JPH10128062A - Waste gas treating agent for incineration equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the discharge of dioxins from a municipal waste incineration equipment and the elution of a heavy metal from a fly ash collected from a waste gas by using a treating agent containing an adsorbent composed of a powdery hydrophilic inorganic porous material having carbon carried on the surface. SOLUTION: The absorbent used for the waste gas treating agent is formed from the one obtained by carrying carbon on the inorganic porous material having high specific surface area. The dioxins are effectively adsorbed thereon because of the wide carbon surface. As the inorganic porous material to be used, a hydrophilic material other than carbon such as silicic acid, aluminum silicate, magnesium silicate, aluminum hydroxide is exemplified and aluminum hydoxide obtained by drying and pulverizing an amorphous aluminum hydroxide waste generated in an Alumite(R)-treating process can be used. The inorganic porous material having >=50cm<2> /g to >=800cm<2> /g specific surface area measured by the BET method is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing generation of dioxins in exhaust gas discharged from an exhaust gas treatment step of a municipal waste incineration plant and elution of heavy metals from fly ash generated from the exhaust gas. It is. In addition, the said incineration equipment in this invention means an incinerator and a melting furnace.

[0002]

2. Description of the Related Art In recent years, environmental pollution by dioxins has been regarded as a problem. This is compared to other pollutants,
This is because the toxicity of dioxins is extremely high. For example, most toxic is said to strongly 2,3,7,8 four dioxin chloride (hereinafter, abbreviated as TCDD.) LD ₅₀ in guinea pigs is 2 [mu] g / kg. Furthermore, dioxins not only have a very strong acute toxicity as described above, but also have been confirmed to be potent carcinogens and teratogenic substances. For example, the TCD
In the case of D, 0.01 to 0.07 μg / kg / day
There is a report that it shows carcinogenicity even in such a small amount. Also, 1
It has been confirmed that administration of TCDD at a dose of 〜１０10 μg / kg to the mother of a pregnant rat causes malformation, and has been found to be a unique and highly teratogenic substance.

The sources of the above-mentioned dioxins include municipal solid waste incinerators, industrial processes such as steel mills and metal refining industries, exhaust gas from automobiles, chlorine bleaching processes in the paper parve industry, and chemical industrial products such as pesticides. And so on. Among these sources, dioxins generated from municipal solid waste incineration facilities are the largest in Japan.

In the case of municipal solid waste treatment plants, various organic substances and chlorides such as plastic, garbage, and wood are contained in the garbage. When these refuse are incinerated, some of the organic substances are not completely decomposed into carbon dioxide, and the unburned organic substances are discharged to an exhaust gas treatment step, which becomes a precursor of dioxins. On the other hand, chlorine in chloride is discharged as gaseous components such as chlorine gas and hydrogen chloride gas. It is said that these chlorine-containing gas components react with the above-mentioned dioxin precursor through a complicated reaction route to produce dioxins. In addition, metal salts such as chloride steel contained in fly ash blown up in the exhaust gas treatment process serve as a catalyst,
It is said that the production of dioxins is further promoted. Therefore, it is generally considered that unburned organic substances are converted into dioxin precursors in an incinerator, and dioxins are synthesized in a low-temperature region such as a boiler or a dust collector.

[0005] In Japan, the land area is small and the amount of waste generated is extremely large. Therefore, the incineration rate of general waste is higher than in Europe and the United States, and most of the general waste is landfilled after incineration. Therefore, Japan is considered to be a country with a large amount of dioxins generated worldwide. Incidentally, in Japan, about 48 million tons of general waste (1988) and about 310 million tons of industrial waste (1985) are discharged. In the year 2000, general waste was about 8,000
With 10,000 tons, industrial waste is expected to reach about 600 million tons. Of this, about 70% of general waste is incinerated and about 20% is directly disposed of. In addition, about 40% of industrial waste is recycled, about 30% is reduced in volume by incineration, etc., and is disposed of, and about 30% is directly disposed of at final disposal sites. As described above, it has been clarified that a large amount of dioxins may be generated when these general wastes and industrial wastes are incinerated. In the future, emission regulations for dioxins emitted from incineration facilities will be greatly strengthened.

