JP3552994B2 - Low NOx burner - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a low NOx burner, and more particularly to a low NOx burner capable of reducing nitrogen oxides (hereinafter referred to as “NOx”) generated during combustion.
[0002]
[Prior art]
In recent years, air pollution has become a major social problem, and prevention thereof has been demanded by society.
Along with this, in particular, suppression of NOx generation is becoming an indispensable condition for burners mounted in boilers, incinerators, and the like.
In urban areas, NOx emission standards are 80 ppm or less for liquid fuels (O ₂ = 0% converted value; the same applies hereinafter). However, in the near future, this standard value will become even more severe. It is getting.
On the other hand, in the field of marine equipment, NOx regulations for main marine diesel engines have been implemented from the viewpoint of marine pollution prevention, and similar measures have been taken for auxiliary equipment such as burners installed in boilers and incinerators. Is expected to be implemented.
[0003]
[Problems to be solved by the invention]
By the way, as a method of reducing the NOx value in the conventional burner, for example, a self-exhaust gas circulation system, a water / steam spray system, a two-stage combustion system, a rich-burn combustion system, a split flame system, a thin-film flame system, an external exhaust gas circulation system, etc. However, depending on these conventional burners, it is difficult to suppress NOx to 80 ppm or less even when a fuel with a low nitrogen content such as kerosene, light oil, or heavy fuel oil A is used as the fuel. there were.
In the case of the external exhaust gas circulation system, the amount of circulated exhaust gas is easily affected by the draft, and it is difficult to adjust the circulation rate. Therefore, the reliability of the NOx reduction rate is lacking, and the flame tends to be unstable due to the mixing of the exhaust gas. There was a problem that.
Further, as a side effect of these methods, there is a problem that the flame becomes longer and the combustion chamber must be enlarged, which increases the volume of a boiler, an incinerator and the like, and increases initial costs.
[0004]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the conventional low NOx burner, and has as its object to provide a low NOx burner capable of reducing the length of a flame and suppressing generation of NOx. .
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a low NOx burner according to the present invention is provided with an atomizer holder having a fuel spray atomizer at a tip thereof at a center position of the combustion cylinder, and a combustion flowing through the combustion cylinder so as to externally fit the atomizer holder. In a low NOx burner in which an auxiliary air cylinder having an auxiliary air hole for taking in a part of air for use is provided and a radial flow type swirler is provided at a tip position of the auxiliary air cylinder between the combustion cylinder and the atomizer holder, a radial flow type is provided. The swirler is configured by arranging a plurality of blades between a front plate and a rear plate having a disk shape of different diameters, the outer diameter of the front plate is smaller than the inner diameter of the combustion cylinder, and The outer diameter of the rear plate is larger than the inner diameter of the hole opening at the center of the front plate, and the inner diameter of the hole opening at the center of the rear plate is set to be equal to or larger than the inner diameter of the hole opening at the center of the rear plate. Is characterized in that it is larger than the outer diameter of .
[0006]
In this low NOx burner, a strong swirling vortex is generated by primary air introduced through a radial flow type swirler provided at a tip end of an auxiliary air cylinder between a combustion cylinder and an atomizer holder, and fuel is generated in the swirling vortex. As fuel is injected, active mixing of fuel and air is performed just before the flame is formed, which promotes gasification of the sprayed fuel particles and reduces the turbulence that spreads radially in the combustion space. In the violent mainstream region, the mixing of air and fuel is promoted, and further, the mixing with the secondary air is activated in this region. Due to these effects, a local high-temperature region is less likely to be formed, and NOx is reduced. At the same time, the flame is shortened, and the required minimum amount of auxiliary air introduced through the auxiliary air cylinder can cool the fuel spray atomizer and prevent backflow due to swirling vortex.
[0007]
The radial swirler is configured by arranging a plurality of blades between a front plate and a rear plate each having a disc shape having a different diameter, and the outer diameter of the front plate is determined by the inner diameter of the combustion cylinder. Is smaller than the outer diameter of the rear plate, and the inner diameter of the hole opening at the center of the front plate is equal to or larger than the inner diameter of the hole opening at the center of the rear plate. By making the diameter larger than the outside diameter of the auxiliary air cylinder, it is possible to determine the optimal ratio between primary air and secondary air, and to prevent backflow while generating swirling vortices downstream. Can be.
