JP3176004B2 - Low NOx gas fired burner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly used for a steam boiler, a hot water boiler and the like, and relates to a low NOx gas burning burner using gas as a fuel.

[0002]

2. Description of the Related Art Conventionally, in a burner of a steam boiler or a hot water boiler, as a measure for reducing NOx (nitrogen oxide),
Methods such as exhaust gas circulation combustion, hydrogenation combustion, and steam injection combustion are employed.

In other words, the exhaust gas recirculation combustion system aims to reduce NOx by recirculating a part of the exhaust gas to a burner to lower the oxygen partial pressure. In addition, 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 circulated by itself, the recirculation rate of the exhaust gas is reduced under a low load condition, so that an effective reduction of NOx cannot be achieved. Further, in any case, it is necessary to increase the blowing function power more than necessary, and there is a problem in cost.

In the hydrogenated combustion and steam injection combustion systems,
The blowing of water may cause corrosion of the can body, and the boiler efficiency also decreases. Further, a water blowing device such as a pump is required separately, which causes a problem in cost. Of course, in the steam injection combustion system, if the steam generated by the boiler is used,
When the boiler efficiency is reduced and the steam generated by the boiler is not used or cannot be used, a steam generator or the like is separately required, resulting in a significant increase in cost.

On the other hand, in a gas-fired burner using gas as a fuel, a low-NOx gas-fired burner in which the amount of generated NOx is on the order of 50 ppm is adopted by employing a method such as split combustion, concentration combustion, and self-recirculation combustion. Has been put to practical use. However, the low NOx gas-fired burner has an output of 400,000 kca.
1 / h to 2,000,000 kcal / m ³ h and furnace load of 250
NO when applied to a boiler of 10,000 kcal / m ³ h or more
It was difficult to suppress the generation amount of x to 40 ppm (O ₂ = 0% conversion) or less. In particular, gas-fired burners are stricter in regulation than oil-fired burners, and are extremely problematic.

The present invention provides a low-N boiler capable of greatly reducing the generation of NOx even in a high-load combustion boiler without causing such problems in boiler function and cost.
It is an object to provide an Ox gas fired burner.

[0008]

In order to achieve the above object, a low NOx gas-fired burner of the present invention has a burner throat ring at the center thereof, which coincides with the axis of the combustion chamber and communicates with the combustion chamber, A wind box provided with a primary air supply chamber communicating with the burner throat ring and a secondary air supply chamber formed around the primary air supply chamber, provided in the wind box,
A primary air supply mechanism that controls the amount of primary air supplied to the primary air supply chamber to less than the theoretical air amount and supplies primary air to the burner throat ring in a swirling flow, and a secondary air supply around the burner throat ring A predetermined interval is provided to communicate the chamber and the combustion chamber, and the secondary air is ejected toward the downstream center of the primary combustion portion by the primary air, and the jet air flow from the secondary air nozzle is upstream of the primary air. At the side, a plurality of secondary air nozzles inclined with respect to the axis of the combustion chamber so as not to interfere with each other, and a secondary air nozzle provided in the wind box and having a secondary air nozzle that is larger than the primary air amount into the combustion chamber from the secondary air nozzle. A secondary air supply mechanism that supplies secondary air, and a secondary air supply mechanism that is located at the center of the wind box and guides the swirled primary air to the burner throat ring and swirls part of the primary air inside The cone to be introduced is arranged concentrically at the center of the cone, and the gas is ejected in the centrifugal direction to premix with the primary air in the cone, and the premixed gas mixture is substantially centrifuged into the combustion chamber from the cone tip. And a stem mechanism for jetting in the direction.

