Method for Crushing Waste Gypsum

Abstract

To provide a crushing method which effectively separates paper pieces and gypsum and suppresses injury of mill mesh that is used for crushing when crushing waste gypsum.SOLUTION: Waste gypsum is crushed by using two sets of mills. Either mill 2 includes a projection port 18 on one end part and a discharge port 19 on the other end part, and rotates a rotation shaft 10 which is provided with a hammer 12 within a casing 16. The mill on the first step causes opening of the mesh 22 to be (12 to 30) mm and the mill on the second step causes opening of the mesh to be (3 to 12) mm. The waste gypsum is put into the mill on the first step, the waste gypsum which passes through the mesh of the mill on the first step is put into the mill on the second step, paper pieces and foreign matters are provided from discharge ports of the mill on the first step and the mill on the second step, and the waste gypsum powder is obtained from the mesh of the mill on the second step.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This invention relates to a method for crushing waste gypsum.

Background Art

[0002] The inventor has been considering the recovery of gypsum from waste gypsum boards. Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2020-65975) shows an example of a method for recovering gypsum. First, the waste gypsum board is crushed, then ground to an appropriate particle size, and the gypsum particles and paper pieces are separated. The obtained gypsum particles are calcined and then mixed with water to form a gypsum slurry. Gypsum dihydrate is precipitated from this gypsum slurry, and the gypsum dihydrate particles are separated by a solid-liquid separation device. Metal foreign substances such as metal fittings and hard foreign substances such as mortar and concrete are mixed in the waste gypsum board. Therefore, the metal foreign substances and hard foreign substances in the gypsum slurry are separated by the difference in specific gravity. Among the materials obtained from the waste gypsum board, the valuable ones are gypsum dihydrate and paper pieces. In this specification, metal foreign substances and hard foreign substances are collectively referred to as weight foreign substances.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is preferable that paper pieces and gypsum can be separated during the crushing process of waste gypsum. The inventor has confirmed that an impact mill that rotates a rotating shaft equipped with hammers inside a casing is suitable for this purpose. That is, the waste gypsum board is introduced from near one end of the casing, crushed by the rotating hammers, and the crushed gypsum lumps are discharged from the mesh of the casing. Since paper pieces are difficult to be crushed, they do not pass through the mesh and are sent by the hammers to near the other end of the casing and discharged.

[0005] Waste gypsum boards contain, in addition to gypsum and board paper, metal pieces such as fittings, and heavy foreign matters such as mortar and concrete. In order to separate the paper pieces from the gypsum, it is preferable to reduce the opening of the mesh. However, such a mesh is thin and has limited mechanical strength, so it is easily damaged by heavy foreign matters. Since the opening of the mesh is provided by punching or the like, the opening diameter (diameter) of the mesh is equal to or greater than the thickness of the mesh. When the opening is reduced, the thickness of the mesh also becomes smaller.

[0006] An object of the present invention is to effectively separate paper pieces from gypsum when crushing waste gypsum, and to suppress damage to the mesh of the mill used for crushing.

Means for Solving the Problems

[0007] In the present invention, waste gypsum is crushed using two mills, a first-stage mill and a second-stage mill. Each mill has an inlet at one end and an outlet at the other end, and a casing having a mesh between the inlet and the outlet, and is a mill that rotates a rotating shaft equipped with hammers inside the casing. In the first-stage mill, the opening of the mesh is set to be 12 mm or more and 30 mm or less, and in the second-stage mill, the opening of the mesh is set to be 3 mm or more and 12 mm or less, and the opening of the mesh of the second-stage mill is made smaller than the opening of the mesh of the first-stage mill. Waste gypsum is introduced from the inlet of the first-stage mill. The waste gypsum that has passed through the mesh of the first-stage mill is introduced from the inlet of the second-stage mill. Paper pieces and foreign matters are obtained from the outlets of the first-stage mill and the second-stage mill. Waste gypsum granules are obtained from the mesh of the second-stage mill. The sizes of these openings are values empirically obtained by the inventor in order to separate gypsum from paper pieces while reducing damage to the mesh. The thickness of the mesh is approximately the same as the opening diameter of the mesh.

