Manufacturing method of anhydrous gypsum and manufacturing device of anhydrous gypsum

Abstract

To obtain anhydrous gypsum with minimal coloring while reducing carbon dioxide emissions from discarded gypsum products.SOLUTION: A method comprises a step of stirring substances originating from gypsum products together with liquid water at temperatures of 205°C or higher.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing anhydrous gypsum and an apparatus for producing anhydrous gypsum. [Background technology]

[0002] Conventional technologies for recycling discarded gypsum board include the following: Discarded gypsum board is crushed to produce a crushed material. Since gypsum board is primarily composed of gypsum dihydrate, the crushed material contains gypsum dihydrate. The crushed material is then placed in a kiln, where impurities such as wallpaper and glue are burned and removed. A thermal reaction produces gypsum hemihydrate.

[0003] In addition, in the technology of Patent Document 1, gypsum dihydrate is obtained from waste gypsum by the following process. First, the waste gypsum is coarsely pulverized. Paper is roughly removed from the coarsely pulverized waste gypsum. The coarsely pulverized waste gypsum is mixed with water to prepare a slurry. The slurry is wet-pulverized using a planetary ball mill. The slurry is passed through a mesh to remove remaining paper fibers. Sodium citrate is added to the slurry, and the slurry is heated at 135°C and 0.3 MPa while stirring in an autoclave for 1.5 hours. At this stage, all of the gypsum in the slurry is gypsum hemihydrate. This gypsum hemihydrate slurry is stirred at 80°C for 4 hours. The slurry is then filtered and subjected to solid-liquid separation to obtain a cake. The cake is washed with water. As a result, gypsum dihydrate with an average particle size of 42 μm is obtained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-273599 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method of burning crushed waste gypsum in a kiln has the following problems: it takes a long time to heat the kiln and process the material; the resulting gypsum contains ash from paper combustion and is brown in color; and the combustion releases a large amount of carbon dioxide.

[0006] The technology of Patent Document 1 can obtain gypsum dihydrate, but it cannot obtain type II anhydrous gypsum, which can be used as an additive for cement or as a filler for resins and paints. [Means for solving the problem]

[0007] The present disclosure can be realized in the following forms.

