Method for drying granular material and method for producing ammonium sulfate

Abstract

A method for drying granular material using a dryer having a bottom plate with a plurality of holes formed therein is provided, which can prevent the holes from being blocked by the granular material in a wet state to be dried. [Solution] A method for drying granular material using a dryer having a bottom plate with multiple holes formed therein, comprising a dried raw material placing step in which dried granular material is placed on the bottom plate, a wet raw material introducing step in which wet granular material is introduced on top of the dried granular material, and a drying step in which gas is blown into the granular material through the multiple holes to dry the wet granular material.

Description

[Technical Field]

[0001] The present invention relates to a method for drying granular material and a method for producing ammonium sulfate. [Background technology]

[0002] When coke oven gas discharged from a coke oven is refined to produce fuel gas, the coke oven gas is brought into contact with dilute sulfuric acid to remove ammonia. By bringing this coke oven gas into contact with dilute sulfuric acid, an aqueous ammonium sulfate solution (hereinafter referred to as "ammonium sulfate mother liquor") is produced. The ammonium sulfate mother liquor is concentrated in a crystallizer. As a result, ammonium sulfate is crystallized in the crystallizer, and the ammonium sulfate is recovered and then dried. In this way, ammonium sulfate granules are produced.

[0003] As a technique for producing ammonium sulfate from ammonium sulfate mother liquor, Patent Document 1 discloses a technique for dissolving ammonium sulfate crystals precipitated in a transfer pipe by heating the ammonium sulfate in the transfer pipe during the crystallization process. According to Patent Document 1, dissolving the ammonium sulfate crystals precipitated in the transfer pipe prevents clogging of the transfer pipe and improves the operating rate of the ammonium sulfate crystallization process.

[0004] Furthermore, Patent Document 2 discloses a drying method for powder or granular material, in which powder or granular material before drying is supplied to a first drying chamber, where it is dried while preventing agglomeration by an airflow, and then the powder or granular material is supplied to a second drying chamber, where it is dried while preventing agglomeration by supplying gas. According to Patent Document 2, by using the first and second drying chambers, powder or granular material having a target dryness and substantially free of agglomeration can be obtained. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-216276 [Patent Document 2] Japanese Patent Application Publication No. 10-318673 Summary of the Invention [Problem to be solved by the invention]

[0006] In the technology disclosed in Patent Document 1, when ammonium sulfate in a water-containing state is introduced into a dryer having a bottom plate with a plurality of holes formed therein in order to dry the ammonium sulfate, the holes become clogged, causing a problem that the ammonium sulfate cannot be dried.

[0007] The drying method disclosed in Patent Document 2 requires the use of two drying chambers, which results in a problem of a complicated dryer configuration. Furthermore, Patent Document 2 does not disclose any measures to prevent clogging of holes in a dryer having a bottom plate with multiple holes formed therein.

[0008] The present invention has been made in view of the above-described conventional techniques, and an object of the present invention is to provide a method for drying granular material, which can suppress clogging of holes by the wet granular material to be dried in a dryer having a bottom plate with a plurality of holes formed therein. Another object of the present invention is to provide a method for producing ammonium sulfate using the method for drying granular material. [Means for solving the problem]

[0009] The means for solving the above problems are as follows. [1] A method for drying granular material using a dryer having a bottom plate with a plurality of holes formed therein, comprising: a dry raw material placing step of placing the dried granular material on the bottom plate; a wet raw material introducing step of introducing the wet granular material on the dried granular material; and a drying step of blowing gas into the granular material through the plurality of holes to dry the wet granular material. A method for drying granular material, comprising: [2] A method for drying granular material according to [1], wherein the average particle size of the granular material after drying placed in the dried raw material placing step is larger than the average particle size of the granular material in a wet state. [3] A method for drying granular material according to [2], wherein the particle size of the granular material placed in the drying raw material placing step after drying is 1.4 mm or more. [4] A method for drying granular material described in [2] or [3], further comprising a particle size separation process for classifying the granular material dried in the drying process into multiple particle sizes, and the granular material after drying that is placed in the dried raw material placing process is the granular material classified in the particle size separation process. [5] A method for drying granular material according to any one of [1] to [4], wherein the height of the granular material placed in the drying raw material placing step after drying is 6 mm or more. [6] The method for drying granular material according to any one of [1] to [5], wherein the granular material is ammonium sulfate crystallized from an aqueous solution of ammonium sulfate. [7] A method for producing ammonium sulfate using the method for drying granular material according to any one of [1] to [5], wherein the granular material is ammonium sulfate, and in the water-containing raw material introducing step, water-containing ammonium sulfate crystallized from an aqueous ammonium sulfate solution is introduced into the dryer and dried to produce ammonium sulfate. [Effects of the Invention]

