JP2019131434A - Method for producing fly ash for concrete, and method for producing cement composition - Google Patents

Abstract

To provide a method for producing a fly ash for concrete, capable of obtaining the fly ash available as an admixture for concrete from an unburned carbon-containing coal ash with relatively simple work, and to provide a method for producing a cement composition using the same.SOLUTION: A method for producing a fly ash for concrete includes: a flotation sorting step of preparing a slurry that contains an unburned carbon-containing coal ash and water, and then conducting flotation sorting of the unburned carbon and coal ash to obtain a water-containing coal ash; a dehydration drying step of conducting dehydration drying of the water-containing coal ash to obtain a dried coal ash; and a classification step of conducting dry classification of the dried coal ash.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing concrete fly ash and a method for producing a cement composition.

  It is known that coal ash (also called fly ash) generated from a pulverized coal-fired boiler has an effect of improving the durability of concrete. For this reason, utilization of coal ash as an admixture for concrete has been studied. However, coal ash contains unburned carbon (also called unburned carbon), and this unburned carbon adsorbs an air entraining agent (AE agent), which is one of admixtures for concrete. There are things to do. For this reason, when using coal ash with a large amount of unburned carbon, it is necessary to add a large amount of an air entraining agent.

  For these reasons, coal ash with low unburned carbon content is used as an admixture for concrete, but coal ash with high unburned carbon content is partially used as cement raw material. However, it is often landfilled as industrial waste. Therefore, a method for producing fly ash useful for concrete by removing unburned carbon from unburned carbon-containing coal ash having a high content of unburned carbon has been studied.

As a method for removing unburned carbon in coal ash containing a large amount of unburned carbon, a floating sorting method is known. The floating sorting method is to prepare a slurry containing coal ash containing unburned carbon and water, and to float hydrophobic unburnt carbon in the slurry and collect it as a floated material. Is settled in a slurry and recovered as a sediment.
For example, in Patent Document 1, water is added to coal ash to form a slurry, and after adding a collecting agent to the slurry, a shearing force is applied to the slurry and the collecting agent to generate bubbles in the slurry. Discloses a method in which the unburned carbon content of coal ash is adhered to and floated.

Patent Document 2 discloses performing a classification step of removing coarse coal ash particles in advance before performing the floating sorting step.
In Patent Document 3, as a method for treating pulverized coal boiler ash, pulverized coal boiler ash is subjected to floating separation treatment and wet classification treatment. It is disclosed that the coarse particles are used as a cement raw material and the fine particles classified by wet classification are used as a cement admixture.

JP 2007-7485 A JP-A-8-57351 JP-A-7-213949

In the floating sorting method as disclosed in Patent Document 1, fine coal ash fine particles with high activity are collected as floating matter together with unburned carbon, and the activity of sediment coal ash is reduced. There was a problem that sometimes.
Moreover, as disclosed in Patent Document 2, when coarse particles are removed by the classification process before the floating sorting process, the coal ash after classification has a relatively increased content of unburned carbon. Thus, it may be difficult to sufficiently remove unburned carbon in the floating sorting process. Furthermore, when coarse particles are removed by the classification process, the fine particles of coal ash adhering to the coarse particles of coal ash are easily recovered along with unburned carbon in the floating sorting process. In some cases, the activity decreased.
In addition, as described in Patent Document 3, the method of wet classification of the sediment generated in the floating sorting step requires drying the coarse and fine fractions classified by the wet classification, respectively. Therefore, there is a problem that the operation becomes complicated and the cost for drying becomes high.

  The present invention has been made in view of the above-described circumstances. JIS A 6201 (fly ash for concrete) which can be used as an admixture for concrete from unburned carbon-containing coal ash by a relatively simple operation. ) To provide a fly ash for concrete that can meet the quality standards, and a method for producing a cement composition using the fly ash.

  In order to solve the above-mentioned problems, the method for producing fly ash for concrete according to the present invention prepares a slurry containing coal ash containing unburned carbon and water, and the unburned carbon and coal ash. A floating selection step of obtaining hydrous coal ash by floating selection, a dehydration drying step of dehydrating and drying the hydrous coal ash to obtain dry coal ash, and a classification step of dry-classifying the dry coal ash It is characterized by.

