JPS60126508A - Finely powdered coal burning device - Google Patents

Abstract

PURPOSE:To avoid the increasing of unburnt content in a ash and reduce the NOx by a method wherein a finely powdered coal flow is formed arround an air flow, a flame holding member having a specific shape is provided at the top position where the both fluids are supplied. CONSTITUTION:An oxygen-containing gas supply pipe 30 and a cylindrical sleeve 20 are provided, and a finely powdered coal flow 21 is flowed along the outer side of the pipe 30. The pipe 30 and the sleeve 20 are arranged on the axis 104 of a burner throat 10. A flame holding member 50 formed to be smaller difference in diameter than that of the air supply pipe 30 is provided at the furnace side opening end of the air supply pipe 30. By the bluff-body effect due to the flame holding member 50, a finely powdered coal turbid flow (circulating flow) is generated where the finely powdered coal is ignited and the flame holding function is performed. Meanwhile, a generated gas content such as a carbon hydride gas and the like are partially ignited, thermally decomposed and oxidized by the air flow I , and changed to a mixed gas IIIhaving a high reactivity, then a high temperature reducing atmosphere is formed. The atmosphere is diffused with surrounding an exhaust gas 41, then gradually mixed with an oxidate such as a high temperature small quantity remaining oxygen and OH radical and the like, thus, a zone IV is formed. Further, the zone IV is contacted with a main burner burning gas, and mixed, then a NO contained in the burning gas is reduced to N2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion device for negative pulverized coal, and particularly to a combustion device such as a boiler suitable for reducing nitrogen oxides in exhaust gas and unburned matter in ash.

Due to recent changes in the energy supply and demand situation, there is an urgent need to develop combustion technology that is compatible with common fuels in thermal power generation facilities that require large amounts of energy sources.

In particular, in so-called pulverized coal direct combustion equipment that burns pulverized coal, high-efficiency, pollution-free combustion technology that can handle a wide variety of foreign brands of coal is required.

Coal contains a large amount of organic nitrogen compounds compared to gas and oil, and therefore, generation of NOx (so-called Fuel Nox) due to oxidation of the organic nitrogen compounds during combustion becomes a problem.

Initially, it was thought that this NO fuel production was extremely inevitable, but recent boar research results show that fuel
It has been suggested that it is possible to suppress the production of NO. In other words, nitrogen compounds in fuel (denoted as Fuel N) undergo the following oxidation and reduction process to become NO! The above reaction route depends on the oxygen concentration, the concentration ratio of breath and energy, etc.

On the other hand, hydrocarbon gas generated as so-called volatile matter from pulverized coal passes through highly reactive and short-lived hydrocarbon radicals (.HC) in the early stage of combustion. As described above, this .He also reacts with 02 and NO, and follows the following reaction path.

In both cases, XN is involved in the NO decomposition/reduction process, and the efficient reduction of NO to NO is possible in the presence of a certain amount of oxygen and at a low air ratio ((1) It is confirmed that the condition will progress.

In order to take advantage of the above reaction, the present inventors have developed a so-called in-furnace denitrification combustion method that has an extremely low air ratio burner downstream of the main combustion zone and performs complete combustion downstream of the main combustion zone. recent years,
This method has been applied to various types of combustion.

However, although this method can be suitably implemented for gas and oil fuels, it is difficult to use coal due to equipment limitations.
It turned out that there were various problems.

This is due to the fact that combustion of coal particles is essentially different from combustion of gas or oil. That is, after the coal particles release their volatile content, they proceed to burn the remaining solids (called char). This determines the overall combustion time, but it is known that even with the same coal, chars with different combustion speeds are formed depending on the temperature rise at the initial stage of combustion. If char is formed without going through a rapid temperature increase process, the amount of unburned matter including char with a slow combustion rate will increase, and therefore a long combustion time will be required.

An object of the present invention is to provide a pulverized coal combustion apparatus that can eliminate the drawbacks of the prior art described above, avoid an increase in unburned content in ash, and reduce NO emissions.

