Note: Descriptions are shown in the official language in which they were submitted.
OPTIMIZATION OF GAS TURBINE COMBUSTION SYSTEMS LOW LOAD
PERFORMANCE ON SIMPLE CYCLE AND HEAT RECOVERY STEAM
GENERATOR APPLICATIONS
Cross-Reference to Related Applications
[0001] This application is a continuation-in-part of US Application Serial No.
13/542,222, filed
on July 5, 2012, which is a continuation-in-part of US Application Serial No.
12/463,060 filed on
May 8, 2009. This application also claims the benefit of US Application Serial
No. 61/601,876,
filed on February 22, 2012.
Technical Field
[0002] The present disclosure relates to an automated system to sense the
operating condition of
a combustion system and to make preset adjustments to achieve desired
operation of the turbine
thru out an optimized load range.
Background
[0003] Lean premixed combustion systems have been deployed on land based gas
turbine
engines to reduce emissions, such as NOx and CO. These systems have been
successful and, in
some cases, produce emission levels that are at the lower limits of
measurement capabilities,
approximately 1 to 3 parts per million (ppm) of NOx and CO. Although these
systems are a great
benefit from a standpoint of emission production, the operational envelope of
the systems is
substantially reduced when compared to more conventional combustion systems.
As a
consequence, the control of fuel conditions, distribution and injection into
the combustion zones
has become a critical operating parameter and requires frequent adjustment,
when ambient
atmospheric conditions, such as temperature, humidity and pressure, change.
The re-adjustment
of the combustion fuel conditions, distribution and injection is termed
tuning.
[0004] Controlled operation of a combustion system generally employs a manual
setting of the
operational control elements of a combustor to yield an average operational
condition. These
settings may be input through a controller, which as used herein shall refer
to any device used to
control the operation of a system. Examples include a Distributed Control
System (DCS), a fuel
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turbine controller, a programmable logical controller (PLC), a stand-alone
computer with
communication to another controller and/or directly to a system,
[0005] These settings are satisfactory at the time of the setup, but
conditions may change and
cause unacceptable operation in a matter of hours or days, Tuning issues are
any situation
whereby any operational parameters of a system are in excess of acceptable
limits, Examples
include emissions excursion outside of allowable limits, combustor dynamics
excursion outside
of allowable limits, or any other tuning event requiring adjustment of a
turbine's operational
control elements. Other approaches use a formula to predict emissions based on
gas turbine's
operating settings and select a set point for fuel distribution and/or overall
machine fuel/air ratio,
without modifying other control elements, such as fuel gas temperature. Still
other approaches
employ a remote connection to the site by tuning experts, that will
periodically readjust the tune,
from the remote location. These approaches do not allow for continuous timely
variation, do not
comprehensively take advantage of actual dynamics and emission data or do not
modify fuel
distribution, fuel temperature and/or other turbine control elements,
100061 Another variable that impacts the lean premixed combustion system is
fuel
composition. Sufficient variation in fuel composition will cause a change in
the heat release of
the lean premixed combustion system. Such change may lead to emissions
excursions, unstable
combustion processes, or even blow out of the combustion system,
[0007] In recent years, over-capacity of power generation, even that using
F-class firing
temperature gas turbines, has resulted in much of the installed gas turbine
fleet running in a
cyclic mode versus baseload operation. This means that many gas turbine
operators are forced to
shut their equipment down overnight, when power prices are so low that the
losses incurred
running overnight far outweigh the costs of starting the equipment every
morning. This
operation process has an impact on the maintenance of the equipment as each
stop / start cycle
causes a resulting load cycle on the equipment.
[0008] To combat this situation, gas turbine operators are investigating
ways of running their
equipment overnight while incurring the smallest economic loss possible. One
viable solution is
to lower the minimum load a gas turbine can achieve while still maintaining
acceptable
emissions levels. This method of operation is commonly referred to as
"Turndown,"
[0009] "Turndown" has been used within the power generation industry for
many years. As
such, nothing directly related to this mode of operation is included as part
of this patent. What is
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novel is the approach used by the ECOMAXTm tuning controller to tune the
combustion system
while in turndown, as well as the method incorporated within ECOMAXTm to
mitigate
detrimental effects on the combined-cycle heat recovery steam generator (HRSG)
caused by low
steam flows and high gas turbine exhaust temperatures. The system is also
applicable to simple.
cycle operation; however, most simple cycle systems are applied to peak power
generation and
have a desirable shut ¨ down process in the operating plan,
[0010] Often, as
gas turbine loads are reduced, HRSG steam flows reduce while gas turbine
exhaust temperatures rise, This combination, in conjunction with inadequate
intra-stage
attemperation flow capacity, often results in excessively high HRSG outlet
steam temperatures
(steam turbine inlet steam temperatures). In many cases these steam
temperatures approach
material limitations and can lead to pre-mature component failure, On the
other extreme, steam
conditioning / attemperation systems with adequate condensate flows can
provide enough
condensate to keep the superheat outlet temperature within specifications at
the point of entrance
into a steam turbine; however, localized over-attemperation can occur, This
over-attemperation
often leads to condensate impacting directly on steam piping downstream of the
attemperator,
causing excessive thermal fatigue in the piping sections immediately
downstream of
desuperheaters / attemperators,
[0011] To date
efforts have focused on manually (if at all) modifying a gas turbine's fuel-to-
air (Fa) ratio to keep the HRSG design constraints satisfied, However, factors
such as ambient
temperature changes, turbine component degradation, etc., can necessitate
periodic manipulation
of the gas turbine's f/a ratio, at low loads, to ensure acceptable HRSG inlet
conditions.
Automated manipulation of the f/a ratio of a gas turbine utilizing real-time
HRSG operational
information, as well as real-time gas turbine operational information,
provides an efficient means
to maximize HRSG component life.
[0012] It is
understood that manipulation of a gas turbine's fuel-air ratio will directly
affect
the engine's "tune", and as such any approach to accomplish this must be
accompanied by
another automated turbine control scheme to "re-tune" the turbine as-needed.
[0013] Mis-
operation of the combustion system manifests itself in augmented pressure
pulsations or increasing of combustion dynamics. Pulsations can have
sufficient force to destroy
the combustion system and dramatically reduce the life of combustion hardware.
Additionally,
improper tuning of the combustion system can lead to emission excursions and
violate emission
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permits, Therefore, a means to maintain the stability of the lean premixed
combustion systems,
on a regular or periodic basis, within the proper operating envelope, is of
great value and interest
to the industry, Additionally, a system that operates by utilizing near real-
time data, taken from
the turbine and HRSG sensors, would have significant value to coordinate
modulation of fuel
composition, fuel distribution, fuel gas inlet temperature, and/or overall
machine Va. ratio (HRSG .. =
inlet temperature and airflow).
Summary
[OM] Provided
herein is a system and method for tuning the operation of a turbine and
optimizing the mechanical life of a heat recovery steam generator. Provided
therewith is a
turbine controller, sensor means for sensing operational parameters, control
means for adjusting
operational control elements. The controller is adapted to tune the operation
of the gas turbine in
accordance preprogrammed steps in response to operational priorities selected
by a user. The
operational priorities preferably comprise optimal heat recovery steam
generator life,
[0015] The
present disclosure provides a controller and method for optimizing the fuel-
air
ratio of a gas-turbine combustor toward mitigating the detrimental effects of
the turbine's
exhaust conditions on the expected life of a Heat Recovery Steam Generator
(HRSG) system,
especially during low-load conditions. The gas turbine consumption system is
of the type having
sensor means for measuring operational parameters of the turbine and control
means for
controlling various operational elements of the turbine. The operational
parameters of the turbine
which are received by the controller include combustor dynamics, turbine
exhaust temperature
(overall fuel/air ratio), turbine exhaust emissions, and various heat recovery
steam generator
(HRSG) steam conditions, The operational control elements may include the fuel
gas blend ratio
(ratio of non-pipeline quality fuel gas to pipeline quality fuel gas), fuel
distribution within the
combustion system, fuel temperature and turbine exhaust temperature. The
turbine/power plant
system can also include a distributed control system (DCS) communicating with
the sensor
means and the control means. The tuning controller is normally connected to
the turbine system
through the DCS (although the tuning controller can connect directly to the
gas turbine
controller),
[0016] The
tuning controller operates by receiving data from the sensor means,
Operational
priorities for the turbine are set within the controller and are typically
selected from optimum
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NOx emissions, optimum power output, optimum combustor dynamics, optimum fuel
gas blend
ratio, and / or optimum HRSG life, The data received from the turbine sensors
is compared to
stored operational standards within the controller, The selected operational
standards are based
on the set operational priorities. A determination is made as to whether the
turbine operation
conforms to the operational standards. In addition, upon the data being out of
conformance, a
determination is made of the dominant tuning criteria again based on the
preset operational
priorities. Once the logical determinations arc made, the tuning controller
communicates with the
operational control means through the DCS to perform a selected adjustment in
an operational
parameter of the turbine, The selected operational adjustment is based on the
dominant tuning
criteria and has a preset fixed incremental value and defined value range.
