Transcript From natural gas to decarbonised energy carriers

Power cycles with CO2 capture –
combining solide oxide fuel cells
and gas turbines
Dr. ing. Ola Maurstad
SINTEF Energy Research
Outline of the presentation
 A technology status for power plants with CO2 capture
(efficiencies, capture costs, timeframes)
 A hybrid SOFC/GT power cycle with CO2 capture
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Commercial power cycles
 The dominating technology for new power generation
plants based on natural gas: the combined cycle (CC)
 It combines a gas turbine cycle with a steam turbine and
achieves electrical efficiencies close to 60 % (LHV)
 The specific investment cost is around $500/kWe
 Compared to coal fired power plants the emissions of CO2
is only around 50 % per kWh electricity (due to the higher
efficiency and the lower carbon content of natural gas)
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Gas fired power plants with CO2
capture
 To fulfill the Kyoto agreement Norwegian emissions of CO2
must be reduced
 The electricity consumption is increasing yearly
 Norway has large reserves of natural gas
 We also have geological structures under the sea with
great storage capacity for CO2
 The less costly alternative would be to use CO2 for
enhanced oil recovery (EOR)
 Therefore, one option in reducing the emissions are gas
fired power plants with CO2 capture
 Other options include renewable energy, energy efficiency
and energy modesty
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Principles for power plants with CO2
Exhaust, 0.3-0.5% CO
capture
2
1
Power plant
Conventional
CO2
capture
2H2  O2  2H2O
Coal
Oil
Natural gas
2
Gasification
Reforming
Watershift
H2  CO
Power plant
Oxy-fuel combustion
CH 4  O2  CO 2  2 H 2O
Power plant
Hydrogen-rich fuel
H 2  CO2
O2
3
CO2
capture
CO2
storage
Exhaust,
0.1-0.5% CO2
Air separation
Water
removal
1: Post-combustion principle
2: Pre-combustion principle
3: Oxy-fuel principle = direct stoichiometric combustion with oxygen
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Efficiency potential
incl. CO2 compression (2%-points)
65
63
61
59
57
55
53
51
49
47
45
43
1
2
3
4 5
6
7
8
9 10 11 12 13 14 15
Time until commercial plant in operation
Year
given massive efforts from t=0
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Risk for not succeeding
AZEP
High
Chemical Looping Combustion
SOFC+CO2 capture
Medium
Oxy-fuel
Combined Cycle
Pre-comb.
NG reform.
Low
Post-comb.
amin-abs.
CC
0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 ..
2.4 (Norway)
Combined Cycle additional cost €-cent/kWhel
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Risk for not succeeding
AZEP
High
Chemical Looping
Combustion
SOFC+CO2 capture
Medium
Oxy-fuel
Combined Cycle
Pre-comb.
NG reform.
Post-comb.
amin-abs.
