Patent Application
20050211142
1. Technical Field
The present invention relates to a burner, a fuel combustion method by the burner, and a method of retrofitting a boiler provided with an existing burner to turn it into a boiler with the burner made according to the present invention.
2. Description of Prior Art
For burners used for boilers or the like, it is required to cope with load change, cope with various coals, reduce the concentration of nitrogen oxides (NOx), reduce unburned fuel, etc. In order to satisfy those requirements, various methods of controlling combustion conditions have been developed. For example, some of them are a method of apportioning a flow quantity of air between secondary air and tertiary air by air resistors, a method of changing swirl number, etc.
As one of methods of controlling combustion conditions, a method of adjusting a secondary air flow rate and adjusting an air jetting direction by making a partition wall partitioning secondary air and tertiary air movable is proposed (see a patent document 1, for example).
Patent Document 1: JP 60-26922 B (Claims)
The patent document 1 discloses that since it is possible to control the flow of secondary air by moving the partition wall in the burner axial direction, secondary flame can be burned under the best condition from a viewpoint of low NOx emission and combustion efficiency.
An object of the invention is to enable a burner to be cooled while reducing NOx.
A burner according to the present invention comprises a primary nozzle for supplying fuel and primary air, a tubular secondary nozzle provided outside the primary nozzle so as to embrace or contact with the primary nozzle, a tubular tertiary nozzle provided outside the secondary nozzle so as to embrace or contact with the secondary nozzle, and a tubular partition wall partitioning the secondary nozzle and the tertiary nozzle and provided therebetween, wherein a flow path change member is provided on the partition wall, which flow path change member is made so as to jet outwardly a fluid flowing in the tertiary nozzle, and the partition wall is made movable in parallel with the burner axis direction. The secondary nozzle is supplied with secondary air and the tertiary nozzle is supplied with tertiary air. In the invention, the burner axis means the central axis of the tubular primary nozzle.
By moving the partition wall provided with the flow path change member in a direction in parallel with the burner axis, a cross-sectional area of a tertiary air jet of the tertiary nozzle changes, and a flow rate and a flow speed of the tertiary air change. The change in flow rate of the tertiary air changes a flow rate and a flow speed of the secondary air. By the change in flow rate of the tertiary air or a flow rate of the secondary air, the combustion conditions change. As a result, it is possible to lower the temperatures of burner constituent components.
The burner of triple tube construction, which is an objective of the invention, is constructed so that fuel is ignited with primary air to form reducing flame and make NOx small, and the secondary air and tertiary air are mixed with the reducing flame to burn the unburned fuel contained in the reducing flame. The burner is known as an in-flame 2-stage combustion burner or an in-flame NOx reduction burner. In this burner, delay in mixing of the tertiary air makes a region of the reducing flame large, whereby low NOx emission is promoted. Many burners of this construction each have a stabilizer provided at the outlet of the tubular primary nozzle, as shown in the patent document 1, and in the present invention, also, it is possible to provide a stabilizer at the outlet of the primary nozzle. Of flame stabilizers, there are an inner flame stabilizing ring in which a ring-shaped projection is formed at the inside of the outlet of the tubular primary nozzle and an outer flame stabilizing ring in which a tubular projection is provided outside the outlet of the tubular primary nozzle so as to throw out in the burner axis direction, and it is preferable to provide both of them. Provision of the stabilizer forms a flow recirculation region due to turbulent flow eddy in a wake flow thereof or in a flow downstream of the stabilizer, and the flow recirculation involves fuel, for example, pulverized coal particles to make them into flash points for high temperature gas and promote ignition of the pulverized coal. H ere, the secondary air bears a role to cool the stabilizer and adjust a mixing ratio of fuel and air.
As the flow path change member, such a member is desirable that has a taper-shaped inclined plane so that the tertiary air flows, while changing gradually the flow direction from a flow parallel with the burner axis to an outward flow. Further, the rear side, that is, the side in contact with the secondary air, of the flow path change member is desirable to be formed so that it inclines along the inclined plane of the tertiary nozzle. By forming the flow path change member in this construction, when the flow path change member is moved so that the tertiary air jet cress-sectional area becomes small, the secondary air jet cross-sectional area increases according to the movement thereof.
