JP5103311B2 - Low NOx combustion apparatus and burner used therefor - Google Patents

Description

  The present invention is mainly used for small multi-tube once-through boilers and the like, and in particular, a premixed gas obtained by mixing fuel and combustion air is injected at high speed in the form of a vertically long thin film and burned. By forming a vertically thin film flame along one heat transfer surface of the combustion chamber, the generation of NOx and CO can be greatly suppressed even when the fuel is burned at a low air ratio under high load combustion conditions. The present invention relates to a low NOx combustion apparatus and a burner used therefor.

Conventionally, boilers using gas or oil as fuel have been required to reduce emissions of NOx, CO, etc. as harmful combustion waste due to problems such as air pollution. In recent years, has the global warming due to greenhouse gases of CO ₂ in question, has been strongly demanded reduce emissions of CO _2.

Therefore, even in a small combustion apparatus compact boiler which accounts for about 10% of domestic CO ₂ total emissions, combustion equipment to reduce emissions of CO ₂ to attained the NOx reduction and CO reduction is determined It has been.

Generally, small boiler (e.g., multi-tube once-through boiler of small) In like, miniaturization increasingly willing combustion chamber is very compact, very furnace load is 1000kW / m ³ ~10000kW / m ³ The combustion conditions are very high. For this reason, in the combustion at a low air ratio, the generation of CO cannot be suppressed, so the air ratio is set to about 1.25 to 1.4.

  Conventional techniques for reducing NOx include a diffusion combustion system using a divided flame, a premixed combustion system, and the like (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3).

By the way, in the high air ratio region where the air ratio is 1.25 or more, the premixed combustion method has a flame cooling effect superior to the diffusion combustion method, and therefore, generation of NOx can be suppressed.
However, in the low air ratio region where the air ratio is 1.25 or less, the premixed combustion method cannot suppress the generation of NOx because the combustion speed increases and the flame temperature rises compared to the diffusion combustion method.

  Therefore, in a small boiler or the like, the premixed combustion method is generally used because the fuel cannot be burned at a low air ratio because CO is generated in the low air ratio combustion under a high load combustion condition as described above. This is the most excellent low NOx combustion method.

When low air ratio combustion is possible in a small boiler or the like, the exhaust gas heat loss can be suppressed, the boiler can be made highly efficient and the fuel consumption can be suppressed, and accordingly, the amount of CO ₂ emission can be reduced.
However, with the conventional technology, it has been very difficult to suppress the generation of CO and the generation of NOx under high-load combustion conditions.

JP 2003-302012 A Japanese Patent Laid-Open No. 2007-120839 JP 2007-309578 A

  The present invention has been made in view of such problems, and its purpose is to generate NOx and CO even when fuel is burned at a low air ratio under high load combustion conditions such as a small boiler. An object of the present invention is to provide a low NOx combustion apparatus and a burner used therefor which can be largely suppressed.

To achieve the above object, the invention of claim 1 of the present invention has a rectangular cross-sectional shape surrounded by a heat transfer surface of a water cooling wall structure or a water cooling jacket structure comprising a plurality of water tubes and fins. Are provided at a position eccentric to the center of the combustion chamber in the width direction at one end of the combustion chamber, and a premixed mixture of fuel and combustion air is injected into the combustion chamber at high speed for combustion. A combustion apparatus comprising a vertically long and narrow burner, wherein the burner injects the premixed gas in a vertically thin film form with an aspect ratio of 50: 1 or more and at a high speed of 50 m / sec or more , The ratio of the width of the combustion chamber to the width of the vertical thin film premixed gas jetted at high speed is 25: 1 or more, and the vertical thin film flame formed in the combustion chamber is on the side where the burner is eccentric due to the Coanda effect . To be formed along the heat transfer surface of the combustion chamber There is a butterfly.

