influence of ash deposition in oxyfuel corrosion experiments
TRANSCRIPT
Influence of Ash Deposition in Oxyfuel Corrosion Experiments
Axel Kranzmann*, Maria Mosquera Feijoo*, Alba Baselga Zapater**Federal Institute for Material Science and Testing, Berlin;Universidad Ramón Llul, Institut Químic de Sarrià
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Open questions in corrosion
Influence of gas velocity above surfaceInfluence of steam pressureTime – which experimental time an which experiment is representative
for the individual component or plant.Influence of dual conditions like both side on a separating wall (pipe wall
in steam power plants).Influence of an ash layer on high temperature corrosion.A deductive model or a reliable inductive models which predict
material loss on base of material chemistry and microstructuredoes not exist.How to extrapolate from laboratoy data to the field ?
…(more questions exist)
This presentation contributes to
Influence of an ash layer on high temperature corrosion in oxyfuel flue gas.
Influence of dual corrosion (pipe wall in steam power plants) Exists! But not much laboratory experiments were performed for coal
plant superheater tubes A deductive model or an reliable inductive models which predicts
material loss does not exist and is still a vision.
Example: Tube with inner pressureGas diffusion.Educt towards steel.Products into gas phase.
Gas corrosion.
Local gas-ash/slag/Metalequilibrium.
Ash-Magnetite reaction.
Pressure, temperature, flow.
Steam oxidation
H+
Fe + H2O
CO2
SO2O2
H2O
Mm(SO4)n
{ }{ }
}{ .Na,..M:1n2,mCa,..Mn,Fe,M:1n1,m...Cr,Fe,M:3n2,m
2
3
⊂==
⊂==
⊂==
+
+
+
C
SO
Oxyfuel-SteamDual conditions
MClx
SiO2Al-Si-O
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Gas
Gas
Thermocouples type K. Nickel-Chrome/ Nickel-Aluminium
SpecimenTitaniumattachingparts
Aluminum oxide(Al2O3) ceramic.
Gas injectionpipes of1.4571 steel
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Dual gas coupon experiment– an upgrade from simple ISO coupon experiment towards technical conditions.
Specimen Geometry
Circular couponsActive Diameter / mm: 15 Tickness/ mm: 2,65 – 2,96Active Surface area: 1.767 cm2
Ash layer > 1 mg/cm2
Oxyfuel flue gas:27 H2O-60 CO2-1 SO2-10 N2-2 O2
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3 mm
20 mm
15 mm
Phases Ash Weight%
CaSO4 40Fe2(SO4)3 20FeSO4 20SiO2 10Fe2O3 3.3Al2O3 1.9CaO 4.8
Brownmillerite
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Oxyfuel Flue GasOxyfuel Flue Gas
Oxyfuel Flue Gas
Single-atmosphere
Steam
Ash
Dual-atmosphere
SealingSpecimen
Scheme of Test Idea
Comparison of ashand no ash in Oxyfuel flue gas.
Influence of steamthe oxidation in Oxyfuel flue gas.
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I)
Both surfaces loaded with Oxyfuel flue gas.
One surface area covered with ash.
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24 h, 600 °C, oxyfuel ash – no ash comparison
Ash no Ash
Similar to air or steamOxidation. Density oflocal corrosion scale isvery inhomogeneous.
Continuous internal oxidationAsh reacts with the epitaxiallygrown oxide.
20 µm
Ash No Ash
240 h, 600 °C, oxyfuel test gas both faces
Continuous thicker inner oxidationAsh is completely mixed with theexternal grown oxide.
Oxyfuel oxidation
Expressedinternalcorrosion
Haematite
Magnetite
Magnetiteplus FeCr-Spinel
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Development in the first 240 h
24 h
Oxyfuel Flue Gas
240 h
Internal oxidation upto 15 µm deep.
Comparable to steamoxidation.
Thicker oxide!Nests of Hämatite andin the Ash!
Thicker oxide!Pores were formed in deeper oxidesnear the interface to the metal.
SomeSulfur
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II)
Dual Conditions
One surface in contact with steam and ash free
One surface in contact with flue gas and ash
H+
Fe + H2O
CO2
SO2O2
H2O
Mm(SO4)n
C
SO
MClx
SiO2Al-Si-O
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Dual condition experiment24 h, 600 °C
Flue gas + ash Steam
20 µm
Fast local corrosion,general island formation,oxidation depth up to20 µm. Single Haematiteislands visible.
Continuous layer ofless than 15 µm thickness.
Inner corrosion linked tomore sulfur in contact withmetal.
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Dual condition experiment240 h, 600 °C
Flue gas + ash Steam
Buckling of the outer layerappeared indicatingcompressive growthstresses. Haematite is notforming an layer.
The internal oxide layerseems to be thinner thanafter 24 h annealing time.
Haematite –Ashis strongly fixed onthe external Magnetite
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Development in the first 240 h, VM12SHCFlue gas
Steam
8 to 14 µm continuous innercorosion zone
Much thinner external corrosionbut spallation
Up to 20 µm inner oxidationzonePartially locallizedLocal corrosion noodles growtogether
2424 h h
Ash
24240 h h
Thinner inner corrosionlayerSpalation effects even in the inner corrosion layer.
