United States
Environmental
Protection Agency
Office of Enforcement
and Compliance
Assurance (2201 A)
EPA 325-F-012-002
S1 Enforcement Alert
' PROffc ^J
Volume 10, Number 5
Office of Civil Enforcement
August 2012
EPA Enforcement Targets Flaring
Efficiency Violations
Purpose
EPA is devoting significant enforcement resources to
correcting regulatory noncompliance at flares. This Alert
is intended to inform flare owners and operators of this
enforcement initiative and to educate them on proper flare
operation. EPA hopes this Alert will spur improvement of flare
operating practices, including better control and monitoring
of supplemental gas, air, and steam, and thereby reduce
harmful emissions to the environment. Better flare operation
practices will have the potential to improve public health by:
1) reducing emissions of toxic air pollutants that may pose
a health risk; and 2) reducing volatile organic compound
emissions which will in turn reduce the formation of ozone
which is potentially harmful to vulnerable populations
including the young, elderly, and those with respiratory
problems. Moreover, improving flare combustion efficiency
can result in cost savings due to reduced steam usage.
Introduction
Chemical and petroleum facilities generate waste gases
that need to be controlled safely, economically, and in a
manner that protects the public health and the environment.
The law requires facilities to use good air pollution control
practices to minimize the emission of waste gases, see
EPA's October 2009 Enforcement Alert, http://www.epa.
gov/compliance/resources/newsletters/civil/enfalert/flaring.
pdf
j. _n j._ ^^
EPA investigations have found
flares that were operated so
poorly that there was likely no
combustion taking place at all.
In these circumstances the flare
Because, not all waste
gases can be prevented or
recovered, various control
technologies are used
to reduce the impact of
these waste streams on the
environment; one common
technology is flaring. A flare
is a mechanical device used to combust and thereby destroy
volatile organic compounds, toxic compounds, and other
pollutants at refineries and other industrial sites.
was merely venting pollution
directly to the atmosphere.
Federal requirements for flares are found in the
New Source Performance Standards (NSPS) in
§ 60.18 and National Emission Standards for
Hazardous Air Pollutants (NESHAP) in § 63.11.
At a minimum, these rules require flares to be:
• Designed and operated with no visible emissions
using EPA Method 22 (except for periods not to
exceed 5 minutes in 2 hours);
• Operated with a flame present at all times, confirmed
by the use of a thermocouple or equivalent device;
• Used only when the net heating value of the gas to be
combusted is 300 BTU per standard cubic foot (BTU/
scf) or greater (if the flare is steam- or air-assisted),
or 200 BTU/scf or greater (if the flare is nonassisted);
and
• Designed for and operated with an exit velocity less
than 60 feet per second (ft/sec). An exit velocity of
greater than 60 ft/sec but less than 400 ft/sec may
be used if the net heating value of the gas being
combusted is sufficiently high.
Through its inspection and enforcement programs,
EPA has identified many instances where flares have been
improperly monitored and operated. The consequences
are lower combustion efficiency and potentially significant
quantities of excess emissions of volatile organic chemicals,
sometimes including hazardous air pollutants.
Flare Design Characteristics
Flares are specifically designed to combust gases. Many
flares employ steam or air to promote mixing of oxygen
within the Vent Gas to ensure
combustion occurs without smoke.
There are many parameters that
affect the combustion efficiency of
a flare. One important parameter is
the heating value of the gases that
are to be combusted, often measured
in BTU/scf. The heating value is a
measure of the combustibility of the
gas. Generally, it is easier to maintain a stable flame and
achieve high efficiency for gas streams with higher heating
Smoke is an
indication that
hydrocarbons are
not being combusted
completely.
http://www.epa.gov/compliance/resources/newsletters/civil/enfalert/index.html
-------
Enforcement Alert
values. The NSPS and NESHAP requirements regulate the
net heating value and require gases contain at least 300 BTU/
scf if they are being combusted in an air or steam assisted
flare. If this heating value minimum cannot be met by the
Vent Gases alone, then supplemental gas, such as natural
gas, must be added.
