JP7406994B2 - Method for manufacturing cement composition - Google Patents

Description

The present disclosure relates to a method for producing a sulfur-based composition and a cement composition, a system for producing a cement composition, and a cementitious solidifying material.

Cement clinker is manufactured using limestone, clay, silica, iron oxide, etc. as main raw materials. In the production of cement clinker, in addition to these main raw materials, various industrial by-products and industrial wastes are effectively used as raw materials and fuel. However, depending on the selection of raw materials, cement clinker may contain very small amounts of heavy metals such as cadmium, chromium, and lead derived from various raw materials and fuels.

Among heavy metals, hexavalent chromium, unlike other heavy metals, exists in the form of stable oxo anions such as chromate ions (CrO ₄ ^2- ), and is poorly soluble even under high pH conditions. Does not form hydroxides. For this reason, hexavalent chromium is classified as a heavy metal whose elution measures are relatively difficult. It is known that the amount of hexavalent chromium leached increases especially when volcanic ash clay soil such as Kanto loam is targeted for ground improvement.

Cement clinker or cement is sometimes used as a raw material for solidifying materials such as ground improvement materials. The amount of hexavalent chromium leached from improved soil is limited to 0.05 mg/L or less according to soil environmental standards. In Patent Document 1, a reducing gypsum composition obtained by drying a slurry containing calcium sulfite hemihydrate and dihydrate gypsum obtained in a flue gas desulfurization process is blended into a cement-based solidifying material to produce hexavalent chromium. A technology has been proposed to reduce solidified soil to trivalent chromium and render it harmless.

Japanese Patent Application Publication No. 2007-246306

Since commercially available sulfite compounds such as calcium sulfite are expensive, the use of commercially available products increases the manufacturing cost of the cement composition. On the other hand, although using a reducing gypsum composition as a cement-based solidifying material as in Patent Document 1 is effective in reducing the elution of hexavalent chromium from solidified soil, It is necessary to produce.

Therefore, the present disclosure provides a manufacturing method that can easily and stably manufacture a sulfur-based composition that has a reducing effect that is effective in reducing the elution of hexavalent chromium. The present invention also provides a method and system for producing a cement composition using this method for producing a sulfur-based composition. The present invention also provides a cement-based solidifying material that can reduce the elution of hexavalent chromium.

A method for manufacturing a sulfur-based composition according to one aspect of the present disclosure includes a manufacturing process of generating a gas containing sulfur dioxide gas and/or hydrogen sulfide, and a step of absorbing sulfur dioxide gas and/or hydrogen sulfide contained in the gas into a raw material slurry. A slurry preparation step of obtaining a slurry containing a sulfur-based compound, and adding a total of 0.01 to 10 mass of glycol-based compounds to the raw material slurry and/or the slurry containing a sulfur-based compound, based on the solid content contained in the raw material slurry. % addition step, and a slurry concentration adjustment step of adjusting the solid content concentration of the slurry containing the sulfur-based compound to 0.1 to 95% by mass.

In the above manufacturing method, a slurry (sulfur-based composition) containing a sulfur-based compound effective in reducing the elution of hexavalent chromium is obtained using sulfur dioxide gas and/or hydrogen sulfide contained in the gas. Here, when the sulfur-based composition is oxidized, its ability to reduce hexavalent chromium may decrease. Since the above manufacturing method includes the addition step of adding a predetermined amount of the glycol compound to the raw material slurry and/or the slurry containing the sulfur compound, oxidation of the sulfur compound can be suppressed. Thereby, a sulfur-based composition having the ability to reduce hexavalent chromium can be easily and stably produced. Note that the sulfur-based composition in the present disclosure may be in the form of a slurry or in a solid form such as a powder.

A method for producing a cement composition according to one aspect of the present disclosure provides a method for producing a cement composition, which includes a step of obtaining a cement composition using a sulfur-based composition obtained by the above-described production method and a cement clinker. do.

The above-mentioned sulfur-based composition is used in the method for producing the cement composition. With the above manufacturing method, a cement composition capable of reducing the elution of hexavalent chromium can be easily and stably manufactured.

A system for manufacturing a cement composition according to one aspect of the present disclosure includes a cement clinker firing section for firing raw materials to obtain cement clinker, and converting sulfur dioxide gas and/or hydrogen sulfide contained in exhaust gas from the cement clinker firing section into a raw material slurry. a slurry preparation section for obtaining a slurry containing a sulfur-based compound; and a pulverization section for obtaining a cement composition by pulverizing a mixture containing a cement clinker and a slurry containing a sulfur-based compound. The slurry preparation section includes an addition section that adds a total of 0.01 to 10% by mass of a glycol compound to the raw material slurry and/or the slurry containing a sulfur compound, based on the solid content contained in the raw material slurry. , and a slurry concentration adjustment section that adjusts the solid content concentration of the slurry to 0.1 to 95% by mass.

The above manufacturing system includes a slurry preparation section that uses sulfur dioxide gas and/or hydrogen sulfide contained in the gas to obtain a slurry containing a sulfur-based compound effective in reducing elution of hexavalent chromium. The slurry preparation section includes an addition section that adds a predetermined amount of the glycol compound to the raw material slurry and/or the slurry containing the sulfur compound. Therefore, oxidation of sulfur-based compounds can be suppressed. Thereby, a cement composition capable of reducing the elution of hexavalent chromium can be easily and stably produced.

A cementitious solidifying material according to one aspect of the present disclosure includes cement particles and particles containing a sulfur-based composition, the sulfur-based composition contains a sulfite compound, and the particles containing the sulfur-based composition include: It includes a core part containing a sulfite compound, and a covering part that covers at least a part of the surface of the core part and contains a glycol compound. Since this cement-based solidifying material includes a coating portion containing a glycol compound that covers a core portion containing a sulfite compound, oxidation of the sulfite compound can be suppressed. Therefore, the cement-based solidifying material of the present disclosure can reduce the elution of hexavalent chromium.

According to the present disclosure, it is possible to provide a manufacturing method that can easily and stably manufacture a sulfur-based composition that has a reducing effect that is effective in reducing the elution of hexavalent chromium. Furthermore, it is possible to provide a method and system for producing a cement composition using this method for producing a sulfur-based composition. Further, it is possible to provide a cement-based solidifying material that can reduce the elution of hexavalent chromium.

FIG. 1 is a diagram showing a cement composition manufacturing system according to one embodiment. It is a figure showing the manufacturing system of the cement composition concerning another embodiment.

Hereinafter, one embodiment of the present disclosure will be described with reference to the drawings as the case may be. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents. In the description, the same reference numerals will be used for the same elements or elements having the same function, and redundant description will be omitted in some cases. Further, the dimensional ratio of each element is not limited to the ratio shown in the drawings.

<First embodiment of method for producing sulfur-based composition and cement composition>
A method for producing a sulfur-based composition according to an embodiment of the present disclosure includes a production process of producing a sulfur-containing gas containing sulfur dioxide gas and/or hydrogen sulfide, and a production process of producing a sulfur-containing gas containing sulfur dioxide gas and/or hydrogen sulfide. A slurry preparation process to obtain a slurry containing sulfur-based compounds (hereinafter sometimes referred to as "sulfite slurry") by absorption into the raw material slurry, and a slurry preparation process in which the raw material slurry and/or the sulfite slurry are mixed based on the solid content contained in the raw material slurry. The method includes an addition step of adding a total of 0.01 to 10% by mass of glycol compounds, and a slurry concentration adjustment step of adjusting the solid content concentration of the slurry containing the sulfur compound to 0.1 to 95% by mass.

Examples of sulfur-containing gases in the manufacturing process include exhaust gas containing sulfur dioxide gas generated from kilns that burn cement clinker and magnesia clinker, exhaust gas containing sulfur dioxide gas generated from thermal power generation facilities or smelting factories for ferrous and non-ferrous metals, and sulfur gas. Combustion gas containing high concentration of sulfur dioxide obtained by combustion, gas containing sulfur dioxide obtained by heating and decomposing waste containing sulfur such as waste gypsum board, etc. can be used. Two or more of these gases can also be used in appropriate combination. By using such a gas, a sulfur-based composition can be produced at low cost. Sulfur-containing gas includes gas containing sulfur dioxide and/or hydrogen sulfide generated by heating sulfur-containing waste such as waste gypsum board at 500 to 1400°C, and gas containing sulfur dioxide and/or hydrogen sulfide, which is generated by decomposing the above-mentioned sulfur-containing waste using microorganisms. It may also be a gas (decomposed gas) containing sulfur dioxide gas and/or hydrogen sulfide produced by this process.

The sulfur-containing gas may include exhaust gas at a temperature of 700 to 1200° C. extracted from the bottom of the cement kiln between the calciner. It is preferable that the exhaust gas contacts the raw material slurry at a temperature of 400° C. or lower. For example, before the slurry preparation step, there may be a cooling step of cooling the exhaust gas to 400° C. or lower, preferably 300° C. or lower, and more preferably 200° C. or lower. Thereby, sulfite compounds can be efficiently obtained from exhaust gas having a high sulfur concentration.

