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Dear Participants
WELCOMETo a discussion on
FSSS/ Boiler Protection SystemBasic ConceptsandStandards
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CONTENT Basic concept
Function of BMS
Furnace purge procedure
STANDARDS / NFPA
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MainFunctions
Furnace purge before boiler light-up
Oil firing: Permissives, Sequences and Protections
Coal firing: Permissives, Sequences and ProtectionsMaster Fuel Trip (MFT) or Boiler Trip
Post-Trip Purge Fans Trip
Runback: Graded Mill TrippingRunback: Graded Mill Tripping
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SG (Steam Generator)CONTROLS
BACK
BURNER
MANAGEMENT
SYSTEM
BOILERPROTECTIONS
MILLING
SYSTEM
FUEL OILSYSTEM
UNIT PURGE
SEC. AIR DAMPER
CONTROL
SOOT BLOWERCONTROL
AUX. PRDS
CONTROL
HP-BYPASSCONTROL
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Some DefinitionsBoiler Control System:
Deals with Regulating Control
Burner Management System (BMS):
Deals with Furnace Safety and Start/Stop of Fuel
Preparation and Burning Equipment
BMS Logic:Deals with Control System which would give
output based on external inputs and internal logic
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Burner management system
Burner management system is
designed to ensure the execution
of a safe ,orderly operatingsequence in the startup and
shutdown of fuel firing
equipments and to prevent errors
of omission safe operating
procedure.
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Function of BMSTO PROVIDE SAFETY TO BOILER.
TO PROVIDE ORDERLY SEQUENCE IN
THE S/U & S/D OF FUEL FIRING EQUIPMENTS.
PREVENT S/U OF FUEL FIRING EQUIPMENTS
UNLESS CERTAIN PERMISSIVE INTERLOCKSHAVE BEEN SATISFIED.
CONTINUOUS FLAME MONITORING.
FAULT DETECTION AND ASSOCIATE S/D.INITIATE MFT UNDER CERTAIN CONDITION OF
LOAD COMBINATION.
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Basic Concepts of BMS
BMS is an independent and discreet logic systemspecially designed for safety and protection duringstarting , shutdown, low load and emergencyconditions.
BMS system has been designed to provide increasedsafety, reliability, flexibility and over all performance ofthe boiler.
The system is intended to protect against malfunction
of fuel firing equipment and associated systems. In some phases of operation, the BMS shall provide
permissive interlocks only to ensure safe startup ofequipment.
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The Burner Management system monitors the presenceor absence of the forced draft fan running and verifies air
flow is being produced, ensures the water level in theboiler drum is satisfactory, and verifies that there is atleast one flame in the furnace.
The Burner Management alarm system provides for afirst out cause of trip allowing operators to readily
identify the reason for an unexpected boiler tripcondition.
The Burner Management System controls the airregisters, igniters and fuel oil valves for each burner, as
well as monitoring of the flame signals for each burner inservice.
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Function of BMS Controls boiler purge, fuel headers, and burner field devices,
allowing sequential control of the start-up and shutdown of anyburners.
Continuous monitoring of supervisory interlocks, fuel valve positions,flame status and field devices.
The control strategy normally utilize de energize to trip method. Smart alarms provide fail to open, fail to start, fail to close, andfail to stop information.
Flame monitoring equipment provides the logic controller with flamestatus of burners and/or igniters.
Prevent firing unless a satisfactory furnace purge has first been
completed.
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Prohibit start-up of the equipmentunless certain permissive interlockshave first been completed.
Monitor and control the correctcomponent sequencing during start-
up and shut-down of the equipment. Conditionally allow the continued
operation of the equipment onlywhile certain safety interlocksremaining satisfied.
Provide automatic supervision whenthe equipment is in service and
provide means to make a MasterFuel Trip (MFT) should certainunacceptable firing conditions occur.
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SIMPLIFIED BLOCK DIAGRAM OFBURNER MANAGEMENT SYSTEM.
