JP2002031312A - EQUIPMENT AND METHOD FOR LOW-NOx COMBUSTION IN REFUSE GASIFYING AND MELTING FACILITY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the NOx content of the exhaust gas from a refuse gasifying and melting facility by elaborating a plan to improve the two-stage combustion method, used in the secondary combustion chamber of the facility. SOLUTION: A low-NOx combustion equipment is incorporated in a refuse gasifying and melting facility provided with a gasifying furnace 6, which performs partial oxidization and combustion on the refuse supplied from a dryer 3 that dries the refuse at a low air ratio, a melting furnace 10 which burns and melts unburned components and solid contents (char) generated in the furnace 6, the secondary combustion chamber 14 in which the unburned components from the furnace 10 are completely burned, and an exhaust gas treating facility which treats the exhaust gas from the chamber 14. The combustion equipment supplies a waste combustion gas 30, subjected to flue-gas treatment to the secondary combustion chamber 14 on the downstream side of the melting furnace 10 as a gas for complete combustion, by keeping the inside of the furnace 10 in a reduction atmosphere (lower than the theoretical air ratio). Also the exhaust gas from the dryer 3 is used as the gas for complete combustion of the combustion chamber 14, instead of the waste combustion gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refuse incineration and melting facility, and reduces unburned components such as nitrogen oxides (hereinafter referred to as NOx) and carbon monoxide (hereinafter referred to as CO) in exhaust gas. The present invention relates to a technique relating to a combustion apparatus and a method suitable for the present invention.

[0002]

2. Description of the Related Art In recent years, a refuse gasification and melting system that can simultaneously reduce the volume of refuse and detoxify refuse ash has attracted attention. FIG. 7 shows a system of a fluidized bed waste gasification and melting system according to the prior art. The refuse is put into a dust hopper 1 from a storage pit (not shown), and a predetermined amount of refuse is supplied to the gasification furnace by a quantitative feeder 2 through a dryer 3, a pipe 4, and a sealing mechanism 5. 6. The refuse supplied to the gasification furnace 6 undergoes a partial oxidation reaction with the air supplied to the fluidized bed 8 through a pipe 7, and combustible gas such as CO and hydrogen,
A solid char and a small amount of tar are formed.

The solid char containing unburned components and ash is powdered by vigorous mixing and agitation with a fluid medium (usually sand) in a fluidized bed 8 and is melted together with generated gas and tar through a flue 9. The ash is sent to the furnace 10, reacts with oxygen in the air supplied through the pipe 11, burns, the ash in the solid is melted, and discharged as harmless slag through the discharge pipe 12. The melting furnace 10 is provided with an auxiliary burner 12-1 using gas or oil as a fuel in order to cope with a wide range of refuse, especially low calorific value refuse.

The high-temperature combustion gas from the melting furnace 10 is supplied to a slag screen 13 (which is a water-cooled or air-cooled pipe for preventing ash scattering) provided at the outlet of the melting furnace 10 and a secondary combustion chamber. Through 14, the heat is recovered by the heat recovery unit 15 and the air heater 16. Thereafter, the exhaust gas becomes clean exhaust gas by the dust collector 17 and is exhausted through the induction blower 18 and the chimney 19.

[0005] On the other hand, the dryer 3 raises the temperature of the refuse by using gas or oil fuel or by using the exhaust gas to remove moisture in the refuse. Facilities. The exhaust gas from the dryer 3 is
The air is supplied to the secondary combustion chamber downstream of the melting furnace 10 near the outlet 14 through the induction blower 20 and the pipe 21.

Generally, it is necessary to maintain a high temperature of 1350 ° C. or higher in the melting furnace 10 in order to slag ash in solids from the gasification furnace 6. For this reason, it is usually kept in an oxidizing atmosphere (air ratio of 1 or more). In this method, since no reduction region is formed downstream of the melting furnace 10, N
There is a problem that the Ox concentration increases.

