JP2000061252A - Combustion exhaust gas treating agent and treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amt. of sodium hydroxide required to neutralize acidic gases in a scrubbing tower, to reduce the amt. of circulating water forced to be discharged from the scrubbing tower and to reduce the concn. of dioxins in exhaust gas by using a combustion exhaust gas treating agent contg. slaked lime, activated carbon and a heavy metal fixing agent. SOLUTION: Waste combustion gas generated from an incinerator 1 is passed through a waste gas temp. reducer 2 to reduce the temp., dust is collected in a dust collector 3, acidic gaseous components are neutralized by scrubbing with a sodium hydroxide soln. or the like in a waste gas scrubber 4 and the treated gas is discharged from a stack 6 into the air. In the discharge passage of the waste combustion gas, a treating agent contg. slaked lime, activated carbon and a heavy metal fixing agent is blown into the waste gas on this side of the dust collector 3. The slaked lime is allowed to react with the acidic components in the waste gas and compds. such as calcium chloride and calcium sulfate formed by this reaction are collected in the dust collector 3. The amt. of the slaked lime added to the waste gas is preferably 0.5-2.5 g/Nm3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a treatment agent and a treatment method for combustion exhaust gas generated from an incineration facility for municipal waste, and more particularly, to releasing the combustion exhaust gas to the atmosphere through a dust collector and a smoke washing tower. It is possible to perform the neutralization treatment of the acidic gas in the exhaust gas and the dioxin concentration reduction treatment, the heavy metal immobilization treatment in the collected fly ash, and the salt concentration reduction treatment in the smoke washing tower circulating water with one agent. The present invention relates to a treatment agent for combustion exhaust gas and a method for treating combustion exhaust gas using the treatment agent.

[0002]

2. Description of the Related Art Since combustion exhaust gas generated from an incinerator for municipal waste contains soot dust and acid gases such as hydrochloric acid and sulfur oxides, the exhaust gas temperature reducing device 2 as shown in FIG.
After lowering the temperature with, collect dust (fly ash) with a dust collector 3 such as an electric dust collector or a tap filter, and then wash with a caustic soda solution etc. with an exhaust gas washing device (smoke washing tower) 4. After the acid gas component is neutralized (wet process), it is discharged from the chimney 6 to the atmosphere (in the figure, 1 is an incinerator, and 5 is an induction fan). The fly ash collected by the dust collector 3 is disposed of at the final disposal site. Prior to that, in order to prevent the heavy metal in the fly ash from eluting at the final disposal site, It is obligatory to perform an intermediate treatment for immobilization (insolubilization). As the immobilization treatment, a chemical treatment method in which a heavy metal fixing agent is added to fly ash and kneaded is known as the simplest treatment method.

[0003]

As described above, since a large amount of acid gases such as hydrochloric acid and sulfur oxides are contained in the combustion exhaust gas of municipal waste and the like, the smoke washing tower 4 is operated by the wet method described above. It is necessary to neutralize, but in this case, a large amount of caustic soda is required. Further, in order to prevent scale failure in the smoke washing tower due to sodium chloride or sodium sulfate generated by the neutralization reaction, it is necessary to forcibly discharge a part of the circulating water in the smoke washing tower to reduce the concentration.

That is, in the wet-type smoke washing tower 4, acidic gas components such as hydrochloric acid and sulfur oxides in the exhaust gas are neutralized with circulating water containing caustic soda to form sodium chloride and sodium sulfate, Be absorbed. Along with driving
The concentration of these reaction products in the circulating water rises, and if the concentration exceeds the solubility, it will be deposited as scale in the smoke washing tower, which will hinder the operation. Therefore, in order to prevent such an increase in concentration, it is necessary to forcibly blow a part of the circulating water and discharge it, and replenish the replenishing water in proportion to the discharge amount.

In order to reduce the amount of dioxins in the exhaust gas, in order to prevent activated metal from being added to the flue in front of the smoke washing tower or the circulating water of the smoke washing tower, or to prevent the elution of heavy metals from fly ash, It is also necessary to add a heavy metal fixing agent to the fly ash collected by the dust collector 3 and knead it.

As described above, conventionally, the neutralization treatment of the acidic gas in the combustion exhaust gas and the reduction treatment of the dioxins concentration, the fixing treatment of the heavy metals in the fly ash collected, and the circulating water of the smoke washing tower are carried out. For each processing such as salt concentration reduction processing, various incidental equipment is required in the exhaust gas discharge system path, etc., management items increase for these operations, and the burden of maintenance work is also great. There was a problem that became.

