JP3428461B2 - Removal method of dioxins in exhaust gas - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dioxins contained in exhaust gas from waste incinerators, waste melting furnaces and other waste treatment furnaces, and steel furnaces and other industrial heating and melting furnaces. TECHNICAL FIELD The present invention relates to a method for removing dioxins in exhaust gas for removing gases.

[0002]

2. Description of the Related Art Exhaust gas discharged from waste incinerators, waste melting furnaces and other waste treatment furnaces, and steelmaking furnaces and other industrial heating / melting furnaces has acidic gases such as HCl and SOx. In addition to the substances, harmful substances such as dust (soot dust), NOx, heavy metals, and dioxins (hereinafter, also referred to as DXNs) are included.

[0003] Among them, it is known that dioxins can be removed by operating a dust collector such as a bag filter (hereinafter also referred to as BF) in a temperature range of 200 ° C or lower. The removal mechanism is that dioxin is adsorbed on the dust in the exhaust gas and the dust adsorbing the dioxin is collected by the dust collector.

[0004]

However, in the above-mentioned method, the removal rate of dioxins varies considerably, and the "Minimization of Dioxins related to waste treatment prevention announced by the Ministry of Health and Welfare in January 1997. It is very difficult to achieve the standard value (emission concentration: 0.1 ng-TEQ / Nm ^{3 in} the case of all newly installed stations) indicated in the “Guidelines (new guidelines)” in a stable manner.

It is considered that the reason why the removal rate is not stable is that the properties of the dust acting as an adsorbent in the exhaust gas are not constant and change depending on the operating conditions. Therefore, today, in order to stably clear the standard value and to remove dioxins to a high degree, the dust collector is operated at low temperature, which is advantageous for adsorption, and the dust collector inlet flue is used as a fine adsorbent. A method of blowing powdered activated carbon is used.

However, in this case, since the expensive activated carbon is continuously used, the running cost is significantly increased, and the temperature reducing device is required in front of the dust collecting device for low temperature operation. Not only the cost but also the running cost will increase.

On the other hand, when a catalytic denitration device or a white smoke prevention device is installed after the dust collector, the exhaust gas discharged from the dust collector needs to be reheated to about 200 ° C., which increases energy cost. There is also a problem.

The present invention solves the above problems, and an object of the present invention is to provide a method for removing dioxins in exhaust gas stably, highly efficiently and efficiently in a dust collector. It is a thing.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have paid attention to the fact that unburned carbon contained in dust in incineration exhaust gas has the same fixed carbon as activated carbon as a main component.
The present inventors have completed the present invention by finding that the dust contains various substances having the ability to adsorb dioxins, and that the dust is improved in the ability to adsorb dioxins by being pulverized.

[0010] That is, the method of removing the exhaust gas dioxins of the present invention, the exhaust gas treatment system leading to the dust collector from the processing furnace, after taking out the dust in the exhaust gas that has settled before reaching the dust collector to the outside of the system It is returned to the dust collector of the exhaust gas treatment system . Also, the exhaust gas is gas cooled
Dust collected through the tower to the dust collector and taken out of the system
Return to the gas cooling tower or dust collector of the exhaust gas treatment system
It is characterized by In addition, the dust that settled in the exhaust gas treatment system
To remove the gas from the system and return it to the exhaust gas treatment system.
At that time, dust is transported by the transport air from the air supply device.
It is characterized by returning it through piping.

Further, it is characterized in that the dust taken out of the system is pulverized by a pulverizing means and the powdery dust is returned to the exhaust gas treatment system. In addition, in an exhaust gas treatment system that guides the exhaust gas from the treatment furnace to a dust collector, the dust in the exhaust gas is pulverized by a pulverization means arranged in the system. The main adsorbed substances contained in the dust are considered to be unburned carbon and oxides such as silica with a porous surface, but in addition to these, many components also aggregate and adsorb. It is believed that there are many adsorbents, such as aggregates that create an easy surface condition.

