JP2020023415A - Manufacturing method of cement composition, and manufacturing system of cement composition - Google Patents

Abstract

To provide a manufacturing system of a cement composition capable of manufacturing inexpensively a cement composition effective for elution reduction of hexavalent chromium.SOLUTION: A manufacturing system 300 of a cement composition includes a pulverization part 50 for obtaining a cement composition by mixing a compound containing cement clinker and sulfite slurry containing a sulfite compound, and a desulfurization part 60 for obtaining sulfite slurry by desulfurizing at least a part of exhaust gas generated from a different factory 200 on a site different from a cement factory 100 including the pulverization part 50.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a method for producing a cement composition, and a system for producing a cement composition.

  Cement clinker is manufactured mainly from limestone, clay, silica, iron oxide, and the like. 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 fuels. However, depending on the selection of raw materials, very small amounts of heavy metals such as cadmium, chromium, and lead derived from various raw fuels may be mixed into the cement clinker.

Among the heavy metals, hexavalent chromium, unlike other heavy metals, exists as a stable oxoanion such as chromate ion (CrO ₄ ²⁻ ), and is hardly soluble even under high pH conditions. Do not form hydroxides. For this reason, hexavalent chromium is classified as a heavy metal whose elution countermeasures are relatively difficult. It is known that the amount of hexavalent chromium eluted increases especially when volcanic ash-like clay such as Kanto loam is targeted for ground improvement.

  Cement clinker or cement is sometimes used as a raw material for soil improvement materials. The amount of hexavalent chromium eluted from the ground improvement soil is limited to 0.05 mg / L or less based on soil environmental standards. In Patent Document 1, a reducing gypsum composition obtained by drying a slurry containing calcium sulfite hemihydrate and gypsum dihydrate obtained in a flue gas desulfurization step is mixed with a cement-based solidifying material to form hexavalent chromium. There has been proposed a technology for reducing trivalent chromium to render the solidified soil harmless.

JP 2007-246306 A

  Since commercially available sulfites such as calcium sulfite are expensive, using a commercially available product increases the production cost of the cement composition. On the other hand, as described in Patent Document 1, the use of a reducing gypsum composition in a cement-based solidifying material is effective in reducing the elution of hexavalent chromium from solidified soil, but the use of a reducing gypsum composition It needs to be produced. Thus, the present disclosure provides a method and system for producing a cement composition capable of producing, at low cost, a cement composition effective for reducing the elution of hexavalent chromium.

  The method for producing a cement composition according to an aspect of the present disclosure includes a pulverizing step of mixing and cementing a cement clinker and a sulfurous acid slurry containing a sulfite compound to obtain a cement composition, and the sulfurous acid slurry performs a pulverizing step. Includes sulfite compounds obtained by desulfurizing exhaust gas generated at another factory located on a site different from the cement factory.

  In this production method, a cement composition is produced by mixing a sulfurous acid slurry containing a sulfurous acid compound obtained by desulfurizing exhaust gas generated in another factory with a cement clinker. As described above, since a sulfite compound effective for reducing the dissolution of hexavalent chromium is obtained from exhaust gas generated at another factory, it is possible to produce a cement composition effective for reducing the dissolution of hexavalent chromium at low cost. it can.

  It is preferable that the sulfurous acid slurry is obtained without going through an oxidation treatment step of oxidizing a sulfurous acid compound after the desulfurization step of absorbing sulfurous acid gas in the exhaust gas. A gypsum slurry containing a sulfite compound and gypsum may be obtained by oxidizing a part of the sulfurous acid slurry. If the gypsum slurry thus obtained is used for the production of a cement composition, the production cost of the cement composition can be further reduced.

  In the pulverizing step, it is preferable to mix gypsum together with the sulfurous acid slurry to obtain a cement composition. This allows the properties of the cement composition to be adjusted flexibly. It is preferable that the sulfurous acid slurry, the gypsum, and the cement clinker are simultaneously mixed and pulverized. As a result, the calcium sulfite is finely pulverized, and the reducing action of hexavalent chromium can be enhanced.

  The proportion of the solid content in the sulfurous acid slurry is preferably 0.1 to 95% by mass. Thereby, the handleability of the sulfurous acid slurry can be maintained satisfactorily, and the pulverization efficiency can be improved by mixing an appropriate amount of water with the cement clinker and pulverizing the mixture. In addition, the gypsum contained in the cement composition is prevented from being excessively converted into gypsum gypsum, has excellent fluidity and strength, and is hardly solidified even when stored for a long period of time.

The sulfurous acid slurry contains at least one sulfurous acid 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 as a solid content. It is preferable to contain a compound and at least one salt selected from the group consisting of calcium sulfate dihydrate, calcium hydroxide, calcium carbonate, and magnesium hydroxide. By containing such a component, a cement composition capable of further reducing the elution of hexavalent chromium can be produced. From the same viewpoint, the sulfite slurry preferably contains a double salt of calcium sulfite and calcium sulfate.

  When the cement composition is 100 parts by mass, it is preferable to mix 0.1 to 20 parts by mass of the sulfurous acid slurry with the cement clinker in terms of anhydride of the sulfurous acid compound. Thus, the pulverization can be performed sufficiently smoothly while maintaining the elution of hexavalent chromium at a sufficiently low level.

  The sulfurous acid slurry is preferably obtained by absorbing a sulfurous acid gas contained in an exhaust gas into an aqueous solution containing an alkaline earth metal and / or an alkali metal salt different from Ca, and then mixing a calcium compound. Thereby, the effect of scaling by calcium sulfite can be reduced and the stability of the process can be improved.

  The sulfite slurry may contain calcium sulfite obtained by treating industrial wastewater containing a water-soluble sulfite containing at least one of an alkali metal and an alkaline earth metal different from Ca with a calcium compound. Thereby, the sulfites can be more effectively used, and the production cost of the cement composition can be further reduced.