[0008] (1) According to one aspect of the present disclosure, there is provided a method for producing anhydrous gypsum, the method comprising: (a) stirring a material resulting from a gypsum product with liquid water at a temperature of 205°C or higher; In this embodiment, fine particle anhydrous gypsum is obtained by stirring gypsum dihydrate contained in a substance derived from a gypsum product together with liquid water in an environment of 205° C. or higher. Therefore, compared to an embodiment in which a substance derived from a gypsum product is burned, it is possible to obtain anhydrous gypsum with less coloration while reducing carbon dioxide emissions. (2) In the above-described method for producing anhydrous gypsum, an embodiment may include (b) a step of classifying the mixture of the liquid water and substances resulting from the gypsum product that has undergone the step (a) into gypsum particles and liquid water, and impurities larger than the gypsum particles. By adopting such an embodiment, it is possible to easily separate the target anhydrous gypsum from impurities that are contained in the discarded gypsum product and are larger than the fine particles of anhydrous gypsum. (3) In the method for producing anhydrous gypsum of the above aspect, the step of stirring the substance resulting from the gypsum product together with liquid water may be performed at a temperature of 210°C or higher. By adopting such an embodiment, the proportion of anhydrous gypsum in the resulting product can be increased compared to an embodiment in which the step of stirring the substances resulting from the gypsum product with liquid water is performed at a temperature below 210°C. (4) In the above-described method for producing anhydrous gypsum, an embodiment may include a step of raising the temperature inside the furnace by blowing steam into the furnace into which the substances originating from the gypsum products have been charged, before the step of stirring the substances originating from the gypsum products together with the liquid water. By adopting this configuration, the temperature of the liquid water and the substances resulting from the gypsum products can be raised more efficiently than in a configuration in which the temperature of the liquid water and the substances resulting from the gypsum products is raised from room temperature by heating only from outside the furnace. (5) The method for producing anhydrous gypsum according to the above embodiment may further include a step of filtering the gypsum particles and liquid water obtained by the classification step using a filter press. In this embodiment, gypsum dihydrate contained in a substance resulting from a gypsum product is stirred with liquid water in an environment of 205° C. or higher, thereby obtaining fine particles of anhydrous gypsum having a particle size within a certain range. Therefore, by selecting an appropriate filter, it is possible to remove water from the resultant product without losing a large amount of the produced anhydrous gypsum and in a short time, compared to an embodiment in which anhydrous gypsum having an uncontrolled particle size is provided as the processing target. (6) In the method for producing anhydrous gypsum of the above form, the classification step may include a step of treating the mixture of the liquid water and the substance resulting from the gypsum product with a slit saver, and a step of treating the mixture treated with the slit saver with a wedge wire that can classify objects with dimensions smaller than the dimensions that the slit saver can classify. In this embodiment, gypsum dihydrate contained in a substance resulting from a gypsum product is stirred with liquid water in an environment of 205°C or higher, thereby obtaining fine particles of anhydrous gypsum having a particle size within a certain range. Therefore, by treating with an appropriate slit saver and wedge wire, moisture can be removed from the resulting product without losing a large amount of the produced anhydrous gypsum and in a short time, compared to an embodiment in which anhydrous gypsum whose particle size is not controlled is provided as the target for classification. Furthermore, because classification is performed in two stages using a slit saver and a wedge wire, classification can be performed in a shorter time than if classification were performed in one stage using only a slit saver or a wedge wire. (7) According to another aspect of the present disclosure, there is provided a manufacturing apparatus for manufacturing anhydrous gypsum, the apparatus including a processing section for stirring a substance resulting from a gypsum product together with liquid water at a temperature of 205°C or higher. The present disclosure can be realized in various forms other than the anhydrous gypsum manufacturing method and manufacturing apparatus, for example, a gypsum recycling method, a gypsum manufacturing method, an apparatus for implementing the method, etc. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing an anhydrous gypsum manufacturing system 1 according to a first embodiment of the present disclosure. [Figure 2] 1 is a flowchart showing a method for producing anhydrous gypsum. [Figure 3] 1 is a table showing the anhydrite content of samples obtained as a result of subcritical processing at various temperatures. [Figure 4] 1 is an X-ray diffraction analysis chart of Sample 1 treated at 190°C. [Figure 5] 1 is an X-ray diffraction analysis chart of Sample 2 treated at 200°C. [Figure 6] 1 is an X-ray diffraction analysis chart of Sample 3 treated at 210°C. [Figure 7] 1 is an X-ray diffraction analysis chart of Sample 4 treated at 220°C. [Figure 8] 1 is an X-ray diffraction analysis chart of Sample 5 treated at 230°C. [Figure 9] 1 is a table showing the weight loss rate of the resultant product of subcritical treatment carried out at each temperature. [Figure 10] 3 is a histogram showing the particle size distribution of anhydrous gypsum obtained by performing the process of FIG. 2 with the subcritical treatment temperature set to 230° C. in step S300. [Figure 11] 3 is a table showing the density, porosity, and specific surface area of ​​anhydrous gypsum obtained by performing the process of FIG. 2 with the subcritical treatment temperature set to 230° C. in step S300. DETAILED DESCRIPTION OF THE INVENTION

[0010] A. First embodiment: A1. Anhydrite production system configuration: FIG. 1 is a block diagram showing an anhydrous gypsum manufacturing system 1 according to a first embodiment of the present disclosure. The anhydrous gypsum manufacturing system 1 receives discarded gypsum products and produces anhydrous gypsum. The discarded gypsum products are, for example, gypsum boards that have been used as wall materials for houses. The gypsum boards are mainly composed of gypsum dihydrate. The anhydrous gypsum manufacturing system 1 includes a crushing unit, a subcritical processing unit 300, a classification unit 400, and a drying processing unit 500.

[0011] The crushing unit receives discarded gypsum products and crushes them. In this specification, the crushed gypsum products are referred to as powder. The crushing unit includes a crusher 120 and a separator 130.

[0012] The crusher 120 crushes the discarded gypsum products. The separator 130 roughly removes impurities from the crushed gypsum products. The separator 130 is equipped with a magnetic separator and a trommel. The separator 130 uses the magnetic separator to remove iron from the crushed gypsum products. The separator 130 uses the trommel to sift the crushed gypsum products and separate large impurities. The gypsum products mainly contain gypsum dihydrate. The discarded gypsum products still contain minute impurities such as fine wallpaper and glue that were attached to the gypsum products.

[0013] The subcritical treatment unit 300 includes a subcritical treatment chamber. The subcritical treatment unit 300 can agitate powder obtained by crushing discarded gypsum products with liquid water at a temperature of 205°C or higher in the subcritical treatment chamber. The powder is agitated with water under a high pressure of 17 atmospheres or higher.

