RU2714648C1 - Reactor for wood raw material torrefication - Google Patents

Abstract

FIELD: forestry.

SUBSTANCE: invention can be used in timber industry for processing wood wastes. Reactor for wood raw materials torrefication includes housing closed from above and from sides by metal enclosure with insulation 9, with heating chamber and torrefication chamber. Reactor is mounted on supports 1, 2, 3, on which at an acute angle to horizon there rigidly installed are guides 4, on which drums 5 with loaded wood raw material can slide under action of gravity. Movement control of drums 5 is carried out by means of cutouts 6, 7, 8, made with possibility of vertical movement. Reactor is heated by furnace boilers 14 and 15, flue gases and gaseous products are removed through chimney 10. Drum 5 is made from stainless steel sheet in form of welded cylinder with bottom, to which in drum 5 cavity one end is welded with perforated pipe, forming annular cavity for loading of wood raw material. To limit spontaneous rolling of reels 5 there is limiting stop 16 having slots for forks of forklift truck 13, providing for removal of drums from guides 4.

EFFECT: disclosed reactor ensures high quality of the end product while reducing power consumption.

5 cl, 2 tbl, 11 dwg

Description

The invention relates to wood processing, in particular to torrefaction, and can be used in the forest industry for processing wood waste to obtain useful constituent components used as fuel.

A known complex for continuous heat treatment of solid small particles, mainly dispersed wood materials, in which preliminary preparation of the processed material is carried out, preparation of a gaseous heat carrier, simultaneous supply of heat carrier and material particles into the channel of the heat treatment chamber, drying of wood particles in direct contact with the heat carrier, joint removal of flow solid particles and gas mixture, the temperature of the coolant at the inlet to the heat treatment channel supports m within 500 ÷ 600 ° C, and the oxygen content in the coolant, such as flue gases was kept below 8 wt. %, while the supply of material for drying is supported in an amount that ensures the temperature of the stream at the outlet of the channel is not lower than 200 ° C, and the residence time of the particles of material in the heat treatment channel is maintained within 6–40 seconds (RF patent No. 2596683, publ. September 10, 2016).

In this complex for continuous heat treatment of solid small particles using a powerful fan of 90-100 kW, a flow of solid wood particles is fed into a gaseous coolant having a temperature of 500-600 ° C, which, together with the coolant, is driven through an annular, closed pipe of large diameter (1200 mm) and at the outlet of the pipe channel, the temperature should be at least 200 ° C.

The well-known thermal aerodynamic method of heat treatment provides high quality of the finished product, but has an extremely high energy intensity due to the high aerodynamic resistance, since it is necessary to spend 90-100 kW of electricity to move a small amount of solid wood particles in a gaseous coolant (5-7 kg per second).

An industrial installation that implements a patent for an invention of the Russian Federation 2596683 is designed, manufactured and put into operation in the city of Shelekhov, Irkutsk Region and has shown its effectiveness in the quality of the finished product, but it is energy-intensive.

A device for processing biomass is known in which the processing of biomass involves loading biomass into a torrefaction system, heating the biomass containing moisture to a temperature of torrefaction. The torrefaction system comprises a first processing device and a second processing device. In the first device, the biomass is heated to a temperature of 260-310 ° C for a first period of time and fed to the second processing device at a temperature of 230-280 ° C for a second period of time that is longer than the first period of time. In this case, the temperature in the second device is kept lower than the highest temperature in the first device. The first period of time is preferably a maximum of 3 minutes, and the second period of time is at least 3 minutes. (patent for the invention of the Russian Federation No. 2596743, publ. 09/10/2016).

With this method of heat treatment in forced-rotation drums, as described in RF patent for invention No. 2596743, when the biomass is first heated in one rotating drum during heat treatment and then moved to a second rotating drum, very large energy inputs for forced rotation are required for subsequent heat treatment drums and moving biomass from one drum to another.

There are known reactors for wood torrefaction described in sufficient detail (https://studref.com/307805/tehnika/reaktory_torrefikatsii, found on the Internet on February 25, 2019, see the Appendix to the application). As a result of the analysis, the following disadvantages by types of reactors can be given, namely:

- low quality of the finished product due to clumping of raw materials;

- burned out the finished product;

- high energy intensity of the process due to the high resistance during the aerodynamic transfer of raw materials, the movement of raw materials through the auger, the high engine power during rotation of the drums.

