JPS582509A - Combustion method of pulverized coal - Google Patents

Abstract

PURPOSE:To reduce NOx, by transporting pulverized coal to a combustion nozzle from a crusher and by reducing the concn. of oxygen in the waste combustion gas to be jetted out of a combustion nozzle to below the concn. of oxygen in the air. CONSTITUTION:Combustion air 11 is supplied to a pulverized coal combustion burner 17 as secondary and tertiary air. Fuel coal is transported to the pulverized coal combustion burner 17 through the inside of a pulverized coal supply duct 24 using combustion primary air afger the coal have been pulverized by stock coal crusher 21. A part of combustion gas 10 extracted by a primary air blower 22 is used as the primary air for the combustion of the pulverized coal. Thus, the concn. of oxygen in the primary air can be reduced to below the oxygen concn. of the atmospheric air, because the waste combustion gas is used as the primary air, and reduction of quantity of NOx to be generated at the combustion of the pulverized coal can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion method for pulverized coal, and particularly to a combustion method suitable for reducing nitrogen oxides (hereinafter referred to as NOX) generated during combustion of pulverized coal.

In fossil fuels, C,! (In addition to fuel components such as
0XFi, NOX generated during combustion of gas and liquid fuels
There is a desire to reduce this as much as possible.

NOxFi is generated when various fuels are combusted, and depending on its generation form, there are two types of NOx: thermal/I/NOX and fuel NOX.
classified into types. Thermal NOXe-! , is produced when nitrogen in the combustion air is oxidized by oxygen, and fueue and 4NOx are produced when the N content of fuel is oxidized with oxygen. Conventional combustion methods for suppressing the generation of N9X include a multistage combustion method in which combustion air is divided into multiple stages and injected, and an exhaust gas recirculation method in which combustion exhaust gas with a low oxygen concentration is mixed into the combustion region. These low N
The common principle of the OX combustion method is to suppress the reaction between nitrogen and oxygen by lowering the temperature of the combustion flame. Among the two types of NOX mentioned above, thermal NOX is the one whose generation amount is reduced by lowering the combustion temperature, and fuel NOX is generated in Combustion II! less dependent on degree. Therefore, the 4th Flame Control Law, which aims to reduce the flame temperature, is as follows:
Although it is effective in reducing NOx from Mehoku, which has a low N content, nearly 80% of the NOx generated is from fuel NOx.
It has little effect on pulverized coal combustion, which is X.

The purpose of the present invention is to take into account the unique combustion properties of ζ pulverized coal,
The object of the present invention is to provide a combustion method that reduces NOx generated during pulverized coal combustion by further improving the conventionally developed combustion method.

The combustible components in coal can be broadly classified into volatile components and solid components. According to the unique properties of this coal, the combustion mechanism of pulverized coal consists of a thermal decomposition process of the pulverized coal in which volatile components are released, a combustion process of the released volatile components, and a combustible solid component (hereinafter referred to as char) after the thermal decomposition. It consists of the combustion process. The combustion rate of volatile components is higher than that of solid components, and volatile components are burned in the initial process of combustion. Further, during the thermal decomposition process, the N content in the coal is divided into those that are released as volatiles and those that remain in the char, similar to the combustible components. Therefore, NOX from the volatile N fraction of 2-L NOXH1 generated during J pulverized coal combustion and NO'X from the N fraction in the char.
It's 4 years old. Among these two types of 7UEL NOX,
Since the reaction between the fuel NOXi from the char, the solid fuel as a reducing agent, and NOX progresses within the char, the amount generated is small, and NOX from volatile components accounts for most of the fuel NOX. Therefore, as a method for suppressing fuel NOx generated during combustion of pulverized coal, a combustion method that is effective in suppressing 7UEL NOx generated from volatile components is the most effective method.

It is known that volatile N becomes nitrogen-containing radicals (reaction intermediates) such as CN and NH during combustion. In addition to reacting with oxygen to become NOX, these radicals can also react with generated NOX to become a reducing agent that decomposes N-0X into nitrogen. This NOX reduction effect of nitrogen-containing radicals becomes significant under low oxygen concentrations.

As is clear from the above explanation, NOx during pulverized coal combustion
As a reduction method, the combustion area of volatile components is made to have a low oxygen concentration atmosphere. The combustion method is the most effective.