[0008]
Further, the secondary air passage formed between the outer edge of the front plate of the radial flow type swirler and the inner peripheral surface of the combustion cylinder is partially closed by a plurality of divided plates at a plurality of positions, and a plurality of secondary air passages are formed. Air holes can be formed.
[0009]
As a result, the secondary air is divided and supplied, and this action causes a lean combustion to reduce the generation amount of NOx.
[0010]
Further, the throttle can be formed such that the inner diameter of the opening at the tip end of the combustion cylinder is smaller than the inner diameter of the other portion.
[0011]
Thereby, the reduced secondary air can be collided and mixed at an early stage, thereby further reducing NOx and shortening the flame.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a low NOx burner according to the present invention will be described below with reference to the drawings.
[0013]
1 to 4 show a first embodiment of a low NOx burner according to the present invention.
[0014]
This low NOx burner is provided with a combustion cylinder 1 having a cylindrical or polygonal shape and through which combustion air B flows, and an atomizer holder 2 disposed at a center position of a front end opening of the combustion cylinder 1. At the same time, the fuel spray atomizer 3 is attached to the tip of the atomizer holder 2.
[0015]
The combustion cylinder 1 is configured such that combustion air B is supplied into the combustion cylinder 1 and the air is ejected from an opening at the end.
[0016]
The fuel spray atomizer 3 provided at the center position of the combustion cylinder 1 is configured to be supplied with liquid fuel from the rear, atomized by the fuel spray atomizer 3, and sprayed.
[0017]
An auxiliary air cylinder 5 having a plurality of auxiliary air holes 5a for taking in a part of the combustion air B flowing through the combustion cylinder 1 is provided so as to fit the atomizer holder 2 to the outside. A radial swirler 4 is provided at the distal end of the auxiliary air cylinder 5 between the holders 2.
[0018]
The electrode rod 7 is attached along the outer peripheral surface of the atomizer holder 2, and the tip of the electrode rod 7 is connected to the fuel atomizer 3 through an auxiliary air hole 5 a formed on the rear surface of the auxiliary air cylinder 5. Provide it near the tip.
[0019]
The radial swirler 4 is configured such that a plurality of blades 4b are formed between a front plate 4a and a rear plate 4c having a disc shape having different diameters to form a swirling air passage.
In this case, the relationship between the front plate 4a and the rear plate 4c having a disc shape with different diameters is as follows: the outer diameter of the front plate 4a is D1, the inner diameter of the combustion cylinder 1 is D, and the outer diameter of the rear plate 4c is D3. , D>D1> D3, that is, the outer diameter D1 of the front plate 4a is set smaller than the inner diameter D of the combustion cylinder 1 and larger than the outer diameter D3 of the rear plate 4c.
When the inside diameter of the hole opening at the center of the front plate 4a is D2 and the inside diameter of the hole opening at the center of the rear plate 4c is D4, the opening at the center of the front plate 4a satisfies the relationship of D2 ≧ D4. The inner diameter D2 of the circular hole is set to be larger than or equal to the inner diameter D4 of the circular hole opened at the center of the rear plate 4c.
Further, the outer diameter D3 of the rear plate 4c is set to be larger than the outer diameter D5 of the auxiliary air cylinder 5.
[0020]
On the other hand, the plurality of blades 4b joined between the front plate 4a and the rear plate 4c are joined at an angle θ with respect to the radial axis as shown in FIG. A swirling air passage 4d is formed between the blade 4b and the rear plate 4c.
[0021]
Further, a difference between the outer diameter D1 of the front plate 4a and the inner diameter D of the combustion cylinder 1 is provided between the front plate 4a of the radial swirler 4 disposed in the combustion cylinder 1 and the combustion cylinder 1. A ring-shaped space is formed, and this space is used as a secondary air passage 6.
