Patent Description:
The background information herein below relates to the present disclosure but is not necessarily prior art.

Recent environmental regulation norms require measurement and control of NOx and CO in the flue gas from power plants driven on fossil fuel. Control of NOx emission requires a reduction of NOx using selective catalytic reduction (SCR) and Selective non-catalytic reduction (SNCR). In both these cases, ammonia (NH<NUM>) is sprayed at a high temperature (> <NUM>) to reduce NOx to nitrogen and water. Due to fluctuations in the combustion processes and loading of the power plants, there are wide variations in both NOx and NH<NUM> (ammonia slip) concentrations in the flue gas. The in-situ and real-time measurements of flue gas mixtures are thus required for regulatory requirements and active combustion control of the boilers.

Presently, the measurements are carried out through sampling of the flue gas from the stack (hot/cold extraction) and carrying out the measurement in an analyser installed at a distance of <NUM>-<NUM> from the sampling point. A major drawback of this technique is the change in the stoichiometry of the sampled gas or condensations due to fluctuations in the sampling line temperature. To prevent such changes in stoichiometry, salt formations, or condensations, the sampling line is kept at a constant pre-determined high temperature (based on the dew point of the gas mixtures) using automatic temperature (for tropical climates) or heater power (for cold climates) control. Regular monitoring and adjustments with test gas are required to ensure the fidelity of the measurement process. It leads to higher operational and maintenance costs for this type of system.

To mitigate the challenges due to complex gas sampling and conditioning processes, in-situ probes have been developed to measure the gas species concentrations directly in the gas flow path. This real-time measurement enables the active control of the combustor in synchronization with the load curve based on power demand.

<CIT> relates to internal combustion engine diagnostics and discloses a diagnostic system for measuring temperature, pressure, CO2 concentration and H2O concentration in a fluid stream. It is known from this reference that a laser source can be housed in an enclosure and a probe for sampling the gas is used. For example, it describes that a first laser light source is coupled to a first end of a first pitch optic cable. A second laser light source is coupled to a first end of a second pitch optic cable. A lens is disposed proximate to a second end of each of the first and the second pitch optic cables for directing the first and second lights through a sampling chamber to a mirror. A first catch optic cable has a second end disposed proximate the lens for receiving light output from the first laser light source that is reflected from the mirror. A second catch optic cable has a second end disposed proximate the lens for receiving light output from the second laser light source that is reflected from the mirror.

<CIT> relates to a flue gas analyzer for the stacks of industrial furnaces. It discloses an apparatus for measuring the concentration of each gas in a mixture in a common sample chamber of H2 O, CO2, and CO wherein infrared radiation is passed through the sample chamber along a path to impinge upon an infrared detector.

<CIT> relates to internal combustion engine diagnostics and discloses apparatuses and methods for determining the spatial and temporal nonuniformities of CO2 in an intake fluid stream.

<CIT> relates to gas analysers e.g. for analysing the carbon monoxide content of flue gas. It is directed towards a gas analysing equipment which avoids the problems of taking gas samples from a flue and avoids the problems known in in situ equipment employing a beam splitter and two detectors where the detectors must be substantially identical in character.

<CIT> discloses a method for correcting the wavelength and the tuning range of a laser spectrometer, in which the light from a wavelength-tunable laser diode is detected and evaluated after it has passed through a gas.

<CIT> relates to semiconductor device manufacture and it discloses an apparatus and method for depositing one or more layers on a substrate using a line of electromagnetic radiation. It discloses optics arrangement continuous wave electromagnetic radiation source and substrate to focus the radiation on substrate.

However, all such systems have various problems, including signal deterioration, an inability to penetrate deeply, high cost, and the need for several probes.

The existing in-situ system uses tunable diode lasers (TDLs) and direct optical absorption spectroscopy (DOAS) technique for the measurement of gas species concentrations. The flue gas diffuses in the diffusion probe through a set of filters that form the measurement zone of the system. The laser radiation from one end of the probe is reflected at the other end using retro-reflectors, thereby forming a measurement path-length which is approximate twice the length of the probe. There are two major limitations with this method: the first limitation is the measurement of low concentrations at high temperatures. At high flue gas temperatures, the line-strength of the absorbing gas molecules decreases resulting in the decrease in measurement sensitivity of the concentrations and degradation of the signal-to-noise ratio. The second limitation is the reliability of the lasers. This mainly manifests as drift in the laser frequencies due to thermal conduction from the stack wall. Additional cooling mechanisms are required to prevent the laser drifts which results in higher operational costs of the in-situ measurement system.

