EP1099084A1

EP1099084A1 - Reactor for wood retification

Info

Publication number: EP1099084A1
Application number: EP99931345A
Authority: EP
Inventors: Dominique Guillin
Original assignee: Fours et Bruleurs Rey
Current assignee: Fours et Bruleurs Rey
Priority date: 1998-07-17
Filing date: 1999-07-13
Publication date: 2001-05-16
Also published as: FR2781180A1; AU4789399A; FR2781180B1; CA2337357A1; BR9912160A; WO2000004328A1

Abstract

The invention concerns the technical sector of transforming wood by torrefaction of wood material of plant origin. More particularly it concerns a reactor characterised in that it comprises: a sealed chamber operating discontinuously; means for high stirring (10, 12) of the atmosphere for heating the wood; a loading system whereon the wood is maintained under 'ongoing and adaptable' mechanical stress (9, 14). Said reactor provides an industrial method for crosslinking wood.

Description

Wood retification reactor

The present invention relates to the technical sector of the transformation by roasting of woody materials of plant origin.

French patent FR 2,512,053 (ARMINES) describes a process for obtaining from wood a new material having new properties with greater ease of use, while retaining all of the potential thermal energy of the woody material. from the start, for a significantly increased calorific value.

According to this patent, a vegetable woody material, such as wood, is subjected to a roasting treatment in a neutral atmosphere, at a temperature between 200 and 280 ° C., preferably 240 and 260 ° C.

This treatment applies to any woody product of plant origin, including woody forest or agricultural waste. If the product is too fine, agglomeration is carried out beforehand, for example in sawdust croquettes or the like.

The duration of the treatment depends on the particle size and the temperature. For 1 cm3, for example 30 min. at 280 ° C but 1 h at 250 ° C and 2 h at 230 ° C. A friable brown product is obtained, different from both charcoal and "red" charcoal obtained by carbonization at low temperature. Among other things, the release of acetic acid from the wood is obtained.

French patent 2,591,611 (ARMINES) describes a new material known as “thermocondensed” obtained by the control and / or inhibition at all times of the exothermic reactions which occur in the material during the heat treatment of wood. The method consists in treating chips less than 50 mm or sawdust, anhydrous, by intimate contact with a non-oxidizing gaseous medium at a controlled temperature, maintained between 220 and 280 ° C, for at most 30 min., Then at cool the material to less than 200 ° C, preferably to 120 ° C, in a non-oxidizing medium. These conditions make it possible to avoid any carbonization.

This patent also describes a furnace with circulation of hot gases according to a mode “with cross currents” compared to the treated material.

Patent 2 604 942 (ARMINES) describes a process for manufacturing lignocellulosic material with small dimensional variations for variable hygrometric states, from solid wood or bot fibers. This process consists of “cross-linking” the wood fibers. This involves carrying out chemical bridging (covalent bonds) between the macromolecular chains of the wood fibers.

This retification is carried out by heat treatment in an atmosphere and at controlled temperature, for a limited period.

The aforementioned patent indicates on page 5 and page 6 the various complex physicochemical modifications which occur during the implementation of this process. A new product is obtained having a very high resistance to humidity (very high dimensional stability).

The teaching of the three aforementioned patents, and in particular of FR 2 604 942, is incorporated here by reference and the skilled person can usefully refer to it.

Patent FR 2 751 579 is also known, which describes a process for treating wood with a glass transition stage.

The patent FR 2 751 580 describes a wood retification process, according to which, during at least one heat treatment step, the existing quantity of at least one of the gases resulting from the decomposition of the hemicellulose is monitored, and this step is interrupted as soon as said quantity begins to become constant.

These documents describe in particular temperature / time cycles suitable for the implementation of a wood retification process according to the aforementioned ARMINES patents. The teaching of these patents is also incorporated here by reference.

Finally, patent FR 2 757 097 is known, which describes a device for treating wood at high temperature, in a reducing atmosphere, by a gas heating system with recirculation of air in the combustion chamber, to effect combustion of the hydrocarbons. This process extracts the "tars" that the presence of water then forces to condense and does not specify the exact purpose of the treatment, which is a simple heating / cooling of wood simply stacked freely on carts. In any event, this patent provides for the introduction of water and an atmosphere comprising up to 3% of oxygen, which therefore cannot be applied to retification.

