JPH06147447A - Method for reducing dioxine and the like generated at refuse incinerator - Google Patents

Abstract

PURPOSE:To reduce dioxine and the like by a method wherein an outlet part of an air pre-cooling device is rapidly cooled in such a way as a temperature of discharged gas becomes a specified temperature. CONSTITUTION:Secondary combustion air is blown into a lower part of a secondary combustion chamber 15, not-yet burn gas generated in a drying zone and combustion gas of high temperature got from a combustion zone are mixed to each other in a longitudinal direction at a lower part of the secondary combustion chamber 15 and the not-yet burned gas is burned again while occurrence of thermal NOx caused by a rapid partial combustion being restricted. Then, a rapid horizontal mixing with a tertiary combustion air is carried out and a complete combustion of the not-yet burned gas at the secondary combustion chamber 15 is approximately accomplished, resulting in that CO can be reduced. Then, either water or air is injected at the upper part of the secondary combustion chamber 15 or the adjacent installed gas cooling chamber 17 and an outlet of a downstream side air pre-cooling device 23 is rapidly cooled in such a way that a temperature of the discharged gas at the outlet becomes about 200 to 250 deg.C. With such an arrangement, it is possible to reduce dioxine and the like.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for reducing dioxins in a refuse incinerator.

[0002]

2. Description of the Related Art Generally, combustible waste discharged from homes is collected and incinerated in a refuse incinerator for disposal (see, for example, Japanese Patent Laid-Open No. 3-28617).

Such an incinerator has a hopper to which waste is supplied by a waste crane, a hopper chute for guiding the waste from the hopper, and a dust feeder having a waste extruder for transferring the waste of the hopper chute. It is provided with a dry stoker that dries the dust supplied by the dust supply device, a combustion stoker that burns the dust from the dry stoker, and a post-combustion stoker that burns the dust from the burning stoker and burns it.

The dry stoker, the combustion stoker, and the post-combustion stoker form a combustion chamber. This combustion chamber is provided below the furnace body. An exhaust gas cooling chamber is formed in the upper part of the furnace body, and an exhaust port for discharging the exhaust gas is formed in the upper end of the gas cooling chamber.

High-temperature primary combustion air is blown into the dry stoker, the combustion stoker, and the post-combustion stoker from their respective lower air blowing ports. In the dry stoker, the waste is transferred to the front while being stirred and unraveled, is transported from the dry stoker to the combustion stoker, and is further burned by the combustion stoker while being stirred and unraveled, and is transferred to the front and post-combusted. Carried to the stalker.

A blower called a furnace cooling fan provided near the exit of the furnace is operated so as to blow air at room temperature when the combustion temperature rises, and is guided to the exhaust gas cooling chamber above the furnace body. The exhaust gas was being cooled.

That is, only when the combustion temperature due to the primary combustion rises, combustion was controlled by blowing cooling air as the exhaust gas temperature control at the furnace outlet of the refuse incinerator.

[0008]

As described above, the blower provided in the vicinity of the furnace outlet is called a furnace cooling fan, and is operated so as to blow when the furnace temperature becomes high, and the furnace temperature is controlled. However, it was not combustion control.

In the secondary combustion of the conventional refuse incinerator, it is better to make the residence time longer by bringing the hot exhaust gas and the unburned gas into contact with each other by devising the shape of the furnace body. However, the reburning air has not been actively blown in for secondary combustion of the exhaust gas.

Under such circumstances, in recent years, due to problems such as dioxins, it has been required to achieve complete combustion of refuse. A higher level of complete combustion control has come to be required from the conventional furnace temperature control, which only requires the furnace temperature to be within a certain range. The achievement of complete combustion is evaluated by the CO concentration in the exhaust gas, the remaining amount of carbon in the exhaust gas, and the like.

While the purification of the exhaust gas is demanded in this way, the dust in the combustion zone on the combustion stoker of the furnace body is burned in the state of being completely burned or close to it, and almost completely burned high temperature exhaust gas is generated. However, since the garbage that has not dried sufficiently is burned in the dry bed on the dry stoker, exhaust gas containing unburned gas at a relatively low temperature of incomplete combustion is likely to be generated.

Therefore, in order to achieve complete combustion of dust, more stable combustion on the primary combustion side (dust supply amount, primary combustion air amount control) and unburned gas in the high-temperature exhaust gas left behind in primary combustion are used. In the secondary combustion section, it is required to mix with secondary combustion air to promote secondary combustion.

