1. Field of the Invention
The invention relates to a method and apparatus for controlling operation of a furnace-based-system, and specifically relates to a method and apparatus for optimizing combustion within a furnace to minimize unwanted byproduct emissions by relating a concentration of one or more unwanted byproducts exhausted through a zone of an exhaust portion of the furnace to combustion conditions in a primary zone within the furnace.
2. Discussion of Prior Art
In general, tangentially-fired (“T-fired”) boilers include a furnace in which a combination of a combustible fuel and air is combusted to generate heat for producing steam that can be used for any desired purpose such as driving a steam turbine to produce electricity for example. The combustible fuel and air are introduced into in a horizontal furnace plane within the furnace from multiple locations about the perimeter of the furnace in such a manner that the fuel and air are directed tangentially to a focal region in the furnace plane within the furnace of the boiler. The focal region is substantially concentric with the furnace, resulting in the formation of a spiraling fireball from combustion of the fuel and air mixture about the focal region within the furnace. T-fired boilers promote thorough mixing of the combustible fuel and air, stable flame conditions within the furnace of the boiler and long residence time of the combustion gases in the furnace.
Ever more stringent state and federal environmental regulations require emissions from T-fired boilers to include fewer unwanted byproducts than were previously allowed. Unwanted byproducts such as oxides of nitrogen (“NOx”), carbon monoxide (“CO”), and possibly other byproducts such as unburned carbon (commonly expressed as loss-on-ignition or “LOI”) must be kept below limits established by these regulations. Traditional boiler control systems have relied upon the monitoring of the exhaust from the furnace as a whole (i.e., the collective bulk exhaust resulting from operation of all burners operating simultaneously) to detect unacceptable levels of unwanted byproducts. A combustion anomaly was said to exist when the levels of one or more unwanted byproducts surpassed a predetermined limit for that byproduct. Based on the measured quantity of the unwanted byproduct in the collective exhaust the supply of fuel and/or air to the entire array of burners was adjusted in an attempt to operate the boiler within regulatory limits. Such control methods fail to consider the individual contribution of each burner and/or air injector to the combustion anomaly.
More recent attempts have utilized a separate sensor at the exhaust of the T-fired boiler for each individual burner and/or individual air injector. Complex computer models are required to trace the quantities of byproducts sensed from each individual sensor back to its respective individual burner and/or air injector. Developing the required computer model to perform the calculations for tracing sensed quantities back to contributions from each individual burner and/or air injector is very time consuming and expensive. Further, the computer models aimed at identifying the precise contribution of each burner and/or air injector to a quantity sensed by the respective sensor may be inaccurate due to the myriad of other contributing factors that can affect combustion and the production of unwanted byproducts. A different computer model may also be required for a boiler for various different operating conditions, requiring many different computer models to control operation of the boiler under all of the different operating conditions and adding to the complexity.
Accordingly, there is a need in the art for a method and apparatus for monitoring and controlling operation of a furnace to minimize unwanted byproduct emissions. The method and apparatus can optionally relate a byproduct quantity sensed within an exhaust zone back to a zone within a furnace that is a primary contributor to the sensed byproduct quantity.
The following summary presents a simplified summary in order to provide a basic understanding of some aspects of the systems and/or methods discussed herein. This summary is not an extensive overview of the systems and/or methods discussed herein. It is not intended to identify key/critical elements or to delineate the scope of such systems and/or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
One aspect of the present invention provides a method of optimizing operation of a furnace within a system to control emission of an unwanted byproduct. The method includes associating each of a plurality of different furnace zones inside of the furnace with at least one exhaust zone from among a plurality of different exhaust zones through which an exhaust composition travels to exit the furnace. The method includes receiving, from at least one of a plurality of sensors in communication with each of the plurality of different exhaust zones, a signal indicative of an amount of the byproduct in the exhaust composition exiting the furnace through at least one of the exhaust zones that is in excess of a predetermined limit. The method includes identifying an offending furnace zone from among the plurality of furnace zones as a function of the signal from the at least one of the plurality of sensors. The offending furnace zone includes an oxygen level contributing to the amount of the byproduct in excess of the predetermined limit. The method includes initiating a relative adjustment of at least one of: an amount of oxygen being introduced into the offending furnace zone, and an angular orientation of an oxygen injector introducing oxygen into the offending furnace zone relative to a focal region within the furnace.
