Flare System

 Aker Kvaerner Powergas Pvt. Ltd.

Flare system Satish K. Saxena Sept. 2005

Typical flow diagram

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 2

System protection •

Primary protection -

•

Secondary protection -

•

Control system

Hard wired trip protection

Tertiary protection -

Safety valves, rupture disk

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 3

Reliving Scenarios -

Fire

-

Refrigeration failure

-

Power failure

-

Vaporis aporisation ation in exchan exchangers gers

-

Steam failure

-

Overfilling

-

C.W. failure

-

Tube rupture

-

Inst. Air failure

-

Entrance of volatile liquid

-

Reflux failure

-

-

Side reflux failure

Chemical reaction (Run away reaction)

-

Closed outlet

-

Liquid expansion

-

Air cooler fan failure Control valve failure

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 4

Reliving devices 

Safety – Safety  – Relief  Relief valve.



Rupture disk.



Emergency de-pressurisation.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 5

i) Safety valves Types

-

Conventional.

-

Balance bellows.

-

Pilot operated. Set pressure equals to design pressure/MAWP of equipment.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 6

Allowable Back pressure depends upon the type of safety valve. ∆P = 3% of set pressure of safety valve.

ii) Rupture disk “Rupture Disk is most preferred, fool prove, safety d e v i c e , o p e n s i n s t a n t an e o u s l y t o p r o t e c t t h e s y s t em a g a in s t o v er p r es s u r i s at i o n . It i s d es i g n e d t o b u r s t w h e n d i f f er en t i a l p r e s s u r e ac r o s s t h e d i s k e x c e ed s a p r e d et e r m i n e d v a l u e at p r e d e t e r m i n e d t e m p e r at u r e . R u p t u r e d i s k s a r e u s e d i n g a s , l i q u i d , h i g h l y c o r r o s i v e, h ig h l y v i s c o u s an d c o n g eal in g s e r v i c es . It is i n s t a l le d i n v a r io u s c o m b i n a t i o n s , s o l e s a f et y d e v i c e , w i t h s a f et y v a l v e , e it h e r i n l e t o r i n p a ra ll el d e p e n d i n g u p o n t h e c r i t i c al i t y o f s y s t e m . ---Continue-- 

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 7

Rupture disk APPLICATIONS:

T h e u s e o f r u p t u r e d i s k a s p r e s s u r e -r e li ev i n g d e v i c e i s p r e f er r e d i n t h e f o l l o w i n g c a s es : 

W h e r e p r es s u r e r i s e i s s o r a p i d t h a t t h e i n e r t i a o f a s a f e t y v a l v e w ould be a disadvantage.



W h e r e m i n u t e l e ak a g e o f p r o c e s s f l u i d ( To x i c , h i g h l y i n f l a m m a b l e, s a f e t y v a lv e o p e n s t o a t m o s p h e r e) c a n n o t b e t o l e r at e d u n d e r o p e r a t in g c o n d i t i o n s .



S er v i c e c o n d i t i o n s l e d t o d e p o s i t i o n , w h i c h c a n m a k e s af et y valve ino perative.



C o l d a m b i e n t c o n d i t i o n c o u l d p r e v e n t a s af e t y v a l v e t o o p e r at e .



S o l i d c o n t a i n i n g g a s m a k es s a f et y v a l v e i n o p e r a b l e.



C o r r o s i v e g a s e s s p o i l t h e s a f e t y v a l v e i n t e rn a l s . ---Continue---

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 8

Rupture disk 

R u p t u r e d i s k i s u s e d a s s o l e s af et y d e v i c e i n f o l l o w i n g c a s es : --Ins tantaneou s relief is r equired . --A s a n a d d i t i o n a l s a f e g u a r d f o r p r e s s u r e r el i ev e  .