[0014] The classifying unit 400 classifies the mixture of liquid water and powder into gypsum particles and liquid water, and impurities larger than the gypsum particles. The classifying unit 400 includes a slit saver 420 and a wedge wire 440.

[0015] The slit saver 420 can classify objects. The slit saver 420 of the present embodiment receives a fluid mixture and separates objects having a size greater than 1.0 mm from objects having a size less than 1.0 mm.

[0016] The slit saver 420 includes multiple sets of rotating units and multiple sets of fixed units, each of which includes a large number of plates of the same shape arranged at intervals in the thickness direction. In the fixed units, each plate is rectangular, 3.0 mm thick, and 1.0 mm apart. In the rotating units, each plate is oval, 1.0 mm thick, and 3.0 mm apart. The multiple sets of rotating units and multiple sets of fixed units are arranged alternately. The fixed units arranged side by side with a rotating unit between them form a sieve. The tip of each plate in the fixed units is approximately in contact with the rotation axis of the adjacent rotating unit.

[0017] Each of the multiple sets of rotating units is arranged so that the tips of the multiple plates arranged in the thickness direction are positioned in the gaps between the multiple plates of the adjacent fixed unit. When the slit saver 420 is operating, the rotating units rotate around a rotation axis parallel to the arrangement direction of the multiple plates. As a result, the slit saver 420 allows only those particles of the mixture that are smaller than the gaps between the plates to pass downward from among the mixture introduced from above into the multiple sets of fixed units arranged side by side. By rotating each rotating unit while meshing the multiple plates, the gaps between the multiple plates of the fixed unit are prevented from being blocked by particles contained in the mixture.

[0018] The wedge wire 440 can classify objects. More specifically, the wedge wire 440 is supplied with the mixture processed by the slit saver 420 and can classify the mixture into sizes smaller than the size of the objects that the slit saver 420 can classify. The wedge wire 440 of this embodiment is supplied with a fluid mixture and can separate particles having a size greater than 20 μm from particles having a size less than 20 μm.

[0019] The wedge wire 440 comprises a large number of rods having the same shape and triangular cross sections. The rods are arranged at a predetermined interval, with one side of the triangle of the cross section facing upward and in a position that defines the same plane. In this embodiment, the gap between the tips of the triangles of the rods arranged side by side is 20 μm. The wedge wire 440 allows only the mixture introduced above the rods arranged side by side that is smaller than the gap between the rods to pass downward. As a result, a slurry composed of gypsum fine particles with a particle size of 20 μm and water is produced.

[0020] The drying treatment unit 500 dries the slurry processed in the classification unit 400 to produce gypsum powder. The drying treatment unit 500 has a filter press 520 and a drying oven 540. The filter press 520 filters the slurry to separate water from the slurry. As a result, a cake of gypsum powder is produced. The drying oven 540 dries the cake of gypsum powder. As a result, anhydrous gypsum powder is produced.

[0021] A2. Manufacturing method of anhydrite: Fig. 2 is a flowchart showing a method for producing anhydrous gypsum. The process in Fig. 2 is carried out in an anhydrous gypsum production system 1 (see Fig. 1). Anhydrous gypsum is produced by the process in Fig. 2.

[0022] In step S100, discarded gypsum products are crushed by the crushing unit to prepare a powdery material. Specifically, the crusher 120 crushes the discarded gypsum products. As a result, compared to a case in which the gypsum products are not crushed and are fed into the subcritical treatment chamber of the subcritical treatment unit 300, gypsum products of various sizes can be accommodated in the subcritical treatment chamber and the filling rate of the gypsum products in the subcritical treatment chamber can be increased. Impurities are roughly removed from the crushed gypsum products by the separator 130. As a result, a powdery material is produced. The gypsum contained in the gypsum products is gypsum dihydrate. Therefore, the powdery material produced in step S100 also contains gypsum dihydrate.

[0023] In step S200, the powdery material obtained in step S100 is introduced into the subcritical processing chamber of the subcritical processing unit 300. Steam generated in a steam boiler is blown into the subcritical processing chamber into which the powdery material has been introduced, thereby raising the temperature inside the subcritical processing chamber.