However, even if an attempt is made to promote the secondary combustion, in the control for sending the primary combustion air to the secondary combustion section for cooling the furnace, since the secondary combustion air is not blown in particularly when the temperature of the furnace is lowered, The supply amount of the secondary combustion air is insufficient with respect to the primary combustion air amount, or the wind speed for mixing cannot be obtained, which is far from achieving complete combustion. For example, the CO concentration is 10 to 10 at the normal furnace temperature. The peak value may be 100 times higher.

On the other hand, for the production of dioxins in the municipal solid waste incinerator, dioxins contained in the components of the municipal solid waste have passed through the incinerator without undergoing thermal decomposition / oxidative decomposition, Those produced by gas-phase reaction after the incinerator exit and gas-solid reaction involving fly ash surface, 300 ° C in the exhaust gas cooling process
Some are generated in the vicinity.

It has been confirmed that reduction of unburned carbon in exhaust gas due to complete combustion and reduction of residence time of fly ash at around 300 ° C. are effective for suppressing these generations.

Therefore, the object of the present invention is to provide a method for reducing dioxins in a refuse incinerator, which enables complete combustion in the refuse incinerator and shortens the residence time of exhaust gas near 300 ° C. based on the above facts. To provide.

[0017]

SUMMARY OF THE INVENTION According to the present invention, primary combustion air is supplied to a combustion chamber to burn dust, and residual unburned gas in exhaust gas generated in the combustion chamber is burned in a secondary combustion chamber to generate exhaust gas. In the combustion method of a refuse incinerator, in which the soot is cooled in the gas cooling chamber and the air preheater, and the soot and dust in the exhaust gas is removed by the electrostatic precipitator or bag filter, the amount of secondary combustion air corresponding to the primary combustion air in the exhaust gas To the residual unburned gas in the vertical direction, and then a predetermined amount of tertiary combustion air is supplied to the residual unburned gas in the exhaust gas at a wind speed that is about twice the wind speed of the secondary combustion air. Direction, then the exhaust gas is rapidly cooled in the gas cooling chamber to bring the temperature of the exhaust gas at the outlet of the air preheater to about 200-
The temperature is set to 250 ° C.

[0018]

In the present invention, secondary combustion air is blown into the lower portion of the secondary combustion chamber, and unburned gas generated in the drying zone and high temperature combustion gas from the combustion zone are vertically generated in the lower portion of the secondary combustion chamber. And re-combustion of unburned gas while suppressing generation of thermal NOx due to rapid partial combustion.

Next, in the upper part of the secondary combustion chamber, rapid horizontal mixing is performed by the tertiary combustion air, almost complete combustion of unburned gas in the secondary combustion chamber is achieved, and CO can be reduced.

Then, in the gas cooling chamber arranged above or adjacent to the secondary combustion chamber, water or air is injected, and the exhaust gas temperature at the outlet of the air preheater on the downstream side is about 200-.
It is rapidly cooled to 250 ° C.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a refuse incinerator according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 indicates a refuse incinerator. This waste incinerator 1 is supplied with waste by a waste pit 1A, a loading door 1B provided on the waste loading side of this waste pit 1A, a waste crane 1C provided above the waste pit 1A, and this waste crane 1C. Hopper 2
A hopper chute 3 that guides garbage from this hopper 2,
A dust supply device having a waste extruder 4 for transferring the waste of the hopper chute 3, a drying stoker 5 for drying the waste supplied by the dust supply device, and a combustion stoker 6 for burning the waste from the drying stoker 5. It is provided with a post-combustion stoker 7 which burns the waste from the combustion stoker 6 and burns it with fire.

The waste extruder 4 is provided below the hopper chute 3. Dry stoker 5, Burning stoker 6,
The post combustion stoker 7 is housed in a furnace body 8 and
A discharge port 9 for discharging combustion gas is formed at an upper end of the furnace body 8. A cooling water supply port 10, a secondary combustion air blower 11, a cooling water supply port 10, and a secondary combustion are formed on a side wall surface of the furnace body 8. A blower 12 for tertiary combustion air is provided between the blowers 11 for air, and an auxiliary combustion burner 13 is provided at the lower end of the furnace body 8.

