JP2000053456A - Prevention of aggregation and solidification caused by moisture absorption of fly ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent aggregation and solidification caused by moisture absorption at industrially low cost with simple operation by adding a specific quantity of water-insoluble inorganic fine powder to fly ash collected from a waste gas from a pulverized coal combustion boiler. SOLUTION: The water-insoluble inorganic fine powder by 0.1-10 wt.% is added. As the adding method, a method for adding the inorganic fine powder into the fly ash using a system as fixed quantity powder supply device at a transporting near to a dust collector as possible, in the transporting systems of the fly ash after the dust collector of the waste gas by using an aeration equipment for discharging the fly ash or a mixing equipment by air for uniformalizing the fly ash, which is installed side by side with a fly ash storage tank in a thermal power plant or the like, is preferable. As the inorganic fine powder, lime stone fine powder free from the adverse effect on the hydraulic reaction of cement and having blotter effect is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing fly ash collected from exhaust gas from a pulverized coal combustion boiler from coagulating and condensing due to moisture absorption.

[0002]

2. Description of the Related Art Conventionally, if fly ash absorbs moisture excessively, coagulation and consolidation will occur, and the coagulated and consolidated fly ash will not be able to be discharged from a storage tank or the like. It is known that fly ash has a high risk of agglomeration and consolidation, particularly when handling in a high-temperature and high-humidity environment under various adverse conditions.

[0003] In view of the above, various means have conventionally been proposed for preventing cohesion and consolidation of fly ash due to moisture absorption.

For example: 1) Fly ash is heated at a temperature of 500 ° C. or more for 30 minutes or more. 2) Add a small amount of water of 0.4% or less to fly ash, mix and then air dry. 3) Wash fly ash with sufficient water and dry. 4) The fly ash is fluidized by aeration, and wet air is forcibly fed into the fluidized fly ash. 5) After crushing coarse ash (such as cinder sand and pond ash) collected at the same time as fly ash with a pulverized coal-fired boiler to a fineness equivalent to or higher than that of fly ash, pulverize the crushed material of the coarse ash. Ash 4
Replace with about 0%. Such methods have been proposed.

[0005] However, the above methods 1) to 4) are very effective methods for losing the cohesion and solidification ability of fly ash at the laboratory level. It is not a method that can be economically processed. In the method 5), the amount of coarse ash generated is extremely small (about several percent) compared to the amount of fly ash, and therefore, it is equivalent to fly ash when industrially implemented. A problem arises in that the required amount of coarse ash pulverized material is insufficient.

Accordingly, an object of the present invention is to produce a large amount of fly ash industrially at low cost and with a simple operation.
It is an object of the present invention to provide a method for eliminating or relaxing the coagulation and solidification ability of the fly ash due to moisture absorption.

[0007]

Means for Solving the Problems In order to achieve the above object, the present inventors first studied again the causative substance causing fly ash to coagulate and consolidate, and based on the research results, Assuming a method that can eliminate or alleviate the flocculation ability of fly ash,
The present invention was completed by confirming the effect of the method by a test.

[0008] That is, the main soluble salts contained in fly ash are calcium sulfate and sodium sulfate, and it is known that trace amounts of potassium sulfate and magnesium sulfate are further contained. Here, conventionally, calcium sulfate, ie, soluble anhydrous gypsum (III type anhydrous gypsum) and / or hemihydrate gypsum (β type hemihydrate gypsum) (hereinafter referred to as “air-hardening Gypsum), which hydrated to form dihydrate gypsum when it absorbed moisture, and it was thought that the hydration reaction at this time caused fly ash to coagulate and solidify.

However, when the present inventors conducted tests, various phenomena that could not be explained by the conventional gypsum hydration theory (see Test Examples 1 to 3 described later) were found, and the gypsum hydration theory could not be denied. Since it has disappeared, further research has been conducted.The causative substance of fly ash coagulation is sodium sulfate, another main component of soluble salts contained in fly ash. As a result, a high-concentration aqueous solution of sodium sulfate is generated, and when this deliquescent liquid is formed at the contact point between the fly ash particles, the deliquescent liquid forms a cross-link between the fly ash particles,
It has been concluded that this cross-linking phenomenon is the mechanism of cohesion and consolidation of fly ash.