Also known are drums that do not rotate and are called retorts that are installed in a thermally insulated casing. Raw materials are loaded into the drums and they are subjected to heat treatment including drying, thermal modification, and, if necessary, torrefaction and further cooling. Since the drums do not rotate, there is no intensive mixing of the raw materials, while the finely chopped wood raw materials have extremely low thermal conductivity, which inevitably leads to the burning of raw materials on the walls of the drum, and in the center of the drum the wood raw materials are crumpled. The known device cannot provide the possibility of obtaining a torreficate with homogeneous properties. Known equipment is manufactured by Uraltehdrevugol LLC, Nizhny Tagil (MPRU-40, MPRU-60).

Patent research on the application to determine the prior art was carried out according to the following headings of the IPC: C 10L 5/44, C 10 B 47/30. As a result of patent research, the following technical solutions were also identified in this technical field that were taken into account in the analysis: CN 107434977, CN 107325825, CN 206308313, CN 208266115.

A known unit for torrefaction, comprising at least one torrefaction zone, which is a separate area in the compartment of the torrefaction unit, located in front of the heating zone with respect to the biomass inlet in the torrefaction unit, which contains means for separately controlling the temperature in said separate areas in which the temperature of the preheated biomass is kept almost constant at the desired torrefaction temperature for the desired torrefic time and where the desired torrefaction temperature is in the range from 220 to 600 ° C, and the torrefaction zone includes cooling means that are connected to a vessel or unit containing a cooling medium, where the cooling medium is water. (RF patent No. 2615169 , published on 04.04.2017).

In the known device, the presence of a screw moving the wood pulp through the heating, torrefaction and cooling zone requires a high energy consumption and the cost of overcoming the friction of wood raw materials relative to the surfaces of the screw and pipe.

In Onega, the Arkhangelsk region, a plant for the production of torrefied fuel pellets, which are obtained from wood lignin-containing waste, was built. The equipment is designed and manufactured in Finland. The energy intensity of the process of obtaining the finished product is also extremely high due to the electromechanical drive of the mechanisms of movement of raw materials.

The closest technical solution selected by the applicant as a prototype is a reactor for torrefaction of wood raw materials at low temperature, which contains a housing with a heating chamber and a torrefaction chamber, which are equipped with rotary drums (patent for the invention of the Russian Federation No. 2559491, publ. 10.08 .2015).

This device provides a fairly high quality product, however, it has high energy consumption and significant mass-overall dimensions.

An object of the invention is to reduce the energy intensity upon receipt of torrefied wood.

EFFECT: reduced energy intensity of a device for producing torrefied wood while ensuring high quality of torreficate.

The technical problem is achieved in that the reactor for torrefaction of wood raw materials contains a housing with a heating chamber and a torrefaction chamber, in which the drums with removable covers are rotatably disposed, characterized in that the reactor is additionally equipped with inclined guides that enable the drums to rotate by rolling them under the action gravity, in addition to the torrefaction chamber, a cooling section is made, while the guides at the boundaries of the heating chamber, torrefaction and the section are cooled They contain cut-offs made with the possibility of vertical movement, in the upper part of the reactor there is a pipe for exhausting gases leaving the reactor, and a perforated pipe is installed along the axis of each drum, which forms an annular cavity for loading the feedstock and interacts with one end face with a removable cover made with the possibility of removal of gaseous products from the cavity of the drum.

Drums and perforated pipes are made of metal.

Perforated pipes have through holes with a diameter of preferably 1-3 mm.

The guides are installed at an acute angle to the horizon, preferably at an angle of 7-10.

Comparison of the claimed technical solution with the prototype shows that it differs in the following features:

- the reactor is additionally equipped with inclined guides;

- the drums are mounted on inclined rails with the possibility of rotation by rolling under the action of gravity;

- in the reactor, in addition to the torrefaction chamber, a cooling section is made;

- guides at the borders of the heating chamber, torrefaction and the cooling section contain cutoffs;

- in the upper part of the reactor a pipe is made for the removal of exhaust gases;

- a perforated pipe is installed along the axis of each drum;

- the perforated pipe forms an annular cavity in the drum for loading raw materials;

- the perforated pipe interacts at one end with a removable lid, made with the possibility of removal of gaseous products from the cavity of the drum.

