Abstract
Gasification of biomass in fixed bed gasifiers is a well-known technology, with its origins dating back to the beginning of 20th century. It is a technology with good prospects, in terms of small scale, decentralized power co-generation. However, the understanding of the process is still not fully developed. Therefore, assessment of the changes in the design of a gasifier is typically performed with extensive prototyping stage, thus introducing significant cost. This study presents experimental results of gasification of a single pellet and bed of particles of raw and torrefied wood. The procedure can be used for obtaining design parameters of a fixed bed gasifier. Results of two suits of experiments, namely pyrolysis and CO2 gasification are presented. Moreover, results of pyrolysis of pellets are compared against a numerical model, developed for thermally thick particles. Pyrolysis time, predicted by model, was in good agreement with experimental results, despite some differences in the time when half of the initial mass was converted. Conversion times for CO2 gasification were much longer, despite higher temperature of the process, indicating importance of the reduction reactions. Overall, the obtained results could be helpful in developing a complete model of gasification of thermally thick particles in a fixed bed.
Highlights
Nowadays the importance of renewable energy sources, such as biomass, is increasing due to the increased international pressure to gradually phase out the fossil fuels
This is especially the case for the torrefaction performed within the course of this study, with residence time of 15 min
This could be attributed to the way of performing torrefaction—i.e., bed of torrefied material was not packed and there was no flow of gas through the bed of material
Summary
Nowadays the importance of renewable energy sources, such as biomass, is increasing due to the increased international pressure to gradually phase out the fossil fuels. Torrefaction is a process of thermal valorization of solid fuel in order to enhance its fuel properties subsequently allowing low-grade fuels, such as biomass, to become a tradable commodity [4]. Energies 2020, 13, 3018 sometimes called slow pyrolysis and it typically takes place at temperatures between 250 ◦ C and 300 ◦ C with residence times ranging between 10 min and 60 min [4,17,18,19,20,21,22,23,24,25,26]. Some literature sources treat torrefaction as mild pyrolysis, which is a thermal decomposition of the organic material under the absence of oxygen [27]. Released volatile organic compounds are typically unstable and are a subject of secondary reactions such as cracking, recombination or re-polymerization [30], with the latter taking place even in the pyrolysis oil [28]
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