In this case, as shown in FIG. 2, a plurality of divided plates 6b are arranged along the circumferential direction of the ring-shaped secondary air passage 6, thereby dividing the ring-shaped secondary air passage 6 into a plurality of divided air passages. A plurality of secondary air holes 6a are formed by being partially closed by a plate.
[0022]
Next, the operation of the low NOx burner will be described.
Combustion air B supplied from a blower (not shown) is supplied from the rear of the combustion cylinder 1, circulates in the combustion cylinder 1, and has primary combustion air B <b> 1, secondary air B <b> 2, and It is divided into three types of auxiliary air B0.
That is, a part of the combustion air B is sucked into the auxiliary air cylinder 5 from the auxiliary air hole 5a formed on the outer peripheral portion or the rear surface of the auxiliary air cylinder 5, becomes the auxiliary air B0, and passes through the auxiliary air cylinder 5. Then, it flows into the combustion space 9 through the opening formed at the center of the radial swirler 4 and further through the swirling mixer 8.
Further, another part of the combustion air B passes through the swirling air passage 4d formed in the radial swirler 4 and passes through the swirling mixing section 8 of the radial swirler 4 as primary air B1, It flows into the combustion space 9.
Further, the remaining combustion air B flows through the secondary air holes 6a formed in the outer peripheral portion of the radial swirler 4 and flows into the space 9 between the combustion chambers as secondary air B2.
[0023]
As described above, the combustion air B flowing in the combustion cylinder 1 is divided into three types, that is, the auxiliary air B0, the primary air B1, and the secondary air B3. After being introduced, the fuel injected by the fuel spray atomizer 3 is ignited and burned.
That is, the fuel supplied to the fuel spray atomizer 3 via the atomizer holder 2 is injected from the injection hole of the fuel spray atomizer 3 and flows into the combustion space 9 through the swirl mixer 8 together with the auxiliary air B0. . Then, the flame formed in the combustion space 9 is maintained by the primary air B1, and is further completely burned in the combustion space 9 by the secondary air B2.
[0024]
Next, the operation of the radial swirler 4 will be described.
A part of the combustion air B passes through the swirling air passage 4d of the radial swirler 4 and further flows as primary air B1 through the swirling mixer 8 in the radial swirler 4 into the combustion space 9. Since the primary air B1 flows from the outside toward the inside in the radial direction while having an angle θ, a strong swirling vortex is generated in the swirling mixing unit 8.
Since fuel is injected during the swirling vortex, active mixing of fuel and air is performed immediately before the flame is formed, and gasification of the injected fuel spray 12 is promoted.
Furthermore, the swirling vortex due to the primary air B1 forms a recirculation region 10 on the central axis of the combustion space 9 and is kept flame.
The outer peripheral region of the recirculation region 10 is the main flow region 11 formed by the action of the swirling vortex, and is a region with severe turbulence. However, the main flow of the fuel spray 12 is not in the recirculation region 10 but almost in this region. Since the gas passes through the highly turbulent region, the mixing of the fuel and the combustion air becomes active.
Further, since this flow radially spreads between the combustion chambers 9, the flow collides with the subsequent secondary air B <b> 2 and the mixing becomes active.
By the above operation, a local high-temperature region is hardly formed, NOx is reduced, and flame shortening is realized.
[0025]
Next, the dimensions of the radial swirler 4 will be described.
In order to reduce NOx, the air distribution between the primary air B1 and the secondary air B0 is important. In this embodiment, the air distribution of the primary air B1 is smaller than that of a burner using another baffle type flame stabilizer. Allocation ratio is increasing.
The outer diameter D1 of the front plate 4a of the radial swirler 4 is set smaller than the inner diameter D of the combustion cylinder 1 and larger than the outer diameter D3 of the rear plate 4c for the following reasons.
That is, if D = D1, the secondary air passage 6 will not be secured, and the secondary air will not flow. Since the secondary air is required by spray combustion, it is necessary to satisfy D> D1. In order for the primary air B1 to pass through the swirling air passage 4d, it is necessary to change the flow direction inward in the radial direction. However, when D1 = D3, most of the primary air B2 becomes the secondary air B2 and almost no primary air B1 flows. Therefore, by setting D1> D3, an optimal ratio between the primary air B1 and the secondary air B2 is secured.
