JP2000051633A - Method for treating exhaust gas from incinerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating exhaust gas from an incinerator which can cool the combustion gas of waste promptly. SOLUTION: Waste is burned in an incinerator 1, and the high temperature exhaust gas G generated in the process is cooled by passing it through the first and second cooling filter layers 3, 5 comprising a group II metal hydroxide which are installed in the first pipe line 4 and the second pipe line 6. After that, the cooled exhaust gas G is introduced into a soot and dust removing apparatus installed in the third pipe line 7 to be an exhaust gas channel. Calcium hydroxide, magnesium hydroxide, barium hydroxide (octa-hydrate), strontium hydroxide (octa-hydrate), and others can be used as the group II metal hydroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rapidly cooling exhaust gas from a waste incinerator.

[0002]

In recent years, industrial waste, general waste, or solid waste produced from these wastes has been developed.
Dioxins generated when incinerating (RDF) and the like have become a social problem. The main cause of dioxins generated by burning waste is that chlorine-based compounds such as vinyl chloride contained in waste during combustion in incinerators become precursors to chlorophenol and chlorobenzene. 250-400 by catalytic reaction on fly ash
In the exhaust gas treatment process, chlorinated aromatic compounds such as chlorophenol and chlorobenzene form unburned carbon, air, moisture, and inorganic materials at low temperatures of 250 to 350 ° C. It is known that there are two types, namely, so-called de novo synthesis generated in the presence of chlorine and the like. Of these dioxins, the synthesis rate from the precursor during combustion is high, but the combustion gas is generated from the incinerator to the temperature control tower in the range of 600 to 250.
While there is only a reaction time of about several seconds passing through a temperature range of about ℃, the residence time of fly ash in the exhaust gas treatment system where de novo synthesis occurs is very long,
It is thought that in actual incinerators, there are more dioxins generated by the latter reaction. In addition, chlorine, in particular, waste amount of 1
It is needless to say that chlorine of not less than% is required, but a metal component serving as a catalyst is also required. Among such metal components, fine powder particles such as copper chloride or fly ash plays an important role as a catalyst. Is becoming apparent.

[0003] That is, from these facts, dioxins are characterized as chlorine compounds under the condition of coexistence of oxygen with a characteristic temperature of about 650 to 7 which is much higher than the decomposition and formation temperature.
Decomposition starts at about 50 ° C. and is expected to be substantially decomposed at about 850 ° C. On the other hand, if it is 250 ° C. or less, no synthesis is performed. In order to further suppress the synthesis, it is considered effective to remove chlorine (the compound) as much as possible and to reduce copper chloride having a large catalytic activity.

[0004] Therefore, as measures against such dioxins, the present situation is to raise the combustion temperature of the refuse incinerator itself and to remove chlorine in the refuse incinerator. However, raising the combustion temperature of the refuse incinerator itself or removing chlorine from the refuse incinerator basically suppresses the generation of dioxin inside the incinerator, and waste The combustion exhaust gas contains chlorine-based gases such as hydrogen chloride gas and chlorine gas, NO _x ,
As described above, a large amount of corrosive gas such as O _x is contained, and de novo synthesis occurs in this exhaust gas treatment step. Therefore, in the exhaust gas treatment process, slaked lime is carried on the bag filter to remove corrosive gas. However, the bag filter used for collecting chlorine-based gas and the like generally has a service temperature of about 200 ° C. Therefore, it cannot be used immediately after the outlet of a high temperature refuse incinerator, and the pressure loss of exhaust gas is large. For this reason, a temperature control tower is provided in the exhaust gas channel,
The temperature of the exhaust gas flowing through the temperature control tower is reduced by spraying steam with a scrubber or the like, and then the exhaust gas is passed through a bag filter. However, the exhaust gas immediately after being discharged from the stack of the refuse incinerator is about 700 ° C., and in the temperature control tower of the type that sprays steam described above,
Since the cooling rate of the exhaust gas is not fast, the exhaust gas will stay for a long time in the temperature range of 250 to 600 ° C., which is the synthesis temperature of dioxins, and there is a possibility that dioxins may be generated in the exhaust gas channel. As a countermeasure, it is conceivable to rapidly cool the exhaust gas by supplying a large amount of water vapor.However, to rapidly cool the exhaust gas requires a very large amount of water vapor, and the amount of gas flowing through the exhaust gas passage is greatly increased. In addition to the increase, the amount of gas flowing through the bag filter also increases, so that it is not practical, such as an extremely large-scale device, and the load on the bag filter also increases. Furthermore, it would be desirable if chlorine-based gas and the like could be removed while cooling quickly in the cooling device, because the generation of dioxins in the exhaust gas passage could be further suppressed.