[0006] As a countermeasure against dioxins in incineration facilities, currently considered methods are roughly classified into the following five (A) to (E). (A) Removal of causative substances in garbage. (B) Production suppression under combustion conditions. (C) Suppression of generation in heat recovery and cooling processes. (D) Suppression of generation and removal during exhaust gas treatment. (E) Detoxification of fly ash. Among these methods, the technologies that have been actively studied in recent years are:
(D) Generation suppression and removal in the exhaust gas treatment process. One of the first measures taken during the exhaust gas treatment process is to reduce the temperature of the dust collector. According to the dioxin generation prevention guidelines, the temperature of the dust collector is set to 250 to 280 ° C for the existing furnace and 200 for the new furnace.
It is shown to be below ℃. However, electric dust collectors, which have been widely used in existing incinerators, cannot reduce the temperature much, and it has been found that dioxins are generated by corona discharge. The system has a dust collector. Further, a method of adsorbing dioxins in exhaust gas using activated carbon or activated coke to reduce the emission of dioxins into the atmosphere has been attempted, and some of them have been commercialized. Furthermore, as a recent technology, it has been studied to oxidize dioxins by introducing an oxidizing agent or an oxidation catalyst in an exhaust gas treatment process. Further, it has been studied to inject a chemical such as H ₂ S, NH ₃ , and triethanolamine for suppressing the catalytic activity of fly ash in the exhaust gas treatment process. However, research on dioxin countermeasures has only just begun, and there is no completely established technology at present.

[0007] In addition to the above problems of dioxins, the problem of heavy metals has become a major environmental problem.
That is, cadmium (Cd), lead (Pb), chromium (Cr), mercury (Hg), arsenic (As), copper (Cu), and the like are included in color-printed paper and cellophane contained in garbage. Cadmium, lead, zinc (Z
n), chromium, mercury, arsenic, and the like, and by incineration of these, ash enriched with heavy metals is obtained. In incineration plants, this ash is increasingly collected in the form of main ash consisting of garbage and fly ash collected by bag filters. Although both the main ash and the fly ash contain heavy metals, heavy metals are particularly easy to elute in the fly ash. This is for the following reason. That is, in the refuse incineration plant, slaked lime or quick lime is blown in the middle of the exhaust path to capture hydrogen chloride gas generated during incineration. Since these are combined with hydrogen chloride gas to form calcium chloride, the concentration of hydrogen chloride gas in the exhaust gas can be reduced. However, since unreacted slaked lime and quick lime remain in the exhaust gas, fly ash collected from such an exhaust gas by a dust collector or the like becomes highly alkaline with a pH of 12 or more. Fly ash contains a high concentration of lead, and this lead has the property of becoming water-soluble as a plumbate under high alkalinity. Become. Therefore, in the refuse incineration plant, fly ash is mixed with cement, added with water, kneaded, cured and solidified and disposed of, or landfilled with main ash in order to prevent harmful metals from being eluted. . However, since the cement is alkaline, when a large amount of cement is added to such fly ash, the elution of lead is not suppressed. Therefore, there are various problems in the conventional treatment method of simply solidifying with cement, and secondary pollution may occur unless the use is limited.

[0008]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method for preventing the emission of dioxins from municipal waste incineration equipment and the elution of heavy metals from fly ash collected from exhaust gas. It is to provide.

[0009]

Means for Solving the Problems The present inventors have made intensive studies to solve such a problem, and as a result, have arrived at a method capable of achieving this object. That is, the present invention
An exhaust gas treating agent comprising an adsorbent composed of a powdery hydrophilic inorganic porous material having carbon supported on its surface,
And a method of separating and removing the adsorbent from exhaust gas after blowing the treating agent in an exhaust gas treatment step of an incineration facility.

