methods for eliminating corrosion in sulphur...

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

1

2

3

4

5

6

7

8

9

10

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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