  According to the method for producing fly ash for concrete of the present invention configured as described above, the floating sorting step is performed on the unburned carbon-containing coal ash before performing the classification step. The fine particles of coal ash adhering to the coarse particles of coal ash are difficult to be recovered as unburned carbon. For this reason, the unburned carbon content in the unburned carbon content-containing coal ash can be selectively removed. In addition, the hydrous coal ash obtained in the floating sorting step is dehydrated and dried in the dehydration drying step to obtain dry coal ash, and then dry classification in the classification step, so that coarse particles in the dry coal ash are removed and fine Highly active coal ash fine particles can be efficiently recovered.

Here, in the method for producing fly ash for concrete according to the present invention, the coal ash containing the unburned carbon content has a content ratio of particles having a particle diameter of 45 μm or more within a range of 10 mass% or more and 45 mass% or less. The L value in the Hunter Lab color system is preferably 40 or more.
In this case, since the unburned carbon-containing coal ash has a particle size of 45 μm or more and the content of coarse particles is in the above range, the coal ash is suspended in a state where fine particles of coal ash are attached to the coarse particles. The sorting step can be carried out, and the hydrous coal ash obtained in the floating sorting step has a high content of fine particles of coal ash. For this reason, coal ash with high activity can be obtained by the subsequent dehydration drying process and classification process. In addition, since the L value in the Hunter Lab color system indicating the unburned carbon content of the unburned carbon-containing coal ash is set to 40 or more, in the floating sorting step, the unburned carbon ash contained in the sediment coal ash The content of the fuel carbon can be reduced to such an extent that there is no practical problem in using it as fly ash for concrete.

Moreover, in the method for producing fly ash for concrete according to the present invention, the slurry contains a scavenger for unburned carbon, and the content of the scavenger relative to coal ash containing the unburned carbon is 0.2. It is preferable that the water content relative to the coal ash containing the unburned carbon content is in the range of 300% by mass to 1500% by mass.
In this case, since the slurry contains the unburned carbon content collector, water, and unburned carbon-containing coal ash in the above range, the unburned carbon contained in the unburned carbon-containing coal ash in the floating sorting step. Minutes can be efficiently recovered as floating objects.

In the method for producing fly ash for concrete according to the present invention, the L value in the Hunter Lab color system of the dry coal ash was further measured and measured between the dehydration drying step and the classification step. It is preferable to include an inspection step of sending the dry coal ash having the L value of 45 or more to the classification step.
In this case, since the classification process can be performed on dry coal ash that has been confirmed to have a high L value of 45 or more in the inspection process, the content of unburned carbon is low and it is used as an admixture for concrete. Possible fly ash can be obtained more reliably.

In the method for producing fly ash for concrete according to the present invention, in the classification step, the dry coal ash is preferably classified so that the content of particles having a particle diameter of 45 μm or more is less than 10% by mass. .
In this case, the coal ash obtained by the classification step includes 90% by mass or more of fine particles of coal ash having a particle size of less than 45 μm and high activity, and therefore can be advantageously used as fly ash for concrete.

The manufacturing method of the cement composition of this invention is characterized by including the process of mixing the fly ash for concrete obtained by the above-mentioned manufacturing method, and cement.
According to the method for producing a cement composition of the present invention having such a configuration, since the fly ash for concrete obtained by the above production method is used, the cement composition obtained by this production method is unburned. The carbon content is reduced, the amount of air entraining agent (AE agent) used can be reduced, and the strength development is also good.

  The present invention has been made in view of the above-described circumstances. JIS A 6201 (fly ash for concrete) which can be used as an admixture for concrete from unburned carbon-containing coal ash by a relatively simple operation. It is possible to provide a method for producing a fly ash for concrete that can obtain a fly ash that meets the quality standards, and a method for producing a cement composition using the fly ash.

It is a flowchart which shows the manufacturing method of the fly ash for concrete which concerns on one Embodiment of this invention.

  Hereinafter, the manufacturing method of the fly ash for concrete which is this embodiment of this invention, and the manufacturing method of a cement composition are demonstrated.

<Method of manufacturing fly ash for concrete>
FIG. 1 is a flowchart showing a method for producing concrete fly ash according to an embodiment of the present invention.
As shown in FIG. 1, the concrete fly ash manufacturing method according to the present embodiment includes a floating sorting step S01, a dehydration drying step S02, an inspection step S03, and a classification step S04.

