JP2016079192A - Coal manufacturing method for fuel, coal ash evaluation method and coal ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coal manufacturing method for fuel capable of preventing generation of adhesion of coal ash at low cost.SOLUTION: The coal manufacturing method for fuel of the present invention is a method for manufacturing coal for fuel by mixing raw material coal and includes a process for mixing raw material coal so that a value of evaluation value D=(2×W+1.3×A×W)/W, where Wis the percentage content of magnesium in ash of coal for fuel in terms of magnesium oxide, Wis the percentage content of sodium in terms of sodium oxide and Wis the percentage content of sulfur in terms of sulfur trioxide by using factor A=0 is preset determination threshold or more. The determination threshold is preferably 0.3 or more. The coal evaluation method determines that the one having the determination value D of the preset determination threshold or more is good. The coal ash of the present invention is a coal ash generated by burning coal and has the determination value D is 0.3 or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for preparing fuel coal, a method for evaluating coal ash, and coal ash.

  In coal combustion facilities using coal as fuel, such as coal-fired power generation facilities, about 100 kg or more of coal ash is generated per 1 ton of coal. For example, a million kilowatt-class coal-fired power plant generates several hundred tons of coal ash every day.

  Coal ash contains silica and alumina as main components and contains Fe, Ca, K, Na, Mg, S and the like as trace components. Such coal ash is used, for example, as a cement raw material, a concrete admixture, soil, or a drainage improving material.

  Transfer from a coal combustion facility with a large amount of coal ash production to a coal ash utilization facility such as a cement production plant is mainly carried out by ships. Such loading and unloading of coal ash to a ship is generally performed by pneumatic transportation. However, a phenomenon called so-called occupancy may occur in which coal ash aggregates and blocks (blocks) in the ship during transportation, making unloading difficult.

  When such an occupancy occurs, it is necessary to pulverize the coal ash that has been consolidated manually, which not only requires labor costs, but also increases the ship's berthing period and generates berthing charges and operation of the ship. This leads to a decrease in the rate and causes a significant increase in cost.

Coal ash is broadly divided into clinker ash recovered from the combustion chamber and fly ash recovered from the combustion exhaust gas. The main cause of the occupancy is dihydrate gypsum (calcium sulfate produced mainly on the fly ash surface). It is reported that particle crosslinking is caused by dihydrate: CaSO ₄ -2H ₂ O) (Shunichiro Uchida et al., “Elucidation of coal ash consolidation mechanism”, Taiheiyo Cement Research Report, No. 151).

When specifically described, the sulfur compounds in the coal are mostly decomposed during the combustion of coal, the sulfur content will be oxidized sulfur dioxide (SO _2). A part of this sulfur dioxide is further oxidized to sulfur trioxide (SO ₃ ). When the temperature of the exhaust gas decreases and becomes below a certain temperature (so-called acid dew point), sulfur trioxide reacts with water vapor to become sulfuric acid (H ₂ SO ₄ ) mist and adheres to the coal ash surface. When this sulfuric acid further reacts with calcium in coal ash, gypsum (calcium sulfate: CaSO ₄ ) is generated, and this gypsum becomes dihydrate gypsum (CaSO ₄ -2H ₂ O) by moisture absorption to form a crosslinked structure. Inconvenience occurs due to coal ash consolidation.

  As a method for preventing the staying, a water-insoluble inorganic fine powder having a blotting paper effect is added to preferentially absorb moisture in the inorganic fine powder, and coal ash absorbs moisture to produce dihydrate gypsum. A method of suppressing this has been proposed (see Japanese Patent Laid-Open No. 2000-53456). However, if such a method of mixing additives is employed, the production cost of coal ash increases.

Further, the content of calcium oxide (CaO) in fly ash is 3.5% by mass or more, and the ratio of the content of iron oxide (Fe ₂ O ₃ ) to the content of calcium oxide is 2 or less. A method has been proposed in which calcium oxide is preferentially absorbed by calcium oxide by mixing different types of raw material coal to suppress the formation of dihydrate gypsum (Japanese Patent Laid-Open No. 2012-126913). However, when the content of calcium oxide is increased, there is a drawback in that the production of calcium sulfate that causes crosslinking is promoted, so that there is a possibility that a sufficient staying prevention effect cannot be obtained.

