JPS6257685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention particularly relates to a radiant tube combustion method and apparatus with low emissions (concentrations) of NOx and black smoke.

(Prior Art) Conventionally, as shown in FIGS. 5a and 5b, a radiant tube 2 inserted through a furnace wall 1 of a heat treatment furnace has been used.
A burner main body 3 is connected to the end of the radiant tube 2, and a fuel injection pipe 5 having a flame stabilizing plate 4 at the tip
Provided so as to coincide with (coaxial center) the tube axis T of
A combustion device has been proposed in which fuel G is ejected from a fuel ejection pipe 5 and, at the same time, combustion air A is ejected from a combustion air ejection passage 6 formed on the outer periphery of the fuel ejection pipe 5.

However, in this combustion device, unburned matter, especially black smoke, is likely to be generated when the combustion rate is low.

In other words, even though the combustion air A is at a high temperature (500°C or higher), its temperature is lower than that of the flame (900-1200°C), so the low-density flame flows into the upper flow of the radiant tube 2 due to buoyancy, and the high-density combustion air The force that flows to the lower flow acts on A. Especially at low load combustion rates,
Since the ejection flow velocity of the fuel G and combustion air A and the gas flow velocity within the radiant tube 2 are reduced, the buoyancy of the flame becomes dominant. Therefore, when combustion begins, fuel G cross-mixes with combustion air A and moves to the upper flow in an air-starved combustion state. The airflow also shifts to the lower flow. Then, the flow inside the radiant tube 2 becomes a two-phase flow consisting of an upper flow of flame containing a large amount of unburned matter macroscopically and a lower flow of combustion air, and flows downstream while being laminarly mixed. However, when going downstream, the amount of heat removed from the tube 2 becomes larger than the combustion heat, so the gas temperature decreases, making it difficult to burn unburned components, and making it easier to generate black smoke.

Additionally, large amounts of NOx are likely to be generated during high-load combustion rates of high-temperature combustion air (500°C or higher).

That is, the combustion of the radiant tube 2 causes the fuel G
Since the combustion chamber is narrow for the amount of fuel, the combustion chamber load factor is large, exceeding 10×10 ⁶ kcal/m ³ h.
Therefore, in the past, in order to improve combustion efficiency, the main focus was on uniformly mixing fuel G and combustion air A at an early stage to achieve rapid combustion. The temperature increases,
This makes it easier for NOx to be generated.

For this reason, not only does the environment of the combustion equipment deteriorate with NOx, black smoke, etc., but the black smoke also adheres to the heat exchanger tubes of the recuperator, reducing heat exchange ability and increasing pressure loss. Further, unburned carbon is deposited in the lower layer of the radiant tube 2, and the heat transfer ability of the radiant tube 2 in the furnace is reduced. Further, there are problems such as the exhaust gas temperature becoming high and the durability of the recuperator becoming poor.

Further, as shown in FIGS. 6a and 6b, the fuel injection pipe 5 is connected to the fuel injection pipe 5' provided along the fuel axis which is offset above the tube axis T of the radiant tube 2. A combustion device has been proposed in which, at the same time as fuel G is injected, combustion air A is ejected from a combustion air ejection passage 6' formed along an air axis offset below the tube axis T. ing.

However, with this combustion device, the amount of NOx is small at high load combustion rates, but at low load combustion rates, the buoyancy of the flame becomes dominant, resulting in an extremely large amount of black smoke. be.

Therefore, when adopting a high-temperature recuperator with improved exhaust heat recovery rate, the upper limit of the combustion air temperature is restricted by the NOx regulatory concentration and black smoke concentration. It is difficult to employ a requioperator. Measures to reduce NOx by adding evaporation to high-temperature combustion air increase running costs, which reduces the investment benefits of high-efficiency waste heat recovery.

(Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a radiant tube combustion method and apparatus with good turndown characteristics of low NOx and black smoke. be.

(Structure of the Invention) Therefore, in the combustion method according to the present invention, combustion air is ejected along the air axis of the radiant tube, which is offset above the tube axis, and at the same time The structure is such that the fuel is injected along the fuel axis which is deviated from the center.

Further, in the combustion device according to the present invention, the combustion air jet passage is formed along the air axis of the radiant tube, which is offset to the upper side of the tube axis, and the combustion air jet passage is formed along the air axis of the radiant tube, which is displaced to the lower side of the tube axis. A fuel injection pipe is provided along the axis.

(Effects of the Invention) According to the present invention, the combustion air ejection axis is offset toward the upper side and the fuel ejection axis is offset toward the lower side with respect to the tube axis of the radiant tube. As a result, rapid mixing of fuel and combustion air at high load combustion rates is avoided, resulting in slow combustion, which suppresses NOx.

