JP4901668B2 - Coal-fired power generation system and hexavalent chromium elution control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coal thermal power generating system capable of suppressing the elution of chromium (VI) from coal ash without requiring an expensive installation investment and without using any chemical agent, and to provide a method for suppressing the elution of chromium (VI) from the coal ash in the coal thermal power generating system. <P>SOLUTION: The coal thermal power generating system is provided with a coal ash sealing container capable of sealing the coal ash in an air-tight state, a coal ash feeding means feeding the coal ash to the coal ash enclosing container and an exhaust gas transferring means transferring the exhaust gas transferred in a system from a heat exchange unit to a dust collector to the coal ash enclosing container. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a coal-fired power generation system and a hexavalent chromium elution suppression 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 and hexavalent chromium 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 hexavalent chromium compounds) 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 suppression 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-fired power generation system having a heat exchange unit downstream of the combustion boiler, the coal ash enclosure container capable of enclosing the coal ash in a sealed state, and the coal ash enclosure container A coal-fired power generation system comprising coal ash supply means for supplying to the coal ash and exhaust gas transfer means for transferring the exhaust gas moving through the system from the heat exchange unit to the dust collector into the coal ash enclosure.

  Here, the “coal ash supply means (coal ash supply device)” may be any known supply means capable of supplying coal ash to the “coal ash enclosure”. Specifically, as the coal ash transfer means, a screw conveyor for transferring coal ash, a transfer means for floating coal ash in water, a pipe (pipe) for transferring coal ash, and coal ash are transferred. Although the transfer means etc. comprised from the air blower used as motive power are mentioned, it is not limited to these.

  According to the invention of (1), the coal ash collected by the dust collector is put in a coal ash enclosure that can be sealed in a sealed state, and the coal ash enclosure is filled with a heat exchange unit to a dust collector. It is possible to introduce exhaust gas moving through the system. The system from the heat exchange unit to the dust collector is in a reducing atmosphere where the oxygen concentration of the exhaust gas is 1% to 10%, and the exhaust gas temperature in the system is 200 ° C to 600 ° C. The temperature is such that hexavalent chromium is easily reduced to trivalent chromium. Therefore, when hexavalent chromium is present in the coal ash placed in the coal ash enclosure, the hexavalent chromium is easily reduced to trivalent chromium.

  As described above, according to the present invention, a coal ash enclosure, coal ash supply means, and exhaust gas transfer means are provided in an existing coal-fired power generation system, no chemical is required, and a large amount of capital investment is made. Without requiring, elution of hexavalent chromium from coal ash can be suppressed.

  (2) Furthermore, a denitration device that removes nitrogen oxides in the exhaust gas is provided, and the exhaust gas transfer means transfers the exhaust gas that moves in the system from the heat exchange unit to the denitration device in the coal ash enclosure. The coal-fired power generation system according to (1) to be transferred.

  (3) Further, a denitration device that removes nitrogen oxides in the exhaust gas is provided, and the exhaust gas transfer means puts the exhaust gas that moves in the system from the denitration device to the dust collector into the coal ash enclosure. The coal-fired power generation system according to (1) to be transferred.

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

  In the invention of (2), the temperature of the exhaust gas in the system from the heat exchange unit to the denitration apparatus is 350 ° C. to 600 ° C., and the oxygen concentration of the exhaust gas is 2% to 3% in a reducing atmosphere. Suitable conditions for reducing hexavalent chromium to trivalent chromium are provided.

  The temperature of the exhaust gas 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 is 2% to 3% in a reducing atmosphere. The invention also has conditions that facilitate the reduction of hexavalent chromium to trivalent chromium.

  (4) Furthermore, it has exhaust gas return means connected to the coal ash enclosure, and returns the exhaust gas in the coal ash enclosure to the system from the heat exchange unit to the dust collector (1) The coal thermal power generation system according to any one of (3).