[0024] By performing this type of treatment, the temperature of the powder can be raised to the treatment temperature in step S300 more efficiently than in a case where the water and powder are raised from room temperature only by heating from outside the subcritical treatment chamber. For example, the subcritical treatment chamber of the subcritical treatment section 300 of this embodiment can raise the temperature of the powder inside to 220°C or higher within 50 minutes by injecting appropriately adjusted steam. Furthermore, by increasing the boiler capacity, the time required to raise the temperature of the powder to the treatment temperature can be reduced to about 30 minutes.

[0025] Furthermore, the above process can reduce carbon dioxide emissions and running costs compared to a method in which the temperature of water and powdery material is raised from room temperature only by heating from outside the subcritical treatment chamber. For example, when an electric heater is used, the efficiency of the power plant is 30-40%, and losses also occur in the electric heater. On the other hand, the thermal efficiency of a steam boiler is 85% or more. Furthermore, heating by combustion produces carbon dioxide, NOx, and SOx, and the thermal efficiency is about 50%.

[0026] In the case where the pulverized waste gypsum is burned in a kiln, it takes a long time to heat the treatment kiln, so the equipment cannot be operated and stopped frequently. In other words, the equipment needs to be operated continuously. However, in this embodiment, steam generated in a steam boiler is injected to raise the temperature inside the subcritical treatment chamber, so batch treatment is possible. Therefore, it is easy to operate the anhydrite production system 1 when necessary and to shut down the anhydrite production system 1 at other times.

[0027] In step S300, the powdery material obtained in step S100 is stirred with liquid water at 205°C or higher by the subcritical processing unit 300. The weight ratio of powdery material to water fed into the subcritical processing unit chamber of the subcritical processing unit 300 is, for example, 1:1. In the process of step S300, unlike the mode in which gypsum hemihydrate is produced, no substances other than the powdery material to be treated and water are added. As a result, anhydrous gypsum is produced from gypsum dihydrate via α-gypsum hemihydrate, as follows: In addition, organic matter contained in the powdery material obtained in step S100 is broken down into smaller molecules. The process in step S300 is referred to as "subcritical processing" in this specification. [ka]

[0028] In step S300, the powdery material is stirred together with liquid water in an environment of, for example, 210° C. Therefore, compared to a mode in which the reaction proceeds while the powdery material is stirred in a gas without liquid water, no large lumps of gypsum are produced, and no large amounts of excessively small gypsum particles are produced, resulting in fine particles of anhydrous gypsum with sizes falling within a certain range.

[0029] For example, by performing the treatment at 210° C. or higher in step S300, the following effect can be obtained: the proportion of anhydrous gypsum in the resultant product can be increased compared to an embodiment in which the step of stirring the powdery material with liquid water is performed at a temperature lower than 210° C. The relationship between the treatment temperature in step S300 and the yield of anhydrous gypsum will be described later in the examples.

[0030] In step S400, the mixture of liquid water and powdery material is classified into gypsum particles and liquid water, and impurities larger than the gypsum particles. Specifically, first, in step S420, the mixture of liquid water and powdery material is processed by a slit saver 420. As a result, impurities having a size exceeding 1.0 mm are removed from the mixture of liquid water and powdery material. Note that the construction waste input into the anhydrous gypsum manufacturing system 1 in step S100 contains various impurities such as stones and wood chips.

[0031] Thereafter, in step S440, the mixture treated by the slit saver 420 is treated by the wedge wire 440. As a result, impurities having a size exceeding 20 μm are removed from the mixture of liquid water and powder. Note that in step S400, a portion of the water used in the subcritical treatment in step S300 may be discharged to the outside of the anhydrite manufacturing system 1 as steam or liquid water.

[0032] By stirring the dihydrate gypsum contained in the powdered material with liquid water in an environment of 205°C or higher, fine particles of anhydrous gypsum are obtained, with particle sizes falling within a specific range. This provides the following advantages compared to an embodiment in which the particle size of the anhydrous gypsum to be classified is not controlled and a wide range of particle sizes is provided. Specifically, impurities can be removed by processing with an appropriate slit saver 420 and wedge wire 440. Furthermore, in the subsequent step S500, moisture can be removed from the resulting product in a short time without losing a large amount of the anhydrous gypsum. Many of the glass fibers from the insulation material contained in construction waste and the paper used to form the gypsum board are smaller than 1 mm, making classification extremely difficult using conventional techniques. However, this method can remove these impurities in a short time. Furthermore, because classification is performed in two stages using the slit saver 420 and wedge wire 440, classification that improves product quality can be performed in a shorter time than with a single stage using only the slit saver 420 or wedge wire 440.

