JPH05296411A - Nitrogen oxide reducing burner - Google Patents

Abstract

PURPOSE:To enable an effective restriction of occurrence of NOx, soot dust and CO to be carried out. CONSTITUTION:Primary air 12 of which volume is lower than a theoretical combustion air volume is supplied from a burner throat 4 into a combustion chamber 2 while being circulated. Secondary air 18 of which volume is higher than that of the primary air is supplied from a plurality of air injection nozzles 16 arranged at a side part of the burner throat 4 into the combustion chamber 2. The air injection nozzles 16 are spaced apart by a predetermined amount at a circumferential annular region of the burner throat 4 in such a manner that the secondary air 18 is injected toward a center of a downstream side of a primary combustion part 14 with the primary air 12 and further that injection air flows 18' from the air injection nozzles 16 may not interfere from each other at their upstream side and further inclined by about 10 deg. to 30 deg. in respect to an axis of the combustion chamber 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a nitrogen oxide reduction burner preferably used in a relatively small boiler.

[0002]

2. Description of the Related Art In conventional burners, methods such as exhaust gas circulation combustion, hydrogenated combustion, and steam injection combustion are adopted as measures for reducing nitrogen oxides (NOx).

That is, the exhaust gas recirculation combustion system is intended to reduce NOx by recirculating a part of exhaust gas to the burner section to lower the oxygen partial pressure, and the hydrogenated combustion and steam injection combustion systems are NOx is reduced by blowing water and steam into the combustion chamber to lower the flame temperature.

[0004]

However, in the exhaust gas recirculation combustion system, when the exhaust gas is forcedly circulated by the combustion blower, the exhaust gas recirculation amount is set in order to avoid instability of the flame and contamination of the combustion air system. It cannot be increased to a certain extent or more, and NOx reduction cannot be sufficiently achieved. Further, when the exhaust gas is self-circulated, under low load conditions, the recirculation rate of the exhaust gas is reduced, and thus effective NOx reduction cannot be achieved. Further, in any case, it is necessary to raise the blowing function more than necessary, which causes a problem in cost.

In addition, in the hydrogenated combustion and steam injection combustion methods, there is a risk that can body corrosion may occur due to the blowing of water, and the boiler efficiency also decreases. Further, a water blowing device such as a pump is additionally required, which causes a problem in cost. On the other hand, in the steam injection combustion method, if the steam generated by the boiler is used, the boiler efficiency decreases, and if the steam generated by the boiler is not used or cannot be used, a steam generator or the like is required separately, resulting in a significant cost increase. Becomes

The present invention is extremely practical in that it is possible to significantly reduce the generation of NOx without causing such a problem in terms of boiler function and cost and to effectively suppress the generation of soot and CO. The purpose is to provide a good burner.

[0007]

A nitrogen oxide reduction burner of the present invention which has solved this problem is a primary combustion air for supplying primary air in a swirling flow from a burner throat into a combustion chamber in a smaller amount than the theoretical combustion air amount. A supply mechanism and a secondary combustion air supply mechanism for supplying secondary air in an amount larger than the primary air amount into the combustion chamber from a plurality of air ejection nozzles provided on the side of the burner throat, and particularly, air The jet nozzle jets secondary air toward the annular area around the burner throat toward the center of the downstream side of the primary combustion section by the primary air, and the jet air flows from the air jet nozzle interfere with each other on the upstream side. In order not to do so, it is proposed to arrange them at a predetermined interval in a state of being inclined with respect to the axis of the combustion chamber.

[0008]

[Operation] Two-stage combustion is performed by the supply of primary air and secondary air, and NO is produced by the mixing and diffusion of the oxidizing flame and the reducing flame.
The generation of x, CO, and dust is effectively suppressed. Such a suppressing effect is particularly exhibited by arranging the air ejection nozzles in parallel on the annular region in the above-described inclined state. That is, in such an arrangement, as shown in FIG. 3, in the upstream region where the jet air flow of the secondary air does not interfere without being diffused, the oxidizing flame due to the jet air flow partially encroaches around the reducing flame. By setting the boundary area of both flames to be large,
Since effective suppression of Ox and the like is achieved, suppression of NOx and the like becomes insufficient when the boundary region between both flames is small as shown in FIG.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to the embodiments shown in FIGS.

This embodiment is a once-through boiler (steam boiler or the like) having a combustion chamber surrounded by a spiral water pipe wall, and particularly has a relatively small capacity (oil amount of 30) which makes it difficult to reduce NOx. The present invention is applied to a burner installed in a boiler of up to 150 kg / h).

