JP2007291312A - Method of inhibiting elution of harmful trace elements and elution inhibitor for adding to coal for use in the inhibiting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of inhibiting the elution of harmful trace elements from combustion residues of coal. <P>SOLUTION: The method of inhibiting the elution of harmful trace elements is a method of inhibiting the elution of harmful trace elements from combustion residues of coal by adding an elution inhibitor for adding to coal to coal as fuel wherein as the elution inhibitor for adding to coal is used an elution inhibitor comprising as the main component one or more kinds selected from the group consisting of limestone, slaked lime and quicklime and the elution inhibitor for adding to coal is preferably added in an amount of a range of not less than 0.3 pt.mass to less than 10 pts.mass based on 100 pts.mass coal. The addition of the elution inhibitor may be carried out within a combustion boiler. As another alternative, the addition may be carried out in the state of pulverized coal before introducing the same into the boiler. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a toxic trace element elution control method that suppresses leaching of toxic trace elements from combustion residues of coal, which is a fuel in a coal-fired power generation system, and an elution inhibitor for coal addition used therefor.

  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 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.
JP 2003-164886 A JP 2003-200132 A JP 2002-194328 A JP 2005-134098 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 which is a fuel 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 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 the elution of harmful trace elements, and an elution inhibitor for coal addition used therefor.

  (1) A toxic trace element elution control method for suppressing elution of toxic trace elements from combustion residues of coal by adding an elution inhibitor for coal addition to coal as fuel in a coal thermal power generation system. A method for suppressing the elution of harmful trace elements, wherein an elution inhibitor containing at least one selected from the group consisting of limestone, slaked stone, and quicklime is used as the coal elution inhibitor.

  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 limestone, 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.

  (2) The harmful trace element elution suppressing method according to (1), wherein the coal elution inhibitor is added in a range of 0.1 parts by mass or more and less than 10 parts by mass with respect to 100 parts by mass of the coal.

  (3) The harmful trace element elution suppression method according to (1), wherein the coal-elution additive is added in an amount of 0.1 parts by mass or more and 6.0 parts by mass or less with respect to 100 parts by weight of the coal.

  (4) The harmful trace element elution suppression method according to (1), wherein the coal elution inhibitor is added in the range of 0.1 parts by weight to 1.0 part by weight with respect to 100 parts by weight of the coal.

  According to the inventions of (2) to (4), 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 suppressing effect of harmful trace elements becomes insufficient. There is no improvement. Moreover, since there is a possibility that a large amount of coal ash adheres to the inner wall of the furnace (slagging) due to a melting point drop on the surface of the coal ash, the addition amount of the elution inhibitor for coal addition is 6.0 parts by mass or less. Preferably, it is less than 1.0 part by mass.

  (5) From (1) above, the coal-elution inhibitor is added so that the pH of the aqueous solution produced by adding 10 parts by mass of coal ash to 100 parts by mass of water is 12.0 or more. (4) The harmful trace element elution suppression method according to any one of (4).

  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. For this reason, according to the invention described in (5), it is possible to effectively prevent elements such as selenium, boron and arsenic from eluting from coal ash.

  (6) The harmful trace element according to any one of (1) to (5), wherein the coal-fired power generation system is a pulverized coal combustion type power generation system, and the coal addition elution inhibitor is added to a combustion boiler. Elution suppression method.

  (7) The harmful effect according to any one of (1) to (5), wherein the coal-fired power generation system is a power generation system of a pulverized coal combustion system, and the elution inhibitor for coal addition is added upstream from within the combustion boiler. Trace element elution suppression method.

  (8) The coal thermal power generation system is a pulverized coal combustion type power generation system, and the elution inhibitor for coal addition is added in the vicinity of a heat exchange unit arranged downstream of the combustion boiler (1) to (5) The method for suppressing the elution of harmful trace elements according to any one of the above.

  The inventions of (6) to (8) prescribe the addition position of the dissolution inhibitor for coal addition. In this invention, the elution inhibitor for coal addition is added in the state of coal, and in the invention of (6), it adds in a combustion boiler as a preferable addition position. 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, in the invention of (7), the elution inhibitor for coal addition is added upstream from within the 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.

  Moreover, in the invention of (8), the elution inhibitor for coal addition is added in the vicinity of the heat exchange unit arranged downstream of the combustion boiler. This heat exchange unit is also referred to as a furnace upper dividing wall, a superheater, a reheater, or the like, and is an area where 850 ° C. to 900 ° C. is maintained. Thus, “addition to coal” in the present invention is preferably substantially added in a state where the atmospheric temperature is 850 ° C. or higher.

