Refining conversion technologies: Among the classic and modern cracking routes, which process is the most widely used in oil refineries for converting heavy gas oils to gasoline and lighter products?

Introduction:
Crude fractions above the naphtha range must be converted to yield gasoline, LPG, and light olefins. Several historical and modern cracking technologies exist; identifying the dominant contemporary workhorse is essential for refinery literacy.

Given Data / Assumptions:

• Feed: vacuum gas oil and heavy gas oils.
• Objective: high gasoline yield and propylene/butylene by-products.
• Comparison across thermal and catalytic methods.

Concept / Approach:
Fluidised catalytic cracking (FCC) uses a circulating, powdered zeolite catalyst in a riser reactor, enabling continuous operation and regeneration. It largely displaced early fixed-bed (Houdry) and moving-bed (T.C.C.) systems and supplanted purely thermal approaches (Dubbs) due to higher selectivity and flexibility.

Step-by-Step Solution:

Verification / Alternative check:
Refinery capacity summaries worldwide show FCC as one of the largest conversion unit capacities after crude distillation and hydrotreating.

Why Other Options Are Wrong:

• Dubbs: Thermal, largely obsolete for gasoline manufacture.
• T.C.C. / Houdry: Early catalytic systems, replaced by FCC.
• Visbreaking: Mild thermal cracking to reduce resid viscosity, not the main gasoline maker.

Common Pitfalls:
Assuming “older named” processes are still the mainstay; technology migrated to FCC.

Final Answer:
Fluidised-bed catalytic cracking (FCC)