JPS6064110A - Low nox burner - Google Patents

Abstract

PURPOSE:To carry out effectively gaseous phase reduction of NOx, by a method wherein a vortex forming component is arranged to an end part of a furnace side of either a path of gas or fuel and a reductive atmosphere is formed favorably by dividing a gas flow from a fuel flow through the vortex. CONSTITUTION:A furnace side opening of a pulverized coal pipe is made into an outward frame cap 100 constituted so as to expand the diameter of the opening toward an end of the opening. A sleeve 42 and the other sleeve 43 are arranged on an external circumferential part of the pulverized coal pipe 41 and further on an external circumferential part of the sleeve 42 respectively so that they form annular paths for passing of gas. Although a pulverized coal flow 10 consisting of primary air and pulverized coal is burnt by injecting the same into a furnace through the pulverized coal pipe 41, the pulverized coal flow 10 is controlled from dispersing outward through a flow of an eddy 103 to be formed in the frame cap 100, and a high temperature reductive flame 105 is formed centering around the center axis 104 of a burner, through which gaseous phase reduction of NOx is made into N2. A circulating vortex as shown by a symbol A in an illustration is formed by making a little secondary air 20 spout at turning strength which is different from that of tertiary air, the tertiary air B is once separated from the pulverized coal flow 10 through the circulating vortex and mixes with the high temperature reductive flame 105 at its rear flow.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion device that reduces nitrogen oxides (hereinafter abbreviated as “NOX”), and particularly relates to a combustion device that can achieve a significant reduction in NOx during combustion of pulverized coal.

Due to recent changes in fuel conditions, the number of thermal power plants that use coal as fuel is increasing.

In this case, the coal is finely pulverized, for example, into pulverized coal with a fi of about 70% passing through 200 meshes, and has good combustibility.

We are trying to improve controllability. This pulverized coal combustion technology itself has been established for a long time, and now it is possible to burn it as efficiently as heavy oil. Various gas and oil type pulverized coal combustors have been developed and are in use, but the most basic and most suitable type for high-load, high-efficiency combustion is the pulverized coal combustor.
An example is an annular air swirl type burner having a pulverized coal supply pipe as the central axis. In the burner, the coal is pulverized into fine powder by a mill, and then transported by air flow using conveying air that accounts for about 20% of the combustion air, and then introduced into the furnace through the burner port.

The remaining combustion air is normally given a certain amount of swirl in the vicinity of the burner mouth in a heavily or double annularly separated state and is ejected from around the pulverized coal jet.

Pulverized coal is flame-stabilized and steady combustion is maintained by the recirculation flow near the burner throat generated by this moderate swirling flow and, in some cases, by the addition of an impeller. For simply burning pulverized coal, this type of combustor usually satisfies the intended purpose.

However, as is well known, NO, which is produced as a by-product of combustion,
Since x is often generated in high-load combustion burners and is one of the causes of air pollution, some basic burner improvements or overall combustion improvements in the furnace have been carried out. A particular problem in pulverized coal combustion is NOx (hereinafter referred to as Fuel NOx) caused by organic nitrogen (hereinafter referred to as Fuel N) that is contained in large amounts (usually 1 to 2 wt%) in pulverized coal. and
It accounts for most of the NOx in exhaust gas.

Here, the adult cow reactions of NOx from Fuel N and N2 are as shown in the following equations (LL (2)), and both reactions are performed competitively.

+02 Fuel N - NOx = - (1) -1-N.

Fuel N-m-g-(2) Therefore, in order to give priority to the generation of N2 and maintain high-temperature load combustion to a certain extent, securing a high-temperature reducing flame is an important point.

The combustion method, which is generally called two-stage combustion, is an application of this combustion reaction.It creates an air-deficient state in the burner zone to form a high-temperature reducing flame, and then injects the insufficient amount from the after-air port downstream of the nokuichi-na zone. This improves combustion throughout the furnace and reduces NOx emissions. Currently, in the case of a new boiler for general coal, 2
The NOx emission concentration has been suppressed to about 0.00 ppm.

However, in the combustion of pulverized coal, a considerable amount of boiler (furnace) space is required to completely burn unburnt coal particles (char) remaining together with reducing air in the air-deficient burner zone by after-air. Therefore, although the above combustion method is in principle an extremely effective low NOx combustion method, it has certain limitations.

