JPH0957230A - Treatment of waste incinerating furnace fly ash and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detoxicate dioxin and the like contained in fly ash discharged from a waste incinerating furnace. SOLUTION: In this treatment of the fly ash of the waste incinerating furnace by which the fly ash recovered from the waste incinerating furnace is heated to thermally decompose organic fluorine compounds such as dioxin contained in the fly ash, fly ash is granulated, and then the granulated fly ash is fed to a boiler, and is heated to 400-600 deg.C by waste combustion gas passing through the boiler. The granulated diameter of the fly ash is made 3-50mm. Further, there are provided a granulator 8 for granulating the fly ash recovered by a dust collector 3, a heater 6 installed in the boiler and for heating the fly ash, and a fly ash conveyor 5 for conveying the fly ash discharged from the dust collector 3 to the granulator 8 and then to the heater 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fly ash treatment method and a treatment apparatus for detoxifying organic chlorine compounds such as dioxins contained in fly ash discharged from a refuse incinerator.

[0002]

2. Description of the Related Art Conventionally, extremely toxic dioxins and precursors of dioxins such as chlorobenzene and chlorophenol are contained in fly ash discharged and collected from a refuse incinerator that incinerates municipal waste and combustible waste. Organic chlorine compounds such as substances (collectively referred to as organic chlorine compounds such as dioxins) are included.

As a method for detoxifying dioxins contained in this fly ash, Japanese Patent Laid-Open No. 2-78479 discloses a method in which a reducing atmosphere such as nitrogen or a low oxygen atmosphere of 5% or less is used in a sealed conveyor. At the same time, the fly ash is indirectly reheated by the sensible heat of the electric heater or the high-temperature exhaust gas to thermally decompose the organic chlorine compounds such as dioxins contained in the fly ash, and the fly ash is heated to as much as 200 after the heat treatment. A technique of rapidly cooling to below ℃ is disclosed.

Thus, even if chlorine remains in the fly ash after the heat treatment, the re-synthesis of dioxins is prevented and the fly ash is rendered harmless.

Further, in Japanese Patent Laid-Open No. 7-157723, fly ash is supplied into a fly ash heating device installed in the lower part of the boiler on the exit side of the refuse incinerator, and the fly ash is directly supplied by combustion exhaust gas passing through the lower part of the boiler. Techniques for heating are disclosed. This allows
The harmful organic chlorine compounds such as dioxins contained in the fly ash are heated to 400 to 600 ° C. and thermally decomposed to render the fly ash harmless.

[0006]

SUMMARY OF THE INVENTION
In the detoxification treatment method disclosed in JP-A-2-78479, an inert gas such as nitrogen is required to create a low oxygen atmosphere,
Moreover, since electric energy is required for heating by the electric heater, there is a problem that the processing cost is high.

In the method of directly heating fly ash by combustion exhaust gas disclosed in Japanese Patent Laid-Open No. 7-155723, since the fly ash is a fine powder, the combustion exhaust gas passing through the boiler causes the fly ash to be scattered. cause. For this reason, the heating device had to be installed in the lower part of the boiler with a low gas flow rate. As a result, the heat transfer efficiency is lowered and the fly ash processing capacity is limited.

Further, since powder fly ash has a low thermal conductivity, the fly ash moving in the heating device cannot be stably heated to 400 to 600 ° C., and it takes a considerable time to render it harmless. There was a problem.

Further, when heating, if the low melting point condensable substance contained in the fly ash is grasped and the proper heating temperature is not set, the low melting point condensable substance will melt in the heating device. There is a problem that the powder fly ash is fused on a large scale and interferes with the subsequent fly ash transportation.

The present invention has been proposed to solve the above-mentioned problems of the prior art, in which fly ash recovered from a refuse incinerator is supplied into a boiler and heated by exhaust gas passing through the boiler. In addition, when pyrolyzing organic chlorine compounds such as dioxins contained in fly ash to make them harmless, heating efficiency is high, fly ash processing capacity is large, and there is no restriction on the installation location of the fly ash heating device. It is intended to provide a highly reliable fly ash treatment method and treatment device.