The existing system for gas analysis is not suitable for deep penetration into large measurement zones (> <NUM>) due to difficulties in optical alignment. Signal degradation occurs in the existing system due to vibration. The conventional system also needs high-cost corrosion-resistant high-temperature mirrors. Also, the conventional system is not suitable if the laser source needs to be maintained at a fixed temperature.

Therefore, there is a need of a system for in-situ gas analysis that alleviates one or more aforementioned drawbacks.

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
A primary object of the present disclosure is to provide a system for in-situ gas analysis.

Another object of the present disclosure is to provide a system for in-situ gas analysis, which allows accurate measurement of low gas concentrations at high temperatures.

Yet another object of the present disclosure is to provide a system for in-situ gas analysis, which does not require additional cooling mechanisms.

Another object of the present disclosure is to provide a system for in-situ gas analysis, which does not involve difficulties in optical alignment.

Yet another object of the present disclosure is to provide a system for in-situ gas analysis, which provides real-time measurement.

Another object of the present disclosure is to provide a system for in-situ gas analysis, which measures the gas concentrations directly in the gas flow path.

Yet another object of the present disclosure is to provide a system for in-situ gas analysis, which does not involve condensation of gas.

Another object of the present disclosure is to provide a system for in-situ gas analysis, which incurs low operational and maintenance cost.

Yet another object of the present disclosure is to provide a system for in-situ gas analysis, which is not affected by vibration.

Another object of the present disclosure is to provide a system for in-situ gas analysis, which should be resistant to high temperature.

Yet another object of the present disclosure is to provide a system for in-situ gas analysis, which should be resistance to corrosion.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

There is provided a a system for in-situ gas analysis in a flue gas region according to appended independent claim <NUM>. The system comprises an enclosure, a laser beam source housed in the enclosure, a tubular probe insertable for probing in the flue gas region, a detector and a processing unit. The laser beam source is configured to generate laser beams. The tubular probe comprises optical waveguides, a dead zone, a measurement zone and a reflection chamber. The optical waveguides are configured to receive and conduct laser beams generated by the laser beam source. The dead zone configured to support and isolate the optical waveguides contained therein from surrounding flue gases. The optical waveguides extend up to and project the generated laser beams from the farther end of the dead zone. The measurement zone is configured to receive the projected laser beams by the optical waveguides. The measurement zone is configured to allow the flue gas to pass therethrough and get exposed to the projected laser beams. The reflection chamber is located at the farther end of the measurement zone. The reflection chamber comprises a first focusing lens for focusing the projected laser beams that are exposed to the flue gases in the measurement zone and at least two mirrors, positioned as defined in independent claim <NUM>, for reflecting back the focused laser beams towards the optical waveguides. The detector is configured to detect the reflected laser beam and generate at least one corresponding sensed signal. The processing unit is configured to process the sensed signal from the detector for computing composition of the flue gas.

Preferably, the laser beam source is configured to allow tuning of the frequency spectrum of the laser beam generated for identification of particular molecules present in the flue gas being analyzed.

Advantageously, the tubular probe comprises an insulation-cum-support tube along the dead zone for thermally insulating as well as structurally supporting the optical waveguides. Further, preferably, the insulation-cum-support tube consists of a first shield, a second shield and an air jacket defined by the space between the first shield and the second shield. The air jacket is configured to allow compressed air at ambient temperature to flow therethrough.

In an embodiment, the enclosure is temperature-stabilized and is configured to be positioned external to the flue gas region.

Typically, the detector includes a laser-optical sensor.

Preferably, the measurement zone is provided with a diffuser which allows diffusion of flue gases from the surrounding flue gas region into the measurement zone. Alternatively, the measurement zone is an open path cell.

Typically, the optical waveguides include a plurality of transmitting cables for transmitting the generated laser beams and projecting the generated laser beams into the measurement zone and at least one receiving cable for receiving the reflected laser beam and transmitting the reflecting beam to the detector.

