JP6672884B2 - Method for producing anhydrous gypsum - Google Patents

Description

  The present disclosure relates to a method for producing anhydrous gypsum.

  As the number of demolition of houses using gypsum board increases year by year, the amount of waste gypsum increases. Accordingly, there is a growing need for a technology for treating waste gypsum. For this reason, various studies for effectively utilizing waste gypsum have been made.

  Waste gypsum usually contains paper and an organic admixture together with gypsum dihydrate. For this reason, if it is added to the cement-based material as it is, there is a concern that strength developability may be reduced or the setting properties may fluctuate. Therefore, a method has been proposed in which waste gypsum is heated to carbonize and decompose the paper and the organic admixture, and the gypsum component is recovered as hemihydrate gypsum or anhydrous gypsum (see Patent Documents 1 to 7).

JP-A-10-36149 Japanese Patent No. 3108922 JP-A-2002-68740 JP 2008-1567 A JP 2006-199576 A JP 2002-87816 A JP 2013-224251 A

  When the waste gypsum is heated, carbonization and decomposition of the paper and the organic admixture progress. On the other hand, when the temperature becomes 1200 ° C. or more, partial decomposition of the gypsum progresses, and there is a concern that SOx is generated. For this reason, in the conventional manufacturing method, in order to advance the reform of waste gypsum while suppressing the decomposition of gypsum, it was necessary to lower the heating temperature as much as possible and lengthen the heating time. For this reason, the production efficiency tends to decrease.

  Therefore, an object of the present invention is to provide a production method capable of efficiently producing anhydrous gypsum from waste gypsum while sufficiently suppressing the generation of SOx.

  According to the study of the present inventors, it was found that there is a difference in the reaction initiation temperature and the reaction rate between the carbonization and decomposition reaction of paper and the organic admixture and the decomposition reaction of gypsum. Based on such knowledge, it was found that by supplying waste gypsum to the combustion flame, paper and the organic admixture were quickly carbonized and decomposed before the gypsum decomposed, and anhydrous gypsum was obtained efficiently. Thus, the present invention has been completed.

  That is, the present invention is a method for producing anhydrous gypsum having a heating step of heating waste gypsum containing dihydrate gypsum to obtain anhydrous gypsum, in the heating step, the waste gypsum is supplied toward a combustion frame and heated. And a method for producing anhydrous gypsum.

  In this production method, the waste gypsum is supplied toward the combustion frame and heated, so that the temperature rise rate of the waste gypsum can be sufficiently increased. It is presumed that, by this, before the gypsum contained in the waste gypsum is decomposed, the paper and the organic admixture can be quickly carbonized and decomposed to promote the modification to the anhydrous gypsum. Therefore, it is possible to efficiently produce anhydrous gypsum from waste gypsum while sufficiently suppressing the generation of SOx.

  In the heating step, it is preferable to supply and heat the waste gypsum so as to contact the combustion flame. Thereby, the temperature rise rate of the waste gypsum can be further increased. Therefore, it is presumed that while further suppressing the decomposition of gypsum contained in the waste gypsum, the paper and the organic admixture can be carbonized and decomposed in a shorter time to sufficiently promote the modification to the anhydrous gypsum. .

  The heating time in the heating step is preferably not more than 20 minutes. Thus, the decomposition of gypsum in the heating step can be further suppressed, and anhydrous gypsum can be produced with a high yield.

  Before the heating step, it is preferable to have a drying step of preheating and drying the waste gypsum to reduce the ignition loss to 12% by mass or less. As a result, since the conversion to anhydrous gypsum in the heating step proceeds more smoothly, the quality of the obtained anhydrous gypsum becomes better, and the amount of evaporation of water in the heating step can be reduced, thereby stably producing the anhydrous gypsum. Can be continued.

  F. Of anhydrous gypsum obtained in the heating step It is preferable that CaO is 1% by mass or less and the total carbon content is 0.5% by mass or less. Thereby, the obtained anhydrous gypsum can be made high quality.

  Advantageous Effects of Invention According to the present invention, it is possible to provide a production method capable of efficiently producing anhydrous gypsum from waste gypsum while sufficiently suppressing the generation of SOx. This can contribute to the construction of a waste gypsum recycling system.

