JP7606930B2 - Pilot Burner - Google Patents

Description

The present invention relates to a pilot burner that can handle a variety of gas types through fuel conversion, etc., and is less susceptible to pressure fluctuations in the main burner.

Because pilot burners are ignited prior to the ignition of the main burner for a heating furnace or boiler, they must have both strong flame-holding capabilities and a flame of sufficient length. It is particularly important to avoid the flame being blown out due to negative pressure fluctuations in the main burner's combustion air flow, and delays in ignition of the main burner due to insufficient flame length.

There are two types of pilot burners: the premix type, in which gas fuel and combustion air are mixed in advance and then burned, and the nozzle mix type, in which gas fuel and combustion air are mixed at the tip of the burner and then burned.

Recently, the nozzle mix method has been used because it does not require a device to mix gas fuel and combustion air and is less likely to cause flashback problems (for example, Patent Document 1).

Patent Document 1 discloses a nozzle mix type pilot burner that is characterized by having a Kanthal rod for electric spark ignition in the center of the burner, an ultraviolet flame detector at the rear end of the burner, a combustion air ejection tube on the outer periphery of the Kanthal rod, and a gas fuel ejection tube with swirling blades with a twist angle of 20° to 50° inside on the outer periphery of the combustion air ejection tube, with the combustion air ejection speed in the range of 10 to 60 m/sec and the gas fuel ejection speed being 1/2 or less of the combustion air ejection speed.

The pilot burner of the above invention ensures reliable flame ignition, has excellent flame stability, and forms a flame concentrated in the center of the burner, so flame detection by an ultraviolet flame detector is also effective.

JP 2001-272010 A

However, in the pilot burner of Patent Document 1, while it is sufficient if the type of gas fuel is fixed, when the gas fuel is switched to coke oven gas (COG), liquefied natural gas (LNG), or liquefied propane gas (LPG), the following problems arise.

Since LNG and LPG have a higher calorific value per unit volume ( ^m3 ) than COG, when burning the same amount of heat, the flow rate is 1/4 to 1/2 of that of COG. This slows down the flow rate through the swirl vanes, weakens the swirling force, and causes insufficient mixing with the combustion air, resulting in an unstable flame.

In addition, since the nozzle mix method is considered to have weaker flame holding power than the premix method, there was also a need for a method to reduce the effect of negative pressure fluctuations in the main burner's combustion air flow on the flame being blown out.

In order to solve the above problems, the pilot burner of the present invention is a double tube with an inner tube located at the center of the burner and a concentric outer tube on the outer periphery of the inner tube, in which combustion air flows through the inner tube and gas fuel flows through the area surrounded by the inner tube and the outer tube, and a flame is generated in front of the tip of the inner tube. It is characterized by having a throttle section at the tip of the inner tube to reduce the amount of combustion air flowing out in front of the tip of the inner tube, multiple horizontal holes in the middle of the inner tube so that the combustion air flows from the inner tube into the gas fuel in the area surrounded by the inner tube and the outer tube, and swirl vanes in the area surrounded by the inner tube and the outer tube between the multiple horizontal holes and the tip of the inner tube.

Furthermore, it is preferable that the ratio of the total area of the multiple horizontal holes to the area of the inner diameter of the constriction portion is 2.5 to 4.0.

It is also preferable to provide a constriction nozzle at the tip of the outer tube, which incorporates multiple constrictions at a predetermined opening angle from the inner diameter of the constricted portion of the inner tube so that the inner diameters of the multiple constrictions increase in sequence.

Furthermore, it is preferable that the aperture nozzle incorporates the multiple apertures at a predetermined interval.

Furthermore, it is preferable that the shape of the multiple apertures is a wavy circle.

The pilot burner of the present invention has a throttle section at the tip of the inner tube, which reduces the amount of combustion air flowing out in front of the tip of the inner tube, and some of the combustion air flows into the gas fuel in the area surrounded by the inner and outer tubes through multiple horizontal holes provided in the middle of the inner tube, creating a premixed state, and the apparent flow rate increases as it passes through the swirl vanes, increasing the swirl force and flame retention.

Furthermore, it was confirmed that if the ratio of the total area of the multiple side holes to the area of the inner diameter of the constriction portion is 2.5 to 4.0, the combustion air flows sufficiently from the side holes into the gas fuel in the area surrounded by the inner and outer tubes.

