JP2008275181A - Method of inhibiting elution of harmful trace element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of inhibiting elution of harmful trace element from combustion residue of coal. <P>SOLUTION: The elution of harmful trace element from combustion residue of coal is inhibited by adding an elution preventing agent for coal addition to fuel coal, and further adding an elution prevent agent for ash addition to coal ash. The elution preventing agent including at least one or more kinds of components selected from limestone, slaked lime and calcined lime at its main component, is used as the elution preventing agent for coal addition, and the elution preventing agent including aluminum sulfate as an essential component, is added as the elution preventing agent for ash addition. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a toxic trace element elution suppression method that suppresses leaching of toxic trace elements from combustion residues of coal as fuel in a coal-fired power generation system.

  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. A part of the coal ash, which is a residue after combustion, is used as civil engineering and building materials such as concrete and soil improvement materials from the viewpoint of effective use of resources, but the surplus is disposed of in landfills.

  By the way, coal used as a fuel 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, or a method of solidifying coal ash with cement or the like is performed (see Patent Documents 1 to 3).

  Further, in Patent Document 4, coal is burned in the combustion path (A), the exhaust gas is treated with an electric dust collector, and the resulting dust collection ash is used as a main fuel in the combustion furnace (B). Disclosed is a method for treating combustion ash by which the incinerated ash that has been burned again with the addition of a calcium source has a boron content of 1.0 mg / l or less by a dissolution test method based on Notification No. 18 of the 2003 Environment Agency. According to this treatment method, since coal ash is burned again in a combustion furnace to which a calcium source can be added, elution of boron contained in the incinerated ash can be suppressed. It is said that it can be used soon.

Furthermore, Patent Document 5 discloses an elution inhibitor containing aluminum sulfate, sodium thiosulfate, and iron powder as essential components as an elution inhibitor for contaminants in fly ash. And the use of quicklime are disclosed.
JP 2003-164886 A JP 2003-200132 A JP 2002-194328 A JP 2005-134098 A JP 2002-239522 A

  However, the conventional techniques described in Patent Document 1 to Patent Document 3 reduce the elution concentration of harmful trace elements by adding an additive to coal ash that is a combustion residue. In this case, there is a problem that silos, water tanks, mixing devices, etc. are required on a large scale as equipment for adding and mixing additives to coal ash, resulting in high processing costs and new equipment space. is there.

  Further, in the conventional techniques described in Patent Document 1 to Patent Document 3, although prevention of elution of heavy metals has been studied, studies on prevention of elution of light elements such as boron and fluorine have been insufficient.

  About the processing method of patent document 4, dust collection ash obtained with the combustion furnace is burned again with limestone etc., and possibility that the processing cost of dust collection ash will become high is high. Furthermore, the means for adding limestone has not been clarified and may require additional equipment. Moreover, in the processing method of patent document 4, the combustion temperature at the time of a coal ash process is as low as 700 to 900 degreeC, and cannot implement it suitably in a high temperature furnace. In addition, this treatment method cannot be suitably implemented even in a pulverized coal combustion furnace or the like. Moreover, the element used as the object of elution prevention is restricted to boron, and cannot be used as a general elution prevention method for trace metals.

  The elution inhibitor described in Patent Document 5 contains aluminum sulfate, sodium thiosulfate, and iron powder as essential components. For this reason, it is necessary to blend in advance and the cost also increases. Moreover, the elution prevention level is insufficient with this elution inhibitor alone, and there is a problem that the elution prevention level of arsenic and boron is particularly inferior. Moreover, when using quicklime together, this is added to the fly ash and the combined use to coal and coal ash is not examined.

  The present invention has been made in view of the above-described problems, and does not require a large initial investment, and does not require large-scale additional equipment. Elution of harmful trace elements from coal combustion residues in a coal-fired power generation system An object of the present invention is to provide a method for suppressing elution of harmful trace elements.

(1) A toxic trace element elution suppression method for suppressing leaching of toxic trace elements from coal combustion residues as fuel in a coal-fired power generation system,
To the coal, an elution inhibitor containing one or more selected from the group consisting of limestone, slaked stone, and quicklime is added as an elution inhibitor for coal addition,
Furthermore, a harmful trace element elution suppression method, comprising adding an elution inhibitor containing aluminum sulfate as an essential component to coal ash obtained after combustion of the coal as an elution inhibitor for ash addition.