Each incremental
change is input over a set period of time, which is sufficient for the turbine
to gain operational
stability. Once the time period passes, operational data is again received
from the turbine sensor
means to determine if an additional incremental change is desired, Generally
speaking, upon
completing the adjustments within the defined range, a further operational
parameter adjustment
is selected, again based on the dominant tuning criteria, and a further fixed
incremental
adjustment is made within a defined range and over a set period of time, The
tuning process
continues by the controller receiving operational data to determine if the
operation is conforming
to the operational standards or whether an additional incremental adjustment
is required. The
operational parameters being adjusted by the tuning controller are preferably
the fuel/air ratio
within the gas turbine, the combustor fuel distribution split within the
nozzles of the combustor,
the fuel gas inlet temperature, and/or the fuel gas blend ratio,
[0017] It is
understood that the tuning controller, when Optimum HRSG life is selected by
the
plant operator, will first evaluate what changes (if any) need to be made to
the gas turbine f/a
ratio to mitigate potential HRSG mechanical concerns and make these necessary
changes.
Subsequent to this optimization process, the tuning controller will tune the
gas turbine, if needed,
using the standard parameters of fuel splits, fuel gas temperature, and/or
fuel gas composition
(Note: gas turbine f/a ratio is not an option).
[0018] In a
further aspect of the disclosure, the system performs a method for
determination
of the dominant gas turbine combustion system tuning scenario through the use
of Boolean
hierarchical logic and multiple levels of control settings,
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[0019] In
another aspect of the disclosure, the method performed relates to automated
control
of the gas turbine inlet fuel temperature through automated modification of
the fuel gas
temperature control set point within a Distributed Control System (DCS),
[0020] In a
still further aspect of the disclosure, a method for automated control of a
gas
turbine inlet fuel temperature is defined by automated modification of the
fuel gas temperature
control set point within the fuel gas temperature controller.
[0021] In
another aspect of the disclosure a method for communicating turbine control
signals
to a gas turbine controller is accomplished through the use of an existing gas
turbine
communication link with an external control device, such as, for example a
MODBUS Serial or
Ethernet communication protocol port existing on the turbine controller for
communication with
the Distributed Control System (DCS).
100221 In a
still further aspect of the disclosure a method for modification of a gas
turbine
combustion system is defined by a series of auto tuning settings via a user
interface display,
which utilizes Boolean-logic toggle switches to select user-desired
optimization criteria. The
method is preferably defined by optimization criteria based on Optimum
Combustion Dynamics,
Optimum NOx Emissions, Optimum Power, Optimum Heat Rate, Optimum CO Emissions,
Optimum Heat Recovery Stearn Generator (HRSG) Life, Optimum Gas Turbine Fuel
Blend
Ratio or Optimal Gas Turbine Turndown Capability whereby toggling of this
switch changes the
magnitude of the combustor dynamics control setting(s).
Brief Description of Drawings
[0023] For the
purpose of illustrating the invention disclosed herein, the drawings show
forms
that are presently preferred. It should be understood that the invention is
not limited to the
precise arrangements and instrumentalities shown in the drawings of the
present disclosure.
[0024] Fig, 1
shows an exemplary embodiment of a schematic representation of an
operational plant communication system encompassing the gas turbine engine
system,
incorporating a gas turbine tuning controller as well as communication with
various elements of
the HRSG via plant DCS.
[0025] Fig. 2
shows an exemplary embodiment of a functional flow chart for the operation of
a tuning controller according to the present disclosure,
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[0026] Fig. 3
shows an exemplary embodiment of a user interface display for selecting the
optimization mode within the present disclosure,
[0027] Fig, 4
shows an exemplary schematic of the inter-relationship of various optimization
mode settings,
100281 Fig. 5
shows an exemplary overview schematic of the process steps utilized to
determine the alarm signals triggered according to the present disclosure,
100291 Fig, 6
shows an exemplary process overview of the steps to determine allowable
turbine tuning parameters.
[0030] Fig. 7
shows a further detailed exemplary process according to the steps shown in
Fig,
6.
[0031] Fig, 8
provides a further detailed exemplary schematic of the steps the present
disclosure utilizes to determine the dominant tuning concern,
[0032] Fig. 9
shows a first example schematic of the determination of the system's dominant
tuning concern, given various alarm inputs into the present disclosure,
[0033] Fig, 10
shows a second example schematic of the determination of the system's
dominant tuning concern, given various alarm inputs into the present
disclosure,
100341 Fig, 11
shows a third example schematic of the determination of the system's
dominant tuning concern, given various alarm inputs into the present
disclosure,
[0035] Fig, 12
shows a fourth example schematic of the determination of the system's
dominant tuning concern, given various alarm inputs into the present
disclosure,
[0036] Fig, 13
shows a first operational example of operational tuning of a gas turbine
engine
system as contemplated by the present disclosure,
[0037] Fig, 14
shows a second operational example of operational tuning of a gas turbine
engine system as contemplated by the present disclosure.
100381 Fig, 15
shows a third operational example of operational tuning of a gas turbine
engine
system as contemplated by the present disclosure,
[0039] Fig, 16
shows a fourth operational example of operational tuning of a gas turbine
engine system as contemplated by the present disclosure.
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Detailed Description
100401 The
present disclosure generally relates to systems and methods for tuning the
operation of combustion turbines, In the depicted embodiments, the systems and
methods relate
to automatic tuning of combustion turbines, such as those used for power
generation. Persons of
ordinary skill in the art will appreciate that the teachings herein can be
readily adapted to other
types of combustion turbines, Accordingly, the terms used herein are not
intended to be limiting
of the embodiments of the present disclosure. Instead, it will be understood
that the
embodiments of the present disclosure relate generally to the field of
combustion turbines, and in
particular for systems, methods and computer readable media for tuning of
combustion turbines,
100411 Fig, 1 is
a communication diagram for a gas turbine engine (not shown), within which
a tuning controller 10 of the present disclosure operates. A distributed
control system (DCS) 20
serves as the main communication hub, As an alternative, a plant using the gas
turbine controller
as a DCS, may also have the tuning controller 10 communicate directly to the
gas turbine
controller 30, As a further alternative, the tuning controller 10 can
communicate directly with
the gas turbine controller 30, irrespective if the gas turbine controller 30
is functioning as a DCS.
Most of the turbine control is performed through the DCS 20, A turbine
controller 30
communicates directly with the gas turbine and with the DCS 20, In the present
disclosure,
information relevant to turbine operation, e.g., turbine dynamics, turbine
exhaust emissions, etc.
are directed through the DCS 20 to the tuning controller 10. The tuning
controller 10 is
contemplated to be a stand-alone PC used to run as a programmable logical
controller (PLC).
The tuning controller 10 is preferably a separate computer from the turbine
controller 30 and
does not normally communicate directly with the turbine controller 30, except
through the DCS
20, However; as mentioned above, the tuning controller 10 can be configured to
directly
communicate with the gas turbine controller 30,
[00421 Referring
now to Figs, 1 and 2, the tuning controller 10 is contemplated to be a stand-
alone PC used to run as a programmable logical controller (PLC). The tuning
controller 10 is
preferably a separate computer from the turbine controller 30 that is in
constant communication
from with the turbine controller 30. The signals from the tuning controller 10
may also be
transferred to the turbine controller 30 or other controls within the system
by the use of an
external control device, such as a MODBUS Serial or Ethernet communication
protocol port
existing on or added to the system.
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[0043] The
relevant operational data is received from sensor means associated with the
turbine, For example, the turbine exhaust emission reading is taken from stack
emissions by a
continuous emissions monitoring system (CEMS) 40, which is connected to the
DCS.
