Biochars produced with fast/flash pyrolysis in conical spouted bed reactor: potential for carbon sequestration
Keywords:Lignocellulosic biomass; biochar; Van Krevelen diagram; Carbon sequestration
With the objective of verifying the potential for environmental applications of different chars produced by fast/flash pyrolysis in a conical spouted bed reactor (CSBR), data/information was taken from previous studies, including 23 pyrogenic carbonaceous materials (PCM) produced with different anatomic parts of eight lignocellulosic biomasses as feedstocks, as follows: pinewood sawdust (Pin); poplar wood (Po); eucalyptus (Euc); orange waste (Ow); acacia (Ac); gorse (Car); rice husk (Rh) and; brow species mixture (Mix). These PCMs were classified according to Van Krevelen diagram (VK) (based on their O/C and H/C molar atomic ratios) and according to Spokas’ approach (based on their O/C molar atomic ratio). Since PCMs obtained with fast/flash pyrolysis tends to have underdeveloped structures as a result of short operation residence time (SRT) (0.05-0.11 s) and high heating rate (HR) (10³-104 °C/s), their properties are not favorable, for instance, for carbon sequestration. Even though, based on the O/C and H/C atomic ratios, all 23 PCMs met the international standards established by the Initiative Biochar Certificate (IBI) (H/C ≤ 0.7) and by the European Biochar Certificate (EBC) (O/C ≤ 0.4; H/C ≤ 0.7), being entitled to be named biochars. When the focus is placed on carbon sequestration applications, according to the EBC criterium (C ≥ 50%), besides the O/C and H/C ratio limits, four biochars obtained with rice husk biomasses were not eligible since their Carbon (C) content is <50%. Mix biochar (O/C=0.25; H/C=0.35; T=500°C) was also excluded according to Spolas’ criterium which requires O/C <0.2. The remaining 18 biochars were stable with half lifetime ≥1000 years and for these biochars, the atomic ratios and the final temperature achieved during pyrolysis (O/C, H/C, T°C respectively) were: Pin: (0.19; 0,57, 450°C), (0.10; 0.42, 500°C), (0.05; 0.19, 600°C), (0.05; 0.19, 500°C), (0.05; 0.19, 500°C), (0.16;0.51, 400°C), (0.11; 0.40, 500°C); Ac: (0.16; 0.35, 500°C); Car: (0.06; 0.34, 500°C); Euc: (0.13; 0.35, 500°C); Ow: (0.15; 0.60, 425°C), (0.15; 0.48, 500°C), (0.13; 0.43, 600°C); Po: (0.16; 0.60, 435°C), (0.14; 0.61, 455°C), (0.10; 0.55, 485°C), (0.08; 0.51, 505°C), (0.14; 0.56, 525°C). A more restrictive raking still focusing on carbon soil sequestration was made, prioritizing higher temperatures for pyrolysis (500 ≤ T ≤ 600°C), higher C content (C ≥ 50%) and O/C < 0.2, as follows: Pin (0.05; 0.19, 600°C) > Car (0.06; 0.34, 500°C) > Euc: (0.13; 0.35, 500°C) > Ow: (0.13; 0.43, 600°C) > Po: (0.14; 0.56, 525°C) > Ac: (0.16; 0.35, 500°C). However, the potential for environmental applications of these six biochars must be experimentally demonstrated since applications of biochars produced through CSBR are seldom reported in literature.
Copyright (c) 2020 Renato Rocha Batista, Gartzen Lopez, Marcia Marques
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