A method for processing of wood raw material, and a crusher for wood raw material

Abstract

 A method for treating wood raw material (301), wherein the wood raw material (301) is introduced between a pair of rollers (350, 360) and the wood raw material (301) is pressed by the pair of rollers (350, 360), wherein the wood raw material (301) is crushed into crushed pieces (303). In the method, moisture is pressed out of the wood raw material (301) to dry the crushed pieces (303), and moisture is separated from the crushed pieces (303). Further, a system for crushing wood raw material is presented, comprising a crusher with a pair of rollers (350, 360), which pair of rollers is arranged to press the material. In the system, the pair of rollers (350, 360) is arranged to press the wood raw material (301) to reduce the moisture content, wherein the pair of rollers (350, 360) is arranged to crush the wood raw material (301) into crushed pieces (303). Furthermore, the system comprises a conveyor (304) arranged in connection with said crusher to separate moisture from the crushed pieces (303).

Description

Field of the invention

[0001] The invention relates to the pre-treatment of stumps and small timber at the initial end of raw material production, particularly in a forest (at the forest end), for use by power plants, biorefineries and the pulping industry, among other things. With the pre-treatment, it is possible to improve the qualitative properties of the raw material as well as to increase the cost efficiency of long-haul transportation. Furthermore, the method can be used to expand the raw material potential available for the forest industry.

Background of the invention

[0002] The use of biomass in various further processing plants, for example for the production of biofuel or as fuel for a boiler, is an increasing trend. In particular, the use of wood material as a renewable energy source with neutral carbon dioxide emissions has increased and partly replaced the use of non-renewable energy sources which generate carbon dioxide emissions, such as oil and natural gas, and according to some assessments peat, too. In order to collect wood material that might otherwise decompose in forests, such as stumps and logging residues, for utilization, so-called energy wood has also become favoured for further processing but has turned out to be more difficult to use than the materials used before.

[0003] A delivery of stumps and other energy wood may also often contain material that is problematic for the processing of the material, such as rocks of various sizes, sand and clay, which may cause various problems in the further processing plants. The rocks, sand, clay, and other similar non-combustible material may be conveyed as loose material with the stumps and other combustible energy wood, and furthermore, rocks may also be found partly or totally inside a stump. Said problematic materials also impair the production capacity; for example, they reduce the combustion capacity in boilers. Furthermore, in boilers, particularly detrimental problems are caused by non-combustible material clogging the grate or corresponding structures and the ash removal devices. Also, in deliveries of raw material for the chemical industry and the pulping industry, bark of wood material is detrimental. In general, it is known to separate loose metal material from wood chips by means of magnets, or also other loose material by a blower, as presented for example in CA 1,083,930. When the wood raw material comprises stumps, it is known, for example from CA 1,112,213, to remove the loose material from the stumps at the harvesting stage by shaking.

[0004] Another problem in utilizing biomass as a source of energy for a further processing plant lies in the fact that the dry solids content of the biomass supplied to the further processing plant may occasionally be so low that the utilization of said biofuel is no longer economically viable. For example, the use of particularly moist energy wood as fuel is usually not economically viable. The efficiency of the combustion process and thereby the control of the process are significantly dependent on the dry solids content of the biomass. Not only the moisture content but also a high unforeseeable variation in the moisture content may be a significant problem in view of the control of the process in the energy industry as well as in the chemical and pulping industries. Moreover, the treatment of biomass may be difficult, if the size of raw material pieces varies to a great extent or if the raw material contains too large pieces.

[0005] Also, in view of the transportation of the raw material, its moisture content, impurities and the varying size of pieces may cause problems. The moisture is water bound to the raw material, and its transportation is normally not economically viable. Similarly, impurities, such as rocks and loose soil, may unnecessarily increase the transportation costs. As a result of the varying size of pieces, in turn, part of the transportation capacity may be left unused, because the raw material cannot be loaded in the hauling equipment as tightly as when raw material pieces of equal size are loaded. When the wood raw material comprises small timber, it is known not only to store and dry the wood raw material but also to chip it to small chips at the forest end of the process before the transportation. When the wood raw material contains stumps, it is known to chop and crush the stumps into very small crushed pieces before the transportation, and to separate the loose material by blowing, for example as presented in CA 1,083,930. It is also known to remove metal parts from the chips by using magnets.

[0006] According to the prior art, the use of biomass, particularly wood, after the chipping comprises combustion, use as filling material, and composting as soil conditioner. In these uses, it is advantageous that the pieces are small in size. The devices of prior art, particularly the device according to EP 0 876 843, are designed to produce pieces of a relatively small size, ranging from 15 to 120 mm. The small size of pieces is secured by applying a suitable sieve or another arrangement in the crusher after the crushing. It should be noted that due to the end use of the devices, they produce material pieces of a small size. However, the use of wood raw material pieces of such a size is limited to the above-mentioned purposes and does not comprise, for example, the use of the raw material pieces in the pulping industry or the chemical industry. Application in these industries requires pieces of a larger size and a purer raw material.

