WO2014067577A1

WO2014067577A1 - Endoscope for high-temperature processes and method of monitoring a high-temperature thermal process

Info

Publication number: WO2014067577A1
Application number: PCT/EP2012/071632
Authority: WO
Inventors: Jesper Cramer
Original assignee: Force Technology
Priority date: 2012-10-31
Filing date: 2012-10-31
Publication date: 2014-05-08

Abstract

A method of monitoring a high-temperature thermal process, comprising: recording a sequence of images by means of a camera (103) operatively receiving light signals via an optical system; and performing image processing to determine the spatial expanse of a combustion zone and communicating a control signal indicative of the spatial expanse to a system controlling the high-temperature thermal process; wherein the apparatus has a predominant response to light in the wavelength range between 600 nm and 1400 nm; and wherein the image processing involves temporal filtering that enhances relatively slowly varying intensities and attenuates relatively rapidly varying fluctuations. An apparatus (100) for recording such a sequence of images comprises an endoscope (109) for inspection through a hole in a wall of a chamber wherein the process takes place.

Description

Endoscope for high-temperature processes and method of monitoring a high -temperature thermal process The ever increasing demand for energy in the form of heat and electricity has brought attention to the combustion processes or other thermal processes where fuel, e.g. in the form of waste in various forms, is converted into useful energy. The rising awareness of the unwanted consequences of our energy use calls for a more efficient utilisation of the fuels with fewer environmental impacts. This is the case both for the combustion of traditional fossil fuels and for the combustion of biomass and waste. When the fuel is burning, the location of the combustion zone and the time needed to achieve complete combustion are not totally fixed, but will vary depending on variations in fuel and combustion conditions.

The combustion process can be optimised when such variations are measured and when the combustion conditions are controlled. Early signals will give the benefit of early control where the needed changes are smaller and the operation is thus more stable.

The combustion chamber has high temperatures, typically above 1000 degrees Celsius. Inside the chamber, where the high-temperature processes take place, the combination of heated or burning matter, flames, particles and gases makes the environment inside the chamber very aggressive to any type of technical installations, including apparatuses for visual data acquisition (and/or inspection), and the walls as such of the chamber. To extract heat energy from the combustion processes or other thermal processes, the combustion chamber or furnace is typically equipped with tubes conveying a liquid and/or gas e.g. water and/or steam. The tubes are typically built into the walls of the chamber. The distance between the tubes is typically 20 mm. A hole drilled in the wall between the tubes (also denoted water tubes) must be smaller than 20 mm. This poses a challenge when devices for measurements or data acquisition are to be placed for controlling and optimizing the combustion process. Combustion processes in furnaces are controlled and optimized by spot temperature measurements, measurements of gases such as oxygen and carbon monoxide and by measurements of the expanse of the fuel.

Related prior art

The below prior art methods disclose acquisition of infrared signals from a combustion zone.

JP1 1063453 (A) and JP 10267243 (A) and JP62245935 (A) disclose acquisition of infrared images with a camera placed outside a furnace and looking through a window in the furnace wall

JP8018837 (A) discloses a bulky cooling device that cools a camera.

US 5,510,772 discloses acquisition of infrared signals from potential fire in the open landscape, giving signal to fire alarm.

CN 2,251 ,719 discloses a high temperature endoscope for clearly inspecting the furnace wall to avoid explosion danger www.cesvco-endoscopes.com and www.lenoxinst.com disclose an endoscope with a relatively large diameter. When images are recorded with a camera placed outside the furnace, looking through a window of the furnace wall, it is conventionally not possible to obtain a proper field of view that covers the furnace where combustion takes place. One reason is that the distance between the tubes installed on or in the walls of the furnace, is too narrow. The tubes are then an obstacle to obtaining such a proper field of view.

If a camera is placed outside the furnace, an image of the combustion zone can be achieved only if a window can be made in a furnace wall giving a view to the combustion zone. This allows a poorer viewing angle and thus a poorer image of the combustion process.

A cooling device for the whole camera makes the overall proportions of the camera even larger and does not improve the possibility of recording a good image of the combustion process.

A device that is suitable for recording infra-red signals from possible fire in the open landscape will not be suitable for recording image signals from a combustion process occurring in a furnace because of the proximity and hence exposure of the device to high temperatures in the furnace.

A high-temperature endoscope that is suitable for seeing through the furnace wall is not necessarily suitable for being installed in a furnace wall cooled with water tubes unless the diameter of the endoscope is small enough to go between the water tubes of the wall. The wave length of infrared light needs larger dimensions of optical equipment than the wave length of near-infrared light. Therefore an infrared endoscope and camera solution cannot get a sufficiently small diameter. A camera recording visual light will not be able to record a useful image of the burning or heated matter on the grate since flames or particles are present and since they significantly reduce the visibility in the chamber. An endoscope with an outer diameter larger than approximately 30, 20, or 1 1 mm is generally not suitable for installation in a furnace wall with tubes since the endoscope is not small enough to go between the tubes of the wall as the tubes are conventionally installed at a distance from each other of typically 20 mm. It should be noted that the tubes could be spaced further apart at some locations of the wall, but that comes with an economic cost and can cause other technical problems.

