JP2013202434A - Method for disposing of fluidized bed-system boiler ash and disposer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method, for disposing of fluidized bed-system boiler ash, which can make an effective use of fluidized bed-system boiler ash, and at the same time, remove mercury from an exhaust gas simultaneously.SOLUTION: A fluidized bed-system boiler ash disposer 1 comprises a dust collection device 3 which recovers a boiler ash from an exhaust gas G1 of a fluidized bed-system boiler 2 burning coal C, a slurry making means which makes a slurry S1 by adding water W to the boiler ash (fly ash) FA recovered by the dust collection device 3, and a wet scrubber 5 which adds alkali AL to an exhaust gas G3 of the dust collection device 3 or an exhaust gas G7 of an activated coke reclaiming tower 24 and cleans the exhaust gas G3 or G7 while adding the slurry S1 created by the slurry making means. It is possible to provide a floatation machine 8 which separates the slurry S4 discharged from a surface modifier 7 into an unburnt carbon UC and an ash content A other than the former. The ash content A containing gypsum GY separated by a floatation method, can be used as an incorporation material for cement and the unburnt carbon UC adsorbing the mercury can be discarded.

Description

  The present invention relates to a method and apparatus for effectively removing ash discharged from a fluidized bed boiler and efficiently removing mercury in exhaust gas.

  There are two types of combustion systems at coal-fired power plants: a pulverized coal combustion system and a fluidized bed combustion system. At present, the pulverized coal combustion method is the mainstream, but in recent years, the construction of a circulating fluidized bed power plant that can use low-grade coal, biomass, etc. as fuel has also been promoted.

  Also in the cement manufacturing facility, as shown in FIG. 3, a circulating fluidized bed boiler 22 is installed, and fuel coal C is introduced into the boiler 22 together with limestone L for removing sulfur oxides to flow. It is burned while generating steam for private power generation. The exhaust gas G1 of the boiler 22 is dust-removed by the electric dust collector 23, and the recovered boiler ash A is used as a cement raw material. Since the circulating fluidized bed boiler 22 efficiently performs heat transfer in the fluidized bed, the amount of NOx generated is low due to low-temperature combustion at about 800 to 900 ° C.

  However, since the ash discharged from the fluidized bed boiler contains a large amount of unburned carbon compared to the ash of the pulverized coal-fired boiler, its use is limited as a cement raw material and a cement mixture, The process is tight.

  On the other hand, as described above, since a large amount of limestone is added to perform desulfurization, the fluidized bed boiler contains a large amount of quick lime in the ash, and therefore cannot be used as an admixture for cement. In addition, it is pointed out that the current equipment has difficulty in dealing with mercury contained in boiler exhaust gas.

  Accordingly, the present invention has been made in view of the above-described problems in the prior art, and is a fluidized bed boiler ash that can effectively use fluidized bed boiler ash and can simultaneously remove mercury in exhaust gas. An object of the present invention is to provide a processing method and a processing apparatus.

  In order to achieve the above object, the present invention provides a method for treating a fluidized bed boiler ash, wherein the exhaust gas from a fluidized bed boiler that burns coal is removed to recover the boiler ash, and the recovered boiler ash is treated with water. Is added to form a slurry, and after adding alkali to the gas containing volatile components in the exhaust gas of the fluidized bed boiler after dust removal, wet cleaning is performed while further adding the slurry.

And according to the present invention, after adding the alkali to the gas containing the volatile components in the exhaust gas after recovering the boiler ash from the exhaust gas of the fluidized bed boiler, the recovered boiler ash is further added in the form of a slurry. While being wet-cleaned, the lime content put into the fluidized bed boiler is converted to gypsum, and SO ₂ contained in the gas containing volatile components in the exhaust gas is removed as alkali sulfate and also contained in the boiler ash Mercury in the exhaust gas can also be adsorbed and removed by unburned carbon. At this time, it is possible to avoid excess CaO remaining in the boiler ash by supplying the fluidized bed boiler with limestone that balances with the amount of SO ₂ generated in the fluidized bed boiler.

  In the fluidized bed boiler ash treatment method, the gas containing a volatile component in the exhaust gas of the fluidized bed boiler may be the exhaust gas itself of the fluidized bed boiler after the dust removal, or after the dust removal. After the volatile component of the fluidized bed boiler is adsorbed on the adsorbent, the adsorbent can be heated to form a gas containing the volatile component desorbed.

  In the method for treating fluidized bed boiler ash, the slurry obtained by the wet cleaning can be separated into unburned carbon and other ash by a flotation method.

  Moreover, the ash content other than the unburned carbon separated by the flotation method can be used as an admixture for cement, and the unburned carbon can be discarded. As a result, an admixture for cement that does not contain CaO can be obtained, and the unburned carbon adsorbed with mercury can be discarded, so that mercury can be safely landfilled.

