CA2799830A1

CA2799830A1 - Method and system for monitoring steam generation tube operation conditions

Info

Publication number: CA2799830A1
Application number: CA2799830A
Authority: CA
Inventors: Hua Nmn Xia; Aditya Kumar; Guanghua Wang
Original assignee: General Electric Co
Current assignee: BL Technologies Inc
Priority date: 2012-12-20
Filing date: 2012-12-20
Publication date: 2014-06-20
Anticipated expiration: 2032-12-20
Also published as: CA2799830C

Abstract

A system for monitoring the operating conditions of a steam generator is described. The system comprises a network in communication with a workstation, a plurality of fiber optic sensors for sensing strain information of tubes in a steam generator and communicating this information to the workstation, and a camera for detecting temperature in a plurality of tubes in a steam generator, and for communicating the temperatures to the workstation, wherein the workstation is configured to determine the operating conditions of the steam generator.

Description

METHOD AND SYSTEM FOR MONITORING STEAM GENERATION TUBE OPERATION
CONDITIONS
FIELD
[0001] The present disclosure relates generally to steam generators. More particularly, the present disclosure relates to monitoring steam generators during operation.
BACKGROUND

[0002] The following background discussion is not an admission that anything discussed below is citable as prior art or common general knowledge.

[0003] A steam generator is used in various applications and processes including, for example, for driving a turbine to create electricity, or in steam assisted gravity drainage for recovery of oil in oil sands as are found in Alberta, Canada.

[0004] A heat recovery steam generator (HRSGs) is a type of steam generator that uses heat exchangers to recover heat from a hot gas stream to generate steam. A
type of HRSG is a once-through steam generator (OTSG). OTSGs are favoured in some oil sands applications.
Unlike HRSGs, OTSGs do not have boiler drums. An OTSG comprises one or more high carbon steel tubes or tube coils that pass through different, but connected, heating sections, namely, radiant and convection sections. In an OTSG, the water to be heated and converted into steam is pumped in a continuous path through the tubes through the radiant and convection sections.
Heat is generated by combusting fuel in a combustion chamber. The combustion chamber is located directly adjacent to the radiant section. The heat from the combustion chamber is forced through the radiant section, through the convection section and out an exhaust stack.

[0005] Cold or mild temperature water is first pumped through the convection section where heat exchange with the hot combustion flue gas pre-heats the water. To maximize heat transfer to the water, the coiled carbon steel tubes in the convection section are tightly arranged next to one another in stacks or layers to maximize water surface area to water volume.

[0006] HRSGs and OTSGs comprise one or more pipes that pass through heating regions.
Water is pumped through the pipes and heated as it traverses the heating regions. OTSGs are harsh environments that can experience up to 1000 degrees Celsius in a radiant regions and 500-1000 degrees Celsius in a steam convection region.

[0007] Pre-heated water or water/steam mixture exits the convection section and continues to the radiant section where it is further heated by the hot air and by the radiation emitted from the combustion of fuel. The radiant section consists of a large number of tubes in a shell through which hot air and combusted gas are forced. The tubes in the radiant section are straight and arranged circumferentially around the interior of the radiant section to form a hollow cylindrical structure. No tubes are present in the centre of the cylinder so as to allow combusted gas and hot air to pass therethrough.

[0008] During operation, deposits can accumulate in the interior of the tubes or tube coils that carry water or steam or a mixture thereof, through the sections. The accumulation of deposits in the interior of the tubes is called fouling and is caused by particles in the water or scaling due to the presence of silica, carbonate, and other minerals in the water. Heat accelerates the accumulation of deposits or fouling. Fouling may reduce the performance of the HRSG and OTSG by degrading the thermal exchange efficiency of the tubes, or parts thereof, at different radiant and convection sections. Deposits on the interior of the tubes also restrict the flow of water. Localized fouling can product hot spots that continue to foul and may lead to a ruptured pipe.
INTRODUCTION

[0009] The following is intended to introduce the reader to the detailed description to follow and not to limit or define the claims.

[0010] This specification describes a system for monitoring the operating conditions of a steam generator. The system comprises a network in communication with a workstation; a plurality of fiber optic sensors for sensing temperature or strain information of tubes in a steam generator; instrumentation connected to the fiber optic sensors for obtaining the strain information therefrom and communicating the strain information to the workstation through the network; a camera for detecting the temperature in a plurality of tubes in a steam generator, and for communicating the temperatures to the workstation through the network;
wherein, the workstation is configured to determine the operating conditions of the steam generator. In another embodiment of the system the fiber optic sensor is a high-temperature fiber optic sensor. In another embodiment of the system the fiber optic sensors sense the strain information of tubes in a radiant section of the steam generator. In another embodiment of the system the camera senses the temperature of tubes in a radiant section of the steam generator.

[0011] Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

[0013] Figure 1A is an illustration of a once-through steam generator.

[0014] Figure 1B is a cross section of a convection section of a circuit of the once-through steam generator depicted in Figure 1A.

[0015] Figure 1C is a cross section view of a radiant section of a circuit of the once-through steam generator depicted in Figure 1A.

[0016] Figure 2 is a perspective side view of a segment of a fiber optic sensor.

[0017] Figure 3 is a cross section view of an exemplary embodiment of a fiber optic sensor disposed within a hermetical cable package.

[0018] Figure 4 is a perspective side view of a cable package disposed within a guide tube and affixed to a tube according to an embodiment of the present invention.

