JPS58182005A - Combustion method for low nox - Google Patents

Abstract

PURPOSE:To improve a heat efficiency and besides to decrease a quantity of NOx to be exhausted, by reducing NOx by means of a reducing intermediate product in a first flame. CONSTITUTION:In a reducing burner 1, a combustion is conducted in an air-fuel ratio of 1 or less, preferably 0.4 or not more than 0.4, to form a first flame F1, and a reducing intermediate product, a radical, such as CO, or NH2, CN and the like, is produced in the first flame F1. Meanwhile, a primary burner 2 is annularly disposed around the reducing burner 1, and a second flame F2 is formed in an air-fuel ratio of about 1 or more in a manner to surround the first flame F1, which results in sharing a heat load of a combustion device. A plurality of inactive gas jet nozzles 13 are located between a reduction burner mounting part and a primary burner mounting part, the jetting of inactive gas through the nozzle 13 forms a layer of an inactive gas stream between the first and the second flame, and it is effective when this method prevents the two flames F1 and F2 from being mixed together at a stage where the intermediate product is in an insufficient produdcing state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion method that reduces the amount of nitrogen oxide emissions, and more particularly to a combustion method that can maintain the amount of nitrogen oxide emissions at a low rate and increase thermal efficiency.

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 the amount of nitrogen oxides emitted.

Conventional NOx reduction combustion methods include: (a) Exhaust gas recirculation method in which a portion of exhaust gas is mixed with combustion air to lower oxygen partial pressure and combustion humidity.

(b) A two-stage combustion method in which 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 amount of air is supplied in the second and subsequent stages.

(c) A method of lowering the combustion temperature by cooling the combustion air.

Various methods have been proposed, but they still 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 these methods.

Recently, as part of the bias combustion method, reducing intermediate products generated in burners with extremely low air ratios have been
A method for reducing and removing Ox during the combustion stage, that is, an in-furnace denitrification method, has been developed and is attracting attention.

Figure 1 shows this combustion method. In the figure, a main burner 2 is arranged around a flame holding plate 3 at the center of a burner throat 4 formed at the center of a front wall 5 of the furnace. Furthermore, a plurality of reduction burners 1 are arranged around this main burner installation part so as to surround this main burner installation part. In the main burner a, the air-fuel ratio is set to about 1 or more, and a second flame (main burner flame) F2 is formed which mainly receives the heat load. On the other hand, in the surrounding reducing burners, the air-fuel ratio is extremely reduced, and a first flame (reducing burner flame) F is formed so as to surround the second flame F2.

As a result, NOx in the second flame is reduced to harmless N by the reducing intermediate product formed in the first flame.

When the combustion apparatus shown in Fig. 1 is used as a boiler, the second flame that receives the heat load is located in the center of the furnace, and this flame F
A low-temperature first flame F is located between the furnace wall surface 10 and the furnace wall surface 10. Since most of the heat transfer within the furnace occurs through the wall surface 1o, the presence of the low temperature first flame between the high temperature second flame F2 and the wall surface 1o will reduce heat transfer efficiency.

An object of the present invention is to provide a low NOx combustion method that solves the above-mentioned problems, has high thermal efficiency, and can reduce the amount of NOx emissions.

In short, this invention improves thermal efficiency by forming a high-temperature second flame around a low-temperature first flame that burns in a reducing atmosphere. Generated well and a considerable amount of NO in the second flame
This is a low NOx combustion method in which a layer of inert gas is formed between the first flame and the second flame so that both flames mix when x occurs.

Embodiments of the present invention will be described below with reference to the drawings.

In FIGS. 2 and 3, reduction burners are arranged in an annular manner around a flame holding plate 3 at the center of a burner opening 4 formed at the center of the front wall 5 of the furnace. In this reducing burner, combustion is carried out at an air-fuel ratio of 1 or less, preferably 0.4 or less, and a first flame F is formed. a
Generates radicals such as O, NH2, and ON.

On the other hand, a main burner 2 is arranged in an annular manner around the reduction burner, and the air-fuel ratio is approximately 1 or more, and a second flame F2 is formed so as to surround the first flame back, reducing the heat load of the combustion device. bear. In this case, since heat is transferred to the horizontal medium to be heated through the wall surface 10 of the combustion device, the heat transfer efficiency is increased in the method of the present invention in which a high temperature second flame is formed near the wall surface 10. Note that in this case, a certain amount of time is required until the reducing intermediate product is produced in the first flame F.

If the mixture is mixed with the second flame too quickly, the amount of reducing intermediate products produced will be insufficient, resulting in a decrease in the NOx reduction rate.

For this reason, a plurality of inert gas injection nozzles 13 are arranged between the reduction burner installation part and the main burner installation part, and the nozzles 13
A layer of inert gas flow is formed between the first flame and the second flame by injecting inert gas from the flame, and the two flames F and F mix at a stage when intermediate products are not sufficiently produced. It is effective to prevent this. Moreover, the purpose can be sufficiently achieved by recirculating and using the exhaust gas discharged from the combustion apparatus as the inert gas.

By carrying out the present invention, thermal efficiency can be increased, and NOx reduction efficiency can be made the same as or higher than that of the conventional technology.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a combustion device showing a conventional low NOx combustion method, FIG. 2 is a sectional view of a combustion device showing an embodiment of the present invention, and FIG. 3 is a front view of FIG. 2. 1... Reduction burner 2... Main burner 13... Inert gas injection nozzle F... First flame (7)

Claims (1)

[Claims] 1. A second flame surrounding a first flame burning in a reducing atmosphere.
A flame is formed and the reducing intermediates in the first flame generate N
A low NOx combustion method characterized by OX t-reduction. 2. The low NOx combustion method according to claim 1, characterized in that a layer of inert gas flow is formed between the first flame and the second flame. 3. The low NOx combustion method according to claim 2, characterized in that exhaust gas from a combustion device is recirculated and used as the inert gas. 4. The first flame is formed by one or more reduction burners located approximately at the center of the combustion burner device, and the second flame is formed by a plurality of main burners located in an annular shape surrounding these reduction burners. A low NOx combustion method according to claim 1, characterized in that: 5. The low NOx combustion method according to claim 4, wherein a plurality of 5° inert gas injection nozzles are arranged in an annular shape surrounding the reduction burner and located inside the ring of the main burner.