Corrosion Due to Elemental Sulfur in Sour Gas Production and Claus - PowerPoint PPT Presentation

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: pdclark@ucalgary.ca 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 H 2 O Fe + S 8 FeS FeS O 2 (Air) Fe 2 O 3 + SO 2 + Energy (∆H = -1,226 kJ) The Fe 2 O 3 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 iron sulfide sulfur steel ‘mackinawite’ iron sulfide sulfur steel ‘mackinawite’ S-deficient FeS (1-x) FeS is pyrophoric when “non-stoichiometric” dry and finely divided

Mechanistic Overview of Steel / Sulphur Corrosion 2e - non-stoichiometric e - conducting FeS layer

Effect of Moisture and Steel / Sulfur Contact (free-standing H 2 O) (2-3 wt% moisture) - Contact and moisture are essential for corrosion -

Effect of Temperature on The Rate of Wet Sulfur Contact Corrosion PANAMA CANAL > 20 o C most TRANS-ATLANTIC of the time TRANS-PACIFIC

Partial Oxidation of FeS and Formation of Sulfuric Acid Partial FeS + O 2 (Air) Fe 2 (SO 4 ) 3 oxidation Fe 2 (SO 4 ) 3 + H 2 O 2 Fe 3+ [6 H 2 O] + 3 SO 4 2- [6 H 2 O] Solvolysis Fe 3+ (H 2 O) 6 Fe 2+ (H 2 O) 5 OH + [H + ] Iron sulfate forms acidic solutions (pH ≈ 1 -2) which corrode steel •

Two Examples of Sulfur Deposition in Sour Gas Production Facilities S 8 Deposition within a Sour Gas Flow Line + S 8 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 H 2 S 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 O 2 (Air) (ppmv) FeS Protective Coating CH 4 / H 2 S / CO 2 High P H 2 S S 8 (S 8 / H 2 O) Sour Gas 2 Fe 2+ (S) + ½ O 2 2 Fe 3+ + O 2- 2 Fe 3+ + H 2 S 2 Fe 2+ + 2 H + + 1 / 8 S 8 2 H + + O 2- H 2 O • The protective FeS coating becomes a catalytic layer • The reaction is fast at high P; the amount of sulfur (H 2 O) formed depends on amount of O 2 ingress

Sulfur Formation and Corrosion in Amine Plants CH 4 H 2 S – CO 2 FeS ~40°C ~130°C Steam Condensate - - R 3 NH HS / HS x CH 4 /H 2 S- + CO 2 O 2 (ppmv) + - Amine Contactor: H 2 S + ½ O 2 H 2 O + 1 / 8 S 8 R 3 NH HS X R 3 N, H 2 S - + - - pH >10 Regenerator: R 3 NH HS X R CO 2 H + HS 2 O 3 / HSO 4 • 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 Process gas gas Brick failure Fe + S 2 FeS 2 S 8 H 2 S H 2 + ½ S 2 ½ S 2 Fe + H 2 S H 2 + FeS FeS 2 • O 2 is very rapidly consumed by H 2 S in the flame • Steel is oxidized by sulfur forming a mixture of FeS and FeS 2

The Chemical Function of the WHB Ferrule T < 400°C H 2 O Steam Furnace H 2 S, S 8 , H 2 gases T < 400°C H 2 O, N 2 (T > 1,000°C) 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 H 2 O (CH 4 combustion) S 8 S 8 • 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 Insulation Tail Gas TGU Incinerator Line Support (“heat” sink) S 8 + H 2 O (l) FeS Corrosion Products • Inadequate heating at line support allows water condensation H 2 O (l) Rapid Fe/S corrosion: Fe + 1 / 8 S 8 FeS • H 2 O (l) Aqua Claus reaction: 2 H 2 S + SO 2 [H 2 S x O y ] 3 / 8 S 8 + 2 H 2 O • • Highly acidic aqueous solution is formed

Field Pictures of Corroded Claus Tail Gas Line Pictures provided to ASRL by:

Mechanisms for Deterioration of Concrete in Sulfur Pits AIR Concrete O 2 N 2 O 2 H 2 S (H 2 O) SO 2 S 8 H 2 S + S 8 H 2 S x Liq S 8 Solid/ liquid S 8 Liquid S 8 T ºC = 130ºC 90→130 • Migration of H 2 S, SO 2 , O 2, H 2 O and S (vap) into internal pore structure of the concrete followed by chemical reactions.

Formation of Sulfur Inside the Concrete Detailed Chemistry Concrete pore H 2 S + O 2 SO 2 + H 2 O structure 1 / 8 S 8(vap) + ½ O 2 SO 2 2 H 2 S + SO 2 3 / 8 S 8 + H 2 O “H 2 SO 4 ” Claus chemistry intermediates “H 2 S 2 O 3 ” [strong acids] “CaO” CaSO 4 , CaS 2 O 3 Concrete Lower density, higher volume unconsolidated products.

