[FoRK] Authoritative explanation of gas spike in 2007/8?
meltsner at alum.mit.edu
Sun Oct 11 12:09:49 PDT 2009
And for those who have been following at home, a really brief and
probably misremembered intro to refining:
* Crude oil is a mix of lots of interesting molecules. Sometimes
there's asphalt in it, sometimes there's wax ("napthenic", IIRC)
* Refining was originally a process by which crude was heated up to
extract relatively consistent groups of molecules. Whatever was left
was sold for asphalt and similar apps.
* These days, most refineries have the capability of breaking
(cracking) the heavier molecules into the more desirable light ones --
you can do this with heat (thermal) or the more efficient way is to
use various clever catalysts. Some of these catalysts will be
poisoned by the common impurities in the heavier oils, so you need to
add more equipment to get that stuff out first.
* [There may also be a capability at some plants to combine light
molecules into more desirable heavier ones, e.g. butane and propane
into gasoline, IIRC]
* A smaller number of refineries can remove sulfur and other
impurities from their outputs, but this is a significant investment.
* Alaskan crudes are really heavy and gunky -- you need the right
sort of refinery to convert them efficiently into salable products --
and tend to be close to a somewhat oozy solid at room temperature
* Saudi crudes (and a few others) are light and fluffy, and really
easy to refine
* A fully-equipped refinery can take practically any crude and turn
it into salable products
* Other refineries can only work efficiently with relatively light
crudes and have limited cracking and impurity removal .
So, it's easy to see how a demand for one really clean fraction would
cause trouble if there was a mismatch between refining capabilities
and the available grades of crude.
The stats on refinery capacity, by the way, are scary. I would have
liked to see an age distribution as well, but the number of
refineries has dropped by 50% since I was at Chevron, which is scary
all by itself. The older plants are unlikely to be fully equipped
with the latest refining equipment, so even bringing them out of
mothballs may just make the problem more complicated.
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