Abstract:

To utilize agricultural and forestry waste to prepare high-quality biochar fuel at low cost， using cedar sawdust （CS） as raw material， pressurized torrefaction experiments were conducted using a micro high-pressure reactor to study fuel quality and the changes in physicochemical structure as well as pyrolysis kinetics. The results showed that，compared with atmospheric torrefaction at the same temperature （230 ℃）， the fixed carbon content of pressurized torrefied semi-char increased. Pressure promoted the conversion of volatile substances to fixed carbon in biomass. The volatile content in CS-290-1.5 decreased from 84.09% of CS to 45.74%， and calorific value increased to 28.15 MJ·kg^-1， the fuel quality significantly increased. The oxygen-carbon and Hydrogen-carbon ratios decreased to 0.24 and 0.85， which had basically reached the fuel quality range of bituminous coal. Temperature played an important role in the volatile matter removal and carbonization. Fourier-transform infrared spectroscopy results showed that oxygen-containing groups in solid products decreased， while C=C increased. The deoxygenation and aromatization reactions between biomass components were strengthened. Raman experimental results showed that the higher temperature under pressure led to an increase in condensation reaction from small to large aromatic rings in torrefied semi-char， resulted in an increase in graphitization degree. As temperature increased， the specific surface area and total pore volume of solid semi-char showed a gradual increase trend. CS-290-1.5 had a specific surface area of 40.02 m²·g^-1， suggesting that the raise in temperature promoted volatile matter removal and the generation of small molecule gases， thereby increasing pores and combustion reactivity. According to pyrolysis kinetics calculation， the activation energy of pressurized torrefied semi-char significantly increased at a later stage of pyrolysis reaction. The cross-linking reaction in torrefied semi-char was enhanced， resulting in the generation of more substances with high thermal stability. The determination results of gas composition indicated that compared to atmospheric pressure， pressurized torrefaction was more conducive to the deep decomposition of cellulose and hemicellulose of biomass， promoting the removal of a large number of oxygen-containing groups， and releasing in the form of H₂O， CO and CO₂. To sum up， using gas pressure could enhance the deoxygenation and quality improvement of pine sawdust， which provided a theoretical basis for the energy efficient utilization of aromatic plant waste.

Key words: aromatic plants, biomass, pressurized torrefaction, deoxygenation, activation energy

摘要：

为利用农林废弃物以低成本制备高品质生物焦燃料，以雪松木屑（cedar sawdust， CS）为原料，采用微型高压反应釜进行加压烘焙试验，研究烘焙半焦燃料品质的提高和物化结构、热解动力学特性变化以及气体产物组分分布。结果表明，与同温度下（230 ℃）常压烘焙相比，加压烘焙半焦的固定碳含量均有所提高，压力促进了生物质中挥发性物质向固定碳的转化。CS-290-1.5半焦的挥发分从CS原样的84.09%降至45.74%，热值增加到28.15 MJ·kg^-1，燃料品质显著增加，且氧碳比、氢碳比降低至0.24和0.85，基本达到烟煤的燃料性能范围。温度对挥发分的脱除以及脱氧增碳效果起着重要的作用。傅里叶变换红外光谱结果显示，烘焙半焦中含氧基团减少，C=C增加，生物质组分间的脱氧及芳构化反应加强。拉曼试验结果表明，加压下温度的提高使烘焙半焦中小芳香环向大芳香环的缩聚程度提高，石墨化程度增加。随温度升高，固体半焦比表面积与总孔体积呈逐渐增加趋势，CS-290-1.5比表面积高达40.02 m²·g^-1，温度的提高促进了挥发分脱除与小分子气体的生成，导致孔隙数量增加，燃烧反应性增强。热解动力学计算表明，加压烘焙半焦在热解反应后期的活化能显著增加，烘焙半焦中交联反应增强，生成更多热稳定性高的物质。气体组分测定结果表明，相比常压加压烘焙更有利于生物质中纤维素和半纤维素组分的深度分解，促进了含氧基团的大量脱除，更多的以H₂O、CO、CO₂等形式释放。综上表明，借助气体压力增强松木木屑脱氧提质，为芳香类植物废弃物高值能源化利用提供了理论依据。

关键词: 芳香植物, 生物质, 加压烘焙, 脱氧, 活化能