KR20220136487A - Flame image analysis for furnace combustion control - Google Patents

Abstract

The operation of the combustion control system of the furnace is responsive to image analysis, and correlation of the flame produced by combustion in the furnace, outside the furnace or in the furnace, to correlate the image with the carbon monoxide content of the flame. Controlled by regulation of oxygen and/or fuel flow into the furnace.

Description

FLAME IMAGE ANALYSIS FOR FURNACE COMBUSTION CONTROL

The present invention relates to a furnace for controlling and/or reducing the emission of carbon monoxide from a furnace, in which the material is heated and the heating can result in the formation of carbon monoxide (a furnace is a sealed closed chamber such as a combustion chamber in which fuel and gaseous oxidant are burned). space) for the operation of the combustion control system.

Operations in which the material is heated in the furnace can lead to the formation of carbon monoxide in the furnace. Mechanisms that allow carbon monoxide to form include incomplete combustion of fuel in a furnace; incomplete combustion of combustible materials when the material to be heated in the furnace is also intended to be burned; and/or transformation of the carbonaceous material present in or on the material to be heated. Examples of such transformations include pyrolysis and/or incomplete combustion of carbonaceous materials.

When carbon monoxide is formed in the furnace, the release of carbon monoxide out of the furnace is usually undesirable. Various techniques exist for removing carbon monoxide from gaseous offgas leaving the furnace, such as absorption of carbon monoxide into an absorbent, or addition of reactants to the offgas that react with carbon monoxide. Such techniques present problems such as cost and difficulty of implementation and control.

The present invention provides an efficient method for avoiding the emission of carbon monoxide from a furnace. The present invention also provides an efficient method for controlling the operation of a furnace to achieve improved efficiency and production rates.

One aspect of the invention is a method of heating a material in a furnace, the method comprising:

(A) derived from carbonaceous material by heating a material comprising carbonaceous material in a furnace having a flue using heat generated by combustion in the furnace of fuel and gaseous oxidizer fed into the furnace producing carbon monoxide that is formed in the furnace, a flame that can extend out of the furnace from the flue;

(B) the flame from images of the flame taken outside or inside the furnace by a digital camera located outside the furnace, by electronically expressing at least one parameter corresponding to the intensity of the flame and corresponding to the concentration of carbon monoxide in the flame. characterizing a concentration of carbon monoxide in the flame and determining the characterized concentration of carbon monoxide in the flame from predetermined correlations of actual concentrations of carbon monoxide in the flame to the expressed values of the at least one parameter;

(C) comparing the characterized concentration of carbon monoxide in the flame as characterized according to step (B) to a pre-established threshold concentration value for said concentration;

(D) when the characterized concentration of carbon monoxide in the flame exceeds the pre-established threshold concentration value, while continuing to characterize the concentration of carbon monoxide in the flame from images of the flame taken by a digital camera outside the furnace, An amount of oxygen supplied into the furnace available for reaction, an amount of fuel, or an amount of both oxygen and fuel is used to lower the characterized concentration of carbon monoxide in the flame below a pre-established threshold concentration value for a predetermined length of time. adjusting to an effective amount or amounts.

Another aspect of the invention is a method of heating a material in a furnace, the method comprising:

(A) heating a material containing a carbonaceous material in a furnace having a flue using heat generated by combustion in the furnace of a fuel and gaseous oxidizer fed into the furnace, thereby reducing carbon monoxide derived from the carbonaceous material generating - a flame is formed in the furnace that can extend out of the furnace from the flue;

(B) from images of the flame taken outside or inside the furnace by a digital camera located outside the furnace by electronically expressing at least one parameter corresponding to the intensity of the flame and corresponding to the concentration of carbon monoxide in the flame. characterizing a concentration of carbon monoxide in the flame and determining the characterized concentration of carbon monoxide in the flame from predetermined correlations of actual concentrations of carbon monoxide in the flame to expressed values of at least one parameter;

(C) comparing the characterized concentration of carbon monoxide in the flame as characterized according to step (B) to a pre-established threshold concentration value for said concentration;

(D) carbon monoxide in the furnace when the characterized concentration of carbon monoxide in the flame exceeds the pre-established threshold concentration value, while continuing to characterize the concentration of carbon monoxide in the flame from images of the flame taken by a digital camera outside the furnace adjusting the amount of oxygen supplied into the furnace available to react with the furnace to an amount effective to lower the characterized concentration of carbon monoxide in the flame below a pre-established threshold concentration value for a predetermined length of time.

