1. K.Hack, GTT-Technologies ExMente Workshop, 21st and 22nd July 2008
Summary of the Project OptiCorr Modelling of Hot Corrosion of Heat Exchanger Components
K.Hack, GTT-Technologies ExMente Workshop, 21st and 22nd July 2008

2. Fotographs: Courtesy VTT - Technology
Motivation
Precipitate formation in a superheater of a bio-mass incinerator
Fotographs: Courtesy VTT - Technology

3. A very complex overall process

4. - Overview of the Thermochemical Modelling including Database Work
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

5. Phases and Components in the System
Gas Phase
Ash deposit
Metal
HCl, SO2
O2, H2O
Volatile
compounds:
ZnCl2, PbCl2
KCl, NaCl
Sulfates resp.
KOH, NaOH
etc.
Fe, Ni, Cr, C
Mo, Si, Al
Precipitates
Carbides
MC, M23C6
M7C3
Nitrides
TiN
etc.
Solid state
Liquid state
Silicates
Sulfates, Chlorides
(Ca, K, Na, Pb, Zn)
Others (oxides...)

6. Available tools (1): FactSage
Stoichiometric reactions
Complex equilibria
Phase diagrams
Data assessment

7. Available tools (2): InCorr and SaltCorr/CorrApp
Calls ChemApp
after each
diffusion step.
metal diffusion
(Cr, Fe, Ni...)
oxygen diffusion

8. ChemSheet Available tools (3): ChemSheet The principle method
Thermodynamic Data
ChemApp
Excel Worksheet
ChemSheet
An example
application

9. 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

10. 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

11. 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 !)

12. 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

13. Contents 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

14. Assessment work: One Compositional Axis

15. Assessment work: Two Compositional Axes

16. 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

17. One-dimensional mappings: Speciation in gases (1)
Ar(g)
H2O(g)
O2(g)

18. One-dimensional mappings: Speciation in gases (2)
SO3
SO2
H2SO4

19. Two-dimensional mappings: Two Compositional Axes (2)

20. Two-dimensional mappings: Two Compositional Axes (3)
Note the constant
potentials :
T and P(Cl2).

21. Two-dimensional mappings: Potential diagram (1)

22. Two-dimensional mappings: Potential diagram (3)

23. The Salt Corrosion Model

24. Model picture One-dimensional diffusion (across the salt melt)Fe
Fe + Cl2(l) = FeCl2(l)
2FeCl2(l) + 1.5O2(g) = Fe2O3(s) + 2Cl2(g)
Cl2(g) = Cl2(l)
Ar(g) - O2(g)
KCl(l) - ZnCl2(l)
Gas
Melt
Metal
K+ - Zn2+ - Cl-
One-dimensional diffusion (across the salt melt)
is coupled with the local equilibrium concept.

25. Results of the Simulation, I
Incubation period
(after 5 min)

26. Results of the Simulation, II
Fe-Oxide
Solidified Saltmelt Fe
Oxide formation
near surface
(after 10 min)

27. The Gas Corrosion Model

28. Low Chromium Steels sulfidation corrosion oxidation outer scale
SO2 and / or O2
sulfidation
corrosion
oxidation
outer scale
original surface
inner scale
sulphides and/or
oxides

29. Model picture Two-dimensional diffusion is coupled with
the local equilibrium concept.

30. Fe3O4 grain boundaries FeCr2O4 Results of the simulation, I
y [m]
x [m]
Fe3O4 [at.%]
FeCr2O4 [at.%]
grain boundaries
Fe3O4
FeCr2O4

31. Cr in Fe-BCC Cr2O3 Results of the simulation, II Cr in Fe-BCC (at.%)
y [m]
x [m]
Cr in Fe-BCC (at.%)
Cr2O3 (at.%)
Cr in Fe-BCC
Cr2O3

32. Mean Thickness of the Oxide Scale

33. The Gas Precipitation Model

34. Model Picture Heat exchanger 1, T1 Flue Gas with Aerosols, T0 .
sticking effects
Flue Gas with Aerosols, T0 .
Combustion chamber
Heat exchanger n, Tn
sticking effects

35. 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
Input box for sticking coefficient

36. Summary of the Gas Precipitation Model: Results

37. Summary of the Gas Precipitation Model: Results

38. Summary of the Gas Precipitation Model: Results

39. 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

40. THANK YOU for your attention !

42. 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

43. 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, Fe-
Ce 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-,CrO42- system
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),
other sulphides are treated as stoichiometric

44. 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

45. Classification of subsystems:
2 The Salt Subsystem
Components:
KCl-ZnCl2-FeCl2-MnCl2-FeCl3-K2SO4-ZnSO4-FeSO4-MnSO4-Fe2(SO4)3-K2CrO4-ZnCrO4-MnCrO4-FeCrO4-Fe2(CrO4)3 plus
NaCl-PbCl2-Na2SO4-PbSO4-Na2CrO4-PbCrO4
Phases:
Liquid with all components
Solid solutions, e.g. K2SO4-K2CrO4, NaCl-KCl
Stoichiometric solids (Possibly add OH !)

46. 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

47. 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

48. One-dimensional mappings: Speciation in gases (1)

49. One-dimensional mappings: Speciation in gases (1)

50. One-dimensional mappings: Speciation in gases (2)

51. One-dimensional mappings: Speciation in gases (2)

52. One-dimensional mappings: Speciation in gases (3)

53. One-dimensional mappings: Speciation in gases (3)

54. 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 .003

55. One-dimensional mappings: Alloy investigations (2)

56. One-dimensional mappings: Alloy investigations (2)

57. One-dimensional mappings: Alloy investigations (2)

58. One-dimensional mappings: Alloy investigations (2)

59. Two-dimensional mappings: Compositional Axes (1)

60. Two-dimensional mappings: Compositional Axes (2)

61. Two-dimensional mappings: Compositional Axes (3)

62. One-dimensional mappings: Alloy investigations (1)
Alloy 625 : Ni 68.1, Cr 19, Mo 8.9, Fe 2.8, Si 1.8

63. One-dimensional mappings: Alloy investigations (2)

64. One-dimensional mappings: Alloy investigations (3)

65. Two-dimensional mappings: Potential diagram (1)

66. Two-dimensional mappings: Potential diagram (2)

67. Two-dimensional mappings: Potential diagram (2)

68. 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

69. Two-dimensional mappings: Potential diagram (2)

70. Two-dimensional mappings: Potential diagram (4)