JP2009074771A - Coal fired power generation system and method of reducing elution of hexavalent chromium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coal fired power generation system not requiring a large amount of plant investment and restraining the elution of hexavalent chromium from coal ash without using chemicals, and a method of reducing the elution of hexavalent chromium from coal ash in the coal fired power generation system. <P>SOLUTION: This coal fired power generation system includes: a combustion boiler for burning coal; and a dust collector provided on the downstream from the combustion boiler for scavenging coal ash generated by burning the coal from exhaust gas generated by burning the coal, wherein the combustion boiler has a heat exchange unit on the downstream from the combustion boiler. The system includes a coal ash supply means for supplying coal ash scavenged by the dust collector into a system from the vicinity of the heat exchange unit to the dust collector. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 for burning coal, and a dust collector that is provided downstream of the combustion boiler and collects coal ash generated by combustion of the coal from exhaust gas generated by combustion of the coal, The combustion boiler is a coal thermal power generation system having a heat exchange unit downstream of the combustion boiler, and the coal ash collected by the dust collector is placed in the system from the vicinity of the heat exchange unit to the dust collector. Coal thermal power generation system with coal ash supply means to supply.

  Here, "coal ash supply means (coal ash supply device)" is a known supply capable of supplying coal ash (dust) to the system from the vicinity of the heat exchange unit to the dust collector without allowing air to flow in. Any means (supplying device) may be used. Specifically, the supply is constituted by a pipe (pipe) connected to the system and capable of transferring coal ash into the system, and a blower serving as power for transferring coal ash into the system. Examples thereof include, but are not limited to, a supply means that extracts exhaust gas from the vicinity of the heat exchange unit, winds up coal ash with the wind of the extracted exhaust gas, and sends it to the vicinity of the heat exchange unit.

  According to the invention of (1), the coal ash collected (collected) by the dust collector is supplied into the system from the vicinity of the heat exchange unit to the dust collector. The exhaust gas in the system from the vicinity of the heat exchange unit to the dust collector is in a reducing atmosphere with an oxygen concentration of 1% to 10%, and the exhaust gas temperature in the system is 200 ° C to 600 ° C. The exhaust gas has conditions that facilitate reducing hexavalent chromium to trivalent chromium. For example, when coal ash is supplied near the heat exchange unit, the time required for the coal ash to be collected by the dust collector is 5 to 50 seconds, and hexavalent chromium is present in the coal ash. In this case, a part of hexavalent chromium in the coal ash is reduced to trivalent chromium. Therefore, the degree of elution of hexavalent chromium can be reduced.

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

  (2) Further, a denitration device that removes nitrogen oxides in the exhaust gas is provided, and the coal ash supply means sends the coal ash collected by the dust collector from the vicinity of the heat exchange unit to the denitration device. The coal-fired power generation system according to (1), which is supplied into the system.

  (3) Further, a denitration device for removing nitrogen oxides in the exhaust gas is provided, and the coal ash supply means is configured to connect the coal ash collected by the dust collector from the denitration device to the dust collector. The coal-fired power generation system according to (1), which is supplied inside.

  The inventions of (2) and (3) specifically define the place where the coal ash is supplied by the coal ash supply means.

  The temperature of the exhaust gas in the system from the vicinity of the heat exchange unit to the denitration apparatus is 350 ° C. to 600 ° C., and the oxygen concentration of the exhaust gas in the system is in a reducing atmosphere of 1% to 6%. The invention has conditions that facilitate the reduction of hexavalent chromium to trivalent chromium. Furthermore, for example, when coal ash is supplied near the denitration device, the time required for the coal ash to be collected by the dust collector is 5 to 50 seconds, and hexavalent chromium was present in the coal ash. In some cases, part of the hexavalent chromium is reduced to trivalent chromium. Thereby, the degree of elution of hexavalent chromium can be reduced.

  The temperature in the system from the denitration device to the dust collector is 350 ° C. to 200 ° C., and the oxygen concentration of the exhaust gas in the system is in a reducing atmosphere of 4% to 10%. Since the reduction reaction of hexavalent chromium generally proceeds under a temperature condition of 250 ° C. or higher, in the invention of (3), it is possible to reduce hexavalent chromium to trivalent chromium depending on the conditions. Further, according to the invention of (3), since coal ash is supplied into the system after the denitration device, it is possible to reduce the load on the denitration device.

  (4) a combustion boiler that burns coal, and a dust collector that is provided downstream of the combustion boiler and collects coal ash generated by combustion of the coal from exhaust gas generated by combustion of the coal, The combustion boiler supplies a coal ash collected by the dust collector into the system from the vicinity of the heat exchange unit to the dust collector in a coal thermal power generation system having a heat exchange unit downstream of the combustion boiler. A hexavalent chromium elution reduction method for suppressing elution of hexavalent chromium from the coal ash by performing coal ash supply treatment.

  The invention of (4) captures the invention of (1) as a hexavalent chromium elution reduction method, and the same effect as the invention of (1) can be obtained. In the present invention, the coal ash supply process can be performed by the “coal ash supply means” described in (1) above, and the transferred coal ash is manually collected from the vicinity of the heat exchange unit. This includes processing to supply the system up to the system.

