Method for producing hemihydrate gypsum

Abstract

This method for producing hemihydrate gypsum comprises the steps of: starting firing raw material gypsum in the atmosphere and in an open state, and adding a chloride to the raw material gypsum when the temperature of the raw material gypsum is in a range of room temperature or higher and 120°C or less; and firing the raw material gypsum at a temperature higher than 120°C after adding the chloride.

Description

Method for producing hemihydrate gypsum

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

[0002] Hemihydrate gypsum is produced by firing dihydrate gypsum, the raw material, in a kiln or furnace. During the firing process, the water of crystallization evaporates from the raw material gypsum (dihydrate gypsum), transforming it into hemihydrate gypsum. Two types of hemihydrate gypsum are known: α-type hemihydrate gypsum, which is produced by pressurized firing in water or steam using an autoclave, and β-type hemihydrate gypsum, which is produced by atmospheric pressure firing in the air.

[0003] The resulting hemihydrate gypsum can be mixed with an appropriate amount of water to form a slurry, which then solidifies back into dihydrate gypsum. Hemihydrate gypsum is used, for example, as a raw material for gypsum board.

[0004] Patent Document 1 discloses a technique for producing α-type hemihydrate gypsum by adding a grain size adjusting salt such as calcium chloride to gypsum and increasing the pressure and temperature. Patent Document 2 discloses a technique for maintaining the fluid state of gypsum with steam during firing and heating it while continuously adding gypsum with added chloride until dehydrated.

[0005] JP-A-48-102095 JP-A-49-93410

[0006] Beta-type hemihydrate gypsum may disintegrate when mixed with water to form a slurry. When hemihydrate gypsum disintegrates, the surface area of ​​the particles increases, requiring a large amount of water for mixing. Furthermore, the resulting slurry may harden rapidly, making it difficult to handle.

[0007] Patent documents 1 and 2 do not take into consideration the disintegration of particles when hemihydrate gypsum and water are mixed to form a slurry. Specifically, the hemihydrate gypsum in Patent Document 1 is α-type hemihydrate gypsum, which does not have the problem of particle disintegration. Patent Document 2 is a technology that realizes continuous single-stage firing at low temperatures, and it is difficult to apply it directly to other firing methods.

[0008] The present invention aims to provide a method for producing hemihydrate gypsum that can suppress the disintegration of particles when mixed with water to form a slurry.

[0009] A method for producing hemihydrate gypsum according to one embodiment includes the steps of: starting the firing of raw gypsum in the atmosphere and in an open state; adding chloride to the raw gypsum when the temperature of the raw gypsum is in the range of room temperature or more and 120°C or less; and firing the raw gypsum at a temperature higher than 120°C after adding the chloride.

[0010] According to the method for producing hemihydrate gypsum of the present invention, it is possible to produce hemihydrate gypsum that can suppress particle disintegration when mixed with water to form a slurry.

[0011] Figure 1 is a flowchart showing an example of a method for producing hemihydrate gypsum according to the embodiment. Figure 2 is a graph showing an example of the calcination profile of hemihydrate gypsum according to the embodiment. Figure 3 is a graph showing an example of the calcination profile of hemihydrate gypsum according to another example of the embodiment. Figure 4 is a graph showing an example of the calcination profile of hemihydrate gypsum according to a comparative example.

[0012] Embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure.

[0013] (Embodiments) Figure 1 is a flowchart showing an example of a method for producing hemihydrate gypsum according to the embodiment. Figure 2 is a graph showing an example of the calcination profile of hemihydrate gypsum according to the embodiment. Figure 3 is a graph showing an example of the calcination profile of hemihydrate gypsum according to another example of the embodiment. Figure 4 is a graph showing an example of the calcination profile of hemihydrate gypsum according to a comparative example. The method for producing hemihydrate gypsum according to the embodiment is to produce dihydrate gypsum (CaSO4). ４ ・2H ２ The raw material gypsum (O) is calcined to produce β-type hemihydrate gypsum (CaSO4). ４ ・ 1 / 2H ２ The process for manufacturing O) will be explained.

