JP2006162185A - Coal burning boiler and combustion method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simultaneously reduce NOx and CO by refinement of the structure and arrangement of an after air nozzle, in a coal burning two-stage combustion boiler. <P>SOLUTION: This coal burning boiler is constituted by arranging a contraction flow part for gradually reducing in an outer diameter toward an outlet jetting port on the inside of a main after air nozzle. A sub-after air nozzle is arranged on the downstream side of the main after air nozzle, and NOx and CO are simultaneously reduced by arranging a mechanism for adjusting the total quantity of air supplied to the main and sub-after air nozzles and a mechanism for adjusting the ratio of an air quantity supplied to the main and sub-after air nozzles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a two-stage combustion type coal fired boiler, and more particularly to a coal fired boiler provided with a main after air nozzle and a sub after air nozzle.

  Boilers are required to reduce the concentration of nitrogen oxides (NOx), and a two-stage combustion method is applied to meet this requirement. This combustion method is a method of supplying air for complete combustion from an after air nozzle after burning fuel in a state where air is insufficient.

  Several structures have been proposed for after-air nozzles to improve air mixing and combustion conditions. For example, a structure has been proposed in which an after air nozzle has a contracted portion in which the outer diameter of the air flow path gradually decreases toward the air outlet (see, for example, Patent Document 1). Further, a configuration has been proposed in which the after air nozzles are arranged in two stages in the main flow direction of the combustion gas (see, for example, Patent Document 2).

JP-A-10-122546 (Claims, FIG. 1) Japanese Patent Laid-Open No. 10-153302 (FIG. 1)

  In recent boilers, simultaneous reduction of not only NOx but also NOx and carbon monoxide (CO) is required. Although the conventional two-stage combustion boiler can reduce one of NOx and CO, it is difficult to reduce both NOx and CO at the same time.

  An object of the present invention is to provide a coal fired boiler capable of simultaneously reducing NOx and CO, and a combustion method thereof.

  The present invention provides a coal-fired boiler having an after-air nozzle that completely burns combustion gas on the downstream side of a burner that burns coal fuel such as pulverized coal and air in an air-deficient state. In the main after air nozzle with a large amount of air supply, provided in the main after air nozzle with a large amount of air supply, a constricted portion whose flow path outer diameter decreases toward the air outlet of the outlet is provided, and the downstream side in the flow direction of the main after air nozzle In addition, it is a coal fired boiler provided with a sub-after air nozzle with a small air supply amount.

  The present invention is a combustion method in which two-stage combustion of coal fuel is performed by the boiler having the above-described configuration, and the amount of air supplied to the main after-air nozzle is adjusted at that time so that the jet flow velocity by the main after-air nozzle can be adjusted. .

  The present invention also performs two-stage combustion of coal fuel with the boiler having the above-described configuration, and maintains the amount of air supplied to the burner within a predetermined range in which the amount of NOx generated is reduced, and the main after-air nozzle and other sub-afters In this combustion method, the distribution of the amount of air supplied to the air nozzle is adjusted to adjust the jet flow velocity of the main after-air nozzle.

  In the boiler according to the present invention, the main after-air nozzle with a large air supply amount is provided with a contraction portion for increasing the jet flow velocity, and the sub-after air nozzle with a small air supply amount is provided downstream thereof, so that the air flow distribution of both nozzles is provided. By adjusting this, NOx and CO can be reduced simultaneously.

  In the present invention, it is desirable to provide a member for defining the minimum flow path area of the contracted portion inside the main after air nozzle. The main after-air nozzle is composed of primary and secondary nozzles that supply air in a straight flow or swirl flow, and a tertiary nozzle that supplies tertiary air provided outside the primary and secondary nozzles. It is preferable that the tertiary nozzle has a velocity component in the center direction toward the center axis of the after-air jet. It is desirable to provide a mechanism for adjusting the total amount of air supplied to the main after-air nozzle and the sub-after air nozzle and a mechanism for adjusting the ratio of the amount of air supplied to the main and sub-after air nozzles.

  It is preferable that a plurality of main after-air nozzles and sub-after-air nozzles are arranged on the front wall and the rear wall of the boiler. Further, it is desirable that the sub-after air nozzle is disposed immediately above the main after-air nozzle, or between the plurality of main after-air nozzles, on the downstream side or near the furnace side wall. Other features of the present invention will become apparent from the following examples.