1 is a schematic diagram showing how the present invention can be implemented on a furnace apparatus;
Figure 2 is a chart showing the sequence of steps of the present invention.

The present invention is useful for heating any material that can be heated in a furnace. Examples of such materials include iron ore and other compounds, as well as ferrous metals such as iron and steel, including scrap as well as finished products. Further examples include non-ferrous metals, such as aluminum and copper, and their ores and other compounds, including scrap as well as finished products. Heating of any such materials is employed to prepare them for further chemical and/or physical treatment.

The present invention is also useful for heating a material in which some or all of the material is melted. In such operations, the material may include any of the aforementioned metals, metal oxides, and other metal compounds. Other examples include products that are melted together in a glassmaking furnace to form molten glass; Such materials include pieces of recycled glass, known as cullets, and raw materials, known as batches, that are melted together to make glass, typically sodium oxide, potassium oxide, and silicates of sodium and potassium. includes Another example of such an operation is a cement kiln, in which raw materials, typically comprising lime or limestone, and silica and/or aluminosilicate (clay) and other desired additives, are heated together so that they melt and react with each other. to form the compounds that make up cement.

The present invention is also useful for heating materials in which some or all of the material is to be burned, such as in an incinerator. Materials that can be heated in the practice of this aspect of the invention include all combustible products, such as carbonaceous fuels, and solid waste.

Any of the materials processed in accordance with the present invention have the property that they contain some carbonaceous material, so heating the material may cause carbon monoxide to form in the furnace from the carbonaceous material. The carbonaceous material present may be an organic compound present in the material being heated and/or may include some or all of the material that is heated in the furnace and then combusted. For example, scrap comprising aluminum, copper, iron and/or steel may have carbonaceous material thereon, such as paints or other organic coatings, organic food and/or human excrement, and the like. The cullet present in the glassmaking material can retain thereon organic matter, which is a residue of food or other organic matter that was present on the cullet before it was recycled as a cullet.

Carbon monoxide that forms in the furnace can be caused by incomplete combustion of fuel in the furnace; incomplete combustion of combustible materials when the material to be heated in the furnace is also intended to be burned; and/or transformation of the carbonaceous material in or on the material to be heated, examples of such transformations including pyrolysis or incomplete combustion of the carbonaceous material. can Just as carbon monoxide emissions from a furnace are undesirable regardless of the source of the carbon monoxide, the present invention is useful regardless of the source or mechanism by which the carbon monoxide at risk of being emitted from the furnace is formed therefrom.

Referring to FIG. 1 , a furnace 1 is shown in cross section. Although the illustrated furnace has a shape typical of a furnace that can be rotated about a horizontal axis in the embodiment shown in FIG. 1 , the present invention may also be practiced with any other type and shape of furnace. In the furnace 1, the material to be heated is marked with 2. Material 2 is heated by heat from flame 4 formed in the furnace by combustion of fuel 13 and oxidant 12 in burner 11 . Suitable fuel 13 may be any combustible carbonaceous material, preferred examples of which include methane, natural gas, and atomized fuel oil. Suitable oxidizing agents fed at 12 include oxygen, such as air, oxygen-enriched air, and any gaseous product containing a stream having an oxygen content of at least 50% by volume, preferably at least 90% by volume. Streams with such elevated oxygen content are commercially available from any of several suppliers of atmospheric gases. Although one flame 4 is shown, a furnace in which the present invention may be practiced may include more than one burner 11 and more than one flame 4 .

The furnace 1 comprises at least one flue 6 through which gaseous products can exit the furnace 1 . The gaseous products exiting the flue 6 include gaseous products of combustion between the oxidant 12 and the fuel 13, such as carbon dioxide and water vapor, and may contain volatile organic compounds (VOCs) and may contain carbon monoxide. In a practical application of the present invention, if there is only one flue 6 , a flame 15 can extend from the outlet 7 of the flue 6 . If more than one flue 6 is present, there may be a flame 15 extending from at least one outlet 7 of the at least one flue 6 . Carbon monoxide may be present in flame 15 and may or may not burn completely in flame 15 .

The furnace 1 may include a sight port 10 in the wall of the furnace, through which the flame 4 inside the furnace 1 can be observed from outside the furnace 1 .