[0011]

The invention of claim 1 relates to a refuse incinerator for heating fly ash recovered from a refuse incinerator to thermally decompose organic chlorine compounds such as dioxins contained in the fly ash. In a fly ash treatment method, fly ash is granulated, and then the granulated fly ash is supplied into a boiler and heated to 400 to 600 ° C. by combustion exhaust gas passing through the boiler. This is the fly ash treatment method.

Fly ash discharged from the refuse incinerator is collected and collected by an electric dust collector or the like. The collected fly ash is granulated by a fly ash granulator.

Then, even if the granulated fly ash (hereinafter referred to as the granulated fly ash) is supplied into the boiler and the granulated fly ash is exposed to the combustion exhaust gas passing through the boiler, the bulk density increases. Therefore, the granulated fly ash does not scatter.

Further, the granulated fly ash has a higher bulk density and a higher thermal conductivity than the non-granulated powder fly ash. Therefore, the granulated fly ash can be uniformly and efficiently heated in a short time.

By setting the heating temperature at this time to 400 to 600 ° C., the thermal decomposition temperature of the dioxins in the fly ash becomes higher than the thermal decomposition temperature, and the dioxins are rendered harmless.

When the heating temperature is lower than 400 ° C., the organic chlorine compounds such as dioxins in the fly ash are not thermally decomposed and are not rendered harmless. When the heating temperature exceeds 600 ° C, the fly ash is partially melted and the fly ash is fused, which makes it difficult to convey the fly ash and requires extra heat energy for heating, which is not preferable. .

According to a second aspect of the present invention, there is provided the fly ash treatment method, wherein the fly ash has a particle size of 3 to 50 mm.

By setting the granulation particle size of the fly ash to 3 to 50 mm, even if the granulated fly ash is exposed to a large amount of combustion exhaust gas passing through the boiler, the granulated fly ash does not scatter. As a result, the restrictions on the installation location of the fly ash heating device in the boiler are eliminated, and the thermal conductivity is increased by granulation, and the fly ash processing capacity can be greatly increased.

Even if the granulated fly ash is heated and the low melting point cohesive substance in the fly ash is melted, since fusion occurs between the granulated fly ash particles, the impact between the particles causes fusion between the particles. Fly ash is transported smoothly because the garments are easily broken.

When the diameter of the fly ash is less than 3 mm, when the fly ash is conveyed by using a fly ash conveying device such as a screw conveyor, the granulated fly ash enters the gap between the casing and the screw and is granulated. Fly ash is mechanically destroyed or is deposited on the inner wall of the casing, which increases transport resistance, which is not preferable.

Granulation If the fly ash diameter exceeds 50 mm, it becomes difficult to granulate to a uniform particle diameter, uneven heating occurs, and the heat transfer area per unit weight decreases, so that the heating efficiency is reduced. descend.

According to a third aspect of the present invention, as a fly ash treatment apparatus capable of performing such fly ash treatment, in a fly ash treatment apparatus of a refuse incinerator equipped with a dust collector, dust is collected by the dust collector. The fly ash granulator that granulates fly ash, the fly ash heating device that is installed in the boiler, and heats the granulated fly ash whose upper surface is opened in the boiler, and the fly ash that is collected from the dust collector. A fly ash processing apparatus comprising a fly ash granulating device and a fly ash transporting device for transporting to a fly ash heating device.

After being granulated to a predetermined particle size and strength by the fly ash granulating device, the fly ash is conveyed by the fly ash conveying device into the fly ash heating device installed in the boiler.

Since the upper surface of this fly ash heating device is open to the inside of the boiler, the granulated fly ash is in direct contact with the combustion exhaust gas and efficiently heated above the thermal decomposition temperature of dioxins in a low oxygen atmosphere. Therefore, dioxins are thermally decomposed and rendered harmless.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a situation in which a fly ash treatment apparatus according to an embodiment of the present invention is incorporated in a refuse incinerator to perform fly ash treatment.

In FIG. 1, 1 is a boiler, 2 is a harmful gas treatment device, 3 is a dust collector, 4 is a chimney, 5 is a fly ash conveying device, 6 is a fly ash heating device, and 7 is a fly ash heating device. A screw feeder provided, 8 is a fly ash granulating device, 10 is an induced blower, 11 is a flow of combustion exhaust gas, 12 is a flow of fly ash, and 13 is a fly ash pit.

