This work studies the defluidization time and the agglomerates generation in a Bubbling Fluidized Bed (BFB) reactor during Cynara Cardunculus L. gasification using, separately, two different bed materials, silica sand and sepiolite (Mg 8 Si 12 O 30 (OH) 4 (OH 2 ) 4 8H 2 ). The high adsorption capacity and the elemental composition of the sepiolite make it suitable as an alternative bed material in order to reduce agglomeration. Experiments were performed on a stainless steel lab-scale BFB reactor operating with air as gasifying agent at different air excess ratios (u/u mf ). A quartz reactor was alternatively used for the visualization of bed material and biomass during gasification, allowing to observe the agglomerate formation process. Pressure signals were analyzed both in time and frequency domain to determine the defluidization time.Furthermore, the shape and size of the bed material after the experiments were evaluated.Higher defluidization times in the case of sepiolite were measured. Particle sizes were affected by the type of bed material and the air excess and agglomerates of different shapes were formed for sepiolite and silica sand.

Gasification of Cynara cardunculus L. was performed in a bubbling fluidized bed (BFB) using air as the gasifying agent and magnesite and olivine as different bed materials. Temperature was varied during the experiments (700-800 ºC) with fixed biomass feeding and air flow rates.The effect of using the magnesite and olivine on the gas and tar composition, carbon and biomass conversion, and cold gas efficiency was investigated. The product gas showed high hydrogen content (13-16 %v/v) for both magnesite and olivine in the temperature range studied.Higher heating value and gas yield were improved with increasing the temperature from 700 to 800 ºC. Biomass and carbon conversion were greater than 75%, giving values higher than 90 % for both 700 and 800 ºC in magnesite and for 800 ºC in olivine. Indane and cresols were the main tar compounds at low temperature while naphthalene was the dominant tar species at the high temperatures. Gasification performance was better with magnesite at 700 ºC while olivine showed better properties at 800 ºC.

h i g h l i g h t sJetsam and flotsam behavior of fuel particles was analyzed using pressure signals. Cynara cardunculus L. was gasified in a lab-scale FB using sepiolite and silica sand. Agglomeration mechanisms: cap-clinker formation and entire bed defluidization. Wide band energy and attractor comparison tool showed similar results. Wide band energy can identify and characterize each agglomeration mechanism. a b s t r a c tThe bed material and the fuel particles are the main actors in the agglomeration process in a bubbling fluidized bed reactor during a gasification conversion. The physical and chemical reactions between them determine whether the bed operates under a proper fluidization condition or the quality of the fluidization is deteriorated due to agglomerates appearance inside the bed. This work analyzes the pressure signals of a fluidized bed during Cynara cardunculus L. gasification in a reactor with an inner diameter of 52.8 mm. Jetsam and flotsam behavior of fuel particles is analyzed using sepiolite and silica sand as bed materials, respectively. The wide band energy and the attractor comparison tool are used to detect agglomeration, and, as a consequence, the defluidization of the bed. Similar defluidization times are obtained employing both methods. The wide band energy analysis shows that, for jetsam fuel particles, the endogenous bubbles produced by the fuel devolatilization inside the bed change the energy distribution, while for flotsam fuel particles, the cap-clinker agglomerate formed is detected by high frequencies in the power spectrum.

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Two-phase heat transfer model of a beam-down gas-solid fluidized bed solar particle receiver.

SynopsisThe percolation model has been applied to the study of gelation of the TGDDM-DDS system (tetraglycidyldiaminodiphenylmethane-~~nodipheny~ulfone) at a mass concentration of 100-30. For each temperature the experimental viscosity curves are satisfactorily described by a percolation law. Using the degree of chemical reactions, X, as a variable, a very clear change in the reaction mechanism with temperature can be shown. Then a rate of advancement of effective reactions, Y, is defined. This value only takes intermolecular-type reactions into account, and is probably the only variable on which viscosity depends in a percolation law:We obtain Y, = 0.45 and p = 2.0. Comparing X , and Y, a t the gel point, we obtain information on the proportion of intramolecular reactions with temperature. It is also demonstrated that the critical percolation threshold agrees closely with the gel point determined experimentally on log G" = f ( t ) curves.

Nitrate solar salt as heat transfer medium for thermochemical conversion of biomass.• Solid carbonaceous materials promotes the molten salt degradation.• Shift from endothermicity to exothermicity process due to solid carbonaceous material.• Higher gas yield is obtained when using molten salt as heating medium.• Less complex bio-oil composition compared with fixed bed pyrolysis.