[0008] Preferably, the opening of the mesh of the first-stage mill is set to be 14 mm or more and 20 mm or less, and the opening of the mesh of the second-stage mill is set to be 5 mm or more and 10 mm or less. These opening sizes are within the empirically optimal range for separating gypsum from paper pieces and reducing damage to the mesh.

[0009] In this invention, waste gypsum is crushed with a hammer and separated into paper pieces and gypsum particles. While moving from the inlet to the outlet, the waste gypsum is repeatedly struck by the hammer, and the gypsum falls off from the paper pieces. Since the opening of the mesh of the first-stage mill is as large as 12 mm or more and 30 mm or less, the crushed gypsum lumps are quickly discharged from the mesh. Also, since the mesh can be made thick, damage to the mesh caused by heavy foreign matters can be suppressed. The paper pieces and heavy foreign matters are discharged from the outlet of the first-stage mill, and the amount of gypsum adhering to the paper pieces is small. Although heavy foreign matters also enter the second-stage mill, since they are small foreign matters that have passed through the mesh of the first-stage mill, they rarely damage the mesh. The gypsum lumps are further crushed in the second-stage mill to become gypsum particles, and are separated into paper pieces, heavy foreign matters, and gypsum particles.

[0010] In this invention, waste gypsum is separated into paper pieces and gypsum by a two-stage mill equipped with a rotary impact hammer. Here, by setting the opening of the mesh in the first-stage mill to be 12 mm or more and 30 mm or less, and the opening of the mesh in the second-stage mill to be 3 mm or more and 12 mm or less, the paper pieces and gypsum can be sufficiently separated, and damage to the mesh can also be suppressed.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Best Mode for Carrying Out the Invention

[0012] Examples for carrying out the present invention are shown below. The scope of this invention should be determined based on the description in the claims, taking into account the description in the specification and well-known techniques in this field, in accordance with the understanding of those skilled in the art. The scope of this invention is not limited by the examples.

Examples

[0013] Figures 1 to 6 show the method for crushing waste gypsum boards in the examples. Figure 1 shows the process from the recovery of gypsum dihydrate from waste gypsum boards. The waste gypsum boards are put into the first-stage mill 2 and crushed. If necessary, before the first-stage mill 2, the waste gypsum boards are roughly crushed by a chain crusher or the like to a size that can be put into the mill 2. The waste gypsum boards are roughly crushed in the first-stage mill 2 and separated into a mixture of paper pieces and heavy foreign substances, and gypsum lumps. The gypsum lumps that have passed through the mesh of the first-stage mill 2 are put into the second-stage mill 3, and the gypsum lumps are further crushed to separate the paper pieces and heavy foreign substances. The paper pieces and heavy foreign substances obtained from the mills 2 and 3 are further separated by a specific gravity separation device 4 such as a cyclone or a vibrating screen into gypsum, paper pieces, and heavy foreign substances.

[0014] The gypsum granules discharged from the mesh of the second-stage mill 3 are crushed by a crushing device 5 if necessary, or the paper pieces and heavy foreign substances are further separated from the gypsum by a specific gravity separation device, a magnetic separator, etc. The gypsum is stored at one end in a silo 6 and calcined by a calciner 7 to obtain hemihydrate and / or anhydrous type III gypsum. Then, it is mixed with an aqueous medium in a crystallization device 8 to form a gypsum slurry and precipitate gypsum dihydrate particles. The gypsum slurry is separated into solid and liquid by a solid-liquid separation device 9 such as a filter press into gypsum dihydrate particles and filtrate, and the filtrate is refluxed to, for example, the crystallization device 8. The present invention lies in crushing waste gypsum by two-stage series mills 2 and 3, and other points can be changed as appropriate.