[0010] By using the method for drying granular material according to the present invention, it is possible to prevent the holes formed in the bottom plate from being clogged, thereby reducing the number of times the dryer is stopped to wash the bottom plate with water, and thereby increasing the operating rate of the dryer. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional schematic view of a dryer that can carry out the method for drying granular material according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating a method for producing ammonium sulfate. [Figure 3] FIG. 3 is a graph showing the relationship between the height of the dried raw material and the number of washing operations. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be specifically described below through embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these embodiments. The method for drying granular material according to this embodiment will be described below using an example in which it is applied to drying ammonium sulfate. However, the method for drying granular material according to this embodiment is not limited to ammonium sulfate, and can also be applied to other granular materials.

[0013] Ammonium sulfate, an example of a granular material, is recovered from an ammonium sulfate mother liquor. Ammonium sulfate is crystallized by concentrating the ammonium sulfate mother liquor produced by contacting coke oven gas with dilute sulfuric acid, and is recovered as a slurry of ammonium sulfate. The slurry of ammonium sulfate is dehydrated using a centrifuge until the water content is 0.1 to 5% by mass. The ammonium sulfate dehydrated in this manner becomes the hydrated ammonium sulfate that is dried by the method for drying granular material according to this embodiment.

[0014] 1 is a cross-sectional schematic diagram of a dryer that can carry out the granular material drying method according to this embodiment. The dryer 10 is used to dry ammonium sulfate 22 in a water-containing state.

[0015] The dryer 10 has a cylindrical container 12 with a bottom and a bottom plate 16 having a plurality of holes 14 formed therein. The bottom plate 16 is provided at a fixed distance from the bottom surface of the container 12. A gas 24 is introduced into the region between the bottom surface of the container 12 and the bottom plate 16 through a vent 18 formed on the side surface of the container 12. In this embodiment, the gas 24 is air heated to 180 to 190°C. By introducing the gas 24 through the vent 18, the gas 24 is blown into the container 12 through the holes 14.

[0016] In the method for drying granular material according to this embodiment, first, a dried raw material placing step is carried out in which ammonium sulfate dried in the dryer 10 is placed on the bottom plate 16 of an empty container 12. In the dried raw material placing step, ammonium sulfate 26 classified to a particle size of 1.4 mm or more and less than 4.75 mm in a particle size separation step described below is placed. In the dried raw material placing step, ammonium sulfate 26 is placed until the placement height reaches 6 mm or more.

[0017] After the dry raw material placing step is performed, a wet raw material adding step is performed in which wet ammonium sulfate 22 is added into the container 12 from above the placed ammonium sulfate 26. The wet ammonium sulfate 22 is added from one side of the container 12.

[0018] A drying step is carried out in which gas 24 is blown into the ammonium sulfate 22 in a wet state that has been introduced in the wet raw material introduction step to dry it. The ammonium sulfate 22 in a wet state introduced into the container 12 from one side moves to the other side opposite the one side while being dried in the container 12. The dried ammonium sulfate 22 is discharged from an outlet 19 formed on the other side.

[0019] As described above, in the method for drying granular material according to this embodiment, a dry raw material placing step is performed in which dried ammonium sulfate 26 is placed on the bottom plate 16 before a wet raw material adding step is performed in which wet ammonium sulfate 22 is added to the container 12. As a result, the dried ammonium sulfate 26 is placed near the holes 14, ensuring gaps between the granular materials, thereby suppressing clogging of the holes 14. On the other hand, if wet ammonium sulfate 22 is added to the container 12 without placing dried ammonium sulfate 26, the areas near the holes 14 will be blocked by the wet ammonium sulfate 22, and gaps will not be ensured between the granular materials, making the holes 14 more likely to be clogged.

