Thermal drying process for wood under 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); -Adjusting the moisture content of the wood (S2) by heating-saturating (S3) the drying chamber (1) with CO2 -heating (S4) the CO2 circulating in the drying chamber (1) according to a first phase, then heating 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 of stabilization -Decreasing according to a second phase (S6) the temperature of the heating chamber (1) to the setpoint temperature T1 as long as the measured moisture content of the wood is greater than the final target moisture content value Hc.

Description

Title of the invention: [Process for thermal drying of wood under CO2 atmosphere]

[0001] The present invention relates to a method for thermally drying wood under a CO2 atmosphere, in particular but not limited to the industrial drying of timber, round wood and / or logs. It also relates to an installation for implementing said drying method and the product obtained.

[0002] Here, the term "timber, round timber and logs" means wood intended for use in secondary wood processing industries, in particular for industry, construction, carpentry, or for urban, industrial, collective and domestic exterior and interior design.

[0003] Although various solutions for drying timber, round wood and / or logs exist, the known solutions rarely allow for industrial application associated with a low energy balance. Indeed, the known solutions are generally used on a small scale, due to the problem of consuming a minimum of energy while obtaining wood with a low percentage of water.

[0004] Another disadvantage of existing solutions is the duration of the drying process, which often represents a significant duration of several days, or even several weeks, a factor limiting effective use for industrial use.

[0005] 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 low residual moisture in the dried wood and ensuring the integrity of the internal structure of the wood during and after drying.

[0006] Current drying processes and installations also have the disadvantage of only sequestering a very small quantity of CO2 in the wood to be dried.

[0007] The present invention overcomes these drawbacks.

[0008] It relates to a process for thermally drying wood implemented using a drying installation comprising at least one drying chamber.

[0009] According to a general definition of the invention, the drying process comprises the following steps: -Acquisition of metrological data and parameters of the wood to be dried; -Adjust the hygrometry of the wood by heating up to a first set temperature Tl according to a chosen temperature gradient G1 if the hygrometry of the wood is greater than 30%, in order to extract the free water from the wood to be dried; -If the measured wood humidity is less than or equal to 30%, saturate the drying chamber with CO2 even if the set temperature Tl is not reached; - heating the CO2 circulating in the drying chamber up to the set temperature Tl in the drying chamber according to a first phase, then heating according to a second phase the CO2 circulating in the drying chamber until the measured hygrometry of the wood reaches a chosen intermediate target value Hi, the heating being carried out up to a second set temperature T2 limit of 10 to 120°C according to a chosen temperature gradient G2 depending on the specific drying profile of the wood to be dried making it possible to extract the specific bound water from the wood to be dried; -Decrease in a first phase the temperature of the heating chamber to a third setpoint temperature T3 chosen for stabilization, when the measured hygrometry of the wood reaches the chosen intermediate target value Hi, said setpoint temperature T3 being maintained for a chosen period of time until the measured hygrometry is stable and within a chosen range of values ​​HX; and -Decrease the temperature of the heating chamber in a second phase to the set temperature Tl as long as the measured hygrometry of the wood is higher than the final target hygrometry value Hc, if the measured hygrometry of the wood is lower than or equal to the final target hygrometry value Hc, maintain the measured temperature equal for a chosen stabilization period.

[0010] By way of non-limiting example, the wood belongs to the group formed by round wood, logs, timber, wood shaped into boards.

[0011] In practice, the step of acquiring metrological data and parameters of the wood to be dried includes the following sub-steps: -Fill the drying chamber with the object to be dried; -Measure the temperature of the wood on the surface and at the core; -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.

[0012] The step of adjusting the wood hygrometry includes the following sub-steps: -Measuring the wood hygrometry in real time; - If the measured humidity is greater than 30%, increase the temperature of the drying tube from ambient temperature until the measured humidity is less than or equal to 30%, the temperature increase being carried out according to a chosen temperature gradient Gl, and limited to a first set temperature Tl; and -If the measured humidity is less than or equal to 30%, saturate the drying chamber with CO2.

[0013] the CO2 saturation step comprises the following sub-steps: -Check that the set temperature Tl is reached in the drying chamber; -Inject CO2 from CO2 supply means; -Measure the partial pressure of CO2 using measuring means, placed at the outlet of the CO2 supply means and at the outlet of the installation; -Compare partial pressure of CO2 at the inlet and outlet; and - Stop CO2 injection and activate CO2 recycling means when the CO2 partial pressure ratio at the inlet / outlet is greater than or equal to a chosen target R value.

[0014] the reheating step comprises the following sub-steps: - Increase the temperature of the drying chamber according to a chosen temperature gradient G2, with a set temperature T2 as the limit temperature; - Activate the activation / deactivation of CO2 flow reversal means according to a chosen frequency Fl configured to reverse the direction of the CO2 flow in the drying chamber; -Activate means of dehumidification of the drying chamber; -Measure the wood's humidity in real time; and -if the measured hygrometry of the wood is less than or equal to an intermediate hygrometry value Hi of the wood, stabilize the temperature of the drying chamber even if the set temperature T2 is not reached.

[0015] the step of decreasing the temperature according to a first phase comprises the following sub-steps: - when the measured hygrometry of the wood reaches the chosen intermediate target value Hi, reduce the temperature in the drying chamber to a chosen stabilization setpoint temperature T3; - Stabilize the measured hygrometry of the wood to be dried within a range of target hygrometry values ​​HX; and - when the target humidity range HX is reached, stabilize the wood temperature reached for a chosen duration D, even if the set temperature T3 is not reached.

