JPH04256416A - Treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To cool the exhaust gas exhausted from the waste incineration furnace to low temp. of <= about 200 deg.C incapable of generating dioxin in the dust collector with very compact device and to remote an acibic halide in the exhaust gas. CONSTITUTION:Exhaust gas exhausted from a waste incineration furnace M and primarity cooled to about 300 deg.C is introduced into the treating tank 1 packed with particulates as a secondary cooling treatement to form fluidized layer or jitted layer S and the mixed solution of alkali and water is sprayed into the treating tank 1, then the exhaust gas is coded to disired temp. of <=about 200 deg.C by vaporizing water of the mixed solution and simultaneously an a acidic halide is allowed to react an alkali to separate and remote this reaction product by a dry dust collector 5.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for treating exhaust gas discharged from municipal garbage incinerators and the like.

0002

[Prior Art] In urban garbage incinerators, the exit temperature of exhaust gas is usually as high as 900°C, so the exhaust gas is cooled to a temperature of around 300°C using a heat exchange method using air or water. The exhaust gas is then led to a dry dust collector, where fine particles such as ash are removed from the exhaust gas and released into the atmosphere.

In addition, in this method, in order to remove acidic halides such as hydrogen chloride gas contained in the exhaust gas, alkaline powder such as slaked lime is generally blown into the duct in front of the dry dust collector, and this is mixed with acidic halides. A reaction with the halide is caused, and reaction products such as calcium chloride are separated and removed together with the ash in the gas using the dust collector.

By the way, it has recently been pointed out that the exhaust gas from garbage incinerators contains dioxins, and in December of last year (1990), the Ministry of Health and Welfare compiled and announced guidelines for controlling emissions. . According to this report, in order to reduce dioxins, complete combustion of garbage is desired, and it is also desirable to lower the temperature inside the dust collector as much as possible. In particular, it is pointed out that at the current temperature of around 300 degrees Celsius, there is a risk that the largest amount of dioxins will be produced inside the dust collector.

[0005] Therefore, in order to reduce the above dioxins,
After the high-temperature exhaust gas from the garbage incinerator is primarily cooled to a temperature of around 300°C using a heat exchange method using air or water, it is further subjected to a secondary cooling treatment that also serves to remove acid halides. A multistage cooling method that cools the material to a temperature of about 200° C. or lower and then introduces it to a dry dust collector is attracting attention.

[0006] In the secondary cooling treatment in this method, the exhaust gas after primary cooling is introduced into the vertical treatment tower from the top of the tower, and an alkali such as caustic soda or slaked lime is introduced from the two-fluid nozzle also installed at the top of the tower. It is designed to spray water containing water in the form of a mist. The sprayed water evaporates as it descends inside the tower, and the exhaust gas is cooled to a temperature of about 200° C. or less. The thus cooled exhaust gas is led from the bottom of the tower to a dry dust collector together with the salts and ash produced by the reaction between the alkali and the acidic halide in the exhaust gas, where the salts and ash are removed. removed and released into the atmosphere.

[0007]

However, in the conventional secondary cooling treatment described above, although the water sprayed from the top of the tower is successfully evaporated and the exhaust gas is cooled to the desired temperature,
A fairly large treatment tower is required. For example, for exhaust gas with a displacement of about 40,000 Nm3/hour assuming a general garbage incinerator, the diameter is 4.5 m and the height is 20 to 20 m.
This will be an extremely large treatment tower of approximately 25m.

[0008] In an incinerator, the related equipment is usually housed inside the building, so it is difficult to install such a tall and space-consuming treatment tower, and even if it could be installed, the construction cost would be enormous. As described above, the conventional secondary cooling treatment has had major problems that must be overcome in terms of equipment and economy.

[0009] In view of these problems, the present invention has been developed to process exhaust gas discharged from urban garbage incinerators and the like, which has been primarily cooled to a temperature of about 300°C, before introducing it into a dry dust collector. By applying a specific secondary cooling treatment that does not pose the problems in terms of equipment or economy like conventional methods, it is possible to easily cool the dust collector to a temperature of about 200°C or less, which can suppress the generation of dioxin. The object of the present invention is to provide a novel exhaust gas treatment method that can simultaneously remove acid halides from the exhaust gas.