It was also confirmed that the use of a constriction nozzle with multiple constrictions at the tip of the outer tube, in which the inner diameter of the multiple constrictions increases in sequence at a specified opening angle from the inner diameter of the constricted part of the inner tube, can respond to fluctuations in negative pressure from the main burner.

Furthermore, they discovered that the flame pressure can be adjusted by installing a throttling nozzle that incorporates the multiple throttling plates at a specified interval, and confirmed that the effect of negative pressure from the main burner can be reduced depending on the gas fuel.

Furthermore, by providing a throttling nozzle in which the throttling blades have a wavy circular shape, the turbulence of the swirling flow is further increased, the mixing of the gas fuel and the combustion air is promoted, and the flame holding power is increased.

FIG. 2 is a cross-sectional view of one embodiment of a pilot burner of the present invention. FIG. 2 is an enlarged cross-sectional view of the tip of the pilot burner of FIG. 1. FIG. 4 is a cross-sectional view of a second embodiment of the pilot burner of the present invention. FIG. 4 is an enlarged cross-sectional view of the tip of the pilot burner of FIG. 3. 1 is a diagram showing an appropriate relationship between the distance from the constriction portion of the inner tube of the constriction nozzle and the constriction diameter. FIG. FIG. 13 is a front view of an example of a wave-shaped circular aperture shape used in a aperture nozzle. FIG. 13 is an example of a development of the shape and phase of a wave-shaped circular aperture used in a aperture nozzle.

Below, an embodiment of the pilot burner of the present invention will be explained with reference to the drawings.

One embodiment of the pilot burner of the present invention will be described with reference to Figures 1 and 2. The pilot burner 1 has a double-tube structure with an inner tube 2 located in the center and an outer tube 3 concentric with the inner tube 2. Combustion air A supplied from a combustion air connection 9 flows through the inner tube 2, and gas fuel G supplied from a gas fuel connection 10 flows between the inner tube 2 and the outer tube 3.

An electrode rod 5 is fixed to the inner surface of the inner tube 2 while being insulated by an insulator 7, and penetrates the narrowed portion 20 at the tip of the inner tube 2. The electrode rod 5 is connected to an ignition plug 11 in an electrically conducting state, and the ignition plug 11 is connected to a high-voltage transformer (not shown), and is connected to the tip of the electrode rod 5 and the tip of the inner tube 2 with a voltage of, for example, 6000 V, and is configured to generate an electric spark in the gap between the bent tip of the earth electrode rod 6, generating a flame in the mixture of combustion air A and gas fuel G in front of the tip of the inner tube 2.

In this embodiment, the rear end of the pilot burner 1 is sealed with a plug 12, but instead of the plug 12, a sight glass or a flame detector for detecting flames may be installed.

The combustion test of the pilot burner 1 of the present invention was carried out with a constant combustion heat value of 10 Mcal/h and an air ratio of 1.1, using COG, LNG and LPG gas fuels G. The flow rate of the combustion air A was 12 m ³ /h and the pressure was 1 kPa. On the other hand, the flow rates of the COG, LNG and LPG gas fuels G were 2.2 m ³ /h for COG, 1.0 m ³ /h for LNG and 0.45 m ³ /h for LPG, due to the relationship between the heat value of the gas fuel G, and the pressure was 0.4 to 0.5 kPa, which was about half the pressure of the combustion air A.

A constriction section 20 is provided at the tip of the inner tube 2, and the area of the outlet for the combustion air A is reduced, thereby reducing the amount of air flowing out from the tip. In this embodiment, the inner diameter of the inner tube 2 is 16 mm, and the inner diameter of the constriction section 20 is 10 mm, so the area ratio is reduced to 0.39. A reduction in the area ratio by the constriction section 20 of about 0.3 to 0.5 was favorable.

Eight horizontal holes 22 with an inner diameter of 6 mm are drilled on the circumference of the inner tube 2, and part of the combustion air A flows from these horizontal holes 22 into the gas fuel G in the area surrounded by the inner tube 2 and the outer tube 3, becoming a premixed gas fuel. In the case of the above test conditions, about 1/3 of the flow rate of the combustion air A flows out from the throttle nozzle 20, and about 2/3 flows from the horizontal holes 22 into the gas fuel G in the area surrounded by the inner tube 2 and the outer tube 3. The flow rate of the premixed gas fuel in the area surrounded by the inner tube 2 and the outer tube 3 is about 8 to 10 m ³ /h, which solves the problem of reduced swirl force that occurs when gas fuel is switched in a conventional nozzle mix type pilot burner.

