JP2003322321A - Combustion method for stoker type refuse incinerator and stoker type refuse incinerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the generation of hazardous substances including NOx and CO in exhaust gas by using low-air-ratio combustion and to prevent the production of clinkers on an incinerator wall and damage to the incinerator wall by blowing the exhaust gas as recirculation gas into an incinerator after heat recovery. <P>SOLUTION: This stoker type refuse incinerator 1 comprises a drying stoker 10a, a combustion stoker 10b and an after-combustion stoker 10c. Primary combustion air A1 having a primary air ratio of 1.0-1.2 is supplied to the stoker 10 and after-combustion gas G' generated on the after-combustion stoker 10c is extracted to the outside of the incinerator, while part of exhaust gas G" is blown as recirculation gas into a flow area on the downstream side of a primary combustion chamber 12 and combustion gas G generated on the drying stoker 10a and the combustion stoker 10b is stirred and mixed with the recirculation gas to form a reduction zone 25 between the primary combustion chamber 12 and a secondary combustion chamber 13. Furthermore, after- combustion gas G' extracted from an upper space of the after-combustion stoker 10c is blown as circulation gas into the secondary combustion chamber 13. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refuse incinerator for incinerating mainly municipal solid waste and industrial waste, and more particularly to a stoker type refuse incinerator equipped with a stoker comprising a dry stoker, a burning stoker and a post-burning stoker. Regarding the improvement of the combustion method and the stoker-type waste incinerator, by performing low air ratio combustion to suppress harmful substances such as NOx and CO in the exhaust gas, and part of the exhaust gas after heat recovery is used as a recirculation gas for the furnace. The present invention relates to a combustion method for a stoker-type refuse incinerator and a stoker-type refuse incinerator that prevent clinker generation on the furnace wall and damage to the furnace wall by blowing air into the furnace.

[0002]

2. Description of the Related Art Generally, as a method for treating municipal solid waste and industrial waste (hereinafter referred to as "garbage"), so-called incineration occupies the mainstream, and a stoker type waste incinerator or a fluidized bed type waste incinerator is used. Many treatment methods using are used. Among them, the stoker-type waste incinerator is a waste incinerator that has a large number of operating records and has an excellent practical utility that it can burn waste relatively stably. In addition, many stoker-type waste incinerators with large capacity and automatic operation type are used so that a large amount of waste can be incinerated continuously as the amount of waste discharged in large cities increases. There is.

FIG. 2 is a schematic system diagram of a waste treatment plant equipped with a conventional stoker-type refuse incinerator 30, which is a stoker-type refuse incinerator 3
0, waste heat boiler 31, superheater 32, economizer 33,
Deaeration heater 34, bag filter 35, and induced draft fan 3
It is composed of 6 etc., and incinerates waste such as municipal waste and industrial waste in the stoker-type refuse incinerator 30 to reduce the volume and volume, and at the same time, to remove the high temperature generated in the stoker-type refuse incinerator 30. The combustion gas is converted into a waste heat boiler 31, a superheater 32,
Heat is recovered by the economizer 33 and the deaeration heater 34, passed through the bag filter 35 to form clean gas, and then sent to the chimney (not shown) from the induced draft fan 36.

The stoker-type refuse incinerator 30 includes a furnace body 37, a refuse supply hopper 38, a stoker 39, a drying stoker 39a, a combustion stoker 39b, and a post-combustion stoker 39.
c, stoker lower hopper 40, primary combustion chamber 41, secondary combustion chamber 42, ash outlet 43, exhaust gas outlet 44, primary combustion air supply pipe 45, primary combustion air blower 46, secondary combustion air supply pipe 47, secondary The combustion air blower 48, the damper 49, the oxygen concentration detector 50, the recirculation gas supply pipe 51, the recirculation gas blower 52, the heat exchanger 53 and the like are included, and a large amount of residual oxygen generated on the post-combustion stoker 39c is included. The post-combustion stage gas G'being taken out and blown into the furnace to dry the stoker 39a and the combustion stoker 39b.
The drying / combustion stage gas G generated above is stirred and mixed to form a uniform reduction zone in the furnace to suppress the generation of NOx,
After that, the secondary combustion air A2 is blown into the furnace to completely burn unburned gas such as CO and reduce the generation of dioxins.

