JPH09264516A - Fuel two stage supply type low nox burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sharply restrict production of NOx by limiting combustion temperature without use of a big volume of an inactive gas owing to a fact that surface temperature of a flame is lowered and hence combustion is sloughly performed by cooling the surroundings of a flame hole upon combustion in each burner. SOLUTION: A side wall 16 in a furnace is constructed as a water cooled wall, and further surroundings of flame holes 6, 7 of a primary burner 1 and a secondary burner 2 are cooled upon combustion with a burner 3. Hereby, surface temperature of a flame upon combustion of a fuel is lowered and hence the combustion is slowly done so that Combustion temperature is limited without use of a big volume of an inactive gas as in the prior art to inexpensively sharply restrict production of NOx.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-stage fuel supply type low NOx burner applied to various heating furnaces, combustion furnaces, boilers and the like.

[0002]

2. Description of the Related Art A conventional combustion furnace 30 of a two-stage fuel combustion system is shown in FIGS. That is, a burner 34 including a primary burner 32 and a secondary burner 33 is arranged on one end side of the furnace wall 31 which is laterally oriented. Wind box 35 of this burner 34
Is supplied with almost the same amount of combustion air as is required to burn the total amount of fuel supplied from the primary nozzle 36 and the secondary nozzle 37, and a portion of the total fuel is injected from the primary nozzle 36. The remaining portion is sprayed from the secondary nozzle 37, and is burned by the burner 34.

According to this method, fuel is supplied to both nozzles 36 and 37.
When dividedly supplied, the primary fuel injected from the primary nozzle 36 is the theoretical amount of air required to burn all the supplied fuel, that is, the primary combustion is at a high air ratio of 1.7 or more. The combustion temperature in the burner 32 becomes extremely low, and the generation of thermal NOx and prompt NOx is suppressed. Further, the secondary fuel injected from the secondary nozzle 37 sucks the combustion gas (primary combustion exhaust gas) having a low oxygen concentration existing around the jet flow due to the injection energy of the secondary nozzle 37, so that the secondary fuel is discharged. After the fuel is diluted, it is secondarily burned.

Due to this effect, when the temperature in the furnace is low,
The secondary combustion of the secondary burner 33 is performed slowly, the combustion temperature is lowered and the generation of thermal NOx is suppressed, and the production of prompt NOx is suppressed because the secondary fuel is diluted.

In such a combustion system, the primary nozzle
If an inert gas is mixed in advance with the fuel to be supplied to at least one of the 36 and the secondary nozzle 37, local heat generation at the boundary surface between the fuel and its surroundings will be suppressed, resulting in a slower combustion. It is possible to suppress the generation of NOx as a whole.

That is, referring to FIG. 7, the effect of suppressing NOx generation based on an experimental example will be described. The solid curve shows the conventional combustion system, and an air ratio of 1.15 using an inert gas (N ₂ gas).
Shows the effect of suppressing the generation of NOx when implemented in
At that time, the mixing ratio of the inert gas is 40% by volume with respect to the fuel. Here, the solid curve A shows the case where the inert gas is mixed in advance in all the fuels supplied to both nozzles 36 and 37, and the solid curve B shows the case where the inert gas is mixed only in the secondary nozzle 37. . The solid curve C is the case where no inert gas is mixed in any fuel.

As can be seen from the solid curve, in contrast to the solid curve C containing no inert gas, both nozzles 36 and 37 have a real curve A containing inert gas, and the secondary nozzle 37 is inert. In any case of the real curve B in which the gas is mixed, the NOx concentration is lowered and the NOx is reduced by mixing the inert gas.
Can be achieved.

[0008]

However, according to the above-mentioned method of mixing the inert gas, it is possible to expect further reduction of NOx by increasing the mixing ratio of the inert gas. When the low NOx burner is used for various heating furnaces and boilers of an actual machine, various equipments for inert gas and required power thereof are increased, which is uneconomical in cost.

That is, the combustion exhaust gas is used as the inert gas, and the combustion exhaust gas is used as the primary burner 32 or the secondary burner.
If you try to return it to 33, you will need piping equipment and a blower for that purpose.