According to a second aspect of the present invention, there is provided a burner for use in the low NOx combustion apparatus according to the first aspect, wherein the burner is formed in a vertically long, rectangular parallelepiped shape having an open end, and is a combustion air. A part of the combustion cylinder that flows in as secondary combustion air, and a vertically long inlet section and an inlet section in which the cross-sectional shape is tapered and a part of the combustion air flows in as primary combustion air A vertically long jet having a vertical slit-like jet passage and a suction hole for sucking a part of the secondary combustion air that has flowed into the combustion cylinder into the jet passage on both side surfaces of the tip portion A secondary part that is disposed in the combustion cylinder in a state in which the tip of the ejection part is located in the opening on the tip side of the combustion cylinder and is supplied into the combustion cylinder between the tip of the ejection part and the tip of the combustion cylinder Premixing with a slit-like gap that ejects part of the combustion air forward A gas injection nozzle and a gas manifold that is disposed in an inlet portion of the injection nozzle and injects fuel in a state of intersecting a flow of primary combustion air in the inlet portion, and a premixed gas of fuel and combustion air is The ratio of the width of the combustion chamber to the width of the vertical thin film premixed gas jetted at a high speed in the form of a vertically long thin film with an aspect ratio of 50: 1 or more and at a high speed of 50 m / sec or more. Is characterized by a ratio of 25: 1 or more .

The low NOx combustion apparatus of the present invention is a vertically long combustion chamber in which a transverse cross-sectional shape surrounded by a heat transfer surface of a water cooling wall structure or a water cooling jacket structure consisting of a plurality of water tubes and fins is formed in a rectangular shape. At one end, a vertically narrow burner is disposed at a position eccentric from the center position in the width direction of the combustion chamber, and the aspect ratio of the fuel / combustion air premixed gas from the burner is 50: 1 or more. It is jetted at a high speed of 50 m / sec or more in the form of a vertically long thin film, and the vertically thin thin film flame is formed along the heat transfer surface of the combustion chamber on the side where the burner is eccentric. On the upstream side of the vertical thin film flame formed along the heat transfer surface of the chamber, it is slow combustion just before blow-off due to high-speed injection of premixed gas, and it becomes a vertical thin film flame with good heat dissipation. Therefore, the rise in flame temperature is suppressed and thermal NO It is possible to suppress the occurrence, also, CO in the downstream side of the elongated thin-film flames, because the turbulence degree is high by high-speed jet flow of the premixed gas, a mixture is promoted CO combustion gas The oxidation to ₂ can be completed quickly.
As a result, the low NOx combustion apparatus of the present invention greatly suppresses the generation of NOx and CO even when fuel is burned at a low air ratio of 1.1 to 1.2 under high load combustion conditions. be able to.
In the low NOx combustion apparatus of the present invention, the ratio of the width of the combustion chamber and the width of the vertically thin film-like premixed gas injected from the burner at a high speed is 25: 1 or more. The flame is surely and satisfactorily formed along the heat transfer surface of the combustion chamber on the side where the burner is eccentric, and the above-described effects can be more reliably exhibited.

The burner of the present invention is configured to be able to inject a premixed mixture of fuel and combustion air in a vertically thin film shape with an aspect ratio of 50: 1 or more and at a high speed of 50 m / sec or more. A flame having a large surface area is formed, and radiation heat dissipation is improved, the temperature of the flame can be suppressed, and the effect of reducing the flue gas is increased and the effect of reducing NOx is increased.
Further, the burner according to the present invention divides combustion air into primary combustion air and secondary combustion air and mixes them with fuel in multiple stages, so that the reaction speed at the initial stage of combustion can be suppressed and NOx can be reduced. it can.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 and 2 show a low NOx combustion apparatus according to an embodiment of the present invention, and the low NOx combustion apparatus is disposed in a facing manner to form a pair of water cooling walls that form a combustion chamber S1 and a heat exchange chamber S2. 1, an upper header 2 and a lower header 3 that are disposed at the upper and lower positions of both water cooling walls 1 and in which the upper and lower ends of the water pipes 1a of both water cooling walls 1 are connected in a continuous manner, respectively, A heat transfer water tube group 4 including a plurality of heat transfer water tubes 4a disposed in the exchange chamber S2 and having upper and lower ends connected to the upper header 2 and the lower header 3 in communication with each other, and the combustion chamber S1 A premixed gas G ′ formed by mixing the fuel G and the combustion air A is provided at one end (upstream end of the combustion chamber S1) at a position eccentric from the central position L in the width direction of the combustion chamber S1. A vertically long and narrow burner 5 which is burned by being injected into the combustion chamber S1 in a vertically long thin film at high speed. The steam boiler (multitubular once-through boiler) is provided so as to cover the entire burner 5 and includes a wind box 7 for supplying the combustion air A supplied from the air supply duct 6 to the burner 5. ing.

