Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PhD : selection by topics

Engineering science >> Thermal energy, combustion, flows
2 proposition(s).

Study of biomass mixture reactivity (ash and carbon matrix)

Département Thermique Biomasse et Hydrogène (LITEN)

Laboratoire de Préparation de la Bioressource

01-01-2019

SL-DRT-19-0258

francoise.defoort@cea.fr

The context is the thermochemical valorization of unused biomass waste (agricultural or forestry residues) in energy vectors (combustion, gasification for 2G biofuels). These biomasses have properties (composition and ash content) inducing liquid phases that may or may not be desirable depending on the processes. The objective is to formulate biomass mixtures based on the thermodynamic equilibrium between solid and liquid phases to adapt the proportion of liquid to the needs of the processes. The main lock to check is to obtain a chemical reactivity. Dilution of the existing phases of the resources to be blended will not produce the desired effect. Furthermore, it must be verified that the carbon matrix of the biomass mixture has a gasification / combustion kinetics compatible with the processes. The thesis will focus on the study of the presence of liquid phase in the ashes of biomasses and their mixtures by melting / quenching then characterization SEM-EDX and XRD, the kinetics of chemical reaction of ashes by X-ray diffraction at high temperature, the kinetics of combustion/gasification of the carbon matrix of biomasses and their mixtures in thermobalance by thermogravimetric analysis TGA and study of the grain size of biomasses on chemical reactivity (ash, carbon matrix) The results obtained on the ashes may give rise to a chemical reactivity model and those on the carbon matrix can then be integrated into the kinetic models already developed in the laboratory, which will extend the validity of the latter to biomass mixtures.

Study and Optimisation of combined cold and heat production for thermal networks

Département Thermique Biomasse et Hydrogène (LITEN)

Laboratoire Systèmes Solaires Haute Température

01-10-2019

SL-DRT-19-0691

nicolas.lamaison@cea.fr

Heating demand represents a major part of the total energy consumption (about 40% in France for example). In parallel, residential and tertiary cold demand keeps increasing (+80% for the next 10 years at the European scale). Moreover, the ever-increasing integration of photovoltaic or wind electricity may eventually lead to over voltage and thus instabilities of the power grid. Finally, it is well proven that energy storage is more efficient and cheaper using thermal rather than electrical means. Thus, smart synergies must be found between these two energy carrier. In that context, the present PhD thesis aims at studying the combined production of cold and heat for District Thermal Networks (DTN) using a thermal/electrical co-optimization framework. First, we will focus on the different production/conversion technologies available for the thermal and electric carriers such as simultaneous heating and cooling heat pumps (SHC-HP), absorption heat pumps (A-HP), electrical resistance, etc? and for storage. We will define the advantages and breakdowns of each system depending on the domain of application. The most promising system in terms of applicability will be then studied in details in a second phase. We will particularly develop a sizing methodology, based on MILP methods (Mixed Integer Linear Programming). With the latter, the potential conflictual objectives of production (heat vs cold) will be accounted for in the problem formulation and thus in the sized system. To do so, a physico-mathematical systematic approach accounting for uncertainties will be implemented. Finally, we will study the system from an operational point of view both numerically and experimentally, notably to evaluate the real level of performance of the sized system.

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