Low
CC
1
2
3
4 5
6
7
8
9 10 11 12 13 14 15
Time until commercial plant in operation
Year
given massive efforts from t=0
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Working principle of a SOFC
Source: http://www.seca.doe.gov/
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The solide oxide fuel cell (SOFC)
CH 4  H 2O  CO  3H 2
CH 4  CO2  2CO  2 H 2
Fuel
H 2O  CO  H 2  CO2
H 2  O2  H 2O  2e
900-1000 °C
1 O  2e  1 O 2
2 2
2 2
Reforming
Water/gas shift
Anode
Electrolyte
ZrO2
Oxygen ions
Cathode
Air
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Electrons
Technology status of SOFCs
 The major developers of SOFCs is Siemens
Westinghouse, but several others
 The cost of the SOFCs is the major barrier for market
introduction
 SECA – Solid State Energy Conversion Alliance
 A 10-year program led by Dept. of Energy, USA to accelerate the
commercialization of SOFCs
 Cost target for 3-10 kW module by 2010: $ 400/kW
 Projected costs assuming mass production of existing cell designs
are $1500-4500
 SECA yearly budget is around 20 million $
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Combining
SOFCs and
gas turbines
CH 4  H 2O  CO  3H 2
CH 4  CO2  2CO  2 H 2 Reforming
H 2O  CO  H 2  CO2
Water/gas shift
Fuel
H 2  O 2  H 2O  2e
Anode
900-1000 °C
Electrolyte
ZrO2
1 O  2e  1 O 2
2 2
2 2
Vann
Heat
exchanger
Cathode
Air
Natural gas
SOFC with
internal reforming
Compressor
Air
Oxygen ions
Combustor
Turbine
Exhaust
~
Scale 250 kW-10 MW
Efficiency (net AC/LHV) ~60-70%
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Electrons
Benefits of SOFC/GT systems
 Electrical efficiencies as high as those for combined cycle
plants at much smaller scale (1/1000)
 Very low emissions of NOx, SOx
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Technology status
SOFC/GT system
 220 kWe demonstration system
in operation at NFCRC, USA
 Designed and fabricated by
Siemens Westinghouse (operational in 2000)
 53 % electrical efficiency (net AC/LHV) achieved
 Conceptual designs by SW have shown electrical
efficiencies approaching 60 % (300 kW to 20 MW
systems)
 More complex and/or expensive systems in the literature
promise much higher efficiencies (e.g. 70 %)
 Other planned demonstration systems have not always
appeared on schedule ...
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Adding CO2 capture to the process
 The SOFC is especially well
suited for capture of CO2
 CO2 is present only in the anode
exit stream (not mixed with
nitrogen), and at high partial
pressure
 The afterburner oxidizes the rest
of the fuel so that the exhaust
consists only of CO2 and H2O
 The water vapor is then
condensed by cooling and
removed => resulting in a pure
stream of CO2, ready for
compression
Fuel cell section
After-burning section
Air in
Air in
Air out
Air out
Exhaust
gas
Seal
Exhaust
Leak path
Fuel from
pre-reformer
Source: Shell Technology Norway AS
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Simplified system description
Natural gas
Efficiency (net AC/LHV): 65 – 68 %
1
Exhaust
6
5
Exhaust turbine
Afterburner
SOFC unit
2
CO2,H2O
Anode side
9
Cathode side
3
4
Depleted air
10
11
12
Exit air
14
8a
8b
Air turbine
Air compressor
7
Air
13
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The SOFC unit with recirculation
Resirculation stream
2c
Ejector
Prereformer
Natural gas
2
2a
SOFC
stack
2b
Anode exit
Anode
3
Preheated air
9
Cathode exit
Cathode
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10
Afterburner solutions
 Several solutions are possible (both mature and unmature
technologies)
 Cryogenic separation
 Chemical absorption
 Second SOFC
 Oxygen permeable membrane
 Hydrogen permeable membrane
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Solution 1: Second SOFC
Anode inlet
3
Anode outlet
Reactions (2)-(3)
O 2
Cathode inlet
11
4
Cathode outlet
O 2  4e   2O 2
12
Solution 2: Oxygen conducting
membrane reactor
Sweep
Permeate
3
Feed
11
Reactions (2)-(3)
e
4
O 2
Retentate
O 2  4e   2O 2
12
Solution 3: Hydrogen conducting
membrane reactor
Feed
Retentate
Reaction (2) and:
3
Sweep
11
H 2  2H   2e 
H
e
O 2  4H   4e 
 2H 2 O
4
Permeate
12
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Technology status SOFC/GT with
CO2 capture
 No demonstration system exists
 Aker Kværner and Shell are working with the technology
in cooperation with Siemens Westinghouse
 A demonstration system for an atmospheric SOFC with
CO2 capture was planned operational in Kollsnes, Norway
before 2004 – has not appeared
 Specific investment cost for a SOFC/GT system with CO2
capture based on today’s equipment has been estimated
to $5000-8000/kWe
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Technological challenges
 Development of low-cost and reliable SOFC (and
afterburner) units
 Component matching and system integration
 Development of suitable micro gas turbines for small scale
solutions
 Development of new power converters
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Thank you for your attention!
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