JP2017149619A - Method for producing anhydrous gypsum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method by which anhydrous gypsum can be efficiently produced from waste gypsum while sufficiently suppressing generation of SOx.SOLUTION: A method for producing anhydrous gypsum, including a heating step of heating waste gypsum including dihydrate gypsum to obtain anhydrous gypsum, is provided in which the waste gypsum is supplied toward a combustion flame and is heated in the heating step.SELECTED DRAWING: None

Description

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

  As the number of demolished houses where gypsum board is used increases year by year, the amount of waste gypsum generated has increased. Accordingly, there is an increasing need for techniques for treating waste gypsum. For this reason, various studies have been made to effectively use waste gypsum.

  Waste gypsum usually contains paper and organic admixture together with dihydrate gypsum. For this reason, there is a concern that, if it is added as it is to a cement-based material, the strength development property is lowered or the setting property is fluctuated. Thus, a method has been proposed in which waste gypsum is heated to carbonize and decompose the paper and organic admixture, and the gypsum content is recovered as hemihydrate gypsum or anhydrous gypsum (see Patent Documents 1 to 7).

Japanese Patent Laid-Open No. 10-36149 Japanese Patent No. 3108922 JP 2002-68740 A JP 2008-1567 A JP 2006-199576 A JP 2002-87816 A JP2013-224251A

  When the waste gypsum is heated, carbonization and decomposition of the paper and the organic admixture proceed. On the other hand, when the temperature exceeds 1200 ° C., partial decomposition of the gypsum proceeds and there is a concern that SOx is generated. For this reason, in the conventional manufacturing method, in order to advance modification | reformation of waste gypsum, suppressing decomposition | disassembly of gypsum, it was necessary to make heating temperature low and lengthen a heating time. For this reason, production efficiency tends to be low.

  Then, an object of this invention is to provide the manufacturing method which can manufacture anhydrous gypsum efficiently from waste gypsum, fully suppressing generation | occurrence | production of SOx.

  According to the study by the present inventors, it was found that there is a difference in reaction initiation temperature and reaction rate between carbonization and decomposition reaction of paper and organic admixture and decomposition reaction of gypsum. Based on this knowledge, we have found that by supplying waste gypsum toward the combustion frame, paper and organic admixture can be quickly carbonized and decomposed before gypsum decomposition occurs, and anhydrous gypsum can be obtained efficiently. 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, wherein the waste gypsum is supplied toward the combustion frame and heated. A method for producing anhydrous gypsum is provided.

  In this manufacturing method, since waste gypsum is supplied and heated toward a combustion flame | frame, the temperature increase rate of waste gypsum can fully be made high. Thus, it is presumed that the paper and the organic admixture can be quickly carbonized and decomposed to promote the modification to anhydrous gypsum before the decomposition of the gypsum contained in the waste gypsum occurs. Accordingly, anhydrous gypsum can be efficiently produced from waste gypsum while sufficiently suppressing the generation of SOx.

  In the heating step, waste gypsum is preferably supplied and heated so as to come into contact with the combustion flame. Thereby, the temperature increase rate of waste gypsum can be further increased. Therefore, it is presumed that the paper and organic admixture can be carbonized and decomposed in a shorter time and the conversion to anhydrous gypsum can be sufficiently promoted while further suppressing the decomposition of dihydrate gypsum contained in waste gypsum. .

  The heating time in the heating step is preferably 20 minutes or less. Thereby, decomposition | disassembly of the dihydrate gypsum in a heating process can be suppressed further, and an anhydrous gypsum can be manufactured with a high yield.

  Before the heating step, it is preferable to have a drying step in which waste gypsum is preheated and dried to reduce the loss on ignition to 12% by mass or less. As a result, the modification to anhydrous gypsum proceeds more smoothly in the heating process, so that the quality of the obtained anhydrous gypsum becomes better, and the amount of moisture evaporation in the heating process can be reduced, so that stable production is possible. Can continue.

  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.

