Claims:1. A method (500) for measuring a plurality of parameters corresponding to an exhaust emission of a combustion process, the method (500) comprising:
obtaining (502) a spectroscopic signal associated with the exhaust emission;
generating (504), via optical wavelength separation, an absorption spectrum signal from the spectroscopic signal, wherein the absorption spectrum signal corresponds to a plurality of species in the exhaust emission;
identifying (506) a plurality of spectral features in the absorption spectrum signal, wherein the plurality of spectral features comprises a plurality of spectral responses and a plurality of interfering spectral responses; and
simultaneously determining (508) a plurality of parameters based on the plurality of spectral features and a spectroscopic model.
2. The method (500) of claim 1, further comprising controlling (510) the exhaust emission based on the plurality of parameters.
3. The method (500) of claim 1, wherein simultaneously determining (508) the plurality of parameters is further based on an operating range of at least one of the plurality of parameters.
4. The method (500) of claim 1, further comprising:
generating, by a single tunable laser, a laser beam having one or more laser modulation depths, and
passing the laser beam through the exhaust emission to obtain the spectroscopic signal.
5. The method (500) of claim 4, wherein the laser beam comprises a wavelength modulated laser beam, and wherein a wavelength of the wavelength modulated laser beam is tuned to a spectral feature adapted to determine one or more of the plurality of parameters.
6. The method (500) of claim 5, wherein generating (504) the absorption spectrum signal comprises:
determining the absorption spectrum signal based on the spectroscopic signal; and
generating a derivative spectroscopic signal based on a first harmonic and a second harmonic of the absorption spectrum signal.
7. The method (500) of claim 1, further comprising developing a spectroscopic model, wherein developing the spectroscopic model comprises:
generating a plurality of reference absorption spectrum signals (514) based on a reference exhaust emission having one or more of the plurality of species, wherein the plurality of reference absorption spectrum signals corresponds to a plurality of reference parameter sets, and wherein each of the plurality of reference parameter sets comprises a plurality of reference parameters;
identifying a reference feature set (516) in each of the plurality of the reference absorption spectrum signals to generate a plurality of reference feature sets, wherein each reference feature set comprises a plurality of reference spectral features; and
establishing a correspondence (518) between the plurality of reference feature sets and the plurality of reference parameter sets to generate the spectroscopic model.
8. The method (500) of claim 7, wherein simultaneously determining (508) the plurality of parameters comprises:
selecting a reference feature set having a plurality of reference spectral features from plurality of reference feature sets in the spectroscopic model based on the plurality of spectral features via use of a regression technique;
identifying a reference parameter set having a plurality of reference parameters from the plurality of reference parameter sets corresponding to the selected reference feature set; and
selecting the plurality of reference parameters of the reference parameter set as the plurality of parameters.
9. The method (500) of claim 7, wherein simultaneously determining (508) the plurality of parameters comprises:
selecting at least two reference feature sets from the plurality of reference feature sets in the spectroscopic model based on the plurality of spectral features via use of a regression technique;
identifying a reference feature set among the at least two reference feature sets based on an operating range of at least one of the plurality of parameters;
identifying a reference parameter set having a plurality of reference parameters from the plurality of reference parameter sets corresponding to the selected reference feature set; and
selecting the plurality of reference parameters of the reference parameter set as the plurality of parameters.
10. The method (500) of claim 1, wherein the plurality of parameters comprises a temperature value, a pressure value, a concentration value of a species, or combinations thereof and wherein the plurality of species comprises at least one of NO2, H2O, and O2.
11. The method (500) of claim 10, wherein the plurality of parameters comprises at least a concentration of NO2 and a temperature value.
12. A system (100) for simultaneous spectroscopic measurements, the system (100) comprising:
a launcher unit (116) comprising:
a single tunable laser (134) configured to generate a wavelength modulated laser beam;
a beam shaping subunit (136) coupled to the single tunable laser (134) and configured to convey the wavelength modulated laser beam through exhaust emission to generate a spectroscopic signal, wherein the exhaust emission comprises a plurality of species, and wherein the spectroscopic signal corresponds to a plurality of parameters of the exhaust emission;
a receiver unit (118) comprising:
a wavelength separation subunit (140) configured to generate an absorption spectrum signal based on the spectroscopic signal;
a detector (142) coupled to the wavelength separation subunit (140) and configured to identify a plurality of spectral features in the absorption spectrum signal, wherein the plurality of spectral features comprises a plurality of spectral responses and a plurality of interfering spectral responses;
a data storage unit (120) configured to store a laser tuning function, a spectroscopic model, and an operating range of one or more of the plurality of parameters; and
a processor unit (122) communicatively coupled to the data storage unit (120) and the detector (142) and configured to simultaneously determine a plurality of parameters based on the plurality of spectral features and, the spectroscopic model.
13. The system (100) of claim 12, further comprising a controller (124) communicatively coupled to the processor unit (122) and configured to control the exhaust emission based on the plurality of parameters.
