Patent Application
20180195715
The present disclosure relates to a combustion burner and a boiler equipped with the same.
As a combustion burner for combusting pulverized coal fuel, there is known a burner where a plurality of flame holders, which are referred to as “splitters”, are disposed at an outlet of a fuel nozzle of the burner. In the burner, a recirculation region is formed on a downstream side of the splitters to maintain combustion of pulverized coal. In this manner, ignition and flame holding (hereinafter referred to as “internal ignition” or “internal flame holding”) are performed in the vicinity of a center axis of the fuel nozzle so that reduced combustion is performed under an air deficiency condition to realize low NOx combustion.
To enhance flame holding performance, it is preferable that a flame holder have a long edge length of splitter length. However, when the number of splitters is increased, a blocking rate of an outlet of a burner and hence, pressure loss of the burner is increased. Further, even when the number of splitters is increased while reducing a width of the splitters so as to ensure the edge length of splitter length, the splitters are disposed close to a wall portion of the fuel nozzle and hence, there is a possibility that ignition occurs at an outer periphery of the fuel nozzle. A combustion air supply nozzle and the like are disposed outside the fuel nozzle so that a large amount of oxygen is present, and therefore when external ignition occurs, there is a risk that a large amount of NOx is generated.
The following PTL 1 and PTL 2 disclose combustion burners where splitters are formed into a comb shape when the splitters are viewed in a front view from the downstream side.
When the splitters are formed into a comb shape as described in the above-mentioned respective patent literatures, an edge length of splitter length can be ensured.
However, the splitter described in PTL 1 is configured to introduce pulverized coal to the outer peripheral side of a nozzle so that external ignition is performed. Accordingly, low NOx combustion cannot be realized with such a configuration.
In the technique disclosed in PTL 2, air is injected from the splitter. Accordingly, combustion performed in a fuel nozzle is promoted so that reduced combustion is inhibited and hence, low NOx combustion cannot be realized.
The present disclosure is made under such circumstances, and it is an object of the present disclosure to provide a combustion burner where an edge length of splitter length of a splitter is increased and flame holding performance is enhanced so that low NOx combustion can be realized by internal flame holding, and a boiler equipped with the same.
To solve the problems described above, a combustion burner and a boiler equipped with the same according to the present disclosure adopt the following solutions.
That is, according to one aspect of the present disclosure, there is provided a combustion burner which includes: a fuel nozzle through which a fuel gas obtained by mixing a fuel and air with each other is blown into a furnace; and a plurality of splitters configured to divide a fuel gas flow by a widened portion where a width of the widened portion increases as the widened portion extends in a direction of the fuel gas flow, the splitters being disposed in the fuel nozzle on a distal end side of the fuel nozzle such that longitudinal axes of the splitters extend from a side of one wall portion of the fuel nozzle to a side of the other wall portion which is disposed on a side opposite to said one wall portion, wherein the plurality of splitters include: a slitted splitters configured to slit which partially reduces a width of the widened portion at a downstream end in the fuel gas flow, and a non-slitted splitters configured to adjacently to the slitted splitters, the non-slitted splitters having the widened portion, and the widened portion at a downstream end in the fuel gas flow having a fixed width in a direction of the longitudinal axis.
The slitted splitter has the slit so that an edge length of splitter length of the slitted splitter is increased whereby flame holding performance is enhanced. Accordingly, internal flame holding where a flame is held on the inside of the fuel nozzle is strengthened.
The non-slitted splitter forms a recirculation region on the downstream of the widened portion and thus has a flame holding function, but also has a function as a guide member which guides a fuel to the slitted splitter disposed adjacently to the non-slitted splitter by making use of inclined surfaces of the widened portion. Accordingly, internal flame holding by the slitted splitter is further strengthened.
Further, according to another aspect of the present disclosure, there is provided a combustion burner which includes: a fuel nozzle through which a fuel gas obtained by mixing a fuel and air with each other is blown into a furnace; and a plurality of splitters configured to divide a fuel gas flow by a widened portion where a width of the widened portion increases as the widened portion extends in a direction of the fuel gas flow, the splitters being disposed in the fuel nozzle on a distal end side of the fuel nozzle such that longitudinal axes of the splitters extend from a side of one wall portion of the fuel nozzle to a side of the other wall portion which is disposed on a side opposite to said one wall portion, wherein the splitter includes a plurality of slitted splitters having a slit which partially reduces a width of the widened portion at a downstream end in the fuel gas flow, and the slitted splitters disposed adjacently to each other respectively include wide surfaces having no slit, and the wide surfaces of the widened portions of the slitted splitters oppositely face each other.
