JP3026671B2 - Exhaust gas combustion furnace and combustion control method for exhaust gas combustion furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas furnace for burning carbon monoxide contained in exhaust gas and a method for controlling the combustion of the exhaust gas furnace.

[0002]

2. Description of the Related Art As an example of such an exhaust gas combustion furnace,
The following description will be made by taking a cupola exhaust gas combustion furnace provided on the exhaust side of the cupola as an example. Cupola is a melting furnace that obtains molten cast iron by melting coke by burning coke.This exhaust gas contains a large amount of carbon monoxide gas, and in general, an exhaust gas combustion furnace is installed. It is processed. Then, heat is recovered from the combustion exhaust gas discharged from the exhaust gas combustion furnace by an air preheater or the like, and is separately used. Now, a conventional exhaust gas combustion furnace is provided with a combustion zone and a dilution cooling zone. Explaining the treatment state in each zone, in the combustion zone, the excess air ratio is reduced, combustion is performed at a high temperature (about 1,100 ° C.) close to the theoretical combustion temperature, and the residence time in this zone is increased to increase the carbon monoxide gas. Was trying to complete combustion. On the other hand, in the dilution cooling zone, dilution air was introduced to lower the temperature of the exhaust gas to about 800 ° C., which is the heat-resistant temperature of the subsequent heat recovery device such as an air preheater.

[0003]

However, today,
NOx generated by the combustion treatment is regarded as a major problem from the viewpoint of air pollution prevention and the like, and reduction of NOx generated from such an exhaust gas combustion furnace is a major problem. Here, in the exhaust gas combustion furnace having the above-described configuration, in the dilution cooling zone, since the exhaust gas temperature has decreased to 800 ° C.,
Although there was almost no generation of Ox, the generation of high levels of NOx could not be avoided in the combustion zone due to the combustion state such as a high processing temperature and the residence time. Accordingly, an object of the present invention is to provide an exhaust gas combustion furnace capable of suppressing NOx contained in exhaust gas discharged from the exhaust gas combustion furnace to a low level, and a method of controlling the combustion of the exhaust gas combustion furnace.

[0004]

In order to achieve the above object, the exhaust gas combustion furnace according to the present invention is characterized by a primary combustion chamber in which exhaust gas to be treated flows in and a primary combustion process is performed, and a primary combustion chamber for treating the primary combustion chamber. And a secondary combustion chamber in which the exhaust gas is subjected to a secondary combustion process.In the connection passage where the exhaust gas flows from the primary combustion chamber to the secondary combustion chamber, heat radiation from the primary combustion chamber to the secondary combustion chamber is provided. Secondary combustion air supply means for preventing and providing a radiant heat reflecting surface for reflecting radiant heat to the primary combustion chamber, providing a throttle portion for narrowing a flow path cross-sectional area of the connection flow path, and supplying secondary combustion air to the connection flow path Is provided in the throttle section. Further, the characteristic means of the combustion control method for an exhaust gas combustion furnace according to the present invention is characterized in that, in the combustion control of the above-described exhaust gas combustion furnace, the amount of primary combustion air supplied to the primary combustion chamber is reduced by the theoretical amount of carbon monoxide contained in the exhaust gas. The primary combustion process is performed while controlling the temperature in the primary combustion chamber at around 900 ° C. by controlling the combustion air amount to 60 to 80% of the amount of combustion air, and the theoretical combustion air amount with respect to the remaining carbon monoxide in the secondary combustion chamber. The secondary combustion air is supplied to perform secondary combustion processing on the remaining carbon monoxide. Then, the operation and effect thereof will be described below.