Therefore, we can assume that the claimed technical solution meets the criterion of "novelty."

The invention can be implemented using well-known technical means, therefore it meets the criterion of "industrial applicability".

When evaluating the inventive step, the applicant took into account the following additional materials.

The dissertation for the degree of Candidate of Technical Sciences A. Timerbaeva, supervisor, Doctor of Technical Sciences, Safin RR, “Heat treatment of crushed wood in plate-type reactors”, which provides a detailed analysis of the heat exchange processes that occur in the design different reactors. An abstract based on the analysis of patent information which examines intellectual property in the field of energy wood torrefaction, patented in Russia in 2013-2018. Author: Gornostaev Vitaliy Nikolaevich Leading Engineer, Head of the Department of Intellectual Property and Invention Protection, Petrozavodsk State University, Petrozavodsk, Republic of Karelia.

An analysis of the aforementioned prior art, as well as other known reactors for heat treatment of ground wood raw materials, showed that they have common problems, namely, high energy costs for ensuring the operation of torrefaction plants.

In the proposed device, a drum raised to a certain height, filled with feedstock, rolls along inclined guides under the action of gravity, sequentially without any electromechanical drive, rotates discretely and passes sequentially through the drying zones of the raw materials, heat treatment and the cooling section.

It should be noted that the drum is heated by heat exchange both from its outer surface and from its inner surface through a perforated pipe mounted along the axis of the drum. At the same time, a constant and intensive alteration of the raw material occurs in the drum, in which there is no sticking of the raw material into lumps, the likelihood of burnout or underburning of the finished product is reduced, and there is no burning of the raw material to the walls of the drum.

Engineering calculations show that the energy intensity in the proposed device is 2.5 to 3 times lower than that of the above heat treatment methods. Namely, the installation (the city of Shelekhov) - costs at a productivity of 3.6 tons / hour, with an electricity price of 6 rubles / kW amount to 180 rubles per ton of product. At the plant in Onega, costs are 175 rubles per ton of product.

When conducting patent information research, the claimed combination of features, providing the claimed technical result, was not identified, therefore, the claimed technical solution meets the criterion of "inventive step".

Figure 1 schematically shows the inventive device, where A is the drying section, B is the torrefaction section, C is the cooling section, D is the channel for supplying the drums, Figure 2 shows the drum, Figure 3 shows the locking device of the drum, .4, FIG. 5, FIG. 6, FIG. 7, FIG. 8 shows an experimental setup for conducting pilot tests; FIG. 9, 10 shows the finished product, which was obtained in an experimental installation from pine chips, Fig.11 - finished product obtained from sawdust aspen.

The reactor is mounted on supports 1, 2, 3, on which guides 4 are rigidly mounted at an acute angle to the horizon from 7-10.

The drums 5 can slide along the guides 4 under the action of gravity. In the drums 5 is placed wood raw materials, mainly waste logging, sawmilling and woodworking in the form of small pieces of wood chips and sawdust, or a mixture thereof.

To control the retention of the drums 5 from rolling under the action of gravity along the guides 4, cut-offs 6, 7, 8 are provided, made with the possibility of vertical movement by lowering and raising them. When lowering the cutters 6,7,8 is ensured that the drums 5 roll down.

The reactor is closed at the top and sides with a metal fence with a heater 9.

To remove flue gases from the reactor, including those generated from furnace boilers 14, 15, the reactor is equipped with a chimney 10.

The temperature of the flue gases in the chamber of torrefaction of wood raw materials is measured and regulated by temperature sensors 11, and in the heating chamber by temperature sensors 12.

The loading of the drums 5 with wood raw materials and the unloading of finished torrefied products is carried out by the manipulator and then the drums 5 are fed into the reactor by a forklift 13 from the left side and the same forklift 13 from the right side of the reactor, the finished drums 5 are removed.

To ensure the required drying temperature, a furnace boiler 14 is used, and for torrefaction of raw materials, a furnace boiler 15 is used.

To limit the spontaneous rolling of the drums 5 is a limit stop 16 having slots for the legs of the forklift 13, in order to remove the drums from the guides 4.

In FIG. 2 shows a drum 5, which is made of stainless steel sheet in the form of a welded cylinder with a diameter of 1.0 to 2.5 meters, a length of 2.0-3.0 meters and a bottom 17 that is hermetically welded to the cylindrical base of the drum 5.