F o l l o w i n g a r e t h e ap p l i c a t i o n s , w h e r e r u p t u r e d i s c i s u s e d i n s e r i es , of s afety valve at up -str eam . --T o p r o t e c t t h e s a f e t y v a l v e a g ai n s t c o r r o s i o n . --To preven t leakage of c orro siv e, tox ic and valuable m aterial. --T o p r e v e n t t o t a l l o s s o f m a t er i al f r o m t h e s y s t e m f o l l o w i n g rupturing o f rupture disc. --T o p r o t e c t t h e s a f et y v a l v e b e c o m i n g i n o p e r ab l e d u e t o c o n g e al i n g of m aterial.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 9

iii) Emergency 





Vapor De-pressurisation

De-pressurisation during fire minimises the risk of failure of equipment even at lower than its design pressure, due to reduction in “Yield Strength” of its material of construction with increase of wall temperature during fire. De-pressurisation also reduces the risk of increasing the internal pressure of equipment exceeding the “Rupture pressure” during external fire, thus preventing the occurrence of major leak of hazardous chemicals, which leads to safety and environment hazards. De-pressurisation helps in reducing the wall temperature thus reduces the risk of pre-mature failure of equipment.

-----Continue-Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 10

Conditions for requirement of “Emergency Vapor De-pressurisation” 





“All the process equipment, as part of a system, should have atleast total cumulative inventory of 3 to 5 cubic meters of Butane or more volatile liquid under normal operating conditions, shall be provided w ith remotely operated depressurisation assembly.” As per the API-521 (Clause 3.19.1), the release capacity should be such that the continuous vapour depressurisation should reduce the equipment pressure to 50% of its design pressure within 15 minutes. The API-521 (Clause 3.19.1), further states that when fire is controlling contingency, it may be appropriate to limit the provision of depressurisation facility only for the equipment and sections which operate 250 lbs/square inch and above, where the size and volume of a system is significant. The depressurisation is limited to 100 lbs/square inch or 50% of the design pressure, whichever is lower, within 15 minutes time (for vessels with wall thickness 1” or more, thinner vessel requires higher depressurisation rate, means lower than 15 minutes). ---ContinueAker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 11

Emergency Vapor De-pressurisation Type of vapor de-pressurisation:



Controlled de-pressurisation.



Uncontrolled de-pressurisation.

-----Continue----

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 12

Emergency Vapor De-pressurisation

Q MAX., UNCONTROLLED DEPRESSURISATION

   Q  ,    E    T    A    R    W    O    L    F    N    O    I    T    A    S    I    R    U    S    r    S    h    /    E    3    R    P    E    M    S   D

    D     E     L     L    O     R     T     N    O    C     N     U

FLARE CAPACITY, Q MAX., CONTROLLED DEPRESSURISATION CONTROLLED  ALLOWABLE TIME

TIME, MINUTES

FIG.3

DEPRESSURISATION TIME (AREA UNDER BOTH THE CURVES WITHIN THE STIPULATED TIME ARE SAME, MEANS VOLUME HANDLED ARE SAME)

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 13

Flare load summary Flare load summary :

1) Normal

2) Emergency

C.W. FAILURE FIRE PROCESS UPSET Depressurisation Unit no. T/HR MW TEMP T/HR MW TEMP T/HR MW TEMP T/HR MW TEMP 1

UNIT A

2

UNIT B

3

UNIT C

*

IT IS NOT NECESSARY THAT IF MASS FLOW IS HIGHER, THE FLARE LOAD WILL BE GOVERNING.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 16

Streams requiring disposal 

 

Vapor and liquid relief from safety valve and rupture disk. De-pressurised vapors.  Any operational inflammable waste stream does not have suitable outlet.

“Venting Vs. Flaring” Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 17

Venting considered only, otherwise flaring 







  

Release occurs only in extreme emergency conditions. Release vapor / gas is lighter than Air (< 0.9 times the air). No risk and consequences of accidental flame ignition. Concentration of toxic / corrosive components in dispersed clouds do not reach in harmful level. Condensation of corrosive vapor should not occur. Stream should be free of liquid. Hot gas venting should not ignite.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 18

Flaring Vs. Venting Considerations are to be made, based on the followings, whether to vent or flare the disposed streams.



Impact of environment.



Safety and integrity of disposal system ( Products are not combustible).



Local regulations.



Economic evaluations.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 19

Common Vs. segregated flare systems Segregated flare system may be required in following cases: 

    

Release at various pressure levels, economic reasons to reduce the size of flare headers, sub-headers and stack. Widely differing potentials for liquid release. Corrosive and non-corrosive streams. Meet plant layouts / economics. Cold dry gas with wet gas. Contents of one stream may react with contents of other stream led to chemical reactions, producing heat .

