3235-6347-PROJECT

INDEX

SR.NO. PARTICULARS PAGE NO.

1 INTRODUCTION

2

2 SIGNIFICANCE

3

3 OPERATION

4

4 EQUIPMENT

5

5 FURNACE PURGE

7

6 LIGHTING UP WARM UP ELEVATION

10

7 LIGHTING UP HEAVY OIL ELEVATION

16

8 MILL

18

9 FAN CONTROL

25

10 CONTROLS OF WIND BOX DAMPER

26

11 FSSS PROTECTION TO BOILER

27

12 FSSS ANNUNCIATIONS

28

13 CARE OF FSSS

29

INTRODUCTION

Furnace safeguard supervisory system popularly called FSSS

continuously monitors the operations related to fuel admission and some

other vital parameters to ensure safety of the Boiler.

Generally furnace oil or any kind of fuel is susceptible to explosion

hazards. Majority of explosion occurs during start up, shut down and

low load operations. There are many steps that must be followed by the

operator to admit a fuel in to the furnace safely and properly. In high

capacity boilers, where fuel input rate is very high major furnace

explosions can result from the ignition of unburnt fuel accumulated in

the first one or two seconds. Human reaction time to such situations is

inadequate. So there a proper burner management system called as FSSS

is installed in the Boilers. Every operation related to fuel admission is

accomplished through FSSS.

SIGNIFICANS

The furnace explosion occurs due to:

a) Improper purging of the furnace and air.

b) Inadequate ignition procedures.

c) Maintaining fuel supply for too long a period without establishing

combustion.

d) Re-lighting burners too soon after previous flame out.

e) Introduction of main fuel without ensuring adequate ignition

energy.

So furnace burning any and all kinds of fuels is susceptible to

explosion hazards. FSSS helps in achieving basic objectives repeatedly

without error to safe-guard the furnace against hazardous effect by

means of

a) Ensuring certain Safe condition established and proved in the

furnace before light up can proceed.

b) In the case of unstable furnace flame condition, to help the

operator to introduce additional ignition energy.

c) In the event of flame failure fuel supply is immediately cut off and

furnace, air and gas paths purged before any attempt is made to

relight the burners.

OPERATION

Furnace safeguard supervisory system comprises of controls,

indications, logic to carry out following:

1) To start and complete furnace purge when all technological

conditions are fulfilled.

2) To start and monitor igniters.

3) To start warm up or heavy oil guns when permissive condition

exits. The guns are allowed to burn so long as proper

combustion conditions are ensured.

4) To start mills and coal feeders when safe conditions exist.

5) To trip out mills and coal feeders when satisfactory conditions

cease.

6) To trip out all boiler fines when boiler safety is threatened

7) To monitor furnace flame.

8) To start and stop igniter and scanner fans.

9) To indicate auxiliary and fuel air damper close and modulation

indications.

10) To release damper interlocks for secondary air control.

11) To provide boiler trip signal to other equipment such as PA

fans, turbine generator etc.

EQUIPMENT

So, FSSS system is designed to offer a maximum safety, minimum

trips, minimum power consumption and maximum life for the

component used. The logic is functionally divided into unit logic,

elevation logic and corner logic.

Unit Logic: it supervises the overall furnace condition by monitoring all

critical parameters of fuel firing system and also supervises furnace

purge.

Elevation Logic: start up and stopping actions for the elevation are

carried out through this logic.

Corner Logic: it controls and supervises the corner was that is oil

valves, atomizing valves.

FSSS Equipment can be group under three heads:

Operating and indicating console insert on the operators desk: this

consist of all the switches for initiating controls and also indications of

status of all fuel firing equipment and their auxiliaries. The operator is

mainly concerned with this desk only provided other two are functioning

properly.

Relay logic cabinets:

This cabinet consists of relays, timers, circuit breakers for AC,

DC, and control supplies flame scanner. The control the process

logic.

Field Equipment:

Field equipment are those which help in actual operation of fuel

firing equipment and those which provide the status to the operating

consol and relate logic cabinet. Field equipments are trip was valves

on the main oil headers, hydro motor valves on oil lines of individual

corner, oil guns and atomizing medium of oil gun assembly, igniters,

flame scanners, pressure and temperature switches, scanner fans,

igniter fans, mill discharge valves, hot air gate, cold air gate, tram

iron gate, seal air gate etc. the connection form field equipment to

relay logic cabinet is through cables. Connection from operating

console to relay logic cabinet is by cables for easy maintenance.

