JPH11304109A - Boiler combustor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize production level of NOx, CO and smoke soots (unburnt component) in combustion gas at the boiler outlet by keeping the mixture correctly at the after air port regardless of variation in the combustion conditions, e.g. burner air ratio. SOLUTION: A sub-airport 3 for varying the area of air channel and reduction burning fuel is provided between burners 2a, 2b and a main airport 4 on the downstream side. Since the area of air channel of the sub-airport 3 is enlarged, by the combustion conditions of the burner, such that the after air through force will be equivalent to base conditions even it the quantity of after air is increased when it is increased over a base value on the upstream side, good mixing takes place in the central part of a furnace and NOx is not increased. When the quantity of after air is decreased below the base value on the upstream side, good mixing takes place similarly to base conditions by limiting the area of air channel of the sub-airport 3 thereby ensuring the through force. Consequently, generation of CO and smoke soots (unburnt component) is not increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler combustion apparatus suitable for minimizing the generation levels of nitrogen oxides (NOx), carbon monoxide (CO) and dust (unburned components) at the boiler outlet. About.

[0002]

2. Description of the Related Art A burner used in a boiler combustion apparatus is generally of a two-stage combustion type for the purpose of reducing the concentration of NOx in boiler exhaust gas. The two-stage combustion type burner supplies combustion air to the burner in two stages, burns the fuel at an air ratio of 1 or less (usually 0.75 to 0.95), and then flows the after-air port on the downstream side. This is a configuration in which insufficient air is supplied to the section to complete combustion.

The two-stage burner burns fuel in a low air ratio state from the burner section to the after-air port section, and as a result, has an effect of reducing both thermal NOx and fuel NOx. Therefore, it is possible to reduce the NOx concentration of the combustion gas regardless of the type of fuel such as gas, oil, and pulverized coal.

In general, the higher the two-stage combustion ratio, the higher the effect of reducing the NOx concentration of the combustion gas. However, if the two-stage combustion ratio is increased beyond a certain ratio, the NOx concentration tends to increase. This is because if the two-stage combustion ratio is too high, the air ratio to fuel in the burner section becomes too low, and unburned fuel not combusted in the burner section burns rapidly in the after-airport section, and NOx is regenerated. That's why.

As a method for suppressing the regenerated NOx, there is a method in which after-air ports are provided in multiple stages and the after-air is supplied in a divided manner. FIG. 4 shows a configuration of a typical two-stage after-airport in a counter-burning type burner used in a furnace of a pulverized coal-fired boiler.

The furnace 31 has two burners 32a and 32b,
It is installed on the wall of the furnace at the opposing position and has two upper and lower after-air ports 33a, 3b above the upper burner 32b for the purpose of lowering the NOx of the combustion gas by effectively utilizing the space of the furnace 31.
3b are installed opposite each other.

The combustion air preheated from the FDF 36 via the air heater 37 is distributed to the burner section and the after-air port section by the wind box 39 and charged into the furnace 31 while the flow rate is adjusted by the damper 38. In the two-stage combustion zone from the burner section to the after-air ports 33a and 33b, the furnace is operated at a stoichiometric air ratio or lower, so that the furnace 3
In 1, unburned gas remains. The unburned gas mixes with the after-air downstream of the after-air port (above the furnace) to complete combustion. The combustion exhaust gas exiting the furnace 31 is discharged from a chimney 42 via a denitration device 41 and an air heater 37.

[0008]

The conventional two-stage combustion burner shown in FIG. 4 has the same shape of after air ports 33a, 33.
Since b was installed in multiple stages, at the same two-stage combustion ratio, increasing the air amount at the upstream air port 33a decreases the air amount at the downstream air port 33b, and the downstream after-air does not have sufficient penetration force. Therefore, there is a problem that the effect of supplying after air in multiple stages cannot be exhibited.

As described above, the prior art two-stage combustion burner does not take into consideration the appropriate mixing of the after-air and the unburned gas in the after-air port portion due to the change in the burner air ratio, and the combustion in the combustion gas is not considered. There has been a problem that the NOx concentration increases, or that the CO concentration and unburned components increase.

[0010] An object of the present invention is to appropriately maintain the mixing at the after-airport section irrespective of a change in combustion conditions such as a burner air ratio, so that NOx, CO and soot (not yet) in the combustion gas at the boiler outlet section. (Fuel content) is minimized.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a boiler having a burner for burning fuel together with primary air and an after-air port for supplying combustion air, the burner and the most downstream after-air port. The problem is solved by a boiler combustion device having a variable air passage area between the main air port and at least one or more sub air ports for reducing and burning fuel.

The means for varying the area of the air flow path of the sub-air port may be configured such that the air flow path of the sub-air port is divided into multiple stages, and a flow path opening / closing means for each of the divided air flow paths is provided. it can.

