Vanadium

 Vanadium is a metal present in all crude oils. The levels found in residual fuels depend mainly on the crude oil source, with those from Venezuela and Mexico having the highest levels. Problems associated with high vanadium are largely overcome by good engine design, correct fuel treatment (water removal) and correct engine operating conditions.

 The actual level is also related to the concentrating effect of the refinery processes used in the production of residual fuel. Most residual fuels have vanadium levels of less than 150 mg/kg. In general, residual fuel contains a small amount of sodium when delivered, typically below 50 mg/kg. The presence of sea water increases this value by approximately 100 mg/kg for each per cent sea water. Normally sea water can be removed from the fuel by gravitational separation in the settling tank and centrifugal purification. Very occasionally, sodium hydroxide used in the refining process may be a source of contamination. Some of the sodium may be present in an oil soluble form that cannot be removed on board ship. Particular attention is paid to the amounts of sodium and vanadium in the fuel as these elements have a low "striction" temperature. This is the temperature at which the ash becomes semi-liquid and can adhere to components in the combustion system if the component temperatures are high enough. The melting point of the ashes depends on the constituents of the ash.

 There are no practical methods by which vanadium can be removed from fuel on board ship. Therefore the only practical way to restrict vanadium is by limiting its content in the fuel purchasing arrangement. One possible operational solution for older engines which are sensitive to vanadium and sodium is the use of a fuel additive which acts as a combustion modifier.