As shown in FIG. 1, the burner 1 of this embodiment has a combustion chamber 2 (diameter 565 mm, axial length 1150 m).
m) is attached to the end furnace wall 2a, the fuel spray nozzle 5 and the ignition electrode 6 are provided in the burner throat 4 (burner throat ring diameter 109 mm) provided in the center of the furnace wall 2a, and immediately below it. Distribute and diffuser 7
(Diameter 100 mm) and the following primary combustion air supply mechanism 8 and secondary combustion air supply mechanism 9 are provided.

That is, the primary combustion air supply mechanism 8 is
As shown in FIGS. 1 and 2, a primary air wind box 10 communicating with the burner throat 4 is disposed on the furnace wall 2a. Swivel vanes 11 in the wind box 10
Are provided so that the primary air 12 can be supplied to the combustion chamber 2 from the burner throat 4 while being swirled. The swirl number S of the primary air 12 is determined by the diameter of the burner throat 4, the shape of the swirling vane 11, etc., but normally, the swirl number S of the swirling flow is designed to be 0.3 to 0.6. Preferably. If the swirl number S is less than 0.3, the flame becomes long and the combustion chamber 2 becomes large, and if it exceeds 0.6, the fuel sprayed from the nozzle 5 (kerosene in this embodiment) burns. Peripheral wall 2b of chamber 2
This is because there is a risk of collision with carbon and carbonization. The swirl number means the degree of swirl defined by S = Gφ / (Gx / (d / 2)) (Gφ: angular momentum in jet, Gx: axial momentum in jet, d: burner throat Diameter). In addition, the entrance portion 10 of the wind box 10
An air flow rate control damper 13 is provided at a so that the primary air supply amount from the burner throat 4 can be adjusted to be equal to or less than the theoretical combustion air amount. It is set to 1 to 0.6.

According to such a primary combustion air supply mechanism 8,
Since the air 12 is supplied to the combustion chamber 2 in a state less than the theoretical combustion air amount, when the spray oil from the fuel spray nozzle 5 is ignited by the discharge of the ignition electrode 6, the primary combustion section 14 that performs reduction combustion and vaporization combustion is generated. Will be formed. In the primary combustion section 14, since the primary air 12 is supplied in a swirling flow, the combustion gas 12 ′, which is the reducing gas generated, is regenerated together with the formation of the negative pressure section by the diffuser 5. By being circulated, the residence time is increased, vaporization of the spray oil is promoted, and stable combustion is continued.

The secondary combustion air supply mechanism 9 is shown in FIG.
As shown in FIG. 2, the furnace wall 2a is provided with a plurality of air ejection nozzles 16 ... And a secondary air window box 17 surrounding the wind box 8 and communicating with the ejection nozzles 16. Secondary air 18 for each nozzle 1
It is configured so as to be ejected from 6 into the combustion chamber 2.
The nozzles 16 are arranged in parallel in the peripheral annular region of the burner throat 4 at a predetermined interval, and are arranged along the axis of the combustion chamber 2 to eject the secondary air 18 toward the downstream center of the primary combustion section 14. On the other hand, the tilted posture is a predetermined angle θ. Further, an air volume control damper 19 is provided at the inlet portion 17a of the wind box 17, and all the nozzles 16
The amount of secondary air jetted from ... can be adjusted according to the amount of primary air supply. This secondary air ejection amount is larger than the primary air supply amount and is set to an amount obtained by subtracting the primary air supply amount from the predetermined required air amount (for example, assuming that the required combustion air ratio is 1.2, the primary air ratio is 1.2). Is 0.3, the secondary air ratio is 0.9). The burner 1 is three-position controlled, on / off controlled, and proportionally controlled. In this embodiment, the burner 1 is three-position controlled, and the supply amount of the primary air 12 and the secondary air 18 (air amount control dampers 13 and 19). The opening degree) is automatically controlled according to the boiler load.

By the way, the air flow 18 'ejected from each nozzle 16 is gradually diffused toward the downstream side, but the mutual intervals, the number of nozzles 16 and the inclination angle θ are as follows.
The jet air streams 18 '... Do not interfere with each other on the upstream side, diffuse and interact with each other on the downstream side, and enter below the recirculation region of the primary combustion gas 12' (hereinafter referred to as "proper secondary air supply mode"). As described above, it is appropriately set according to the recirculation force of the primary combustion gas 14, the shape of the combustion chamber 2, and the like.
In general, it is preferable to arrange four or five nozzles 16 ... In an inclined posture of 10 to 30 ° at equal intervals, and in this embodiment, four nozzles (bore diameter 35.6 mm) 16 ...
They are arranged at equal intervals in a tilted posture of °. The secondary air 1
The jet speed of 2 is also a condition necessary to secure the above-mentioned proper secondary air supply form, and generally, it should be set to 15 m / s or more under the minimum load condition in the boiler. Is preferred, in this example 1
It is set to 5 m / s.

