Optimizing Reactor Performance with 3D Printed Baffled Logpile Structures: Enhanced Heat Transfer and Reduced Pressure Drop

Significance 

The optimization of reactor performance is a fundamental challenge in Chemical Engineering and has significant implications for efficiency and cost-effectiveness in industrial processes. An important aspect of this optimization involves the design of catalytic materials and reactor geometries that enhance heat transfer, maintain adequate residence time distribution, and minimize pressure drop. Traditional approaches, such as using randomly packed beds of catalyst pellets, often struggle with inadequate radial heat transfer, leading to the necessity of reducing reactor diameters. This, in turn, requires multi-tubular configurations to maintain production capacity, which are both complex and costly. Recent advancements have explored cellular structures like honeycomb monoliths and foams that provide better heat transfer due to their high thermal conductivity and reduced point contacts. Despite these improvements, limitations persist, especially in catalyst holdup when using washcoating methods. Newer approaches have suggested packed foams and Periodic Open Cellular Structures (POCS), which achieve higher catalyst holdup and enhanced heat transfer. However, these too come with design constraints related to the particle and cell sizes of the foams. A promising and innovative solution to these challenges lies in additive manufacturing, particularly 3D printing of catalytic materials. This technique eliminates the need for a backbone structure and allows for unprecedented design freedom. Using methods such as Direct Ink Writing (DIW), intricate logpile structures can be created with independent control over particle size and porosity. While previous studies have shown the potential of these structures, their application in optimizing heat transfer and minimizing pressure drop in reactors remains underexplored. To this end, new study published in Chemical Engineering Journal and led by Professor Martin van Sint Annaland from the Eindhoven University of Technologyand conducted by PhD candidate Leon R.S. Rosseau, Timothy van Lanen, and Dr. Ivo Roghair investigated the use of 3D printed baffled logpile structures. These structures incorporate porous baffles that induce a cross-flow regime, which is expected to enhance heat transfer while maintaining a low pressure drop. By designing and experimentally testing eighteen novel cylindrical 3D printed structures, the study aims to quantify the heat transfer and pressure drop trade-offs, providing a comprehensive understanding of their performance.

The researchers performed this study to explore the untapped potential of 3D printing technology in chemical reactor design. By leveraging the design flexibility of 3D printing, they sought to create catalytic structures that can be tailored to specific process requirements. The study’s goal was to demonstrate that porous baffles within 3D printed logpile structures could significantly enhance heat transfer while reducing pressure drop, thus offering a superior alternative to conventional packed bed reactors. This research not only addresses the existing limitations of reactor design but also paves the way for more efficient and cost-effective industrial chemical processes.

The researchers conducted a series of experiments to evaluate the heat transfer and pressure drop characteristics of eighteen novel 3D printed baffled logpile structures. These structures were designed using polyethylene terephthalate glycol (PETG) due to its higher glass transition temperature and thermal conductivity compared to polylactic acid (PLA). The structures were printed using a Prusa MK3S Fused Deposition Modelling (FDM) machine. The cylindrical modules, each with an inner diameter of 44.2 mm and a height of 205 mm, were tested in a stainless steel tube. Nitrogen gas was introduced from the bottom through a porous distributor, with flow rates controlled by a Bronkhorst F-201AV mass flow controller. The top of the tube was sealed with a lid containing thermowells and a gas outlet, and pressure drop measurements were taken using a Keller Series PD-23 differential pressure transmitter. The tube’s side wall was equipped with electrical tracing to regulate the temperature, ensuring steady state conditions for accurate data collection. The experiments focused on evaluating the heat transfer performance of the structures by setting the electrical tracing to a target temperature of 353 K and recording axial temperature profiles at various flow rates. The researchers found that structures with 50 µm baffle gap spacing demonstrated superior heat transfer performance compared to a packed bed of pellets. This was attributed to the enhanced cross-flow regime induced by the porous baffles, which improved the fluid-phase heat transfer contribution. The results indicated that the number of baffles per unit length was a critical design variable. Reducing this parameter led to comparable heat transfer performance but significantly lower pressure drop, highlighting the effectiveness of porous baffles in optimizing reactor performance.

Pressure drop measurements involved increasing the flow rate in steps and recording steady state values. The data showed that porous baffles achieved a heat transfer performance only slightly lower than conventional solid baffles while offering a substantially reduced pressure drop. This finding underscored the advantage of using porous baffles, as they provide a more favorable heat transfer pressure drop trade-off compared to non-porous baffles. Additionally, the positioning of consecutive baffles at an angle was found to further improve this trade-off, demonstrating that tailored designs can meet specific process requirements effectively. The authors introduced new design variables such as the number of baffles per unit length and baffle rotation angle. These variables were systematically varied to understand their impact on reactor performance. For instance, reducing the number of baffles per unit length resulted in a significant decrease in pressure drop, up to 80%, while maintaining comparable heat transfer performance. This was a remarkable finding as it suggested that fewer baffles could achieve efficient heat transfer with much lower pressure drop, making the design more practical for industrial applications. Moreover, the researchers also explored the effect of rotating the baffles. They found that rotating the baffles in the split-recombine structure increased the convective heat transfer contribution significantly while reducing the pressure drop. This optimized design was able to offer an effective radial thermal conductivity up to three times higher than that of a packed bed of monodisperse spheres at the same pressure drop. The findings from these rotated configurations demonstrated the potential for further enhancing reactor performance through innovative structural designs enabled by 3D printing. To facilitate reactor design considerations, the experimental data was correlated, providing valuable insights into the performance characteristics of the structures under different operating conditions and design parameters. The correlations were likely specific to the current scale of the experiments, but they laid the groundwork for future studies and potential scale-up of the technology. The researchers noted that while the current findings were promising, additional simulations and experiments at different scales would be necessary to fully understand and exploit the potential of these novel 3D printed structures.

