a load of wood, in particular of timber, implementing the method according to the invention, comprising:
The heat generation means comprise for example at least one grate furnace and a heat exchanger in which the energy produced by the combustion of a fuel with an oxidant is recovered.
In a particular form of implementation, the stabilization system according to the invention moreover comprises means for reintroducing the residual gas which is output from the heat generation means into a treatment cycle, these reintroduction means comprising means for condensing the steam H2O present in said residual gas, and means for passing said residual gas through the heat exchanger where said residual gas reaches the temperature of the treatment in progress.
This system can moreover comprise means for compressing the residual gas, so as to condense and recover the carbon dioxide in liquid phase, as well as means for concentrating the carbon dioxide in the residual gas.
In a practical embodiment example of the stabilization system according to the invention, the wood treatment means comprise at least one kiln module comprising two removable end partitions in order to allow a transfer of loads of wood to be treated, through one and/or the other of said two ends.
The kiln module can be substantially in the form of a parallelepiped and comprise fixed vertical side partitions comprising double walls in order to provide a space in which the treatment gas and the gas extracted after treatment are conveyed. The external walls of the vertical side partitions are thermally insulated.
Advantageously there can be provided an assembly of a plurality of kiln modules, characterized in that intermediate mobile end partitions are arranged so that they can be removed, the removable end partitions of the assembly of modules being kept closed during the treatment. Intermediate mobile partitions can be installed in order to define several distinct treatment zones comprising for example a drying zone and a high temperature stabilization zone.
The kiln module preferably comprises a ceiling with double walls between which a treatment-gas distribution system is arranged. This gas distribution system comprises means for receiving hot treatment gas originating from the heat generation means and means for extracting this gas after passing inside the kiln module and treatment of the load of wood. The internal wall of the ceiling can be adjustable in height so as to compensate for a variable height in the load of wood to be stabilized.
The system according to the invention can also comprise means for delivering the gas extracted from the kiln module after treatment towards reactor means within heat generation means, in order to be purified there, as well as exhaust fan means for maintaining the kiln module treatment volume under low pressure.
There can also be provided a pressure drop compensation system installed on a treatment gas duct between the heat generation means and the means for treating the load of wood.
The gas distribution system comprises for example means for alternating the extraction of the loaded gases through one and the other of the side walls of the kiln module. These alternation means comprises a four-way mechanism arranged at the junction of the connections of the duct supplying the hot gas, the duct for extracting the loaded gas after treatment, and ducts connected to the fixed vertical walls of the kiln module.
The stabilization method according to the invention uses a completely neutral gas, at the temperatures and pressures of the method, which makes it possible to raise the temperature of the wood well beyond its self-ignition limits. This gas is advantageously carbon dioxide CO2. The CO2 is the final phase of carbon combustion, and is therefore non-flammable.
The carbon dioxide is used in the method as:
The carbon dioxide CO2 used in the method according to the invention has advantageously originated from the heat production method utilized in the heat generator.
According to yet another aspect of the invention, a wood is proposed, in particular a timber, having the characteristics of a wood which has been subjected to the stabilization method according to the invention.
Other advantages and characteristics of the invention will become apparent on examining the detailed description of an embodiment which is in no way limitative, and the attached drawings in which:
A description will now be given, with reference to the abovementioned figures, of an embodiment example of a stabilization system according to the invention, at the same time as the method implemented in this method.
The stabilization system S comprises, with reference to
The heat generator 2 is a system, with reference to
Depending on the combustion principle applied, the concentration of CO2 in the residual gas is more or less high. If the combustion is carried out under oxidant (or combustive) air, the residual gas comprises a large percentage of nitrogen: approximately 4 volumes of nitrogen to 1 volume of CO2. If the combustion is carried out under O2, the residual gas comprises more than 95% CO2.
According to the type of installation and its function the oxidant (or combustive) can be ambient air as it is, air enriched with O2, at a more or less high percentage, industrial O2, or also the three subsequent combustion methods, during a cycle, as a function of the rise in temperature and the guarantee of safety.
Given the chosen combustion method, the thermal yield is different: from a minimum yield with oxidant air to the maximum yield with industrial O2. It is the combustion method which determines the CO2 recovery procedure.
If the residual gas after the condensation of H2O comprises more than 90% CO2, it is recovered as it is in order to:
When the residual gas after the condensation of H2O comprises less than 30% CO2 the two methods for concentrating the CO2 must be implemented. The gaseous residue is recycled in the generator 2 during the treatment cycle. The CO2 concentration method is used until the quantity collected is sufficient for the high-temperature phase. The liquid CO2 is stored 25 in order to be used in the method. The CO2 store increases as the treatment cycles proceed, and there is therefore an economic benefit to draw off the surplus of marketable quality.
