Coking feed selection: determine the most suitable feedstock for a delayed coking or fluid coking unit when the objective is to produce petroleum coke along with lighter products.

Introduction / Context:
Coking is a deep-conversion thermal process used to upgrade the heaviest, most refractory fractions of crude by cracking them into lighter products (naphtha, gas oils) and solid carbon (petroleum coke). Feed selection determines yields, coke quality, and unit performance.

Given Data / Assumptions:

• Process: delayed or fluid coking.
• Potential feeds: vacuum residue, light gas oil, diesel, naphtha.
• Goal: maximize conversion of heavy molecules and produce coke.

Concept / Approach:
Vacuum residue (vacuum bottoms) contains the highest boiling, polynuclear aromatic, asphaltenic, and metal-rich species that are unsuitable for distillation-based upgrading. Coking targets precisely this stream to break large molecules, reject carbon as coke, and generate usable lighter products. Lighter streams like diesel, LGO, or naphtha are not appropriate feeds for a coker and are more valuable elsewhere in the refinery.

Step-by-Step Solution:

Verification / Alternative check:
Refinery flow schemes route VDU bottoms to delayed coking, visbreaking, resid hydrocracking, or deasphalting; among these, coking is the classic route for coke production.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing feed suitability with temporary recycle streams; process design prioritizes the heaviest, least valuable fractions for coking.

Final Answer:
Vacuum residue