JP2017042709A - Treatment method for fluidized bed boiler ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reuse ash discharged from a fluidized bed boiler while achieving increase of use thereof at a low cost.SOLUTION: A treatment method for fluidized bed boiler ash is provided in which water is added to fly ash FA contained in an exhaust gas of a fluidized bed boiler for burning coal thereby forming slurry, unburned carbon UC is removed from the slurry, modified ash A1 which is obtained by solid-liquid separation of the slurry after removal of the unburned carbon UC, is cured, and thus, solidified modified ash A2 is obtained. The modified ash A2 can obtain a sufficient strength in reusing the ash as an earthwork material. After a surface of the unburned carbon or the like in the slurried fly ash FA is modified, the unburned carbon is removed from the slurry by floatation, whereby removal efficiency of the unburned carbon can be enhanced. Strength of the modified ash can be increased by adding sodium hydroxide solution and/or potassium hydroxide solution to the slurry after removal of the unburned carbon.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a coal ash regeneration process, and more particularly to a method for regenerating ash discharged from a fluidized bed boiler.

  Conventionally, it has been proposed to add an alkali activator such as lime to coal ash and regenerate it in large quantities as earthwork materials such as embankments and roadbed materials (for example, Patent Document 1).

  On the other hand, there are two types of boilers used in coal-fired power plants: pulverized coal combustion type and fluidized bed type. At present, the pulverized coal combustion type is the mainstream, but in recent years, the construction of a circulating fluidized bed type power plant that can use low-grade coal, biomass, etc. as fuel has also been promoted.

JP 2009-006250 A

  In the technique described in Patent Document 1 and the like, there is a problem that, in order to recycle coal ash as an earthwork material, the strength is insufficient and the addition of an alkali activator is indispensable, resulting in high operating costs. there were.

  In addition, the ash discharged from the fluidized bed boiler contains a large amount of unburned carbon compared to the ash from the pulverized coal combustion boiler, so the use is limited as a cement raw material and as a cement mixture. The process was tight.

  Therefore, the present invention has been made in view of the above-described problems in the prior art, and an object of the present invention is to reuse ash discharged from a fluidized bed boiler at low cost while expanding applications.

  As a result of extensive research, the present inventors have found that the above problems can be solved by regenerating fluidized bed boiler ash as an earthwork material among coal ash, and have made the present invention. . That is, in the method for treating fluidized bed boiler ash according to the present invention, water is added to the boiler ash contained in the exhaust gas of the fluidized bed boiler that burns coal to form a slurry, and unburned carbon is removed from the slurry. The modified ash obtained by solid-liquid separation of the slurry after removal of the unburned carbon is cured.

  According to the present invention, after removing unburned carbon, it is possible to obtain a modified ash having sufficient strength to be used as an earthwork material, for example, by curing at room temperature without adding an alkali activator. The operating cost can be kept low. Moreover, the apparatus which removes unburned carbon by making the conventional coal ash into a slurry can be used as it is.

  In the fluidized bed boiler ash treatment method, the solid-liquid separation can be performed with a filter press. Thereby, the water-powder ratio is reduced, the boiler ash is more closely adhered, and a denser and higher-strength earthwork material can be obtained.

  By adding sodium hydroxide and / or potassium hydroxide to the slurry after removing unburned carbon, the strength of the modified ash can be further increased without increasing the operating load of the apparatus used for solid-liquid separation. .

  By removing unburned carbon from the slurry by a flotation process, the removal efficiency of unburned carbon can be improved.

  It is preferable that the boiler ash is recovered from the exhaust gas of a circulating fluidized bed boiler having a relatively high unburned carbon content because the strength of the earthwork material can be further increased.

  As described above, according to the present invention, fluidized bed boiler ash can be reused at low cost while expanding its application.

It is the schematic which shows an example of the processing apparatus for enforcing the processing method of the fluid bed type boiler ash which concerns on this invention.

  Next, an embodiment of a fluidized bed boiler ash processing method according to the present invention will be described with reference to FIG.

  FIG. 1 shows an example of a treatment apparatus for carrying out the method for treating fluidized bed boiler ash according to the present invention. The treatment apparatus 1 is an exhaust gas from a fluidized bed boiler (not shown, hereinafter referred to as “boiler”). A dissolution tank 2 for adding water W to a fly ash FA, which is boiler ash recovered from the slurry, and a stirring tank 3 for adding a collector Co to the slurry S1 discharged from the dissolution tank 2 and stirring the slurry S1; A surface reformer 4 that modifies the surface of unburned carbon or the like contained in the fly ash FA by applying a shearing force to the slurry S2 from the stirring tank 3, and further foams in the slurry S3 from the surface reformer 4 Flotation machine 5 which adds agent B to generate bubbles and performs flotation, filter press 6 to obtain unburned carbon UC by solid-liquid separation of floss F from flotation machine 5, and flotation machine Reforming tail T from 5 by solid-liquid separation Composed of a filter press 7 to obtain the A1.