In the grate furnace or furnaces 20, “vegetable biomasses” are burned, in all solid fuel forms CB (with dimensions greater than sawdust and crushed materials). These are all so-called “energy wood” forms (logs, billets, wood chips, slabs, edgings, reconstituted briquettes which are stable in combustion, granules, etc.).
The solid fuel is preferably densified biomass [Bio-D]® which, due to its densification method, is a carbon concentrate (85% instead of 50% for the “energy” biomass) and therefore an energy concentrate. The densified biomass [Bio-D]® makes it possible to achieve a greater yield of CO2 during a cycle.
The accumulation of CO2 recovered allows utilization in various additional methods. The withdrawal of its atmospheric equivalent in greenhouse gas, in each application and each use, is an enormous gain for the ecosystem. The carbon dioxide CO2 is produced once and used several times in methods which would have produced it in another fashion.
The oxidant (or the combustive) used is preferably industrial oxygen, especially if the system must be used in a complex with energy co-generation. The thermal ratio is then substantially greater. The oxidant can also be “atmospheric” air enriched or not enriched, in installations where only the stabilization of the wood is sought.
The energy recovered in the exchanger 21 makes it possible to reheat the CO2 intended to be used for the wood treatment, it is also used in order to produce steam at a high pressure for the co-generation of electricity 26. This electricity is used for the stabilization method according to the invention, which renders it autonomous.
If the stabilization method according to the invention is utilized in order also to achieve the co-combustion of waste, the energy produced is greater than the needs of the system. The excess co-generated energy can be marketed and used in additional facilities of the complex.
The wood treatment kiln 10 is for example produced, with reference to
This characteristic makes possible, with reference to
The ends 11, 12 are mobile and removable, and they close the treatment volume VT when the load of wood B has entered. When several kiln modules 10.1, 10.2, 10.3, 10.4 are assembled, it is the ends 11.1, 10.4 of the assembly which are closed, as illustrated by
Whether for one kiln module or several assembled modules 10.1, 10.2, 10.3, 10.4, a single generator 2 with its specific peripherals will supply the treatment gas GT and the energy necessary to the system.
The ceiling 13 of the kiln module 10; 10.1, 10.2, 10.3, 10.4 also has double walls 130, 131 between which the gas distribution system SD is organized; SD1, SD2, SD3, SD4. This distribution system is designed in order to receive the hot gas GT originating from the heat generator 2 and extract this loaded gas GC after it has passed through the treatment technical volume VT. The low/internal wall, which relates to the technical treatment volume, is mobile in order to be adjusted to a suitable height, to compensate for variable heights of the load of wood B to be stabilized.
The floor of the kiln module 10 is equipped with rails 15A, 15B, with reference to
The gas extracted GC is delivered to the reactor 23 in the heat generator 2 in order to be purified before its reuse. This extracted gas is then loaded with gasified elements during the raising of the temperature of the wood to be treated. The CO2 gas used for the treatment of the wood is thus continuously recycled. It is recovered at the outlet of the generator 2 with the CO2 produced by the combustion methods in the reactor (combustion of the solid fuel and of the elements of the wood which have been gasified during the treatment).
The gas extracted after treatment of the wood comprises CO2 introduced from the steam originating from the wood, and combustible volatile molecules, gasified during the raising of the temperature of the load of wood.
The combustible gas parts will be reduced to their native elements in the thermal reactor, where all their available energy will be produced. The steam is purified by passing through the solid fuel reactor 23, it is condensed to pure water after recovery of the thermal energy. The recovered thermal energy makes it possible to produce a quality of steam which will be used for the co-generation of electricity 26.
The residual heat, after co-generation, is used for the stabilization method. The treatment gas being permanently recycled, this residual heat is recovered. There is a surplus of heat during the recycling methods, this heat can be utilized in the additional facilities of a complex, for example:
The treatment volume VT of the kiln module 10 is maintained under low pressure by an exhaust fan 50 independent of the kiln. It is situated on the outside of the duct 5 for extraction of the gases from the kiln module 10 and delivery to the heat generator 2. It is this extraction of the loaded gases GC which creates the low pressure in the treatment volume VT of the kiln module 10. The loaded gas GC is delivered to the reactor 23 in the generator 2 which purifies this gas in a permanent recycling method. The CO2 is recovered at the outlet of the generator 2 by the methods described above. The recovered CO2 is in liquid phase, its temperature lies between −85 and −100° C.
