JPH1025113A - Production of gypsum dihydrate from scattered ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain industrially useful gypsum dihydrate by slurring scattered ash discharged from an incinerator followed by treating the resultant slurry with sulfuric acid. SOLUTION: Scattered ash produced from an incinerator is made into a slurry with water, in advance; and the slurry is subjected to solid-liquid separation process to obtain a cake. Secondly, water is added to the cake into a slurry, and sulfuric acid is then added to the slurry to neutralize it. The respective concentrations of the above two kinds of slurry are pref. <=40wt.%. When the latter slurry is to be neutralized, the slurry is pref. brought to pH4-10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing dihydrate gypsum from exhaust gas discharged from a waste incinerator (hereinafter abbreviated to an incinerator) during waste incineration.

[0002]

2. Description of the Related Art Waste incineration is an excellent method from the viewpoint of reduction of waste volume and sanitation. More than 70% of the total waste disposal in Japan is incinerated. Have been. However, treatment of incinerated residue, that is, treatment of incineration ash, is one of the major challenges facing the country.

[0003] Japanese waste 1 supervised by the Ministry of Health and Welfare
According to 994, the amount of general waste in 1991 was about 50 million tons nationwide, of which about 36,000 tons were incinerated.

[0004] Although there is a difference in the type or capacity of the incinerator, for example, in the case of the stalker furnace, fly ash of 2 to 4% of the weight of the waste at the time of incineration is generated, and in the case of the fluidized bed furnace, about 10%. % Fly ash is said to be generated.

At present, these fly ash, together with incineration ash discharged from under the incinerator, are generally landfilled at a final disposal site. However, at the final disposal site,
In addition to the above-mentioned incinerated ash and fly ash, in some cases, non-combustible waste and the like may be landfilled, and the receiving capacity is enormous. For this reason, municipalities such as municipalities are struggling to secure land for new final disposal sites, and many local governments have determined that securing land for disposal sites is hopeless in the future. How to reduce the burden on disposal sites was a major issue for each local government.

As a measure to reduce the burden on the final disposal site, recycling of non-combustible waste such as bottles, cans, and metals has recently been promoted along with legal improvement. In addition, incineration ash has been tried to be used as civil engineering materials by treatment such as melting and elution. However, regarding fly ash, for example, Chemical Equipment, May 1995, p.
Although a melting system has been proposed, as described on page 32, it has just been developed,
A proposal for a specific effective use method is desired.

[0007]

The present inventors have conducted various studies on the effective use of fly ash. As a result, they have found that fly ash can be slurried, and sulfuric acid can be added to be used as gypsum. The present invention has been reached.

That is, according to the present invention, fly ash generated from an incinerator is previously slurried with water, the slurry is solid-liquid separated to obtain a cake, and water is again added to the cake to form a slurry. The present invention relates to a method for producing gypsum from fly ash, which is characterized by adding sulfuric acid to a slurry and neutralizing the slurry.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

[0010] The incinerator mentioned here refers to one that incinerates industrial waste, household waste and the like. Various dust collectors, such as electric dust collectors and bag filters, collect floating air generated when neutralizing acidic substances in exhaust gas discharged at this time with inorganic calcium compounds such as calcium carbonate, slaked lime, quicklime and dolomite. What is collected by such as is called fly ash. The present invention is a method of slurrying the fly ash and neutralizing the slurry with sulfuric acid.

The present inventors have focused on the Ca component contained in fly ash, and have attempted to make effective use of dihydrate gypsum using sulfuric acid.

[0012] However, fly ash has a smaller particle size than incineration ash, is light, has a scattering property and a hygroscopic property, and further contains various components. There are various fly ash as shown in the analysis examples of Table 1 depending on the incinerator.

[0013]

[Table 1] When these fly ash are used directly for building materials, for example, when used as a raw material for lightweight aggregates, Na, Mg, and Cl contents are generally 0.1% each though they vary depending on the application.
It is required that the content be reduced to about 1% by weight or less.

For example, when mixed with cement mortar, it becomes one factor causing an alkali-aggregate reaction, which undesirably leads to a decrease in crushing strength of the product.

When used for the production of gypsum board,
It is known that when Na and Mg each exceed 0.1% by weight, a whitening phenomenon occurs and problems such as bending of a gypsum board occur.

Therefore, according to the study by the present inventors, even if water is used as fly ash to remove soluble components, the Cl content is reduced to 0.1.
It is difficult to reduce the content to 5% by weight or less, and further to 0.1% by weight or less even after acid washing, a large amount of water to be dissolved is required, which is industrially difficult and economically practical. is not.