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 20

Disposal of H2S rich gas “Gas stream rich in H 2S should not be combined with gas streams free of H2S”. Because off:



H2S spread in entire flare network, shall call for “NACE” materials for entire system. H2S attack on the CS will make “Pyrophoric” substance that can lead to fire hazard in presence of explosive mixture (Auto ignition temperature is very low for “Pyrophoric” substance).

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 21

Disposal of Oxygen rich gas “Stream rich in oxygen should not be put into the common flare header”.







Oxygen forms explosive mixture with hydrocarbons, leads to explosion, if fire source is available. Oxygen converts H2S in elemental sulfur that plugs, obstruct free flow of gas.  As well,H2S produces “Pyrophoric” substance by reacting with pipe material. If Oxygen laden H/C gas ,already in explosive range, pass can create fire hazards either due to “pyrophoric” substance or by “Static electricity”. Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 22

Conventional flare system FLARE SYSTEM PILOT

PILOT FLARE TIP PSV

IGNITION LINE

PSV

DRY SEAL

F.G PURGE

PSV

1:200

F.G PURGE

1:200

B.L

PSV

WATER

H/C

K.O DRUM

PUMP

WATER

LIQUID SEAL DRUM

WATER

PLANT AIR FLAME FUEL GAS

FRONT GENERATOR

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 23

FLARE STACK

Component of “Flare network” 

Flare tip with pilots.



Dry gas seal.



Flare stack.



Liquid seal.



Flame front generator.



Knock-out drum.



Flare header and sub-headers.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 24

Problem encounter in flare system 









Glaring: Causes inconvenience to the surrounding population and feeling of unnecessary waste of resources. Noise: Causes inconvenience to the surrounding population and prolonged exposure to excessive noise may cause mental irritation, fatigue and even deafness. Radiation: Effects the surrounding population, properties and vegetation, also effects the working of operating staff in near vicinity. Ground level concentration (GLC)  : Long term effects of toxic, combustion products on population, structures and plant and animals. Smoke: Causes considerable amount of environmental pollution.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 25

Daily noise exposure limit Daily exposure, hrs

OSHA Noise regulation dBA

NIOSH Noise regulation dBA

8

90

85

4

95

90

2

100

95

1

105

100

0.5

110

105

0.25

115

110

OSHA – Occupational Safety and Health Administration. NIOSH – National Institute of Occupational Safety and Health. Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 26

Recommended flare radiation levels Permissible radiation level, BTU/Hrxft 2, (Including solar radiation)

Conditions/exposure times as per  API-RP-521(1)

Bruzutowski & sommer

Continuous exposure of personnel

2 hrs.

1500

Emergency action lasting for several minutes without proper clothes

Less than two hrs.

2000

Emergency action lasting up to 1 minute.

Less than 20 Sec.

500

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 27

Recommended “GLC” levels Pollutants

Period of measurement

Max. permissible level, PPM.

CO

8 hrs average

9.0

1 hr average

35.0

Annual arithmetic avg. mean

0.03

24 hrs. avg.

0.14

Annual geometric mean

75 µ g/m 3

24 hrs avg.

260 µ g/m3

H2S

1hr avg.

0.03

NO2

Annual arithmetic mean

0.05

Hydrocarbon

3 hrs avg.

0.24

SO2

Particulate matter

These levels of pollutants are as per “OSHA” standards Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 28

Types of flare system (Tip controls efficient burning) 

Conventional : – Conventional



“Coanda” effect flare:- High pressure gas



Jet –Mix flare :- These are multiple nozzles and arms. The flare gas is

flare consists of pipe stack with flare tip and pilot at top. The kinetic energy of the gas does not aid to air mixing for improving the burning efficiency. injected from a narrow slot follows a profile of curved surface. The “tulip” of coanda profile aids in formation of hollow cylinder of gas entrains air up to 20 times of gas volume helps in efficient burning. This creates both turbulence and sucking of air. spread out to the ambient air at high velocity promoted rapid turbulence mixing with air and thus produces efficient burning.



