Patent Grant
8714970
This application is a national stage of International Application No. PCT/AU2010/001236, filed Sep. 21, 2010, and claims priority to Australian Application No. 2009 904605 filed Sep. 21, 2009.
The field relates to combustion monitoring and control systems, and related processes.
In any combustion reaction, it is desirable to ensure that the ratio of fuel to air is appropriate for achieving complete combustion of the fuel. Combustion in the presence of too much excess air tends to increase NOX production (and CO2 if there is too much excess air and too little water), while combustion with insufficient air may result in CO production or result in unburnt fuel in the form of soot and/or slag.
A problem, however, is the difficulty in being able to accurately monitor and control a combustion process. For example, changes in fuel and air composition during combustion can occur rapidly. The typical method of controlling combustion is by measurements on the exhaust gases which are ineffective since there can be a significant time delay between the moment of combustion and the time at which a need for correction is detected. Another problem is that there is no reliable way of determining the amount of combustible material (or potential energy content) in a given amount of fuel. This is a significant problem in the combustion of solid fuels (such as pulverised coal), which may contain different amounts of impurities in different samples of fuel being fed to a burner. As a result, it can be very difficult to work out the volume of air required for achieving complete combustion of a sample of fuel.
There is also a growing need for technologies that help reduce greenhouse gas emissions, and to use fuels such as coal more efficiently and effectively in energy production. Attempts have been made to minimise the release of pollutants (such as CO, CO2 and NOX) by improving the cleaning of flue gases after combustion. Attempts have also been made to develop more thermally efficient systems that use less coal to generate the same amount of power (e.g. using higher grade coal), together with improved techniques for effluent treatment and residue use and/or disposal. However, none of these approaches address the problem of detecting and correcting imbalances in fuel/air composition to minimise the production of undesirable gases.
There have been other attempts at monitoring and controlling combustion. WO 88/02891 describes a video image processing method for flame monitoring in a combustion process. Video cameras capture images of the flame from the side. The video signal is continually processed to find an ignition area of the flame (based on the gradient of pixel intensities). Temporal changes in the location of the ignition area are used to control the boiler. However, this technique focuses on a specific characteristic of the flame, and does not control combustion based on any physical characteristics of the inputs (e.g. fuel) used for combustion.
Another approach is described in WO 96/34233, which relates to a method of measuring the amount of pulverised fuel in a boiler for controlling a combustion process. Furnace cameras measure the distribution of heat radiation emitted by the flame over a predefined area. An irradiance value is determined for a point within the flame area at a set distance away from the ignition point of the flame. The air feed rate to the burner is determined simultaneously. The fuel feed rate is determined based on the irradiance value and the air feed rate (which enables the amount of pulverised fuel in the flame to be determined). The air feed rate is adjusted according to changes in the fuel feed rate. This technique does not control combustion based on any physical characteristics of the inputs used for combustion.
It is therefore desired to address one or more of the above problems, or to at least provide a useful alternative to existing combustion control techniques.
A combustion control system (and related process) is described. In general terms, the system performs image analysis to identify one or more physical attributes of solid fuel particles (e.g. pulverised coal) to determine a combustibility level of the fuel (representing its potential energy content). The combustion process is configured and controlled based on the combustibility of the fuel. The system may further involve performing analysis of various optical characteristics of products resulting from the combustion process, and making appropriate adjustments to configuration parameters for controlling the combustion process.
One described embodiment relates to a combustion control system, including:
A key advantage of the combustion control system is the ability to detect changes in the circumstances affecting a combustion process in close to real time (based on an analysis of the changes in the combustibility characteristics of the fuel used for combustion over time, as well as one or more optical characteristics representing an end result of the combustion over time). Other benefits and advantages can be appreciated from the following description.