[0016] the step of decreasing the temperature according to a second phase comprises the following sub-steps: - Deactivate CO2 flow reversal means and CO2 recycling means; - if the measured hygrometry of the wood is higher than the final target value Hc, reduce the temperature of the drying chamber to the set temperature Tl according to a chosen gradient G3 by progressive deactivation of heating means; -if the measured hygrometry of the wood is less than or equal to the final target value Hc, stabilize the temperature measured in the drying chamber even if the set temperature Tl is not reached.

[0017] 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.

[0018] Thus, the drying process makes it possible to obtain rapid drying of the wood, with a low deformation rate, less energy-intensive, while allowing adaptability to any type of wood thanks to the monitoring, control and retro-adjustment steps.

[0019] The drying process uses a generation of CO2 heat-transfer gas flow injected into the drying chamber of the wood load at atmospheric pressure, followed by closed-loop heating, with a system for monitoring numerous physical measurements including recording of pressure, hygrometry, temperature, mass of the drying chamber at different points and connected to a feedback loop allowing adjustment of the operation of the installation to obtain the optimal conditions for drying the wood.

[0020] Such a drying process has the advantage of being short in time, reproducible on a large scale for industrial use, energy efficient and allows a final hygrometry of the dried wood to be obtained between 0% and 22%.

[0021] Advantageously, the drying method / installation 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%.

[0022] The Applicant has also observed that the drying process / installation according to the invention makes it possible to obtain dried wood with lower moisture uptake, a reduction in the colouring of the dried wood, as well as the limitation / absence of the appearance of cracks during drying.

[0023] Other advantages and characteristics of the invention will appear on examining the description and the drawings in which:

[0024] [Fig.l] schematically represents a wood drying installation in accordance with the invention;

[0025] [Fig.2] represents in isolation two embodiments of the CO2 supply means of the installation according to the invention;

[0026] [Fig.3] represents the drying chamber of the installation according to the invention;

[0027] [Fig.4] represents an internal immersion heater module of the heating system in accordance with the invention;

[0028] [Fig.5] represents a single-suction fan of the heating system according to the invention;

[0029] [Fig.6] schematically represents the general stages of the drying process according to the invention;

[0030] [Fig.7] schematically represents the sub-steps allowing Filling of the chamber / sensor data acquisition;

[0031] [Fig.8] schematically represents the sub-steps allowing the elimination of free water from the wood to be dried in accordance with the invention;

[0032] [Fig.9] schematically represents the sub-steps allowing the injection of CO2 saturation of the drying chamber according to the invention;

[0033] [Fig. 10] schematically represents the sub-steps relating to the drying step under CO2 in accordance with the invention;

[0034] [Fig. 11] schematically represents the sub-steps relating to the CO2 cooling step in accordance with the invention; and

[0035] [Fig. 12] schematically represents the sub-steps relating to the step of evacuating CO2 from the drying chamber according to the invention.

[0036] With reference to Figures 1 to 5, the drying installation according to the invention comprises 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, CO2 supply means 3, gas circulation means 4 allow the renewal of the atmosphere inside the drying chamber 1, and to extract from the drying chamber and recycle the heat transfer gaseous fluid comprising CO2 and water in the form of steam, several metrology measurement units forming metrology means 5, and finally a computer control system 6 equipped with an application programming interface API.

[0037] The installation has a drying chamber 1 composed of one or more hollow cylindrical drying tubes allowing the introduction of the round wood to be dried.

[0038] By way of non-limiting example, the drying chamber 1 comprises a closed tube of 2,000 liters insulated with internal atmospheric recirculation. For example, the reactor is constituted by: - a 5.5 meter long steel tube, closed by two steel plates (not shown) 700 mm in diameter and 3 mm thick, one bolted to flanges with 1 inspection tap closed by a 220 mm diameter steel plate bolted to the flange, and the other equipped with a hinged door bolted to the flange on articulated studs, with an inspection tap, and finally closed by a tap / valve; - a roller railway (not shown) consisting of a series of ten rollers 4 cm in diameter and 15 cm in length spaced every 70 cm and fixed by a bolted plate; and - a threaded end closed by a cap bolt, for the installation of the sensors, at the ends and in the center, fixed on the axis of the upper generator of the chamber.

[0039] According to one embodiment, the drying chamber 1 according to the invention comprises a safety valve 103 arranged in the medial position of the 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.

[0040] In practice, the critical pressure at the valve can be 1.5 bar.

[0041] According to a particular embodiment of the invention, the drying chamber has an inclination of 1%, having a drain solenoid valve with a swan neck, which allows the evacuation of water in liquid form during drying.

[0042] The drying installation further comprises a heating system 2, equipped with a conduit comprising a gas circulation inlet from CO2 supply means 3, the conduit then leading to first circulation means or recirculation fan comprising a sheath 203a, a turbine 203b, as well as an inlet 203c and an outlet 203d allowing the circulation of the gas mixture towards the chamber 1 in a direction F in the heating system 2, from a heater 205 or reheating cell, said recirculation fan allowing the evacuation of the atmosphere thus heated towards an injection module (206a) giving into the drying chamber 1.

[0043] According to a first alternative embodiment, the drying chamber 1 is made up of a plurality of drying tubes, connected to a heating system 2 common to the drying tubes.

[0044] According to a second alternative embodiment, the drying chamber 1 consists of a plurality of drying tubes, connected to a plurality of heating systems 2.

