JPH0752006B2 - How to treat municipal waste incineration ash - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for treating incinerated ash of municipal waste, and more specifically, the incinerated ash of municipal waste is subjected to melting treatment to form slag, reduced melting, and discharge treatment. Together with a method for reducing NO _x .

[Conventional technology]

Municipal solid waste was conventionally disposed of by landfill, but it has become difficult to secure land for landfill, and it is now incinerated and then incinerated ash is disposed of. However, the incineration of garbage produces about 10% of incinerated ash, and even the site for landfill disposal of ash is becoming tight. In addition, environmental problems such as the scattering of finely divided ash, the leaching of heavy metals, and the unpleasant odor caused by unburned substances have occurred during the landfill disposal of ash.

Therefore, a method is adopted in which waste incineration ash is melted and treated to reduce the volume at the time of landfill, at the same time prevent molten metal leaching of powder, and decompose unburned materials to achieve environmental protection at once. .

In that case, an arc furnace or a burner furnace is often used. However, when such high temperature heating is performed in the atmosphere, a large amount of NO _X gas is generated, and secondary pollution in the environment is often generated.

2-5% of unburned carbohydrates in the incineration ash
It is known that it contains a carbon source, which reacts with air in the melting process of ash to form a reducing atmosphere, and can maintain a sufficiently reducing atmosphere from the viewpoint of mass balance. However, these carbon sources are vaporized by thermal decomposition prior to the melting of the ash, and there is a problem in maintaining the reducing atmosphere on average on the period until the melting of the ash.

[Problems to be Solved by the Invention]

The present invention, in the melting of refuse incineration ash using plasma,
It is intended to provide a method for completely melting a refuse incineration ash while suppressing generation of NO _X generated under a high temperature oxidizing atmosphere.

Further, the present invention provides a method for completely maintaining the inside of the furnace in a reducing atmosphere throughout the process of forming the molten slag of ash as described above.

[Means for Solving the Problems]

The present invention, when melting the municipal waste incineration ash with a plasma torch, always adds a carbon source or a carbohydrate source, which is more than the amount oxidized by the amount of air supplied, separately to the incinerator ash melting treatment furnace, and reduces it. A method for treating municipal waste incineration ash, which is characterized by melting the incineration ash in a neutral atmosphere.

In this case, the carbon source or the carbohydrate source may be added to the relatively low temperature part in the melting furnace on average over time.

Note that coke, coal, charcoal, etc. can be used as the carbon source, and waste such as combustible waste and sewage sludge can be used as the carbohydrate source.

[Action]

When a plasma furnace is used to heat at high temperature in the atmosphere, NO _X is generated by the following reaction.

However, ΔG ^O : Free energy change (cal / mol) T: Absolute temperature (K).

When obtaining the equilibrium partial pressure from these equations NO _X NO _X at 1600 ° C. vicinity required slag melt obtained Figure 2 is several thousand ppm.

On the other hand, when a carbon source or a carbohydrate source such as combustible waste or sewage sludge is charged into the plasma furnace and burned, the atmospheric O ₂
Reacts with the carbon source and the carbohydrate source together with the water in the incinerated ash according to the following equation to form a reducing atmosphere.

n _O2 O ₂ ＋ ncC ＋ n _H2O H ₂ O → m _CO CO ＋ m _CO2 CO ₂ ＋ m _H2 H ₂ ＋ m _H2O H ₂ O …… (3) n _O2 O ₂ ＋ n _Cel (C ₆ H ₁₀ O ₅ ) n ＋ n _H2O H ₂ O → m _CO CO ＋ m _CO2 CO ₂ ＋ m _H2 H ₂ ＋ m _H2O H ₂ O (4) In the reaction system of these reactions, the water gas reaction of the following equation is established.

CO + H ₂ O = CO ₂ + H ₂ ΔG ^O = −8600 + 7.65T (5) If equations (3) or (4) and (5) are combined,
The concentration of each component in the reaction system when the supply amount of each substance in the reaction system of formula (3) or (4) is given is uniquely determined.

For example, in an incinerator ash melting furnace for municipal solid waste, which uses 20 Nm ³ / h of air as plasma gas, the water content is about 10% during the melting process.
When coke is added to the ash prepared as above, the atmospheric components in the furnace change as shown in FIG. That is, about 6k
A reducing atmosphere is formed by adding more than g / h of coke.

NO _x generated once by the following reaction under reducing atmosphere
Is reduced.

The NO _X concentration in the atmosphere shown in FIG.
Obtained from equation (7) and shown in FIG. Such high concentration of NO _X in an oxidizing atmosphere is significantly reduced.

As described above, in the high-temperature melting of municipal waste incineration ash, adding a carbon source such as coke, coal, charcoal, etc., or a carbohydrate source such as combustible waste, sewage sludge, etc., forms a reducing atmosphere and suppresses the generation of NO _X. Although it can be done, it is necessary to devise it in actual implementation.