The system may further include:
Representative embodiments of the present invention are herein described, by way of example only, with reference to the accompanying drawings, wherein:
A combustion control system 100, as shown in
The first and second set of sensors 104 and 106 are each made up of one or more different sensors, and each includes at least one image sensor adapted for capturing a sequence of optical images and generating image and/or video data representing the captured sequence of images. Each image sensor may include one or more of a solid-state matrix sensor, a charge-coupled device (CCD) sensor, and a complementary metal-oxide-semiconductor (CMOS) active pixel sensor. For example, an image sensor may be part of a video camera. The controller 102 may be a standard computer, a portable computing device (e.g. a laptop), or a specialised computing device for controlling a combustion process as described herein. The controller 102 includes a processor that operates under the control of commands or instructions generated by the fuel analysis module 108, combustion analysis module 110 and combustion control module 112. The term processor is used in this specification to refer to either a collection of one or more microprocessors, one or more hardware components of a device, or an entire device that is configured for performing the acts in the combustion control process 300 shown in
The fuel analysis module 108, combustion analysis module 110 and combustion control module 112 may be provided by computer program code. Those skilled in the art will appreciate that the processes performed by the modules 108, 110 and 112 can also be executed at least in part by dedicated hardware circuits, e.g. Application Specific Integrated Circuits (ASICs) or Field-Programmable Gate Arrays (FPGAs).
In the representative embodiment shown in
The fuel analysis module 108 controls a processor of the controller 102 to perform pre-processing of the sample data to enhance and clarify the represented images. Pre-processing may involve applying one or more of the following enhancement techniques to the data in an image (or video frame): scaling, resizing, image/frame correction or enhancement, colour correction or enhancement, edge detection, grey level stretch, noise elimination, erosion/dilation, thinning, split and merge, merge small regions, background split, merge and split on shape, polygonal approximation, classification of concavities, split large clusters into simple clusters, supplementary cost functions for two or three touching particles, image binarisation, skeleton, distance function, split based on skeleton histogram. The fuel analysis module 108 then controls a processor of the controller 102 to analyse the sample data.
Coal is non-homogenous, and typically contains a combination of carbon particles and other elements (or impurities) bonded together. The carbon content of coal indicates the amount of potential energy that can be released by the coal during combustion. An advantage of burning coal with higher energy content is that less CO2 will be produced. However, another way to enhance combustibility is to pulverise the coal into fine particles for combustion. The particles of pulverised coal may relate to different chemical elements, each of which may have different combustibility characteristics, and each of which can be detected based on their individual physical characteristic including colour, intensity, texture, size, shape, weight and density.
For each image (or frame) represented by the sample data, the fuel analysis module 108 identifies individual particles of pulverised coal (for at least some of the particles detected within the image of the sample). The fuel analysis module 108 then analyses each particle to determine attributes for one or more predefined physical characteristics (such as colour, intensity, texture, size, shape, weight and density). This analysis enables the fuel analysis module 108 to identify the main types of elements comprised in the sample of coal, and based on the combustibility characteristics of these elements, the fuel analysis module 108 generates an index value for each sample representing an estimated energy content within each sample of coal (e.g. based on the amount and combustibility of the material in each sample).
The following description outlines how the combustibility index value may change depending on the attributes for key predefined physical characteristics of fuel particles in a sample:
The index values generated by the fuel analysis module 108 for each sample may be stored in one or more memory components, which may be part of the controller 112. The combustion control module 112 accesses index values for a sequence of samples, and detects and analyses changes in the index value (for different samples) over time. The combustion control module 112 generates or adjusts one or more configuration parameters (based on the index value changes) for controlling a combustion process. In a representative embodiment, this involves adjusting configuration parameters responsible for controlling one or more of the following:
In a representative embodiment, the configuration parameters are adjusted to increase or decrease a current rate of combustion to a level more appropriate for the combustibility of the fuel at the time. For example, the current rate of combustion may be adjusted so that it is appropriate for achieving complete combustion with the current sample of fuel (to minimise over production of products from combustion such as CO, CO2, NOX, SOX, soot and/or slag).
