There has been a significant increase in the application of
advanced control strategies in the power industry. This session presents recent
results in applying several of these strategies, including predictive control,
robust H-infinity control, and neuro-fuzzy control to various power plant
subsystems. Integrative efforts in overall power plant control and optimization
will be presented, as well.
P013-“Dynamic NOx/Heat Rate
Optimization”
Don Labbe, Bill
Hocking, Invensys
Entergy White Bluff Units 1 & 2 are split furnace 850 MW PRB
coal fired drum units constructed in the early 80’s. The plants were recently
retrofitted with a modern DCS and achieved significant control and ramp rate
improvement. Entergy desired to further improve unit heat rate and lower NOx
emissions while maintaining or enhancing ramp rate capability. This required a
dynamic optimization approach that addressed unit limitations such as O2 and
steam temperature control during unit ramping, coal mill changes and soot
blowing. A dynamic optimization system combining Model Predictive Control and
Neural Nets operating at high execution rates was integrated with the DCS. The
system provides tighter regulation of the critical ramping variables thus
allowing the reduction of “operator margin” for heat rate improvements of
greater than ½% and NOx reductions of greater than 20%. Through the dynamic
multi variable control structure these improvements are maintained during
dispatch operation, which is nearly continuous for these units. The system provides
the added benefit of lower peak steam temperatures while raising the average
steam temperatures, thus enhancing ramp rate capability while improving heat
rate.
P050-"Advanced Control of Drum
Level and Bypass Pressure on a Combined Cycle Heat Recovery Steam
Generator"
John Sorge,
Southern Company, Pascale Bendotti, EdF, Joe Baas, Alabama Power Company, and
Cyrus Taft, EPRI I&C Center.
Many
combined-cycle power plants are changing from base load operation to daily
cycling operation due to the sharp increase in natural gas prices. Daily cycling requires that the plant control
systems perform well during all phases of the operating regime from startup to
full load. Although conventional control
techniques based on proportional-integral-derivative (PID) controllers have
performed adequately over the years, advanced multivariable control techniques
offer the possibility of better control system performance. This paper reports on an advanced control
demonstration project on a combined cycle heat recovery steam generator
(HRSG). The application is the
intermediate pressure (IP) drum level control and the IP steam bypass pressure
control. The plant control system is an
Emerson Ovation distributed control system and the advanced controller is
implemented in an Ovation workstation as a C program. A previous paper described the application
selection and the plant model identification process. In this paper the focus is on the H infinity
controller design, implementation and testing on a development system. Plant test results are expected to be
included.
P026 - Robust Hybrid Control Strategy
for the Boiler/Turbine Unit Full Operating Range in a Coal-Fired Power Plant”
Kai Zheng,
Joseph Bentsman,
Multi-input-multi-output
(MIMO) robust controllers recently designed for the megawatt output/throttle
pressure control in a coal-fired power plant boiler/turbine unit have
demonstrated performance and robustness noticeably superior to that of the
currently employed nonlinear PID-based controller. These controllers, however,
have been designed only for the range of 150-185 MW around the 185 MW nominal
operating point, exhibiting a significant loss of performance in the lower range
of 120-150 MW. Through system identification, the reason for the latter
performance drop has been found in the current work to be a noticeable dependence
of the boiler/turbine unit steady state gains on the operating point. This
dependence induces significant modeling uncertainty that degrades system
performance. This problem is addressed in the present work via two control
strategies. The first one employs the single robust controller based on the
middle (150MW) operating point in place of the 185 MW one. This effectively
reduces the modeling uncertainty over the entire range to approximately 50% of
that associated with the previous design.
The second one uses hybrid controller synthesized through partitioning
the full operating range into two sub-ranges and designing a robust controller
for each of them. This permits attainment of the desired overall performance,
while further reducing the modeling uncertainty to approximately 25% of that
associated with the previous designs. Fast, smooth, and reliable switching
between two controllers, as dictated by the setpoint change, is performed by a
recently developed robust bumpless transfer algorithm. The single controller strategy
features simplicity and ease of use, while the hybrid controller approach
provides better robustness in face of uncertainty due to plant aging, soot
deposits, etc. As demonstrated by simulation results, each strategy provides an
adequate solution to the problem of robust control of a boiler/turbine unit over
the full operating range.
