EA021142B1 - Method of recovering wood fibres from wood fibre and/or wood chipboard panels for re-use thereof - Google Patents

Abstract

A method of recycling structural wood panels such as fibre board recovering the constituent wood fibres for re-use as a substitute for virgin wood fibre. The wood panels are shredded and mixed with water to form a slurry, which is then heated by passing an electric current through the slurry to weaken the bonding between the wood fibres. The heating may be at a pressure higher than atmospheric. After heating, the slurry may be rapidly depressurized for example by spraying through a nozzle, to dry and separate the fibres. Apparatus is described for carrying out the method as a continuous process.

Description

(57) A method for recycling structural wood panels such as fiberboard restoring composite wood fibers for reuse in place of natural wood fiber is claimed. Wood panels are crushed and mixed with water to form a suspension, which is then heated by passing an electric current through the suspension to weaken the adhesion between the wood fibers. Heating can be performed under atmospheric pressure. After heating, the suspension can quickly release pressure, for example, by spraying it through a nozzle to dry and break the fibers. The device is described for performing the method in the form of a continuous process.

021142 Β1

FIELD OF THE INVENTION

The invention relates to the recycling of structural materials of wood, such as fiberboard and particleboard. More specifically, the invention relates to the recovery of constituent wood fibers from defective structural wood materials for reuse in place of natural wood fiber. This invention does not apply to pulping processes that recover fiber from lignocellulosic materials for the manufacture of paper or paperboard.

State of the art

Combined wood-based fiberboards and wood-based panels (panels) are usually used as raw materials for the manufacture of furniture, carpentry, commercial equipment and structures. They are mass-produced in many parts of the world (over 22 million tons annually). They usually contain a matrix of peeled wood fibers, wood chips or shavings bonded together under high pressure and temperature, usually with the addition of resin or glue. The most famous of these types of panels are Medium Density Fiberboard (HDF) and High Density Fiberboard (HDF).

Wood-fiber boards and particle boards are suitable for their intended purpose, but are not directly applied explicitly for effective reuse. More than 170,000 tons of fiberboard are aimed at introducing a waste stream in the UK annually from the primary and secondary processing process (commercial and industrial waste streams). Significantly more when consumer waste is taken into account.

The treatment of these waste streams is more problematic with the commonly used technique of applying a topcoat to cardboard during or after manufacture. Clamping devices and fittings, such as inserts and loops that can be applied to products made from fiberboard, also add complexity to the identification of an effective recycling process.

There is currently no viable economic way to recover wood fiber from these waste streams, and therefore it is destroyed either by burying or burning. This contributes to the unsustainable use of buried waste and the loss of potential recycle.

SUMMARY OF THE INVENTION

The term slurry is used throughout this document to describe a material that consists of water and a mixture of cardboard, which ranges from small parts of a moist, homogeneous fibrous cardboard to individual wood fibers that are held in water.

The term structural wood material is used to describe a material, such as a fiberboard and a particleboard, which is made by artificially joining together fibers, wood chips or other small particles of lumber.

The present invention is a method of recovering composite wood fibers from waste and sorted structural wood materials, preferably in a continuous process, such that the recovered fiber is of suitable quality that is to be recycled / reused in the manufacturing industry of fiberboards (instead of natural wood fiber) and other intended uses, including but not limited to insulation materials, fillers for plastic / cement mixtures, absorbent chips and material for growing horticultural crops.

The method uses: (ί) the addition of water or the absence of additives to the mass of defective composite structural wood material and (ίί) the application of (conductive) electric current heating to this mass. The benefit of using electric current heating is that it is a uniform and penetrating thermal effect generated by this technique, without burning or charcoal of wood fiber. The waste is preferably mechanically broken into pieces (crushed) before applying heat or adding water to increase the efficiency of the process. Additionally, mechanical destruction of the plate material is applied to the aqueous suspension of the plate material before the fibers dry. Surface reagents can be used to speed up the impregnation of parts of the fiberboard with added water. In order to optimize conductivity and improve heating efficiency, electrolytes can be added to water.