  According to the invention of (4), the exhaust gas is returned to the system again without being discharged out of the system, and the exhaust gas treatment is performed, so that harmful substances such as sulfur oxides in the exhaust gas are released out of the system. Can be prevented.

  (5) The coal ash enclosure is connected to the exhaust gas transfer means, and has a spiral exhaust gas ejection pipe in which a jet port for ejecting the exhaust gas is formed in the coal ash enclosure. The coal thermal power generation system according to any one of (4).

  (6) The coal ash enclosure is connected to the exhaust gas transfer means, and has an exhaust gas ejection pipe in which a plurality of ejection ports for ejecting the exhaust gas are formed in the coal ash enclosure, and the exhaust gas ejection The pipe is bent a plurality of times in the coal ash enclosure, and the portion sandwiched between the adjacent bent portions in the exhaust gas ejection pipe is substantially parallel to the other portion sandwiched between the adjacent bent portions in the vertical or horizontal direction. The coal-fired power generation system according to any one of (1) to (4) formed as described above.

  The inventions of (5) and (6) define the shape of the exhaust gas ejection pipe in which the ejection port for ejecting the exhaust gas into the coal ash enclosure is formed.

  According to the invention of (5), the coal ash enclosure has the spiral exhaust gas jet pipe in which the jet port for jetting the exhaust gas is formed, and the exhaust gas is efficiently discharged into the coal ash by the spiral exhaust gas jet pipe. Can be spouted.

  According to the invention of (6), the coal ash enclosure has an exhaust gas ejection pipe formed with a plurality of ejection ports for ejecting exhaust gas, and the exhaust gas ejection pipe is bent a plurality of times in the coal ash enclosure, The portion sandwiched between adjacent bent portions in the exhaust gas ejection pipe is formed to be parallel to each other in the vertical or horizontal direction with other portions sandwiched between adjacent bent portions. Therefore, in this invention, exhaust gas can be efficiently injected to coal ash.

  (7) A combustion boiler that burns coal, 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, and the coal ash In a coal-fired power generation system having a heat exchange unit downstream of the combustion boiler, and supplying the coal ash to the coal ash enclosure After the coal ash supply process, the exhaust gas transfer process for transferring the exhaust gas moving in the system from the heat exchange unit to the dust collector into the coal ash enclosure, the coal ash supply process and the exhaust gas transfer process , Elution of hexavalent chromium to suppress elution of hexavalent chromium from the coal ash by performing a sealing process for sealing the coal ash enclosure for a predetermined time Control method.

  The invention of (7) captures the invention of (1) as a hexavalent chromium elution suppression method, and the same effect as the invention of (1) can be obtained. Note that the coal ash supply process and the exhaust gas transfer process performed before the sealing process may be performed simultaneously, or one of them may be performed as a pre-process and the rest as a post-process.

  (8) The coal-fired power generation system includes a denitration device that removes nitrogen oxides in the exhaust gas, and the exhaust gas transfer process uses the exhaust gas that moves in the system from the heat exchange unit to the denitration device. The hexavalent chromium elution suppression method according to (7), which is a process of transferring into a coal ash enclosure.

  The invention of (8) captures the invention of (2) as a hexavalent chromium elution suppression method, and the same effect as the invention of (2) can be obtained.

  (9) The coal-fired power generation system includes a denitration device that removes nitrogen oxides in the exhaust gas, and the exhaust gas transfer treatment uses the exhaust gas that moves in the system from the denitration device to the dust collector. The hexavalent chromium elution suppression method according to (7), which is a process of transferring into a coal ash enclosure.

  The invention of (9) captures the invention of (3) as a hexavalent chromium elution suppression method, and the same effect as the invention of (3) can be obtained.

  (10) The hexavalent chromium elution suppression method according to any one of (7) to (9), wherein an average particle diameter of the coal ash supplied to the coal ash enclosure by the coal ash supply process is 1 μm to 100 μm.

