JP4834719B2 - Waste disposal method - Google Patents

Description

  The present invention relates to a method for treating waste such as fly ash generated when melting general waste and industrial waste in a melting furnace, for example.

When the waste is melted, neutralization is performed by bringing slaked lime into contact with the exhaust gas in order to remove acidic gas in the exhaust gas. Generally, the acidic gas is hydrogen chloride, and calcium chloride is generated by a neutralization reaction with slaked lime.
Therefore, the fly ash generated by the melting treatment of the waste generally consists of neutralized products and soot of acid gas and slaked lime in the exhaust gas, and most of the neutralized products are calcium chloride. The dust contains scattered matter, alkali components, and heavy metals.
When fly ash having such a composition is directly put into a melting furnace as waste, calcium chloride is decomposed to generate hydrogen chloride, and a large amount of slaked lime is required to neutralize the hydrogen chloride. This increases the load on the equipment. Furthermore, there is a possibility that corrosion of equipment and piping is promoted by increasing the concentration of hydrogen chloride.

  In order to solve the above problems, there has been proposed a method in which fly ash is washed with water to remove a water-soluble component such as a neutralized product of acid gas and slaked lime and an alkali component and then melt-processed.

JP-A-9-192625 JP 2000-144271 A JP 2003-10814 A JP 2003-320336 A JP 2004-298777 A

  In the method of washing fly ash with water, it is necessary to dissolve heavy metals by using acid-added water as washing water because heavy metals such as lead cannot be removed simply by washing with water. However, this requires a large amount of acid to be used, resulting in high processing costs. When washing with water to which an acid has been added, many components in fly ash are eluted in the washing water, so There is a problem that the amount of residue generated by the processing step of the waste cleaning liquid after processing increases.

As a means for solving the above-described conventional problems, the present invention adds 1 to 10 parts by mass of washing water to 1 part by mass of waste, thereby washing the waste with water to remove water-soluble components and washing. A water washing process for adjusting the chlorine concentration of the residue to 4 to 10% by mass with respect to the solid content, and gasifying harmful metals contained in waste as a chloride by melting the washing residue adjusted for the chlorine concentration . and a melting step of removing, in which fly ash generated from the molten process is to provide a method of processing waste is circulated in the washing step as part of the waste. The waste that is the subject of the present invention is generally fly ash. In the washing process, the washing water is preferably added in an amount of 1 to 10 parts by mass with respect to 1 part by mass of the waste. Also in the above washing residue, in order to adjust to 4 to 10 wt% of chlorine concentration of the solid content may perform melting treatment in terms of the addition of a predetermined amount of chlorine-rich product. In this case, it is desirable to use fly ash as the high chlorine content.

[Action]
When waste such as fly ash is washed with water, water-soluble components such as alkali components and neutralized products of acid gas and slaked lime contained in the fly ash are eluted into water and removed. As described above, most of the neutralized product is calcium chloride.

  In the water washing process, by adjusting the mixing ratio of washing water and waste (fly ash) appropriately, the residual amount of the neutralized product is adjusted, and the chlorine concentration in the residue after washing is determined as the solid content. It adjusts to 4-10 mass% with respect to. Or after removing the said neutralization product excessively at a water-washing process process, you may adjust a chlorine concentration to 4-10 mass% with respect to solid content by adding a high chlorine content to a washing residue anew. It is desirable to reuse fly ash as a high chlorine content.

When the waste whose chlorine concentration is adjusted to 4 to 10% by mass with respect to the solid content is melt-treated in this way, harmful metals such as lead in the waste are gasified as highly volatile chlorides. Removed. In the case of waste whose chlorine concentration is less than 4% by mass with respect to the solid content, there is a shortage of chlorine to completely convert harmful metals into chlorides, and the removal rate of harmful metals decreases, while the chlorine concentration is low. When it exceeds 10 mass% with respect to solid content, there exists a possibility that an installation, piping, etc. may be corroded by excess chlorine.
The slag generated by the melting treatment of the waste does not substantially contain harmful metals, and can be used as cement aggregate or roadbed material.

