Method for the thermal drying of wood in a co2 atmosphere

Abstract

The invention relates to a thermal drying process for wood implemented comprising the following steps: -Acquisition of metrological data and parameters of the wood to be dried (S1); -saturating (S2) the drying chamber (1) with CO2; -Adjusting the moisture content of the wood (S3) by heating; -heating (S4) the CO2 circulating in the drying chamber (1) according to a first phase, then reheating according to a second phase the CO2 circulating in the drying chamber (1) until the measured moisture content of the wood reaches a chosen intermediate target value Hi; -Decreasing (S5) the temperature of the heating chamber (1) to a chosen third setpoint temperature T3 for stabilization; -Decreasing according to a second phase (S6) the temperature of the heating chamber (1); and the wood dried directly by the process according to the invention.

Description

[0001] The present invention relates to a process for thermal drying of wood by CO 2 sequestration as well as the dried wood directly obtained by the process, in particular but not limited to the industrial drying of industrial wood, energy wood, logs, and similar lignocellulosic material.

[0002] Here, "industrial wood" means wood intended for use in secondary wood processing sectors, particularly for industry, construction, carpentry, or for urban, industrial, collective and domestic exterior and interior design.

[0003] “Wood” means any lignocellulosic material or similar compound capable of sequestering CO2.

[0004] Here, "CO2 sequestration" means any substitution, CO2 trapping, chemical reaction between CO2 / wood polymers / water or complexation, or stable accumulation of CO2 or carbonation of wood or water contained in wood with compounds such as wood to be dried or similar receiving material.

[0005] A system is known as taught by documents WO2020127026 and FR3090835A1, using wood drying cells under CO2 atmosphere to implement a process for drying wood under CO2 atmosphere.

[0006] This process has the disadvantage of not being able to maintain uniformity in the temperature of the gas mixture in the drying chamber, resulting in poor uniformity in the drying of the wood.

[0007] This method also has the disadvantage of not being able to limit the presence of water in the liquid state in said drying chamber, nor of guaranteeing that the temperature of the drying environment is uniform in use at all points in the drying chamber.

[0008] Although various solutions for drying timber, roundwood and / or logs exist, known solutions rarely allow for industrial applications associated with a low energy balance. Indeed, known solutions are generally used on a small scale, to consume a minimum of energy while obtaining wood with a low percentage of water, and do not allow for drying with a neutral or negative carbon balance.

[0009] Another disadvantage of existing solutions is the duration of use of a drying installation, several days or even several weeks, a factor limiting its effective use for industrial purposes.

[0010] Furthermore, current processes too often struggle to achieve the objective of raising the temperature so that it is uniform throughout the core of a mass of wood, while achieving precise hygrometry of the dried wood and ensuring the integrity of the internal structure of the wood during and after drying.

[0011] Current drying processes and installations also have the disadvantage of only allowing a very small quantity of CO2 to be sequestered in the wood to be dried.

[0012] All the known drying methods mentioned above also cause deformation of the resulting wood, frequently including deformations of the planed timber such as warping, but also at the level of the knots of said material with detachments. These deformations also present numerous disadvantages during the future use of the dried material.

[0013] Disadvantages in use include, but are not limited to, unequal force distribution at any point of said material which may cause structural weaknesses, deformations rendering the material unusable, accelerated wear of the material over time, and significant volume shrinkage between the undried state and the dried state, and therefore poor material yield from the drying process.

[0014] The present invention overcomes these drawbacks.

[0015] The invention relates to a method for thermally drying wood carried out using a drying installation comprising at least one drying chamber.

[0016] According to a general definition of the invention, said method comprises the following steps: Acquire metrological data and parameters of the wood to be dried by measurement via metrological means; Activate CO2 supply means configured to saturate the drying chamber with CO2 and have a circulating gas mixture; Check that the CO2 saturation in the circulating gas mixture is sufficient to start a drying cycle by verification via CO2 / CH4 measurement means at an exhaust duct; Activate heating means to adjust the wood humidity by heating when a sufficient measured CO2 saturation is reached. If the wood humidity is greater than 30%, heat with a temperature limit according to a first set temperature T1, according to a chosen temperature gradient G1 in order to extract the free water from the wood to be dried and activate circulation means;If the wood humidity is less than 30%, heat with a temperature limit according to a first set temperature T2, according to a chosen temperature gradient G2 in order to extract the bound water from the wood to be dried and activate the circulation means; Stabilize the temperature of the CO2 circulating in the drying chamber according to a first phase when a humidity less than or equal to 30% is measured, activate the recycling means then increase according to a second phase the temperature of the CO2 circulating in the drying chamber until the measured humidity of the wood reaches a chosen intermediate target value Hi, the heating means being activated so that the reheating is carried out with a limit temperature defined by a second set temperature T2 of 120°C according to a chosen temperature gradient G2, and according to the specific drying profile of the wood to be dried allowing the bound water to be extracted from the wood to be dried;Maintaining the humidity of the wood to be dried by deactivating the recycling means and modulating the activity of the heating means to reduce the temperature of the heating chamber according to a first phase, up to a third setpoint temperature T3 for stabilization chosen according to a temperature gradient G3, when the average humidity measured by the wood humidity measuring means reaches the intermediate target value Hi chosen, unless one of the measured humidity values ​​of the wood is greater than Hi+A%, A being a chosen value, said setpoint temperature T3 being maintained for a chosen duration of time D until the measured humidity value of the wood initially greater than Hi+A% is stable and within a range of values ​​lower than Hi+A%;- Deactivate the heating means, to reduce the temperature of the heating chamber in a second phase, when the average measured hygrometry of the wood reaches the final target hygrometry value Hc.;

[0017] For example, the humidity value Hi+A% has an A value between 1% and 2.5%.

