Method for on-line measurement of fuel heat content of fuel in a combustion turbine system

The fuel heat content of fuel is measured on-line while a combustion turbine system is running by measuring data from the combustion turbine system during combustion of the fuel. The measured data are corrected using a standard correction algorithm. The fuel heat content of the fuel is determined using at least a portion of the corrected data. From the measurement of the fuel heat content, any changes in the fuel heat content are determined. Also, any changes in the control and operational parameters attributable to the change in fuel heat content are determined.

BACKGROUND OF THE INVENTION
 The present invention relates to measuring fuel heat content of fuel, and
 more particularly, to measuring fuel heat content while a combustion
 turbine system is on-line and/or running.
 The measurement of the fuel heat content of fuel is an important factor in
 controlling the combustion of the fuel. However, in a deregulated power
 generation market, it is desirable that power production be as inexpensive
 as possible. In an effort to produce inexpensive power, typically, the
 most inexpensive fuel is used. Unfortunately, these inexpensive fuels have
 fuel heat content that varies dramatically from the rated heating value of
 the fuel. Therefore, controlling the combustion of these inexpensive fuels
 has become increasingly complex.
 Typically, the fuel heat content is measured by performing various tests on
 the fuel in a laboratory or other controlled setting. These tests can
 include calorimetric, stoichiometric, constituent analysis and catalytic
 combustion. In general, the laboratory tests provide a fuel heat content
 measurement for the fuel under controlled conditions and do not provide an
 on-line determination of the fuel heat content while the combustion
 turbine system is on-line and running. An on-line measurement of the fuel
 heat content would allow the control parameters associated with the
 combustion turbine system to be adjusted such that the maximum operational
 efficiency of the combustion turbine system is achieved. In addition, an
 on-line measurement of the fuel heat content would allow control
 parameters associated with the combustion turbine system to be adjusted to
 avoid damage or increased wear caused by the changes of temperature and
 pressure in the combustion turbine system that are associated with a
 change in the fuel heat content. Therefore, a need exists for a method of
 measuring the fuel heat content while the combustion turbine system is
 on-line and running.
 Presently, fuel heat content monitors are available that can measure the
 fuel heat content while the system is on-line. The fuel heat content
 monitor is a separate device that requires installation and additional
 data monitoring. However, these fuel heat content monitors are expensive.
 As such, in an effort to produce energy at the lowest price, the added
 cost of these fuel heat monitors and the cost associated with monitoring
 the heat fuel content data makes the use of the heat fuel content monitors
 impractical. Therefore, a need also exists for a method of measuring fuel
 heat content that does not require the purchasing of expensive equipment.
 Also, a need exists for a method of measuring fuel heat content that uses
 conventionally monitored data and does not entail the costs associated
 with additional data monitoring.
 In combustion turbine systems, many control and operational parameters are
 measured, such as, but not limited to, temperature, pressure and fuel
 flow. Typically, changes in the fuel heat content result in changes in the
 measured parameters. During monitoring of these parameters, it is
 important that any change in these measured parameters that is
 attributable to changes in the fuel heat content be readily determined.
 Such a determination can prevent unrequired maintenance on the combustion
 turbine system. Since unrequired maintenance can increase the cost of the
 power generation, it is desirable that only required maintenance be
 performed on the combustion turbine system in order to keep the power
 generation costs to a minimum. Therefore, a need exists for an on-line
 measurement of the fuel heat content that determines whether changes in
 the control and operational parameters are attributable to changes in the
 fuel heat content.
 BRIEF SUMMARY OF THE INVENTION
 An exemplary embodiment of the present invention provides a method for
 determining a change in fuel heat content of fuel used in a combustion
 turbine system. The method includes measuring data from the combustion
 turbine system during combustion of the fuel while the combustion turbine
 system is on-line and running. The measured data is corrected using a
 standard correction algorithm. A heat rate is calculated using at least a
 portion of the corrected data. A change in the calculated heat rate is
 determined. A compressor efficiency and a pressure ratio is calculated
 using at least a portion of the corrected data. The calculation of the
 compressor efficiency and the pressure ratio is based on the determination
 of a change in the calculated heat rate. A change in the calculated
 compressor efficiency and the calculated pressure ratio is determined. A
 temperature rise across a hot section of the combustion turbine system is
 calculated using at least a portion of the corrected data. The calculation
 of the temperature rise across the hot section is based on the
 determination of a change in the compressor efficiency and the pressure
 ratio. A change in the temperature rise across the hot section of the
 combustion turbine system is determined. A fuel heat content is calculated
 using at least a portion of the corrected data. The calculation of the
 fuel heat content is based on the determination of a change in the
 temperature rise across the hot section. A change in the fuel heat content
 is calculated, and a mathematical model of the operation of the combustion
 turbine system is changed based on the determination of a change in the
 fuel heat content.