Combustion dynamics is sensed using a dynamic pressure sensing probe located
within the
combustion region of the turbine combustor. As shown, a continuous dynamics
monitoring
system (CDMS) 50 is provided and communicates with the DCS, The CDMS 50
preferably uses
either direct mounted or wave guide connected pressure or light sensing probes
to measure the
combustion dynamics. Another relevant operational parameter is the fuel gas
temperature.
Again, this temperature information is directed to the tuning controller 10
through the DCS 20
from the fuel heating controller 60, Since part of the tuning operation may
include adjustment of
the fuel temperature, there may be a two-way communication between the tuning
controller 10
and the fuel heating unit 60, The DCS 20 communicates with a fuel blend ratio
controller 70 to
adjust the ratio of pipeline quality gas to non-pipeline quality gas (for
subsequent consumption
within the gas turbine). There exists in direct communication between the fuel
blend ratio
controller 70 and the tuning controller 10 via the DCS 20. Last, as part of
this disclosure, certain
key operating parameters of the HRSG 80 are sent to the tuning controller 30
via the DCS 20. If
the tuning controller 10 determines that various parameters of the HRSG 80 are
outside of
allowable ranges, changes to the gas turbine f/a ratio are sent from the
tuning controller 10
through the DCS 20 to the gas turbine controller 30.
100441 Relevant
operational data from the turbine and HRSG is collected several times per
minute. This data collection allows for near real-time system tuning. Most
relevant turbine and
HRSG operational data is collected by the tuning controller 10 in near real-
time. However, the
turbine exhaust emissions sensor means is typically received by the tuning
controller 10 with a 2
to 8 minute time lag from current operating conditions. This time lag
necessitates the need for
the tuning controller 10 to receive and buffer relevant information, for a
similar time lag, before
making operational tuning adjustments. This tuning controller 10 tuning
adjustment time lag
assures that all of the operational (including exhaust emissions) data is
representative of a stable
turbine operation before and after any adjustments have been made, Once the
data is deemed
stable, the tuning controller 10 determines whether there is a need for
adjustment of tuning
parameters. If no adjustment is necessary, the tuning controller 10 maintains
the current tuning
and waits to receive the next data set. If changes are desired, tuning
commences, First, HRSG
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operational data are compared against HRSG component mechanical limits, If any
HRSG
mechanical limits (or margin against such limits) are violated, the tuning
controller 10 will alter
the gas turbine f/a ratio through the DCS 20 to the turbine controller 30.
Subsequently, if there is
sufficient margin in the key operational characteristics of the gas turbine
(namely exhaust
emissions and combustor dynamics), the tuning controller 10 can send a command
(if applicable)
to the fuel gas ratio controller 70 (through the DCS 20) to increase the ratio
of non-pipeline
quality gas to pipeline quality gas,
100451 All
determinations of the need for turbine tuning are performed within the tuning
controller 10, The tuning operation is started based on an "alarm" created by
receipt of
operational data outside of preset operational criteria, In order for the
tuning operation to be
initiated, the alarm ¨ and thus the data anomaly ¨ must continue for a
predetermined period of
time,
100461 One
example of a tuning adjustment is the variation of the fuel nozzle pressure
ratio to
adjust combustion dynamics. With the requirement of higher firing temperatures
to achieve
greater flame temperatures and efficiency, turbine combustors must release
more energy in a
given combustor volume. Better exhaust emissions are often achieved by
increasing the mixing
rate of fuel and air upstream of the combustion reaction zone, The increased
mixing rate is often
achieved by increasing the pressure drop at the fuel nozzle discharge. As the
mixing rate
increases in combustors, the turbulence generated by combustion often leads to
noise within the
combustor and may lead to the generation of acoustic waves. Typically,
acoustic waves are
caused when the sound waves of the combustion flames are coupled with the
acoustic
characteristics of the combustor volume or the fuel system itself,
[00471 Acoustic
waves may affect the internal pressure in the chamber. Where pressure
near a fuel nozzle rises, the rate of fuel flowing through the nozzle and the
accompanying
pressure drop decreases, Alternatively, a decrease in pressure near the nozzle
will cause an
increase in fuel flow, In cases where a low fuel nozzle pressure drop allows
fuel flow
oscillation, a combustor may experience amplified pressure oscillations, To
combat the pressure
oscillations within the combustor, combustion dynamics are monitored and the
fuel air ratio and
fuel nozzle pressure ratio may be modified to reduce or eliminate unwanted
variations in
combustor pressure, thereby curing an alarm situation or bringing the
combustion system back to
an acceptable level of combustion dynamics.
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[0048] As shown in Fig. 2, the data received from the sensing means for the
HRSG
operational parameters (80), combustor dynamics (50), turbine exhaust
emissions (40), and other
relevant turbine operating parameters (30) are directed through the DCS (20)
to the tuning
controller (10). These input values are then compared to standard or target
operational data for
the turbine, The stored operational standards are based, at least in part, on
the operational
priority settings for the turbine, These priority settings are defined on the
main user interface 12
of the tuning controller 10 and are shown graphically in Fig, 3, Based on the
priority settings, a
series of adjustments are made to the operation of the turbine by the turbine
controller 10
connected through the DCS 20. The adjustments are directed to the control
means, including the
fuel heating unit 60 (Fig, 1), fuel blend ratio controller 70, and various
other operational
elements 90 of the turbine (Fig. 2),
[0049] The
interface display 12 shown in Fig, 3 is comprised of switches (each having an
On/Off indication), These switches allow the user to specify the desired
tuning priorities for the
operation of the turbine, The switched operational priorities include optimum
NOx emissions
14, optimum power 16, optimum combustor dynamics 17, optimum fuel blend ratio
18, and
optimum HRSO life 19, Each of these switches is set by the user to adjust the
preferred
operation of the turbine, Within the tuning controller are functions that
operate within the
priorities set by the switches, Preferably, if both the optimum NOx emissions
switch 12 and the
optimum power switch 14 are set to "On", the controller 10 will run in the
optimum NOx mode,
not optimum power. Thus, to run in optimum power mode, the optimum NOx
emissions switch
12 must be "Off', Optimum dynamics 17 can be selected at any time, It is
explicitly noted that
other User-Interface Toggle Switches (not shown) may be used, including
parameters such as
Optimum Heat Rate, Optimum CO emissions, Optimum Heat Recovery Steam Generator
(HRSO) Life, Optimum Gas Turbine Fuel Blend Ratio, Optimal Gas Turbine
Turndown
Capability, etc,
100501 Fig, 4
shows a graphical representation of the interrelationship of the interface
display
switches. As shown, switching one parameter "On" will alter the alarm limits
to a different level
than their "Off' level, In the example shown in Fig, 4, the alarm limits are
shown with both
Optimum NOx and optimum power in the "On" position and in the "Off' position,
These points
on the graph are then modified by the selection of optimum dynamics
(represented throughout by
the symbol 5) in either the "On" or "Off" position, The points shown on the
graph of Fig. 4
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represent an exemplary set of limits for dynamics, based on the user's
selected operational
priorities,
100511 Returning
to Fig, 2, there is shown a representation of the logical flow of the
determinations and calculations made Within the tuning controller 10. The
tuning controller 10
receives the actual operating parameters of the turbine through the turbine
controller 30,
combustor dynamics through the CDMS 50, turbine exhaust emissions through the
CEMS 40,
and relevant HRSG operating parameters 80. This sensor data is directed to the
tuning controller
through the DCS 20, The received sensor data is compared to stored operational
standards to
determine if the turbine operation is conforming to the desired settings. The
operational
standards are based on the preset operational priorities of the turbine,
defined by the switches 14,
16, 17, 18, and 19 on the main user interface display 12 of the tuning
controller 10 (Fig, 3),
100521 Based on
the preset operational priorities, a hard-coded hierarchical Boolean-logic
approach determines the dominant tuning criteria based on operational
priorities. From this
logical selection, the tuning controller 10 implements a fixed incremental
adjustment value for
changing an operational parameter of the turbine within a maximum range of
adjustment (e.g.,
high and low values). The tuning changes are made in a consistent, pre-
determined direction
over a pre-determined increment of time and are dependent on the dominant
tuning criteria at
present. It is contemplated that no formulaic or functional calculations are
made to determine the
magnitude of tuning adjustments; rather, the incremental adjustments, the
direction of the
adjustments, the time span between adjustments, and the maximum range for the
adjustments for
each parameter and for each tuning criteria are stored in the tuning
controller 10.