  The invention of (10) defines the range of the average particle diameter of coal ash that effectively suppresses the elution of hexavalent chromium from the coal ash.

  (11) The sealing process is any one of (7) to (10), wherein after the coal ash supply process and the exhaust gas transfer process, the coal ash enclosure is sealed within a range of 5 minutes to 60 minutes. The hexavalent chromium elution suppression method of description.

  The invention of (11) defines the time for the sealing treatment that effectively suppresses the elution of hexavalent chromium from the coal ash.

  (12) The hexavalent chromium elution suppression method according to any one of (7) to (11), wherein after the sealing treatment, a reducing gas is sealed in the coal ash sealing container and reacted for 5 minutes to 60 minutes. .

  According to the invention of (12), after the sealing treatment, the reducing gas is sealed in the coal ash sealing container and reacted for a predetermined time or more, so hexavalent chromium can be reduced more effectively. Thereby, the elution inhibitory effect of hexavalent chromium can be heightened more.

  According to the present invention, an existing coal-fired power generation system is simply provided with a coal ash enclosure, a coal ash supply means, and an exhaust gas transfer means, so that no chemical is required and no large capital investment is required. In addition, elution of hexavalent chromium from coal ash can be suppressed.

  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, the coal ash process part 18 which processes the coal ash produced | generated by combustion of pulverized coal, and the reduction process part 20 which reduces the hexavalent chromium in coal ash 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 141 (mil) that converts coal into pulverized coal that can be combusted with pulverized coal, 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 via 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 1 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 flow path 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, as will be described later, coal ash is supplied by a coal ash supply means 202 (see FIG. 1). Supplied to the ash enclosure 201. 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 recovery silo 183 is a facility for temporarily storing fly ash collected by the dust collector 182 and fly ash discharged from the coal ash enclosure 201 by the coal ash discharge means 205 as will be described later. .

<A-5: Reduction processing unit>
The reduction treatment unit 20 includes a coal ash enclosure container 201 that can enclose the fly ash collected by the dust collector 182 in the coal ash treatment unit 18 in a sealed state, and the fly collected by the dust collector 182. Coal ash supply means 202 for supplying ash to the coal ash enclosure 201 and exhaust gas transfer means for transferring exhaust gas moving from the vicinity of the economizer, which is a heat exchange unit, to the denitration device 181 into the coal ash enclosure 201 203. Further, the reduction processing unit 20 includes exhaust gas return means 204 that returns exhaust gas in the coal ash enclosure 201 to the system from the vicinity of the economizer to the denitration device 181, and fly ash that has been reduced from the coal ash enclosure 201. And a coal ash discharging means 205 for discharging to the coal ash recovery silo 183.

  The coal ash enclosure 201 is a container that can enclose the fly ash collected by the dust collector 182 in the coal ash treatment unit 18 in a sealed state. Specifically, the coal ash enclosure container 201 is a container that can be switched between a sealed state and an open state, and may have a lid that can be opened and closed intermittently, for example. That is, the coal ash enclosure 201 has a structure capable of preventing the transferred (supplied) exhaust gas from flowing out of the container for a certain period. However, the coal ash enclosure 201 is not limited to these, and is resistant to the contents of the transferred exhaust gas and the collected fly ash and the like, and encloses the contents in a sealed state. Any container is possible if possible.

  Further, the coal ash enclosure 201 may be connected to the exhaust gas transfer means 203 and may have a spiral exhaust gas ejection pipe in which an ejection port for ejecting the exhaust gas is formed in the coal ash enclosure 201. Furthermore, as shown in FIG. 3, the coal ash enclosure 201 is connected to the exhaust gas transfer means 203, and an exhaust gas ejection pipe in which a plurality of jets 201a for ejecting the exhaust gas into the coal ash enclosure 201 is formed. 201b, the exhaust gas jet pipe 201b is bent a plurality of times in the coal enclosure, and the portion sandwiched between the adjacent bent parts of the exhaust gas jet pipe 201b is sandwiched between the adjacent bent parts of the exhaust gas jet pipe 201b. It may be formed so as to be substantially parallel to each other in the vertical or horizontal direction.

