JPH10288325A - Generation restraint method of dioxins contained in exhaust gas in refuse incinerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute secondary combustion, cooling and agitation of combustion exhaust gas generated during refuse incineration in a refuse incinerator properly and restrain a blowing-through rise of an unburnt gas and restrain the generation of dioxins. SOLUTION: The lower part of a flue 5 which discharges combustion exhaust gas generated from a combustion chamber 2 of a refuse incinerator is use as a gas mixing chamber 8 while mixing and agitation air blowing nozzles 9 and cooling air blowing nozzles 11 are provided on a side wall on both sides and or on a side wall in front and rear. A secondary combustion air blowing group 10, which is directed at the opposed side walls, is provided on the left side of the lower part of the gas mixing chamber located above a dry fire grate 3a of the combustion chamber 2 or on the right side of a side wall, thereby generating a revolving air current by the air blown in from each nozzle group 10 in the gas mixing chamber and mixing an unburnt gas with the combustion gas to a satisfactory extent. The unburnt gas is burnt secondarily with high efficiency by the secondary combustion air from the secondary combustion air blowing nozzles 10, thereby restraining the generation of dioxins from the exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling dioxins contained in combustion exhaust gas generated when incinerating waste in a waste incinerator.

[0002]

2. Description of the Related Art In a refuse incinerator, when a small amount of dioxins is contained in the combustion exhaust gas discharged from the incinerator when incinerating various kinds of refuse such as municipal waste and industrial waste, the human body may be damaged. Adversely affect. Therefore, in order to prevent the occurrence of pollution problems, it is necessary to suppress dioxins in the combustion exhaust gas generated from the refuse incinerator.

[0003] The dioxins in the combustion exhaust gas are generated by incomplete combustion, and when the gas temperature reaches about 300 ° C in an exhaust gas treatment facility or the like, the dioxins are catalyzed on the dust surface. It is said that some are synthesized.

It is known that as means for suppressing the generation of dioxins from the exhaust gas from a refuse incinerator, it is effective to raise the refuse combustion temperature, secure the refuse combustion residence time, and mix and stir the flue gas. ing. Hereinafter, a conventional flue gas mixing and stirring means for suppressing the generation of dioxins will be described.

FIG. 5 is a schematic vertical sectional view of a refuse incinerator showing a conventional method for suppressing the generation of dioxins, and FIG. 6 is a sectional view of FIG.
FIG. 4 is a cross-sectional view taken along a line A. As shown in the drawing, a grate 3 including a dry grate 3a, a combustion grate 3b, and a post-combustion grate 3c is provided in the combustion chamber 2 of the incinerator 1.
Primary air is blown into each of 3b and 3c from below.

[0006] The refuse charged on the dry grate 3a into the combustion chamber 2 from the refuse inlet 1a of the incinerator 1 is the dry grate 3a,
It moves sequentially over the combustion grate 3b and the post-combustion grate 3c, during which it is dried and burned. The incineration ash is discharged at outlet 7.
The flue gas is discharged to the outside of the furnace through a flue 5 connected to a gas discharge port 4 at an upper portion of the combustion chamber 2, and is cooled by cooling water injected from a nozzle (not shown), or And heat is recovered and discharged.

[0007] A plurality of air blows into the front side wall 5a and the rear side wall 5b of the flue 5 connected to the combustion chamber 2 in the direction of movement of the dust on the grate 3 near the gas outlet 4. Nozzles 6 and 6 are provided facing each other toward the center of the flue 5.

The air injection nozzles 6 and 6 supply secondary combustion air (air for preventing incomplete combustion of combustion exhaust gas) and cooling air (air for controlling the combustion temperature in the furnace). Supply and air for mixing and agitation (air for mixing and agitating the combustion exhaust gas to eliminate incomplete combustion). Subsequent combustion, cooling and mixing take place.

[0009]

As described above, in the conventional refuse incinerator, the air blowing nozzles 6 provided on the front side wall 5a and the rear side wall 5b near the gas outlet 4 of the flue 5 are used. Secondary combustion, cooling, and mixing of the combustion exhaust gas are performed by the secondary air blown from 6, so that there is an advantage that the apparatus is simple and the equipment cost is low, but there are the following problems.

(1) Above the dry grate 3a of the combustion chamber 2,
There is unburned gas generated in the drying stage of the refuse, and the unburned gas rises and blows out along the side walls of the combustion chamber 2 and the flue 5 to be discharged. From a hydrodynamic point of view, the flue gas near the air injection nozzles 6, 6 is drawn by local decompression caused by the high-speed air ejected from the nozzles 6, 6, so that the unburned gas is conventionally blown by air. Nozzles 6, 6
Was thought to mix with the air from. However, according to the study of the present inventors, since the high-temperature combustion exhaust gas in the combustion chamber 2 becomes a strong updraft, a phenomenon that the hot exhaust gas blows through the gap between the adjacent blowing nozzles 6 and 6 as unburned gas is generated. It turns out that it cannot be avoided.