First, unburned carbon which is considered to have the highest adsorption capacity will be described. Most of unburned carbon in the exhaust gas exists in the form of flakes. This unburned carbon is the same carbonaceous material as activated carbon, 1) its surface is non-polar, 2)
Since it can be seen that the specific surface area reaches the same level as that of powdered activated carbon (about 600 to 1000 m ² / g), it is considered that the ability to adsorb dioxins is high.

Moreover, unburned carbon is dust (generally 1-3
g / Nm ³ ) usually contains more than 1% (w / w), and it is considered that the amount of dioxins contained in exhaust gas is small (generally 1-10 ng-TEQ / Nm ³ ). If
Both quality and quantity are considered to be sufficient as an adsorbent.

However, the activated carbon powder has an average particle size of 10 to 20.
In contrast to μm, flaky unburned carbon is usually several mm to several cm in length on one side, and because it has a huge and planar structure, it is difficult to mix and stir in gas, and it is huge. Is extremely small compared to the amount of powder activated carbon which is usually sprayed (50 to 300 mg / Nm ³ ).

Therefore, the unburned carbon has a low contact efficiency with the exhaust gas, and in the case of BF, most of the unburned carbon reaches the hopper without reaching the filter layer on the surface of the filter cloth which is effective as a reaction site. It is considered to settle.

Further, it is considered that the amount and shape of unburned carbon generated from the furnace are constantly changing, and the contact efficiency with the exhaust gas is also changing accordingly. On the other hand, the powdered activated carbon is extremely fine and large in quantity as compared with the flaky unburned carbon as described above, and furthermore, the spray amount can be controlled,
It is considered that the contact efficiency with the exhaust gas is high and constant, and in the case of BF, it reaches the filtration layer without settling in the hopper and is uniformly attached thereto.

From the standpoint of adsorption of dioxins to the adsorbent, it is clear that it is advantageous that the gas-solid contact efficiency is high and constant and that the gas is uniformly present in the filtration layer, and basically, such conditions are satisfied. The removal rate of dioxins is high and stable. A certain amount of activated carbon powder (BF150 ℃ 50
It is considered that this is the reason why the removal rate of dioxins becomes stable at a high level when spraying more than mg / Nm ³ ).

From the above, the biggest cause of variation in the removal rate of dioxins by the dust collector when only unburned carbon is present is that gas-solid contact efficiency due to the shape of unburned carbon and unburned carbon It is considered that this is a change in gas-solid contact efficiency due to a change in the amount generated.

Next, components other than unburned carbon will be described. It is considered that various oxides with adsorption ability are contained in the dust, and although the adsorption ability is lower than that of unburned carbon, the adsorption of dioxins by these also contributes to the dioxins removal performance of the dust collector. It is thought that For example, it is known that oxides such as silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) whose presence in dust is confirmed exhibit an adsorbing ability depending on the surface structure. It is conceivable that many substances other than oxides have the ability to adsorb dioxins, and it is considered that these also contribute to the adsorption performance of dioxins. The results of component analysis of stoker incineration fly ash as an example of dust are as follows.

[0020]

[Table 1] From the above knowledge, in the present invention, the dust once taken out of the system is to be returned to the exhaust gas treatment system, thereby effectively utilizing the dioxin adsorption capacity of the dust, the exhaust gas It is possible to adsorb dioxin contained therein and improve the efficiency and the removal stability of dioxins in the dust collector.

Further, the dust (that is, the adsorbent, and in particular, the flaky unburned carbon) is pulverized outside or inside the system, whereby the adsorbent is mixed in the exhaust gas.・ Promotes agitation (in the case of BF, in addition to that, evenly adheres to the filter layer) to generate gas-solid contact efficiency comparable to that of spraying powdered activated carbon, and to sufficiently adsorb the dioxin adsorbents. Can be pulled out.

As a result, the standard value can be stably cleared without spraying the powdered activated carbon or by spraying a smaller amount of the powdered activated carbon than the amount conventionally required, and it is expected to be further improved in the future. It becomes possible to easily deal with the setting of target values due to the tightening of regulations.