  (9) A coal addition elution inhibitor that suppresses the elution of harmful trace elements from the combustion residue by adding to coal as fuel in a coal-fired power generation system, and consists of limestone, slaked stone, and quicklime. An elution inhibitor for coal addition, comprising at least one selected from the group.

  The invention of (9) captures the invention of (1) above as an elution inhibitor for coal addition, and the same effect as the invention of (1) can be obtained.

  (10) The elution inhibitor for coal addition according to (9), wherein the elution inhibitor for coal addition is granular or powdery.

  (11) The elution inhibitor for coal addition according to (10), wherein the average particle size is 10 μm to 100 μm.

  (12) The elution inhibitor for coal addition according to (10), wherein the average particle size is 10 μm to 80 μm.

  (13) The elution inhibitor for coal addition according to (10), wherein the average particle size is 10 μm to 60 μm.

  (14) A coal addition elution preventing solution, which is a slurry containing the coal addition elution inhibitor according to (10) to (13) or a mixed liquid in which the coal addition elution inhibitor is dispersed in water.

  According to the aspect of (10), by making the elution inhibitor for coal addition granular or powdery, addition becomes easy, mixing is also made uniform, and the elution prevention effect can be enhanced. Especially, mixing to coal can be made easy by making an average particle diameter into 10 micrometers from 100 micrometers like the aspect of (11), and the elution prevention effect can be heightened especially. 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 as in the embodiment (12), and further preferably 10 μm to 60 μm as in the embodiment (13). 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, in the aspect of (14), by adding the elution prevention solution for coal addition in the state of the slurry containing the granular or powdery coal elution prevention agent for coal addition, or the mixed liquid which disperse these in water, The same effects as the effects (10) to (13) can be obtained. Among these, the slurry-like coal-elution preventing solution for coal addition is easy to handle, which is preferable.

  According to the toxic trace element elution control method of the present invention and the elution inhibitor for coal addition used therein, a large amount of initial investment is not required, and large-scale additional equipment is not required. Elution of harmful trace elements from the residue can be suppressed.

<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 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: Harmful Trace Element Elution Control Method of the Present Invention>
The harmful trace element elution suppression method of the present invention is a harmful effect of suppressing the elution of harmful trace elements from the combustion residue of coal by adding an elution inhibitor for coal addition to coal as fuel in a coal thermal power generation system. This is a trace element elution suppression method, and uses an elution inhibitor containing as a main component one or more selected from limestone, slaked stone, and quicklime as the elution inhibitor for coal addition. It demonstrates using said pulverized coal combustion facility 1. FIG.

  This step includes a coal supply step S10 for supplying coal, a pulverized coal generation step S20 for pulverizing the supplied coal to generate pulverized coal, and a pulverized coal combustion step for generating coal ash by burning the pulverized coal. S30 and a coal ash treatment step S40 that collects and stores the coal ash, and each of these steps includes a coal supply unit 12, a pulverized coal generation unit 14, a pulverized powder of the above-described pulverized coal combustion facility 1, respectively. This is performed in the charcoal combustion unit 16 and the coal ash treatment unit 18. And the elution inhibitor addition process S50 for coal addition which is the feature of the present invention is preferably performed in any of the coal supply process S10, the pulverized coal generation process S20, and the 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 can be 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 to the case where a coal addition 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 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 dividing 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 850 ° C. to about 900 ° 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 powder having an average particle size in the range of 1 μm to 100 μm.

<Coal ash treatment process 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.

<Coal dissolution elution inhibitor addition step S50>
As shown in FIG. 1, the coal addition elution inhibitor adding step S50, which is a step of adding the coal addition elution inhibitor, which is a feature of the present invention, is preferably the above coal supply step S10, pulverized coal generation step S20. The pulverized coal combustion step S30 is performed (S51, S52, S53 in FIG. 1 respectively).

  In addition, the addition place of the elution inhibitor for coal addition will not be specifically limited if it is a 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, It may be performed in a transfer path between the pulverized coal combustion step S30 and the like.

  Specifically, for example, a method for supplying and mixing the coal-elution elution inhibitor on the belt conveyor being transferred when transporting from the coal feeder 122 to the coal pulverized coal machine 141, and a coal addition elution 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 to the furnace 161 together with combustion air 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 less than 1.0 part by mass. 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 less than 10 parts by mass 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 conditions of 1300 ° C. to 1500 ° C. in the furnace 161, the surface of the coal ash mainly composed of silica and alumina is softened (melted), and the viscous coal ash particles are in contact with the 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.