The present invention solves the above-mentioned conventional problems, reduces the required amount of caustic soda for neutralizing acid gas in the smoke washing tower, reduces the forced discharge amount of the circulating water of the smoke washing tower, A treatment agent for combustion exhaust gas capable of reducing the concentration of dioxins and preventing the elution of heavy metals in the collected fly ash with a single agent, and a method for treating combustion exhaust gas using such a treatment agent The purpose is to do.

[0008]

The flue gas treatment agent of the present invention is characterized by containing slaked lime, activated carbon and a heavy metal fixing agent.

Among the treatment agents of the present invention, slaked lime contributes to the neutralization treatment of acid gas, reduces the amount of caustic soda used in the smoke washing tower, and reduces the amount of scale components produced, thereby circulating water in the smoke washing tower. Reduce the forced discharge of water.

Activated carbon also reduces the concentration of dioxins in the exhaust gas that adsorbs the dioxins in the combustion exhaust gas and releases it to the atmosphere. The activated carbon is preferably a powdered active material.

The heavy metal fixing agent fixes heavy metals in soot dust and prevents elution of heavy metals from fly ash collected by the dust collector.

The flue gas treatment method of the present invention is a method for treating flue gas discharged from an incinerator by sequentially passing it through a dust collector and a wet cleaning device (smoke washing tower) to be introduced into the dust collector. The treatment chemical of the present invention is blown into the combustion exhaust gas.

When the treatment chemical of the present invention is added in front of the dust collector, slaked lime in the chemical reacts with acidic components such as hydrochloric acid and sulfur compounds in exhaust gas, and calcium chloride and calcium sulfate produced by the reaction are collected in the dust collector. Captured in. The amount of slaked lime added is 0.5 to 2.5 g / Nm with respect to combustion exhaust gas.
³ is preferable.

Further, the activated carbon in the treatment agent adsorbs dioxins, and the heavy metal fixing agent fixes the heavy metal in the dust. It is preferable that the addition amount of this activated carbon is 50 to 250 mg / Nm ³ with respect to the combustion exhaust gas, and the addition amount of the heavy metal fixing agent is 0.01 to 1 g / Nm ³ with respect to the combustion exhaust gas. The heavy metal fixing agent is preferably phosphoric acid, a phosphoric acid salt, or a dithiocarbamic acid derivative.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

In accordance with the method of the present invention, by blowing the treating agent of the present invention containing slaked lime, activated carbon and a heavy metal fixing agent in front of the dust collector 3 in a combustion exhaust gas discharge passage as shown in FIG. Slaked lime in the treatment agent reacts with acidic components such as hydrochloric acid and sulfur oxides in the exhaust gas, and the compounds of calcium chloride and calcium sulfate produced by this reaction are collected by the dust collector 3. The amount of slaked lime added is preferably such that it has the same molar equivalent as the acidic gas in the exhaust gas, especially hydrochloric acid. For example, when the concentration of hydrochloric acid is 800 ppm, the added amount of slaked lime is about 1.02 g / Nm ³ . Is preferred.

Usually, the reaction between acid gas and slaked lime is a reaction between gas and solid, so even if added theoretically in the same molar equivalent, it does not react completely. Therefore, in the dry treatment as in the present invention, it is necessary to excessively add the acidic gas in the exhaust gas in order to completely remove it by adding slaked lime. In that case, the fly ash collected by the dust collector 3 is required. The content of unreacted slaked lime in the product will increase, the pH of fly ash will rise, and lead and other substances will be eluted in large amounts, and this will cause scale problems in the water collection facility at the final disposal site.

In the present invention, the purpose of adding slaked lime is merely to reduce the salt load of the circulating water of the smoke washing tower 4 in the subsequent stage, and it is not necessary to neutralize all the acidic gas components in the exhaust gas. To reduce the elution of lead from the fly ash and the scale hindrance of the water collection facility at the final disposal site, it is not necessary to add slaked lime excessively, and the molar equivalent to hydrochloric acid in the exhaust gas may be about the same.

Thus, when slaked lime is added in the same molar amount as hydrochloric acid in the exhaust gas, hydrochloric acid is consumed by a reaction of about 40 to 60% of the theoretical amount. That is, the concentration of hydrochloric acid gas in the acid gas in the exhaust gas brought into the smoke washing tower 4 is about 40 to 60 in the conventional case.
%, Which significantly reduces the amount of caustic soda used for neutralization. Further, since the amount of the neutralization reaction product, which is a scale component, is also reduced, the forced blow amount per unit time can be reduced, and the amount of makeup water can be reduced.

