Boiler Emergency Control Procedure

8/12/2019 Boiler Emergency Control Procedure

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INTRODUCTION

BOILER EMERGENCY CONTROL PROCEDURE

Objective of the emergency control

i) Maintain equipment in maximum state of reliability.

ii) Minimize personnel casualties and secondary damage to vital machinery.

Three steps in emergency operations

i) Minimization of equipment damage.

ii) Restoring bac the equipment in service.

iii) !arrying out the necessary repairs.

BOILER EMERGENCIES

i) "oiler trip out #M$T).

ii) %isturbance in boiler drum &ater level.

iii) 'ater pumps failure.

iv) (igh &ater level

v) !arry over.vi) Reheater protection upon loss of load

vii) Minor tube leaage.

viii) Major tube burst.

ix) $.%. fan failures.

x) .%. fan troubles.

xi) $urnace explosion.

xii) (igh furnace pressure.

IMPORTANT BOILER SAFETIES

) Master $uel trip #M$T).

ii) *artial fuel trip.

iii) *urge.


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BOILER TRIP

+ boiler trip command #M$T) stops all fuel inputs by tripping

+ll of the pulverizer

+ll feeders

+ll oil guns

+ll ignitor

!loses the ignitor, light oil and heavy trip valves

+ boiler trip command #M$T) is initiated by any of the follo&ing conditions being present.

-oss of unit %.!. po&er #for more than sec)

-oss of +.!. po&er at any elevation #for more than sec) in service / no feeder established.

-o& drum &ater level.

(igh drum &ater level

"oth $.%. fans are off

"oth .%. fans are off

0nit air flo& is less than 12 3 of full load air flo& before boiler loading has been above 12 3

-o& furnace pressure.

(igh furnace pressure

Turbine trip

-oss of all fuel

0nit flame failure #trip)

Manual trip

"oth the trip push buttons on the control console depressed.

Loss of fuel

Trip circuit becomes on once a minimum of three of the four igniters at any elevation are proved

on.

Once the trip circuit is on, loss of fuel trip &ill occur if 4

+ll feeders are off

+nd


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5ither the igniter trip valve is not open or more than one of the four igniter valves are not

open at any elevations

+nd

5ither the heavy oil trip valve is not open or more than one of the four heavy oil nozzle

valves are not open at all elevations +", !% and 5$

+nd

5ither the light oil trip valve is not open or more than one of the four heavy oil

nozzle valves are not open at all elevations +",

+nd

0nit +! po&er is not available

Unit flame failure

%uring light up and until any main fuel either coal or heavy oil is in service at a fire ball

condition, the optical flame scanner do not tae part in overall flame failure protection system

unit flame failure signal is initiated &hen there is no fireball conditions at all elevations

and either any feeder is on or any heavy oil nozzle valve is not closed at any elevation # +" or

5$ ) &here less than three of the four associated igniters are proven O6

5levation no fireball condition

-oss of +! po&er failure for more than sec

6earest oil elevation less than1 no nozzle valves, oil guns and igniter are proven

5levation7s both coal feeders are off

Trip valve operation

Trip valve is to cut off oil supply to furnace in M$T condition

*ermissive to open trip valves

+ll the igniter valves are proven closed

gniter oil supply pressure is adequate

"oiler trip circuit is reset

The trip valve closed automatically

On boiler trip #M$T) conditions


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gniter oil pressure going lo& &hen any of the gniter valve is open for more than

t&o seconds

light oil trip valve permissive for opening


+ll &arm8up oil nozzle valves are closed

'arm up fuel supply pressure is adequate

light oil trip valve Tripping conditions

"oiler trip out conditions

'arm up fuel pressure is lo& for more than sec, any &arm up oil nozzle valve is

not closed

'arm up air to oil differential pressure is lo& for more than sec

(eavy oil trip valve permissive for opening


+ll (eavy oil nozzle valves are closed

(eavy fuel supply pressure is adequate

light oil trip valve Tripping conditions

"oiler trip out conditions

(eavy fuel pressure is lo& for more than sec &hen either recirculation valve is

closed or any (eavy oil nozzle valve is not closed

9team to (eavy oil differential pressure is lo& for more than sec

arious !oiler "ontrol s#stem

-ight oil pressure control

(eavy oil pressure control

(eavy oil temperature control

*ulveriser temperature control

*ulveriser air flo& control

!ombustion control

*rimary air pressure control

Total air flo& control


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+uxiliary air damper control

$uel air damper control

(eavy oil 4 'arm up oil damper control

$urnace draft control.

superheater steam temperature control

Reheater steam temperature control

+uxiliary *R%9 pressure control

+uxiliary *R%9 temperature control

%rum level control

!"% expander level control

BOILER INTERLOC$ SYSTEM

Control % Interlo"& for Air 'eater

6o interloc provided can be started from local:M!!:remote independently

Tri((in) interlo"&

On motor protections

"earing temperature ; .>. Common O(erational Pro!lems of Boiler % Au+iliaries?

