CO2NET Lectures on Carbon Capture and Storage
1. Climate Change, Sustainability and CCS2. CO2 sources and capture3. Storage, risk assessment and monitoring4. Economics5. Legal aspects and public acceptance
Prepared by Utrecht Centre for Energy research
Contents lecture 2:CO2 sources and capture
• CO2 sources• CO2 capture/decarbonisation routes• Separation principles• CO2 capture technologies in power cycles +
consequences on the power cycle• Comparison of different CO2 capture technologies• CO2 transport
CO2 emissions from fossil fuel use
Source: IEA WEO 2004
0
4000
8000
12000
16000
20000
power industry transport residential +services
othersectors
CO
2 em
issi
ons
(Mt/y
r)
20302002
CO2 emissions industry and power
Source: IEA GHG 2002a
Total: 13.44 Gt/y in 2000.
CO2 emissions by region
Source: IEA GHG 2002a
CO2 source distribution
Source: IEA GHG 2002b
Scale CO2 emissions
Source: IEA GHG 2002a
Purity CO2 sources
• Ammonia 100%• Hydrogen 10-100%• Ethylene oxide 100%• Gas processing 100%• Cement 15-30%• Iron and steel 15%• Ethylene 10-15%• Refineries 3-13%• Power 3-15%
CO2 sources and capture
• CO2 capture targets: large, stationary plants.• Power production
– Large sources, representing large share total emissions
• Industrial processes– Large sources, some emitting pure CO2
• Synthetic fuel production (Fischer-Tropsgasoline/diesel, Dimethyl ether (DME), methanol, ethanol)– Target sources in future?
Power plants
• Pulverised coal plants (PC) • Natural gas combined cycle (NGCC) • Integrated coal gasification combined
cycle (IGCC)• Boilers fuelled with coal, natural gas, oil
and biomass
Pulverised coal plant (PC)
Source: TVA
Natural gas combined cycle(NGCC)
HRSG
Gas turbine Steam turbine
compressor
Flue gas
Fuel
Air
CombustionChamber
Integrated coal gasification combined cycle (IGCC)
Source: Gottlicher, 2004
Power plant overview
1600-170043-45 (up to 52%)250-350IGCC
500-70055-58 (up to 65%)100- 500NGCC1000-125040-46 (up to 50%)500 –1000PC
Capital cost (€/kWe)
Efficiency (% LHV)
Capacity (MWe)
Plant
(efficiencies forecasted for 2010-2020)
CO2 emission + concentration
CO2 emission factors: coal 95 kg/GJ natural gas 56 kg/GJ
0.0
0.1
0.2
0.3
0.40.5
0.6
0.7
0.8
0.9
PC NGCC IGCC
CO
2 em
issi
on (k
g/kW
h)
min max
[CO2]=12-15% [CO2]=3-4%
Contents
• CO2 sources• CO2 capture/decarbonisation routes• Separation principles• CO2 capture technologies in power cycles +
consequences on the power cycle• Comparison of different CO2 capture
technologies• CO2 transport
Post-combustion capture
Separation of CO2 from mainly N2 in flue gas from combustion process (end-of-pipe)
energy conversion CO2 capture
flue gas
power
air
fuel
CO2
exhaust
Pre-combustion capture
Conversion of fossil fuels in syngasand separation of CO2 from H2 in shifted syngas prior to combustion
reforming/ partial
oxidation
water gas shift
syngas
steam/oxygen
fuel CO2CO2 capture
CO2
energy conversion
power
air
H2 exhaust
H2
Oxyfuel (denitrogenated) combustion
Separation of O2 from N2 in air and convert fuel in O2 environment
energy conversion Condenser
power
fuel
O2
CO2
H2Oair separation
air
N2
CO2
H2O
CO2 capture routes: summary
• Post-combustion capture: separation CO2-N2• Pre-combustion capture: separation CO2-H2• Oxyfuel combustion: separation O2-N2
[CO2] (%)p (bar)
75-95%20-40%3-15%~1 bar10-80~1 bar
Oxyfuelcomb.(exhaust)
Pre-comb. (shifted syngas)
Post-comb.(flue gas)
Contents
• CO2 sources• CO2 capture/decarbonisation routes• Separation principles• CO2 capture technologies in power cycles +
consequences on the power cycle• Comparison of different CO2 capture
technologies• CO2 transport
Separation principles
• Absorption: fluid dissolves or permeates into a liquid or solid.
