JP2003329228A - Waste incinerator - Google Patents

Abstract

(57) [Problem] To provide a waste incinerator that generates little NOx even when oxygen-enriched air is used as air blown from below a grate or a fluidized bed. SOLUTION: The stoker is divided into three of a dry stoker 3, a burning stoker 4, and a post-burning stoker 5,
From the lower part of each stoker, oxygen-enriched air is blown through oxygen-enriched air supply pipes 18, 19, and 20. The oxygen concentration in the oxygen-enriched air is set to be highest in the oxygen-enriched air supply pipe 18 and lowest in the oxygen-enriched air supply pipe 20. For this reason, a large amount of oxygen is supplied to the dry stoker 3 which has a large amount of unburned components, requires a large amount of oxygen for combustion, and has a low temperature, so that the combustion is stabilized. Then, in the post-combustion stoker 5 where the combustion is almost completed and the temperature is high, the amount of oxygen to be blown is small. Thus, the amount of generated NOx can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grate type or fluidized bed type waste incinerator for incinerating waste such as municipal waste.

[0002]

2. Description of the Related Art A grate type or fluidized bed type waste incinerator is widely used as an incinerator for incinerating waste such as municipal waste. A schematic diagram of a typical one is shown in FIG. The dust 2 thrown into the hopper 1 is sent to the drying stoker 3 through the chute, is dried by the air from below and the radiant heat in the furnace, and is heated and ignited. The waste 2 that has ignited and started combustion is sent to the combustion stoker 4,
It is gasified by the combustion air sent from below and partly burns. Then, the post-combustion stoker 5 completely burns the unburned components. Then, the ash remaining after the combustion is taken out from the main ash chute 6.

Combustion is carried out in the main combustion chamber 7, and the combustion exhaust gas is separated into a main flue 9 and a sub flue 10 and discharged due to the presence of the intermediate ceiling 8. The exhaust gas passing through the main flue 9 contains almost no unburned components and contains approximately 10% oxygen.
The exhaust gas passing through the secondary flue 10 contains about 8% unburned components. These exhaust gases are mixed in the secondary combustion chamber 11 and secondary combustion is performed to completely burn unburned components.
The exhaust gas from the secondary combustion chamber 11 is sent to the waste heat boiler 13 after the dust having a large particle size is removed in the dust removing chamber 12.
After heat exchange, it is discharged to the outside through the temperature reducing tower, bag filter, etc.

When incinerating municipal solid waste in such a grate type or fluidized bed type waste incinerator, since the municipal solid waste consists of many substances having different properties, the combustion state in the furnace is kept constant. However, it is unavoidable that the temperature and the concentration of the combustion gas in the main combustion chamber 7 become uneven in distribution in terms of time and space.

Particularly, in the dry area on the dry stoker, depending on the property of dust, a large amount of water vapor may be generated or flammable components in the dust may be temporarily reduced to make ignition unstable. A phenomenon called CO spike may occur due to the phenomenon. This is because the flame disappears and unburned gas containing a large amount of CO flows into the secondary combustion chamber,
Here again, it is a phenomenon that the material is not completely burned and is released to the outside.
The CO spike also occurs when combustion in the main combustion chamber 7 becomes unstable. When a CO spike occurs, exhaust gas containing harmful substances is released to the outside of the furnace, which is not preferable in terms of pollution prevention.

Further, when the flame temperature in the main combustion chamber 7 becomes high, dust is welded to the intermediate ceiling 8 and the furnace wall, and deposits called clinker are generated to narrow the flow path of the gas in the furnace or make it huge. There is a problem that the clinker drops on the bottom of the furnace and damages the grate and the like. Further, if the state of the flame is unstable, the flame is easily blown off, and it is difficult to perform high-load combustion.

In order to solve such problems and to effectively utilize the sensible heat of the exhaust gas, the exhaust gas or a mixed gas of the exhaust gas and air is blown into the upper part of the stoker in the main combustion chamber, and the flame holding effect thereof is provided. Proposes a method of burning unburned matter near the stoker (lower part of the furnace) to stabilize the combustion state and prevent combustion near the ceiling to prevent clinker generation and melting damage of refractory on the ceiling. Has been done.

Attempts have also been made to improve the combustion of waste by stabilizing the combustion state by enriching the air blown from under the stoker with oxygen. Then, a technique combining these is disclosed in JP-A-2002-13.
No. 715.

