SINTEF Energy Research Power cycles with CO 2 capture – combining solide oxide fuel cells and gas turbines Dr. ing. Ola Maurstad

SINTEF Energy Research

Power cycles with CO2 capture – combining solide oxide fuel cells and gas turbines

Dr. ing. Ola Maurstad


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


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)


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


Power plant Conventional

CO2

capture

Coal

Oil

Natural gas

CO2 storage

1

Gasification Reforming

Water-shift

CO2

capture Power plant Hydrogen-rich fuel2

Air separation Power plant Oxy-fuel combustion

Waterremoval

3

Exhaust, 0.3-0.5% CO2

Exhaust, 0.1-0.5% CO2

OHOH 222 22

COH 2 22 COH

OHCOOCH 2224 2

2O

1: Post-combustion principle2: Pre-combustion principle3: Oxy-fuel principle = direct stoichiometric combustion with oxygen

Principles for power plants with CO2 capture


65E

ffic

ienc

y po

tent

ial

incl

. CO

2 com

pres

sion

(2%

-poi

nts)

Year1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Time until commercial plant in operationgiven massive efforts from t=0

43

45

47

49

51

53

55

57

59

61

63

Combined Cycle

Post-combustion amin-absorption

Pre-combustion, NG reforming

Chemical Looping Combustion

AZEP

Oxy-fuel Combined Cycle

SOFC+CO 2 ca

pture


Post-comb.amin-abs.

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 ..

CC

Pre-comb. NG reform.

AZEP

Combined Cycle additional cost €-cent/kWhel

Chemical Looping Combustion

Oxy-fuelCombined Cycle

Low

Medium

High

SOFC+CO2 capture

Risk for not succeeding

2.4 (Norway)


Risk for not succeeding

Post-comb.amin-abs.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

CC

Pre-comb. NG reform.

AZEP

Chemical LoopingCombustion

Oxy-fuelCombined Cycle

Low

Medium

High

SOFC+CO2 capture

Time until commercial plant in operationgiven massive efforts from t=0

Year


Working principle of a SOFC

Source: http://www.seca.doe.gov/


Anode

Cathode

ElectronsElectrolyte ZrO2

Oxygen ions

Fuel

Air

eOHOH 222

2

222 2

1221 OeO

222

224

22422

3

COHCOOH

HCOCOCH

HCOOHCH

ReformingWater/gas shift

900-1000 °C

The solide oxide fuel cell (SOFC)


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 $


~

Heat exchanger

SOFC withinternal reforming

Natural gas

Vann

Air

Compressor Turbine

ExhaustCombustor

Scale 250 kW-10 MWEfficiency (net AC/LHV) ~60-70%

Anode

Cathode

ElectronsElectrolyte ZrO2

Oxygen ions

Fuel

Air

eOHOH 222

2

222 2

1221 OeO

222

224

22422

3

COHCOOH

HCOCOCH

HCOOHCH

ReformingWater/gas shift

900-1000 °C

Combining SOFCs and gas turbines


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


Technology status SOFC/GT system

220 kWe demonstration systemin operation at NFCRC, USA

Designed and fabricated bySiemens 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 ...


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

Air in

Air out

Fuel cell section

Fuel frompre-reformer

Exhaust gas

Air in

Air out

After-burning section

Exhaust gas

Air in

Air out

After-burning section

Seal

ExhaustLeak path

Source: Shell Technology Norway AS


Simplified system descriptionNatural gas

Air

CO2,H2O

SOFC unit

7

After-burner

Cathode side

Anode side

12

8a

2

3 4

13

Depleted air9

14

5

1

Exit air

6

8b

Air turbineAir compressor

Exhaust turbine

Exhaust

10 11

Efficiency (net AC/LHV): 65 – 68 %


The SOFC unit with recirculation

Cathode

Anode

2b

2c

2a

3

109

2

Preheated air

Natural gas

Cathode exit

Anode exit

Resirculation stream

Ejector

SOFCstack

Pre-reformer


Afterburner solutions

Several solutions are possible (both mature and unmature technologies)

Cryogenic separation Chemical absorption Second SOFC Oxygen permeable membrane Hydrogen permeable membrane


11Cathode outlet

Anode outlet

Solution 1: Second SOFC

3Anode inlet

Cathode inlet

4

12

11Retentate

Permeate

Solution 2: Oxygen conducting membrane reactor

3Sweep

Feed

4

12

Reactions (2)-(3)

e 2O

Reactions (2)-(3)

22 2O4eO

2O

11Permeate

Retentate

Solution 3: Hydrogen conducting membrane reactor

3Feed

Sweep

4

12

Reaction (2) and: 2e2HH2

H

O2H4e4HO

2

2

e

22 2O4eO


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


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


Thank you for your attention!

Documents

SINTEF Energy Research Power cycles with CO 2 capture – combining solide oxide fuel cells and gas turbines Dr. ing. Ola Maurstad