Fre,uent tri(s on flame failure


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>. !hec for proper combustion

. !hec for correct total air flo&

1. !hec for correct coal air ratio

@. !hec for correct &ind box to furnace %*

A. !hec for proper functioning of 9+%!

B. !hec for healthiness of flame scanners

. !hec for correct total air flo&

. !hec for correct burner tilt position

1. !hec for correct feed &ater temperature at 5conomiser inlet

@. !hec for slagging:scaling #external) on &ater &all, 9( / R( tubes

A. Operate &all blo&ers:-R9" at regular interval as per requirement

B. !hec for inside scaling in &ater &alls / 9(:R( tubes

. Maintain stable combustion

. 9tudy R( protection logic

1. nitially eep (*:-* "ypass valves on manual mode. +fter stable

combustion and sufficient flo& only they should be put on +uto

@. !hec for proper functioning of these valves on Manual and +uto7

A. !hec protection closing circuit for any malfunctioning

B. Maintain correct (* "ypass do&nstream temperature


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Tri((in) of Unit on /i)/-lo. 1rum le2el 0

>. !hec for sudden opening:leaage of &ater&all:economiser tube

. !hec for tripping of any one of running "$*s

1. !hec for malfunctioning of drum level auto control

@. !hec for closure of any valve in feed &ater circuit

A. !hec for opening of (* "ypass valve on fast opening mode.

B. !hec for sudden thro& off:raising of load

. +void sudden stress to boiler tubes

. Maintain rate of pressurisation:de8pressurisation as recommended during

hydraulic test of boiler

1. Maintain rate of rise:drop of temperature as recommended during start8

up:shut do&n #follo& start up curve)

@. Monitor drum:9(:R( metal temperatures during start up:shut do&n

A. %O67T T+E5 M--9 6TO 95R=!5 06-599 $-O' 9

59T+"-9(5% T(RO0F( R5(5+T5R

B. Maintain proper &ater chemistry regime as per recommendations.


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3*3*4* Boiler 1rum (ressure 1ro((in) su11enl# 0

>. !hec for interruption of coal to the furnace due to choing in the burner

. !hec for tripping of feeder:mill

1. !hec for disturbed combustion inside furnace

@. !hec for any boiler tube leaage

A. !hec for opening of boiler drains, vent, safety valves

B. !hec for choing in mills:drop in air flo& through mill


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C. !hec for proper +ir distribution and functioning 9+%!

D. !hec for leaages through peep holes, manholes, seal &ater trough etc.

>2. !hec for tube failures.

>.>.>


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3*6*3*3* Su(er/eater-Re/eater-E"onomiser-Tu!e failure 0

>. !hec for indications for overheating of the failed tubes and the nearby

tubes

. !hec for failure of &eld joint

1. !hec the tube thicness of the failed tube and the nearby tubes

@. !hec the healthiness of nearby long retractable soot blo&er for steam

passing

A. !hec for possibility of choing:loss of adequate flo& through the tubes

B. !hec for foreign materials:obstructions in the connected headers


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the boiler design to prevent the follo&ing safety hazards.

G 5quipment must be designed to protect against electrical shoc from

exposure to control po&er.

G "oiler control must assure a sufficient quantity and duration of pre8purge

airflo& through the boiler prior to ignition to prevent boiler explosions.

G "oiler control must assure a sufficient quantity and duration of post8purge

airflo& through the boiler during shutdo&n to prevent boiler explosions.

G "oiler control must assure a sufficient quantity of combustion air and

prevent excessive fuel during boiler operation to prevent boiler explosions.

G "oiler control must limit the number of retries &hen igniting the boiler pilot.

The industry standard is to allo& three attempts at achieving pilot ignition

prior to necessitating a boiler purge cycle.


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CONTROL LOOPS0

GENERAL* *rovide controls in accordance &ith applicable codes.

CONTROL LOOP TYPES* + single control loop includes a controlled

variable sensor, controlled variable transmitter, controller, automatic8manual control

station, and final control element. !ontrol loops used for boilers may be of the

pressure, temperature, liquid level type, or flo& type.

