JP2742847B2 - High-performance comprehensive exhaust gas treatment method - 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 treating exhaust gas discharged from an incinerator of municipal solid waste and industrial waste, an industrial furnace, and the like. The present invention relates to a treatment method excellent in removing harmful substances such as heavy metals and dioxins.

[0002]

2. Description of the Related Art Exhaust gas from incinerators for municipal solid waste and industrial waste includes dust, acid gases (HCl, SOx, HF, etc.), and heavy metals (Hg, Cd, P).
b, As, Zn, etc.) and harmful substances such as dioxins. Such exhaust gas has been conventionally treated by the following method.

A first method is shown in a flowchart of FIG. The exhaust gas from the incinerator is cooled in a waste heat recovery boiler or a water jet cooling tower, and then treated in a dry electric dust collector (EP) and a wet smoke cleaning device. This method is widely used as a method for removing heavy metals such as dust, acid gas, and mercury with high efficiency. However,
In this method, a dry electric precipitator (EP) has 200
There is a problem that dioxin is regenerated at a temperature of at least 250C, especially at a temperature of at least 250C, and dioxin cannot be sufficiently removed.

A second method is a bag filter method shown in the flowchart of FIG. The exhaust gas is cooled in a waste heat recovery boiler or a water jet cooling tower and then passed through a temperature control tower or a slurry spray tower. Slaked lime slurry is introduced in the slurry spray tower. Subsequently, slaked lime is introduced and processed by a bag filter. Bag filter ash is cement solidified,
Landfill dumping. This method has become mainstream in Japan and overseas since the guidelines on dioxin emission reduction (December 1990) were issued. However, in this method, the removal of mercury is unstable, and the removal of dioxin is also unstable depending on fly ash.
In addition, the greatest challenge of this method is the harmless stabilization of the bag filter ash. According to this method, the collected ash is cement-solidified using a heavy metal fixing agent. Problems.

A third method is the EDV method (simultaneous dust / smoke washing wet processing method) shown in the flowchart of FIG. The exhaust gas is cooled in a waste heat recovery boiler or a water jet cooling tower, and then processed in a dust removing tower and an absorption tower. Slaked lime is introduced in the dust removal tower, and caustic soda is introduced in the absorption tower. Subsequently, it is processed in a wet electric precipitator. This method
Acid gas and mercury removal rates are better than bag filters. Also, the collected ash is superior to the bag filter in that it can be harmlessly stabilized by wastewater treatment, and the amount of collected ash can be reduced to about 1/4 of that in the case of a bag filter (as cement solidified). ing. However, dust removal is inferior to bag filters. For the removal of dioxin, a performance close to that of a bag filter is obtained, but the removal rate is unstable.

A fourth method is shown in the flowchart of FIG. In this method, a wet smoke washing treatment is further performed in addition to the above second method. In this method, the removal rate of acid gas and mercury is improved as compared with the second method. However, since the collected ash from the bag filter is also cemented, there is a problem similar to the second method.

The fifth method is shown in the flowchart of FIG. The exhaust gas is cooled by a waste heat recovery boiler,
Next, it is treated by a dry electric precipitator and is subjected to a wet smoke treatment.
Subsequently, it is processed by a bag filter. A small amount of activated carbon / slaked lime is introduced upstream of the bag filter to reduce dioxins. The dry electric precipitator treatment and the wet smoke treatment are performed in front of the bag filter in order to prevent the bag filter from being burned out by sparks from the boiler. This method requires the treatment of collected ash with an electrostatic precipitator and a bag filter, the treatment of drainage of wet smoke, and the process is extremely complicated.

The present invention solves the above various problems and provides an exhaust gas treatment method capable of efficiently removing harmful substances such as dust, acid gas, heavy metals and dioxins in exhaust gas. Aim.

[0009]

Means for Solving the Problems The exhaust gas treatment method of the present invention has been devised to achieve the above-mentioned object. In treating the combustion exhaust gas, water is injected (1) into the exhaust gas and the exhaust gas is treated. Dissolve and remove heavy metals, dissolve heavy metals
Solid-liquid separation of the acidic water, detoxifying the separation liquid containing heavy metals
Heat treatment of the separated solid containing dioxin.
And / or detoxification by cement solidification method
Alkali is added to the exhaust gas after water injection , treated in the dust removal tower (2), and acid gas is alkali-absorbed in the gas absorption tower (3).
Subsequently, an alkali is added to the exhaust gas, the dust is removed by a bag filter (4), and the clean exhaust gas is released.The collected ash containing the excess alkali is transferred to the dust removal tower (2). It is.

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

In the present invention, water injection into combustion exhaust gas (1)
Then, since a large amount of acidic gas is contained in the exhaust gas, the injected water dissolves these gases and becomes acidic at pH <2. Therefore, at the same time, heavy metals in the exhaust gas can be dissolved and removed from the exhaust gas.

