Combustion Rotation System for Fuel-Injection Boilers
A combustion rotation system that utilizes the placement, direction, and/or unbalanced fuel injection flow rates to the burners in a fuel-injection power boiler, such as pulverized coal, oil or gas fired boiler, to achieve Inboard/Outboard (I/O) rotation of the combustion mass or other types of mixing of the combustion mass. The over fired air (“OFA”) ports may also be placed, directed, and/or operated to contribute to the rotation of the combustion mass. The fuel-injection combustion rotation system may also be controlled while the boiler is operation, and controlled automatically, through a master control system. The fuel-injection combustion rotation system induces multiple vortex rotation of the combustion mass, which is more efficient and effective than attempting to rotate the entire combustion mass in a single vortex.
The present invention claims priority to U.S. Provisional Patent Application Ser. No. 61/100,949 entitled “Method and System for Multiple Vortex Combustion Rotation in a Coal Fired Boiler” filed 29 Sep. 2008, which is incorporated herein by reference.
FIELD OF THE INVENTIONThe present invention relates to industrial boilers and, more particularly, relates to a combustion rotation system for an industrial fuel-injection boiler in which the burners and over fire air (OFA) ports are located, directed and operated to induce multiple rotational vortexes in the combustion mass inside the combustion section of the fuel-injection boiler.
BACKGROUND OF THE INVENTIONFor decades, industrial fuel-injection boilers have been operated with balanced fuel injection profiles that produce rising, non-rotating combustion masses inside the combustion section of the boiler. No systems are presently available for rotating or otherwise mixing the combustion mass in conventional fuel-injection boilers. U.S. Pat. No. 7,185,594 describes a combustion rotation system for a chemical recovery boiler in which supplemental air is injected into the combustion chamber to induce rotation of the combustion mass. This approach is not amenable for use in a fuel-injection boiler, such as a pulverized coal, oil or gas boiler, because injection of supplemental air to induce rotation of the combustion mass would change the air-fuel mixture in the boiler and impart other undesirable combustion characteristics. U.S. Pat. No. 5,809,910 describes a waste incinerator using over fire air (OFA) ports to rotate the combustion mass to more completely incinerate the contaminants in the waste product. This boiler is not a fuel injection boiler and describes rotating the entire combustion mass in a single vortex combustion rotation. Therefore, there remains a need for a combustion rotation system suitable for fuel-injection boilers, such as coal, oil and gas boilers.
SUMMARY OF THE INVENTIONThe present invention may be implemented in a combustion rotation system in or for an industrial fuel-injection boiler with a combustion section, first and second opposing boiler walls, and a plurality of burners. Each burner is supported on the first or second boiler wall and configured for injecting a mixture of fuel and air into the boiler. Each burner has an associated fuel-injection flow rate controller. The flow rate controllers are set in a coordinated manner to impart an unbalanced fuel-injection profile to induce multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
In addition, each column of burners typically has one or more over-fire air ports located above the column of burners, and each over-fire air port has an associated flow rate controller. The over-fire air port flow rate controller may be set to impart an unbalanced air injection profile consistent with the unbalanced fuel-injection profile imparted by the fuel-injection rate controllers to assist the burners in inducing the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
In a typical configuration, the burner locations on the first boiler wall are directly opposing the burner locations on the second boiler wall and the burners on each boiler wall are arranged into inboard columns and outboard columns. For an inboard/outboard rotational technique, the flow rate controllers are set to induce an unbalanced fuel-injection profile between the inboard columns and outboard columns on the first boiler wall, an unbalanced fuel-injection profile between the inboard columns and outboard columns on the second boiler wall, an unbalanced fuel-injection profile between the inboard columns on the first boiler wall and the inboard columns on the second boiler wall, and an unbalanced fuel-injection profile between the outboard columns on the first boiler wall and the outboard columns on the second boiler wall.
