Download For fuels used directly

Major Roles for Fossil Fuels
in an Environmentally
Constrained World
Robert H. Williams
Princeton University
Sustainability in Energy Production and
Utilization in Brazil: The Next Twenty Years
Universidade Estadual de Campinas
Campinas
Sao Paulo, Brazil
18-20 February 2002
OUTLINE OF PRESENTATION
• Climate change context to motivate considerations of:
--electricity + hydrogen economy
--relative roles of renewables and decarbonized fossil energy
•
•
•
•
•
Prospects for geological storage of CO2
H2 production technology, with focus on coal
H2 costs as automotive fuel
Is decarbonization of natural gas worthwhile?
Conclusions and implications for Brazil
CLIMATE CLIMATE CHALLENGE
(IS92a “BAU” Scenario of IPCC)
Increase in global energy use/capita, 1997-2100:
For primary energy up 2.0X ( 1/3 US level in 1997)
For electricity up 2.6X (½ US level in 1997)
For “fuels used directly” up 1.4X (¼ US level in 1997)
Global CO2 emissions:
Total:
6.2 GtC (1997, actual, 37% coal)  20 GtC (2100, 88% coal)
From electricity generation:
1.9 GtC (1997)  5 GtC (2100)
From “fuels used directly”:
4.3 GtC (1997)  15 GtC (2100)
Cumulative emissions, 1990-2100: 1500 GtC
Allowable Cumulative Carbon Emissions to Reach Various Targets
1600
1400
1200
1000
Gt C
WRE350a
WRE450a
800
WRE550a
WRE650a
WRE750a
600
400
200
0
1980
2000
2020
2040
2060
2080
2100
2120
Renewables/Decarbonized Fossil Energy Competition,
Carbon-Constrained World
For electricity:
 Renewables will be strong competitors for decarbonized fossil fuels—esp. wind
(central station), PV (distributed, grid-connected)
 Electric storage problem “solved” at large scales (CAES)
For fuels used directly (2/3 of CO2 emisions today):
 Biomass--regionally important but limited global potential relative to challenge
 Poor near-term and long-term economic prospects for making H2 via water-splitting
(electrolysis or thermochemical cycles) from renewables—relative to H2 from fossil
fuels with CO2 removal and sequestration
GLOBAL PERSPECTIVE ON BIOMASS
According to World Energy Assessment, long-term biomass energy potential
~ 100 – 300 EJ/y (for comparison: global primary energy use~ 400 EJ/y, 1997)
Biomass contributions to energy in IS92a:
 ~ 130 EJ/y in 2050 (compared to 655 EJ/y from fossil fuels)
 ~ 205 EJ/y in 2100 (compared to 865 EJ/y from fossil fuels)
Although it can make important regional contributions, biomass alone
cannot adequately decarbonize fuels used directly to the extent needed
to solve climate change problem
Implications of Renewable/Fossil Energy
Competition for Carbon Management
• No carbon problem if fossil fuels = conventional oil/NG
• Most of climate change challenge posed by coal [and, to
lesser extent, unconventional oil (e.g., tar sands, heavy oils)]
• Most of climate change challenge posed by “fuels used
directly” and will be severe even if electricity is 100%
decarbonized in this century
• But gasification-based H2 production/CO2 sequestration
technologies offer good prospects for decarbonizing lowquality fossil energy feedstocks at attractive costs
• Are there options for storing the CO2 byproduct of H2
production that are adequate to raise the decarbonization/CO2
sequestration strategy to the status of a major contender in the
energy race to achieve near-zero emissions of greenhouse
gases?