The method uses the use of high temperatures in the range of 30-99 ° C (and preferably in the range of 80-99 ° C) on a suspension (mixture) of water and structural wood material. The use of high temperature, when using electric heating, reduces the adhesive (both added resin and natural lignin) adhesion between lignocellulosic elements, thereby allowing easy separation of composite wood fibers from each other.

The method preferably further utilizes the use of a continuous system.

The method can additionally apply the use of elevated temperatures (above 100 ° C) in a sealed compartment with electric current heating.

The method may further apply the use of rapid pressure relief through a high pressure nozzle (or a set of nozzles), as an aid to drying the reduced fibers. The fiber separation effect also occurs during pressure relief, which helps to process materials and facilitates more efficient additional drying if required. This drying method can work either as a result of a rapid depressurization of a sealed compartment of electric current heating, or when used as an additional independent pressure subsystem inside a continuous process line that uses electric current heating under ambient pressure.

The invention is important because of the sustainability perspective because it offers the potential to reduce the environmental burden of an important element of the lumber supply chain, creating added value and extending the life of long wood fibers.

The continuous nature of the processes is a very preferred factor, which ensures the significance of the process for the required large volume of the technological sector of composite fiberboards, where the capacity of the feedstock for industry can reach more than 40 tons per hour.

In addition, the method in accordance with this invention allows the separation of commonly used upper layers of the surface from the wood fiber element of structural timber. These top layers are used during or after manufacture as a means of further appealing to marketable products, such as fiberboard. These topcoats typically include plywood, paper foil, paint or other type of laminate and must be removed before the regenerated wood fiber can be reused. This invention addresses this requirement. There is a choice of waste pretreatment using mechanical methods such as sandblasting, high pressure jetting or planing. However, where these methods are not practical, flotation separation (including foam separation) can be used after applying electric current heating. Alternatively (or additionally), separation can be achieved by using air sorting technologies (such as cyclone separators) during or after the fibers have dried.

This invention has general application in such combined fiberboards that are widely manufactured and used. This will provide a new source of raw materials for the manufacture of composite fiberboards, such as fiberboard, which are currently very susceptible to the use of raw materials for the recycled lumber industry. The fiber recovered through this process will have comparable quality to a fiber made from natural wood fibers made from wood chips or sawn timber, typically used by the cleaning process. The resulting fiber from this inventive process can be applied in a flexible manner in terms of their physical characteristics; length, moisture content, etc. can be controlled. An effective method in which this invention provides for wood fiber to be recycled is currently important because it reduces the need for natural wood and inadequate natural resources.

Benefits

This technology enables the recovery of wood fibers from defective structural wood material so that the recovered fibers remain of suitable quality for re-incorporation into the wood-fiber board or other product. This process is repeatable in such a fiberboard made with a reduced fiber content that can be directly reused for its intended purpose. It offers environmental and economic benefits over other recycling / destruction methods, such as composting / burning with energy recovery, whereby the fibers lose their properties after one cycle.

In one aspect, this invention provides for the continuous recovery of large volumes of wood fiber from a defective structural wood material, thereby making it possible to introduce the reduced fiber directly into the fiberboard production process. This is a significant advantage over batch processing, which will be unable to deliver the recovered fiber in a manner suitable for production throughputs ranging from 10-40 tons per hour. This invention also provides for flexibility and moisture control of the recovered fibers, therefore, offering multiple entry points into the production line of a fiberboard (which may differ in equipment). Reconstituted fibers can also be dried and packaged in bales for more efficient storage and use in specialized alternative stores.

This invention differs from the invention disclosed in the international patent application ЖО 03/026859 A1, by which the material of defective boards is processed in a low-volume group method using a chemo-thermomechanical process.

The use of electric current heating is a highly efficient and cost-effective means of heating in terms of both capital costs and current costs. It provides 2 021142 an advantage over the technology proposed by Τηναίά (UK patent No. 2410746 B), by which electromagnetic radiation is proposed as a means of helping to scale down and restore wood fibers from defective lignocellulosic cardboard material.

The technological effect of this electric current heating technique will include a more controlled temperature profile and a more homogeneous suspension heating profile during cardboard processing and such a more predictable recovery cycle without the risk of burning or charcoal of the material and with a reduced production risk of fire.

