Making lighter work of heavier oil

Refiners are now entering an era of processing heavier crudes to meet increasing demand for high quality transportation fuels. However, these heavier crudes present many new operational challenges, including their higher percentage of residue. This is more difficult to upgrade economically using either traditional hydrogen-addition technologies such as fixed-bed residue desulphurisation or well-established carbon-rejection technologies such as delayed coking.

Fixed-bed residue desulphurisation technology is characterised by its relatively low conversion rate of 25%. Although delayed coking offers higher conversion, it is non-selective and produces a high yield of coke, which is ever more difficult to market. Heavier residue processing at higher conversion can also lead to fouling (sludge) in the products (fuel oils) and in the unit’s hardware. The latter can reduce the efficiency of the heat exchangers or cause a pressure drop build-up in the reactor section, both of which potentially lead to premature unit shutdown and loss of margin.

In countries like China, the increasing demand for transportation fuels means greater reliance on imported heavier crude oils from countries such as Venezuela.

Fixed-bed residue desulphurisation integrated with fluidised catalytic cracking and delayed coking is the main residue upgrading technology in Chinese refineries today. However, Chinese refiners need higher residue conversion to meet demand while maintaining a low carbon footprint. “This is what we call the bottom-of-the-barrel upgrading challenge,” says David McNamara, Technical Manager, Residue Upgrading, CRI/Criterion Marketing Asia Pacific Pte Ltd. “Every refiner worldwide will have to convert more of the bottom of the barrel into high-quality transportation fuels and do so with lower greenhouse gas emission levels.”

Shell Global Solutions and Criterion Catalysts & Technologies have a platform of different technologies to help refiners address this challenge. “Our approach is to design a customised solution for each specific refinery or unit operation. The days of applying an off-the-shelf solution to fit all are gone,” says McNamara. “By customising, we try to help refiners obtain as much as possible from their existing hardware without major investment.

Many of our solutions are customised drop-in packages, for example, an improved catalyst system with Shell Global Solutions reactor internals to provide optimal catalyst utilisation and pressure drop control. These can be retrofitted during a normal unit turnaround (typically one month), so the unit does not need to be shut down for a lengthy period and incur high margin losses.

“We have adopted what we call the 4Cs approach – chemistry, composition, conditions and catalyst – to design optimal solutions to help our customers meet the residue upgrading challenge,” he continues. “Understanding the residue’s chemistry is crucial to the customised approach. Each refiner has a different process configuration, crude slate and environmental demands. We need to understand how best to make the right chemistry happen to achieve the required conversion rates and product specifications while minimising side reactions that will deactivate the catalyst. It is a very fine balance.”

It is also very important to characterise the residue’s composition properly, for example, by analysing for saturates, aromatics, resins and asphaltene content. This gives a better idea of the upgrading quality of the feed and its fouling behaviour. Vacuum residue (the bottom of the bottom of the barrel) is far more likely to destabilise during processing and cause fouling in a residue upgrading unit than atmospheric residue. As refiners aim for higher conversion of heavier oils, controlling fouling becomes the key parameter influencing an achievable on‑stream factor.

“Operating conditions play an important role in both controlling the rate of catalyst deactivation and influencing the rate of fouling. If an operation has a high fouling tendency, we can factor that into the catalyst design, for example, by custom designing the active sites to ensure higher asphaltene removal selectivity, as asphaltenes would otherwise cause fouling,” says McNamara.

By understanding these variables, Criterion can design the most suitable catalyst solution for a particular refiner. “We use the 4Cs approach to learn as much as possible about the feed’s reactivity and fouling tendency, and the unit operation, including any limitations, then use this information as key input in developing the customised design,” he adds.

However, customised catalysts need to be properly utilised once loaded in the unit. Shell Global Solutions reactor internals are well established at helping to optimise catalyst utilisation in hydroprocessing units, including fixed-bed residue desulphurisation operations. For example, the Shell Global Solutions High Dispersion tray is a proven technology for optimal liquid and gas distribution in multiple refinery hydroprocessing applications and is now being more widely applied in fixed-bed residue desulphurisation applications targeting heavier oil processing.