  ADVANTAGE OF THE INVENTION According to this invention, the production method which can manufacture anhydrous gypsum efficiently from waste gypsum, fully suppressing generation | occurrence | production of SOx can be provided. This can contribute to the establishment of a recycling system for waste gypsum.

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

  In the following, embodiments of the present invention will be described with reference to the drawings as the case may be. However, the following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted in some cases. The dimensional ratios in the drawings are not limited to the illustrated ratios.

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

  As the waste gypsum, for example, waste materials generated at a gypsum board manufacturing factory, gypsum board scraps generated at a new construction site, waste materials generated at a demolition site, and the like can be used. However, waste materials generated at the site of demolition work include inorganic building waste materials other than gypsum. It is preferable to perform a pretreatment process that reduces the content of such inorganic building waste before the heating process. The content of inorganic building waste is preferably less than 10% by mass. Moreover, the paper and cloths affixed to the gypsum board surface burn in the heating process. For this reason, it is not necessarily removed 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 clogging in a reformer that reforms the waste gypsum and that can be easily discharged from a silo or a tank. As such a particle size, it is 50 mm or less, for example, Preferably it is 10 mm or less, More preferably, it is 5 mm or less. As a result, handling is improved, and the supply to the reformer can be continued sufficiently stably.

  In the heating process, waste gypsum is supplied toward the combustion flame and heated. Such a heating process can be performed using a reformer having a burner and capable of supplying waste gypsum toward the combustion flame from the burner. The type and shape of the reformer are not particularly limited. An example of the reformer is a cocurrent rotary kiln. The 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 showing an example of a reformer. The reformer 100 includes a burner 12, and heats the waste gypsum 30 to reform it into anhydrous gypsum 32, a supply unit 20 that supplies the waste gypsum 30 to the cocurrent flow rotary kiln 10, Is provided.

  The co-current rotary kiln 10 is provided with a kiln hood 11, a drum body 17, and a settling chamber 14 in communication from the upstream side to the downstream side. A burner 12 is attached to the kiln hood 11 of the parallel flow 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 cocurrent rotary kiln 10 are not particularly limited. The length L of the drum body 17 along the direction of the rotation axis is preferably 1 to 10 m, more preferably 2 to 6 m, from the viewpoint of achieving both the downsizing of the reformer and sufficient production capacity. The inner diameter φ of the drum body 17 of the cocurrent rotary kiln 10 is, for example, 1 to 3 m. From the viewpoint of allowing anhydrous gypsum to be discharged in a short time, it is preferable that the inclination angle of the drum 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, the tilt angle is more preferably 1 to 5 °, and the rotation speed is more preferably 2 to 7 rpm.

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

  The burner 12 may be a variable burner capable of arbitrarily adjusting the direction of the combustion frame 16. By adjusting the direction of the frame to the optimum position according to the particle size of the waste gypsum 30, it becomes easy to find the optimum heating condition. As a result, it can be more efficiently modified to anhydrous gypsum. As an example of the variable burner, there is 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 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 so as to pass through the combustion frame 16. However, it is not essential that all of the supplied waste gypsum 30 contacts the combustion frame 16 or passes 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. And most of the dihydrate gypsum contained in the waste gypsum 30 is promptly modified into anhydrous gypsum. These reactions can be completed before the gypsum decomposes. Therefore, it is considered that dihydrate gypsum can be efficiently modified to anhydrous gypsum while suppressing the generation of SOx generated with the decomposition of gypsum.

  FIG. 2 is a cross-sectional view taken along the line II-II in the reformer 100 of FIG. A combustion frame 16 is formed in the vicinity of the center in the radial direction on the upstream side of the drum body 17 of the parallel flow 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 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 until it has left the periphery of the combustion frame 16 even after being deposited near the bottom of the drum body 17. Waste gypsum 30 that does not come into contact with the combustion frame 16 is also deposited near the bottom of the drum body 17 and then exposed to the high temperature of the combustion frame 16 around the combustion frame 16. By being exposed to high temperature in this way, carbonization and decomposition of paper and organic admixture and reforming to anhydrous gypsum proceed rapidly.

