WO1989005847A1

WO1989005847A1 - Method and device for the torrefaction of vegetable ligneous material

Info

Publication number: WO1989005847A1
Application number: PCT/FR1988/000625
Authority: WO
Inventors: Roger Gerard; Jean-Paul Cimetiere
Original assignee: Sotraveg
Priority date: 1987-12-22
Filing date: 1988-12-20
Publication date: 1989-06-29
Also published as: FR2624876B1; YU233188A; EP0345336A1; FR2624876A1; ES2009673A6; PT89321A

Abstract

The present invention relates to a process for the torrefaction of ligneous material of vegetable origin wherein, continuously and in a unique sealed vessel: the material is dried in a first oven (2) in the presence of vapor in order to remove the water and the acetic acid, up to a temperature of 180°C approximately, and in a second oven (3), the temperature is raised up to 280°C in order to torrefy the material in a water vapor-laden atmosphere; the water being taken from the vapor issued from the drying step.

Description

METHOD AND DEVICE FOR ROASTING MATERIAL

VEGETABLES

The present invention relates to a process for roasting vegetable woody material, in particular wood in logs, sticks, chips, reconstituted or agglomerated in granules or in any other form; but it also applies to everything that is of plant origin and can constitute biomass.

The roasting of wood and other woody materials is a technique that has been known for a long time and was the subject of in-depth studies at the beginning of this century. It has been found, in fact, that between charcoal distilled at high temperature (that is to say beyond 300º0 and wood), there was an intermediate state of matter where not only were the disadvantages of charcoal reduced and wood, but new properties were obtained; it was discovered that the wood is roasted when brought to a temperature between 100ºC and 290 ° C, and that the roasting has optimal qualities when it is carried out in temperatures of the order of 270 to 290 ° C; the product obtained is not very hygroscopic, dense, easy to handle and clean, it has a lower calorific value than charcoal distilled at high temperature, but at least 21 000 kjoule / kg and its calorific yield at equal volume is significantly higher than that of charcoal.

These properties were used in the late 1930s because they made the use of gas engines economically preferable to the use of petrol engines. After the Second World War, roasted wood lost its interest for many years, notably for the following reasons:

- the gasifiers, where it was used, themselves posed the risk of explosion due to the significant releases of hydrogen,

- the product obtained was quite heterogeneous:

a) the bowls being a very poor conductor of heat, it is difficult to obtain a uniform temperature throughout its mass, during the treatment,

b) from a temperature of around 250ºC, the wood enters a mainly exothermic reaction which is difficult to control. It follows a very rapid rise in temperature which exceeds the maximum roasting temperature and the wood begins to carbonize,

Many devices have been developed with the aim of controlling roasting but without giving any real satisfaction either because of the excessive complexity of the installations, or because of the risk of fire or explosion as a consequence of the very rapid ignition of the particles. of wood in suspension in the presence of oxygen, an inflammation which is communicated to the whole mass, that is to say very high production costs,

- and above all the massive exploitation of the oil slicks, very early after 1945, caused the replacement of gasifier engines by petrol engines. Among the devices produced at this time, there is in particular patent FR-A-993,131, which describes an installation for manufacturing roasted combustible agglomerates. The wood is cut into small fragments which are dehydrated, then sieved, roasted and finally agglomerated and cooled. However, the installation described in this document cannot be used for wood chips with a volume much greater than the fragments, since the patent provides for agglomeration of the products which includes a phase and a device for cooling the roasted material, which avoids the risk of ignition, on the other hand the recirculation in the roasting oven of part of the gases released during roasting does not allow good control of the treatment which in practice limits the maximum roasting temperature to around 260ºC.

However, at present, certain industries need energy and seek to avoid the use of petroleum; this is the case of metallurgical reduction in which the oxidized metal is reduced in the presence of reducing bodies.

This reduction is commonly carried out with coal which has unsaturated carbon, or in the gas phase with reducing bodies such as hydrogen, but never or very difficult with petroleum which produces saturated hydrocarbons.

Faced with the explosion dangers of reduction in the gas phase (hydrogen) and the ever increasing costs of coal extraction, wood roasting is a solution to the search for fuel and presents a new economic interest.

