RELATED APPLICATIONS

This application claims the benefit of 35 USC §119(e) to United States Provisional Patent Application Serial No. 61/457591 , filed 26 April 2011.

FIELD OF THE INVENTION

This invention relates to a method and apparatus used to measure the flow of a stream of high temperature, high dust load gas coming out of a combustion process. More preferably, the present invention is geared towards the measurement of gas flow volumes and/or velocities in the steel making industry, cement industry, and/or any other industry employing intense combustion processes, where the quantities of off-gas emitted from conversion vessels are large, and which may be at a high temperature and contain particulates.

BACKGROUND OF THE INVENTION

Currently the steel industry, and other intense combustion industries, does not have a direct method of precisely and continuously measuring the volume of the large quantity of off-gases coming out of furnace conversion vessels. In particular, as a result of hindrances imposed on the classical methods of gas flow measurement resulting from furnace process conditions, such as extremely high temperatures, inconsistent gas composition, inconsistent particulate content, and the presence of flame conditions at the point of measurement, heretofore the accurate measurement of furnace gas velocity and/or volumetric sensing has proven largely ineffective.

Active cross correlation flow sensors make use of a light source that emits a beam through an off-gas stream or flow and a detector located across the flow stack. Such sensors sense the light modulation resulting from the interaction of the light beam with the particles and gaseous species present in the flow. Recently, optical techniques involving non-intrusive laser sensors _, have been developed to provide more real-time measurements of steel furnace off-gas flow constituents and/or temperatures. Optical devices for such analysis have been reported for a variety of wavelength spectrum, including those disclosed in United States Patent No. 6,611 ,319; U.S. Patent No. 6,369,881; U.S. Patent No. 5,672,827; United States Patent Application Publication No. 2003/0685244; and United States Patent Application Publication No. 2006/0421700. Such conventional devices typically contain one or more pairs of laser light emitters 4a,4b and receptors 6a,6b which are positioned on opposite sides of a gas flue duct 20. The emitter/receptor pairs 4,6 are provided downstream from the conversion vessel, as for example shown in Figure 1 and are frequently used to quantitatively analyse individual gas constituents. Shining rays of laser light through the off-gas stream or flow 8 has, however, proven problematic and, as shown by other types of measurements, mainly gas composition measurement, frequently results in inconsistent readings due to the high and variable content of particulates in the gas stream. In addition, the required alignment precision of the optical components used in laser techniques suffers from vibration effects produced in the steel fabrication processes and other intense combustion environments, making it necessary to increase servicing of the system.

For industrial combustion processes, Mid-IR laser systems which operate at wavelengths beyond 3.0 micrometers have certain advantages including a more immediate response time compared to extractive methods. Mid-IR laser systems have shown reasonably good transmission characteristics even through gas streams containing particulate matter. Mid-IR range lasers, however, have certain disadvantages that severely limit their applicability in industrial environments. Typically Mid-IR lasers use a Pb-salt diode which must be operated with cryogenic cooling, thereby adding complexity and cost. Further, since Mid-IR energy propagates poorly through fiber optic cables, the cryogenic cooled laser transmitter must be located very near the process off-gas stream. This in turn requires the use of motorized mirror reflectors because of the proximity limitations. The operation of reflective mirrors and cryogenic cooling systems in hot, dusty industrial environments associated with steel making furnaces is very problematic and is often unworkable.

Sensors which operate by the analysis of Near-IR laser beams with wavelengths in the range of about 0.7 to 3.0 micrometers have certain advantages compared to Mid-IR lasers in industrial applications. Near-IR range lasers provide an immediate response and can operate at room temperature. Hence, Near-IR lasers do not require complex cryogenic cooling systems. Unlike Mid-IR, Near-IR laser beams can be transmitted through fiber optic cable. As a result, the laser source can be located in a clean control room and not directly in the harsh industrial environment.

