JPH0350407A - Extremely low nox combustion method - Google Patents

Abstract

PURPOSE:To reduce causes of regeneration of NOx by mixing an alcoholic oxygen-containing fuel into air at an air port, thereby adding a function of positively decomposing by-produced nitrogen-containing compounds in an upper space of a burner. CONSTITUTION:In a boiler device, an incomplete combustion condition exists in a burner zone on the lower side of a boiler. Even if combustion air in only charged in a multistep manner, under this condition, a large quantity of NOx is regenerated because the mixing of the combustion air takes place through diffusion. On the other hand, when a fluid jet from a lower after air port 31, which has an oxygen partial pressure controlled by an exhaust gas from a recirculating gas system 300 and a stoichiometric oxygen ratio restricted to or below 1 by mixing an alcohol and a combustion gas from an alcohol mixing system 200, is mixed with a combustion gas from an upper burner zone, nitrogen-containing compounds such as NH3 and HCN are decomposed easily by the oxygen contained in the alcohol, so that conversion of these compounds to NO is suppressed to a low level. Thus, causes of regeneration of NOx at the final stage, namely, in a complete combustion region in the vicinity an upper after air port 32 are removed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an ultra-low NOx combustion method, and is particularly suitable for reducing nitrogen compounds in the exhaust gas of boiler equipment using pulverized coal as fuel. Concerning combustion methods.

[Prior Art] In the combustion of fuel containing organic nitrogen compounds such as pulverized coal, when the combustion is performed with an air ratio of 1 or more (ie, excess air), the conversion rate of nitrogen in the fuel to NOx increases. For this reason, the so-called two-stage combustion method is widely used, in which the first stage is first subjected to incomplete combustion, and the remaining air necessary for complete combustion is branched from the burner zone and introduced at the subsequent stage. An example of typical structural characteristics is shown in FIG. 2 using a commercial boiler as an example.

In FIG. 2, a burner group 20 is arranged in the lower part of the boiler furnace 10 and forms a main combustion area with combustion air and, for example, pulverized coal. An air injection port 30 for complete combustion (hereinafter referred to as an after air port) is arranged above it.

In this method, the burner zone is temporarily maintained in a state of incomplete combustion, so NOx (hereinafter referred to as
It is called Fuel NOX. ) generation is considerably small (can be suppressed. However, in this method, NO precursors such as NHx and HCN, which are simultaneously generated in the burner zone, are suppressed from regenerating NOX by air from the after-air port. It is extremely difficult to do this, and the only way to solve these problems is to expand the space above the burner ■0.
The only option is to gradually reduce the number of precursors. However, needless to say, this method has its own limitations from the viewpoint of making the height of the boiler furnace more compact.

[Problem to be solved by the invention]

In other words, the conventional combustion method described above does not have a function of actively decomposing byproducts such as NH, HCN, etc., which are precursors of NOX.

An object of the present invention is to provide a combustion method capable of solving the problems of the prior art described above and reducing NOx in exhaust gas without requiring an increase in the size of a combustion device such as a boiler furnace.

[Means to solve the problem]

The above purpose is to place an air port in the main combustion area of the fuel and the downstream side of the combustion gas to inject air for complete combustion in a small amount (in both stages) with respect to the gas flow, and to This is achieved by mixing alcohol-based oxygen-containing fuel into the air of an air boat located on the upstream side of the flow, and adding a function to actively decompose by-product nitrogen-containing compounds in the upper space V0 of the bar. .

[Effect]

Oxygen-containing fuel such as alcohol can partially oxidize NH, HCN, etc. due to the action of oxygen in its molecules, and by mixing alcohol, the space above the burner V*
By maintaining proper oxygen partial pressure and N stoichiometric air ratio, N
Precursors such as H, HCN, etc. are decomposed and the regeneration of No in the complete combustion region at the final stage is sufficiently suppressed.

〔Example〕

FIG. 1 is a boiler apparatus and its system diagram for carrying out the combustion method of the present invention. In FIG. 1, a boiler furnace 10
A burner group 20 is installed at the bottom of the burner, forming a main combustion area using paddy combustion air and pulverized coal.

Above the burner group 20 (on the downstream side of the gas flow),
A lower after air port 31 and an upper after air port 32 are installed. That is, the after air port is multi-staged into two stages.

Combustion air is introduced from the air system 100 into the lower after-air port 31 and the upper after-air port 32, and oxygen-containing alcohol fuel is supplied to the lower after-air port 31 from the alcohol mixing system 200. Recirculated exhaust gas is supplied from a circulating gas system 300.

In this boiler equipment, in the burner zone at the bottom of the boiler,
It is in an incomplete combustion state, and hydrocarbon gas such as CH4, C
In the case of pulverized coal, the so-called incomplete combustion components and nitrogen-containing compounds, which are composed of solids such as char, and H-poor o and Co2 are included.

Even if only combustion air is introduced in multiple stages in this state, the mixing form is diffusion mixing, so a large amount of NOX ( Mainly NO) is regenerated.

On the other hand, the oxygen partial pressure is adjusted by the exhaust gas from the recirculating gas system 300, and the alcohol mixing system 200
In the mixing of the fluid jet from the lower after-air port 31, where the stoichiometric oxygen ratio is suppressed to 1 or less due to the mixing of alcohol and combustion gas from the upper burner zone, and the combustion gas from the upper burner zone, NH ,,
Nitrogen-containing compounds such as HCN are easily decomposed, and migration to No can be suppressed to a low level. This eliminates the NO0 regeneration factor in the complete combustion region near the final stage, that is, the upper stage after-air port 32.

As the alcohol-based oxygen-containing fuel in the present invention, methyl alcohol is most suitable from the viewpoint of cost and combustion efficiency.

In the combustion method according to the present invention, the size of the reaction space V0 is
The same level as the conventional example is required, and the boiler furnace volume is not necessarily smaller than the conventional example, but the reaction space V
This method is advantageous over conventional methods because nitrogen-containing compounds such as NH, HCN, etc. are effectively decomposed.

〔Effect of the invention〕

As described above, according to the present invention, the NOx regeneration factor due to the mixing of alcohol-based fuel is reduced, and the Fuel NOx
Ultra-low NOx combustion has been achieved by reducing

It is possible to reduce the consumption of reducing agents such as

[Brief explanation of drawings]

Fig. 1 is a commercial boiler furnace and its main system diagram for implementing the method of the present invention, and Fig. 2 is a commercial boiler furnace and its main system diagram showing a typical example of the conventional two-stage combustion method. . 10... Boiler furnace, 20... Burner group, 30... After airport, 31...
...Lower after air port, 32...Upper after air port, 100...Air system, 2
00...Alcohol-containing strain, 300...
...Recirculating exhaust gas system.

Claims (1)

[Claims] (1) In a device that burns hydrocarbon fuel containing organic nitrogen compounds such as pulverized coal, there is at least two stages of complete combustion in the main combustion region of the fuel and the downstream side of the combustion gas with respect to the gas flow. A combustion method characterized by arranging an air port for introducing air and mixing an alcohol-based oxygen-containing fuel into the air in the air port located upstream of the air port in the gas flow direction.