WO2005039842A1

WO2005039842A1 - Method for preparing fiberboards from wood fibers

Info

Publication number: WO2005039842A1
Application number: PCT/DE2004/002146
Authority: WO
Inventors: Klaus E. Radzimanowski; Roberto Fasan
Original assignee: Schenkmann-Piel Engineering-Gmbh
Priority date: 2003-10-07
Filing date: 2004-09-25
Publication date: 2005-05-06
Also published as: DE502004012474D1; ATE507949T1; EP1670623A1; EP1670623B1; DE10347052A1

Abstract

The invention relates to a method for preparing fiberboards from wood fibers. According to the inventive method, chopped wood particles are treated by admixing saturated steam. Once the wood particles are size-reduced to wood fibers, superheated steam is admixed, thereby drying and conveying the wood fibers. The wood fibers are removed from the superheated steam or saturated steam in a first separator (5). The dried wood fibers are fed to a sizing section (18) by means of a gaseous transport medium, the flow velocity being increased upstream of the sizing section (18). The increased kinetic energy of the wood fibers allows for an even sizing thereof. The superheated steam from the first separator (5) is fed to a distributor chamber (9) in order to enable its reuse.

Description

Process for the production of fiberboard from wood fibers

The invention relates to a method for producing fiberboard from wood fibers.

According to the prior art, the wood fibers for the production of the fiberboard are obtained in such a way that raw wood is shredded into so-called wood chips in a chipper. These wood chips are then subjected to saturated steam treatment, possibly after preheating. This damping process plasticizes the natural wood binders such as resins or lignin, which reduces their binding power. At the same time, the integrated wood fibers are softened during this damping process.

After this pretreatment, the wood chips are shredded in a mill under saturated steam and the actual fibers are obtained in the form of thin and fine threads. The mixture of saturated steam and fibers is then blown through pipes into a so-called current dryer, where liquid glue is injected and the saturated steam with hot air from e.g. 170 ° C is mixed.

It is known from EP 0 823 870 B1 to add superheated steam to the saturated steam / fiber mixture for drying and conveying. Due to the measure proposed there, the supply of dry hot air to the saturated steam / fiber mixture can be dispensed with, since the now mixed, unsaturated superheated steam is able to dry the saturated steam / fiber mixture and can also take over the transport of the mixture in the pipelines. The now saturated steam or superheated steam fiber mixture is fed to a pressure-resistant cyclone, which separates the fibers from the superheated steam. The superheated steam is fed to a superheated steam distributor, from where it can be fed to different uses in an energy-saving manner.

The fibers obtained in this way can then, if necessary by carrying out further process steps, be fed to a molding and pressing line in which the fiberboard is produced by curing the glue. Further treatment steps for the wood fibers include, for example, bunkering, sifting with the help of an air classifier or renewed separation in a separator arranged after the classifier.

The fiber drying after the gluing according to EP 0 823 870 B1 by admixing hot steam or also by the known admixture of hot air has the disadvantage that a certain part of the amount of glue is lost through pre-curing and volatilization and as a binder in the pressing of the Fiberboard is no longer available. The amount of liquid glue injected must be increased accordingly. Since the cost of the glue (binder) is very high in relation to the costs, the glue represents an essential cost factor in the production of the fiberboard.

In contrast to the so-called wet gluing described above, methods for dry gluing are also known. For example, EP 0 728 562 discloses a method for dry gluing of pneumatically conveyed particles. In this case, the wood fibers are first dried to the required final moisture in a dryer and then fed to a gluing section via a delivery line which has a cross-sectional reduction. The gluing section is provided with glue nozzles. In order to achieve a uniform wetting of the particles, the wetting section is a diffuser section formed, which is to cause a cross-sectional expansion and thus a turbulent flow of the fibers in the section. Due to the turbulent flow, the formation of fiber aggregates should be avoided, since these fiber aggregations lead to glue stains in the fiberboard surface and can cause damage to the press belts of the press.

The invention has for its object to provide a method for producing fiberboard from wood fibers, in which a uniform glue distribution is achieved with the lowest possible production costs.