For this reason, a so-called two-stage combustion method is employed in which the inside of the melting furnace 10 is set to a reducing atmosphere (air ratio is 1 or less) and air for complete combustion is supplied from the downstream of the melting furnace 10.
Methods for measuring Ox reduction have also been proposed. However, in this method, depending on the supply position and supply method of the two-stage combustion air, C
An unburned component such as O may increase.

Further, if pure air is used as the two-stage combustion air, the temperature inside the secondary combustion chamber 14 becomes too high, which causes a problem that thermal NOx having a strong temperature dependency is increased.

As described above, when the inside of the melting furnace 10 is brought into a reducing atmosphere by using the two-stage combustion method, if the air ratio is too low, the inside of the melting furnace 10 becomes low temperature and the slag does not melt. .

[0010]

As described above,
The following problems occur in the waste gasification and melting equipment in the conventional technology.

(1) When the inside of the melting furnace is set to an oxidizing atmosphere, N
When the Ox concentration increases and (2) the melting furnace is set to a reducing atmosphere and the two-stage combustion method is adopted, the air ratio in the melting furnace is set to 0.7.
In the following, the temperature in the melting furnace decreases, and the slag becomes difficult to flow down. (3) Similarly, even if the two-stage combustion method is adopted,
If the exhaust gas from the melting furnace is not sufficiently mixed, unburned components such as CO will increase. (4) If pure air is used as the air for the two-stage combustion, thermal NOx will increase.

It is an object of the present invention to provide a low NOx device that reduces nitrogen oxides in exhaust gas by adopting a two-stage combustion method and improving the solution to solve the above-mentioned problems.

[0013]

In order to solve the above problems, the present invention mainly employs the following configuration.

A dryer for drying the refuse received from the upstream side; a gasifier for partially oxidizing and burning the refuse supplied from the dryer at a low air ratio; an unburned component and solids generated in the gasifier; A melting furnace for burning and melting a portion (char), a secondary combustion chamber for completely burning unburned components from the melting furnace, and an exhaust gas treatment facility for treating exhaust gas from the secondary combustion chamber. A refuse gasification / melting facility, wherein the inside of the melting furnace has a reducing atmosphere (less than the theoretical air ratio), and the exhaust gas is subjected to the exhaust gas treatment as a complete combustion gas in the secondary combustion chamber downstream of the melting furnace. NOx combustion equipment in a refuse gasification and melting facility that supplies water in multiple stages.

A dryer for drying the refuse received from the upstream side; a gasifier for partially oxidizing and burning the refuse supplied from the dryer at a low air ratio; and an unburned component generated in the gasifier. A melting furnace for burning and melting the solid content (char), a secondary combustion chamber for completely burning unburned components from the melting furnace, and an exhaust gas treatment facility for processing exhaust gas from the secondary combustion chamber. A refuse gasification and melting facility provided with a reducing atmosphere (less than the theoretical air ratio) inside the melting furnace, and discharged from the dryer as a complete combustion gas into the secondary combustion chamber downstream of the melting furnace. NOx combustion equipment in a refuse gasification and melting facility that supplies dryer exhaust gas in multiple stages.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A low NOx combustion apparatus and method in a waste gasification and melting facility according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a system configuration of a low NOx combustion device in a waste gasification and melting facility according to a first embodiment of the present invention, which is a system configuration when using combustion exhaust gas as a complete combustion gas.

According to FIG. 1, refuse is put into a dust hopper 1 from a storage pit, and a predetermined amount of refuse is supplied to a gasification furnace by a quantitative feeder 2 through a dryer 3, a pipe 4, and a seal mechanism 5. 6. The refuse supplied to the gasification furnace 6 undergoes a partial oxidation reaction with the air supplied to the fluidized bed 8 through a pipe 7 to generate a combustible gas such as CO and hydrogen, a solid char, and a small amount of tar. I do.