As shown in FIG. 1, the pair of water cooling walls 1 are formed by arranging a plurality of water pipes 1a in a straight line and connecting adjacent water pipes 1a with strip-like fins 1b extending in the vertical direction. In addition, a vertically long combustion chamber S1 having a rectangular cross section formed between the inner wall surfaces (heat transfer surfaces) of the two water-cooling walls 1 and a heat exchange chamber S2 communicating therewith are formed. It has become.
Further, a fireproof wall 8 into which the burner 5 is inserted is provided at the upstream end portion (the right end portion in FIG. 1) of both the water cooling walls 1.

As shown in FIG. 2, the upper header 2 and the lower header 3 are each formed in a rectangular box shape. The upper header 2 has upper ends of the water pipes 1a of the two water cooling walls 1, and the lower header. 3, the lower ends of the water pipes 1a of the water cooling walls 1 are connected in a continuous manner.
The upper header 2 is connected to a steam pipe for guiding the generated steam to a steam separator (not shown), and the lower header 3 is connected to a water supply pipe (not shown). . Further, a refractory 9 is lined on the lower surface side of the upper header 2 and the upper surface side of the lower header 3 to protect the upper header 2 and the lower header 3 from high-temperature combustion gas, as well as the combustion chamber S1 and the heat. The upper surface side and the lower surface side of the exchange chamber S2 are closed.

  As shown in FIG. 1, the heat transfer water tube group 4 is disposed in a heat exchange chamber S2, and has a plurality of pipes whose upper end and lower end are connected to the upper header 2 and the lower header 3 in communication with each other. It consists of a heat transfer water tube 4a. The plurality of heat transfer water tubes 4a forming the heat transfer water tube group 4 are arranged at a constant pitch in the heat exchange chamber S2. Therefore, a combustion gas passage through which the combustion gas from the combustion chamber S1 passes is formed in the clearance between the heat transfer water tube group 4 and the two water cooling walls 1 and the clearance between the heat transfer water tube group 4.

As shown in FIG. 1, the burner 5 is provided at one end portion (upstream end portion) of the combustion chamber S1 at a position eccentric from the center position L in the width direction of the combustion chamber S1, and is inserted into the fire wall 8. The premixed gas G ′ of the fuel G and the combustion air A is jetted at a high speed in the form of a vertically thin film, and along the heat transfer surface in the combustion chamber S1 on the side where the vertically thin film flame F is eccentric. To be formed.
This phenomenon is called the Coanda effect (a phenomenon in which when the fluid flows on the surface of the object, it flows along the surface of the object so as to stick to it), the jet width of the thin-film premixed gas G ′ and the combustion chamber S1 It depends on the width ratio and the jet velocity of the premixed gas G ′.
Therefore, the burner 5 is configured to inject the premixed gas G ′ at a high speed of 50 m / sec or more in the form of a vertically long thin film having an aspect ratio of 50: 1 or more. The burner 5 is configured such that the ratio of the width of the combustion chamber S1 to the width of the vertically thin film-like premixed gas G ′ injected at a high speed is 25: 1 or more.

  Specifically, as shown in FIG. 1, the burner 5 is inserted into a fire wall 8 and a vertically long combustion cylinder 10 in which a part of the combustion air A flows as secondary combustion air A2; An injection nozzle 11 which is disposed in the combustion cylinder 10 and injects a premixed gas G ′ formed by mixing fuel G and combustion air A into the combustion chamber S 1, and is disposed in the inlet of the injection nozzle 11. And a gas manifold 12 for injecting fuel G into the injection nozzle 11, and the premixed gas G ′ is in the form of an elongated thin film with an aspect ratio of 50: 1 or more and at a high speed of 50 m / sec or more. In addition to the injection, the ratio of the width of the combustion chamber S1 to the width of the vertically thin film-like premixed gas G ′ injected at high speed is 25: 1 or more, and the vertically thin film-like flame F is introduced into the combustion chamber S1. It is to be formed.