The present inventors have focused on the Ca component in fly ash, and have found a method for utilizing this Ca component. The Ca component is hydrogen chloride or S generated as exhaust gas during incineration.
The Ox component is made into calcium chloride, sulfate, sulfite, etc. by adding an inorganic calcium compound, but an excess of 2 to 3 times the theoretical equivalent amount of the inorganic calcium compound is generally used. ing.

The fly ash also contains water-soluble substances such as NaCl and MgCl _{2 which} are problematic for building materials. For this reason, water is added to fly ash to form a repulp slurry, having a slurry concentration of 5 to 40% by weight and a residence time of 0.5 to 4%.
After stirring for a time, preferably 1 to 2 hours, at a temperature of 10 to 50 ° C., solid-liquid separation is performed to obtain a treated cake.

The separation apparatus used in the present invention is not particularly limited. However, in order to wash the cake as necessary, a device provided with a device capable of washing the cake, such as a belt filter or a horizontal belt filter, is preferably used. And a centrifuge.

The obtained treated cake is again slurried by adding water in a reaction tank, and then neutralized with sulfuric acid to obtain gypsum dihydrate (CaSO ₄ .2H ₂ O). However, usually the resulting crystal shape is fine and needle-like. In order to improve this, a crystal modifier is generally used, and in the presence of gypsum as a seed crystal, it is necessary to grow the crystal to have a crystal shape with a uniform particle size. However, fly ash contains a large amount of various impurities as described above, and therefore the crystal growth of gypsum is not constant, and it is preferable to set detailed conditions for each fly ash.

According to the study of the present inventors, the conditions for crystal growth differ depending on the fly ash, but the temperature is 20 to 50.
℃, slurry concentration 40 wt% or less, pH for neutralization treatment
It is preferable to carry out the reaction within a range of 4 to 10, more preferably within a range of 5 to 9. By using a crystal growth agent under these conditions, the growth of crystals can be further promoted.

Various types of crystal growth agents are known. Among inorganic phosphates, organic substances containing phosphorus, low-molecular-weight polycarboxylates and the like, low-molecular-weight polycarboxylates containing no phosphorus are used. Use is preferred, including environmental measures.

Constituents of the low molecular weight polycarboxylate include monomers such as acrylic acid, methacrylic acid, maleic acid, itaconic acid and fumaric acid, and monomers copolymerized therewith with vinyl alcohol, vinyl ether, olefin and vinyl. Compounds having an unsaturated bond such as sulfonic acid, styrene sulfonic acid, and hydroxyethyl methacrylic acid are preferred. Of course, there is no problem to use a commercially available modifier such as a crystal modifier or a scale inhibitor, and it is more economically preferable in consideration of the price and the like. The amount of the crystal growth agent is preferably in the range of 10 to 100 ppm by weight based on the amount of gypsum to be formed. Further, the amount of the gypsum to be formed as a seed crystal using gypsum is 0.5-2.0
Double amounts are preferred.

The resulting neutralized slurry is separated by a solid-liquid separator to obtain a gypsum cake. If necessary, cake washing may be performed.

Although the separation apparatus used in the present invention is not particularly limited, the apparatus is preferably provided with equipment capable of washing cake, for example, a belt filter, a horizontal belt filter and A centrifuge is preferred.

The gypsum thus obtained is not inferior to by-products such as phosphogypsum and waste gypsum.
Even when used alone, it can be used satisfactorily.

Hereinafter, the present invention will be described in detail with reference to FIG. FIG. 1 shows a preferred embodiment for carrying out the present invention. In FIG. 1, fly ash 1 is guided to a repulp tank 2, slurried together with water 3, and guided to a solid-liquid separator 4. In the solid-liquid separator 4, if necessary, the cake is further washed with washing water 5, and the obtained cake 6 is sent to the reaction tank 7. In the reaction tank 7, the sulfuric acid 8, the crystal modifier 9 and the seed crystal 10 are supplied. Further, the slurry concentration can be adjusted to a predetermined concentration by adding water 11. The sulfuric acid 8 has a predetermined reaction temperature, prevents the generation of fine gypsum due to local reaction, and has an 80-deg.
The use of a concentration of less than or equal to% by weight is preferred.

As the seed crystal 10, there is no problem even if gypsum is newly added, but it is not a problem to take out a part of the obtained gypsum and recycle it. This is a preferred method.