The solid char containing unburned components and ash is powdered by vigorous mixing and stirring with the fluidized medium (usually sand) in the fluidized bed 8 and is melted together with the produced gas and tar through the flue 9. The ash is sent to the furnace 10 and reacts and burns with oxygen in the air supplied through the pipe 11. The ash in the solid is melted and discharged as harmless slag through the discharge pipe 12. In this case, the amount of air supplied through the pipe 11 is controlled by the damper 11-1 so that the air ratio in the melting furnace 10 becomes 1.0.
Control to be less than. The melting furnace 10 is provided with an auxiliary burner 12-1 using gas or oil as a fuel in order to cope with a wide range of waste, particularly low calorific value waste.

The high-temperature combustion gas from the melting furnace 10 is supplied to a slag screen 13 provided at the outlet of the melting furnace 10 (this is used for the most upstream two-stage combustion in which ash is prevented from scattering and a combustion exhaust gas supply hole is provided). Through the secondary combustion chamber 14, the heat is recovered by the heat recovery unit 15 and the air heater 16. After that, it becomes clean exhaust gas by the dust collector 17, and is exhausted through the induction blower 18 and the chimney 19,
A part of the combustion exhaust gas that has exited from the induction blower 18 is supplied in multiple stages (two stages in this embodiment) into the secondary combustion chamber 14 downstream of the melting furnace 10 via a recirculation blower 29 and a pipe 30. .

As described above, the fuel is supplied to the upstream side (lower side) through the slag screen 13 into the secondary combustion chamber 14. On the other hand, on the downstream side (upper side), the temperature atmosphere is 80
It is supplied to a position near 0 to 1000 ° C. A pipe 22 for supplying NH ₃ from the middle of the pipe 30 for the combustion exhaust gas
Is connected. Further, a damper 23 for controlling the amount of the two-stage combustion gas to each stage is provided. In this embodiment, the flue gas from the refuse gasification and melting furnace is used, but in refuse incineration equipment, several refuse gasification and melting furnaces are generally set in the same place, and other refuse gasification Combustion exhaust gas from a melting furnace may be used.

Next, FIG. 2 shows a system configuration of a low NOx combustion device in a waste gasification and melting facility according to a second embodiment of the present invention. FIG. 2 shows a system configuration when a dryer exhaust gas is used as a complete combustion gas. 2 has many parts in common with the system configuration shown in FIG. 1, and the description of FIG. 1 is cited for this common part. The feature of the second embodiment of the present invention shown in FIG. 2 is the configuration related to the dryer, and therefore, the related configuration will be described.

The dryer 3 raises the temperature of the refuse by using gas or oil fuel and removes the water in the refuse, and is a facility for low heat generation, that is, refuse having a large amount of water. The exhaust gas from the dryer 3 is supplied to the induction blower 2
0, the secondary combustion chamber 14 downstream of the melting furnace 10 via the pipe 21
Are supplied in multiple stages (two stages in this embodiment). As in the case of using the combustion exhaust gas in the first embodiment, the gas is supplied to the upstream side (lower side) through the slag screen 13 into the secondary combustion chamber 14. On the other hand, downstream side (upper side)
Is supplied to a position where the temperature atmosphere is around 800 to 1000 ° C. The pipe 21 for the exhaust gas of the dryer is filled with N
Pipe 22 for supplying and H ₃ are connected. Further, a damper 23 for controlling the amount of the two-stage combustion gas to each stage is provided.
Is installed.

Here, although not shown, it is also possible to use both the exhaust gas as the complete combustion gas on the upstream side and the dryer exhaust gas as the complete combustion gas on the downstream side. In the use of both exhaust gases, the exhaust gases may be used in reverse.

At this time, the meaning of the terms used in the description of the embodiments of the present invention will be mentioned. In the present embodiment, nitrogen oxide (NOx) is taken up. However, nitrogen is nonflammable, but when it becomes high temperature, it can become an air pollutant (a cause of acid rain and photochemical smog) as nitrogen oxide. There are two types of thermal NOx: nitrogen in air generated under high-temperature conditions and fuel NOx generated by oxidation from nitrogen compounds in fuel. Regarding NOx generated by combustion,
The production increases as the combustion temperature increases and the oxygen concentration increases. The stoichiometric air amount refers to a theoretically calculated minimum amount of air required for combustion, and the amount of air actually supplied during combustion is referred to as an actual air amount. And
The air ratio refers to the ratio of the actual air amount to the theoretical air amount.