Hereinafter, the present invention will be described more specifically with reference to examples.
<Test Example 1: Small scale test>
<Example 1>
3 parts by weight of limestone was mixed with 100 parts by weight of Chinese bituminous coal (hereinafter referred to as coal A). This mixture was pulverized by an impeller mill to obtain a powder having 74 μm under 80 wt%, 40 μm under 50 wt%, and 20 μm under 25 wt%.
This powder (limestone-containing pulverized coal) was supplied to a pulverized coal combustion furnace and burned. As the pulverized coal combustion furnace, a self-burning vertical furnace having an inner diameter of 30 cm and a furnace length of 2.5 m was used, and the amount of powder charged was 5 to 6 kg / h. The furnace temperature at this time reached 1300 ° C.
After combustion, the discharged coal ash was collected with a bag filter at the rear stage of the combustion furnace.

The collected coal ash was subjected to elution operation according to Environment Agency Notification No. 46 to prepare a test solution, and the concentration of each trace element in this test solution was measured. The measurement results are shown in Table 1.
Selenium and arsenic were measured by atomic absorption, fluorine was measured by ion chromatography, and boron was measured by ICP mass spectrometry.

<Comparative Example 1>
In Example 1, coal ash was collected and evaluated in the same manner as in Example 1 except that limestone was not added to Coal A. The measurement results are shown in Table 1.

<Example 2>
In Example 1, coal ash was collected and evaluated in the same manner as in Example 1 except that Australian bituminous coal (coal B) was used instead of coal A. The measurement results are shown in Table 1.

<Comparative example 2>
In Example 2, coal ash was collected and evaluated in the same manner as in Example 2 except that limestone was not added to Coal B. The measurement results are shown in Table 1.

  As is apparent from the measurement results shown in Table 1, when the method of the present invention is carried out, the elution concentration of each trace element from coal ash can be reduced. Therefore, it was confirmed that the elution concentration of the trace elements contained in the coal ash can be reduced by a simple operation of adding an additive such as limestone to the coal before putting it into the mill.

<Test Example 2: Actual machine test>
<Example 3>
The apparatus as shown in FIG. 1 and FIG. 2 was used, and the elution inhibitor (limestone) was added at the position of the coal supply part in FIG. The limestone was adjusted so that the Ca content (% by mass) in the ash was the ratio shown in Table 2. Moreover, about the coal ash collect | recovered by the coal ash collection | recovery silo 183, the elution density | concentration of a trace element (selenium, boron, and arsenic) is shown in Table 2 with the decreasing rate after that. Here, Australian coal was used as coal. Moreover, the numerical value of each elution amount in Table 2 is the elution amount after addition / the elution amount not added. Here, the post-addition elution amount corresponds to the example of the present invention, and the non-addition elution amount corresponds to the comparative example, which is a system to which the elution inhibitor of the present invention is not added. The unit of elution concentration is [mg / L], and the unit of decrease rate is [%].

  In addition, the measurement result of the elution concentration shown below is the same as that of Test Example 1 in which the elution operation was performed according to Environment Agency Notification No. 46, a test solution was prepared, and the concentration of each trace element in this test solution was measured. . Moreover, among each trace element, selenium and arsenic were performed by atomic absorption method, fluorine was performed by ion chromatography, and boron was performed by ICP mass spectrometry.

  Moreover, ECO which is a sampling location of Table 2 is the primary economizer 161d in FIG. Further, EP (dust collector) first stage to EP (dust collector) fourth stage are respective dust collectors of the dust collector 182 composed of four stages in series.

  According to the results in Table 2, it can be seen that an elution preventing effect is recognized in selenium, boron and arsenic. The reduction rate in parentheses is a reference value, and even if this figure exceeds the regulation value, these ash is mixed with other ash and disposed of, so the regulation value as ash is cleared, so there is no problem .

<Test Example 3: Examination of particle size difference / small-scale test>
<Example 4>
Mixing 100 parts by weight of Australian charcoal pulverized to a particle size of 200 μm with 1.0 part by weight of limestone pulverized to a particle size of 45 μm, converting to JIS ash, and performing an elution operation according to Environment Agency Notification No. 46 to prepare a test solution, The concentration of each trace element in this test solution was measured. The results are shown in Table 3.
Of the trace elements, fluorine was measured by ion chromatography, and boron was measured by ICP mass spectrometry.