[0007] Increased use of wood for energy production, among other things, and various rulings (e.g. customs rulings, forest conservation rulings) restricting the availability of wood have impeded the availability of wood raw material. The possibility that wood raw material which has conventionally been channelled for use in the pulping industry might end up in energy production in future, may decrease the supply of raw materials for the forest industry. The decreasing supply of raw materials may require that the raw material is utilized more efficiently. For example in the energy production, the specific heat of the raw material decreases significantly as the moisture content of the raw material increases. Furthermore, the increasing demand for wood raw material may set problems of supply for the pulping industry. For example, the capacity of debarking drums at pulp mills may become a limiting factor, if supplementary quantities of wood raw material can only be obtained by processing in a barking drum. The opportunity to use wood raw material in a different way makes it possible for the wood industry to utilize pulp mills at a higher capacity and to optimize the exploitation of wood better.

[0008] The procurement of raw material for use in the production of energy by means of arrangements of prior art is a long-term process. To achieve a sufficient degree of dryness requires special long-term storage. This means that high costs on the acquisition and harvesting of raw material as well as interest expenses on these costs are tied up in the storages. For example for stumps, storing for even longer than 12 months is required by the current method of energy production. Furthermore, such storing requires landing sites of a large surface area. This surface is excluded from other forestry for the time of the storage. For example stumps are first stored in heaps in a wood lot and subsequently in mounts along a forest truck road. The logging chain also requires several turns to the wood lot, which may delay and hamper the forest renewal.

[0009] Furthermore, new uses for wood raw material, for example, as raw material for the chemical industry, require measures for the quality control different from before. Current methods, in which the quality is degraded by variations in the size of pieces and in the moisture content, are not adequate for this purpose.

Brief summary of the invention

[0010] It is an aim of the present invention to reduce the above-described problems by pre-treating wood raw material by a crusher for drying the raw material, and by removing moisture from the crushed pieces. Such a pre-treatment improves the quality of the raw material, as the raw material is dried and impurities are separated. In an embodiment, moisture is removed by means of a conveyor. In an embodiment, impurities are removed from the crushed pieces by sieving.

[0011] In an embodiment, the raw material is pre-treated already at the initial end of the production chain, for example in the forest (at the forest end). The pre-treatment can be implemented, for example, by crushing the stumps at the harvesting stage in the forest or in a roadside landing (in a terminal). After the crushing, the crushed pieces may have a size of, for example, 10 to 40 cm. It has been found that a crushed stump dries in a storage heap considerably faster and drier than a stump that has not been pre-treated. Furthermore, in connection with the crushing, possibly assisted by sieving, the impurities of the stumps remain to a great extent in the forest or in the terminal, which improves the quality at the use end and may save transportation costs. After the crushing and pressing presented in the method, the crushed pieces can be baled. The baling enables better conservation of the quality of the raw material, as well as cost-effective long-haul transportation. The quality conservation, in turn, enables, among other things, the application of stump wood for also other uses than energy production, for example as raw material for the pulping and chemical industries. This improves the supply of raw material for the forest industry.

[0012] The method for processing of wood raw material according to the invention is characterized in what will be presented in the characterizing part of the independent claim 1. The system for crushing wood raw material according to the invention is characterized in what will be presented in the characterizing part of the independent claim 9. Furthermore, the use of a waste crusher for crushing wood raw material according to the invention is characterized in what will be presented in the independent claim 13.

Description of the drawings

[0013] In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1

shows a process of prior art for collection, transportation and use of wood raw material,

Fig. 2a

shows a process for collection, transportation and use of wood raw material according to one embodiment,

Fig. 2b

shows an advantageous embodiment of a process for pre-treatment of wood raw material,

Fig. 2c

shows a process for collection, transportation and use of wood raw material according to another embodiment,

Fig. 3a

illustrates the crushing of wood raw material in a side view,

Fig. 3b

shows the feed chute of a crusher of wood raw material seen from above,

Fig. 4a

shows the rollers of a crusher according to an advantageous embodiment of the invention seen from above,

Fig. 4b

shows the rollers of a crusher according to an advantageous embodiment of the invention in an end view,

Fig. 5a

shows an example of sieving of wood raw material in a side view, and

Fig. 5b

shows the example of Fig. 5a of the sieving of wood raw material seen from above.

[0014] In Figures 1 to 5, the same numerals or symbols are used for corresponding parts.