[0019] Figure 5 is a schematic depiction of a monitoring system and a portion of the once-through steam generator of Figure 1A according to an embodiment of the present invention.

[0020] Figure 6 is a flowchart of a process for monitoring the operating conditions of tubes with a fiber optic sensor in the once-through steam generator of Figure 1A in accordance with an embodiment of the present invention.

[0021] Figure 7 is a block diagram of an illustrative system for determining location data for pipes of the once-through steam generator of Figure 1A;

[0022] Figure 8 is a flowchart of an example method for determining location data for pipes of the HRSG of Figure 1A;

[0023] Figure 9 is a view of sample images for calibrating a camera according to the method of Figure 1A;

[0024] Figure 10 through Figure 12 are views of camera lens distortion parameters for calibrating a camera according to the method of Figure 8;

[0025] Figure 13 and Figure 14 are perspective views of tubes in the interior of a radiant section of a HRSG, showing the identification of landmarks, and a projection from the landmarks, respectively, according to the method of Figure 8;

[0026] Figure 15 is a schematic view of a pipe template transformation, for adjusting a location according to the method of Figure 8;

[0027] Figure 16 and Figure 17 are schematic views of projected locations of the pipe templates, for adjusting location data according to the method of Figure 8;
and

[0028] Figure 18 through Figure 21 are perspective views of pipes in the interior of a HRSG, depicting location data for pipes, according to the method of Figure 8.

[0029] Figure 22 shows another example embodiment of a system for monitoring the operating conditions of a once-through steam generator as shown in Figure 1A.
DETAILED DESCRIPTION

[0030] In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments.
However, it will be apparent to one skilled in the art that these specific details are not required. In other instances, well-known electronic structures and circuits are shown in block diagram form in order to not obscure the understanding. For example, specific details are not provided as to whether the embodiments described herein are implemented as a software routine, hardware circuit, firmware, or a combination thereof.

[0031] FIG. 1A illustrates an example HRSG, in particular a once-through steam generator (OTSG) 100, for use with a method and system for monitoring the operating conditions therein.
An HRSG is an energy recovery heat exchange system that recovers heat from a hot gas stream generated by a gas turbine. The energy from the hot gas stream generates steam for electricity production or for various industrial processes. A specialized type of HRSG that does not include a boiler drum is an OTSG. An OTSG converts water (also referred to as feed water) to high-pressure and high-temperature steam.

[0032] In the OTSG 100, cold or pre-heated water may follow a continuous path without segmented sections for components such as economizers, evaporators, and super heaters. In the OTSG 100, preheating, evaporation, and superheating of the water may take place consecutively, within one continuous circuit 102. Water is pumped through the circuit 102, shown as arrow "A" in FIG. 1A, at a cold end 104 of the OTSG 100. As the water flows through the OTSG 100, it is heated and changes phase as it extracts heat from the gas flow shown as arrow 106. Superheated steam flows through the hot end 108 of the OTSG 100, shown as =
arrow "B" in FIG. 1A. The circuit 102 includes one or more tubes that are exposed to one or more convection sections 110, and one or more radiant sections 112, also referred to as furnaces, together referred to as heating sections.

[0033] For example, the temperature in the radiant section 112, or furnace, of an OTSG can reach up to 1,000 C (degrees Celsius). The water or steam in the interior of tubes used in an OTSG may reach 300 C and a pressure of 1800 pounds per square inch gage (psig), limiting the use of traditional fouling detection techniques as described above.

[0034] Individual sections of the OTSG 100 may be larger or smaller based on the heat load received from the gas turbine. The location of the pipes as built or observed during operation may differ from locations according to computer-aided design (CAD) models of the HRSG
system or components thereof. Furthermore, the location of the pipes may be affected due to expansion and contraction of pipes due to operating conditions and heat, and manufacturing variations.

[0035] FIG. 1B shows a cross-section of the convection section 110 of the circuit 102 as shown in FIG. 1A. Disposed within the circuit 102 are one or more tubes 109 which run the length of the circuit. Between the tubes 109 themselves and the walls of the circuit 102 is air. To maximize heat transfer to the water, the coiled carbon steel tubes in the convection section 110 are tightly arranged next to one another in stacks or layers to maximize water surface area to water volume.

[0036] FIG. IC shows a cross-section of the radiant section 112 of the circuit 102 as shown in FIG. 1A. Disposed within the circuit 102 are one or more tubes 109 which run the length of the circuit. Between the tubes 109 themselves and the walls of the circuit 102 is air. The radiant section 112 consists of a large number of tubes 109 through which hot air and combusted gas are forced. The tubes 109 in the radiant section 112 are straight and arranged circumferentially around the interior of the radiant section 112 to form a hollow cylindrical structure. No tubes are present in the centre of the cylinder so as to allow combusted gas and hot air to pass therethroug h.

[0037] FIG. 2 shows an embodiment of a fiber optic sensor 210 comprising a strand of optical fiber 212 that reflects particular wavelengths of light and transmits all other wavelengths of light. The optical fiber 212 comprises a core 214 and a cladding 216. The cladding 216 comprises a material with a low refractive index, such as silicon dioxide, which encases the core 214, and an outer coating material, such as polyimide or metal. To achieve the desired reflective / transmission properties in the optical fiber 212, the refractive index of the core 214 is periodically varied. These variations are known as Bragg gratings (gratings) 218. Gratings 218 can be created by, for example, inscribing the core 214 with an intense ultraviolet source such as an ultraviolet laser. U.S. Patent 7,574,075, incorporated herein by reference in its entirety, describes a fiber Bragg grating and fabrication method of same. The gratings are, generally, 5-millimeters in length and the distance between the gratings is, generally, 50 millimeters.