Pressure* *ressure control loops may be used for the control of boiler

pressure or fuel oil pressure. $or the control of boiler pressure, the final control element

regulates fuel flo& to the boiler in response to boiler drum steam pressure. $or the

control of fuel oil pressure, the final control element is usually a pressure reducing

control valve that regulates in response to do&nstream pressure.

Tem(erature* Temperature control loops may be used for the control of

steam temperature from boilers or fuel oil temperature from fuel oil heaters.

Le2el* -iquid level control loops may be used for the control of boiler drum

&ater level.

Flo.* $lo& control loops may be used for the control of fuel flo& into the

boiler burners, burner draft airflo&, feed &ater into a boiler, or steam flo& out of a boiler.

AIR TO FUEL7RATIO* $urnish controls to automatically provide the proper

fuel to air ratio over the entire boiler operating range from maximum turndo&n to

Maximum !ontinuous Rating #M!R). *rovide cross8limited #lead8lag) controls bet&een

air and fuel to increase airflo& before increasing fuel flo& and to decrease fuel flo&

before decreasing airflo&.

!onsider full metering controls, &hich measure directly both airflo& and fuel

flo&, for all boilers &ith capacities greater than A.C gigajoule:h #A,222,222 "tu:h).

!onsider an oxygen analyzer, for trim only, for all boilers &ith capacities greater than


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A.1 gigajoule:h #@,222,222 "tu:h). !onsider !O trim for all boilers &ith capacities

greater than A.


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T/ree

n this control, $eed $lo& transmitter measures feed flo& and its output is connected tothe computing relay to &hich is connected steam flo& signal. %ifference bet&een steam flo&

and feed flo& is then fed to drum -evel control, to &hich drum level signal is also connected.

9ince actual measurement of feed flo& is carried out, this control circuit gives very stable and

high quality performance.

%rum level control circuits used in *o&er *lants no& a days control the feed flo& by

varying the $eed *ump scoop instead of $eed !ontrol valve on loads above 123

INDIIDUAL ITEM RE8UIREMENTS

Controllers* "oilers use three types of controllers. These are digital #e.g.

microprocessor or computer based), analog, and pneumatic. 0se the follo&ing

guidelines in selecting the type of controller to be used?

G 0se the type of controller that is the most economical and reliable.


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G $or plants &ith many control loops use digital type of controllers.

G $or the expansion of existing controls &ithin a plant use the existing

technology. This may be either digital, analog electronic, or pneumatic

controllers.

G 0se pneumatic controllers in hazardous areas.

G +void use of pneumatic controllers in the control room.

G 'hen using digital control avoid depending on a single or a fe& control

devices for the entire plant &ithout having a bacup. + redundant

controller might not be required if only a single controller controls one loop.

(o&ever, if a single controller controls a large number of loops then

provide redundancy so that if the controller fails another controller &ill

automatically tae over.

Pro"ess Controllers* *rocess controllers use one or several of the follo&ing

control modes?

G On8off

G *roportional

G ntegral #also called reset)

G %erivative #also called rate)

Most digital controllers have all of the above control modes included. They

are also usually provided &ith anti8reset &indup. +nalog and p neumatic controllers

often do not include all three control modes or anti8reset &indup.

Control Mo1es* n general, use the follo&ing control modes for the indicated

control loop.

G $lo& 88 0se proportional plus integral.

G -evel 88 0se proportional plus integral.

G *ressure and Temperature 88 0se proportional plus integral. 0se

proportional plus integral plus rate &hen the application requires a quic

response time


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De1i"ate1 Alarms* *rovide a separate &indo& that includes all dedicated

alarms associated &ith an area. Typical dedicated alarms are summarized in Table B8.

Flame Dete"tors* *rovide the flame detector best suited for the fue l and

flame. $or gas fired boilers al&ays use an ultraviolet #0=) self8checing flame scanner.

%o not use a flame detector that is activated by hot refractory.

*rovide a separate flame detector for each burner. -ocate the flame detector

so that it &ill be activated only by its o&n burner and not by an adjacent burner or hot

refractory.

