= ∆pCC/pCII x 100% If the relative combustion chamber pressure drop declines below limit PP.BK.01 for more than 5s at speeds above the turbine speed S.TURB.70, the individual alarm “RELA
Trang 1DRAWING/DOCUMENT STATUS FOR REFERENCE
PROJECT :
CAMAU 1 750MW COMBINED CYCLE POWER PLANT
PETRO VIETNAM CPMB
s
DRAWING TITLE :
System Description Combustion Chamber Instrumentation
Ursprung/Original Ursprung-Nr./Original-No Urspr.-PKZ-Nr Orig.-PC
Datum
Date
Name Maßstab
Scale N/A A4 UA/DCC Type XS00
gezeich
Drawn 06-04-10 STEENM Benennung/Title
Inhaltskennzeichen Contents Code bearb
Coord 06-04-10 LIEDTKE
geprüft
Abtlg
Dept P415 sgd
System Description Combustion Chamber Instrumentation
Zähl.-Nr
Reg.-No 355020
Dienstst./Dept UNID Index/Rev Version
Blatt-Nr./Page-No
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Refer also to:
List of Control Settings (SREL) 3.1-0210
List of Measuring Instruments 3.1-0220
P+I Diagram, Gas Turbine 3.1-1010
P+I Diagram, Combustion Chamber 3.1-3010
Settings, limits, and measuring ranges of the items of
equipment referred to here are given in the List of
Measuring Instruments and List of Control Settings (SREL)
This description only gives guideline values
Function
The tasks of the measuring instruments associated with
the combustion chamber system are described in this
Section These measuring instruments are used to detect
the pressure drop across the combustion chamber,
combustion process instabilities (known as humming),
flashback, and flame out
Pressure Drop across the Combustion
Chamber
Wear phenomena can occur during long-term operation
of the gas turbine (for example, increased gaps in the
combustion chamber hot gas casing) As a result of these
wear phenomena, less air reaches the burners This
jeopardizes stable premix combustion
The relative combustion chamber pressure drop can
generally be considered an indication of combustion
chamber cooling air and combustion air flows It is
dependent on the combustion chamber geometry, but in
the upper load range is virtually independent of the
momentary GT output The relative combustion chamber
pressure drop changes as a result of wear or damage to
the burner or combustion chamber parts (changes in
geometry, changes in flow cross-section) Long-term
monitoring of the relative combustion chamber pressure
drop is performed to assess the condition of the
combustion chamber
The differential pressure across the combustion
chamber ∆pCC is measured by differential pressure
transducer MBM10CP101 (cf 3.1-3010) and compressor
outlet pressure pCII (absolute pressure) by pressure
transducer MBA12CP101 (cf 3.1-3010) Signals from
these instruments are used to calculate the relative
combustion chamber pressure drop (in percent):
∆pCC rel. = (∆pCC/pCII) x 100%
If the relative combustion chamber pressure drop
declines below limit PP.BK.01 for more than 5s at speeds
above the turbine speed S.TURB.70, the individual alarm
“RELATIVE COMBUSTION CHAMBER PRESSURE DROP <MIN” is annunciated
Monitoring of Measuring Points
If a positive or negative measuring range violation is detected for measuring point MBA12CP101 or MBM10CP101, the individual alarm “HYBRID BURNER DATA ACQUISITION FAULTED” is annunciated
Flame Monitoring
Fuel must never be fed into the gas turbine combustion chamber for an impermissibly long period without combustion taking place The purpose of flame monitoring
is to determine whether the main fuel is in fact burning in the combustion chamber, i.e., whether a flame is present
On fuel oil startup, the ignition gas flame must not trigger the signal “FLAME ON”
Flame detectors are mounted on the combustion chamber for this purpose, their signals are processed in the respective evaluation units (generation of limits) These limits are used by the downcircuit interlock logic for actuating the fuel shutoff valves
When the gas turbine is started up on fuel oil, ignition gas is briefly used to ignite the fuel oil flames in the combustion chamber Because the ignition gas and natural gas flames have a nearly identical radiant intensity, an evaluation unit with sensitivity set to detect natural gas flames may also be triggered by ignition gas flames to issue a “FLAME ON” signal
In the event that fuel oil flames fail to ignite, it is possible that unburned fuel oil could continue to be carried into the combustion chamber and exhaust section (boiler) beyond the end of the ignition monitoring period
A separate flame monitoring system is therefore provided for each fuel to ensure that fuel oil and natural gas flames are reliably detected
Flame monitoring employs two flame detectors located somewhat offset from one another on the circumference of the combustion chamber Each is mounted tangentially and monitors formation of the respective flames in the combustion chamber A group of about 2 – 4 burners is covered by each flame detector
Each flame detector consists of an optical sensor unit and an optoelectronic converter comprising two photo-sensitive elements These 2-color sensors cover the spectral range from UV to IR For this reason it is possible
to monitor all types of fuel including gas
The intensity of the light emitted by the combustion flames is subject to stochastic scattering (for example caused by non-uniform supply of combustion air or the flow
of fuel) Because of this characteristic of flame radiation,
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the flame sensor distinguishes between uniform light (for