[0045] In practice, the heater 205 is of the immersion heater type sold under the reference “electric heater 237537 with immersion tube” by the company VULCANIC© with a power of 7 W and comprises an inlet 206 through which the gases to be heated enter the heater 205, an open cylindrical conduit 208 made of steel, in which an immersion heater 209 is inserted and fixed on one of the openings, and finally a second outlet opening 207 for the gases thus heated. Downstream of the conduit 208 before the outlet orifice 207 are arranged a thermostat 210 allowing the regulation of the temperature of the immersion heater 209 as well as a temperature measuring probe 211.

[0046] By way of non-limiting example, the heating system 2 comprises a spiral duct circuit, made of galvanized steel sheet, approximately 8 m long, supplying a heating extraction box equipped with a fan 203 of the helical type with a low-pressure remote motor of 9.5 NmVmn, as well as a thermostatically controlled heater 205 of 2 x 3.5 kW, the whole insulated by a 20 cm thick glass wool envelope.

[0047] The drying chamber further comprises metrology means 5, allowing the measurement of various physical characteristics. The instruments included in drying chamber 1 are, for example:

[0048] - at least two individualized scales 503a / 503b / 503c / 503d, distributed under the chamber and allowing the monitoring of the mass of the drying tube, and thus knowing the mass of the load of wood being dried, indicating the progress of the drying;

[0049] - at least two individual temperature transmitters placed on the wood, arranged in the center of the log 501a / 501b / 501c as well as at the periphery of the latter 502a / 502b / 502c, thus allowing precise monitoring in real time of the temperature at several points of the chamber 1, as well as in the load of wood, in order to avoid damaging the log during drying and to optimize drying by fine regulation;

[0050] - three individual hygrometer / thermometer assemblies arranged upstream 504a, at center 504b, and downstream 504c in drying chamber 1;

[0051] - a pressure transmitter assembly 506a and pressure gauge 506b allowing recording the pressure inside the drying chamber 1.

[0052] Each metrological measurement includes a set value or a group of set values ​​to be respected, specific to each type of wood.

[0053] The heating installation according to the invention then comprises a gas mixture circulation circuit having circulation means 213a, 213b for forcing the circulation of the gas mixture in a closed circuit, through the drying chamber 1.

[0054] By way of non-limiting example, the circulation means 213a, 213b comprise a first fan 213a allowing the circulation of the gas mixture towards the drying chamber 1, and a second fan 213b allowing the circulation of the gas mixture outside the drying chamber 1 towards the gas mixture circulation circuit.

[0055] In practice, first circulation means 213a may be of the medium pressure, single-suction centrifugal fan type with duct 203b and turbine 203a made of sheet steel, said fan comprising a turbine 203a with forward-inclined blades made of galvanized sheet steel, the fan 203 being capable of withstanding a maximum temperature of the air to be transported from -20°C to 250°C.

[0056] The first fan 213a is integrated into an injection module 206a, and arranged at the outlet of the heating means 2.

[0057] The injection module 206a is configured to inject the gas mixture into the drying chamber 1, and is connected to CO2 supply means 3 and to the heating means 2.

[0058] Said injection module 206a comprises the first fan 213a, a circulation duct 204 connected to the first inlet 201 of the drying chamber 1 and to the second inlet 202 of the drying chamber 1, each inlet 201, 202 respectively comprising a solenoid valve EV3, EV4 configured to alternately allow the circulation of CO2 in the drying chamber 1, when one solenoid valve EV3, EV4 is in the closed position, the other solenoid valve EV3, EV4 is in the open position, thus allowing the injection of the gas mixture at each end of the drying chamber 1.

[0059] The second fan 213b is integrated into an evacuation module 206a, and arranged at the outlet of the heating means 2.

[0060] The evacuation module 206b is arranged at the outlet of the heating chamber 1, and connected to the first outlet 204 and to the second outlet 205 of the drying chamber 1, each outlet 204, 205 respectively comprising a solenoid valve EV2, EV1 configured to alternately allow the circulation of CO2 towards the second fan 203b connected to an outlet 701 of the drying installation, and configured to allow the circulation of the gas mixture at the outlet of the drying chamber 1 so that when one solenoid valve EV2, EV1 is in the closed position, the other solenoid valve EV2, EV1 is in the open position, the circulation of the gas mixture then taking place alternately at each end of the drying chamber 1 according to a frequency chosen during the drying of the wood.

[0061] The injection module 206a and the evacuation module 206b form a flow inversion module 206 configured to allow the circulation of CO2 in a first circulation direction in the drying chamber 1 between a first inlet 201 of the drying chamber 1 and a first outlet 204 of the drying chamber 1, and in a second circulation direction between a second inlet 202 of the drying chamber 1 and a second outlet 205 of the drying chamber 1, and capable of uniformizing the thermal distribution in the drying chamber 1.

[0062] Indeed, the solenoid valves EV1, EV2, EV3, EV4 of the injection module 206a and of the evacuation module 206b are configured to pass from an open position to a closed position alternately, so that when a solenoid valve EV3, EV4 is in the open position in the injection module 206a, the solenoid valve EV1, EV2 of the evacuation module 206b in the open position is arranged at the other end of the drying chamber 1.

[0063] Advantageously, the alternating circulation of CO2 in the injection module 206a and the evacuation module 206b makes it possible to maintain uniformity of the temperature of the gas mixture in the drying chamber 1 and thus allow drying of the wood and uniform sequestration of the CO2 in the wood.

