JP2000202395A - Treatment of ash collected by two-step-in-series type bag filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating ashes collected by a bag filter and by which elution of heavy metals can easily be prevented while the addition amount of a chemical agent is suppressed to the minimum and the running cost and the landfilling amount can be lowered. SOLUTION: In a flue gas treatment method wherein at first fly ashes are collected by passing a flue gas, which is emitted by incinerating wastes or melting and solidifying wastes and which contains incinerator fly ashes or melted fly ashes, through a bag filter 6 in the prior stage and then acidic gases in the flue gas are absorbed and removed by spraying slaked lime to the resultant flue gas from which the fly ashes are removed and passing the flue gas through a bag filter 8 in the posterior stage, about 10 wt.% concentration of a slurry is produced by adding an iron salt 15 of 0.1% or higher based on conversion into Fe to fly ashes 11 under stirring and water as a pH adjusting agent, to fly ashes collected in the bag filter in the posterior stage, and the pH value of the slurry is controlled to be 6-12 by adding an iron salt while stirring the slurry.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating ash collected in a bag filter, and more particularly, to a method of connecting incinerated fly ash and molten fly ash discharged from a waste incineration facility and a melting and solidification facility in series.
The present invention relates to a method of treating collected ash collected by a bag filter at a stage.

[0002]

2. Description of the Related Art Conventionally, in a facility for incinerating or melting and solidifying waste, there is only one bag filter, and the generated incineration fly ash and molten fly ash are collected, and slaked lime is blown upstream of the bag filter. In addition, a reaction tower is provided and sprayed with slaked lime slurry to simultaneously absorb and remove hydrogen chloride and sulfur oxides, which are acidic gases. This requires only one bag filter, and is advantageous in terms of equipment cost and space.
This is a widely used technique. In the case of a bag filter, a layer of fly ash and slaked lime is formed on the filter cloth surface, and high-efficiency dust collection by the layering and close solid-gas contact when the combustion exhaust gas passes through the layered layer cause the acidic gases hydrogen chloride and sulfur. The advantage is that the absorption and removal of the oxide can be performed simultaneously.

However, when attempting to remove hydrogen chloride and sulfur oxides with high efficiency, the amount of slaked lime to be added is equivalent to [the number of moles of slaked lime added to the moles of hydrogen chloride and sulfur oxide flowing into the bag filter. , The molar ratio is HCl / Ca (OH) ₂ = 1/2 and the sulfur oxide is SO
x / Ca (OH) ₂ = 1) or more. For example, considering removal of 90% or more, about 2 equivalents of slaked lime are added to hydrogen chloride and sulfur oxide of the acid gas. It was necessary. Therefore, most of the collected ash from the bag filter contained a large amount of unreacted slaked lime and exhibited alkali having a pH of 12 or more. This alkaline fly ash is easy to elute the lead compounds contained in the fly ash,
In this case, the landfill standard value was exceeded in most cases. This is because the lead compound dissolves as hypochlorite ion (HPbO ₂ ) when the pH value becomes 12 or more.

[0004] Even when cement is solidified as an intermediate treatment of the alkaline fly ash, lead often exceeds the landfill standard value, and even if a liquid chelate is added, especially when a low boiling heavy metal such as molten fly ash is added. When a certain amount of lead is concentrated and the lead content is high, the amount of the expensive liquid chelating agent to be added increases, and there is a disadvantage that the running cost is increased. When an iron salt (one of ferrous sulfate, ferric sulfate, ferric chloride, ferric polysulfate and the like or a mixture thereof) is added to the alkaline fly ash, the iron is added for the original purpose. Before the dissolution prevention effect due to the coprecipitation effect of the salt, the salt is consumed in a large amount to adjust the pH to the optimal pH range of 8 to 11, resulting in an increase in running costs and landfill disposal. This is due to unreacted slaked lime contained in the alkaline fly ash in a large amount. In addition, when adjusting the pH of the alkaline fly ash with an acid such as sulfuric acid, in addition to a large amount of addition, since the unreacted slaked lime is a solid, there is a place where the center of the unreacted slaked lime does not react in a wet state. Even if the pH is once adjusted to a predetermined range, the pH often returns to the alkali side again, making it difficult to adjust the pH.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and prevents harmful heavy metals, particularly lead, contained in incineration and molten fly ash from being eluted by a simple and minimal additive chemical. It is an object of the present invention to provide a method for treating ash collected in a bag filter, which can reduce the running cost and reduce the amount of landfill disposal.