[0033] In step S500, a drying process is performed by drying process unit 500. Specifically, in step S520, the gypsum particles and liquid water obtained in step S400 are filtered by filter press 520. As a result, water is separated from the slurry, and a gypsum powder cake is obtained. Because the organic matter contained in the powder material has been broken down into smaller molecules in step S300 and the viscosity of the slurry has decreased, water can be removed from the slurry in a short time by filter press 520. Thereafter, in step S540, the gypsum powder cake is dried in drying furnace 540, and anhydrous gypsum powder is produced.

[0034] In step S300, the gypsum dihydrate contained in the powdery material is stirred with liquid water in an environment of 205°C or higher, thereby obtaining fine particles of anhydrous gypsum having a particle size within a certain range. Therefore, by selecting an appropriate filter in step S520, it is possible to remove water from the resultant product without losing a large amount of the produced anhydrous gypsum and in a short time, compared to a mode in which anhydrous gypsum with an uncontrolled particle size is provided as the processing target.

[0035] In this embodiment, gypsum dihydrate contained in a powdery material is stirred with liquid water in an environment of 205°C or higher, thereby obtaining fine particle anhydrous gypsum (see S300 in FIG. 2). Therefore, the target anhydrous gypsum can be separated from impurities contained in discarded gypsum products and larger than the fine particle anhydrous gypsum by classification (see S400 in FIG. 2). As a result, compared to an embodiment in which a powdery material is burned to remove impurities by combustion, high-quality, less-colored anhydrous gypsum can be obtained that does not contain combustion ash from the impurities, while reducing carbon dioxide emissions.

[0036] The anhydrous gypsum manufacturing system 1 in this embodiment is also called a “manufacturing apparatus.” The subcritical processing section 300 is also called a “processing section.”

[0037] A3. Working Example: FIG. 3 is a table showing the anhydrous gypsum content of samples obtained as a result of subcritical treatment performed at various temperatures. 400 g of gypsum dihydrate powder and 600 g of water were introduced into the subcritical treatment section 300, and the treatment temperature was set to various temperatures between 190°C and 230°C. The treatment time was 5 minutes. However, for sample 4, which was treated at a temperature of 220°C, 300 g of gypsum dihydrate powder and 300 g of water were introduced, and subcritical treatment was performed for 15 minutes. The type of gypsum contained in the obtained material was confirmed using an X-ray diffraction device.

[0038] FIG. 4 is an X-ray diffraction analysis chart of Sample 1 treated at 190°C. The upper part of FIG. 4 shows the X-ray diffraction analysis chart of Sample 1. The lower part of FIG. 4 shows the diffraction patterns of gypsum anhydride, gypsum dihydrate, and gypsum hemihydrate. The X-ray diffraction analysis chart of Sample 1 closely matches the diffraction pattern of gypsum dihydrate. Furthermore, a slight peak of gypsum anhydride is observed in the X-ray diffraction analysis chart of Sample 1. No peak of gypsum hemihydrate is observed in the X-ray diffraction analysis chart of Sample 1. For this reason, it is thought that in Sample 1, a small amount of gypsum anhydride was produced from the gypsum hemihydrate, and the remaining gypsum hemihydrate was converted back to gypsum dihydrate (see the upper and lower parts of Reaction Formula (1) above).

[0039] FIG. 5 is an X-ray diffraction analysis chart of Sample 2 treated at 200°C. The configurations of each of FIGS. 5 to 8 are the same as those of FIG. 4. The X-ray diffraction analysis chart of Sample 2 closely matches the diffraction pattern of gypsum dihydrate. Furthermore, a slight peak of gypsum anhydride is observed in the X-ray diffraction analysis chart of Sample 2. No peak of gypsum hemihydrate is observed in the X-ray diffraction analysis chart of Sample 2. For this reason, it is thought that in Sample 2 as well, a small amount of gypsum anhydride was produced from gypsum hemihydrate, and the remaining gypsum hemihydrate was converted back to gypsum dihydrate (see the upper and lower lines of reaction equation (1) above).

[0040] It is believed that the dehydration of gypsum begins to occur around 97°C. However, at around 100°C, the reaction from gypsum hemihydrate to gypsum dihydrate is thought to occur more frequently than the reaction from gypsum dihydrate to gypsum hemihydrate (see the upper part of the above reaction formula (1)). For this reason, it is thought that only a small amount of gypsum hemihydrate exists in the environment, and as a result, there is almost no anhydrous gypsum produced via gypsum hemihydrate (see the lower part of the above reaction formula (1)).

