JP5171184B2 - Coal-fired power generation system and method for increasing the average particle size of fly ash - Google Patents

Description

  The present invention relates to a coal-fired power generation system and a method for enlarging the average particle size of fly ash.

  In the coal thermal power generation system, coal ash such as clinker ash and fly ash is generated as a by-product by combustion of coal used as a raw material. Clinker ash falls from the furnace and is also called bottom ash. Fly ash is the remaining dust.

  Fly ash (dust) is collected with high efficiency (for example, 95% or more) mainly by a dust collector such as an electric dust collector. This fly ash has been conventionally disposed of in landfills, but in recent years, it has been effectively used as a concrete admixture, a cement raw material, and a ground improvement agent from the viewpoint of environmental conservation.

  However, in addition to carbon, coal contains harmful elements such as boron, fluorine, selenium, arsenic and hexavalent chromium (hereinafter referred to as boron, fluorine, selenium, arsenic and hexavalent chromium). Therefore, fly ash also contains harmful trace elements. Therefore, in order to make effective use of fly ash, techniques for suppressing the elution of harmful trace elements have been studied.

For example, in Patent Document 1, among a plurality of dust collection stages arranged in an electric dust collector, fly ash is collected from a specific dust collection stage, and a plurality of exhaust ash is installed in the vertical direction of exhaust gas. A method for preventing elution of harmful trace elements in fly ash by collecting fly ash from the dust collection stage located on the most upstream side of the exhaust gas among the dust collection stages is disclosed.
JP 2006-35123 A

  However, even if it is possible to prevent harmful trace elements from being collected from being collected, depending on the performance of the dust collector, the dust collector cannot collect fly ash with a small average particle size. There is a possibility that fly ash containing elements is released from the chimney into the atmosphere. That is, when fly ash having an average particle size smaller than the separation limit particle size of the dust collector is present, fly ash containing harmful trace elements passes through the dust collector and is released into the atmosphere from the chimney. For this reason, since the average particle diameter of fly ash is small, when an existing dust collector cannot remove fly ash, it is necessary to strengthen new facilities. However, when a new facility is provided, a problem such as an increase in cost and a problem that the installation space is insufficient occur.

  Therefore, a large amount of initial investment is not required, and a coal-fired power generation system that makes the fly ash average particle size larger than the separation limit particle size or the average particle size of fly ash without the need for large-scale additional equipment. There is a need for a way to increase it.

  The present invention has been made in view of the above-mentioned problems, and does not require a large initial investment, and does not require a large-scale additional facility, and can increase the average particle size of fly ash. An object of the present invention is to provide a power generation system or a method for increasing the average particle size of fly ash.

  (1) In a coal thermal power generation system comprising: a combustion boiler that burns coal; and a dust collector that is disposed downstream of the combustion boiler and removes fly ash contained in exhaust gas generated by combustion of the coal. The dust collector has a first opening in the vicinity of a portion from which the fly ash is removed, and is disposed downstream of the combustion boiler and upstream of the dust collector, and has a second opening that forms an opening. A downstream portion having, a fly ash transfer pipe communicating from the first opening to the second opening, and suction means for sucking the inside of the fly ash transfer pipe from the first opening toward the second opening , Comprising a coal-fired power generation system.

  (2) The coal dust power generation system according to (1), wherein the dust collector has a first opening in the vicinity of a portion where fly ash having a large average particle diameter is removed from the fly ash.

  Fly ash generated by coal combustion is discharged downstream from the combustion boiler and upstream from the dust collector, and the average particle size is smaller than the separation limit particle size of the dust collector. May contain fly ash.