In order to make the partition wall move easily without making the burner construction complicated, it is desirable for the partition wall to be composed of a fixed wall and a movable wall, and for the movable wall to be move sliding on the surface of the fixed wall. Concretely, it is desirable to be composed of a portion that the tertiary air flows in parallel with the burner axis as the fixed wall and a portion that the parallel flow changes in flow direction outward as the movable wall, that is, the latter portion is a portion on which the flow path change member is provided. It is desirable for the fixed wall to provide guide rollers thereon. It is preferable to provide a stopper or stoppers for stopping movement of the movable wall on at least one of the fixed wall and the movable wall. Since the flow path change member and the partition wall in the vicinity of the flow path change member are apt to be heated to a high temperature, it is preferable to provide fins for cooling them there. As a means for moving the movable wall, a bar-shaped member is provided, which bar-shaped member is mounted on the movable wall and moved forward and backward in the burner axis direction by manual or automatic means. At this time, extension of one end of the bar-shaped member out of the wind box of the burner makes its maintenance easy and its failure uneasy. It is possible to move the movable wall by pulling and pushing the end of the bar-shaped member by hand. Further, it is possible to easily move it forward and backward to provide gears on the end portion of the bar-shaped member and use a handle having another gear mounted thereon and meshed with the gears. Still further, by providing a motor or motors instead of the handle, it is possible to save power for movement and to make it automatic by control.
The burner according to the invention can be used for a burner using oil, gas, pulverized coal etc. as fuel, particularly, it is suitable for a burner using pulverized coal. In a pulverized coal burner, sometimes combustion is assisted when a load is low by providing an oil burner for assisting combustion inside a primary nozzle. In the burner according to the invention, also, such an oil burner can be provided.
For the burner according to the invention, it is possible to add a tertiary air bypass mechanism by which a part of tertiary air is caused to bypass the tertiary nozzle into another nozzle. The tertiary air bypass mechanism is formed so that when the partition wall partitioning the secondary nozzle and the tertiary nozzle is moved to a predetermined position, a part of the tertiary air bypasses the tertiary nozzle into another nozzle. By making a hole in the movable wall while making a hole in the fixed wall so as to communicate with the above-mentioned hole when the movable wall is moved to the predetermined position, the part of the tertiary air can bypass the tertiary nozzle into the secondary nozzle. One hole formed in each of the fixed wall and the movable wall is sufficient, however, it is preferable to provide a plurality of holes in a circumferential direction in order to increase a flow rate of the tertiary air.
By forming a hole in the primary nozzle and connecting the hole with the hole formed in the fixed wall by a bypass pipe, it is possible to flow the tertiary air into the primary nozzle. By forming the bypass pipe so that the tertiary air flows along the inner wall of the primary nozzle and jets in the flow direction of fuel, it is possible to cool the stabilizer by the tertiary air flowing in the primary nozzle.
Another of the aspects of the present invention is a combustion method in which the partition wall partitioning the secondary nozzle and the tertiary nozzle is moved to reduce the tertiary air jet cross-sectional area of the tertiary nozzle when the temperature of the flow path change member becomes higher than a set temperature in the case where fuel is burned by using the above-mentioned burner, thereby a flow speed of the tertiary air is increased. Further, another of the aspects of the present invention is a combustion method in which the partition wall is moved to increase the tertiary air jet cross-sectional area and make the flow speed of the tertiary air slow when ash comes to deposit on the burner during combustion. Further, another of the aspects of the present invention is a method of moving the partition wall to decrease the tertiary air jet cross-sectional area of the tertiary nozzle and increase the flow rate of secondary air when the burner is out of service without fuel supply to the burner. Further, another of the aspects of the present invention is a method of causing a part of, tertiary air to be supplied to the tertiary nozzle to bypass the tertiary nozzle into the secondary nozzle or the primary nozzle while stopping of fuel supply to the burner. Further, another of the aspects of the present invention is a method of conducting an operation of making the tertiary air jet cross-sectional area small to increase the momentum of tertiary air and increasing the quantity of tertiary air in the case where the NOx concentration is high or fuel of bad combustibility is used.
Further another of the aspects of the present invention is a method of retrofitting a boiler provided with an existing burner having a tubular partition wall which partitions a secondary nozzle and a tertiary nozzle and is fixedly provided, wherein a part or all of the partition wall is removed and a tubular partition wall provided with a flow path change member is arranged for the fixed partition wall so as to be movable.
