JPS6014256B2 - Low NOx burner for hydrogen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low N○× burner for hydrogen, and more particularly to a burner capable of burning hydrogen while mixing a portion of combustion air into the fuel.

In the combustion of hydrogen, diffusion combustion (combustion without premixing of fuel air) generates a large amount of N0x, while combustion with premixing air increases the amount of N○k generated as the primary mixed air ratio increases. It is well known that it decreases.

However, in premix combustion of hydrogen, the primary air ratio is set to 0. If it is made larger than the main limit, it will easily backfire up to the air mixing start position inside the burner, and in a burner that sucks air into the fuel gas by the flow velocity of the fuel gas itself (for example, in practice, It is difficult to completely prevent flashbacks unless the intake air vents (as in household combustion appliances) are closed. In other words, N due to adjustment of premixed air
○× suppression and flashback suppression have a mutually contradictory relationship, and it is extremely difficult to achieve both. Specifically, as shown in Figure 1, unless the primary air is increased to 0.6 or more, N○×
cannot be significantly suppressed. Figure 1 shows the level of N○× in the exhaust gas when three types of fuel, hydrogen, propane, and propylene, are burned in a cylinder burner at an output of 2 arc cal/min. , Mouth is C3 day 6, Ha is C3H
Indicates B. However, as the primary air ratio of the air/hydrogen premixed air increases, the combustion speed increases and reaches the maximum at the primary air ratio of around 0.6 as shown in Figure 2, so both NOx and flashback are suppressed at the same time. In the case of hydrogen, the current situation is that it is an extremely difficult problem to solve in principle. Incidentally, FIG. 2 is a graph showing the relationship between the primary air ratio and the combustion speed when various fuels are combusted, and symbols A to C in the figure represent the same things as in FIG. 1, respectively. It is known to use premix burners in order to avoid flashbacks.

In particular, when an internal premix burner is used, air is mixed from the inside and outside of the combustion gas, resulting in characteristics somewhat similar to premix combustion. However, the internal pre-mixing burner requires a compressor and a pressure reducing valve to eject primary air under pressure, making it inconvenient and unsuitable for household gas appliances. SUMMARY OF THE INVENTION An object of the present invention is to provide a burner that basically uses suction and mixing of air with fuel gas and that does not cause backfire inside the burner.

The means basically used in the present invention, the suction mixing means of air using a combustion scale gas, is already widely used for combustion gases having a slow burning rate.

For example, for city gas (4,50 cal/N〆) and LP gas (25,000 Kcal/N〆), fuel gas is delivered at a pressure of about 80 and 280 mercury columns, respectively, and at the base of the burner, the fuel gas is delivered to the required combustion level. Approximately more than half of the air is premixed. However, when the same method is adopted with hydrogen or a fuel gas mainly composed of hydrogen, the maximum combustion speed occurs when premixing more than half of the combustion air, as shown in Figure 2. It becomes easy to backfire, and it quickly reaches the air intake hole. In other words, for general fuel gas, the maximum combustion speed appears when all the required air is introduced (^, = 1), whereas for hydrogen, the increase in combustion speed when air is insufficient (reaching about 2 MSO's for hydrocarbon fuel) is unique. This is a phenomenon.
For this reason, converting general-purpose combustion equipment to hydrogen would require hydrogen to be used under the most dangerous conditions for generating a child mixture, which would be impractical. In order to avoid premixing and obtain the same NOK suppression effect as with premixing, it is necessary to ensure that hydrogen and air first meet outside the burner and that considerable mixing occurs before ignition. It is. In the present invention, an air pipe is provided inside the tip of the burner, and air is sucked in by the fuel gas that meets the burner. The amount of suction air is 0.5 to 0 as the primary air ratio.
．． The most preferable value is about 8, and the amount can be changed depending on the fuel gas nozzle flow rate and the angle between the nozzle inner wall and the air pipe. The fuel gas flow rate can be accelerated by adjusting the burner diameter by giving the burner nozzle an appropriate inclination as shown in FIG. 3. At this time, the inclination is preferably 1C. ~450. However, FIG. 3 is a drawing showing the nozzle tip of the burner of the present invention, where 1 is a fuel gas inlet pipe, 2 is an air pipe, and 3 is a fuel gas outlet. In the burner, depending on how close the air pipe entrance part is to the maximum fuel gas flow velocity part,
The suction effect of the gas flow can be adjusted. The mechanism by which low N○x is achieved when the burner of the present invention is used will be explained below.