[0010] Therefore, even if a deliquescent solution of sodium sulfate is formed on the surface of fly ash, it is theoretically considered that coagulation does not occur unless cross-links are formed between the fly ash particles. The test was proceeded based on the idea that the condition should be such that the substance can not be present as a liquid by absorbing the substance (this will be referred to as "blotting paper effect").

Thus, the fly ash is preliminarily added and mixed with the water-insoluble inorganic fine powder having no harm to the hydration-hardening reaction of the cement and having a blotting paper effect, and then the fly ash absorbs moisture into the inorganic fine powder. A method of preventing coagulation and consolidation due to moisture absorption of fly ash by absorbing the aqueous sodium sulfate solution generated on the surface of the fly ash and preventing cross-linking between the fly ash particles by the aqueous sodium sulfate solution. I came to draft it. This is the same idea as a technique for preventing a freshly formed candy from forming a bridging due to sticky surface and becoming a large lump by dusting fine powder.

[0012] Here, since candy is a food, fly ash is often used by mixing it with cement, just as it is essential that the fine powder to be dried is a fine powder suitable for food. Therefore, it is an essential condition that the fine powder does not harm the hydration hardening reaction of the cement. Also,
The present invention relates to a fine powder having no or little ability to adsorb or absorb sodium sulfate deliquescent, or a water-soluble fine powder which dissolves itself in deliquescent and cannot exert a blotter effect. Since the above-mentioned purpose cannot be achieved, it is also an essential requirement that the powder be a water-insoluble fine powder having a blotting paper effect.

The present invention specifically relates to fly ash obtained by collecting dust from the exhaust gas of a pulverized coal combustion boiler such as a thermal power plant, which, when fly ash is generated, harms the hydration hardening reaction of cement. In this method, 0.1 to 10% by weight of a water-insoluble inorganic fine powder having a blotting paper effect is added and mixed to prevent coagulation and consolidation of fly ash due to moisture absorption.

The method of adding and mixing the inorganic fine powder to fly ash includes aeration equipment for discharging fly ash provided in a fly ash storage tank of a thermal power plant or the like, or uniform fly ash. Using a mixing device or the like with air for the formation of air, preferably, the inorganic fine powder is fly using a quantitative feeder for powder to a transfer system as close to the dust collector as possible in a fly ash transfer system after the exhaust gas dust collector. The addition to the ash is preferred because the inorganic fine powder added during several stages of transfer via a transfer system or storage tank at the subsequent stage is naturally stirred and mixed into the fly ash. However, the addition position and the addition method of the inorganic fine powder are not particularly limited to the above-mentioned methods, and may be added and mixed by any means as long as the aggregation and consolidation ability of fly ash can be eliminated.

The type of the inorganic fine powder to be added is preferably a fine powder satisfying the following conditions in addition to the above conditions. Fine powder that can eliminate the flocculation ability of fly ash by adding and mixing a small amount (preferably several%). Fine powder that can be obtained inexpensively anywhere in the country and that has no supply concerns including distribution. Desirably, when mixed into cement, it should be a fine powder that promotes the hydration hardening reaction of cement.

The most suitable fine powder that satisfies the above-mentioned conditions is limestone fine powder, but is not limited to limestone fine powder, and is a non-water-soluble inorganic fine powder that does not harm the hydration hardening reaction of cement. Fine powders other than limestone fine powder may be used as long as they are fine powders that can eliminate or reduce the cohesion and consolidation ability of fly ash, that is, fine powders that can be expected to have a blotting paper effect.

Note that limestone fine powder is a fine powder that has been met with enormous demand for flue gas desulfurization or asphalt addition, so it can be obtained inexpensively anywhere in the country and has no supply concerns including distribution. It is a powder.