At that time, the operating temperature of the dust collector, which has conventionally promoted the adsorption reaction only in the low temperature region around 150 ° C., may be shifted to a higher temperature side. That is, the amount of suction dust, the dust suction method, and the adsorption capacity such as the specific surface area of activated carbon when activated carbon is used, and the balance between these and the operating temperature, the optimum operating conditions that sufficiently correspond to the target value. Can be set.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a general equipment configuration in a waste incineration / melting treatment plant, in which a boiler 2 and an air preheater 3 are installed as exhaust gas cooling / heat recovery equipment from an incinerator 1 and the like, and a bag filter and an electrostatic precipitator are installed. The dust collector 4 is installed. Moreover, in order to operate the dust collector 4 in a temperature range of 200 ° C. or less as a measure for suppressing the emission of dioxins, a gas cooling tower 5 is installed in front of the dust collector 4.

The dust 6 settled / accumulated or collected at the bottom of each facility is usually discharged out of the system and landfilled as incinerated ash or dust ash. In the method for removing dioxins in exhaust gas of the present invention, A part of such dust 6 is sprayed into the inlet flue of the dust collector 4 or the inside of the gas cooling tower 5 by the transportation air from the air supply device 7 such as a compressor or a blower. Excess dust 6 in adjusting the spray amount
Is sent to the melting furnace exhaust gas treatment system or the drying furnace exhaust gas treatment system.

By doing so, the adsorbent mainly composed of unburned carbon contained in the dust 6 at 1% (w / w) or more adsorbs dioxins in the exhaust gas at a high rate. The dust 6 adsorbing dioxins and the like is collected by the dust collector 4, and the dedioxin and the exhaust gas from which dust is removed flow out toward the subsequent treatment device (not shown).

At that time, while the dust 6 passes through the transportation pipe, the flaky unburned carbon and the like are easily pulverized and mixed into powder by mixing with ash, which is the main component of the dust, so that the dioxin of the dust 6 is generated. The adsorption capacity is even higher, and the removal rate of dioxins is high. The transport speed of dust 6 is usually 15 to 20 m / s, but 13 m / s,
Even with a passage time of 0.3 s, unburned carbon easily powderizes to an average particle size of about 20 μm, which is comparable to powdered activated carbon.

In the method shown in FIG. 2, the dust 6 is collected by a cutting device 8 such as a screw conveyor.
To the inlet flue or inside the gas cooling tower 5. According to such a method, when the dust 6 is cut out by the cutting device 8, flaky unburned carbon or the like is rubbed,
Powdered by receiving stress such as shearing.

In the method shown in FIG. 3, after the dust 6 is cut out by the cutting device 8 such as a screw conveyor, the air is fed from the air supply device 7 to the inlet flue of the dust collector 4 or the inside of the gas cooling tower 5. Supply to. According to such a method, since the dust 6 is pulverized in two stages, the particle size becomes smaller.

In the method shown in FIG. 4, the dust 6 is crushed by a crushing device 9 such as a mill, and then the inlet flue of the dust collecting device 4 or the gas cooling tower 5 is moved by the transportation air from the air supply device 7.
Supply to inside. Even with such a method, the dust 6 is pulverized in two stages, and thus the particle size becomes smaller.

In the method shown in FIG. 5, after the dust 6 is crushed by the crushing device 9 such as a mill, it is supplied to the inlet flue of the dust collecting device 4 or the inside of the gas cooling tower 5 by the cutting device 8 such as a screw conveyor. To do. Even with such a method, the dust 6 is pulverized in two stages, and thus the particle size becomes smaller.

In the method shown in FIG. 6, a powdering device 10 for passing exhaust gas as a swirling flow is separately provided,
The dust originally contained in the exhaust gas is swirled in the powdering device 10, and then is directly sent to the dust collecting device 4 while being carried on the gas flow.

