In which oil refinery unit does high-temperature distillation occur?

High-temperature distillation primarily occurs in the coker unit of an oil refinery. The coker is designed to convert heavy crude oil residues into lighter, more valuable products through a process known as coking. This involves subjecting the feedstock to high temperatures, which breaks down larger, heavier molecules into smaller fractions, allowing for the production of valuable products such as gasoline and diesel.

While the distillation column, crude unit, and reforming unit play crucial roles in the refining process, they operate under different principles. The distillation column is used for separating mixtures based on differences in boiling points, but the conditions aren't as extreme as in a coker. The crude unit processes raw crude oil into various fractions, but it does so without reaching the high temperatures characteristic of coking. The reforming unit, aimed at improving the quality of gasoline, operates under catalytic processes that involve moderate temperatures, distinct from the high temperatures utilized in coking.

Thus, the coker is the correct answer as it specifically employs high-temperature distillation techniques to transform heavy residues into lighter, more marketable products.