[0006]

According to the present invention, an exhaust gas containing incinerated fly ash or molten fly ash generated by incineration or melting and solidification of waste is firstly filtered by a bag filter in the first stage. Through which the fly ash is collected and then sprayed with slaked lime to the exhaust gas after the fly ash is collected and passed through a bag filter at a later stage to absorb and remove the acidic gas in the exhaust gas. To the fly ash collected by the bag filter described above, an iron salt of 0.1% or more in terms of Fe per fly ash and the collected ash collected by a subsequent bag filter as a pH adjuster are added, and water is added to wet fly ash. This is a method for treating bag filter ash, which is characterized by kneading in a state.

Further, in the present invention, waste gas incinerated or melted ash generated by incineration or melting and solidification of waste is first passed through a bag filter in the former stage to collect fly ash.
Then, fly ash is sprayed with slaked lime to the exhaust gas after collection, and then passed through a bag filter at the subsequent stage.In a method of treating exhaust gas to absorb and remove acidic gas in the exhaust gas, the fly ash collected by the bag filter at the preceding stage is removed. Then, water is added to prepare a slurry liquid of about 10 wt%, iron salt is added with stirring, and subsequently, ash collected by a bag filter at the subsequent stage is added to adjust the pH value of the slurry liquid to 6 to 12. This is a method for treating ash collected by a bag filter. In the treatment method, it is preferable to use one of ferrous sulfate, ferric sulfate, ferric chloride, or ferric polysulfate or a mixture thereof as the iron salt.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, in a facility for incinerating or melting and solidifying waste, first, as a method for collecting generated incineration fly ash or molten fly ash, a facility in which two bag filters are connected in series (Japanese Patent Publication No. 7-103980). Publications). In other words, the main function of the former bag filter is to collect fly ash containing low-boiling heavy metals generated from the incinerated material or solidified material. Sprayed lime in the form of powder or slurry is sprayed between the bag filters of the subsequent stage, and the absorption and removal of hydrogen chloride and sulfur oxides, which are acidic gases, by laminating slaked lime formed on the filter cloth surface of the latter bag filter Is the main function. By doing so, of course, the dust collected by the bag filter at the previous stage contains heavy metals, but has no unreacted slaked lime (when a small amount of slaked lime is added mainly for the purpose of protecting the bag filter) However, the dust collected from the bag filter at the subsequent stage is separated into dust that contains little heavy metal but contains much unreacted slaked lime.

[0009] By doing so, the collected dust in the former stage can be used in an optimum pH range of 6 to 12 (for example, JP-A-8-3903).
No. 8), it is possible to start from the acidic side and easily adjusted by adding an alkali. The present invention is characterized in that "reactive alkali ash", which is a second-stage bag filter ash, is used as the alkaline agent. By using this "reactive alkali ash" for the intermediate treatment of fly ash in the previous stage,
Since it is not necessary to add a new alkali to the ash treatment, it is possible to reduce the running cost and the amount of landfill disposal. In addition, this “reactive alkali ash” slightly absorbs CO ₂ in the exhaust gas and indicates a pH of 12 units lower than the pH of slaked lime, and the pH adjustment has a buffering effect on the amount of “reactive alkali ash” added. It has been found that it is easy to adjust to an optimum pH value.

On the other hand, the "reacted alkali ash" contains a large amount of unreacted alkali and is effective even at high alkalinity. When a liquid chelate is added, the concentration of heavy metals is very low. Elution could be prevented by kneading in a wet state by adding a small amount of 0.1%. The details of the principle of making heavy metals in waste insoluble by the present invention are unknown, but iron salts and "reactive alkali ash"
It is considered that the alkali component acts to form a precipitate of iron hydroxide, into which heavy metals in the ash are taken. The mechanism of incorporation is the adsorption of iron hydroxide of heavy metals in ash,
Substitution with the iron hydroxide crystal lattice Fe ion is considered.