Federal regulations prohibit extended periods of smoking
at flares. Adding the proper amount of steam or air to
avoid smoke is beneficial, but adding excessive amounts is
detrimental. Excess steam or air mixed with the Vent Gas
cools the flame and dilutes the Vent Gas thereby lowering
the heating value. Steam addition is usually measured as the
ratio of pounds of steam per pounds of Vent Gas (Ib/lb). There
is no single steam-to-Vent Gas
ratio that is appropriate for all
flares. The types of compounds
being combusted, and to some
extent the flare design, determine
the proper ratio. There are,
however, general guidelines
that suggest approriate ratios,
with the most important
being the manufacturers'
recommendations, which tend
to be between 0.1 and lib steam per Ib of Vent Gas.
Vent Gas is the mixture
of gases that are to be
combusted, usually found
just inside the flare. The
Vent Gas consists of
combustible process gases.
supplemental gas, inert
compounds, purge/sweep
gases, and other material.
Too little steam -
Smoke due to poor
mixing and lack
of oxygen ^
Good Combustion
-Turbulent, Hot Flame
Too much steam -
Diluting and
cooling the flame
In addition to the numeric standards governing flares
(e.g., net heating value, exit velocity), there are NSPS and
NESHAP general provisions that require process and pollution
control equipment be operated using good air pollution
control practices to minimize emissions, and in accordance
with the equipment's design. Since it would be impossible
for EPA to list all "common practice" actions for equipment
owners (e.g., keep equipment from freezing, keep electrical
equipment dry), these two narrative standards minimally
require a flare operator to follow the equipment manufacturers'
specifications, and to stay abreast of and apply the current state
of scientific knowledge on flare operation and combustion to
minimize emissions.
[Federal requirements for equipment operators' I
general duty are found in the NSPS and NESHAP.
• "At all times, including periods of startup, shutdown, and malfunction
I ...the operator shall operate and maintain any affected source,
including associated air pollution control equipment in a manner
consistent with safety and good air pollution control practices for
minimizing emissions." See, e.g., 40 CFR § 63.6(e), 40 CFR § 60. ll(d).
• "Operators of control devices that are used to comply with the
provisions of this subpart shall monitor these control devices to
ensure that they are operated and maintained in conformance with
their design. See, e.g., 40 CFR § 63.172(e), 40 CFR § 60.482-10.
A number of studies have been conducted to assess
flare efficiencies and to identify the factors that affect flare
performance. One simple and critical parameter already
mentioned is the steam-to-Vent Gas ratio. Another parameter
with an even better correlation to combustion efficiency for
steam assisted flares is the heating value of the combustion
zone gas. EPA's recent settlements define combustion zone
gas as all Vent Gas, pilot gas, and all steam just outside the
flare tip, where combustion is supposed to take place. This
parameter is not to be confused with the net heating value of
Vent Gas found in current regulations which does not include
steam or pilot gas and is measured just inside the flare. In
the enforcement context, EPA may analyze the heating value
of the combustion zone gas to estimate a flare's combustion
efficiency. A finding of low combustion efficiency is
indicative of a potential failure to comply with the general
duty provisions discussed above.
Recent Flare Testing and the Net Heating Value of the
Combustion Zone Gas.
• The net heating value in the combustion zone (NHVcz) gas
correlates well with combustion efficiency for steam assisted
flares. It is a better indicator of efficiency than the heating
value of the Vent Gas alone.
• NHVcz is currently not a regulatory requirement, and is
different from the current Vent Gas heating value minimum
standards of 200 and 300 BTU/scf.
• NHVcz is calculated using the Vent Gas heating value, the
flow rates of Vent Gas, steam and the pilot gas (as per recent
settlements).