[0038] Because of the harsh environment and extreme heat in an OTSG 100, a high-temperature fiber optic sensor 210 is preferably used. An example of a high-temperature fiber optic sensor 210 is a tetrahedral fiber Bragg grating sensor. U.S. Patent 8,180,185, which is 10 herein incorporated by reference in its entirety, describes a tetrahedral fiber optic sensor for a harsh environment. The tetrahedral fiber optic sensor comprises microcrystalline and silicon dioxide tetrahedral structure gratings which are better able to tolerate high temperatures while keeping their structural integrity and reducing thermal drift in the wavelengths of light reflected and refracted by the gratings.

[0039] FIG. 3 shows an example embodiment of a high-temperature fiber optic sensor 210 encased in a hermetical cable package 220 which, together, form a sensor cable package 222, according to the present invention. The hermetical cable package 220 comprises three concentric metal layers. An inner metal layer 224 is disposed circumferentially about the high-temperature fiber optic sensor 210. The inner metal layer 224 comprises gold, nickel and aluminum and has a thickness of 10-20 micron meters. A middle metal layer 226 is disposed circumferentially about the inner metal layer 224. The middle metal layer 226 comprises stainless steel or INCONEL and has an outside diameter of less than 1 millimetre and an inside diameter of more than 0.25 millimetres. The outer metal layer 228 is disposed circumferentially about the middle metal layer 226 and has an outside diameter of less than 1.5 millimetres and an inner diameter of more than 1 millimetre. The outer metal layer 228 is composed of INCONEL. The gaps between the three metal layers can contain air, or thermal conductive filling material, or fluid. A conventional pulling method is used to thread the fiber optic sensor 210 through the inner metal layer 224.

[0040] FIG. 4 shows an example embodiment of the sensing cable package 222, substantially the same as shown in FIG. 3, affixed to, or integrated with, the tube 109 according to the present invention. Prior to affixing or integrating the sensing cable package 222 to the tube 109, the surface of the tube 109 is first cleaned of all oxides. A guide tube 240 is affixed to the tube 109 by spot welding at multiple locations along the tube 109. The tube 109 and the guide tube 240 are welded together using shims 242 therebetween so that it affixes the sensing cable package 222 along the length of the tube 109. A shim 242 may be approximately 20mm wide and have a curvature on one of its faces sufficient to adapt to the curvature of the tubes 109 to which it is being affixed. The sensing cable package 222 is inserted or threaded into the guide tube 240. In an example embodiment, a sensing cable package 222 can be from 20 to 30 feet in length. Multiple sensing cable packages 222 can be combined together, end to end, to span the entire length of the tube 109. The guide tube 240 may be sprayed with thermal sprays to mitigate potential delamination of the guide tube 240 from the shims 242, and the shims 242 from the tube 109. The first thermal spray may consist of a base coat of Metco 443, the second thermal spray may consist of alumina.

[0041] FIG. 5 shows an example embodiment of a plurality of fiber sensing cable packages 222 affixed to the tubes 109 of the radiant section 112 of the OTSG 100 of FIG. 1A according to the present invention. The cable packages 222 are affixed to the tubes 109 by shims 242 and connected to instrumentation 250 for monitoring the operating conditions of the tubes 109. The sensing cable packages 222 run along the lengths of at least a portion of each tube 209 within the guide tubes 240. The fiber optic sensors 210 of the sensing cable packages 222 are optically connected to a junction box 254 which transmits signals from the fiber optic sensors 210 to a signal processing unit 256, such as an optical sensing interrogator, sm125 from Micron Optics Inc. The optical sensing interrogator 256 may comprise a broadband or tunable light source 258 and a photodetector 260. The photodetector 260 can be arranged as an array to provide multi-channel optical spectral analysis functionality. For high accuracy spectral analysis, an optical sensing interrogator is normally integrated with a NIST standard gas calibration cell.
The optical sensing interrogator 256 is connected to a central processing unit (CPU) 262 which includes a display 264. The CPU 262 can be connected to a network 406. The light source 258 emits a broadband spectrum light. The spectrum of light emitted by the light source 258 can be controlled by either tuning a filter or by tuning a laser cavity. In an example embodiment the light source 258 is a tunable fiber laser that can provide 80-100nm wide spectral range.

[0042] FIG. 6 is a flowchart of a process 300 for monitoring the operating conditions of the tubes 209 in the OTSG 200 of the system of Figure 5, according to the present invention. The process 300 comprises the steps of emitting 302 light into a plurality of fiber optic sensors 210, detecting 304 the refracted wavelengths of the light, converting 306 the detected wavelengths of multiplexed signals into individual sensor signals using a peak tracking algorithm, communicating 308 the signal to a central processing unit 262 (CPU), processing 310 the signal to determine the operating conditions of the tubes 209, and displaying 312 the operating conditions on a display.

[0043] In the step of emitting 302, the light is emitted by the light source 258 through the junction box 254 and into each of the fiber optic sensors 210. The light travels down the core 214 of each of the fiber optic sensors 210. Upon encountering gratings 218, certain wavelengths of the light reflect and the other wavelengths refract. What wavelengths reflect and refract depends upon the properties of the grating 218 the spacing between the gratings 218, and the operating conditions of the tubes 209. The refracted wavelengths cascade through each grating 218 and travel back up the core 214 of the fiber optic sensors 210, through the junction box 254 and into the optical sensing interrogator 256.