However, Near-IR range lasers also have certain disadvantages that limit their applicability. Near-IR range laser beams have poorer transmission characteristics than Mid-Range IR, in particulate, containing gas streams. As a result, Near-IR based sensors have been less effective in some industrial environments. These limitations restrict Near-IR range lasers in situ capability where the laser energy is to be transmitted directly through the combustion off-gas stream in close proximity to the combustion source, and where low particulate off-gas streams are produced.

Passive cross correlation flow sensors make use of a light receptor only, and receive and sense wavelength energy which is emitted by the exhausted furnace off- gas itself. A passive cross correlation optical flow meter therefore does not require a light source since the detectors collect the thermal radiation emitted by the hot gases and/or particles present in the hot flow. The applicant has appreciated that the near real-time calculation of the off-gas stream or flow velocity and/or volume in harsh environments by means of cross correlation methods can be attempted using optical techniques that capitalize on the hot particle laden flow absorption and emission radiation properties. The technique can also employ the absorption and emission radiation from the gaseous species. Such optical techniques may be non-intrusive by nature since they do not interfere with the off-gas flow. Furthermore, such flow velocity and/or volume measurements can also be undertaken using active or passive cross correlation methods depending on the type of components employed.

United States Patent 5,986,277, to Bourque et al. describes one method and an apparatus used to measure the flow velocity and the temperature of a thermally charged spray used in plasma spray processes. The system of Bourque et al. is used with thermal spraying, and in particular, plasma spraying such as those used to produce protective coatings. Bourque et al. describes an apparatus which includes a lens inside a sensor head near a torch. The sensor focuses the electromagnetic radiation from a small area of the discharge spray plume into two optical fibers, which in turn transmit the light to optical sensors that generate a pair of signals proportional to the radiation intensity. In between the fiber optics and the pair of sensors, the light is filtered using two bandpass filters with adjacent wavelengths. The velocity is calculated using a cross correlation method, and the particle temperature is determined by a two-color pyrometer technique.

Bourque et al. uses a specific range of the electromagnetic radiation, and which is characteristic of the heat radiation emitted by the heated particles moving in the spray. In addition, the area of view is generally believed to be relatively small, with reliance given to the predictable and good flow behavior of the spray to measure its velocity. In contrast, the applicant has appreciated that using a small area of view in an industrial or steel making furnace, where the level of turbulence in the off-gases is higher, would increase the probability of measuring other secondary turbulent flow velocities, other than that of the main flow, leading to inaccuracies.

Heretofore, conventional active flow measuring devices have proven largely ineffective for use in the steel industry due to the harsh operational environment. In addition, conventional passive application systems suffer from the high turbulence shown by the off-gases exiting from furnaces.

Accordingly, the applicant has recognized that the need for accurate off-gas flow velocity and/or volume measurement exists, and the benefits from achieving the foregoing objects may be measurable in direct financial-operational benefits through deceased operating costs, and/or by the possible reduction in discharged emissions per ton of product through the better understanding and control of industrial furnace fume systems.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a sensor arrangement for accurately measuring and/or calculating the volume or velocity of flow of gases emitted from furnace conversion vessels. More preferably, the sensor arrangement is provided as part of a system to assist in calculating and/or determining the mass balance and the energy balance within the conversion vessel, with the one possible final objective of allowing the dynamic control of the process, and/or as better monitoring or control of emissions through the associated fume system.

Accordingly, one object of the current invention is to provide an improved apparatus and method to overcome the disadvantages and limitations of the prior art devices, and which is operable to obtain rapidly velocity or flow volume measurements of the high temperature process off-gas stream emitted by intense combustion processes, and preferably y but not limited to processes used in the steel making industry.

More preferably, the current invention provides a system and/or method to obtain accurate off-gas velocity or flow measurements in a close vicinity to a furnace combustion source, without the need of using electromagnetic radiation emitters of a particular wavelength or band.

