JP7759753B2 - System and method for controlling combustion in a furnace - Google Patents

Description

The present invention generally relates to a system for measuring temperatures inside a furnace, such as a rotary furnace, tilting rotary furnace, or reverberatory furnace, among others, utilizing at least one multi-wavelength pyrometer, and to a method for controlling combustion inside such a furnace based on temperatures measured inside the furnace by at least the multi-wavelength pyrometer. The present invention is preferably for use in the ferrous and non-ferrous metals production sector.

Furnaces, in which materials are heated, preferably to their melting temperature, consume a large amount of energy. Furthermore, the temperature to which materials are heated inside a furnace is a significant factor in the quality of the resulting product and the lifespan of the refractory lining that lines the interior of the furnace's heating chamber (the enclosed space defined by the furnace vessel where the materials are heated). Several attempts have been made to measure the temperature inside a furnace to provide better control over the heating process. Some solutions use thermocouples attached to the exterior of the furnace vessel. However, the temperatures measured by these thermocouples are approximations rather than the exact temperature inside the vessel. Other solutions involve drilling holes in the vessel wall and refractory lining into which different heating measurement devices, such as thermocouples or thermometers, are inserted to be closer to the material inside the heating chamber. However, because these temperature measurement devices never directly contact the material being heated and are separated by at least one layer of refractory material, these solutions also only provide an approximation of the material's temperature. Additionally, the drilled holes made in the vessel with such solutions significantly weaken the refractory lining, which may lead to catastrophic failure of the entire vessel's refractory lining and unnecessary or premature refurbishment.

Some other solutions perform measurements of the temperature of the refractory lining from outside the vessel through its opening during vessel downtime, in other words when the vessel is empty. From that measurement, the temperature that the material will reach during furnace operation can be estimated. Again, the obtained temperature can only be considered an approximation of the temperature that will be reached in the refractory material. Moreover, these solutions are time-consuming, as measurements must be performed when the vessel is empty, and reduce overall process productivity insofar as downtime periods are extended to perform the temperature measurements.

The lack of precise control over the temperatures reached by the refractory material, and therefore the material being heated inside the furnace, results in a lack of real control over the final properties and quality of the manufactured product, and also contributes to an increased proportion of oxidized material (dross) due to the very high temperatures reached.

Furthermore, a lack of control over the temperature inside the furnace can similarly result in a lack of control over the combustion of fuel and oxidizer occurring inside the heating chamber, which can lead to the formation of large amounts of carbon monoxide and other undesirable gases, such as methane or hydrogen, inside the furnace. Carbon monoxide is a colorless, odorless, and tasteless flammable gas that is slightly less dense than air and highly toxic to humans and animals. Mechanisms by which carbon monoxide is formed inside the furnace include incomplete combustion of the fuel, incomplete combustion of the combustible material when the material to be heated in the furnace is intended to be burned as well, and/or conversion of carbonaceous material present in or on the material to be heated. Examples of such conversion include pyrolysis and/or incomplete combustion of the carbonaceous material.

Various techniques exist for removing carbon monoxide from the gaseous off-gas exiting the furnace, such as absorbing the carbon monoxide in an absorber or adding a reactant to the off-gas that reacts with and neutralizes the carbon monoxide. Such techniques present drawbacks, including cost and difficulty in implementation and control.

Therefore, due to the lack of control over the actual temperature reached by the material being heated inside the furnace, it is not possible to effectively control the combustion of the fuel and oxidizer being burned inside the furnace to heat the material to be heated, melted, or combusted.

The present invention provides a simple and efficient system that can accurately measure the true, current temperature of the refractory material inside the heating chamber during furnace operation, allowing the heating process to be optimized to operate at the maximum operating temperature of the refractory material. It further provides a method for controlling combustion inside the furnace, optimizing the consumption of fuel and gaseous oxidizer used to heat the material, as well as avoiding or at least minimizing carbon monoxide emissions from the furnace. It further allows for improved efficiency and production rates, and provides better control over the characteristics and quality of industrial products.

A first object of the present invention is a system for measuring the temperature inside a furnace. The furnace comprises a vessel defining a heating chamber in which material is heated. The furnace further comprises a retractable door, at least one burner configured to burn a fuel and a gaseous oxidizer, and a flue through which an exhaust flame extends out of the heating chamber. Each burner of the furnace generates a corresponding flame inside the heating chamber that heats the material. The fuel can reach the furnace in the form of a gas, liquid, or liquefied gas, but is in a gaseous state when burned by the burner. If additional oxidizer is required due to the presence of carbonaceous material in the material to be heated, it can be provided through an extra oxidizer lance located near the burner itself.

The system further includes at least one multi-wavelength pyrometer coupled to the furnace. The at least one multi-wavelength pyrometer is aimed at a portion of the vessel's refractory lining that is not in direct contact with the material being heated, so that the beam emitted by the multi-wavelength pyrometer is projected directly onto the portion of the refractory lining of the heating chamber. This type of pyrometer can provide more precise temperature measurement capabilities than conventional single-wavelength pyrometers when operating in an atmosphere with dense smoke and suspended metal particles, such as those typically encountered in furnaces when ferrous or non-ferrous materials are heated. The at least one multi-wavelength pyrometer is configured to measure the temperature of the corresponding portion of the refractory lining during furnace operation, i.e., during heating of the material inside the heating chamber performed by at least one burner of the furnace. The multi-wavelength pyrometer can determine the temperature of the portion of the refractory lining by capturing the spectral radiation emitted by the refractory lining at a wide wavelength at the same time and location within the portion. The temperature is then determined by the ratio of these signals, which gives the current temperature of the portion of the refractory lining. This temperature of the refractory lining section provides reliable information about the temperature that the material being heated will reach.

Having precise control of the refractory lining temperature is an important aspect of this type of furnace, as during the material heating operation, the refractory lining conducts a tremendous amount of heat to the material being heated. Therefore, the higher the temperature that the refractory material can reach without damaging the refractory lining, the greater the heat transfer to the material being heated. Therefore, controlling the temperature of the refractory lining provides better control of the heating process within the furnace.

