JP2000227214A - Low pollution combustion method and apparatus used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low pollution combustion method and an apparatus used therefor capable of effectively removing dioxins and heavy metals in fly ash discharged from an incinerator and of exhausting clean waste gas. SOLUTION: There are provided an incinerator 12 for combusting waste 11 at high temperature, a dust collector 14 for collecting soot dust 13 in waste gas exhausted from the incinerator 12, a washing tank 16 for suspending in water fly ash 15 collected in the dust collector 14 and moving heavy metals to a water phase, and dewatering means 18 for dewatering water contained in slurry like sludge 17 from the washing tank 16. Dewatered cake 19 after the dewatering is returned again to the incinerator 12 for further combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an incinerator for municipal waste,
The present invention relates to a low-pollution combustion method capable of removing harmful substances in exhaust gas discharged from various types of incinerators that burn general and industrial waste such as industrial waste incinerators and sludge incinerators, and a device used therefor, particularly contained in the exhaust gas. The present invention relates to a technique for suppressing the resynthesis of chlorinated aromatic compounds such as nitrogen oxides and dioxins.

[0002]

2. Description of the Related Art Exhaust gas discharged from various incinerators, such as municipal garbage incinerators, industrial waste incinerators, and sludge incinerators, depends on the types of incineration objects and incineration conditions. , Nitrogen oxides, dioxins and P
Hazardous substances such as harmful chlorinated aromatic compounds represented by CBs and highly condensed aromatic hydrocarbons may be contained, causing damage to the human body, animals and plants as environmental hormones, and destroying the natural environment. As a serious social problem.

FIG. 6 schematically shows a conventional waste incineration facility. As shown in Fig. 6, supplied waste (incineration)
01 is quantitatively supplied to an incinerator 02, and is burned in a state where the residence time is 2 seconds or more at 800 ° C. or more and is cut off from the outside air, and the burned incineration ash 03 is transferred to an incineration ash storage facility 04, One exhaust gas 05 is supplied to an exhaust gas cooling facility 06.
After being cooled to 200 ° C. or lower, in the exhaust gas treatment equipment 07 having dust removing means provided on the downstream side, dioxins are decomposed and removed together with dust removal,
After that, it is discharged from the chimney 08.

As a method of treating the exhaust gas treatment equipment 17, various methods such as an activated carbon adsorption method, a thermal decomposition method, and a catalytic cracking method have been proposed as a method for removing organic chlorine compounds such as dioxin in exhaust gas. I have. On the other hand, fly ash accompanying the exhaust gas is present in the exhaust gas, and low-boiling heavy metals such as lead, zinc, and cadmium, and dioxins are present in the fly ash. Need to be processed. Conventionally, the collected fly ash is indirectly heated at a high temperature of 400 to 600 ° C., or is brought into contact with a catalyst at a high temperature (200 to 550 ° C.) to decompose and remove dioxins.

[0005] However, the former method of indirect heating, which has been conventionally proposed, has a problem that the heat exchange efficiency is low and the size of the apparatus is large. However, there is a problem that the catalyst is required. In order to decompose dioxins with a predetermined amount of catalyst, the exhaust gas must be heated to a high temperature (200 to 5).
(50 ° C.), and the cost required for heating is enormous. Further, there is a problem that the durability of the catalyst is lacked due to dusts containing nitrogen oxides, sulfur oxides, and heavy metals contained in the combustion exhaust gas.
In particular, when the treatment is performed at a high temperature, the heavy metal having a low boiling point is scattered outside the system by heating, which is a problem.

[0006] In view of the above problems, the present invention provides dioxins in fly ash discharged from an incinerator,
An object of the present invention is to provide a low-pollution combustion method capable of efficiently removing heavy metals and discharging clean exhaust gas, and an apparatus used therefor.