Next, the present invention will be described with reference to the drawings. FIG. 1 is a flow process diagram of a gasification and melting plant incorporating the method for treating bag filter collected ash of the present invention. In FIG. 1, waste is first introduced into a gasification furnace, partially burned and gasified, and a gasification product is introduced into a swirling melting furnace 2 and burns at a high temperature. Is discharged. On the other hand, the combustion exhaust gas containing the molten fly ash is heat-recovered sequentially through the boiler 3, the air preheater 4, and the economizer, and then introduced into the dust-collecting bag filter 6 at the preceding stage to collect the molten fly ash. The exhaust gas from which the molten fly ash has been removed is slaked lime powder 7
Is added to the latter-stage de-HCl and SO ₄ bag filter 8 to collect the reacted alkali ash, and then discharged from the chimney 9.

The molten fly ash collected by the bag filter 6 at the former stage is stored in a storage tank 11, and the reactive alkali ash collected by the bag filter 8 at the latter stage is stored in a storage tank 12.
The stored molten fly ash is treated with iron salt 1 in the treatment tank 13.
5. The treatment is performed by the treatment method of the present invention in which a reaction alkali ash and water are added and kneading treatment is performed to obtain an intermediate treatment ash 18.
On the other hand, the remaining reaction alkali ash is
The chelating agent 17 and water are added and the mixture is kneaded to obtain an intermediate ash 19.

[0013]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. Example 1 Shredder dust (combustible debris generated when cutting grass) was burned at a high temperature in the gasification and melting furnace plant shown in FIG. 1, and the first-stage bag filter collection ash generated when gasification and melting was performed. "Reactive alkaline ash" of the second stage bag filter ash
Various tests were performed by using. Table 1 shows the chemical composition of the raw ash.
Table 2 shows the results of the dissolution test of raw ash according to Notification No. 13 of the Environment Agency.

[0014]

[Table 1]

[0015]

[Table 2]

The first-stage bag filter collected ash exhibits weak acidity because slaked lime is not added, and Cd, Pb, Cu,
Zn, was concentrated at a high concentration. The “reacted alkali ash” contained a large amount of unreacted slaked lime, exhibited alkalinity of pH 12, and had a very small heavy metal concentration because heavy metals were almost completely removed by the first-stage bag filter. From the results of the dissolution test of this raw ash, the ash collected by the first-stage bag filter was Hg, P
b, Cd, exceeds the landfill reference value, and Zn, Cu
Was also eluted at a high concentration. In addition, the elution of "reactive alkali ash" slightly eluted Pb, but was within the landfill standard value. While stirring the 10% slurry liquid of the first-stage bag filter collected ash, ferric polysulfate [@Fe ₂ (OH) _n (SO
₄ ) _{3-n / 2} ｝ _n ] is 7.25% per ash (0.1% in terms of Fe).
8%), 14.5% (1.6% in Fe), 29%
(3.2% in terms of Fe), followed by the addition of "reactive alkali ash", and the pH value at a stable place was set at the "set pH value".
And The amount of “reactive alkali ash” added and the “set pH”
FIG. 2 shows the relationship between the "values".

Polysulfur having a set pH value in the range of pH 6 to 12
Ferric acid [｛Fe_Two(OH)_n(SO _Four)_{3-n / 2}｝_n〕as well as
The amount of "reactive alkali ash"
A processing test was performed. Table 3 shows the standard values for landfill
Table 4 shows examples of the added amounts. Set pH value
In all cases of pH 6-12, heavy metal elution value is detected
The result of clearing the limit value or landfill standard value was obtained.
Was. From Table 3, each ferric polysulfate [@Fe_Two(OH)_n
(SO_Four)_{3-n / 2}｝_n] To the amount, "reactive alkali ash"
May be added in the amount of ± 50%. Addition of “reactive alkali ash”
It turns out that the pH can be adjusted easily because of the range of the amount
did.

