Flare Modeling Parameters
Flare Modeling Parameters
Flare Modeling Parameters
The District has developed an Excel spreadsheet that can generate both screening and refined
flare parameters. The screening method previously used was developed by EPA and has been
used for since ~1980 to evaluate flares. With the need to evaluate flares against the new PM2.5
National Ambient Air Quality Standards (NAAQS) and /or Significant Impact Levels (SILs), the
current screening method has become too conservative for the purposes of evaluating flare
impacts against more stringent NAAQS.
Refined Method:
A refined method was developed using algorithms found in American Petroleum Institute (API),
Standard 521 (Flare Designing Method). API is a leader in the development of petroleum and
petrochemical equipment and operating standards covering topics that range from drill bits to
environmental protection. To ensure that this new method does not over estimate flare modeling
parameters several modifications were included:
1) EPAs maximum flame deflection of 45 degrees was added to reduce the flare exit velocity.
Please note: this is in addition to the calculated flame distortion adjustment and,
2) The lowest flame velocity estimated between the calculated and that based on the provided
flare diameter was used.
These adjustments provide a level of conservatism to the modeling parameters ensuring that
impacts are not underestimated.
Default Parameters:
The default parameters are based on natural gas and should be adjusted based on the gas
being flared. Specifically, the following parameters should be adjusted based on specific gas
information or the information provided in the included tables: 1) Allowable radiation, 2 ) Fraction
of heat radiated, 3) Heating value, 4) Gas specific density, 5) Molecular weight, and 6) Ratio of
Specific Heats.
When adjusting other default parameter (Flowing Gas Temp., Wind Speed, & Mach #) the
reviewing agency should be consulted.
1) The Flowing Gas Temp. is considered to be at standard temperature (70 ).
2) The Wind Speed was derived based on meteorological sites in the San Joaquin Valley.
3) The Mach # is based on literature research conducted during the development of the
methodology. The research would indicated that most subsonic flares can reach a mach #
between 0.2 and 0.5 while sonic flares could reach a mach # >1.0. The Mach # can be effected
by the flare design, quality of gas being flared and flame stability. To be conservative it is
recommended that the mach # be set to the lowest possible value. As the mach # has a direct
effect on the maximum possible exit velocity being calculated.
Enclosed flares should be modeled as normal point sources (stacks). The information below should only be used for open
flares where the flame is visible.
Modeling Parameters
Exit Velocity
20
m/sec
Exit Temp
1273
K
Eff Diameter
1.96
meters
Eff Height
15.62
meters
Flare Eff. Diameter Calculation
ds = 9.88 E-4 (QH)^0.5
Input
125
Input
9.144
Flare Height (m)
16485187.5 J/sec
15.62 Heff
1 Hr
60 min
1 min
60 sec
Default Parameters
1.58
0.25
55.53
0.056
19.5
293.15
8.9
0.2
101.325
1.27
x 13. m
L
15.14 m
Wind 8.9 m/sec
y
5.21 m
yc
2.61 m
Heff
14.36 m
6.5 m
Height
9.14 m
xc
D
24.83 m
2.27 m
Dia.
H1
11.75 m
21.88 m
R1
28.38 m
R
Note: The estimated flare parameters were generated using the calculation methodology provided in ANSI/API Standard
521. A publically available reference to these calculations can be found in a book by Arun Datta "Process engineering and
design using Visual Basic" starting on page 330. A snippet can be found at http://www.scribd.com/doc/86470056/372/Lowerexplosive-limit-of-mixtures.
Minimum Distance
The minimum distance from the center of the are to the point of exposureis estimated as follows
D = ( * F * Q / 4 * K)0.5
=
1.00
F=
0.25
Q=
48,976.64
kW
K=
1.58
D=
24.83
m
81.47
= fraction of heat intensityfttransmitted (for a conservative analysis, the value of
Where:
Heat release, Q
For gases with known compositions, the heat release is estimated as follows:
Q = (W / 3.6 ) * wiqi
W=
wi =
3175.15
qi =
55.53
48,976.64
Q=
Where:
Q = heat release, kW
W = gas ow rate, kg/hr
wi = mass fraction of component i
qi = heating value of component i, MJ/kg (Table 3)
If the gas composition is not known, the heating value of the gas can be assumed as 50 MJ/kg. Heating values of
commonly used gases are presented in Table 3.
