JP5036467B2 - Coal-fired power generation system and hexavalent chromium elution reduction method - Google Patents

Description

  The present invention relates to a coal thermal power generation system and a hexavalent chromium elution reduction method.

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

  By the way, coal used as fuel contains a trace amount of harmful elements such as boron, fluorine, selenium, arsenic, hexavalent chromium and the like in addition to carbon (hereinafter, the harmful elements are referred to as “toxic trace elements”). For this reason, in consideration of the environment, the allowable concentration of harmful trace elements from coal ash is regulated by law.

  In particular, hexavalent chromium among harmful trace elements has a great adverse effect on the human body and has been a cause of large-scale soil contamination in the past. For this reason, the allowable concentration of elution of hexavalent chromium from coal ash (hereinafter referred to as “hexavalent chromium” includes a hexavalent chromium compound) is strictly regulated.

  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 hexavalent chromium contained in coal ash to below a regulation value is examined.

  For example, an elution inhibitor is proposed to suppress the elution of hexavalent chromium from cement by adding artificial zeolite impregnated with one of aqueous solutions of sodium sulfite, sodium bisulfite, and calcium sulfite to cement. (See Patent Document 1).

  Moreover, in patent document 2, after making the cement-solidified soil which has a hexavalent chromium elution amount exceeding a soil environmental standard contact carbon dioxide, at least 1 sort (s) chosen from a carbide | carbonized_material and organic substance is added, and it bakes. A method for treating hexavalent chromium-contaminated soil is disclosed.

  Further, Patent Document 3 discloses a method for treating hexavalent chromium-containing soil, wherein the soil containing hexavalent chromium is heat-treated at 200 ° C. to 600 ° C. in a reducing atmosphere.

  In addition, Patent Document 4 discloses a method for reducing hexavalent chromium in a cement clinker, characterized by heat-treating a cement clinker containing hexavalent chromium at 650 ° C. to 1100 ° C. in a reducing atmosphere. Yes.

According to the inventions described in Patent Documents 2 to 4, it is said that the elution amount of hexavalent chromium can be reduced below the soil environment standard by a simple method.
JP-A-2005-112706 JP 2002-219451 A JP 2003-334532 A JP 2004-018339 A

  However, the cost of purchasing sodium sulfite, sodium bisulfite, and calcium sulfite used in the prior art described in Patent Document 1 is high, and in a thermal power plant, these chemicals are actually used to convert hexavalent chromium. It is difficult to suppress elution. In addition, even if an attempt is made to reduce the purchase cost of the drug by providing the above-mentioned drug manufacturing facility, naturally, a large amount of capital investment is required for the installation of the manufacturing facility.

  The inventions described in Patent Documents 2 and 3 are methods for treating hexavalent chromium-contaminated soil, and are not directly applicable to a method for treating coal ash. Furthermore, in the inventions described in Patent Documents 2 to 4, heat treatment is performed on hexavalent chromium-contaminated soil or cement clinker, and this treatment requires a large cost.

  The present invention has been made in view of the above-described problems, and does not require a large amount of capital investment, and is capable of suppressing elution of hexavalent chromium from coal ash without using a chemical. An object is to provide a power generation system and a hexavalent chromium elution reduction method for suppressing elution of hexavalent chromium from coal ash in the coal thermal power generation system.

(1) A combustion boiler that burns coal, a first dust collector that is provided downstream of the combustion boiler and collects fly ash generated by combustion of the coal from exhaust gas generated by combustion of the coal ; A coal-fired power generation system provided with an upstream side of the first dust collector and a second dust collector that collects cinder ash generated by combustion of the coal from the exhaust gas ,
A coal thermal power generation system comprising coal ash supply means for supplying the cinder ash collected by the second dust collector to the upstream side in the vicinity of the second dust collector .