The acidic water in which the heavy metal is dissolved is treated as a waste liquid as follows. That is, first, the acidic water is solid-liquid separated by a centrifuge, a screw brace, a filter press, or the like. The heavy metal exists on the liquid side, and is treated by a conventional treatment method (a combination treatment of a liquid chelate method, a sodium hydrosulfide method, an alkali coagulation method, sand filtration, chelate, and the like). On the other hand, since sludge (solid) contains ss-shaped dioxin, it is treated by a heat treatment method, a cement solidification method, or the like.

An alkali is added to the exhaust gas from which the heavy metals have been removed as described above, and the acid gas still contained is neutralized to form a salt, which is removed by the dust removing tower (2). Slaked lime is generally used as the alkali, but is not necessarily limited thereto. Gas absorption tower to further remove acidic gas
Perform alkali treatment in (3). The preferred alkali is, but is not necessarily limited to, caustic soda.

An alkali is added to the exhaust gas, and the exhaust gas is collected by a bag filter (4). The alkali is usually 2 stoichiometric.
Add ~ 3 equivalents. The preferred alkali is slaked lime.
Activated carbon can be added together with the alkali. In the present invention, the bag filter ash containing excess alkali is transferred to the dust removal tower (2), and the alkali is effectively reused. This reduces the consumption of alkali and solves the problem of treating alkali. In addition, the amount of landfill solids in the collected ash from the bag filter can be significantly reduced.

[0015]

EXAMPLE A comparison was made between the processing method of the present invention in FIG. 1, the bag filter processing method in FIG. 3, and the EDV processing method in FIG.

Table 1 shows various performances of the obtained combustion exhaust gas treatment.

[0017]

[Table 1] As described above, the treatment method of the present invention is superior to the conventional bag filter treatment method and EDV treatment method in removing harmful substances such as dust, acid gases (HCl, SOx), heavy metals (Hg), and dioxins. Was. In particular, there was a remarkable effect on the dioxin removal rate. Also,
Slaked lime consumption and landfill solids were also significantly reduced as compared to the conventional bag filter processing method.

[0018]

As described above, the method for treating combustion exhaust gas according to the present invention comprises the steps of: (1) injecting water into the exhaust gas to dissolve and remove heavy metals in the exhaust gas;
(2), acid gas is alkali-absorbed in the gas absorption tower (3), alkali is then added to the exhaust gas, and the dust is removed by the bag filter (4) to discharge the clean exhaust gas. Compared to the bag filter processing method and the EDV processing method,
It is excellent at removing harmful substances such as dust, acid gas, heavy metals and dioxin, and has a remarkable effect particularly on the dioxin removal rate. In addition, the bag filter collected ash containing excess alkali is transferred to the dust removal tower (2) and reused, so that the consumption of slaked lime and the amount of landfill solids can be significantly reduced as compared with the conventional bag filter processing method. it can. Water is also injected into the exhaust gas to remove heavy metals in the exhaust gas.
After dissolving and removing, the acidic water in which heavy metals are dissolved is solid-liquid
Separation and detoxification of the separation liquid containing heavy metals
Detoxification of separated solids containing xinx, so heavy metals and
Release of harmful substances such as dioxin out of the system
Can be processed without delay.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flowchart of an exhaust gas treatment method of the present invention.

FIG. 2 is a diagram showing a flowchart of a conventional exhaust gas treatment method.

FIG. 3 is a view showing a flowchart of a conventional exhaust gas treatment method.

FIG. 4 is a view showing a flowchart of a conventional exhaust gas treatment method.

FIG. 5 is a view showing a flowchart of a conventional exhaust gas treatment method.

FIG. 6 is a view showing a flowchart of a conventional exhaust gas treatment method.

[Explanation of symbols]

 (1)… Water injection (2)… Dust removal tower (3)… Gas absorption tower (4)… Bag filter

Claims (2)

(57) [Claims] In treating flue gas, water is injected into the flue gas to dissolve and remove heavy metals in the flue gas, and the acidic water in which the heavy metals are dissolved is solid-liquid separated to contain the heavy metals.
Detoxify the separated liquid and remove the dioxin-containing separated solid.
By heat treatment and / or cement setting
Detoxification treatment, alkali is added to the exhaust gas after the above water injection, treated in the dust removal tower (2), alkali gas is absorbed in the gas absorption tower (3), and then alkali is added to the exhaust gas to make a bag. The filter (4) collects dust and discharges clean exhaust gas.The collected ash containing excess alkali is collected by the dust removal tower (2).
An exhaust gas treatment method, wherein the method is carried out. 2. A separation liquid containing a heavy metal is subjected to liquid chelation.
Method, sodium hydrosulfide method, alkali coagulation method, sand filtration and / or
Or the detoxification treatment by chelation.
the method of.