Inside the furnace body 8, the primary combustion chamber 1 above the drying stoker 5, the combustion stoker 6, and the post-combustion stoker 7 is installed.
4 and the secondary combustion chamber 15 near the blower 11 for secondary combustion air
And a tertiary combustion chamber 16 above the secondary combustion chamber 15, and a gas cooling chamber 17 above the tertiary combustion chamber 16.

The blower 11 for secondary combustion air is provided directly above the primary combustion chamber 14 of the furnace body 8. The secondary combustion air blowing nozzle 11A is provided on the upper side and the lower side of the secondary combustion chamber 15.

The secondary combustion air blown from the secondary combustion air blowing nozzle 11A extends vertically from the lower portion of the secondary combustion chamber 15 of the furnace body 8 toward the upper portion while drawing an S-shape (meandering shape). It is mixed with the upflow of exhaust gas.

The tertiary combustion chamber 16 and the gas cooling chamber 17 of the furnace body 8
The cross section in the vicinity is configured in a circular shape, and as shown in FIG. 2, on the wall surface of the tertiary combustion chamber 16 of the furnace body 8, a plurality of tertiary combustion air blowing nozzles 12A to which air is sent from the blower 12 for tertiary combustion air are provided. They are circumferentially provided at predetermined intervals.

The blowing direction of each tertiary combustion air blowing nozzle 12A has a predetermined inclination angle with respect to the wall surface of the furnace body 8 and the same inclination angle with respect to the tangential direction of the furnace body 8. A vortex flow of the secondary combustion air is generated within 8.

When the diameter of the tertiary combustion chamber 16 becomes large, it is advisable to change the blowing angle of the tertiary air blowing nozzle 12A in order to prevent the central portion from blowing through and increase the mixing efficiency.

Then, one end of the air supply pipe 18 is connected to the dust pit 1A, and the other end side is branched midway, and the first branch pipe 18A connected to the lower portion 8A of the drying stoker 5 of the furnace body 8 is burned. The second branch pipe 18B connected to the lower portion 8B of the stoker 6 and the third branch pipe 18B connected to the lower portion 8C of the post-combustion stoker 7.
It constitutes a branch pipe 18C.

An under furnace conveyer 26 is provided on the lower portion 8A of the drying stoker 5 and the lower portion 8B of the combustion stoker 6. This lower furnace conveyor 26 and the lower part 8 of the post combustion stoker 7
C communicates with the main ashing conveyor 27. The main ash discharging conveyor 27 is in communication with the ash bunker 27.

An air volume adjusting damper (not shown), a primary combustion air blower 20, and a primary combustion air temperature adjusting damper 20A are provided in the middle of the air supply pipe 18. A primary combustion air distribution first damper 21A is provided in the middle of the first branch pipe 18A, a primary combustion air distribution second damper 21B is provided in the middle of the second branch pipe 18B, and a primary combustion air distribution is provided in the middle of the third branch pipe 18C. The distribution third dampers 21C are provided respectively.

Further, a discharge duct 22 is connected to the discharge port 9 of the furnace body 8, and an air preheater 23 and an electrostatic precipitator 24 are provided in this order in the middle of the discharge duct 22. A heat exchange air pipe 25 passing through the air preheater 23 and a hot water generator 19 are connected to both sides of the primary combustion air temperature adjusting damper 20A of the air supply pipe 18.

Exhaust duct 22 through air preheater 23
The exhaust gas therein and the primary combustion air in the heat exchange air pipe 25 and the hot water generator 19 are heat-exchanged, the temperature of the primary combustion air in the air supply pipe 18 becomes high, and the exhaust gas in the exhaust duct 22 cools. To be done.

A slaked lime tank 29 is connected to a duct 28 connecting the air preheater 23 and the electrostatic precipitator 24 via a pipe 31. The slaked lime in the slaked lime tank 29 is supplied by a slaked lime blower 30.

Below the electric dust collector 24, a dust collecting ash humidifier 32 is provided. The lower part of the dust collecting ash humidifier 32 communicates with the ash bunker 27. An induction blower 34 is provided on the downstream side of the electric dust collector 24 via a duct 33. The induction blower 34 communicates with the chimney 35.