[0064] The Applicant has observed that the use of the flow inversion module 206 also makes it possible to limit the presence of water in the liquid state in the drying chamber 1, and thus make the use of an inclined chamber and a system optional. gooseneck type disposal to remove liquid water that may accumulate at the base of the drying chamber 1.

[0065] Furthermore, such drying uniformity makes it possible to obtain a shrinkage of less than 5%, unlike a standard shrinkage of 10 to 15% with conventional drying means.

[0066] According to a particular embodiment, the drying installation according to the invention further comprises a recirculation module 206c, arranged between the evacuation module 206b, recycling means 600, and the heating means 2, and comprising a solenoid valve EV5 configured to allow / prevent the recirculation of the dehumidified gas mixture towards the drying chamber 1.

[0067] The recirculation module 206c is configured to allow the reinjection of a gas mixture into the injection module 206a, or the sending of the gas mixture to an outlet 701 of the drying installation.

[0068] Furthermore, the CO2 recycling means 600 allow the separation of the water vapor and the gaseous CO2 present in the atmosphere extracted from the chamber 1 during drying, in order to be able to eliminate the water while recovering the CO2 in order to be stored, or to be directly reused in the installation.

[0069] 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 mixture, which is then recovered by gravity in liquid form and eliminated.

[0070] For example, the recycling means 600 allow the drying of the internal atmosphere extracted from the drying chamber 1 via a thermal condensation installation of the water vapor by cooling, on a cold wall equipped with a heat exchanger. The system therefore allows the reinjection of the dehydrated atmosphere into the drying chamber 3.

[0071] 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.

[0072] 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.

[0073] In practice, the heat exchanger of the recycling means 600 also makes it possible to reheat the dehydrated gas mixture before reinjection via the injection module 206a.

[0074] According to a particular embodiment of the invention, the heat exchanger is configured to reheat the cooled gas mixture after water extraction to a temperature of 50°C for reinjection into the drying chamber 1.

[0075] Advantageously, the recycling means 600 make it possible to control the hygrometry of the gas mixture and thus minimize the environmental variations of the wood to be dried, thus optimizing the drying of the wood and the sequestration of CO2, while limiting the energy expenditure to maintain a low temperature difference between the CO2 leaving the heating means 2 and coming from the recirculation module 206c.

[0076] In practice, the CO2 gas recovered by the recycling means 600 can be stored, or directly reinjected into the drying chamber 1.

[0077] According to a particular embodiment of the invention, the drying chamber 1 comprises an inlet, which is followed by a so-called “breathing” conduit comprising a non-return valve followed by a breathing solenoid valve for the drying chamber 1, which allows the injection of air coming from outside the installation into the drying chamber 1.

[0078] The drying installation according to the invention further comprises an outlet 701 connected to the evacuation module 206b.

[0079] According to a first embodiment of the invention, the outlet 701 is connected to a second drying installation, and has a solenoid valve 700a configured to allow / prevent the circulation of the gas mixture at the outlet, solenoid valve 700a being equipped with a counting device consisting of a pressure gauge / thermometer assembly 302 and volume meter / flow meter 303 configured to measure the quantity of CO2 at the outlet of the installation.

[0080] According to a second embodiment of the invention, the outlet 701 is connected to a recycled CO2 storage installation, and has a solenoid valve 700b configured to allow / prevent the circulation of the gas mixture at the outlet, solenoid valve 700b being equipped with a counting device consisting of a pressure gauge / thermometer assembly 302 and volume meter / flow meter 303 configured to measure the quantity of CO2 at the outlet of the installation.

[0081] According to a third embodiment of the invention, the outlet 701 is connected to a second drying installation, and has a solenoid valve 700a configured to allow / prevent the circulation of the gas mixture at the outlet, solenoid valve 700a being equipped with a counting device consisting of a pressure gauge / thermometer assembly 302 and volume meter / flow meter 303 configured to measure the quantity of CO2 at the outlet of the installation, and connected to a recycled CO2 storage installation, and has a solenoid valve 700b configured to allow / prevent the circulation of the gas mixture at the outlet, solenoid valve 700b ... bitmeter 303 configured to measure the quantity of CO2 at the installation outlet 701.

[0082] In practice, the counting module further comprises means for measuring the partial pressure of CO2 700b, arranged at the outlet (701) of the installation, and configured to record and transmit the partial pressure of CO2 measured in the installation to a computer system (6) for controlling the drying installation.

[0083] The drying installation further comprises CO2 supply means 3, which comprise a source of CO2 belonging to the group formed by biogenic CO2, CO2 of fossil origin.

[0084] According to a first embodiment of the invention, the CO2 supply means 3 have at least one CO2 supply unit 301 comprising two locations for standard "Air-Liquid" type shells, each containing 34 kg of liquid CO2 compressed to 50 bar, and the corresponding expansion device(s), i.e. a gaseous CO2 expansion device consisting of a primary pressure regulator (not shown) allowing the pressure to change from 70 bar to 3 bar (0.5 m3 / h), a secondary flow regulator-regulator allowing the pressure to change from 3 bar to 0.3 bar (5 m3 / h). The supply means 3 then have a cut-off solenoid valve 304 preceded by an atmospheric CO2 metering device 302 / 303, the solenoid valve controlling the supply to a fixed atmospheric pipe 306.