Detailed description of the invention

[0015] According to the prior art, wood raw material is used in power plants and biorefineries. A power plant refers to a station that produces energy, for example thermal and/or electric energy. A biorefinery refers to a production facility that refines biomass. Biomass refers to virgin materials or recycled materials (waste materials) originating from plants, such as trees or grass. Biomass comprises especially materials of wood origin. A refining production plant may be, for example, a facility that produces chemical, mechanical or thermomechanical pulp, or biofuel. Such pulp can be used, among other things, for papermaking or for making thermal insulation materials.

[0016] Figure 1 illustrates the manufacture and use of wood raw material according to the prior art in a schematic view. The manufacture and use are geographically divided into the forest end and the use end. At the forest end, the forest grows or is grown, which is indicated by reference numeral 10 in Fig. 1. After the growth, wood is harvested 11 and stored 12. The storage 12 in the wood lot typically takes place in roadside landings or the like, whereas the harvesting 11 of wood raw material takes place in the forest. Typically, the aim is to keep the distance between the wood harvesting site and the roadside landing small. Moreover, the wood raw material can be dried 13a. The drying and storage are technically similar events, because during long-term storage, the wood also dries. In this context, drying 13a refers to long-term storage, whereas storage refers to short-term storage between the harvesting 11 and the transportation 14, or storage in which drying is prevented by tarpaulins, or the like. According to the prior art, the drying may take for example longer than a year, in the case of stumps. The process steps at the forest end are shown by diagonal hatching in Fig. 1. Figure 1 shows the production process particularly when the wood raw material comprises stumps.

[0017] After the drying or storage, the raw material is transported 14 to the use end. The transportation 14 comprises at least the loading 14a of the raw material to a means of transportation at the forest end, the hauling of the raw material, and the reception of 14c of the raw material at the use end. Furthermore, during the transportation, the raw material can be moved from one means of transportation to another. At the use end, the raw material is processed 15 to a desired size of pieces and composition, and is transferred 16 to the subsequent process steps 17. For processing the material to the desired size of pieces and composition, a suitable processing means, for example a crusher or a chopper, is applied. The process steps at the use end are shown by horizontal hatching in Fig. 1. The process steps 16 and 17 are not significant for the invention. In addition to the transfer 16, they may comprise the production of pulp or biofuel from the wood raw material, or the combustion of the wood raw material.

[0018] The forest end and the use end of the process are typically very different with respect to the size of the area. The use end may be a single production plant, and the forest end may be a large forest area (of even several hundreds of square kilometers). Moreover, typically at least part of the forest end is geographically far (tens to hundreds of kilometers) away from the use end.

[0019] As presented in the background of the invention, in the transportation step 14, the raw material typically contains non-combustible material as impurities, and moisture bound to the raw material during the growth and/or storage. Furthermore, there is great variation in the size of the raw material pieces, which reduces the utilization degree of the transportation capacity, because voids are left in the load space of the transportation means. Said non-combustible material is typically mineral soil (for example rocks, sand, gravel, and clay). Of these, particularly problematic materials are normally rocks, because they may e.g. break equipment, and clay, which binds water to the material. Metal may also cause problems both in a crusher and in further processing, if it is not detected and removed from the incoming material. Particularly in the case of wood raw material, the raw material typically also contains detrimental non-combustible material in addition to energy wood. For example loads of stumps, that is, loads that comprise stumps, typically contain rocks of various sizes, which may be present both as loose rocks and possibly also in rocks left inside the stumps. Logging residue, in turn, contains non-combustible material particularly for the reason that the logging residue is typically stored in roadside landings to wait for transportation. Thus, the bottom layers of the energy wood storage are in contact with the soil material. Furthermore, it is possible that rocks are placed as weights onto a heap of logging residue. Thus, these rocks placed as weights may end up in a delivery of energy wood.

[0020] Figure 2a shows one embodiment of a process for producing and using wood raw material according to the invention. It has been found that after the growth 10 and harvesting 11 of wood, it is advantageous to pre-treat 20 the wood raw material before the storage 12. After the harvesting 11 and the pre-treatment 20, the wood raw material is stored 12 and can be dried 13b. It can be concluded from Figs. 1 and 2a that the invention relates particularly to that part of the process which takes place at the forest end, between the harvesting 11 and the transportation 14. However, it should be noted that the pre-treatment process presented in this application may also be suitable for use in other locations than those mentioned above for carrying out the process. Furthermore, the pre-treatment 20 may affect the way in which the transportation 14 or processing 15 is implemented. For example, in the pulping industry, the processing 15 may comprise the application of debarking drums which is not necessary as a process step for crushed wood raw material.

[0021] Figure 2b shows an advantageous pre-treatment process 20 in more detail. In this pre-treatment process, the wood raw material is crushed 22 by a crusher. The crusher used may be a crusher specially designed for this purpose, or a crusher modified from a commercial crusher (for example, Arjes Raptor XL) to be suitable for this purpose. Such a crusher can be, for example, a waste crusher. A waste crusher refers to a crusher that is arranged for crushing construction waste, such as wood, glass, rock material, or asphalt, or municipal or industrial waste. In general, the material to be crushed in crushers is introduced between a pair of rotating rollers, wherein the material is crushed by cutting protrusions provided in the roller. In connection with the crushing, the rollers also compress the material to be crushed.

