Fuel Oil Service System:
Once the oil is purified and stored in the day tanks, the fuel is drawn to the engine through the service system. The system consists of the following components.
- Fuel oil circulation pumps:
They have a discharge pressure of about 4 bar. These pumps circulate the oil through the system continuously even when the engine is stopped for a short duration so that the impurities/sediments in the fuel oil will not get settle down in the pipelines.
- Fuel oil booster pumps:
There should always be a positive pressure at the suction of the fuel pumps mounted on the engine. Hence the booster pumps are provided to boost the pressure up to 8 bar.
- Heater (steam/electric) & Viscotherm (viscosity monitoring device)
Fuel oil is to be supplied to the engine at a viscosity of about 12 to 14 cst and to maintain and control the viscosity heaters are provided. These can be either steam heated or electric heated. The viscotherm senses the viscosity of oil going to the engine and in case of higher viscosity, it allows more steam to the steam heater by opening the valve on the steam inlet to the steam heater.
- Final fuel filter (duplex type):
A very fine fuel filter (of about 2 microns) is provided just before the engine so that all impurities are removed from fuel oil before entering the engine.
- Fuel return line and deaerator:
Since the load on the engine is varying at different speeds of the ship, the fuel oil requirements also vary at different loads. to avoid any cavitations in the pipelines due to variations in the volume of flow, always excess fuel is supplied to the fuel pumps of engines and this excess fuel will be returned back to the system from the fuel pumps. through the return line.
Since the fuel oil is heated (when the engine is running on HFO) there will be oil vapours in the system which cause cavitation in the pipelines. To avoid cavitation, a deaerator is provided in the return line so that any oil vapours in the system will get condensed.
- Operation of engine on LDO (light diesel oil)
The engine will be run on LDO, when the engine will be stopped for a long time (like when ship reaches a port for loading and unloading) so that the impurities of HFO will not get settled down in pipe line. Since LDO is more purified oil and is having a viscosity of 12-14 cst, no heating is required during operation on LDO.