Patent Application
20240230229
The present invention relates to a method for the thermal drying of wood by CO2 sequestration in addition to the dried wood directly obtained using the method, in particular but not exclusively, for the industrial drying of industrial wood, fuel wood, logs and similar lignocellulosic material.
The term “industrial wood” is used here to refer to wood intended for use in the secondary wood processing sectors, in particular for industry, construction, joinery, or for exterior and interior fittings for urban, industrial, collective and domestic use.
“Wood” means any lignocellulosic material or similar compound capable of sequestering CO2.
The term “CO2 sequestration” means in this case any substitution, trapping of CO2, chemical reaction between CO2/wood polymers/water or complexation or stable accumulation of CO2 or carbonation of wood or of water contained in wood with compounds such as wood to be dried or similar receiving material.
A system as taught by document WO2020127026, using wood drying cells under a CO2 atmosphere, is known, in order to implement a method of drying wood under CO2 atmosphere.
The disadvantage of this method is that the temperature of the gas mixture in the drying chamber cannot be maintained uniformly, resulting in poor uniformity of drying of the wood.
The disadvantage of this method is also that it does not make it possible to limit the presence of water in the liquid state in said drying chamber, or to guarantee that the temperature of the drying environment is uniform during use at all points in the drying chamber.
Although various solutions exist for drying timber, roundwood and/or logs, the known solutions are only rarely suitable for industrial applications and have a low energy balance. The known solutions are indeed generally used on a small scale, to consume a minimum amount of energy while obtaining wood with a low water content, and do not make it possible to achieve drying with a neutral or negative carbon balance.
Another disadvantage of the existing solutions is the length of time it takes to operate a drying installation, several days or even several weeks, a factor that limits its effective use for industrial applications.
Furthermore, current methods all too often struggle to achieve the objective of raising the temperature so that the latter is homogeneous right to the core of a mass of wood, while achieving precise humidity of the dried wood and guaranteeing the integrity of the wood's internal structure during and after drying.
Another disadvantage of the current drying processes and installations is that only a very small amount of CO2 can be sequestered in the wood to be dried.
All the known drying methods mentioned above also cause warping of the wood thus obtained, frequently including warping of the edges such as tiling, but also at the level of the knots of said material with detachment. These distortions also have numerous disadvantages when the dried material is used in the future.
Disadvantages in use include, but are not limited to, uneven distribution of forces at all points in said material, which may cause structural weaknesses, distortions rendering the material unusable, accelerated wear of the material over time, and significant shrinkage in terms of volume between the undried state and the dried state, and therefore poor material yield from the drying process.
The aim of the present invention is to overcome these problems.
The invention relates to a method of thermally drying wood using a drying installation comprising at least one drying chamber.
According to a general definition of the invention, said process comprises the following stages:
By way of example, the humidity value Hi+A % has a value A of between 1% and 2.5%.
In practice, the stage of acquisition of the metrological data and parameters of the wood to be dried comprises the following sub-stages:
In addition, the stage of activation of the means of supply of CO2 comprises a sub-stage of verifying the CO2 saturation of the circulating gas mixture in the drying chamber.
In practice, the stage of activation of the means of heating to adjust the humidity of the wood comprises a sub-stage of real-time monitoring of wood humidity, and the heating stage comprises a sub-stage of real-time monitoring of wood humidity.
According to one embodiment of the invention, the stage of activation of the means of recycling comprises a sub-stage of implementing an activation/deactivation sequence of a flow reversal module at a selected frequency F1
In practice, the stage of reducing the temperature of the heating chamber in a second phase furthermore comprises a sub-stage of shutting down the flow reversal module at the same time as the means of recycling.
The process according to the invention furthermore comprises a CO2 discharge stage, configured to desaturate the drying chamber with CO2 to extract the dried wood.
By way of a non-limiting example, the heating stage comprises a temperature limit according to a first setpoint temperature T1 between 50° C. and 60° C., according to a selected temperature gradient G1 of 2° C./hour.
By way of a non-limiting example, the temperature increase stage comprises a temperature limit defined according to a second setpoint temperature T2 less than or equal to 120° C., according to a selected temperature gradient of between 1° C./hour and 3° C./hour.
