JPS61223411A - Catalyst burning method for pulverized coal - Google Patents

Abstract

PURPOSE:To enable to achieve low NOx burning and high efficient burning simultaneously by burning residual combustibles with remaining burning air after promotion of low air oxidation and thermal decomposition of pulverized coal. CONSTITUTION:After air-fuel mixture composed of pulverized coal and air to convey coal is passed through a honeycomb-like catalyst layer 13, the mixture is injected into a furnace. In the catalyst layer 13, thermal decomposed gas generated from coal is oxidized by oxygen in primary air and gas temp. in the layer is raised up. The quantity of coal is increased corresponding to raised temp. and further, temp. is raised up by gas oxidation and thermal decomposition of coal is promoted simultaneously. Secondary air is utilized to run completely the combustible air-fuel mixture ejected from the catalyst layer. Thereby, oxidation of pulverized coal under low air ratio is promoted and volatile matter is enabled to spout before pulverized coal is injected into the furnace and therefore, improved performance of ignitability and burning of pulverized coal and also low NOx burning are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for burning pulverized coal, and particularly to a method for efficiently burning pulverized coal, which has inferior ignitability and combustibility compared to other fuels.

[Background of the invention]

The characteristics of pulverized coal combustion are that coal is more heat resistant than other fossil fuels, and contains a large amount of nitrogen in the fuel, producing a large amount of nitrogen oxides (hereinafter referred to as NOx), which are air pollutants, during combustion. It is something that happens.

Two types of combustion methods have been developed to reduce this NOx. The basic idea common to these low NOx combustion methods is to convert nitrogen in the fuel into harmless nitrogen (N2) in a low air ratio flame lacking combustion air. The N content in the fuel is
In the low air ratio region, in the early stage of combustion in the coexistence of 03, it is oxidized to NO, and relatively downstream after 02 has been consumed, it is released as NH. Here, 02 from the outside does not mix into the low air ratio region, and 0. When the shortage condition is saved, NO becomes NH
, decreases with . When 02 is mixed quickly and the region of 0° deficiency is difficult to be preserved, the generated NH is also oxidized to No. Therefore, creating a stable low air ratio flame and speeding up the consumption of 0□ here is a key technology for achieving low NOx combustion. However, slowing down the mixing of 02 naturally tends to deteriorate the combustibility, and it is difficult to achieve high efficiency combustion and low NOx at the same time.

Furthermore, coal with low volatile content has poor ignitability;
Formation of a low air ratio flame itself is difficult.

Regarding the catalytic combustion of gases, there have already been many research publications*,
11 At the 3rd Symposium on Fixed Combustion Systems held in the United States, Mr. J. P. Kiraselling et al. Development J (J, P.

Kesselring at al 'Catalyt
ic Combustion System Deval
opment for 5tationary 5ou
rcaApplications'Proceedi
ngs of the Th1rdStationar
y 5source Combustion Sympo
sium). However, there is no example yet of using a catalyst for combustion of pulverized coal.

[Purpose of the invention]

An object of the present invention is to simultaneously achieve the aforementioned low NOx combustion and high efficiency combustion. Another object of the present invention is to provide a combustion technology that makes it easier to burn even coal with a low volatile content.

[Summary of the invention]

The main point of the present invention is that a combustion catalyst is installed in a burner that burns pulverized coal to oxidize volatile components released from pulverized coal at a low air ratio, and here, low air oxidation of pulverized coal and heat After promoting decomposition, the remaining combustion air is used to burn the remaining combustibles.

[Embodiments of the invention]

The present invention will be explained in more detail below using an example.

FIG. 1 shows one embodiment of a pulverized coal combustion burner using the present invention. The burner of this embodiment was composed of a fuel jet nozzle 11 and a secondary air nozzle 12. fuel nozzle 1
1 consists of a combustion catalyst 13 and a heat insulating material 14. A mixture of pulverized coal and primary air for conveying the pulverized coal was passed through the honeycomb-shaped catalyst layer 13 and then injected into the combustion furnace. The heat insulating material 14 was installed to prevent heat generated within the catalyst layer 13 from being radiated to the secondary air around the outer periphery of the fuel nozzle 11. The temperature of the pulverized coal-primary air mixture at the inlet of the catalyst bed was set to 270° C. at which thermal decomposition of the pulverized coal began. Catalyst layer 13
In the first layer, pyrolysis gas from one coal is oxidized by oxygen in the primary air, and the gas temperature in the first layer increases. The continuous oxidation-pyrolysis process in which the amount of pyrolysis gas from the coal increases by the amount of temperature rise, and this gas is further oxidized and the temperature rises at the same time promotes the pyrolysis of the coal. The process continues until the oxygen in the air is consumed, and a mixture of pulverized coal containing combustible gas is ejected at the outlet of the catalyst layer.

The secondary air was used to completely burn the combustible mixture ejected from the catalyst layer. To improve flame retention,
A swirl flow generator 15 was installed to blow out secondary air as a swirl flow.

FIG. 2 is a cross-sectional view of the fuel nozzle 11. Combustion catalyst 1
3 was covered with a heat insulating material 14. A wear-resistant honeycomb 16 was installed on the air-fuel mixture inlet side of the combustion catalyst 13. Combustion catalyst 1
3 is abrasion due to collision of pulverized coal in the air-fuel mixture, reducing catalyst life. Abrasion due to the collision of this pulverized coal occurs at the inlet of the catalyst layer.

The wear loss is most severe in the run-up section and is usually observed to be several times more than in the fully developed laminar flow section within the catalyst layer. In this embodiment, a wear-resistant honeycomb 16 was installed in the catalyst layer 13 in order to suppress the decrease in life due to this wear.

In this embodiment, a metal honeycomb or other ceramic honeycomb may of course be used depending on the degree of wear caused by SiC.

〔Effect of the invention〕

According to the present invention, oxidation of pulverized coal is promoted at a low air ratio,
Furthermore, since the volatile matter can be released before the pulverized coal is ejected into the furnace, it is possible to improve the ignitability of the pulverized coal, improve the combustibility, and achieve low NOx combustion.

[Brief explanation of drawings]

FIG. 1 is a cutaway perspective view of a burner used in an embodiment of the present invention, and FIG. 2 is a cutaway perspective view of a combustion catalyst installation part. 11...Fuel nozzle, 12...Secondary air nozzle, 1
3... Combustion catalyst, 14... Heat insulating material, 15... Swirling flow generator, 16... Wear-resistant honeycomb.

Claims (1)

[Claims] 1. In the pulverized coal combustion method, a mixture of air and pulverized coal that is less than the theoretical amount of air required for complete combustion of pulverized coal,
A catalytic combustion method for pulverized coal, which is characterized by passing the pulverized coal through a combustion catalyst layer, then ejecting it into a combustion furnace, and burning the pulverized coal at a high air ratio in the furnace.