The SO ₂ concentration (by volume) of the sulfur-containing gas is preferably 500 ppm to 20%. Thereby, a sufficient amount of sulfur-based compounds can be obtained from the sulfur-containing gas. Further, the SO ₂ concentration of the sulfur-containing gas may be controlled to 500 ppm to 20% by adjusting the sulfur content of the raw material or fuel. Thereby, the SO ₂ concentration of the sulfur-containing gas can be controlled in a simple manner. The raw material may contain a sulfur-containing raw material containing at least one selected from the group consisting of waste gypsum board, waste tires, and desulfurization slag, or may burn sulfur as a fuel. Note that the SO ₂ concentration of exhaust gas in the present disclosure is a volume-based value.

In the slurry preparation step, the sulfur-containing gas generated in the manufacturing step is absorbed into the raw material slurry to obtain a slurry containing sulfur-based compounds. The slurry containing the sulfur-based compound contains, as a solid content, at least one selected from the group consisting of calcium sulfite hemihydrate, calcium bisulfite (Ca(HSO ₃ ) ₂ ), and a double salt of calcium sulfite and calcium sulfate. It may include one type of sulfite compound and sulfur-based compounds such as calcium sulfate dihydrate, calcium sulfide, and calcium polysulfide.

The raw material slurry preferably contains at least one salt selected from the group consisting of calcium hydroxide, calcium carbonate, and magnesium hydroxide. By containing such components, it is possible to produce a cement composition that can further reduce the elution of hexavalent chromium. From the same viewpoint, the slurry containing the sulfur-based compound preferably contains a double salt of calcium sulfite and calcium sulfate.

The manufacturing process may be a cement clinker manufacturing process for manufacturing cement clinker. The raw material slurry contains an inorganic powder containing a calcium compound generated in the cement clinker manufacturing process, and preferably contains 10 to 98% by mass of the calcium compound as CaO based on the entire inorganic powder. This makes it possible to easily prepare a slurry containing a sulfite compound. Moreover, the manufacturing cost of the cement composition can be sufficiently reduced.

The manufacturing method of this embodiment uses fine powder mainly composed of CaCO ₃ generated when clinker raw materials are crushed, dust particles containing CaO and/or Ca(OH) ₂ generated in the chlorine bypass section, and dust particles. A raw material slurry is prepared using one or more selected from the group consisting of washed dust particles obtained by washing with water, and sludge containing cement and/or cement hydrate (for example, ready-mixed concrete sludge obtained at a ready-mixed concrete factory). It is preferable to have a raw material slurry preparation step of preparing a raw material slurry. Thereby, the manufacturing cost of the cement composition can be sufficiently reduced. From the viewpoint of stabilizing the operation in the slurry preparation process, the solid content concentration of the raw material slurry is, for example, preferably 0.1 to 50% by mass, more preferably 0.5 to 30% by mass, and even more preferably 1 to 20% by mass. Preferably, 3.0 to 15% by weight is most preferred.

In the addition step, 0.01 to 10% by mass of a glycol compound is added to the raw material slurry and/or the slurry containing a sulfur compound obtained in the slurry preparation step, based on the solid content contained in the raw material slurry. . When the glycol compound is added to both the raw material slurry and the slurry containing the sulfur compound, the total amount of each added amount is within the above numerical range. By adding a glycol compound, it is possible not only to delay agglomeration of fine powder during pulverization and promote pulverization, but also to prevent oxidation of fine particles of a sulfur compound having a reducing effect. From this point of view, the amount of glycol compounds added may be 0.05 to 5% by mass in total, or even 0.1 to 3% by mass, based on the solid content contained in the raw material slurry. good.

When adding an organic compound other than a glycol compound, the amount of the organic compound including the glycol compound may be 0.01 to 15% by mass based on the solid content in the raw material slurry.

The glycol compound preferably contains at least one selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, and glycerin. By using such glycol-based compounds, it is possible to reduce the amount of electricity required for pulverization when manufacturing cement compositions, increase the strength of cement compositions, and improve the powder fluidity of dry powder using sulfur-based compounds. Can be done. The glycol compound may be obtained from waste coolant or waste liquid or residue obtained in a recycling and decomposition process of waste PET bottles. The addition step of adding the glycol compound may be performed by blending a composition such as waste liquid containing the glycol compound into the raw material slurry or the slurry containing the sulfur compound.

In the addition step, the glycol compound may be added to either the slurry containing the sulfur compound or the raw material slurry, or the glycol compound may be added to both the slurry containing the sulfur compound and the raw material slurry. good. From the viewpoint of sufficiently suppressing oxidation of the sulfur-based compound, the glycol-based compound may be added to the raw material slurry.

The manufacturing method of this embodiment adds a flocculant to the slurry containing sulfur-based compounds obtained in the slurry preparation process, from the viewpoint of promoting precipitation of fine sulfur-based compounds contained in the slurry and quickly reducing the water content. It may have a mixing step of mixing. This facilitates coagulation and precipitation of the sulfur-based compounds, allowing smooth and rapid handling of the slurry and adjustment of the water content. The flocculant preferably contains at least one selected from the group consisting of an aluminum-based flocculant, an iron-based flocculant, and a polymer flocculant.

The manufacturing method of this embodiment includes a slurry concentration adjustment step of adjusting the solid content concentration of the slurry containing a sulfur-based compound obtained in the slurry preparation step. In the slurry concentration adjustment step, the solid content concentration of the slurry is adjusted to 0.1 to 95% by mass. As a result, it is possible to maintain good handling properties of the slurry, and an appropriate amount of water is mixed into the cement clinker, so that pulverization can be made smooth. In addition, excessive conversion of gypsum contained in the cement composition into hemihydrate gypsum is suppressed, and a cement composition can be produced that has excellent fluidity and strength development and is difficult to solidify even when stored for a long period of time.

In the slurry concentration adjustment step, from the viewpoint of suppressing clogging of the slurry and stabilizing operation, the solid content concentration of the slurry containing sulfur compounds is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass. It is preferably 3 to 28% by weight, more preferably 10 to 25% by weight. In addition, from the viewpoint of preventing oxidation of sulfur-based compounds (preventing gypsum formation), the pH of the slurry is preferably adjusted to 4 to 8, more preferably 4 to 7, and even more preferably 5.0 to 6.5. 5.5 to 6.0 is most preferred. It is preferable to include a pH adjustment step of adjusting the pH of the slurry while monitoring the scaling situation and the oxidation degree (gypsumization degree) of the sulfur-based compound.

The solid content concentration of the slurry may be adjusted based on at least one of the temperature of the cement clinker obtained in the cement clinker manufacturing process, the temperature of the cement composition at the exit of the cement mill, and the loss on ignition of the cement composition. . Thereby, a cement composition with reduced variation in properties can be stably produced.

In the slurry concentration adjustment step, the solid content concentration may be adjusted by precipitating sulfur-based compounds and removing supernatant water, or by performing filtration or centrifugation. The water concentration of the slurry containing the sulfur-based compound is reduced to 60% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. At this time, the solid content concentration of the slurry containing the sulfur-based compound can be increased to 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more. By adding the above-mentioned flocculant, the precipitation rate of the sulfur-based compound is increased, and supernatant water can be easily removed and centrifuged in a shorter time, so that the water content can be stably and efficiently reduced.

In the slurry preparation step, it is preferable to obtain a sulfite slurry containing calcium sulfite by treating at least a portion of the exhaust gas generated in the cement clinker manufacturing step using a lime-gypsum method. In addition, we heat and decompose exhaust gas containing sulfur dioxide gas generated from thermal power plants and ferrous and non-ferrous metal smelting plants, highly concentrated sulfur dioxide gas obtained by burning sulfur, and waste containing sulfur such as waste gypsum board. Gases containing sulfur dioxide gas obtained by the above methods can be used, and these exhaust gases can also be used in appropriate combinations. By these methods, a slurry containing calcium sulfite can be obtained through a simple process.

In the slurry preparation process, sulfur dioxide gas and hydrogen sulfide are absorbed into an aqueous solution containing an alkaline earth metal and/or alkali metal salt different from Ca, and then a calcium compound is mixed to obtain a slurry containing calcium sulfite. You can. Thereby, the influence of scaling due to calcium sulfite can be further reduced and the stability of the process can be improved.

The exhaust gas obtained in the slurry preparation step after at least a portion of the sulfur-containing gas such as sulfur dioxide gas has been absorbed may be introduced into the cement kiln. This makes it possible to detoxify harmful substances contained in the exhaust gas and to effectively utilize the exhaust gas, thereby reducing the manufacturing cost of the cement composition (cement solidifying material). Furthermore, the release of NOx and the like can be further reduced.

The manufacturing method of this embodiment may include a drying step of drying the slurry to obtain dry powder. In the drying step, the water in the slurry containing the sulfur-based compound containing water is reduced or removed to obtain a dry powder of the sulfur-based compound in which the water content is reduced to, for example, less than 5% by mass, preferably less than 3% by mass. . The heating temperature of the sulfite slurry in the drying step is, for example, 180°C or lower, preferably 150°C or lower, and more preferably 120°C or lower. Thereby, it is possible to suppress volatilization of glycol compounds and to sufficiently suppress oxidation of sulfite compounds contained in the dry powder.

