Patent Description:
Large scale production of Medium Density Fiberboard (MDF) began in the <NUM>'s. High Density Fiberboard (HDF) is a similar product, although with a density which is usually higher than MDF. MDF/HDF is used in various applications such as furniture and flooring. Today, many tonnes of used MDF/HDF containing objects are thrown away every year and thereafter burned since methods for recycling such objects are not known.

In publication <CIT> is disclosed a method of manufacturing a fiberboard method from straw comprising the steps of: cutting the straw to a length of about two inches to about four inches; softening the straw by contacting the straw with steam under elevated pressure for a period of time between <NUM> seconds and two minutes; and mechanically refining the softened straw to produce fibers capable of being used in the manufacture of cellulosic fiberboard products.

In publication <CIT> is disclosed a wet strength wastepaper recycling chemical and mechanical pulping method including material preparation, steaming, first extrusion soaking, second extrusion soaking, latency and defibering and purifying, screening and concentrating.

An object of the invention is to provide a method for recycling MDF or HDF containing material in order to produce fibers suitable for production of new MDF/HDF.

These and other objects are achieved by the present invention by means of a method according to the independent claim.

According to a first aspect of the invention, there is provided a method for producing recycled fibers from MDF or HDF containing material, for instance for use in MDF or HDF production or for use as strengthening fibers in containerboard. The method comprises steaming the MDF or HDF containing material for a predetermined time to obtain steamed material, subjecting the steamed material to a pulping process to obtain a slurry, screening the slurry to remove oversize particles to obtain a screened slurry, dewatering the screened slurry to obtain dewatered fibers and fluffing the dewatered fibers to obtain said recycled fibers.

It is understood that the MDF or HDF containing material refers to objects which at least partly consist of MDF or HDF, such as pieces or chips of recycled furniture, recycled flooring or raw board reject, i.e. pieces of MDF or HDF board which is rejected in an MDF or HDF sheet forming line. It is furthermore understood that the term oversize particles include, but is not limited to, to non-fibrous material such as plastic, paper, metal or the like which are part of the raw material (MDF or HDF containing material). Also including wood pieces coming from other types of panelboards as well as water proof glued pieces of MDF and HDF.

The method according to the first aspect of the invention is normally carried out continuously together with an MDF or HDF sheet forming line, supplying recycled fibers thereto. It is however possible to carry out the method batch-wise and supply recycled fibers to an MDF or HDF sheet forming line at a later time.

The invention is based on the insight that recycled fibers suitable for MDF or HDF production can be surprisingly effectively released from MDF or HDF containing material, in particular recycled material, by steaming and pulping the material. The invention is furthermore based on the insight that such steaming and pulping leaves non-desirable particles such as plastic, paper or metal largely unaffected size-wise which allows these oversize particles to be removed by means of screening.

In embodiments, the MDF or HDF containing material is provided in the form of chips having an area of less than <NUM><NUM><NUM>, preferably less than <NUM><NUM>. The chips typically have a thickness which is substantially less than their length, but may be from <NUM>,<NUM> up to <NUM>.

In embodiments, the method further comprises providing the MDF or HDF containing material by means of reducing the size of an MDF or HDF containing object, for instance into chips.

In embodiments, the predetermined time is <NUM>-<NUM>, preferably <NUM>-<NUM>. The steaming may be carried out using steam having a temperature in the range of <NUM>-<NUM>. The steaming is normally carried out at atmospheric pressure, i.e. with <NUM> steam, but it is understood that the steam could be slightly cooled off before reaching the MDF or HDF containing material. The steaming may alternatively be performed at slightly above <NUM> (i.e. at slight overpressure). Considering that MDF or HDF containing material from recycled furniture or flooring often comprises plastic, it is not suitable to use an excessively high steam temperature (much above <NUM>). The steaming is preferably carried out at <NUM> % consistency or more.

In embodiments, the pulping process is performed at <NUM>-<NUM>. The pulping process may be performed at a consistency <NUM>-<NUM> %, preferably about <NUM> %.

In embodiments, the screening comprises using a coarse screen and/or a fine screen, wherein the coarse screen has larger perforations than the fine screen. Coarse screening and/or fine screening may comprise more than one screens and/or screening stages. The coarse screen/-s may have holes having a diameter of <NUM>-<NUM>. The fine screen/-s may have slots having a width of <NUM>-<NUM> or holes having a diameter of <NUM>-<NUM>.

Before screening stages there can be a high consistency cleaner to remove heavy particles.

In embodiments, the dewatering is carried out to a consistency of at least <NUM> %, preferably around <NUM> %.

In embodiments, the fluffing comprises using a fluffer having a gap of <NUM>-<NUM>, preferably <NUM>-<NUM>, such as <NUM>.

According to a second aspect of the invention there is provided a method for producing MDF or HDF boards comprising producing recycled fibers using the method according first aspect of the invention or embodiments thereof, coating the recycled fibers with at least one binding agent, drying the coated recycled fibers, and after said drying, forming MDF or HDF sheets using the dried fibers, or in other words feeding the fibers to an MDF or HDF forming line. It is understood that coating the fibers with at least one binding agent refers to applying a glue or adhesion or binding agent to the fibers to allow the fibers to adhere or bind to each other further downstream in the process.

