Clean Coal
Oxymoron or Key to Energy Independence?
Michelle Chesebro
[email protected]
Current Coal Usage
• 50% of the energy in
the U.S. is generated
from coal
• More than 500 coalfired power plants in
U.S. with average age
of 35 years
• U.S. supplies of coal
projected to last from
164 -250 years
Economics and Security of Supply
• Coal is plentiful and cheap
• Coal is found in abundance in countries
with stable governments
– United States, India, China
• MIT concluded that coal will continue to be
used to meet the world’s energy needs in
significant quantities.
Greenhouse Gases
• Among fossil fuels, coal is
the most carbon-intensive
so electricity generated
by coal produces high
CO2 emissions
• U.S. coal-burning power
plants contribute 1.5
billion tons per year of
CO2
• Globally, coal is
responsible for 40% of
CO2 emissions
China’s Contribution to
Greenhouse Gases from CO2
• International Energy Agency now predicts
China will surpass the U.S. in CO2
emissions by 2009, 10 years earlier than
previous projections
• China uses more coal than the U.S., the
E.U. and Japan combined
• China is bringing new coal-fired power
plants online almost every week
Proposed Solution
• Carbon Capture & Sequestration (CCS) – can
reduce CO2 emissions significantly while using
coal to meet energy needs
• Components:
Initial Step: Coal Gasification
• Coal put in gasifier with oxygen and steam
where heat and pressure are used to form
a synthetic gas, known as “syngas”
• CO2 can then be captured
– Before combustion (IGCC)
– After combustion (Pulverized Coal plants)
Product: Syngas
• Composition – Carbon Monoxide and
Hydrogen
• Potential Uses
– Power Generation (IGCC)
– Fertilizers & Methanol
– Natural Gas
– Gasoline & Diesel Fuels (Fischer-Tropsch)
Post-Combustion Capture
• Used in conventional pulverized coal-fired
power (PC) plants that produce flue gases
• CO2 separated out from flue gas
• 80-95% captured (but low concentrations
to begin with in flue gas)
Post-Combustion Process
• Flue gas is passed through an absorber
where a solvent removes most of the CO2
• CO2-containing solvent goes to stripper
and is heated to release the CO2
• New process being used by American
Electric Power: chilled ammonia used as
solvent – can process larger amounts of
CO2, but requires less energy
Post Combustion
Pre-Combustion Capture
• Integrated Gasification Combined-Cycle
(IGCC) technology
• Used in new power plants and well suited
for high grade bituminous coal
• 90% of CO2 removed
IGCC Process
• Coal gasification to produce syngas
• Syngas cooled and cleaned to remove
particulates and other emissions
• Electricity generation
– Syngas then combusted with air or oxygen to drive
gas turbine
– Exhaust gases are heat exchanged with water/steam
to drive steam turbine
• By introducing steam between cooler and gas
clean-up, CO converted to CO2 which can be
captured and stored before combustion
IGCC Process
1.
2.
3.
4.
5.
Coal burned to produce syngas
Syngas burned in combustor
Hot gas drives gas turbines
Cooling gas heats water
Steam drives steam turbines
Competing Technologies
• Because of the differences in coal type, a
wide range of technologies will need to be
deployed. We should not jump on the
IGCC bandwagon too quickly for research
& development $$$, but continue to fund a
variety of options
• Clear preference for IGCC or SCPC
(Super Critical Pulverized Coal) cannot be
justified at this time
Comparison of IGCC and SCPC
• Reasons to prefer IGCC
– Potential tightening of air quality standards for other pollutants
reduced by IGCC, such as SO2, NOx and mercury
– Likelihood of a future carbon charge
– Possible federal or state financial assistance for IGCC
• Reasons to prefer SCPC
– Near-term opportunity for higher efficiency
– Capability to use lower cost coals
– Ability to cycle the power plant more readily in response to grid
conditions
– Confidence in reaching capacity factor/efficiency performance
goals
Retrofitting Costs
• Major technical modifications required
regardless of which technology is used
• Based on today’s engineering estimates, cost of
retrofitting for IGCC appears to be cheaper than
retrofitting for SCPC
• Variables
– Timing and size of carbon charge
– Difference in retrofit cost
• Very possible that old plants will just have to be
bulldozed because retrofitting will prove to be
cost-prohibitive
Another Option – UCG
• Underground Coal Gasification
• Addresses other environmental concerns
associated with coal mining
Other Technologies
• Oxygen fired pulverized coal combustion