 Advantageously, the method described hereinabove measures the fuel heat
 content of fuel while a combustion turbine system is on-line and running,
 and the method measures the fuel heat content without the purchasing of
 expensive equipment. Also, the method described hereinabove measures fuel
 heat content using conventionally monitored data and does not entail the
 costs associated with additional data monitoring. Further, the method
 described hereinabove provides an on-line measurement of the fuel heat
 content that determines whether changes in the control and operational
 parameters are attributable to changed in the fuel heat content.

DETAILED DESCRIPTION OF THE INVENTION
 Exemplary embodiments of the present invention involve a method for
 determining the fuel heat content and/or changes in the fuel heat content
 of fuel used in a combustion turbine system 100 (FIG. 1) while the
 combustion turbine system 100 is on-line and running. The fuel heat
 content is a desirable factor in controlling the combustion of fuel. The
 measurement of the fuel heat content provides the amount of fuel required
 to produce a measurable amount of energy, such as, the amount of fuel
 required to generate a kilowatt hour (kwh) of power measured in, for
 example, gallons/kwh, liters/kwh or cubic centimeters/kwh. In this
 disclosure, the measurement of the amount of fuel required to produce a
 measurable amount of energy is called fuel heat content, but, in the art,
 this measurement can also be referred to as heating value, such as, low
 heating value (LHV) and high heating value (HHV).
 In FIG. 1, a highly simplified combustion turbine system 100 comprises a
 gas turbine 110. It should be appreciated that the present invention is
 not limited to a gas turbine 110 and includes all combustion turbine
 systems 100 that consume fuel to operate. In one embodiment, the gas
 turbine 110 uses natural gas as a fuel. However, it should be appreciated
 that the fuel in other combustion turbine systems 100 is not limited to
 natural gas. Other suitable fuels may, for example, include gasoline,
 kerosene, diesel fuel, wood, coal and jet fuel.
 As shown in FIG. 1, the gas turbine 110 includes an inlet port 120 and an
 exit port 130. The inlet port 120 is the location where a combustion gas
 is introduced into the combustion turbine system 100. The combustion gas
 is combined with the fuel in the combustion turbine system 100. The fuel
 and the combustion gas are combined in a ratio that is known in the art
 and can be controlled via control parameter s of t he combustion turbine
 system 100. In one embodiment, the combustion gas comprises air. The exit
 port 120 is the location where the exhaust from the gas turbine 110 exits
 the combustion turbine system 100. In one embodiment, the exhaust gas
 includes various end products of the combustion process that is carried
 out in the combustion turbine system 100.
 The combustion gas is provided to a compressor 160. The fuel is provided
 via fuel inlets 150 to the compressor 160. The fuel inlets 150 are
 controlled by fuel flow controls 140. The combustion gas and the fuel are
 mixed in the compressor 160 and supplied to a hot section 170. In the hot
 section 170, the combination of the fuel and the combustion as is ignited,
 and the exhaust is fed to the exit port 130 after the combustion has taken
 place. The combusted fuel mixture produces a desired form of energy, such
 as, for example, electrical, heat and mechanical energy. In one
 embodiment, the combusted fuel mixture produces electrical energy measured
 in kilowatt hours (kwh). However, the present invention is not limited to
 the production of electrical energy and encompasses other forms of energy,
 such as, mechanical work and heat.
