Partial conversion, or “mild” hydrocracking, has been used by refiners for years to produce incremental middle distillate yields while upgrading feedstock for fluid catalytic cracking (FCC). Unfortunately, the combination of low pressure and high temperatures needed for hydroconversion often results in heavy, high-aromatic diesel products with low cetane quality.
Old problem – new solution
To resolve the issue, Topsoe re-invented partial conversion hydrocracking. We developed our Staged Partial Conversion process (SPC) to produce low-sulfur FCC feed – and to enable ULSG production without gasoline post-treatment – while co-producing high-quality EN 590 diesel.
The SPC process incorporates a staged reaction system in which a portion of the heavy gas oil product from the lead hydrodesulfurization (HDS) reactor is bypassed on flow control. This reduces the net charge rate to the second series flow hydrocracking (HDC) reactor. SPC allows the net conversion level in the second reactor to be substantially higher than the overall gross conversion requirement for producing FCC feed. Increased conversion dramatically improves middle distillate product quality.
A high gas/oil ratio creates a favorable operating environment within the HDC reactor.
Severity in the lead reactor is controlled, depending on the minimum HDS requirement for the FCC feed, to make ultra-low sulfur gasoline. Severity in the lag reactor is controlled independently to meet ultra-low sulfur kerosene and diesel fuel requirements, such as smoke point, density, and cetane quality.
The SPC prevents the risk of “overtreating” the FCC feed and delivers the FCC feed and ULSD quality you want. At a lower cost and with less hydrogen consumption than conventional MHC units.
Staged Partial Conversion Process Layout