Next, a combustion control method by the refuse incinerator thus constructed will be described with reference to FIGS. 1 to 4. In the present embodiment, high-temperature primary combustion air is blown into the lower portion 8A of the drying stoker 5, the lower portion 8B of the combustion stoker 6, and the lower portion 8C of the post-combustion stoker 7, respectively, and the waste supply amount and the primary combustion air amount are controlled. , The dry stoker 5, the combustion stoker 6, and the post-combustion stoker 7 are stably combusted to generate an exhaust gas, which is discharged from the furnace body 8
It rises inside and reaches the inside of the secondary combustion chamber 15.

Usually, the flow velocity of the upward flow of the exhaust gas is about 2
~ 3 m / sec. On the other hand, the amount of the secondary combustion air from the secondary combustion air blower 11 corresponding to the primary combustion air is set in the secondary combustion chamber 15 such that the blowing speed of the secondary combustion air is about 6 to 8 times the flow velocity of the upward flow of the exhaust gas. In the lower part of the secondary combustion chamber 15, the unburned gas generated in the drying zone and the high temperature combustion gas from the combustion zone are vertically mixed to suppress generation of thermal NOx due to rapid partial combustion. While reburning unburned gas.

Here, the injection amount of the secondary combustion air is set to 1: 0.4 to 0.6 when the primary combustion air amount is 1.
Further, as for the secondary combustion air, the air at room temperature was used for the purpose of conventionally used for cooling the furnace, whereas in the present embodiment, the secondary combustion air is mainly used for the secondary combustion. Since it is blown in, the secondary combustion air is also set to a high temperature,
The secondary combustion is made more effective.

Further, the exhaust gas produced by the secondary combustion rises together with the exhaust gas produced by the primary combustion,
It reaches the tertiary combustion chamber 16. On the other hand, blower 1 for tertiary combustion air
The secondary combustion air is blown into the tertiary combustion chamber 16 from 2 through the plurality of tertiary combustion air blowing nozzles 12A with the blowing speed thereof being set to a value about twice as high as the blowing speed of the secondary combustion air.

Here, the injection amount of the tertiary combustion air is set to 1: 0.3 to 0.4 when the primary combustion air amount is 1.
In the tertiary combustion chamber 16, mixing of the tertiary combustion air with the residual unburned gas in the exhaust gas which has not yet been burned by the secondary combustion is promoted.

In this case, the tertiary combustion air is kept at room temperature to make the cooling of the exhaust gas more effective, and the tertiary combustion air at room temperature swirls into the furnace body 8 through the plurality of tertiary combustion air injection nozzles 12A. Since it is blown in like this, the promotion of the mixing of the tertiary combustion air and the residual unburned gas in the exhaust gas is made effective.

In this state, the tertiary combustion is promoted in the tertiary combustion chamber 16. Then, the exhaust gas generated by the primary combustion, the secondary combustion, and the tertiary combustion is guided to the gas cooling chamber 17, and is rapidly cooled by the cooling water sprayed from the cooling water supply port 10.

The quenching here is performed at the outlet 2 of the air preheater 23.
This is for setting the exhaust gas temperature of 3 A to about 200 to 250 ° C., and is performed by changing the amount of spray water from the cooling water supply port 10.

Thereafter, the exhaust gas is guided to the discharge port 9, further cooled from the discharge duct 22 through the air preheater 23, and reaches the electrostatic precipitator 24. The inlet temperature of the electrostatic precipitator 24 is set to about 200 to 250 ° C.

In the electrostatic precipitator 24, soot and dust in the exhaust gas are removed and the amount is reduced to a reference value or less. Then, the cooled and purified exhaust gas is discharged to the chimney 35 by the induction blower 34.

On the other hand, the dust completely burned to ash in the combustion chamber 14 is humidified and cooled by the sealing water in the main ash discharging conveyor 27. Further, since the dust of the electrostatic precipitator 24 is fine and has a small specific gravity, it is humidified by the dust collector humidifier 32 and discharged by the main ash discharging conveyor 27.

Ash residue from the incinerator and electrostatic precipitator 2
The dust of No. 4 is stored in the ash bunker 27. By preheating the air with the exhaust gas and passing the preheated air to the hot water generator 19, the heat required by the preheating utilization facility is recovered.

By blowing slaked lime into the exhaust gas leaving the air preheater 23, the hydrogen chloride contained in the exhaust gas is reduced to a reference value or less. The hydrogen chloride that has reacted with the slaked lime is collected and removed by the electrostatic precipitator 24 as calcium chloride.

