JP2001137638A - Melt exhaust gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce dioxins in a molten exhaust gas without using an adsorbent such as activated carbon or the like, and to easily recover a collected dust ash in a molten exhaust gas treatment. Provide a way. SOLUTION: The incineration ash of an incinerator is melted in a melting furnace 1, and caustic soda is sprayed in a gas cooling tower 3 to fix an acid gas component in an exhaust gas as a reaction product with the caustic soda in the molten fly ash. The dust fly 4 collects and removes the molten fly ash and the reaction product, and blows the fly ash such as the fly ash discharged from the incinerator into the bag filter 5 together with the exhaust gas. While collecting dust, dioxins in exhaust gas are adsorbed and removed by incineration fly ash, and the dust ash of the bag filter 5 is melted together with the incineration ash in the melting furnace 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for melting waste, and more particularly to a method for treating molten exhaust gas for removing harmful substances from the exhaust gas.

[0002]

2. Description of the Related Art In recent years, due to the improvement in the accuracy of analytical techniques, the state of contamination by dioxins (hereinafter referred to as DXNs), which are extremely small amounts of extremely toxic chemical substances present in the environment, has gradually surfaced, and has become a major social problem. I have. The largest source of DXNs is municipal solid waste incinerators, of which dust ashes account for an overwhelming amount (more than 80%). Currently, only the exhaust gas emitted from the chimney is regulated, and at present, there is no regulation on dust ash, which accounts for most of the emission. However, there is no doubt that efforts to reduce the burden on the environment as much as possible by reducing not only the exhaust gas from the chimney but also the total amount of emission itself are surely necessary in the future.

[0003] Under such a background, as one of the detoxifying methods of dust ash containing a large amount of DXNs, ash melting treatment has been attracting attention, and DXNs produced by installing an incinerator and a melting furnace together. It is conceivable that the method of complete detoxification will increase in the future. The molten waste gas contains toxic substances such as soot, NOx, heavy metals and DXNs in addition to acidic substances such as HCl and SOx. Generally, in incineration exhaust gas treatment,
Acid gas (HCl, SOx) is neutralized and removed by spraying slaked lime powder, which is an alkaline agent, into the flue of the bag filter, and heavy metals and DXNs are obtained by operating the bag filter in a temperature range of 200 ° C or less. It is known that it can be adsorbed and removed from incinerated fly ash. As a means for removing harmful substances in these exhaust gases, it has become mainstream to employ a bag filter having a high dust collection efficiency and a high reaction rate.

[0004] In response to this flow, it is common practice to employ a bag filter in the treatment of molten exhaust gas.

[0005]

However, molten fly ash does not have the capability of adsorbing and removing DXNs unlike incinerated fly ash, because the chemical composition of the fly ash differs greatly from that of incinerated fly ash. Table 1 shows a composition table of both components.

[0006]

[Table 1] Therefore, in a bag filter for treating molten exhaust gas, D
In order to remove XNs, it is necessary to newly blow in an adsorbent such as powdered activated carbon. Unlike incineration, waste melting has the concept of not only reducing the volume of waste but also recycling resources.Molten fly ash, which is a concentrated mixture of chlorides and heavy metals, contains as much impurities as possible. It is desirable to collect in a state that does not contain and return to the yamamoto.

However, when the bag filter is operated by the above method, unreacted slaked lime powder, a neutralized reaction product thereof, and powdered activated carbon are mixed in the collected dust ash in addition to the molten fly ash. However, there was a problem that it would be very difficult to implement Yamamoto reduction. The present invention has been made to solve the above-described problems, and can reduce DXNs in a molten exhaust gas without using an adsorbent such as activated carbon, and can greatly reduce the total amount of DXNs emitted from a melting facility. Further, it is another object of the present invention to provide a method for treating a molten exhaust gas in which collected dust ash can be easily reduced at the hillside.

[0008]

In order to solve the above-mentioned problems, a method for treating molten exhaust gas according to the present invention comprises introducing a molten exhaust gas discharged from a melting furnace to a dust collector to collect and remove molten fly ash. The exhaust gas is blown into the bag filter together with the incinerator fly ash, and the incinerator fly ash is collected and the DXNs in the exhaust gas are adsorbed and removed by the incinerator fly ash. Is what you do.