New devices, (described in the document "Gui de Techni que de l a Carbonisation" printed in

Edi ti ons Edisud in 1985) were made. The roasting is carried out in a neutral atmosphere to avoid the presence of oxygen favoring the spontaneous combustion of wood, from a temperature of 250ºC. The wood is roasted either in a rotary kiln or in a succession of vertical ovens; each oven corresponding to a determined heating temperature, that is to say in a single vertical oven brought successively to different temperatures, these ovens corresponding to a production of batch roasted wood,

To reduce production costs, a continuous roasting device has been developed in which the wood is dried in a first horizontal oven and then roasted in a second oven separate from the first. However, these installations still have many drawbacks:

- they are complex and very expensive,

- the roasting temperature, beyond 250ºC, is still poorly controlled, or at the cost of significant consumption of neutral gas,

- the product obtained is of poor cleanliness: a thin layer of coal dust covers the wood.

The object of the present invention is a process for roasting wood and other woody materials of plant origin, continuously, in a simple, automatic, non-polluting roasting device, giving a clean, homogeneous and stable product.

The subject of the invention is a continuous roasting process of wood and other vegetable woody materials in which first of all in a first compartment, the wood is heated to dry it and extract the acetic acid, then in a second compartment the temperature of the previously dried wood is raised and brought to the roasting temperature of the wood being, in each compartment, stirred by giving it a slow movement which leads it from the entry to the exit of said compartment, characterized in that:

- drying and roasting are carried out in a single, reed enclosure,

- the drying temperature of the wood between the inlet and the outlet of the compartment is gradually brought to the maximum temperature of 185ºC, the heating being carried out by a first stream of preheated gas charged essentially with steam and circulated by a first fan ,

- the roasting temperature is gradually brought to the maximum temperature of 285ºC, in an atmosphere mainly charged with steam in order to control the rise in the temperature of the compartment, the heating being carried out by a second stream of gas preheated and circulated by a second fan, in that:

- The drying gas, charged with water vapor, is partly recirculated in the drying compartment, partly recirculated in the roasting compartment, partly partly evacuated in order to eliminate the excess vapor from the enclosure, and that:

- the roasted wood is poured into a tank filled with a solution containing water in order to cool the product obtained,

- the cooled wood is taken from the tank and transported out of the enclosure to a storage and bagging unit, The invention is also remarkable for the following characteristics:

- the gas pressure in the roasting compartment is slightly higher than that prevailing in the drying compartment so that the drying gas does not flow into the roasting compartment,

- the drying gas is partly recycled in the drying fan, partly evacuated and led into the cooling tank in order to collect in the tank part of the water extracted from the wood, partly recycled in the roasting circuit, and partly recycled between the outlet of the drying compartment and the inlet of the roasting compartment, and in that the roasting gas, at the outlet of the roasting compartment is completely recycled in the roasting fan,

- the drying gas at the outlets is saturated with water vapor.

- the roasting gas, at the outlet, is added with water vapor and recirculated in the roasting fan,

- water is supplied to the roasting oven to ensure a minimum quantity of water vapor in the compartment.

The invention also relates to the device for roasting wood or other woody material of plant origin, according to the method defined above comprising successively a drying oven and a horizontal roasting oven, superimposed, communicating with one another, each internally comprising a perforated cylindrical drum movable in rotation about its longitudinal axis provided means of advancement of the wood, characterized in that it comprises:

- a closed tank of raw material, communicating with the inlet of the drying oven so that the gas circulation between said oven and the tank is reduced to the maximum,

- a communication chute between the two drying and roasting ovens,

a cooling tank essentially comprising water, disposed under the outlet of the roasting oven, the tank being intended to receive the roasted material, the water being intended to cool and rinse said material, the water level being at a height ensuring the closure of the outlet of the roasting oven, said tank being in communication with a means of removing and transporting the material of the carrier strip type or the like, and in that each oven comprises supply lines and respective outlet for drying and roasting gases, fitted with manual and / or automatic flow control valves,

- the assembly constituting a single sealed enclosure.

