JP2014129204A - Expansible material and expansible composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient method of use capable of making more ash generated during coal combustion by a pressure fluidized bed boiler to be a utilization object regardless of the magnitude of variations of ingredients.SOLUTION: An expansible material is a baked product of (A) PFBC ash of 100 pts.mass, (B) caustic lime of 300 to 1000 pts.mass or a calcium salt generating 300 to 1000 pts.mass of calcium oxide by thermal decomposition with baking, and has a percentage content of free caustic lime of 40 to 80 mass%.

Description

  The present invention relates to effective use of calcined ash generated by pressurized fluidized bed combustion of coal.

  Due to the energy situation, attempts are being made to actively use so-called low-grade coal that has been avoided as a fuel for power generation in coal-fired power generation. A pressurized fluidized bed boiler has begun to be used as a device suitable for burning low-grade coal. This pressurized fluidized bed boiler is a fluidized bed of a mixture of massive coal and limestone that has not been pulverized and burned under pressure. It has excellent thermal efficiency and can be burned at low temperatures, so it can be used for nitrogen oxides and sulfur oxides. It is difficult to generate vaporized substances such as Further, the characteristics of the ash after burning coal fuel in the boiler (hereinafter referred to as “PFBC ash”) are also considerably different from the coal ash derived from pulverized coal burned in a conventional pulverized coal combustion boiler or the like. That is, PFBC ash has a more angular particle shape than coal ash obtained by combustion of a conventional pulverized coal boiler or the like. In addition, since desorption due to vaporization is unlikely to occur, those containing sulfur or particularly low-grade coal are likely to be enriched with a high concentration of calcium, and these substances form crystalline compounds, resulting in a crystalline production rate. There is a tendency to increase considerably. In this way, it has physical and chemical characteristics that are far from conventional coal ash, so it is not suitable for seeking a place of use for conventional coal ash users, and promising effective utilization measures have been found. It's not a situation. As a few known PFBC ash industrial applications and resource recycling technologies, soil improvement materials containing PFBC ash having a specific average particle size as an active ingredient (see, for example, Patent Document 1), cement use amount. About half (mass) of the concrete composition that can be replaced with PFBC ash obtained under specific conditions (see, for example, Patent Document 2), and the specific PFBC ash is mixed with Portland cement and used as a non-shrinkable cement Only a few examples such as technology (see, for example, Patent Documents 3 and 4) are disclosed. Among these, the non-shrinkage cement mixed with PFBC ash uses low-grade coal as a fuel, so that the quantitative variation of the components contained in the coal itself is very large. For this reason, the components contributing to the formation of expansive hydrates such as limes and gypsum in the PFBC ash and the amount thereof can vary considerably depending on the fuel lot. When PFBC ash with a low content of the expandable hydrate-forming component is used, no shrinkage may be achieved by hydration. Conversely, PFBC ash with a high content of the hydrate-forming component is used. In some cases, overexpansion may occur, causing cracks in mortar or concrete.

  On the other hand, when only the PFBC ash having a specific component content as the expansive hydrate-forming component is selectively used, there is a possibility that most of the PFBC ash deviating from this component content may not be effectively used, which is expensive. There was no choice but to dispose of it at a high disposal cost.

Japanese Patent Laid-Open No. 11-112247 Japanese Patent Laid-Open No. 11-147747 JP 2009-208986 A JP 2010-228930 A

  The present invention is an effective utilization measure of PFBC ash capable of making more PFBC ash to be used regardless of the variation in the content of the components in view of the above situation, without increasing the processing cost and It is an object of the present invention to provide an inflatable substance that does not require complicated operations and complicated processes and can express a stable desired expansibility.

  As a result of repeated studies to solve the above problems, the present inventor baked a mixture of a specific amount of PFBC ash and quicklime regardless of the amount of the components contained therein, so Since the intumescent material was obtained, it was found that PFBC ash can be utilized as the intumescent material, and the present invention was completed.

