Patent Application
20140263772
Embodiments of the invention are directed to monitoring pulverizers and in particular to detecting a combustion-related condition in a pulverizer based on calculating a heat balance of the pulverizer.
Coal is used as a fuel in many power plants. Before the coal is introduced into the power plant it typically undergoes a pulverization process to reduce the size of the coal from relatively coarse chunks to a fine powder. This is done to increase the reactivity of the coal by increasing the effective surface area, to reduce surface moisture on the coal, and to make transportation of the coal into the furnace forming part of the power plant easier.
There are times during a pulverization process that the coal may ignite resulting in a fire inside a pulverizer. Fires can damage the pulverizer and cause safety risks to personnel, as well as causing delays in a power-providing system relying on the fine coal powder.
According to the aspects illustrated herein, there is provided a system for detecting a combustion-related condition in a pulverizer includes a pulverizer configured to receive coal chunks via an inlet, to grind the coal chunks into coal powder and to output the coal powder via an outlet. The system includes sensors configured to detect heat input characteristics supplied to the pulverizer and heat output characteristics emitted from the pulverizer. The system also includes a controller configured to determine, based on signals from the sensors, whether a combustion-related condition exists in the pulverizer based on a heat balance function including the heat input characteristics and the heat output characteristics.
According to the other aspects illustrated herein, a method for detecting a combustion-related condition in a pulverizer includes measuring, with sensors, input heat characteristics of a pulverizer and output heat characteristics of the pulverizer. The method also includes detecting a combustion-related condition in the pulverizer by performing a heat balance operation including the input heat characteristics and the output heat characteristics.
According to other aspects illustrated herein, a pulverizer control system inclused a processor configured to receive as inputs sensor signals corresponding to input heat characteristics of a pulverizer and output heat characteristics of the pulverizer, to determine whether a combustion-related condition exists in the pulverizer based on a heat balance equation including the input heat characteristics and the output heat characteristics, and to perform at least one of generating a signal indicating that a combustion-related condition exists in the pulverizer or controlling the pulverizer to take corrective action based on determining that the combustion-related condition exists in the pulverizer.
The above described and other features are exemplified by the following figures and detailed description.
Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:
A coal feed inlet 114, also referred to as a coal chunk inlet, coal inlet or inlet 114, extends into the housing 111 to allow coal chunks 141 to be inserted into the coal grinding bowl 115 in the housing 111. Drying and transport air is provided from an air duct 118 into the housing 111 which prevents ground coal powder 142 from falling down below the bowl and to direct the ground coal powder 142 up and away from the coal grinding bowl 115 towards a collection chute 112 and out a coal powder outlet 113. In addition, one or more additional air inlets may be provided to direct seal air flows into the housing 111, which keep the coal 141 and 142 from entering components such as bearings, gears and other moveable components under the bowl 115. From the coal powder outlet 113 the coal powder may be provided to a power generation system to burn the coal powder to generate electrical power, heat or any other type of power.
In embodiments of the invention, sensors 123a to 123f are positioned at multiple locations around the pulverizer 110 to detect characteristics of the pulverizer 110. In particular, the sensors 123a to 123f are configured to detect characteristics of the pulverizer 110 related to a heat balance algorithm or equation that represents heat sources supplied to the pulverizer 110 and heat emitted by the pulverizer 110. In
While some examples of sensors and sensor location have been provided in
The pulverizer control system 130 monitors and controls operation of the pulverizer 110. The monitoring system 131 may include processing circuitry that receives data from the sensors 123a to 123e and controls the drive assembly 117 via the motor control system 133 according to the sensor data as well as user inputs or control data from systems external to the pulverizer control system 130. A combustion detection system 132 receives as inputs the sensor data corresponding to heat, humidity and flow data, for example, and generates a heat balance algorithm based on the received sensor data, or feeds the received sensor data into a predetermined heat balance algorithm. If a predetermined imbalance or characteristic is detected in the heat balance algorithm, the combustion detection system 132 determines that there is a combustion-related condition in the housing 111. The combustion detection system 132 may generate a warning or notice to a user that there is a combustion-related condition, or the combustion detection system 132 may send control signals to the motor control system 133 and the intake/output control system 134 to automatically control the rotation of the drive assembly 117, to halt air inflow via the air inlet 118, to halt coal chunk 141 input via the coal chunk inlet 114 and to halt coal powder output from the coal powder outlet 113.