[0044] Each grating 218, in effect, acts as an individual temperature and / or strain sensor.
In an embodiment of this invention, each grating 218 is arranged to reflect slightly different wavelengths of light from the other gratings 218 that are also along the length of the fiber optic sensor 210. In this way, reflected light from a particular grating 218 (and therefore the temperature and pressure sensed by that particular grating at a particular measurement location along the tube 209) can be differentiated from the light reflected by the other gratings 218. The range of light wavelengths each grating 218 is arranged to reflect, depends upon the number of gratings 218 in the fiber optic sensor 210, the bandwidth of the light source 258, and the variance in wavelengths, due to temperature and pressure strains, the gratings 218 are expected to reflect.

[0045] In the step of detecting 304, the light detectors 260 in the interrogator 256 detect the refracted wavelengths of light.

[0046] In the steps of converting 306 and communicating 308, the detected wavelengths of light are converted into a digital signal and communicated to the CPU 262. In example embodiments, communication may occur through any or all of sending and / or receiving electrical signals, optical signals, or wireless signals.

[0047] In the step of processing 310 and displaying 312, the CPU 262 processes the signal to determine the operating conditions of the tube 209 at a specific point in time and displays 209 the operating conditions on a display 264.

[0048] A grating typically has a sinusoidal refractive index variation over a defined length.
The reflected wavelength AB of the pulse of light is defined by the equation AB = 270, where neis the effective refractive index of the fiber Bragg grating, and A is the grating period.

[0049] The bandwidth is defined by the equation AA = [287i07/]
AB,where 7r Sno is the variation in the refractive index (i.e. n2 ¨ n1), and n is the fraction of power in the fiber core.

[0050] High-temperature fiber optic sensors 210, as described in this embodiment, may be multi-functional. They are sensitive to both temperature and strain such that a change in either or both at any grating point along the length of the fiber optic sensor 210 causes a relative shift in the wavelength of light reflected at that grating 218. If the wavelength shift at time initial t(0) is k(t(0)), then, the wavelength shift of fiber optic sensors 210 in response to both temperature and strain at any moment, t, is defined according to the following equation:
AAB (t) = Kee(t) + KtAT(t), AAB(t) = 2.(t) ¨ A(t(0)), and AT(t) = T(t) ¨
T(t(0)), where KE is the fiber sensor strain sensitivity E(t) is the thermal strain effect at time t Kt is the temperature sensitivity, and AT is the relative temperature variation at time t.

[0051] Where a fiber optic sensor is under a pressure strain-free condition, whether the fiber optic sensor experiences either a linear or nonlinear wavelength shift depends upon the external temperature. In general, a polynomial function up to order 3 could satisfy most of the calibration needs for the following equations AAB (t) = a + b = AT(t) + c = AT2(t) + d = AT3(t), where a,b,c and dare constants determined during calibration.

[0052] If the fiber optic sensor 210 is under a pressure strain due to the way in which the sensor package is deployed, the wavelength shift is just a function of the surface temperature of the tube 209. In such a case, the temperature sensitivity, Kt will be dominated by the coefficient of thermal expansion of the sensor package and tube. A fiber optic sensor 220 can detect thermal strains and the instrumentation 250 can measure the extent to which, a tube 209 deforms or ruptures.

[0053] A pressure strain due to tube deformation at a constant temperature is described by the following equation: A(T , t) = A(T) + K EE(t). The shift in the wavelength of reflected light is occurs slowly which reflects the gradual mechanical deformation of the tube.

[0054] A pressure strain due to a tube rupture is described by the following equation:
A(T , t) = A(T 0) + Ks(t) , where To is a specific steam tube operation temperature. In this event, the fiber optic sensor long-term trend suddenly returns to strain-free status, or induces some discontinuous drop in the fiber optic sensor response.

[0055] Both a slow response, a varied response, and an unexpected discontinuous response, are combined when conducting tube thermal degradation analysis. For example, the average tube temperature from all of the fiber optic sensors can be used to determine the general trend of the degree of fouling formation, while each individual fiber optic sensor in each tube can be used for local hot spot detection.

[0056] In the step of converting 306, the reflected wavelengths are multiplexed through wavelength domain signal analysis technology.

[0057] In the step of processing 310, the above-noted equations are used to determine various operating conditions of the tube 209. Operating conditions include, but are not limited to, the local temperatures and changes in local temperatures of a point on the tube 209 at each grating 218; the local strain and changes in local strain of a point on the tube 209 at each grating 218; thermal trends of a tube 209; localized hot spots; dynamic thermal events; and transient thermal events.

[0058] Prior to deploying fiber optic sensors 210 as shown in Figure 5, each fiber optic sensor 210 needs to be calibrated in a laboratory. During calibration, the calibration variables a,b,c, and d are determined through running simulations. When the fiber sensing package 210 is deployed in a steam generator, the strain on the fiber optic sensor 210 needs to be equivalent to the strain on the fiber optic sensor 210 in the laboratory during calibration so that the calibration variables a,b,c, and d are correct.

[0059] FIG. 7 illustrates an example system 400 for determining pipe locations in a HRSG, such as the OTSG 100. According to example embodiments of the invention, the system 400 may include camera(s) 402, a data store 404, a network 406, and a workstation 410.