By way of a non-limiting example, the temperature reduction stage of the heating chamber in a first phase comprises a temperature limit according to a first setpoint temperature T3 between 50° C. and 100° C., according to a selected temperature gradient G3 of 2° C./hour.
Advantageously, the drying process according to the invention also makes it possible to obtain a shrinkage of the wood of less than 5%, whereas the standard shrinkage with conventional drying means is 10 to 15%.
The invention also relates to a dried wood obtained directly using the process according to the invention, comprising lignin, cellulose and hemicellulose.
According to a second general definition, the dried wood obtained directly by the process according to the invention contains less than 20% measured average humidity, and the ultrastructure of the cell wall of the wood is retained in the dried state compared with the state before drying.
The Applicant has also observed that implementation of the process according to the invention by a drying installation makes it possible to obtain dried wood according to the invention, having less reabsorption of humidity, a reduction in the colour of the dried wood, as well as the limitation/absence of the appearance of cracks during drying.
In addition, the drying process according to the invention makes it possible to obtain uniform drying and a shrinkage of less than 5%, while limiting the presence of water in the liquid state in the drying chamber.
Other advantages and characteristics of the invention will appear on examination of the description and drawings in which:
With reference to
According to a stage of acquisition of the metrological data and parameters of the wood to be dried S1, metrological data and parameters of the wood to be dried are acquired by the measurement of the metrological means 5.
In addition, the various parametric data are measured in order to calibrate the setpoint values to be applied.
In practice, the stage of acquisition of the metrological data and parameters of the wood to be dried S1 comprises the following sub-stages:
For instance, the wood to be dried is inserted into the drying chamber 1 and the drying chamber is subsequently sealed hermetically.
In practice, the difference between the surface temperature of the wood and core temperature of the wood must be less than or equal to 20° C. throughout the entire drying process.
In addition, the sub-stage of measuring the weight of the wood to be dried S16 enables the loss of mass involved in implementing the drying process to be calculated and the quantity of water extracted to thus be quantified, taking into account the quantity of CO2 sequestered.
By way of a non-limiting example, the maximum quantity of CO2 sequestered is 250 kg/m3 of wood.
According to a stage of CO2 saturation S2 of the drying chamber 1, means of supply of CO2 3 are activated in order to allow the injection of CO2 from a CO2 source into the drying chamber 1.
In practice, the CO2 saturation stage S2 comprises a sub-stage of verification S21 of the CO2 saturation in the circulating gas mixture, in order to ensure that said minimum CO2 saturation to initiate a drying cycle is achieved.
A gas mixture is defined as the total sum of the compounds of the gaseous and liquid environment circulating in the drying chamber 1 at a time t.
In practice, verification of the CO2 saturation S21 is implemented by measurement via means of measurement of CO2/CH4 56 in a discharge duct of the drying module C1.
According to one embodiment, when the ratio R═P[CO2] input/P[CO2] output is between 0.8 and 1.2, the minimum CO2 saturation is achieved.
According to an alternative embodiment, verification of the CO2 saturation S21 is implemented by measurement of the percentage CO2 in the circulating gas mixture.
According to a wood humidity adjustment stage S3, means of heating 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 means of heating 2 are activated when the minimum CO2 saturation is achieved.
The wood humidity adjustment stage S3 furthermore comprises a sub-stage of real-time measurement of wood humidity S31.
In practice, if the measured humidity of the wood exceeds 30%, the process according to the invention comprises a sub-stage of heating S32 via the means of heating 2, the implementation parameters of which comprise an upper temperature limit according to a first setpoint temperature T1 not to be exceeded, in addition to a selected temperature gradient G1 in order to extract the free water from the wood to be dried until the measured humidity of the wood is less than or equal to 30%.
The sub-stage of heating S32 furthermore comprises activation of means of gas circulation 4.
By way of a non-limiting example, the first setpoint temperature T1 is between 50° C. and 60° C.
By way of a non-limiting example, the chosen temperature gradient G1 is 2° C./hour.
If the humidity of the wood is less than or equal to 30%, a drying stage S4 is implemented directly, and involves increasing the temperature of the circulating gas mixture, the implementation parameters of which comprise an upper temperature limit according to a second setpoint 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 means of gas circulation 4.
