Peter D. Clark
Director of Research, Alberta Sulphur Research Ltd. and Professor Emeritus of Chemistry, University of Calgary
and
N. I. Dowling
Senior Research Scientist, Alberta Sulphur Research Ltd. Contact: [email protected]
Corrosion Due to Elemental Sulfur in Sour Gas Production and Claus Sulfur Recovery Systems
MESPON 2016 Abu Dhabi, United Arab Emirates, October 9 – 11, 2016
Wet Sulfur Contact Corrosion of Carbon Steel
The Safety Moment: Iron Sulfide and Fire
Fe + S8 FeS H2O
FeS
O2 (Air)
Fe2O3 + SO2 + Energy (∆H = -1,226 kJ)
The Fe2O3 becomes red hot igniting any flammable material (sulfur)
Result: Fires inside the Claus plant (catalyst beds), sulfur pits, tanks, sulfur forming plants and more
Electrochemical Mechanism of Sulfur Corrosion
steel sulfur iron sulfide ‘mackinawite’
S-deficient FeS(1-x) “non-stoichiometric” FeS is pyrophoric when
dry and finely divided
steel sulfur iron sulfide ‘mackinawite’
Mechanistic Overview of Steel / Sulphur Corrosion
non-stoichiometric e- conducting FeS
layer
2e-
Effect of Moisture and Steel / Sulfur Contact
- Contact and moisture are essential for corrosion -
(free-standing H2O) (2-3 wt% moisture)
Effect of Temperature on The Rate of Wet Sulfur Contact Corrosion
> 20oC most of the time
PANAMA CANAL TRANS-ATLANTIC
TRANS-PACIFIC
Partial Oxidation of FeS and Formation of Sulfuric Acid
FeS + O2 (Air) Fe2 (SO4)3 Fe2 (SO4)3 + H2O 2 Fe3+ [6 H2O] + 3 SO4
2- [6 H2O]
Partial oxidation
Solvolysis
Fe3+ (H2O)6 Fe2+ (H2O)5 OH + [H+]
• Iron sulfate forms acidic solutions (pH ≈ 1-2) which corrode steel
S8 Deposition within a Sour Gas Flow Line+
Two Examples of Sulfur Deposition in Sour Gas Production Facilities
S8 Deposition in a Gas Plant Inlet Separator*
+ Photograph courtesy of John Morgan, John M. Campbell & Company * Photograph courtesy of Mark Townsend, Burlington Resources
Sulfur Deposition Arising from Oxidation of ppm Level H2S
Sources: 1. Chesnoy, A.-B., and Pack, D.J., S8 Threatens Natural Gas Operations, Environment, OGJ, V.95, No.17, pp.74-79, Apr. 28, 1997. 2. Courtesy of PG&E, Technological and Ecological Services (TES), San Ramon, California
Natural Gas Distribution Regulator Cage 2 200-mm ANSI 600 Turbine Meter 1
Magnified Image of Elemental Sulfur on Restrictor Valve
Surface 2
Elemental sulfur confirmed by SEM/EDX analysis
In Situ Formation of Sulfur in Sour Gas Equipment
FeS Protective Coating
H2S S8
O2 (Air) (ppmv)
High P Sour Gas
CH4 / H2S / CO2 (S8 / H2O)
2 Fe2+ (S) + ½ O2 2 Fe3+ + O2-
2 Fe3+ + H2S 2 Fe2+ + 2 H+ + 1/8 S8 2 H+ + O2- H2O
• The protective FeS coating becomes a catalytic layer
• The reaction is fast at high P; the amount of sulfur (H2O) formed depends on amount of O2 ingress
Sulfur Formation and Corrosion in Amine Plants
Steam Condensate
• Sulfur is formed at FeS layer in the contactor and then transported around the amine loop • Degradation occurs in the regenerator; ionic species enhance corrosion
~130°C
CH4 H2S – CO2
~40°C FeS
CH4/H2S- CO2
O2 (ppmv)
R3 NH HS / HSx
+
- -
Contactor: H2S + ½ O2 H2O + 1/8 S8 R3 NH HSX
Regenerator: R3 NH HSX R CO2 H + HS2O3 / HSO4 + - pH >10 - -
Amine R3N, H2S
-
+
“Combustion” of Steel with Sulfur in the Claus Furnace
S8
Process gas
Acid gas
Air
Ceramic brick
• O2 is very rapidly consumed by H2S in the flame
• Steel is oxidized by sulfur forming a mixture of FeS and FeS2
Fe + S2 FeS2 H2S H2 + ½ S2 Fe + H2S H2 + FeS FeS2
½ S2
Brick failure
The Chemical Function of the WHB Ferrule
Ceramic ferrule
H2O T < 400°C
Steam
T < 400°C H2S, S8, H2
H2O, N2
Furnace gases
(T > 1,000°C)
• The alumina ferrule is chemically inert to all species
• Steel (Fe) is relatively inert to sulfur and other species < 400°C.
