Monitoring flammable materials in gas streams

Abstract

1. A method and device for monitoring combustible material in a high temperature gas stream and generating a control signal, wherein a controlled injection of an oxidant is injected into the gas stream by a lance (8) extending between a window of a monitoring device (9) and a flow path (3) of the gas stream, the lance (8) defining a line of sight between the window and the gas stream in the flow path (3), in the presence of combustible material in the gas stream, the combustible material combusts with the oxidant in a flame (10) in the gas stream forward of the lance (8), one or more characteristics of the flame that correlate with a concentration of combustible material in the gas stream are detected by the monitoring device (9) through the line of sight and the window, the monitoring device (9) processing the one or more detected flame characteristics and generating a control signal based on the one or more detected flame characteristics.

Description

[Technical Field]

[0001] The present invention relates to a method for monitoring the presence of combustible materials in a gas stream. [Background technology]

[0002] It is known in the art to monitor flames inside combustion furnaces and use the monitoring results to control the combustion process within the furnace.

[0003] EP-A-2843340 proposed a method for detecting combustion gases in the atmosphere of a furnace heated by a burner and an oxygen supply. According to this known method, oxygen is injected at a high velocity into the combustion furnace to generate an airflow (circulation) in the furnace atmosphere. The combustion gases to be detected are ignited by the presence of said oxygen, and the spectrum of the resulting flame is used to detect the presence of said combustion gases in the furnace atmosphere. In practice, this known method exhibits a number of drawbacks. In most industrial combustion furnaces, the volume occupied by the combustion space and the flow patterns that usually occur in the combustion atmosphere are such that an excessive amount of oxygen or an excessive oxygen injection rate, typically both, is required to generate a sufficient airflow in the furnace atmosphere so that combustion gas detection can be reliably performed, as opposed to relying on temporary local accumulations of combustion gases in the atmosphere. Injecting oxygen in the amount and / or rate required for reliable detection would not only be expensive, but would also significantly affect the actual purpose for which the combustion furnace is operated, in that it could result in, for example, excessive oxygenation of the charge and altered temperature profiles in the furnace. In addition, it is typically not possible to separate the spectrum of the flame generated through the oxygen injection and the spectrum of the flame or flames generated by the main burner of the combustion furnace, which again makes the detection of combustion gases by the described method unreliable.

[0004] Monitoring the presence of combustion gases in the exhaust gases of a combustion furnace is also known in the art. From ES-A-2207389, a method is known that does not have the drawbacks of the first-mentioned known method. According to ES-A-2207389, oxygen is injected into the exhaust gases of a combustion furnace for melting aluminum charges, which may contain organic substances, and the temperature change caused by said oxygen injection in the exhaust gases is detected, and the oxygen / fuel ratio of the burners in the furnace is adjusted depending on the detected temperature change. As disclosed in ES-A-2207389, the oxygen / fuel ratio of the burners in the furnace is adjusted depending on whether the detected temperature change is positive or negative, which method has limited accuracy and can lead to frequency changes in the oxygen / fuel ratio of the burners in the furnace and unstable furnace operation. Using the value of the temperature change that has occurred provides some improvement, but remains inaccurate when it fails to take into account other factors that may affect the detected temperature change, such as periodic (e.g., burner power changes) or non-periodic (fragment type) changes in the temperature at which the exhaust gases leave the melting furnace. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need for a more reliable and accurate method for detecting combustible materials in the combustion gases generated by a combustion process.

[0006] It is an object of the present invention to overcome at least some of the problems associated with the above-referenced prior art methods. [Means for solving the problem]

[0007] The ability to detect combustible substances in gases is not only of interest for gases generated by combustion processes, so the solution proposed by the present invention is also applicable to gases other than combustion gases that are available at temperatures similar to those of combustion furnace exhaust gases.

[0008] The present invention specifically relates to a method for monitoring combustibles in a gas stream flowing at a temperature of at least 550° C. along a flow path extending from a gas inlet to a gas outlet, the flow path therefore not including any equipment or devices, such as a combustion furnace, that generate the gas stream being monitored.

[0009] The temperature of the gas stream flowing along the flow path is preferably at least 600°C, more preferably at least 700°C. The temperature may reach up to 1500°C or even up to 1800°C.

[0010] The combustible material in the gas stream is monitored by a monitoring device including a window, the lance extending between the window of the monitoring device and a flow path of the gas stream and defining a line of sight between the window and the gas stream within the flow path.

[0011] According to the invention, a controlled jet of oxide having an oxygen content of 22-100% by volume is injected into a gas stream by a lance. In the presence of combustible material in the gas stream, the combustible material burns with the injected oxide in a flame in the gas stream ahead of the lance.