[0020] Furthermore, when gas 24 is blown into container 12 with dried ammonium sulfate 26 placed therein, a fluidized bed is formed in which dried ammonium sulfate 26 and gas 24 are mixed. By forming this fluidized bed and drying ammonium sulfate 22 in a water-containing state, it becomes possible to efficiently dry ammonium sulfate 22 in a water-containing state while suppressing clogging of pores 14.

[0021] Fig. 2 is a schematic diagram illustrating a method for producing ammonium sulfate. A method for drying granular material according to this embodiment and a method for producing ammonium sulfate using the method for drying granular material will be described with reference to Fig. 2. Hydrated ammonium sulfate 22, which has been crystallized from an ammonium sulfate mother liquor and dehydrated, is transported to a dryer 10 by a conveyor 30. The hydrated ammonium sulfate 22 is placed in a container 12 in which dried ammonium sulfate 26 has been placed in a drying raw material placing step.

[0022] The ammonium sulfate 22 in a water-containing state is dried by the gas 24 in the container 12. The dried ammonium sulfate 22 is discharged from the discharge port 19. The temperature of the dried ammonium sulfate 22 discharged from the discharge port 19 is measured on the conveyor 32, and the dry state of the ammonium sulfate 22 is determined.

[0023] If the temperature of ammonium sulfate 22 is 100°C or higher, it is determined that ammonium sulfate 22 has been sufficiently dried. On the other hand, if the measured temperature of ammonium sulfate 22 is less than 100°C, it is determined that the drying of ammonium sulfate 22 is insufficient, and ammonium sulfate 22 is dissolved again in ammonium sulfate mother liquor or dried again in dryer 10. Note that, taking a safety factor into consideration, it may also be determined that ammonium sulfate 22 has been sufficiently dried when the temperature of ammonium sulfate 22 discharged from outlet 19 is 105°C or higher. In this manner, ammonium sulfate 22 in a water-containing state is continuously dried and produced using dryer 10.

[0024] The dried ammonium sulfate 22 is then transported by a conveyor 32 to a sieving device 34. The sieving device 34 is composed of an upper sieve 36 with a mesh size of 4.75 mm and a lower sieve 38 with a mesh size of 1.4 mm. The sieving device 34 carries out a particle size separation step in which the dried ammonium sulfate 22 is classified into a plurality of particle sizes.

[0025] In the particle size separation step, a sieving device 34 is used to classify the ammonium sulfate into, for example, ammonium sulfate 25 having a particle size of less than 1.4 mm, ammonium sulfate 26 having a particle size of 1.4 mm or more and less than 4.75 mm, and ammonium sulfate 27 having a particle size of 4.75 mm or more. Ammonium sulfate 25 is ammonium sulfate that falls below the sieve of sieve 38. Ammonium sulfate 26 is ammonium sulfate that falls below the sieve of sieve 36 and falls above the sieve of sieve 38. Ammonium sulfate 27 is ammonium sulfate that falls above the sieve of sieve 36.

[0026] The selling price of ammonium sulfate varies depending on its particle size. Ammonium sulfate 25 with a particle size of less than 1.4 mm is sold at a relatively low price, while ammonium sulfate 26 with a particle size of 1.4 mm or more but less than 4.75 mm is sold at a higher price than ammonium sulfate with a particle size of less than 1.4 mm. For this reason, ammonium sulfate 25 and ammonium sulfate 26 classified in the particle size separation process are sold at different selling prices as shown above. On the other hand, ammonium sulfate 27 has no buyers, so it is dissolved again in ammonium sulfate mother liquor.

[0027] In the dry raw material placing step, a portion of the ammonium sulfate 26 having a particle size of 1.4 mm or more and less than 4.75 mm obtained in the particle size separation step is used in the dry raw material placing step. In this way, in the dry raw material placing step, it is preferable to use ammonium sulfate having a particle size of 1.4 mm or more from which fine particles having a particle size of less than 1.4 mm have been removed. Here, ammonium sulfate having a particle size of 1.4 mm or more is ammonium sulfate that can be sieved onto a sieve 38 with a mesh size of 1.4 mm.