A perforated pipe 18 with a diameter of 70-120 mm is welded to the bottom 17 of the drum 5, in which through holes 19 with a diameter of 1-3 mm are made along the entire length, through which moisture is removed from the wood raw material, as well as pyrolysis gases generated during torrefaction.

The perforated pipe 18 forms an annular cavity in the drum 5 for loading wood raw materials, therefore, heating of the wood raw material occurs simultaneously by heat exchange both through the outer surface of the drum 5 and through the walls of the perforated pipe 18.

The open end part of the drum 5 is equipped with a removable cover 21, has a stamped or welded mouthpiece 20, the outer diameter of which corresponds to the diameter of the removable cover 21.

In the center of the removable lid 21, a hole 22 is made, which, when the removable lid 21 is mounted on the perforated pipe 18, is fixed by a diametrical locking device 23, well known in practice for retorting the use of barrels with a removable lid.

The diametrical locking device 23 is a U-shaped flexible collar that slips around the perimeter of the removable cover 21 mounted on the mouthpiece 20 of the drum 5 from the side of its open end part and the free end of the perforated pipe 18. The diametrical locking device 23 is installed vertically and tightly fixes the removable the cover 21 with the help of the hook 24, on which the clamp of the locking lever 25 is thrown. By pulling the diametrical locking device 23 and the clamp of the locking lever 25, a reliable fixation is ensured. cover 21 and, accordingly, the tightness of the drum 5 is ensured. After fixing the removable cover 21, a plug 26 is installed on the perforated pipe 18. To prevent wood from entering the perforated pipe 18, the plug 26 is installed on the perforated pipe 18 when loading the drum 5. After fixing cover 21 diametrically locking device 23, and loading the drum 5, the plug 26 is removed, opening the hole 22 and the open end of the perforated pipe 18.

At the cooling section C, where the drums 5 with the finished product are cooled to a temperature of 80 ° C, nozzles 27 are provided for spraying cooling water.

To simulate the heat treatment process in the reactor and obtain the results and modes of thermal modification, torrefaction of crushed wood waste, preferably not more than 5 mm in cross section and 50-60 mm long, such as wood chips and sawdust, a complete experimental cycle was developed, manufactured and passed research experimental installation (hereinafter - EU) which is presented in Fig.4, Fig.5, Fig.6, Fig.7, Fig. 8.

The experimental setup is made in the form of a thermally insulated casing of sheet metal with a thickness of 3 mm, in the cavity of which a heater, for example, perlite, is placed (Fig. 4, section G-G).

The control unit is made on the pipe base 28, in the form of runners, which allow sliding the control unit to the desired location by sliding.

The tube base 28 is rigidly welded to the bottom of the lower part of the housing 29, to which the upper part of the housing, made in the form of a lifting cover 31, is attached through a hinge 30.

The lifting cover 31 has the possibility of lifting relative to the hinge 30 using the bracket 32 to which the cable 33 is attached and it is possible to raise and lower the lifting cover 31 to load and unload two drums 5.

Raising and lowering the lifting cover 31 is a mechanical winch 34, which transmits the force to the cable 33 through a vertical rack 35 and block 36.

In section GG (Fig. 4) on the upper and lower parts of the EU, it is evident that the upper 31 and lower 29 parts of the EU housing are made in two layers of metal 37 with thermal insulation 9 inside, for example, in the form of a well-known insulation - perlite, which is filled up between welded and tight metal sheets 37 with a thickness of 3 mm.

A temperature sensor 12 is installed in the lifting cover 31, which transmits an electrical signal to the digital control panel 38.

To adjust the required temperature in the temperature range 130-350 ° C, an electric blower fan 39 is used, which, depending on the required temperature set on the digital control panel 38, sets and regulates the required burning temperature of firewood in the lower part of the combustion chamber 40, located in the lower part of the housing 29, where there is an air supply valve 41, adjustable by a lever 42, which is either completely closed and prevents the air supply, or partially or completely open for air supply by the valve 41 and intensification Oren firewood.

The loading of firewood or any other type of solid fuel to ensure the temperature required for thermal modification (130-190 ° C) or torrefaction temperature (230-290 ° C) is made through the loading hatch 43, which is mounted on hinges 44 and has the ability to recline fully into the ground for convenience, loading firewood and is fixed in the closed position after loading the required number of firewood with the help of a lowering and rotating stop - latch 45, made in the form of a L-shaped movable latch.