When municipal refuse, industrial waste, etc. are incinerated in a refuse incinerator (not shown), high temperature combustion exhaust gas (usually about 1000 ° C.) is generated. The combustion exhaust gas usually contains fly ash of about several grams / Nm ³ .

The generated exhaust gas is guided to the boiler 1 and the sensible heat of the exhaust gas is heat-exchanged. The exhaust gas temperature after heat exchange in the boiler 1 (exhaust gas temperature at the outlet of the boiler 1) is about 30.
It becomes 0-400 degreeC.

After that, the exhaust gas is guided into the harmful gas treatment device 2 and sprayed with the slaked lime slurry to remove harmful gas components such as HCl and SO ₂ in the exhaust gas.

Next, the exhaust gas is guided into the dust collector 3 such as an electric dust collector, the fly ash in the exhaust gas is collected and discharged from the lower part of the dust collector 3, and the exhaust gas is discharged from the chimney 4 to the atmosphere. Is discharged.

The fly ash discharged from the lower part of the dust collector 3 is
Fly ash granulation device 8 by fly ash transfer device 5 such as a conveyor
And is granulated in the fly ash granulator 8 to 3 to 50 mm. As the fly ash granulating device 8, a disk pelletizer having a higher granulation efficiency (productivity) than the drum pelletizer is desirable.

Further, since the fly ash alone is inferior in granulation property,
Before loading into the fly ash granulation device 8, a proper amount of binder and water may be added to ensure a predetermined granulation strength and granulation efficiency.

The granulation strength at this time may be such that it is not mechanically broken during transportation by the fly ash transporting device 5, and if the strength is extremely higher than this, the mechanical strength of the fly ash transporting device 5 will be high. It causes trouble and is not preferable.

A fly ash hopper (not shown) for temporarily storing the granulated fly ash is provided in the fly ash granulator 8 and is supplied to the fly ash heating device 6 in the next step. The feed rate can be freely controlled without being affected by the granulation rate.

The granulated fly ash stored in the fly ash hopper is transported to the fly ash heating device 6 by the fly ash transport device 5 such as a belt conveyor. The fly ash transfer device 5 may be a device other than the belt conveyor as long as it is a transfer device that does not mechanically break the granulated fly ash.

According to the investigation of the inventors, 400 g
In order to heat to ~ 600 ° C, the temperature of the exhaust gas supplied to the fly ash heating device 6 should be in the range of 500 ° C or higher to 800 ° C, and the sensible heat of the combustion exhaust gas passing through the boiler 1 serves as a heating source. It turned out to be fully available. In the present embodiment, as shown in FIG. 1, the fly ash heating device 6 is installed on the upstream side in the boiler 1.

The fly ash heating device 6 is installed so as to penetrate the inside of the boiler, and since the upper surface of this device 6 is open, it directly contacts the combustion exhaust gas passing through the upstream side in the boiler 1. , Granulated fly ash is efficiently heated.

In addition, the fly ash heating device 6 is provided with a screw feeder 7, and by rotating the screw feeder 7, the granulated fly ash is stirred and mixed, and the fly ash heating device 6 is supplied with an inlet. The sensible heat of the exhaust gas is more efficiently transferred to the granulated fly ash and heated because the sensible heat of the exhaust gas moves from the section to the exit section.

The heating time of the granulated fly ash is determined by the moving speed of the fly ash heating device 6 and can be controlled accurately by controlling the number of revolutions of the screw feeder 7. It can range from 10 to 60 minutes. At this time, a temperature range of 500 ° C. or higher to 80
Since the exhaust gas passing through the boiler 1 at 0 ° C. is used,
The granulated fly ash is heated in the range of 400 to 600 ° C.

In the present invention, since the heating is controlled as described above, it is not necessary to use an electric heater or the like as an auxiliary heat source.

[0041]

【Example】

Confirmation test (1): Investigation of influence of heating time In this test, a small electric furnace was used to measure HCl concentration of 1000.
Fly ash was heated in a simulated exhaust gas with ppm and water content of 20%, and the effect of heating time on the decomposition of dioxins was investigated.