In embodiments of the method according to the second aspect of the invention, the method further comprises providing new biomass fibers from biomass material, coating the new biomass fibers with a binding agent, drying the coated new biomass fibers and mixing the new biomass fibers with the recycled fibers before said coating, or after said coating, or after said drying, such that new biomass fibers and recycled fibers are both fed to said MDF or HDF sheet forming line. In other words, the MDF/HDF production is based on recycled and new fibers. The method normally comprises producing the new biomass fibers from biomass such as tree material, bagasse, straw or any other type of biomass suitable to be used as basis for MDF/HDF production. Such process steps are well known in the art and will not be described in further detail here. Alternatively, the new fibers may be provided from another location and/or from a previous batch. As described above, the new biomass fibers are mixed with the recycled fibers before said coating, or after said coating, or after said drying. In other words, it is foreseeable that the new and recycled fibers are coated together (mixing before/during the coating) or that the fibers are dried together (mixing after said coating or during drying) or pre-treated separately (mixing after drying). In other embodiments, the MDF/HDF production is based solely on recycled fibers.

In embodiments of the method according to the second aspect of the invention, the coating is carried out using a blowline, in which said at least one binding agent is injected/sprayed.

According to a third aspect there is provided a system for producing recycled fibers from recycled MDF or HDF material, for instance for use in MDF or HDF production or for use as strengthening fibers in containerboard. The system comprises a steaming apparatus provided with an inlet for said MDF or HDF containing material and at least one steam inlet connected to a source of steam to provide steam to said material, a pulping apparatus connected to an outlet of said steaming apparatus and being configured to subject the steamed material to a pulping process to provide a slurry, a screening system connected to an outlet of said pulping apparatus and being configured to remove oversize particles from said slurry, a dewatering apparatus connected to an outlet of said screening system and being configured to dewater the slurry, and a fluffer connected to an outlet of said dewatering apparatus and being configured to fluff the dewatered slurry to produce said recycled fibers.

In embodiments of the system according to the third aspect, the steaming apparatus is an atmospheric steamer using low pressure steam or steaming to the pulping apparatus is in low steaming pressure. The screening system may comprise a coarse screen and/or a fine screen/-s, wherein the coarse screen has larger perforations than the fine screens. Such a screening system is known in the art and will not be described in further detail here. The dewatering apparatus may be a twin-roll press, a screw press, a twin-wire press, or any other suitable apparatus known to the person skilled in the art. The fluffer may be of the atmospheric/open type and may furthermore be of the low or high consistency type.

According to a fourth aspect there is provided a system for producing MDF or HDF boards. The system comprises a system for producing recycled fibers according to the third aspect, coating means configured to coat the recycled fibers with at least one binding agent, drying means configured to dry the coated recycled fibers, an MDF or HDF sheet forming line connected to the drying means to receive dried coated recycled fibers.

The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features. Further, all features and advantages of embodiments described above with reference to the first, second, third or fourth aspects may be applied in corresponding embodiments of any of the other aspects.

Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, which show presently preferred embodiments of the invention, wherein:.

<FIG> shows a flowchart of an embodiment of the method according to the first aspect of the invention. The method comprises reducing <NUM> the size of one or more provided MDF or HDF containing object into chips having an area of less than <NUM><NUM><NUM>, preferably less than <NUM><NUM>, for instance 40x40 mm, and having a thickness less than their length/width. The reducing step is optional, since the MDF/HDF containing object may alternatively have been reduced in size to chips beforehand, such that pre-produced chips are provided to the steaming <NUM>. The chips are steamed <NUM> for a predetermined time, preferably <NUM>-<NUM> minutes, preferably at atmospheric conditions with <NUM> steam, to obtain steamed material. The steaming can be done as pre-steaming before the pulping process in the pulping apparatus. The steaming is preferably carried out at <NUM> % consistency or more. The steamed material is thereafter subjected to a pulping process <NUM>, preferably at a temperature of <NUM>-<NUM> and at a consistency of about <NUM> %, to obtain a slurry. The slurry is thereafter screened using a fine screening system 4b, optionally with a preceding coarse screening 4a, to remove oversize and undesired particles. The screened slurry is thereafter dewatered <NUM> to a consistency of at least <NUM> %, preferably around <NUM> %. The dewatered material is refined/fluffed <NUM> to obtain recycled fibers. The recycled fibers may optionally be coated <NUM> with at least one binding agent as part of the method. Between the pulping process <NUM> and the screening system 4a, 4b optionally a high consistency cleaning (HCC) stage 3b in a high consistency cleaning (HCC) device 3b can be located.

