JPH08285230A - Low pressure loss type low nox pulverized coal burner and pulverized coal combustion device - Google Patents

Abstract

PURPOSE: To provide a low NOx burner, capable of achieving the reduction of NOx without increasing a pressure loss of combustion air stream in the part of the burner and without reducing the diameter of the throat part of the burner. CONSTITUTION: A separation preventing vane 39 is installed in a secondary air flow passage 20 and at least either fluid of combustion air and exhaust gas is conducted to flow through a bypass passage 40, produced between the vane 39 and a burner wall 38, to blow the fluid through the outlet opening of the flow passage 40 into the direction of rear stream. As a result, the separation area of flow, which is produced by the sudden contraction of tertiary air 26 when there is no separation area-preventing vane 30, can be blown off by the fluid. Accordingly, the effective sectional area of the tertiary air flow passage 20 is increased and the pressure loss of the flow of combustion air 26a, 26b, passing through the flow passage 20, is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulverized coal combustion device,
Ultra low NO especially in burners requiring low NOx combustion
Low pressure loss type low NO which is capable of stable combustion at x and is suitable for reducing pressure loss of combustion air.
x Pulverized coal burner.

[0002]

2. Description of the Related Art As a pulverized coal combustion system used in a conventional boiler, etc., a pulverized coal machine (hereinafter referred to as a mill) having a built-in classifier pulverizes the coal, and the pulverized coal having a size smaller than a predetermined size is classified. A combustion system that directly supplies pulverized coal burner with carrier air has been put to practical use.

A two-stage combustion method (air staging) is a typical NOx reduction technique for this pulverized coal combustion system. This two-stage combustion method has an external type and an internal type. The external type is a fuel-rich condition in which the air ratio in the burner zone of the combustion furnace (the ratio of required air to fuel is 1 is a stoichiometric equivalent) is 1 or less. The NOx is reduced by reducing the generated NOx by maintaining the above condition, and the unburned fuel is completely burned by injecting air from the air charging hole provided in the downstream of the burner zone. Further, the internal two-stage combustion method is to swirl secondary and tertiary air to delay mixing of pulverized coal flow that is ignited and burned only with primary air and air, and the air ratio is changed only in the primary air. A two-stage combustion method in a burner zone in which a fuel rich condition of 1 or less is maintained, NOx produced is reduced to reduce NOx, and unburned fuel is completely burned by swirled secondary and tertiary air. Is. Pulverized coal low NOx burners based on these combustion methods (for example, JP-A-60-1)
No. 76315, JP-A-62-172105) have been put into practical use.

FIG. 7 shows a system diagram of a pulverized coal burning boiler equipped with the pulverized coal low NOx burner. Fuel coal is temporarily stored in a coal bunker 1 and then processed into pulverized coal by a mill 2. On the other hand, the primary air that conveys this pulverized coal to the burner 4 in the wind box 3 is pressurized by a PAF (Primary Air Fan) 5 and then heated by a heat exchanger 6 provided at the boiler outlet to generate high temperature boiler combustion exhaust gas. Heat exchange with, about 30
After being heated to 0 ° C., it is sent to the mill 2. The temperature-elevating air is sent to the burner 4 together with the pulverized coal after evaporating the water adhering to the coal inside the mill 2. The primary air temperature at the inlet of the burner 4 drops to about 80 ° C.

Combustion air such as secondary air and tertiary air is supplied by the FDF 8 through the heat exchanger 9 to the wind box 3 in which the burner 4 is arranged. Further, high temperature air for combustion remains in a part of the boiler exhaust gas and is supplied to the bottom of the boiler furnace 11 by the GRF (exhaust gas mixing fan) 10.

Two types of cross-sectional structural views of a conventional pulverized coal low NOx burner provided in the pulverized coal burning boiler of FIG. 7 by the conventional internal two-stage combustion method are shown in FIGS. 8 and 9. In FIGS. 8 and 9, a half cross section is shown with respect to the central axis of the burner. The burner in FIG. 8 has a flow path for secondary air and a flow path for tertiary air adjacent to each other, and the burner in FIG. 9 has a flow path for secondary air and a flow path for tertiary air separated from each other.