Continuous inneroxidation.
Buckling even for thisstill thin layer.
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Development in the first 240 h
AshFlue gas
Steam
24240 h h2424 h h
Ash
High amountof Sulfur
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The ash layer supports the formation of a continuousinternal oxidation layer.
The outer (epitactical) corrosion layer envelops ash particle. A partly reaction between ash and Magnetite isforms Haematite.
Haematite is also formed on the ash free surface. It mightbe a product supported by the Sulfates in the ash.
Haematite formation is neglegtible under Dual conditions.
Only under dual conditions the ash layer supports grainboundary attack caused by sulphur which and buckling on the steam side.
79
25
47
05
101520253035404550
O/O 24h O/O 240h S/O 24h S/O 240h
Thickness loss - Total Steel Material loss / µm
Uncertainty in the order of ±3 µm (± 5 Pixels).
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Oxide scales are comparable but material loss seems to besmall in oxyfuel atmosphere.
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Inconsistence?
Similar Oxide scale thickness after the oxyfuel-oxyfuel corrosion experiment than in the steam –oxyfuel experiment.
But the material loss shows vice versa data!
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Points to discuss
- Why the ash induces a more homogeneousinner corrosion layer?
- What reacts with Magnetite at 600 °C an partly consumes the outer Magnetite layer?
- Why we observe thick oxide scales but a very small material loss in case of oxyfuelcorrosion?
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- Why the ash induces a more homogeneousinner corrosion layer?
- Hypothesis- More homogeneous partials pressure of
SO2 and O2.- Diffusion of ash constituents- …?
Not answered yet!
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What reacts with Magnetite at 600 °C an partly comsumes the outer Magnetite layer?
Mainly the oxyfuel flue gas – but SO2 partial pressure is influenced by the ash.
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Why we observe thick oxide scales but a very small material loss in case of oxyfuel corrosion?
Result of volume increase by dissolving Carbon in the Martensite structure.
Martensite structure
aa
“c“
Leng
tha,
c /n
m0.28
0.31
Carbon content in at%0 10.7
0.29
0.30
c
a
Range for Martensite
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0.991
1.011.021.031.041.051.061.071.081.09
1.1
0 1 2 3 4 5 6 7 8 9 10
Relative change in volume
at% C in Martensite structure.
Max. 26 µm growthper mm specimenthickness.
In mass %
Cr Co W Si Mn C V P Al S
VM12 Steel 11.7 1.51 1.47 0.51 0.28 0.14 0.2 0.02 0.01 <0.01
0.6
6.5
7.2
7 9
25
47
0
10
20
30
40
50
60
70
80
O/O 24h O/O 240h S/O 24h S/O 240h
Thickness loss - Total Steel Material loss / µm
Uncertainty in theorder of ±3 µm (± 5 Pixels).
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Oxide scales are comparable but material loss seems to be small in oxyfuel atmosphere. * Kinetik PhD Thesis D. Hünert, BAM, 2009 andCorrosion +Thermodynamik D. Young, Eurocorr 2013.
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Influence of Ash Deposition in OxyfuelCorrosion Experiments
Ash supports the formation of the innercorrosion layer
Ash reacts with the epitaxial oxide layer
Ash doesn`t prevent the uptake of Carbonby the steel.
The total material loss in µm could be evenhigher than in pure steam oxidation.
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Thank you for showing an interest in our work.
Expectation
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Working conditions
to face*
Component fora technology Experiment
Simulate theworking conditions.
Draw conlusions on
Functionality, Lifetime, interaction, improvements, ….
Type of Experiments (only high temperature T > boiling temperature of Acids and Water)
Waterwalltube
Super-heatertube
Steamsampler
Waterwall
Steamturbineblade
Gas turbineblade
Ash, Slag
Steam
Flue gas
Stress
Air
Coupon (ISO)
Dual corrosioncoupon
Tube simulationexp.
Double ring test
Tensile Test
Ash, Slag
Steam
Flue gas
Stress
Air
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* Knowledge on the external influences and the ageing of the material. Corrosion: material composition, corrosion rates in relation to chemical activitiesor fugacities, solubility of impurities in the surface near volume, Diffusion constants, microstructure change during exposure, influence of stress
FIncreased solubilityfor soluble atoms likeH+ or C in Fe
Grain size and shapeGrowth, recristallization)
Variable: T, p
Shape (creep, plasticity,viscose flow)
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Same environmental conditionon each surface = Single conditions
or full/half embedded in ash/slag
One experiment: T, p , flow rate, gas mixture = constant
ISO Coupon Test
Steam
Oxyfuelgas
With and withoutash deposit
Temperature 600 °C
Gas tiedsealing
Dual corrosion condition flue gas experiment
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Example: Simple tube with inner pressure
Gas diffusionEduct towards steelProducts into gas phase
Gas corrosion
Local gas-ash/slag/Metall equilibrium
Ash-Magnetite reaction
pressure
Steam oxidation
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