After the completion of the reaction, the slurry is allowed to grow sufficiently by the addition of seed crystals, and is further led to an aging tank 12 so as to be uniform in terms of particles, and is allowed to stay there to grow the crystals. As long as the aging tank 12 and the neutralization tank 7 have a residence time of about 1 to 3 hours, there is no particular problem with one or a plurality of tanks. Needless to say, it is preferable to be independent of each other.

The gypsum slurry 13 thus formed is extracted from the aging tank 12 and sent to a solid-liquid separator 14.
Gypsum 15 is obtained. In addition, depending on the degree of purification of the gypsum, cake washing (not shown) is performed as necessary.
It is also possible to carry out.

[0031]

The present invention will be described below in detail with reference to examples. Example 1 Fly ash generated in a stalker furnace was analyzed and found to have the composition shown in Table 2.

The fly ash 1 was quantitatively guided at 100 kg / h to a repulping tank 2 having an effective volume of 1 m ³ (material: SUS-304, equipped with a stirrer) and repulped at 400 kg / h of water.
Filtration was performed with a 0.3 m ² horizontal belt filter (solid-liquid separator 4). Cake washing 5 was performed at 100 L / h. In addition, when the amount of the obtained cake and the attached moisture were measured every 50 hours, the results shown in Table 3 were obtained. further,
The cake 6 is continuously supplied to the reaction tank 7 (effective volume 1.5 m).
³ , material SUS-316L, with stirrer), pH6
-8, sulfuric acid 8 having a concentration of 40% by weight was added, and a crystal modifier 9 (sodium polyacrylate, having a molecular weight of about 40) was added.
00) was added at a rate of 20 g / h. Water 11 was added to adjust the slurry concentration in the reaction tank 7 to 25 to 30% by weight. 200 L / h of recycled slurry from aging tank 12 as seed crystal 10 (specific gravity of slurry: about 1.2)
Was supplied. The slurry in the reaction tank 7 is allowed to overflow into the aging tank 12 (effective volume 2.0 m ³ , material SUS-316L, with a stirrer) to promote crystal growth.
The generated slurry 13 is withdrawn from the aging tank 12 and solid-liquid O.D. The mixture was filtered through a 5 m ² belt filter (solid-liquid separator 14) to obtain gypsum dihydrate 15.

The crystal form of the gypsum obtained is 1 in the longitudinal direction.
It was a twin crystal with a size of 50 to 250 µ and a width of 40 to 80 µ and had uniform particles. Further, when analyzed by an X-ray diffractometer, no peak other than gypsum was observed.

The production of the above-mentioned gypsum was carried out continuously for 300 hours since there is no particular problem.

[0035]

[Table 2]

[0036]

[Table 3] Chemical analysis of the resulting gypsum obtained gave the results in Table 4. Judging from the results, it is considered that the gypsum is comparable to phosphate gypsum and excreted gypsum. Note that the analysis value is an average value of values obtained by analyzing a sample every 8 hours.

[0037]

[Table 4] Test Example 1 A cement setting test was performed using the gypsum obtained in Example 1.

The same Portland cement clinker was used as the cement clinker used in the test.
The test was performed based on R-5201.

Table 5 shows the test results. The dihydrate gypsum obtained in Example 1 gave no inferior results as compared with phosphate gypsum and waste gypsum, and was suitable for gypsum for cement. You can see that it can be used.

[0040]

[Table 5] Test Example 2 The gypsum obtained in Example 1 was fired in a gypsum test pot (firing capacity: 5 kg), and the gypsum test was performed based on JIS R-9112. Table 6 shows the test results. As is clear from Table 6, the gypsum obtained in Example 1 is a gypsum gypsum having a high tensile strength, and is not inferior to gypsum gypsum and drainage gypsum. It turns out that it can be used conveniently.

[0041]

[Table 6]

[0042]

The present invention is a method for producing industrially useful dihydrate gypsum by slurrying fly ash discharged from an incinerator and subjecting it to sulfuric acid treatment.

Conventionally, fly ash has been considered difficult to treat, and has no disposal method other than dumping and landfill at the final disposal site. It provides a method that can be reused as gypsum, which is one of the industrially important raw materials, and its industrial significance and contribution to environmental measures are great.

Further, it can be treated for building materials such as gypsum board and / or cement gypsum.

[Brief description of the drawings]

FIG. 1 is a block flow diagram illustrating an example of an apparatus suitable for implementing the present invention.