It is a schematic diagram which shows an example of a reformer. FIG. 2 is a sectional view taken along line II-II in the reformer of FIG. 1. It is a schematic diagram which shows another example of a reformer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as necessary. However, the following embodiments are exemplifications for describing the present invention, and are not intended to limit the present invention to the following contents. In the description, the same elements or elements having the same functions will be denoted by the same reference symbols, and duplicate description will be omitted in some cases. The dimensional ratios in the drawings are not limited to the illustrated ratios.

  The method for producing anhydrous gypsum of the present embodiment has a heating step of heating waste gypsum containing gypsum to obtain anhydrous gypsum. The waste gypsum preferably contains gypsum dihydrate as a main component. Waste gypsum may include, in addition to dihydrate gypsum, hemihydrate gypsum, anhydrous gypsum, and organic substances such as paper and organic admixtures. The content of gypsum in waste gypsum may be, for example, 50% by mass or more, or may be 60 to 90% by mass. The content of the organic matter in the waste gypsum may be, for example, 5% by mass or less or 3% by mass or less in terms of the amount of carbon. The ignition loss in the waste gypsum is, for example, 15% by mass or more, and may be 15 to 30% by mass.

  As the waste gypsum, for example, waste materials generated in a gypsum board manufacturing plant, scraps of gypsum board generated in a new construction site, waste materials generated in a demolition work site, and the like can be used. However, waste materials generated at the demolition work site include inorganic building waste materials other than gypsum. It is preferable to perform a pretreatment step of reducing the content of such inorganic building waste before the heating step. The content of the inorganic building waste is preferably less than 10% by mass. Moreover, the paper and cloths stuck on the gypsum board surface burn in the heating step. For this reason, it is not always necessary to remove it before the heating step. However, it may be removed by performing a pretreatment step such as sieving after pulverization.

  The particle size of the waste gypsum is preferably a size that does not cause blockage in the reformer for reforming waste gypsum and facilitates discharge from a silo or a tank. Such a particle size is, for example, 50 mm or less, preferably 10 mm or less, and more preferably 5 mm or less. Thereby, the handleability is improved, and the supply to the reformer can be performed sufficiently stably.

  In the heating step, waste gypsum is supplied toward the combustion flame and heated. Such a heating step can be performed using a reformer having a burner and capable of supplying waste gypsum from the burner toward the combustion flame. The type and shape of the reformer are not particularly limited. An example of a reformer is a co-current rotary kiln. A co-current rotary kiln is preferably used because it can be easily supplied and discharged, and can be heated uniformly.

  FIG. 1 is a schematic diagram illustrating an example of a reforming apparatus. The reforming apparatus 100 has a burner 12, and a co-current rotary kiln 10 that heats the waste gypsum 30 to reform it into anhydrous gypsum 32; a supply unit 20 that supplies the waste gypsum 30 to the co-current rotary kiln 10; Is provided.

  In the co-current rotary kiln 10, a kiln hood 11, a drum body 17, and a sedimentation chamber 14 are provided in communication from the upstream side to the downstream side. A burner 12 is attached to a kiln hood 11 of the co-current rotary kiln 10. A fuel supply unit for supplying fuel is connected to the burner 12 (not shown). As the fuel, any of gaseous fuel (such as city gas), liquid fuel (such as heavy oil), and solid fuel (such as pulverized coal) may be used. From the viewpoint of easy handling, a liquid fuel that generates less dust is preferable.

  The shape and size of the co-current rotary kiln 10 are not particularly limited. The length L of the drum main body 17 along the rotation axis direction is preferably 1 to 10 m, and more preferably 2 to 6 m, from the viewpoint of achieving both reduction in the size of the reformer and sufficient production capacity. The inner diameter φ of the drum body 17 of the co-current rotary kiln 10 is, for example, 1 to 3 m. From the viewpoint of allowing the anhydrous gypsum to be discharged in a short time, it is preferable that the inclination angle of the drum main body 17 with respect to the horizontal plane is 0.5 to 8 °, and the rotation speed is 1 to 10 rpm. From the same viewpoint, it is more preferable that the inclination angle is 1 to 5 ° and the rotation speed is 2 to 7 rpm.

  The supply unit 20 is configured by, for example, a pipe. The pipe is inserted into the co-rotary rotary kiln 10 from the upper wall surface of the kiln hood 11, and its tip is disposed inside the drum main body 17. The waste gypsum 30 flows through the pipe forming the supply unit 20 and is supplied into the co-current rotary kiln 10 from the opening at the tip of the pipe. The supply unit 20 supplies the waste gypsum toward the combustion frame 16 in the drum main body 17. The supply unit 20 may be configured to supply the waste gypsum to the combustion frame 16 by dropping it by gravity, or to supply the waste gypsum to the combustion frame 16 by discharging the waste gypsum together with the flowing gas. It may be configured to do so.