14. The system (100) of claim 12, wherein the single tunable laser (134) is further configured to generate a laser beam having one or more laser modulation depths.
15. The system (100) of claim 12, wherein the wavelength separation subunit (140) is further configured to generate a derivative spectroscopic signal based on a first harmonic and a second harmonic of the absorption spectrum signal.
16. The system (100) of claim 12, wherein the processor unit (122) is further configured to simultaneously determine the plurality of parameters based further on an operating range of at least one of the plurality of parameters.
17. The system (100) of claim 12, wherein the processor unit (122) is further configured to:
select a reference feature set having a plurality of reference spectral features from a plurality of reference feature sets in spectroscopic model based on the plurality of spectral features via use of a regression technique;
identify a reference parameter set having a plurality of reference parameters corresponding to the selected reference feature set; and
select the plurality of reference parameters of the reference parameter set as the plurality of parameters.
18. The system (100) of claim 12, wherein the processor unit (122) is further configured to:
select at least two reference feature sets from a plurality of reference feature sets in the spectroscopic model based on the plurality of spectral features via use of a regression technique;
identify a reference feature set among the at least two reference feature sets based on an operating range of one or more of the plurality of parameters;
identify a reference parameter set having a plurality of reference parameters corresponding to the selected reference feature set; and
select the plurality of reference parameters of the reference parameter set as the plurality of parameters.
19. The system (100) of claim 12, wherein the plurality of parameters comprises at least one of a temperature value, a pressure value, and a concentration value of a species and wherein the species comprises at least one of NO2, H2O, and O2.
20. The system (100) of claim 19, wherein plurality of parameters comprises at least a concentration of NO2 and a temperature value.
, Description:BACKGROUND
[0001] Embodiments of the present specification relate generally to spectroscopic measurements, and
more particularly to systems and methods for simultaneous measurement of multiple parameters
corresponding to one or more species in an exhaust emission.
[0002] Emission of gaseous effluents from industrial plants and combustion based machinery are
constrained by regulatory limits. Analysis of gaseous emissions from the exhaust chamber aids in
controlling the operation of the industrial plants. Also, currently available techniques for determining the
health of an engine are based on the analysis of emission of gaseous effluents from the engine such as a gas
turbine.
[0003] Analysis of the gaseous effluents typically includes determination of a temperature and pressure
within a combustion/exhaust chamber of the engine. Further, concentration of water, carbon dioxide, and
other gases in the effluents are also used to comply with the legal requirements.
[0004] Use of conventional techniques such as a thermocouple for determining the temperature may
not be optimal for certain applications. This is especially true when the operating temperature is very high
and in applications where field measurements of transients effects are necessary. For example, in gas
turbines operating at a temperature of about 1300 degree centigrade, frequent recalibration may be required
to compensate for temperature drifts. Further, thermocouples have a limited operating lifetime and
therefore need to be frequently replaced. Thermocouples may obstruct the path of the exhaust emission
and typically measure stagnation temperature. Thermocouples may not be optimal for measuring stream
temperature of exhaust emission.
[0005] Other presently available methods use spectroscopic techniques to measure operating
parameters such as temperature and pressure. Spectroscopic techniques are also useful in determining the
concentration of gaseous components in the effluents. A commonly used spectroscopic technique is laser
absorption spectroscopy that is based on a tunable laser source. The tunable laser is tuned over the spectrum
having absorption lines of the gaseous components to be analyzed. However, the efficiency of laser
absorption spectroscopy at higher operating pressures may be diminished. Moreover, use of spectroscopic
techniques in a combustion chamber of a gas turbine may be a challenging task due to harsh environmental
conditions.
BRIEF DESCRIPTION
[0006] In accordance with one aspect of the present specification, a method for measuring a plurality
of parameters corresponding to an exhaust emission of a combustion process is presented. The method
includes obtaining a spectroscopic signal associated with the exhaust emission. The method further
includes generating, via optical wavelength separation, an absorption spectrum signal from the
spectroscopic signal, where the absorption spectrum signal corresponds to a plurality of species in the
exhaust emission. Moreover, the method also includes identifying a plurality of spectral features in the
absorption spectrum signal, where the plurality of spectral features includes a plurality of spectral responses
and a plurality of interfering spectral responses. In addition, the method includes simultaneously
determining a plurality of parameters based on the plurality of spectral features and a spectroscopic model.
[0007] In accordance with another aspect of the present specification, a system for simultaneous
spectroscopic measurements is presented. The system includes a launcher unit having a single tunable laser
configured to generate a wavelength modulated laser beam. and a beam shaping subunit coupled to the
single tunable laser and configured to convey the wavelength modulated laser beam through exhaust
emission to generate a spectroscopic signal, where the exhaust emission includes a plurality of species, and
where the spectroscopic signal corresponds to a plurality of parameters of the exhaust emission. The system
further includes a receiver unit having a wavelength separation subunit configured to generate an absorption
spectrum signal based on the spectroscopic signal. The receiver unit further includes a detector coupled to
the wavelength separation subunit and configured to identify a plurality of spectral features in the absorption
spectrum signal, where the plurality of spectral features includes a plurality of spectral responses and a
plurality of interfering spectral responses. The system includes a data storage unit configured to store a
laser tuning function, a spectroscopic model, and an operating range of one or more of the plurality of
parameters. Moreover, the system includes a processor unit communicatively coupled to the data storage
unit and the detector and configured to simultaneously determine a plurality of parameters based on the
plurality of spectral features and the spectroscopic model.
