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17 páginas.- 16 figuras.-5 tablas..- 50 referencias., The impact of biochar modification on its behavior towards the adsorption and cracking of naphthalene (in a mixture naphthalene/toluene) as tar model compound has been investigated. Both tar adsorption and cracking may be considered alternative tar cleaning technologies which enable its further energetic use. Biochars were produced using different feedstocks and process conditions to tune their physico-chemical and morphological properties. Beech wood, representative of woody biomass, and almond shell and rice husk, representative of agricultural residues, were used. Furthermore, beech wood was also washed with deionized water and doped with KCl and FeSO4. Biochars were produced at 700 degrees C under several atmospheres (pure N2 and mixtures of N2, CO2, H2O, and CO), resulting in different physico-chemical properties and thus naphthalene adsorption and cracking behavior. Naphthalene adsorption experiments were performed at 250 degrees C and naphthalene cracking experiments were carried out at 750 degrees C and 850 degrees C. The performance of the investigated biochars towards naphthalene adsorption and cracking depended strongly on the production conditions, with biochars produced under reactive atmosphere (including N2, CO2, and H2O) yielding the best behavior. For naphthalene adsorption, an easily accessible high surface area seemed to be the dominant parameter determining the biochar adsorption capacity. Wood doping with FeSO4 resulted in biochars with higher adsorption capacity due to the formation of mesopores and Fe clusters within these mesopores that could likely enhance the adsorption capacity. In the case of naphthalene cracking, biochars produced under reactive atmosphere (G1) with untreated wood and H2O-washed wood showed the highest naphthalene conversion. In this case, the specific surface area was not the most relevant parameter determining the biochars performance. Wood doping with KCl had a negative impact on naphthalene cracking, while wood doping with FeSO4 impacted positively when the biochar was produced in N2 atmosphere, but negatively when produced in reactive atmosphere (G1), likely due to the oxidation state of Fe. Biochars from agricultural residues and woody biochars, produced under the same conditions, performed similarly.

Biomass combustion is an important pathway of energy generation from renewable resources. Even though biomass combustion is an established conversion process, there is a high potential for further optimization of the used technologies. In particular, the advantage of numerical methods for the improvement of biomass combustion systems is not used to its full extent, because the simulation of these complex systems requires various sub-models for the thermo-chemical conversion of the biomass and sufficient computational resources for the combustion simulation. However, simulations are a valuable tool to enhance the design and operating conditions of biomass combustion systems with regard to high efficiency, low emissions and high flexibility. In addition, comparison of experimental and numerical results leads to a better understanding of the processes involved in biomass combustion. The present study gives a comprehensive overview of simulations of biomass combustion systems based on computational fluid dynamics that are available in the literature. It focusses on systems with fixed bed and covers various technologies (moving bed, pellet boilers, wood log stoves) as well as a wide range of sizes from laboratory reactors to industry scale. Besides woody biomass, also alternative fuels such as straw or municipal solid waste are considered. All relevant sub-models for the thermo-chemical conversion of the fuel on the one hand and for the gas-phase combustion on the other hand are discussed in detail. The recent advances in the concerned research fields are described.

In the framework of a European project, a straw combustion boiler in conjunction with an organic Rankine cycle is developed. One objective of the project is the enhancement of the combustion chamber by numerical methods. A comprehensive simulation of the combustion chamber is prepared, which contains the necessary submodels for the thermo-chemical conversion of straw and for the homogeneous gas phase reactions. Part I introduces the modelling approach for the thermal decomposition of the biomass inside the fuel bed, whereas part II deals with the simulation of the gas phase reactions in the freeboard.