水热氧化预处理对棉秆成型颗粒理化性质的影响

以棉秆为研究对象,经180～280℃水热氧化预处理后热压制备成型颗粒。利用热重分析、X射线衍射(XRD)及傅里叶变换红外光谱(FTIR)等分析手段,考察了水热氧化预处理温度对棉秆成型颗粒理化性能及燃烧性能的影响。结果表明:随着水热氧化温度的升高,棉秆的固相产物产率降低,半纤维素于180℃之前完全分解,无定形纤维素于200℃完全分解,结晶纤维素于260℃完全分解,水热氧化固相产物的纤维素结晶度呈现逐渐减小的趋势,而木质素相对含量增加;棉秆成型颗粒的固定碳含量、热值和能量密度增加,但燃烧性能变差。水热氧化预处理后棉秆成型颗粒的表观密度保持在1300kg/m³左右,抗压强度则随着水热氧化温度的增加而下降,其中180℃水热氧化预处理后棉秆成型颗粒的抗压强度相比原料成型燃料增加了183.33%。本研究范围内,经180℃水热氧化预处理后获得的棉杆成型颗粒的燃烧性能和物理性能最佳,其热值为17.76MJ/kg,能量密度为23.44GJ/m³,抗压强度达11.90MPa,可作为优质生物质成型燃料使用。

Effect of hydrothermal oxidation pretreatment on the physicochemical properties of fuel pellets prepared from cotton stalks

Cotton stalk (CS) was first pretreated by hydrothermal oxidation (HTO) process in an autoclave at 180—280℃ and then densified to prepare fuel pellets. The effect of HTO temperature on the physicochemical properties of the resulted CS pellets was investigated by thermogravimetric analyzer, X-ray diffractometer (XRD) and Fourier transform infrared spectrometer (FTIR), etc. The results indicated that the resulted CS yield decreased with the increase of HTO temperature. The hemicellulose contained in CS decomposes completely before HTO temperature reached to 180℃, the amorphous cellulose decomposed before 200℃, the crystalline cellulose decomposed before 260℃, and the relative content of the lignin gradually increased. The cellulose crystallinity of the resulted CS showed a decreasing trend as HTO temperature increases. The fixed carbon yield, the calorific value and the energy density of the resulted CS pellet increased, but the combustion characteristic became worse. The apparent density of the resulted CS pellet remained around 1300kg/m3, and the compressive strength decreased with increasing HTO temperature. The compressive strength of the pellet prepared from CS pretreated at 180℃ was the maximum, which increased by 183.33% compared with that from the raw material. The key factors affecting the compressive strength were crystalline cellulose which could act as a skeleton support and pseudo-lignin which acted as binder. The fuel pellet from CS pretreated at 180℃ showed the best combustion characteristic and physical properties with the calorific value of 17.76MJ/kg, the energy density of 23.44GJ/m³, and the compressive strength of 11.9MPa. The resulted indicated that the biomass pellets could be used as high-quality solid fuels.