FR2775292A1 - Heat treatment of lignocellulose-containing materials by pyrolysis in a non-renewed atmosphere - Google Patents

Abstract

The materials are carbonized in a non-renewed atmosphere in a pyrogenic reaction. Carbonization is continuous and the materials are preheated and cooled in a non-renewed atmosphere. A vessel (1) forms a tunnel furnace supplied with heat (3) and with a chimney (4). A cylindrical tube (2) passes longitudinally through the furnace, with preheating and cooling zones at its ends The materials are mixed during the pyrogenic reaction and dried before the pyrogenic reaction. The tube contains a number of containers (17) in which the lignocellulose material is placed. These containers are driven in rotation by the tube and have a number of openings around their circumference. The containers are in the form of closed conical casks. The tube diameter is sufficient to allow the casks to pass through and to contain seven casks: five in the furnace and one in each of the preheating and cooling zones. The chimney contains means of treating the pyrogenic reaction vapors. A reservoir of pyrogenic reaction vapors is collected at the bottom of the chimney, to reduce the suction effect of the chimney and to feed the preheating zone. The cooling zone is cooled by a cold water circuit. The containers are placed in clusters. Alternatively, the material passes through the tube driven by an endless screw. The tube has hot pipes and cold pipes. The heating device rotates.

Description

 The present invention relates to a method of heat treatment of any material or material, simple or composite, comprising lignocellulosic fibers and a device for carrying out this method. The purpose of this process is to generate a thermo-chemical decomposition of the essential components, in particular wood into a solid residue with a high carbon content, that is to say to carry out carbonization.

 The prior art already knows such processes, described for example in French patent application No. 2,512,053. This document relates to a roasting process intended to produce a material with high calorific value.

 It has the drawback of being very complex to implement since the heat treatment is carried out under an inert atmosphere, of nitrogen for example.

 The method according to the invention intends to remedy this drawback by proposing not to carry out a complete carbonization of the woody materials, but a partial carbonization, of the pyrogenation type under an non-renewed atmosphere, while remaining at the limit of the exothermic pyrolysis of the material, without ever exceeding it. The non-renewal of the pyrogenation atmosphere is obtained according to the preferred embodiment of the invention by placing the woody materials in transported containers (or continuously according to the process) in the pyrogenation oven.

 Another important advantage of the process is the possibility offered to recover and recycle large quantities of dry or wet lignocellulosic materials hitherto landfilled or incinerated due to their low calorific value or their possible contamination by an agent toxic.

 The device according to the invention also has the advantage of being able to operate continuously.

 The pyrogenized material obtained by the process according to the invention has multiple applications; chemically and physically inert, but having many physical qualities (thermal, sound insulation, etc.), it can be used as a filler or as an adjuvant in composite materials such as cement-based compositions for example.

 Other advantages will emerge from the description given below of the invention with reference to the appended figures in which - Figures la to Id represent the device carrying out the method according to the invention respectively seen in perspective, from the front, from the side, and from above - FIG. 2 represents a preferred embodiment of the device according to the invention seen in longitudinal section according to which the material to be pyrogenized is placed in drums driven in rotation by the oven; - Figure 3 shows a cross section of a preferred embodiment of the hearth of the device according to the invention; - Figure 4 shows another embodiment of the device according to the invention seen in longitudinal section, according to which the material to be pyrogenized is placed in drums driven in rotation by an endless screw passing through the oven; - Figure 5 shows another embodiment of the containers according to which the containers are introduced by cluster into the oven; - Figure 6 shows another embodiment of the continuous transit device for the material to be pyrogenized through the oven; - Figure 7 shows another embodiment of the pyrogenation device further provided with a dryer, and - Figure 8 shows another embodiment of the material heating device according to which heat distribution tubes are placed within matter.

 The method according to the invention is a method of heat treatment of materials made up of lignocellulosic fibers, comprising a step of carbonization of said materials.

 It is characterized in that said carbonization step is carried out partially under an unrenewed atmosphere. This operation constitutes a pyrogenation.

 The purpose of this pyrogenation is to obtain inert matter chemically and physically.

 According to a characteristic of the invention, this pyrogenization is carried out continuously.

 Preferably, the pyrogenation step is preceded by a step of preheating the material, and is completed by a step of cooling the material, both carried out under an unrenewed atmosphere, so that the material does not completely enter into combustion. .

 For more efficiency, it is preferable to stir the material to be pyrolized throughout the duration of the thermochemical treatment.

 The method can also comprise a step of drying the material before or at the start of introduction into the oven if the material to be pyrolized has a high humidity.

 The device implementing the method may have different embodiments. The description given below presents, in a nonlimiting manner, a preferred mode and a few additional examples of devices implementing the method according to the invention.

 The device carrying out the process according to the invention illustrated in FIG. 1 consists of an enclosure (1) thermally insulated forming a tunnel oven supplied with heat by a hearth (3) and a chimney (4) for discharging the gases of combustion of the hearth (3).

