Which refinery process is considered semi-batch (opposed to continuous)?

• A. Hydrocracking
• B. Delayed coking
• C. Catalytic reforming
• D. Distillation

Answer: (B)

In refinery operations, semi-batch means the process runs in distinct cycles rather than a constant, unbroken flow. Delayed coking fits this idea because it uses coke drums in cycles: a batch of heavy residue is charged into a drum, heated and cracked to produce liquids, gases, and solid coke. After a set period, the drum is isolated, the coke is removed, and another batch is charged into a drum for the next cycle. While one drum is on line, others are prepared or emptied, so throughput happens in steps rather than a continuous stream.

In contrast, hydrocracking and catalytic reforming are designed for steady-state, continuous operation where feed is constantly fed and products are continuously withdrawn. Distillation columns are also normally continuous separators, where a steady feed and continuous product streams are maintained to separate components by boiling point. So delayed coking is the semi-batch process among these options.