Investigation on hydrothermal-pyrolysis process to eliminate S-pollution from corncob residue utilization: Experiment and life cycle assessment

Abstract

Corncob residue (CR) is characterized by high S and moisture content, which results in large SOx emissions in the thermal process (incineration/pyrolysis). This study investigated a new hydrothermal-pyrolysis method (HT-PY) to obtain high-quality products (phenol-rich and low moisture content bio-oil, S-free char). Compared with S content of CR, the S content of hydrochar obtained from 300 ℃-HT decreased 63.33 %. After pyrolysis, the S and volatile-sulfur (VS) content of char obtained from 300HT-550PY decreased 84.45 % and 95.24 %, only 0.14 % and 0.01 %. Compared with direct pyrolysis of CR, Hydrothermal pre-treatment improved the decomposition of organic-S in solid phase and eliminate the S-emissions of gas phase. Basing on the experimental data and process simulation, life cycle assessment, and economic cost analysis of CR-HT-PY were also provided benefits. The steam of the hydrothermal unit recovered to the heat supply of furfural production (30796.21 MJ). And the HT-PY system exhibited the lowest GWP and AP environmental impact, SO2 emissions of CR-HT-PY was merely emitted during the hydrothermal process (0.32 kg/ton CR), decreased 98.03 % (15.92 kg SO2/ton CR) compared with direct pyrolysis. The carbon utilization efficiency was also increased by 41.37 % due to higher-quality products. In addition, due to the high value of S-free char, the total economic efficiency of CR-HT-PY was more than twice that of other systems.