example radiation of the combustion chamber lining) and
light emitted by flames Signals from the uniform light
sources are not registered by the flame detector
The optical sensor unit and the optoelectronic converter
are not housed in a common enclosure The flame signal is
fed from two sensor units via fiberoptic Y-cables to four
optoelectronic converters The optoelectronic converters
convert radiant energy into electric signals that are
forwarded to the evaluation units Two of the evaluation
units are set to the intensity of natural gas flames and two
to the intensity of the fuel oil flames
The following tasks are performed by the evaluation
units:
− Monitoring and evaluation of flame detectors
− Setting the flame identity signals (natural gas and fuel
oil)
− Generation of limits for the signal “FLAME ON”
− Monitoring the function of the evaluation units
The evaluation units are equipped with changeover
contacts and internal relays route the detected flame
signals into the I&C system via the respective
normally-open relay contacts If a flame signal is detected and then
exceeds an adjustable limit, the changeover contacts close
(“FLAME ON”) If the flame signal drops below the
non-adjustable limit, the changeover contacts open (“FLAME
OFF”) The magnitude of the switching hysteresis varies
with the difference between the lower, fixed limit and the
upper, adjustable limit Opening of the changeover
contacts only occurs when violation of the lower limit
persists for longer than one second
Operational Functions
Natural Gas Startup and Operation of the Gas Turbine
on Natural Gas
Natural gas is supplied to the diffusion burners to ignite
the flames Each natural gas diffusion burner is equipped
with two ignition electrodes that are supplied with voltage
for a defined period If the signal “NG FLAME ON” is not
issued by both natural gas flame monitors after the ignition
flame cutout safety delay has elapsed or at any time during
subsequent operation on natural gas, the supply of natural
gas is shut off by trip
Fuel Oil Startup and Operation of the Gas Turbine on
Fuel Oil
Ignition gas (for example, propane) is fed to the natural
gas diffusion burners to ignite the fuel oil If the signal “FO
FLAME ON” is not issued by both fuel oil flame monitors
after the stipulated ignition flame cutout safety delay has
elapsed or at any time during subsequent operation on fuel oil, the supply of fuel is shut off by trip
The fuel oil flame monitors are set such that the ignition gas flames do not cause annunciation of the signal “FO FLAME ON”
Flame Monitor Signals on Fuel Changeover
When a second fuel valve opens (NG ESV OPEN and
FO DM ESV OPEN), all four flame monitors are active Consequently the lower sensitivity of the natural gas flames has priority for the duration of the fuel changeover Trip is triggered if none of the four flame monitors signal “FLAME ON”
Monitoring of Flame Monitors
In the event of conflicting signals from the two flame monitors for a given fuel (fuel oil or natural gas), the alarm
“FLAME MONITORING FAULTED” is annunciated after a delay of K.FLAMM.01 has elapsed The period K.FLAMM.01 must be somewhat longer than the ignition flame cutout safety delay
The non-coincidence monitoring alarm of the fuel oil flame monitors is suppressed during operation on natural gas to prevent response of non-coincidence monitoring of the fuel oil flame monitors in this mode
Monitoring of the Combustion Chamber, Acceleration and Humming
Combustion instability is manifested in gas turbines by increased combustion chamber pressure fluctuation amplitudes, also known as humming, and/or combustion chamber accelerations
High acceleration levels must be promptly detected and suppressed to prevent damage to the gas turbine This is achieved by:
− Changeover to diffusion mode (fuel oil)
− Output reduction
− Triggering of trip
Acceleration is detected using piezoelectric sensors MBM10CY101 to MBM10CY103 mounted on the combustion chamber
To protect the gas turbine, measurement of combustion chamber acceleration is implemented in all machines with tiled annular combustors; in addition, the duration of acceleration is recorded cumulatively Combustion chamber tiles must be inspected if the cumulative durations
of these phenomena exceed certain limits
Limits GW1 to GW4 (acronym based on the German term) are generated from the average of the above-mentioned measurements for acceleration monitoring purposes
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At speeds above S.TURB.70, limits GW1 and GW2 as
well as acceleration monitoring are enabled, however they
are initially suppressed for delay K.BRACC.03
Limit GW1 is suppressed for the time period
K.BRACC.01 during activation and deactivation of
water/emulsion injection when operating on fuel oil GW1 is
not suppressed in the event of water injection system trip,
because this trip can also be caused by measures to
suppress combustion chamber acceleration
Limits GW1 and GW2 are suppressed for the duration
of changeover FO DM ↔ FO PM using a staggered
deactivation delay of K.ACC.06 Analogously time interval
K.ACC.05 is used in the case of changeover from NG DM
↔ NG DM/PM DMO, NG DM/PM DMO ↔ NG PM, and NG
DM ↔ NG PM
On fuel changeover, limits GW1 and GW2 are
suppressed during the time in which either the natural gas
system or the fuel gas system is being shut down
No interlocks are provided for GW3, i.e., it is thus
always active
GW4 is provided for early detection of high acceleration