0010

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the present inventors used a treatment tank filled with powder and granular material during the secondary cooling treatment, and after the primary cooling, The exhaust gas is introduced to form a fluidized bed or spouted bed of the powder and granules, and water containing alkali is sprayed into this layer to evaporate the water and cause the alkali to mix with the acidic halides in the exhaust gas. By allowing the reaction to proceed simultaneously on the particle surface of the powder or granular material, the exhaust gas is cooled to a desired temperature of about 200°C or less as water evaporates, and acidic halides are removed at the same time as this cooling. As a result, without increasing the size of the conventional device,
Having learned that it is possible to achieve a good secondary cooling treatment, we have completed this invention.

That is, in the present invention, exhaust gas discharged from a garbage incinerator and primarily cooled to a predetermined temperature is introduced into a treatment tank filled with granular material to form a fluidized bed or spouted bed of the granular material. water containing an alkali is sprayed into this layer, and the evaporation of this water and the reaction between the alkali and the acidic halide in the exhaust gas are simultaneously carried out on the particle surface of the powder and granular material. The exhaust gas which has been secondarily cooled to a temperature is guided to a dry dust collector together with the fine powder containing the products of the reaction, where the fine powder is removed and then released into the atmosphere. This relates to the processing method.

0012

[Operation] In the present invention, when the exhaust gas after primary cooling is introduced into the processing tank filled with powder and granules, a fluidized bed or spouted bed of the powder and granules is formed by the fluid action of the exhaust gas. When water containing alkali is sprayed into this layer and evaporation of this water and reaction between the alkali and the acidic halide in the exhaust gas occur simultaneously on the particle surface of the powder, the exhaust gas is sprayed. The cooled exhaust gas is then guided to a dry dust collector together with fine powder containing the reaction product of the alkali and acidic halide, where the above-mentioned Fine powder is removed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the configuration of an apparatus to which the exhaust gas treatment method of the present invention is applied. In the figure, 1 is a processing tank for secondary cooling treatment, 2 is a mixing tank for alkali and water, 3 is an alkali storage tank, 4 is a water storage tank, and 5 is a dry dust collector.

The treatment tank 1 has a powder filling chamber 12 partitioned by a rectifying plate 11 at the bottom of a vertical container body 10, and above the chamber 12, alkali and water are introduced from a water injection pipe L1. A spray nozzle 14 is provided for discharging the mixed liquid toward the collision plate 13, and an exhaust gas inlet 15 is provided below. Furthermore, an outlet 16 is provided in the upper part of the main body 12 to lead out the exhaust gas introduced into the main body.

In addition, in the mixing tank 2, the alkali in the storage tank 3 is transferred to a pipe L2 into a container 22 equipped with an agitator 21.
In addition, the water in the storage tank 4 is supplied through the pipe L3, mixed by the stirrer 21, and this mixed liquid is supplied to the spray nozzle 14 by the pump P1 through the water injection pipe L1. It's summery.

In such an apparatus configuration, the exhaust gas G1 discharged from a city garbage incinerator M or the like and which has been primarily cooled to a temperature of about 300° C. by a known means such as a heat exchange method using air or water is For the next cooling treatment, the treatment tank 1
When the powder and granules enter the filling chamber 12 through the rectifying plate 11, the powder and granules are made to flow or jet due to the fluid action, forming a fluidized bed or spouted bed S of the powder and granules. Form.

Here, from the spray nozzle 14 to the mixing tank 2
When you spray a mixture of alkali and water prepared in
This liquid mixture hits the collision plate 13 and scatters in the form of mist, and is dispersed within the fluidized bed or spouted bed S described above. Since the powder in the fluidized bed or spouted bed S is heated to a high temperature by the exhaust gas G1, the water in the liquid mixture that comes into contact with the particle surface is quickly evaporated, and this evaporation causes the particle surface to Alkali adhering to reacts well with acidic halides in the exhaust gas.

Reaction products such as halogen salts generated in this reaction are detached from the particle surfaces of the powder and granules due to friction because the powder and granules are in intense friction with each other due to the fluid action of the exhaust gas, and the reaction products such as halogen salts are released from the exhaust gas. At the same time, it scatters above the container body 10.

The exhaust gas G2 thus led out from the outlet 16 is cooled to a temperature of about 200° C. or less as the water evaporates. This exhaust gas G2 is then
The fine powder Pd containing a halide salt, which is a reaction product of an alkali and an acidic halide, an unreacted alkali, and ash in the exhaust gas, is guided to the dry dust collector 5 through a pipe L4.

