JP3490221B2 - Method for producing molten solid from fly ash generated during sludge incineration - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to sludge as soluble phosphorus fertilizer, which uses fine powder in soot dust as a raw material when collecting and treating soot dust generated when incinerating sewage sludge in a fluidized bed furnace. The present invention relates to a method for producing a melt-solidified body.

[0002]

2. Description of the Related Art In a sewage treatment plant, soot dust in waste gas discharged when incinerating sewage sludge generated by sewage treatment in a fluidized bed furnace is generally a gas cyclone dust collector, an electric dust collector, a bag filter. Etc. or by cleaning with a wet gas scrubber.

Apart from wet dust collection, fly ash collected by dry dust collection is conventionally humidified to prevent scattering, or kneaded with cement for stabilization. After it is applied, it is often dumped in a landfill site and disposed of in landfill.

In recent years, however, it has become difficult to secure landfill disposal sites for incinerated ash and fly ash with the increase in incineration of general waste and industrial waste. Therefore, incineration ash and fly ash are subjected to treatments such as firing and melting and solidification to be used as construction materials for research in various fields.

In the step of incinerating sewage sludge in a fluidized bed furnace, classification is performed by utilizing the flow velocity of exhaust gas. That is,
Most of the earth and sand contained in the sludge is carried out of the furnace as soot dust and separated from the exhaust gas and collected. Furthermore, the large-grained sand and fluidized sand remaining in the furnace are gradually pulverized due to heat history and carried out of the furnace.Therefore, a large amount of earth and sand is captured as fly ash from the ash content of organic components generated by combustion. It

[0006]

When the waste such as sewage sludge and combustible construction waste materials is incinerated in a fluidized bed furnace, soot dusts are collected and treated in fly ash. Heavy metals are often contained in the ash content, and dioxins are also attached in some cases.

Therefore, fly ash is often not suitable for landfilling to the extent that it is humidified to prevent it from scattering, and it is necessary to detoxify and stabilize the entire amount of soil and sand. Such a treatment requires a large amount of cost and requires securing landfill sites.

On the other hand, since fly ash generated when incinerating sewage sludge in a fluidized bed contains a large amount of phosphorus components, the present inventor first adjusted the components of fly ash to form a molten ash. Proposed to produce phosphorus fertilizer and return it to green farmland, and filed a patent application in Japanese Patent Application No. 8-145833. According to this method, fly ash can be used as a raw material to produce fused phosphorus fertilizer effective as a phosphate fertilizer, and fly ash can be effectively utilized.

However, sediment is mixed in the sewage, and the sewage sludge generated in the sewage treatment step also contains the sediment. Since the content of such earth and sand greatly differs depending on whether it is fine weather, rainy weather, or groundwater level, the composition of fly ash also varies. Table 1 shows an example of fluctuations in the composition of fly ash.

[0010]

[Table 1]

As is clear from Table 1, the contents of SiO ₂ and P ₂ O ₅ in fly ash both fluctuate greatly. Therefore, when manufacturing the fused phosphorus fertilizer using fly ash, not only is it troublesome to adjust the components, but it is not necessary to use Si that is unnecessary as the fused phosphorus fertilizer.
Since it contains a large amount of O ₂ , it contains a large amount of Ca as a component regulator.
As a result of requiring O, MgO, P ₂ O _5, etc., there is a problem that the cost becomes high.

Therefore, an object of the present invention is to solve the above-mentioned problems, to collect fly ash generated when incinerating sewage sludge in a fluidized bed furnace, and to adjust its components to produce a soluble phosphorus fertilizer. In doing so, the composition of the fly ash can be adjusted stably regardless of the amount of fly ash and the composition of the composition. Another object of the present invention is to provide a method capable of producing a melted and solidified sludge as the above.