100531 As shown
in Fig, 2, when Optimum HRSG Life 19 is not selected by the operator, the
tuning controller 10 determines whether the emissions are in compliance 100
and whether the
combustor dynamics are at acceptable levels 102. If both are in compliance
with the set
operational standards, the tuning controller 10 waits for the next data set
from the CEMS 40 or
the CDMS 50, and for other turbine operational data 90, If both are in
compliance with the set
operational standards and possess sufficient operational margin, and Optimum
Fuel Blend Ratio
18 is selected, the tuning controller 10 will send a command to the fuel blend
ratio controller 70
to increase the ratio of non-pipeline quality gas to pipeline quality gas. If
the received data is
non-conforming with the operational standards, i,e, above or below alarm
levels, as is the case
with step 104 of Fig. 2, the tuning operation moves to the next tuning step of
first determining
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the dominant tuning concern 106, The logical adjustment of turbine operation
is defined by the
dominant tuning criteria 106, which is based, at least in part, on the preset
operational priorities
set within the user interface 12, as will be discussed below with respect to
Fig. 8.
[0054] If Optimum
HRSG Life 19 is selected by the operator, the first decision the tuning
controller makes is an assessment of the margin of pertinent HRSG parameters
(including but not
limited to high pressure superheat outlet steam temperature, hot reheat outlet
steam temperature,
high pressure superheat steam desuperheater margin against saturation (degrees
Fahrenheit of
temperature immediately downstream of attemperator compared to saturation
temperature), hot
reheat steam desuperheater margin against saturation) against design limits.
These temperature
margins are compared against allowable margins as defined by the user, If the
actual
temperature margins are less than the allowable margins, the tuning controller
10 will
automatically adjust the turbine controller's f/a ratio 122. In this
particular case, the tuning
controller 10 has first adjusted the gas turbine's f/a ratio for an external
reason (HRSG
component life), This change can adversely affect the gas turbine's current
state-of-tune,
Therefore, the normal gas turbine tuning scheme is performed by the tuning
controller 10;
however, changes to the turbine's f/a ratio are not allowed. The remaining gas
turbine tuning
scheme is defined below,
10055] In a preferred
operation, the tuning controller 10 will first attempt to change the
turbine combustor fuel splits 108, The fuel split determines the distribution
of the fuel flow to
the fuel nozzles in each combustor, It should be noted that while the current
embodiment
indicates the presence of two adjustable fuel circuits, this approach can be
utilized for one, two
or more fuel circuits. If these adjustments do not resolve the tuning issue
and do not place the
operational data back into conformance with the operational standards, a
further adjustment is
performed. In certain situations or if the efficacy of fuel split changes on
resolving high
combustor dynamics is low, the next incremental adjustment is a change of the
fuel gas
temperature set point. In this adjustment step, the tuning controller 10 sends
a modified fuel gas
inlet temperature signal to the DCS 20, which is directed to the fuel heating
unit 60,
[0056] Referring
again to Fig. 2, if modification of the combustor fuel splits and/or fuel gas
inlet temperature does not resolve the tuning issue 110, the tuning controller
10 will then alter
the overall fuel/air ratio 112, This approach makes changes to the turbine
thermal cycle utilizing
fixed incremental changes over pre-determined amounts of time. The step is
intended to adjust
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the exhaust temperature (up or down) by adjusting the air to fuel ratio in
accordance with
predetermined, standard control curves for the turbine operation, which are
maintained within the
memory of the tuning controller 10, If changes made to the gas turbine's
overall fuel/air ratio do
not resolve the tuning issue 114 or if Optimum HRSG Life 19 is enabled and
HRSG mechanical
concerns exist, the tuning controller 10 will adjust the fuel blend ratio 116,
[00571 In the
present disclosure, it is contemplated that all control changes directed by
the
tuning controller 10 are fed back to the turbine system (30, 90), fuel gas
temperature controller
60, and fuel blend ratio controller 70 through the DCS 20. However, the tuning
controller 10 can
be configured to communicate directly with the turbine controller 30, These
changes are
implemented directly within the various controller means within the system or
through the
turbine controller 30. When the operational data is returned to the desired
operational standards,
the tuning settings are held in place by the tuning controller pending an
alarm resulting from
non-conforming data received from the sensor means through the DCS,
[0058] The
adjustments sent from the tuning controller 10 to the turbine controller 30 or
the
associated controller (60, 70) means are preferably fixed in magnitude, Thus,
the adjustments
are not recalculated with new data or optimized to a target, The adjustments
are part of an "open
loop", Once started, the adjustments move incrementally to the preset maximum
or maximum
within a specified range, unless an interim adjustment places the operation
data into conformance
with the operational standards. Under most circumstances, when the full
incremental range for
one operational parameter is completed, the tuning controller moves on to the
next operational
parameter, which is defined by the preset operational priorities. The specific
order of operational
control elements is not fixed, and can be determined by operational
priorities, The logic of the
tuning controller drives the operational control element adjustment based on a
"look-up" table
stored within the memory of the tuning controller and preset operational
primities,
[0059] The
tuning controller preferably addresses one operational parameter at a time,
For
example, the dominant tuning criteria dictates the first adjustment to be
made. In the preferred
example discussed above, the fuel distribution/split parameter is first
adjusted. As indicated in
Fig, 2, the fuel split of fuel circuit 1 is first addressed, followed by the
split for fuel circuit 2.
Again, this method can be applied to any combustion system with one or more
adjustable fuel
circuits, The fuel gas inlet temperature adjustment generally follows the fuel
split adjustments
when needed, Within each step, there is an incremental adjustment, followed by
a time lag to
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permit the adjusted turbine operation to stabilize, After the time lag, if the
current operational
data analyzed by the tuning controller indicates that turbine operation still
remains outside of the
operational standards, the next incremental adjustment within the step is
made. This pattern
repeats for each step, Under most circumstances, only when one adjustment step
is completed
does the tuning controller move onto the next operational parameter. It should
be noted that there
exists an over-riding loop whereby the tuning controller 10 will directly
increase the non-
pipeline quality gas blend ratio (through the fuel blend ratio controller 70)
if key turbine
operational characteristics possess ample operational margin (against alarm
conditions) 118. The
control methodology of this over-riding control loop is identical to that
mentioned above for fuel
splits and turbine f/a ratio ¨ a change is made in a pre-defined direction, a
pre-defined amount, in
a pre-defined amount of time,
[0060] The
tuning controller preferably controls combustion operation to maintain proper
tuning in variable conditions of ambient temperature, humidity and pressure,
all of which vary
over time and have a significant effect on turbine operation. The tuning
controller may also
maintain the tuning of the turbine during variation in fuel composition.
Variation in fuel
composition may cause a change in the heat release, which can lead to
unacceptable emissions,
unstable combustion, or even blow out, The tuning controller will adjust the
fuel composition
entering the turbine indirectly through changes in the fuel blend ratio 116,
100611 Another
aspect regarding fuel splits within the combustor deals directly with
combustion systems having a series of outer nozzles (of the same type,
controlled by an outer
fuel split affecting circumferential distribution of fuel within the outer
fuel nozzles) in
combination with a center nozzle (of same or different type compared to outer
nozzles,
controlled by an inner / center fuel split). Within this framework, the center
nozzle can either
operate with a "rich" or "lean" fuel-to-air ratio, as compared to the f/a of
the outer fuel nozzles.