Further, in the above-described conventional fuel two-stage combustion type combustion furnace 30, even in a boiler having a water cooling wall,
The water cooling wall extends to the tips of the nozzles 36 and 37, and there is no cooling effect near the tips of the secondary burner 33. That is, low NO
The secondary burner 33 of the x-burner originally burns the fuel in a diluted state and burns it at a low temperature to reduce NOx, but like a boiler or a heating furnace with a very high furnace load. When the furnace temperature was high, the NOx suppressing effect decreased as the furnace temperature increased.

The main cause of this is that the ignition is accelerated as the temperature becomes higher and the combustion is started before the secondary fuel is sufficiently diluted with the combustion gas, so that it is generated from the primary burner 32 and the secondary burner 33. It was found that the amount of NOx rapidly increased as the temperature increased and the NOx suppression effect decreased as the furnace temperature increased.

Therefore, an object of the present invention is to provide a two-stage fuel supply type low NOx burner which can solve the above problems.

[0013]

A means for solving the problems in the present invention is to provide a furnace main body with a primary burner and a secondary burner, and to provide a cooling device for cooling the firing port of each of these burners. When burning in the burner, the surroundings of the heating port are cooled so that the surface temperature of the flame when burning the fuel is lowered, thus the combustion is slow and without the use of large amounts of inert gas. Therefore, the combustion temperature can be suppressed and the generation of NOx can be significantly suppressed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. The two-stage fuel supply type low NOx burner according to the embodiment of the present invention is applied to various heating furnaces, combustion furnaces, boilers, etc., and FIG. 4 shows the combustion of the two-stage fuel combustion system used in this experiment. Furnace 14 is shown.

In this combustion furnace 14, the side wall of the furnace facing sideways
A heat insulating material 17 is sprinkled around the inner surface of 16 and a cooling water 18 is supplied to the outer surface of the inner wall 16 of the furnace, so that the heat insulating material is
The outside is cooled through 17 and the inner wall 16 of the furnace.

A burner 3 is provided at one end of the combustion furnace 14.
This burner 3 is composed of a primary burner 1 and a secondary burner 2 arranged around the primary burner 1, and a cooling device for cooling the combustion ports 6, 7 of the primary burner 1 and the secondary burner 2. There is.

As shown in FIGS. 1 and 2, the primary burner 1 is a disk-shaped water cooling wall 8 arranged so as to close a circular opening formed on one end side of the combustion furnace 14, and this water cooling wall 8 The large-diameter cylinder 9 that penetrates the center of the large-diameter cylinder 9, the primary nozzle 4 that partially penetrates the large-diameter cylinder 9, and the insertion portion 9a of the large-diameter cylinder 9
A first water cooling jacket 10 covering the inside and the outside, a primary supply pipe 11 for supplying the cooling water 8a into the water cooling wall 8, and a primary discharge pipe for discharging the used cooling water 8a from the water cooling wall 8.
12, a jacket supply pipe 13 for supplying the cooling water 10a to the first water cooling jacket 10, and a jacket discharge pipe 15 for discharging the used cooling water 10a from the first water cooling jacket 10. The tip opening of the first water-cooling jacket 10 serves as the above-mentioned firing port 6 of the primary burner 1.

The secondary burner 2 includes a plurality of (four in the figure) small diameter cylinders 20 arranged around the large diameter cylinder 9 and each small diameter cylinder 20.
Secondary nozzle 5 inserted into the secondary nozzle 5, a second water cooling jacket 21 arranged at the tip of the secondary nozzle 5, and a secondary supply pipe for supplying cooling water 21a to the second water cooling jacket 21.
22 and a secondary discharge pipe 23 for discharging the used cooling water 21a from the second water cooling jacket 21, and the opening of the tip of the second water cooling jacket 21 is used as the heating port 7 of the secondary burner 2. ing.

The cooling device comprises a water cooling wall 8, a first water cooling jacket 10 and a second water cooling jacket 21.
A wind box 25 is provided in the opening, and the wind box 25 is supplied with an air amount substantially the same as that required to burn all the fuel supplied from the primary nozzles 4 and the secondary nozzles 5. Further, a part of the total fuel is injected from the primary nozzle 4, and the remaining part is injected from the secondary nozzle 5, so that the burner 3
Is burned by.

