1. L. Douglas Smoot & Robert E. Jackson
Combustion Resources, Inc
Provo, UT
Joseph D. Smith
Systems Analysis and Solutions, LLC
Owasso, OK
IFRC International Pacific Rim
Combustion Symposium
26-29 September 2010
Maui, Hawaii 1
2. • 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
3. • 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 Systems
3
5. • 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
Waste
Fuel Gas
+ Supplemental
Fuel Gas
+ Purge
Gas
6. • Structural
– Diameter
– Length
• Operational
– Flow Rates:
waste fuel purge gas
supplemental fuel steam
pilot fuel/air combustion air
• External
– Wind velocity, ambient air conditions
6
15. • Fuel – Air Only
Fuel/(Fuel + Air) = Stoichiometric Ratio
• Flare Gas – Air (Combustion Zone Gas)
Fuel/(Flare Gas + Air) = Flammability Ratio (FR)m
• FRm includes inert diluents
Purge Gas
Carbon Dioxide (from pilot fuel/air)
Steam
15
18. 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 Tad)
– 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
19. • 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
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
21.
22.
23.
24.
25.
26.
27. Draft - Enforcement Confidential
Comparison of Recent data t Pohl’s data for
97-98% Combustion Efficiency Points
E
D
A11
B
A19
MPC TxCity 9/09
28. 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)
HeatingValue(BTU/scf)
Series1
Pow er (Series1)
29. What about Flare Flame Shape as effected by wind and Combustion Efficiency?