Refinery Operations

The Keys to Maximizing Diesel Production

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Single stage with recycle yields a typical conversion of approximately 98 per cent. Diesel is the major product of hydrocracking and its yield can be typically as high as 75 per cent (weight basis) in a two stage hydrocracking. Diesel obtained from hydrocracking can be almost free from sulfur and can therefore meet stricter regulatory specifications such as Euro V without further treatment.

Feed for hydrocracking can be light vacuum gas oil (LVGO) and heavy vacuum gas oil (HVGO) from heavy coker gas oil (HCGO) from coker unit, or visbreaking gas oil (VBGO) from the visbreaking unit. Fluidized Catalytic Cracking Fluidized catalytic cracking (FCC) is a process in which a heavier oil fraction is converted to lighter fractions such as LPG (rich in C3 and C4 olefins), FCC gasoline, light cycle oil (LCO) in a catalytic process.


The unconverted fraction is removed as heavy cycle oil (HCO), which is used as a cutter stock for fuel oil blending. LCO has a boiling range of diesel but has a lower cetane index due to higher aromatics contents. It may also have a higher sulfur quantity than required by regulatory specifications. Therefore, it has to be hydrotreated to reduce the sulfur level and increase its cetane index by the saturation of aromatics. The hydrotreated LCO is added to diesel pool.


Coking is a thermal cracking process that converts vacuum residue, a heavy oil fraction, into valuable lighter products such as fuel gas, LPG, naphtha, light coker gas oil (LCGO), heavy coker gas oil (HCGO). Petroleum coke is also produced in the process.

LCGO boils in the boiling range of diesel and, therefore, undergoes the process of hydrotreating to produce diesel. HCGO boils in the boiling range of vacuum gas oil (VGO). Hence, it can be fed to the FCC unit or hydrocracker unit. Hydrocracker produces diesel as a major product. The FCC unit also produces diesel through hydrotreating of LCO.