This invention includes an additional high-pressure pump unit in which ohmic heating elements can be implemented in one piece. The unit may alternatively form a discrete compartment after applying electric current heating. The rapid depressurization of this unit through a high-pressure nozzle grill designed to allow the passage of water and suspended wood fiber involves the instantaneous evaporation of a substantial portion of the bound moisture contained within and between the wood fibers. The effect of fiber separation is also attested. This drying effect is achieved at a relatively low energy and cost burden. Additional drying may also be required or desirable depending on the use of the reconstituted fiber.

Brief Description of the Drawings

In the drawing, a schematic representation of a preferred process for recovering wood fiber from a defective wood fiber board.

Detailed process description

DVPSP and other defective structural wood material can be categorized into two separate types; those that are not processed, that is, have no coating applied to the surface (raw cardboard), or those that are processed, that is, have veneer, foil, paint or other form of laminated material applied to the surface and / or edges. This invention allows the treatment of these wastes together, that is, mixed streams of waste and processed and unprocessed material, being processed simultaneously or by rejecting the material of the treated waste through an initial cleaning compartment in which the top surface layer is removed by mechanical means.

Each waste recycling plant is likely to have an impact on the specifications for the incoming waste, depending on the commercial activities within its service area, for example, a furniture manufacturing group or a major retail distribution center (where waste materials can be obtained after return shipping from multiple specialized stores).

If required, the mechanical breaker compartment (1.1) forms the beginning of this invention with the most likely grinding operation to be used. Removal of the upper layers of surfaces is best achieved by grinding the material to a relatively uniform size, where each part has an approximate size of 80 mm x 80 mm. However, electric current heating is most effective when the average size of the crushed parts of the fiberboard is less than 20 mm x 20 mm. This provides a more uniform distribution of steam water in the cavity of the heater by electric current. Taking into account these changes, the optimal dimensions of the waste parts were set between 25 mm x 25 mm and 45 mm x 45 mm. Removal of metallic or other solid pollutants will be considered immediately after grinding by induction magnet (1.2a) to remove ferrous metal and eddy current separator (1.2b) to remove colored pollutants (screws, nails, fittings, hinges and other inserts that can be found in partially processed or consumer waste fiberboard).

After grinding, the material is calibrated using an automated strainer (1.3). A mesh conveyor that uses a degree of vibration will remove dust and small particles. Dust extraction (1.4) is used at this stage to maintain safe working conditions.

Then the material is fed into the bath (1.5) with a dropwise supply of the solution, which contains hot water at a temperature above 30 ° C with an optimal operating range between 80 and 99 ° C. The purpose of this compartment is to ensure that sufficient water is absorbed in the defective fiberboard to enable efficient and predictable conductive heating operation. Water may contain added surfactants to increase or accelerate the wetting of the fiberboard. Water may also contain added salts (for example, NaCl in a solution of 0.05 M) to increase the conductivity of the resulting suspension.

Initial grinding (1.1) involves a large surface area of the fiberboard, which is exposed to water when immersed in a bath with a dropwise solution, therefore, the time required for sufficient absorption to occur is reduced. It is preferable to limit water absorption to the required minimum in order to reduce the cost and energy involved in removing it again later in the process. Depending on the mixture of waste streams processed, moisture absorption will be optimized between the higher moisture content required to maximize the efficiency of electric current heating and the lower moisture content, to minimize the energy required to dry the treated fibers. In one example, the moisture content of a fiberboard can be increased from about 8% yy (wet basis weight / total weight) to about 70% yyy.

Then the waste material is transferred to a continuous feed hopper, which introduces parts of the fiberboard into the electric heating section (1.6). Electric heating provides for rapid and homogeneous absorption of heat in parts of a wood-fiber board. The feed to this compartment will be controlled by a screw plug, injection pump, or similar device that maintains constant throughput. The screw plug also acts as a seal to ensure that no unwanted leakage will occur from the heating compartment, which can operate at elevated (above atmospheric) pressure. You can use a high-pressure discharge pump to raise the internal pressure of this compartment, preferably to a value between 1.0 and 20 atm (to prevent boiling) depending on the requirements of the process temperature.