The first aspect of the present invention relates to a burner device, which includes a hot air outlet provided in a burner throat portion of a side wall of the furnace, and a pulverized coal airflow outlet provided adjacent to the hot air outlet. , a bluff body member (e.g. made of ceramic) provided at the hot air outlet and/or the pulverized coal air stream outlet;
an inert gas or/and air jet port provided outside or adjacent to the outer periphery of the pulverized coal air flow jet port, and a recirculation vortex of the pulverized coal flow is provided downstream of the bluff body member. It is characterized in that it is formed and ignited, and a high temperature strongly reducing atmosphere is formed in its wake.

The second aspect of the present invention is that the burner device is installed downstream of the main combustion burner as a denitrification burner, and is equipped with a main combustion burner, a low air ratio burner, and an after air port in order along the gas flow direction in the furnace. , in a pulverized coal combustion device that forms a main combustion zone, a denitrification combustion zone, and a complete combustion zone, respectively, corresponding to the burner, the above-mentioned specific burner device is used as a nuclear low air ratio burner (denitration burner). be.

That is, when a denitrification burner is arranged in correspondence with the main burner, air is supplied near the central axis of the denitrification burner to rapidly raise the temperature of the char, and exhaust gas is supplied to the outer peripheral side of the pulverized coal flow. This is designed to maintain a fuel-excess and low-oxygen condition in the area where the partially combusted gas of the denitrification burner and the main burner combusted gas come into contact.

In a typical embodiment of the present invention, in a furnace such as a boiler that burns pulverized coal, when pulverized coal is distributed to a plurality of burners and combusted, 1) along the gas flow in the furnace, the most downstream 2) Regarding the structure of the burner, the average air ratio of the burner placed on the side is 0.6 or less. (■) The hot air (2)
00°C or higher), (II) a pulverized coal airflow is ejected in an annular or layered manner adjacent to the hot air outlet, (lIN) the tip of the pulverized coal pipe or/and the hot air supply pipe; A cap (mouthpiece) or a bluff body effect member in place of it is installed in the pulverized coal pipe, and (4) a structure is provided adjacent to the pulverized coal pipe to blow out high-temperature, inert gas such as combustion exhaust gas around it in an annular or layered manner. , 3) A three-stage combustion method is proposed in which air or a mixture of air and exhaust gas sufficient for complete combustion in the entire furnace is introduced further downstream of the burner.

In the present invention, when no bluff body member is provided,
Due to the lack of swirling of the pulverized coal flow, the ignition or flame holding properties are poor, and therefore, in the absence of a rapid heating process of the char (coal particles), a flame-retardant char is formed.
This makes it difficult to achieve complete combustion due to after-air pressure.
This results in an increase in unburned content in the ash.

Note that if a flame is used as a denitrification burner due to lack of air inside the flame and a high air ratio layer is formed around its outer periphery (outer ring or outer layer), the combustion gas from the main burner upstream (above the furnace) and the denitrification In the flame mixing section, the reducing intermediate products of the liver and kidneys gather at the center of the denitrification flame9, and are surrounded by a high air ratio layer.
! It cannot work effectively in reducing the

The present invention is particularly suitable for use in combustion devices that require high efficiency, low NO, and operation over a wide range of combustion load bands, such as boiler furnaces for commercial large-capacity thermal power generation.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of a denitrification burner used in the present invention. This burner device consists of a supply pipe 30 for oxygen-containing gas (hereinafter referred to as air) provided on the central axis 104 of a burner throw 10 on the side wall of a furnace 60, and a pulverized coal flow 21 provided on the outside thereof. Cylindrical sleeve 2 through which
0, an exhaust gas passage 40 provided between the sleeve 20 and the burner throat 100, and a wind box 40A communicating with the exhaust gas passage 40. A flame stabilizing member 50 that forms a step having a diameter smaller than that of the two-gas supply pipe 30 is provided at the contact portion).

The pulverized coal flow 21 consists of pulverized coal, conveying air and/or exhaust gas.