That is, in the stoker-type refuse incinerator 30, the primary combustion air A1 supplied from below the stoker 39 is used.
Of the primary air ratio of 0.9 to 1.0, and
The post-combustion stage gas G ′ having a high oxygen concentration generated on the post-combustion stoker 39c is extracted from the inside of the furnace, and the extracted post-combustion stage gas G ′ is cooled by the heat exchanger 53 to reduce its temperature, and then is primarily used as a reflux gas. Blow into the downstream region of the combustion chamber 41,
The post-combustion stage gas G ′ stirs and mixes the drying / combustion stage gas G generated on the drying stoker 39 a and the combustion stoker 39 b, and the combustion gas (drying / drying / drying) is generated between the primary combustion chamber 41 and the secondary combustion chamber 42. Reduction zone 54 in which the temperature and composition of the mixture of combustion stage gas G and post-combustion stage gas G ') are uniform
And the minimum required secondary combustion air A2 (secondary air ratio is 0.3 to 0.4) is blown from the secondary combustion air blower 46 into the secondary combustion chamber 42 to generate the primary combustion air A1. And a combustion gas in the secondary combustion chamber 42 (a gas in which the drying / combustion stage gas G and the post-combustion stage gas G'are mixed, with the total air amount of the secondary combustion air A2 and the air ratio being about 1.3). ) The unburned gas and unburned substances inside are completely burned.

Therefore, according to the stoker type refuse incinerator 30, the drying / combustion stage gas G generated in the primary combustion chamber 41
Is satisfactorily and reliably agitated and mixed twice by the post-combustion stage gas G ′ blown into the furnace and the secondary combustion air A2. As a result, the unburned gas and unburned substances in the combustion gas (gas in which the drying / combustion stage gas G and the post-combustion stage gas G'are mixed) are completely burned without blowing a large amount of combustion air into the furnace. It is possible to suppress the generation of NOx, CO, dioxins and the like.

[0007]

However, even in the conventional stoker-type refuse incinerator 30, the following (1) to (1)-
The problem as shown in (6) remains. (1) In order to form the reduction zone 54 in the furnace, the primary combustion air A1 must be completely combusted in a state where the supply amount of the primary combustion air is 1.0 or less. It has to be adopted, and there is a problem that the cost of remodeling becomes high when introducing it into an existing furnace. (2) If the quality of the refuse supplied to the furnace is low, it is difficult to completely combust it with the supply amount of the primary combustion air A1 being 1.0 or less in the primary air ratio. There is a problem that it is difficult to form the reduction zone 54 therein. (3) As the recirculation gas blown between the primary combustion chamber 41 and the secondary combustion chamber 42, the post combustion stage gas G ′ above the post combustion stoker 39 c (this post combustion stage gas G ′ is HCl or SO
Since a corrosive gas such as x is small and a large amount of residual oxygen is contained in the furnace, the amount is limited. As a result, stirring of the drying / combustion stage gas G generated on the drying stoker 39a and the combustion stoker 39b
In some cases, the mixing cannot be sufficiently performed, and in this case, it is not possible to form a uniform reduction zone 54 in the furnace, and NOx
However, there is a problem that the occurrence of the above cannot be sufficiently suppressed. (4) The temperature of the reduction zone 54 formed by blowing in the post combustion stage gas G ′ (reflux gas) has the highest temperature. Therefore, in the stoker-type refuse incinerator 30 that does not have a furnace wall cooling structure such as a water cooling wall (boiler), the temperature of the reduction zone 54 becomes equal to or higher than the melting point of ash when the quality of the refuse is high, and clinker generation and furnace wall fireproofing occur. There is a problem of causing damage to things. (5) The post-combustion stage gas G ′ (reflux gas) extracted from the upper space of the post-combustion stoker 39 c is the recirculation gas blower 52.
Must be cooled to 300 ° C. or less by the heat exchanger 53 from the service temperature of. As a result, an installation space for installing the heat exchanger 53 is required. (6) Secondary combustion air A2 having a secondary air ratio of 0.3 to 0.4
In case of blowing air into the furnace at room temperature, a stoker type waste incinerator 3
The combustion gas (drying / combustion stage gas G in the secondary combustion chamber 42 depends on the scale of 0 and the quality of the waste supplied to the furnace.
And the gas in which the post combustion stage gas G ′ is mixed) may not be sufficiently stirred and mixed. When the secondary combustion air A2 is heated in order to promote the stirring and mixing of the combustion gas in the secondary combustion chamber 42, it is necessary to add an air preheater or increase the capacity. As a result, there is a problem that the cost becomes high and the amount of steam used in the air preheater increases, leading to a decrease in power generation efficiency.

The present invention has been made in view of such problems, and an object thereof is to sufficiently suppress generation of harmful substances such as NOx and CO in exhaust gas by performing low air ratio combustion. At the same time, by blowing the exhaust gas after heat recovery into the furnace as recirculation gas, it is possible to prevent clinker generation on the furnace wall and damage to the furnace wall, and the combustion method of the stoker type waste incinerator and the stoker type waste incinerator. To provide.