One advantage of the combustion control system 100 is that the analysis carried out by fuel analysis module 108 can provide almost real time feedback on changes in the combustibility characteristics of a sample of fuel. In contrast, current industry practice is to take fuel samples to a laboratory for analysis on a weekly/monthly basis to assess the combustibility of the fuel, and make relevant adjustments to the configuration parameters based on the analysis results.
Another advantageous aspect of the combustion control system 100 is the ability to visually detect the changing dynamics of combustion and making changes to relevant configuration parameters based on the detected changes, and the index value (as described above), over time.
In the representative embodiment shown in
In the same way as the fuel analysis module 108, the combustion analysis module 110 also controls a processor of the controller 102 to perform pre-processing of the combustion data to enhance and clarify the represented images. The combustion analysis module 110 then controls a processor of the controller 102 to analyse the combustion data. For each image (or frame) represented by the combustion data, the combustion analysis module 110 determines attributes for one or more predefined visual characteristics of a product resulting from the combustion process. The reference to a product includes a reference to the flame, temperature and gases that are produced as a result of the combustion process. The combustion analysis module 110 analyses one or more of the following optical characteristics of the flame (and other control factors including the amount of air, amount of fuel, combustibility of the fuel, and temperature of the combustion). Based on the changes to any of these optical characteristics over time (and together with the changes in the index value over time), the combustion control module 112 determines the need for and level of adjustment to any of the control factors:
The combustion analysis module 110 also analyses optical characteristics of temperature variations (or temperature gradients) inside the combustion chamber resulting from the combustion process. For example, in a representative embodiment, at least one of the second set of sensors 106 is adapted with an optical filter to enable visibility of a distribution of heat radiation (i.e. including the infrared spectrum) inside the combustion chamber 216. Another sensor 106 is adapted with a different optical filter to enable visibility of at least one of smoke particles, hot air currents, and slag being formed inside the combustion chamber 216. Based on the changes to any of these optical characteristics over time (and together with the changes in the index value over time), the combustion control module 112 determines the need for and level of adjustment to any of the control factors.
The combustion analysis module 110 also analyses optical characteristics of an exhaust gas produced as a result of the combustion process. For example, in a representative embodiment, the second set of sensors 106 includes different image sensors that are each adapted with a different optical filter for detecting the presence and/or intensity of one or more specific wavelengths in the combustion chamber 216 which represents the presence or absence of a particular type of exhaust gas (e.g. including CO, CO2, NOX and SOX). This is based on the understanding that different molecules comprised in the exhaust gases produced in combustion can either enhance or retard the reflection of certain wavelengths of light, which can serve as a optical signature that can be detected by an image sensor. Based on the changes to any of these optical characteristics over time (and together with the changes in the index value over time), the combustion control module 112 determines the need for and level of adjustment to any of the control factors.
For example, detecting the presence of NOX or CO in the combustion chamber 216 may indicate there is insufficient air in the combustion chamber, which may trigger the combustion control module 112 to increase a primary or secondary air feeding rate into the combustion chamber 216. Also, detecting the presence of an excessive amount of CO2 in the combustion chamber 216 (relative to the amount of CO2 expected from complete combustion of the fuel of known combustibility) may indicate that there is too much air and too little water, which may trigger the combustion control module 112 to decrease a primary or secondary air feed rate into the combustion chamber 216.
In one configuration of the combustion control system 110, step 306 proceeds to step 308, where the combustion control module 112 analyses the changes in the index value for each sample over time and generates or adjusts one or more configuration parameters (e.g. an excess air feeding rate, fuel feeding rate and temperature) for controlling the combustion process.
In another configuration of the combustion control system 100, step 306 proceeds to step 310, where the combustion analysis module 110 generates combustion data including data representing images (or frames) of various dynamic optical characteristics of the combustion process within the combustion chamber 216 (e.g. flame dynamics, temperature dynamics and the presence of certain exhaust gases produced as a result of the combustion process). At step 312, based on the changes to any of these optical characteristics over time (and together with the changes in the index value over time), the combustion control module 112 determines the need for and level of adjustment to any of the control factors. Process 300 ends after steps 308 and 312, and is repeated again from step 302 to process the sample data and combustion data in respect of a different sample of the fuel.