OPTIONS FOR CO2 DISPOSAL
Deep Ocean Disposal (> 3 km)
 Most discussed option
 Reduces rapid transient CO2 buildup in atmosphere
 Significantly reduces long-term atmospheric CO2 concentration (> 50%)
 Many environmental concerns (e.g., ocean life impacts of pH changes, impacts of CO2
hydrate particles on benthic organisms, ecosystems)
Depleted Oil & Natural Gas Fields
 Large capacity (~ 500 GtC)
 Most secure option if original reservoir pressure not exceeded
 Some opportunities for enhanced oil/natural gas resource recovery
 Geographically limited option
Deep Beds of Unminable Coal
 CO2 injection can be used for enhanced methane recovery from unminable coal beds
 CO2 will remain in place (adsorptivity of CO2 on coals much higher than for CH4)
 Geographically limited option
Deep Saline Aquifers
 Deep saline aquifers (> 800 m) widely available geographically
 Enormous potential if closed aquifers with structural traps are not required
 Uncertainties about storage security, but time scales for reaching near-surface fresh-water aquifers
are long (~ 2000 y)
GLOBAL CAPACITY FOR CO2 STORAGE
IN DEEP SALINE AQUIFERS
If aquifers with structural traps are needed:
~ 50 GtC (C. Hendriks, Carbon Dioxide Removal from Coal-Fired Power Plants, Dept. of
Science, Technology, and Society, Utrecht University, The Netherlands, 1994)
If large open aquifers with good top seals can also be used:
Up to 2,700 GtC (IEA GHG R&D Programme)
~13,000 GtC (C. Hendriks, Carbon Dioxide Removal from Coal-Fired Power Plants, Dept. of
Science, Technology, and Society, Utrecht University, The Netherlands, 1994)
For comparison:
Projected emissions from fossil fuel burning, 1990-2100, IS92a: ~ 1500 GtC
Reasonable target for sequestration, 21st century ~ 600 GtC
Carbon content of remaining exploitable fossil fuels (excluding methane hydrates):
~ 5,000 - 7,000 GtC
EXPERIENCE WITH CO2 DISPOSAL
ENHANCED OIL RECOVERY: 74 projects worldwide; often profitable in mature
oil-producing regions; 4% of US oil so produced—mostly using CO2 from
natural reservoirs piped up to 800 km, but Weyburn (Canada) uses 1.5 million
tonnes/y of CO2 piped 300 km from North Dakota coal gasification plant
ENHANCED COAL BED METHANE RECOVERY: 1 commercial project in
San Juan Basin (US)
ACID GAS DISPOSAL: 31 acid gas (H2S + CO2) disposal projects in Canada
TWO PROJECTS FOR AQUIFER DISPOSAL OF CO2 ASSOCIATED
WITH OFF-SHORE NATURAL GAS PRODUCTION:
 Sleipner Project in North Sea (since 1996)
 Natuna Project in South China Sea (planned for 2005-2010)
EXPERIENCE WITH & PLANS FOR AQUIFER CO2 DISPOSAL
AT LARGE SCALES
NG Field
Firm
CO2 in
gas (%)
Disposal Rate
t CO2/y
t C/y
Destination
of CO2
OnStream
Sleipner West,
Norway, North
Sea
Statoil
($50-$80
million
project)
9.5%
1M
0.3 M
Sleipner East,
Utsira Formation
(800 m depth)
1996
(20 y life)
Natuna,
Indonesia,
South China Sea
Pertamina
& Exxon/
Mobil
71%
> 100 M
> 30 M
Two aquifers
north of
Natuna field
~ 2005?
CAN NEAR-ZERO GHG/AIR POLLUTANT EMISSIONS
BE REALIZED AT ACCEPTABLE COST?
Plausibly yes, if H2  major energy carrier complementing electricity—
(CO2 recovery costs low in H2 manufacture)
Requirements:
· Large, widely available, secure, and environmentally acceptable storage
capacity for CO2—geological storage options promising
· Technology for manufacturing H2 from abundant fossil fuel sources
· H2 competitive as energy carrier need technologies that:
—put high market value on H2 (e.g., fuel cells in transport)
—provide H2 at competitive costs
· H2 must be produced centrally to minimize cost of CO2 disposal
WHY COAL?