For this reason, a so-called dual register type burner has been developed in which each burner is configured to perform low NOx combustion based on the above-mentioned principle, instead of controlling the combustion of the entire boiler. FIG. 1 shows this dual register type burner. In the figure, the pulverized coal is injected into the furnace through the pulverized coal pipe 41 as a pulverized coal flow 1o together with air for transporting the air (minus air). This pulverized coal stream is injected into the furnace and combusted at a low air ratio to produce reducing intermediates and reduce some of the NOx in the gas phase. On the other hand, the secondary air 20 that has been given a swirling force by the air vane 71 passes through the secondary air register 61 to the outer periphery of the flame, and the tertiary air register 62 to the outer periphery of the flame. The tertiary air 3o supplied through the air is injected. In this way, air is supplied to the flame after gas-phase reduction, and unburned matter is combusted. As a result, two-stage combustion is performed in the burner alone, and NOx is reduced to 40
It has been demonstrated that it is reduced to about 0 ppm (reduction rate of about 40%). This type of burner has low NO
In order to achieve the It is required that the air and flame (or gas) mix to effectively burn unburned components. However, in this type of burner, although the secondary air 20 and tertiary air 30 are usually separated by a sleeve, in reality, the pulverized coal flow, secondary air jet, and tertiary air jet are separated near the burner throat outlet. It has been found that it is impossible to mix easily and maintain sufficient separation of the high-temperature reducing flame in the early stages of combustion, and it is extremely difficult to further reduce NOx in this type of combustion apparatus.

This invention was constructed in view of the above-mentioned problems,
An object of the present invention is to provide a combustion device with significantly improved NOx reduction rate.

In short, this invention arranges a vortex forming member on the furnace side end of the gas passage and/or the fuel passage, and uses this vortex to separate the gas and fuel flow to form a good reducing atmosphere, thereby reducing NOx gas. The object of the present invention is to provide an apparatus that can effectively perform phase reduction.

First, before showing embodiments of the present invention, some of the technical points that led to the present invention will be explained. As mentioned earlier, in order to produce a two-stage combustion effect with a single burner, maintain high efficiency combustion, and sufficiently suppress unburned content in the ash, the following technical points must be met. Further improvements are needed.

(1) Avoid spreading the pulverized coal flow as much as possible.

(2) Maintain the high-temperature reducing flame of the pulverized coal airflow produced by (1).

(3) Separate the outermost air from the initial combustion zone formed in (1) and (2) as much as possible. (NOx Suppression by High Temperature Reducing Flame) (4) (After 3 hours of operation, after a certain residence time, the high temperature reducing flame and the outermost air are mixed well (reduction of unburned matter).

Among the above, (LL (2) is for pulverized coal flow, (3)
(4) is a technical point in terms of fluid dynamics regarding the outermost air, but (1), (2), or (3) and (4) each generally have contradictory problems.

For example, in order to suppress the diffusion shown in (1), the chrysanthemum-shaped impeller that is normally used cannot be used, and therefore, a new method is required to achieve the high-temperature reducing flame in (2). or,
In order to achieve air separation in (3), (4)
In other words, in order to dramatically improve the reduction of NOx for each burner, we need to create a two-stage combustion effect by simply delaying the mixing of the outermost air. It is necessary to deviate from the conventional concept of causing a problem, and this invention aims to provide a technical solution to the above-mentioned items (1) to (4).

FIG. 2 shows an embodiment of the invention.

First, the furnace-side opening of the pulverized coal pipe 41 is fitted with an outward-facing frame cap (
(hereinafter simply referred to as "frame cap") 100. The frame cap 100 may be formed integrally with the pulverized coal pipe 41 or may be formed separately and then attached to the end of the pulverized coal pipe. Further, the frame cap may be configured such that the chrysanthemum pieces are opened and closed using a plurality of frame cap constituent pieces to change the diameter of the frame cap.