[0007]

Means for Solving the Problems According to the invention of claim 1 of the present invention which solves the above-mentioned problems, dust in exhaust gas discharged from an incinerator which burns waste at a high temperature is collected and collected. The dust fly ash is washed with water to form a slurry, the water in the slurry sludge is dewatered into a dewatered cake, and the dewatered cake is returned to the incinerator and burned again.

[0008] The invention of claim 2 is characterized in that, in claim 1, the dewatered cake is granulated and the granulated product is returned to the combustion furnace.

A third aspect of the present invention is characterized in that, in the first aspect, a cement-based compound is added to the sludge to form a solidified cement, and the solidified cement is returned to a combustion furnace.

[0010] The invention of claim 4 is characterized in that, in claim 1, heavy metals in the washing wastewater from the washing tank are removed by coagulation sedimentation and reused as a washing liquid.

[0011] The invention of claim 5 is characterized in that, in claim 4, salt in wastewater from the coagulated sediment is removed by a reverse osmosis membrane.

The invention of claim 6 provides an incinerator for burning waste at a high temperature, a dust collecting device for collecting dust in exhaust gas discharged from the incinerator, and a dust collecting device for the dust collecting device. A washing tank for suspending the fly ash in the washing tank, and a dehydrating means for dehydrating the water in the slurry sludge from the washing tank.The dewatered cake after dehydration is returned to the incinerator again and burned again. It is characterized by making it.

[0013] The invention of claim 7 is characterized in that, in claim 6, an apparatus for granulating the dewatered cake is provided, and the granulated material is returned to the combustion furnace.

The invention of claim 8 is characterized in that, in claim 6, a cement solidifying means for adding a cement compound to the sludge is provided, and the solidified cement is returned to the combustion furnace.

According to a ninth aspect of the present invention, in the sixth aspect, a coagulating sedimentation unit is provided for removing heavy metals from the washing wastewater from the washing tank.

A tenth aspect of the present invention is characterized in that, in the ninth aspect, a reverse osmosis membrane is provided for removing a salt content in the waste liquid from the coagulation and sedimentation means.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

According to the present invention, fly ash contained in exhaust gas discharged after burning waste in a high-temperature incinerator is separated by a dusting device, and the separated fly ash and the like are washed with water in a washing tank.
The heavy metal is transferred to the aqueous phase, and the remaining water in the slurry-like sludge is removed to form a dewatered cake. The dewatered cake is burned again in an incinerator, and silicon (Si), calcium (C)
a), aluminum (Al) is separated as bottom ash of an incinerator. That is, in a high-temperature incinerator, the silicon (Si), calcium (Ca), and aluminum (Al) are soared by the air flow in the furnace and are discharged as fly ash together with the exhaust gas outside the incinerator. In a furnace, dioxins and the like contained in fly ash are decomposed again at a high temperature after being burned, and then discharged as bottom ash. At this time, fly ash is suspended in the washing tank, heavy metals (eg, mercury, lead) contained in the fly ash are positively removed by washing with water, water is removed, and then the dehydrated cake is put into an incinerator. I have. At this time, the dehydrated cake may be granulated and sent to the bottom of the incinerator so as not to be scattered.

It is also possible to add a cement compound to the sludge to form a solidified cement, and to put the solidified cement into an incinerator instead of a dewatered cake. Thus, by returning in a solid state, it is not scattered by the flame in the incinerator, and is not discharged out of the incinerator together with the exhaust gas.

Further, dioxins and the like contained in the dewatered cake and cement solidified product are decomposed by high-temperature decomposition in an incinerator to reduce the concentration of dioxins in exhaust gas.

According to the present invention, fly ash can be treated in a closed system, and heavy metals such as mercury (Hg), lead (Pb), and cadmium (Cd) are removed, thereby providing a low-pollution combustion method. be able to.

