4. INVESTIGATION RESULTS
On the basis of analysis results of fuel oils taken from the sampling spots, Table 2 shows values of the properties at the sampling spot No. 1 (at bunkering) and the sampling spot No. 8 (at engine inlet) and separation efficiency of each item.
Figure 2 to 9 show value changes of density, kinematic viscosity, water, sodium, asphaltene, dry sludge, aluminum + silicon and vanadium.
On vessel "A" the values of items dropped greatly from the sampling spot No.6 to No. 8 on the fuel circulation line. It is presumed that fuel oil with low viscosity was contaminated on the fuel supply line for some reason. Therefore, the value changes from the sampling spot No.6 to No.8 on vessel "A" were disregarded.
4.1 Changes of Density and Kinematic Viscosity
Expect for vessel "A", due to evaporation of light contents, both density and kinematic viscosity tend to increase slightly as the fuel oil flows closer to engine inlet. On average, value of density increases 0.004%, while value of kinematic viscosity increases 0.9% respectively.
4.2 Changes of Water and Sodium
The highest separation efficiency of water content throughout all systems is 72.7% and the lowest is -200.0%; on average 53.5%. Overall, the effects of the settling tanks and the service tanks are distinct and the purifiers come next.
On vessel "J", however, the value of the water content increases at the outlet purifier. It is presumed that the purifier was not in good condition or the sampling procedures were improper. The highest separation efficiency of sodium content throughout all systems is 43.5% and the lowest is -0.2%; on average 22.7%.
Except for vessel "C" and vessel "J", the separation efficiency of sodium shows a similar tendency as water and greater effects are seen on Vessel "D", "E" and "G". Although on vessel "C" and "J" the water content is removed relatively well, there are no noticeable changes in sodium values.
In many cases sodium is generally introduced into the fuel oil due to ingress of sea water. However, it is presumed that the high sodium content on these vessels were attributed to different causes other than sea water.
4.3 Changes of Asphaltene and Dry Sludge (TSE)
The highest separation efficiency of asphaltene content throughout all systems is 12.1%, and the lowest is -14.2%, on average 2.0%. At any rate, the changes of asphaltene content are confined to within a narrow range and there are no noticeable changes throughout all pre-treatment systems.
The highest separation efficiency of dry sludge (TSE) is 66.7%, and the lowest is -22.5%, on average 50.4%. The removal effect is observed on the fuel oil supply line, and on the contrary the values of sludge tend to increase on the circulation line. This is because heat instability causes an excessive sludge generation in the fuel oil as the fuel oil circulates on the circulation line at high temperature.
4.4 Changes of Al + Si (Aluminum + Silicon)
The highest separation efficiency of aluminum and silicon contents is 81.5%, and the lowest is 0.0%, on average 59.7%. Al + Si removal rates of each pre-treatment device are shown in Table 3. For removing FCC compounds composed of aluminum and silicon elements, effects of the purifiers are outstanding and the settling tanks and the service tanks stand second. Meanwhile, the removing effects of the second and the third filters are relatively low.
This is because most of catalytic fines with a large particle size are removed before entering the service tank. Depending on the amount and size of particles, the most part of actual removing amount can be removed before entering the service tank.
4.5 Changes of Vanadium
The highest separation efficiency of vanadium contents is 6.3%, and the lowest is -22.1%, on average 0.3%. There are almost no changes seen in the values of vanadium just as observed in the values of asphaltene.
5.CONCLUDING SUMMARY
On the basis of survey results, the effects of the pre-treatment systems and the considerations to be taken when examining the effects are described below.
5.1 Current State of Shipboard Fuel Oil Pre-treatment Systems
Specific properties responsible for abnormalities in the combustion chambers and the exhaust gas systems of the diesel engines are water, micro carbon residue, FCC (catalytic fines), dry sludge, vanadium, and sodium. Among these properties water, FCC (catalytic fines) and dry sludge can be removed in the pre-treatment system.
Most of the separation effects are achieved before entering the service tanks, and in particular, effects of the purifiers are outstanding. However, reports from ships often indicate that actual separation efficiencies vary considerably from purifier to purifier.
Fuel additives should be used for the properties like sulfur, micro carbon residue, sodium, asphaltene and vanadium which cannot be removed by present pre-treatment systems. Therefore, it is necessary to include a fuel additive supplying device when determining the arrangement of the pre-treatment systems.
5.2 Responding to FCC Catalysis Fines
Al + Si contents in the samples of fuel oil used in the investigation ranged between 2.3 to 48.2 mg/kg (on average 20.6 mg/kg), and it was found that the removal effects were noticeable on the fuel oil supply line, in particular effects of the purifier were distinct.
The volume flow rates through the purifiers were throttled to 12% to 66% (50.1% on average) of the rated flow rate, and the separation efficiencies were 12 to 75% (on average 43.2%). Although the separation efficiencies varied, effects of the purifiers were larger as the volume flow rates through the purifiers were smaller and Al + Si contents were larger.
