KR101365923B1 - Recycling technology - Google Patents

Abstract

A method of recovering processed wood panels, such as fiber boards, recovers component wood fibers for reuse as a substitute for solid wood fibers. The wood panel is crushed and mixed with water to form a slurry, which is then heated by passing an electric current through the slurry to weaken the bond between the wood fibers. Heating may be carried out above atmospheric pressure. After heating, the slurry can be rapidly depressurized, for example by spraying through a nozzle, to dry and separate the fibers. An apparatus for performing the method as a continuous process is described.

Description

Regeneration technology {RECYCLING TECHNOLOGY}

FIELD OF THE INVENTION The present invention relates to the recycling of engineered wood materials such as fiber boards and particle boards. More specifically, the present invention relates to the recovery of component wood fibers from waste processed wood material for reuse as a replacement for solid wood fibers. The present invention is not directed to a pulping process for recovering fibers from wood fiber material for paper or cardboard production.

Wood-based synthetic fiber boards and particle boards (panels) are commonly used as raw materials for furniture manufacturing, joinery, shop fittings, and construction. They are mass produced in more than one part of the world (more than 22 million tonnes per year). These typically comprise a matrix of refined lumber fibers, wood chips or prawns that are bonded together under high pressure and temperature, usually by the addition of a resin or adhesive. The most prominent these panel types are medium density fiber boards (MDF) and high density fiber boards (HDF).

Fiber boards and particle boards are fitted for this purpose but do not readily provide themselves for effective regeneration. More than 170,000 tonnes of MDF are considered to enter waste streams annually in the UK from primary and secondary processing activities (commercial and industrial waste streams). Significantly greater amounts are considered when posting consumer waste.

The handling of these waste streams is further problematic by commonly used techniques of applying surface finish processing to boards during or after manufacture. Fixtures and fittings, such as inserts and hinges that can be applied to products made from fiber boards, also add complexity to the identification of effective regeneration processes.

There are currently no viable economic processes for recovering wood fibers from these waste streams and are therefore disposed of by landfill or incineration. This contributes to the non-persistent use of landfills and the loss of regeneration potential.

The term “slurry” is used throughout this specification to describe a material consisting of water and board mixtures ranging from small pieces of wet solid boards to individual wood fibers held in water.

The term "engineered wood material" is used to describe materials such as fiber boards and particle boards that are constructed by artificially joining together fibers, chips, or small particles of wood.

The present invention preferably recovers component wood fibers from waste and rejected engineered wood materials in a continuous process such that, although the recovered fibers are not limited to these, insulating materials, filler / bonder composite materials for plastics, leak absorbers and The fiber board manufacturing industry including horticultural growth media (replacement for wood fiber) and other end use applications are directed to methods that are of sufficient quality to be recycled / reused.

The method utilizes (i) the addition of water with or without additives to the mass of waste composite engineered wood material and (ii) the application of resistive (conductive) heating to the same mass. The benefit of applying resistive heating is the uniform, invasive heating effect produced by this technique without burning or charcoal wood fibers. Waste material is preferentially mechanically crushed (crushed) prior to heat application or water addition to aid process efficiency. Further mechanical collapse of the board material is applied to the water board slurry before the drying of the fiber occurs. Surface agents can be used to accelerate the impregnation of fiber board debris with added water. The electrolyte can be added to water to optimize conductivity and improve heating efficiency.

The method utilizes the use of high temperatures in the range of 30 ° C. to 99 ° C. (preferably in the range of 80 ° C. to 99 ° C.) on slurries (mixtures) of water and engineered wood materials. Application of high temperatures using resistive heating reduces the adhesion (added resin and natural lignin) bonds between lignocellulosic elements and thus allows the component wood fibers to be easily separated from each other.

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

The method may further utilize the use of elevated temperatures (greater than 100 ° C.) in the pressurized resistance heating module.

The method may further utilize the use of rapid decompression via a high pressure nozzle (array of nozzles) as an aid in drying the recovered fibers. The fiber separation effect is also induced during decompression, which aids in material handling and facilitates more efficient make-up drying if required. This drying method can be operated as a result of rapid depressurization from the pressure resistant heating module or can be used as a subsequent independent pressure subsystem in a continuous process line using resistance heating at ambient pressure.