DRAWINGS
[0008] These and other features and aspects of embodiments of the present invention will become better
understood when the following detailed description is read with reference to the accompanying drawings
in which like characters represent like parts throughout the drawings, wherein:
[0009] FIG. 1 is a block diagram of a system for simultaneous measurement of multiple parameters
corresponding to one or more species in an exhaust emission, in accordance with aspects of the present
specification;
[0010] FIG. 2 is a graphical representation of an absorption spectrum having a plurality of spectral
features, in accordance with aspects of the present specification;
[0011] FIG. 3 is a graphical representation of a portion of the absorption spectrum of FIG. 2, in
accordance with aspects of the present specification;
[0012] FIG. 4 is a flow chart illustrating a method for simultaneous measurement of multiple
parameters, in accordance with aspects of the present specification; and
[0013] FIG. 5 is a flow chart illustrating another method for simultaneous measurement of multiple
parameters, in accordance with aspects of the present specification.
DETAILED DESCRIPTION
[0014] As will be described in detail hereinafter, systems and methods for simultaneous measurement
of multiple parameters using spectroscopic methods are presented. More particularly, the systems and
methods are directed towards simultaneous measurement of multiple parameters related to one or more
species in exhaust gas emission of a combustion process. The exhaust gas emission is generated by a
combustion based machine such as, but not limited to, an internal combustion engine, an external
combustion engine, or a boiler. A spectroscopic signal is generated by facilitating interaction of a laser
beam with the exhaust gas emission. An absorption spectrum signal corresponding to species present in
the exhaust emission is obtained from the spectroscopic signal. A plurality of spectral features in the
absorption spectrum signal is identified. Moreover, parameters corresponding to the species are
simultaneously determined based on the plurality of spectral features. These parameters may then be
employed to control combustion in the gas turbine.
[0015] The term ‘combustion process’ refers to a chemical process facilitating reaction of a fuel with
an oxidizer to generate exhaust emission with heat. The term ‘spectrum signal’ as used herein refers to a
frequency domain signal represented as a series or a graph. Also, the term ‘spectral feature’ as used herein
refers to a numerical quantity derived from a spectrum signal. The term ‘species’ refers to a gaseous
component present in the exhaust emission. Further, the term ‘parameter’ generally refers to a property of
a species (such as a gaseous component composition, for example) or a property of the exhaust emission
(such as temperature or pressure, for example) expressed as a numerical quantity. Moreover, the term
‘spectroscopic model’ refers to a model designed using offline spectroscopic experiments to relate spectral
features to parameters that correspond to a species in the exhaust emission. The term ‘reference spectral
feature’ refers to a predetermined spectral feature that is used for building a spectroscopic model. In
addition, the term ‘reference parameter’ refers to a predetermined (or known) parameter value used in the
offline experiments. The term ‘reference feature set’ is used to refer to a plurality of reference spectral
features, while the term ‘reference parameter set’ refers to a plurality of reference parameters. Further, the
term ‘reference set’ refers to a reference feature set corresponding to a reference parameter set.
[0016] FIG. 1 is a block diagram of a gas turbine system 100 configured to simultaneously measure
multiple parameters related to one or more species in an exhaust emission of a combustion process, in
accordance with aspects of the present specification. It may be noted that in the present specification, the
simultaneous measurement of multiple parameters related to one or more species in the exhaust emission
of the combustion process is described with reference to a combustion process in a gas turbine. However,
use of the system 100 may also find application in combustion processes of other machines and/or systems.
The gas turbine system 100 includes an exhaust chamber 102 having an input window 104 and an output
window 106. The exhaust chamber 102 receives a laser beam 110 via the input window 104 and facilitates
interaction of the laser beam 110 with exhaust emission 108 to generate a spectroscopic signal 112. The
exhaust emission 108 includes a plurality of species. In one embodiment, the plurality of species includes
at least one of NO2, H2O, and O2. The spectroscopic signal 112 is extracted from the exhaust chamber 102
through the output window 106.
[0017] The gas turbine system 100 further includes a spectroscopic measurement subsystem 114 that
is operatively coupled to the exhaust chamber 102. The spectroscopic measurement subsystem 114 is
configured to receive the spectroscopic signal 112 from the exhaust chamber 102 and simultaneously
determine a plurality of parameters corresponding to one or more of the species in the exhaust emission
108. These parameters include, but are not limited to, a temperature value, a pressure value, a concentration
value of a species, or combinations thereof.