  According to the invention of (1), since the elution inhibitor is added not at the coal ash after combustion but at the stage of coal during combustion or before combustion, it can be easily applied by improving existing equipment. . In addition, the timing of addition will not be specifically limited if it is the addition to the state of coal, Any of the coal supply part mentioned later, a pulverized coal production | generation part, and a pulverized coal combustion part may be sufficient. This pulverized coal combustion section includes the vicinity of the heat exchange unit arranged downstream of the combustion boiler.

  Further, in the present invention, the elution inhibitor for coal addition includes one or more selected from the group consisting of calcium compounds such as limestone, slaked stone, quicklime, and preferably the group consisting of limestone, slaked stone, quicklime. It is characterized by using an elution inhibitor containing one or more selected as a main component. One or more selected from the group consisting of calcium compounds such as limestone, slaked stone, and quicklime are readily available, and harmful elements such as boron, fluorine, selenium, arsenic, hexavalent chromium, among others, boron , Fluorine, selenium and arsenic elution can be effectively suppressed.

And in this invention, the elution inhibitor containing as an aluminum sulfate essential component is further added to the coal ash obtained after combustion of coal as an elution prevention for ash addition, It is characterized by the above-mentioned.
As described in the above cited reference 5, aluminum sulfate dissolves in water when it coexists and functions as an electrolyte. In addition, aluminum polycondensation ions are formed in the process of producing aluminum hydroxide through hydrolysis. It is thought that it works to insolubilize pollutants by forming as a polymer and condensing while putting pollutants there. This can also be estimated from the fact that aluminum sulfate is used as a sewage precipitation agent (flocculating agent). However, usually, when aluminum sulfate is added to coal ash, the pH of coal ash decreases due to the gypsumization of calcium and acidification with sulfuric acid due to the sulfuric acid component contained. Due to this pH decrease, trace components such as boron are easily eluted. Therefore, even in the method of the cited document 5, prevention of boron elution is insufficient.

  However, according to the method of the present invention, CaO in coal ash is increased and the high alkali is maintained (about pH 12 to 13) by the addition of the above-mentioned coal dissolution additive. Even when aluminum sulfate is added thereto, a high pH can be maintained by the buffering action of CaO, so that the elution suppressing effect can be maintained even when the surroundings are in a high pH region. That is, the elution of boron, fluorine, selenium, and arsenic can be effectively suppressed without being affected by the pH drop. As a result, for example, when coal ash is used as a soil conditioner or the like, there is an excellent effect that re-elution due to acid rain or the like can be prevented.

  That is, the feature of the present invention is that the elution prevention effect due to the addition of aluminum sulfate can be sufficiently brought out by adding Ca to the coal in advance. This makes it possible to obtain a sufficient elution-preventing effect even in coal types with a high trace substance content that have been difficult in the past (eg, Chinese coal, Indonesian coal, etc.), and the applicable types of coal are greatly expanded. .

  In addition, there is a problem that only the addition of the coal dissolution elution inhibitor described above is insufficient to suppress the elution of fluorine, but as in the present invention, by using aluminum sulfate addition to coal ash, Also for fluorine, the amount of elution can be significantly suppressed (see Examples described later).

  The aluminum sulfate in the present invention includes not only a single crystal but also its hydrated salt. For example, 27, 18, 16, 10, hexahydrate is known as the hydrated salt, and these are all included in the aluminum sulfate in the present invention.

  Further, the elution inhibitor for ash addition is preferably aluminum sulfate alone, but may contain other substances (for example, aluminum hydroxide) as long as the effect thereof is not impaired.

(2) With respect to 100 parts by mass of coal, the dissolution additive for coal addition is added in a range of 0.1 parts by mass or more and 10 parts by mass or less,
The harmful trace element elution suppression method according to (1), wherein the ash addition elution inhibitor is added in an amount of 0.3 to 10 parts by mass with respect to 100 parts by mass of the coal ash.