FIG. 3 shows a state in which the slag screen 13 is blown into the furnace. From this figure, by arranging the blowing positions of the adjacent pipes alternately, almost the entire area of the cross section is covered, and almost the entire outer surface of the adjacent pipe is covered with a combustion exhaust gas or a dryer exhaust gas of 150 ° C. or less. Therefore, burning of the piping can be prevented.

FIG. 4 shows the effect of non-catalytic NOx removal of NOx by NH ₃ . In this figure, the horizontal axis indicates the temperature of the atmosphere, and the vertical axis indicates the NOx concentration in the exhaust gas. Also,
The molar ratio of NH ₃ to NO is used as a parameter. From this figure, it can be seen that the minimum value of the NOx concentration is around 800 to 1000 ° C. in the ambient temperature. For this reason, the combustion exhaust gas or the dryer exhaust gas according to the present invention contains NH ₃
, It is necessary to properly distribute the supply of the two-stage combustion gas to each stage.

FIG. 5 shows the relationship between the air ratio and the adiabatic flame temperature. From this figure, the adiabatic flame temperature becomes maximum at an air ratio of around 1.0, that is, at the theoretical amount of air, and decreases even if it is large or small. In order to adopt a two-stage combustion method (air ratio less than 1.0) and maintain the temperature in the melting furnace at or above the ash melting temperature, the air ratio in the melting furnace is 0.7 or more and less than 1.0 , Desirably, should be controlled to 0.8 or more and 0.95 or less.

FIG. 6 shows a comparison of the NOx concentration between the case where the air ratio in the melting furnace is less than 1.0 (in the present invention) and the case where the air ratio in the melting furnace is 1.0 or more (prior art) in the test furnace. As a result, it was found that when the inside of the melting furnace was set to a reducing atmosphere (air ratio less than 1.0), it was reduced by about half as compared to an oxidizing atmosphere (air ratio of 1.0 or more). Note that the values of the present invention shown in FIG. 6 are experimental results when a dryer exhaust gas was used as the complete combustion gas.

As described above, the embodiments of the present invention include those having the following configuration, function, and operation as summarized below.

The first feature of the present embodiment is that the combustion exhaust gas or the dryer exhaust gas is used as the two-stage combustion air and supplied to the secondary combustion chamber downstream of the melting furnace in two or more stages. It is. When the flue gas or the dryer exhaust gas is used as the two-stage combustion gas, the O ₂ concentration in the flue gas is about 10%, and the O ₂ concentration in the dryer exhaust gas is generally 15%.
Since it is before and after (10 to 19%), the combustion reaction temperature is lowered as compared with the case where pure air (O ₂ concentration is 21% by volume percentage and 23% by weight percentage) as air in the atmosphere is used. Therefore, generation of thermal NOx can be suppressed. Further, by supplying the combustion exhaust gas or the dryer exhaust gas in multiple stages, the mixing of the combustion gas from the melting furnace with the combustion exhaust gas or the dryer exhaust gas in the secondary combustion chamber is promoted, and unburned components such as CO Slip-through can be prevented.

The second feature of this embodiment is that the most upstream two-stage combustion gas is blown into the secondary combustion chamber from a plurality of slag screens provided at the outlet of the melting furnace. And
As a method of supplying the gas for the two-stage combustion on the most upstream side, a combustion exhaust gas or a dryer exhaust gas is supplied to a plurality of slag screens, which are pipes inserted into a secondary combustion chamber at a melting furnace outlet, and the exhaust gas is supplied to a plurality of holes. , The mixing with the combustion gas from the melting furnace is promoted, and the unburned components such as CO can be reduced. In addition, when the gas flow from the holes is blown out perpendicularly to the combustion gas from the melting furnace, mixing is further promoted, and the piping (slag screen) installed in a high temperature field is improved.
Exhaust gas (temperature is usually 150 ° C. or less) from the pipes adjacent to the surface of
° C or less), and slag screen burning can be avoided.