JP 2000-53456 A JP 2012-126913 A

Shunichiro Uchida et al. “Elucidation of coal ash consolidation mechanism” Taiheiyo Cement Research Report, No. 151 p. 50-59, 2006

  In view of the above inconveniences, the present invention provides a coal preparation method for fuel that can suppress the occurrence of coal ash set-up at a low cost, a coal ash evaluation method that can more accurately determine the ease of occurrence of settling, and the occurrence of settling-off. The issue is to provide coal ash.

The coal preparation method for fuel of the present invention made to solve the above-mentioned problem is a method for preparing coal for fuel by mixing raw material coal, and the magnesium oxide equivalent mass content of magnesium in the ash content of the coal for fuel the W _Mg, sodium oxide reduced mass content of sodium W _Na, and sulfur trioxide reduced mass content of the sulfur is taken as W _S, with coefficients a = 0 or 1, by the following formula (1) The method includes a step of mixing raw coal so that the value of the determination value D to be expressed is equal to or greater than a predetermined determination threshold value.
_{D = (2 × W Mg +} 1.3 × A × W Na) / W S ··· (1)

In the fuel coal obtained by the fuel coal preparation method, the determination value D calculated from the contents of magnesium, sodium and sulfur is equal to or higher than the determination threshold. Magnesium, sodium, and sulfur in the ash content of the fuel coal are each oxidized by the combustion of the fuel coal, and magnesium oxide (MgO), sodium oxide (Na ₂ O), and sulfur trioxide in the coal ash immediately after combustion. It exists as (SO ₃ ). That is, also in the coal ash obtained by the combustion of the fuel coal obtained by the fuel coal preparation method, the determination value D is equal to or greater than the determination threshold value. When this coal ash absorbs moisture, sulfur trioxide reacts with moisture (H ₂ O) to produce sulfuric acid (H ₂ SO ₄ ). This sulfuric acid reacts preferentially with the magnesium oxide (MgO) or sodium oxide (Na ₂ O) to produce magnesium sulfate (MgSO ₄ ) or sodium sulfate (Na ₂ SO ₄ ). Furthermore, since this coal ash contains a certain amount or more of magnesium and sodium with respect to sulfur, most of the sulfuric acid can be consumed for the production of magnesium sulfate (MgSO ₄ ) or sodium sulfate (Na ₂ SO ₄ ). , Generation of gypsum (CaSO ₄ ) can be suppressed. Magnesium sulfate and sodium sulfate produced here do not cause coal ash particles to settle, and therefore do not cause occupancy. Therefore, by burning the coal for fuel obtained by the method for preparing coal for fuel, it is possible to suppress bridging due to moisture absorption of gypsum and to produce coal ash that is less likely to occur. Moreover, since the said coal preparation method for fuels only mixes raw material coal and does not use an additive, it can suppress generation | occurrence | production of coal ash occupancy at low cost.

The determination threshold is preferably 0.3 or more. Thus, when the value of the determination threshold is within the above range, the sulfuric acid produced in the coal ash is sufficiently consumed by the production of magnesium sulfate (MgSO ₄ ) or sodium sulfate (Na ₂ SO ₄ ). Therefore, it is not necessary to select raw coal excessively, and cheap and stable coal for fuel can be provided.

Moreover, the evaluation method of the coal ash of the present invention made in order to solve the above problems is an evaluation method of coal ash generated in a coal combustion facility, and the magnesium oxide equivalent mass content of magnesium in the coal ash is calculated. W _Mg, sodium oxide reduced mass content of sodium W _Na, and sulfur trioxide reduced mass content of the sulfur is taken as W _S, with coefficients a = 0 or 1, expressed by the following formula (1) The determination value D is determined to be a non-defective product when the determination value D is equal to or greater than a predetermined determination threshold value.
_{D = (2 × W Mg +} 1.3 × A × W Na) / W S ··· (1)

  The coal ash evaluation method evaluates coal ash on the basis of the ratio of the content of magnesium oxide and sodium oxide that can consume the generated sulfuric acid to the content of sulfur trioxide that generates sulfuric acid by moisture absorption. The ease of occupancy due to the formation of dihydrate gypsum of coal ash can be determined relatively accurately.