Summary

There is provided an apparatus for visual inspection through a hole in a wall of a chamber for high-temperature processes and comprising: an elongated member that has a proximal end and a distal end and comprises a duct extending between the proximal end and the distal end; an endoscope arranged in the duct to extend from the distal end of the duct to its other, proximal end; and a camera coupled with the endoscope to receive light from the proximal end of the endoscope and convert it into an output signal; wherein the apparatus has a response to light that is predominant in the wavelength range between 600 nm and 1400 nm.

The chamber in which the high-temperature process takes place may be a combustion chamber of a combustion plant or the gasification chamber for a gasification process. The process may convert waste, biomass and/or fossil fuels into heat energy. Alternatively, the process may be an industrial process for thermal treatment or treatment by flames or gas of products or intermediate products. Inside the chamber, the high-temperature processes involve high temperatures, typically above about 1000 degrees Celsius, but high temperatures can also be those above about 600 degrees Celsius, or 800 degrees, or above about 1200 degrees Celsius.

The apparatus can be installed with its elongated member extending through or partially through the hole in the wall of the chamber which is typically of considerably small diameter, of about 10 mm to 20 mm. The diameter of the hole is typically limited by technical installations, such as cooling channels, in the wall of the chamber. Typically, the hole needs to be made for the apparatus to enable that the interior of the chamber can be inspected by the apparatus from the outside. The available space for such a hole and thus its diameter may be up to about 30, 40 or 50 mm. The response to light that is predominant in the wavelength range between 600 nm and 1400 nm enables a sufficiently good image resolution where heated or burning subject-matter can be distinguished from flames. Inspection at wavelengths of visible light would not enable such distinction. Inspection at wavelengths of infrared light would require equipment and in particular an optical system with a considerably large aperture that would not fit within the available space for inspection given by the technical installations within the chamber. However, the wavelength range between 600 nm and 1400 nm enables a sufficiently good image resolution where heated or burning subject-matter can be distinguished from flames. An apparatus with this feature can be installed within many existing chambers. Moreover, the ability to introduce the elongated member of the apparatus where cooling of the chamber wall is needed enables establishment of a direct view with a good viewing angle and thus the possibility of viewing a large portion or substantially the entire the combustion zone. The viewing of the entire combustion zone gives a complete overview of the conversion of subject- matter and the inspection thus provide very valuable information for the control of the conversion process.

The wavelength range between 600 nm and 1400 nm corresponds roughly to the so-called near-infrared range. The near-infrared wavelength range is also abbreviated NIR or IR-A. It is defined as electromagnetic radiation in the wavelength range of 700 nm-1400 nm.

The response to light that is predominant in the wavelength range between 600 nm and 1400 nm is the camera's response in its output signal to light transmitted through the optical system of the apparatus. The optical system of the apparatus comprises the endoscope and the camera and optionally i) an optical adapter placed between the endoscope and the camera, and/or ii) an optical filter, and/or iii) a protective lens in front of the endoscope, and/or iv) any optical coatings.

Generally, the spectral response to light received via the endoscope has a band-pass characteristic with its pass-band located within the wavelength range between 600 nm and 1400 nm. The pass-band, with a relatively high transmittance, may be defined to be located between two cut-on wavelengths, outside which the filter has a relatively low transmittance.

With appropriate computer processing of the signals from the camera it is possible to compute (optionally visualize) the location and expanse and optionally the intensity of the combustion zone. Thereby signals for more instant control of the combustion process can be outputted to a control system which will in turn improve the combustion or the gasification process as the case may be. In general, earlier signals for optimisation and control of a combustion process are achieved. Moreover, when the combustion process is improved, energy output of a boiler of the system can be improved and undesired emissions can be reduced. In some embodiments the predominant response is located within the wavelength range between 600 nm and 1000 nm or 600 nm and 900 nm or between 700 nm and 1000 nm or 800 nm and 1000 nm.

In some embodiments the apparatus comprises an optical long-pass filter or an optical band-pass filter that attenuates transmission of light below its pass-band. In some embodiments the filter is a long-pass filter with a cut-on wavelength in the range between 600 nm and 1200 nm. In some embodiments the cut-off wavelength is in the range between 700 nm and 1000 nm. In some embodiment the cut-off wavelength is specified as 715 nm or 1000 nm. In some embodiments the response is established by an optical longpass filter or an optical bandpass filter with its lower cut-on wavelength located in the range 600 nm to 800 nm.