According to such a method, the flaky unburned carbon in the exhaust gas is pulverized by the swirling flow, and the gas-solid contact efficiency is improved. In the powdering device 10, 5
Although unburned carbon and the like can be suitably crushed and pulverized by running dust on the wall surface at a swirling speed of about m / s, the exhaust gas treatment equipment in the preceding stage of the dust collector 4, for example, the gas cooling tower 5 itself. It is also possible to have a swirl flow generation function.

Each of the above-mentioned methods is sufficiently effective, but by combining the method of any one of Embodiments 1 to 5 with the method of Embodiment 6, it is possible to further improve the dioxin removal performance. You can

The effect of removing dioxin by the method of the present invention as described above will be shown below. (Test Example 1) As shown in FIG. 7, the dust-containing exhaust gas 13 guided from the incinerator 11 through the actual incinerator bag filter 12 to the chimney is branched at the inlet side of the bag filter 12,
The dust in the exhaust gas was pulverized by introducing it into the powdering device 14 and passing it as a swirling flow, and then introducing it into the bag filter 15. The test gas is municipal waste incineration exhaust gas, the exhaust gas temperature is 150 ° C, and the exhaust gas amount is 400 Nm ³ / h (we
t). (Test Example 2) As shown in FIG. 8, in the same manner as in Test Example 1, the dust-containing exhaust gas 13 branched on the inlet side of the actual incinerator bag filter 12 was collected in advance at the inlet flue of the bag filter 15. The dust 16 that has been stored is pulverized by pipe transportation with compressed air from the compressor 17 at 150 ° C. (pipe passage speed 13 m / s, pipe passage time 0.3 s, air pressure 0.05 kgf / cm ² ), and the feeder Blown through 18. (Comparative Example 1) As shown in FIG. 9, the dust-containing exhaust gas 13 branched at the inlet side of the actual incinerator bag filter 12 was introduced directly into the bag filter 15 as in Test Example 1. (Comparative Example 2) As shown in FIG. 10, in the same manner as in Test Example 1, the dust-containing exhaust gas 13 branched at the inlet side of the actual incinerator bag filter 12 was mixed with the powdered activated carbon 19 at the inlet flue of the bag filter 15. Was sprayed with 50 mg / Nm ³ (wet).

The results are shown in Table 2 below. In Comparative Example 1 in which the dust-containing exhaust gas 13 was directly introduced into the bag filter 15, the new standard (0.1 ng-TEQ / Nm ³ ) was not satisfied, but Test Example 1 in which dust in the exhaust gas was powdered by a swirling flow In Test Example 2 in which dust outside the system was sent by transportation air, all were sufficiently cleared, and dioxins (DXNs) equivalent to Comparative Example 2 in which powdered activated carbon was sprayed (50 mg / Nm ³ -wet) A removal effect was obtained.

[0037]

[Table 2] From these, preferably, by mixing powdered dust with the exhaust gas, without spraying powdered activated carbon, or only by spraying a smaller amount of powdered activated carbon than conventionally required, the reference value You can see that it can be cleared stably.

Although the operating temperature of the dust collector 15 (exhaust gas temperature) is 150 ° C. here,
Even if the temperature is shifted to a high temperature of about 250 ° C., the removal rate of dioxins can be sufficiently improved and stabilized.

Therefore, the incineration of waste as described above
It is possible to reduce initial cost, running cost, and thermal energy in the melt processing plant (initial cost = gas cooling tower facility cost, activated carbon spray facility cost, exhaust gas reheating facility cost, running cost =
Activated carbon cost, etc., thermal energy = BF outlet exhaust gas reheating).

[0040]

Industrial Applicability As described above, according to the present invention, by returning the dust once taken out of the system to the exhaust gas treatment system, the dioxin adsorption capacity of the dust can be effectively utilized, and the dioxin in the exhaust gas can be effectively utilized. It is possible to remove the dioxins, and it is possible to improve the dioxins removal efficiency and the removal stability in the dust collector.