(more promising for lower quality coals)
– Burning coal in oxygen-rich atmosphere to
produce a pure stream of CO2
• Chemical looping combustion
– Continually looping two stage reaction
process that provides two waste streams from
coal combustion
– The first contains carbon dioxide and water,
and the CO2 can be compressed for storage
Transport of Captured CO2
• Compressed to supercritical fluid
– Dense as liquid
– Gas-like viscosity
• Transported through pipelines
• Or further cooled and transported in
marine tankers like LNG
Sequestration
Storage of Captured CO2
• Deep geologic formations such as saline
aquifers
• Depleted oil and natural gas fields
• Ocean
– Dissolving CO2 deeper than ½ mile
– Depositing liquefied CO2 on sea floor 2 miles
down
Carbon Options
1. CO2 pumped into disused coal fields displaces methane which can be
used as fuel
2. CO2 can be pumped into and stored safely in saline aquifers
3. CO2 pumped into oil fields helps maintain pressure, making extraction
easier
Storage Concerns
• Leakage presents an immediate hazard to
humans and ecosystems (CO2 is an
asphyxiant)
• Possibilities
– Blow-out at injection well
– Slow leak through faulty well or ground
fractures
• Even slow leaks negate the benefit of
burying the CO2 in the first place
Regulatory Framework for Storage
• Must include:
– Site selection
– Injection and surveillance
– Eventual transfer of liability to the government
• The goal of energy independence cannot
be allowed to trump global warming
concerns. Even if a regulatory framework
is developed for the U.S., who will be the
global carbon police?
Status of CCS Projects
• Current IGCC Projects – used primarily for
enhanced oil & gas recovery, not CO2 storage
– Sleipner in Norway
– Weyburn in Canada
– In Salah in Algeria
• Need large-scale demonstration before this can
be considered a viable proposal
• Large-scale electricity generation – proposed
projects:
– FutureGen in the U.S.
– ZeroGen in Australia
– A number of proposals in Europe and Canada
Price of Coal
• Coal is plentiful and currently cheap
because the health and environmental
costs are borne by the public, not the
industry
• But price will increase
– Charge for CO2 emissions to account for
health and environmental costs
– Deploying carbon capture and storage will
increase price of coal-fired power by at least
50%, with some estimating twice that amount
Grandfathering Loophole
• Utilities may be tempted to invest in new
power plants without capture in the hope
that these plants will be grandfathered in
– Expectation of free CO2 allowances under
future carbon emissions regulations
– Benefit when electricity prices increase as a
result of a carbon control regime
• Congress needs to close the loophole
Coal to Liquid
• The bigger hurdle for energy independence is finding a
replacement for gasoline. Other countries have used a
process for turning coal into gasoline (Nazi Germany and
the apartheid government of South Africa).
• Coal  Gasifier  Syngas
• Fischer-Tropsch Process
– Syngas  Reactor  Hydrocarbons
– Hydrocarbons cooled = liquid fuel
• Concern – Coal to Liquid (CTL) development has no
near-term plan to capture any of the CO2 it produces.
Until it does, using the label “clean coal” is inaccurate.
Liquid Fuel from Coal
• Second approach – direct coal liquefaction 
coal is pulverized and mixed with oil and
hydrogen in a pressurized environment
CTL
• CTL with carbon capture
– Will be incredibly expensive and will require
government subsidies
– If 85% of the CO2 is captured, the liquid fuel
that is produced will have the same emissions
as a gallon of regular diesel
• CTL without carbon capture
– May be economically viable without
government subsidies
– Will be a disaster in terms of global warming
Concerns
• Technological issues for both capture and
sequestration are not trivial and we are still at
least five to ten years away
• Any sequestration method still has the potential
for leaks
– Impact to human health – high concentrations of CO2
causes loss of consciousness
– CO2 makes water in aquifers acidic enough to
dissolve certain types of rocks releasing toxins that
seep into drinking water
– Any leak at all reduces the benefits of carbon capture
technology, because there is no way to recapture the
leaked CO2 and store it again
Big Picture
• Federal funding should
continue so that we can
learn more about the
costs and risks of burying
CO2
• However, “coal is the fuel
of the past, not the
future.” (Jeff Goodell)
Clean coal technology is
not a long-term solution
to America’s (or the
world’s) energy problems.