  According to the invention of (1), the dust collector has the first opening in the vicinity of the portion from which the fly ash is removed, and the downstream portion is disposed downstream of the combustion boiler and upstream of the dust collector to form an opening. The fly ash transfer pipe communicates from the first opening to the second opening, and the suction means sucks the fly ash transfer pipe from the first opening toward the second opening. . Accordingly, fly ash is transferred from the first opening to the second opening. Here, the fly ash having a small average particle diameter present in the downstream part is immediately after having been transferred from the combustion part in the boiler and is not completely cooled and solidified, and at least the surface is in a molten state. For this reason, the fly ash with a small average particle size is merged with the surface of the fly ash with a relatively large average particle size, so that the average can be obtained without a large initial investment and without requiring a large-scale additional equipment. Fly ash with a large particle size can be produced. That is, the average particle size of fly ash can be increased.

  Moreover, according to the invention of (2), since the fly ash transferred to the downstream portion has a large average particle size, it is possible to efficiently capture the fly ash having a small average particle size.

  Here, the “downstream part arranged downstream of the combustion boiler and upstream of the dust collector” means a furnace upper dividing wall, a superheater, a reheater, or a economizer corresponding to a heat exchange unit, which will be described later Or an exhaust passage or the like. In this downstream part, it is preferable that the fly ash that has passed through the combustion part of the combustion boiler is not completely cooled and solidified, and the fly ash is maintained in a molten state.

  In addition, “fly ash having a large average particle size among fly ash” means that, for example, in the case of an electric dust collector, if there are a plurality of collection stages, the fly ash is collected in the collection stage upstream of the exhaust gas. It is a fly ash. In addition, in the case of the heavy dust collector, if the exhaust gas flows in the apparatus in the horizontal direction, it is fly ash that has settled to the inlet side of the apparatus. Thus, even if it is the same dust collector, the average particle diameter of fly ash may differ with the taking-out position. Even in this case, the fly ash transferred to the downstream portion in the present invention has a large particle size among all the fly ash taken out by the dust collector. The fly ash transferred to the downstream portion preferably has a particle size of 110% or more and 300% or less with respect to the average particle size in all fly ash (for example, when the average particle size is 35 μm, 40 μm or more and 100 μm or less).

  (3) The coal-fired power generation system according to (1) or (2), wherein pulverized coal is used as the coal.

  The invention of (3) stipulates that the fuel used in the coal-fired power generation system according to the present invention is pulverized coal. In the coal-fired power generation system according to the present invention, when pulverized coal is used as the fuel, the average particle size of fly ash is reduced, so it is very significant to increase the average particle size of fly ash. That is, with the coal-fired power generation system according to the present invention, even if the fuel is fly ash having a small average particle size because of pulverized coal, the average particle size can be increased.

  (4) The coal-fired power generation system according to any one of (1) to (3), wherein the downstream portion is a heat exchange unit disposed downstream of the combustion boiler.

  In the invention of (4), the position where the fly ash having a large average particle size is transferred is defined as the position of the downstream portion. According to invention of (4), the downstream part to which the fly ash with a large average particle diameter is transferred is a heat exchange unit arrange | positioned downstream of a combustion boiler. This heat exchange unit is called a furnace upper dividing wall, a superheater, a reheater, and a economizer, and is an area where a temperature of 450 ° C. to 900 ° C. is maintained. As described above, since the high temperature region is maintained in the heat exchange unit, the fly ash having a small average particle diameter melted in the combustion section in the boiler is not completely cooled and solidified, so that the surface of the fly ash having the large average particle diameter is not cooled. It is possible to merge. Accordingly, fly ash having a large average particle size can be generated. That is, the average particle size of fly ash can be increased without making a large initial investment and without requiring a large-scale additional facility.

  (5) Fly ash in a coal-fired power generation system comprising: a combustion boiler that burns coal; and a dust collector that is disposed downstream of the combustion boiler and removes fly ash contained in exhaust gas generated by combustion of the coal The fly ash removed by the dust collector is provided between the combustion boiler and the dust collector, and the exhaust gas passes through the fly ash removed by the dust collector. The method of enlarging the average particle diameter of fly ash by making it transfer to a part.