The production method has a desulfurization step of obtaining a sulfurous acid slurry by absorbing a sulfurous acid gas into a raw material slurry, and an oxidation treatment step of oxidizing the sulfurous acid slurry to obtain a slurry containing gypsum. Preferably, the processing steps are bypassed. Also has an analysis step of analyzing the SO ₂ content in the solid content of the sulfite slurry obtained in the desulfurization step, depending on the analysis result of the SO ₂ content, or sulfite slurry to bypass the oxidation process not It is preferred to determine This makes it possible to adjust the production amounts of the sulfite compound and the gypsum as needed. Therefore, the production cost of the cement composition can be stably reduced.

  It is preferable to have a slurry concentration adjusting step of adjusting the ratio of the solid content of the sulfurous acid slurry to 30 to 95% by mass. As a result, the handling cost of the sulfurous acid slurry can be improved while the transportation cost can be reduced, and the introduction of excessive moisture into the cement composition can be suppressed.

  In the above production method, it is preferable to prepare an aqueous solution or slurry containing magnesium sulfite from the sulfur dioxide gas contained in the exhaust gas, and mix the aqueous solution or slurry with a calcium compound to obtain a sulfurous acid slurry. Thereby, the effect of scaling by calcium sulfite can be reduced and the stability of the process can be improved.

The above production method is characterized in that fine particles containing CaCO ₃ as a main component, dust particles containing CaO and / or Ca (OH) ₂ generated in a chlorine bypass part, and dust particles are generated when a raw material for cement clinker is crushed. A raw material slurry preparing step of preparing a raw material slurry for desulfurizing the exhaust gas using at least one selected from the group consisting of water-washed dust particles obtained by washing water and sludge containing cement and / or cement hydrate. Is preferred. Thereby, the production cost of the cement composition can be sufficiently reduced.

  It is preferable that the above-mentioned production method has a transportation step of transporting the exhaust gas or the sulfurous acid slurry from another factory to a cement factory.

  A cement composition manufacturing system according to an aspect of the present disclosure includes a pulverizing unit that obtains a cement composition by mixing a mixture including a cement clinker and a sulfurous acid slurry including a sulfite compound, and a cement plant including a pulverizing unit. A desulfurization unit for desulfurizing at least a part of the exhaust gas generated at another factory on a different site to obtain the sulfurous acid slurry.

  In this production system, a cement composition is produced by mixing a sulfurous acid slurry containing a sulfurous acid compound obtained by desulfurizing exhaust gas generated in another factory with a cement clinker. As described above, since a sulfite compound effective for reducing the dissolution of hexavalent chromium is obtained from exhaust gas generated at another factory, it is possible to produce a cement composition effective for reducing the dissolution of hexavalent chromium at low cost. it can.

  In the above production system, it is preferable that a ratio of a solid content in the sulfurous acid slurry is 0.1 to 95% by mass. Thereby, the handleability of the slurry can be maintained satisfactorily, and an appropriate amount of water can be mixed with the cement clinker, so that the pulverization can be smoothly performed. Further, by this, the gypsum contained in the cement composition is suppressed from being excessively gypsum-formed gypsum, is excellent in fluidity and strength development, and produces a cement composition that is difficult to solidify even when stored for a long time. it can.

The sulfurous acid slurry includes, as solid components, at least one sulfurous acid compound selected from the group consisting of calcium sulfite hemihydrate, calcium bisulfite (Ca (HSO ₃ ) ₂ ), and double salts of calcium sulfite and calcium sulfate. And at least one salt selected from the group consisting of calcium sulfate dihydrate, calcium hydroxide, calcium carbonate, and magnesium hydroxide. By containing such a component, a cement composition capable of further reducing the elution of hexavalent chromium can be produced. From the same viewpoint, the sulfite slurry preferably contains a double salt of calcium sulfite and calcium sulfate.

  It is preferable that the production system includes a sulfurous acid slurry preparation unit that obtains a sulfurous acid slurry by absorbing sulfurous acid gas into the raw material slurry, and an oxidation processing unit that oxidizes the sulfurous acid slurry to obtain a slurry containing gypsum. This makes it possible to adjust the production amounts of the sulfite compound and the gypsum as needed. Therefore, the production cost of the cement composition can be stably reduced.

  It is preferable that the production system includes a slurry concentration adjusting unit that adjusts a ratio of a solid content of the sulfurous acid slurry to 30 to 95% by mass. Thereby, the transportation cost of the sulfurous acid slurry can be reduced.

  A first preparation unit that absorbs sulfurous acid gas contained in exhaust gas into an aqueous solution containing an alkaline earth metal different from Ca and / or a salt of an alkali metal to obtain a sulfite compound different from calcium sulfite; A second preparation unit for mixing a sulfite compound and a calcium compound to obtain a sulfite slurry containing calcium sulfite. Thereby, the influence of scaling by calcium sulfite can be reduced, and the stability of the manufacturing system can be improved.

The production system includes a fine particle powder containing CaCO ₃ as a main component, a dust particle containing CaO and / or Ca (OH) ₂ generated in a chlorine bypass portion, which is generated when a raw material for cement clinker is crushed, and the dust particle. It is preferable to provide a raw material slurry preparation unit that prepares a raw material slurry using at least one selected from the group consisting of water-washed dust particles obtained by washing water and sludge containing cement and / or cement hydrate. Thereby, the production cost of the cement composition can be sufficiently reduced.

  It is preferable that the production system includes a transport unit that transports the exhaust gas or the sulfurous acid slurry from another factory to a cement factory.

  ADVANTAGE OF THE INVENTION According to this indication, the manufacturing method and manufacturing system of a cement composition which can manufacture the cement composition effective in reduction of the elution of hexavalent chromium at low cost can be provided.

It is a figure showing one embodiment of a manufacturing system of a cement constituent. FIG. 3 is a view showing another embodiment of a system for producing a cement composition. It is a figure which shows another embodiment of the manufacturing system of a cement composition.