• Adsorption: attachment of fluid to a surface (solid or liquid).
• Cryogenic (low-temperature distillation): separation based on the difference in boiling points
• Membranes: separation which makes use of difference physical/chemical interaction with membrane (molecular weight, solubility)
Absorption versus adsorptionChemical versus physical
Chemical Adsorption Physical Adsorption
Chemical Absorption Physical Absorption
Physical absorption
• Van der Waals forces• Governed by Henry’s law: p = Kc*c
p = partial pressure (Pa)Kc = Henry’s law constant (Pa/(mol/l)) (function of T and solvent)c = concentration in solvent (mol/l)
• Suited for processes with high partial pressure (>5 bar).• Absorption occurs at high pressure and low temperature.
Desorption occurs by pressure decrease.
Chemical absorption
• Covalent bond. In case of CO2, acid-base reaction (exothermic).
• CO2 loading is characterised by a saturation effect due to limited amount of reactive components.
• Suited for low to moderate CO2 partial pressures at low temperatures.
• More selective separation than physical absorption.• Most common absorbents: alkanolamines
CO2 + 2 R-NH2 ⇔ R-NH3+ + R-NHCOO-N-C bond is much stronger than Van der Waals forces
• Regeneration (desorption) occurs at increased temperature
Chemical versus physical absorption
concentration
Physical (Henry’s law)
Chemicalpartial pressure
p2
p1
c1ph c1ch c2ch c2ph
Low partial pressure (p1):
C1ph < C1chChemical absorption deserves preference
p2: reverse
~ 5 bar
Chemical versus physical absorption: example
• Inputs: – Flue gas NGCC (4 vol%, 1.1 bar) → p(CO2) = 4400 Pa– Kc (CO2) for Selexol (physical solvent) @ 21°C:
5.4.105 Pa/(mol/l)– MEA concentration (chemical solvent): 30 weight% =
12 mol%
• Outputs: – c (CO2) in Selexol = 8.10-3 mol/l– c (CO2) in MEA = 5.35.10-2 mol/l
• Higher loading with chemical absorbents!
Physical adsorption
• Van der Waals forces• Can be performed at high temperature• Adsorbents: zeolites, activated carbon and
alumina• Regeneration (cyclic process):
– Pressure Swing Adsorption (PSA)– Temperature Swing Adsorption (TSA) – Electrical Swing Adsorption (ESA)– Hybrids (PTSA)
Chemical adsorption
• Covalent bonds• Adsorbents: metal oxides, hydrotalcites• Example: carbonation (>600°C) -
calcination (1000°C) reactionCaO + CO2 ⇔ CaCO3
• Regeneration (cyclic process): – Pressure Swing Adsorption– Temperature Swing Adsorption
Cryogenic separation: principles (1)
• Distillation at low temperatures. Applied to separate CO2 from natural gas or O2from N2 and Ar in air.
-219, 0.0015-183O2
-183, 0.12-162CH4
-210, 0.125-196N2-199, 0.69-186Ar
-57, 5.18 NA (sublimation)CO2
Triple point (°C, bar)Boiling point (°C@p0)
substance
CO2 phase diagram
Cryogenic CO2 separation
−
+−=
s
s
CO
ONCO pp
py
yys .1
2
22
2
sCO2 = CO2 separation factor (%)
y = molar fraction
p = total pressure
ps = condensation/sublimation pressure CO2 (function of T)
Cryogenic CO2 separation: pT requirements for 90% recovery
Source: Gottlicher 2004
Cryogenic CO2 separation: applications
• Suitable for oxidising and reducing gas streams with high CO2 concentrations:– Bulk separation CO2/CH4 in natural gas: 1-80% CO2
@ high pressure (up to 200 bar). – Bulk separation CO2/H2 in syngas: 20-40% CO2 @
10-80 bar– Purification of flue gas oxyfuel combustion: 75-95%
CO2 @ ~1 bar. Contaminants: N2, Ar, O2 (non-condensible) SO2 and NOx (high boiling points)
• Not feasible for bulk separation CO2/N2 in flue gas: 3-15% CO2 @ ~1 bar (too low!)