  The coal ash supply means 202 is means (apparatus) for supplying fly ash collected by the dust collector 182 to the coal ash enclosure 201.

  The coal ash supply means 202 includes a pipe (pipe) connected to the coal ash enclosure 201 and capable of transferring fly ash to the container, and a blower serving as power for transferring fly ash to the container. The means which is done is mentioned. That is, a means for providing a blower for transferring fly ash to the container is provided in a pipe for transferring fly ash to the container. Examples of other coal ash supply means 202 include a screw conveyor that supplies fly ash to the container, or a means that floats fly ash in water and supplies the ash to the container. Further, the coal ash supply means may be a means for supplying fly ash that has been conveyed in advance to the coal ash enclosure 201. However, the coal ash supply means is not limited to these, and any supply means (supply device) can be used as long as fly ash collected by the dust collector 182 can be supplied to the coal ash enclosure 201. )

  The exhaust gas transfer means 203 is a means (apparatus) for transferring exhaust gas moving in 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 into the coal ash enclosure 201. is there. Specifically, the exhaust gas transfer means 203 is a pipe connecting 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 and the coal ash enclosure 201. (Pipe). The exhaust gas transfer means 203 preferably has a blower for transferring the exhaust gas, and more preferably has a structure capable of intermittently transferring the exhaust gas.

  In the present embodiment, the exhaust gas transfer means 203 is a means for supplying the coal ash enclosure 201 with exhaust gas moving in the system from the vicinity of the primary economizer 161d or the secondary economizer 161e to the denitration device 181. The exhaust gas moving in the system from the denitration device 181 to the dust collector 182 may be a means for supplying the coal ash enclosure container 201 with the exhaust gas.

  The exhaust gas return means 204 is connected to the coal ash enclosure 201, and returns the exhaust gas in the coal ash enclosure 201 from the vicinity of the primary economizer 161d or the secondary economizer 161e to the dust collector 182. It is. Specifically, the exhaust gas return means 204 connects the inside of the system from the vicinity of the primary economizer 161d or the secondary economizer 161e to the dust collector 182 and the coal ash enclosure 201 in the same manner as the exhaust gas transfer means 203. Pipe (pipe). The exhaust gas transfer means 203 preferably has a blower for discharging the exhaust gas, and further preferably has a structure capable of discharging the exhaust gas intermittently.

  Coal ash discharging means 205 is means for discharging fly ash reduced from the coal ash enclosure 201 to the coal ash collection silo 183. Specifically, the coal ash discharge means 205 is configured by a screw conveyor or the like, similar to the coal ash supply means 202.

<B: Hexavalent chromium elution suppression method of the present invention>
The hexavalent chromium elution suppression method of the present invention collects coal ash generated by combustion of coal from a combustion boiler for burning coal and exhaust gas provided downstream of the combustion boiler and generated by combustion of the coal. In the coal thermal power generation system including a dust collector 182 and a coal ash enclosure container 201 capable of sealing the coal ash in a sealed state, the combustion boiler has a heat exchange unit downstream of the combustion boiler. Coal ash supply process for supplying coal ash to the coal ash enclosure container 201, and exhaust gas transfer process for transferring the exhaust gas moving in the system from the heat exchange unit to the dust collector 182 into the coal ash enclosure container 201 And after the coal ash supply process and the exhaust gas transfer process, the sealing process for sealing the coal ash enclosure container 201 for a predetermined time is performed. Ri, wherein is a method of suppressing the elution of hexavalent chromium from coal ash, the method will be described with reference to pulverized coal burning facility 1 described above.