Nearby, it comes into contact with the pulverized coal flow 21 supplied through the outer cylindrical sleeve 20, and due to the bluff body effect of the flame stabilizing member 50, a turbid flow (circulating flow) of pulverized coal is generated, which is ignited in this area and at the same time Demonstrates flame function. Pulverized coal flow 2
1 is a so-called premixture as a whole, and therefore various operating conditions for maintaining a flame for a given composition (e.g., jet flow velocity, etc.) are extremely limited, but the air flow 31
By installing the flame stabilizing member 50 at the jetting contact portion of the pulverized coal flow 21 and the pulverized coal flow 21, good early ignition can be obtained regardless of the above-mentioned operating conditions.

On the other hand, volatile components such as hydrocarbon gas generated from pulverized coal are partially ignited, thermally decomposed, and partially oxidized by air flow I (the partial oxidation zone is indicated by I■), making them highly reactive. The mixture becomes a mixture ■, forming a high-temperature reducing atmosphere, which is surrounded by exhaust gas 41, diffuses, and gradually mixes with a small amount of oxygen therein, a small amount of high-temperature residual oxygen, and oxidizing substances such as OH radicals. (Zone IV), further contacts and mixes with the main burner combustion gas, and removes N in the combustion gas.
O is reduced to N2.

In the above embodiment, if the shape of the flame stabilizing member 50 has a bluff body effect (generating a recirculating vortex on the downstream side of a nonlinear object), the shape of the flame stabilizing member 50 may be such that a stepped portion is provided at the tip of the air supply pipe as shown in the figure. In addition to the cylindrical portion provided therein, various shapes such as a plate shape, a cap (mouthpiece) shape, etc. may be used. In addition, the exhaust gas 44)+ has a low oxygen concentration (02 is 10 v
Other gases may be used as long as they have a volume of 6 vol or less, preferably 6 vol or less. In addition to the annular structure shown in FIG. 1, the burner structure may be a layered structure. Further, in order to facilitate the adjustment of the mixture with the main burner combustion gas, a swirling means such as a vane may be provided in the passage 40 so as to swirl the exhaust gas 4@width. Note that normal combustion can also be performed by supplying air instead of the exhaust gas 4 to the passage 40 between the burner throw 10 and the pulverized coal pipe 20.

According to the above burner device, by providing the flame stabilizing member 50 at the tip of the air supply #I30, the pulverized coal flow can be quickly and stably ignited even at an extremely low air ratio, and the carrier fluid 41 (e.g. exhaust gas) can be ignited quickly and stably. Stable ignition and flame holding are possible without being affected by conditions, etc. In addition, by forming a pulverized coal flow 21 in the air flow 310 times and igniting it early in the vicinity of the flame stabilizing member, high-temperature strong reducing radicals can be formed. A high denitrification rate can be obtained by effectively dispersing NOx in the exhaust gas and causing it to come into contact with and react with the NOx-containing gas such as the main combustion exhaust gas. Further, the burner of the present invention can obtain char with good combustibility even at an extremely low air ratio by early igniting pulverized coal, and therefore can prevent a rapid increase in unburned content in the ash when reducing NOx. Therefore, for example, the height of the boiler furnace can be lowered, and the space and equipment cost of the device can be reduced.

The burner of the present invention is particularly suitable as a denitrification burner installed downstream of the main burner, but it can also be used as a normal combustion burner in a combustion system in which this burner is arranged in multiple stages and an after air port is provided in the downstream. It is also possible to use it as

Next, FIG. 2 is an explanatory diagram showing an embodiment of a combustion apparatus d in which the burner of the present invention is used as a denitrification burner and is arranged downstream of the main burner. In the figure, a main combustion burner (referred to as main burner) group 71, a denitrification burner group 72, and an after air port 73 are sequentially provided on the opposing side walls of the furnace 600 in the direction of gas flow.