[0012] In this context, a fluid jet is considered "controlled" when the jet flows at a controlled or determined flow rate and / or velocity.

[0013] According to the present invention, one or more characteristics of a flame that correlate with the concentration of combustible material in a gas flow are detected by a monitoring device through a line of sight and a window, and the monitoring device then processes the one or more detected flame characteristics and generates a control signal based on the one or more detected flame characteristics.

[0014] Since the monitoring is carried out in the flow path downstream of any equipment where a gas flow is generated, said monitoring is possible without any risk of interference from processes taking place within said equipment with the detection of one or more flame characteristics.

[0015] The flow path is typically located within or defined by the gas line.

[0016] The controlled injection of oxide has multiple functions. First, the controlled injection provides oxygen, which, together with any combustible materials in the gas stream, initiates a flame in the gas stream. Furthermore, because the controlled injection provides the oxygen in a controlled manner, the flame also initiates in a controlled manner, thus making monitoring of any combustible materials present more reliable. Additionally, the controlled injection of oxide shields the monitoring device from the gas stream, thus preventing it from being damaged or fouled by the gas stream, its components, and / or its temperature, thereby increasing the durability and reliability of the method.

[0017] The method according to the invention can be carried out with any oxide having an oxygen content of at least 22% by volume, such as oxygen-enriched air, but oxides with higher oxygen contents are preferred in order to more easily ignite combustible materials in the gas stream. The controlled injection oxide may have an oxygen content of at least 30% by volume, preferably at least 60% by volume, more preferably at least 90% or at least 98% by volume oxygen.

[0018] Similarly, the method may be carried out by injection of the oxide into the gas stream at ambient or non-cryogenic sub-ambient temperatures, but typically above 0°C, with controlled injection of the oxide at higher temperatures making ignition of combustible material in the gas stream easier. Thus, the oxide used in the method according to the invention may be at ambient temperature or above, for example pre-heated to a temperature of at least 100°C, at least 150°C, at least 200°C, etc., and particularly up to 600°C or up to 650°C.

[0019] According to a preferred embodiment of the present invention, the controlled injection of oxide is 0.1 Nm 3 / h~50.0Nm 3 / h, more preferably 0.2 to 25.0 Nm 3 / h.

[0020] According to an advantageous embodiment, the lance is positioned so that the line of sight forms an angle of 5° to 175°, preferably 25° to 155°, more preferably 45° to 135° with the flow direction of the gas stream, the angle being defined as the angle between the line of sight and the gas flow in the flow direction of the controlled jet and the gas stream. Thus, when the angle is less than 90°, the oxide jet is injected partially co-currently with the gas stream, and when the angle is greater than 90°, the controlled jet is injected partially counter-currently with the gas stream. When the angle is 90°, the controlled oxide jet is injected perpendicular to the gas stream flow along the flow path.

[0021] The extent to which the lance extends into the flow passage can vary, and is typically between 0% (eg, when the downstream end of the lance is flush with the outer wall of the flow passage) and 50% of the cross-sectional diameter of the flow passage.

[0022] Heating exhaust gases from a thermal treatment is known from EP-A-2701716, in that the exhaust gases are passed through a combustion chamber where heat is generated by burning a fuel with an oxide containing at least 25% oxygen by volume. The exhaust gases can thereby be heated to temperatures between 200 and 1700°C, specifically between 400 and 800°C. According to one embodiment, combustible substances in the exhaust gases are used as fuel and burned in the combustion chamber by the oxide without the addition of additional fuel. The combustion chamber may have an extended exhaust gas escape tube with a refractory wall. A burner lance may be used to inject fuel and oxide, or oxide alone, into the combustion chamber, through which the fuel and oxide can be provided coaxially. The burner lance may be equipped with an ignition system and monitored by an infrared or ultraviolet probe. Monitoring any combustible substances present in the exhaust gas is not disclosed or suggested in EP-A-2701716.

[0023] Control parameters according to the present invention, generated by a monitoring device based on one or more detected flame characteristics, may be used in a variety of ways or combinations of ways, for example, the control parameters may be communicated to a user interface to allow an operator to verify or record the combustible content of the gas stream.

[0024] The control parameter may be compared to a predetermined reference value or a predetermined reference range in a processing unit, which may or may not be integrated into the monitoring device, and an alarm signal may be generated if the generated control parameter is higher or lower than the reference value (depending on the nature of the control parameter and whether the reference value is a predetermined maximum or a predetermined minimum value) or if the generated control parameter falls outside the predetermined range.

