JPH09206725A - Treatment of waste gas and flying ash from incineration furnace or melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To save resources with a device for capturing the flying ashes in the waste gases produced from an incineration furnace, etc., and separates and recovers lead compds. by adding an acid thereto by recovering the acid in the waste gases after the removal of the flying ashes and using this acid for the sepn. and recovery of the lead compds., thereby reutilizing the recovered lead and zinc. SOLUTION: After the waste gases produced from the melting furnace A are cooled by a cooling means 1, the capturing of the molten flying ashes and dust is executed by a dust collector 2. The device is provided with a flying ash treating system C consisting of a recovering system C1 for separating and recovering the lead compds. and a zinc recovering system C2 for separating and recovering the zinc compds. in order to recover the lead and zinc included in the molten flying ashes. The molten flying ashes are first put into a mixing tank 12 and are mixed with water 13 to form a slurry in order to allow the smooth extraction by the acid in the post stage. This slurry is introduced into an acid extracting tank 14 where the acid is added to the slurry and the precipitate (lead precipitate) is separated. The acid recovered by cleaning in a water cleaning column 3 is used as the acid to be added at that time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas and fly ash generated from an incinerator or a melting furnace in a municipal solid waste incinerator, an industrial waste incinerator, or the like.

[0002]

2. Description of the Related Art When incinerating municipal waste or industrial waste in an incinerator in an incinerator as described above, exhaust gas containing incinerated fly ash and acid is generated. After incineration, incineration ash remains in the incinerator. The exhaust gas is discharged to the atmosphere after removing incineration fly ash by a dust collector and further removing the above-mentioned acid by neutralization by alkali cleaning. Further, the incinerated fly ash and the incinerated ash may be melted in a melting furnace in order to reduce the volume. in this case,
Exhaust gas containing molten fly ash and acid is generated from the melting furnace. This exhaust gas is also discharged after removing the molten fly ash with a dust collector and neutralizing the acid by alkali cleaning. The fly ash such as incineration fly ash or molten fly ash is a salt or low boiling heavy metal gasified in the process of treatment in an incinerator or a melting furnace (often volatilized in the form of chloride or metal vapor). However, it is cooled and condensed after being discharged from the furnace, and often contains salts (compounds of chlorine and sulfur with sodium and potassium) and heavy metal (particularly lead and zinc) compounds.
If the fly ash is landfilled without being treated, the harmful heavy metals as described above may be eluted and cause environmental pollution. Therefore, conventionally, the following processing is performed.
First, an acid is added to the fly ash to separate and collect a lead compound. Next, a zinc compound is separated and collected by adding an alkaline neutralizing agent to the residue obtained after separating and collecting the lead compound from the fly ash. Such a method is disclosed, for example, in JP-A-6-170354.

According to the above method, lead and zinc can be recovered, which is useful for environmental protection, and by reusing the recovered lead and zinc, it is also useful for resource saving.

[0004]

However, in the above-mentioned conventional method, there is a problem that an acid is required for separating and recovering the lead compound, resulting in an increase in running cost.

The method for treating exhaust gas and fly ash from an incinerator or a melting furnace of the present invention is provided to solve the above-mentioned problems of the prior art. An object of the present invention is to, when exhaust gas is generated from an incinerator or a melting furnace, remove fly ash and acid from the exhaust gas to enable discharge in a state where the environment can be preserved. Another object is to make it possible to conserve the environment by separating and collecting lead compounds from the fly ash, and to make resource saving by reusing the collected lead compounds. Another purpose is to further protect the environment by separating and recovering the zinc compound from the residue after separating and recovering the lead compound from the fly ash, and to reuse the recovered zinc compound. To save resources. Another purpose is to collect and recover the lead compound by recovering the acid from the exhaust gas after the fly ash is removed from the furnace and using the acid as the acid for separating and recovering the lead compound. The goal is to keep running costs low. Other objects and advantages will be more readily apparent from the drawings and the following description associated therewith.

[0006]

In order to achieve the above object, a method of treating exhaust gas from an incinerator or a melting furnace and fly ash in the present invention is to remove fly ash from the exhaust gas generated from the incinerator or the melting furnace. In a method of treating exhaust gas and fly ash from an incinerator or a melting furnace, which includes a step of collecting and a step of adding an acid to the collected fly ash to separate and recover a lead compound, the fly ash was removed. The acid contained therein is recovered from the subsequent exhaust gas, and the acid is used for separating and recovering the lead compound.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The drawings showing the embodiments of the present invention will be described below. In FIG. 1 showing a treatment system of exhaust gas from a melting furnace and fly ash, A shows a melting furnace for melting incineration fly ash or a mixture of incineration fly ash and incineration ash, and a furnace for electric melting, for example, an arc furnace And a furnace for performing combustion melting, for example, a burner type melting furnace. B is an exhaust gas treatment system (see symbols 1 to 7) for treating exhaust gas emitted from the melting furnace so that it can be emitted into the atmosphere, and C is heavy metal from the molten fly ash collected in the exhaust gas treatment system. Fly ash treatment system (see reference numbers 11 to 26) for recovering the ash, and D produces an alkaline neutralizing agent used in the fly ash treatment system C using the exhaust gas treated liquid or the fly ash treated liquid as a raw material. The generation system for each is shown.

