What is the DEMEX unit primarily used for in a refinery?

The DEMEX unit is primarily used in a refinery to provide feedstock for the Delayed Coker Unit. This unit plays an integral role in the oil refining process, particularly in converting heavier fractions of crude oil into lighter, more valuable products. The DEMEX process focuses on extracting specific components from the heavier oil fractions, which are then used as feed for the Delayed Coker, a unit responsible for cracking heavy oils into lighter hydrocarbons and petroleum products.

In contrast, the other options refer to different processes or functions within a refinery that do not align with the primary operation of the DEMEX unit. For instance, cooling crude oil and storing refined products are functions that pertain more to other systems within the refinery layout, while separating volatile compounds typically relates to different distillation processes, rather than the specific role of the DEMEX in providing suitable feedstock for cokers.