JP2007101035A - Burner for liquid fuel of boiler with exhaustion port along center axis of furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a burner which effectively reduces NOx without increasing CO and soot, in a combustion furnace having exhaustion ports along an axis of a furnace. <P>SOLUTION: The burner is equipped with: a spray nozzle 3 for spraying fuel toward the furnace; an inner cylinder 2 in which a tip end side of the spray nozzle is stored; and an outer cylinder 1 provided on an outer circumference side of the inner cylinder. A plurality of air nozzles 7 are provided in a downstream end face of the outer cylinder which extend further toward a downstream side. A blowout port for blowing out main air for combustion into the furnace is formed in a downstream end face of these air nozzles. When inside of the furnace is separated by a plane produced with a line drawing through the axis of the furnace and connecting the axis and the exhaust port of the furnace and a line positioned at ±100°, the burner has air nozzles only on the exhaust port side of the furnace, and a combustion guide 8 is provided in the downstream of the air nozzles so as not to overlap these nozzles. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a low-NOx burner for liquid fuel that can suppress NOx generated by combustion.

  Conventionally, in order to suppress NOx generated by combustion, a burner using a gaseous fuel containing no N component in the fuel has been put to practical use. This type of burner is easy to control the flame and in the fuel. Since it contains no N component, it has the feature that NOx generated by combustion can be easily suppressed, but there is a problem that running gas is expensive because expensive gas fuel is used.

  Therefore, although it is difficult to suppress NOx in order to reduce running costs, an external exhaust gas recirculation method that uses a relatively low-cost liquid fuel and can reduce the amount of NOx generated during combustion of this type of liquid fuel. Burners using water spraying or a combination of both have been employed.

However, these methods not only increase the equipment cost, but also tend to decrease thermal efficiency and durability, and in recent years, a low-NOx burner for liquid fuel that can be more easily reduced in NOx has been proposed ( For example, see Patent Document 1).
Patent No. 3527456

  The burner described in Patent Document 1 has the structure shown in FIG. 5, and is a burner that uses flame splitting, concentration combustion, and exhaust gas internal recirculation as a principle of NOx suppression.

In particular, the combustion gas in the furnace to which the burner is attached is guided directly below the burner from the hydrodynamic effect of the jet of combustion air, and NOx generation during combustion is suppressed by low oxygen combustion by mixing the combustion gas and combustion air. Since the exhaust gas recirculation method is the main NOx suppression mechanism, it works well in a forward-flow type combustion furnace such as a flue tube type, but depending on the structure of the furnace, the function may not be fully demonstrated.

For example, in a furnace that has a combustion gas outlet in the immediate vicinity of the burner attachment, such as a reversal combustion furnace, or a combustion furnace that has an exhaust outlet along the central axis of the furnace (commonly called an Ω-flow furnace) Because the draft force of the furnace flue is stronger than the draft force produced by the burner combustion air jet, the combustion exhaust gas does not return to the burner and NOx suppression is not achieved, and conversely the combustion air exiting the jet outlet In some cases, the exhaust gas is pulled out to the exhaust port immediately and the combustibility is deteriorated.

Also, in a combustion furnace with an exhaust port along the center axis of the furnace, the flame of the burner extends along this axis and flows to the exhaust port side, so before the combustion is completed, it enters the furnace exhaust port and the water pipe And because it is cooled by a water-cooled wall, it causes soot generation and CO increase.

However, even in such a furnace, it is desired to comply with recent strict environmental regulations, and burners and furnace structures have been improved.

An object of the present invention is to provide a burner capable of effectively reducing NOx without causing an increase in CO and soot in a combustion furnace having an exhaust port along the central axis of the furnace.

The burner of the present invention is a burner attached to a boiler having an exhaust port that is elongated along the central axis of the furnace, and includes a spray nozzle that sprays fuel toward the furnace, and an inner cylinder member that houses the tip side of the spray nozzle. An outer cylinder member disposed on the outer peripheral side of the inner cylinder member, and an air nozzle extending further downstream is provided on the downstream end face of the outer cylinder member, and these air nozzle downstream end faces are provided in the furnace. The burner is formed with a jet outlet for jetting combustion main air (hereinafter referred to as secondary air), and the furnace passes through the central axis of the furnace and the line connecting this axis and the furnace exhaust furnace is ± 100 When divided into two planes formed from a line of °, a plurality of air nozzles are provided only on the end face on the exhaust port side.