[0041] However, the reaction from gypsum hemihydrate to anhydrous gypsum is an almost irreversible reaction (see the bottom of reaction equation (1) above). For this reason, it is thought that if a very long period of time is taken, anhydrous gypsum will gradually accumulate and a sufficient amount of anhydrous gypsum can be obtained, even in an environment of 100°C. Furthermore, although no example is given here, in an environment of 180°C, the reaction from gypsum hemihydrate to anhydrous gypsum will also reach a detectable level, so it is thought that a sufficient amount of anhydrous gypsum can be obtained in a more realistic time.

[0042] FIG. 6 is an X-ray diffraction analysis chart of Sample 3 treated at 210°C. The X-ray diffraction analysis chart of Sample 3 closely matches the diffraction pattern of gypsum anhydride. In the X-ray diffraction analysis chart of Sample 3, a slight peak of gypsum dihydrate is also observed. In the X-ray diffraction analysis chart of Sample 3, no peak of gypsum hemihydrate is observed.

[0043] FIG. 7 is an X-ray diffraction analysis chart of Sample 4 treated at 220°C. In the X-ray diffraction analysis chart of Sample 4, there are almost no peaks other than those of anhydrous gypsum. That is, in the X-ray diffraction analysis chart of Sample 4, there are very few peaks of gypsum dihydrate. In the X-ray diffraction analysis chart of Sample 4, there is no peak of gypsum hemihydrate.

[0044] FIG. 8 is an X-ray diffraction analysis chart of Sample 5 treated at 230°C. In the X-ray diffraction analysis chart of Sample 5, there are almost no peaks other than those of anhydrous gypsum. That is, in the X-ray diffraction analysis chart of Sample 5, there are very few peaks of gypsum dihydrate. In the X-ray diffraction analysis chart of Sample 5, there is no peak of gypsum hemihydrate.

[0045] The reason why no peak of gypsum hemihydrate is observed in Samples 1 to 5 is considered to be as follows: The gypsum hemihydrate produced by the hydrothermal reaction in the subcritical treatment section 300 is considered to be rehydrated to become gypsum dihydrate as follows (see also the upper part of reaction formula (1)). [ka]

[0046] The weight of water in gypsum dihydrate is 20.9%. Therefore, if the weight loss rate when a mixture of gypsum dihydrate and anhydrous gypsum is heated is WL (0≦WL≦1), the anhydrous gypsum content can be calculated using the following formula: X(%) = (WL×100-20.9) / (0-20.9) ··· (1)

[0047] FIG. 9 is a table showing the weight loss rate of the resultant product of subcritical processing performed at each temperature. The material obtained as a result of processing by the subcritical processing unit 300 at each temperature was dried at 50°C to remove adhering water. Then, it was further heated at 240°C to remove water of crystallization. The weight loss rate was calculated as the ratio of the difference between the weight after heating and the weight before heating to the weight before heating (see the rightmost column in FIG. 9). Then, the anhydrous gypsum content was calculated using formula (1). The anhydrous gypsum content in each sample is shown in the rightmost column in FIG. 3.

[0048] From Figure 3, it appears that in Sample 1, where the subcritical treatment temperature was 190°C, and Sample 2, where the subcritical treatment temperature was 200°C, a small amount of gypsum anhydride was produced, with the remainder being gypsum dihydrate derived from gypsum hemihydrate. In Sample 3, where the subcritical treatment temperature was 210°C, it appears that approximately 90% became gypsum anhydride, and around 10% became gypsum dihydrate derived from gypsum hemihydrate. In Sample 4, where the subcritical treatment temperature was 220°C, and Sample 5, where the subcritical treatment temperature was 230°C, almost only gypsum anhydride was produced.

[0049] From the above, it can be seen that the temperature of the subcritical treatment in the subcritical treatment section 300 is preferably 205°C or higher, more preferably 210°C or higher, and even more preferably 215°C or higher.

[0050] Generally, gypsum begins to gradually decompose above 900 to 1000°C, becoming calcium oxide CaO and sulfur trioxide SO3. Since the subcritical treatment in the subcritical treatment section 300 is intended to obtain gypsum, the upper limit of the temperature in the subcritical treatment in the subcritical treatment section 300 will be obvious to those skilled in the art. Furthermore, since the subcritical treatment in the subcritical treatment section 300 involves stirring gypsum together with liquid water, the pressure in the subcritical treatment in the subcritical treatment section 300 will also be obvious to those skilled in the art.

