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Combustion for Low Emission Applications of Natural Gas

Periodic Reporting for period 1 - CLEAN-Gas (Combustion for Low Emission Applications of Natural Gas)

Reporting period: 2015-01-01 to 2016-12-31

The scientific goal of CLEAN-Gas is to develop new experimental and numerical tools for improving natural gas combustion in innovative burners.

Due to its widespread availability and its environmental and technological benefits, Natural Gas is of great interest to the European Energy policy. Therefore a deep understanding and high-level training in the experimental and numerical tools for investigating natural gas combustion in new burners are of upmost importance for future developments.

Forecasters predict that natural gas consumption in the EU will double over the next 25 years. European natural gas consumption currently represents approximately 17% of world consumption. European gas imports are expected to reach slightly over 80% of total consumption by 2030. To tackle this challenge, the EU is investing heavily in natural gas equipment, as demonstrated by the construction of the Nabucco pipeline in Turkey. The use of natural gas makes it possible to divide CO2 emissions nearly by 2 compared to coal. It also enables the use of gas turbines with an efficiency close to 50%. Natural gas is present in all sectors from companies/business to personal/private sector.

Natural gas is a fossil fuel whose energy conversion is mainly achieved by combustion. The combustion process induces two main side effects: the production of greenhouse gases (CO2) and the emission of pollutant species such as nitrogen oxides (NOx) and soot particles. Conventional techniques used to reduce these emissions, already low compared to usual fossil fuels, are often post-combustion treatments and they include CO2 storage, flue gases cleaned up by catalytic and non-catalytic conversions. Another solution is to act directly on the combustion process in order to limit pollutant emissions at the source while maximizing combustion efficiency. New processes are currently using this strategy, for example regenerative burners, flameless combustion, combustion of highly diluted mixtures or oxy-combustion.

These processes, already used in some industrial units, are still poorly understood and very difficult to transpose from one industry to another. Therefore, it is extremely important to develop academic and research studies on these new combustion processes to make best use of existing resources while limiting their environmental impact. These new processes are very different from existing technologies and constitute real technological breakthroughs.

These points show that deep understanding and detailed experiments and modelling of the combustion processes are of paramount importance. In particular, the appropriate description of the interactions between the combustion process, and the system aerodynamics is crucial in order to develop innovative combustion systems. Considering the complex nature of these phenomena, the use of both experimental investigations and Computational Fluid Dynamics (CFD) is acknowledged to be essential for the development and implementation of such novel combustion technologies.
The project involves the development of a comprehensive kinetic mechanism to model the pyrolysis, oxidation, and combustion of natural gas with predictive capabilities in a wide range of operating conditions. Special attention has been devoted to thermodynamic data and to the chemistry of pollutant species, particularly PAHs, carbonaceous particles (soot) and NOx. The kinetic mechanism has been improved also for unconventional combustion conditions, such as diluted MILD (Moderate or Intense Low oxygen Dilution) conditions, on the basis of the coupling of kinetic simulations with Uncertainty Quantification (UQ) and Principal Component Analysis (PCA).

The complex interactions between kinetics and turbulence have been studied especially in MILD combustion regime conditions by developing simulation tools able to provide high-fidelity numerical experiments. Particular attention was devoted to the application/extension of the EDC approach to Large Eddy Simulations. Moreover, the LES methodology was extended to the Thickened Flame (TF-LES) model using a flame-wrinkling factor to further investigate flame/turbulence interactions.

Since in many industrial devices lean-premixed flames are stabilized by a swirling flow, during the project several experiments studied the dynamics of flame stabilization and the flame response to flow disturbances, using a loudspeaker to generate the flow modulations. Thermo-acoustic instabilities, blow-off and flashback limits were experimentally characterized during the project. A specific burner is under investigation to provide a reliable dataset of turbulent flames experiments for the validation of numerical simulation tools in the pressurized conditions of interest for gas turbine combustion.

Finally, a multi-physics LES tool has been used for the simulation of industrial-scale combustion devices, with the aim to study the combustion process. Particular attention was devoted to the role of radiative energy transfer and to the effect of different configurations (oxygen enrichment, CO2 dilution, high pressure) on the emissions from turbulent methane flames.
Main outcomes of the program are skilled people, scientific and transferable knowledge.

Fundamentally, the highest outcome of the program is skilled people. They will be well-trained candidates in Natural Gas combustion and its applications in a general context of environmental needs. After following the research program in an international environment, they should become high quality scientists/experts mastering the necessary tools and methodologies from a cross approach perspective (theory, computation and experimentation), and professionals able to address the main challenges in the domain.

The second outcome is scientific knowledge and expertise. Providing around 8 research doctoral work per year, all connected together and gathered into a group of high-level international universities, within their usual research activities research groups, will certainly increase scientific knowledge in combustion. The multi-scale (from micro-phenomenon to macro) and multi domain approach (chemistry to fluid mechanics) will contribute greatly to the knowledge development. Novel functionalities and new innovative routes may be identified and developed both in the numerical approach and in the practical applications themselves. Moreover, great enhancement in experimental set-ups is expected from the partnership. Publications, conference participations, seminars or other such communication should be significant and will be taken as a success indicator for the program.

The third main outcome concerns the transfer of such knowledge. Based on scientific studies and the company environment, products should be developed for direct application to the market. Intellectual property right and patents will be addressed and clearly defined in each doctoral work. The number of patents will be an additional indicator of success.

A fourth outcome will be an international thematic network and community among T.I.M.E. Association but also beyond. By working together, sharing events and setting up an alumni group, a real network within the Combustion Science community, especially for Natural Gas, will be generated. Partners already have some collaboration together, but CLEAN-Gas will be the chance to develop new common and unified perspectives.
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