[0018]

Test Examples Hereinafter, test examples that led to the discovery of the present invention will be described.

-Method of Measuring Aggregation-Consolidation Ability of Fly Ash- First, before describing the test examples, a method of measuring the aggregation-consolidation ability of fly ash performed in the test examples will be described.
This is a method according to the method of measuring the standard softness of the cement paste in the “setting test of cement” described in JIS R 5201.

Specifically, (1) Fly ash is lightly packed in a cement paste container so that the penetration depth of the standard rod is about 35 mm. (2) Subsequently, the cement paste container filled with fly ash is placed in a humidity box having a relative humidity approaching 100% as much as possible to absorb the fly ash and to determine the penetration depth of the standard rod into the fly ash. Measure the change over time. (3) The change over time of the penetration depth of the standard rod is regression-analyzed by Boltzmann equation, and the final value obtained as a result is defined as the final value of the standard rod penetration depth of the fly ash. The above method measures the increase in cohesive force due to the cohesion and consolidation of fly ash as an increase in the viscosity of fly ash, and the higher the value of the final value of the standard rod penetration depth, the higher the cohesion of the fly ash. It means fly ash in which the performance has been eliminated or alleviated.

-Fly ash used in the test example- The fly ash used in the test example was a fresh fly ash immediately after collecting dust and having a flocculation ability. Fly ash was tested on fly ash that was fresh and isolated from the air, because on a laboratory scale, when left in air, it gradually absorbed moisture and lost its ability to coagulate.

-Test example which is the basis for denying the conventional gypsum hydration theory-[Test example 1] After adding a small amount of water to fly ash having coagulation and consolidation ability and mechanically forcibly stirring it, Fly ash that was rapidly dried in a dryer adjusted to 70 ° C. was produced, and the change over time of the penetration depth of the standard rod was measured for the fly ash by the method described above. FIG. 1 shows the measurement results. For comparison, untreated fly ash (fly ash without any means of eliminating or relaxing coagulation and consolidation ability) and a small amount of water were added and mechanically agitated, followed by natural drying. FIG. 1 also shows the measurement results of the fly ash obtained as described above (the fly ash in which the means for preventing coagulation and consolidation by the method of the conventionally proposed 2) was used.

FIG. 1 shows that the flocculence of fly ash lost by the addition and mixing of a small amount of water was measured at 70 ° C.
It is recognized that the plant has been revived by forced drying. This means that the air-set gypsum is converted to dihydrate gypsum by reacting with a small amount of water while stirring, and the flocculation ability of fly ash is eliminated by depriving the hydration hardening power of the air-set gypsum in advance. According to the conventional gypsum hydration theory, gypsum once transferred to dihydrate gypsum was transferred to hemihydrate gypsum again by forced drying at 70 ° C.
The transition from gypsum to gypsum hemihydrate cannot theoretically occur.

Test Example 2 Fly ash was prepared by adding a small amount of water to fly ash having coagulation and consolidation ability, mechanically forcibly stirring the mixture, and then heat-treating for 2 hours in an electric furnace adjusted to 300 ° C. And about this fly ash,
The change with time of the penetration depth of the standard bar was measured by the above method.
FIG. 2 shows the measurement results. For comparison, in the same manner as in Test Example 1 above, measurement was performed on an untreated fly ash and a fly ash obtained by adding a small amount of water, mechanically stirring the mixture, and then naturally drying it. The results are also shown in FIG.

FIG. 2 shows that the heat treatment at 300 ° C. does not restore the flocculation ability of fly ash at all. If the conventional gypsum hydration theory is correct,
When heated at 00 ° C., calcium sulfate contained in fly ash is transferred to soluble anhydrous gypsum (type III anhydrous gypsum), and the flocculence of fly ash should be restored. In addition, it is the temperature at which gypsum changes to hemihydrate gypsum.
It was also confirmed that the flocculation ability of fly ash was not restored even at 100 ° C. drying.

