JP2007330929A - Method for manufacturing civil engineering and construction material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing civil engineering and construction materials, by which an initial investment can be decreased, they can be manufactured at low costs and harmful trace elements can be restrained from being eluted from them. <P>SOLUTION: The method for manufacturing civil engineering and construction materials by using coal ash being combustion residues of coal to be used as fuel in a coal-burning power generation system comprises: a coal ash recovery step of burning coal and recovering coal ash as combustion residues; and a civil engineering and construction material production step of producing civil engineering and construction materials from the recovered coal ash and raw materials for the civil engineering and construction materials. The coal ash recovery step comprises a limestone addition step of adding an elution inhibitor consisting of limestone to coal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a civil engineering building material, and more particularly to a method for manufacturing a civil engineering building material using coal ash.

  There are various methods for burning coal in a coal-fired power generation system. Among them, so-called pulverized coal combustion in which particles obtained by finely pulverizing coal are blown into a furnace and burned is mainly employed. And the coal ash used as the residue after combustion is used as a part of raw materials of civil engineering building materials, such as concrete and a soil improvement material, from a viewpoint of effective use of resources.

  By the way, coal contains a trace amount of harmful elements such as boron, fluorine, selenium, arsenic and hexavalent chromium in addition to carbon. For this reason, in consideration of the environment, the allowable concentration of harmful trace elements from coal ash is regulated by law.

  However, there are over 100 coal types exported to Japan per year, and not all of them meet the above-mentioned regulatory values. For this reason, the technique for reducing the elution density | concentration of the harmful trace element contained in coal ash to below a regulation value is examined.

For example, a method of adding a trace element elution inhibitor such as a chelating agent to coal ash and a method of solidifying coal ash with cement or the like are performed (see Patent Documents 1 to 3).
JP 2003-164886 A JP 2003-200132 A JP 2002-194328 A

However, the above prior art has the following problems.
In order to add additives to coal ash and mix them, large-scale facilities such as silos, water tanks, and mixing devices and equipment space are required. For this reason, a large initial investment is required. Moreover, since the additive added to coal ash is expensive, manufacturing cost rises.

  Further, although prevention of elution of heavy metals has been studied, studies on prevention of elution of light elements such as boron and fluorine are insufficient.

  The present invention has been made in view of the above problems, and provides a method for manufacturing a civil engineering building material that can reduce the initial investment amount, can be manufactured at low cost, and can suppress the elution of harmful trace elements. With the goal.

  The present inventors have found that alkaline coal ash can be produced at low cost by adding limestone to coal, and have completed the present invention. Specifically, the present invention provides the following.

(1) A civil engineering and building material manufacturing method using coal ash, which is a combustion residue of coal as fuel in a coal-fired power generation system,
A coal ash recovery step of burning the coal and recovering coal ash as a combustion residue, and a civil engineering and building material generation step of generating the civil engineering and building material from the coal ash and a civil engineering and building material raw material,
The said coal ash collection | recovery process is a civil engineering building material manufacturing method which has a limestone addition process which adds the elution inhibitor consisting of limestone to the said coal.

  According to the invention of (1), first, coal ash which is a combustion residue of coal in a coal-fired power generation system is recovered, and civil engineering and building materials are generated from the coal ash and civil engineering and building material raw materials.

  Here, since an elution inhibitor made of limestone was added to coal, elution of harmful trace elements such as boron, fluorine, selenium, arsenic, and hexavalent chromium, especially boron, fluorine, selenium, and arsenic can be effectively suppressed. . Moreover, since limestone can be obtained at low cost, civil engineering and building materials can be manufactured at low cost.

Moreover, when an elution inhibitor is added and reacted in the coal ash state after combustion, it is necessary to newly install equipment for adding and reacting.
Therefore, according to the invention of (1), since the elution inhibitor is added during combustion or in the state of coal before combustion, it can be dealt with simply by improving the existing equipment. For this reason, the initial investment amount can be reduced.

  The addition of limestone is not particularly limited as long as it is an addition in a coal state, and may be performed in any of a coal supply unit, a pulverized coal generation unit, and a pulverized coal combustion unit described later. This pulverized coal combustion section includes the vicinity of a heat exchange unit (so-called economizer) disposed downstream of the combustion boiler.