According to the invention, the camera 21 is located outside the furnace 1 . The camera 21 comprises an aperture 22 through which the camera 21 receives images. In one embodiment of the invention, the camera 21 is positioned relative to the furnace 1 such that the diaphragm 22 of the camera 21 faces towards the flame 15 . In another embodiment of the present invention, the camera 21 is configured such that the aperture 22 of the camera 21 is aligned with the sight port 10 so that the camera 21 takes an image of the flame 4 inside the furnace 1 . It is positioned relative to the furnace 1 so as to be able to receive it.

The camera 21 is a digital camera, wherein the camera 21 detects one or more characteristics of the object (in this case, the detected characteristics include at least the intensity of the flame towards which the camera 21 is directed), and detects It means that the image corresponding to the specified characteristic is expressed electronically in digital form. Digital cameras with this capability are commercially available. These may be standalone units, or they may be part of an item of equipment that also has additional functional capabilities (eg, telephony, timekeeping, etc.).

Still referring to FIG. 1 , a control device 25 controls the flow rate of oxidant 12 and fuel 13 to burner 11 (or to multiple burners if more than one burner 11 is present). do. Optionally but preferably, a lance 27 is provided for discharging the supplemental oxidant into the furnace 1 when additional oxidant is to be put into the furnace 1 . The flow of oxidant through the lance 27 is controlled by a control device 29 . The oxidizing agent that may be introduced into the furnace 1 through the lance 27 may be air, oxygen-enriched air, or a higher purity oxidant having an oxygen content of at least 50% by volume and even at least 90% by volume. The oxygen content of the oxidizing agent fed into the furnace 1 via the lance 27 may be the same or different with respect to the oxygen content of the oxidizing agent 12 fed into the furnace 1 .

In FIG. 1 , block 23 refers to a complete system performing the sequence of steps presented as 31 , 33 and 35 in FIG. 2 . The system may reside in one integrated device, or the components performing certain steps may be physically separated from other components and connected to each other by suitable cables or by cableless wireless connections. Some or all of the components may be included in the camera 21 . However, for ease of function and because of the possibility that the camera 21 may be located in an environment that is hot and dusty and thus potentially harsh to components such as the processor, the camera 21 is physically isolated from other components. , and the camera 21 is preferably connected by cable or wireless connection to a component that performs step 31 at least first following the acquisition of an image by the camera 21 . As can be seen in FIG. 1 , system 23 is coupled to camera 21 to receive input from camera 21 , system 23 includes control device 25 and (if present) control device ( 29 ), providing a signal to the control devices 25 , 29 .

In operation, combustion is carried out inside the furnace 1 in the presence of the material 2 in the furnace 1 . A flame is formed in the furnace, which may appear as a flame 15 extending from the opening 7 of the flue 6 . In one embodiment of the present invention, the camera 21 faces the flame 15 , an image of the flame 15 is received through the aperture 22 . In another embodiment of the invention, the camera 21 is directed towards the furnace 1 , so that an image of the flame 4 inside the furnace 1 is received at the aperture 22 via the sight port 10 . Flame 15 or 4 can be very bright, so aperture 22 and exposure must be adjusted to avoid blooming of the image. In some situations, it may be desirable to be able to dynamically adjust the exposure of an image so that proper resolution is achieved when the image is very dark. In most situations, such dynamic adjustment is not necessary. The view factor and resolution of the camera image should be such that the image size is at least 50 x 50 pixels, preferably at least 300 x 300 pixels. One skilled in the art can readily determine the appropriate image resolution and image view factor for a given distance of camera 21 from flame 15 or 4 and for a given size of flame 15 or 4 . The camera 21 generates a digital electronic image of the flame 15 or flame 4 based on at least one parameter of the flame, such as the intensity of the flame 15 or flame 4 . The electronic image is transmitted electronically by the camera 21 to the device performing step 31 .

In step 31 , the signal corresponding to the image of the flame 15 or 4 is one or more values indicative of the intensity or varying intensities of the flame, which may include various values over the area of the flame within the field of view of the camera 21 . is converted to Intensities are detected and digitally represented to produce an array of values corresponding to the detected intensities. The detected intensity parameter also corresponds to the concentration of carbon monoxide present in the flame.