That is, when the carbon source or the carbohydrate source is mixed with the refuse incineration ash and supplied to the melting furnace, the carbon source or the carbohydrate source reacts with oxygen in the furnace or thermally decomposes in the process of melting the ash to reach the slag. In some cases, the gas is exhausted to the outside of the melting furnace and the inside of the furnace cannot be completely maintained in a reducing atmosphere.
Since the purpose of this method is to melt and incinerate the refuse incineration ash, a reducing atmosphere must be maintained during the whole process.

That is, in the present invention, ash is added near the highest point in the furnace where the ash should be melted, and a carbon source or a carbohydrate source is continuously provided around the furnace or at a relatively low temperature part such as an inlet from the feeder. The reducing gas is added and the atmosphere in the furnace is filled with the reducing gas for all the time when the melting furnace is in operation.

〔Example〕

Municipal solid waste incineration ash was processed using the municipal solid waste incineration ash melting furnace (output 250 KW, processing capacity 200 kg / h) using the plasma torch shown in Fig. 1. In FIG. 1, the incineration ash melting furnace 5 is supplied with municipal waste incineration ash from the raw material supply port 1, is heated by the plasma torch 6, and the molten incineration ash 8 is accumulated at the furnace bottom and discharged from the molten ash extraction port 7. To be done. The exhaust gas is dedusted by the cyclone 9, cooled in the cooling tower 10 and discharged.

The NO _X concentration in the exhaust gas was measured while preheating the melting furnace with compressed air of 20 Nm ³ / h as plasma gas with an output of 180 KW 4
000 ppm NO _X was detected. In the atmosphere, CO and H ₂
Was not detected.

Therefore, a coke with a water content of 10% was introduced from the hopper 2 through the gate 3 at an addition rate of 10 kg / h, charged into the melting furnace 5 with the feeder 4, and pyrolyzed. As a result, the gas partial pressure in the atmosphere was
The NO _x concentration in the exhaust gas was reduced to 50 ppm with 15% CO and 5% H ₂ .

Example 2 In the same melting furnace as in Example 1, the melting furnace was operated with an output of 180 KW and compressed air of 20 Nm ³ / h as plasma gas, and dried to obtain 10 kg of municipal solid waste incineration ash having a water content of 20% every 5 minutes. The continuous melting process was performed at the feed rate.

At that time, in the comparative example, coke having a water content of 10% was uniformly mixed and added to the incineration ash at an addition rate of 20 kg / h.

On the other hand, in the examples, the same coke was added at an addition rate of 0.5 kg every 1.5 minutes between additions of incinerated ash so that the coke was always located at the charging port of the feeder 4.

FIG. 5 shows the results of continuous sampling and analysis of NO _X components in the exhaust gas in Comparative Example and Example.

In the Example, the NO _X concentration in the exhaust gas is uniform between 30 and 60 ppm, whereas in the Comparative Example, the NO _X concentration is high as a whole,
High concentrations of 100 ppm or more were occasionally detected.

The gas partial pressure in the atmosphere of this example was 27% CO, H ₂
Was 18%, and H ₂ O and CO ₂ were 12% and 5%, respectively.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY According to the present invention, NO _X generated during volume reduction of incinerated ash of municipal waste can be significantly reduced.

Further, there is an effect that a carbon source, combustible waste, sewage sludge or the like can be effectively used to obtain a high-calorie exhaust gas.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional side view showing a municipal solid waste combustion ash melting furnace using a plasma torch as an example to which the present invention is applied, and FIG. 2 is a graph showing the relationship between temperature and NO _X partial pressure,
4 and 5 are graphs showing the relationship between the added amount and the partial pressure, and FIG.
The figure is a time chart of the embodiment. 1 ... Raw material supply port 2 ... Hopper 3 ... Gate 4 ... Feeder 5 ... Incinerator ash melting furnace 6 ... Plasma torch 7 ... Molten ash outlet 9 ... Cyclone 10 ... Cooler

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Hayashi 2-3-2 Uchisaiwaicho, Chiyoda-ku, Tokyo Kawasaki Steel Co., Ltd. Tokyo headquarters (72) Inventor Kentoshi Yamazaki 1-1-1, Uchisaiwaicho, Chiyoda-ku, Tokyo No. 3 in Tokyo Electric Power Co., Inc. (56) Reference JP-A-60-152813 (JP, A)

Claims (3)

[Claims] 1. When melting and treating municipal waste incineration ash with a plasma torch, a carbon source or a carbohydrate source, which is more than the amount oxidized by the amount of air supplied, is always added separately to the incinerator ash melting treatment furnace. A method for treating municipal waste incineration ash, which comprises melting the incineration ash in a reducing atmosphere. 2. The method for treating municipal waste incineration ash according to claim 1, wherein a carbon source or a carbohydrate source, which is separately added, is added to a relatively low temperature portion in the melting furnace on an average time basis. . 3. The method according to claim 1 or 2, wherein the separately added carbon source or carbohydrate source is one or more selected from coke, coal, charcoal, combustible waste, and sewage sludge.