1. FOR SUPER CRITICAL BOILERS
ADVANCED C&I SYSTEMS
FOR SUPER CRITICAL BOILERS

2. V.R.Krishnakumar T.R.Rajagopalan P.Rajesh NTPC-SRHQ Operation Services
Presentation By
V.R.Krishnakumar
T.R.Rajagopalan
P.Rajesh
NTPC-SRHQ
Operation Services

3. Present Operational Scenario
Availability Based Tariff implemented
Continuous Availability and Operational Reliability of Units are very crucial and linked to Tariff
Fast response to load changes demanded from Control centre is assuming greater significance

4. AREAS IDENTIFIED FOR IMPROVEMENT in SC BOILERS
Temperature measurement
MS Temperature Control using advanced controllers
Intelligent Soot Blowing Systems
Fire side corrosion monitoring

5. COMMONLY USED TEMP. TRANSDUCERS
Thermocouples
Type J
Type K
Type R
RTDs
PT 100
Cu 53

6. RTDs
A resistor that has a very large temp.coefficient installed in a metal protection sheath
The output of the resistor varies proportionately with temp.
Pt is most commonly used as it has a high melting point
It has a well defined resistance vs temp. relationship

7. THE ISSUES IN STEAM TEMP. MEASUREMENT
Drift in thermocouples over a period of time
RTDs have much better accuracy, but higher cost and poor durability for rugged applications
Performance acceptance test of power plants warrants measurement within a certainty of 0.5ºC at 550 ºC
The temp.gradient over a T/C has a large effect on its performance
3 ºC under estimation of MS temp.at 538 ºC increases heat rate by about 0.1 per cent

8. THE ISSUES IN STEAM TEMP. MEASUREMENT contd..
6 ºC over estimation of MS temp. can reduce life expectancy of boiler tubes by up to 28%
Non-homogeneous T/Cs will give difft. Outputs at difft. immersion depths
To achieve 0.5ºC accuracy it is necessary to calibrate T/C at various insertion depths and use only those which show same output at difft. insertion lengths
PT100s are capable of meeting the accuracy but their life expectancy in the industrial environment is not known

9. STUDIES ON TEMP.SENSORS (1) at PG & E and Duke Power
(2) at South African energy company Eskom

10. RECOMMENDATIONS
Develop a database to keep history records of all calibration data
For Performance tests T/Cs may not be used at least for critical m/m like MS, RH, FW, Bled steam etc.
A project should be initiated to scan international trends in temp.m/m
T/Cs should be calibrated in situ to avoid inhomogeneity effects
There are some internationally reputed suppliers for PT100 RTDs suitable for steam applications

11. STEAM TEMPERATURE CONTROL - ISSUES
Use of conventional PID controllers results in temperature excursions during load fluctuations and takes around 30 minutes to stabilize the temp
This affects the life of critical components in Boiler as well as Turbine
This also affects the heat rate/ economy of generation

12. Main Steam Temp.Control
EPRI study in Mid American’s George Neal Station

13. RECOMMENDATIONS
Use of Advanced controllers such as Multi Variable Controllers / Fuzzy Logic Controllers in steam temp control applications
Optimization/Tuning of important boiler controls may be taken up periodically
SH and RH steam sensors may be checked for proper response on line. T/Cs exhibiting time constants in excess of 30 seconds may be removed and checked

14. PREDICTIVE ADAPTIVE CONTROLLER
The dynamic modeling method is used to represent the process and models the process dead time also
Controller adapts to the changes in gain, time constants and time delay(dead time) happening in the process with MW changes
A custom gain scheduling that would automatically load different sets of PID tuning values depending on MW change

15. BENEFITS COMPARED TO CONVENTIONAL PID
Performance improvement of around 50% i.e. deviations within 6 to 9 ºC from set point compared to 12 to 19 ºC during ramp load changes of 5-10 MW/min

16. SHIFT IN CONTROL PHILOSOPHY FOR SC BOILERS?
Firing control based on metal /steam temperature measurement rather than MW/Load set point
This may result in better match of load and firing especially during ramp load changes

17. FIRE SIDE CORROSION MONITORING
Superheaters and Reheaters can fail due to corrosion by molten alkali sulfates
Higher steam temperatures result in increased susceptibility to this corrosion
On-line electrochemical corrosion monitors developed for low temp.applications can be adopted for monitoring of tube corrosions in SC Boilers
Continuous monitoring is attractive as the trend shows variations with load and coal quality

18. FIRE SIDE CORROSION MONITORING contd..
Local gas velocity and particulate loading also influence corrosion rates
EPRI study results reveal that the corrosion resistance of SS310 (25%Cr) is superior to that of SS316 (18% Cr)

19. INTELLIGENT SOOT BLOWING (ISB)
Conventional Soot Blowing based on a time schedule rather than actual fouling conditions in the boiler
ISB Uses a combination of modeling, neural networks, expert systems and heat flux sensors installed inside furnace
Heat flux sensors serve as a tool to deal with spatial firing differences
ISB based on heat flux sensors has a positive impact on tube life and also helps in better control of Steam temp.

20. THANK YOU ALL