Mercury Hg

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Mercury (Hg)

• The Elemental Challenge to
• Coal-Based Electricity Generation

Rev. 11/1/01
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The Mercury Issue
The committee estimates that over 60,000
children each year are born at risk for adverse
neurodevelopmental effects due to in utero
exposure to methylmercury. National Research
Council of the National Academy of Sciences
(NRC/NAS) July 2000
3
Whats at Stake?

• Uncertain compliance costs for all coal-based
  generation
• EPA 67,700 to 70,000 per pound removed
• RDI estimate 0.5 - 7.8 billion annually
• Adverse public reaction to fish advisories,
  mercury rain, exaggerated risk

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Ultimate Coal Killer?
Some experts fear this may be the beginning of
the end for coal, since the ultimate pollution
control method for mercury in coal is to switch
to gas as a fuel. As a leading industry source
puts it, Everybody has been looking at ozone,
fine particulate and climate change in relation
to coal use, but mercury may be the ultimate coal
killer.
Electricity Daily - April 1998
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Glossary, Sources and Statistics
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Glossary

• Element (Hg is a trace element in coal)
• Elements were created when Earth formed they are
  basic building blocks of chemical compounds
• trace-- found only in minute quantities
• Ubiquitous present everywhere (air, land, water)
• Neurotoxin substance harmful to brain
• Bioaccumulation the building up of a substance
  faster than the body can eliminate it
• Biomagnify to increase in concentration up the
  food chain

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Glossary

• Volatile vaporizes easily
• Speciation changing into different chemical
  forms (species). Common Hg species are
• HgO (elemental)
• Hg2 or HgII (oxidized or ionic)
• Methylmercury (CH3Hg, aka MeHg, which is
  organic)
• Hgp (particulate)
• Cycling movement through air, land, and water

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Glossary

• Fate what happens to the mercury where it goes
• Methylation transformation of Hg to MeHg
• MeHg is organic caused by anaerobic bacteria
• Acute vs. chronic immediate vs. long term
• High dose vs. low dose exposurelarge vs. small
• Reference Dose (RfD) amount that can be consumed
  daily for life without appreciable risk of
  adverse effects

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The Mercury Cycle
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Global Hg Cycle
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Sources of Hg

• Natural primary source
• Degassing of Earths crust
• Ocean and volcanic activity
• Anthropogenic or man-made
• Municipal and medical waste
• Combustion (utility, vehicle, other)
• US utilities emit 52 tons per year
• Chlor-alkalai production plants
• Gold mining, smelting
• Preservatives (medical, agricultural)
• Legacy wastes

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Atmospheric Transport and Fate

• Mercury can travel great distances for at least a
  year (Hg0) as a global pollutant
• Some local deposition occurs
• Source attribution is extremely difficult

13
Atmospheric Transport and Fate

• EPA estimates rely heavily on computer models,
  using generalized, non-specific sites
• RELMAP for regional scale transport
• ISC3 for local scale analysis
• IEM-2M for watershed and waterbody analysis
• Many analyses have significant limitations due to
  current state-of-the-science concerning (1)
  mercury fate and transport in land and water
  environments and (2) variability between
  waterbodies.

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Total Global Natural and Manmade Hg Emissions
5,500 tons
US EPA 12/97
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Estimated Global Anthropogenic Mercury Emissions
Source EPRI 9/00
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• Mercury Health Impacts

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Mercury Health Impacts

• Mercury is a Hazardous Air Pollutant
• Not a criteria pollutant no National Ambient
  Air Quality Standard (NAAQS) established
• Human exposure pathways
• inhalation Mad Hatters Disease
• ingestion primary public health focus, through
  fish consumption
• Methylmercury specie of greatest concern
• This neurotoxin can impair the brain and nervous
  system
• It bioaccumulates in tissues
• It biomagnifies up the food chain

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Methylmercury (Hg) Health Impacts

• Brain is the critical target organ
• Cerebrum, cerebellum
• Other target sites?
• Cardiovascular system
• Immune system
• Kidneys

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Observed MeHg Health Effects

• High dose/ acute exposure
• (Iraqi and Japanese poisoning incidents)
• Brain damage
• Mental retardation
• Seizure disorder
• Deafness
• Blindness

• Low dose/ chronic exposure
• (focus of EPA utility emission concerns)
• Attention deficit
• Visual/spatial problems
• Verbal memory problems
• Fine motor problems
• Low muscle tone

NRC/NAS Report 7/00
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Suspected MeHg Health Effects

• Cardiovascular impacts
• Alters blood pressure regulation
• Alters heart rate variability
• Immune system impacts?
• Reproductive system impacts?
• Genetic damage?
• Potential carcinogen?

NRC/NAS Report 7/00
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The Reference Dose (RfD)

• An estimate of daily exposure to MeHg that is
  likely to be without an appreciable risk of
  harmful effects during a lifetime
• The RfD is necessary to determine fish MeHg
  tissue levels for the purpose of determining
  consumption levels and fish advisories

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What Do State Mercury Fish Advisories Really Mean?