  According to the invention of (2), elution of the above-mentioned harmful trace elements can be suppressed more effectively. It is not preferable that the addition amount of the dissolution inhibitor for coal addition is less than 0.1 parts by mass, since the elution suppression effect of harmful trace elements becomes insufficient. There is no significant improvement. Moreover, since there is a risk of causing a large amount of coal ash to adhere to the furnace inner wall (slagging) due to a melting point drop on the surface of the coal ash, the addition amount of the elution inhibitor for coal addition should be 6.0 parts by mass or less. The amount is preferably 1.0 part by mass or less.

  Further, if the addition amount of the ash addition elution inhibitor is less than 0.3 parts by mass, the effect of inhibiting the elution of harmful trace elements is insufficient, which is not preferable. Even if it exceeds 10 parts by mass, the pH is lowered. Therefore, no significant improvement is observed in the elution suppressing effect of harmful trace elements.

  In addition, in this invention, the said elution inhibitor for coal addition is added so that pH of the aqueous solution produced | generated by adding 10 mass parts of coal ash with respect to 100 mass parts of water may become 12.0 or more. It is preferable. Elements such as selenium, boron, and arsenic have the property that the amount of elution from coal ash is less under conditions of higher pH. Therefore, it is possible to effectively prevent elements such as selenium, boron and arsenic from eluting from the coal ash.

  The coal-adding dissolution inhibitor is preferably granular or powdery, preferably has an average particle size of 10 μm to 100 μm, more preferably an average particle size of 10 μm to 80 μm, and an average particle size Is particularly preferably 10 μm to 60 μm. Moreover, you may use the elution prevention solution for coal addition which is the slurry containing the elution inhibitor for coal addition, or the liquid mixture which disperse | distributed the said elution inhibitor for coal addition in water.

  By making the elution inhibitor for coal addition granular or powdery, the addition becomes easy and the mixing is made uniform to enhance the elution prevention effect. Among these, by making the average particle size from 10 μm to 100 μm, mixing with coal can be facilitated, and the elution preventing effect can be particularly enhanced. When the average particle size is less than 10 μm, it is not practical as an elution inhibitor for coal addition, and when the average particle size exceeds 100 μm, only a small effect is obtained by adjusting the particle size. The average particle diameter is more preferably 10 μm to 80 μm, and still more preferably 10 μm to 60 μm. By setting the average particle size to 80 μm or less, the particle size can be adjusted by using a coal pulverized coal machine conventionally provided in a coal-fired power generation system of a pulverized coal combustion method, which is efficient. Furthermore, by setting the average particle size to 60 μm or less, it is possible to use the limestone powder used in a desulfurization apparatus that is conventionally provided in a coal-fired power generation system. The effect by adjusting can be sufficiently obtained. Moreover, the same effect as the above can be obtained by adding the coal-elution-preventing solution in the form of a slurry containing a granular or powdery coal-elution-preventing agent, or a mixed solution in which these are dispersed in water. . Among these, the slurry-like coal-elution preventing solution for coal addition is easy to handle, which is preferable.

(3) The coal-fired power generation system is a pulverized coal combustion type power generation system,
Add the coal dissolution elution inhibitor in the combustion boiler or upstream thereof,
The harmful trace element elution suppression method according to (1) or (2), wherein the ash addition elution inhibitor is added to coal ash collected by a dust collector.

  The invention of (3) prescribes the addition position of the dissolution inhibitor for coal addition and the dissolution inhibitor for ash addition. In this invention, the elution inhibitor for coal addition is added in the state of coal, and it adds to a combustion boiler as a preferable addition position, for example. Thereby, the elution inhibitory effect of a harmful trace element can be improved by the high temperature heating by combustion. In the present invention, “inside the combustion boiler” includes addition to the piping when the combustion boiler is recirculating exhaust gas. Moreover, you may add the elution inhibitor for coal addition upstream from the inside of a combustion boiler. “Upstream from inside the combustion boiler” is, for example, a coal supply unit and a pulverized coal generation unit, which will be described later. According to this aspect, since it can be added in the state of fuel coal or pulverized coal, the addition can be performed with simpler equipment, and even existing equipment can be easily applied.