This combustion technique may be extended to boilers with larger numbers of columns of burners. In a first illustrative configuration, the number of columns on each boiler wall is four and the number of rotational vortexes is two. In a second illustrative configuration, the burners locations on the first boiler wall are directly opposing the burner locations on the second boiler wall. In a third second illustrative configuration, the number of columns on each boiler wall is six and the number of rotational vortexes is three. In a fourth illustrative configuration, the number of columns on each boiler wall is eight and the number of rotational vortexes is four.
In another combustion rotation technique, the fuel-injection lateral locations on the first boiler wall are laterally offset from the fuel-injection lateral locations on the second boiler wall to assist in the inducement of the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler. In addition, one or more of the fuel-injection directions may be horizontally tilted to assist in the inducement of the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler. As another technique, one or more of the fuel-injection directions may be vertically tilted to assist in mixing of the combustion mass inside the combustion section of the boiler. As yet another technique, the fuel-injection flow controllers may be set to impart a vertically unbalanced fuel injection profile along one or more of the columns to assist in mixing of the combustion mass inside the combustion section of the boiler. These techniques may be implemented individually or in various combinations to rotate and mix the combustion mass. A master controller may also be used to rotate and/or mix the combustion mass and/or actuate boiler cleaning equipment while the boiler is in operation in response to measured boiler parameters, such as temperature, pressure, gas analysis, and heat flux.
The present invention may be implemented in a combustion rotation system that utilizes the placement, direction, and/or unbalanced fuel injection flow rates to the burners in a fuel-injection power boiler, such as pulverized coal, oil or gas fired boiler, to achieve rotation of the combustion mass and other types of mixing of the combustion mass. The over fired air (“OFA”) ports may also be placed, directed, and/or operated to contribute to the rotation of the combustion mass. For example, in a typical boiler configuration with four opposing columns of burner and OFA ports on opposite walls of the boiler, the jets are located, directed and/or operated to produce two counter-rotating inboard/outboard vortices in the combustion mass. The fuel-injection combustion rotation system may also be controlled while the boiler is operation, and controlled automatically, through a master control system.
U.S. Pat. No. 7,185,594 describes a combustion rotation system for a chemical recovery boiler in which supplemental air is injected above the combustion chamber to induce rotation of the combustion mass. While the injection of supplemental air into a chemical recovery boiler does not adversely affect the combustion process, this approach is not amenable for use in a fuel-injection boiler because the injection of additional air into the boiler to rotate the combustion mass would change the air-fuel mixture and impart other undesirable combustion characteristics.
The present invention solves this problem by placing, directing and/or controlling the air/fuel flow rate to the combustion burners involved in the combustion process to induce rotation of the combustion mass in the combustion section of the boiler without adversely affecting the air-fuel mixture. The placement, direction, and injection flow rates to the OFA ports may also be selected or controlled to assist in combustion rotation. The fuel-injection combustion rotation system induces multiple vortex rotation of the combustion mass, which is more efficient and effective than attempting to rotate the entire combustion mass in a single vortex.
As opposed to the chemical recovery boiler, a fuel-injection boiler, such as a pulverized coal, oil or gas fired boiler, introduces the fuel and combustion air through the same jet or burner. This means that one cannot just add additional air ports to rotate the combustion mass, as taught in U.S. Pat. No. 7,185,594, since this would result in an increase in the air/fuel ratio. This is not desirable because increasing the air/fuel ratio will increase the flue gas through the boiler resulting in multiple problems inside the boiler and in the back-end air pollution equipment. Altering the air/fuel ratio would also reduce the efficiency of the boiler, which is typically designed to obtain a desired air/fuel ratio prior to the injection of supplemental air for combustion rotation.
Rather than adding supplemental air to impart combustion rotation, the fuel-injection combustion rotation system utilizes the setup (i.e., placement, direction and/or flow rates) of the burners to impart combustion rotation, which is a significant adaptation and improvement over the supplemental air approach to imparting combustion rotation in a chemical recovery boiler. For some boilers, this means some burners become high flow burners while others become low flow burners. The high flow burners will flow more fuel/air than the low flow burners. In a coal fired boiler, the minimum amount of coal may be passed to the low flow burners based on the minimum allowable coal flow for the supply pipe, while the flow to the high flow burners is increased above the conventional level. This type of unbalanced fuel injection profile is quite the opposite of traditional practice where a lot of trouble is taken to balance the fuel flow to each burner.