[0060] With reference to FIG. 7, in an example embodiment, CAD model(s) 426 may be entered into the workstation 410 by a terminal or remote workstation 428. In other example embodiments of the invention, the CAD model(s) 426 may already be present in the workstation 410. The CAD model(s) 426 may comprise the three-dimensional design and construction

[0061] According to an example embodiment of the invention, the workstation 410 may comprise one or more memories 412, one or more processors 420, and one or more input/output interfaces 422. In accordance with an example embodiment of the invention, the

[0062] According to an example embodiment, one or more cameras 402 may be in angles. Furthermore, once the location data for a tube 109 has been determined, then thermal measurements may be taken continually to measure critical parameters related to pipe fouling and deterioration such as pipe temperatures, thermal trends, localized hot spots, dynamic and transient events, and the like. While the camera(s) 402 are most useful for monitoring the OTSG
100 during operation, the camera(s) 402 can also be used when maintenance is being performed on the tubes 109 to measure the residual heat from the tubes 109.

[0063] In an example embodiment, the camera(s) 402 may be located in a housing mounted on the inner wall of the circuit 102, just outside the OTSG 100 radiant section 112. This location reduces the amount of heat to which the camera(s) 402 are exposed. In an embodiment, the housing and camera(s) 402 can be cooled with air from outside the circuit 102.
In another embodiment, the camera housing can be insulated from the inside of the circuit 102 to reduce the amount of heat to which the camera(s) 402 are exposed.

[0064] In an example embodiment, the camera(s) 402 are arranged so as rotate about one or more axis to view different sections of the pipes and to view the pipes at different angles.

[0065] The camera(s) 402 may include equipment for communication with the workstation 410 via a network 406, or by other direct or wireless inputs to the workstation 410. In other example embodiments, the camera(s) 402 may communicate directly with the workstation 410 via input/output interfaces 422. In an example embodiment, a local or remote data store or memory device or system 412 may be utilized for saving images or other data associated with the pipes of the OTSG 100. In an example embodiment, the data store or memory device or system 412 may also be utilized for storing and/or retrieving CAD model(s) 426 for use with the calculation module(s) 418.

[0066] According to an example embodiment, the system 400 may be utilized for determining location data for tubes 109 of the OTSG 100. For example, images of the one or more tubes 109 of the HRSG 122, that are in the field of view of the camera(s) 402, may be loaded into the memory 412 of the workstation 410. The images may then be used together with the CAD model(s) 426 according to the method described below. The method may be carried out by the calculation module(s) 418. According to an example embodiment, location data associated with the one or more tubes 109 of the OTSG 100 may be determined based at least in part on the CAD model(s) 426 and the images. According to another example embodiment, the system may be utilized for continuous monitoring and diagnosing of fouling of tubes 109 of an HRSG, and for determining location data for the fouled tubes 109.

[0067] According to an example embodiment of the invention, the location data may be output, stored and/or used to monitor and diagnose hot spots or other symptoms of fouling. The location data may be used by technicians to anticipate, schedule, or facilitate the repair or maintenance of the OTSG 100, to change or control one or more operations associated with the OTSG 100, to integrate the monitoring with other processes, and to improve steam generation efficiency. Location data can also be used to improve the accuracy of the thermal images taken by the camera(s) 402 by correcting for tubes 109 distance and viewing angles.

[0068] FIG. 8 is a flowchart illustrating an example of a method for monitoring changes in temperature according to thermal images of tubes 109 in a HRSG and determining a location of a diagnosed anomaly or potential fouling. The method includes determining location data for tubes 109 in a HRSG.

[0069] Optionally, the system may be used with optical, or non-IR, cameras. When using IR
or non-IR cameras, camera lens distortion may affect the determined location data as by the use of a wide angle or macro lens. To address these effects, the method may include calibrating the camera to reduce a camera lens distortion characteristic such as, for example, tangential distortion and radial distortion. Calibrating the camera lens, shown as 502 in FIG. 8, may be achieved by using a camera calibration toolbox, as for example, Jean-Yves Bouguet, Camera Calibration Toolbox for Matlab.

[0070] FIG. 9 illustrates example images 602 of a planar checkerboard used for camera calibration. The calibrated image is shown at 604. To incorporate sufficient information for the calibration, images of the checkerboard in different sizes, positions, rotations and viewpoints should be provided.

[0071] FIG. 10 through FIG. 12 show the radial, tangential, and combined lens distortion functions, respectively. FIG. 10 shows the tangential component of the camera lens distortion characteristic. FIG. 11 shows the radial component of the camera lens distortion characteristic.
FIG. 12 shows the complete camera lens distortion characteristic, which is the combination of the tangential and radial distortion characteristics.

[0072] According to one example, the relations among the image, the CAD
model, lens distortions and other calibration parameters may be represented in Equation 1.
u d = D asy yx00] ry73) [I (1) Z'

[0073] where u and v are image points (coordinates), function DO is the lens distortion function, a, and a3, are focal length of the camera, s is the skew parameter, x0 and yo are the image center, X' Y' and Z' are the 3D points (coordinates) in the camera coordinate system, and i3 is the lens distortion parameter.