The burner according to the present invention is the in-flame 2-stage combustion type and excellent for reduction of NOx. According to the present invention, it is possible to suppress ash deposit on the burner or damage of the burner due to heat while reducing NOx. In the present invention, by fixing the jet direction of tertiary air to a constant outward direction and changing the momentum of the tertiary air, the size or region of flow recirculation can be optimized within a range in which it does not become small, and it is possible to keep the combustion condition better. Further, even if a flow rate of tertiary air is kept constant, it is possible to make the flow speed at a downstream end of a guide sleeve high, so that the guide sleeve can be cooled. Further, by controlling independently the momentum and the flow rate of the tertiary air, the size of flame and the size of flow recirculation determined mainly by the momentum, and the size of a reducing region determined by the flow rate can be controlled independently, and a good combustion condition can be kept.
The burner and the method of using the burner according to the present invention will be explained hereunder, referring to the Drawings.
A stabilizer 10 having a tubular shape is provided on an end of the primary nozzle 4. An air resistor (or air resistors) 7 is provided upstream of the tertiary nozzle 9. Further, a tertiary damper 35 and a secondary damper 34 are provided upstream of the tertiary nozzle 9 and the secondary nozzle 8, respectively.
By moving the movable wall 2 and the guide sleeve 3 provided on the end thereof forward and backward, that is, in a parallel direction to the burner axis, the flow rate and flow speed of the tertiary air, the flow rate and flow speed of the secondary air and a ratio of the tertiary air flow rate and the secondary air flow rate are changed, whereby it is possible to control the combustion conditions. This is the same as changing a ratio of tertiary air momentum and secondary air momentum. In the present invention, by keeping a jet angle of the tertiary air constant and changing an outlet cross-sectional area for the tertiary air, it is possible to change the flow rate and flow speed of the tertiary air. By directing always the tertiary air outward, the size of flow recirculation formed downstream of the stabilizer 10 and the guide sleeve 3 can be always made large, so that the combustion conditions can be always kept good. The momentum of the tertiary air is a main factor for determining the size of flame and the size of flow recirculation. The flow rate of the tertiary air is a main factor for determining the size of a reducing region. Since the momentum and the flow rate of tertiary air can be controlled independently, it is possible to make a combustion condition suitable for improvement on flame stabilization and NOx reduction. Further, it is possible to change independently the momentum of tertiary air and the flow rate of secondary air, whereby the secondary air can be used for other objects such as cooling of the stabilizer 10, air supply to the fuel flowing in the primary nozzle, etc.
The movable wall 2 has a possibility that the temperature thereof rises when the flow rate of tertiary air is small. Damage due to burning or deformation are apt to occur when the temperature of the member rises higher than a temperature that the member subjected to heat is sustainable to the heat. It is better to use material of high heat resistance for the movable wall 2.
Hereunder, first of all, a burner adjusting method at time of trial operation of the burner will be explained. Immediately after the burner is installed on the boiler, in some cases an intended flow rate does not flow. Causes for this are considered to be manufacturing errors of the burner, asymmetry of upstream ducts, setting errors of the resistors, the dampers installed on the burner, etc. Further, in some cases, it is necessary to set a flow rate of air according to deviation of fuel for each burner. Therefore, by adjusting the air resistor 7 of the tertiary nozzle 9, the tertiary damper 35, the secondary damper 34 and the movable wall 2, combustion conditions suitable for reduction of NOx, CO, unburned fuel, soot, corrosion, and the metal temperature of the burner part are made. Hereunder, examples of the adjusting method are shown.
In the case where flame stabilization is bad, the following operations are conducted to improve the stabilization of flame:
(1.1) In the case where the momentum of tertiary air is small: The movable wall 2 is moved to a near side or to the left side in
(1.2) In the case where the momentum of secondary air is small:
When the flow rate of secondary air can be allowed to be increased, it is good that the air resistor 7 of the tertiary nozzle 9 is closed to make swirling strong, or the movable wall 2 is moved to the near side to make the flow speed of the tertiary air high. The increase in flow rate and momentum of the secondary air makes the flow recirculation region downstream of the stabilizer 10 large and raises the stabilization of flame. However, when the secondary air increases too much, on the contrary in some cases the flow recirculation is made small. An optimum flow rate exists for the secondary air.
In
In the case where the concentration of NOx is high, adjustment is conducted the following method.
(2.1) Since making the stabilization of flame high decreases the concentration of NOx, setting for increasing the stability of flame is taken.
