Abstract
Co-hydrothermal carbonization (Co-HTC) is an emerging technology for processing multiple waste streams together to improve their fuel properties in the solid product, known as hydrochar, compared to the hydrothermal carbonization (HTC) of those individual streams. Sulfur is considered one of the most toxic contaminants in solid fuel and the combustion of this sulfur results in the emission of SOx. It was reported in the literature that, besides the fuel properties, Co-HTC reduced the total sulfur content in the hydrochar phase significantly. However, the transformation of different forms of sulfur has not yet been studied. Therefore, this study investigated the transformation of different forms of sulfur under the Co-HTC treatment. In the study, the Co-HTC of food waste (FW) and two types of coal wastes (middle bottom (CW1) and 4 top (CW2)) were conducted at 180 °C, 230 °C and 280 °C for 30 min. Different forms of sulfur were measured by using elemental analysis (total sulfur), and a wet chemical method (sulfate sulfur and pyritic sulfur). The organic sulfur was measured by the difference method. The results showed that a maximum of 49% and 65% decrease in total sulfur was achieved for CW1FW and CW2FW, respectively, at 230 °C. Similar to the total sulfur, the organic sulfur was also decreased about 85% and 75% for CW1FW and CW2FW, respectively. Based on these results, a sulfur transformation mechanism under Co-HTC treatment was proposed.
Highlights
Co-hydrothermal carbonization (Co-HTC) is a process where blended biomass or coal-biomass blend is treated at high temperature (180–280 ◦ C) and autogenous vapor pressure (10–64 bar) in the residual moisture
Our previous studies showed that the Co-HTC treatment of food waste (FW) and coal waste (CW) blend at 180–280 ◦ C for 30 min improved solid fuel properties compared to their individual hydrothermal carbonization (HTC) [1,3]
Sulfate sulfur, which constitutes less than 10% of total sulfur, increased with the HTC temperature in both the raw coal waste samples
Summary
Co-hydrothermal carbonization (Co-HTC) is a process where blended biomass or coal-biomass blend is treated at high temperature (180–280 ◦ C) and autogenous vapor pressure (10–64 bar) in the residual moisture. Our previous studies showed that the Co-HTC treatment of food waste (FW) and coal waste (CW) blend at 180–280 ◦ C for 30 min improved solid fuel properties compared to their individual hydrothermal carbonization (HTC) [1,3]. This synergistic effect was due to the generation of acidic solutions by dehydration and decarboxylation reactions during the hydrothermal carbonization of FW, which catalyzed the degradation of CW and resulted in lower hydrochar yields. The techno-economic analysis of a scaled-up plant (81,175 kg/h solid handling capacity) was studied and the process was found to be economically feasible [4]
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