The drying stage S4 of the drying process comprises sub-stages involving:
According to one embodiment, the stage of activation S42 of the means of recycling 600 furthermore comprises initiating an activation/deactivation sequence of a flow reversal module at a selected frequency F1, configured to reverse the direction of the flow of circulating gas mixture in the drying chamber 1 at a selected frequency in two directions of circulation.
In practice, the means of heating 2 are activated so that heating is carried out with a limit temperature defined by a second setpoint temperature T2 of 120° C. according to a selected temperature gradient G2, and as a function of the specific drying profile of the wood to be dried enabling the bound water to be extracted from the wood to be dried in a more precise manner.
Setpoint temperatures T1 and T2 are temperature limits that each drying module C1 may not exceed during these phases.
In practice, the setpoint temperature T2 is less than or equal to 120° C.
By way of a non-limiting example, the chosen temperature gradient G2 is between 1 and 3° C./hour.
In practice, the intermediate target value Hi chosen for the measured humidity of the wood is equal to the desired final target humidity Hc+1.5 to 2.5%.
In addition, achieving the chosen intermediate value Hi is made possible by controlling the means of recycling 600 via a high hysteresis (hys-h) and a low hysteresis (hys-b). These two parameters make it possible to activate the means of recycling 600 in corroboration with the humidity measured in the drying chamber 1 in order to avoid activating/deactivating the means of recycling 600 or of supply of CO2 3 in the event of a humidity measurement fluctuating between a value above and below the chosen intermediate value Hi.
In practice, the temperature gradient G2 is chosen as a function of the specific drying profile of the wood to be dried, enabling the bound water to be extracted from the wood to be dried, as well as dynamically, so as to be adjusted as the chosen intermediate target value Hi for wood humidity is approached.
By way of a non-limiting example, the pressure measured in the drying chamber is between 0.8 and 1 bar.
In a holding stage of the wood to be dried S5, the temperature in the drying chamber 1 is stabilised.
The holding stage of the wood to be dried S5 is implemented by deactivating S51 the means of recycling 600, and by adjusting the activity of the means of heating 2 to reduce the temperature S52 of the heating chamber 1 in a first phase down to a third stabilisation setpoint temperature T3 chosen according to a temperature gradient G3, when the average humidity of the wood measured via the means for measuring the humidity 54 of the wood reaches the chosen intermediate target value Hi, the humidity is stabilised S53.
In practice, if one of the measured humidity values of the wood is greater than Hi+A %, said setpoint temperature T3 is maintained for a selected period of time until the measured humidity value of the wood greater than Hi+A % initially is stable and within a range of values less than or equal to Hi+%.
By way of a non-limiting example, the third setpoint temperature T3 is between 60 and 100° C.
By way of a non-limiting example, the range of target humidity values is between a final target humidity value Hc and an intermediate target humidity value Hi, i.e. the target wood humidity value Hc+A %.
In practice, the value A is between 1 and 2.5%.
In practice, when the measured humidity is stable and below Hi, the temperature of the drying chamber 1 is stabilised S54, and is maintained for a selected period of time D, even if the setpoint temperature T3 is not reached.
By way of a non-limiting example, the duration D is 2 hours.
Advantageously, stabilisation of the temperature for a selected period D when the measured humidity reaches a value within a selected range of target humidity values less than or equal to Hi allows hygroscopic rebalancing of the wood to be dried.
In a cooling stage under CO2 S6, the temperature in the drying chamber 1 is reduced according to selected conditions.
In practice, the temperature reduction stage in a second phase S6 comprises a sub-stage of deactivation S61 of the means of recycling 600.
According to one embodiment of the invention, the sub-stage of deactivation S61 also comprises shutting down the flow reversal module.
By way of a non-limiting example, the chosen temperature gradient G3 is 2° C./hour.
In practice, the temperature gradient G3 is chosen in an identical manner, regardless of the specific drying profile of the wood to be dried, the latter profile also being dynamic, so as to be adjusted as the chosen final target value Hc for wood humidity is approached.
By way of a non-limiting example, the final target value Hc for wood humidity is between 0% and 18%.
