JPH0116885Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a combustion device that reduces nitrogen oxide emissions.

Nitrogen oxides (hereinafter abbreviated as "NOx") are one of the air pollutants, and various combustion methods and combustion devices have been proposed and put into practical use to reduce their emissions.

Conventional NOx reduction combustion methods include: (a) Exhaust gas recirculation method, which mixes a portion of exhaust gas with combustion air to lower oxygen partial pressure and lower combustion temperature.

(b) A two-stage combustion method in which the combustion air is divided into two or more stages, the air supply amount in the first stage is less than the theoretical air amount, and the insufficient air is supplied in the second stage and thereafter; ) Various methods have been proposed, such as lowering the combustion temperature by lowering the temperature of the combustion air, but all of them have problems such as a significant decrease in thermal efficiency and unstable combustion. The reality is that it is difficult to further significantly increase the NOx reduction rate using only this method.

Recently, as a bias combustion method, an in-furnace denitrification method has been developed and is attracting attention, in which NOx is reduced and removed during the combustion stage using reducing intermediate products generated in a burner with an extremely low air-fuel ratio.

This combustion method mainly reduces NOx generated in the main burner, which is responsible for the heat load, using reducing intermediate products generated from the reduction burner, which performs combustion at an extremely low air-fuel ratio. There are also problems such as combustion becomes unstable and a large amount of unburned matter is generated.

Furthermore, if the reducing burner flame and the main burner flame come into contact too quickly, the air-fuel ratio of the burner flame will increase due to the combustion air of the main burner, turning it into a "main burner flame," making it impossible to reduce NOx. Not only this, but also the amount of NOx generated itself increases. In other words, in this method, it is necessary to control the air-fuel ratio of the burner flame in which the intermediate product is to be produced as accurately as possible, and to separate the two flames until the reducing intermediate product is produced. It is important to prevent "flaming".

The purpose of this invention is to provide a combustion device configured in view of the above-mentioned needs. Specifically, it is possible to efficiently generate intermediate products in the reduction burner, and to improve the production of intermediate products in the main burner flame after the intermediate products have been generated. An object of the present invention is to provide a combustion device configured to achieve good mixing with a reducing burner flame.

In short, the idea is to arrange an air supply cylinder and an inert gas supply cylinder whose supply amount is controlled via a valve to the reduction burner arranged around the main burner, and to reduce part of the total length of the reduction burner flame. The surrounding area is covered with inert gas, the air-fuel ratio is controlled without being affected by the amount of oxygen present in the furnace, and reducing intermediate products are generated, and after the intermediate products are generated, the main burner is This is a combustion device configured to reduce NOx in the main burner flame into a gas phase by mixing it with the flame.

Examples of this invention will be described below based on the drawings.

1 and 2, a flame holding plate 3 is arranged at the center of the burner throat 4 of the front wall 5 of the furnace, and a plurality of main burners 1 (not shown) are arranged around this flame holding plate 3. In the case of , 4 pieces) are arranged.
8 is a manifold that supplies fuel 11 (for example, natural gas) to each burner. Since the combustion of gas is limited by the combustion capacity of a single burner tube, the number of main burners corresponding to the maximum load is provided as shown in the figure. 2
are reduction burners arranged around the main burner 1. An air supply cylinder 20 is provided around the reduction burner 2 so that the central axis of the burner 2 and this axis are the same, and an inert gas supply cylinder is provided at the end of the air supply cylinder 20 on the furnace side. 21
are arranged on the same axis. Reference numeral 22 denotes an air supply pipe for supplying the combustion air 10 to each air supply cylinder 20, 23 indicates a valve provided in each air supply pipe 22, 24 indicates an inert gas supply pipe, and 25 indicates an inert gas supply pipe in the same pipe. It is a valve installed.

In this combustion apparatus, combustion air 10 that has flowed into the wind box 7 is given a swirling force by the air register 6, and is injected from the throat 4 as combustion air for the main burner 1 to form the main burner flame _F1 . In this case, the air-fuel ratio in the main burner 1 is approximately 1.4-1.5.