In a simplified construction, an off-gas velocity measuring device is provided which allows for fast response analysis of the flow velocity and/or volume of a furnace off-gas by using at least one, and more preferably two or more detectors. The detectors include a suitable radiation receiver/sensor, and which may be of an identical design, and which may or may not be calibrated. Preferably the device receiver/sensors operate to detect one or more signatures of the natural energy emissions or radiation energy of the gas and/or particle components in the off-gas stream. In a preferred mode of operation of the velocity measuring device, the receiver/sensors of multiple detectors are positioned at spaced locations along the combustion gas flow path or process off-gas stream. The device operates to determine the time-of-flight between the two or more spaced receiver/sensors of a selected feature of the spectrum of radiation or electromagnetic energy emitted by the high temperature process off-gas stream. By using time-of-flight measurement, the present system advantageously operates independently of the off-gas stream chemical composition and/or the dust load entrained therein.

More preferably, the method provided by the present invention measures the flow velocity of the off-gas stream whereby at two or more regions along the off-gas stream, wherein the emitted radiation is received by receiver/sensors. Preferably, the receiver/sensors are provided as optical probes which transmit by way of optical fiber cables, radiation which is emitted across substantially the entire width of the off- gas stream to at least one detector. In between the optical fiber cables and the detector, one or more bandpass filters may be provided. Preferably, the bandpass filters are selected to transmit only a preselected feature of the received radiation within an electromagnetic (EM) spectrum range to the detectors.

The detectors are used to generate electrical signals proportional to the measured radiation. These signals are transmitted to and received by a data acquisition module or other suitable processor and/or computer which is used to determine the time delay between signals. The processor or computer preferably also correlates the signals received from the receiver/sensors with their relative positioning and/or dimensions of an off-gas duct to calculate the velocity and/or volume of the off-gas flow.

In another preferred mode of operation, the device operates as a targeted application. The properties and conditions of the off-gases at the point of measurement will determine the objective range or band of the electromagnetic spectrum to be measured, be it mid-IR, near-IR, visible or UV and/or the width of the band as well. For the selection of the specific detectors, at least two photodetectors with a wide working wavelength range are preferable. A variant of the application to suit the measurement of a specific emission line or band of the electromagnetic spectrum, embodies a combination of photodetector and a bandpass filter is chosen. In an alternate construction of the invention, the device includes two or more, and preferably only a pair of calibrated spectrometer detectors.

In a simplified construction, the optical probes are preferably located within an off-gas duct of a flue gas system in an orientation generally perpendicular to the direction of the off-gas stream flow and separated by a known distance, one downstream relative to the other. The optical probes can furthermore be introduced to a certain depth inside the off-gas flue or duct.

In accordance with one aspect, the apparatus consists of two preferably identical optical probes focusing the radiation from two spaced areas of measurement from the off-gas flow, and which are each optically coupled to an associated fiber optic cable. The fibre optic cable operates to transmit the radiation energy or light collected and focused by the probes to at least one and more preferably two detectors. Each detector is associated with and provided for receiving the light from an optic fiber cable. The data acquisition module and a computer/processor operate to run a cross correlation velocity calculation program to provide substantially near real-time data measurements of flue gas, flow velocity and/or volume flow. Although not essential, preferably an associated bandpass filter is located between each detector and its associated fiber optic cable or optical probe. The bandpass filters are used to isolate and allow for the selective measurement of a single electromagnetic spectrum feature.

Accordingly, in one aspect, the present invention resides in a furnace control system for the optimization of furnace combustion operations, the system including: a combustion gas flow sensor assembly comprising, a first optic sensor disposed at a first position relative to a combustion gas flow, a second optic sensor disposed at a second position relative to said combustion gas flow, the second position being spaced a predetermined distance from said first position, each of the first and second optic sensors operable to receive radiation energy from the combustion gas flow, at least one photodetector optically coupled to at least one associated one of the first and second optic sensors, the at least one photodetector operable to generate electric signals in proportion to the radiation energy received from the associated optic sensors, a data compiler communicating with the at least one photodetector for compiling energy at least one profile of radiation energy sensed by each of first and second optic sensors based on the generated electric signals, a processing assembly for correlating at least a portion of the compiled energy profile of energy sensed by the second sensor and outputting a signal representative of at least one of the combustion gas velocity and the combustion gas volume based on a time difference between the correlated portions.