(Floating sorting process)
In the floating sorting step S01, first, a slurry containing unburned carbon-containing coal ash containing unburned carbon and water is prepared.
As the unburned carbon-containing coal ash, for example, coal ash generated from a pulverized coal burning boiler or the like can be used. The unburned carbon-containing coal ash has a particle content of 45 μm or more in the range of 10% by mass to 45% by mass, and the L value in the Hunter Lab color system is 40 or more. preferable.

  When the content of coarse particles having a particle size of 45 μm or more contained in the unburned carbon-containing coal ash is less than 10% by mass, the content of fine particles having a particle size of 45 μm or less is relatively increased, and the floating sorting step S01 Therefore, there is a risk that the amount of fine particles of coal ash collected as floating matter together with unburned carbon will increase. On the other hand, when the content of particles having a particle diameter of 45 μm or more exceeds 45% by mass, the adhesion between the unburned carbon and the coal ash particles becomes strong, and the removal rate of the unburned carbon in the floating sorting step S01 is increased. May decrease. In order to further reduce the amount of fine particles of coal ash collected as floating matter together with unburned carbon, and to improve the removal rate of unburned carbon, the content of particles having a particle diameter of 45 μm or more is 15% by mass. It is preferable that it exists in the range of 40 mass% or less. In addition, the content rate of the particle | grains whose particle diameter is 45 micrometers or more can be obtained by the method of reading from the cumulative particle size distribution curve of the particle size distribution measured using the laser diffraction type particle size distribution meter. In addition, the content rate of the particle | grains 45 micrometers or more obtained by this method is the method described in the appendix B (45 micrometer sieve residue test method (net sieve method)) of JISA6201: 2015 (fly ash for concrete). Is approximately the same value as the 45 μm sieve residue measured by.

  In the Hunter Lab color system, the L value generally represents lightness. In the unburned carbon-containing coal ash, the L value is considered to correlate with the amount of unburned carbon on the coal ash surface. That is, a low L value (low brightness = close to black) indicates that the unburned carbon content of coal ash is high. If the L value is less than 40, the unburned carbon content cannot be sufficiently floated and sorted in the floating sorting step S01, and a large amount of unburned carbon may remain in the coal ash. The L value of the unburned carbon-containing coal ash is preferably in the range of 40 to 60.

  The slurry of the unburned carbon content-containing coal ash and water preferably contains an unburned carbon content collector. It is preferable that the collection agent has a specific gravity lighter than water, is hydrophobic, and has an affinity for unburned carbon. As the collecting agent, liquid hydrocarbons can be used. Examples of liquid hydrocarbons include petroleum oils such as kerosene, gasoline, light oil, and heavy oil.

  The slurry can be prepared by mixing unburned carbon-containing coal ash, water, and a scavenger. There is no restriction | limiting in particular in the order of mixing. For example, water and unburned carbon-containing coal ash may be mixed, and the resulting mixture and a scavenger may be mixed, or water and a scavenger may be mixed, and the resulting mixture and unburned Carbon-containing coal ash may be mixed, unburned carbon-containing coal ash and scavenger may be mixed, and the resulting mixture and water may be mixed, or unburned carbon-containing You may mix coal ash, water, and a collection agent simultaneously.

  The content of the scavenger with respect to the unburned carbon-containing coal ash is preferably in the range of 0.2% by mass or more and 15% by mass or less. If the content of the scavenger is less than 0.2% by mass, the efficiency of floating sorting of unburned carbon and coal ash may be reduced. On the other hand, even if the content of the scavenger exceeds 15% by mass, the addition effect of the scavenger is saturated, and the scavenger tends to adhere to the coal ash. May become difficult to separate. The content of the scavenger with respect to the unburned carbon-containing coal ash is preferably in the range of 0.4% by mass to 12.5% by mass.

  The water content relative to the unburned carbon-containing coal ash is preferably in the range of 300% by mass to 1500% by mass. If the water content is less than 300% by mass, the amount of solid content in the slurry is relatively increased, so that the viscosity of the slurry is increased and it is difficult to efficiently separate coal ash and unburned carbon. There is a risk. On the other hand, if the water content exceeds 1500% by mass, it is necessary to increase the equipment scale of the floating sorting apparatus. Moreover, the dehydrated efficiency in the dehydration drying process may be reduced for the hydrous coal ash obtained in the floating sorting process. The water content relative to the unburned carbon-containing coal ash is preferably in the range of 370% by mass to 1000% by mass.