The mechanism of dioxin removal by the exhaust gas treating agent according to the present invention will be described. As described above, dioxins generated in incineration facilities are organic chlorinated substances generated by reacting unburned organic substances with gaseous components containing chlorine such as chlorine gas or hydrogen chloride gas. These dioxins are extremely hydrophobic substances, and are known to be adsorbed by hydrophobic substances such as carbon and activated carbon. Therefore, to date, a method of adsorbing and removing dioxins generated from an incinerator using activated carbon has been widely studied. However, the fine pores of activated carbon are generally very small pores having a pore diameter of 20 ° or less, so that dioxins are hardly diffused and cannot exhibit sufficient adsorption ability. Also,
Since activated carbon itself is a lump of carbon, it has a very high flammability and may cause a dust explosion when blown into an exhaust gas treatment process. In addition, activated carbon is a very expensive chemical and the treatment cost is too high to be used as a waste treatment agent. On the other hand, the adsorbent for dioxins used in the treating agent of the present invention has a large carbon surface because it supports carbon on an inorganic porous material having a high specific surface area, and effectively adsorbs dioxins. be able to. This is the same principle as increasing the catalytic ability by supporting a catalytic substance on a porous substance. Furthermore, since the pore diameter of the inorganic porous material used in the present invention is mainly distributed in a region of 20 ° or more, dioxins are easily diffused, and dioxins are effectively adsorbed on the carbon surface. . In addition, the adsorbent used in the present invention contains a large amount of carbon in the pores of the nonflammable inorganic substance, so that chain combustion of carbon is prevented and dust explosion is unlikely to occur.

Next, the mechanism of stabilizing heavy metals by the exhaust gas treating agent according to the present invention will be described. The mechanism of stabilizing heavy metals by the exhaust gas treating agent of the present invention is based on the fact that the inorganic porous substance stabilizes adsorption of heavy metals. Low-boiling metals such as lead, cadmium and mercury evaporate from the incinerator and are discharged together with the exhaust gas. Most of the evaporated heavy metal is condensed or adsorbed on the fly ash surface when the fly ash in the exhaust gas is collected by an electric dust collector or a bag filter, and is collected together with the fly ash. However, these heavy metals adsorbed and collected by the fly ash ionize and dissolve in the water when the fly ash is exposed to water, so that secondary pollution occurs as it is. Since the inorganic porous material used in the present invention is a material having hydrophilicity, it can effectively adsorb ionized heavy metals. On the other hand, activated carbon, which is generally used as an adsorbent for dioxins, has a very strong hydrophobicity and cannot adsorb ionized heavy metals.
Furthermore, if the adsorbent used in the present invention is blown into the exhaust gas treatment step or disposed as a filter in the exhaust gas treatment step, not only can heavy metals be eluted from fly ash, but also the heavy metal vapor in the exhaust gas can be effectively removed. Can be collected.

As described above, the adsorbent used in the exhaust gas treating agent according to the present invention is a composite material of a hydrophilic inorganic porous substance and a hydrophobic activated carbon. It has an excellent property that it can simultaneously perform adsorption treatment with heavy metal ions of a substance.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The inorganic porous material used in the present invention will be described. The inorganic porous substance used in the present invention is a hydrophilic substance other than activated carbon, such as silicic acid, aluminum silicate, magnesium silicate, and aluminum hydroxide.
In addition, the ability to adsorb heavy metals depends on the specific surface area of the inorganic porous material, and the larger the specific surface area, the more the ability to stabilize heavy metals. In particular, an inorganic porous substance having a specific surface area of 50 m ² / g or more is preferable for effectively preventing elution of heavy metals, and a substance having a specific surface area of 100 m ² / g or more is more preferable. However, if the specific surface area is too large, it becomes bulky and handling becomes troublesome, so that the specific surface area is preferably 800 m ² / g or less. The inorganic porous material used in the present invention may be a synthetic product or a natural product. Synthetic products include synthetic silicic acid, synthetic aluminum silicate, synthetic magnesium silicate, synthetic aluminum hydroxide,
There are synthetic zeolites and the like. Activated clay as a natural product,
There are acid clay, allophane, bentonite, diatomaceous earth, natural zeolite, activated clay, and the like. A substance whose specific surface area is further increased by treating these substances with acid is also effective.

The specific surface area according to the present invention will be described below. The specific surface area referred to in the present invention is the BET of the nitrogen substitution method.
It is a value measured by the method. The BET method uses a catalyst or catalyst alone,
This is a very commonly used method for measuring the specific surface area of a porous substance such as zeolite. The BET method is a method in which gas molecules such as nitrogen are adsorbed on the surface of a substance, and the specific surface area is measured from the amount of the adsorbed nitrogen. As the type of gas molecules to be adsorbed, nitrogen, argon, or the like is used. In the present invention, the values are measured by a replacement method using nitrogen gas.