In another aspect, the present invention resides in a system for measuring industrial furnace combustion gas velocity and/or volume along a gas flue pipe, the system comprising, a combustion gas flow sensor assembly comprising, a first optic sensor disposed at a first position along said gas flue pipe for receiving radiation energy emitted from combustion gasses flowing adjacent the first optic sensor, a second optic sensor disposed at a second position along said gas flue pipe spaced a predetermined distance from said first position, said second sensor operable for receiving radiation energy emitted from combustion gasses flowing adjacent the second optic sensor, an associated photodetector optically coupled to each of the first and second optic sensors, each photodetector operable to generate electric signals proportional to the radiation energy received by the associated first and second optic sensors at the first and second positions, respectively, a data compiler for compiling energy profiles of radiation energy sensed by each of first and second optic sensors, a processing assembly for comparing at least part of the compiled energy profiles and calculating sensed energy time delay therebetween, and outputting the sensed energy time delay as an output of at least one of the combustion gas velocity and the combustion gas volume moving along said gas flue pipe.

In a further aspect, the present invention resides in An industrial furnace gas flow sensor assembly for sensing at least one of a combustion gas flow velocity and a combustion gas flow volume along a gas flue pipe, the sensor assembly comprising, a first optic sensor disposed at a first position along said gas flue pipe for receiving electromagnetic energy emitted from combustion gasses flowing adjacent the first optic sensor, a second optic sensor disposed at a second position along said gas flue pipe spaced a predetermined distance from said first position, said second sensor operable for receiving electromagnetic energy emitted from combustion gasses flowing adjacent the second optic sensor first and second photodetectors each photodetector optically coupled to an associated one of the first and second optic sensors, and operable to generate electric signals is proportion to the electromagnetic energy sensed there by, a data compiler for compiling energy profiles of radiation energy sensed by each of first and second optic sensors, a processor for comparing at least portion of the compiled energy profiles correlating a time difference between the energy profiles and the predetermined distance and outputting a signal representative of at least one of the combustion gas velocity and the combustion gas volume moving along said gas flue pipe. BRIEF DESCRIPTION OF THE DRAWINGS

Reference may now be had to the following detailed description, taken together with the accompanying drawings in which:

Figure 1 shows schematically an off-gas sensor arrangement in accordance with the prior art;

Figure 2 is a schematic view of the apparatus which incorporate an off-gas sensor assembly for detecting and monitoring a flue gas stream velocity and/or volume in accordance with a preferred embodiment of the invention;

Figure 3 is a schematic view of an optic sensor used in the apparatus of Figure 2, in accordance with a preferred embodiment of the invention;

Figures 4 and 5 illustrate schematically the apparatus for detecting and monitoring a flue gas stream velocity and/or volume, in accordance with further embodiments of the invention;

Figures 6a, 6b and 6c show graphically the correlation of signal properties between two spaced sensors over time in calculating off-gas flow velocities;

Figure 7 illustrates schematically the off-gas sensor assembly shown in Figure 2 installed for use in an industrial electric arc furnace (EAF); and

Figure 8 illustrates schematically the off-gas sensor assembly of Figure 2 mounted in a water cooled flue duct of an industrial basic oxygen furnace (BOF).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is made to Figure 2 which illustrates an assembly 10 used in the continuous and real-time monitoring of high temperature off-gas flow 8 velocities and/or volumes from an electric arc steel making furnace 50 (Figure 7) in accordance with a preferred embodiment of the invention. The assembly 10 includes a pair of identical optic sensors or probes 12a, 12b; two fiber optic cables 14a, 14b and a pair of photodetectors 18a, 18b; a protecting compartment 30 preserving the electronic components from the harsh environment.

As will be described, the photodetectors 18a, 18b are electronically coupled with a data acquisition module 22, which in turn communicates with a computer 24. The computer 24 is further agreeable to control inputs respecting the combustion parameters of the steel making furnace 50. Optionally, the photodetectors 18a, 18b and data acquisition module 22 are housed within.

