Abstract
In this paper, the yields and composition of solid and condensable products that were obtained by microwave-assisted torrefaction of softwood, wheat straw, and peat fuel pellets, defined as main- and side-stream torrefaction products, were studied. The torrefaction process, at temperatures varied in the range of 200–300 °C, was performed using a laboratory-scale torrefactor of original construction. Water-enriched fractions were distilled off from condensable products to isolate tar fractions, the fuel characteristics of which were compared with those of solid fractions. Py-GC/MS/FID, GC/MS/FID, thermal analysis, elemental analysis, and wet chemistry methods were used to characterize the main- and side-stream torrefaction products, with a focus on their valorization according to the biorefinery approach. The simultaneous development of the destruction and condensation processes in lignocarbohydrate complexes during microwave treatment leads to an increase in the relative portion of aromatic compounds in torrefied biomass, increasing the higher heating value (HHV) of the solid fractions. The increase up to 60% of the heat amount that was liberated due to the thermal oxidative conversion of solid fractions vs. that of the non-treated ones was established by DSC tests. The heat that was liberated by the combustion of the tar fractions was much lower than that of solid fractions, which was explained by the composition of tars, influencing their thermal conversion.
Highlights
Publisher’s Note: MDPI stays neutralThe European strategic long-term vision for the modern, competitive, and climate neutral economy is executed in accordance with the Paris Agreement, reaching net-zerogreenhouse gas (GHG) emissions as early as possible and by 2050 at the latest [1]
Its contribution to climate change accounts for 40% of the global CO2 emissions from energy use and about 72% of the total greenhouse gas (GHG) emissions from the electricity sector [3]
The mass balance of the fractions that were obtained as a result of MW-assisted torrefaction, coupled with the data of the water content in the starting biomass, testified that drying was the dominant but not the single process of biomass transformation by MWassisted processing at 200 ◦ C
Summary
The European strategic long-term vision for the modern, competitive, and climate neutral economy is executed in accordance with the Paris Agreement, reaching net-zero. GHG emissions as early as possible and by 2050 at the latest [1]. The propriety of this long-term strategy was supported by the decisions of the 26th United Nations Climate. Among other fossilbased energy resources, coal is the single biggest contributor to anthropogenic climate change. Its contribution to climate change accounts for 40% of the global CO2 emissions from energy use and about 72% of the total greenhouse gas (GHG) emissions from the electricity sector [3]. According to the Glasgow summit decisions, 750 coal-fired power with regard to jurisdictional claims in published maps and institutional affiliations
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