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Olivine is one of the refractory materials well-suited for fluidized-bed reactor technology. However, this material agglomerates at high temperatures due to the presence of sticky molten ash. The aim of this work is to investigate the mechanism of olivine agglomeration in fluidized-bed reactors and to determine the risk factors for agglomeration. A laboratory fluidized-bed reactor was designed to study the agglomeration effect between the ash and the refractory bed material. A systematic experiment was performed to determine the agglomeration ratio as a function of different parameters (operating time, bed materials, ash content, temperature, gas flow and additives). The mechanism of adhesion between the molten ash and the bed material is described, and the optimization of parameters to prevent this agglomeration is determined.

Biomass gasification is more suitable than combustion for Combined Heat and Power (CHP) applications. In this field, fluidized bed reactor technology ensures good mixing of continuously fed fuel and provides homogeneous temperature distribution in the reactor. The aim of the gasification is to produce clean syngas, thus it is important to investigate the influence of various operating conditions on the property of gas products and tar evolution. Usually, temperature and catalytic bed composition are the most studied parameters. In spite of the advantages of fluidized beds, biomass gasification suffers from technical problems such as slagging and fouling due to the high ash content and the formation of low melting point compounds and eutectic composition. The understanding of bed agglomeration requires the investigation of natural phases of biomass mineral matter and bed material. Due to the abundance of ash in biomass and its low degree of crystallization, supplementary methods have to be used beside XRD, LA-ICP-MS and SEM–EDX analysis to characterise interactions between ashes and fluidized bed material.

Steam gasification of Miscanthus X Giganteus (MXG) at high heating rate in a fluidised bed reactor with the use of olivine as catalyst was investigated. The effects of temperature (815–880 °C) on the yields and the compositions of syngas and tars were determined. The experimental results show that the gas yields and the content of H 2 increase with the temperature, while the yields of tar, char and the content of CO, CO 2 and CH 4 in the product gas decrease. Noteworthy is that about 1.1 m 3 of dry gas (at ambient conditions) per kg of dry ash free biomass were obtained with about 46% of H 2 and 24% of CO by volume at 880 °C. The tars composition was determined by FTIR, NMR and GC/MS. The identification of different compounds shows mainly the presence of simple molecules. This may be facilitating the possibility of complete tar reforming process (hot gas cleaning), to improvement of the syngas yield and the decrease of the formation of pollutants.

The Miscanthus X giganteus (MXG) presents many advantages (high yield, perennial crop, easy harvesting…) so it can be considered as a good candidate in terms of renewable energy sources. Several works have been carried out and were devoted to the MXG, especially in the agricultural field, but this study is the first which deals with gasification in order to produce syngas. The catalytic steam gasification of MXG in a fluidised bed reactor into presence of olivine based catalysts was investigated. Three parameters were studied, the temperature (800 °C and 900 °C), the pellets size (6 mm and 8 mm) and the nature of catalyst (olivine and Ni/olivine). Noteworthy is the efficiency shown by the Ni/olivine at 800 °C, which leads to the production of 1.7 m 3 kg − 1 daf of gas, containing 50% of H 2 . Ni/olivine catalyst was characterised by XRD, TPR and SEM-EDX in order to monitor its structural changes during the process. Moreover, a solvent system of tar recovery was tested, which allows to obtain a more representative set of the whole tars. Then, the tars composition was determined by GC/MS. The identification of different compounds shows the presence of different PAHs, in majority naphthalene.