[0009]

In order to achieve the above object, the invention described in claim 1 of the present invention is a dry stoker,
In a stoker-type refuse incinerator, which has a stoker consisting of a combustion stoker and a post-combustion stoker, and supplies primary combustion air from each stoker individually into the primary combustion chamber above the stoker, the primary combustion supplied from below the stoker The supply amount of air is 1.0 to 1.2 in terms of primary air ratio,
The post-combustion stage gas generated on the post-combustion stoker is drawn out of the furnace, and a part of the exhaust gas after heat recovery is blown into the downstream side basin of the primary combustion chamber as a recirculation gas, and a dry stoker and Drying generated on the burning stoker
The combustion stage gas is agitated and mixed to form a reduction zone between the primary combustion chamber and the secondary combustion chamber, and the post combustion stage gas extracted from the upper space of the post combustion stoker is used as reflux gas for the secondary combustion chamber. It is characterized in that it was blown into.

According to the second aspect of the present invention, the post-combustion stage gas extracted from the upper space of the post-combustion stoker is subjected to heat recovery by a heat exchanger to reduce the temperature, and then the secondary combustion air at room temperature is used. The feature is that they are mixed and blown into the secondary combustion chamber.

According to the third aspect of the present invention, the supply amount of the secondary combustion air is 0.2 to 0.4 in the secondary air ratio, and the total air ratio is 1.2 to 1.4. The feature is that the unburned gas and unburned materials in the secondary combustion chamber are completely burned in this state.

According to a fourth aspect of the present invention, the primary combustion air supplied to the drying stoker, the primary combustion air supplied to the combustion stoker, and the recirculation gas supplied to the downstream side region of the primary combustion chamber are Characterized by controlling the amount of recirculated gas blown into the downstream region of the primary combustion chamber so that the total amount of oxygen held by each is equal to or less than the amount of oxygen required as theoretical combustion air for waste. There is.

The invention according to claim 5 of the present invention comprises a stoker comprising a dry stoker, a combustion stoker, and a post-combustion stoker, and the primary combustion air is supplied individually from below each stoker into the primary combustion chamber above the stoker. In the stoker-type waste incinerator, the recirculation gas passage and a recirculation gas passage that guide a part of the exhaust gas discharged from the waste incinerator and recovered in heat to the downstream region of the primary combustion chamber as a recirculation gas. A recirculation gas blower installed in the exhaust gas, a recirculation gas passage that draws out the post-combustion stage gas generated on the post-combustion stoker and uses this as recirculation gas to the secondary combustion chamber on the downstream side of the primary combustion chamber, and It is characterized by including a recirculation gas blower provided in the gas passage and a heat exchanger arranged in a portion of the recirculation gas passage upstream of the recirculation gas blower.

According to a sixth aspect of the present invention, a secondary combustion air supply pipe is connected to a portion of the recirculation gas passage on the upstream side of the recirculation gas blower, and a secondary combustion stage gas flowing in the recirculation gas passage is provided with a secondary combustion air supply pipe. It is characterized in that the secondary combustion air is mixed.

According to a seventh aspect of the present invention, the ambient temperature air branched from the outlet side of the primary combustion air blower is connected to the secondary combustion air supply pipe connected to the upstream side of the reflux gas blower in the reflux gas passage. It is characterized in that it is supplied as secondary combustion air, and the ambient temperature air is mixed with the post-combustion stage gas flowing in the recirculation gas passage and blown into the secondary combustion chamber.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a schematic system diagram of a waste treatment plant equipped with a stoker type waste incinerator 1 for carrying out the method of the present invention.
It is composed of a stoker type waste incinerator 1, a waste heat boiler 2, a superheater 3, an economizer 4, a degassing heater 5, a bag filter 6 and an induced draft fan 7, etc. While incinerating waste such as waste to reduce the volume and volume, the high-temperature combustion gas generated in the stoker-type refuse incinerator 1 is used as a waste heat boiler 2, a superheater 3,
Heat is recovered by the economizer 4 and the deaeration heater 5, passed through the bag filter 6 to form clean gas, and then sent from the draft fan 7 to a chimney (not shown).