According to the secondary combustion air supply mechanism 9, since the secondary air 18 is blown in the above-mentioned proper secondary air supply mode, the secondary combustion air is diffused at the downstream side of the recirculation region of the primary combustion gas 12 '. The secondary combustion section 20 is formed, and complete combustion in the combustion chamber 2 is achieved. That is, the jet air streams 18 '... Diffusely mix on the downstream side to perform uniform slow combustion, and the upstream side of the jet air streams 18' ... do not diffuse the air to perform remarkable oxidative combustion. Therefore, as shown in FIG. 3, an oxidizing flame (transparently visible) is present around the reducing flame (bright flame) 21 in the upstream portion where the jet air streams 18 '... Do not diffuse and do not interfere with each other.
The flame form that 22 has partially penetrated (hereinafter referred to as “appropriate flame form”).
That is, the reducing flame 21 and the oxidizing flame 22 are clearly distinguished and mixed in the annular region immediately below the nozzle 16, and the boundary area between the two flames 21 and 22 is large.

Therefore, by the supply of the primary air 12 and the secondary air 18 as described above, the reducing flame 21 and the oxidizing flame 22 are clearly distinguished and mixed on the upstream side, and both flames 21 are advanced toward the downstream side. , 22 is gradually diffused and mixed, and is subjected to two-stage combustion, so that NOx can be significantly reduced even in a relatively small-capacity oil-fired boiler with high-load combustion, which makes it difficult to reduce NOx. CO,
Generation of soot and dust can also be satisfactorily suppressed.

In the configuration of the above embodiment, the load 1
When a combustion experiment was carried out under the conditions of 00% and 50%, the proper flame form (FIG. 3) was confirmed, and as shown in FIGS. 4 to 6, the NOx generation amount (ppm (O ₂ = 0% conversion, The same shall apply hereinafter)), CO generation amount (ppm), small scale No. It was confirmed that these (main indicators of the dust generation rate) were significantly reduced. 4 to 6, the solid line shows the case of 100% load, and the chain line shows the case of 50% load. As is clear from the results of the burning experiment using such kerosene as fuel, according to the burner 1 of the present invention, the strictest regulations of Tokyo among prefectures (NOx <80 ppm for oil burning, gas burning) And N
Ox <60 ppm) can be sufficiently cleared, and even in the case where oil burning will be regulated at the same level as gas burning in the future, this can be sufficiently dealt with.

Further, as a comparative example, the air ejection nozzle 16
When the number of ... Is increased to eight, which is twice the number in the above-mentioned embodiment, and an experiment is conducted under the same conditions, as shown in FIGS.
The reduction rate of Ox, CO, and soot was significantly reduced. In this experiment, since the number of nozzles was doubled, the jetted air streams 18 '... also interfered with each other even on the upstream side, and as shown in FIG.
Therefore, the boundary area between the annular flame 21 and the oxidative flame 22 is significantly smaller than that in the case of FIG. 11 to 13, the solid line shows the case of 100% load, and the chain line shows the case of 50% load.

Further, as another comparative example, an experiment was carried out also when the nozzle inclination angle θ was set to 0 °, but an appropriate flame form was not obtained, and the reduction rate of NOx and the like was further reduced as compared with the case of the above comparative example. .. Further, due to poor mixing, the small scale No. It was also high, and the amount of CO generated also increased.

From the results of such comparative experiments, the effect of reducing NOx and the like is achieved especially by injecting the secondary air 18 in the above-mentioned appropriate secondary air supply form and obtaining the above-mentioned appropriate flame form. Guessed. Therefore, it is necessary to set the number of the air ejection nozzles 16 ... and the inclination angle θ so that a proper secondary air supply mode and a proper flame mode can be obtained according to the combustion conditions and the like.

The present invention is not limited to the above-mentioned embodiments, and can be appropriately improved and changed without departing from the basic principle of the present invention.

