IT202200022869A1 - Screening device for the production of calibrated wood chips for use in boilers and pellet stoves - Google Patents

Description

Description of the industrial invention entitled:

?SCREENING DEVICE FOR THE PRODUCTION OF CALIBRATED WOOD CHIPS FOR USE IN BOILERS AND PELLET STOVES?

DESCRIPTION

The present invention relates to a device for screening raw wood chips, obtained by pre-screening wood chips with a 10x10 mm grid, in order to obtain calibrated wood chips, i.e. of controlled dimensions, so that they are suitable for use as fuel in pellet stoves and boilers.

Through a process called ?chipping?, the wood is mechanically chopped into small pieces called ?chips? of non-uniform size.

Raw wood chips are produced with a selected range of forestry chippers capable of producing raw wood chips with a high percentage of calibrated wood chips (suitable for domestic stoves and boilers).

The wood thus transformed constitutes raw wood chips, i.e. a vegetal biomass which, like pellets or firewood, is considered a 100% ecological green biofuel.

The calibrated wood chip, the production of which is the object of the present invention, is the result of the sifting of the raw wood chip and has a width [l] between 3 and 12 mm, a length [L] between 3 and 25 mm and a thickness [H] not exceeding 7 mm and is suitable for use as fuel in boilers and pellet stoves.

The interest in the market is enormous, considering that the national pellet requirement is currently covered by 87% by imports from Austria, the Balkans, Russia, Canada and New Zealand. It follows that the development of this new fuel, produced with local raw materials, could contribute both to the increase of the country's energy self-sufficiency and to the increase of forest maintenance activities, with beneficial effects on the regulation of runoff in forest areas and on the rural economy.

It should be noted that the size of the various chips is of crucial importance, otherwise blockages of the feed screws of pellet stoves and boilers occur.

At the moment, the raw wood chips on the market are not intended for fueling pellet-fired stoves and boilers because the problem of the dimensional non-homogeneity of the fuel has not been resolved.

According to the current technique, the raw wood chip is obtained mainly with vibrating screens based on vibrating grids, designed to separate the smaller flakes from the wood chips.

However, the vibrating screens of the current technique do not allow the elimination of elements with abnormal dimensions compared to the dimensional standard of the calibrated wood chips such as under- and over-sizes. The raw wood chips, generated by the current screening process of the woody material, in fact have elements with non-uniform geometries. In particular, the narrow and long ones (L?10 mm and L?25 mm) are not eliminated with traditional screening techniques. With these screens, the selection of the material occurs exclusively by falling into perforated elements with a known section or by crossing grids. The result is that the elongated wood chips (L?25 mm), which are those that cause blockages in the feed screws of pellet stoves and boilers, are not completely eliminated from the mass, so the raw wood chips obtained with the current screening technique are not suitable for use as fuel in place of pellets.

Current technologies are structured for the selection of raw materials in which the selection process is carried out exclusively by means of calibrated hole grids. The selection process is mainly implemented for the production of wood fiber panels in which the selection based on the diameter of the raw material and not the longitudinal dimensions is essential.

Patent CN203304177 (Shaking screener for wood chips) describes a squaredisc-shaped machine body type machine with centrifugal advancement of the material and selection by falling through a passage inside an area with calibrated holes.

Patent CN215612307 (Wood chip cleaning device for artificial board production) describes an industrial-type system for processing waste materials even in the presence of impurities. This system is equipped with sensors for the elimination of stones and metals and includes fans for the removal of plastic materials. The material is then selected by gravity through a passage inside an area with calibrated holes. Different dimensional types of materials are obtained, used both for the production of wood-fiber panels and for other applications in the construction sector.

Patent CN208407613 (Wood shavings classified screening machine) describes a machine for the selection of wood materials for the production of wood panels from recycled materials. Up to five different dimensional types of materials are obtained by means of vibrating advancement on calibrated hole grids.

Patent CN206953222 (Wood chip screening system with jumbo size wood chip secondary chipper) describes a composite board production plant and refers to a wood chip screening system with calibrated hole grids and a jumbo size wood chip secondary chipper.

Patent CN108057509 (Wood chip separation device) describes a machine for the elimination of sawdust and dust from woody material and subsequent selection into two fractions. The separation occurs by gravity through a grid.

None of the patents cited contain a system for selecting wood material based on the length of the scales.

The purpose of the present invention is to select the so-called calibrated wood chip, that is, a woody material divided into flakes of such a size that it can be used as fuel in stoves and boilers currently fueled by pellets. The invention is an integral part of a new production process that goes from the selection of the wood rounds suitable for the production of calibrated wood chips, to the choice of the most suitable forestry chippers, to their optimal setting for the production of "raw wood chips" with the maximum percentage of calibrated wood chips inside it, to then move on to its drying and finally to the actual sifting and subsequent packaging.