  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 Then, a pulverized coal combustion process S30 for generating coal ash, a coal ash treatment process S40 for storing the coal ash, and a coal ash supply process S50 for performing a coal ash supply process for supplying the coal ash to the coal ash enclosure 201 And after the coal ash supply process and the exhaust gas transfer process, an exhaust gas transfer process S60 for performing an exhaust gas transfer process for transferring the exhaust gas moving in the system from the heat exchange unit to the dust collector 182 into the coal ash enclosure 201. , A sealing process S70 for performing a sealing process for sealing the coal ash enclosure 201 for a predetermined time, and an exhaust gas return process for returning the exhaust gas in the coal ash enclosure 201 to the system. The exhaust gas return process step S80 to perform, and a coal ash discharge process step S90 to perform the coal ash discharge process for discharging the coal ash in the coal ash enclosure 201 in coal ash recovery silo 183.

  Here, the coal supply step S <b> 10 is performed in the coal supply unit 12 of the pulverized coal combustion facility 1. The pulverized coal generation step S <b> 20 is performed in the pulverized coal generation unit 14. The pulverized coal combustion step S30 is performed in the pulverized coal combustion unit 16. The coal ash treatment step S40 is performed in the coal ash treatment unit 18. The coal ash supply process S50, the exhaust gas transfer process S60, the sealing process S70, the exhaust gas return process S80, and the coal ash discharge process S90 are performed in the reduction processing unit 20. Hereinafter, each step will be described.

<Coal supply process S10>
First, in the coal supply step S <b> 10, 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 S20, 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 step S <b> 30, 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 450 ° 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 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 deposited on a hopper (not shown) and then transferred to the coal ash recovery silo 183 and supplied to the coal ash enclosure 201 by the coal ash supply means 202. The 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>
The coal ash supply processing step S50 which is one of the features of the present invention performs a coal ash supply process in which fly ash collected by the dust collector 182 is supplied to the coal ash enclosure 201 by the coal ash supply means 202. It is a process. As shown in FIG. 1, the coal ash supply processing step S <b> 50 is performed by the reduction processing unit 20 that overlaps a part of the coal ash processing unit 18.

  The average particle size of fly ash supplied by the coal ash supply means 202 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 size exceeds 100 μm, the exhaust gas does not enter the fly ash, so the reduction reaction from hexavalent chromium to trivalent chromium does not proceed.

<Exhaust gas transfer process S60>
The exhaust gas transfer processing step S60, which is one of the features of the present invention, is performed after the coal ash supply processing step S50, from the vicinity of the primary economizer 161d or the secondary economizer 161e in which the exhaust gas transfer means 203 is a heat exchange unit. This is a step of performing exhaust gas transfer processing for transferring the exhaust gas moving through the system up to 181 into the coal ash enclosure 201.

  In the present embodiment, the exhaust gas transfer processing step S60 transfers the exhaust gas moving in the system from the vicinity of the primary economizer 161d or the secondary economizer 161e to the denitration device 181 into the coal ash enclosure 201. The exhaust gas moving in the system from the denitration device 181 to the dust collector 182 may be transferred into the coal ash enclosure 201.

  Further, in the present embodiment, in the exhaust gas transfer processing step S60, a process of transferring the exhaust gas moving in the system from the vicinity of the primary economizer 161d or the secondary economizer 161e to the denitration device 181 into the coal ash enclosure 201 is performed. However, in addition to the exhaust gas, an elution suppression additive treatment (step) may be performed in which a fuel additive capable of preventing elution of harmful trace elements is added to the coal ash enclosure 201. This treatment not only suppresses elution of hexavalent chromium from fly ash, but also prevents elution of harmful trace elements such as fluorine and boron from fly ash.

  Furthermore, in this embodiment, although the exhaust gas transfer process step S60 is performed after the coal ash supply process step S50, the coal ash supply process step S50 and the exhaust gas transfer process step S60 may be performed at the same time. The coal ash supply process S50 may be performed after the transfer process S60.

