JP2565620B2 - Combustion method of pulverized coal - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates, Ri engaging <br/> combustion how the pulverized coal, relates to the preferred combustion methods from reducing in particular nitrogen oxides (hereinafter referred to as NOx).

[0002]

2. Description of the Related Art NOx produced during combustion of fossil fuel is
It is classified into fuel NOx and thermal NOx. Fuel NOx is generated by oxidizing a nitrogen component (hereinafter referred to as N component) contained in fuel, and thermal NOx is generated by oxidizing nitrogen in the air. Coal has a high N content, and nearly 80% of NOx generated during combustion is fuel NOx. On the other hand, the combustion technology that has been developed in the past is typified by the two-stage combustion method and the exhaust gas recirculation method.
The mainstream is effective in reducing thermal NOx by suppressing the oxidation of nitrogen in the air by lowering the combustion temperature.

Fuel NOx generated during combustion of pulverized coal
The generation route of is described as follows according to the combustion mechanism. Pulverized coal combustion consists of the processes of ignition, pyrolysis, gas combustion, and solid combustion. The initial region of combustion is the region where ignition and pyrolysis proceed, and the N content present in the coal is divided into those that volatilize as a gas and those that remain in the solid. In the combustion region following pyrolysis, gas combustion in which volatile matter in coal burns and solid combustion in which solids that released volatile matter burn progresses, and N content released as gas and N content in solids also burn. Partly converted to NOx and part to nitrogen in the region.

N released as a gas during the thermal decomposition of coal
Some of the components become hydrogen cyanide (HCN) and ammonia (NH ₃ ), and these nitrogen compounds are oxidized to NOx in a high temperature and high oxygen concentration atmosphere. It has the property of selectively reducing NOx in the coexistence to form nitrogen (N ₂ ). By utilizing this property, it is possible to improve the conventionally developed two-stage combustion and reduce the NOx in the pulverized coal combustion, and a burner based on the two-stage combustion principle has been developed. The two-stage combustion is a reducing region with a low air ratio in the first stage, which is a method of reducing N content in coal to N ₂ as much as possible. To further reduce NOx, generation of NOx in the combustion flame It is necessary to clearly distinguish and control the region, the reducing agent generation region for NOx reduction, and the NOx reduction region.

[0005]

The object of the present invention is NO.
The object of the present invention is to provide a method for burning pulverized coal and a burner for combustion, which has a great effect of suppressing generation of x and reduces the emission of unburned components.

[0006]

The present invention is directed to the outer periphery of a pulverized coal nozzle for injecting a fuel mixture composed of pulverized coal and primary air.
Is equipped with a secondary air nozzle that ejects secondary air, and its outer circumference
The tertiary air nozzle for jetting tertiary air is provided, the pulverized
Expand the tip of the charcoal nozzle to the outside and connect it to the secondary air nozzle.
A swirler is provided in each of the tertiary air nozzles to provide the secondary air.
And pulverized coal bar in which tertiary air is swirled and ejected
Burns the pulverized coal with
And NOx from the nitrogen content of the prior <br/> Symbol pulverized in coal burning in the fine coal <br/> burner tip air amount below theoretical air amount near the fuel mixture by the secondary air made of air It forms a pre-combustion zone that produces ammonia and cyan compounds, and
To the combustion exhaust from the pre-stage combustion region and the tertiary air
Forming a post-combustion region for combustion that reduces NOx more
It is a combustion method of pulverized coal, characterized in that that.