[0014] Here, "hemihydrate gypsum" refers to α-type hemihydrate gypsum and β-type hemihydrate gypsum. α-type hemihydrate gypsum can be produced by pressurizing dihydrate gypsum, such as natural gypsum, in water or steam using an autoclave. β-type hemihydrate gypsum can be produced by calcining dihydrate gypsum, such as natural gypsum, in atmospheric pressure. In this embodiment, unless otherwise specified, "hemihydrate gypsum" refers to β-type hemihydrate gypsum. Hemihydrate gypsum is also called calcined gypsum.

[0015] As shown in Figure 1, in the method for producing hemihydrate gypsum according to this embodiment, first, raw gypsum for producing hemihydrate gypsum is prepared (step ST1).

[0016] As raw material gypsum, dihydrate gypsum (CaSO4) containing at least one of chemical gypsum, raw ore, or recycled gypsum. ４ ・2H ２ O) is used. Chemical gypsum is gypsum synthesized in the chemical industry and includes gypsum produced as a by-product, such as flue gas desulfurization gypsum. Raw material is natural raw material that is found in nature.

[0017] Recycled gypsum includes gypsum recovered from waste gypsum boards generated in-house by gypsum board manufacturers, as well as waste gypsum boards generated during new construction and demolition. The raw material gypsum may be a mixture of chemical gypsum or raw material with recycled gypsum.

[0018] Next, the calcination of the raw gypsum (dihydrate gypsum) is started (step ST2). In this embodiment, the calcination of the raw gypsum is carried out in the atmosphere and in an open state without pressurization. In the calcination process of the raw gypsum, conventional calcination equipment used by those skilled in the art, such as a kettle or rotary kiln, is used.

[0019] Next, chloride is added to the raw gypsum when its temperature is within a predetermined temperature range (step ST3). The temperature range for adding the chloride is, for example, above room temperature and below the primary boiling temperature, for example, below 120°C. "Room temperature" refers to the temperature at which firing begins, for example, around 25°C. Adding chloride at room temperature also includes cases where chloride is added to the raw gypsum before firing begins. The chloride includes, for example, at least one of calcium chloride, potassium chloride, sodium chloride, zinc chloride, barium chloride, ammonium chloride, and magnesium chloride.

[0020] The graphs shown in Figures 2 to 4 show time on the horizontal axis and the temperature of the gypsum on the vertical axis. Figure 2 schematically shows the calcination profile when chloride is added at a temperature of 100°C or lower, for example, at room temperature. Figure 3 schematically shows the calcination profile when chloride is added at a temperature of 120°C or lower than the primary boiling point in the comparative example. Figure 4 schematically shows the calcination profile in the comparative example, when no chloride is added.

[0021] As shown in Figure 2, when chloride is added at room temperature, the raw gypsum is heated by the firing apparatus, and the temperature of the raw gypsum rises roughly in proportion to the passage of time, from the start of firing to a temperature of about 100°C (time t1).

[0022] Subsequently, the slope of the temperature profile in the temperature range of approximately 100°C to 110°C is smaller than the slope of the temperature profile in the temperature range below 100°C. This is because, for example, in the temperature range above 100°C, primary boiling begins, and the crystalline water contained in the raw gypsum boils, so the heat of vaporization of the crystalline water suppresses the temperature rise of the gypsum.

[0023] As shown in Figure 3, if chloride is added after firing has started, for example, when the temperature has risen to 120°C (time t11), the temperature of the gypsum will drop to, for example, 100°C (time t12). In the example shown in Figure 3, the temperature at which the slope of the temperature profile becomes smaller after the addition of chloride is expressed as the "primary boiling temperature".

[0024] In contrast, as shown in Figure 4, in the comparative example without chloride addition, the temperature rises roughly proportionally with the passage of time from the start of firing to approximately 130°C (time t21). Subsequently, the slope of the temperature profile in the temperature range of approximately 130°C to 140°C is smaller than the slope of the temperature profile in the temperature range below 130°C. The primary boiling temperature in the comparative example without chloride addition is approximately 130°C.