Here, the dioxins contained in the fly ash of the present invention include polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCD).
Fs) is a general term for Fs), which is said to be generated in trace amounts when a chlorine compound and a certain organic chlorine compound are burned, and is a chemically colorless crystal. Depending on the number of chlorine, there are dichloride to octachloride.
and 135 kinds s, among these, particularly tetrachloride dibenzo -p- dioxin (T ₄ CDD) is known as having the strongest toxicity. In addition, as harmful chlorinated aromatic compounds, in addition to dioxins, various organic chlorine compounds (for example, aromatic compounds such as phenol and benzene (for example, chlorobenzenes, chlorophenol and chlorotoluene) ), Chlorinated alkyl compounds, etc.).

PCBs (polychlorinated biphenyls)
Is a generic term for compounds in which several chlorine atoms are added to biphenyl, and there are isomers depending on the number of chlorine substitutions and substitution positions.
Typical are 2,6-dichlorobiphenyl, 2,2'-dichlorobiphenyl, 2,3,5-trichlorobiphenyl, etc., which are highly toxic and may generate dioxins when incinerated. Also known as

Next, a preferred embodiment of a low-pollution combustion apparatus for implementing the combustion system of the present invention will be described.
The present invention is not limited to this. The combustion furnace is not particularly limited as long as it is a known incinerator, and examples thereof include a stoker furnace and a fluidized bed furnace.

[First Incineration System] FIG. 1 is a schematic diagram of a first combustion system provided with a low-pollution combustion apparatus for implementing the low-pollution combustion method of the present invention. As shown in FIG.
The incinerator 12 burns various wastes 11 such as municipal waste, industrial waste, and sludge at a high temperature.
A dust collector 14 for collecting dust in exhaust gas 13 discharged from the incinerator 12 and fly ash 15 collected by the dust collector 14 are suspended in water, and heavy metals are washed and drained. And a dewatering means 18 for dewatering the water in the slurry sludge 17 from the water rinsing tank 16. The dewatered cake 19 after dehydration is returned to the incinerator 12 again. Burn it.

According to such a combustion system, after the heavy metals in the fly ash are removed, the fly ash is returned to the combustion furnace as a dehydrated cake again.
i), as a solid matter of calcium (Ca) and aluminum (Al), is discharged out of the incinerator as incineration main ash (bottom ash) 20.

As a result, the heavy metals in the fly ash are removed by washing with water, and the sludge 17 free of heavy metals is dehydrated and then returned to the incinerator 12 for burning. Ca) or the like can be treated as bottom ash. Also, dehydrated cake 1
The dioxins contained in 9 are also decomposed in a high temperature incinerator, thereby enabling clean combustion.

[Second Incineration System] FIG. 2 is a schematic view of a first combustion system provided with a low-pollution combustion apparatus for implementing the low-pollution combustion method of the present invention. As shown in FIG.
In the combustion system of the above, a granulating device 21 for granulating the dehydrated cake 19 is provided to form a granulated product 22.
Is returned to the combustion furnace 12.

In this embodiment, since the granulated material 22 is used, the incinerator 12 is used to prevent the cake of the first system shown in FIG. Is settled in the inside, and can be treated as bottom ash. At the time of combustion, the dioxins contained in the granules 22 are also decomposed in the high temperature incinerator, thereby enabling clean combustion.

[Third Incineration System] FIG. 3 is a schematic view of a first combustion system provided with a low-pollution combustion apparatus for implementing the low-pollution combustion method of the present invention. As shown in FIG.
In the combustion system, a cement solidifying means 24 for adding a cement compound 23 to the sludge 17 is provided,
The solidified cement 25 is returned to the combustion furnace 12.

In the present embodiment, since the solidified cement 25 is used, the cement is settled into the incinerator 12 more easily than the cake of the first system shown in FIG. 1 and can be treated as bottom ash. . At the time of combustion, dioxins contained in the solidified cement 25 are also decomposed in a high-temperature incinerator, thereby enabling clean combustion.