Next, a method for producing an adsorbent used in the treatment agent according to the present invention will be described. Various methods are conceivable as a method for producing the adsorbent. For example, a simple method in which an inorganic porous substance and carbon powder such as activated carbon are kneaded with water or a solvent, dried, and subsequently crushed may be used. However, the following method is most desirable in order to effectively support carbon inside the pores of the inorganic porous material. That is, first, the inorganic porous material is impregnated with an organic substance such as fats and oils, petroleums, proteins, and fats. By heat-treating such a substance, the impregnated organic substance is carbonized. As a method of carbonizing an organic substance, a method of steaming by heating the inorganic porous material impregnated with the organic substance as described above in a state where the oxygen source is intentionally cut off is desirable. In this case, a part of the organic matter evaporates when heated, and when this vapor is condensed in a cooling device and returned to the inorganic porous material again, which is called reflux, the organic matter is efficiently converted into carbon. And generation of gas can be prevented. However, such a steaming method requires a large-scale apparatus, so the efficiency is somewhat lowered.However, the organic substance is impregnated by heating the inorganic porous substance impregnated with the organic substance in the open state to partially burn the organic substance. It can also be carbonized. In this case, a general heating device such as an electric furnace, a rotary kiln, and an incinerator can be used as the heat treatment device. Inorganic porous materials impregnated with organic substances, such as activated clay waste used as an adsorbent in oil and fat refining processes and zeolite catalyst waste used in petroleum refining and cracking processes The use of such a method is a preferable method because the cost is low and the waste is effectively used. As described above, the treatment agent of the present invention can utilize waste generated in a fat or oil refining process or a petroleum refining process as an adsorbent, and is therefore more advantageous in cost than using activated carbon.

The method of using the treating agent of the present invention will be described below. The most common use of the treating agent of the present invention is to blow the treating agent in powder form into a flue of an exhaust gas treatment step of an incinerator. When blowing, it is more effective to blow simultaneously with an acidic gas remover such as slaked lime and other heavy metal stabilizers, or to mix and blow with them.
Further, the treating agent can be packed in a container in a powder state or in a molded state, and this can be disposed in an exhaust gas treatment step as a filter. Furthermore, fly ash collected from the exhaust gas after injecting the treating agent of the present invention into the flue gas of the exhaust gas treatment step, since heavy metals are stabilized, so long as an appropriate amount of treating agent is injected, Elution of heavy metals is prevented. By kneading the collected fly ash with water, the heavy metals can be more effectively stabilized.

[0017]

By using the waste treating agent of the present invention,
Dioxins discharged from incinerators for industrial waste and municipal waste can be reduced, and elution of heavy metals from fly ash recovered from exhaust gas can be prevented.

[0018]

EXAMPLES Examples of the present invention will be described below, but they do not limit the contents of the present invention.

[Example 1] Stalker type, hydrochloric acid treatment type
Is dry, dust collection is bag filter, gas emission
Is 5000Nm^Three/ Hr, discharge of fly ash is 20kg / h
The experiment was performed in the municipal solid waste incinerator which is r. Slaked lime (ratio
35m surface area^Two/ G special slaked lime (Okutama Industry Co., Ltd.)
Company name: Tamacalc), normal special name slaked lime is specific surface
Product is 15m ^Two/ G) and adsorbent (produced in oil and fat refining process)
Activated clay waste obtained by steaming)
As the treatment agent according to the present invention, the adsorption in the treatment agent
0.5, 1.2, 10, 20, 60% by weight
It was made to become. Acid gas remover in exhaust gas treatment process
Above incinerator of the type in which slaked lime is blown as a dry process
The treatment agent was replaced with slaked lime in the flue of the exhaust gas treatment process.
I blew it. The blowing rate is 20kg / hr
Was. In this case, the temperature at the cooling device outlet was 200 ° C.
Was. At this time, the dioxin
The emission concentration and the amount of fly
Heavy metals (Pb, Cd, Cr) from ash⁶⁺) Of elution amount
Table 1 shows the results measured by the Office Notification No. 13 method. Also,
As a comparative example, only the slaked lime was subjected to the exhaust gas treatment of the incinerator.
The results when the gas is blown into the flue of the process are also shown.

[0020]

[Table 1]

As is clear from Table 1, when the treating agent according to the present invention is blown into the flue of the exhaust gas treatment step of the incinerator, dioxins at the outlet of the electric precipitator are compared with the case where only slaked lime is blown. It can be seen that the emission concentration of methane is greatly reduced. Also, heavy metals from recovered fly ash,
In particular, it can be seen that the elution of lead is also effectively suppressed.