The present invention has been made in view of these problems, and an object of the present invention is to provide an exhaust gas treatment method for a refuse incinerator capable of rapidly cooling waste combustion exhaust gas.

[0006]

As a result of intensive studies in view of the above-mentioned object, the present inventor has found that the exhaust gas flow path of a refuse incinerator, in particular, the I.V.
By providing a cooling filter composed of a Group I metal hydroxide, the calorific value of the exhaust gas is deprived due to the decomposition reaction of the hydroxide, and the exhaust gas passing therethrough is rapidly cooled to a temperature of 250 ° C. or less where dioxins are not generated. I found that I can do it. Further, they have found that the group II metal hydroxide can also remove chlorine-based gas in the exhaust gas while cooling the exhaust gas. The present invention has been made based on these.

That is, in the method for treating exhaust gas of a refuse incinerator according to the first aspect of the present invention, waste is burned in a refuse incinerator, and high-temperature exhaust gas generated at this time is cooled by flowing through the cooling filter. Then, it is introduced into a dust removal device provided in the exhaust gas channel.

According to a second aspect of the present invention, there is provided a method for treating an exhaust gas from a refuse incinerator, wherein the exhaust gas having a temperature of 600 ° C. or more flows through the cooling filter.

According to a third aspect of the present invention, there is provided a method for treating exhaust gas from a refuse incinerator, wherein the exhaust gas is cooled to 250 ° C. or less by the cooling filter in the first or second method.

Further, the method for treating exhaust gas of a refuse incinerator according to claim 4 is the method according to any one of claims 1 to 3, wherein the Group II metal hydroxide is selected from calcium, magnesium, barium and strontium. It is a hydroxide of one or more selected metals or a hydrate thereof.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of an exhaust gas treatment method for a refuse incinerator according to the present invention will be described in detail with reference to the apparatus shown in FIGS.

FIG. 1 shows an example of an exhaust gas treatment apparatus of a refuse incinerator to which the method of the present invention can be applied. In FIG. 1, reference numeral 1 denotes a heat-resistant refuse incinerator made of metal or ceramic. A waste stocker (not shown) communicates with the end of the inlet 2 on the upper side of 1 so that a fixed amount of waste is supplied to the refuse incinerator 1. Reference numeral 3 denotes a first cooling filter layer provided immediately after the chimney 1a of the refuse incinerator 1 by the first pipeline 4.
In the first cooling filter layer 3, a plurality of first filters 3 a made of a Group II metal hydroxide are provided. Further, on the downstream side of the first cooling filter layer 3, A second cooling filter layer 5 is arranged via a second conduit 6, and a plurality of second filters 5 a made of a Group II metal hydroxide are also provided in the second cooling filter layer 5. . Further, reference numeral 7 denotes a third pipe connected to the second cooling filter layer 5, and the third pipe 7 serves as a discharge path for removing dust and soot such as fly ash such as a bag filter or an electric dust collector. (Not shown) and communicates with the external environment.
In the present embodiment, an exhaust gas flow path is constituted by the first conduit 4, the second conduit 6, and the third conduit 7.

In this embodiment, the waste includes not only general waste and industrial waste but also solid waste (RDF). This refuse solid fuel is a fuel obtained from waste (Refuse Derived F
uel), which is a waste form that does not contain metal pieces, glass pieces, or other removable inorganic substances and can be used as fuel as it is, especially after crushing garbage and combustible garbage It is dried to improve the calorific value and preservability, and it is compressed and molded into pellets to improve the preservability and transportability.Deodorization is preferably performed by adding slaked lime or quick lime before drying. And the generation of harmful gases.

In the above-described apparatus, the group II metal hydroxide that causes an endothermic reaction in the filters 3a and 5a of the cooling filter layers 3 and 5 basically means that two hydroxyl groups are bonded to an alkaline earth metal. For example, it is generated with heat generation by a hydration reaction of an alkaline earth metal oxide. As the Group II metal hydroxide as described above, calcium hydroxide, magnesium hydroxide,
Barium hydroxide (octahydrate), strontium hydroxide (octahydrate) and the like can be used. Specifically, calcium hydroxide has a decomposition temperature in the range of about 400 to 500 ° C., and water Magnesium oxide has a decomposition temperature in the range of about 350-420 ° C., and barium hydroxide (octahydrate)
A dehydration temperature in the range of about 80-170 ° C, and 650-750.
Strontium hydroxide (octahydrate) has a dehydration temperature of about 90-150 ° C and a dehydration temperature of about 47 ° C.
It has been experimentally confirmed to have a decomposition temperature of 5 to 575 ° C. These Group II metal hydroxides may be used in the form of granules or aggregates, and in some cases, powders.

