JPS6029845B2 - Low NOx burner with excellent combustibility - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low N○k burner with excellent combustibility, and particularly proposes a low N○○ burner that can perform combustion at a high distance even during turndown.

Conventionally used burners aimed at low NOk include exhaust gas circulation type burners and two-stage combustion type burners.

The former has a slow combustion rate due to the effect of low NO widening, and the latter has a low NOx effect only when the primary and secondary air ratio is optimal, so for example, the flame When changing the primary/secondary air ratio in order to change the length, there was a drawback that it became difficult to obtain a low N○×. In short, if both try to achieve low N0x,
The variable nature of the frame in preparation for turndown was either poor or non-existent. This can be explained in more detail as follows. ■Regarding combustibility: This is common to all secondary gas burners, but even if the combustion condition is good under the design conditions, good combustibility cannot be obtained in a turndown condition narrowed down from the design conditions.

For example, when the flow rate is reduced to 1/3 from the design condition, the flow velocity ejected from the nozzle becomes 1/3 for both air and gas. (
The momentum of the ejected gas (as the cross-sectional area of the ejecting part is constant) is expressed as (mass) x (velocity), so when compared with the designed optimal combustion condition, it is 1'9, and the air and gas At the same time, the mixing state of the flame deteriorates and the energy possessed by the flame decreases, resulting in a flame temperature pattern that differs greatly from the design conditions. Moreover, the heating capacity inside the furnace was reduced, making it impossible to create a uniform furnace temperature distribution. For this reason, good combustibility could not be obtained below the design condition of 1/mirror steepness.

On the other hand, in the case described above, if high speed is unnecessarily set in the design conditions to ensure combustibility, the required pressure will be proportional to the flow velocity, so a large amount of power (such as a blower) will be required.
It is not practical because it requires Regarding the variable nature of the combustion flame: In conventional gas burners, the flame length could be changed by changing the ratio of primary and secondary air, for example.

However, under flow conditions reduced from the design conditions, the miscibility of air and gas worsens and the momentum rapidly decreases, so sufficient variable properties cannot be achieved. ■Regarding low N○x properties: In conventional gas burners, when pursuing low N○x properties, it was not possible to have desirable combustibility and flame variable properties.

As mentioned above, conventional gas burners cannot have low N○×, flame variable properties, good combustibility, and uniform temperature distribution in the furnace over a wide range of use (when there is a large turndown). .

The present invention is a burner developed for the purpose of overcoming the drawbacks of the prior art described above, and in particular, provides high-speed combustion properties to a low N○× burner, and also provides excellent combustion properties even when it is turned down. It is designed so that it can hold.

The low N○× burner of the present invention will be described in detail below based on the preferred embodiment shown in the drawings. The low N○× burner of the present invention has a fuel gas feeding section in the center, a primary air feeding section around it, and a secondary air feeding section outside. - Of the above-mentioned structure, the self-combustion gas supply section is composed of a gas nozzle hole whose tip side is flared and a corresponding conical nozzle core whose tip side is flared; The secondary air supply section is composed of a tapered annular primary air nozzle hole and a correspondingly provided annular nozzle core with a pointed tip, and the secondary air supply section is arranged in a ring with a plurality of tapered tip ends. It is composed of a group of secondary air nozzle holes and a conical nozzle core with a pointed tip provided correspondingly to the secondary air nozzle hole group, and a premixing space is interposed in the front surface of each feeding section, and the primary air is A plurality of secondary air holes are provided around the central hole to provide a combustion space and correspond to the secondary air supply portion, and a plurality of secondary air holes are located between the secondary air holes. The present invention is characterized by a configuration in which a baffle is provided with combustion gas recirculation holes.

In the structure described above, the fuel gas is supplied to the fuel gas supply section 1
0 and is supplied to one part of the fuel gas nozzle hole which is widened at the end and is suitable for this.

