located below a chimney tray to ensure close-to-ideal vapour/liquid distribution throughout the catalytic bed underneath. EquiFlow quench systems (Hy-Quench-XM, Hy-Quench-NG) feature a more compact design.* This results in smaller reactors in grassroot configurations and increased catalyst volume for existing reactors. These quench systems provide higher thermal efficiency over a wider range of operating conditions, resulting in longer catalyst cycles and/or higher throughput operation. To mitigate the effect of fouling, the EquiFlow smart fil - tering tray system (Hy-Clean) limits recurrent pressure drop problems while ensuring a perfect gas/liquid distribution in reactors.* It will prevent plugging of the bed by catching and retaining feed impurities that are often responsible for crust formation between the different catalyst layers. Notably, with the use of Hy-Clean, there is no additional pressure drop compared to conventional distributors or quench sys- tems. Overall, Hy-Clean will enable a significant increase in catalyst cycle length, leading to higher profitability. Reduction in reactor operating temperature and pressure drop with Axens’ EquiFlow reactor internals also result in lower CO 2 footprint associated with specific unit operation. *Note: EquiFlow, Hy-Quench-XM, Hy-Quench-NG, and Hy-Clean are marks of Axens. A Jeff Johns, Becht Advisor, jjohns@becht.com, Jeff Kaufman, Becht Advisor, jkaufman@becht.com, Steve DeLude, Becht Advisor, sdelude@becht.com, Gene Roundtree, Becht Advisor, groundtree@becht.com Improved understanding of feed quality, reactor and flow modelling through reactor systems (CFD modelling) has allowed licensors and catalyst vendors to improve their internals and tailor their catalyst systems. Improved feed filtration systems reduce particulate and fouling on top catalyst beds. Improved distribution trays/internals and quench mix- ing allow better utilisation of loaded catalysts and reduce the risk of partial bed bypassing and/or hot spot formation. These increase the potential operating range for the reac- tor. In addition, the best new internals designs take up less space (allowing more room for active catalyst). They are designed for easy assembly and disassembly, reducing unit downtime during a turnaround and catalyst replacement. We also note that when new internals are installed in existing reactors, the upgrade should strongly consider new bed temperature indicators (TIs) for better tempera- ture control and reactor monitoring. Finally, graded/tailored catalyst loads, including specifically designed materials for fine particulate and/or maximum metals trapping, allow sustained operation with high catalyst activity and reduced fouling/pressure drop. A Andrew Layton, Principal Consultant, andew.layton@ kbc.global Since 1990, flow distribution has become increas - ingly important as product quality moves to ppm levels. Distributor tray design has changed to mitigate the impact of levelness and flow rate issues using better chimney
design. Adding spray nozzles to the trickle bed flows has improved coverage. Distributor trays often lose effective- ness over time due to thermal cycling, poor gasketing, poor construction, and few sites following optimum checking procedures during changeout. This situation has led to poor performance and activity losses exceeding 50%, often a bigger effect than changing to a better catalyst. The design of the beds has also been improved to optimise mass velocity and bed height. For example, increasing bed depth will cause some loss of good distribution as no bed is perfectly loaded, and the impact worsens as the bed gets longer. The bed loading procedures have improved with the advent of faster, more effective dense loading machines. New unit designs take turnaround and loading needs into account, including improved distributor tray access and, sometimes, more direct access to each bed rather than top loading only. This is also a better option from a safety view- point. In addition, the newer units no longer use interbed dump tubes, which created maldistribution issues. A vari- ety of approaches are now used to mitigate fouling issues in the reactor, including: • Separate foulant collection trays • Multiple bed grading with differing sizes, higher surface area, high metals capacity • Scale traps, or surface area enhancers, can be justified in severe cases if they increase surface area in the right spot with modified design and size, depending on the foulant • Bypass devices, which alleviate pressure drop by permit- ting partial bypass as pressure drop builds. Note that tackling a fouling problem in the reactor is a mitigation instead of a solution to the root cause. To improve operations, the following upstream factors should be examined: • Analyse and size-check foulants • Modify procedures to minimise foulant movement • Upgrade construction materials • Optimise filter design and focus on the right streams to filter, but not necessarily all • Minimise tankage feed • Solve upstream corrosion issues, usually at the primary fractionator • Improve desalter designs • Careful use of chemicals and consideration of down- stream effects • Collectively, this forms part of the unit’s KPI monitoring to track reliability. A Torkil Ottesen Hansen, Senior Technology Director, Topsoe, TIH@topsoe.com Examples of reactor internals that improve reactor per- formance by means of reduced fouling and pressure drop build-up include dedicated scale catchers like Topsoe’s pro- prietary HELPsc that can be installed in the reactor head to capture particulates brought in with the feed before they plug the catalysts beds. Another example would be improved distributor trays with capacity for sediments without obstructing the distribution. Continuous development of reactor internals technology will permit use of more complicated feeds in the future. The
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Catalysis 2023
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