[0018] In practice, the stage of acquiring metrological data and parameters of the wood to be dried includes the following sub-stages: Fill the drying chamber with the object to be dried; Measure the surface and core temperature of the wood; Measure the humidity of the wood to be dried; Measure the temperature of the drying chamber; Measure the humidity of the drying chamber; and Measure the weight of the wood to be dried.

[0019] Furthermore, the step of activating the CO2 supply means comprises a sub-step of verifying the CO2 saturation of the gas mixture circulating in the drying chamber.

[0020] In practice, the step of activating the heating means to adjust the hygrometry of the wood includes a sub-step of monitoring the hygrometry of the wood in real time and the heating step includes a sub-step of monitoring the hygrometry of the wood in real time.

[0021] According to an embodiment in accordance with the invention, the step of activating the recycling means comprises a sub-step of implementing an activation / deactivation sequence of a flow inversion module according to a chosen frequency F1.

[0022] In practice, the step of reducing the temperature of the heating chamber according to a second phase further comprises a sub-step of stopping the flow inversion module at the same time as the recycling means.

[0023] The method according to the invention further comprises a CO2 evacuation step, configured to desaturate the drying chamber with CO2 to extract the dried wood.

[0024] By way of non-limiting example, the heating step comprises a temperature limit according to a first set temperature T1 between 50°C and 60°C, according to a chosen temperature gradient G1 of 2°C / hour.

[0025] By way of non-limiting example, the temperature increase step comprises a temperature limit defined according to a second set temperature T2 less than or equal to 120°C, according to a chosen temperature gradient G2 between 1°C / hour and 3°C / hour.

[0026] By way of non-limiting example, the step of reducing the temperature of the heating chamber according to a first phase comprises a temperature limit according to a first set temperature T3 between 50°C and 100°C, according to a chosen temperature gradient G3 of 2°C / hour.

[0027] Advantageously, the drying process according to the invention also makes it possible to obtain a shrinkage of less than 5% of the wood, whereas the standard shrinkage with conventional drying means is 10 to 15%.

[0028] The invention also relates to a dried wood directly obtained by the process according to the invention, comprising lignin, cellulose and hemicellulose.

[0029] According to a second general definition, the directly dried wood obtained by the process according to the invention contains less than 20% of average measured humidity, and in that the ultrastructure of the cell wall of the wood is preserved in the dried state compared to the state before drying.

[0030] The Applicant also observed that the implementation of the method according to the invention by a drying installation makes it possible to obtain dried wood according to the invention, has low moisture uptake, a reduction in the coloring of the dried wood, as well as the limitation / absence of the appearance of cracks during drying.

[0031] Furthermore, the drying method according to the invention makes it possible to obtain drying uniformity, as well as shrinkage of less than 5% while limiting the presence of water in the liquid state in the drying chamber.

[0032] Other advantages and characteristics of the invention will appear on examining the description and the drawings in which: [ Fig 1 ] schematically represents the steps of the process implemented by the drying installation in accordance with the invention; [ Fig 2 ] schematically represents the sub-steps of the chamber filling step / acquisition of sensor data of the process implemented by the drying installation according to the invention; [ Fig 3 ] schematically the sub-steps of the CO2 chamber saturation step of the process implemented by the drying installation according to the invention; [Fig 4] schematically represents the sub-steps of the wood hygrometry adjustment step of the process implemented by the drying installation in accordance with the invention; [ Fig 5 ]schematically represents the sub-steps of the step of maintaining the wood to be dried in the process implemented by the drying installation in accordance with the invention; [ Fig 6 ] schematically represents the sub-steps of the CO2 cooling step of the process implemented by the drying installation according to the invention; [ Fig 7 ] schematically represents the sub-steps of the CO2 drying step of the process implemented by the drying installation according to the invention; [ Fig 8 ] schematically represents a drying installation capable of implementing the method according to the invention; and [ Fig 9 ] represents a front view of the drying installation capable of implementing the method according to the invention.

[0033] In reference to the figures 1 à 7 ,the method of drying and sequestering CO 2 in wood according to the invention is carried out in a drying installation comprising at least one drying module C1 integrating at least one drying chamber 1, heating means 2 as well as CO 2 supply means 3, and comprises a succession of steps.

[0034] According to a step of acquiring metrological data and parameters of the wood to be dried S1, metrological data and parameters of the wood to be dried are acquired by measuring metrological means 5.

[0035] In addition, the measurement of the various parametric data is carried out to calibrate the setpoint values ​​to be applied.

[0036] In practice, the stage of acquiring metrological data and parameters of the wood to be dried S1 includes the following sub-stages: Fill the drying chamber with the object to be dried S11; Measure the surface and core temperature of the wood S12; Measure the humidity of the wood to be dried S13; Measure the temperature of the drying chamber S14; Measure the humidity of the drying chamber S15; and Measure the weight of the wood to be dried S16.

[0037] For example, the wood to be dried is inserted into drying chamber 1, and then the drying chamber is hermetically sealed.

[0038] In practice, the difference between the surface temperature of the wood and the core temperature of the wood must be less than or equal to 20°C throughout the drying operation.

[0039] In addition, the sub-step of measuring the weight of the wood to be dried S16 allows the calculation of the mass loss relating to the implementation of drying and thus quantifies the quantity of water extracted by taking into account the quantity of CO 2 sequestered.

[0040] As a non-limiting example, the maximum quantity of CO2 sequestered is 250kg / m3 of wood.

[0041] According to a CO 2 saturation step S2 of the drying chamber 1, CO 2 supply means 3 are activated in order to allow the injection of CO 2 from a CO 2 source into the drying chamber 1.

[0042] In practice, the CO 2 saturation step S2 includes a sub-step S21 of verification of the CO 2 saturation in the circulating gas mixture, to ensure that said minimum CO 2 saturation for starting a drying cycle is reached.

[0043] The term circulating gas mixture is understood to mean the total sum of the components of the gaseous and liquid environment circulating in the drying chamber 1 at a time t.