[0051] FIG. 10 is a histogram showing the particle size distribution of anhydrous gypsum obtained by performing the process of FIG. 2 with the subcritical treatment temperature set to 230°C in step S300. As can be seen from FIG. 10, approximately 93% of the obtained anhydrous gypsum has a particle size of 20 μm or less. Therefore, by treating with the wedge wire 440, the anhydrous gypsum manufacturing system 1 can remove moisture from the resultant product in step S500 in a short time without losing a large amount of the produced anhydrous gypsum. As can be seen from FIG. 10, approximately 7.5% or less of the obtained anhydrous gypsum has a particle size of 1 μm or less. Therefore, by treating with the filter press 520, the anhydrous gypsum manufacturing system 1 can remove moisture from the resultant product in a short time without losing a large amount of the produced anhydrous gypsum.

[0052] Fig. 11 is a table showing the density, porosity, and specific surface area of ​​anhydrous gypsum obtained by setting the temperature of the subcritical treatment in step S300 to 230°C and performing the treatment in Fig. 2. The anhydrous gypsum powder obtained by setting the temperature of the subcritical treatment in step S300 to 230°C and performing the treatment in Fig. 2 had the density, porosity, and specific surface area shown in Fig. 11.

[0053] B. Other Embodiments: B1. Alternative Embodiment 1: (1) In the above embodiment, discarded gypsum products are input into the anhydrous gypsum manufacturing system 1 to produce anhydrous gypsum (see S100 in FIG. 1). However, anhydrous gypsum may be produced from substances derived from gypsum products, such as semi-finished gypsum products and waste generated in the manufacturing process of gypsum products, and may also be produced from other materials containing gypsum dihydrate.

[0054] (2) In the above embodiment, the crushing unit includes the crusher 120 (see the upper part of FIG. 1). The discarded gypsum products are crushed by the crusher 120 (see the upper part of FIG. 2). However, the crushing unit may be configured not to include the crusher 120. In such an embodiment, the discarded gypsum products are fed into the subcritical treatment chamber of the subcritical treatment unit 300 without being crushed. Even in such an embodiment, it is possible to obtain finely divided anhydrous gypsum with little coloring.

[0055] (3) In the above embodiment, the powdery material is stirred with liquid water at 205°C or higher by the subcritical processing unit 300 (see S300 in FIG. 2). The weight ratio of the powdery material to the water fed into the subcritical processing unit chamber of the subcritical processing unit 300 is 1:1. However, the weight ratio of the water to the powdery material fed into the subcritical processing unit chamber may be less than 1. However, the weight ratio of the water to the powdery material is preferably 0.7 or more, more preferably 0.8 or more, and even more preferably 0.9 or more.

[0056] (4) In the above embodiment, water vapor is blown into the subcritical processing chamber into which the powder obtained in step S100 has been introduced, and the temperature inside the furnace is raised (see step S200 in FIG. 2). The water used in the subcritical processing may be introduced into the subcritical processing chamber in a liquid state or in a water vapor state.

[0057] (5) In the above embodiment, the classification in step S400 is performed outside the subcritical processing chamber of the subcritical processing section 300 using the slit saver 420 and the wedge wire 440 (see FIG. 1). However, the classification may be performed in the same environment as the subcritical processing in the subcritical processing section 300.

[0058] (6) In the above embodiment, the slit saver 420 receives a mixture of fluid and separates particles having a size greater than 1.0 mm from particles having a size less than 1.0 mm (see FIG. 1). However, the size of objects that the slit saver can classify may be other sizes. However, the size of objects that the slit saver can classify is preferably any of dimensions between 0.5 and 1.5 mm, more preferably any of dimensions between 0.7 and 1.3 mm, and even more preferably any of dimensions between 0.9 and 1.2 mm.

[0059] (7) In the above embodiment, the wedge wire 440 receives a fluid mixture and separates it into particles having a size greater than 20 μm and particles having a size less than 20 μm (see FIG. 1). However, the size of the objects that the wedge wire can classify may be other sizes. However, the size of the objects that the wedge wire can classify is preferably any size between 10 and 30 μm, more preferably any size between 15 and 25 μm, and even more preferably any size between 18 and 22 μm.

