1 Metal Dusting Corrosion in SMR plants
Metal Dusting Corrosion in Steam Reforming PlantsJ. Bohle, Dr. C. Beyer, U. Wolf, Dr. D Ulber
Steam Reforming Technology User Conference
Labuan, Malaysia
March 5-7, 2007
2 Metal Dusting Corrosion in SMR plants
Metal Dusting Corrosion (MDC)Metal Dusting Corrosion (MDC)
Disintegration of metals and alloys into a dust of graphite and metal particles after carbon ingress and over-saturation.
3 Metal Dusting Corrosion in SMR plants
OverviewOverview
Phenomena of Metal Dusting Corrosion (MDC)
Mechanism involved / Reactions
Material considerations
Examples of MDC in Steam Reforming Plants
Prevention of MDC
Influence of MDC on process design
Literature
4 Metal Dusting Corrosion in SMR plants
Steps in Metal Dusting CorrosionSteps in Metal Dusting Corrosion
Diffusion of reducing / carburizing gas through oxide protection layers to metal surface
Formation & supersaturation of carbides
Dissociation into metal particles and graphite
Diffusion of catalytically active metal particles
Loss of carbon, metal, metal carbide, metal oxide
5 Metal Dusting Corrosion in SMR plants
Phenomena involved in MDCPhenomena involved in MDC
Gas-phase and gas-metal reactions (T, p, composition fi)
Diffusion of reducing gas, carbon and metals (T, fi)
Flow and temperature distribution (vel, T) – equipment design
Catalytically active components in gas and metal
Thermodynamic & mechanical stability of protective layers
Stresses / fractures imposed on surfaces by gradients
Metal crystallographic structure
Sulfidic components in gas
6 Metal Dusting Corrosion in SMR plants
ReactionsReactions
Carburization reactions
CO + H2 <-> C + H2O aC =K1*pCO*(pH2/pH2O)
2 CO <-> C + CO2 aC =K2*(p2CO/pCO2)
CH4 <-> C + 2 H2 aC =K3*(pCH4/p2H2)
Gas-phase reactions
H2O + CO <-> CO2 + H2
H2O + CH4 <-> CO + 3 H2
aC carbon activity
Ki equilibrium constant
Pi partial pressure
7 Metal Dusting Corrosion in SMR plants
Potential for Metal Dusting CorrosionPotential for Metal Dusting Corrosion
8 Metal Dusting Corrosion in SMR plants
Temperature rangePromoting componentsTemperature rangePromoting components
450°C < MDC temp. range < 800°C / Boudouard temp.
At [Fe/Ni] > ~ 2/3 mass-frac, metal dusting is retarded at the lower regimes of the metal dusting temp. range
MDC promoting gas components (negative impact on metal oxide protection layer)
9 Metal Dusting Corrosion in SMR plants
Material ConsiderationsMaterial Considerations
Surface oxide stability is enhanced by alloying elements such as Cr, Al, Si, Ti, Mo providing a barrier to carbon diffusion
Carbon and alloying elements diffusion is influenced by crystallographic structure and surface condition (e.g. grain size)
Surface coatings or surface finish (grinding) can provide added stability by influencing the carbon diffusion and/or physical resistance to mechanical and thermal effects
10 Metal Dusting Corrosion in SMR plants
Material ConsiderationsMaterial Considerations
Fe-based and Ni-based metals show different behaviour
Empirical equation of alloying material resistance to MDC (Parks & Schillmoller)
Crequiv. = Cr % + 3 x (Si % + Al %)
Inclusion of the effects of other alloying elements such as Ti, Mo, Ni outstanding
Preferred material Nicrofer® 6025 HT – alloy 602 CA
No alloy is MDC resistant under all conditions
11 Metal Dusting Corrosion in SMR plants
Where can Metal Dusting Corrosion occur?Where can Metal Dusting Corrosion occur?
Reducer Sockets
Transfer Line at Reformer Outlet
Process Gas Boiler (PGB) Inlet chamber
PGB tube inlet section (ferrules) and tube sheet
PGB bypass tube, bypass flow control device
PGB outlet chamber
Heat Exchanger d/s of PGB, e.g. Feed Preheater
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SMR Outlet System – Reducer SocketsSMR Outlet System – Reducer Sockets
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Manifold, Transfer LineGas BarriersManifold, Transfer LineGas Barriers
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Process Gas Boiler„Cold“ Bypass DesignProcess Gas Boiler„Cold“ Bypass Design
15 Metal Dusting Corrosion in SMR plants
Process Gas BoilerFlow and temperature distributionProcess Gas BoilerFlow and temperature distribution
16 Metal Dusting Corrosion in SMR plants
Process Gas Boiler Flow and temperature distributionProcess Gas Boiler Flow and temperature distribution
Temperature distribution in outlet chamber mixing zone of a process gas boiler
below 450°C
450 – 1000°C
Gastemperatures:
Bypass open
Bypass closed
17 Metal Dusting Corrosion in SMR plants
Inserts in PGB tubes for temp. controlInserts in PGB tubes for temp. control
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
0 2000 4000 6000 8000 10000
Distance from Inlet (mm)
Tem
pe
ratu
re (
°C)
Feedgas
Wall medium
Steam Cooling
300
310
320
330
340
350
360
370
380
390
400
0 2000 4000 6000 8000 10000
Distance from Inlet (mm)
Tem
pe
ratu
re
(°C
)
Wall inside
Wand outside
Steam Cooling
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Measures against MDC Pro & ConsMeasures against MDC Pro & Cons
Avoid metal wall temperatures in MDC temperature range
Use of non-metallic materials in critical areas
Change gas atmosphere– Introduction of process gas (for purge) in critical areas– Catalytically activated refractory (Lurgi Patent)
Material science, Protection layers
Sulfidic compounds in gas
Design for easy maintenance / replacement
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Influence of MDC on process designInfluence of MDC on process design
Process efficiency / consumption figures
Steam to Carbon Ratio
Steam Superheater for Process Gas Cooling
Export Steam Value
Gas-heated Steam Reformer design
20 Metal Dusting Corrosion in SMR plants
Literature ReferencesLiterature References
R.T. Jones, K.L. Baumert; Metal Dusting – An Overview of Current Literature; Corrosion 2001; No. 01372
H.J. Grabke, E.M. Müller-Lorenz; Occurrence and Prevention of Metal Dusting on Stainless Steel; Corrosion 2001; No. 01373
F. Hohmann; Improve Steam Reformer Performance; Hydrocarbon Processing; 03/1996; p. 71-74
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