  As shown in FIG. 3, the combustion cylinder 10 is formed into a rectangular oblong shape having a rectangular cross section with the tip (left end of FIG. 3A) open, and on both side surfaces thereof. The secondary air hole 10a for supplying a part of the combustion air A supplied from the blower (not shown) through the air supply duct 6 into the wind box 7 into the combustion cylinder 10 as the secondary combustion air A2 is provided. It is formed at regular intervals in the vertical direction.

As shown in FIG. 3, the injection nozzle 11 has a vertically long inlet portion 11a having a tapered cross-sectional shape and a vertically long discharge formed continuously with the inlet portion 11a to form a vertically oriented slit-like discharge passage. And a flange portion 11c connected to the opening side end of the inlet portion 11a. The flange portion 11c contacts the rear end of the combustion cylinder 10, and the tip of the ejection portion 11b is the opening on the front end side of the combustion cylinder 10. Is located at the center position in the combustion cylinder 10.
Further, on both side surfaces of the ejection portion 11b of the ejection nozzle 11, a part of the secondary combustion air A2 supplied into the combustion cylinder 10 from the secondary air hole 10a is ejected in a slit shape of the ejection portion 11b. A vertically long suction hole 11d for sucking into the passage is formed at regular intervals in the vertical direction.
Further, a part of the secondary combustion air A2 supplied into the combustion cylinder 10 from the secondary air hole 10a is ejected forward between the tip of the ejection part 11b of the injection nozzle 11 and the tip of the combustion cylinder 10. A slit-like gap is formed, and in the flow passage of the secondary combustion air A2 formed between the combustion cylinder 10 and the injection nozzle 11, a rectifying plate 11e is vertically arranged at regular intervals. Is arranged.

As shown in FIG. 3, the gas manifold 12 is formed in a flat and vertically long box shape with a sharpened tip, and the tip is inserted into the inlet 11 a of the injection nozzle 11, and the rear end side A fuel gas supply pipe (not shown) connected to a fuel gas supply source (not shown) is connected to the both sides of the tip of the gas manifold 12 on the inner surface of the inlet 11a of the injection nozzle 11 and the gas manifold. A fuel injection hole 12a is formed between the front end portion 12 and the outer surface of the front end portion 12 so as to intersect the inflow passage of the primary combustion air A1.
Further, the gas manifold 12 has a distance between the outer surface of its tip and the inner surface of the inlet 11a of the injection nozzle 11 at a distance that allows the primary combustion air A1 to be sucked effectively by the injection of the fuel G from the fuel injection hole 12a. Are arranged.

  A pilot burner 13 for igniting the premixed gas G ′ ejected from the burner 5 is provided in the vicinity of the burner 5 so that the pilot flame faces the tip of the burner 5. The pilot burner 13 is stopped after the premixed gas G ′ is ignited.

According to the burner 5, a part of the combustion air A supplied from the blower (not shown) through the air supply duct 6 into the wind box 7 enters the inlet 11 a of the injection nozzle 11 as the primary combustion air A 1. The primary combustion air A1 in which the fuel G that flows in and is supplied to the gas manifold 12 from a fuel gas supply pipe (not shown) flows in the inlet 11a of the injection nozzle 11 from the fuel injection hole 12a of the gas manifold 12 The fuel G and the primary combustion air A1 are mixed in a state where they intersect with each other, and this premixed gas G ′ is ejected from the opening at the tip of the ejection portion 11b of the ejection nozzle 11 in the form of a vertically long thin film, and the pilot burner 13 Are ignited and burned to form a vertically long flame F.
Further, according to the burner 5, a part of the combustion air A supplied into the wind box 7 flows into the combustion cylinder 10 as the secondary combustion air A2 from the secondary air hole 10a of the combustion cylinder 10, The secondary combustion air A2 formed between the combustion cylinder 10 and the injection nozzle 11 flows in the flow path of the secondary combustion air A2 toward the tip opening of the combustion cylinder 10, and a part of the secondary combustion air is in the middle. A2 is sucked into the injection nozzle 11 from the suction hole 11d of the injection nozzle 11 and mixed with the premixed gas G ', and the remaining secondary combustion air A2 is supplied to the front end of the injection portion 11b of the injection nozzle 11 and the front end of the combustion cylinder 10. Is injected into the combustion chamber S1 through a slit-like gap formed between the two. Since the burner 5 divides the combustion air A and mixes it with the fuel G in a multistage manner, the reaction speed at the initial stage of combustion can be suppressed and NOx can be reduced. Further, the burner 5 is injected with the secondary combustion air A2 in the combustion cylinder 10 from a slit-like gap formed between the tip of the injection portion 11b of the injection nozzle 11 and the tip of the combustion cylinder 10. The diffusion of the flame F is suppressed.

