Effect of hydrothermal pretreatment on deashing and pyrolysis characteristics of bamboo shoot shells

Bamboo shoot shells (BSS) were treated at hydrothermal temperatures of 160 °C, 180 °C, and 200 °C with residence times of 6 h, 8 h, and 10 h. The variation of ash-forming elements and the influence of deashing behavior on fuel and pyrolysis characteristics of BSS hydrochars were originally investigated during hydrothermal pretreatment (HTP) process. The results showed that HTP decreased 53.82–64.00% of BSS ash because 95.2–96.5% of K, 61.3–82.1% of Mg, 22.0–39.2% of Al, 23.7–51.8% of Fe, and 28.8–43.6% of Ca were removed. This improved fusion characteristics of BSS ash and reduced the risk of deposition, slagging and scaling. With increase in hydrothermal temperatures and residence times, the contents of fixed carbon, C, and high heating value of BSS hydrochars increased, while the contents of volatiles and O decreased. HTP shifted pyrolysis process of BSS to high temperature zone, and increased their activation energy and the amount of all gaseous products, including CO groups, C–O–C groups, alkyls, H2O, and CO. In conclusion, HTP is helpful for BSS to be used as feedstocks of bioenergy and biomaterials due to decrease of ash contents and improvement of thermal stability. •Hydrothermal pretreatment decreases 53.82–64.00% of ash content.•The removal ratios of ash-forming elements are K > Mg > Ca > Fe > Al > Si.•Hydrothermal pretreatment increases the activation energy.•Hydrothermal pretreatment delays the initial decomposition temperature.•Hydrothermal treatment aggravates the release of gaseous products during pyrolysis.