In order for the combustion air A to flow sufficiently from the horizontal holes 22 into the gas fuel G in the area surrounded by the inner tube 2 and the outer tube 3, it is preferable that the ratio of the total area of the horizontal holes 22 to the area of the inner diameter of the throttle section 20 is 2.5 to 4.0. In this embodiment, the ratio was 3.2.

This premixed gas fuel passes through the swirl vanes 4, which are located in the area surrounded by the inner tube 2 and the outer tube 3 between the multiple horizontal holes 22 of the inner tube 2 and the tip. Because the flow rate is higher than that of the initial gas fuel G, the flow rate increases after passing through the swirl vanes 4, increasing the swirling force and stabilizing the flame.

The swirl vanes 4 have grooves with a twist angle of 20° to 50° and are fixed by welding or other methods to the tip of the inner tube 2. The outer tube 3 is divided using a screw-type mechanism, and the front part is placed over the inner tube 2, forming a flow path in the concave part with a twist angle of 20° to 50°.

When gas fuel G is converted from COG to LNG or LPG, in a conventional pilot burner, the flow rate in the area surrounded by the inner tube 2 and outer tube 3 is lower than in the case of COG, and the flow rate of the gas fuel G passing through the swirl vane is slow, resulting in a weak swirl force and insufficient mixing with the combustion air A, resulting in an unstable flame. However, in the present invention, due to the configuration of the constriction section 20 at the tip of the inner tube 2, the multiple horizontal holes 22, and the swirl vane 4, part of the combustion air A flows from the multiple horizontal holes 22 of the inner tube 2 into the gas fuel G in the area surrounded by the inner tube 2 and outer tube 3, creating a premixed state, increasing the apparent flow rate, and increasing the swirl force, restoring the mixture with the combustion air A, stabilizing the flame, and improving flame stability.

Another embodiment of the pilot burner of the present invention will be described using Figures 3 and 4. Note that this embodiment is the same as the pilot burner of Example 1 except that a throttle nozzle 8 is added, so the parts described in Example 1 will be omitted.

The throttle nozzle 8 may be connected to the tip of the outer tube 3 by screwing, or may be integrated into the outer tube 3.

The restriction nozzle 8 incorporates three circular restrictions with different inner diameters: a first restriction 80, a second restriction 82, and a third restriction 84. With regard to the inner diameter of each restriction and its interval, the present inventors have obtained the following findings as a result of extensive research into further improving flame retention against fluctuations in negative pressure from the main burner.
1) The following relationship exists between the distance L from the throttle portion 20 of the inner tube 2 to the tip of the throttle nozzle 8 and the difference (D1-D2) between the inner diameter D1 of the throttle nozzle 8 and the inner diameter D2 of the throttle portion 20 of the inner tube 2, and the inner diameter of each throttle is determined on the line that forms this angle.
tan(α/2)=(D1-D2)/2L
In this embodiment, L = 54 mm, D1 = 28 mm, and D2 = 10 mm, so the angle α is 19°, which is the opening angle of the cone. If the angle α is small, the interval between the multiple throttles becomes large, which reduces the generation of turbulence in the swirling flow and decreases the flame holding power. Conversely, if the angle α is large, the interval between the multiple throttles becomes small, which reduces the generation of turbulence in the swirling flow and decreases the flame holding power. Therefore, the range of the angle α is preferably 14° to 24°.
2) The interval between the orifices depends on the inner diameter D1 of the orifice nozzle 8, and is preferably in the range of 0.25×D1 to 0.65×D1. In this embodiment, the interval between d1 and d2 is preferably in the range of 7 mm to 18.2 mm. The thickness of each of the orifices 80, 82, and 84 was approximately 3 mm.
3) In order to sufficiently generate turbulence in the swirling flow, a plurality of restrictors (2 to 4) are necessary. In the present embodiment, taking into account the manufacturing costs, etc., three restrictors were appropriate.

Figure 5 shows the appropriate relationship between the distance from the throttle part of the inner tube to each throttle of the throttle nozzle in this embodiment and the throttle diameter. The range enclosed by two straight lines is the appropriate range, and the distance and diameter of the three throttles selected in this embodiment are indicated by circles. In this embodiment, L2 = 15 mm, d1 = 8 mm, and d2 = 13 mm.

In Example 2, we described a constriction nozzle 8 incorporating three circular constrictions with different inner diameters, but we discovered that changing the shape of the constriction from circular to wavy circular creates more turbulence in the swirling flow and increases the flame retention, as we will explain below.