[0015] Figure 2 shows the structure of the first-stage mill 2. Except that the opening size of the mesh is small, the same applies to the second-stage mill 3. A plurality of rows of hammers 12 are provided on the rotating shaft 10. The striking surface of the hammer 12 is inclined from the axial direction of the rotating shaft 10, and the waste gypsum is sent from the right to the left in Figure 2. The rotating shaft 10 is rotated by the motor 14, and 15, 15 are bearings that support the rotating shaft 10. The rotating shaft 10 and the hammer 12 are housed, for example, in a steel casing 16. There is an inlet 18 on one end side of the casing 16, and a waste gypsum board (not shown) is put in. If it is difficult for the waste gypsum board to pass through the inlet 18, the waste gypsum board is pre-crushed by a chain crusher (not shown) or the like. There is a discharge port 19 on the other end side of the casing 16, and paper pieces and heavy foreign matters that have not been crushed to a size that can pass through the opening of the mesh 22 by the hammer 12 are discharged.

[0016] For example, below the casing 16, a mesh 22 having a large number of openings is provided. The gypsum lumps crushed by the hammer 12 and crushed to a size that can pass through the openings are discharged from the outlet 21 at the bottom of the cover 20. Note that the mesh 22 may be provided not only below the casing 16 but also on the entire circumference.

[0017] Figures 3 and 4 show the openings 25 of the mesh 22. 24 is a metal plate such as steel, and for example, circular openings 25 are provided by punching or the like. The thickness t of the metal plate 24 is approximately the same as the opening diameter D (diameter) of the opening 25. The opening ratio of the mesh 22 (the total area of the openings 25 divided by the area of the mesh 22 including the openings 25 when looking at the mesh 22 from above) is, for example, 20% or more and 50% or less, preferably 30% or more and 40% or less. The higher the opening ratio, the higher the crushing efficiency, but the strength of the mesh 22 decreases.

[0018] In the first-stage mill 2, the opening diameter D is set to be 12 mm or more and 30 mm or less, preferably 14 mm or more and 20 mm or less. When the thickness t of the mesh 22 is 12 mm or more, preferably 14 mm or more, it is hardly damaged by metal foreign matters, hard foreign matters such as mortar and concrete in the waste gypsum board. Also, due to the specifications of the gypsum board, the thickness of the waste gypsum board is often 12.5 mm or 9 mm. Therefore, when the opening diameter D is 12 mm or more, preferably 14 mm or more, the crushed gypsum lumps can easily pass through the opening 25. The rotary impact hammer 12 crushes the waste gypsum and separates it into paper pieces and gypsum lumps. While the waste gypsum is being moved within the casing 16, the gypsum adhering to the paper pieces is repeatedly struck and falls off from the paper pieces and is discharged from the mesh 22. Therefore, the amount of gypsum adhering to and discharged with the paper pieces is small. Empirically, when the opening diameter D is 12 mm or more, 90% or more of the gypsum component can be taken out from the opening 25. When the opening diameter D is 30 mm or less, preferably 20 mm or less, the paper pieces and heavy foreign matters entering the second-stage mill 3 can be reduced, and it is possible to prevent large-sized heavy foreign matters from mixing into the second-stage mill 3 and damaging the mesh. If the opening of the mesh of the mill 2 is less than 12 mm, not only the mesh will be damaged, but also the amount of gypsum discharged from the discharge port 19 together with the paper pieces will increase.

[0019] Since the paper pieces are tough, they are difficult to be crushed into small sizes, and most of them are discharged from the discharge port 19. Most of the heavy foreign matters such as metal fittings, mortar, and concrete are also discharged from the discharge port 19. However, some of the paper pieces and heavy foreign matters are put into the second-stage mill 3 from the outlet 21 together with the gypsum lumps.