Membranes: principle
feed “X-rich”
permeate site
membrane
retentate siteresidue “X poor”
sweep gas (co- or countercurrent)
X X
Membranes: important mechanisms
Knudsen Diffusion (porous)
Molecular Sieving (porous)
Solution-diffusion/ Ionic conductivity
(non-porous)
Non-porous membranes: physics
• Fick’s law for solution-diffusion process:
Q = K.A.Δp/l
Q = flux (mol/hr)K = permeability (mol/m*hr*Pa)A = membrane area (m2)Δp = pressure difference (Pa)l = membrane thickness (m)
Membrane characteristics
• Permeability determines required membrane area
• Selectivity (ratio of permeabilities) determines the purity of the end-product. At low selectivity, recycle or multi-stage plants may offer a solution.
• Permeability and selectivity are negatively correlated. Optimum!
• Stability is major issue. Solution: porous support such as glass, ceramic or metal
Membrane classifications
• Organic versus inorganic. Organic membranes are not resistant to high temperatures in contrast to inorganic membranes.
• Inorganic membranes: – metallic (transition metals, Pd)– microporous (SiO2, C, zeolite) – ion transport/conducting (ceramic)
• Porous versus non-porous (dense) • Self-supporting versus composite
Source: Rautenbach and Albrecht 1989
Organic membrane applications
• Polymeric membranes (commercial): – CO2/CH4 separation (high CO2 partial
pressure)– CO2/N2 separation (post-combustion).
Partial pressure in flue gas and membrane selectivity are low. This requires compression/recycling, which makes it uneconomic.
Inorganic membrane applications
• Metallic membranes (pre-combustion capture):– CO2/H2 separation by means of composite Pd-alloys.
• Microporous membranes (pre-combustion capture):– CO2/H2 separation. The selectivity is currently not
sufficient to enable the production of more than 99.99% H2.
• Ion transport membranes (pre-combustion capture + oxyfuel combustion):– CO2/H2 separation (proton conducting membranes) – O2/N2 separation (oxygen conducting membrane)
Ion transport membranes
permeate
retentate(compressed air)
e- ↓ ↑ O2-
O2 + 4e-→ 2O2-
2O2-→ O2 + 4e-
Mixed oxygen conducting
(both ionic and electronic conductivity)
permeate
retentate(compressed air)
↑ O2-
O2 + 4e-→ 2O2-
H2 + O2-→ H2O + 2e-
permeate
retentate
e- ↑ ↑ H+
H2→ 2H+ + 2e-
O2 + 4H+ + 4e-→ 2H2O
e-
Oxygen conducting
(only ionic conductivity)
Mixed proton conducting
(both ionic and electronic conductivity)
Membrane absorption
Source: Feron, TNO-MEP
Combining capture routes and technologies: CO2 capture toolbox
Source: Feron, TNO
Capture method
Post-combustion decarbonisation
Pre-combustion decarbonisation
Denitrogenated conversion
Principle of separation
Membranes • Membrane gas absorption • Polymeric membranes • Ceramic membranes • Facilitated transport
membranes • Carbon molecular sieve
membranes
CO2/H2 separation based on: • Ceramic membranes • Polymeric membranes • Palladium membranes • Membrane gas
absorption
• O2-conducting membranes
• Facilitated transport membranes
• Solid oxide fuel cells
Adsorption • Lime carbonation/calcinations
• Carbon based sorbents
• Dolomite, hydrotalcites and other carbonates
• Zirconates
• Adsorbents for O2/N2 separation, perovskites
• Chemical looping Absorption • Improved absorption liquids
• Novel contacting equipment • Improved design of
processes
• Improved absorption liquids
• Improved design of processes
• Absorbents for O2/N2 separation
Cryogenic • Improved liquefaction • CO2/H2 separations • Improved distillation for air separation
Contents
• CO2 sources• CO2 capture/decarbonisation routes• Separation principles• CO2 capture technologies in power cycles +