  Further, the “civil engineering building material” is not particularly limited as long as it is a material that can be used for civil engineering construction, and specifically includes a soil improvement material, an artificial aggregate, and the like. In addition, the coal ash obtained in the process of the manufacturing method of this invention can also be used as environmental purification materials, such as a water quality improvement material.

(2) In the civil engineering and building material manufacturing method according to (1),
The coal thermal power generation system is a pulverized coal combustion type power generation system,
The said limestone addition process is a civil engineering building material manufacturing method which is a process of adding the said elution inhibitor in a combustion boiler.

  According to invention of (2), since the elution inhibitor was added in the combustion boiler, the elution inhibitor is heated to a high temperature by coal combustion. Thereby, coal ash is melted and harmful trace elements in coal ash are enclosed. In addition, harmful trace elements are insolubilized by calcium oxide generated from calcium carbonate. Due to the above action, the elution of harmful trace elements can be further suppressed.

  Here, “inside the combustion boiler” includes the piping in the case where the combustion boiler is in an embodiment in which the exhaust gas is recirculated.

(3) In the civil engineering and building material manufacturing method according to (1) or (2),
The coal thermal power generation system is a pulverized coal combustion type power generation system,
The said limestone addition process is a civil engineering building material manufacturing method which is a process of adding the said elution inhibitor upstream from a combustion boiler.

  According to the invention of (3), since the elution inhibitor is added into the combustion boiler, the elution inhibitor is heated to a high temperature by coal combustion. Thereby, coal ash is melted and harmful trace elements in coal ash are enclosed. In addition, harmful trace elements are insolubilized by calcium oxide generated from calcium carbonate. Due to the above action, the elution of harmful trace elements can be further suppressed.

  Moreover, since an elution inhibitor is added in the state of raw coal or pulverized coal, the equipment can be simplified and even existing equipment can be easily handled.

  Here, “upstream from the combustion boiler” is, for example, a coal supply unit and a pulverized coal generation unit described later.

(4) In the civil engineering building material manufacturing method according to any one of (1) to (3),
The said limestone addition process is a civil engineering and building material manufacturing method which is a process of adding the said elution inhibitor in 0.1 to 20 mass parts with respect to 100 mass parts of said coal.

If the amount of elution inhibitor added is too small, the effect of inhibiting the elution of harmful trace elements will be insufficient, while if too large, coal ash will adhere to the inner wall of the furnace due to the melting point drop on the coal ash surface (slagging). Not only there is a fear, but a significant improvement in the elution suppression effect of harmful trace elements is not recognized, which is disadvantageous in terms of cost.
Therefore, according to the invention of (4), since the elution inhibitor is added in the range of 0.1 to 20 parts by mass with respect to 100 parts by mass of coal, harmful trace elements can be sufficiently suppressed and inexpensive. In addition, civil engineering and building materials can be manufactured, and slugging can be suppressed.

(5) In the civil engineering and building material manufacturing method according to any one of (1) to (4),
The coal thermal power generation system is a pulverized coal combustion type power generation system,
The said limestone addition process is a civil engineering building material manufacturing method which is a process added to the heat exchange unit vicinity arrange | positioned downstream from a combustion boiler.

  According to the invention of (5), since the elution inhibitor is added downstream from the fuel boiler, the leaching of harmful trace elements without causing problems such as a large amount of coal ash adhering to the furnace inner wall (slagging). Can be suppressed.

  (6) A soil improvement material produced by the civil engineering and building material production method according to any one of (1) to (5).

  (6) The soil improvement material of description is manufactured by the civil engineering and building material manufacturing method mentioned above. Therefore, it is possible to reduce the initial investment amount, to manufacture at a low cost, and to suppress the elution of harmful trace elements.

  Moreover, in the soil improvement material, there is a concern about acidification due to acid rain. Therefore, according to the invention of (6), since calcium oxide produced by heating limestone is contained, the progress of acidification can be suppressed by its buffering action.

  Here, “soil improver” is mainly used for improving soil in civil engineering buildings, but is also preferably used for various purposes such as improvement of soil for agriculture and forestry, improvement of contaminated soil, etc. It can be done.

  (7) An artificial bone produced by the method for producing civil engineering and building materials according to any one of (1) to (5).

  The artificial aggregate described in (7) is manufactured by the above-described civil engineering and building material manufacturing method. Therefore, it is possible to reduce the initial investment amount, to manufacture at a low cost, and to suppress the elution of harmful trace elements.

