L. Douglas Smoot & Robert E. Jackson
Combustion Resources, Inc
Provo, UT
Joseph D. Smith
Systems Analysis and Solutions, LLC
Owasso, OK
IFRC International Pacific RimCombustion Symposium
26-29 September 2010Maui, Hawaii 1
•
Environmental Protection Agency –
Mr. Brian Dickens -
Technical Discussions
–
Financial Support
•
Eastern Research Group, Inc.–
Mr. Paul Buellesbach
•
Technical Review–
Dr. Ahti
Suo-Att
ha
–
Mr. Larry Berg
•
Mr. Scott Smith, Zeeco–
Flare Photograph
2
•
Identify & Quantify Generalized Flare Performance Parameters for Allowing High Flare Combustion Efficiency–
Open, single-stage, steam-assisted flares
–
How do Vent LHV and Flare LHV affect flare performance?–
How much steam can be effectively added to reduce smoke?
–
For various fuels, purge gases
•
Apply Mass and Energy Balances
•
Approach Applicable to other Flare Systems3
4
•
Vent Gas =
•
Flare Gas = vent gas + pilot fuel/air + steam
•
Adiabatic Temperature = maximum temperature of a flare gas –
air mixture
•
Flammability Ratio = volume fraction of fuel in the flare gas –
air mixture (includes steam, purge gas)
•
Lower Heating Value = heat of combustion of a stoichiometric, fuel–air mixture with water vapor product 5
WasteFuel Gas
+ SupplementalFuel Gas
+ PurgeGas
•
Structural–
Diameter
–
Length •
Operational–
Flow Rates:
waste fuel
purge gassupplemental fuel
steam
pilot fuel/air
combustion air•
External–
Wind velocity, ambient air conditions
6
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛++
Δ=
S
S
P
P
F
F
FCFf
MWW
MWW
MWWVol
HWLHV)(
))(()(
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛++
Δ=
S
FS
P
FP
F
FC
MWWW
MWWW
MWVol
H)/()/(1)(
)(
(LHV)f
independent of mass flow rates, flare diameter and height(ΔHC
)F
near-constant for typical hydrocarbons (weight basis)
For small purge flow, value of steam/fuel to maintain (LHV)f
⎟⎠⎞
⎜⎝⎛=⎥
⎦
⎤⎢⎣
⎡−
Δ=⎟⎟
⎠
⎞⎜⎜⎝
⎛≈⎥
⎦
⎤⎢⎣
⎡+ VG
SMWMW
VolLHVMWH
WW
WWW
F
S
F
SCF
F
S
PF
S
)(
Increasing purge flow adds to supplemental fuel requirement 7
Kanary, GlassmanFuel Mol. Weight LHV kcal/g Stoich
vol. % Lean Flam Limit, % stoich. (avg
= 54)
Benzene 78.1 9.56 0.0277 48
1, 3-Butadiene 54.1 10.87 0.0366 54
n-Butane 58.1 10.92 0.0312 58
2-Butene 56.1 10.82 0.0377 53
Cyclohexane 84.2 10.47 0.0227 57
Cyclopentane 70.1 10.56 0.0271 55
n-Decane 142.3 10.56 0.0133 56
Ethane 30.1 11.34 0.0564 53
n-Heptane 100.2 10.62 0.0187 56
n-Hexane 86.2 10.69 0.0216 56
Kerosene 154.0 10.30 --- 53
Methane 16.0 11.95 0.0947 58
n-Nonane 128.3 10.67 0.0147 58
n-Octane 114.2 10.70 0.0165 58
n-Pentane 72.1 10.82 0.0255 55
l-Pentene 70.1 10.75 0.0271 42
Propane 44.1 11.07 0.0402 51
Propene 42.1 10.94 0.0444 54
Toluene 92.1 9.78 0.0227 53
xylene 106.0 10.30 --- 56
Gasoline 73 octane 120.0 10.54 --- ---8
Fuels MethanePropaneButadienen-octane
Purge Gas Mass Flow Rate3 levels
Steam/Vent Gas1, 2.5, 4
Flare Gas LHV50 –
400
9
(Tad
, LHVflare
, LHVvent
, FR)
0
500
1000
1500
2000
2500
3000
3500
4000
0 50 100 150 200 250 300 350 400 450 500
Flare Gas Lower Heating Value (BTU/scf)
Add
iaba
tic F
lam
e Te
mpe
ratu
re (F
)
MethanePropeneButadienen-OctaneLog (all data)
R2 = 0.9816
Flare Gas Lower Heating Value (BTU/scf)
Adi
abat
ic F
lam
e Te
mpe
ratu
re (F
)
10
Purge Gas (1, 2, 3X), Steam/Vent Gas (1, 2, 3)
0
500
1000
1500
2000
2500
3000
3500
4000
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Vent Gas Lower Heating Value (BTU/scf)
Add
iaba
tic F
lam