  (6) The fly ash having a large average particle diameter among the fly ash removed by the dust collector is provided between the combustion boiler and the dust collector from the dust collector and downstream through which the exhaust gas passes. The method of enlarging the average particle diameter of the fly ash as described in (5) which is made to transfer to a part.

  The inventions of (5) and (6) are based on the inventions of (1) and (2). Similar to the inventions of (1) and (2), fly ash having a large average particle diameter can be produced. That is, the average particle size of fly ash can be increased without making a large initial investment and without requiring a large-scale additional facility.

  (7) The method for enlarging the average particle size of fly ash according to (5) or (6), wherein pulverized coal is used as the coal.

  The invention (7) captures the invention (3) as a method. Similar to the invention of (3), by applying the method for enlarging the average particle size of fly ash according to the present invention to the case where the fuel is pulverized coal, the fly ash having a small average particle size because the fuel is pulverized coal. Even so, the average particle size can be increased.

  (8) The said downstream part is a heat exchange unit arrange | positioned downstream of the said combustion boiler, The method of expanding the average particle diameter of the fly ash in any one of (5) to (7).

  The invention (8) captures the invention (4) as a method. Similar to the invention of (4), fly ash having a large average particle diameter can be generated. That is, the average particle size of fly ash can be increased without making a large initial investment and without requiring a large-scale additional facility.

  According to the present invention, the average particle size of fly ash can be increased without making a large initial investment and without requiring a large-scale additional facility.

  Hereinafter, an embodiment showing an example of the present invention will be described with reference to the drawings.

<Configuration of coal combustion plant in coal-fired power generation system>
FIG. 1 is a schematic explanatory view showing a coal combustion plant 10 in a coal thermal power generation system. Here, as shown in FIG. 1, the coal combustion plant 10 includes at least a combustion boiler 40 that burns coal, and electric dust collection that removes fly ash (dust) contained in exhaust gas generated by burning the coal. Device 90.

  Further, the coal combustion plant 10 includes a coal bunker 20 for storing coal supplied from a coal silo (not shown) by a coal transportation facility, a pulverized coal machine 30, and an exhaust passage (provided downstream of the combustion boiler 40). 50), a denitration device 60 provided in the exhaust passage 50, an air preheater 70, a gas heater (for heat recovery) 80, an induction fan 210, a desulfurization device 220, and a gas heater (for reheating) ) 230, a desulfurization ventilator 240, and a chimney 250. FIG. 2 is an enlarged view of the vicinity of the combustion boiler (furnace) 40.

  The pulverized coal machine 30 pulverizes the coal supplied from the coal bunker 20 via the coal feeder 25 to a fine particle size to form pulverized coal. Then, by mixing the pulverized coal and air, the pulverized coal is preheated and dried to facilitate combustion. Air is blown onto the formed pulverized coal, whereby the pulverized coal machine 30 supplies the pulverized coal to the combustion boiler 40.

  The combustion boiler 40 burns the pulverized coal supplied from the pulverized coal machine 30 together with the forcibly supplied air. By burning pulverized coal, coal ash such as clinker ash and fly ash is generated and exhaust gas is generated. As will be described later, fly ash is removed by an electrostatic precipitator 90.

  The combustion boiler 40 will be described in detail with reference to FIG. 2. In FIG. 2, the combustion boiler 40 has a substantially inverted U shape as a whole, and the exhaust gas (combustion gas) is inverted U along the arrow in the figure. After moving in the shape of a letter, after passing through the secondary economizer 41e, it is reversed again into a U-shape. An exhaust passage 50 (the last arrow in FIG. 2) of the combustion boiler 40 is connected to the denitration device 60 in FIG.

  Below the combustion boiler 40, a burner 41a for burning pulverized coal in the vicinity of the burner zone 41a 'in the combustion boiler 40 is arranged. Moreover, the 1st superheater 41b is arrange | positioned by the U-shaped top part vicinity in the combustion boiler 40, and also the 2nd superheater 41c is arrange | positioned from there. Furthermore, from the vicinity of the terminal end of the second superheater 41c, a primary economizer 41d and a secondary economizer 41e are 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 retained by exhaust gas.