  "Artificial aggregates" include back walls for rock walls, revetments, retaining walls, ground pile piles (sand compaction pile, sand for sand drain method), road base materials for road construction, lightweight for concrete It can be used as general aggregate for civil engineering and construction such as aggregate (sand, gravel substitute). The “artificial aggregate” in the present specification is not necessarily limited to those used in combination with cement.

In general, in an aggregate containing material such as concrete, there is a concern about an alkali aggregate reaction induced by an alkali metal salt such as sodium oxide or potassium oxide. When this alkali-aggregate reaction occurs, the inside of the aggregate-containing material locally expands, causing problems such as cracking, strength reduction, and elasticity reduction of the aggregate-containing material.
Therefore, according to the invention of (7), since the dissolution inhibitor made of limestone is added, since the calcium oxide produced by heating the limestone is contained in the aggregate-containing material, the aggregate-containing material is cracked, Does not cause problems such as reduced strength and reduced elasticity.

  (8) A method for suppressing soil acidification using coal ash recovered by burning coal and limestone.

  (9) A method for preventing an alkaline aggregate reaction using coal ash recovered by burning coal and limestone.

According to the present invention, since an elution inhibitor made of limestone is added to coal, it is effective for the elution of harmful trace elements such as boron, fluorine, selenium, arsenic and hexavalent chromium, especially boron, fluorine, selenium and arsenic. Can be suppressed. Moreover, since limestone can be obtained at low cost, civil engineering and building materials can be manufactured at low cost.
Moreover, since the elution inhibitor is added during combustion or in the state of coal before combustion, it can be dealt with simply by improving existing equipment. For this reason, the initial investment amount can be reduced.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  The civil engineering and building material manufacturing system used in the present invention includes a pulverized coal combustion facility 1 that burns coal and collects coal ash as a combustion residue, and civil engineering and building material generation that generates civil engineering and building materials from coal ash and civil engineering and building materials. And a facility.

<A: Configuration of pulverized coal combustion facility in coal-fired power generation system>
FIG. 1 is a block diagram showing a pulverized coal combustion facility 1 in a coal-fired power generation system. FIG. 2 is an enlarged view of the vicinity of the furnace 161 in the pulverized coal combustion unit 16.

  As shown in FIG. 1, a pulverized coal combustion facility 1 includes a coal supply unit 12 that supplies coal, a pulverized coal generation unit 14 that converts the supplied coal into pulverized coal, and a pulverized coal combustion unit that burns pulverized coal. 16 and a coal ash treatment unit 18 for treating coal ash which is a combustion residue generated by combustion of pulverized coal.

[A-1: Coal supply section]
The coal supply unit 12 includes a coal bunker 121 that stores coal, and a coal feeder 122 that supplies the coal stored in the coal bunker 121. The coal bunker 121 stores coal to be supplied to the coal feeder 122. The coal feeder 122 continuously supplies the coal supplied from the coal bunker 121 to the coal pulverized coal machine 141. Moreover, this coal feeder 122 is provided with the apparatus which adjusts the supply_amount | feed_rate of coal, and, thereby, the amount of coal supplied to the coal pulverizer 141 is adjusted. Further, a coal gate is provided at the boundary between the coal bunker 121 and the coal feeder 122, thereby preventing air from the coal feeder from flowing into the coal bunker.

[A-2: Pulverized coal generation unit]
The pulverized coal generation unit 14 includes a coal pulverized coal machine (mill) 141 that converts coal into pulverized coal capable of pulverized coal combustion, and an air supply unit 142 that supplies air to the coal pulverized coal machine 141.

  The coal pulverized coal machine 141 pulverizes the coal supplied from the coal feeder 122 through the coal supply pipe to form fine pulverized coal, and is supplied from the pulverized coal and the air supply unit 142. Mix with fresh air. Thus, by mixing pulverized coal and air, the pulverized coal is preheated and dried to facilitate combustion. Air is blown onto the formed pulverized coal, thereby supplying the pulverized coal to the pulverized coal combustion unit 16.

  Examples of the type of the coal pulverized coal machine 141 include a roller mill, a tube mill, a ball mill, a beater mill, an impeller mill, and the like. However, the type of the coal pulverized coal machine 141 is not limited to these and may be any mill used in pulverized coal combustion.

[A-3: Pulverized coal combustion section]
The pulverized coal combustion unit 16 includes a furnace 161 that combusts the pulverized coal generated by the pulverized coal generation unit 14, a heater 162 (heat exchange unit) that heats the furnace 161, and an air supply that supplies air to the furnace 161. Machine 163.