[0020] Since no large-sized heavy foreign matter is fed into the second-stage mill 3, the mesh may be thinner than that of the first-stage mill 2. In the second-stage mill 3, while moving from the inlet 18 to the outlet 19, the gypsum lumps are repeatedly struck by the hammers 12, so that the paper pieces and the gypsum are further separated from each other, and the heavy foreign matter is also separated from the gypsum. Then the gypsum lumps are crushed into gypsum granules. And according to the inventor's experience, when the opening diameter D of the mesh 22 of the second-stage mill 3 is 3 mm or more and 12 mm or less, preferably 5 mm or more and 10 mm or less, the paper pieces and the heavy foreign matter can be sufficiently separated from the gypsum, and the damage of the mesh can also be prevented. In the second-stage mill 3, the opening of the mesh is made smaller than that of the mesh of the first-stage mill 2.

[0021] In addition, the gypsum granules obtained from the second-stage mill 3 may be further crushed by the crushing device 5, and after crushing, other components may be further separated from the gypsum by a magnetic separator, a specific gravity separation device, etc.

[0022] The size of the opening of the mesh 22 will be described. For a circular opening 25, the diameter D of the opening is taken as the size of the opening. For an opening other than circular, for example, the diameter of the inscribed circle of the opening is taken as the size of the opening. For example, for the opening 30 in Fig. 5 and the opening 40 in Fig. 6, the diameter D of the inscribed circle shown by the dashed line is taken as the size of the opening.

[0023] The following effects are obtained in the embodiment. · While moving from the inlet 18 to the outlet 19 of the mills 2 and 3, the rotating hammers 12 repeatedly strike the waste gypsum. Due to the strikes, the gypsum falls off from the paper pieces, and the gypsum and the paper pieces can be effectively separated. · By setting the opening of the mesh of the first-stage mill 2 to be 12 mm or more and 30 mm or less, preferably 14 mm or more and 20 mm or less, the crushed gypsum lumps can be quickly discharged through the mesh, and the mesh can be made thick, so that the damage of the mesh can also be prevented. · By setting the opening of the mesh of the second-stage mill 3 to be 3 mm or more and 12 mm or less, preferably 5 mm or more and 10 mm or less, and making it smaller than the opening of the mesh of the first-stage mill, paper pieces and heavy foreign matters can be sufficiently separated from the gypsum. Since large heavy foreign matters have already been separated by the first-stage mill 2, even if the opening of the mesh is made smaller, the mesh of the second-stage mill 3 is less likely to be damaged.

Explanation of symbols

[0024] 2, 3 mills 4 Specific gravity separation device 5 Crushing device 6 Silo 7 Calciner 8 Crystallization device 9 Solid-liquid separation device 10 Rotating shaft 12 Hammers 14 Motor 15 Bearings 16 Casing 18 Inlet 19 Outlet 20 Cover 21 Exit 22 Mesh 24 Metal plate 25 Opening 30, 40 Openings

Claims

1. A method for crushing waste gypsum using two mills, a first-stage mill and a second-stage mill, wherein each of the mills has an inlet at one end and an outlet at the other end, and between the inlet and the outlet, a casing having a mesh, and rotates a rotating shaft equipped with hammers inside the casing to crush waste gypsum. In any of the mills, the mesh is made of a metal plate and has an opening composed of a plurality of holes. In the first-stage mill, the opening of the mesh is set to be 12 mm or more and 30 mm or less. In the second-stage mill, the opening of the mesh is set to be 3 mm or more and 12 mm or less, and the opening of the mesh of the second-stage mill is made smaller than the opening of the mesh of the first-stage mill. Waste gypsum is introduced from the inlet of the first-stage mill. The waste gypsum that has passed through the mesh of the first-stage mill is introduced from the inlet of the second-stage mill. Paper pieces and foreign matters are obtained from the outlets of the first-stage mill and the second-stage mill. A method for crushing waste gypsum, characterized in that waste gypsum particles are obtained from the mesh of the second-stage mill.

2. In the first-stage mill, the opening of the mesh is set to be 14 mm or more and 20 mm or less. In the second-stage mill, the opening of the mesh is set to be 5 mm or more and 10 mm or less. The method for crushing waste gypsum according to Claim 1, characterized by this.

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