• No uniform approach
• No uniform reference dose
• Increase in the number of state advisories is not
  necessarily evidence of health effects or
  increased risk, but of increased concern and
  caution

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What Reference Dose Is Correct For MeHg?
Although other federal agencies disagree, EPAs
RfD for methylmercury is 0.1 microgram/kilogram/da
y The NRC/NAS committee determined that the
reference dose used by the EPA is scientifically
justifiable for the protection of human health.
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How Protective Is the RfD?
The reference dose is intended to protect the
most sensitive individuals in the population. An
estimate based solely on the central tendency of
the distributionwould not provide a protective
reference dose. NRC/NAS 7/00
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• Coal, Control, and Cost Issues

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Coal Mercury Content

• Content varies by type of coal and by seam
• EPRIS initial analysis of EPAs Information
  Collection Request (ICR) data indicates that 90
  of US coal has Hg content of 0.02 to 0.26 ppm
• Coal in one Chinese province has Hg
  concentrations as high as 55.0 ppm

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Utility Mercury Emissions

• US power plants release about 45 tons annually
• 1/3 of US total
• 1 percent of global total
• Information Collection Request indicates possibly
  only 45 tons
• Utilities emit elemental and inorganic Hg
• Methylmercury is organic it doesnt come from
  stack
• No link between utility emissions and local
  impact
• Technology effective 0 - 90

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Mercury in Flue Gas 3 Types

• 1. Gaseous elemental mercury (Hg0)
• Generally escapes capture
• 2. Gaseous ionic mercury (HgII)
• Some scrubbers can remove up to 95
• 3. Particle-bound mercury (Hgp)
• Fabric filters, ESPs remove 10-80
• Some scrubbers can remove up to 95
• (usually Mercuric chloride, HgCl2)

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What Happens During Combustion?
Zygarlicke, UND-EERC
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Potential Control Approaches

• Coal cleaning, pretreatment, or blending
• Mercury specific flue gas cleaning tech, such as
  activated carbon injection (ACI)
• Multi-pollutant flue gas cleaning tech
• NOx control systems
• SO2 control systems
• Fine PM control systems
• Augmenting Hg control systems

EPA 5/00
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What Are the Costs of Control?

• Mercury Control System Key Cost Criteria
• Retrofit factor of 1.2 for installation costs
• Lost revenue of 3/ton from flyash sales in the
  carbon injection process
• Prices for consumables
• Activated carbon 0.55/lb
• Fly ash disposal 29.94/ton
• Parasitic power 46 mills/kWh
• NETL/DOE 5/00

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There Is No Simple Solution
The challenge of reducing mercury emissions from
power plants today is that no uniform method or
technology exists. Current pollution controls
were designed for other types of pollutants, and
their effectiveness in reducing mercury emissions
can vary from boiler to boiler. Depending upon
the power plant, reduction levels can range from
90 percent to zero. DOE Techline 8/14/00
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Major Factors for Hg Fate

• Determined by
• Coal chemistry
• Coal cleaning
• Boiler/burner characteristics
• Temperature
• Speciation
• Post-combustion pollution control
• Ambient air, water

• Possible fates
• Vaporize (HgO) and enter global pool for eventual
  deposit
• Bound by sorbents
• Deposit in ash
• Emitted as Hgp , Hg II, other Hg compound for
  eventual deposit
• Possible methylation

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Why Can Waste Incinerators Control Mercury
Emissions?

• 1. They have different feedstock

• With higher concentration of Hg
• And higher concentration of Chlorine

2. Control is more cost-effective due to higher
concentrations

• 3. Combustor characteristics are different

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Uncertainties and Research Needs
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Uncertainties

• How much Hg comes from natural or background
  sources?
• How much Hg is in US coals?
• How much Hg do utilities emit?
• How far is Hg transported?
• All long-range transport, or does some of it
  deposit closer to the source?
• If so, how much?

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Uncertainties

• Is there a relationship between decreased utility
  emissions and a change in the concentration of
  MeHg in fish?
• How much MeHg in fish tissue comes from US
  sources?
• Will regulation/control make any difference in
  fish tissue concentrations?

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Uncertainties
Given the current scientific understanding of
the environmental fate and transport of this
element, it is not possible to quantify how much
of the MeHg in fish consumed by the U.S.
population is contributed by U.S. emissions
relative to other sources of Hg (such as natural
sources and re-emissions from the global pool.)
As a result, it cannot be assumed that a change
in total mercury emissions will be linearly
related to any resulting change in MeHg in fish,
nor over what time period these changes would
occur. EPA 3rd Great Waters Report 6/00
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Research Needed

• Determine relationship between fish mercury
  concentration and Hg concentration in
  water/sediment (important for TMDL)
• Determine relationship between change in
  emissions and resulting change in fish MeHg
  levels
• Determine actual US fish consumption and MeHg
  concentrations in key subpopulations

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Research Needed

• Determine how other regulations impact coal-based
  power plant Hg emissions
• Conduct full-scale testing of activated carbon
  injection (ACI) technology
• Assess power plant control options
• Conduct detailed economic evaluation of control
  technologies

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EPAs Regulatory Determination(RD)

• Based on the available information, the
  Administrator finds that regulation of Hazardous
  Air Pollutant emissions from coal- and oil-fired
  electric utility steam generating units under
  section 112 of the Clean Air Act is appropriate
  and necessary.
• Announced 12/14/00 published in Federal Register
  12/20/00

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EPAs Regulatory Preferences

• MACT (Maximum Achievable Control Technology)
  means a focus on the best
• New at least as stringent as the emission
  control that is achieved in practice by the best
  controlled similar source
• Existing at least as stringent as the average
  emission limitation by the best performing 12 of
  emission sources
• Probably the least desirable outcome, and
  possibly the most difficult to justify
• Multi-emissions legislation

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Where Do We Go From Here?
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Preparing for State Responses to Federal Mercury
Initiatives

• Discourage states from acting prematurely
• National approach is necessary for global
  pollutant
• National approach is necessary to prevent
  patchwork of state and local laws that could
  raise cost of electricity or reduce reliability

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CEED Regulatory Primer

• Designed for state and local policy makers
• Provides the facts
• Makes the case for a national approach