A typical wall fired pulverized coal boiler contains multiple levels of burners on opposing walls. These burners on are arranged above each other in vertical stacks or columns and positioned so that there are similar columns of burners on opposite sides of the boiler (i.e., directly across the boiler. If the outer burners are chosen as the high flow burners, then the inner burners will be the low flow burners to impart rotation vortexes into the combustion mass. The opposite wall will have the opposite arrangement with high flow going to the inboard burners and low flow to the outboard burners. In this way the opposing jets will not interfere with each other. The resulting flow pattern produces two counter rotating inboard/outboard vortices. The spin is reinforced as the flue gases flow up and past each level of the burner and OFA jets, which are similarly operated. Even though the burner flows are biased, the total fuel flow and air/fuel ratio per level typically remains approximately the same as in the conventional balanced fuel injection technique, although these parameters may be altered and re-optimized if desired. In particular, the total fuel flow and air/fuel ratio may be optimized for efficiency, pollution control, or other desired characteristics to take advantage of the higher efficiency combustion obtained with combustion rotation.
Rotating the combustion mass significantly increases the mixing between the air and fuel, which leads to an increase in combustion efficiency enabling more complete combustion reducing the amount of carbon monoxide generated in comparison to the conventional balanced fuel injection technique. The spiraling upward movement of the combustion mass increases the residence time for the fuel in the combustion section of the boiler, enabling it to burn more completely. The improved combustion results in a greater heat release in the furnace and a reduction of un-burnt fuel in the ash. All of these are desirable improvements.
NOx that is generated as part of combustion is considered a major pollutant. Hence reducing NOx is highly desired. NOx forms through two mechanisms. One is the oxidation of the N2 in the atmosphere at high temperatures while the other is through a series of chemical reactions that combine the N in the fuel with the O2 in the atmosphere. In order to control the NOx production, combustion engineers have staged the combustion. This is done by removing some percentage of the air in the burner zone and introducing it further in the furnace. To do this, multiple openings known as air ports are made in the boiler wall. These ports are referred to as Over Fired Air (“OFA”) ports. Typically these air ports are lined up vertically with the burners and are opposing OFA ports on the other side of the boiler. In the fuel-injection combustion rotation system, the certain OFA ports may be blocked off so that there are high air flow to OFA ports above the high flow burners and no flow to the OFA ports above the low flow burners.
Computation Fluid Dynamics (CFD) is widely used today to model the complex combustion and fluid flow processes in a boiler. The boiler shown in
In case 1 the high flow burners (HI) flowed 34% more coal than the base case while the low flow burners (LO) flowed 34% less. The ratio between the HI and LO flow burners was 2:1. In the case of the OFA the total number of ports used was reduced from 8 to 4 hence doubling the flow per port. The enhanced mixing results in a 73% reduction in carbon monoxide (CO) and an 81% reduction of unburnt carbon in the ash. However the NOx generation went up by 13%. This is due to the fact that more of the nitrogen came in contact with the air due to the better mixing.
To offset this more of the secondary (2RY) air was move to the OFA resulting in a 159% increase in OFA. This results in substoicheometric conditions in the burner zone resulting in an higher CO at the superheater exit giving a 33% reduction versus 73% in case 1. As expected the NOx generation went down by 47% from the base case. These results show that the superior mixing of this I/O system allows one to hold the CO generation down while allowing one to move more air to the OFA elevation to reduce NOx. Without this type of aggressive mixing the CO generation will go up. This is well known to people working with combustion.