  In the conventional burner, the combustion air from the secondary air port of the air nozzle is ejected so as to be distributed substantially evenly around the central axis of the furnace, so that the central axis of the furnace and the central axis of the flame are substantially the same. It was considered a match. However, as shown in FIG. 6, in the Ω flow type once-through boiler having an exhaust port along the central axis of the furnace, the flame flutters to the exhaust port side due to the draft force generated when the combustion exhaust gas flows along the road, and the center of the furnace Often formed off axis.

For this reason, a convection heat transfer zone of a water tube group in which soot is generated when a part of the flame comes into contact with the water tube near the exhaust port or combustion gas is arranged outside the water tube that forms the furnace before the combustion is completed To increase CO.
Further, if the combustion exhaust gas is exhausted from the exhaust port at an early point, the force for circulating the combustion exhaust gas to the burner becomes weak, and the suppression of NOx generation is also reduced.

  Even if the low NOx burner shown in FIG. 5 is employed, the force of circulating the combustion exhaust gas to the burner is weak, and the expected result cannot be obtained.

On the other hand, according to the present invention, the combustion air from the secondary air port is intensively jetted in the form of creating an air curtain along the exhaust port of the furnace, and the flame generated by this secondary air is also curtain-shaped. Because it is thin and fast, it prevents the combustion gas that has not been completely combusted from flowing to the exhaust port and prevents unburned oil droplets and oil droplets that are in the middle of combustion from reaching the exhaust-side water pipe.

In addition, since flame formation concentrates on one side of the furnace and collides with the refractory material on the hearth at a high speed, the high-temperature combustion gas reverses and rises on the opposite side of the flame flow, and the vaporized fuel In addition to promoting combustion and suppressing the generation of soot, the temperature and amount of combustion exhaust gas circulated to the burner source is increased, and as a result, suppression of NOx generation due to combustion is promoted.

Conversely, if the secondary air port is concentrated on the side opposite to the exhaust port, the reverse flow combustion gas that can be reversed to the flame forming side is sucked into the exhaust port on the way, so the speed of the combustion exhaust gas returning to the burner Since the temperature decreases and the temperature of the fuel decreases, the fuel vaporization / ignition becomes slow, soot is easily generated, and the amount of combustion exhaust gas circulated also decreases, so that the effect of suppressing NOx generation also decreases.

This is because even when most of the secondary air ports are provided on the exhaust port side and one part is mounted on the opposite side, the secondary air ejected from here and the resulting flame flow obstruct the flow of the inversion combustion gas. As a result, the effect of suppressing NOx generation decreases.

In the burner, the jet direction of the secondary air is directed toward the furnace center axis, and the air flow is not excessively brought close to the exhaust port.

As the secondary air ejected from the air nozzle moves away from the nozzle port, the flow velocity decreases and widens, so when approaching the exhaust port in this area, it is sucked and exhausted without contributing to combustion, not only worsening combustibility but also thermal efficiency. Will be lowered. In a commercial combustor machine, three-position and four-position control is common and is designed with rated combustion, so this phenomenon is particularly likely to occur in a low combustion region.

  In addition, the provision of a plurality of secondary air nozzles in the circumferential direction is not only for the purpose of suppressing NOx by dividing the flame by the jet air exiting from these nozzles, but also for the combustion exhaust gas recirculated to the nozzle origin. This is to improve the mixing of the oil droplets sprayed from the fuel nozzle, flowing between the nozzles, to promote the vaporization and ignition of the fuel, and to suppress the NOx by the low oxygen combustion.