To rotate the drums 5, made for experimental installation from standard barrels of 200 liter capacity with a removable cover 21, and a diametrical locking device 23, which is latched onto the hook 24 due to the locking lever 25, three rotating shafts 46 are provided. At one end of three rotating shafts 46, three rotating sprockets 47 are installed, which, due to the chain transmission 48 from the drive sprocket 49, are driven by a gear motor 50, which has the ability to control the desired rotational speed of the ring-shaped drums 5 filled with finely chopped wood raw materials in the form of wood chips and / or sawdust.

The rotation of the drums 5 is carried out according to a predetermined program that fully simulates the process of thermal modification and torrefaction of raw materials in the inventive reactor.

As a boiler, which provides the temperature necessary for thermal modification and torrefaction of wood raw materials, a combustion chamber 40 is used.

A chimney 10 is installed in the lifting cover 31, through which flue gases from the combustion of firewood, gaseous products released from the drums 5 and excess heat are removed.

Table 1 shows the modes of heat treatment of wood raw materials that were used on EU.

In FIG. 9, 10 shows the finished product, which was obtained on EU from pine chips, FIG. 11 - finished product from sawdust aspen.

The inventive device operates as follows.

To load the wood raw material of the drum 5, the removable cover 21 is removed. For this, the diametrical locking device 23 is removed by opening the locking lever 25 and removing it from the hook 24. The drum 5 is placed on the bottom 17, and on the free end of the perforated pipe 18 is put on the plug 26, which when loading wood raw materials prevents it from falling into the perforated pipe 18.

The loading of wood raw material into the drum 5, which is mounted vertically on the bottom 17, is carried out on a special loading conveyor (not shown in the figure) through a dispenser pipe, which pours a strictly defined amount of raw material into the annular cavity of the drum 5, the level of which should reach the level of the mouthpiece 20. Next, a removable cover 21. is put on. In this case, the plug 26 is removed from the perforated pipe 18 and the perforated pipe 18 is inserted into the hole 22 on the removable cover 21. Then, a diametrical locking device is put on. 23. 23. A clamp of the lever-latch 25 is thrown onto the hook 24 and the removable cover 21 is securely fixed on the drum 5, preventing atmospheric oxygen from entering it, and, as a result, ensuring such a tightness inside the drum 5 that prevents the spontaneous combustion of raw materials at high temperatures 130- 290 ° C (up to a maximum of 350 ° C).

To ensure a continuous cycle, the total number of drums 5 should be at least two times greater than the number of drums 5 located in the areas of drying A, thermal modification or torrefaction B and cooling C, and should preferably be 50-60 pieces.

The loader 13 places the drums 5 filled with wood raw material in the channel D onto the guides 4. The cutter 6 is lowered and the cutter 7 is raised and the drums 5 roll up to the cutter 7 and then the loader 13 loads the following drums completely filling the drying section A to zone D.

Before loading the first drum 5, furnace boilers 14, 15 of the corresponding sections of drying and thermal modification - torrefaction, are launched into operation, providing heating to a predetermined temperature. Furnace boilers 14, 15 operate on wood waste, taken for example in the form of firewood, cut.

The temperature of the heat flow in the drying section And should be in the range of 150-190 ° C, and in the area of thermal modification and torrefaction of raw materials - 200-300 ° C.

After the raw materials are dried within 40-75 minutes, the cutter 7 is lowered and the drums 5 are rolled up to the cutter 8 as the channel D is loaded.

Next, the loader 13 again loads the drums 5 with wood raw materials to the drying section A through the channel D. Thermal modification of the raw materials is carried out at a heat flow temperature from the furnace boiler 15 at a temperature of 200-220 ° C, lasting 40-60 minutes, and the raw materials are torrefied at a thermal temperature flow 290-300 ° C, torrefaction time is 30-40 minutes. A feature of the claimed design is that the coolant for drying and torrefaction is simultaneously supplied both to the outer surface and to the inside of the drums 5 through a perforated pipe 18 made of metal. This ensures uniform heating of the raw material, and through the through holes 19 of the perforated pipe 18, pyrolysis gases and water vapor are removed from the cavity of the drums 5, which are then removed from the reactor through the pipe 10.

