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Corrosion Due to Elemental Sulfur in Sour Gas Production and Claus Sulfur Recovery Systems 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] 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 H2O FeS 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 steel sulfur sulfur FeS is pyrophoric when dry and finely divided iron sulfide ‘mackinawite’ iron sulfide ‘mackinawite’ S-deficient FeS(1-x) “non-stoichiometric” Mechanistic Overview of Steel / Sulphur Corrosion 2e- non-stoichiometric e- conducting FeS layer Effect of Moisture and Steel / Sulfur Contact (free-standing H2O) (2-3 wt% moisture) - Contact and moisture are essential for corrosion - 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 + H2O Partial oxidation Fe2 (SO4)3 2 Fe3+ [6 H2O] + 3 SO42- [6 H2O] Solvolysis Fe3+ (H2O)6 • Fe2+ (H2O)5 OH + [H+] Iron sulfate forms acidic solutions (pH ≈ 1-2) which corrode steel Two Examples of Sulfur Deposition in Sour Gas Production Facilities S8 Deposition within a Sour Gas Flow Line+ + Photograph courtesy of John Morgan, John M. Campbell & Company S8 Deposition in a Gas Plant Inlet Separator* * Photograph courtesy of Mark Townsend, Burlington Resources Sulfur Deposition Arising from Oxidation of ppm Level H2S 200-mm ANSI 600 Turbine Meter 1 Natural Gas Distribution Regulator Cage 2 Magnified Image of Elemental Sulfur on Restrictor Valve Surface 2 Elemental sulfur confirmed by SEM/EDX analysis 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 In Situ Formation of Sulfur in Sour Gas Equipment O2 (Air) (ppmv) FeS Protective Coating High P Sour Gas H2S CH4 / H2S / CO2 (S8 / H2O) S8 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 CH4 H2S – CO2 FeS ~40°C ~130°C Steam Condensate R3 NH HS / HSx + CH4/H2SCO2 O2 (ppmv) Contactor: H2S + ½ O2 + - Regenerator: R3 NH HSX • • H2O + pH >10 1/ 8 Amine S8 R3N, H2S - + - R3 NH HSX - R CO2 H + HS2O3 / HSO4 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 “Combustion” of Steel with Sulfur in the Claus Furnace Ceramic brick Air Acid gas Process gas Brick failure Fe + S2 FeS2 H2S H2 + ½ S2 Fe + H2S H2 + FeS S8 ½ S2 FeS2 • O2 is very rapidly consumed by H2S in the flame • Steel is oxidized by sulfur forming a mixture of FeS and FeS2 The Chemical Function of the WHB Ferrule T < 400°C H2O Furnace gases (T > 1,000°C) Steam T < 400°C H2S, S8, H2 H2O, N2 Ceramic ferrule • The alumina ferrule is chemically inert to all species • Steel (Fe) is relatively inert to sulfur and other species < 400°C. The Importance of Purging Sulfur From a Claus Unit During Shutdowns Steam Hot Purge (CH4 combustion) H2O S8 S8 • 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 Tail Gas Insulation TGU Incinerator Line Support (“heat” sink) S8 + H2O(l) FeS Corrosion Products • Inadequate heating at line support allows water condensation • Rapid Fe/S corrosion: Fe + 1/8 S8 H2O(l) H2O(l) • Aqua Claus reaction: 2 H2S + SO2 • Highly acidic aqueous solution is formed FeS [H2SxOy] 3/ 8 S8 + 2 H2O Field Pictures of Corroded Claus Tail Gas Line Pictures provided to ASRL by: Mechanisms for Deterioration of Concrete in Sulfur Pits AIR Concrete O2 N2 H2S Solid/ liquid S8 T ºC = 90→130 • H2S + S8 O2 (H2O) H2Sx SO2 S8 Liq S8 Liquid S8 130ºC Migration of H2S, SO2, O2, H2O and S (vap) into internal pore structure of the concrete followed by chemical reactions. Formation of Sulfur Inside the Concrete Detailed Chemistry Concrete pore H2S + 1/ 8 O2 structure S8(vap) + ½ O2 SO2 3/ S 8 8 2 H2S + SO2 “H2 SO4” “H2 S2O3” “CaO” Concrete SO2 + H2O + H2O Claus chemistry intermediates [strong acids] CaSO4, CaS2O3 Lower density, higher volume unconsolidated products. Secondary Corrosion Processes at Concrete Pit Reinforcing Steel Fe H2O, Fe S8 O2, H2O Fe CaO Fe2 (SO4)3 Fe2O3, H2SO4 FeS Fe Secondary Corrosion CaO Enhanced Sulfur Formation at Steel Fe + H2SO4 FeSO4 + H2 2 H2S + SO2 CaO + H2SO4 CaSO4 + H2O H2S + ½ O2 Fe2O3 Fe2O3 3/ 8 S8 + 2 H2O 1/ S 8 8 + H2O Primary Corrosion in Sulfur Tanks – Air Drafted Systems N2 Insulation S8(vap) SO2 • Poor roof insulation (or poor heating) may result in inner roof temperature of < 100°C Consequences O2 • S8 solid deposition and water / H2SXOY condensation (from SO2 / H2O) • Fe / S8 corrosion Liquid S8 SO2 Steam To scrubbers Air / SO2 / S8(vap) Air (H2O) ~ 140°C Fe + 1/8 S8 Steam coil • H2O or H2SXOY FeS Acid corrosion 2 Fe + H2SXOY 2 Fe SXOY + H2 Secondary Corrosion on Sulfur Tank Roofs – Air Drafted Tanks Air (H2O) < 100°C Air / SO2 / S8(vap) To scrubbers FeS corrosion layer Oxidation of FeS N2 Insulation O2 SO2 [H2O] S8(liq) O2 SO2 T = 140°C 2 FeS + 3/2 O2 Fe2O3 + 2/8 S8 2 FeO + 3/8 S8 2 FeS + SO2 Continued Sulfur Corrosion Fe + 1/8 S8 (H2O) FeS • 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. Rupture of Steam Coils in Sulfur Tanks Air Air / SO2 (H2S) Steam Coil Corrosion Fe + H2S FeS + H2 S8 (H2S) FeS S8(l) inlet Fe FeS ~ 140°C S8(liq) (H2S) Mechanical erosion "Clean surface" Fe Steam H2S (S8(liq)) New FeS Steam coil Condensate / Steam Fe • Mechanical erosion of FeS layer leads to thinning of carbon steel coils and eventual rupture Shipping Sulfur By Rail Steel Box S8 • Polymer coating to prevent iron-sulfur corrosion OR • Keep sulfur dry by adding a cover or roof Aluminum Box [Don’t do it!] S8 Aluminium (mp=660°C) • 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 Corrosion and Acidity Generation in a Ship Hold - a Potentially Deadly Combination - H2SO4 Thiobacilli S8 H2SO4 S 8 H 2O Corrosion: H 2O FeS / Sulfur layer may become H2S FeS + H2SO4 saturated > 1000 ppmv. FeSO4 + H2S denser than air — remains in the bottom of the hold. Sulfur Loading to Limewashed Hold Development of Zinc-modified Limewash COMBINE LIMEWASH AND Zn2+ Chemistry: Improved barrier plus additional benefit from release of Zn2+ in event of acidity build-up Advantage: • SUCCESSFULLY FIELD TESTED IN SHIP TRIAL Mitigation of Corrosion by Zn2+: Fe + 1/8 S8 Zn (OH)2 + FeS 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