[0009] With this configuration, in the bag filter, D
XNs can be adsorbed and removed by effectively utilizing the adsorbing ability of incinerated fly ash, and DXNs adsorbed and removed can be decomposed by melting the dust ash of the bag filter in a melting furnace. In addition, the dust collected by the dust collector does not contain unreacted slaked lime powder, reaction products, and powdered activated carbon unlike conventional ones. The amount can be greatly reduced, and the amount of DXNs discharged from the melting facility can be significantly reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a melting furnace 1 melts waste, and the waste includes incineration ash discharged from an incinerator (not shown). An exhaust gas treatment system 2 for treating molten exhaust gas discharged from the melting furnace 1 includes a gas cooling tower 3 as a temperature reducing device, a dust collector 4, and a bag filter 5. The dust collector 4 is constituted by an electric dust collector or a bag filter.

In the exhaust gas treatment system 2, the molten exhaust gas discharged from the melting furnace 1 is led to a gas cooling tower 3, where cooling water and caustic soda are sprayed into the exhaust gas, and the exhaust gas is cooled to a predetermined temperature range (200 ° C. or lower). At the same time, the acid gas component in the exhaust gas is fixed in the molten fly ash as a reaction product with caustic soda. The exhaust gas that has passed through the gas cooling tower 3 is guided to a dust collector 4 to collect molten fly ash and the reaction products. As described above, the acidic gas component in the exhaust gas is taken out of the system together with the molten fly ash as a reaction product with the caustic soda, and therefore does not circulate in the system unlike the conventional method. This will be described in detail later.

[0012] Dust collected ash separately collected in an incinerator, or boiler ash or gas-cooled ash discharged from other equipment is blown into the bag filter 5 together with exhaust gas. Since incinerated fly ash such as dust ash contains fixed carbon by several% (weight ratio), it has a higher DXNs adsorption capacity than molten fly ash containing almost no fixed carbon. The bag filter 5 collects the incineration fly ash, and the exhaust gas passes through the incineration fly ash forming a layer on the filter surface, whereby solid-gas contact is efficiently performed, and the incineration fly ash adsorbs and removes dioxins in the exhaust gas. I do. The collected ash from the bag filter 5 is supplied to the melting furnace 1 and melted together with the incinerated ash to thermally decompose DXNs to render it harmless.

Therefore, by effectively utilizing the incinerated fly ash having DXNs adsorption capacity, not only is the adsorbent such as activated carbon unnecessary, but also the amount of DXNs discharged from the melting facility as dust ash is greatly reduced. . By the way, when the method of spraying slaked lime powder in the bag filter 5 and removing the acid gas is used in the same manner as in the conventional incineration exhaust gas treatment, when the dust ash of the bag filter 5 is melted, the acid gas component is re-gasified in the melting furnace. And is circulated through the system to be concentrated. However, as described above, in the present embodiment, the acidic gas component in the exhaust gas is taken out of the system together with the fly ash as a reaction product with the caustic soda, so that it is possible to prevent circulation in the system. .

FIG. 2 shows another embodiment of the present invention, wherein the temperature reducing device 6 comprises a waste heat recovery device such as a waste heat boiler, an air preheater or a gas cooling tower. It can be configured by a combination. A gas cooling tower 7 is arranged on the upstream side of the bag filter 5, and a wet scrubber 8 is provided on the downstream side. The gas cooling tower 7 reduces the temperature of the gas flowing into the bag filter 5 to a predetermined temperature range (200 ° C. or lower). The lower the temperature, the more the DXNs resynthesis reaction is suppressed and the DXNs removal rate is improved. be able to.

In this configuration, the temperature of the molten exhaust gas discharged from the melting furnace 1 is reduced to a predetermined temperature range by the temperature reducing device 6 and then guided to the dust collector 4 to collect the molten fly ash. The exhaust gas which has been cooled to a predetermined temperature range (200 ° C. or lower) in the gas cooling tower 7 is blown into the bag filter 5 together with the incineration fly ash discharged separately from the incinerator, and the incineration fly ash is collected by the bag filter 5. DXNs in exhaust gas is adsorbed and removed by incineration fly ash.

