NOx
Understanding NOx and
Air Regulatory Drivers for NOx Control
March 6, 2014
Raymond R. Allen, PE
Evergreen Environmental Consulting LLC
9633 Octavia Ave. – Baton Rouge, LA 70809
Office: 225-778-5813 – Cell: 225-590-0491
[email protected]
www.evergreenenvironmentalconsulting.com
New “100 ppb” 1-hr NO2 NAAQS
 It’s a NO2 standard and not a NOx standard!
 Final rule for the new 1-hour NO2 National Ambient Air Quality Standard
(NAAQS) in February 9, 2010 Federal Register – Effective April 12, 2010
1-hr NO2 NAAQS is attained at a given receptor location when the 3???  The
th-percentile of the annual distribution of daily
year
average
of
the
98
Explained
in Slide 7
maximum 1-hour NO2 concentrations does not exceed 100 ppb
 Industry legally challenged this new standard, but the U.S. Court of
Appeal – DC Circuit upheld the new NO2 1-hr NAAQS in July 2012
 In January 2012 EPA designated all areas of the country as
“unclassifiable/attainment” for the 2010 1-hr NO2 NAAQS.
FYI: Even though data from EPA’s extensive national network of NO2 ambient monitors
indicate Attainment with the 1-hr NO2 NAAQS across the U.S., some facilities that are
now seeking NSR permits find it very difficult to demonstrate 1-hr NO2 NAAQS compliance
due to EPA’s overly-conservative dispersion modeling guidelines and policies
2
History of the NO2 NAAQS
39 Years!
1985 EPA Finding: No Changes to NO2 NAAQS Warranted
1996 EPA Finding: No Changes to NO2 NAAQS Warranted
Source: Integrated Science Assessment for Oxides of Nitrogen – Health Criteria – First External Review Draft – 11-2013
3
Design Value: 1-hr NO2 NAAQS
NO/NO2/NOx Monitor
2009 calendar year of 1-hr NO2 monitoring data
Ambient-Air
Monitoring Station
365 days
The 1-hr NO2 NAAQS is attained at a given monitor location when the 3-year average of the 98th-percentile
(8th highest) of the annual distribution of daily maximum 1-hour NO2 concentrations does not exceed 100 ppbv
24 hr
High
1
365 daily max 1-hr NO2 concentrations sorted high to low
2
3
4
5
6
7
8
9
10
11
12
The 98th percentile “cut point” for 365 data points ≥ 365 x (1-0.98) ≥ 7.3 = 8th highest value
= 8th highest daily maximum 1-hr NO2 concentration recorded during calendar year 2009
Ambient Monitor Design Value: A
statistic that describes the air quality status
of a given location (Attainment or NonAttainment) with a NAAQS
4
Low
A similar exercise was performed
with 2010 and 2011 1-hr NO2
data. The three 8th highest dailymaximum 1-hr NO2 results for
2009-2011 are averaged:
2009 8th HDM: 98 ppb
2010 8th HDM: 102 ppb
2011 8th HDM: 97 ppb
NO2 Design Value = 99 ppbv
1-hr NO2 NAAQS Attainment
New 1-hr NO2 NAAQS Challenges
 Air Permitting Perspective: Demonstrating compliance with
the NO2 1-hr NAAQS has proven to be an extreme challenge
for air dispersion modelers, and as a result some major plant
expansions may have to rely on retrofit NOx control projects
in order to legitimately “net out” of NSR review for NOx
 EPA Modeling Guidance Still Overly-Conservative: “Additional Clarification
Regarding Application of [40 CFR 51] Appendix W Modeling Guidance for the
1-hour NO2 National Ambient Air Quality Standard” issued March 1, 2011 and
a prior memo dated June 29, 2010 – some key issues:
NO
NO2
 Handling the conversion of NO to NO2 in the ambient air
 Establishing a realistic 1-hr background NO2 concentration for use in air quality
demonstrations involving dispersion modeling
HEADS UP: The 1-hr NO2 NAAQS is not the only new NOx-based
challenge to NSR permitting - NSR rules now link both Ozone and
PM-2.5 ambient air standards with NOx emission increases
5
NOx Regulatory Definitions
 SIP Definition from 40 CFR 51.50: “Nitrogen Oxides (NOx) means nitrogen oxides
as defined in 40 CFR 60.2 and all oxides of nitrogen except N2O [nitrous oxide].