  In the present invention, the coal thermal power generation system is a pulverized coal combustion type power generation system, and the coal addition elution inhibitor may be added in the vicinity of a heat exchange unit disposed downstream of the combustion boiler. . This heat exchange unit is also referred to as a furnace upper partition wall, a superheater, a reheater, or the like, and is an area where 450 ° C. to 500 ° C. is maintained. Thus, the “addition to coal” in the present invention is preferably performed in the state where the atmospheric temperature in the furnace is 850 ° C. to 900 ° C. or 450 ° C. to 500 ° C.

  Moreover, in this invention, it is preferable to add the elution inhibitor for ash addition to the coal ash collect | recovered from the dust collector. The dust collector will be described later. As a result, the existing equipment can be used as it is, and it is not necessary to add new equipment. In addition, the coal ash collect | recovered with the dust collector is the meaning including not only the addition in a dust collector but the addition before and behind that (for example, the addition in any place of the coal ash process part 18 in FIG. 1).

  According to the harmful trace element elution control method of the present invention, a large amount of initial investment is not required, and the elution of harmful trace elements from coal combustion residues in a coal-fired power generation system is suppressed without requiring a large-scale additional facility. can do.

<A: Configuration of pulverized coal combustion facility in coal-fired power generation system>
Hereinafter, an embodiment showing an example of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a pulverized coal combustion facility 1 in a coal-fired power generation system. Here, as shown in FIG. 1, the 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 that burns pulverized coal. The combustion part 16 and the coal ash process part 18 which processes the coal ash produced | generated by combustion of pulverized coal are provided. FIG. 2 is an enlarged view of the vicinity of the furnace 161 in the pulverized coal combustion unit 16.

<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 substantially inverted U shape as a whole, and after the combustion gas moves in an inverted U shape along the arrow in the figure. Then, it is reversed again into a U-shape, and the outlet of the furnace 161 (the last of the arrows in FIG. 2) is connected to the denitration device 181 and the dust collector 182 in FIG. In the pulverized coal combustion facility according to the present embodiment, the height of the furnace 161 is 30 m to 70 m, and the total length of the exhaust gas passage ranges from 300 m to 1000 m.

  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. Further, near the top of the U-shape in the furnace 161, a furnace upper dividing wall 161b, a final superheater 161b ′, and a first reheater 161f (all of which are heat exchange units) are arranged, and further placed horizontally from there. A primary superheater 161c (heat exchange unit) is subsequently arranged. Further, a second reheater 161f ′ is provided in parallel with the horizontal primary superheater 161c, and from the vicinity of the terminal end of the horizontal primary superheater 161c, a primary economizer 161d (heat exchange unit). A secondary economizer 161e (heat exchange unit) is 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. In the present embodiment, in the furnace 161, the primary economizer 161d and the secondary economizer 161e are separately installed in two stages, but the present invention is not limited to such a form. That is, the furnace 161 may have only a single economizer.

<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 device 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 device (not shown).

  The coal ash collection silo 183 is a facility that primarily stores the coal ash collected by the dust collector 182. The coal ash stored here is input to the kneader 184 while adjusting the input amount.

  The kneader 184 is an apparatus for kneading the coal ash charged from the coal ash recovery silo 183 together with the ash addition elution inhibitor 20. Thereby, reaction with coal ash and the elution inhibitor 20 for ash addition is accelerated | stimulated. The kneader 184 kneads coal ash and the ash addition elution inhibitor 20, but may be kneaded with a liquid such as water in addition to these. In addition, the elution suppression process process which throws this elution inhibitor 20 for ash addition into coal ash is explained in full detail later.

  The ash addition elution inhibitor 20 is added to coal ash or sludge generated in a coal-fired power generation system to suppress the elution of harmful trace elements, and contains aluminum sulfate as an essential component.

  The storage unit 185 is a tank for curing the coal ash kneaded by the kneader 184.

<B: Harmful Trace Element Elution Control Method of the Present Invention>
An example of a preferred embodiment of the present invention will be described using the pulverized coal combustion facility 1 described above.

  This process includes a coal supply process for supplying coal, a pulverized coal generation process for pulverizing the supplied coal to generate pulverized coal, and a pulverized coal combustion process for generating coal ash by burning the pulverized coal; And a coal ash treatment process for collecting and storing the coal ash. Each of these processes includes a coal supply unit 12, a pulverized coal generation unit 14, and a pulverized coal combustion unit 16 of the pulverized coal combustion facility 1, respectively. , And the coal ash treatment unit 18. And the elution inhibitor addition process for coal addition which is the feature of the present invention is preferably performed in any of the above-described coal supply process, pulverized coal generation process, and pulverized coal combustion process. The ash addition elution inhibitor addition step is preferably performed in the coal ash treatment step described above.