 The combustion turbine system 100 is typically controlled via various
 control parameters from an automated and/or electronic control system (not
 shown) that is attached to the combustion turbine system 100. A detailed
 description of the automated and/or electronic control system (not shown)
 that controls the combustion turbine system 100 is beyond the scope of
 this disclosure. However, it should be appreciated that the determination
 of the fuel heat content and changes in the fuel heat content can be
 supplied to the automated and/or electronic control system (not shown) to
 be used for control calculations or mathematical control model algorithms
 used to control the combustion turbine system 100.
 As shown in FIG. 2, one embodiment of a method for on-line determination of
 fuel heat content of fuel used in combustion turbine system 100 (FIG. 1)
 includes measuring data from the combustion turbine system 100 while the
 combustion turbine system 100 is on-line and running (step 210). The
 measured data is corrected using a standard correction algorithm (step
 220). The fuel heat content is determined using the corrected data (step
 230).
 In the combustion turbine system 100, data are measured (step 210) from a
 variety of areas in and on the gas turbine 110 (FIG. 1). The measurement
 of the data provides information relating to the operation of the
 combustion turbine system 100. From these data measurements, the
 combustion turbine system is controlled to maximize the operational
 efficiency of the combustion turbine system 100. It should be appreciated
 that the measurement of the data is taken in real-time while the
 combustion turbine system 100 is on-line and running. The on-line
 measurement of the data allows various control parameters to be adjusted
 in real-time such that the combustion turbine system operates at the
 maximum operational efficiency at all times. In addition, the measured
 data can be collected such that statistical modeling and analysis can be
 performed on the measured data, as will be described herein below. In this
 case, the measured data are sampled per predetermined time periods and
 these measurements are archived for analysis.
 In the combustion turbine system 100 as shown in FIG. 1, the measurement of
 the data includes measuring a flange to flange output in the gas turbine
 110. The flange to flange output is measured on a generator (not shown) of
 the gas turbine 110. The power that is extracted by the gas turbine 110
 drives the compressor 160 and the generator (not shown). The flange to
 flange output is the electrical power that is made by the generator (not
 shown). In particular, the flange to flange output is the power generated
 from the gas turbine 110 less any excitation and/or compressor 160 usage.
 A fuel flow into the gas turbine 110 from the fuel inputs 150 is measured
 by transducers (not shown) in the area of the fuel flow controls 140. The
 fuel flow measures the amount of fuel that is provided to the gas turbine
 110 over a specified period of time.
 A heating value of the fuel is assumed. In one embodiment, the heating
 value is not a measured quantity of data but is assumed to be the heating
 value rating provided by the supplier of the fuel. Typically, the supplier
 provides a heating value, as part of the fuel specifications, such as, a
 low heating value (LHV) and a high heating value (HHV). In a preferred
 embodiment, the assumed heating value is the low heating value (LHV).
 The inlet temperature and pressure of the combustion gas are measured at
 inlet port 120. In addition, the relative humidity of the combustion gas
 can be measured at the inlet port 120. The outlet temperature and pressure
 are measured at the exit port 130. It should be appreciated that these
 temperature, pressure and humidity measurements are provided by
 transducers that are attached on or near the combustion turbine system
 100. More particularly, the transducers (not shown) are respectively
 positioned near the inlet port 120 and exit port 130. The data
 measurements can be provided using devices known in the art including, for
 example, transducers, flow meters, sensors, thermocouples, thermistors and
 other electronic measuring devices.
 The temperature at the outlet of the compressor 160 is measured. In
 addition, the exhaust temperatures of the gases exiting the hot section
 170 are also measured. It should be appreciated that the exhaust
 temperature at the hot section 170 and the outlet temperature at the exit
 port 130 can comprise the same measurement in one embodiment of the
 present invention. In addition, the present invention may encompass data
 measured from and around the combustion turbine system 100 that are
 different than the data described herein.
 As illustrated in FIG. 2, once the data are measured (step 210) from the
 combustion turbine system 100 (FIG. 1), the data are corrected using a
 standard correction algorithm (step 220). The measured data are corrected
 using the standard correction algorithm to remove any anomalies in the
 data caused by ambient conditions under which the combustion turbine
 system 100 is operating. In addition, the correction of the measured data
 allows all data to be compared regardless of the ambient conditions under
 which the data were collected. For example, in one embodiment, the
 standard correction algorithm corrects the data based on the ambient
 temperature, pressure, relative humidity and elevation. It should be
 appreciated that other ambient conditions can be used with the standard
 correction algorithm. It should also be appreciated that the ambient
 conditions are measured in a similar manner to all measured data, such as,
 using various sensors and other data collection devices.
