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

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

A very complex overall process

- 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

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...)

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

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

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

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

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

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 !)

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

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

Assessment work: One Compositional Axis

Assessment work: Two Compositional Axes

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

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

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

Two-dimensional mappings: Two Compositional Axes (2)

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

Two-dimensional mappings: Potential diagram (1)

Two-dimensional mappings: Potential diagram (3)

The Salt Corrosion Model

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.

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

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

The Gas Corrosion Model

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

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

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

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

Mean Thickness of the Oxide Scale

The Gas Precipitation Model

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

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

Summary of the Gas Precipitation Model: Results

Summary of the Gas Precipitation Model: Results

Summary of the Gas Precipitation Model: Results

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

THANK YOU for your attention !

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

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

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

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 !)

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

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

One-dimensional mappings: Speciation in gases (1)

One-dimensional mappings: Speciation in gases (1)

One-dimensional mappings: Speciation in gases (2)

One-dimensional mappings: Speciation in gases (2)

One-dimensional mappings: Speciation in gases (3)

One-dimensional mappings: Speciation in gases (3)

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

One-dimensional mappings: Alloy investigations (2)

One-dimensional mappings: Alloy investigations (2)

One-dimensional mappings: Alloy investigations (2)

One-dimensional mappings: Alloy investigations (2)

Two-dimensional mappings: Compositional Axes (1)

Two-dimensional mappings: Compositional Axes (2)

Two-dimensional mappings: Compositional Axes (3)

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

One-dimensional mappings: Alloy investigations (2)

One-dimensional mappings: Alloy investigations (3)

Two-dimensional mappings: Potential diagram (1)

Two-dimensional mappings: Potential diagram (2)

Two-dimensional mappings: Potential diagram (2)

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

Two-dimensional mappings: Potential diagram (2)

Two-dimensional mappings: Potential diagram (4)