<Example 5>
The test was performed in the same manner as in Example 4 except that the particle size was 75 μm. The results are shown in Table 3.

<Comparative Example 3>
The test was performed in the same manner as in Example 4 except that the particle size was 150 μm. The results are shown in Table 3.

  As is apparent from Table 3, the elution amounts of fluorine and boron are smaller in Example 4 or Example 5 than in Comparative Example 3. From the above findings, it is suggested that the smaller the particle size when adding limestone, the greater the effect of suppressing the elution of trace elements.

<Test Example 3: Examination of particle size / actual machine test>
<Example 6>
100 parts by mass of Chinese coal pulverized to 74 μm and 1 part by weight of limestone pulverized to 45 μm were mixed and burned in an electric heating type drop tube furnace. The coal ash after combustion was sampled, and a test solution was prepared by elution operation according to the Environment Agency Notification No. 46, and the concentration of each trace element in the test solution was measured. The results are shown in Table 4.
Of the trace elements, fluorine was measured by ion chromatography, boron was measured by ICP mass spectrometry, and selenium and arsenic were measured by atomic absorption.

<Comparative example 4>
The same experiment as in Example 6 was performed without adding limestone to Chinese charcoal. The results are shown in Table 4.

  As is clear from Table 4, in Example 6, it was possible to significantly suppress the elution of trace elements as compared with Comparative Example 4. That is, it was found that when limestone having a particle size of 45 μm was used as an elution inhibitor for coal addition, the elution of trace elements could be suitably suppressed.

<Test Example 4: Effect on pH>
<Example 7>
2 parts by weight of limestone was added to 100 parts by weight of Australian coal and burned in a pulverized coal combustion furnace. Coal ash was collected in an electric dust collector, and an elution operation was performed according to the Environment Agency Notification No. 46 to prepare a test solution. After measuring the pH, the concentration of each trace element in the test solution was measured. The results are shown in Table 5.
Of each trace element, boron was measured by ICP mass spectrometry, and selenium and arsenic were measured by atomic absorption.

<Reference Example 1>
Without adding limestone to Australian coal, it is burned in a pulverized coal combustion furnace, coal ash is recovered in an electric dust collector, and the CaO content (%) in coal ash is the CaO in coal ash obtained in Example 7. Slaked lime was added so as to have the same content (%). About this, elution operation by the said Environmental Agency notification 46 was performed, and the test solution was created. Table 5 shows the pH of the test solution and the elution amount of trace elements.

<Comparative Example 5>
The test was performed in the same manner as in Reference Example 1 except that slaked lime was not added during the preparation of the test solution. Table 5 shows the pH of the test solution and the elution amount of trace elements.

As is apparent from Table 5, the coal ash of the coal burned with the addition of limestone has a pH of 13 or higher, whereas when slaked lime is added to the coal ash, the pH is 13 or lower. . Correspondingly, in boron, selenium, etc., the elution from coal ash of coal burned by adding limestone is less than the elution amount when slaked lime is added to coal ash. This was comparable. Even when slaked lime was added until the solution was saturated, the pH was about 12.4 and did not change any more.
From the above, by adding limestone and burning coal, a chemical change occurs for some reason, the pH of coal ash rises to 13 or more, and the elution suppression effect of boron, selenium, arsenic, etc. is enhanced. I understood that.

<Test Example 5: Relationship between pH and elution amount>
<Example 8>
2 parts by weight of limestone was mixed with 100 parts by weight of Australian charcoal and burned in a pulverized coal combustion furnace. The coal ash after combustion was collected from the last stage of the electric dust collector. The elution operation according to the Environment Agency Notification No. 46 was performed to prepare a test solution, and after measuring the pH, the concentration of each trace element in the test solution was measured. The results are shown in Table 6.
Of each trace element, boron was measured by ICP mass spectrometry, and selenium and arsenic were measured by atomic absorption.

  From the results shown in Table 6, it can be seen that the elution amount of trace elements varies depending on the pH of each coal ash. As an overall tendency, the higher the pH, the lower the elution amount. For boron, the elution amount tends to decrease at pH 12.0 or higher. For selenium, pH 12.0 compared to pH 11.7, pH 12.2. Compared to 5, the elution amount is halved at pH 13.0. Furthermore, it can be seen that the amount of elution of arsenic is greatly reduced at pH 12.5 compared to pH 12.0.