(2.2) In the case where although flame is sufficiently stabilized, it is desired to further reduce the concentration of NOx, it is effective to delay mixing of air. In order to delay the mixing of air, it is effective to decrease the flow rate of the secondary air and increase the flow rate of the tertiary air. To carry out it, it is considered that the secondary damper 34 is closed, or the movable wall 2 is moved so that the tertiary air outlet is opened. Further, it can be achieved by increasing the momentum of tertiary air. The delay of mixing of air can be attained also even by closing the air resistor 7 of the tertiary nozzle 9 and making swirling of tertiary air strong. In this case, it is necessary to close the secondary damper 34 so that the flow rate of the tertiary air does not decrease.
In the case where unburned fuel is much, adjustment is conducted in the following method.
(3.1) There is a possibility that unburned fuel becomes much without conducting stabilization of flame. Therefore, it is effective to take a setting similar to the setting for improvement on the stabilization of flame.
(3.2) In the case where although flame is sufficiently stabilized, it is desired to further reduce the unburned fuel, it is effective to increase secondary air. In this case, there is a possibility that the momentum of tertiary air decreases and the stabilization of flame decreases when the secondary damper 34 is opened. Therefore, it is effective to increase the flow speed of tertiary air by moving the movable wall 2 to the near side or to make the swirling strong by closing the air resistor 7 of the tertiary nozzle 9.
(3.3) For reduction of unburned fuel, it is effective to raise a burner air ratio. The flow rate of air increases by raising the burner air ratio, mixing of air and fuel becomes better, and the concentration of NOx becomes high. In order to reduce the concentration of NOx, the method described in the example 2 can be applied.
To reduce corrosion, adjustment is conducted by the following method:
(4.1) Being short in air around the wall makes the concentration of reducing gas higher and corrosion speed high. To supply air to around the wall, it is effective to increase the flow rate of tertiary air. Therefore, it is effective to open the movable wall 2 to make the flow path area of the tertiary nozzle 9 wide and increase the flow rate of tertiary air. Further, to make air reach to around the wall by increasing the momentum of tertiary air, it is possible to close the secondary damper 34.
(4.2) Since it is also possible to make the stabilization of flame bad and to decrease reducing gas, it is possible to perform an operation reverse to that in the example 1.
(4.3) The reducing gas can be reduced and corrosion can be reduced, also, by increasing an air quantity of the burner close to the wall that is apt to corrode. Therefore, it is effective to adjust air distribution by adjusting the movable wall 2, the resistor, and the damper for each burner, thereby making the operation condition into such an operation condition that the pressure loss of the burner that is better for an air quantity to be increase is reduced.
In the case where it is desired to change greatly kinds of fuel, adjustment is conducted by the following method:
(5.1) When kinds of fuel are greatly changed, pulverization and an amount of volatile matters in the fuel change, so that it is better to change the damper opening, the position of the movable wall 2 and the setting of the air resistor 7 in order to keep the stabilization of flame and reduce NOx. In the case where fuel is changed from a fuel of good combustibility to a fuel of bad combustibility, there is a possibility that the stabilization of flame decreases. In this case, it is better to conduct such an operation that the stabilization of flame becomes good.
(5.2) The fuel of bad combustibility has a high possibility that the concentration of NOx becomes high, so that it is better to conduct such an operation that NOx is reduced.
In the case where ashes in fuel deposit, operations are taken by the following method:
(6.1) In the case where the stabilization of flame is good and ashes in the fuel melt and deposit around the burner, the movable wall 2 is moved forward (to an opposite side to the near side) to increase the outlet cross-sectional area for tertiary air, decrease the flow speed of the tertiary air and reduce the stabilization of flame. By operating in this way, the combustion temperature decreases, so that deposition of ashes is reduced. At the same time, secondary air also increases, the temperature around the stabilizer 10 decreases and the ashes can be prevented from melting.
(6.2) In the case where molten ash deposits on the wall of boiler, it is better to supply air to around the wall. Therefore, it is better to operate so that air is supplied around the wall by moving the movable wall 2 to the near side to change the jetting direction of tertiary air outward.