[0009]

However, as far as is known so far, all of the techniques for improving the combustion of waste by enriching the air blown from under the stoker with oxygen are known as stokers. Oxygen-enriched air is blown evenly over the whole. However, the amount of oxygen required for combustion is not uniform over the entire stoker, and in general, a large amount of oxygen is required immediately after the waste material has ignited, but the waste material is above the stoker. When it progresses and reaches the latter stage of the stoker, most of the combustion has already been completed and the temperature is high, so much oxygen is not required for combustion.

Therefore, an oxygen-rich portion is generated in the high temperature portion, which causes a problem that a large amount of NOx is unavoidable. In addition, a local high temperature field is generated in the furnace, which causes a problem of burning the grate and the furnace wall. This situation applies not only to the grate type waste incinerator but also to the fluidized bed type waste incinerator.

The present invention has been made in view of the above circumstances. Even when oxygen-enriched air is used as the air blown from under the grate or under the fluidized bed, NOx generation is small and the oxygen content is substantially reduced. The object is to provide a waste incinerator that consumes less energy.

[0012]

A first means for solving the above-mentioned problems is a grate type or fluidized bed type waste incinerator, in which at least a grate or a fluidized bed is provided in a main combustion chamber. In the case of supplying oxygen-enriched air from a part, the oxygen concentration in the oxygen-enriched air is adapted to decrease in the traveling direction of the waste (waste incinerator). Item 1).

In the present means, the oxygen concentration in the oxygen-enriched air is made to decrease in the traveling direction of the waste, so that oxygen is required at the early stage of combustion of the waste that requires a large amount of oxygen. Oxygen-enriched air (or non-enriched air) with low oxygen concentration is supplied at high temperature where high-concentration oxygen-enriched air is supplied and does not require much oxygen near the end of combustion. ) Is used. Therefore, while realizing stable combustion, it is possible to reduce the generation of NOx and avoid burnout of the grate and the fluidized bed.

The simplest method for changing the oxygen concentration is to perform each grate or fluidized bed.
The oxygen concentration may be changed within the same grate or within the fluidized bed.

A second means for solving the above-mentioned problems is as follows.
A grate type or fluidized bed waste incinerator, which supplies oxygen-enriched air from at least a portion below the grate or fluidized bed to the main combustion chamber, and produces exhaust gas or a mixed gas of exhaust gas and air, In the method of blowing into the upper part of the grate or the fluidized bed of the main combustion chamber, the oxygen concentration in the oxygen-enriched air is arranged to decrease in the traveling direction of the waste. The incinerator (claim 2).

In addition to the first means, this means is provided with a mechanism for blowing the exhaust gas or a mixed gas of the exhaust gas and air into the grate of the main combustion chamber or the upper part of the fluidized bed. Therefore, the gasification of the waste is promoted by the flame holding action of the gas blown by the exhaust gas circulation equipment. Further, the combustion in the main combustion chamber is stable, the CO generation at the furnace outlet is reduced, and the combustion in the vicinity of the ceiling is reduced, so that the refractory on the ceiling is melted or clinker is generated. Can be reduced.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a waste incinerator which is an example of an embodiment of the present invention. The dust 2 thrown into the hopper 1 is sent to the drying stoker 3 through the chute, dried by the oxygen-enriched air from below and the radiant heat in the furnace, and is heated to ignite. The dust 2 that has ignited and started combustion is sent to a combustion stoker 4, and is gasified by the combustion air sent from below, and a part thereof burns. Then, the post-combustion stoker 5 completely burns the unburned components. Then, the ash remaining after the combustion is taken out from the main ash chute 6.

The combustion is carried out in the main combustion chamber 7, and the combustion exhaust gas is separated into the main flue 9 and the sub flue 10 and discharged due to the presence of the intermediate ceiling 8. The exhaust gas passing through the main flue 9 contains almost no unburned components and contains approximately 10% oxygen.
The exhaust gas passing through the secondary flue 10 contains about 8% unburned components. These exhaust gases are mixed in the secondary combustion chamber 11 and secondary combustion is performed to completely burn unburned components.
The exhaust gas from the secondary combustion chamber 11 is sent to the waste heat boiler 13 after the dust having a large particle size is removed in the dust removing chamber 12.
After the heat is exchanged, it is attracted by the attracting fan 15 via the exhaust gas treatment facility 14 including a temperature reducing tower, a bag filter, etc., and is diffused from the chimney 16 to the atmosphere.