  Next, unburned carbon and coal ash in the slurry are recovered by floating sorting. Unburnt carbon is levitated into the slurry and recovered as a floated material (floss). Coal ash is settled in the slurry and recovered as a sediment (tail). As a method for levitating the unburned carbon component, air is introduced into the slurry, and bubbles are attached to the unburned carbon component, whereby the unburned carbon component is levitated. It is possible to use a method in which air bubbles are entrained and the air bubbles are attached to the unburned carbon content, whereby the unburned carbon content is levitated. When air is introduced into the slurry, the amount of air introduced is preferably in the range of 0.5 L / min to 5 L / min with respect to 1 L of the slurry. If the amount of air introduced is too small, there will be fewer bubbles adhering to the unburned carbon, and the recovery rate of unburned carbon may be reduced. On the other hand, if the amount of air introduced is too large, the bubbles may adhere to the coal ash, and the coal ash may be recovered together with the unburned carbon as floating matter, which is not preferable.

  Since the unburned carbon content recovered as a floating substance in the floating sorting step S01 contains a relatively large amount of carbon, it can be used as a fuel for cement production, for example.

(Dehydration drying process)
In the dehydration drying step S02, the coal ash (hydrated coal ash) recovered as a sediment in the floating sorting step S01 is dehydrated, made into a cake, and then dried to obtain dry coal ash.
As a dehydrator for dehydrating the hydrous coal ash, for example, a filter press or a centrifugal dehydrator can be used. Moreover, as a dryer for drying cake-like hydrous coal ash, a hot-air circulation type dryer, an electric furnace, and a rotary kiln can be used, for example. As a heat source for the dryer, exhaust heat from the cement production facility can be used.

(Inspection process)
In inspection process S03, L value in Hunter Lab color system of dry coal ash obtained by dehydration drying process S02 is measured, and dry coal ash whose measured L value is 45 or more is sent to classification process S04. That is, in the inspection step S03, the amount of unburned carbon mixed in the dry coal ash is judged by the L value, and when the L value is 45 or more (OK), it is mixed in the dry coal ash. Since there is little unburned carbon content, it sends to classification process S04.

  On the other hand, when the L value is less than 45 (NG), it is not sent to the classification step S04 because there is a large amount of unburned carbon mixed in the dry coal ash. In the present embodiment, in this case (NG), the dry coal ash is sent to the floating sorting step S01, and in the floating sorting step S01, the unburned carbon component and the coal ash are floated again. However, the processing method of the dry coal ash whose L value is less than 45 is not limited to this. For example, dry coal ash having an L value of less than 45 and dry coal ash having an L value of 55 or more may be mixed so that the L value does not become less than 45, and the resulting mixture may be sent to a classification step. .

(Classification process)
In the classification step S04, the dry coal ash sent from the inspection step S03 is dry-classified to remove coarse particles having a large particle size, whereby fine particles having a small particle size and relatively high activity are used as fly ash for concrete. to recover. The coarse particles removed in the classification step S04 can be used as a cement raw material, for example.

  In the classification step S04, it is preferable to classify the dried coal ash so that the content of particles having a particle diameter of 45 μm or more is less than 10% by mass. If the content of particles having a particle diameter of 45 μm or more of the dried coal ash (fly ash) after classification is 10% by mass or more, the activity of fly ash may be reduced. In order to obtain fly ash having high activity, the classification condition is preferably such that the content of particles having a particle diameter of 45 μm or more is 8% by mass or less, and preferably 5% by mass or less. Particularly preferred. On the other hand, when the content ratio of particles having a particle diameter of 45 μm or more is set to an excessively low value, a large amount of coal ash is removed, the fly ash recovery rate decreases excessively, and the unburned coal ash is relatively unburned. The carbon content may increase. For this reason, the classification conditions are preferably such that the content of particles having a particle diameter of 45 μm or more is 0.5% by mass or more, and particularly preferably 1.0% by mass or more.