At this time, the cross-sectional area of the fuel gas supply section is adjusted by moving the gas nozzle adjusting rod 3 connected to the conical gas nozzle core 2 provided for adjusting the cross-sectional area of the combustion gas nozzle hole 1. Ru. The primary air is supplied through the primary air supply pipe 11 to four tapered primary air nozzle holes into which the primary air is supplied.

The cross-sectional area of this primary air supply section is determined by a primary air nozzle adjustment rod 6 connected to an annular nozzle core 5 with a pointed tip provided corresponding to an annular primary air nozzle hole 4 with a tapered cross section. It can be freely adjusted by moving it. Similarly 2
The secondary air is introduced from the secondary air supply pipe 12 and is ejected from the secondary air nozzle hole 7, which has a tapered conical cross section. The cross-sectional area of the secondary air supply section is adjusted by moving a secondary air nozzle adjustment rod 9 connected to a conical nozzle core 8 with a pointed tip provided in accordance with the shape of the secondary air nozzle hole 7. Ru. The above-mentioned fuel gas and primary air are mixed in the premixing chamber 16 at the outlet of each nozzle hole 1, 4, and the center hole 13 of the baffle 20 provided in front of the premixing chamber 16 is used as the primary combustion chamber to perform combustion in an air-deficient state. do.

A plurality of annularly arranged secondary air holes 14 are provided near the outer periphery of this baffle 20, and at the same time, these correspond to the secondary air nozzle holes 7, and the recirculated combustion gas is The secondary air combined with the air is blown out. Further, a combustion gas recirculation hole 15 is provided between each secondary air hole 14 of this baffle 20, and a part of the combustion gas is ejected from the secondary air nozzle at high speed from this combustion gas recirculation hole 15. Reflux occurs due to the suction effect of secondary air. However, this fuel gas recirculation also occurs through the combustion gas recirculation hole 15 due to the suction effect of the fuel gas and primary air. Note that 18 in the drawings indicates a nozzle holder, and 19 indicates a sealing chamber. In the invention described above, the flow velocity of the ejected fuel gas and air is approximately proportional to the square root of the pressure (Pg, Pa, respectively) of the fuel gas and air in front of the nozzle.

Therefore, if it is desired to keep the flow rate of ejected gas and air constant, the rods 3, 6, and 9 may be adjusted so that Pg and Pa are respectively constant. Also, when changing the flow rate of ejected gas or air, the rods 3, 6, and 9 are adjusted in order to change Pg and Pa to certain values. Because of this configuration, the burner of the present invention can increase the momentum of the frame even under conditions that are far below the design conditions by keeping the flow velocity of fuel gas and air constant or controlling it to a certain target value. This makes it possible to have good combustibility. in short,
The burner of the present invention can fully satisfy the characteristics required of a burner as shown in Table 1, and can exhibit this not only in the designed state but also in any turndown state. .

Table 1 The reason why the burner of the present invention described above has low N○× is as follows.
It can be considered as follows.

In conventional burners, high-speed combustion is possible under design conditions, but the flow rate decreases during turndown.
Therefore, the combustibility deteriorates, and in such a state, normal combustion cannot be achieved unless there is a considerable excess of air. As a result, 02 was excessive, inviting a no or an oath. On the other hand, the burner of the present invention has a two-stage combustion/exhaust gas recirculation structure, and also has a variable flow rate structure for each/Zulu feeding section, so it can be used from high load to low load. It can achieve high-speed combustion in the entire range up to , has good air/gas mixing characteristics, and always achieves low 02 combustion, and even when there is a so-called turndown, the same low N○× minimum value as under the design conditions is achieved. You can get it. In addition, in the nozzle of the present invention, the structure of the fuel gas nozzles 1 and 2 is shaped to widen toward the injection direction. The liquid can be discharged while spreading outward in the form of a shaped film.