In other words, the heat content of pulverized coal! A combustion method that creates a low oxygen concentration atmosphere in the combustion zero initial region including the process 't''↑ becomes effective.

A typical pulverized coal burner is comprised of a primary air pipe 1, a secondary air pipe 2, a tertiary air pipe 3, and an ignition device 4, as shown in FIG. Inside the primary air pipe 1, pulverized coal and primary air for transporting the pulverized coal from the pulverized coal supply device to the burner flow. Combustion air flows through the depleted air pipe 2 and the tertiary air pipe 3, the flow rate of which is regulated by elephant dampers 5 and 6 installed respectively.

In the conventional exhaust gas recirculation method, primary air, secondary air, and tertiary air are mixed in with the combustion exhaust gas and gas in the burner, and the oxygen concentration in the combustion air is uniformly lowered, or new air is added to the combustion air. A method has been adopted in which a combustion exhaust gas supply pipe is installed between the primary air pipe 1 and the secondary air pipe 2. However, with the method of uniformly lowering the oxygen concentration in the combustion air, the combustion speed becomes lower and the flame becomes longer.
The combustion furnace becomes larger. In addition, the method of installing a flue gas supply pipe in Shinku has problems such as poor mixing of flue gas and pulverized coal, which reduces the effect of reducing NOx.

The present invention has been made to solve the above-mentioned problem, and is characterized by a pulverized coal combustion method in which the gas ejected from a fuel nozzle is a combustion exhaust gas having a lower oxygen concentration than air.

Embodiment 2 of the present invention will be explained in the second part. Fig. 2 shows an example in which the present invention is applied to a pulverized coal combustion boiler 25, in which pulverized coal is burned in the combustion chamber 7. After the combustion gas lO passes through the ninth heat exchanger group 8 that generates water vapor, it exchanges heat with the combustion air 11 in the air preheater i, heats the combustion air 11t, and then releases it into the atmosphere. be done.

Air preheater 9
After being heated within, it passes through the combustion air supply pipe 12,
The air is supplied into the wind box 16. Furthermore, the combustion air 11' is fed into the pulverized coal combustion burner 17 installed in the wind box 16 as secondary air and tertiary air.
After being distributed to an appropriate flow rate by the tertiary air damper 15, it is ejected from the secondary air pipe and the tertiary air pipe.

The fuel coal is stored in the coking coal storage 1 - 8 , and guided by the coking coal supply device 20 to the coking coal dressing device 21 through the coking coal supply pipe 19 . After the fuel coal is pulverized by the coking coal pulverizer 21 to a particle size suitable for combustion,
The primary air for combustion passes through the pulverized coal supply pipe 24 and is transported into the pulverized coal combustion burner 17 having a nozzle at the tip.
It will be done. The fuel coal is injected into the combustion chamber 7° by the pulverized coal combustion burner 17, and is combusted by primary air, secondary air, and tertiary air.

A part of the combustion gas lO is extracted by the secondary air blower 22, and the extracted combustion gas is separated from other combustion gases by the primary air supply pipe 23, and the pulverized coal produced by the coking coal pulverizer 21 is pulverized. At the same time as being transported to the coal combustion burner 17, it is used as primary air for pulverized coal combustion. The oxygen concentration in the primary air, that is, the combustion exhaust gas, obtained in this way is usually 10% by volume or less, and the initial region of pulverized coal combustion is lower than when atmospheric air is used as the primary air. It is possible to create an oxygen concentration atmosphere. In other words, since the thermal decomposition of pulverized coal and the combustion of volatile components can proceed under low oxygen concentration, NO generated during pulverized coal combustion can be reduced.
'It is effective in reducing X.

Since it is possible to create a low oxygen concentration atmosphere in the initial region of charcoal combustion, NOx generated during pulverized coal combustion can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a typical burner used for pulverized coal combustion, and FIG. 2 is an explanatory diagram of the present invention when applied to a pulverized coal combustion boiler.

Claims (1)

[Claims] 1. A combustion device having a gas for transporting pulverized coal, a fuel nozzle for ejecting a mixed airflow of the pulverized coal and gas, an air nozzle for ejecting air for burning the pulverized coal, and a pulverizer for pulverizing the fuel coal. A pulverized coal combustion method characterized in that pulverized coal is conveyed from a pulverizer to a fuel nozzle, and the gas ejected from the fuel nozzle is a combustion gas having a lower oxygen concentration than air.