Patent Application
20110056416
1. Field of the Invention
The invention relates generally to a method and apparatus for controlling operation of a boiler that generates steam to drive a turbine or provide process steam or heating, and more specifically to method and apparatus for monitoring and controlling combustion within a boiler by sensing a plurality of operating conditions at a common location with a common sensor.
2. Description of Related Art
One method of generating electricity includes driving a turbine generator with steam. A boiler for generating the steam commonly includes a furnace with an array of individual burners for burning the hydrocarbon fuel in the presence of oxygen to raise the temperature of water and produce the steam to be delivered to the turbine. The combustion performance of an individual burner provided to the furnace can affect the combustion performance locally within the furnace, and thereby affect the overall performance of the boiler as a whole.
If one or more of the burners is not operating in an optimal manner, a condition referred to as a combustion anomaly, the boiler can emit unsatisfactory levels of by products such as oxides of nitrogen (“NOX”), carbon monoxide (“CO”), mercury (“Hg”), and possibly other byproducts such as unburned carbon (commonly expressed as loss-on-ignition or “LOI”). The combustion anomaly can also result in fuel-rich gases and high local gas temperatures that can contribute to the formation of difficult to remove ash deposits called slag, or can cause boiler tube-wall wastage through corrosion and thermal fatigue. In such circumstances the offending burner(s) must be singled out from the array of burners, and then adjusted to optimize performance of the boiler. Once the offending burner(s) is identified, the performance of that burner can be optimized by means of combustion control, which can include varying the flow rate at which the hydrocarbon fuel is introduced to the burner, the flow rate at which air is introduced to the burner, the rotational velocity component, i.e. spin, of the feed, the angle of injection, an additive level or other suitable variable that can rectify the combustion anomaly.
Traditional boiler control systems have relied upon the monitoring of the exhaust from the furnace as a whole (i.e., the collective exhaust resulting from operation of all burners operating simultaneously) to detect combustion anomalies. In response to the detection of a combustion anomaly based on a measured quantity from this collective exhaust the supply of fuel and/or air to the entire array of burners could be adjusted in an attempt to optimize operation of the boiler. Such control methods fail to consider the local effects each burner has on the boiler, and fails to attribute the individual contribution of each burner to the combustion anomaly.
More recently, attempts have been made to trace a combustion anomaly back to one or more offending burners, from among the entire array of burners that is/are the primary cause of the combustion anomaly. Determining the presence of a combustion anomaly and identifying the offending burner(s), however, is typically not determined as a function of a single operating condition, such as a measured temperature, at a particular location within the boiler. Instead, to identify, or at least narrow down the location of the offending burner(s), such control methods rely on a plurality of measured operating conditions sensed at various different locations within the boiler.
Arrays of individual sensors are disposed at various different locations throughout the boiler to monitor different operating conditions at each of those different locations. For example, the concentration of carbon monoxide (“CO”) has been monitored by an array of sensors disposed at an exhaust port of the boiler downstream of the furnace exit. Further, an array of temperature sensors has been disposed adjacent to a nose of the furnace provided to the boiler to monitor the temperatures near the burners. The temperatures near the burners to which the temperature sensors are exposed are typically too high for the CO concentration sensors to be co-located with the temperature sensors. Thus, the array of CO concentration sensors is spatially located away from the temperature sensors at another, distant location of the boiler where they are subjected to much lower temperatures that will not damage the CO concentration sensors. But in order to consider both the measured CO concentration and the measured temperature at a common location in the boiler to evaluate a combustion anomaly, one of these measured operating conditions was required to be mapped to correspond to an equivalent value at the location of the other operating condition. In other words, the CO concentration measured by each CO concentration sensor adjacent the exhaust port, for example, was adjusted to correspond to the value of the CO concentration that could be expected to be measured at the location of each respective temperature sensor. Thus, the measured temperature and the equivalent CO concentration at a common location in the boiler could be used to determine whether a combustion anomaly has occurred, and if so, which of the burners is contributing to the combustion anomaly.
Such attempts have improved boiler control over the traditional methods of controlling the boiler solely on the CO concentration at the exhaust port. But the mapping of a sensed operating condition from one location to another location within the boiler introduces a degree of error in evaluating a combustion anomaly, limiting the ability to effectively identify the offending burner(s). Further, the mapping requires the use of many mathematical models and robust control equipment, making boiler control expensive and complex.
Accordingly, there is a need in the art for a method and apparatus for controlling operation of a boiler to optimize performance thereof. The method and apparatus can allow for sensing a plurality of operating conditions at a common location within the boiler to detect a combustion anomaly and allow for optimization of boiler operation.
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.