Furthermore, the present invention is a fluidized bed type boiler ash treatment apparatus, which is a dust collector that collects boiler ash from the exhaust gas of a fluidized bed boiler that burns coal, and water that is collected in the boiler ash collected by the dust collector. And a wet scrubber for washing while adding the slurry generated by the slurrying means after adding alkali to the gas containing the volatile component in the exhaust gas of the dust collector It is characterized by providing. According to the present invention, similarly to the above-described invention, the lime content charged into the fluidized bed boiler is converted to gypsum, and SO ₂ remaining in the exhaust gas is removed as alkali sulfate, and unburned carbon contained in the boiler ash. Thus, mercury in the exhaust gas can be adsorbed and removed.

  The fluidized bed boiler ash treatment apparatus may include a flotation machine that separates the slurry discharged from the wet scrubber into unburned carbon and other ash.

  As described above, according to the present invention, it is possible to provide a fluidized bed boiler ash treatment method and treatment apparatus that can effectively use fluidized bed boiler ash and simultaneously remove mercury in exhaust gas. .

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram which shows one Embodiment of the processing apparatus of the fluidized bed boiler ash which concerns on this invention. It is a whole block diagram which shows the modification of the processing apparatus of the fluid bed type boiler ash which concerns on this invention. It is a flowchart for demonstrating the processing method of the conventional fluidized bed boiler ash.

  Next, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an embodiment of a treatment apparatus for fluidized bed boiler ash according to the present invention. This treatment apparatus 1 collects exhaust gas G1 of a circulating fluidized bed boiler (hereinafter referred to as “boiler”) 2. The electric dust collector 3, the gas gas heater 4 for raising the temperature of the exhaust gas G 4 of the wet scrubber 5 with the heat held by the exhaust gas G 2 of the electrostatic dust collector 3, and the fly ash FA recovered by the electric dust collector 3 after adding alkali AL to the exhaust gas G 3 From the wet scrubber 5 that cleans the exhaust gas G3 while adding the slurry S1 of (boiler ash), the stirring tank 6 that adds and collects the collector Co to the slurry S2 discharged from the wet scrubber 5, and the stirring tank 6 The surface reformer 7 that modifies the surface of unburned carbon or the like contained in the fly ash FA by applying a shearing force to the slurry S3, and the slurry S4 from the surface reformer 7 Furthermore, a flotation machine 8 for adding a foaming agent B to generate bubbles to perform flotation, and a filter press 9 for obtaining unburned carbon UC by solid-liquid separation of the floss F from the flotation machine 8; , And a filtration separation device 10 for solid-liquid separation of the tail T from the flotation machine 8.

  The boiler 2 is installed for a coal-fired power plant or private power generation. The boiler C 2 is put into the boiler 2 together with limestone L for desulfurization and burned while flowing to generate steam. Since this boiler 2 has high adaptability to fuel and low environmental load, it is also suitable for direct combustion of biomass.

  The electric dust collector 3 is provided for recovering the fly ash FA in the exhaust gas G1 from the boiler 2. The electrostatic precipitator 2 preferably has a heat resistance of at least 150 ° C. or higher in order to recover heat from the exhaust gas G2 by the gas gas heater 4 at the subsequent stage. A bag filter can be used instead of the electric dust collector 3.

  The gas gas heater 4 is provided for heating the air taken in from the surroundings by the exhaust gas G2 discharged from the electrostatic precipitator 3 and using the high-temperature air heated by the gas gas heater 4 for raising the temperature of the exhaust gas G4 of the wet scrubber 5. . Instead of the gas gas heater 4, a heat recovery device, a reheater, a heat pipe, a Jungstrom (registered trademark) heat exchanger (manufactured by Alstom Co., Ltd.), or the like can be used.

The wet scrubber 5 cools the exhaust gas G3 with moisture or the like contained in the fly ash FA slurry S1 collected by the electric dust collector 3, collects fine powder contained in the exhaust gas G3, and wets the SO ₂ remaining in the exhaust gas G3. 5 is prepared for reacting with the alkali AL added in the preceding stage of 5 and Ca (OH) ₂ in the slurry S1 for desulfurization. As the alkali AL, potassium hydroxide, sodium hydroxide, or the like can be used.

  The agitation tank 6 is provided for adding a collection agent Co such as light oil to the slurry S2 from the wet scrubber 5 and agitating and mixing with the filtrate W ′ from the filtration / separation apparatus 10.

  The surface reformer 7 modifies the surface of unburned carbon or the like in the slurry S3 by applying a shearing force to the slurry S3 from the stirring tank 6.

  The flotation machine 8 adds the foaming agent B to the slurry S4 supplied from the surface reformer 7 to generate bubbles, causes the unburned carbon contained in the slurry S4 to adhere to the bubbles and floats up, and the slurry S4 Provided to separate unburned carbon from the. Above the flotation machine 8, an air supply device for supplying air for generating bubbles is provided.