[0026]
The following is a method for setting the inner diameter D2 of the circular hole opening at the center of the front plate 4a of the radial swirler 4 to be equal to or larger than the inner diameter D4 of the circular hole opening at the center of the rear plate 4c (D2 ≧ D4). There is a reason.
In other words, if D2 <D4, the primary air B1 has a greater effect of blowing not only downstream but also upstream. Therefore, by setting D2 ≧ D4, a swirling vortex is reliably generated on the downstream side, and a backflow is prevented as much as possible.
[0027]
Next, the auxiliary air cylinder 5 will be described.
The auxiliary air B0 cools the atomized fuel atomizer 3 and, at the same time, flows a minimum amount of air to prevent backflow by the primary air B1.
That is, although the central part of the vortex becomes negative pressure due to the swirling flow, a part of the combustion gas in the downstream region is involved, but this combustion gas is prevented from being involved in the upstream.
The auxiliary air B0 is introduced from the auxiliary air hole 5a opened in the outer periphery of the auxiliary air cylinder 5 and the rear plate, and the amount of passage is determined by the size of this passage area.
[0028]
Next, the plurality of secondary air holes 6a and the dividing plate 6b will be described.
When the secondary air passage 6 is closed by the dividing plate 6b, a region that is difficult to contact with the secondary air and a region that is difficult to contact are formed in the combustion space 9.
The action of such divided secondary air causes a lean burn, thereby reducing the amount of NOx generated. Since the swirling air described above has a large effect of radially expanding, the downstream portion located at the dividing plate 6b has no flow of the secondary air B2. Therefore, when observing the flame from the downstream side, it is as if the flame is divided. Looks like.
[0029]
Next, FIG. 5 shows a second embodiment of the low NOx burner of the present invention.
[0030]
This low NOx burner has a throttle 13 formed between the combustion cylinder 1 and the radial swirler 4 to reduce the diameter of the front end of the combustion cylinder 1 without disposing the dividing plate 6b. The configuration is the same as that of the low NOx burner of the first embodiment.
[0031]
In this low NOx burner, the secondary air B2 is not divided, unlike the low NOx burner of the first embodiment, and flows uniformly from around the radial swirler 4.
Since the throttle 13 is formed such that the inner diameter of the opening portion at the tip end of the combustion cylinder 1 is smaller than the inner diameter of the other portion, the secondary air B2 can be contracted. The primary air B1 and the fuel, which radially expands, can collide and mix the secondary air B2 that has been contracted at an early stage, so that low NOx and short flame can be realized.
[0032]
As described above, the low NOx burner of the present invention has been described based on a plurality of embodiments. However, the present invention is not limited to the configuration described in the above embodiment, and the configuration may be appropriately changed without departing from the gist of the present invention. It can be changed.
For example, the fuel spray atomizer 3 in the above-described embodiment is a pressure injection valve that injects a liquid fuel such as petroleum, but may be a type that injects a fuel such as gaseous fuel or a premixed gas, in addition to fuel such as petroleum. Further, a two-fluid injection valve using steam or air as a spray medium may be used.
Similarly, the fuel spray atomizer 3 has been described as a single-hole type atomizer, but the invention is not limited thereto, and a multi-hole type atomizer may be used. As a result, the possibility of realizing rich-and-lean combustion increases, and an effect of increasing the NOx reduction effect can be expected.
[0033]
【The invention's effect】
According to the low NOx burner of the present invention, a strong swirling vortex is generated by the primary air introduced through the radial swirler provided at the distal end of the auxiliary air cylinder between the combustion cylinder and the atomizer holder. Because fuel is injected into the swirling vortex, active mixing of fuel and air is performed just before the flame is formed, which promotes gasification of the sprayed fuel particles and radially in the combustion space. In the turbulent mainstream region that spreads, the mixing of air and fuel is promoted, and furthermore, the mixing with secondary air becomes active in this region, and these effects make it difficult for local high-temperature regions to be formed. , NOx is reduced, flame shortening is realized, and cooling of the fuel spray atomizer and backflow due to swirling vortex can be prevented by the minimum necessary auxiliary air introduced through the auxiliary air cylinder.