Nitrogen oxides should be reported on an equivalent molecular weight basis as
nitrogen dioxide (NO2)” [NO2 Molecular Weight = 46.0]
 NSPS Definition from 40 CFR 60.2: “Nitrogen oxides means all oxides of nitrogen
except nitrous oxide, as measured by test methods set forth in this part”
[Reference Method 7 series – 7, 7A, 7B, 7C, 7D, 7E]
CLARIFICATION: Most current-day NOx stack tests are conducted per Reference Method 7E,
an instrumental technique basically identical to a NOx/O2 CEMS. Method 7E is capable of providing
the stack gas total NOx concentrations (ppmvd @ stack O2d) as well concentrations for NO and NO2
individually – ensure your stack tester provides speciated NO and NO2 test
data because it may be needed for an NO2 ambient-air compliance demonstration. Method 7E
reports NOx mass emissions “as NO2”. All NOx mass emission calculations used for regulatory
purposes should likewise assume all measured stack-gas NOx exists in the form of NO2 (MW = 46.0)
6
Key NOx Components: NO and NO2
Nitric Oxide
MW = 30.01
The Greenhouse Gas Nitrous
Oxide (N2O) is NOT NOx
Nitrogen Dioxide
MW = 46.01
SIMPLIFYING ASSUMPTION: Most of
our focus today is on current regulatory drivers
to install NOx emission controls on new and
existing industrial combustion processes. In
this context, you can generally treat NOx as a
simple two-components mix of NO and NO2
7
Other NOx Components
Potential PM-2.5
Precursors
Nitric Oxide
MW = 30.01
Nitrous Acid – HNO2
Dinitrogen
Trioxide – N2O3
Does the scientific evidence really support
regulating secondary PM-2.5 formed from NOx?
Dinitrogen
Tetroxide – N2O4
Dinitrogen
Pentroxide – N2O5
Nitric Acid – HNO3
Trinitramide
N(NO2)3
REPEATING: Generally treat NOx as a simple two-component mixture of NO and NO2
HOWEVER: As upcoming slides show, in the ambient air certain NOx constituents can
potentially undergo reactions to form two other criteria pollutants: Ozone and PM-2.5
8
Three Stages of NOx Chemistry
Fuel
Air
COMBUSTION
PROCESS NOx
SNAPSHOT OF
IN-STACK NOx
Combustion
process NOx
formation is
addressed in our
next presentation
by Tom which
focuses on NOx
emission controls
ISR: A helpful
parameter in PSD
modeling is the
in-stack molar
ratio of NO2 to
total NOx
N2 + O 2
NOx
NOx = NO + NO2
NO2 (ppmv)
ISR =
NOx (ppmv)
POST-STACK NOx
AMBIENT-AIR REACTIONS
1. NO to NO2 Conversion
NO
NO2
2. Ozone Formation
NOx + VOC uv O3
3. PM-2.5 Formation
NOx + Other
PM-2.5
What happens in the Black Box?: NSR regulations now require us
to consider the impact of NOx emissions on ambient-air NO2, Ozone & PM-2.5
9
NO
NO2 Equilibrium in Ambient Air
 Stack test data vary significantly, but as a rough rule of thumb, the NO2-to-NOx ISR
is ~ 0.1 (stack gas has 10% NO2 and 90% NO) - EPA modeling guidance allows a
conservatively-high default ISR of 0.5 (50/50 spilt of NO/NO2)
 For emitted NOx EPA’s 1-hr NO2 modeling guidance assumes that when chemical
equilibrium is achieved in the ambient air, the ratio of NO2-to-NOx is 0.8 (emitted
NOx ends up as 80% NO2 and 20% NO in ambient air)
 NO-to-NO2 reaction goes both ways, but the ultimate outcome is a post-stack
conversion of NO-to-NO2 via several chemical reactions, including reactions that
form ozone and PM-2.5 pollution
 EPA’s models are based on ozone
reacting as a as a strong “NO
scavenger” which converts NO to NO2
– hence higher ozone levels increase
the rate of NO-to-NO2 conversion – is
this always true? See slide after next
10
Black Box Model of NOx in the Ambient Air
INPUTS
Combustion stack-gas with NOx
consisting mostly of NO with much
less NO2 (e.g. NO2/NOx ISR ~ 0.10 )
OUTPUTS
Unfavorable Conditions?