In another representative embodiment, the first set of sensors 104 may include one or more sensors adapted for monitoring a physical condition of one or more mechanical components. For example, the sensors 104 may be adapted to monitor an extent of wear of a mechanical component in a grinder, mill, crusher 206 or pulveriser 210. The fuel analysis module 108 (or alternatively a separate analysis module of the system 100) may process a sequence of images (or frames) detected by the sensors 104 to determine whether the relevant mechanical component (e.g. by its shape or working characteristics, such as vibration) is within acceptable operating parameters. If the fuel analysis module 108 determines (based on the images) that the relevant mechanical component is damaged or is no longer operating effectively (e.g. due to mechanical wear, vibration or other damage), the fuel analysis module 108 may generate an alert signal, instruction or message to indicate that the relevant part requires maintenance or replacement.
In another representative embodiment, the first set of sensors 104 may include one or more special-purpose sensors adapted for monitoring a composition of the material collated at the bottom of the combustion chamber 216 (e.g. via opening 230). The special-purpose sensors may be configured to sample relevant parameters from the deposited material at regular time intervals (e.g. on a continuous basis). The relevant parameters may include a chemical composition of the material (such as the presence of carbon or other elements representing constituents of unburnt fuel). Sample data obtained by the special-purpose sensors are communicated to the fuel analysis module 108 (or alternatively a separate analysis module of the system 100) for analysis, which determines whether the combustion process within the combustion chamber 216 is resulting in any quantity of unburnt fuel (and possibly a rate at which the amount of unburnt fuel is being accumulated inside the combustion chamber, e.g. increasing or decreasing in volume over time). The fuel analysis module 108 may then make relevant adjustments to any of the factors described above for controlling the combustion process to enable a greater amount of fuel to undergo complete combustion.
In another representative embodiment, the second set of sensors 106 may include one or more sensors for detecting the presence of CO2 produced by the combustion process inside the combustion chamber 216. The sensors provide data representing an amount of CO2 produced (e.g. within each sampling timeframe) to the combustion analysis module 110. There are two ways for lowering the production of CO2 in a combustion process using coal fuel. One is to make the combustion process more efficient, and the other is to mix wood into the coal fuel. The combustion analysis module 110 may respond to the sensors 106 detecting a presence of CO2 by controlling the efficiency of the combustion process (as described above), or to control a fuel composition adjustment means (not shown in the FIGS.) to inject an amount of wood (e.g. fine wood chips or particles) into the coal fuel supplied to the primary and/or secondary grinders/burners 212 and 218. The amount of wood injected into the coal fuel is determined based on a predefined relationship (e.g. a proportional relationship) based on the amount of CO2 detected by the sensors 106.
Any of the processes or methods described herein can be computer-implemented methods, wherein the described acts are performed by a computer or other computing device. Acts can be performed by execution of computer-executable instructions that cause a computer or other computing device (e.g. controller 102 or the like) to perform the described process or method. Execution can be accomplished by one or more processors of the computer or other computing device. Multiple computers or computing devices can cooperate to accomplish execution.
One or more computer-readable media can have (e.g. tangibly embody or have encoded thereon) computer-executable instructions causing a computer or other computing device to perform the described processes or methods. Computer-readable media can include any computer-readable storage media such as memory, removable storage media, magnetic media, optical media, and the like. Any related data structures used by the processes or methods described herein can also be stored (e.g. tangibly embodied on or encoded on) on one or more computer-readable media.
This section provides a detailed description of a specific exemplary embodiment of the combustion control system 100. The system 100 performs three stages of processing or analysis independently or concurrently. The first stage is establishing the combustibility indices of the pulverised coal and/or solid fuel. The second stage involves combustion flame dynamics analysis. The third stage involves emission reduction procedures as well as savings in the fuel quantity.
