共查询到18条相似文献,搜索用时 125 毫秒
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用稻壳、法国梧桐树叶在不同热解条件下制得生物质焦样,通过压汞法获得生物质焦的孔隙结构实验数据,采用热力学模型对生物质焦的孔隙结构进行数学建模,并计算了相应的分形维数。计算结果表明,生物质焦的孔隙结构越复杂,分形维数越大。 相似文献
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不同秸秆生物炭的孔隙结构及其差异 总被引:1,自引:0,他引:1
基于低温氮气吸附的研究方法,对水稻秸秆、玉米秸秆、小麦秸秆制备的生物炭进行了孔结构研究,用BET方程、BJH方程和t-plot方法分别计算得到生物炭的比表面积、孔径分布和微孔数据,利用FHH模型计算了孔隙分形维数。研究表明:不同温度不同材料都对生物炭的孔结构有较大影响,随着热解温度的升高水稻秸秆生物炭和小麦秸秆生物炭的BET比表面积和总孔容呈先增加后降低的趋势,而玉米秸秆生物炭的孔隙度随着热解温度升高持续增加;3种秸秆生物炭的孔径分布均以中孔为主,孔隙内部以Ⅱ型孔为主;水稻秸秆、玉米秸秆、小麦秸秆制备的生物炭都具有很好的分形特征,分形维数(D)分别为2.545 4~2.669 3、2.629 7~2.689 5、2.577 3~2.597 2,表明这3种生物炭孔隙结构比较复杂,非均质性强,其中水稻秸秆生物炭和小麦秸秆生物炭均在500 ℃条件下有较高的分形维数,分别是2.669 3和2.597 2,玉米秸秆生物炭则在700 ℃条件下有较高的分形维数,为2.689 5。 相似文献
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利用氮气等温吸附/脱附法(-196℃)和扫描电镜(SEM)等研究了热解过程中生物质颗粒孔隙结构的演化规律,并用分形维数来描述焦颗粒内部孔隙表面形态的复杂程度。结果表明,热解温度对生物质焦的孔结构和表面形态有显著影响。热解过程中孔网络结构在发生演变,孔的形状发生了一定变化,且孔径有先变小后变大的趋势。高温导致焦颗粒发生塑性变形,使得孔隙扩大和孔表面更加光滑。随着温度的升高,生物质焦的BET比表面积先增大后减小,500℃以前,孔容积的变化规律与比表面积相近。通过分形FHH方程回归得到的分形维数能较好地表征颗粒内部孔隙表面的分形特征。其分形特征与热解温度密切相关,分形维数的变化与BET比表面积有一定关联。 相似文献
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认识和表征中药材的孔隙结构,对优化其中有效成分的提取过程有指导作用.今利用SEM、压汞法等考察了根类中药材甘草、黄芪、丹参的饮片及粉末在不同溶剂环境下的孔隙结构.研究结果表明,三种药材的粉末均主要由致密组织和薄壁组织组成,与未处理的情况相比,水溶胀会使薄壁组织含量增加,孔容和比表面积增大,乙醇溶胀不会带来明显的显微结构变化,孔容和比表面积有所减小.对压汞法实验数据的拟合证实三种药材均具有典型的热力学分形特征,分形维数在2.30~2.90之间.对于同一种药材,在水中的分形维数比未处理和在乙醇中的大.中药材分形维数是孔隙结构的综合反映,分形维数越大,孔径的分布范围越宽、小孔越多,越有利于传质.测定分形维数为表征中药材的整体孔隙结构提供了一种手段. 相似文献
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结合压汞曲线来研究砂岩储层的分形维数,利用实验说明了致密气藏存在分形特性,通过推导计算了致密气藏分形维数,对于复杂的微小孔隙发育的砂岩孔隙结构,分形维数接近3.基于实验证实分形的基础上,考虑基质孔隙和裂缝存在分形特性,并考虑到致密气藏的应力敏感性,基于致密气在纳米级孔隙中的非达西流动特点,建立了新的分形致密气藏渗流模型,通过对模型进行求解的基础上研究了具有分形特性的致密气藏渗流规律.绘制并分析了不同参数影响下的压力动态典型曲线.通过分析表明,基质和裂缝分形参数都对压力动态产生影响,但影响的流动时期和阶段不同.传统的气藏模型是本文所建模型的特例. 相似文献
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用氮气等温吸附/脱附(77 K)方法测量了淮南低变质煤及其在850℃条件下燃烧得到半焦的内部孔隙结构.通过分析得到有关煤焦颗粒内部孔隙结构的参数及其与燃尽率之间的关系.由吸附/脱附曲线判断煤焦孔洞的形状呈多样性.结合吸附理论,认为分形BET和分形Freundlich方程回归得到的分形维数分别表征颗粒内部大中孔表面分形维数和微孔体积分形维数.发现在燃烧过程中煤焦的表面分形维数及体积分形维数具有不同的变化趋势. 相似文献
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Study on coal chars combustion under O2/CO2 atmosphere with fractal random pore model 总被引:1,自引:0,他引:1
When predicting the variation of pore structure during O2/CO2 combustion of coal chars using the random pore model (RPM), it is impossible to calculate exactly the structure parameter ψ from the pore characteristics. The values of structure parameter ψ, which were calculated based on its fractal feature at various carbon conversions, should be almost constant. However, this investigation exhibited a drastic increase of ψ at the end of combustion reaction. In this work, structure parameter ψ of the RPM was modified according to the experimental analysis and a new model, fractal random pore model (FRPM), was constructed. Compared with other models such as RPM, discrete random pore model (DRPM), the Struis model (Model I) and the Liu model (Model II), it was found that fractal random pore model was more accurate to describe coal chars combustion, especially at higher conversions. Using the FRPM, O2/CO2 isotherm combustion of coal chars were analyzed at different temperatures. 相似文献