〔effect〕
In the present invention, hazardous metals in the waste are removed by gasification during the melting process as a highly volatile chloride without using an acid, so that the waste can be processed at a low processing cost and melted. Slag generated by processing can also be reused.

The present invention is described in detail below.
〔waste〕
The waste targeted by the present invention includes incineration ash and fly ash generated when heat treatment such as incineration, thermal decomposition, melting, etc. is performed on general waste and industrial waste, or sludge and pulverization generated from a wastewater treatment process Examples include fine powder generated from the process and the separation process, and fumes generated from the incinerator. For example, the fly ash is collected from the melting furnace by a dust collector. Examples of the dust collector include a gravity dust collector, an inertia dust collector, a cyclone, a bag filter, and an electric dust collector.

Alkaline components contained in the above waste include slaked lime, calcium chloride, caustic soda, caustic potash, sodium carbonate, potassium carbonate, etc., mainly alkali metal and alkaline earth metal compounds such as sodium and potassium, and heavy metals are lead. Zinc, cadmium, chromium, cobalt, copper and the like are exemplified. The heavy metal is contained in the waste as a simple substance or a compound.
Fly ash, which is a kind of waste, contains a large amount of about 48% by mass of calcium chloride, which is a main component of a neutralized product of acid gas and slaked lime.

  Examples of the acid gas source contained in the waste include organic chlorine compounds such as trichlorethylene and dioxin, inorganic chlorine compounds such as sodium chloride and calcium chloride, and sulfur compounds such as sulfur, sulfate and sulfite. Generates hydrogen chloride and sulfurous acid gas from sulfur or sulfur compounds.

[Washing process]
In the present invention, the waste is washed with water. Specifically, the waste is put into a washing tank equipped with a stirrer, and water is injected, and stirring and washing are performed. The neutralized product, alkali component, or acid gas source contained in the waste is substantially removed by the washing process.

  In the water washing treatment step, the chlorine concentration of the washing residue is adjusted to 4 to 10% by mass with respect to the solid content. For that purpose, washing water is added in an amount of 1 to 10 parts by mass with respect to 1 part by mass of the waste. Alternatively, after excessively removing the neutralized product containing chlorine from the waste, a predetermined amount of high-chlorine content such as calcium chloride, magnesium chloride, fly ash is added again to adjust the chlorine concentration of the cleaning residue to the solid content. It adjusts to 4-10 mass% with respect to.

  After the water washing treatment, solid-liquid separation is performed by solid-liquid separation means such as a centrifugal separator, a filter press, a vacuum dehydrator or the like. In the case of adding the above-described high chlorine content, it is usually added to a washing residue which is a solid phase (including slurry) after solid-liquid separation.

[Melting process]
The washing residue (solid phase) subjected to the solid-liquid separation after the water washing treatment is melted in a melting furnace. The heat source of the melting furnace is roughly divided into a method using fossil fuel such as heavy oil and coke and a method using electricity. A method using fossil fuel includes a rotary kiln method, a coke bed method, or a surface melting method, and a method using electricity includes an arc method and a plasma method.

During the melting process, harmful metals such as lead contained in the cleaning residue react with chlorine contained in the cleaning residue to become highly volatile chlorides, which are gasified and discharged together with fly ash from the melting furnace.
The discharged fly ash is circulated in the washing process and merged with other waste or washed with fly ash alone. If desired, a part of the fly ash is added to the washing residue as described above. Used to adjust the chlorine concentration of the cleaning residue. Furthermore, the cycle in which the discharged fly ash is combined with other wastes and washed with water, the chlorine concentration is adjusted, and the melting treatment is performed again can be repeated many times.