As we can see, a lot of complex research has aimed to discover, for more than fifteen years, processes for developing wood by transforming it into new products with new properties.

Reading the prior art, which will be referred to, reveals the complexity and the physicochemical finesse of these studies and the sensitivity of the processes which result therefrom.

Indeed, the processes are required to remain between narrow or very narrow operating margins, which can be achieved in the laboratory, but which become impractical or too expensive on an industrial scale.

The present invention relates to a wood retification reactor, therefore intended for the industrial implementation of the retification process as described in the prior art.

As we saw above, the constraints of retification are multiple and very restrictive.

We have seen that this is a heat treatment of wood (or more generally of woody materials of plant origin) which must be carried out under an inert atmosphere. The reactor will therefore have to prevent imperatively any oxygen and therefore ambient air entry, both to respect the process and for safety requirements (risk of spontaneous ignition). One can naturally think of providing the reactor with oxygen sensors and of monitoring this oxygen. But the problem is then that the known sensors or oxygen analyzers resist poorly the inevitable humidity of the retification process, and above all are influenced by VOC emissions (volatile organic compounds such as methane, various hydrocarbons etc ... ). It is therefore the combination of humidity and VOCs that poses the most serious problem.

Extremely precise monitoring of the temperature / time curve is also required. This implies, on an industrial scale, that we are able to solve a major difficulty, which is to carry with a very high precision (of the order of the degree Celsius) the entire mass of wood (several tons ), simultaneously, at the same temperature of the cycle, then to pass with the same temperature / time precision to the next zone of the cycle, etc ... remarkably insulating material from the thermal point of view.

The difficulty is all the more severe since the same precision must be obtained not only during temperature rises, but also during the cooling phase (s).

An obvious solution would be to lengthen all the phases to allow the temperature more time to homogenize in the mass. This would be to forget that, on an industrial scale, one cannot envisage such a lengthening of the process, on the one hand because of the energy cost, and on the other hand because of the longer immobilization of the wood, which would lead to very low yield. Above all, too long a treatment period at high temperature would trigger reactions in the wood, which would become uncontrollable and degrade the mechanical properties of the final product.

Another difficulty encountered relates to the deformation of the mass of wood subjected to such a heat treatment. The object of the process is among other advantages to obtain a dimensionally very stable wood; this objective would naturally be meaningless if the wood came out deformed or warped from the retification reactor.

This accumulation of major difficulties linked to each other (for example, the more brutal the thermal shock, which is economically desirable, the more the strain stress will be strong ...) is undoubtedly the explanation of why none retification reactor exists to date, despite the great interest of this technology.

These problems have been solved, according to the invention, by a reactor which is characterized by:

- a sealed enclosure for continuous or discontinuous operation;

means of strong mixing of the atmosphere used for heating the wood;

a loading system on which the wood is kept under an “evolving” mechanical constraint.

The oven includes means for injecting inert gas such as nitrogen to create and maintain the inert atmosphere. These means are known.

By “evolutionary”, we designate here a mechanical stress capable of accompanying and compensating for the shrinkages that the wood undergoes as a function of temperature cycles.

The term “inert” atmosphere denotes here the fact that an inert gas, preferably nitrogen, is injected from the start of the cycle start, the nitrogen progressively replacing oxygen until it becomes an atmosphere of 'pure nitrogen (in any case, without oxygen, but containing VOCs and moisture, as well as other extracted products such as methanol or acetic acid).

According to a preferred embodiment, the "progressive" constraint is exerted by hydraulic cylinders. According to another less preferred embodiment, the jacks are replaced by springs carried on the loading carriages, these springs being tensioned at the start of the treatment and having to be both able to withstand the temperature cycles and to exert a constant or very substantially constant compressive force. In practice, these springs will be made of stainless steel.

According to another embodiment, the strong mixing of the atmosphere is obtained by centrifugal turbines.

According to a particularly preferred embodiment of the invention, a system of flaps is provided, the reversal of which makes it possible to reverse the direction of passage of the flow of treatment gas through the charge.