FURNACE PURGE

Furnace purge is required after a boiler trip out, before relighting

the boiler to expel all unburnt full particles, vapor etc, form the boiler so

that when spark is introduced during light up, possibility of explosion

are avoided.

FSSS ensure a proper furnace purge in following manner:- “Purge

Ready” signal when appear only when following conditions are fulfilled.

110V AC and 220V DC supply to FSSS panel is switch on.

Boiler Drum water level normal.

At least one ID and one FD fan running.

Establish 30% full load air flow as seen in total air flow recorder.

Igniter trip valve closed.

Warm up trip valve closed.

Heavy oil trip valve closed.

All igniter valves closed.

All warm up and oil gun valve closed.

All auxiliary air damper modulating to maintain air flow can

adequate wind box to furnace differential processing?

All coal mills off.

All raw coal feeders off.

All flame scanners show no flame.

All mill hot air gates closed and cold air damper are less than 5

degree open.

No boiler trip command.

When above conditions are met, signal “purge ready” will

disappear, even during purging process. When signal “purge ready”

appears, press button “push to purge after the expiry of purging time

signal “purge complete” appears.

454

LIGHTING UP WARM UP ELEVATION

Now we are ready for Boiler light up.

a) Lighting up warm up elevation AB

Elevation AB has capability to be used for either burning light oil

or heavy oil. So select “light oil” on the consol for AB elevation ensure

warm up oil tips are provided is guns of that particular elevation.

b) I] Igniter trip valve:

Press igniter trip valve “open” push button igniter trip valve oil

open provided the following condition are fulfilled.

Igniter oil supply pressure adequate (more than 12.1 kg/cm2)

All igniter valves closed.


In addition, instrument air supply must be available to actuate trip

valve.

If igniter fan is not started, it will start when first igniter start

Command is given.

II] Opening light oil trip valve:

Light oil trip valve will open if following condition is met:

No boiler trip.

Elevation AB LO valves on guns is closed.

Light oil pressure adequate i.e. they should not less than 1.4

kg/cm2 for more than 25 sec. and light oil trip valve open push button

pressed.

The following figure shows logic diagram for “warm up oil trip

valve control”. Before Boiler light up with Light Diesel oil, LOTV must

be open by giving “open” command from push button switch on the

desk.

Output form “OPEN” push button switch goes to an AND gate.

Other input to this gate are_

1. No Boiler Trip

2. All Corner Valves closed

3. LDO Pressure Adequate

4. LOTV “Close” command not persisting

When all these inputs are TRUE, OPEN command causes AND

gate to give a TRUE output causing LOTV to open.

LOTV closes when

1. Close command through push button switch is initiated OR

2. Boiler trips OR

3. After a delay of 3 second when any warm up oil elevation’s Corner

valve is NOT CLOSE AND

i) If LDO Pressure drops to LOW valve OR

ii) If P between atomizing air and LDO is low.

Dia fig3 455

c) Starting Igniter:

When igniter is started for 1st 10 sec period, oil and atomizing air

are admitted though the valve and simultaneously a spark is applied. The

spark lights up the oil spray and flame is sensed by flame sensor in the

igniter. This happen within 10 secs, the valve is held ‘open’ allowing

igniter to continue.

There are no separate igniter start push buttons, pressuring any one

pair of oil gun start or stop push button will give starting impulse to all

four igniter of that elevation. To start the oil guns press either 1and 3 or

2 and 4 start button. This gives commands for igniter start provided the

following condition is met:

DC power available.


Burner tilt horizontal and air flow less than 40%.

Igniter trip valve open.

L.O. trip valve are open.

Igniter start causes following gives a start command to spark plug.

This command holds for 10 secs by which time if flame is in the igniters.

Now in this way at least three igniters on selected elevations are

proved command is given for selected LO guns to advance and light up

provided:

o Atomizing air valve open

o Warm up oil valve open.

o Corresponding igniter proved.

Under this condition, first one gun will advance, atomizing air will

open the next gun of will undergo similar operation with time log off

25 secs in this at least three guns have to be proved, otherwise oil guns

will trip out. When guns trips , the gun will not retract , it must be

retracted locally immediately to avoid any fire accident.

Warm up guns will trip under following conditions:

Pressing stop push button.

