Practical measures for managing fertilizer cargoes, addressing issues like caking and compaction to ensure cargo remains acceptable and fit for use.
Fertilizer cargoes are hygroscopic and can absorb moisture during transport, leading to two main issues: compaction and caking. Compaction results from the weight of stowed cargo pressing granules together and is usually reversible, while caking occurs when the cargo gets wet, forming chemical or molecular bonds like crystal bridges, and is often irreversible.
Distinguishing between them is crucial: if the cargo breaks into free-flowing granules under light pressure, it is compaction; if it resists breaking or turns to powder, it is caked. This distinction affects whether the cargo is commercially acceptable and whether claims may arise.
Action to take if caked
If the cargo is proven to be caked, the severity of such caking needs to be assessed. When assessing the severity, numerous factors should be considered, including:
- What is the end use? If used in mechanical spreaders, then free-flowing nature will be important. However, for manual spreading it is likely to be less important.
- Nature of the fertilizer itself – such as its moisture content, hygroscopicity, temperature, chemical composition and mechanical strength.
- External influences – typically the compaction pressure, ambient conditions, storage time and handling procedure.
Severe caking can occur upon loss of moisture subsequent to a wetting incident. The cargo may be wet at the time of discharge but would be expected to become hard-caked once it dries out in the future.
Prevention
To prevent or minimize caking whilst on board the vessel:
- Keep the cargo dry.
- Weathertight hatch covers and accesses are essential.
- Avoid working the cargo during rain.
The production process, use of anti-caking agents and storage arrangements ashore also influence the cargo’s vulnerability to caking.