The exhaust gas passing through the bag filter 5 is led to a wet scrubber 8 to absorb and remove acidic gas components in the exhaust gas. The dust collected from the bag filter 5 is supplied to the melting furnace 1,
DXNs is pyrolyzed by melting with incineration ash. Therefore, since the molten fly ash is solely recovered by the electric precipitator without containing unreacted slaked lime powder, activated carbon powder, neutralization reaction products and the like as in the prior art, the dust ash can be easily reduced to the yamamoto. Other functions and effects are the same as those of the previous embodiment.

FIG. 3 shows another embodiment of the present invention. In this configuration, the temperature of the molten exhaust gas discharged from the melting furnace 1 is reduced to a predetermined temperature range by the temperature reducing device 6, and slaked lime powder is sprayed into the exhaust gas in a route from the temperature reducing device 6 to the dust collector 4. The acidic gas component in the exhaust gas is fixed in the molten fly ash as a reaction product with slaked lime powder, and guided to the dust collector 4 to collect the molten fly ash.

The exhaust gas which has been cooled to a predetermined temperature range (200 ° C. or lower) in the gas cooling tower 7 is blown into the bag filter 5 together with the incineration fly ash discharged separately from the incinerator, and the incineration fly ash is collected by the bag filter 5. DXNs in exhaust gas is absorbed and removed by incineration fly ash. Bag filter 5
Is supplied to the melting furnace 1 and melted together with the incinerated ash to thermally decompose DXNs.

[0019]

As described above, according to the present invention, dioxins can be adsorbed and removed by effectively utilizing incinerated fly ash, an adsorbent such as activated carbon is not required, and the amount of dust ash to be discharged and DXNs amount can be greatly reduced. Further, the fly ash is collected without containing the unreacted slaked lime powder, activated carbon powder, neutralization reaction products, and the like as in the prior art, so that the dust ash can be easily reduced to the yamamoto.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an exhaust gas treatment method according to an embodiment of the present invention.

FIG. 2 is a flow sheet showing an exhaust gas treatment method according to another embodiment of the present invention.

FIG. 3 is a flow sheet showing an exhaust gas treatment method according to another embodiment of the present invention.

[Description of Signs] 1 Melting furnace 2 Exhaust gas treatment system 3 Gas cooling tower 4 Dust collector 5 Bag filter 6 Temperature reduction device 7 Gas cooling tower 8 Scrubber

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasutatsu Sadamoto 2-1-1, Toyosu, Koto-ku, Tokyo Ishikawajima-Harima Heavy Industries Co., Ltd. Tokyo 1st Factory (72) Inventor Junya Nishino Isogo-ku, Yokohama-shi, Kanagawa No. 1 Shin-Nakahara-cho Ishikawashima-Harima Heavy Industries Co., Ltd. Machinery and Plant Development Center (72) Inventor Takeshige Creation Plan 2-1-1, Toyosu, Koto-ku, Tokyo Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo No. 1 Factory (72) Inventor Shiro Baba 2-1-1 Toyosu, Koto-ku, Tokyo Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo No. 1 Factory (72) Inventor Tetsuo Kimura 2-47 Shishitsuhigashi, Namiwa-ku, Osaka-shi, Osaka Kubota Corporation (72) Inventor Shiro Uebayashi 2-47 Shishitsuhigashi, Naniwa-ku, Osaka-shi, Osaka Kubota Co., Ltd. 1-47, Shikitsu-Higashi 1-chome, Naniwa-ku, Osaka-shi, Japan (72) Inventor Masato Kurata 2-47, Shikitsu-higashi 1-chome, Naniwa-ku, Osaka, Osaka F-term (reference) 4D002 AA21 AC04 AC10 BA04 BA05 BA13 BA14 CA01 DA02 DA12 DA66 EA02 GA02 GB03

Claims (1)

[Claims] 1. An exhaust gas discharged from a melting furnace is guided to a dust collector to collect and remove molten fly ash, and then the exhaust gas is blown into a bag filter together with an incinerator fly ash. A method for treating molten exhaust gas, comprising collecting dust and dioxins in exhaust gas by incineration fly ash, and melting the collected ash of the bag filter in a melting furnace.