[Fourth Incineration System] FIG. 4 is a schematic view of a first combustion system provided with a low-pollution combustion apparatus for implementing the low-pollution combustion method of the present invention. As shown in FIG.
A coagulating sedimentation unit 27 for removing heavy metals in the washing wastewater 26 from the washing tank 16 is provided,
The heavy metal 28 is precipitated and removed.

In the present embodiment, the heavy metal 28 is precipitated and removed by the coagulating / precipitating means 27 and can be prevented from being discharged to the outside as it is.

[Fifth Incineration System] FIG. 5 is a schematic view of a first combustion system provided with a low-pollution combustion apparatus for implementing the low-pollution combustion method of the present invention. As shown in FIG.
In the combustion system of (1), a reverse osmosis membrane 30 for removing the salt in the effluent 29 from the coagulation sedimentation means 27 for removing heavy metals in the washing phase 25 from the washing tank 16 is provided,
The treated water 32 from which water has been removed is reused in the washing tank 16 again.

In the present embodiment, the wastewater 29 from the coagulation and sedimentation means 27 is used to remove salts by a reverse osmosis membrane (RO membrane) 30 and is used again for washing in the washing tank 16.

[0036]

As described above, according to the first aspect of the present invention, dust in exhaust gas discharged from an incinerator burning waste at a high temperature is collected, and the collected flying dust is collected. The ash is washed with water to form a slurry, the water in the slurry sludge is dewatered to form a dewatered cake, and the dewatered cake is returned to the incinerator again and burned again. Since it is returned to the incinerator as a dehydrated cake and burned, silicon (Si), which is originally treated as incineration ash,
Calcium (Ca) and the like can be treated as bottom ash, and dioxins contained in the dehydrated cake are also decomposed in a high-temperature incinerator, thereby enabling clean combustion.

According to the second aspect of the present invention, in the first aspect, the dewatered cake is granulated, and the granulated material is returned to the combustion furnace. Scattering is prevented, and it can be settled inside the incinerator and efficiently treated as bottom ash.

According to the third aspect of the present invention, in the first aspect, a cement-based compound is added to the sludge to form a solidified cement, and the solidified cement is returned to the combustion furnace. The ash is also prevented from being scattered again in the fly ash and settled into the incinerator so that it can be efficiently treated as bottom ash.

According to the fourth aspect of the present invention, in the first aspect, the heavy metals in the washing wastewater from the washing tank are removed by coagulation sedimentation and reused as the washing liquid, so that the heavy metals are formed as precipitates. Can be removed.

According to the invention of claim 5, in claim 4, since the salt in the waste liquid from the coagulation and sedimentation is removed by the reverse osmosis membrane, the wastewater from the coagulation and sedimentation means is removed by the reverse osmosis membrane. The salt can be removed and used again for washing in the washing tank.

According to the invention of claim 6, an incinerator for burning waste at a high temperature, a dust collecting device for collecting dust in exhaust gas discharged from the incinerator, and a dust collecting device A washing tank for suspending the collected fly ash in the washing, and a dehydrating means for dehydrating water in the slurry sludge from the washing tank, the dewatered dewatered cake is returned to the incinerator again, Because it burns again, heavy metals in fly ash are removed by washing with water,
Since it is returned to the incinerator as dehydrated cake and burned, silicon (Si) and calcium (C
a) and the like can be treated as bottom ash, and dioxins contained in the dewatered cake are also decomposed in a high temperature incinerator, thereby enabling clean combustion.

According to the invention of claim 7, in claim 6, the apparatus for granulating the dewatered cake is provided, and the granulated material is returned to the combustion furnace. Is prevented from re-scattering to the inside of the incinerator and can be efficiently treated as bottom ash.

According to the eighth aspect of the present invention, in the sixth aspect, a cement solidifying means for adding a cement compound to the sludge is provided, and the solidified cement is returned to the combustion furnace. The fly ash is prevented from being scattered again and settled in the incinerator so that it can be efficiently treated as bottom ash.

