It is impossible to use the heavy fuel oil directly from the bunker tank without treating it. There are different methods used on a ship to treat the fuel before using it for combustion. Some of the most used methods are:
Heating & Draining
The fuel delivered to the ship is stored in the bunker tank where it is heated by supplying steam to the coils installed in the bunker tanks. Heating is an essential process, which makes it an integral part of fuel oil treatment. The average temperature maintained for heavy fuel oil bunker tanks is around 40ºC.
After transferring it to a settling tank, the fuel is further heated to ensure it is at an appropriate temperature to enter the separators. Once the fuel is transferred to the service tank from the separator, the oil temperature is >80ºC. The main intention is to ensure the smooth pumpability of the fuel oil at different processes and to separate the maximum quantity of water from fuel by draining the settling and service tanks and using purifiers.
For the removal of water and sludge from the heavy-grade oil, fuel oil purifiers are used. Depending upon the owner’s choice, either conventional or modern purifiers (computer-driven fuel cleaning systems) can be installed on a ship.
The oil flow remains continuous even during the sludge discharge process. Purification of heavy fuel oil is considered to be the most critical treatment process and is carried out on all commercial ships.
The heating and purification process is used to separate water from the fuel. However, the solid impurities such as fine metal particles which can cause abrasion wear in the fuel system must also be removed. A fine filter is placed in the fuel oil supply line, which blocks the fine metal particles. These are full-flow units and the substance used inside the filters is usually natural, or synthetic fibrous woollen felt material.
Just like the automotive industry where fuel additives are popular, the maritime industry also uses chemicals in fuels for different jobs; However, this process is not much popular.
The main types of residual fuel additives for marine heavy fuel oil are:
• pre-combustion additives such as demulsifiers, dispersants
• combustion improvers
• ash modifiers