Next, a sleeve 42 is disposed around the outer periphery of the pulverized coal pipe 41, and another sleeve 43 is disposed around the outer periphery of the pulverized coal pipe 41 to form an annular passage for gas passage. Like conventional sleeves, these sleeves have a shape that does not enlarge the diameter at the tip, that is, the entire sleeve is formed into a cut-off cylindrical shape. 101゜10
If 2 is formed, gas separation can be performed more effectively as will be described later. In addition, by gradually increasing the thickness of the member walls of both the frame cap and the funnel-shaped part toward the open end on the furnace side, the outer diameter part of the frame cap and the funnel-shaped part expands toward the open end at a steeper angle than the inner diameter part. It may be configured to do so.

In the apparatus configured as above, the pulverized coal flow 10 consisting of sub-air and pulverized coal passes through the pulverized coal pipe 41 into the furnace.
t1. However, in this pigeon house, no impeller is installed for the stuffing tube, and the pulverized coal flow is suppressed from spreading outward by the small vortex 103 formed in the frame cap 100. Therefore, a high-temperature reducing flame 105 is formed near the burner centering on the burner axis 104. NOx is reduced by radicals such as ・NH, ・ON and reducing intermediate products such as CO in this high-temperature reducing flame.
2 by gas phase reduction. In other words, since the flame cap can prevent pulverized coal from dispersing, the high-temperature reduction zone can be brought closer to the burner side compared to conventional burners, and even when secondary air and tertiary air are injected using conventional sleeves. Since a high temperature reduction region is formed upstream of the mixing point of these airs, relatively good gas phase reduction can be achieved.

However, it is more effective to inject secondary air and tertiary air as follows. In other words, the secondary air damper 321.
Secondary air 20. by controlling a tertiary air damper 331 and/or installing secondary and tertiary individual air fans. Tertiary air 30
The secondary air and the tertiary air are separated from the high-temperature reducing flame 105 by independent control of the pressure and air volume upstream of the vane 71 and the tertiary air register 62.

In this case, it was confirmed that good results could be obtained by operating the tertiary air 30 at a pressure of 120 mmAg or higher on the upstream side of the air register 62. Also, it is effective to set the volume of tertiary air and secondary air to approximately 4=1 at this time.
I was able to recognize it.

As a result, the tertiary air 30 maintains a strong swirling force and appropriate air volume, and both the secondary air and tertiary air are injected into the furnace at a wide angle at the burner throat, and a high-temperature reducing flame is formed near the burner as described above. Combined with this, the mixing of the two is slight and good gas phase reduction can be achieved. Further, on the downstream side of this high-temperature reducing flame, the injection energy of secondary air and tertiary air also decreases and flows toward the burner axis 104, where unburned air is combusted.

In addition, when converting a burner with a small throat diameter to the burner according to the present invention, it is extremely effective to form funnel-shaped portions 101 and 102 at the tips of each sleeve 42 and 43 in order to back up the above air supply system. It is.

It has also been confirmed through experiments that a fixed circulating vortex as shown by A in the figure can be formed by blowing out a small amount of secondary air 20 with a swirling strength different from that of tertiary air.

Due to the existence of this circulating vortex A, the outermost air (tertiary air B in this example) is once turned into a pulverized coal flow around this circulating vortex.
O is separated very effectively, and the presence of this vortex improves mixing with the wake of the high-temperature reducing flame 105 formed by the pulverized coal flow in its wake.

Furthermore, the exhaust gas passage 50 is effective for spatially separating the pulverized coal flow and the secondary air, does not necessarily require a large amount of exhaust gas, and is less problematic than conventional burners from a practical standpoint. Must not be.

FIG. 3 shows a supply system for each gas and pulverized coal to the burner shown in FIG. 2. The code 200 in the figure is -=, -, J-
i08 &+) + 18 octopus, M4 or critical lead A S le,
301 is an exhaust gas recirculation fan, 302 is a secondary air fan, and 303 is a tertiary air fan.

The burner device of this invention is highly effective for older boilers that do not have an after air port formed in the boiler furnace, and can achieve significant NOx reduction without modifying the boiler body. It is effective not only for this type of boiler but also for two-stage combustion type boilers and in-furnace denitrification type boilers.

Figure 4 shows each type of boiler, (a) is the unmeasured type, (
b) is a two-stage combustion type, and (C) is an in-furnace denitrification type.

In the figure, reference numeral 400 indicates a burner according to the present invention, 410 indicates an after-air port, and 420 indicates a burner exclusively used for denitration by lowering the air ratio of the nozzle according to the present invention.