The present invention further relates to the first pulverized coal and the primary air.
Outside the first pulverized coal nozzle that ejects a fuel mixture consisting of
A secondary air nozzle that ejects secondary air around the circumference is provided
A tertiary air nozzle that ejects tertiary air is installed around the
2nd pulverized coal, air and oxygen concentration around 3-5% by volume
Fuel mixture consisting of combustion exhaust gas adjusted to
A second pulverized coal nozzle is provided, and the first pulverized coal nozzle is provided.
Of the secondary air nozzle and the tertiary air
Each nozzle is equipped with a swirler, and the secondary air and the tertiary air
With a pulverized coal burner that swirls the air and ejects it.
The pulverized coal is burned and sprayed from the first pulverized coal nozzle.
The pulverized coal bar depends on the fuel mixture to be discharged and the secondary air.
Pre-combustion near the tip
And a combustion zone from the pre-combustion zone to form a calcination zone.
The latter stage combustion region is formed in the latter stream of the former stage combustion region by the tertiary air.
To form a zone, which is defined by the front combustion region and the rear combustion region.
Therefore, the primary combustion region that burns at an air ratio of 1 or more is configured,
Is the second pulverized coal nozzle on the outer periphery of the primary combustion region?
Combustion with an air ratio of less than 1 by the fuel mixture ejected from
Secondary combustion zone to generate reducing thermal decomposition products
To form a flame in the primary combustion region and the flame in the secondary combustion region.
Combining with the flame on the downstream side to form the third combustion zone
It is a method of burning pulverized coal, characterized by:

[0008]

As described above, the N content in coal becomes a compound such as NOx, nitrogen (N ₂ ), ammonia (NH ₃ ), hydrogen cyanide (HCN) in the thermal decomposition process. Among these compounds, NH ₃ has a property of selectively reducing NOx even in the coexistence of oxygen, and it is a known fact in the field of flue gas denitration technology that NOx has a high reducing effect. Therefore, in order to effectively reduce NOx in the combustion gas containing oxygen using coal, a large amount of NH ₃ is generated from the coal and this is converted into N 2.
It is sufficient to react with Ox, and NOx reduction during coal combustion is
NH ₃ generation method and NH ₃ and NOx mixing method are major technical problems. However, the type of nitrogen compound in which N content in coal is converted during thermal decomposition depends on the thermal decomposition conditions of coal,
In order to generate a large amount of the desired NH ₃ , it is necessary to set the optimum thermal decomposition conditions for NH ₃ production. As a result of intensive studies by the inventors, in the temperature region close to the coal combustion temperature, the oxygen concentration in the coal pyrolysis atmosphere has a great influence on the NH ₃ conversion rate of N content in the coal, and it is optimal to maximize the NH ₃ conversion rate. It was confirmed by the pyrolysis experiment of pulverized coal that the oxygen concentration was high.

The point of the present invention is to utilize a thermal decomposition product from coal for the reduction of NOx. Therefore, a portion of the coal for combustion is burned in an oxygen concentration atmosphere in which the NH ₃ conversion rate of N content in the coal is maximized. Pyrolysis and mixing this with NOx-containing combustion gas.

In the combustion method of the present invention, pulverized coal and 1
A pre-combustion region formed by secondary air and secondary air, and
Formed by combustion exhaust from the first-stage combustion zone and tertiary air
The primary combustion region composed of the latter-stage combustion region
A flame having is formed. In addition, in the combustion method of the present invention
In addition, the primary combustion region and the secondary combustion region
A flame composed of the tertiary combustion region is formed. And
The NOx generation region, the pulverized coal thermal decomposition product generation region for NOx reduction, and the NOx reduction reaction region are clarified in the flame . The primary combustion region is a complete combustion region in which the first pulverized coal is completely burned with air having a theoretical air amount or more, and most of the fuel is burned therein. In this region, since the air ratio is burned at 1 or more, the unburned fuel remaining in the combustion ash becomes very small and at the same time a large amount of NOx is generated. The secondary combustion region is a combustion region of pulverized coal ejected with a mixed gas of combustion exhaust gas and air, in which combustion with an air ratio of less than 1, that is, thermal decomposition of the second pulverized coal proceeds. Since this region is an oxygen-deficient reducing region, the proportion of N content in the pulverized coal that is oxidized to NOx is very small, and ammonia (NH ₃ ), which is an intermediate product of N content in the combustion process, Hydrogen cyanide (HCN) etc. are generated. The third combustion region is a region where the thermal decomposition product of pulverized coal generated in the secondary combustion region reacts with NOx generated in the primary combustion region and surplus oxygen in the primary combustion region. Reduction reactions and oxidation reactions of hydrocarbons, carbon monoxide, hydrogen, unburned solids, etc. proceed.

