Title of Invention

"A NON-CONTACT METHOD AND DEVICE TO DETERMINE THE GAS TEMPERATURE IN A COMBUSTION CHAMBER OF STEAM GENERATOR"

Abstract

The invention determines combustion chamber gas temperature in a steam raising system. Quasi-distributed optical sensing array means disposed within the combustion chamber are used for determining the gas temperature. The shift in characteristic reflected spectrum of interrogated light is indicative of the gas temperatures at the individual sensor points Planar profile of combustion chamber gas temperature is deduced from the point temperatures determined using the optical sensing array.

Full Text

-2- FIELD OF INVENTION The present invention generally relates to a measurement system which uses optical media with Bragg gratings. More particularly, the present invention relates to a non-instrusinic,non-contact hi-fidality method to determine the gas temperature in a typical furnace, in particular a combustion chamber of a steam generator. The invention further discloses a multipoint optical device adaptable to carry-out the innovative method. BACKGROUND OF THE INVENTION Steam generating units are employed universally by Power Plants, Industries and Refineries to produce steam for their operation. The steam generators are designed so as to be capable to fire fuel oil, fuel gas or coal. The fuels are admitted in the combustion chamber of the steam generator only after determining that the combustion chamber has attained the requisite ignition temperature. The products of combustion that is to say, the high temperature flue gas-proceed through various heat absorbing elements located in the first pass and second pass of the steam generator. -3- Since the steam generators in a plant requires to be operated at a relatively high temperature and pressure, conditions within the combustion chamber must be continuously monitored. One of the monitorable conditions constitutes flue gas temperature which indeed is critical parameter to be consistently monitored through sensing and acquiring characteristic data. Flue gas temperature sensing in a steam generator is normally accomplished with one or more temperature monitoring devices operated by electric or mechanical means. One such monitoring device is the thermocouple- a device based on thermoelectric effect, a plurality of which is disposed throughout the combustion chamber and heat transfer surface. The thermocouples are placed in the steam generator in such a way that they are separated by protective sheaths. The sheaths are provided to protect the relatively fragile thermocouple junctions from the hostile environment inside the steam generator. Consequently, the thermocouples do not really sense the process temperature directly, but instead respond to the heat transmitted, and thus, the sensing of temperature is influenced by the time lag inherent in conductive heat transfer . Accordingly, a substantial delay in thermocouple response, generally occurs corresponding to the changes in temperature within the combustion chamber. This phenomenon is particularly true during system startup when combustion reaction initially results in a rapid -4- temperature rise which must be detected in order to confirm combustion establishment. In addition, heat transfer time lag affect thermocouple response to the changes in operating conditions during normal system operation. Moreover, the thermocouples are basically effective for spot measurement. As an alternative to thermocouples, mechanical devices like acoustic pyrometers are occasionally used to measure the gas temperature. The acoustic pyrometer is externally mounted on the combustion chamber. The pyrometer is connected to the combustion chamber via a purgeable lance tube which normally extends from the pyrometer into the chamber internals. A major limitation of monitoring devices like acoustic pyrometer, arises from the difficulty encountered in keeping the lance tube free of obstructions. Further, the acoustic signals generated from the auxiliary components of the steam generator for example, soot blowers, and those from the steam leaks in the combustion chamber, also influence the measured data to a considerable extent. Thus, the acoustic pyrometer can only provide an averaged value of the measurand, particularly, in the path between the receiver and the transmitter. There are already known various constructions of sensing arrangements, for example, U.S. Pat. No. 4,806,012, entitled "Distributed, Spatially Resolving Optical Fiber Strain Gauge", discloses -5- a sensing device capable of sensing stresses within a structure which comprises an optical fiber containing a plurality of periodic Bragg gratings of different original periodicities. Thus each reflecting light in a narrow range around a central wavelength can be determined by the respective periodicity. Such bragg gratings are disposed at different regions of the structure so as to be subjected to different stresses, temperatures and strains depending on their locations in the structure, and undergoing strain-related changes in their periodicities including in their central wavelengths of reflection. During the use of this known sensing arrangement, light is launched into the optical fiber in a wavelength range, such that, the wavelengths of interest with respect to all of the Bragg gratings under all conditions can be embraced. Then, the light returned back to the launching end of the fiber is examined , or the light reaching the other end is examined, respectively for the presence or the absence or diminishing or otherwise of intensity, in respect of the altered light around each central wavelengths of the gratings, the alteration being taking place due to the stresses existing at the respective locations of the structure, thereby the magnitude of such stresses is determined. Prior to installation of the optical fibre core in the structure,the individual Bragg gratings are provided in the optical fiber core, by exposing the optical fiber core through the cladding to an -6- interference pattern of two ultraviolet light beams , the light frequency and/or orientation of the light beams relative to the optical fiber longitudinal axis for each of the gratings, being such that, the interference pattern maxima and minima extend through the fiber in directions normal to the longitudinal axis, and that the periodicity (e.g. the distance between two consecutive maxima) being that desired for the particular grating. However, this approach is particularly advantageous, in the applications in which the number of locations along the optical fiber to be monitored for stresses in the structure is relatively small, because the device entails an important drawback in that each of the gratings has to have assigned to it a considerable amount of the available spectrum (i.e. not only its relatively narrow wavelength or frequency band but also the separation from the adjacent wavelength or frequency band assigned to another grating by an amount sufficient to avoid overlapping or crosstalk between the adjacent channels under all circumstances, that is, even when the centra! wavelengths of the adjacent channels have moved, as a result of the stresses applied at the locations of the associated gratings, toward one another to the maximum extent). Such allocation of larger spectrum to each of the gratings, severely limit the number of grating sensors that can be employed within each sensing optical -7- fiber. For example, if a solid state device, such as an edge-emitting diode or a laser diode is used as the light source, which