Sulphur (sulfur) is a major dry bulk cargo, with global seaborne trade of approximately 35 to 45 million tonnes per year, principally moving from oil and gas refining regions where sulphur is recovered as a by-product of fuel desulphurisation to fertilizer producers worldwide who use sulphur as a feedstock for sulphuric acid and ammonium phosphate fertilizers. The IMSBC Code regulates sulphur shipments under multiple schedule entries reflecting the different commercial forms of the product.
Schedule structure
The IMSBC Code includes the following schedule entries for sulphur:
- Sulphur (UN 1350): bulk crushed lump, granulated, or prilled sulphur. Group B (chemical hazard, flammable but not explosive).
- Sulphur (formed, solid): solidified blocks of sulphur produced by molten sulphur cooling and breakage. Generally lower fines content than crushed material. Group B.
All commercial sulphur grades are classified Group B due to flammability and dust hazards. The Group B classification means the cargo is not subject to liquefaction (TML/MC) testing but is subject to chemical hazard handling provisions.
Cargo properties
Elemental sulphur is a yellow crystalline solid with a melting point of 115 degrees Celsius and an ignition temperature of approximately 232 degrees Celsius. The principal commercial forms are:
- Crushed lump sulphur: irregular fragments of approximately 5 to 50 millimetres broken from solid blocks at the production facility. Typical of older Canadian, US, and Middle Eastern production.
- Prilled sulphur: small uniform spherical pellets of approximately 2 to 5 millimetres formed by spraying molten sulphur into a cooling tower. Lower dust generation than crushed lump.
- Granulated sulphur: granules of approximately 2 to 6 millimetres formed by drum or fluid bed granulation. The dominant modern commercial form, with low dust generation and good flow properties.
- Formed sulphur: cast solid blocks broken to handleable size. Less common in modern trade.
Bulk density is approximately 1.0 to 1.3 tonnes per cubic metre. Stowage factor is approximately 0.75 to 1.0 cubic metres per tonne.
Hazards
Sulphur presents three principal marine carriage hazards:
- Dust ignition: fine sulphur dust forms an explosive mixture in air. Loading and discharge operations must control dust accumulation, and ignition sources (smoking, hot work, electrical sparks) must be eliminated. Modern granulated and prilled sulphur produces less dust than crushed lump but the hazard is not eliminated.
- Bulk fire: a sulphur fire can be initiated by spark, friction, or external heat source and propagates through the bulk cargo at moderate rates. Sulphur fires generate sulphur dioxide which is toxic and corrosive.
- Hydrogen sulphide release: some petroleum-derived sulphur cargoes release residual hydrogen sulphide (H2S) during the voyage, particularly if the cargo was stored under elevated temperatures before loading. H2S is acutely toxic at low concentrations and the IMSBC Code requires appropriate ventilation and gas monitoring.
Hold preparation and loading
Holds must be clean, dry, and free of oils, organic residues, and incompatible cargo residues. Bare steel surfaces should be intact (sulphur does not react with steel directly but accumulated moisture and SO2 can cause corrosion over time). Bilge wells should be clean and dry.
Loading is by shore conveyor and shiploader. Granulated and prilled sulphur self-trims; crushed lump may require some bulldozer trimming for hatch closure. Loading rates of 2,000 to 6,000 tonnes per hour are typical at major export terminals.
Critical pre-loading procedures:
- Hot work permits suspended throughout loading and voyage.
- All ignition sources (smoking, naked flames, faulty electrical equipment) controlled.
- Cargo temperature monitored at loading; abnormally high temperatures (above 60 degrees Celsius) warrant investigation.
Voyage handling
The cargo is generally not ventilated during voyage unless there is a specific need to remove H2S accumulation. Hold atmosphere monitoring for H2S and SO2 may be required for petroleum-derived sulphur cargoes. Cargo temperature should be monitored where practical. Continuous bilge inspection ensures any moisture ingress is identified early and pumped out before it can react with sulphur to form dilute sulphurous acid.
Discharge
Discharge is by grab-fitted shore cranes at receiving ports including major fertilizer manufacturing centres in Morocco (OCP), Saudi Arabia (Ma’aden), Tunisia, India, Brazil, and the United States. Discharge rates of 800 to 2,500 tonnes per hour per grab are typical. Hold cleaning after discharge requires fresh-water washing to remove sulphur residues, with care to ensure complete drying before any subsequent dissimilar cargo is loaded.
Major routes
Sulphur seaborne trade flows include:
- Canada (Vancouver, Prince Rupert) export of recovered Alberta gas-plant sulphur to Asian fertilizer producers.
- Saudi Arabia, UAE, Qatar, and Iran export of refinery-recovered sulphur to South Asia, Africa, and Latin America.
- Russia (Black Sea ports) export of Astrakhan and other gas-plant sulphur to global markets.
- Kazakhstan (via Russian and Iranian transit) export to global fertilizer producers.
- United States (Gulf Coast) export of refinery sulphur to Latin America and South Asia.
Receiving ports are typically dedicated fertilizer-plant berths with covered conveyor systems and shore storage capable of handling sulphur’s specific hazards.