An embodiment of this flap system is shown in FIG. 3 and is schematically described in FIG. 6. The system described is not limiting, and other means of reversing the flow will appear clearly to those skilled in the art. job.

The function of this reversal is to ensure that the flow of process air which has just been heated by the electrical resistors does not always pass through the mass of wood in the same direction; this would indeed cause an asymmetry in the heat treatment of the load, since the hottest air would attack the load always on the same side. The inversion (for example every 5 minutes) causes the load to be alternately attacked on each side by the hottest air.

This inversion principle is important in order to achieve satisfactory temperature uniformity of the charge.

According to one embodiment, the hot retification air circulates around the mass of wood then is directed by at least one fan to a cooler where the condensates, mainly water, methanol and acetic acid, extracted from the wood being condensed treatment. The air leaving the condenser is then returned to the process air flow, mixed with this flow, then reheated with the flow and returned to the load. Preferably, the cooler is a finned air / air heat exchange condenser or a similar device of known type.

According to yet a preferred embodiment of the invention, this condenser is used, in addition to its condensate removal function, to cool the load of wood during the temperature reduction phases. By this dual function of the condenser, the reactor according to the invention therefore solves one of the problems posed in a simple manner.

According to a preferred variant, the reactor further comprises a double enclosure wall into which cold ambient air is injected, this wall becoming a cold radiator and participating in the cooling of the inert atmosphere circulating around the load of wood. , with the desired speed.

The invention allows a precision, in temperature uniformity, of the order of 1, 5 to 2 or 2.5 ° C, which meets the specifications. This is remarkable, in the case of loads of the order of 8 m3 and the complex and demanding temperature / time cycle which will be described below.

The heating consists of batteries of electrical resistors, the only ones capable of ensuring, in the current state of technology, the heating of the air subjected to the desired strong mixing (that is to say, heating of the air with thermal inertia also as low as possible), according to the cycles described in the patents FR 2 751 579 and 2 751 580 mentioned above.

In order to avoid any entry of air, and therefore of oxygen, the enclosure and the access doors are gas tight.

Another important aspect of the invention resides in the mode of loading.

It is a trolley on which the stacks of pieces of wood are placed, separating each layer with wooden or metal slats; the voids thus created between each layer allow better access of the mixed air to the entire load. Above all, the upper layer is prestressed by hydraulic cylinders (or any similar system, like the springs worn mentioned above), which is transmitted to the whole load, so as to subject it to the “evolutionary” stress described above.

Without this essential provision, the other essential provision which is the violent mixing of the treatment atmosphere would only have led to thermal shocks which would have deformed the wood.

Those skilled in the art will understand that the result of this prestressing was absolutely not certain. Indeed, it was certain that the wood subjected to thermal shocks deforms; on the other hand, nothing indicated that it was enough to prestress it according to the invention to prevent any deformation. In particular, it would have been more likely that residual stresses remained, rendering the wood unusable. This is all the more the case since the wood leaves the reactor at 0% humidity. It would have been logical to fear that the inevitable resumption of humidity would result in a warping of the wood and therefore significant losses during machining. This serious drawback does not occur, since according to the invention the dimensional stability of the product obtained does not exceed +/- 2% which is remarkably low, taking into account the cycles undergone.

Without wishing to be bound by any theory, the Applicant attributes this surprising result to the combination of the retification process and the “evolutionary” constraint exerted for example by the jacks.

The reactor for wood retification is also characterized by the fact that the method of loading wood into the reactor comprises at least one carriage on which the stacks of pieces of wood are placed, separating each layer by wooden or metal slats , and preferably two carriages arranged on either side of the reactor enclosure.

In this configuration, the reactor according to the invention operates on the principle of discontinuous heating. The reactor enclosure has two access doors, one at each end. While a carriage and its constrained load undergo treatment after entering the enclosure from one side, another load is prepared on a second trolley on the other side. When the first carriage leaves on its side, the second will enter and the cycle can start again. It is understood that the cycle must be as short as possible to reduce the waiting time.

However, the reactor according to the invention can also be adapted to continuous treatment, as illustrated by FIG. 7 and its commentary.