[0025] The control parameters may be communicated to upstream and / or downstream equipment, where the generated control parameters are effectively used as control parameters for the control of said equipment and / or the process performed therein. It should be understood that upstream equipment is equipment located upstream of the gas inlet of the flow path in the flow direction of the gas flow. An example of such upstream equipment is equipment that generates a gas flow, such as a combustion equipment that generates a gas flow of hot combustion gases. It should be understood that downstream equipment is located downstream of the gas outlet of the flow path in the flow direction of the gas flow. An example of downstream equipment may be downstream gas processing equipment for processing the gas flow, for example, but not limited to, equipment for cleaning or purifying the gas flow. Downstream equipment may also be equipment for utilizing the gas flow, for example, by chemically changing it.

[0026] The one or more flame characteristics detected by the monitoring device may include the radiation intensity of a flame generated in the gas stream following injection of a controlled jet of oxide therein. The monitoring device may thus detect the radiation intensity of said flame in the visible and / or invisible range, preferably in the visible or infrared spectral range, preferably a combination of both, for example in the wavelength range of 400-1000 nm.

[0027] The monitoring device may also include a temperature sensor in contact with the gas stream, such as a thermocouple, for measuring the temperature of the gas stream in addition to one or more characteristics of the flame detected by the monitoring device through the line of sight and the window. According to a preferred embodiment, the temperature sensor is positioned in a controlled jet of oxide having an oxygen content of 22-100% by volume, which controlled jet is injected into the gas stream, and the temperature sensor then measures the temperature of a flame generated in the gas stream by combustion of combustible material in the gas stream with the oxide in the controlled jet when the gas stream contains such combustible material.

[0028] According to one such embodiment, a temperature sensor is located within a lance defining a line of sight, where the controlled injection of oxide within which the temperature sensor is located is the same as the controlled injection injected by said lance, and the temperature sensor measures the temperature of a flame, one or more characteristics of which are detected by a monitoring device through the line of sight and window.

[0029] According to an alternative embodiment, the controlled injection of oxide where the temperature sensor is located is a second controlled injection different from the controlled injection of oxide injected by the lance (corresponding to the first controlled injection). In that case, the monitoring device also includes a separate injector for injecting a further (second) controlled injection of oxide where the temperature sensor is located into the gas flow. The first and second controlled injections may be injected into the gas flow at adjacent locations or at spaced locations.

[0030] For example, according to the process described in WO-A-2010 / 022964, the monitoring device may use the temperature measured by the temperature sensor as: (a) an additional input for generating a control signal, i.e., the monitoring device generates the control signal based on both one or more flame characteristics detected by the monitoring device through the line of sight and the window and the temperature measured by the temperature sensor; (b) as a verification input, from which the monitoring device generates an alarm signal when the temperature measured by the temperature sensor indicates a significantly different level of combustible material in the gas flow compared to the level of combustible material in the gas flow corresponding to the value of the one or more flame characteristics detected by the monitoring device through the line of sight and the window; or (c) as a backup input, from which the monitoring device generates the control signal based on the temperature measured by the temperature sensor when the monitoring device is unable to generate a control signal based on one or more flame characteristics detected by the monitoring device through the line of sight and the window.

[0031] According to one embodiment, the monitoring device detects and / or processes one or more flame characteristics intermittently, for example, to reduce the energy consumption of the monitoring device. According to a preferred embodiment, the monitoring device detects and processes one or more flame characteristics continuously.

[0032] The one or more flame characteristics detected by the monitoring device and / or the control signals generated by the monitoring device based on the one or more flame characteristics are efficiently stored in a data storage device, so that the stored data can later be retrieved and used, for example, to improve the performance of upstream equipment generating the gas flow, in post-incident assessments, or to optimize future process controls, particularly by automated learning processes.

[0033] The one or more detected flame characteristics and / or generated control signals are typically communicated to and may be displayed on / by one or more user interfaces. The user interfaces may be part of a mobile device such as a cell phone, tablet, etc. The user interfaces may also be located at a local or remote control station.

[0034] The method according to the invention can be used to monitor combustibles in a wide range of gas streams, provided that the gas stream has a temperature of at least 550° C., as mentioned above. The method according to the invention is particularly useful for monitoring combustibles in flue gas streams from combustion equipment.