By including the dry powdering step, it becomes possible to more easily produce a sulfur-based composition and a cement composition or a cement-based solidifying material containing the same by just a mixing operation without going through a pulverization step. Also, long-distance transportation allows production of cement compositions at locations other than cement factories. In addition, sulfur-based compounds are used for purposes other than cement compositions, such as neutralizing acidic wastewater generated in mining wastewater and the steel industry, and as reducing materials for reducing harmful substances contained in soil and water. can do.

The drying may be performed by drying the slurry with reduced water content while stirring in a vacuum dryer. This makes it possible to produce dry powder with an appropriate particle size. The dry powder may be added to and mixed with a pulverized product containing cement clinker and gypsum to obtain a cement composition or a cement-based solidifying material. By drying it, it becomes possible to transport it over long distances and mix it in a mixer, making it easier to manufacture cement compositions, reducing agents, cement-based solidifying materials, and the like.

A method for producing a cement composition according to one embodiment includes, after the above-described method for producing a sulfur-based composition, a step of obtaining a cement composition or a cement-based solidifying material using a sulfur-based composition and a cement clinker. For example, a pulverization step is performed to obtain a cement composition or a cementitious solidifying material. That is, in the pulverization step, a cement composition or a cementitious solidifying material is obtained by pulverizing a mixture containing a cement clinker and a slurry containing a sulfur-based compound. In this way, since the sulfur-based compounds effective in reducing the elution of hexavalent chromium are obtained from the sulfur-containing gas, it is possible to easily produce a cement composition or a cement-based solidifying material that is effective in reducing the elution of hexavalent chromium. be able to. In the pulverization step, it is preferable to mix gypsum to obtain a cement composition or a cement-based solidifying material. This makes it possible to easily adjust the composition of the cement composition or cement-based solidifying material.

When the cement composition (cement solidifying material) is 100 parts by mass, the cement clinker contains 0.1 to 20 parts of the slurry in terms of anhydride of reducing sulfur compounds (for example, sulfite compounds and sulfides). It is preferable to mix parts by mass. Thereby, the pulverization can be performed sufficiently smoothly while maintaining the elution of hexavalent chromium at a sufficiently low level.

<First embodiment of cement composition manufacturing system>
A cement composition manufacturing system according to one embodiment includes a cement clinker firing section that burns raw materials to obtain cement clinker, and a raw material slurry that absorbs sulfur dioxide gas and/or hydrogen sulfide contained in exhaust gas from the cement clinker firing section. The present invention includes a slurry preparation section for obtaining a slurry containing a sulfur-based compound, and a pulverization section for obtaining a cement composition by pulverizing a mixture containing cement clinker and slurry.

In the above production system, for example, a slurry containing a sulfur-based compound is obtained from gas generated when producing cement clinker from raw materials and raw material slurry. Then, a mixture containing cement clinker and this slurry is pulverized to obtain a cement composition. In this way, the sulfur-based compounds that are effective in reducing the elution of hexavalent chromium are obtained from the exhaust gas generated in the cement clinker firing section, making it possible to easily and inexpensively produce cement compositions that are effective in reducing the elution of hexavalent chromium. can be manufactured.

From the viewpoint of stably absorbing sulfur dioxide gas and/or hydrogen sulfide contained in exhaust gas, the solid content concentration of the raw material slurry used in the slurry preparation section is preferably 0.1 to 50% by mass, and 0.5 to 30% by mass. It is more preferably 1 to 20% by weight, most preferably 3.0 to 15% by weight.

The above manufacturing system includes a slurry concentration adjustment section that adjusts the solid content concentration of the slurry obtained in the slurry preparation section. In the slurry concentration adjusting section, the water content is adjusted to 60% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. At this time, the solid content concentration of the slurry can be increased to 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more. As a result, it is possible to maintain good handling properties of the slurry, and an appropriate amount of water is mixed into the cement clinker, so that pulverization can be made smooth. In addition, this prevents the gypsum contained in the cement composition from becoming excessively hemihydrated gypsum, producing a cement composition that has excellent fluidity and strength development and is difficult to solidify even when stored for a long period of time. can.

The slurry consists of calcium sulfite hemihydrate, calcium bisulfite (Ca(HSO ₃ ) ₂ ), double salt of calcium sulfite and calcium sulfate, calcium sulfide, and calcium polysulfide as solid contents. It is preferable to contain at least one sulfur-based compound selected from the group consisting of a dihydrate of calcium sulfate, calcium hydroxide, calcium carbonate, and at least one salt selected from the group consisting of magnesium hydroxide. By containing such components, it is possible to produce a cement composition that can further reduce the elution of hexavalent chromium. From the same viewpoint, the slurry preferably contains a double salt of calcium sulfite and calcium sulfate.

The slurry preparation section absorbs sulfur dioxide gas and/or hydrogen sulfide into an aqueous solution containing a salt of an alkaline earth metal and/or an alkali metal different from Ca to obtain a sulfite compound different from calcium sulfite. It is preferable to mix the compound and the calcium compound to obtain a slurry containing calcium sulfite (a sulfur-based compound having Ca as a constituent element). Thereby, the influence of scaling due to calcium sulfite can be reduced and the stability of the manufacturing system can be improved.

The slurry preparation section washes with water fine powder mainly composed of CaCO ₃ that is generated when the raw material is crushed, dust particles containing CaO and/or Ca(OH) ₂ that are generated in the chlorine bypass section, and dust particles. It is preferable to include a raw material slurry preparation section that prepares a raw material slurry using at least one selected from the group consisting of water-washed dust particles obtained by washing, and sludge containing cement and/or cement hydrate. Thereby, the manufacturing cost of the cement composition can be sufficiently reduced.

Preferably, the manufacturing system includes a first control unit that adjusts the sulfur content in the raw material and controls the SO ₂ concentration of the exhaust gas to 500 to 20,000 ppm. This makes it possible to obtain a sufficient amount of sulfite compounds from the exhaust gas.

The manufacturing system includes a second control that controls the solid content concentration of the slurry based on at least one of the temperature of the cement clinker obtained in the cement clinker firing section, the exit temperature of the cement mill, and the ignition loss of the cement composition. It is preferable to include a section. Thereby, a cement composition with reduced variation in properties can be stably produced.

In the above manufacturing system, it is preferable that the exhaust gas includes gas extracted between the kiln bottom of the cement kiln and the calciner, and that the exhaust gas includes a cooling unit that cools the exhaust gas to 400° C. or lower. Thereby, sulfite compounds can be efficiently obtained from exhaust gas having a high sulfur concentration.

Preferably, the manufacturing system includes a flow path that introduces the exhaust gas obtained in the slurry preparation section, after at least a portion of the sulfur dioxide gas has been absorbed, into the cement kiln. This makes it possible to effectively utilize waste heat and reduce the manufacturing cost of the cement composition. Furthermore, the release of NOx and the like can be further reduced.

The above manufacturing system may obtain sulfur dioxide gas in a heating section different from the cement clinker firing section. That is, the exhaust gases containing sulfur dioxide gas obtained from the cement clinker firing section and the heating section different therefrom may be introduced into the slurry preparation section together or individually.

The slurry preparation section includes an addition section that adds a glycol compound to the slurry containing the sulfur compound and/or the raw material slurry. The amount of the glycol compound added is 0.01 to 10% by mass based on the solid content contained in the raw material slurry. When a glycol-based compound is added to both the slurry and the raw material slurry, the total amount of each addition is within the above numerical range. By adding a glycol compound, it is possible not only to delay agglomeration of fine powder during pulverization and promote pulverization, but also to prevent oxidation of fine particles of a sulfur compound having a reducing effect. From the viewpoint of suppressing oxidation of fine particles of sulfur-based compounds and reducing manufacturing costs, the amount of glycol-based compounds added may be 0.05 to 5% by mass in total, based on the solid content contained in the raw material slurry, and may be 0. It may be .1 to 3% by mass. The types of glycol-based compounds that can be added and the route for obtaining them are as described in the first embodiment of the method for producing the sulfur-based composition and cement composition described above. The addition section may be configured to add the glycol compound to the raw material slurry before absorbing sulfur dioxide gas, or may be configured to add the glycol compound to the slurry containing the sulfur compound. may have been done.

The above manufacturing system may include a mixing section for adding a flocculant to the slurry containing the sulfur-based compound in the slurry preparation section. By adding a flocculant, the precipitation of fine sulfur-based compounds contained in the slurry can be promoted, and the water content can be quickly reduced. The types of flocculants that can be added are as described in the first embodiment of the method for producing the sulfur-based composition and cement composition described above.