The burner of FIG. 8 has a mixed flow 15 of primary air and pulverized coal 15 with a venturi 13 around the starter burner 12.
The flame stabilizer 14 is installed between the primary air flow passage 16 and the secondary air flow passage 19, and the secondary air flow passage 19 and the tertiary air flow passage 20 are provided on the outer periphery of the primary air flow passage 16. FIG. 9 also shows a cross section of a burner in which a flame stabilizer 14 is installed in a primary air flow passage 16 having a venturi 13, and a secondary air flow passage 19 and a tertiary air passage are provided on the outer periphery of the primary air flow passage 16. Air passage 20
Shows the case where the two are separated. The burner shown in FIG. 8 is a secondary air flow provided with a secondary air air register 22 in which a mixed flow 15 of primary air and pulverized coal accelerated by a venturi 13 provided in a primary air flow path 16 around a starter burner 12 is provided with a secondary air air register 22. Secondary air 25 and tertiary air 26 are replenished from the passage 19 and the tertiary air flow passage 20 provided with the tertiary air air register 23, respectively, and the pulverized coal is burned. At this time, the secondary air 25 and the tertiary air 26 are respectively transferred to the air register 2
It is supplied into the furnace 17 while being swirled by 2 and 23.

The burner shown in FIG. 9 supplies the tertiary air 26 away from the center of the burner, delays the mixing of the tertiary air 26 into the combustion region, and creates a large reduction region to reduce NOx generation during combustion. It is the one. The detour for making a U-turn at the outlet of the secondary air flow path 19 in the furnace toward the primary air flow path 16 is provided in order to supply the tertiary air away from the burner center. In addition to the reason for providing the U-turn flow passage, in addition to reducing NOx in the exhaust gas, the secondary air flow passage 19 is cooled by the secondary air 25 passing through the portion facing the furnace 17. However, it may prevent the slag from adhering to this portion. As a result, the combustion gas can be further reduced in NOx than the burner shown in FIG.

[0009]

With the NOx reduction technology such as the internal two-stage combustion method described in the above-mentioned prior art,
NOx emissions at the boiler outlet up to around 100-150ppm (fuel ratio = fixed carbon / volatile matter value is 2, standard coal with 1.5% nitrogen content in coal, 5% or less unburned in ash) It can be lowered. However, while the regulation of the NOx emission amount contained in the combustion exhaust gas becomes strict as an environmental measure, the NOx emission concentration at the boiler outlet is required to be a low value of 100 ppm or less. In addition to this, in Japan, where dependence on coal imports is close to 100%, stable low N
The establishment of Ox technology is indispensable.

Although various improvements have been proposed as measures to reduce NOx in order to reduce NOx emissions to 100 ppm or less, these improved burners can burn at low NOx and have improved performance, but The burner structure tends to be complicated and the diameter of the burner throat part tends to be large because the burner structure is carefully devised to achieve them. Regarding the new installation, it can be dealt with by increasing the diameter of the burner throat part (opening of the boiler water wall where the burner is installed) for attaching the burner to the boiler furnace, but the latest burner throat part for conventional burners can be used. If a low NOx burner is to be installed, the burner throat portion is small and the burner diameter must be reduced accordingly. Therefore, there is a problem that the air flow path becomes narrow, the pressure loss in the burner portion of the combustion air flow increases, and the power of auxiliary equipment such as FDF (Forced Draft Fan) increases.

A phenomenon in which a pressure loss occurs in the burner portion of the combustion air flow will be described with reference to FIGS. 10 and 11. FIG. 10 shows an internal two-stage combustion type pulverized coal burner used in the pulverized coal boiler of FIG. 7. The combustion tertiary air 26 has its air flow rate adjusted by the air register 23, is swirled in the air flow, and is then ejected toward the inside of the furnace 17. At this time, in the burner throat portion 28, as shown in FIG. 10, due to the influence of the contraction flow, a separation region 31 where the fluid is separated from the burner wall surface 29 of the burner throat portion 28 is formed,
The effective channel cross section is reduced. Therefore, the flow of the tertiary air 26 is accelerated, and the pressure loss of the flow of the tertiary air 26 for combustion in this portion increases.