  FIG. 1 is a configuration diagram of a furnace portion of a pulverized coal burning boiler according to an embodiment of the present invention. The wall of the furnace is surrounded by an upper furnace ceiling 44, a lower hopper 47, a side furnace front wall 45, a furnace rear wall 46, and a furnace side wall 48 shown in FIGS. A water pipe (not shown) is installed. A part of the combustion heat generated in the furnace combustion space 23 is absorbed by the water pipe. Combustion gas generated in the furnace combustion space 23 flows upward from below and is discharged as a gas 43 after combustion. The combusted gas 43 passes through a rear heat transfer section (not shown), and the heat contained in the gas is further recovered here.

  A burner 36 is installed in the lower part of the furnace, where an air-deficient flame 37 is formed. The burner 36 includes a pulverized coal nozzle that ejects a mixed flow 42 of burner primary air and pulverized coal, a secondary nozzle that ejects secondary air for the burner, and a tertiary nozzle that ejects tertiary air. The coal is pulverized to approximately 150 μm or less in a pulverizer (not shown), and then conveyed by the primary air for burner, and a mixed flow 42 of the primary air for burner and pulverized coal is jetted from the burner 36 into the furnace. The burner secondary and tertiary air 41 is simultaneously ejected from the burner 36 via the burner wind box 38.

  A main after air nozzle 34 is installed above the burner 36. A sub-after air nozzle 35 is installed on the downstream side of the main after-air nozzle. The structure of the main after air nozzle 34 is a contracted flow type structure in which the air flow is directed toward the central axis direction of the main after air nozzle near the jet outlet. Details of the structure will be described later with reference to FIGS. Most of unburned components such as CO generated from the air-deficient flame 37 formed in the burner portion are completely burned (oxidized) by mixing with air from the main after-air nozzle. However, NOx is generated when unburned components and main after-air air are mixed. This NOx is mainly thermal NOx. The amount of NOx generated is related to the flow rate of air ejected from the main after air nozzle (maximum flow rate of the contracted portion), and adjustment of the flow rate of main after air is important. Furthermore, if the main after-air air ejection conditions are set so that the NOx is low, the oxidation tends to be insufficient and CO tends to be generated. It is necessary to set conditions.

  The combustion air 49 is distributed to the burner secondary and tertiary air 41 and the after-air air 40 by an air flow rate distribution adjusting mechanism a51. The after air 40 is distributed by the air flow rate distribution adjusting mechanism c53 to the air flowing to the front wall side after air and the air flowing to the rear wall side after air. A nose 39 is often provided on the upper portion of the furnace rear wall 46. Due to the effect of the nose 39, the flow of the combustion gas around the auxiliary after air nozzle 35 becomes asymmetric. By adjusting the distribution of after-air flowing to the front wall side and the rear wall side, NOx and CO can be reduced even in an asymmetric flow field.

  The after-air air 40 further adjusts the amount of air supplied from the main / sub-after air by a main / sub-after-air air flow distribution adjusting mechanism 50. Thereby, the jet flow velocity (maximum flow velocity of the contracted portion) of the main after-air can be adjusted. When the jet flow rate is too high, the amount of sub-after air is increased, and when the jet flow rate is too low, the reverse is performed. At this time, the jet flow velocity of the sub-after air also changes. However, since the sub-after air ejected from the sub-after air nozzle has a lower gas temperature and lower flow rate than the main after-air, the influence on the generation of NOx (thermal NOx) is small. Further, since the main after-air air amount can be adjusted by adjusting the flow rate of the sub-after air, the secondary and tertiary air flow rates supplied to the burner can always be constant. This means that the combustion conditions of the air-deficient flame 37 formed in the burner part can always be operated under the optimum conditions where the amount of NOx generation is minimized.

  As a result, it is possible to always keep the NOx generated in the burner portion to a minimum and at the same time keep the air blowing conditions of the main after-air nozzle so that the overall performance of NOx and CO is optimized.

