During hydraulic fracturing (“fracking”), part of the process involves injecting sand to keep pores of a well open. When the well is brought back online after fracking, some of that sand burps back up to the surface and into a separator.

A separator sits on the surface and separates the oil, gas, and water using heat from an internal fire tube. Gas gets siphoned off and funneled to a sales meter and then eventually to homes and businesses. Oil and water collect in onsite tanks and are eventually hauled a
Source: NDT