  The furnace 161 is heated by a heater 162 (heat exchange unit), and combusts the pulverized coal supplied from the coal pulverized coal machine 141 via the pulverized coal pipe together with the air supplied from the air supply unit 163. By burning pulverized coal, coal ash is generated and discharged to the coal ash treatment unit 18 together with the exhaust gas.

  The furnace 161 will be described in detail with reference to FIG. 2. In FIG. 2, the furnace 161 has a generally inverted U shape as a whole, and after the combustion gas moves in an inverted U shape along the arrow in the figure. After passing through the secondary economizer 161h, it is again reversed into a U shape, and the outlet of the furnace 161 (the last arrow in FIG. 2) is connected to the denitration device 181 and the dust collector 182 in FIG.

  Below the furnace 161, a burner 161a for burning pulverized coal is disposed in the vicinity of the burner zone 161a 'in the furnace 161. In addition, a cage wall 161b, a first superheater 161c, and a first reheater 161d are sequentially arranged along the flow path near the top of the U-shape in the furnace 161, and a second regenerator is disposed downstream of the cage wall 161b. A heater 161e and a second superheater 161f are arranged in parallel. From the vicinity of the end of the second superheater 161f, a primary economizer 161g and a secondary economizer 161h are provided in two stages. Here, the economizer (also referred to as ECO) is a heat transfer surface group provided for preheating boiler feedwater using heat held by combustion gas. The cage wall 161b, the first superheater 161c, the first reheater 161d, the second reheater 161e, the second superheater 161f, the primary economizer 161g, and the secondary economizer 161h are: Constructs a heat exchange unit.

[A-4: Coal ash treatment unit]
The coal ash treatment unit 18 includes a denitration device 181 that removes nitrogen oxides in the exhaust gas discharged from the pulverized coal combustion unit 16, a dust collector 182 that removes soot in the exhaust gas, and coal ash collected by the dust collector 182. A coal ash recovery silo 183 for primary storage.

  The denitration apparatus 181 removes nitrogen oxides in the exhaust gas. That is, ammonia gas is injected as a reducing agent into exhaust gas at a relatively high temperature (300 to 400 ° C.), and nitrogen oxides in the exhaust gas are decomposed into harmless nitrogen and water vapor by the action of a denitration catalyst, so-called dry ammonia contact. A reduction method is preferably used.

  The dust collector 182 is a device that collects coal ash in the exhaust gas with an electrode. The coal ash collected by the dust collector 182 is conveyed to the coal ash collection silo 183. Further, the exhaust gas from which the coal ash has been removed is discharged from the chimney after passing through a desulfurization apparatus (not shown).

  The coal ash collection silo 183 is a facility that primarily stores the coal ash collected by the dust collector 182.

<B: Structure of civil engineering building material generation facility>
The civil engineering and building material generation facility is a facility for generating civil engineering and building materials using the coal ash stored in the coal ash recovery silo 183. Such a facility may be appropriately selected from conventionally known facilities according to the type of civil engineering and building material to be generated. In addition, when it is a thing which can use coal ash itself like a soil improvement material, it is not necessarily required to utilize a civil engineering building material production | generation facility.

  Moreover, the civil engineering and building material generation facility used in the present invention may be disposed integrally with the pulverized coal combustion facility 1 described above or may be disposed separately. However, as a civil engineering and building material generation facility, it is preferable to use an already installed facility rather than newly constructing a coal-fired power generation system in that the initial investment can be further reduced.

<C: Civil engineering building material manufacturing method>
The civil engineering and building material manufacturing method of the present invention includes a coal ash recovery process that generates coal ash from coal, and a civil engineering and building material generation process that generates civil engineering and building materials from the coal ash and civil engineering and building materials.

[C-1: Coal ash recovery process]
The case where this coal ash collection | recovery process is performed using said pulverized coal combustion facility 1 is demonstrated below.

  The coal ash recovery step includes coal supply step S10 for supplying coal, pulverized coal generation step S20 for pulverizing the supplied coal to generate pulverized coal, and fine powder for burning coal and generating coal ash. The coal combustion step S30 and the coal ash treatment step S40 that collects and accommodates the coal ash, each of which includes the coal supply unit 12 and the pulverized coal generation unit of the pulverized coal combustion facility 1 described above, respectively. 14, pulverized coal combustion unit 16, and coal ash treatment unit 18. And the limestone addition process S50 which is the characteristics of this invention is preferably performed in any one of said coal supply process S10, pulverized coal production | generation process S20, and pulverized coal combustion process S30.