Thereby, the volume of the boiler including the combustion chamber, the incinerator and the like can be reduced, and a low NOx burner that can reduce the initial cost can be obtained.
[0034]
The radial swirler is configured by arranging a plurality of blades between a front plate and a rear plate each having a disc shape having a different diameter, and the outer diameter of the front plate is determined by the inner diameter of the combustion cylinder. Is smaller than the outer diameter of the rear plate, and the inner diameter of the hole opening at the center of the front plate is equal to or larger than the inner diameter of the hole opening at the center of the rear plate. By making the diameter larger than the outside diameter of the auxiliary air cylinder, it is possible to determine the optimal ratio between primary air and secondary air, and to prevent backflow while generating swirling vortices downstream. Can be.
[0035]
Further, the secondary air passage formed between the outer edge of the front plate of the radial flow type swirler and the inner peripheral surface of the combustion cylinder is partially closed by a plurality of divided plates at a plurality of positions, and a plurality of secondary air passages are formed. By forming the air holes, the secondary air is supplied in a divided manner, and this action causes a lean combustion to reduce the amount of generated NOx.
[0036]
Further, by forming a throttle so that the inner diameter of the front end opening of the combustion cylinder is smaller than the inner diameter of the other portion, the reduced-flow secondary air is collided and mixed at an early stage, thereby further lowering the flow. NOx and flame reduction can be realized.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a first embodiment of a low NOx burner according to the present invention.
FIG. 2 is a side view of the same.
FIG. 3 is a side longitudinal sectional view taken along line AA of FIG. 2;
FIG. 4 is an explanatory diagram showing a state of fuel and air flow of the low NOx burner.
FIG. 5 is a sectional view showing a second embodiment of the low NOx burner of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Combustion cylinder 2 Atomizer holder 3 Fuel spray atomizer 4 Radial swirler 4a Front plate 4b Blade 4c Rear plate 4d Swirling air passage 5 Auxiliary air cylinder 5a Auxiliary air hole 6 Secondary air passage 6a Secondary air hole 6b Divider 7 Electrode Rod 8 Swirling mixing section 9 Combustion space 10 Recirculation area 11 Swirl main flow area 12 Fuel spray 13 Restrictor B Combustion air B0 Auxiliary air B1 Primary air B2 Secondary air D Combustion cylinder inner diameter D1 Front plate outer diameter D2 Front plate inner diameter D3 Rear plate outer diameter D4 Rear plate inner diameter

Claims (3)

The center position of the combustion tube (1), the atomizer holder having a fuel spray atomizer (3) (2) and the atomizer holder (2) so as to fitted to the tip, flowing combustion tube (1) in the combustion An auxiliary air cylinder (5) having an auxiliary air hole (5a) for taking in a part of the working air (B) is provided, and the auxiliary air cylinder (5) between the combustion cylinder (1) and the atomizer holder (2) is provided. In a low NOx burner provided with a radial flow type swirler (4) at the tip position, the radial flow type swirler (4) is placed between a front plate (4a) and a rear plate (4c) having a disc shape with different diameters. The outer diameter (D1) of the front plate (4a) is smaller than the inner diameter (D) of the combustion tube (1), and the rear plate (4c). And the inner diameter (D2) of the circular hole opening at the center of the front plate (4a) is made larger than the outer diameter (D3) of the rear plate. Center and opening to the inside diameter of the circular hole (D4) or more of 4c), further, the outer diameter of the rear plate (4c) (D3), that is larger than the outer diameter of the auxiliary air cylinder (5) (D5) Features a low NOx burner. A secondary air passage (B2) formed between the outer edge of the front plate (4a) of the radial swirler (4) and the inner peripheral surface of the combustion tube (1) is formed by a plurality of split plates (6b) . The low NOx burner according to claim 1 , characterized in that a plurality of secondary air holes (6a) are partially closed at a plurality of locations. The low NOx burner according to claim 1 or 2, wherein the throttle (13) is formed such that the inner diameter of the front end opening of the combustion cylinder (1) is smaller than the inner diameter of the other part.

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