In the present specification and claims, the term “combustion-related condition” refers to combustion, such as smoldering or flame and to conditions identified as leading to combustion and being precursors of combustion in a pulverizer 110. Accordingly, the combustion detection system 132 detects conditions corresponding to an existing flame, such as an imbalance in a heat balance equation above a threshold corresponding to a flame, and the combustion detection system 132 detects combustion-related conditions that lead to flames in the pulverizer 110, such as high humidity levels at the outlets 113 of the pulverizer 110, the pulverizer 110 operating at a threshold coal-flow level that may lead to overflow of coal into the drive assembly 117 or any other combustion-related condition.
In one embodiment of the invention, the algorithm used to compute a heat balance or energy balance in the pulverizer 110 is as follows:
In this embodiment, m=mass flow of one or more of air, water vapor and coal, h=enthalpy of the air, water vapor, and/or coal and Q=energy flux, or change in energy. When there is no fire in the pulverizer 110, the net energy flux Q is zero. In one embodiment, the fire detection system determines that there is a flame in the pulverizer 110 when Q=+/−0.05. In one embodiment, to calculate the heat balance, the following are measured: dry air entering the pulverizer 110 via the inlet 114; water vapor in the air stream of the inlet 114, dry air of the drying and transport air stream at the inlet 118 and thermal energy contributed to the pulverizer 110 as a function of the grinding process.
Air enters the pulverizer 110 through several sources. These include hot air supplied via the mill inlet duct 114, or coal chunk inlet 114, and the drying and transport air introduced via the air inlet 118 to prevent infiltration of coal into the drive assembly 117. In an embodiment in which the pulverizer 110 operates under suction, ambient air from the coal chunk inlet 114 may infiltrate the drive assembly 117 components to replace seal air. The inlet air provided via the mill inlet duct 114, or coal chunk inlet 114, is drawn into the mill inlet duct from external sources. At least a portion of the air may be passed through a heat exchanger to raise its energy level of the air. The remainder of the mill inlet air is bypassed around the air heater and reintroduced as tempering air upstream of the mill inlet duct 114. Dampers on both a hot air stream and a tempering air stream control the total quantity of air to the mill while the relative quantities contributed by each is controlled based on the temperature measured at the mill outlet. The quantity and temperature of the air reaching the mill inlet duct 114 are measured so that their respective values are known.
The humidity ratio of air entering the inlet 114 and exiting the outlet 113 is measured, and the mass flow of water in the incoming air stream to the inlet 114 is determined as well as the mass flow of dry air in the incoming air stream to the inlet 114. In addition, the humidity of air entering the inlet 118 may also be added to the air entering the inlet 114 in the humidity ratio. Once this is known, the change in enthalpy of water vapor and dry air from the pulverizer inlet to pulverizer outlet temperatures can be determined. The sources of thermal energy into the pulverizer 110 have been identified and their respective contributions defined. The total energy into the pulverizer 110 is simply expressed as: Qin=ΔHa+Qgrind. This equation is the enthalpy of the total moist air stream entering the pulverizer 110 plus energy from the grinding.
Then, moisture evaporated from the surface of the coal may be measured by measuring outlet humidity (and based on the humidity ratio), the coal passing through the pulverizer 110 may be measured, such as by measuring the flow of coal chunks 141 into the pulverizer 110, and losses through the housing 111 may be measured, such as by temperature sensors 123b and 123c.
In embodiments of the invention, the pulverizer control system 130 may include any one computer or multiple computers interconnected via a network to monitor and control the pulverizer 110. The pulverizer control system 130 may include one or more processors and supporting logic and other circuitry, as well as memory and other computer-readable media that store computer programs to control operation of the pulverizer 110, to receive and analyze sensor signals and to detect fires in the pulverizer 110. Components of the pulverizer control system 130 may be connected to each other and to the pulverizer 110 via wires or wirelessly.