[0060] (8) In the above embodiment, the mesh size of the sieve provided in the filter press 520 is, for example, 1 μm. However, the mesh size of the sieve provided in the filter press may be other sizes (see FIG. 1). However, the mesh size of the sieve provided in the filter press is preferably any size between 0.5 and 4 μm, more preferably any size between 0.7 and 2.5 μm, and even more preferably any size between 0.8 and 1.5 μm.

[0061] (9) In the above embodiment, after filtration by filter press 520, the gypsum powder cake is dried in drying oven 540 (see S540 in FIG. 2). However, the gypsum powder cake may be shipped as a product, and drying in drying oven 540 may not be performed.

[0062] B2. Alternative Embodiment 2: In the above embodiment, the mixture of liquid water and powder is classified into gypsum particles, liquid water, and impurities larger than the gypsum particles (see S400 in FIG. 2). However, classification of the impurities does not have to be performed. That is, the mixture after the processing of step S300 may be used as a product.

[0063] B3. Alternative Embodiment 3: In the above embodiment, the powdery material is stirred with liquid water in an environment of 210°C (see S300 in FIG. 2). However, the subcritical treatment in the subcritical treatment section 300 may be performed at other temperatures, such as 205°C. However, the subcritical treatment is preferably performed at 210°C or higher, more preferably at 215°C or higher, and even more preferably at 220°C or higher.

[0064] B4. Alternative Embodiment 4: In the above embodiment, steam is injected into the subcritical treatment chamber into which the powder obtained by crushing the gypsum product has been introduced, thereby raising the temperature inside the subcritical treatment chamber (see S200 in FIG. 2). However, the temperature of the environment in which the subcritical treatment is carried out may be raised by heating from outside the chamber, or the injection of steam and heating from outside the chamber may be used in combination.

[0065] B5. Alternative Embodiment 5: In the above embodiment, filtration is performed using filter press 520 to separate water from the slurry (see S520 in FIG. 2). However, water may be removed from the slurry by other methods, such as drying by heating or by blowing hot air, without performing filtration using filter press 520. Also, the mixture processed in step S300 may be used as a product without removing water.

[0066] B6. Alternative Embodiment 6: The mixture of liquid water and powder is processed by the slit saver 420 and then processed by the wedge wire 440 (see S420 and S440 in FIG. 2). However, in removing impurities from the mixture of liquid water and powder, processing may be performed only by the slit saver or only by the wedge wire.

[0067] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features of the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0068] 1...anhydrous gypsum manufacturing system, 100...crushing section, 120...crusher, 130...separator, 300...subcritical processing section, 400...classifying section, 420...slit saver, 440...wedge wire, 500...drying processing section, 520...filter press, 540...drying furnace

Claims

1. A method for producing anhydrous gypsum, (a) A method for producing anhydrous gypsum, comprising the step of stirring a substance resulting from a gypsum product with liquid water at a temperature of 205°C or higher.

2. The method for producing anhydrous gypsum according to claim 1, further comprising: (b) a step of classifying the mixture of liquid water and substances resulting from the gypsum product that has been subjected to the step (a) into gypsum particles and liquid water, and impurities larger than the gypsum particles.

3. The method for producing anhydrous gypsum according to claim 1, The method for producing anhydrous gypsum, wherein the step of stirring the substance resulting from the gypsum product with liquid water is carried out at a temperature of 210°C or higher.

4. The method for producing anhydrous gypsum according to any one of claims 1 to 3, further comprising: A method for producing anhydrous gypsum, comprising the step of raising the temperature inside the furnace by blowing steam into the furnace into which the substance originating from the gypsum product has been charged, before the step of stirring the substance originating from the gypsum product together with the liquid water.

5. The method for producing anhydrous gypsum according to any one of claims 1 to 3, further comprising: A method for producing anhydrous gypsum, comprising a step of filtering the gypsum particles and liquid water obtained by the classification step using a filter press.

6. The method for producing anhydrous gypsum according to any one of claims 1 to 3, The classification step includes: treating the mixture of liquid water and material resulting from the gypsum product with a slit saver; and treating the mixture treated with the slit saver with a wedge wire capable of classifying objects into sizes smaller than the sizes of objects that can be classified by the slit saver.

7. A manufacturing apparatus for manufacturing anhydrous gypsum, A manufacturing apparatus including a processing unit that stirs substances resulting from gypsum products together with liquid water at a temperature of 205°C or higher.

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