JP2695589B2 - Exhaust gas and dust collection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acidic gas (such as HC, for example, an incinerator for solid waste such as municipal solid waste and industrial waste, a coal-fired boiler, a waste liquid incinerator, an electric furnace, a non-ferrous melting furnace, etc.
1, SOx, NOx, HF), and heavy metals (for example, Pb, Zn, C) in the dust entrained in the exhaust gas.
d, Hg), and exhaust gas discharged from various furnaces and dust ash.

[0002]

2. Description of the Related Art With the increase in the amount of municipal waste and industrial waste discharged and the increase in the incineration rate, the amount of incineration exhaust gas and dust ash, incinerator ash, and the amount of exhaust gas and dust ash generated in various factory facilities increase,
Acid gases and heavy metals contained in them are new sources of environmental pollution.

Of these, in particular, the exhaust gas of the organic refuse incinerator contains a lot of harmful acidic gases such as HCl, SOx, NOx and HF, and the ash contains a lot of low boiling heavy metals such as mercury, zinc and lead. When they are contained and released into the environment, they dissolve in rainwater or the like to become acid rain, and harmful heavy metals are eluted from ash, and various prevention techniques have been developed.

For example, in order to collect the acidic gas, an alkali washing tower system, a semi-wet lime milk moving packed bed reaction system, and a dry slaked lime blowing system are adopted in various places.

As a method for detoxifying ash, "Environmental Facility" No. 21 (1985) p. 79 to 84, a method of kneading and solidifying with concrete, a method of reacting a heavy metal extracted from ash with water with carbon dioxide to carbonate, a method of mixing with asphalt to solidify are described.

In Japanese Patent Publication No. 61-47154, a waste ash containing a heavy metal is mixed with an alkaline component in the presence of an iron salt and mixed, and the mixture is granulated or allowed to stand at a temperature of 300. It is disclosed that the heavy metal is fixed as a mixed hydroxide with an iron salt by maintaining the temperature at or below ° C.

It is said that the heavy metal in the ash is fixed to a considerable extent, and there is an advantage that it can be safely dumped.

However, in this heavy metal fixing method, an alkali is directly added to the treated ash and mixed, so that an expensive alkali is required for the treatment, and the mixing is insufficient. Partly the pH becomes high and p
When H is 11.5 or more, heavy metals cannot be fixed, the efficiency of immobilization decreases, and moreover, the treatment time of 2 days is required at around room temperature, and the treatment time becomes long or the treatment facility becomes huge. There are drawbacks.

Further, since alkali is added to the treated ash, there is a drawback that the harmful acid gas contained in the exhaust gas cannot be collected at all.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to collect various combustible substances containing an acidic gas component and a heavy metal component from exhaust gas and exhaust gas containing an acidic gas generated from equipment for incineration or melting and carbonization. Another object of the present invention is to provide an economical method for detoxifying dust ash and incineration residue containing heavy metals.

[0011]

The present invention follows the first step of detoxifying acid gas in exhaust gas by spraying alkali or alkali and powdery divalent iron salt into exhaust gas from a processing furnace. And a second step of collecting dust in the exhaust gas to which the alkali or alkali and powdery divalent iron salt has been added, and water, divalent iron salt and
And a third step of stirring and heating after adding an acid .

[0012]

[Function] By adding an alkali to the exhaust gas containing dust, SOx, HCl, etc. at the upstream side of the dust collector, acidic harmful substances such as SOx and HCl in the exhaust gas react with the alkali and are removed from the exhaust gas. To be done.

Further, since the alkali is added to the air flow which is the exhaust gas, the mixing of the dust containing the heavy metal and the alkali is promoted, which is preferable for the subsequent ferrite treatment.

Further, depending on the concentration of SOx or HCl in the exhaust gas, a large amount of alkali must be added. As a result, if the pH of the mixture of dust and dust containing heavy metals and alkali becomes high, it becomes unsuitable for the ferrite formation reaction. . In such a case, an acid is added to accelerate the ferritization reaction.

When a powdery divalent iron salt is used as the divalent iron source for the next operation, it is effective to add it to the exhaust gas in the same manner as the alkali to enhance the mixing effect.

Next, the ferritizing treatment of the collected ash will be described.