[0022] Now, it has been surprisingly found that when such a crusher is used for crushing wood raw material into crushed pieces, the deformation work effective on the wood raw material during crushing by compressing is focused particularly on the wet points in the wood. This deformation work heats and thereby also dries the wood raw material. Thus, it has been found that in crushing by compressing, the moisture content of the wood material is decreased and also levelled out. In a corresponding way, after the crushing, the size of the crushed pieces is more uniform than before the crushing. Furthermore, impurities, such as non-combustible loose matter and bark, are separated from the raw material by crushing. If the crushed wood raw material is to be used in the pulping industry and the chemical industry, the size of the crushed pieces may be preferably 10 to 40 cm. The size of the pieces generally refers to the size of an opening, through which the piece can pass. Thus, the size of the crushed pieces in the direction of at least one dimension, the middle one in the order of magnitude, is advantageously 10 to 40 cm. It is also possible that the size of the crushed pieces in the direction of the two smallest dimensions is 10 to 40 cm, or that the size of the crushed piece in all three dimensions is between 10 and 40 cm. More advantageously, the size of the pieces may be 12 to 40 cm, and most advantageously 15 to 40 cm. Commonly available crushers do not necessarily produce pieces of such a large size, but the crushers may need to be modified, for example by removing sieves or the like from them.

[0023] In connection with the crushing 22, chopping of the material into smaller parts, debarking, removal of loose material, and drying take place. It has been found that during the above-described crushing, the moisture content is typically reduced by about 15%. The moisture released from the wood in the crusher is at least partly pressed out of the wood raw material and remains in the crusher or is vaporized. The released moisture can be separated from the crushed pieces, for example, by bringing (dropping) the crush onto a conveyor, wherein moisture possibly present on the surface of the crushed pieces is transferred to the conveyor or onto the ground, and vaporized moisture is entrained in the air.

[0024] Wood has been found to dry when it is pressed by a crusher. During the pressing, water is compressed out of the tissue of the wood. Furthermore, the wood raw material becomes warmer, wherein part of the moisture is vaporized. Moisture, such as water or steam, is separated from the compressed wood raw material, or crushed pieces. After the compressing, the crushed pieces can expand to at least some extent. Because some moisture has been removed from the crushed pieces, the crushed pieces do not absorb all the moisture back to their tissue.

[0025] The water pressed out of the wood raw material can be discharged from the crusher for example by means of gravity, wherein the water runs down from the crusher. The water can be led, for example, to the ground. The water can be led through a conveyor that is permeable to water or that guides water to the ground. Crushed pieces can also be led down by gravity. The crushed pieces can be led, for example, onto a conveyor. The conveyor is arranged to carry the crushed pieces away from under the crusher and to lead water to the ground. The conveyor is thus arranged to remove moisture from the crushed pieces. The conveyor may be, for example, a belt conveyor. The belt of the belt conveyor may be arranged to be permeable to water. The belt of the belt conveyor may be arranged to guide water away from the crushed pieces. The removal of moisture from the material flow discharged from the crusher and comprising crushed pieces and moisture, such as water and/or steam, reduces the moisture content of the remaining material, or crushed pieces, with respect to the moisture content of the uncrushed material, or the wood raw material.

[0026] The crusher exerts a compressive force on the wood raw material, deforming the wood raw material. Causing such a deformation requires work. This work is stored in the compressed piece in the form of at least one of the following: elastic energy, permanent deformation energy, and heat. Because the crushing is performed with great forces, all the energy is not stored in the form of elastic energy or deformation energy, and the wood raw material being crushed is heated. The heating speeds up the drying, because part of the moisture is vaporized. Moisture in the form of steam is also separated from the crushed pieces by leading the crushed pieces onto the conveyor. Thus, the crushed pieces can be led, for example by gravity, onto the conveyor, wherein the crushed pieces are dropped onto the conveyor. Because steam is water in gaseous form, due to the uplift caused by the air the gravity has no significant effect on steam, wherein the moisture in the form of steam is separated from the crushed pieces when the crushed pieces are led onto the conveyor.

