Flare Stack

by

S Choudhary

SIZING A SUBSONIC FLARE STACK Project Client Unit No.

EIL Job No. Location Tag No.

Item Name

Qty

Prepared by Reviewed by Ref Co Code Date

API 52 521 Fi Fifth Ed Edition Ja Jan 20 2007 & Addendum, Ma May 20 2008

BASIC DATA

Mass Flow Rate

qm

kg/h

45360

 Absolute Pr within flare tip,

P2

kPa

101.3 Fig. 7 Flame Length Length Vs Heat Release Release

 Average Molecular Mass Flowing Temperature Compressibility Factor  Mach No. at flared tip Heat of combustion

M T Z Ma

K kgJ/kg

Wind Velocity

u∞

m/s

Fraction of Heat radiated Fraction of radiated heat trans thru atm.

F τ

Maximum allowable radiation

K

kW/m

Grade Distance from CL of flare stack to point being considered

r

m/s

Ration of specific heatts in the gas

k

46.1 422 1 0.2 50000 8.9 0.3 1

2

6.3 45.7 1.4

CALCULATION OF FLARE TIP DIAMETER

Flare tip inside diameter 

d

m

Q L

kW m

0.4677577

Fig. 9 Approx. Flame Distortion due to lateral wind

CALCULATION OF FLAME LENGTH

Heat Liberated Flame Length ( from Fig 7 of API 521)

630000 50

CALCULATION OF FLAME DISTORTION CAUSED BY WIND VELOCITY

Vapour Volumetric Flow rate Exit velocity at flare tip From fig 9 of API 521 From fig 9 of API 521

qvap

m3/s

u j

m/s

9.463841148 55.1005451

u∞/u j

0.161522903

∑∆y/L ∑∆x/L ∑∆y ∑∆x

0.36 0.85 18 42.5

CALCULATION OF FLARE STACK HEIGHT

Min. distance from the epicentre of the flame to the object being considered

Overall Height of Stack

D r' h' h

m m m m

48.87264093 24.45 42.31704777 33.31704777 Fig C.1 Dimensional references for Flare stack

CALCULATION OF NOISE LIMIT

Speed of sound in the gas abs. Static Pr upstream of the Restriction abs. Static Pr upstream of the Restriction Pressure Ratio Noise Level from Fig 18

c

L

m/s psia psia Pr dB dB

76.28936831

L30 r Lp

dB m dB

130.2893683 120 102.5634811

Cuft/lb TPD

12.03259803 1088.64

2

10*ln(0.5*qm*c /3600) Noise Level at 30 m Distance from the sound source (tip) Sound Pressure at distance r 

326.486042 48 16 3 54

CALCULATION OF GROUND LEVEL C ONCENTRATION

Specific Voume of Toxic Gas Wt Discharge of Pollutant Component Vertical Diffusion Coefficient

V M Dz

Horizontal Diffusion Coefficient

Dy

 Air Velocity at Grade Stack Height Environmental Factor 

mu H

mph ft

5 109.3078995 0.25

Cocentration at Grade

Cmax

ppm

810.6250958

Dist from stack to the point of max concent.

X

m

2.865708405

0.13 0.13

CALCULATION OF AIR REQUIREMENT FOR SMOKELESS FLARING

 Air Flow rate  Air Flow rate

kgmole/hr kg/hr

Efficiency of Blower

Power Rating of Blower 

kW

CALCULATION OF STEAM REQUIREMENT FOR SMOKELESS FLARING

1712.34 178768296 0.5 57.8085984