JPH0738935B2 - Method of removing mercury from exhaust gas of refuse incinerator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for removing mercury from exhaust gas discharged from a refuse incinerator.

[Prior Art] Since exhaust gas emitted from a refuse incinerator contains highly toxic mercury, it is necessary to remove it. Conventionally, the removal of mercury from the exhaust gas emitted from a refuse incinerator has been carried out by a method of using a solid scavenger arranged in a flue. It is known that a metal sulfide or a chloride thereof, particularly a copper sulfide is effective as a solid collector used in this method. Then, for the purpose of enhancing the trapping effect, these trapping agents are used in the form of powder or supported on a carrier. The former method increases the surface area of the scavenger to increase the exposed surface area which reacts with mercury in the exhaust gas, and the latter method increases the amount of the scavenger to enhance the scavenging effect.

[Problems to be Solved by the Invention] However, in any of the conventional methods, there is a problem in that the solid scavenger must be separately prepared, and the cost becomes high. In addition, the former method has a problem that the cost for pulverizing the scavenger into fine powder is high. The latter method has a problem that it is necessary to handle the carrier carrying the scavenger, and the amount of solids to be handled increases by the amount of the carrier, which is troublesome.

An object of the present invention is to provide a method for removing mercury from exhaust gas of a refuse incinerator that solves the above problems.

[Background of Invention Completion] It is already known that the frequency distribution of each component in the exhaust gas of a refuse incinerator is as shown in FIG. The source of Figure 2 is 43 of the 1980 edition of the Tokyo Metropolitan Institute of Waste Management Research Report.
It is the “Survey of Dust Properties in Incineration Plants” (especially page 46) published on page 56. As shown in FIG. 2, the exhaust gas contains metals such as Cd, Pb, Zn, and Cu that are effective in removing mercury, and these metals are contained in large amounts in the state of fine particles smaller than 1 to 3 μm. There is. Therefore, it is understood that by separating the fine particle ash from the dust collecting ash in the exhaust gas, it is possible to obtain the fine particle ash containing a large amount of the above metal, which is effective for removing mercury. However, vaporized mercury in the exhaust gas has already adhered to the particulate ash in such collected ash, and because of the relationship with other components in the particulate ash, such particulate ash is
It was considered to have no vapor mercury removal effect.

On the other hand, the present inventors conducted various studies and conducted the following experiments. That is, fine ash of 1 to 3 μm obtained by classifying the dust ash from the exhaust gas emitted from the waste incinerator,
The time required to reach 20% breakthrough after passing through the air at various temperatures containing mercury 0.5 mg / Nm ³ in the mercury trap, that is, the amount of mercury in the air that passed through the mercury trap. Is 20% of the amount of mercury in the air before passing through the mercury trap.
The time to reach was measured. For comparison with this, a solid scavenger made of copper sulfide is held on a carrier made of X-type zeolite, which is placed in a mercury scavenger, which contains 0.5 mg / Nm ³ of mercury. Air at various temperatures was passed and the time to reach 20% breakthrough was measured. These results are shown in FIG. It can be seen from FIG. 3 that the effect of removing mercury by the particulate ash is almost the same as that of copper sulfide. As a result, the inventors of the present invention have obtained the finding that the particulate ash still has the effect of removing vaporous mercury, and completed the present invention.

[Means for Solving the Problems] A method for removing mercury from exhaust gas of a refuse incinerator according to the present invention is a method of classifying dust ash from exhaust gas emitted from a refuse incinerator to separate fine ash, Is supplied again into the exhaust gas at the upstream side of the dust collector and at the downstream side of the refuse incinerator, and vapor mercury is adhered and fixed to the particulate ash to be removed.

In the above, the particulate ash to be supplied into the exhaust gas again on the upstream side of the dust collector and on the downstream side of the dust incinerator may be supplied as it is, but in order to increase the dust collection efficiency in the post process, It is preferable to adjust the particle size by controlling the humidity to agglomerate the particles.

[Operation] When the collected ash from the exhaust gas discharged from the waste incinerator is classified to separate fine ash, and the fine ash is supplied again into the exhaust gas upstream of the dust collector and downstream of the waste incinerator. The mercury vapor in the exhaust gas adheres to and is immobilized on the particulate ash that has the effect of removing vaporous mercury. Since the particulate ash with mercury attached becomes coarse particles, when the particulate ash is classified by separating it after being collected by the dust collector,
It is discharged together with coarse-grained ash and appropriately treated.