In some embodiments the response, which may be defined as a bandpass characteristic, is established by an optical longpass filter of the edge type with a cut-on wavelength of about 715 nm in combination with a camera that is sensitive to visible light, but gradually becomes less responsive to light at wavelengths longer than about 600 nm. In some embodiments the long-pass filter gradually has a lower transmittance at wavelengths longer than about 1400 nm e.g. gradually lower from 1700 nm, 2200 nm or 2700 nm. An optical long-pass filter of the edge type has a relatively steep slope with a lower transmittance towards shorter wavelengths. They are usually specified by their cut-on wavelength at -3dB of peak transmission.

In some embodiments the predominant response descends with a higher order slope towards shorter wavelengths and descends with a lower order slope towards longer wavelengths. In embodiments such a response provides sufficient attenuation of visible light that could otherwise impinge on the camera's sensor with such high intensity that it would be hard, if not impossible, to distinguish or detect heated or burning subject matter in the chamber in the camera's output signal. The visible wavelength range is typically defined as the range of about 390 nm to about 750 nm.

In some embodiments the camera has a spectral response that exhibits a predominant response in the visible wavelength range and a lower response in the near-infrared range.

Such a camera is expediently useful since its lower response in the near- infrared range is often sufficient to record image signals representing burning subject-matter, and since such cameras are commercially available at lower prices than cameras configured to have a predominant response in the near- infrared or infrared range.

In some embodiments an optical longpass filter of the edge type is arranged in front of such a camera or elsewhere in the optical system. The edge type filter has a relatively steep slope with a lower transmittance towards shorter wavelengths and gives sufficient attenuation of the camera's predominant response in the visible wavelength range so that the lower response in the near-infrared range becomes sufficiently useful for distinguishing heated or burning subject matter from flames.

In general, a camera is coupled with the endoscope to receive light from the proximal end of the endoscope and to convert light impinging on its image sensor to an output signal which is typically an electric output signal with digital or analogue image information. In some embodiments the endoscope is coupled with the camera such that substantially the entire disc of light emanating from the endoscope impinges on and within the boundaries of the image sensor of the camera. Conventionally, the optical system is configured such that all pixels of the image sensor receive light from the optical system. Thereby the resolution of the camera is fully utilized. However, when as claimed, the entire, circular, disc of light emanating from the endoscope impinges on and within the boundaries of the image sensor of the camera, the viewing angle defined by the optical system is fully utilized. Thereby, since inspection takes place through the wall of the chamber making it difficult to get a wide field of view and since the thermal processes typically take place over a great expanse, the thermal process is much better covered for the visual inspection. Since, typically, the image sensor has a square shape, some pixels outside the disc are not utilized, but with today's pixel count in camera sensors, this is not an actual problem.

In some embodiments the endoscope is coupled with the camera such that substantially the entire disc of light emanating from the endoscope impinges on and within the boundaries of the image sensor of the camera by means of an optical adapter (not shown) which may be a part of the endoscope. The size of the disc on the sensor can be set by selecting an appropriate magnification ratio of the endoscope and/or converter and/or by selecting an appropriate distance between the camera's image sensor and the optical endoscope and/or converter.

In general the elongated member is also designated a lance or a lance endoscope. In some embodiments the elongated member comprises a channel configured to convey a refrigerant from its proximal end to its distal end. Thereby, the endoscope can be cooled to lower the temperature inside the endoscope and thus protect the endoscope and optionally other optical components inside the endoscope from excessive temperatures. The refrigerant can be liquid, e.g. distilled water or a gas, such as air, e.g. pressurised gas. In some embodiments the endoscope is configured with a further channel for returning the refrigerant to the proximal end. In other embodiments the endoscope comprises an outlet coupled with the channel for discharging the refrigerant to the space in front of the endoscope.

In some embodiments the combination of the cooling of the endoscope, e.g. with water, and a small outer diameter, e.g. smaller than 30, 25, or 20 mm, allows that the apparatus can be installed with the endoscope looking into the a combustion chamber of a furnace since the endoscope can fit between water tubes of the furnace wall or the boiler wall.

In some embodiments the elongated member has an outer wall enclosing a first tube; wherein the interior of the first tube is coupled to an inlet for supply of a forward flow of refrigerant and, at the distal end, to a space between the outer wall and the first tube to establish a passage for a reverse flow of the refrigerant; and wherein the space between the outer wall and the first tube is coupled to an outlet for discharging refrigerant. Thereby the refrigerant, which is cooler at the supply end, runs in its forward direction in a more centrally located channel, closer to the endoscope which is susceptible to excessive temperatures; then it returns in a more peripherally located channel, closer to the outer wall of the endoscope. This configuration gives an efficient cooling of the endoscope. In some embodiments, the refrigerant is coupled to flow in the opposite direction. In some embodiments the first tube has one or more openings or bores in the wall of the distal end of the first tube to establish a passage from the interior of the first tube to the space between the outer wall and the first tube. Thereby a passage for the reverse flow is established. The most distal end of the first tube can then be fixated to hold the first tube in a fixed position. In some embodiments the outer wall of the elongated member, the lance, is a tube e.g. with a circular cross-section. In some embodiments the first tube is arranged substantially concentrically with the outer wall.

