JP2759306B2 - Nitrogen oxide reduction burner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In a conventional burner, as a measure for reducing nitrogen oxides (NOx), systems such as exhaust gas recirculation combustion, hydrogenation combustion, and steam injection combustion are employed.

[0003] That is, the exhaust gas recirculation combustion system aims to reduce NOx by recirculating a part of the exhaust gas to a burner portion to lower the oxygen partial pressure. Water and steam are blown into the combustion chamber to lower the flame temperature, thereby reducing NOx.

[0004]

However, in the exhaust gas recirculation combustion system, when the exhaust gas is forcibly circulated by a combustion blower, the exhaust gas recirculation amount is reduced in order to avoid instability of the flame and contamination of the combustion air system. It cannot be increased to a certain degree or more, and it is not possible to achieve a sufficient reduction in NOx. Further, when the exhaust gas is self-circulated, the recirculation rate of the exhaust gas is reduced under a low load condition, so that it is impossible to effectively reduce NOx. Further, in any case, it is necessary to increase the blowing function power more than necessary, and there is a problem in cost.

[0005] In the hydrogenation combustion and the steam injection combustion system, there is a possibility that corrosion of the can body may occur due to the blowing of water, and the boiler efficiency also decreases. Further, a water blowing device such as a pump is required separately, which causes a problem in cost. On the other hand, in the steam injection combustion system, if the steam generated by the boiler is used, the boiler efficiency will be reduced. If the steam generated by the boiler is not used or cannot be used, a steam generator or the like will be required separately, resulting in a significant cost increase. Becomes

According to the present invention, the generation of NOx can be significantly reduced without causing such problems in boiler function and cost, and the generation of dust and CO can be effectively suppressed. The purpose is to provide a simple burner.

[0007]

According to the present invention, there is provided a nitrogen oxide reducing burner in which a primary air having a swirl number of 0.3 to 0.6 is swirled into a combustion chamber from a burner throat. A primary combustion air supply mechanism for supplying a stream of air, and a secondary combustion air supply mechanism for supplying secondary air 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. In particular, the plurality of air ejection nozzles are provided in the peripheral annular region of the burner throat by injection from the air ejection nozzles.
The outgoing air flow is not diffused upstream and
In order to eject secondary air toward the downstream center of the primary combustion section by primary air without interfering with the primary chamber, the secondary air is arranged at a predetermined interval in a state inclined with respect to the axis of the combustion chamber,
From each air jet nozzle around the reducing flame in the combustion section
Oxidation flame due to jet air flow is clearly distinguished
It is proposed to make a configuration so as to generate a flame form that bites into the target. The swirl number refers to a degree of turning defined as described later.

[0008]

[Function] Two-stage combustion is performed by the supply of the primary air and the secondary air.
The generation of x, CO, and dust is effectively suppressed. Such a suppression effect is particularly achieved by arranging the air ejection nozzles in parallel with each other in the inclined state on the annular region. That is, as shown in FIG. 3, in the area where the jet airflow of the secondary air is not diffused and interferes with each other, as shown in FIG. 3, each air jet nozzle surrounds the reducing flame in the primary combustion section. partially eating write flameless state where oxidizing flame by ejecting airflow is clearly distinguished
By exhibiting the form and increasing the boundary area between both flames, effective suppression of NOx and the like is achieved. When the boundary region between both flames is small as shown in FIG. Is insufficiently suppressed.

[0009]

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

This embodiment relates to a once-through boiler (steam boiler or the like) having a combustion chamber surrounded by a helical water pipe wall, and in particular, has a relatively small capacity (oil amount 30) for which it is difficult to reduce NOx. The present invention relates to an example in which the present invention is applied to a burner mounted on a boiler of about 150 kg / h).

