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Coal: An Old Source Facing New Challenges Daniel Cohan Rice University October 4, 2014.
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Transcript of Coal: An Old Source Facing New Challenges Daniel Cohan Rice University October 4, 2014.
Coal: An Old Source Facing New Challenges
Daniel Cohan
Rice University
October 4, 2014
Outline
• Overview of coal and its use• Emissions from coal• Controlling emissions from coal• Other impacts of coal• Costs of coal
2
Overview of Coal and its Use
4
How Coal Forms
• Plants die in swamp forests and are buried by sediment as peat
• Heat and pressure expel water and gases
• Coal becomes more carbon and energy rich over millions of years
Graphic from Univ of Kentucky
5
6
Western coals becoming increasingly prevalent
• Thick seams in West for large-scale mining
• Appalachian coals heavily utilized before, most accessible reserves already tapped
• Western coals have lower sulfur content, lower price– Transportation costs,
bottlenecks are issueUS EIA, AEO 2012
Powder River Basin Coal supplies many TX power plants
7
http://www.wildearthguardians.org/images/content/pagebuilder/Powder_River_Basin_distribution_legend-2.jpg
8
U.S. uses 1,045,878,000 tons of coal for electric generation each year• 3.5 tons/person/year (~50 times
our weight)
100 tons1 ton
360 tons12 tons
9
U.S. Coal Use Trends
• Historically, large use by industry, homes, transportation
• Now power plants predominate
US EIA, AEO 2006
Coal supplies 34% of electricity for the Texas ERCOT grid
10
Natural gas45%
Coal34%
Nuclear12%
Wind9%
Other0%
Electricity Generation (MWh) in ERCOT, 2012
Coal is big share of US electricity capacity, but most growth is natural gas & renewables
11
Most U.S. coal-fired electricity is from decades-old power plants
12
Cohan and Douglass, 2011
Emissions from Coal
14
IPCC
Projected climate change depends on CO2 emissions
15
IPCC, WGI SPM, 2013
Electricity Generation: Biggest source of greenhouse gases in U.S.
16
Highest CO2 emissions from coal(This is life cycle CO2equivalent basis, so
includes CH4 leaks, etc)
17
Greenhouse gas impact per kWh:Coal >> Natural gas >> Solar, biomass, wind, nuclear
Weisser, “A guide to life-cycle greenhouse gas emissions from electric supply technologies.” Energy, 2007
Old coal plants emit far more NOx than other options in Texas
18-
0.5
1.0
1.5
2.0
2.5
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
NO
x E
mis
sion
Rat
e (l
b/M
Wh
)
TXU legacy coal
Other old coal
New coal
10 cleanest old coal
Natural gas
Cohan, 2013
Emissions from Texas power plants
NOx contributes to excess ozone in Texas cities (standard is 75 ppb)
19
0
20
40
60
80
100
120
8-h
r O
zon
e D
esig
n V
alu
e (p
pb
)
Houston-Galveston-Brazoria (88)
Dallas-Fort Worth (87)
Beaumont-Port Arthur (80)
San Antonio (80)
Tyler-Longview-Marshall (79)
Waco (75)
Austin-Round Rock (74)
Corpus Christi-Victoria (72)
El Paso (72)
Cohan, 2013
20
Ground-level Ozone Impacts
• Health effects– Strong oxidant, irritates lungs– Linked to asthma and other
respiratory illnesses– Recently linked to mortality
• Damage to vegetation & crops• Greenhouse gas• Non-attainment of EPA standards
Old coal plants emit far more SO2 than other options in Texas
21-
2.0
4.0
6.0
8.0
10.0
12.0
14.0
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
SO2
Em
issi
on R
ate
(lb/M
Wh)
TXU legacy coal
Other old coal
New coal
10 cleanest old coal
Natural gas
Cohan, 2013
Emissions from Texas power plants
22
SO2 contributes to fine particulate matter
• Particulate matter: airborne particles composed of a variety of chemical compounds
• Particulate matter is likely the leading cause of illness and mortality from air pollution
Controlling emissions from coal-fired electricity
Timeline of US cap-and-trade policies for air pollutants
http://www.epa.gov/airmarkets/progress/ARPCAIR10_01.html
25
U.S. Power Plant Emissions Trends
NOx Emissions SO2 Emissions
http://www.epa.gov/airmarkt/progress/datatrends/index.html
US EPA Policies for CO2 from Power Plants
• Historically, CO2 was not regulated
• 2007: Supreme Court in Massachusetts v. EPA ruled Clean Air Act can cover CO2
• 2013: Proposed New Source Performance Standards of 1000-1100 lb CO2/MWh
– Attained by new natural gas plants– Would require partial capture of CO2 from coal
• 2014: Proposed Clean Power Plan, with CO2 targets for each state– For Texas: 39% reduction by 2030 26
Clean Power Plan CO2 Reduction Targets
27
US Power Plant CO2 Trends
28
http://www.epa.gov/airmarkt/progress/datatrends/index.html
29
Power Plant NOx Control:Selective Catalytic Reduction (SCR)
• Ammonia is injected after boiler to convert NOx to N2 and water– Requires catalyst– Specific temperature
range
• ~85% NOx reduction
29
www.de-nox.com
Flue Gas Desulfurization (“Wet Scrubber”) for SO2
US DOE National Energy Technology Laboratory
Rainfall Acidity, 1994
Rainfall Acidity, 2009(Note the reductions in acidity in regions where coal is heavily used for electricity; results from SO2 & NOx controls under Acid Rain Program)
Post-combustion carbon capture
33
FIGURE 12.1 Flowsheet of the monoethanolamine (MEA) process for CO2 capture.