[0085] The CO2 supply means 3 then comprise a gas circulation device 307 making it possible to draw air at ambient temperature towards the heating system 2. The circulation device 307 comprises an air compressor 308 ejecting pressurized air towards a pipe dividing into two, and the first division of which allows the circulation of compressed air towards a pressure reducer 309 which then allows the circulation of air at reduced pressure towards the solenoid valves 101b and 102a, respectively present at the inlet 101 and outlet 102 of the drying chamber 1.A second division of the pipe allows the circulation of compressed air towards a pressure reducer 310 which reduces the pressure of the injected air towards a solenoid valve 311 allowing the control of the quantity of air introduced into the circuit, which then comprises a non-return valve 312 and opening into the atmospheric circulation pipe 306 which joins the conduit 204 of the heating system 2 upstream of the circulation means 213a.

[0086] According to an alternative embodiment of the invention, the atmospheric circulation pipe 306 directly joins at least one injection module 206a connected to the drying chamber 1.

[0087] According to another alternative embodiment, the CO2 supply means 3 comprise at least one so-called “new” CO2 supply module, and one so-called “recycled” CO2 supply module, connected to the drying installation by a connection system (30, 31) to a CO2 source comprising at least one electronic valve (EVC1, EVC2) configured to allow the injection / stopping of CO2 injection into the drying installation.

[0088] New CO2 means CO2 in a pressurized bottle (301).

[0089] Recycled CO2 means CO2 from a CO2 supply from a methanization facility exhaust, an industrial chimney type CO2 supply, and an annex CO2 sequestration wood drying facility.

[0090] According to a non-limiting example, the CO2 supply means (3) belong to the group formed by a CO2 injection system from CO2 in a pressurized bottle (301), a CO2 supply from the evacuation of a methanization installation, a CO2 supply of the industrial chimney type, and a wood drying installation by annexed CO2 sequestration, or a combination of them.

[0091] The CO2 supply means 3 comprise a counting device consisting of a pressure gauge / thermometer 302 and volume meter / flow meter 303 assembly. The injected and decompressed CO2 supply conduit then comprises a non-return valve and finally joins an atmospheric circulation pipe 306 to the heating means 3.

[0092] The counting module further comprises means for measuring the partial pressure of CO2 700a, arranged at the outlet of the CO2 supply means (3) and at the outlet (701) of the installation, and configured to record and transmit the partial pressure of CO2 measured in the installation to a computer system (6) for controlling the drying installation.

[0093] By way of example, the means for measuring the partial pressure of CO2700a,700b comprise a device of the gas chromatograph type 700a, arranged at the outlet of the CO2 supply means, and configured to analyze the composition of the gas mixture at the outlet of said CO2 supply means and thus measure the quantity of CO2 at the inlet of the installation.

[0094] Advantageously, by comparing the quantity of CO2 at the installation inlet and at the outlet 701, it is possible to measure the CO2 saturation rate circulating in said installation and thus guarantee a minimum saturation rate to optimize the drying environment in the drying chamber 1.

[0095] The drying installation furthermore 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 different metrology means 5, in order to adjust the instructions sent to the components of the installation.

[0096] The computer control system 6 is configured to control the supply means 3, circulation means 213a, 213b, reheating means 2, and recycling means 600. according to appropriate programs, setpoints 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 setpoints in the event of a deviation.

[0097] In practice, the computer control system 6 equipped with an application programming interface API is configured to: -Acquire metrological data and parameters of the wood to be dried by measuring metrological means 5; -Activate the heating means 2 to adjust the hygrometry of the wood by heating up to a first set temperature Tl according to a chosen temperature gradient G1 if the hygrometry of the wood is greater than 30%, in order to extract the free water from the wood to be dried and activate the circulating means 203a, 203b; -If the measured wood humidity is less than or equal to 30%, activate the CO2 supply means 3 configured to saturate the drying chamber 1 with CO2 even if the set temperature Tl is not reached; - stabilize the temperature of the CO2 circulating in the drying chamber 1 according to a first phase up to the set temperature T1, activate the recycling means 600 then increase according to a second phase the temperature of the CO2 circulating in the drying chamber 1 until the measured hygrometry of the wood reaches a chosen intermediate target value Hi, the heating means 2 being activated so that the reheating is carried out up to a second set temperature T2 limit 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; - Deactivate the recycling means 600 and modulate the activity of the drying means 2 to reduce the temperature of the heating chamber 1 according to a first phase, down to a third chosen stabilization setpoint temperature T3, when the measured hygrometry of the wood reaches the chosen intermediate target value Hi, said setpoint temperature T3 being maintained for a chosen period of time until the measured hygrometry is stable and included in a chosen range of values ​​HX; and - Deactivate the heating means 2, to reduce the temperature of the heating chamber 1 according to a second phase, down to the set temperature Tl as long as the measured hygrometry of the wood is higher than the final target hygrometry value Hc, if the measured hygrometry of the wood is lower than or equal to the final target hygrometry value Hc, reactivate the heating means 2 so as to keep the measured temperature stable for a chosen stabilization period.

[0098] With reference to Figures 6 to 12, the CO2 drying and sequestration installation thus described with reference to figures 1 to 5 implements a process for drying and sequestering CO2 in the wood comprising a succession of steps according to the following sequence:

[0099] According to a first step of acquiring the metrological data and parameters of the wood to be dried SI, measure the different parametric data to calibrate the setpoint values ​​to be applied, via metrology means 5.

[0100] In practice, the step of acquiring metrological data and parameters of the wood to be dried SI includes the following sub-steps: -Fill the drying chamber with the object to be dried SI 1; -Measure the surface and core temperature of the wood S12; -Measure the hygrometry of the wood to be dried S13; -Measure the temperature of the drying chamber S14; -Measure the humidity of the S15 drying chamber; and -Measure the weight of the wood to be dried S16.