According to one aspect, the invention provides a method of controlling operation of a system that includes a boiler with a plurality of burners. The method includes sensing a plurality of operating conditions at a first common location along the boiler. At least one of the plurality of operating conditions sensed at the first common location is indicative of a combustion anomaly occurring during operation of the boiler. The method includes tracing the combustion anomaly back to an offending burner that is at least partially responsible for the combustion anomaly based on a model that takes into consideration at least two of the plurality of operating conditions sensed at the first common location. The method includes adjusting at least one of a process input and a boiler configuration to establish a desired value of the operating conditions at the first common location.
According to another aspect, the invention provides a system that includes a steam-driven turbine and a boiler. The boiler includes a plurality of burners arranged in an array to burn a hydrocarbon fuel. The system includes a plurality of sensors, each adapted to sense a plurality of operating conditions at a common location within the boiler and to transmit a signal indicative of a combustion anomaly when one or more of the operating conditions falls outside of a predetermined range of suitable values indicative of desired combustion. The system includes an actuator for controlling at least one of a process input and a boiler configuration to affect operation of at least one of the burners. The system includes a controller in communication with the plurality of sensors to receive the signals indicative of the combustion anomaly, wherein, responsive to receiving the signals the controller traces the one or more operating conditions outside of the predetermined range of suitable values to identify an offending burner contributing to the combustion anomaly and controls the actuator to adjust the at least one of the process input and the boiler configuration to bring the one or more operating conditions into the predetermined range of suitable values.
According to yet another aspect, the invention provides a system including a steam-driven turbine and a boiler. The boiler includes a plurality of burners arranged in an array to burn a hydrocarbon fuel. The system includes a plurality of non-invasive sensors each adapted to remotely sense a plurality of operating conditions at a common location within the boiler and to transmit a signal indicative of a combustion anomaly when at least one of the operating conditions falls outside of a predetermined range of suitable values indicative of desired combustion. The system includes a controller in communication with the plurality of non-invasive sensors to receive the signals indicative of the combustion anomaly. The controller includes a computer-accessible memory storing a model that relates the operating conditions falling outside of the predetermined range of suitable values from one or more of the sensors to at least one offending burner contributing to the combustion anomaly. The system includes an actuator to be controlled by the controller for controlling at least one of a flow rate of the hydrocarbon fuel introduced to the offending burner, a flow rate of air introduced to the offending burner, a flow rate of an additive introduced to the boiler through an injector, and an angle of the injector for introducing the additive into the boiler to bring the operating conditions into the predetermined range of suitable values.
The invention may take physical form in certain parts and arrangement of parts, embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:
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.
A method of optimizing operation of a fuel fired boiler is described below in detail. The method includes the use of a plurality of different sensors at different spatial locations within a fuel fired boiler furnace to track in-furnace combustion conditions and the relative differences between the performance of individual burners. Each of the sensors can be used to sense a plurality of operating conditions at the different spatial locations to make adjustments to individual burners and yield an optimized boiler performance. The optimized operating burner conditions can vary from one burner to another. This means that one or both of the air flow and fuel flow, for example, can vary from burner to burner and that the air to fuel ratio to individual burners is not predetermined. Rather, each burner can be individually biased and adjusted to meet boiler performance objectives as indicated by the in-furnace sensors as described in detail below. Optimized performance includes, for example, reduced NOx emissions, reduced LOI emissions, increased efficiency, increased power output, improved superheat temperature profile, reduced slagging, reduce waterwall wastage, and/or reduced opacity relative to un-optimized operation of the boiler. Corrective actions such as burner adjustments, boiler configuration adjustments, or both can include, for example, fuel flow, air flow, fuel to air ratio, burner register settings, overfire airflows, the orientation of injectors 55 for introducing an additive (including air or fuel) into the furnace, and other furnace input settings.
Referring to the drawings,
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 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 into the furnace 18 to bring the operating conditions sensed by an array of sensors 38 (
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 a region adjacent to the burners 28 and then to the exhaust port 37 in a direction generally indicated by arrow 39 shown in
Substantially-balanced combustion is achieved when a flue gas has substantially-uniform operating conditions across the cross-section of the exhaust port 37 of the furnace 18 as described below with reference to
Referring also to
Each sensor 38 can optionally be any non-invasive sensor capable of sensing a plurality of operating conditions at a common location within the furnace 18 without physically protruding into the interior of the furnace, and without physically contacting or consuming combustion products to sense the operating conditions. Thus, the non-invasive embodiment of the sensor can measure the plurality of operating conditions at the common location within the furnace from a remote spatial location. Each sensor 38 can sense a qualitative or quantitative value of two or more operating conditions at substantially the same location within the furnace 18, which can optionally be a location where the sensor would be damaged when exposed to the operating conditions if physically located at that location. For example, if the operating conditions to be sensed at the common location include a temperature and a quantity of carbon monoxide, the temperature sensed at the common location is greater than a maximum temperature that a carbon monoxide sensor can withstand.