  The boiler is installed for a coal-fired power plant or private power generation, and fuel coal is introduced into the boiler together with limestone for desulfurization and burned while flowing to generate steam. The coal combustion ash and limestone are recovered as boiler ash. Both boiler ash generated in the circulating fluidized bed type and pressurized fluidized bed type contains more calcium and sulfur than pulverized coal type coal ash. Although there is a lot of unburned carbon, its characteristics are considered to be close.

  The dissolution tank 2 is provided for adding the water W to the fly ash FA recovered from the exhaust gas from the boiler to generate the slurry S1.

  The agitation tank 3 is provided to generate the slurry S2 by adding a collection agent Co such as light oil to the slurry S1 from the dissolution tank 2 and agitation and mixing with the filtrate FI from the filter press 7.

  The surface reformer 4 modifies the surface of unburned carbon or the like in the slurry S2 and finely pulverizes particles by applying a shearing force while adding a hydrophobic agent to the slurry S2 from the stirring tank 3. To produce slurry S3.

  The flotation machine 5 adds the foaming agent B to the slurry S3 supplied from the surface reformer 4 to generate bubbles, and causes the unburned carbon contained in the slurry S3 to adhere to the bubbles and float to the slurry S3. Is provided for separation into floss F containing unburned carbon and tail T containing fly ash from which unburned carbon has been removed. The flotation machine 5 is provided with an air supply device (not shown) that supplies air for generating bubbles.

  The filter press 6 is provided for solid-liquid separation of the floss F discharged from the flotation machine 5, and collects unburned carbon UC to the cake side.

  The filter press 7 is provided for solid-liquid separation of the tail T containing ash other than unburned carbon including gypsum discharged from the flotation machine 5, and the modified ash A1 is recovered in the separated cake. The separated filtrate FI is reused in the stirring tank 3 or the like.

  Next, a processing method according to the present invention using the processing apparatus 1 having the above configuration will be described with reference to FIG.

  First, fly ash FA is supplied to the dissolution tank 2 and slurried with water W. Next, in the stirring tank 3, the collecting agent Co is added to the slurry S1 discharged from the dissolution tank 2 and stirred, and the pH is adjusted to 5 or more and 10 or less by supplying sulfuric acid or carbon dioxide gas. Next, after applying a shearing force to the slurry S <b> 2 in the surface reformer 4, the obtained slurry S <b> 3 is supplied to the flotation machine 5. Here, the application of the shearing force is performed in order 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 5 to perform the flotation operation. The floss F from the flotation machine 5 is solid-liquid separated by the filter press 6, and the unburned carbon UC can be used as fuel. . On the other hand, the tail T from the flotation machine 5 is solid-liquid separated by the filter press 7 to obtain the modified ash A1. Further, the filtrate FI dehydrated by the filter press 7 can be supplied to the stirring tank 3 and reused.

  Here, when the tail T is subjected to solid-liquid separation, an alkali additive AL such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) may be added. The reason why the alkali additive AL is added is to increase the strength of the modified ash finally obtained. Such an alkali additive AL may be added to, for example, the slurry-like tail T before solid-liquid separation, or the aqueous solution may be sprayed using a washing process by the filter press 7. The alkaline water that has been subjected to solid-liquid separation can be reused again as part of the alkali additive AL.

  The modified ash A1 discharged from the filter press 7 is cured to obtain a modified ash A2. Curing may be, for example, 10 ° C. or more at room temperature, and is preferably performed for 3 days or more. One day may be sufficient if the temperature is higher. The obtained modified ash A2 can be used as civil engineering and port materials such as aggregates, roadbed materials, backfilling materials, etc. after being crushed and classified as necessary.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

  First, the 1st Example of the processing method of the fluidized bed boiler ash which concerns on this invention using the processing apparatus 1 which has the said structure is described, referring FIG.

  In this example, water W was added to fly ash FA having the properties shown in Table 1 to produce slurry S1 having a fly ash FA concentration of 20% by mass.

  Next, 5% by weight of light oil of fly ash FA was used as the collecting agent Co, and the collecting agent Co was added to the slurry S1 and stirred to produce a slurry S2. Next, 0.82% by weight of fly ash FA MIBC (methyl isobutyl carbinol) is used as the foaming agent B, and the foaming agent B is added to the slurry S3 whose surface of the slurry S2 has been modified and floated. The operation was performed to recover the froth F containing unburned carbon UC and to obtain the tail T. Next, the tail T was subjected to solid-liquid separation with a filter press (set pressure 7 kN) to obtain modified ash A1, which was then cured at 20 ° C. for 2 weeks to produce modified ash A2.

  As a result, Floss F having an unburned carbon UC amount of 67.4% by mass and modified ash A2 having an unburned carbon UC amount of 12.7% by mass were obtained. The amount of floss F was 18% by mass of the whole slurry discharged from the flotation machine 5, and the tail T was 82% by mass.

  Table 2 shows the properties of the modified ash A2 (Example 1) obtained by crushing the tail T after curing. The particle size of fly ash FA was 2.36 mm or less, whereas the modified ash A2 had a larger particle size due to solidification, and was in accordance with the Japanese Industrial Standard (JIS A 5001) specified for crushed stone for roads. It was found that the particle size distribution of S-20 was generally matched.