The present invention is important from a sustainable deployment standpoint as it provides the potential to reduce the environmental burden of critical components of the wood product supply chain while creating added value and extending service life for long length wood fibers.

The continuous nature of the process is a very desirable factor that allows the process to be related to the solid demands of the synthetic fiber board manufacturing sector, where the raw feedstock throughput can reach more than 40 tonnes per hour.

In addition, the method according to the invention makes it possible to separate the surface finish machining typically found from the wood fiber elements of the processed wood product. These finishings are used during or after manufacturing as a means of adding value to 'goods' products, such as fiber boards. These finishes typically include veneers, paper foils, paints or other types of 'laminates' and must be removed before the recovered wood fibers can be reused. The present invention addresses this request. An option exists to pretreat the waste using mechanical methods such as sanding, high pressure water jetting or planning. However, if these methods are not practical, floating separation (including bubble separation) can be used after the application of resistance heating. Alternative (or additional) separation may be accomplished via the use of an air separation technique (such as a cyclonic separator) during or after drying of the fiber.

The present invention has a general purpose in which composite boards are widely manufactured and used. This will provide a new source of raw materials for the manufacture of composite boards, such as MDF, which are currently highly sensitive to the use of recycled wood feedstock. The fibers recovered from this process may have a 'quality' corresponding to that of the wood fibers made from chips or logs by conventionally used purification processes. The fibers resulting from the process of the present invention can be applied in a flexible manner in terms of their physical properties, where the length, moisture content and the like can be controlled. An effective way of allowing wood fibers to be recycled in the present invention is important in this regard as it reduces the demand for solid wood, scarce natural resources.

Advantages

This technique allows the recovery of wood fibers from waste engineered wood materials so that the recovered fibers remain in suitable quality for reintroduction into the fiber board or for other manufacturing. This process is iterative in that the fiber boards produced with the recovered fiber content as appropriate can be recycled on their own. This provides environmental and economic advantages over other regeneration / disposal methods such as composting / incineration with energy recovery, whereby the fibers are 'lost' after a single cycle.

In one aspect, the present invention allows for continuous recovery of solid wood fibers from waste engineered wood materials, thus allowing recovered fibers to be introduced directly into the MDF manufacturing process. This is a significant advantage over 'batch' processing, which may not be possible to supply recovered fibers in a manner suitable for manufacturing throughput ranging from 10 to 40 tonnes per hour. The present invention also allows for flexibility and control of the water content of the recovered fibers, thus providing a plurality of input points into the fiber board manufacturing process line (which may vary between facilities). Recovered fibers can also be dried and packaged for more efficient storage and use in alternative application markets.

The invention differs from the invention disclosed in international patent application WO 03/026859 A1, wherein the waste board material is treated in a low volume batch using a chemical-thermo-mechanical process.

The use of resistive heating is a highly efficient and cost effective heating means both in terms of capital and operating costs. This offers advantages over the technique proposed by Jawaid (patent GB 2410746 B), where electromagnetic radiation is proposed as a means of assisting the recovery and degradation of wood fibers from waste lignocellulosic board material. .

The operational benefit from this resistive heating technique is a more predictable recovery cycle with a more controlled temperature profile during the processing of the board and a more homogeneous heating profile of the slurry and thus a reduced operational fire risk without the risk of burning or charring the material. It may include.

The present invention includes an optional high pressure pumping unit in which a resistive heating element can be integrated. The unit may alternatively form a separate module after resistive heating is applied. Rapid release of pressure from this unit via a high pressure nozzle array designed to allow passage of water and suspended wood fibers allows for instantaneous evaporation of a substantial portion of the original moisture contained in and between the wood fibers. . Fiber separation effects are also seen. This drying effect is achieved with a relatively low energy and cost burden. Supplementary drying may also be required or desirable depending on the application for the recovered fiber.

1 is a schematic diagram of a preferred process for recovering wood fibers from a waste fiber board.