[0028] In granular materials, fine particles have a stronger adhesive force than coarse particles, filling the gaps between the coarse particles and reducing the air permeability of the granular material. Therefore, by using ammonium sulfate with a particle size of 1.4 mm or more from which fine particles less than 1.4 mm have been removed, the decrease in air permeability of the ammonium sulfate placed near the holes 14 is suppressed, thereby further reducing clogging of the holes 14. Note that in this embodiment, coarse particles with a particle size of 4.75 mm or more are removed due to a loss of business partners, but the ammonium sulfate 26 used in the dry raw material placing step may contain such coarse particles of ammonium sulfate.

[0029] Furthermore, since fine particles are removed and ammonium sulfate classified to a predetermined particle size is obtained in this manner, the method for drying granular material according to this embodiment preferably includes the particle size separation step described above. This makes it possible to obtain ammonium sulfate 26 after drying with an adjusted particle size that can further suppress clogging of pores 14, and the ammonium sulfate 26 can be used in the drying raw material placing step.

[0030] As described above, by using the method for drying granular material according to this embodiment, it is possible to prevent the holes 14 formed in the bottom plate 16 from being blocked by the wet granular material. This reduces the number of times the dryer 10 is stopped and the bottom plate 16 is washed with water to eliminate the blockage, thereby increasing the operating rate of the dryer 10. If the operating rate of the dryer 10 can be increased, it becomes possible to improve the productivity of ammonium sulfate in the method for producing ammonium sulfate that uses the method for drying granular material according to this embodiment.

[0031] Note that the present invention is not limited to the above-described embodiment and various modifications can be made. In the above-described embodiment, the dried raw material placing step illustrates an example in which ammonium sulfate 26 is placed until the placement height reaches 6 mm or more, but the present invention is not limited to this. Even if even a small amount of ammonium sulfate 26 is placed in the dried raw material placing step, the ammonium sulfate 26 placed near the holes 14 ensures gaps, thereby preventing clogging of the holes 14 compared to when no ammonium sulfate 26 is placed. Therefore, if dried ammonium sulfate 26 is placed in the dried raw material placing step, clogging of the holes 14 can be prevented more than in the past, regardless of the placement height.

[0032] Furthermore, in the dry raw material placing step, an example has been shown in which a portion of ammonium sulfate 26 having a particle size of 1.4 mm or more and less than 4.75 mm is used, but this is not limiting. The average particle size of the dried ammonium sulfate placed in the dry raw material placing step may be the same as the average particle size of ammonium sulfate in a hydrated state. Even if the average particle size is the same, by using dried ammonium sulfate, voids between the granular materials are secured near the holes 14, thereby suppressing clogging of the holes 14. In this embodiment, the average particle size is the median diameter, which can be calculated as the particle size at which the mass cumulative distribution is 50%.

[0033] However, as mentioned above, fine particles have a higher adhesive strength than coarse particles, filling the gaps between the coarse particles and reducing the air permeability of the granular material. For this reason, it is preferable to use dried ammonium sulfate from which fine particles have been removed, which has a larger average particle size than ammonium sulfate in a hydrated state, in the dry raw material placing step. This prevents the air permeability of ammonium sulfate placed near the holes 14 from decreasing, further preventing clogging of the holes 14. [Example]

[0034] Next, examples will be described. In the examples, wet ammonium sulfate 22 was dried using the dryer 10 shown in FIG. 1 (diameter of holes 14: 2 mm) under drying conditions such that the production rate of dried ammonium sulfate was 3.7 t / h. In invention examples 1 to 4, a dried raw material placing step was carried out in which dried ammonium sulfate 26 having a particle size of 1.4 mm or more and less than 4.75 mm was placed in an empty container 12, followed by a wet raw material adding step in which wet ammonium sulfate 22 was added, and a drying step. In invention examples 1 to 4, the placement height of the placed ammonium sulfate 26 was changed, and wet ammonium sulfate 22 was dried under the same other drying conditions.

[0035] In the comparative example, the step of adding wet raw material, in which wet ammonium sulfate 22 was added, and the drying step were carried out without carrying out the dry raw material placing step, to dry the ammonium sulfate 22. In each of the inventive examples and comparative examples, the drying of the ammonium sulfate 22 was carried out for 8 weeks, and the number of times that the holes 14 were clogged and the water washing operation was carried out during this period was confirmed.