The object is achieved with the features of claim 1. According to the proposed method, shredded wood particles, preferably in the form of wood chips, are treated by adding saturated steam to reduce the binding power of the wood-based binders. The wood chips treated in this way are then comminuted in a mill to obtain the wood fibers. Hot steam is then added to dry and promote the wood fibers. The mixture of wood fibers and steam is then fed to a first separator, for example in the form of a cyclone, in order to separate the wood fibers from the superheated steam or saturated steam. The wood fibers separated in this way with a final moisture content of preferably 3 to 20%, ideally 10 to 12%, are fed into a conveyor line in which the wood fibers are transported to a gluing section of the conveyor line by means of a gaseous transport medium. Before reaching the gluing section, the wood fibers pass an acceleration section in which

Flow rate is increased. This is preferably achieved by reducing the cross section of the delivery line immediately before the gluing section. A multiplicity of gluing nozzles are provided in the gluing section, which can extend both along the circumference of the conveying line and along the flow direction of the wood fibers. Due to the high kinetic energy of the previously accelerated wood fibers, a good swirling of the individual particles and an even distribution of the glue on the particles is achieved. This prevents the formation of clumps of fibers, so that glue stains and, in particular, damage to subsequent system parts such as press belts are prevented.

The wood fibers glued in this way are now fed to a molding and press line. If appropriate, this takes place after a gaseous medium has been admixed again and, if appropriate, after carrying out further process steps such as bunkering, classifying and / or separating the wood fibers from the gaseous medium.

In a preferred embodiment, the wood fibers are glued at an increased flow rate. In this case, the flow rate essentially corresponds to the flow rate that is reached in the acceleration section. If the flow of the wood fibers is accelerated by reducing the flow cross-section, the flow cross-section in the gluing section corresponds approximately to the flow cross-section at the end of the acceleration section.

After the gluing, the wood fibers are preferably passed through a dwell section of the conveying line. The dwell section serves to further even out the gluing or wetting of the wood fibers.

The pneumatic conveying of the wood fibers in the conveying line is expediently carried out by air, which is preferably heated and has a temperature of approximately 60 ° C. to 120 ° C., preferably 90 ° C.

In order to prevent the glue from caking in the gluing section, a covering surface of the gluing section is cools. As a result, a condensate film can form on the casing surface, which prevents the glue from sticking.

In a preferred embodiment, after the gluing, the wood fibers are subsequently dried by means of mixed, heated air. The mixed heated air has a temperature of 60 ° C to 120 ° C.

The amount and the state variables of the superheated steam fed upstream of the first separator are preferably selected such that the saturated steam which is initially present is completely converted into the superheated steam state. For the purposes of this patent application, saturated steam or wet steam or saturated steam is a steam state corresponding to the wet steam area of the known steam tapes. Superheated steam or superheated steam refers to unsaturated steam that is capable of absorbing further steam and is adjacent to the wet steam area.

After separation in the first separator, the superheated steam is preferably fed to a distribution chamber, from which at least a partial volume flow I is withdrawn for return to the saturated steam / fiber mixture, the partial volume flow I being overheated in a heat exchanger.

Due to the supply of superheated steam after the first separator, there are no longer any flue gas quantities that would otherwise have to be cleaned with loss of energy. Rather, the energy contained in the superheated steam can be used efficiently.

Due to the energy supplied in the heat exchanger, a further partial volume flow II of the superheated steam can be removed, for example for preheating the wood chips, so that a corresponding energy saving also results here. Another partial volume flow III can, if necessary, be removed for preheating the air for a classifier. Furthermore, a partial volumetric flow IV of the classifier air can be admixed directly The moisture content of the air in the classifier increases, so that the fibers to be sifted become hotter and the processing times of the press line are reduced accordingly.

Furthermore, a partial volume flow V of the superheated steam can be taken from the distribution chamber to heat the air, which conveys the wood fibers through the gluing section. The partial volume flow V is fed to a heat exchanger in which ambient air is heated. Another partial volume flow VΣ of the superheated steam can be taken from the distribution chamber for heating the air, by means of which the glued wood fibers are dried. This air supplied for drying can also be used as a conveying medium for the glued wood fibers. The remaining, possibly still existing, excess energy in the superheated steam distributor can be used for example for domestic water heating, building heating or for other heating purposes.

The wood fibers can preferably be pre-glued before being fed to the first separator or to the first separator group. Thus, the process uses so-called wet gluing on the one hand and dry gluing on the other. The degree of pre-gluing is set in such a way that an optimum is achieved with regard to the total consumption of the glue and a uniform gluing of the wood fibers.

In a preferred embodiment, the wood fibers are exposed to high-frequency vibrations, so-called microwaves, for drying. This type of drying is expediently carried out after the wood fibers have been glued in the dwell section.

The invention is illustrated, for example, using a schematic process diagram.

For the production of wood fibers for the production of fiberboard raw wood is first crushed in a chipper 1 and the wood chips produced are fed to an autoclave 2. Inside the autoclave 2, the wood chips are treated in batches with saturated steam at a pressure of approx. 8 bar and a temperature of approx. 150 ° C. The steam treatment plasticizes the wood binders and softens the wood fibers.