  The secondary and tertiary air 41 supplied to the burner is distributed to the air flowing to the burner on the front wall side and the air flowing to the burner on the rear wall side by the air flow rate distribution adjusting mechanism b52, similarly to the after-air air 40. The

  FIG. 2 is a cross-sectional view showing an example of a detailed structure of the main after-air nozzle. The basic structure of the main after air nozzle of FIG. 2 is a cylindrical shape with the jet central axis 8 as an axis of symmetry. The nozzle is surrounded by the windbox outer cylinder 1 and the windbox outer wall 13, and combustion air flows from the windbox opening 5 as indicated by an arrow 6. Air flows along the direction of the arrow 6 and is ejected from the ejection port 4 to the combustion space 23 in the furnace. The ejected air is mixed with the combustible gas in the furnace combustion space 23 to burn the combustible gas. A water pipe 14 is provided around the spout 4. A contracting member 2 is provided on the side of the outlet 4 of the after air nozzle. The contraction member 2 has a structure in which the diameter gradually decreases toward the jet port 4 side. By this contracted member 2, a velocity component toward the nozzle central axis is given to the air flow indicated by the arrow 6, and the contracted portion 3 is formed. A member 7 that defines the minimum flow path area of the contracted flow portion is provided near the inlet of the contracted flow portion 3. The flow velocity of the air in the contracted portion is defined by the area of the portion having the smallest opening area in the contracted portion. In the configuration of FIG. 2, the flow velocity of the contracted portion is maximized at the tip of the member 7 that defines the minimum flow path area of the contracted portion. The member 7 that defines the minimum flow path area of the contracted flow portion in FIG. 2 has a configuration in which the outer diameter gradually decreases toward the jet port 4. This is to reduce the turbulence of the flow in the contracted flow part 3. By reducing the disturbance, it is easy to suppress a rapid increase in NOx. The member 7 that defines the minimum flow path area of the contracted portion is fixed to the support material 9. The support member 9 is fixed to the windbox outer cylinder 1 through a guide 12. An overheat preventing material 10 is provided inside the member 7 that defines the minimum flow path area of the contracted portion. This is to prevent the support material 9 from being burned out by the radiant heat from the flame formed in the in-furnace combustion space 23. When the flame radiant heat formed in the in-furnace combustion space 23 is weak, or when the support material 9 can be cooled by another method, the overheat prevention material 10 is not necessarily required.

  FIGS. 3A and 3B show an example of the arrangement of the main after air nozzle and the sub after air nozzle. FIG. 3A is a cross-sectional view taken along the line AA of FIG. 1 and shows the arrangement of the main after-air nozzles 34. FIG. 3B is a cross-sectional view taken along the line B-B in FIG. 1 and shows the arrangement of the sub-after air nozzles 35. A plurality of main after air nozzles 34 are usually arranged at right angles or almost right angles to the flow of the burner combustion gas, and the same number is arranged on the furnace front wall 45 side and the furnace rear wall 46 side. The simplest arrangement method of the sub-after air nozzle 35 is to arrange it directly above the main after-air 34.

Next, modifications of the main after-air nozzle structure and modifications of the arrangement of the after-air nozzle will be described, but the present invention is not limited to these modifications.
[Modification 1 of main after-air nozzle structure]
FIG. 4 is a modified example of the detailed structure of the main after-air nozzle. The cooling air flow path for cooling the support material 9 for the member that defines the minimum flow path area of the reduced flow portion, and the reduced flow member 2 are shown in FIG. It has a flow path for cooling air for cooling, which is different from FIG.

  A cooling air hole 20 is provided in the support material 9 for the member that defines the minimum flow path area of the contracted portion. A part of the air introduced from the windbox opening 5 becomes a flow of cooling air as indicated by an arrow 25 and is discharged from the cooling air hole 20. In the process, it collides with the support material 9 of the member that defines the minimum flow path area of the contracted portion, and this support material 9 can be cooled. Further, a part of the air discharged from the cooling air hole 20 collides with the member 7 that defines the minimum flow path area of the contracted portion, and this member can be cooled.

  Further, in FIG. 4, a cooling air guide plate 21 is provided in the vicinity of the contracted portion 3. Thereby, the cooling air flows between the cooling air guide plate 21 and the contracted flow member 2 through the cooling air introduction port 58, and the contracted flow member 2 can be cooled. Further, since this cooling air flows on the outermost peripheral side of the jet port 4, it can be used to remove coal ash adhering to the periphery of the jet port 4. When the amount of coal ash adhering to the periphery of the jet nozzle 4 increases, the amount of air flowing between the contracted flow member 2 and the cooling air guide plate 21 is temporarily increased to facilitate removal of the adhering ash. Can be used.

