This was the case at S-Oil’s Onsan refinery in Ulsan, South Korea. This leading refiner was dissatisfied with the cycle length of its hydrocracker, and installing Shell reactor internals and next-generation catalysts from Criterion Catalysts & Technologies (Criterion) proved to be a robust, high-value solution. S-Oil calculates the value to its operations as in excess of $20 million a year.
S-Oil’s Onsan facility is the fifth largest refinery in the world and has an extremely complex configuration that includes a hydrocracker, a residue fluidised catalytic cracking unit, an aromatics complex and a state-of-the-art lubricants base oils plant. This enables it to produce high-value light oil products such as gasoline, diesel and kerosene, as well as petrochemicals and group 2 and 3 lubricants base oils.
With a corporate goal of becoming the most competitive oil refiner in Asia Pacific, S-Oil is continually striving to maximise its performance and profitability. So, when the cycle length of its hydrocracker was curtailed, management took steps to rectify the situation by working with Criterion and Shell Global Solutions.
The single-stage, two-reactor, 170-bar, 75,000-bbl/d hydrocracker was originally licensed from another vendor. The unit’s most valuable output is unconverted oil, which is routed to the wax hydroisomerisation unit and then the hydrofinishing unit to make Group 3 base oils. It also produces large amounts of middle distillates and smaller quantities of less-valuable liquefied petroleum gas and naphtha.
S-Oil had desired a cycle length of 36 months but the unit had only achieved 32 months in the previous cycle and other cycles had been even shorter. Pretreatment limitations meant that, at the end of run, the unconverted oil quality tended to decline. Consequently, S-Oil had to derate the base oil unit to maintain product quality and there was little opportunity for deeper processing of vacuum gas oil (VGO).
Meng Loong Chua, Senior Technical Service Engineer, Criterion Catalysts & Technologies, was part of the team that investigated the unit. He explains that, on the pretreatment portion, the existing catalyst was suboptimal in stability and losing activity too quickly over the cycle. There was also suboptimal catalyst utilisation that resulted in the short cycle length. “We found that there was a high radial temperature spread over the catalyst beds,” he says.
“This indicates low uniformity of vapour–liquid distribution and suggests that the catalyst bed is not being used efficiently, which can shorten cycle life.” In the cracking reactor, there was extra activity left in the last cycle and this provided the opportunity to optimise the cracking catalyst towards more middle distillate production and better hydrogenation for the unconverted oil production.
To address these issues, the team replaced the internals in both the hydrocracker’s reactors. The new hardware that it fitted included Shell high dispersion (HD) trays, Shell ultra-flat quench (UFQ) interbed internals, Shell catalyst support grids and Shell bottom baskets.
In addition, Criterion tailored a stacked-bed catalyst system that was designed to deliver balanced activity and selectivity, an optimal product slate and significantly better-quality unconverted oil. This was informed by a series of pilot plant tests that used S-Oil’s actual feeds (see below)