• NHVcz is closely related to another parameter, the Lower
Flammability Limit of the Combustion Zone.
• Recent testing provides insight into NHVcz and its relation-
ship to efficiency:
o "TCEQ 2010 Flare Study", Texas Commission on
Environmental Quality, August 1, 2011.
http://www.tceq.texas.gov/assets/public/implementation/
air/rules/Flare/2010flarestudy/2010-flare-study-final-report.
pdf
o "Performance Test of a Steam-Assisted Elevated Flare
with Passive FTIR" for Texas City and Detroit, Marathon
Petroleum Corporation, September 2009 and July 2010.
http://www.epa.gov/compliance/resources/publications/
civil/programs/caa/texascity-report.pdf
http://www.epa.gov/compliance/resources/publications/
civil/programs/caa/detroit-report.pdf
o "PFTIR Tests of Steam-Assisted Elevated Flares - Port
Arthur", Flint Hills Resources Port Arthur, LLC, June 2011
http://www.epa.gov/compliance/resources/publications/
civil/programs/caa/portarthur-report.pdf
August 2012
-------
Enforcement Alert
Factors Affecting Flare Performance:
1. Flame Quenching in the Combustion Zone
Mixing is important because the Vent Gas and oxygen must be well mixed to complete combustion.
Studies indicate that the assist-to-gas (steam-to-Vent Gas or air -to-Vent Gas) ratios are critical to combustion efficiency.
Generally speaking, steam-to-Vent Gas ratios ranging between approximately 0.2 and 1.0 will result in the highest
efficiency. Supplying a mass of air less than approximately 7 times the stoichiometric mass of air will result in the
highest efficiencies.
Problems occur when flame quenching takes place, sometimes termed "oversteaming" or "overaeration," which
occurs at high assist-to-gas ratios. The problems occur because:
• Facilities mistakenly believe that excess steam or air will allow good combustion.
• Facilities fail to reduce steam or air when Vent Gas flow transitions from high to low.
• Facilities have minimum steam addition rates to protect the flare tip from overheating. During low waste gas flow,
the resulting steam-to-Vent Gas ratio can be very high, causing oversteaming.
• The steam control equipment associated with a steam-assisted flare lacks adequate flow adjustment precision, which
results in excess steam now at low waste gas flow.
• The air blower associated with an air-assisted flare lacks adequate flow adjustment, which results in excess air at
low waste gas flow.
These problems lead to significantly lower flare combustion efficiencies.
To correct these potential problems, facilities can use one or a combination of techniques, including:
• Continuously measure the flow rate of the waste gas and continuously measure, and then control, the steam or air
being added as assist gas. Follow the manufacturer's recommendations and publicly available documents in setting
proper assist gas rates.
• Utilize automatic damper actuators or variable frequency drives on the air supply system.
• Reduce the "minimum" or "cooling" steam rates as low as possible while still being protective of the physical
integrity of the flare.
Factors Affecting Flare Performance:
2. Low Heat Value in Vent Gas
Vent Gas Heating Value is important because sufficient combustible material must be present to maintain flame
stability and achieve high efficiency.
Problems occur because facilities use flares to control waste gases that have low heating value without adding
supplemental fuel to raise the Vent Gas heating value to the regulatory minimum of 200 BTU/scf or 300 BTU/
scf. See, e.g., 40 CFR 60.18(c)(3)(ii). This issue is not to be confused with NHVcz and flame quenching discussed
above. Low heating value in Vent Gas occurs because:
• Facilities use flares to control a variety of streams with varying quality. When only one or a few low-flow sources
are venting to the flare, the volumetric flow and combustible material concentrations can be minimal.
• Batch processes are inherently variable and will have periods of very low flow or high inert (e.g., nitrogen)
concentrations. Inert gas lowers the heating value of the gas mixture.
• Supplemental fuel requirements can be costly; facilities may choose not to incur that cost and will combust the
low heating value stream alone.