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

  The method for producing a cement composition according to an embodiment of the present disclosure includes a pulverizing step of mixing and pulverizing a cement clinker and a sulfurous acid slurry containing a sulfite compound to obtain a cement composition. The sulfurous acid slurry contains a sulfurous acid compound obtained by desulfurizing exhaust gas generated at another factory located on a site different from the cement factory where the pulverizing step is performed. The type of the other factory is not particularly limited as long as it has a plant that produces exhaust gas containing sulfurous acid gas. For example, it may be other than a cement plant, and may be a thermal power plant or a plant (steel mill) in the steel industry. In such a separate factory, combustion of heavy oil or coal containing sulfur generates exhaust gas containing sulfur dioxide. In such an exhaust gas flue gas desulfurization step, for example, a sulfurous acid slurry containing a sulfite compound can be used by bringing a raw material slurry containing lime into contact with the exhaust gas.

  In the pulverizing step, a cement composition may be obtained by mixing a cement clinker, a sulfurous acid slurry, and gypsum, and then pulverizing a compound containing these. In another example, in the grinding step, the mixing and grinding of the cement clinker, the sulfurous acid slurry, and the gypsum may be performed simultaneously. As yet another example, in the pulverizing step, after the cement clinker is pulverized to some extent, the sulfurous acid slurry and the gypsum are blended, and the resulting blend may be further pulverized.

  The manufacturing method of the present embodiment may include a firing step of firing the raw materials to manufacture a cement clinker. As a raw material of the cement clinker, for example, limestone can be mentioned. The sulfurous acid slurry can be obtained in a desulfurization step in which the raw material slurry absorbs sulfurous acid gas contained in the exhaust gas.

Examples of the sulfite compound contained in the sulfite slurry include calcium sulfite (for example, hemihydrate), calcium bisulfite (Ca (HSO ₂ ) ₂ ), a double salt of calcium sulfite and calcium sulfate, and magnesium sulfite. The content of the sulfite compound (in terms of anhydride) 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, particularly based on the entire solid content. It is preferably at least 70% by mass.

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

  When the sulfite slurry contains an appropriate amount of calcium sulfate, the amount of gypsum in the pulverizing step can be reduced or omitted. The content of calcium sulfate dihydrate in the sulfurous acid slurry is, for example, 70% by mass or less, preferably 50% by mass or less, and more preferably 30% by mass or less based on the whole solid content. From the viewpoint of obtaining a sulfurous acid slurry containing the above components in a suitable range, the pH is preferably 3.0 to 11.0, more preferably 4.0 to 9.0, and more preferably 5.0 to 7.0. 0 is more preferred.

  In one example, the ratio of the solid content in the sulfurous acid slurry is preferably 0.1 to 95% by mass. The ratio of the solid content in the sulfurous acid slurry is more preferably 1 to 70% by mass, still more preferably 3 to 50% by mass, and particularly preferably 5 to 40% by mass. Within such a range, the mixture of the sulfurous acid slurry and the cement composition can be sufficiently uniform while maintaining the handleability of the sulfurous acid slurry at a high level. The method may include a slurry concentration adjusting step of dehydrating the sulfurous acid slurry or adding water to the sulfurous acid slurry to adjust the solid content ratio to 30 to 95% by mass.

  A gypsum slurry containing gypsum may be obtained by performing an oxidation treatment step of bringing a part of the sulfurous acid slurry obtained in the desulfurization step into contact with air or oxygen. The gypsum slurry is dehydrated to form gypsum, which may be used in the grinding step. The ratio of oxidizing the sulfurous acid slurry may be adjusted according to the supply and demand balance between the sulfurous acid slurry and the gypsum slurry or gypsum. Thereby, the production cost of the cement composition can be further reduced.

The other part of the sulfurous acid slurry may bypass the oxidation treatment step. Further, it may comprise an analysis step of analyzing the SO ₂ content in the solid content of the sulfite slurry obtained in the desulfurization step. It is preferable to determine whether or not the sulfurous acid slurry obtained in the desulfurization step bypasses the oxidation treatment step according to the analysis result of the SO ₂ content in the analysis step. This makes it possible to adjust the amounts of the sulfite compound (calcium sulfite) and the gypsum according to the properties of the sulfite slurry. Therefore, the production cost of the cement composition can be stably reduced. SO ₂ concentration in the solids content of the sulfite slurry is 5 to 50 mass%, for example.

  The type of cement clinker obtained in the cement production process is not particularly limited, and may be any of various portland cements specified in JIS R 5210: 2003 “Portland cement”. According to the cement composition of the present embodiment, the elution of hexavalent chromium can be sufficiently suppressed. The total chromium content of the cement clinker may be, for example, from 20 mg / kg to 250 mg / kg, from 80 mg / kg to 200 mg / kg, or from 100 to 150 mg / kg. The amount of the water-soluble hexavalent chromium of the cement clinker measured according to the method described in the Cement Institute 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 the present embodiment can be 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, low heat Portland cement, and the like. Further, 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 pulverizing step, a cement composition may be obtained by blending and pulverizing a cement clinker, a sulfurous acid slurry and, if necessary, gypsum. The gypsum to be blended may be in any form of gypsum dihydrate, gypsum hemihydrate and anhydrite. Each form of gypsum may be blended alone or in combination of a plurality of types. The order of blending the cement clinker, the sulfite slurry and the gypsum is not particularly limited, and two of these may be blended first and then the remaining one blended, or three may be blended simultaneously. . The mixing amount of gypsum may be about 3 to 10% by mass in terms of SO _{3 with} respect to cement clinker. The gypsum may be prepared by oxidizing and dehydrating a part of the sulfurous acid slurry.

  The pulverization in the pulverization step may be performed by a finishing mill such as a ball mill or a vertical mill. Into the finishing mill, a cement composition is manufactured by introducing a cement clinker, a sulfurous acid slurry, gypsum, a grinding aid, and the like, and mixing 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 still more preferably 1 to 5% by mass.