[0013]

The method of the present invention utilizes the flow rate of the exhaust gas in the process of collecting and treating soot dust generated when incinerating sludge, and the fly ash particles of the soot dust are partially classified. The critical particle size (D ₇₅ ) of 75% is 5 to 2
By setting the particle size in the range of 0 μm and classifying, coarse particles of D ₇₅ or more are captured, and then fine powder of less than D ₇₅ is collected, or the above dust is captured by a dust collector, and the captured dust is scattered. The ash particles are subjected to wind classification by setting the critical particle size (D ₇₅ ) at which the partial classification efficiency is 75% within the range of 5 to 20 μm, whereby coarse particles of D ₇₅ or more and fine particles of less than D ₇₅ are obtained. When the fine powder of less than D ₇₅ collected in this way is melted and then solidified by cooling, CaO, MgO is added to the fine powder.
And / or a salt thereof is mixed as a component of the melt-solidified body so that the alkaline earth component is 40% or more and the soluble magnesium is 12% or more, and phosphoric acid and / or a salt thereof is melt-solidified. As a body component, a mixture of solute phosphoric acid is added to 17% or more, and the mixture is melted at a temperature of 1350 ° C. or higher and then cooled and solidified to produce a sludge melt solidified body as a fused phosphorus fertilizer. It has a special feature.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of the present invention, the fly ash particles of the soot dust are collected by utilizing the flow rate of the exhaust gas in the process of collecting the soot dust generated when the sewage sludge is incinerated in a fluidized bed furnace, by that portion classification efficiency is classified by setting a range limit particle diameter at 75% of (D ₇₅₎ of 5 to 20 [mu] m, after captured by D ₇₅ or more coarse particles, for example cyclones, of less than D ₇₅ The fine powder is collected by, for example, an electric dust collector. Alternatively, the soot dust is trapped by a dust collector, and the fly ash particles of the trapped soot dust are classified by wind force by setting the critical particle size (D ₇₅ ) at which the partial classification efficiency is 75% within the range of 5 to 20 μm. As a result, it is divided into coarse particles of D ₇₅ or more and fine particles of less than D ₇₅ .

The classification of fly ash particles has a partial classification efficiency of 7
The reason why the critical particle size (D ₇₅ ) of 5% is set within the range of 5 to 20 μm is that when D ₇₅ exceeds 20 μm, sand or the like is mixed in the collected fly ash, resulting in the inclusion of SiO ₂ . The ratio increases, while the P ₂ O ₅ content decreases, making it unsuitable as a raw material for fused phosphorus fertilizer. When D ₇₅ is less than 5 μm, it is difficult to industrially collect such ultrafine particles and it becomes impractical.

Table 2 shows the chemical composition of all the dust collected from the exhaust gas generated when incinerating sewage sludge in a fluidized bed furnace. In Table 3, D ₇₅ is set within the range of 5 to 20 μm. It is the chemical composition of finely divided EP ash having a D of less than _75, which is classified by an electrostatic precipitator.

[0017]

[Table 2]

[0018]

[Table 3]

As is clear from a comparison between Tables 2 and 3, finely divided EP ash having a D of less than ₇₅ contains a large amount of P ₂ O ₅ which is an essential component of the fused phosphorus fertilizer. . The amount of EP ash generated at this time was 22 to 28% of the entire soot dust, and the particle size was 16 μm or less.

The sludge melted and solidified as the fused phosphorus fertilizer is produced by the method described below using the fine powder classified as described above and having a D less than ₇₅ . On the other hand, classified coarse particles of D ₇₅ or more are reused as backfill soil after excavation of civil engineering, or by molding and firing into bricks or pellets, and reused as raw materials for civil engineering and construction materials. To be done.

[0021] Soluble phosphorus fertilizer is widely used as a phosphate material suitable for the agricultural situation in Japan where there are many acidic soils. According to the Fertilizer Control Law, the components of fused phosphorus fertilizer are 17% or more of soluble phosphoric acid, 40% or more of alkali content, and 1% of soluble soluble soil.
It is set at 2% or more. On the other hand, the classified fine fly ash powder having a D < _{75 or} less has a low alkali content, that is, the total amount of CaO and MgO, and a low content of soluble magnesium (MgO 2).

Therefore, in the present invention, when the fly ash fine powder having a D of less than ₇₅ is melted and then solidified by cooling, CaO, MgO and / or a salt thereof is added to the fine powder as a component of the melt-solidified body. Alkaline earth components such as MgO are mixed in an amount of 40% or more and slightly soluble magnesia is 12% or more. Further, phosphoric acid and / or a salt thereof is used as a component of the melt-solidified body, Mix and adjust the ingredients so that the amount becomes 17% or more.

Next, the mixture in which the components are adjusted as described above is melted at a temperature of 1350 ° C. or higher in an electric furnace, a flat furnace, etc., then water-crushed, dehydrated and ground to a predetermined particle size. In this way, a sludge melt solidified body as the fused phosphorus fertilizer is produced.