 The enclosure (1) forming the tunnel oven, consists of a box (7) of elongated shape and square or rectangular section placed on a metal frame (8). The box (7) comprises a thermal insulation (9) made of light refractory materials with low thermal conductivity fixed on the interior walls of the box. This box (7) with a width of about ten meters closed has four openings: the first (14) to allow the entry of hot gases from the hearth (3); the second (15) for the evacuation of fumes to the chimney (4) and the other two (16 and 16 ') at each end of the enclosure (1) to allow on the one hand the introduction of the material to pyrogenize through the opening (16) and on the other hand the recovery of the pyrogenized material through the opening (16 ').

 The temperature of the oven (16) and (16 ') gradually increases to 300 C and then decreases.

 According to a preferred version of the invention illustrated in FIG. 2, a cylindrical tube (2) driven in rotation is used as a heat exchanger between the hot gases and the material to be pyrogenized which passes continuously through the oven.

 Under the box (7) and in the frame (8) pass rotating drive shafts (10) maintained by rolling bearings (11). The shafts have rollers (12) at each ends supporting the cylindrical tube (2) and allowing it to rotate. A variator gear motor (13) fixed at the end of one of the shafts and its holding arm with elastic studs complete this device.

 The box (7) is surmounted by a chimney (4) for evacuating the combustion gases from the hearth.

 According to this preferred version, the material to be pyrogenized is introduced before the start of the heat treatment in containers (17) in the form of drums.

 The rotating metallic cylindrical tube (2) is of sufficient diameter to allow the passage of these barrels containing the material to be pyrogenized and protrudes from the ends of the enclosure (1) to form a preheating zone at the inlet and a zone cooling at the outlet. In addition, the cylindrical tube comprises near each end two wheels (18) whose treads are in contact with the rollers which support and drive the tube while allowing its expansion. The space (19) between the tube and the walls of the tunnel furnace serves as a conduit for the hot gases.

 The barrels, preferably seven in number in the device, five of which are in the oven proper and one in each preheating and cooling zone have a slightly conical shape so that they advance by themselves during rotation. of the cylindrical tube (2) and that the material they contain is stirred automatically and regularly.

Their forward speed depends on two factors the taper and the speed of rotation of the cylindrical tube (2).

 The containers (17) containing the material to be pyrogenized are hermetically closed during their transit through the cylindrical tube (2), in order to prevent the heated material from coming into contact with the ambient air and from being consumed.

 However, the containers (17) have a plurality of calibrated openings, distributed around their circumference to allow the evacuation of water vapor and volatile organic compounds emitted by the material to be hot pyrogenized as well as toxic agents including the material first can be impregnated.

 The containers (17) are therefore subjected to a slight internal pressure which prevents air from entering. When they leave the pyrogenator, the barrels are then cooled until their temperature is lower than the ignition temperature of the lignocellulosic material in order to be able to empty them without risk of combustion.

 In a preferred version of the invention, the device is further provided with a network for suction of the pyrogenation vapors comprising a collection hood (20) situated above the inlet of the cylindrical tube (2) provided with an entry door which is opened only when a new barrel (17) is introduced into the cylindrical tube, a pipe (5) and a pump (6), for example a centrifugal fan which ensures the suction of vapors from pyrogenation in the tube (2) via the pipe (5) and blows at high speed at the bottom (22) of the chimney flue (4) thus increasing the natural draft of the chimney by depressive effect .

This aspiration has a triple function: to prevent vapors and other volatile organic compounds from spreading in the room during the introduction of a new barrel (17) into the tube (2) and to ensure the heating of the first barrel by heat of these vapors and produce a "Venturi" effect at the bottom (22) of the chimney (4).

 The chimney (4) can also be provided with a device for treating pyrogenation vapors, not shown here.

 The cooling of the cooling zone of the tube (2) can be carried out by a water circuit, not shown here.

 In a preferred version of the invention, the hearth (3) is a wood hearth. It communicates the hot gases to the tunnel oven through a wide opening (14). This hearth as shown in Figure 3 consists of a metal casing (23) lined with insulating refractory materials and has in the lower part an inclined grid consisting of metal strips (26) between which the primary air passes. This grid can be shaken manually by the action of a lever outside the hearth and driving a camshaft (27) on which the upper part of the grid rests. The pieces of wood preferably constituting the fuel are introduced into the hearth (3) by a central chute (28) inclined so as to load the top of the grid and equipped with a tilting loading trough (29) acting as a valve. closing in these two extreme positions. The flames can develop by passing on each side of this chute. This hearth also includes adjustable secondary air introduction ducts (30) and a door (31) for access to the grate for ignition and ash removal. The primary air is introduced under the grid through a draft regulator (32) which also serves as a non-return valve.

 FIG. 4 illustrates another embodiment of the device according to the invention in which the containers (17) are driven not by the rotation of the tube (2), but by one or more endless screws (33) passing longitudinally through the oven . Each container (17) is provided with one or more racks (34) longitudinal or round so as to rotate on itself as it advances.

