JP2865958B2 - Detoxification method of fly ash - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detoxifying fly ash generated by incineration of refuse or combustion of coal or the like.

[0002]

2. Description of the Related Art In a conventional method for detoxifying fly ash, after mixing fly ash and water, a combustion exhaust gas is blown into a mixture of fly ash and water to neutralize a slurry, and then a polymer condensing agent is mixed. And then dehydrated and solid-liquid separated.

[0003] That is, as shown in FIG.
The washing water supplied to the mixing tank 3 from the tank and the fly ash supplied to the mixing tank 3 from the fly ash supply pipe 2 are mixed in the mixing tank 3 by the stirrer 3a, washed with water, and washed with ash. The slurry becomes a slurry in which harmful substances such as heavy metals adhering to the cleaning water migrate to the washing water side. This slurry is supplied into the reaction tank 10 and mixed with the combustion exhaust gas blown from the exhaust gas supply pipe 9 in the reaction tank 10 by the stirrer 10a to neutralize the slurry. The neutralized slurry is supplied into the mixing tank 5, mixed with the polymer flocculant supplied from the polymer flocculant supply pipe 4 in the mixing tank 5 by the stirrer 5 a, and the fly ash is converted into floc floc. I do. The slurry containing the aggregated flocs is supplied into the dehydrator 6 and subjected to a dehydration action, whereby a dehydrated cake 7 and a separated liquid 8 are obtained.

[0004]

In the above conventional method,
After mixing the washing water and fly ash to wash the fly ash, the combustion exhaust gas is blown in to neutralize the slurry, and then the polymer flocculant is mixed and dewatered. Can not perform effective dehydration. The reason why good coagulated floc cannot be obtained is that carbon dioxide gas (CO ₂ ) in the combustion exhaust gas blown into the slurry to perform neutralization converts calcium hydroxide (Ca (OH) ₂ ) in the slurry into calcium carbonate (CaCO ₃ ). This calcium carbonate is considered to be preventing the formation of aggregated floc.

For this reason, the water content of the dewatered cake obtained by dewatering the slurry is as high as 80 to 90%, and the concentration of suspended substances (SS) such as CaCl and Ca (OH) ₂ in the separated liquid is high. Become.

An object of the present invention is to provide a method for detoxifying fly ash which can solve the above problems.

[0007]

SUMMARY OF THE INVENTION According to the present invention, fly ash contained in flue gas is washed with water to transfer harmful substances such as heavy metals adhering to the surface of the fly ash to the wash water side. In the method of detoxifying fly ash, which treats the washing water after detoxification, the fly ash is washed with water, and then a polymer flocculant is added to a mixture of fly ash and water to aggregate the ash to form flocs. In addition,
The mixture is dehydrated and solid-liquid separated, and the separated liquid is neutralized by blowing combustion exhaust gas.

[0008]

According to the present invention, fly ash generated by combustion is washed with water to transfer harmful substances such as heavy metals adhering to the surface to the washing water side, and the mixture of the fly ash and water immediately polymer aggregates. The agents are mixed, dehydrated and separated into solid and liquid. As a result, the washed fly ash forms a good floc and can be effectively dewatered.

Further, the combustion exhaust gas is blown into the effectively dehydrated separated liquid as described above to neutralize the separated liquid, thereby reducing the chemical cost required for the subsequent neutralization. Further, by performing neutralization with the combustion exhaust gas, calcium carbonate in the separated liquid is converted into calcium bicarbonate to prevent scale from adhering to pipes and the like.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. Reference numeral 3 denotes a mixing tank that accommodates the stirrer 3a and is supplied with the washing water from the washing water inflow pipe 1 and the fly ash from the fly ash supply pipe 2. The mixing tank 3 includes a stirrer 5a.
The polymer coagulant is supplied from a polymer coagulant supply pipe 4 into the mixing tank 5. Reference numeral 6 denotes a dehydrator connected to the mixing tank 5 to perform solid-liquid separation. Separated water 8 obtained by the dehydrator 6 is supplied into the reaction tank 10. Reaction tank 1
Numeral 0 houses a stirrer 10a, and combustion exhaust gas is blown into the reaction tank 10 from an exhaust gas supply pipe 9.