The slitted splitters are disposed adjacently to each other, and the wide surfaces having no slit oppositely face each other so that a fuel guided by the wide surface of one splitter is introduced to a downstream side of the other splitter. In this way, a fuel is guided between the wide surfaces disposed adjacently to each other in an oppositely facing manner so that flame holding is strengthened on both splitters.
Further, the splitter does not inject air and hence, there is no possibility that a flow of the guided fuel is inhibited.
A surface forming the slit of the slitted splitter may be formed of an inclined surface which deflects the fuel gas flow in the direction of the longitudinal axis.
The inclined surface forming the slit deflects the fuel gas flow in the direction of the longitudinal axis of the splitter. Accordingly, the fuel gas flow can become turbulent also in the direction of the longitudinal axis and hence, flame holding performance can be further enhanced. Particularly, the slit can be three-dimensionally formed by respective surfaces forming the slit and hence, flame holding performance can be enhanced.
The splitters may be disposed at different positions in the direction of the fuel gas flow.
The splitters are disposed at different positions in the direction of the fuel gas flow, that is, the splitters are disposed in a displaced manner toward the upstream side and toward the downstream side in the direction of the fuel gas flow. Accordingly, compared to a case where the splitters are disposed at the same position in the direction of the fuel gas flow, an area which the widened portions of the splitters occupy can be reduced. With such a configuration, an increase in speed of a fuel gas can be suppressed so that a flow speed of a fuel gas toward the downstream side in the direction of the fuel gas flow can be approximated to a combustion speed of a fuel gas toward the upstream side so that ignition can be performed at an early stage before the fuel gas further flows toward the downstream side and hence, flame holding performance of the flame can be enhanced.
Ignition can be performed at the early stage by the splitters positioned on the upstream side in the fuel gas flow, and ignition or flame holding can be strengthened by the splitters positioned on the downstream side in the fuel gas flow.
Further, the splitters positioned on the upstream side in the fuel gas flow can introduce a fuel to the recirculation region for the splitters on the downstream side so that ignition or flame holding by the splitters on the downstream side can be strengthened. In this case, it is preferable that the non-slitted splitters be disposed on the upstream side, and the slitted splitters be disposed on the downstream side.
A flow straightening plate which is configured to separate a wall surface side of the fuel nozzle and the splitter from each other may be disposed at an end portion of the splitter in the longitudinal direction.
At the end portion of the splitter in the longitudinal direction, there is a possibility that ignition occurs using the end portion as a base point so that external ignition occurs at an outer peripheral portion of the fuel nozzle. A combustion air supply nozzle and the like are disposed outside the fuel nozzle so that a large amount of oxygen is present, which causes a large amount of NOx to be generated when external ignition occurs.
In view of the above, the flow straightening plate is provided, which separates the wall surface side of the fuel nozzle and the splitter from each other. Accordingly, external ignition, where ignition is performed at the end portion of the splitter, can be suppressed so that internal ignition and flame holding can be further strengthened.
The splitter may have a corner-removed portion, where a corner portion is removed, at a downstream end corner portion of the widened portion.
If a splitter has an corner portion at the downstream end corner portion of the widened portion, there is a possibility that the splitter receives radiation from the inner peripheral surface side of the fuel nozzle so that ignition occurs using the corner portion as a starting point whereby external ignition occurs at the outer peripheral portion of the fuel nozzle. A combustion air supply nozzle and the like are disposed outside the fuel nozzle so that a large amount of oxygen is present. Accordingly, when external ignition occurs, a large amount of NOx is generated.
In view of the above, the corner portion-removed portion, where the corner portion is removed, is formed on the splitter so as to suppress ignition or flame holding.
As the corner portion-removed portion, a tapered portion where a corner portion is chamfered can be named, for example.
According to another aspect of the present disclosure, there is provided a boiler which includes: a furnace; any one of the above-described combustion burners provided in the furnace; a flue provided on a downstream side of the furnace; and a heat exchanger provided in the flue.
With the provision of the combustion burner described above, it is possible to provide a boiler which performs low NOx combustion.
With the formation of the slit, an edge length of splitter length of the splitter on a front surface can be increased and, at the same time, a fuel can be guided to a recirculation region which is formed by the adjacent splitter, whereby flame holding performance at a center region of the fuel nozzle is enhanced, and low NOx combustion brought about by internal flame holding can be realized.
Hereinafter, embodiments according to the present disclosure are described with reference to drawings.
Hereinafter, a first embodiment of the present disclosure is described with reference to
A combustion burner of this embodiment combusts a pulverized coal fuel (fuel) obtained by pulverizing mainly coal by a mill, and is provided in a boiler (not shown in the drawing). A plurality of combustion burners are provided for the boiler which includes heat exchange such as a superheater and an evaporator in a flue, and the combustion burners form flames in a furnace.