[0044] In practice, the verification of CO 2 saturation S21 is implemented by measurement via CO 2 / CH4 measuring means 56 at the level of an evacuation duct of the drying module C1.

[0045] According to one embodiment, when the ratio R= P[CO 2 ] input / P[CO 2 ] output is between 0.8 and 1.2, the minimum CO 2 saturation is reached.

[0046] According to an alternative embodiment, the verification of the CO 2 saturation S21 is implemented by measuring the percentage of CO 2 in the circulating gas mixture.

[0047] According to a wood humidity adjustment step S3, heating means 2 are activated to adjust the humidity of the wood to be dried, so that the measured humidity of the wood is less than or equal to 30%. The heating means 2 are activated when the minimum CO2 saturation is reached.

[0048] The wood hygrometry adjustment step S3 further includes a sub-step of measuring the wood hygrometry in real time S31.

[0049] In practice, if the measured hygrometry of the wood is greater than 30%, the method according to the invention comprises a heating sub-step S32 via the heating means 2, the implementation parameters of which include an upper temperature limit according to a first set temperature T1 not to be exceeded, as well as a chosen temperature gradient G1 in order to extract the free water from the wood to be dried until the measured hygrometry of the wood is less than or equal to 30%.

[0050] The heating sub-step S32 further comprises the activation of gas circulation means 4.

[0051] As a non-limiting example, the first set temperature T1 is between 50°C and 60°C.

[0052] As a non-limiting example, the chosen temperature gradient G1 is 2°C / hour.

[0053] If the hygrometry of the wood is less than or equal to 30%, a drying step S4 is implemented directly, and consists of increasing the temperature of the circulating gas mixture, the implementation parameters of which include an upper temperature limit according to a second set temperature T2 not to be exceeded, and according to a chosen temperature gradient G2, in order to extract the bound water from the wood to be dried and activate the gas circulation means 4.

[0054] The drying step S4 of the drying process comprises sub-steps comprising: stabilize S41 the temperature of the CO 2 circulating in the drying chamber 1 according to a first phase when the measured hygrometry of the wood is less than or equal to 30%; activate S42 of the recycling means 600; measure in real time the hygrometry of the wood S43; and increase S44, according to a second phase, the temperature of the CO 2 circulating in the drying chamber 1 until the measured hygrometry of the wood reaches a chosen intermediate target value Hi.

[0055] According to one embodiment, the activation step S42 of the recycling means 600 further comprises the start of an activation / deactivation sequence of a flow inversion module according to a chosen frequency F1, configured to reverse the direction of the flow of the gas mixture circulating in the drying chamber 1 according to a chosen frequency in two circulation directions.

[0056] In practice, the heating means 2 are activated so that the heating is carried out with a limit temperature defined by a second set temperature T2 of 120°C according to a chosen temperature gradient G2, and according to the specific drying profile of the wood to be dried, making it possible to extract the bound water from the wood to be dried more precisely.

[0057] The set temperatures T1 and T2 are temperature limits that each drying module C1 cannot exceed during these phases.

[0058] In practice, the set temperature T2 is less than or equal to 120°C.

[0059] As a non-limiting example, the chosen temperature gradient G2 is between 1 and 3°C / hour.

[0060] In practice, the intermediate target value Hi chosen for the measured hygrometry of the wood is equal to the desired final target hygrometry Hc + 1.5 to 2.5%.

[0061] Furthermore, reaching the chosen intermediate value Hi is made possible by controlling the recycling means 600 through a high hysteresis (hys-h) and a low hysteresis (hys-b). These two parameters make it possible to activate the recycling means 600 in corroboration with the hygrometry measured in the drying chamber 1 in order to avoid activation / deactivation of the recycling means 600 or the CO 2 3 supply in the event of a hygrometry measurement fluctuating between a value higher and lower than the chosen intermediate value Hi.

[0062] In practice, the temperature gradient G2 is chosen according to the specific drying profile of the wood to be dried, allowing the extraction of bound water from the wood to be dried, and dynamic, so as to be adjusted when approaching the intermediate target value Hi of hygrometry of the chosen wood.

[0063] As a non-limiting example, the pressure measured in the drying chamber is between 0.8 and 1 bar.

[0064] According to a step of maintaining the wood to be dried S5, the temperature in the drying chamber 1 is stabilized.

[0065] The step of maintaining the wood to be dried S5 is implemented by deactivating S51 the recycling means 600, and by modulating the activity of the heating means 2 to reduce the temperature S52 of the heating chamber 1 according to a first phase, down to a third set temperature T3 for stabilization chosen according to a temperature gradient G3, when the average hygrometry measured of the wood via the hygrometry measuring means 54 of the wood reaches the intermediate target value Hi chosen, the hygrometry is stabilized S53.

[0066] In practice, if one of the measured hygrometry values ​​of the wood is greater than Hi+A%, said set temperature T3 is maintained for a chosen period of time until the measured hygrometry value of the wood greater than Hi+A% initially is stable and within a range of values ​​less than or equal to Hi+A%.

[0067] As a non-limiting example, the third set temperature T3 is between 60 and 100°C.

[0068] As a non-limiting example, the range of target hygrometry values ​​is between a final target hygrometry value Hc, and an intermediate target hygrometry value Hi, i.e. the target wood hygrometry value Hc + A%.

[0069] In practice, the value A is between 1 and 2.5%.

[0070] In practice, when the measured humidity is stable and lower than Hi, the temperature of the drying chamber 1 is stabilized S54, and maintained for a chosen period of time D, even if the set temperature T3 is not reached.

[0071] As a non-limiting example, duration D is 2 hours.

[0072] Advantageously, stabilizing the temperature for a chosen duration D when the measured hygrometry reaches a value within a chosen target hygrometry value range less than or equal to Hi allows a hygroscopic rebalancing of the wood to be dried.

[0073] According to a CO2 cooling step S6, the temperature in the drying chamber 1 is reduced according to selected conditions.