After the wood chips have been steamed, they are fed to a mill 3, which is also under saturated steam, in which the softened chips are shredded using suitable grinding units and the fine wood fibers are exposed.

The pressurized saturated steam-wood fiber mixture is then fed via a pipeline 4 to a first separator 5 working as a cyclone, where the wood fibers are separated from the medium to be conveyed.

Before this, superheated steam, which has passed through a heat exchanger 8 for overheating, is blown into the pipeline 4 via a feed 6 with the aid of a fan 7. The state variables of the superheated steam supplied and its defects are selected so that the saturated steam is converted into superheated superheated steam while the wood chips are drying.

The superheated superheated steam, which is fed to the first separator 5 at the same time as the wood fibers, leaves the separator 5, which is still overheated, and reaches a distribution chamber 9, where several partial volume flows can be removed. The largest partial volume flow I is fed to the already mentioned heat exchanger 8, is superheated there and, as already described, is blown into the pipeline 4 by means of the fan 7. A second partial volume flow II is fed to the chipper 1 via a pipeline 10 and serves to preheat the wood chips. The fiber material separated from the first separator 5 is then transferred to a compensating screw 12 via a feed 11. The moisture content of the wood fibers is approximately 3% to 20%, preferably 10% to 12%.

Starting from the compensating screw 12, the processed wood fibers reach a feed line 15 via a feed 13 and a lock 14.

The conveying line 15 is charged with heated air by means of a heat exchanger 16, which has approximately 60 to 120 °, preferably 90 °. The heated air serves as transport air and leads the wood fibers along the delivery line 15 in the direction of the arrows 17 to the gluing section 18. Immediately before the gluing section 18, the conveying line 15 has a reducing section 19, which reduces the flow cross section AI of the conveying line 15 to a flow cross section A2 and thus increases the speed of the conveyed wood fibers. The gluing section 18 adjoining the reducing section 19 is designed as a pipe section with a constant diameter and a correspondingly constant flow cross section A2. The flow cross section of the pipe section can also be made slightly smaller or larger along the conveying direction. The length of the gluing section Ll is 20 to depending on the system capacity

30 meters. Due to the reduction of the flow cross-section from AI to A2 immediately before the glueing gate 18, the wood fibers reach a speed of approx. 30 to 60 m / s.

In the conveying direction there are one along the gluing section 18

A large number of glue nozzles 20 arranged spirally around the circumference are provided. The number and arrangement of the glue nozzles 20 can be adapted depending on the type of glue and the amount of glue. The glue or binder is diluted to the viscosity required for spraying. The gluing section 18, which is designed as a pipe section, consists of a high-quality section polished material to prevent glue deposits on an inner lateral surface along the gluing section 18. Furthermore, to avoid caking, the pipe section is designed as a double-walled pipe with an inlet I and an outlet 0 for a cooling medium. The temperature of the cooling medium is set in such a way that a condensate forms from the inner wall of the pipe.

Following the gluing section 18, a dwell section 21 is formed, which also has a flow cross section A2 and extends over a length of approximately 15 to 30 m. The dwell section 21, which is designed as a pipe section, is also made of high-quality polished material, so that glue deposits are avoided.

Following the dwell section 21, the glued wood fibers pass through a mixing chamber 22 with baffles, which bring about a uniform mixing of the glued fibers with an additionally supplied air stream. The guide bleaches are spaced parallel in the conveying direction. The air flow supplied has a temperature of 60 to 120 ° and is supplied to the mixing chamber 22 via a separate feed line 23. Downstream of the mixing chamber 22 is a further delivery line 24, in which the glued fibers are subsequently dried by means of the hot air supplied. This post-drying is necessary because water is added to the wood fibers when the glue is added and the final moisture content was increased by gluing. The conveying line has a substantially larger flow cross section A3 than the flow cross section of the gluing section and the dwell section, so that the transport speed is reduced at this point and the dwell time in this section is greater.

By means of a switch 25 it is also possible to feed the wood fibers separated in the first separator 5 into the delivery line 24 via a further feed line 26 and thus to to bypass glue section 18. In this case, the wood fibers coming from the mill 3 are fed to wet gluing (not shown in FIG. 1) before the first separator 5, so that gluing in the gluing section 18 is no longer necessary. However, it can also be expedient to add a first part of the glue required for the fiberboard before the first separator 5 and a second part of the glue in the gluing section 18.

The post-dried wood fibers pass through the conveying line 24 into a second separator 27. The separated air is fed to a filter unit 28 and then released into the environment. The glued wood fibers are transferred to an air classifier 29 in which larger wood components or lumps of glue are separated and removed from the process as so-called heavy goods.