P051-“A New Advanced Coordinated Controller
for Boiler and Turbine of Coal Fired Power Plant”
Luc Deprugney; A. Girard, S. Maurin, Electricite DeFrance
Research & Development and H. Jestin, Electricite De France Cordemais Plant
Cordemais
Power Plant/Unit 5 is a 600MW once-through coal-fired plant. Designed to
operate at base load, the boiler is very sensitive to load transients.
Particularly, non linear rises in waterwall temperatures are frequently
observed at the bottom of the boiler even during slow load drops. This is the
main reason why the existing controller that coordinates the boiler and the
turbine aims at protecting the boiler to the detriment of turbine performance
(this control strategy is generally called turbine-following strategy). As a
consequence, the plant does not provide ancillary services to the grid.
From a fleet
optimization point of view, this inability strongly penalizes EDF. Therefore,
EDF started up a project in order to allow Cordemais 5 to provide ancillary
services, in spite of its boiler sensitivity.
The first
stage of the project consisted in retuning the existing controller. However,
the results of this optimization were not satisfactory at all. Indeed, the
boiler-turbine system is a very complex non-linear and multivariable process
that is not easy to control with PID-based controllers. As a result, EDF
decided to develop and implement a new advanced controller (NAC).
The NAC
could not be implemented in the existing DCS (MicroZ – YOKOGAWA), for it is
essentially matrix-based. As a consequence, it was implemented in an industrial
PC dedicated to the NAC. The operators can switch from the existing controller
to the NAC thanks to a bumpless transfer system that was developed.
This
document describes the stages that led to the implementation of the NAC at Cordemais
5.
The first
part deals with the principles of the NAC and presents simulation results:
·
Limitations
of the turbine following strategy at Cordemais 5
·
Innovative
principles of the NAC – How to cope with boiler sensitivity.
·
Process
modeling.
·
Comparison
between existing controller and NAC in simulation.
The second
part sums up the principles of the interconnection between MicroZ and the
industrial PC.
The final
part shows the results obtained on-site with the NAC, and details the economic
benefits achieved. Cordemais 5 now has an ancillary services mode, which is
compatible with a safe operation of the process (in particular regarding boiler
sensitivity).
P023-”Intelligent Sootblowing (ISB)
in the Coal Fueled Electric Power Industry – EPRI Perspective”
Jeff
Stallings, Rabon Johnson, EPRI I&C Center
As the Electric Power continues to evolve, power producers are
driven toward improved production while striving to meet changing EPA
requirements. Meeting these requirements
has in most cases prompted plants to equip their units with SCR’s, FGD systems
and simultaneously deploy advanced technology to maximize production. Intelligent Sootblowing, one of those
technologies, is the process of controlling sootblowers to operate only when
and where needed. ISB includes use of
water in the furnace to control fouling and slagging from burning today’s
fuels. EPRI is promoting and
collaborating on ISB projects with various power producers and over the past
several years tested and demonstrated ISB technology. This paper discusses lessons learned and
benefits realized from those projects.
The paper presents a brief history of sootblowing technology, discusses
various ISB technologies in use today, and the benefits and savings documented
in the various ISB projects. The paper
also includes a projection of where EPRI expects the technology to be deployed
and integrated in plants in the future.
P021-“Optimization Systems-‘Out of
Control?’”
Jeff Williams,
Emerson Process Controls Inc, Power & Water Solutions.
A western US Utility utilizing
The facility has four units; this unit recently upgraded the
control and instrumentation with a modern distributed control system (DCS) for
the integrated automation of boiler control, burner management (BMS), feed pump
turbine control (BFPT), data acquisition functions (DAS), wet scrubber control
(FGD), steam turbine control, motor and pump start/stop , and balance of plant
functions. The steam generator is CE / Alstom design with six levels of burners
arranged in the T-fired configuration. This unit was commissioned in 1976 and
has a 520 MW GE turbine generator. Unit 3 would be the first of a fleet wide
initiative to deploy software optimization to improve environmental levels of
NOx while maintaining heat rate.