Process Considerations for the Safe Process Considerations for the Safe Process Considerations for the Safe Process Considerations for the Safe Design of Sulphur Tanks and Design of Sulphur Tanks and Design of Sulphur Tanks and Design of Sulphur Tanks and
Collection SystemsCollection SystemsCollection SystemsCollection Systems
Ken Sourisseau, P. Eng.Shell Canada Energy
Figure 1Figure 1Figure 1Figure 1---- Simplified Claus ProcessSimplified Claus ProcessSimplified Claus ProcessSimplified Claus Process
Condenser
ClausReactor
Reheater
steam
steamTail Gas
Sulphur
Acid Gas
Air
WHBRF steamsteam
Figure 2Figure 2Figure 2Figure 2---- Liquid Sulphur HandlingLiquid Sulphur HandlingLiquid Sulphur HandlingLiquid Sulphur Handling
Pit DegassingPit DegassingPit DegassingPit Degassing
External DegassingExternal DegassingExternal DegassingExternal Degassing
Liquid Sulphur HazardsLiquid Sulphur HazardsLiquid Sulphur HazardsLiquid Sulphur Hazards
• Severe burns• Combustion product, SO2 is highly toxic• Production method results in H2S and
SO2 being dissolved in liquid– Degassing in storage creates explosive
vapours– Degassing in storage creates toxic
atmosphere
Mitigation of Personnel HazardsMitigation of Personnel HazardsMitigation of Personnel HazardsMitigation of Personnel Hazards
• Exposure to Toxic Vapour– Use of sulphur seal legs– Improvement in lookbox design– Elimination of lookboxes
• Exposure to Molten Sulphur– Proper tracing and steam supply– Packing glands for rod-out connections
Figure 3Figure 3Figure 3Figure 3Sulphur Seal LegSulphur Seal LegSulphur Seal LegSulphur Seal Leg
• Sulphur flow down centre pipe• Returns up annulus• Length of seal leg should
ensure blower deadhead cannot blow seal
• Proper heat tracing required on outside of return pipe
Figure 4 Figure 4 Figure 4 Figure 4 –––– Lookbox EvolutionLookbox EvolutionLookbox EvolutionLookbox Evolution
b) Newest Stylea) Second Generation
Figure 5 Figure 5 Figure 5 Figure 5 –––– Sulphur Sight GlassSulphur Sight GlassSulphur Sight GlassSulphur Sight Glass
Figure 6 Figure 6 Figure 6 Figure 6 ---- Inline Sulphur Site GlassInline Sulphur Site GlassInline Sulphur Site GlassInline Sulphur Site Glass
Figure 7 Figure 7 Figure 7 Figure 7 –––– Effective Heat TracingEffective Heat TracingEffective Heat TracingEffective Heat Tracing
Courtesy of Controls Southeast Inc.
Figure 8 Figure 8 Figure 8 Figure 8 –––– Heat Tracing Large PipeHeat Tracing Large PipeHeat Tracing Large PipeHeat Tracing Large Pipe
Figure 9 Figure 9 Figure 9 Figure 9 –––– Liquid Sulphur ViscosityLiquid Sulphur ViscosityLiquid Sulphur ViscosityLiquid Sulphur Viscosity
Liquid Sulphur Viscosity
0.001
0.010
0.100
1.000
10.000
100.000
120 130 140 150 160 170 180
Temperature (oC)
Vis
co
sit
y (P
a s
)
Figure 10 Figure 10 Figure 10 Figure 10 ---- Steam Ingress to Sulphur Steam Ingress to Sulphur Steam Ingress to Sulphur Steam Ingress to Sulphur RundownRundownRundownRundown
Prevention of Explosive AtmospheresPrevention of Explosive AtmospheresPrevention of Explosive AtmospheresPrevention of Explosive Atmospheres
• Sweep air required in rundown vessel• Degas liquid sulphur in pit or in external
degas vessel• In pit degas start-up concerns
– Increase air flow rate– Start degassing before pit is full
Storage Tank ConsiderationsStorage Tank ConsiderationsStorage Tank ConsiderationsStorage Tank Considerations
• Properly degassed sulphur should provide no problems, small H2S venting
• Proper heat tracing of roof and vents • Undegassed sulphur may create
explosive atmosphere in tank– Proper rim and centre vents recommended– Steam purge may create larger problem
Prevention of Pyrophoric DepositsPrevention of Pyrophoric DepositsPrevention of Pyrophoric DepositsPrevention of Pyrophoric Deposits
• Prevent formation by having oxidizing atmospheres
• Undegassed sulphur to rundown tanks creates a reducing atmosphere
• Steam purge creates wet conditions more conducive to pyrophoric deposits
• Pyrophoric deposits on tank roofs easily ignited when tank inbreathing
Prevention of CorrosionPrevention of CorrosionPrevention of CorrosionPrevention of Corrosion
• Keep surfaces hot to prevent water and/or sulphur deposition
• Use stainless steel for surfaces that can be uncovered of liquid sulphur
• Consider removal of sulphur tank heating coil in favour of external tank tracing