Most combustion tuning keeps the combustion system either on a "lean center
nozzle" or a "rich
center nozzle" mode of operation. In some circumstances, better flame
stability can be achieved
with a "rich center nozzle" fuel split profile when compared to a "lean center
nozzle"; however,
this normally results in higher NOx emissions, Therefore, a hybrid fuel
schedule is of particular
interest, whereby the combustion system utilizes a "lean center nozzle" fuel
split schedule at
higher load conditions (where flame stability is less of a concern but NOx
emissions are more of
a concern) transitioning to a "rich center nozzle" fuel split schedule at
lower load and turndown
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conditions (where flame stability is more of a concern and NOx is less of a
concern), The
system of the present disclosure determines which fuel split schedule is
employed (rich or lean
center nozzle) at each operating point (allowing for the use of a hybrid fuel
split schedule), and
adjusts the fuel split schedule (Fuel Circuit 1 Split and Fuel Circuit 2
Split) in the proper
direction, Again, changes made are of fixed magnitude in fixed time intervals,
10062] Another
point regarding fuel splits deals directly with combustion systems having a
series of outer nozzles (of same or different type, controlled by an outer
fuel split affecting
circumferential distribution of fuel within the outer fuel nozzles) with no
center nozzle. Within
this framework, a subset of these outer nozzles (referred to generally as
minor circuit 1) can
either operate with a "rich" or "lean" fuel-to-air ratio, as compared to the
f/a of the remaining
outer fuel nozzles (referred to as major circuit 1). Most combustion tuning
keeps the combustion
system either on a "lean minor circuit 1" or a "rich minor circuit 1"
circumferential fuel split
mode of operation, In some circumstances, better flame stability can be
achieved with a "lean
minor circuit 1" fuel split profile when compared to a "rich minor circuit I"
fuel split profile;
however, this can result in higher NOx emissions, Therefore, a hybrid fuel
schedule is of
'particular interest, whereby the combustion system may utilize a "rich minor
circuit 1" fuel split
schedule at higher load conditions (where flame stability is less of a concern
but NOx emissions
are more of a concern) transitioning to a "lean minor circuit 1" fuel split
schedule at lower load
and turndown conditions (where flame stability / CO is more of a concern and
NOx is less of a
concern). The system of the present disclosure determines which fuel split
schedule is employed
(rich or lean minor circuit 1) at each operating point (allowing for the use
of a hybrid fuel split
schedule), and adjusts the fuel split schedule (Fuel Circuit 1 Split and Fuel
Circuit 2 Split, if
applicable) in the proper direction. Again, changes made are of fixed
magnitude in fixed time
intervals,
[0063] One
further aspect regarding fuel splits deals directly with combustion systems
having
one or more annular rings of fuel nozzles (of same or different type,
controlled by an
circumferential fuel split affecting circumferential distribution of fuel
within each ring of fuel
nozzles), whereby a second family of fuel splits may be available (if more
than one annular ring
of fuel nozzles exists)which adjusts the relative (radial) amount of fuel to
each of the radially
concentric fuel rings (ring 1, ring 2, etc.), Within this framework, a subset
of each ring's fuel
nozzles (referred to as minor circuit ring 1, minor circuit ring 2, etc.) can
either operate with a
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"rich" or "lean" fuel-to-air ratio, as compared to the f/a of the remaining
ring's fuel nozzles
(referred to as major circuit ring I, major circuit ring 2, etc.), Most
combustion tuning keeps the
combustion system either on a "lean minor circuit ring 1" or a "rich minor
circuit ring 1" (and
similar approaches for rings 2, 3, etc,) circumferential fuel split mode of
operation. In some
circumstances, better flame stability can be achieved with, using ring 1 as an
example, a "lean
minor circuit ring 1" fuel split profile when compared to a "rich minor
circuit ring 1" fuel split
profile; however, this can result in higher NOx emissions, Therefore, a hybrid
fuel schedule is of
particular interest, whereby the combustion system may utilize a "rich minor
circuit ring I" fuel
split schedule at higher load conditions (where flame stability is less of a
concern but NOx
emissions are more of a concern) transitioning to a "lean minor circuit ring
1" fuel split schedule
at lower load and turndown conditions (where flame stability / CO is more of a
concern and NOx
is less of a concern). The system of the present disclosure determines which
fuel split schedule
is employed for each ring, if applicable (rich or lean minor circuit ring 1,
rich or lean minor
circuit ring 2, etc.) at each operating point (allowing for the use of a
hybrid fuel split schedule),
and adjusts the fuel split schedule (Fuel Circuit 1 Split and Fuel Circuit 2
Split, if applicable) in
the proper direction. Again, changes made are of fixed magnitude in fixed time
intervals,
[0064] Fig. 5
provides a schematic that details the framework for determining the dominant
tuning concern 106, as included in Fig, 2, Future steps will be described
below with respect to
Fig, 8, First, relevant emissions parameters 120 and combustor dynamics 122
are received by
the tuning controller 10 from the CEMS 40 and CDMS 50, as detailed above, The
relevant
emissions parameters 120 and combustor dynamics 122 are then compared to
allowable tuning
limits 124 that are also provided to the tuning controller 10. The allowable
tuning limits are in
the form of preset ranges that may be adjusted using the tuning interface 12
of Fig. 3 and
determined according to the logic set forth below with respect to Figs. 6 and
7. The output of
this comparison is a series of "True" alarms 126 of various tuning concerns,
where an alarm
condition is indicated if the sensed operational data 120, 122 is above or
below a given alarm
range set forth in the tuning limits 124,
[0065] Alarm
conditions may have more than one level or tier, For example, there may be
varying degrees of severity of an alarm, such as: high "11"; high-high "HH";
high-high-high
"HHH" and low "L"; low-low "L"; low-low-low "LLL", The "True" logical alarms
126 are
subsequently ranked according to their level of importance (e.g. high ¨ high
"HH" alarms are
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more important than high "H" alarms, etc.) in step 130, If more than one
tuning concern shares
the same level, the tuning concerns will then be ranked according to the user
preferences as set
forth below with respect to Fig. 8, If only one "True" alarm emerges, this
will be selected and
used as the dominant tuning concern 106 to initiate the tuning process as set
forth in Fig, 2.
However, the results of the process of Fig, 5, namely the ranked "True" alarms
130, will be
processed through user determined criteria, as shown in Fig, 8, before a
dominant tuning concern
106 is confirmed,
[00661 In Fig,
6, a flow chart is provided to explain how the allowable tuning limits 124 are
determined. Once determined, the tuning limits 124 are compared to the
operational data 120,
122 as set forth above and shown in Fig, 5, First, the User Interface Toggle
Switches 14, 16, 17
corresponding to those in the interface display 12 of Fig, 3, are compared
against each other,
utilizing an internal hierarchy to allow passage of the alarm constraints
relative to the most
significant toggle switch, Thus, depending on which switches are in the "On"
position, different
tuning limits will be included in the allowable tuning limits 124. Each of
Optimum NOx,
Optimum Power and Optimum Dynamics has a collection of preset limits (denoted
by the
numerals 134, 136 and 138 in Fig, 6), depending on whether the corresponding
toggle switch 14,
16, 17 is in the "On" of "Off' position, There is also an internal set of
default limits 140 to be
used when none of the toggle switches are in the "On" position,
[0067] The
internal hierarchy will determine which tuning limits shall take precedence in
the
event that competing toggle switches 14, 16 or 17 are in the "On" position, In
the present
example, the hierarchy ranks Optimum NOx 14 above Optimum Power 16, Optimum
Dynamics
17 may be selected at any time and will simply alter the tuning limits of the
other selections
given, such as is shown in Fig, 4, If Optimum NOx 14 and Optimum Power 16 are
both in the
"On" position, the tuning limits for Optimum NOx 134 will be used.
Additionally, the tuning
limits for Optimum Dynamics 138 are utilized if this toggle switch 17 is
activated, If no User
Interface Toggle Switches 14, 16, 17 are active, default tuning limits 140 are
provided as the
allowable tuning limits 124, All of the tuning limits 134, 136, 138 and 140
that may be used to
construct the allowable tuning limits for the tuning controller 10 may be
developed by the end
user and programmers and are then preferably hard coded into the tuning
controller 10 for a
given application. The methodology outlined in Fig. 6 is meant to provide an
exemplary
framework for incorporation of a number of different User Interface Toggle
Switches, such as
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those options set forth above with respect to Fig. 3 including Optimum HRSG
Life 19, whereby
only a subset are specifically outlined in this disclosure.
[0068] Fig, 7
shows a specific example of the flow chart of Fig. 6 given for the
determination
of a subset of the system's allowable tuning limits. In this example, the
tuning limits for High
NOx, High HighN0x, High Class 1 613's, High Class 2 6P's will be determined
based on preset
tuning limits and the user's preferences. The various exemplary tuning limits
are provided for
Optimum NOx 134, Optimum Power 136, Optimum Dynamics 138, and No Optimal
Settings
140 are given corresponding numerical values (shown respectively in blocks
152, 154, 156 and
158). The corresponding numerical values given for each criterion vary, such
that the allowable
limits 124 will be different depending on which toggle switches 14, 16 or 17
are selected, By
way of example, the Optimum NOx 134, 152 and Optimum Power 136, 154 give
limits for NOx,
but also provide limits for Dynamics that are to be used in the event that
Optimum Dynamics
138, 156 is not selected. However, in the event that the Optimum Dynamics
toggle 17 is
selected, the Class 1 olp's and Class 2 OP's values provided therefore 156
shall be used instead of
the values listed with respect to Optimum NOx 134, 152 and Optimum Power 136,
154,
100691 In this
particular example, the toggle switches for Optimum NOx 14 and Optimum
Dynamics 17 are selected, with the switch for Optimum Power 16 left in the
"Off' position.