LOCALCONTROL
BOXAIR
DAMPER
B
M
S
FUEL
V/V
FLAMEDETECTOR
IGNITER
ABC
DAS
MILLCONTROL
C.C.R
BOILER
PLANT
IGNITION
CONTROL
PANEL
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BURNER GROUP-EACH STEAM GENERATOR HAS FOUR BURNERGROUPS.EACH GROUP COMPRISES FOUR OIL BURNER WITH
ASSOCIATE PF BURNER LOCATED ABOVE AND BELOW.
MILL GROUP- THERE ARE EIGHT MILL GROUPS PER STEAMGENERATOR EACH GROUP COMPRISES A MILL ,ITS ASSOCIATED
COAL FEEDER AND A SEAL AIR FAN.
AIR DAMPER-
AIR DAMPER ARE DIVIDED AS FOLLOWS-
1-FIVE ELEVATION OF FOUR SECONDARY AIR.
2- 4 ELEVATION OF 4 AIR TO OIL/S.A.D3-8 ELEVATION OF 4 AIR TO P.F. BURNER.
4-TWO ELEVATION OF FOUR OVERFIRE AIR.
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RELATIONSHIP OF MILL GROUP,ELEVATION NUMBERS GROUPNUMBERS.BURNER NOZZLE NOZZLE MILL GROUPGROUP ELEVATION TYPE GROUP
NUMBER NUMBER4 13---------------------------SECONDARY AIR
12---------------------------COAL--------------------------- -F
11---------------------------OIL AND S/A
3 10 --------------------------COAL-----------------------------E9 --------------------------SECONDARY AIR
8---------------------------COAL------------------------------D
2 7-------------------------- OIL AND S/A
6---------------------------COAL------------------------------C
5---------------------------SECONDARY AIR
4---------------------------COAL------------------------------B
1 3---------------------------OIL AND S/A2---------------------------COAL------------------------------A
1-------------------------- SECONDARY AIR
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STANDARDS AND CODES
Prescriptive standards such as NFPA have done well at
identifying what interlocks should be implemented based
upon lessons learned from previous incidents and near
misses.
In todays microprocessor-based world, it is more important
to know how to properly implement the prescriptive based
interlocks.
The logic solver was comprised of relays with simple and
well-defined failure modes, it was very easy to understand
what level of risk reduction the BMS provided.
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NFPA Burner Management Systems (BMS) associated with fired
devices in the power boilers are defined as Safety
Instrumented Systems (SIS) if they contain sensors, a logic
solver and a final control element according to NFPA.
By actively embracing the concept that a BMS may in fact
be a SIS, companies can ensure that these systems are
designed, maintained, inspected and tested per both the
applicable prescriptive standards (API, NFPA, etc.).
A BMS can be designed that meets all requirements of the
prescriptive standards such as NFPA.
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Standard FollowedNational Fire ProtectionAuthority (NFPA) of USA
Code 85 of 2001
This code is an amalgamation of earlier codes 8501 to
8506 applicable for various types of boilers and
combustion
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IBR RequirementsFuel supply should be shut off when:
Flame failure occurs
Failure to ignite fuel within a pre-determinedtime
Abnormal drum level
Trip of Draft fansIncrease in Boiler Pressure
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BMS Logic HardwareNo specific stipulation regarding type of
hardwareNFPA stipulations are not retroactive
Existing system if giving trouble free operation
can continue to work even if not PLC/DCSbased
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Some Requirements ofNFPABurner Management System (BMS) Logic shall:
be such that single failure does not prevent shutdown
evaluate and address failure of components
diagnose improper logic functionshave a direct operable device for MFT which would work
irrespective of BMS logic
be protected from unauthorised logic changes
be provided with independent logic, I/O, power supplyand hardware etc for each boiler separately
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Interesting Insights toNFPANFPA recognises that:It is not possible to encompass all specific
hardware applications
The code should not be considered a cookbook
No standard can guarantee elimination ofFurnace explosion or implosion
Basic cause of Furnace Explosion is ignition ofaccumulated combustibles in the furnace
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