The device is also remarkable for the following characteristics:

- It includes a plurality of evacuation pipes for products extracted from drying:

- at least one recycling line taking gas from the outlet side of the compartment and circulating the gas in the drying fan,

- at least one recirculation line divided into two sub-lines: . a water vapor recycling line, recirculating a fraction of gas, saturated with water in the roasting fan;

a pipe for recycling the water vapor recirculating a fraction of gas saturated with water in the communication chute;

- at least one evacuation and recovery pipe for supersaturated water vapor and condensates in the cooling tank; the flows in these pipes being under the control of known instruments: pressure, temperature sensors, flow meters, valves, solenoid valves, or the like;

- It includes a roasting gas evacuation pipe which takes the gas from the side of the inlet of the roasting compartment and recirculates all of the gas in the roasting fan.

- The drying gas supply pipes are arranged along the compartment, each supply pipe being arranged downstream of a discharge pipe so that the circulation of the gas is against the flow of the movement of the material.

the communication chute between the two ovens is short, vertical, cylindrical, and is surrounded by a circular groove supplied with drying gas supersaturated with water vapor, in order to form a ring of gas insulating the two compartments, the means for advancing the wood is a rib which develops in a helix from the entry to the exit of the drum, and extending substantially from the wall of the drum towards the central axis of said drum,

_ the drying drum comprises at least one helical disc coaxial with the central axis, extending at most over 360 °, the same as that of the rib,

the roasting drum comprises at least one helical disc coaxial with the central axis, extending at most over 360 °, the same as that of the rib.

- The discs are arranged at the location of the rib so that they form an extension of the rib up to the axis of rotation.

- the drying drum has three boxes separated by two discs.

- the roasting drum has three boxes separated by two discs

- The compartments are equipped with measuring, command and control devices of known types connected to a programmable controller, in order to operate automatically.

The present invention provides the following advantages:

the device is of simple design and its realization represents moderate investments,

- its operation can be fully automated,

- the release of polluting gases into the atmosphere is completely eliminated, the consumption of cooling water is low due to the recovery of the water extracted from the roasted material,

- The invention can be used as well with pieces of wood, plates, sticks, or other, as with plants of other origin and compacted: compost, grass, straw, stalks of cereals etc.

- the tank is used to clean the products of any particles.

In the following description, an example of wood roasting will be described, but of course, this example is not limiting.

In order to better understand the invention, the following drawing shows:

FIG. 1: a schematic profile view of the roasting device according to the invention,

FIG. 2: a schematic side view of the roasting device of FIG. 1,

- Figure 3: a graph illustrating the evolution of the temperature according to the method of the invention.

As seen in Figures 1 and 2, the roasting device according to the invention comprises a single enclosure 1, internally comprising two ovens or compartments: a drying compartment 2 and a roasting compartment 3; the two compartments are separated by a communication chute 4.

The enclosure 1 is sealed so that there can be no entry or exit of gas with the atmosphere which is not controlled. The drying compartment 2 has at one end 5, an inlet pipe 6, intended to receive the bowls.

In the exemplary embodiment, this inlet pipe communicates with a closed volume 7 in which a large quantity of wood to be treated is stored; this pipe is controlled by a wheel of the vane type 8 controlled by a motor not shown, but any other known device for regulating the supply can be used.

Preferably the volume 7 is sealed, in order to avoid the ingress of water, but still in practice care is taken to limit gas exchanges between the compartment 2 and the volume 7 as much as possible in order to avoid thermal losses with the mass of waiting wood and the volume of gas present in this volume. To this end, the power supply by paddle wheel can be replaced by any other means making an airlock and limiting exchanges. On the other hand, we also use the large mass of waiting wood to make a buffer between the two volumes.

At the opposite end 9, the enclosure comprises a vertical overflow 10 intended for discharging the roasted wood; this weir plunges into a cooling water tank 11 so that the water level is always above the outlet section of the weir, there is no communication of the roasting compartment with the outside air . The roasted wood, at the outlet of the roasting compartment, falls by gravity into the weir and then into the bin.

To evacuate the cooled roasted wood, it is planned to install a conveyor belt 12 in the cooling tank 11: under the progressive accumulation of wood in the weir, part of the wood sinks, is distributed in the tank, and reaches the strip.

The compartments are both in the form of a drum 13, 14 cylindrical perforated or trommel, substantially horizontal, movable in rotation about their central longitudinal axis 15, 16. The drums are each driven by a motor 17, 18 of known type and held by rollers not shown.

Each drum is internally provided with a helical rib 19, 20 which extends from the inlet 23, 24 to the outlet 25, 26 of said drum 2,3 and the rib extends from the lateral perforated wall 21, 22 of the drum towards the axis 15, 16.

