气化过程中谷壳焦颗粒孔隙结构及分形特性的演化

Evolution of pore structure and fractal characteristics of rice husk char particles during gasification

为了深入揭示生物质焦在气化反应中的行为变化及反应机理,该文利用氮气物理吸附法和扫描电镜等技术研究了气化过程中谷壳焦颗粒孔隙结构和表面形态的演化,并用分形维数描述了焦颗粒内部孔隙表面形态的复杂程度。结果表明,谷壳气化焦的吸附特性曲线在整体上均呈现出II型等温线特征,表明焦颗粒具有较为连续和完整的孔分布系统。随着气化反应的进行,谷壳焦的BET比表面积和微孔比表面积均呈现出先增大后减小的变化趋势,并在气化转化率为48.6%时取得最大值210.45和147.14m2/g。孔容积的变化规律与比表面积相近。随着气化转化率的增大,焦颗粒的平均孔径迅速减小,在转化率为35.4%时达到最小值2.94nm,之后稍有增大。分形FHH(Frenkel-Halsey-Hill)模型适用于生物质气化焦颗粒孔隙表面分形特征的研究。气化过程中焦颗粒孔隙表面分形维数的变化趋势与平均孔径的变化趋势相反,两者呈现出较好的线性关系。研究结果可为实际生物质气化过程的数值模拟和运行参数的优化等提供参考。

The changes in pore structure and fractal characteristics of rice husk char particles during gasification were studied by N2 physisorption method and scanning electronic microscopy（SEM）.The results showed that the adsorption isotherms of rice husk gasified chars were all type II isotherms with hysteresis loops,indicating that the chars consisted of continuous and complete system of pores.As the gasification conversion rate increased,the BET surface area and micropore area first increased to reach the maxima of 210.45 and 147.14 m^2/g at the conversion of 48.6% and then decreased.Pore volume showed a similar tendency to BET surface area.The average pore diameter decreased significantly and then increased slowly with increase of gasification conversion rate and reached the minimum of 2.94 nm at the conversion rate of 35.4%.The fractal Frenkel-Halsey-Hill（FHH） model was capable of predicting the pore surface fractal characteristics of the gasified char particles.The evolution of pore surface fractal dimension（Ds） was opposite to that of average pore diameter（dave）.There was a good linear relationship between Ds and dave.The results can provide valuable information for the numerical simulation and the optimization of operating parameters of the actual biomass gasification process