That is, this invention is the expansible composition represented by following [1]-[3], and the expansible composition represented by [4].
[1] A calcined product of (A) 100 parts by mass of PFBC ash and (B) 300 to 1000 parts by mass of quicklime or a calcium salt that generates 300 to 1000 parts by mass of calcium oxide by pyrolysis by calcining. An expandable substance having a quicklime content of 40 to 80% by mass.
[2] The expansive substance according to the above [1], which contains anhydrous gypsum in the fired product.
[3] The expansible material according to [1] or [2] above, wherein the baked product contains calcium silicate and calcium aluminate.
[4] An expandable composition comprising any of the expandable substances [1] to [3] as an active ingredient.

  According to the present invention, it is possible to provide an optimum use destination of PFBC ash that has not been effectively used so far. For example, the PFBC ash is derived from the combustion of low-grade coal and has been almost disposed of so far. Even simple PFBC ash can be recycled as an expandable material, for example, as a material for civil engineering and construction, without making full use of complicated processing processes.

The expansive substance of the present invention is obtained by firing a mixture containing a specific amount of PFBC ash and quicklime as a material to be fired. The PFBC ash used for the material to be fired is an ash produced as a by-product when a mixture of coal and limestone is burned in a pressurized fluidized bed boiler. Here, the mixing amount of coal and limestone used for combustion in the boiler is not particularly limited. From the viewpoint of combustion efficiency, the addition of approximately 0.02 to 0.14 (both mass ratio) of limestone to coal 1 is shown as one recommended example, but it is only an example, and the structure and capacity of the boiler used The recommended value varies depending on the setting output. Although the thing of the said mass ratio also becomes object in this invention, it is not limited to illustrated mass ratio. In addition, the quality of coal, which is a combustion source of PFBC ash used in the present invention, is not particularly limited, and may be low-grade coal that is disliked in ordinary coal-fired power generation. Moreover, the limestone mixed with coal and used for combustion can use any limestone, and the purity etc. are not specifically limited. The properties of PFBC ash are not only affected by the chemical characteristics of such a material to be baked, but also divided into ash that has a difference in properties such as BM ash and FA ash depending on the location where it is generated in the combustion boiler. Among these, the FA ash is collected mainly by a dust collector leading from the upper part of the boiler, and the content of CaO and SO ₃ as chemical components tends to be higher than that of conventional coal ash. Moreover, since BM ash is taken out from each position of the boiler, the limestone used as the fluid medium inside the pressurized fluidized bed boiler has an overwhelmingly large CaO content as a chemical component, and the particle shape is also angular. Many are irregularly shaped. The PFBC ash that can be used in the present invention can be any of BM ash and FA ash, or both, regardless of the blending ratio. Further, it is not necessary to pre-treat the PFBC ash discharged from the boiler during use.

  The expansive substance of the present invention is a fired mixture of 300 to 1000 parts by weight of quick lime or a calcium salt that generates 300 to 1000 parts by weight of calcium oxide by pyrolysis by firing with respect to 100 parts by weight of such PFBC ash. The product is fired. The calcium salt that can be used is not limited as long as it is a substance that generates calcium oxide by thermal decomposition at about 1250 ° C. to 1500 ° C. in the atmosphere, and the residual product vaporizes and leaves. Specific examples include calcium carbonate, calcium hydroxide, calcium hydrogen carbonate, calcium acetate, and the like, and two or more of these can be used in combination with calcium oxide. Moreover, if the amount of quicklime is less than 300 parts by mass with respect to 100 parts by mass of the PFBC ash, the amount of expansion as that of a conventional expansive substance that can be added to the cement composition may not be obtained, which is not preferable. Also, if the amount of quick lime exceeds 1000 parts by mass with respect to 100 parts by mass of PFBC ash, the material to be baked will be very hygroscopic, so consider the effects on the calcination and carefully store it. Is necessary, and the amount of lime in the material to be baked is considerably high, which reduces the amount of PFBC ash used. Moreover, as long as the expansive substance of this invention does not lose the effect of this invention, the mixture containing components other than the said PFBC ash and quicklime can be used for baking. Examples of such components include sulfates.