According to the invention of (1), Shinda ash trapped (dust collection) by the second dust collector is fed to and upstream in the vicinity of the second dust collector. The exhaust gas in the system from the vicinity of the heat exchange unit to the first dust collector is in a reducing atmosphere having an oxygen concentration of 1% to 10%, and the exhaust gas temperature in the system is 200 ° C. to 600 ° C. The exhaust gas in the system has conditions that make it easy to reduce hexavalent chromium to trivalent chromium. Accordingly, by supplying the cinder ash collected by the second dust collector provided upstream of the first dust collector to the vicinity of the second dust collector and upstream , elution of hexavalent chromium Can be reduced.

As described above, according to the present invention, hexavalent chromium from Cinda Ash can be obtained only by providing coal ash supply means in an existing coal-fired power generation system, without the need for chemicals, and without requiring large capital investment. Elution can be suppressed.

(2) The second dust collector includes a economizer that is provided downstream of the combustion boiler and preheats boiler feed water using heat retained by exhaust gas generated by combustion of the coal, The ash includes ECO ash collected by the economizer, and the coal ash supply means supplies the ECO ash in the vicinity of the economizer and upstream thereof (1). .

(3) further comprising a economizer that is provided downstream of the combustion boiler and preheats boiler feed water using heat held by exhaust gas generated by combustion of the coal;
The second dust collector includes an air preheater provided downstream of the economizer,
The cinder ash includes AH ash collected by the air preheater,
The coal ash supply means is the coal thermal power generation system according to (1) , wherein the AH ash is supplied into the system from the vicinity of the economizer to the air preheater .

(4) disposed downstream of the combustion boiler, further comprising the economizer for preheating using heat possessed by the exhaust gas boiler feedwater generated by the combustion of the coal, the second dust collector, the A denitration device that is provided downstream of the economizer and removes nitrogen oxides in the exhaust gas, the cinder ash includes denitration device ash collected by the denitration device, and the coal ash supply means includes The coal-fired power generation system according to (1), wherein the denitration device ash is supplied into the system from the vicinity of the economizer to the denitration device.

(5) a combustion boiler that burns coal, a first dust collector that is provided downstream of the combustion boiler and collects fly ash generated by combustion of the coal from exhaust gas generated by combustion of the coal; A coal-fired power generation system provided with an upstream side of the first dust collector and a second dust collector that collects cinder ash generated by combustion of the coal from the exhaust gas. Hexavalent that suppresses elution of hexavalent chromium from the cinder ash by performing coal ash supply processing for supplying the cinder ash collected by the dust device to the vicinity of the second dust collector and upstream. Chromium elution reduction method.

(6) The second dust collector includes a economizer that is provided downstream of the combustion boiler and preheats boiler feedwater using heat held by exhaust gas generated by combustion of the coal, Ash includes ECO ash collected by the economizer. In the coal ash supply process, the ash is supplied from the ECO ash in the vicinity of the economizer and upstream. The method for reducing elution of hexavalent chromium according to (5), which suppresses elution of valent chromium.

(7) The second dust collector is further provided with a economizer that is provided downstream of the combustion boiler and preheats boiler feed water using heat held by exhaust gas generated by combustion of the coal. An air preheater provided downstream of the economizer, and the cinder ash contains AH ash collected by the air preheater, and the coal ash supply process, The hexavalent chromium elution reduction method according to (5), wherein elution of hexavalent chromium from the AH ash is suppressed by supplying the system from the vicinity of the heater to the air preheater .

(8) The second dust collector is further provided with a economizer that is provided downstream of the combustion boiler and preheats boiler feed water using heat held by exhaust gas generated by combustion of the coal. A denitration device that is provided downstream of the economizer and removes nitrogen oxides in the exhaust gas, and the cinder ash includes denitration device ash collected by the denitration device, in the coal ash supply process The elution of hexavalent chromium from the denitration apparatus ash is suppressed by supplying the denitration apparatus ash into the system from the vicinity of the economizer to the denitration apparatus. Method.

  According to the present invention, elution of hexavalent chromium from coal ash can be achieved only by providing coal ash transfer means in an existing coal-fired power generation system, without requiring chemicals and without requiring large capital investment. It is possible to suppress.