[0005]

In this exhaust gas combustion furnace, a two-stage combustion system having primary and secondary combustion chambers is employed, and a radiant heat reflecting surface and a throttle portion are provided to reduce NOx. That is,
The effect of the heat radiation prevention surface prevents heat radiation from the primary combustion chamber and reflects the radiant heat to maintain the combustion temperature in the room, improve the stability of combustion in the primary combustion chamber, and complete the combustion And the residence time can be shortened. Therefore, desired processing can be performed even if this chamber is kept at a lower temperature than before. Further, by providing the secondary combustion air supply means in the throttle section, secondary combustion air is supplied to the connection flow path having a reduced cross-sectional area, so that the exhaust gas and the secondary combustion air are Are sufficiently mixed, and also in the combustion in the secondary combustion chamber, the completion of the combustion is promoted and the residence time is shortened. Therefore, the effect of reducing NOx can be obtained only from these factors.

Further, when this exhaust gas combustion furnace is used, the total amount of carbon monoxide in the primary combustion chamber is 60 to 80%.
% Combustion at about 900 ° C. and the remaining carbon monoxide combustion in the secondary combustion chamber, the primary combustion chamber becomes a reducing atmosphere and operates at a lower temperature than before. It will be. Therefore, from the configuration of the exhaust gas combustion furnace, further by appropriate selection of the combustion method, reduction of excess air ratio, selection of low combustion temperature,
Since it becomes easy to satisfy the conditions effective for NOx reduction, such as a reduction in the residence time of the combustion gas in a high temperature range, a low NOx operation can be further achieved.

[0007]

Accordingly, an exhaust gas combustion furnace capable of suppressing NOx contained in exhaust gas discharged from an exhaust gas combustion furnace to a low level and a combustion control method for the exhaust gas combustion furnace can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exhaust gas combustion furnace 1 of the present application and a combustion control method thereof will be described with reference to the drawings. FIG. 3 shows a configuration of a cupola exhaust gas system including the exhaust gas combustion furnace 1. That is, as shown, the cupola exhaust gas system includes a cupola 3, a cyclone 4, an exhaust gas combustion furnace 1, an air preheater 5, a waste heat boiler 6, a gas cooler 7, a bag filter 8, a dust collecting fan 9, a chimney 10 And the like.

Next, the structure and operation of the exhaust gas combustion furnace 1 will be described. FIG. 1 is a longitudinal sectional view of the exhaust gas combustion furnace 1, and FIG. 2 is a transverse sectional view of a throttle unit 11 provided in the furnace. First, the general configuration and capacity of the exhaust gas combustion furnace 1 will be described in a bulleted manner. Exhaust gas condition: Exhaust gas amount 19,000 Nm ³ / H Exhaust gas temperature 500 ° C Carbon monoxide concentration 16% Combustion method: Primary combustion chamber 12 and secondary combustion chamber 1 in combustion zone
Primary combustion requirement Combustion treatment of 70-80% of the amount of carbon monoxide contained in exhaust gas Combustion temperature 900 ± 20 ° C Secondary combustion requirement Combustion treatment of complete combustion of residual carbon monoxide Combustion temperature 870 ± 20 ° C Dilution requirement After the secondary combustion, dilute air is charged and the combustion furnace exit temperature is 7
80 ± 20 ° C. Attached burner: Main body pilot burner 14 (20 × 10 ⁴ Kcal / H) Constant ignition Auxiliary burner (not shown) (200 × 10 ⁴ Kcal / H) For heating the furnace body at startup

Next, the configuration of the exhaust gas combustion furnace 1 will be described in detail. The combustion furnace 1 is configured as an empty tower having a steel plate shell lined with brick or castable refractory material. As shown in the figure, a primary combustion chamber is sequentially arranged from an exhaust gas inlet 15 into which exhaust gas from the cupola 3 flows. 12, a connection flow path 16, a secondary combustion chamber 13, and a dilution chamber 17 are provided. The primary combustion chamber 12 is provided with a primary combustion air blowing nozzle 18 as primary combustion air supply means for supplying primary combustion air to this portion, and also includes a main body pilot burner 14 and an auxiliary burner (not shown). Is provided.