[0009]

The primary air supplied to the primary air supply chamber by the primary air supply mechanism is guided by the cone while turning, and is guided from the burner throat ring to the combustion chamber. In addition, a part of the primary air is given a swirling force and introduced into the cone, and after being premixed with the gas ejected into the cone from the stem,
It is ejected from the tip of the cone into the combustion chamber. The gas mixture gas ejected from the tip of the cone is ignited and burned together with the primary air ejected from between the cone and the burner throat ring. At this time, since the primary air is supplied to the combustion chamber in a state smaller than the theoretical combustion air amount, a primary combustion section performing reduction combustion is formed in the combustion chamber. Needless to say, in the primary combustion section, the combustion gas, which is the reducing gas generated by the swirling of the primary air and the like, is recirculated, so that the residence time increases and stable combustion is continued. On the other hand, the secondary air supplied to the secondary air supply chamber by the secondary air supply mechanism is blown from the secondary air nozzle toward the downstream center of the primary combustion section. As a result, a secondary combustion section is formed by diffusion combustion on the downstream side of the recirculation region of the primary combustion gas, and complete combustion in the combustion chamber is achieved. That is, on the downstream side of the jet air flow, the air diffuses and mixes, and uniform slow combustion is performed. On the upstream side of the jet air flow, remarkable oxidative combustion is performed without air diffusion. Thus, by the supply of the primary air and the secondary air, the reducing flame and the oxidizing flame are clearly distinguished and mixed on the upstream side, and the flames are gradually diffused and mixed toward the downstream side. Since the two-stage combustion is performed in a certain state, the generation of NOx, CO, and the like can be significantly reduced even in the gas-fired high-load combustion where it is difficult to reduce NOx.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a hot water boiler equipped with a low NOx gas-fired burner according to an embodiment of the present invention (output: 500,000 kcal)
/ H, furnace load: about 2.5 million kcal / m ³ h). In FIG. 1, reference numeral 1 denotes a boiler body made of a metal plate for storing boiler water, 1a denotes a can plate forming a boiler body, 2 denotes a furnace which is immersed in can water to form a combustion chamber 3, 4 Is a burner mounting flange.

As shown in FIG. 1, the low-NOx gas-fired burner is mounted on a burner mounting flange 4 so as to coincide with the axis of the combustion chamber 3.
, A primary air supply mechanism 6, a secondary air nozzle 7, a secondary air supply mechanism 8, a cone 9, and a stem mechanism 10.

The wind box 5 is disposed so as to coincide with the axis of the combustion chamber 3, and is fixed to the burner mounting flange 4 as shown in FIGS. 1 and 2, and comprises an inner side wall, an outer side wall and an outer peripheral wall. The box-shaped main body 11 is fixed to the center of the inner wall so as to be aligned with the axis of the combustion chamber 3,
A cylindrical burner throat ring 12 communicating with the combustion chamber 3
And a partition cylinder 15 and an annular plate 16 which are arranged in the main body 11 and partition the inside of the main body 11 into a primary air supply chamber 13 communicating with the burner throat ring 12 and a secondary air supply chamber 14 located outside the primary air supply chamber 13. And so on. FIG.
In the figure, 17 is a refractory attached to the inner wall, 18 is a burner plate attached to the center of the outer wall, and this burner plate 18 has a cone 9, a stem mechanism 10, a pilot burner 19 and a flame detector ( (Not shown) is attached.

The primary air supply mechanism 6 is provided in the wind box 5 to control the amount of primary air supplied to the primary air supply chamber 13 to a theoretical amount of air or less, and to send the primary air 20a to the burner throat ring 12. It is supplied in a swirling flow. Specifically, the primary air supply mechanism 6 forms a communication part 21 for communicating the primary air supply chamber 13 and the secondary air supply chamber 14 with the partitioning cylinder 15 as shown in FIGS. A manual or automatic primary air amount adjusting damper 22 is provided in the section 21, and a plurality of swirling vanes 23 are annularly arranged in parallel in the primary air supply chamber 13. That is, a part of the combustion air 20 supplied to the secondary air supply chamber 14 by the secondary air supply mechanism 8 described later is guided from the communication part 21 to the primary air supply chamber 13, and this is used as primary air 20 a and the swirl vanes 23 To supply the gas to the burner throat ring 12. The opening degree of the primary air amount adjusting damper 22 is set so that the primary air amount supplied from the primary air supply chamber 13 to the combustion chamber 3 is equal to or less than the theoretical air amount. The air 20a is 0.1% of the theoretical combustion air amount.
It is set to be 5 to 0.8. The number of swirls of the primary air 20a is determined by the inner diameter of the burner throat ring 12, the shape of the swirl vane 23, and the like. Usually, the swirl number S of the swirling flow is designed to be 0.3 to 0.8. It is preferable to keep it. Here, the swirl number means a 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).