The Blaine specific surface area of the cement composition obtained by the pulverization treatment is preferably 2500 to 6000 cm ² / g, more preferably 3000 to 5000 cm ² / g. When the Blaine specific surface area is 2500 cm ² / g or more, it is easy to achieve excellent strength development. On the other hand, if the Blaine specific surface area is 6000 cm ² / g or less, the viscosity when used as a concrete or solidified material slurry can be easily controlled to a suitable range.

  The form of gypsum contained in the cement composition is preferably gypsum dihydrate or anhydrous gypsum (type II). Of the gypsum contained in the cement composition, the proportion of hemihydrate gypsum is preferably 90% by mass or less, more preferably 60% by mass or less, based on the total amount of gypsum dihydrate and anhydrous gypsum. It is more preferably at most 20 mass%, most preferably at most 20 mass%.

You may have the raw material slurry preparation process of preparing a raw material slurry. In the raw material slurry preparation step, the raw material slurry may be prepared using dust particles containing CaO and / or Ca (OH) ₂ obtained from the bleed gas from the chlorine bypass section, or may be obtained by washing the dust particles with water. A raw material slurry may be prepared using water-washed dust particles.

The raw material slurry may be prepared by collecting an inorganic compound generated in a cement factory. Examples of such an inorganic compound include fine particle powder containing CaCO ₃ as a main component, which is generated when pulverizing a raw material for cement clinker, dust particles containing CaO and / or Ca (OH) ₂ generated in a chlorine bypass section, and Washed dust particles obtained by washing the dust particles with water are exemplified. The raw material slurry may be prepared by mixing sludge containing cement and / or cement hydrate. As the sludge, for example, ready-mixed sludge obtained at a ready-mixed concrete factory can be mentioned.

  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, the sulfurous acid gas can be sufficiently absorbed in the desulfurization step. Examples of the calcium compound include calcium carbonate, lime (slaked lime and quick lime), and the like.

The SO ₂ concentration of the exhaust gas in another factory may be, for example, 200 to 100,000 ppm or 1000 to 20,000 ppm. By using the exhaust gas containing SO ₂ at such a concentration, a sufficient amount of the sulfite compound can be obtained from the exhaust gas while maintaining the stability of the desulfurization step.

  The desulfurization step may be performed in a cement factory, or may be performed in another factory located on a site different from the cement factory. When the desulfurization step is performed in a cement factory, a transfer step of transferring exhaust gas containing sulfurous acid gas generated in another factory to a cement factory by a pipeline, for example, is performed. The sulfurous acid slurry can be prepared by performing a desulfurization step of the exhaust gas transported to the cement factory. On the other hand, when the desulfurization step is performed in another factory, a transport step of transporting the sulfurous acid slurry prepared in another factory using, for example, a pipeline, a ship, a lorry, or the like is performed.

  The manufacturing method of the present embodiment uses a sulfurous acid slurry obtained by absorbing the sulfurous acid gas contained in the exhaust gas generated in another factory into the raw material slurry, so that a cement composition capable of reducing the elution of hexavalent chromium can be produced at low cost. Can be manufactured. The sulfurous acid slurry also contributes to the desulfurization of the exhaust gas, and since the sulfurous acid compound is used as a slurry without drying, a series of processes of desulfurization and production of the cement composition can be simplified. In addition, since a sulfite slurry can be used instead of water injection at the time of pulverizing the cement composition, and since the slurry is in the form of a slurry, the mixing property between the sulfite compound and the cement clinker is improved, thereby shortening the pulverization process and simplifying the equipment. In addition, there is an advantage that the production cost of a cement composition effective for reducing the elution of hexavalent chromium can be significantly reduced.

  The method for producing a cement composition of the present embodiment may be performed using a cement composition production system described below, or may be performed using another cement composition production system. The description of the cement composition manufacturing system described below can be applied to the cement composition manufacturing method of the present embodiment.

  FIG. 1 is a diagram showing one embodiment of a system for producing a cement composition. The cement composition manufacturing system 300 includes a cement factory 100 and another factory 200 installed on a site different from the cement factory 100. The cement plant 100 includes a cement kiln unit 10 that includes a cement kiln unit 10 that sinters raw materials to produce a cement clinker, a bypass unit 12 that bleeds exhaust gas, and a preheater unit 16 that includes one or more cyclones. A pulverizing section 50 for pulverizing a compound containing the sulfurous acid slurry to obtain a cement composition. The separate factory 200 includes the exhaust gas generator 20 and a desulfurization unit 60 that desulfurizes at least a part of the exhaust gas generated by the exhaust gas generator 20 to obtain a sulfurous acid slurry.

  The separate factory 200 may be installed at a location geographically distant from the cement factory 100 including the cement firing unit 70 and the crushing unit 50. The cement factory 100 and the separate factory 200 may be separated by, for example, a road, or may be separated by the sea, a river, or a mountain. The cement factory 100 manufactures a cement clinker by the cement firing unit 70 and manufactures a cement composition using the cement clinker. On the other hand, the type of the other factory 200 is not particularly limited as long as it has facilities for producing exhaust gas containing sulfurous acid gas. For example, it may be a factory different from a cement factory, and may be a thermal power plant or a factory (steel mill) in the steel industry. The exhaust gas generator 20 may be, for example, a combustion device, a boiler, a gas turbine, or a sintering furnace.

  The preheater section 16 provided in the cement firing section 70 of the cement plant 100 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 extracts exhaust gas from between the kiln butt 10a of the cement kiln section 10 and a bottom cyclone (cyclone at the bottom) or a calciner (not shown) of the preheater section 16. This bypass section 12 may be a chlorine bypass section. The cement clinker produced in the cement kiln section 10 is cooled to, for example, 40 to 220 ° C., preferably 80 to 150 ° C. in the cooling section 11 and introduced into the silo 18.