Moving local switch from ‘Remote’ to any other position.

Gun advanced or engaged limit switches are released.

Corresponding igniters trip out.

Air or oil is elevating valve are closed.

Oil valve is not proven to be open within 90seconds.

Any boiler trip command.

At any time when warm up guns are in service, it more than

one igniter is off all warm up guns oil trip.

LIGHTING UP HEAVY OIL ELEVATION

I] Lighting up Heavy Oil Elevation.

Healy oil can be fired on any three elevation AB,CD and EF.

Heavy oil guns are supposed to be self sustaining. Once three oil guns

are tilt, their flow (gun loading in that particular elevation) is more than

30% or Boiler load more than 30% and flame scanners are sensing flame

under these condition light oil can be withdrawn without affecting oil

guns.

II] Now the heavy oil valves open under following condition are met.

Header oil pressure adequate.

All heavy oil hydra motor valve of AB, CD, EF oil guns are

proven closed.


Heavy oil pressure not low less than 1.4 kg/cm2 for more than 2

secs. When valve open signals open appears on the panel.

Starting igniter command oil materialize only when heavy oil is

ready for light up with oil temperature more than 1050C .

Now taking heavy oil guns service in elevation AB.

Gun will advance provided:

Atomizing steam isolating valve open.

Heavy oil manual isolating valve open.

Heavy oil igniter on.

Under this condition oil gun advance.

MILL

FSSS controls the salve starting, running and stopping of mills.

a) Pulverizer Ready for start

This is common to all six mills signal pulverizer ready will appear

when all the following conditions are fulfilled.

Mills outlet temperature is less than 900C.

Seal air valve open.

Cold air gate open.

Feeder inlet gate open,

Pulverizer discharge valve open.

Tramp iron hopper gate open.

No Pulveriser trip command.

Burner tilt horizontal and air flow less than 40% for

subsequent mills, the first R.C. feeder ON. Energizes relay by

passing burner tilt and air flow conditions.

Dia fig 4. 456

b) Ignition permissive :

It is presumed that P.A. fan is running, seal air fan is running, P.A.

header pressure is normal before we can actually start the mill, another

conditions that of providing sufficient ignition energy near the burner

nozzle of the mill has to be ensured so that, once coal flow is established

through mill, the pulverized coal will light up inside the boiler without

any loss of time.

At least three oil guns (Heavy oil or warm up) are in service for the

first mill to be started A or B, C or D, E or F.

For second mill to be start ignition energy is given by either:-

Three oil Guns being in service adjacent to mill or

Boiler load is more than 30%.

Adjacent mill running with RC feeder speed in excess of

5rpm or Pulverizer A or C in service at igniter than 50%

loading.

This ignition energy must be continuously available for three

minutes after starting RC feeder.

Even though the logic permits removal of ignition energy after

three minutes operationally it will be required for even longer period till

boiler flame conditions are stable.

The following figure shows Logic Diagram for Ignition Permissive

for Pulverizer A and B. Similar requirements are applicable for other

Pulverizers:

1) Pulverizer B is running with 50% loading AND Boiler Load is More

than 30% OR

a) Elevation AB in service with 3 out of 4 Guns established.

2) Puloverizer B Ignition Permissive is available if

a) Pulverizer A or C running at 50% loading AND Boiler load is

more than 30% OR

b) Oil Elevation AB in service with 3 out of 4 Guns established.

Dia fig. 457

Actual starting of the mill

If conditions are met and if local key release push button is

released mill can be started by pressing the start push button on console.

As soon as mill starts, cold air damper opens full.

Hot air gate can now be opened provided temperature after mill

still remains less than 900C. If the temperature exceeds 900C, the

white signal ‘ Pulverizier ready’ will disappear but the mill will

continue to run. Pulversier ready can disappear for other reason

also.

However if discharge damper closes mill will trip immediately.

After opening the hot air gate, cold air and hot air damper can be

regulated to achieve an after mill temperature of 600C to750C and

P.A. fan flow about 52 T/hrs. During manipulation of air, take care

load P.A. fan so, that P.A. header pressure does not fall below

650mm.

If the ignition energy continuous to be present after starting mill,

feeder can be started and mill loaded.

As soon as feeder is started, signal given to panel to modulate fuel

air accelerator to speed of feeder. When feeder stops, fuel air

damper is shut. This is to facilitate quick light up of fuel when a

mill is started.