By making the amount of pulverized coal which is completely burned in the primary combustion zone larger than that of the pulverized coal which is thermally decomposed in the secondary combustion zone, the emission of unburned fuel can be reduced, and the high temperature in the primary combustion zone can be achieved. Since the thermal decomposition product generated in the secondary combustion region is oxidized by the excess oxygen heated to the above, the chemical reaction in the tertiary combustion region can be efficiently promoted.

In one embodiment of the present invention, the pulverized coal combustion exhaust gas is used for adjusting the oxygen concentration, and the mixing ratio of the combustion exhaust gas and the combustion air is controlled so that the oxygen concentration in the thermal decomposition atmosphere is controlled. Is adjusted.

Further, in one embodiment of the present invention, in order to facilitate adjustment of oxygen concentration in the pyrolysis zone, the above-mentioned mixed gas is used for transporting pulverized coal and jetted into the pyrolysis zone of pulverized coal in a combustion furnace. It is used to

Further, in order to more effectively bring out the effect of the present invention, a pulverized coal jetting gas which is thermally decomposed in the secondary combustion region,
That is, the oxygen concentration of the air-fuel mixture of combustion exhaust gas and air is preferably 3 to 5% by volume. That is, NO even in the presence of oxygen
In order to efficiently generate NH ₃ capable of selectively reducing x in the thermal decomposition reaction of pulverized coal, it is necessary to select thermal decomposition conditions. As a result of intensive studies by the inventors, the oxygen concentration in the thermal decomposition atmosphere was determined. It was discovered that NH ₃ is most often generated from pulverized coal when 3 to 5%. Therefore, the oxygen concentration in the secondary combustion region is set to 3 to 5% by volume, that is, the oxygen concentration of the air-fuel mixture is adjusted to 3 to 5% by volume, and the mixing ratio of the air and the combustion exhaust gas is adjusted so that the tertiary combustion is performed. It is possible to effectively promote the NOx reduction reaction that proceeds in the region.

Further, a reaction temperature of 900 ° C. or higher is suitable for effectively reacting NH ₃ and NOx in the presence of oxygen, and therefore the pulverized coal pyrolysis product and the NOx-containing combustion gas are burned. It is preferable to mix them in a furnace to accelerate the NOx reduction reaction.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a pulverized coal combustion method and a burner for combustion according to the present invention will be described below with reference to the drawings.

In FIG. 1, a pulverized coal combustion burner comprises a pulverized coal nozzle 01, a secondary air nozzle 02 and a tertiary air nozzle 0 for supplying a fuel mixture composed of pulverized coal and primary air.
And 3. Before combustion by the fuel mixture and secondary air near the burner tip with a combustion air amount less than the theoretical air amount
Stage combustion region is formed, subsequent combustion zone by then flow into the combustion effluent from the tertiary air and the front combustion region. In the first-stage combustion region, ammonia and cyan compounds are produced in addition to NOx from the N content in the coal, and in the latter-stage combustion region, these nitrogen compounds react to reduce NOx.

In FIG. 2, the pulverized coal combustion burner comprises two pulverized coal nozzles 12, 13, a secondary air nozzle 17, a tertiary air nozzle 18, and an igniter 16. The tip of the pulverized coal nozzle 12 is expanded outward. Most of the fuel pulverized coal is ejected from the pulverized coal nozzle 12 which ejects the fuel mixture composed of the pulverized coal and the primary air for carrying and ejecting the pulverized coal, the secondary air nozzle 17, the tertiary air nozzle 1
A secondary combustion region 21 having an air ratio of 1 or more is formed at the tip of the burner by the secondary air and the tertiary air ejected from 8. The primary combustion region 21 is a primary combustion region formed by the fuel mixture of the pulverized coal nozzle 12 and secondary air, and a secondary combustion region formed by combustion exhaust from the primary combustion region and tertiary air. And a region. Pre-combustion area
In the area, expansion of the pulverized coal nozzle tip and swirling flow of secondary air
Due to the action, it consists of pulverized coal and primary air downstream of the pipe expansion section.
Due to the circulating flow of fuel mixture and secondary air,
A high temperature flame is formed, which promotes the generation of NH _3.
To be done. Further, in the present embodiment, the secondary air nozzle 17 and the tertiary air nozzle 18 are provided on the outer periphery of the pulverized coal nozzle 12 in order to shorten the flame in the primary combustion region 21 and to make it independent of other combustion regions. And a secondary air swirl vane 14 and a tertiary air swirl vane 15 for giving a swirl flow to the combustion air are installed in the respective nozzles. The pulverized coal nozzle 13 is installed on the outer periphery of the tertiary air nozzle 18,
From the nozzle 13, a fuel mixture composed of a combustion exhaust gas and air whose oxygen concentration is adjusted to 3 to 5% by volume and a pulverized coal is ejected. The fuel mixture ejected from the nozzle 13 forms a secondary combustion region 22 on the outer periphery of the primary combustion region 21, and is included in the heat and mixture transmitted from the primary combustion region 21 in this region. The thermal decomposition reaction of pulverized coal proceeds with oxygen, and a reducing thermal decomposition product is generated.