[0027] On the conveyor, the crushed pieces are carried 23 to a sieve, in which the crushed pieces are sieved 24. By the sieving, impurities, such as soil and other fines, are removed from the crushed pieces. The sieving can also be used to separate bark parts of the wood which are impurities in view of pulping but raw material in view of energy recovery from wood. In this way, the use of the wood raw material can be taken into account and the raw material can be treated accordingly already at the forest end. Furthermore, a part of the same raw material batch can be separated for use, for example, in the refining industry and part for the use of the energy industry. In this way, for example when raw material is pre-treated for the refining industry, the bark material can be stored 12c temporarily at the forest end, and this bark material can be included in the crushed pieces to be supplied to the energy industry. In a corresponding manner, when supplying crushed pieces to the energy industry, it is possible to utilize the stored 12c bark material. By crushing, faster drying of the raw material is achieved, and the quality of the raw material is improved by reducing and levelling out the moisture content as well as by removing impurities, such as bark and loose material. Furthermore, sieving can be used for removing impurities from the crushed pieces already at the forest end.

[0028] Such pre-treatment enables baling 29 and/or other packing of the crushed pieces for transportation and further treatment. The crushed pieces can be baled after the storage 12 or drying 13b, before the transportation 14, or the baling can be left out, as illustrated in Figs. 2a and 2c. It is also possible that time is consumed between the baling 29 and the transportation 14, wherein bales of crushed pieces are stored at the forest end, as shown by the reference numeral 12b. By baling and packing the crushed pieces, it is possible to secure that their quality is preserved better also in the storage. The bales of crushed pieces can be, for example, wrapped in a moisture-tight material, wherein the moisture content of the baled crushed pieces is preserved and levelled out for further treatment. In such a case, the further treatment may be pulping or chemical industrial use. For combustion plants, the aim is normally to keep the crushed pieces as dry as possible. The bales can thus be wrapped in, for example, a mesh or another material permeable to moisture. The baling 29 can be implemented in a known way by a suitable baler, for example a Flexus Balasystem device. Furthermore, the baling 29 can further intensify the transportation efficiency, because baled crushed pieces take less space than non-baled crushed pieces.

[0029] Figure 2c shows another embodiment of a process for producing and using wood raw material according to the invention. The difference to the above-presented process shown in Fig. 2a is the fact that after the harvesting 11 of the wood raw material, the raw material is stored 12, followed by pre-treatment 20. After the pre-treatment, the crushed pieces can be dried 13b. In this embodiment, the apparatus performing the pre-treatment 20 can be brought to the storage location, and the costs for transportation of the apparatus are thus lower than in the embodiment of Fig. 2a.

[0030] Figure 3a shows an embodiment of crushing 22 wood raw material. Figure 3a shows a crusher for raw material according to an advantageous embodiment of the invention in a side view. In Fig. 3a, the wood raw material 301 has been fed into the crusher. The crusher comprises a feed vessel for wood raw material, delimited by edges 302. The crusher also comprises crushing rollers 350 and 360 which are arranged to crush the wood raw material 301. The crushing parts of the roller 360 are shown by broken lines, because they are not present in the sectional plane illustrated by Fig. 3a. Wood raw material 301 is introduced between the rollers, wherein the rollers crush the wood raw material into crushed pieces 303. The crusher can be provided with scrapers 307 for scraping the crushed pieces off the rollers. The crushed pieces enter the conveyor partly from between these scrapers. In a crusher according to an advantageous embodiment of the invention, the feed vessel is provided with openings 308, from which the wood material can also enter the conveyor. A conventional crusher for wood raw material does not comprise such openings. Uncrushed or chopped wood raw material can also enter the conveyor through such openings. Chopped wood raw material refers to wood raw material which has been removed from the rest of the wood raw material by means of crushing rollers, or wood raw material from which some wood raw material has been removed by crushing rollers, but which has not been guided between the crushing rollers. Also this wood material is called crushed pieces in the present description. After the crushing, the crushed pieces 303 are led to a conveyor 304, for example a belt conveyor. The conveyor can be driven, for example, by a belt pulley 305. The structure of the crushing rollers may influence the size of the crushed pieces obtained.

[0031] Because the raw material typically comprises rocks and other loose material, rocks and other loose material 306 may also be present in the crushed pieces 303. To separate this, the crushed pieces are sieved. The sieving arrangement will be described in more detail further below. Figure 3b shows, in a principle view from above, the feed vessel and the openings 308 provided in it, of a crusher according to an advantageous embodiment of the invention. The size of the openings corresponds to the size of the crushed pieces obtained from the process, and it may be advantageously 10 to 40 cm, more advantageously 12 to 40 cm, and most advantageously 15 to 40 cm. Furthermore, it has been found that the edges of the crusher, particularly hooks 353, 363 (Figs. 4a and 4b), remove roundish pieces from stumps, which pieces thus have a different shape than roots. In view of further use, it is advantageous that the crushed pieces include such removed, chopped pieces. It has thus been found that the openings 308 may be advantageously semi-circular in shape, wherein the crushed pieces may comprise such chopped wood raw material.

