Xiaopeng Bai

Co-pelletizing characteristics of torrefied wheat straw with peanut shell

The co-pelletizing characteristics of torrefied wheat straw and peanut shell with adding water were investigated. The physicochemical and friction characteristics of biochar were determined to investigate the mechanism of biochar inter-particle cohesive bonding. Results showed that optimized process conditions were obtained with 15% peanut shell and 10% water content. The volume density, maximum breaking force of pellets initially decreased and then increased, while energy consumption increased with increasing temperature. The main factors contributing to the cohesion of mixing pellet were the peanut shell content, water content and friction characteristics of biochar. The moisture absorption of the pellet was improved significantly, while the water absorption of pellets did not always decrease with increased temperature. Peanut shell is an effective and inexpensive binder in the preparation of good-quality biochar pellets. Biochar pellets derived from torrefaction temperature of 275-300°C showed superior qualities for application as renewable biofuels.

Changes in the physicochemical structure and pyrolysis characteristics of wheat straw after rod-milling pretreatment

Pyrolysis is increasingly used for raw biomass conversion. In this study, the effects of rod-milling pretreatment (RMP) on the physicochemical properties and pyrolysis characteristics of wheat straw (WS) was found. The mechanism behind these changes was further analyzed. RMP appreciably reduced the particle size and cellulose crystallinity, and increased the specific surface area and pore volume of WS. Under RMP, with an increasing conversion rate α, the activation energy E was expressed as a para-curve, whereas it was expressed as a tangent curve for samples that underwent hammer-milling pretreatment (HMP). At the same α, the thermal degradation temperature for RMP was lower than that for HMP. The E value clearly decreased with RMP, and increased following a wave-like pattern with increased rod-milling strength (RMS). The lowest E value (118.69 or 108.97 kJ/mol) was obtained with a milling time of 60 min. Hence, RMP is an environmental-friendly and effective method for improving the efficiency of pyrolysis.

Combined different dehydration pretreatments and torrefaction to upgrade fuel properties of hybrid pennisetum ( Pennisetum americanum ×P. purpureum )

Different dehydrating methods combined with torrefaction were investigated to find the underlying mechanism that how dehydration process influence the degree of hornification. Hybrid pennisetum was selected as the experiment material. Oven-dried sample (ODS), crushed dried sample (CDS), and sun-cured dried sample (SDS) were torrefied under the temperature of 275 °C and 300 °C with the duration time of 60 min. The results showed that, changes in elevated carbon content and higher heating value (HHV) and reduced oxygen content of SDS were the most obvious under identical torrefaction conditions. Fuel ratio of SDS was enhanced most under 300 °C. It also had the highest devolatilization index (Di). The combination of sun-cured dried with torrefaction under 300 °C caused lowest degree of irreversible hornification happened during dehydrating process, and different hornification degrees caused by different dehydrating methods effect the enhancement of fuel properties of lignocellulosic biomass material.

Effects of combined pretreatment with rod-milled and torrefaction on physicochemical and fuel characteristics of wheat straw

The mechanism of rod-milling combined with torrefaction as well as its effects on physicochemical and fuel properties of wheat straw were investigated. Rod-milling and hammer-milling samples were torrefied under three temperatures (250, 275, and 300 °C) with a duration time of 30 min. The results indicated that combined rod-milling and torrefaction pretreatment (CRT) significantly elevated carbon content, higher heating value, fuel ratio, and reduced oxygen content and atomic H/C and O/C ratios in wheat straw. Moreover, CRT significantly reduced cellulose crystallinity, and increased the specific surface area and pore volume of wheat straw, which lowered the wheat straws degrading pyrolysis temperature. These peak values appeared under 300 °C. Devolatilization index (Di) was improved by rod-milling pretreatment under identical torrefaction conditions except 275 °C. Therefore, the combination of rod-milling with torrefaction under 300 °C has the advantage of enhancing fuel properties of lignocellulosic biomass materials.