POWER January 2011 - 65

COMMENTARY
Anticipating the New Utility
MACT Rules
By Paul S. Farber, PE, DEE
I
t's been almost three years since the U.S. Court of Appeals
for the D.C. Circuit issued its decision vacating the Environmental
Protection Agency's (EPA) Revision Rule and the
Clean Air Mercury Rule. Since then, the utility industry has
been in a holding pattern with respect to the control of hazardous
air pollutant (HAP) emissions. However, the time draws
near for the EPA to issue its new National Emission Standard
for Hazardous Air Pollutants (NESHAP) regulating HAP emissions
from coal- and oil-fired electric generating units (EGUs).
According to a 2009 consent decree, the EPA must publish its
proposed Utility NESHAP by March 16, 2011. Emission limits
included in the NESHAP must be based on the application of
maximum achievable control technology (MACT).
Forecasting What the New Rules Will Cover
Based on our knowledge of the utility industry, our experience
with EGUs and air pollution control (APC) systems, and a review
of the regulatory history, our predictions are as follows.
First, the Utility NESHAP will include MACT standards for
both new and existing coal- and oil-fired EGUs. The EPA could
also publish an alternative NESHAP for facilities that are
classified as an area, or minor, source of HAP emissions.
Second, the Clean Air Act allows the EPA to divide source
categories into subcategories based on differences in class,
type, or size. In the past, the agency has established subcategories
based on emission characteristics that affect control
technology selection and effectiveness. In our opinion, combustion
processes, fuel characteristics, and emissions from
coal-fired EGUs with dissimilar control technology configurations
are different enough to justify subcategorization. We
think the EPA will subcategorize coal-fired boilers by fuel for
the fuel-related HAPs and that it may further subcategorize
boilers by combustion design for non-fuel-related HAPs.
Third, the EPA likely will expand the number of HAPs regulated
by the Utility NESHAP to include mercury, non-mercury
trace metals, acid gases (hydrochloric acid and hydrogen
fluoride), dioxins and furans (D/F), and non-D/F organic
compounds. Due to emissions monitoring limitations, it is
unlikely that the EPA will require continuous monitoring of
the individual non-mercury trace metals and organic HAP
compounds. It will probably regulate certain HAP categories
using surrogates. The most likely surrogates include filterable
particulate matter less than 10 microns (PM10) as a
surrogate for the non-mercury trace metals and CO as a surrogate
for the non-D/F organics.
Finally, the EPA likely will establish the MACT standards for
each regulated HAP, or surrogate, based on a statistical analysis
of available emissions data. As part of this rulemaking effort, the
EPA initiated an Information Collection Request (ICR) that included
a request that several existing EGUs conduct stack testing
for a variety of HAP compounds. The EPA will probably develop
64
the EGU MACT standards using an approach similar to the one
used in the recently proposed Industrial Boiler NESHAP.
Possible Control Strategies for MACT Compliance
Assuming the Utility NESHAP looks something like what we
are predicting, utilities will have to consider the following
APC strategies for MACT compliance.
Mercury. Regardless of how the EPA subcategorizes the
coal-fired EGUs, it is likely that mercury MACT will reflect an
emission rate based on at least 90% reduction from mercury
in the fuel. Bituminous-fired units may meet their mercury
MACT requirement with flue gas desulfurization (FGD) alone.
These units may need to consider an activated carbon injection
(ACI) system upstream of the unit's particulate control
system if additional mercury control is needed.
Acid Gases. Acid gas emissions are generally a function of
the coal's chlorine and fluorine content. FGD control systems
designed to capture SO2
also effectively capture acid gases. The
acid gas MACT standard for bituminous-fired units will likely require
FGD control. Subbituminous-fired units tend to generate
fewer acid gas emissions; however, based on a review of information
available from the EPA's ICR Part I (Facility Descriptions),
more than 12% of the existing subbituminous-fired units are
equipped with SO2
controls. Therefore, compliance with the acid
or acid gas control.
gas MACT standard for subbituminous-fired units will likely require
some type of SO2
Non-mercury Trace Metals. Almost all existing coalfired
boilers are equipped with either an electrostatic precipitator
or fabric filter baghouse for PM control. Although the
PM MACT standard could be very stringent, we think the MACT
standard for existing coal-fired boilers should be achievable
with either control system.
Organic HAPs. It is expected that the Utility MACT will
have both a D/F emission limit and a non-D/F organic HAP
emissions standard. If the EPA includes D/F emission limits
in the Utility NESHAP, the challenge may be demonstrating
compliance with the emission limit. ACI control systems may
provide D/F emissions control, if needed. If the Utility NESHAP
regulates non-D/F organic HAPs, CO will be probably be
used as a surrogate.
Although stricter MACT emission limits are expected, APC
technologies should be available to meet the MACT standards.
However, because of the interactions between, and
the co-benefits afforded by, conventional APC technologies
in the service of controlling HAP emissions, the biggest challenge
may be developing compliance strategies that address
all HAP standards while avoiding the inclination to focus on
a single HAP to the detriment of another. ■
-Paul S. Farber, PE, DEE (paul.s.farber@sargentlundy
.com) is an environmental engineer at
Sargent & Lundy LLC in Chicago.
www.powermag.com
POWER | January 2011
http://www.powermag.com
POWER January 2011

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