As shown in Fig. 4, the gas introduced from the fuel gas introduction pipe 1 is ejected from the outlet 3, and the gas is ejected from the outside side of the burner.
Diffusion flame with excess air at high temperature while mixing with air 7 [Flame 5]
burns as.

At this time, if there is no air supply from the inside, all the hydrogen will burn as a diffusion flame, resulting in a high NO amount corresponding to ^, = 0 in Figure 1.
Gives a wide level. However, when the primary air is sucked from the inner air pipe 2, a high-speed sub-air mixture is generated at the center directly above the burner, and a high-temperature excess fuel flame (flame 6) is generated at a slightly elevated position. Using the burner of the present invention, this 6
It is possible to generate a flame, but this requires certain conditions, such as when the amount of primary air is too small. <0.4, the flame will not ignite due to lack of air, and combustion will occur only in the high temperature diffusion flame on the outside, which may result in a high N0k level. Therefore, in such cases, the gas flow rate, air Adjust the tube opening position, diameter, etc. and confirm that the inner 6 flames are generated.

With the 6-flame, which is a reducing flame inside the flame, there is a significant air shortage, so the generation of N○× hardly occurs. After the reaction of 6 flames is completed, the external secondary air gradually mixes and reacts with the remaining hydrogen, forming a low-temperature excess air flame [4 flames] that is extinguished. At this stage, the flame is already at a low temperature, so even if there is sufficient air, there is little generation of NOx. The main reaction process in this burner, that is, 6 flames → 4 flames, is essentially the main reaction process in the two-stage combustion method, which is N in the 1st flame → 2nd flame.
This corresponds well to the OK suppression mechanism (the first flame becomes a fuel-excess flame when the temperature is high, and the second flame becomes an air-excess flame when the temperature is low). The burner of the present invention is utilized exclusively as a low NO wide burner for hydrogen. In other words, as shown in Figure 1, it is a peculiarity of hydrogen that N○× can be reduced by air particle mixing.
Other fuels have almost no effect on reducing N○x due to air premixing, or in some cases may even have a high N○x effect.
It is possible that it may become k. Furthermore, when the burner of the present invention is applied to hydrocarbons such as LP gas, the mixing of LP gas with air is not as rapid as with hydrogen, so the mixing at the inner 6 flame position is poor, ignition is delayed, and the 6 flame is The flame lifts significantly and burns after almost reaching the outer 5 or 4 flames, which reduces the effect of the inner suction mixture. The burner of the present invention can burn hydrogen easily and safely with extremely low NOx generation, and can be used as a household/commercial burner for hydrogen.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the primary air ratio and the concentration of N○× generated when various fuels are burned, and Figure 2 is a graph showing the relationship between the primary air ratio and the combustion rate. It is a graph. Further, FIG. 3 is a cross-sectional view of the tip of the burner of the present invention, and FIG. 4 shows the state of flame when hydrogen is burned using the burner of the present invention. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 By holding the air pipe inside the burner gas pipe, the inner air pipe reaches the nozzle tip so that the fuel gas and the inner air meet for the first time at the nozzle tip in the burner nozzle which is made into a double pipe. The upstream side of the inner air pipe is open to the air, and the outer wall of the outer gas pipe is arranged at the tip of the nozzle so that the fuel gas flow flowing through the outer gas pipe quickly mixes with the inner air flow immediately after jetting out of the nozzle. A low NOx burner for hydrogen, characterized by being inclined toward the tube core.