[0101] For example, the wood to be dried is inserted into the drying chamber 1, then the drying chamber is hermetically sealed.

[0102] In practice, the difference between the surface and core temperature of the wood must be less than or equal to 20°C.

[0103] Furthermore, the sub-step of measuring the weight of the wood to be dried S16 allows the calculation of the loss of mass relating to the implementation of the drying and thus quantifies the quantity of water extracted by taking into account the quantity of CO2 sequestered.

[0104] As a non-limiting example, the maximum quantity of CO2 sequestered is 250kg / m3 of wood.

[0105] According to a second step of adjusting the hygrometry of the wood S2, capable of eliminating free water from the wood, if the hygrometry of the wood is greater than 30%, the drying chamber 1 is heated to a first set temperature T1 according to a chosen temperature gradient Gl.

[0106] In practice, if the wood humidity is less than or equal to 30%, a third CO2 saturation step S3 is implemented, even if the set temperature T1 has not yet been reached.

[0107] The step of adjusting the hygrometry of the wood S2 includes the following sub-steps: -Measure wood hygrometry in real time S21;

[0108] - If the measured humidity is greater than 30%, increase the temperature of the tube drying of the ambient temperature S22 until the measured humidity is less than or equal to 30%, the temperature increase being carried out according to a chosen temperature gradient Gl, and limited to a first set temperature Tl; and

[0109] -If the measured humidity is less than or equal to 30%, saturate the drying chamber 1 with CO2 S3.

[0110] By way of non-limiting example, the first set temperature T1 is between 50°C and 60°C.

[0111] As a non-limiting example, the chosen temperature gradient G1 is 2°C / hour.

[0112] According to a third saturation step S3 of the drying chamber with CO2, the CO2 supply means 3 inject CO2 into the drying chamber 1 until the CO2 saturation reaches a chosen value.

[0113] The CO2 saturation step S3 comprises the following sub-steps: -Check that the set temperature Tl is reached in the drying chamber S31; -Inject S32 the CO2 from CO2 supply means 3; -Measure using measuring means 700a, 700b, arranged at the outlet of the CO2 supply means 3 and at the outlet 701 of the installation the partial pressure of CO2 S33; -Compare partial pressure of CO2 at inlet and outlet S34; and - Stop CO2 injection and activate CO2 recycling means when the CO2 partial pressure ratio at the inlet / outlet is greater than or equal to a chosen target R value S35.

[0114] In practice, the injection is implemented via an injection module 206a.

[0115] By way of example, the CO2 saturation in the drying chamber 1 is measured by gas chromatography, by punctures carried out via metrology means 5 arranged at the inlet and outlet of the drying chamber 1.

[0116] As a non-limiting example, when the ratio R= P[CO2] inlet / P[CO2] outlet is between 0.8 and 1, the CO2 saturation is sufficient, the CO2 injection is stopped.

[0117] According to a fourth drying step S4, heating S4 the CO2 circulating in the drying chamber 1 up to the set temperature T1 in the drying chamber 1 according to a first phase, then heating according to a second phase the CO2 circulating in the drying chamber 1 until the measured hygrometry of the wood reaches a chosen intermediate target value Hi, the heating being carried out up to a second set temperature T2 limit of 120°C according to a chosen temperature gradient G2 according to the specific drying profile of the wood to be dried making it possible to extract the specific bound water from the wood to be dried

[0118] The reheating step S4 comprises the following sub-steps: - Increase the temperature of drying chamber 1 according to a chosen temperature gradient G2, with a limit temperature of T2 S41 - Activate the activation / deactivation of CO2 flow reversal means according to a chosen frequency Fl S42 configured to reverse the direction of the CO2 flow in the drying chamber 1; -Activate dehumidification means S43 of drying chamber 1; -Measure the hygrometry of S44 wood in real time; and -if the measured hygrometry of the wood is less than or equal to an intermediate hygrometry value Hi of the wood, stabilize S45 the temperature of the drying chamber 1 even if the set temperature T2 is not reached.

[0119] Furthermore, the temperature increase S41 is carried out in two phases.

[0120] A first phase consists of heating the CO2 circulating in the drying chamber 1 up to the set temperature T1 in the drying chamber 1.

[0121] A second phase consists of heating, according to a second phase, the CO2 circulating in the drying chamber 1 until the measured hygrometry of the wood reaches a chosen intermediate target value Hi, the heating being carried out up to a second limit set temperature T2 according to a chosen temperature gradient G2 as a function of the specific drying profile of the wood to be dried, making it possible to extract the specific bound water from the wood to be dried.

[0122] By way of non-limiting example, the second set temperature T2 is between 100 and 120°C.

[0123] As a non-limiting example, the chosen temperature gradient G2 is between 1 and 7°C / hour.

[0124] 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%.

[0125] In practice, the temperature gradient G2 is chosen 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, and dynamic, so as to be adjusted when approaching the intermediate target value Hi of hygrometry of the chosen wood.

[0126] By way of non-limiting example, the pressure measured in the drying chamber is between 0.8 and 1 bar.

[0127] According to a fifth step of reducing the temperature according to a first phase S5 of the drying chamber 1, the temperature of the heating chamber (1) is reduced until the wood to be dried reaches a measured hygrometry included in a chosen target hygrometry value range HX, the temperature reduction having a minimum limit value defined as a third setpoint temperature T3 for stabilization.

