Summary of
the Project OptiCorr
Modelling of Hot Corrosion
of Heat Exchanger Components
K.Hack, GTT-Technologies
ExMente Workshop, 21st and 22nd July 2008
Motivation
Precipitate formation in a superheater of a bio-mass incinerator
Fotographs: Courtesy VTT - Technology
GTT-Technologies
OptiCorr
deposits
FBC
A Problematic
very complex
overallinprocess
and recovery boilers
Alkali aerosol particles &
coarse mode particles
Chloride vapours
Turbulent flow in
staggered tube array
Condensation on
aerosol particles
Sulphation
Thermophoresis
SO2
HCl
Condensation
on deposit
layer
Coarse particle
sticking
Sintering &
removability by
sootblowing
GTT-Technologies
Boundary
layer
Corrosion
Heat
transfer
Diffusion
in porous
deposits
OptiCorr
Contents
-
Overview of the Thermochemical Modelling
including Database Work
-
One- and two-dimensional Phase Maps
related to OptiCorr
-
Simulation of various Aspects
of Boiler Corrosion
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Phases and Components in the System
Gas Phase
HCl, SO2
O2, H2O
Volatile
compounds:
ZnCl2, PbCl2
KCl, NaCl
Sulfates resp.
KOH, NaOH
etc.
GTT-Technologies
Ash deposit
Solid state
Liquid state
Silicates
Sulfates, Chlorides
(Ca, K, Na, Pb, Zn)
Others (oxides...)
Metal
Fe, Ni, Cr, C
Mo, Si, Al
Precipitates
Carbides
MC, M23C6
M7C3
Nitrides
TiN
etc.
OptiCorr
Available tools (1): FactSage
Stoichiometric reactions
Complex equilibria
Fe - Cr - V - C System
T = 850°C, wt.% C = 0.3, Ptot = 1 atm
<F*A*C*T>
0.05
 – fcc + M23C6
‚ – fcc + M7C3 + M23C6
ƒ – bcc + fcc + M7C3 + M23C6
„ – bcc + MC + M7C3 + M23C6
bcc + MC
+ M23C6
0.02
„
bcc + MC + M7C3
23
C
3
+
M
C
6
bcc
+ fcc
+ MC
+ M7C3
7
bcc + M7C3
0.01
M
bcc + fcc + MC
+
Phase diagrams
Data assessment
bcc + MC
0.03
fcc + MC
fcc + MC + M7C3
fcc + bcc
+ M7C3
fcc + M7C3
‚
fcc
0.00
0.00
0.02
0.04
0.06
0.08
0.10
ƒ
bc
c
mass fraction V
0.04
bcc + M23C6

fcc + bcc
+ M23C6
0.12
0.14
0.16
mass fraction Cr
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Available tools (2): InCorr and SaltCorr/CorrApp
Calls ChemApp
after each
diffusion step.
metal diffusion
(Cr, Fe, Ni...)
oxygen diffusion
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Available tools (3): ChemSheet
Thermodynamic Data
The principle method
ChemApp
ChemSheet
Excel Worksheet
An example
application
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Database work:
Classification of Subsystems
1 The Metal Subsystem
2 The Salt Subsystem
3 The Oxide Subsystem
4 The Sulphide Subsystem
Compilation, critical evaluation
and new assessements
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Contents of subsystems:
1 The Metal Subsystem
Components:
Fe-Cr-Ni-Mn-C-Si-Al-Mo plus S-O as well as Cl
and possibly K-Na-Pb-Zn-Ca (add Ce on request
by RAU)
Phases:
FCC_A1 (Fe,Cr,...)1(Va,C,S,O)1
BCC_A2 (Fe,Cr,..)1(Va,C,S,O)3
plus carbides, e.g. M23C6, M7C3, M3C2 etc
NOTE: Additional work was put into a smaller
Ni-based alloy database
GTT-Technologies
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Contents of subsystems:
2 The Salt Subsystem
Components:
K,Zn,Fe,Fe3+,Cr,Cr3+,Ni// Cl,SO4,CrO4 plus
Na,Pb // Cl,SO4,CrO4
Phases:
Liquid with all components
Solid solutions, e.g. K2SO4-K2CrO4, NaCl-KCl
Stoichiometric solids
(To be done: Add more cat-ions and OH !)