The combustion air supply nozzle 4 forms a flow passage through which only a secondary air passes. Air is supplied through the combustion air supply nozzle 4 such that the air travels in a straight line toward the inside of the furnace. That is, air flowing out from the combustion air supply nozzle 4 is made to flow parallel to a fuel gas flowing out from the fuel nozzle 3 so as not to intersect with the fuel gas flowing out from the fuel nozzle 3. Although not shown in the drawing, a tertiary combustion air nozzle, through which combustion air is supplied, is disposed outside the combustion air supply nozzle 4.
As shown in
A plurality of splitters 5, 6, 7 are disposed in the fuel nozzle 3, and five splitters are disposed in this embodiment. Each of the splitters 5, 6, 7 is disposed such that a longitudinal axis thereof extends from the side of a lower wall portion (one wall portion) 3a of the fuel nozzle 3 to the side of an upper wall portion (the other wall portion) 3b which is disposed on a side opposite to the lower wall portion 3a. That is, each of the splitters 5, 6, 7 is a vertical splitter which is disposed so as to extend in the vertical direction. Upper and lower ends of the splitters 5, 6, 7 are fixed to wall portions of the fuel nozzle 3 by support members 8 respectively.
The fuel nozzle 3 includes a nozzle angle adjusting mechanism which is rotatable in the up-and-down direction together with the splitters 5, 6, 7. In this embodiment, vertical splitters are used so that even when an angle of the nozzle is adjusted in the up-and-down direction, a flow of a fuel gas is not largely deflected, which is preferable.
The splitters 5, 6, 7 are members having a function of dividing a fuel gas flow, but do not have a function of injecting air from the inside.
The splitters include: slitted splitters 5 and 6 disposed in the center and on both ends in the horizontal direction; and non-slitted splitters 7 adjacently disposed on both sides of the slitted splitter 5 disposed in the center. In this way, each non-slitted splitter 7 is disposed at a position where the non-slitted splitter 7 is disposed adjacently to the slitted splitters 5, 6.
As shown in
The widened portions 10 have an approximately triangular shape as shown in
As shown in
In this embodiment, assuming an equivalent circle diameter of an opening of the fuel nozzle 3 as “D”, the predetermined distance S is set to 0.001 D or more and 1.0 D or less, and more preferably set to 0.03 D or more and 0.5 D or less. It is further preferable to set the predetermined distance S to 0.05 D or more and 0.3 D or less.
A lower limit value and an upper limit value of the predetermined distance S is determined based on the following viewpoint. When the predetermined distance S becomes lower than the lower limit value, a distance between the slitted splitters 5, 6 and the non-slitted splitters 7 becomes extremely small. Accordingly, even when these splitters are displaced from each other so as to ensure a sufficient cross-sectional area of a flow passage, an advantageous effect of such a configuration cannot be obtained. On the other hand, when the predetermined distance S exceeds the upper limit value, a recirculation region formed by the non-slitted splitters 7 disappears before reaching the slitted splitters 5, 6 so that an advantageous effect cannot be obtained where a fuel gas is guided to the recirculation region formed by the non-slitted splitters 7 from the slitted splitters 5, 6.
The predetermined distance S may be adjusted by moving the non-slitted splitters 7 positioned on the upstream side in the direction of the fuel gas flow as indicated by arrows A in
As shown in
As shown in
It is preferable that the slits SL be formed at a center portion of the splitters 5, 6 in the longitudinal direction so as to allow ignition or flame holding to be performed at a position as close as possible to the center side of the fuel nozzle 3, and that the slits SL be not formed at both upper and lower end portions of the splitters 5, 6.
Assuming a length of the splitters 5, 6 as L0, a range L1 where the slits SL are formed is set such that an expression L1/L0 becomes 0.8 or less, and is preferably 0.5 or less.
As shown in
According to the combustion burner 1 having the configuration described above, the following manner of operation and advantageous effects can be acquired.
With the use of the slitted splitters 5, 6 having the slits SL, an edge length of splitter length is increased so that flame holding performance is enhanced. Accordingly, internal flame holding where a flame is held on the inside of the fuel nozzle 3 is strengthened. The non-slitted splitters 7 form a recirculation region on the downstream of the widened portion 10 and thus have a flame holding function, but also have a function as a guide member which guides fuel to the slitted splitters 5, 6 disposed adjacently to the non-slitted splitters 7 by making use of the inclined surfaces of the widened portion 10. Accordingly, internal flame holding by the slitted splitters 5, 6 is further strengthened. In this way, internal flame holding is strengthened by the combination of the slitted splitters 5, 6 and the non-slitted splitters 7 so that reduced combustion is promoted whereby NOx generated in a flame region of the burner can be reduced.
