Download Elemental Sulfur Corrosion in Sour Gas and Claus Sulfur Recovery

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