Thus, the values from Optimum NOx for High NOx and High HighNOx 152 are
provided. Also,
because Optimum Dynamics 17 is also selected, the Dynamics values for High
Class 1 OP's and
High Class 2 OP's 138, 156 replace those OP's values provided with respect to
Optimum NOx
134, 152, As a result, the allowable tuning limits 124 are provided as shown
in block 160.
These allowable tuning limits 124 correspond to those used in Fig. 5, as
described above, to
determine whether information from the CEMS 40 and CDMS 50 is in an alarm
state or
operating normally.
[0070] Fig. 8,
shows a further schematic for the process of incorporating a user's priorities
and the "True" alarm conditions received for determining the dominant tuning
concern 106. It is
this tuning concern 106 which dictates the turbine operational changes the
turbine controller 10
performs, as shown in Fig, 2,
[0071] First, a
determination is made of all potential dominant tuning issues 142, These
include, but are not limited to: combustor blowout, CO emissions, NOx
emissions, Class I
combustor dynamics (Class 1 OP's), Class 2 combustor dynamics (Class 2 OP's),
and HRSG
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mechanical life, The list of potential dominant tuning issues 142 is
determined by the user and
programmer and may be based on a number of factors or operational criteria, By
way of
example, Class 1 and Class 2 combustor dynamics 6P's refer to combustion
dynamics occurring
over specific ranges of acoustic frequencies, whereby the range of frequencies
is different
between Classes 1 and 2, Indeed, many combustion systems can possess different
acoustic
resonant frequencies corresponding to Class 1 and Class 2, and variations in
these 2 dynamics
classes may be mitigated utilizing different turbine operational parameter
changes for each
different turbine and / or combustor arrangement. It should also be noted that
certain combustion
systems may have none, 1, 2, or greater than 2 different "classes" (frequency
ranges) of
combustor dynamics which can be tuned, This disclosure utilizes a system
whereby 2 different
combustor dynamics classes are mentioned, However, it is fully intended that
this disclosure can
be broadly applied to any number of distinct dynamics frequency classes (from
0 to greater than
2),
[0072] After
determination of the potential dominant tuning issues 142, these issues are
ranked in order of significance 144 according to the end user's needs as well
as the detrimental
effects that each tuning concern can have on the environment and / or turbine
performance. The
relative importance of each potential dominant tuning concern can be different
with each end
user, and for each combustor arrangement. For example, some combustion systems
will
demonstrate an extreme sensitivity to combustor dynamics, such that normal
daily operational
parameter variations can cause a normally benign dynamics tuning concern to
become
catastrophic in a very short amount of time, In this case, one or both of the
dominant dynamics
tuning concerns (Class 1 and Class 2) may be elevated to Priority I (Most
Important), By way of
example in Fig, 7, combustor blowout is listed as the most important Dominant
Tuning Concern
144, This ranking is used to determine the dominant tuning concern in the
event that there are
multiple alarms with equal levels of severity. This ranking of Dominant Tuning
Concerns 144,
from most to least important, provides the overall framework where the
specific Boolean Logic
Hierarchy 148 is created, For example, assuming Class 1 and Class 2 613's obey
generally
monotonic behavior relative to perturbations in system operational parameters,
a High-High
"HH" Class 2 OP's alarm may be more significant than High "H" Class 1 OP's
alarm,
Additionally, in the example given in Fig, 8 for the Boolean Logic Hierarchy
148, High "H"
NOx emissions is more significant than High "H" Class 2 dynamics, This means
that if both
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High "H" NOx and High "H" Class 2 dynamics are both "in alarm" (Logic = True),
in the
absence of other alarms being "True", the autotuning system will tune for High
"H" NOx
because it is the dominant tuning concern, Finally, it can be seen that
Blowout is ranked above
NOx Emissions and both are ranked above Class 1 OP's, Thus, if there were high
"H" alarms
returned for all three categories, Blowout would be the dominant tuning
concern, followed by
NOx Emissions and then Class 1 OP's, This Boolean Logic Hierarchy 148 will be
what is
compared to the "True" alarms 130 returned by comparing the allowable tuning
limits 124 to the
operational data 120, 122 as set forth above with respect to Fig, 5,
100731 All
"True" tuning alarms 130 are provided as ranked by severity (e.g. HHH above
HH,
etc,), The "True" tuning alarms 130 are then compared with the hard-coded
Boolean Logic
Hierarchy 148, in step 150 to determine which tuning will become the "True"
Dominant Tuning
Concern 106. This one "True" Dominant Tuning Concern 106 is now passed into
the remainder
of the autotuning algorithm, as detailed in Fig, 2, as the Dominant Tuning
Concern 106 to be
mitigated by operational changes,
100741 'Thus the
tuning controller 10 may be configured to optimize the mechanical life of a
Heat Recovery Steam Generator (HRSG) through the manipulation of the gas
turbine exhaust
temperature (turbine fuel air (f/a) ratio) when key HRSG operational
characteristics indicate
insufficient design margin against over-temperature (at steam outlet
conditions) and / or over-
attemperation (at intra-stage desuperheater). The HRSG will have sensors for
measuring
operational parameters of the boiler, and the turbine having sensor means for
measuring
operational parameters of the turbine, as discussed above, The HRSG
operational parameters
include high pressure and/or hot reheat steam outlet temperatures and/or high
pressure and/or hot
reheat intra-stage desuperheater outlet temperatures and pressures, The
turbine operational
parameters include combustor dynamics and turbine exhaust emissions. Using
.the logic applied
above with respect to alarm levels, the turbine controller will adjust various
operational control
elements, such as fuel distribution and / or fuel-to-air (f/a) ratio, as
needed,
100751 The
control system for optimizing HRSG life is set forth above in Fig, 1 and
(optionally) relies on the turbine controller 10 communicating through the
DCS20 to the sensor
means and the control means listed above to control the operational control
elements of the
turbine. In order to maximize HRSG life in light of other potential
operational priorities, a user
will select operational priorities for HRSG and / or other turbine operation,
selected from the
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group comprising optimum NOx emissions, optimum power output, optimum
combustor
dynamics, optimum HRSO life, and / or optimum fuel blend ratio (ratio of non-
pipeline quality
gas to pipeline quality gas). The below examples will be provided for
instances where the
Optimum HRSG Life 19 is selected in the control panel shown in Fig, 3, such
that Optimum
HRSG Life is an operating priority, potentially in addition to other selected
priorities.
[0076] During
operation, the turbine controller will receive operational data from the gas
turbine sensor means and the HRSG sensor means. The operational data will be
compared to
stored operational standards, based on the selected operational priorities.
Using this comparison,
the turbine controller will determining if both the HRSG and gas turbine
operation conform to
the operational standards,
100771 To the
extent that either the HRSG or gas turbine operational parameters are not
within allowable limits, the tuning controller 10 will determine the dominant
toning criteria for
non-conforming operation of the HRSG and / or the gas turbine, based on the
preset operational
priorities. With the
dominant tuning criteria determined, the turbine controller 10 will
communicate with the selected operational control elements to perform a
selected adjustment in
the operational control element of the gas turbine, The operational control
element may be
combustor fuel distribution split within the nozzles of the combustor, fuel
gas inlet temperature,
fuel/air ratio within the turbine, and / or gas fuel blend ratio (fuel
composition), The adjustment
to the operational control element will be based on the dominant tuning
criteria and have a fixed
incremental value and defined range, each incremental change input over a set
period of time
sufficient for the turbine to gain operational stability,
[0078] The
sensing process will be repeated in open loop fashion, such that the turbine
controller will subsequently receive further data regarding the operational
parameters from the
HRSG and gas turbine sensor means upon passage of a set period of time to
determine if an
additional incremental change is desired. If additional tuning is required,
further incremental
adjustments will be made to the operational control element within a defined
range. To the
extent that the range of available adjustments to a particular control element
are exhausted, the
tuning controller 10 will select a further operational control element
adjustment based on the
dominant tuning criteria, the further selected adjustment having a fixed
incremental value and
defined range, with each incremental adjustment made over a set period of time
sufficient for the
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turbine to gain operational stability. The sensing and adjustment (if needed)
process will be
continued during the operation of the turbine and HRSG,
10079] In one
embodiment, the system can be programed with stored operational data, such
that the mechanical life of an HRSG is optimized in the tuning process by
first adjusting the fuel-
to-air ratio of the gas turbine in increments to change the HRSG hot gas inlet
conditions to
provide sufficient design margin in key HRSG operational parameters (i.e.