MDF and other engineered wood material waste are divided into two distinct types-unfinished, ie unpainted (raw board) or finished, ie veneers, foils, applied to surfaces and / or edges, Paint or other forms of laminate-may be classified. The present invention can treat these wastes together, i.e., an initial 'wash' module in which a mixed waste stream of both finished and unfinished materials is removed simultaneously or via surface finishes by mechanical means. It is processed by converting the finished waste material via diesel.

Each waste recovery treatment facility is disposed of depending on commercial activity within its catchment area, such as, for example, a group of furniture manufacturers or distribution centers at major retailers where waste material can be received after multiple shipments from multiple discount stores. There is a possibility of operating a specification for introducing a substance.

If desired, mechanical breakdown module 1.1 may form the beginning of the invention with grinding, which is the most possible task to be used. Removal of the surface finish is best achieved by grinding the material to a relatively uniform size, with each fragment having an approximate dimension of 80 mm x 80 mm. However, resistive heating is most efficient when the average size of the crushed fiber board fragments is less than 20 mm x 20 mm. This allows for a more even distribution of interstitial water across the resistance heater cavity. In view of these variations, the optimum waste fragment size parameter is set as 25 mm x 25 mm to 45 mm x 45 mm. Removal of metal or other solid contaminants can be achieved by grinding and non-ferrous contaminants (screws, nails, fixtures, hinges and other inserts that can be found in partially processed or post consumer fiber board waste) with induction magnets (1.2a) for ferrous metal removal. May be processed immediately after the eddy current separator 1.2b.

After grinding, the material is sorted via an automated sieve 1.3. Mesh conveyors using vibration levels will be able to remove dust and fines. Dust extraction (1.4) is used at this point to maintain a safe working environment.

The material is then fed into an immersion tank 1.5 containing hot water at a temperature above 30 ° C. with an optimum operating range of 80 ° C. to 99 ° C. The purpose of this module is to allow fiber board waste to absorb a sufficient volume of water so that conduction heating can operate efficiently and predictably. The water may include a surfactant added to enhance or accelerate the wetting of the fiber board. The water may also include added salts (eg, NaCl in 0.05 M solution) to enhance the conductivity of the resulting slurry.

Initial crushing 1.1 allows the larger surface area of the fiber board to be exposed to water when immersed in the immersion tank, thus reducing the time required for sufficient absorption to occur. It is desirable to limit the water uptake to the minimum required to reduce the cost and energy involved in removing it again later in the process. Depending on the mixture of waste streams to be treated, moisture absorption may be optimized between the higher moisture content required to maximize resistive heating efficiency and the lower moisture content to minimize the energy required to dry the treated fiber. In one example, the moisture content of the fiber board can be increased from approximately 8% wwb (wet basis / total weight) to approximately 70% wwb.

The waste material is then transported in a continuous feed hopper that introduces the fiber board fragments into the resistive heating module 1.6. The resistance heater will allow rapid and homogeneous heat absorption into the fiber board fragments. The feed into this module may be controlled by plug screws, displacement pumps or similar devices that maintain a constant throughput. The plug screw also acts as a seal to ensure that no unwanted emissions occur from the heating module that can operate under elevated (over atmospheric) pressure. A high pressure discharge pump may be used to increase the internal pressure of this module, preferably from 1.0 atm to 20 atm (to prevent boiling) depending on process temperature requirements.

The heating module may take the form of an angled insulated cylindrical container of 0.2 m to 20 m length, typically having a diameter of 50 mm to 500 mm. Based on a typical throughput of 5 tonnes per hour of waste fiber boards, these dimensions may be approximately 15 m in length with a diameter of 220 mm. This will allow the slurry to remain in the heating module for a period of several minutes, typically about 3 minutes depending on the operating temperature.

The electrodes are located on the interior of the process vessel of the molded array of two or more electrodes configured to maximize the heating and penetration potential of the system. The molded array is tailored to the flow rate, power requirements and conductivity of the slurry and can be controlled to optimize the heater temperature for the desired throughput, input temperature and conductivity of the slurry. The resistive heater will typically be able to operate in the range of 20 kW to 1500 kW. The slurry is maintained at a temperature of at least 50 ° C., preferably at least 90 ° C. while remaining in the vessel. If the vessel is pressurized, the operating temperature can be increased up to 160 ° C.

