Figure No. 6: Blending
Most engine manufacturers believe that the addition of small quantities of used lubricants, i.e., less than 5%, may be tolerated [9]. This allows a ship operator to dispose of the ship's own used oils in a simple and uncomplicated method.
It should be noted that refiners rarely ever have significant volumes of used oil at their disposal. Furthermore, some producers and suppliers of marine fuels have said "that it is their policy to not knowingly supply marine fuels containing used lubricants at all". There is some new drive recently, however, to ban the use of used lubricants from blending fuels completely [10].
3.4 Blending Marine Fuel Oils
Nearly all marine fuel oils are blended from components, either at the refinery, at the terminal, or in a barge. Some years ago even on board blending was executed.
Most blends are 3 component blends. This is inevitable because viscosity and density limits must be met without uneconomic "quality give away ".
Refinery blending is the most reliable approach. It is normally executed in tanks equipped with effective mixing tools. The accuracy of the mixing process, furthermore, is controlled by the refinery's own lab. A refinery nominally produces one of the "35" categories of ISO 8217: 1996 or higher only, according to the quality of available residual material and diluents.
Blending of all other categories reasonably is executed at the terminal in tanks or by means of an in-line blender. Both methods allow for sufficient precision in meeting the specification, even for three component blends. In blending, it is important to consider that significant differences in viscosity, density and temperatures of the components make it difficult to achieve the necessary homogeneity of the blend.
It is, therefore, crucial to control this process by adequate methods, in particular with dumbbell blends .
Blending with the help of an in-line blender into a barge is agreeable provided the compatibility of the components is well known and the barge is vetted by a chartered surveyor for cleanliness and good order of tanks, scales and tank calibrations before loading.
Blending of components loaded into a barge from different supply points and circulated for some time with the barge's own cargo pumps is more problematic for a variety of parameters out of the supplier's and the receiver's control. It normally takes a couple of hours of circulation to achieve a homogeneous mix of the components. Also, the blending easily can fail when for example hot residual material has been pumped on top of a distillate or diluent of much lower temperature. In case the product supplied has been blended in a barge the receiver must check the density and the viscosity to assure homogeneity of the relevant tank contents.
Barge blending cannot be totally avoided in case technical problems on the terminal exclude other options or, in case the data of a blend loaded already demonstrate that a re-adjustment of the stem is inevitable.
Responsible fuel suppliers ensure by application of commensurate procedures that the sophisticated blending process leads to satisfactory results. Off specification blends when delivered result in delays and significant costs in case reblending or the exchange of the product becomes necessary.
3.5 Transport and Transfer
It is a long time ago that ships regularly sailed to the fuel, i.e., to a refinery or a bunker terminal. These days it is normal that the fuel sails to the ship: by barge.
Barge transport regrettably, offers a wide variety of options where to manipulate the fuel in quality and quantity, or to cheat the customer otherwise [11].
Shortening the chain of accountabilities, therefore, between refinery tank and ship tank contributes to a satisfactory probability of receiving unproblematic fuels. Tank to ship no doubt is the safest method. However, this is not always feasible. In consequence, other approaches like barge transport and even barge blending must be executed in a way controlled to a degree that the process can be rated safe. Own vigilance is indispensable, and competent ship staff should be nominated to witness all relevant activities on the barge and at the ship's manifold.