  As the dry classifier, a centrifugal classifier that classifies using the centrifugal force of particles and an inertia classifier that classifies using the inertial force of particles can be used. Further, as the centrifugal classifier, a forced vortex type, a semi-free vortex type, and a free vortex type can be used. The forced vortex classification device is a classification device that includes a rotating body inside the device and forcibly forms a vortex by rotating the rotating body at a high speed. The semi-free vortex classifier is a classifier provided with a guide plate for generating a vortex inside the apparatus instead of a rotating body. The free vortex classifier is a classifier that generates vortices by blowing a gas in a tangential direction inside the apparatus, as represented by a cyclone. Among these classifiers, a forced vortex centrifugal classifier is preferable. In the forced vortex centrifugal classification device, the particle size of the powder after classification can be adjusted with high accuracy by adjusting the rotational speed of the rotor (rotor).

  According to the concrete fly ash manufacturing method of the present embodiment configured as described above, the floating sorting step S01 is performed on the unburned carbon-containing coal ash before the classification step S04. The fine particles of coal ash adhering to the coarse particles of coal ash are difficult to recover as unburned carbon. For this reason, the unburned carbon content in the unburned carbon content-containing coal ash can be selectively removed. In addition, since the hydrous coal ash obtained in the floating sorting step S01 is dehydrated and dried in the dehydration drying step S02 to obtain dry coal ash, dry classification is performed in the classification step S04, so that coarse particles in the dry coal ash are removed. Fine and highly active coal ash fine particles can be efficiently recovered.

  Moreover, in the manufacturing method of the fly ash for concrete of this embodiment, since inspection process S03 is further included between dehydration drying process S02 and classification process S04, L value is as high as 45 or more in inspection process S03. The classification step S04 can be performed on the dry coal ash for which the above is confirmed. As a result, it is possible to more reliably obtain fly ash that has a low unburned carbon content and can be used as an admixture for concrete. Note that the inspection process S03 is not necessarily performed at all times. For example, when continuously performing the floating sorting step S01 and the dehydration drying step S02 on the unburned carbon-containing coal ash having the same particle content of 45 μm or more and the same L value, usually obtained drying Since the L value of coal ash is stable, the inspection step S03 may not be performed.

  Moreover, in the manufacturing method of the fly ash for concrete of this embodiment, the content rate of the coarse particle | grains whose particle diameter contained in unburned carbon containing coal ash is 45 micrometers or more is in the range of 10 mass% or more and 45 mass% or less. By doing so, the floating sorting step S01 can be performed in a state where the unburned carbon-containing coal ash fine particles are adhered to the coarse coal ash particles, and the hydrous coal ash obtained in the floating sorting step S01 is coal The content of fine particles of ash increases. For this reason, coal ash with high activity can be obtained by subsequent dehydration drying step S02 and classification step S04. In addition, since the L value in the Hunter Lab color system that indicates the unburned carbon content of coal ash containing unburned carbon is 40 or more, in the floating sorting step S01, the unburned carbon ash contained in the sediment coal ash The content of the fuel carbon can be reduced to such an extent that there is no practical problem in using it as fly ash for concrete.

  In the method for producing fly ash for concrete according to the present invention, the slurry contains an unburned carbon content collector, and the slurry contains unburned carbon content collector, water, and unburned carbon-containing coal ash. By including in the above-mentioned range, the unburned carbon content contained in the unburned carbon content-containing coal ash can be efficiently recovered as a floating matter in the floating sorting step S01.

  In the method for producing fly ash for concrete according to the present invention, in the classification step S04, the dry coal ash is classified so that the content of particles having a particle diameter of 45 μm or more is less than 10% by mass. The resulting coal ash contains 90% by mass or more of fine particles of coal ash having a particle size of less than 45 μm and high activity, and thus can be advantageously used as an admixture for concrete.

<Method for producing cement composition>
The manufacturing method of the cement composition of this embodiment includes the process of mixing the dry coal ash (fly ash for concrete) after classification obtained as mentioned above and cement.
The substitution rate of fly ash (the content of fly ash with respect to the total amount of fly ash and cement) is preferably in the range of 1% by mass to 10% by mass. When the substitution rate is less than 1% by mass, it is difficult to obtain the effect of using fly ash. Moreover, when a substitution rate exceeds 10 mass%, there exists a possibility that the compressive strength when hardening a cement composition may reduce.

