Manufacturers claim that approximately 70 to 90% of Al + Si contents can be removed when the volume flow rates are set at 25%. However, the results of the investigation show that there are large difference between the data and the results of actual vessels tests. It is considered that the flow rates through the purifiers are the main attributing factors of the removal capabilities.
In marine heavy fuel oil currently available on the market Al + Si contents is approximately 20 mg/kg on average. Therefore, only 30 to 60 % separation efficiencies are required to reduce aluminum + silicon contents to the recommended values of engine manufacturers (7 to 15 mg/kg) at engine inlet. Usually single operation is conducted on board with consideration given to keeping the standby unit of purifier. However, when using fuel oil with high Al + Si contents, the purifier is set in parallel operation with throttling the flow rate as small as possible.
Vessel "D" is an example of this operation procedure. Although the flow rate was throttled to 12%, only 75% separation efficiency was attained. From this result we plan to examine a detailed relationship between operating conditions and separation efficiencies of the purifiers because the separation efficiencies changes extensively depending on other conditions other than flow rates. Furthermore, when operating the purifiers routinely on board, it is difficult to maintain a maximum operating performance at all times, so some margin should be allowed for processing fuel oil.
5.3 Examination of Pre-treatment Devices
Each device of pre-treatment systems including purifiers does not always display its expected capability, and properties of fuel oil, specification of device, operating procedures are assumed to be contributors for inadequate performance. To provide better fuel oil for the engine, it is necessary to examine maintenance conditions, operating procedures, and adaptability of devices.
6.CONCLUDING REMARKS
To respond degraded fuel oils, it is vital to examine the extent of the effects of shipboard fuel oil pre-treatment systems. The results of the investigation obtained so far suggest that there is much room for improvement in practical operation and arrangement of pre-treatment systems. Moreover, it is anticipated that effects of pre-treatment system will vary with properties of fuel oil.
We plan to continue the investigation in the future and further results of these surveys will be reported when another opportunity is arises.