Further, a fly ash transfer pipe 170 is connected to the opening 42 at an opening (second opening) 42 which is a side surface of the combustion boiler 40 and has an opening formed in the vicinity of the primary economizer 41d. Is provided.

  The denitration device 60 disposed on the exhaust passage 50 is for removing nitrogen oxides in the exhaust gas. That is, so-called dry ammonia, ammonia gas is injected as a reducing agent into exhaust gas at a relatively high temperature (300 ° C 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. A catalytic reduction method is preferably used. The exhaust gas is cooled by exchanging heat with air for combustion in an air preheater (AH) 70, recovered by the gas heater 80, and then sent to the electric dust collector 90.

  The electric dust collector (EP) 90 is a device that collects coal ash in the exhaust gas with an electrode. The electric dust collector 90 will be described in detail with reference to FIGS. 3 and 4. As shown in FIG. 3, the electrostatic dust collector 90 has an inlet throttle duct 92 and an outlet throttle duct 94 formed on each of the left and right sides. A box-shaped sealed chamber 96, three rectangular insulator chambers 98 disposed on the sealed chamber 96, a plurality of high-voltage transformer rectifiers 102 disposed on the insulator chamber 98, and a pair disposed on the sealed chamber 96 The striking device 104, the perforated plate 106 in the sealed chamber 96 and facing the inlet throttle duct 92, and a partition plate provided on the back of the perforated plate 106, the in-plane direction of which is A large number of dust collecting electrodes 108 arranged in a row along the entrance / exit direction, and discharge electrodes connected between the dust collecting electrodes 108 and connected to a discharge electrode support insulator 110 disposed in the insulator chamber 98. Electrode 112 and Four dust collection hoppers 114, 115, 116, 117 (117 are shown) arranged at the lower part of the sealed chamber 96 and facing the arrangement positions of a plurality of electrostatic electrode groups each composed of an assembly of the two electrodes 108, 112. And an inspection floor 118 is provided on the floor surface around each static electrode group.

  As shown in FIG. 4, the operation principle of the electrostatic precipitator 90 is that the dust collecting electrode 108 is connected to the + side of the DC high-voltage power supply created by the high-voltage transformer rectifier 102 and charged positively, and the discharge electrode is connected to the − side. 112 is connected. Therefore, when exhaust gas flows in from the inlet throttle duct 92 and fly ash contained in the exhaust gas passes between the dust collection electrodes 108, the fly ash is charged to-by the-charge discharged from the discharge electrode 112, It is adsorbed on the surface of the dust collecting electrode 108 and deposited there.

  Further, after the ventilation of the exhaust gas is stopped and the power supply is shut off, when the hammering device 104 is vibrated, the fly ash adsorbed and deposited on the dust collecting electrode 108 is placed in any one of the dust collecting hoppers 114 to 117. It falls and is collected by the fly ash collection | recovery apparatus 120 shown in FIG. 1 through the dust collection hoppers 114-117.

In the case of the electric dust collector 90, fly ash falling on the dust collection hoppers 114 and 115 which are dust collection hoppers on the inlet throttle duct 92 side among the dust collection hoppers 114 to 117 has a large average particle diameter. An opening (first opening) 114 b is formed on the side surface 114 a of the dust collection hopper 114. That is, the electrostatic precipitator 90 has an opening 114b in the vicinity of a portion where fly ash having a large average particle diameter is removed from fly ash. A fly ash transfer pipe 170 is connected to the opening 114b. The fly ash transfer pipe 170 communicates from the opening 114b to the opening 42. On the fly ash transfer tube 170, as shown in FIG. 1, a suction device (suction means) 180 is provided so as to suck in the direction from the opening 114b to the opening 42.