As used herein, the term "vessel" refers to a container of various sizes and shapes designed to hold materials at high temperatures, e.g., above the material's melting point. These vessels are widely used in many industrial applications, for example, in the metal manufacturing sector. As known in the art, these vessels are typically made of metal and lined with a refractory material (which may be installed in the form of bricks lining the interior surface of the vessel or cast directly onto the interior surface of the vessel) to protect the metal components of the vessel from the high-temperature materials placed therein. For example, the refractory material used to install the inner protective layer of the vessel may be a magnesia (MgO)-based refractory material incorporating various magnesia aggregates and, ultimately, some binder. Other refractory materials may include _andalusite ( _Al2SiO5 )-based refractory materials, magnesia combined with carbon-based refractory materials, etc. The operating temperatures of the refractory material may reach 2000°C or even higher. In particular, the operating temperatures of refractory materials in the steel manufacturing industry can range between 1500 and 1800°C.

As used herein, the term "material" may refer to any material or substance that can be heated in a furnace. Examples of such materials include metals (e.g., ferrous metals such as iron and steel), metal ores (e.g., iron ore), and other metal compounds, combinations of metal compounds, or combinations of metal and non-metal compounds. These metallic materials include scrap as well as final products. Additional examples of materials include non-ferrous metals such as aluminum and copper, and ores and their other compounds, including scrap as well as final products. Heating such materials prepares them for subsequent chemical and/or physical processing steps.

As used herein, the term "heat chamber" means an enclosed space defined by the walls of a container in which material is heated. The temperature reached inside the heat chamber may be high enough to heat, melt, or combust the material.

In some embodiments, the furnace may further include a resistor to heat the material inside the heating chamber. In this way, the combined effect of the burner and resistor can accelerate the heating process.

In some embodiments, the fuel used to be burned by the burners of the furnace can be selected from the group including natural gas, propane, butane, heavy oil, light oil, coke oven gas (COG), blast furnace gas (BFG), biogas, other synthetic gases of various compositions, and any combination thereof. The fuel can also be any other substance or combination of substances capable of producing heat or power upon combustion.

In some embodiments, the gaseous oxidant can be selected from the group including pure oxygen, low-purity oxygen, oxygen-enriched air, or any combination thereof. The gaseous oxidant may also be other gaseous reactants that include oxygen and have the ability to remove electrons from other reactants, preferably fuel, during oxidation-reduction reactions.

In some embodiments, the furnace is a horizontally oriented furnace, and at least one multi-wavelength pyrometer is directed toward a portion of the refractory lining at the end of the heating chamber, located at a distance from the level reached by the liquid form of the material being heated. As used herein, the term "horizontally oriented furnace" refers to a furnace whose front-to-rear axis is substantially parallel to the floor of the industrial facility in which it is installed, or is at a small inclination angle, such as an inclined rotary furnace. Preferably, at least one multi-wavelength pyrometer projects an infrared beam to measure the temperature on a portion of the refractory lining at the end of the heating chamber, located close to the surface of the material, e.g., 20-30 cm above the surface, within a region defined by an angle of -60° to 60° relative to an axis perpendicular to the surface of the material. The region of the refractory lining located at the end of the vessel is a region of the refractory material that typically reaches higher temperatures, and therefore, it may be advisable to measure the temperature in this region to avoid reaching temperatures that may exceed the working temperature of the refractory material. Additionally, measuring the temperature of areas of the refractory lining that are in close proximity to the material being heated may be advisable as these areas offer the highest heat transfer coefficient to the material being heated.

In some more preferred embodiments, the furnace is selected from the group including, among others, a rotary furnace, an inclined rotary furnace, and a reverberatory furnace. All of these furnaces are oriented substantially horizontally relative to the floor of the facility in which they are located. In particular, a rotary furnace refers to a substantially horizontal furnace that rotates about its front-to-rear axis. An inclined rotary furnace is a rotary furnace that has the ability to tilt vertically relative to its front-to-rear axis. A reverberatory furnace is a horizontally oriented furnace that isolates the material being heated or processed from contact with fuel, but not from contact with combustion gases. In some cases, a reverberatory furnace can also be tilted vertically during the transfer process of already-melted material, and once the material has been transferred, the furnace resumes its horizontally oriented position.

In some embodiments, at least one multi-wavelength pyrometer is a two-color infrared thermometer. Two-color infrared thermometers simultaneously measure the energy emitted by the portion of the refractory lining onto which they are projected, in two adjacent infrared spectral bands. They typically use a layered "sandwich" detector with dual photodiodes to obtain two separate signals. Two-color infrared thermometers can obtain accurate temperature readings even when the radiation picked up by the detector is attenuated by up to 90% due to visual obstructions created by airborne particles, dust, smoke, etc. This makes them particularly useful in environments such as the heating chamber of this type of furnace.

In some embodiments, at least one multi-wavelength pyrometer is coupled to the retractable door or the vessel wall. In some embodiments, there may be at least one multi-wavelength pyrometer coupled to the retractable door of the furnace and at least one other multi-wavelength pyrometer coupled to the furnace wall. The multi-wavelength pyrometers can be inserted into holes located in the retractable door and/or vessel wall, which are connected to the heating chamber by corresponding intervening portholes, and the beam generated by the pyrometer can be transmitted and received through the portholes.

In some embodiments, the system includes two or more multi-wavelength pyrometers that perform redundant temperature measurements to improve the reliability of the measurements obtained. In such embodiments, the multi-wavelength pyrometers may be directed at the same portion of the refractory lining, adjacent portions of the refractory lining, or separate portions of the refractory lining, where the separate portions are in close proximity to the surface of the material and are located at the ends of the heating chamber, bounded by an angle between -60° and 60° with respect to an axis normal to the surface of the material. The system may calculate an arithmetic mean of the temperatures measured by all or some of the multi-wavelength pyrometers to obtain more accurate and reliable measurements.

