JP5063203B2 - Gas burner - Google Patents

Description

  The present invention relates to a gas burner having a function of improving combustion performance during low load operation.

  Conventionally, various proposals have been made for techniques for reducing harmful combustion exhaust materials generated by combustion in combustion equipment and the like, particularly for techniques for reducing NOx. As an example, a partially premixed gas burner that supplies combustion air separately from primary and secondary is used, and a thin-film cylindrical premixed airflow is formed in the downstream area of the premixer jet port. There is a method for reducing NOx by combusting secondary air for combustion from the outside toward the mixed airflow and forming a large number of small flames to completely burn without generating local high temperature parts. This is known from US Pat.

  In this prior art, secondary air is diverted from a primary air supply line and blown into the primary combustion section through a large number of small holes so that secondary combustion is simultaneously performed in the primary combustion section. Therefore, combustion exhaust gas and secondary air cannot be mixed and supplied to the combustion section for complete combustion. Further, since it is difficult to improve the straightness of the flame, for example, when a burner used for a small once-through boiler is used, there is a problem that it is difficult to improve the combustion efficiency.

  Therefore, as shown in FIGS. 4 (a) and 4 (b), the present inventors are provided with a Laval nozzle forming portion 60 at a position extending coaxially with the fuel injection port 52 in the distal end portion of the outer cylinder 50, and forming the Laval nozzle. A diverted air circulation part 54 is formed between the outer peripheral edge 62 of the blowing part 61 of the part 60 and the inner surface 50a of the outer cylinder 50, and in front of the outlet of the diffuser 64 connected to the throat part 63 of the Laval nozzle forming part 60. A gas burner 70 having a structure in which a secondary combustion gas suction portion 65 having a plurality of secondary combustion gas suction holes 66 formed by mixing the air branched in the circulation portion 54 and combustion exhaust gas is provided is disclosed in Japanese Application No. 2006-11936). In the figure, black arrows indicate fuel gas, white arrows indicate air, and hatched arrows indicate air-fuel mixture.

  However, in the gas burner 70 according to the invention of the prior application, it is effective if the cross section orthogonal to the combustion gas traveling direction of the combustion chamber is circular or square (aspect ratio is 1: 1), but the cross section of the combustion chamber is rectangular and vertical and horizontal. When the ratio is large (for example, when the combustion chamber is long and narrow), the exhaust gas recirculation flow in the width direction becomes weak or the flame does not reach the heat transfer surface at the upper and lower ends in the vertical direction. Since there is a problem that heat transfer is not performed, an improved version of this is obtained by the prior invention (Japanese Patent Application No. 2006-297697).

  However, the improved gas burner of the invention of the prior application has a problem that the flame becomes slightly unstable during operation at a low load, and the CO and NOx values tend to increase. In general, a general small once-through boiler product is required to operate with a "50,100"% load or a "30,50,100"% load. Therefore, the gas burner according to the invention of the prior application exhibits high performance when performing rated operation, but when operating at low load, the combustion gas flow rate becomes slow and backfire occurs, or fuel and air are not sufficiently mixed. The flame becomes unstable and needs to be improved.

Japanese Patent No. 3417367

  The present invention has been made to solve such problems, and provides a gas burner configured to ensure a gas flow rate corresponding to a load during operation and to obtain a stable combustion effect even at a low load. It is intended to do.

In order to achieve the above object, a gas burner according to the present invention comprises:
A Laval nozzle forming portion is provided at a coaxial line extending position with the fuel gas supply means in the distal end portion of the outer cylinder, and a shunt air circulation portion is formed between the suction portion opening edge of the Laval nozzle forming portion and the inner surface of the outer cylinder, In the gas burner in which a secondary combustion gas suction part is provided in front of the diffuser outlet of the Laval nozzle forming part by mixing the air branched in the diverted air circulation part and the combustion exhaust gas,
The flame holding plate provided in the secondary combustion gas suction part is provided so as to be able to expand and contract with respect to the flame ejection flow path in the secondary combustion gas suction part.

In the present invention, it is preferable that the flame holding plate has a configuration in which a drive mechanism is operated by a control device so that a movable portion thereof is automatically operated according to a supply amount of fuel gas (second invention). In addition, the flame holding plate has a base end portion pivotally attached to a portion connected to the outlet of the diffuser, and a pair of the flame holding plates are arranged opposite to each other, and the flame holding plates are connected to each other at the end portion. In addition, when an operation force is applied by the flame ejection adjusting means connected to the outer surface of one of the flame holding plates, both the flame holding plates can be tuned and moved from the pivot point so that the opening width can be varied. (3rd invention).