[0074] In practice, the step of reducing the temperature according to a second phase S6 comprises a sub-step of deactivation S61 of the recycling means 600.

[0075] According to one embodiment of the invention, the deactivation sub-step S61 further comprises stopping the flow inversion module.

[0076] As a non-limiting example, the chosen temperature gradient G3 is 2°C / hour.

[0077] In practice, the temperature gradient G3 is chosen identically, regardless of the specific drying profile of the wood to be dried, this being also dynamic, so as to be adjusted when approaching the final target value Hc of hygrometry of the chosen wood.

[0078] As a non-limiting example, the final target value Hc for wood hygrometry is between 0% and 18%.

[0079] The method according to the invention further comprises a step S7 of evacuating the atmosphere from the drying chamber including the CO 2 , configured to desaturate the drying chamber 1 with CO 2 and thus extract the dried wood when the measured hygrometry of the wood is less than or equal to the final target hygrometry value Hc, and after stabilization of the temperature for the chosen duration.

[0080] All the steps of the process are controlled and carried out via a succession of fully automated commands by a computer control system 6 comprising the application programming interface API. The API executing a control program, it sends different instructions to each of the control components and receives the recording data from the metrology means 5 of the drying installation in real time from the start to the end of the process, which make it possible to adjust the control components in order to optimize the drying in the event of a deviation from the setpoint values.

[0081] The drying profile is specific for each type of wood, each type of wood therefore having a hygrometric evolution curve at the heart of the wood as a function of its own drying time and the specific associated temperature increase sequencing, which dictate the temperature increase profile to be applied during the heating phases, and serves as a basis for comparison with the recorded metrology measurements so that the computer control system 6 retro-adjusts these same measurements to set values, in order to obtain optimal and industrial drying of the wood.

[0082] In practice, the temperature gradients G1, G2, G3 are modulated by the computer control system 6, so as to control the evolution of the hygrometry in the heartwood of the wood during drying.

[0083] In practice, since the humidity in the wood to be dried varies, the ambient humidity, the average humidity, the minimum humidity and the maximum humidity are monitored by metrology means 5.

[0084] Recording the control of the sequences of setpoint values ​​associated with the observed measurements makes it possible to establish a specific drying hygrometric profile for the type of wood to be treated, and thus define the retro adjustments by the control computer system 6 for wood of the same type during subsequent drying operations, and thus industrialize the drying while maintaining the conservation of the macromolecular structure of the dried wood with a substitution of the bound water by CO 2 .

[0085] Furthermore, each passage from one stage to another stage is only dependent on the hygrometric target to which the current stage is conditioned and not on whether the set temperature of the current stage is reached or not.

[0086] The process thus described also makes it possible to obtain dried wood, also called dried cellulosic material.

[0087] Advantageously, the dried lignocellulosic material is little deformed during drying under CO2 and has dimensional stability in the dried state.

[0088] The lignocellulosic material dried by implementing the method according to the invention comprises lignin, cellulose and hemicellulose, and has an average measured humidity of less than 20%, while having an ultrastructure of the cell wall of the wood structurally preserved in the dried state compared to the state before drying.

[0089] Variations in water content in cell walls normally cause wood to deform. Wood "swells" when it absorbs water, and it contracts when it loses water. These dimensional variations of a wood sample, which cause a change in volume, are not the same in the three reference directions: radial, tangential, and longitudinal.

[0090] The dried cellulosic material has a tangential shrinkage of less than 5% and a radial shrinkage of less than 4%.

[0091] In addition, the dried lignocellulosic material exhibits less swelling upon moisture recovery (rehumidification), in fact the swelling of the material is 50% lower than that observed through conventional drying.

[0092] Advantageously, low tangential and radial shrinkage allows material savings of up to 20% when lignocellulosic material is used.

[0093] By way of non-limiting example, the use of the lignocellulosic material according to the invention in the manufacture of floor coverings makes it possible to reduce dimensional variations when said floor coverings are exposed to variations in hygrometry.

[0094] Advantageously, the use of dried wood-type lignocellulosic material makes it possible to obtain manufactured products with improved mechanical properties, with less swelling following moisture uptake and improved durability, while limiting material losses during manufacturing linked to deformations, detachments, cracks, which results in a yield between 40 and 50% during the transformation of wood via conventional drying. In other words, 50 to 60% less waste is obtained per cubic meter of transformed wood.

[0095] Instrumentation and control based on metrology measurements of the internal environment of drying chamber 1 and the wood make it possible to avoid damaging the wood during drying, any drying inducing unavoidable material shrinkage, although reduced by drying in a CO2-saturated atmosphere. In the event of poor control, the structural quality of the dried wood thus obtained can be significantly impacted.

[0096] Cracks and sagging of the wood may appear as a result of poor control and thus compromise the structural integrity of the dried wood obtained by the process according to the invention, thus generating a product not according to the invention.

[0097] The process according to the invention therefore makes it possible, via fine regulation of the hygrometry of the wood, to obtain dried wood with precise hygrometry, with shrinkage less than or equal to 5%, a negligible deformation rate, and with a limitation, or even elimination of the appearance of cracks in the wood thus dried.

[0098] In reference to the figures 8 et 9 ,the method according to the invention can be implemented by a drying installation under CO 2 atmosphere comprising at least one drying module C1, each drying module C1 having several functional groups among which a heating chamber 1 comprising at least one drying tube into which the wood to be dried is introduced, heating means 2, CO 2 supply means 3, gas circulation means 4 allowing the renewal of the atmosphere inside the drying chamber 1, several metrology measurement units forming metrological means 5, and finally a computer control system 6 equipped with an application programming interface API.

[0099] The drying module C1 has a drying chamber 1 composed of one or more hollow cylindrical drying tubes allowing the introduction of the wood to be dried.