The angle of the contracting member 2 may change in the middle of the contracting part. In the configuration of FIG. 4, the angle near the inlet of the contracted portion is large. Further, the angle near the outlet of the contracted portion is small. The shape of the guide 12 has a structure in which a part of the outer peripheral portion is cut away. If the shape of the guide 12 is as shown in FIG. 4, the turbulence of the air flow flowing into the contracted portion 3 can be reduced, which is effective in reducing NOx.
[Modification 2 of main after-air nozzle structure]
FIG. 5 is a sectional view showing another modified example of the main after-air nozzle. A primary nozzle 30 is disposed at the center of the main after-air nozzle, a secondary nozzle 31 is disposed outside the primary nozzle 30, and a contracted-flow tertiary nozzle 29 is disposed outside the secondary nozzle 2. In the main after-air nozzle having this structure, primary air flows in the direction indicated by arrow 16, and secondary air flows in the direction indicated by arrow 17 outside the primary nozzle. The tertiary air ejected from the contracted tertiary nozzle 29 flows in the direction indicated by the arrow 15 and merges with the secondary air flow indicated by the arrow 17 at the outlet of the secondary nozzle 31 and flows into the furnace combustion space 23. . Here, the ejection direction of the secondary nozzle 31 is parallel to the jet central axis 8. Further, a turning force is given to the flow of the secondary air indicated by the arrow 17 by the secondary air register 32. Since the contracted flow tertiary nozzle 29 is installed in the direction of the jet central axis 8, a contracted flow can be formed.

Pulverized coal contains ash in the fuel. In this case, if a contracted flow is formed at the outlet of the main after-air nozzle, ash melted in the high-temperature combustion gas may adhere to the vicinity of the water pipe 14 at the outlet of the air port. As ash deposits grow to form clinker, flow may be hindered or water pipes may be damaged due to falling. In such a case, when the clinker is small, the flow rate of the tertiary air is reduced, the flow rate of the secondary air is increased, and the temperature of the clinker is lowered, thereby generating thermal stress and peeling off.
[Modification 1 of after-air nozzle arrangement]
FIG. 6 shows a modified example of the arrangement of the main after air nozzle and the sub after air nozzle. FIG. 6A is a cross-sectional view taken along the line AA of FIG. 1 and shows the arrangement of the main after air nozzle. FIG. 6B is a cross-sectional view taken along the line BB of FIG. In FIG. 6, the sub-after air nozzle 35 is disposed on the downstream side between the main after-air nozzles 34. The unburned components that pass between the main after air nozzles 34 are likely to be discharged from the furnace without being mixed with the air ejected from the main after air nozzle 34, and are likely to cause an increase in CO emission. When the sub-after air nozzle 35 is disposed downstream of the main after-air nozzle 34 as shown in FIG. 6, the air ejected from the sub-after-air nozzle 35 is mixed with unburned components passing between the main after-air nozzles 34. Since it becomes easy, reduction of CO becomes easy.
[Modified example 2 of after-air nozzle arrangement]
FIG. 7 is also a modified example of the arrangement of the main after air nozzle and the sub after air nozzle. (A) of FIG. 7 is AA sectional drawing of FIG. 1, and shows arrangement | positioning of the main after air nozzle. FIG. 7B is a cross-sectional view taken along the line B-B in FIG. In this example, the sub-after air nozzle 35 is disposed in the vicinity of the furnace side wall 48. When the unburned components pass between the main after-nozzle 35 and the furnace side wall 48, CO is most likely to be generated. This is because the gas temperature near the furnace side wall 48 is low and the oxidation rate of CO and unburned components is the slowest here. In the configuration of FIG. 7, in order to efficiently oxidize unburned components passing between the main after nozzle 34 and the furnace side wall 48, the sub after air nozzle 35 is arranged on the furnace side wall 48 side. By arranging the sub-after air nozzle 35 on the furnace side wall side with respect to the main after-nozzle 34, oxidation of unburned components passing between the main after-nozzle 35 and the furnace side wall 48 is facilitated, and CO can be reduced.
[Verification of the effect of the present invention]
FIG. 8 shows the results of examining the relationship between the flame temperature and the amount of NOx generated. The flame temperature is the highest temperature in a region where unburned components generated from a flame with insufficient air and air ejected from the main after air are mixed and burned. In FIG. 8, circles indicate experimental results, and curves indicate calculation results. NOx correlates strongly with flame temperature. As the flame temperature increases, NOx increases exponentially. In particular, when the flame temperature exceeds 1500 ° C., the increase in NOx is remarkable.