A throttle portion 11 is provided between the primary combustion chamber 12 and the secondary combustion chamber 13. Is half of the cross-sectional area of the flow passage of the primary combustion chamber 12. further,
The ring-shaped surface on the lower side of the aperture portion 11 functions as a radiation heat reflecting surface 11a. A secondary combustion air supply means for supplying secondary combustion air for secondary combustion to the secondary combustion chamber 13 through the connection flow path 16 is provided on the inner peripheral surface 11b of the protrusion constituting the throttle portion 11. A secondary combustion air header 19 and a secondary combustion air blowing nozzle 20 directly connected to the header 19 are opened. Here, the secondary combustion air blowing nozzle 20 is
As shown in FIG. 2, twelve are provided in the circumferential direction, and the blowing directions are provided horizontally in the longitudinal direction of the furnace and at an inclination of 10 degrees with respect to the radial direction. By employing this configuration, the secondary combustion air is introduced in a vortex state, and good mixing is performed.

[0012] Between the secondary combustion chamber 13 and the dilution chamber 17,
A dilution air blowing nozzle 21 for supplying dilution air is provided. Further, a gas outlet 22 for sending out the exhaust gas at the top of the dilution chamber 17 in the lateral direction is provided.

The throttle height of the throttle portion 11 reflects the radiant heat to maintain the combustion temperature in the primary combustion, thereby speeding up the completion of combustion and shortening the residence time. The throttle portion 11 prevents the emission of combustion heat upward. The inner diameter of the primary combustion chamber 12 is set to D for the purpose of shortening the residence time by accelerating the completion of combustion in the secondary combustion, and achieving sufficient mixing of the exhaust gas and the combustion air by the so-called Venturi tube effect by the throttle unit 11. _1, when the inner diameter of the narrowed portion 11, ^{_{D 2 D 2 2 / D 1}} 2 ≦ 1 /
It is set to 2.

The main configuration of the exhaust gas combustion furnace 1 has been described above. The operation state and the NOx reduction state will be described below. Primary combustion state Primary combustion air is blown into cupola exhaust gas introduced from the gas inlet 15, ignited by the main body pilot burner 14, and burned in the primary combustion chamber 12. Here, the amount of carbon monoxide burned in the primary combustion is 60 to the total amount of carbon monoxide.
The primary combustion air amount is controlled to be 60 to 80% of the theoretical combustion air amount so as to be 80%. In this combustion state, since there is no excess oxygen, a reducing atmosphere is formed in the primary combustion chamber 12 by the residual carbon monoxide. The combustion temperature is about 9 which is lower than the theoretical combustion temperature of about
It is kept as low as 00 ° C. The upward heat radiation is prevented by the effect of the ring-shaped heat radiation preventing surface 11a provided in the throttle portion 11, the combustion temperature is maintained, and the stability of combustion in the primary combustion chamber 12 is enhanced. At the same time, the completion of combustion is faster, and the residence time is shorter. Due to such factors, NOx in the primary combustion is suppressed to a low level.

Secondary combustion condition After the primary combustion, secondary combustion air is blown from the secondary combustion air header 19 provided inside the throttle portion 11 and a plurality of secondary combustion air blowing nozzles 20 directly connected thereto. The remaining carbon monoxide (20 to 40% of the total carbon monoxide amount) is burned in the secondary combustion chamber 13. Here, the combustion temperature is controlled at a temperature slightly lower than the primary combustion temperature (about 900 ° C.). In the secondary combustion, where the cross-sectional area is shrunk by the throttle portion 11 and the exhaust gas flow rate is fast,
The secondary combustion air is blown from the tip of the throttle portion, and the exhaust gas and the secondary combustion air are sufficiently mixed by the so-called Venturi tube effect, and the residual carbon monoxide is completely burned. Therefore, the completion of combustion is promoted, the residence time is shortened, and the generation of NOx is suppressed.

After the combustion of the residual carbon monoxide in the secondary combustion chamber 13 is completed, dilution air is added to the dilution air in the combustion exhaust gas.
1 to lower the temperature of the exhaust gas to 800 ° C., which is the heat-resistant temperature of the heat recovery device such as the air preheater 5 that follows.
At this temperature, there is almost no generation of NOx.

