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94716008 burner-management-system-et-2008
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94716008 burner-management-system-et-2008



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  • 1. BURNER MANAGEMENT SYSTEM(BMS) The BMS shall be designed to perform the following functions:- 1. Prevent firing unless a satisfactory furnace purge has first been completed. 2. Prohibit start-up of the equipment unless certain permissive interlocks have first been completed. 3. Monitor and control the correct component sequencing (manual or automatic) during start-up and shut-down of the equipment. 4. Conditionally allow the continued operation of the equipment only while certain safety interlocks remaining satisfied. 5. Provide component condition feedback to the operator and, if so equipped, to the plant control systems and/or data loggers. 6. Provide automatic supervision when the equipment is in service and provide means to make a Master Fuel Trip (MFT) should certain unacceptable firing conditions occur. 7. Execute a MFT upon certain adverse unit operating conditions. 8. Because the flue gas path is to be treated the same as a fuel line, the BMS must monitor the status of the valves and associated equipment and include them in the permissives and safety logic. Operation:- Per NFPA 8501, section 2-1.3(b):- a common cause of furnace explosions is “Fuel leakage into an idle furnace and the ignition of the accumulation by a spark or other source of ignition”. Proper attention to the design of the interlocks and trip system to provide a safe light up of the boiler furnace is required. Philosophy used at Vindhyachal St-2, 3 : -energize to open & De- energize to close.
  • 2. Basic components of a BMS/FSSS system:- a) Control & supervision of :- 1) Furnace purge. 2) SAD modulation 3) Light oil ON-OFF. 4) Heavy oil ON-OFF. 5) Tube mill & Raw coal feeder. b) Flame scanner intelligence & checking. c) Overall boiler flame failure protection. d) Boiler trip protection. Furnace Purge:- Before any fuel firing is permitted, either initially or after a boiler trip, a satisfactory furnace purge cycle must be completed. As indicated in NFPA 8501, section 6-2.4.1(i):- the purge shall be “...sufficient for at least eight air changes” of the furnace. Purge Permissives:- 1. All LONV’s & HONV’s closed . 2. LOTV & HOTV closed. 3. All Mills OFF & PA Fans OFF. 4. All scanners show no flame. 5. “No bolier trip condition” exists. 6. All mill outlet gates are closed. 7. Air flow between 30% & 40% of MCR. 8. All Aux air dampers in modulating position. Purge air flow (NFPA 8501, section 6-2.4.1(h): The total furnace airflow shall not be reduced below the purge rate airflow (70% of the maximum continuous airflow capacity). Reducing airflow below these limits will lead to a MFT, and a new furnace purge will be required. Note:-Non-availability of any above during execution of purge cycle of 9mins. will reset the purge counter & purging has to restarted.
  • 3. Selection of Fuel Oil type & permissives: 1. All of the above mentioned. 2. Oil gun is in place in the burner. 3. Oil pressure & temperature is normal 4. Fuel oil atomizing interlocks are satisfied 5. Fuel oil atomizing medium is provided to the burner 6. Oil control valve is in light-off position. Other Conditions: 1. No MFT condition after purge 2. All flame scanners report no flame 3. All air dampers are in light-off position. Start permissive for Oil system(LOTV/HOTV) 1. HORV open 2. All HONV closed & Supply hdr Pr. Adeq. & Temp. adeq. & No MFT. Trip conditions for LOTV/HOTV 1. MFT 2. Any LONV/HONV not closed & LO/ HO hdr pr V.Low (2/3 logic) 3. Atom.air /Steam pr. V.Low(2/3 logic) & no LO/HO elev. in start or stop. 4. HO hdr temp. V.Low & any HONV not closed for >2sec 5. HORV not open(for HO only) 6. Loss of unit critical power(+24VDC) Failure to meet any of these conditions shall prevent the burner light-off operation. Shutdown:- Per NFPA 8501, section 6-2.4.5:- The normal shutdown cycle for the boiler shall accomplish the following in the order listed: (a) Shut off fuel supply to the main burner. (b) Interrupt spark and shut off fuel supply to igniter, if in operation.