  The burner 12 may be a variable burner that can arbitrarily adjust the orientation of the combustion frame 16. By adjusting the direction of the frame to an optimal position according to the particle size of the waste gypsum 30, it is easy to find the optimal heating conditions. Thereby, it can be more efficiently modified into anhydrous gypsum. As an example of the variable burner, one in which the tip of the burner is bent with respect to the axis of the burner tube main body and the direction of the combustion frame can be changed by rotating the burner tube main body around the axis. The variable burner is not limited to such a form, and is not particularly limited as long as the direction of the combustion frame 16 can be changed.

  The supply unit 20 supplies the waste gypsum 30 toward the combustion frame 16 of the burner 12. Most of the waste gypsum 30 supplied into the co-current rotary kiln 10 contacts the combustion frame 16 before contacting the inner wall surface of the co-current rotary kiln 10. The waste gypsum 30 may be supplied to pass through the combustion frame 16. However, it is not essential that all of the supplied waste gypsum 30 contact the combustion frame 16 or pass through the combustion frame 16.

  The waste gypsum 30 supplied toward the combustion frame 16 of the burner 12 is heated at a sufficiently high heating rate. As a result, the paper and the organic admixture contained in the waste gypsum 30 in contact with the combustion frame 16 of the burner 12 are quickly carbonized and decomposed. Most of the dihydrate gypsum contained in the waste gypsum 30 is promptly reformed into anhydrous gypsum. These reactions can be completed before the gypsum decomposes. Therefore, it is considered that dihydrate gypsum can be efficiently modified into anhydrous gypsum while suppressing generation of SOx accompanying the decomposition of gypsum.

  FIG. 2 is a sectional view taken along the line II-II in the reforming apparatus 100 of FIG. A combustion frame 16 is formed near the center in the radial direction on the upstream side of the drum main body 17 of the co-current rotary kiln 10. The waste gypsum 30 supplied from the supply unit 20 toward the combustion frame 16 passes through the combustion frame 16 and accumulates near the bottom on the upstream side of the drum main body 17.

  The waste gypsum 30 that has passed through the combustion frame 16 is exposed to the high temperature of the combustion frame 16 even after it is deposited near the bottom of the drum body 17 until it leaves the periphery of the combustion frame 16. The waste gypsum 30 not in contact with the combustion frame 16 also accumulates near the bottom of the drum body 17 and is exposed to the high temperature of the combustion frame 16 around the combustion frame 16. By being exposed to such a high temperature, the carbonization and decomposition of the paper and the organic admixture and the modification to the anhydrous gypsum proceed rapidly.

  The drum body 17 is continuously rotating in the direction P. Since the rotation axis of the drum main body 17 is inclined by 0.5 to 8 degrees with respect to the horizontal plane, the upstream side is higher than the downstream side. For this reason, the waste gypsum 30 gradually moves to the downstream side of the drum main body 17 while being stirred by the rotation of the drum main body 17 of the co-current rotary kiln 10.

  The external flame of the combustion frame 16 has, for example, a temperature of 1200 ° C. or more, which is a gypsum decomposition temperature. Since the decomposition reaction of gypsum does not occur instantaneously, the carbonization and decomposition of the paper and the organic admixture contained in the waste gypsum 30 that has come into contact with the external flame and the waste gypsum 30 that has passed near the external flame can be rapidly advanced. . The waste gypsum 30 is supplied by the supply unit 20 toward the combustion frame 16. For this reason, even if the waste gypsum 30 contains fine particles, it is possible to sufficiently suppress the fine particles from floating as a dust in the exhaust gas without coming into contact with the combustion frame 16 due to the air current in the drum body 17. be able to. The fine particles are instantaneously reformed by coming into contact with the combustion flame 16 or passing near the combustion flame 16.

  When not in contact with the combustion frame 16, the time required for carbonizing and decomposing the paper and the organic admixture tends to be long. If the heating time is long, the gypsum decomposition reaction tends to proceed. For this reason, it is preferable that the waste gypsum 30 contacts the combustion frame 16.