As discussed above, the pulverizer control system 130 and the combustion detection system 132 may detect conditions that may lead to fires prior to the fire being detected in the pulverizer 110. For example, the monitoring system 131 may detect a high humidity level at the outlet 113. The high humidity levels may lead to clumping of coal particles, which may lead to clogging of the outlet 113 or junctions and pathways downstream of the outlet 113, which may lead to fires. The pulverizer control system 130 may then generate a signal or message to warn of the humidity levels or potential fire, or may control the pulverizer 110 or external air supply systems to address the problem.
In another example, the pulverizer control system 130 may detect a flow of coal chunks 141 that is at a predetermined threshold corresponding to coal chunks 141 potentially falling out of the bowl 115 and into the drive system 117, which may in turn lead to fires. In particular, when the pulverizer 110 is operating at its drying capacity, high inlet temperatures and spillage may precede a fire. In such an embodiment, the pulverizer control system 130 may generate a warning or control the pulverizer 110 or external coal supply systems to address the fire to reduce the flow of coal into the pulverizer 110. While examples of preemptive fire-condition detection have been provided, embodiments of the invention encompass using sensors to detect any condition indicating a potential for fires and combustion in the pulverizer 110.
In block 302, input heat balance characteristics of the pulverizer are detected. Input heat balance characteristics include the temperature, humidity and flow rate of air entering the pulverizer with coal chunks and the temperature, humidity and flow rate of air entering the pulverizer from below the grinding bowl. Another input heat balance characteristic is the thermal energy contributed to the pulverizer as a function of the grinding process.
In block 303, output heat balance characteristics are sensed. Output heat balance characteristics include the temperature, humidity and flow rate of air leaving the pulverizer via an outlet, such as the outlet from which coal powder leaves the pulverizer. Other output heat balance characteristics include convection and radiation energy of the pulverizer.
In block 304, a combustion-related condition is detected based on applying the input heat balance characteristics and output heat balance characteristics in a heat balance algorithm. In one embodiment, the input and output heat balance characteristics are compared with each other, and a difference is compared to a threshold value. The threshold value may be selected to correspond to a value at which a fire is likely in the pulverizer. For example, in one embodiment, the threshold value corresponds to a difference, such as five percent, between the heat input characteristics and heat output characteristics. In such an embodiment, if a difference of five percent or greater is detected, then it may be determined that there is a fire in the pulverizer. In one embodiment, a difference greater than zero but less than five percent may be considered a combustion-related condition that should be monitered or addressed to prevent the occurance of a fire.
In block 305, the pulverizer is controlled based on the heat balance algorithm. For example, if it is determined that there is a fire or combustion-related condition in the pulverizer, inputs of air or coal may be halted, or outputs of air or coal may be halted.
Embodiments of the invention are directed to systems and apparatuses for detecting a combustion-related condition in a pulverizer and methods for detecting a combustion-related condition in a pulverizer. Embodiments are also directed to controllers, processors and other circuitry that detect combustion-related conditions in a pulverizer as well as computer-readable media that control a processor to detect a combustion-related condition in a pulverizer.
In one embodiment, a system for detecting a combustion-related condition in a pulverizer includes a pulverizer configured to receive coal chunks via an inlet, to grind the coal chunks into coal powder and to output the coal powder via an outlet. The system may include sensors configured to detect heat input characteristics supplied to the pulverizer and heat output characteristics emitted from the pulverizer. The system may also include a controller configured to determine, based on signals from the sensors, whether a combustion-related condition exists in the pulverizer based on a heat balance function including the heat input characteristics and the heat output characteristics.
In one embodiment, the system includes a grinding bowl in which the coal chunks are ground into the coal powder and a drying and transport air inlet located beneath the grinding bowl and configured to supply drying and transport air around the edges of the grinding bowl. In such an embodiment, the heat input characteristics measured by the sensors may include a temperature and a humidity level of the drying and transport air at the drying and transport air inlet.