The slurry preparation section includes a slurry concentration adjustment section that adjusts the water content of the slurry containing the sulfur-based compound. The slurry concentration adjustment section reduces the water content to 60% by mass or less, preferably 50% by mass or less, more preferably 40% by mass or less, by precipitating sulfur-based compounds and removing supernatant water, or by performing filtration or centrifugation. It may be configured to reduce the amount. Thereby, the solid content concentration of the slurry containing the sulfur-based compound can be increased to 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more. Adding a flocculant increases the precipitation rate of sulfur-based compounds, making it easier to remove supernatant water and centrifugation in a shorter time, making it possible to stably and efficiently reduce the water content from slurry. .

The slurry preparation section may include a drying section that dries the slurry to obtain dry powder containing a sulfur-based compound. The drying section may be configured to, for example, dry the slurry with reduced water content while stirring it using a vacuum dryer, thereby producing dry powder with an appropriate particle size. This makes it possible to transport it over long distances or mix it with other powders in a mixer, making it easier to manufacture cement compositions and reducing agents.

The cement composition obtained by the production system of this embodiment contains a sulfur-based compound that has a reducing effect effective in reducing the elution of hexavalent chromium, and therefore can be suitably used as a cement-based solidifying material. That is, the above-described cement composition manufacturing system may be a cement-based solidifying material manufacturing system. In this case, "cement composition" in the above description may be read as "cement solidifying material". Furthermore, a cement solidifying material may be prepared by blending gypsum, slag, etc. into the cement composition obtained by the above-described cement composition manufacturing system.

<Second embodiment of method for producing sulfur-based composition and cement composition>
The method for producing a cement composition according to the present embodiment includes a cement clinker production process in which cement clinker is produced by firing raw materials containing sulfur, and sulfur dioxide gas and/or sulfide contained in exhaust gas generated in the cement clinker production process. A slurry preparation step in which a slurry containing a sulfur-based compound is obtained by absorbing hydrogen into the raw material slurry; an addition step in which a glycol-based compound is added to the raw material slurry and/or a slurry containing a sulfur-based compound; A mixing step of adding a flocculant to a slurry containing a compound, a slurry concentration adjustment step of adjusting the solid content concentration of the slurry containing a sulfur-based compound to 0.1 to 95% by mass, and a slurry containing a cement clinker and a sulfur-based compound. and a grinding step to obtain a cement composition. As an example, in the pulverization step, a cement composition may be obtained by blending gypsum with a slurry containing a cement clinker and a sulfur-based compound, and then pulverizing the mixture containing these. As another example, in the pulverization step, the slurry containing cement clinker and a sulfur-based compound and gypsum may be blended and pulverized at the same time. As yet another example, in the pulverization step, after pulverizing the cement clinker to some extent, a slurry containing a sulfur-based compound and gypsum may be blended, and the resulting mixture may be further pulverized.

Examples of raw materials include sulfur-containing raw materials and clinker raw materials. However, it is not essential to use a sulfur-containing raw material, and the fuel may contain sulfur. A slurry containing a sulfite compound as a sulfur compound (hereinafter sometimes referred to as "sulfite slurry") contains, for example, calcium sulfite as the sulfite compound. For example, a cement clinker production process that uses raw fuel containing sulfur to produce cement clinker generates exhaust gas containing sulfur dioxide gas. By bringing this exhaust gas into contact with the raw material slurry, sulfite slurry can be efficiently produced. In particular, the gas between the bottom of the cement kiln and the calciner contains a lot of sulfur oxides, so if the exhaust gas from this period is used, it is possible to produce sulfite slurry containing a lot of sulfite compounds with a sufficiently high efficiency. be able to. Note that "between the kiln bottom and the calcination furnace" in the present disclosure includes the kiln bottom, the calcination furnace, and the space between these.

When a chlorine bypass section is installed as equipment for extracting exhaust gas from the kiln bottom of the cement kiln section to the calcining furnace, the exhaust gas may be obtained by extracting the gas from the chlorine bypass section. Alternatively, it may be obtained by extracting exhaust gas from the bottom of a cement kiln. Since such exhaust gas has a high temperature (for example, 500 to 1400°C), a cooling step may be included in which the exhaust gas is cooled to 400°C or lower. By bringing such exhaust gas into contact with the raw material slurry, a sulfite slurry can be efficiently prepared. A sulfite slurry may be obtained by a lime-gypsum method using a slurry containing lime as the raw material slurry.

The manufacturing method of the present embodiment combines a raw material slurry with water, fine particle powder mainly composed of _CaCO3 generated when crushing a clinker raw material, and CaO and/or Ca(OH) ₂ generated in a chlorine bypass section. A raw material slurry prepared using one or more selected from the group consisting of dust particles containing dust particles, washed dust particles obtained by washing the dust particles with water, and sludge containing cement and/or cement hydrate. It may have a preparation step. The raw material slurry preferably contains 10 to 98% by mass of the calcium compound as CaO based on the entire inorganic powder containing the calcium compound.

Examples of the sulfite compounds contained in the sulfite slurry include calcium sulfite (for example, hemihydrate), calcium bisulfite (Ca(HSO ₃ ) ₂ ), a double salt of calcium sulfite and calcium sulfate, and magnesium sulfite. The content of sulfite compounds (anhydride equivalent) in the sulfite slurry is preferably 5% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, especially Preferably it is 70% by mass or more.

The sulfite slurry may contain components other than sulfite compounds. Such components include calcium hydroxide, calcium carbonate, magnesium hydroxide, calcium sulfate, and the like. It may contain at least one of these components. Calcium sulfate may include any of a dihydrate (dihydrate gypsum), a hemihydrate (hemihydrate gypsum), and an anhydride (anhydrite).

When the sulfite slurry contains an appropriate amount of calcium sulfate, the addition of gypsum in the grinding process can be reduced or omitted. The content of calcium sulfate dihydrate in the sulfite slurry is, for example, 30% by mass or less based on the total solid content. From the viewpoint of producing a sulfite slurry containing each of the above-mentioned components in a suitable range, the pH thereof is preferably 4 to 8, more preferably 4 to 7, even more preferably 5.0 to 6.5, and 5.5. ~6.0 is most preferred.

In the slurry concentration adjustment step, the water content of the sulfite slurry is reduced to 60% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. At this time, the solid content concentration of the slurry containing the sulfur-based compound can be increased to 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more. Within this range, the sulfite slurry and cement clinker can be mixed sufficiently uniformly while maintaining the ease of handling the sulfite slurry at a high level.

The solid content concentration of the slurry is determined by the temperature Tr of the cement clinker obtained in the cement clinker manufacturing process, the temperature of the cement composition at the exit of the cement mill (Tm, 40 to 140°C), and the ignition loss (Ig, ig.loss) (slurry concentration adjustment step). This makes it possible to control the temperature during grinding in a cement mill within a suitable range (40 to 140°C) and produce a cement composition with stable quality while reducing the amount of water sprayed in the cement mill. can.

The desulfurization gas obtained in the slurry preparation process, after at least a portion of the sulfur dioxide gas has been absorbed into the sulfur dioxide slurry, may be introduced into the cement kiln via the cooler section, preheater section, calciner, etc. of the cement clinker. good. This makes it possible to recover the sulfur dioxide gas that has not been absorbed into the sulfur dioxide slurry again as exhaust gas, making it possible to effectively utilize the sulfur content. Moreover, by performing heat recovery, the manufacturing cost of the cement composition can be reduced. Further, when the exhaust gas contains a trace amount of NOx (nitrogen oxides), the amount of NOx released can be further reduced.

In the addition step, for example, a glycol compound is added to the raw material slurry and/or the sulfite slurry. In the mixing step, for example, a flocculant is added to the sulfite slurry. As the flocculant and the organic compound, those listed in the first embodiment can be used.

The cement clinker obtained in the cement clinker production process is not particularly limited in its type, and may be any of the various Portland cements specified in JIS R 5210:2003 "Portland cement". According to the cement composition of this embodiment, the elution of hexavalent chromium can be sufficiently suppressed. The total chromium content of the cement clinker may be, for example, 20 mg/kg to 250 mg/kg, 80 mg/kg to 200 mg/kg, or 100 to 150 mg/kg. The amount of water-soluble hexavalent chromium in the cement clinker measured according to the method described in the Cement Association Standard Test Method JCAS I-53-2018 may be, for example, 3 to 40 mg/kg, or 10 to 40 mg/kg. kg, or 20 to 30 mg/kg.

The cement composition manufactured by the manufacturing method of this embodiment can be made into Portland cement specified in JIS R 5210 "Portland cement". Examples of such Portland cement include ordinary Portland cement, early strength Portland cement, moderate heat Portland cement, and low heat Portland cement. Furthermore, at least one selected from blast furnace slag, fly ash, and siliceous material may be added to these Portland cements to form a mixed cement.

In the pulverization step, cement clinker, sulfite slurry and, if necessary, gypsum may be blended and pulverized to obtain a cement composition. The gypsum to be mixed may be in the form of dihydrate gypsum, hemihydrate gypsum, or anhydrite gypsum. Each type of gypsum may be blended singly or in combination of multiple types. The order of blending cement clinker, sulfite slurry, and gypsum is not particularly limited, and two of these may be blended first and then the remaining one, or the three may be blended at the same time. . The amount of gypsum to be blended may be about 3 to 10% by mass based on SO ₃ based on the cement clinker. Gypsum may be prepared by oxidizing and dehydrating a portion of a sulfite slurry.