would be highly desirable because of the relatively low cost and reliability of such device, it would only cover a wavelength range of few tens of nm. On the other hand, each of the optical sensors of the type disclosed in the above-cited reference, would require up to 5 nm of bandwidth to cover the entire measurement bandwidth. Thus, only a limited number of sensors can be associated with each optical source disclosed in the US-patent under discussion. OBJECTS OF THE INVENTION It is therefore, an object of the invention to propose a non-instrusinic, non-contact, hi-fidility method to determine the gas temperature in a typical furnace, in particular, a combustion chamber of a steam generator. Another object of the invention is to propose a multipoint optical sensing device to determine the gas temperature in any typical furnace, in particular, a combustion chamber of a steam generator. A still another object of the invention is to propose a non-instrusinic, non-contact, hi-fidility method to determine the gas temperature in a -8- typical furnace, in particular, a combustion chamber of a steam generator which makes use of the proportional change in a physical property of the optical sensing device. A further object of the invention is to propose a multipoint optical sensing device which consists of an array of multipoint sensors arranged in a single optical device. A still further object of the invention is to propose a non-instrusinic, non-contact, hi-fidility method to determine the gas temperature in a typical furnace, in particular, a combustion chamber of a steam generator which generates a planar gas temperature profile from the measurand information derived from the multipoint optical sensing device. SUMMARY OF THE INENTION The present invention provides an optical fiber-based apparatus, for measuring a gas temperature in a high-temperature environment like a steam generator combustion chamber, and a method of using the optical fiber-based apparatus for such measurement. More particularly and in accordance with exemplary embodiments, the optical fiber-based apparatus comprises -9- an optical fiber-based sensor including an optical fiber which has a plurality of fiber gratings disposed thereon at appropriate locations along the longitudinal axis of the optical fiber. The gratings exhibit exceptional thermal stability and do not degrade at conditions prevailing inside the steam generator combustion chamber, thereby enabling the optical fiber-based sensor of the present invention to be used for measuring flue gas temperature in high temperature environment of steam generator combustion chamber. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING: Figure: 1 shows a schematic diagram of an optical fibre-based apparatus according to the present invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION: As shown in fig 1, the method determines the temperature of flue gas in the combustion chamber by adapting an optical sensing device having atleast four quasi-distributed optical sensing array means (1). The array means (1) is disposed within the combustion chamber (2) of the steam generator. Light originating from a light source when launched into the optical sensing array means (1), undergoes -10- reflection at each of the sensor locations. As the sensor array means (1) of the device undergoes deformation in its geometric structure due to the effect of the gas temperature in contact with the array means (1), the extent of light reflection from the device undergoes a relative change. As the light passes through the optical sensor array means, characteristic of the reflected spectrum undergoes a change. An interrogator (3) is disposed at the end of the optical array to determine the gas temperatures at each of the sensor points as a function of the shift in the reflected peaks of the received interrogating light signal. A signal processor (4) is arranged to deduce a planar profile of the temperature of flue gas in the combustion chamber, based on the point temperatures determined using the optical sensing array. -11- WE CLAIM: 1. A non-instrusinic, non-contact, hi-fidality method to determine the gas temperature in a typical furnace, in particular a combustion chamber of a steam generator, the method comprising the steps of: - providing a multipoint optical sensing array means, being interposed in the combustion chamber; - providing a light source and launching light from the light-source to the optical sensing array means, the array means having a plurality of quasi-distributed optical sensors; - acquiring data in respect of a change in the characteristic of the reflected spectrum of light corresponding to a deformation in the original geometric structure of the sensing array means upon fluctuations in flue-gas temperature inside the combustion chamber; - arranging an interrogator downstream of the array means which capture the data relating to the gas temperatures at each sensor point as a function of the shift in the reflected peaks of the received interrogating light signals; and - -12- - providing a signal processor operably connected to the interrogator, to generate a planar profile of the temperature of flue gas in the combustion chamber based on the captured data respecting to the gas-temperatures at each sensor point. 2. A multipoint optical sensor device to determine the gas temperature in a typical furnace, in particular a combustion chamber of a steam generator, the device comprising: -a light source for launching light beams at different directions; -atleast four quasi-distributed optical sensors forming an array means (1) interposed in the combustion chamber (2), the array means (1) being susceptible to geometric deformation in structure corresponding to changes in temperature of flue-gas in the combustion chamber (2), the deformed structure of the sensing array means (1) emitting a reflected spectrum of light with changed characteristic, the changes being in registration 4 with the geometrical deformation in the structure of the sensing means; -an interrogator (3) disposed downstream of the optical sensing array means (1) for acquiring data in respect of the gas temperature at each sensor point of the array means (1), -13- the acquired data representing a shift in the reflected peaks of the interrogating light signals, and - a signal processor (4) operably connected to the interrogator (3) for receiving data from said interrogator (3) to generate a planar profile of the temperature of flue gas based on the data respecting to the point temperatures captured at each sensor means. 3. A non-instrusinic, non-contact, hi-fidality method to determine the gas temperature in a typical furnace, in particular a combustion chamber of a steam generator, as substantially described herein and illustrated with reference to the accompanying drawing. 4. A multipoint optical sensor device to determine the gas temperature in a typical furnace, in particular a combustion chamber of a steam generator, as substantially described herein and illustrated with reference to the accompanying drawings The invention determines combustion chamber gas temperature in a steam raising system. Quasi-distributed optical sensing array means disposed within the combustion chamber are used for determining the gas temperature. The shift in characteristic reflected spectrum of interrogated light is indicative of the gas temperatures at the individual sensor points Planar profile of combustion chamber gas temperature is deduced from the point temperatures determined using the optical sensing array.