[0036] When hole 14 becomes clogged, the pressure in the area sandwiched between the bottom surface of container 12 and bottom plate 16 increases. Therefore, the pressure in this area was measured, and when the measured pressure reached a predetermined pressure or higher, blockage of hole 14 was detected and a water washing operation was performed. The drying conditions and the number of water washing operations (number of water washing operations in two weeks) for invention examples 1 to 4 and the comparative example are shown in Table 1 below.

[0037] [Table 1]

[0038] As shown in Table 1, the number of water washing operations in Examples 1 to 4, in which the dried raw material placing step was carried out, was less than the number of water washing operations in Comparative Example 1, in which the dried raw material placing step was not carried out. From this result, it was confirmed that by carrying out the granular material drying method according to this embodiment, which includes the dried raw material placing step, clogging of holes 14 can be suppressed and the number of water washing operations required to clear the clogging can be reduced.

[0039] Figure 3 is a graph showing the relationship between the height of the dried raw material and the number of washing operations in the example. As shown in Figure 3, the number of washing operations decreased as the height of the dried raw material increased up to a height of 19 mm. From this result, it was confirmed that, up to a height of 19 mm, clogging of the holes 14 could be further suppressed as the height of the dried raw material increased.

[0040] On the other hand, even when the height of the dried raw material was increased from 19 mm to 26 mm, the number of water washing operations did not change. From this result, it was confirmed that the effect of suppressing clogging of holes 14 is sufficient when the height of the dried raw material is 19 mm, and that even if it is increased further, the effect of suppressing clogging of holes 14 does not change. Therefore, it was confirmed that the height of the dried raw material in the dried raw material placing step is preferably 19 mm or less, and by doing so, clogging of holes 14 can be suppressed without unnecessary placement of ammonium sulfate 26, which is the dried raw material, and the operating rate of dryer 10 can be increased. [Explanation of symbols]

[0041] 10 Dryer 12 containers 14 holes 16 Bottom plate 18 Ventilation hole 22, 25, 26, 27 Ammonium sulfate 24 Gases 30, 32 Conveyors 34 Sieving device 36, 38 sieve

Claims

1. A method for drying granular material using a dryer having a bottom plate with a plurality of holes formed therein, a dried raw material placing step of placing the dried granular material on the bottom plate; a step of introducing the granular material in a wet state onto the dried granular material; a drying step of blowing gas into the granular material through the plurality of holes to dry the granular material in a water-containing state; A method for drying granular material, comprising:

2. 2. The method for drying granular material according to claim 1, wherein the average particle size of the granular material after drying placed in the drying raw material placing step is larger than the average particle size of the granular material in a wet state.

3. 3. The method for drying granular material according to claim 2, wherein the granular material placed in the drying raw material placing step has a particle size of 1.4 mm or more after drying.

4. The method further includes a particle size separation step of classifying the granular material dried in the drying step into a plurality of particle sizes, 3. The method for drying granular material according to claim 2, wherein the granular material after drying placed in the drying raw material placing step is granular material classified in the particle size separation step.

5. The method further includes a particle size separation step of classifying the granular material dried in the drying step into a plurality of particle sizes, 4. The method for drying granular material according to claim 3, wherein the granular material after drying placed in the drying raw material placing step is granular material classified in the particle size separation step.

6. 6. The method for drying granular material according to claim 1, wherein the granular material after drying placed in the drying raw material placing step has a placement height of 6 mm or more.

7. The method for drying granular material according to any one of claims 1 to 5, wherein the granular material is ammonium sulfate crystallized from an aqueous ammonium sulfate solution.

8. 7. The method for drying granular material according to claim 6, wherein the granular material is ammonium sulfate crystallized from an aqueous solution of ammonium sulfate.

9. A method for producing ammonium sulfate using the method for drying granular material according to any one of claims 1 to 5, the particulate material is ammonium sulfate; In the water-containing raw material charging step, water-containing ammonium sulfate crystallized from an aqueous ammonium sulfate solution is charged into the dryer and dried to produce ammonium sulfate.

10. A method for producing ammonium sulfate using the method for drying granular material according to claim 6, the particulate material is ammonium sulfate; In the water-containing raw material charging step, water-containing ammonium sulfate crystallized from an aqueous ammonium sulfate solution is charged into the dryer and dried to produce ammonium sulfate.

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