Stage 1—Combustibility Index
The first stage involves various image capture and processing steps and generating a combustibility index value based on an analysis of the material properties of the fuel. Table 1 summarises the key processes performed under the control of the system 100 in stage 1:
Coal (brown and black) is non-homogeneous and has numerous other elements/impurities bonded together. To convert the chemical bondage into heat energy, during combustion in any industrial boiler (mainly in power stations) the carbon content is obtained through laboratory analysis. The combustion control system 100 quantifies the coal composition online in real time and further analyses the crushed coal and powdered/pulverised coal to calculate its combustibility index for tabulation or designated by a serial number to establish its energy content. This provides a reliable and fully repeatable guide to the fuel's oxygen demand for maximum utilisation of its energy content, during all stages of combustion and oxidation. The higher the energy content is utilised the lesser the emission of CO2. The following presentations explain the energy content of coal utilisation versus CO2 reduction.
Every chemical element that is a part of the non-homogenous coal composition has its own specific colour and intensity as well as specific grain size and shape. A lump of coal contains a combination of any number of carbon particles and impurities. During grinding the lumps are crushed and powered to very fine grain sizes. Different elements have different densities and weights. These different elements form their own specific fine grains and have their specific colour, intensities, shape and size. By separating these individual grains using split and merge image processing techniques the composition of these main elements are tabulated. Wrong and inconsistent particle size distribution produces carbon monoxide resulting in wrong boiler balance, very poor combustion, pressure problems and eventually oxidises into CO2. The system analyses the size and shape of the fuel online in real time, automatically analyses the fuel quality and impurities to determine its combustibility indices and the energy content.
The combustion control system 100 includes design and build of different types of cameras with specific settings and filters to capture different target data such as the fuel quality, burner performance, various blowers including soot blowers, combustion flame etc. The camera housing design built with 2 separate cooling systems and a nozzle prevents condensation of dust and suspended particles on the lens. The cameras can be used up to 1400° Celsius. The cameras are designed for pre-investigation to find the right position for mounting online cameras. They can be approximately 1.5 meters long to reach through all types of walls mounted on rails equipped with automatic temperature sensors. If the temperature is too high (temporary peaks or stoppage in the cooling systems), the camera automatically rolls out. The system 100 also includes monitoring systems designed for heat resistance, including a liquid and air cooled camera housing with a number of features to record true and reliable variation in the images and adjust features (such as light, contrast, volume, distribution, movement, dynamics etc.) being monitored, where variations in their behaviour/pattern provide the information required and co-related to the measured data from the fuel feeding, the combustion parameters and measurement readings, and the exhaust gas analysis and speed/volume.
The invention relates to online analysis of the quality of ground coal in a specially designed mill/grinder, changing the shape of the particles in a way that increases their ability to react in a controlled method and changes their behaviour in the combustion chamber.
The processing board is a PC-bus frame grabber card for most advanced computers and digital control systems (DCS) that control the operation of the boiler. The board can implement image acquisition, true/pseudo colour image display, graphic overlays, transparent manipulation, transformation, zoom, roam, real-time operation, change pixel aspect ratio and conduct many other important and relevant functions. The on-board frame memory includes multiport VRAM and is directly mapped with and has access to the memory space of the host computer. Each individual data bank contains a minimum of 8 layers of information (each pixel contains 8-bits). Table 2 describes the key functional elements of the system 100.
The system 100 automatically acquires series of images (in excess of 50 to 100 per second) from the online video cameras at periodic sequences, performs a number of filtering and enhancing routines, abstracts regions and borders for qualitative and quantitative analysis, carries out numerous segmentation sub-routines and constructs the flame in binary format. A series of shape analysis are automatically carried out for statistics and dynamic parametric calculations to isolate fuel quality, status of combustion and process information such as temperature distribution and pressure distribution. The analysis is further enhanced by Multivariate Data Modelling techniques.
