JP3816243B2 - Burner - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion apparatus, and more particularly to a combustion apparatus suitable for reducing nitrogen oxides in exhaust gas.
[0002]
[Prior art]
As an effective means for reducing nitrogen oxide (NOx) in the exhaust gas of a pulverized coal fired boiler, a so-called flame denitration technique for reducing NOx in a flame has been put into practical use. FIG. 3 is a side sectional view of a burner suitable for effectively performing exhaust gas denitration in the furnace 116.
[0003]
The burner has three flow paths, and a mixed fluid 105 of fuel (pulverized coal) and carrier gas is introduced into the inner fuel flow path 101. A combustion air supply flow path is provided on the outer periphery of the fuel flow path 101, and the combustion air supplied from the wind box 115 is divided into the secondary air 106 and the tertiary air 107, and the secondary air flow path 102. Are introduced into the furnace 116 from the tertiary air flow path 103. The secondary air passage 102 and the tertiary air passage 103 are respectively provided with a secondary air swirler 111 and a tertiary air swirler 113 for jetting combustion air from the burner port while swirling.
[0004]
Further, a flow path separator 112 is installed between the secondary air flow path 102 and the tertiary air flow path 103, and the timing at which the tertiary air 107 is mixed with the mixed fluid 105 by the flow path separator 112 is set. The secondary air is delayed from the timing of mixing with the mixed fluid 105 to form a reduction region with excess fuel inside the flame. A flame holder 110 is provided on the outer peripheral portion of the outlet of the fuel flow path 101. The flame is formed by the flame holder 110 from the burner port, and combustion proceeds rapidly in the reduction region.
[0005]
FIG. 4 shows the O ₂ concentration distribution, temperature distribution, and NOx temperature distribution in the flame in the combustion test in the test furnace using the burner shown in FIG. As the combustion progresses, O ₂ is rapidly consumed in the flame, and the O ₂ concentration decreases with increasing distance from the burner. Although NOx is produced in a large amount in the vicinity of the burner, the reduction reaction is promoted as the O ₂ concentration decreases, so the NOx concentration rapidly decreases as the distance from the burner increases.
[0006]
In order to further promote NOx reduction in the furnace 116, a two-stage combustion method is applied. FIG. 5 shows an example of a boiler fuel combustion system to which the two-stage combustion method is applied. The mixed fluid 105 of pulverized coal and transport gas is introduced into the furnace 116 through the burner 122. After the combustion air 124 is distributed and adjusted by the burner air flow rate adjustment damper 125 and the two-stage combustion air flow rate adjustment damper 126, the burner wind box 115 and the two-stage combustion wind box 128 are respectively burner 122 and two-stage. It is introduced into the furnace 116 via the combustion air supply device 129. In the example of FIG. 5, a part of the exhaust gas 130 discharged from the furnace 116 is returned to the furnace 116 as the recirculation gas 131 and used for reheat steam temperature control.
[0007]
[Problems to be solved by the invention]
By combining the above-mentioned furnace denitration burner and the two-stage combustion method, the NOx concentration in the exhaust gas is 120 ppm NOx for coal with a fuel ratio (fixed carbon / volatile content) of 2.5 or less and a nitrogen content of 2.0% or less. It has reached the level of (O ₂ 6% conversion). The above-mentioned NOx concentration reduction technology is mainly concerned with the conversion of nitrogen content in coal into NOx, that is, the amount of fuel NOx. With the decrease in the NOx concentration level, the so-called thermal NOx concentration ratio that N _{2 in} the air reacts with O ₂ at a high temperature and can no longer be ignored.
[0008]
In order to suppress the thermal NOx concentration, it is known that lowering the flame temperature and lowering the O ₂ concentration in the combustion field are effective. Therefore, so-called exhaust gas mixing, in which a part of boiler exhaust gas is recirculated and mixed with combustion air, is one of practical techniques effective for thermal NOx suppression.
[0009]
FIG. 6 shows an example of a fuel combustion system of a boiler that produces exhaust gas mixture. In the system diagram of FIG. 6, members having the same functions as those shown in the system diagram of FIG.