Fay & Golomb textbook
• Reaction of liquid solvent MEA with CO2 • C2H4OHNH2 (“MEA”) + H2O + CO2 ↔ C2H4OHNH3
+ + HCO3-
• Need 1 mole MEA per mole CO2 captured• Huge material flows: 400 kg/s MEA for 500MW plant
Forward Reaction @ 40-65°C (flue gas must be cooled)
Reverse Reaction @ 100-120°C (needs steam; hurts efficiency)
34
CO2 Transport
• Pipelines– Some CO2 pipelines already exist for
enhanced oilfield recovery– Similar impacts as other hydrocarbon pipelines
• Ships– CO2 could be liquefied for ship transport
• Road or rail– Probably not cost-effective
35
Methods for storing CO2 in deep underground geological formations
SRCCS Figure TS-7
36
Global distribution of large stationary sources of CO2
Prospective areas in sedimentary basins where suitable saline formations, oil or gas fields, or coal beds may be found.
SRCCS Figure TS-2b
37
Geological Storage Capacity
• For comparison, global anthropogenic emissions are about 28 GtCO2/year
IPCC, 2005
Cost of CCS vs. other CO2 control options
38
Coal Impacts beyond Air and Climate
40
Mountaintop Removal Mining• In much of Appalachia, coal seams may
be hundreds of feet beneath surface• 500 feet or more of a mountain summit
may be removed to access coal
Coal Ash Pond Spill, Kingston (TN) Power Plant, December 2008
Associated Press41
Ash from Coal Power Plants
42
Coal Ash• Ash from coal combustion: 10% of original
volume of coal (U.S. EPA)– Fly ash (74%): Mixed with exhaust gas;
captured by various technologies– Bottom ash (20%): Large, settles to bottom– Boiler slag (6%): Ash that melts by heat
• 1,300 coal ash dumps in U.S.– Mercury, lead, arsenic, and selenium in ash– Lack of federal regulation– $5-11 billion/year estimated clean-up costs
N.Y. Times, “Hundreds of Coal Ash Dumps Lack Regulation,” 1/6/200943
Solid Wastes from Coal Power Plants
• Coal combustion generates ~129 million tons/year of wastes in US; ~35% reused
US EPA Coal Combustion Products Partnership
44
Cost of Coal Electricity
New coal costs more than gas, wind, or geothermal; with carbon capture, it costs more than solar
Alternatives to coal in Texas
47
Cost1
Cost with incentives2
Cost with incentives + $25/ton CO2 3
SO2 4
(lb)
NOx 5
(lb) CO2 6
(lb) Hg 7
(10-5 lb) Water use 8
(gal)
Legacy coal 2011 $39.63 $39.63 $66.34 9.18 1.48 2,137 8.9 300 Coal with UBS retrofits 9
$42.89 $42.89 $70.02 4.36 1.23 2,170 0.9 309
Coal with SCRs 10 $45.29 $45.29 $72.42 4.36 0.59 2,170 0.9 309 Natural gas $65.90 $65.90 $79.51 0.01 0.36 1,089 0.0 270 Geothermal $76.10-
$88.20 $65.10- $77.20
$65.65- $77.75
0.17 0.00 44 0.0 5
Coastal wind $51.00-$83.40
$40.00- $72.40
$40.00- $72.40
0.00 0.00 0 0.0 1
Solar $140.30 $77.90-$101.18
$77.90- $101.18
0.00 0.00 0 0.0 26
Energy efficiency $35.00 $35.00 $35.00 0.00 0.00 0 0.0 0
Cohan, 2013
Costs per MWh generated
Externality costs of coal(National Research Council, 2009)
• 3.2 cents/kWh due to health and other impacts of air pollution– 1.7 cents/kWh by 2030 as emissions are cut– Natural gas impacts are ~0.2 cents/kWh– Other studies estimate much higher impacts from coal
• Wide uncertainty on climate impacts (up to 10 cents/kWh)
• Additional impacts from coal mines and transport
48
Projections of coal use depend on climate policy
49
GHG15 scenario: US sets CO2 emission price, rising to $44/ton by 2035
US EIA Annual Energy Outlook 2012
Summary of challenges to coal• Old coal plants provide affordable
electricity, but:– Need to control NOx, SO2, and mercury
– Retrofit carbon capture is very expensive– EPA Clean Power Plan will require CO2 cuts
• New coal plants aren’t cost competitive with natural gas or some renewables– Need carbon capture to meet EPA’s proposed
New Source Performance Standards• Impacts to air, climate, land, and water
50