In an embodiment, the optical waveguides include a plurality of sets of transmitting cables and a plurality of receiving cables. The plurality of sets of transmitting cables includes at least a first set of transmitting cables and a second set of transmitting cables for transmitting and projecting first generated laser beams containing a first frequency band and second generated laser beams containing a second frequency band respectively. The plurality of receiving cables includes a first receiving cable and a second receiving cable for receiving and transmitting a corresponding first reflected laser beam and a corresponding second reflected laser beam respectively. Accordingly, as the reflection chamber comprises at least two mirrors positioned one after the other along the longitudinal axis of the reflection chamber, the first mirror is configured to reflect the first generated laser beam and the second mirror is configured to reflect the second generated laser beam. Further, the detector comprises a second focusing lens for focusing a plurality of reflected laser beams including the first reflected laser beam and the second reflected laser beam. Accordingly, the dead zone comprises a first collimation lens assembly positioned at the farther end of the dead zone.

In an embodiment, the enclosure houses a plurality of gas cells provided for calibration, with one gas cell per laser beam source.

Preferably, the optical waveguides are made of chalcogenic cylindrical raw material such as As-Se, As-Se-Te, or Ge-Sb-Se, or are hollow waveguides.

The first focusing lens is formed by a group of lens which includes convex lens and fresnel lens.

The system for in-situ gas analysis of the present disclosure will now be described with the help of the accompanying drawing, in which:.

Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the invention which is only limited by the scope of the appended claims. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises", "comprising", "including" and "having" are open-ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated.

When an element is referred to as being "mounted on", "engaged to", "connected to" or 'coupled to" another element, it may be directly on, engaged, connected or coupled to the other element. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

Terms such as "inner", "outer", "beneath", "below", "lower", "above", "upper" and the like, may be used in the present disclosure to describe relationships between different elements as depicted from the figures.

Conventional methods of measurement of the concentration of gases involve sampling of gases from the source and transporting them to the analyser located <NUM>-<NUM> away. The stoichiometry of the sample gas, salt formations, or condensation changes due to fluctuations in the sampling line temperature. In order to counteract such a change, the sampling line is kept at a constant pre-determined high temperature. Such systems incur high operating and maintenance costs for regular monitoring and adjustment with a test gas, which is necessary to ensure the accuracy of the measuring process. To mitigate these challenges, in-situ gas analysis is proposed.

While in-situ analysis of flue gases in combustion chambers and the like using LASER is known, the desired accuracy of the analysis of flue gases could not be achieved due to the depth of the chambers at which the gases are desired to be analyzed. When the light moves to depths of <NUM> and beyond, the light is subject to scattering, diffraction, etc. by the vibrating gas molecules, which are produced at high temperatures, i.e., <NUM> and above. Moreover, it is also desired to keep the light source at room temperature. Hence, the source cannot be exposed to the high temperatures within or in direct contact with the combustion chamber. Thus, a system for in-situ gas analysis is required, which has improved accuracy and which eliminates or mitigates the aforementioned issues.

An example outside the scope of the invention and a preferred embodiment of the present invention will now be described with reference to <FIG>. In <FIG>, an example of a system <NUM> for in-situ gas analysis in a flue gas region <NUM> comprises an enclosure <NUM>, a laser beam source <NUM> housed in the enclosure <NUM>, a tubular probe insertable for probing in the flue gas region <NUM>, at least one detector <NUM> and a processing unit. The laser beam source <NUM> is configured to generate laser beams. Thus, the enclosure <NUM> is positioned external to the flue gas region <NUM>. The tubular probe comprises optical waveguides <NUM>, a dead zone <NUM>, a measurement zone <NUM> and a reflection chamber <NUM>. The optical waveguides <NUM> are configured to receive and conduct laser beams generated by the laser beam source <NUM>. The dead zone <NUM> configured to support and isolate the optical waveguides <NUM> contained therein from surrounding flue gases. The optical waveguides <NUM> extend up to and project the generated laser beams from the farther end of the dead zone <NUM>. The measurement zone <NUM> is configured to receive the projected laser beams by the optical waveguides <NUM>. The measurement zone <NUM> is configured to allow the flue gas to pass therethrough and get exposed to the projected laser beams. The reflection chamber <NUM> is located at the farther end of the measurement zone <NUM>. The reflection chamber <NUM> comprises a first focusing lens <NUM> for focusing the projected laser beams that are exposed to the flue gases in the measurement zone <NUM> and a mirror <NUM> for reflecting back the focused laser beams towards the optical waveguides <NUM>. The detector <NUM>, typically placed in a probe head <NUM>, is configured to detect the reflected laser beam and generate at least one corresponding sensed signal. The processing unit is configured to process the sensed signal from the detector <NUM> for computing composition of the flue gas.

