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[tashaqsc]

Hi All

I'm hoping i can draw experience from the group on this - Im looking for information regarding
1. Factors that can affect stability (IP390 test) result post cracking ie. is a shift from equilibruim possible while product remains in tankage?
2. The effect of cutter stocks on fuel oil (in particular would the addition of parrafinic material result in drastic changes to stability).


Any info would help. Thanks

[kkala]

...
1. Factors that can affect stability (IP390 test) result post cracking ie. is a shift from equilibruim possible while product remains in tankage?
2. The effect of cutter stocks on fuel oil (in particular would the addition of parrafinic material result in drastic changes to stability)...

It seems that fuel oil components are not in "perfect" equilibrium. There is a tendency to brake down fuel oil stability, which is accelerated by heating, contact with water, contact with air, even by some of the additives for treatment, resulting in precipitated sludge or gum.
α. Unsaturated hydrocarbons are quick to react with O2 (from air or water), usually forming insuluble material in the form of sludge much faster. Also they tend to polymerize when heated, forming gums.
β. Heavy oils are more unstable due to intensive prior treatment. Their free carbon and insoluble materials may remain in suspension for long time. But blended with lighter distillates will make them precipitate (sludge).
γ. Blending of oils (distillates, residuals) will affect their stability and result in sludge. This occurs even if two fuel oils are blended.
Asphaltene is often precipitated when residual and distillate oils are blended (more distillate will bring more sludge). This will happen in case that a fuel oil is blended with parrafin.
δ. Aromatic compounds cause less slug due to their ability to solve; Thermally cracked oils have a higher percentage in aromatics, so they develop less sludge compared to catalytically cracked oils.
ε. Even well handled "pure" fuel oils are to develop sludge and gum in storage, but in a much longer time.
Above is taken from "Fuel oil manual" by Paul F Schmidt (Industrial Press, 1985), Chapter 18, Stability of fuel oils. More info can be found here.
I have also seen than residual fuel oils not having undergone cracking (straight run atmospheric residues, SRAR) are much more stable than cracked fuel oils. Cracked oil is not used in internal combustion engines for electric generation here, SRAR oil is used after treatment (water & sludge removal).