The above and other purposes, as will be explained below, are achieved with a device for screening raw wood chips in accordance with claim 1. Said device, which allows the production of wood chips of controlled dimensions, so that they are suitable for use as fuel in pellet stoves and boilers, is of the type that provides for the passage of said raw wood chips over grates/sieves. Said grates/sieves can be inclined and are subjected to vibration, so as to guide the passage of the raw wood chips over said grates/sieves so that the parts of said raw wood chips, of dimensions not compliant with use as fuel in pellet stoves and boilers are separated for other uses. Said device is characterized in that it comprises:

- a first grid/sieve, equipped with holes, suitable for selecting the raw wood chips, eliminating dust and flakes that are too small; - a second grid/sieve, which has a plurality of parallel channels on the bottom of which there are openings for selecting and discarding elements that are too long.

This selection occurs following the alignment of the scales with the prevalent dimension aligned with the direction of said channels.

Preferred embodiments and non-trivial variants of the present invention form the subject of the dependent claims.

It is understood that all attached claims form an integral part of this description.

The invention in question solves the drawbacks in question as it allows for the production of a substitute product for wood pellets, which can be used for the same purposes.

At the moment, the uncalibrated wood chips on the market are not intended for fueling pellet stoves and boilers because current technology has not resolved the problem of the dimensional inhomogeneity of the fuel.

The present invention guarantees the dimensional uniformity of the calibrated wood chips, eliminating all the long and deformed elements and making it usable in boilers and stoves traditionally fueled with wood pellets.

It will be immediately obvious that countless variations and modifications can be made to what has been described (for example, relating to shape, dimensions, arrangements and parts with equivalent functionality) without departing from the scope of protection of the invention, as appears from the attached claims.

The present invention will be better described by some preferred embodiments, provided by way of example and not of limitation, with reference to the attached drawings, in which:

- FIG. 1 shows the fundamental parts of the device according to the present invention;

- FIG. 2 shows the part of the device that performs the final screening.

With reference to FIG. 1, (1) indicates a device for screening calibrated wood chips, i.e. a vibrating screen with special grids/sieves (2, 3) for screening raw wood chips.

These grids/sieves (2, 3) are inclined at an angle of between -15? and 30?, preferably between 0? and 15?, so that the combined effect of vibrations and gravity moves the wood chips forward.

A first grid/sieve (2), equipped with a plurality of holes (2a), allows the wood chip to be selected in relation to the size of the flakes. In particular, it allows the elimination of dust and flakes that are too small.

According to a preferred embodiment, called first metal grid/sieve (2), with dimensions of for example 500x500 mm, it is substantially a sieve with said holes (2a) of circular section, with a diameter of approximately 3 mm, and is suitable for the elimination of dust and flakes of dimensions smaller than 3 mm.

This second grid/sieve (3), with dimensions of for example 500x700 mm, has a plurality of parallel channels (3a) on the bottom of which there are openings (4) for the selection and discarding of elements that are too long.

According to a preferred embodiment, said parallel channels (3a) have a width (or lumen) of between 10 and 15 mm, preferably 12 mm, a depth of 10 mm and have two discharge openings (4) in the terminal part, of a square or rectangular shape, made on the bottom of the channels (3a) themselves and of a width equal to the lumen of the channel and a length equal to 10 mm.

The first grid/sieve (2), the one with 3 mm holes (2a), is positioned on a plane parallel to, but raised by approximately 20 mm, with respect to the plane of the second grid/sieve (3).

The selection process of the calibrated wood chips requires that the raw wood chips (to be sifted) are poured directly onto the first grid/sieve (2). The raw wood chips, due to the vibrations and inclination of the first grid/sieve (2), move towards the second grid/sieve (3), i.e. the one equipped with channels (3a). The material falls from the first grid/sieve (2), onto the second grid/sieve (3), distributing itself fairly uniformly between all the channels (3a), and advances due to the vibrations and inclination towards the end of the channels (3a). In the channels (3a) the wood chips are oriented with the prevailing size in a direction parallel to the channels (3a), so that the flakes with a length [L] less than 25 mm fall through the discharge openings (4) of the channels (3a) and go on to constitute the actual calibrated wood chips, while the excess dimensions run through the channels (3a) to the bottom, where they are collected as excess dimensions for other energy uses.

The sieve according to the invention preferably comprises a system for unblocking the product along the channels (3a), represented by rotating brushes with plastic bristles (not shown), which slide at regular intervals along the channels (3a) to eliminate any blockages and a system of compressed air nozzles (not shown) placed under the level of the channels (3a) and oriented towards the openings (4) of the channels (3a) themselves.