As shown in FIGS. 1 and 3, the secondary air nozzle 7 is formed of a metal cylinder, and is disposed in parallel with a predetermined annular space (concentric area) around the burner throat ring 12. It is penetrated and fixed to the refractory 17 and the inner wall of the main body 11 so as to communicate the secondary air supply chamber 14 and the combustion chamber 3. The secondary air nozzle 7 is provided with a secondary air 20b.
Is inclined at a predetermined angle θ with respect to the axis of the combustion chamber 3 in order to cause the primary air 20a to jet toward the downstream center of the primary combustion section 33. By the way, the jet airflow 20b 'from each secondary air nozzle 7 is gradually diffused toward the downstream side.
The number and the inclination angle θ are such that the jet airflows 20b 'do not interfere with each other on the upstream side, but diffuse and interfere with each other on the downstream side, and enter below the recirculation region of the primary combustion gas (hereinafter, referred to as the following). As in the case of “appropriate secondary air supply form”), it is appropriately set according to the recirculation force of the primary combustion gas, the shape of the combustion chamber 3 and the like. Generally, four or five nozzles are used for 20 to 25 nozzles.
It is preferable to arrange them at equal intervals in an inclined posture of °. In this embodiment, five nozzles (outside diameter 34 mm, wall thickness 3 m
m stainless steel pipes) are arranged at equal intervals in a 20 ° inclined posture. In addition, the ejection speed of the secondary air 20b is a condition necessary to secure the above-described appropriate secondary air supply form, and generally, the rating (load 1) of the boiler concerned.
00%) under a load condition of 40 m / s to 80 m / s.
It is preferable to set s.

The secondary air supply mechanism 8 is provided in the wind box 5 and supplies a secondary air 20b larger than the primary air amount into the combustion chamber 3 from the secondary air nozzle 7. Specifically, as shown in FIGS. 1 and 2, the secondary air supply mechanism 8 connects the air supply duct 24 to the secondary air supply chamber 14 and connects the air supply duct 24 to the secondary air supply chamber 14.
A damper 26 for automatically adjusting the air flow, the opening of which is controlled by a motor 25, is provided therein, and the air for combustion 20 supplied from the air supply duct 24 to the secondary air supply chamber 14 by the blower is automatically controlled according to the combustion load. It is configured to be.
The amount of secondary air 20b supplied from the secondary air nozzle 7 to the combustion chamber 3 is larger than the amount of primary air.

The cone 9 is disposed at the center of the wind box 5 and guides the primary air 20a swirled by the swirl vanes 23 to the burner throat ring 12 while swirling a part of the primary air 20a. Is to be introduced. Specifically, the cone 9 has a cylindrical shape, is disposed at the center of the wind box 5 so as to coincide with the axis of the combustion chamber 3, and is attached to the inner surface of the burner plate 18. A centering guide (not shown) is attached to the outer peripheral surface of the cone 9 so that the gap between the outer peripheral edge of the flame holding plate 28 and the inner peripheral surface of the burner throat ring 12 is uniform. Further, a plurality of cone vanes 27 are provided at the base end of the cone 9, and a part of the primary air 20 a in the primary air supply chamber 13 is introduced into the cone 9 while swirling. . This corn vane 27 is used for the primary air 20 supplied into the corn 9.
In addition to applying a swirling force to a to uniformly mix the gas G in the cone 9 with the gas G, the jetting direction of the premixed gas from the tip of the cone 9 is also determined. Further, an annular flame holding plate 28 facing the inner peripheral surface of the burner throat ring 12 is provided at the tip of the cone 9, and the flame holding plate 28 has a slit for preventing burnout over the entire circumference. Notches for the pilot burner 19 and for flame monitoring are formed. The flame holding plate 28 and the burner throat ring 12
The flow rate of the primary air 20a ejected from the gap into the combustion chamber 3 is 15 m / s to 30 m / s when the boiler load is 50%.
It is preferable to set s.