[0128] In practice, the step of reducing the temperature according to a first phase S5 comprises the following sub-steps: - when the measured hygrometry of the wood reaches the chosen intermediate target value Hi, reduce the temperature in the drying chamber 1 to a chosen set temperature T3 for stabilization S51; - Stabilize the measured hygrometry of the wood to be dried within a target hygrometry value range HX S52; and - when the target humidity value range HX is reached, stabilize the wood temperature reached for a chosen duration D, even if the set temperature T3 is not reached S53.

[0129] By way of non-limiting example, the third set temperature T3 is between 60 and 100°C.

[0130] By way of non-limiting example, the range of target hygrometry values ​​HX is between a final target hygrometry value Hc, and a final target hygrometry value 1.1 Hc (i.e. 110% of Hc).

[0131] During this step of reducing the temperature according to a first phase S5, when the measured hygrometry of the wood reaches the chosen intermediate target value Hi, said temperature of the drying chamber is reduced to a set limit temperature T3.

[0132] In practice, when the measured hygrometry is stable and within a chosen range of HX values, the temperature of the drying chamber is stabilized and maintained for a chosen period of time D, even if the set temperature T3 is not reached.

[0133] As a non-limiting example, the duration D is 2 hours.

[0134] Advantageously, stabilizing the temperature for a chosen duration D when the measured hygrometry reaches a value within a chosen target hygrometry value range HX allows hygroscopic rebalancing of the wood to be dried.

[0135] According to a sixth step, the step of decreasing the temperature according to a second phase S6, the temperature of the heating chamber 1 is decreased to the set temperature T1 (T1 less than T3) as long as the measured hygrometry of the wood is greater than the final target hygrometry value Hc, if the measured hygrometry of the wood is less than or equal to the final target hygrometry value Hc, maintain the measured temperature equal for a chosen stabilization period.

[0136] In practice, the step of reducing the temperature according to a second phase S6 comprises the following sub-steps: - Disable CO2 flow reversal means and CO2 recycling means S61 - if the measured hygrometry of the wood is higher than the final target value Hc, reduce the temperature S62 of drying chamber 1 to the set temperature Tl according to a chosen gradient G3 by progressive deactivation of heating means 2; -if the measured hygrometry of the wood is less than or equal to the final target value Hc, stabilize the temperature measured in the drying chamber 1 for a chosen duration, even if the set temperature Tl is not reached S63.

[0137] As a non-limiting example, the chosen temperature gradient G3 is 2°C / hour.

[0138] In practice, the temperature gradient G3 is chosen to be identical, regardless of the specific drying profile of the wood to be dried, and dynamic, so as to be adjusted when approaching the final target value Hc of hygrometry of the chosen wood.

[0139] As a non-limiting example, the final target value Hc is between 0% and 18%.

[0140] The method according to the invention further comprises a CO2 evacuation step S7, configured to desaturate the drying chamber with CO2 to extract the dried wood when the measured hygrometry of the wood is less than or equal to the final target value Hc, and after stabilization of the temperature for the chosen duration.

[0141] All the steps of the process are controlled and carried out via a succession of fully automated commands by the computer control system 6 comprising an 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 instruments 5 of the drying installation, 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.

[0142] 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 the drying time specific to it and the associated specific 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 retro control system 6 adjusts these same measurements to setpoint values, in order to obtain optimal and industrial drying of the wood load.During each of the temperature increase phases S2, S4 and decrease S5, S6, the thermostat 210 of the heater 205 as well as the real-time metrology measurement recording systems, allow the adjustment of the power of the heater 205 by feedback effect of the thermostat 210 on the heater 205 as well as the modulation of the CO2 circulation systems.

[0143] In practice, temperature gradients G1, G2, G3 of the first phase 901 and of the second phase 902 of drying are modulated by the control means 6, so as to control the evolution of the hygrometry in the heartwood of the piece of wood during drying. drying.

[0144] In practice, since the humidity in the wood to be dried is variable, the following are monitored by metrology measurements: ambient humidity, average humidity, minimum humidity, and maximum humidity, for example.

[0145] 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 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 CO2.

[0146] By way of non-limiting example, the retro adjustments made by the control means 6 are obtained by modifying the operation of the heater 205, the circulation means 213a, 213b of the gas mixture. These readjustments allow on the one hand the maintenance of a maximum temperature delta of 20°C between the temperature recorded at the heart of the wood and the temperature of the atmosphere of the drying chamber 1, and on the other hand, to adapt the drying of a wood species to a specific profile.

[0147] The method according to the invention also allows the optimization of the substitution of CO2 for H2O linked to the cellulose of the wood to be dried. This CO2 / H2O substitution makes it possible to guarantee the “structural” molecular integrity of the “cellulose lamination, hemicellulose and lignite”, and thus of the dried wood. Fine and precise multi-parameter control of the drying environment, the hygrometry of the wood to be dried and the temperature in the drying chamber 1 is therefore necessary.

[0148] The instrumentation and control based on metrology measurements of the internal environment of the drying chamber 1 and of the wood make it possible to avoid damaging the wood during drying, any drying inducing an unavoidable shrinkage of material, although reduced by the substituted CO2. In the event of poor control, the structural quality of the dried wood thus obtained can be significantly impacted.

[0149] Cracks, as well as 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.

[0150] The method according to the invention therefore makes it possible, via fine regulation of the hygrometry of the wood, to obtain dried wood of 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.