  The filter press 9 is provided for solid-liquid separation of the floss F containing unburned carbon discharged from the flotation machine 8, and collects unburned carbon UC adsorbed with mercury on the cake side.

  The filtration / separation apparatus 10 is provided for solid-liquid separation of the tail T containing ash other than unburned carbon containing gypsum discharged from the flotation machine 8, and the ash A containing gypsum GY is recovered in the separated cake. Is done. The separated filtrate W ′ is reused in the stirring tank 6 or the like.

  Next, a treatment method according to the present invention using the fluidized bed boiler ash treatment apparatus 1 having the above configuration will be described with reference to FIG.

The boiler 2 is supplied with coal C as fuel and an appropriate amount of limestone L for desulfurization, and the coal C is burned while flowing. Thereby, SO ₂ produced by the combustion of coal C reacts with CaO produced from limestone L and is desulfurized as CaSO ₃ . The limestone L supplied here is not supplied excessively as in the prior art, but is set to an amount that balances with the amount of SO ₂ produced by the combustion of coal C. Further, mercury in the combustion gas is adsorbed to unburned carbon in the fly ash FA generated by the combustion of coal C.

  The exhaust gas G1 of the boiler 2 is removed by the electric dust collector 3, and water W is added to the recovered fly ash FA to form a slurry S1, which is then supplied to the wet scrubber 5. On the other hand, the exhaust gas G2 of the electrostatic precipitator 3 is introduced into the gas gas heater 4, and heat exchange with the exhaust gas G4 of the wet scrubber 5 is performed to raise the temperature of the exhaust gas G4. By recovering heat from the exhaust gas G2 in the gas gas heater 4, the amount of water evaporation in the wet scrubber 5 can be minimized. The exhaust gas G4 from the wet scrubber 5 is heated by the gas gas heater 4 and then released to the atmosphere as the exhaust gas G5.

After adding alkali AL to the exhaust gas G3 from the gas gas heater 4, the wet scrubber 5 is brought into contact with the slurry S1. Thereby, SO ₂ contained in the exhaust gas G3 becomes alkali sulfate (potassium sulfate, sodium sulfate, etc.) and dissolves in water in the wet scrubber 5, and quick lime contained in the fly ash FA reacts with water. The slaked lime generated in this manner and the SO ₂ remaining in the exhaust gas G3 react and desulfurize as described below to produce gypsum (CaSO ₄ .2H ₂ O). Also, gypsum is generated from CaSO ₃ generated by the boiler 2.
CaO + H ₂ O → Ca (OH) ₂
SO ₂ + Ca (OH) ₂ → CaSO ₃ · 1 / 2H ₂ O + 1 / 2H ₂ O
CaSO ₃ · 1 / 2H ₂ O + 1 / 2O ₂ + 3 / 2H ₂ O → CaSO ₄ · 2H ₂ O

  In the stirring tank 6, the collection agent Co is added to the slurry S2 discharged from the wet scrubber 5 and stirred. After the shearing force is applied to the slurry S3 in the surface reformer 7, the slurry is supplied to the flotation machine 8. . The reason why shear force is applied to the slurry S3 is to improve the flotation floatability by modifying the surface of unburned carbon or the like in the fly ash FA.

  Next, the foaming agent B is added to the flotation machine 8 and the flotation operation is performed. The floss F from the flotation machine 8 is solid-liquid separated by the filter press 9 and the unburned carbon UC adsorbing mercury Hg is removed. Collect and discard. On the other hand, the tail T from the flotation machine 8 is solid-liquid separated by the filtration / separation device 10, and the ash A containing gypsum GY is used as an admixture for cement. The filtrate W ′ dehydrated by the filtration / separation apparatus 10 can be supplied to the stirring tank 6 and reused.

  Next, a modified example of the fluidized bed boiler ash treatment apparatus according to the present invention will be described with reference to FIG.

  The fluidized bed boiler ash treatment device 21 includes a catalyst tower 22 for denitration between the electrostatic precipitator 3 and the gas gas heater 4, and a desulfurization device 23 and an activity between the gas gas heater 4 and the wet scrubber 5. The coke regeneration tower 24 is provided, and other components are the same as those of the processing apparatus 1 shown in FIG. Therefore, in the processing device 21, the same components as those of the processing device 1 are denoted by the same reference numerals, and description thereof is omitted.

  The catalyst tower 22 is provided to remove NOx remaining in the exhaust gas G2 from the electrostatic precipitator 3, and a titanium / vanadium catalyst or the like can be used.