• Facilities conduct compliance tests under themaximum conditions where problems with low heating values are
unlikely. In practice, flares are not always operated at these "ideal" rates.
These problems lead to lower flare combustion efficiencies.
To correct these potential problems, facilities can:
• Ensure that the Vent Gas meets the current regulatory heating value limits of 300 BTU/scf for assisted flares, and
200 BTU/scf for unassisted flares, at all times. This will require evaluating the heating value of Vent Gas over the
full range of operating scenarios.
• Determine the heating value of the Vent Gas as a whole, not only the hydrocarbons in the Vent Gas, just before it
leaves the flare tip. The heating value evaluation includes nitrogen and any other compounds that make up the gas
mixture that is present just inside the flare tip.
• Monitor the Vent Gas flow and automatically supply supplemental fuel if the Vent Gas does not have sufficient
heating value.
• Evaluate other control options and limit flare use to true emergency situations.
August 2012 3
-------
Enforcement Alert
Well Operating Flare - High Combustion Efficiency
Marathon, BP North America, and Ongoing
Enforcement
Two recent judicial settlements, one with the Marathon
Petroleum Company and another with BP North America,
include injunctive relief designed to address potential
oversteaming issues and limit the level of future flaring. See,
http: //www. epa. go v/compliance/re source s/case s/civil/caa/
marathonrefining.html and http://www.epa.gov/compliance/
resources/cases/civil/caa/bp-whiting.html. These settlements
highlight, in addition to liability related to the general duty
provisions discussed above, potential New Source Review
(NSR) liability at flares. This liability stems from periods
of low combustion efficiency that result in higher pollutant
emissions. A source's failure to recognize and account for
these emissions can result in NSR violations. In addition, oil
refiners face possible NSPS Subpart J/Ja liability because of
the potential of burning non-compliant gas in flares.
Flare compliance is an ongoing priority for EPA generally
and under the Air Toxics National Enforcement Initiative
specifically, http://www.epa.gov/compliance/data/planning/
initiatives/initiatives.html#airtoxic. EPA encourages any
company that believes it may have operated flares in a manner
that resulted in poor combustion efficiency to expeditiously
disclose and correct violations.
If Vent Gas is being sent to a flare but there is no visible flame,
or if only a steam plume is visible, the flare may be operating at
low combustion efficiency, ft is better for the environment for a
flare to produce a farge orange/yeffow flame than no flame at aff
when Vent Gas is present.
Penalties for Violations
Violating federal requirements for flares can result in
a penalty, under the Clean Air Act, of up to $37,500 per
violation, per day. To knowingly violate a flare requirement,
including knowingly making a false or fraudulent statement
or omiting material information required concerning a flare
and its operation, can subject a person to criminal prosecution.
Convictions can result in fines, imprisonment, or both.
Conclusion
EPA Enforcement is investigating and seeking resolution
of low heating value and excess steam or air addition at
industrial flares. When flaring is unavoidable, Vent Gas must
be monitored and its heating value adjusted as necessary in
order to meet the current regulatory standards for the heating
value of Vent Gas. Moreover, monitoring the Vent Gas and
steam or air flow and applying steam or air and supplemental
gas in an amount that results in high combustion efficiency
helps assure compliance with the general duty requirements.
Finally, flare owners are expected to operate in accordance
with the manufacturer's recommendations and publicly
available documents, including the long-available literature
from EPA, and generally available documents regarding the
current state of scientific knowledge on flare operation and
combustion.
Poorly Operating/Over Steamed Flare - Low Combustion
Efficiency
Disclaimer: This document puts EPA regulatory provisions in context with plain language. Nothing in this Enforcement Alert revises or replaces any
regulatory provisions in the Rule, any other part of the Code of Federal Regulations, the Federal Register, or the Clean Air Act. For more information
go to: www.epa.gov/compliance.
August 2012
------- |