The stoker type refuse incinerator 1 comprises a furnace body 8, a refuse supply hopper 9, a stoker 10, and a drying stoker 1.
0a, combustion stoker 10b, post-combustion stoker 10c, stoker lower hopper 11, primary combustion chamber 12, secondary combustion chamber 1
3, ash outlet 14, exhaust gas outlet 15, primary combustion air supply device 16, recirculation gas passage 17, recirculation gas blower 18,
Reflux gas passage 19, reflux gas blower 20, heat exchanger 21,
It is composed of a secondary combustion air supply pipe 22, a damper 23, an oxygen concentration detector 24, etc., and supplies the primary combustion air A1 supplied below the stoker 10 with a primary air ratio of 1.0 to.
1.2, and a part of the exhaust gas G ″ recovered by the waste heat boiler 2 is blown into the furnace as a recirculation gas so that the reduction zone 25 is provided between the primary combustion chamber 12 and the secondary combustion chamber 13. And further, the post-combustion stage gas G ′ generated on the post-combustion stoker 10c is extracted from the inside of the furnace to form a recirculation gas, and the recirculation gas is subjected to a secondary combustion with a secondary air ratio of 0.2 to 0.4. The air A2 is mixed and blown into the secondary combustion chamber 13.

The stoker 10 is a dry stoker 10.
a, a combustion stoker 10b, and a post-combustion stoker 10c, and a stoker lower hopper 11 is arranged below each stoker 10a, 10b, 10c. Each of these stokers 10a, 10b, 10c has a movable grate (not shown) and a fixed grate (not shown) like the conventionally known stokers.
Are alternately arranged and each movable grate is reciprocated in the front-rear direction at a constant pitch by a drive device (not shown) such as a fluid pressure cylinder, thereby stirring the dust on the stalker 10 on the upstream side. To move to the downstream side. The stoker 1 is located above the stoker 10.
The stoker 1 is driven by the primary combustion air A1 supplied from below.
Primary combustion chamber 12 that burns refuse that progressively advances over 0
And a secondary combustion chamber 13 for burning unburned gas and unburned substances produced by burning in the primary combustion chamber 12.

The primary combustion air supply device 16 is branchedly connected to each stoker lower hopper 11 under the stoker 10, and supplies the primary combustion air A1 below the respective stokers 10a, 10b, 10c. Tube 26,
Supply of the primary combustion air blower 27 connected to the primary combustion air supply pipe 26 and the primary combustion air A1 which is provided at the branch portion of the primary combustion air supply pipe 26 and is supplied below the respective stokers 10a, 10b, 10c. It is composed of a plurality of dampers 23 and the like for adjusting the amount, and by changing the opening degree of the damper 23, the supply amount of the primary combustion air A1 supplied below each of the stokers 10a, 10b, 10c can be adjusted. Has become. In this embodiment, the supply amount of the primary combustion air A1 supplied from below the stoker 10 is 1.0 to 1.0 in terms of the primary air ratio (primary combustion air amount / theoretical combustion air amount).
It is set to 1.2.

The recirculation gas passage 17 extracts a part of the exhaust gas G ″ which has been heat-recovered by the waste heat boiler 2 or the like and guides it as a recirculation gas to the downstream side region of the primary combustion chamber 12. The recirculation gas injection port 17a formed in the furnace wall in the downstream region of the primary combustion chamber 12, the exhaust gas duct between the economizer 4 and the degassing heater 5, and the recirculation gas injection port 17a are connected to each other. Recirculation gas supply pipe 17 to be connected
b of the exhaust gas G ″ (exhaust gas G ″ having an oxygen concentration of 3.5% to 6%) that is heat-recovered on the downstream side of the economizer 4 by the recirculation gas blower 18 provided in the recirculation gas supply pipe 17b. A part of the gas is sucked into the recirculation gas supply pipe 17b, and the sucked exhaust gas G ″ is blown into the downstream region of the primary combustion chamber 12 from the recirculation gas blowing port 17a as a recirculation gas. The blowing amount of the circulating gas is adjusted by the damper 23 provided in the recirculating gas supply pipe 17b. Note that a part of the exhaust gas G ″ is blown into the downstream region of the primary combustion chamber 12 as the recirculating gas. , The drying / combustion stage gas G generated on the drying stoker 10a and the combustion stoker 10b is stirred and mixed, and the combustion gas (drying / combustion stage gas G is generated between the primary combustion chamber 12 and the secondary combustion chamber 13).
This is because a reducing zone 25 having a uniform temperature and composition of the mixed gas of the exhaust gas G ″ and the exhaust gas G ″ is formed. By forming the reducing zone 25, generation of NOx can be suppressed. In the present embodiment. The air ratio in the downstream region of the primary combustion chamber 12 (oxygen ratio = oxygen amount of the primary combustion air A1 supplied to the dry stoker 10a and the combustion stoker 10b + the amount of oxygen contained in the recirculation gas / theoretical combustion) (Oxygen amount of air) is 1.0 or less, preferably an air ratio of 0.8 to 1.
The amount of recirculated gas (exhaust gas G ″) is adjusted so that a uniform reduction zone 25 of 0 can be formed. The recirculated gas amount Q at this time is obtained by the following formula: Q × recirculated gas Concentration of oxygen + (amount of primary combustion air supplied to dry stoker 10a + amount of primary combustion air supplied to combustion stoker 10b) x 0.21 = reference air amount x 0.2
1 x reduction zone 25 air ratio