According to a preferred arrangement, the continuous reactor enclosure is divided into several modules in order to be able to process loads of very different volumes without requiring heating and cooling of the entire enclosure, which would be an expense (and a time) perfectly useless. This will be described in more detail with reference to Figure 7.

According to a nonlimiting example, the batch reactor can be adapted to accommodate loads of 1, 5, 3, 4.5 or 6 m, as shown in Figures 1 to 4. In these figures, we see in effect that all the systems such as jacks, mixers (engines and turbines), and the like, are distributed over the length of the reactor, according to an arrangement making it possible to treat the different lengths of charge above, and above all impose the same temperature uniformity throughout the reactor enclosure, whether the charge is 1.5 m, 3 m, 4.5 m or 6 m. This is essential to avoid any heterogeneity, for example on an edge of the load, etc.

Naturally, the air circuits must include valve and distribution systems adapted to supply one, two or three modules.

The cycle can be fully programmed, and a PLC (or man-machine interface) controls the various functions which have just been described.

The temperature rise and fall cycles will, in a preferred embodiment, be those described in the aforementioned patent FR 2 751 580, in particular in FIG. 1 of this patent. Other characteristics and advantages of the invention will appear better on reading the description which follows, and with reference to the appended drawing, in which:

FIG. 1 represents a general sectional view from above of the reactor in discontinuous operating version according to the invention

2 shows a side view in partial section along -> A of the reactor in discontinuous operating version according to the invention shown in Figure 1

3 shows a side view in section (excluding condenser) along BB of the reactor in discontinuous operating version according to the invention shown in Figure 1

FIG. 4 represents a general side view in partial section of the reactor in discontinuous operating version according to the invention

Figure 5 reproduces by way of nonlimiting example Figure 1 of the aforementioned patent 2 751 580, applicable both to continuous and discontinuous mode

Figure 6 (Figures 6 a and 6 b) schematically shows the operation of the flow reversing flaps visible in Figures 2 and 3, applicable to both continuous and discontinuous mode

- Figure 7 shows a schematic side view of a reactor according to the invention, suitable for continuous operation.

In the figures, the same references have the same meanings, which are as follows.

1 Watertight door

2 Set of trolleys (trolley 2a, trolley 2b) Cooling fan

Condenser circulation fan

Hydraulic central

Condenser cooling fan

Condenser

Cooling fan

Load clamping cylinders

Brewers

Safety valve

Air flow reversal system

Table (flow measurement, nitrogen injection, pressure regulation)

Load clamping device (shown in clamping position)

Load of treated wood on carriage 2a

Load of wood awaiting treatment on the trolley 2b

Brewer's turbine

Flow reversing flaps, position 1

Flow reversing flaps, position 2 It will be understood that position 1 of the flaps corresponds to circulation in one direction, and position 2 in the "opposite" direction, as shown diagrammatically in FIGS. 6a and 6b.

20 Pivot pivot axis

21 Connecting rod between the flaps, for simultaneous tilting of the two flaps

22 Electric heating resistance

PMB bottom dead center of the clamping device 14

TDC top dead center of the clamping device 14

T in Figure 1, shows a view of zones 2-3-4 without the interior sheet metal

P in FIG. 1, represents a view of zone 1 without the structure of the ceiling

The operation of the reactor according to the invention will be obvious to those skilled in the art on reading the above and the figures, as well as the following example.

According to a preferred construction method, the jacks 9 are mounted on the top of the reactor and exert their action vertically, through the roof structure, by clamping devices 14, in particular of the plate type shown.

The cylinders are programmed via the automaton to compensate for deformations and / or other dimensional or stress reactions of the wood during the temperature / time cycle.

In Figure 6, which consists of Figures 6a and 6b, there is shown the inversion of the treatment atmosphere flow through the set of flaps. In FIG. 6 a, the flaps 19 are in the so-called “2” circulation position and the turbine and the flaps direct the flow as indicated. The hottest flux is located to the right of the figure (contact with resistor 22 right, before attacking the load). The coolest flow is on the left (flow having passed through the load before meeting the left resistance 22). There is therefore a temperature gradient in the load, from the right (warmer) to the left (slightly less warm). This causes asymmetry in the heat treatment. To restore symmetry, the set of flaps is reversed by the link 21 or any similar system, to reach the reverse or "opposite" circulation position called "1" which corresponds to FIG. 6b, flaps 18.