Therefore, the surface area of the flame generated by mixing with the primary combustion air increases, and the amount of heat radiation increases accordingly. Therefore, the average maximum flame temperature of that frame becomes lower, and N○
× Effectively reduces Moreover, in the case of the nozzle of the present invention, since the gas nozzle 2 has a conical structure with a widening end, a strong negative pressure area is created near the center of the subcombination chamber 16 on the front surface of the nozzle. Therefore, the combustion gas combusted in the primary combustion chamber flows into the center of the sub-mixing chamber 16. Therefore, in general, in this type of frame, the localized high temperature that tends to occur in the frame disappears, and the frame temperature decreases. In this regard, in conventional burners, the temperature of the outer periphery of the frame decreases due to heat radiation to the surroundings, but the center part has the disadvantage that there is no heat radiation and tends to become overheated, which weakens the reduction in N○×. The burner of the present invention described above can control the cross-sectional areas of the combustion gas, primary air, and secondary air injection nozzles in the range from fully closed to fully open, so that the flow rate can be reduced from the design condition to a minute flow rate ( Even during turndown, the jet flow velocity can be controlled arbitrarily, so good combustibility can always be maintained.

{2) Primary, secondary air flow rate ratio, fuel gas, primary, 2nd
Next, by controlling the air flow rate and nozzle flow rate,
Since the length can be controlled, uniform temperature distribution within the furnace can be obtained at all times.

(The combustion gas recirculating from the 3' combustion gas recirculation hole reaches the negative pressure part formed on the central axis of the baffle 20 due to the suction action of the secondary air and the suction action of the mixture of fuel gas and primary air. Because of the inflow, low N○× can be achieved under any circumstances.

As explained above, according to the low N○× burner of the present invention,
Low N○ in a wide range of use (when turning down significantly)
× is obtained, flame variable property, good combustibility,
In addition, a uniform temperature inside the furnace can be obtained.

[Brief explanation of the drawing]

Figure 1 of the drawings is a cross-sectional view of the low N○× burner of the present invention, Figure 2 is a cross-sectional view taken along the line A-A in Figure 1, and Figure 3 is a cross-sectional view taken along the line B-- in Figure 1.
It is a sectional view taken in the direction of the arrow B. 1...Fuel gas nozzle hole, 2...Nozzle core for fuel gas nozzle, 3...Gas nozzle adjustment rod, 4...Primary air nozzle hole, 5... Nozzle core for primary air nozzle, 6... Primary air nozzle adjustment rod, 7... Secondary air nozzle hole, 8...
...Nozzle core for secondary air nozzle, 9... Rod for secondary air nozzle adjustment, 10... Fuel gas supply pipe, 11... Primary air supply pipe, 12...2
Next air supply pipe, 13...Baffle center hole, 14...
...Secondary air hole, 15...Combustion gas recirculation hole, 16...Premixing chamber, 17...Primary combustion chamber, 18...Nozzle holder , 19... Seal chamber, 20... Baffle. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 A fuel gas supply section is arranged in the center, a primary air supply section is arranged around it, and a secondary air supply section is arranged concentrically on the outside, and a combustion gas recirculation butthole is provided in front of the fuel gas supply section. In the burner, the fuel gas supply section has a variable nozzle cross-sectional area structure consisting of a gas nozzle hole whose tip side is flared and a corresponding conical nozzle core, and the primary air supply The section has a variable nozzle cross-sectional area structure consisting of an annular primary air nozzle hole tapering at the tip side and a corresponding annular nozzle core with a pointed tip, and the secondary air supply section The nozzle has a variable cross-sectional area structure consisting of a group of secondary air nozzle holes arranged in an annular arrangement with tapered sides and a corresponding conical nozzle core with a pointed tip. A plurality of secondary air holes provided on the front surface of each of the secondary air discharge sections corresponding to the front surface of the secondary air discharge section around a central hole that provides a primary air combustion space on the front surface of each of the above-mentioned feeding sections whose The combustibility is characterized by the fact that a plurality of combustion gas recirculation holes are arranged concentrically with a plurality of combustion gas recirculation holes sandwiched between adjacent air, and are arranged with premixed air interposed therebetween. Excellent low NOx burner.