Claims

Claims

1. Method for thermal drying of wood implemented using a drying installation comprising at least one drying chamber (1), said method comprising the following steps: -Acquisition of metrological data and parameters of the wood to be dried (SI); -Adjust the wood humidity (S2) by heating up to a first set temperature Tl according to a chosen temperature gradient G1 if the wood humidity is greater than 30%, in order to extract the free water from the wood to be dried; -If the measured wood humidity is less than or equal to 30%, saturate (S3) the drying chamber (1) with CO2 even if the set temperature Tl is not reached; - heating (S4) the CO2 circulating in the drying chamber (1) up to the set temperature T1 in the drying chamber (1) according to a first phase, then heating according to a second phase the CO2 circulating in the drying chamber (1) until the measured hygrometry of the wood reaches a chosen intermediate target value Hi, the heating being carried out up to a second set temperature T2 limit of 100 to 120°C according to a chosen temperature gradient G2 depending on the specific drying profile of the wood to be dried making it possible to extract the specific bound water from the wood to be dried; -Decrease according to a first phase (S5) the temperature of the heating chamber (1) to a third setpoint temperature T3 chosen for stabilization, when the measured hygrometry of the wood reaches the chosen intermediate target value Hi, said setpoint temperature T3 being maintained for a chosen period of time until the measured hygrometry is stable and included in a chosen range of values ​​HX; and -Decrease according to a second phase (S6) the temperature of the heating chamber (1) to the set temperature Tl as long as the measured hygrometry of the wood is higher than the final target hygrometry value Hc, if the measured hygrometry of the wood is lower than or equal to the final target hygrometry value Hc, maintain the measured temperature equal for a chosen stabilization period.

2. Method according to claim 1, characterized in that the wood belongs to the group formed by round wood, log, timber, shaped wood boards.

3. Method according to claim 1 or 2, characterized in that the step of acquiring the metrological data and parameters of the wood to be dried (SI) comprises the following sub-steps: - Filling the drying chamber with the wood to be dried (SI 1); - Measuring the temperature of the wood at the surface and at the core (S 12); - Measuring the hygrometry of the wood to be dried (S 13); - Measuring the temperature of the drying chamber (S 14); - Measuring the hygrometry of the drying chamber (S 15); and - Measuring the weight of the wood to be dried (S 16).

4. Method according to any one of claims 1 to 3, characterized in that the step of adjusting the hygrometry of the wood (S2) comprises the following sub-steps: -Measuring the hygrometry of the wood in real time (S21); -If the measured hygrometry is greater than 30%, increase the temperature of the drying tube from ambient temperature (S22) until the measured hygrometry is less than or equal to 30%, the increase in temperature being carried out according to a chosen temperature gradient Gl, and limited to a first set temperature Tl; and -If the measured hygrometry is less than or equal to 30%, saturate the drying chamber (1) with CO2 (S3).

5. Method according to any one of claims 1 to 4, characterized in that the CO2 saturation step (S3) comprises the following sub-steps: - checking whether the measured hygrometry is less than or equal to 30%; - Injecting (S32) the CO2 from CO2 supply means (3); - Measuring using measuring means (700a, 700b), arranged at the outlet of the CO2 supply means (3) and at the outlet (701) of the installation the partial pressure of CO2 (S33); - Comparing the partial pressure of CO2 at the inlet and at the outlet (S34); and - Stopping the injection of CO2 and activating CO2 recycling means when the ratio of partial pressure of CO2 at the inlet / outlet is greater than or equal to a chosen target value R (S35).

6. Method according to any one of claims 1 to 5, characterized in that the reheating step (S4) comprises the following sub-steps: -Increasing the temperature of the drying chamber (1) according to a temperature gradient G2 chosen, with a set temperature T2 as the limit temperature (S41); - Trigger the activation / deactivation of CO2 flow reversal means according to a chosen frequency Fl (S42) configured to reverse the direction of the CO2 flow in the drying chamber (1); - Activate dehumidification means (S43) of the drying chamber (1); - Measure the wood hygrometry in real time (S44); and - if the measured wood hygrometry is less than or equal to an intermediate wood hygrometry value Hi, stabilize (S45) the temperature of the drying chamber (1) even if the set temperature T2 is not reached.

7. Method according to any one of claims 1 to 6, characterized in that the step of decreasing the temperature according to a first phase (S5) comprises the following sub-steps: - when the measured hygrometry of the wood reaches the chosen intermediate target value Hi, reducing the temperature in the drying chamber (1) to a chosen stabilization setpoint temperature T3 (S51); - Stabilizing the measured hygrometry of the wood to be dried in a target hygrometry value range HX (S52); and - when the target hygrometry value range HX is reached, stabilizing the temperature of the wood reached for a chosen duration D, even if the setpoint temperature T3 is not reached (S53).

8. Method according to claim 7, characterized in that the step of decreasing the temperature according to a second phase (S6) comprises the following sub-steps: - Deactivating the CO2 flow reversal means and the CO2 recycling means (S61); - if the measured hygrometry of the wood is higher than the final target value Hc, reducing the temperature (S62) of the drying chamber (1) to the set temperature Tl according to a chosen gradient G3 by progressive deactivation of heating means (2); - if the measured hygrometry of the wood is lower than or equal to the final target value Hc, stabilizing the temperature measured in the drying chamber (1) even if the set temperature Tl is not reached (S63).

9. Method according to any one of claims 1 to 8, characterized in which further comprises a CO2 evacuation step (S7), configured to desaturate the drying chamber with CO2 to extract the dried wood.

Images