[0035] In combustion facilities, thermal energy is generated by combustion. The presence of combustible substances in the exhaust gas of a combustion facility indicates incomplete combustion in the facility, i.e., suboptimal furnace operation as far as energy generation in the furnace is concerned. Such suboptimal furnace operation may be due, for example, to fluctuations in the composition of the combustible furnace charge (such as in a waste incinerator or blast furnace) or to the presence of combustible substances in the charge being melted, such as metal scraps that are uncontrollably released during the melting process. According to the present invention, the presence of combustible substances in the exhaust gas of such combustion facilities can be reliably monitored. In some cases, incomplete combustion in the furnace is intentionally sought, specifically to chemically reduce the atmosphere inside the furnace. In such cases, the exhaust gas of a combustion facility actually contains combustible substances, and the method and device according to the present invention can be advantageously used to monitor the concentration or level of combustible substances in the exhaust gas and fluctuations of said concentration or level, for example due to the presence of combustible substances in the charge, such as metal scraps that are uncontrollably released.

[0036] According to the present invention, the efficiency of a combustion facility can be improved by monitoring the presence of combustible materials in the exhaust gas stream from the combustion facility and using control signals generated by a monitoring device to adjust the combustion stoichiometry within the combustion facility.

[0037] Combustion facilities of particular interest to the present invention include furnaces for (re)melting non-ferrous metals (such as furnaces for melting aluminum, copper, lead and tin and their alloys), furnaces for melting or re-melting iron and iron alloys, furnaces for recovering metals from electronic waste (e-waste), cement or lime kilns, waste incineration kilns or blast furnaces, electric arc furnaces, boilers, etc. According to a preferred embodiment, the method according to the present invention is used to monitor combustibles in flue gas streams from furnaces for melting non-ferrous metals, furnaces for melting or re-melting iron or iron alloys or furnaces for recovering metals from e-waste.

[0038] When the method is used to monitor combustibles in a gas stream that is a flue gas stream from a combustion facility, the control signal generated by the monitoring device may be communicated to the upstream combustion facility, where the control signal may be advantageously used to adjust the combustion stoichiometry within the combustion facility. Such an embodiment of the invention may be used specifically to reduce or avoid the presence of combustibles (unburned materials or products of partial combustion such as CO) that exit the combustion facility as part of the flue gas stream, thereby improving the energy efficiency of the combustion facility. The method makes it possible to achieve this objective in a fast, accurate, and reliable manner: Speed: The monitoring device instantly detects one or more characteristics of a flame occurring in situ in the flowing exhaust gas stream. There is no need to sample the exhaust gas. As a result, very low latency times can be achieved. Accuracy: Monitoring is performed in the exhaust gas stream downstream of a gas-stream generating installation, specifically a combustion installation. The flame in the gas stream observed by the monitoring device is therefore shielded from one or more flames in the installation process, specifically the combustion installation (including any radiation from the combustion installation). Higher accuracy is therefore achieved. A controlled injection of an oxide with a higher oxygen content than air is used to generate the flame in the gas stream. Higher accuracy is achieved when the flame is generated in ambient air, specifically compared to an uncontrolled amount of ambient air. Reliability: High temperature exhaust gas streams, particularly high temperature flue gas streams, can be corrosive and / or dirty and can contain high levels of condensable materials. If a flame is generated in the gas stream, the flame can also generate soot. In accordance with the present invention, greater reliability and durability is achieved in that the window of the monitoring device is spaced from the gas stream, and the window and line of sight are protected from corrosion, erosion, or deposition from the gas stream and the flame therein by a controlled injection of oxide flowing through the lance.

[0039] When the monitoring device detects the presence of combustible material in the flue gas stream downstream of the combustion equipment, or detects the presence of combustible material in the flue gas stream at a level above a predetermined level, the control signal generated by the monitoring device can be used to change / adjust / regulate the combustion stoichiometry within the combustion equipment to ensure that the oxygen supplied to the combustion equipment is sufficient to ensure substantially complete combustion or complete combustion of any combustible material inside the combustion equipment. This can be achieved by increasing the rate at which combustion oxides are supplied to the combustion equipment without changing the rate at which combustibles are supplied to the equipment, by reducing the rate at which combustibles, specifically fuel, are supplied to the combustion equipment without changing the rate at which combustion oxides are supplied to the combustion equipment, or by increasing the ratio of combustion oxides to combustibles (specifically fuel) supplied to the combustion equipment. When a combustion equipment is intentionally operated with incomplete combustion and the monitoring device detects a higher than expected level of combustible material in the combustion exhaust gas stream, i.e., a level higher than a predetermined level, the control signal generated by the monitoring device can similarly be used to change / adjust / regulate the combustion stoichiometry within the combustion equipment to ensure a sufficient, albeit intentionally incomplete, combustion level of combustible material inside the combustion equipment, thus, for example, optimizing combustion energy production within the combustion equipment while ensuring the presence of a non-oxidizing atmosphere within said equipment.