  The low NOx combustion apparatus configured as described above uses the gas fuel G as the fuel G, supplies it to the burner 5, and controls the flow rate so that the air ratio becomes 1.1 to 1.2. Combustion air A is supplied to the burner 5 to be mixed with the gas fuel G and burned.

According to the low NOx combustion apparatus, the premixed gas G ′ of the gas fuel G and the combustion air A ejected from the burner 5 is injected into the combustion chamber S1 at a high speed in the form of a vertically long thin film and ignited by the pilot burner 13. Burned.
At this time, the burner 5 is provided at one end portion of the combustion chamber S1 at a position eccentric from the center position L in the width direction of the combustion chamber S1, so that the premixed gas G ′ has an aspect ratio of 50: 1 or more. And a ratio of the width of the combustion chamber S1 to the width of the vertically long thin film premixed gas G ′ injected at a high speed is 25: 1 or more. Therefore, the vertically long thin film-like flame F formed in the combustion chamber S1 is formed along the heat transfer surface in the combustion chamber S1 on the side eccentric by the Coanda effect.

In the flame F formed along the heat transfer surface in the combustion chamber S1, in the vicinity of the injection nozzle 11, the premixed gas G 'is injected at a high speed exceeding the flame propagation speed, so that a flame is formed in the mainstream. In other words, the flame F slowly propagates from a side flow with a slow flow velocity, that is, combustion just before blow-off (blow-off).
Moreover, the flame F is a vertically long thin film-like flame F having a large surface area, and therefore has a good radiation heat dissipation property. However, since the flame F follows the heat transfer surface of the combustion chamber S1, the contact heat dissipation property is also good. Can also suppress the temperature of the flame F.
Further, when the flame F is shifted to one water cooling wall 1 (heat transfer surface) of the combustion chamber S1, the combustion gas is recirculated in the combustion chamber S1 space between the other water cooling wall 1 and the flame F. A flow G ″ is generated. This recirculation flow G ″ of the combustion gas returns to the vicinity of the tip of the burner 5 and joins with the main flow, which has the effect of slowing the combustion.

Thus, in the low NOx combustion apparatus, slow combustion occurs on the upstream side of the flame F because of the high-speed injection flow, and turbulence degree on the downstream side of the flame F because of the high-speed injection flow. As a result, the mixing of combustion gas is improved and the change from CO to CO ₂ can be completed quickly.
Therefore, in this low NOx combustion apparatus, even if the fuel G is burned at a low air ratio of 1.1 to 1.2, the combustion speed is suppressed on the upstream side of the flame F as compared with the normal premixed combustion method. Therefore, the temperature rise of the flame F can be mitigated and the generation of thermal NOx can be suppressed, and the combustion can be completed quickly on the downstream side of the flame F, so that the residual CO can be suppressed.

  Then, the combustion gas generated in the combustion chamber S1 flows into the heat exchange chamber S2 from the combustion chamber S1, and moves downstream in the combustion gas passage while contacting the heat transfer water tube group 4 and the both water cooling walls 1. In the meantime, heat is applied to both water cooling walls 1 and the plurality of heat transfer water tubes 4a forming the heat transfer water tube group 4 by contact heat transfer, and then passes through a flue (not shown) connected to the heat exchange chamber S2. Discharged outside the boiler.