The material may come out of the resistance heater via a water column or tower to maintain pressure in the heater.

After passing through the resistance heater, the material may still contain a loose 'clump' (cluster or bundle) of unseparated fibers. Thus, the material may require some additional agitation to reach a completely homogeneous state.

De-clumping or de-agglomeration can be achieved by feeding material into a rotating cylinder that may or may not be warned. Rotating cylinders can also be used to selectively capture the remaining debris of the waste laminate. Airflow systems may also be used that introduce a physical barrier into the free passage of the fiber. This may achieve the effect of releasing individual fibers from residual clumps at this stage.

After unclumping the material is dried (1.7). After drying, any residual debris of the waste laminate can be removed in the air cyclone prior to packaging and packing the recovered fibers 1.8. Alternatively, the recovered fibers can be fed directly to a further manufacturing process at the same location.

In the case of more liquid slurry exiting the resistance heater, declumping of the fiber is typically accomplished via mechanical agitation by the use of an inline ribbon blender module. Suspension separation techniques can be applied to remove any residual waste laminate. This leads to mechanical dehydration of the slurry. After mechanical dehydration, the material is subjected to clumping and drying. Declumping or deagglomeration and subsequent processes may then be performed as described above. If the liquid slurry is still under pressure, it can be pumped into one of two (or more) pressure vessels, once filled, which are alternately isolated from the continuous system. From these pressurized holding tanks, the slurry is pumped through an array of spray nozzles, where a sudden explosive pressure release occurs that 'blows' the brittle matrix of each waste fiber board fragment so that the individual component fibers are released. The material after the spray is further dried as required. After drying any residual debris of the waste laminate can be removed in the air cyclone.

Claims (19)

A method of recovering wood fibers from fiber board material,
Mixing the ground fiber board with water to form a slurry,
Passing a current through the slurry to heat the fiber board thereby weakening the bond between the wood fibers in the fiber board. The method of claim 1, wherein the slurry is heated to a temperature of 30 ° C. to 99 ° C. 7. The method of claim 2, wherein the slurry is heated to a temperature of 80 ° C. to 99 ° C. 4. The method of claim 1, wherein the heating is performed at a pressure higher than atmospheric pressure. The method of claim 4, wherein the heating is performed at a pressure of 1 to 20 atm (0.1 to 2.0 MPa). The method of claim 4 or 5, wherein the slurry is heated to a temperature of 30 ° C. to 160 ° C. 7. The method of claim 1, wherein the slurry mixing step further comprises adding an electrolyte. 6. The method of any of claims 1 to 5, wherein the slurry mixing step further comprises adding a surface agent. The method according to any one of claims 1 to 5, wherein the average size of the pieces of the crushed fiber board is in the range of 25 mm to 45 mm. 6. The method of claim 1, further comprising separating the finish from the fiber board prior to mixing the ground fiber board with water to form the slurry. 7. The method according to any one of claims 1 to 5, wherein after heating the slurry is subjected to rapid depressurization. 6. The method of any one of claims 1 to 5, wherein the heating step further comprises transporting the slurry through a vessel carried out in a continuous process. An apparatus for recovering wood fibers from fiber board material,
The apparatus comprises a heating vessel for holding a slurry of crushed fiber board mixed with water, the heating vessel including electrodes for passing a current through the slurry to heat the slurry. The apparatus of claim 13, wherein the heating vessel is sealed to enable pressurization at pressures above atmospheric pressure. The apparatus of claim 13, further comprising two or more holding tanks, wherein the apparatus is configured such that the slurry can be pumped into one of the two or more holding tanks while the slurry is under pressure. . The apparatus of claim 15, wherein the apparatus further comprises an array of spray nozzles, wherein rapid and explosive pressure relief occurs when a liquid slurry is pumped from the holding tank to the spray nozzle array. 15. The apparatus of claim 13 or 14, further comprising a tank in which the fiber board can be wetted by water before the slurry is introduced into the heating vessel. delete delete

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