[0018]

[Table 3]

[0019]

[Table 4]

Example 2 A test was performed in the same manner as in Example 1 except that ferrous sulfate heptahydrate was added as an iron salt to the ash. While stirring the 10% slurry liquid of the first stage bag filter collected ash,
Ferrous sulfate heptahydrate (FeSO ₄ .7H ₂ O)
% (0.8% in Fe conversion), 8% (1.6 in Fe conversion)
%) And 16% (3.2% in terms of Fe), followed by the addition of "reactive alkali ash", and the pH value at a stable place was set as the set pH value. FIG. 4 shows the relationship between the “reacted alkaline ash” and the set pH value. Relative amount of setting pH value in the range of pH6~12 ferrous heptahydrate sulfate (FeSO ₄ · 7H ₂ O) and "reaction alkaline ash", performed ash treatment test in the same manner as in FIG. 3 Was. Ferrous sulfate heptahydrate (FeSO ₄・
7H ₂ O) was added by adding an aqueous solution obtained by adding 2 parts by weight of water to 1 part by weight and sufficiently kneading in a wet state by further adding water. Table 5 shows the amount of the elution that cleared the landfill standard value, and Table 6 shows the examples.

In all cases where the set pH value was pH 6 to 12, a result was obtained in which the elution value of the heavy metal was sufficiently below the detection limit value or the landfill standard value. Table Each sulfate from 5 Ferrous heptahydrate _{(FeSO 4 · 7H 2 O)} " react alkaline ash" for weight may in amount of ± 50%, "the reaction alkaline ash"
It has been found that the pH can be easily adjusted because of the range of the amount added.

[Table 5]

[0022]

[Table 6]

Example 3 First-stage bag filter ash generated when municipal waste (municipal waste) was incinerated in a stoker-type incineration plant.
Various tests were performed using the "reacted alkali ash" of the ash collected from the stage bag filter. The chemical composition of the raw ash is shown in Table 7, and the results of the raw ash elution test according to the Environment Agency Notification No. 13 are shown in Table 8.

[0024]

[Table 7]

[0025]

[Table 8]

The ash collected in the first-stage bag filter exhibits neutrality because slaked lime is not added, and Cd, Pb, Cu, Z
n, was concentrated at a high concentration. "Reactive alkali ash"
The unreacted slaked lime was contained in a large amount and exhibited alkalinity of pH 12, and heavy metals were almost completely removed by the first-stage bag filter, so that the heavy metal concentration was very small. From the results of the dissolution test of this raw ash, the ash collected by the first-stage bag filter was Pb, Cd,
Exceeded the landfill standard value, and Zn and Cu were also eluted at a high concentration. The elution of "reactive alkali ash" was within the reference value for landfill, although Pb was slightly eluted. While stirring a 10% slurry liquid of the collected ash from the first-stage bag filter, ferric polysulfate [{Fe ₂ (OH) _n (SO ₄ ) _{3-n / 2} ｝ _n ] was added at 7.25% per ash. (0.8% in Fe), 14.5%
(1.6% in Fe conversion), 29% (3.2% in Fe conversion)
%), Followed by “reactive alkali ash”,
The pH value at the stable place was set as the set pH value. FIG. 5 shows the relationship between the “reacted alkaline ash” and the set pH value.

Polysulfur having a set pH value in the range of pH 6 to 12
Ferric acid [｛Fe_Two(OH)_n(SO _Four)_{3-n / 2}｝_n〕as well as
The amount of "reactive alkali ash"
A processing test was performed. Table 9 shows the reference values for landfill
Table 10 shows examples of the added amounts. Set pH
In all cases where the pH was between 6 and 12, the elution value of heavy metals was detected.
The result of clearing the output limit value or landfill standard value is obtained.
Was done. From Table 10, each ferric polysulfate [@Fe_Two(O
H)_n(SO_Four)_{3-n / 2}｝_n] To the amount "reaction alkali
"Ash" may be added in an amount of ± 50%.
Since there is a wide range of addition, pH adjustment can be performed easily.
found.

[0028]

[Table 9]

[0029]

[Table 10]

Example 4 "Reactive alkali ash" shown in Tables 1 and 2 had a landfill standard value cleared, but diethyldithiocarbamic acid (C
₂ H _{5) 2} NCS ₂ - was treated test by liquid chelating agent having a functional group. A liquid chelating agent was added to "reactive alkali ash" in an amount of 0.01 to 0.1% / ash and kneaded. In addition, the liquid chelating agent was diluted and added to humidified water. The next day, a dissolution test was performed according to the Environment Agency Notification No. 13 method. Table 11 shows the fillings, and the addition of a liquid chelating agent at 0.03% / ash or more showed an elution-suppressing effect.

