JP3189032B2 - Treatment of exhaust gas from garbage incinerators - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for treating exhaust gas from a refuse incinerator.

[0002]

2. Description of the Related Art Conventionally, methods for removing harmful substances such as mercury in exhaust gas from a refuse incinerator include a wet method and a dry method.

In the wet method, as shown in the flowchart of FIG. 1, high-temperature exhaust gas (about 200 to 300 ° C.) passed from an incinerator through an electric precipitator is guided to a catalytic denitration device to be denitrated, and then subjected to a scrubber or the like. In a cleaning device, exhaust gas is brought into contact with an aqueous alkaline solution, and harmful substances in the exhaust gas are absorbed by water and removed. However, in this wet method, among mercury and mercury compounds in exhaust gas, water-soluble mercuric chloride (HgCl ₂ ) can be captured, but non-water-soluble metal mercury (Hg ⁰ ) is captured. Can not. In addition, since a separate wastewater treatment facility is required to treat the scrubber wastewater that has absorbed mercury compounds and remove mercury, it is necessary to strictly control the process,
In addition, there is a disadvantage that the cost is high.

In the dry method, as shown in a flowchart of FIG. 2, slaked lime (Ca) is added to high-temperature exhaust gas from a garbage incinerator.
(OH) ₂ ) fine powder is sprayed to react slaked lime with acidic gases (SO _x , HCl, etc.) in the exhaust gas, and then activated carbon fine powder is sprayed in the exhaust gas to remove metallic mercury in the gas. Then, the reaction product and the activated carbon fine powder adsorbing mercury are removed by a bag filter. Although this method is advantageous over the wet method in that it does not require the treatment of scrubber wastewater, it also has its own disadvantages. That is, slaked lime shows a high removal rate for mercuric chloride, but a low removal rate for metallic mercury. Therefore,
In order to adsorb and remove metallic mercury, it is necessary to use a large amount of expensive activated carbon, which increases the cost. Also, activated carbon is
At a temperature of 180 ° C or higher, the adsorption capacity is significantly reduced, and it is extremely disadvantageous to spray the activated carbon directly into the high-temperature exhaust gas after slaked lime spraying. In the case where catalytic denitration is performed, the catalytic denitration reaction at 200 ° C. or higher performed after passing through the bag filter is inhibited. Further, the high cost of processing the ash collected in the bag filter formed by spraying a large amount of slaked lime is a major drawback of the dry method.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for removing exhaust gas from a waste incinerator containing mercury at low cost and with high efficiency without using expensive equipment. Purpose.

[0006]

Means for Solving the Problems The present inventor has conducted intensive studies while paying attention to the current state of the prior art as described above, and as a result, fly ash (BF deposited ash) from a garbage incinerator deposited on a bag filter. When contacting the waste gas with the waste incinerator, B
It has been found that F sedimentary ash exhibits an extremely high mercury adsorption ability, and mercury contained in exhaust gas is removed at a high removal rate. Also, since the exhaust gas that has passed through the bag filter contains substantially no mercury, it is possible to absorb and remove and purify harmful substances in the exhaust gas into water simply by washing it with a scrubber or other washing device. Also headlined.

That is, the present invention provides the following method for treating exhaust gas from a refuse incinerator: After sending the exhaust gas from the garbage incinerator directly to the bag filter on which the incinerator fly ash was deposited to remove metallic mercury,
A method for treating exhaust gas from a garbage incinerator, wherein the treatment gas is washed by an exhaust gas washing device to remove an acid gas.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been completed based on the novel findings summarized in Examples 1 and 2 described below.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 3 is a flowchart showing the outline of the method of the present invention. In the method of the present invention, the hot exhaust gas from the incinerator is sent to a bag filter. Fly ash (incinerator fly ash without spraying slaked lime) is previously deposited on the bag filter. In this state, when the mercury-containing exhaust gas comes into contact with fly ash deposited on the bag filter, mercury in the exhaust gas is captured by the fly ash and removed from the exhaust gas. In the present invention, a sufficient mercury removal rate can be obtained even when the exhaust gas temperature is as high as about 200 ° C., and when the exhaust gas temperature is lowered, the mercury removal rate is further improved.

The exhaust gas from which mercury has been removed is washed by a known exhaust gas cleaning device such as a scrubber to remove acidic gases (SO _x , HCl, etc.). The washing wastewater is treated by a known wastewater treatment method such as a coagulation sedimentation treatment method.

The exhaust gas after the treatment is released from the chimney into the atmosphere.

When the composition of fly ash from the incinerator falls below a predetermined value (3% or more as calcium chloride and 3% or more as a carbon-based adsorbing substance), or an aid for facilitating sifting of BF deposited ash For spraying drugs such as
When the active ingredient in the F ash does not reach the predetermined value, the calcium chloride is formed in the BF ash by spraying calcium chloride or adding calcium hydroxide to the exhaust gas and reacting with HCl in the exhaust gas. Activated carbon may be supplied to make up for the insufficient carbon-based adsorptive substance.