The brushes will be conveniently oriented with the axis of rotation perpendicular to the channels (3a) and parallel to the plane of the second grid/sieve (3), so that the tangential speed of the ends of the bristles, at the point of contact, is parallel to the channels (3a) themselves. The direction of rotation must be such as to push the flakes in the opposite direction to the direction of advancement of the material.

Compressed air, programmed regularly, removes any blockages from the channel openings (3a).

In summary, the raw wood chip undergoes an initial screening through the first grid/sieve (2), which eliminates dust and pieces smaller than the holes (2a) (3mm). The wood chip, stripped of the smaller parts, passes, due to vibrations and inclination, onto the second grid/sieve (3); again due to the combined effect of vibrations and inclination, it passes through the channels (3a) of the second grid/sieve (3), with the wood chip flakes orienting themselves with the prevailing size in a direction parallel to the channels (3a). Once they reach the openings (4), the pieces [L] less than 25 mm long are discharged into a container below and constitute the calibrated wood chip suitable for use in pellet stoves and boilers, while those of greater length exit from the channels (3a) and are collected as overmeasures for other energy uses.

Preferred embodiments of the invention have been described, but they are naturally susceptible to further modifications and variations within the scope of the same inventive idea. In particular, numerous variants and modifications, functionally equivalent to the previous ones, will be immediately evident to those skilled in the art, which fall within the scope of the invention, as highlighted in the attached claims in which the reference signs placed in brackets cannot be interpreted as limiting the claims themselves. Furthermore, the word "comprising" does not exclude the presence of elements and/or phases other than those listed in the claims. The preceding article "a", "an" or "an" element does not exclude the presence of a plurality of such elements. The simple fact that some features are cited in different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims (11)

1. Device (1) for screening raw wood chips, suitable for obtaining calibrated wood chips, or chips of controlled dimensions, so that they are suitable for use as fuel in boilers and pellet stoves, of the type which involves the passage of said raw wood chips to be screened over grids/sieves (2, 3), said passage occurring through the combined effect of the inclination and vibration to which said grids/sieves (2, 3) are subjected, in which the parts of said raw wood chips, of dimensions not compliant with use as fuel in boilers and pellet stoves are separated for other uses, characterised in that said device (1) comprises: - a first grid/sieve (2), equipped with holes (2a), suitable for selecting said raw wood chips, eliminating dust and flakes that are too small; - a second grid/sieve (3), which has a plurality of parallel channels (3a) on the bottom of which there are openings (4), for the selection and discarding of elements that are too long, where the selection occurs following the alignment of the scales with the prevalent dimension aligned with the direction of said channels (3a). 2. Device (1) for screening raw wood chips according to claim 1, characterised in that said first grid/sieve (2), suitable for selecting the raw wood chips, in relation to the size of the flakes of said raw wood chips, eliminating dust and flakes that are too small, is provided with holes (2a) of 3 mm diameter. 3. Device (1) for screening raw wood chips according to claim 1, characterised in that said second grid/sieve (2) has dimensions 500x700 mm. 4. Device (1) for screening raw wood chips according to claim 1, characterised in that pairs of openings (4) are made in the terminal part of said channels (3a). 5. Device (1) for screening raw wood chips according to claim 1, characterised in that said channels (3a) have a lumen between 10 and 15 mm. 6. Device (1) for screening raw wood chips according to claim 5, characterised in that said channels (3a) have a lumen of 12 mm. 7. Device (1) for screening raw wood chips according to claim 1, characterised in that said openings (4), made on the bottom of said channels (3a), are two discharge openings (4), rectangular or square, made on the bottom of the channels (3a) themselves and with a width equal to the lumen of the channel and a length equal to 10 mm. 8. Device (1) for screening raw wood chips according to at least one of claims 1 to 7, characterised by comprising a system for unblocking the raw wood chips along the channels (3a), represented by rotating brushes with plastic bristles, which slide at regular intervals along the channels (3a) to eliminate any blockages. 9. Device (1) for screening raw wood chips according to at least one of claims 1 to 8, characterised by the fact that it comprises a system for releasing the product from the openings (4), represented by a system of compressed air nozzles, positioned under the level of the channels (3a) and oriented towards the openings (4) of the channels (3a) themselves, in such a way that the compressed air, programmed regularly, removes any blockages. 10. Device (1) for screening raw wood chips according to at least one of claims 1 to 8, characterised in that said first and second grid/sieve (2, 3) are inclined at an angle ? between -15? and 30?. 11. Device (1) for screening raw wood chips according to claim 10, characterised in that said first and second grid/sieve (2, 3) are inclined at an angle ? between 0? and 15?.