[0031]

[Table 11]

[0032]

As described above, according to the conventional method, a large amount of heavy metals and a large amount of unreacted slaked lime are mixed in the collected ash. And the amount of landfill disposal has increased accordingly. According to the present invention, by using the “reactive alkali ash” of the latter-stage bag filter used for the exhaust gas treatment for the treatment of the dust collection ash at the previous stage of the in-line two-stage bag filter, the pH can be newly increased.
Without adding an alkali agent as a regulator, and because of the buffering effect of "reactive alkali ash" on pH adjustment to unreacted slaked lime, pH adjustment is easy, and by treating in an optimum pH range, iron salt The addition amount was also small, and the running cost and the amount of landfill disposal could be reduced.

[Brief description of the drawings]

FIG. 1 is a flow diagram of a gasification and melting plant incorporating the method of the present invention.

FIG. 2 is a graph showing the relationship between the amount of reaction alkaline ash added and the set pH value in the example.

FIG. 3 is a route diagram showing a procedure of an ash treatment test.

FIG. 4 is a graph showing the relationship between the amount of reaction alkali ash added and a set pH value in Example 2.

FIG. 5 is a graph showing the relationship between the amount of reaction alkaline ash added and the set pH value in Example 3.

[Explanation of symbols]

1: gasifier 2: turning melting furnace, 3: boiler, 4: air preheater, 5: economizer 6: dust collecting bag filter, 7: slaked lime powder, 8: de HCl, bag filter for SO ₄ , 9: chimney, 11, 12: ash storage tank, 13, 14: treatment tank, 15: iron salt, 16: water, 17: chelating agent, 1
8, 19: intermediate treated ash

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinya Abe 11-1 Haneda Asahimachi, Ota-ku, Tokyo Inside Ebara Works Co., Ltd. (72) Inventor Kazuyuki Inoue 11-1 Haneda Asahi-cho, Ota-ku, Tokyo Stock Company EBARA F-term (reference) 4D002 AA02 AA19 AA28 AB01 AC04 BA02 BA03 BA14 CA01 CA11 DA05 DA12 DA14 DA22 DA66 DA70 GA02 GA03 GB06 GB08 GB09 HA10 4D004 AA37 AA46 AC05 BA02 CA12 CA15 CA28 CA29 CA34 CA35 CC03 CC06 CC10 CC12 DA

Claims (3)

[Claims] 1. Exhaust gas containing incinerated fly ash or molten fly ash generated by incineration or melting and solidification of waste is first passed through a bag filter at a preceding stage to collect fly ash, and then fly ash is collected. In a method of treating exhaust gas in which slaked lime is sprayed on the subsequent exhaust gas and passed through a bag filter at a later stage to absorb and remove acidic gas in the exhaust gas, fly ash collected by the bag filter at the former stage is added to the fly ash with Fe 0.1% or more iron salt in conversion,
A method for treating ash collected from a bag filter, comprising adding ash collected by a bag filter at a later stage as a pH adjuster, adding water, and kneading the ash in a wet state. 2. Exhaust gas containing incinerated fly ash or molten fly ash generated by incineration or melting and solidification of waste is first passed through a bag filter at a preceding stage to collect fly ash, and then fly ash is collected. In the exhaust gas treatment method of spraying slaked lime onto the subsequent exhaust gas and passing it through a subsequent bag filter to absorb and remove the acidic gas in the exhaust gas, water is added to the fly ash collected by the preceding bag filter to add 10 wt. % Of a slurry liquid, and iron salt is added thereto with stirring, and subsequently, ash collected by a bag filter at the subsequent stage is added to adjust the pH value of the slurry liquid to 6%.
A method for treating ash collected from a bag filter, wherein 3. The iron salt comprises ferrous sulfate, ferric sulfate,
3. The method of claim 1, wherein one of ferric chloride and ferric polysulfate or a mixture thereof is used.