  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. Coal that supplies the coal ash processing unit 18 that processes the coal ash generated by the combustion of the pulverized coal, the combustion unit 16, and the coal ash (fly ash) from the vicinity of the heat exchange unit described later to the dust collector 182 And an ash supply unit 20. 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.

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

  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 again reversed into a U-shape, and the outlet of the furnace 161 (the last arrow in FIG. 2) is connected to the denitration device 181 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 collects (collects) fly ash (dust) out of the coal ash in the exhaust gas and the denitration device 181 that removes nitrogen oxides in the exhaust gas discharged from the pulverized coal combustion unit 16. A dust collector 182 and a coal ash collection silo 183 that primarily stores fly ash collected by the dust collector 182 are provided.

  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 fly ash in the exhaust gas with an electrode. Fly ash is the remaining soot from the coal ash produced by the combustion of coal. The fly ash collected by the dust collector 182 is accumulated in a hopper (not shown) and conveyed to a coal ash recovery silo 183, and also near the primary economizer 161d or a secondary node by a coal ash supply means 201 described later. It is supplied into the system from the vicinity of the carbonizer 161e to the denitration device 181. The exhaust gas from which the fly ash has been removed is discharged from the chimney after passing through a desulfurization device (not shown). The dust collector 182 is preferably provided in a plurality of stages.

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

<A-5: Coal ash supply unit>
The coal ash supply unit 20 includes coal ash supply means 201 that supplies fly ash collected by the coal ash processing unit 18 into a system from a coal saver that is a heat exchange unit to a dust collector 182.

  The coal ash supply means 201 supplies fly ash collected by the dust collector 182 into the system from the vicinity of the heat exchange unit of the primary economizer 161d or the secondary economizer 161e to the dust collector 182. Specifically, the coal ash supply means 201 is configured to collect fly ash collected by the dust collector 182 in the system from the vicinity of the primary economizer 161d or the secondary economizer 161e of the furnace 161 to the denitration apparatus 181. Or it supplies in the system | strain from the denitration apparatus 181 to the dust collector 182. FIG.

  As the coal ash supply means 201, for example, it is connected in the system from the vicinity of the heat exchange unit of the primary economizer 161d or the secondary economizer 161e to the dust collector 182 to transfer fly ash into the system. The supply means comprised from the possible pipe | tube (pipe) and the air blower used as the motive power which transfers fly ash in the said system is mentioned. That is, it is an apparatus provided with a blower for transferring fly ash into the system on a pipe for transferring fly ash into the system. Examples of the other coal ash supply means 201 include supply means for extracting the exhaust gas from the vicinity of the heat exchange unit, winding up the coal ash with the extracted wind of the exhaust gas, and sending it to the vicinity of the heat exchange unit. The coal ash transfer means is a supply means for supplying the fly ash transported in advance into the system from the vicinity of the heat exchange unit of the primary economizer 161d or the secondary economizer 161e to the dust collector 182. May be. However, the coal ash transfer means is not limited to these, and any type can be used as long as fly ash collected by the dust collector 182 can be supplied into the system without inflowing air. A supply means (supply device) may be used.

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

<B: Hexavalent chromium elution reduction method of the present invention>
The hexavalent chromium elution reduction method of the present invention collects coal ash produced by combustion of coal from a combustion boiler for burning coal and exhaust gas provided downstream of the combustion boiler and produced by combustion of the coal. A coal thermal power generation system having a heat exchanging unit downstream of the combustion boiler, and the coal ash collected by the dust collecting unit 182 from the vicinity of the heat exchanging unit. This is a method for suppressing elution of hexavalent chromium from the coal ash by performing the coal ash supply process to be supplied into the system up to the dust collector 182, and this method is performed using the pulverized coal combustion facility 1. I will explain.

  The method for suppressing elution of hexavalent chromium from coal ash includes coal supply step S10 for supplying coal, pulverized coal generation step S20 for pulverizing the supplied coal to generate pulverized coal, and burning this pulverized coal The pulverized coal combustion step S30 for generating coal ash, the coal ash treatment step S40 for collecting (collecting) fly ash from the coal ash and storing the fly ash, and the fly collected by the dust collector 182 The coal ash supply processing step S50 for transferring ash into the system is included, and each of these steps includes the coal supply unit 12, the pulverized coal generation unit 14, the pulverized coal combustion unit 16, the coal of the pulverized coal combustion facility 1, respectively. This is performed in the ash treatment unit 18 and the coal ash supply unit 20. Hereinafter, each step will be described.