Another aspect of the present invention provides a furnace-based system. The system includes a furnace which includes a plurality of burners arranged in an array for burning a combination including a combustible fuel and oxygen within the furnace. The system includes a plurality of overfire oxygen injectors for injecting overfire oxygen into the furnace in a direction tangential to a focal region within the furnace, wherein the overfire oxygen injectors are adjustable to adjust the direction that the overfire oxygen is injected into the furnace relative to the focal region. The system includes an exhaust port for exhausting an exhaust composition from the furnace. The exhaust port includes a plurality of exhaust zones. The system includes a plurality of sensors that are operable to sense an amount of an unwanted byproduct in the exhaust composition exiting the furnace through the plurality of exhaust zones. The system includes a controller that is operable to receive signals from the plurality of sensors indicative of the amount of the unwanted byproduct in the exhaust composition exiting through at least one of the exhaust zones and to identify, based on the signals received from the plurality of sensors, a furnace zone with an oxygen level that is contributing to the amount of the unwanted byproduct sensed exiting through the at least one of the exhaust zones.
Another aspect of the present invention provides a system for generating electric power. The system includes a steam-driven turbine and a boiler for producing steam to drive the turbine. The boiler includes a furnace. The furnace includes a plurality of burners arranged in an array for burning a combination including a combustible fuel and oxygen within the furnace. The system includes a plurality of overfire oxygen injectors for injecting overfire oxygen into the furnace in a direction tangential to a focal region within the furnace, wherein the overfire oxygen injectors are adjustable to adjust the direction that the overfire oxygen is injected into the furnace relative to the focal region. The system includes an exhaust port for exhausting an exhaust composition from the furnace. The exhaust port includes a plurality of exhaust zones. The system includes a plurality of sensors that are operable to sense an amount of an unwanted byproduct in the exhaust composition exiting the furnace through the plurality of exhaust zones. The system includes a controller that is operable to receive signals from the plurality of sensors indicative of the amount of the unwanted byproduct in the exhaust composition exiting through at least one of the exhaust zones and to identify, based on the signals received from the plurality of sensors, a furnace zone with an oxygen level that is contributing to the amount of the unwanted byproduct sensed exiting through the at least one of the exhaust zones.
The foregoing and other aspects of the invention will become apparent to those skilled in the art to which the invention relates upon reading the following description with reference to the accompanying drawings, in which:
a is a cross-sectional view of the furnace shown in
b is a cross-sectional view of the furnace shown in
c is a cross-sectional view of the furnace shown in
Example embodiments that incorporate one or more aspects of the invention are described and illustrated in the drawings. These illustrated examples are not intended to be a limitation on the invention. For example, one or more aspects of the invention can be utilized in other embodiments and even other types of devices. Moreover, certain terminology is used herein for convenience only and is not to be taken as a limitation on the invention. Still further, in the drawings, the same reference numerals are employed for designating the same elements.
An example embodiment of a power generating system 10 is shown schematically in
A second fan 30 supplies secondary air to the burners 28 through an air conduit 32 and a windbox 33. The secondary air is heated before being introduced into the furnace 18 upon passing through a regenerative heat exchanger 34, transferring heat from a boiler exhaust line 36 to the air conduit 32. Secondary air can optionally be introduced into the furnace 18 in addition to the primary air when there is insufficient oxygen present within the furnace 18 to allow complete combustion of the fuel being burned, a condition referred to herein as an oxygen deficiency. The secondary air is introduced into the furnace 18 in a region referred to herein as a combustion zone 42, in which the combination of the coal or other combustible fuel and oxygen from the air introduced into the furnace 18 is combusted. A region vertically above the combustion zone within the furnace 18 is utilized to supply surplus oxygen, referred to herein as overfire oxygen, to promote complete oxidation of partially oxidized byproducts such as oxide CO to fully oxidized byproducts such as CO2, for example. This region in which overfire oxygen is introduced is referred to herein as the overfire region 44.
As shown in
A plurality of second oxygen injectors 49 can be adjustably coupled at various locations about the inner perimeter of the furnace 18, allowing the second oxygen injectors 49 to pivot relative to a focal region 60 (
The boiler 12 also includes a network of actuators that are operable to control at least one of a process input and a boiler configuration to affect the combustion occurring within the furnace 18. The actuators can be adjusted to regulate the process inputs such as a flow rate of fuel and/or air such as the SOFA, for example, into the furnace 18. For instance, valves 41 (
According to alternate embodiments, the configuration of the boiler 12 itself can be adjusted instead of, or in addition to the actuators in an attempt to bring the values of the operating conditions to within the predetermined range of suitable values. For example, the furnace 18 can optionally be provided with an additive injector 55 that penetrates a wall of the furnace 18, thereby extending into the furnace 18 for injecting a desired additive from a reservoir 57 into the furnace 18, and optionally into the primary combustion zone. A myriad of additives (such as a combustion additive, or magnesium oxide for slag) could be used, and any specifics about additives should not be considered to be a limitation upon the invention. The additive can be injected into the furnace 18. The angle at which the additive injector 55 introduces the additive into the furnace 18 can be adjusted to affect the operating conditions within the furnace 18.