Furthermore, when the particulate ash separated from the dust ash is supplied again into the exhaust gas on the upstream side of the dust collector and on the downstream side of the refuse incinerator, the mercury vapor already attached to the particulate ash and fixed, and again. It is possible to prevent the mercury vapor, which has been fixed after adhering to the dust ash before it reaches the dust collector, from being vaporized again.

In this method, since the fine particles separated from the dust ash of the exhaust gas are used, it is not necessary to separately prepare the solid scavenger, and the work of crushing the separately prepared solid scavenger into fine powder is required. unnecessary. Further, it is not necessary to handle the carrier carrying the solid scavenger.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a process flow according to the present invention. First
In the figure, waste is incinerated in an incinerator (1) and the exhaust gas is sent to a dust collector (2). The exhaust gas contains fly ash and vaporous mercury. The exhaust gas is sent to the dust collector (2), where it is subjected to dust collection processing, and then discharged from the chimney into the atmosphere. The collected ash is sent to a classifying device (3) consisting of a small cyclone and classified,
The coarse particle ash of 3 to 5 μm is discharged from the coarse particle outlet by centrifugal force and appropriately treated. On the other hand, particulate ash smaller than 3 μm is discharged from the particulate ash outlet, and the waste incinerator (1)
It is supplied again into the exhaust gas in the flue connecting the dust collector (2) and the dust collector (2). Coarse-grained ash is 50-60% of dust-collected ash, and fine-grained ash is 40-50%. The particulate ash to be supplied again into the exhaust gas is conditioned by the humidity control device (4) in order to improve the dust collection efficiency in the dust collector (2) in the subsequent process, and is supplied in a state in which the particles are agglomerated and coarsened. To be done. However,
The particulate ash may be supplied as it is into the exhaust gas.
Also in this case, since vaporized mercury adheres to the fine particle ash to form coarse particles, it is discharged together with the coarse particle ash from the coarse particle outlet of the classifier.

The vaporized mercury adheres to the aggregated particulate ash supplied in the exhaust gas. Aggregated particulate ash to which vaporous mercury has adhered may also adhere to fly ash. The agglomerated particulate ash to which vapor mercury has adhered is sent to the dust collector (2) together with the exhaust gas, and is collected there. When the dust ash is classified by the classifier, the vaporized mercury-adhered fine particle ash becomes coarse particles, and thus is discharged from the coarse particle outlet of the classifier (3) and appropriately treated.

In the above, a separately prepared solid scavenger may be arranged in the flue connecting the dust incinerator (1) and the dust collector (2). Also in this case, the amount of the solid scavenger is smaller than that in the case of using it alone.

[Effects of the Invention] According to the method for removing mercury from the exhaust gas of the refuse incinerator of the present invention, since the fine particles separated from the dust ash of the exhaust gas are used as described above, the solid scavenger is separately provided. There is no need to prepare it at low cost. Moreover, since it is not necessary to separately pulverize the solid scavenger prepared into fine powder or to handle the carrier carrying the solid scavenger, the work is simplified and the cost is reduced. In addition, mercury vapor that has already adhered to the particulate ash and has been immobilized, and mercury vapor that has been immobilized and adhered to the particulate ash before it reaches the dust collector after being supplied again is prevented from revaporizing. Therefore, the efficiency of removing mercury from the exhaust gas is improved.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention, FIG. 2 is a graph showing a frequency distribution of components in dust ash collected from exhaust gas of a refuse incinerator, and FIG. 3 is exhaust gas of the refuse incinerator. 3 is a graph showing the mercury removal effect of fine particle ash and copper sulfide separated from the dust collecting ash collected from. (1) …… Garbage incinerator, (2) …… Dust collector.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location 7704-3K F23J 15/00 J (72) Inventor Toshio Hama 5th Nishikujo, Konohana-ku, Osaka City, Osaka Prefecture 3-28 Hitachi Shipbuilding Co., Ltd. (72) Inventor Kanji Ota 5-3 28 Nishi Kujo, Konohana Ward, Osaka City, Osaka Prefecture (2) Hitachi Shipbuilding Co., Ltd. (72) Naoko Hirata, Nishikonohana-ku, Osaka City, Osaka Prefecture Kyujo 5-chome 3-28 Hitachi Shipbuilding Co., Ltd. (56) Reference JP-A-55-155732 (JP, A) JP-A-1-159514 (JP, A)

Claims (1)

[Claims] 1. A dust ash from an exhaust gas discharged from a refuse incinerator is classified to separate fine particle ash, and the fine particle ash is reused in the exhaust gas upstream of the dust collector and downstream of the waste incinerator. A method for removing mercury from the exhaust gas of a refuse incinerator, which comprises supplying and fixing vaporized mercury to the particulate ash to fix it.