The pulverization in the pulverization step may be performed with a finishing mill such as a ball mill or a vertical mill. A cement composition is manufactured by putting cement clinker, sulfite slurry, gypsum, grinding aid, etc. into the finishing mill and mixing them while grinding. The cement composition thus obtained contains a sulfite compound. Therefore, the content of hexavalent chromium in the cement composition can be reduced. The content of the sulfite compound in the cement composition is, for example, preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass.

The Blaine specific surface area of the cement composition obtained by pulverization is preferably 2,500 to 6,000 cm ² /g, more preferably 3,000 to 5,000 cm ² /g. If the Blaine specific surface area is 2500 cm ² /g or more, it will be easier to achieve excellent strength development. On the other hand, if the Blaine specific surface area is 6000 cm ² /g or less, the viscosity can be easily controlled within a suitable range when used as a concrete or cement-based solidifying material slurry.

The form of gypsum contained in the cement composition is preferably dihydrate gypsum or anhydrite (type II). Among the gypsum contained in the cement composition, the proportion of gypsum hemihydrate may be 98% by mass or less, and preferably 0.1 to 95% by mass, based on the total amount of gypsum dihydrate and anhydrite. It is more preferably 5 to 85% by mass, and even more preferably 10 to 30% by mass.

The raw material slurry may be prepared by recovering inorganic compounds generated during the cement clinker manufacturing process. Examples of such inorganic compounds include fine particle powder mainly composed of CaCO ₃ generated when clinker raw materials are crushed, dust particles containing CaO and/or Ca(OH) _{2 generated in the chlorine bypass section, and dust particles containing CaO and/or Ca(OH) 2} generated in the chlorine bypass section. Examples include water-washed dust particles obtained by washing particles with water. The raw material slurry may be prepared by adding sludge containing cement and/or cement hydrate. Examples of the sludge include ready-mixed concrete sludge obtained at a ready-mixed concrete factory.

The raw material slurry may contain an inorganic powder containing a calcium compound. It is preferable that the calcium compound is contained in an amount of 10 to 98% by mass as CaO based on the entire inorganic powder contained in the raw material slurry. Thereby, sulfur dioxide gas can be sufficiently absorbed in the slurry preparation process. Examples of calcium compounds include calcium carbonate and lime (slaked lime and quicklime).

The SO ₂ concentration (Sg) of the exhaust gas is preferably 500 to 20,000 ppm, more preferably 1,000 to 15,000 ppm, and still more preferably 2,000 to 10,000 ppm. This makes it possible to obtain a sufficient amount of sulfite compounds from the exhaust gas while maintaining process stability. The SO ₂ concentration (Sg) of the exhaust gas may be controlled by changing the amount of sulfur-containing raw material used to adjust the sulfur content of the raw material. Sulfur-containing raw materials include waste gypsum board, waste tires, desulfurization slag, gypsum, cokes, sulfur-containing wastes, sulfur-containing by-products, and the like. The SO ₂ concentration of the exhaust gas may be controlled by adjusting the ratio of the sulfur-containing raw material to the total raw material. Note that in this embodiment, the waste gypsum board may include paper adhering to the surface of the gypsum board.

The SO ₂ concentration of the exhaust gas has a good correlation with the SO ₃ concentration of the powder sampled from the bottom cyclone provided in the preheater section. Therefore, the sulfur content of the raw material may be adjusted based on the SO ₃ concentration to control the SO ₂ concentration of the exhaust gas (feedforward control). Further, the control based on the SO ₃ concentration of the powder in the bottom cyclone and the control based on the SO ₂ concentration of the exhaust gas may be performed in combination.

The manufacturing method of this embodiment allows the sulfite slurry obtained by absorbing sulfur dioxide gas contained in the exhaust gas generated from the cement clinker manufacturing process into the raw material slurry to be directly blended into the cement clinker, so it does not require the installation of large-scale new equipment. A cement composition that can reduce the elution of hexavalent chromium can be easily produced without the need for The sulfite slurry also contributes to desulfurization of exhaust gas, and since the sulfite compound is used as a slurry without drying, a series of processes for desulfurization and production of a cement composition can be simplified. In the addition process, glycol-based compounds are added to the raw material slurry and/or slurry, which not only delays the agglomeration of fine powder during pulverization and accelerates pulverization, but also suppresses oxidation of fine particles of sulfuric acid compounds. can. Furthermore, by including a mixing step in which a flocculant is added, it is possible to promote flocculation and precipitation of solids and suppress scaling.

In the slurry concentration adjustment step, the slurry concentration can be easily and stably adjusted depending on the use of the sulfur-based compound slurry. In addition, the sulfite slurry can be used instead of water injection when crushing the cement composition, and since it is in the form of a slurry, the sulfite compound and cement clinker have good miscibility, shortening the manufacturing process and simplifying equipment. In addition, there is an advantage that the manufacturing cost of a cement composition that is effective in reducing the elution of hexavalent chromium can be significantly reduced.

The method for manufacturing a cement composition of this embodiment may be performed using the cement composition manufacturing system according to each embodiment, or may be performed using another cement composition manufacturing system. The descriptions of each cement composition manufacturing system are applicable to the method for manufacturing a cement composition of this embodiment.

<Second embodiment of cement composition manufacturing system>
FIG. 1 is a diagram showing an embodiment of a cement composition manufacturing system. A cement composition manufacturing system 100 includes a cement kiln section 10 that produces cement clinker by firing sulfur-containing raw materials and clinker raw materials, a bypass section 12 that extracts exhaust gas, and a preheater section 16 that has one or more cyclones. A composition comprising a cement clinker firing section 70, a slurry preparation section 60 that absorbs sulfur dioxide gas contained in exhaust gas from the cement clinker firing section 70 into a raw slurry to obtain a sulfite slurry containing calcium sulfite, and a cement clinker and a sulfite slurry. A pulverizing section 50 is provided to obtain a cement composition by pulverizing a substance.

The preheater section 16 brings the raw material into contact with the exhaust gas from the cement kiln section 10 to preheat the raw material. The bypass section 12 bleeds exhaust gas containing sulfur dioxide gas from between the kiln bottom 10a of the cement kiln section 10 and the bottom cyclone (cyclone at the bottom) or calciner (not shown) of the preheater section 16. This bypass section 12 may be a chlorine bypass section. Cement clinker produced in the cement kiln section 10 is cooled to 40 to 220° C. in the cooling section 11 and introduced into the silo 18.

The slurry preparation section 60 cools the exhaust gas extracted from the bypass section 12 and the exhaust gas extracted from the kiln bottom 10a to, for example, 400° C. or lower, preferably 100 to 200° C., and collects dust particles containing agglomerated chlorine compounds. A cooling unit 17 that generates sulfur dioxide, a dust collection unit 19 that removes at least a portion of dust particles contained in the exhaust gas to obtain exhaust gas containing sulfur dioxide gas, and a dust collection unit 19 that brings the exhaust gas and raw material slurry containing calcium compounds into contact with each other to remove sulfur dioxide gas. It includes a slurry preparation section 30 that obtains a sulfite slurry containing calcium sulfite as a compound, and a raw material slurry preparation section 34 that prepares a raw material slurry.

In the cement kiln section 10, coal, petroleum coke, and the like are burned and the raw materials react to generate exhaust gas containing sulfur dioxide. Between the kiln bottom 10a of the cement kiln section 10 and the preheater section 16, the gas extracted from the bleed pipe constituting the bypass section 12 is recovered as exhaust gas. The concentration of sulfur dioxide in the exhaust gas from the bypass section 12 may be, for example, about 100 to 5000 ppm on a volume basis (standard state). Note that the concentration of sulfur dioxide in the present disclosure is a concentration on a volume basis (standard state) unless otherwise specified.

The exhaust gas may be extracted from the kiln bottom 10a. The temperature of the exhaust gas extracted from the kiln bottom 10a may be, for example, 700 to 1200°C, and the concentration of sulfur dioxide may be 500 to 20,000 ppm. The exhaust gas extracted from the kiln bottom 10a and the exhaust gas from the bypass section 12 are introduced into the cooling section 17, either together or individually, and are cooled to, for example, about 100 to 200° C. (cooling step). Cooling in the cooling unit 17 may be performed by mixing outside air (air) or the like with the exhaust gas, or may be performed by a cooler using heat from cooling water, air, or the like.

By cooling the exhaust gas, volatile chlorine compounds and the like aggregate on the surfaces of dust particles originally contained in the exhaust gas. At least a portion of such dust particles are removed by the dust collection section 19 (dust collection step). The dust collecting section 19 includes, for example, a bag filter. If the exhaust gas may contain dust particles, the exhaust gas may bypass the dust collection section 19 and be introduced directly into the slurry preparation section 30.