e Te
mpe
ratu
re (F
)
MethanePropeneButadienen-Octane
Vent Gas Lower Heating Value (BTU/scf)
Adi
abat
ic F
lam
e Te
mpe
ratu
re (F
)
11
)]/()/[()]/()/()/[()/()(
PPFF
SSPPFFFv MWWMWW
MWWMWWMWWLHVLHV+
++=
•
Required Vent (LHVv
) Heating Values always greater than flare LHVF
• With no steam, values equal
• Flare temperature does not correlate with vent LHV
12
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Steam/Vent Gas Ratio
Fuel
Flo
w (l
bm/h
r)
MethanePropeneButadienen-Octane
Steam/Vent Gas Ratio
Req
uire
d Fu
el F
low
(lbm
/hr)
13
0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200 250 300 350 400 450
Flare Gas Lower Heating Value (BTU/scf)
Lim
iting
Ste
am/V
ent G
as R
atio
MethanePropeneButadienen-Octane
Flare Gas Lower Heating Value (BTU/scf)
Max
imum
Ste
am/V
ent G
as R
atio
14
(Without Purge Gas)
•
Fuel –
Air OnlyFuel/(Fuel + Air) = Stoichiometric Ratio
•
Flare Gas –
Air (Combustion Zone Gas)Fuel/(Flare Gas + Air) = Flammability Ratio (FR)m
•
FRm
includes inert diluentsPurge GasCarbon Dioxide (from pilot fuel/air)Steam
15
16
17
Adi
abat
ic F
lam
e Te
mpe
ratu
re (F
)
Mixture Flammability Ratio FRm
For Steam-assisted Flares:•
Flare Operating criteria established via application of mass and
energy balances and hydrocarbon flammability limits
–
Recommended standards not dependant on stack diameter or capacity
–
Flare gas lower heating value (LHV)f
appropriate energy standard for setting flare gas energy level (correlates with adiabatic flame temperature, Tad
)–
Vent gas heating value (LHVg) not appropriate energy standard (low correlation to T
ad)–
Minimum LHVf
(ca. 200 Btu/ft3) required to maintain efficient combustion above lean flammability limit
–
LHVf
values above ~300 Btu/ft3
restrict steam use, S/V mass ratio < 2–
Appears to be a “Maximum Steam/Vent mass ratio”
based on LHVf
–
Fuel requirements to maintain flare gas LHV reach extreme levels
for steam rates above S/V ~ 3/1
–
With negligible purge rate, maximum steam rate can be calculated
directly to maintain LHVf
≥
200 Btu/ft3
•
Recommended Standards for Steam-assisted flares–
200 ≤ LHV(flare gas) ≤ 300 Btu/ft3
– (S/V)max ≤ 3 18
•
Currently, these standards are only applicable to steam- assisted flares
•
Only apply to hydrocarbon fuels (not hydrogen, acetone, ammonia, alcohols)
•
These do not guarantee high combustion/destruction efficiency
•
Applicable to “similar”
waste and supplemental fuels•
Considers “inert”
purge gas
•
Correlation of flare combustion efficiency data required to to establish flare standards
•
Fuel tendencies of soot formation not considered
Generalized Application of this method can reduce or eliminate limitations!
20
Recent Flare Test Data
•
Work by EPA with John Zink and Marathon illustrate applicability of these methods
•
Next few slides were taken from a recent report issued by Marathon Oil Company
Draft -
Enforcement Confidential
Comparison of Recent data t Pohl’s data for 97-98% Combustion Efficiency Points
ED
A11B
A19
MPC TxCity
9/09
Combining Recent Marathon Data with earlier Pohl Data, is there an equation which relates “Exit velocity”
to “Flare Gas
Heating value”
for Combustion Efficiency > 98%?
Pohl & MPC Data
y = 326.2x0.1635
0
100
200
300
400
500
600
700
800
0.1 1 10 100
Exit Velocity (ft/s)
Hea
ting
Valu
e (B
TU/s
cf)
Series1
Pow er (Series1)
What about Flare Flame Shape as effected by wind and Combustion Efficiency?