果冻传媒

Iron powder combustion, a promising green energy alternative, involves millions of micro-reactors burning in a vastly different process than traditional fuels. To harness this potential, a deep understanding of individual iron particle combustion is essential. The PhD research of Leon Thijs sheds new light on the mechanisms driving iron powder combustion, revealing that while oxygen transport plays a key role, unexpected mass loss occurs due to vaporization, even below the boiling point鈥攃hallenging assumptions about iron鈥檚 zero-emission potential and pushing the boundaries of sustainable energy.

Currently, 80% of the global energy relies on fossil fuels, contributing to climate change and geopolitical conflicts. There is a consensus nowadays that we should transition to renewable energy sources like hydro, solar, wind, and geothermal energy. However, these sources face challenges such as fluctuating production, seasonal mismatches, and geographic limitations in energy storage and transport. To address these issues, cost-effective and green energy carriers are needed. Among options like ammonia, hydrogen, batteries, and metal powders, iron powder is promising. It is carbon-free, recyclable, compact, cost-competitive, and widely available. The Metal-enabled Cycle of Renewable Energy suggests using iron for sustainable, long-distance transport and long-term storage of clean energy.

Self-sustained micro-reactor

Iron powder, typically in the order of 10-100 micrometers, can potentially be combusted in existing coal-fired power stations with minimal modifications. The resulting iron oxide can be captured and reduced back to iron powder using renewable energy where and when it is available. This iron powder can then be transported back to power and heat generation facilities, closing the sustainable energy cycle. But the question is, how does an iron powder flame burn, how can it be stabilized and what about unwanted emissions? To answer such questions, we need to understand and predict the combustion process up to the single particle level. Burning iron powder involves millions of particles, creating a process vastly different from conventional gaseous and coal combustion. In iron powder combustion, each iron particle remains in the condensed phase, acting as a self-sustained micro-reactor that consumes oxygen and releases heat. To fully understand this process, it is crucial to understand the combustion behavior of these individual iron particles.

Understanding key processes

Thijs aims to develop this understanding by investigating the key processes that govern the combustion of individual iron particles using advanced numerical models, using models with different levels of detail and combining simulations on both small (nanometer) and large (micrometer) scales and comparing results with experiments.

In this study, he systematically examined the impact of three mechanisms on the oxidation process. The rate at which an iron particle burns, is determined by the interaction of three key mechanisms:

1.         Oxygen transport to the surface: Oxygen molecules from the surrounding gas must reach the iron particle's surface.

2.         Oxygen consumption at the surface: Once at the surface, the iron particle needs to absorb and react with the oxygen molecules.

3.         Internal transport of iron and oxygen atoms: Inside the iron particle, iron and oxygen atoms need to move and react with each other.

The research has shown that by considering oxygen transport to the surface as the rate-limiting process, our models can reasonably replicate the experimentally observed temperature changes over time for individual iron particles burning in normal air. Additionally, it was shown that a small but significant amount of iron evaporates during combustion, affecting its zero-emission potential. To improve model accuracy and applicability across various conditions, it is essential to include the other two key processes. Since these processes are influenced by atomic-scale phenomena, molecular dynamics simulations were performed. These simulations explored the surface interactions between iron particles and incoming oxygen molecules, as well as the transport properties of atoms within the particle.

ERC funding

Research into iron combustion is a big part of the Power & Flow group of the Mechanical Engineering department. Thijs is the first PhD candidate who graduated within the ERC project of Prof. Philip de Goey. Read more on this research in /en/news-and-events/news-overview/05-05-2023-philip-de-goey-receives-erc-proof-of-concept-grant-for-research-into-metal-fuels.

Title of PhD thesis:. Supervisors: Prof. Philip de Goey, Prof. Jeroen van Oijen, and Assistant Prof. Xiaocheng Mi.

An interview with Leon Thijs

What is the most relevant outcome from your research and how could thisimpact society?

The transition to renewable energy requires not only the production of solar and wind energy but also efficient methods for storing and transporting large amounts of energy. Iron powder is considered a promising energy carrier because it is carbon-free, widely available, and recyclable. To design and optimize real-world iron-fuel burners, a thorough understanding of the fundamentals of fine iron particle combustion is necessary. In my research, we developed several models to enhance this understanding, giving us a clearer picture of how individual particles burn. This knowledge is crucial for improving processes in large-scale iron powder burners. For example, it was previously believed that no iron was lost through evaporation during combustion due to its heterogeneous burning nature. However, our research has shown that, despite the particle temperature staying below its boiling point, a small but non-negligible mass loss occurs through evaporation under certain conditions. This could impact the recyclability of iron and potentially compromise its zero-emission characteristics. Our models now allow us to better predict when this evaporation might happen and how to prevent it.

Question 2:

What was the most significant finding from your research, and what aspects turned out to be most important to you?

I wouldn鈥檛 say I have one single significant finding; rather, it is the collective impact of the results that has progressively enhanced our understanding of single iron particle combustion. For me, the most important achievement is that we have significantly advanced our understanding over the past few years. With this knowledge and the developed models, we can now take a major step toward realizing iron powder combustion. Of course, there is still much to learn, and we have established clear directions for continuing this research.

Question 3:

What was your motivation to work on this research project?

Working on a topic that contributes to the energy transition provided an additional sense of purpose to my daily work, as this is a highly relevant issue. Additionally, since this was a relatively new field, there was much to explore, and we were at the forefront of understanding this technique, which was truly exciting. 

Question 4:

What was the greatest obstacle that you met on the PhD journey?

The greatest obstacle during my PhD was the lack of experimental data. When developing a model, you need experimental data to validate it and support certain hypotheses. Since this research was in a new field, there was limited data available, making it challenging to validate our hypotheses. Over time, more experimental data became available, which sometimes disproved our assumptions (a positive outcome, as it meant we learned new things). 

Question 5:

What did you learn about yourself during your PhD research journey? Did you develop additional new skills over the course of the PhD research?

Thanks to the excellent supervision of my (co-)promoters and collaborators, I became a better scientist during my PhD. Additionally, by presenting my work at several international conferences, I significantly improved my soft skills, such as presenting my results. I also had the opportunity to acquire new technical skills. We initiated a collaboration with Imperial College London, where I learned to use molecular dynamics simulations. These simulations provided deeper insights into atomic interactions, which are crucial for advancing our understanding

Question 6:

What are your plans for after your PhD research?

Although I really enjoyed my PhD and like working at the university, I have decided to leave academia and move to industry.  I will start on October 1st at the R&D department of Canon Production Printing in Venlo, where I will be working on developing models related to inkjet printing.