Air Assisted flare:- These are provided with special mixing heads. Air is blow into the stack through a concentric pipe results in turbulence mixing of air, ensuring efficient burning. --Continue--Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 29

Flare tips BURNER

 AIR

 AIR

HP GAS FLARE GAS LP GAS

EXTERBNAL COANDA TIP (KALDAIR)

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 30

CONVENTIONAL TIP

Types of flare system (Tip controls efficient burning) 

Steam assisted flare :-

This flare achieves the smokeless

capability by mixing steam with the effluent. The steam is introduced at various points to suck secondary air and turbulence to improve mixing. The steam also reduces flame temperature by dilution and thus reduces the thermal radiation.

Reaction takes place ;

CnH2n+2

+2nH2O ==== nCO2 + (6n+2) H2

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 31

Flare tips STEAM NOZZLE WIND SHIELD

JET-MIX NOZZLE

STEAM

H.P. GAS

L.P. GAS

STEAM FLARE GAS

STEAM ASSIST/GLASS-ASSIST TIP (JOHN ZINK)

LRGO TIP

JET-MIX TIP

TIP (JOHN ZINK)

(NATIONAL AIR OIL)

COANDA PROFILE

SLOT

STEAM

    K     N     A     T     D     E     C     U     D     N     I

STEAM

FLARE GAS

COANDA STEAM-SSIST (KALDAIR)

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 32

Dry gas seal Dry gas seal controls the Oxygen ingress in the flare system and also reduces the quantity of gas required for the purging. There are basically four types of Dry gas seals.  

Labyrinth seal.  Arrestor seal.



Fluidic seal @.



Molecular seal @.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 33

Dry gas seals OUTLET

FLARE TIP

 AIR DRAIN

 AIR

DRAIN PURGE GAS

LABYRINTH SEAL

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 34

INLET

 AIRRESTOR SEAL

Dry gas seals OUTLET

 AIR

SEAL

DRAIN

PURGE GAS

FLUIDIC SEAL

INLET DRAIN

MOLECULAR SEAL

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 35

Flare header sizing Sub headers are sized for 0.9 mach number, main flare header for 0.7 to 0.8 mach number, stack is sized for 0.5 mach at peak flaring and 0.2 Mach for normal flaring. •

Most of times main flare header/sub-headers sizes are controlled by allowable back pressure rather than maximum allowable velocity as stated above.

** All connections to main flare header are from the top in order to avoid back flow of condensate.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 36

Liquid seal drum •

•

Prevents the flash back from travelling up-stream. Dry gas seal cannot prevent flash back. Protect system against air ingress during vacuum pulling.

•

Provides positive sealing.

•

Avoids pulsation in flame flare tip.

•

Protect system against explosion.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 37

Liquid seal drum design ( Normally vertical)

•

API RP-521 recommends sizing should be based on gas flow area  3 Times inlet pipe cross sectional area.

4

( D 

2

)

3.

D-

Drum diameter, M

d-

Inlet pipe diameter, M

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

d 

2

Page 38

d 

2

4

--- Continue---

•

Disengaging height 2 to 3 Times the diameter.

•

Minimum seal height: 4” w.c.

•

Pipe height = 10 feet.

•

Slotted / V-Notches dip tube controls surging flow.

•

Seal height : 1.75 Times the back pressure.

•

Design pressure = 7.0 kg/cm2g,

•

Design temperature = As per header design.

•

Minimum water flow = 1.25 dm 3/sec.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 39

Knock-out drum Liquid from the flare gas is required to be separated out before it is routed for flaring because:

•

•

•

Liquid particles 90 burn in flare unnoticed except marginally change in flame colour. Liquid particles 90 to 400 light.

burning droplet visible in day

Liquid particles 400 gives fire balls, Therefore, liquid requires separation before it enters flare stack for burning.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 40

Knock- out drum design Normally “Horizontal”. - Diameter : i) Single flow

 D

2

W  

360 (dL



dV ). M . P / T 

- Diameter : ii) Double flow 0.7 times diameter calculated above. ---- Continue----

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 41

•

Length : ---Decided on liquid hold – up basis. ---Normally 10 minutes Hold-up for liquid, removed by pump, on/off operations.

•

Design pressure : •

•

7.0 kg/cm2g, withstanding internal explosion.