Oxidation of the reducing thermal decomposition products generated in the secondary combustion zone 22 and NO generated in the primary combustion zone 21
A third combustion zone 23 in which the reduction reaction of x takes place is formed in the wake of the first and second combustion zones.

The packed Experimental Example 1 Japanese domestic coal and domestic coal to 1000 ° C. char produced by heating in an inert atmosphere (flammable solids retained during coal pyrolysis) a platinum holder and 1000 ° C. The NH ₃ conversion rate of N content in coal and N content in char was measured by quantifying NH ₃ generated when heated. Figure 3 shows the oxygen concentration in the thermal decomposition atmosphere at 1 to 7% by volume.
It is the result of studying the effect of the atmospheric oxygen concentration on the NH ₃ conversion rate by varying the oxygen concentration within the range. The horizontal axis shows the oxygen concentration during pyrolysis, and the vertical axis shows the NH ₃ conversion rate of N content in coal and char. As is clear from FIG. 3, the NH ₃ conversion rate is greatly affected by the oxygen concentration, and there is an optimum oxygen concentration that maximizes the NH ₃ conversion rate. NH ₃ conversion in coal N content is maximized at an oxygen concentration of about 3 vol%, N content in the char is NH ₃ conversion is maximized at an oxygen concentration of about 5% by volume.

[0021] Experimental Example 2 Figure 4 is a example of the experimental results using the experimental apparatus and the same apparatus to obtain a 1, the same manner as in Example 1 in the coal in the oxygen concentration in the pyrolysis atmosphere and the N content of NH ₃ This is the effect on conversion rate. In this example, in order to examine the effect of coal type, an experiment of thermal decomposition reaction of Australian coal and Chinese coal was tried. The thermal decomposition temperature is 1000 ° C. as in Example 1. As is clear from FIG. 4, although there is a slight difference in the optimum oxygen concentration range depending on the type of coal, the oxygen concentration in the thermal decomposition atmosphere is about 3 for both Australian and Chinese coals, similar to the Japanese domestic coals of Example 1.
The NH ₃ conversion rate of N content in coal is maximized near volume%.

As is clear from the above examples, in order to effectively utilize the thermal decomposition products of coal as NOx reducing agents, it is necessary to control the oxygen concentration in the thermal decomposition atmosphere of coal to an optimum value. .

[0023]

As described above , according to the first invention.
For example, depending on the mixture of pulverized coal, primary air and secondary air
The pre-combustion region that burns with less than the theoretical air amount
Formed in the wake of the combustion exhaust from the pre-combustion zone and 3
A second-stage combustion region is formed by the secondary air. Pre-combustion area
Increasing the flame temperature by mixing secondary air into the area
To easily release combustible components in pulverized coal to reduce unburned content.
Can be reduced. As a result, the unburned component reduction effect and
It is possible to achieve pulverized coal combustion that has a great effect of reducing NOx.
Wear. According to a second invention, the shape according to the first invention is formed.
Pulverized coal, air and flue gas are formed around the combustion area
Pyrolytic coal pyrolysis region whose oxygen concentration was adjusted by the mixture of
Zone is formed, which improves the conversion rate to ammonia.
Improve to. As a result, the NOx reduction effect is even greater and
It is possible to achieve pulverized coal combustion with less unburned content.