lowering or raising
the temperature of the hot gas inlet), The tuning can then continue as may be
required as a result
of these changes made to the turbine's f/a ratio, For example, the HRSG may be
provided with
sensor means for measuring operational parameters of the associated boiler,
including high
pressure and/or hot reheat outlet steam temperatures as well as high pressure
and/or hot reheat
intra-stage desuperheater outlet temperatures and pressures. The gas turbine
having will also
have sensor means for measuring operational parameters of the turbine,
including stack
emissions and combustion dynamics from the turbine and control means for
various operational
elements of the turbine, including fuel distribution and / or fuel temperature
and / or fuel blend
ratio and / or fuel-to-air ratio, Optionally, the tuning controller 10,
Various sensor means and
control means may either be connected directly or via a distributed control
system (DCS), The
control system may also be provided with means for setting operational
priorities for turbine
operation, selected from the group comprising optimum NOx emissions, optimum
power output,
optimum combustor dynamics, optimum fuel blend ratio, and / or optimum HRSG
life, such as
that shown in Fig. 3 discussed above. Using this tuning system, operational
priorities are
selected, operational parameters are sensed and tuning occurs using the
methods discussed herein
with respect to optimizing HRSG life and turbine operation, provided that in
this instance, f/a
ratio is the predetermined first operational control element to be adjusted to
optimize HRSG life,
while other operational control elements may be adjusted in order to keep the
combustion turbine
within the allowable limits for each operational parameter.
[0080] A method
of optimizing the mechanical life of an HRSG through tuning the operation
of a gas turbine, is now disclosed using the systems described herein, The
method first includes
establishing a communication link between the turbine controller 10 and
(optionally) the DCS 20
and receiving data from the HRSG and / or gas turbine sensor means regarding
the status of
various operational parameters of the HRSG and the turbine. The operational
parameter values
are then compared to set of standard data to determine if adjustment to
operational control
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elements is required in order to bring the operation of the turbine or HRSG
into allowable limits,
If tuning is needed, the tuning controller will communicate with the selected
operational control
elements to perform a defined incremental adjustment of the selected control
element. The
system then receives, at the tuning controller, via the sensor means and DCS
operational
parameter data regarding the operation of both the HRSG and the turbine from
the sensor means
and determines if the adjustment conforms turbine operation to a set standard
or if a further
incremental adjustment is desired,
100811 The sensed
data from the HRSG may include steam outlet temperatures and / or steam
superheater intra-stage attemperator over-saturation conditions, The
operational control element
that is adjusted to modify the values of these sensed parameters may be the
fuel-to-air ratio of the
turbine, Once the HRSG values are within allowable limits, if further tuning
is required to bring
the operation of the turbine within its allowable limits, This will be done
according to the tuning
methods described above, preferably without further modification to the f/a
ratio, such that the
operational control elements of fuel gas temperature, fuel splits or fuel
blend ratio,
[0082] The tuning of
the system may be adapted for method for tuning a premixed
combustion system wherein there exists two distinct modes of operation, The
turbine being
tuned (not shown) may have an outer ring of identical fuel nozzles utilizing
an outer nozzle fuel
split to modulate the circumferential fuel distribution within these outer
nozzles, an inner fuel
nozzle which utilizes an inner nozzle fuel split to adjust the fuel-to-air
ratio of the inner to outer
nozzles, The outer an inner nozzles discussed herein are known to those
skilled in the art and not
specifically recounted herein, The two distinct modes of operation comprise a
"lean" inner
nozzle mode whereby the f/a ratio of the inner nozzle is less than the f/a
ratio of the outer fuel
nozzles, and a "rich" inner nozzle whereby the f/a ratio of the inner nozzle
is greater than the f/a
ratio of the outer fuel nozzles. The method for tuning a system having these
distinct modes
comprises selecting, at the tuning controller 10 of a hybrid fuel split
schedule for varying modes
based on the turbine load, The "lean" center nozzle fuel split schedule will
be at higher load
conditions and the "rich" fuel split schedule will be used at lower load and
turndown conditions,
where the turbine is being operated at the lowest level possible in order to
maintain operation of
the HRSG,
100831 The method may
include the steps disclosed above along with making, at the tuning
controller 10, a determination of whether the current mode of operation is
utilizing either a
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"lean" or "rich" inner nozzle mode of operation, and selecting the direction
of adjustment for
Fuel Circuit Split 1 and / or Fuel Circuit Split 2 when a tuning issue exists,
depending on which
mode of operation is being utilized at the current operating conditions and
preset operational
parameters stored within the turbine controller,
10084] All of
the methods provided above can be conducted using Boolean-logic toggle
switches, such as those shown in Fig, 3, to select user-desired optimization
criteria. One of the
optimization criteria is Optimum HRSG Life, whereby toggling of this switch to
a "1" ("TRUE")
allows the tuning controller to improve HRSG mechanical operating margins,
such as steam
outlet temperature and / or steam superheater intra-stage attemperator
saturation temperature
margin, through changes in the HRSG inlet conditions via modifications to the
gas turbine fuel-
to-air ratio, These changes may be made using the methods and systems
disclosed above.
10085] A method
for tuning a premixed combustion system is also provided whereby there
exists an outer ring of fuel nozzles utilizing an outer nozzle fuel split to
modulate the
circumferential fuel distribution within these outer nozzles, utilizing two
modes of operation: a
"lean minor circuit I" subset of the outer nozzles whereby the f/a ratio of
this outer fuel nozzle
subset is less than the f/a ratio of the remaining outer fuel nozzles, and a
"rich minor circuit 1"
inner nozzle whereby the f/a ratio of this outer fuel nozzle subset is greater
than the f/a ratio of
the remaining outer fuel nozzles, The method includes usage of a hybrid fuel
split schedule, with
a "rich minor circuit 1" fuel split schedule at higher load conditions, and
usage to a "lean minor
circuit 1" fuel split schedule at lower load and turndown conditions. The
method may also
include varying other operational control elements, as described herein, in
order to bring the
operation of the turbine or HRSG into allowable limits,
100861 The
method may also include usage of a hybrid fuel split schedule, with a "lean
minor
circuit 1" fuel split schedule at higher load conditions, and usage to a "rich
minor circuit 1" fuel
split schedule at lower load and turndown conditions. Further, the method may
include making a
determination, at the tuning controller 10, if the current mode of operation
is utilizing either a
"lean minor circuit 1" or "rich minor circuit 1" mode of operation, and
adjusting, using
operational control elements for fuel splits, the Fuel Circuit Split 1 and /
or Fuel Circuit Split 2 in
the proper direction, when a tuning issue exists, depending on which mode of
operation is being
utilized at the current operating conditions,
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[0087] A method
is also provided for tuning a premixed combustion system, using similar
systems and steps as described above, whereby there exists one or more annular
rings of fuel
nozzles (of same or different type, controlled by an circumferential fuel
split affecting
circumferential distribution of fuel within each fuel nozzle ring), In the
current system, it is
contemplated that a second family of fuel splits may be available (if more
than one annular ring
of fuel nozzles exists), which adjusts the relative (radial) amount of fuel to
each of the radially
concentric fuel nozzle rings (ring 1, ring 2, etc,), utilizing two modes of
operation: a "lean minor
circuit ring 1" subset of the ring 1 fuel nozzles whereby the f/a ratio of
this ring 1 fuel nozzle
subset is less than the f/a ratio of the remaining fuel nozzles of ring I, and
a "rich minor circuit
ring 1" subset of the ring 1 fuel nozzles whereby the f/a ratio of this outer
fuel nozzle subset is
greater than the f/a ratio of the remaining fuel nozzles of ring 1, The tuning
method comprises ,
use of a hybrid fuel split schedule, with a "lean minor circuit ring 1" fuel
split schedule at higher
load conditions, usage of a "rich minor circuit ring 1" fuel split schedule at
lower load and
turndown conditions, and similar usage of "rich" and "lean" fuel split
schedules, one at high
loads and the other at lower load / turndown conditions, for each of the
remaining fuel nozzle
rings of the combustion system. Each of the fuel schedules may be pre-
programmed into the
tuning controller 10 and selected based on sensed operational parameters of
the system,
[0088] The
method may also be modified, depending on operational priorities and user
input
to the tuning controller 10, to include usage of a hybrid fuel split schedule,
with a "rich minor
circuit ring 1" fuel split schedule at higher load conditions, usage to a
"lean minor circuit ring 1"
fuel split schedule at lower load and turndown conditions, and similar usage
of "rich" and "lean"
fuel split schedules, one at high loads and the other at lower load / turndown
conditions, for each
of the remaining fuel nozzle rings of the combustion system,
[0089] A method
is also provided for tuning a premixed combustion system, such as that
disclosed above, whereby there exists one or more annular rings of fuel
nozzles (of same or
different type, controlled by an circumferential fuel split affecting
circumferential distribution of
fuel within each fuel nozzle ring), whereby a second family of fuel splits may
be available (if
more than one annular ring of fuel nozzles exists) which adjusts the relative
(radial) amount of
fuel to each of the radially concentric fuel nozzle rings (ring 1, ring 2,
etc,), utilizing two modes
of operation: a "lean minor circuit ring 1" subset of the ring 1 fuel nozzles
whereby the f/a ratio
of this ring 1 fuel nozzle subset is less than the f/a ratio of the remaining
fuel nozzles of ring 1,
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and a "rich minor circuit ring 1" subset of the ring 1 fuel nozzles whereby
the f/a ratio of this
outer fuel nozzle subset is greater than the f/a ratio of the remaining fuel
nozzles of ring 1. The
method first comprises the step of determining if the current mode of
operation is utilizing either
a "lean minor circuit ring 1" or "rich minor circuit ring 1" mode of
operation, making a similar
determination of the current mode of operation, either "rich" or "lean" minor
fuel circuit
operation, for each of the remaining fuel nozzle rings of the combustion
system. Once these
determinations are made, the method comprises the step of adjusting, via the
tuning controller 10
and selected operational control element, Fuel Circuit Split 1 and/or Fuel
Circuit Split 2 in the
proper direction, when a tuning issue exists, The direction of adjustment is
determined based on
which mode of operation is being utilized at the current operating conditions.