[0100] The drying chamber is connected to the heating means 2 by an inlet duct 206a, and has an outlet duct 206b configured to evacuate a CO 2 , or CO 2 / H 2 O gas mixture from said drying chamber 1 depending on the progress of the drying.

[0101] In practice, the inlet duct 206a is arranged at a first end of the drying chamber 1 and the outlet duct 206b at a second end of the drying chamber 1 so as to allow longitudinal circulation of the CO2 gas mixture relative to the wood to be dried.

[0102] By way of non-limiting example, the drying chamber 1 comprises a closed, heat-insulated tube with internal atmospheric recirculation.

[0103] According to a particular embodiment of the invention, the drying chamber 1 comprises a minimum volume of 10m3 saturable with CO2.

[0104] According to one embodiment, the drying chamber 1 comprises metrological means 5 configured to measure parameters belonging to the group formed by hygrometry of the wood to be dried, hygrometry in the drying chamber 1, temperature of the wood to be dried, temperature in the drying chamber 1, pressure in the drying chamber 1.

[0105] According to one embodiment, the drying chamber 1 comprises at least one probe for measuring the temperature and humidity in the drying chamber 53.

[0106] By way of non-limiting example, the drying chamber 1 comprises two probes for measuring the temperature and humidity in the drying chamber 53.

[0107] According to one embodiment, the drying chamber 1 comprises at least one probe for measuring the hygrometry of the wood to be dried 54.

[0108] By way of non-limiting example, the drying chamber 1 comprises two probes for measuring the hygrometry of the wood to be dried 54.

[0109] In practice, the drying chamber 1 further comprises a control box 61 configured to receive and process the data recorded by the hygrometry measuring probes of the wood to be dried 54.

[0110] According to one embodiment, the drying chamber 1 further comprises a pressure measuring probe 55 in said drying chamber 1, allowing the emergency evacuation of part of the atmosphere contained in the drying chamber 1 in the event of critical pressure therein.

[0111] In practice, each metrological measurement includes a set value or a group of set values ​​to be respected, specific to each species or application of the wood to be dried.

[0112] In practice, the critical pressure can be 1.5 bar.

[0113] The drying chamber 1 further comprises door closing sensors 62, configured to detect the closing status of the doors for inserting the wood to be dried.

[0114] As a non-limiting example, the drying chamber 1 is 5.5m long with a circulation diameter of 2.4 metres, cylindrical or quasi-cylindrical in shape and contained in a maritime container insulated with 60mm thick wood wool panels. This box is connected from one end to the other by a heat-insulated pipe, a heating system 2 and four centrifugal circulation fans capable of withstanding temperatures of up to 250°C.

[0115] The drying module C1 further comprises operating means configured to operate and control the drying in each drying module C1 and corresponding to any means arranged outside the drying chamber 1 allowing the operation thereof.

[0116] The drying module C1 comprises CO 2 3 supply means configured to control the injection of the CO 2 gas mixture from at least one CO 2 source.

[0117] The CO 2 supply means 3 comprise a conduit connected on the one hand to the CO 2 source, and on the other hand to the heating means 2, said conduit being equipped with a solenoid valve 701 allowing the control of the injection of CO 2 into the drying module C1.

[0118] In practice, a command is sent to the solenoid valve 701, and triggers its opening in order to supply the drying installation with CO2.

[0119] In practice, the CO 2 supply means 3 further comprise metrological means 5 configured to measure parameters belonging to the group formed by flow rate of the injected circulating CO 2 gas mixture, temperature of the injected circulating CO 2 gas mixture.

[0120] According to one embodiment, the CO2 3 supply means comprise at least one probe for measuring the temperature and the circulating flow rate 51.

[0121] The drying installation further comprises CO2 supply means 3, which comprise a source of CO2 belonging to the group formed by biogenic CO2, non-biogenic CO2.

[0122] According to another alternative embodiment, the CO 2 supply means 3 comprise at least one so-called “direct” CO 2 supply module, and one so-called “recycled” CO 2 supply module, connected to the drying module C1 and configured to allow the injection / stopping of the injection of CO 2 into the drying module C1.

[0123] Direct CO2 means CO2 from a CO2 source in gas form which has not been purified at the outlet of the off-gas or industrial chimney and whose gas mixture containing CO2 is directly used by the drying module C1 without phase change of the CO2.

[0124] Recycled CO2 means CO2 from a CO2 feed from a CO2 source such as bottled and liquefied CO2.

[0125] In practice, the CO 2 supply means 3 consist of at least one CO 2 injection system from CO 2 coming from the distribution system D1 to the heating means 2.

[0126] The drying module C1 further comprises heating means 2, connected to the CO2 supply means 3 on the one hand, and to the drying chamber 1 on the other hand by an inlet conduit 206a.

[0127] In practice, the heating means 2 are of the immersion heater type and more particularly of the “in-line electric heater” type.

[0128] For example, the immersion heater has a power of 90 kW, and comprises an inlet through which the gases to be heated enter, an open cylindrical or quasi-cylindrical steel conduit, into which an immersion heater is inserted, and finally a second outlet opening for the gases thus heated. The immersion heater also comprises a thermostat for regulating the temperature of the immersion heater.

[0129] According to a first embodiment, the drying means 1 consist of a plurality of drying modules C1, connected to heating means 2 common to several drying modules C1.

[0130] According to an alternative embodiment, the drying means 1 consist of a plurality of drying modules C1, each connected to individual heating means 2.

[0131] The inlet conduit 206a comprises a solenoid valve 702 configured to control the injection of the CO2 gas mixture into the drying chamber 1, as well as gas circulation means 4.

[0132] In practice, the gas circulation means 4 of the inlet duct 206a comprise at least one fan 41 capable of operating bilaterally in two directions of circulation of the gas mixture, either towards the drying chamber 1, and from the drying chamber 1.