The combustion conditions for changing the air flow area of the sub air port of the present invention include a burner air ratio, a burner air ratio, a total air ratio used in the burner and the after air port,
There are methods using the burner air ratio, the total air ratio used in the burner and the after-air port, and any one of the boiler load and the fuel property as parameters.

[0014]

Table 1 shows the difference in the behavior of the after-air between the prior art and the present invention with respect to the change in the amount of the after-air at the upstream side of the two-stage after-air port.

[0015]

[Table 1]

In both the burner of the present invention and the prior art burner shown in FIG. 4, when the set burner air ratio is a base value (the after-air amount at that time is also a base value), the burner air ratio is lower than the base value. In this case, the after-air amount increases, and when the burner air ratio is higher than the base value of the set burner air ratio, the after-air amount decreases.

However, when the amount of after-air on the upstream side is increased from the base value due to the combustion conditions of the burner, the penetration force increases with the increase in the amount of after-air in the prior art, and the front and rear of the can at the central part of the furnace are located. The after-airs injected from the device interfere with each other. Thus, in the burner of the related art, the combustion air jet from the after-air port flows to the burner zone side (downside of the furnace). Therefore, NOx tends to increase due to the reduction of the NOx reduction region and the NOx regeneration phenomenon.

On the other hand, in the burner of the present invention, when the after-air amount on the upstream side is increased due to the combustion condition of the burner, even if the after-air amount is increased, the after-air porting force becomes equal to the base condition. Since the area of the air flow path of the (sub air port) is increased, good mixing is performed even in the central part of the furnace, and NOx does not rise.

If the amount of upstream after-air is reduced below the base condition, the burner of the prior art reduces the after-air penetration force, causing the unburned gas to pass through at the center of the furnace, resulting in CO and soot (unburned). ) The level shows an increasing trend. On the other hand, in the burner of the present invention, by performing the operation of reducing the air flow path area of the after-air port (sub-air port) to secure the penetration force, good mixing is performed similarly to the base condition, so that CO generation is generated. The amount and dust (unburned matter) do not increase.

Further, when the after-air port is made one step,
When the amount of air supplied from the after-air port is increased, a portion having a high oxygen concentration locally occurs, and it takes time for the high-concentration oxygen to diffuse. By using an airport and varying the amount of combustion air from the upstream after-air port (sub-air port) in accordance with combustion conditions, it is possible to adjust the after-air penetration force to be appropriate. The downstream after-air port (main air port) has a function of diffusing combustion air.

[0021]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of an embodiment of the present invention. This figure shows the configuration of a pulverized coal-fired boiler combustion device. Burners 2a, 2b are installed in the furnace 1 in two-stage opposition,
A sub air port 3 and a main air port 4 are provided opposite to each other above the lower burner 2b for the purpose of reducing NOx of combustion gas by effectively utilizing the space of the furnace 1.

The combustion air preheated from the FDF 6 via the air heater 7 is distributed to the burner section and the after-air port section by the air damper 8 and the wind box 5, and is charged into the furnace 1.

In the two-stage combustion zone in the furnace 1 from the burner section to the sub air port 3, fuel is burned at a stoichiometric air ratio or less, so that unburned gas remains in the furnace 1.
The unburned gas mixes with the sub-after-air 11 and the main after-air 12 downstream of the after-air port portion (above the furnace) to complete the combustion. The flue gas discharged from the furnace 1 is discharged from the chimney 15 via the denitration device 13 and the air heater 7.

FIG. 2 is a sectional view of the sub air port 3 according to the present invention. The sub air port 3 has flow paths 3a, 3b, 3
c is divided into three, and the slide flow path 3a, 3b,
The opening and closing of 3c is adjusted.

FIG. 3 is a sectional view of the main air port 4 according to the embodiment of the present invention. The main air port 4 is provided with a primary sleeve 22 to which the first divided air 21 is supplied and a secondary sleeve 24 to which the second divided air 23 is supplied to the outer periphery of the primary sleeve 22 so that the combustion air can be supplied in two parts. Is provided as a dual type after-airport structure.

The primary sleeve 22 of the main air port 4 is provided with a slide damper 26 for adjusting the amount of air supplied from the opening 22a. The secondary sleeve 24 also has a slide damper 2 for opening and closing the opening 24a.
7 are provided. The slide dampers 26 and 27 are driven by driving devices 28 and 29, respectively. The secondary sleeve 24 is provided with an air register 30 for imparting a swirling force and a penetrating force to the combustion air. The air register 30 is controlled by the register driver 31 to optimize the swirling force and penetration force of the combustion air, thereby minimizing the passage of unburned gas in the furnace 1 near the after-airport portion. It becomes possible.