The stem mechanism 10 is disposed concentrically at the center of the cone 9 and ejects gas G in the centrifugal direction to premix with the primary air 20a in the cone 9 and to mix the premixed gas mixture. The gas is blown from the tip of the cone 9 into the combustion chamber 3 in a substantially centrifugal direction. Specifically, as shown in FIG. 1, the stem mechanism 10 is attached to the center of the burner plate 18 in a penetrating state in a state coinciding with the axis of the combustion chamber 3, and includes a gas supply pipe, a control valve (not shown), and the like. A stem 29 connected to a gas supply source via a shaft, a support shaft 30 attached to the stem 29 and coinciding with the axis of the stem 29, and a stem 29 attached to the support shaft 30 so as to be movable in the axial direction. Gas adjusting disk 3 for adjusting the amount of gas ejected from the nozzle and ejecting gas G in the centrifugal direction
And a disk 32 attached to the tip of the support shaft 30 and positioned at the opening of the tip of the cone 9 to determine the jetting direction and jetting speed of the gas mixture in the cone 9. The direction of the gas mixture jetted from the cone 9 into the combustion chamber 3 depends on the angle of the cone vane 27 and the disc 32.
Can be adjusted by changing the position of the gas mixture gas.
° is preferable. Further, it is preferable to set the ejection speed of the gas mixture gas to be 12 m / s or more when the load is low (load 50%).

Next, the operation of the low NOx gas-fired burner will be described. The combustion air 20 from the blower is supplied to the secondary air supply chamber 14 of the wind box 5 through the air supply duct 24 and the air volume automatic adjustment damper 26, and then flows into the primary air supply chamber 13 from the communication portion 21. It is divided into a primary air 20a and a secondary air 20b supplied from the secondary air supply chamber 14 to the combustion chamber 3 via the secondary air nozzle 7. Primary air 20a flowing into the primary air supply chamber 13
Are swirled by swirling vanes 23 and are further divided into those for premixing and those for flame stabilization. That is, after a part of the primary air 20a is given a swirling force by the cone vane 27 and introduced into the inside of the cone 9 and premixed with the gas G (natural gas 13A) ejected from the stem 29 in the centrifugal direction, The gas is ejected in a substantially centrifugal direction from the gap between the tip of the cone 9 and the disc 32 and supplied to the combustion chamber 3. Also, the remaining primary air 20a
Is guided along the outer peripheral surface of the cone 9 while turning,
The fuel is injected into the combustion chamber 3 from a gap between the flame holding plate 28 and the burner throat ring 12. Then, the tip of the cone 9 and the disk 32
The gas mixture gas ejected from the gap of the primary air 20 ejected from the gap between the flame holding plate 28 and the burner throat ring 12
The fuel gas is ignited and burned by the pilot burner 19 together with a.
The flame shape is a hollow thin-film swirling flame because gas and air are ejected in a ring shape.

At this time, since the primary air 20a is supplied to the combustion chamber 3 in a state smaller than the theoretical air amount, a primary combustion section 33 that performs diffusion and reduction combustion is formed in the combustion chamber 3. In the primary combustion section 33, since the primary air 20a is supplied in a swirling flow, the generated combustion gas, which is a reducing gas, is re-used together with the formation of the negative pressure section by the flame holding plate 28. The fuel is circulated, so that the residence time is increased and stable combustion is continued. Of course, the gas G is sufficiently premixed with a part of the primary air 20a, and the primary air 20a is supplied from between the flame holding plate 28 and the burner throat ring 12.
Is supplied in a swirling manner, so that a uniform primary combustion section 33 is formed, the generation of a heat spot is effectively prevented, and the generation of thermal NOx due to the heat spot can be suppressed.