After 50 seconds of feeder starting relay energizes to permit feeder

to be controlled by boiler pressure auto.

PULVERIZER START

When ignition energy available and Pulverizer ready condition are

establish for the respective Pulverizer. The Pulverizer may be place in

service as follows:

a) Start the Pulverizer by pressing start push button

b) When Pulverizer is proven on as indicated by its on indication

or by amp on UCR open, hot air gate and allow pulverize to

come adequate temp (750C) and PA flow of about 52 T/hr with

the help of cold air damper.

c) When Pulverizer is up to temp 1400C start feeder and set at

minimum and associated elevation of fuel air damper proven

close.

Coal flow must be proven either by coal flow detector or

satisfactory Pulverzier amp within 5 secs after feeder started. When

minimum of the two feeders are establish at greater than 50% loading,

associated elevation of oil guns may be shutdown provided feeder has

been on for minimum 3 of 3 minute.

FAN CONTROL

Igniter and scanner fans:

Igniter fan:-

Igniter can be started from control desk otherwise it get set started

automatically when any igniter or oil elevation start is initiate at least

one ID and more than one FD fan must be service for the igniter fan to

start on stopping igniter fan from control desk will remove the

associated igniter fan service provided all of igniter valve are closed.

Scanner Fan Control:-

It can be started from control desk otherwise it get started

automatically when the scanner air duct to differential pressure falls

below 4.5”w.g. low differential pressure more than 10 secs will alarm,

the scanner emergence damper open on interlock when both ID/FD fan

are off, this allows the fan to draw ambient air for the cooling scanner

when unit is bottled up on stopping fan from control desk will remove

the scanner fan from service provided the scanner duct to furnace desk.

Pressure is above 4.5”w.g.

CONTROLS THE WIND BOX DAMPERS

1] Auxiliary Air Dampers:

During furnace purge and when load is less than 30%. FSSS

modulates are auxiliary air dampers to maintain a low wind box

pressure (30mm).

When load increases beyond 30% the modulation is for a higher

wind box pressure (60mm), which is achieve by closing dampers

near elevation not in service.

When warm up oil is in service, the auxiliary air damper of AB

elevation opens to a predetermined position.

When heavy oil is in service, the auxiliary air is allowed to be

controlled by opening depending on oil pressure.

When one FD fan trips, then all auxiliary and fuel air damper open

wide.

2] Fuel air dampers:

All the air dampers are shut on elevations where there are no

feeders in service.

After starting of feeder, the fuel air damper of that elevation

is allowed to be controlled with feeder speed.

FSSS PROTECTS THE BOILER

By tripping out all fuel i/p under the following condition:

Loss of D.C. to FSSS

Furnace pressure inadequate.

Less than fire ball load and loss of A.C. on any elevation in

service.

Drum level high or low.

Flame failure trip.

Both PA fan off.

Low air flow.

In this way FSSS protect the boiler hence it is said to be furnace

safeguard supervisory system.

FSSS ANNUNCIATIONS

F.S.S.S. Provide the following Annunciations/ contacts:

Both ID & FD fans (one pair) off.

Air flow is less than 30% when boiler load is less than 30%.

Scanner fault alarm.

Stand by scanner fan started.

Furnace pressure high/low.

Both P.A. fans off when any pulverizer is ON.

Drum level high/low.

Turbine trip.

Heavy oil Header Pressure low.

Loss of A.C. power.

CARE OF FSSS

To get maximum utilization out of FSSS the following are

recommended:

These notes serve as a guide for boiler operation engineers. Relay

numbers have been given for their understanding only. No repair o

tinkering on FSSS panel is allowed by operation engineers. Relay logic

panel must be handled by only the control maintenance engineers

deputed for the purpose.

All check and repair must be based on engineering drawing.

FSSS panel and console must be kept clean. Periodic vacuum

cleaning or air blowing is advised.

FSSS panel must be kept closed and locked if necessary.

Earth fault relay occur in the panel wiring and relays. Frequent

source or fault lie in the field equipment and connecting with FSSS

must be periodically inspected; leakages eliminated, kept clean and

smooth working should be constantly at relay panel to make good

failures of field equipment.

Gun advance retract mechanisms, limit switches, hydra motor

valve, trip valves pressure, temperature switches etc. require

periodic cleaning, lubrication and other appropriate maintenance.