Oxy-fuel Combustion: Near, Intermediate & Long term

Adel F. Sarofim

University of Utah

Reaction Engineering International

Seventh Annual MIT Carbon Sequestration Forum

Cambridge, MA

October 31 & November 1

Outline

• Oxy-fuel combustion principles• External Recycle for Retrofit Applications• Internal Recycle for New Plants• New Concept• Concluding comments

Oxy-fuel Combustion Options (adapted from Wall, 06)

Hot RFG

Cold RFG

Furnace Heat Extraction

Gas Cleanup

Coal + O2

Stack

Compression / Sequestration

CO2

Nitrogen is eliminated from air to produce CO2 stream for sequestration. Oxygen is diluted with recirculated flue gas. Several options exist for location of recirculation stream. Cold RFG or external RFG is option best suited to retrofit. Hot RFG or internal RFG is option available for new plants.

Cold RFG: Retrofit of Existing Boilers (adapted from Kobayashi, ’05)

The basis for oxy-fuel combustion is to have oxygen mimic air by mixing 1 mole of oxygen with R moles of recirculated flue gases

R is the volume (molar) ratio of recirculated flue gas to oxygen1

R1 + R

Issues: What are the impacts on gas composition, heat transfer, NOx & SOx emission?

Retrofit of boiler (Stromberg, 2004)

Compositions and volume for bituminous coal (CH1.1O0.2N0.017S0.015) fired with air and oxygen (0% excess air)

Air Firing Oxy-Firing

CO2 17 % by volume 64%

H2O 8.9% 34%

NOx 2770xCR* ppm 10,700xCR* ppm

SOx 2470 ppm 9400 ppm

Moles 1 0.26

CR* = fractional conversion of coal nitrogen to NOx

The ratio R of recirculated CO2 to Oxygen is between 2 and 3 if the adiabatic temperature or maximum heat flux

for air combustion is to be matchedCase O2, eff TAF

K pc pw ε, T=1500 K

L=15 mqmax, kW/m2

Air 21% 2302 0.16 0.089 0.51

0.68

0.68

0.68

812

O2R=1

51% 3176 0.64 0.34 3,946

O2

R =235% 2330 0.64 0.34 1,140

O2

R=327% 1891 0.64 0.34 496

Detailed analyis for a 50 MWe plant shows a match for the furnace at a value of ~ 3.3 (Payne et al., ’89)

= R

NO concentration relative to unstaged combustion in air. Results based on Air Liquide/B &W 1.5MWt study for oxy-firing staged and unstaged (US

regulations are 0.14 lbs/million Btu ~ 84 ppm for air firing) (Wall et al., ’06)

0

20

40

60

80

100

120

Air-case Oxy-case 1 Oxy-case 2

Unstaged Staged US Regulation100

63

47

29 3124

100

x N

Ox/(

NO

xfo

r uns

tage

dai

r com

bust

ion)

Primary reason for the reduction is the partial destruction of the NO recycled through the flame. Some enhanced capture of SO2 by ash was also observed as a result of the higher SO2 driving force.

Options for Control of trace gas contaminants

Oxy-fuel flow chart by Okawa et al., 1999

Combustion

Modification for NOx

Disposal with CO2?

Separation during CO2condensation?

SOx, Hg Control?

Constraints on composition for piping CO2

•CO2 > 95%•H2O < 100 ppm•H2S (or SO2) < 1450 ppm•N2 < 4%•HC < 5%Concentration limits for on-site sequestration are uncertain, both technical and regulatory.The nitrogen limit is determined by the difficulties of separating non-condensables from CO2 during compression and imposes severe constraints on furnace inleakage for retrofits.