[0010]
A part of the exhaust gas 130 discharged from the furnace 116 is returned to the fuel combustion system by the gas recirculation fan 132 as the recirculation gas 131, and a part thereof is a recirculation gas flow rate adjustment damper 133 for reheat steam temperature control. Is introduced into the furnace 116 from the bottom of the furnace, and the other part is adjusted to a predetermined flow rate by the exhaust gas mixing flow rate adjusting damper 134 and then mixed with the combustion air 124 by the mixer 135.
[0011]
The combustion air mixed with the recirculated gas is adjusted to a predetermined flow rate by the air flow rate adjusting dampers 125 and 126 and then guided to the burner wind box 115 and the two-stage combustion wind box 128, respectively. As shown in FIG. 3, the mixture of the combustion air 124 and the recirculation gas 131 is guided from the wind box 115 to the furnace 116 through the secondary air flow path 102 and the tertiary air flow path 103. . A part of the secondary air 106 and the tertiary air 107 are gradually mixed with the pulverized coal and the carrier gas in the mixed fluid 105 formed on the inner peripheral side of the flow of the combustion air 124 while the flame is gradually mixed. To form.
[0012]
However, when exhaust gas is mixed with the combustion air 124, the O ₂ concentration in the wind box 115 is uniformly reduced. Therefore, in the process of forming a flame as described above, the combustibility of fuel near the burner is reduced. descend. The reduction in fuel combustibility leads to a reduction in the combustion rate in the reduction region formed in the vicinity of the burner and the function of denitration in the flame, resulting in an increase in the NOx concentration.
[0013]
That is, the exhaust gas mixture for suppressing the generation of thermal NOx increases the amount of fuel NOx generated, resulting in no effect in suppressing the generation of finished NOx. The above problem is caused by a decrease in fuel combustibility due to exhaust gas mixing. The same applies to the invention disclosed in Japanese Patent Laid-Open No. 60-30912, which discloses mixing exhaust gas with the tertiary air 107.
[0014]
The publication describes a low NOx burner that mixes exhaust gas with air or supplies it alone to the outer periphery of the secondary air, and its purpose is to prevent the generation of thermal NOx in the flame outermost peripheral zone. . However, the low NOx burner described in the above publication does not have the outer flame stabilizer 110 described in the prior art of the present application (FIG. 3), and the ignition flame holding region immediately after being ejected from the fuel flow path to the furnace. It is in an unstable state. Furthermore, mixing exhaust gas into the air from the outer periphery of the secondary air or supplying it alone in such a situation results in a shortage of air to stably burn the fuel and disturbance to the secondary air. Fuel combustibility will decrease.
[0015]
In the prior art shown in FIG. 5 in which the exhaust gas generated by the combustion of fuel in the furnace 116 is again introduced into the furnace 116 from the bottom of the furnace 116, there is a phenomenon that the NOx generation amount decreases by increasing the exhaust gas input amount. It has been confirmed. However, since this method is a mechanism in which NOx is lowered by lowering the temperature in the entire furnace, the effect of reducing the amount of NOx produced is small. In addition, since the exhaust gas is introduced from the vicinity of the bottom burner, which has the lowest ambient temperature and the most severe conditions in terms of ensuring flame stability, an increase in the amount of exhaust gas input causes a destabilization of the flame. Yes.
[0016]
The subject of this invention is providing the combustion apparatus which can reduce a thermal NOx density | concentration effectively, maintaining flame stability and the combustibility of a fuel, and not reducing the denitration performance in a flame.
[0017]
[Means for Solving the Problems]
The above object of the present invention is achieved by introducing the recirculation gas from the outermost peripheral portion of the burner that does not affect the flammability in the vicinity of the burner.
That is, the present invention provides a primary flow path for feeding the carrier gas and the solid fuel to the furnace, a flame stabilizer provided at the tip portion of the primary flow path, multiple combustion air provided outside of the primary flow path The burner is provided with a combustion air flow path for introducing the exhaust gas, and an exhaust gas recirculation flow path for introducing a part of the combustion exhaust gas, which is further provided on the outer periphery of the combustion air flow path.