Water for kneading is added to the collected ash, and divalent iron and acid are added to this wet mixture to uniformly disperse both of them. The pH of this mixture is 7.0-11.5.
By adjusting the temperature to 30 ° C. to 99 ° C. after the adjustment, the divalent iron in the mixture gradually crystallizes and turns into ferrite. Ferrite is a chemical formula of MFe ₂ O
₄ (M: Fe, Zn, Pb, and other metals), the divalent iron in the mixture forms the iron oxide crystal lattice called ferrite, and the heavy metal is originally an iron atom. Instead of iron, it is taken in and fixed at the position that should be occupied by.

The reaction formula is expressed as follows.

Neutralization reaction: M ²⁺ + 2Fe ²⁺ + 6OH ⁻ → M
Fe ²⁺ (OH) ₆ (1) Oxidation reaction: MFe ₂ (OH) ₆ + 1 / 2O ₂ → MFe ₂
O ₄ + 3H ₂ O (2) In the above reaction formula, if the pH is less than 7.0, OH − in the reaction of the formula (1) will be insufficient and the ferrite formation reaction will not proceed. Also, the pH is 1
If it exceeds 1.5, heavy metals such as lead take the form of HPbO ₂ ^{− and} are not incorporated in the ferritization reaction. Also,
When there is no oxygen or when there is no contact with oxygen, and when the mixture is not stirred, for example, when it is allowed to stand, the O
₂ is insufficient and the reaction does not proceed.

Furthermore, in order to promote the oxidation reaction (2) in the ferrite formation reaction, at least heating is effective and heating at 30 ° C. or higher is required.

When the heating temperature is 100 ° C. or higher, the solubility of oxygen in water in the oxidation reaction (2) is almost zero and the oxidation reaction does not proceed. Therefore, the heating temperature needs to be lower than 100 ° C. is to <br/> 2 Ataitetsushio及beauty acid added into Chirihai, be mixed in the form of an aqueous solution are preferred over process, 2 Ataitetsushio is sulfate, as chlorides, also, Sulfuric acid, hydrochloric acid can be used as the acid, and slaked lime or the like can be used as the alkali added in the upstream measurement of the exhaust gas from the dust collector.

[0022] The amount of 2 Ataitetsushio及beauty acid to dust collection ash, it takes more than the chemical equivalent required for the reaction, typically function well at about up 10 to 200% may play. However, since the amount of addition depends on the form of the heavy metal and the like, it is preferable to determine after the preliminary test.

[0023]

EXAMPLES Example 1 FIG. 1 shows an outline of the processing equipment used.

In the figure, reference numeral 12 denotes a powder ejection device provided in an exhaust gas duct on the upstream side of the electrostatic precipitator 13,
Slaked lime C was supplied as an alkali into the exhaust gas E from the incinerator through the powder ejection device 12 to cause a reaction with hydrogen chloride and sulfur oxides in the exhaust gas.

Here, slaked lime C was sprayed as a powder at a ratio of 2.0 times the reaction molar equivalent ratio to HCl. By this operation, 95% of HCl in the exhaust gas was removed.

The supplied slaked lime, reacted calcium chloride, and calcium sulfate were collected by the electric dust collector 13 together with the incinerator fly ash.
Collected by. The collected ash A (hereinafter referred to as EP ash) is passed through a rotary ash discharging valve 14 and is passed through an EP ash storage tank 15
Was stored in the reactor 1 and discharged from the quantitative cut-out feeder 16 below the EP ash storage tank 15 and received in the reactor 1. This E
P ash A has a pH of 1 due to the addition of alkali into the exhaust gas.
Since it was 2.0, the sulfuric acid F in a weight ratio of 3% was received as an aqueous solution from the tank 3, and the pH of the mixture was adjusted to 11.5. This is mixed with air in the reactor 1 at a rate of 10 liter / min per 1 kg of dry matter of the mixture,
While ventilating from the air inlet 4, the temperature of the mixture is 70 ° C.
It was heated by the heating device 6 so as to be, and continuously stirred using the stirrer 7, and the results shown in Table 1 and Table 2 were obtained.

Table 1 shows the content of heavy metals in the collected ash A,
Table 2 shows the results of the leaching test of the ash after the treatment in comparison with the concrete solidification method and the asphalt solidification method, together with the ocean dumping standard. For the dissolution test method, refer to the Environmental Agency Notification No. 13 (19
1973) was used.

[0028]

[Table 1] As shown in Table 2, in the case of this example, all the heavy metals were below the ocean dumping standard, and showed particularly excellent results in Pb, Zn, and hexavalent Cr as compared with the concrete solidification method and the asphalt solidification method. ing.