<Sealing process S70>
The sealing process S70 is a process of performing a process of sealing the coal ash enclosure container 201 in a sealed state for a predetermined time after the coal ash supply process S50 and the exhaust gas transfer process S60. That is, in the sealing process S70, after the fly ash supplied by the coal ash supply means 202 and the exhaust gas transferred by the exhaust gas transfer means 203 are sealed in the coal ash enclosure container 201, the coal ash enclosure container 201 is filled for a predetermined time. It is the process of performing the process which encloses in a sealed state.

  In this embodiment, the sealing process S70 is performed after the coal ash supply process S50 and the exhaust gas transfer process S60, but the seal process S70 includes the coal ash supply process S50 and the exhaust gas transfer process S60. You may make it carry out simultaneously.

  The oxygen concentration of the exhaust gas in 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 of 2% to 3%, and the temperature of the exhaust gas in the system Is 200 ° C. to 600 ° C. Therefore, the exhaust gas in the system has conditions that facilitate reducing hexavalent chromium to trivalent chromium. Therefore, when hexavalent chromium is present in the fly ash by the sealing treatment step S70, the 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 prevented, existing facilities can be used effectively, which is advantageous in terms of cost.

  The time for sealing the coal ash enclosure 201 in a sealed state is preferably in the range of 5 minutes to 60 minutes. In less than 5 minutes, hexavalent chromium in fly ash is not sufficiently reduced to trivalent chromium. If it is 60 minutes or more, the reduction reaction of hexavalent chromium to trivalent chromium proceeds completely and no further reduction treatment is performed, so that no further effect can be obtained, which is economically disadvantageous.

<Exhaust gas return processing step S80>
The exhaust gas return processing step S80 is a step of performing a process of returning the exhaust gas in the coal ash enclosure 201 to the system from the vicinity of the primary economizer 161d or the secondary economizer 161e to the denitration device 181 after the sealing process S70. is there.

  In addition, in the exhaust gas transfer processing step S60, when the exhaust gas moving through the system from the denitration device 181 to the dust collector 182 is transferred to the coal ash enclosure container 201, the exhaust gas return process step S80 is performed in the coal ash enclosure container 201. The exhaust gas may be returned to the system from the denitration device 181 to the dust collector 182.

<Coal ash emission treatment process S90>
The coal ash discharge treatment step S90 is a step of performing a process of discharging fly ash in the coal ash enclosure 201 to the coal ash recovery silo 183 after the sealing treatment step S70.

  In the present embodiment, the method of reducing hexavalent chromium in coal ash using only exhaust gas is shown, but the present invention is not limited to this. That is, for example, after the sealing treatment step S70, reducing gas may be enclosed in the coal ash enclosure 201 and reacted within a range of 5 minutes to 60 minutes to reduce hexavalent chromium.

  Moreover, when coal ash contains calcium oxide etc. and shows alkalinity, the hexavalent chromium in coal ash may not be fully reduced by exhaust gas. In such a case, the coal ash is preferably neutralized with carbon dioxide gas or the like in advance, and then the coal ash and the exhaust gas are reacted.

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 a schematic block diagram which shows a part of pulverized coal combustion facility in the coal thermal power generation system which shows one embodiment of this invention. It is drawing which shows an example of a coal ash enclosure container.

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 Heater 163 Air supply machine 18 Coal ash processing part 181 Denitration device 182 Dust collector 183 Coal ash recovery silo 20 Reduction processing unit 201 Coal ash enclosure container 202 Coal ash supply means 203 Exhaust gas transfer means 204 Exhaust gas return means 205 Coal ash discharge means S10 Coal supply process S20 Pulverized coal production process S30 Pulverized coal Combustion process S40 Coal ash treatment process S50 Coal ash supply process S60 Exhaust gas transfer process S70 Sealing process S80 Exhaust gas return process S90 Coal ash discharge process

Claims (11)