  The desulfurization device 23 is provided to bring the exhaust gas G4 into contact with the active coke AC as an adsorbent, and to adsorb and remove SOx contained in the exhaust gas G4 by the active coke AC. SOx in the exhaust gas is adsorbed and removed by the activated coke AC as sulfuric acid, and when ammonia is injected into the exhaust gas G4, SOx is adsorbed as an ammonium salt. A trace amount of mercury contained in the exhaust gas G4 is also adsorbed and removed by the activated coke.

  The activated coke regeneration tower 24 is provided to regenerate the activated coke AC having a lowered activity, and desorbs adsorbed substances such as sulfuric acid, ammonium salt, and mercury by hot air to restore the activity. During heat regeneration, nitrogen gas is supplied to purge the desorbed material from the activated coke AC.

  In this processing device 21, NOx remaining in the exhaust gas G2 from the electrostatic precipitator 3 is removed by the catalyst tower 22, and then the exhaust gas G3 is introduced into the gas gas heater 4 to exchange heat with the exhaust gas G5 from the desulfurization device 23. Thereafter, SOx and mercury are removed by the desulfurizer 23. On the other hand, the exhaust gas G7 generated in the active coke regeneration tower 24 contains desorbed SOx, mercury, and the like. Alkali AL is added to the exhaust gas G7, and SOx contained in the exhaust gas G7 becomes alkali sulfate and dissolves in water in the wet scrubber 5. Further, the exhaust gas G8 from the wet scrubber 5 is returned to the inlet of the electrostatic precipitator 3. The exhaust gas G6 after heat exchange with the gas gas heater 4 is released to the atmosphere.

  The operation procedure of each apparatus after the wet scrubber 5 is the same as that of the processing apparatus 1, and also in this processing apparatus 21, the floss F from the flotation machine 8 is finally solid-liquid separated by the filter press 9. The unburned carbon UC adsorbed with mercury Hg is recovered and discarded, and the tail T from the flotation machine 8 is solid-liquid separated by the filtration / separation device 10 and the ash A containing gypsum GY is used as an admixture for cement. can do.

  In the above embodiment, the case where the ash discharged from the circulating fluidized bed boiler is effectively used and the mercury in the exhaust gas is removed from the boiler is described as an example. However, the present invention is not limited to the circulating fluidized bed type. The present invention can also be applied to other types of fluidized bed boilers.

DESCRIPTION OF SYMBOLS 1 Fluidized bed type boiler ash processing equipment 2 Circulating fluidized bed type boiler 3 Electric dust collector 4 Gas gas heater 5 Wet scrubber 6 Stirrer tank 7 Surface reformer 8 Flotation machine 9 Filter press 10 Filtration separator 21 Fluidized bed type boiler ash Treatment unit 22 Catalytic tower 23 Desulfurization unit 24 Activated coke regeneration tower AC Activated coke AL Alkali B Foaming agent C Coal Co Collection agent F Floss FA Fly ash G1 to G8 Exhaust gas GY Gypsum L Limestone T Tail UC Unburned carbon W Water W 'Filtrate

Claims (7)

Dust is removed from the exhaust gas from a fluidized bed boiler that burns coal, and boiler ash is recovered.
Water is added to the recovered boiler ash to form a slurry,
A method for treating fluidized bed boiler ash, comprising adding an alkali to a gas containing a volatile component in the exhaust gas of the fluidized bed boiler after dust removal and then performing wet cleaning while adding the slurry.   The method for treating fluidized bed boiler ash according to claim 1, wherein the gas containing a volatile component in the exhaust gas of the fluidized bed boiler is the exhaust gas itself of the fluidized bed boiler after the dust removal. .   The gas containing the volatile component in the exhaust gas of the fluidized bed boiler is a volatilization that is desorbed by heating the adsorbent after adsorbing the volatile component of the fluidized bed boiler after the dust removal to the adsorbent. The method for treating fluidized bed boiler ash according to claim 1, wherein the gas contains a sexual component.   4. The method for treating fluidized bed boiler ash according to claim 1, 2 or 3, wherein the slurry obtained by the wet cleaning is separated into unburned carbon and other ash by a flotation process. .   The fluidized bed boiler ash according to any one of claims 1 to 4, wherein the ash content other than the unburned carbon separated by the flotation method is used as an admixture for cement, and the unburned carbon is discarded. Processing method. A dust collector for recovering boiler ash from the exhaust gas of a fluidized bed boiler that burns coal;
Slurrying means for adding water to the boiler ash recovered by the dust collector to form a slurry;
A fluidized bed boiler ash comprising: a wet scrubber which is washed while adding a slurry generated by the slurrying means after adding alkali to a gas containing volatile components in the exhaust gas of the dust collector Processing equipment.   The apparatus for treating fluidized bed boiler ash according to claim 6, further comprising a flotation machine for separating the slurry discharged from the wet scrubber into unburned carbon and other ash.

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