(Coal supply process S10)
First, in the coal supply process, the coal stored in the coal bunker 121 is supplied to the coal pulverized coal machine 141 by the coal feeder 122. The coal supplied to the coal pulverized coal machine 141 is specifically bituminous coal, subbituminous coal, lignite, or the like, but is not limited to these coals and may be any coal that can perform pulverized coal combustion. Good.

(Pulverized coal production process S20)
Next, in the pulverized coal generation step, the coal supplied from the coal feeder 122 is pulverized by the coal pulverized coal machine 141, thereby generating pulverized coal. The generated pulverized coal is supplied to the furnace 161. At this time, the average particle size of the pulverized coal formed in the pulverized coal generation step may be a particle size range generally used in pulverized coal combustion, and generally 74 μm under 80 wt% or more. The degree of pulverization. This range can also be applied when an elution inhibitor is added.

(Pulverized coal combustion process S30)
Next, in the pulverized coal combustion process, the pulverized coal generated by the coal pulverized coal machine 141 is burned by the furnace 161. As shown in FIG. 2, the coal ash generated by the combustion of pulverized coal in the burner zone 161a ′ rises along the direction of the arrow, and along with the exhaust gas, the cage wall 161b, the first superheater 161c, the first recycle The heater 161d, the second reheater 161e, the second superheater 161f, the primary economizer 161g, and the secondary economizer 161h are sequentially passed. As described above, the vicinity of the first reheater 161d and the second reheater 161e is a region where the temperature is maintained from 850 ° C. to 900 ° C., and the heat possessed by the combustion gas is used. Heat is exchanged by passing through a heat transfer surface group provided to preheat boiler feedwater, and the temperature decreases. Then, it is sent to a denitration device 181 and a dust collector 182 at the subsequent stage. The coal ash produced in this pulverized coal combustion process is usually in the form of powder having an average particle size in the range of 1 μm to 100 μm.

(Coal ash treatment step S40)
Thereafter, the coal ash generated by burning pulverized coal is discharged to the denitration device 181 together with the exhaust gas, and sent to the coal ash recovery silo 183 through the dust collector 182. The dust collector 182 is preferably provided in a plurality of stages.

(Limestone addition process S50)
As shown in FIG. 1, the limestone addition step S50, which is a step of adding an elution inhibitor made of limestone, which is a feature of the present invention, is preferably the coal supply step S10, the pulverized coal generation step S20, and the pulverized coal combustion step. This is performed for any of S30 (S51, S52, and S53 in FIG. 1 respectively).

  In addition, the addition place of an elution inhibitor will not be specifically limited if it is the state of coal, For example, the transfer path between coal supply process S10 and pulverized coal production | generation process S20, pulverized coal production | generation process S20, and pulverized coal combustion You may perform by the transfer path between process S30, etc.

  Specifically, for example, a method of supplying and mixing an elution inhibitor onto a belt conveyor that is being transferred when transporting from the coal feeder 122 to the coal pulverized coal machine 141, and an elution inhibitor of the coal pulverized coal machine 141 A method of directly charging into a coal hopper (not shown), a method of supplying an agent charging port in a pipe between the coal pulverized coal machine 141 and the furnace 161, a method of directly charging the furnace 161 with combustion air, and a heater 162, cage wall 161b constituting a part of furnace 161, first superheater 161c, first reheater 161d, second reheater 161e, second superheater 161f, primary economizer 161g, And a method of adding it in the vicinity of the heat exchange unit such as the secondary economizer 161h, but is not limited thereto. As described above, the method of the present invention does not require a new facility, and can be applied by a slight improvement of the existing facility. Therefore, the existing facility can be used effectively, which is advantageous in terms of cost.

The elution inhibitor used in the present invention is made of limestone (CaCO ₃ ). The elution inhibitor is preferably granular or powdery in that it can be easily added and the mixing can be made uniform to improve the elution prevention effect. In particular, the average particle size is preferably 10 μm to 100 μm, and more preferably 10 μm to 70 μm.