  The shorter the heating time in the heating step, the more the productivity can be improved while suppressing the decomposition of gypsum. From such a viewpoint, the heating time is preferably 20 minutes or less, more preferably less than 10 minutes, further preferably less than 7 minutes, and particularly preferably less than 5 minutes. The lower limit of the heating time is not particularly limited, but is preferably 1 minute or more, more preferably 2 minutes or more, from the viewpoint of sufficiently progressing the modification to anhydrous gypsum.

  After the waste gypsum 30 comes into contact with the combustion frame 16, the kiln bottom temperature of the co-current rotary kiln 10 is preferably 500 to 1000 ° C. in order to sufficiently dehydrate the gypsum in the co-current rotary kiln 10. The co-current rotary kiln 10 preferably has a structure capable of maintaining the above-described heating time and kiln bottom temperature.

  The anhydrous gypsum 32 (waste gypsum 30) deposited on the bottom on the upstream side of the drum main body 17 moves to the downstream side of the drum main body 17 while being stirred. As shown in FIG. 1, the anhydrous gypsum 32 generated by being heated in the drum main body 17 is discharged to the outside of the co-current rotary kiln 10 via the settling chamber 14 connected to the downstream side of the drum main body 17. . Thus, anhydrous gypsum can be manufactured.

  In the method for producing anhydrous gypsum according to another embodiment, a drying step may be provided before the heating step. In the drying step, it is preferable that the waste gypsum is preheated and dried, and the loss on ignition of the dried gypsum is 12% by mass or less. By performing the drying step, dehydration and dehydration of waste gypsum, and carbonization and decomposition of paper and organic matter progress more smoothly, so that the quality of finally obtained anhydrous gypsum can be improved. The loss on ignition of waste gypsum obtained in the drying step is more preferably 10% by mass or less, and more preferably 7% by mass or less.

  Even if the loss on ignition in the drying step is reduced to less than 2% by mass, the quality of the finally obtained anhydrous gypsum does not change much. Therefore, from the viewpoint of production efficiency, the loss on ignition of waste gypsum obtained in the drying step is preferably 2% by mass or more. The ignition loss can be measured by JIS R 5202: 2010 “5.2. Method other than blast furnace cement and blast furnace slag” in “5.

  FIG. 3 is a schematic diagram showing another example of the reformer. A method for producing anhydrous gypsum having a drying step and a heating step can be performed using the reformer 110 in FIG. The reforming apparatus 110 includes a dryer 45 for drying the waste gypsum 30 on the upstream side in addition to the configuration of the reforming apparatus shown in FIG. The waste gypsum once stored in the raw material tank 40 is supplied to the dryer 45. The type of the dryer 45 is not particularly limited, and examples thereof include a rotary kiln, a kettle oven, a flash drying oven, and a fluidized bed drying oven.

  The drying temperature in the dryer 45 is, for example, 70 to 450 ° C, preferably 100 to 400 ° C, and more preferably 120 to 350 ° C. It is preferable that the dryer 45 has a structure capable of realizing such a temperature condition. The waste gypsum dried in the dryer 45 is transferred to the supply unit 20 by the belt conveyor 50. Then, as described above for the reforming apparatus 100, the waste gypsum is supplied from the supply unit 20 to the co-current rotary kiln 10, and the waste gypsum is reformed into anhydrous gypsum.

  Before the waste gypsum is put into the co-current rotary kiln 10, the waste gypsum is preliminarily dried in the dryer 45, whereby the water content of the waste gypsum can be reduced. Thereby, while reforming of waste gypsum in the co-current rotary kiln 10 is promoted, carbonization and decomposition of paper and organic matter are also promoted, and the quality of anhydrous gypsum finally obtained can be improved.

  Downstream of the sedimentation chamber 14, a dust collecting unit 60, a product silo 70 for storing anhydrous gypsum, and a dust collecting unit 60 are provided. The anhydrous gypsum obtained by the co-current rotary kiln 10 is transferred to a product silo 70 by a belt conveyor 66.

  In the production method of the present embodiment, a recovery step of recovering anhydrous gypsum from the exhaust gas of the co-current rotary kiln 10 may be performed. The collecting step can be performed by the dust collecting unit 60 in FIG. That is, smoke exhaust generated in the co-current rotary kiln 10 is introduced into the dust collecting unit 60. Specifically, the smoke exhaust is introduced into the cyclone 62 via the pipe 61, and the coarse dust is collected. The exhaust gas from the cyclone 62 is introduced into an electric precipitator 64 via a pipe 63. In the electric dust collector 64, fine dust that cannot be collected by the cyclone 62 is collected.