On the other hand, fuel 12 is supplied to the reduction burner 2 via a manifold 9, and an air supply pipe 2
Combustion air 10 is supplied via 2. In this case, the air-fuel ratio of the reduction burner is about 0.4 or less, and in some cases, the valve 23 is fully closed to supply no air at all. An example in which a fixed amount of air is supplied to the burner 2 will be described below. F in the diagram
is the reducing burner flame formed by such a low air-fuel ratio. On the other hand, an inert gas G, for example, a fuel gas 12, is supplied from the inert gas supply cylinder 21, the amount of which is controlled by a valve. This inert gas G is injected into the furnace so as to surround each reducing burner flame _F2 . As a result, the entire length of the reducing burner flame F is covered with the inert gas G as shown by the dotted line in FIG. 2, and contact with the combustion air supplied from the throat 4 for the main burner 1 is cut off. Ru.
That is, by covering the flame F ₂ with the inert gas G, the flame F ₂ burns almost exclusively with the air supplied from the air supply tube 20 . Therefore, the air-fuel ratio of the reduction burner 2 depends on the supply amount of the fuel 12 and the valve 23.
Almost complete control can be achieved by adjusting the supply of combustion air 10 by adjusting the amount of combustion air 10 . Under such control, the combustion in the reduction burner 2 is performed by extremely reducing the air-fuel ratio or by setting the air-fuel ratio to 0, so the combustion is slow and the intermediate production of CN, NH, etc. used for reducing NOx is reduced. Objects do not occur upstream of the flame. Since the region where this intermediate product is produced is covered with the inert gas G, there is no risk of "main burner flame formation" due to contact with the main burner flame _F1 .

On the other hand, since the flame temperature of the main burner flame F ₁ is higher on the downstream side, NOx is more likely to be generated on this downstream side. Therefore, the main burner flame F ₁ and the reduction burner flame F ₂ are respectively located on the downstream side of the flame. The NOx reduction efficiency is higher when the mixture is mixed at the location where NOx is likely to be generated, the so-called burnout location. In other words, the inert gas G supplied from the inert gas supply cylinder 21 covers the reducing burner flame F2 only for the flame length in which reducing intermediate products are to be produced, and after that, the inert gas G is used to inject energy into the reducing burner flame _F2. The supply amount of the inert gas G is adjusted by the valve 25 so that the two flames are actively mixed. came into contact with reducing intermediates
NOx is reduced to _N2 in the gas phase to achieve low NOx reduction.

In other words, the O ₂ surrounding the main burner is not consumed by the reduction burner, and the intermediate products generated in the reduction burner are wrapped in inert gas G and mixed in at the burnout point of the main burner, thereby achieving optimal NOx removal. It is something that makes you do. To achieve this, the ejection speed of the inert gas is changed in response to the distance of the flame burnout position from the burner nozzle being expanded or contracted depending on the load, so that the reducing components can safely reach the flame burnout position. The amount of gas supplied is controlled by a valve.

By implementing this idea, the part of the reducing burner flame that should generate reducing intermediate products is almost completely covered with inert gas, making it possible to accurately control the air-fuel ratio of the reducing burner flame and reduce NOx. It is possible to generate just the right amount of intermediate products required for gas phase reduction.

[Brief explanation of the drawing]

FIG. 1 is a front view of a combustion device according to this invention, and FIG. 2 is a sectional view taken along line A--A in FIG. 1. 1... Main burner, 2... Reduction burner, 10...
Combustion air, 20...Air supply tube, 21...Inert gas supply tube, _F1 ...Main burner flame, _F2 ...Reduction burner flame, G...Inert gas.

Claims (1)

[Scope of utility model registration request] In a device in which a reducing burner is arranged near the main burner and nitrogen oxides generated in the main burner are reduced with a reducing intermediate product generated in the reducing burner, a plurality of main burners with an air ratio of 1 or more are arranged in a first A plurality of reduction burners are arranged on a virtual circumference of the first virtual circle, and a plurality of reduction burners are arranged on a second virtual circumference coaxially surrounding the first virtual circle, and each reduction burner is connected to the air surrounding the respective reduction burner. An inert gas supply cylinder surrounds this air supply cylinder and the supply amount is adjusted via a valve.
NOx combustion equipment.