  The exhaust gas that has passed through the electrostatic precipitator (EP) 90 is guided to the desulfurization device 220 via the induction fan 210. The desulfurization apparatus 220 sprays a mixed liquid of limestone and water onto the combustion gas, thereby absorbing the sulfur oxide contained in the combustion gas into the mixed liquid to generate a desulfurized gypsum slurry, and dehydrating the desulfurized gypsum slurry. By processing, desulfurized gypsum is produced | generated, and the produced | generated desulfurized gypsum is collect | recovered with the desulfurization gypsum collection | recovery apparatus 222 connected to this apparatus.

  The air from which the sulfur oxide has been removed by the desulfurization device 220 is heated by the gas heater 230 and guided to the chimney 250 via the desulfurization ventilator 240. The gas heater 230 is configured to effectively discharge the combustion gas from the chimney by using the chimney effect by heating the temperature of the combustion gas lowered by the desulfurization apparatus 220.

  Next, fly ash (hereinafter referred to as fly ash A) having a large average particle diameter is transferred by the fly ash transfer pipe 170, and fly ash (hereinafter referred to as fly ash B) in the vicinity of the primary economizer 41d is transferred to the surface of the fly ash A. ) Is melted and united to produce fly ash (hereinafter, fly ash C).

  When the inside of the dust collection hopper 114 is sucked by the suction force of the suction device 180, the fly ash A that has dropped on the dust collection hopper 114 is sucked into the fly ash transfer pipe 170. The sucked fly ash A is discharged through the fly ash transfer pipe 170 from the opening 42 to the vicinity of the primary economizer 41d provided in the combustion boiler 40. Fly ash B exists in the vicinity of the primary economizer 41d having a temperature of 450 ° C to 500 ° C. This fly ash B is not completely cooled and solidified after passing through the combustion part of the combustion boiler 40, and the surface is melted. Then, fly ash B melts and coalesces on the surface of fly ash A, and new fly ash C is generated. That is, fly ash A and B combine to produce fly ash C having a large average particle size.

  Moreover, it is preferable that the average particle diameter of the fly ash A to be transferred is 1 μm or more and 100 μm or less. If it is less than 1 μm, the average particle size is too small and the newly generated fly ash C has a small average particle size. Even if it exceeds 100 μm, no further effect is obtained.

  The average particle size of fly ash B in the vicinity of the primary economizer 41d is preferably 1 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less.

  Although the fly ash transfer pipe 170 is connected to the dust collection hopper 115, it is sufficient that it is connected to at least one dust collection hopper as well as only one dust collection hopper.

  In addition, although the electric dust collector 90 is provided as a dust collector, the dust collecting hopper may be another type of dust collector, for example, a gravity dust collector or fly that is separated by natural sedimentation by fly ash gravity. It may be an obstacle type dust collector or a centrifugal dust collector that separates on an obstacle by a force such as inertial force, centrifugal force, electrostatic force or the like acting on the ash, or by a diffusion movement of particle groups. When the type of the dust collector is changed, naturally, an opening connected to the fly ash transfer pipe 170 is provided in the vicinity of the portion of the fly ash from which the fly ash having a large average particle diameter is removed.

  The fly ash transfer pipe 170 is connected to the combustion boiler 40 in the vicinity of the primary economizer 41d. However, if the fly ash A is in a meltable state, for example, the burner zone 41a in the combustion boiler. It may be connected to the combustion boiler 40 in the vicinity, or may be connected to the exhaust passage 50. In this case, the temperature of the place where the fly ash A is transferred is preferably in the range of 400 ° C. or higher. If the temperature of the place where the fly ash A is transferred is less than 400 ° C., the fly ash B is completely cooled and solidified, and the surface of the fly ash B may not be maintained in a molten state.

  The suction device 180 may employ any known means as long as it sucks the fly ash transfer pipe 170 from the opening 42 toward the opening 114b.