The air ratio of the main burner 71 varies depending on the properties of the coal, etc.
The air ratio of the denitrification burner 72 may be 1 or more or 1 or less, but in order to form a strong reducing atmosphere, the air ratio of the denitrification burner 72 is smaller than that of the main burner, and is preferably 0.6 or less, particularly preferably 0.3 to 0. It is .5. The amount of air supplied to the acta air boat 73 may be sufficient as long as it is sufficient to completely burn the unburned content in the main burner and the denitrification burner (the air ratio as a whole is 1 or more).

Further, it is preferable that the ratio of the secondary air 31 to the tertiary air 41 of the denitrification burner 72 is 2 or more. Further, it is preferable that the secondary air and the tertiary air be supplied while being swirled, and in this case, it is more preferable to supply them with their swirling directions reversed.

FIG. 3 shows a preferred example of the main burner 71 used in the combustion apparatus shown in FIG.
It is described in No. 47. In other words, the cono burner includes a pulverized coal pipe 141 provided on the central axis 104 of the burner throat 10, and annular passages 150 and 12 sequentially arranged outside the pulverized coal pipe 141.
0, the secondary air damper 221 and vane 171 provided in the annular passage 120, and the cylindrical sleeve 14.
3 and a tertiary air damper 231 and a tertiary air register 162 provided in the passage 130 between the burner throat 100, and the furnace side opening of the fine powder tube x4x is configured to expand its diameter toward the opening end. It has 7 frame caps and 100 frames. Also sleeve 142.143
Similarly to the frame cap 100, the frame cap 100 also has funnel-shaped portions 101 and 102 whose diameter increases toward the open end.

In the burner with the above configuration, the pulverized coal flow 21 consisting of secondary air and pulverized coal is injected into the furnace through the pulverized coal pipe 141 in the center and burned, contrary to the case shown in FIG. In this case, no impeller is installed in the pulverized coal pipe 141, and the pulverized coal flow is suppressed from spreading outward by the small vortex 103 formed in the frame cap 100, and at the same time it is ignited here. Burner axis 10
A high-temperature reduction flame 105 is formed near the burner with the flame 104 centered thereon. NOx is reduced to N2 in the gas phase by radicals such as .NH2 and .CN and reducing intermediate products such as CO in this high-temperature reducing flame. In other words, by preventing the diffusion of pulverized coal with the flame cap, the high-temperature reduction zone can be brought closer to the burner tip compared to conventional burners.
Even if secondary air and tertiary air are injected using a conventional sleeve, a high-temperature reduction region is formed upstream of the mixing point of these airs, making it possible to perform good gas phase reduction.

Downstream of the high-temperature reduction zone, secondary air is pumped through a damper 221.
The secondary air and the tertiary air are adjusted by the high-temperature reducing flame 105 and rotated by the vane 171, and the tertiary air is adjusted by the damper 231 and the air register 162 and supplied around the high-temperature reducing flame 105, respectively. It can be supplied separately from 105. In this case, the pressure of the tertiary air 130 is, for example, 120 m on the upstream side of the air register 162.
It has been found that good results can be obtained by operating the system at a temperature of 1.5 kg or more, and it has been confirmed that it is effective to set the air volume of tertiary air and secondary air to approximately 4=1.

As described above, the tertiary air 130 maintains a strong swirling force and appropriate air volume, and the secondary air 130 at the burner throat
Since both the 01 tertiary air 130 and the tertiary air 130 are injected into the furnace at a wide angle, even if a high-temperature reducing flame is formed near the burner tip as described above, the mixing of the high-temperature reducing flame and secondary or tertiary air is slight near the burner tip. Therefore, good gas phase reduction can be performed. On the other hand, 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.

Still, by blowing out a small amount of secondary air 120 with a swirling strength or swirling direction different from that of tertiary air 130,
It has also been confirmed through experiments that a fixed circulating vortex as shown by A in the figure can be formed. This circulating vortex A
Due to the presence of the outermost air (in this example, tertiary air B
) is once separated from the pulverized coal flow 21 very effectively around this circulating vortex, and due to the existence of this vortex, the downstream part is separated from the high temperature reducing flame 105 formed by the pulverized coal flow. Mixing can be improved. Note that the exhaust gas passage 150 that recirculates the combustion furnace outlet gas is effective for spatially separating the pulverized coal flow and the secondary air, but does not necessarily require this large amount of exhaust gas.

