c i for super critical

8/4/2019 C I for Super Critical

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ADVANCED C&I SYSTEMS

FOR SUPER CRITICALBOILERS



Presentation By

V.R.Krishnakumar

T.R.Rajagopalan

P.Rajesh

NTPC-SRHQ

Operation Services



Present Operational Scenario

Availability Based Tariff implemented

Continuous Availability and OperationalReliability of Units are very crucial andlinked to Tariff

Fast response to load changes

demanded from Control centre isassuming greater significance



AREAS IDENTIFIED FORIMPROVEMENT in SC BOILERS

Temperature measurement

MS Temperature Control usingadvanced controllers

Intelligent Soot Blowing Systems

Fire side corrosion monitoring



COMMONLY USED TEMP.TRANSDUCERS

Thermocouples

Type J

Type K

Type R

RTDs

PT 100

Cu 53



RTDs

A resistor that has a very largetemp.coefficient installed in a metal

protection sheathThe output of the resistor variesproportionately with temp.

Pt is most commonly used as it has a

high melting pointIt has a well defined resistance vs temp.relationship



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 ruggedapplications

Performance acceptance test of power plantswarrants measurement within a certainty of

0.5ºC at 550 ºCThe temp.gradient over a T/C has a largeeffect on its performance

3 ºC under estimation of MS temp.at 538 ºC

increases heat rate by about 0.1 per cent



THE ISSUES IN STEAM TEMP.MEASUREMENT contd..

6 ºC over estimation of MS temp. can reducelife 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 tocalibrate T/C at various insertion depths and

use only those which show same output at difft. insertion lengths

PT100s are capable of meeting the accuracybut their life expectancy in the industrialenvironment is not known



STUDIES ON TEMP.SENSORS(1) at PG & E and Duke Power

(2) at South Africanenergy company Eskom



RECOMMENDATIONS

Develop a database to keep history records of all calibration data

For Performance tests T/Cs may not be usedat least for critical m/m like MS, RH, FW, Bledsteam etc.

A project should be initiated to scan

international trends in temp.m/mT/Cs should be calibrated in situ to avoidinhomogeneity effects

There are some internationally reputed

suppliers for PT100 RTDs suitable for steama lications



STEAM TEMPERATURECONTROL - ISSUES

Use of conventional PID controllersresults in temperature excursions

during load fluctuations and takesaround 30 minutes to stabilize the temp

This affects the life of criticalcomponents in Boiler as well as Turbine

This also affects the heat rate/economy of generation



Main Steam Temp.Control

EPRI study in Mid Americans George NealStation



RECOMMENDATIONS

Use of Advanced controllers such as Multi Variable Controllers / Fuzzy Logic Controllers

in steam temp control applicationsOptimization/Tuning of important boilercontrols may be taken up periodically

SH and RH steam sensors may be checked

for proper response on line. T/Cs exhibitingtime constants in excess of 30 seconds maybe removed and checked



PREDICTIVE ADAPTIVECONTROLLER

The dynamic modeling method is used torepresent the process and models the process

dead time alsoController adapts to the changes in gain, timeconstants and time delay(dead time)happening in the process with MW changes

A custom gain scheduling that wouldautomatically load different sets of PID tuningvalues depending on MW change



BENEFITS COMPARED TOCONVENTIONAL PID

Performance improvement of around50% i.e. deviations within 6 to 9 ºC

from set point compared to 12 to 19 ºCduring ramp load changes of 5-10MW/min



SHIFT IN CONTROL

PHILOSOPHY FOR SCBOILERS?

Firing control based on metal /steamtemperature measurement rather thanMW/Load set point

This may result in better match of load

and firing especially during ramp loadchanges



FIRE SIDE CORROSIONMONITORING

Superheaters and Reheaters can fail due tocorrosion by molten alkali sulfates

Higher steam temperatures result inincreased susceptibility to this corrosion

On-line electrochemical corrosion monitorsdeveloped for low temp.applications can be

adopted for monitoring of tube corrosions inSC Boilers

Continuous monitoring is attractive as thetrend shows variations with load and coalquality



FIRE SIDE CORROSIONMONITORING contd..

Local gas velocity and particulateloading also influence corrosion rates

EPRI study results reveal that thecorrosion resistance of SS310 (25%Cr)is superior to that of SS316 (18% Cr)



INTELLIGENT SOOTBLOWING (ISB)

Conventional Soot Blowing based on a timeschedule rather than actual fouling conditionsin the boiler

ISB Uses a combination of modeling, neuralnetworks, expert systems and heat fluxsensors installed inside furnace

Heat flux sensors serve as a tool to deal withspatial firing differences

ISB based on heat flux sensors has a positiveimpact on tube life and also helps in bettercontrol of Steam temp.



THANK YOU ALL

c i for super critical

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