The process according to the invention furthermore comprises a stage of discharge S7 of the atmosphere from the drying chamber, including the CO2, configured to desaturate the drying chamber 1 in CO2 and thus extract the dried wood when the measured humidity of the wood is less than or equal to the final target value humidity Hc, and after stabilisation of the temperature for the selected period.
All the stages of the process are controlled and carried out via a succession of fully automated commands by a computerised control system 6, which includes the application programming interface (API). As the API executes a control program, it sends various instructions to each of the control components and receives the recording data from the metrological means 5 of the drying installation in real time from the start to the end of the process, which enable adjustment of the control components in order to optimise drying in the event of any deviation from the setpoint values.
The drying profile is specific to each type of wood, with each type of wood therefore having a hygrometric evolution curve at the heart of the wood as a function of its particular drying time and the associated specific temperature increase sequences, which dictate the temperature increase profile to be applied during the heating phases, and serves as a basis for comparison with the metrological measurements recorded so that the computerised control system 6 retrospectively readjusts these same measurements back to the setpoint values, in order to obtain optimum industrial drying of the wood.
In practice, the temperature gradients G1, G2, G3 are varied by the computerised control system 6, so as to control changes in humidity in the heartwood of the wood during drying.
In practice, as the humidity in the wood to be dried varies, the ambient humidity, average humidity, minimum humidity and maximum humidity are monitored by the metrological means 5.
By recording control of the setpoint values associated with the measurements observed, it is possible to establish a hygrometric drying profile specific to the species of wood to be treated and thus define the retrospective adjustments by the computerised control system 6 for wood of the same species during subsequent drying operations, and thus industrialize drying while preserving the macromolecular structure of the dried wood with the substitution of bound water by CO2.
In addition, each transition from one stage to another is dependent only on the humidity target that applies to the current stage and not on whether or not the setpoint temperature of the current stage is achieved.
The process described above furthermore makes it possible to obtain dried wood, also known as dried cellulosic material.
Advantageously, the dried lignocellulosic material exhibits little warping during drying under CO2 and is dimensionally stable in the dried state.
The lignocellulosic material dried by implementing the process according to the invention comprises lignin, cellulose and hemicellulose, and has an average measured humidity of less than 20%, while the ultrastructure of the cell wall of the wood is structurally retained in the dried state compared with the state before drying.
Variations in water content in the cell walls normally lead to warping of the wood. Wood “swells” when it absorbs water, and contracts when it loses water. These dimensional variations in a sample of wood, causing a variation in volume, are not the same in the three reference directions: radial, tangential and longitudinal.
The dried cellulosic material has a tangential shrinkage of less than 5% and a radial shrinkage of less than 4%.
Furthermore, the dried lignocellulosic material exhibits less swelling when humidity is reabsorbed (rehumidification); indeed, swelling of the material is 50% less than that observed with conventional drying.
Advantageously, low tangential and radial shrinkage enables savings in material of up to 20% when the lignocellulosic material is used.
By way of a non-limiting example, the use of lignocellulosic material according to the invention in the manufacture of floor coverings makes it possible to reduce dimensional variations when the said floor coverings are exposed to variations in humidity.
Advantageously, the use of lignocellulosic material of the dried wood type makes it possible to obtain products with improved mechanical properties, with less swelling following reabsorption of humidity and improved durability, while limiting material losses during manufacture linked to warping, delamination and cracks, resulting in a yield of between 40 and 50% when the wood is processed using conventional drying. In other words, 50 to 60% less waste is obtained per cubic metre of wood processed.
The instrumentation and control based on metrological measurements of the internal environment of the drying chamber 1 and of the wood, make it possible to avoid damaging the wood during drying, with all drying resulting in unavoidable material shrinkage, albeit minimised 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 affected.
Cracks and sagging of the wood may appear as a result of poor control, thereby compromising the structural integrity of the dried wood obtained by the process according to the invention, thus generating a product not in accordance with the invention.
The process according to the invention therefore makes it possible, by fine adjustment of the humidity of the wood, to obtain dried wood of precise humidity, with a shrinkage of less than or equal to 5%, a negligible rate of warping, and with a limitation, or even elimination, of the onset of cracks in the wood thus dried.