Part of the exhaust gas on the outlet side of the induction fan 15 is
It is guided to the nozzle group 17 provided in the main combustion chamber 7 and blown above the stoker in the main combustion chamber 7. If necessary, air is mixed with the exhaust gas in the exhaust gas circulation system,
Exhaust gas enriched with oxygen is blown in. As a result, the unburned gas generated from the dust 2 is combusted immediately above the stoker, and the combustion is stabilized.

In the waste incinerator shown in FIG. 1, the stoker is divided into three parts, a dry stoker 3, a combustion stoker 4, and a post-combustion stoker 5, and from the bottom of each stoker, oxygen enrichment is performed. Oxygen-enriched air is blown in through the air supply pipes 18, 19, 20. That is, as shown in the figure, each oxygen-enriched air supply pipe 18, 19, 20
In front of, the air and oxygen are mixed to create oxygen-enriched air, which is blown into the underside of the stoker.

The oxygen concentration in these oxygen-enriched air is the highest in the oxygen-enriched air supply pipe 18 (preferably 24).
.About.26%), and the lowest in the oxygen-enriched air supply pipe 20 (desirably 21-23%). Therefore, a large amount of unburned matter is required for combustion, and a large amount of oxygen is supplied to the drying stoker 3 having a low temperature, so that combustion becomes stable. Then, in the post-combustion stoker 5 in which the combustion is almost completed and the temperature is high, the amount of oxygen blown is small. As a result, the combustion can be stably performed as a whole, and the amount of NOx generated can be reduced.

In the above embodiment, the one having the exhaust gas circulation system has been described, but the present invention can be applied to the waste incinerator having no exhaust gas circulation system. In addition, the inside of the furnace can be monitored and NOx in exhaust gas can be monitored.
By monitoring the concentration or the CO concentration and adjusting the oxygen concentration in the oxygen-enriched air according to the situation, the pollution reduction of the exhaust gas is further promoted. As a specific example, it is preferable to take the action shown in Table 1. (Table 1)

[0023]

[Table 1]

[0024]

As described above, according to the present means,
Even when oxygen-enriched air is used as the air blown from under the grate or under the fluidized bed, it is possible to provide a waste incinerator that generates less NOx.

[Brief description of drawings]

FIG. 1 is a diagram showing a waste incinerator that is an example of an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional waste incinerator.

[Explanation of symbols]

1 ... Hopper, 2 ... Garbage, 3 ... Dry stoker ... 4 ... Combustion stoker, 5 ... Post-combustion stoker, 6 ... Main ash chute, 7
... main combustion chamber, 8 ... intermediate ceiling, 9 ... main flue, 10 ... secondary flue, 11 ... secondary combustion chamber, 12 ... dust removal chamber, 13 ... waste heat boiler, 14 ... exhaust gas treatment facility, 15 ... induction fan , 16 ...
Chimney, 17 ... Nozzle group, 18, 19, 20 ... Oxygen-enriched air supply pipe

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F23L 9/02 F23L 9/02 // F23C 10/00 F23H 11/10 F23H 11/10 F23C 11/02 301 F term (reference) 3K023 JA02 JD02 KA02 KB01 KB12 KD01 3K061 HA03 HA17 HA21 HA27 HA29 3K064 AA01 AB03 AD08 AE01 BA09 3K065 AA01 AA11 AB01 AC01 GA03 GA07 GA13 GA14 GA22 GA23 GA26 GA33 GA53

Claims (2)

[Claims] 1. A grate or fluidized bed waste incinerator for supplying oxygen-enriched air to the main combustion chamber from at least a portion below the grate or fluidized bed, wherein the oxygen enrichment is performed. A waste incinerator characterized in that the oxygen concentration in the air is lowered as it goes in the direction of progress of the waste. 2. A grate type or fluidized bed type waste incinerator, wherein oxygen-enriched air is supplied to the main combustion chamber from at least a part below the grate or fluidized bed, and the exhaust gas or the exhaust gas and air In a system in which a mixed gas is blown into the grate of the main combustion chamber or the upper part of the fluidized bed, the oxygen concentration in the oxygen-enriched air is made to decrease as it goes in the traveling direction of the waste. Characteristic waste incinerator.