  As described above, the electrostatic precipitator 90 has the opening 114b in the vicinity of the part from which fly ash having a large average particle diameter is removed from the fly ash, and the primary economizer 41d of the combustion boiler having the opening 42 is Arranged downstream of the combustion boiler 40 and upstream of the electrostatic precipitator 90, the fly ash transfer pipe 170 communicates from the opening 114b to the opening 42, and the suction device 180 is directed from the opening 114b to the opening 42. Then, the inside of the fly ash transfer pipe 170 is sucked. Accordingly, fly ash having a large average particle diameter is transferred to the opening 42 from the opening 114b. Here, the fly ash having a small average particle diameter present in the vicinity of the opening 42 is in a state where at least the surface is melted by the residual heat of the combustion boiler 40. For this reason, the fly ash with a small average particle size is combined with the surface of the fly ash with a large average particle size, so that the average particle size can be obtained without a large initial investment and without requiring a large-scale additional equipment. Can produce large fly ash. That is, the average particle size of fly ash can be increased.

  In the present embodiment, the case where fly ash having a large average particle size among the fly ash is transferred by the fly ash transfer pipe 170 is described as an example, but the present invention is not limited to this. That is, the fly ash transferred by the fly ash transfer pipe 170 may be a fly ash having a relatively small average particle diameter after the electrostatic precipitator 90.

It is a schematic block diagram which shows the coal combustion plant in the coal thermal power generation system which shows one Embodiment of this invention. FIG. 2 is an enlarged view of the vicinity of a combustion boiler in FIG. 1. It is the perspective view which partially fractured | ruptured the electrostatic precipitator in the coal thermal power generation system which shows one Embodiment of this invention, and showed the inside. It is explanatory drawing which shows the operation principle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Coal combustion plant 20 Coal bunker 30 Pulverizer 40 Combustion boiler 41d Primary economizer 41e Secondary economizer 50 Exhaust passage 60 Denitration device 70 Air preheater 80 Gas heater 90 Electric dust collector 114,115,116,117 Dust collection Hopper 116 Fly ash recovery device 118 Floor 130 Gas heater 140 Desulfurization ventilator 170 Fly ash transfer pipe 180 Suction device 210 Induction ventilator 220 Desulfurization device 222 Desulfurization gypsum recovery device 230 Gas heater 240 Desulfurization ventilator 250 Chimney

Claims (6)

In a coal thermal power generation system comprising: a combustion boiler that burns coal; and a dust collector that is disposed downstream of the combustion boiler and removes fly ash contained in exhaust gas generated by combustion of the coal.
The dust collector has a first opening in the vicinity of a portion where fly ash having a large average particle diameter is removed from the fly ash ,
A downstream portion disposed downstream of the combustion boiler and upstream of the dust collector and having a second opening forming an opening;
A fly ash transfer pipe communicating from the first opening to the second opening;
A coal thermal power generation system comprising: suction means for sucking the fly ash transfer pipe from the first opening toward the second opening. The coal-fired power generation system according to claim 1 , wherein pulverized coal is used as the coal. The coal-fired power generation system according to claim 1 , wherein the downstream portion is a heat exchange unit disposed downstream of the combustion boiler. An average particle of fly ash in a coal thermal power generation system comprising: a combustion boiler that burns coal; and a dust collector that is disposed downstream of the combustion boiler and removes fly ash contained in exhaust gas generated by combustion of the coal A method of expanding the diameter,
The fly ash removed from the fly ash having a large average particle diameter in the fly ash of the dust collector is removed from the dust collector through the opening provided in the vicinity of the part. A method of enlarging the average particle size of fly ash by transferring it to the downstream part through which the exhaust gas passes, provided between the dust collector. The method for enlarging the average particle size of fly ash according to claim 4 , wherein pulverized coal is used as the coal. The said downstream part is a heat exchange unit arrange | positioned downstream of the said combustion boiler, The method to expand the average particle diameter of the fly ash of Claim 4 or 5 .

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