consequences on the power cycle• Comparison of different CO2 capture
technologies• CO2 transport
Integration of CO2 capture technologies in power cycles
Pre-combustionNGCC + Chem/Phys. absorption
OxyfuelAZEPOxyfuelChemical looping combustion
OxyfuelSOFC-GT
Pre-combustionSorption enhanced reforming
Pre-combustionMembrane reforming
Pre-combustionIGCC + Physical absorption
Post-combustionNGCC + Chemical absorption
Post-combustionPC + Chemical absorption
CO2 capture routeTechnology
State-of-the-art
Advanced
Post-combustion capture: chemical absorption
Sources: Herzog, MIT (left), ABB Lummus Crest (right)
Post-combustion capture: Integration in NGCC
Gas turbine Steam turbine
compressor
Flue gas
Fuel
Air
CombustionChamber
Knock-out drum
FilterAbsorber Stripper
Water wash
pumps
Heatexchangers
MEA rich
Other gasstreams
Reboiler loop
Feed gas
Cooler
Condenser
MEA lean
CompressorTransport
HRSGHRSG
Gas turbine Steam turbine
compressor
Flue gas
Fuel
Air
CombustionChamber
Knock-out drum
FilterAbsorber Stripper
Water wash
pumps
Heatexchangers
MEA rich
Other gasstreams
Reboiler
Feed gas
Cooler
Condenser
Reclaimer
MEA lean
CompressorTransport
Gas turbine Steam turbine
compressor
Flue gas
Fuel
Air
CombustionChamber
Knock-out drum
FilterAbsorber Stripper
Water wash
pumps
Heatexchangers
MEA rich
Other gasstreams
Reboiler loop
Feed gas
Cooler
Condenser
MEA lean
CompressorTransport
HRSG
Source: Peeters, UU
Post-combustion capture: Impact on efficiency (1)
ηpost-capture = efficiency of plant with post-combustion CO2 captureηreference = efficiency of plant without CO2 captureWcapture = power requirements of flue gas fan + pumps (MWe)Qcapture = heat requirements CO2 regeneration (MWth)α = ratio incremental power reduction to incremental heat
output (MWe/MWth) Wcompression = power requirements of CO2 compression (MWe)E = fossil fuel input (MWth)
ECW
EQ
EW ncompressiocapturecapture
referencecapturepost −−−=−α
ηη
Efficiency reference plant
ηreference = efficiency of plant without CO2 captureP = net power output (MWe)E = fossil fuel input (MWth)
Considering fossil energy consumption, CO2 capture might best be performed at power plants with high electric efficiency
EP
reference =η
Power requirements flue gas fan
Source: Bolland and Undrum, 2003
Power loss due to heat extraction for CO2 regeneration
Source: Bolland and Undrum, 2003
CO2 compression work
Source: Bolland and Undrum, 2003
Post-combustion capture:Impact on efficiency
Source: IEA GHG, 2005
Post-combustion capture:Impact on capital costs
Source: IEA GHG, 2005
Post-combustion capture:Impact on electricity costs
Source: IEA GHG, 2005
COE coal Fluor wo capture = 4.4 c/kWh, increase ≈ 40%
COE gas Fluor wo capture = 3.1 c/kWh, increase ≈ 40%
Pre-combustion capture: reactions
• Steam reforming of natural gas:CH4 + H2O ⇔ CO + 3H2 ΔH298= -206 KJ/mol(general: CxHy + xH2O ⇔ xCO + (x+y/2)H2)
• Water gas shift (WGS) reaction: CO + H2O ⇔ CO2 + H2 ΔH298= 41 KJ/mol
• Overall reaction:CH4 + 2H2O ⇔ CO2 + 4H2 ΔH298= -165 KJ/mol
• Partial oxidation of natural gas:CH4 + ½O2 ⇔ CO + 2H2 ΔH298= 36 KJ/mol(general:CxHy + x/2O2 ⇔ xCO + y/2H2)
Pre-combustion capture: Integration in IGCC
Source: IEA GHG
additional components
Pre-combustion capture: Integration in NGCC
additional components
Source: Kvamsdal, 2004
Pre-combustion capture: Impact on efficiency (1)
ηpre-capture = efficiency of plant with pre-combustion CO2 captureηCC H2 = efficiency of combined cycle fired on hydrogen rich
gasηconversion = efficiency of fossil fuel conversion into syngasQn = heat demanding processes e.g. WGS reaction, ATR
