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Vanadium & Sodium Levels

Vanadium and Sodium graph

No economical process exists for removing vanadium from either crude oil or residual fuel. Vanadium is a metal present in all crude oils in an oil-soluble form.
The levels found in residual fuels depend mainly on the crude oil source, with those from Venezuela and Mexico having the highest levels. The actual level is also related to the concentrating effect of the refinery processes used in the production of the residual. Most residual fuels have vanadium levels of less than 150 mg/kg. Some fuels however, have a vanadium level greater than 400 mg/kg.
In general, fuel when delivered contains a small amount of sodium, typically below 50 mg/kg. The presence of seawater increases this value by approximately 100 mg/kg for each percent of seawater. If not removed in the fuel treatment process, a high level of sodium will give rise to post-combustion deposits in the turbocharger. Although potentially harmful, these can normally be removed by water washing.
High temperature corrosion and fouling can be attributed to vanadium and sodium in the fuel. During combustion, these elements oxidise and form semi-liquid and low melting salts that adhere to exhaust valves and turbochargers. In practice, the extent of hot corrosion and fouling are generally maintained at an acceptable level by employing the correct design and operation of the diesel engine. Temperature control and material selection are the principal means of minimising hot corrosion. It is essential to ensure exhaust valve temperatures are maintained below the temperatures at which liquid sodium and vanadium complexes are formed and for this reason valve face and seat temperatures are usually limited to below 450°C.
When a fuel is bunkered with a vanadium level greater than that recommended by the engine designer, there is a risk that hot corrosion and fouling may occur. One operational solution is by the use of a fuel additive, and numerous ash-modifying compounds are available. They should be used with care as situations can arise where the effect of the ash-modifier, by incorrect application, can cause further problems in the downstream post-combustion phase.

Damaged exhaust valve

Do not run with vanadium levels above specification for extended periods. Watch for a sodium (Na) to vanadium (V) ratio of 1:3, as the lowest melting point corrosive sodium/vanadium/oxide salts are formed.  
Vanadium, Sodium and Ash will cause fouling in the Turbocharger.
The above image shows the effect of hot corrosion on exhaust valves.

Off-line Bunker Fuel

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