JPH0251085B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a combustion method for reducing nitrogen oxides (NO _x ), which is particularly efficient in a compact combustion furnace.
The present invention relates to the above method capable of reducing NO _x .

An example of a conventional combustion method for reducing nitrogen oxides (hereinafter abbreviated as NO _x ) is shown in Figure 1.

In Figure 1, 01 is the combustion furnace, 02 is the combustion air duct, 03 is the main burner, 04 is the auxiliary air compartment, 05 is the afterburner, 06 is the afterburning air compartment, 07 is the combustion air, and 08 is the main Burner combustion air, 09 is auxiliary air, 10 is afterburning air (),
11 is afterburning air (), 12 is fuel, 13 is main burner fuel, 14 is afterburning fuel, 15 is main combustion flame, 16 is auxiliary combustion flame, 17 is A area, 18 is B area, 19 is region C, and 20 is a flue.

In FIG. 1, most of the total amount of fuel 12 sent by a fuel supply facility (not shown) is blown into the combustion furnace 01 from the main burner 03, and the remainder is used as afterburning fuel 14. It is blown into the combustion furnace 01 from the afterburner 05.

On the other hand, combustion air 07 is fed from a blowing facility (not shown) and blown into the combustion furnace 01 from the main burner 03, the auxiliary air compartment 04, the afterburner 05, and the afterburning air compartment 06, respectively.

The amount of main burner combustion air 08 blown from the main burner 03 is less than the theoretical air amount of the main burner fuel 13, and the amount of auxiliary air 09 blown from the auxiliary air compartment 04 is the amount of main burner combustion air 08. The sum is approximately equal to or slightly larger than the theoretical air amount of the main burner fuel 13.

The amount of afterburning air ( ) 10 blown from the afterburner 05 is less than the theoretical air amount of the afterburner fuel 14 and in the B area 18.
Creates a NO _x reducing atmosphere.

Afterburning air compartment 0
Afterburning air blown from 6 () 1
No. 1 is used to completely burn the unburned matter generated in the B region 18 of the NO _x reducing atmosphere, and the amount of the injection is an appropriate amount depending on the combustion situation.

NO _x reduction by such conventional combustion methods is
It is done as follows.

Main burner fuel 1 blown from main burner 03
3 is combusted by main burner combustion air 08,
A main combustion flame 15 is formed, but while unburned fuel remains due to lack of air, it becomes a low-temperature flame and NO _x generation is suppressed. Unburnt fuel is A in combustion furnace 01
In region 17, combustion is completed by auxiliary air 09 blown in from auxiliary air compartment 04 provided in the upper stage on the same central axis as the fuel injection direction of main burner 03. As a result, the amount of NO _x in the exhaust gas decreases at the outlet of region A 17, resulting in a low-oxidation atmosphere. This NO _x reduction method is usually called an over-fire air method (OFA method) or a two-stage combustion method.

Main combustion flame 1 that completed combustion in area A 17
5 exhaust gas is a small amount of afterburning air () 10 blown from an afterburner 05 provided downstream of the auxiliary air compartment 04.
(below the theoretical air amount of the afterburning fuel 14) and the afterburning fuel 14 form an incomplete combustion sub-combustion flame 16, and the combustion furnace 0
Create a NO _x reduction atmosphere in area B 18 in 1,
NO _x generated from the main combustion flame 15 is reduced. In addition, in the B area 18 in the NO _x reduction atmosphere, unburned matter is generated at the same time, but the afterburning air ( ) 11 blown from the afterburning air compartment 06 provided downstream of the B area 18 Completely burned.

As a result, NO _x in the exhaust gas in the C region 19
The amount is further significantly reduced compared to the amount of NO _x in the A region 17. Therefore, the exhaust gas is discharged from the flue 20 to the outside of the furnace as clean combustion exhaust gas with low _NOx content and unburned matter.

As mentioned above, the conventional NO _x reduction combustion method is
This is an extremely effective NO _x reduction method that combines the OFA method and in-furnace denitrification method using afterburning.
Of these, in-furnace denitrification by afterburning is
The longer the residence time of the exhaust gas in the reduction region, the more effective it is, and the NO _x reduction rate tends to be higher.

However, from the test research and actual test results to date, the peak of the NO _x reduction rate due to afterburning is almost constant regardless of the NO _x value level, and in order to increase the overall NO _x reduction effect, It was found that it is necessary to increase the NO _x reduction by the OFA method as much as possible and keep the absolute value of NO _x at the entrance of the afterburning region low.

Figure 5 (described later) shows the experimental results (OFA
The relationship between the NO _x reduction rate (according to the method) and the distance L between the center of the main burner 03 and the auxiliary air compartment 04 (data α in Figure 5) is shown.
In order to increase the NO _x reduction effect by the OFA method, the center of the main burner 03 and the auxiliary air compartment 04 must be
It is necessary to make the distance L large.

However, in the conventional NO _x reduction combustion method, the auxiliary air compartment 04 is mostly
Since it is located on the same axis as the fuel injection direction of the main burner 03 and above the uppermost part of the main burner 03, it is designed to reduce the _NO If the distance L is increased, the height of the boiler inevitably increases, which is a drawback.

The present invention provides a combustion method for reducing NO _x that can effectively reduce NO _x without increasing the height of the boiler.

