How does a retort extract oil from crushed oil shale?

A retort extracts oil from crushed oil shale through a process called pyrolysis. Because oil shale contains kerogen rather than free-flowing oil, it must be heated to break the chemical bonds of the kerogen macromolecules.12

In a surface retort, the crushed shale is placed in a specially designed vessel that facilitates rapid heating in an oxygen-free environment. The rock is heated to temperatures typically ranging from 480 to 550 °C (900 to 1,020 °F). This thermal treatment liberates liquid and gaseous hydrocarbons, along with nitrogen, sulfur, and oxygen compounds.1

Various methods are used to transfer the necessary heat to the shale, including:
* Internal-combustion: Burning gases or a portion of the shale itself to generate heat.1
* Hot-recycled-solids: Circulating heated inert materials or burned shale through the retort.1
* Conduction through a wall: Applying heat electrically or by burning fuel outside the retort wall.1
* Externally generated hot gas: Injecting remotely heated gas into the retort zone.1
* Reactive fluids: Using chemically reactive fluids, such as high-pressure hydrogen, to heat and stabilize the hydrocarbons.13