Effects of additives and hydrothermal pretreatment on the pelleting process of rice straw: Energy consumption and pellets quality
2019
Xia, Xianfei | Zhang, Ke | Xiao, Hongru | Xiao, Suwei | Song, Zhiyu | Yang, Zhengyu
Pelleting is an appealing approach to enhance energy density of biomass for renewable fuel production. To overcome these two challenges: high energy consumption of pelleting and low product calorific value of pellets, the pretreatment of raw biomass is a necessary process prior to pelleting. In this study, the rice straw was pretreated by hydrothermal carbonization (HTC) firstly, then the economic additives: crude glycerin and paraffin were added. Afterward, the pretreated biomass was pelletized using mixed-level orthogonal array design to evaluate energy consumption and pellets quality. Finally, the pelleting condition was optimized based on the analysis of range and variance, thermogravimetric analysis and scanning electron microscope (SEM) evaluation. Experimental results indicated that additive type was a more influential factor than HTC pretreatment and adding ratio in terms of reducing energy consumption and improving pellet quality. Compared to the non-pretreated rice straw, pelleting energy of the selected hydrothermally pretreated sample with 4% paraffin addition reduced 37.26%, pellet density (ratio of pellet mass to volume) enhanced by 7.71%, and calorific value (heat released by combustion of unit pellet mass) increased by 68.10%, while the tensile strength (the crushing resistance and mechanical stability of the pellets) just loss by 4.33%. Combustion and micro-bonding characteristics also show that this rice straw pellet fuel has a great potential as an alternative fuel for coal.
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