According to the ninth aspect of the present invention, in the sixth aspect, a coagulating sedimentation means for removing heavy metals in the washing wastewater from the washing tank is provided, so that heavy metals can be removed as precipitates. it can.

According to the tenth aspect, the ninth aspect is provided.
In the above, since a reverse osmosis membrane for removing salts in the effluent from the coagulation / sedimentation means is provided, the wastewater from the coagulation / sedimentation means is removed with a reverse osmosis membrane to remove salts, and is used again for water washing in a water washing tank. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a first combustion system according to the present invention.

FIG. 2 is a schematic diagram of a second combustion system according to the present invention.

FIG. 3 is a schematic diagram of a third combustion system according to the present invention.

FIG. 4 is a schematic diagram of a fourth combustion system according to the present invention.

FIG. 5 is a schematic diagram of a fifth combustion system according to the present invention.

FIG. 6 is a schematic diagram of a combustion system according to the prior art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Waste 12 Incinerator 13 Dust 14 Dust collection device 15 Fly ash 16 Rinse tank 17 Slurry sludge 18 Dehydration means 19 Dehydration cake 20 Incineration ash (bottom ash) 21 Granulator 22 Granulated material 23 Cement compound 24 Cement Solidification means 25 Cement solidified material 26 Washing drainage 27 Coagulation sedimentation means 28 Heavy metal 29 Drainage 39 Reverse osmosis membrane 31 Salt content 32 Treated water

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuo Sato 12 Nishikicho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Heavy Industries, Ltd. Yokohama Works (72) Inventor Hiroki Honda 1-8-8, Sachiura Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture Address 1 F term in Yokohama Research Laboratory, Mitsubishi Heavy Industries, Ltd. 3K070 DA01 DA02 DA07 DA16 DA27 DA36 DA37 DA40 DA44 DA45 DA76 4D004 AA02 AA37 AA46 AB03 AB06 AB10 CA10 CA34 CA50 CB50 CC06 CC13

Claims (10)

[Claims] 1. A method for collecting dust in exhaust gas discharged from an incinerator that burns waste at a high temperature, washing the collected fly ash with water to form a slurry, and removing water in the slurry sludge. A low-pollution combustion method, comprising dewatering a dewatered cake, returning the dewatered cake to the incinerator again, and burning it again. 2. The low-pollution combustion method according to claim 1, wherein the dewatered cake is granulated and the granulated product is returned to a combustion furnace. 3. The low-pollution combustion method according to claim 1, wherein a cement-based compound is added to the sludge to form a solidified cement, and the solidified cement is returned to a combustion furnace. 4. The low-pollution combustion method according to claim 1, wherein heavy metals in the washing wastewater from the washing tank are removed by coagulation sedimentation and reused as a washing solution. 5. The low-pollution combustion apparatus according to claim 4, wherein the salt in the effluent from the coagulated sediment is removed by a reverse osmosis membrane. 6. An incinerator for burning waste at a high temperature, a dust collector for collecting dust in exhaust gas discharged from the incinerator, and fly ash collected by the dust collector for washing with water. A washing tank for turbidity, and a dehydrating means for dehydrating water in slurry sludge from the washing tank, wherein the dewatered cake after dehydration is returned to the incinerator again and burned again. Pollution combustion equipment. 7. The low-pollution combustion device according to claim 6, further comprising a granulating device for granulating the dewatered cake, and returning the granulated material to a combustion furnace. 8. The low-pollution combustion apparatus according to claim 6, wherein a cement solidifying means for adding a cement compound to the sludge is provided, and the solidified cement is returned to a combustion furnace. 9. The low-pollution combustion apparatus according to claim 6, further comprising a coagulating sedimentation unit for removing heavy metals in the washing effluent from the washing tank. 10. The low-pollution combustion apparatus according to claim 9, further comprising a reverse osmosis membrane for removing a salt in the effluent from the coagulation sedimentation means.