  In the present invention, in a gas burner capable of increasing the NOx value reduction effect by high-speed jetting of a mixture of fuel gas and air while dividing and supplying combustion air in multiple stages with a simple configuration and performing multistage combustion, the low load combustion During operation, the flame can be burned with a stable flame by restricting the flame ejection passage that ejects in accordance with the load.

  According to the present invention, when operating at a low load, the combustion gas (by controlling automatically so as to narrow the outlet interval by the flame holding plate provided in the combustion section so as to match the supply amount of the supplied fuel gas. The flow rate of the premixed gas) is ejected without decreasing, and the flame is stabilized and combustion can be performed effectively. Therefore, even if the operation is performed at a low load, unstable combustion can be avoided and an increase in the NOx value can be suppressed. In addition, the flame can be burned in a vertically long and very thin state even when operated at a low load, which is more effective as a gas burner used for a small once-through boiler.

  Next, specific embodiments of the gas burner according to the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing a main part of a gas burner according to an embodiment of the present invention. FIG. 2 is a diagram showing an outline of the flame ejection adjusting means for operating the flame holding plate, and FIG. 3 is a perspective view showing the burner partially cut away.

  A gas burner 10 according to this embodiment includes an outer case 11 (corresponding to an outer cylinder in the present invention) having a rectangular cross section provided with a mounting structure (not shown) that can be mounted on a burner mounting portion of a combustion device, and the outer case 11. The mixing means 20 for mixing the combustion gas and the combustion air provided so as to jet the flame with the axial center line Q aligned, the fuel gas supply means 30, and the ejection of the flame at the flame ejection section are adjusted. It is comprised with the flame ejection adjustment means 40. FIG.

  The outer case 11 is formed in a flat rectangular shape with a front-side open rectangular section of the required internal method, and the mixing means 20 and the fuel gas supply means 30 are incorporated on the axis Q of the outer case 11. Yes. An air supply port by a blower is connected to the rear end (direction opposite to the combustion side) of the outer case 11 although a specific structure is not shown.

  The mixing means 20 is dimensioned to fit within the outer case 11 as described above, and has a Laval nozzle shape (hereinafter referred to as “Laval nozzle forming portion 21”) in the longitudinal direction (axial direction) as shown in FIG. The center line is arranged on the axis Q of the outer case 11 so that the front end protrudes from the front end of the outer case 11.

  The Laval nozzle forming portion 21 is formed in a flat cross-sectional shape that constricts an inlet portion 22 (corresponding to the suction portion of the present invention) toward an intermediate throat portion 23, and an inner wall surface of the outer case 11 is formed at an opening edge 22a. 12 and the air circulation part 15 (corresponding to the diversion air circulation part of the present invention) is arranged at a required interval. In addition, a secondary combustion gas suction portion 25 is provided at the tip of the diffuser 24 and is formed in a required length in the axial direction with an area larger than the opening area. The Laval nozzle forming portion 21 is effective in sucking the primary air by supplying the fuel gas from the gas ejection hole 34 of the fuel gas supply means 30 to the space between the inlet portion 22 and the outer surface of the box of the fuel gas supply means 30. It is arranged with the distance which can be done automatically. The Laval nozzle forming portion 21 is supported by a support member (not shown) on the outer surface portion so that the posture can be maintained with respect to the outer case 11.

  The secondary combustion gas suction part 25 formed to be connected to the tip of the Laval nozzle forming part 21 protrudes from the tip of the outer case 11 on both sides of the part connected to the outlet of the diffuser 24. A pair of flame holding plates 25a, 25b are provided at intervals, and a plurality of suction holes 26 for secondary combustion gas are provided in the longitudinal direction in both flame holding plates 25a, 25b.

  The pair of flame holding plates 25a and 25b in the secondary combustion gas suction part 25 are pivotally supported by support shafts 27 and 27 along the longitudinal axis at the base end part, and the flame jet adjusting means 40 is used as the axis of the burner. The flow path of the combustion flame can be expanded and contracted toward the core Q.