Further, by pulverizing the dust, its ability to adsorb dioxins can be further enhanced. As a result, the standard value can be stably cleared without spraying the powdered activated carbon or by spraying a smaller amount of the powdered activated carbon than conventionally required. Since the dust collector can be operated at high temperature, the initial cost, running cost, and thermal energy cost in the waste incineration / melting processing plant can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a method for removing dioxins in exhaust gas according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a method for removing dioxins in exhaust gas according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a method for removing dioxins in exhaust gas according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a method for removing dioxins in exhaust gas according to a fourth embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a method for removing dioxins in exhaust gas according to a fifth embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a method for removing dioxins in exhaust gas according to a sixth embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a flow of Test Example 1 for testing the effects of dioxins according to the method of the present invention.

FIG. 8 is an explanatory diagram showing a flow of Test Example 1 for testing the effects of dioxins according to the method of the present invention.

FIG. 9 is an explanatory view showing the flow of Comparative Example 1 for testing the effect of dioxins by the conventional method.

FIG. 10 is an explanatory diagram showing a flow of Comparative Example 2 for testing the effect of dioxins by the conventional method.

[Explanation of symbols]

1 incinerator 4 Dust collector 6 dust 8 cutting device 9 crusher 10 powdering equipment 17 Air supply device

─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Takeshige Sosaku 2-1-1 Toyosu, Koto-ku, Tokyo Ishikawa Shima Harima Heavy Industries Ltd. Tokyo 1st factory (72) Inventor Shiro Baba 2 Toyosu, Koto-ku, Tokyo 1st-1 Ishikawa Shima-Harima Heavy Industry Co., Ltd. Tokyo 1st factory (72) Inventor Takeo Kobayashi 1 Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Ishikawajima Harima Heavy Industry Co., Ltd. Technical Research Institute (72) Inventor Tetsuo Kimura Osaka 2-47 Shikizu Higashi 1-chome, Naniwa-ku, Osaka, Japan Kubota Co., Ltd. (72) Inventor Tetsuo Kiyota 1-2-47 Shiketsu Higashi 1-chome, Naniwa-ku, Osaka, Osaka (72) Inventor Sato Jun 2-47 Shikazuhigashi, Naniwa-ku, Osaka-shi, Osaka Prefecture Kubota Corporation (72) Inventor Masato Kurata 1-2-47 Shikitsuhigashi, Naniwa-ku, Osaka-shi, Osaka Prefecture Within Kubota Corporation (56) Reference Patent flat 5-203127 (JP, A) JP flat 4-197423 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) B01D 53 / 34-53/85 B01J 20/00-20/34

Claims (5)

(57) [Claims] 1. An exhaust gas treatment system from a treatment furnace to a dust collector
2. A method for removing dioxins in exhaust gas, wherein the dust in the exhaust gas settled to reach the dust collector is taken out of the system and then returned to the dust collector of the exhaust gas treatment system . 2. Exhaust gas passes through a gas cooling tower to a dust collector.
Then, the dust taken out of the system is cooled by the gas in the exhaust gas treatment system.
Claims characterized by returning to a waste tower or dust collector
Item 2. A method for removing dioxins in exhaust gas according to Item 1. 3. The dust settled in the exhaust gas treatment system is discharged to the outside of the system.
When taking it out and returning it to the exhaust gas treatment system,
Stroke through the transportation pipe with the transportation air from the air supply device.
Discharge according to claim 1 or 2, characterized in that
Method for removing dioxins in gas. 4. The dust taken out of the system is used as a powdering means.
More pulverized and returned powder dust to the exhaust gas treatment system
In the exhaust gas according to claim 1 or 2, characterized in that
How to remove dioxins. 5. Exhaust gas that directs exhaust gas from the processing furnace to a dust collector
In the gas treatment system, the dust in the exhaust gas is placed in the system.
Exhaust gas characterized by being pulverized by different pulverizing means
How to remove medium dioxins.