<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. The vicinity of this heat exchange unit is an area where the temperature is maintained at about 450 ° C. to about 900 ° C., and passes through a heat transfer surface group provided for preheating boiler feedwater using the heat held by the combustion gas. As a result, heat exchange occurs 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 collecting device 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 S40>
Thereafter, the coal ash generated by burning pulverized coal is discharged together with the exhaust gas to the denitration device 181 and sent to the dust collector 182. The fly ash collected from the exhaust gas by the dust collector 182 is accumulated in a hopper (not shown) and then transferred to the coal ash recovery silo 183. In addition, the coal ash supply means 201 performs a primary section as a heat exchange unit. It is transferred into the system from the vicinity of the carbonizer 161d or the secondary economizer 161e to the dust collector 182. The exhaust gas from which the fly ash has been removed is discharged from the chimney after passing through a desulfurization device (not shown).

<Coal ash supply process S50>
In the coal ash supply process S50, which is one of the features of the present invention, the fly ash collected by the dust collector 182 is collected from the vicinity of the primary economizer 161d or the secondary economizer 161e, which is a heat exchange unit. It is a processing step of transferring into the system up to the apparatus 182. As shown in FIG. 1, the coal ash supply processing step S <b> 50 is preferably performed in the coal ash supply unit 20 that overlaps a part of the pulverized coal combustion unit 16 and a part of the coal ash processing unit 18. That is, the coal ash supply processing step S <b> 50 is performed in the pulverized coal combustion unit 16, the piping (inside the system) between the pulverized coal combustion unit 16 and the coal ash processing unit 18, and the coal ash processing unit 18.

  The system from the vicinity of the primary economizer 161d or the secondary economizer 161e, which is a heat exchange unit, to the dust collector 182 is in a reducing atmosphere with an oxygen concentration of 1% to 10%, and the internal temperature is 200 ° C to 600 ° C. Therefore, the above system is in a condition that hexavalent chromium can be easily reduced to trivalent chromium. When coal ash is supplied near the heat exchange unit or when coal ash is supplied near the denitration device 181, the time until the coal ash is collected by the dust collector 182 is 5 to 50 seconds, respectively. Or 3 to 30 seconds, and sufficient time can be ensured for the reduction reaction of a part of hexavalent chromium. Therefore, even when hexavalent chromium is present in fly ash, hexavalent chromium is easily reduced to trivalent chromium.

  As described above, the present invention treats fly ash discharged from a coal-fired power generation system with a slight improvement of existing facilities provided in the coal-fired power generation system, thereby producing hexavalent chromium from fly ash. Since elution can be easily reduced, existing facilities can be used effectively, which is advantageous in terms of cost.

  The average particle diameter of the fly ash transferred by the coal ash supply means 201 is preferably 1 μm or more and 100 μm or less, and more preferably 1 μm or more and 50 μm or less. When the average particle size is less than 1 μm, the effect of adjusting the average particle size can hardly be obtained. When the average particle diameter exceeds 100 μm, the exhaust gas does not contact the inside of the fly ash, so the reduction reaction from hexavalent chromium to trivalent chromium does not proceed.

  The amount of fly ash transferred by the coal ash supply means 201 is preferably 10% by mass or less with respect to the amount of fly ash collected by the dust collector 182. If it exceeds 10% by mass, fly ash exceeding the processing amount of the dust collector 182 is present in the exhaust gas, which is not preferable.

  In the present embodiment, fly ash is transferred from coal ash, but other coal ash, specifically, at least one selected from the group of ECO ash, AH ash, and denitration device ash is used. What is contained may be transferred into the system from the vicinity of the heat exchange unit to the dust collector 182.