levels during operation on natural gas near base load
In addition, measuring points MBM12CP107,
MBM12CP110, and MBM12CP115 are provided for
detection of combustion chamber humming and are
connected directly to the analysis system The analysis
system is not part of this system and is therefore not
described in this document
Operation on Natural Gas
If violation of limit GW1 persists for duration K.ACC.01,
output is abruptly reduced by the increment E.LEIST.32 If
violation of this limit persists, output is again reduced
repeatedly and abruptly by the same increment each time
K.BRUMM.05 has elapsed
If violation of limit GW2 persists for duration K.ACC.02,
output is reduced once by increment E.LEIST.33
If violation of limit GW4 persists for duration K.ACC.09,
output is reduced by increment E.LEIST.32
Natural gas system trip is triggered if violation of the
respective limit GW1 or GW2 persists for the time
K.BRUMM.03 and K.ACC.01 (or K.BRUMM.04 and
K.ACC.02) after the onset of the first output reduction
Gas turbine trip is triggered immediately if GW3 is
violated
Operation on Fuel Oil
If violation of limit GW1 persists for duration K.ACC.01, output is abruptly reduced by the increment E.LEIST.32 If violation of this limit persists, output is again reduced repeatedly and abruptly by the same increment each time K.BRUMM.05 has elapsed If violation of this limit persists despite several output reductions, rapid changeover to diffusion mode is initiated after time periods K.BRUMM.09 and K.ACC.01 have elapsed If the gas turbine is being operated with water injection at this time, the water injection system is automatically tripped to prevent extinguishing of the flames
If violation of limit GW2 persists for duration K.ACC.03, output is reduced by increment E.LEIST.33 If violation of this limit continues, rapid changeover to diffusion mode is initiated after time periods K.BRUMM.10 and K.ACC.03 have elapsed If the gas turbine is being operated with water injection at this time, the water injection system is automatically tripped to prevent extinguishing of the flames
If violation of GW2 persists for a further time period of K.BRACC.02, K.BRUMM.10, and K.ACC.03, the fuel oil system trips
Gas turbine trip is triggered immediately if GW3 is violated
Monitoring of Burner Temperature
If fuel quality does not meet the standards stipulated by Siemens (cf specification “Fuel”), gradual coking may occur on the FO diffusion burner nozzles and the baffles of the axial swirler Such gradual coking changes the shape and appearance of the flames, this in turn can cause overheating and ultimately damage to the burners
If fuel oil premix burner supply lines sustain damage, for example formation of cracks at weld beads or even pipe fracture, this also causes formation of flames or overheating in the region of the axial swirler
In the standard design, monitoring is not performed in the operating modes natural gas diffusion, natural gas premix and fuel oil diffusion
Flashback is detected using two thermocouples per burner that monitor burner temperature Temperature is measured at the axial swirler
Differential temperatures are calculated from the mean
of the compressor outlet temperature and the temperatures
at the axial swirlers If at least one differential temperature exceeds TT.BRENNER.M01, the individual alarm
“BURNER TEMPERATURE >MAX” is annunciated
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If a differential temperature exceeds the setting
TT.BRENNER.U01 for a period of at least 1s during
operation in diffusion mode, startup of the premix burners
is blocked and the alarm “PM BLOCKED” is annunciated
This interlock is deactivated when the differential
temperature drops below TT.BRENNER.U01
Burner Temperature Monitoring in Fuel Oil
Premix Mode
If one differential temperature exceeds the setting
TT.BRENNER.U01 during operation in FO PM for a period
of at least one second, rapid changeover from FO PM →
FO DM is initiated and the individual alarms “BURNER
TEMPERATURE MONITORING RESPONSE”, “PM
BLOCKED”, and “BURNER INSPECTION NECESSARY”
are annunciated Changeover back to FO PM is blocked by
an interlock Continued operation of the GT is permissible
in FO diffusion mode as well as NG diffusion or NG premix
mode
Failure of Burner Temperature Monitoring
A pretrip alarm is annunciated if individual temperature
measuring points at the axial swirlers fail This does not
restrict the availability of the machine, however If
acquisition of one axial swirler temperature measurement
sustains a channel fault the individual alarm “BURNER TEMPERATURE MONITORING FAULTED” is annunciated
If both thermocouples of a given burner are defective, the individual alarm “PM BLOCKED” is annunciated If this fault occurs during operation in FO PM, rapid changeover from FO PM → FO DM is initiated The machine cannot be returned to fuel oil premix mode until these channel faults have been rectified
In the event of failure of/faults to one or both compressor thermocouples, a fixed value is used for calculating means instead of the defective measurement (max value selection)
Ignition System
Flames are ignited electrically Each burner is equipped with two ignition electrodes, their tips are located at the outlet of the NG diffusion burner Dedicated ignition transformers (MBM12GT001 to MBM12GT024) supply the voltage required for ignition to the spark electrodes of the respective burners When the ignition voltage is applied, an arc forms between the tips of the two electrodes