These ribs 19, 20 are intended to drive the wood in the manner of an endless screw with the rotation of the drum 13, 14 in a slow and continuous advancement movement from the inlet to the outlet of the drum, and to ensure regular and repetitive brewing of the wood, which ensures good temperature uniformity in the wood.

Thus when the wood enters the inlet 23 of the drying drum 13, it is driven and stirred in the drum, which it crosses longitudinally; when it reaches the outlet 25 of the drum it falls into the chute 4 which separates the two compartments and enters the inlet 24 of the roasting drum. There, it is again stirred and driven by the rib 20 and gradually reaches the outlet 26 of the drum, from where it comes out to fall by gravity into the weir 10.

The drums are perforated to allow the circulation of drying and roasting gases. Each compartment has pipes for supplying and evacuating the drying and roasting gases:

- The drying compartment 2 comprises a supply line 27, and evacuation lines 28, 29, 29 '. The supply line 27 is connected to a drying fan 30. The exhaust line 28 is connected to the inlet of the drying fan 30 in order to recycle part of the drying gas. The drying fan has at its outlet a gas burner of known type, for example a propane burner or the like. This burner is intended to heat the drying gas to a temperature of around 165 ° C minimum to 185ºC maximum.

Upon ignition, the gas in the drying compartment is air; this air is heated by the burner. Due to the evaporation of the water contained in the wood, the combustion of the heating gas, and the recycling, the drying gas is depleted in oxygen and enriched in water and carbon dioxide, to the point that there is practically no more oxygen.

The supply lines 27 ', 27 ", are arranged downstream of the discharge lines 28', 28", so that the circulation current is against the current of the movement of progression of the wood, or from downstream to upstream. This arrangement makes it possible to obtain a water content in the wood coming out of the compartment, practically constant, and avoids the circulation of the drying gas in the roasting compartment.

According to the invention, there are also provided conduits 29, 29 ′ discharging the excess water vapor, and drying condensates. These pipes are preferably arranged on the side of the inlet of compartment 2 in order to evacuate the part of the gas which is richest in water vapor, and in condensates. Line 29 is connected to the cooling tank in order to recover the condensate, that is to say the condensed drying water vapor, and the other products dissolved in this water, and to dissolve by bubbling the other gases coming from the drying. (acetic acids in particular).

This arrangement makes it possible to achieve a significant saving in water consumption since the evaporated water represents approximately 30% of the weight of the raw wood.

On the other hand, a pipe 29 ′ is preferably arranged at the upper part of the compartment and the withdrawn steam is recirculated on the one hand in the roasting circuit by the fan 37, on the other hand at the level of the chute. communication 4. The flow rate in the fan 37 is controlled by an automatic valve controlled by the temperature prevailing in the roasting oven 3.

Flow, pressure and temperature regulators not shown but of known type are provided in these conduits 27, 27 ', 27 ", 28, 28', 28" and 29, 29 'so that the maximum drying temperature is around 180 ° C and a maximum of 185ºC.

It is considered that roasting begins when the wood hardly releases any more water, that is to say when its moisture content reaches a determined minimum threshold H. Depending on the species and for pieces of wood of a volume average of the order of 10 × 3 × 3 m ^-6 , that is to say platelets, this threshold is reached for drying temperatures varying between 170 and 185ºC. At 165 ° C drying is generally not sufficient.

In addition, according to the invention, provision is made to control the temperature in the drying drum 13 by placing internally along the drum, discs 31 forming a partition, separating two adjacent boxes. In the example illustrated, two discs 31 are provided, which separate the drum 13 into three boxes 32, 33, 34.

These discs are helical and have the same pitch as that of the helical rib 19; and they are preferably located on the rib.

Thus in the embodiment shown, the first box 32 has no hot gas inlet, and two discharge outlets 29, the second box 33 has a hot gas inlet 27 "and two recirculation outlets 28, the third box has two hot gas inlets 27 'and a recirculation outlet 28.

This realization makes it possible to heat the wood very gradually as illustrated by the lower curve of FIG. 3; the greatest amount of steam is released in the first box without significant increase in temperature and all the steam is recovered in 29, 29 ', in the second box, the actual heating begins and the wood still releases a large amount of water, in the third box, heat is mainly used to heat the wood which has lost most of its water.

