Module-11B Flare System

7/25/2019 Module-11B Flare System

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February 5, 2016 Technomanage / UKD & SNM 1

Training Program on

Basic Process Engineering Practices

For

Technip India Ltd.

By

The Technomanage Group

And Mr. S.N.Mitra

Module !!B Flare System


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Flaring is a com"ustion control process in #hich #aste gases arepiped to a remote$ usually ele%ated location and "urned in an open&lame in the open air.

A specially designed "urner tip$ au'iliary &uel$ and steam or air areused to promote mi'ing &or nearly complete com"ustion ()*+ ,-.

The &laring process can produce undesira"le "yproducts$ including

noise$ smo/e$ heat radiation$ light$ S0'$ N0'$ 10$ and an undesired

source o& ignition. 2o#e%er$ proper design can minimi3e these.

4hat is Flaring5

Flare 6.0 7rum4ater

seal

Flare Tip

Flare 2eader

Process E8uipment

Process E8uipment


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February 5, 2016 Technomanage / UKD & SNM #

Process plant can "e su"9ected to e'cessi%e o%erpressure or

underpressure due to process upset conditions.

Sa&ety :al%es or ;upture 7iscs pre%ent the e8uipment &rom

reaching o%erpressure condition i.e. protects it &rom e'ceeding

design pressure "y releasing the e'cess gases.

The gases released in a process plant is generally ha3ardous.

Primary purpose o& &lare system is to sa&ely ta/e the released

gases to a &lare stac/ and "urn it.

Flare system is also used &or "urning gases due to emergency

%enting. E'ample o& emergency %enting Gas &laring #hen a

consumer shuts do#n.

Purpose o& Flare System


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February 5, 2016 Technomanage / UKD & SNM $

1auses o& 0%erpressure

E'ternal &ire

Bloc/ed :al%e

Process a"normality or maloperation

E8uipment or ser%ice < utility &ailure

1hanges in am"ient conditions

;una#ay chemical reaction

Flare system is used to destroy &lamma"le$ to'ic or corrosi%e

%apors$ &rom relie& %al%es or emergency %enting.


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Flare System 7esign Factors

6ey design &actors to ensure &lare sa&ety and per&ormance

include=

Smo/eless operation

Flame sta"ility

Flare si3e$ capacity$ stac/ diameter

Thermal radiation

Noise le%el

;elia"le pilot and ignition system

Flash"ac/ protection


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Flare Net#or/ 1omponents

4ater

seal

Flare Tip

Flare 6.0 7rum

Incinerator

Mol Seal

Pilot

Burner

Flare

Ignition

System

Fuel Gas (>?- Pump

P1

@nit Flare 27;Fuel Gas

Process (@nit !-

@nit Flare 27;Fuel Gas

Process (@nit >-

Main

Flare

27;Flare

Stac/

Air


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Flares are generally categori3ed in t#o #ays=

!- "y the height o& the &lare tip (i.e.$ ground or ele%ated- and>- "y the method o& enhancing mi'ing at the &lare tip (i.e.$ steam

assisted$ airassisted$ pressureassisted$ or non assisted-.

Ele%ating the &lare can pre%ent potentially dangerous

conditions o& high radiation at ground le%el or operating area o&

a process unit. The distance and heighto& the &lare stac/ is set

"y radiation calculations (API ;P >!-

Further$ the products o& com"ustion can "e dispersed a"o%e

#or/ing areas to reduce the e&&ects o& noise$ heat$ smo/e$ ando"9ectiona"le odors. 7ispersion and ground le%el concentration

o& pollutants &rom &lare also may set the height o& the &lare

stac/.

Flare Types


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February 5, 2016 Technomanage / UKD & SNM '

1rac/ing can occur #ith the &ormation o& small hot particles o&

car"on that gi%e the &lame its characteristic luminosity. I& there is an

o'ygen de&iciency and i& the car"on particles are cooled to "elo#

their ignition temperature$ smo/ing occurs.Nonassisted &lares are

more prone to smo/ing.

Flare Types$ 1ontd...

The nonassisted &lare is 9ust a &lare tip #ithout an au'iliarypro%ision &or enhancing the mi'ing o& air into its &lame. Its use is

generally limited to gas streams that "urn readily #ithout

producing smo/e.

Non assisted &lares

Smo/e pro"lem


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February 5, 2016 Technomanage / UKD & SNM (

Assisted &lares

In assisted &lares$ induction o& air &or com"ustion and mi'ing are

enhanced "y %arious means descri"ed "elo#.

Steam is in9ected into the com"ustion 3one to promote tur"ulence

&or mi'ing and to induce air into the &lame.