[0040] According to a preferred embodiment, the control signals generated by the monitoring device are used to adjust the combustion stoichiometry within the combustion facility by adjusting the fuel flow rate and / or combustion oxide flow rate to the combustion facility within 10 seconds, preferably within 4 seconds, and more preferably within 3 seconds of detection by the monitoring device of one or more detected flame characteristics based on the corresponding control signals generated.

[0041] The oxide used as the combustion oxide in the combustion facility that produces the combustion gas stream may have the same chemical composition as the oxide that is injected by controlled injection into the gas stream according to the present invention or a different chemical composition.

[0042] When the oxide used as the combustion oxide has a higher oxygen content than ambient air, the energy efficiency of the combustion equipment is typically improved relative to air-fired operation of the combustion equipment. Thus, according to a preferred embodiment, an oxide having an oxygen content of 22 to 100% by volume is supplied to the combustion equipment from an oxide source as the combustion oxide.

[0043] Oxide from two different oxide sources can be used as the combustion oxide in the combustion facility and for the controlled injection of oxide injected by a lance into the gas flow, respectively. When an oxide having an oxygen content of 22 to 100% by volume is used as the combustion oxide in the combustion facility, it is advantageous to use an oxide from the same oxide source as the combustion oxide in the combustion facility, on the one hand, and as the controlled injection of oxide injected by a lance into the gas flow, on the other hand.

[0044] The invention also relates to a device for monitoring combustible substances in a gas stream, adapted for use in the method according to the invention.

[0045] The device according to the present invention includes a lance, a sensor, and a processing unit. The lance has a first end near a window of the monitoring device and an open second end facing away from the window. The lance defines a line of sight between the window and the open second end of the lance. The lance further exhibits an oxide inlet at or on the side of the first end of the lance. The sensor is located behind the window and is capable of detecting one or more characteristics of a flame located through the lance and the window in front of the second end of the lance. The processing unit is programmed to process the one or more detected flame characteristics and generate a control signal based on the one or more detected flame characteristics. In use, the oxide inlet of the lance is fluidly connected to an oxide source via a flow controller capable of adjusting the oxide flow rate to the lance. The device also advantageously includes a transmitter for transmitting the generated control signal.

[0046] According to a preferred embodiment, the sensor is capable of detecting visible or invisible radiation intensities, such as infrared radiation, preferably a combination of visible and infrared radiation intensities.

[0047] The monitoring device may be programmed to detect and / or process one or more flame characteristics intermittently or continuously.

[0048] The monitoring device preferably also includes a thermocouple positioned to detect the temperature at or adjacent the second end of the lance, where the processing unit of the device is in data communication with the thermocouple to receive the temperature detected by the thermocouple. According to one embodiment, the thermocouple is positioned within the lance. According to an alternative embodiment, the thermocouple is positioned within a tube adjacent the lance.

[0049] According to basic embodiments of the methods and devices of the present invention, the control signal generated by the monitoring device based on one or more detected flame characteristics correlating with the concentration of combustible material in the gas stream is a binary signal, one of two binary signals being a value corresponding to a level of combustible material in the gas stream above a predetermined threshold, and the second of the two binary signals being a value corresponding to a level of combustible material in the gas stream below said threshold. For example, particularly when complete or substantially complete combustion is sought in a combustion facility producing a hot gas stream, one of the binary signals may be generated when the monitoring device does not detect combustible material in the gas stream, and the other of the binary signals may be generated when the monitoring device detects combustible material in the gas stream.

[0050] According to a preferred more advanced embodiment of the invention, the control signal is non-binary. In such a case, the non-binary control signal is advantageously such that the value of the concentration of the combustible substance in the gas flow can be derived from the value of the control signal. For example, the control signal and the concentration may exhibit a linear dependence on each other.

[0051] The invention and its advantages are described in more detail in the following non-limiting examples with reference to FIGS. [Brief explanation of the drawings]

[0052] [Figure 1] FIG. 1 is a schematic diagram of an installation including a combustion furnace and a monitoring device for use in accordance with the present invention. [Figure 2] FIG. 2 is a schematic diagram of a monitoring device suitable for use in accordance with the present invention. [Figure 3] FIG. 3 is a schematic diagram of monitoring equipment suitable for use in accordance with the present invention. [Figure 4] FIG. 4 is a schematic diagram of monitoring equipment suitable for use in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0053] The melting process shown in FIG. 1 is carried out in a so-called Short Rotary Drum Furnace (SRF) 1.

[0054] A metal charge 2 to which additives such as coke, iron, fluorspar, etc. are added is loaded into the furnace 1 .