In some embodiments the elongated member comprising the first tube is made from stainless steel. The combination of a stainless steel lance with cooling passages can withstand the high temperatures, typically of above 1000 degrees Celsius, in a combustion chamber, and the very aggressive combination of flames, particles, and gases. In some embodiments the apparatus comprises a housing coupled with the elongated member and accommodating the camera; wherein the camera housing has an outer wall and comprises a first passage for supplying a refrigerant to the elongated member and a second passage for receiving a refrigerant from the elongated member. Thereby the housing itself can be cooled by the same refrigerant flow as the refrigerant flow in the elongated member.

In some embodiments the first passage is located more centrally to the housing and the second passage is located closer to the outer wall of the housing. In some embodiments the housing has a tubular shape and comprises a third tube of substantially the same diameter, which diameter is, however, slightly smaller than that of the camera housing. Thereby the second passage can be established as the space between the inside of the outer wall and the outside of the third tube. This provides efficient cooling of the outside wall of the camera housing. The third tube has a sufficiently large diameter to enclose and accommodate the camera. In some embodiments the first passage is established by a fourth tube with a substantially smaller diameter than that of the third tube. The fourth tube can be arranged along the inner periphery of the third tube to provide space for the camera. The fourth tube is coupled to convey the refrigerant in the forward direction.

In some embodiments the housing is made from stainless steel and is welded to the elongated member or lance. Thereby the passages of the housing and the lance can be coupled accurately and reliably together.

In some embodiments the elongated member has an end-portion at its distal end and an outer wall enclosing a second tube; wherein the interior of the second tube is coupled, at the proximal end, to an inlet for supply of a forward flow of a purging agent; and wherein the second tube, at the distal end, is coupled to the end-portion for discharge of the purging agent into space in front of the end-element.

Thereby there is established a passage for the purging agent that is discharged in front of the lance to establish a flow that blows away particles from heated or burning subject matter. The purging agent may be pressurised air.

In some embodiments the interior of second tube establishes the duct for the endoscope.

In some embodiments the second tube encloses a third tube that establishes the duct for the endoscope and protects the endoscope from the flow, and turbulence, of the purging agent. There is thereby established a passage for the purging agent in the space between the second pipe and the third pipe. This is expedient especially when the purging agent is delivered at high pressure (high flow velocity) which could otherwise cause undesired movements (flapping) of the endoscope, which could, in turn, create undesired image blurring. In some embodiments the distal end comprises an element that is made from a ceramic material having the property of being machineable or comprises a ceramic portion having the property of being machineable.

The ceramic end-element protects the most distal end of the lance from excessive heating where it is difficult to establish a sufficiently distal flow of refrigerant. The ceramic end-element can stand the high temperatures and serves as thermal insulation for the most distal end of the lance. In embodiments, where the lance has a tubular shape, it is especially convenient that the ceramic is a machineable type since it then can be shaped by lathing, which is a relatively inexpensive production method compared to e.g. casting.

In some embodiments the elongated member has, at its distal end, a central aperture for the endoscope to receive light and has circumferentially arranged holes for discharge of a cleaning agent. Thereby the endoscope can receive light through the central aperture, while purge air can be discharged close to that central aperture, where the optical aperture is located and where a purge flow is especially needed. In some embodiments the apparatus comprises an image processor operatively coupled with the camera and configured to determine the spatial expanse of a high-temperature zone and light intensity of the high- temperature zone and communicating control signals indicative of the spatial expanse and light intensity; wherein image processing involved in determining the spatial expanse comprises temporal filtering that enhances relatively slowly varying intensities and attenuates relatively rapidly varying fluctuations.

It has been discovered by means of the above apparatus that burning subject matter is hard to distinguish from flames since the above apparatus has a greater response towards the visible light wavelength range. However, flames flare (fluctuate and move back and forth), whereby at some time instances the burning subject matter is viewable and at other times not, since it is covered by flames. The temporal low-pass filtering across several images in a sequence can attenuate the intensity levels caused by flames and thereby enhance, relatively, intensity levels caused by heated or burning subject matter. This improves the performance of an algorithm of computing the spatial expanse of a high-temperature zone and improves the reliability of the control signal indicative of the spatial expanse, which in turn improves controllability of the thermal processes in the chamber. In general, the high- temperature zone can be defined by a certain level of intensity in the image.

There is also provided a method of monitoring a high-temperature thermal process processing subject matter on a grate and comprising: recording a sequence of images by means of an camera operatively receiving light signals via an optical system; and wherein the combination of the camera and the optical system is installed to view at least a portion of the combustion grate; and performing image processing on an image of the sequence to determine the spatial expanse of a combustion zone and communicating a control signal indicative of the spatial expanse to a system controlling the high-temperature thermal process; wherein the apparatus has a predominant response to light in the wavelength range between 600 nm and 1400 nm; and wherein the image processing involves temporal filtering that enhances relatively slowly varying intensities and attenuates relatively rapidly varying fluctuations. In some embodiments, the step of performing image processing comprises determining the spatial expanse of a combustion zone and its light intensity and communicating a control signal indicative of the spatial expanse and the light intensity to a system controlling the high-temperature thermal process.