That is, the present invention blows main combustion fuel and air from a plurality of main combustion fuel and air injection nozzles, and blows auxiliary air, afterburning fuel and air, and afterburning air from each injection nozzle. In the nitrogen oxide reduction combustion method in which fuel is combusted in a nitrogen oxide reduction combustion method, the auxiliary air is injected from upstream of the most downstream nozzle among the plurality of main combustion fuel and air injection nozzles in the main combustion fuel and air injection direction. This relates to a nitrogen oxide reduction combustion method characterized by blowing in different directions.

More specifically, in the method of the present invention, an auxiliary air compartment equipped with an auxiliary air jetting nozzle that can freely move the jetting direction vertically and horizontally is shown in FIG. 2A and FIG. 2B, which is a sectional view thereof. As shown in the figure, the auxiliary air injection nozzle is installed between the upper and lower parts of the top main burner, and the auxiliary air injection nozzle can be adjusted from outside the combustion furnace so that the auxiliary air blowing direction does not match the fuel blowing direction from the main burner. This is what I did. As a result, effective _NOx reduction can be achieved without increasing the height of the boiler compared to the conventional method.

The method of the present invention can be applied to boilers, various industrial furnaces, etc.

One embodiment of the method of the present invention is shown in FIGS. 2-4. FIG. 2A is a conceptual diagram, FIG. 2B is a sectional view of FIG. 2A, and FIG. 4 is a view taken along the - arrow in FIG.

In FIGS. 3 and 4, 101 is a combustion furnace;
102 is a combustion air duct, 103 is a main burner,
104 is an auxiliary air compartment (equipped with an auxiliary air jet nozzle that can be freely moved vertically and horizontally), 105 is an afterburner, 106 is an afterburning air compartment, 107 is combustion air, and 108 is main burner combustion air. , 10
9 is auxiliary air, 110 is afterburning air (), 111 is afterburning air (), 112 is fuel, 113 is main burner fuel,
114 is afterburning fuel, 115 is main combustion flame, 116 is sub-combustion flame, 117 is A area, 1
18 is a B area, 119 is a C area, and 120 is a flue.

Note that the members indicated by reference numerals 101 to 120 correspond to the members indicated by reference numerals 1 to 20 in FIG. 1 showing the conventional example, and have substantially the same structure.

The difference between the above example and the conventional example is that the auxiliary air compartment 104 equipped with an auxiliary air jetting nozzle that can be freely moved vertically and horizontally is
As shown in Figures A and B, the auxiliary air 109 from the auxiliary air compartment 104 is arranged between the top stage main burner and the next stage main burner so as not to interfere with the main combustion flame 115 in the furnace. The NOx is blown into the A region 117 in order to reduce _NOx .

The effect of the NO _x reduction combustion method of the present invention is different from that of the conventional method.
It is the same as the NO _x reduction combustion method, but has the following effects.

An auxiliary air compartment 104 equipped with an auxiliary air blowing nozzle that can be freely moved vertically and horizontally from the outside of the combustion furnace 101 is disposed between the top stage main burner and the next stage main burner, and the auxiliary air compartment 104 is installed inside the furnace. Auxiliary air 109 blown into
However, in order to avoid promoting the generation _{of NOx} from the main combustion flame 115, the blowing direction of the auxiliary air 109 is adjusted by an auxiliary air injection nozzle, as shown by the ← mark in FIG. Therefore, the main burner 103
Even if the distance L between the centers of the auxiliary air compartment 104 and the auxiliary air compartment 104 is set small, the NO _x reduction effect will not be impaired.

Figure 5 is obtained from the combustion test results of the test furnace. In Figure 5, NO _x1 is the amount of NO _x generated by combustion in the main burner only (ppm), NO _x2 is the amount of NO _x generated by the OFA combustion method (ppm), and L is the distance between the centers of the main burner and the auxiliary air compartment ( m),
L _B indicates the main burner height (m), auxiliary air 09,
The amount of 109 is calculated as (auxiliary air amount/total air amount) x 100 = 20 (%), and α is the data from the conventional method shown in Figure 1 as described above.
β is the data obtained by the method of the present invention shown in FIGS. From Figure 5, the NO _x reduction effect of OFA combustion is:
The auxiliary air compartment 104 is connected to the main burner 10
It can be seen that the case where the burner is disposed on the fuel injection direction axis of No. 3 and above the uppermost stage main burner 103 shows a slightly higher tendency, but there is no significant difference. Therefore, the auxiliary air compartment 1
04 between the top stage main burner and the next stage main burner, compared to the former, the distance L from the center of the main burner 103 can be reduced while the NO _x reduction effect is comparable, so the boiler height can be reduced. NO _x can be reduced without increasing the temperature.

[Brief explanation of drawings]

Fig. 1 shows the conventional NO _x reduction combustion method, Figs. 2 to 4 show an embodiment of the method of the present invention, and Fig. 5 shows the experimental results to confirm the effectiveness of the method of the present invention. This is a chart showing the data.

Claims (1)

[Claims] 1 Main combustion fuel and air are blown in from multiple main combustion fuel and air injection nozzles, and auxiliary air, afterburning fuel and air, and afterburning air are blown in from each injection nozzle to combust the fuel. In the nitrogen oxide reduction combustion method, the auxiliary air is directed from upstream of the most downstream nozzle among the plurality of main combustion fuel and air injection nozzles in a direction different from the injection direction of the main combustion fuel and air. A nitrogen oxide reduction combustion method characterized by blowing.