In some embodiments, the system further includes a heating control module communicatively coupled to the at least one multi-wavelength pyrometer and the at least one burner. The heating control module is configured to receive temperature measurements from the at least one multi-wavelength pyrometer and to modify at least one of the amount of fuel and the amount of gaseous oxidizer burned by the at least one burner in the heating chamber based on the received temperature measurements. To do so, the heating control module can compare the received measurements with a predetermined temperature and adjust the amount of fuel and/or gaseous oxidizer to be burned based on the results of the comparison.

Preferably, the predetermined temperature is the maximum service temperature of the refractory lining. This maximum service temperature is the highest temperature that the refractory material can reach without thermal degradation of its properties. By using the maximum service temperature of the refractory lining, material processing times, as well as fuel and oxidant consumption, are significantly reduced, with improved optimization of the heating process.

For example, the heating control system can adjust the amount of gaseous oxidizer, e.g., oxygen, delivered to the furnace for combustion by the burner by increasing or decreasing the amount of gaseous oxidizer relative to the amount of fuel supplied to the burner. Alternatively, the heating control system can adjust the amount of fuel, e.g., natural gas, available in the furnace for combustion by the burner by increasing or decreasing the amount of fuel relative to the amount of gaseous oxidizer supplied to the burner. Therefore, the heating control module adjusts the amount of fuel and/or gaseous oxidizer injected for combustion by the burner based on the measured temperature. Preferably, the heating control module adjusts the amount of fuel and/or gaseous oxidizer burned in the furnace based on the measured temperature, while maintaining a corresponding stoichiometric relationship between the fuel and the oxidizer. In this manner, the amount of at least one of the fuel and the gaseous oxidizer can be increased or decreased to change the heating power of the flame inside the combustion chamber to increase or decrease the temperature inside the combustion furnace. Thus, the heating process can be optimized by exposing the refractory material to a preset temperature at any time during the heating process. Additionally, by adjusting the amount of fuel and/or gaseous oxidant during the heating process, the energy consumption of the combustion furnace can be optimized. Moreover, by optimizing the heating process, the refractory lining and materials are exposed to a substantially constant temperature during most of the heating process (except for the period until the refractory material first reaches a predetermined temperature), avoiding the presence of temperature peaks or dips that could affect the quality or properties of the final product.

In some embodiments, the system includes at least one digital camera located outside the furnace or mounted on the retractable door or wall of the vessel. These cameras are configured to take images of the flame inside the heating chamber and/or the exhaust flame. Preferably, the camera located outside the furnace is configured to take images of the exhaust flame, while the camera mounted on the furnace is configured to take images of at least one of the flames generated by the burner inside the heating chamber. The retractable door and/or wall may have drilled holes with corresponding portholes through which the respective cameras are inserted.

In some embodiments, the heating control module is configured to receive an image of the flame from the camera and determine the carbon monoxide concentration in the flame based on at least one parameter of the flame in the image. For example, the at least one parameter may be selected from the group including flame intensity, flame area, flame length, flame color coordinates (U, V), and any combination thereof.

In some embodiments, the heating control module is configured to vary at least one of the amount of fuel and the amount of gaseous oxidant burned by at least one burner in the heating chamber based on a combination of the measured temperature and the carbon monoxide concentration in at least one of the flame inside the heating chamber and the exhaust flame.

Therefore, the heating control module can adjust the amount of fuel and/or gaseous oxidizer injected to be burned by the burner based on the measured temperature alone or based on a combination of the measured temperature together with the amount of carbon monoxide determined from the flame image. In such an embodiment, the heating control module is configured to find a compromise between the amount of fuel and the amount of gaseous oxidizer to be burned in the heating chamber in such a way that the temperature of the refractory material is as close as possible to a predetermined temperature while at the same time minimizing carbon monoxide emissions. Preferably, carbon monoxide emissions should tend toward zero, provided that the current temperature of the refractory material is as close as possible to the predetermined temperature.

Carbon monoxide formed within the heating chamber and exiting the heating chamber via the flue can be produced by any one or more of several possible mechanisms, such as incomplete combustion of fuel in the burner, incomplete combustion of combustible material if the material to be heated is also intended to be burned in the furnace, and/or conversion of carbonaceous material in or on the material to be heated; examples of such conversion include pyrolysis or incomplete combustion of carbonaceous material. When the material to be heated includes carbonaceous material, such carbonaceous matter may be organic compounds. For example, scrap containing aluminum, copper, iron, and/or steel may have carbonaceous matter deposited thereon, such as paint or other organic coatings, organic food, and/or human waste. Cullet present in glassmaking materials may have organic material deposited thereon, which may be residues of food or other organic matter that was present on the cullet before it was recycled as cullet.

In some embodiments, the material to be heated in the combustion chamber of the combustion furnace includes a metal.

In some embodiments, at least a portion of the materials being heated in the furnace are combusted or melted. In those cases, at least a portion of the materials are melted, and the furnace can be considered a melting furnace. For example, the materials to be melted can include any metal, such as iron, steel, metal oxides, and other metal compounds. Another example includes products being melted together in a glass-making furnace to form molten glass. Such materials include recycled glass pieces known as cullet, and raw materials known as batch that are melted together to make glass. Such materials 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 containing lime or limestone, silica and/or aluminosilicates (clay), and other optional additives, are heated together to melt and react with each other to form the compounds that make up cement. If some or all of the materials are to be burned, the furnace can be considered an incinerator. Materials that can be heated for combustion include all combustible products, such as carbonaceous fuels and solid waste.

A second object of the present invention is a method for controlling combustion in a furnace. The method includes providing a system as described above and measuring the temperature of a portion of the refractory lining of the heating chamber with at least one multi-wavelength pyrometer during operation of the furnace. A heating control module then receives the measured temperature and compares it to a preset temperature of the refractory lining. Based on the results of the comparison, the heating control module adjusts at least one of the amount of fuel and the amount of gaseous oxidant burned by the burner in the heating chamber. Preferably, the predetermined temperature is the maximum operating temperature of the refractory lining.