Moreover, the coal ash of the present invention made to solve the above problems is coal ash produced by coal combustion, and the magnesium oxide equivalent mass content of magnesium is W _Mg , and the sodium oxide equivalent mass content of sodium is the rate W _Na, and sulfur trioxide reduced mass content of the sulfur is taken as W _S, with coefficients a = 0 or 1, the value of the judgment value D represented by the following formula (1) 0.3 It is the above.
_{D = (2 × W Mg +} 1.3 × A × W Na) / W S ··· (1)

  In the coal ash, the content of magnesium and sodium is larger than a certain value with respect to the sulfur trioxide equivalent mass content of sulfur, so that the sulfuric acid produced by moisture absorption of sulfur trioxide is reduced by the production of magnesium sulfate or sodium sulfate. Can be consumed. Thereby, even if the said coal ash absorbs moisture, it is hard to generate | occur | produce.

  Here, “magnesium oxide equivalent mass content of magnesium”, “sodium oxide equivalent mass content of sodium”, and “sulfur trioxide equivalent mass content of sulfur” in coal ash are the ash content of coal. Or it is a value based on the dry mass of coal ash, and it is a value measured by the elution test of the sample (coal ash) which ashed the coal of measurement object, or the coal ash of measurement object. The “elution test” refers to measurement using an ion chromatograph of ions eluted in water by dispersing the material in distilled water having a mass of 10 times the sample and shaking for 6 hours. . In addition, “good product” of coal ash refers to a material that is difficult to settle due to moisture absorption.

  As described above, according to the present invention, coal ash occupancy can be suppressed inexpensively and effectively.

It is a schematic diagram which shows the structure of the coal combustion facility for manufacturing the coal ash of one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Coal ash]
The coal ash according to an embodiment of the present invention is coal ash generated by combustion of coal, wherein the magnesium oxide equivalent mass content of magnesium is W _Mg , the sodium oxide equivalent mass content of sodium is W _Na , and sulfur trioxide reduced mass content of the sulfur is taken as W _S, with coefficients a = 0 or 1, the value of the judgment value D represented by the following formula (1) is greater than a predetermined determination threshold.
_{D = (2 × W Mg +} 1.3 × A × W Na) / W S ··· (1)

  As a minimum of the above-mentioned judgment threshold, 0.3 is preferred, 0.5 is more preferred, and 0.8 is still more preferred. In the case of the coefficient A = 0, 0.9 is particularly preferable. On the other hand, as the upper limit of the determination threshold, 1.5 is preferable, 1.3 is preferable, and 1.2 is more preferable. When the determination threshold is less than the lower limit, sulfuric acid produced by the reaction of sulfur trioxide with water cannot be sufficiently consumed by magnesium oxide and sodium oxide, and there is a possibility that the occurrence of seizure cannot be sufficiently suppressed. On the other hand, when the determination threshold value exceeds the upper limit, the cost for obtaining such a composition increases, and the coal ash may become expensive. In particular, 1 can be used as a preferable determination threshold when the coefficient A = 1.

[Coal ash evaluation method]
Moreover, the evaluation method of the coal ash which concerns on one Embodiment of this invention is the magnesium oxide conversion mass content rate of magnesium, W _Mg , the sodium oxide conversion mass content rate of sodium is W _Na , and sulfur trioxide conversion mass content of sulfur. the rate is taken as W _S, the value of the judgment value D represented by the above formula (1) is determined to be nondefective what is the determination threshold value or more set in advance.

  In addition, since the content rate of sodium in the coal ash obtained by burning general coal is sufficiently smaller than the content rate of magnesium, the coefficient A is set to 0 in the above formula (1), and the content rate of sodium is ignored. Thus, the determination value D may be calculated.

Here, the coal ash immediately after being generated in the coal combustion facility is oxidized with magnesium, sodium and sulfur, and contains each in the form of magnesium oxide, sodium oxide and sulfur trioxide. Thus, sulfur trioxide conversion mass content W _S of the magnesium oxide reduced mass content W _Mg, sodium oxide reduced mass content W _Na and sulfur sodium of the magnesium can be measured by performing as dissolution test .

[Manufacturing method of coal ash]
The method for producing coal ash includes a step of preparing fuel coal by the fuel coal preparation method according to one embodiment of the present invention, and a step of burning the fuel coal obtained in the fuel coal preparation step. Prepare.