GTT-Technologies
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Contents of subsystems:
3 The Oxide Subsystem
Components:
FeO, Fe2O3, CrO, Cr2O3, NiO, MnO, Mn2O3,
MoO3, K2O, Na2O, PbO, ZnO
Phases:
Liquid with all components (only for completeness)
Solid solutions, e.g. wustite
(Fe,Fe3+,Ni,Mn,Va)(O) corundum (Fe,Cr)2O3,
Fe-spinel FeO.(Fe,Cr)2O3
Stoichiometric solids, e.g. the pure oxides
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Assessment work: One Compositional Axis
[87Chu]
1800
BCC_A2 + LIQUID
LIQUID
FCC-A1 + LIQUID
Te
m 1300
pe
rat
ur
e,
K
BCC_A2 + LIQUID
CeFe2
FCC-A1 + LIQUID
800
Ce2Fe17
FCC-A1 + CeFe2
300
0
.2
.4
.6
.8
1
mole fraction Ce
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Assessment work: Two Compositional Axes
Co
[81Zha]
0.8
[79Dom]
mo
le
fra
cti
on
Co
0.6
FCC-A1
0.4
SIGMA
0.2
BCC_A2
Fe
0.8
0.6
0.4
0.2
Cr
mole fraction Fe
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Calculational results (available in GuideBook):
- One-dimensional mappings
Gases used in the corrosion experiments
- Two-dimensional mappings
Alloy and Salt systems
Alloys under corrosive conditions
- The Process Model calculations
An overview
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One-dimensional mappings: Speciation in gases (1)
Ar(g)
H2O(g)
O2(g)
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One-dimensional mappings: Speciation in gases (2)
SO3
GTT-Technologies
SO2
H2SO4
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Two-dimensional mappings: Two Compositional Axes (2)
KCl - NiCl2 - ZnCl2
Liquidus Surface between 300 and 1000 °C
NiCl2
GTT-Technologies
0. 9
0. 1
0. 8
0. 2
0. 7
0. 3
0. 6
0. 4
0. 5
0. 5
0. 4
0. 6
0. 3
0. 7
0. 2
0. 8
0. 1
0. 9
KCl
0.9
0.8
0.7
0.6
0.5
mole fraction
0.4
0.3
0.2
0.1
ZnCl2
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Two-dimensional mappings: Two Compositional Axes (3)
Fe - K - Zn - Cl 2
o
-5
320 C, p(Cl 2) = 10 atm
LIQUID + KCl + ZnK 2Cl4
0. 3
0. 7
Note the constant
potentials :
T and P(Cl2).
0. 2
0. 8
0. 1
0. 9
K
0. 5
0. 5
LIQUID + ZnK2Cl4
0. 4
0. 6
LIQUID + KCl
0. 4
0. 8
0. 2
0. 7
0. 3
0. 6
LIQUID
Fe
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0. 9
0. 1
LIQUID + FeCl2
0.9
0.8
0.7
0.6
0.5
mole fraction
0.4
0.3
0.2
0.1
Zn
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Two-dimensional mappings: Potential diagram (1)
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Two-dimensional mappings: Potential diagram (3)
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The Salt Corrosion Model
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Model picture
Gas
Ar(g) - O2(g)
2FeCl2(l) + 1.5O2(g) = Fe2O3(s) + 2Cl2(g)
KCl(l) - ZnCl2(l)
Melt
Cl2(g) = Cl2(l)
K+ - Zn2+ - ClFe + Cl2(l) = FeCl2(l)
Metal
Fe
One-dimensional diffusion (across the salt melt)
is coupled with the local equilibrium concept.
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Results of the Simulation, I
50m
ZnCl2 - KCl
#
Fe
Incubation period
(after 5 min)
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Results of the Simulation, II
Fe-Oxide
Solidified Saltmelt
Fe
Oxide formation
near surface
(after 10 min)
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The Gas Corrosion Model
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Low Chromium Steels
SO2 and / or O2
sulfidation
corrosion
outer scale
inner scale
oxidation
original
surface
sulphides and/or
oxides
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Model picture
outer
scale (Fe3O4)
inner
scale (Fe3O4,FeCr2O4)
p(O2) Fe O
3
4
p(O2) FeCr O
2
4
p(O2) Cr O
2
intercrystalline
oxidation (Cr2O3)
Deff
3
moving
interface
Dx
Dy
DGB
steel B
5 µm
(550°C, 72h, air) 5µm
Two-dimensional diffusion is coupled with
the local equilibrium concept.
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Results of the simulation, I
Fe3O4
Fe3O4 [at.%]
y [m]
x [m]
grain boundaries
FeCr2O4
FeCr2O4 [at.%]
y [m]
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x [m]
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Results of the simulation, II
Cr in Fe-BCC
Cr in Fe-BCC (at.%)
x [m]
y [m]
Cr2O3 (at.%)
Cr2O3
x [m]
y [m]
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Mean Thickness of the Oxide Scale
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The Gas Precipitation Model
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Model Picture
Heat exchanger 1, T1
sticking effects
Flue Gas with Aerosols, T0
Combustion chamber
.