In some embodiments the temporal filter has a time-constant in the range of 0.2 seconds to 3 seconds

In some embodiments the time-constant is approximately 1 second. However, it may be approximately 0.8 seconds or 1 .2 or 1 .3 seconds, e.g. in the range 0.4 seconds to 2 seconds or 0.6 seconds to 1 .4 seconds.

Brief description of the figures

In the below an exemplary embodiment is described with reference to the drawing in which:

fig. 1 schematically shows an apparatus with a camera and a lance for an optical endoscope;

fig. 2 shows the spectral response of the camera and the overall spectral response of the apparatus;

fig. 3a and 3b show the spectral transmittance of an optical filter;

fig. 4 shows the distal end of the apparatus in detail;

fig. 5 shows a system configured to control the combustion zone in a furnace; and

fig. 6 shows a flowchart for a method of processing images recorded with a predominant sensitivity to light in the near-infrared spectral range.

Detailed description

Fig. 1 schematically shows an apparatus with a camera and a lance for an optical endoscope. The apparatus is shown in a longitudinal cross-sectional view. The apparatus 100 comprises an elongated member 101 , also denoted a lance 101 , and a housing 102 accommodating a camera 103. The lance 101 has a proximal end, closest to the housing 102, and its other end is denoted its distal end. The lance 101 comprises a duct 104 extending between the proximal end and the distal end. The duct 104 is arranged centrally in the lance, as can be seen in the cross-sectional lance view 105, but it may be arranged at an outer, non-central position.

As can be seen from the cross-sectional lance view 105, the lance has an outer wall 106 enclosing a first tube 107 which encloses a second tube 108. The interior of the second tube 108 establishes the duct 104 accommodating the optical endoscope 109. As can be seen from the cross-sectional housing view 1 10, the housing has a cylindrical cross-section and has an outer wall 1 1 1 that encloses a third tube 1 12. Also, the housing comprises a fourth tube 1 13 that is arranged at a non- central position to give space for the optical system 1 14 comprising among other things the camera 103.

The fourth tube 1 13 is coupled at its first end to an inlet 1 16 for supply of a refrigerant. At its other end, the fourth tube 1 13 is coupled to the lance and in particular to the passage established between the first tube 107 and the second tube 108 of the lance 101 . Thereby a passage for conveying a refrigerant in a forward direction is established.

At its distal end, the first tube 107 has holes or cuts in its tube wall to establish a passage to a further passage formed by the space between the outer wall 106 of the lance and the outside of the first tube 107. This further passage is coupled to yet a further passage, of the housing 102, established in the space between the outer wall 1 1 1 of the housing 102 and the third tube 1 12. Thereby a passage for conveying a refrigerant in a reverse direction is established. This yet further passage is coupled to an outlet 1 17 for discharge of the refrigerant.

The refrigerant then flows closest to the endoscope in its forward direction, when it is coolest and returns closer to the periphery of the lance and the housing when it has been heated by the heat radiation on the lance from the thermal processes. In some embodiments the flow of the refrigerant is reverse by configuring the outlet 1 17 as an inlet and the inlet 1 16 as an outlet. For the purpose of conveying a purge agent to the most distal end of the lance, the interior of the second tube 108 is coupled, at the proximal end, to an inlet 1 18 for supply of a forward flow of a purging agent. As can be seen the second tube 108 is coupled to the inlet 1 18 via a compartment or space of the housing 102 that also accommodates portions of the optical system and the camera 103. At the distal end the second tube 108 is terminated for discharge of the purging agent into space in front of the end-element. Additionally, the purging agent e.g. air serves as a cooling agent for the endoscope. The purging agent has a much lower temperature than the temperature which the lance is exposed to, the temperature of the purging agent may be below 50 degrees Celsius, e.g. below about 30 degrees, or below about 20 degrees.

The optical system comprises the endoscope 109, an optical adaptor 1 19 thereof, a filter 120, and the camera 103. This optical system or components thereof is/are configured with a response to light that is predominant in the wavelength range between 600 nm and 1400 nm. In some embodiments the filter 120 is embodied with the optical endoscope or with the camera 103.

In some embodiments the filter 120 is integrated with the camera 105 and/or with the camera's image sensor.