FIG. 11 shows the flow velocity distribution in the vicinity of the burner throat section 28 of the conventional internal two-stage combustion type pulverized coal burner. As described with reference to FIG. 10, at the inlet portion of the burner throat portion 28, that is, the outlet portion of the air register 23, the flow path of the tertiary air 26 is rapidly reduced, so that the air flow near the wall surface of the tertiary air flow path 20. Since the peeling area 31 of the secondary air 2 is generated, the tertiary air 2 near the wall surface of the tertiary air flow path 20 at the outlet of the air register 12
The flow velocity distribution 32 of No. 6 is as shown in FIG. 11, backflow occurs, and the separation region 31 (see FIG. 10) has a negative pressure.

Thus, in the prior art, in order to reduce the pressure loss in the burner throat portion 28 portion of the tertiary air flow passage 20, there is no way but to increase the effective flow passage cross section. As mentioned above, the new burner can be dealt with by increasing the diameter of the burner throat part. However, when the latest low NOx burner is installed in the burner throat part for the conventional burner, the burner part of the combustion air flow is Pressure loss increases and FDF (Forced Draft F
There was a problem that the power of auxiliary equipment such as an) increased.

An object of the present invention is to provide a low NOx burner that achieves low NOx without increasing pressure loss in the burner portion of the combustion air flow. Another object of the present invention is to enable a low NOx burner to be installed in a burner throat part for an existing burner without reducing the burner throat part diameter.

[0015]

The object of the present invention is achieved by the following constitutions. That is, in a pulverized coal burner provided in a combustion device that supplies fuel and combustion air to a burner port provided in a furnace wall, a feed fluid is introduced into an air introduction passage located at the outermost periphery of the burner. A separation prevention vane that prevents the generation of a region that separates from the burner wall surface that forms the flow path is provided in the air input flow path near the wall surface, and the input air is provided between the separation prevention blade and the burner wall surface,
A low pressure loss type low NOx pulverized coal burner in which at least one fluid flow path of exhaust gas is formed and an opening for blowing the fluid is formed near the wall at the flow path outlet.

In the above low pressure loss type low NOx pulverized coal burner of the present invention, the exhaust gas of the fuel burned in the furnace is used as the exhaust gas to be injected between the separation preventing blade and the burner wall surface forming the air injection passage at the outermost periphery of the burner. It can be circulated and used. In addition, a configuration is provided in which a flow rate adjusting damper is provided in a fluid passage formed at a burner wall surface interval that forms an air input passage at the outermost periphery of the separation prevention blade and the burner, or a portion of the swirling flow of combustion air is supplied. be able to. Further, the corner portion, which is the flow path changing portion of the air input flow path, may be chamfered so that the air flow in the air input flow path on the outermost periphery of the burner forms a smooth flow. Further, a pulverized coal combustion apparatus equipped with the low pressure loss type low NOx pulverized coal burner is also within the scope of the present invention.

[0017]

According to the present invention, the separation area preventing blade is installed in the combustion air input passage, and at least one of combustion air and exhaust gas is caused to flow in the fluid passage formed between it and the burner wall surface. The fluid is blown in the wake direction from the outlet opening of the. As a result, when there is no separation area preventing vane, the fluid can blow off the separation area of the flow formed by the rapid reduction of the injected combustion air.
Therefore, the effective flow passage cross section of the combustion air input flow passage becomes large, and the pressure loss of the combustion air flow passing therethrough becomes small.

Further, the flow velocity of the fluid flowing through the fluid passage formed between the separation region preventing blade and the burner wall surface does not pass through the air register normally installed in the combustion air passage, and the passage resistance is small. Since the fluid passes through the fluid passage formed between the separation area preventing vane and the wall surface of the burner, it can be jetted to the wake side at a higher speed than the fluid passing through the air register.
By this high-speed jet, the separation region 31 shown in FIG. 10 can be canceled out, and by increasing the turbulence intensity,
The effect of reducing the thickness of the boundary layer between the burner wall surface and the fluid is obtained. Due to this effect, it becomes possible to sufficiently secure the cross section of the combustion air flow path, so that it is possible to suppress the maximum flow velocity and reduce the pressure loss in the air flow path.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. The burner of this embodiment is applied to the pulverized coal burning boiler shown in FIG. 7. FIG. 1 shows a cross-sectional view of a low pressure loss type low NOx pulverized coal burner according to this example. The pulverized coal burner is a coaxial swirl burner, which is an improvement of the conventional pulverized coal burner shown in FIG. 8 to a low pressure loss type. Regarding the constituent members shown in FIG. 1, members having the same functions as those described in FIG. 8 and the like are designated by the same reference numerals, and the description thereof will be omitted.