[0018] In a presently contemplated configuration, the spectroscopic measurement subsystem 114
includes a launcher unit 116, a receiver unit 118, a data storage unit 120, a processor unit 122, and a
controller 124. The various units in the spectroscopic measurement subsystem 114 are coupled to one
another through a communication bus 126. In one embodiment, the launcher unit 116 includes a single
tunable laser 134 and a beam shaping subunit 136. Further, in one embodiment, the beam shaping subunit
136 includes a telescope and/or other optical components for directing the laser beam 110 to the input
window 104 of the exhaust chamber 102. The launcher unit 116 includes an optic fiber coupler 138
configured to convey a laser beam emitted by the single tunable laser 134 to the beam shaping subunit 136.
[0019] The launcher unit 116 and the single tunable laser 134 in particular is configured to generate the
laser beam 110 and convey the laser beam 110 through the input window 104 of the exhaust chamber 102.
Specifically, in one embodiment, the laser beam 110 generated by the single tunable laser 134 is a
wavelength modulated laser beam. This wavelength modulated laser beam 110 is channeled to the exhaust
chamber 102 where the wavelength modulated laser beam 110 interacts with the exhaust emission 108 to
generate the spectroscopic signal 112. The spectroscopic signal 112 includes a spectrum signal
corresponding to an absorption spectrum representative of a plurality of parameters corresponding to one
or more species in the exhaust emission 108.
[0020] Additionally, in certain embodiments, the single tunable laser 134 is configured to generate the
laser beam 110 such that the laser beam 110 has one or more laser modulation depths. Moreover, in some
embodiments, the single tunable laser 134 is configured to generate the laser beam 110 having
characteristics determined by a quantitative non-linear laser tuning function. The single tunable laser 134
may employ one or more of these laser tuning functions to generate the laser beam 110. In one embodiment,
the data storage unit 120 is configured to store these laser tuning functions. Also, in some embodiments,
interactions between the single tunable laser 134 and the exhaust emission 108 result in generation of the
spectroscopic signal 112 having a derivative spectroscopic signal representative of a first harmonic and a
second harmonic of the absorption spectrum signal.
[0021] As noted hereinabove, the optic fiber coupler 138 is used to operatively couple the single tunable
laser 134 and the beam shaping subunit 136. More particularly, the optic fiber coupler 138 is configured
to convey the laser beam generated by the single tunable laser 134 to the beam shaping subunit 136. In one
embodiment, the beam shaping subunit 136 includes optical elements and/or telescope arrangements for
shaping the laser beam received from the single tunable laser 134. Moreover, the beam shaping subunit
136 is configured to convey the shaped laser beam into the exhaust chamber 102 through the input window
104. This arrangement advantageously allows operation of the spectroscopic measurement system 114 in
harsh operating conditions such as extreme temperature values.
[0022] The receiver unit 118 is communicatively coupled to the exhaust chamber 102 and configured
to receive the spectroscopic signal 112 from the exhaust chamber 102 via the output window 106. In
addition, the receiver unit 118 is configured to generate an absorption spectrum signal 144 using the
spectroscopic signal 112 and identify a plurality of spectral features 128 in the absorption spectrum signal
144. As previously noted, the spectral feature is a numerical quantity that is derived from a spectrum signal.
[0023] In the embodiment of FIG. 1, the receiver unit 118 is depicted as including a wavelength
separation subunit 140 and a detector 142. The wavelength separation subunit 140 is configured to receive
the spectroscopic signal 112 from the exhaust chamber 102 and generate the absorption spectrum signal
144 using the spectroscopic signal 112. In one embodiment, the wavelength separation subunit 140 includes
optical elements arranged in a suitable configuration to generate the absorption spectrum signal 144.
Further, the detector 142 is communicatively coupled to the wavelength separation subunit 140 and
configured to receive the absorption spectrum signal 144 from the wavelength separation subunit 140. In
addition, the detector 142 is configured to detect a plurality of spectral features 128 in the absorption
spectrum signal 144.
[0024] In one embodiment, the spectral features 128 in turn include a plurality of spectral responses
corresponding to the plurality of species in the exhaust emission 108 and a plurality of interfering spectral
responses resulting from overlapping of adjacent spectral responses among the plurality of spectral
responses. In another embodiment, the spectral features 128 include other interfering spectral responses
generated based on two or more of the plurality of spectral responses. By way of example, an area under a
spectral response may be considered as a spectral feature 128. In another example, a separation value
between two spectral responses may be representative of a spectral feature 128. In some embodiments, the
plurality of spectral features 128 may also include one or more derived features that are derived based on
the plurality of spectral responses.
[0025] The processor unit 122 is communicatively coupled to the detector 142 and the data storage unit
120 and configured to receive the plurality of spectral features 128 from the receiver unit 118. Further, the
processor unit 122 is configured to simultaneously determine a plurality of parameters 130 that correspond
to the plurality of species in the exhaust emission 108. In particular, the processor unit 122 is configured
to determine the parameters 130 based on the spectral features 128, a spectroscopic model, and an expert
system. The processor unit 122 is also configured to employ an optimization technique to extract an
optimum solution from the spectroscopic model using the spectral features 128. Further, the optimum
solution may be used to obtain the parameters corresponding to the exhaust emission 108. In one
embodiment, the optimization technique is used to determine a reference feature set corresponding to the
plurality of spectral features 128 from the spectroscopic model. In addition, a reference parameter set
corresponding to the determined reference feature set is obtained from the spectroscopic model. The
processor unit 122 is configured to determine the plurality of parameters 130 based on the reference
parameter set.