The upper surface SL1 and the lower surface SL2 which are the inclined surfaces forming the slit SL deflect a fuel gas flow in the direction of the longitudinal axis of the splitters 5, 6. Accordingly, the fuel gas flow can become turbulent also in the direction of the longitudinal axis and hence, flame holding performance can be further enhanced. Particularly, the slit SL can be three-dimensionally formed by respective surfaces forming the slit SL and hence, flame holding performance can be enhanced.
The splitters 5, 6, 7 are disposed at different positions in the direction of the fuel gas flow. Accordingly, compared to a case where the splitters 5, 6, 7 are disposed at the same position in the direction of the fuel gas flow, an area occupied by the widened portions 10 of the splitters can be reduced. With such a configuration, an increase in speed of a fuel gas can be suppressed so that a flow speed of a fuel gas toward the downstream side in the direction of the fuel gas flow can be approximated to a combustion speed of a fuel gas toward the upstream side, ignition can be performed at an early stage before the fuel gas further flows toward the downstream side, and hence, flame holding performance of the flame can be enhanced.
The non-slitted splitters 7 positioned on the upstream side in the fuel gas flow guide a fuel to the recirculation region for the slitted splitters 5, 6 on the downstream side so that ignition or flame holding by the slitted splitters 5, 6 on the downstream side can be strengthened. In this way, when a main function of a splitter is to guide pulverized coal, it is preferable to use the non-slitted splitter 7 as the splitter.
By providing the flow straightening plates 15, each of which separates the wall surface side of the fuel nozzle 3 and the splitters 5, 6, 7 from each other, external ignition, where ignition is performed at the upper end portion or the lower end portions of the splitters 5, 6, 7, can be suppressed so that internal ignition and flame holding can be further strengthened.
In this embodiment, the non-slitted splitters 7 are disposed on the upstream side, and the slitted splitters 5, 6 are disposed on the downstream side, but the non-slitted splitters 7 and the slitted splitters 5, 6 may be disposed in a reversed arrangement, that is, the non-slitted splitters 7 may be disposed on the downstream side, and the slitted splitters 5, 6 may be disposed on the upstream side. This configuration is adopted when a fuel is used which is expected to ignite at an early stage. Ignition is performed at the early stage by the slitted splitters 5, 6 disposed on the upstream side, and the non-slitted splitters guide a fuel gas to a recirculation region formed by these slitted splitters 5, 6.
Further, as shown in
Next, a second embodiment of the present disclosure is described with reference to
This embodiment differs from the first embodiment with respect to a point that tapered portions, where corner portions of the splitters 6 are removed, are formed on the splitters 6, and is the same in other respects. Accordingly, components in common are given the same reference numerals, and description thereof is omitted.
As shown in
The tapered portion 20 may have any shape provided that the corner portion is removed. As shown in
In this embodiment, unlike in the first embodiment, two flow straightening plates 15a, 15b are provided. The respective flow straightening plates 15a, 15b are disposed at height positions symmetrical with each other with respect to a center position of the fuel nozzle 3 in the height direction, and are formed of plate bodies extending in the horizontal direction.
According to this embodiment, the tapered portion 20, where the corner portion is removed, is formed so that it is possible to suppress a phenomenon that the splitter 6 receives radiation from the inner peripheral surface side of the fuel nozzle 3 so that ignition occurs at the corner portion as a starting point whereby external ignition occurs at an outer peripheral portion of the fuel nozzle 3.
The tapered portion (corner-removed portion) 20 may be also formed on other splitters. That is, the tapered portion 20 may be also formed on the slitted splitter 5 disposed at the center or on the non-slitted splitters 7.
In the embodiments described above, five splitters are used. However, the present disclosure is not limited to such a configuration. Two to four splitters may be used, or six or more splitters may be used. The optimum number of splitters is designed depending on a size of a fuel nozzle.
In the respective embodiments described above, the description is made with respect to a case where the splitters 5, 6, 7 are vertical splitters extending in the up-and-down direction as one example. However, the present disclosure is also applicable to a case where the splitters 5, 6, 7 are lateral splitters extending in the horizontal direction.
Further, in the embodiments described above, the description has been made mainly with respect to a case where the fuel is pulverized coal. However, the fuel is not limited to pulverized coal, and the present disclosure is also applicable to a case where the fuel is petroleum coke, a petroleum residue or a biomass fuel (in the form of a solid or slurry).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-179764 | Sep 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/072564 | 8/1/2016 | WO | 00 |
