Pyrolysis behaviors of anaerobic digestion residues in a fixed-bed reactor with rapid infrared heating

Fast pyrolysis via rapid infrared heating may significantly enhance the heat transfer and suppress the secondary reaction of the volatiles. The effects of various pyrolysis temperatures on pyrolysis behaviors of anaerobic digestion residues (ADR) were studied in this research utilizing a fixed-bed reactor equipped with rapid infrared heating (IH), as well as to compare the pyrolysis products produced by rapid infrared heating (IH) to those produced by conventional electric heating (EH). Thermogravimetric (TG) analysis revealed that pyrolysis of ADR occurred in three decomposition stages. The results of pyrolysis experiments showed that increasing temperature first raised the bio-oil yield for IH and EH, peaking at 500–600 °C, but thereafter decreased the yield. In contrast to the findings achieved with EH, infrared heating (IH) presented a greater overall bio-oil yield but a lower gas yield. The bio-oil produced by IH increased from 8.35 wt.% at 400 °C to 12.56 wt.% at 500 °C before dropping to 11.22 wt.% at 700 °C. Gaseous products produced by IH have a higher heating value than those generated by EH. Nitrogenous compounds, ketones, and phenols make up the majority of the bio-oil. In the IH bio-oil, nitrogen compounds rose with increasing temperature, while those varied slightly in the EH bio-oil. The phenols content in IH bio-oil was much more than that of EH, exhibiting values of 8.63% and 2.95%, respectively. The findings of the FTIR spectra of biochar indicated that as the temperature increased, the chains of aliphatic side professedly reduced and the structure of biochar became considerably ordered for both heating techniques. The Raman spectra of IH biochar showed that the ratio of A_G/A_D rose progressively from 0.17 to 0.20 as pyrolysis temperature rose from 500 to 700 °C.