Mass flow rate in lb. per hour
W=V*D
V=
125000
D=
0.056
W=
7000.00
lb. per hour,
3,175.15
kg per hour,
Where
W = mass flow rate in lb. per hour,
V = flow rate in scf/hr,
D = gas specific density (Table 4)
SG = Specific Gravity (Table 4)
1.09
m3/sec
Where:
F = actual volumetric ow, m3/sec
W = mass ow rate, kg/h (Table 4)
MW = molecular weight of the owing gas (Table 4)
T = temperature of the owing gas, K
Where:
Uj = are tip exit velocity, m/sec
d = are stack diameter, m
Flame distortion caused by wind velocity is calculated as follows
U = Ux / Uj
Ux =
Uj =
U=
8.9
Calculated
Provided
56.25
0.158
96.02
0.093
Where:
U = velocity factor
Ux = wind velocity, m/sec
Flame vertical length, y, is estimated by using the following equation
y = L * [ -0.0392 + (0.1267 / U0.5) + ( 0.0178 / U) - (0.003 / U1.5)]
L=
15.14
Calculated
Provided
U=
0.158
0.093
y =
5.21
7.01
m
Where:
y = Flame vertical length
L = ame length, m
U = velocity factor
Calculated
Provided
2.61
3.50
Calculated
Provided
6.50
6.07
xc = 1/2 * x
xc =
Where:
yc = vertical distance of ame center from the top of are stack, m
xc = horizontal distance of ame center from the top of are stack, m
Value of K at any location where personnel with appropriate clothing may be continuously exposed
C2H2
Air
26
29
Density - (lbm/ft3)
(kg/m3)
1.0921)
0.06821)
2)
1.170
0.07292)
1.2051)
0.07521)
2)
1.293
0.08062)
Alcohol vapor
Ammonia
Argon
Arsine
Benzene
Blast furnace gas
Butadiene - C4H6
NH3
17.031
Ar
39.948
C6H6
78.11
0.7171)
0.7692)
1.6611)
1.78372)
0.04481)
0.04802)
0.10371)
0.1113532)
11)
58.1
Butylene (Butene)
C4H8
56.11
Carbon dioxide
CO2
44.01
Carbon disulphide
0.59
1.38
2.69
2.6961
1.02
1.87
3.486
1.2502)
0.20643
0.07802)
2.4891)
2.52)
2.504
1.8421)
1.9772)
0.15541)
0.1562)
0.1482)
0.11501)
0.12342)
1.1651)
1.2502)
0.07271)
0.07802)
0.9667
0.048
0.63
0.18691)
2.486
0.0342)
0.44
C4H6
C4H10
Carbureted Water
Gas
Chlorine
Coal gas
Coke Oven Gas
Combustion
products
Cyclobutane
Cyclohexane
Cyclopentane
Cyclopropane
0.9
1.601
Butane
Carbon monoxide
Specific Gravity1)
- SG -
2.0061
1.94
1.5189
76.13
CO
Cl2
28.01
70.906
2.9941)
0.582)
1.112)
0.0692)
1.938
84.16
2.422
1.451
Decane
Deutrium - D2
Digester Gas
(Sewage or Biogas)
Ethane
Ether vapor
Ethyl Alcohol
Ethyl Chloride
Ethylene
Fluorine
Helium
4.915
0.07
0.062
0.8
1.2641)
0.07891)
1.0378
2.586
0.0786
C2H6
30.07
C2H5Cl
46.07
64.52
C2H4
28.03
1.260
He
4.02
0.16641)
0.17852)
N-Heptane
Hexane
Hydrogen
Hydrogen Chloride
Hydrofluoric acid
Hydrochloric Acid
Hydrogen Sulfide
Illuminating gas
Isobutane
Isopentane
Krypton
Marsh gas
Mercury vapor
Methane
CH4
2.23
2)
2)
0.010391)
0.0111432)
0.9683
1.31
0.138
HCl
100.2
86.17
2.016
36.5
0.08992)
1.5281)
0.00562)
0.09541)
H2S
36.47
34.076
1.632)
1.4341)
0.08951)
3.459
2.973
0.0696
1.268
2.37
1.261
1.1763
0.4
2.01
2.48
2.89
0.555
6.94
0.04171)
0.04472)
0.5537
H2
3.742)
Methyl Alcohol
Methyl Butane
Methyl Chloride
16.043
0.6681)
0.7172)
32.04
72.15
50.49
Natural gas
1.74
19.5
0.7 - 0.92)
0.89992)
1.2491)
1.1651)
1.25062)
Neon
Nitric oxide
Ne
NO
20.179
30
Nitrogen
N2
28.02
0.044 0.0562)