Further, the secondary air 20b is supplied from the secondary air nozzle 7 to the secondary air 20b.
Is blown toward the downstream center of the primary combustion section 33,
On the downstream side of the recirculation region of the primary combustion gas, a secondary combustion portion 34 is formed by diffusion combustion, and complete combustion in the combustion chamber 3 is achieved. That is, the jet airflow 20b '
On the downstream side, air diffuses and mixes, and uniform slow combustion is performed. On the upstream side of the jet airflow 20b ', reduction combustion with a theoretical air amount or less is performed. Therefore, the jet air flow 20
In the upstream part of b ', the oxidizing flame (visually transparent) partially enters the surroundings of the reducing flame (bright flame), and the flame is present in the annular area immediately below the secondary air nozzle 7. Therefore, the reducing flame and the oxidizing flame are clearly distinguished and mixed, and the boundary area between the two flames is large.

As described above, by supplying the primary air 20a and the secondary air 20b, the reducing flame and the oxidizing flame are clearly distinguished and mixed on the upstream side, and both flames gradually decrease toward the downstream side. Since two-stage combustion is performed in a state of diffusion and mixing, even in high-load combustion where it is difficult to reduce NOx, NOx can be significantly reduced and generation of CO and the like can be suppressed well. can do.

FIG. 4 shows the structure of the above embodiment.
A combustion experiment was performed under the conditions of 100% and 50% load, and the relationship between the primary air amount, the NOx generation amount (ppm (O ₂ = 0% conversion, the same applies hereinafter)) and the CO generation amount (ppm) was graphed. The solid line shows the case of 100% load, and the chain line shows the case of 50% load. As is clear from the graph, it was confirmed that the low NOx gas-fired burner according to the present invention significantly reduced the NOx generation amount and the CO generation amount even in the high load combustion. In the configuration of the above embodiment, the maximum temperature in the combustion chamber 3 (the secondary combustion section 34 indicates the maximum temperature) is rated (load 100%).
Was 1130 ° C. or less. By the way, N of gas G fuel
As a measure against thermal NOx as a measure against Ox, the temperature is 1
It is known that when the temperature is 300 ° C. or lower, the generation amount of NOx becomes very small. Therefore, the temperature of the combustion chamber 3 becomes 1130
C. or less in the above embodiment.
It is understood that the amount of x generation is very small.

The present invention is not limited to the above-described embodiment, but can be appropriately modified and changed without departing from the basic principle of the present invention.

For example, in the above embodiment, the primary air supply chamber 13 and the secondary air supply
And a communication portion 21 that communicates with the air supply duct 24.
A part of the combustion air 20 supplied to the secondary air supply chamber 14 is guided from the communication part 21 to the primary air supply chamber 13, but the communication part 21 is omitted in other embodiments. The primary air supply chamber 13 is connected to another air supply duct provided with a damper, and the primary air supply chamber 13 and the secondary air supply chamber 14 are separately connected to the primary air 20a and the secondary air 20b from the respective air supply ducts. You may make it supply.

In the above embodiment, the inside of the box-shaped main body 11 is partitioned by the partition cylinder 15 and the annular plate 16 to form the primary air supply chamber 13 and the secondary air supply chamber 14, but the partition cylinder It may be divided by only 15.

In the above embodiment, the gas adjusting disk 31 is disposed at the opening of the tip of the stem 29,
The gas G is ejected in the centrifugal direction from the gap between the gas and the gas adjusting disk 31. In other embodiments, the distal end opening of the stem 29 is closed and the outer peripheral wall of the distal end of the stem 29 is closed. A plurality of nozzle holes may be formed in each of the nozzles, and gas G may be ejected from each nozzle in the centrifugal direction.