  As the flame ejection adjusting means 40, one end of a tilting operation rod 43 is connected to a projecting piece 42 projecting perpendicularly to the outer surface of one flame-holding plate 25a, and the rod 43 extending rearward is connected. For example, a rack gear 44 is connected to the rear end portion. The rack gear 44 meshes with a pinion 45a attached to the output shaft of the motor 45, and the rod 43 is advanced and retracted so that the flame holding plate 25a can tilt inward from an upright state. Has been. In addition, the pair of flame holding plates 25a and 25b has a bracket 25d attached to the outer surface at the end in the longitudinal direction, and a pair of links 46 and 46 that are pivotally attached to the bracket 25d at the other end. Is engaged with a guide slot 28a formed in an end plate 28, 28 provided so as to surround both ends of the secondary combustion gas suction part 25 or a member (not shown) provided outside the end plate 28. The other flame-holding plate 25b is tilted symmetrically with respect to one flame-holding plate 25a which is connected to the guide pin 46a in a V-shape and is tilted by the rod 43 via the links 46, 46. Have been to. In addition, instead of using the link 46 for the synchronous drive of the flame holding plates 25a and 25b, each may be driven by the motor 45 via the operation rod 43.

  For example, a stepping motor is preferably used as the driving motor 45 for operating the tilting operation rod 43 in the flame ejection adjusting means 40. The motor 45 is driven by a separately installed control device 49 in conjunction with a fuel gas supply means 30 described later.

  The fuel gas supply means 30 is a flat box shape with a sharpened tip 33 which can be inserted into the inlet portion 22 of a Laval nozzle forming portion 21 (mixing means 20) disposed inside the outer case 11. A gas supply pipe 32 connected to the fuel gas supply unit is attached to the rear end portion. A plurality of gas ejection holes 34 are formed on both side surfaces of the tip 33 at a predetermined interval in an air-fuel mixture inflow passage formed by the inner surface of the inlet portion 22 of the Laval nozzle forming portion 21 and the outer surface of the gas supply box 31. It is provided in a crossing direction. The gas supply box 31 is provided to be movable in the front-rear direction by a required distance at the mounting portion, and is configured to be driven forward and backward by a linear actuator 35 (for example, a small electric cylinder). The combustion state can be adjusted by changing the mixing ratio of air and fuel gas. The linear actuator 35 is connected to and controlled by a control device 49 so as to be interlocked with the drive of the flame holding plate operating motor 45 in the flame ejection adjusting means 40.

  Further, although not shown in the drawings (the same applies hereinafter), a plurality of rectifying plates are arranged in the gas supply box 31 as necessary so that the ejection of the fuel gas from each gas ejection hole 34 is evenly averaged. Is formed. On the other hand, a plurality of rectifying plates are attached to the outer surface of the gas supply box 31 or the inner surface of the inlet portion 22 of the Laval nozzle forming portion 21 in parallel with the air flow direction so that the sucked air (air mixture) is not evenly distributed to the throat portion 23. It is preferably adapted to flow. It is desirable to provide a rectifying plate also on the air circulation part side in the outer case 11.

  The gas burner 10 of the present embodiment configured as described above is used by being attached to a small once-through boiler, for example. At this time, city gas is used as the fuel and is supplied by the fuel gas supply means 30 (gas supply box 31). On the other hand, the soot is controlled so that the air ratio becomes 1.0 to 1.2, and the air and the fuel gas are supplied. Are mixed and supplied to the combustion section.

  As shown in FIG. 1, the combustion air A with respect to the fuel gas G supplied from the gas supply box 31 is opened in the outer case 11 at the opening edge 22 a of the inlet portion 22 (suction portion) of the Laval nozzle forming portion 21. Is divided into the outer air circulation part 15 and the inside of the inlet part 22. Mixing of the air introduced into the inlet portion 22 of the Laval nozzle forming portion 21 with the primary air into which the fuel gas ejected from the gas ejection holes 34 of the gas supply box 31 flows is promoted and premixed gas G ′. It flows into the throat part 23 from the suction part (inlet part 22). The premixed gas G ′ compressed at the suction portion (inlet portion 22) is further compressed at the narrow throat portion 23 and is ejected from the diffuser 24 outlet at high speed. In the secondary combustion gas suction part 25 connected to the outlet of the diffuser 24, the flow path rapidly expands, so that a part of the premixed gas G ′ ejected forms a recirculation region, and the main stream goes straight. The premixed gas G ′ traveling straight is ignited and burned by an ignition means attached to a burner (not shown).

  On the other hand, the air A which is diverted to the air circulation part 15 outside the Laval nozzle forming part 21 in the outer case 11 flows in the outer case 11 as it is and reaches the flame holding plates 25a and 25b in the secondary combustion gas suction part 25. The suction gas is sucked by the attracting action accompanying the discharge force of the premixed gas G ′ ejected from the provided suction hole 26 and is supplied to the combustion section as the secondary combustion gas G ″. At this time, around the burner generated in the combustion section The combustion exhaust gas is also sucked and recombusted at the same time. By doing this, a secondary combustion gas G ″ with a low oxygen concentration can be created and supplied toward the flame of the combustion section, thus realizing combustion with a low local high temperature. Therefore, it is possible to further reduce NOx.