Black Box
VOC & Other Emissions (e.g. CO, NH3)
Ambient Air NOx Pollution with
mostly NO2 and much less NO
(e.g. NO2/NOx Ratio ~ 0.80 )
Ambient Air Ozone Pollution
Ambient Air Secondary PM-2.5
Pollution (nitrate-based)
Sunlight & Clear Skies (or not)
Reactions of VOC, NOx and other chemicals in the ambient air are highly-complex and very
dependent on uncontrollable factors. In general, the presence of Unfavorable Conditions
yields higher levels of all the NOx-related pollutants NO2, O3 and secondary PM-2.5
FOUL CONDITIONS THAT EXASCERBATE NOx-DRIVEN POLLUTION FORMATION
 Hot summer days, daylight hours, clear skies and high sunlight intensity
 Low wind speeds & highly stable meteorology (e.g. Pasquill Stability Class F)
 Presence of higher than normal short-term NOx and VOC emission levels
 Presence of Highly Reactive VOC (HRVOC) emissions
11
NO
NO2 Reality Check
Baton Rouge State Capital Site AAMS – June 2012 Data Averaged by Hour of the Day
60
0.90
0.80
50
0.70
40
0.60
NO2-to-NOx Ratio
30
0.50
0.40
20
0.30
1-hr avg NO2
0.20
10
0.10
0
Hour of the Day
NO2 –to-NOx Molar Ratio
ppbv NO2 or ppbv ozone
1-hr avg ozone
June 2012
Hourly Avg
Ozone
(ppbv)
June 2012
Hourly Avg
NO2
(ppb)
June 2012
Hourly Avg
NO2-to-NOx
Molar Ratio
0.00
Question: Does this slide show that ozone follows EPA’s stated model of reality
by “scavenging NO” to increase both NO2 levels and the NO2-to-NOx ratio?
12
New Source Review (NSR) and NOx
OPTION: If making a
NO2 NAAQS and/or PSD
increment modeling
demonstration becomes
too problematic,
consider installing
retrofit NOx controls and
“netting out” of NSR –
the result is federal
BACT and/ or LAER will
not be required
 NSR permitting is pollutant-specific (NOx, O3, PM-2.5, etc)
 Prevention of Significant Deterioration (PSD) = NSR for
NAAQS attainment pollutants – CAA Title I Part C
 Air quality demonstration via dispersion modeling and ambient
monitoring must show future project won’t cause exceedances of
any NAAQS or PSD increment
 Best Available Control Technology (BACT) required on
project-affected emission units with actual annual emissions
increase of the subject PSD pollutant – case-by-case review
 Non-attainment New Source Review (NNSR) = NSR for
NSR
Regulatory
Drivers for
New NOx
Controls
NAAQS non-attainment pollutants – CAA Title I Part D
 Emission offsets of at ratio > 1:1 required for NSR pollutant – offset
ratio depends on the NA pollutant and the NA area classification
 Lowest Achievable Emission Rate (LAER) technology
required on project-affected emission units with actual annual
emissions increase of NNSR pollutant – most stringent available
13
NSR Applicability Triggers Involving NOx
Wow!
Notes
1. No NO2 non-attainment areas exist in the U.S. Shown here are requirements if such an area is ever designated by EPA.
2. No SIL exists for O3. A more in-depth air study is typically required if a VOC or NOx emission increases exceed 100 tpy.
3. PM-2.5 SILs from 40 CFR 51.165(b)(2). January 2013 Court ruling vacated and remanded other PM-2.5 SILs and SMC,
(was set at 4 μg/m3). Vacated regulations are 40 CFR 51.166(k)(2) & (i)(5)(i)(c) and 52.21(k)(2) & (i)(5)(i)(c).
4. Offset ratio shown for direct PM-2.5. Preamble to the 2008 PM-2.5 Rule identified inter-pollutant offset ratios for direct
PM-2.5 to NOx: Eastern US: 200 ton NOx to 1 ton direct PM-2.5; Western US: 100 ton NOx to 1 ton direct PM-2.5
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NOx Control Driver: NSPS – CAA§111
 Federal New Source Performance Standards (NSPS) codified at 40
CFR Part 60 require technology-based emission controls for certain
categories of industrial facilities when the facilities are either new,
modified or reconstructed after a specified effective date
 NSPS Subpart Ja – Petroleum Refinery Heaters – Post May 14, 2007
(Court-Ordered Stay on Much of NSPS Ja Lifted November 13, 2012)
 Natural Draft Process Heaters Rated to Fire > 40 MMBtu/hr HHV-basis
o
o
Either
Or
40 ppmvd NOx @ 0% O2 – 30-day rolling average
0.040 lb NOx/MMBtu HHV-basis – 30-day rolling average
 Forced Draft Process Heaters Rated to Fire > 40 MMBtu/hr HHV-basis
o
o
Either
Or
60 ppmvd NOx @ 0% O2 – 30-day rolling average
0.060 lb NOx/MMBtu HHV-basis – 30-day rolling average
Are the alternative NSPS Ja Process Heater
NOx limits equivalent? See the next slide
15
40 ppmvd NOx @ 0% O2 = 0.04 lb NOx/MMBtu?