Documents:

01007-kol-2006-abstract.pdf

01007-kol-2006-claims.pdf

01007-kol-2006-correspondence others.pdf

01007-kol-2006-description(complete).pdf

01007-kol-2006-drawings.pdf

01007-kol-2006-form-3.pdf

01007-kol-2006-form1.pdf

01007-kol-2006-form2.pdf

01007-kol-2006-g.p.a.pdf

1007-KOL-2006-(03-11-2011)-ABSTRACT.pdf

1007-KOL-2006-(03-11-2011)-AMANDED CLAIMS.pdf

1007-KOL-2006-(03-11-2011)-AMANDED PAGES OF SPECIFICATION.pdf

1007-KOL-2006-(03-11-2011)-DESCRIPTION (COMPLETE).pdf

1007-KOL-2006-(03-11-2011)-EXAMINATION REPORT REPLY RECIEVED.pdf

1007-KOL-2006-(03-11-2011)-FORM 1.pdf

1007-KOL-2006-(03-11-2011)-FORM 2.pdf

1007-KOL-2006-(03-11-2011)-FORM 3.pdf

1007-KOL-2006-(03-11-2011)-OTHERS.pdf

1007-KOL-2006-(03-11-2011)-PA.pdf

1007-KOL-2006-(06-07-2012)-CORRESPONDENCE.pdf

1007-KOL-2006-CORRESPONDENCE.pdf

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