[0133] Alternatively, the inlet duct 206a comprises at least two ducts connected to the drying chamber 1, each duct comprising at least one fan 41. These fans 41 are configured to each operate in one direction of circulation, i.e. at least one fan towards the drying chamber 1 and one fan from the drying chamber in the inlet duct 206a.

[0134] The heating means 2 are also connected to an outlet duct 206b connecting an outlet end of the drying chamber 1 to said heating means 2, and forming a closed-loop circulation duct of the CO 2 gas mixture.

[0135] The outlet conduit 206b comprises a solenoid valve 706 configured to control the discharge of the CO2 gas mixture into the drying chamber 1, as well as gas circulation means 4.

[0136] In practice, the gas circulation means 4 of the outlet duct 206b comprise at least one fan 42 capable of operating bilaterally in two directions of circulation of the gas mixture, either towards the drying chamber 1, and from the drying chamber 1.

[0137] Alternatively, the outlet duct 206b comprises at least two ducts connected to the drying chamber 1, each duct comprising at least one fan 42. These fans 42 are configured to each operate in one direction of circulation, i.e. at least one fan towards the drying chamber 1 and one fan from the drying chamber towards the heating means 2.

[0138] By way of non-limiting example, the circulation means 4 of the fan type 41, 42, are of the medium pressure, single-intake centrifugal fan type with a duct and turbine made of sheet steel, said fan comprising a turbine with forward-inclined blades made of galvanized sheet steel, the fan 51 being capable of withstanding a maximum temperature of the air or CO 2 to be transported of -20°C to 250°C.

[0139] The circulation means 4 of the inlet duct 206a in combination with the circulation means 4 of the outlet duct 206b form a flow inversion module capable of allowing the circulation of the CO2 gas mixture from the heating means 2 to the drying chamber 1 in a first operating direction and from the drying chamber 1 to the heating means 2 in a second operating direction, and thus forcing the circulation of the CO2 gas mixture in a closed circuit, through the drying chamber 1 in two circulation directions.

[0140] Advantageously, the alternating circulation of the CO 2 in the inlet duct 206a and outlet duct 206b in two circulation directions makes it possible to circulate the CO 2 longitudinally in the direction of the length of the drying chamber 1 with an injection and an extraction advantageously positioned at the ends of the drying chamber 1 and thus maintain a uniformity of the temperature of the gas mixture in the drying chamber 1 and thus allow drying of the wood and uniform treatment of the CO 2 in the wood.

[0141] The Applicant observed that the use of the flow inversion module and more particularly the circulation of CO2 longitudinally in the drying chamber 1 in an alternative manner makes it possible to limit the presence of water in the liquid state in the drying chamber 1, and thus makes the use of an inclined drying chamber and a swan-neck type elimination system optional for eliminating water in liquid form which may accumulate at the base of the drying chamber 1.

[0142] Furthermore, such uniformity of drying makes it possible to obtain a tangential shrinkage of less than 5% and a radial shrinkage of less than 4%, unlike an average standard shrinkage of around 10 to 15% with conventional drying methods. The invention also makes it possible to greatly limit the deformation of the square-edged timbers and, more particularly, prevents the knots in the wood from deforming during drying. This reduced deformation of the wood during drying could represent a material saving of up to 20% depending on the applications.

[0143] In practice, the fans 41, 42 of the inlet duct 206a and the outlet duct 206b are coupled to frequency variators which advantageously make it possible to reduce the rotation speed as a function of the wood species to be dried, and therefore the flow rate of the circulating gas mixture as a function of the humidity level of the wood and the temperature of the circulating gas mixture and thus optimize the drying uniformity.

[0144] The outlet conduit 206b further comprises a bypass for sampling the circulating gas mixture 45 and integrating CO 2 / CH 4 measuring means 56, configured to measure the proportion of CO 2 relative to the total volume of gas in circulation and the proportion of CH 4 circulating during the drying phase of the drying module C1 in CO 2 , and thus verify the CO 2 saturation in the entire circuit of the drying module C1.

[0145] Advantageously, monitoring the CO 2 / CH 4 of the gas mixture during drying makes it possible to record the evolution of the concentration of the different compounds in the circulating gas mixture and thus allow the operation of the drying module 1 to be adjusted, but also to ensure the safety of the drying module C1 in the event of a drastic increase in the quantity of CH 4 .

[0146] In practice, if the quantity of CH 4 in the gas mixture circulating during drying is greater than 3.5%, the drying module C1 C2 is immediately drained.

[0147] The outlet conduit 206b further comprises metrological means 5 configured to measure parameters belonging to the group formed by flow rate of the injected circulating CO2 gas mixture, temperature of the injected circulating CO2 gas mixture, and hygrometry of the circulating gas mixture.

[0148] According to one embodiment, the outlet duct 206b comprises at least one probe for measuring the temperature and the circulating flow rate 51.

[0149] By way of non-limiting example, the outlet conduit 206b comprises at least one probe for measuring the temperature and the circulating flow rate 51 arranged upstream and one probe for measuring the temperature and the circulating flow rate 51 arranged downstream of the CO 2 recycling means 600.

[0150] According to one embodiment, the outlet duct 206b comprises at least one temperature and humidity measuring probe 53.

[0151] By way of non-limiting example, the outlet duct 206b comprises at least one temperature and humidity measuring probe 53 arranged upstream and one temperature and humidity measuring probe 53 arranged downstream of CO2 recycling means 600.

[0152] In practice, the outlet duct 206b comprises at least one temperature and humidity measuring probe 53 arranged upstream and one temperature and humidity measuring probe 53 arranged downstream of CO 2 recycling means 600, and at least one temperature and circulating flow rate measuring probe 51 arranged upstream and one temperature and circulating flow rate measuring probe 51 arranged downstream of CO 2 recycling means 600.

[0153] Advantageously, such an arrangement makes it possible to monitor the composition of the circulating gas mixture but also the activity of the CO2 recycling means 600 as well as their modulation.