At the decomposition temperature or higher, such a Group II metal hydroxide releases water, contrary to the hydration reaction, and absorbs heat as it returns to the oxide. Therefore, when it comes into contact with the exhaust gas at a high temperature (not less than its decomposition temperature), a decomposition reaction or the like occurs. That is, calcium, magnesium, barium,
When a group II metal such as strontium is M, 2M
A dehydration endothermic reaction of (OH) ₂ → 2MO + 2H ₂ O− (caloric value) occurs. For example, in the case of calcium, slaked lime (Ca
As (OH) ₂ ) is converted to quicklime (CaO), heat is absorbed from the surroundings. In the case of octahydrate of a Group II metal hydroxide such as barium hydroxide or strontium hydroxide, a dehydration reaction accompanying the drying of the added water occurs prior to the dehydration endothermic reaction described above. This also absorbs heat. In addition, the group II metal hydroxide is 500 to 700 ° C.
When it comes in contact with corrosive gas such as chlorine gas at high temperature, it reacts with chlorine gas (Cl ₂ ) and II such as calcium chloride
Since it is immobilized on the surface as a group III metal chloride, it also exhibits the ability to remove chlorine-based gas in exhaust gas. In addition, such NO _x can be removed by a reaction similar. In addition, it also has the effect of converting copper chloride, which is fine particles and fly ash, into copper oxide. The amount of the Group II metal hydroxide used for such cooling filter layers 3 and 5 depends on the surface area per unit weight thereof.
It is preferable to use about 200 g to 1 kg per 1 m ³ of the flow rate. Particularly, since the reaction rate of this dehydration endothermic reaction is slow, it is preferable to use a sufficient amount of Group II metal hydroxide for long-term use.

The first cooling filter layer 3 made of a Group II metal hydroxide as described above is provided, for example, in a cylindrical container 4a formed in a first conduit 4 as shown in FIG. It has a structure in which a plurality of first filters 3a made of a group II metal hydroxide granule 11 are formed by filling the first filter 3a into the second filter 3a. The second cooling filter layer 5 may have the same configuration as the first cooling filter 3 described above. For example, the first cooling filter layer 3 and the second cooling filter layer 5 may be used.
Since the temperature of the exhaust gas G flowing through the first cooling filter layer 3 is naturally high in the first cooling filter layer 3 and low in the second cooling filter layer 5, for example, calcium and magnesium such as calcium and magnesium are provided in the first cooling filter. The second cooling filter is composed of hydroxide octahydrate of barium and strontium hydroxide so that it can absorb heat even at a low temperature.
By making the endothermic onset temperature of the Group II metal hydroxide constituting the cooling layer different, the exhaust gas G can be cooled more efficiently.

Next, the cooling filter layers 3, 5 as described above
The waste gas incinerator exhaust gas treatment method of
Then, slaked lime is used for the first cooling filter
Slaked lime and barium hydroxide octahydrate
The case where a mixture of the above is used will be described as an example. Apparatus shown in FIG.
, The refuse incinerator 1 burns refuse solid fuel
And high temperature (about 600-700 ° C) exhaust gas G
From the first cooling filter layer 3 through the first conduit 4
To reach. The filter 3a of the first cooling filter layer 3
Slaked lime is used as group II metal hydroxide 11
Therefore, its decomposition start temperature is about 400-500 ° C.
If the temperature of the exhaust gas G is high, a dehydration endothermic reaction occurs
Since it is converted to quicklime, the calorie of exhaust gas G is absorbed and
Cools quickly. In the initial stage, slaked lime
The heat of the specific heat of the body is also absorbed. Furthermore, in exhaust gas G
Chlorine gas such as hydrogen chloride gas and chlorine gas contained
NO _xCorrosive gases such as are also sorbed and removed by slaked lime.
In addition, fine particles and fly ash of copper chloride are converted into copper oxide. Continued
The exhaust gas G passes through the second pipe 6 and passes through the second cooling filter.
The layer 5 is reached. The filter of the second cooling filter layer 5
Ruta 5a is composed of slaked lime and hydroxyl as group II metal hydroxide 11.
Exhaust gas G is used in combination with barium octahydrate
If the temperature is higher than about 400-500 ° C, slaked lime and water
Dehydration reaction of barium oxide octahydrate by endothermic dehydration reaction
The exhaust gas G is further cooled. Also, the temperature of the exhaust gas G
Even if the temperature drops below 400 ° C,
Drying of barium hydroxide octahydrate if higher than 170 ° C
The exhaust gas G is further cooled by the dehydration reaction.