In the above embodiment, a part of the exhaust gas G ″ at the exit of the economizer 4 is extracted and used as the recirculation gas, but in other embodiments, the bag filter is used. The exhaust gas G ″ at the 6 outlet, the exhaust gas G ″ at the outlet of the degassing heater 5 or the exhaust gas G ″ at the outlet of the waste heat boiler 2 may be extracted and used as a recirculation gas.

The reflux gas passage 19 is connected to the post-combustion stoker 1
The post-combustion stage gas G ′ (containing a large amount of residual oxygen) generated on 0c is drawn out of the furnace and introduced as a reflux gas into the secondary combustion chamber 13 downstream of the primary combustion chamber 12. Yes, a suction chamber 19a formed in the furnace wall above the post-combustion stoker 10c so as to communicate with the primary combustion chamber 12, a plurality of reflux gas injection ports 19b formed in the furnace wall of the secondary combustion chamber 13, and suction The post-combustion stage gas G above the post-combustion stoker 10c is constituted by a recirculation gas blower 20 provided in the recirculation gas supply pipe 19c. 'Is sucked into the suction chamber 19a, and after the suction, the combustion stage gas G'
Is used as a recirculation gas from the recirculation gas injection port 19b into the secondary combustion chamber 13. The post-combustion stage gas G'above the post-combustion stoker 10c is drawn out of the furnace because NOx is generated when the post-combustion stage gas G'having a high oxygen concentration flows above the combustion stoker 10b. . In addition, after the withdrawal, the combustion stage gas G ′ is blown into the secondary combustion chamber 13 as the reflux gas because
This is because it promotes the stirring and mixing of the combustion gas that has risen inside (the gas in which the drying / combustion stage gas G and the exhaust gas G ″ are mixed).

The heat exchanger 21 is arranged in a portion of the recirculation gas passage 19 upstream of the recirculation gas blower 20 (in the suction chamber 19a in this example), and after combustion is taken out from above the post combustion stoker 10c. The temperature of the stage gas G '(reflux gas) is reduced.

The secondary combustion air supply pipe 22 is a portion of the recirculation gas passage 19 upstream of the recirculation gas blower 20 (the recirculation gas supply pipe 1 between the recirculation gas blower 20 and the heat exchanger 21).
9c) is connected in a branched manner so that the secondary combustion air A2 at room temperature can be mixed with the post-combustion stage gas G ′ flowing in the reflux gas passage 19. The secondary combustion air A2 mixed with the post-combustion stage gas G ′ flowing in the recirculation gas passage 19
Is the combustion gas in the secondary combustion chamber 13 (drying / combustion stage gas G
The amount of unburned gas and unburned substances in the mixed gas of the post-combustion stage gas G'and the exhaust gas G "is adjusted to an appropriate amount. The secondary combustion air A2 is adjusted. The oxygen concentration in the exhaust gas G ″ discharged from the exhaust gas outlet 15 of the stoker-type refuse incinerator 1 is detected by the oxygen concentration detector 24, and a damper provided in the secondary combustion air supply pipe 22 based on the detected value. It is performed by controlling 23.
In this embodiment, the supply amount of the secondary combustion air A2 is 0.2 to 0.4 in the secondary air ratio, and the total air ratio is 1.2.
Unburned gas and unburned matter in the combustion gas (gas mixture of drying / combustion stage gas G, post-combustion stage gas G ′ and exhaust gas G ″) in the secondary combustion chamber 13 in a state of up to 1.4. Is designed to burn completely.

In the above-mentioned embodiment, the ambient temperature air in the atmosphere is fed by the recirculation gas blower 20 to the secondary combustion air supply pipe 2.
2 is used as the secondary combustion air A2, but in another embodiment, the room temperature air branched from the outlet side of the primary combustion air blower 27 as shown by the broken line in FIG. May be supplied to the secondary combustion air supply pipe 22 as the secondary combustion air A2.

Thus, the above-mentioned stoker type refuse incinerator 1
In this case, the dust introduced into the furnace from the dust supply hopper 9 is sequentially advanced on the drying stoker 10a, the combustion stoker 10b, and the post-combustion stoker 10c, while the primary combustion air blower 27 sends the primary combustion air supply pipe 26. Also, primary combustion is performed by the primary combustion air A1 supplied to the primary combustion chamber 12 through the respective stokers 10a, 10b, 10c.

