Method for Crystallizing Gypsum

Abstract

To provide a method which, when a gypsum slurry derived from a waste gypsum board is crystallized, reduces the heating cost of the gypsum slurry and eliminates bubbles in a crystallization tank.CONSTITUTION: Gypsum particles obtained by calcining a waste gypsum board after crushing are mixed with water to form a gypsum slurry, and gypsum particles are precipitated from the gypsum slurry in a crystallization tank. Heating steam is blown into the gypsum slurry at a height of up to 1 / 5 from the liquid level of the gypsum slurry in the crystallization tank to heat the gypsum slurry and eliminate bubbles on the liquid level of the gypsum slurry.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] The inventors have proposed recovering gypsum from waste gypsum board (for example, Patent Document 1: WO2012 / 176688). The waste gypsum board is crushed by a crusher and calcined to obtain hemihydrate and / or anhydrous type III gypsum. This gypsum is mixed with water or the like, and particles such as dihydrate gypsum are precipitated in a crystallization tank, and the gypsum is recovered by solid-liquid separation.

[0003] The type of gypsum precipitated in the crystallization tank varies depending on the liquid temperature. For example, below 90°C, dihydrate gypsum precipitates, and when the liquid temperature is increased, hemihydrate gypsum, anhydrous type III gypsum, etc. precipitate. In the range from room temperature to 90°C, larger particle-sized dihydrate gypsum with higher industrial value precipitates as the temperature is higher. Therefore, the gypsum slurry in the crystallization tank is heated, but heating requires costs.

[0004] The waste gypsum board contains components such as surfactants, foams when made into a gypsum slurry, and may overflow from the crystallization tank. Also, when the gypsum particles are covered with foam, the dissolution into the slurry is delayed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problems of this invention are to reduce the heating cost of the gypsum slurry when crystallizing the gypsum slurry derived from waste gypsum board and to eliminate the foam in the crystallization tank.

Means for Solving the Problems

[0007] In a method for crystallizing gypsum, in which gypsum particles obtained by calcining crushed waste gypsum board are mixed with water to form a gypsum slurry, and gypsum particles are precipitated from the gypsum slurry in a crystallization tank, steam is blown into the gypsum slurry at a height from the liquid surface of the gypsum slurry in the crystallization tank to 1 / 5 of the upper part, thereby heating the gypsum slurry and eliminating bubbles on the liquid surface of the gypsum slurry.

[0008] When steam is blown into the gypsum slurry, the thermal efficiency is higher than flowing the heated heat medium into a jacket surrounding the crystallization tank for indirect heating. Further, when steam is blown into the upper part of the gypsum slurry, the bubbles in the upper part of the gypsum slurry are heated, expanded and burst. Therefore, defoaming can be achieved simultaneously with heating the gypsum slurry.

[0009] To maintain the gypsum slurry at a predetermined temperature, in addition to blowing steam, the crystallization tank may be covered with a heating jacket, and a heated heat medium may be circulated in the jacket. However, preferably, in order to reduce the heating cost, the gypsum slurry is maintained at a predetermined temperature by steam, and no other heat source is provided in the crystallization tank.

[0010] Preferably, a plurality of crystallization tanks are provided in series, a gypsum slurry mixed with water is supplied to the crystallization tank on the most upstream side, the gypsum slurry is moved from the upstream side to the downstream side, and steam is blown only into the crystallization tank on the most upstream side. When steam is supplied to the crystallization tank on the most upstream side, the slurry temperature can also be maintained near a predetermined value in the crystallization tank on the downstream side. Further, since foaming occurs in the crystallization tank on the most upstream side, the bubbles may be removed in the crystallization tank on the most upstream side.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

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

Example

[0013] Examples are shown in FIGS. 1 and 2. FIG. 1 shows the process from the crushing of waste gypsum board to the recovery of gypsum. In the first pretreatment step 2, waste gypsum board (not shown) is roughly crushed by a crusher 10. The crushed pieces are passed through a sieve 16, and the gypsum powder is separated as the undersize component. While the oversize component is conveyed by a sorting conveyor 18, foreign matters such as metal, wood chips, and mortar are removed by manual sorting or the like. The crushed pieces from which foreign matters have been removed are conveyed by a metering conveyor, and magnetic adherends such as metal are removed by a magnetic separator 25. Then, they are crushed into gypsum granules by a fine crusher 30, and for example, paper pieces are removed by a sieve built into the fine crusher 30. Next, the gypsum granules are conveyed by an air flow through a magnetic separation pipe 32, and small metal objects such as screws and nails are separated by a magnet installed in the magnetic separation pipe 32. The gypsum granules that have passed through the magnetic separation pipe 32 are stocked in a silo 40.

[0014] In the calcination step 4, the gypsum granules are calcined by a calciner 50 to be changed into hemihydrate and / or anhydrous type III gypsum. The calcined gypsum is processed in a crystallization step 6. The calcined gypsum is mixed with an aqueous medium such as gypsum slurry in a mixer 61, and for example, crystallized in four serially connected crystallization tanks 62 to 65 to precipitate dihydrate gypsum particles. Note that when the temperature of the crystallization tanks 62 to 65 is increased above 90°C, hemihydrate gypsum or the like can be precipitated. The crystallization tank 62 is on the most upstream side, and the larger the number, the more downstream it is. Then, the gypsum slurry is circulated between the crystallization tanks 62 to 65. In the example, the gypsum slurry is returned from the crystallization tank 65 to the crystallization tank 62, but the reflux of the gypsum slurry from the crystallization tank 65 to the crystallization tank 62 may be omitted.