(MWth)Qm = heat producing processes e.g. syngas cooling (MWth) α = ratio incremental power reduction to incremental heat
output (MWe/MWth) Wcompression = power requirements of CO2 compression (MWe)Wmisc = miscellaneous power requirements e.g. ASU,
compression of oxygen/fuel gas (MWe)E = fossil fuel input (MWth)
EW
EW
EQ
EQ miscncompressiommnn
conversionHCCcapturepre −−+−=∑∑
−
ααηηη
2
Pre-combustion capture: Impact on efficiency (2)
0%
2%
4%
6%
8%
10%
12%
14%
IGCC dry IGCC slurry NGCC
effic
ienc
y pe
nalty
(%)
minmax
Composed from various sources
Pre-combustion capture:process integration
• Le Chatelier principle: by removing one of the products (CO2 or H2), the equilibrium will shift to the product site. – Membrane shift reactor: integration WGS with H2 separation.– Membrane reforming: integration reforming, WGS and H2
separation.– Sorption enhanced shift reactor: integration WGS and CO2
separation by adsorbents– Sorption enhanced reforming: integration reforming, WGS
and CO2 separation• Membranes/adsorbents allow high temperature
separation
Pre-combustion capture: Membrane reforming
CO2, H2O,Membrane
ReactionResidual gas
Permeate hydrogenH2
Feed stream
H2 H2H2 H2
High-pressure side
Low-pressure side
Catalyst particles
Sweep
CH4 + 2H2O ⇔ CO2 + 4H2
Source: ECN
In order to sustain this endothermic reaction, heat is supplied by burning natural gas (or hydrogen) in a furnace
Pre-combustion capture: Membrane reforming integrated in
CC (1)
Source: Norsk Hydro
Pre-combustion capture: Membrane reforming integrated in
CC (2)
Source: Norsk Hydro
Pre-combustion capture: Sorption enhanced reforming
CH4 + H2O H2 + CO2
catalyst adsorbent catalyst adsorbent
CO2CO2 CO2C
O2CO2
steam
airsteamnatural gas
generatorgas
turbine
SERP reactorin adsorptionmode
waterknock out
CO2
H2 +steam
SERP reactorin desorptionmode
Source: ECN
Principle
Integration in CC
Oxyfuel combustion: State-of-the-art configuration
Source: Andersson, Maksinen, Chalmers University
Oxyfuel combustion: Impact on efficiency (1)
ηoxyfuel = efficiency of oxyfuel combustion plantη reference O2 = efficiency of reference plant with near
stoiciometric combustion with O2. Different heat transfer and expansion characteristics!
WO2 = power requirements for O2 production (ASU) and compression (MWe)
Wcompression= power requirements of CO2 compression (MWe)
EW
EW ncompressioO
Oreferenceoxyfuel−−= 2
2ηη
Oxyfuel combustion: Impact on efficiency (2)
0%
2%
4%
6%
8%
10%
12%
14%
PC NGCC
effic
ienc
y pe
nalty
(%)
minmax
Composed from various sources
Oxyfuel combustion: Improvements for NGCC
• Disadvantages oxyfuel combustion in NGCC:– high energy requirements ASU– developing turbines with CO2/H2O as working fluid
• Advanced concepts:– Alternative oxygen production technologies
(membranes or oxygen carriers) – Allow for the use of conventional turbines using N2
as main working fluid
Oxyfuel combustion: Advanced concepts (AZEP)
Source: Norsk Hydro
Option: afterburner
Oxyfuel combustion:Chemical looping combustion
Oxyfuel combustion:Chemical looping combustion in CC
Source: Wolf, KTH
Solid oxide fuel cell (SOFC)
Source: Shell
H2 + O2-→ H2O+ + 2e-
CO + O2-→ CO2 + 2e-
O2 + 4e-→2O2-
SOFC-GT hybrids
Source: Siemens
SOFC features
• Promises high efficiency (60-70%) power generation at small scale (modular system), e.g. for distributed combined heat and power
• Current capital costs are high (>2000 €/kWe, small-scale NGCC ~ 1000 €/kWe)
• Status: various demonstration units with capacities in kW-MW range.
• Good opportunities for CO2 capture
CO2 capture at SOFC(-GT)
• SOFC is in fact oxyfuel concept, as nitrogen is separated from oxygen by the electrolyte.