  Since the burner is rectangular and has a large vertical ratio corresponding to the shape of the combustion chamber (not shown), the flame burned as described above is thin in the width direction and has a vertical shape. Combustion is performed, and the air-fuel mixture is injected at a high speed, so that the secondary combustion gas G ″ flows toward the main flow of the pre-mixed gas G ′, and acts to suppress the diffusion of the flame. Therefore, it is possible to make the flame straight, so that the surface of the flame becomes large and the surface area of the flame becomes large, and the flame flow path is like a small once-through boiler. Even if it is narrow and bends, the flame reaches up and down and the heat absorption effect on the heat transfer surface can be enhanced.

  Moreover, in the gas burner 10 of the present embodiment, since the flame injection adjusting means 40 is attached to the secondary combustion gas suction portion 25, when the combustion load amount is reduced from the rated load at which combustion is performed as described above, The flame ejection adjusting means 40 is operated in conjunction with the supply amount of the fuel gas G, and the flame holding plates 25a and 25b in the secondary combustion gas suction section 25 are tilted inward, so that the flame ejection channel 29 is in accordance with the load. Narrowed.

  That is, when the supply amount of the fuel gas becomes smaller than that at the rated load based on data (relation between the combustion load amount and the optimum inclination angle) input in advance in the control device 49, the motor 45 in the flame ejection adjusting means 40 is operated. Then, the pinion 45a on the output shaft is rotated to advance the operation rod 43 with the rack gear 44 engaged therewith. Then, the rod 43 is tilted inward from the support shaft 27 to which one flame holding plate 25a is attached via the projecting piece 42 to which the end of the rod 43 is connected (indicated by a two-dot chain line in FIG. 2). At this time, the other flame holding plate 25b is tilted through the links 46 and 46 connected from the flame holding plate 25a operated by the rod 43, and the connecting portion of both the links 46 and 46 is connected to the guide slot 28a. Since it is connected to the engaging guide pin 46a, it operates synchronously, and the flame ejection passage 28 is narrowed according to the combustion load of the burner. Therefore, the flow velocity of the premixed airflow can be ensured, the diffusion of the flame can be suppressed, the instability can be prevented, and stable combustion can be achieved.

  In the above description, the flame ejection adjusting means 40 that tilts the flame holding plate is described as operating by motor drive, but the drive for tilting the flame holding plate is not limited to this. It is also possible to use manual operation (for example, rotating a screw shaft or lever operation) or other power (for example, a hydraulic cylinder).

Sectional drawing which represents typically the principal part of the gas burner which concerns on one Embodiment of this invention. The figure which shows the outline | summary of the flame ejection adjustment means which operates a flame-holding board Perspective view showing part of the burner's exterior Schematic view (a) and plan view (b) of a gas burner according to the invention of the prior application

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Gas burner 11 Outer case 20 Mixing means 21 Laval nozzle formation part 25 Secondary combustion gas suction part 25a, 25b Flame holding plate 26 Secondary combustion gas suction hole 27 Support shaft of flame holding plate base end part 29 Flame ejection flow path 30 Fuel gas supply means 31 Gas supply box 40 Flame ejection adjustment means 42 Projection piece 43 Operation rod 44 Rack gear 45 Motor 45a Pinion 46 Link 49 Control device

Claims (3)

A Laval nozzle forming portion is provided at a coaxial line extending position with the fuel gas supply means in the distal end portion of the outer cylinder, and a shunt air circulation portion is formed between the suction portion opening edge of the Laval nozzle forming portion and the inner surface of the outer cylinder, In the gas burner in which a secondary combustion gas suction part is provided in front of the diffuser outlet of the Laval nozzle forming part by mixing the air branched in the diverted air circulation part and the combustion exhaust gas,
A gas burner, wherein a flame holding plate provided in the secondary combustion gas suction part is provided so as to be able to expand and contract with respect to a flame ejection flow path in the secondary combustion gas suction part.   2. The gas burner according to claim 1, wherein the flame holding plate is configured such that a drive mechanism is operated by a control device so that a movable portion thereof automatically operates in accordance with a supply amount of fuel gas. The flame holding plate is connected with a pair of opposing ends of which the base end portion is pivotally attached to a portion connected to the outlet of the diffuser , and the flame holding plates are connected to each other at the end portion, When an operation force is applied by a flame ejection adjusting means connected to the outer surface of one flame holding plate, both the flame holding plates are configured to move in synchronization with the pivot point as a base point so that the opening width can be varied. The gas burner according to claim 1 or 2.

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