That is, the waste introduced into the furnace from the waste supply hopper 9 is continuously supplied onto the dry stoker 10a by the waste supply pusher (not shown), and the primary combustion is supplied from below the dry stoker 10a. The air A1 is heated and dried by the radiant heat from the primary combustion chamber 12 in a high temperature state, and at the same time, combustion starts in a part of the dust. As a result, water in the dust is evaporated and unburned gas such as CO and HC is released. Next, the dried refuse is continuously sent from the dry stoker 10a onto the combustion stoker 10b, where the primary combustion air A1 supplied from below the combustion stoker 10b raises the flame to burn the combusted stoker 10b. At the downstream end, it just reaches the burnout point. Then, the dust that has burned out at the downstream end of the combustion stoker 10b continues to be burned by the post-combustion stoker 10.
c, and the so-called "primary combustion air A1" supplied from the bottom of the post-combustion stoker 10c there causes so-called "combustion combustion" to produce incinerated ash with almost no unburned content, and then the ash is discharged from the ash outlet 14 and discharged. .

In this stoker type refuse incinerator 1,
In the state where the supply amount of the primary combustion air A1 supplied below the stoker 10 is 1.0 to 1.2 in terms of the primary air ratio, the stoker 10
After burning and burning the above garbage, a post-burning stoker 1
The post-combustion stage gas G '(combustion gas G'having almost no corrosive gas and high oxygen concentration) generated above 0c is drawn from the upper space of the post-combustion stoker 10c into the suction chamber 19a by the reflux gas blower 20. I am trying. In addition, in this stoker-type refuse incinerator 1, the drying / combustion stage gas G with a large amount of volatile and unburned components generated on the drying stoker 10a and the burning stoker 10b is guided to the primary combustion chamber 12 above the stoker 10. , Exhaust gas G ″ in the downstream region of the primary combustion chamber 12
Stirring and mixing with (recirculation gas). That is, in the stoker-type refuse incinerator 1, the heat recovered exhaust gas G ″ (oxygen concentration of 3.5 to 6 is provided downstream of the economizer 4).
% Of the exhaust gas G ″) is sucked into the recirculation gas supply pipe 17b by the recirculation gas blower 18, and the sucked exhaust gas G ″ is used as the recirculation gas.
The dry / combustion stage gas G generated from the dry stoker 10a and the combustion stoker 10b is blown into the downstream region of the primary combustion chamber 12 from a and stirred and mixed. Therefore, between the primary combustion chamber 12 and the secondary combustion chamber 13, the reduction zone 25 (the air ratio is 0 where the combustion gas (the gas in which the drying / combustion stage gas G and the exhaust gas G ″ are mixed) has a uniform temperature and composition. .8 to 1.0
Therefore, the reduction zone 25) is formed, and the generation of NOx can be sufficiently suppressed.

On the other hand, the post-combustion stage gas G '(reflux gas) withdrawn from the upper space of the post-combustion stoker 10c is cooled by the heat exchanger 21 to have its temperature reduced, and then, in the secondary combustion air supply pipe 22. Is mixed with the secondary combustion air A2 (secondary combustion air A2 having a secondary air ratio of 0.2 to 0.4), passed through the recirculation gas blower 20 and the recirculation gas blowing port 19b.
Is blown into the secondary combustion chamber 13. At this time, the mixed gas of the post combustion gas stage G ′ and the secondary combustion air A2 blown into the secondary combustion chamber 13 has a temperature of about 200 ° C. and an oxygen concentration of 15 to 20%.

In the secondary combustion chamber 13 into which the post combustion stage gas G'and the secondary combustion air A2 are blown, the combustion gas (drying / combustion stage gas G and exhaust gas rising from the reduction zone 25 G ″ mixed gas) is agitated / mixed to promote uniform temperature and composition, and the total air ratio is 1.2 to 1.
At a low air ratio of 4, unburned gas such as CO in the combustion gas is completely burned and unburned substances such as dioxins are completely decomposed. As a result, it is possible to completely burn unburned gas and unburned substances in the combustion gas without supplying a large amount of combustion air into the furnace, and to sufficiently suppress the generation of NOx, CO, and dioxins. You can

The exhaust gas G ″ completely combusted in the secondary combustion chamber 13 is heat-recovered by the waste heat boiler 2, the superheater 3, the economizer 4, and the degassing heater 5, and the temperature is 180 ° C. to 25 ° C.
After being cooled to a temperature of 0 ° C. and passing through the bag filter 6 to become clean gas, it is sent to a chimney (not shown) by an induction draft fan 7 and discharged into the atmosphere from the chimney.
The exhaust gas G ″ discharged from the waste heat boiler 2 has an oxygen concentration of 3.5 to 6%, and after the necessary amount is extracted as a recirculation gas, the rest is treated by the bag filter 6 and the like. Emitted from the chimney into the atmosphere.