Several cameras monitor the entire combustion process inside the boiler and are correlated to the changes in the boiler settings. Special hardware filters are used on the cameras to enhance information that is partly hidden by burning gas and/or intense light to enhance the flames to isolate the burner's performance. The system 100 processes all video files and includes several special designed algorithms:
The technology provides extensive analysis for stage wise reduction in excess air to save substantial amounts of fuel or alternately increases higher heat/steam production for the same amount of fuel.
Stage 2—Flame Dynamics Analysis
The second stage involves analysis of various characteristics of the flame, including by-products produced by the flame. Table 3 summarises the key processes performed under the control of the system 100 in stage 2:
Instead of the human eye, system 100 uses a camera that provides high speed and high accuracy non-touch measurement, and analyses the information required to control combustion dynamics with low excess oxygen a factor that is vital for minimizing emission. In order to comprehensively control combustion it is extremely important to quantify the quality of the fuel and its combustibility indices and its energy content. The system 100 automatically analyses the fuel's energy content and controls all stages of the combustion to enhance the fuel's chemical bondage conversion to heat energy at the same time as controlling the emission of gasses for the CO2 and other gas reduction procedures. “Blow-outs”, “Cold sections”, “Dynamic turbulence” and “Convection” are monitored and optimised for effective combustion and also emission reduction. This is a phenomenon of dynamics and shape in vertical movement and circulatory, and “off-lets” (suction) temporary explosions and implosions. The optimal combustion is a combination of flame shape, oxygen positioning, semi-turbulent, but controlled dynamics—vertically controlled by the exhaust fan, (but circular and pressure distribution is very individual) and often some secondary air in the right place that produces the post-oxidation—in old burners this is often produced by a “leak” that sucks air half way up and—even such “leaks” can be seen with the combustion camera of the present invention when mounted to monitor secondary combustion.
A unique feature of the system 100 is that it records, in real time and online, numerous parameters of the combustion such as fuel bed (amount of fuel present), temperature gradients, pressure gradients, turbulence (mixing) and excess air. Good combustion depends on H2O and CO2 and bad combustion produces different poisonous gases like Nitrogen/sulphur complexes, and CO depending on type of fuel and type of combustion technology (furnace, boiler etc). Optimised combustion must balance CO (too little oxygen) and CO2 (too “much” oxygen and too little water).
The key algorithms used by the system 100 include:
Important for optimising combustion is the positioning of the excess air/oxygen in the required location of the combustion zone, meaning where it is required and not how much is available. Excess air in the wrong location does not contribute to combustion; it only cools the boiler (less steam) and dilutes the emissions (good for monitoring but bad for energy production). Image analyses provide reliable advice about where the excess air is required based on the dynamics of combustion. The key parameters used by the system 100 include:
The system 100 automatically measures and analyses soot and slag build up on the super-heaters that cause loss of suction. The system 100 can also recirculate exhaust gas to cool the super-heaters as well as minimise O2 to enhance dynamics if secondary air registers are available. The system 100 can also analyse (e.g. after the final mill) the size distribution of fuel particles, which may be monitored continuously or sampled numerous times under different operating and environmental conditions.
Stage 3—Emission Reduction and Fuel Savings
The third stage involves the system making various adjustments to parameters controlling the fuel and/or process of combustion to reduce emissions and to reduce fuel consumption. Table 4 summarises the key processes performed under the control of the system 100 in stage 3:
The relationship between the important parameters and the combustion are:
The system 100 analyses the images to isolate each pressure zone and their intensities to calculate the movement of the oxygen cell, fuel combustion and emitted gas intensities. During combustion the fuel undergoes the following phases:
The key advantages of the combustion control system 100 can include one or more of the following:
Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.
The word ‘comprising’ and forms of the word ‘comprising’ as used in this description and in the claims does not limit the invention claimed to exclude any variants or additions.
In this specification, including the background section, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge, or known to be relevant to an attempt to solve any problem with which this specification is concerned.
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| Publishing Document | Publishing Date | Country | Kind |
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