The camera is connected to a connector 1 14 for establishing electrical connection with the camera comprising communicating image signals and control signals to and from the camera Fig. 2 shows the relative spectral response of the camera and the overall relative spectral response of the apparatus. A diagram 201 comprises an abscissa axis, along which wave lengths from 400 nm to 1000 nm are indicated, and an ordinate axis along which relative responses from 0.0 to 1 .0 are indicated. The curve 202 shows the relative response of the camera 103 as specified by a manufacturer. The relative response as depicted by the curve 202 is measured, relative to a maximum response, as intensity levels in the electrical output signal from the camera in response to an influx of monochromatic light on the camera's image sensor at respective wavelengths. As illustrated by the curve 202, the camera 103 has a spectral response that exhibits a predominant response in the visible wavelength range, below approximately 600 nm, and a lower response in the near- infrared range above 600-700 nm, but below 1000-1400 nm.

The band of curves 203, 204 and 205 depicts a relative response as mentioned above, but with different optical long-pass filters in front of the camera. These curves depict the overall relative spectral response of the apparatus. The optical long-pass filters filter the influx of light before it is incident on the camera's image sensor. The curves 203, 204 and 205 represent filters with a low, medium and high cut-on wavelength.

The above curves serve to illustrate different embodiments. In other embodiments, other cut-on wavelengths and/or or other orders of filter slope are selected to configure the apparatus with a response to light that is predominant in the wavelength range between 600 nm and 1400 nm.

In some embodiments, compared to the shown spectral response, the camera has a spectral response that is relatively greater in the wavelength range above 700 nm and up to about 800 nm or 900 nm. In some embodiments, the camera has a relatively lower spectral response in the wavelength range below 700 nm.

Fig. 3a and 3b show the spectral transmittance of an optical filter. In general, transmittance, at a specified wavelength, is the fraction of the amount of light at that wavelength that passes (is transmitted) through the filter relative to the amount of incident light at that wavelength.

Diagrams 301 and 302 comprise an abscissa axis, along which wave lengths from 200 nm to 1200 nm and 200 nm to 5200 nm are indicated, respectively, and an ordinate axis along which transmittance (internal transmittance) from 0.99 to 10^"5 are indicated. Curves 303 and 304 depict the transmittance for an optical filter at over a relative narrow and a relatively wide wavelength range, respectively. As can be seen in diagram 301 the optical filter has a long-pass filter characteristic. The filter's cut-on wavelength is specified to be 715 nm. The filter is a so-called edge filter with a relatively steep slope towards shorter wavelengths.

This can also be seen in diagram 302, although at longer wavelengths the filter has an attenuated (lower) transmittance compared to the wavelength range immediately above the cut-on wavelength. The attenuated response at longer wavelengths plays only an insignificant role, since the attenuated transmittance sets in only somewhat above the near-infrared range (above 1000 nm to 1400 nm). Thus, the filter can be considered a long-pass filter, although it has, to some extent, a band-pass characteristic.

In some embodiments the cut-on wavelength is in the range between 600 nm and 1200 nm. In some embodiments the cut-on wavelength is in the range between 700 nm and 1000 nm.

Fig. 4 shows the distal end of the apparatus in detail. This distal end is the distal end of the elongated member or lance of the apparatus. It is shown in a longitudinal cross-sectional view. Reference numeral 106 designates the outer wall of the lance; numeral 107 designates the first tube; and numeral 108 designates the second tube. Bore or hole 406 establishes a passage between the passage between the second tube 108 and the first tube 107 and the passage between the outer wall 106 and the first tube 107. In some embodiments the outer wall 106, the first tube 107 and the second tube 108 are made from stainless steel, however other metals or other materials may be used.

At the distal end, there is an end-portion 403 also denoted a metal tip 403.

In some embodiments the end-portion 403 is made from the same material as the outer wall and the first and second tube, e.g. stainless steel, however, it can be made from another type of metal or from another material. The tubes and the outer wall are welded to the metal tip 403.

The metal tip 403 has a longitudinal bore (duct) with a nominal diameter, but with longitudinally extending protrusions 405 (e.g. three protrusions spaced 120 degrees apart) that reduce the diameter of the cylinder where the protrusions are located to establish contact faces for frictionally holding the endoscope or a cladding thereof in a fixed position. Space between the longitudinally extending protrusions establishes longitudinally extending passages for the purge agent. This passage is illustrated by the dotted arrows 408.

The longitudinal bore of the metal tip 403 has a larger diameter than the nominal diameter towards the distal end (a counterbore).

Further to the distal end, there is a second end-element 402 also denoted a ceramic tip 402. The ceramic tip is rotational symmetric. It has a central, longitudinal bore with a cone shaped, gradually wider opening towards the distal end. It has an outer diameter that is substantially the same as an outer diameter of the metal tip 403 and towards the proximal end it has a reduced diameter such that the ceramic tip 402 can be accommodated in the counterbore of the metal tip 403. The ceramic tip can be securely fixed to the metal tip in different ways e.g. by frictional coupling and/or by glue and/or by a locking element e.g. a ring accommodated in a depression in the counterbore and a corresponding depression in the ceramis tip.