[0032] An advantageous structure for the crushing rollers is shown in Figs. 4a and 4b. Figure 4a shows a pair of rollers of a crusher according to Fig. 3a in a view from above. The rollers 350 and 360 are provided with crushing edges 351 and 361. The edges may be, for example, rectangular in shape. In Fig. 4a, only some of these edges are shown and indicated with reference numerals, for clarity. The crushing edges 351 and 361 are connected to edge supporting structures 352 and 362. Some crushing edges are provided with hooks 353 and 363. The hooks 353 and 363 pull the material to be crushed to the actual crushing edges 351 and 361 and may also chop the material to be crushed. The crushing rollers 350 and 360 are arranged to rotate around their shafts 354 and 364. In Fig. 4a, the distance left between the supporting structures 352 is indicated with the symbol d₁. In a corresponding manner, the distance d₁ may be left between the supporting structures 362. It is obvious that these distances affect the size of the crushed pieces obtained. The scrapers of Fig. 3a could be provided between the supporting structures 352 or between the supporting structures 362, respectively.

[0033] Figure 4b shows a pair of crushing rollers in an end view. The distance between the crushing edge 351 and the roller 360 is indicated with the symbol d₂, and it is obvious that this distance also affects the size of the crushed pieces to be obtained. The size of the crushed pieces can also be affected by the number of edges 351 on the circumference of the roller in the sectional plane transverse to the roller (in Fig. 4b, eight edges are provided on the circumference of the roller in the sectional plane shown), as well as by the diameter of the rollers.

[0034] For removing moisture, it is also advantageous to heat the wood raw material by the crusher. The heating of the piece depends, among other things, on the deformation work to which it has been subjected. In a known way, the specific deformation energy depends on the magnitude of the deformations and the stress (or pressure) prevailing in the piece. The deformation energy, in turn, also depends on the volume in which the deformations take place. Consequently, the quantity of the deformation energy is affected by the magnitude of the deformation, the magnitude of the stress, and the volume in which the deformations take place. If the piece is subjected to heating by compressing, that is, crushing it, it is thus advantageous to apply a high pressure (stress) and a large surface area at the edge of the crusher. Preferably, almost the whole edge presses the material to be crushed. The stress applied is affected by the forces of crushing. It is possible that when wood raw material is crushed into pieces of a large size, a greater stress is required than when wood raw material is crushed into pieces of a smaller size. It is thus possible that when pieces are crushed into crushed pieces of a large size, the pieces are heated more than when the raw material is crushed into pieces of a smaller size. Thus, the drying caused by heating may be more efficient in pieces of a large size than in pieces of a small size.

[0035] With reference to Fig. 4a, the rollers 350 and 360 constitute said pair of rollers. The surface area of the edges 351, 361 pressing the wood raw material is arranged relatively large. In Fig. 4a, the edge 351 has a rectangular shape. In this context, the shape refers to the shape of the surface that directs a force on the wood raw material by pressing. The cross-sectional shape of the edge 351 of the roller 350 is thus rectangular when the sectional plane of said cross-section is transverse to such a line segment that is directed from the central axis of the roller to the center of the edge 351 transversely to the central axis of the roller. The shape of said cross-section is affected by the hook 353, if the edge 351 comprises a hook 353. The edge 351 may be substantially flat, convex or concave. A concave edge may be provided to match the shape of a corresponding other roller.

[0036] When wood raw material is introduced between the pair of crushing rollers 350, 360, the edge 351 presses the wood raw material towards the roller 360, wherein the wood raw material is compressed. In a corresponding manner, the edge 361 presses the wood raw material towards the roller 350. In the embodiment of Fig. 4a, the edges 351 and 361 as well as the supporting structures 352 and 362 are arranged on the rollers in such a way that a space is left between four edges 351 of the first roller closest to each other, into which space the edge 361 of the second roller presses the wood raw material. Such a space is left, for example, at the left edge of the roller 350 in Fig. 4a. In a corresponding manner, a space is left between the four edges 361 of the second roller closest to each other, into which space the edge 351 of the first roller presses the wood raw material. Such compressing and space is also illustrated in Fig. 3a. Such a pair of crushing rollers may be arranged, for example, in a waste crusher, wherein the waste crusher can be used for crushing wood raw material.

[0037] By the size of the edges of the rollers it is possible to define the size of the crushed pieces. By the size of the edges of the rollers, it is also possible to affect the deformation energy and thereby the heating of the material. Preferably, the crushing rollers 350, 360 and their edges 351, 361 are selected in such a way that the size of the crushed pieces is within the above-described limits. Furthermore, the large size of pieces makes it possible to use the crushed pieces in at least one of the following: the pulping industry and the chemical industry.