The two compliance options for the NSPS Ja Process
Heater NOx limits are shown to be basically equivalent
16
NOx Control Driver: NSPS – CAA§111
 NSPS Subpart KKKK – Stationary Combustion Turbines Post February 18, 2005
 Proposed Revision to NSPS Subpart KKKK in August 29, 2012 Federal Register
Partial List of Current NSPS Subpart KKKK Combustion Turbine NOx Emission Standards
Large GT > 250 MWe
Proposed NSPS KKKK has no
changes to existing NOx limits,
but does propose compliance with
all NOx limits during startups,
shutdowns and malfunction
• NOTE: EPA is NOT claiming that the NSPS 4K optional NOx
concentration-based limits and the useful-power-output
limits are equivalent – instead, the power output option
rewards facilities with a high level of thermal efficiency
• QUESTION:
In the case highlighted above, what thermal
efficiency “cutoff” dictates whether it’s best to go with the 4K
power-output-based NOx emission limit? See next slide
17
Selecting the Best GT NOx Limit Option
FYI – A PSD BACT level for Greenhouse Gas (GHG) emissions for a
utility combustion turbine in Louisiana was recently set at a heat rate of
7,630 Btu/kW-hr (or thermal efficiency of 44.7%)
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NOx Control Driver: Other NSPS
 NSPS Subparts D, Da, Db & Dc – Boilers of all types and IGCC Units
 Useful power output-based NOx limits added (June 13, 2007 Federal Register)
 NSPS Subpart JJJJ – Spark-Ignition IC Engines (gasoline or gaseous fuel)
 Rule modified multiple times – last revision in the June 28, 2011 Federal Register
 Rule is complex and confusing – EPA website has requirements summary spreadsheet
 NSPS Subpart IIII – Compression-Ignition IC Engines (diesel fuel)
 Rule modified multiple times – last revision in the June 28, 2011 Federal Register
 Rule is complex and confusing – EPA website has requirements summary spreadsheet
 NSPS Rules Not Covered Today: Many other NSPS rules exist covering
combustion equipment not directly addressed in this presentation,
including dryers, calciners and multiple types of incinerators
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NOx Control Driver: Ozone NA SIPs – NOx RACT
 CAA Section 110 requires States to develop and implement State
Implementation Plan (SIP) rules to bring NAAQS non-attainment areas
into attainment – these SIP rules implement Reasonably Available
Control Technology (RACT)
 From a NOx perspective the only NAAQS pollutant currently of
concern is Ozone, given that there are no NO2 non-attainment areas
designated in the U.S., and it is not expected EPA would use a NOx
emission reduction strategy to address PM-2.5 non-attainment areas
 NOx RACT may be a fairly simple set of NOx emission standards, such
as the Louisiana NOx RACT standards shown on the next slide
 In more difficult Ozone non-attainment areas, such as Houston, NOx
RACT has evolved into a stringent NOx cap-and-trade program
&
20
Example: Louisiana NOx RACT Rules
NOTE 1: RACT rules generally
adhere to technology-based
emission limits developed by EPA.
The NOx RACT limits shown here,
from LAC 33:III.Chapter 22, have
been implemented in the BR O3 NA
area. The BR area has recently been
designated as an attainment area for
the 8-hr ozone NAAQS. All RACT
rules remain in place after an area
achieves attainment because of the
CAA’s anti-backsliding provisions
NOTE 2: Louisiana’s NOx RACT limits apply only
during the ozone season (May 1st to September 30th)
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NOTE 3: Louisiana’s NOx RACT
rule has averaging plan provisions
that allow for over-control of certain
sources, while other sources remain
uncontrolled – a “bubble” concept
NOx Control Driver: CSAPR
 Cross-State Air Pollution Rule (CSAPR) replaces EPA’s 2005 Clean Air
Interstate Rule (CAIR), which was vacated by U.S. Court of Appeals – DC
Circuit in 2012 – the U.S. Supreme Court agreed to hear this case in June 2013
and EPA’s opening merits brief filed in September 2013 (www.epa.gov/crossstaterule )
 CSAPR imposes SO2 and NOx cap-and-trade programs on power plants located
in the eastern U.S. and establishes new C&T allowances – the allocation of
allowances amongst affected States and individual utility units is a big issue!