[0026] As previously noted, the spectroscopic model relates the plurality of spectral features to a
corresponding plurality of parameters. In one embodiment, the spectroscopic model is represented as a
suitable data structure such as, but not limited to, a table. In one embodiment, the spectroscopic model may
be in the form of a two-dimensional (2D) table having a plurality of rows. In the two-dimensional table,
each row may include a reference feature set and a corresponding reference parameter set. In another
embodiment, additionally, each row may also include a corresponding operating mode of the gas turbine,
and corresponding operating ranges of one or more of the plurality of parameters 130.
[0027] Also, the expert system includes a database of a plurality of operating modes of the gas turbine
and operating ranges for parameters corresponding to each of the operating modes. In one embodiment,
the spectroscopic model and the expert system are stored in the data storage unit 120. In some
embodiments, the spectroscopic model may relate the plurality of spectral features 128 to a corresponding
plurality of parameters that is associated with one of the plurality of operating modes and/or operating
ranges of the plurality of parameters.
[0028] In accordance with aspects of the present specification, the spectroscopic model may be
developed a priori by the processor unit 122 based on a quantitative non-linear tuning function and a
reference exhaust emission. It may be noted that the reference exhaust emission includes known
compositions of species, where the species have a corresponding plurality of reference parameters. In this
example, a laser beam may be generated by the launcher unit 116. Further, this laser beam may be directed
towards the reference exhaust emission to generate a reference spectroscopic signal. Also, a reference
absorption spectrum signal may be generated using the reference spectroscopic signal.
[0029] Moreover, developing the spectroscopic model may entail identifying a plurality of reference
spectral features in the reference absorption spectrum signal. Additionally, developing the spectroscopic
model includes establishing a correspondence between the plurality of reference spectral features and the
plurality of reference parameters. It may be noted that the spectroscopic model includes a plurality of
reference sets, where each reference set in turn includes a corresponding plurality of reference spectral
features and a plurality of reference parameters. In one embodiment, an off-line experiment may be
performed to determine the plurality of reference sets for either a specific gas turbine system or for a class
of gas turbine systems. In another embodiment, the expert system may be developed over a period of time
by observing the operating modes of the gas turbine under various operating conditions. It may be noted
that the operating modes are characterized by the operating ranges of the parameter values and a rate of
change of parameter values. In certain embodiments, the spectroscopic model may also be constrained by
the expert system while determining the plurality of parameters using the optimization technique.
[0030] With continuing reference to the spectroscopic model, the processor unit 122 is configured to
identify a plurality of reference spectral features based on the plurality of spectral features and the
spectroscopic model. The plurality of reference spectral features corresponds to a reference set among the
plurality of reference sets of the spectroscopic model. In certain embodiments, the processor unit 122 may
use a regression technique to identify the plurality of reference spectral features that corresponds to the
plurality of spectral features. In particular, the regression technique selects the reference set that is in close
proximity to the spectral features in a statistical sense. In one embodiment, the proximity is quantified by
a mean squared error. Additionally, the processor unit 122 is configured to identify a plurality of reference
parameters that corresponds to the plurality of reference spectral features. The plurality of reference
parameters is selected as the plurality of parameters.
[0031] In some embodiments, the processor unit 122 may be configured to select at least two reference
feature sets based on the spectroscopic model via use of the regression technique. In this example, the
processor unit 122 is configured to select reference spectral features corresponding to one of the two
reference feature sets based on the operating range of at least one of the plurality of parameters 130. The
processor unit 122 is also configured to identify a plurality of reference parameters that corresponds to the
selected reference spectral features. The plurality of reference parameters is selected as the plurality of
parameters.
[0032] Also, the processor unit 122 may include one or more processors. The terms ‘processor unit’,
‘one or more processors,’ and ‘processor’ are used equivalently and interchangeably. The processor unit
122 includes at least one arithmetic logic unit, a microprocessor, a general purpose controller, or a processor
array to perform the desired computations or run the computer program.
[0033] While the processor unit 122 is shown as a separate unit in the embodiment of FIG. 1, one or
more of the units 120, 124, 136, 140, 142, may include a corresponding processor unit. In this example,
the processor unit 122 may be configured to perform the functions of the various units of the spectroscopic
measurement system 114. In other embodiments, the single tunable laser 134, the beam shaping subunit
136, and the wavelength separation subunit 140 may be communicatively coupled to one or more processors
that are disposed at a remote location, such as a central server or cloud based server via a communications
link such as a computer bus, a wired link, a wireless link, or combinations thereof.