<FIG> flowchart of an embodiment of the method according to the first aspect of the invention and corresponds to the embodiment of the method as above referring to <FIG> but the steaming <NUM> has been omitted and the steaming is done by introducing steam S from a steam source S directly to the pulping process <NUM> in the pulping apparatus at the pulping consistency, due to which difference this embodiment of <FIG> does not fall within the scope of the claim <NUM>. The method comprises reducing <NUM> the size of one or more provided MDF or HDF containing object into chips having an area of less than <NUM><NUM><NUM>, preferably less than <NUM><NUM>, for instance 40x40 mm, and having a thickness less than their length/width. The reducing step is optional, since the MDF/HDF containing object may alternatively have been reduced in size to chips beforehand, such that pre-produced chips are provided. The steaming is done by introducing steam S from a steam source S directly to the pulping process <NUM> in the pulping apparatus at the pulping consistency. The material is subjected to a pulping process <NUM>, preferably at a temperature of <NUM>-<NUM> and at a consistency of about <NUM> %, to obtain a slurry.

The slurry is thereafter screened using a fine screening system 4b, optionally with a preceding coarse screening 4a, to remove oversize and undesired particles. The screened slurry is thereafter dewatered <NUM> to a consistency of at least <NUM> %, preferably around <NUM> %. The dewatered material is fluffed <NUM> to obtain recycled fibers. The recycled fibers may optionally be coated <NUM> with at least one binding agent as part of the method. Between the pulping process <NUM> and the screening system 4a, 4b optionally a high consistency cleaning (HCC) stage 3b in a high consistency cleaning (HCC) device 3b can be located.

<FIG> shows a flowchart of an embodiment of the method according to the second aspect of the invention. The method comprises the same method steps <NUM>-<NUM> as shown in <FIG> and explained above. The method further comprises a coating step <NUM>, which is similar to the coating <NUM> in <FIG> in that at least one binding agent such as resin and wax is added, except that new biomass fibers may be provided <NUM> and optionally be mixed <NUM> with the recycled fibers. The new biomass fibers may be produced from biomass such as tree material, bagasse, straw or any other type of biomass suitable to be used as basis for MDF/HDF production. The process steps involved in producing the new biomass fibers are well known to the person skilled in the art and will not be described in further detail herein. The coated fibers are thereafter dried <NUM>, and after said drying, fed to an MDF or HDF sheet forming line <NUM>. As indicated by the dotted arrows in the figure, the new biomass fibers may alternatively be subjected to a separate coating step <NUM> and be mixed <NUM> with the recycled fibers after coating <NUM> or may be subjected to separate coating and drying steps <NUM>, <NUM>, and be mixed <NUM> with the recycled fibers after the drying step <NUM>. The process steps involved in an MDF or HDF sheet forming are well known to the person skilled in the art and will not be described in further detail here.

<FIG> shows a schematic illustration of an embodiment of a system according to the third aspect. The system comprises an optional size reduction apparatus <NUM>, for instance a hammermill, and a steaming apparatus <NUM> being an atmospheric steamer provided with an inlet for said MDF or HDF containing material and at least one steam inlet connected to a source of low-pressure steam to provide steam to said material. A pulping apparatus <NUM> is connected to an outlet of the steaming apparatus <NUM> and is configured to subject the steamed material to a pulping process to provide a slurry. An optional coarse screening system 23a is connected to an outlet of the pulping apparatus <NUM> and is configured to remove oversize particles from the slurry. A fine screening system 23b is connected to an outlet of the coarse screening system 23a or (in embodiments without a coarse screen) to the pulping apparatus <NUM> and is configured to remove smaller particles from the slurry. The coarse screen has holes with a diameter of <NUM>-<NUM>. The fine screen has slots having a width of <NUM>-<NUM> or holes having a diameter of <NUM>-<NUM>. The outlet of the fine screening system is connected to an optional pulp tank <NUM> in which the slurry may be stored prior to being fed to a dewatering apparatus <NUM>, which is a screw press or similar. The water pressed out from the dewatering apparatus may be fed to an optional water tank <NUM> from which it is recycled for use in the pulping apparatus. An atmospheric refiner <NUM> is connected to an outlet of the dewatering apparatus <NUM> and is configured to refine the dewatered slurry to produce said recycled fibers. The refiner has a fillings gap of <NUM>-<NUM>, preferably about <NUM>. Between the pulping apparatus <NUM> and the screening system 23a, 23b optionally a high consistency cleaning (HCC) stage 3pb in a high consistency cleaning (HCC) device 3b can be located.

Claim 1:
Method for producing recycled fibers from MDF or HDF containing material, wherein said MDF or HDF containing material is provided in the form of chips having an area of less than <NUM><NUM><NUM>, preferably less than <NUM><NUM><NUM>, comprising
- providing said MDF or HDF containing material by means of reducing (<NUM>) the size of an MDF or HDF containing object into said chips,
- steaming (<NUM>) said MDF or HDF containing material for a predetermined time to obtain steamed material;
- subjecting the steamed material to a pulping process (<NUM>) to obtain a slurry;
- screening (4a, 4b) the slurry to remove oversize particles to obtain a screened slurry;
- dewatering (<NUM>) the screened slurry to obtain dewatered fibers, and
- fluffing (<NUM>) the dewatered fibers to obtain said recycled fibers.