RECOMMENDED BOILER INSTRUMENTATION

BOILER CONTROL PANEL INDICATORS9 RECORDERS AND

TOTALI:ERS*

The instrumentation in Table B8> represents the minimum

recommended requirements for a boiler plant. This instrumentation selection is based

primarily on boiler operation safety concerns. Refer to 6$*+ CA2, Standard for the

Prevention of Furnace Explosions/mplosions in !ultiple Burner Boilers for further

instrumentation concerns for boiler plants in the >1.>C gigajoule:h #>,A22,222 "tu:h) or

above range and +9M5 !9%8>, Controls and Safety Devices for Automatically Fired

Boilers for boiler plants belo& >1.>C gigajoule:h #>,A22,222 "tu:h). The indicators and

recorders can be either dedicated or shared devices. Totalizers must be dedicated

devices. 9hared device selection may be either by means of pushbuttons, a selector

s&itch, or by entering commands on a eyboard. *rovide the follo&ing in the display of

information associated &ith a shared device.

G 6ame of process variable

G nstrument number

G 0nits

G *rocess variable value

9tore the process data in a storage device such as a computer dis or tape if

a dedicated recorder or totalizer is not provided. -abel the computer dis or tape as to

process variable, instrument number, date, time, and units. The time label must include


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hours, minutes, and seconds. 9tore the data so that it can be retrieved selectively. n

selective retrieval as a minimum include the name of process variable, instrument

number, date and desired time interval. nclude maximum and minimum points and

alarms &ith the data to be recorded. *rovide a dedicated printer or printer:plotter on

&hich the recorded and totalized data can be presented on paper on demand. %ata

storage, retrieval, and printing must meet federal, state, and local environmental

documentation requirements.

+n instrumentation item is not applicable if the equipment that it services is

not included in the plant. $or example, if an air preheater is not provided then an air

preheater outlet temperature indicator does not have to be furnished.

BOILER CONTROL PANEL ALARMS AND S'UTDO5NS*

The alarms and

shutdo&ns in Table B 8 represents the minimum recommended requirements for a

boiler plant. These &ere selected based primarily on boiler operation safety concerns.

Refer to 6$*+ CA2, 9tandard for thePrevention of Furnace Explosions/mplosions in

!ultiple Burner Boilers for further information for boiler plants in the >1.>C gigajoule:h

#>,A22,222 "tu:h) or above range and +9M5 !9%8>, Controls and Safety Devices for

Automatically Fired Boilers for boiler plants belo& >1.>C gigajoule:h #>,A22,222 "tu:h).

*rovide a separate &indo& in an annunciator system for each dedicated alarm. *rovide

a dedicated common trouble alarm &indo& to &hich the non8dedicated alarms are

&ired. nclude a first8out listing to sho& &hich device connected to the common trouble

alarm tripped first. *rovide instrumentation to sho& &hich device shut the equipment

do&n first during a system shutdo&n.

+n alarm or shutdo&n is not applicable if the equipment that it services is not

included in the plant. $or example, if the boiler is gas fired only, a lo& fuel oil pressure

alarm is not required. Refer also to paragraphs 1 8A and @8.B.

BOILER CONTROL PANEL CONTROLLERS*

*rovide controllers as

required for the proper operation of the boiler plant. !ontrollers required for a typical


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boiler plant include steam header pressure #plant master and boiler master), boiler drum

&ater level #feed&ater flo&), fuel flo&, combustion air flo& and boiler furnace draft.

BOILER PROTECTIONS AND FURNACE SAFEGUARD

AND SUPERISORY SYSTEM

There are three distinct systems for the Operation and !ontrol of "oiler in >2 M' and

A22 M' "oilers. These are

>. Measurement and process control system for the control of "oiler *rocesses. This system

is provided mainly for measurement and of mechanical properties such as *ressure,

temperature, $lo& and level of &ater and steam. $uel and +ir flo& control, $urnace %raft

control, %rum level control, coordinated master pressure control etc are some of the

controls and measurements included in this system,

. "oiler nterloc system is mainly used for the sequential and interlocing !ontrol of %

fans, $% $ans and *+ $ans and some other equipment of the "oiler.

1. $urnace 9afeguard and 9upervisory 9ystem, popularly called $999, continuously monitors

the operations related to fuel admission and some other vital parameters to ensure safety

of the "oiler. Fenerally furnace oil or any ind of fuel is susceptible to explosion hazards.

Majority of explosions occurs during start up, shout do&n and lo& load operations. There

are many steps that must be follo&ed by the operator to admit fuel in to the furnace

safely and properly. f left to the judgement of the operators, there is a high probability

of error. +dequacy of ignition energy is an important factor &hich should not be left for

to operator interpretation. n high capacity boilers, &here fuel input rate is very high,

major furnace explosions can result from the ignition of unburnt fuel accumulated in first

> or seconds. (uman reaction time to such situations is inadequate. !onsidering these

facts a proper "urner Management 9ystem, called $999 is installed in the "oilers. 5very

operation related to fuel admission is accomplished through $999. 9ystem -ogic allo&s

fuel admission only if it is safe. The system logic also senses any lielihood of dangerous

situation and preempts fuel admission is such situations.