<Coal supply process>
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 can be pulverized coal combustion. Good.

<Pulverized coal production process>
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 to the case where a coal addition elution inhibitor is added.

<Pulverized coal combustion process>
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 pulverized coal is burned in the burner zone 161a ′, and the temperature at this time ranges from 1300 ° C. to 1500 ° C., and the coal ash generated by the combustion rises in the direction of the arrow. And the exhaust gas through the furnace upper partition wall 161b, the final superheater 161b ', the first reheater 161f, the second reheater 161f', and the horizontal primary superheater 161c (all of which are heat exchange units). The primary economizer 161d (heat exchange unit) and the secondary economizer 161e (heat exchange unit) are sequentially passed. As described above, the vicinity of the heat exchange unit is an area where the temperature is maintained at about 450 ° C. to about 500 ° C., and heat transfer provided for preheating boiler feedwater using the heat held by the combustion gas. By passing through the plane group, heat is exchanged, and the temperature decreases. The time required for the exhaust gas to reach from the burner zone 161a ′ to the vicinity of the economizer is approximately 5 to 10 seconds. 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 a powder having an average particle size in the range of 1 μm to 100 μm.

<Coal ash treatment process>
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.

<Elution inhibitor addition process for coal addition>
As shown in FIG. 1, the coal addition elution inhibitor adding step, which is a step of adding the coal addition elution inhibitor, which is the first feature of the present invention, is preferably the above coal supply step, pulverized coal production step. The pulverized coal combustion process is performed (S31, S32, and S33 in FIG. 1 respectively).

  In addition, the addition place of the elution inhibitor for coal addition is not particularly limited as long as it is in the state of coal. You may carry out by the transfer path between processes, etc.

  Specifically, for example, a method for supplying and mixing coal dissolution elution inhibitor on a belt conveyor being transferred when transporting from coal feeder 122 to coal pulverized coal machine 141, and a coal addition dissolution inhibitor A method of directly feeding into a coal hopper (not shown) of the coal pulverized coal machine 141, a method of supplying an agent charging port in a pipe between the coal pulverized coal machine 141 and the furnace 161, and directly with the combustion air to the furnace 161 A method of charging, a furnace upper dividing wall 161b, a final superheater 161b ′, a first reheater 161f, a second reheater 161f ′, a horizontal primary superheater 161c, which constitute a part of the furnace 161; However, the method is not limited to these. 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 for coal addition of the present invention contains one or more selected from the group consisting of calcium compounds such as limestone (CaCO ₃ ), slaked stone (Ca (OH) ₂ ), quicklime (CaO) and the like. Further, the dissolution inhibitor for coal addition is preferably granular or powdery, specifically, the average particle size is preferably 10 μm to 100 μm, more preferably 10 μm to 80 μm, and more preferably 10 μm to 60 μm. More preferably. When the average particle size is less than 10 μm, the average particle size is too fine and is not practical as an elution inhibitor for coal addition. When the average particle size exceeds 100 μm, the effect of adjusting the average particle size can hardly be obtained. Moreover, when making an average particle diameter into 80 micrometers or less, the particle size of the elution inhibitor for coal addition can be adjusted using the coal pulverized coal machine 141, and it is efficient. Furthermore, when the average particle size is 60 μm or less, the limestone powder used in the desulfurization apparatus can be used as it is, so that it is economical and by adjusting the particle size of the coal-added dissolution inhibitor. A sufficient effect can be obtained.

  It is preferable that the addition amount of the coal addition elution inhibitor to the coal is 0.1 to 10 parts by mass with respect to 100 parts by mass of the coal. The amount is more preferably 1 part by mass or more and 6.0 parts by mass or less, and particularly preferably 0.1 part by mass or more and 1.0 part by mass or less. When the amount is less than 0.1 parts by mass, it is not possible to substantially obtain the effect obtained by adding the dissolution additive for coal addition. On the other hand, the elution inhibitor for coal addition is preferably 10 parts by mass or less, and preferably 6.0 parts by mass or less from the viewpoint of preventing slugging and fouling in order to reduce the melting point of coal ash. More preferably, it is 1.0 mass part or less.