.
.
Heat exchanger n, Tn
sticking effects
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Summary of the Gas Precipitation Model: User interface
The dust load from the combustion chamber
Input box for transfer coefficient
The temperature input box using StepIndex variable
The gas composition as from
the combustion chamber
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Input box for sticking coefficient
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Summary of the Gas Precipitation Model: Results
Condensed Phases, Trans=1, Stick=0.1
s-Ca,Mg,Na\SO4/CaSO4
s-Ca,Mg,Na\SO4/(Na2SO4):2.000
Al2O3_corundum(alpha(s4)
1.E+06
AlF3(s)
Na5Al3F14(s)
Amount in mol
SiO2_quartz(l)(s)
Al6Si2O13_mullite(s)
NaAlSi3O8_low(s)
1.E+03
NaAlSi3O8_high(s2)
Na2SO4(s)
NaCl_halite (rock sal(s)
CaSO4_anhydrite(s)
Fe2O3_hematite(s)
1.E+00
300
NiSO4(s)
400
500
600
T in K
GTT-Technologies
700
800
900
(NiO)(Fe2O3)(s)
ZnAl2O4(s)
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Summary of the Gas Precipitation Model: Results
s-Ca,Mg,Na\SO4/CaSO4
Condensed Phases, Trans=0.9, Stick=0.2
s-Ca,Mg,Na\SO4/(Na2SO4):2.000
Al2O3_corundum(alpha(s4)
1.E+06
AlF3(s)
Amount in mol
SiO2_quartz(l)(s)
Al6Si2O13_mullite(s)
Na2SO4(s)
1.E+03
CaSO4_anhydrite(s)
Fe2O3_hematite(s)
Fe2(SO4)3(s)
NiSO4(s)
1.E+00
300
400
500
600
T in K
GTT-Technologies
700
800
900
ZnAl2O4(s)
ZnSO4(s2)
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Summary of the Gas Precipitation Model: Results
s-Ca,Mg,Na\SO4/CaSO4
Condensed Phases, Trans=0.1, Stick=0.1
s-Ca,Mg,Na\SO4/(Na2SO4):2.000
Al2O3_corundum(alpha(s4)
1.E+06
SiO2_quartz(l)(s)
Amount in mol
Al6Si2O13_mullite(s)
1.E+04
Na2SO4(s)
Al2(SO4)3(s)
CaSO4_anhydrite(s)
1.E+02
Fe2O3_hematite(s)
Fe2(SO4)3(s)
1.E+00
300
NiSO4(s)
400
500
600
T in K
GTT-Technologies
700
800
900
ZnAl2O4(s)
ZnSO4(s)
OptiCorr
SUMMARY of OptiCorr Project
- New and improved databases
- Use of ChemApp in advanced environments
- Process models for improved understanding
of phase formation
- under molten salt layer
- in an oxygen containing atmosphere
- on cooling of gas
Outlook on future options:
* improved database needed on salts (experiments!)
* better model for the combustion process
and the precipitation possibly coupled with CFD
GTT-Technologies
OptiCorr
THANK YOU for your attention !
GTT-Technologies
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GTT-Technologies
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Final actions:
- Applied calculations guided by the
other
project partners, e.g. „open system“
calcs., but also „point tests“, a simple
gas
precipitation model using ChemSheet
- One-dimensional mappings for all test
alloys (without corrosive environment)
- Potential diagrams for test alloys
under
various conditions
GTT-Technologies
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Database work executed :
- Metal Subsystem
in close co-operation with HUT: Mietinen database rejected, GTT own
database improved, especially Fe-Mn-S subsystem thoroughly
checked, FeCe added on request by RAU, Fe-Co-Cr and Ni-Co-Cr re-assessed
- Salt Subsystem
using the quasi-chemical next nearest neighbour interaction model
from
CRCT Montreal: K+,Zn2+,Fe2+,Fe3+,Cr2+,Cr3+,Ni2+//Cl-,SO42-,CrO42system
has been assessed or estimated
- Oxide Subsystem
data needed could be taken from FACT database
- Sulphide Subsystem
FeS-MnS subsystem was taken from literature (including solid
solutions),
GTT-Technologies
other sulphides are treated as stoichiometric
OptiCorr
Classification of subsystems:
1 The Metal Subsystem
Components:
Fe-Cr-Ni-Mn-C-Si-Al-Mo plus S-O as well as Cl
and possibly K-Na-Pb-Zn-Ca (add Ce on request
by RAU)
Phases:
FCC_A1 (Fe,Cr,...)1(Va,C,S,O)1
BCC_A2 (Fe,Cr,..)1(Va,C,S,O)3
plus carbides, e.g. M23C6, M7C3, M3C2 etc
NOTE: Additional work was put into a smaller
Ni-based alloy database
GTT-Technologies
OptiCorr
Classification of subsystems:
2 The Salt Subsystem
Components:
KCl-ZnCl2-FeCl2-MnCl2-FeCl3-K2SO4-ZnSO4FeSO4-MnSO4-Fe2(SO4)3-K2CrO4-ZnCrO4MnCrO4-FeCrO4-Fe2(CrO4)3 plus
NaCl-PbCl2-Na2SO4-PbSO4-Na2CrO4PbCrO4
Phases:
Liquid with all components
Solid solutions, e.g. K2SO4-K2CrO4, NaCl-KCl
Stoichiometric solids
GTT-Technologies
(Possibly add OH !)