  FIG. 9 shows the results of an experiment on the relationship between the maximum flow velocity of the contracted flow portion and the flame temperature using the main after-air nozzle having the configuration shown in FIG. The burner air ratio was substantially constant in the range of ± 2% of the reference condition, and the furnace air ratio was changed. As the maximum flow velocity of the contracted portion increases, the flame temperature gradually increases. When the flow velocity of the contracted portion exceeds a certain value, the flame temperature increases rapidly. This means that the NOx increases slowly until the maximum flow velocity of the contracted flow part reaches a certain value, but if the value exceeds a certain value, the increase in NOx becomes abrupt. Note that CO decreased conversely as the maximum flow velocity in the contracted portion increased.

  When the maximum flow velocity of the constricted part is low, NOx is low but CO is high. On the other hand, when the maximum flow velocity of the contracted flow portion is too high, CO is low, but NOx increases rapidly. Until the flow velocity reaches a certain value, CO decreases as the flow velocity increases. However, since the increase in NOx is gradual, the overall performance of NOx and CO improves with the maximum flow velocity of the contracted portion.

  FIG. 10 shows the results of measuring the relationship between NOx and CO under three conditions: when the flow velocity of the contracted portion is slow (low speed), when optimal (optimum speed), and when fast (high speed). There is an optimum condition just before reaching a certain value, and at this time, the overall performance of NOx and CO is the best. The overall performance of NOx and CO is reduced whether the flow rate is faster or slower than the optimum value.

  FIG. 11 shows the results of comparing the performances of NOx and CO in the case of using the main after-air nozzle configured as shown in FIG. 2 and the main after-air nozzle of the prior art. The burner air ratio and furnace air ratio were within the range of ± 2% of the reference conditions. The configuration of the prior art is obtained by removing the contracted-flow tertiary nozzle 29 from the configuration of FIG. Reference numeral 106 indicates a result when the secondary nozzle is not swiveled in the conventional configuration, reference numeral 105 indicates a result when the secondary nozzle is swiveled in the conventional configuration, and reference numeral 104 indicates that the nozzle diameter is changed. Is the result of when. Reference numeral 101 denotes a result of the configuration of the present invention (FIG. 2), which is a result when the maximum flow velocity of the contracted portion is optimized. It can be seen that in the configuration of the present invention, both NOx and CO are reduced as compared with the prior art. It is desirable to optimize the flow velocity of the reduced flow part at the same time as making the reduced flow type main after air nozzle as shown in FIGS.

  FIG. 12 shows the relationship between the flow rate of the main after-air air and NOx and CO in comparison with the prior art. The flow velocity here is the flow velocity at the after-air jet outlet in the prior art. The relationship between the flow velocity, NOx and unburned components in the prior art is shown in FIG. 8 of Japanese Patent Laid-Open No. 2003-254510. The flow velocity in the present invention is the maximum flow velocity at the contracted portion. Reference numeral 121 represents conventional NOx, and reference numeral 123 represents conventional CO. Reference numeral 122 represents NOx in the present invention, and reference numeral 124 represents CO in the present invention.

  As the flow rate increases, NOx increases while CO decreases. This is seen in both the present invention and the prior art. The difference between the present invention and the prior art is that the increase in NOx is slow until the flow velocity reaches a certain value. For this reason, it has an optimum value for the total performance of NOx and CO under a certain flow rate condition. In the prior art, even when the flow rate is relatively low, the NOx increase rate when the flow rate is increased is large. For this reason, the total performance of NOx and CO does not change much even if the flow rate is changed.