S8
S8
Steam
H2O Hot Purge (CH4 combustion)
The Importance of Purging Sulfur From a Claus Unit During Shutdowns
• Ceramic brick and catalyst retains sulfur after unit shut down
• Conditions must be maintained to prevent condensation of sulfur in places other than the condensers
Corrosion in Off-Gas Line Below Water Dew Point
• Inadequate heating at line support allows water condensation
• Rapid Fe/S corrosion: Fe + 1/8 S8 FeS
• Aqua Claus reaction: 2 H2S + SO2 [H2SxOy] 3/8 S8 + 2 H2O
• Highly acidic aqueous solution is formed
H2O(l)
H2O(l)
Tail Gas Insulation
TGU Incinerator
Line Support (“heat” sink) S8 + H2O(l)
FeS Corrosion Products
Field Pictures of Corroded Claus Tail Gas Line
Pictures provided to ASRL by:
Mechanisms for Deterioration of Concrete in Sulfur Pits
Liquid S8 130ºC
Concrete
• Migration of H2S, SO2, O2, H2O and S (vap) into internal pore structure of the concrete followed by chemical reactions.
H2S + S8 H2Sx Solid/ liquid S8
T ºC = 90→130
AIR
Liq S8
H2S S8 SO2
O2 O2 N2
(H2O)
Formation of Sulfur Inside the Concrete
Detailed Chemistry
H2S + O2 SO2 + H2O 1/8 S8(vap) + ½ O2 SO2 2 H2S + SO2 3/8 S8 + H2O “CaO” CaSO4, CaS2O3
Lower density, higher volume unconsolidated products.
Concrete pore
structure
“H2 SO4” “H2 S2O3”
Concrete
Claus chemistry intermediates [strong acids]
Secondary Corrosion Processes at Concrete Pit Reinforcing Steel
Fe
Fe CaO
CaO
Fe2 (SO4)3 Fe2O3, H2SO4
Fe H2O,
S8
Fe FeS
O2, H2O
Secondary Corrosion Enhanced Sulfur Formation at Steel Fe + H2SO4 FeSO4 + H2 CaO + H2SO4 CaSO4 + H2O
2 H2S + SO2 3/8 S8 + 2 H2O H2S + ½ O2 1/8 S8 + H2O
Fe2O3
Fe2O3
Primary Corrosion in Sulfur Tanks – Air Drafted Systems
Air / SO2 / S8(vap) To scrubbers Air (H2O)
Insulation
• Poor roof insulation (or poor heating) may result in inner roof temperature of < 100°C • S8 solid deposition and water / H2SXOY condensation (from SO2 / H2O) • Fe / S8 corrosion Fe + 1/8 S8 FeS • Acid corrosion
2 Fe + H2SXOY 2 Fe SXOY + H2
Steam coil
Steam ~ 140°C
Liquid S8 SO2
SO2
N2
S8(vap) O2
H2O or H2SXOY
Consequences
Secondary Corrosion on Sulfur Tank Roofs – Air Drafted Tanks
Air (H2O) < 100°C
Insulation
T = 140°C
S8(liq)
SO2
SO2
N2
O2
Air / SO2 / S8(vap) To scrubbers
O2
[H2O]
FeS corrosion layer
Oxidation of FeS 2 FeS + 3/2 O2 Fe2O3 + 2/8 S8 2 FeS + SO2 2 FeO + 3/8 S8 Continued Sulfur Corrosion Fe + 1/8 S8 FeS (H2O)
• Without roof heating, T may fall to < 100°C, allowing H2O or H2SXOY condensation. • Partial oxidation of FeS may reform S8 at surface. • Corrosion at “cool” roof surface may result from condensed acids (H2SXOY), sulfur deposited or formed by chemical reaction.
