Distillate treatment consists of processes designed to remove contaminants, including nitrogen and sulfur compounds.  Treatment also improves physical properties, including thermal stability and color stability, to transform distillates into products of greater purity and market quality.  Often, these processes rely on catalytic reactions.  Catalysts are different in physical & chemical properties depending on the treated distillates.  For instance, to treat kerosene, liquid catalysts are needed to accelerate the process; on the other hand, to treat naphtha in the Hydrotreating Unit and diesel in the Hydrodesulfurization Unit, solid catalysts are needed along with hydrogen under high temperatures and pressure.

Since the naphtha derived from the CDU contains low octane numbers along with unsuitable quality for gasoline blending, it undergoes a process to split it into light naphtha and heavy naphtha, which then proceed to different treatment units.  Light naphtha proceeds to the Isomerization Unit (ISOM) to raise the octane number from 65-70 to 88-89, which contain no aromatics contaminants, thus making it suitable for blending into low-aromatics gasoline.  On the other hand, heavy naphtha proceeds to the Continuous Catalyst Regeneration Unit (CCR) to raise its octane number from 40-50 to 102-103.

The residue from the CDU, commonly termed long residue, enters the High Vacuum Unit (HVU), where Vacuum Gas Oil or VGO (a type of diesel) is distillated from the short residue inside the Fractionation Tower under high temperature and vacuum.

VGO is then fed into the Fluidized Catalytic Cracking Unit (FCCU) at elevated temperatures to crack molecules into high-octane gasoline and diesel.  Out of this process, coke forms on the catalysts.  To revive these catalysts and reuse them, the coke is burned in the Regenerator unit.  An option is to feed light residue into the Hydrocracking Unit (HCU) under high temperature and pressure to crack the molecules and improve their quality to high-value White Oil, namely naphtha, kerosene, and diesel.

As for the short residue derived from the HVU, it proceeds to the Thermal Cracking Unit (TCU) for quality improvement up to the market-dictated values with a process under a high temperature – high pressure environment.  Emerging is residue with lower viscosity plus some gasoline and diesel.  Thaioil has planned, however, to stop TCU operation once it has to produced 0.5-percent-weight sulfur residue consistent with the International Marine Organization (IMO) standard, since the quality of the TCU residue is not suitable to produce such product.  The key objective of the residue conversion process is to lower the volume of low-quality residue while raising the volume of white oil products, including gasoline and diesel, which have premium market values and increasing flexibility for choosing various crude types.  Finally, such residue conversion process also enhances gross refining margins over hydro-skimming refineries.

As a rule, a complex refinery yields assorted middle distillates commonly used for fuel blending, thus giving rise to various combinations for premium products.  Nevertheless, each product need to be blended with precision, additives & dyes injection to meet market need and product standards.  Thaioil currently uses in-line blending for blending gasoline and diesel, leveraging a computerized system of blending ratio control in parallel with online analysis for controlling product quality.  This efficiently modulates proportions to yield products meeting quality requirements.  For Fuel oil, it is blended by batch blending.