  In the co-current rotary kiln 10, since the waste gypsum from the supply unit 20 is supplied toward the combustion frame 16 of the co-current rotary kiln 10, the fine particles are also sufficiently reformed. Therefore, both the coarse dust and the fine dust collected in the dust collecting section 60 contain anhydrous gypsum as a main component. Therefore, both of these dusts can be transferred to the product silo 70 by the belt conveyor 66. As described above, by recovering anhydrous gypsum from flue gas generated in the co-current rotary kiln 10, the yield of anhydrous gypsum is improved, and high productivity can be obtained.

  The dust collecting unit 60 is not limited to the above-described embodiment, and may use a known dust collecting unit such as a filter dust collector (bag filter) in addition to a cyclone (centrifugal dust collector) and an electric dust collector. These dust collectors may be used alone or in combination of two or more.

  The anhydrous gypsum obtained in each of the above embodiments contains Type II anhydrous gypsum as a main component. In addition, one or both of anhydrous type I gypsum and type III anhydrous gypsum may be included. Also, a small amount of one or both of the hemihydrate gypsum and the gypsum may remain.

  The anhydrous gypsum obtained in each of the embodiments described above has f. CaO (free lime) may be contained, and its content is preferably 1% by mass or less, more preferably 0.3% by mass or less. Thus, f. By reducing the content of CaO, it can be suitably used as a cementitious additive. F. Since CaO is generated by decomposing anhydrous gypsum at high temperature, f. If the content of CaO is low, the decomposition of gypsum is suppressed in the co-current rotary kiln 10, and the amount of generated SOx is sufficiently reduced. In addition, f.CaO is measured by the Japan Cement Association Standard Test Method JCAS I-01 "Method for Quantifying Free Calcium Oxide".

  The anhydrous gypsum may contain a carbon content, and its content (total carbon content) is preferably 0.5% by mass or less. By reducing the total carbon content in this way, it can be suitably used as a cementitious additive. The total carbon content can be measured by the infrared absorption method of JIS R 1603 “Chemical analysis method of fine silicon nitride powder for fine ceramics”.

  In the method for producing anhydrous gypsum according to each of the above-described embodiments, the conversion of waste gypsum to anhydrous gypsum can be promoted while suppressing the decomposition of gypsum. For this reason, the heating time of waste gypsum can be shortened. Therefore, anhydrous gypsum can be produced in a very short time in a high yield. Further, the reformer can be sufficiently miniaturized, and the waste gypsum can be reformed into anhydrous gypsum with high efficiency.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said Embodiment at all.

  The content of the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

(Examples 1 to 4)
A waste gypsum reformer including a co-current rotary kiln and a supply unit as shown in FIG. 1 was prepared. Using this reformer, waste gypsum was modified in the following procedure to produce anhydrous gypsum.

  The waste gypsum board was crushed to a size of 4 mm or less to remove a part of the paper to prepare a granular sample. The density, chemical composition, morphology and properties of this granular sample were as shown in Table 1. 30 g of the granular sample and 300 mL of water were placed in a beaker, and stirred for 1 minute with a hand mixer to check for the presence of foaming. As a result, a large amount of foam was generated, and it was confirmed that the foam had foaming properties. The presence of effervescent indicates that the waste gypsum contains an organic admixture.

  The granular sample was supplied from a supply section into a co-current rotary kiln (inner diameter φ: 1.4 m, length L: 4.0 m, inclination: 3 °) to perform a heating step. The regenerated heavy oil as a fuel was supplied to the burner within a range of a fuel consumption of 54 to 77 L / hour, and the kiln bottom temperature of the co-current rotary kiln was adjusted as shown in Table 2. As shown in FIG. 1, the granular sample was supplied such that the granular sample and the combustion frame were in direct contact. The supply amount of the granular sample was 1.1 tons / hour. The residence time (heating time) during which the granular sample stayed in the co-current rotary kiln was adjusted by changing the rotation speed of the co-current rotary kiln. The residence time (heating time) in each example was as shown in Table 2. Thus, the waste gypsum was modified to obtain anhydrous gypsum.