[0015] Note that the gypsum granules may be put into an aqueous medium flowing through a trough or the like without using the mixer 61. Also, instead of the multi-stage crystallization tanks 62 to 65, a single large crystallization tank may be used.

[0016] In the filtration step 10, the gypsum slurry is extracted from the crystallization tank 65 or the like, passed through a sieve to remove paper pieces. Then, the gypsum slurry is subjected to solid-liquid separation by a filter to extract gypsum powder such as dihydrate gypsum. The remaining liquid component is circulated to, for example, the mixer 61 to replenish the process water lost as the crystal water or the adhering water of the gypsum powder.

[0017] Figure 2 shows the crystallization tanks 62 and 63. The crystallization tanks 64 and 65 in the third and fourth stages are configured in the same manner as the crystallization tank 63 in the second stage. The gypsum slurry 70 is stored in the crystallization tanks 62 and 63, and the gypsum slurry is supplied from the slurry supply pipe 71 connected to the mixer. Further, the crystallization tanks 62, 63, etc. are connected by the circulation pipe 72, and the gypsum slurry is moved to the precipitation tank on the lower stage, for example, by natural flow. The gypsum slurry is circulated to the uppermost precipitation tank 62 from the lowermost precipitation tank 65 by the circulation pipe 74. Blades 76 and drive motors 75 are provided in each precipitation tank 62 - 65 to stir the gypsum slurry 70. When the hemihydrate and / or anhydrous type III gypsum derived from the waste gypsum board is made into a slurry, bubbles 78 are generated particularly in the uppermost crystallization tank 62 due to the influence of surfactants or the like in the gypsum board.

[0018] The outlet of the steam introduction pipe 84 is arranged at the liquid level of the uppermost precipitation tank 62 or at a position immediately below the liquid level, generally at a height from the liquid level of the slurry 70 to 1 / 5 of the upper part, and the heating steam is blown into the gypsum slurry 70. The heating steam may be blown into the gypsum slurry from directly above the liquid level as in the case of the steam introduction pipe 86 shown by the dashed line. 82 is a steam generator such as a boiler. Also, the temperature T of the gypsum slurry 70 is measured by the temperature sensor 88 to control the steam generator 82.

[0019] The heated steam blown in from the steam introduction pipes 84 and 86 is, for example, at 130°C and 1 atm, and those at 100 - 150°C and 0.2 - 2 atm are easier to handle. The pressure here indicates the difference from atmospheric pressure, and 0.2 - 2 atm is 1.2 - 3 atm (pressurized steam) as absolute pressure. Also, since the heated steam often exceeds 100°C, it is superheated steam. When the temperature of the gypsum slurry in the topmost crystallization tank 62 is reduced to slightly less than 90°C by the heated steam, all the crystallization tanks 62 - 65 can be maintained at the required temperature except in cold regions. And blowing in the heated steam consumes less energy cost than indirectly heating the crystallization tank 62 with a jacket or the like.

[0020] When the heated steam is blown in, the slurry near the liquid surface is heated, and as a result, the bubbles 78 also expand and burst. Therefore, the bubbles 78 can be eliminated simultaneously with the heating of the gypsum slurry 70. Although the gypsum slurry is diluted by the blowing in of the heated steam, it can usually be heated within the range where it goes out of the system as the crystal water or adhering water of the precipitated gypsum dihydrate. Therefore, except in cold regions, there is no need to use a heating jacket or the like in combination.

Explanation of Symbols

[0021] 2 Pretreatment Process 4 Calcination Process 6 Crystallization Process 8 Filtration Process 10 Crusher 11 Inlet 16 Sieve 18 Sorting Conveyor 20 Quantitative Conveyor 25 Magnetic Separation Device 30 Fine Crusher 32 Magnetic Separation Pipe 40 Silo 50 Calciner 61 Mixer 62 - 65 Crystallization Tanks 70 Gypsum Slurry 71 Slurry Supply Pipe 72, 74 Circulation Pipes 75 Motor 76 Blades 78 bubbles 80 ventilation holes 82 steam generator 84, 86 steam inlet pipes 88 temperature sensor

Claims

1. In a method for crystallizing gypsum dihydrate, gypsum particles obtained by calcining waste gypsum board after crushing are mixed with water to form a gypsum slurry, and gypsum dihydrate particles are precipitated from the gypsum slurry under stirring in a crystallization tank, wherein at a height from the liquid surface of the gypsum slurry in the crystallization tank to 1 / 5 of the upper part, hot steam is blown into the gypsum slurry to heat the gypsum slurry to a predetermined temperature higher than room temperature and not exceeding 90 °C and to eliminate the bubbles on the liquid surface of the gypsum slurry. A method for crystallizing gypsum dihydrate, characterized in that

2. The method for crystallizing gypsum dihydrate according to claim 1, characterized in that the gypsum slurry is maintained at a predetermined temperature by the hot steam, and no other heat source is provided in the crystallization tank.

3. A method for crystallizing gypsum dihydrate according to claim 1 or 2, characterized in that a plurality of crystallization tanks are provided in series, a gypsum slurry mixed with water is supplied to the crystallization tank on the most upstream side, the gypsum slurry is moved from the upstream side to the downstream side, and hot steam is blown only into the crystallization tank on the most upstream side.

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