Info Centre >> Fuel and Lube Oil Technical Manual >> 4. Fuel Oil - Test Results >> 4.9 Ash
Residual fuels have more ash-forming constituents than any other as they are concentrated from the residue of crude oil refining processes. Vanadium and other materials such as silicon, aluminium, nickel, sodium and iron are the main contributing components. Typically, the ash value is in the range 0.03-0.07 % m/m as shown.
During onboard treatment, ash level may be reduced as a result of the settling tank and the centrifuges. This is because of the partial removal of catalyst fines (aluminium and silicon), sodium if in the form of salt water and iron if in the form of debris.
Less than 1% of residual fuels contain an ash level greater than 0.1 %. Excessive ash levels are invariably caused by the inclusion of some waste material in the fuel which will increase the tendency for engine fouling. Attention should be paid to water washing when operating on a high ash fuel. Ash-modifying fuel additives can also assist cleanliness of the exhaust system.
High ash levels may be associated with waste lube oil in the fuel. This is a contentious issue and there is as yet no clear picture as to what is acceptable. If there is any doubt, if other parameters are also high (eg. water) or the estimated lube oil content is >5% then fuels containing waste lubes should be rejected.
Comment:
Generally acceptable to process a fuel with ash content 25% above the limit. V, Zn + Mg are generally oil soluble and cannot be reduced. Be careful if Na:V is 1:3.