In the case where the temperature of the stabilizer 10 is high, the following operation is conducted:
When the temperature of the stabilizer 10 is high, it is effective to make the flow speed of secondary air high. In order to increase the flow rate of secondary air, the tertiary damper 35 or the air resistor 7 is closed. In this case, there is such a possibility that the momentum of tertiary air decreases and the stabilization of flame decreases. Therefore, the movable wall 2 is moved to the near side instead of closing the tertiary damper 35 and the air resistor 7. Thereby, both of keeping the stabilization of flame and reduction of the temperature of the stabilizer can be achieved.
Decrease of the minimum load of the boiler is conducted as follows:
Boiler load not always is 100%, but it is changed according to power demands. If it can be run at a very low load, the operation efficiency of the boiler increases. Usual burners are designed so that the performance is good at a load of 100%. When the load is low, respective flow rates of fuel and air entering the furnace from the burner decrease, so that there is a possibility that the momentums thereof come to be unbalanced and the stabilization of flame decreases. For example, when the momentum of tertiary air is low, it is effective to increase the momentum by moving the movable wall 2 to the near side. This operation is the same as the method of increasing the stabilization of flame as described in the example 1. However, when the stabilization of flame is increased under the low load operation, in some cases, the combustibility becomes bad at a high load. It is better to set in such a range that the combustibility does not become bad even at a high load.
A merit of driving the movable wall 2 by the motor 6 is that the movable wall 2 is controlled according to the algorithm of combustion adjustment described in the embodiment 1, and an optimum combustion condition can be always kept. As others, as explained hereunder, it is possible to provide a suitable operation condition by changing flow rate conditions.
In some cases, the burner is out of service without fuel being supplied. Under such a condition, there is a possibility that the burner being out of service is heated by radiation heat from other burners and the temperatures of the guide sleeve 3, the stabilizer 10, etc. rise. To prevent this phenomenon, it is necessary to supply air to the burner even when it is out of service. When a flow rate of air to be supplied to the burner being out of service is large, an air adjustment quantity becomes small. Therefore, it is necessary to make small the flow rate of air to be supplied to the burner being out of service. When the flow rate is decreased under the condition that the movable wall 2 is fixed, the flow speeds of tertiary air and secondary air decrease, and it is impossible to sufficiently cool the guide sleeve 3 and the stabilizer 10.
In the present invention, the burner is turned into the condition as shown in
In the above-described embodiments, the tertiary nozzle is provided with the air resistor 7. However, it is possible to form it without provision of such an air resistor 7. The air resistor 7 is for controlling a combustion field by swirling the tertiary air, because in the present invention the same effect can be attained by moving the movable wall 2 forward and backward in the burner axis direction. Further, the air resistor 15 of the secondary nozzle is not essential, either. In this case, the secondary damper 34 is necessary because any method of adjusting a flow rate of secondary air comes not to exist thereby.
A construction of a controller used for the embodiment 2 is shown in
In the case where the concentration of oxygen in the air carrying fuel is low, it is good to take such a construction that the smaller the tertiary air jet sectional area of the tertiary nozzle 9 becomes with the movable wall 2 being moved to the n ear side, the more the flow rate of bypass air increases. When lignite is used, since the fuel is easy to catch fire, the fuel is carried with flue gas. When the burner load is high, even if the oxygen concentration of primary air is low, stable combustion is possible because the gas temperature is high inside the combustion apparatus, for example, the boiler. However, when the load decreases, the gas temperature inside the combustion apparatus lowers and unburned fuel increases and lift-off occurs unless the oxygen concentration of the primary air becomes high. In such a low load case, tertiary air flows into the primary nozzle 4, so that it is possible to effect stable combustion. Although such a construction that tertiary air always bypasses and flows into the primary nozzle 4 is also considered, combustion is promoted when the load is high and the possibility of explosion and ash deposit becomes high, so that it is better to take the construction that the smaller the load becomes, the more the flow rate of air is increased.
Further, in a similar manner to the example of
In some cases, the pulverized coal burner is provided with an oil burner formed so as to spray oil 21 for assisting combustion from an atomizer 31.
Further, it is preferable to provide a stopper 2 on the movable wall 2. Thereby, it is possible to prevent the movable wall 2 form moving forward too much due to sensor failure or the like. Although not shown in
Further, in
In
An example of other use of the burner according to the present invention will be explained. In
The present invention makes it possible to cool the burner while reducing NOx by controlling the combustion condition optimum. The possibility of utility of the burner according to the present invention is large to make thermal failure of the burner less.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-086006 | Mar 2004 | JP | national |