Reference numeral 7 denotes a dehydrated cake obtained by solid-liquid separation in the dehydrator 6. In the next step, the treatment liquid 11 discharged from the reaction tank 10 is treated with an acid / alkali chemical in the next step in order to remove heavy metal ions and the like so that the water quality can be released while maintaining the pH at a constant value. You. The polymer flocculant to be supplied into the mixing tank 5 includes Diafloc AP520, A
P630 (trade name) or the like can be used.

In this embodiment, the fly ash is supplied to the mixing tank 3.
Inside, the mixture is mixed with the washing water by the stirrer 3a and washed with water, and harmful substances such as heavy metals attached to the surface thereof become slurry which has migrated to the washing water side. This slurry is supplied into the mixing tank 5 and mixed with the polymer flocculant by the stirrer 5a in the mixing tank 5 to form flocculent flocks of fly ash. At this time, since CaCO ₃ that inhibits the formation of aggregate flocs is not present in the slurry,
Fly ash effectively agglomerates into flocs.

As described above, the slurry in which the flocculated floc is effectively formed is supplied into the dehydrator 6 and subjected to the solid-liquid separation action, whereby the dehydrated cake 7 and the separated liquid 8 are obtained. Since the flocculated floc is effectively formed in the slurry as described above, the dehydration by the dehydrator 6 is sufficiently performed, and the dewatered cake 7 having a low water content is obtained, and the concentration of the suspended substance is reduced. A separation liquid 8 is obtained.

[0014] concentration is lower separation liquid 8 in the floating material is fed into the reaction vessel 10, is mixed with combustion exhaust gas that has been blown by the agitator 10a, the neutralizing shown in CO ₂ by reduction 1 in the combustion exhaust gas receive.

[0015]

Embedded image

If CO ₂ is further blown into the separation liquid 8, the pH of the separation liquid drops, so that CO ₃ ²⁻ in the separation liquid 8 changes to HCO ₃ ⁻ , and the calcium carbonate ( CaCO ₃ is replaced by calcium bicarbonate (Ca (HC)
O ₃ ) ₂ ). This prevents the scale from adhering to a pipe or the like.

As described above, in the present embodiment, the floc formation is inhibited by mixing the fly ash slurry washed with water in the mixing tank 3 with the polymer flocculant in the mixing tank 5. The slurry is treated with the polymer flocculant in the absence of CaCO ₃ , and effective floc formation can be performed. Therefore, the dehydrator 6
In the dehydration cake 7 with low moisture content
And a separation liquid 8 having a low concentration of suspended substances.

Further, since the separated liquid 8 is neutralized by the combustion exhaust gas in the reaction tank 10, the calcium carbonate in the separated liquid 8 is converted into calcium bicarbonate, and the generation of calcium carbonate scale in piping or the like is prevented. Can be suppressed. In addition, since the concentration of the suspended substance in the separation liquid 8 is low, the amount of chemicals for processing the separation liquid in the next step can be reduced.

[0019]

According to the present invention, since the polymer flocculant is added immediately after the fly ash is washed with water, the fly ash which is difficult to flocculate with the conventional method can be effectively flocculated with the polymer flocculant. By performing dehydration thereon, a dehydrated cake having a low moisture content and a separated liquid having a low suspended substance concentration can be obtained.

Further, since the separated liquid having a low suspended solids concentration is neutralized by the combustion exhaust gas, scale adhesion can be prevented, and the amount of chemicals required for processing the separated liquid in the next step can be reduced. .

[Brief description of the drawings]

FIG. 1 is a system diagram of one embodiment of the present invention.

FIG. 2 is a system diagram of a conventional fly ash detoxification method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Washing water inflow pipe 2 Fly ash supply pipe 3 Mixing tank 4 Polymer flocculant supply pipe 5 Mixing tank 6 Dehydrator 7 Dehydration cake 8 Separation liquid 9 Exhaust gas supply pipe 10 Reaction tank 11 Treatment liquid

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-176493 (JP, A) JP-A-62-289291 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C02F 1/56 B09B 3/00

Claims (1)

(57) [Claims] 1. Fly ash generated by combustion is washed with water to transfer harmful substances such as heavy metals adhering to the surface to the washing water side, and the washing water after detoxifying the fly ash is treated. In the method for detoxifying fly ash, the fly ash is washed with water, and then a polymer flocculant is added to a mixture of fly ash and water to aggregate ash to form flocs. A method for detoxifying fly ash, comprising separating a liquid and neutralizing the separated liquid by blowing a combustion exhaust gas.