In the above embodiment, the low NOx gas-fired burner is applied to a hot water boiler, but may be applied to a steam boiler or the like, or to a boiler in which the combustion chamber 3 is oriented horizontally or vertically. It goes without saying that you can do it.

[0028]

As is apparent from the above description, according to the present invention, the generation of NOx and CO can be greatly suppressed, and the generation amount of NOx can be reduced even in high load combustion. It can be suppressed to 40 ppm or less. Further, since the flame of the two-stage combustion system and the primary combustion part is a thin-film swirling flame having a hollow shape, an increase in the flame temperature can be suppressed and the heat load distribution to the furnace becomes uniform. Further, since the gas and a part of the primary air are sufficiently mixed in the cone and supplied to the combustion chamber, it is advantageous in combustion and there is no fear of flashback. In addition, since the cone and the stem are used, the pressure of the gas ejection portion is lower than that using the gas nozzle, and there is no need to supply a high-pressure gas, and sufficient combustion can be performed with the low-pressure gas. In addition, rapid combustion and the like are suppressed by a two-stage air supply system (two-stage combustion) and a uniform combustion method.
Combustion noise also decreases.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view of a low NOx gas-fired burner according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is a graph showing measurement results of NOx generation amount and CO generation amount.

[Explanation of symbols]

3 is a combustion chamber, 5 is a wind box, 6 is a primary air supply mechanism, 7 is a secondary air nozzle, 8 is a secondary air supply mechanism, 9
Is a cone, 10 is a stem mechanism, 12 is a burner throat ring, 13 is a primary air supply chamber, 14 is a secondary air supply chamber,
20a is primary air, 20b is secondary air, 33 is a primary combustion section, and G is gas.

Continuation of front page (56) References JP-A-52-140920 (JP, A) JP-A-56-82306 (JP, A) JP-A-60-191103 (JP, A) JP-A-4-110508 (JP) JP-A-50-55933 (JP, A) JP-A-5-118519 (JP, A) JP-A-53-134233 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB Name) F23D 14/02 F23C 11/00 323-324 F23D 14/24 F23D 14/70

Claims (1)

(57) [Claims] 1. A burner throat ring (12) having a central portion aligned with the axis of the combustion chamber (3) and communicating with the combustion chamber (3).
A wind box (5) having a primary air supply chamber (13) communicating with the burner throat ring (12) and a secondary air supply chamber (14) formed around the primary air supply chamber (13);
The primary air (20a) is provided in the wind box (5) to control the amount of primary air supplied to the primary air supply chamber (13) to be less than or equal to the theoretical air amount, and swirl the primary air (20a) to the burner throat ring (12). A primary air supply mechanism (6) to be supplied, and a secondary air supply chamber (14) arranged around the burner throat ring (12) at predetermined intervals so as to communicate the secondary air supply chamber (14) and the combustion chamber (3). (20b) is ejected toward the downstream center of the primary combustion section (33) by the primary air (20a), and the jet airflow (20b ') from the secondary air nozzle (7) is located upstream of the primary air combustion section (33). Are provided in a plurality of secondary air nozzles (7) inclined with respect to the axis of the combustion chamber (3) so as not to interfere with each other, and in the wind box (5). Primary air volume in room (3) A large secondary air (20b) two for supplying secondary air supply mechanism (8) is disposed in the central portion of the wind box (5), turning the primary air (20
a) which guides a) to the burner throat ring (12) and introduces a part of the primary air (20a) into the interior while swirling it; and a concentrically arranged gas at the center of the cone (9). (G) is spouted in the centrifugal direction and cone (9)
And a stem mechanism (10) for premixing with the primary air (20a) therein and ejecting the premixed gas mixture gas from the cone (9) tip into the combustion chamber (3) in a substantially centrifugal direction. Low NOx gas fired burner.