Test Example 3 Commercially available hemihydrate gypsum (calculated gypsum, β
Gypsum-type gypsum) and soluble anhydrous gypsum (type-III anhydrous gypsum) prepared by heating at 300 ° C. for 2 hours in the same manner as the method for measuring the cohesion and consolidation ability of fly ash, respectively. And the change with time of the penetration depth of the standard bar was measured.
FIG. 3 shows the measurement results.

From FIG. 3, it is recognized that air-set gypsum such as type III anhydrous gypsum and β type hemihydrate gypsum do not coagulate and solidify in a short period of time when fly ash coagulates and solidifies.
From the above, it has been found that the reaction of the air-set gypsum is extremely slow in the presence of water having a degree of moisture absorption, and does not agglomerate and compact in a short period of time when fly ash is agglomerated.

From the above Test Examples 1 to 3, the conventional gypsum hydration theory had to be denied. Therefore, the present inventors have focused on sodium sulfate, which is another main component of soluble salts contained in fly ash, and when this sodium sulfate absorbs moisture, it deliqueshes to produce a high-concentration aqueous sodium sulfate solution. When the deliquescence was formed at the contact points between the fly ash particles, the deliquescence formed a bridge between the fly ash particles, and this cross-linking phenomenon was considered to be the mechanism of cohesion and consolidation of the fly ash.

According to the description of sodium sulfate tide, for example, when a small amount of water is added to fly ash and mechanically stirred, the aqueous sodium sulfate solution generated by the addition of water forms cross-links between fly ash particles. Without penetrating into the interior of the particles through the cracks or pores of the fly ash particles, they are lost from the surface of the fly ash particles. Then, in the subsequent natural drying, the aqueous solution of sodium sulfate that has permeated into the fly ash particles is dried at that position, and the fly ash is dried while leaving the sodium sulfate inside the fly ash particles. The caking ability is eliminated or alleviated. However, as in Test Example 1, after a small amount of water was added to fly ash and mechanically forcedly stirred and then dried at 70 ° C., water was evaporated not only on the surface but also inside the fly ash particles. This causes the water vapor pressure inside the fly ash particles to rise, so that the aqueous sodium sulfate solution that has permeated the inside of the corners gushes out onto the fly ash surface again, causing sodium sulfate to precipitate on the fly ash surface, resulting in aggregation of the fly ash. Explain that consolidation ability has been restored.

Therefore, the present inventors proceeded with the discussion based on the above description of sodium sulfate tide, and even if sodium sulphate liquor is formed on the surface of fly ash, the liquor is absorbed by another substance and fly ash is absorbed. The following test was performed on the assumption that coagulation and consolidation would not theoretically occur unless a crosslink was formed between the particles.

Test Example 4 Four types of fine powders shown in Table 1 were added to fly ash having agglomeration and consolidation ability by 0, 1, 3, 5, 10 and 20% by weight, respectively. Then, the mixture was shaken vigorously in a polyethylene bag for 3 minutes, and then the change over time in the penetration depth of the standard rod was measured in the same manner as described above. The respective measurement results are shown in FIGS. FIG. 8 shows the relationship between the final value of the standard rod penetration depth and the amount of each fine powder added.

[0032]

[Table 1] Although the heavy calcium carbonate described in Table 1 is a fine limestone powder, it is described as heavy calcium carbonate in the tables and figures in order to distinguish it from light calcium carbonate.

FIG. 8 shows that the ultimate value of the penetration depth of the standard rod increases as the amount of the fine powder added increases. This means that the flocculence of fly ash, which had hindered the invasion of the standard bar in the case of no addition, was lost and improved so that the standard bar could penetrate deeper. The mechanism of this improvement is that the fine powder previously added to and mixed with the fly ash absorbs the sodium sulfate aqueous solution generated on the surface as the fly ash absorbs moisture, and cross-links are formed between the fly ash particles by the sodium sulfate aqueous solution. In order to prevent
It is considered that the cohesion and consolidation ability of fly ash was eliminated or reduced.