• Various configurations can be applied to capture CO2 from the anode off-gas: – Post-fuel cell capture of CO2 using cryogenics or
absorption– Pre-fuel cell capture of CO2– Post-fuel cell off-gas oxidation (conversion of
remaining CO and H2 into CO2 and H2O)
Pre-fuel cell CO2 capture
Source: Jansen and Dijkstra, 2004
Post-fuel cell off-gas oxidation (1)
Source: Maurstad, 2004
Afterburner configurations
Source: Maurstad, 2004
Contents
• CO2 sources• CO2 capture/decarbonisation routes• Separation principles• CO2 capture technologies in power cycles +
consequences on the power cycle• Comparison of different CO2 capture
technologies• CO2 transport
Technology comparison:efficiency with CO2 capture
20%
30%
40%
50%
60%
70%
PC-po
st
PC-ox
y
IGCC
-pre
NGCC
-post
NGCC
-pre
NGCC
-oxy
ATR-
SEW
GS MRAZ
EP CLC
SOFC
-GT
net e
lect
ric e
ffici
ency
(% L
HV) max
min
Composed from various sources
Technology comparison:energy penalties
Composed from various sources
30%
40%
50%
60%
70%
PC-po
st
PC-ox
y
IGCC
-pre
NGCC
-post
NGCC
-pre
NGCC
-oxy
PC-po
st ad
v.
IGCC
-pre a
dv.
NGCC
-post
adv.
ATR-
SEWG
S MRAZ
EP CLC
SOFC
-GTn
et e
lect
ric e
ffici
ency
(% L
HV)
with CO2 capture reference plant
state-of-the-art advanced
Technology comparison:electricity production costs
Composed from various sources
01234567
PC-po
st
PC-ox
y
IGCC
-pre
NGCC
-post
NGCC
-pre
NGCC
-oxy
PC-po
st ad
v.
IGCC
-pre a
dv.
NGCC
-post
adv.
ATR-
SEWG
S MRAZ
EP CLC
SOFC
-GTe
lect
ricity
cos
ts (€
ct/k
Wh)
capital fuel O&M
state-of-the-art advanced
Technology comparison:CO2 recovery
Composed from various sources
0.00
0.20
0.40
0.60
0.80
1.00
PC-po
st
PC-ox
y
IGCC
-pre
NGCC
-post
NGCC
-pre
NGCC
-oxy
PC-po
st ad
v.
IGCC
-pre a
dv.
NGCC
-post
adv.
ATR-
SEW
GS MR AZEP CL
C
SOFC
-GT
CO
2 pr
oduc
tion
(kg/
kWh)
CO2 capture CO2 emissions
state-of-the-art advanced
CO2 captured versus avoided
0 0.2 0.4 0.6 0.8 1
ReferencePlant
CapturePlant
CO2 produced (kg/kWh)
Emitted
Captured
CO2 avoided
CO2 captured
CO2 avoidance costs = (COEcap- COEref)/(Eref - Ecap)
Source: Herzog, MIT
Technology comparison: CO2 mitigation costs
Composed from various sources
0
10
20
30
40
50
60
PC-po
st
PC-o
xy
IGCC
-pre
NGCC
-pos
t
NGCC
-pre
NGCC
-oxy
PC-p
ost a
dv.
IGCC
-pre a
dv.
NGCC
-pos
t adv
.
ATR-
SEWG
S MRAZ
EP CLC
SOFC
-GTC
O2
miti
gatio
n co
sts
(€/t
CO
2)
state-of-the-art advanced
Choice of reference system
3.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
0.00 0.20 0.40 0.60 0.80 1.00
CO2 emission (kg/kWh)
elec
trici
ty c
osts
(€ct
/kW
h) PC IGCCNGCC
Source: based on Herzog, MIT
No CCS
With CCS
Summary: Post-combustion capture
• Chemical absorption is currently most feasible technology
• Technology is commercially available, although on a smaller scale than envisioned for power plants with CO2 capture (>500 MWe)
• Energy penalty and additional costs are high with current solvents. R&D focus on process integration and solvent improvement.
• CO2 capture between 80-90%• Power cycle itself is not strongly affected (heat
integration, CO2 recycling)• Retrofit possibility
Summary: Pre-combustion capture
• Chemical/physical absorption is currently most feasible technology
• Experience in chemical industry (refineries, ammonia)• Energy penalty and additional costs physical absorption
are lower in comparison to chemical absorption• CO2 capture between 80-90%• Need to develop turbines using hydrogen (rich) fuel• No retrofit possibility• Advanced concepts to decrease energy penalty/costs:
– sorption enhanced WGS/reforming– membrane WGS/reforming
Summary: Oxyfuel combustion• Cryogenic air separation is currently most feasible
technology• Experience in steel, aluminum and glass industry• Energy penalty and additional costs are comparable
to post-combustion capture• Allows for 100% CO2 capture • NOx formation can be reduced• FGD in PC plants might be omitted provided that SO2
can be transported and co-stored with CO2• Boilers require adaptations (retrofit possible). R&D
issues: combustion behaviour, heat transfer, fouling, slagging and corrosion.
