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 ID: 187760
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Slide1
Coal: An Old Source Facing New Challenges
Daniel CohanRice UniversityOctober 4, 2014Slide2
Outline
Overview of coal and its useEmissions from coalControlling emissions from coalOther impacts of coalCosts of coal
2Slide3
Overview of Coal and its UseSlide4
4
How Coal Forms
Plants die in swamp forests and are buried by sediment as peatHeat and pressure expel water and gasesCoal becomes more carbon and energy rich over millions of years
Graphic from Univ of KentuckySlide5
5Slide6
6
Western coals becoming increasingly prevalent
Thick seams in West for large-scale miningAppalachian coals heavily utilized before, most accessible reserves already tappedWestern coals have lower sulfur content, lower priceTransportation costs, bottlenecks are issue
US EIA, AEO
2012Slide7
Powder River Basin Coal supplies many TX power plants
7
http://www.wildearthguardians.org/images/content/pagebuilder/Powder_River_Basin_distribution_legend-2.jpgSlide8
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 tons
1 ton
360 tons
12 tonsSlide9
9
U.S. Coal Use TrendsHistorically, large use by industry, homes, transportation
Now power plants predominate
US EIA, AEO 2006Slide10
Coal supplies 34% of electricity for the Texas ERCOT grid
10Slide11
Coal is big share of US electricity capacity, but most
growth is natural gas & renewables
11Slide12
Most U.S. coal-fired electricity is from decades-old power plants
12
Cohan and Douglass, 2011Slide13
Emissions from CoalSlide14
14
IPCCSlide15
Projected climate change depends on CO
2 emissions15
IPCC, WGI SPM, 2013Slide16
Electricity Generation: Biggest source of greenhouse gases in U.S.
16Slide17
Highest CO
2 emissions from coal(This is life cycle CO
2equivalent 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, 2007Slide18
Old coal plants emit far more NOx
than other options in Texas18
Cohan, 2013
Emissions from Texas power plantsSlide19
NOx
contributes to excess ozone in Texas cities (standard is 75 ppb)19
Cohan, 2013Slide20
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Ground-level Ozone Impacts
Health effectsStrong oxidant, irritates lungsLinked to asthma and other respiratory illnessesRecently linked to mortalityDamage to vegetation & crops
Greenhouse gas
Non-attainment of EPA standardsSlide21
Old coal plants emit far more SO
2 than other options in Texas
21
Cohan, 2013
Emissions from Texas power plantsSlide22
22
SO2
contributes to fine particulate matterParticulate matter: airborne particles composed of a variety of chemical compounds
Particulate matter is likely the leading cause of illness and mortality from air pollutionSlide23
Controlling emissions from coal-fired e
lectricitySlide24
Timeline of US cap-and-trade policies for air pollutants
http://www.epa.gov/airmarkets/progress/ARPCAIR10_01.htmlSlide25
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U.S. Power Plant Emissions Trends
NOx Emissions SO2
Emissions
http://www.epa.gov/airmarkt/progress/datatrends/index.htmlSlide26
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 CO22013: Proposed New Source Performance Standards of 1000-1100 lb CO
2
/MWh
Attained by new natural gas plants
Would require partial capture of CO
2
from coal
2014: Proposed Clean Power Plan, with CO
2
targets for each state
For Texas: 39% reduction by 2030
26Slide27
Clean Power Plan CO
2 Reduction Targets27Slide28
US Power Plant CO2 Trends
28
http://www.epa.gov/airmarkt/progress/datatrends/index.htmlSlide29
29
Power Plant NOx Control:
Selective Catalytic Reduction (SCR)Ammonia is injected after boiler to convert NOx to N
2
and water
Requires catalyst
Specific temperature range
~85% NO
x
reduction
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www.de-nox.comSlide30
Flue Gas Desulfurization
(“Wet Scrubber”) for SO2
US DOE National Energy Technology LaboratorySlide31
Rainfall Acidity, 1994Slide32
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)Slide33
Post-combustion carbon capture
33
FIGURE 12.1
Flowsheet
of the
monoethanolamine
(MEA) process
for CO
2
capture.
Fay & Golomb textbook
Reaction of liquid solvent MEA with CO
2
C
2
H
4
OHNH
2
(“MEA”) + H
2
O + CO
2
↔ C
2
H
4
OHNH
3
+
+ HCO3-
Need 1 mole MEA per mole CO
2
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)Slide34
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CO2 Transport
PipelinesSome CO2 pipelines already exist for enhanced oilfield recoverySimilar impacts as other hydrocarbon pipelinesShips
CO
2
could be liquefied for ship transport
Road or rail
Probably not cost-effectiveSlide35
35Slide36
36Slide37
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Geological Storage CapacityFor comparison, global anthropogenic emissions are about 28 GtCO
2/year
IPCC, 2005Slide38
Cost of CCS vs. other CO
2 control options
38Slide39
Coal Impacts beyond Air and ClimateSlide40
40
Mountaintop Removal Mining
In much of Appalachia, coal seams may be hundreds of feet beneath surface500 feet or more of a mountain summit may be removed to access coalSlide41
Coal Ash Pond Spill, Kingston (TN) Power Plant, December 2008
Associated Press
41Slide42
Ash from Coal Power Plants
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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 technologiesBottom ash (20%): Large, settles to bottomBoiler slag (6%): Ash that melts by heat1,300 coal ash dumps in U.S.Mercury, lead, arsenic, and selenium in ashLack of federal regulation$5-11 billion/year estimated clean-up costs
N.Y. Times, “Hundreds of Coal Ash Dumps Lack Regulation,” 1/6/2009
43Slide44
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
44Slide45
Cost of Coal ElectricitySlide46
New coal costs more than gas, wind, or geothermal; with carbon capture, it costs more than solarSlide47
Alternatives to coal in Texas
47
Cohan, 2013
Costs per MWh generatedSlide48
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 cutNatural gas impacts are ~0.2 cents/kWhOther studies estimate much higher impacts from coalWide uncertainty on climate impacts (up to 10 cents/kWh)Additional impacts from coal mines and transport
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Projections of coal use depend on climate policy
49
GHG15 scenario: US sets CO
2
emission price, rising to $44/ton by 2035
US EIA Annual Energy Outlook 2012Slide50
Summary of challenges to coal
Old coal plants provide affordable electricity, but:Need to control NOx, SO
2, and mercuryRetrofit carbon capture is very expensiveEPA Clean Power Plan will require CO2 cutsNew coal plants aren’t cost competitive with natural gas or some renewablesNeed carbon capture to meet EPA’s proposed New Source Performance Standards
Impacts to air, climate, land, and water
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