  The drum body 17 continuously rotates in the direction P. Since the rotation axis of the drum body 17 is inclined by 0.5 to 8 ° 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 body 17 while being agitated by the rotation of the drum body 17 of the cocurrent rotary kiln 10.

  The external flame of the combustion flame | frame 16 has the temperature of 1200 degreeC or more which is a gypsum decomposition temperature, for example. 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 in contact with the external flame and the waste gypsum 30 that has passed through the vicinity of the external flame can be rapidly advanced. . The waste gypsum 30 is supplied toward the combustion frame 16 by the supply unit 20. For this reason, even if the waste gypsum 30 contains fine particles, the fine particles are suspended by the airflow in the drum body 17 and are sufficiently suppressed from being discharged as dust in the exhaust gas without contacting the combustion frame 16. be able to. The fine particles are instantly reformed by coming into contact with the combustion flame 16 or passing through the vicinity of the combustion flame 16.

  Without contact with the combustion flame 16, the time required for carbonization and decomposition of the paper and organic admixture tends to be longer. When the time for heating becomes longer, the decomposition reaction of gypsum tends to proceed. For this reason, it is preferable that the waste gypsum 30 contacts the combustion frame 16.

  As the heating time in the heating step is shorter, productivity can be improved while suppressing 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. Although there is no restriction | limiting in particular in the minimum of heating time, From a viewpoint of fully progressing the modification | reformation to an anhydrous gypsum, it is preferable that it is 1 minute or more, and it is more preferable that it is 2 minutes or more.

  After the waste gypsum 30 comes into contact with the combustion frame 16, the kiln bottom temperature in the cocurrent rotary kiln 10 is preferably 500 to 1000 ° C. in order to sufficiently dehydrate the gypsum in the cocurrent rotary kiln 10. The cocurrent 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 of the drum body 17 on the upstream side moves to the downstream side of the drum body 17 while being stirred. As shown in FIG. 1, the anhydrous gypsum 32 generated by heating in the drum body 17 is discharged to the outside of the cocurrent rotary kiln 10 via the settling chamber 14 connected to the downstream side of the drum body 17. . In this way, anhydrous gypsum can be produced.

  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, the waste gypsum is preheated and dried, and the loss on ignition of the gypsum after drying is preferably 12% by mass or less. By performing the drying step, the dehydration and dehydration of the waste gypsum and the carbonization and decomposition of the paper and organic matter proceed more smoothly, so that the quality of the finally obtained gypsum can be improved. The ignition loss of the waste gypsum obtained in the drying step is more preferably 10% by mass or less, and more preferably 7% by mass or less.

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

  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 of FIG. The reformer 110 includes a dryer 45 for drying the waste gypsum 30 on the upstream side in addition to the configuration of the reformer shown in FIG. The waste gypsum once stored in the raw material tank 40 is supplied to the dryer 45. The kind of dryer 45 is not specifically limited, A rotary kiln, a kettle furnace, an airflow drying furnace, a fluidized bed drying furnace, etc. can be illustrated.

  The drying temperature in the dryer 45 is 70-450 degreeC, for example, Preferably it is 100-400 degreeC, More preferably, it is 120-350 degreeC. The dryer 45 preferably has a structure capable of realizing such temperature conditions. Waste gypsum dried in the dryer 45 is transferred to the supply unit 20 by the belt conveyor 50. And as the description of the above-mentioned reformer 100, it is supplied from supply part 20 to cocurrent flow type rotary kiln 10, and waste gypsum is reformed to anhydrous gypsum.

  Before the waste gypsum is put into the cocurrent rotary kiln 10, the amount of water in the waste gypsum can be reduced by preliminarily drying the waste gypsum in the dryer 45. As a result, the reforming of the waste gypsum in the cocurrent flow type rotary kiln 10 is promoted, and the carbonization and decomposition of paper and organic matter are also promoted, and the quality of the anhydrous gypsum finally obtained can be improved.

  On the downstream side of the settling chamber 14, a dust collection unit 60, a product silo 70 for storing anhydrous gypsum, and a dust collection unit 60 are provided. The anhydrous gypsum obtained in the cocurrent rotary kiln 10 is transferred to the product silo 70 by the belt conveyor 66.