After the wood raw material in the drums 5 has undergone thermal modification or torrefaction, the cutter 8 is lowered and the drums 5 with the finished product roll up to the stop 16.

In the cooling section C, the cooling of the drums 5 is carried out, as a rule, with water in a finely dispersed jet-drop method using nozzles 27.

When the temperature of the finished product in the drum 5 reaches less than 80 ° C, at which spontaneous combustion is impossible, the loader 13 picks up the drum 5 and takes it to the unloading area of the finished product.

The average estimated cycle time of the completion of the process in the reactor using the inventive drums 5, completely filled with wood raw material, which is preferably taken wet finely ground wood raw materials in the form of wood chips or sawdust, as well as their mixtures, determined on the basis of the experimental process carried out on an experimental installation, is 150-200 minutes (including cooling in the cooling section C).

This is due to the fact that the reactor for thermal modification and torrefaction of wood waste is a continuous device, where, after rolling one drum 5 to the stop 16 of the cooling section C, the loader 13 takes it to the finished goods warehouse to unload the finished product, and immediately replenishes the drum 5, filled with fresh wood raw material, places it in the channel D instead of the drum 5 which has rolled down earlier (having passed the full cycle).

The average duration of the torrefaction cycle in section B of one drum is 20-30 minutes, which is determined on the basis of studies performed on an experimental installation.

Table 2 shows the comparative estimated efficiency of energy consumption.

In FIG. 9, 10 and 11 show the obtained torreficate from pine shavings and aspen sawdust, which has a homogeneous structure, which can be obtained only if the raw materials are uniformly heated throughout the heat treatment cycle.

Thus, in the claimed technical solution, a high degree of quality of the finished product is achieved, ensured by the uniformity of heating, with a significant reduction in energy consumption. The reduction in energy costs is due to the fact that energy is spent only on heating the drums, and woodworking waste (cutting, shaving, etc.) is used for heating, and energy is not wasted on driving the rotation of the drums and forced movement of raw materials through the technological zones, and these energy costs , studies show, can reach 25-30%.

Table 1

No. Name of wood raw materials, humidity 60-90% Duration of a cycle, min. Total min drying thermal modification torrefaction cooling 1 sawdust 1.1 spruce 45-60 25-30 20-35 60 150-175 1.2 Pine 45-55 25-35 20-35 60 150-175 1.3 larch 55-60 35-40 25-30 60 175-190 1.4 Birch 55-65 30-40 25-30 60 175-195 1.5 aspen 55-60 25-35 20-25 60 155-180 2 Chips, maximum fraction 10 * 20 * 50mm 2.1 spruce 55-65 30-35 20-25 60 165-185 2.2 Pine 60-65 30-35 20-25 60 175-190 2.3 larch 65-70 35-40 25-30 60 185-200 2.4 Birch 65-70 35-40 25-30 60 185-200 2.5 aspen 55-60 30-35 20-25 60 175-180

table 2

No. p / p Name Energy consumption kWh / ton 1 Installation in the city of Shelekhov, Irkutsk region. thirty 2 Installation in Onega 28.5 3 The inventive reactor 21-23

Claims (5)

1. The reactor for torrefaction of wood raw materials contains a housing with a heating chamber and a torrefaction chamber, in which the drums with removable covers are rotatably disposed, characterized in that the reactor is further provided with inclined guides that enable the drums to rotate by rolling them by gravity, additionally a cooling section is made behind the torrefaction chamber, while the guides at the boundaries of the heating chamber, torrefaction and the cooling section contain cutoffs made with with the possibility of vertical movement, in the upper part of the reactor a pipe is made for the removal of gases leaving the reactor, and a perforated pipe is installed along the axis of each drum, which forms an annular cavity for loading the feedstock and interacts at one end with a removable cover configured to remove gaseous products from the cavity of the drum. 2. The reactor according to claim 1, characterized in that the drums and perforated pipes are made of metal. 3. The reactor according to claim 1, characterized in that the perforated pipes have through holes with a diameter of 1-3 mm 4. The reactor according to claim 1, characterized in that the guides are installed at an angle from 7-10 ° to the horizon. 5. The reactor according to claim 1, characterized in that the wood raw material is a waste of logging, sawmilling and woodworking in the form of small pieces of wood chips, or sawdust, or a mixture thereof.

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