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FLARE RADIATION Analysis y

Flare System Design

Flare Radiation

depends on fraction of heat radiated from the flame · Gas composition · Flame type · St t of air-fuel mixing State f i f l i i · Soot/smoke formation · Quantity of fuel being burned · Flame temperature · Flare burner design

Flare System Design

Flare Radiation basic calculation

Radiant Epicentre Q F D K Heat release KW fraction of heat radiated distance to point radiant heat flux kw/m2

D H

Receptor point perpendicular to D K= FQ/4D2

Vary H to meet radiation limit

Flare System Design

Fraction of heat radiated

Year Author

f factor

Many different methods for predicting 1964 1967 1969 1973 1979 1980 1981 1984 1987 1987 Kent Tan API single point Brzustowski and Sommer Leahey et al. Oenbring and Sifferman Becker d Laing B k and L i Leahey and Davies Cook et al. Chamberlain

Flare System Design

Flare Radiation basic calculation

Computer software now allows detailed l l ti d t il d calculations ; · multipoint analysis · transmissivity (humidity) · Ø angle of incidence for inclined receptor points p p · receptor emissivity · shielding · view angle · temperature calculations

Ø

Flare System Design

D H

Flare Radiation view angle

Partial view

Partial view stack store

Flare System Design

Flare Radiation view angle

Roof sees entire flame

stack store

Flare System Design

Radiation ­ Recommended Limits

Radiation Level w/m2 1270 0 1900 3100 4730 6300 9460 Radiation Level btu/ft2 400 00 600 1000 1500 2000 3000 Temp Above ambient C 12 19 31 46 61 89 Duration

Helicopter dec s e copte decks no rotors acceptable Uncomfortable f U f bl for long periods Several minutes 30-60 seconds Few seconds only must retreat t t t

Flare System Design

Radiation Isopleths - sizing the stack

Flare System Design

Radiation Isopleths - Flaresim

Can also calculate similar plots for temperatures and noise levels

Flare System Design

Meeting Flare Radiation Limits

Increase length of flare boom Increase height of flarestack Provide radiation shielding Provide water sprays p y Reduce flaring rate Use high velocity tips

Flare System Design

Flare Shielding

Plan View with shielding

Flare System Design

Water Curtains

high pressure atomised water is sprayed behind the burners to absorb upto 70% of the incident radiation

Flare System Design

Water Curtains

Too much water ?

May M require a relight...... ... i li ht

Flare System Design

Radiation

Sonic vs Pipeflare

Up to 5 times as much radiation from a pipeflare

Radiation level

Sonic

PIPEFLARE

Distance along boom Flare System Design

Radiation

Scenario Power failure

Reducing Red cing Flare Rate

Flow 258000 220000 125000 45000 98000 245000 6500 => flare design flow 85% design flow 48% 17% 38% 95% 3%

Cooling Water failure Fire Zone 1 Fire Zone 2 Fire Zone 3 Depressuring Zone 1 Depressuring Zone 2 p g

Probably very little reduction possible.

Flare System Design

Radiation

Scenario

Reducing Red cing Flare Rate

Flow 445000 258000 220000 125000 45000 98000 6500 => flare design flow 58% of design 49% 28% 10% 22% 1.5%

Depressuring Zone 1 Power failure Cooling Water failure Fire Zone 1 Fire Zone 2 Fire Zone 3 Depressuring Zone 2 p g

DP of Zone 1 is by far the highest flow reducing this will result in a smaller flare system, saving $$$$$$

Flare System Design

Summary on Radiation Limits

Evaluate the radiation levels expected and reduce stack size by .. provide radiation shielding where needed Provide water sprays Review relief loads and reduce flaring rate Use high l it tips U hi h velocity ti if possible. ibl

Flare System Design

Information

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