In conclusion, the study led by Professor Martin van Sint Annaland and his team demonstrated how 3D printed baffled logpile structures can effectively address long-standing challenges in reactor design, such as inadequate heat transfer and high pressure drops, which are common issues with traditional packed bed reactors. The ability of the 3D printed structures to improve heat transfer while maintaining or reducing pressure drop has profound practical implications. Enhanced heat transfer allows for more efficient chemical reactions, which can lead to increased production rates and improved product quality. The reduction in pressure drop, on the other hand, decreases the energy required to pump fluids through the reactor, leading to significant energy savings and lower operational costs. This dual benefit of improved heat transfer and reduced pressure drop can enhance the overall efficiency and cost-effectiveness of chemical processes, making them more sustainable and economically viable. One of the most important practical implications of the study is the design flexibility offered by 3D printing. The ability to tailor the geometry of catalytic materials to specific process requirements means that reactors can be customized for a wide range of applications. This customization can optimize reactor performance for specific reactions, thereby improving yield and selectivity. Additionally, the ability to easily modify design variables, such as baffle gap spacing and the number of baffles per unit length, allows for rapid prototyping and optimization, which can accelerate the development of new chemical processes. Moreover, the authors’ findings have significant implications for various industries, including petrochemical, pharmaceutical, and environmental engineering. For instance, in the petrochemical industry, where efficient heat transfer is crucial for processes like cracking and reforming, the use of 3D printed catalytic structures could lead to substantial improvements in reactor performance. In the pharmaceutical industry, where precise control over reaction conditions is essential, customized 3D printed reactors could enhance the production of high-value chemicals and drugs. Additionally, the environmental engineering sector could benefit from more efficient catalytic converters and reactors for pollution control and waste treatment.

Optimizing Reactor Performance with 3D Printed Baffled Logpile Structures: Enhanced Heat Transfer and Reduced Pressure Drop - Advances in Engineering

About the author

Leon R.S. Rosseau

Doctoral Candidate, Chemical Engineering and Chemistry, Chemical Process Intensification
Eindhoven University of Technology
The Netherlands

About the author

Professor Martin van Sint Annaland

Eindhoven University of Technology
The Netherlands

Martin van Sint Annaland studied Chemical Engineering at the University of Twente (UT, Enschede, The Netherlands) where he obtained his MSc (1994) and PhD (2000) degrees. His thesis on ‘A novel reverse flow reactor coupling endothermic and exothermic reactions’ was supervised by professors Hans Kuipers and Wim van Swaaij. In 2000 Van Sint Annaland joined the UT research group Fundamentals of Chemical Reaction Engineering (FCRE) as an Assistant Professor. In 2006 he was appointed Associate Professor. In 2010 he moved to the Department of Chemical Engineering and Chemistry at Eindhoven University of Technology (TU/e, The Netherlands), where he was appointed Full Professor. Martin van Sint Annaland chairs the research group Chemical Process Intensification.

Martin van Sint Annaland chairs the research group Chemical Process Intensification that develops novel multi-functional reactor concepts based on improved fundamental knowledge using validated advanced (multi-phase) reactor models. This is achieved by employing a combination of state-of-the-art numerical models (using the multi-level modeling approach), advanced (non-invasive) experimental techniques, and experimental demonstration of novel reactor concepts (proof of concept). Important research themes of the group include:

  1. Integration of reaction and separation. The focus here is on membrane reactors, chemical looping processes and sorption-enhanced processes and combinations thereof. Both (high temperature) packed bed and fluidized bed membrane reactors and packed bed and fluidized bed chemical looping processes are studied for many different applications.
  2. Integration of endothermic and exothermic reactions. This comprises for instance the rapid cycling reverse flow reactor to couple the endothermic propane dehydrogenation with the exothermic combustion of methane/carbon deposits. Another example is the packed bed membrane reactor with a dual function catalyst to couple the oxidative coupling and steam reforming of methane. A third example is the Cu-Ca process for sorption-enhanced steam methane reforming coupled with chemical looping.
  3. Integration of heat exchange exploiting dynamic reactor operation. This theme entails reverse flow (membrane) reactors and dynamically operated packed beds e.g. for cryogenic separation of CO2 from flue gasses, and chemical looping combustion for power production) or liquid injection (viz. induced condensing agents in gas phase polyolefin reactors).

Reference

Leon R.S. Rosseau, Timothy van Lanen, Ivo Roghair, Martin van Sint Annaland, Experimental demonstration of the heat transfer — pressure drop trade-off in 3D printed baffled logpile structures, Chemical Engineering Journal, Volume 482, 2024, 149092,

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