  The combustion guide according to claim 4 prevents the oil droplets sprayed from the fuel nozzle and having a large momentum from passing through the air jet and reaching the water cooling wall with insufficient vaporization, and is ignited and formed in the guide. Control the direction of the flame and suppress the fire spreads in the radial direction of the furnace and approaches the exhaust port. In addition, the combustion guide is red-hot, which promotes the vaporization of fuel oil droplets by this radiant heat, separates the air jet and flame flow from the combustion gas flow, and returns the combustion gas to the burner as a reverse flow. This is to promote the flow.

  Switching to this burner can be expected to significantly reduce NOx without increasing CO and soot generation in Ω flow type once-through boilers, which occupy most of the commercially available once-through boilers.

  Next, specific embodiments of the low-NOx burner for liquid fuel according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a longitudinal sectional view and a side view on the nozzle side of a low-NOx burner for liquid fuel according to the first embodiment of the present invention.

  FIG. 4 shows an example of a combustion guide attached downstream of FIG.

  FIG. 7 shows a longitudinal sectional view of an example of an Ω flow type once-through boiler 100 to which the burner and the combustion guide are attached. Combustion air is sent from an air blower (not shown) to the wind box 102, appropriately distributed by the burner 101, and jetted to the furnace 103.

  1 includes a spray nozzle 3 for spraying fuel toward the furnace, an inner cylindrical member 2 in which the tip end side of the spray nozzle is accommodated, and an outer cylindrical member 1 disposed on the outer peripheral side of the inner cylindrical member. A burner in which an air nozzle 5 extending further downstream is provided on the downstream end face of the outer cylinder member, and an outlet for ejecting combustion main air into the furnace is formed on the air nozzle downstream end face. Yes, as shown in the side view, when the inside of the furnace passes through the center axis of the furnace, and is divided into two planes made of a line passing through this axis and the furnace exhaust port and a line of ± 110 °, only the end surface on the exhaust port side Indicates a burner with multiple air nozzles.

  Combustion air sent to the wind box 102 enters the outer cylinder 1, and 10% or less of the air is sent from the primary air port 4 to the inner cylinder 2, but all the remaining air is jetted air from the air nozzle 5 into the furnace. It is ejected in the intended direction.

  The flame ignited in the combustion guide in FIG. 4 extends strongly to the refractory material 111 at the lower end of the furnace in the form of a curtain at the exhaust port of the furnace, reverses upon hitting the refractory material, and enters the burner base of the throat refractory material 110 as high-temperature combustion exhaust gas. Circulate.

  The combustion gas that has been returned to the burner due to the draft force generated by the combustion air is drawn directly downstream of the burner to promote fuel vaporization and ignition, and to suppress NOx generation during combustion due to a decrease in the oxygen concentration of the combustion air.

  Concentration of the air nozzle to the furnace exhaust port side suppresses the flow of the flame to the exhaust port as shown in the schematic diagram of FIG. 7 and promotes the circulation of the combustion gas.

  FIG. 8 shows NOx values at the time of A heavy oil rated combustion when concentrated as described above and when air nozzles are uniformly arranged circumferentially on the end surface of the outer cylinder member. It can be seen that the concentrated arrangement has a greater NOx suppression effect than the uniform arrangement.

  Further, FIG. 9 shows an example in which the generation of soot at the time of low combustion of A heavy oil when the position of the air nozzle is on the exhaust port side and on the other side is compared. Soot generation is clearly lower when the air nozzle is on the exhaust side, and the NOx concentration is also lower, although not shown. This tendency does not change with rated combustion.

  FIG. 2 shows an example of a burner in which the air nozzle 6 is inclined at an angle θ ° toward the furnace center axis so that the flame does not approach the exhaust port and the circulation flow is not obstructed. This angle θ is 0 to 15 °, preferably 5 to 10 °.

  FIG. 3 is an example of a burner having a nozzle constituting the outlet of the air nozzle 7 and having a nozzle whose outermost plate is inclined at an angle η ° so that the flame does not approach the exhaust port while maintaining the circulation flow. This angle η is 15 to 40 °, preferably 25 to 35 °.