Anyone skilled in the art will understand that reversing the flaps reverses the direction of the gradient.

The inversion is carried out approximately every 5 minutes, or according to any other suitable frequency.

FIG. 7 represents a reactor according to the invention, suitable for continuous operation.

The charges A, B H, I, enter and circulate in the direction indicated.

The reactor is, according to a preferred non-limiting mode, limited to five modules

30 drying

40 preheating

50 retification

60 phase one cooling

70 cooling phase two

The modules are isolated by watertight doors E. All the systems which have just been described, mutatis mutandis, are used. The indicative temperatures are shown in the figures for clarity, as seen, some modules can be divided (dotted line) into, for example, two cells placed at different temperatures, there is also shown in Figure 7 a diagram not limiting heat recovery by an appropriate series of return circuits 80, 90, 100. These circuits, which use known heat exchangers, not shown, will be understood by any person skilled in the art.

It will also be understood that the retification module 50 has priority because its temp cycle. / time is fixed and imperative and therefore determines the number of charges in the downstream and upstream modules.

Example of batch processing:

A load of 8 m3 of spruce was treated, in pieces of thickness 27 mm for 100 mm in width and 6 m in length.

The green wood has been dried to reduce its moisture content by approx. 30-40% (initial content) at approx. 12% at the inlet of the reactor in Figures 1 to 6.

The reactor is loaded, the watertight doors are closed, and the treatment cycle of FIG. 6 is started with nitrogen injection. The whole treatment is carried out with a slight nitrogen overpressure.

We go up in a first step to 80 ° C and level at 80 ° C: total 2h. the brewers are at 35,000 m3 / h / 1.5 m long zone. The flow is reversed every 5 minutes.

Then rise to 170 ° C and level at 170 ° C; total 2 h. Same conditions.

We then go up to 230 ° C and level, duration 1 hour. Same conditions.

Then cooled to outlet conditions, 50 ° C and 0% humidity. The conditions are the same, except that, on the one hand, the cooling of the double side wall is carried out, and that on the other hand, the condenser cooling fan is raised in speed so that the treatment atmosphere (hot nitrogen plus H20 plus VOC) condenses the condensates and is cooled before being returned to the stream. We therefore operate a double cooling, internal and external.

A brown product is obtained, having excellent mechanical properties and a dimensional stability of 1.8%.

The invention relates to the reactors which have just been described, as well as the process for treating wood or woody materials combining retification and placing of the load under "progressive" stress, and finally the load-carrying carriages on which are worn, according to a particular embodiment, means for exerting this evolutionary constraint during a retification process, such as stainless steel springs capable of compressing the load with a constant or very substantially constant force during the treatment, and finally the new products thus obtained.

Claims

1 Reactor for wood retification, which is characterized by:

a sealed enclosure for continuous or discontinuous operation;

- means of strong mixing of the atmosphere used for heating wood;

a loading system on which the wood is kept under an “evolving” mechanical constraint, and

which is characterized by the fact that the heating consists of batteries of electrical resistances

2 Reactor for the retification of wood, according to claim 1, which is characterized by the fact that one exerts on the load of wood in treatment a mechanical stress known as "evolutionary", capable of accompanying and compensating for the withdrawals which undergoes wood as a function of temperature cycles.

3 Reactor for the retification of wood, according to claim 1 or 2, which is characterized in that the "evolutionary" constraint is exerted by hydraulic cylinders.

4 Reactor for wood retification, according to any one of claims 1 to 3, which is characterized in that the jacks 9 are mounted on the top of the reactor and exert their action vertically, through the roof structure, by clamping devices 14.

5 Reactor for the retification of wood, according to any one of claims 1 to 4, which is characterized in that the jacks 9 are programmed by means of the automaton to compensate for deformations and / or other dimensional reactions or stress of the wood during the temperature / time cycle. 6 Reactor for the retification of wood, according to any one of claims 1 to 4, which is characterized in that the evolutionary stress is exerted by springs carried by the load-carrying carriages, in particular stainless steel springs.