[0032]

As is apparent from the above description, according to the present invention, the supply amount of the primary combustion air supplied from below the stoker is 1.0 to 1.2 in terms of the primary air ratio, and the after combustion stoker is above the stoker. The post-combustion stage gas generated in
A portion of the exhaust gas after heat recovery is blown into the downstream basin of the primary combustion chamber as recirculation gas, and the recirculation gas stirs and mixes the drying stoker and the drying / combustion stage gas generated on the combustion stoker to perform primary combustion. A reduction zone is formed between the combustion chamber and the secondary combustion chamber, and after the temperature of the post-combustion stage gas extracted from the upper space of the post-combustion stoker is reduced, the secondary combustion stage gas has a secondary air ratio of 0. The secondary combustion air of 2 to 0.4 is mixed, and after the secondary combustion air is mixed, the combustion stage gas is blown into the secondary combustion chamber as the reflux gas, and the total air ratio is 1.2 to
In the state of 1.4, the unburned gas and unburned substances in the secondary combustion chamber are completely burned. As a result, the present invention provides
The following excellent effects can be achieved. (1) Without reducing the primary air ratio of the primary combustion air supplied from below the stoker to 1.0 or less, the air ratio in the furnace is 1.0.
The following reduction zones can be formed. as a result,
It is not necessary to use a high-performance stoker when introducing it into an existing furnace, and it is possible to use a conventional stoker. (2) Without reducing the primary air ratio of the primary combustion air supplied from below the stoker to 1.0 or less, the air ratio in the furnace is 1.0.
Since the following reduction zones can be formed, the waste on the stoker can be efficiently dried and burned even when the waste quality of the waste supplied to the furnace is low, and the N
Generation of Ox can be suppressed. (3) Exhaust gas having a low oxygen concentration (oxygen concentration of 3.
Since 5% to 6% of exhaust gas) is used as the recirculation gas, even if the amount of oxygen in the gas for stirring and mixing supplied to the furnace is the same as in the conventional case, it is supplied to the furnace. The amount of recirculated gas is increased, the stirring / mixing effect can be enhanced, a uniform reduction zone can be formed, and the generation of NOx can be sufficiently suppressed. (4) Exhaust gas with a low oxygen concentration (oxygen concentration of 3.
5% to 6% of exhaust gas) is used as the recirculation gas, so it is necessary to prevent the formation of locally high oxygen concentration in the part of the furnace where the recirculation gas is blown. You can As a result, it is easy to form a uniform reduction zone, and the effect of suppressing NOx can be obtained. (5) Exhaust gas having a low oxygen concentration (oxygen concentration of 3.
5% to 6% of exhaust gas) is used as the recirculation gas, and thus N ₂ and CO ₂ which are surplus components in the recirculation gas.
As a result, the cooling effect can be obtained by increasing the gas amount while maintaining the air ratio in the reduction zone at about 0.8 to 1.0. As a result, it is possible to prevent the temperature in the reduction zone from rising too high, and even if the stoker-type refuse incinerator does not have a wall cooling structure such as a water cooling wall (boiler), clinker generation and damage to the furnace wall refractory Can be prevented. (6) After the post-combustion stage gas (reflux gas) extracted from the upper space of the post-combustion stoker is cooled by the heat exchanger,
Since it is cooled by being mixed with the secondary combustion air at room temperature, it is possible to reduce the capacity of the heat exchanger and
Cost reduction and installation space reduction are possible. (7) Since the secondary combustion air is mixed with the post-combustion stage gas (reflux gas) extracted from the upper space of the post-combustion stoker, the secondary combustion air is heated without using the air preheater. Therefore, the stirring and mixing of the combustion gas in the secondary combustion chamber can be promoted, and the secondary air ratio can be reduced. (8) Since a part of the exhaust gas discharged from the stoker-type waste incinerator is used as the recirculation gas, the stirring / mixing effect is promoted compared to the conventional one, and the conventional air ratio is 1.3. It becomes easier to complete combustion in the air conditioner, and the total air ratio can be further reduced. (9) By performing low-air-ratio combustion, the amount of exhaust gas discharged from the stoker-type refuse incinerator decreases, and the installed capacity of exhaust gas treatment equipment and induced draft fans installed downstream of the stoker-type refuse incinerator. Can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic system diagram of a refuse treatment plant equipped with a stoker type refuse incinerator for carrying out the method of the present invention.