[0034] Moreover, the controller unit or controller 124 is communicatively coupled to the processor unit
122 and configured to receive the plurality of parameters 130 from the processor unit 122. Further, the
controller unit 124 is configured to generate a control signal 132 based on the plurality of parameters 130.
The controller 124 is further configured to modify the operation of the gas turbine based on the control
signal 132 to control the exhaust emission 108. In one embodiment, the control signal 132 is a correction
signal that may be employed to control one or more operating parameters of the gas turbine. The control
of the operating parameter may include increasing a value of that operating parameter of the gas turbine
when the control signal has a positive value and decreasing the value of the operating parameter when the
control signal has a negative value, in one example. Also, the magnitude of the control signal 132 may be
used to determine a step size for controlling/changing the operating parameter of the gas turbine. In one
embodiment, if the concentration and/or rate of emissions of a certain species exceeds permissible levels,
for example, the controller 124 is further configured reduce a power output of the gas turbine based on the
control signal 132. In another embodiment, the controller 124 may halt the operation of the gas turbine
based on the control signal 132.
[0035] The data storage unit 120 may be a database or a data repository. For example, the data storage
unit 120 may be a dynamic random access memory (DRAM) device, a static random access memory
(SRAM) device, flash memory or other memory devices. In one embodiment, the memory unit may include
a non-volatile memory or similar permanent storage device, media such as a hard disk drive, a floppy disk
drive, a compact disc read only memory (CD-ROM) device, a digital versatile disc read only memory
(DVD-ROM) device, a digital versatile disc random access memory (DVD-RAM) device, a digital versatile
disc rewritable (DVD-RW) device, a flash memory device, or other non-volatile storage devices. A nontransitory
computer readable medium may be encoded with a sequence of instructions to enable at least one
processor unit to perform analysis of exhaust emission 108 of a gas turbine and generate the control signal
132 for controlling the gas turbine operation.
[0036] Furthermore, one or more of the units 116, 118, 120, 136, 140, 134, 142 may be standalone
hardware components. Other hardware implementations such as field programmable gate arrays (FPGA),
application specific integrated circuits (ASIC) or customized chip may be employed for one or more of the
units of the system.
[0037] It may be noted that the spectroscopic measurement subsystem 114 employs a single laser to
simultaneously measure temperature, pressure, and species concentration of the exhaust emission 108 using
wavelength modulated spectroscopy measurements. The simultaneous measurements include acquiring
spectroscopic signals and use of interfering gas signatures to enable the simultaneous estimation of the
plurality of parameters 130.
[0038] FIG. 2 is a graphical illustration 200 of a plurality of spectral amplitudes that are representative
of spectral features, in accordance with aspects of the present specification. The graph 200 includes an xaxis
202 representative of a wavelength in cm-1 and a y-axis 204 representative of an amplitude. The graph
200 includes a curve 206 that is representative of the absorption spectrum signal 144 generated by the
system 100 of FIG. 1. The curve 206 exhibits a plurality of peak responses 208, 210, 212, 214, 216
corresponding to a plurality of spectral features obtained from the absorption spectrum signal. In the
example of FIG. 2, the peaks 208, 210, 212 correspond to spectral responses that are associated with a
plurality of species present in the exhaust emission 108 of FIG. 1. Also, the peaks 214,216 correspond to
interfering spectral responses that are generated due to an overlap of the peaks 208, 210, 212. By way of
example, the interfering spectral response 214 is generated due to an overlap of the peaks 208 and 210,
while the interfering spectral response 216 is generated due to an overlap of the peaks 210 and 212. In the
example of FIG. 2, spectral amplitude values corresponding to the peaks 208, 210, 212, 214, 216 are
representative of the spectral features.
[0039] It may be noted that different spectral features corresponding to different gaseous components
in the exhaust emission having varying temperature, concentration and/or pressure values exhibit unique
peak responses as signatures. Typically, these signatures are used for either estimating temperature or
concentration of a species. In accordance with aspects of the present specification, a combination of a
plurality of peak responses may be employed to simultaneously determine multiple relevant quantities.
[0040] Further, a plurality of interfering responses may also be used as signatures in the simultaneous
determination of the plurality of parameters. By way of example, the peaks 208, 212 are observed in the
absorption spectrum signal when moisture is present in the exhaust emission and the peak 210 is observed
in the absorption spectrum signal when NO2 is present in the exhaust emission. The peaks 214, 216 are
enhanced when the both moisture and NO2 are present in addition to the peaks 208, 210, 212. In one
example, the peaks 208, 212 may be employed to estimate a concentration of moisture in the exhaust
emission when temperature is known. In another example, the peak 210 is sufficient to determine a
concentration of NO2 in the exhaust emission when the temperature is known. In accordance with
exemplary aspects of the present specification, the peaks 208, 210, 212 are used to simultaneously estimate
the respective concentrations of moisture and NO2 in the exhaust emission. Further, the interfering peaks
214, 216 may be used together with the peak responses 208, 210, 212 to simultaneously provide robust
estimates of temperature, concentrations of moisture and NO2.