The ceramic tip also has a protrusion (or nose) 414 that deflects the purging agent as it discharges right in front of the endoscope. Thereby there is established a passage for the purging agent that is discharged in front of the lance to establish a flow that blows away particles from heated or burning matter; the aperture of the endoscope is thereby kept free from particles.

Fig. 5 shows a system configured to control the combustion zone in a furnace chamber. The furnace chamber 502 has an inlet 503 for waste or fuel, a conveyor grate 505 for moving the waste or fuel across a number of controllable combustion sections 506 and an outlet 504 for removing slag. Flue gas from the combustion process escapes through a first boiler draft 507. To extract heat from the combustion process, a tube system 508 is installed in or with the walls of the combustion chamber. The tube system is configured to circulate a liquid and/or gas e.g. water and/or steam. The tube system is coupled to a heat exchanger (not shown) and/or another system (not shown) to supply energy in a suitable form. To extract the heat energy, the tubes are installed close to each other; typically spaced 20-60 mm apart. Generally, the waste or fuel in any form is denoted matter 513. Flames are designated 509.

The controllable combustion sections 506 also denoted controllable sections 506 are typically installed inside the combustion chamber as parts of the combustion plant. The controllable sections 506 can be controlled in various ways. In some embodiments the sections are controlled by means of the respective section's:

- Grate speed, and/or - Primary air, and/or

- Secondary, air

And/or the plant's fuel feed rate, which is the rate at which fuel or matter is fed into the chamber through inlet 503, e.g. by means of a conveyor.

In some plants each controllable section has a conveyor grate with a respective controllable speed at which waste or matter is moved across the grate. Primary air and secondary air is also controllable, which means that the flow and/or temperature of air discharged above the section, respectively below the section are controllable.

The apparatus 100 is installed with its lance through a hole in a wall of the chamber 502. Due to its configuration that allows it to be installed or to view through a narrow space or hole it is possible to establish a field of view that covers the entire grate area or the most important portions thereof, where combustion takes place. The apparatus thereby comes very close to a high temperature zone 509 inside the chamber. Conventional apparatuses are typically installed further up the first boiler draft 507 or closer to the inlet 503 or outlet 504, which prevents a good field of view to the combustion grate.

The apparatus 100 is coupled to an image processor 510 that is configured to compute the spatial expanse and/or location of burning or heated subject matter on the grate 505. The image processor operates in accordance with the method described below. The result of the computation is transmitted to a system controller 512 via an interface 51 1 . In some embodiments the system controller 512 and the image processor 510 are two different systems running on separate hardware. The interface 51 1 serves to interface the two systems in terms of hardware and software. The system controller 512 controls the controllable sections 506 in response to measurements in the plant and different settings and the location and/or spatial expanse of the burning matter as computed by the image processor 510. Thus, the system controller 512 controls grate speed and/or primary air, and/or secondary air as described above and/or the plant's fuel feed rate.

Fig. 6 shows a flowchart for a method of processing images recorded with a predominant sensitivity to light in the near-infrared spectral range. In the images recorded by the apparatus 100, both burning matter 510 (i.e. matter with sufficiently high temperature to emit radiation in the near-infrared range) and flames 509 will appear. The flames will cast shade over the matter, but since the flames flare the matter will appear temporary temporarily in the sequence of images. The below method computes an estimate of a zone within which the matter 510 is burning. According to the method, the appearance of flames 509 is attenuated by use of a temporal low-pass filter.

The method acquires images in a sequence in step 601 and performs temporal low-pass filtering in step 602 where the acquired images are input to the temporal low-pass filter. In some embodiments the temporal low-pass filter is of the MR (infinite impulse response) type and in other of the FIR (finite impulse response) type. Output from the temporal low-pass filter is a filtered image that is updated each time an image is acquired. The low-pass filter should not be set with too slow a time constant, since the flames then cast a shadow across the image and cover for potential information of burning matter in the image. The purpose of the low-pass filter is to emphasize the more stationary, high intensity areas on the grate, as these high intensity areas represents where the subject matter burns, and thus where a combustion zone is located on the grate. To emphasize the more stationary areas, the filter removes the fastest changes in the flames for example with a time constant of approximately 1 second.

The filtered image or sequence of filtered images output from step 602 is subjected to a processing step 603 wherein a perspective correction is computed. The images recorded by the camera via the endoscope have a so-called fish-eye distortion due to the optics of the endoscope 109 and/or the optical adapter 1 19. In some embodiments a model for computing this correction is a model proposed by Ciaran Hughes et al. in Review of Geometric Distortion Compensation in Fish-Eye Cameras, ISSC 2008, Galway.

Output from step 603 is a geometrically corrected image or sequence of images; which in turn is input to step 604 wherein a temperature zone is computed. Steps thereof comprise: i) image reduction; ii) computation of the location of combustion zone; and iii) computation of the combustion zone's fronts.