The operation of the above-described embodiment will be described below. In the wind box 25, the amount of fuel supplied from the primary nozzles 4 and the secondary nozzles 5 is almost the same as the amount required for combustion. The combustion air is supplied, and further, a part of the total fuel is injected from the primary nozzle 4 and the remaining part is injected from the secondary nozzle 5, and is burned by the burner 3.

When the burner 3 is burned in this way, the water supply wall 11, the water supply wall 13, the water supply wall 13 for the jacket, the water supply wall 8 for the jacket, the water supply wall 8 for the first jacket, and the water supply wall for the first water jacket respectively.
10. Cooling water 8a, 10a, 21a is supplied to the second water cooling jacket 21 to cool the surroundings of the heating ports 6, 7.

In this way, when burning by the burner 3,
By cooling the surroundings of the firing ports 6, 7 of the primary nozzle 4 and the secondary nozzle 5 with the cooling water 8a, 10a, 21a, it is possible to suppress the combustion temperature and suppress the generation of NOx.

FIG. 3 shows a graph obtained by the experiment. In the present experiment using the combustion furnace 14 in the above-described embodiment, the relationship between the area of the water cooling wall and the NOx generation amount was examined, and the effect of water cooling, that is, the influence of the furnace temperature on NOx generation was examined in advance. In the figure, the solid line of X is a curve showing the temperature in the furnace, and the solid line of Y is a curve showing the NOx concentration.

As a result, it was found that the lower the area ratio of the water cooling wall, the higher the temperature inside the furnace, and the NOx concentration increases accordingly. The broken line of Z is a curve showing the NOx concentration according to the embodiment of the present invention. Compared to the case where the inner wall 16 of the furnace is simply a water cooling wall, the surroundings of the combustion ports 6 and 7 are cooled and burned. As a result, it can be seen that the NOx concentration is remarkably reduced.

As described above, according to the embodiment of the present invention,
In addition to making the inner wall 16 of the furnace a water-cooling wall, at the time of combustion by the burner 3, by cooling the surroundings of the firing ports 6, 7 of the primary burner 1 and the secondary burner 2 with cooling water 8a, 10a, 21a, Can lower the surface temperature of the flame when it burns, and therefore, the combustion is performed slowly, so that it is possible to use the combustion exhaust gas without using a large amount of inert gas as in the conventional case and to use the combustion exhaust gas with the primary burner 1 or the secondary burner. Even if it is an inexpensive and simple device, the combustion temperature can be suppressed and NO
It is possible to significantly suppress the generation of x.

[0026]

As is apparent from the above description, the present invention is provided with the cooling device for cooling the burner ports of the primary burner and the secondary burner installed in the furnace body. Since it can lower the surface temperature of the combustion chamber and therefore burns slowly, there is no need to use a large amount of inert gas as in the past and there is no need to install equipment to return the combustion exhaust gas to the primary burner or secondary burner. Even with a simple and inexpensive device, the combustion temperature can be suppressed and the generation of NOx can be significantly suppressed.

[Brief description of drawings]

FIG. 1 is an overall vertical sectional view showing an embodiment of the present invention.

FIG. 2 is a front view of the same.

FIG. 3 is a graph showing a change in NOx concentration.

FIG. 4 is a schematic vertical sectional view of a combustion furnace used in the same experiment.

FIG. 5 is a vertical sectional view showing a conventional two-stage fuel supply type low NOx burner.

FIG. 6 is an enlarged vertical sectional view of the same.

FIG. 7 is a graph showing a NOx generation suppressing effect.

[Explanation of symbols]

 1 Primary Burner 2 Secondary Burner 3 Burner 4 Primary Nozzle 5 Secondary Nozzle 6 Firing Port 7 Firing Port 8 Water Cooling Wall 10 First Water Cooling Jacket 14 Combustion Furnace 21 Second Water Cooling Jacket

Front page continued (72) Inventor Kazunori Nakamura 5-3-28 Nishikujo, Konohana-ku, Osaka City, Osaka Prefecture Hitachi Shipbuilding Co., Ltd. (72) Inventor Katsuhiko Yamazaki 5-3-28 Nishijojo, Konohana-ku, Osaka Issue Hitachi Shipbuilding Co., Ltd.

Claims (1)

[Claims] 1. A two-stage fuel supply type low-N type fuel supply system, comprising a primary burner and a secondary burner in a furnace body, and a cooling device for cooling the firing port of each burner.
Ox burner.