In some embodiments, the heating control system can adjust the amount of gaseous oxidizer, e.g., oxygen, available in the furnace for combustion by the burner by increasing or decreasing the amount of gaseous oxidizer relative to the amount of fuel supplied to the burner. In some other embodiments, the heating control system can adjust the amount of fuel for combustion by the burner by increasing or decreasing the amount of fuel relative to the amount of gaseous oxidizer supplied to the burner. Thus, the heating control module adjusts the amount of fuel and/or gaseous oxidizer injected for combustion by the burner based on the measured temperature and, in turn, based on the difference between the measured temperature and a preset temperature. Preferably, the heating control module will adjust the amount of fuel and/or gaseous oxidizer injected for combustion by the burner based on the measured temperature and maintaining a corresponding stoichiometric relationship between the fuel and oxidizer.

In some embodiments, when the measured temperature exceeds the preset temperature, the method includes varying at least one of the amount of fuel and the amount of gaseous oxidizer effective to reduce the temperature of the refractory lining to equal the preset temperature for a predetermined period of time.

In some embodiments, when the measured temperature is less than the preset temperature, the method includes varying at least one of the amount of fuel and the amount of gaseous oxidizer effective to raise the temperature of the refractory material to equal the preset temperature for a predetermined period of time.

In some embodiments, the heating control module receives images of at least one of the flame inside the heating chamber and the exhaust flame from at least one digital camera. Each burner in the furnace generates a flame that heats the material inside the heating chamber. For example, the heating control module may receive only images from an external camera that takes images of the exhaust flame, or may receive only images from one or more cameras coupled to the furnace that take pictures of one or more flames inside the heating chamber, or may receive images of both the exhaust flame and the flame inside the heating chamber.

The heating control module then determines a carbon monoxide concentration in the flame based on at least one parameter of the flame in the image and compares the determined carbon monoxide concentration to a preset carbon monoxide concentration. The at least one parameter of the flame can be flame intensity, flame area, flame length, flame color coordinates (U, V), and any combination thereof, among other parameters. The heating control module then causes the at least one burner to vary at least one of the amount of fuel and the amount of gaseous oxidizer burned in the heating chamber based on a combination of the results of the temperature comparison and the results of the carbon monoxide concentration comparison.

More specifically, the heating control module is configured to find a compromise between the amount of fuel and the amount of gaseous oxidant burned in the heating chamber in such a way that the temperature of the refractory lining is as close as possible to a predetermined temperature while simultaneously minimizing carbon monoxide emissions. In this way, the heating process is optimized while minimizing carbon monoxide concentrations.

In some embodiments, when the measured temperature exceeds the preset temperature and/or the carbon monoxide concentration exceeds the preset carbon monoxide concentration, the method includes varying at least one of the amount of fuel and the amount of gaseous oxidant burned in the heating chamber to an amount effective to reduce the carbon monoxide concentration in the heating chamber so long as the temperature of the refractory lining remains as close as possible to the preset temperature for a predetermined period of time.

In some embodiments, when the measured temperature is less than the preset temperature and/or the carbon monoxide concentration exceeds the preset carbon monoxide concentration, the method includes varying at least one of the amount of fuel and the amount of gaseous oxidant burned in the heating chamber to an amount effective to reduce the carbon monoxide concentration in the heating chamber so long as the temperature of the refractory lining remains as close as possible to the preset temperature for a predetermined period of time.

The system for measuring the temperature inside a furnace and the method for controlling combustion inside the heating chamber of a furnace described herein offer several advantages and/or differences compared to conventional devices and techniques. In particular, the solution should be able to accurately measure the current temperature of the refractory lining inside the heating chamber during furnace operation. By maintaining the refractory material at a predetermined operating temperature throughout the entire heating process, the method for controlling combustion inside a furnace can optimize the consumption of fuel and gaseous oxidizer used to heat the material, which in turn can avoid or at least minimize carbon monoxide emissions from the furnace. This further allows for improved efficiency and production rate of the heating process and provides better control over the characteristics and quality of the industrial product.

To complete the description and to provide a better understanding of the invention, a set of drawings is provided, which form an integral part of the description, illustrate various embodiments of the invention, and should not be construed as limiting the scope of the invention, but merely as examples of how the invention may be put into practice.
The drawings include the following figures:

1 illustrates a system for measuring the temperature inside a rotary furnace, according to certain embodiments of the present invention. 1 illustrates a system for measuring the temperature inside a rotary furnace, which also measures the carbon monoxide concentration inside the rotary furnace, according to certain embodiments of the present invention. 1 illustrates a system for measuring the temperature inside a reverberatory furnace, according to certain embodiments of the present invention. 1 illustrates a flow diagram of a method for controlling combustion in a furnace, in accordance with certain embodiments of the present invention.

FIG. 1 illustrates a system 100 for measuring the temperature inside a rotary furnace 101. It should be understood that the system 100 of FIG. 1 may include additional components, and that some of the components described herein may be removed and/or modified without departing from the scope of the described system 100. Moreover, implementation of the system 100 is not limited to such embodiments.

The furnace 101 depicted in this embodiment is a rotary furnace having a shape typical of a furnace that can rotate about its front-to-rear axis, but the present invention may be practiced equally well with other types of furnaces, including horizontally oriented furnaces, and furnaces having different shapes.

The rotary kiln 101 comprises a vessel 102 defining a heating chamber 103 in which a material 104, e.g., iron, is heated above its melting temperature (approximately 1540°C). The furnace 101 further comprises a retractable door 105 through which the raw material is introduced, one burner 106 that burns a fuel (e.g., natural gas) and a gaseous oxidant (e.g., oxygen) in a stoichiometric relationship (e.g., 2.1 moles of _O2 per mole of natural gas to optimize combustion operation) to generate a heating flame 108 that heats the material 104, and a flue or chimney 107 coupled to the retractable door 105, through which an exhaust flame 109 extends from the heating chamber 103. Through the flue 107, off-gases generated inside the heating chamber 103 also exit with the exhaust flame 109. 1 depicts only one burner 106 located within the retractable door 105, the furnace 101 may include a different number of burners that generate a corresponding number of heating flames within a heating chamber that may be located within the retractable door and/or within the furnace walls. The burners 106 receive fuel and gaseous oxidant from respective sources not shown in this figure.

