Comparison of atmospheric and gas-pressurized oxidative torrefaction of heavy-metal-polluted rice straw

The oxidative torrefaction of rice straw polluted by heavy metals was carried out in a tube reactor (atmospheric pressure, AP) and an autoclave (gas-pressurized, GP), in order to compare the effects of the torrefaction temperature, carrier gas composition, and reactor type on torrefled products' properties. Compared with the AP, the GP-torrefled rice straw had a lower solid yield, volatile matter, fixed carbon, hydrogen and oxygen contents, lower overall colour change (Delta E), combustion characteristic factor (S-N), but a higher bulk density, higher heating value, ash and carbon content, higher combustion temperatures (T-i and T-f) and fuel ratio. The weight loss, volatile matter, element, higher heating values and combustion characteristics of the AP-torrefled rice straw showed good correlations with its colour parameters, which indicating that it is technically feasible to identification and prediction by the human eye of AP-torrefled RS at the industrial level. However, higher amount of typical heavy metals remained in the GP-torrefled solid products with lower biological availability, indicating that GP torrefaction can be utilized as a low-cost and safe pre-treatment for heavy-metal-polluted rice straw at the industrial scale. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The oxidative torrefaction of heavy metal-polluted rice straw was studied under different conditions to compare the effects on torrefled products' properties. The results showed that rice straw torrefaction under gas-pressurized conditions had better combustion performance, while the identification and prediction of atmospheric pressure torrefied rice straw could be achieved through color parameters. Gas-pressurized torrefaction can be used as a low-cost, safe pre-treatment for heavy metal-polluted rice straw.