This takes one of two main forms. In both cases the
two base components HFO and MDO are added
together sequentially into a tank that is then
mechanically mixed to provide a homogenous
product. The difference in sparge blending is that the blend in the tank is recycled. The oil re-enters the
tank via a sloping tube with holes cut in it to
enhance the dispersion effect. This method improves
total homogenisation of the fuel and allows
representative samples to be taken from the recycle
pipework for analysis.
The drawback with both these methods is the time
delay to fully mix the components. On occasions this
can sometimes take as long as 1 hour. After this a
sample frequently has to be extracted and taken for
analysis which incurs a further delay. In addition
batch blending is only really practical as a shore
based system. The bunkering barge therefore can
only carry pre-blended grades of fuel; although
sparge mixing can be performed on the bunkering
barge. The accuracy of the blend is totally reliant on
the accuracy to specification of both base oils, and
the equipment performing the sequential metering.
In some cases the volumes to be added are
calculated by tank level of the base oils. Batch
blending however is still a viable method where
market demand is small and /or intermittent.