In order to add slaked lime to the same molar equivalent as hydrochloric acid in the exhaust gas, 0.5 to 2.5 of slaked lime is added to the exhaust gas.
It is preferable to add about g / Nm ³ .

When the treatment agent of the present invention is blown in front of the dust collector 3, the activated carbon in the treatment agent adsorbs the dioxins generated by incineration of the dust, and the dioxins in the exhaust gas discharged from the chimney to the atmosphere. Reduce the concentration. As this activated carbon, “GL50” manufactured by Norit Co., which has excellent adsorption performance for dioxins, is suitable. The amount of the activated carbon added is preferably about 50 to 250 mg / Nm ^{3 with} respect to the exhaust gas.

By the way, dioxins discharged from the incinerator to the atmosphere include dioxins produced in the incinerator and dioxins produced by resynthesizing the precursors of the dioxins in the dust collector. When activated carbon and caustic salt are added to the exhaust gas,
It is described in JP-A-9-220438 that the latter dioxins precursor is also adsorbed and removed by activated carbon.

Therefore, in the present invention, a caustic alkali salt may be further added together before the dust collector, whereby the re-synthesis of dioxins in the dust collector can be prevented and the dioxins discharged into the atmosphere can be prevented. The concentration can be further reduced.

When the treatment chemical of the present invention is blown in front of the dust collector 3, the heavy metal fixing agent in the treatment chemical fixes the heavy metal in the dust and prevents elution.

As described above, in the case of the conventional chemical treatment method, the fly ash collected by the dust collector is mixed with the humidifying water and the heavy metal fixing agent by using a kneader, so that a chemical injection facility is required. The kneadability of the fly ash and the chemical in the kneader became a problem, but by blowing the treatment chemical containing the heavy metal fixing agent in front of the dust collector according to the present invention, the fly ash and the heavy metal fixing agent were kneaded. Eliminates the need for processing. Therefore, the chemical injection equipment to such a kneader becomes unnecessary, and
Since the fly ash and the chemical are uniformly mixed, the problem of the kneading ability of the kneading machine is solved.

Examples of the heavy metal fixing agent include phosphoric acid, phosphates such as sodium phosphate, potassium phosphate, calcium phosphate, ammonium phosphate, aluminum phosphate, and dithiocarbamic acid derivatives such as dithiocarbamate. Particularly, when a phosphate is used, it is excellent in the elution preventing effect of heavy metals under low pH conditions and the stability of the effect for a long period of time, and is extremely effective in preventing elution at the final disposal site.

The amount of the heavy metal fixing agent added is preferably 0.01 to 1 g / Nm ³ with respect to the exhaust gas.

In the present invention, it is preferable that the treatment chemicals containing slaked lime, activated carbon and heavy metal fixing agent are added to a region where the temperature of the exhaust gas discharged from the incinerator is 400 ° C. or higher. In the method of the present invention, the treatment agent of the present invention is blown into the flue in front of the dust collector where the temperature of the exhaust gas is 400 ° C or higher.

On the other hand, when the treatment agent of the present invention is blown into the dust collector, the temperature of the exhaust gas becomes less than 400 ° C., and the fly ash acts as a catalyst to convert the dioxin precursor into dioxin. This is not desirable.

The flue gas treating agent of the present invention can be prepared, for example, by mixing slaked lime, activated carbon and a heavy metal fixing agent so as to have the above-mentioned preferable addition amounts, and the form thereof is powder or powder. It may be in the form of a slurry in which is dispersed in water.

[0031]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Example 1 As shown in FIG. 1, an exhaust gas from a fully continuous stalker furnace with an incineration capacity of 100 ton / 24 hr is subjected to wet gas treatment by an electric dust collector and a smoke washing tower, and then discharged. With an exhaust gas amount of 35500 Nm ³ / hr and a design inlet hydrochloric acid concentration of 700 mg / Nm ³ ), slaked lime 53.75 wt%, powder activated carbon “GL50” manufactured by Nippon Norit Co., Ltd.
7.70% by weight, dibasic calcium phosphate (CaHPO ₄
2H ₂ O) 38.40% by weight of the treating agent was added to the flue in front of the dust collector at 1.30 g / Nm ^{3 with} respect to the amount of exhaust gas.
Continuous infusion.