In addition, any examples of means used are only specific illustrations of means that can be used for embodiment of the invention. The Person skilled in the art will understand that these examples are not limitative and are not restricted to the examples mentioned, but extend to any example of means, the implementation of which yields the same technical effect.
With reference to
The drying module C1 has a drying chamber 1 consisting of one or more hollow cylindrical drying tubes for introducing the wood to be dried.
The drying chamber is connected to the means of heating 2 by an inlet duct 206a, and has an outlet duct 206b configured to discharge a CO2 or CO2/H2O gas mixture from said drying chamber 1 depending on the state of progress of the drying.
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.
By way of a non-limiting example, the drying chamber 1 comprises a closed, heat-insulated tube with internal atmospheric recirculation.
According to a particular embodiment of the invention, the drying chamber 1 comprises a minimum volume of 10 m3 that is saturable with CO2.
According to one embodiment, the drying chamber 1 comprises metrological means 5 configured to measure parameters belonging to the group formed by humidity of the wood to be dried, humidity in the drying chamber 1, temperature of the wood to be dried, temperature in the drying chamber 1 and pressure in the drying chamber 1.
According to one embodiment, the drying chamber 1 comprises at least one sensor for measuring the temperature and humidity in the drying chamber 53.
By way of a non-limiting example, the drying chamber 1 comprises two sensors for measuring the temperature and humidity in the drying chamber 53.
According to one embodiment, the drying chamber 1 comprises at least one sensor for measuring the humidity of the wood to be dried 54.
By way of a non-limiting example, the drying chamber 1 comprises two sensors for measuring the humidity of the wood to be dried 54.
In practice, the drying chamber 1 also comprises a control box 61 configured to receive and process the data recorded by the sensors measuring the humidity of the wood to be dried 54.
According to one embodiment, the drying chamber 1 also comprises a pressure measurement sensor 55 in said drying chamber 1, enabling emergency discharge of part of the atmosphere contained in the drying chamber 1 in the event of critical pressure therein.
In practice, each metrological measurement includes a setpoint value or a group of setpoint values to be respected, specific to each species or application of the wood to be dried.
In practice, the critical pressure may be 1.5 bar.
The drying chamber 1 also comprises door closure sensors 62, configured to detect the closure status of the doors for inserting the wood to be dried.
By way of a non-limiting example, the drying chamber 1 is 5.5 m in length with a circulation diameter of 2.4 metres, cylindrical or virtually cylindrical in shape and enclosed in a maritime container insulated with wood wool panels 60 mm thick. This box is connected from one end to the other by a heat-insulated insulated pipe, a heating system 2 and four centrifugal circulation fans capable of withstanding temperatures of up to 250° C.
The drying module C1 furthermore 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 enabling operation thereof.
The drying module C1 comprises means of supply of CO2 3 configured to control the injection of the CO2 gas mixture from at least one CO2 source.
The means of supply of CO2 comprise a pipe connected on the one hand to the CO2 source, and on the other hand to the means of heating 2, said pipe being equipped with a solenoid valve 701 for controlling the injection of CO2 into the drying module C1.
In practice, a command is sent to the solenoid valve 701, triggering its opening in order to supply the drying installation with CO2.
In practice, the means of supply of CO2 3 also comprise metrological means 5 configured to measure parameters belonging to the group formed by the flow rate of the injected circulating CO2 gas mixture and the temperature of the injected circulating CO2 gas mixture.
According to one embodiment, the means of supply of CO2 3 comprise at least one sensor for measuring the temperature and circulating flow rate 51.
The drying installation furthermore comprises means of supply of CO2 3, comprising a CO2 source belonging to the group formed by biogenic CO2 and non-biogenic CO2.
According to another alternative embodiment, the means of supply of CO2 3 comprise at least one so-called “direct” CO2 supply module, and a so-called “recycled” CO2 supply module, connected to the drying module C1 and configured to allow the injection/stopping of the injection of CO2 into the drying module C1.
Direct CO2 denotes CO2 originating from a source of CO2 in the form of gas that has not been purified on exiting the off-gas or industrial chimney and the gas mixture of which containing CO2 is used directly by the C1 drying module without any change in the phase of the CO2.