  The combustion guide of FIG. 4 prevents the oil droplets sprayed from the fuel nozzle and having a large momentum from passing through the air jet and reaching the water cooling wall while being insufficiently vaporized, and to be ignited and formed in the guide. This is a cylindrical tube with an appropriate diameter D and length L necessary to control the direction of the fire and to suppress the fire spreading in the radial direction of the furnace and approaching the exhaust port. In addition, since this pipe is heated by a flame or circulating combustion gas, the vaporization of the fuel oil droplets is further promoted by the heat radiated from this pipe. Further, since the air jet / flame flow is separated from the flow of the combustion gas, the flow of the combustion gas recirculated to the burner as an inverted flow is also promoted.

  In this combustion guide, if the distance between the outside of the circumferentially arranged air nozzles and the central axis of the furnace is R, the diameter D is 2.4R or more and 2.8R or less, and the length L is 100mm or more and 500mm or less. Metal tube.

  FIG. 10 shows an example of carrying out A heavy oil rated combustion in an optimized state using the burner of claim 3 and the combustion guide of claim 4. It can be seen that the NOx, CO, and soot values sufficiently satisfy the current environmental regulations.

It is sectional drawing and a side view of the burner of embodiment of Claim 1. It is sectional drawing and a side view of the burner of embodiment of Claim 2. It is sectional drawing and side view of the burner of embodiment of Claim 3. It is sectional drawing and a side view of the combustion guide of embodiment of Claim 4. It is sectional drawing and a side view of the burner of embodiment shown by the reference patent 3527456. It is a flame cross-sectional schematic diagram of the conventional burner in an Ω flow type once-through boiler. It is a flame cross-sectional schematic diagram of the burner of the present invention in an Ω flow type once-through boiler. Comparison chart of NOx in A heavy oil rated combustion of burners with air nozzles arranged evenly in the circumferential direction and concentrated arrangement on the exhaust side Comparison chart of soot in A fuel oil low combustion of burner in which air nozzles are concentrated and arranged opposite to the exhaust nozzle side Figure of exhaust gas properties in A heavy oil rated combustion when the burner of the present invention is optimized

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner cylinder 2 Outer cylinder 3 Nozzle assembly 4 Primary air port 5 Claim 1 type main air nozzle 6 Claim 2 type main air nozzle 7 Claim 3 type main air nozzle 8 Combustion guide
100 Ω flow once-through boiler
101 Conventional burner
102 wind box
103 Furnace (combustion chamber)
104 water pipe
105 Combustion gas chamber
106 Smoke chamber
107 Exhaust duct
108 water chamber
109 Steam room
110 Higuchi refractory material
111 Furnace refractory
112 Proposed burner

Claims (4)

  A burner attached to a boiler having an exhaust port that is elongated along the central axis of the furnace, and a spray nozzle (3) that sprays fuel toward the furnace, an inner cylinder member that houses the tip side of the spray nozzle, and the inner cylinder An outer cylinder member 1 disposed on the outer peripheral side of the member (2), and an air nozzle (5) extending further downstream is provided on the downstream end face of the outer cylinder member (1). The burner has a jet outlet that ejects main combustion air into the furnace at the downstream end face of the nozzle. The burner passes through the central axis of the furnace, and the line connecting the furnace exhaust port with this axis is ± 100 ° A burner characterized by having a plurality of air nozzles only on the end surface on the exhaust port side when divided into two planes formed by lines.   A plurality of air nozzles (6) provided in a biased manner as described above are provided on the downstream end face of the outer cylinder member at intervals in the circumferential direction of the face, and the central axis of these air nozzles is the furnace central axis. The burner according to claim 1, wherein the burner has an inclination of 0 to 10 °.   In the plurality of air nozzles (7) arranged as described above, the shape of the nozzle outlet is not limited, but the plate that forms the outlet shape, the plate that is the outermost side from the central axis of the furnace is the central axis of the furnace The burner according to claim 1, wherein the burner has an inclination of 20 ° to 40 °. In the burner, if the distance between the outer circumference of the air nozzles arranged on the circumference and the furnace center axis is R, the combustion guide (8) having a diameter of 2.4R to 2.8R and a length of 100mm to 500mm. The burner according to claim 1, wherein the burner is attached downstream of the air nozzle so as not to overlap the nozzle.

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