An enlarged schematic view of the optical probes 12a, 12b is shown in Figure 3. Each probe 12 is provided with a lens assembly 32 includes electromagnetic energy collector 36 positioned at an inner end of a lens tube 38, and which is sealed at its outer end by a lens 40. The lens 40 is selected so as to collect and focus electromagnetic radiation which is emitted by the furnace off-gas flow onto the collector 36. The lens tube 38 encases the lens 40 and collector 36, and in turn protected by the probe outer shell 34. Optionally, the outer shell 34 is specially designed to prevent or minimize intrusion of off-gas particles into the probe 12. In this regard, the lens tube 38 and/or shell 34 may be provided with suitable back flow or gas purging systems to periodically clear any debris or particles which may accumulate on the surface of the lens 40.

Figure 2 shows the optical probes 12a, 12b as being placed open to the high temperature process off-gas stream or flow 8. The probes 12a,2b are preferably mounted perpendicularly to the direction 100 of the flow 8 at longitudinally spaced locations along the flue duct 20 by predetermined separation distance L. Optionally, the probes 12a, 12b can be introduced to a certain depth inside the off-gas flue duct 20 to measure the emitted radiation of the off-gases, preferably reaching upto the center line of the flue duct 20.

Figures 2 and 3 show best the collector 36 of each probe 12a, 12b as being optionally coupled to an associated fiber optic cable 14a, 14b. The radiation emitted by the off-gas flow 8 is thus focused by the lens 40 of the optical probe 12a, 12b onto the energy collectors 36 and transmitted with fiber optic cables 14a, 14b. The fiber optic cables 14a, 14b are selected to transmit the light and/or electromagnetic energy over a long distance to a pair of photodetectors 18a, 18b enclosed inside the protective compartment 30 that can be located far from the point of measurement. Each photodetector 18a, 18b operates to generate electrical signals that are proportional to the intensity of the sensed radiation energy measured by each associated sensor 12a, 12b at the area of measurement. Presently, the protective compartment 30 also encloses the data acquisition module 22. The module 22 is electromagnetically connected to the photodetectors 18a, 18b and receives, manages and converts the analog signals from the photodetectors 18a, 18b during sensing operations. The data acquisition module 22 may be provided with an internal or external processor, but is most preferably electronically in communication with the computer 24 used to control overall furnace operations. The computer 24 performs a cross correlation calculation required to determine the time delay between the signals receive from each probe 12a, 12b. This time delay represents the time-of-flight of the moving off-gas flow 8 to travel the distance L between optical probes 12a, 12b. The computer 24 may thus calculate the flow velocity of the off-gas 8, and, by comparing the velocity to predeterminable geometries of the gas flue duct 20, its volumetric flow. This output is to be displayed to a user, and/or sent as output signals directly to an automated furnace control program providing an indication of the flow velocity and/or flow volume of an off-gas flow 8 along the flue duct 20.

Figures 2 and 6a to 6c show a preferred embodiment of the invention, where the photodetectors 18a, 18b receive data and provide signals from the associated sensors 12a, 12b which represent electromagnetic radiation measurements the off- gas energy signature of the entire width of the off-gas stream 8, across the whole of the flue duct 20 diameter adjacent each sensors 12a, 12b. Figures 6a and 6b illustrate respectively, sample radiant energy data sensed during furnace operations by each sensor 12a, 12b over time.

While sensing the entire width of the off-gas stream radiant energy profile presents a preferred embodiment, the invention is not so limited. Depending on the availability of photodetectors 18a, 18b, however, the range of emitted radiant energy can be selected to cover only a defined wavelength range, namely restricted to one or more of UV, visible, near-IR or mid-IR.

A second embodiment of the invention is shown in Figure 4, wherein like reference numerals are used to identify like components. In Figure 4, the fiber optic cables 14a, 14b transmit collected radiant energy from the associated optical probes 12a, 12b (shown in Figure 2) first through an associated one of a pair of identical bandpass filters 44a,44b. Each bandpass filter 44a,44b in turn is optically coupled to a photodetector 18a, 18b by a fiber optic coupling. The bandpass filters 44a,44b are employed to select only a specific emission line or band of the sensed electromagnetic spectrum. This configuration allows the assembly 10 to focus on a single component of the off-gas stream 8, such as the emissions from CO or CO ₂ , depending on the furnace applications.