  In the manufacturing method of this embodiment, you may perform the collection | recovery process which collect | recovers anhydrous gypsum from the flue gas of the cocurrent flow type rotary kiln 10. FIG. The collection step can be performed by the dust collection unit 60 of FIG. That is, the dust collection unit 60 is introduced with the flue gas generated in the cocurrent rotary kiln 10. Specifically, the flue gas is introduced into the cyclone 62 via the pipe 61, and coarse dust is collected. Exhaust gas from the cyclone 62 is introduced into the electric dust collector 64 via the pipe 63. The electric dust collector 64 collects fine dust that could not be collected by the cyclone 62.

  In the parallel flow type rotary kiln 10, since the waste gypsum from the supply unit 20 is supplied toward the combustion frame 16 of the parallel flow type rotary kiln 10, the fine particles are also sufficiently reformed. For this reason, the coarse dust and fine dust collected by the dust collection unit 60 both contain anhydrous gypsum as a main component. Accordingly, both of these dusts can be transferred to the product silo 70 by the belt conveyor 66. Thus, by recovering anhydrous gypsum from the flue gas generated in the cocurrent flow type rotary kiln 10, the yield of anhydrous gypsum can be improved and high productivity can be obtained.

  The dust collection unit 60 is not limited to the above-described embodiment, and a known dust collection unit such as a filtration dust collection (bag filter) may be used in addition to the cyclone (centrifugal force dust collector) and the 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 to this, one or both of type I anhydrous gypsum and type III anhydrous gypsum may be included. One or both of a small amount of hemihydrate gypsum and dihydrate gypsum may remain.

  The anhydrous gypsum obtained in each of the above-described embodiments is f. CaO (free lime) may be contained, and the content thereof is preferably 1% by mass or less, and more preferably 0.3% by mass or less. Thus, f. By reducing the content of CaO, it can be suitably used as a cement-based additive. F. Since CaO is generated when anhydrous gypsum decomposes at high temperature, f. If the content of CaO is low, decomposition of gypsum is suppressed in the cocurrent flow rotary kiln 10, and the amount of SOx generated is sufficiently reduced. In addition, f.CaO is measured by Cement Association standard test method JCAS I-01 “Quantitative method of free calcium oxide”.

  Anhydrous gypsum may contain carbon, and its content (total carbon content) is preferably 0.5% by mass or less. Thus, it can use suitably as a cement-type additive by reducing the total carbon amount. 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 manufacturing method of anhydrous gypsum according to each of the above-described embodiments, it is possible to promote the modification from waste gypsum to anhydrous gypsum while suppressing decomposition of gypsum. For this reason, the heating time of waste gypsum can be shortened. Therefore, anhydrous gypsum can be produced in a high yield in a very short time. In addition, the reforming apparatus can be sufficiently downsized to reform waste gypsum to 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 contents 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 1-4)
A waste gypsum reforming device including a cocurrent rotary kiln and a supply unit as shown in FIG. 1 was prepared. Using this reformer, waste gypsum was modified by 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, and a granular sample was prepared. Table 1 shows the density, chemical composition, form, and properties of the granular sample. A granular sample (30 g) and water (300 mL) were placed in a beaker, stirred with a hand mixer for 1 minute, and examined for foaming. As a result, it was confirmed that a large amount of foam was generated and foamed. The foaming property indicates that the waste gypsum contains an organic admixture.

  The granular sample was supplied from a supply unit into a cocurrent rotary kiln (inner diameter φ: 1.4 m, length L: 4.0 m, inclination: 3 °) to perform a heating process. Recycled heavy oil as a fuel was supplied to the burner in a range of fuel usage of 54 to 77 L / hour, and the kiln bottom temperature of the cocurrent rotary kiln was adjusted as shown in Table 2. As shown in FIG. 1, the granular sample was supplied so that the granular sample and the combustion frame were in direct contact with each other. The supply amount of the granular sample was 1.1 ton / hour. The residence time (heating time) for the granular sample to stay in the cocurrent rotary kiln was adjusted by changing the number of rotations of the cocurrent rotary kiln. The residence time (heating time) in each example was as shown in Table 2. In this way, waste gypsum was modified to obtain anhydrous gypsum.

