Changes of chemical and mechanical behavior of torrefied wheat straw

Abstract

13The purpose of the study was to investigate the influence of torrefaction on the grindability of wheat straw. 14 Straw samples were torrefied at temperatures between 200 ˚C to 300 ˚C and with residence times between 0.5 to 15 3 hours. Spectroscopic information obtained from ATR-FTIR indicated that below 200 ˚C there was no obvious 16 structural change of the wheat straw. At 200-250 ˚C hemicelluloses started to decompose and were totally 17 degraded when torrefied at 300 ˚C for 2 hours, while cellulose and lignin began to decompose at about 270-300 18 ˚C. Tensile failure strength and strain energy of oven dried wheat straw and torrefied wheat straw showed a clear 19 reduction with increasing torrefaction temperature. In addition, Hardgrove Grindability Index (HGI) of wheat 20Page 2 of 23 straw torrefied at different conditions was determined on a standard Hardgrove grinder. Both results showed an 21 improvement of grindability in the torrefaction temperature range 250-300 ˚C, which can be well explained by 22 the findings from FTIR analysis. At a torrefaction temperature of 260 ˚C and with a residence time of 2 hours, 23 wheat straw samples produced similar HGI values as coal (RUKUZN) with 0% moisture content. Under this 24 condition, the Anhydrous Weight Loss (AWL%) of the wheat straw sample was 30% on dry and ash free basis 25 (daf), and the higher heating value of the torrefied wheat straw was 24.2 MJ kg -1 (daf). The energy loss 26 compared to the original material was 15% (daf). 27

Torrefied Biomass Pellets—Comparing Grindability in Different Laboratory Mills

“…Bridgeman et al [16] measured the modified HGI of torrefied willow and found values between 24 and 51 mainly depending on the difference in TF time (10 vs. 60 min) while the TF temp was in both cases at 290 • C. The pellets from torrefied willow analysed here had a HGI of 34 which is between the two HGIs measured by Bridgeman et al [16] probably due to a higher TF temp (308 • C) at similar TF time (9 min). Interestingly, the results obtained by Bridgeman et al [16] and Shang et al [34] compare well to the results obtained here even though the torrefaction in these two studies was done in lab-scale reactors as compared to the pilot-scale torrefaction which might affect homogeneity of the product.…”

“…Regarding a comparison with standardized Hardgrove coals by applying the modified HGI method, forest residue and straw had the highest value (HGI = 55) which reflects a low energy input, better grindability and potentially a higher throughput while spruce and beech had the lowest HGI values (HGI = 25 and 21 respectively) being not so favourable for grinding. Similar to the method used here with 50 cm 3 samples, Shang et al [34] investigated the HGI of torrefied wheat straw at different TF temp with a residence time much higher (2 h) than any of the TF time used here. The HGI of the pellets made from straw torrefied at 270 • C for 30 min analysed here (HGI = 55) is therefore slightly below the value observed by Shang et al [34] for straw torrefied at 250 • C for 2 h (HGI ≈ 60).…”

“…Similar to the method used here with 50 cm 3 samples, Shang et al [34] investigated the HGI of torrefied wheat straw at different TF temp with a residence time much higher (2 h) than any of the TF time used here. The HGI of the pellets made from straw torrefied at 270 • C for 30 min analysed here (HGI = 55) is therefore slightly below the value observed by Shang et al [34] for straw torrefied at 250 • C for 2 h (HGI ≈ 60). Bridgeman et al [16] measured the modified HGI of torrefied willow and found values between 24 and 51 mainly depending on the difference in TF time (10 vs. 60 min) while the TF temp was in both cases at 290 • C. The pellets from torrefied willow analysed here had a HGI of 34 which is between the two HGIs measured by Bridgeman et al [16] probably due to a higher TF temp (308 • C) at similar TF time (9 min).…”

Thermal Pre-Treatment of Sewage Sludge in a Lab-Scale Fluidized Bed for Enhancing Its Solid Fuel Properties

“…In addition, Shang et al [41] performed torrefaction of wheat straw and concluded that the upper limit of temperature, i.e., 300 °C, is the desired temperature for torrefaction. Contrarily, Jeeban et al [42], in their study, concluded that the optimum temperature range for torrefaction of sewage sludge was 300-350 °C, although the torrefaction of sewage sludge was performed in a fixed bed.…”

Influence of torrefaction on chemical compositions of empty fruit bunch (EFB) biomass using microwave heating

“…Whereas, the cellulose and lignin began decompose about 270 to 300 °C. The tensile failure strength and strain energy are clear reduce due to the increasing temperature (Shang et al, 2012). Then, in this study, the effect of torrefaction towards compositions of hemicellulose, cellulose and lignin will be investigated.…”