Air
Steam coil Steam
~ 140°C S8(liq)
Rupture of Steam Coils in Sulfur Tanks
Air / SO2 (H2S)
(H2S)
Condensate / Steam
• Mechanical erosion of FeS layer leads to thinning of carbon steel coils and eventual rupture
Steam Coil Corrosion
Fe + H2S FeS + H2
S8 (H2S) FeS
Fe
Mechanical erosion
Fe "Clean surface"
H2S (S8(liq))
Fe
New FeS
S8(l) inlet
FeS
Shipping Sulfur By Rail
S8 S8
Steel Box Aluminum Box [Don’t do it!]
• Polymer coating to prevent iron-sulfur corrosion
OR
• Keep sulfur dry by adding a cover or roof
• Aluminum will melt if S8 catches fire
• Al/S8 react explosively at T of burning sulfur to form Al2S3
• Al2S3 reacts with water producing H2S Al2S3 + 3 H2O Al2O3 + 3 H2S
Aluminium (mp=660°C)
Thiobacilli H2SO4
S8 S8
H2SO4
H2O H2O
Corrosion: FeS / Sulfur layer may become H2S saturated > 1000 ppmv.
FeS + H2SO4 FeSO4 + H2S
denser than air — remains in the bottom of the hold.
Corrosion and Acidity Generation in a Ship Hold - a Potentially Deadly Combination -
Sulfur Loading to Limewashed Hold
Development of Zinc-modified Limewash
Chemistry:
Advantage:
• SUCCESSFULLY FIELD TESTED IN SHIP TRIAL
COMBINE LIMEWASH AND Zn2+
Improved barrier plus additional benefit from release of Zn2+ in event of acidity build-up
Mitigation of Corrosion by Zn2+: Fe + 1/8 S8 FeS Zn (OH)2 + FeS ZnS + Fe (OH)2
• ZnS is a perfect insulator stopping e-transfer at iron surface
Effect of Soluble Zn2+ on Wet Sulfur Corrosion
solution phase addition of Zn2+
soluble Zn2+ inhibits S corrosion at concentrations even as low as 1 x 10-2 M
Inhibition works by in-situ formation of insoluble ZnS barrier at steel / S contact area
Zn2+ + S2- ZnS ( stoichiometric )
ASRL Member Companies 2016 - 2017
Aecom Technology Corporation Air Liquide Global E&C Solutions / Lurgi Ametek Process & Analytical Instruments/Controls Southeast AXENS BASF Catalysts LLC Bechtel Corporation Black & Veatch Corporation BP Brimstone STS Ltd. Canadian Energy Services/PureChem Services ConocoPhillips Company CB&I Chevron Energy Technology Company Denbury Resources Inc. Devco Duiker CE E.I. du Pont Canada Company / MECS Inc. Enersul Inc. Euro Support BV ExxonMobil Upstream Research Company Flint Hills Resources Fluor Corporation / GAA HEC Technologies Hexion Inc. Husky Energy Inc. Industrial Ceramics Limited IPAC Chemicals Limited
Jacobs Canada lnc. / Jacobs Nederland B.V. KT – Kinetics Technology S.p.A. Linde Gas and Engineering (BOC) Lubrizol Canada Ltd. Nova Chemicals OMV Exploration and Production GmbH Optimized Gas Treating, Inc. Ortloff Engineers, Ltd. Oxbow Sulphur Canada ULC. (former ICEC) Petro China Southwest Oil and Gas Field Company/RINGT Phillips 66 Company Porocel Industries, LLC Porter McGuffie, Inc. Prosernat Riverland Industries Ltd. Secure Energy Services Shell Canada Energy SiiRTEC Nigi S.p.A. Sulfur Recovery Engineering (SRE) Sulphur Experts Inc. TECHNIP The Petroleum Institute / Abu Dhabi National Oil Company (ADNOC) Total S.A. UniverSUL Consulting WorleyParsons