 As mentioned above, the correction of the measured data is provided so that
 the data measured on different days can be compared. The data are
 corrected based on certain ambient conditions to reflect a standard day.
 The standard day and standard correction algorithm can be measured and
 determined by a standards organization, such as, the international
 standards organization (ISO). In addition, as an alternative to using
 correction information of a standards organization, it should be
 appreciated that a correction algorithm and standard day can be calculated
 by sampling and measuring data over various conditions to provide the
 correction information and, thus, the correction information need not be
 supplied by a standards organization.
 After the measured data are corrected (step 220), the corrected data or a
 portion of the corrected data are used to determine the fuel heat content
 (step 230) of the fuel used in the combustion turbine system 100 (FIG. 1).
 The fuel heat content is determined via a calculation. The calculation of
 the fuel heat content uses a calculated value of the heat rate
 (HR.sub.new) and a previously calculated heat rate (HR.sub.old). Since the
 calculation of the heat rate is made in real time while the gas turbine
 110 is operating, the calculated values of the heat rate (HR.sub.new) and
 (HR.sub.old) are continually being calculated and are available for the
 calculation of the fuel heat content. The calculation for the heat rate is
 further explained herein below. The fuel heat content (FHC) is calculated
 using the following algorithm:
 ##EQU1##
 In one embodiment, the fuel heat content is provided to a mathematical
 model of the combustion turbine system 100. The mathematical model is used
 to control the combustion turbine system 100 to provide the highest
 operational efficiency. In controlling the combustion turbine system 100,
 various parameters can be adjusted, such as, the fuel flow, the ratio
 mixture of the fuel to the combustion gas and the compression of the fuel
 mixture. It should be appreciated that other parameters can be used during
 control of the combustion turbine system 100 and the present invention is
 not limited to only those parameters described herein.
 In addition, the determination of the fuel heat content can be used to
 provide fuel heat content data for statistical modeling and analysis. In
 this case, the fuel heat content is determined on a predetermined time
 basis and archived for analysis/modeling purposes. It should be
 appreciated that the determination of fuel heat content is provided in
 real-time while the combustion turbine system 100 is on-line and
 operating. This real-time feedback of the fuel heat content allows control
 parameters to be adjusted to maximize the operational efficiency of the
 combustion turbine system 100.
 In the exemplary methods described herein, various data are compared to
 determine whether a change in the data has occurred. The determination of
 a change is provided by measuring or calculating the data and providing
 statistical analysis and modeling of the measured and/or calculated data.
 The measured and/or calculated data are archived in, for example, a
 database. Noise boundaries are calculated based on an historical analysis
 of the measured and/or calculated data. The noise boundaries include
 control limits that are calculated based on statistical analysis, and the
 noise boundaries provide a boundary in which the data can vary and still
 be statistically within the limits. A change is determined to occur if the
 measured and/or calculated data fall outside the control limits of the
 noise boundaries. It should be appreciated that all types of statistical
 analysis and modeling are encompassed by the present invention. It should
 also be appreciated that the determination of a change in various measured
 and/or calculated data avoids unrequited maintenance from being done on
 the combustion turbine system 100. In this regard, the determination of
 changes in measured and/or calculated data can result in finding the
 portion of the combustion turbine system that is the cause of the change,
 and therefore, maintenance can be limited to that certain portion of the
 combustion turbine system 100, or the mathematical model can be altered to
 reflect the change in the data. Specifically, in one embodiment of the
 present invention, data are measured and data are calculated to determines
 changes in the operation of the combustion turbine system 100 that can be
 attributable to a change in the fuel heat content.