The amount of the dissolution inhibitor added to the coal is preferably in the range of 0.1 to 20 parts by mass with respect to 100 parts by mass of coal.
[C-2: Civil engineering building material generation process]
In the civil engineering and building material generation step, civil engineering and building material is generated using the coal ash stored in the coal ash recovery silo 183. This step may be appropriately performed according to a conventionally known procedure depending on the type of civil engineering and building material to be generated.

  For example, a sea sand substitute material using the artificial aggregate of the present invention has a powder amount of 87% by mass of coal ash as an artificial aggregate, 10% by mass of cement, and 3% by mass of viscosity. It is manufactured by adding 20% by mass to 24% by mass of water, mixing them, and granulating them by applying a predetermined pressure. However, the artificial aggregate of the present invention is not necessarily added with cement or the like. For example, a mixture obtained by adding about 15% by mass of water of coal ash to coal ash and mixing it with a predetermined pressure is used. It may be manufactured by granulating with. The sea sand substitute produced in this manner has excellent strength and drainage, and also has excellent adsorption performance for various trace elements. Therefore, it can be preferably used for various purposes such as soil improvement materials (for civil engineering and construction, agriculture and forestry), water quality improvement materials and the like.

  According to the embodiment of the present invention described above, the elution of harmful trace elements such as boron, fluorine, selenium, arsenic and hexavalent chromium can be suppressed by adding an elution inhibitor. This mechanism first lowers the melting temperature of coal ash by adding an elution inhibitor made of limestone. That is, the surface of the coal ash mainly composed of silica and alumina is softened (melted) by the high temperature in the furnace 161, and the viscous coal ash particles are brought into contact with the trace elements and taken into the coal ash. Therefore, it is estimated that the elution concentration decreases. Thus, in the present invention, by adding an elution inhibitor before the combustion stage, the high temperature of the furnace in the pulverized coal combustion section is effectively used to suppress the elution of trace elements from the coal ash. is there.

It is a schematic block diagram of the pulverized coal combustion facility in the coal thermal power generation system concerning one embodiment of the present invention. It is an enlarged view of the vicinity of the furnace in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pulverized coal combustion facility 12 Coal supply part 14 Pulverized coal production | generation part 16 Pulverized coal combustion part 18 Coal ash processing part 121 Coal bunker 122 Coal feeder 141 Coal pulverized coal machine 142 Air supply machine 161 Furnace 162 Heating machine 163 Air supply machine 181 Denitration equipment 182 Dust collector 183 Coal ash recovery silo S10 Coal supply process S20 Pulverized coal generation process S30 Pulverized coal combustion process S40 Coal ash treatment process S50 Limestone addition process

Claims (9)

A method for producing civil engineering and building materials using coal ash, which is a combustion residue of coal as fuel in a coal-fired power generation system,
A coal ash recovery step of burning the coal and recovering coal ash as a combustion residue, and a civil engineering and building material generation step of generating the civil engineering and building material from the coal ash and a civil engineering and building material raw material,
The said coal ash collection | recovery process is a civil engineering building material manufacturing method which has a limestone addition process which adds the elution inhibitor consisting of limestone to the said coal. In the civil engineering and building material manufacturing method according to claim 1,
The coal thermal power generation system is a pulverized coal combustion type power generation system,
The said limestone addition process is a civil engineering building material manufacturing method which is a process of adding the said elution inhibitor in a combustion boiler. In the civil engineering and building material manufacturing method according to claim 1 or 2,
The coal thermal power generation system is a pulverized coal combustion type power generation system,
The said limestone addition process is a civil engineering building material manufacturing method which is a process of adding the said elution inhibitor upstream from a combustion boiler. In the civil engineering building material manufacturing method in any one of Claim 1 to 3,
The said limestone addition process is a civil engineering and building material manufacturing method which is a process of adding the said elution inhibitor in 0.1 to 20 mass parts with respect to 100 mass parts of said coal. In the civil engineering building material manufacturing method in any one of Claim 1 to 4,
The coal thermal power generation system is a pulverized coal combustion type power generation system,
The said limestone addition process is a civil engineering building material manufacturing method which is a process added to the heat exchange unit vicinity arrange | positioned downstream from a combustion boiler.   The soil improvement material manufactured by the civil engineering building material manufacturing method in any one of Claim 1 to 5.   An artificial aggregate manufactured by the civil engineering and building material manufacturing method according to any one of claims 1 to 5.   A method for suppressing soil acidification using coal ash recovered by burning coal and limestone. A method for preventing an alkali-aggregate reaction using coal ash recovered by burning coal and limestone.

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