The firing temperature of the object to be fired is preferably 1250 ° C. to 1500 ° C. and the firing time is generally 30 minutes to 120 minutes in order to stably generate a predetermined amount of free quick lime, but neither is limited to the stated value. . The firing apparatus is not particularly limited as long as it can be fired at the above temperature, and examples thereof include an electric furnace, a furnace, and a rotary kiln. It is desirable that the fired product is gradually cooled from the maximum temperature to a certain temperature range in order to stably grow calcium oxide crystals. As the slow cooling temperature zone, it is desirable to obtain an appropriate value by a preliminary experiment or the like because it is influenced by the firing furnace structure, the amount of firing treatment, and the like. An example of a standard is a temperature 200 to 300 ° C. lower than the maximum temperature. After this temperature zone has passed, a rapid cooling treatment such as removal from the furnace may be performed. Since the fired product after cooling is usually in the form of a lump, it is desirable to pulverize and adjust the size using a classifier if necessary. Since a more appropriate expansion property can be easily obtained, the grain size is recommended to be 2000 to 7000 cm ² / g in terms of the Blaine specific surface area, but is not limited to the particle size. The particle size can be adjusted by changing the pulverization time of the baked product after cooling with a pulverizing medium such as a ball mill, a vibration mill, a rod mill, or a pin mill, or by appropriately performing classification or sieving after pulverization.

  Moreover, the expansive substance of this invention is the said baked material, Comprising: It is essential that free quicklime content is 40-80 mass%. By setting it as this free quicklime content rate, the expandability of the grade which can prevent shrinkage | contraction of a cement composition when it mixes with cement etc. can be provided, for example. If the free lime content is less than 40% by mass, the expansion force is insufficient, and for example, it is difficult to suppress self-shrinkage of the cement composition, which is not preferable. On the other hand, if the content of free lime exceeds 80% by mass, the weathering resistance of the fired product is lowered and the possibility of deterioration is increased, which is not preferable.

Further, the expandable material of the present invention preferably contains anhydrous gypsum. The anhydrous gypsum content in the expandable material is not particularly limited. In the case where only PFBC ash and quicklime are fired, the gypsum content tends to hardly exceed 3% by mass in view of the chemical component composition, and therefore it is preferable that at least about 2% by mass is contained. Moreover, gypsum may be previously contained in the material to be fired. Here, gypsum refers to any one or more of anhydrous gypsum, dihydrate gypsum, hemihydrate gypsum, and CaSO ₄ . The gypsum content in the material to be baked is not particularly limited, but it is preferably less from the viewpoint of promoting the use of PFBC ash and ensuring a predetermined expansibility. (Non-contained is also possible.) By containing anhydrous gypsum in the expansive substance, it is possible to improve the medium-to-long-term expansion.

The expansible material of the present invention preferably further contains calcium silicate and calcium aluminate. The contents of calcium silicate and calcium aluminate in the expandable material are not particularly limited. Preferably, when the calcium silicate is contained in an amount of 10 to 40% by mass and the calcium aluminate is contained in an amount of 5 to 20% by mass, there is a possibility that the expansion of the expansion can be enhanced by containing the calcium silicate without substantially impairing the expansion of the expansion. In general, calcium silicate, which has a slower hydration reaction than quick lime, and calcium aluminate, which has a quick hydration reaction as quick lime, contain free calcium lime that is substantially surrounded by calcium aluminate and calcium silicate. It is difficult to cause an early hydration reaction after contact with water, and hydration progresses easily with the hydration reaction and strength development of combined hydraulic materials such as cement. Expansion becomes easy to give. The method for containing a predetermined amount of calcium silicate or calcium aluminate in the expandable composition is not particularly limited. Since PFBC ash is likely to contain SiO ₂ and Al ₂ O ₃ , it can also be a source of calcium silicate and calcium aluminate. Moreover, if it is a component which contributes to formation of calcium silicate or calcium aluminate, even components other than PFBC ash can be included in the material to be fired.

  Moreover, the expansive substance of the present invention may contain components other than free quick lime, anhydrous gypsum, calcium silicate and calcium aluminate as long as the effects of the present invention are not lost. Examples of such components include calcium ferrite, calcium aluminosilicate, and Irwin.