[0038] The wood raw material that has been heated during the crushing also transfers heat to other pieces in the vicinity and to the edges 351, 361. Thus, the large crushing surface (contact surface) of the edge 351 of the crusher on the piece to be crushed has another advantage. Because the pieces to be crushed are heated, heat is transferred from the pieces to be crushed to the crushing edges. The edges are thus heated. In a corresponding manner, the heated edges transfer heat to the next pieces to be crushed. Furthermore, water that is pressed out of the wood raw material may be compressed onto the roller. Thus, the heated roller also heats the water, and the evaporation of water is intensified. Furthermore, the heat being transferred to other pieces to be crushed levels out the drying of the raw material during crushing, wherein the quality of the crushed pieces obtained from the process is more homogeneous.

[0039] It has been found that during the above-described crushing, the moisture content is typically reduced by about 15%. Thus, the moisture content of the crushed pieces is typically about 15% lower than the moisture content of uncrushed wood raw material. The moisture content refers to the mass of the moisture contained in the wood raw material or in the crushed pieces in relation to the total mass. Said figure indicating the reduction in the moisture content does not refer to percentage units. For example, the moisture content of wood raw material may be about 30%, wherein when the moisture content is reduced by about 15%, the remaining moisture content of the crushed pieces is about 25%. In many cases, moisture can also be removed and the moisture content reduced more, or significantly more. Thus, the ratio of the moisture content of the crushed pieces to the moisture content of the wood raw material is not greater than 85%. The ratio of the moisture content of crushed pieces dried by the method to the moisture content of wood raw material may also be lower or significantly lower.

[0040] In commercial arrangements, the size of the crushed pieces is arranged to be relatively small (smaller than 120 mm according to EP 876 843). This can be implemented for example by means of a sieve or an opening which, in the arrangement of Fig. 3a, would return too large crushed pieces to be crushed further and prevent their entry onto the conveyor. In the pre-treatment method according to the present invention, such sieving is not done but large crushed pieces are led from the crusher directly onto the conveyor without sieving. Furthermore, the crusher is provided with openings 308, by means of which a greater part of the crushed pieces of a desired size can move from the crusher onto the conveyor. The pressing effected in connection with the crushing dries the raw material, and the compressed moisture is brought either in the form of water onto the ground or in the form of steam with air off the conveyor. It is obvious that also other kinds of crushing rollers or other kinds of crushers can be used as long as sufficient compressing for drying and a sufficient size of pieces for further use is achieved by crushing.

[0041] Figures 5a and 5b show an advantageous embodiment for sieving the crushed pieces. The crushed pieces 303 are conveyed by the conveyor 304 to a sieve 501. In the sieve, crushed pieces which are too small for further use and loose material are carried through the sieve, for example, into a hood 505, and the crushed pieces are passed across the sieve 501 to a second conveyor 504. The hood 505 may be provided with a vacuum, for example by means of a suction pipe 506, wherein this vacuum further intensifies the sieving. The hood 505 is not necessarily needed, but the small pieces and the loose material can also be collected by another collector or be directed onto the ground. Figure 5a shows sieving in a side view and Fig. 5b in a top view. The sieving is advantageously performed by using bars 510 as the sieve 501, spaced so that pieces which are too small for further use can pass through the bars. Preferably, the spacing of the bars can be about 10 to 20 mm. It has been found that the above-described crushing process produces crushed pieces including small pieces on one hand and large pieces on the other hand. Consequently, the spacing of the bars can be advantageously much smaller than the desired size of the crushed pieces, which is advantageously 10 to 40 cm. This two-fold size distribution may be due to the fact that the compression wood tissue contained in the roots of a tree is not always ground to a significant extent in the crusher. The bars 510 of the sieve 501 can be shorter than the sieve in the longitudinal direction, wherein such bars can be aligned in rows and subsequent rows of bars as a sieve 501. Figures 5a and 5b show a sieve 501 comprising three rows of bars. The sieve may be arranged in an angle α to the horizontal plane 502, wherein the raw material is passed on the sieve, along the bars, by the effect of gravity, as shown in the figure. With too large an angle, in turn, the sieving is not necessarily sufficient. Advantageously, the angle α is about 20 to 60 degrees and preferably about 45 degrees. The bars of the sieve may be arranged to vibrate so that the movement of the material may be facilitated and the likelihood of blinding of the sieve may be reduced. The vibration can be effected, for example, by dropping crushed pieces 303 and loose material 306 onto the sieve 501. It has been found that even about 90% of the soil contained in the crushed pieces can be removed by the described sieving. The width of the sieve can be selected according to the width of the conveyor. The length of the sieve is limited, among other things, by achieving a sufficient sieving degree and by the manufacturing costs. It has been found that sufficient sieving can be provided with a sieve length of at least about 1.5 meters.

[0042] After an advantageous pre-treatment process 20, the crushed pieces thus have a smallish size, are clean and slightly drier than untreated raw material. It is known that wood raw material pieces of a small size are dried faster than wood raw material pieces of a large size. Consequently, the drying 13b of pre-treated material takes less time than the drying 13a of untreated material. The saving in time reduces the costs of capital tied up in the raw material and thereby improves the cost efficiency of the process. The saving in time also reduces the use of forested soil for landing or drying purposes. This intensifies forestry compared with long storage periods and accelerates forest renewal after the harvesting. In addition to saving time, the need for drying area may also be reduced, because the crushed and sieved raw material may take less space than uncrushed raw material. This may further intensify forestry and accelerate forest renewal.