  As described above, in the melting treatment, harmful metals such as lead in the cleaning residue react with chlorine in the cleaning residue to form a highly volatile chloride and are gasified and removed. Thus, the chlorine concentration in the washing residue is adjusted to 4 to 10% by mass with respect to the solid content. The basis for this is shown in FIG. FIG. 1 is a graph showing the relationship between the concentration of chlorine contained and the volatilization rate (removal rate) of lead by melting treatment for fly ash containing 0.4 mass% of lead. According to FIG. 1, a volatilization rate of about 95% by mass or more is ensured when the contained chlorine concentration is 4% by mass or more, and the volatility is 100% by mass and the lead is almost completely obtained when the contained chlorine concentration is 10% by mass or more. Removed. Therefore, when the contained chlorine concentration exceeds 10% by mass, the effect of removing lead is saturated, and when the contained chlorine concentration is higher than that, there is a possibility that equipment, piping, etc. are corroded.

Since the slag generated by the melting process contains almost no harmful metal such as lead, it can be effectively used as a cement aggregate or a roadbed material.
Furthermore, since the waste cleaning liquid generated by the water washing process contains toxic metals, the pH is made alkaline and removed as hydroxide sludge, or after appropriate post-treatment such as passing through an ion exchange membrane. Release into the river.

Examples of the present invention will be described below, but the present invention is not limited to the examples.
FIG. 2 shows an apparatus system used for the processing of the present invention. In the apparatus system shown in the figure, wastes such as fly ash are transferred by a conveyor 1 and put into a water washing tank 2. The waste is washed with water.

The contents of the tank 2 after the water washing treatment are sent to the centrifugal dehydrator 6 by the pump 5, and centrifugal dehydration is performed. The dehydrated cleaning residue is introduced into the melting furnace 9 after adjusting the chlorine concentration in the chlorine adjusting tank 11.
Drainage discharged from the centrifugal dehydrator 6 is introduced into the wastewater treatment facility 8 from the drainage channel 7.

In the melting furnace 9, the cleaning residue is melted, and fly ash generated in the melting process is collected by the dust collector 10. Examples of the dust collector 10 include a bag filter and a cyclone.
The collected fly ash is circulated and put into the water washing tank 2 or a part thereof is circulated into the chlorine adjusting tank 11 and added to the washing residue after centrifugal dehydration to adjust the chlorine content. .

Specific examples of the processing method of the present invention will be described below.
As waste, fly ash generated by melting treatment of industrial waste was used. The fly ash was subjected to elemental analysis by fluorescent X-ray analysis to obtain the elemental composition. The results are shown in Table 1.

<Washing process>
The fly ash was washed with water by the water washing tank 2. The amount of washing water at this time was set to 10 parts by mass with respect to 1 part by mass of fly ash, and stirring and washing were performed at room temperature for 60 minutes.
After the washing treatment, the contents were dehydrated by the centrifugal dehydrator 6 and the washing residue was put into the melting furnace 9 to perform the melting treatment.
The washing residue was sampled and dried by heating at 110 ° C. for 2 hours, and the dried product was subjected to elemental analysis by fluorescent X-ray analysis. The results are shown in Table 2.

  According to Table 2, 5.1% by mass of chlorine and 0.6% by mass of lead are contained with respect to the solid content of the cleaning residue. Therefore, according to this specific example, the chlorine concentration of the cleaning residue is in the range of 4 to 10% by mass with respect to the solid content, so that adjustment of the chlorine concentration in the chlorine adjusting tank 11 is unnecessary. Moreover, when Table 1 and Table 2 are compared, chlorine is reduced from 28.0% by mass to 5.1% by mass and sodium, an alkali component, is reduced from 5.3% by mass to 0.7% by mass by the water washing treatment. In addition, it is observed that potassium decreases from 1.6% by mass to 0.8% by mass.