  The coal addition elution inhibitor is preferably added so that the melting point of coal ash produced as a result of combustion is 1200 ° C. or higher, and more preferably 1300 ° C. or higher. Since the melting point of coal ash is 1200 ° C. or higher, it is possible to prevent the coal ash from being excessively melted inside the furnace 161 and causing slagging and fouling. Furthermore, by adding so that the melting point of coal ash becomes 1300 ° C. or higher, the effect of preventing the occurrence of such slugging and fouling can be obtained more strongly.

  The melting point of coal ash is greatly affected by the components of coal ash. That is, when there is a large amount of iron (III) oxide, calcium oxide, magnesium oxide, sodium oxide, potassium oxide, etc. in the coal ash, the melting point of the coal ash tends to be relatively low, When a large amount of silicon oxide, aluminum oxide, titanium oxide or the like is present, the melting point of coal ash tends to be relatively high. In addition of the dissolution inhibitor for coal addition, the melting point of coal ash can be adjusted by adjusting the content of these components in the coal ash.

Moreover, in this invention, adding the elution inhibitor for coal addition so that pH of the aqueous solution produced | generated by adding 10 mass parts of coal ash with respect to 100 mass parts of water may become 12.0 or more. You can also. Elements such as selenium, boron and arsenic have the property that the higher the pH of coal ash, the less likely it is to elute from coal ash. For this reason, it can suppress effectively that these elements elute from coal ash by making pH of coal ash 12.0 or more.
The limestone is preferably added so that the pH of the aqueous solution adjusted under the above conditions is 12.5 or more, and more preferably 13.0 or more. By adding limestone to such a pH, it is possible to further enhance the elution suppressing action of elements such as selenium, boron and arsenic.

  In the present invention, by adding the above-described coal dissolution additive, the elution of harmful trace elements contained in coal ash can be suppressed regardless of the type of trace elements. Specific examples of trace elements that can prevent elution include, but are not limited to, boron, fluorine, selenium, and arsenic. Among these, elution of boron, selenium and arsenic can be particularly preferably suppressed. This mechanism first lowers the melting temperature of coal ash by the addition of an elution inhibitor for coal addition, which is a compound containing calcium. That is, under the high temperature condition of 1300 ° C. to 1500 ° C. in the furnace 161, the surface of coal ash mainly composed of silica and alumina is softened (melted), and the coal ash particles having viscosity come into contact with trace elements. Thus, it is estimated that the elution concentration is reduced by being taken into the coal ash. In this way, in the present invention, by adding the anti-elution agent for coal addition by the stage of combustion, the high temperature of the furnace in the pulverized coal combustion part is effectively used, and the elution of trace elements from the coal ash is suppressed. To do.

  In addition, when limestone, slaked lime, or quicklime is used as an elution inhibitor for coal addition, calcium oxide derived from these elution inhibitors for coal addition in the exhaust gas cooling process or in the collected coal ash Reacts with selenium oxide, arsenic trioxide, boron oxide, etc. present in coal ash to produce poorly soluble or insoluble compounds such as calcium selenite, calcium arsenate, calcium borate, Elution of trace elements in coal ash can be suppressed.

  In addition, when the dissolution additive for coal addition is added only in the vicinity of the superheater, the temperature in the vicinity of the superheater is 850 ° C. to 900 ° C., which is a relatively low temperature. Only happens. For this reason, it is also effective to add the elution inhibitor for coal addition only to the vicinity of the superheater.

<Elution inhibitor addition step S21 for ash addition>
As shown in FIG. 1, the ash addition elution inhibitor addition step S21, which is a step of adding the ash addition elution inhibitor 20 as the second feature of the present invention, is preferably performed in the above coal ash treatment step. (For example, S21 in FIG. 1).

