Method of recovering paper scrap and gypsum granules from waste gypsum board

Abstract

In the present invention, when recovering paper scrap and gypsum granules from a waste gypsum board, the gypsum granules are separated from paper scrap while the generation of paper dust from pulverization is kept to a minimum. After having been crushed, the waste gypsum board is separated by means of a first sieve into over-sieve paper scrap and under-sieve components. The under-sieve components from the first sieve are pulverized by means of a pulverizer, and the under-sieve components having been pulverized by the pulverizer are sieved by means of a second sieve and are separated into over-sieve components composed of a mixture of paper scrap and gypsum granules, and under-sieve components composed of gypsum granules. The over-sieve components from the second sieve are fed onto a conveying surface of a belt conveyor, the conveying surface moving diagonally upward, and the paper scrap is conveyed upward along with the conveying surface of the belt conveyor and collected from the upper part of the belt conveyor, and the gypsum granules are caused to roll diagonally downward on the conveying surface and are collected from the lower part of the belt conveyor.

Description

Method for recovering paper pieces and gypsum granules from waste gypsum board

[0001] The present invention relates to a method for separating and recovering paper chips and gypsum particles from waste gypsum board.

[0002] The inventors have commercialized the recovery of gypsum powder and paper from waste gypsum board. First, the waste gypsum board is crushed to produce paper chips and gypsum granules. Next, the paper chips are recovered as an oversized component using a sieve such as a vibrating sieve, and the gypsum granules are recovered as an undersized component. The gypsum granules are further crushed and sieved into paper chips and gypsum granules. The gypsum granules are converted into hemihydrate and / or anhydrous type III gypsum by calcination, which is then dissolved in a gypsum slurry in a mixing tank, and gypsum powder such as gypsum dihydrate is precipitated in a crystallization tank. The precipitated gypsum powder is filtered, and the filtrate is returned to the mixing tank, for example. Through the above process, paper chips and gypsum powder can be recovered from waste gypsum board.

[0003] Patent Publication No. 2023-00603

[0004] When the material is sieved after crushing, large gypsum particles remain in the sieved components. If the gypsum particles are mixed with the paper pieces, the value of the paper pieces decreases. Therefore, if the crushing is intensified, paper powder is generated, which mixes with the gypsum particles and reduces the purity of the gypsum particles. It is difficult to sufficiently separate the paper pieces from the gypsum particles while suppressing the generation of paper powder using only crushing and sieving.

[0005] An object of the present invention is to separate the gypsum particles from the paper chips while suppressing the generation of paper dust due to pulverization when recovering the paper chips and gypsum particles from waste gypsum board.

[0006] The method of recovering paper pieces and gypsum particles from waste gypsum board of this invention includes the steps of crushing the waste gypsum board and then separating it using a first sieve into paper pieces that pass through the sieve and an under-sieve component; crushing the under-sieve component that passed through the first sieve using a crusher; sieving the under-sieve component crushed by the crusher using a second sieve to separate it into an over-sieve component consisting of a mixture of paper pieces and gypsum particles and an under-sieve component consisting of gypsum particles; and feeding the over-sieve component that passed through the second sieve onto the conveying surface of a belt conveyor whose conveying surface moves obliquely upward, conveying the paper pieces upward together with the conveying surface of the belt conveyor and recovering them from the top of the belt conveyor, and rolling the gypsum particles obliquely downward on the conveying surface to recover them from the bottom of the belt conveyor.

[0007] In this invention, flat paper pieces that have high friction with the belt are transported diagonally upward along the conveying direction on the conveying surface of the belt conveyor and can be collected from the top of the belt conveyor. Gypsum granules, which are bulkier than paper pieces, roll on the conveying surface of the belt conveyor, and because they are soft, the corners are cut off by rolling, forming a shape that is closer to a sphere, making them easier to roll. As a result, the gypsum granules can be collected from the bottom of the belt conveyor. In this invention, the belt conveyor can separate the paper pieces from the gypsum granules. This separation does not involve crushing the paper pieces, so the amount of paper powder mixed into the gypsum granules does not increase.