Claims (19)

[Claims] 1. A method for removing dioxins and heavy metals in exhaust gas from an incinerator, comprising an adsorbent comprising a powdery hydrophilic inorganic porous material having carbon supported on the surface and inside the pores. Exhaust gas treatment agent for stabilization of chemicals. 2. The exhaust gas treating agent according to claim 1, wherein the inorganic porous substance is at least one selected from silicic acid, aluminum silicate, magnesium silicate, and aluminum hydroxide. 3. The exhaust gas treating agent according to claim 2, wherein the inorganic porous substance is a synthetic substance. 4. An inorganic porous material comprising: treating clay minerals such as acid clay, activated clay, kaolin, bentonite, allophane, and diatomaceous earth; The exhaust gas treating agent according to claim 1, wherein the agent is a substance from which impurities such as are removed. 5. The exhaust gas treating agent according to claim 2, wherein the inorganic porous substance is aluminum hydroxide obtained by drying and pulverizing amorphous aluminum hydroxide waste generated in the alumite treatment step. 6. The exhaust gas treating agent according to claim 1, wherein the specific surface area of the inorganic porous substance measured by the BET method is from 50 m ² / g to 800 m ² / g. 7. The exhaust gas treating agent according to claim 1, wherein the pore diameter of the inorganic porous substance is mainly distributed in a region of 20 ° or more. 8. The adsorbent impregnates the inorganic porous substance with the organic substance and then heat-treats the organic substance to carbonize the organic substance present on the surface of the inorganic porous substance and inside the pores. The exhaust gas treating agent according to claim 1, which is obtained. 9. An adsorbent heat-treats an inorganic porous material impregnated with an organic material in a state where the supply of air from the outside is cut off or restricted, so that the surface of the inorganic porous material and the inside of the pores are formed. The exhaust gas treating agent according to claim 8, which is obtained by carbonizing an existing organic substance. 10. When the inorganic porous material impregnated with the organic material is subjected to heat treatment, the organic material is carbonized while the evaporated organic material is circulated and brought into contact with the inorganic porous material again to form a surface of the inorganic porous material. The exhaust gas treating agent according to claim 9, which is supported inside the pores. 11. An inorganic porous material impregnated with an organic material is heated or burned in an open air state or an air supply state, and finally carbon remains on the surface of the inorganic porous material and inside the pores. 9. The exhaust gas treating agent according to claim 8, wherein the organic substance is carbonized by stopping the heat treatment or the combustion in the step. 12. The exhaust gas treating agent according to claim 8, wherein the inorganic porous material impregnated with the organic material is activated clay after being used in a step of purifying fats and oils. 13. The exhaust gas treating agent according to claim 8, wherein the inorganic porous material impregnated with an organic material is a zeolite catalyst after being used in a petroleum refining process. 14. The method according to claim 1, further comprising mixing slaked lime.
14. The exhaust gas treating agent according to any one of items 13 to 13. 15. The exhaust gas treating agent according to claim 14, wherein the slaked lime has a specific surface area of 30 m ² / g or more. 16. The treatment agent contains 0.5% by weight of the adsorbent.
The exhaust gas treating agent according to claim 14, which contains at least 60% by weight or less. 17. The exhaust gas treating agent according to claim 1, which is blown into a flue of an exhaust gas treating step of a municipal solid waste incinerator, and the exhaust gas treating agent together with fly ash is collected by an electric dust collector or a bag filter. A method for removing dioxins from exhaust gas of an incineration plant, characterized in that the dioxins are separated from the exhaust gas by the method. 18. The exhaust gas treating agent according to any one of claims 14 to 16 is blown into a flue of an exhaust gas treating process of a municipal solid waste incinerator, and the exhaust gas treating agent is added together with fly ash to an electric dust collector or a bag filter. A method for simultaneously removing dioxins and acid gas from exhaust gas of an incineration plant, wherein the acid gas is separated from the exhaust gas. 19. The method according to claim 17 or 18, wherein after dioxins are removed or dioxins and acid gas are simultaneously removed, the dioxins are collected together with the exhaust gas treating agent in an electric precipitator or a bag filter. A method for treating fly ash in an incinerator, comprising stabilizing heavy metals by kneading the fly ash with water.