The vessel 102 and the retractable door 105 are made of a metal or metal alloy capable of withstanding very high temperatures, and their interior surfaces are lined with a layer of refractory lining 110, which may be installed in the form of bricks lining the interior surface of the vessel 102 or may be poured directly onto the interior surface of the vessel 102. The refractory lining 110, for example, this layer of MgO-based refractory material, protects the vessel 102 and the retractable door 105 from heat, pressure, and chemical attack caused by the hot molten material placed therein. The layer of refractory lining 110 substantially covers the interior surfaces of the vessel 102 and the retractable door 105. The MgO-based refractory material has a maximum operating temperature of 2000°C.

The system 100 further includes a two-color infrared thermometer 111 coupled to the retractable door 105. More specifically, the two-color infrared thermometer 111 is inserted into an observation port (not shown in this figure) of the retractable door 105. The two-color infrared thermometer 111 is oriented with respect to the vessel 102 so that the infrared beam emitted by the thermometer 111 is projected onto a portion 112 of the refractory lining 110 that is not in direct contact with the material 104 to be heated. The two-color infrared thermometer 111 captures infrared radiation emitted by the portion 112 of the refractory lining 110 using dual photodiodes at two wavelengths at the same time and location within the portion 112. The temperature of the portion 112 of the refractory lining 110 is then determined by the ratio of these two signals (each of the two signals captured by the dual photodiodes at two different wavelengths). Preferably, portion 112 will be located at the end of vessel 102, in other words, in front of retractable door 105, at a distance "d" from surface 113 of material 104 to be heated, since this area of refractory lining 110 reaches the highest temperature. This portion will likewise be determined by the surface delimited by angles "-α" to "α" relative to axis 114 normal to surface 113 of material 104. More preferably, distance "d" will be in the range between 20 cm and 30 cm, and angle "α" will be in the range between 30° and 60°.

The system 100 further includes a heating control module 115 communicatively coupled to the two-color infrared thermometer 111 and the burner 106. The heating control module 115 receives the temperature measured by the two-color infrared thermometer 111 and modifies the amount of natural gas and/or oxygen burned by the burner 106 in the heating chamber 103 based on the received measurement. To do so, the heating control module 115 compares the received measurement with a predetermined temperature and adjusts the amount of natural gas and/or oxygen to be burned based on the results of the comparison. By way of example, the predetermined temperature may be the maximum operating temperature of the MgO-based refractory material, i.e., 2000°C, or another temperature lower than but close to this maximum operating temperature, such as 1900°C or 1950°C. Since the melting temperature of iron is approximately 1540°C, these operating temperatures of the refractory lining (the temperature inside the heating chamber will be similar to the temperature of the refractory material) will be high enough to melt iron.

For example, the heating control module 115 can increase or decrease the amount of natural gas being burned to adjust the current temperature of the refractory lining 110 to the preset temperature. Simultaneously, or alternatively, the heating control module 115 can increase or decrease the amount of oxygen being burned to adjust the current temperature of the refractory lining 110 to the preset temperature. Preferably, the heating control module 115 can increase or decrease the amount of oxygen or natural gas being burned to adjust the current temperature of the refractory lining 110 to the preset temperature while maintaining a stoichiometric relationship between the oxygen and natural gas.

The system 100 may include an injection control module (not shown) configured to control the flow of oxygen and fuel to the burner 106 (or to multiple burners if the system 100 includes more than one burner 106). The injection control module may act on the valves of the respective fuel and oxidizer injectors (not shown) of the burner 106 to regulate the amount of fuel and/or gaseous oxidizer burned inside the heating chamber 103.

During the heating process of the material 104, the temperature of the portion 112 of the refractory lining 110 is measured by a two-color infrared thermometer 111, and the power of the burner 106 is adjusted based on the measurement so that it continues to provide energy to the furnace 101 to promote the melting of the material 104 within the heating chamber 103. When the refractory lining 110 reaches a preset temperature (preferably the maximum operating temperature of the refractory lining 110), the power of the burner 106 is adjusted so that the temperature does not exceed or fall below the preset temperature or a certain margin above or below the preset temperature. In particular, if the temperature exceeds the preset temperature or margin, the burner 106 will reduce its power to a minimum (e.g., by reducing the amount of fuel and oxidizer burned) or may even shut down; if the temperature falls below the preset temperature or margin, the burner 106 will increase its power (e.g., by increasing the amount of fuel and oxidizer burned).

FIG. 2 illustrates a system 200 for measuring the temperature inside a rotary furnace 201, which also measures the carbon monoxide (CO) concentration inside a heating chamber 203 of the furnace 201. It should be understood that the system 200 of FIG. 2 may include additional components, and that some of the components described herein may be removed and/or modified without departing from the scope of the described system 200. Moreover, implementation of the system 200 is not limited to such embodiments.

1 , plus a digital camera 217 located outside the furnace 201 and positioned relative to the furnace 201 so as to aim the aperture of the camera 217 at the exhaust flame 209 and capture images of the exhaust flame 209. The system 200 also includes an observation port in the wall of the vessel 202, through which the heating flame 208 inside the heating chamber 203 is observed by another digital camera 218, which captures images of the heating flame 208. Both cameras 217 and 218 are communicatively coupled to the heating control module 215 so that the captured images can be sent to the heating control module 215.

The aperture and exposure of cameras 217 and 218 can be adjusted manually or automatically to prevent image blooming due to the high light intensity emitted by flames 208 and 209. Cameras 217 and 218 create digital electronic images of flames 208 and 209 based on at least one parameter of the flames, such as the intensity of flames 208 and 209. The electronic images are electronically transmitted by cameras 217 and 218 to heating control module 215.