The operation of the exhaust gas combustion furnace 1 will be described below. The data for each gas is shown in Table 1.

[0018]

[Table 1]

As a result, it is understood that the treatment for carbon monoxide has been sufficiently completed. Further, the effect of reducing NOx under such operating conditions will be described. The NOx generation amount in a single-stage combustion system employed in a conventional exhaust gas combustion furnace having a combustion zone and a dilution zone is 120 pp.
m (O ₂ : 0% conversion value), a two-stage combustion in which a throttle portion 11 is provided at a partition between primary combustion and secondary combustion according to the present invention, and secondary air is blown out from the tip of the throttle portion. In this method, the amount of NOx generated is about 45 ppm (O ₂ : 0%
(Converted value), which is less than half.

In the above embodiment, the exhaust gas combustion furnace 1
Is formed in a vertical shape, but this can be arbitrarily configured such as a horizontal type. Further, the secondary combustion air supply means may have a structure in which a secondary combustion air header 19 is provided outside the outer shell and only a plurality of secondary air blowing nozzles 20 directly connected to the secondary combustion air header 19 are built therein.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an exhaust gas combustion furnace.

FIG. 2 is a cross-sectional view of a throttle section.

FIG. 3 is an overall flow chart of a cupola exhaust gas treatment system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust gas combustion furnace 11 Throttle part 11a Radiation heat reflection surface 12 Primary combustion chamber 13 Secondary combustion chamber 16 Connection flow path 19 Secondary combustion air supply means 20 Secondary combustion air supply means

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Nishi 1-4-2 Nakamichi, Higashinari-ku, Osaka-shi, Osaka Inside Osaka Gas Engineering Co., Ltd. No.4-2, Osaka Gas Engineering Co., Ltd. (56) References JP-A-3-17416 (JP, A) JP-A-5-196218 (JP, A) JP-A-63-315821 (JP, A) ( 58) Field surveyed (Int.Cl. ⁷ , DB name) F23G 7/06 ZAB F23G 5/00 ZAB F23G 5/14 ZAB F23G 5/50 ZAB

Claims (3)

(57) [Claims] An exhaust gas combustion furnace for combusting carbon monoxide contained in exhaust gas, comprising: a primary combustion chamber (12) in which an exhaust gas to be treated flows in and undergoes a primary combustion process; A secondary combustion chamber (13) in which the exhaust gas treated in (12) is subjected to secondary combustion processing, and a connecting flow path () through which the exhaust gas flows from the primary combustion chamber (12) to the secondary combustion chamber (13). 16) a radiant heat reflecting surface (11) for preventing heat radiation from the primary combustion chamber (12) to the secondary combustion chamber (13) and reflecting radiant heat to the primary combustion chamber.
a) and a throttle section (11) for reducing the cross-sectional area of the connection flow path (16), and a secondary combustion air supply means (2) for supplying secondary combustion air to the connection flow path (16). 19) and (20) with the throttle unit (1)
Exhaust gas combustion furnace provided in 1). 2. The exhaust gas combustion furnace according to claim 1, wherein a cross-sectional area of the connecting flow passage is not more than half of a cross-sectional area of the primary combustion chamber. 3. The combustion control method for an exhaust gas combustion furnace (1) according to claim 1, wherein the amount of primary combustion air supplied to the primary combustion chamber (12) is reduced by the amount of carbon monoxide contained in the exhaust gas. 60 of theoretical combustion air volume
The primary combustion process is performed while maintaining the temperature in the primary combustion chamber (12) at around 900 ° C., and the remaining carbon monoxide is theoretically reduced in the secondary combustion chamber (13). A combustion control method for an exhaust gas combustion furnace, wherein secondary combustion air is supplied in an amount equal to or greater than a combustion air amount, and the remaining carbon monoxide is subjected to secondary combustion processing.