  Examples of cement mixed with fly ash include ordinary Portland cement, early-strength Portland cement, ultra-early strong Portland cement, moderately hot Portland cement, and low heat Portland cement. Cement compositions are concrete such as gypsum, quick-setting admixtures, setting modifiers, air entraining agents (AE agents), antifoaming agents, thickeners, rust inhibitors, antifreeze agents, shrinkage reducing agents, aggregates, etc. Various kinds of admixtures that are used as admixtures may be included.

  As a mixing apparatus for mixing fly ash and cement, for example, a known mixing apparatus used for manufacturing a cement composition such as a Henschel mixer, a V-type mixer, a mixing apparatus by circulating a tank, or the like may be used. it can.

  According to the method for producing a cement composition of the present embodiment configured as described above, since the concrete fly ash obtained by the above production method is used, the cement composition obtained by this production method is The unburned carbon content is reduced, the amount of air entraining agent (AE agent) used can be reduced, and the strength development is also good.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.

  The effects of the present invention will be described below with reference to examples.

In this example, five types of unburned carbon-containing coal ash A to E having different R45, L value, MB (methylene blue) adsorption amount, and activity index shown in Table 1 below were prepared as raw material coal ash. .
In addition, R45 means the content rate (mass%) of the particle | grains whose particle diameter is 45 micrometers or more. R45 was determined from the cumulative particle size distribution curve obtained from the particle size distribution measured using a laser diffraction particle size distribution meter.
The L value means the L value of the Hunter Lab color system. The L value was measured using a color difference meter (Minolta, model: CR210).
The MB adsorption amount was measured in accordance with the Cement Association standard test method JCAS I-61: 2008 (fly ash methylene blue adsorption amount test method).
The activity index was measured in accordance with JIS A 6201: 2015 (fly ash for concrete) and its annex C (flow value ratio and activity index test using fly ash mortar). The age of the mortar specimen was 28 days.

In this example, each step of the floating selection step, the dehydration drying step, and the classification step was performed as follows under the conditions shown in Table 2 below unless otherwise specified.
Specifically, in the flotation step, the unburned carbon-containing coal ash 800 and 5000 g of water are put into a flotation apparatus equipped with a stirrer, and then 60 g of kerosene is added as a scavenger, Was stirred for 10 minutes under the condition of a rotational speed of 850 rpm to obtain a slurry. After stopping the stirrer, air was supplied to the flotation device for 5 minutes under the condition of a supply amount of 10 L / min, and the floated material (unburned carbon content) and the sediment (hydrated coal ash) were recovered.
In the dehydration drying step, the hydrous coal ash was dehydrated using a filter press to form a cake, and then heated at 105 ° C. for 120 minutes using a ventilator to obtain dry coal ash.
In the classification process, using a forced vortex centrifugal classifier (Nisshin Engineering Co., Ltd., turbo classifier, model TC400), the 45 μm sieve residue is in the range of 8% by mass or more and less than 10% by mass. The rotor rotation speed was adjusted within a range of 1000 to 3000 rpm and classified.

[Invention Examples 1-5, Comparative Examples 1-5]
In Invention Examples 1 to 5, as shown in Table 3 below, each of the floating sorting step, the dehydration drying step, and the classification step was performed in this order on the unburned carbon-containing coal ash A to E. Table 3 shows the R45, L value, MB adsorption amount, and activity of the coal ash after the dehydration drying process and the classification process.

  In Comparative Examples 1 to 5, as shown in Table 3 below, the unburned carbon-containing coal ash A to E was subjected to the floating sorting process and the dehydration drying process, and the classification process was not performed. Table 3 shows the R45, L value, MB adsorption amount, and activity of the coal ash after the dehydration drying process.

  As shown in Table 3, the fly ash obtained in Examples 1 to 5 of the present invention in which the classification process was performed after the dehydration drying process was compared with the fly ash obtained in Comparative Examples 1 to 5 in which the classification process was not performed. The activity was improved in comparison. This is considered to be because coarse particles of coal ash having relatively low activity were removed by the classification process. Moreover, the amount of MB adsorption was higher in the fly ash obtained in Invention Examples 1 to 5 than in the fly ash obtained in Comparative Examples 1 to 5. This is considered to be because the content of relatively fine unburnt carbon increased due to the removal of coarse coal ash particles by the classification process.