[0041] FIG. 3 is a graphical illustration 300 of one spectral feature, in accordance with aspects of the
present specification. In particular, the spectral feature depicted in FIG. 3 is an area under an absorption
spectrum signal. The graph 300 includes an x-axis 302 representative of a frequency in Hertz and a y-axis
304 representative of an amplitude. The graph 300 includes a curve 306 representative of an absorption
spectrum signal such as the absorption spectrum signal 144 of FIG. 1 generated by the gas turbine system
100 of FIG. 1. The curve 306 includes a pulse response 308. In the example of FIG. 3, an area 310 under
the pulse response 308 is representative of a spectral feature. Additional spectral features may also be
derived from the curve 306 based on area values corresponding to the other pulse responses or amplitude
values of the pulse responses.
[0042] Referring now to FIG. 4, a flow chart 400 illustrating a method for simultaneous measurement
of multiple parameters, in accordance with aspects of the present specification, is presented. In one
example, the method for simultaneous measurement entails simultaneous measurement of parameters such
as, but not limited to, a concentration of nitrogen dioxide, a concentration of moisture, a temperature value
in an exhaust chamber, a pressure value in the exhaust chamber, or combinations thereof. The method 400
of FIG. 4 is described with reference to the elements of FIGs. 1-3.
[0043] At step 402, a plurality of spectral features is received. In certain embodiments, the spectral
features may be obtained from a high resolution look up table 414. In one example, these spectral features
may be representative of measured spectral features. Also, in certain examples, the five spectral peaks 208,
210, 212, 214, 216 corresponding to the absorption spectrum signal 206 of FIG. 2 are representative of the
five measured spectral features. In another example, the area under one of the peaks 208, 210, 212, 214,
216 may be considered as a sixth spectral feature. Further, at step 402, a plurality of reference sets is also
retrieved from the high resolution look up table 414. Each of the plurality of reference sets includes a
plurality of reference spectral features and corresponding reference parameters. In this example, the
reference spectral features correspond to five reference spectral amplitudes or peaks that have been
determined a priori through an offline experiment and stored in the data storage unit 120 of FIG. 1. It may
be noted that the look up table 414 may be designed based on a spectroscopic model having a plurality of
reference feature sets and corresponding plurality of parameter sets. The spectroscopic model may be
developed via use of an offline spectroscopic experimental setup as previously described.
[0044] Moreover, at step 404, a plurality of error values corresponding to the plurality of reference sets
is determined. In particular, the error values may be determined based on the five measured spectral peaks.
In one example, the error values may be determined using equation (1).
?????? ??
(1)
[0045] In equation (1), e is an error value corresponding to one reference set. In particular, the error
value e is representative of a proximity of the plurality of reference spectral features of that reference set to
the corresponding plurality of measured spectral features. Also, i is a summation index, wi is a weight
factor, ki is a normalizing factor, pi is a measured spectral feature, and pi
LUT is a reference spectral feature.
The summation index parameter i represents an ith component value among a plurality of component values.
[0046] Subsequently, at step 406, the error e is minimized using an optimization technique to determine
an optimal solution. In certain embodiments, a minimum error value among the plurality of error values
corresponding to the reference sets is selected and identified as the optimal reference set. The reference
feature set that corresponds to the optimal reference set is representative of the plurality of spectral features.
Some non-limiting examples of optimization techniques used to determine the optimal reference feature set
include a gradient descent technique, a recursive least squares technique, and the like.
[0047] In certain scenarios, the optimization technique may identify more than one reference feature
set as the optimal reference set. In such an example, one of these reference feature sets is identified as the
optimal reference feature set based on one or more operating parameters of the gas turbine, as indicated by
optional step 408. Some non-limiting examples of the operating parameters of the gas turbine that are used
to identify the optimal reference feature set include moisture fraction changes, a burner mode of the gas
turbine, a rate of change of emission, and the like.
[0048] Furthermore, at step 410, a plurality of reference parameters corresponding to the identified
optimal reference feature set is selected as the plurality of parameters of the exhaust emission. Additionally,
these parameters may be used for controlling the exhaust emission of the gas turbine, as indicated by step
412.
[0049] FIG. 5 is a flow chart 500 of another method for simultaneous measurement of multiple
parameters, in accordance with aspects of the present specification. The method 500 is described with
referenced to the components of FIGs. 1-3.
[0050] The method 500 includes obtaining a spectroscopic signal associated with the exhaust emission,
as indicated by step 502. The method further includes generating, via optical wavelength separation, an
absorption spectrum signal from the spectroscopic signal. The absorption spectrum signal corresponds to
a plurality of species in the exhaust emission 108 from a gas turbine, as indicated by step 504. Furthermore,
at step 504, a laser beam 110 is passed through the exhaust emission 108 in the exhaust chamber 102 of the
gas turbine to generate the spectroscopic signal 112. In one embodiment, the launcher unit 116 and the
single tunable laser 134 in particular is used to generate of the laser beam 110. Also, the laser beam 110
may be a wavelength modulated laser beam. In such an embodiment, a wavelength of the wavelength
modulated laser beam is tuned to a spectral feature adapted to determine one or more of the plurality of
parameters of exhaust emission 108. The wavelength separation subunit 140 is configured to receive the
spectroscopic signal 112 from the output window 106 of the exhaust chamber 102. In addition, at step 504,
a derivative spectroscopic signal based on a first harmonic and a second harmonic of the absorption
spectrum signal is generated.