[0025] As shown in Figures 2 and 3, in this embodiment, by adding a chloride with good hydrophilicity, the primary boiling temperature is lowered and the crystal water contained in the raw gypsum boils efficiently. After adding the chloride in a temperature range of room temperature to 120°C, the crystal water contained in the raw gypsum boils until time t2 or time t13, thereby suppressing the temperature rise of the gypsum.

[0026] In this embodiment, the primary boiling temperature in the calcination profile of the raw gypsum can be lowered by adding chloride. Furthermore, in this embodiment, the primary boiling time can be shortened compared to the comparative example without chloride addition.

[0027] Here, primary boiling time refers to the time required for the primary boiling of the raw gypsum. Specifically, it is the time when the slope of the temperature profile shown in Figures 2 to 4 is smaller than, for example, the slope below 100°C. In the example shown in Figure 2, the primary boiling time is the time from time t1 to time t2 when the primary boiling is completed. In the example shown in Figure 3, the primary boiling time is the time from time t11 to time t13. In the comparative example shown in Figure 4, the primary boiling time is the time from time t21 to time t22.

[0028] Furthermore, the predetermined temperature range for adding chloride is not limited to room temperature or above 120°C, but may be, for example, 90°C or above 120°C. More preferably, it may be a temperature range of 110°C or above 120°C.

[0029] As the boiling of the water of crystallization progresses and the heat of vaporization of the water of crystallization becomes relatively small with respect to the heating of the firing apparatus, the temperature of the gypsum rises to a temperature higher than the primary boiling temperature. Then, heating is continued until a predetermined temperature below the secondary boiling temperature is reached, and firing is completed (step ST4). For example, as shown in FIG. 2, the slope of the temperature profile after time t2 becomes abruptly larger than the slope of the temperature profile from time t1 to time t2. For example, time t2 is the time when the virtual line obtained by approximating the firing profile in the primary boiling temperature range as a straight line intersects the virtual line obtained by approximating the firing profile after time t2 as a straight line. Similarly, in the example shown in FIG. 3, the slope of the temperature profile after time t13 becomes abruptly larger than the slope of the temperature profile from time t12 to time t13.

[0030] In this embodiment, the secondary boiling temperature is, for example, about 190°C. The secondary boiling temperature is the temperature at which anhydrous gypsum (CaSO ４ ·1 / 2H ２ O) is produced from hemihydrate gypsum (CaSO ４ ). In this embodiment, hemihydrate gypsum can be produced by completing the firing below the secondary boiling temperature. By the above process, hemihydrate gypsum (CaSO ４ ·1 / 2H ２ O) can be produced by firing raw material gypsum.

[0031] The hemihydrate gypsum obtained by the production method of this embodiment is mixed with water and formed into a slurry. The obtained slurry is poured, for example, into a line where the base paper flows and is sandwiched by the base paper above and below. The base paper and the slurry are formed into a plate shape through between the molding rolls arranged above and below or between the upper and lower plates, dried and cured on a conveyor belt, and then roughly cut and formed. The roughly cut board is dried in a dryer to remove excess moisture and then cut to the product dimensions to be manufactured as a gypsum board.

[0032] The gypsum products to which the hemihydrate gypsum obtained by the production method of this embodiment is applied are not limited to gypsum boards. The hemihydrate gypsum obtained by the production method of this embodiment can be used, for example, in gypsum plaster, gypsum-based putty, gypsum-based adhesives, gypsum-based SL (self-leveling) materials, etc.

[0033] In this embodiment, when mixing hemihydrate gypsum and water to form a slurry, the disintegration of particles can be suppressed. More specifically, in the manufacturing method of this embodiment, the primary boiling temperature during calcination can be lowered by adding chloride, so the particle size of the primary particles of hemihydrate gypsum becomes larger and the specific surface area (surface area per unit mass volume) of hemihydrate gypsum becomes smaller compared to when chloride is not added. Then, the primary particles of hemihydrate gypsum aggregate to form secondary particles.