Turning now to the drawings, in which like numerals refer to similar elements throughout the figures,
The boiler 10 includes a pair of opposing boiler walls 11, 12 extending in the “x” direction that support a number of opposing burners 20 that inject a mixture of air and fuel, such as pulverized coal, oil or natural gas, into the combustion section of the boiler. The boiler walls also support a number over-fire air (“OFA”) ports 22 that inject air into the combustion section of the boiler above the level of the burners. The burners 20 and OFA ports 22 on opposing sides of the boiler in a conventional boiler are stacked in vertical columns directly across from each other. The lower row of burners is sometimes referred to as the primary (1RY) burners, the next level is sometimes referred to as the secondary (2RY) burners, and the upper level is sometimes referred to as the tertiary (3RY) burners. In a boiler with four levels of burners, the lower pair of rows may be referred to as the primary (1RY) burners, and the upper pair of rows may be referred to as the secondary (2RY) burners.
In the conventional fuel injection boiler, the burners and OFA ports on the first wall 11 are positioned directly across from a mirror-image set of burners and OFA ports on the opposing wall 12, and each burner and OFA port is directed horizontally, parallel to the “z” direction at various vertical levels. In addition, each opposing pair of burners is typically operated at the same injection rate, which results in a “balanced” injection profile. Each opposing pair of OFA ports is also operated at the same injection rate in the balanced injection profile. This results in a non-rotating combustion mass that travels inward toward the middle of the boiler and upward toward the heat exchangers, as shown in
The heat exchanger section 14 at the top of the boiler 10 has multiple wing walls also known as division panels 24 that come off the front walls. These act like flow straighteners that tend to destroy any rotation in the flow gas. Due to a relatively short distance from the OFA ports 22 ports to the bottom of the wing walls in a typical fuel-injection boiler, there is insufficient space to stack more than one or two levels of OFA ports between the burners and the division panels. Therefore, it is not possible to use the OFA ports alone to impart significant rotation to the combustion mass, as described for certain chemical recovery boilers in U.S. Pat. No. 7,185,594.
As shown in
As shown on
Referring to
It should be appreciated that two vortices can be created using high and low flow burner jet flows in a boiler with four columns of burners as shown in
More specifically,
This same technique can be expanded to a boiler with eight columns of burners and OFA ports on opposing boiler walls.
For a new plant or a plant in which physical modifications can be made, staggered burner placement can also be used to rotate the combustion mass, which can reduce the number of columns of burners required to produce the same number of vortices. For this technique, the opposing burners and OFA are not directed directly at each other, but are instead offset to induce mixing in the combustion mass. The burners and OFA ports may be strategically located horizontally (x direction), vertically (y direction), or both horizontally and vertically in addition to varying the flow rates (z direction). Strategic placement of burners can eliminate the need for low flow burners and associated piping and support structures. For example,
This same technique can be expanded to a boiler with any number of columns of burners and OFA ports on opposing boiler walls.
In addition to the techniques described above, one or more of the burners and OFA jets may be injected into the boiler at a vertically and/or horizontally tilted angle to impart desired mixing in the combustion mass. Angling the burners can be implemented in combination with staggered columns and/or flow rate adjustment to further induce mixing of the combustion mass. Examples of burner and OFA jets that are tilted horizontally (in the x-z plane) are shown in
As another design option, the angle of burner and/or OFA injection can be varied from port-to-port in the vertical direction as shown in
As an alternative to, or addition to, the combustion rotation techniques described above, the burner and OFA jets may also be tilted or angled vertically (in the y-z plane) as shown in
Those skilled in the art will appreciate that the basic concept of adjusting the burner flow rates, positions, injection angles, and nozzle rotation to rotate and otherwise mix the combustion mass may be implemented with a range of different specific burner and OFA port configurations. Those conceptual examples shown in the figures are merely illustrative. In general, the equipment required to implement these combustion rotation techniques include an air/fuel mixture and fuel injection flow rate controller for each burner to be controlled with flow rate adjustment, a fuel injection flow rate controller for each OFA port to be controlled with flow rate adjustment, jet nozzle rotating equipment for each burner and OFA port to be rotated, and jet pointing equipment for each burner and OFA port to be directionally controlled. Jet nozzles may be rotated with motor driven gear assemblies. The jet pointing equipment may include mounting structures for supporting the burner or OFA jet in a desired orientation. Directional nozzles may also be use to direct burner or OFA jets in desired directions. The directional nozzles may be rotated with motor driven gear assemblies to change the pointing directions of the jets. In general, the mounting structures and nozzles may be fixed, in which case they are physically changed to make adjustments, or these structures may be manually adjustable or motorized for remotely controlled adjustment while the boiler is in operation.