In step 33, the detected intensity parameter is compared with a pre-established correlation of the intensity parameter to the actual concentration of carbon monoxide in the flame. Pre-established correlations can be achieved by simultaneously measuring the concentration of carbon monoxide in the flame through established techniques such as gas sampling using a gas sampling probe followed by analysis of the sampled gas, or continuous emission monitoring, and detected by a camera 21 . by observing the values of the expressed parameters derived in step 31 from the values based on the intensity as determined and recording together the measured concentrations and parameter values, where they can be read together, for example on a computer or in a created catalog; can be established In this way, each intensity parameter expressed by the system corresponds to an actual concentration value of carbon monoxide in the flame. Determination of the existing correlation between the expressed parameters and the measured carbon monoxide concentration may have already been carried out during the initial setup of the system in the furnace and usually need not be repeated in a given furnace each time the furnace is operating. However, an operator may find it desirable to establish a new set of correlations for different furnaces as well as for a given furnace in situations where the conditions under which a given furnace should be operated will be significantly different.

The system described herein can be used to achieve any of several methods of controlling furnace operation. One such method is to control carbon monoxide emissions by controlling the oxygen supply to the furnace, which is now described:

The operation of the furnace will have a pre-established value for the concentration of carbon monoxide in the flame, so values of carbon monoxide concentration above that value are unacceptable and must be lowered. Typical values for excess carbon monoxide may range from 3% to 30% by volume, although the value may vary depending on the location, the nature of the material 2 being heated in the furnace 1, or other conditions. Pre-established values are arbitrary values of significance to the operator, such as values indicating an undue risk of environmental damage, or a risk violation of applicable environmental regulations, or an undesirable imbalance of economic and thermodynamic conditions within the furnace. based on a factor or group of factors of

In step 33, a pre-established value for the concentration of carbon monoxide in the flame (which may also be referred to as a threshold or set point) is stored, and the detected intensity parameter corresponding to the concentration of carbon monoxide in the flame at any one point in time is It is compared with a pre-established threshold. The comparison may be performed at any desired rate, but preferably the comparison is performed at a rate of once every 2 to 5 seconds. Preferably the comparison is performed automatically by a suitably programmed controller.

If the detected and treated intensity parameter corresponds to an actual carbon monoxide concentration in the flame that exceeds a pre-established threshold, the system takes an action that results in additional oxygen being provided in the furnace 1 . 2 , this action is represented in step 33 as generating a signal which activates the combustion control system 35 to have additional oxygen present in the furnace 1 . The additional oxygen will react with the carbon monoxide present in the furnace, so less carbon monoxide leaves the furnace 1 through the flue 6 in the flame 15 or otherwise. By any of several modes, additional oxygen may be provided into the furnace 1 to react with the detected excess carbon monoxide. For example, one such mode is the control system 35 of oxygen 12 fed into furnace 1 through burner 11 without increasing the flow rate of fuel 13 into furnace 1 . to increase the quantity. Another possible mode is through make-up feed line 29 (shown in FIG. 1 ), make-up oxidant, or an increased amount of make-up oxygen, also without increasing the flow rate of fuel 13 into furnace 1 . is to supply Another possible mode is to reduce the amount of fuel 13 fed into the furnace 1 without reducing the amount of oxygen 12 or make-up oxygen 27 fed into the furnace 1 . Alternatively, any combination of these modes may be implemented simultaneously.

A preferred embodiment is to provide supplemental oxygen 27 so that the operator does not have to adjust the stoichiometric ratio of fuel and oxidant supplied via one or more burners 11 . The replenishment supply line 27 is preferably introduced into areas where carbon monoxide is not particularly desirable, such as near the area where the interior of the furnace 1 connects with the upstream end of the flue 6, or a relatively higher amount of It should be positioned to feed the oxidizing agent into areas within the furnace where carbon monoxide may be present.

The provision of additional oxygen continues until the detected and treated value indicative of the carbon monoxide concentration in the flame is reduced to a value below the previously established threshold value. If desired, the additional oxygen should be less than the pre-established threshold, such as 0.5% to 2% below the pre-established threshold, in order to minimize the number of times the provision of additional oxygen must be initiated and then stopped. should be provided until

Steps 31, 33, and 35 may be performed on suitably programmed controllers connected to each other by means of suitable cables or by wireless connections. Instead, they can all reside within one piece of hardware.

As can be seen, the system described herein also provides for supply of oxygen (oxidizer), fuel, or both oxygen and fuel, to achieve desired combustion characteristics in the furnace or to perform control of furnace operation from start-up. By adjusting, it can be used to perform other methods of controlling the operation of the furnace. In this embodiment of the present invention, one or more than one setpoint (typically at one burner, or at each of several burners if the furnace has multiple burners) corresponding to the fuel flow rate and oxygen flow rate in the furnace. 3 to 10 setpoints) are pre-established in the controller.

