(a) Distillation Products from Crude Oil and their Uses on a Vessel:
- Fuel Oil (Bunker Fuel): The primary fuel used for powering the main propulsion engine and generators on most commercial vessels. Bunker fuel comes in various grades with different sulfur contents.
- Marine Diesel Oil (MDO): A lighter distillate fuel used for auxiliary engines, generators, and deck machinery on board ships. MDO has a lower sulfur content compared to bunker fuel and offers better combustion characteristics.
- Marine Gasoil (MGO): A very low sulfur content diesel fuel used in emission-controlled engines or in areas with strict emission regulations. MGO is similar to MDO but with even lower sulfur levels.
- Lubricating Oils: A variety of lubricating oils are derived from crude oil and used for various purposes on board. These include engine oil for internal combustion engines, gear oil for gearboxes and transmissions, and hydraulic oil for hydraulic systems.
- Asphalt: While not directly used on board in its final form, asphalt, also known as bitumen, is a product of crude oil distillation. It can be used for waterproofing applications on some vessels or for shore-based maintenance projects.
(b) Aluminium & Silicon Oxides in Fuel according to ISO 8217:
(i) How They Get There:
Aluminium (Al) and silicon (Si) oxides can enter marine fuels through various pathways:
- Natural Contamination: Trace amounts of these elements can be present naturally in the crude oil itself due to geological formations.
- Refinery Processes: During the refining process, some clay-based materials used for catalysts or adsorbents might contribute aluminium and silicon oxides to the final fuel product.
- Storage and Handling: Contamination can occur during storage and transportation due to contact with tanks, pipelines, or equipment containing these materials.
(ii) Effect on Engine Performance:
The presence of aluminium and silicon oxides in fuel can have several negative consequences for engine performance:
- Abrasive Wear: These hard oxide particles can act as abrasives, increasing wear and tear on engine components like pistons, cylinder liners, and injector nozzles.
- Deposit Formation: Aluminium and silicon oxides can contribute to deposit buildup on pistons, injector tips, and exhaust valves. These deposits can hinder proper fuel injection, reduce combustion efficiency, and lead to power loss.
- Increased Maintenance Needs: The abrasive wear and deposit formation caused by these contaminants can necessitate more frequent engine maintenance and component replacements.
(iii) How They Are Removed from Fuel:
There are several methods for removing or reducing aluminium and silicon oxides in marine fuels:
- Centrifugation: High-speed centrifuges can separate out solid contaminants, including some oxide particles, from the fuel oil.
- Microfiltration: Fine filters can trap smaller oxide particles that might not be removed by centrifuges.
- Fuel Additives: Specific fuel additives can be used to disperse or agglomerate these oxides, preventing them from causing wear or deposit formation.
- Careful Storage and Handling: Implementing proper storage and handling practices to minimize contamination from tanks and equipment can help prevent the introduction of these oxides in the first place.
The specific method chosen for removing aluminium and silicon oxides will depend on the severity of contamination, economic factors, and the fuel treatment capabilities available on board the vessel. Following the guidelines set forth in ISO 8217, which specifies the maximum allowable limits for various contaminants in marine fuels, helps ensure fuel quality and protects engines from wear and tear.