Refinery Automation Institute, LLC
COVID-19 pandemic and OPEC oil war are decimating fuel demand and cratering prices. But it will not last forever, so when the time comes, be prepared. Part of that preparation is being flexible to run any type of crude with minimum headaches.
Given that crude oil comprises 60% or more of the operating costs of a refinery, how can we improve the economics?
This paper examines degradation of crude stored for a long time, e.g. crude bought from the SPR, standard methods of valuing a crude oil using assays, is there a thing such as ‘bad’ oil that can’t be fixed by blending, crude compatibility to avoid asphaltene precipitation, and on-line crude blend optimization.
Typical SPR Salt Crude Storage
Typical underground concrete crude storage
The crude oil stored at US SPR is in salt caverns solution-mined in salt formations which provide impermeable walls and a relatively constant storage temperature of approximately 17 degrees C.
Other countries also use underground storage in abandoned mines, salt rock formation, and purpose built concrete underground storage tanks to maintain a constant temperature and minimize contamination.
Degradation of crude oil occurs when:
– Heating above 30 deg C, the light hydrocarbons such as Butane and Natural Gasoline may evaporate; this lowers the potential yield of gasoline and lowers the price of the crude. With SPR underground tanks, this is not an issue because of the year-round constant temperature of about 17 degrees C in the SPR underground salt caverns.
– Mixing two crudes with differing fuel fraction yields; it may lower the refiner yield of the most profitable products and thus lower the crude blend value to the refiner. This is determined by examining the resulting blend “assay” of the two or more different crudes.
– Mixing “incompatible” crudes or hydrocarbon such as highly paraffinic crude; this may precipitate asphaltenes, which will form a sludge, which coats the tank walls and internals of pipes and pumps. This does not render the crude unusable; it is a headache, and it just increases the cost of pumping and sludge removal, and maintenance costs.
It is common worldwide practice for the last 50 years to blend together a multiplicity of crude oils to economically optimize the crude feed “diet” to specific refineries requirements (in terms of yields and qualities).
Typically, a refinery will blend 4 to 11 different crude oils in a “feed” tank or do an in-line blending of different crudes (Fig. 4). For in-line blending, we use an on-line crude mix property analyzer (a Lab in a suitcase) installed on the blender pipe to control precisely and automatically the proportion of each crude oil in the mix based on each crude property assays.