  In the ash addition elution inhibitor addition step S21, it is preferable to add the ash addition elution inhibitor 20 within a range of 0.3 parts by mass to 10 parts by mass with respect to 100 parts by mass of coal ash. In addition, among each process which comprises the above-mentioned coal ash processing process, the elution suppression process process which adds the elution inhibitor 20 for ash addition is not limited to S21, From the pre-process of a denitration process, the pre-process of a stirring process Any time between. For example, the ash addition elution inhibitor 20 may be added to the coal ash collected by the dust collector 182 (each stage in the case of multiple stages).

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
The apparatus as shown in FIG. 1 and FIG. 2 was used and the elution inhibitor 30 for coal addition (limestone) was added to the position of the coal supply part 12 in FIG. 1 (S31). Moreover, the elution inhibitor 20 for ash addition (14-18 hydrate salt of aluminum sulfate) was added to the position of the kneading machine 184 of the coal ash treatment section 18 in FIG. 1 (S21). Here, Australian coal was used as coal.

  In addition, limestone was added so that it might become 1 mass part with respect to 100 mass parts of coal, and the aluminum sulfate hydrate was added so that it might become 2 mass parts with respect to 100 mass parts of coal ash.

  Table 1 shows the results of measuring the elution concentrations of trace elements (selenium, boron, and arsenic) for the coal ash to which the coal addition elution inhibitor 30 and the ash addition elution inhibitor 20 were added. The unit of elution concentration is [mg / L] in all cases. In Comparative Example 1, neither coal dissolution elution agent 30 nor ash addition dissolution agent 20 was added, and Comparative Example 2 was obtained by adding only coal addition dissolution agent 30 (ash addition). No elution inhibitor 20 is added). The first to fourth stages in the table mean the first to fourth stages of the EP (dust collector 182), and the dust collector 182 composed of four stages in series from the upstream first stage to the downstream fourth stage. It is a measurement result about the ash collected from each dust collector.

  According to the results shown in Table 1, in the example in which the ash addition elution inhibitor 20 was further added as compared to the addition of only the coal addition elution inhibitor 30 (Comparative Example 2), the elution suppression was further greatly reduced. ing. In particular, with respect to fluorine, the elution preventing effect was not recognized in Comparative Example 2, but the elution preventing effect was obtained in the Examples. Accordingly, it can be seen that the method of the present invention can be applied to a wide range of coal types (coal species containing a large amount of harmful trace elements) and can be applied to a wide range of harmful trace elements.

  Since this invention can reduce the harmfulness (environmental load) of coal ash discharged from a pulverized coal combustion furnace such as a thermal power plant, it is a technology that enables further effective utilization and safe disposal of coal ash.

It is a schematic block diagram of the pulverized coal combustion facility in the coal thermal power generation system which shows one Embodiment of this 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 121 Coal bunker 122 Coal feeder 14 Pulverized coal production | generation part 141 Coal pulverized coal machine 142 Air supply machine 16 Pulverized coal combustion part 161 Furnace 162 Heating machine 163 Air supply machine 18 Coal ash processing part 181 Denitration equipment 182 Dust collector 183 Coal ash recovery silo 20 Elution inhibitor for ash addition 30 Elution inhibitor for coal addition S21 Elution inhibitor addition process for ash addition S31, S32, S33 Elution inhibitor addition process for coal addition

Claims (3)

A toxic trace element elution suppression method that suppresses leaching of harmful trace elements from combustion residues of coal as fuel in a coal-fired power generation system,
To the coal, an elution inhibitor containing one or more selected from the group consisting of limestone, slaked stone, and quicklime is added as an elution inhibitor for coal addition,
Furthermore, a harmful trace element elution suppression method, comprising adding an elution inhibitor containing aluminum sulfate as an essential component to coal ash obtained after combustion of the coal as an elution inhibitor for ash addition. With respect to 100 parts by mass of coal, the dissolution additive for coal addition is added in the range of 0.1 to 10 parts by mass,
The harmful trace element elution suppression method according to claim 1, wherein the elution inhibitor for ash addition is added in a range of 0.3 parts by mass to 10 parts by mass with respect to 100 parts by mass of the coal ash. The coal-fired power generation system is a pulverized coal combustion type power generation system,
Add the coal dissolution elution inhibitor in the combustion boiler or upstream thereof,
The harmful trace element elution suppression method according to claim 1 or 2, wherein the ash addition elution inhibitor is added to coal ash recovered by a dust collector.

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