Heating control module 215 converts the digital signals corresponding to the images of flames 208 and 209 into one or more values representing the intensity or intensity change of the flames, which may include various values for the area of the flame within the field of view of cameras 217 and 218. The intensity is detected and digitally represented to create a series of values corresponding to the detected intensity. There is a direct relationship between the detected intensity parameter and the concentration of carbon monoxide present in the flame. Similarly, there are direct relationships that can be used between other flame parameters, such as flame area, flame size, and color coordinates (U, V), and the concentration of carbon monoxide in the flame. Moreover, there are other direct relationships between some combinations of the mentioned flame parameters and the CO concentration of the same flame. Therefore, these other parameters or combinations of parameters can be used to derive the CO concentration.

In such an embodiment, the heating control module 215 compares the detected intensity parameters to preset correlations of the intensity parameters to the actual concentration of CO in the flames 208 and 209. These preset intensity-CO concentration correlations can be established in advance by simultaneously measuring the concentration of CO in the flames via established techniques, such as gas sampling using a gas sampling probe, followed by analysis of the sampled gas or continuous emission monitoring, and observing the value of a rendered parameter derived from the intensity-based value as detected by a camera, and recording the measured concentration and parameter value together where they can be retrieved, such as in a computer or written catalog. In this way, each intensity parameter rendered by the system corresponds to an actual concentration value of CO in the flame. Determination of an existing correlation between the rendered parameter and the measured CO concentration may have already been performed during initial setup of the system in the furnace and typically does not need to be repeated for a given furnace each time the furnace is operated. However, operators may find it preferable to establish a new set of correlations not only for different furnaces, but also for a given furnace in situations where the conditions under which a given furnace will operate will vary significantly.

The system 200 further includes a lance 216 for injecting supplemental oxidizer into the heating chamber 203 when additional oxidizer is needed to enter the heating chamber 203. This additional oxidizer is used to react with existing CO within the heating chamber 203, thereby reducing its concentration. The flow of oxidizer through the lance 216 can be controlled by the same injection control module that manages the injection of the burner 206, or by a separate injection control module, all managed by the heating control module 215. The oxidizer passing through the lance 216 can be oxygen, air, oxygen-enriched air, or a higher purity oxidizer having an oxygen content of at least 50% by volume, or even at least 90% by volume. The oxygen content of the oxidizer supplied into the furnace 201 through the lance 216 can be the same or different from the oxygen content of the oxidizer supplied to the burner 206.

During the heating process of material 204, the temperature of portion 212 of refractory lining 210 is measured, and the power of burner 206 is adjusted so that it continues to provide energy to furnace 201 to promote melting of material 204 within heating chamber 203. When refractory lining 210 reaches a preset temperature, the power of burner 206 is adjusted (increased or decreased) so as not to exceed or fall below the preset temperature or a certain margin above or below said preset temperature. Accordingly, the amount of fuel and/or gaseous oxidant injected to be burned by the burner will be adjusted during the melting process as described for the embodiment of FIG. 1.

At the same time that the temperature of the refractory lining 210 is being controlled as described in the previous paragraph, the CO concentration is similarly measured by the heating control module 215. A value for the concentration of CO in the flame is preset, whereby CO concentration values higher than the preset value are considered unacceptable and should be reduced. For example, a CO concentration of 3% by volume or greater may be considered unacceptable for several reasons, such as being dangerous, harmful to the environment, violating environmental regulations, or representing an undesirable imbalance in the furnace's economic and thermodynamic conditions.

When the detected and processed intensity parameters of the flames 208, 209 correspond to an actual CO concentration above a preset threshold, the system takes action that results in injecting additional oxidizer into the furnace 201 via the lance 216. The additional oxygen should react with the CO present in the heating chamber 203 so that at least a portion of the detected excess CO is burned inside the furnace 201 and less CO exits the furnace 201 via the flue 207. This extra oxidizer is independent of the oxidizer required to burn the fuel and can be changed at any time to suit the detected CO level. CO is typically produced during the first phase of the heating process. In particular, CO is typically produced during the first 15-20 minutes, corresponding to the loading of the raw material and the beginning of heating as the carbonaceous material is burned. During the remaining time, no CO is typically produced because all the carbonaceous material has already been burned.

Preferably, the system will have a lance 216 to provide additional oxidant into the furnace 201 to react with the detected excess CO so that the operator does not have to adjust the stoichiometric ratio of oxidant and fuel supplied through the burner 206, although other methods of injecting additional oxidant can be used. For example, the heating control module 215 may increase the amount of oxidant supplied into the furnace 201 using the burner 206 and/or lance 216 without increasing the fuel flow rate. Alternatively, the heating control module 215 may decrease the amount of fuel supplied into the furnace 201 without decreasing the amount of oxidant supplied into the furnace 201.

The injection of additional oxidizer will continue until the detected and processed value representing the CO concentration in the flame falls to a value below the aforementioned preset threshold. More preferably, to minimize the number of times additional oxidizer injections must be performed, additional oxidizer should be provided until the detected and processed value falls below a preset threshold, such as 0.5% to 2% below the preset threshold.

As an example, when natural gas is used as the fuel and oxygen is used as the gaseous oxidant, a stoichiometric relationship of 2.1 moles of oxygen per mole of natural gas can be used. With this stoichiometric relationship, all of the natural gas is burned inside the furnace 201, resulting in (theoretically) no CO emissions. However, excess CO may be detected due to the presence of carbonaceous material in the material being heated 204 or other causes. The amount of oxygen in the heating chamber 203 should then be increased so that the additional oxygen reacts with the excess CO and burns it. Therefore, the heating control module 215 can inject the additional oxygen through the lance 216 to increase the stoichiometry to 2.2 (or higher) moles of oxygen per mole of natural gas for a period of time. This allows the CO to be burned without increasing or decreasing the fuel being burned by the burner 206, so that the temperature of the refractory lining 210 can be maintained at a predetermined temperature. Because the injection of additional oxidizer is independent of the burner, the burner stoichiometry to manage the temperature of the refractory lining 210 and the injection of additional oxidizer to reduce CO concentration can be managed separately by the heating control module 215.

Figure 3 illustrates a system 300 for measuring the temperature inside a reverberatory furnace 301, in accordance with certain embodiments of the present invention. It should be understood that the system 300 of Figure 3 may include additional components, and that some of the components described herein may be removed and/or modified without departing from the scope of the described system 300. Moreover, implementations of the system 300 are not limited to such embodiments.