The main burner 71 in FIG.
When used as a main burner, as shown in Figure 3, the pulverized coal flow is supplied to the central axis of the burner, and a combustion flame is formed surrounding it with air or exhaust gas. Even if reducing radicals are generated, they are quickly oxidized due to the presence of an air layer, and the combustion gas containing NO in the main burner does not come into direct contact with these radicals, making it a non-light-emitting burner for use as a denitrification burner. Become.

Then (Figure 2), in this denitrification burner, air is supplied to the burner center shaft, and pulverized coal is supplied to the burner, which ignites early and generates strong reducing radicals, which is the opposite of the case described above. Strongly reducing radicals are generated so as to surround the air flow around the central axis, and the exhaust gas containing these radicals comes into direct contact with the combustion gas from the main burner, so that sufficient denitration can be achieved.

As described above, according to the present invention, the pulverized coal flow can be quickly and safely ignited even at extremely low air ratios, the danger of explosion due to flame detector malfunction etc. can be eliminated, and the pulverized coal flow can be formed in the air flow conduit. However, by igniting it early near the flame-holding member, high-temperature strongly reducing radicals can be formed.
Furthermore, a high denitrification rate can be obtained by effectively dispersing these strong reducing radicals into the exhaust gas, and causing them to come into contact with and react with NO and other gases contained in the main combustion exhaust gas.

Furthermore, early ignition of pulverized coal allows char with good combustibility to be obtained even at extremely low air ratios, making it possible to prevent a rapid increase in unburned content in the ash in the low range of NO operation. Furthermore, by using this burner as a denitrification burner in a three-stage combustion device, it is possible to supplement the denitrification function of the main burner and obtain an even higher denitrification rate.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the burner device used in the present invention, FIG. 2 is an explanatory diagram showing an embodiment of the pulverized coal combustion device of the present invention, and FIG. It is a sectional view showing an example of composition of a main burner used in an apparatus. 10... burner throat, 20... pulverized coal pipe, 21
...Pulverized coal flow, 30...Air supply pipe, 31...Air flow, 40...Exhaust gas flow record, 40A-...Exhaust gas, 4
DESCRIPTION OF SYMBOLS 1... Exhaust gas flow, 50... Bluff body member (flame holding member), 60... Boiler furnace, 71... Main burner group, 72... Denitrification burner group, 73... After air port. Figure 3 Nz1 N51

Claims (2)

[Claims] (1) A hot air nozzle provided in the burner throat portion of the furnace side wall, a pulverized coal airflow nozzle provided adjacent to the hot air nozzle, and the hot air nozzle or/and the pulverized coal. A bluff body member provided at the airflow jetting port, and an inert gas or/and air jetting port provided outside or adjacent to the outer periphery of the pulverized coal airflow jetting port, A pulverized coal combustion device characterized in that a pulverized coal flow is ignited by forming a recirculating vortex at the pulverized coal flow, and a high temperature strongly reducing atmosphere is formed in its wake. (2) The furnace is equipped with a main combustion burner, a low air ratio burner, and an after air port in sequence along the gas flow direction, and forms a main combustion zone, a denitrification combustion zone, and a complete combustion zone, respectively, corresponding to the burners. In the charcoal combustion apparatus, the low air ratio burner includes a hot air jet port, a pulverized coal airflow jet port provided adjacent to the hot air jet port, and a pulverized coal air flow jet port provided adjacent to the hot air jet port and/or the pulverized coal jet port. a bluff body member provided at the airflow outlet; and an inert gas or/and air outlet provided outside or adjacent to the outer periphery of the pulverized coal airflow outlet; A pulverized coal combustion device characterized in that it forms a recirculating vortex of a pulverized coal flow in its wake, ignites it, and forms a high-temperature, strongly reducing atmosphere in its wake.