01 fsss basic concept and std

April 11, 2023 PMI Revision 00 1

Dear Participants

WELCOME

To a discussion on

FSSS/ Boiler Protection SystemBasic Concepts

and Standards


CONTENT

• Basic concept • Function of BMS• Furnace purge procedure• STANDARDS / NFPA


Main Functions

•Furnace purge before boiler light-up

•Oil firing: Permissives, Sequences and Protections

•Coal firing: Permissives, Sequences and Protections

•Master Fuel Trip (MFT) or Boiler Trip

•Post-Trip Purge Fans Trip•Runback: Graded Mill Tripping•Runback: Graded Mill Tripping


SG (Steam Generator) CONTROLS

BACK

• BURNER MANAGEMENT SYSTEM

• BOILER PROTECTIONS

• MILLING SYSTEM

• FUEL OIL SYSTEM

• UNIT PURGE

• SEC. AIR DAMPER CONTROL

• SOOT BLOWER CONTROL

• AUX. PRDS CONTROL

• HP-BYPASS CONTROL


Some Definitions•Boiler 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 operating sequence in the startup and shutdown of fuel firing equipments and to prevent errors of omission safe operating procedure.

April 11, 2023 7

Function of BMS TO 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 INTERLOCKS HAVE BEEN SATISFIED. CONTINUOUS FLAME MONITORING. FAULT DETECTION AND ASSOCIATE S/D. INITIATE MFT UNDER CERTAIN CONDITION OF LOAD COMBINATION.


Basic Concepts of BMS• BMS is an independent and discreet logic system

specially designed for safety and protection during starting , shutdown, low load and emergency conditions.

• BMS system has been designed to provide increased safety, reliability, flexibility and over all performance of the 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 of equipment.


• The Burner Management system monitors the presence or absence of the forced draft fan running and verifies air flow is being produced, ensures the water level in the boiler drum is satisfactory, and verifies that there is at least one flame in the furnace.

• The Burner Management alarm system provides for a “first out” cause of trip allowing operators to readily identify the reason for an unexpected boiler trip condition.

• The Burner Management System controls the air registers, igniters and fuel oil valves for each burner, as well as monitoring of the flame signals for each burner in service.


• If the flame quality degrades to 60% of maximum signal strength a poor flame alarm is issued to the alarm system. When a flame quality signal is below 40% for 4 seconds the burner will trip.

• The Burner Management System lights off the initial burner and cuts out burners automatically based on an operator selected sequence.

• It determines when burners need to be cutout based on the steam pressure signal from the ACC (Automatic Combustion Control) system.

• It also provides an interface to the ACC system to tell it when there is a state of change that can affect how the ACC will respond or perform.


Function of BMS

• Controls boiler purge, fuel headers, and burner field devices, allowing sequential control of the start-up and shutdown of any burners.

• 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,” and

“fail to stop” information.• Flame monitoring equipment provides the logic controller with flame

status of burners and/or igniters. • Prevent firing unless a satisfactory furnace purge has first been

completed.


• Prohibit start-up of the equipment unless certain permissive interlocks have first been completed.

• Monitor and control the correct component sequencing during start-up and shut-down of the equipment.

• Conditionally allow the continued operation of the equipment only while certain safety interlocks remaining satisfied.

• 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.

April 11, 2023 13

SIMPLIFIED BLOCK DIAGRAM OF

BURNER MANAGEMENT SYSTEM.

LOCAL CONTROL

BOX AIR DAMPER

BMS

FUELV/V

FLAMEDETECTOR

IGNITER

ABC

DAS

MILLCONTROL

C.C.R

BOILER PLANT

IGNITION CONTROL

PANEL

April 11, 2023 14

BURNER GROUP-EACH STEAM GENERATOR HAS FOUR BURNER GROUPS.EACH GROUP COMPRISES FOUR OIL BURNER WITH ASSOCIATE PF BURNER LOCATED ABOVE AND BELOW.

MILL GROUP- THERE ARE EIGHT MILL GROUPS PER STEAM GENERATOR 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.D

3-8 ELEVATION OF 4 AIR TO P.F. BURNER.

4-TWO ELEVATION OF FOUR OVERFIRE AIR.

April 11, 2023 15

RELATIONSHIP OF MILL GROUP, ELEVATION NUMBERS & GROUP

NUMBERS.BURNER NOZZLE NOZZLE MILL GROUP

GROUP ELEVATION TYPE GROUP

NUMBER NUMBER 4 13---------------------------SECONDARY AIR

12---------------------------COAL--------------------------- -F

11---------------------------OIL AND S/A

3 10 --------------------------COAL-----------------------------E

9 --------------------------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/A

2---------------------------COAL------------------------------A

1-------------------------- SECONDARY AIR


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 today’s 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.


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.


Standard Followed

National Fire Protection Authority (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


IBR Requirements

Fuel supply should be shut off when:Flame failure occursFailure to ignite fuel within a pre-determined

timeAbnormal drum levelTrip of Draft fansIncrease in Boiler Pressure


BMS Logic Hardware

No specific stipulation regarding type of hardware

NFPA stipulations are not retroactiveExisting system if giving trouble free operation

can continue to work even if not PLC/DCS based


Some Requirements of NFPA

Burner Management System (BMS) Logic shall:be such that single failure does not prevent shutdownevaluate and address failure of componentsdiagnose improper logic functionshave a direct operable device for MFT which would work

irrespective of BMS logicbe protected from unauthorised logic changesbe provided with independent logic, I/O, power supply

and hardware etc for each boiler separately


Interesting Insights to NFPA

NFPA recognises that:It is not possible to encompass all specific

hardware applicationsThe code should not be considered a “cook

book”No standard can guarantee elimination of

Furnace explosion or implosionBasic cause of Furnace Explosion is ignition of

accumulated combustibles in the furnace

01 fsss basic concept and std

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