[0008] Preferably, the gypsum granules recovered from the bottom of the belt conveyor are re-ground in a grinder together with the under-sieve component of the first sieve. The re-ground gypsum granules are then sieved through a second sieve. Since the gypsum granules recovered from the bottom of the belt conveyor tend to have large particle sizes, re-grounding the gypsum granules makes it possible to make the particle sizes uniform with the gypsum granules that initially passed through the second sieve.

[0009] Particularly preferably, the second sieve is a vibrating sieve with openings of 6 mm to 12 mm. If the openings are less than 6 mm, clogging is likely to occur when processing waste gypsum board wet with rainwater, etc. If the openings are more than 12 mm, a large amount of paper fragments will be mixed in with the under-sieve component.

[0010] 3. A process diagram from crushing waste gypsum boards to recovering gypsum dihydrate powder in an example. 4. A diagram showing the separation of paper chips and gypsum particles by a belt conveyor in an example. 5. A photograph showing the paper chips (FIG. 3(A)) and gypsum particles (FIG. 3(B)) separated in an example.

[0011] Examples for carrying out the present invention are shown below. The scope of the present invention should be determined based on the claims, taking into account the description in the specification and well-known techniques in this field, and in accordance with the understanding of those skilled in the art. The scope of the present invention is not limited by the examples.

[0012] Examples are shown in Figures 1 to 3. In this specification, the opening (mesh size) of a sieve is the diameter of the opening if the opening is circular, the length of one side if the opening is square, and the root of the product of the lengths of the short side and the long side if the opening is rectangular.

[0013] Figure 1 shows an example of recovering paper chips and gypsum dihydrate powder from waste gypsum board. At a minimum, it is sufficient to crush and pulverize the waste gypsum board and separate the paper chips from the gypsum particles; subsequent calcination and crystallization are not required. In Figure 1, the waste gypsum board is crushed using a crusher 2 to obtain paper chips and gypsum particles. The crusher can be of any type. The paper chips and gypsum particles obtained by crushing are placed on a first sieve 4, such as a vibrating sieve, and separated into the oversized paper chips and the undersized component (mainly gypsum particles, including the paper chips).

[0014] The undersize fraction obtained from sieve 4 is fed into crusher 5, and the crushed gypsum particles are sieved using a second sieve 8 consisting of a vibrating sieve or the like. The type of crusher 5 is arbitrary. The undersize fraction of sieve 8 is mostly gypsum and is fed into calciner 10. The oversize fraction of sieve 8 includes paper chips and gypsum particles, and is fed into belt conveyor 6. The paper chips are collected from the top of belt conveyor 6, and gypsum particles with slightly larger particle sizes are collected from the bottom, and are fed back into crusher 5. The process using belt conveyor 6 can separate the paper chips and gypsum particles, and generates almost no paper dust.

[0015] The openings of the second sieve 8 are preferably 6 mm or more and 12 mm or less. If the openings are less than 6 mm, clogging is likely to occur when processing waste gypsum board wet with rainwater, etc. If the openings are more than 12 mm, a large amount of paper fragments will be mixed in with the undersize components. The openings of the first sieve 4 are made larger than the openings of the second sieve 8.

[0016] In order to separate metal pieces such as nails, gravel, sand and other non-magnetic foreign matter mixed in with the waste gypsum board, it is preferable to carry out a process for separating metallic foreign matter, non-magnetic foreign matter, etc. at an appropriate location, for example, between the crusher 2 and the calciner 10.

[0017] In the calciner 10, the gypsum granules are calcined to produce hemihydrate and / or anhydrous type III gypsum, which is then mixed with water such as a gypsum slurry in a mixing tank 12, and, for example, gypsum dihydrate particles are precipitated in a crystallization tank 14. In a filter 16, gypsum dihydrate powder and the like are recovered from the gypsum slurry in the crystallization tank 14, and the filtrate is refluxed, for example, to the mixing tank 12. Note that, in the crystallization tank 14, other gypsum such as hemihydrate may be precipitated instead of gypsum dihydrate.