Summary: Oxyfuel combustion (2)
• Boilers require adaptations (retrofit possible). R&D issues: combustion behaviour, heat transfer, fouling, slagging and corrosion.
• Application in NGCC: new turbines need to be developed with CO2 as working fluid (no retrofit)
• R&D focus on development of new oxygen separation technologies. Advanced concepts to decrease energy penalty/costs: – AZEP (separate combustion deploying oxygen membranes) – Chemical looping combustion (separate combustion
deploying oxygen carriers).
Contents
• CO2 sources• CO2 capture/decarbonisation routes• Separation principles• CO2 capture technologies in power cycles +
consequences on the power cycle• Comparison of different CO2 capture
technologies• CO2 transport
CO2 transport
• Pipelines are most feasible for large-scale CO2 transport– Transport conditions: high-pressure (80-150 bar) to
guarantee CO2 is in dense phase • Alternative: Tankers (similar to LNG/LPG)
– Transport conditions: liquid (14 to 17 bar, -25 to -30°C)– Advantage: flexibility, avoidance of large investments– Disadvantage: high costs for liquefaction and need for
buffer storage. This makes ships more attractive for larger distances.
Pipeline versus ship transport
Source: IEA GHG, 2004
Pipeline design
52
22 322
dlqf
dlvfp
πρ
ρ ==∆
µρvdRe =
Δp = pressure drop (Pa)
Re = Reynolds number
f = friction factor
v = average fluid velocity (m/s)
q = volumetric flow (m3/s)
l = pipe length (m)
d = (internal) pipeline diameter (m)
ρ = fluid density
µ = fluid viscosity
As a consequence of friction and elevation differences, pressure drop occurs along the pipeline:
Pipeline optimisation
• Small diameter: large pressure drop, increasing booster station costs (capital + electricity)
• Large diameter: large pipeline investments
• Optimum: minimise annual costs (sum of pipeline and booster station capital and O&M costs plus electricity costs for pumping).
• Offshore: pipelines diameters and pressuresare generally higher as booster stations are expensive
CO2 density as function of p,T
0
200
400
600
800
1000
1200
0 50 100 150 200 250 300 350
Pressure (bar)
Den
sity
CO
2 (k
g/m
3)
0102030405060708090100110120130140150160170180190
Source: Hendriks, Ecofys
CO2 quality specifications
• USA: > 95 mol% CO2• Water content should be reduced to
very low concentrations due to formation of carbonic acid causing corrosion
• Concentration of H2S, O2 must be reduced to ppm level
• N2 is allowed up to a few %
CO2 transport costs
0
1
2
3
4
5
0 50 100 150 200 250 300 350
distance (km)
tran
spor
t cos
ts (€
/t C
O2)
0.1 Mt/yr1 Mt/yr2 Mt/yr4 Mt/yr10 Mt/yr20 Mt/yr40 Mt/yr
Source: Damen, UU
Risks pipeline transport
• Major risk: pipeline rupture. CO2 leakage can be reduced by decreasing distance between safety valves.
• CO2 is not explosive or inflammable like natural gas
• In contrast to natural gas, which is dispersed quickly into the air, CO2 is denser than air and might accumulate in depressions or cellars
• High concentrations CO2 might have negative impacts on humans (asphyxiation) and ecosystems. Above concentrations of 25-30%, CO2 is lethal.
Safety record pipelines• Industrial experience in USA: 3100 km CO2
pipelines (for enhanced oil recovery) with capacity of 45 Mt/yr
• Accident record for CO2 pipelines in the USA shows 10 accidents between 1990 and 2001 without any injuries or fatalities. This corresponds to 3.2.10-4 incidents per km*year
• Incident frequency of pipelines transmitting natural gas and hazardous liquids in this period is 1.7.10-4 and 8.2.10-4, respectively, with 94 fatalities and 466 injuries
Conclusion: CO2 transport is relatively safe.