The roasting compartment 3 comprises a supply pipe 35 for roasting gas and a discharge pipe 36 for this gas.

The supply line 35 is connected at 35 'to the outlet side 26 of the drum 14, and the discharge line 36 is connected downstream of the connections 35' to the side of the drum inlet 24 so that the current from the roasting gas is against the current of the advancement movement of the wood. The exhaust pipe 36 is connected to the inlet of a roasting fan 37 in order to recycle all of the outgoing roasting gas.

In addition, according to the invention, a gas pipe 38 is provided between the evacuation pipe 29 ′ for the drying gases and the fan 37. It is this pipe which, by supplying the fan, with gas very rich in vapor. of water, allows to really control the roasting.

The roasting fan 37 has at its outlet a gas burner, of a type known per se, for example a propane or other burner, intended to heat the roasting gas to the maximum temperature of 290ºC.

The roasting gas is composed as follows:

- gas recirculated in 36

- gas from the combustion of the burner,

- gas saturated with water vapor coming at 38 from the outlet 29 '.

The two compartments 2, 3 of the enclosure 1 are superimposed, the roasting compartment 3 being at a lower level relative to the drying compartment 2. In the embodiment, compartment 3 is under the drying compartment 2 in the same vertical plane, as illustrated in FIG. 2, but this is not compulsory: they can for example be in perpendicular planes. In this way, the wood can flow by gravity from one compartment 2 to another 3.

Between the two compartments there is a communication chute 4; this chute is preferably vertical, short and cylindrical. According to the invention, provision is made to surround the chute 4 with a groove 39 provided with an inlet 40 for drying gas supplied by line 29 '; this chute forms a ring of gas which surrounds the wood coming from the drying drum and prevents very hot roasting gas from circulating towards the drying compartment and causing a thermal shock on the dried wood, capable of initiating the reaction exothermic. In addition, in order to avoid the flow of drying gas to the roasting compartment, the pressure in the latter compartment is preferably maintained slightly higher than that prevailing in the preceding compartment: there is therefore constantly a slight depression between the bottom and the top of the enclosure. However, this arrangement is not essential and the two compartments can be isobars and the steam introduced into the chute can flow into the roasting compartment: it is then evacuated with the roasting gas, at 36.

The main function of this chute is to separate the drying and roasting treatments, which constitutes a condition for the good quality and regularity of the roasted product: on the one hand, the wood is gradually dried in the presence of an atmosphere charged with water vapor , and on the other hand, immediately after and without temperature variation between the treatments, the steam comes from an atmosphere charged with water vapor, the steam coming from the drying by a separate pipe.

The supply lines 35, 35 ′, 40, the evacuation lines 36, and the recirculation lines 38 are provided with control, measurement and command means of a type known and not described, for example valves, solenoid valves, flow meters, thermometers, pressure sensors, and the like so that the temperature in the roasting drum gradually increases from the temperature of 180ºC at inlet 24, to the temperature of 280ºC at outlet 26.

In order to control the change in temperature in the roasting drum 14, there are internally, along the drum, helical discs 41, forming a partition separating the drum into two adjacent boxes.

These discs are of the same design as the discs 31: not even that of the rib 20, and located on the rib.

In the example illustrated, two discs 41 are provided, separating the drum 14 into three boxes 42, 43, and 44. The box 42 has a discharge outlet 36, the box 43 only has a gas inlet 35 'and the box 44 only has a gas inlet 35 'Of course, this arrangement can be modified and the compartment may include one or more than two discs.

This realization makes it possible to heat the wood very gradually as illustrated by the upper curve of Figure 3: the evolution is linear up to 280 ° C, and then it remains constant until the exit.

What is remarkable is the regularity of the temperature rise, especially between around 250 and 280ºC.

Indeed, we know that from the temperature of 250ºC, the wood enters into a spontaneous exothermic reaction; this reaction leads to a very rapid increase in temperature in the roasting oven: when the temperature is allowed to exceed 290ºC, the wood immediately enters the carbonization phase, which should be avoided. According to the invention, the main purpose of supplying water vapor to the roasting compartment is to control the temperature increase, the water vapor here having the function of absorbing the production of heat from the exothermic reaction.