 In FIG. 3, the determination of a change in the fuel heat content includes
 a calculation of the heat rate (step 310). The heat rate is a
 determination on the efficiency of the operation of the entire combustion
 turbine system 100 (FIG. 1). The heat rate (HR) is calculated using the
 inputs of the flange to flange output (FFO) (step 312), the fuel flow (FF)
 (step 314) and the low heat value (LHV.sub.assumed) which is assumed. The
 heat rate is calculated using the following algorithm:
 ##EQU2##
 The assumed LHV may comprise the heating value supplied by the fuel
 supplier. The fuel supplier calculates the LHV using various techniques
 know in the art. It should be appreciated that the fuel supplier can
 provide a LHV and a high heating value (HHV) with the fuel. In another
 embodiment, the assumed heating value can be the HHV or another heating
 value that has been calculated from various other data. In addition, as
 described above, the measured data used to calculate the heat rate are
 corrected using a correction algorithm.
 In addition, the heat rate can be calculated if the heat losses in the
 compressor 160 (FIG. 1), the gas turbine 110 and the generator (not shown)
 are known. For example, the algorithm for the heat rate (HR) can be as
 follows:
 ##EQU3##
 In this embodiment, the power output is the flange to flange output (FFO).
 Also, if the power output, compressor loss, turbine loss and generator
 loss are known, any change in the heat rate can be attributable to the
 fuel heat content. For example, if the power output and all other heat
 losses remain constant but the heat rate increases one percent (1%), the
 actual fuel heat content is one percent (1%) less than the assumed LHV or
 the previously calculated fuel heat content.
 Once the heat rate has been calculated from the corrected data, a
 determination is made as to whether the heat rate has changed (step 320).
 The determination of a change in the heat rate is accomplished, as
 described above, using statistical analysis of the heat rate data. If the
 calculated heat rate falls outside the control limits of the noise
 boundaries, the heat rate has not changed (step 322), and no operational
 anomalies relating to the operation of the combustion turbine system 100
 exist.
 If the heat rate has changed, a compressor efficiency and a compressor
 pressure ratio (P.sub.ratio) are calculated (step 330). Therefore, the
 calculation is based on the determination of a change in the heat rate.
 The compressor efficiency provides the operational efficiency of the
 compressor 160 (FIG. 1). The compressor pressure ratio (P.sub.ratio)
 provides the ratio of the inlet to the exit pressures to the compressor
 160. These calculated parameters determine if a problem exits within the
 compressor 160 that is causing the change in the heat rate.
 The calculation of the compressor efficiency and the compressor pressure
 ratio (P.sub.ratio) uses the inputs of the compressor inlet and outlet
 temperatures (step 332), the compressor inlet and outlet pressures (step
 334) and the relative humidity (step 336). It should be appreciated that
 the measured data used to calculate the compressor efficiency and the
 compressor pressure ratio (P.sub.ratio) are corrected with a correction
 algorithm, as described above. The calculation of the compressor
 efficiency is calculated by the ratio of an actual efficiency to an
 adiabatic efficiency which are calculated using the inlet and out
 temperatures, inlet and outlet pressures and any change in entropy and/or
 free energy. In addition, the compressor pressure ratio (P.sub.ratio) is
 calculated using the ratio of the outlet pressure to the inlet pressure.
 Once the compressor 160 efficiency and the compressor pressure ratio
 (P.sub.ratio) have been calculated, a determination is made as to whether
 the compressor efficiency and the compressor pressure ratio (P.sub.ratio)
 have changed (step 340). The determination of the change of the compressor
 efficiency and the compressor pressure ratio (P.sub.ratio) (step 340)
 involves comparing the calculated compressor efficiency and the calculated
 compressor pressure ratio (P.sub.ratio), respectively, with the
 statistical analysis of previously calculated compressor efficiency and
 the compressor pressure ratio (P.sub.ratio). If the calculated compressor
 efficiency or calculated the compressor pressure ratio (P.sub.ratio) fall
 outside the control limits of the noise boundaries, a problem may exist in
 the compressor 160 that is causing the change in the heat rate.
 If no change in the compressor efficiency or the compressor pressure ratio
 (P.sub.ratio) exists, a problem with the compressor 160 may not exist and
 may not be causing the change in the heat rate. As such, a temperature
 rise (T.sub.rise) across the hot section 170 is calculated (step 350).
 Therefore, the calculation is based on the determination of a change in
 the compressor efficiency or the compressor pressure ratio (P.sub.ratio).