The process input(s) associated with each individual burner 28 can optionally be adjusted independent of the process input(s) of other burners 28 to affect the combustion performance of the individual burners 28. Likewise, the boiler configuration, such as the injection angle of a first additive injector 55 can be adjusted independently of another additive injector (not shown). This independent adjustment of the boiler configuration can primarily affect the combustion performance of a burner 28 adjacent to the first additive injector 55 without significantly affecting the combustion performance of another burner 28 spatially separated from the first additive injector 55. Thus, the combustion performance of each of the burners 28 can be adjusted and corrected individually to promote substantially-balanced combustion.
A flue gas including gaseous combustion products such as fully combusted fuel in the form of CO2, in addition to undesirable byproducts such as NOx and CO compositions, for example, travels in a substantially vertical direction upward within the furnace 18. The flue gas travels upward beyond a nose 35 that protrudes into an interior chamber defined by the furnace 18, and then generally vertically downward through an exhaust port 37 leading to the exhaust line 36. The exhaust port 37 is said to be “downstream” of the burners 28 as the flue gas travels from the combustion zone 42 and overfire region 44 to the exhaust port 37. As shown in
A furnace plane 72 portion of the furnace 18 shown in
With continued reference to
A plurality of sensors 70 can be positioned at various locations adjacent to the exhaust port 37 for sensing an amount of the byproduct in the exhaust gasses exiting the furnace 18 through at least one of the exhaust zones 78 that is in excess of a predetermined limit. For example, the sensors 70 can be operable to sense an amount of CO, or a concentration of CO within the exhaust gasses exiting the furnace 18 through each of the exhaust zones 78. In the illustrative embodiments described herein the sensors 70 are operable to sense an amount or concentration of CO, and can sense when the amount or concentration of CO exceeds a predetermined upper limit deemed acceptable to be discharged from the furnace 18. However, alternate embodiments can optionally utilize sensors 70 operable to sense any operating parameter such as temperature, pressure, or the amount or concentration of any other byproduct included in the exhaust gasses exiting the furnace 18 through the exhaust port 37. However, for the sake of brevity the examples discussed below include a CO sensor 70 for sensing an amount of CO included in the exhaust gasses.
Sensed amounts of CO above a predetermined upper limit within one or more of the exhaust zones 78 is indicative of an oxygen depletion in the corresponding furnace zone(s) 76. Referring once again to the embodiment shown in
An example of a method of optimizing operation of a boiler to control emission of an unwanted byproduct is described with reference to
In general, the controller 90 (
a-6c also illustrates the relative adjustment of the angular orientation of the second oxygen injector(s) 49 during optimization of boiler operation. The adjustment of the angular orientation of the second oxygen injector(s) in the direction of arrow 102 in
a will be described as the starting configuration of the furnace 18. In this configuration, each of the second oxygen injectors 49 introducing the SOFA into the furnace 18 has an angular orientation (indicated by arrows 104) to tangentially supply the SOFA to the focal region 60. In
To counter the flow of oxygen within furnace zone I and promote substantially-uniform oxidation of CO across the furnace plane 72, the sensor(s) 70 transmit a signal indicative of this sensed condition to be received by the controller 90 (
According to alternate embodiments, the adjustment described above as being initiated by the controller 90 can optionally be displayed via the display 88 (
The furnace 18 continues to operate and an excess amount of CO exiting through exhaust zone I is again sensed. In this instance, however, the amount of CO is now increasing within exhaust zone I in the direction of arrow 120 as shown in
Similar adjustments continue to occur during operation of the furnace 18, and for each of the furnace and exhaust zones 76, 78 to ensure a substantially uniform distribution of oxygen within the overfire region 44 disposed vertically above the combustion zone 42 (
The invention has been described with reference to the example embodiments described above. Modifications and alterations will occur to others upon a reading and understanding of this specification. Example embodiments incorporating one or more aspects of the invention are intended to include all such modifications and alterations insofar as they come within the scope of the appended claims.