Steam assisted &lares

Air assisted &lares

Some &lares use &orced air to pro%ide the com"ustion air and the

mi'ing re8uired &or smo/eless operation.

Pressure assisted &lares

Gas pressure is /ept high at the "attery limit o& the &lare to promote

mi'ing at the "urner tip.

Flare Types$ 1ontd...


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Flare 2ard#are 1omponents

Sa&ety ;elie& andFlare 2eader

Steam

Assisted

Flare


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Steps on 7esigning Flare System

7etermine

1ontrolling Load

For Each ;elie&

Estimate

4orst Scenario

For the Plant

Identi&y 1ases

For 0%erpressure

Identi&y Systems

For ;elie&

Protection

Select Set

Pressures

Line Si3ing

PI7

For Flare System

Select Stac/

2eight$ 7iameter

And 7istance

Select Type 0&

Flare Tip$

Seals

Piping LayoutE8uipment

Speci&ication


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The &irst step is to analy3e the causes o& o%erpressure in

%arious e8uipment and systems and calculate the loads dueto sa&ety %al%e popping.

E'ternal &ire

Process a"normality or maloperation

E8uipment or ser%ice < utility &ailure

1hanges in am"ient conditions

;una#ay chemical reaction

0nce the loads are calculated$ they are systematically

ta"ulated under a"o%e heads.

The chances o& simultaneously occurring &ailures dictate the

&lare load

7etermining Flare Load in a Plant


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February 5, 2016 Technomanage / UKD & SNM 1#

E'amples o& Sa&ety :al%e Si3ing 1ases

Fire 1ase re8uired to "e estimated &or %essels > &eet &rom

ground. 2eat &lu' due to &ire is ta/en as >! or CD. MBtu! (!**C- gi%es the e8uation

>!$ ' F ' A .+> 4here 2eat a"sorption in #etted area.

A 4etted area in s8. &t.

F En%ironment Factor

(F! &or "are sur&ace$ .!

.C &or

insulated sur&ace- NFPA

>!$ ' F ' A .+D 4here

(F.C &or "are #ater sprayed$

"uried or insulated sur&ace-


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February 5, 2016 Technomanage / UKD & SNM 1$


Bloc/ed Flo# inad%ertently closed "loc/ %al%e$ &ailed

shut control %al%e$ po#er &ailure$ pump &ailure #ith

upstream %essel le%el a&&ected.

Tu"e rupturedi&&erential pressure "et#een shell side and

tu"e side to "e e%aluated.

1ontrol %al%e &ailure due to air &ailure or other causes.

Po#er &ailure resulting pump &ailure$ instrument air

&ailure$ &ailure o& agitator in %essel etc.


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Steam related &ailure can cause e'cessi%e steam

pressure due to &ail open %al%e$ stoppage o& steam supply#ith lo# %apori3ation and rising le%els$ high %apor load

due to e'cess steam.

;e&lu' &ailure causes %apor o%erload. Since column is at

ground le%el &ire case usually controls.

Thermal relie& Bloc/ed li8uid line #ith heat load li/e

steam tracing or solar radiation.

;una#ay chemical reaction should "e specially

e%aluated &rom licensor in&ormation. @sually this case or

&ire case controls the PS: si3ing.



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0%erpressure= Bloc/ed 7ischarge 1ase

Bloc/discharge&rom #ellhead

0il mani&old

This can happen #hen there is a sudden closure o& %al%e in

any &lo#ing pipeline. In this case$ the sa&ety %al%es pro%ided

on pipeline or e8uipment need to "e designed on &ull &lo#

rate


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February 5, 2016 Technomanage / UKD & SNM 1%

2eat E'changer Tu"e Failure

Tu"e Side Shell Side

4hen there is a #ide di&&erence in design pressure "et#een

the t#o e'changer sides and the lo# pressure side isdesigned at a pressure less than t#othird o& design

pressure o& high pressure side$ a relie& %al%e is re8uired at

the lo# pressure side


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February 5, 2016 Technomanage / UKD & SNM 1'

@tility Failure E'ample 1ooling 4ater Failure

Feed

Top product

;e"oiler

1ondenser

Bottom product

7istillation1olumn

4hen there is a sudden &ailureo& cooling #ater in o%erhead

condensers o& distillation

column$ the column pressure

starts increasing due to loss o&re&lu' a&ter ! minutes.

To o%ercome this$ a relie& %al%e

is re8uired that can %ent theadditional 8uantity o& %apor

generated to &lare.


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February 5, 2016 Technomanage / UKD & SNM 1(

1ontrol E8uipment Failure 0%ersupply o& 2eat

Feed

Top product

;e"oiler

1ondenser

Bottom product

7istillation1olumn

4hen the control o& &uel supplyor steam supply to re"oiler

&ails$ there could "e e'cessi%e

heating resulting in rise in

column temperature and o%erpressuri3ation.