The dust particles collected in the dust collecting section 19 are washed with water in the water washing section 31 to reduce the salt content. The washed dust particles whose salt content has been reduced in the water washing section 31 contain, for example, CaO and/or Ca(OH) ₂ . The water-washed dust particles are introduced into the raw material slurry preparation section 34 and are effectively utilized not only for desulfurizing exhaust gas but also as a raw material for calcium sulfite. Note that the dust particles collected in the dust collecting section 19 may be introduced into the raw material slurry preparation section 34 as they are without being washed with water.

The exhaust gas from which at least some of the dust particles have been removed in the dust collection section 19 is introduced into the slurry preparation section 30. The slurry preparation section 30 is, for example, a bubbling tank, and brings the raw material slurry into contact with the exhaust gas. Thereby, sulfur dioxide is incorporated into the raw material slurry, and a sulfite slurry can be obtained. Furthermore, it is possible to effectively utilize sulfur dioxide, whose release into the atmosphere is regulated. In this way, the slurry preparation section 30 also functions as a flue gas desulfurization section. Note that the means for contacting the raw material slurry with the exhaust gas is not limited to bubbling, but may also be a method of spraying the raw material slurry.

The raw material slurry is continuously or intermittently supplied to the slurry preparation section 30 from the raw material slurry preparation section 34 . The raw material slurry preparation section 34 is supplied with fine particle powder mainly composed of CaCO ₃ generated in a raw material crushing section 82 that crushes water and a clinker raw material (for example, limestone). Furthermore, in addition to the above-mentioned dust particles and water-washed dust particles, sludge containing cement or cement hydrate may be introduced into the raw material slurry preparation section 34 . Examples of the sludge include ready-mixed concrete sludge obtained at a ready-mixed concrete factory (raw material slurry preparation step).

An addition section for adding a glycol compound is connected to the slurry preparation section 30. The type and function of the glycol compound are the same as in the above-mentioned "first embodiment of the method for producing a sulfur composition and a cement composition."

The desulfurization gas desulfurized in the slurry preparation section 30 is introduced into the cooling section 11, flows through a flow path that exchanges heat with the cement clinker, and is introduced into the cement kiln section 10. Thereby, the sulfur dioxide gas remaining in the desulfurization gas can be effectively utilized. Furthermore, when the desulfurization gas contains NOx, release of NOx into the atmosphere can be suppressed. Further, a part of the desulfurization gas whose dust particles have been reduced in the dust collection section 19 may bypass the slurry preparation section 30 and be introduced into the cement kiln section 10 through a flow path passing through the cooling section 11.

At least a portion of the sulfite slurry prepared in the slurry preparation section 30 is introduced into the slurry concentration adjustment section 36. The slurry concentration adjustment section 36 is configured to be able to adjust the solid content concentration in the sulfite slurry by dehydration or water addition. The solids concentration in the sulfite slurry may be from 0.1 to 95% by weight. The content of sulfite compounds (in terms of anhydride) based on the total solid content in the sulfite slurry is, for example, 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, and still more preferably 20% by mass or more. % by mass or more.

Another part of the sulfite slurry prepared in the slurry preparation section 30 is introduced into the coagulation and sedimentation section 91. An addition section for adding a glycol compound is connected to the coagulation/sedimentation section 91. By providing such an additive part, oxidation of the sulfite compound having a reducing effect can be suppressed. Note that it is not essential to connect the addition section to both the slurry preparation section 30 and the coagulation/sedimentation section 91, and the addition section may be connected to only one of them.

The amount of the glycol compound added is 0.01 to 10% by mass based on the solid content contained in the raw material slurry. When the glycol compound is connected to both the raw material slurry preparation section 34 and the coagulation/sedimentation section 91, the total value of the amount added to each is adjusted within the above-mentioned numerical range. The above-mentioned addition amount is preferably 0.05 to 5% by mass in total, more preferably 0.1% in total from the viewpoint of reducing the manufacturing cost of the cement composition while sufficiently suppressing the oxidation of the sulfite compound. ~3% by mass.

A mixing section for adding a flocculant is connected to the coagulation and sedimentation section 91 . The types and functions of the flocculant and glycol compound are the same as in the first embodiment described above. In the coagulation-sedimentation section 91, by adding a flocculant from the mixing section, precipitation of fine sulfite compounds contained in the sulfite slurry is promoted. Thereby, a sulfite slurry with a high solid content can be easily and quickly obtained.

A portion of the sulfite slurry whose solid content has been concentrated in the coagulation-sedimentation section 91 is introduced into the dehydration section 37 to further reduce water content. The dewatering section 37 may be configured with, for example, a sedimentation tank that separates the supernatant liquid. Thereby, the solid content concentration in the sulfite slurry can be adjusted. Since the sulfite slurry contains the organic compound supplied from the addition section, the rate of solid content precipitation is high. Therefore, the solid content concentration can be adjusted smoothly and quickly. The coagulation and sedimentation section 91 may include a centrifugal separator, a filter, and the like. Note that another part of the sulfite slurry whose solid content has been concentrated in the coagulation-sedimentation section 91 may be introduced into the slurry concentration adjustment section 36.

The sulfite slurry whose water content has been reduced in the dewatering section 37 is introduced into the drying section 93. By further reducing the water content in the drying section 93, dry powder can be obtained. The dry powder obtained in this manner may include a core portion containing a sulfite compound and a coating portion that covers at least a portion of the core portion. This coating preferably contains a glycol compound. Thereby, oxidation of the sulfite compound contained in the core portion can be suppressed. The heating temperature of the sulfite slurry in the drying section 93 is, for example, 180°C or lower, preferably 150°C or lower, and more preferably 120°C or lower. By heating at such a heating temperature, it is possible to suppress volatilization of glycol compounds and to sufficiently suppress oxidation of sulfite compounds contained in the dry powder.

The dry powder is mixed with a pulverized product (cement composition) containing cement clinker and gypsum in the mixing section 94 . As a result, a cement composition can be easily produced by only a mixing operation without going through the crushing section 50. The cement composition thus obtained may be stored in the silo 54 together with the cement composition produced through the crushing section 50. In addition, in this embodiment, although the coagulation-sedimentation part 91, the dehydration part 37, and the drying part 93 are separately provided, these may be comprised integrally as a drying part.

Still another part of the sulfite slurry prepared in the slurry preparation section 30 is dehydrated in the dehydration section 44 and introduced into the blending section 51.

The solid content concentration in the sulfite slurry in the slurry concentration adjustment section 36 is determined based on the temperature Tr of the cement clinker, the temperature Tm of the cement composition derived from the cement mill 52, and the ignition loss Ig of the cement composition. controlled by. Specifically, the measured values of the temperature Tr of the cement clinker, the temperature Tm of the cement composition, and the ignition loss Ig of the cement composition are input to the control unit 38 as input signals. The control unit 38 selects one of the three input signals and outputs a control signal related to the target value of the solid content concentration in the sulfite slurry to the slurry concentration adjustment unit 36. The control unit 38 may select the signal that adjusts the solid content concentration most among the plurality of input signals. The slurry concentration adjustment section 36 adjusts the solid content concentration in the sulfite slurry based on the control signal from the control section 38 . The control unit 38 may have table data showing the relationship between the above-mentioned three measured values and the solid content concentration of the sulfite slurry, or may have correlation equation data.

It is not essential to separately provide the slurry preparation section 30 and the slurry concentration adjustment section 36. In another embodiment, the solid content concentration may be adjusted in the slurry preparation section 30. In this case, the control signal from the control section 38 may be input to the slurry preparation section 30. Further, the measured value inputted to the control unit 38 is any one selected from the temperature Tr of the cement clinker, the temperature Tm of the cement composition derived from the cement mill 52, and the ignition loss Ig of the cement composition. There may be one or two.

The sulfite slurry whose solid content concentration has been adjusted and the cement clinker stored in the silo 18 are introduced into the blending section 51 in the crushing section 50. The cement clinker may be introduced after being stored in the silo 18, or may be introduced directly from the cooling section 11. The temperature Tr of the cement clinker introduced into the blending section 51 is, for example, 40 to 220°C.

In the blending section 51, gypsum may be blended as needed. The sulfite slurry contains at least one sulfite compound selected from the group consisting of calcium sulfite hemihydrate, calcium bisulfite (Ca(HSO ₃ ) ₂ ), and a double salt of calcium sulfite and calcium sulfate. is preferred. In this case, when the cement composition is 100 parts by mass, the sulfite slurry is added to the cement clinker, preferably from 0.1 to 20 parts by mass in terms of the anhydride of the sulfite compound (or in terms of the anhydride of calcium sulfite). The amount is preferably 0.15 to 15 parts by weight, more preferably 0.2 to 10 parts by weight, particularly preferably 0.25 to 5 parts by weight. Thereby, the blend can be smoothly pulverized while maintaining the content of sulfite compounds in the resulting cement composition. When a double salt of calcium sulfite and calcium sulfate is included, the calcium sulfite in the double salt may be contained in the above-mentioned mass proportion. The blending ratio of gypsum to 100 parts by mass of cement clinker may be about 1.5 to 20 parts by mass in terms of SO ₃ .