Exhaust gas was sampled at points A, B and C in FIG. 1 to measure the concentration of dioxins and hydrochloric acid in the exhaust gas (point A is slightly upstream of the injection point of the treatment chemical). . In addition, the fly ash collected by the dust collector was subjected to an elution test according to the Environmental Agency Notification No. 13 to analyze heavy metals in the eluate. Furthermore, for a certain period (24 hours) of the smoke washing tower
Of make-up water and 25 wt% sodium hydroxide solution (25
% NaOH) consumption was measured.

The results are shown in Tables 1 and 2.

Comparative Example 1 Exhaust gas was sampled in the same manner as in Example 1 without injecting the treatment chemicals, and the concentration of dioxins and the concentration of hydrochloric acid in the exhaust gas were measured. In addition, a fly ash dissolution test was conducted in the same manner, and 25% NaOH consumption of makeup water was examined, and the results are shown in Tables 1 and 2.

Comparative Example 2 Treatment was carried out in the same manner as in Example 1 except that only slaked lime was injected into the flue in front of the dust collector in an amount of 0.7 g / Nm ³ with respect to the amount of exhaust gas. Is the same as the injection amount of slaked lime in the treatment agent in Example 1.), and the fly ash collected by the dust collector was subjected to the dissolution test in the same manner as in Example 1, and the results are shown in Table 2. Indicated.

[0037]

[Table 1]

[0038]

[Table 2]

The following is clear from Table 1.

That is, in Example 1, the concentration of dioxins at the point C was greatly reduced by the injection of the treatment chemical of the present invention. On the other hand, in the case of Comparative Example 1 in which no chemical is added,
The dioxin concentration at point C is higher than that at point A,
This is presumably because the dioxin precursor in the exhaust gas was resynthesized in the dust collector.

In addition, in Example 1, the concentration of hydrochloric acid in the exhaust gas at point B was decreased by the injection of the treatment chemical of the present invention,
Along with this, the amount of makeup water supplied to the smoke washing tower and the amount of 25% NaOH consumed also decreased as compared with the case of Comparative Example 1 in which no chemical was added.

Further, the following is clear from Table 2.

That is, in Example 1, the elution of heavy metals was prevented by injecting the treatment chemical of the present invention. On the other hand, Comparative Example 1 in which no chemical is added has a problem of heavy metal elution, and Comparative Example 2 in which only slaked lime is added cannot prevent the elution of heavy metals.

[0044]

As described in detail above, according to the present invention, the required amount of caustic soda for neutralizing the acid gas in the smoke washing tower is reduced, the forced discharge amount of the circulating water of the smoke washing tower is reduced, There is provided a combustion exhaust gas treatment agent capable of reducing the concentration of dioxins of the above and preventing the elution of heavy metals in the collected fly ash with one agent. Further, combustion exhaust gas can be efficiently treated using such a treatment agent.

[Brief description of drawings]

FIG. 1 is a system diagram showing a general combustion exhaust gas discharge system passage.

[Explanation of symbols]

1 incinerator 2 Exhaust gas temperature reduction device 3 dust collector 4 Exhaust gas cleaning device (smoke washing tower) 5 attraction fans 6 chimney

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Claims (5)

[Claims] 1. A flue gas treating agent comprising slaked lime, activated carbon and a heavy metal fixing agent. 2. A method for treating combustion exhaust gas discharged from an incinerator by sequentially passing through a dust collector and a wet cleaning device to treat the combustion exhaust gas introduced into the dust collector with the treatment chemical according to claim 1. A method for treating combustion exhaust gas, which comprises blowing in the gas. 3. The treatment chemical according to claim 2, wherein the addition amount of slaked lime in the treatment chemical is 0.5 to 2.5 g / Nm ³ with respect to the combustion exhaust gas. A feature of combustion exhaust gas treatment chemicals. 4. The method according to claim 2 or 3, wherein the treatment chemical is added so that the amount of activated carbon added to the treatment chemical is 50 to 250 mg / Nm ³ with respect to the combustion exhaust gas. Combustion exhaust gas treatment chemicals. 5. The heavy metal fixing agent in the treatment agent according to claim 2, which is one or more selected from the group consisting of phosphoric acid, a phosphate and a dithiocarbamic acid derivative. The amount of the heavy metal fixing agent in the treatment agent is 0.0 with respect to the combustion exhaust gas.
A treatment agent for combustion exhaust gas, which is added so as to be 1 to 1 g / Nm ³ .