Design temperature : •

20oC above the maximum temperature of any release.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 42

Pilot ignition System For pilot ignitions various devices are available, most common are:



Flame front generator



Piezometer



Ballistic spark ignition

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 43

Flame front generator FLAME FRONT GENERATOR

IGNITION FAILURE

PURGE FAILURE PURGE GAS R

G

PILOT ON/OFF,  GREEN/RED R

IGNITION  AUTO/MANUAL

R

ON PB OFF

POWER

CONROL  PANEL PURGE

IGNITION PG

FLARE GAS 1/2"Ø PG

1/2" Ø 1" Ø TO PILOTS

WINDOW

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 44

PLANT AIR

Flare gas purging system 



 All the dead ends of flare sub-headers / main header requires gas purging. The dry gas seal also requires continuous purging to avoid air ingress in the flare header due to chimney effect and during vacuum pulling. Normally gas for purging should be heavier than the air. The rate of purge flow should be sufficient to overcome any tendency of “Flash back” (1.0 fps min with H/C and up to 10.0 fps for hydrogen. Higher purge is required for the hydrogen because it has highest “Flame propagation ----- Continue--velocity”). Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 45

Flare gas purging system 





In order to control the purge rate, a sample point is provided below the dry gas seal to monitor the oxygen content. As per API-521, oxygen should be less than 6%V. Any increase in oxygen content calls for increase in purging rate. Purge gas lighter than air is more effective than heavier gas. In case of heavier than air purge gas, there is no buoyancy mechanism causing air entry into the stack, and there is thus no incentive to include a dry gas seal.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 46

“Zero Flaring/ flare gas recovery” Concept 

Local environmental regulations



Substantial reduction of CO 2 and NOx emissions



Reduction in CO2 – Taxes (in some countries)



Increase flare tip lifetime



No loss in fuel gas purging



No need of pilot gas



Increased profit due to the sales value of flare gas



 Less noise and light disturbances



 Achieving status of clean environment.

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 47

Instantaneous Ignition System Requirement of an instantaneous ignition system, otherwise the pilot burner needs to be kept on.

Ballistic

spark ignition technology

Continuous

sparking ignition system

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 48

PPA possible option

PSH

0.8 MMSCFD

Recovery Comp.

Flash Gas

29 psig 1st Stage FGC

LP PSH

1 MMSCFD

0.05 MMSCFD

HP

0.2 MMSCFD Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 49

ATM VENT “A” ATM VENT “B”

2nd Stage FGC

Tapti possible option

PSH

To suction of Booster Compressor

?? MMSCFD

LP

1st stage Recovery Comp.

?? MMSCFD

?? MMSCFD

HP

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 50

2nd  stage Recovery Comp PSH

Waste gas to pilot

Concept of “Box flare” Concept of box flare has been derived for the plants (Refinery and gas processing units) where substantial quantity of gas is required to be flared for quite some time. The concept of “Box flare” attends all the problems normally encountered with “conventional flare”. In “Box flare”, controlled combustion of flare gas is carried out inside the enclosed chamber and during peak flaring there is auto diversion of flare gas to conventional elevated flare stack. 

Glaring: Controlled combustion inside the enclosed chamber, invisible from outside. --Continue--

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 51

Concept of “Box flare” 







Noise: - Enclosed chamber is provided with noise insulation from outside, which arrests noise emission from the burning. Radiation :-Enclosed chamber provided with refractory inside, acts as the barrier, does not allow heat radiation at outside working area. Ground Level Concentration:- Chimney at the top of box flare and controlled complete combustion helps in controlling the GLC rising above the dangerous level. Smoke :- Combustion is controlled by stages to ensure that gas should burn completely. Besides, there is check to divert the excess gas above its capacity towards elevated flare, thus ensures no smoke to emit from box flare. Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 52

Box flare BOX FLARE

FLARE TIP

DRY SEAL 1:200

1:200 B.L

ELEVATED STACK WATER

K.O DRUM

WATER

SEAL DRUM

ELEVATED FLARE

PIC

WATER PIC

PIC

SEAL DRUM (FOR BOX FLARE)

BOX (ENCLOSED BURNING)

Aker Kvaerner Powergas Pvt. Ltd. Sept,2005

Page 53

CLOSED CHAMBER