System 300 may be similar to systems 100 and 200 of FIGS. 1 and 2, but may be installed in a reverberatory furnace 301 of FIG. 3. The reverberatory furnace 301 isolates the material being heated or processed from contact with fuel, but not from contact with combustion gases. The furnace 301 includes six burners: four air-fuel burners 306a and two oxygen-fuel burners 306b. In such an embodiment, there is a camera 317 located outside the vessel 302 to capture images of the exhaust flame 309, and a camera 318 coupled to or located proximate to the vessel 302 to capture images through an observation port of the heating flame 308. In particular, the camera 318 captures images of the heating flame resulting from the merging of the flames 308 generated by the six burners 306a-b before the heating flame exits through the flue 307. The flue is fluidly coupled to the vessel 302 instead of being coupled to the retractable door 305. Both cameras 317 and 318 are communicatively coupled to heating control module 315 such that they can transmit captured images to heating control module 315, from which heating control module 315 can derive the CO concentration inside heating chamber 303. Two-color infrared thermometer 311 is similarly configured to measure the temperature of portion 312 of refractory lining 310 within heating chamber 303 during operation of furnace 301.

Based on the measured temperature of portion 312 and the CO concentration in flames 308, 309 and corresponding deviations from the respective preset temperatures and maximum CO concentrations, heating control module 315 can vary at least one of the amount of fuel and the amount of gaseous oxidant burned by burners 306a-b within heating chamber 303, as described for the embodiment of FIG. 2.

Figure 4 shows a flow diagram of a method 400 for controlling combustion in a furnace, in accordance with certain embodiments of the present invention. Although Figure 4 will be described with reference to the system of Figure 1, the method 400 for controlling combustion in a furnace may also be implemented in the systems of Figures 2 and 3.

In step 401 of method 400, a system 100 is provided for measuring the temperature inside a furnace 101. Method 400 may also be practiced equally well with other types of horizontally oriented furnaces and furnaces having different geometries.

In step 402 of method 400, the multi-wavelength pyrometer 111 measures the temperature of the portion 112 of the refractory lining 110 within the heating chamber 103 during operation of the furnace 101. There may be two or more multi-wavelength pyrometers 111 measuring different portions of the refractory lining 110, and the resulting temperature may be the average of all measured temperatures.

In step 403 of method 400, the heating control module 115 receives the measured temperature and compares it to a preset temperature, which may be less than or equal to the maximum operating temperature of the refractory material of the refractory lining.

In step 404 of method 400, the heating control module adjusts at least one of the amount of fuel and the amount of gaseous oxidant burned by the burner 106 in the heating chamber 103 based on the results of the comparison.

In some embodiments, the heating control module 115 can adjust the amount of gaseous oxidizer, e.g., oxygen, available in the furnace 101 to be burned by the burner 106 by increasing or decreasing the amount of gaseous oxidizer relative to the amount of fuel supplied to the burner 106. In some other embodiments, the heating control module 115 can adjust the amount of fuel available in the furnace 101 to be burned by the burner 106 by increasing or decreasing the amount of fuel relative to the amount of gaseous oxidizer supplied to the burner 106. Thus, the heating control module 115 adjusts the amount of fuel and/or gaseous oxidizer injected to be burned by the burner 106 based on the measured temperature and, in turn, based on the difference between the measured temperature and a preset temperature.

In some embodiments, when the measured temperature exceeds the preset temperature, the method includes varying at least one of the amount of fuel and the amount of gaseous oxidizer by an amount effective to reduce the temperature of the refractory lining 110, and therefore the temperature within the heating chamber 103, to equal the preset temperature for a predetermined period of time.

In some embodiments, when the measured temperature is lower than the preset temperature, the method includes varying at least one of the amount of fuel and the amount of gaseous oxidizer by an amount effective to raise the temperature of the refractory lining 110, and thus the temperature within the heating chamber 103, to equal the preset temperature for a predetermined period of time.

In some embodiments, the heating control module receives images of at least one of the flame inside the heating chamber and the exhaust flame from at least one digital camera. Each burner in the furnace generates a flame that heats the material inside the heating chamber. For example, the heating control module may receive only images from an external camera that takes images of the exhaust flame, or may receive only images from one or more cameras coupled to the furnace that take pictures of one or more flames inside the heating chamber, or may receive images of both the exhaust flame and the flame inside the heating chamber.

In some embodiments, the method includes receiving, in a heating control module, an image of at least one of a flame inside the heating chamber and an exhaust flame from at least one camera, and determining, by the heating control module, a CO concentration in the flame based on at least one parameter of the flame in the image. The CO concentration in the flame corresponds to a CO concentration in the heating chamber. The heating control module then compares the determined CO concentration with a preset CO concentration and causes at least one burner to vary at least one of the amount of fuel and the amount of gaseous oxidizer burned in the heating chamber based on a combination of the results of the temperature comparison and the results of the carbon monoxide concentration comparison. Preferably, the heating control module is configured to find a compromise between the amount of fuel and the amount of gaseous oxidizer burned in the heating chamber in such a way that the temperature of the refractory material is as close as possible to a predetermined temperature while simultaneously minimizing carbon monoxide emissions. Preferably, carbon monoxide emissions should tend to zero, provided that the current temperature of the refractory material is as close as possible to the predetermined temperature.

The heating control module 115, 215 includes hardware and software logic to perform the functions described above. More specifically, the heating control module 115, 215 may incorporate a processing device, which may be at least one of a central processing unit (CPU), a semiconductor-based microprocessor, a graphics processing unit (GPU), a field-programmable gate array (FPGA) configured to retrieve and execute instructions, other electronic circuitry suitable for retrieving and executing instructions stored on a machine-readable storage medium, or a combination thereof. The processing device may retrieve, decode, and execute the instructions stored on the machine-readable storage medium to perform the functions described above. The machine-readable storage medium may be located within the heating control module 115, 215, or may be located remote from but accessible to the heating control module 115, 215 for execution (e.g., via a computer network). As used herein, a "machine-readable storage medium" may refer to any electronic, magnetic, optical, or other physical storage device for containing or storing information, such as executable instructions, data, etc.