A formulation including cement clinker, sulfite slurry, and optionally gypsum is introduced into cement mill 52. The cement mill 52 may be a ball mill or a vertical mill. The temperature of the cement mill 52 tends to rise due to frictional heat during pulverization. Water is sprinkled into the cement mill 52 so that the temperature inside the cement mill 52 does not rise excessively. Therefore, by containing an appropriate amount of water in the sulfite slurry, excessive temperature rise within the cement mill 52 can be suppressed. Therefore, blending the sulfite compound in the form of a slurry also contributes to reducing the amount of water sprayed into the cement mill 52.

The temperature Tm of the cement composition at the exit of the cement mill 52 may be 20°C to 180°C, preferably 40°C to 150°C, more preferably 50°C to 140°C, even more preferably 60°C to The temperature is 95°C. If the temperature Tm becomes too low, water in the sulfite slurry tends to cause a hydration reaction with the cement composition. On the other hand, if the temperature Tm becomes too high, calcium sulfite tends to be oxidized and change to calcium sulfate. That is, by setting the temperature Tm within the above-mentioned temperature range, the drying of the blend proceeds at a sufficient speed while suppressing the oxidation of calcium sulfite. Also, cement clinker, calcium sulfite and gypsum can be mixed sufficiently uniformly.

The thus obtained cement composition capable of reducing the amount of hexavalent chromium eluted is stored in the silo 54. The ignition loss Ig (ig.loss) of the cement composition may be, for example, 1.0 to 8.0% by mass. At least a portion of this cement composition may be used as a cementitious solidifying material or as a raw material for a cementitious solidifying material.

A measuring device for measuring the SO ₂ concentration Sg of the exhaust gas is installed downstream of the dust collecting section 19 . Furthermore, a measuring device for measuring the SO ₃ concentration Sp in the dust is installed at the bottom of the kiln 10a. The SO ₂ concentration Sg is controlled to 500 to 20,000 ppm by adjusting the sulfur content of the raw material. The sulfur content of the raw material may be adjusted by changing the supply amount of the sulfur-containing raw material or by changing the sulfur concentration in the sulfur-containing raw material.

Specifically, the measured values of the SO ₂ concentration Sg in the exhaust gas and the SO ₃ concentration Sp in the dust are input to the control unit 84 as input signals. The control unit 84 selects one of the two input signals and outputs a control signal related to the target value of the SO ₂ concentration Sg of the exhaust gas to the sulfur-containing raw material supply amount adjustment unit 86. The control unit 84 may derive a control signal regarding the target value based on the input signals of the SO ₂ concentration Sg and the SO ₃ concentration Sp. The supply amount adjustment section 86 adjusts the supply amount of the sulfur-containing raw material based on the control signal from the control section 84 . The control unit 84 may have table data showing the relationship between the above two measured values and the supply amount of the sulfur-containing raw material, or may have correlation data. The control unit 84 may adjust the supply amount of the sulfur-containing raw material based on either the SO ₂ concentration Sg of the exhaust gas or the SO ₃ concentration Sp in the dust.

In this embodiment, the crushing section 50 includes a blending section 51 and a cement mill 52, but is not limited thereto. For example, in a modified example, the cement clinker, sulfite slurry, and optionally blended gypsum may be directly input into the cement mill 52, where they may be blended and pulverized. In addition, cement clinker and gypsum are mixed in the blending section 51, and on the belt conveyor that conveys the resulting blend from the blending section 51 to the cement mill 52, sulfite slurry is sprinkled on the blend, and the cement mill 52 crushes the blend. You may go.

In another modification, a control unit may be provided that adjusts the blending ratio of sulfite slurry to cement clinker depending on the chromium content of the cement clinker derived from the cement kiln unit 10. The chromium content of the cement clinker may be measured by sampling from the silo 18 at a predetermined frequency, or may be calculated from the chromium content contained in the raw material introduced into the cement clinker firing section 70.

The control unit calculates the amount of sulfite slurry to be added to the cement clinker based on the input value of the chromium content of the cement clinker determined as described above. The control unit may have table data showing the relationship between the cement chromium content and the blending amount of the sulfite slurry, or may have correlation equation data between the two. The control unit calculates the blending amount of the sulfite slurry using such data. Based on the calculation result, the control unit controls, for example, a flow rate adjustment valve that adjusts the flow rate of the sulfite slurry. In this way, the blending ratio of sulfite slurry to cement clinker can be adjusted. Such control can be performed using simple equipment since the slurry has fluidity.

The cement composition manufacturing system 100 and its modifications may be used based on the contents of each of the above-mentioned cement composition manufacturing methods. Therefore, the content described in the method for producing a cement composition also applies to the system for producing a cement composition. Furthermore, the description of the manufacturing system 100 and its modifications also applies to each method of manufacturing the cement composition described above. The cement composition manufacturing system of the present disclosure is capable of manufacturing a slurry containing sulfur-based compounds and desulfurizing exhaust gas at the same time. It is no longer necessary to provide a dedicated tank, weighing machine, or transportation equipment. Therefore, the installation cost and operating cost of the equipment can be sufficiently reduced. However, the present disclosure does not exclude those equipped with such equipment.

<Third embodiment of cement composition manufacturing system>
FIG. 2 is a diagram showing another embodiment of a cement composition manufacturing system. The cement composition manufacturing system 101 in FIG. 2 includes a slurry preparation section 30A instead of the slurry preparation section 30 that prepares a sulfite slurry containing calcium sulfite. In the slurry preparation section 30A, an aqueous solution or slurry containing magnesium sulfite is prepared, and then the slurry and a calcium compound are mixed to prepare a sulfite slurry containing calcium sulfite. Since the other elements are the same as the cement composition manufacturing system 100, the differences from the cement composition manufacturing system 100 will be explained.

In the slurry preparation section 30A, exhaust gas containing sulfur dioxide gas is absorbed into an aqueous solution containing magnesium hydroxide. This yields an aqueous solution or slurry containing magnesium sulfite. Since magnesium sulfite has a higher solubility in water than calcium sulfite, it can suppress solid content clogging. Raw material slurry is added from the raw material slurry preparation section 34 to the aqueous solution or slurry containing magnesium sulfite. The raw material slurry is, for example, fine powder mainly composed of _CaCO3 generated when clinker raw materials are crushed, dust particles containing CaO and/or Ca(OH) ₂ generated in the chlorine bypass section, and dust particles that are washed with water. and sludge containing cement and/or cement hydrate. Thereby, the slurry preparation section 30A can obtain a sulfite slurry containing calcium sulfite.

The slurry preparation section 30A needs to maintain a certain degree of airtightness in order to prevent exhaust gas from being released to the outside. For this reason, it is preferable to reduce the maintenance frequency. In this embodiment, among sulfite compounds, magnesium sulfite, which has a higher solubility in water than calcium sulfite, is first produced, and then a sulfite slurry containing calcium sulfite is prepared. Therefore, the frequency of maintenance of the slurry preparation section 30A due to scaling of calcium sulfite can be reduced, and the stability of the process can be improved.

In this embodiment, magnesium hydroxide is used in the slurry preparation section 30A, but the present invention is not limited to this, and any salt capable of producing a sulfite compound having a higher solubility in water than calcium sulfite can be used. . As such salts, it is possible to use salts of alkaline earth metals or alkali metals different from Ca and Mg, such as potassium hydroxide and sodium hydroxide.

<Cement solidifying material>
A cementitious solidifying material according to one embodiment contains cement particles and particles containing a sulfur composition. The cement particles may be particles of cement clinker, Portland cement, or the like. Particles containing a sulfur-based composition include a core portion containing a sulfite compound, and a coating portion that covers at least a portion of the surface of the core portion and contains a glycol-based compound. The sulfite compound may include at least one selected from the group consisting of calcium sulfite hemihydrate, calcium bisulfite (Ca(HSO ₃ ) ₂ ), and a double salt of calcium sulfite and calcium sulfate. In addition to the sulfite compound, the core portion may contain at least one salt selected from the group consisting of calcium sulfate dihydrate, calcium hydroxide, calcium carbonate, and magnesium hydroxide.

The core portion may be a portion that does not contain a glycol compound. On the other hand, the shell part is a part containing a glycol compound, but may contain components other than the glycol compound. Particles containing a sulfur-based composition in a cementitious solidifying material can suppress oxidation of the sulfite compound contained in the core portion by having a shell portion. For example, the particles containing the sulfur-based composition may be dry powder obtained in the drying section 93 of FIG. 1 or 2. A cementitious solidifying material may be obtained by blending such dry powder with Portland cement. Alternatively, for example, a slurry obtained in the slurry concentration adjusting section 36 of FIGS. 1 and 2 or the like may be mixed with cement particles and dried.

The cementitious solidifying material of this embodiment may be a cement composition obtained by the above-mentioned cement composition production method or production system, or may be obtained using these cement compositions as raw materials. good. The cementitious solidifying material may contain particles other than cement particles and particles containing a sulfur-based composition. Such particles include, for example, granular gypsum, slag, calcium carbonate, clinker dust, fly ash, silica fume, metakaolin, and the like.