The graph of FIG. 4 is a graph comparing the combustion performance of the steam boiler using the low NOx combustion apparatus of the present invention, the burner of the present invention, and the steam boiler employing the conventional premixed combustion system previously developed by the applicant. It is. The steam boiler using the low NOx combustion apparatus of the present invention, the burner of the present invention and the steam boiler adopting the conventional premixed combustion system are operated under the same conditions, and the fuel G used is natural gas / LPG. It was used.
As is apparent from the graph of FIG. 4, the steam boiler using the low NOx combustion apparatus of the present invention and the burner of the present invention generate NOx and CO as compared with the steam boiler adopting the conventional premixed combustion system. Was able to be greatly suppressed.

  In the above-described embodiment, the combustion chamber S1 is formed by the heat transfer surface of the water-cooled wall 1 structure. In other embodiments, the heat transfer surface of the water-cooled jacket structure is used. The combustion chamber S1 may be formed (not shown).

1 is a schematic cross-sectional view of a low NOx combustion apparatus according to an embodiment of the present invention. It is a partially cutaway side view of the low NOx combustion apparatus. The burner of a low NOx combustion apparatus is shown, (A) is a cross-sectional view of the burner, and (B) is a partial side view of the burner. It is the graph which compared the combustion performance of the steam boiler which employ | adopted the conventional premixed combustion system which the steam boiler using the low NOx combustion apparatus of this invention, the burner of this invention, and this applicant developed previously.

Explanation of symbols

  1 is a water cooling wall, 1a is a water pipe, 1b is a fin, 5 is a burner, 10 is a combustion cylinder, 11 is an injection nozzle, 11a is an inlet portion, 11b is an ejection portion, 11d is a suction hole, 12 is a gas manifold, and A is combustion Air for primary combustion, A1 for primary combustion, A2 for secondary combustion, F for flame, G for fuel, G 'for premixed gas, L for the center in the width direction of the combustion chamber, and S1 for the combustion chamber.

Claims (2)

A vertically long combustion chamber surrounded by a heat transfer surface of a water cooling wall structure or a water cooling jacket structure consisting of a plurality of water pipes and fins, and a longitudinal direction of the combustion chamber at one end of the combustion chamber A combustion apparatus comprising a vertically long and narrow burner that is provided at a position eccentric from a central position and injects and burns a premixed mixture of fuel and combustion air into a combustion chamber at high speed, In addition, the premixed gas is injected in the form of a vertically thin film having an aspect ratio of 50: 1 or more and at a high speed of 50 m / sec or more, and the width of the combustion chamber and the width of the vertically mixed thin premixed gas to be injected at a high speed The ratio of the ratio is 25: 1 or more, and a vertically thin film-like flame formed in the combustion chamber is formed along the heat transfer surface of the combustion chamber on the side where the burner is eccentric due to the Coanda effect. A low NOx combustion device. The burner used in the low NOx combustion apparatus according to claim 1, wherein the burner is formed in a vertically long and flat rectangular shape with an open end, and a part of the combustion air is used as secondary combustion air. An inflowing combustion cylinder, a longitudinal inlet portion in which a cross-sectional shape is tapered and a part of the combustion air flows in as primary combustion air, and a slit-like jet passage that is vertically connected to the inlet portion And a vertically long jet part formed with a suction hole for sucking a portion of the secondary combustion air that has flowed into the combustion cylinder into the jet passage on both side surfaces of the tip part, and the tip of the jet part burns A portion of the secondary combustion air that is disposed in the combustion cylinder in a state of being located in the opening on the tip end side of the cylinder and is supplied into the combustion cylinder between the tip of the ejection portion and the tip of the combustion cylinder is ejected forward A premixed gas injection nozzle formed with a slit-like gap and an injection nozzle And a gas manifold that injects fuel in a state intersecting with the flow of primary combustion air in the inlet, and has an aspect ratio of 50: 1 or more for the premixed mixture of fuel and combustion air The ratio of the width of the combustion chamber to the width of the premixed gas in the form of a vertically long thin film that is injected at a high speed is 25: 1 or more. A burner characterized by that.

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