Crude oil is not supposed to be transported in large amounts by rail, especially through densely populated areas. Pipelines should be the default conduit for crude.
A train carrying more than 100 tankers of crude oil derailed in southern West Virginia on Monday, sending at least one tanker into the Kanawha River, igniting at least 14 and sparking a house fire…
There’s also the stabilization dilemma. Normally, light crude contains diluted gases and volatile liquids. The gases are mostly saturated hydrocarbons ranging from methane (CH4) to butane and isobutane (C4H10) and even neopentane (C5H12). Starting with n-pentane and isopentane, we’re dealing with liquids, assuming normal conditions, that is 20°C and atmospheric pressure. Note that isopentane boils at 28°C and n-pentane at 36°C so guess what happens to them in summer. Obviously, untreated light crude is explosive because of these flammable gases and vapors, and Bakken oil is particularly rich in these.
Some of the gases are separated from the crude at once at the production site, and some of them – methane plus some ethane – are still flared, as is the case in the Bakken. But heavier gases are too valuable to flare. The dilemma is whether to “stabilize” crude – to remove the most volatile flammable components – before transportation or to take extra precautions during transportation and let refiners extract the lightest fractions. After all, gasoline and jet fuel are also explosive but they get safely moved over large distances, although for them, too, pipelines are safer than rail cars.
One of the main dangers of transportation by car is the risk of a BLEVE (Boiling liquid expanding vapor explosion). When a pipeline leaks and ignition follows, you get a nasty fire. But often when railcars crash, one catches fire and starts to heat the tankers nearby, which are as yet intact. You then get a huge buildup of pressure inside which the pressure relief valve is not designed to handle, leading to a catastrophic rupture of the vessel, resulting in a BLEVE. And BLEVEs are very, very bad.
Thanks – I did not know much about BLEVE but now that you’ve explained it to me and I’ve read up on it a little, it seems so obvious and it’s clearer to me why propane-butane tanks used for home cooking can explode so devastatingly. I wonder if some kind of emergency disengagement system is used on trains: if a tank car catches fire in motion, first it gets decoupled from the one behind it, then from the one before.