[0154] The drying module C1 further comprises CO 2 recycling means 600 arranged at the outlet duct 206b allowing the separation of the water vapor and the gaseous CO 2 present in the atmosphere extracted from the chamber 1 during drying, in order to be able to eliminate the water while recovering the CO 2 in order to be stored, or to be directly reused in the installation.

[0155] By way of non-limiting example, condensation recycling means 600 are used, reducing the temperature of the binary water vapor / CO2 gas mixture extracted from the drying chamber 1 to a chosen temperature, allowing the condensation of the water in the gas mixture, which is then recovered by gravity in liquid form and eliminated. In practice, the recycling means 600 allow the drying of the internal atmosphere extracted from the drying chamber 1 via thermal condensation of the water vapor by cooling, on at least one heat exchanger equipped with at least one cold battery, it will be possible to advantageously place several cold batteries configured in series to increase the dehumidification capacity of each drying module C1. The system therefore allows the reinjection of the dehydrated atmosphere into the drying chamber 1.

[0156] In practice, each heat exchanger includes at least one EV evaporator and at least one CO condenser.

[0157] According to one embodiment of the invention, the heat exchanger of the recycling means 600 is only active when the hygrometry of the circulating gas mixture is between two threshold values.

[0158] In practice, the heat exchanger of the CO2 recycling means 600 is only active during the drying phase, and when the measured hygrometry of the circulating gas mixture is between a maximum threshold value and a minimum threshold value.

[0159] For example, the humidity threshold values ​​in drying chamber 1 are 20% for the minimum threshold and 100% for the maximum threshold.

[0160] According to one embodiment of the invention, the recycling means 600 comprise a heat exchanger type system comprising at least two cold batteries, configured in series to gradually extract the water from the gas mixture, each cold battery being capable of extracting a chosen percentage of the water from said gas mixture.

[0161] Advantageously, a series of cold batteries makes it possible to limit the humidity in the drying chamber 1, and thus make it possible to limit the duration of the drying cycle, making it possible to resolve the performance problem of a conventional heat exchanger when the humidity is higher than the critical operating value, and thus to reduce the duration of each cycle, causing the operation of each drying module C1 over a shorter period and limiting the associated energy expenditure.

[0162] According to one embodiment, the recycling means 600 further comprise a discharge outlet configured to discharge the condensed water or condensates, said discharge outlet incorporating a water flow meter 57.

[0163] The water flow meter 57 is configured to record the discharge rate of the water to be removed, and thus makes it possible to correlate the quantity of water removed with the difference between the initial and final humidity level of the wood for a drying cycle.

[0164] In practice, the heat exchanger of the recycling means 600 also allows the dehydrated gas mixture to be reheated before reinjection into said installation.

[0165] According to a particular embodiment of the invention, the heat exchanger is configured to reheat the cooled gas mixture after extraction of the water to a temperature differential of 50°C with the temperature of the circulating gas mixture, for reinjection into the drying chamber 1.

[0166] For example, maintaining a humidity level in the drying chamber 1 below a chosen value makes it possible to shorten the drying cycle for which the means 213a, 213b for circulating CO 2 in the drying module(s) C1 can represent 5 to 20% of the energy expenditure.

[0167] Advantageously, the recycling means 600 make it possible to control the hygrometry of the gas mixture and thus control the quality of the drying of the wood, thus optimizing the drying process and the quality of the material obtained, while limiting the energy expenditure and maintaining a low temperature difference between the CO 2 leaving the heating means 2 and coming from the recirculation module 206c.

[0168] In practice, the CO2 gas recovered by the recycling means 600 can be stored in storage means, or directly reinjected into the drying chamber 1.

[0169] According to a particular embodiment of the invention, the drying chamber 1 comprises at least one evacuation circuit, which is followed by a so-called “breathing” conduit comprising at least one breathing solenoid valve 704, 705 of the drying chamber 1, which allows the injection of air coming from outside the installation into the drying chamber 1 and the evacuation of the gas mixture contained in said drying chamber 1.

[0170] The evacuation circuit further comprises circulation means 4 of the fan type 43, as well as CO 2 / CH 4 measuring means 56, configured to measure the proportion of CO 2 relative to the total volume of gas in circulation and the proportion of CH 4 circulating during the phase of filling the drying module C1 with CO 2 , and thus verify the CO 2 saturation in the entire circuit of the drying module C1 during said filling, and configured to allow the emptying of the drying chamber 1.

[0171] According to one embodiment, the drying module C1 further comprises an additional discharge outlet connected to the drying chamber 1 and comprising at least one fan 44 followed by an outlet solenoid valve 703 as well as a sensor for measuring the circulating gas flow rate and temperature 51, and configured to allow the measurement of the flow rate and temperature of the gas mixture during the emptying of the drying chamber 1.

[0172] By way of non-limiting example, the circulation means 4 of the fan type 43, 44, of the additional evacuation outlet and of the evacuation circuit are of the medium pressure and single suction centrifugal fan type with duct and turbine made of sheet steel, said fan comprising a turbine with forward inclined blades made of galvanized sheet steel, the fan 51 being capable of withstanding a maximum temperature of the air or CO 2 to be transported of -20°C to 250°C.

[0173] The drying module C1 also integrates a computer control system 6 comprising an application programming interface API. The application programming interface allows, on the one hand, the management of the sending of instructions to each of the components of the installation, and on the other hand to integrate the data received by the various metrological means 5, in order to adjust the instructions sent to the components of the installation.

[0174] In practice, the C1 drying module also includes an energy consumption meter.

[0175] The computer control system 6 is configured to control the supply 3, circulation 4, heating 2, and recycling 600 means according to appropriate programs, setpoint values ​​and drying times depending on the quality of the desired dried wood, and processing means to measure, compare and readjust the operating parameters to the setpoint values ​​in the event of a deviation.