[0018] The separation of paper chips and gypsum granules by a belt conveyor 6 will be explained with reference to Figure 2. The belt conveyor 6 drives an endless belt 20 with a pair of pulleys 22, 22, one of which is a drive pulley and the other a driven pulley, for example. The endless belt 20 is, for example, a flat belt made of natural rubber with teeth on the backside that mesh with the teeth of the pulley 22. The endless belt 20 may be a low-friction steel belt, a stepped belt with horizontal protrusions to increase friction with the conveyed material, a flat belt with upward protrusions on both sides, or the like, and the shape and material of the endless belt 20 are optional.

[0019] The conveying surface 21 of the endless belt 20 conveys clumps of gypsum particles 24 and paper chips 26. The conveying direction of the endless belt 20 (hereinafter referred to as "belt 20") is diagonally upward, and in the case of a flat belt made of natural rubber, the inclination angle for separating the paper chips from the gypsum particles is preferably 7° to 30°. The inclination angle is made smaller for belts with low friction such as steel belts, and larger for stepped belts with high friction. The inclination angle was empirically determined so that the paper chips rise together with the belt 20 and the gypsum particles roll on the belt 20 and fall.

[0020] The oversized component is charged onto the belt 20, for example, from a chute 28, and the charge position is preferably between the center position in the longitudinal direction of the belt 20 and a position in the lower half position in the longitudinal direction of the belt 20 so that the gypsum granules do not move to the upper end of the belt conveyor 6. A skirt or the like may be provided at the lower end of the chute 28 to prevent paper pieces from scattering.

[0021] When the sieved-over component is placed on the conveying surface 21, the flat paper chips 26, which have high friction with the belt 20, are conveyed diagonally upward along the conveying direction and are collected, for example, from the upper end of the conveyor 6. The gypsum granules 24, which are bulkier than the paper chips 26, roll on the conveying surface 21, and because they are soft, their corners are cut off and they become nearly spherical, making them easier to roll. As a result, the gypsum granules 24 can be collected, for example, from the lower end of the conveyor 6. Most of the gypsum powder generated by the corners of the gypsum granules 24 being cut off is also collected from the lower end of the conveyor 6. The paper chips 26 and gypsum granules 24 can be collected by free fall from the end of the belt 20 or by vacuum suction, etc.

[0022] The gypsum granules recovered from the conveyor 6 have a large particle size, so they are pulverized in a pulverizer 5 together with the undersize component of the first sieve 4.

[0023] Figure 3(A) shows paper scraps collected from the top of the conveyor 6, and Figure 3(B) shows gypsum granules collected from the bottom of the conveyor 6. The gypsum granules have rounded corners and are easy to roll. This allows the paper scraps and gypsum granules to be easily separated and collected.

[0024] 2 Crusher 4, 8 Sieve 5 Pulverizer 6 Belt conveyor 10 Calciner 12 Mixing tank 14 Crystallization tank 16 Filter 20 Endless belt 21 Conveying surface 22 Pulley 24 Gypsum granules 26 Paper pieces 28 Chute

Claims

1. A method for recovering paper chips and gypsum granules from waste gypsum board, comprising the steps of: crushing waste gypsum board, and then separating the paper chips that pass through a first sieve and an under-sieve component using a crusher; crushing the under-sieve component that passed through the first sieve using a crusher; sieving the under-sieve component crushed by the crusher using a second sieve to separate it into an over-sieve component consisting of a mixture of paper chips and gypsum granules and an under-sieve component consisting of gypsum granules; and feeding the over-sieve component that passed through the second sieve onto the conveying surface of a belt conveyor whose conveying surface moves diagonally upward, transporting the paper chips upward together with the conveying surface of the belt conveyor and recovering them from the top of the belt conveyor, and rolling the gypsum granules diagonally downward on the conveying surface to recover them from the bottom of the belt conveyor.

2. The method for recovering paper chips and gypsum granules from waste gypsum boards according to claim 1, wherein in the crushing step, the gypsum granules recovered from the bottom of the belt conveyor are re-crushed by the crusher together with the undersize components of the first sieve.

3. A method for recovering paper chips and gypsum particles from waste gypsum boards according to claim 2, characterized in that the second sieve is a vibrating sieve with openings of 6 mm or more and 12 mm or less.

Images