The third feature of this embodiment is that ammonia (hereinafter referred to as NH ₃ ) is added to the combustion exhaust gas or the dryer exhaust gas, and the amount of the two-stage combustion gas supplied to each stage is adjusted by a damper or the like. It is to control. Then, by adding NH ₃ to the combustion exhaust gas or the dryer exhaust gas, non-catalytic denitration by NH ₃ occurs, and the NOx reduction reaction is promoted.
However, the non-catalytic denitration reaction with NH ₃ depends on the temperature of the atmosphere, and is most effective at 800 to 1000 ° C. For this reason, in order to supply the combustion exhaust gas containing NH ₃ or the dryer exhaust gas to the optimum position, it is necessary to control the amount of the two-stage combustion gas supplied to each stage with a damper or the like.

The fourth feature of this embodiment is that, even when the inside of the melting furnace is set to a reducing atmosphere, the air ratio in the melting furnace is set to 0.7 or more and less than 1.0, and the temperature in the melting furnace is set to ash melting. Do not drop below the temperature. When the melting furnace is set to a reducing atmosphere by using the two-stage combustion method, the temperature in the melting furnace is reduced when the air ratio is excessively reduced due to the relationship with the adiabatic flame temperature. It is possible that:
Therefore, it is necessary to control the air ratio in the melting furnace to 0.7 or more and less than 1.0, preferably 0.8 or more and 0.95 or less.

[0034]

The effects of the present invention are as follows.

(1) Since the amount of gas supplied to the melting furnace can be reduced, the volume of the melting furnace can be reduced. For this reason, it is possible to reduce costs for manufacturing the melting furnace. The volume reduction rate corresponds to the air ratio, and is about 1/4 at an air ratio of 0.9.

(2) When an auxiliary burner using kerosene or the like as a fuel is used in the melting furnace, the inside of the melting furnace has a reducing atmosphere, so that thermal NOx can be reduced from the auxiliary burner. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a low NOx combustion device in a waste gasification and melting facility according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a low NOx combustion device in a waste gasification and melting facility according to a second embodiment of the present invention.

FIG. 3 is a view showing a state of blowing out the combustion gas when a slag screen is used as a two-stage combustion gas supply port in the present embodiment.

FIG. 4 is a graph showing the effect of non-catalytic NOx removal of NOx by NH ₃ in the present embodiment.

FIG. 5 is a graph showing the relationship between the air ratio and the adiabatic flame temperature.

FIG. 6 is a graph comparing the NOx concentration according to the present invention with the NOx concentration according to the prior art.

FIG. 7 is a system configuration diagram of a waste gasification and melting facility according to a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Dust supply hopper 3 Dryer 5 Seal mechanism 6 Gasification furnace 8 Fluidized bed 10 Melting furnace 11 Combustion air piping 12 Slag discharge pipe 12-1 Burning auxiliary burner 13 Slag screen 14 Secondary combustion chamber 16 Air heater 18 Induction blower 19 Chimney 20 Induction blower for dryer 21 Dryer exhaust gas pipe 22 NH ₃ supply pipe 23 Two-stage combustion gas damper 24 Push-in ventilator 29 Recirculation blower 30 Combustion exhaust gas recirculation pipe