[0034] As a result, in this embodiment, the disintegration of secondary particles can be suppressed when mixing hemihydrate gypsum and water to form a slurry. Furthermore, because hemihydrate gypsum has a small specific surface area, the amount of water mixed with hemihydrate gypsum (the appropriate amount of water when forming the slurry) can be suppressed. In addition, the occurrence of problems such as rapid hardening when forming the slurry can be suppressed, making it easier to handle when manufacturing gypsum products using hemihydrate gypsum.

[0035] The manufacturing methods shown in Figures 1 and 2 are merely examples and can be modified as appropriate. For example, in the process of manufacturing gypsum board using the obtained hemihydrate gypsum, a hemihydrate gypsum crushing step may be performed as needed. Furthermore, the slurry formation step may include adhesive aids, hardening accelerators, foam for weight reduction, other additives, admixtures, etc.

[0036] (Example 1) Table 1 shows the amount of water mixed, particle size distribution, and primary boiling temperature for hemihydrate gypsum in Example 1 and Comparative Example 1. In Example 1, hemihydrate gypsum was obtained by adding chloride within a predetermined temperature range during firing, performing primary boiling, and then secondary boiling. In Example 1, calcium chloride was used as the chloride, and the amount of chloride added to the gypsum raw material was 0.15 wt%. Comparative Example 1 used hemihydrate gypsum obtained without adding chloride during firing. Other manufacturing conditions for Comparative Example 1 were the same as those for Example 1.

[0037] In both Example 1 and the Comparative Example, chemical gypsum was used as the raw material. A predetermined amount of raw gypsum was weighed, placed in a firing apparatus, and fired in the open atmosphere.

[0038] The "amount of mixed water" shown in Table 1 is the appropriate amount of water when hemihydrate gypsum and water are mixed to form a slurry, and it was measured in accordance with JIS R 9112. Also, the particle size distribution was measured using a laser diffraction / scattering type device. The "powder" in the particle size distribution indicates the ratio of particles with a particle size of 11 μm or less for the calcined hemihydrate gypsum before forming the slurry. Also, the "slurry" in the particle size distribution indicates the ratio of particles with a particle size of 11 μm or less in the state of a slurry obtained by mixing hemihydrate gypsum and water.

[0039] As described above, the primary boiling temperature of Example 1 shown in Table 1 indicates the temperature when the slope of the temperature profile becomes small after adding chloride (see FIGS. 2 and 3). Similarly, the primary boiling temperature of the comparative example is also the temperature when the slope of the temperature profile becomes small.

[0040]

[0041] As shown in Table 1, the hemihydrate gypsum according to Example 1 can suppress the amount of mixed water compared to the hemihydrate gypsum according to the comparative example without adding chloride. That is, the hemihydrate gypsum according to Example 1 has less particle disintegration when forming a slurry compared to the comparative example, so the amount of mixed water is suppressed. Also, it can be said that by adding chloride, the primary particles of hemihydrate gypsum become larger and the specific surface area of hemihydrate gypsum is smaller, thus suppressing the amount of mixed water.

[0042] Also, in both Example 1 and the comparative example, no particles with a particle size of 11 μm or less were detected in the particle size distribution of the powder. In the particle size distribution of the slurry (state of the slurry), the ratio (17.35%) of particles with a particle size of 11 μm or less in Example 1 is a very small value compared to the comparative example (64.57%). That is, in the comparative example without adding chloride, particle disintegration occurs when mixing with water to form a slurry, whereas for the hemihydrate gypsum according to Example 1, it was shown that particle disintegration is suppressed when mixing with water to form a slurry by adding chloride.

[0043] In the calcination profile of the raw gypsum according to Example 1, the primary boiling temperature is 105°C. In Comparative Example 1, where no chloride was added, the primary boiling temperature was 130°C. This demonstrates that adding chloride lowers the primary boiling temperature during calcination.

