JPS58187709A - Pulverized coal burning system utilizing nitrogen in coal - Google Patents

Abstract

PURPOSE:To reduce NOx contained in combustion gas in a pulverized coal burning device by utilizing the nitrogen content in coal for the reduction of NOx. CONSTITUTION:Coal generating a large quantity of ammonia upon heat decomposition which is a step of combustion is selected rather than coal burnt as main fuel and used as a fuel. At the same time, ammonia is generated from the selected coal so as to be utilized for the rediction of NOx generated from the coal which is the main fuel. First, domestic coal or Chinese coal is carried by carrier air through a pulverized coal supply hole 1, and ejected through a pulverized coal nozzle 3 and burnt so as to be used as the main fuel. Then, Australian coal having an ammonia conversion rate of the nitrogen content in coal higher than that of the domestic coal or Chiness coal, is conveyed by carrier air, and ejected through a pulverized coal nozzle 4 and burnt. By this procedure, a flame containing a large quantity of ammonia which reduces NOx produced due to the main fuel through the nozzle 3 wraps a flame containing a large quanaity of NOx through nozzle 3, and a reduction reaction of NOx is caused at the tip end of the flame to attemp to reduce NOx.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulverized coal combustion method that utilizes nitrogen in rounded coal to reduce NOx generated during pulverized coal combustion.

The NOx generated during a combustion fire can be divided into two types: thermal NOx, which is caused by nitrogen in the fuel (hereinafter referred to as 7UEL Not), and nitrogen generated in the air (hereinafter referred to as thermal NOx). Broadly classified. Most of the NOx generated during coal combustion is fuel NOx.

Nitrogen present in coal is divided into two types: one that volatilizes as a gas through thermal decomposition, which is a process of combustion, and the other that remains in solid form. In addition to the nitrogen released as a gas during thermal decomposition, cyanide and ammonia-based compounds are included, and these nitrogen compounds are oxidized to NOx in a high-temperature, high-oxygen atmosphere. However, ammonia has a suitable reaction temperature.

If the oxygen concentration is set, it has the property of selectively reducing Not to nitrogen even in the presence of oxygen present in normal combustion gas.

The low NOx combustion technology that has been developed so far is
These methods are typified by the staged combustion method and the exhaust gas recirculation method, and are effective in suppressing thermal Now by lowering the combustion temperature.

On the other hand, if AN'&-A utilizes the above-mentioned property of selectively reducing NOx to nitrogen even in the presence of oxygen under appropriate conditions, it can be used as a thermal NOx countermeasure. By improving the two-stage combustion, it is possible to reduce NOx in pulverized coal combustion as a fuel NOx countermeasure. A pulverized coal combustion burner based on the two-stage combustion tube principle has already been developed, but in order to fully satisfy the strict environmental regulations, it is necessary to further develop technology to reduce NOx.

An object of the present invention is to provide a pulverized coal combustion system that uses nitrogen in coal to reduce NOx in combustion gas in a pulverized coal combustion apparatus.

The main point of the present invention is to reduce NOx by utilizing the nitrogen content in one coal to reduce 1kNOx.

Of the nitrogen present in coal, one of the compounds released as a gas during thermal decomposition, which is one of the combustion processes, contains 1 ammonia, which is oxidized and becomes NOx in a high-temperature, high-oxygen atmosphere. . However, under appropriate conditions, it has the property of selectively reducing NOx even in the presence of oxygen.

Therefore, it is conceivable to use coal as a source of ammonia for use in the reduction reaction using ammonia, which is one method of reducing NOx.

In other words, when it comes to coal that is burned as the main fuel, we select coal that generates a large amount of ammonia during pyrolysis, which is one of the combustion processes, and then generate ammonia from that coal. If used to reduce NOx, it becomes possible to achieve low NOxt.

According to this method, the combustion zone of the main fuel coal is completely combusted regardless of the generation of NOx, and the N
It is possible to reduce Ox with ammonia from coal, which generates a large amount of ammonia. Therefore, it is possible to prevent the amount of unburned matter from increasing.

Another advantage is that there is no need to newly install an ammonia supply system for KNOx reduction in the pulverized coal combustion device, and the pulverized coal supply system that already exists can be used.

It can be used as a supply system for NOx reducing agent.

However, the amount of ammonia generated during thermal decomposition, which is a process of combustion, differs depending on the type of coal. Therefore, in order to realize the above technology, it is necessary to select an appropriate coal and use it as a NOx reducing agent.

Hereinafter, the content of the present invention will be explained with reference to FIG. 1, and an embodiment will be explained with reference to FIG. 2.

