Abstract
A thermosyphon-fixed bed reactor was designed and constructed to investigate the temperature distribution of the cassava rhizome and its decomposition behavior. To study the properties of torrefied char obtained from this reactor, cassava rhizome was torrefied in five different configurations, including the thermosyphon-fixed bed reactor, a laboratory reactor in compact bulk arrangement with N2 as the purge gas and without any purge gas, and another one in a hollow bulk arrangement with and without purge gas. It was found that the use of thermosyphons with a fixed bed reactor improved the uniform temperature distribution. The average heating rate to the cassava rhizome bed was 1.40 °C/min, which was 2.59 times higher than that of the fixed bed reactor without thermosyphons. Compared to the other configurations, this reactor gave the highest higher heating value (HHV) and the lowest mass yield of 23.97 MJ/kg and 47.84%, respectively. The water vapor produced in this reactor played an autocatalyst role in the decomposition reaction. Finally, the thermosyphon-fixed bed reactor gave an energy yield in the range of 70.43% to 86.68%. The plot of the HHV ratio–mass yield diagram indicated the difference of torrefied char obtained from different reactors. The thermosyphon-fixed bed reactor produced torrefied biomass with the highest HHV ratio compared to that of other reactors at the same energy yield.
Highlights
Torrefaction is a biomass upgrading process using a thermal degradation reaction
In terms of process parameters, it is revealed that the increase of temperature and resident time resulted in the increase of higher heating value (HHV), grindability, and hydrophobicity [4,5,6,7,8,9,10,11,12,13,14]
The average heating rate to the cassava rhizome bed was 1.40 ◦ C/min, which was quite low compared to the heating rate of the electrical heated fixed bed reactor reported by Budde et al [21] (10 ◦ C/min.)
Summary
Torrefaction is a biomass upgrading process using a thermal degradation reaction. Since the process temperature is in a range of 200–300 ◦ C, the torrefaction process is sometimes called mild pyrolysis [1,2,3]. The outstanding advantage is the higher retained energy of the residual solid product, compared to that of the other pyrolysis process, i.e., carbonization. These advantages lead to a number of studies on both process parameters and reactor design torrefaction. The increase of particle size resulted in the decrease of the weight loss of biomass [16,17]. The compact bulk arrangement resulted in the higher degree of decomposition and value of HHV compared with that of the hollow bulk arrangement. This result was explained, in that water produced during torrefaction
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