Preferably, the laser beam source <NUM> is configured to allow tuning of the frequency spectrum of the laser beam generated, using direct optical absorption spectroscopy (DOAS) or wavelength modulation spectroscopy (WMS) or frequency modulation spectroscopy (FMS), for identification of particular molecules present in the flue gas being analyzed.

In an embodiment, the enclosure <NUM> is temperature-stabilized and is configured to be positioned external to the flue gas region. In an embodiment, the enclosure <NUM> houses a plurality of gas cells <NUM> provided for calibration, with one gas cell <NUM> per laser beam source <NUM>.

A plurality of parabolic mirrors <NUM> can be used to direct the laser beam emanating from the laser beam sources <NUM> into each of the optical waveguides <NUM>. Preferably, each of the laser beam sources <NUM> is a QCL, i.e., quantum cascade laser or tunable diode lasers (TDLs).

Typically, the first focusing lens <NUM> formed by a group of lens which includes convex lens and fresnel lens.

The tubular probe is mounted using a mounting flange <NUM>. The mounting flange <NUM> is provided with a circumferential sealing means.

The laser beam projected from the optical waveguides <NUM> interacts with the high-temperature flue gases in the measurement zone <NUM>. Further, the first focusing lens <NUM> of the reflection chamber <NUM> collimates the laser beam traveling within the measurement zone <NUM>. The mirror <NUM> of the reflection chamber <NUM> reflects the laser beam towards the optical waveguides <NUM> parallel to the incident light. The optical waveguides <NUM> transmit the light coming from the measurement zone <NUM> into the detector <NUM>. The detector <NUM> generates signals corresponding to the light and transmits to the processing unit. The processing unit analyses the signals thus received for identifying contents of the flue gases that are analyzed. The processing unit is preferably disposed within the temperature-controlled optical source enclosure <NUM>.

In an advantageous embodiment, as shown in <FIG>, the tubular probe comprises an insulation-cum-support tube <NUM> along the dead zone for thermally insulating as well as structurally supporting the optical waveguides <NUM>. The insulation-cum-support tube <NUM> consists of a first shield 32a, a second shield 32b and an air jacket 32c defined by the space between the first shield 32a and the second shield 32b. Compressed air at ambient temperature is made to flow through air jacket 32c.

The dead zone <NUM> comprises a first collimation lens assembly <NUM> positioned at the farther end of the dead zone <NUM>. The first collimation lens assembly <NUM> aligns each of the beams in its intended direction of impingement on the first focusing lens <NUM>.

Preferably, the measurement zone <NUM> is provided with a diffuser <NUM> which allows diffusion of flue gases from the surrounding flue gas region into the measurement zone <NUM>. Alternatively, the measurement zone <NUM> is an open path cell.

Typically, the detector <NUM> includes a laser-optical sensor <NUM>.

Typically, as shown in <FIG>, the optical waveguides <NUM> include a plurality of transmitting cables (60a) for transmitting the generated laser beams and projecting the generated laser beams into the measurement zone <NUM> and at least one receiving cable 60b for receiving the reflected laser beam and transmitting the reflecting beam to the detector <NUM>.

In an embodiment, as shown in <FIG>, the optical waveguides <NUM> include a plurality of sets of transmitting cables and a plurality of receiving cables. The plurality of sets of transmitting cables includes at least a first set of transmitting cables 601a and a second set of transmitting cables 602a. The first set of transmitting cables 601a transmits and projects first generated laser beams containing a first frequency band. The second set of transmitting cables 602a transmits and projects second generated laser beams containing a second frequency band. The plurality of receiving cables includes a first receiving cable 601b and a second receiving cable 602b. The first receiving cable 601b receives and transmits a first reflected laser beam corresponding to the first frequency band. The second receiving cable 602b receives and transmits a second reflected laser beam corresponding to the second frequency band.

According to the invention, and as shown in <FIG>, the reflection chamber <NUM> comprises at least two mirrors 54a, 54b positioned one after the other along the longitudinal axis of the reflection chamber <NUM>. A first mirror 54a is configured to reflect the first generated laser beam and a second mirror 54b is configured to reflect the second generated laser beam. Further, the detector <NUM> comprises a second focusing lens <NUM> for focusing a plurality of reflected laser beams including the first reflected laser beam and the second reflected laser beam. In an embodiment, the detector <NUM> may include a second collimation lens assembly (not shown).

