Defluidization and agglomeration of a fluidized bed reactor during Cynara cardunculus L. gasification using sepiolite as a bed material

Abstract

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.

Cynara cardunculus L. gasification in a bubbling fluidized bed: The effect of magnesite and olivine on product gas, tar and gasification performance

“…In the present study this value was 11.38 % (dry basis) including added kaolin which had been mixed with the C. cardunculus L (Table 1) to prevent agglomeration. Previous gasification studies had reported some agglomeration problems when gasifying this energy crop due to the high amounts of alkali metals such as K and Na [23][24][25][26]. The amount of kaolin added was 3 wt.% of the biomass loaded into the feeding system.…”

“…The agglomerates were found to be formed by a melted phase rich in sodium, potassium, calcium, magnesium and silicon. Serrano et al [26] used silica sand and an alternative bed material, sepiolite, in order to compare the defluidization time and agglomerates during cardoon gasification at different air velocities and observed that the sepiolite delayed the defluidization time by up to an order of magnitude compared with silica sand. These studies show that the use of different bed materials such as magnesite, olivine or sepiolite can delay agglomeration and suggest that dolomite can be used to completely avoid it.…”

Agglomeration detection by pressure fluctuation analysis during Cynara cardunculus L. gasification in a fluidized bed

“…In this sense, a previous work of Serrano et al [30] showed different agglomeration and defluidization processes for Cynara cardunculus L. gasification. On the one hand, jetsam behavior of fuel particles was found in a bed formed by sepiolite particles.…”

“…Similar results were obtained for the rest of fluidization velocities. Finally, the defluidization time for all the tests is compared to previous results reported by [30].…”

“…At this point, biomass feeding was stopped and signals were acquired for another 300 s. After this time, the electrical furnaces and the air supply were shut down and the reactor was cooled down. More detailed information about the experimental setup is described in [30].…”