While the world reliance on combustion is set to continue, to satisfy our energy needs, we need to advance combustion science to develop new technologies that can handle CO2
-neutral fuels efficiently, and without producing pollutants. Some examples of new combustion technologies have been proposed recently, and implemented in some practical devices. However, these low-emissions combustion regimes are very complex and very difficult to predict, making impossible to transpose solutions from one industrial configuration to another. What we aim to accomplish in CLEAN is to combine the most recent advances in computer science and high performance computing, to decode the complexity of turbulent reacting flows and develop new models that can be used, with confidence, to develop fuel-flexible, efficient and clean combustion technologies.
Born in 1980. PhD in Chemical and Material Engineering (Università di Pisa), Master in Chemical Engineering (Università di Pisa). Post-docs at University of Utah and the Von Karman Institute. Associate Professor at the Aero-Thermo-Mechanics Department (ULB), Vice-president of the Belgian Section of the Combustion Institute, Chair of the ULB-VUB Research Group « Combustion and Robust Optimization ». Prof. Parente has been awared with the Fonds Renard for sustaining research (2011) and with prestigious national and international grants and programs, notably: European Research Council, Marie Curie Innovative Training Network, EU Horizon 2020.
1. Climate change, renewable energies and the storage challenge
The energy supply is one of the great societal challenges we are facing. When talking about energy conversion, we do not often recognize the role combustion plays today. If we think for a moment about our everyday life, the products we use, how we get to work or home, to meetings, to visit family and friends and go on holiday, we soon realize that almost any activity has a power signature. Most of this energy, about two thirds, comes today from combustion.
Combustion is, however, the major source of air pollution and a major contributor to CO2 and climate change. A recent UN report indicated that the concentration of CO2 in the atmosphere has reached 405.5 parts per million (ppm). If we continue on this slope, in 50 years we will pass the 500 ppm level, entering in a very dangerous zone of climate change, with temperature increase likely above 3 °C and catastrophic effects for our planet. As of today, we have almost depleted our carbon urgent to limit the temperature increase to 1.5°C, as recommended by the COP21 in Paris, to limit climate change effects. Without further ado, it is time to act.
New developments in renewable energy are fundamental to assure the energy needs of future generation, within a sustainable growth model. Yet, one fundamental challenge affects a society solely relying on renewable sources, their intrinsic intermittency. We all know that wind and solar energies are characterized by daily and seasonal changes, and they have very strong spatial dependency; likewise, geothermal and hydroelectric sources are only available at specific sites and impose precise constraints in terms of exploiting infrastructures. Thus, the intermittent nature of renewable sources requires the development of storage solutions that can guarantee the availability of the required energy supply when renewable sources are not available.
Battery-based storage is very effective for short-term storage: batteries have among the best electrical roundtrip efficiencies and they should therefore be used in case of interday and intraday storage. Their energy reservoir is however limited to a few hours by the high capacity cost.
Long-term energy storage (seasonal storage) and energy intensive processes (long-range passenger transportation and manufacturing processes) require, on the other hand, high energy densities (tens of MJ per kg), which can realistically only be provided though the transformation of chemical energy into heat and work.
We are left, then, with an apparently unsolvable paradox, namely, the awareness of the significant negative impact of combustion-based technologies and, at the same time, the acknowledgement that the world reliance on combustion is set to continue, to satisfy our energy needs. The objective of CLEAN is centered on the solution of this paradox, to show that there is no inconsistency between the renewable technologies and novel combustion technologies for new energy carriers.
2. The future energy mix and the integration of renewable sources and combustion
The future energy mix will include a variety of fuels. Power-to-X (P2X) technologies allow to store the excess renewable energy in the form of chemical compounds, characterized by the very high energy densities and, thus, representing ideal candidates for long-term storage and energy-intensive industrial processes and transportation. These chemical compounds are generally referred to as Smart Energy Carriers (SEC), and they include hydrogen (the easiest molecule that can be formed by water electrolysis), ammonia (an effective way to store hydrogen in liquid form by combining it with atmospheric nitrogen), methane (combining hydrogen with recycled carbon dioxide coming from capture and storage processes), but also methanol and other synthetic fuels for targeted applications (for air and ground transport, power generation, …). The availability of SECs can potential lead to a seamless integration of renewable sources and combustion technologies (Figure 1), in the framework of a circular economy model, where the dependency on fossil fuel sources can be progressively dismissed, as Figure 1 indicates.
The availability of different fuel sources is an attracting opportunity. It can contribute to decarbonize the power supply, accommodate the fluctuating demand of energy and to shape a more secure energy supply for the future, with less geopolitical inhomogeneities.
Interestingly, energy storage in smart new energy carriers makes the role of combustion crucial. For the power-to-X concept to be effective and viable, novel combustion technologies shall be developed, to accommodate the expected fuel flexibility without compromising the energy efficiency and pollutant emissions. This is far from being the case today. Indeed, industrial process are optimized considering the specificity of the used fuel. Making them “fuel flexible” will be a major engineering challenge for the next decades.
One possible solution is to imagine to tailor fuels to technologies, but this might have limitations depending on the local availability of fuel building blocks (e.g. carbon dioxide). A better approach is to develop technologies that can operate efficiently and without harmful emissions regardless of the fuel. We collectively indicate these technologies with the name of MILD combustion.
3. Novel combustion technologies
Figure 2 – The energy trilemma: our society needs an affordable, secure and environmentally friendly energy supply.
To meet the long-term objective of CO2 neutrality and mitigate the effects of global warming, the combustion field requires profound innovation. MILD combustion technologies potentially offer a solution to this, for the ability of guaranteeing fuel-flexibility, while ensuring very high energy efficiency and virtually zero pollutant emissions (figure 2).
MILD combustion originates from a change in perspective in combustion science, cultivated in the last decades. Previously, it was not considered possible to obtain both high efficiency and low pollutant emissions and a trade-off had to be accepted between the two, because the problem was only studied from an energetic perspective. Nowadays, combustion is treated and controlled as a chemical reactor, which allows to simultaneously meet environmental and energetic needs, and to accommodate the flexibility of fuel resources expected in future years (Figure 3). Some examples of MILD combustion technologies have been designed in recent years, and implemented in some devices. However, these low-emissions combustion regimes are very complex and very difficult to predict, making impossible to transpose solutions from one industrial configuration to another.