By using a sufficient amount of the group II metal hydroxide 11 for the exhaust gas G in the first and second cooling filters 3 and 5, the exhaust gas G is rapidly cooled to 250 ° C. or less. This makes it possible to prevent the chlorine gas contained in the exhaust gas G from reacting to synthesize dioxins via chlorophenol, chlorobenzene and the like.

After the exhaust gas G has been cooled in this way, the exhaust gas G flows through the third pipe 7 and is removed by a dust removal device (not shown) such as a bag filter or an electric dust collector. Various corrosive gases, as well as fine powder of a Group II metal hydroxide such as calcium hydroxide discharged from the first and second cooling filters 3 and 5 are collected and released to the external environment.

The first and second cooling filters 3, 5
When the calcium hydroxide (hydrated lime) and barium hydroxide octahydrate, which are the Group II metal hydroxides 11 in the inside, are sufficiently converted to calcium oxide (quick lime) and barium oxide by endotherm, take out the filters 3 and 5 and remove the new ones. Can be replaced with Calcium oxide (quick lime) and barium oxide in the used filters 3 and 5 easily react by supplying water such as steam due to the repetition of the hydration reaction, and remove the heat taken from the exhaust gas G. Since it is released and returned to slaked lime and barium hydroxide octahydrate, it can be used again as a filter. At this time, it is desirable from the viewpoint of energy to reuse the heat generated during the hydration reaction as a heat source.

As described in detail above, in the method for treating exhaust gas from a refuse incinerator according to the present embodiment, the waste is burned in the refuse incinerator 1, and the high-temperature exhaust gas G generated at this time is discharged to the first exhaust gas channel. Group II metal hydroxide 11 is connected to the pipes 4 and 6.
First and second cooling filter layers 3 and 5 made of
The high temperature exhaust gas G is passed through the first and second cooling filter layers 3 and 5.
After being cooled by flowing the waste gas, the waste gas is introduced into the dust removal device provided in the third pipe line 7 serving as the exhaust gas passage, so that the exhaust gas G from the refuse incinerator 1 undergoes a dioxin generation reaction. Can be quickly cooled to no more than about 250 ° C. In addition, the effect of removing corrosive gas such as chlorine-based gas and converting fine particles of copper chloride into fly ash can be expected. In particular, in the present embodiment, the first cooling filter layer 3 is provided with the chimney 1 where the temperature of the exhaust gas G is 600 ° C. or more.
Since the exhaust gas G is provided near the outlet of a, the dehydration and endothermic reaction of the group II metal hydroxide 11 occurs efficiently.
It can be cooled quickly to below ℃.

Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and various modifications can be made. For example, in the above embodiment, the two cooling filter layers of the first cooling filter layer 3 and the second cooling filter layer 5 are provided, but this cooling filter layer can cool the exhaust gas G to 250 ° C. or less. If so, the number may be one, or three or more. Further, the incinerator is not limited to the one in the above-described embodiment, and it goes without saying that it can be applied to various types of incinerators.

[0023]

The present invention will be described in more detail with reference to the following specific examples. Example 1 A cooling filter having a thickness of 10 cm was prepared using 500 g of slaked lime granules. In FIG. 1, only one of them is used, and at a combustion chamber temperature of about 900 to 1050 ° C., an exhaust gas of about 30
The exhaust gas temperature before and after the cooling filter at a flow rate of 0 liter / min was measured every hour. The results are shown in Table 1 together with the combustion chamber temperature and the temperature difference before and after the filter.

