FLARE RADIATION Analysis y Flare System Design Flare Radiation depends on fraction of heat radiated from the flame • Gas composition • Flame type • State St t off air-fuel i f l mixing i i • Soot/smoke formation • Quantity of fuel being burned • Flame temperature • Flare burner design Flare System Design Flare Radiation basic calculation Radiant Epicentre D H Q F D K Heat release KW fraction of heat radiated distance to point radiant heat flux kw/m2 Receptor point perpendicular to D K= FQ/4πD2 Vary H to meet radiation limit Flare System Design Fraction of heat radiated f factor Many different methods for predicting Year Author 1964 1967 1969 1973 1979 1980 1981 1984 1987 1987 Kent Tan API single point Brzustowski and Sommer Leahey et al. Oenbring and Sifferman B k and Becker d LLaing i Leahey and Davies Cook et al. Chamberlain Flare System Design Flare Radiation basic calculation Computer software now allows d t il d calculations detailed l l ti ; • multipoint analysis • Τ transmissivity (humidity) D • Ø angle of incidence for inclined receptor p points p • ε receptor emissivity • shielding H • view angle • temperature calculations Ø Flare System Design 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 Radiation Level btu/ft2 Temp Above ambient C Duration 1270 0 400 00 12 Helicopter e copte dec decks s no rotors 1900 600 19 acceptable 3100 1000 31 Uncomfortable U f bl ffor long periods 4730 1500 46 Several minutes 6300 2000 61 30-60 seconds 9460 3000 89 Few seconds only mustt retreat 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 ? M require May i a relight…… 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 Red cing Flare Rate Reducing Scenario Flow Power failure 258000 Cooling Water failure 220000 85% design flow Fire Zone 1 125000 48% Fire Zone 2 45000 17% Fire Zone 3 98000 38% Depressuring Zone 1 245000 95% Depressuring p g Zone 2 6500 3% Probably very little reduction possible. Flare System Design => flare design flow Radiation Red cing Flare Rate Reducing Scenario Flow Depressuring Zone 1 445000 => flare design flow Power failure 258000 58% of design Cooling Water failure 220000 49% Fire Zone 1 125000 28% Fire Zone 2 45000 10% Fire Zone 3 98000 22% 6500 1.5% Depressuring p g Zone 2 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 U hi Use high h velocity l it titips if possible. ibl Flare System Design