  That is, the coal thermal power generation system of the present invention collects coal ash generated by combustion of coal from a combustion boiler that burns coal and exhaust gas that is provided downstream of the combustion boiler and generated by combustion of the coal. A coal thermal power generation system having a heat exchange unit downstream of the combustion boiler, wherein the coal ash is introduced into the system from the vicinity of the heat exchange unit to the dust collector. The coal thermal power generation system provided with the coal ash supply means to supply may be sufficient.

  In addition, the hexavalent chromium elution reduction method of the present invention captures coal ash produced by combustion of coal from a combustion boiler for burning coal and exhaust gas provided downstream of the combustion boiler and produced by combustion of the coal. A coal-fired power generation system having a heat exchange unit downstream of the combustion boiler, the coal ash collected by the dust collector from the vicinity of the heat exchange unit. It may be a hexavalent chromium elution reduction method that suppresses elution of hexavalent chromium from the coal ash by performing coal ash supply processing to be supplied into the system up to the dust collector.

  The coal ash of the coal thermal power generation system and the hexavalent chromium elution reduction method is an ash containing at least one selected from the group of fly ash, ECO ash, AH ash, and denitration device ash.

  Here, the coal ash collected by the primary economizer 161d and the secondary economizer 161e of the furnace 161 is ECO ash, the coal ash collected by an air preheater (AH) (not shown) is AH ash, and the denitration device 181. The coal ash collected at the plant is called denitrification equipment ash, and these are collectively called Cinder Ash.

  In the coal thermal power generation system and the hexavalent chromium elution reduction method, the place where the collected fly ash, ECO ash, AH ash, and denitration equipment ash are supplied is more than the device (place) where each ash is collected. An upstream location is preferred. For example, in the case of fly ash, it is preferably supplied into the system from the vicinity of the primary economizer 161d and the secondary economizer 161e, which are heat exchange units, to the dust collector 182. In the case of ECO ash, it is preferable to be supplied near the primary economizer 161d and the secondary economizer 161e. In the case of AH ash, it is preferably supplied into the system from the vicinity of the primary economizer 161d and the secondary economizer 161e to the air preheater. In the case of the denitration apparatus ash, it is preferably supplied into the system from the vicinity of the primary economizer 161d and the secondary economizer 161e to the denitration apparatus 181. By taking much reduction time, it is possible to suppress elution of hexavalent chromium from coal ash, while returning the exhaust gas that has not been processed in the predetermined exhaust gas treatment facility to the predetermined exhaust gas treatment facility or later, There is a possibility of placing a burden on the exhaust gas treatment facility at the later stage.

  Furthermore, in the hexavalent chromium elution reduction method of the present invention, when supplying coal ash into the system from the vicinity of the heat exchange unit to the dust collector 182, heavy oil combustion ash, crude oil combustion ash, naphtha combustion ash, coke In addition, at least one reducing agent selected from the group consisting of coal and wastewater treatment sludge may be added. Thereby, hexavalent chromium in coal ash can be reduced efficiently. The addition amount when adding the reducing agent is preferably 0.01 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of coal ash. If a reducing agent exceeding 5 parts by mass is added, the furnace 161 may be damaged. Even if a reducing agent of less than 0.01 parts by mass is added, a substantial effect cannot be obtained.

  In the hexavalent chromium elution reduction method of the present invention, the coal ash is supplied into the system from the vicinity of the heat exchange unit to the dust collector 182 and recovered by the dust collector 182, and then the recovered coal ash is further collected. It may be heated. Specifically, in the coal ash recovery silo 183, a method of heating using auxiliary steam generated in the pulverized coal combustion facility 1, a method of heating in a dedicated combustor, and the like can be given. Thereby, elution of hexavalent chromium can be further reduced.

