ABB PSPG-E7
SteamTMax
Precise control of main and reheat ST
© ABB Group
May 8, 2014 | Slide 1
© ABB
SteamTMax
Challenge
•
mS
•
matt



© ABB Group
May 8, 2014 | Slide 2
© ABB
Tin
Tout
Live steam and reheated steam temperatures are controlled
process variables critical in steam generation control
They need to be regulated with high precision in order to prevent
unnecessary material stress (thermal stress) in thick-walled
components, especially in steam generators and turbines
Traditionally, the live steam (and reheated steam) temperature
control was done by means of a PI-PI cascade arrangement or
some other simple control structure
SteamTMax solution
ABB’s State Controller with observer
Evaporator
Feed water
control
1st Superheater
Temperature
control
2nd Superheater
Temperature
control
Setpoint Controller
© ABB Group
May 8, 2014 | Slide 3
© ABB
Reheater
Temperature
control
G
SteamTMax
Classic temperature control
Superheater
Attemperator
•
m Sm
Tin
•
m att
-
PI
+ -
M
Tout
+
PI
TSP
Classic PI-PI cascade control:
 The primary controller (master) calculates the required inlet temperature
necessary to obtain the desired outlet temperature
© ABB Group
May 8, 2014 | Slide 4
© ABB

The subordinate controller (slave) regulates the inlet temperature by means
of the spray attemperator

This configuration delivers good performance in superheaters with low-order
and fast transient behavior. However, performance is moderate in
superheaters with wider warm-up span, higher-order behavior and/or
substantial dead time
SteamTMax
Internal structure
Attemperator
•
mS
Tin
T1
T2
T out
T3
T diff
+
–
K1
•
mW
T^ 1
K2
T^ 2
K3
^
T
3
K4
^
T4
Observer
R0
R1
R2
R3
+
T SP
RPI
4,5
M
State Space Controller
© ABB Group
May 8, 2014 | Slide 5
© ABB

Model of the plant: The observer calculates the theoretical internal temperatures
in the superheater, making them available to the controller to be used as interstate variables

Non-linear load-dependent behavior: The “K” and “R” vectors are dynamically
calculated to provide optimum performance at any load operation point

Performance: Thanks to its predictive capability and ultra-fast integration
component, the state controller delivers improved performance without
sacrificing robustness.
SteamTMax
Melody function block
set point and
process variables
plant characteristics
SCO
parameterization
SCO incl. PI-PI-cascade
backup system
controller
configuration
internal control
variables
PI-PI cascade
parameterization
Dynamic parameter calculation
based on pole positioning
(Ackermann)
© ABB Group
May 8, 2014 | Slide 6
© ABB
correcting
variable (Ysp)
binary logic and
feedback values
SteamTMax
Integration and commissioning
Superheater
Attemperator
•
mS
Tin
•
matt
State Space
Controller
with Observer


© ABB Group
May 8, 2014 | Slide 7
© ABB
PI
+

-
PI
+ -
M
Linearization
Tout
TSP
The SCOT is normally implemented parallel to a simpler control:
 In existing systems (e.g. SCOT as optimization solution) it runs parallel to the
existing control structure
 In new implementations or complete control logic replacement (e.g. new
power units or full retrofits) the integrated PI-cascade backup system is used
This simplifies commissioning and avoids disturbances to the process during
controller parameterization and fine tuning procedures
Switch-over between controllers takes place smoothly thanks to the built-in
tracking mode logic
SteamTMax
Integration and commissioning
© ABB Group
May 8, 2014 | Slide 8
© ABB

An accurate identification of the
plant is a key factor to achieve
maximum performance of the
controller

ABB’s plant identification tool
for superheaters is designed to
simplify the identification
process and to deliver high
accurate plant characteristics
SteamTMax
Increased efficiency as a result of higher temperatures
PI-PI-cascade
Tout
State Controller
with Observer (SCOT)
Physical Temperature Limit
DCS max Temperature
Outlet Temperature
∆T Set Point
Temperature SP
Time



© ABB Group
May 8, 2014 | Slide 9
© ABB
Increasing the live steam and reheated steam operation temperature results
in an immediate increment of unit efficiency
With a higher set point, however, the margin between the operation point
and max. admissible temperature is reduced
This is no problem thanks to the improved performance that the state controller delivers
SteamTMax
Benefits
Attemperator

•
mS
Tin
T1
T2
Tout
T3
Tdiff
+
–
K1
•
m
W
Observer
T^1
K2
T^2
K3
^
T
3
K4

^
T
4
-
R0
R1
R2
R3
+
TSP
RPI
4,5
M
State Space Controller


© ABB Group
May 8, 2014 | Slide 10
© ABB
Fatigue of thick-walled components
(especially in the turbine and steam
generator) is greatly reduced
Load change rates can be increased
without risk of exceeding temperatures
limits. As a result, the power unit is better
suited to rapidly respond to load demand
changes
Improved precision (no overshoot) and
speed while correcting temperature
deviations minimizes actuator work and
helps reducing unit oscillations caused by
back coupling with other control loops in
the system
Effective for any superheaters; highly
effective for superheaters with wide warmup span (e.g. >70°K for coal, >100°K for
gas/oil fired power plants) and/or a
significant dead time and slow transient
behavior