[0055] An open flame 7 is generated inside the furnace 1 to directly heat the charge 2 and melt the metal or metals contained in the charge 2. The resulting liquid metal phase is struck and then directed to a metallurgical processing step (not shown).

[0056] The SRF 1 is filled with a metal charge 2 on the longitudinal axis of the furnace drum via a front door. Exhaust gases exit the furnace through the rear opening of the furnace drum on the furnace drum axis. The exhaust gas drawn from the SRF 1 is collected in a vertical exhaust gas channel 3 connected directly to the rear opening before being redirected to a cyclone (not shown) and an exhaust filtration device (not shown). The SRF 1 is fitted with one water-cooled oxygen-gas burner 4 with a nominal power of 3 MW. Natural gas 5 and oxygen 6 are injected through the burner tip to generate a flame 7 inside the furnace 1.

[0057] The process shown can be used, for example, to melt tin, in other words the charge placed in the furnace 1 is a tin charge.

[0058] Nominal natural gas flow is 250-300 Nm 3 / h. The nominal oxygen gas flow is 450-700 Nm 3 / h. Nominal exhaust gas flow is 2300~2700Nm 3 / h, and the nominal exhaust gas temperature is estimated to vary between 1100 and 1500°C. The CO content in the exhaust gas varies dynamically during the dissolution process from 0 to 30% by volume.

[0059] To detect and quantify the CO content in the exhaust gas, a monitoring device 9 is installed at one end of a lance 8 that is mounted on the exhaust gas channel 4 outside the furnace drum. The second end of the lance 8 is open and positioned inside the exhaust gas flow so that the monitoring device 9 can "watch" the exhaust gas flow through the lance 8. At ambient temperatures, the monitoring device 9 has a CO content of 1-30 Nm3 A controlled flow of substantially pure oxygen (at least 99% by volume oxygen) of 1000 kJ / h is injected into the exhaust gas stream towards it through lance 8. Lance 8 is connected to an oxygen source, in this case oxygen reservoir 12, although the oxygen source could also be an oxygen pipeline or an air separation unit.

[0060] Thus, oxygen is injected into the exhaust gas stream, causing the CO contained in the exhaust gas to combust and produce a further flame 10 of size, temperature and radiation commensurate with the amount of CO contained in the exhaust gas.

[0061] For the avoidance of any doubt, the term "flame" as used herein includes both visible flames and diluted flames (also known as flameless combustion).

[0062] While viewing the flame 10 through the lance 8, the monitoring device 9 captures at least one of these flame characteristics (dimensions, temperature and radiation) and generates a control signal proportional to the amount of CO contained in the exhaust gas. The generated control signal is sent to a digital data processing unit 11, such as a programmable logic controller (PLC), for data processing. The processed data is used as a control signal for adjusting the proportion of oxygen and natural gas injected through the burner 4, according to the method described in WO 2010 / 022964. In this way, the time lapse between the detection of one or more flame characteristics of the flame 10 and the adjustment step in the furnace 1 is kept very short (less than 10 seconds, preferably less than 4 seconds or even less than 3 seconds).

[0063] Thus, by optimizing the operation of the furnace 1 and keeping the presence of combustibles such as CO in the exhaust gas stream to a minimum, a reduction of up to 20% in the consumption of a particular natural gas may be achieved.

[0064] FIG. 2 shows a monitoring unit suitable for use in the present invention.

[0065] The monitoring unit includes a monitoring device 9 with a window 91 through which one or more characteristics of a flame located in front of the window 91 can be detected by the monitoring device 9.

[0066] The injection lance 8 extends forward from the window 91. At the end of the lance 8 facing the monitoring device 9 (the upstream end of the lance 8), the lance 8 is provided with an oxygen inlet 81 through which oxygen can be pumped into the lance 8 at a controlled rate. The opposite tip 82 (downstream end) of the lance 8 is open-ended. Because the lance 8 is straight and has no internal blockages, the lance 8 defines a clear line of sight between the window 91 of the monitoring device 9 and the open end 82 of the lance 8. The lance 8 is further provided with a flange 83 at which the monitoring unit can be mounted onto a gas flow pipe, such as an exhaust gas channel of a combustion facility.

[0067] When flange 83 is mounted on the gas flow tube through which a hot gas stream flows and a controlled flow of oxygen is supplied to lance 8 via oxygen inlet 81, the oxygen is injected into the hot gas stream as a controlled oxygen jet. When the hot gas stream contains combustible material, a flame is generated where the combustible material contacts the controlled jet of oxygen. Via a line of sight through lance 8 and window 91, monitoring device 9 detects one or more characteristics of the flame. For example, monitoring device 9 can be constructed and programmed to detect the flame's radiation intensity at a wavelength corresponding to CO combustion. The detected intensity thus indicates the concentration of CO in the gas stream. Monitoring device 9 then generates a control signal based on the detected radiation intensity.