[0014]

By using fly ash effectively, a chemical for removing mercury becomes unnecessary. Alternatively, even when such a drug is used, the amount used can be reduced.

Even at a high temperature of 200 ° C. or more, not only mercuric chloride but also metallic mercury can be removed at a high removal rate.

Since spraying of slaked lime for acid gas treatment is not performed, the amount of bag filter ash produced is greatly reduced.

[0017]

EXAMPLES Examples are shown below to further clarify the features of the present invention.

In the following embodiment using a simulated exhaust gas containing metallic mercury but not containing other impurity components, the washing and removing treatment of the acidic gas from the gas after the mercury removal and the treatment of the washing wastewater are carried out. Although not shown, these post-treatments can be easily carried out by established methods.

Example 1 In the present invention, the high ability to remove metallic mercury by fly ash at high temperatures is due to the fact that calcium chloride and a carbon-based adsorbing substance (unburned porous carbon component,
About 0 to 500 m ² / g and has an adsorption characteristic similar to activated carbon).

In order to further clarify the relationship between these contents and the mercury removal rate, mercury removal by pseudo BF deposited ash was performed in the following manner.

Activated carbon (specific surface area of about 800 m) is substituted for kaolin (inactive substance) by calcium chloride and carbon-based adsorbent.
² / g) was added at an equal ratio to prepare a pseudo BF sedimentary ash, and the effect of removing mercury in the high-temperature gas was confirmed using the apparatus shown in FIG.

Simulated exhaust gas containing metallic mercury 0.15 mg / Nm ³ was heated from line 1 to 350 ° C. by a heater in a preheating tube 3.
After that, the mixture was supplied to a glass tube 5 provided with a filter 7 and heated to 200 ° C. by a heater. The temperatures of the preheating tube 3 and the glass tube 5 were adjusted while measuring the temperature with a thermocouple. In the filter 7, a powder layer (filter cake layer) having a thickness of about 5 mm was formed from the simulated BF deposited ash prepared above. In this state, the simulated exhaust gas discharged from the filter 7 was absorbed into the absorption liquid 9 for mercury analysis and the gas meter 1.
1 and taken out of the system via the suction pump 13.

FIG. 5 shows the mercury removal effect. When the contents of calcium chloride and activated carbon are 5%, mercury removal rates as high as about 80% have been achieved.

Example 2 In order to clarify the ability to remove mercury by fly ash (corresponding to BF deposited ash when slaked lime was not sprayed), mercury in exhaust gas was removed in the following manner.

In the same manner as in Example 1 except that a mixture obtained by mixing fly ash (slaked lime was not sprayed) and slaked lime collected in a garbage incinerator at a predetermined ratio was used instead of pseudo BF sedimentary ash, Simulated mercury-containing exhaust gas was treated.

FIG. 6 shows the results. It is clear that slaked lime has little effect on mercury removal, whereas fly ash has an excellent mercury removal effect.

Table 1 shows the contents of calcium chloride and carbon in each mixture.

[0028]

[Table 1]

Example 3 A simulated exhaust gas containing mercury was treated in the same manner as in Example 1 except that the thickness of the fly ash layer on the bag filter was variously changed. Table 2 shows the results.

[0030]

[Table 2]

As is evident from the results shown in Table 2, in the method of the present invention, if the layer thickness of the BF deposited ash is about 3 mm or more, a sufficient mercury removing effect can be obtained.

In the normal operation of the bag filter of the embodiment, the BF sedimentary ash has a thickness of about 5 to 15 mm.
It is clear that sufficient mercury removal rates can be obtained even in actual facilities.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a known wet treatment method for exhaust gas from a refuse incinerator.

FIG. 2 is a flowchart showing a known dry treatment method of exhaust gas from a refuse incinerator.

FIG. 3 is a flowchart showing a method for treating exhaust gas from a refuse incinerator according to the present invention.

FIG. 4 is a flowchart showing an apparatus used in a process for removing mercury in high-temperature exhaust gas according to the first embodiment.

FIG. 5 is a graph showing a mercury removal effect in Example 1.

FIG. 6 is a graph showing a mercury removal effect in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exhaust gas introduction line 3 ... Preheating tube 5 ... Glass tube 7 ... Filter 9 ... Absorbent for mercury analysis 11 ... Gas meter 13 ... Suction pump

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B01D 53/81 (72) Inventor Teruaki Fujikawa 2-16-10 Ohnodai, Osaka Sayama-shi, Osaka (56) References JP-A-7-70 328378 (JP, A) JP-A-7-139719 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/34-53/88

Claims (2)

(57) [Claims] 1. A method for treating exhaust gas from a garbage incinerator.
Te, garbage incinerator to bag filter incinerator fly ash was deposited
A method for treating exhaust gas from a garbage incinerator, comprising removing the metallic mercury by sending the exhaust gas from the garbage without treatment, and then removing the acidic gas by washing the treated gas with an exhaust gas washing device. 2. The composition of the incinerator fly ash is calcium chloride.
At least 3% and at least 3% as a carbon-based adsorbent
The exhaust gas treatment according to claim 1, wherein the exhaust gas is treated.
Method.