  The expansible composition of the present invention contains the expansible substance as an active ingredient, and exhibits expansibility by hydration. The expandable composition of the present invention is, for example, a diluting component for adjusting the expansion force when the free quick lime is produced in a large amount in the fired product obtained by firing the PFBC ash, quick lime, etc. Ingredients that provide the necessary self-hardness for diverting a component that compensates for the desired expansion to a desired level, such as a static crushed material using expansion pressure In addition, for example, when it is desired to adjust the onset of expansion, for example, a hydration reaction promoting component or a retarding component can be mixed with the fired product. Specific components that can form an expandable composition by mixing with the fired product include, for example, gypsum, various portland cements, alkali metal salts, carboxylic acids, and salts thereof. The expansible composition of the present invention can be suitably used by mixing with a hydraulic composition containing various cements as a main binding component, specifically, cement paste, mortar or concrete. Moreover, the thing with a high expansion pressure can be used also for a static crushing material.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the described examples.

  [Preparation of fired product] Using the PFBC ash (P1, P2) and quick lime (commercial product) or fine limestone powder (commercial product) of the chemical components shown in Table 1, dry mixing was performed to obtain the composition shown in Table 2. . About 3 g of the mixture was filled in a cylindrical mold having an inner dimension of 20 mm in diameter and 30 mm in height, and pressure-molded with a pressure of 19.6 MPa to produce a briquette, which was to be fired.

[Baking of the object to be baked]
About 80 g of the produced briquette is put together in a platinum dish, heated to 1400 ° C. at a heating rate of about 10 ° C./min using an electric furnace, held at that temperature for 15 minutes, and then 1200 ° C. over 15 minutes. The temperature was lowered to a temperature, and the fired product was taken out of the furnace. Next, the fired product that was brought to a temperature near room temperature by being left outside the furnace was pulverized by a disk mill. The mineral phase of the pulverized product was examined by powder X-ray diffraction, and the theoretical composition of the mineral phase was calculated from the Borg equation based on the chemical analysis value of the pulverized product. The results are shown in Table 3.

[Preparation of expandable composition]
The crushed material or the pulverized material is mixed with anhydrous gypsum powder and / or ordinary Portland cement as necessary to the blending amount shown in Table 4, and the powder size is adjusted to about 3000 (± 500) cm ² / g. Thus, an expandable composition was produced.

[Evaluation of expandable composition]
30 parts by weight of the expansible composition, 420 parts by weight of ordinary Portland cement (commercially available product), 1350 parts by weight of ISO standard sand and 225 parts by weight of water are defined as “Expansion” defined in Annex I of Concrete Expansion Material of JIS A6202. A test specimen was prepared by kneading according to a method according to “Method for testing expansibility of material by mortar”, and the amount of expansion was measured. Moreover, the compressive strength was measured by the method according to the "mortar compressive strength test of the expansion material for concrete" prescribed | regulated by JISA6202 with respect to the test body produced similarly. For reference, a mortar specimen was also prepared for a kneaded material prepared by mixing a commercially available lime-based expanded material for mortar / concrete with the same kneaded material mixture as described above instead of the expandable composition shown in Table 4 ( The specimen 10), the amount of expansion and the compressive strength were examined by the same method. The above evaluation results are shown in Table 5. Each evaluation test was performed in a room at about 20 ° C.

From the results of Table 5, any of the mortar specimens using the expansible composition of the present invention has an expansibility equal to or greater than that of a commercially available lime-based expansive material for mortar / concrete or an expansibility defined in JIS A6202. It can be seen that the 7-day-old mortar, which is the quality standard, exhibited an expansibility sufficiently satisfying 250 × 10 ⁻⁶ or more, and the strength development was comparable to a commercially available expansive material.

Claims (4)

(A) A calcined product of 100 parts by mass of PFBC ash and (B) 300 to 1000 parts by mass of quick lime or a calcium salt that generates 300 to 1000 parts by mass of calcium oxide by thermal decomposition by calcining, and the content of free quick lime Is an expansible substance having a mass of 40 to 80% by mass. The expansive substance according to claim 1, which contains anhydrous gypsum in the fired product. The expandable substance according to claim 1 or 2, wherein the fired product contains calcium silicate and calcium aluminate. The expansible composition which uses the expansive substance in any one of Claims 1-3 as an active ingredient.