In addition, all of the injection parameters illustrated above can be changed from burner to burner and OFA port to OFA port as desired to impart mixing and rotation to the combustion mass. For example, the positions, flow rates, and angles of injection for the burners and the OFA ports can selected as design considerations for a new plant. In addition, most of these parameters can be changed for an existing plant, in some cases requiring equipment upgrades such as jet pointing equipment. Once control equipment is in place for some or all of these parameters, some or all of the parameters can be changed while the boiler is on operation, for example by turning burner and OFA jets on and off, adjusting the flow rates, and adjusting injection angles. One or more of these parameters can also be changed continually or continuously (modulated) in accordance with predefined patterns, measured performance characteristics, and/or feedback signals.
The fuel mixture supplied to the burners and boiler cleaning equipment, such as water canons and sootblowers, can also be controlled in accordance with predefined patterns, measured performance characteristics, and/or feedback signals. As shown in
More specifically,
Claims
1. A combustion rotation system in or for an industrial fuel-injection boiler having a combustion section, comprising:
- a boiler having first and second opposing walls;
- a plurality of burners, each burner supported on the first or second boiler wall and configured for injecting a mixture of fuel and air into the boiler;
- wherein each burner has an associated fuel-injection flow rate controller; and
- wherein flow rate controllers are set to impart an unbalanced fuel-injection profile to induce multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
2. The combustion rotation system of claim 1, wherein:
- the burners have locations on the first and second boiler walls;
- the burners locations on the first boiler wall are directly opposing the burner locations on the second boiler wall;
- the burners on each boiler wall are arranged into inboard columns and outboard columns;
- the flow rate controllers are set to induce an unbalanced fuel-injection profile between the inboard columns and outboard columns on the first boiler wall;
- the flow rate controllers are set to induce an unbalanced fuel-injection profile between the inboard columns and outboard columns on the second boiler wall;
- the flow rate controllers are set to induce an unbalanced fuel-injection profile between the inboard columns on the first boiler wall and the inboard columns on the second boiler wall; and
- the flow rate controllers are set to induce an unbalanced fuel-injection profile between the outboard columns on the first boiler wall and the outboard columns on the second boiler wall.
3. The combustion rotation system of claim 1, wherein:
- the burners on each boiler wall are arranged into columns;
- each column of burners has one or more over-fire air ports located above the column of burners;
- each over-fire air ports has an associated flow rate controller; and
- the over-fire air port flow rate controllers are set to impart an unbalanced air injection profile consistent with the unbalanced fuel-injection profile imparted by the fuel-injection rate controllers to assist the burners in inducing the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
4. The combustion rotation system of claim 1, wherein:
- the burners have locations on the first and second boiler walls;
- the burners locations on the first boiler wall are directly opposing the burner locations on the second boiler wall;
- the burners on each boiler wall are arranged into columns;
- the number of columns on each boiler wall is four and the number of rotational vortexes is two, or the number of columns on each boiler wall is six and the number of rotational vortexes is three, or the number of columns on each boiler wall is eight and the number of rotational vortexes is four.
5. The combustion rotation system of claim 1, further comprising:
- a plurality of sensors for measuring boiler parameters; and
- a master controller for adjusting the fuel injection profile in response to the measured boiler parameters.
6. The combustion rotation system of claim 1, further comprising:
- a plurality of sensors for measuring boiler parameters; and
- a master controller for activating boiler cleaning equipment in response to the measured boiler parameters.