 One can also imagine introducing the material to be pyrogenized in any other container of different shape or comprising partitions, vertical or horizontal or even in bundles or in clusters. FIG. 5 illustrates an exemplary embodiment of a cluster (35) of containers. This cluster comprises for example four containers. It is furthermore provided with a handling beam (36) allowing the clusters of the tube (2) to be entered or removed.

 FIG. 6 illustrates another embodiment of the device for the continuous transit of the material to be pyrogenized through the furnace according to which the material is introduced in bulk into the tube (2), fixed or in rotation, without the intermediary of a container .

 The transit of the material and the mixing are ensured by an endless screw (37). The wood flow rate is calculated so that the pyrogenization is carried out without total carbonization of the material.

 According to another version of the invention illustrated in Figure 7, one can add to the heating device, a drying device (38) of the material to be pyrogenized, if the latter has too high a humidity level. The drying heat can come from the fireplace (3).

 The operating principle of the dryer is substantially identical: the wet wood (39) passes through a rotating cylinder (40) using an endless screw (41), and dries up as it progresses.

 Preferably, the air, before being evacuated by the chimney (4), passes through a heat exchanger (42).

 According to another version of the invention illustrated in FIG. 8, the heat transfer device can be modified so that the heat is transmitted to the material conveyed by the screw (37) by hot pipes (43) and that the cooling is produced by cold pipes (44).

 According to this version, the oven is equipped with an insulated fireplace (45) and casing.

 According to another version of the invention, not shown here, the heat transfer device can be of the rotary heat type. Thus, the gaseous mixture whose oxygen content is limited is injected into the stationary oven (2) to carry out the pyrogenization of the material.

Claims (24)

 CLAIMS 1. Process for the thermal treatment of materials comprising lignocellulosic fibers comprising a step of carbonization of said materials, characterized in that the carbonization is carried out partially under an unrenewed atmosphere, thus carrying out pyrogenation. 2. Method according to claim 1, characterized in that the carbonization is carried out continuously. 3. Method according to claim 1 or 2, characterized in that it further comprises a step of cooling said materials under a non-renewed atmosphere. 4. Method according to any one of claims 1 to 3, characterized in that it further comprises a step of preheating said materials under a non-renewed atmosphere. 5. Method according to any one of claims 1 to 4, characterized in that said materials are mixed during the pyrogenation phase. 6. Method according to any one of claims 1 to 5, characterized in that it further comprises a drying step before the pyrogenization step. 7. Device for implementing the method according to any one of claims 1 to 6, characterized in that it consists of an enclosure (1) forming a tunnel oven supplied with heat by a hearth (3) and a chimney (4) for evacuating combustion gases. 8. Device according to claim 7, characterized in that the oven is traversed longitudinally by a tube (2) of substantially cylindrical shape. 9. Device according to claim 8, characterized in that the tube (2) is rotated. 10. Device according to any one of claims 8 or 9, characterized in that the tube (2) has at its ends a preheating zone and a cooling zone. 11. Device according to any one of claims 8 to 10, characterized in that the tube (2) contains a plurality of containers (17) in which are arranged said materials comprising lignocellulosic fibers. 12. Device according to claim 11, characterized in that said containers (17) are rotated by the tube (2). 13. Device according to any one of claims 1 1 or 12, characterized in that said containers (17) have a plurality of openings distributed around their circumference. 14. Device according to any one of claims 1 1 to 13, characterized in that said containers (17) are closed drums of conical shape. 15. Device according to claim 14, characterized in that the tube (2) is of a sufficient diameter to allow the passage of said barrels and in that it contains seven barrels, five in the oven proper and one in each zone preheating and cooling. 16. Device according to any one of claims 7 to 15, characterized in that the chimney (4) is provided with a device for treating pyrogenation vapors. 17. Device according to any one of claims 7 to 16, characterized in that it comprises a network for suction of the pyrogenation vapors. 18. Device according to claim 17, characterized in that said suction network of the pyrogenation vapors terminates at the bottom (22) of the chimney (4) in order to increase the depression effect of the chimney (4). 19. Device according to any one of claims 17 or 18, characterized in that said vapor suction network supplies heat to the preheating zone of the tube (2). 20. Device according to any one of claims 10 to 19, characterized in that the cooling zone of the tube (2) is cooled by a cold water circuit. 21. Device according to any one of claims 1 1 to 14, characterized in that said containers (17) are arranged in a cluster (35). 22. Device according to any one of claims 7 to 10, characterized in that said materials comprising lignocellulosic fibers pass through the tube (2) by means of an endless screw (37). 23. Device according to any one of claims 8 to 10, characterized in that the tube (2) comprises hot pipes (43) and cold pipes (44). 24. Device according to any one of claims 7 to 10, characterized in that it comprises a rotary heat device.