  Further, from the results of Table 3, unburned carbon-containing coal ash A to C in which R45 is in the range of 10% by mass to 45% by mass and the L value in the Hunter Lab color system is 40 or more is used. The fly ash obtained in Examples 1 to 3 of the present invention has a high activity index of 80 or more and a low MB adsorption amount of 0.3 mg / g, which confirms that it is particularly useful as a fly ash for cement. It was done.

[Evaluation of fly ash]
The fly ash obtained in Invention Examples 1 and 2 and Comparative Example 1 and ordinary Portland cement were mixed at the substitution rate shown in Table 4 below (the fly ash content relative to the total amount of fly ash and ordinary Portland cement). Thus, a cement composition was obtained. The setting time, compressive strength, and presence / absence of black spots were measured for the obtained cement composition. The results are shown in Table 4.

The setting time and compressive strength were measured according to JIS R 5201 (cement physical test method).
The presence or absence of black spots was measured as follows.
In accordance with JIS R 5201, a cement composition, standard sand and water were mixed to prepare a mortar. The prepared mortar was filled in a mold for measuring compressive strength (4 cm × 16 cm) and cured. The surface 64 cm ² (= 4 cm × 16 cm) of the obtained cured mortar was visually observed to confirm the presence or absence of black spots. The case where one or more black spots were confirmed on the surface of the cured mortar was determined to be “present”.

  Moreover, as Reference Example 1, the setting time, compressive strength, and the presence or absence of black spots were measured in the same manner for the above ordinary Portland cement alone (without fly ash substitution). The results are shown in Table 4.

As shown in Table 4, the cement composition containing fly ash of Comparative Example 1 having a relatively low activity index has a compressive strength of 49. 5% when the fly ash substitution rate is 5 mass%. It decreased rapidly to 6 N / mm ² . On the other hand, the cement composition containing fly ash according to Examples 1 and 2 of the present invention showed a stable compressive strength when the fly ash replacement rate was in the range of 1 to 7 mass%, and the fly ash replacement rate was 7. The compressive strengths at 28 days of mass% were 53.2 N / mm ² (Invention Example 1) and 53.1 N / mm ² (Invention Example 2), respectively, and exhibited high strength development.

[Comparative Examples 6-7]
In Comparative Examples 6 to 7, as shown in Table 5 below, the unburned carbon-containing coal ash AB was subjected to the classification process, the floating selection process, and the dehydration drying process in this order. Table 5 shows the R45, L value, MB adsorption amount, and activity of the coal ash after the classification step and after the dehydration drying step.

  As shown in Table 5, the fly ash obtained in Comparative Examples 6 and 7 in which the classification process, the floating selection process, and the dehydration drying process were performed in this order is the activity after the floating selection process → dehydration drying process. The index was lower than after the classification process. This is considered to be because the fine particles of limestone having high activity were removed together with unburned carbon in the floating sorting process.

  In Table 6 below, R45, L value, MB adsorption amount, and activity of unburned carbon-containing coal ash AB used in Invention Examples 1-2 and Comparative Examples 6-7 and the obtained fly ash are shown. , Respectively.

As shown in Table 6, the fly ash obtained in Examples 1-2 of the present invention has a lower MB adsorption amount and a higher activity index than the fly ash obtained in Comparative Examples 6-7. It was confirmed to be particularly useful as a fly ash for cement.
The reason why the MB adsorption amount of fly ash obtained in Comparative Examples 6 to 7 is high is that the coarse particles of coal ash are removed by the classification step, so that the content of unburned carbon is relatively large. This is thought to be because the unburned carbon content could not be sufficiently removed in the floating sorting process. The reason why the activity index of the fly ash obtained in Comparative Examples 6 to 7 was decreased was that the coarse particles of coal ash were removed by the classification step, thereby adhering to the coarse particles of coal ash. This is thought to be because the fine particles of coal ash were collected together with unburned carbon in the floating sorting process.