A combustion boiler that burns coal;
A dust collector that is provided downstream of the combustion boiler and collects fly ash having a particle size of 100 μm or less among the coal ash generated by the combustion of the coal from the exhaust gas generated by the combustion of the coal ;
A fly ash enclosure that can enclose the fly ash in a sealed state;
A fly ash supply means for supplying the fly ash to the fly ash enclosure,
A heat exchange unit that is provided downstream of the combustion boiler and exchanges heat of exhaust gas generated by combustion of the coal and heat of boiler feed water for supplying water to the combustion boiler;
Coal-fired power system comprising a gas transfer means to transfer the gas to move the system from the heat exchange unit to the dust collecting device to the fly ash enclosure. 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 exhaust gas transfer means transfers the exhaust gas moving in the system from the heat exchange unit to the denitration apparatus into the fly ash enclosure. 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 exhaust gas transfer means transfers the exhaust gas moving through the system from the denitration device to the dust collector into the fly ash enclosure. The exhaust gas return means connected to the fly ash enclosure and further comprising an exhaust gas return means for returning the exhaust gas in the fly ash enclosure to the system from the heat exchange unit to the dust collector. Or a coal-fired power generation system. The fly ash enclosure is connected to the exhaust gas transfer means, and has a spiral exhaust gas ejection pipe in which a spout for ejecting the exhaust gas is formed in the fly ash enclosure. Or a coal-fired power generation system. The fly ash enclosure is connected to the exhaust gas transfer means, and has an exhaust gas ejection pipe in which a plurality of ejection ports for ejecting the exhaust gas are formed in the fly ash enclosure.
The exhaust gas jet pipe is bent a plurality of times in the fly ash enclosure.
5. The structure of claim 1, wherein a portion sandwiched between adjacent bent portions in the exhaust gas ejection pipe is formed to be substantially parallel to each other in a vertical or horizontal direction with another portion sandwiched between adjacent bent portions. The coal-fired power generation system described. A dust collector that collects fly ash having a particle size of 100 μm or less from a combustion boiler that burns coal and coal ash that is provided downstream of the combustion boiler and is generated by combustion of the coal from exhaust gas that is generated by combustion of the coal An apparatus, a fly ash enclosure that can enclose the fly ash in a hermetically sealed state, and heat supplied to the combustion boiler that is provided downstream of the combustion boiler and that is generated by the combustion of the coal. In a coal-fired power generation system comprising a heat exchange unit for exchanging heat with boiler boiler water ,
A fly ash supply process for supplying the fly ash to the fly ash enclosure,
Exhaust gas transfer processing for transferring the exhaust gas moving in the system from the heat exchange unit to the dust collector into the fly ash enclosure,
Hexavalent chromium elution suppression that suppresses elution of hexavalent chromium from the coal ash by performing a sealing process in which the fly ash enclosure is sealed for a predetermined time after the fly ash supply process and the exhaust gas transfer process. Method. The coal-fired power generation system includes a denitration device that removes nitrogen oxides in the exhaust gas, and the exhaust gas transfer process encloses the exhaust gas that moves in the system from the heat exchange unit to the denitration device in the fly ash The hexavalent chromium elution suppression method according to claim 7, wherein the hexavalent chromium elution suppression method is a process of transferring to a container. The coal-fired power generation system includes a denitration device that removes nitrogen oxides in the exhaust gas, and the exhaust gas transfer treatment encloses the exhaust gas that moves in the system from the denitration device to the dust collector into the fly ash. The hexavalent chromium elution suppression method according to claim 7, wherein the hexavalent chromium elution suppression method is a process of transferring to a container. The hexavalent seal according to any one of claims 7 to 9 , wherein, in the sealing process, after the fly ash supply process and the exhaust gas transfer process, the fly ash enclosure is sealed in a range of 5 minutes to 60 minutes. Chromium elution suppression method. Furthermore, after it said sealing process, by sealing a reducing gas in the fly ash enclosure, reacting or longer and 60 minutes or 5 minutes, hexavalent chromium elution suppressing method according to claim 7 to 10.

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