Figure 6 shows an example of a front view of a circular corrugated orifice shape used in a orifice nozzle. The corrugated circular orifice shape is a shape in which a corrugation is added to the circular orifice of Example 2. Figure 6(a) is a shape in which 12 semicircular irregularities are added with a radius of about 2 mm from a base point of a diameter of 16 mm, Figure 6(b) is a shape in which 14 semicircular irregularities are added with a radius of about 2 mm from a base point of a diameter of 18 mm, and Figure 6(c) is a shape in which 16 semicircular irregularities are added with a radius of about 2 mm from a base point of a diameter of 21.7 mm. By making the shape into a corrugated circle, the swirling flow is further disturbed by the circular orifice, which promotes mixing of the gas fuel G and the combustion air A and increases the flame retention.

Note that the circular waveform is not limited to the semicircular shape shown in Figure 6, but includes triangular and rectangular irregularities, and may be any shape that causes turbulence in the swirling flow.

Also, while any shape that causes turbulence in the swirling flow is acceptable, if the phase of the concaves and convexes of the three orifices is aligned, the turbulence of the swirling flow will be small, so attention must be paid to the relationship between the incidence angle of the swirling flow and the phase of the convexities and convexities of the orifices during the design stage.

Figure 7 shows an example of a development of the shape and phase of a wavy circular orifice used in a throttling nozzle. In this embodiment, the swirl vanes 4 allow gas fuel G or flame to flow into the throttling nozzle 8 at an angle of 35°, as shown by the dashed line. The convex parts from the base point of the aperture of each orifice are shown in black, and the concave parts in white. In Figure 7(a), if the phases of the concave parts of the three orifices are aligned in the center of the development, two parts of the swirling flow will have overlapping phases of the concave parts, resulting in a NG region where the turbulence of the swirling flow is weak. In Figure 7(b), if the phases of the concave parts of the three orifices are not aligned in the center of the development, there will be no overlapping phases of the concave parts in the swirling flow, resulting in a good phase arrangement where all the swirling flows are sufficiently turbulent.

The pilot burner of the present invention has been described above based on the examples, but the present invention is not limited to the structure and shape described in the above examples, and the structure and shape can be changed as appropriate without departing from the spirit of the invention.

The pilot burner of the present invention can merge some of the combustion air to increase the swirling force and stabilize the flame, even when the flow rate passing through the swirl vanes is low due to fuel conversion from gas fuel. In addition, the throttle nozzle strengthens the flame holding power against the blowing out of the flame due to negative pressure fluctuations in the main burner combustion air flow, making it suitable as a pilot burner for the main burner.

REFERENCE SIGNS LIST 1 Pilot burner 2 Inner tube 3 Outer tube 4 Swirl vane 5 Electrode rod 6 Earth electrode rod 7 Insulator 8 Throttle nozzle 9 Combustion air connection 10 Gas fuel connection 11 Spark plug 12 Plug 20 Throttle section 22 Horizontal hole 80 First throttle 82 Second throttle 84 Third throttle A Combustion air G Gas fuel

Claims (5)

A pilot burner consisting of a double tube with an inner tube located at the center of the burner and a concentric outer tube around the outer periphery of the inner tube, in which combustion air flows through the inner tube and gas fuel flows through the area surrounded by the inner tube and the outer tube, generating a flame in front of the tip of the inner tube, characterized in that it has a throttle section at the tip of the inner tube to reduce the amount of combustion air flowing out in front of the tip of the inner tube, multiple horizontal holes in the middle of the inner tube so that the combustion air flows from the inner tube into the gas fuel in the area surrounded by the inner tube and the outer tube, and swirl vanes in the area surrounded by the inner tube and the outer tube between the multiple horizontal holes and the tip of the inner tube. The pilot burner described in claim 1, characterized in that the ratio of the total area of the multiple horizontal holes to the area of the inner diameter of the throttle portion is 2.5 to 4.0. The pilot burner according to claim 1 or 2, characterized in that a throttling nozzle is provided at the tip of the outer tube, incorporating multiple throttling blades at a predetermined opening angle from the inner diameter of the throttling portion of the inner tube so that the inner diameters of the multiple throttling blades increase in sequence. The pilot burner according to claim 3, characterized in that the multiple throttles are assembled at a predetermined interval. The pilot burner according to claim 3 or 4, characterized in that the shape of the multiple throttles is a wavy circle.

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