In this document, the term "comprise" and its derivatives (e.g., "comprising") should not be understood in an exclusive sense, i.e., these terms should not be interpreted to exclude the possibility that what is being described and defined may include additional elements, steps, etc. The term "another," as used herein, is defined as at least a second or more. The term "coupled," as used herein, unless otherwise indicated, is defined as connected, whether directly without any intervening elements or indirectly with at least one intervening element. Two elements may be mechanically or electrically coupled or communicatively linked through a communications channel, pathway, network, or system.

The present invention is clearly not limited to the particular embodiments described herein, but equally encompasses any variations that may be considered by one skilled in the art (e.g., with regard to the selection of materials, dimensions, components, configurations, etc.) within the overall scope of the invention as defined in the claims.

100, 200, 300 System 101, 201, 301 Furnace 102, 202, 302 Vessel 103, 203, 303 Heating chamber 104, 204 Material 105, 205, 305 Openable door 106, 206, 306 Burner 107, 207, 307 Flue 108, 208, 308 Flame/heating flame 109, 209, 309 Discharge flame 110 , 210, 310 Refractory lining 111, 211 Multi-wavelength pyrometer/two-color infrared thermometer 112, 212, 312 Part 113 Surface 114 Vertical axis 115, 215, 315 Heating control module 216 Lance 217, 218, 317, 318 Camera 311 Two-color infrared thermometer 400 Methods 401, 402, 403, 404 Steps

Claims (10)

A system (200) for controlling combustion in a furnace (201), comprising:
The furnace (201)
a container (202) defining a heating chamber (203) in which a material (204) is heated;
An opening and closing door (205);
at least one burner (206) configured to burn a fuel and a gaseous oxidant, each burner (206) generating a flame (208) inside the heating chamber (203) that heats the material (204);
a flue (207) through which an exhaust flame (209) extends outward from the heating chamber (203);
Equipped with
The system (200)
at least one multi-wavelength pyrometer (211) coupled to the furnace (201);
a heating control module (215) communicatively coupled to the at least one multi-wavelength pyrometer (211) and the at least one burner (206);
At least one camera (217, 218) located outside the furnace (201) or attached to the retractable door (205) or to a wall of the vessel (202);
Equipped with
the at least one multi-wavelength pyrometer (211) is directed toward a portion (212) of the refractory lining (210) of the heating chamber (203) that is not in direct contact with the material (204), whereby the at least one multi-wavelength pyrometer (211) is configured to measure the temperature of the portion (212) of the refractory lining (210) during operation of the furnace (201);
the heating control module (215) is configured to receive a measured temperature of the portion (212) of the refractory lining (210) from the at least one multi-wavelength pyrometer (211);
the at least one camera (217, 218) is configured to take images of at least one of the flame (208) and the exhaust flame (209) inside the heating chamber (203);
the heating control module (215) is configured to receive the image from the at least one camera (217, 218) and determine a carbon monoxide concentration in at least one of the flame (208) and the exhaust flame (209) based on at least one parameter in the at least one of the flame (208) and the exhaust flame (209) in the image ;
the heating control module (215) is configured to vary at least one of the amount of fuel and the amount of gaseous oxidant burned by the at least one burner (206) in the heating chamber (203) based on a combination of the measured temperature and the determined carbon monoxide concentration .
System (200). The system (200) of claim 1, wherein the furnace (201) is a horizontally disposed furnace, and the at least one multi-wavelength pyrometer (211) is directed toward the portion (212) of the refractory lining (210) at the end of the heating chamber (203) and positioned at a distance above the surface of the material (204) when the material (204) becomes liquid. The system (200) of claim 1 or 2, wherein the furnace (201) is selected from the group including a rotary furnace, an inclined rotary furnace, and a reverberatory furnace. The system (200) described in any one of claims 1 to 3, wherein the at least one multi-wavelength pyrometer (211) is a two-color infrared thermometer. The system (200) of any one of claims 1 to 4, wherein the at least one multi-wavelength pyrometer (211) is coupled to the retractable door (205) or a wall of the vessel (202). The system (200) of any one of claims 1 to 5, wherein the at least one parameter is selected from the group including flame intensity, flame area, flame length, flame color coordinates (U, V), and any combination thereof. A method (400) for controlling combustion in a furnace, comprising:
Providing (401) a system (200) according to any one of claims 1 to 6 ;
measuring (402) the temperature of a portion of the refractory lining of the heating chamber with the at least one multi-wavelength pyrometer during operation of the furnace;
comparing (403) the measured temperature with a preset temperature of the refractory lining by the heating control module;
receiving, in the heating control module, an image of at least one of the flame and the exhaust flame inside the heating chamber from the at least one camera;
determining, by the heating control module, a carbon monoxide concentration in at least one of the flame and the exhaust flame based on at least one parameter in the at least one of the flame and the exhaust flame in the image;
comparing, by the heating control module, the determined carbon monoxide concentration with a preset carbon monoxide concentration;
varying, by the heating control module, at least one of the amount of fuel and the amount of gaseous oxidant burned by the at least one burner in the heating chamber based on a combination of the results of the comparison of temperature and the results of the comparison of carbon monoxide concentration ;
The method (400) includes: 8. The method (400) of claim 7 , wherein the preset temperature is a maximum use temperature of the refractory material of the refractory lining. 9. The method (400) of claim 7 or 8, wherein when the measured temperature exceeds the preset temperature, the method (400) includes varying, by the heating control module, at least one of the amount of fuel and the amount of gaseous oxidant to the amount effective to reduce the temperature of the refractory lining to equal the preset temperature for a predetermined period of time. 10. The method (400) of any one of claims 7 to 9, wherein when the measured temperature is lower than the preset temperature, the method (400) includes varying, by the heating control module , at least one of the amount of fuel and the amount of gaseous oxidant to the amount effective to raise the temperature of the refractory lining to equal the preset temperature for a predetermined period of time.