[0090] Figs, 9-
12 provide exemplary visual representations of the autotuning system interface
depicting how the Boolean Logic Hierarchy works in practice. Fig, 9 shows the
alarms returned
in connection with the example set forth above with respect to Fig. 8. Namely,
alarms are
returned for Class 2 8P's at the levels of H 162, HR 164 and HHH 166, In
addition, alarms for
NOx 168 and Class 1 SF's 170 are returned at the H level, Since more extreme
levels trump
conflicts of different alarms at the same level, the HHH Class 2 OP's is the
priority and therefore
the dominant tuning concern 172.
10091] Figs, 10-
12 show various further examples of the dominant tuning concern for
different "True" alarm levels under the user defined hierarchy 144 of Fig, 8.
Fig, 10 shows high
pressure steam at maximum operating temperature and the high pressure steam
desuperheater at
saturation conditions (placing water into the steam pipe), with no other
alarms active. Thus,
HRSG Mechanical Life Optimization is the dominant tuning concern. Fig, 11
shows a Class
26P's at an H level, with NOx at both an II and HH condition, thus making High
NOx as the
dominant tuning concern, Finally, Fig. 12 shows both Class 1 OP's and Class 2
OP's at the H
level, Referring to the user ranking of dominant tuning issues 144 in Fig, 8,
Class 1 OP's is
ranked as a priority above Class 2 OP's and thus, although the severity of the
alarms is equal,
Class 1 OP's becomes the dominant tuning concern,
[0092] In Figs.
13 ¨16, there is shown various examples of the operational results of a tuning
operation of a tuning controller of the present disclosure based on
operational data from a
running turbine system, In Fig. 13, the dominant tuning concern is high Class
2 OP's, and a
change in the combustor fuel split El is made in reaction to a high Class 2
(SF's alarm generated
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when the combustor dynamics moves outside of the set operational priorities
for optimum
dynamics. The actual combustor dynamics data received by the turbine
controller 10 from, for
example, the CDMS 50 is designated as 200 in the graph. The moving average for
the
combustor dynamics is identified in the graph as 202. When the combustor
dynamics exceed the
dynamics alarm limit value 204 for a set period of time TA an alarm goes off
within the tuning
controller, This alarm causes the first event El and a resulting incremental
adjustment in the
combustor fuel split tuning parameter 206, As illustrated, the incremental
increase in the fuel
split causes a corresponding drop in the combustor dynamics 200, with the
average combustor
dynamics 202 dropping below the dynamics alarm limit 204. As time continues,
the tuning is
held by the tuning controller and the average combustor dynamics 202 maintains
its operational
position below the dynamics limit 204. Thus, no further adjustments necessary
or alarms issued.
[0093] In Fig.
14, the tuning criteria is High NOx emissions, As NOx emissions data 210 is
received from the tuning controller, an alarm is generated after the passage
of time TA. The
alarm is caused by the NOx emissions 210 exceeding the operational standard or
tuning limit
212. The alarm activates a first event El resulting in an incremental increase
in the fuel split
214. After a period of time TB from the first event El, the NOx alarm is still
activated due to the
NOx emissions 210 exceeding the preset tuning limit 212. This continued alarm
after time TB
causes a second event E2 and a second incremental increase in the fuel split
value 214, This
second increase is equal in magnitude to the first incremental increase, The
second event E2
causes the NOx emissions level 210 to drop below the preset limit 212 within
the review time
period and halts the alarm. As the NOx emissions 210 remains below the limit
212, the fuel split
214 tuning is held and the operation of the turbine continues with the defined
operational
parameters,
[0094] In Fig,
15, the tuning criteria is Blowout, with the alarm created by a low NOx
reading
received by tuning controller. As shown, the NOx tuning limit 220 is defined.
Upon passage of
the set time period TA from receiving NOx level data 222, the alarm is
generated and a first
event El occurs. At the first event El, the fuel split level 224 is
incrementally adjusted
downward. After a set passage of time TB from event El additional NOx
emissions data 222 is
received and compared to the preset alarm level 220. Because the NOx is still
below the alarm
level 220, a second event E2 occurs resulting in a further incremental
reduction in the fuel split
value 224. A further passage of time TC from event E2 occurs and additional
data is received,
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Again, the NOx data 222 is low, maintaining the alarm and resulting in a
further event E3, At
event E3, the fuel split value 224 is again reduced by the same incremental
amount, This third
incremental adjustment results in the NOx emissions 222 rising above the
preset limit 220 and
results in removal of the alarm, The fuel split 224 tuning value set after
event E3 is held in place
by the tuning controller 10.
100951 In Fig,
16, the tuning criteria is again Blowout, whereby the NOx emissions data 230
received by the tuning controller 10 is again tracking along the lower
emissions limit 232. At the
first tuning event El, the fuel split value 234 is incrementally dropped to
result in a
corresponding increase in the NOx emissions 230 over the lower limit 232.
After this first
incremental adjustment, the NOx emissions for a period of time holds above the
limit 232 and
then begins to again fall. At the second tuning event E2, the fuel split value
234 is again adjusted
by the designated fixed incremental value, This second adjustment then places
the fuel split
value 234 at its defined minimum within the preset range of allowable values
(determined as a
hard coded limit within the tuning controller 10). Because this limit is
reached, the tuning
operation moves to the next operational parameter, which is normally the
second fuel circuit
adjustment. In the example provided, this second circuit value (not shown) is
already at its set
maximum/minimum and is therefore not adjusted. Thus, the tuning operation
moves on to the
next operational parameter, load control curves 236, As shown, at event E2 an
incremental
adjustment is made in the load control curve value 236. The increase in the
load control curve
value 236 results in a corresponding increase in the NOx emission 230 to a
value above the
minimum 232 and removes the alarm. Upon removal of the alarm, the tuning
settings are held
and no further adjustments are made. The tuning controller 10 then proceeds to
receive data
from the sensor means, through the DCS, and continues to make comparisons with
the set
operational standards (including the minimum NOx emissions limit EL),
[0096] The
present invention has been described and illustrated with respect to a number
of
exemplary embodiments thereof, It should be understood by those skilled in the
art from the
foregoing that various other changes, omissions and additions may be made
therein, without
departing from the spirit and scope of the present invention, with the scope
of the present
invention being described by the foregoing claims.
hils I tueouit).1 29