The desulfurization unit 60 provided in the separate factory 200 includes a sulfur dioxide slurry preparation unit 30 that brings an exhaust gas containing a sulfur dioxide gas into contact with the exhaust gas and a raw material slurry containing a calcium compound to obtain a sulfur sulfite slurry containing calcium sulfite as a sulfite compound, A raw material slurry preparing unit 34 for preparing a raw material slurry is provided. The raw material slurry preparing unit 34 is supplied with water and fine particle powder containing CaCO ₃ as a main component from a crushing unit 82 provided in the cement plant 100 and crushing a raw material (eg, limestone). In addition, the raw material slurry preparation unit 34 cleans the bleed gas from the bypass unit 12 to, for example, 400 ° C. or less, preferably 100 to 200 ° C., and cleans the dust particles containing a chlorine compound that aggregates by cleaning the dust particles. Sludge containing the obtained washed dust particles, cement or cement hydrate (raw con sludge obtained at a ready-mixed concrete factory, etc.) may be supplied (raw material slurry preparation step). Each raw material blended in the raw material slurry may be transferred from the cement plant 100 to another plant 200 by a pipeline, a lorry, a ship, or the like, or may be one produced at another plant 200.

  The sulfurous acid slurry preparing unit 30 is, for example, a bubbling tank, and brings the raw material slurry continuously or intermittently supplied from the raw material slurry preparing unit 34 into contact with the exhaust gas containing the sulfurous acid gas. Thereby, the sulfurous acid gas is taken into the raw material slurry, and a sulfurous acid slurry can be obtained. Further, it is possible to effectively use sulfurous acid gas whose release to the atmosphere is regulated. Thus, the sulfurous acid slurry preparation unit 30 also functions as a flue gas desulfurization unit. The contact means between the raw material slurry and the exhaust gas is not limited to bubbling, but may be a method of spraying the raw material slurry.

  A part of the sulfurous acid slurry prepared by the sulfurous acid slurry preparation unit 30 is introduced into the oxidation treatment unit 41 and comes into contact with air. In the oxidation treatment section 41, calcium sulfite contained in the sulfite slurry is oxidized to generate gypsum. The gypsum slurry containing gypsum thus generated may be transported from another factory 200 to the cement factory 100 and used in the pulverizing unit 50 or used for another purpose. The other part of the sulfurous acid slurry prepared by the sulfurous acid slurry preparing unit 30 may be conveyed to the cement factory 100 via the conveying unit 90 as the sulfurous acid slurry, bypassing the oxidation treatment unit 41.

  Without preparing the gypsum slurry, the entire amount of the sulfite slurry may be transported from the separate factory 200 to the cement factory 100 via the transport section 90, or based on the supply and demand balance between the sulfite slurry and the gypsum slurry or gypsum. The amount of the sulfurous acid slurry to be oxidized may be adjusted. In FIG. 1, a transport unit 90 shown at the boundary between the separate factory 200 and the cement factory 100 is a transfer unit that transfers fluid between the different factory 200 and the cement factory 100 that are geographically separated from each other. , For example, a pipeline. In another example, it may be a lorry or a ship. When the fluidity of the sulfurous acid slurry is low, a watertight dump may be used.

  Air may be introduced into the sulfurous acid slurry preparation section 30. Thereby, a part of calcium sulfite may be oxidized to obtain calcium sulfate dihydrate. Thereby, a sulfurous acid slurry containing calcium sulfite and calcium sulfate dihydrate can be obtained. When the sulfite slurry contains calcium sulfate dihydrate, the amount of gypsum in the blending section 51 can be reduced or eliminated.

An analysis unit for analyzing the SO ₂ content contained in the solid content of the sulfurous acid slurry obtained by the sulfurous acid slurry preparation unit 30 may be provided. It is preferable to determine whether or not the sulfurous acid slurry obtained by the sulfurous acid slurry preparation unit 30 bypasses the oxidation treatment unit 41 according to the analysis result of the SO ₂ content in the analysis unit. This makes it possible to adjust the amounts of the sulfite compound (calcium sulfite) and the gypsum according to the properties of the sulfite slurry. Therefore, the production cost of the cement composition can be stably reduced. SO ₂ concentration in the solids content of the sulfite slurry is 5 to 50 mass%, for example.

  Part of the sulfurous acid slurry transported by the transport unit 90 from another factory 200 is introduced into the slurry concentration adjusting unit 36. The slurry concentration adjusting section 36 is configured to be able to adjust the solid concentration in the sulfurous acid slurry by dehydration or water addition. The solid content concentration in the sulfurous acid slurry may be 0.1 to 95% by mass, and may be 30 to 95% by mass. The content (in terms of anhydride) of the sulfite compound with respect to the entire 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 further preferably 20% by mass or more. % By mass or more. Note that the slurry concentration adjusting unit 36 may be installed in another factory 200. It is not essential to provide the sulfurous acid slurry preparation unit 30 and the slurry concentration adjustment unit 36 separately. In another embodiment, the concentration of the solid content may be adjusted in the sulfurous acid slurry preparation section 30.

  The other part of the sulfurous acid slurry transported from the different factory 200 by the transport unit 90 is oxidized in the oxidizing unit 42. The oxidation treatment is performed, for example, by bubbling air. Thus, a gypsum slurry containing gypsum is obtained from a sulfite slurry containing calcium sulfite. The gypsum slurry may be dehydrated in the dewatering section 44 to make solid gypsum. The gypsum thus obtained is introduced into the mixing section 51. It is not always necessary to provide both the oxidizing unit 42 and the dewatering unit 44 in the cement factory 100. For example, in another factory 200, the dewatering unit 44 is provided downstream of the oxidizing unit 41 to remove the dehydrated gypsum. It may be transported to the factory 100 and introduced into the crushing unit 50. Alternatively, the gypsum slurry obtained in the oxidation processing section 41 may be transported to the cement factory 100 and introduced into the dewatering section 44 provided in the cement factory 100.

  The sulfurous acid slurry whose solid content concentration is adjusted in the slurry concentration adjusting section 36 and the cement clinker stored in the silo 18 are introduced into the mixing section 51 in the pulverizing section 50. The cement clinker may be introduced once after being stored in the silo 18, or may be introduced directly from the cooling unit 11. The temperature of the cement clinker introduced into the mixing section 51 is, for example, 80 to 150 ° C.