[Explanation of symbols]

 1: Fly ash 2: Repulp tank 3: Water 4: Solid-liquid separator 5: Washing water 6: Cake 7: Reaction tank 8: Sulfuric acid 9: Crystal modifier 10: Seed crystal 11: Water 12: Aging tank 13: Gypsum slurry 14: Solid-liquid separator 15: Gypsum

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 30, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

[0013]

[Table 1] When these fly ash are used directly for building materials, for example, when used as a raw material for lightweight aggregates, Na, Mg, and Cl contents are generally 0.1% each though they vary depending on the application.
It is required that the content be reduced to about 1% by weight or less.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

According to the study of the present inventors, the conditions for crystal growth differ depending on the fly ash, but the temperature is 20 to 50.
℃, slurry concentration 40 wt% or less, pH for neutralization treatment
It is preferable to carry out the reaction within a range of 4 to 10, more preferably within a range of 5 to 9. By using the crystal modifier under these conditions, the growth of crystals can be further promoted.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

Various types of crystal modifiers are known. Among the inorganic phosphates, organic substances containing phosphorus, low-molecular-weight polycarboxylates, etc., low-molecular-weight polycarboxylates containing no phosphorus Is preferred, including environmental measures.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

Constituents of the low molecular weight polycarboxylate include monomers such as acrylic acid, methacrylic acid, maleic acid, itaconic acid and fumaric acid, and monomers copolymerized therewith with vinyl alcohol, vinyl ether, olefin and vinyl. Compounds having an unsaturated bond such as sulfonic acid, styrene sulfonic acid, and hydroxyethyl methacrylic acid are preferred. Of course, there is no problem to use a commercially available modifier such as a crystal modifier or a scale inhibitor, and it is more economically preferable in consideration of the price and the like. The amount of the crystal modifier is preferably in the range of 10 to 100 ppm by weight based on the amount of gypsum to be formed. Further, the amount of the gypsum to be formed as the seed crystal using the formed gypsum 0.5 to 2.0
Double amounts are preferred.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

The fly ash 1 was quantitatively guided at 100 kg / h to a repulping tank 2 having an effective volume of 1 m ³ (material: SUS-304, equipped with a stirrer) and repulped at 400 kg / h of water.
Filtration was performed with a 0.3 m ² horizontal belt filter (solid-liquid separator 4). Cake washing 5 was performed at 100 L / h. In addition, when the amount of the obtained cake and the attached moisture were measured every 50 hours, the results shown in Table 3 were obtained. further,
The cake 6 is continuously supplied to the reaction tank 7 (effective volume 1.5 m).
³ , material SUS-316L, with stirrer), pH6
-8, sulfuric acid 8 having a concentration of 40% by weight was added, and a crystal modifier 9 (sodium polyacrylate, having a molecular weight of about 40) was added.
00) was added at a rate of 20 g / h. Water 11 was added to adjust the slurry concentration in the reaction tank 7 to 25 to 30% by weight. 200 L / h of recycled slurry from aging tank 12 as seed crystal 10 (specific gravity of slurry: about 1.2)
Was supplied. The slurry in the reaction tank 7 is allowed to overflow into the aging tank 12 (effective volume 2.0 m ³ , material SUS-316L, with a stirrer) to promote crystal growth.
The generated slurry 13 was withdrawn from the aging tank 12 and the O.D. The mixture was filtered through a 5 m ² belt filter (solid-liquid separator 14) to obtain gypsum dihydrate 15.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeki Shinozaki 7-1-1, Hikoshimasako-cho, Shimonoseki-shi, Yamaguchi Prefecture Inside Mitsui Toatsu Chemicals Co., Ltd. (72) Tomohiro Hirose 7-7 Honcho, Funabashi-shi, Chiba Address No. 1 Inside Techno Frontier Co., Ltd. (72) Inventor Kazuhiko Yu 7-7-1, Honcho, Funabashi City, Chiba Prefecture Inside Techno Frontier Co., Ltd.

Claims (3)

[Claims] 1. A fly ash generated from an incinerator is previously slurried with water, the slurry is solid-liquid separated to obtain a cake, and water is again added to the cake to form a slurry. A method for producing dihydrate gypsum from fly ash, wherein the gypsum is subjected to a neutralization treatment. 2. The method for producing gypsum dihydrate from fly ash according to claim 1, wherein the concentration of the fly ash in slurry with water and the concentration of the cake in slurry are 40% by weight or less. 3. The method for producing gypsum dihydrate from fly ash according to claim 1, wherein sulfuric acid is added to the slurry and the pH for neutralization treatment is 4 to 10.