According to the above-mentioned structure, the secondary combustion air in an amount corresponding to the primary combustion air is vertically mixed in the furnace body 8 so as to promote the mixing with the residual unburned gas in the exhaust gas. Is supplied as described above, the residual unburned gas in the exhaust gas generated in the primary combustion and the high-temperature combustion gas are gently mixed in the vertical direction to suppress the generation of thermal NOx due to abrupt partial combustion while unburned. The gas is reburned.

Therefore, it is possible to reduce the residual rate of unburned gas in the exhaust gas and burn the dust more completely.
In particular, even when the furnace temperature is lowered, the secondary combustion air is blown in, and the supply amount of the secondary combustion air is the amount corresponding to the primary combustion air amount, so that the amount of the secondary combustion air does not become insufficient,
Alternatively, the wind speed of the secondary combustion air for mixing can be obtained, which is close to the achievement of complete combustion, for example, the CO concentration can be reduced.

The residual unburned gas in the exhaust gas produced in the primary combustion is secondarily burned, and the temperature of the exhaust gas after the secondary combustion is about 800 ° C. to 900 ° C. The residual unburned gas in the exhaust gas can be reburned by feeding the tertiary combustion air into and remixing it.

Therefore, it is possible to reduce the residual rate of unburned gas in the exhaust gas and burn the dust more completely.
In addition, even if the residual unburned gas is almost eliminated from the exhaust gas that has undergone the secondary combustion, the cooling effect by blowing the tertiary combustion air can be obtained.

Therefore, the amount of cooling water supplied to the gas cooling chamber 17 of the furnace body 8 can be reduced, the water content in the exhaust gas can be reduced, and the amount of white smoke discharged from the refuse incinerator 1 can be reduced. .

Further, as a measure against dioxin, for example, even in an existing refuse incinerator, when the exhaust gas temperature at the inlet of the electrostatic precipitator 24 provided in the middle of the discharge duct 22 of the furnace body 8 is designed to be about 200 ° C. This can be dealt with by increasing the capacity of the gas cooling chamber 17 or the amount of water sprayed by the cooling water supply port 10 and quenching.

Even in such an existing refuse incinerator,
By providing the tertiary combustion air supply together with the secondary combustion air supply described above, the cooling capacity of the entire refuse incinerator is improved, and the exhaust gas temperature is improved without modifying the capacity of the gas cooling chamber 17 or the cooling water spraying equipment. A cooling target value can be achieved.

Although the electrostatic precipitator 24 is used in this embodiment, it may be a bag filter. Next, specific examples according to this embodiment are shown in Tables 1 and 2.

Table 1 shows the measured values by the control method of the refuse incinerator according to the present invention, and Table 2 shows the measured values by the control method of the ordinary refuse incinerator which does not perform the tertiary combustion. Table 1
As is clear from the above, the dioxin toxicity conversion value (I-
TEQng / Nm ³ ) is much lower than that of conventional incinerators, 2.6 ng /
It showed Nm ³ .

If a bag filter is used instead of the electrostatic precipitator 24, the dioxins toxicity converted value (I-TEQng / Nm ³ ) in the exhaust gas discharged from the chimney 35 can be 0.5 ng / Nm ³ or less.

[0060]

[Table 1]

[0061]

[Table 2]

As shown in FIG. 5, the gas cooling chamber may be a separate type. In this case, air cooling is also possible. In this case, as shown in Table 3, the dioxins toxicity conversion value (I-TEQng / Nm ³ ) was 2.0 ng / Nm ³ which was lower than that in the above-mentioned Examples.

If a bag filter is used instead of the electrostatic precipitator 24, the dioxin-related toxicity conversion value (I-TEQng / Nm ³ ) in the exhaust gas discharged from the chimney 35 can be reduced to 0.5 ng / Nm ³ or less.

[0064]

[Table 3]

Next, the refuse incinerator of the present invention will be described with reference to FIG. The capacity of the refuse incinerator is 25t / 16
h × 2 furnace = 50t / day, type was quasi-continuous combustion incinerator. The flow is as shown in FIG.

First, FIG. 7 shows the time-dependent change in CO concentration during startup. The CO concentration when started up by the conventional method (hereinafter referred to as a conventional system) which was mixed in one stage is shown by a broken line,
The case where the refuse incinerator of the present invention is used is shown by a one-dot chain line.

