Effects of Chemical Properties and Inherent Mineral Matters on Pyrolysis Kinetics of Low-Rank Coals

Ziqi Zhu,Rihong Cong,Zhengpeng Wu,Lingmei Zhou,Hao Zheng,Yanan Tu

doi:10.3390/pr9122111

Ziqi Zhu, Rihong Cong + Show 4 more

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https://doi.org/10.3390/pr9122111

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Abstract

The kinetics during the pyrolysis process depend on both chemical structure and inherent mineral matters in coal, but normally, only one of these components is investigated in literature. In the present work, four low-rank coals were pyrolyzed in a thermogravimetric analyzer at a heating rate of 10 K/min in a constant nitrogen stream at a temperature up to 900 °C to study the pyrolysis behavior and kinetics. Two of the samples were raw coal (R-YL) and clean coal (C-YL) obtained through the washing process. The results showed that the coal-washing process mainly affected the inorganic part (mineral matters) and structure in coal, which did not largely change the chemical properties. The pyrolysis behavior in primary stage (before 550 °C) was mainly affected by the chemical properties of coal, while the pyrolysis behavior in higher temperature also depended on inherent mineral matters. The kinetics of four coals were obtained using the Coats–Redfern (CR) method with five theoretical models. The difference of E value was almost negligible for R-YL and C-YL, also showing that the coal-washing process did not largely change the chemical properties. The higher frequency factor A for clean coal C-YL showed a more porous structure due to the coal-washing process. The apparent activation energy E in the third stage was affected by the thermodynamic property of inherent minerals.

Highlights

The continued development of the world economy requires more and more energy consumption, a large part of which comes from coal, especially in China [1,2]
The catalytic effects caused by mineral matter can be represented by the index of basicity or the alkali index [12], where a high index of basicity indicates strong catalytic effects. It is defined in the following way: the sulfur content was low, the pyrite and pyrrhotite can be detected by X-ray Diffraction (XRD)
The present study mainly focused on the effects of chemical properties and inherent mineral matters on the pyrolysis kinetics of low-rank coals

Summary

Introduction

The continued development of the world economy requires more and more energy consumption, a large part of which comes from coal, especially in China [1,2]. The typical characteristics of low-rank coals, such as a high moisture content, low calorific value and high volatile content, restrict the direct utilization of lowrank coals. The common utilization technologies of low-rank coal include combustion, liquidation, gasification and pyrolysis. The moisture content of low rank coal can be significantly reduced and the calorific value can be greatly increased, which can largely upgrade the quality of low-rank coal. It is the first step in the process of combustion, liquidation and gasification. It is important to obtain the kinetic parameters and influence factors during the coal pyrolysis process

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Conclusion