The Shell Global Solutions filter tray is another important reactor internal designed to trap physical foulants entrained in the residue feed for the duration of a typical cycle in a fixed-bed residue desulphurisation unit. Installed in the front end of these units, the filter tray removes physical foulants (particulates, scale, corrosion products, etc.) by a deep bed filtration/sedimentation mechanism, which controls pressure drop build-up sufficiently to avoid it becoming cycle limiting when processing heavier crude.

Shell Global Solutions can also draw on its in-house residue upgrading process design and operating experience in developing customised solutions. One of the key features of the Shell-Global-Solutions-designed fixed-bed residue desulphurisation unit is that it has multiple beds, which enable the temperature to be controlled more efficiently. With three beds per reactor and a quench between beds, refiners can operate each section of the reactor at the same temperature and thereby control catalyst deactivation more effectively than in the single fixed-bed residue desulphurisation units that are more commonplace.

The Shell HYCON residue upgrading unit at Pernis refinery in the Netherlands has been operating for over 20 years. It is the only unit in the industry incorporating a fixed-bed residue desulphurisation unit that can successfully process 100% vacuum residue. The front end of the unit is designed to remove the heavy metals (nickel and vanadium) in the feed. It features a daily fresh catalyst addition/spent catalyst withdrawal operation for constant metals removal.

The Shell HYCON unit’s hybrid design provides residue conversions of up to 70% with a cycle length of 22 months. This also remains a record in the industry.

Shell Global Solutions also offers customised debottlenecking solutions for fluidised catalytic cracking units. In most cases, fixed-bed residue desulphurisation units are operated as feed pretreatment units for the fluidised catalytic cracking unit. The advent of heavier crude processing results in lower conversion of the residue, which means additional feed of lower quality for routing to the fluidised catalytic cracking unit. Under these circumstances, debottlenecking of the fluidised catalytic cracking unit is required to maintain good unit economics.

For grassroots heavier oil (residue) upgrading units, more refiners are turning to the well-established ebullated-bed hydroconversion technology, which provides conversion approaching 80% of vacuum residue. This trend is being driven not only by the heavy oil upgrading challenge but also by the greater need to upgrade more vacuum residue, as its traditional market outlets such as asphalt and high-sulphur fuel oil are eroding.

Shell has experience of operating both types of ebullated-bed unit licensed technologies: Axens’ H-OilRC and Chevron Lummus Global’s LC-FINING technology. Additionally, Criterion has over 40 years’ experience in ebullated-bed catalysts and currently supplies customised catalysts to H-OilRC and LC-FINING units. A recent enhancement of Criterion’s customised approach is an alliance with Headwaters Technology Innovation Group to exclusively offer HCAT^® liquid molecular catalyst technology together with Criterion ebullated-bed catalysts.

Being a liquid, HCAT nanocatalyst intimately mixes with the feed and is therefore not limited by the diffusion effects that occur in larger solid catalysts. It effectively brings the active site to the heavy oil molecules. Moreover, the intimate mixing with the vacuum residue feed means that HCAT catalyst also enters the thermal zone of the ebullated-bed reactor thereby catalytically enhancing, along with the solid catalyst, the conversion and the selectivity of the residue upgrading process in the entire reactor volume.

Combined with Criterion’s ebullated-bed solid catalysts, HCAT technology can help to increase vacuum residue conversion and improve product quality while effectively controlling fouling. It is another good example of a customised drop-in solution for maximising the unit on-stream factor during heavier oil processing.

The combined package of Shell Global Solution process design expertise and advanced reactor internals and Criterion’s customised catalysts offers refiners cost-effective, easy-to-implement residue upgrading solutions for getting more out of their existing and new units when rising to the heavy oil upgrading challenge. “With this combination of process expertise, high-quality reactor hardware and customised catalysts at our disposal, we can apply the right technology to the right feed in the right residue upgrading unit,” concludes McNamara.