As shown in FIG. 1, a burner 1 of this embodiment has a combustion chamber 2 (having a diameter of 565 mm and an axial length of 1150 m).
m), a fuel spray nozzle 5 and an ignition electrode 6 are provided at a burner throat 4 (a burner throat ring diameter of 109 mm) provided at the center of the furnace wall 2a. Arrange and diffuser (flame holding plate) 7
(Diameter 100 mm) and the primary combustion air supply mechanism 8 and the secondary combustion air supply mechanism 9 as described below.

That is, the primary combustion air supply mechanism 8 includes:
As shown in FIGS. 1 and 2, a primary air wind box 10 communicating with the burner throat 4 is provided on the furnace wall 2 a. A swirl vane 11 is provided in the wind box 10.
Are provided so that the primary air 12 can be supplied from the burner throat 4 into the combustion chamber 2 while swirling. The swirl number S of the primary air 12 is determined by the diameter of the burner throat 4, the shape of the swirl vane 11, and the like. In the present invention, the swirl number S of the swirl flow is 0.3.
It is designed to be 0.6. If the swirl number S is less than 0.3, the flame becomes long and the combustion chamber 2 becomes large. If the swirl number S exceeds 0.6, the fuel sprayed from the nozzle 5 (kerosene in this embodiment) burns. Perimeter wall 2b of room 2
This is because there is a risk of carbonization due to the collision of The swirl number means the degree of swirl defined by S = Gφ / (Gx / (d / 2)) (Gφ: angular momentum in the jet, Gx: axial momentum in the jet, d: burner throat Diameter). In addition, the entrance 10 of the wind box 10
a is provided with an air flow control damper 13 so that the primary air supply amount from the burner throat 4 can be adjusted to be less than the theoretical combustion air amount. It is set to 1 to 0.6.

According to the primary combustion air supply mechanism 8,
Since the air 12 is supplied to the combustion chamber 2 in a state smaller than the theoretical combustion air amount, when the ignition electrode 6 discharges the spray oil from the fuel spray nozzle 5 to ignite the primary combustion unit 14 that performs the reduction combustion and the vaporization combustion. Will be formed. In the primary combustion section 14, since the primary air 12 is supplied in a swirling flow, the generated combustion gas 12 ', which is a reducing gas, is regenerated in conjunction with the formation of the negative pressure section by the diffuser 7. By being circulated, the residence time is increased, the 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, a plurality of air ejection nozzles 16 are provided on the furnace wall 2a, and a secondary air window box 17 surrounding the wind box 10 and communicating with the ejection nozzles 16 is provided. The secondary air 18 is configured to be ejected from each nozzle 16 into the combustion chamber 2. The nozzles 16 are arranged in parallel in the annular area around the burner throat 4 at a predetermined interval.
Is inclined at a predetermined angle θ with respect to the axis of the combustion chamber 2 in order to eject the gas toward the downstream center of the primary combustion section 14. Also, the entrance 1 of the wind box 17
An air flow control damper 19 is provided at 7a so that the amount of secondary air ejected from all the nozzles 16 can be adjusted according to the amount of primary air supplied. The secondary air ejection amount is set to be larger than the primary air supply amount and set to an amount obtained by subtracting the primary air supply amount from a predetermined necessary air amount (for example, assuming that the necessary combustion air ratio is 1.2 and the primary air ratio is 1.2). Is 0.3, the secondary air ratio is 0.9.) The burner 1 is controlled by three positions, on / off control, and proportional control. In this embodiment, the burner 1 is controlled by three positions, and the primary air 1 is controlled.
2 and the supply amount of the secondary air 18 (air volume control dampers 13, 1)
9) is automatically controlled in accordance with the boiler load.