<Test Example 6: Relationship between coal ash addition amount and melting point>
<Example 9>
0.50 parts by weight of limestone was added to 100 parts by weight of Australian charcoal and burned in an electrically heated drop tube furnace. After combustion, the coal ash was collected, the composition of the coal ash was analyzed, and the melting point in the coal ash was measured. The results are shown in Table 6.

<Example 10>
The test was performed in the same manner as in Example 9 except that 1.00 parts by weight of limestone was added to 100 parts by weight of Australian coal. The results are shown in Table 7.

<Example 11>
The test was performed in the same manner as in Example 9 except that 2.25 parts by weight of limestone was added to 100 parts by weight of Australian coal. The results are shown in Table 7.

<Comparative Example 6>
The test was performed in the same manner as in Example 9 except that 10.00 parts by weight of limestone was added to 100 parts by weight of Australian coal. The results are shown in Table 7.

From Table 7, the melting point of coal ash sufficiently exceeds 1300 ° C. when the amount of limestone added is 1.0% or less, and sufficiently exceeds 1200 ° C. even when it is 2.25% or less. From this, it can be seen that when the amount of limestone added is 2.25% or less, the risk of slagging and fouling associated with a decrease in the melting point of coal ash is low.
On the other hand, when the amount of limestone added is 10.00%, the melting point of coal ash is below 1200 ° C., indicating that the risk of slagging and fouling is high.

  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 S10 Coal supply process S20 Pulverized coal production process S30 Pulverized coal combustion process S40 Coal ash treatment process S50 Coal leaching inhibitor addition process

Claims (14)

A harmful trace element elution suppression method for suppressing the elution of harmful trace elements from the combustion residue of coal by adding an elution inhibitor for coal addition to coal as a fuel in a coal thermal power generation system,
A method for inhibiting harmful trace element elution, wherein an elution inhibitor containing at least one selected from the group consisting of limestone, slaked stone and quicklime is used as the elution inhibitor for coal addition.   The harmful trace element elution suppression method according to claim 1, wherein the elution inhibitor for coal addition is added in a range of 0.1 parts by mass or more and less than 10 parts by mass with respect to 100 parts by mass of the coal.   The harmful trace element elution suppression method according to claim 1, wherein the elution inhibitor for coal addition is added in a range of 0.1 parts by mass or more and 6.0 parts by mass or less with respect to 100 parts by weight of the coal.   The harmful trace element elution suppression method according to claim 1, wherein the elution inhibitor for coal addition is added in an amount of 0.1 parts by weight or more and 1.0 part by weight or less with respect to 100 parts by weight of the coal.   5. The coal addition additive is added so that the pH of an aqueous solution produced by adding 10 parts by mass of coal ash to 1 part by mass of water is 12.0 or more. The method for suppressing the elution of harmful trace elements according to crab.   6. The harmful trace element elution suppression method according to any one of claims 1 to 5, wherein the coal-fired power generation system is a power generation system of a pulverized coal combustion system, and the elution inhibitor for coal addition is added into a combustion boiler.   6. The harmful trace element elution suppression method according to claim 1, wherein the coal-fired power generation system is a power generation system of a pulverized coal combustion system, and the elution inhibitor for coal addition is added upstream from within the combustion boiler. .   The coal-fired power generation system is a power generation system of a pulverized coal combustion system, and the elution inhibitor for coal addition is added in the vicinity of a heat exchange unit arranged downstream of the combustion boiler. To suppress the elution of harmful trace elements. A coal addition elution inhibitor that suppresses the elution of harmful trace elements from the combustion residue by adding to coal as fuel in a coal thermal power generation system,
An elution inhibitor for coal addition, comprising at least one selected from the group consisting of limestone, slaked stone, and quicklime.   The coal elution inhibitor for coal addition according to claim 9, wherein the coal elution inhibitor is granular or powdery.   The coal dissolution elution agent according to claim 10, wherein the average particle size is 10 µm to 100 µm.   The coal-elution-preventing agent according to claim 10, wherein the average particle size is 10 µm to 80 µm.   The coal dissolution elution agent according to claim 10, wherein the average particle size is 10 µm to 60 µm. An elution preventing solution for coal addition, which is a slurry containing the coal elution inhibitor for coal addition according to claim 10 or 13 or a mixed solution in which the elution inhibitor for coal addition is dispersed in water.

Images