When the cement solidifying material is 100 parts by mass, the content of cement particles may be 50 parts by mass or more, and may be 60 parts by mass or more. When the cementitious solidifying material is 100 parts by mass, the content of particles containing the sulfur-based composition is preferably 0.1 to 20 parts by mass, more preferably 0.15 to 15 parts by mass in terms of anhydrous sulfite compound. parts, more preferably 0.2 to 10 parts by weight, particularly preferably 0.25 to 5 parts by weight. When a double salt of calcium sulfite and calcium sulfate is included, the calcium sulfite in the double salt may be contained in the above-mentioned mass proportion.

When the cementitious solidifying material contains granular gypsum, the content of gypsum is preferably 3 to 20 parts by mass in terms of SO ₃ when the cementitious solidifying material is 100 parts by mass. The gypsum may be anhydrite. When the cementitious solidifying material contains granular blast furnace slag, the content of blast furnace slag is preferably 2 to 50 parts by mass, and preferably 5 to 30 parts by mass, when the cementitious solidifying material is 100 parts by mass. It is preferable.

Although several embodiments have been described above, the present disclosure is not limited to the above-described embodiments. For example, it is not essential to provide the control units 38 and 84, and an operator may perform these controls manually. Further, for example, sulfur dioxide gas obtained in a heating section different from the cement clinker firing section or exhaust gas containing the same may be introduced into the slurry preparation section. That is, the exhaust gas containing sulfur dioxide gas obtained from the cement clinker firing section and a heating section different from this may be introduced into the slurry preparation section together or individually. Moreover, the content of each embodiment may be applied to another embodiment.

(Reference example 1)
A raw material slurry (0.4 L) having a solid content concentration of 10% by mass was prepared by blending commercially available CaCO ₃ powder and water. Bleed gas was collected from the chlorine bypass section of a cement composition manufacturing device. The sampled bleed gas was cooled to about 200° C., and then dust particles were removed using a bag filter. The concentration of sulfur dioxide in the bleed gas after removing dust particles was 1500 ppm (by volume). This bleed gas was blown into the raw material slurry to cause bubbling, and the sulfur oxides in the bleed gas were absorbed into the raw material slurry. This resulted in a sulfite slurry containing calcium sulfite. The solid content concentration of the obtained slurry was about 10% by mass.

The sulfite slurry was filtered to recover solids. The recovered solids were dried under an air atmosphere at about 40°C. The X-ray pattern of the obtained solid content was measured using an X-ray diffractometer (manufactured by Bruker AXS, accelerating voltage: 30 kV, current: 10 mA, tube: Cu). The X-ray pattern was subjected to Rietveld analysis using analysis software (Topas (R), manufactured by Bruker AXS Co., Ltd.), and was analyzed for CaCO ₃ , Ca(OH) ₂ , CaSO ₃ .0.5H ₂ O, and CaSO ₄ .2H ₂ O was quantified. As a result, it was confirmed that the solid content contained 5% by mass of CaCO ₃ , 5% by mass of CaSO ₄ .2H ₂ O, and 90% by mass of CaSO ₃ .0.5H ₂ O. On the other hand, Ca(OH) ₂ was not detected.

From this analysis result, it was confirmed that the sulfite slurry after being brought into contact with the exhaust gas containing sulfite contained calcium sulfite. By using the sulfite slurry thus obtained in the pulverization process, it is possible to produce a cement composition that can reduce the elution of hexavalent chromium.

According to the present disclosure, there is provided a method for producing a sulfur-based compound that can easily produce a cement composition that is effective in reducing elution of hexavalent chromium. Further, a method and system for producing a cement composition effective in reducing elution of hexavalent chromium are provided. Furthermore, a cement solidifying material capable of reducing the elution of hexavalent chromium is provided.

10... Cement kiln part, 10a... Kiln bottom, 11... Cooling part, 12... Bypass part, 16... Preheater part, 17... Cooling part, 18... Silo, 19... Dust collection part, 30, 30A... Slurry preparation part, 31 ...Water washing section, 34... Raw material slurry preparation section, 36... Slurry concentration adjustment section, 37... Dehydration section, 38... Control section, 38, 84... Control section, 44... Dehydration section, 50... Grinding section, 51... Blending section, 52... Cement mill, 54... Silo, 60... Slurry preparation section, 70... Cement clinker baking section, 82... Raw material crushing section, 84... Control section, 86... Supply amount adjustment section, 91... Coagulation sedimentation section, 93... Drying section , 94...mixing section, 100...manufacturing system.

Claims (15)

A manufacturing process that generates a gas containing sulfur dioxide gas and/or hydrogen sulfide;
The sulfur dioxide gas and/or hydrogen sulfide contained in the gas is absorbed into the raw material slurry to form calcium sulfite hemihydrate, calcium bisulfite (Ca(HSO ₃ ) ₂ ), and calcium sulfite and calcium sulfate. A slurry preparation step for obtaining a sulfite slurry containing at least one sulfite compound selected from the group consisting of double salts;
an addition step of adding a total of 0.01 to 10% by mass of a glycol-based compound to the raw material slurry and/or the sulfite slurry, based on the solid content contained in the raw material slurry;
a slurry concentration adjustment step of increasing the solid content concentration of the sulfite slurry to adjust the solid content concentration to 40 to 95% by mass;
A method for producing a cement composition, comprising a pulverizing step of obtaining a cement composition containing the sulfite compound using the sulfite slurry having a solid content concentration of 40 to 95% by mass and cement clinker. Claim 1, wherein the content of the sulfite compound (in terms of anhydride) with respect to the total solid content of the sulfite slurry obtained in the slurry concentration adjustment step is 5% by mass or more, and the solid content concentration is 40 to 95% by mass. A method of manufacturing the cement composition described. The method for producing a cement composition according to claim 1 or 2, wherein in the pulverizing step, the sulfite slurry, the cement clinker, and gypsum are blended and pulverized to obtain the cement composition. The sulfite slurry has, as a solid content,
The sulfite compound;
The cement composition according to any one of claims 1 to 3, comprising at least one salt selected from the group consisting of calcium sulfate dihydrate, calcium hydroxide, calcium carbonate, and magnesium hydroxide. How things are manufactured. According to any one of claims 1 to 4, in the slurry preparation step, the sulfurous acid slurry is obtained by treating at least a portion of the gas containing the sulfurous acid gas and/or hydrogen sulfide with a lime-gypsum method. A method for producing a cement composition. In the slurry preparation step, the gas containing sulfur dioxide gas and/or hydrogen sulfide is absorbed into an aqueous solution containing a salt of an alkaline earth metal and/or an alkali metal different from Ca, and then a calcium compound is mixed therein. The method for producing a cement composition according to any one of claims 1 to 5, wherein the sulfite slurry containing the sulfite compound having calcium as a constituent element is obtained. Fine particle powder mainly composed of _CaCO3 generated when clinker raw material is crushed, dust particles containing CaO and/or Ca(OH) ₂ generated in the chlorine bypass section, and water-washed dust obtained by washing the dust particles with water. The method according to any one of claims 1 to 6, comprising a step of preparing the raw material slurry using at least one selected from the group consisting of particles and sludge containing cement and/or cement hydrate. A method of manufacturing the cement composition described. The method for producing a cement composition according to any one of claims 1 to 7, wherein the gas contains sulfur dioxide gas, and the SO ₂ concentration of the gas is 500 ppm to 20%. The method for producing a cement composition according to any one of claims 1 to 8, wherein the gas includes exhaust gas at a temperature of 700 to 1200°C extracted from the bottom of a cement kiln between a calciner and a calciner. The gas is one or both of a gas containing sulfur dioxide gas and/or hydrogen sulfide generated by heat treatment of sulfur-containing waste at 500 to 1400 ° C. or decomposition treatment by microorganisms, and a combustion gas generated by burning sulfur. A method for producing a cement composition according to any one of claims 1 to 9, comprising: The method for producing a cement composition according to any one of claims 1 to 10, wherein in the slurry preparation step, the gas contacts the raw material slurry at a temperature of 400° C. or lower. The cement composition according to any one of claims 1 to 11, wherein the desulfurization gas obtained in the slurry preparation step after at least a portion of the sulfur dioxide gas and/or hydrogen sulfide has been absorbed is introduced into a cement kiln. How things are manufactured. The method for producing a cement composition according to any one of claims 1 to 12, comprising a drying step of drying at least a portion of the sulfite slurry at 180° C. or lower to dry powder. According to any one of claims 1 to 12, in the pulverizing step, the cement composition is obtained by adding a sulfur-based composition obtained by drying at least a part of the sulfite slurry at 180 ° C. or lower to dry powder. A method of manufacturing the cement composition described. In the slurry concentration adjustment step, the solid content concentration of the sulfite slurry is adjusted based on the temperature of the cement clinker obtained in the cement clinker manufacturing process, the temperature of the cement composition at the exit of the cement mill, and the ignition loss of the cement composition. The method for producing a cement composition according to any one of claims 1 to 14, which is adjusted based on at least one selected from the group consisting of:

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