 EPA developed CAIR/CSAPR under the “good neighbor” provisions of the CAA
to reduce ozone and PM-2.5 pollution in downwind non-attainment areas
NOTE : There are
three different types of
emission allowances
under the CSAPR capand-trade program
22
Map of CSAPR-Affected U.S. States
NOTE : All U.S.
States fall into 1 of 4
possible categories
of requirements
under CSAPR’s capand-trade program
Climate
Change is
Real
Folks!
1. Submit CSAPR caption ideas to [email protected]
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Final NOx Control Driver: Consent Decree
As the petroleum refining industry is already keenly aware, regulators are using the Consent
Decree process to extract emission reductions and impose other requirements on industry.
The following definitions from a refinery CD are typical of NOx controls required:
 “Current Generation Ultra-Low NO Burners shall mean the Current Generation Ultra-Low NOx
Burners that are designed to achieve a NOx emission rate of 0.020 to 0.040 lb/MMBtu HHV when
firing natural gas at 3% stack oxygen at full design load without air preheat, even if upon installation
actual emissions exceed 0.040 lb/MMBtu HHV”
 “Next Generation Ultra-Low NO Burners or Next Generation ULNBs shall
mean those burners that are designed to achieve a NOx emission rate of less
than or equal to 0.020 lb/MM Btu HHV when firing natural gas at 3% stack
oxygen at full design load without air preheat, regardless of whether upon
installation actual emissions exceed 0.020 lb/MM Btu HHV”
 “Qualifying Controls for the purposes of NOx control technology for heaters
and boilers, shall mean: SCR or SNCR; Current Generation or Next Generation
Ultra-Low NO Burners; or other technologies or combination of technologies
which COMPANY X demonstrates, to EPA’s satisfaction, will reduce NOx
emissions to 0.040 lbs. per MMBtu or lower. NOx control technology may
include the permanent shutdown of a heater or boiler with revocation of its
federally enforceable operating and construction permits”
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Take-Aways & Closing Remarks
NOx
 EPA revoked the 1-hr O3 NAAQS in favor of an 8-hr O3 NAAQS after many years
of deliberation, primarily because of the complexity of inter-pollutant
reactions in the ambient air – we are now faced with a similar quandary with
the new 1-hr NO2 NAAQS – did EPA fail to learn a lesson from the previous
problems we experienced while implementing the 1-hr ozone NAAQS?
 The federal NSR rules make the presumption that PM-2.5 formation from NOx
precursors is significant enough to require PSD review for PM-2.5 with only a
40 ton/yr NOx emissions increase – is this approach based on sound science?
 As a result of EPA’s overly-conservative NO2 dispersion modeling policies, it is
difficult to make NO2 ambient-air compliance demonstrations – because of
this and other NSR permitting obstacles associated with NOx, some facilities
are choosing to legitimately avoid NOx NSR permitting altogether by installing
retrofit NOx controls and “netting out” of the NSR permitting process
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Take-Aways & Closing Remarks
NOx
 A skilled air permitting and compliance engineer should be fully capable of:
 Comparing alternative NOx emission limits on an “apples-to-apples” basis
 Characterizing and quantifying a combustion unit’s thermal efficiency, if necessary
 Characterizing and quantifying NOx emissions performance during periods of start-
up, shut down, and malfunction
 The Heater & Boiler MACT rules (40 CFR 63 Subparts 5D & 6J) were not
covered today because they do not contain specific NOx emission limits – one
admonition, however, is that when conducting heater or boiler tune-ups under
these rules, ensure nothing is changed that will negatively impact the NOx
performance of any LNBs, ULNBs or any other inherent or add-on NOx controls
 CONCLUSION: There are numerous regulatory drivers that will require the
installation of NOx controls on new and existing combustion units over the
next several years – make sure the best NOx control technology is selected by
gaining a firm understanding of how NOx control technologies work
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