Recycled CO2 refers to CO2 originating from a CO2 supply derived from a CO2 source, such as CO2 packaged in cylinders and liquefied.
In practice, the means of supply of CO2 3 consist of at least one system for injection of CO2 from CO2 originating from a distribution system towards the means of heating 2.
The drying module C1 furthermore comprises means of heating 2, connected to the means of supply of CO2 3 on the one hand, and to the drying chamber 1 on the other hand via an inlet duct 206a.
In practice, the means of heating 2 are of the immersion heater type and more particularly of the “in-line electric heater” type.
By way of example, the immersion heater has a power rating of 90 kW and comprises an inlet through which the gases to be heated enter, an open cylindrical or virtually cylindrical steel duct into which an immersion heater is inserted, and finally a second outlet opening for the gases thus heated. The immersion heater furthermore comprises a thermostat for regulating the temperature of the immersion heater.
According to a first embodiment, the means of drying 1 consist of a plurality of drying modules C1, connected to means of heating 2 common to several drying modules C1.
According to an alternative embodiment, the means of drying 1 consist of a plurality of drying modules C1, each connected to individual means of heating 2.
The inlet duct 206a comprises a solenoid valve 702 configured to control the injection of the CO2 gas mixture into the drying chamber 1, in addition to means of gas circulation 4.
In practice, the means of gas circulation 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, i.e. towards the drying chamber 1, and from the drying chamber 1.
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 each configured to operate in one direction of circulation, i.e. at least one fan towards the drying chamber 1 and one fan from the drying chamber into the inlet duct 206a.
The means of heating 2 are also connected to an outlet duct 206b connecting an outlet end of the drying chamber 1 to said means of heating 2, and forming a closed loop circulation duct for the CO2 gas mixture.
The outlet duct 206b comprises a solenoid valve 706 configured to control the discharge of the CO2 gas mixture into the drying chamber 1, in addition to means of gas circulation 4.
In practice, the means of gas circulation 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, i.e. towards the drying chamber 1, and from the drying chamber 1.
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 each configured to 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 means of heating 2.
By way of a non-limiting example, the means of circulation 4 of the fan type 41, 42, are of the medium-pressure, single-suction centrifugal fan type with a sheet steel casing and impeller, said fan comprising an impeller with forward-inclined blades made of galvanised sheet steel, the fan 51 being capable of withstanding a maximum temperature of the air or CO2 to be transported of −20° C. to 250° C.
The means of circulation 4 of the inlet duct 206a in combination with the means of circulation 4 of the outlet duct 206b form a flow reversal module capable of allowing the circulation of the CO2 gas mixture from the means of heating 2 to the drying chamber 1 in a first direction of operation and from the drying chamber 1 to the means of heating 2 in a second direction of operation, and thus force the circulation of the CO2 gas mixture in a closed circuit, through the drying chamber 1 in two directions of circulation.
Advantageously, the alternative circulation of the CO2 in the inlet duct 206a and outlet duct 206b in two directions of circulation enables the CO2 to circulate longitudinally in the direction of the length of the drying chamber 1 with injection and extraction positioned advantageously at the ends of the drying chamber 1, thereby maintaining a uniform temperature of the gas mixture in the drying chamber 1 and thus enabling drying of the wood and uniform treatment of the CO2 in the wood.
The Applicant has observed that the use of the flow reversal module and more specifically 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 within the drying chamber 1, and thus make optional the use of an angled drying chamber and a swan-neck type removal system to remove the water in liquid form that may accumulate at the bottom of the drying chamber 1.
In addition, uniform drying of this kind makes it possible to achieve tangential shrinkage of less than 5% and radial shrinkage of less than 4%, in contrast to an average standard shrinkage of around 10 to 15% with conventional drying methods. The invention also drastically reduces warping of the lumber and, in particular, prevents the knots in the wood from distorting during drying. This reduced warping of the wood during drying can represent savings in material of up to 20%, depending on the application.
In practice, the fans 41, 42 of the inlet duct 206a and the outlet duct 206b are coupled to frequency inverters that advantageously enable the speed of rotation to be reduced as a function of the species of wood 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 optimise the uniformity of drying.