[0044] (Example 2) Table 2 shows the amount of water mixed, particle size distribution, primary boiling temperature, and primary boiling time for the hemihydrate gypsum according to Example 2. In Example 2, the amount of chloride added was kept constant at 0.15 wt%, and hemihydrate gypsum was prepared by varying the temperature at which chloride was added in the calcination profile of the raw gypsum from room temperature to 150°C. The above-mentioned various characteristics were measured for each of the hemihydrate gypsums with different chloride addition temperatures.

[0045] The amount of water mixed, particle size distribution, and primary boiling temperature shown in Table 2 are the same as those in Example 1 described above, and repeated explanations are omitted. The primary boiling time shown in Table 2 is the time at which the slope of the temperature profile becomes smaller. When the chloride input temperature is above room temperature but below 100°C, the primary boiling time corresponds, for example, to the time from time t1 to time t2 in Figure 2. When the chloride input temperature is 100°C or higher, it corresponds to the time from time t11 to time t13 in Figure 3.

[0046] As shown in Table 2, the amount of water mixed in hemihydrate gypsum (Examples 2-1 to 2-5) formed with a chloride input temperature between room temperature and 120°C was smaller than the amount of water mixed in hemihydrate gypsum (Comparative Examples 2-1 and 2-2) formed with a chloride input temperature of 130°C or higher. In other words, it was shown that by setting the chloride input temperature to a range between room temperature and 120°C, particle disintegration during slurry formation was suppressed compared to the case where the chloride input temperature was 130°C or higher, resulting in a smaller specific surface area of ​​hemihydrate gypsum.

[0047] In all hemihydrate gypsum formed with chloride added at temperatures between room temperature and 150°C, no particles smaller than 11 μm were detected in the particle size distribution of the powder. In the particle size distribution of the slurry, the proportion of particles smaller than 11 μm in Examples 2-1 to 2-5 was in the range of approximately 17.35% to 29.72%, which is significantly smaller than the proportion of particles smaller than 11 μm in Comparative Examples 2-1 and 2-2 (62.24% or more). This demonstrates that by setting the chloride added at temperatures between room temperature and 120°C, particle disintegration can be effectively suppressed when mixing with water to form a slurry.

[0048] The primary boiling temperatures in Examples 2-1 to 2-5 are lower than those in Comparative Examples 2-1 and 2-2. Furthermore, the primary boiling time tends to decrease as the chloride addition temperature increases.

[0049] From the above results, it is preferable that the temperature range for adding chloride be between room temperature and 120°C. More preferably, the temperature range for adding chloride is between 100°C and 120°C. Even more preferably, the temperature range for adding chloride is between 110°C and 120°C. This lowers the primary boiling temperature and shortens the primary boiling time. Adding chloride increases the particle size of the primary particles of hemihydrate gypsum and decreases the specific surface area of ​​hemihydrate gypsum. As a result, when mixing the obtained hemihydrate gypsum with water to form a slurry, the amount of water mixed can be reduced and particle disintegration can be suppressed.

[0050] (Example 3) Table 3 shows the amount of chloride added, the amount of water mixed, and the particle size distribution for the hemihydrate gypsum according to Example 3. In Example 3 (Examples 3-1 to 3-7), hemihydrate gypsum was prepared by varying the amount of chloride added from 0.01 wt% to 0.5 wt%. The temperature at which the chloride was added in Example 3 was room temperature. That is, in Example 3, the chloride was added to the raw gypsum at room temperature and the mixture was fired. In Comparative Example 3, hemihydrate gypsum was prepared without adding chloride (amount of chloride added: 0 wt%).

[0051]

[0052] As shown in Table 3, in Examples 3-1 to 3-7, the amount of water added decreases as the amount of chloride added increases. Also, as the amount of chloride added increases, the proportion of particles with a particle size of 11 μm or less in the particle size distribution of the slurry decreases.