The sensors 38 can also transmit signals indicative of a combustion anomaly when one or more of the sensed operating conditions falls outside of a predetermined range of suitable values indicative of a desired, balanced combustion of the fuel-air mixture. The sensed value of the operating condition can be obtained from absolute measurement, relative measurement, and drawing from analysis of fluctuations in combustion quality. Examples of suitable non-invasive sensors 38 for sensing the operating conditions include, but are not limited to, a quantum cascade laser (“QCL”) paired with an optical detector 45 for receiving laser light 51 from the QCL, tunable diode laser or other optical sensor, a radiation sensor, and any other sensor that can measure operating conditions at a common location remotely located from the sensor itself.
Although the sensors 38 are described in detail below as including a combination of QCL and optical detector 45, other embodiments can include any suitable sensor that can withstand the conditions at the common location where the plurality of operating conditions is to be sensed. Further, two sensors could optionally be co-located according to alternate embodiments to sense their respective operating condition at the common location. Examples of such alternate embodiments of sensors 38 include, but are not limited to LOI sensors, temperature sensors, CO sensors, CO2 sensors, NOx sensors, O2 sensors, THC sensors, volatile organic compounds (“VOC”) sensors, sulfur dioxide (SO2) sensors, heat flux sensors, radiance sensors, opacity sensors, emissivity sensors, moisture sensors, hydroxyl radicals (OH) sensors, sulfur trioxide (SO3) sensors, particulate matter sensors, and emission spectrum sensors.
A method of controlling operation of the system 10 specific to the boiler 12, which includes a plurality of burners 28, in accordance with an embodiment can be understood with reference to
The value of the operating conditions as determined by the QCL and its respective optical detector 45 can be recorded in a computer-accessible memory at 105. Recording the value of the operating conditions preserves the sensed value of the operating conditions for comparison with those sensed values during a subsequent iteration of the present method to determine whether the combustion anomaly has been improved.
At least one of the plurality of operating conditions (both operating conditions in the present example) sensed at the first common location can be compared at step 107 to a range of predetermined acceptable values for those operating conditions. If the sensed value of each operating conditions falls within the respective predetermined ranges of acceptable values, the boiler 12 is operating properly and substantially-balanced combustion is achieved. Combustion is maintained at step 109 and the method returns to step 100 to continue monitoring of the operating conditions at the first common location.
If, however, it is determined at step 107 that one or more of the operating conditions falls outside the predetermined range of acceptable values for that operating condition, such a condition is indicative of a combustion anomaly occurring during operation of the boiler 12. During the combustion anomaly the flue gas exiting the exhaust port 37 of the furnace 18 of the boiler 12 does not exhibit substantially-balanced combustion.
At step 110 in
The value of each of the sensed operating conditions can optionally be used in tracking the combustion anomaly back to the offending burner(s) 28, and can optionally be used to identify the one or more burners 28 providing the most significant contributions to the combustion anomaly. For instance, a burner 28 vertically aligned with a QCL embodiment of a sensor 38 and a respective optical detector 45 may contribute more significantly to an under-temperature condition at the common location where the temperature is measured than another burner 28 horizontally offset from the QCL and respectively optical detector 45. Further, if an amount of CO detected by the sensor 38 at the first common location where the temperature was also sensed exceeds a maximum allowable value, it can be determined that an oxygen deficiency exists within the furnace 18. Based on the fluid dynamics within the particular furnace configuration this oxygen deficiency can be traced back to one or more burners 28 that are operating without sufficient levels of oxygen.
In response to tracing the combustion anomaly back to an offending burner at step 110 in
The adjustment made at step 115 can be recorded at 117 to develop a real-time data model for correlating future deviations of the operating conditions sensed at the first common location within the furnace 18 to particular adjustments of process inputs and/or boiler configurations. The mathematical model can be updated in response to each adjustment to reflect the cause and effect of such adjustments on the operating conditions sensed at the first common location in the furnace 18 for subsequent iterations to correct future combustion anomalies.
To illustrate substantially-uniform operating conditions across the cross-section of the exhaust port 37 during substantially-balanced combustion, the exhaust port 37 in
The operating conditions of the flue gas exiting via each zone are affected differently by the combustion of each burner 28 at different spatial locations within the furnace 18. Thus, the adjustments to the process input and/or boiler configuration brought about by the method described above with reference to
The adjustment of the process input and/or boiler configuration as described with reference to
Finally, following yet another iteration of the method described with reference to
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.