7 Reactor for the retification of wood, according to any one of claims 1 to 6, which is characterized in that the strong mixing of the atmosphere is obtained by centrifugal turbines.

8 Reactor for the retification of wood, according to any one of claims 1 to 7, which is characterized in that there is provided a system of flaps whose periodic inversion (18, 19) allows to periodically reverse the process gas flow through the feed, to periodically reverse the temperature gradient in the feed.

9 Reactor for the retification of wood, according to any one of claims 1 to 8, which is characterized in that the shutter system is placed under the brewer's turbine and comprises two shutters mechanically connected by a link.

10 Reactor for wood retification according to any one of claims 1 to 9, which is characterized in that the hot retification atmosphere circulates around the mass of wood and is then directed by at least one fan to a condenser where condensate condensates, mainly VOC, methanol and acetic acid, extracted from the wood being treated.

1 1 Reactor for wood retification, according to any one of claims 1 to 10, which is characterized in that the treatment atmosphere leaving the condenser is mixed with the treatment flow and then heated with this flow before being returned to the load.

12 Reactor for wood retification, according to any one of claims 1 to 9, which is characterized in that the condenser is a finned air / air heat exchange condenser or the like. 13 Reactor for wood retification, according to any one of claims 1 to 11, which is characterized in that this condenser is used, in addition to its condensate removal function, to cool the load of wood during the phases of temperature drop, by cooling the treatment atmosphere.

14 Reactor for the retification of wood, according to any one of claims 1 to 13, which is characterized in that the reactor also comprises a double enclosure wall into which cold ambient air is injected, during of the cooling phase.

15 Reactor for the retification of wood, according to any one of claims 1 to 14, which is characterized in that the enclosure and the access doors are gas tight.

16 Reactor for the retification of wood, according to any one of claims 1 to 15, which is characterized in that the method of loading the wood into the reactor comprises at least one carriage on which the stacks of pieces of wood are placed , separating each layer with wooden slats

17 Reactor for the retification of wood, according to any one of claims 1 to 16, which is characterized in that the method of loading the wood into the reactor comprises two carriages arranged on either side of the enclosure of the reactor.

18 Reactor for the retification of wood, according to any one of claims 1 to 17, which is characterized in that it operates according to the principle of discontinuous heating.

19 Reactor for the retification of wood, according to any one of claims 1 to 18, which is characterized in that the reactor enclosure comprises two access doors, one at each end adapted so that, while a trolley and its constrained load undergo the treatment after entering the enclosure from one side, another load is prepared on a second trolley on the other side. 20 Reactor for wood retification, according to any one of claims 1 to 19, which is characterized by the fact that the reactor enclosure is divided into several modules in order to be able to treat loads of very different volumes without imposing heating and cooling of the entire enclosure

21 Reactor for wood retification, according to any one of claims 1 to 20, which is characterized by the fact that the cycle can be fully programmed, and an automaton (or man-machine interface) controls the various functions of the cycle.

22 Reactor for the retification of wood, according to any one of claims 1 to 21, which is characterized in that it operates according to a principle of continuous treatment.

23 Reactor for wood retification, according to any one of claims 1 to 22, which is characterized by the fact that it comprises several drying, preheating, retification, phase one cooling and phase two cooling modules, separated by doors. waterproof.

24 Reactor for the retification of wood, according to any one of claims 1 to 23, which is characterized by the fact that it comprises subdivisions into cells in said modules, except the retification module.

25 Reactor for the retification of wood, according to any one of claims 1 to 24, which is characterized in that it comprises circuits for recovering the heat of retification.

26 Reactor for the retification of wood, according to any one of claims 1 to 25, which is characterized in that it comprises means for injecting inert gas such as nitrogen.

27 A method of treating wood or woody materials, characterized in that it combines retification and loading under "evolving" constraints, in an inert atmosphere. 28 load-bearing carriages for use in the reactor according to any one of claims 1 to 26 or in the method according to claim 27, on which are carried means for exerting said evolutionary stress, during the retification process, as stainless steel springs capable of compressing the load with a constant or very substantially constant force during said treatment.

29 New products characterized in that they are obtained in the reactor according to any one of claims 1 to 26 or by the process according to claim 27, or using at least one carriage according to claim 28.