[0068] Alternatively, or in combination with said radiation intensity, the monitoring device 9 may detect IR (infrared) radiation from the flame as a flame characteristic and use the detected IR radiation to generate a control signal.

[0069] The monitoring unit of FIG. 3 differs from the monitoring unit of FIG. 2 in that, in addition to the lance 8, it includes an additional oxygen tube 100 having a thermocouple 101 mounted therein. The thermocouple 101 is in data communication with the monitoring device 9. The controlled flow of oxygen delivered through the oxygen inlet 81 is split between the lance 8 and the tube 100, each of which injects a separate, controlled jet of oxygen into the hot gas stream. If combustible material is present in the gas stream, a flame will be generated in the gas stream where the combustible material comes into contact with the injected oxygen. Through the line of sight of the lance 8 and the window 91, the monitoring device 9 detects one or more flame characteristics as described above. Additionally, through the thermocouple 101 in the tube 100, the monitoring device 9 further detects the flame temperature, which can be used as a further input for the monitoring device 9 to generate a control signal, as a possible backup input for generating a control signal, or as a safety check to verify the prima facie accuracy of one or more characteristics of the flame detected through the line of sight and the window 91.

[0070] The monitoring unit of FIG. 4 differs from the monitoring unit shown in FIG. 3 in that the tube 100 is not fluidly connected to the oxygen inlet 81 of the lance 8. In that case, the tube 100 with the thermocouple positioned therein may be separately supplied with a controlled jet of oxidizing gas, which is then injected into the gas stream. Alternatively, a relatively small amount of sweep gas may be flowed through the tube 100 with the thermocouple positioned therein, or no gas may be flowed at all.

[0071] According to an embodiment not shown, the thermocouple may be positioned within the lance 8 .

[0072] The method according to the present invention was used to monitor combustibles in the exhaust gas stream emitted from a laboratory-scale furnace.

[0073] The temperature of the exhaust gas exceeded 1000° C. The carbon monoxide content in the exhaust gas varied from 0 to 12% by volume.

[0074] The oxide used was pure oxygen.

[0075] A monitoring unit was mounted on the furnace exhaust pipe. The monitoring device included a photosensor located behind a window in the monitoring device of the unit. The photosensor was capable of measuring radiation intensity in the visible and IR ranges. Thus, when a flame occurred at the downstream end of the oxygen lance, which defined a line of sight between the window and the downstream end, the monitoring device detected the intensity of flame radiation in the visible and IR ranges through the line of sight and the window.

[0076] In the first set of tests, oxygen was injected into the gas stream at different flow rates within the furnace exhaust gas temperature range and with varying known concentrations of CO in the gas stream. This procedure also determined the oxygen flow rate through the lance, and therefore the oxygen injection rate, that provided the most significant temperature rise due to burning combustible materials with oxygen in the gas stream. Under certain test conditions, a flow rate of 0.25 Nm 3 An oxygen flow rate value of 1 / h was found to be optimal for all CO levels. In other words, the oxygen flow rate provided an increase in the maximum exhaust gas temperature detected by the thermocouple for all CO levels. The magnitude of the increase in maximum temperature itself increased with increasing CO levels in the gas stream. In addition, the oxygen flow rate also provided the highest detected flame radiation intensity detected by the photosensor for all CO levels, whereby the level of detected radiation intensity also increased with increasing CO levels in the gas stream.

[0077] The first set of tests was used to calibrate the monitoring unit.

[0078] In a second set of tests, the calibrated monitoring device was used to monitor CO in the hot exhaust gas stream from a furnace operating at various power levels and combustion stoichiometries. Upon detecting a radiation intensity corresponding to a CO level in the exhaust gas stream that exceeded a predetermined acceptable upper limit, the monitoring device generated a control signal for a corresponding adjustment of the furnace's oxygen-fuel ratio.

[0079] A second set of tests confirmed that, after calibration with the test results, the monitoring device could be used to reliably determine the CO content in an unknown flue gas stream, remote from the flue gas stream and without the interference of a furnace flame.

[0080] A comparison of the CO levels determined by the monitoring device based on flame radiation and the CO levels determined based on the temperature rise detected by the thermocouple confirmed the accuracy and reliability of the monitoring device of the present invention.