The heating compartment will typically be in the form of an angular insulated cylindrical chamber between 0.2-20 mV in length with a diameter between 50 and 500 mm. Based on a typical throughput of five tons per hour of defective wood fiber boards, these dimensions will be approximately 15 m in length with a diameter of 220 mm. This will allow the suspension to remain in the heating compartment for a few minutes: usually about 3 minutes depending on the operating temperature.

The electrodes are placed on the inside of the process chamber in a grid of a certain shape of two or more electrodes, which is configured to maximize the heating and penetrating potential of the system. A lattice of a certain shape is made according to customer specifications for costs, power consumption and conductivity of the suspension, and it can be controlled to optimize the temperature of the heater for given flow capacities, input temperatures and conductivity of the suspension. An electric current heater will typically operate in the range of 20-1500 kW. The suspension is maintained at a temperature of at least 50 ° C and preferably at least 90 ° C, while it remains in the chamber. If the chamber is sealed, the operating temperature can be increased to 160 ° C.

Material may exit the heater by electric shock through a water meter or water tower to maintain pressure inside the heater.

After passing through an electric current heater, the material may still contain loose lumps (bundles or bundles) of undivided fibers. Therefore, the material may require that some additional mixing reach a completely homogeneous state.

Splitting or crushing can be achieved by feeding material into a rotating cylinder, which can be heated or not heated. The rotating cylinder can also be used to selectively capture the remaining parts of the defective laminate. Aerodynamic equipment that introduces physical barriers into the free passage of fibers can also be used. This will achieve the effect of releasing individual fibers from the remaining lumps at this stage.

After breaking, the material is dried (1.7). Then, drying up any remaining pieces of defective laminated material can be removed in an air cyclone before packing and packing of the restored fibers (1.8). Alternatively, the recovered fibers can be immediately fed into a further production process at the same location.

In the case of a larger quantity of liquid suspension exiting the heater by electric current, the fiber breaks are achieved by mechanical stirring, usually using a continuous belt mixer module. The flotation separation technique can be applied to remove any residual defective laminated material. This is accompanied by mechanical drainage of the suspension. After mechanical drying, the material is subjected to separation and drying. The splitting or fragmentation and subsequent processes can then be performed as described previously. Where the liquid suspension is still under pressure, it can be pumped into one of two (or more) pressure chambers, which are sequentially isolated from the continuous system after they are filled. From these sealed collection tanks, the suspension is pumped through a spray nozzle grill, in which a sudden and explosive pressure release occurs, which blows the loose matrix of each defective part of the fiberboard so that the individual fiber components are released. After spraying, the material is then dried as required. Then, dried up any remaining parts of the defective laminated material can be removed in an air cyclone.

Claims (12)

CLAIM 1. The method of recovery of wood fibers from wood-fiber and / or wood-4 021142 particle boards for reuse, in which the crushed structural wood material of wood-fiber and / or wood chip boards is mixed with water to form a suspension and pass an electric current through suspension for heating the crushed wood material and thus weakening the adhesion between the wood fibers in the wood material. 2. The method according to claim 1, in which the suspension is heated to a temperature between 30 and 99 ° C. 3. The method according to claim 2, in which the suspension is heated to a temperature between 80 and 99 ° C. 4. The method according to claim 1, in which the heating is performed under pressure above atmospheric. 5. The method according to claim 4, in which the heating is performed under a pressure of between 1 and 20 atm (0.1 and 2.0 MPa). 6. The method according to claim 4 or 5, in which the suspension is heated to a temperature between 30 and 160 ° C. 7. The method according to any of the preceding paragraphs, in which an additional electrolyte is added at the stage of mixing the suspension. 8. A method according to any one of the preceding claims, in which a surfactant is further added at the stage of mixing the suspension. 9. The method according to any of the preceding paragraphs, in which the structural wood material is milled to an average size of parts in the range of 25-45 mm. 10. The method according to any of the preceding paragraphs, in which impurities are additionally separated from the suspension before or after the heating step. 11. A method according to any one of the preceding claims, wherein after heating the suspension is subjected to a rapid depressurization. 12. The method according to any of the preceding paragraphs, in which the heating step is performed in a continuous mode during the transfer of the suspension through the heating chamber.