To o%ercome this$ a relie& %al%e

is re8uired that can %ent theadditional 8uantity o& %apor

generated to &lare.


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Selecting the Set Pressure

7epending on temperature rating o& the e8uipment and

material o& construction$ design pressure or ma'imum

allo#a"le #or/ing pressure (MA4P- is decided.

The set pressure o& sa&ety %al%e is to "e e8ual or lo#er

than design pressure. It is guided "y codes li/e API >.


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;elie& Line Si3ing Guidelines

No PS: inlet line pressure drop should "e greater than C,

o& the set pressure.

PS: discharge side should "e at least one si3e higher

than the inlet side.

PS: discharge side pressure drop should not "e more

than !, o& the set pressure.

Bac/ pressure on sa&ety %al%e should not e'ceed !, o&

set pressure. For "ello#s type sa&ety %al%e it can "e

higher. There should "e no restriction on relie& lines &ull "ore L0

%al%es$ no ;estriction ori&ice$ no &lame arrestor etc.

Be a#are o& limitations o& sonic &lo#. Sonic &lo# limits

ma'imum possi"le &lo# in a line. 7o not e'ceed , o&

sonic %elocity.


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Flare System 2ard#are and Net#or/ 7esign

A&ter completing the design o& process systems$ a &inal &lare

and relie& analysis o& process system should "e done.

A comparati%e study o& &lare and relie& loads should "e

determined and the #orst scenario &oreseen.

Based on the #orst conditions$ &lare load is designed.

Based on the controlling &lare load$ the &lare e8uipment and

system hard#are are designed

Net#or/ o& relie& lines &rom numerous e8uipment #ith

main &lare header

Flare / o drum

Li8uid trans&er pumps

Flare stac/ are designed.


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February 5, 2016 Technomanage / UKD & SNM 2#

Flare stac/s are o& three types=

Sel& Supported 7erric/ Supported Guy Supported

Flare Stac/s


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The height and distance o& a &lare is determined "y the ground

le%el limitations o&=

thermal radiation intensity$

luminosity$

noise$

height o& surrounding structures$ and

the dispersion o& the e'haust gases.

API ;P >! sets the guidelines &or radiation and dispersion

calculations.

Stac/ 2eight


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Solar ;adiation

API ;P >! pro%ides guidelines &or radiation limits &or

estimating stac/ height.

An industrial &lare is normally si3ed &or a ma'imum heat

intensity o& !$>$ Btu


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Flare height may also "e determined "y the need to sa&ely disperse

the %ent gas in case o& &lameout.

The height in these cases #ould "e "ased on dispersion modeling

&or the particular installation conditions.

The minimum &lare height normally used is C &eet.

Stac/ 2eight 1ontd..


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1old :ent

In cases #here the sa&ety relie& %al%es are small in num"er and

%enting possi"ilities are minimal$ cold %enting o& natural gas

can "e carried out in stead o& &laring.

The gas should "e mainly methane (much lighter than air- so

that it goes up and disperses in the air much a"o%e operating

le%el.

1old %enting is also done &or atmospheric storage tan/s or

#here ade8uate "ac/ pressure &or &lare system is not a%aila"le.

Fl i & At h i T /


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February 5, 2016 Technomanage / UKD & SNM 2'

Atmosphericstorage tan/

:ent stac/

Atmospheric Storage Tan/ designed as per API H can

not tolerate "ac/ pressure o& &lare system. They need to

"e %ented.

Atmospheric Storage Tan/s &or re&rigerated li8uids

designed as per API H> ( mm #ater- can "e

connected to &lare.

Flaring &rom Atmospheric Tan/s

)e*r+geraed

-mo.her+c

Sorage an

Fare .ac

1 d d G id li


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1odes and Guidelines

API ;P > Si3ing$ selection$ and installation o& pressure

relie%ing de%ices in re&ineries

Part I Si3ing and Selection$ !**C.

Part II Installation$ !**D.

API ;P >! Guide &or pressurerelie%ing and depressuring

systems$ !**.

API ;P >H Flanged Steel Sa&ety ;elie& :al%es$ Fourth

Edition$ !**.

API ;P > Seat Tightness o& Pressure ;elie& :al%es$ Third

Edition$ !**!.

API Std > :enting atmospheric and lo# pressure storage

tan/s= Nonre&rigerated and re&rigerated$ !**+.

API ;P >>! @se o& pressure%acuum %ent %al%es &or

atmospheric Loss$ First Edition$ !*HH.

Documents

Module-11B Flare System