Coal resources abundant globally:
Recoverable coal
~ 200,000 EJ
(580 y supply at current fossil energy use rate)
Recoverable natural gas
Conventional
Unconventional
~ 12,000 EJ
~ 33,000 EJ
Coal prices low [1997 NG price for US electric generators: 2.1 X
coal price; projected (2020): 3.7 X coal price]; not volatile
Environmental issues  need radical technological innovation
Gasification  near-zero emissions of air pollutants/GHGs
Residual environmental, health, safety problems of coal mining
MAKING H2 FROM FOSSIL FUELS
Begin with”Syngas” Production:
Oxygen-Blown Coal Gasification:
Steam-Reforming of Natural Gas
CH0.82O0.07 + 0.47 O2 + 0.15 H2O 
 0.56 H2 + 0.85 CO + 0.15 CO2
CH4 + H2O  CO + 3H2
Followed by Syngas Cooling & Water-Gas Shift Reaction:
CO + H2O  H2 + CO2,
Net Effect:
CH0.82O0.07 + 0.47 O2 + 1.00 H2O 
 1.40 H2 + 1.00 CO2
CH4 + 2 H2O  CO2 + 4 H2
Followed by CO2/H2 Separation via Physical or Chemical Process
HHV efficiency [(H2 output)/(Total primary fuel input)]:
~ 70% for coal
~ 80% for natural gas
Separated CO2 Can Be Disposed of at Relatively Low Incremental Cost
H2 Production from Coal with CO2/H2S Cosequestration
Air
separation
unit
Quench +
scrubber
Gasifier
oxygen
air
High temp.
WGS
reactor
CO-rich
raw syngas
coal slurry
Syngas
expander
CO2-lean
exhaust
gases
Steam
turbine
steam
Syngas
cooling
HRSG
H2 product
Gas turbine
Low temp.
WGS
reactor
H2- and
CO2-rich syngas
air
compressed
purge gas
Pressure
swing
adsorption
lean
solvent
N2 for NOx control
CO2 + H2S
to storage
Conventional hydrogen 2 (1-7-02)
CO2/H2S
physical
absorption
CO2/H2S
drying and
compression
rich
solvent
Solvent
regeneration
NG price:
2.44 $/GJ HHV
Hydrogen Cost vs. Carbon Tax
70 bar
Hydrogen Cost ($/GJ HHV)
8.5
8.0
CO2 -sulfur
co-sequestration
7.5
7.0
6.5
6.0
CO2 venting
5.5
Coal, conventional technology
Natural gas, steam reforming
5.0
4.5
0
20
40
60
Carbon Tax ($/tonne C)
80
100
Fig. L2ab
•
With CO2 venting, cost of H2 from NG SMR always lower than H2 from coal
•
But, even at today’s low NG prices (2.44 $/GJ), H2 from coal with CO2-sulfur
co-sequestration is comparable to H2 from NG
•
Note: 70 bar conventional technology is commercially available today
NG price:
3.4 $/GJ HHV
Hydrogen Cost vs. Carbon Tax
70 bar
Hydrogen Cost ($/GJ HHV)
8.5
8.0
7.5
CO2 -sulfur
co-sequestration
7.0
6.5
6.0
5.5
CO2 venting
Natural gas, steam reforming
Coal, conventional technology
5.0
4.5
0
20
40
60
Carbon Tax ($/tonne C)
•
80
100
Fig. L2ac
At NG prices (3.4 $/GJ) likely to be typical 20 y from now, cost of H2 from
coal with CO2-sulfur co-sequestration is significantly lower than H2 from NG
SMR
Consumer Fuel Costs for Gasoline ICE Cars and H2 Fuel Cell Cars
(excluding retail fuel taxes)
Fuel cost (¢/liter, gasoline
equivalent)
Cost of driving (¢/km)
Production
cost
Cost to
consumer
Gasoline ICE
(6.7 l/100km)
H2 fuel cell car
(2.9 l/100 km ge)
Gasoline
23
30
2.0
-
H2 from coal,
CO2 vented
21
50
-
1.4
H2 from coal,
CO2 seq.