  • 4. (c) For oil: 1. Where used, open the recirculating valve. 2. Shut off atomizing medium, if desired. (d) For gas, vent piping between safety shutoff valves to atmosphere. (e) Perform a post purge of the boiler furnace enclosure. (f) Shut down fan, if desired.” Normal Boiler Shutdown A normal shutdown is initiated by operating BOILER SHUTDOWN switch. This will initiate the shut down sequence listed above. Boiler Master Fuel Trip Any of the following conditions shall cause a boiler trip to occur. This results in the shutdown of all fuel and requires another furnace purge cycle before any attempt at re-lighting. 1. Loss of unit 220VDC power for >2sec. 2. Loss of unit critical power(+24VDC) 3. All forced draft fans OFF. 4. All Induced draft fans OFF. 5. Drum water level V.High for >10Sec. 6. Drum water level V.Low for >5Sec. 7. Air flow<30%of MCR. 8. Furnace pressure V.low(2/3 logic). 9. Furnace pressure V.High(2/3 logic). 10. Loss of Reheater protection. 11. Less than fireball & loss of AC in any elevation in service 12. Emergeny PB pressed 13. Loss of all fuel 14. Unit flame failure. 15. Water wall circulation not proper 16. All SRAPH Off. 17. All BFP’s Off for >10Sec.
  • 5. MFT will initiate:- 1. Cut-off fuel.(Close HOTV/LOTV, mills, feeders, mill outlet gates, PA general inlet gates, all HONV/LONV & PA fans.) 2. A feed forward signal to furnace draft control for 30sec. 3. Transfer Aux. air control to manual and open all aux. air dampers. 4. All fuel air dampers are transferred to manual and opened fully. 5. Illuminate the appropriate indicator lights and alarms. 6. Return the system to the pre-purge state Boiler restart will be inhibited until all pre-purge requirements are satisfied. First-out trip system:- 1. The first cause of boiler trip is indicated and cuase of trip memory is set, blocking successive trip commands/reasons. 2. This gets reset only after successful 9 min. purge cycle completion. Post purge excursion protection:- 1. After expiry of 9 mins. of purge cycle 2. If all above purge permissives(except pt. no. 7) & air flow >30% MCR. 3. Furnace press. V.Hi, V.low exits. Then, “Post purge fan trip” command is issued to FD & ID fans. This is reset after opening opening of any HO/LO valve. Alarms:- The following is a list of recommended alarm conditions: 1. Any boiler or burner trip signal 2. High or low water level 3. High furnace pressure 3. Partial Loss of flame (For the typical two scanner system, one indicates “no flame”) 5. Main fuel shutoff valves closed
  • 6. 6. Loss of control system power 7. Unsuccessful burner shutdown Suggested color design: Oil guns sequence:- Pair mode or elevation mode A predefined time of 70 secs given for oil at an elevation to prove. Gap of 15 secs. between commands of two guns in pair. How BMS is implemented:- a) Field devices b) CER / Remote devices c) Human interface Field devices- It includes Mechanical parts: Valves, dampers, power cylinders, pumps, piping/ impulse lines, instrument air, Positioners, E/P converters, AFR, ALR etc Electrical parts: Ignitor(HEA and its excitor), Solenoids, limit switches and associated cables. Electronic parts: Flame scanners, Level / temperature/ pressure switches, transmitters and associated cables. CER / Remote devices: It includes Relays, wiring, sold state devices, power supply source & distribution system(110VAC, 220VDC), power isolation devices(fuses, breakers etc), contactors, control panel, I/O modules, Programmable modules, PLC, Flame scanner remote electronics and other instrumentation required to implement BMS Purge Permissives indicating lights: white Purge Available indicating light: green Purge in progress indicating light: Amber Purge complete indicating light: White MFT reset indicating light: red
  • 7. logics/Philosophy, 24VDC power supply if solid state or Digital control system is used for logic building. Human interface: It includes For conventional UCB- Various selection blocks, On/Off switches, indication lamps, alarm/ annunciation, recorders/ indicators For modern UCB- CRT/LVS based. Operation/ view of BMS devices thru mouse or touch screen. Trend/ bar chart/ mimic / alarm report tells operator about field status. Subloops of BMS:- 1) Unit control panel 2) MFT panel 3) SADC controls 4) Oil gun controls 5) Mill controls(one of each mill) 6) RCF controls 7) Flame scanner electronics panel Logic implementation in BMS panel:- a) Three channels for MFT conditions, with 2/3 logic for final trip command to all slave devices. b) Slave commands to fuel cut-off and start permissives are sent thru two routes( one being hardwired, other one is thru software) c) Modern controls build BMS logics on digital systems(PLC or DCS) and use relays/ contactors for interfacing with field devices. d) Most of the parameters used for BMS have 3 sensors in field for 2/3 voting. e) These sensor status are multiplied in MFT panel for use in three channels(3 x 3) f) Monitoring of protection instruments for discrepancy in their status( only one out of three reports or none of the status for a instrument is available)
  • 8. g) Sequence control for oil gun & mill startup/ shutdown incorporating all protections & interlocks. h) Positioning of Secondary air dampers(Fuel & aux. air) during furnace purge/ shutdown conditions, cut-in of oil / coal and as per BLI(for aux. air in normal operation to maintain proper windbox to furnace DP).