Lucio DE FUSCO's PhD Thesis

Assessment of ash agglomeration and fouling in combustion by theoretical and experimental biomass fuels characterization

Among the priorities of the EU, there is the need for harvesting large amounts of renewable energy to progress the transition to a lowcarbon economy. Flexible biomass provision is envisaged for energy system predictability and for the valorization of renewable feedstock.
Nevertheless, biomass is greatly varying in its physical and chemical properties: especially, the variability in the inorganic matter (ash) concentration has an impact on the fuel behavior in conversion plants, e.g. in combustion, inducing operational challenges. Consequently, the
use of opportunity fuels such as agro-residues and bio-refinery wastes, is limited. In fact, the current characterization of biomass has a limited value for operational decisions.

The objective of this Thesis, developed in collaboration with ENGIE Electrabel, is to develop tools for biomass characterization with a focus on ash challenges in combustion: agglomeration, slagging and fouling.

After the introduction, a model to compute the fuel propensities to induce agglomeration - slagging issues as a function of the ash composition is presented. Such simplified model is applied to characterize unconventional Mediterranean fuels. As a second step, a more fundamental approach based on equilibrium phase diagrams (e.g. K2OSiO2-CaO) and thermochemical equilibrium calculations is proposed and applied to ten opportunity fuels. Computational and experimental tools are integrated with the development and the validation of a 5-step fuel
characterization methodology applied to four woody fuels, including tests in a circulating fluidized bed pilot reactor. A detailed study on fouling of sunflower husks burned with mineral additives, including tests in a drop tube furnace, is finally addressed.

The characterization tools developed and validated in this Thesis allow, given a specific fuel, the preliminary evaluation of the risk of ash challenges in combustion: the key for an efficient fuel screening with the objective of operational excellence.

Membres du jury :

Prof. Hervé Jeanmart (UCL), promoteur
Prof. Laurent Delannay (UCL), président
Dr. Véronique Dias (UCL), secrétaire
Prof. Francesco Contino (VUB)
Prof. Julien Blondeau (VUB)
Dr. Yves Ryckmans (ENGIE Lab, Belgique)
Dr. Françoise Defoort (CEA, France)
Prof. David Chiaramonti (UniFi, Italie)