Status•Existing Pilot Scale (< 5 MWt)

•EER (CA), 3.2 MW; IFRF (Neth.), 2.5 MW; IHI (Japan); Air Liquide, B&W (OH), 1.5 MW; CANMET (Canada), 0.3 MW; Alstom (CT), 3.0 MW CFB

•Planned Pilot Demonstration (>20 MWt)•Vattenfall 30 MWt Schwarze Pumpe Germany. Groundbreaking 5/06Japan (IHI) –Australia (Queensland) Oxy-Fired Retrofit with oxygen plant, CO2 compression and sequestration (including combustion and heat transfer evaluation); PF boiler (Callide A 30 MWe Unit owned by CS Energy).•Hamilton (OH) B&W 24 MWe retrofit

•Economic Assessmets•Many

Outline

• Oxy-fuel combustion principles• External Recycle for Retrofit Applications• Internal Recycle for New Plants• New Concepts • Concluding Comments

New Plant Design with Internal Flue Gas Recycle (Kobayashi, ’05)

Aspirating (A) burner for having oxygen designed to mimic air at fuel jet (Kobayashi, 2005)

BOC burner

The A burner is one of a number of burners using internal gas recirculation widely used in industry (30% of glass making furnaces)

New concept (DOC) being introduced in steel industry (Kobayashi, 2005)

(DOC)

Possible Applications of DOC Concept to Utility Boilers(N. B. flue gas stream leaving furnace has 26% of volume of air blown

furnace)

Five partial division walls

Tangential firing, oxygen and fuel alternating with height

Six front wall and five rear

NOx ports

Four rows front and rear wall

burners

Opposed wall firing = Fuel injection

= Oxygen injection

Outline

• Background• Oxy-fuel combustion principles• External Recycle for Retrofit Applications• Internal Recycle for New Plants• New Concepts• Concluding Comments

Energy flows for Conventional Lignite-Fired Boiler (Stromberg, 2004)

Energy Flows for the case of Oxy-Fuel Firing Showing Losses with Air Separation Unit and CO2 Compression

(Stromberg, ’04)

vs. 865 MW - 42.7%

Cost of Producing Oxygen (Kobayashi, 2005)

• Current technologies to produce 95% purity oxygen require ~ 200 Kwh/ton O2

• Theoretical energy required to compress oxygen from 0.21 to 1 atmosphere is about 30 KWh/ton O2

• There is potential for enormous savings with innovative designs– Chemical looping combustion being pursued by several

groups [Chalmers (Sweden), GE-EER (USA), Zaragosa(Spain), KIER (Korea), NNTU (Norway),…) using Fe, Mn, Cu, Ni based oxygen carriers.

– CO2 in-furnace capture and recovery using solid sorbents (e.g., CO2 wheel and lithium sulfate or hydrotalcite)

– New concept by Praxair using oxygen transport membranes appears to be exciting alternative.

Oxygen Transport Membranes Integrated into Boiler Offer Potential for Major Cost Reduction

(Kobayashi, 2005)

O2 Flux = C⋅ln(P1/P2)

High fluxes can be obtained with P1/P2 > 3 achievable by compressing air to 14.3 atmospheres to produce pure O2 corresponding to an ideal compression power of 250 kwh/ton O2 at 80°F

OR by using air at 1 atmand dilute oxygen combustion at 7% O2

(P1)

(P2)

P is oxygen partial pressure

Conceptual sketch of OTM-Dilute oxygen combustion (Kobayashi, 2005)

Conceptual OTM furnace design (Kobayashi, 2005)

•OTM boiler reduces air separation power by 90%

•High purity CO2 product reduces cost of capture

One Praxair Concept for OTM FurnaceBecause of the nitrogen elimination greater fraction of energy is

transferred in radiative section (Kobayashi, ’05)

Concluding Comments

• Near Term Prospects– Commitment to oxy-fuel evident from investments of € 50 M

($63.6 M) for Vattenfall pilot and A$ 180 M ($138 M) for Callide retrofit, SaskPower $1.33M for 300MWe ?

– Enhanced oil recover potential niche market for retrofit?• Intermediate and Long Term Prospects depend on

costs vs IGCC or other emerging technologies– Reduction in cost: CFBC or Internal Gas Recycle for capital

costs, ITM for operating costs– In-furnace OTM shows potential for major costs reductions

but faces major technical hurdles

Acknowledgements

Milind Deo, Sho Kobayashi, Lars Stromberg, Terry Wall, Jost Wendt