In the blending unit 51, gypsum other than the gypsum supplied from the dewatering unit 44 may be blended as needed. The sulfite slurry may contain at least one sulfite compound selected from the group consisting of calcium sulfite hemihydrate, calcium bisulfite (Ca (HSO ₃ ) ₂ ), and double salts of calcium sulfite and calcium sulfate. preferable. In this case, when the cement composition is set to 100 parts by mass, the sulfite slurry is added to the cement clinker, preferably in an amount of 0.1 to 20 parts by mass in terms of an anhydride of the sulfite compound (or an anhydride of calcium sulfite). Preferably 0.15 to 15 parts by mass, more preferably 0.2 to 10 parts by mass, particularly preferably 0.25 to 5 parts by mass. Thus, the mixture can be pulverized smoothly while maintaining the content of the sulfite compound in the obtained cement composition. When a double salt of calcium sulfite and calcium sulfate is contained as the sulfite compound, calcium sulfite in the double salt may be contained in the above-mentioned mass ratio. The mixing 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 comprising cement clinker, a sulfite slurry and, optionally, gypsum is introduced into a 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 increase due to frictional heat during pulverization. Water is sprayed into the cement mill 52 so that the temperature inside the cement mill 52 does not rise excessively. Therefore, when the sulfurous acid slurry contains an appropriate amount of water, an excessive rise in temperature in the cement mill 52 can be suppressed. For this reason, blending the sulfite compound in a slurry form also contributes to reducing the amount of water sprayed into the cement mill 52.

  The temperature of the cement composition at the outlet of the cement mill 52 is preferably from 20C to 180C, more preferably from 40C to 150C, and still more preferably from 60C to 90C. If the temperature is too low, the water content of the sulfurous acid slurry causes a hydration reaction with the cement composition, and the strength development tends to decrease. On the other hand, if the temperature is too high, calcium sulfite is oxidized and changes to calcium sulfate, or the amount of hemihydrate gypsum that causes a decrease in fluidity due to dehydration of gypsum to be added is increased. Tend. That is, by setting the temperature in the above-mentioned temperature range, the drying of the composition proceeds at a sufficient speed while suppressing the oxidation of calcium sulfite. In addition, the cement clinker, calcium sulfite, and gypsum can be sufficiently uniformly mixed.

  In the present embodiment, the crushing unit 50 includes the blending unit 51 and the cement mill 52, but is not limited thereto. For example, in a variant, the cement clinker, the sulfurous acid slurry and the optional gypsum may be introduced directly into the cement mill 52 and compounded and ground there. In addition, the cement clinker and the gypsum are blended in the blending unit 51, and on a belt conveyor that conveys the blend obtained from the blending unit 51 to the cement mill 52, a sulfurous acid slurry is sprayed on the blend and crushed by the cement mill 52. May go. In this way, a cement composition that can reduce the elution of hexavalent chromium can be manufactured at low cost. The cement composition obtained by the pulverization in the cement mill 52 is stored in a tank 54.

  In another modification, a control unit that adjusts the blending ratio of the sulfurous acid slurry to the cement clinker according to the chromium content of the cement clinker derived from the cement kiln unit 10 may be provided. 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 of the raw material introduced into the cement firing unit 70.

  The cement composition manufacturing system 300 and its modified examples, and the cement composition manufacturing systems 310 and 320 described below may be used based on the content of the above-described cement composition manufacturing method. Therefore, the contents described in the method for producing a cement composition also apply to the production systems 300, 310, and 320 for the cement composition. The description of the cement composition manufacturing systems 300, 310, and 320 and the modifications thereof also applies to the above-described cement composition manufacturing method. The production system of the cement composition of the present disclosure can perform both the production of a sulfurous acid slurry and the desulfurization of exhaust gas, and further includes a dehydration facility for the sulfurous acid slurry, or a dedicated system for solids after dehydration. There is no need to provide tanks, weighing machines, and transport equipment. For this reason, the introduction cost and operation cost of the equipment can be sufficiently reduced. However, the present disclosure does not exclude those having such equipment.

FIG. 2 is a diagram showing another embodiment of the system for producing a cement composition. The cement composition manufacturing system 310 of this embodiment is provided with a point that the exhaust gas containing the sulfurous acid gas generated from the exhaust gas generator 20 of the separate factory 201 is transported by the transport unit 90, and that the desulfurization unit 60 is provided in the cement factory 101. In that it differs from the cement composition manufacturing system 300 in that The other elements are the same as those of the cement composition manufacturing system 300, and the description of the cement composition manufacturing system 300 applies. In the case of the cement composition manufacturing system 310, the raw material slurry is prepared by introducing the fine particle powder mainly composed of CaCO ₃ obtained in the pulverizing unit 82 into the raw material slurry preparing unit 34 in the cement plant 101. Can be. Therefore, there is no need to transport the raw material of the raw slurry to another factory 201, and the number of transported items can be reduced.

  FIG. 3 is a diagram showing still another embodiment of the system for producing a cement composition. The cement composition manufacturing system 320 of this embodiment includes a first preparation unit 30A and a first preparation unit that prepare an aqueous solution or slurry containing magnesium sulfite instead of the sulfite slurry preparation unit 30 that prepares a sulfite slurry containing calcium sulfite. A cement composition manufacturing system in that a second preparation unit 32 is provided that mixes the aqueous solution or slurry containing magnesium sulfite prepared in Part 30A with a raw material slurry containing a calcium compound to prepare a sulfite slurry containing calcium sulfite. Different from 300. Other elements are the same as those of the cement composition manufacturing system 300, and thus the description of the cement composition manufacturing system 300 is applied.

