methods for eliminating corrosion in sulphur...
TRANSCRIPT
Methods for Eliminating Corrosion in
Sulphur Storage Tanks and Vessels
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Variables with most impact on
tank heating
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• Steam pressure
3.5 to 7 barg generally used
• Maintenance Temperature
Tank Wall – 126°C
Bulk Sulphur – 135°C
• Sweep air
Minimum required to meet tank venting requirements (ejector or free convection)
• Low Liquid Level
Minimum 1m recommended
• Insulation
100mm in shell – 150mm on roof, extend to ground if possible
• Heating of nozzles & heat sinks
MUST consider impact of heat sinks
External Corrosion of Sulphur Tanks
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• Ambient water settling behind the exterior
insulation
Damaged Insulation or poor installation
Tank Wall less than 100°C
Water stagnation leading to corrosion
• Sulphur Spillage around the sulphur tank
Sulphur spill or leak – causing sulphur to collect
on bottom of tank
Sulphur coming in contact with steel can lead to
corrosion issues
External Corrosion of Sulphur Tanks
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Internal Corrosion Mechanisms
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Air
Purge
(H2O)H2O condensation
S8
Porous
Solid S8
H2O (vap)
Inner Fe surface (<100°C)
Expanded
view
SULFUR CORROSION RESULTING FROM SOLID SULFUR DEPOSITION
• Cooling of roof may result from
removing liquid S8 from the tank;
most likely when only a steam coil
is used to heat the sulfur
• Solid sulfur insulates Fe
surface allowing it to cool < 100°C
• H2O diffuses through porous
solid sulfur
• Fe / S8 contact corrosion
Fe + S8 Fe Sx
H2O
140°C Liq. S8
SO2H2S H2O +
H2O SO2O2
Solid S8
140°C Liq. S8
SO2H2S H2O +
H2O SO2O2
Solid S8
Internal Tank Corrosion
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Internal Tank Corrosion
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Internal Tank Corrosion
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Avoiding Internal Corrosion within
Sulphur Storage Tanks
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Proper Utility design is critical
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Heat Input/Output Model
Ground Heat Loss – CFD Model
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Model details: 20m diameter, 1m liquid height
vapor
Liquid
Ground
Heat Input/Output Model
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Sulphur Solidification in Tank
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1. The tanks contain a large amount of sulphur – large thermal capacitance
2. The ground temperature below tank (300mm) at similar temperature to sulphur
3. Tank is typically well insulated
4. Sulphur freezes on tank side walls and top layer – creating insulating layer
Why?
Thermally Engineered Systems
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Thermally Engineered Systems
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Heat Sink –
Must heat
Thermally Engineered Systems
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Thermally Engineered – CFD Model
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Model details: 20m diameter, 1m liquid height
vapor
liquid
ground
Highest sulfur velocity next to perimeter wall and along top surface.
General flow is one large recirculation loop.
Average sulfur velocity = 2.5 m/hr.
Thermally Engineered – CFD Model
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Model details: 20m diameter, 1m liquid height
Sulfur hottest near perimeter and coolest at center.
Average sulfur temperature = 135°C
Difference between perimeter and center temperatures = .56°C
vapor
liquid
ground
Sulphur Temperature Gradients
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0
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2
3
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5
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0 50 100 150 200 250 300 350
∆T
(°F
)
Tank diameter (ft)
Temperature Variation Within the sulfur (∆T tank perimeter to tank center)
Questions?
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