27
56
-
1.6
Electricity Production via Coal IGCC with CO2/H2S Cosequestration
Air
separation
unit
Quench +
scrubber
Gasifier
oxygen
air
High temp.
WGS
reactor
CO-rich
raw syngas
coal slurry
Syngas
expander
CO2-lean
exhaust
gases
Steam
turbine
steam
Syngas
cooling
HRSG
Low temp.
WGS
reactor
Gas turbine
H2- and CO2-rich syngas
air
H2-rich syngas
lean
solvent
N2 for NOx control
CO2 + H2S
to storage
Conventional electricity 2 (1-7-02)
CO2/H2S
physical
absorption
CO2/H2S
drying and
compression
rich
solvent
Solvent
regeneration
Carbon Tax Needed to Induce CO2 Sequestration
in the Production of H2 and Electricity
($/tC)
Energy Carrier
Feedstock for Producing
Energy Carrier
Natural Gas with
CO2 Sequestered
Coal with CO2:
Sequestered
Cosequestered
H2
~ 100
~ 50
~ 30
Electricity
~ 250
~ 80
~ 50
Remaining Global NG & Conv. Oil Resources
Energy Resources
(103 EJ)
Carbon Content
(GtC)
Low
Med
High
Low
Med
High
Conv. oil
9.4
11.1
13.7
179
211
260
Conv. NG
8.7
11.9
16.5
118
162
224
Subtotal
18.1
23.0
30.2
297
373
484
Unconv. NG
33.2
452
Total
56.2
824
CONCLUSIONS
• Stabilizing atmospheric CO2 at 450-550 ppmv requires decarbonizing
both electricity and fuels used directly.
• Although there are many uncertainties, potential CO2 storage capacity
in geological media is probably large enough to make fossil fuels
decarbonization/CO2 sequestration a major energy option for a GHGemissions-constrained world.
• In electricity markets renewables and decarbonized energy systems
will be strong competitors; renewables might well win the economic
race to near-zero emissions.
• Biofuels will be regionally important but the global potential is
inadequate for biofuels to make more than a modest contribution in
addressing the climate change challenge posed by fuels used directly.
CONCLUSTIONS (continued)
•
H2 will probably be needed as a major energy carrier in markets that use
fuels directly.
•
By a wide margin, the least costly route to providing H2 in a GHG
-emissions-constrained world will be from carbonaceous feedstocks.
•
Making H2 from coal will probably be less costly than making it from NG
at typical feedstock prices in 2020 timeframe.
•
If a concerted effort can be directed to decarbonizing coal, it might not be
necessary to decarbonize NG energy systems.
•
The production of H2 from water via electrolysis or complex thermochemical
cycles will play at most marginal roles in providing H2 unless geological
sequestration of CO2 turns out to be a fatally flawed idea.
IMPLICATIONS FOR BRAZIL
•
Prospect of H2 economy as necessary major component of climate mitigation
strategy has major implications for all countries.
•
Brazil has opportunity to support demonstration projects for H2 fueled vehicles
with H2 derived from offpeak hydropower.
•
Additional H2 supplies might be provided by gasification of petroleum
residuals at refineries—e.g., petcoke gasification at Brazilian refineries could
support more than 1 million fuel cell cars.
•
Brazil is one of few places where biomass-derived H2 might eventually
become major option—and if CO2 coproduct were sequestered (so that CO2
emissions would be negative), Brazil could thereby plausibly sell profitably
emission rights to the atmosphere under a global cap-and-trade regime.
Evolving CO2 Plume Front in a Vertical Cross Section
of a Disposal Aquifer
Modeling from: Eric Lindeberg, Escape of CO2 from aquifers, Energy
Conversion and Management, 38 Suppl: 235-240.
Escape of CO2 from an Aquifer with a Spill Point
Located 8 km from the Injector
Modeling from: Eric Lindeberg, Escape of CO2 from aquifers, Energy
Conversion and Management, 38 Suppl: 235-240.