  The anhydrous gypsum after the heating step was evaluated for chemical composition (ig.loss, f.CaO, C), gypsum morphology, and foamability. Ignition loss (ig.loss) was measured by JIS R 5202: 2010 “5.2. Method other than blast furnace cement and blast furnace slag” in “5. f. CaO was measured by the Japan Society of Cement Standard Test Method JCAS I-01 "Method for Quantifying Free Calcium Oxide". Gypsum morphology was confirmed by X-ray diffraction. C (total carbon content) was measured by the infrared absorption method of JIS R 1603 “Chemical analysis method of fine silicon nitride powder for fine ceramics”. Foamability was evaluated in the same manner as in the above-mentioned granular sample. The evaluation results were as shown in Table 2.

  From the results shown in Table 2, in Examples 1 to 4, by supplying waste gypsum toward the combustion flame, the loss on ignition and the total carbon content of waste gypsum were reduced in a short heating time, and the efficiency of anhydrous gypsum was reduced. Could be manufactured. Further, since f.CaO was not generated, it was confirmed that generation of SOx due to the decomposition of gypsum was sufficiently suppressed, and anhydrous gypsum could be obtained with a high yield.

(Examples 5 to 14)
As a step before the heating step, a drying step was performed using a kiln type dryer (φ: 1.4 mx L: 12.0 m). In order to promote the volatilization of water of crystallization contained in the waste gypsum and sufficiently reduce the loss on ignition, the drying temperature was set to 260 to 300 ° C., and the residence time (drying time) in the kiln type dryer was set to 20 minutes. The main component of the waste gypsum after the drying step was hemihydrate gypsum. The loss on ignition of the waste gypsum after the drying step was measured in the same manner as the method for measuring the loss on ignition of anhydrite. The measurement results were as shown in Table 3. After the dried gypsum was once stored in a storage tank, a heating step was performed in a co-current rotary kiln as shown in FIG. 1 in the same manner as in Examples 1 to 4, and the obtained anhydrous gypsum was evaluated. . Table 3 shows the furnace bottom temperature and the residence time (heating time) in each example. Evaluation results of the anhydrous gypsum after the heating step were as shown in Table 3.

  From the comparison results of Tables 2 and 3, it can be seen that by introducing the drying step before the heating step, the loss on ignition and the total carbon content of the anhydrous gypsum are reduced, and anhydrous gypsum having better quality can be obtained. confirmed. In each embodiment, f. Although CaO was slightly generated, the amount thereof was very small and was at a level without any problem.

  As described above, according to the production method of the present invention, anhydrous gypsum can be produced in a shorter time than before without using a large-scale reformer. Further, the amount of generated SOx can be suppressed to a small amount, and anhydrous gypsum can be produced with a high yield. This can contribute to establishing a waste gypsum recycling system.

  Provided is a production method capable of efficiently producing anhydrous gypsum from waste gypsum while sufficiently suppressing the generation of SOx.

DESCRIPTION OF SYMBOLS 10 ... Parallel rotary kiln, 11 ... Kiln hood, 12 ... Burner, 14 ... Sedimentation chamber, 16 ... Combustion frame, 17 ... Drum body, 20 ... Supply part, 30 ... Waste gypsum, 32 ... Anhydrite, 40 ... Raw material tank, 45 dryer, 50, 66 belt conveyor, 60 dust collector, 61, 63 pipe, 62 cyclone, 64 electric dust collector, 70 product silo, 100, 110 reformer.

Claims (5)

A method for producing anhydrous gypsum having a heating step of heating waste gypsum containing gypsum to obtain anhydrous gypsum,
In the heating step, a method for producing anhydrous gypsum, wherein the waste gypsum is supplied toward a combustion frame, and at least a part of the waste gypsum is supplied and heated so as to be in contact with the combustion frame . 2. The method for producing anhydrous gypsum according to claim 1, wherein in the heating step, the waste gypsum is supplied toward the combustion frame by dropping the waste gypsum by gravity from an opening at a tip of a pipe. 3.   The method for producing anhydrous gypsum according to claim 1 or 2, wherein the heating time in the heating step is 20 minutes or less.   The production of the anhydrous gypsum according to any one of claims 1 to 3, further comprising, before the heating step, a drying step of preheating and drying the waste gypsum to reduce the ignition loss to 12% by mass or less. Method.   F. Of the anhydrous gypsum obtained in the heating step The method for producing anhydrous gypsum according to any one of claims 1 to 4, wherein CaO is 1% by mass or less and the total carbon content is 0.5% by mass or less.

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