As described above, according to the present invention, by extracting the fine powder from the fly ash, the amount of silica, which is an unnecessary component, is reduced and the phosphoric acid content is reduced, regardless of variations in the quality and amount of the fly ash. To increase. Therefore, it is possible to adjust the components in a stable manner, reduce the addition amount of alkaline earth or the like, and manufacture the fused phosphorus fertilizer at low cost.

[0025]

Next, the present invention will be described with reference to examples. With respect to 387 kg of fly ash having the composition shown in Table 3, the following amounts of CaO, MgO and / or salts thereof are used as magnesia-based waste brick, calcium carbonate, and phosphoric acid and / or salts thereof are phosphate rock. Was added and mixed well until homogeneous.

Magnesia-based waste brick: 153 Kg charcoal: 135 Kg phosphorus ore: 343 Kg Then, the above mixture was heated and melted at about 1400 ° C. in an electric furnace (three-phase resistance furnace), and then poured into water to about 1
It was pulverized to about 5 to 20 mesh and quenched.

Thus, it was possible to produce a sludge melt-solidified body having the composition of components shown in Table 4, which was a fused phosphorus fertilizer.

[0028]

[Table 4]

[0029]

As described above, according to the present invention,
Fly ash generated when incinerating sewage sludge in a fluidized bed furnace is collected, and when adjusting the composition of the sewage sludge to produce fused phosphorus fertilizer, the composition of the ash is adjusted regardless of the amount and composition of the fly ash. Can be carried out stably, the addition amount of the component adjusting agent such as alkaline earth is small, and the sludge melt-solidified body as the fused phosphorus fertilizer can be produced at low cost, an industrially useful effect. Is brought about.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-3-295884 (JP, A) JP-A-4-87676 (JP, A) JP-A-4-119976 (JP, A) JP-A-4- 124081 (JP, A) JP-A-8-91972 (JP, A) JP-A-8-290145 (JP, A) JP-A-9-255377 (JP, A) JP-A-9-278568 (JP, A) JP-A-9-328384 (JP, A) JP-A-53-122563 (JP, A) JP-A-54-49873 (JP, A) JP-A-56-17993 (JP, A) JP-A-59-164668 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C05B 1/00-C05G 5/00 C02F 11/00-11/20 F23J 1/00-1/08

Claims (2)

(57) [Claims] 1. A limit particle size (D) at which the partial classification efficiency of the fly ash particles of the soot dust reaches 75% by utilizing the flow rate of the exhaust gas in the process of collecting and treating the soot dust generated when incinerating sludge. by classifying set within a range of ₇₅₎ from 5 to 20 [mu] m, after capturing the D ₇₅ or more coarse particles, and the dust collecting fines of less than D _75, the D _75, which is the dust collecting this manner When less than less than a fine powder is melted and then solidified by cooling, CaO, MgO and / or a salt thereof is added to the fine powder as a component of the melt-solidified body, the alkaline earth component is 40% or more, and the soluble magnesium is 12%. Mix as described above, and further add phosphoric acid and / or its salt,
As a component of the melt-solidified body, the soluble soluble phosphoric acid is mixed so as to be 17% or more, and the mixture is melted at a temperature of 1350 ° C. or higher and then cooled and solidified to form a sludge melt-solidified body as a fused phosphorus fertilizer. A method for producing a melted and solidified product from fly ash generated during sludge incineration. 2. In the step of collecting and treating the soot dust generated when incinerating sludge, the soot dust is captured by a dust collector, and the fly ash particles of the soot dust thus obtained have a partial classification efficiency of 75%. By setting the limit particle size (D ₇₅ ) within the range of 5 to 20 μm and performing air classification, the particles are divided into coarse particles of D ₇₅ or more and fine particles of less than D _75, and the D particles thus classified are _When the fine powder of less than ₇₅ is melted and then solidified by cooling, CaO, MgO and / or a salt thereof is added to the fine powder as the component of the melt-solidified body, the alkaline earth component is 40% or more, and the soluble magnesium is 12%. % So that the phosphoric acid and / or its salt is added.
As a component of the melt-solidified body, the soluble soluble phosphoric acid is mixed so as to be 17% or more, and the mixture is melted at a temperature of 1350 ° C. or higher and then cooled and solidified to form a sludge melt-solidified body as a fused phosphorus fertilizer A method for producing a melted and solidified product from fly ash generated during sludge incineration.