Besides improved catalyst systems, what advances in reactor internals are improving efficiency and throughput while also mitigating the effect of fouling and catalyst poisons?Mar-2023
Torkil Ottesen Hansen, Topsoe, TIH@topsoe.com
Examples of reactor internals that improve reactor performance by means of reduced fouling and pressure drop build-up include dedicated scale catchers like Topsoe’s proprietary 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 reactor internals will, in this connection, contribute relatively more to the combined reactor performance. In recent years, some focus areas have targeted renewable feeds fouling and coking potential as well as dealt with the high exotherms. It was necessary to rethink some of the otherwise very successful features used in the ULSD wave and fossil feed processing in general.
Andrew Layton, KBC (A Yokogawa Company), firstname.lastname@example.org
Since 1990, flow distribution has become increasingly 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 effectiveness 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 viewpoint. In addition, the newer units no longer use interbed dump tubes, which created maldistribution issues. A variety 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 permitting 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 downstream effects
• Collectively, this forms part of the unit’s KPI monitoring to track reliability.
Jeff Kaufman, Becht, email@example.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 mixing 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 reactor. 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 temperature 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.
Dinesh-Kumar Khosla, Axens, dinesh-Kumar.firstname.lastname@example.org
Finding the right combination of catalyst and reactor internals is essential for reliable and profitable reactor operation.
In units featuring fixed-bed reactors, along with optimum catalyst design, overall reactor/catalyst performance can be enhanced by using high-efficiency reactor internals. Axens’ proprietary EquiFlow reactor internals ensure a uniform gas/liquid distribution and optimum mixing in the reactor, thereby minimising channelling and hot spots to ensure optimal use of the entire catalyst inventory in the reactor. This enhances catalyst activity, selectivity, and stability, and minimises catalyst changeout frequency while ensuring safe and reliable operation.
EquiFlow distributor trays employ a dispersive system 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 filtering 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 systems. 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 CO2 footprint associated with specific unit operation.
*Note: EquiFlow, Hy-Quench-XM, Hy-Quench-NG, and Hy-Clean are marks of Axens.