Comparing the effect of improving the cohesion and consolidation ability of fly ash by adding the fine powder, it can be seen that the fine silica powder has the smallest improvement effect despite its higher fineness than heavy calcium carbonate. It became. In addition, although silica fume was the finest, the improvement effect was smaller than that of calcium carbonates. This indicates that the characteristics of the substance rather than the fineness contribute significantly to the improvement effect.

In addition, although the two types of calcium carbonate differed greatly in the degree of fineness, the effect of improving the flocculation ability of fly ash was almost the same. This also indicates that the properties of the substance rather than the fineness contribute significantly to the improvement effect.

Considering the above results, since the surface condition and the like differ depending on the type of the fine powder and the degree of hydrophobicity or hydrophilicity differs, the ability to adsorb or absorb the sodium sulfate deliquescent, that is, the blotting paper effect, is reduced. It is thought that it differs depending on the type of fine powder. Therefore, the fine powder to be added needs to be a fine powder having a blotting paper effect, and within the range of Test Example 4, heavy calcium carbonate and light calcium carbonate, and further, silica fume is a fine powder having a blotting paper effect. However, it can be said that the fine silica powder has no blotting paper effect.

The fine powder may be added in an amount of about 0.1 to 10% by weight based on the weight of fly ash. There is an optimum addition amount in the above, and even if it is added more, the sodium sulfate deliquescent solution has been absorbed by the fine powder, so that the improvement effect no longer increases. The optimum addition amount of calcium carbonates is about 2%, and it can be said that the flocculation ability of fly ash has been completely eliminated at this stage.

If the cause of the cohesion and consolidation of the fly ash is the coagulation due to the hydration of the gypsum, the fine powder added to the fly ash impedes the hydration of the air-hardened gypsum. This is not theoretically possible.

Table 2 shows the results of the above Test Example 4 and the results of evaluating the desired properties described in the section [0015] for the fine powders used. Note that the circled numbers in the table are the item numbers described in [0015].

[0040]

[Table 2]

As shown in Table 2, it is found that heavy calcium carbonate, that is, limestone fine powder, is the optimum fine powder satisfying all the items.

Next, the effect of the case where a large amount of coarse ash pulverized matter is substituted for fly ash (the method of preventing coagulation and consolidation by the conventionally proposed method 5) and the addition and mixing of the fine powder of the present invention. The following tests were performed to compare the effects.

Test Example 5 Coarse-grained ash (cinder sand) was previously mixed with a ball mill having a specific surface area of 3,
Crushed to 300 cm ² / g, and the cinder sand fine powder was divided into 0, 2, 5, 10, 20,
After adding 40 and 100% by weight and shaking vigorously in a polyethylene bag for 3 minutes, the change with time of the penetration depth of the standard rod was measured in the same manner as described above. FIG. 9 shows the measurement results. FIG. 10 shows the relationship between the final value of the standard rod penetration depth and the amount of fine cinder sand powder added. For comparison, the relationship between the coagulation-solidification ability of heavy calcium carbonate and the amount of addition found in Test Example 4 is also shown in FIG.

From FIG. 10, it can be seen that the addition of the fine powder of cinder sand and the addition of the fine powder of limestone have a remarkable difference in the effect of improving the cohesion and solidification ability of fly ash. This indicates that the fine powder of cinder sand does not have a so-called blotting paper effect, and the addition and addition of a small amount cannot eliminate or reduce the cohesion and solidification ability of fly ash.
Therefore, the conventional technique of adding a coarse-grained ash is a means of expecting a dilution effect in a broad sense by replacing fly ash with a coarse-grained ash having a small agglomeration and consolidation ability. The amount of the coarse ash pulverized material required for eliminating or relaxing the ash coagulation ability is 2 times the amount of the limestone fine powder having a blotting paper effect.
It is considered that 0 times or more was required.