The outlet duct 206b furthermore comprises a bypass for sampling the circulating gas mixture 45 and incorporating means of measurement of the CO2/CH4 56, configured to measure the proportion of CO2 in relation to the total volume of circulating gas and the proportion of CH4 circulating during the CO2 drying phase of the drying module C1, and thus to check CO2 saturation throughout the circuit of the drying module C1.
Advantageously, monitoring the CO2/CH4 in the gas mixture during drying makes it possible to record changes in the concentration of the various compounds in the circulating gas mixture and thus to adjust the operation of the drying module 1, but also to ensure the safety of the drying module C1 in the event of a drastic increase in the quantity of CH4.
In practice, if the quantity of CH4 in the circulating gas mixture during drying exceeds 3.5%, the drying module C1 C2 is immediately drained.
The outlet duct 206b also comprises metrological means 5 configured to measure parameters belonging to the group formed by the flow rate of the injected circulating CO2 gas mixture, the temperature of the injected circulating CO2 gas mixture and the humidity of the circulating gas mixture.
According to one embodiment, the outlet duct 206b comprises at least one sensor for measuring the temperature and circulating flow rate 51.
By way of a non-limiting example, the outlet duct 206b comprises at least one sensor for measuring the temperature and the circulating flow rate 51 arranged upstream and a sensor for measuring the temperature and the circulating flow rate 51 arranged downstream from the means of recycling 600 of the CO2.
According to one embodiment, the outlet duct 206b comprises at least one sensor for measuring the temperature and the humidity 53.
By way of a non-limiting example, the outlet duct 206b comprises at least one sensor for measuring the temperature and the humidity 53, arranged upstream and a sensor for measuring the temperature and the humidity 53, arranged downstream from the means of recycling 600 of the CO2.
In practice, the outlet duct 206b comprises at least one sensor for measuring the temperature and humidity 53, arranged upstream and one sensor for measuring the temperature and humidity 53, arranged downstream from the means of recycling 600 of the CO2, and at least one sensor for measuring the temperature and the circulating flow rate 51, arranged upstream and one sensor for measuring the temperature and the circulating flow rate 51, arranged downstream from the means of recycling 600 of the CO2.
Advantageously, such an arrangement allows monitoring of the composition of the circulating gas mixture, as well as the activity of the means of recycling 600 of the CO2 and their adjustment.
The drying module C1 also comprises means of recycling 600 of the CO2 arranged at the outlet duct 206b for separating the water vapour 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 for storage or direct reuse in the installation.
By way of a non-limiting example, condensation-type means of recycling 600 are used, reducing the temperature of the binary water vapour/CO2 gas mixture extracted from the drying chamber 1 to a selected temperature, allowing condensation of the water in the gas mixture, which is subsequently recovered by gravity in liquid form and disposed of. In practice, the means of recycling 600 allow the drying of the internal atmosphere extracted from the drying chamber 1 via thermal condensation of the water vapour by cooling, on at least one heat exchanger equipped with at least one cold battery; several cold batteries configured in series can advantageously be used to increase the dehumidification capacity of each drying module C1. The system therefore allows the dehydrated atmosphere to be re-injected into the drying chamber 1.
In practice, each heat exchanger comprises at least one evaporator EV and at least one condenser CO.
According to one embodiment of the invention, the heat exchanger of the means of recycling 600 is only active when the humidity of the circulating gas mixture is between two threshold values.
In practice, the heat exchanger of the means of recycling 600 of the CO2 is only active during the drying phase, and when the measured humidity of the circulating gas mixture is between a maximum threshold value and a minimum threshold value.
For instance, the humidity threshold values in the drying chamber 1 are 20% for the minimum threshold and 100% for the maximum threshold.
According to one embodiment of the invention, the means of recycling 600 comprise a system of the heat exchanger type comprising at least two cold batteries, configured in series to gradually extract water from the gas mixture, each cold battery being capable of extracting a chosen percentage of water from said gas mixture.
Advantageously, a series of cold batteries can be used to limit the humidity in the drying chamber 1, thereby limiting the duration of the drying cycle, solving the performance problem of a conventional heat exchanger when the humidity is higher than the critical operating value, and thereby reducing the duration of each cycle, causing each drying module C1 to operate for a shorter period of time and limiting the associated energy expenditure.