The gaseous/liquid phase change requires a significant amount of energy. This same amount of energy is restored during the liquid/gaseous phase change, it is during this phase change that the condensation of the steam contained in the extracted gas takes place.
The CO2, which must be introduced for the treatment, attains its appropriate heat in the heat exchanger 21 as a function of the temperature programmed by the treatment cycle. The CO2 is thus moderated and suitable for a new treatment cycle, it is sucked in by the low pressure created in the technical volume VT of the kiln module 10, via the gas distribution system SD and so on. A pressure drop compensation system, connected at a significant distance between the generator 2 and the kiln module 10, can be installed on the treatment gas GT duct 4.
The heat generator 2, the kiln module 1 and the gas ducts 4, 5, connecting these two units, are efficiently thermally insulated, in order to reduce the energy losses and make the equipment safe to approach.
The continuous production of CO2 accumulates with the recycled CO2, which induces a superabundance of this gas. CO2 is a strategically important gas in the developing economy, having the properties of a neutral gas for the preservation of certain foodstuffs in the agri-food industry, and as a substitution gas for prohibited refrigerant gases, and as a raw material in technological materials.
With reference to
This mechanism 6 is automatically controlled by the electronic programme for carrying out the treatment. It transfers and alternates the flow/extraction from the one to the other of the vertical walls 16.1, 16.2. This four-way mechanism 6 is produced for example in the form of a parallelepiped the four vertical faces of which are connected facing:
This mechanism 6 comprises a mobile wall 60, centred on its vertical axis 61, which hides the diagonals of the parallelepiped by pivoting about the axis 61. This action alternates the connections of entering and exiting gases to the right-hand 16.2 or left-hand walls 16.1.
In the internal faces of the fixed vertical walls 16.1, 16.2 of the kiln module 10, vertical inlets 52.1, 52.2 are arranged so that the transfers of the flow/extraction gases can take place in the treatment volume VT. These inlets are provided with mobile deflectors, which can be mechanized to provide good distribution of the treatment flow. An upper part of these deflectors is made up of elements which can be closed independently, to make it possible to adjust the height of the ceiling in the treatment volume VT.
The adjustment of the flow of treatment gas GT is carried out by varying the low pressure in the treatment volume VT of the kiln module 10 by varying the power of the extraction motor 50. The object of this heat transfer method is to make the aerodynamics of the gases more fluid and thus to avoid overheating in the zones.
The constant low pressure guarantees that a gas concentration inside the kiln module is impossible. Means of injecting steam into the flow of treatment gas are arranged in order to control the drying of the wood under the best technical conditions. In fact, too-rapid drying would have the consequence of causing physical damage to the treated wood.
The deflectors on the fixed vertical walls can completely block off the inlets, this makes it possible to provide neutral zones when the load of wood to be treated does not occupy all the technical space in the kiln module. In this case, a removable and adjustable partition separates the neutral zone from the active zone in order to save the energy used and reduce the cost of the treatment.
The kiln module 10 can also be arranged so that the mobile end walls can also be shifted in horizontal translation so as to be placed in close proximity to the ends of the load of wood B. This minimizes the treatment volume VT for a given load of wood, which improves the effectiveness of the stabilization method and energy saving.
When the stabilization is carried out, the load of wood B is at too high a temperature to be removed. This temperature must be reduced so as not to risk self-ignition in air and to ensure that it is safe to handle the load B. In order to achieve this reduction in temperature the cycle is continued until the load can be removed in complete safety. The CO2 is introduced at a progressively lower temperature under control of the program, so as not to create thermal shocks detrimental to the load of wood. The condition of recovery of the CO2 in liquid phase makes it possible to lower the temperature of the load of wood very significantly.
The energy which is produced by the heat generator 2, in order to be transferred to the CO2 treatment gas (which transfers part of it to the wood to be treated) is largely recovered by the generator 2, since the treatment gas GT is continuously recycled and therefore the energy that it conveys is also recycled.
The gas used for cooling down the load of wood B, before removing it from the kiln module 10, is also recycled in the generator 2. There is therefore a large quantity of energy available during and at the end of the treatment cycle. This energy can be used in related methods, in particular for drying the wood, energy which can be used in the stabilization method.
The operation of the system can be prolonged and made more profitable by using certain waste as co-fuels with [Bio-D]®, for example, Non-Reusable Used Tyres (NRUT) or polluted timbers, which are subject to a disposal charge tax and which makes the operation more profitable.
This operation of the system allows integration into a synergetic assembly where:
Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without exceeding the scope of the invention.
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| PCT/FR2005/001196 | 5/13/2005 | WO | 00 | 11/29/2007 |
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