The pulverized coal burner 4 includes a nozzle 35 for supplying pulverized coal as a fuel and an air register 2 for supplying air for combustion.
2 and other combustion air supply devices 36.
In this embodiment, the air supply device for combustion will be mainly described.

Pulverized coal nozzle 35 and combustion air supply device 3
There are many combinations with 6. The pulverized coal burner 4 shown in FIG. 1 is an improved version of the conventional pulverized coal burner shown in FIG. 8, but may be an improved version of the pulverized coal burner shown in FIG. 9. However, description of the modified version of FIG. 9 is omitted because it can be easily inferred.

The structural role of each of the pulverized coal burner components shown in FIG. 1 will now be described. Pulverized coal is supplied from the mill 2 (see FIG. 7) by the conveying air (primary air) inside the nozzle 35 located in the central portion of the pulverized coal burner 4. Inside the nozzle 35, a venturi 1 for accelerating the primary air velocity and suppressing flashback from the flame.
3 is inserted. After passing through the venturi 13, the mixed flow 15 of pulverized coal and carrier air is discharged into the furnace 17 from the outlet of the nozzle 35. At this time, mixed flow 1
5 is a free jet to the furnace 17. On the other hand, among the combustion air, the secondary air 25 and the tertiary air 26 are supplied into the furnace 17 from the periphery of the primary air as a swirling jet flow in an annular flow path. The air flow rate distribution ratios of the primary air, the secondary air 25, and the tertiary air 26 are about 20%, about 10%, and about 50% of the total air amount, respectively. About 20% of the remaining air is supplied from the outside of the burner 4 into the furnace 17 as two-stage combustion air. As described above, the flow rate of the tertiary air 26 of the combustion air corresponds to 50% of the total air flow rate. Therefore, by devising this flow path, it is possible to greatly contribute to the power reduction of the fan. I think.

FIG. 1 shows an example in which separation preventing blades 39 are attached in the vicinity of the burner wall surface 38 in the tertiary air passage 20. By laying the separation preventing blade 39, the tertiary air 2
A high-speed jet is formed in the vicinity of the wall of the throat portion 28 of No. 6. In FIG. 1, a bypass flow path 40 formed by the separation preventing blade 39 is provided, a part of the tertiary air 26 is branched, the air register 23 is bypassed, and a part of the tertiary air 26 is flown into the bypass flow path 40. Is shown. Since it does not pass through the air register 23, the flow 26b of the tertiary air 26 in the bypass flow passage 40 has a small flow passage resistance, and therefore can be ejected at a higher speed than the main flow 26a of the tertiary air 26. With this high-speed jet,
It is possible to cancel the peeling area 31 shown in
By increasing the turbulent flow intensity, it is possible to obtain the effect of reducing the boundary layer thickness. Due to this effect, the cross section of the tertiary air flow passage 20 can be sufficiently secured, and thus the tertiary air flow passage 2
The maximum flow velocity at 0 and the pressure loss can be reduced.

FIG. 2 shows the flow velocity distribution of the tertiary air 26 in the vicinity of the burner throat portion 28 of the pulverized coal burner according to this embodiment. In FIG. 11, at the inlet portion of the burner throat portion 28, that is, at the outlet portion of the air register 23, the flow path of the tertiary air 26 is rapidly reduced, and therefore the burner wall surface 29 of the throat portion of the tertiary air flow path 20.
Since the separation region 31 of the air flow is generated in the vicinity,
Although it has been described that the backflow region is generated and the peeling region 31 has a negative pressure, when the peeling prevention blade 39 of this embodiment is installed as shown in FIG. 2, the backflow is as shown in FIG. 11. The peeled area 31 disappears. Further, as compared with the flow velocity of the main flow 26a of the flow of the tertiary air 26, by flowing a small amount of air at a high speed in the bypass flow passage 40, the boundary layer thickness in the vicinity of the burner wall surface 29 of the throat portion can be made thin, so that the tertiary air flow. The cross section of the passage 20 can be effectively used.