  (5) The coal-fired power generation system includes a denitration device that removes nitrogen oxides in the exhaust gas, and the coal ash supply process is configured to remove the coal ash collected by the dust collector from the vicinity of the heat exchange unit. The hexavalent chromium elution reduction method according to (4), which is a process of supplying the system up to the denitration apparatus.

  The invention of (5) captures the invention of (2) as a method for reducing elution of hexavalent chromium, and the same effect as the invention of (2) can be obtained.

  (6) The coal-fired power generation system includes a denitration device that removes nitrogen oxides in the exhaust gas, and the coal ash supply process is configured to collect coal ash collected by the dust collector from the denitration device. The hexavalent chromium elution reduction method according to (4), which is a treatment to be supplied into the system up to the dust device.

  The invention of (6) captures the invention of (3) as a hexavalent chromium elution reduction method, and the same effect as the invention of (3) can be obtained.

  (7) The hexavalent chromium elution reduction method according to any one of (4) to (6), wherein an average particle diameter of the coal ash supplied by the coal ash supply process is 1 μm to 100 μm.

  The invention of (7) defines the range of the average particle diameter of coal ash that can more effectively suppress elution of hexavalent chromium from coal ash. By making the average particle size of the coal ash in the range of 1 μm to 100 μm, it is possible to further suppress the elution of hexavalent chromium.

  (8) A group consisting of heavy oil combustion ash, crude oil combustion ash, naphtha combustion ash, coke, coal, and wastewater treatment sludge when supplying coal ash into the system from the vicinity of the heat exchange unit to the dust collector The method for reducing elution of hexavalent chromium according to any one of claims 4 to 7, wherein at least one reducing agent selected from the group consisting of:

  According to the invention described in (8), when supplying the coal ash into the system from the vicinity of the heat exchange unit to the dust collector, the reduction of hexavalent chromium in the coal ash is performed because a predetermined reducing agent is added. Can be promoted more. Thereby, the effect of reducing elution of hexavalent chromium can be obtained more efficiently.

  (9) The coal ash is supplied into the system from the vicinity of the heat exchange unit to the dust collector, and is recovered by the dust collector, and then the recovered coal ash is further heat-treated. The method for reducing elution of hexavalent chromium according to claim 8.

  According to the invention described in (9), since the coal ash supplied to the system from the vicinity of the heat exchange unit to the dust collector and then recovered by the dust collector is heated, it is not reduced in the coal ash. The remaining hexavalent chromium can be further reduced. Thereby, elution of hexavalent chromium can be further reduced.

  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.

  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 collection silo 183, and also near the primary economizer 161d or a secondary node by a coal ash supply unit 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, and the coal of the above-described 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 additive dissolution 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 (9)

A combustion boiler that burns coal; and a dust collector that is provided downstream of the combustion boiler and collects coal ash generated by combustion of the coal from exhaust gas generated by combustion of the coal, the combustion boiler comprising: A coal-fired power generation system having a heat exchange unit downstream of the combustion boiler,
A coal-fired power generation system comprising coal ash supply means for supplying the coal ash collected by the dust collector into the system from the vicinity of the heat exchange unit to the dust collector. Furthermore, a denitration device for removing nitrogen oxides in the exhaust gas is provided,
The coal-fired power generation system according to claim 1, wherein the coal ash supply means supplies the coal ash collected by the dust collector into the system from the vicinity of the heat exchange unit to the denitration device. Furthermore, a denitration device for removing nitrogen oxides in the exhaust gas is provided,
The coal-fired power generation system according to claim 1, wherein the coal ash supply means supplies the coal ash collected by the dust collector into the system from the denitration device to the dust collector. A combustion boiler that burns coal; and a dust collector that is provided downstream of the combustion boiler and collects coal ash generated by combustion of the coal from exhaust gas generated by combustion of the coal, the combustion boiler comprising: In a coal-fired power generation system having a heat exchange unit downstream of the combustion boiler,
Elution of hexavalent chromium from the coal ash is performed by performing a coal ash supply process for supplying the coal ash collected by the dust collector into the system from the vicinity of the heat exchange unit to the dust collector. A method to reduce elution of hexavalent chromium. The coal-fired power generation system includes a denitration device that removes nitrogen oxides in the exhaust gas,
The hexavalent chromium elution reduction method according to claim 4, wherein the coal ash supply process is a process of supplying the coal ash collected by the dust collector into the system from the vicinity of the heat exchange unit to the denitration apparatus. The coal-fired power generation system includes a denitration device that removes nitrogen oxides in the exhaust gas,
The hexavalent chromium elution reduction method according to claim 4, wherein the coal ash supply process is a process of supplying the coal ash collected by the dust collector into the system from the denitration device to the dust collector.   The method for reducing elution of hexavalent chromium according to any one of claims 4 to 6, wherein an average particle diameter of the coal ash supplied by the coal ash supply process is 1 µm to 100 µm.   When coal ash is supplied into the system from the vicinity of the heat exchange unit to the dust collector, it is selected from the group consisting of heavy oil combustion ash, crude oil combustion ash, naphtha combustion ash, coke, coal, and wastewater treatment sludge The method for reducing elution of hexavalent chromium according to any one of claims 4 to 7, wherein at least one reducing agent is added.   9. The coal ash is supplied into the system from the vicinity of the heat exchange unit to the dust collector, and is recovered by the dust collector, and then the recovered coal ash is further heat-treated. Of reducing hexavalent chromium elution.

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