[0024]

[Table 1]

As is clear from Table 1, it can be seen that the temperature of the exhaust gas is reduced by about 400 ° C. by passing through the cooling filter regardless of the temperature of the exhaust gas. Further, when the cooling filter after the exhaust gas circulation was taken out and the components were inspected, quicklime was detected. From these facts, the decrease in exhaust gas temperature is due to the loss of calorific value of the exhaust gas when calcium hydroxide is converted into quicklime, and the amount (surface area) of the calcium hydroxide granules with respect to the flow rate of the exhaust gas is almost constant. It is considered that the temperature at which the exhaust gas decreases does not fluctuate significantly. This indicates that the amount of calcium hydroxide used should be adjusted according to the desired exhaust gas temperature. Example 2 In the same manner as in Example 1, except that the heat insulating material was wound around the duct serving as the exhaust gas flow path and the temperature of the combustion chamber was changed from 800 to 1050 ° C., the exhaust gas temperature before and after the cooling filter was set to 1
It was measured every hour. The results are shown in Table 2 together with the combustion chamber temperature and the temperature difference before and after the filter.

[0026]

[Table 2]

As is apparent from Table 2, the temperature of the exhaust gas is reduced by about 450 ° C. by passing through the cooling filter regardless of the temperature of the exhaust gas. Further, when the cooling filter after the exhaust gas circulation was taken out and the components were inspected, quicklime was detected. From these facts, the decrease in the exhaust gas temperature is due to the loss of calorific value of the exhaust gas when calcium hydroxide is converted into quicklime, and the decrease in the exhaust gas because the surface area of the calcium hydroxide granules with respect to the flow rate of the exhaust gas is almost constant. It is considered that the temperature does not fluctuate greatly. This indicates that the amount of calcium hydroxide used should be adjusted according to the desired exhaust gas temperature. Comparative Example 1 Exhaust gas temperatures before and after that in Example 1 were measured every hour except that a ceramic was used instead of the cooling filter. Table 3 shows the results together with the combustion chamber temperature and the temperature difference before and after the filter.

[0028]

[Table 3]

[0029]

According to the method for treating exhaust gas of a refuse incinerator according to the first aspect of the present invention, waste is burned in a refuse incinerator, and high-temperature exhaust gas generated at this time is cooled by flowing through the cooling filter. After that, since it is introduced into the dust removal device provided in the exhaust gas channel, the exhaust gas from the refuse incinerator is heated to 250 ° C. or lower at which the generation reaction of dioxins does not occur by the dehydration and endothermic reaction of the Group II metal hydroxide. Can be cooled quickly.

According to a second aspect of the present invention, in the method for treating exhaust gas of a refuse incinerator, the exhaust gas of 600 ° C. or more is passed through the cooling filter. Since the dehydration endothermic reaction occurs efficiently, the exhaust gas can be rapidly cooled.

According to a third aspect of the present invention, in the method for treating exhaust gas from a refuse incinerator, the exhaust gas is cooled to 250 ° C. or less by the cooling filter according to the first or second aspect. Is big.

Further, in the method for treating exhaust gas of a refuse incinerator according to claim 4, the group II metal hydroxide is selected from calcium, magnesium, barium and strontium in any one of claims 1 to 3. Since it is a hydroxide of one or more metals or a hydrate thereof, it is suitable for cooling an exhaust gas having an exhaust gas temperature of 600 ° C. or more by its dehydration endothermic reaction.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an exhaust gas treatment device of a refuse incinerator to which the method of the present invention can be applied.

FIG. 2 is a sectional view showing a cooling filter used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Garbage incinerator 1a Chimney 2 Inlet 3 First cooling filter layer (cooling filter) 4 First pipeline (flow path) 5 Second cooling filter layer (cooling filter) 6 Second pipeline (flow) 7) Third pipeline (flow channel) 11 Group II metal hydroxide G Exhaust gas

Claims (4)

[Claims] Claims 1. A method for burning waste in a refuse incinerator, cooling the high-temperature exhaust gas generated at this time by flowing through the cooling filter, and then introducing the cooled exhaust gas into a dust removal device provided in the exhaust gas channel. Characteristic waste gas treatment method for refuse incinerator. 2. The exhaust gas treatment method for a refuse incinerator according to claim 1, wherein exhaust gas of 600 ° C. or higher is passed through the cooling filter. 3. The exhaust gas from the cooling filter is
The exhaust gas treatment method for a refuse incinerator according to claim 1 or 2, wherein the method is cooled to 50 ° C or lower. 4. The method according to claim 1, wherein the Group II metal hydroxide is calcium,
The refuse incinerator according to any one of claims 1 to 3, wherein the hydrate is a hydroxide of one or more metals selected from magnesium, barium, and strontium, or a hydrate thereof. Exhaust gas treatment method.