In this embodiment, since the separation area 31 shown in FIG. 10 is reduced by the bypass passage 40, even if the tertiary air 26
Even if the distance in the direction orthogonal to the flow of the air (= width of the bypass flow passage 40) or the distance in the direction parallel to the flow of the tertiary air 26 is small, the flow of the tertiary air flow passage 20 in the vicinity where the separation region 31 is formed is small. The effect of increasing the road cross-sectional area is great. For example, assuming that the width of the bypass flow passage 40 is expanded by 10%, the flow passage cross-sectional area of the tertiary air flow passage 20 in that portion is expanded by 20%, and the local flow velocity is reduced by about 20%. Therefore, the pressure loss in this portion can be reduced by about 40% at the maximum, so that the power of the fan can be significantly reduced.

FIG. 3 shows an example in which a flow rate adjusting damper 43 is installed in the bypass flow passage 40. Normally, at the time of high load, the flow rate adjusting damper 43 operates at full opening. However, when the load is low or the burner is stopped, the air flow rate is narrowed down to the minimum, so it is desirable to close the air register 23 in the tertiary air flow path 20. Therefore, the flow rate adjustment damper 43 can control the air flow rate.

Similar to FIG. 3, FIG. 4 shows an example in which the flow rate adjusting damper 43 is attached. However, in order to further reduce the pressure loss of the flow of the tertiary air 26, the flow path changing portion of the tertiary air flow path 20 is changed. The corner portion 20a, which becomes the corner, is chamfered so as to suppress the formation of the circulation area in this portion. By forming the corner portion 20a so that the tertiary air 26 can smoothly flow, the pressure loss of the flow of the tertiary air 26 can be further reduced as compared with FIG.

FIG. 5 shows almost the same structure as in FIG.
The flow of the tertiary air 26 flowing near the burner wall surface 29 of the throat portion 28 of the tertiary air flow path 20 shown in FIG.
An example in which the flow is replaced is shown. The fluid flowing near the burner throat portion 28 does not necessarily have to be combustion air. This is because the purpose is to remove the separation region 31 (see FIG. 10) near the burner throat portion 28, and this fluid does not directly contribute to combustion (oxidation reaction).

The structure shown in FIG. 6 is almost the same as that shown in FIG.
This is an example in which the flow of the tertiary air 26 flowing near the burner wall surface of the tertiary air flow passage 20 shown in FIG. 4 is replaced with the flow of the exhaust gas 45, and the air register 4 is provided in the flow passage 46 of the exhaust gas 45.
7 was placed.

According to the low pressure loss type low NOx pulverized coal burner of the present embodiment, the pressure loss in the burner portion, which cannot be achieved by the ordinary pulverized coal burner, can be greatly reduced. Therefore, if the existing boiler is modified at the throat portion, the auxiliary machine power can be reduced, and the running cost can be significantly reduced.

Also, as a part of environmental measures, the existing low NO
x Older burners that do not take measures against the new low NO
In the past, when replacing with a x-burner, the structure of this low NOx burner was complicated, and it was necessary to remodel and expand the boiler water wall burner port. According to the burner of the invention, it is possible to reduce the amount of ammonia consumed in the denitration device because the burner can be made compact and the NOx in the burner section can be made extremely low while maintaining the NOx emission performance.

Further, in a boiler for foreign countries, it is not necessary to reduce the NOx of the exhaust gas as much as in the domestic case. Therefore, there is a case where only the conventional burner is replaced and a relatively inexpensive measure for reducing the NOx of the exhaust gas is taken. . Even in this case, if the burner according to the embodiment of the present invention is used and the NOx burner can be attached without changing the burner throat diameter, the NOx can be easily reduced.

[0033]

EFFECTS OF THE INVENTION According to the low pressure loss type low NOx pulverized coal burner of the present invention, the pressure loss of the burner portion, which cannot be achieved by the ordinary pulverized coal burner, can be greatly reduced, and the throat portion of the existing boiler can be reduced. Since NOx of the burner can be reduced by modifying the above, the cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a tertiary air separation type low NOx according to an embodiment of the present invention.
Sectional drawing of a pulverized coal burner.