In one embodiment, heat input characteristics include a temperature and humidity of air input to the inlet and heat generated by grinding the coal chunks into coal powder, and the output heat characteristics include a temperature and humidity of air at the outlet, a heat radiation of the pulverizer and a heat convection of the pulverizer.
In one embodiment of the system, the controller is further configured to control operation of the pulverizer based on detecting that a combustion-related condition exists in the pulverizer.
In one embodiment, one of the sensors is a humidity sensor at the outlet, and the controller is further configured to monitor the humidity of air at the outlet to determine whether a precursor condition to a flame in the pulverizer exists based on a humidity level below a predetermined threshold. In one embodiment, the controller is configured to determine whether the combustion-related condition exists in the pulverizer by calculating a difference between a sum of the heat input characteristics and a sum of the heat output characteristics, and by comparing the difference to a predetermined threshold that corresponds to a combustion-related condition.
In one embodiment, the heat balance function is:
, wherein mi is mass flow of air into the pulverizer, mj is mass flow of air out from the pulverizer, hi is enthalpy input to the pulverizer, hj is enthalpy output from the pulverizer and Q is a change in energy. In such an embodiment, the controller may be configured to detect the combustion-related condition by determining that Q is greater than a predetermined threshold. In one embodiment, the combustion-related condition is a flame and the predetermined threshold is +/−0.05.
In one embodiment, a method for detecting a combustion-related condition in a pulverizer includes measuring, with sensors, input heat characteristics of a pulverizer and output heat characteristics of the pulverizer. The method includes detecting a combustion-related condition in the pulverizer by performing a heat balance operation including the input heat characteristics and the output heat characteristics.
In one embodiment, detecting the combustion-related condition in the pulverizer includes calculating a difference between a combination of the input heat characteristics and a combination of the output heat characteristics and determining that the difference is greater than a predetermined threshold. In one embodiment, the method includes controlling the pulverizer to reduce a magnitude of the combustion-related condition based on detecting the combustion-related condition in the pulverizer.
In one embodiment, the heat input characteristics include a temperature and a humidity level of drying and transport air at a drying and transport air inlet, pulverizer configured to flow the drying and transport air upward from beneath a coal grinding bowl. In one embodiment, the heat input characteristics include a temperature and humidity of air input to a coal chunk inlet and heat generated by grinding the coal chunks into coal powder, and the output heat characteristics include a temperature and humidity of air at an outlet of the coal powder, a heat radiation of the pulverizer and a heat convection of the pulverizer.
In one embodiment, the method includes monitoring a humidity of air at a coal powder outlet of the pulverizer to determine whether a precursor condition to a flame in the pulverizer exists based on a humidity level below a predetermined threshold.
Yet another embodiment of the invention includes pulverizer control system including a processor. The processor may be configured to receive as inputs sensor signals corresponding to input heat characteristics of a pulverizer and output heat characteristics of the pulverizer, to determine whether a combustion-related condition exists in the pulverizer based on a heat balance equation including the input heat characteristics and the output heat characteristics, and to perform at least one of generating a signal indicating that a combustion-related condition exists in the pulverizer or controlling the pulverizer to take corrective action based on determining that the combustion-related condition exists in the pulverizer.
In one embodiment, the processor is configured to calculate a difference between a combination of the input heat characteristics and a combination of the output heat characteristics and to determine that a combustion-related condition exists when the difference is greater than a predetermined threshold.
Embodiments of the invention relate to conducting an accurate energy balance analysis with a pulverizer as the control volume. If the heat energy leaving the pulverizer does not equal the heat energy entering the Pulverizer there must be an additional heat source which then indicates a fire. Some technical advantages of embodiments of the invention include the capability to detect a fire at a heat level equal to 5% of heat input regardless of the a fire's location. Embodiments of the invention also reduce the probability of a fire occurding by identifying important precursors. These precursors include high humidity in the outlet pipe which increases the probability of a blocked coal line, which in turn, leads to elevated risk of a fire, and operation of the pulverizer in a regime exceeding its drying capability.
While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