  FIG. 13 relates to the present invention, and is a diagram showing the relationship between the flow velocity of the contracted portion and the overall performance of NOx and CO. If the flow rate is set to an optimum value, NOx and CO can be reduced simultaneously. However, when the flow velocity becomes faster than the optimum value, NOx increases rapidly, and the overall performance of NOx and CO rapidly decreases. Keeping the flow velocity near the optimum value is the key to improving performance. For this purpose, it is effective to always keep the flow velocity of the contracted portion in the main after air nozzle at an optimum value by providing a sub after air nozzle and adjusting the amount of air released to the sub after air nozzle. Also, with this method, the flow velocity of the contracted part in the main after-air nozzle can be controlled without changing the amount of air supplied to the burner, so that the combustion conditions in the burner part are always kept in an optimum state with a small amount of NOx generation. Can do. However, when this method is used, when the flow velocity of the contracted portion in the main after air nozzle is changed, the ejection speed of the air supplied from the sub after air after nozzle also changes. It is desirable to devise the arrangement of the sub-after-air after-nozzles so as to reduce the influence of this change on NOx.

  By calculating the temperature distribution in the furnace, the influence of the arrangement method of the sub-after-air after-nozzle was examined. FIG. 14 shows an example of temperature change in the furnace height direction. The temperature is a cross-sectional average value. A broken line 132 indicates a temperature when the maximum flow velocity of the contracted portion of the main after air nozzle is large. In this case, the maximum value of the temperature in the vicinity of the main after-air exceeds 1500 ° C., and NOx increases. In order to reduce NOx, it is necessary to reduce the amount of air supplied to the main after-air nozzle and to lower the maximum value of the temperature in the vicinity of the main after-air. A solid line 131 represents a temperature change when the amount of air supplied to the main after-air nozzle is reduced and the maximum flow velocity of the contracted portion is optimized. The maximum value of temperature becomes low, and NOx generated from the vicinity of the main after-air can be reduced. However, in this case, if the amount of air supplied to the main after-air nozzle is decreased, the amount of air supplied to the sub-after-air nozzle increases, so that NOx may be generated near the sub-after air.

  A solid line 133 is a temperature near the sub-after air in the configuration of the present invention. Since the sub-after air nozzle is provided on the downstream side of the main after-air nozzle, the ambient temperature near the sub-after air nozzle is lower than 1500 ° C. due to heat radiation to the furnace wall. For this reason, even if the atmospheric temperature changes due to a change in the flow velocity of air ejected from the sub-after air nozzle, the influence on the NOx generation amount is small. By reducing NOx generated near the main after-air, NOx generated from the entire furnace can be reduced.

  Unlike the configuration of the present invention, the solid line 134 is the temperature near the sub-after air when the sub-after air nozzle is installed upstream of the main after-air nozzle. At this time, air from the sub-after air nozzle is ejected into the atmospheric gas having a temperature of around 1500 ° C. Under this condition, if the temperature rises due to an increase in the air flow rate, NOx tends to increase rapidly. For this reason, if the amount of air to the main after-air nozzle is reduced to reduce the NOx generated here, the air flow rate of the sub-after-air nozzle increases, and the NOx generated from the vicinity of the sub-after-air tends to increase. For this reason, it is difficult to reduce NOx generated from the entire furnace.

  According to the present invention, NOx and CO can be simultaneously reduced in a two-stage combustion type coal fired boiler. This has a very large practical effect.