[0053] More specifically, when the amount of chloride added is 0.01 wt% (Example 3-1), although there is no decrease in the amount of water mixed compared to Comparative Example 3, the proportion of particles with a particle size of 11 μm or less in the particle size distribution of the slurry is reduced.

[0054] Furthermore, when the amount of chloride added was 0.5 wt% (Example 3-7), although the amount of water mixed was the same as when the amount of chloride added was 0.3 wt% (Example 3-6), the proportion of particles with a particle size of 11 μm or less in the particle size distribution of the slurry was smaller.

[0055] Therefore, it was shown that when the amount of chloride added is in the range of 0.01 wt% to 0.5 wt%, the proportion of particles with a particle size of 11 μm or less in the particle size distribution of the slurry is smaller compared to Comparative Example 3. In other words, when the amount of chloride added is in the range of 0.01 wt% to 0.5 wt%, particle breakdown is suppressed when hemihydrate gypsum and water are mixed to form a slurry.

[0056] It has been shown that the amount of water added when mixing hemihydrate gypsum and water to form a slurry can be reduced when the amount of chloride added is in the range of 0.05 wt% to 0.5 wt%. Alternatively, since the effect of reducing the amount of water added plateaus when the amount of chloride added exceeds 0.3 wt%, a range of 0.05 wt% to 0.3 wt% is preferred.

[0057] In this disclosure, "wt%" may be replaced with "mass%".

[0058] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included.

[0059] Furthermore, this disclosure may also take the following form.

[0060] (1) A method for producing hemihydrate gypsum, comprising the steps of: (1) starting the firing of raw gypsum in the atmosphere and in an open state, adding chloride to the raw gypsum when the temperature of the raw gypsum is in the range of room temperature or above 120°C or below; and firing the raw gypsum at a temperature higher than 120°C after adding the chloride. (2) The method for producing hemihydrate gypsum according to (1), wherein the amount of chloride added is 0.01 wt% or more and 0.5 wt% or less relative to the raw gypsum. (3) The method for producing hemihydrate gypsum according to (1), wherein the amount of chloride added is 0.05 wt% or more and 0.3 wt% or less relative to the raw gypsum. (4) The method for producing hemihydrate gypsum according to any one of (1) to (3), wherein the chloride includes at least one of calcium chloride, potassium chloride, sodium chloride, zinc chloride, barium chloride, ammonium chloride, and magnesium chloride. (5) The method for producing hemihydrate gypsum according to any one of (1) to (4), wherein the raw material gypsum is dihydrate gypsum comprising at least one of chemical gypsum, raw material, and recycled gypsum. (6) The method for producing hemihydrate gypsum according to any one of (1) to (5), wherein the step of adding the chloride and the step of calcining the raw material gypsum are carried out using the same calcination apparatus.

Claims

1. A method for producing hemihydrate gypsum, comprising the steps of: starting the firing of raw gypsum in the atmosphere and in an open state; adding chloride to the raw gypsum when the temperature of the raw gypsum is in the range of room temperature or higher and 120°C or lower; and firing the raw gypsum at a temperature higher than 120°C after adding the chloride.

2. The method for producing hemihydrate gypsum according to claim 1, wherein the amount of chloride added is 0.01 wt% or more and 0.5 wt% or less relative to the raw material gypsum.

3. The method for producing hemihydrate gypsum according to claim 1, wherein the amount of chloride added is 0.05 wt% or more and 0.3 wt% or less relative to the raw material gypsum.

4. The method for producing hemihydrate gypsum according to claim 1, wherein the chloride comprises at least one of calcium chloride, potassium chloride, sodium chloride, zinc chloride, barium chloride, ammonium chloride, and magnesium chloride.

5. The method for producing hemihydrate gypsum according to claim 1, wherein the raw material gypsum is dihydrate gypsum comprising at least one of chemical gypsum, raw ore, and recycled gypsum.

6. The method for producing hemihydrate gypsum according to claim 1, wherein the step of adding the chloride and the step of firing the raw gypsum are performed using the same firing apparatus.

Images