Thermodynamic characteristics and oxygen threshold limiting the Re-ignition of overfired coal residues in sealed fire zones

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering Pub Date : 2025-02-11 DOI:10.1016/j.csite.2025.105863

Liangzhou Chen , Jian Zhao , Wei Lu , Jinliang Li , Xuyao Qi

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Abstract

This study investigates the thermodynamic properties and oxygen threshold limiting the re-ignition of overfired coal residues within sealed fire zones under controlled oxygen conditions. Thermogravimetric experiments were conducted to analyze re-ignition behavior across varying heating rates and oxygen concentrations. The re-ignition process is delineated into three distinct phases: low-temperature pyrolysis, oxygen adsorption, and combustion. Elevated oxygen concentrations accelerate re-ignition and combustion by lowering ignition and burnout temperatures, shortening combustion duration, and increasing the maximum weight loss rate, indicating a more rapid and intense combustion process. The threshold oxygen concentration for re-ignition suppression was identified between 3 % and 5 %, effectively restricting combustion due to limited oxygen availability. Re-ignition mechanisms shift with oxygen levels, from the A-E model at 5 %, to Jander diffusion at 15 %, and to the shrinking spherical model at 21 %. Below 5 % oxygen, combustion becomes oxygen-limited, with pyrolysis predominating. In this phase, the activation energy fluctuates and significantly decreases around the 5 % threshold, marking a critical shift in the combustion process. These insights offer important guidance for safely reopening fire zones in coal mines and for reducing re-ignition risks.

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本研究调查了在受控氧气条件下，限制密封火区内过火煤渣复燃的热力学特性和氧气阈值。通过热重实验分析了不同加热速率和氧气浓度下的复燃行为。复燃过程分为三个不同阶段：低温热解、氧气吸附和燃烧。氧气浓度升高会降低点火和燃烧温度，缩短燃烧持续时间，增加最大失重率，从而加速复燃和燃烧，表明燃烧过程更加迅速和剧烈。抑制再点火的阈值氧气浓度被确定为 3% 至 5%，由于氧气供应有限，燃烧会受到有效限制。再点火机制随氧气水平的变化而变化，从 5 % 时的 A-E 模型到 15 % 时的詹德扩散模型，再到 21 % 时的收缩球形模型。氧气含量低于 5%时，燃烧受氧气限制，热解占主导地位。在这一阶段，活化能在 5% 临界值附近波动并显著降低，标志着燃烧过程的关键转变。这些见解为安全重开煤矿火区和降低复燃风险提供了重要指导。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Case Studies in Thermal Engineering Chemical Engineering-Fluid Flow and Transfer Processes

CiteScore

8.60

自引率

11.80%

发文量

812

审稿时长

76 days

期刊介绍： Case Studies in Thermal Engineering provides a forum for the rapid publication of short, structured Case Studies in Thermal Engineering and related Short Communications. It provides an essential compendium of case studies for researchers and practitioners in the field of thermal engineering and others who are interested in aspects of thermal engineering cases that could affect other engineering processes. The journal not only publishes new and novel case studies, but also provides a forum for the publication of high quality descriptions of classic thermal engineering problems. The scope of the journal includes case studies of thermal engineering problems in components, devices and systems using existing experimental and numerical techniques in the areas of mechanical, aerospace, chemical, medical, thermal management for electronics, heat exchangers, regeneration, solar thermal energy, thermal storage, building energy conservation, and power generation. Case studies of thermal problems in other areas will also be considered.