FIG. 3 shows a ratio (distribution rate) in which each component contained in the fly ash is distributed into the cleaning waste water and the cleaning residue in the cleaning process.
Referring to FIG. 3, it can be seen that most of chlorine and alkali components that cause corrosion of equipment and piping are eluted and removed in the waste water. Moreover, since lead is an amphoteric metal, it is recognized that it partially elutes in alkaline wastewater (usually pH 11 to 12.5).
Specific examples in the case of actual melting processing are shown below. In this specific example, a mixture of plastic, paper, wood, shredder dust, and sludge is used as waste, and the kneaded product obtained by kneading the waste and the cleaning residue at a solid content of 34: 1 mass ratio is subjected to a melting treatment. I did it. The melting process was performed at 1200 ° C. for 120 minutes.
Table 3 shows the elemental composition of the incineration residue (ash) when the waste used in this specific example was incinerated at 600 ° C. for 3 hours.

The melt was taken out from the melting furnace 9 and then subjected to water granulation to form a small slag.
The component distribution ratio between the slag and the exhaust gas in the melting process is shown in FIG.
Referring to FIG. 4, it can be seen that about 95% by mass of lead is volatilized as a gas and the residual rate in the slag becomes extremely low.
Tables 4 and 5 show the results of the dissolution test (Notification No. 46 of the Environment Agency in 1991) and the soil content test (Notification No. 19 of the Ministry of the Environment in 2003) for the above slag.

Table 4 and Table 5 show that both the dissolution test and soil content test for the slag are much lower than the standard values, and the slag can be safely used for landfill treatment or as cement aggregate or roadbed material. confirmed.
Furthermore, as a semi-reference example, the result of conducting a soil content test on lead contained in the slag generated when only the cleaning residue was melted without kneading the waste was 80 mg / kg, and the standard value was The result was significantly lower.

  The treatment process of the specific example was repeated 20 times by circulating fly ash generated from the melting treatment process to the water washing treatment process. Table 6 shows the relationship between the number of circulations and the lead concentration in the slag generated from each treatment process (measured by a soil content test).

  The reference value of the soil content for lead is 150 mg / kg or less as shown in Table 5, and according to Table 6, it becomes a stable value after the number of circulations of 10 and does not depend on the number of circulations. It is recognized that a lead standard value of 150 mg / kg or less is achieved in the quantity test.

  The treatment method of the present invention is simple and low-cost, can suppress corrosion of equipment and piping, and since the discharged slag is stable and hardly contains harmful metals such as lead, it can be used effectively. Available on top.

It is the graph which showed the relationship between the chlorine content and the volatilization rate (removal rate) of lead by melt processing. It is a figure explaining the apparatus system used for the process of this invention. It is a graph which shows the distribution rate of each component by a washing process. It is a graph which shows the distribution rate of each component by melting of a kneaded material.

DESCRIPTION OF SYMBOLS 1 Conveyor 2 Water washing tank 3 Water supply path 4 Stirrer 5 Pump 6 Centrifugal dehydrator 7 Drainage path 8 Wastewater treatment facility 9 Melting furnace 10 Dust collector 11 Chlorine adjustment tank

Claims (4)

By adding 1 to 10 parts by mass of washing water to 1 part by mass of waste, the waste is washed with water to remove water-soluble components and the chlorine concentration of the washing residue is 4 to 10% by mass with respect to the solid content. A water-washing process to adjust to,
A melting treatment step of gasifying and removing harmful metals contained in the waste as chloride by melting the cleaning residue with adjusted chlorine concentration,
A waste treatment method, wherein fly ash generated from the melting treatment step is circulated to the water washing treatment step as a part of the waste.   The waste treatment method according to claim 1, wherein the waste is fly ash.   In order to adjust chlorine concentration to 4-10 mass% with respect to solid content, the said residue is melt-processed after adding the predetermined amount of a high chlorine content. The waste disposal method described. The waste treatment method according to claim 3 , wherein the high chlorine content is fly ash.