Figure 1 shows the measurement of the conversion rate of nitrogen to ammonia in one coal.The measurement method is to put pulverized coal in a quartz tube and measure the amount of ammonia generated when the heating temperature is about 1000C. , quantified by indophenol spectrophotometry. Coal types KFi, Australian coal, 13i1 internal coal, and Chinese coal were selected, and the atmospheric oxygen concentration was set from 1% to 6%.

4 for any type of coal. The maximum value is reached when the atmospheric oxygen concentration is approximately 3%. However, the ammonia conversion rate depending on the type of coal is about 10% for domestic coal and Chinese coal B, but about 30% for Australian coal C, and there are obvious differences depending on the type of coal.

Therefore, according to Figure 1, it can be seen that if domestic coal or Chinese coal is used as the main fuel, and Australian coal is used as the coal that supplies ammonia, which is the ninth reduction factor in Now, a low NOx effect can be achieved.

Figure 2 shows the results obtained by measuring the concentration of NOx in the exhaust gas of an actual combustion furnace and using only domestic coal as the main fuel.
When Australian charcoal is added to it, it is round compared to E.

When only domestic coal is used, the NOx concentration in the flue gas increases as the atmospheric oxygen concentration increases, but when Australian coal is added, the NOx concentration in the flue gas increases when the atmospheric oxygen concentration is approximately 3%. The NOx content of the plant showed a low value, and it also showed a low value compared to the NOx concentration generated when only domestic coal is burned at other atmospheric oxygen concentrations.

This is because ammonia generated from Australian coal is
Ox is reduced, and the NOx concentration in the combustion exhaust gas decreases, indicating an important point.

FIG. 3 shows a burner of an embodiment of the combustion method of the present invention. Domestic coal or Chinese coal is conveyed through the pulverized coal supply hole 1 by conveying air, and is ejected from the pulverized coal nozzle 3 to be burned as the main fuel. Here, complete combustion is performed regardless of the generation of NOx. Next, the Australian coal is conveyed by conveying air through the pulverized coal supply hole 2), and is ejected and burned from the pulverized coal nozzle 4. Here 1. Transport air with an atmospheric oxygen concentration of 1% to 6% is used. Aust clear charcoal #i #E1 As shown in the figure.

The ammonia conversion rate of nitrogen content in coal is higher than that of domestic coal or Chinese coal. Therefore, the flame containing many NH islands that reduce NOx produced by the main fuel from the pulverized coal nozzle 3 wraps around the flame containing many NOx from the pulverized coal nozzle 3, and the Now reduction reaction occurs at the flame tip. causes low N0x
I was able to figure out t-.

FIG. 4 shows a combustion furnace of one embodiment of the combustion method of the present invention. Burner 5 burns Chinese or domestic coal. Here, complete combustion is performed regardless of the generation of NOx.

Therefore, in the flame 7, a large amount of NOx is generated. On the other hand, in burner 6, the atmospheric oxygen concentration is 1%.
It burns at ~6% and generates a lot of ammonia. Therefore, the flame 8 contains a large amount of ammonia. In this way, flame 7
By arranging the burners 6 and 7 as shown in Fig. 4 so that a region where the flame 8 and the flame 8 are mixed together, the NOx contained in a large amount in the flame 7 is replaced by a group in which a large amount of NOx is contained in the flame 8.

can be used for reduction to achieve low NOx.

As explained above, according to the present invention, a type of coal that generates a large amount of ammonia, which is an effective reducing agent for reducing Not, is selected and used as a reducing agent.

Pulverized coal combustion gas has a low NotK effect.

[Brief explanation of the drawing]

Figure 1 shows the results of measuring the conversion rate of nitrogen to ammonia in one coal, showing the differences depending on the coal type. A diagram comparing the case of using only charcoal and the case of adding Australian charcoal. FIG. 3 is a sectional view of a burner according to an embodiment of the present invention. FIG. 4 is a simplified configuration diagram of a combustion furnace according to an embodiment of the present invention. 1.2...Pulverized coal supply hole, 3.4...Pulverized coal nozzle. 5.6...Pulverized coal combustion burner, 7.8...Pulverized coal combustion 1st product atmosphere 02 (=/-) Fig. 2 0 ml air vertically Concentration replacement Fig. 4 Continuation of page 1 0 shots Name: Takao Hishinuma, 3-1-1 Saiwaimachi, Hitachi-shi Stock% formula% 0 Applicant: Babcock-Hitachi Co., Ltd. 2-6-2 Otemachi, Chiyoda-ku, Tokyo

Claims (1)

[Claims] L: Select coal that generates a large amount of ammonia during thermal decomposition of coal and use it as fuel. A pulverized coal combustion method using nitrogen in coal, which is characterized in that it is used as a reducing agent for Now generated from other combustion.