In the conventional system, a peak of CO concentration exceeding 1000 ppm occurred at the time of startup. As a measure to reduce the CO concentration at the time of startup, the peak of the CO concentration can be reduced to about 700 ppm by using the burner together with the tertiary combustion air.

Further, by using together with the automatic combustion control system using the fuzzy control for the dust supply amount control and the primary combustion air amount control at the start-up, the peak of CO concentration at the start-up is 30
It can be reduced to 0 ppm.

Next, FIG. 8 shows the results of measurement of changes over time in CO concentration and NOx concentration during steady operation, using the conventional system and the dust incinerator of the present invention. Further, FIG. 9 shows changes with time when the refuse incinerator of the present invention is used and when the refuse incinerator of the present invention is used in combination with an automatic combustion control system.

When the refuse incinerator of the present invention is used as compared with the conventional system, the CO concentration is reduced to about 2/3 and NOx is reduced.
The concentration was also reduced to about 2/3. From this, it was confirmed that the refuse combustion furnace of the present invention is a system capable of managing the NOx concentration at a low level while performing the mixing for reducing the CO concentration.

Further, when the automatic combustion control system was used together, the NOx concentration was at the same level as when the waste incinerator of the present invention was used alone, but the CO concentration was reduced to about 1/2.

The measurement results of the amount of organic carbon (TC) (%) in the dust ash when the conventional system and the refuse incinerator of the present invention are used and when the automatic combustion control system is also used are as follows: It was 1.9% in the conventional system, 1.4% in the present invention, and 0.75% in the case of using the automatic combustion control system together.

This data shows that 3
This is an analysis of the composited material by sampling four times every hour. In conventional systems,
Although it was 1.9%, when the refuse combustion furnace of the present invention was used,
It was 1.4%, which was reduced to about 2/3 like the CO concentration. 0.75% when combined with automatic combustion control system
And was further reduced to about 1/2.

From the above, the waste incinerator of the present invention improved the mixing efficiency in the secondary combustion chamber, thermally decomposed most of the unburned components in the exhaust gas, and was able to approach more complete combustion.

Furthermore, by using the automatic combustion control system together, the amount of exhaust gas entering the secondary combustion chamber and the exhaust gas temperature are always stabilized, and the mixing in the secondary combustion chamber works more effectively to ensure complete combustion. It was confirmed that this is a very effective combination (total system).

With respect to the case where the tertiary combustion air is not used and the case where the operation is performed under the condition where the exhaust gas temperature at the inlet of the electrostatic precipitator using the automatic combustion system is controlled at 220 ° C.,
The dioxin homologue concentration in the exhaust gas from the outlet of the electrostatic precipitator was measured. The result is shown in FIG.

When tertiary combustion air was used, in PCDF, H ₇ CDD _S and O ₇ CDD were slightly increased, but other homologues were decreased, and dioxins were decreased as a whole. Since the exhaust gas cooling process and the cooling conditions are the same, it is considered that the use of the tertiary combustion air reduced the dioxins generated up to the outlet of the secondary combustion chamber.

Further, the TEQ when operated without using the tertiary combustion air was 3.3 ng / Nm ³ , and when used, it was 2.6 ng / Nm.
It was decreasing to ³ . From the above, it was confirmed that by using the tertiary combustion air, complete combustion was further achieved at the outlet of the secondary combustion chamber, and it was also effective in reducing dioxins.

Next, the gas cooling chamber 17 and the electrostatic precipitator 24
Since it has been reported that dioxins are also generated in the air preheater 23 installed between them, as a method of reducing dioxins, lower the exhaust gas temperature at the outlet 17 of the gas cooling chamber 17. Can be given.

The exhaust gas temperature at the outlet 17 of the gas cooling chamber 17 is changed by the amount of spray water in the gas cooling chamber 17, and this amount of spray water is controlled by the setting conditions of the exhaust gas temperature at the inlet 24A of the electrostatic precipitator 24.

Therefore, the operating condition was the exhaust gas set temperature at the inlet 24A of the electrostatic precipitator 24. This operating condition,
Table 4 shows the operation results. In the table, EP represents an electrostatic precipitator. The exhaust gas temperature at the inlet 24A of the electrostatic precipitator 24 is set to 20
When set to 0 ℃, 220 ℃, 235 ℃, 250 ℃,
The exhaust gas temperature at the outlet 17 of the gas cooling chamber 17 is 2
The temperatures were 60 ° C, 273 ° C, 285 ° C, and 297 ° C.