(2) Since the air blown from the air blowing nozzles 6 and 6 also serves to cool and mix the combustion exhaust gas, the amount of air blown from the nozzles 6 and 6 is reduced in order to raise the combustion temperature in the furnace. If the amount is reduced, the effect of mixing and stirring the combustion exhaust gas is reduced, so that the generation of dioxins cannot be reduced.

According to experiments, the air blowing speed from the air blowing nozzles 6 and 6 effective for mixing and stirring is 20 to 40 m.
/ Sec. On the other hand, in order to maintain the combustion temperature of the refuse in the combustion chamber 2 at a predetermined temperature (850 to 950 ° C.), the combustion temperature is directly affected by the variation of the combustion state due to the variation of the refuse quality. It is essential to blow cooling air into the combustion chamber 2 for adjustment.

Therefore, it is difficult to satisfy these conditions by the air blown from the same blowing nozzles 6 and 6, and it is inevitable that mixing and stirring must be sacrificed.

(3) Generally, conventional air blowing nozzles 6, 6
Are provided on the front side wall 5a and the rear side wall 5b of the flue 5 connected to the combustion chamber 2 as shown in FIG.
Secondary air is blown from the air blowing nozzles 6 and 6 toward the center of the flue 5. The results of research conducted by the present inventors have been described. It has been found that although the blown secondary air has a cooling effect, the flow of the secondary air is canceled by the upward flow of the high-temperature combustion exhaust gas, so that the mixing and stirring effect is insufficient.

[0015] Accordingly, an object of the present invention is to solve the above-mentioned problems and to appropriately perform secondary combustion, cooling and mixing of combustion exhaust gas generated when incinerating waste in a waste incinerator,
It is an object of the present invention to provide a method capable of suppressing an increase in blow-through of unburned gas, thereby suppressing generation of dioxins.

[0016]

The invention according to claim 1 incinerates refuse supplied to a dry grate in a combustion chamber and sequentially moving on the dry grate, the combustion grate and the post-combustion grate. And the gas mixing chamber in a refuse incinerator in which air is blown into a gas mixing chamber below a flue for discharging generated combustion exhaust gas from the combustion chamber to mix and stir unburned gas in the combustion exhaust gas. A mixing and stirring air blowing nozzle group and a cooling air blowing nozzle group are provided on the left and right side walls and / or the front and rear side walls of the left and right side walls of the lower part of the gas mixing chamber, which is located above the dry grate. The right side wall is provided with a secondary combustion air blowing nozzle group which is blown along the front side wall toward the other opposite side wall, and a cooling air blowing amount from the cooling air blowing nozzle group. Shadow A predetermined amount of secondary combustion air and mixing / stirring air were blown from the secondary combustion air blowing nozzle group and the mixing / stirring air blowing nozzle group without being blown, and were blown from each of the nozzle groups. By cooperation of air for secondary combustion, air for mixing and stirring, and air for cooling,
A swirling flow is generated in the gas mixing chamber, the unburned gas in the combustion exhaust gas is mixed with the combustion gas, and is intensively blown from above the secondary combustion air blowing nozzle group above the dry grate. The secondary combustion air is also characterized in that the unburned gas in the combustion exhaust gas is efficiently secondary-combusted by the secondary combustion air, and thus the generation of dioxins from the combustion exhaust gas is suppressed.

According to a second aspect of the present invention, the flow rate of the secondary combustion air blown from the secondary combustion air blowing nozzle group and the mixing / stirring air blown from the mixing / stirring air blowing nozzle group is reduced. , 20 to 40 m / sec.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. 1 is a schematic vertical sectional view showing one embodiment of the refuse incinerator of the present invention, FIG. 2 is a sectional view taken along line BB of FIG. 1, FIG. 3 is a sectional view taken along line CC of FIG. DD of FIG.
It is a line sectional view. As shown in the drawing, a drying grate 3a, a combustion grate 3b, and a post-combustion grate are provided in a combustion chamber 2 of an incinerator 1.
A grate 3 composed of 3c is provided, and refuse charged from the refuse inlet 1a of the incinerator 1 onto the dry grate 3a in the combustion chamber 2 is dried grate 3a, combustion grate 3b and After moving on the post-combustion grate 3c sequentially, being dried and burned during that time, the incinerated ash is discharged outside the furnace through the discharge port 7, and the flue gas is discharged to the gas discharge port 4 at the upper part of the combustion chamber 2. It is the same as in the related art that is cooled by the cooling water injected from a nozzle (not shown) through the connected flue 5, or passes through the boiler chamber to recover heat, and then is discharged.