[0029]

[Table 2] Then, after ventilating, stirring and heating, it was taken out from the outlet 9 of the reactor 1 hour later, and after ventilation, stirring and heating was taken out from the outlet 9 of the reactor 1 hour later, the ash treatment device 10 having a diameter of about 5 mm was used. Was used for granulation.

Example 2 FIG. 2 shows an example in which an aqueous sulfuric acid solution is added as the acid F in Example 1 to adjust the pH in the reactor 1.

In the same manner as in Example 1, slaked lime C was supplied into the exhaust gas E of the incinerator via the powder jetting device 12 to cause a reaction with hydrogen chloride and sulfur oxides in the exhaust gas. Here, slaked lime C is a powder and has a reaction molar equivalent ratio of 2. to HCl.
Ejected at a rate of 0 times. By this operation, HC in exhaust gas
95% was removed.

The supplied slaked lime, reacted calcium chloride, and calcium sulfate were collected together with the incinerator fly ash by the electrostatic precipitator 13.
Collected by. The collected ash A (hereinafter referred to as EP ash) is passed through a rotary ash discharging valve 14 and is passed through an EP ash storage tank 15
Was stored in the reactor 1 and discharged from the quantitative cut-out feeder 16 below the EP ash storage tank 15 and received in the reactor 1. This E
P ash A has a pH of 1 due to the addition of alkali into the exhaust gas.
Since it was 2.0, the sulfuric acid F in a weight ratio of 3% was received as an aqueous solution from the tank 3, and the pH of the mixture was adjusted to 11.5. This is mixed with air in the reactor 1 at a rate of 10 liter / min per 1 kg of dry matter of the mixture,
While ventilating from the air inlet 4, the temperature of the mixture is 70 ° C.
It was heated by the heating device 6 so as to become, and continuously stirred using the stirrer 7, and the same result as in Example 1 was obtained. Then, the granulation process was performed in the same manner as in Example 3.

[0033]

According to the present invention, the following effects can be obtained.

(1) By adding the alkali to be added on the gas upstream side of the dust collector, the HCl is removed from the exhaust gas.
Since the harmful substances such as the above are removed and the alkali is added in the air flow, the dust collection dust and the alkali are completely mixed, and the elution preventing treatment of the heavy metal can be performed more completely. Further, the alkali can be effectively used for removing harmful substances from the exhaust gas and preventing elution of heavy metals from the dust ash.

(2) The heavy metal can be completely fixed in a short time, the processing time can be greatly shortened, and the processing equipment can be greatly downsized.

(3) Various heavy metals can be treated and removed at the same time.

(4) Regardless of the heavy metal content,
Can process to low concentrations.

(5) Since the ash after the treatment has magnetism, it can be separated by a magnetic separator and its application can be expanded.

(6) The ash after the treatment does not re-elute even if it is dumped in the natural world and is stable even in an acidic atmosphere.

[Brief description of the drawings]

FIG. 1 shows an outline of processing equipment used in an embodiment of the present invention.

[Explanation of symbols]

1 Reactor 2, 3 Tank 4 Air inlet 5 Exhaust fan 6 Heating device 7 Stirrer 8 Motor 9 Discharge port of treated ash 10 Ash treatment device 11 Ash pit 12 Powder ejection device 13 Electrostatic precipitator 14 Rotary valve 15 Ash storage tank 16 Fixed-quantity feeder A Collection ash B Iron sulfate C Slaked lime D Air E Incinerator exhaust gas F Sulfuric acid

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B09B 3/00 B01D 53/34 136Z ZAB B09B 3/00 ZAB 304G (56) Reference JP-A-56-152777 ( JP, A) JP 58-137490 (JP, A) JP 58-137497 (JP, A) JP 6-134436 (JP, A)

Claims (2)

(57) [Claims] 1. A first step of spraying alkali into exhaust gas from a processing furnace to detoxify acidic gas in the exhaust gas, and a second step of collecting dust in the exhaust gas to which the alkali is added While having, for the dust collection dust,
And a third step of stirring and heating after adding water, divalent iron salt and acid , and a method for treating exhaust gas and dust collecting dust. 2. Alkali and powder in the exhaust gas from the processing furnace
Following the first step of spraying powdery divalent iron salt and detoxifying the acidic gas in the exhaust gas, the alkali and powdery divalent iron
Characterized with a second step of dust collecting dust in the exhaust gas with the addition of iron salts, to the dust collected, after adding Mizu及 beauty acid, that a third step of stirring and heating Exhaust gas and dust collection method.