<Method for preparing coal for fuel>
The method for preparing coal for fuel according to an embodiment of the present invention includes a step of analyzing components of each raw coal (usually for each lot), a step of determining a mixing ratio of raw coal, and a step of mixing raw coal Is provided. Examples of the raw material coal include anthracite, bituminous coal, subbituminous coal, and lignite.

(Component analysis process)
Component in the analysis step, measuring the sulfur trioxide conversion mass content W _S of the magnesium oxide reduced mass content W _Mg, sodium oxide reduced mass content W _Na and sulfur sodium magnesium in the ash of raw coal. This component analysis step may be performed by a supplier of each raw material coal.

  By measuring the content of magnesium oxide, sodium oxide and sulfur trioxide in coal ash obtained by ashing raw coal, and dividing by the dry mass of the original raw coal A calculation method can be applied.

(Mixing ratio determination process)
In the mixing ratio determination step, the mixing ratio of the raw coal is determined so that the determination value D represented by the above formula (1) is equal to or higher than the predetermined determination threshold value.

(Raw material coal mixing process)
In the raw material coal mixing step, fuel coal is prepared by mixing raw material coal at the mixing ratio determined in the mixing ratio determination step.

<Coal combustion process for fuel>
In the coal burning process for fuel, the coal ash is obtained by burning the coal for fuel in, for example, a coal burning facility as shown in FIG. More specifically, the coal ash is obtained by mixing clinker ash and fly ash generated by burning the fuel coal.

(Coal combustion facility)
The coal combustion facility in FIG. 1 includes a boiler 1, an economizer 2, a denitration device 3, an air heater 4, an electrostatic precipitator 5, and a desulfurization device 6 that are sequentially disposed in the flue of the boiler. The combustion exhaust gas purified by passing through the economizer 2, the denitration device 3, the air heater 4, the electrostatic precipitator 5, and the desulfurization device 6 is discharged from the chimney 7 to the atmosphere.

  The coal combustion facility of FIG. 1 includes a clinker ash discharged from the boiler 1, a plurality of silos 8 in which fly ash discharged from the economizer 2, the denitration device 3, the air heater 4 and the electric dust collector 5 is stored, and the boiler. 1, the economizer 2, the denitration device 3, the air heater 4, and the electrostatic precipitator 5 are further provided with a transfer device 9 that transfers the ash to any one of the plurality of silos 8.

  In this coal combustion facility, the clinker ash discharged from the boiler 1 and the fly ash discharged from the economizer 2, the denitration device 3, the air heater 4, and the electric dust collector 5 are mixed by being transferred to the same silo 8. It becomes coal ash.

<boiler>
The boiler 1 includes a combustion furnace 10 that burns coal, and a water pipe 11 that is disposed inside the combustion furnace 10 and generates water vapor by heating water with combustion heat of coal. In addition, the boiler 1 includes a clinker recovery unit 12 that recovers clinker ash.

<Economizer>
The economizer 2 is a heat exchanger that heats makeup water supplied to the water pipe 11 and the like by the heat of the combustion exhaust gas discharged from the boiler 1.

  The economizer 2 has an economizer dust collecting portion 13 that collects fly ash separated from the combustion exhaust gas inside the economizer 2 at the bottom thereof, and also functions as a dust collector.

<Denitration equipment>
The denitration device 3 is a selective catalytic reduction denitration device (for example, injecting ammonia into the combustion exhaust gas that has passed through the economizer 2 and allowing the catalyst to pass through, thereby reacting nitrogen oxides with ammonia to convert them into nitrogen gas and water vapor ( SCR: Selective Catalytic Reduction).

  The denitration device 3 also has an SCR dust collection unit 14 that collects fly ash separated inside at the bottom thereof, and also functions as a dust collection device.

<Air heater>
The air heater 4 is a heat exchanger that preheats combustion air supplied to the combustion furnace 10 with heat remaining in the combustion exhaust gas that has passed through the denitration device 3.

  The air heater 4 also has an air heater dust collecting portion 15 that collects fly ash separated inside, and also functions as a dust collecting device.

<Electric dust collector>
The electric dust collector 5 is a device that collects fly ash in the exhaust gas by electrostatic force.