Secondary Corrosion Processes at Concrete Pit Reinforcing Steel Fe CaO H 2 O, O 2 , H 2 O Fe 2 (SO 4 ) 3 Fe Fe Fe 2 O 3 , FeS S 8 H 2 SO 4 Fe CaO Secondary Corrosion Enhanced Sulfur Formation at Steel Fe 2 O 3 2 H 2 S + SO 2 3 / 8 S 8 + 2 H 2 O Fe + H 2 SO 4 FeSO 4 + H 2 Fe 2 O 3 H 2 S + ½ O 2 1 / 8 S 8 + H 2 O CaO + H 2 SO 4 CaSO 4 + H 2 O

Primary Corrosion in Sulfur Tanks – Air Drafted Systems To scrubbers Air / SO 2 / S 8(vap) Air (H 2 O) • Poor roof insulation (or poor heating) may result in inner roof temperature N 2 of < 100 ° C SO 2 Insulation S 8(vap) Consequences O 2 • S 8 solid deposition and water / H 2 S X O Y condensation (from SO 2 / H 2 O) SO 2 Liquid S 8 • Fe / S 8 corrosion ~ 140 ° C Steam H 2 O or Fe + 1 / 8 S 8 FeS H 2 S X O Y Steam coil • Acid corrosion 2 Fe + H 2 S X O Y 2 Fe S X O Y + H 2

Secondary Corrosion on Sulfur Tank Roofs – Air Drafted Tanks Air (H 2 O) < 100 ° C To scrubbers Air / SO 2 / S 8(vap) FeS corrosion layer Oxidation of FeS N 2 SO 2 Insulation 2 FeS + 3 / 2 O 2 Fe 2 O 3 + 2 / 8 S 8 [H 2 O] O 2 2 FeS + SO 2 2 FeO + 3 / 8 S 8 S 8(liq) Continued Sulfur Corrosion O 2 SO 2 (H 2 O) Fe + 1 / 8 S 8 FeS T = 140 ° C • Without roof heating, T may fall to < 100 ° C, allowing H 2 O or H 2 S X O Y condensation. • Partial oxidation of FeS may reform S 8 at surface. • Corrosion at “cool” roof surface may result from condensed acids (H 2 S X O Y ), sulfur deposited or formed by chemical reaction.

Rupture of Steam Coils in Sulfur Tanks Steam Coil Corrosion Air Air / SO 2 Fe + H 2 S FeS + H 2 (H 2 S) S 8 (H 2 S) FeS S 8(l) Fe inlet Mechanical FeS erosion ~ 140 ° C S 8(liq) (H 2 S) "Clean surface" Fe H 2 S (S 8(liq) ) New FeS Steam Condensate / Steam coil Steam Fe • Mechanical erosion of FeS layer leads to thinning of carbon steel coils and eventual rupture

Shipping Sulfur By Rail Steel Box Aluminum Box [Don’t do it!] Aluminium S 8 S 8 (mp=660°C) • Polymer coating to prevent • Aluminum will melt if S 8 iron-sulfur corrosion catches fire OR • Al/S 8 react explosively at T of burning sulfur to form • Keep sulfur dry by adding Al 2 S 3 a cover or roof • Al 2 S 3 reacts with water producing H 2 S Al 2 S 3 + 3 H 2 O Al 2 O 3 + 3 H 2 S

Corrosion and Acidity Generation in a Ship Hold - a Potentially Deadly Combination - H 2 SO 4 Thiobacilli H 2 SO 4 S 8 S 8 H 2 O H 2 O Corrosion: FeS / Sulfur layer may become H 2 S saturated > 1000 ppmv. FeS + H 2 SO 4 FeSO 4 + H 2 S denser than air — remains in the bottom of the hold.

Sulfur Loading to Limewashed Hold

Development of Zinc-modified Limewash COMBINE LIMEWASH AND Zn 2+ Chemistry: Improved barrier plus additional benefit from release of Zn 2+ in event of acidity build-up Advantage : • SUCCESSFULLY FIELD TESTED IN SHIP TRIAL Mitigation of Corrosion by Zn 2+ : Fe + 1 / 8 S 8 FeS Zn (OH) 2 + FeS ZnS + Fe (OH) 2 • ZnS is a perfect insulator stopping e-transfer at iron surface

Effect of Soluble Zn 2+ on Wet Sulfur Corrosion solution phase addition of Zn 2+ soluble Zn 2+ 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 Zn 2+ + S 2- ZnS ( stoichiometric )