[0019]
The present invention also provides a combustion furnace that burns fuel using the burner, an exhaust gas recirculation passage that recirculates exhaust gas discharged from the combustion furnace and introduces it into the burner, and the exhaust gas recirculation passage. Also included is a combustion apparatus provided with the exhaust gas flow rate adjusting means and / or means for adjusting the swirl direction and / or swirl strength of the exhaust gas.
[0020]
Further, the present invention includes a plurality of the burners, an exhaust gas recirculation passage capable of individually or uniformly adjusting the mixed flow rate of the combustion exhaust gas, and a flow rate adjusting means provided in each exhaust gas recirculation passage, A combustion apparatus provided with exhaust gas recirculation flow path switching means is also included.
[0021]
[Action]
Combustion air on the inner periphery side in the combustion air flow that surrounds the pulverized coal flow consisting of fuel (such as pulverized coal, which will be described below as pulverized coal) jetted from the burner into the furnace. The flowing air maintains a high oxygen concentration in the vicinity of the burner with respect to the pulverized coal and its conveying gas, and therefore does not lower the combustibility of the pulverized coal. According to the present invention, the recirculated exhaust gas introduced from the outermost peripheral portion of the fluid ejected from the burner is gradually mixed with the combustion air on the inner peripheral side, and the oxygen concentration in the oxidation flow region downstream of the denitration region in the flame is set. The generation of thermal NOx can be effectively suppressed.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 1 shows a side sectional view of the burner of the present invention. The method of introducing pulverized coal and combustion air and the flow path configuration are the same as those shown in FIG. 3 which is an example of the structure of a burner according to the prior art.
[0023]
A mixed fluid 5 of pulverized coal and carrier gas is introduced into the innermost fuel flow path 1 of the burner. A combustion air supply flow path is provided on the outer periphery of the fuel flow path 1, and the combustion air supplied from the wind box 17 is divided into secondary air 6 and tertiary air 7, and the secondary air flow path 2 Are introduced into the furnace 18 from the tertiary air flow path 3. The secondary air flow path 2 and the tertiary air flow path 3 are respectively provided with a secondary air swirler 11 and a tertiary air swirler 13 for ejecting the combustion air from the burner port while swirling.
[0024]
Also, between the secondary air flow path 2 and the tertiary air flow path 3, the timing at which the tertiary air 7 is mixed with the fuel is delayed from the timing at which the secondary air 6 is mixed with the fuel, and the fuel is reduced excessively inside the flame. A flow path separator 12 for forming a region is installed. A flame holder 10 is provided on the outer periphery of the outlet of the fuel flow path 1. A flame is formed by the flame holder 10 from a burner port, and combustion rapidly proceeds in the reduction region.
[0025]
A feature of the burner according to the present invention is that a recirculation gas passage 4 for recirculating exhaust gas from the furnace 18 is provided on the outer periphery of the tertiary air passage 3. The recirculation gas 8 is guided to a recirculation gas supply chamber 16 through a dedicated recirculation gas supply pipe 15, is given an appropriate swirl by the recirculation gas swirler 14, and is then introduced into the furnace 18.
[0026]
FIG. 2 shows an example of a fuel combustion system of a boiler in which the burner shown in FIG. 1 is used. A mixed fluid 21 of pulverized coal and transporting gas is introduced into the furnace 18 through a burner 22. After the combustion air 24 is distributed and adjusted by the burner air flow rate adjustment damper 25 and the two-stage combustion air flow rate adjustment damper 26, the burner wind box 17 and the two-stage combustion wind box 28 are respectively burner 22 and two-stage. The gas is supplied to the furnace 18 through the combustion air supply device 29.