FIG. 2 is a third air separation type low NOx according to an embodiment of the present invention.
Flow velocity distribution map in the tertiary passage of the pulverized coal burner.

FIG. 3 is a third air separation type low NOx according to an embodiment of the present invention.
Sectional drawing of a pulverized coal burner.

FIG. 4 is a third air separation type low NOx according to an embodiment of the present invention.
Sectional drawing of a pulverized coal burner.

FIG. 5 is a third air separation type low NOx according to an embodiment of the present invention.
Sectional drawing of a pulverized coal burner.

FIG. 6 is a third air separation type low NOx according to an embodiment of the present invention.
Sectional drawing of a pulverized coal burner.

FIG. 7 is a system diagram of a pulverized coal combustion apparatus in which a low NOx pulverized coal burner is used.

FIG. 8 is a sectional view of a conventional tertiary air separation type low NOx pulverized coal burner.

FIG. 9 is a sectional view of a conventional tertiary air separation type low NOx pulverized coal burner.

FIG. 10 is a diagram showing a flow state in a tertiary flow path of a conventional tertiary air separation type low NOx pulverized coal burner.

FIG. 11 is a flow velocity distribution diagram in a tertiary flow path of a conventional tertiary air separation type low NOx pulverized coal burner.

[Explanation of symbols]

4 ... Pulverized coal burner, 13 ... Venturi, 15 ... Mixed flow of pulverized coal and carrier air, 16 ... Primary air flow path, 17 ... Furnace, 19 ... Secondary air flow path, 20 ... Tertiary air flow path, 20a
... Corner portion, 22 ... Secondary air air register, 23 ... Third air air register, 25 ... Secondary air, 26 ... Third air, 28 ... Throat part, 29 ... Burner wall surface of throat part, 35 ... Pulverized coal nozzle, 36 ... Combustion air supply device,
38 ... Burner wall surface, 39 ... Separation prevention blade, 40 ... Bypass passage, 43 ... Flow rate adjusting damper, 45 ... Exhaust gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeki Morita 6-9 Takaracho, Kure-shi, Hiroshima Babcock Hitachi Co., Ltd. Kure Factory (72) Innovator Nobuyasu Mori 3-36 Takaracho, Kure-shi, Hiroshima Babcock Hitachi Ltd. Kure Institute

Claims (6)

[Claims] 1. A pulverized coal burner provided in a combustion device for supplying fuel and combustion air to a burner port provided in a furnace wall, wherein an input fluid is supplied to an air input passage located at the outermost periphery of the burner. A separation preventing blade for preventing a region that separates from the burner wall surface forming the air charging passage is provided in the air charging passage in the vicinity of the wall surface, and charging air is provided between the separation preventing blade and the burner wall surface, A low pressure loss type low NOx pulverized coal burner, characterized in that at least one fluid flow path for exhaust gas is formed, and an opening for blowing the fluid is formed near the wall at the flow path outlet. 2. The low pressure loss according to claim 1, wherein the exhaust gas of the fuel burned in the furnace is used as the exhaust gas to be introduced between the separation prevention blade and the burner wall surface forming the air injection flow path at the outermost periphery of the burner. Type low NOx pulverized coal burner. 3. The low pressure according to claim 1 or 2, wherein a flow rate adjusting damper is provided in a fluid passage formed at a burner wall surface interval forming an air injection passage at an outermost periphery of the burner and the separation preventing blade. Loss type low NOx pulverized coal burner. 4. A part of a swirling flow of combustion air is supplied to a fluid passage formed at a burner wall surface interval forming an air injection passage at an outermost periphery of the burner and a separation preventing blade. The low pressure loss type low N according to claim 1, 2 or 3.
Ox pulverized coal burner. 5. The corner portion, which is a flow path changing portion of the air input passage, is chamfered so that the air flow in the air input passage at the outermost periphery of the burner forms a smooth flow. Item 5. A low pressure loss type low NOx pulverized coal burner according to any one of Items 1 to 4. 6. A pulverized coal combustion apparatus comprising the low pressure loss type low NOx pulverized coal burner according to any one of claims 1 to 5.