 The temperature rise (T.sub.rise) across the hot section 170 determines if
 a problem exits with the hot section 170 that is causing the change in
 heat rate, and the temperature rise (T.sub.rise) is an indirect
 measurement of the gas turbine 110 efficiency. In addition, calculation of
 the temperature rise (T.sub.rise) across the hot section 170 uses the
 inputs of turbine exhaust temperature (step 352) and a compressor outlet
 temperature (step 354). It should be appreciated that the measured data
 used to calculate the temperature rise (T.sub.rise) across the hot section
 170 are corrected with a correction algorithm, as described above. Also,
 the temperature rise (T.sub.rise) across the hot section 170 is calculated
 by subtracting the turbine exhaust temperature from the compressor outlet
 temperature.
 Once the temperature rise (T.sub.rise) across the hot section 170 is
 calculated, a determination is made as to whether a change in the
 temperature rise (T.sub.rise) across the hot section 170 exists (step
 360). The determination of a change in the temperature rise (T.sub.rise)
 across the hot section 170 is made by comparing the calculated temperature
 rise (T.sub.rise) across the hot section 170 to the statistical analysis
 of previously calculated temperature rises (T.sub.rise) across the hot
 section 170. If the temperature rise (T.sub.rise) across the hot section
 170 falls outside the control limits of the noise boundaries, a problem
 may exit with the hot section 170 that is causing the change in the heat
 rate.
 If the temperature rise (T.sub.rise) across the hot section 170 has not
 changed, the fuel heat content is calculated (step 370). Therefore, the
 calculation is based on the determination of a change in the temperature
 rise (T.sub.rise). As described above, the fuel heat content is the
 heating capacity of the fuel used in the combustion turbine system 100. As
 stated above, the calculation of the fuel heat content uses a calculated
 value of the heat rate (HR.sub.new) to a previously calculated value of
 the heat rate (HR.sub.old). The fuel heat content FHC is calculated using
 the following algorithm:
 ##EQU4##
 It should be appreciated that the measured data used to calculate the fuel
 heat content (FHC) are corrected using a correction algorithm, as
 described above.
 After the fuel heat content is calculated, a determination is made as to
 whether the fuel heat content has changed (step 380). The determination of
 the change in fuel heat content is made by comparing the calculated fuel
 heat content with a statistical analysis of the previously calculated fuel
 heat content to determine if the calculated fuel heat content falls
 outside the control limits of the noise boundaries. If the change in fuel
 heat content is not determined, the combustion turbine system 100 can have
 further diagnostic maintenance to determine the cause of the change in the
 heat rate. If the fuel heat content has changed, the change in the heat
 rate may be attributable to the change in fuel heat content. As a result,
 the fuel heat content used in the mathematical model of the operation of
 the combustion turbine system is changed (step 390). Therefore, the change
 in the fuel heat content is determined, and the mathematical mode is
 changed without having to perform unrequired maintenance on the combustion
 turbine system 100 to determine the cause of the change in the heat rate.
 Advantageously, as described herein, a diagnostic tool is provided to
 determine the cause of a change in the heat rate without performing
 unrequired maintenance on the combustion turbine system. It should be
 appreciated that the change in fuel heat content is provided in real time
 while the combustion turbine system 100 is running. As such, the
 mathematical model of the operation of the combustion turbine system 100
 can be used to adjust the control parameters of the combustion turbine
 system 100 in real time to maximize the operational efficiency. Therefore,
 as described herein, a calculated mathematical model is provided with the
 fuel heat content and any changes in the fuel heat content from
 conventionally measured data.
 The foregoing discussion of the invention has been presented for purposes
 of illustration and description. Further, the description is not intended
 to limit the invention to the form disclosed herein. Consequently,
 variations and modifications commensurate with the above teachings, with
 the skill and knowledge of the relevant art, are within the scope of the
 present invention. The embodiment described herein above is further
 intended to explain the best mode presently known of practicing the
 invention and to enable others skilled in the art to utilize the invention
 as such, or in other embodiments, and with the various modifications
 required by their particular application or uses of the invention. It is
 intended that the appended claims be construed to include alternative
 embodiments to the extent permitted by the prior art.