[0074] With reference to FIG. 8, at 506, a CAD model of the OTSG 100 of FIG
1A is registered using an image to generate a projection of the CAD model onto the image. A
projection is used to map real world objects (through the use of points, or coordinates in a matrix) from a thermal image to objects (points, or coordinates in a matrix) in a CAD model. A
projection may refer to a projection matrix that is obtained by receiving several landmarks from the image corresponding to known locations in the CAD model of the system, shown as 504 of FIG. 8. By linking points from the CAD model to points from the image corresponding to these landmarks, the projection matrix may be calculated, shown at 508 of FIG. 8. A
projection matrix of an image of the HRSG system represents how objects from the CAD model may be projected into the image and determines location data for the objects. A projection may be used to determine location data for pipes shown in an image using a CAD model of a HRSG system or a component thereof.

[0075] One or more extrinsic parameters of the camera 402, including the intensity of the pixel, and the angle and distance of the IR camera 402 to the object of interest, may be obtained from the projection matrix. The intensity of each pixel in a given thermal image depends not only on the measured heat, but also on the angle and distance of the IR camera 402 to the part represented by the pixel, also known as extrinsic parameters of the camera 402.
The method may include calibrating the camera 402 to adjust the angle of the camera to each part represented by a pixel of the image and the distance of the camera 402 to each part represented by a pixel of the image, shown as 502 on FIG. 8.

[0076] The projection matrix may be determined by using techniques as described in Richard Hartley and Andrew Zisserman, Multi-view geometry in Computer Vision, Cambridge University Press, 2004. For example, to obtain a projection matrix, several landmarks on the image may be identified, or linked. These landmarks correspond to known locations on the CAD model of the tubes 109. The points of the landmarks from the CAD model may be linked to points of the image. The projection matrix may be determined through the linking of the CAD
model points and image points for these landmarks.

[0077] To determine the projection matrix, the points of the landmarks may be identified.

For example, the endpoints of the top of tubes 1004, illustrated as dots 1006 in FIG. 13, may be identified manually as the landmarks. FIG. 13 and FIG. 14 are perspective views of tubes 109 in the interior of the radiant section 112 of the OTSG 100, showing the identification of landmarks, and the projection from the landmarks, respectively, according to the method of FIG.
8. One point of a landmark may be selected as the reference point having coordinates (0,0,0).
Based on the reference point, the points of all the landmarks in the image may be determined.
The least square algorithm may be used to calculate the projection matrix from the points. The least square algorithm is described in Richard Hartley and Andrew Zisserman, Multi-view geometry in Computer Vision, Cambridge University Press, March 2004.

[0078] The accuracy of the location data may be tested by re-projecting the landmarks from the CAD model points to the image points according to the projection matrix, illustrated as circles 1008 in Fig. 13. In this example, the pipes are sparsely selected to make them clearly visible.

[0079] Once the projection matrix is obtained, given any CAD model point, the corresponding point in the image may be determined. For example, in FIG. 14, the lines 1102 are the estimated positions of the right side of some pipes and the lines 1104 represent the left side of the same pipes. Moreover, the circles 1106 represent rings in the OTSG
100 that may be positioned among different sections of tubes 109. As illustrated in FIG.
14, the tubes and rings are correctly re-projected into the image.

[0080] The location data for the tubes 109 and other components may be accurate at the start of operation, however, operating conditions may reduce this accuracy.
For example, the location may be affected by conditions due to expansion and contraction of tubes 109 due to heat, manufacturing variations, changes in the refraction index due to the heated air in the OTSG 100, or slight movement of the camera 402 over time. Problems due to noises and systematic errors may arise. Accordingly, adjustment or refinement of the location data to address these variations is desirable. To address these variations, in one example, locally fitting a parametric template may be used to adjust the location data for the tubes 109.
Adjusting location data for a tube 109 is shown at 310 of FIG. 8. Adjusting the location data makes the data more robust and may address noise and other systematic errors.

[0081] During operation, using the thermal images, the temperature of a tube 109 may be calculated, shown as 512 of FIG. 8, and changes in temperature may be monitored or tracked to locate, or identify the three-dimensional location of, anomalous "hot spots"
at 514 of FIG. 8, which may indicate the presence of fouling. The adjustment of the location data may be =
continuous, shown as 516 of FIG. 8, so that the location data for anomalies in the tubes 109 may be adjusted continuously to accord with the operating conditions.

[0082]
Tubes 109 closer to the camera may appear to be wider and longer, depending on the orientation of the tubes 109. Since the relevant perspective geometry is known from the projection matrix, a parametric template may be used to refine the location of these tubes 109.
A parametric template may be designed to match to an ideal tube 109 that is orthogonal to the camera's 402 optical axis, shown as 1204 in FIG. 15. This ideal template has a constant value longitudinally (Y axis shown as 1208 in FIG. 15) and has a difference of Gaussians (DOG) shape across the pipe (X axis shown as 1206 in FIG. 15), and thus enables cylindrical objects to be detected. The DOG may be calculated in one dimension, defined in Equation 2:
f (x; i a, o-2) = 1 exp ( x -i ) ) 1 exp( (x_1)2) (2) (721,i2Tr 20-2 where x is the coordinate along the crossline of the pipe (X axis shown as 1206 in Fig. 15), is the mean of both of the Gaussians, which is the coordinate of the middle line (dash line shown as 1204 in FIG. 15) of the pipe, and o-i and a2 are the bandwidth for the two Gaussians respectively.