In addition, in order to ensure roasting in an atmosphere charged with steam, provision is made to supply the roasting oven directly with water 50: it is indeed possible that the steam content in the oven decreases and quickly becomes insufficient ( for example with wood that is already very dry at the entrance to the drying compartment or at the end of treatment when the drying oven is empty): in this case, it is imperative to provide an additional supply, otherwise the quantity of steam introduced in 38 in the roasting circuit would be insufficient and the exothermic reaction would take place without the possibility of control.

In addition, according to the invention, all of the measurement and control instruments are connected to a programmable control cabinet, not shown, in order to constitute a fully automatic roasted wood production installation.

Finally, at the outlet of the drum 14, the roasted wood is poured by gravity through a weir 10 into a cooling tank 1.1 containing water.

The weir 10 plunges into the tank 11 so that the gas from the enclosure 1 cannot escape. One of the walls of the weir is inclined, at an angle of about 45º; the part of the opposite wall 46 plunging into the tank is curved, in order to guide the wood under the inclined wall as illustrated in FIG. 2.

There is under the inclined wall a conveyor belt 12, itself inclined so that the wood is entrained by this band and transported to a storage tank, from where it is then transported in a known manner to the bagging unit.

The function of the cooling tank is to reduce the temperature of the wood from 280 ° C to a lower temperature, preferably ambient, at most 60ºC; water also has the function of washing the wood of impurities which could be on its surface: ash, particles of coal, etc.

In the embodiment, a paddle wheel 48 is shown in the cooling tank. This wheel is intended to drive the roasted wood which floats on the surface of the water downwards and force it to descend and go towards the conveyor belt, according to the arrows in Figure 2.

However, this wheel is not essential and any other means can replace it; it is even possible to foresee nothing: the only weight of the column of roasted wood, in the weir, forcing the wood to plunge into the tank; gradually it moves and, guided by the curved wall, reaches the conveyor belt.

As can be seen, the device according to the invention brings numerous advantages:

- it is simple and inexpensive,

- gas recirculation, and reuse of water for cooling and for roasting: very low water consumption

- two ovens in a single enclosure,

- absence of neutral gas, - No atmospheric pollution since no gas is released directly, the products obtained are always of uniform and constant quality due to the automatic control of the operation, and in addition they are always clean at the outlet of the cooling tank.

In addition, the device makes it possible to roast not only small wooden plates, that is to say of the order of 10 cm long for an average section of 10 cm, but it can also roast pieces in the same way. wood of a much larger volume (logs or other) or fragments of a much lower volume. Only the operating parameters change: duration of treatment, quantity of vapors, etc ... And finally, the device can be used regardless of the species of wood, or whatever the compost of material of woody plant origin.

Claims

1. Continuous roasting process of wood and other woody vegetable materials in which first of all in a first compartment, the wood is heated to dry it and extract the acetic acid, then in a second compartment the temperature of the previously dried wood and it is brought to roasting temperature, the wood being, in each compartment, brewed, giving it a slow movement which leads it from the entry to the exit of said compartment, characterized in that:

- drying and roasting are carried out in a single sealed enclosure,

- the drying temperature of the wood between the inlet (23) and the outlet (25) of the compartment (2) is gradually brought to the maximum temperature of 185ºC, the heating being carried out. by a first stream of preheated gas charged essentially with water vapor and circulated by a first fan (30),

- the roasting temperature is gradually brought to the maximum temperature of 285ºC, in an atmosphere essentially charged with steam in order to control the rise in the temperature of the compartment (3), the heating being carried out by a second stream of preheated gas and circulated by a second fan (37), in that:

- the drying gas, charged with water vapor, is partly recirculated in the drying compartment (2), partly recirculated in the roasting compartment (3), partly partly evacuated so remove excess steam from the enclosure, and in that: - the roasted wood is poured into a container (11) filled with a solution containing water in order to cool the product obtained,

- The cooled wood is taken from the tank (11) and transported out of the enclosure to a storage and bagging unit (7).

2. Roasting method according to claim 1 characterized in that the gas pressure in the roasting compartment (3) is slightly higher than that prevailing in the drying compartment (2) so that the drying gas does not flow not in the roasting compartment.

3. Roasting method according to claim 2 characterized in that the drying gas is partly recycled in the drying fan (30), partly evacuated and led into the cooling tank (11) in order to collect in the tank a part of the water extracted from the wood, partly recycled in the roasting circuit, and partly recycled between the outlet of the drying compartment and the inlet of the roasting compartment, and in that the roasting gas, at the outlet ( 36) of the roasting compartment is completely recycled in the roasting fan (37).