According to one embodiment, the means of recycling 600 furthermore comprise a discharge outlet configured to discharge condensed water or condensate, said discharge outlet incorporating a water flow meter 57.
The water flow meter 57 is configured to record the discharge flow rate of the water to be discharged, and thus makes it possible to correlate the quantity of water discharged to the difference between the initial and final humidity level of the wood for a drying cycle.
In practice, the heat exchanger of the means of recycling 600 can also be used to heat the dehydrated gas mixture before reinjection into said installation.
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 re-injection into the drying chamber 1.
By way of example, maintaining the humidity in the drying chamber 1 below a chosen value makes it possible to shorten the drying cycle, for which the means of circulation 213a, 213b of the CO2 in the drying module(s) C1 may account for 5 to 20% of the energy expenditure.
Advantageously, the means of recycling 600 make it possible to control the humidity of the gas mixture and thus to control the quality of the drying of the wood, thereby optimising the drying process and the quality of the material obtained, while limiting energy expenditure and maintaining a low temperature deviation between the CO2 exiting the means of heating 2 and originating from the recirculation module 206c.
In practice, the CO2 gas recovered by the means of recycling 600 can be stored in means of storage or re-injected directly into the drying chamber 1.
According to a particular embodiment of the invention, the drying chamber 1 comprises at least one discharge circuit, which is followed by a so-called “breathing” duct comprising at least one solenoid valve 704, 705 to allow breathing of the drying chamber 1, permitting air from outside the installation to be injected into the drying chamber 1 and the gas mixture contained in said drying chamber 1 to be discharged.
The discharge circuit furthermore comprises fan-type 43 means of circulation 4, as well as means of measurement of the CO2/CH4 56, configured to measure the proportion of CO2 relative to the total volume of circulating gas and the proportion of CH4 circulating during the phase of filling the drying module C1 with CO2, and thus to check the CO2 saturation throughout the circuit of the drying module C1 during said filling, and configured to allow drainage of the drying chamber 1.
According to one embodiment, the drying module C1 also 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 flow rate and temperature of the gas mixture to be measured when the drying chamber 1 is drained.
By way of a non-limiting example, the fan-type 43, 44 means of circulation 4 of the additional discharge outlet and of the discharge circuit are of the medium-pressure, single-suction centrifugal fan type with sheet steel casing and impeller, said fan comprising an impeller with forward-inclined blades made of galvanised sheet steel, the fan 51 being capable of withstanding a maximum temperature of the air or CO2 to be transported of −20° C. to 250° C.
The drying module C1 also incorporates a computerised control system 6 comprising an application programming interface (API). The application programming interface can be used, on the one hand, to manage the sending of instructions to each of the installation components 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 installation components.
In practice, the drying module C1 furthermore comprises an energy consumption meter.
The computerised control system 6 is configured to control the means of supply 3, of circulation 4, of heating 2 and of recycling 600 according to programmes, setpoint values and drying times appropriate to the required quality of the dried wood, and processing means for measuring, comparing and readjusting the operating parameters to the setpoint values in case of deviation.
The computerised control system 6 also allows monitoring, measurement and recording of all the metrological values measured in a table (including energy consumption), as well as emergency procedures (shutdown without resumption of drying or with resumption of drying).
In practice, the computerised control system 6 is equipped with an application programming interface (API) capable of implementing a drying process.
In practice, during drying, if the pressure measurement sensor 55 in the drying module C1 detects an internal pressure of less than 15% of atmospheric pressure for a specified period, the computerised control system 6 opens the solenoid valve 701 of the means of supply of CO2 3 so as to inject fresh CO2. The drying module C1 furthermore comprises at least one environment sensor arranged outside said module and capable of recording the temperature and humidity in the environment surrounding said drying module.
According to one embodiment of the invention, the computerised control system 6 is also configured to enable control of the dehumidification of the CO2 by activating the means of recycling 600 as a function of a minimum (20%) and maximum (100%) value for the humidity of the atmosphere in the drying chamber 1. This phase is continuous, regardless of the initial humidity of the wood.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2300130 | Jan 2023 | FR | national |
| 2300136 | Jan 2023 | FR | national |