  In the first preparation unit 30A, the aqueous solution containing magnesium hydroxide absorbs the exhaust gas containing the sulfurous acid gas generated in the exhaust gas generator 20 of the different factory 202. Thus, an aqueous solution or slurry containing magnesium sulfite is obtained (magnesium hydroxide method). Since magnesium sulfite has higher solubility in water than calcium sulfite, it is possible to suppress the solid content in the first preparation unit 30A. To the aqueous solution or slurry prepared in the first preparation unit 30A, a raw material slurry containing a calcium compound is added from a raw material slurry preparation unit 34 in a second preparation unit 32 provided downstream of the first preparation unit 30A. Thus, the second preparation section 32 can obtain a sulfurous acid slurry containing calcium sulfite. The sulfurous acid slurry is transported to the cement factory 100 by the transport unit 90, and is used in the same manner as the cement composition manufacturing system 300.

  The first preparation unit 30A needs to maintain a certain degree of hermeticity in order to suppress emission of exhaust gas to the outside. Therefore, it is preferable to reduce the maintenance frequency. In the present embodiment, among the sulfites, magnesium sulfite having a higher solubility in water than calcium sulfite is first generated, and then the sulfite slurry containing calcium sulfite is prepared in the second preparation unit 32. Therefore, the frequency of maintenance of the first preparation unit 30A due to scaling of calcium sulfite can be reduced, and the stability of the process in another factory 202 can be improved.

  In the present embodiment, magnesium hydroxide is used in the first preparation unit 30A. However, the present invention is not limited to this, and a salt that can generate a sulfite compound having higher solubility in water than calcium sulfite may be used. it can. As such a salt, a salt of an alkaline earth metal or an alkali metal different from Ca and Mg can be used, for example, potassium hydroxide and calcium hydroxide.

  Although some embodiments have been described above, the present disclosure is not limited to the above-described embodiments. For example, the first preparation unit 30A and the second preparation unit 32 may be provided in the cement plant 101 of the cement composition manufacturing system 310 to prepare a sulfite slurry containing calcium sulfite from magnesium sulfite. In another example, a first preparation section is provided in another factory, a slurry or an aqueous solution containing magnesium sulfite is transported to a cement factory by a transport section, and a sulfite slurry containing calcium sulfite is transported in a second preparation section provided in the cement factory. May be prepared. Further, as a sulfurous acid source, industrial wastewater containing a water-soluble sulfite containing at least one of an alkali metal and an alkaline earth metal different from Ca generated in a cement plant or another plant may be used in addition to the exhaust gas. The sulfite slurry may include calcium sulfite obtained by treating such industrial wastewater with a calcium compound.

(Reference Example 1)
A raw material slurry (0.4 L) having a solid content of 3% by mass was prepared by mixing commercially available CaCO ₃ powder and water. Bleed gas was collected from the chlorine bypass section of the cement composition manufacturing apparatus. After the extracted gas was cooled to about 200 ° C., dust particles were removed with a bag filter. The concentration of sulfur dioxide in the extracted gas after removing the dust particles was 1500 ppm (by volume). This bleed gas was blown into the raw material slurry for bubbling, and the sulfur oxide in the bleed gas was absorbed by the raw material slurry. As a result, a sulfite slurry containing calcium sulfite was obtained. The solid content of the obtained slurry was about 10% by mass.

The sulfurous acid slurry was filtered to collect a solid content. The collected solid was dried in an air atmosphere at about 40 ° C. Using an X-ray diffractometer (manufactured by Bruker AXS, Inc., acceleration voltage: 30 kV, current: 10 mA, tube: Cu), the X-ray pattern of the obtained solid was measured. The X-ray pattern was subjected to Rietveld analysis using analysis software (Topas®, manufactured by Bruker AXS Corporation), and CaCO ₃ , Ca (OH) ₂ , CaSO ₃ .0.5H ₂ O, and were quantified CaSO ₄ · 2H ₂ O. The analysis results were as shown in Table 1.

(Reference Example 2)
A sulfurous acid slurry was obtained in the same manner as in Reference Example 1, except that a raw material slurry was prepared using Ca (OH) ₂ powder instead of CaCO ₃ powder. In the same manner as in Reference Example 1, the obtained sulfurous acid slurry was subjected to X-ray diffraction. The analysis results were as shown in Table 1.

  As shown in Table 1, in Reference Examples 1 and 2, 9% by mass and 23% by mass of calcium sulfite hemihydrate were detected, respectively. From this result, it was confirmed that the sulfurous acid slurry after contacting the exhaust gas containing sulfurous acid contained calcium sulfite. By using the sulfurous acid slurry thus obtained in the pulverizing step, a cement composition capable of reducing the elution of hexavalent chromium can be produced.

  According to the present disclosure, a method and system for producing a cement composition capable of producing a cement composition effective for reducing elution of hexavalent chromium at low cost are provided.

  DESCRIPTION OF SYMBOLS 10 ... Cement kiln part, 10a ... Kiln bottom, 11 ... Cooling part, 12 ... Bypass part, 16 ... Preheater part, 18 ... Silo, 20 ... Exhaust gas generator, 30 ... Sulfurous acid slurry preparation part, 30 ... Sulfurous acid slurry preparation part, 30A: first preparation unit, 32: second preparation unit, 34: raw material slurry preparation unit, 36: slurry concentration adjustment unit, 41, 42: oxidation treatment unit, 44: dehydration unit, 50: pulverization unit, 51: compounding unit , 52: cement mill, 60: desulfurizing unit, 70: cement firing unit, 82: crushing unit, 90: transport unit, 100, 101: cement factory, 200, 201, 202: separate factory, 300, 310, 320: cement Composition manufacturing system.

Examples of the sulfite compound 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 the sulfite compound (in terms of anhydride) 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, particularly based on the entire solid content. It is preferably at least 70% by mass.