4. Roasting method according to the preceding claim characterized in that the drying gas at the outlets (29,29 ') is saturated with water vapor.

5. Roasting method according to claim 4 characterized in that the roasting gas, at the outlet, is added with water vapor and recirculated in the roasting fan (37).

6. Roasting method according to claim 1 characterized in that the furnace is fed roasting (3) with water to ensure a minimum quantity of water vapor in the compartment (3).

7. Continuous roasting device for wood or other woody material of plant origin according to the method of claim 1 comprising successively a drying oven and a horizontal roasting oven, superimposed, communicating one inside the other, each comprising internally a perforated cylindrical drum movable in rotation about its longitudinal axis provided with means for advancing the wood, characterized in that it comprises:

- a raw material tank (7) closed, communicating with the inlet (23) of the drying oven (2) so that the gas circulation between said oven and the tank is reduced to the maximum,

- a communication chute (4) between the two drying and roasting ovens,

- A cooling tank (11) essentially comprising water, placed under the outlet (26) of the roasting oven, the tank being intended to receive the roasted material, the water being intended to cool and rinse said material, the water level being at a height ensuring closure of the outlet of the roasting oven, said tank being in communication with a means (12) for removing and transporting material of the carrier strip type or the like,

and in that each oven comprises respective supply and outlet pipes for the drying and roasting gases, provided with manual and / or automatic flow control valves,

- the assembly constituting a single sealed enclosure.

8. Roasting device claim 7 characterized in that it comprises a plurality of discharge lines for products extracted from drying:

- at least one recycling line (28) taking gas from the outlet side of the compartment and circulating the gas in the drying fan (30),

- at least one recirculation line (29 ') divided into two sub-lines:

a pipe (38) for recycling water vapor, recirculating a fraction of gas, saturated with water in the roasting fan (37);

a pipe (40) for recycling the water vapor recirculating a fraction of gas saturated with water in the communication trough (4).

- At least one pipe (29) for evacuating and recovering the supersaturated water vapor and condensates in the cooling tank (11), the flows in these pipes being under the control of known instruments: pressure sensors , temperature, flow meters, valves, solenoid valves, or others.

9. Roasting device according to claim 7 characterized in that it comprises a pipe (36) for evacuating the roasting gas which takes the gas from the side of the inlet of the roasting compartment, and recirculates all of the gas in the roasting fan (37).

10. Roasting device according to claim 7 characterized in that the pipes (27 ′, 27 ″) for supplying drying gas are arranged along the compartment (2), each supply line being arranged downstream of a pipe (28 ', 28 ") evacuation so that the gas flow is against the flow of the material.

11. Roasting device according to claim 9 characterized in that the communication chute (4) between the two ovens (2) and (3) is short, vertical, cylindrical, and is surrounded by a circular groove (39), supplied with drying gas (40) supersaturated with water vapor, in order to form a gas ring insulating the two compartments.

12. Roasting device according to claim 7 characterized in that the means for advancing the wood is a rib (19, 20) developing in a helix from the inlet (23,24) to the outlet (25,26 ) of the drum, and extending substantially from the wall (21, 22) of the drum towards the central axis of said drum.

13. Roasting device according to claim 12 characterized in that the drying drum (13) comprises at least one helical disc (31) coaxial with the central axis extending at most over 360º, the same as that of the rib (19).

14. Roasting device according to claim

12 characterized in that the roasting drum comprises at least one helical disc (41) coaxial with the central axis, extending at most over 360 °, the same as that of the rib (20).

15. Roasting device according to claims

13 and 14 characterized in that the discs (31, 41) are arranged at the location of the rib (19, 20) so that they form an extension of the rib up to the axis of rotation (15 , 16).

16. Roasting device according to claim 13 characterized in that the drying drum comprises three boxes (32, 33, 34) separated by two discs (31).

17 Roasting device according to claim 14 characterized in that the roasting drum comprises three boxes (42, 43, 44) separated by two discs (41).

18. Roasting device according to any one of the preceding claims, characterized in that it is provided with measuring, command and control devices, of known types, connected to a programmable automaton in order to operate automatically.