[Invention Examples 6 to 9]
In Inventive Examples 6 to 9, in the classification process, the rotor rotation speed of the forced vortex centrifugal classification apparatus was changed, and the R45 of the fly ash after classification was adjusted to the value described in Table 7 below. Except for this, fly ash was produced in the same manner as in Example 2 of the present invention.
The R45, L value, MB adsorption amount, and activity of the coal ash after the dehydration drying process and the classification process were measured, respectively. The results are shown in Table 7 together with the results of Example 2 of the present invention.

  From the results in Table 7, the fly ash obtained in Invention Example 2 and Invention Examples 7 to 9 obtained by classification so that R45 is less than 10% by mass has a high activity index of 80 or more. It was confirmed to show. In particular, the fly ash obtained in Invention Example 2 and Invention Examples 7 to 8 obtained by classification so that R45 is 1.0% by mass or more shows a low MB adsorption amount of 3 mg / g. It was confirmed. The reason why the amount of MB adsorbed in Invention Example 9 was high was considered to be that the content of unburned carbon in the coal ash was relatively increased by removing a large amount of coal ash.

[Invention Examples 10 to 15]
In inventive examples 10 to 12, fly ash was produced in the same manner as in inventive example 1 except that the amount of kerosene used in the floating sorting step was changed to the amount shown in Table 8 below. The amount of MB adsorbed on the obtained fly ash was measured. The results are shown in Table 8 together with the results of Example 1 of the present invention.

  In Invention Examples 13 to 15, fly ash was produced in the same manner as in Invention Example 2, except that the amount of kerosene used in the floating sorting step was changed to the amount shown in Table 8 below. The amount of MB adsorbed on the obtained fly ash was measured. The results are shown in Table 8 together with the results of Example 2 of the present invention.

  From the results in Table 8, it can be seen that the MB adsorption amount of fly ash varies depending on the amount of kerosene used in the floating sorting step. And if the content rate of kerosene with respect to unburned carbon-containing coal ash (kerosene / unburned carbon-containing coal ash) is 0.2% by mass or more, particularly 0.4% by mass or more, MB adsorption amount of fly ash Was confirmed to decrease significantly.

[Invention Examples 16 to 19]
In Invention Examples 16 to 19, fly ash was produced in the same manner as in Invention Example 1 except that the amount of water used in the floating sorting step was changed to the amount shown in Table 9 below. The amount of MB adsorbed on the obtained fly ash was measured. The results are shown in Table 9 together with the results of Example 1 of the present invention.

  From the results in Table 9, it was confirmed that the MB adsorption amount of fly ash fluctuates depending on the amount of water used in the floating sorting step. And it was confirmed that MB adsorption amount of a fly ash reduces significantly that the content rate of water with respect to unburned carbon content coal ash is 3005 mass% or more, especially 375 mass%.

Claims (6)

Preparing a slurry containing coal ash containing unburned carbon and water, and a floating sorting step to obtain hydrous coal ash by floating sorting the unburned carbon and coal ash;
A dehydration drying step of dehydrating and drying the hydrous coal ash to obtain dry coal ash;
A method for producing fly ash for concrete, comprising a classification step of dry-classifying the dry coal ash.   The coal ash containing the unburned carbon content has a content ratio of particles having a particle diameter of 45 μm or more in a range of 10% by mass to 45% by mass, and an L value in the Hunter Lab color system is 40 or more. The method for producing fly ash for concrete according to claim 1, wherein:   The slurry contains a scavenger for unburned carbon, and the content of the scavenger with respect to coal ash containing the unburned carbon is in the range of 0.2 mass% to 15 mass%, The content rate of the said water with respect to the coal ash containing an unburned carbon content exists in the range of 300 mass% or more and 1500 mass% or less, The manufacturing method of the fly ash for concrete of Claim 1 or 2 characterized by the above-mentioned.   Furthermore, between the dehydration drying step and the classification step, the L value in the Hunter Lab color system of the dry coal ash is measured, and the dry coal ash having the measured L value of 45 or more, The manufacturing method of the fly ash for concrete of any one of Claim 1 to 3 including the test | inspection process sent to a classification process.   5. The concrete according to claim 1, wherein in the classification step, the dry coal ash is classified so that the content of particles having a particle diameter of 45 μm or more is less than 10% by mass. For manufacturing fly ash.   The manufacturing method of the cement composition characterized by including the process of mixing the fly ash for concrete obtained by the manufacturing method of the fly ash for concrete of any one of Claim 1 to 5, and cement.

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