Why all tankers use steam-driven cargo pumps instead of electric pumps? Is the reason only economic or also technical?
Hello @Philip.Argyropoulos, reasons that come in mind:
In steam driven cargo pumps the operator can control the RPM of the pump and hence the flow rate in an easier and more accurate way. This is essential in discharging operations. In electric driven cargo pumps, this would require the installation of huge variable frequency drives. The cost (installation+ bigger generators + fuel oil consumption) is prohibitive in this case and technically it is a more complicated installation.
The fact that the auxiliary boilers can play the two most important roles in discharging operations, at the same time: inerting (exhaust gasses) and steam production (discharging). This is a very good example of efficient engineering systems design. In the case of electric driven cargo pumps the ship would still require inert gas generators. Why not to combine both?
Of course this is not the case for clean product carriers that do not have pump rooms but submerged framo-type pumps in every cargo tank.
For instance, the power output of a SHINKO cargo oil pump turbine of a VLCC is 2,500 KW.
For 3 electric driven cargo oil pumps this would mean 7,500 KW of additional electrical power.
The total electric power available in modern VLCCs is about 3,600 KW (1,200 KW per Diesel Generator) which is almost half of the required power for 3 electric driven cargo oil pumps!