OptiCorr
Classification of subsystems:
3 The Oxide Subsystem
Components:
FeO, Fe2O3, CrO, Cr2O3, NiO, MnO, Mn2O3,
MoO3, K2O, Na2O, PbO, ZnO
Phases:
Liquid with all components (only for completeness)
Solid solutions, e.g. wustite
(Fe,Fe3+,Ni,Mn,Va)(O) corundum (Fe,Cr)2O3,
Fe-spinel FeO.(Fe,Cr)2O3
Stoichiometric solids, e.g. the pure oxides
GTT-Technologies
OptiCorr
Classification of subsystems:
4 The Sulphide Subsystem
Components:
FeS, CrS, Cr2S3, NiS, MnS, MoS, MoS2,
Mo2S3, K2S, Na2S, PbS, ZnS, CaS
Phases:
Liquid with all components (only for completeness)
Solid solutions, e.g. two different (Fe,Mn)S
Stoichiometric solids, e.g. the pure sulphides,
but also FeCr2S4, Fe7S8, Ni3S4, MnS2, Cr3S4,
Cr5S6, Cr6S7, or others
GTT-Technologies
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One-dimensional mappings: Speciation in gases (1)
GTT-Technologies
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One-dimensional mappings: Speciation in gases (1)
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One-dimensional mappings: Speciation in gases (2)
GTT-Technologies
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One-dimensional mappings: Speciation in gases (2)
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One-dimensional mappings: Speciation in gases (3)
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One-dimensional mappings: Speciation in gases (3)
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One-dimensional mappings: Alloy investigations (2)
Steel X20: Fe 86.8, Cr 10.3, Ni .72, Mo .87, V .26, C .18, Si .23, Mn .62, S .00
GTT-Technologies
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One-dimensional mappings: Alloy investigations (2)
GTT-Technologies
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One-dimensional mappings: Alloy investigations (2)
GTT-Technologies
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One-dimensional mappings: Alloy investigations (2)
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One-dimensional mappings: Alloy investigations (2)
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Two-dimensional mappings: Compositional Axes (1)
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Two-dimensional mappings: Compositional Axes (2)
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Two-dimensional mappings: Compositional Axes (3)
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One-dimensional mappings: Alloy investigations (1)
Alloy 625 : Ni 68.1, Cr 19, Mo 8.9, Fe 2.8, Si 1.8
GTT-Technologies
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One-dimensional mappings: Alloy investigations (2)
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One-dimensional mappings: Alloy investigations (3)
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Two-dimensional mappings: Potential diagram (1)
GTT-Technologies
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Two-dimensional mappings: Potential diagram (2)
GTT-Technologies
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Two-dimensional mappings: Potential diagram (2)
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The Partners in the European Project OptiCorr
VTT Chemical Technologies, Espoo, Finland
Joint European Research Center, Petten, Netherlands
Max-Planck-Institut fuer Eisenforschung, Düsseldorf,
Germany
Helsinki University of Technology, Helsinki, Finland
Siegen Technical University, Siegen, Germany
GTT-Technologies, Herzogenrath, Germany
Rautaruukki Oyj, Raahe, Finland
GTT-Technologies
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Two-dimensional mappings: Potential diagram (2)
Fe - Cr - Cl2
mole Cr/(Fe+Cr) = .0325, gas formation not considered
1000
LIQUID-Salt + FCC_A1
FCC_A1
BCC_A2 + FCC_A1
860
LIQUID-Salt
BCC_A2 + LIQUID-Salt
T(C)
720
LIQUID-Salt + FeCl2
BCC_A2
580
BCC_A2 + CrCl2
440
FeCl2 + Cl2Cr
CrCl3 + FeCl2
LIQUID-Salt + CrCl3
300
-30
-24
-18
-12
-6
0
log10(p(Cl2)) (atm)
GTT-Technologies
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Two-dimensional mappings: Potential diagram (4)
GTT-Technologies
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