[Brief description of drawings]

FIG. 1 is a side sectional view of a burner according to the present invention.

FIG. 2 is a side sectional view of a burner according to another embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the NH ₃ conversion rate and the oxygen concentration.

FIG. 4 is a graph showing the relationship between the NH ₃ conversion rate and the oxygen concentration.

[Explanation of symbols]

 01 Pulverized coal nozzle 02 Secondary air nozzle 03 Tertiary air nozzle 04 Ignition burner 05 Swivel blade 06 Swivel blade 07 Ignition auxiliary fuel supply hole 08 Pulverized coal supply hole 09 Secondary air supply hole 10 Tertiary air supply hole 11 Fine powder Charcoal supply hole 12 Pulverized coal nozzle 13 Pulverized coal nozzle 14 Secondary air swirl blade 15 Tertiary air swirl blade 16 Igniter 17 Secondary air nozzle 18 Tertiary air nozzle 21 Primary combustion area 22 Secondary combustion area 23 Third Next combustion area

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Arashi 3-1-1, Saiwaicho, Hitachi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Toru Inada 3-1-1, Saiwaicho, Hitachi, Ibaraki Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Kenichi Soma 3-1-1, Saiwaicho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Kazushi Otsuka 3 Saichocho, Hitachi City, Ibaraki Prefecture 1-1-1, Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Takao Hishinuma 3-1-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (2)

(57) [Claims] 1. A fuel mixture consisting of pulverized coal and primary air
Secondary that ejects secondary air around the pulverized coal nozzle that ejects
The air nozzle is provided, for injecting tertiary air into the outer periphery tertiary
Install an air nozzle and spread the tip of the pulverized coal nozzle outward.
Pipes to the secondary air nozzle and the tertiary air nozzle, respectively.
A swirler is provided to swirl the secondary air and the tertiary air.
The pulverized coal burner is designed to blow out to burn the pulverized coal.
And a fuel mixture consisting of the pulverized coal and primary air.
N nitrogen content in the pulverized coal was burned in air of less theoretical air quantity fine coal burner near the tip by the secondary air
Pre- stage for producing Ox, ammonia and cyan compounds
A combustion region is formed, and the fuel from the preceding combustion region is formed in the subsequent flow.
A combustion method for pulverized coal, which comprises forming a post- stage combustion region in which combustion for reducing NOx is formed by the calcination discharge and the tertiary air . 2. A fuel mixture comprising a first pulverized coal and primary air.
Secondary air is placed around the outer periphery of the first pulverized coal nozzle that ejects aeration.
A secondary air nozzle that jets air is provided, and tertiary air is placed around the nozzle.
A third air nozzle that jets air is provided, and a second
Pulverized coal, air, and fuel with oxygen concentration adjusted to 3-5% by volume
A second pulverized coal which ejects a fuel mixture consisting of burnt exhaust gas
A nozzle is provided, and the tip of the first pulverized coal nozzle is directed outward.
Expand the tube and use the secondary air nozzle and the tertiary air nozzle respectively.
A swirler is installed to swirl the secondary and tertiary air.
Combustion of pulverized coal with a pulverized coal burner
And the fuel mixture ejected from the first pulverized coal nozzle
Of air and the secondary air near the tip of the pulverized coal burner.
A pre-combustion zone is formed that burns at an air amount less than the theoretical air amount.
The combustion exhaust from the pre-stage combustion region and the tertiary air
To form a post-combustion region in the downstream of the pre-combustion region,
An air ratio of 1 due to the front-stage combustion region and the rear-stage combustion region.
The primary combustion region in which the above combustion is performed constitutes the primary combustion region.
Sprayed from the second pulverized coal nozzle onto the outer periphery of the region
Combustion with an air ratio of less than 1 by a fuel mixture produces a reducing
Forming a secondary combustion zone that produces pyrolysis products,
The flame in the primary combustion area and the flame in the secondary combustion area are
A method for burning pulverized coal, characterized in that the pulverized coal is coalesced on the wake side to form a third combustion region .