  The electrostatic precipitator 5 includes a first electrostatic precipitator 16, a second electrostatic precipitator 17, and a third electrostatic precipitator 18 that are arranged in series.

<Desulfurization equipment>
For example, the desulfurization apparatus 6 sprays a slurry in which limestone (CaCO ₃ ) is dispersed in water and makes it contact with the combustion exhaust gas, thereby reacting the limestone with sulfur dioxide (SO ₂ ) in the combustion exhaust gas to thereby form gypsum (CaSO ₄ ). This is a wet desulfurization device (FGD: Fluid Gas Desulfurization) that removes sulfur dioxide from combustion exhaust gas.

<Conveyor>
As the conveying device 9, the clinker collecting unit 12, the economizer dust collecting unit 13, the SCR dust collecting unit 14, the air heater dust collecting unit 15, the first electric dust collecting unit 16, the second electric dust collecting unit 17 and the third electric dust collecting unit. It will not specifically limit if an ash can be transferred from the part 18 to the arbitrary silos 8, For example, a pneumatic transport apparatus, a belt conveyor, a bucket conveyor etc. can be used individually or in combination.

[Action]
The fuel coal obtained by the fuel coal preparation method has magnesium, sodium and sulfur contents satisfying the above formula (1). Due to the combustion of the fuel coal, magnesium and sodium in the fuel coal are each oxidized and remain as magnesium oxide (MgO) and sodium oxide (Na ₂ O) in the coal ash immediately after combustion. Further, sulfur in the fuel coal is oxidized and remains as sulfur dioxide (SO ₂ ) or sulfur trioxide (SO ₃ ). Therefore, the ratio of magnesium, sodium and sulfur content in fuel coal is almost the same as the ratio of magnesium, sodium and sulfur content in coal ash obtained by combustion.

When the coal ash is cooled, the sulfur trioxide reacts with moisture (H ₂ O) to produce sulfuric acid (H ₂ SO ₄ ). When this sulfuric acid reacts with calcium in the coal ash, gypsum (CaSO ₄ ) is produced. Since the coal ash contains a large amount of magnesium oxide and sodium oxide, the sulfuric acid preferentially contains magnesium oxide or sodium oxide. The reaction produces magnesium sulfate (MgSO ₄ ) or sodium sulfate (Na ₂ SO ₄ ).

For this reason, even if sulfuric acid is generated in the coal ash, it is consumed by the production of magnesium sulfate (MgSO ₄ ) or sodium sulfate (Na ₂ SO ₄ ), and thus reacts with calcium in the coal ash to cause gypsum (CaSO ₄ ) It is difficult to generate.

[advantage]
Therefore, the coal ash is unlikely to generate seizure because dihydrate gypsum (CaSO ₄ -2H ₂ O) that cross-links particles hardly occurs even when moisture is absorbed.

  In addition, the fuel coal preparation method used to produce the coal ash only selects and mixes raw material coal combinations, and does not use additives. The coal ash that can be produced can be provided at low cost.

[Other Embodiments]
The said embodiment does not limit the structure of this invention. Therefore, in the above-described embodiment, the components of each part of the above-described embodiment can be omitted, replaced, or added based on the description and common general knowledge of the present specification, and they are all interpreted as belonging to the scope of the present invention. Should.

Coal ash according to another embodiment of the present invention is coal ash produced by coal combustion, wherein magnesium content in terms of magnesium oxide is W _Mg , and sodium content in terms of sodium oxide is W _Na , and sulfur trioxide reduced mass content of the sulfur is taken as W _S, with coefficients a = 0 or 1, the second determination value D2 is equal to or less than a predetermined second determination threshold value represented by the following formula (2) It is a certain coal ash.
_{D2 = W S - (2 ×} W Mg + 1.3 × A × W Na) ··· (2)

As described above, when the second determination value D2 is equal to or less than the predetermined second determination threshold value, even if sulfur reacts with water and sulfuric acid is generated, the sulfuric acid reacts with magnesium oxide and sodium oxide to generate sulfuric acid. Produces magnesium and sodium sulfate. Thus, the coal ash, since the gypsum be moisture to bridge the particles together (CaSO 4 -2H _{2 O)} hardly occurs, it is difficult Itsuki occurs.

