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Fouling of heat exchangers in biomass combustion plants is an operational problem that can lead to a severe decrease of boilers efficiency and availability. To counteract deposition, additives are used to bind the vaporized alkali in high melting temperature structures, such as solid phosphates or aluminum-silicates. Fouling during the combustion of sunflower husks with a combination of P- and Ca-based additive (H3PO4and CaCO3) and Al-silicates additives (kaolin or halloysite) was studied in a test campaign in a Drop Tube Furnace. Fouling tests with additives were compared with reference experiments with the raw fuel (two tests). Thermodynamic equilibrium computationswith FactSage 7.0 and state-of-the-art databases were applied to quantifythe ash molten fractionat 900°C, the mass of liquid per kg of biomass, the K-release rate to the gas phase and finally the condensed mass at 200°C.The use of additives decreased Cl and P (apart from the test with P addition) concentrations in the inner deposits and increasedthe amount of loose deposits on the probe. When computing the enrichment factors of the deposits with respect to the ash injected, K concentration in RAW1 deposits, with respect to RAW1 ash, is enriched of 14% (mol/mol). When using the P+Ca additive, K is depleted in deposits by 46%. With the use of aluminumsilicate additives, K is enriched by 4% for the HAL deposit and depleted of 21% for the KAO case.

In the recent years, a growing interest for low-quality biomass fuels is observed, in both small- and large-scale combustion plants. Such fuels include wood mixtures and forest residues, short-rotation energy crops, herbaceous biomass (e.g. straws) and agricultural or fruit residues. The combustion of these fuels often portends technical operational issues, which include agglomeration of inorganic particles in fluidized beds and ash slag formation in combustors. A simplified fuel characterization approach has been developed in this work, with the objective to define the agglomeration and slagging propensity of biomass fuels for their use in combustion boilers. Among the variables that influence these complex mechanisms, the fuel inorganic composition is considered in this model. The outcome of the model is a parameter in the range 0 - 100 that indicates the specific fuel propensity to induce agglomeration and slagging issues in combustion applications. The model outcomes are validated with experimental results from literature and from laboratory tests in a pilot circulating fluidized bed reactor. The developed tool is build to be used for screening and preliminary selection of solid biomass fuels for combustion., Proceedings of the 23rd European Biomass Conference and Exhibition, 1-4 June 2015, Vienna, Austria, pp. 1782-1786

Among the renewable sources of energy, biomass solid fuels hold a special place. They are indeed at the crossroads between the need for renewable sources on the one hand, and the established know-how on solid fuel combustion on the other hand. Moving from coal to biomass (co-)combustion in an existing pulverised-fuel utility boiler is therefore an effective way to get closer to the current environmental targets. However, biomass and coal present important differences. The size of the particles, the amount and the type of volatiles emitted during pyrolysis, and the composition of the inorganic compounds (ash) are the main differences that significantly impact the combustion of pulverised biomass. A detailed numerical model of a biomass particle undergoing pyrolysis, called SPY, was developed. It combines a detailed chemical mechanism and a physical model of a fibrous particle. The use of apparent kinetic parameters derived from SPY in CFD simulations of utility boilers was proposed to improve their accuracy. A Drop Tube Furnace was designed to reproduce the conditions encountered in utility boilers. Such an experimental tool is useful in the investigation of combustion kinetics and ash deposition phenomena. The fouling of heat exchangers was reproduced, and the deposits were analysed to obtain an insight into their formation and deposition mechanisms. The developed numerical and experimental tools may accurately respond to the current needs in both applied and fundamental research on biomass combustion. (FSA 3) -- UCL, 2013

International audience; Let $\KST$ be the maximal pro-$p$-extension of the cyclotomic $\Z_p$-extension $\K^{cyc}$ of a number field $\K$, unramified outside the places above $S$ and totally split at the places above $T.$ Let $\GST=\Gal(\KST/\K).$ In this work we adapt the methods developed by Schmidt in \cite{schmidt2} in order to show that the group $\GST=\Gal(\KST/\K)$ is of cohomological dimension $2$ provided the finite set $S$ is well chosen. This group $\GST$ is in fact \textit{mild} in the sense of Labute \cite{labute}. We compute its Euler characteristic, by studying the Galois cohomology groups $H^i(\GST,\fq_p)$, $i=1,2.$ Finally, we provide new situations where the group $\GST$ is a free pro-$p$-group.

Deformation extensions slightly branched P; Déformation des extensions peu ramifiées en P