[0081] The efficiency of the method and device according to the invention for monitoring combustibles in high-temperature gas streams was confirmed during long-term tests in an industrial furnace for melting non-ferrous metals, where a reduced atmosphere was maintained. The flame characteristics determined were pixelated multispectral radiation intensities in the visible and near-infrared ranges. The control signal was generated based on the principles described in WO-A-2010 / 022964. The method and device proved to be robust and reliable, and significant energy savings were achieved without increasing the oxidation of the charge.

Claims

1. 1. A method for monitoring flammable materials in a gas stream with a monitoring device, comprising: the gas stream flows along a flow path extending from a gas inlet to a gas outlet at a temperature of at least 550°C, preferably at least 650°C; a lance extends between a window of the monitoring device and the flow path, the lance defining a line of sight between the window and the gas flow in the flow path; a controlled jet of oxide having an oxygen content of 22-100% by volume is injected by the lance into the gas stream, whereby in the presence of combustible material in the gas stream, the combustible material burns with the oxide in a flame in the gas stream ahead of the lance; one or more characteristics of the flame that correlate with a concentration of combustible material in the gas stream are detected by the monitoring device through the line of sight and the window; The method wherein the monitoring device processes the one or more detected flame characteristics and generates a control signal based on the one or more detected flame characteristics.

2. The controlled injection of the oxide is 0.1 Nm ３ / h to 50.0 Nm ３ / h, more preferably 0.2 to 25.0 Nm ３ 10. The method of claim 1, wherein the molten metal is injected into the lance at a flow rate of 10 ...

3. 3. The method of claim 1 or 2, wherein the lance is such that the line of sight forms an angle with the main gas flow direction of between 5° and 175°, more preferably between 25° and 155°, more preferably between 45° and 135°.

4. A method according to any preceding claim, wherein the lance extends into the flow passage between 0% and 50% of the cross-sectional diameter of the flow passage.

5. 5. The method according to claim 1, wherein the control signal is communicated to an upstream equipment generating the gas flow and used as a control parameter in the upstream equipment, and / or is communicated to a downstream gas processing equipment and used as a control parameter for the control of the equipment.

6. 6. The method of any one of claims 1 to 5, wherein the monitoring device detects the visible and / or invisible radiation intensity of the flame, preferably the visible and / or infrared radiation intensity of the flame, preferably a combination of the visible and infrared radiation intensity of the flame.

7. A method according to any one of claims 1 to 6, wherein the gas stream is a flue gas stream from a combustion facility.

8. 8. The method according to claim 7, wherein the combustion facility is selected from the group comprising furnaces for melting non-ferrous metals, furnaces for melting or remelting iron and iron alloys, furnaces for recovering metals from electronic waste, cement or lime kilns, waste incineration kilns or blast furnaces, electric arc furnaces and boilers, preferably selected from furnaces for melting non-ferrous metals, furnaces for melting or remelting iron or iron alloys and furnaces for recovering metals from electronic waste.

9. 9. The method of claims 7 and 8, wherein the control signal is communicated to the upstream combustion equipment and used to adjust the combustion stoichiometry within the combustion equipment, preferably by adjusting the fuel flow rate and / or combustion oxide flow rate to match the combustion equipment within 10 seconds, preferably within 4 seconds, more preferably within 3 seconds.

10. 10. The method according to any one of claims 7 to 9, wherein an oxide having an oxygen content of 22 to 100% by volume is supplied as combustion oxide to the combustion facility from an oxide source, and oxide from the same oxide source is injected into the gas stream by the lance as a controlled jet of said oxide.

11. 1. A device for monitoring combustible materials in a gas stream, comprising: a lance having a first end near a window of the monitoring device and an open second end facing away from the window, the lance defining a line of sight between the window and the open second end of the lance, the lance presenting an oxide inlet at or on a side of the first end of the lance; a sensor located behind the window and capable of detecting one or more characteristics of a flame located through the lance and the window in front of the second end of the lance; a processing unit programmed to process the one or more detected flame characteristics and to generate a control signal based on the one or more detected flame characteristics; Devices that include:

12. The device of claim 11 , further comprising a transmitter for transmitting the generated control signal.

13. 13. A device according to claim 11 or 12, wherein the sensor is capable of detecting visible and / or invisible radiation intensities, preferably visible and / or infrared radiation intensities, more preferably a combination of visible and infrared radiation intensities.

14. 14. A device as claimed in any one of claims 11 to 13, further comprising a thermocouple positioned to detect a temperature at or adjacent the second end of the lance, the processing unit being in data communication with the thermocouple and receiving the temperature detected by the thermocouple.

15. 15. The device of claim 14, wherein the thermocouple is positioned within the lance or within a tube adjacent to the lance.

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