The lower part of the flue 5 is a gas mixing chamber 8, and the secondary air blown into the gas mixing chamber 8 is divided into secondary combustion air, cooling air and mixing and stirring air. The nozzles are blown from respective unique nozzle groups described below.

That is, on each of the front side wall 8a and the rear side wall 8b of the gas mixing chamber 8, a mixing and stirring air blowing nozzle group 9 composed of a plurality of nozzles is directed from the front side wall 8a to the rear side wall 8b. It is provided so that a flow along the left side wall 8c on the left side orthogonal to the moving direction of the refuse is formed, and the rear side wall 8b
From the right side wall 8d on the right side orthogonal to the moving direction of the refuse.

The mixing / stirring air blowing nozzle group 9 further forms a flow along the rear side wall 8b from the left side wall 8c to the right side wall 8d of the gas mixing chamber 8, and
It is preferable that a flow is formed along the front side wall 8a from 8d to the left side wall 8c.

On the right side wall 8d or the left side wall 8c below the gas mixing chamber 8 located above the dry grate 2a of the combustion chamber 2, a secondary combustion air blowing nozzle group 10 composed of a plurality of nozzles is provided. The flow is provided so as to form a flow toward the left side wall 8c along the front side wall 8a or a flow from the left side wall 8c to the right side wall 8d.

In the gas mixing chamber 8, the above-mentioned mixing and stirring air blowing nozzle group 9 and the secondary combustion air blowing nozzle group 10 are described.
In each of the front and rear side walls 8a and 8b, a cooling air blowing nozzle group 11 composed of a plurality of nozzles forms a flow along the left side wall 8c from the front side wall 8a to the rear side wall 8b. It is provided such that a flow along the right side wall 8d is formed from the rear side wall 8b to the front side wall 8a.

The mixing / stirring air, the secondary combustion air blown from each of the mixing / stirring air blowing nozzle group 9, the secondary combustion air blowing nozzle group 10, and the cooling air blowing nozzle group 11. And the cooling air cooperates to generate a swirling flow of air in the gas mixing chamber 8. Therefore, the unburned gas in the high-temperature combustion exhaust gas rising from the combustion chamber 2 is sufficiently mixed and stirred with the combustion gas in the combustion exhaust gas by the swirling flow.

The secondary combustion air blown intensively from the secondary combustion air blowing nozzle group 10 above the dry grate 2a, where it is considered that a large amount of unburned gas is generated, generates unburned gas. Is efficiently and completely burned, and blow-through of unburned gas from the combustion chamber 2 is prevented.

The mixing and stirring air from the mixing and stirring air blowing nozzle group 9 and the secondary combustion air blowing nozzle group 10
The blowing speed of the secondary combustion air from the
It is preferably set to sec. If the blowing speed of the mixing and stirring air is less than 20 m / sec, a sufficient horizontal swirling flow by the mixing and stirring air cannot be obtained. On the other hand, if the blowing speed of the mixing and stirring air exceeds 40 m / sec, no further effect of forming a horizontal swirling flow can be obtained, which is uneconomical.

The temperature inside the combustion chamber 2 is increased to 850 by the cooling air blown from the cooling air blowing nozzle group 11.
It is controlled within the range of ９950 ° C. The temperature in the combustion chamber is 8
If the temperature is lower than 50 ° C., the content of dioxins in the combustion exhaust gas increases, while if the temperature in the combustion chamber exceeds 950 ° C., problems such as damage to the furnace wall of the combustion chamber occur.

The flow rate of the cooling air is not constant during the operation but varies for the purpose. However, the gas mixing chamber 8
The secondary air blown into the air is divided into secondary combustion air, cooling air, and mixing and stirring air, so that the secondary air is not affected by the fluctuation of the cooling air blowing amount. A predetermined amount of secondary combustion air and mixing and stirring air can be blown from the next combustion air blowing nozzle group 10 and the mixing and stirring air blowing nozzle group 9 without causing shortage of air volume and wind speed.

A predetermined amount of the mixing / stirring blown from the independent dedicated mixing / stirring air blowing nozzle group 9, the secondary combustion air blowing nozzle group 10 and the cooling air blowing nozzle group 11. The unburned gas in the combustion exhaust gas is sufficiently mixed with the combustion gas by the air, the secondary combustion air, and the cooling air, and the unburned gas is efficiently and completely burned. As a result, dioxin from the combustion exhaust gas is reduced. The occurrence of species is suppressed.