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F23G 5/30 ZAB F23G 5/30 ZABD ZABK 5/50 ZAB 5/50 ZABF (72) Inventor Shuji Mori Hiroshima Hiroshima 6-9, Takara-cho, Kure-shi, Japan F-term in Babcock Hitachi, Ltd. Kure Plant (reference) 3K061 AA11 AA23 AB02 AB03 AC01 AC19 BA04 BA07 BA10 DA05 EA01 EB06 EB11 EB15 EB16 FA02 FA10 FA21 FA25 3K062 AA11 AA23 AB02 AB03 AC01 AC19 BA03 BB DA25 DB17 3K065 AA11 AA23 AB02 AB03 AC01 BA04 BA07 BA10 HA02 HA03 JA05 JA13 JA15 3K078 AA04 AA07 AA10 BA03 BA22 BA24 CA02 CA06 CA13 CA21 CA22 CA24

Claims (8)

[Claims] 1. A dryer for drying refuse received from an upstream side, a gasifier for partially oxidizing and burning refuse supplied from the dryer at a low air ratio, and an unburned component generated in the gasifier. A melting furnace for burning and melting the solid content (char);
A waste gasification and melting facility comprising a secondary combustion chamber that completely burns unburned components from the melting furnace, and an exhaust gas treatment facility that treats exhaust gas from the secondary combustion chamber, A reducing atmosphere (less than the theoretical air ratio), and supplying the combustion exhaust gas after the exhaust gas treatment as a complete combustion gas to the secondary combustion chamber downstream of the melting furnace in multiple stages. Low NO in melting equipment
x combustion device. 2. A dryer for drying refuse received from an upstream side, a gasifier for partially oxidizing and burning refuse supplied from the dryer at a low air ratio, and an unburned component generated in the gasifier. A melting furnace for burning and melting the solid content (char);
A waste gasification and melting facility comprising a secondary combustion chamber that completely burns unburned components from the melting furnace, and an exhaust gas treatment facility that treats exhaust gas from the secondary combustion chamber, In a reducing atmosphere (less than the theoretical air ratio), and drying exhaust gas discharged from the dryer as a complete combustion gas is supplied in multiple stages to the secondary combustion chamber downstream of the melting furnace. Low NOx combustion equipment in waste gasification and melting equipment. 3. The low NOx combustion apparatus in the waste gasification and melting facility according to claim 1, wherein the complete combustion gas supplied to the secondary combustion chamber in multiple stages is:
A low NOx combustion apparatus in a refuse gasification and melting facility, wherein a slag screen provided at the melting furnace outlet is used as a gas supply facility on the most upstream side. 4. The low NOx combustion apparatus in the refuse gasification and melting facility according to claim 1, wherein ammonia is added to the combustion exhaust gas or the dryer exhaust gas.
x combustion device. 5. The low NOx combustion apparatus in the waste gasification and melting equipment according to claim 1, wherein the amount of gas supplied to each stage of the complete combustion gas supplied to the secondary combustion chamber in multiple stages is controlled. A low NOx combustion apparatus in a refuse gasification and melting facility, comprising control means. 6. A low NOx combustion apparatus in a refuse gasification and melting facility according to claim 3, wherein a gas flow of exhaust gas ejected from said slag screen is orthogonal to a gas flow from a melting furnace. Low NOx combustion equipment in the waste gasification and melting facility. 7. The low NOx combustion apparatus in the waste gasification and melting facility according to claim 1, wherein an air ratio in the melting furnace is set to 0.7 or more and less than 1.0. Low NOx combustion equipment in chemical melting equipment. 8. A dryer for drying refuse received from an upstream side, a gasifier for partially oxidizing and burning refuse supplied from the dryer at a low air ratio, and an unburned component generated in the gasifier. A melting furnace for burning and melting the solid content (char);
Low NOx in a refuse gasification / melting facility comprising: a secondary combustion chamber for completely burning unburned components from the melting furnace; and an exhaust gas treatment facility for treating exhaust gas from the secondary combustion chamber.
A combustion method, wherein the air ratio in the melting furnace is in a range of 0.7 or more and less than 1.0, and the fuel is burnt and melted. A low NOx combustion method in a refuse gasification and melting facility, wherein the exhaust gas of the dryer discharged from the dryer is supplied in multiple stages to complete combustion.