Through $999, startup operations, routine operation and &ithdra&al of the "oiler are

initiated and supervised. $ollo&ing table sho&s the "oiler tripping initiated through $999.


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#i.e. &hen full

load feed line is in service). n some of the >2 M' plants, drum level controller controls [email protected]

3, if it experiences one tube leaage every B months in each of its unit. This &ould be equivalent

to a direct generation loss of A Million for %T*9.

5ach start up of boiler : turbine after attending the problem &ould result in consumption of large

quantity of oil, coal and %M &ater. The start : stop due to the frequent tube leaages &ould

affect the long8term life and performance of boiler and turbine. +nd in case of frequent leaages


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boiler parameters may also be need to be restricted to lo&er value compared to design

parameters and this &ould result in continuous loss in heat rate.

6*< Root Cause of Tu!e Failures0

The boiler pressure parts are subjected to very high steam pressures and flo& internally and high

temperatures and abrasive environment externally. (ence they are liely to fail and cause a

forced outage.

ndia has huge reserves of coal that can be used for po&er generation. "ut the quality of coal is

poor due to very high proportion of highly abrasive ash content. The ash content is as high as @A

3 in ndian coals. The inherent nature of po&er generation process is such that the boiler

pressure parts get a continuous exposure to&ards high temperature flue gases containing abrasive

ash. This erosion leads to tube thinning process, &hich ultimately results in boiler tube rupture

causing a forced outage.

Classifi"ation of Tu!e Failure Causes0+ typical classification of boiler tube failure causes is

sho&n belo& This picture sho&s clear majority of tube failure cases due to erosion and &elding


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CONCLUSION0

$rom the trend sho&n #$ig82).

'e have been able to operate %T*9 units at a record availability and loading factor and maintain

yearly plant loading factor at more than >22 3 &ith lo&est heat rate#$ig8C) in ndia since 2218

2@.

The resultant heat rate is lo&er by .A@ 3 from the base value of 12 Ecal: E'( in 22>82.

The project of providing additional protection to boiler tubes in vulnerable areas can be very

easily replicated across the industry. t can be applied to large utility boilers as &ell as smaller

industrial boiler the benefits to the consumer &ould be immense as mentioned earlier.

*

Dire"t Benefits0

#a) n case of a tube leaage %T*9 looses revenues of Rs. >C Million for this loss of generation.

This loss of generation needs to be bought from external sources at a much higher rate than the


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generation cost of %T*9. (ence prevention of one tube leaage helps the company to continue to

provide subsidy or lo&er tariff to retail consumers.

#b) +lso start up after each tube leaage consumes on an average

>. million for %T*9. +lso these processes generate additional green

house gases.

(ence prevention of one tube leaage provides benefit in terms of

>. -o&er tariff to consumers

. -esser pollution / resource conservation to society at large

SLD>Steam lea& 1ete"tor?0

9-% detects the tube leaage in various zones in the furnace.t uses ultrasonic technique to detect

the tube leaage.>B to >C 9-%7s are placed at various locations in the furnace,the signals from

the above 9-%7s are brought in the *lant control room for monitoring the steam lea in the tubes.

Re1u"tion of Boiler E+it Flue Gas Tem(erature

The ndian po&er sector has al&ays been operating in the deficit regime. The customer has been

facing the brunt of the impact. The po&er costs and availability of quality po&er are the major

issues for the customer. +nd the suppliers have been charging for availability and reliability. n

the regions &here players other than state electricity boards are supplying the po&er directly to

the end user, they have been charging a premium for the consistent supply. (ence the po&er

availability, quality and ultimately the cost are the three issues, &hich the customer has been

dealing &ith to control his o&n costs.

n ndia, the coal based thermal po&er plants are the bacbone of the po&er generation sector.

Out of total generation more than


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to its environmentally clean po&er and non8exhaustive primary energy source. "ut commercially

and economically it is not viable due to high capital investment.

(ence efficiency of the coal8based po&er plant plays a major role in the costs of po&er available

for consumption. The basic coal based po&er generation plants operate on the modified Ranine

cycle. (ere there is a lot of scope for inefficiencies. Or inversely there is a lot of scope for

improvement in the operating efficiency.

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Boiler Emergency Control Procedure

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