From the above Test Examples 4 and 5, it was confirmed that by adding and mixing a small amount (0.1 to 10% by weight) of fine powder to fly ash, the flocculation ability of fly ash can be eliminated or reduced. . Also, it was confirmed that the fine powder to be added at that time needs to be a fine powder having a blotting paper effect, such as limestone fine powder.
Further, fly ash is often used in a state of being mixed with cement, so that it needs to be a fine powder that does not harm the hydration-hardening reaction of cement. Further, the water-soluble fine powder must be a water-insoluble fine powder because it cannot be dissolved in the deliquescent liquid by itself to exert a blotting paper effect.

In consideration of the above, fly-ash collected from the exhaust gas of a pulverized coal-fired boiler is mixed with a water-insoluble inorganic fine powder having no harm to the hydration-hardening reaction of cement and having a blotting paper effect, The present invention has been completed in which the addition and mixing of 0.1 to 10% by weight can prevent coagulation and consolidation of fly ash due to moisture absorption.

[0047]

As described above, the method for preventing coagulation and consolidation of fly ash according to the present invention described above is performed by a simple operation of adding a small amount of fine powder to fly ash and mixing. Since this method can eliminate or alleviate the performance, there is an effect that a large amount of fly ash can be industrially implemented at a low cost.

[Brief description of the drawings]

FIG. 1 shows the time-dependent change of the penetration depth of a standard rod in a fly ash which was rapidly dried at 70 ° C. after a small amount of water was added to the fly ash and mechanically agitated. FIG. 4 is a diagram showing the results of measuring the values of.

FIG. 2 shows Test Example 2, specifically, after adding a small amount of water to fly ash and mechanically stirring it,
It is the figure which showed the result of having measured the time-dependent change of the penetration depth of the standard rod about the fly ash which heat-processed for time.

FIG. 3 shows Test Example 3, specifically, type III anhydrous gypsum and β
It is the figure which showed the result of having measured the time-dependent change of the penetration depth of the standard rod about the type | mold hemihydrate gypsum.

FIG. 4 is a view showing the results of measuring the change over time of the penetration depth of a standard rod with respect to Test Example 4, specifically, fly ash to which various amounts of fine silica powder were added and mixed.

FIG. 5 is a diagram showing the results of measuring the change over time of the penetration depth of a standard rod with respect to Test Example 4, specifically, fly ash to which various amounts of silica fume were added and mixed.

FIG. 6 is a diagram showing the results of measuring the change over time in the penetration depth of a standard rod with respect to Test Example 4, specifically, fly ash to which various amounts of heavy calcium carbonate were added and mixed.

FIG. 7 is a diagram showing the results of measuring the change over time of the penetration depth of a standard rod with respect to Test Example 4, specifically, fly ash to which various amounts of light calcium carbonate were added and mixed.

FIG. 8 is a diagram showing the relationship between Test Example 4, specifically, the amount of various fine powders added to fly ash and the final value of the standard rod penetration depth.

FIG. 9 is a diagram showing the results of measuring the change over time of the penetration depth of a standard rod with respect to Test Example 5, specifically, fly ash to which various amounts of fine cinder sand powder were added and mixed.

FIG. 10 is a view showing the relationship between Test Example 5, specifically, the amount of fine cinder sand powder added to fly ash and the final value of the standard rod penetration depth.

Continuing from the front page (72) Inventor Takao Yamaguchi 1-2-23 Kiyosumi, Koto-ku, Tokyo Japan Consultant Corporation (72) Inventor Yoichi Ishikawa 1-2-23 Kiyosumi, Koto-ku, Tokyo Japan Consultant Corporation (72) Inventor Kazuo Oshima 2-19-1 Shinjuku, Shinjuku-ku, Tokyo F-term within Denki Calltech Co., Ltd. 4G035 AB48 AE19

Claims (2)

[Claims] 1. A non-water-soluble inorganic fine powder which has no harm to the hydration hardening reaction of cement and has a blotting paper effect is added to fly ash collected from exhaust gas of a pulverized coal combustion boiler by 0.1 to 10%. A method for preventing agglomeration and consolidation of fly ash due to moisture absorption, characterized by adding and mixing by weight%. 2. The method according to claim 1, wherein the inorganic fine powder to be added to and mixed with the fly ash is a limestone fine powder.