[0083] Since the perspective geometry of each tube 109 is known, four corners of each tube 109 may be used to determine an affine mapping from the ideal template 1204 to each located template 1202 (the corners being shown as 1210, 1212, 1214, and 1216 in FIG.
15). The parameters of the affine transformation may be estimated using the least squares fitting algorithm. It may be assumed that the angular variations along each pipe are minimal. The affine model may handle width variations along the pipe. The bandwidth of Gaussian filters that form the DOG may be designed so that the highest peak of the template is in the middle of tubes 109 and the lowest peaks of the template is at the two sides of the tubes 109.

[0084]
FIG. 16 and FIG. 17 are schematic views of an example of the use of the tube 109 templates, in the far and near fields, respectively. The tube 109 template is properly located in the image, as shown by regions 1304 of higher weights (and therefore intensity) and regions 1302 of lower weights.

[0085]
To adjust the location of tubes 109, the local maxima of a template score may be used. The local maxima is defined as the weighted sum of intensities with weights given by the DOG template, given by Equation 3:

R(T) = ZpeT l(p(x),p(y)) x w(p(x),p(y)) (3) where T is the template, 14/(=,') is the weight determined by DOG after the affine transformation, p is the pixel inside the template and x, y are the image coordinates of the pixel; 1(=,.) represents the intensity of the image at a given position.

[0086] To find the local maxima, a projected template may be locally adjusted by slightly rotating and shifting the tubes 109. In each instance, a template matching score is obtained.
The local maximum is the one with the highest score, which is also selected as the location of the tubes 109. This process may be defined in Equation 4 as:
Ybest = argMaXyiEr R(yi(T)) (4) where F is the whole set of local rotation and shift parameters and yi is one instance. The final tube 109 location may be determined by Ybest , which corresponds to the local maximum of the template score.

[0087] Equation 4 refines the tube 109 locations individually. This makes the refinement sensitive to the local intensity noises. To overcome this problem, one solution is to combine several neighbor pipes together to refine the location for all of them. Due to the low contrast and blurring of the image, the refinement of a single pipe may be incorrect.
To make it more robust, the response of several pipes may be combined together. Possible rotations and shifts may be enumerated. Then, the local maximum may be selected as the refined position for these pipes.

[0088] For example, the robustness of adjustment or refinement was tested by determining a projection matrix from an image as described above and projecting the tubes 109 into the image. The image was then shifted 5 pixels in both x and y directions, so that the tube 109 locations were inaccurate. To refine the tubes' 109 locations, the estimated template was rotated from -20 to 20 degrees every 5 degrees and was shifted from -5 to 5 pixels every 2 pixels in both x and y directions.

[0089] The refinement results based on a single tube 109 are illustrated in FIG. 18 and FIG.
19. FIG. 18 illustrates the results of near field tubes 109, and FIG. 19 illustrates the results of far field. Lines 1504 are the left side of the tubes 109 and lines 1508 are the right side of the tubes 109. The dotted lines 1502 (for the left side) and 1506 (for the right side) are the tubes' 109 locations, which are not correct due to the shift of the image described above. The solid lines 1504 and 1508 are the results after the refinement. It is observed that the near field tubes 109 are correctly located (FIG. 18), but the ones in the far field are not (FIG. 19). This may be due to the low contrast of the image for the far field tubes 109.

[0090] FIG. 20 and FIG. 21 illustrate the refinement with multiple tubes 109 together. FIG.
20 and FIG. 21 illustrate the results of a two-tube combination and a four-tube combination separately, respectively. It is observed that in both examples (FIG. 20 and FIG. 21), the tubes are located accurately.

[0091] A method includes receiving at least one image, from a camera, of one or more tubes for carrying water in a steam generator such as an HRSG or an OTSG, registering a computer-aided design (CAD) model of the one or more tubes 109 onto the at least one image to generate a projection of the CAD model, and determining location data for the one or more tubes 109 from the projection.

[0092] A system includes a display, at least one processor coupled to the display and configured to receive at least one image, from a camera 402, of one or more tubes 109 for carrying water in a heat recovery steam generator (HRSG) system, register a computer-aided design (CAD) model of the one or more tubes 109 onto the at least one image to generate a projection of the CAD model onto the at least one image, and determine location data for the one or more tubes 109 from the projection.

[0093] The method may include calibrating the camera 402 to reduce a camera lens distortion characteristic. The camera lens distortion characteristic may include tangential distortion and radial distortion. The method may include calibrating the camera 420 to adjust an extrinsic parameter of the camera 402, the extrinsic parameter including at least one of the angle of the camera 402 to each part represented by a pixel of the image and the distance of the camera 420 to each part represented by a pixel of the image. The registering may include receiving an identification of landmarks on the image that correspond to known locations in the CAD model and generating the projection from the landmarks, the projection including a projection matrix from the image to points on the CAD model. The method may further include refining the location of the one or more tubes 109 by adjusting the location using a model based tube 109 template. Adjusting may include constructing a plurality of parametric templates for each of the one or more tubes 109, evaluating the plurality of parametric templates against the location to generate a response, and adjusting the location when the parametric template has a local best fit response. The parametric template may include a rotation parameter and a shift parameter. The adjusting may be dependent on the local best fit response for at least one neighbor tubes 109.

[0094] The image may be a thermal image and the camera 402 may be an infrared camera.
A method may include receiving a sequence of thermal images captured by the infrared camera 402, monitoring the sequence of thermal images for a change of temperature affecting one or more of the tubes 109, and when a temperature change is detected, diagnosing a fouling symptom using the location.

[0095] The HRSG system may be a once-through steam generator (OTSG).