In these embodiments, image analysis parameters are received in step 33 and compared to user defined control level setpoints which also preset flow rate values to be used for the burner and oxidant lance for each level. This last part communicates with the furnace combustion control unit PLC. The user can also select other process parameters such as timers to enable/disable the control level. The user can also select a language to appear on the control panel that the operator will see at this stage, and also select other variables to be controlled. Controller 33 collects data from cameras and associated software, processes this data along with user inputs (limit, oxygen flow set point, natural gas flow set point, delay time), reduces CO emissions and yields furnace output Dynamically adjust the process to increase

The user selects a control variable, selects the start limit, stop limit, and "off-delay" values (any number of each required, typically 1-10 each, and the number of "on-delay" values (typically 1 to 5)) are set. The user also sets the oxygen flow set point and the burner natural gas flow set point for each corresponding limit. When the initial start limit is exceeded by more than the on delay time, the software sets the corresponding oxygen flow set point and natural gas flow set point. The setpoints are processed in the order in which the limits are exceeded. Once the control variable falls below the break limit and the off-delay timer expires, the aforementioned level is set.

When the control variable falls below all interruption limits and the final off delay is complete, the oxygen setpoint is set to zero and the burner fuel setpoint returns to normal control.

When the furnace door is opened, the oxygen set point is set to zero and the burner fuel set point returns to normal control.

The systems and methods described herein enable operators to realize benefits in the operation of the furnace, such as more efficient operation in terms of fuel consumption and reduced cycle times. By monitoring the carbon monoxide content of the flame (and by doing so in real time, this is how the present invention can be used), the operator can supply oxygen and/or fuel to the furnace so that the heat of combustion of the carbon monoxide can be retained in the furnace and used to advantage. The rate can be adjusted, thereby enabling the operator to achieve the same degree of heating and/or melting of the material in the furnace in a shorter cycle time, and allowing the operator to heat and/or heat with less fuel consumption per unit of heated material. or make it possible to achieve melting.

The present invention is, for several reasons, an advantageous method for controlling carbon monoxide emissions from a furnace and for controlling overall furnace operation. One reason is that implementation of the method of the present invention on a working furnace does not require a continuous direct measurement of the concentration of carbon monoxide in the flame. Another reason is that the present invention detects a parameter that characterizes carbon monoxide in a flame, rather than flue gas or exhaust gas, which measurements tend to be more variable and less reliable. In addition, the method of the present invention does not measure the temperature of the flame and is not based on measuring the difference in flame temperature, and thus is more reliable and less susceptible to temperature fluctuations in the flame. Instead, the method of the present invention is based on the correlation of image parameters corresponding to the carbon monoxide concentration in the flame, which is believed to be a novel and efficient mode of operation.

Other advantages include reduced demands on maintenance of the equipment used; little or no furnace downtime and lower installation costs for installation of systems implementing the present invention; and adjusting the oxygen supply, the fuel supply, or both the oxygen supply and the fuel supply when the system detects a condition requiring an increase or other change in the amount of oxygen and/or fuel supplied into the furnace. This will include faster response times.

Claims (1)

A method of heating a material in a furnace comprising:
(A) heating a material comprising carbonaceous material in a furnace having a flue using heat generated by combustion in the furnace of fuel and gaseous oxidizer fed into the furnace, whereby the carbonaceous material is generating carbon monoxide derived from the material, wherein a flame is formed in the furnace that can extend out of the furnace from the flue;
(B) photographed outside or inside the furnace by a digital camera located outside the furnace by electronically expressing at least one parameter corresponding to the intensity of the flame and corresponding to the concentration of carbon monoxide in the flame; characterize the concentration of carbon monoxide in the flame from images of the flame, and determine the characterized concentration of carbon monoxide in the flame from predetermined correlations of actual concentrations of carbon monoxide in the flame to the expressed values of the at least one parameter determining;
(C) comparing the characterized concentration of carbon monoxide in the flame as characterized according to step (B) to a pre-established threshold concentration value for the concentration;
(D) continuing the concentration of carbon monoxide in the flame from images of the flame taken by the digital camera outside the furnace when the characterized concentration of carbon monoxide in the flame exceeds the pre-established threshold concentration value Characterizing the characterized concentration of carbon monoxide in the flame for a predetermined length of time, characterizing the amount of oxygen supplied into the furnace, the amount of fuel, or both oxygen and fuel available to react in the furnace. adjusting an amount or amounts effective to lower below the pre-established threshold concentration value.

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