[0043] In view of refining use of the raw material, it is not necessarily essential that the raw material is as dry as possible but that the moisture level is uniform and known. By the pre-treatment according to the invention, the moisture level can be controlled better, because the drying of the crushed pieces can be significantly reduced by baling and possibly also by wrapping the crushed pieces. Furthermore, the moisture content can be brought at the same time to a significantly lower level by drying 13b the crushed pieces than by drying 13a the non-preteated raw material.

[0044] In connection with the crushing, the impurities of stumps remain largely in the forest or in the terminal, which improves the quality at the power plant end and saves the transportation costs. The transportation costs are also saved by the low moisture content of the material and the uniform size of pieces, enabling better utilization of the transportation capacity. In addition to stumps, also small timber can be pre-treated in the above-described way. Also for small timber, the pre-treatment accelerates the drying. The pre-treatment may also reduce the bark content of the raw material.

[0045] By the presented process for producing and using wood raw material, and by the advantageous pre-treatment process, also other advantages are achieved in addition to those mentioned above: speed, purity, light weight and space requirement. The described pre-treatment process also makes it possible to use stumps in the chemical industry and in pulping. This enables better optimization in the use of wood for the forest industry. For example, the capacity of debarking drums at pulp mills may become a limiting factor, if additional quantities can only be obtained by processing in a barking drum. The presented process makes it possible to obtain additional quantities in other ways.

Claims

1. A method for treatment of wood raw material (301), wherein

- wood raw material (301) is introduced between a pair of rollers (350, 360), and

- the wood raw material (301) is pressed by the pair of rollers (350, 360), wherein the wood raw material (301) is crushed into crushed pieces (303), characterized in that

- moisture is pressed out of the wood raw material (301) to dry the crushed pieces (303), and

- moisture is separated from the crushed pieces (303).

2. The method for treating wood raw material (301) according to claim 1, characterized in

- separating moisture from the crushed pieces (303) by leading the crushed pieces (303) onto a conveyor (304), wherein moisture on the crushed pieces (303) is transferred to the conveyor (304) or onto the ground, and vaporized moisture is entrained in the air.

3. The method for treating wood raw material (301) according to claim 1 or 2, characterized in

- crushing the wood raw material into crushed pieces (303) having a size of 10 to 40 cm.

4. The method for treating wood raw material (301) according to any of the claims 1 to 3, characterized in

- reducing the moisture content by about 15% by the method.

5. The method for treating wood raw material (301) according to any of the claims 1 to 4, characterized in

- carrying out the steps of the method at the forest end to save transportation costs.

6. The method for treating wood raw material (301) according to any of the claims 1 to 5, characterized in baling the crushed pieces (303) to reduce the transportation costs.

7. The method for treating wood raw material (301) according to any of the claims 1 to 6, characterized in sieving the crushed pieces (303) to remove impurities.

8. The method for treating wood raw material (301) according to any of the claims 1 to 7, characterized in that the wood raw material (301) contains stumps.

9. A system for crushing wood raw material, comprising a crusher with a pair of rollers (350, 360), which pair of rollers is arranged to press the material, characterized in that

- the system comprises a conveyor (304),

- the pair of rollers (350, 360) is arranged to press the wood raw material (301) to reduce the moisture, wherein the pair of rollers (350, 360) is arranged to crush the wood raw material (301) into crushed pieces (303), and

- the conveyor (304) is arranged in connection with said crusher to separate moisture from the crushed pieces (303).

10. The system for crushing wood raw material according to claim 9, characterized in that the crusher is arranged to crush the wood raw material (301) into crushed pieces (303) having a size of 10 to 40 cm.

11. The system for crushing wood raw material according to claim 9 or 10, characterized in that the crushing system further comprises means for baling the crushed pieces (303).

12. The system for crushing wood raw material according to any of the claims 9 to 11, characterized in that the crushing system further comprises a sieve (501) for sieving the crushed pieces (303).

13. The use of a waste crusher for crushing wood raw material (301) into crushed pieces (303), characterized in that

- the waste crusher is arranged in connection with a conveyor (304), and

- the conveyor (304) is arranged to separate moisture from said crushed pieces (303).

14. The use according to claim 13, characterized in that

- the waste crusher is arranged to crush the wood raw material (301) into crushed pieces (303) having a size of 10 to 40 cm.

15. The use according to claim 13 or 14, characterized in that

- the waste crusher is provided with openings (308) for removing uncrushed or chopped wood raw material (301) from the crusher.

Drawing