  About anhydrous gypsum after a heating process, chemical composition (ig.loss, f.CaO, C), gypsum form, and foamability were evaluated. The ignition loss (ig.loss) was measured according to “5.2 Cases other than blast furnace cement and blast furnace slag” in “5. Determination of ignition loss” in JIS R 5202: 2010. f. CaO was measured by Cement Association Standard Test Method JCAS I-01 “Quantitative Method for Free Calcium Oxide”. The gypsum form was confirmed by X-ray diffraction. C (total carbon amount) was measured by the infrared absorption method of JIS R 1603 “Chemical analysis method of fine silicon nitride powder for fine ceramics”. The foamability was evaluated in the same manner as the above granular sample. The evaluation results are as shown in Table 2.

  From the results shown in Table 2, in Examples 1 to 4, by supplying waste gypsum toward the combustion frame, the ignition loss of waste gypsum and the total carbon amount are reduced in a short heating time, and anhydrous gypsum is made efficient. Could be manufactured. Moreover, since f.CaO was not produced | generated, generation | occurrence | production of SOx accompanying decomposition | disassembly of gypsum was fully suppressed and it was confirmed that anhydrous gypsum is obtained with a high yield.

(Examples 5 to 14)
As a pre-process of the heating process, a drying process was performed using a kiln-type dryer (φ: 1.4 m × L: 12.0 m). In order to promote the volatilization of crystal water 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 20 minutes. In addition, the main component of the waste gypsum after a drying process was hemihydrate gypsum. The ignition loss of the waste gypsum after the drying process was measured in the same manner as the measurement method of the ignition loss of anhydrous gypsum. The measurement results were as shown in Table 3. The gypsum after drying was once stored in a storage tank, and then the heating step was performed in a cocurrent rotary kiln as shown in FIG. 1 in the same manner as in Examples 1 to 4, and the obtained anhydrous gypsum was evaluated. . The kiln bottom temperature and residence time (heating time) in each example are as shown in Table 3. The evaluation results of anhydrous gypsum after the heating step are as shown in Table 3.

  From the comparison results of Table 2 and Table 3, by introducing the drying process before the heating process, the loss of ignition and the total carbon content of anhydrous gypsum are reduced, and anhydrous gypsum having better quality can be obtained. confirmed. In each example, f. Some CaO was produced, but the amount was very small and there was no problem.

  From the 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. In addition, the amount of SOx generated can be reduced, and anhydrous gypsum can be produced with a high yield. This can contribute to building a recycling system for waste gypsum.

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

DESCRIPTION OF SYMBOLS 10 ... Parallel flow type rotary kiln, 11 ... Kiln food, 12 ... Burner, 14 ... Settling chamber, 16 ... Combustion flame, 17 ... Drum body, 20 ... Supply part, 30 ... Waste gypsum, 32 ... Anhydrous gypsum, 40 ... Raw material tank, 45 ... dryer, 50, 66 ... belt conveyor, 60 ... dust collector, 61, 63 ... piping, 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 dihydrate gypsum to obtain anhydrous gypsum,
The method for producing anhydrous gypsum, wherein in the heating step, the waste gypsum is supplied and heated toward the combustion frame.   The method for producing anhydrous gypsum according to claim 1, wherein in the heating step, the waste gypsum is supplied and heated so as to be in contact with the combustion frame.   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 anhydrous gypsum according to any one of claims 1 to 3, further comprising a drying step in which the waste gypsum is preheated and dried before the heating step so that the loss on ignition is 12% by mass or less. Method.   F. Of the anhydrous gypsum obtained in the heating step. The manufacturing method of the anhydrous gypsum as described in any one of Claims 1-4 whose CaO is 1 mass% or less and total carbon amount is 0.5 mass% or less.

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