The incinerated fly ash or a mixture of the incinerated fly ash and the incinerated ash is placed in a melting furnace A and melted to reduce the volume. In this case, a high temperature exhaust gas of about 1000 ° C. is generated from the melting furnace A.

The exhaust gas is treated in the exhaust gas treatment system B as follows. First, the exhaust gas is cooled by the cooling means 1 so as to have a temperature suitable for the dust collector 2. An example of the cooling means 1 is a cooling air fan that cools the high-temperature exhaust gas with normal temperature air. For example, about 5 times as much air as the amount of the exhaust gas is sent from the fan 1 to lower the temperature of the exhaust gas to about 200 ° C. As the temperature of the exhaust gas decreases, salts and low-boiling heavy metals contained in a gas state condense into molten fly ash. The exhaust gas whose temperature has been lowered is collected by the dust collector 2 such as a bag filter in order to prevent the molten fly ash and other dust contained therein from being discharged together with the exhaust gas. In the dust collector 2, the above-mentioned exhaust gas is removed to a level below the emission standard of molten fly ash and dust into the atmosphere.

The exhaust gas that has passed through the dust collector 2 is washed with water 4 in the water washing tower 3 in order to remove most of the acids contained therein, such as hydrochloric acid gas HCl and sulfur dioxide SO ₂ . Those acids removed by washing are recovered in the water washing tower 3 as an aqueous solution of hydrochloric acid or sulfuric acid. The exhaust gas from which most of the acid has been removed is sent to the alkali washing tower 5.
The alkali washing tower 5 is for reducing the level of the acid remaining in the exhaust gas to a level below the emission standard to the atmosphere. For example, an acid slightly remaining in the exhaust gas after passing through the water washing tower 3 may be used. The hydrochloric acid HCl and the sulfuric acid H ₂ SO ₄ are removed by neutralization with caustic soda 6, for example. The exhaust gas that has been treated in the alkali cleaning tower 5 is discharged into the atmosphere by the exhaust fan 7. The treated liquid in the alkali washing tower 5 is an aqueous solution containing salts such as sodium chloride, potassium chloride and sodium sulfite. The treated liquid can be discharged as waste water as it is, but in this example, it is sent to the generation system D for recycling use of the substance contained therein.

The fly ash treatment system C is for recovering lead and zinc contained therein from the molten fly ash. The fly ash processing system C is a lead recovery system C1 for separating and recovering lead compounds.
(See symbols 11 to 19) and a zinc recovery system C2 (see symbols 21 to 26) for separating and recovering zinc compounds.
The purpose of separating and recovering the respective compounds in each of the lines C1 and C2 is to enable effective utilization of the lead compound and the zinc compound respectively recovered. The recovered lead compounds and zinc compounds can be reused as non-ferrous refining raw materials, respectively.

The operation of the lead recovery system C1 is as follows. The molten fly ash collected by the dust collector 2 is temporarily stored in the storage hopper 11. 12, 1 from the molten fly ash
Lead compounds are separated and collected by the means shown in 4 and 18. That is, the stored molten fly ash is first put into the mixing tank 12 and mixed with water 13 to form a slurry so that the extraction with acid can be smoothly performed in the subsequent step. The slurry is placed in the acid extraction tank 14, there, as shown by the arrow 15,
An acid such as hydrochloric acid HCl or sulfuric acid H ₂ SO ₄ is added to separate the lead-rich precipitate (lead precipitate) from the others. The lead precipitate is separated by the operation in the acid extraction tank 14. That is, the lead compound remains as a lead-rich precipitate in a solid state, and the rest is an aqueous solution. In the acid extraction tank 14, the pH in the tank 14 is adjusted to, for example, about 1 in order to improve the quality of the lead compound obtained. The adjustment is performed by adjusting the amount of the acid added above. The molten fly ash before the addition of acid has a pH of 4 to 6 due to the metal chlorides (PbCl ₂ , ZnCl ₂ , CuCl ₂ , FeCl ₂ etc.) it contains.
It exhibits a degree of acidity. The operation in the tank 14 is also called acid leaching. As the above-mentioned acid to be added, the acid recovered in the water washing tower 3 as shown by the line 16 is used in order to reduce the running cost. Code 17 if not enough
Additional acid is added as shown in. The acid-extracted product is applied to a filter press 18 exemplified as a solid-liquid separation device for separating solid and liquid, and a lead-rich precipitate
19 are recovered. The lead content of the recovered material is, for example, 20 to
40%. The remaining filtrate is the next zinc recovery line C2
Sent to In the case of recovery of the lead compound, for example, 1k
About 0.081 kg of hydrochloric acid (100% hydrochloric acid) is required to recover lead compounds by treating g of fly ash as described above. On the other hand, according to the above-mentioned acid recovery, about 0.055 kg of hydrochloric acid can be recovered from 1 kg of fly ash. Therefore, the recovered hydrochloric acid can cover about 68% of the above required amount. That is, the running cost can be kept low.