  In addition, when the modified ash was produced | generated like Example 1 using the pulverized coal combustion ash shown in Table 1, the modified ash did not solidify and the particle size became 645 micrometers or less.

  Next, among the modified ash A2 obtained as Example 1, one having a particle size of about 20 mm is placed on a scale, and is sandwiched between two points along the diameter of the modified ash A2. A point load was applied, and the strength when the modified ash A2 was destroyed (JSCE Standard “High Strength Fly Ash Artificial Aggregate Loading Test Method (JSCE-C 505-2001))” was measured. The results are shown in Table 3.

  In addition, as Comparative Example 1, 40 ° C. water W was added to fly ash FA so that fly ash FA: water W was 1: 4, kneaded for 30 minutes, and then solidified by filtration using a filter press. Prepared the body.

  As Comparative Example 2, cement and water were added to fly ash FA so that the cement was 10% by weight and the water was 60% by weight. After kneading for 30 minutes, the mixture was poured into a mold and solidified. A solidified body was prepared.

  From Table 3, it was found that the modified ash A2 had a higher crushing strength than Comparative Example 1 in which unburned carbon was not removed, and was comparable to the cement solidified body of Comparative Example 2. This also indicates that removal of unburned carbon is more effective for boiler ash generated in a circulating fluidized bed containing more unburned carbon than a pressurized fluidized bed.

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

  First, a sodium hydroxide (NaOH) solution or a potassium hydroxide (KOH) solution is added to the tail T obtained in the same manner as in the first embodiment, kneaded for 30 minutes, and then filtered with a filter press 7. Two kinds of solidified bodies (Examples 2 and 3) were produced. Next, after crushing these at 20 ° C. for 2 weeks (maintaining the moisturized state), the crushing strength was measured. The concentration of sodium hydroxide and potassium hydroxide in the tail T was adjusted to 0.5N. Table 4 shows the measurement results.

  From Table 4, the modified ash treated by adding potassium hydroxide of Example 3 (KOH-treated product) has the highest crushing strength, and then the modified ash treated by adding sodium hydroxide of Example 2 (NaOH treated product) was found to have a higher crushing strength than the modified ash (water treated product) treated with the water of Example 1. Further, even when a sodium hydroxide solution or a potassium hydroxide solution was added, the filterability in the filter press 7 was not so different from that when water was added. In addition, when water glass was added to the tail T to obtain a 10% water glass solution, filtration could not be performed.

  Furthermore, when the modified ash was produced in the same manner as in Example 2 and Example 3 using pulverized coal combustion ash, the modified ash did not solidify. When 10% of calcium hydroxide was added to pulverized coal combustion ash to produce modified ash in the same manner as in Example 2, the strength could not be measured due to the soft state although solidified.

  As described above, according to the present embodiment, after the fly ash discharged from the fluidized bed boiler is slurried and the surface of unburned carbon in the fly ash is modified, a foaming agent is added. The modified ash is obtained by flotation, obtaining the modified ash from the tail obtained by solid-liquid separation, and curing at room temperature. Therefore, the fly ash discharged from the fluidized bed boiler can be reused as earthwork material.

  Further, the modified ash obtained in this way has the same strength as the cement solidified product obtained by adding cement to fly ash, and the strength is further increased by adding an alkali additive to the tail. Since it can raise, sufficient intensity | strength as earthwork material can be obtained.

  In the above embodiment, the unburned carbon UC is removed from the slurry S3 using the flotation process. However, the fly ash FA is stirred and mixed with water and a non-aqueous solvent having a lighter specific gravity than water. It is also possible to use a method using other water, such as separating the unburned carbon.

1 Treatment device (for fluidized bed boiler ash) 2 Dissolution tank 3 Stirring tank 4 Surface reformer 5 Flotation machine 6, 7 Filter press A1, A2 Modified ash AL Alkaline additive B Foaming agent Co Collection agent F Floss FA Fly ash FI Filtrate T Tail UC Unburned carbon S1-S3 Slurry W Water

Claims (5)

  It is obtained by adding water to boiler ash contained in the exhaust gas of a fluidized bed boiler that burns coal to form a slurry, removing unburned carbon from the slurry, and solid-liquid separation of the slurry after removing the unburned carbon A method for treating fluidized bed boiler ash characterized by curing the modified ash.   The method for treating fluidized bed boiler ash according to claim 1, wherein the solid-liquid separation is performed by a filter press.   The method for treating fluidized bed boiler ash according to claim 1 or 2, wherein sodium hydroxide and / or potassium hydroxide is added to the slurry after removal of unburned carbon.   The method for treating fluidized bed boiler ash according to claim 1, 2 or 3, wherein unburned carbon is removed from the slurry by a flotation process.   The method for treating fluidized bed boiler ash according to any one of claims 1 to 4, wherein the boiler ash is recovered from exhaust gas of a circulating fluidized bed boiler.

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