[0030]

Next, the present invention will be described with reference to examples and comparative examples. According to the method of the present invention, as shown in FIGS. 1 to 4, a mixing and stirring air blowing nozzle group 9 provided on each of the front and rear side walls 8a and 8b and the left and right side walls 8c and 8d of the gas mixing chamber 8 allows the mixing chamber to be mixed. Air for mixing and agitation is blown into the inside of the combustion chamber 2, and a group of secondary combustion air blowing nozzles 10 provided on the right side wall 8 d below the gas mixing chamber 8 and located above the dry grate 3 a of the combustion chamber 2. The secondary combustion air was blown from the right side wall 8d toward the left side wall 8c, and the cooling air was blown by the cooling air blowing nozzle group 11 provided on the front and rear side walls 8a and 8b.

Since dioxins in the combustion exhaust gas discharged from the incinerator 1 are generated by CO due to incomplete combustion, the amount of dioxins generated is examined by using the CO concentration as an index, and the dioxins are blown into the combustion chamber 2. Table 1 shows the amount of secondary air blown, the amount of mixing and stirring air blown into the mixing chamber 8, the amount of secondary combustion air blown, and the amount of cooling air blown.

For comparison, air for mixing and stirring and air for cooling were blown, and air for secondary combustion was not blown, and as shown in FIGS. In the case where the secondary combustion, cooling, and mixing of the combustion exhaust gas were performed by the secondary air blown from the injection nozzle, the CO concentration in the combustion exhaust gas, together with the amount of the primary air and the secondary air injected, is shown in Table 1. Are also shown.

[0033]

[Table 1]

As can be seen from Table 1, the CO concentration in the conventional method was 740 PPM, whereas the CO concentration in the flue gas in the method of the present invention was 35 PPM, which was about It has been reduced by a factor of 20.

[0035]

As described above, according to the present invention,
When incinerating refuse by a refuse incinerator, secondary combustion, cooling and mixing of the combustion exhaust gas generated at the time of incineration are performed properly, and the rise of unburned gas blow-through is suppressed, thereby suppressing the generation of dioxins. Can provide excellent industrial effects.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view of a refuse incinerator showing one embodiment of the method of the present invention.

FIG. 2 is a sectional view taken along line BB of FIG.

FIG. 3 is a sectional view taken along line CC of FIG. 1;

FIG. 4 is a sectional view taken along line DD of FIG. 1;

FIG. 5 is a schematic longitudinal sectional view of a refuse incinerator showing an example of a conventional method.

FIG. 6 is a sectional view taken along line AA of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incinerator 2 Combustion chamber 3 Grate, 3a Dry grate 3b Combustion grate 3c Post combustion grate 4 Outlet 5 Flue 6 Air injection nozzle 7 Incineration ash outlet 8 Gas mixing chamber 8a Front side wall 8b Rear side wall 8c Left side wall 8d Right side wall 9 Air blowing nozzle group for mixing and stirring 10 Air blowing nozzle group for secondary combustion 11 Air blowing nozzle group for cooling

Claims (2)

[Claims] 1. Burning of refuse supplied to a drying grate in a combustion chamber and sequentially moving on the drying grate, the combustion grate and the post-combustion grate, and discharging generated combustion exhaust gas from the combustion chamber. In a refuse incinerator in which air is blown into a gas mixing chamber below a flue to mix and stir unburned gas in the combustion exhaust gas, mixing and stirring is performed on left and right side walls and / or front and rear side walls of the gas mixing chamber. An air blowing nozzle group and a cooling air blowing nozzle group are provided, and are directed to a left side wall or a right side wall of the lower part of the gas mixing chamber, which is located above the drying grate, and to the other opposite side wall. A secondary combustion air blowing nozzle group blown along the front side wall is provided, and the secondary combustion air is blown without being influenced by a cooling air blowing amount from the cooling air blowing nozzle group. Squirting A predetermined amount of secondary combustion air and mixing / stirring air are blown from the nozzle group and the mixing / stirring air blowing nozzle group. The secondary combustion air, mixing / stirring air blown from each of the nozzle groups, and By the cooperation of the cooling air, a swirl flow is generated in the gas mixing chamber, the unburned gas in the combustion exhaust gas is mixed with the combustion gas, and a dry grate is formed from the secondary combustion air blowing nozzle group. Unburned gas in the combustion exhaust gas is efficiently secondary-combusted by the secondary combustion air intensively blown upward, thereby suppressing generation of dioxins from the combustion exhaust gas. To control the generation of dioxins in waste gas from refuse incinerators. 2. The flow rate of the secondary combustion air blown from the secondary combustion air blowing nozzle group and the mixing / stirring air blown from the mixing / stirring air blowing nozzle group is 20 to 40 m / sec. The method of claim 1, wherein