By the way, the jet airflow 18 'from each nozzle 16 is gradually diffused toward the downstream side, but the mutual interval, the number and the inclination angle θ of the nozzles 16 are as follows.
The jet air flow 18 'does not diffuse on the upstream side.
The primary combustion gas 14 diffuses and interferes with each other on the downstream side without interfering with each other, and enters below the recirculation region of the primary combustion gas 12 ′ (hereinafter referred to as “proper secondary air supply form”). Is appropriately set in accordance with the recirculation force of the combustion chamber, the shape of the combustion chamber 2, and the like. Generally, four or five nozzles 16 ...
Are preferably arranged at equal intervals in an inclined posture of 10 to 30 °. In this embodiment, four nozzles (having a diameter of 35.6) are used.
mm) 16 are arranged at equal intervals in a 20 ° inclined posture. Note that the ejection speed of the secondary air 12 is also a condition necessary to secure the above-described appropriate secondary air supply form, and is generally set to be 15 m / s or more under the minimum load condition in the boiler. It is preferable to set it, and in this embodiment, it is set to 15 m / s.

According to the secondary combustion air supply mechanism 9, since the secondary air 18 is blown in the above-mentioned appropriate secondary air supply mode, the secondary combustion by the diffusion combustion is performed downstream of the recirculation region of the primary combustion gas 12 '. The next combustion section 20 is formed, and complete combustion in the combustion chamber 2 is achieved. That is, the jet air flows 18 'are diffused and mixed on the downstream side, and uniform slow combustion is performed. On the upstream side of the jet air flows 18', remarkable oxidative combustion is performed without diffusion of air. Therefore, in the upstream portion where the jet air flows 18 ′ do not diffuse and do not interfere with each other, as shown in FIG.
The flame form that 22 partially penetrated (hereinafter "appropriate flame form")
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 the two flames 21 are mixed toward the downstream side. , 22 are gradually diffused and mixed, so that NOx is significantly reduced even in a high-load combustion and relatively small-capacity oil-fired boiler where it is difficult to reduce NOx. CO,
Generation of dust can also be satisfactorily suppressed.

In the configuration of the above embodiment, the load 1
When the combustion experiment was performed under the conditions of 00% and 50%, the above-mentioned appropriate flame form (FIG. 3) was confirmed. As shown in FIGS. 4 to 6, the NOx generation amount (ppm (O ₂ = 0% conversion, The same applies to the following.)), CO generation amount (ppm), small scale No. (Main indicators of the degree of dust generation) were confirmed to be significantly reduced. 4 to 6, a solid line indicates a case of 100% load, and a dashed line indicates a case of 50% load. As is clear from the results of the combustion experiment using kerosene as a fuel, according to the burner 1 according to the present invention, the strictest regulations of Tokyo among the municipalities (NOx <80 ppm for oil-fired, gas-fired And N
Ox <60 ppm) can be sufficiently cleared, and even if oil-fired regulation is to be performed in the future at the same level as gas-fired regulation, it can be sufficiently dealt with.

As a comparative example, the air jet nozzle 16
.. Were increased to eight, twice the number in the above embodiment, and an experiment was performed under the same conditions. As shown in FIGS.
The reduction rates of Ox, CO, and dust were significantly reduced. In this experiment, since the number of nozzles was doubled, the jet air flows 18 'also interfered with each other on the upstream side as well, and as shown in FIG.
1, and the boundary area between the annular flame 21 and the oxidizing flame 22 is greatly reduced as compared with the case of FIG. In FIGS. 11 to 13, a solid line indicates a case of 100% load, and a chain line indicates a case of 50% load.

As another comparative example, an experiment was conducted even when the nozzle inclination angle θ was 0 °. However, an appropriate flame form was not obtained, and the reduction rate of NOx and the like was further reduced as compared with the comparative example. . Further, due to poor mixing, small scale No. And the amount of CO generated also increased.

From the results of the comparative experiment, it is understood that the effect of reducing NOx and the like can be achieved particularly by blowing the secondary air 18 in the above-described appropriate secondary air supply mode and obtaining the above-described appropriate flame mode. Guessed. Therefore, it is necessary to set the number of the air ejection nozzles 16 and the inclination angle θ, etc., in accordance with combustion conditions and the like so as to obtain an appropriate secondary air supply mode and an appropriate flame mode.