0.0561792)
0.07801)
0.07271)
0.0780722)
0.60 - 0.70
0.697
1.037
0.9669(Pure)
0.9723(Atmospheric)
Nitrogen Dioxide
NO2
46.006
Nitrous Oxide
N2O
44.013
Nitrous Trioxide
N-Octane
Nonane
Octane
NO3
62.005
114.22
0.114
1.53
4.428
3.944
Oxygen
O2
32
Ozone
N-Pentane
Iso-Pentane
Propane
O3
48
72.15
72.15
44.09
C3H8
Propene (propylene)
R-11
R-12
R-22
R-114
R-123
R-134a
Sasol
Sulfur
C3H6
42.1
137.37
120.92
86.48
170.93
152.93
102.03
32.06
Sulfur Dioxide
SO2
64.06
SO3
Sulfur Trioxide
Sulfuric Oxide
SO
C7H8
Toluene
TolueneMethylbenzene
H2O
Water Vapor, steam
Water gas
(bituminous)
Xenon
1)
NTP - Normal Temperature and Pressure
2)
STP - Standard Temperature and Pressure
80.062
48.063
92.141
1.3311)
1.42902)
2.142)
0.08311)
0.0892102)
0.125
1.8821)
0.11751)
1.7481)
0.10911)
2.2791)
2.9262)
0.032
0.135
0.17031)
0.18282)
4.111
0.2435
1.1044
1.66
2.487
1.39
1.5219
1.4523
4.742
4.174
2.985
5.9
5.279
3.522
0.42
1.11
2.264
3.1082
18.016
0.804
5.862)
0.048
0.6218
0.054
0.71
4.53
cp
cv
cp
cv
Ratio of Specific
Heats
=
(kJ/kg K)
(kJ/kg K)
(Btu/lbmoF)
(Btu/lbmoF)
cp / cv
1.32
1.37
0.718
1.67
0.35
0.35
0.24
0.45
0.32
0.27
0.17
0.4
1.11
1.232
1.4
1.13
Specific Heat
Gas or Vapor
Formula
Acetone
Acetylene
Air
Alcohol
C2H5OH
1.47
1.69
1.01
1.88
Alcohol
CH3OH
1.93
1.53
0.46
0.37
1.26
Ammonia
Argon
Benzene
Blast furnace gas
Bromine
Butatiene
Butane
NH3
2.19
0.52
1.09
1.03
0.25
1.66
0.312
0.99
0.73
0.2
0.52
0.12
0.26
0.25
0.06
0.4
0.07
0.24
0.17
0.05
Carbon dioxide
Carbon monoxide
Carbon disulphide
Chlorine
Chloroform
Coal gas
Combustion
products
Ethane
Ether
Ethylene
Freon 22
Helium
Hexane
Hydrochlor acid
Hydrogen
C2H2
C4H10
1.67
1.53
0.395
0.356
1.31
1.667
1.12
1.41
1.28
1.12
1.094
CO2
0.844
1.02
0.67
0.48
0.63
2.14
0.655
0.72
0.55
0.36
0.55
1.59
0.21
0.24
0.16
0.12
0.15
0.16
0.17
0.13
0.09
0.13
1.289
1.4
1.21
1.34
1.15
1.187
1.03
1.24
1.18
1.667
1.06
Ar
C6H6
CO
Cl2
1
C2H6
0.24
C2H4
1.75
2.01
1.53
1.48
1.95
1.23
0.39
0.48
0.4
0.32
0.47
0.33
He
5.19
3.12
1.25
0.75
H2
0.795
14.32
0.567
10.16
3.42
2.43
1.405
Hydrogen Chloride
Hydrogen Sulfide
Hydroxyl
Krypton
Methane
HCl
H2S
0.8
0.57
OH
1.76
0.25
2.22
1.27
0.151
1.7
CH4
Methyl Chloride
Natural Gas
Neon
Nitric Oxide
Nitrogen
Nitrogen tetroxide
Nitrous oxide
CH3Cl
Oxygen
Pentane
Propane
Propene (propylene)
Water Vapor
Steam 1 psia. 120
600 oF
0.135
0.187
1.41
1.32
1.384
0.59
0.45
1.304
0.24
0.56
0.2
0.44
0.23
0.25
1.12
0.21
0.17
0.18
1.1
0.17
1.2
1.27
1.667
1.386
1.4
1.02
1.27
N2O
2.34
1.03
0.995
1.04
4.69
0.88
1.85
0.618
0.718
0.743
4.6
0.69
O2
0.919
0.659
0.22
0.16
C3H8
1.67
1.48
0.39
0.34
1.395
1.07
1.127
C3H6
1.5
1.31
0.36
0.31
1.15
1.93
1.46
0.46
0.35
1.32
1.97
1.5
0.47
0.36
1.31
2.26
1.76
0.54
0.42
1.28
0.64
0.51
0.15
0.12
1.29
0.16
0.097
NO
N2
0.191
0.243
SO2
(ft lbf/lbmoR)
0.15
0.319
0.287
0.22
59.34
53.34
0.39
0.53
0.208
0.1
0.3
0.05
96.5
55.05
0.143
26.5
0.189
0.297
0.12
0.12
0.08
38.86
55.14
0.276
0.06
0.296
51.5
55.08
2.08
386.3
4.12
765.9
0.23
42.4
45.2
0.489
0.518
0.5
0.412
0.277
0.297
0.09
0.18
96.4
30.6
79.1
54.99
35.1
0.26
48.24
0.189
35
0.18
36.8
0.462
0.46
0.5
0.13
24.1