Pyrolysis path and mercury removal mechanism of biochar in different atmospheres

被引：0

作者：

Jia L. ^{[1
]}

Guo J. ^{[1
]}

Wang Y. ^{[1
]}

Zhang Y. ^{[1
]}

Li Z. ^{[1
]}

Liu D. ^{[1
]}

Jin Y. ^{[1
]}

机构：

[1] College of Electrical and Power Engineering, Taiyuan University of Technology, Taiyuan

来源：

Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | 2021年 / 52卷 / 06期

基金：

中国国家自然科学基金;

关键词：

Adsorption mechanism; Biomass char; Mercury; Pyrolysis atmosphere; Reaction path;

D O I：

10.11817/j.issn.1672-7207.2021.06.031

中图分类号：

学科分类号：

摘要：

Pyrolysis process of biomass in three kinds of pyrolysis atmospheres was analysed, aiming at the main components of N2, O2 and CO2 in power plant flue gas. By verifying the proposed reaction path, the pyrolysis evolution mechanism of biomass under the condition of multi-phase components was revealed. Based on a comprehensive study of mercury adsorption characteristics and microscopic characteristics of biochar, the temperature-programmed desorption technique and the adsorption kinetics were employed to systematically explore the reaction mechanism of Hg0 adsorption. The results show that pyrolysis process of biomass can be divided into three stages in N2 atmosphere. Three pyrolysis reaction pathways are possible in O2 atmosphere. There is a critical threshold between 5%-7% O2 volume fraction. The heterogeneous reaction of biomass oxidation is controlled by the diffusion of O2 when the volume fraction is lower than the critical range. When the volume fraction exceeds the critical range, the reaction is accelerated and controlled by kinetics. Above 750℃, CO2 can react directly with the biochar through Boudouard reaction. With the increase of CO2 volume fraction, the gasification reaction can proceed ahead of time and be intensified. There are a large number of parallel first-order reactions during the process of biomass pyrolysis, which constitute obviously different and complex reaction stages. The obtained apparent activation energy E value varies in the range of 30-300 kJ/mol. Compared with N2 pyrolysis atmosphere, Hg0 adsorption capacities of the biochars obtained in O2 pyrolysis atmosphere are worse. CO2 can improve the Hg0 adsorption capacity. When 20% CO2 volume fraction is selected as the pyrolysis atmosphere, biochar formed has the strongest mercury adsorption capacity. During the adsorption process, Hg0 firstly combines with the functional groups on the surface of biochar to form chemical adsorption. When the chemical adsorption is saturated, the physical adsorption occurs. The mercury adsorbed by various ways on the biochar surface is in a mixed form, among which the main products of chemical adsorption are Hg-OM and HgO. © 2021, Central South University Press. All right reserved.

引用

页码：2011 / 2022

页数：11

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