The air required for air separation is fed to a heat exchanger 31 by means of a fan 30, the heat exchanger 30 being supplied with heat for air preheating by means of a third partial volume flow III which is taken from the distribution chamber 10. A fourth partial volume flow IV is fed directly to the preheated air blown into the wind sifter 29 and serves to raise the air humidity in the air sifter 29. For this reason, the temperature of the sighted can

Wood fibers are increased. Partial volume flows V and VI are used to heat the air, which conveys the wood fibers through the gluing section 18 or dries the wood fibers after the gluing section.

After passing through the air classifier 29, the air / wood fiber mixture is fed to a third separator 33 by means of a fan 32, which leaves the heated air as exhaust air. The separated wood fibers can be removed as useful goods and fed to a molding and press line. A further partial volume flow VII can be taken from the distribution chamber 10 with appropriate energy management of the process and can be used for example for hall heating or hot water heating. The partial volume flows can be fed to a wet scrubber (not shown in FIG. 1) for the purpose of removing impurities.

Process for the production of fiberboard from wood fibers

LIST OF REFERENCE NUMBERS

Chipper autoclave mill pipeline first separator supply fan heat exchanger distribution chamber pipeline supply compensating screw supply lock feed line heat exchanger arrow glueing section reducing section glue nozzle residence section mixing chamber supply line delivery line soft supply line separator filter unit air classifier

fan

heat exchangers

fan

separators

Claims

Process for the production of fiberboard from wood fibers

1. A process for the production of fiber boards from wood fibers comprising the following steps: a) treatment of the comminuted wood particles, wood chips vorzugswei ^¬ se, to reduce the bonding force of the wood own binder by admixture of saturated steam; b) crushing the wood chips treated in this way in a mill (3) to obtain the wood fibers; c) admixing superheated steam to the saturated steam / fiber mixture in order to dry and convey the wood fibers; d) feeding the hot steam / saturated steam fiber mixture to a first separator (5) or a first separator group in order to separate the wood fibers from the hot steam or saturated steam; e) pneumatic conveying of the separated wood fibers in a conveying line (15); f) increasing the flow rate of the wood fibers in an acceleration section (19) of the delivery line (15); g) gluing of the wood fibers in a gluing section (18) of the delivery line (15); h) feeding the glued wood fibers to a molding and pressing line, if necessary after re-admixing a gaseous medium and if necessary after carrying out further process steps such as bunkering, classifying and / or separating the wood fibers from the gaseous medium.

2. The method according to claim 1, characterized by the fact that the gluing takes place at an increased flow rate.

3. The method according to claim 1 or 2, characterized in that, after the gluing, the wood fibers are passed through a dwell section (21) of the delivery line (15).

4. The method according to any one of claims 1 to 3, characterized in that the pneumatic conveying takes place by means of heated air.

5. The method according to any one of claims 1 to 4, characterized in that a jacket surface of the gluing section (18) is cooled to form a condensate film.

6. The method according to any one of claims 1 to 5, characterized by the fact that after the gluing, the wood fibers are re-dried by means of mixed, heated air.

7. The method according to any one of claims 1 to 6, characterized in that the saturated steam is converted into the hot steam state by the admixture of superheated steam.

8. The method according to any one of claims 1 to 7, characterized in that the superheated steam after the first separator (5) is fed to a distributor chamber (9), at least a partial volume flow I of which is taken back for return to the saturated steam / fiber mixture, wherein the partial volume flow I is overheated in a heat exchanger (8).

9. The method according to claim 8, characterized in that the distribution chamber (9) takes a partial volume flow II of the superheated steam for preheating the wood chips.

10. The method according to claim 8 or 9, characterized in that a partial volume flow III of the superheated steam for preheating the air for a wind sifter (29) is removed from the distribution chamber (9).

11. The method according to any one of claims 8 to 10, characterized in that a partial volume flow IV of the superheated steam for admixing the air for the air classifier (29) is removed from the distributor chamber (9).

12. The method according to any one of claims 8 to 11, characterized in that a partial volume flow V of the superheated steam is taken from the distributor chamber (9) for heating the air which conveys the wood fibers through the gluing section.

13. The method according to any one of claims 8 to 12, characterized in that the distribution chamber (9) a partial volume flow VI of the superheated steam for heating the air is removed, by means of which the glued wood fibers are dried.

14. The method according to any one of claims 1 to 13, characterized in that the wood fibers are pre-glued before being fed to the first separator (5) or to the first separator group.

15. The method according to any one of claims 1 to 14, characterized in that the wood fibers are exposed to high-frequency vibrations after gluing, preferably in the dwell section 21.