Claims (22)

A pulverizing step of blending and pulverizing a cement clinker and a sulfite slurry containing a sulfite compound to obtain a cement composition,
A method for producing a cement composition, wherein the sulfurous acid slurry contains a sulfurous acid compound obtained by desulfurizing exhaust gas generated at another factory located on a site different from the cement factory where the pulverizing step is performed.   The method for producing a cement composition according to claim 1, wherein the sulfurous acid slurry is obtained without going through an oxidation treatment step of oxidizing the sulfurous acid compound after a desulfurization step of absorbing sulfurous acid gas in the exhaust gas.   The method for producing a cement composition according to claim 1, wherein in the pulverizing step, the cement composition is obtained by mixing gypsum.   The method for producing a cement composition according to any one of claims 1 to 3, wherein a ratio of a solid content in the sulfurous acid slurry is 0.1 to 95% by mass. The sulfurous acid slurry, as a solid content,
At least one sulfite compound selected from the group consisting of calcium sulfite hemihydrate, calcium bisulfite (Ca (HSO ₃ ) ₂ ), and double salts of calcium sulfite and calcium sulfate;
Dihydrate of calcium sulfate, calcium hydroxide, calcium carbonate, and at least one salt selected from the group consisting of magnesium hydroxide,
The method for producing a cement composition according to any one of claims 1 to 4, comprising:   When the cement composition is set to 100 parts by mass, 0.1 to 20 parts by mass of the sulfurous acid slurry is added to the cement clinker in terms of an anhydride of the sulfurous acid compound. The method for producing a cement composition according to the above.   The sulfuric acid slurry is obtained by absorbing a sulfurous acid gas contained in the exhaust gas into an aqueous solution containing an alkaline earth metal and / or an alkali metal salt different from Ca, and then mixing a calcium compound. The method for producing a cement composition according to any one of claims 6 to 6.   The said sulfite slurry contains calcium sulfite obtained by treating an industrial wastewater containing a water-soluble sulfite containing at least one of an alkali metal and an alkaline earth metal different from Ca with a calcium compound. The method for producing a cement composition according to any one of the above. A desulfurization step of obtaining a sulfurous acid slurry by absorbing sulfurous acid gas into the raw material slurry,
An oxidation treatment step of oxidizing a part of the sulfurous acid slurry to obtain a slurry containing gypsum, wherein the other part of the sulfurous acid slurry bypasses the oxidation treatment step. 3. The method for producing a cement composition according to item 1. Has analysis step of analyzing the SO ₂ content in the solid content of the sulfite slurry obtained in the desulfurization step,
In response to said analysis result of the SO ₂ content, the sulfite slurry determines whether to bypass the oxidation step, the manufacturing method of the cement composition of claim 9.   The method for producing a cement composition according to any one of claims 1 to 10, further comprising a slurry concentration adjusting step of adjusting a ratio of a solid content of the sulfurous acid slurry to 30 to 95% by mass.   The method for producing a cement composition according to claim 11, wherein an aqueous solution or slurry containing magnesium sulfite is prepared from the sulfurous acid gas contained in the exhaust gas, and the aqueous solution or slurry is mixed with a calcium compound to obtain the sulfurous acid slurry. The fine particles containing CaCO ₃ as a main component, the dust particles containing CaO and / or Ca (OH) ₂ generated in the chlorine bypass part, and the dust particles generated when the raw material of the cement clinker is crushed are washed with water. A raw material slurry preparation step of preparing a raw material slurry for desulfurizing the exhaust gas using at least one selected from the group consisting of washed water particles obtained and sludge containing cement and / or cement hydrate. 13. The method for producing the cement composition according to any one of the above items 12.   The method for producing a cement composition according to any one of claims 1 to 13, further comprising a transporting step of transporting the exhaust gas or the sulfurous acid slurry from the different factory to the cement factory. A pulverizing unit that obtains a cement composition by mixing a compound including a cement clinker and a sulfite slurry containing a sulfite compound,
A desulfurization unit for desulfurizing at least a part of exhaust gas generated in another plant located on a site different from a cement plant including the pulverizing unit to obtain the sulfurous acid slurry, a cement composition production system.   The cement composition manufacturing system according to claim 15, wherein a ratio of a solid content in the sulfurous acid slurry is 0.1 to 95% by mass. The sulfurous acid slurry, as a solid content,
Calcium bisulfite (Ca (HSO ₃ ) ₂ ) and at least one sulfite compound selected from the group consisting of double salts of calcium sulfite and calcium sulfate;
The system for producing a cement composition according to claim 15 or 16, comprising: at least one salt selected from the group consisting of calcium sulfate dihydrate, calcium hydroxide, calcium carbonate, and magnesium hydroxide.   18. A sulfurous acid slurry preparing section for obtaining a sulfurous acid slurry by absorbing a sulfurous acid gas into a raw material slurry, and an oxidizing section for oxidizing the sulfurous acid slurry to obtain a slurry containing gypsum, the apparatus according to any one of claims 15 to 17. The manufacturing system of the cement composition of Claim.   The system for producing a cement composition according to claim 18, further comprising a slurry concentration adjusting unit for adjusting a ratio of a solid content of the sulfurous acid slurry to 30 to 95% by mass. A first preparation unit for absorbing a sulfurous acid gas contained in the exhaust gas into an aqueous solution containing an alkaline earth metal and / or an alkali metal salt different from Ca to obtain a sulfite compound different from calcium sulfite;
20. The cement composition manufacturing system according to claim 19, further comprising: a second preparation unit that mixes the sulfite compound and the calcium compound to obtain the sulfite slurry containing calcium sulfite. The fine particles containing CaCO ₃ as a main component, the dust particles containing CaO and / or Ca (OH) ₂ generated in the chlorine bypass part, and the dust particles generated when the raw material of the cement clinker is crushed are washed with water. 21. A raw material slurry preparing section for preparing a raw material slurry by using at least one selected from the group consisting of obtained washed dust particles and cement and / or sludge containing cement hydrate. Item 10. A system for producing a cement composition according to item 9.   The cement composition manufacturing system according to any one of claims 15 to 21, further comprising a transport unit configured to transport the exhaust gas or the sulfurous acid slurry from the different factory to the cement factory.

Images