At the inlet of the gas cooling chamber 17, although the exhaust gas temperature of about 900 ° C. is rapidly cooled to 300 ° C. or less by the water spray, the outlet 24B of the electrostatic precipitator 24 is discharged.
The CO concentration in the exhaust gas was 30 ppm or less.

However, the amount of organic carbon in the collected ash is RUN1 when the exhaust gas temperature at the inlet 24A of the electrostatic precipitator 24 is 200.degree.
It was 1.5 to 2.2 times larger depending on other operating conditions. From these, the automatic combustion control system and the refuse incinerator of the present invention complete the thermal decomposition of the unburned components in the exhaust gas in an instant, but the thermal decomposition of the unburned components in the fly ash is important for the residence time. It becomes a different factor and is influenced by the water spray condition of the gas cooling chamber 17.

Therefore, in the case of the upper furnace of the gas cooling chamber, the secondary combustion chamber capacity is set so that the residence time can be about 2 seconds.
In the case of the separate type as well, almost complete combustion is achieved by similarly taking a residence time of about 2 seconds.

[0085]

[Table 4]

Table 5 shows the concentration of dioxins at the outlet 24B of the electrostatic precipitator 24 during the steady operation of RUN1 to RUN4.

[0087]

[Table 5]

The TEQ in a facility equipped with an incinerator-integrated gas cooling chamber is a very low value of 4 ng / Nm ³ or less under any condition. It is considered that the effect of achieving complete combustion by the automatic combustion control system and the present invention is the exhaust gas quenching effect in the gas cooling chamber 17.

The dust collection ash TC (%) and the electrostatic precipitator 2
FIG. 11 shows the TEQ relationship in the exhaust gas from the outlet 24B of No. 4 in FIG. There was a positive correlation between the dust collection ash TC (%) and TEQ.

From this, it is considered that the amount of organic carbon in fly ash affects the production of dioxins. Next, FIG. 12 and FIG. 13 show the concentrations of dioxin analogues when the exhaust gas temperature at the outlet 24B of the electrostatic precipitator 24 is changed to 200 ° C. to 250 ° C. (RUN1 to RUN4).

In RUN 3 and 4 in which the exhaust gas temperature at the inlet 24A of the electrostatic precipitator 24 was set to 235 ° C and 250 ° C,
The ratio of each homologue of dioxins was about the same level.

However, in RUN1 where the temperature was lowered to 200 ° C., the dioxins concentration was high on the contrary. It is considered that this is because the amount of spray water in the gas cooling chamber 17 increased and the evaporation heat load in the gas cooling chamber 17 became too large compared to the set condition.

Table 6 shows the actual evaporation heat load of the gas cooling chamber under each operating condition. Here, the volume of the gas cooling chamber is estimated from 1.0 m below the spray nozzle mounting position to the gas cooling chamber outlet.

From these facts, in the incinerator-integrated gas cooling chamber, rapid cooling of the exhaust gas has a reducing effect on the production of dioxins after the gas cooling chamber, but when the heat load of evaporation is too high, It adversely affects the thermal decomposition of unburned components in the secondary combustion chamber, increasing the amount of organic carbon remaining,
T ₄ CDD _S Dioxin homologues will increase, so it is better not to perform water spraying with an evaporation heat load exceeding 130,000 Kcal / m ³ · h.

[0095]

[Table 6]

FIG. 14 shows the concentration of dioxins homologues in the exhaust gas from the outlet of the electrostatic precipitator at the odor of dioxins homologues in the dust ash of the electrostatic precipitator sampled under the operating conditions of RUN2. Dioxins in the dust collection ash are calculated by subtracting the dust concentration at the outlet from the dust concentration at the electrostatic precipitator at 2.96 g / Nm.
^It was multiplied by ³ and converted per 1 Nm ³ and shown as a value.

As the dioxins to be taken out of the system, PCDD in the collected ash was the largest. The TEQ in the exhaust gas is 2.6 ng / Nm ³ , and the TEQ in the dust ash is 2.4 ng / Nm ^3.
It was Nm ³ , which was a lower value than facilities of the same scale.

This is because the generation control in the combustion chamber was performed by the automatic combustion control system and the present invention, and the exhaust gas temperature at the outlet of the gas cooling chamber was rapidly cooled to 280 ° C. or less. It is considered that this is a synergistic effect of the reduction in the generation of dioxins between dusters.