[0096] Example embodiments of the invention may provide the technical effects of creating certain systems and methods that determine pipe locations in a HRSG.

[0097] In example embodiments of the invention, the system 400 may include any number of hardware and/or software applications that are executed to facilitate any of the operations. In example embodiments, one or more I/O interfaces may facilitate communication between the system 400 and one or more input/output devices. For example, a universal serial bus port, a serial port, a disk drive, a CD-ROM drive, and/or one or more user interface devices, such as a display, keyboard, keypad, mouse, control panel, touch screen display, microphone, etc., may facilitate user interaction with the system 400. The one or more I/O
interfaces may be utilized to receive or collect data and/or user instructions from a wide variety of input devices. Received data may be processed by one or more computer processors as desired in various embodiments of the invention and/or stored in one or more memory devices.

[0098] One or more network interfaces may facilitate connection of the system 400 inputs and outputs to one or more suitable networks and/or connections; for example, the connections that facilitate communication with any number of cameras associated with the system. The one or more network interfaces may further facilitate connection to one or more suitable networks;
for example, a local area network, a wide area network, the Internet, a cellular network, a radio frequency network, a BluetoothTM enabled network, a Wi-Fi Tm enabled network, a satellite-based network, any wired network, any wireless network, etc., for communication with external devices and/or systems. As desired, embodiments of the invention may include the system with more or less of the components illustrated in FIG. 7.

[0099] FIG. 22 shows an example embodiment of a system 1700 for monitoring the operating conditions of the radiant section 112 and of the convection section 110 of the OTSG

100 of FIG. 1. The system 1700 comprises a plurality of the sensing cable packages 222 of FIG.

3, affixed to, or integrated with tubes 109 for monitoring operating conditions in a convection section 110, and one or more thermography imaging cameras 402 positioned proximate to a radiant section 112 for monitoring the operating conditions of tubes 109, therein. The sensing cable packages 222 are ideal for use in the convection section 110 because the tubes 109, therein, are tightly spaced and make a series of turns. The camera 402 is ideal for use in the radiant section 112 because the tubes 109, therein, are straight and all tubes 109 can be viewed by the camera 402 situated at one location. The camera 402 is connected directly to a network 406. The sensing cable packages 222 are connected to instrumentation 250 which communicate with the network 406 through the CPU 262. The network 406 is connected to a workstation 410. The workstation 410 processes information about the operating conditions of the tubes 109 in the radiant section 112, received through the network 406 from the cameras 402. The workstation 410 can also simultaneously process information about the operating conditions of the tubes 109 in the convection section 110 received through the network 406 from the instrumentation 250. In this way, the workstation 410 can, at the same time, monitor the operating conditions of all tubes 109 in all section 110 and 112 of the OTSG
100.
[0100] The above-described embodiments are intended to be examples only.
Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.
Furthermore, The invention is described above with reference to block and flow diagrams of systems, methods, and/or computer program products according to example embodiments of the invention. It will be understood that one or more blocks of the block diagrams and flow diagrams, and combinations of blocks in the block diagrams and flow diagrams, respectively, may be implemented by computer-executable program instructions. Likewise, some blocks of the block diagrams and flow diagrams may not necessarily need to be performed in the order presented, or may not necessarily need to be performed at all, according to some embodiments of the invention.

[0101] These computer-executable program instructions may be loaded onto a general-purpose computer, a special-purpose computer, a processor, or other programmable data processing apparatus to produce a particular machine, such that the instructions that execute on the computer, processor, or other programmable data processing apparatus create means for implementing one or more functions specified in the flow diagram block or blocks. These computer program instructions may also be stored in a computer-readable memory that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means that implement one or more functions specified in the flow diagram block or blocks. As an example, embodiments of the invention may provide for a computer program product, comprising a computer-readable medium having a computer-readable program code or program instructions embodied therein, said computer-readable program code adapted to be executed to implement one or more functions specified in the flow diagram block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational elements or steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions that execute on the computer or other programmable apparatus provide elements or steps for implementing the functions specified in the flow diagram block or blocks.

[0102] Accordingly, blocks of the block diagrams and flow diagrams support combinations of means for performing the specified functions, combinations of elements or steps for performing the specified functions and program instruction means for performing the specified functions. It will also be understood that each block of the block diagrams and flow diagrams, and combinations of blocks in the block diagrams and flow diagrams, may be implemented by special-purpose, hardware-based computer systems that perform the specified functions, elements or steps, or combinations of special-purpose hardware and computer instructions.

[0103] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

WHAT IS CLAIMED IS:

1. A system for monitoring the operating conditions of a steam generator, comprising a network in communication with a workstation;
a plurality of fiber optic sensors for sensing strain information of tubes in a steam generator;
instrumentation connected to the fiber optic sensors for obtaining the strain information therefrom and communicating the strain information to the workstation through the network;
a camera for detecting the temperature in a plurality of tubes in a steam generator, and for communicating the temperatures to the workstation through the network;
wherein, the workstation is configured to determine the operating conditions of the steam generator.

2. The system of claim 1, wherein the strain information is temperature and location data.

3. The system of claim 1, wherein the strain information is pressure strain and location data.

4. The system of claim 1, wherein the fiber optic sensor is a high-temperature fiber optic sensor.

5. The system of claim 1, wherein the fiber optic sensors sense the strain information of tubes in a convection section of the steam generator.

6. The system of claim 1, wherein the camera sense the temperature of tubes in a radiant section of the steam generator.