The positioning and the stability of the various components within the tubular probe, including the cables, the lenses, the mirror can be provided using clamps, brackets, and the like, known in the art.

Preferably, the optical tubes <NUM> of the tubular probe of the present disclosure have a reflective internal surface. The optical tubes <NUM> are hollow fiber/glass tubes having silver coating on the internal surface. In another embodiment, the optical tubes <NUM> are hollow waveguide made of chalcogenic cylindrical raw material such as As-Se, As-Se-Te or Ge-Sb-Se, or are hollow waveguides. The property of having a reflective internal surface prevents the distortion due to diffraction, scattering, and so on, of the light that is transmitted through the optical tubes <NUM> due to any surrounding gases. Due to the low attenuation factor (measured in dB/m) of the optical tubes <NUM>, the range of the tubular probe of the in-situ gas analysis system <NUM> of the present disclosure increases significantly as compared to in-situ gas analysis systems of the prior art. Accurate analysis of flue gases produced in chambers having depths of <NUM> and beyond can be done using the in-situ gas analysis system <NUM> of the present disclosure.

In a typical embodiment, the length of the measurement zone <NUM> is <NUM>, whereas the length of the dead zone can be extended significantly due to the low attenuation factor of the optical tubes <NUM>. Thus, the in-situ gas analysis system <NUM> of the present disclosure requires optical alignment to be maintained only in a measurement zone of typically <NUM>. Also, the optical source <NUM> can be arranged at a sufficient distance from the combustion chamber so that no system for cooling the light sources is required. Moreover, low-cost mirrors can be used in the reflection chamber <NUM>, thereby avoiding the use of the corrosion-resistant mirrors used in the prior art and saving almost three times the cost.

The processing unit may include a repository for storing information such as chemical formulae of gaseous and suspended solid components expected to be detected in the flue gases. The processing unit may include an analog-to-digital convertor, a digital filter module, a time-domain-to-frequency-domain conversion module, a crawler-and-extractor module and so on. The digital filter module may be configured to subject the detected signal to a bandpass filter, an anti-aliasing filter, a noise removal filter and the like. The time-domain-to-frequency-domain conversion module is configured to convert the data from time domain to frequency domain. The crawler-and-extractor module is configured to compare processed data to the information stored in the memory and identify composition of the flue gas, including contained gases, their proportions by weight and so on.

The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present invention, which is limited only by the scope of the appended claims. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable within the scope of the appended claims.

The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of a system for in-situ gas analysis, which:.

The foregoing disclosure has been described with reference to the accompanying embodiments which do not limit the scope of the invention, which is limited only by the scope of the appended claims. The description provided is purely by way of example and illustration.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

Claim 1:
A system (<NUM>) for in-situ gas analysis in a flue gas region (<NUM>), wherein said system (<NUM>) comprises:
• An enclosure (<NUM>);
• A laser beam source (<NUM>) housed in said enclosure (<NUM>), said laser beam source (<NUM>) configured to generate laser beams;
• A tubular probe insertable for probing in the flue gas region (<NUM>), said probe comprising:
∘ optical waveguides (<NUM>) configured to receive and conduct laser beams generated by said laser beam source (<NUM>);
∘ a dead zone (<NUM>) configured to support and isolate said optical waveguides (<NUM>) contained therein from surrounding flue gases, said optical waveguides (<NUM>) extending upto and projecting said generated laser beams from the farther end of said dead zone (<NUM>);
∘ a measurement zone (<NUM>) configured to receive said projected laser beams by said optical waveguides (<NUM>), said measurement zone (<NUM>) configured to allow said flue gas to pass therethrough and get exposed to said projected laser beams; and
∘ a reflection chamber (<NUM>) located at the farther end of said measurement zone (<NUM>), said reflection chamber (<NUM>) comprising a first focusing lens (<NUM>) for focusing said projected laser beams that are exposed to said flue gases in said measurement zone (<NUM>), and at least two mirrors (54a,54b) for reflecting back said focused laser beams towards said optical waveguides (<NUM>) and positioned one after the other along the longitudinal axis of said reflection chamber (<NUM>), wherein a first mirror (54a) is configured to reflect a first generated laser beam and a second mirror (54b) is configured to reflect a second generated laser beam;
• at least one detector (<NUM>) configured to detect said at least one reflected laser beam and generate at least one corresponding sensed signal; and
• a processing unit configured to process said sensed signal from said detector (<NUM>) for computing composition of said flue gas.