It should be noted that the present invention is not limited to the above-described embodiment, and can be appropriately improved and changed without departing from the basic principle of the present invention.

For example, as shown in FIG.
Is provided, and the primary air 12 is supplied to the cone 23.
May be supplied to the combustion chamber 2 from the burner throat 4 by splitting the flows 12a and 12b into and out of the chamber. In this case, the swirl vanes 11a also give swirl to the divided air 12a passing inside the cone 23. Normally, the divided air amount 12a is 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 a concave portion 2c. Further, it goes without saying that the present invention can also be applied to a boiler in which the combustion chamber 2 is turned sideways and in an inverted state.

The number of the air jet nozzles 16, the inclination angle θ, the mutual interval, and the nozzle diameter are within the range in which the appropriate secondary air supply mode and the appropriate flame mode can be obtained. Can be appropriately changed according to the conditions. For example, when the diameter of the combustion chamber 2 is large, it is considered that there may be a case where eight NOx reduction rates are considered to be low as described above. However, in the case of a small boiler to which the present invention is particularly applied, generally, about 4 or 5 would be optimal. In addition, the inclination angles θ, mutual intervals, and nozzle diameters of the nozzles 16 are not necessarily the same. For example, as shown in FIG. 9, the upper and lower headers are connected by water pipe walls 24 and 25 composed of water pipes 24a... 25a. ... from water pipe wall 24, 2
In a multi-tube type once-through boiler configured to discharge combustion gas to a combustion gas passage 27 formed between the five,
The unburned gas easily enters the combustion gas passage 27 from the combustion gas outlet 26 to generate soot, but in such a case, the diameter of the nozzle 16 ′ immediately above the outlet 26 is made larger than the other nozzles 16. By increasing the ejection amount and increasing the ejection amount, it is possible to prevent unburned gas from entering the passage 27.

[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. Can be. In particular, even for small-capacity boilers with high-load combustion, regardless of whether or not they are oil-fired, it will be possible to stay within the currently strictest gas-fired regulatory framework in Tokyo, and regulations will become stricter in the future. It can sufficiently meet the demand for low NOx combustion. Moreover, a boiler can be made much more compact without the necessity of an unnecessarily high-capacity blower or an apparatus for blowing water or steam, which is extremely advantageous in terms of cost.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view showing one 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.

FIG. 3 is a cross-sectional plan view taken along the line III-III in FIG. 1;

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

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

FIG. 6 shows a small scale NO. 6 is a graph showing the measurement results of the above.

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

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

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

FIG. 10 is a cross-sectional plan view corresponding to FIG. 3 in a comparative example.

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

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

FIG. 13 shows a small scale NO. 6 is a graph showing the measurement results of the above.

[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 ... Swirling vane, 12, 12a , 12b ... primary air, 12 '...
Recirculated combustion gas, 14 ... primary combustion section, 16, 16 '... air ejection nozzle, 18 ... secondary air, 18' ... ejection air flow,
20: secondary combustion section, 21: reducing flame, 22: oxidizing flame.

Claims (1)

(57) [Claims] 1. A swirl number of 0.3 to 0.6 of primary air smaller than a theoretical combustion air amount is supplied from a burner throat into a combustion chamber.
A primary combustion air supply mechanism for supplying a swirling flow of
And a plurality of secondary combustion air supply mechanism for supplying more than secondary air primary air amount from the air ejection nozzle in the combustion chamber which is provided on the side of the burner throat, the plurality of air injection nozzles, burner throat The surrounding air
The jet air flow from the jet nozzle expands on the upstream side.
In order to eject the secondary air toward the and the downstream-side center of the primary combustion section by the primary air in the state that does not interfere with each other without dispersion, and arranged at a predetermined distance in a state of being inclined to the axis of the combustion chamber Around the reducing flame in the primary combustion section.
Oxidizing flame caused by the jet air flow from the air jet nozzle becomes clear
As a form of flame that partially digs in a distinct state
A burner for reducing nitrogen oxides, characterized in that: