CN111801527B

CN111801527B - Flame image analysis for furnace combustion control

Info

Publication number: CN111801527B
Application number: CN201880089988.XA
Authority: CN
Inventors: V·科雷亚艾萨内托; E·J·埃文森; K·W·阿尔布雷希特; J·E·凯莉; J·德迭戈里肯; J·维萨斯普尔
Original assignee: Praxair Technology Inc
Current assignee: Praxair Technology Inc
Priority date: 2018-03-02
Filing date: 2018-03-02
Publication date: 2023-01-24
Anticipated expiration: 2038-03-02
Also published as: JP2021515173A; WO2019168542A1; JP7102535B2; MX2020008812A; PL3555527T3; AU2018410969B2; KR102572097B1; EP3974721A1; KR20200118493A; CN111801527A; AU2018410969A1; AU2022203748A1; EP3555527A1; EP3555527B1; BR112020017165A2; ES2904862T3; KR20220136487A; RU2751829C1; WO2019168542A8

Abstract

The operation of a combustion control system of a furnace is controlled by image analysis of a flame produced by combustion within the furnace, either externally of the furnace or within the furnace, to correlate the image with the carbon monoxide content of the flame and adjusting the flow of oxygen and/or fuel into the furnace in response to the correlation.

Description

Flame image analysis for furnace combustion control

Technical Field

The present invention relates to the operation of a combustion control system for a furnace (by furnace is meant an enclosed space, such as a combustion chamber, in which fuel and gaseous oxidant are combusted) in which material is heated and the heating can result in the formation of carbon monoxide to control and/or reduce the emission of carbon monoxide from the furnace.

Background

The operation of heating the material in the furnace may result in the formation of carbon monoxide in the furnace. Mechanisms by which carbon monoxide may be formed include incomplete combustion of the 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 conversion of carbonaceous material present in or on the material to be heated. Examples of such conversions include pyrolysis and/or incomplete combustion of carbonaceous materials.

When carbon monoxide is formed in the furnace, it is generally undesirable for the carbon monoxide to be emitted from the furnace. There are various techniques for removing carbon monoxide from the gaseous exhaust gas leaving the furnace, such as absorbing the carbon monoxide onto an absorbent or adding a reactant to the exhaust gas that reacts with the carbon monoxide. Such techniques present drawbacks such as expense and difficulty of implementation and control.

The present invention provides an efficient method for avoiding carbon monoxide emissions from a furnace. An efficient method for controlling the operation of the heating furnace for improved efficiency and productivity is also provided.

Disclosure of Invention

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

(A) Heating a material containing carbonaceous material in a furnace having a flue in which a flame is formed, using heat generated by combustion in the furnace of a fuel and a gaseous oxidant fed into the furnace, thereby producing carbon monoxide derived from the carbonaceous material, wherein the flame can exit the furnace from the flue;

(B) Characterizing the concentration of carbon monoxide in a flame from an image of the flame taken from inside or outside 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 to the concentration of carbon monoxide in the flame, and determining the characterized concentration of carbon monoxide in the flame from a predetermined correlation of the actual concentration of carbon monoxide in the flame with the expressed value of the at least one parameter;

(C) Comparing the characterized concentration of carbon monoxide in the flame characterized according to step (B) with a pre-set threshold concentration value of the concentration;

(D) When the characteristic concentration of carbon monoxide in the flame exceeds the predetermined threshold concentration value, adjusting an amount of oxygen, an amount of fuel, or an amount of both oxygen and fuel fed into the furnace that is available for reaction in the furnace to one or more amounts thereof that are effective to reduce the characteristic concentration of carbon monoxide in the flame to equal or less than the predetermined threshold concentration value for a predetermined period of time while continuing to characterize the concentration of carbon monoxide in the flame from an image of the flame taken by the digital camera external to the furnace.

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

(B) Characterizing the concentration of carbon monoxide in the flame from an image of the flame taken from inside the furnace or outside 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, and determining the characterized concentration of carbon monoxide in the flame from a predetermined correlation of the actual concentration of carbon monoxide in the flame with the expressed value of the at least one parameter;

(D) When the characteristic concentration of carbon monoxide in the flame exceeds the predetermined threshold concentration value, adjusting the amount of oxygen fed into the furnace available to react with carbon monoxide in the furnace to an amount effective to reduce the characteristic concentration of carbon monoxide in the flame to equal or less than the predetermined threshold concentration value for a predetermined period of time while continuing to characterize the concentration of carbon monoxide in the flame from an image of the flame taken by the digital camera external to the furnace.

Drawings

Fig. 1 is a schematic diagram showing how the invention can be implemented on a furnace installation.

FIG. 2 is a chart showing the sequence of steps of the present invention.

Detailed Description

The present invention may be used to heat any material that may be heated in a furnace. Examples of such materials include ferrous metals such as iron and steel, including finished goods and scrap, as well as iron-containing ores and other compounds. Additional examples include non-ferrous metals such as aluminum and copper, including finished goods and scrap, as well as their ores and other compounds. Any such material is heated to prepare it for further chemical and/or physical treatment.

The invention may also be used to heat materials 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 melt together in a glass making furnace to form molten glass; such materials include recycled glass gobs, known as cullets, and raw materials, known as batches, which are melted together to make glass, and typically include sodium oxide, potassium oxide, and sodium and potassium silicates. Another example of such an operation is a cement kiln, in which raw materials, typically comprising lime or limestone, and silica and/or aluminosilicates (clays) and other desired additives, are heated together so that they melt and react with each other to form cement-constituting compounds.

The invention may also be used to heat materials in which some or all of the material is to be combusted, such as incinerators. 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 treated according to the invention has the following characteristics: they include some carbonaceous material so that heating the material can cause the carbonaceous material to form carbon monoxide in the furnace. The carbonaceous matter present may be organic compounds present in the material being heated and/or may constitute part or all of the material being heated and then combusted in the furnace. For example, scrap material comprising aluminum, copper, iron, and/or steel may carry carbonaceous matter thereon, such as paint or other organic coatings, organic food and/or human waste, and the like. Cullet present in the glassmaking material may carry organic matter thereon, which is a residue of food products or other organic matter present on the cullet prior to recycling the cullet as cullet.

The carbon monoxide formed in the furnace may be produced by any one or more of several possible mechanisms, such as incomplete combustion of the 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 conversion of carbonaceous material in or on the material to be heated, examples of such conversion including pyrolysis or incomplete combustion of the carbonaceous material. The present invention is useful regardless of the source or mechanism of formation of carbon monoxide, as carbon monoxide emitted from the furnace is undesirable regardless of the source of carbon monoxide.

Turning to fig. 1, a furnace 1 is shown in cross-section. Although the depicted furnace has the typical shape of a furnace that is rotatable about an axis that will be horizontal in the embodiment shown in fig. 1, the invention may also be practiced with any other type and shape of furnace. In the heating furnace 1, the material to be heated is indicated as 2. The material 2 is heated by heat from a flame 4 formed in the furnace by combustion of fuel 13 with oxidant 12 at burner 11. Suitable fuels 13 may be any combustible carbonaceous material, preferred examples of which include methane, natural gas, and atomized fuel oil. Suitable oxidants fed at 12 include any gaseous product containing oxygen, such as air, oxygen-enriched air and streams having an oxygen content of at least 50% by volume, preferably at least 90% by volume. Streams having such high oxygen content can be obtained commercially from any of several atmospheric gas suppliers. Although one flame 4 is shown, a furnace that can be used to practice the invention can 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 pass out of the furnace 1. The gaseous products exiting the flue 6 include combustion gaseous products between the oxidant 12 and the fuel 13, such as carbon dioxide and water vapor, and may contain Volatile Organic Compounds (VOC) and may contain carbon monoxide. In the practice of the invention, if only one flue 6 is present, the flame 15 may extend from the outlet 7 of the flue 6. If there are two or more chimneys 6, there may be a flame 15 extending from at least one outlet 7 of at least one chimney 6. Carbon monoxide may be present in the flame 15 and may or may not be completely combusted in the flame 15.

The furnace 1 may comprise an observation opening 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 positioned outside the heating furnace 1. The camera 21 includes an aperture 22 through which the camera 21 receives an image. In one embodiment of the invention, the camera 21 is positioned relative to the furnace 1 such that the aperture 22 of the camera 21 is directed at the flame 15. In another embodiment of the present invention, the camera 21 is positioned relative to the furnace 1 such that the aperture 22 of the camera 21 is aligned with the viewing port 10 such that the camera 21 can receive an image of the flames 4 inside the furnace 1.

The camera 21 is a digital camera, which means that the camera 21 detects one or more features of the object (in this case, the detected features include at least the intensity of the flame at which the camera 21 is directed) and represents, in digital form, an image electronically corresponding to the detected features. Digital cameras having such capabilities are commercially available. They may be stand alone units or may be part of a piece of equipment that also has additional functional capabilities such as telephone, time keeping, etc.

Still referring to fig. 1, the controller 25 controls the flow rates of the oxidant 12 and the fuel 13 to the combustor 11 (or to multiple combustors if more than one combustor 11 is present). Optionally but preferably, lance 27 is provided to discharge supplemental oxidant into furnace 1 when additional oxidant is to be passed into furnace 1. The flow of oxidant through the lance 27 is controlled by a controller 29. The oxidant which can be fed into the furnace 1 through the lance 27 can be air, oxygen-enriched air or oxidant of higher purity having an oxygen content of at least 50% by volume and even at least 90% by volume. The oxygen content of the oxidant fed to the furnace 1 through the lance 27 may be the same as or different from the oxygen content of the oxidant 12 fed to the furnace 1.

In fig. 1, block 23 refers to the complete system performing the sequence of steps shown as 31, 33 and 35 in fig. 2. The system may reside in one integrated device, or 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 these components may be included in the camera 21. However, for functional convenience and because the camera 21 may be located in a potentially hot and dusty environment, and thus may cause damage to components such as the processor, the camera 21 is preferably physically separated from the other components, and the camera 21 is preferably connected by a cable or wireless connection to the components that perform at least step 31, which first follows the acquisition of images by the camera 21. As can be seen in fig. 1, system 23 is connected to camera 21 to receive input from camera 21, and system 23 is connected to control 25 and (if present) control 29 to provide signals to

controls

25 and 29.

In operation, combustion takes place inside the furnace 1 in the presence of the material 2 in the furnace 1. A flame is formed in the furnace, which may be represented by a flame 15 protruding from the opening 7 of the flue 6. In one embodiment of the invention, the camera 21 is directed at the flame 15 such that an image of the flame 15 is received through the aperture 22. In another embodiment of the invention, the camera 21 is directed at the furnace 1 such that an image of the flames 4 inside the furnace 1 is received at the aperture 22 through the viewing port 10. The flame 15 or 4 may be very bright and therefore the aperture 22 and exposure should be adjusted to prevent blooming of the image. In some cases, it may be desirable to be able to dynamically adjust the exposure of an image so that sufficient resolution is achieved when the image is very dark. In most cases, 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 the camera 21 from the flame 15 or 4 and a given size of the flame 15 or 4. The camera 21 creates 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 electronically transmitted 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 converted into one or more values representing the intensity or various intensities of the flame, and may include a series of values over the flame region within the field of view of the camera 21. The intensities are detected and represented numerically to create 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-set correlation of the intensity parameter with the actual concentration of carbon monoxide in the flame. The pre-set correlation may be established by simultaneously measuring the concentration of carbon monoxide in the flame via established techniques such as analysis of the sampled gas after gas sampling using a gas sampling probe, or continuous emission monitoring, and observing the value of the expressed parameter derived in step 31 from the value based on the intensity detected by the camera 21, and recording the measured concentration and parameter value together, where they may be read together, such as in a computer or written directory. Thus, each intensity parameter represented by the system corresponds to an actual concentration value of carbon monoxide in the flame. The determination of the pre-existing correlation between the expressed parameter and the measured concentration of carbon monoxide may already be made during the initial setup of the system of the furnace, and typically does not need to be repeated in a given furnace each time the furnace is run. However, the operator may find it preferable to establish a new set of correlations for different furnaces and at a given furnace, in the event that the conditions under which a given furnace is to be operated will differ significantly.

The system described herein may be used to implement any of several methods of controlling the operation of a furnace. One such method is to control carbon monoxide emissions by controlling the oxygen feed to the furnace, which will now be described:

the operation of the furnace will have a pre-set concentration value of carbon monoxide in the flame, so that a concentration value of carbon monoxide above this value is unacceptable and must be reduced. Typical values for excess carbon monoxide may range from 3 to 30 volume percent, but these values may vary depending on the location, the nature of the material 2 being heated in the furnace 1, or other conditions. The predetermined value is based on any factor or group of factors of significance to the operator, such as a value indicative of a risk of excessive environmental damage, or a risk of violation of applicable environmental regulations, or an imbalance indicative of undesirable economic and thermodynamic conditions in the furnace.

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

When the detected intensity parameter and the processed intensity parameter correspond to an actual concentration of carbon monoxide in the flame that exceeds a predetermined threshold, then the system performs an action that results in the provision of additional oxygen within the furnace 1. In fig. 2, this action is represented as generating a signal in step 33 that activates the combustion control system 35 to cause additional oxygen to be present within the furnace 1. The additional oxygen will react with the carbon monoxide present in the furnace so that less carbon monoxide leaves the furnace 1 via the flue 6 in the flame 15 or otherwise. Additional oxygen may be provided to furnace 1 by any of several modes to react with the detected excess carbon monoxide. For example, one such mode is for control system 35 to increase the amount of oxygen 12 fed into furnace 1 through burner 11, without increasing the flow rate of fuel 13 into furnace 1. Another possible mode is to feed supplemental oxidant or an increased amount of supplemental oxygen through supplemental feed line 29 (shown in FIG. 1) without increasing the flow rate of fuel 13 into furnace 1. Another possible mode is to reduce the amount of fuel 13 fed into the heating furnace 1 without reducing the amount of oxygen 12 or supplemental oxygen 27 fed into the heating furnace 1. Alternatively, any combination of these modes may be implemented simultaneously.

The preferred embodiment is to provide supplemental oxygen 27 so that the operator does not have to adjust the stoichiometric ratio of oxidant and fuel fed through one or more of the burners 11. The supplementary feed line 27 should preferably be positioned such that it feeds the oxidant into a region within the furnace where relatively high amounts of carbon monoxide may be present, or into a region where carbon monoxide would be particularly undesirable, such as near the region of the interior of the furnace 1 that connects with the upstream end of the flue 6.

The supply of additional oxygen is continued until the detected value and the processed value indicative of the concentration of carbon monoxide in the flame decrease to a value equal to or less than the above-mentioned predetermined threshold value. If preferred, additional oxygen should be provided until the detected and processed values are below a predetermined threshold, such as 0.5% to 2% below a predetermined threshold, to minimize the number of times the provision of additional oxygen must be started and then stopped.

Steps

31, 33 and 35 may be performed in suitably programmed controllers connected to each other by suitable cables or by wireless connections. Rather, they may all reside in one piece of hardware.

As noted, the systems described herein may also be used to perform other methods of controlling the operation of a furnace by adjusting the feed of oxygen (oxidant), fuel, or both oxygen and fuel to achieve desired combustion characteristics within the furnace or to perform control of the furnace operation at start-up. In this embodiment of the invention, a set point or more than one set point (typically 3 to 10 set points) is/are preset in the controller, which corresponds to the fuel flow rate and the oxygen flow rate to the furnace (in one burner or in each of several burners if the furnace has multiple burners).

In these embodiments, the image analysis parameters are received and compared to control level set points defined by the user in step 33, who also preset flow rate values to be used in the burner and oxidant lance for each level. The last part is communicated with a heating furnace combustion control PLC. The user may also select other processing parameters such as timers to activate/deactivate the control levels. At this stage, the user may also select the language that the operator will see will appear on the control panel, and may also select other variables to be controlled. The controller 33 collects data from the cameras and related software, processes the data along with user inputs (limits, oxygen flow set point, natural gas flow set point, delay time), and dynamically adjusts the process to reduce CO emissions and increase furnace production.

The user selects the control variables and sets the start limit, stop limit, and "turn-off delay" values (in any number of desired each, typically 1 to 10 each, and the number of "turn-on delay" values (typically 1 to 5)). The user also sets an oxygen flow set point and a burner natural gas flow set point for each corresponding limit. When the on-delay time is exceeded by exceeding the first start limit, the software sets the corresponding oxygen flow set point and natural gas flow set point. When the limit is exceeded, the set points will be processed in sequence. Once the control variable falls below the stop limit and the turn-off delay timer is complete, the previous level is set.

When the control variable falls below all the stop limits and the final turn-off delay ends, the oxygen set point is set to zero and the burner fuel set point is returned to normal control.

If the heating oven door is open, the oxygen set point is set to zero and the burner fuel set point is returned to normal control.

The systems and methods described herein enable an operator to achieve benefits in the operation of a furnace, such as more efficient operation in terms of, for example, fuel consumption and reduced cycle time. By monitoring the carbon monoxide content in the flame (and monitoring in real time, which may make use of the present invention), an operator may adjust the feed rate of oxygen and/or fuel to the furnace so that the heat of combustion of the carbon monoxide may be maintained in the furnace and advantageously utilized, thereby enabling the operator to achieve the same degree of heating and/or melting of material within the furnace in a shorter cycle time and enabling the operator to achieve heating and/or melting with less fuel consumption per unit of material heated.

The present invention is an advantageous method for controlling carbon monoxide emissions from a furnace and for controlling the operation of the entire furnace for several reasons. One reason is that the method of the present invention does not require a continuous direct measurement of the concentration of carbon monoxide in the flame to operate the furnace. Another reason is that the present invention measures detecting parameters that are characteristic of carbon monoxide in the flame, rather than measuring parameters that tend to be more variable and less reliable in flue or exhaust gases. Moreover, 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 is therefore more reliable and less susceptible to temperature fluctuations in the flame. In contrast, the method of the present invention is based on the correlation of image parameters corresponding to the concentration of carbon monoxide in the flame, which is believed to be a novel and effective mode of operation.

Other advantages would include reduced need for maintenance of the equipment used; lower installation costs and little or no downtime for installing a furnace implementing the system of the present invention; and faster response times to adjust the oxygen feed, the fuel feed, or both the oxygen feed and the fuel feed when the system detects a need to increase the amount of oxygen and/or the amount of fuel fed into the furnace or other changed conditions.

Claims

1. A method of heating a material in a furnace, the method comprising:

(A) Heating a material containing carbonaceous material in a furnace having a flue in which a flame is formed, using heat generated by combustion in the furnace of a fuel and a gaseous oxidant fed into the furnace, thereby producing carbon monoxide derived from the carbonaceous material, the flame being extendable out of the furnace from the flue;

(D) When the characteristic concentration of carbon monoxide in the flame exceeds the predetermined threshold concentration value, adjusting an amount of oxygen, an amount of fuel, or an amount of both oxygen and fuel fed into the furnace that is available for reaction in the furnace to one or more amounts thereof that are effective to reduce the characteristic concentration of carbon monoxide in the flame to equal or less than the predetermined threshold concentration value for a predetermined period of time while continuing to characterize the concentration of carbon monoxide in the flame from an image of the flame taken by the digital camera external to the furnace,

wherein the method does not measure the temperature of the flame and is not based on measuring the difference in flame temperature.

2. The method of claim 1, wherein the material comprises a metal.

3. The method of claim 1, wherein in step (a), at least a portion of the heated material is combusted.

4. The method of claim 1, wherein in step (a), at least a portion of the material that has been heated is melted.

5. The method defined in claim 1 wherein in step (D) adjusting the amount of oxygen in the furnace that is available for reaction in the furnace includes increasing the amount of oxygen fed into the furnace relative to the amount of the fuel fed into the furnace.

6. The method defined in claim 1 wherein in step (D) adjusting the amount of oxygen in the furnace that is available for reaction in the furnace includes reducing the amount of the fuel fed into the furnace relative to the amount of oxygen fed into the furnace.

7. The method of claim 1, wherein the flames extend from the flue out of the furnace, and an image of the flames extending from the flue out of the furnace is taken by the digital camera.

8. The method of claim 1, wherein an image of the flame inside the furnace is taken by the digital camera.

9. The method of claim 1, comprising adjusting the amount of oxygen fed into the furnace when the characteristic concentration of carbon monoxide in the flame exceeds the predetermined concentration value.

10. The method of claim 1, comprising adjusting the amount of fuel fed into the furnace when the characteristic concentration of carbon monoxide in the flame exceeds the predetermined concentration value.

11. The method of claim 1, comprising adjusting the amount of oxygen and the amount of fuel fed into the furnace when the characteristic concentration of carbon monoxide in the flame exceeds the predetermined concentration value.

12. A method of heating a material in a furnace according to claim 1, the method comprising:

13. The method defined in claim 12 wherein in step (D) adjusting the amount of oxygen in the furnace that is available to react with carbon monoxide in the furnace comprises increasing the amount of oxygen fed into the furnace relative to the amount of fuel fed into the furnace.

14. A method according to claim 12 wherein in step (D) adjusting the amount of oxygen in the furnace available for reaction with carbon monoxide in the furnace comprises reducing the amount of the fuel fed into the furnace relative to the amount of oxygen fed into the furnace.