In the present embodiment, the air ratio of the optimum burner portion based on the standard coal is 0.85, the air ratio of the sub air port 3 is 0.1, the air ratio of the main air port 4 is 0.25, and the total air ratio is 1.2 (= 0.85 + 0.1 + 0.25). In the base condition in this case, as shown in FIG. 2, the slide damper 18 is set to use two of the three divided flow paths 3a to 3c of the sub air port 3. In the two-stage combustion zone in the furnace 1 from the burner section to the sub air port 3 arrangement part, the burner air ratio is 0.85, and the air is also in the two-stage combustion zone in the furnace 1 from the sub air port 3 to the main air port 4 arrangement part. Ratio 0.85-
Since the low air ratio combustion of 0.95 is performed, the combustion becomes slow and the generation of thermal NOx is suppressed.

Since the two-stage combustion zone has a reducing atmosphere, the reduction reaction of NOx is promoted by the action of the intermediate product generated at the same time as NOx, and the amount of fuel NOx generated is reduced.

In the main air port 4, combustion air equivalent to 0.25 with respect to the air ratio is introduced and mixed appropriately with unburned gas, thereby minimizing the generation of CO and unburned components. . Also, after air 11 and 12 (FIG. 1)
Is divided and supplied in the upper stage and the lower stage, so that the generation of regenerated NOx due to the rapid introduction of air can be minimized.

The optimum ratio of the main after-air injection amount for reducing NOx and unburned components differs depending on the combustion conditions such as the fuel properties. Table 2 shows that the three divided flow passages 3a to 3c of the sub air port 3 are provided. 3 shows the configuration of the sub-airport flow path when the air injection ratio is changed.

[0031]

[Table 2]

As shown in Table 2, when the air ratio of the sub air port 3 is set to 0.12, the input air amount increases by about 20% with respect to the base (0.1). Under such an air ratio condition, the slide damper 18 is set to use all three flow paths 3a to 3c of the sub air port 3. Also, by using only the two flow paths of the sub air port 3 when supplying air under the base condition, the penetration force of the sub-after-air 11 becomes equal to that under the base condition despite the increase in the amount of air. Good mixing is also performed in the center. In addition, under the above conditions, the amount of air in the main air port 4 is reduced by about 8% with respect to the base conditions, but there is no problem because it is within the allowable design range.

On the other hand, the air ratio of the sub air port 3 is set to 0.0
In the case of 8, only about 80% of the combustion air is injected into the base. Under such air ratio conditions,
By setting the two passages of the sub air port 3 to be closed by the slide damper 18 and using only one passage, even if the amount of sub-after-air is reduced, a penetration force equivalent to the base condition can be secured. It does not hinder performance. In this condition also, the air amount of the main air port 4 increases by about 8% in the base condition, but there is no problem because it is within the allowable design range.

[0034]

Effect of the Invention a. By effectively utilizing the furnace space, the two-stage combustion can be effectively performed to the maximum, so that the generation amount of NOx, CO, and dust (unburned components) can be minimized. b. A single boiler can easily handle multiple fuels or multiple coals. c. Two-stage combustion ratio can be set to the optimum value in a wide range for combustion conditions.

[Brief description of the drawings]

FIG. 1 shows a configuration diagram of a boiler combustion device according to an embodiment of the present invention.

FIG. 2 is a sectional view of a sub air port of the boiler combustion device of FIG.

FIG. 3 is a sectional view of a main air port of the boiler combustion device of FIG. 1;

FIG. 4 shows a configuration diagram of a conventional boiler combustion device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Furnace 2a, 2b Burner 3 Sub air port 4 Main air port 5 Wind box 6 FDF 7 Air heater 8 Wind box air damper 11 Sub after air 12 Main after air 13 Denitration device 15 Chimney 17 Actuator 18 Slide damper 21 First split air 22 Primary sleeve 23 First 2 split air 24 Secondary sleeve 26,27 Slide damper 28,29 Drive device 30 Air register 31 Register driver

Claims (7)

[Claims] In a boiler combustion device having a burner for burning fuel together with primary air and an after-air port for supplying combustion air, an air flow passage area is provided between the burner and a main air port which is the most downstream after-air port. And a sub air port for reducing and burning fuel is provided in at least one stage. 2. The boiler combustion device according to claim 1, further comprising means for varying the air flow path area of the sub-air port in accordance with combustion conditions. 3. The air flow path of the sub air port is varied in a multi-stage manner as means for making the air flow path area of the sub air port variable, and flow opening / closing means for each of the divided air flow paths is provided. The boiler combustion device according to claim 2. 4. The boiler combustion apparatus according to claim 2, wherein a burner air ratio is used as a parameter as a combustion condition for changing an air flow area of the sub air port. 5. The boiler combustion apparatus according to claim 2, wherein the combustion conditions for changing the air flow path area of the sub-air port include a burner air ratio and a total air ratio used in the burner and the after-air port as parameters. 6. The boiler combustion according to claim 2, wherein the combustion conditions for changing the air flow path area of the sub-air port include a burner air ratio, a total air ratio used in the burner and the after-air port, and a boiler load as parameters. apparatus 7. The boiler combustion apparatus according to claim 2, wherein fuel properties are used as parameters as combustion conditions for changing the air flow path area of the sub air port.