[0051] Subsequently, at step 506, a plurality of spectral features in the absorption spectrum signal may
be identified. It may be noted that the plurality of spectral features in turn includes a plurality of spectral
responses corresponding to the plurality of species. Further, it may be noted that the plurality of spectral
features includes a plurality of interfering spectral responses generated due to overlapping of adjacent
spectral responses among the plurality of spectral responses.
[0052] Additionally, at step 508, a plurality of parameters corresponding to one or more of the plurality
of species is simultaneously determined based on the plurality of spectral features, a spectroscopic model,
and an operating range of at least one of the plurality of parameters. The parameters include at least one of
a temperature value of the exhaust gas emission, a pressure value of the exhaust gas emission, and a
concentration value of a species. The species includes at least one of NO2, H2O, and O2. It should be noted
that list of parameters and the list of species is not limiting and may include other parameters and species
as well. In addition, at step 508, a reference feature set is selected from a plurality of reference feature sets
in the spectroscopic model based on the plurality of spectral features via use of a regression technique.
Moreover, a reference parameter set having a plurality of reference parameters corresponding to the selected
reference feature set is identified. Further, the plurality of reference parameters of the reference parameter
set is selected as the plurality of parameters.
[0053] In another embodiment, step 508 may include selecting at least two reference feature sets from
the plurality of reference feature sets in the spectroscopic model based on the plurality of spectral features
via use of a regression technique. Subsequently, a reference feature set among the at least two reference
feature sets may be identified based on the operating range of at least one of the plurality of parameters.
Also, a reference parameter set having a plurality of reference parameters corresponding to the selected
reference feature set may be identified. The plurality of reference parameters of the reference parameter
set is selected as the plurality of parameters.
[0054] Subsequently, in step 510, the exhaust emission from the gas turbine may be controlled based
on the plurality of parameters. To that end, the plurality of parameters such as, but not limited to, a
temperature value and the pressure value, may be monitored. The parameters may be compared a
corresponding threshold value. The exhaust emission may be controlled based on the comparison. In one
example, the exhaust emission may be controlled when the one or more of the plurality of parameters
exceed the corresponding threshold value. In this situation, one or more of the operating parameters of the
gas turbine may be altered such that the value(s) of the one or more of the plurality of parameters are within
the corresponding threshold values.
[0055] In one embodiment, the method 500 further includes developing a spectroscopic model, as
indicated by step 512. Specifically, at step 514, a plurality of reference absorption spectrum signals is
generated based on a reference exhaust emission having one or more of the plurality of species. The
plurality of reference absorption spectrum signals corresponds to a plurality of reference parameter sets.
Each of the plurality of reference parameter sets includes a plurality of reference parameters. Further at
step 516, a reference feature set is identified in each of the plurality of the reference absorption spectrum
signals to generate a plurality of reference feature sets. Each reference feature set includes a plurality of
reference spectral features. Subsequently at step 518, a correspondence between the plurality of reference
feature sets and the plurality of reference parameter sets is established to generate a spectroscopic model
illustrated as block 520.
[0056] Various systems and methods for simultaneous spectroscopic measurements of multiple
parameters are presented. These systems and methods provide enhanced control of exhaust emission.
Embodiments of the present specification aid in reducing hardware complexity of the measurement system.
Further, the systems and methods provide enhanced performance when frequent measurements associated
with the exhaust emission are required. The accuracy of online, in-situ measurements of parameters is
improved especially at transient conditions. Moreover, these systems and methods are suitable for use in
harsh environments. Use of the present systems and methods allow accurate measurements of temperature
and concentration values of species, thereby enabling use of wavelength modulated absorption spectrum
based measurement methods. Spectroscopic measurements representative of line-average conditions of the
species provide accurate measurements compared to deriving the mean conditions from measurements
made elsewhere using thermocouples.
[0057] It is to be understood that not necessarily all such objects or advantages described above may
be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will
recognize that the systems and techniques described herein may be embodied or carried out in a manner
that achieves or improves one advantage or group of advantages as taught herein without necessarily
achieving other objects or advantages as may be taught or suggested herein.
[0058] While the technology has been described in detail in connection with only a limited number of
embodiments, it should be readily understood that the specification is not limited to such disclosed
embodiments. Rather, the technology can be modified to incorporate any number of variations, alterations,
substitutions or equivalent arrangements not heretofore described, but which are commensurate with the
spirit and scope of the claims. Additionally, while various embodiments of the technology have been
described, it is to be understood that aspects of the specification may include only some of the described
embodiments. Accordingly, the specification is not to be seen as limited by the foregoing description, but
is only limited by the scope of the appended claims.