First, regarding the no-measure type (a), as mentioned above,
In the case of the two-stage combustion shown in (b), the secondary and tertiary air supplied from each burner functions as after air, and the unburned matter is combusted in advance for each burner, so the conventional two-stage combustion The unburned content in the ash can be effectively suppressed compared to the above. In addition, very recently, as shown in Figure 4 (0), a rich mixture of fuel has been injected into the furnace to locally release NOx.
A combustion method (in-furnace denitrification method) that performs gas phase reduction has been introduced, but this combustion method creates a fuel-enriched region locally in the furnace, and conversely, the main combustion zone tends to have an excess of air. However, by installing the burner according to the present invention in the main combustion zone, a large amount of NOx is generated in the main combustion zone, and as a result, it may be difficult to obtain a sufficient NOx reduction effect. Improved.

FIG. 5 shows the NOx reduction effect of the burner of the present invention. ■ is the minimum NOx emission concentration by the conventional dual air register, and II is the burner according to the present invention when operated under the same operating conditions as the conventional dual air register burner.
is the minimum NOx emission concentration when operating under varying operating conditions.

Note that Japanese charcoal was used in this experiment.

The properties of this Japanese coal were that the fuel ratio (fixed carbon content/volatile content) was approximately 1, the nitrogen content was 1.1%, dry ash free, and the operation was performed at 500 kg-coal/h and a burner excess air ratio of 120%.

By implementing this invention, the high-temperature reduction flame and air can be effectively separated in each burner, so NOx can be effectively reduced in the gas phase, resulting in lower NOx emissions compared to conventional burners. can be significantly reduced.

Furthermore, since the box is removed from each burner, it can be implemented not only in newly installed combustion equipment but also in existing equipment without modifying the combustion equipment itself, so it can be implemented in a wide range of fields.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional low NOx burner, FIG. 2 is a sectional view of a low NOx combustion device according to the present invention, FIG. 3 is a system diagram of fuel and gas supplied to the device in FIG. 2, and FIG. Figures (a) to (c) are sectional views of the boiler furnace, and Figure 5 is a diagram showing the NOx emissions of each combustion device. 10...Pulverized coal flow 20...Secondary air 30...Tertiary air pan--=--Frame cap 101, 102...Funnel-shaped part No. Figure 1 n Figure 2 Procedural amendment (voluntary) November 15, 1980 Kazuo Wakasugi, Commissioner of the Japan Patent Office 1. Indication of the case 1981 Patent Application No. 172:147 2. Title of the invention Low NQx combustion device a 3. Relationship with the case of the person making the amendment Patent applicant residence +9i Mr. 2-6-2 Otemachi, Chiyoda-ku, Tokyo
Name (544) Babcock Hitachi Co., Ltd. 4, Agent Name NK Shibuya Courters Telephone (460) 60
72 Amendment Contents 1, Regarding the "Detailed Description of the Invention" column. (1) Line 5 from the top of page 12 of the specification [12ommAg
Correct the text “J” to 1120mmAqJ. (that's all)

Claims (1)

[Claims] 1. One or more vortex forming members are provided at or near the furnace side end of the fuel passage and/or gas passage of the combustion device to separate the fuel flow and gas flow, and/or the gas flow from each other. A low NOx combustion device characterized by being configured as follows. 2. Claim 1, characterized in that a flame-holding vortex forming member is formed by forming a flame cap whose diameter increases toward the open end of the furnace-side end of the fuel passage.
The low NOx combustion device described in Section 1. 3 3. A patent characterized in that the furnace-side end of the secondary air passage and/or the tertiary air passage is a funnel-shaped part whose diameter increases toward the open end, and this funnel-shaped part is the vortex forming member. A low NOx combustion device according to claim 1 or 2. Any one of claims 1 to 3 is characterized in that a rotating member is arranged in each air passage so that the amount of secondary air and tertiary air supplied can be independently controlled. The low NOx combustion device described in . 5. The low N according to claim 2 or 3, characterized in that the diameter of the opening end of the vortex forming member is variable and the diameter can be adjusted from outside the device.
Ox combustion device. 6. The low 190X combustion device according to claim 1, characterized in that the wall thickness of the vortex forming member is gradually increased toward the open end on the furnace side.