For example, as shown in FIG. 7, the diffuser 7
In place of the cone 23, the primary air 12 is supplied to the cone 23.
It is also possible to divide into the inside and outside of the chamber 12a and 12b to supply the combustion chamber 2 from the burner throat 4. In this case, the swirl vane 11a also swirls the split air 12a passing inside the cone 23. The divided air amount 12a is usually set to be about 1/3 of the total supply amount of the primary air 12. Further, as shown in FIG. 8, the caster portion of the upper furnace wall 2a may not be flat but may be the recess 2c. Further, it goes without saying that the present invention can also be applied to a boiler in which the combustion chamber 2 faces sideways and is in an inverted state.

Further, the number of the air jet nozzles 16 ..., the inclination angle θ, the mutual interval, and the nozzle aperture are within the range in which the proper secondary air supply mode and the proper flame mode are obtained, the combustion conditions, the combustion chamber shape, etc. It can be changed as appropriate. For example, when the diameter of the combustion chamber 2 is large, it may be possible that the number of NOx reduction rate is eight as described above. However, in the case of a small-sized boiler to which the present invention is particularly targeted, generally, about 4 or 5 will be optimal. Further, the inclination angles θ of the nozzles 16, ..., The mutual intervals, and the nozzle apertures may not be the same. For example, as shown in FIG. 9, the upper and lower headers are connected by water pipe walls 24 and 25 formed of water pipes 24 a, ..., 25 a that are arranged in parallel in an annular shape, and a combustion gas outlet 26 formed between the water pipes of the inner water pipe wall 24. … From the water pipe wall 24, 2
In the multi-tube once-through boiler configured to discharge the combustion gas to the combustion gas passage 27 formed between the five,
Although unburned gas easily enters the combustion gas passage 27 from the combustion gas outlet 26 to generate soot, in such a case, the diameter of the nozzle 16 'immediately above the outlet 26 is set to be smaller than that of the other nozzles 16 ... It is possible to prevent the unburned gas from invading the passage 27 by increasing the injection amount and increasing the injection amount.

[0025]

As is apparent from the above description, according to the present invention, the generation of NOx, CO, and dust can be significantly suppressed, and the recent demand for low NOx combustion can be sufficiently satisfied. You can In particular, even for small-capacity boilers with high-load combustion, regardless of whether they are oil-fired or not, it is possible to stay within the strictest gas-fired regulation frame in Tokyo at present, and the regulations will become stricter in the future. It can fully meet the demand for low NOx combustion. In addition, it is not necessary to use an unnecessarily high-capacity blower or a device for blowing water or steam, so that the boiler can be made significantly compact, which is extremely advantageous in terms of cost.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing an embodiment of a burner according to the present invention.

FIG. 2 is a cross-sectional plan view taken along the line II-II of FIG.

3 is a cross-sectional plan view taken along the line III-III in FIG.

FIG. 4 is a graph showing a measurement result of NOx generation amount.

FIG. 5 is a graph showing the measurement results of CO generation amount.

FIG. 6 Small scale NO. 5 is a graph showing the measurement results of the.

FIG. 7 is a vertical sectional side view showing another embodiment.

FIG. 8 is a vertical sectional side view showing still another embodiment.

FIG. 9 is a cross-sectional plan view showing still another embodiment.

10 is a transverse plan view corresponding to FIG. 3 in a comparative example.

FIG. 11 is a graph showing measurement results of NOx generation amount in a comparative example.

FIG. 12 is a graph showing the measurement results of CO generation amount in a comparative example.

13 is a small scale NO. 5 is a graph showing the measurement results of the.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Burner, 2 ... Combustion chamber, 4 ... Burner throat, 9 ... Primary combustion air supply mechanism, 10 ... Secondary combustion air supply mechanism, 10, 17 ... Wind box, 11, 11a ... Swirl vane, 12, 12a , 12b ... Primary air, 12 '...
Recirculation combustion gas, 14 ... Primary combustion part, 16, 16 '... Air jet nozzle, 18 ... Secondary air, 18' ... Jet air flow,
20 ... Secondary combustion part, 21 ... Reduction flame, 22 ... Oxidizing flame.

Claims (1)

[Claims] 1. A primary combustion air supply mechanism for supplying primary air in a swirling flow from the burner throat into the combustion chamber in an amount less than the theoretical combustion air amount, and combustion from a plurality of air ejection nozzles provided on the side of the burner throat. An air supply mechanism for secondary combustion that supplies a larger amount of secondary air to the room, and the air ejection nozzle has secondary air in the peripheral annular region of the burner throat, downstream of the primary combustion section using the primary air. In order to eject the air toward the center of the side and prevent the air streams ejected from the air ejection nozzles from interfering with each other on the upstream side, they are arranged at predetermined intervals in a state inclined with respect to the axis of the combustion chamber. A burner for reducing nitrogen oxide, which is characterized in that