As heating conditions, the granulated fly ash was heated to 500 ° C. for 3 to 60 minutes. The test results are shown in FIG.

In this example, the fly ash granulator 8 was used to granulate the granules to have a particle size of 10 to 20 mm, and the granulated fly ash was heat treated to measure the concentration of dioxins in the granulated fly ash. It is converted to the toxicity equivalent conversion concentration.

In the comparative example, the concentration of dioxins when the powder fly ash discharged from the lower part of the electrostatic precipitator was heat-treated under the same conditions was measured and converted into a toxicity equivalent conversion concentration.

From FIG. 2, it was confirmed that the toxicity equivalent conversion concentration remarkably decreased as the heating time increased in both the examples and the comparative examples. Especially, the decrease of granulated fly ash is remarkable, and the toxicity equivalent conversion concentration is 0.01 ng-Teq in about 10 minutes of heating time.
/ g or less was achieved.

On the other hand, powder fly ash not granulated is 0.01 ng-Teq / g
It took 20 minutes or more to become the following.

Confirmation test (2) In this test, fly ash is granulated under the same conditions as in the confirmation test (1), and the fly ash treatment apparatus shown in FIG. Heating temperature of 500 due to combustion exhaust gas
The concentrations of dioxins in the fly ash were investigated when heated at 20 ° C. for 20 minutes (Example) and when neither granulated nor heated (Comparative Example).

Table 1 shows the test results.

[0049]

[Table 1]

From Table 1, in Examples, the toxicity equivalent conversion concentration in fly ash was 0.003 ng-Teq / g, which was reduced to a sufficiently low value and rendered harmless.

On the other hand, in the comparative example in which the collected ash (fly ash) discharged from the lower part of the electrostatic precipitator was not subjected to the above treatment, the toxicity equivalent conversion concentration was as high as 1.2 ng-Teq / g. there were.

[0052]

According to the present invention, after the fly ash is granulated by the fly ash granulator, the granulated fly ash is supplied to the fly ash heating device installed in the boiler and passes through the boiler. Since it can be accurately heated to 400 to 600 ° C. by the combustion exhaust gas, organic chlorine compounds such as dioxins can be thermally decomposed, and highly reliable detoxification treatment becomes possible.

Granulated fly ash does not scatter even if it is exposed to the exhaust gas passing through the boiler. Therefore, it is possible to eliminate restrictions on the installation location of the fly ash heating device installed in the boiler, and to improve the heat transfer efficiency. It is possible to improve the fly ash processing capacity. Further, even if the low-melting-point cohesive substance in the fly ash is melted, large-scale fly ash fusion does not occur, which enables smooth fly ash treatment.

[Brief description of drawings]

FIG. 1 is a diagram showing a situation in which a fly ash treatment apparatus according to an embodiment of the present invention is incorporated in a refuse incinerator to perform fly ash treatment.

FIG. 2 is a diagram showing the results of an investigation of the effect of heating time on the thermal decomposition of dioxins.

[Explanation of symbols]

 1 Boiler 2 Hazardous gas treatment device 3 Dust collector 4 Chimney 5 Fly ash transport device 6 Fly ash heating device 7 Screw feeder 8 Fly ash granulator 9 Electric heater 10 Induction blower

Claims (3)

[Claims] 1. A method for treating fly ash in a refuse incinerator, which heats fly ash recovered from the refuse incinerator to thermally decompose organic chlorine compounds such as dioxins contained in the fly ash. Then, the granulated fly ash is supplied into the boiler, and 400 to 60 is generated by the combustion exhaust gas passing through the boiler.
A method for treating fly ash in a refuse incinerator, which comprises heating to 0 ° C. 2. The method for treating fly ash in a refuse incinerator according to claim 1, wherein the fly ash has a particle size of 3 to 50 mm. 3. A fly ash treatment apparatus for a refuse incinerator equipped with a dust collector, wherein the fly ash granulator for granulating the fly ash collected by the dust collector and the upper surface installed in the boiler. Equipped with a fly ash heating device that heats the granulated fly ash released in the boiler, a fly ash granulation device that transports the fly ash collected from the dust collector, and then a fly ash transport device that transports it to the fly ash heating device. A fly ash processing device characterized in that