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 Coal dust combustion facility 12 Coal supply part 121 Coal bunker 122 Coal feeder 14 Pulverized coal production part 141 Coal pulverized coal machine 142 Air supply machine 16 Pulverized coal combustion part 161 Furnace 161d Primary economizer 161b Secondary economizer 162 Heater 163 Air supply unit 18 Coal ash treatment unit 181 Denitration device 182 Dust collector 183 Coal ash recovery silo 20 Coal ash supply unit 201 Coal ash supply means S10 Coal supply step S20 Pulverized coal generation step S30 Pulverized coal combustion step S40 Coal ash treatment step S50 Coal ash supply process

Claims (8)

A combustion boiler for burning coal, and a first dust collector for collecting fly ash produced by the combustion of the coal from the exhaust gas produced by combustion of the coal disposed downstream of the combustion boiler, the first A coal-fired power generation system provided with a second dust collector that is provided upstream of the dust collector and collects cinder ash generated by combustion of the coal from the exhaust gas ,
A coal thermal power generation system comprising coal ash supply means for supplying the cinder ash collected by the second dust collector to the upstream side in the vicinity of the second dust collector . The second dust collector includes a economizer that is provided downstream of the combustion boiler and preheats boiler feedwater using heat held by exhaust gas generated by combustion of the coal,
The cinder ash includes ECO ash collected by the economizer,
The coal-fired power generation system according to claim 1 , wherein the coal ash supply means supplies the ECO ash to the vicinity of the economizer and upstream . Further comprising a economizer that is provided downstream of the combustion boiler and preheats boiler feed water using heat possessed by exhaust gas generated by combustion of the coal;
The second dust collector includes an air preheater provided downstream of the economizer,
The cinder ash includes AH ash collected by the air preheater,
The coal-fired power generation system according to claim 1, wherein the coal ash supply means supplies the AH ash into a system from the vicinity of the economizer to the air preheater . The provided downstream of the combustion boiler, further comprising the economizer for preheating the boiler feed water by utilizing the heat held by the exhaust gases produced by the combustion of the coal,
The second dust collector is provided downstream of the economizer, and includes a denitration device that removes nitrogen oxides in the exhaust gas,
The cinder ash includes denitration apparatus ash collected by the denitration apparatus,
The coal-fired power generation system according to claim 1, wherein the coal ash supply means supplies the denitration device ash into the system from the vicinity of the economizer to the denitration device. A combustion boiler that burns coal; a first dust collector that is provided downstream of the combustion boiler and that collects fly ash generated by combustion of coal from exhaust gas generated by combustion of the coal; A coal-fired power generation system including a second dust collector that is provided upstream of the dust collector and collects cinder ash generated by combustion of the coal from the exhaust gas,
Elution of hexavalent chromium from the cinder ash by performing a coal ash supply process for supplying the cinder ash collected by the second dust collector to the upstream side in the vicinity of the second dust collector. To reduce elution of hexavalent chromium. The second dust collector includes a economizer that is provided downstream of the combustion boiler and preheats boiler feedwater using heat held by exhaust gas generated by combustion of the coal,
The cinder ash includes ECO ash collected by the economizer,
The hexavalent chromium elution reduction according to claim 5 , wherein elution of hexavalent chromium from the ECO ash is suppressed by supplying the ECO ash to the upstream of the economizer in the coal ash supply process. Method. Further comprising a economizer that is provided downstream of the combustion boiler and preheats boiler feed water using heat possessed by exhaust gas generated by combustion of the coal;
The second dust collector includes an air preheater provided downstream of the economizer,
The cinder ash includes AH ash collected by the air preheater,
In the coal ash supply process, said AH ash, by supplying into the system until the air preheater from near the economizer, suppress claim 5, wherein the elution of hexavalent chromium from the AH ash Hexavalent chromium elution reduction method. Further comprising a economizer that is provided downstream of the combustion boiler and preheats boiler feed water using heat possessed by exhaust gas generated by combustion of the coal;
The second dust collector is provided downstream of the economizer, and includes a denitration device that removes nitrogen oxides in the exhaust gas,
The cinder ash includes denitration apparatus ash collected by the denitration apparatus,
In the coal ash supply process, the denitration apparatus ash, by supplying from around the economizer into the system until the denitration apparatus, according to claim 5, wherein suppressing the elution of hexavalent chromium from the denitration apparatus ash Of reducing hexavalent chromium elution.

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