[0099]

As described above, according to the present invention,
First, since the amount of secondary combustion air corresponding to the primary combustion air is supplied to the residual unburned gas in the exhaust gas and mixed in the vertical direction,
The high-temperature combustion gas and the unburned exhaust gas burn slowly without causing abrupt partial combustion, and the unburned gas can be reburned while suppressing the generation of thermal NOx.

Next, a predetermined amount of the tertiary combustion air is supplied to the residual unburned gas in the exhaust gas at a wind speed that is approximately twice the wind speed of the secondary combustion air, and the residual unburned gas is mixed in the horizontal direction. It becomes possible to rapidly burn in the horizontal direction to bring it closer to complete combustion, and reduce the CO concentration.

Thereafter, the exhaust gas is rapidly cooled in the gas cooling chamber to bring the exhaust gas temperature at the outlet of the air preheater to about 200 to 250 ° C., so that it is possible to reduce dioxins.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a refuse incinerator according to an embodiment of the present invention.

FIG. 2 is a sectional view of the furnace body showing a tertiary combustion air blowing nozzle of the furnace body of FIG.

FIG. 3 is a perspective view showing an outline of a refuse incinerator according to an embodiment of the present invention.

FIG. 4 is a system schematic diagram of a refuse incinerator according to an embodiment of the present invention.

FIG. 5 is a perspective view showing a modification of the refuse incinerator according to the embodiment of the present invention.

FIG. 6 is a processing flow based on the system of the refuse incinerator according to the embodiment of the present invention.

FIG. 7 is a graph showing a time-dependent change in CO concentration at the time of startup based on the system of the refuse incinerator according to the example of the present invention.

FIG. 8 is a graph showing changes over time in CO and NOx concentrations during steady operation based on the system for a refuse incinerator according to an example of the present invention.

FIG. 9: C during steady operation when the system of the refuse incinerator according to the embodiment of the present invention is used together with an automatic combustion control system
It is a graph which shows changes over time in O and NOx concentrations.

FIG. 10 is a graph showing the concentration of I-TEQ homologues when the system of the refuse incinerator according to the example of the present invention is used together with an automatic combustion control system.

FIG. 11 is a graph showing the concentrations of I-TEQ homologues in the dust ash and the exhaust gas from the outlet of the electrostatic precipitator when the system of the refuse incinerator according to the example of the present invention is used together with the automatic combustion control system.

FIG. 12 is a graph showing the exhaust gas temperature at the outlet of an electric precipitator and the concentration of dioxins homologs when the system of the refuse incinerator according to the example of the present invention is used together with an automatic combustion control system.

FIG. 13 is a graph showing the exhaust gas temperature at the outlet of an electric precipitator and the concentration of dioxins homologs when the system of the refuse incinerator according to the example of the present invention is used together with an automatic combustion control system.

FIG. 14 is a graph showing the concentrations of dioxins homologues in the exhaust gas from the dust collecting ash and the electrostatic precipitator when the system of the refuse incinerator according to the example of the present invention is used together with the automatic combustion control system.

[Explanation of symbols]

 1 Waste incinerator 5 Dry stoker 6 Combustion stoker 7 Post-combustion stoker 8 Furnace body 10 Cooling water supply port 14 Primary combustion chamber 15 Secondary combustion chamber 16 Tertiary combustion chamber 17 Gas cooling chamber 23 Air preheater 24 Electrostatic precipitator

Claims (1)

[Claims] 1. A primary combustion air is supplied to a combustion chamber to burn dust, residual unburned gas in exhaust gas generated in the combustion chamber is burned in a secondary combustion chamber, and the exhaust gas is cooled to a gas cooling chamber and an air preheater. In the combustion method of a refuse incinerator where the dust is removed from the exhaust gas with an electric precipitator or a bag filter, the amount of secondary combustion air corresponding to the primary combustion air is supplied to the residual unburned gas in the exhaust gas. Vertical mixing, and a predetermined amount of tertiary combustion air is supplied to the residual unburned gas in the exhaust gas at a wind speed that is approximately twice the wind speed of the secondary combustion air to mix horizontally, and then the exhaust gas Is rapidly cooled in a gas cooling chamber to bring the exhaust gas temperature at the outlet of the air preheater to about 200 to 250 ° C., a method for reducing dioxins in a refuse incinerator.