Yet, a third embodiment of the invention is shown in Figure 5, used to identify like components. In Figure 5, alternate types of sensors 118a, 118b operate for the measurement of off-gas properties and/or components are used in place of the photodetectors 8a, 18b. . The sensors 118a, 118b may for example be calibrated spectrometer detectors that measure the light intensity of the off-gas 8 over the entire width of the detector's specified electromagnetic spectrum.

In a preferred application, the geometry of the high temperature process off- gas flue duct 20 or pathway and the optic probe separation distance L is preferably pre-calculated and fixed as well.

In operation, the sensors 12a, 12b receive radiant energy from the off-gas flow 8, and output the energy collected via the sensor collectors 36 via the fiber optic cables 14a, 14b to the photodetectors 18a, 18b. Each photodetector 18a, 18b outputs the detected radiant energy as signals to the data acquisition module 22 which compiles the signals for each sensor 12a, 12b, as for example as shown in the plotted output illustrated in Figure 6a (sensor 12a) and 6b (sensor 12b. The output signals will show similar structures representative of sensed characteristics of the off-gas flow 8. As shown in Figures 6a to 6c, profiles of the off-gas flow 8 are output as signals which are shifted by the time-of-flight T _m representing the distance L separating optical probes 12a, 12b. The computer 24 may thus perform a cross correlation function R _xy(T) analyses similarities in the signals received from the sensors 12a, 12b, x(t) and y(t), and calculate a maximum at the point of highest similarity. This maximum represents the time to move between (i.e. across) each sensor 2a, 12b. The flow velocity is then defined as the ratio of the separation between optical probes L by the time-of-flight T _m . To determine the volumetric flow the cross-sectional area of the off-gas flue duct 20 is factored against the calculated flow velocity.

In a preferred mode of operation, the optical probes 12a, 12b and associated photodetectors 18a, 18b analyse the high temperature process off-gas stream 8 from points outside of the gas envelope (i.e. along duct 20), and only detect visible features in the defined bandwidth of the closest vein of gas/flame which will have a very turbulent flow pattern in the direction of gas flow. It has been appreciated that this will not be an impediment but an advantage of the method. In particular, with more turbulent off-gas flow, there exist more pronounced specific features of the signals from the detectors 12a, 12b. As a result, the cross correlation function may be enhanced will work better.

The implementation of the off-gas sensor assembly on the EAF vessel 50 is shown in Figure 7. Where the sensors assembly 10 is mounted for use with EAF furnaces 50, there is the distinct possibility that any holes in the side of the duct 20 through the optical probes 12a, 12b face may become plugged by particulates present in off-gas stream 8. The optical probes may therefore, optionally be protected by a directional purging system.

The implementation of the sensor assembly 10 in the monitoring and control of a BOF type vessel 60 is illustrated in Figure 8. In the BOF vessel 60, the optical probes 12a, 12b are typically mounted on a water cooled duct 20 of the fume system, and optionally may each be provided within their own mounting capsule. As the temperature of the off-gas stream flowing in front of the optical probes 12a, 12b will at times be in excess of 1500°C, the probes 12a, 12b may incorporate provisions for water cooling. While the preferred embodiments illustrate the assembly 10 as including optical probes 12a, 12b which are adapted to passively measure radiant energy from the off-gas flow 8, the invention is not so limited. In an alternate construction, the probes 12a, 12b could be provided as active flow sensors, and include respective electromagnetic light emitters and receptors positioned on opposing sides of the flue duct 20.

While the detailed description describes the assembly 10 as including a pair of optic probes 12a, 12b, in an alternate construction, the apparatus 10 could include additional optic probes to provide redundant and/or verified cross correlation.

While the detailed descriptions describes and illustrates various preferred embodiments of the invention, it is to be appreciated that the invention is not strictly limited to the precise embodiments which are shown. Other variations and modifications will now occur to persons skilled in the art.