FIG. 2 is a schematic system diagram of a waste treatment plant including a conventional stoker-type waste incinerator.

[Explanation of symbols]

1 is a stoker-type refuse incinerator, 10 is a stoker, 10a is a dry stoker, 10b is a combustion stoker, 10c is a post-combustion stoker, 12 is a primary combustion chamber, 13 is a secondary combustion chamber, 17
Is a recirculation gas passage, 18 is a recirculation gas blower, 19 is a recirculation gas passage, 20 is a recirculation gas blower, 21 is a heat exchanger, 22
Is a secondary combustion air supply pipe, 25 is a reduction zone, 27 is a primary combustion air blower, A1 is primary combustion air, A2 is secondary combustion air, G is a drying / combustion stage gas, and G'is a post combustion stage gas (reflux). Gas) and G ″ are exhaust gas (recirculated gas).

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3K061 GA04 HA06 HA17 HA18 HA19                       HA27                 3K062 AA02 AB01 AC01 CB08 DA22                       DB08 DB17                 3K078 AA04 BA03 CA03 CA06 CA12

Claims (7)

[Claims] 1. A stoker-type refuse incinerator comprising a stoker comprising a dry stoker, a combustion stoker, and a post-combustion stoker, and the primary combustion air is individually supplied into the primary combustion chamber above the stoker from below each stoker. The primary combustion air is supplied from below the stoker at a primary air ratio of 1.0 to 1.2, the post-combustion stage gas generated on the post-combustion stoker is drawn out of the furnace, and the primary combustion chamber Part of the exhaust gas after heat recovery is blown into the downstream basin as a recirculation gas, and the recirculation gas stirs and mixes the drying / combustion stage gas generated on the drying stoker and the combustion stoker to mix with the primary combustion chamber and the secondary combustion chamber. A reduction zone is formed between the secondary combustion chamber and the secondary combustion chamber, and the secondary combustion stage gas extracted from the upper space of the secondary combustion stoker is blown into the secondary combustion chamber as reflux gas. Combustion method of stoker type incinerator. 2. The post-combustion stage gas withdrawn from the upper space of the post-combustion stoker is heat-recovered by a heat exchanger to reduce the temperature, and then mixed with the secondary combustion air at room temperature and blown into the secondary combustion chamber. The method of burning a stoker-type refuse incinerator according to claim 1, wherein 3. The unburned gas in the secondary combustion chamber when the secondary combustion air is supplied at a secondary air ratio of 0.2 to 0.4 and the total air ratio is 1.2 to 1.4. The method for burning a stoker-type refuse incinerator according to claim 2, wherein the unburned matter and the unburned matter are completely burned. 4. The total amount of oxygen contained in the primary combustion air supplied to the dry stoker, the primary combustion air supplied to the combustion stoker, and the recirculated gas supplied to the downstream side region of the primary combustion chamber is the total amount of oxygen. The stoker type according to claim 1, wherein the amount of recirculated gas blown into the downstream side region of the primary combustion chamber is controlled so as to be equal to or less than the amount of oxygen required as theoretical combustion air. Combustion method of garbage incinerator. 5. A stoker-type refuse incinerator, comprising a stoker comprising a dry stoker, a combustion stoker, and a post-combustion stoker, wherein primary combustion air is individually supplied into the primary combustion chamber above the stoker from below each stoker. , A recirculation gas passage for guiding a part of the exhaust gas discharged from the refuse incinerator and recovered in heat to the downstream side region of the primary combustion chamber as a recirculation gas, and a recirculation gas blower provided in the recirculation gas passage. , A recirculation gas blower installed in the recirculation gas passage and a recirculation gas passage that draws out the post-combustion stage gas generated on the post-combustion stoker and guides this as recirculation gas to the secondary combustion chamber on the downstream side of the primary combustion chamber. And a heat exchanger arranged upstream of the reflux gas blower in the reflux gas passage, the stoker-type refuse incinerator. 6. A secondary combustion air supply pipe is connected to a part of the recirculation gas passage upstream of the recirculation gas blower so that the secondary combustion air is mixed with the post combustion stage gas flowing in the recirculation gas passage. The stoker-type refuse incinerator according to claim 5. 7. The secondary combustion air supply pipe connected to the upstream side of the reflux gas blower in the reflux gas passage is supplied with room temperature air branched from the outlet side of the primary combustion air blower as the secondary combustion air to produce the reflux gas. The stoker-type refuse incinerator according to claim 6, wherein the post-combustion stage gas flowing in the passage is mixed with the room temperature air and blown into the secondary combustion chamber.