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This paper deals with the gasification reactivity and kinetic modeling of biomass chars derived from a wide range of plant origins. For most chars studied, the gasification reactivity increased with increasing conversion or exhibited a maximum in high conversion range. Common theoretical models could not account for these peculiarities. A semi-empirical gasification kinetic model was proposed on the basis of modifying random pore model, which was found to be capable of describing the experimental data well over the entire conversion range for 14 biomass chars studied. It was found that the fitting parameters introduced in the modified random pore model predicted well the amount of the active potassium (K) in biomass chars. The results led to a reasonable conclusion that the maximum rate at high conversion range was mainly attributed to the catalytic effect of K. 相似文献
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《Fuel Processing Technology》2006,87(10):907-917
This study continues a previous work aiming to explore how fractal analysis may help to understand the textural changes of materials during the manufacture of active carbons. Textural characterization of active carbons is carried out in order to obtain a better understanding of the facts underlying char gasification. The materials selected for study were a series of active carbons obtained from chars by means of gasification with carbon dioxide at 1123 K. These chars were obtained from coals oxidized in air at various temperatures for different periods of time. The data from mercury porosimetry were analyzed using fractal models. The fractal dimensions for the active carbons were calculated by using the methods proposed by Friesen and Mikula, by Zhang and Li and the method of Neimark. This latter method was used to obtain fractal profiles of the chars that were compared with the corresponding fractal profiles of the precursor chars and coals. Pore development during activation depends – together with other factors that remain constant in this study – on the textural properties of the precursor char that, at the same time, are conditioned by the properties of coals. The evolution of the fractal characteristics of the active carbons is also studied. At the same time, a detailed study of pore volume development during activation is presented. These analyses help to clarify the role that various phenomena occurring during activation have on the textural properties of the active carbons. 相似文献
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采用恒温热重分析法对稻草的催化气化反应动力学进行了研究,同时研究了生物质对石油焦气化的催化作用。采用修正随机孔模型对气化反应转化速率与转化率的关系进行了拟合计算,得到生物质焦气化的活化能和指前因子。结果表明,加入催化剂后半焦的气化反应活性增大,活性顺序为:加入K+半焦> 加入Ca2+半焦> 加入Mg2+半焦> 原半焦> 酸洗后半焦,表明了生物质焦能明显提高石油焦的气化活性。不同半焦气化的活化能大小顺序为:加入K+半焦<加入Ca2+半焦<加入Mg2+半焦<原半焦<酸洗后半焦,表明了生物质半焦的加入能降低石油焦气化的活化能。 相似文献
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利用静态氮吸附仪在-196.15 ℃液氮气氛中,测定Ru/Al2O3催化剂的比表面积以及孔结构参数,研究了催化剂的孔容-孔径分布和吸附-脱附等温线。基于FHH多层吸附模型,利用全吸附数据计算出Ru/Al2O3催化剂的表面分形维数。结果表明,3种Ru/Al2O3催化剂的表面分形维数均约2.4,分形维数与比表面积和总孔体积无直接关联。 相似文献
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燃烧过程中石油焦表面形态的变化 总被引:1,自引:1,他引:1
用氮气等温吸附/脱附法对石油焦燃烧过程中表面形态的变化进行了分析.通过BET法和t-plot法对不同燃尽率的石油焦进行了比表面积和孔容积的测定.结果表明,石油焦燃烧过程中孔隙结构变得发达,比表面积和孔容积较原样明显增大且变化趋势基本一致.验证了石油焦燃烧具有分形动力学的行为特征,用FHH模型求得燃烧中表面分形维数值接近3,表明燃烧反应是在空间网格结构的内、外部同时发生的;同时发现,石油焦表面分形维数与比表面积和孔容积在变化趋势上存在明显差异. 相似文献