Why Oil Refineries Shoot Fireballs

At about 6:30 PM last Thursday, if you had been looking skyward in the San Francisco Bay Area, you might have seen, lighting the sky, a fireball.

The skyward flames emanated from an oil refinery operated by Chevron, and caused some to panic on social media and in the community in Richmond, CA, setting off fears that the plant had once more gone up in an inferno, as it has in the past. But it hadn't. The bouts of fire spewing from the plant for the next three hours were a part of operations, according to a Chevron spokesman. "The flaring actually shows that the refinery's safety systems are working properly," Chevron spokesman Braden Reddall said.

What happened at the refinery, was that a machine designed to cool a solvent de-asphalting unit malfunctioned (asphalt is one of the substances found in crude oil and filtered out during refining), and that triggered flaring, according to a Chevron statement. But why the giant fireball?

"The short answer is whenever there is an upset, the pressure vessels in a refinery are protected by pressure levers," Arno de Klerk, an oil refinery expert at the University of Alberta, said. "Those pressure levers would open if something has gone wrong, and of course release the pressure—usually, in the case of a refinery, [as] highly flammable gases that are released into a line. Those gases cannot be released into the atmosphere, so it must go through a flare."

Burning hydrocarbons releases carbon dioxide into the air as a byproduct, though Chevron said that it followed all the regulations. "While we understand there is concern in the community over the flaring at the Richmond refinery, the event was within the air quality safety standards set by the state and federal government," spokesman Reddall said. Data from various sensors around the Chevron plant, which the company makes public, confir​med that. (The sensors look for compounds such as: benzene, carbon disulfide, hydrogen sulfide, sulfur dioxide, toluene and xylene.)

The Bay Area Air Quality Management District (BAAQMD) told me that the flaring was significant enough to warrant investigation—the first such case for the Chevron refinery in more than five years.

"Sometimes flaring is associated with violations [in regulations], sometimes it's an incident that causes no harm," Tom Flannigan, BAAQMD's spokesman, said. "We don't know what the ramifications are, and we anticipate it will take two to three weeks to investigate."

As De Klerk said, flaring is a safety measure in all oil refineries such as the Chevron operation in Richmond, which is what's known as a conversion refinery. Basically, the plant works like this: after the oil is distilled and separated into components (the lighter more valuable fuel is lifted out immediately), the heavier molecules are cracked, and broken down into smaller pieces, making more efficient use of each crude gallon. Then, about 200 hydrocarbons and additives are blended into what becomes mainly jet fuel, liquefied petroleum gas, and diesel.

The de-asphalter is part of the process of dealing with that second group of heavier molecules, and likely requires the use of either butane, propane, or pentane—all highly flammable, and kept in a vacuum—in order to dissolve unwanted compounds.

It's worth noting that a flare could be necessary at any number of points during refining process—each resulting in a flare of a different variety. Some burn bright, tall and look like a fireball such as the one from last week, while others are for all intensive purposes invisible. Despite inevitable environmental risks involved with burning highly pressurized materials, flaring has become a tightly regulated component integral to producing one of our society's most valuable commodities.

"It's like driving a car," Flannigan said. "We want to keep emissions as low as possible, but we know there are going to be emissions. And sometimes cars are very useful tools. So are refineries."