The figure which shows the cross section of the furnace part of the pulverized coal boiler by one Example of this invention, and the supply system of air and pulverized coal. Sectional drawing which shows the structure and air flow direction of the main after air nozzle by one Example of this invention. The figure which shows an example of the arrangement | positioning method of the main and subafter air nozzle in this invention. Sectional drawing of the main after air nozzle by another Example of this invention. FIG. 6 is a cross-sectional view of a main after air nozzle according to still another embodiment of the present invention. The figure which shows the modification of the arrangement | positioning method of the main and subafter air nozzle. The figure which shows the other modification of the main and sub after air nozzle arrangement | positioning method. The figure which shows the relationship between the flame temperature in an after-air combustion part, and NOx production amount. The figure which shows the relationship between the flow velocity of a contracted flow part, and flame temperature when the after air nozzle by one Example of this invention is used. The figure which shows the relationship between NOx and CO when the flow velocity of a contraction part is changed using the after air nozzle by one Example of this invention. The figure which compared the relationship of the characteristic of NOx and CO in this invention with the prior art. The figure which compared the flow rate of after air, NOx, and CO with the structure of this invention, and the prior art. The figure which shows the relationship between the flow velocity of the flow reduction part when using the after air nozzle by one Example of this invention, and NOx and CO comprehensive performance. The figure which shows the example of the calculation result which verified the effect of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Shrinkage member, 3 ... Shrinkage part, 4 ... Jet outlet, 7 ... Member which prescribes | regulates the minimum flow path area of a contraction flow part, 8 ... Jet stream central axis, 23 ... Combustion space in a furnace, 29 ... Shrinkage 3 Next nozzle 30 ... Primary nozzle 31 ... Secondary nozzle 33 ... Secondary air register 34 ... Main after air nozzle 35 ... Sub after air nozzle 36 ... Burner 37 ... Air shortage flame 40 ... After air air 41 ... secondary and tertiary air for burner, 42 ... mixed flow of primary air for burner and pulverized coal, 43 ... gas after combustion, 45 ... front wall of furnace, 46 ... rear wall of furnace, 48 ... side wall of furnace, 49 ... Combustion air, 50 ... Main / sub after-air air flow distribution adjustment mechanism, 51 ... Air flow distribution adjustment mechanism a.

Claims (14)

  A coal-fired boiler comprising a burner for burning coal fuel in an air-deficient state on the furnace wall, and an after-air nozzle for completely burning the combustion gas on the downstream side in the flow direction of the combustion gas by the burner. In the above, the after air nozzles are arranged in a plurality of stages in the combustion gas flow direction so as to maximize the air supply amount of the main after air nozzle provided in the uppermost stream, and flow toward the air outlet in the main after air nozzle. A coal-fired boiler, characterized by having a reduced flow portion whose road outer diameter is reduced.   2. The coal fired boiler according to claim 1, further comprising a member that defines a minimum flow area of the contracted portion inside the main after air nozzle.   2. The main after air nozzle according to claim 1, comprising a primary nozzle, a secondary nozzle provided outside the primary nozzle, and a tertiary nozzle provided outside the primary nozzle, and the tertiary nozzle is arranged in the nozzle central axis direction. A coal fired boiler characterized by being directed and thereby having a velocity component in the central direction.   4. The coal fired boiler according to claim 3, wherein the primary nozzle and the secondary nozzle supply air in a straight flow or a swirl flow.   2. The after-air nozzle air amount adjusting mechanism that adjusts the total amount of air supplied to the after-air nozzle, and the ratio of the amount of air supplied to the main after-air nozzle and the amount of air supplied to the other sub-after air nozzles. A coal fired boiler characterized by comprising a mechanism.   2. The coal fired boiler according to claim 1, wherein the after air nozzle is provided in two stages.   2. The coal fired boiler according to claim 1, wherein a plurality of the main after air nozzles and the other sub after air nozzles are respectively arranged at opposing positions on the front wall of the furnace and the rear wall of the furnace.   The coal-fired boiler according to claim 1, wherein the main after-air nozzle is provided at a right angle or a substantially right angle with a flow of combustion gas by the burner.   The coal-fired boiler according to claim 7, wherein the sub-after air nozzle is disposed immediately above the main after-air nozzle.   The coal-fired boiler according to claim 7, wherein the sub-after air nozzle is disposed on a downstream side between the main after-air nozzles.   The coal fired boiler according to claim 7, wherein the sub-after air nozzle is disposed on a boiler side wall side.   The coal-fired boiler according to claim 7, wherein the sub-after air nozzle is disposed on a boiler side wall side, and the main after-air nozzle is disposed closer to the boiler center than the sub-after air nozzle.   Combustion of a coal fired boiler characterized in that the two-stage combustion of coal fuel is performed by the boiler according to claim 1, and the amount of air supplied to the main after air nozzle is adjusted at that time to adjust the jet flow velocity. Method. The two-stage combustion of coal fuel is performed by the boiler according to claim 1, and the amount of air supplied to the burner is maintained within a predetermined range in which the amount of NOx generated is reduced, and the main after-air nozzle and other sub-after-air nozzles A combustion method for a coal-fired boiler, wherein the distribution of the amount of air to be supplied is adjusted to adjust the jet flow velocity of the main after-air nozzle.

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