Image reduction involves cutting off low intensity areas towards the borders of the image since those areas might distort computation of the combustion zones. In some embodiments this is involves spatial filtering and/or thresholding and/or morphological image operators.

computation of the location of combustion zone involves filtering to estimate a local deviation i.e. to provide an image with local deviations which is subsequently morphologically closed and filled to close the border towards low intensity and to obtain an even image of deviations within the high intensity zone. This image clearly represents a confined area corresponding to the high intensity zone. It may occur that several areas appear in the image, these area are removed if they are not larger than a certain threshold size as they otherwise could disrupt controlling of the combustion zones.

computation of the combustion zone's fronts involves capturing the high intensity zone by means of a so-called alpha-shape and to arrange segments thereof in a forwardly oriented front and a backwardly oriented front (relative to the direction of the grate's movement). There from the absolute locations of the fronts are computed with reference to a fixed point in the combustion chamber. Finally, in step 605, the location of the fronts is communicated to the system controller for control of the controllable combustion zones. The location of the fronts is communicated via the 51 1 by means of suitable parameters.

In some embodiments, additionally, the area of the combustion zone and the intensity or average intensity within the zone is communicated to the system controller by means of suitable parameters.

Claims

1 . An apparatus for visual inspection through a hole in a wall of a chamber for high-temperature processes, comprising:

- an elongated member that has a proximal end and a distal end and comprises a duct extending between the proximal end and the distal end;

- an endoscope arranged in the duct to extend from the distal end of the duct to its other, proximal end;

- a camera coupled with the endoscope to receive light from the proximal end of the endoscope and convert it to an output signal;

wherein the apparatus has a response to light that is predominant in the wavelength range between 600 nm and 1400 nm.

2. An apparatus according to claim 1 , wherein the predominant response is located within the wavelength range between 600 nm and 1000 nm or 600 nm and 900 nm or between 700 nm and 1000 nm or 800 nm and 1000 nm.

3. An apparatus according to any of the preceding claims, wherein the apparatus comprises an optical long-pass filter or an optical band-pass filter that attenuates transmission of light below its pass-band.

4. An apparatus according to any of the preceding claims, wherein the predominant response descents with a higher order slope towards shorter wavelengths and descents with a lower order slope towards longer wavelengths.

5. An apparatus according to any of the preceding claims, wherein the camera has a spectral response that exhibits a predominant response in the visible wavelength range and a lower response in the near-infrared range.

6. An apparatus according to any of the preceding claims, wherein the endoscope is coupled with the camera such that substantially the entire disc of light emanating from the endoscope impinges on and within the

boundaries of the image sensor of the camera.

7. An apparatus according to any of the preceding claims, wherein the elongated member comprises a channel configured to convey a refrigerant from its proximal end to its distal end.

8. An apparatus according to any of the preceding claims, wherein the elongated member has an outer wall enclosing a first tube; wherein the interior of the first tube is coupled to an inlet for supply of a forward flow of refrigerant and, at the distant end, to a space between the outer wall and the first tube to establish a passage for a reverse flow of the refrigerant; and wherein the space between the outer wall and the first tube is coupled to an outlet for discharging refrigerant.

9. An apparatus according to any of the preceding claims, comprising a housing coupled with the elongated member and accommodating the camera; wherein the camera housing has an outer wall and comprises a first passage for supplying a refrigerant to the elongated member and a second passage for receiving a refrigerant from the elongated member.

10. An apparatus according to any of the preceding claims, wherein the elongated member has an end-portion at its distal end and an outer wall enclosing a second tube; wherein the interior of the second tube is coupled, at the proximal end, to an inlet for supply of a forward flow of a purging agent; and wherein the second tube, at the distal end, is coupled to the end-portion for discharge of the purging agent into space in front of the end-element.

1 1 . An apparatus according to any of the preceding claims, wherein the distal end comprises an element that is made from a ceramic material that has the property of being machineable or comprises a ceramic portion that has the property of being machineable.

12. An apparatus according to any of the preceding claims further comprising an image processor operatively coupled with the camera and configured to determine the spatial expanse of a high-temperature zone and

communicating a control signal indicative of the spatial expanse; wherein image processing involved in determining the spatial expanse comprises temporal filtering that enhances relatively slowly varying intensities and attenuates relatively rapidly varying fluctuations.

13. A method of monitoring a high-temperature thermal process processing subject matter on a grate, comprising:

- recording a sequence of images by means of an camera operatively receiving light signals via an optical system; and wherein the combination of the camera and the optical system is installed to view at least a portion of the combustion grate; and

- performing image processing on an image of the sequence to determine the spatial expanse of a combustion zone and communicating a control signal indicative of the spatial expanse to a system controlling the high-temperature thermal process; wherein

- the apparatus has a predominant response to light in the wavelength range between 600 nm and 1400 nm; and wherein

- the image processing involves temporal filtering that enhances relatively slowly varying intensities and attenuates relatively rapidly varying

fluctuations.

14. A method according to claim 13, wherein the temporal filter has a time- constant in the range of 0.2 seconds to 3 seconds.