[0027]
Compared with the system example of the prior art of FIG. 6, in the system example of FIG. 2, a part of the exhaust gas 30 discharged from the furnace 18 is predetermined as a recirculation gas 31 by a recirculation gas adjustment damper 33 by a gas recirculation fan 32. And is returned to the furnace 18 to be used for reheat steam temperature control. A part of the recirculation gas 31 is adjusted to a predetermined flow rate by the burner recirculation gas adjustment damper 34 and then directly introduced into the burner 22. The burner port is connected to the recirculation gas supply pipe 15 shown in FIG.
[0028]
A part of the secondary air 6 and the tertiary air 7 on the inner peripheral side of the burner 22 is gradually mixed with the mixed fluid 5 of the pulverized coal at the center and the conveying gas, and proceeds with combustion in a reducing atmosphere to cause fuel. Suppresses the generation of NOx. On the other hand, the recirculation gas 31 introduced from the outermost periphery of the burner is gradually mixed with the tertiary air 7 to reduce the oxygen concentration in the oxidation region where the tertiary air 7 joins the inner peripheral reduction region, thereby generating thermal NOx. Suppress. By adjusting the flow rate, swirl direction, and strength of the recirculation gas 31, the oxygen concentration in the oxidation region can be adjusted, and thermal NOx can be effectively suppressed.
[0029]
Instead of the outermost peripheral recirculation gas 31, a mixed gas of the recirculation gas 31 and the combustion air 24 may be introduced into the recirculation gas supply pipe 15.
[0030]
In addition, for the highly combustible fuel, the outermost peripheral flow path can be omitted by mixing the recirculation gas with the tertiary air. In this case, it differs from the invention described in JP-A-60-30912 in that there is an outer flame stabilizer 10.
[0031]
【The invention's effect】
According to the present invention, it is possible to suppress the NOx removal efficiency in the flame while suppressing the thermal NOx at the outer periphery of the flame, and further reduce the boiler outlet NOx.
[Brief description of the drawings]
FIG. 1 is a diagram showing a structure example of a burner according to an embodiment of the present invention.
FIG. 2 is a diagram showing a system example of a combustion apparatus according to an embodiment of the present invention.
FIG. 3 is a view showing an example of the structure of a conventional burner.
FIG. 4 shows an example of O ₂ distribution, temperature distribution, and NOx concentration distribution in a combustion field using a burner of the prior art.
FIG. 5 shows an example of a combustion system of the prior art.
FIG. 6 shows an example of a combustion apparatus system according to the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel flow path 4 Recirculation gas flow path 6 Secondary air 7 Tertiary air 10 Flame stabilizer 11 Secondary air swirler 12 Flow path separator 13 Tertiary air swirler 14 Recirculation gas swirler 15 Recirculation gas Supply pipe 16 Recirculation gas supply chamber 17 Wind box 18 Furnace 21 Mixed fluid 22 Burner 24 Combustion air 25 Burner air flow control damper 26 Two-stage combustion air flow control damper 28 Two-stage combustion wind box 29 Two-stage combustion Air supply device 30 Exhaust gas 31 Recirculation gas 32 Gas recirculation fan 33 Recirculation gas adjustment damper 34 Recirculation gas adjustment damper for burner

Claims (3)

A primary flow path for feeding a solid fuel and carrier gas into the furnace, combustion of introducing a flame stabilizer provided at the tip portion of the primary flow path, a multiple of the combustion air which is provided on the outside of the primary flow path burner for the air flow path, it provided further outer periphery of the combustion air flow path, characterized in that a gas recirculation channel for introducing a part of the combustion exhaust gas. A combustion furnace for burning fuel using the burner according to claim 1, an exhaust gas recirculation passage for recirculating exhaust gas discharged from the combustion furnace and introducing it into the burner, and the exhaust gas recirculation passage A combustion apparatus comprising exhaust gas flow rate adjusting means and / or means for adjusting a swirling direction and / or swirling strength of exhaust gas.  A plurality of burners according to claim 1 are provided, and an exhaust gas recirculation passage capable of individually or uniformly adjusting a mixed flow rate of combustion exhaust gas, a flow rate adjusting means provided in each exhaust gas recirculation passage and / or exhaust gas recirculation. A combustion apparatus provided with a circulation flow path switching means.

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