In the dust collector 5, the above-mentioned fine powder Pd is separated and removed from the lower outlet 51, and the thus purified exhaust gas G3 is sent through the pipe L5 and the exhaust pump P2.
released into the atmosphere. On the other hand, the separated and removed fine powder P
d is transported by a screw-type transporter 52 and discharged to the outside by a discharger 6 from its discharge port 53. Since this fine powder Pd contains a portion of unreacted alkali, it may be reused as an alkali raw material to be supplied to the mixing tank 2 if necessary.

In this method, the alkali used to prepare the mixed solution may be easily soluble such as caustic soda, or may be one that forms a slurry such as Mg(OH)2 or Ca(OH)2. It's okay. The amount used is preferably 1.0 to 1.5 times the chemical equivalent of the acid halide in order to sufficiently neutralize the acid halide in the exhaust gas, and As for the alkaline concentration,
It is usually desirable that the amount is about 1 to 5% by weight.

The mixed liquid sprayed from the spray nozzle 14 cools the exhaust gas as the liquid evaporates, and the degree of cooling is determined by the amount of the mixed liquid. The amount of liquid may be adjusted as appropriate through automatic control of the valve V1 and the detector T1 that detects the temperature of the exhaust gas led to the upper part of the processing tank 1.

[0024] The powder and granules to be filled in the processing tank 1 are as follows:
River sand and other mineral materials are generally used, but basic materials such as MgCO3, CaCO3, MgCO3.CaCO3 may also be used in some cases. The particle size of the granular material is usually about 1 to 10 mm. Although it varies depending on the material, the form of the fluidized bed or spouted bed S formed by the fluid action of the exhaust gas G1 is generally determined depending on the particle size of the powder or granular material. In other words, when the particle size is about 1 to 5 mm, it becomes a fluidized bed;
If it is as large as 10 mm, it becomes a spouted bed.

[0025] It should be noted that there is a risk that these powder particles will gradually become pulverized due to friction while forming the fluidized bed or spouted bed S, that is, while cooling the exhaust gas. Therefore, it is recommended to additionally fill the container with new powder over time. In addition, especially when forming a spouted bed, a hollow iron ping-pong ball or the like may be used instead of the powder having the above-mentioned particle size.

In the exhaust gas treatment method based on the above-mentioned device configuration of the present invention, the size of the treatment tank 1 used for secondary cooling is, for example, a particle size of about 4 mm that allows the powder and granules filled therein to form a fluidized bed. In the case of river sand with
The river sand, which has a diameter of about 2.5 m and a height of about 1.8 tons, can be filled with the exhaust gas of about 1 hour (the height of the static bed of powder and granules is about 15 cm, and the height of the fluidized bed is about 15 cm). Saga about 23
It is sufficient to have a chamber with a total length of about 5 m. Therefore, the device is much more compact than the conventional device, and can be easily introduced into urban garbage incineration plants.

[0027]

As described above, according to the exhaust gas treatment method of the present invention, the exhaust gas discharged from the garbage incinerator can be treated with a very compact device without the risk of generating dioxins in the dust collector. It can be easily cooled to an appropriate temperature of 200℃ or less, and acid halides in the exhaust gas can be removed at the same time, so it is easy to apply to general incinerators and is advantageous from an equipment and economic perspective. This method can be used in a wide range of ways.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of an apparatus to which the exhaust gas treatment method of the present invention is applied.

[Explanation of symbols]

1: Processing tank
2: Alkali and water mixing tank 3: Alkali storage tank 4
:Water storage tank 5 :Dry dust collector
G1: Exhaust gas after primary cooling G2: Exhaust gas after secondary cooling G3:
Exhaust gas Pd released into the atmosphere: fine powder
M: Garbage incinerator S: Fluidized bed or spouted bed of powder and granules

Claims (3)

[Claims] 1. Introducing exhaust gas discharged from a garbage incinerator and primarily cooled to a predetermined temperature into a treatment tank filled with granular material to form a fluidized bed or spouted bed of the granular material,
Water impregnated with alkali is sprayed into this layer, and the evaporation of this water and the reaction between the alkali and the acidic halide in the exhaust gas are simultaneously carried out on the particle surface of the powder, thereby allowing the temperature to rise to an appropriate temperature. A method for treating exhaust gas, characterized in that the cooled exhaust gas is led together with fine powder containing the products of the reaction to a dry dust collector, where the fine powder is removed and then released into the atmosphere. Claim 2: The temperature of the exhaust gas after primary cooling is approximately 300.
The method for treating exhaust gas according to claim 1, wherein the temperature is about 200°C or less by a secondary cooling treatment. 3. The method for treating exhaust gas according to claim 1, wherein the granular material is made of river sand or other mineral material and has a particle size of about 1 to 10 mm.