[0176] The computer control system 6 also allows the monitoring, measurement and recording of all the metrological values ​​measured in a table (including energy consumption), as well as emergency procedures (stop without resuming drying or with resuming drying).

[0177] In practice, the control computer system 6 is equipped with an application programming interface API capable of implementing a drying process.

[0178] In practice, during drying, if the pressure measuring probe 55 in the drying module C1 detects an internal pressure lower than 15% of the atmospheric pressure for a chosen duration, the computer control system 6 opens the solenoid valve 701 of the CO 2 supply means 3 so as to inject new CO 2. The drying module C1 further comprises at least one ambient sensor arranged outside of said module, and capable of recording the temperature and humidity in the environment surrounding said drying module.

[0179] According to one embodiment of the invention, the computer control system 6 is further configured to enable the control of the dehumidification of the CO 2 via the activation of the recycling means 600 as a function of a minimum (20%) and maximum (100%) value of the hygrometry of the atmosphere of the drying chamber 1. This phase is continuous regardless of the initial hygrometry of the wood.

Claims

1. Method for thermal drying of wood performed by means of a drying installation, comprising at least one drying chamber (1), wherein the method comprises the steps of: - Acquiring (S1) metrological data and parameters of the wood to be dried by measurement by means of metrological means (5); - Activating (S2) CO2 feeding means (3) configured to saturate the drying chamber (1) with CO2 and disposing of a circulating gaseous mixture; - Verifying (S21) that the CO2 saturation in the circulating gaseous mixture is sufficient to start a drying cycle by verification via CO2 / CH4 measuring means (56) at an outlet line; - Activating (S3) heating means (2) to adjust the moisture of the wood by heating if a sufficient measured CO2 saturation is reached; - If the moisture of the wood is above 30 %, heating (S32), with a temperature limit according to a first desired temperature T1, according to a selected temperature drop G1 in order to extract the free water of the wood to be dried and to activate circulation means (4); - If the moisture of the wood is below 30 %, heating (S4), with a temperature limit according to a first desired temperature T2, according to a selected temperature drop G2 in order to extract the bound water of the wood to be dried and to activate the circulation means (4); the heating (S4) furthermore comprising the following sub-steps: - stabilizing the temperature of the CO2 circulating in the drying chamber (1) according to a first phase (S41) if a moisture of smaller than or equal to 30 % is measured, activating (S42) the recirculation means (600), then increasing, according to a second phase (S44), the temperature of the CO2 circulating in the drying chamber (1) until the measured moisture of the wood reaches a selected intermediate target value Hi, the heating means (2) being activated such that reheating is effected with a limit temperature defined by a second desired temperature T2 of 120 °C according to a selected temperature drop G2, and in response to the specific drying profile of the wood to be dried, allowing to extract the bound water of the wood to be dried; - Maintaining the moisture of the wood to be dried (S5) by deactivating (S51) the recirculation means (600) and modulating (S52) the activity of the heating means (2) for reducing the temperature of the heating chamber (1) according to a first phase up to a third desired temperature T3 of stabilisation selected according to a temperature drop G3 when the mean moisture of the wood measured via the moisture measuring means (54) of the wood reaches the selected intermediate target value (S53), except if one of the measured moisture values of the wood is above Hi+A %, A being a selected value, wherein the desired temperature T3 is maintained during a selected period of time D until the measured moisture value of the wood, that initially was above Hi+A %, is stable and is within a range of values smaller than Hi+A % (S54); - Deactivating (S6) the heating means (2) to reduce the temperature of the heating chamber (1) according to a second phase (S61) when the measured mean moisture of the wood reaches the final target value of moisture Hc.

2. Method according to claim 1, characterized in that the moisture value Hi+A % has a value A between 1 % and 2.5 %.

3. Method according to claim 1 or 2, characterized in that the step of acquiring metrological data and parameters of the wood to be dried (S1) comprises the following sub-steps: - Filling the drying chamber (1) with the wood to be dried (S11); - Measuring the temperature of the wood at the surface and in the core (S12); - Measuring the moisture of the wood to be dried (S13); - Measuring (S14) the temperature of the drying chamber (1); - Measuring (S15) the moisture of the drying chamber (1); and - Measuring the weight of the wood to be dried (S16).

4. Method according to any one of claims 1 to 3, characterized in that the step of activating (S3) heating means (2) for adjusting the moisture of the wood comprises a sub-step (S31) of monitoring the moisture of the wood in real time, and in that the heating step (S4) comprises a sub-step (S43) of monitoring the moisture of the wood in real time.

5. Method according to any one of claims 1 to 4, characterized in that the step of activating (S42) recirculation means (600) comprises a sub-step of performing a sequence of activations / deactivations of a flow inversion module according to a selected frequency F1.

6. Method according to claim 5, characterized in that the step of reducing the temperature of the heating chamber (1) according to a second phase (S61) furthermore comprises a sub-step of stopping (S61) the flow inversion module at the same time as the recirculation means (600).

7. Method according to any one of claims 1 to 6, characterized in that it furthermore comprises a step of evacuating (S7) CO2 which is configured to desaturate the drying chamber (1) of CO2 to extract the dried wood.

8. Method according to any one of claims 1 to 7, characterized in that the heating step (S32) comprises a temperature limit according to a first desired temperature T1 between 50 °C and 60 °C according to a selected temperature drop G1 of 2 °C / hour.

9. Method according to any one of claims 1 to 8, characterized in that the step of increasing the temperature (S44) comprises a temperature limit defined according to a second desired temperature T2 smaller than or equal to 120 °C according to a selected temperature drop G2 between 1 °C / hour and 3 °C / hour.

10. Method according to any one of claims 1 to 9, characterized in that the step of reducing the temperature (S52) of the heating chamber (1) according to a first phase (S52) comprises a temperature limit according to a first desired temperature T3 between 50 °C and 100 °C according to a selected temperature drop G3 of 2 °C / hour.

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