The operation of the zinc recovery system C2 is as follows. Zinc compounds are separated and recovered from the remnants of the lead recovery system C1 by means indicated by reference numerals 21, 23 and 25. That is,
The above filtrate is placed in a neutralization tank 21, and an alkaline neutralizing agent such as caustic soda is added as shown by an arrow 22 to precipitate zinc. The amount of addition is such that the pH is about 9 in order to improve the quality of the obtained zinc-rich precipitate (zinc precipitate). The zinc precipitate is separated in the tank 21 by the addition of the neutralizing agent. That is, a zinc compound such as Zn (OH) ₂ is deposited and precipitated. Next, the aqueous solution containing the precipitate is used in the sulfurization tank 23.
Sodium hydrosulfide 24 is added in order to further precipitate and separate the dissolved zinc and the like. The sodium hydrosulfide 24
ZnS precipitates and precipitates. Above tank 23
The aqueous solution containing the precipitate therein is applied to a filter press 25 exemplified as a solid-liquid separator, and a precipitate 26 rich in zinc is recovered. The content of zinc in the recovered product is, for example, 25 to 40.
%. The treated liquid after the separation and recovery of the lead compound and the separation and recovery of the zinc compound, that is, the filtrate of the solid-liquid separation device 25 is an aqueous solution of salts such as sodium chloride and potassium chloride. This filtrate can be discharged as waste water as it is. However, in this example, the substances contained therein are sent to the production line D for recycling.

In the production system D, the cleaning waste liquid of the alkali cleaning tower 5 is preliminarily removed of unnecessary substances by means indicated by reference numerals 31 and 33. That is, calcium hydroxide 32 is added in the sulfurization tank 31, and a sulfate compound such as gypsum CaSO ₄ is deposited and precipitated. The deposited precipitate is applied to a filter press 33 exemplified as a solid-liquid separator to separate the sulfated precipitate 34. The remaining salt solution is sent to the electrolytic cell 35. Electrolyzer 35
In (1), the filtrate of the filter press 33 and the treated liquid from the fly ash treatment system C are electrolyzed by the electric power 36 from the power source to generate and recover alkali such as caustic soda. As the electric power 36, it is preferable to use the waste power generated by using the waste heat of the waste incineration facility. Of course, normal commercial power can be used. The recovered caustic soda is used as an alkali neutralizer in the zinc recovery system C2 as shown by line 37. If insufficient, an additional alkaline neutralizing agent is added as indicated by reference numeral 38.

Although the examples of the treatment of the exhaust gas from the melting furnace and the molten fly ash have been described above, the same treatment may be performed on the exhaust gas from the incinerator and the incineration fly ash.

[0016]

As described above, according to the present invention, when exhaust gas is generated from the incinerator or the melting furnace A during operation, fly ash is removed from the exhaust gas and further acid is removed. . Therefore, the exhaust gas after removing them has the effect of being able to be discharged into the atmosphere without the problem of causing environmental pollution. Further, the lead ash and the zinc compound can be separated and recovered from the removed fly ash. This has the effect of preventing in advance the risk of fly ash containing lead and zinc being landfilled and causing environmental pollution due to elution of lead and zinc. Not only that, but the recovered lead compounds and zinc compounds can be reused, respectively, which has the effect of saving resources. Moreover, in the case of the separation and recovery of the lead compound, the acid recovered from the exhaust gas is used for the separation and recovery of the lead compound, so the usage cost is zero, and therefore the separation and recovery of the lead compound at a low running cost. There is an effect that can be done. Furthermore, when the exhaust gas is alkali-cleaned so that the acid level is reduced to the extent that it can be discharged into the atmosphere, the acid used for separating and recovering the lead compound is removed from the exhaust gas in advance. In the step of washing with alkali, it is only necessary to neutralize a slight amount of the remaining acid, and therefore the amount of alkali required is small, and there is also an effect that the running cost in this step can be kept low.

[Brief description of drawings]

FIG. 1 is a diagram showing a treatment system for exhaust gas from a melting furnace and molten fly ash.

[Explanation of symbols]

 A Melting furnace B Exhaust gas treatment system 2 Dust collector 3 Water cleaning tower 5 Alkaline cleaning tower C1 Lead recovery system C2 Zinc recovery system

Claims (2)

[Claims] 1. An incinerator or a melting furnace including a step of collecting fly ash from exhaust gas generated from an incinerator or a melting furnace, and a step of adding an acid to the collected fly ash to separate and recover a lead compound. In the method for treating exhaust gas from a furnace and fly ash, the acid contained therein is recovered from the exhaust gas after the fly ash is removed, and the acid is used for separating and recovering the lead compound. Exhaust gas and fly ash treatment method from incinerator or melting furnace. 2. A step of washing the exhaust gas after recovering the acid with an alkali to neutralize the acid remaining in the exhaust gas, and a residue obtained after separating and recovering the lead compound from the fly ash. The method for treating exhaust gas and fly ash from an incinerator or a melting furnace according to claim 1, further comprising the step of adding an alkali neutralizing agent to and separating and recovering the zinc compound.