  The upper limit of the second determination threshold is preferably 0.3%, more preferably 0.2%, and further preferably 0.1%. In particular, when the coefficient A = 0, the upper limit of the second determination threshold is preferably 0.05%, and more preferably 0%. On the other hand, the lower limit of the second determination threshold is preferably -0.2%, preferably -0.1%, more preferably -0.05%. When the second determination threshold exceeds the upper limit, sulfuric acid generated by the reaction of sulfur trioxide with water cannot be sufficiently consumed by magnesium oxide and sodium oxide, and the occurrence of seizure may not be sufficiently suppressed. Conversely, if the second determination threshold is less than the lower limit, the coal ash may be expensive. In particular, 0% can be used as a preferable second determination threshold value when the coefficient A = 1.

  Moreover, the evaluation method of the coal ash which concerns on another embodiment of this invention judges that the 2nd determination value D2 represented by the said Formula (2) is more than the said 2nd determination threshold value set beforehand as non-defective product. Is the method.

  In addition, since the content rate of sodium oxide in coal ash obtained by burning general coal is sufficiently smaller than the content rate of magnesium oxide, the coefficient A = 0 in the above formula (2), and the content rate of sodium oxide May be ignored and the second determination value D2 may be calculated.

Moreover, the coal preparation method for fuel which concerns on another embodiment of this invention is a method of preparing coal for fuel by mixing raw material coal, Comprising: Magnesium oxide conversion mass content of magnesium in fuel raw material coal is set to W _Mg , the sodium oxide reduced mass content of sodium W _Na, and sulfur trioxide reduced mass content of the sulfur is taken as W _S, with coefficients a = 0 or 1, represented by formula (2) A step of mixing raw coal so that the value of the 2 determination value D2 is equal to or greater than a predetermined second determination threshold value.

  Also, instead of mixing all the clinker ash and fly ash obtained by the fuel coal preparation method according to the present invention, conventional fuel coal is burned in a coal combustion facility having a plurality of dust collecting sections, and clinker ash and Coal that can suppress the occurrence of occupancy by producing coal ash by mixing only the fly ash collected in each dust collecting part that is evaluated as good by the coal ash evaluation method according to the present invention. Ashes can also be obtained.

  The present invention is suitably used in a coal combustion facility such as a coal-fired power plant.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Economizer 3 Denitration device 4 Air heater 5 Electric dust collector 6 Desulfurization device 7 Chimney 8 Silo 9 Transfer device 10 Combustion furnace 11 Water pipe 12 Clinker collection part 13 Economizer dust collection part 14 SCR dust collection part 15 Air heater dust collection part 16 1st electricity Dust collector 17 Second electric dust collector 18 Third electric dust collector

Claims (4)

A method of preparing coal for fuel by mixing raw material coal,
Magnesium oxide in terms of mass content of magnesium in the ash of the fuel coal when W _Mg, sodium oxide reduced mass content of sodium W _Na, and sulfur trioxide conversion mass content of sulfur and W _S, factor Preparation of coal for fuel, comprising the step of mixing raw coal using A = 0 or 1 so that the value of determination value D represented by the following formula (1) is equal to or greater than a predetermined determination threshold value Method.
_{D = (2 × W Mg +} 1.3 × A × W Na) / W S ··· (1)   The method for preparing coal for fuel according to claim 1, wherein the determination threshold value is 0.3 or more. An evaluation method for coal ash produced in a coal combustion facility,
When the magnesium oxide in terms of mass content of magnesium in the coal ash W _Mg, sodium oxide reduced mass content of sodium W _Na, and sulfur trioxide conversion mass content of sulfur and W _S, the coefficient A = 0 Alternatively, the coal ash evaluation method is characterized in that, using 1, the determination value D represented by the following formula (1) is determined to be a non-defective product that is equal to or greater than a predetermined determination threshold value.
_{D = (2 × W Mg +} 1.3 × A × W Na) / W S ··· (1) Coal ash produced by the combustion of coal,
Magnesium oxide in terms of mass content W _Mg of _magnesium, sodium oxide reduced mass content of sodium W _Na, and sulfur trioxide reduced mass content of the sulfur is taken as W _S, with coefficients A = 0 or 1 And the value of the judgment value D represented by following formula (1) is 0.3 or more, Coal ash characterized by the above-mentioned.
_{D = (2 × W Mg +} 1.3 × A × W Na) / W S ··· (1)

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