7. The combustion rotation system of claim 1, wherein:
- each burner has an associated fuel-injection lateral location;
- wherein the fuel-injection lateral locations on the first boiler wall are laterally offset from the fuel-injection lateral locations on the second boiler wall to assist in the inducement of the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
8. The combustion rotation system of claim 1, wherein:
- each burner having an associated fuel-injection direction;
- wherein one or more of the fuel-injection directions are horizontally tilted to assist in the inducement of the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
9. The combustion rotation system of claim 1, wherein:
- each burner has an associated fuel-injection direction;
- wherein one or more of the fuel-injection directions are vertically tilted to assist in mixing of the combustion mass inside the combustion section of the boiler.
10. The combustion rotation system of claim 1, wherein:
- the burners on each boiler wall are arranged into columns;
- the fuel-injection flow controllers are set to impart a vertically unbalanced fuel injection profile along one or more of the columns to assist in mixing of the combustion mass inside the combustion section of the boiler.
11. A combustion rotation system in or for an industrial fuel-injection boiler having a combustion section, comprising:
- a boiler having first and second opposing walls;
- a plurality of burners, each burner supported on the first or second boiler wall and configured for injecting a mixture of fuel and air into the boiler;
- wherein each burner has an associated fuel-injection lateral location;
- wherein the fuel-injection lateral locations on the first boiler wall are laterally offset from the fuel-injection lateral locations on the second boiler wall to induce multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
12. The combustion rotation system of claim 11, wherein:
- each burner has an associated fuel-injection flow rate controller; and
- the flow rate controllers are set to impart an unbalanced fuel-injection profile to assist in the inducement of the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
13. The combustion rotation system of claim 12, wherein:
- each burner having an associated fuel-injection direction; and
- one or more of the fuel-injection directions are horizontally tilted to assist in the inducement of the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
14. The combustion rotation system of claim 11, wherein:
- each burner has an associated fuel-injection direction;
- one or more of the fuel-injection directions are vertically tilted to assist in mixing of the combustion mass inside the combustion section of the boiler.
15. The combustion rotation system of claim 11, wherein:
- the burners on each boiler wall are arranged into columns;
- the fuel-injection flow controllers are set to impart a vertically unbalanced fuel injection profile along one or more of the columns to assist in mixing of the combustion mass inside the combustion section of the boiler.
16. A combustion rotation system in or for an industrial fuel-injection boiler having a combustion section, comprising:
- a boiler having first and second opposing walls;
- a plurality of burners, each burner supported on the first or second boiler wall and configured for injecting a mixture of fuel and air into the boiler;
- wherein each burner has an associated fuel-injection direction;
- wherein the fuel-injection directions are set to induce multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
17. The combustion rotation system of claim 16, wherein:
- wherein each burner has an associated fuel-injection lateral location;
- wherein the fuel-injection lateral locations on the first boiler wall are laterally offset from the fuel-injection lateral locations on the second boiler wall to induce multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
18. The combustion rotation system of claim 16, wherein:
- each burner has an associated fuel-injection flow rate controller; and
- the flow rate controllers are set to impart an unbalanced fuel-injection profile to assist in the inducement of the multiple rotational vortexes in the combustion mass inside the combustion section of the boiler.
19. The combustion rotation system of claim 16, wherein one or more of the fuel-injection directions are vertically tilted to assist in mixing of the combustion mass inside the combustion section of the boiler.
20. The combustion rotation system of claim 16, wherein:
- the burners on each boiler wall are arranged into columns;
- the fuel-injection flow controllers are set to impart a vertically unbalanced fuel injection profile along one or more of the columns to assist in mixing of the combustion mass inside the combustion section of the boiler.
Type: Application
Filed: Sep 29, 2009
Publication Date: Mar 31, 2011
Inventor: M. Ishaq Jameel (Beaverton, OR)
Application Number: 12/569,228
International Classification: F23C 5/32 (20060101);