POWER April 2012 - 40

BIOMASS POWER
Has Boiler MACT Improved the
Future for Biomass Power?
The impact of recently released air emissions regulations has stirred heated
debate about forced coal plant closures and the possibility of reduced grid
reliability in some regions. Biomass power may be an unexpected beneficiary
of the new rules.
By Brandon Bell, PE, KBR Power & Industrial
O
n Dec. 23, 2011, the U.S. Environmental
Protection Agency (EPA) released
proposed changes to the Promulgated
Rule of the National Emission
Standards for Hazardous Air Pollutants,
also referred to as Boiler MACT, for both
" Major Source " and " Area Source " facilities.
When Boiler MACT was promulgated
on Mar. 21, 2011, the EPA recognized
some provisions might be too stringent
for facilities covered by the regulation.
Therefore, the very same day, the agency
issued a notice of its intent to reconsider
certain provisions of the just-released rule.
A formal extension of the effective date of
Boiler MACT was announced on May 18,
2011, with a request to the public to supply
data to assist the EPA in its reconsideration
efforts. Affected industries still have
until 2015 to comply with the rule.
The EPA next released the final Mercury
and Air Toxics Standards (MATS) on Dec.
21, 2011. Proposed changes to the CrossState
Air Pollution Rule (CSAPR) were
released Dec. 23, 2011, and immediately
stayed by the U.S. Court of Appeals for the
District of Columbia Circuit on Dec. 30,
two days before the rule's effective date.
Unfortunately, the sometimes-heated
discussions of MATS and CSAPR and
their impact on the reliability of the nation's
power supply have obscured the
possibly positive impact of Boiler MACT
on biomass plants.
Rules Benefit Biomass
It may surprise you to learn that this increased
pressure from the EPA on coalfired
generators (expected to cause 40 GW
to 50 GW worth of coal plant closures),
coupled with the demand for renewable
energy sources, is having an unexpected
side effect: It's making biomass a more attractive
power generation alternative. Furthermore,
the changes the EPA is expected
to make to the Boiler MACT rule will favor
biomass power much more than in the
40
Table 1. Summary of hazardous air pollutants and their limits in the
promulgated Boiler MACT rule. Source: EPA
Combustion technology
Fluidized bed, existing
Fluidized bed, new
Stoker/other, existing
Stoker, new
Dutch oven/suspension, existing
Dutch oven/suspension, new
Fuel cells, existing
Fuel cells. new
Suspension/grate, existing
Suspension/grate, new
earlier version. Those expected improvements
are discussed in greater detail later
in this article.
The revised Boiler MACT regulation
appears to favor biomass power in the impact
it has on required emission reduction
technologies. As it stands, the promulgated
rule will require the addition of multiple
emission reduction systems in order to
meet pollutant limitations. The proposed
regulation removes and reduces many of
the limitations, thus the positive impact on
the economics of biomass plants.
There are three categories of hazardous
air pollutants (HAPs) in the promulgated
Boiler MACT rule, under Major Sources,
that place new limitations on pollutant
emissions from both existing and new biomass
facilities: hydrogen chloride, mercury,
and dioxins/furans (Table 1).
Determining an uncontrolled emission
rate for each of the three HAPs is a major
concern with meeting these limitations.
Biomass typically does not have consistent
characteristics because it is not always
procured from the same source. Due to
sourcing inconsistencies, environmentally
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Hydrogen chloride
limitation (lbm/106 Btu)
0.0350
0.0022
0.0350
0.0022
0.0350
0.0022
0.0350
0.0022
0.0350
0.0022
Notes: dscm = dry standard cubic meter, lbm = pound mass, ng = nanogram.
regulated constituents in the fuel may vary
greatly. For new biomass plants, there is
some consistent data for woody biomass
that could be used to produce baseline
emissions to estimate reduction percentages.
However, for many other biofuels
(including switchgrass, corn stover, and
miscanthus) there is sparse, if any, information
pertaining to the regulated HAPs.
Even with the lack of data, control technologies
will be required to meet the Boiler
MACT requirements.
HAPs Ripe for Removal
For biomass combustion, the control of
mercury and dioxin/furan emissions is
most effective when using a powdered
activated carbon (PAC) injection system.
Mercury can be a particularly difficult pollutant
to control and is generally found in
low concentrations in biomass fuel. After
completing the combustion process, mercury
exists in three forms: an elemental
state (Hg0
), a divalent state (Hg++
), or as
particulate.
Mercury in a particulate form is the
easiest to control, as it will be captured
POWER | April 2012
Mercury limitation
(lbm/106 Btu)
0.000005
0.000004
0.000005
0.000004
0.000005
0.000004
0.000005
0.000004
0.000005
0.000004
Dioxin/furan
limitation (ng/dscm)
0.020
0.020
0.005
0.005
0.200
0.200
4.000
0.003
0.200
0.200
http://www.powermag.com
POWER April 2012

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