In addition, at low load combustion rates, the flame on the lower side rises to the upper side due to buoyancy and mixes with the combustion air blown from the upper side, which suppresses the emission of unburned black smoke. become.

Therefore, a high-temperature recuperator with a high waste heat recovery rate can be used, and low NOx can be achieved by adding steam.
Running costs are no longer required, the environment of the combustion equipment is improved, there is no reduction in the heat exchange capacity of the recuperator, there is no increase in pressure drop in the recuperator, there is no decrease in the heat transfer capacity in the furnace due to carbon accumulation in the radiant tube, and the durability of the recuperator is improved. Sexuality will improve.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIGS. 1a and 1b, a radiant tube 12 inserted through the furnace wall 11 of the heat treatment furnace
The burner main body 13 is connected to the end of the radiant tube 12, and a fuel injection pipe 15 having a flame stabilizing plate 14 at the tip is provided along the fuel axis offset below the tube axis T of the radiant tube 12. , a combustion air jetting passage 16 is formed along the air axis shifted upward from the tube axis T.

Therefore, the combustion air A jetted out from the combustion air jetting passage 16 is mixed and combusted with the fuel G jetted out from the fuel air jetting pipe 15, but in the early stage of combustion, the air A ₁ , A ₂ close to the fuel G and the air are mixed. Since combustion occurs in a insufficient state (air is not supplied from the contact point 17 between the flame holding plate 14 and the radiant tube 12), NOx becomes low at high load combustion rates.

Then, the fuel flow moves to the upper flow due to the buoyancy of the flame, and the remaining combustion air flows A ₃ , A ₄ , A ₅ shift to the lower flow, and in this process, the fuel G and unburned components are completely combusted. , less black smoke is emitted at low load combustion rates.

In addition, the combustion air flow exiting from the lower region of the combustion air flow
A ₁ has the function of burning carbon generated in the vicinity of the contact point 17 between the flame stabilizing plate 14 and the radiant tube 12 together with the high temperature exhaust gas circulation flow G ₁ and preventing carbon accumulation.

2a and 2b show another embodiment in which the base of the fuel injection pipe 15 is aligned with the tube axis T, and the tip portion having the flame stabilizing plate 14 is aligned with the tube axis T of the radiant tube 12. It is installed diagonally and offset to the lower side.

This device can also provide the same functions and effects as the devices shown in FIGS. 1a and 1b.

FIGS. 3 and 4 show a combustion device according to the present invention (□ indicates the device in FIG. 2 a) and a conventional combustion device (○ indicates the device in FIG. 5 a, and △ indicates the device in FIG. 6 a). This is data measuring the relationship between the combustion load factor, NOx, and black smoke (respectively).

1 Combustion conditions (1) Air temperature: 550℃ (inside the burner body) (2) Radiant tube temperature: 850℃ (3) Exhaust gas oxygen concentration: 2.0% (4) 100% combustion: 120×10 ³ kcal/H (5 ) Fuel: Coke oven gas 2 Combustion device (1) Radiant tube inner diameter: 145 mm Length: 6000 mm Shape: U-shaped 3 Experimental furnace width: 760 cm Height: 950 cm Length: 3120 cm As is clear from the figure, main combustion According to the device, it can be seen that when the combustion rate is high, NOx is low and the amount of black smoke is low, and when the combustion rate is low, the amount of black smoke is low.

[Brief explanation of the drawing]

FIG. 1a is a side sectional view of a combustion device according to a first embodiment of the present invention, FIG. 1b is a cross-sectional view taken from FIG. 1a, and FIG. Figure 2b is a cross-sectional view of Figure 2a, Figure 3 is a graph showing the relationship between combustion load factor and NOx, and Figure 4 is a graph showing the relationship between combustion load rate and black smoke. Graph, FIG. 5a is a side cross-sectional view of a conventional combustion device, FIG. 5b is a cross-sectional view of FIG. 5a, and FIG.
FIG. 6a is a side sectional view of a conventional combustion device, and FIG. 6b is a cross-sectional view taken from FIG. 6a. 12...Radiant tube, 13...Burner body, 15...Fuel injection pipe, 16...Combustion air injection passage, T...Tube axis center.

Claims (1)

[Claims] 1. Combustion air is ejected along the air axis of the radiant tube, which is offset above the tube axis, and at the same time, the fuel axis is offset below the tube axis. A radiant tube combustion method characterized in that fuel is ejected along the radiant tube. 2. A combustion air injection passage is formed along the air axis of the radiant tube that is offset above the tube axis, and a fuel injection pipe is formed along the fuel axis that is offset below the tube axis. A radiant tube combustion device characterized in that: