Batch pyrolysis of cotton stalks for evaluation of biochar energy potential

Abstract

The thermal cracking of cotton stalks (CS) through pyrolysis was undertaken using a laboratory scale batch pyrolysis reactor. The distribution of pyrolysis products were studied dependent on the final pyrolysis temperature which ranged from 300 to 800 °C by 100K intervals. The maximum biochar yield of 46.5% was obtained at 400 °C. As the pyrolysis process temperature increased, the solid char product yield decreased. The largest higher heating value (25.845 MJ kg−1) was obtained at 600 °C. All biochar samples produced between 500 and 700 °C had an energy densification ratio of 1.41, indicating a higher mass-energy density than the initial feedstock. A larger share of syngas and bio-oil were produced at higher temperatures, as estimated. Preferential selection of a char based on the energy yield would lead to a selection of the 400 °C product, while selection based on the energy densification ratio would be for a product obtained between 500 and 700 °C. An energy simulation was conducted which determined that the process is self-sustaining at and above 400 °C. Furthermore, the global energy potential was determined from CS pyrolysis, which was estimated at 380 PJ yr−1 could contribute to roughly 0.1% of the actual global total primary energy supply of 576 EJ yr−1.