Abstract The combustion performance of high heating-rate chars is observably affected by the evolution of its physical structure during devolatilization. An effort has been devoted to building understandable relationships between the heating rates of different rank coals, char structure and subsequently detailed combustion characteristics. In this work, the physical structure parameters (internal surface area, porosity, and swelling ratio) of bituminous coals and lignites are qualitatively summarized as a function of heating rates (>104 K/s). Meanwhile, the physical structure effects on char combustion characteristics are investigated separately by using the self-developed kinetics model, where the transient char properties, ash distribution (ash film, ash dilution, and ash vaporization) and char combustion performances are taken into account. The relative importance of the three structure parameters on char burnout is also performed. The internal surface area of high heating-rate chars exerts positive effects on combustion with higher burning temperature and shorter burnout time, whereas the swelling ratio and porosity exert complex effects. The combustion rate initially increases then goes down with char conversion, owing to the integrated effects of formation and destruction of internal surface area. The importance of physical structure parameters on char combustion follows the order: internal surface area > swelling ratio > porosity. These results provide in-depth insight into the effects of physical structure during char combustion and suggest higher heating rates are favorable in industrial boiler applications.

中文翻译：

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高升温速率焦炭物理结构对燃烧特性的影响

摘要 脱挥发分过程中高加热速率焦炭的物理结构演变明显影响其燃烧性能。一直致力于在不同等级煤的加热速率、焦炭结构和随后的详细燃烧特性之间建立可理解的关系。在这项工作中，烟煤和褐煤的物理结构参数（内表面积、孔隙率和膨胀率）被定性地总结为加热速率 (>104 K/s) 的函数。同时，通过使用自行开发的动力学模型，分别研究了物理结构对焦炭燃烧特性的影响，其中考虑了瞬态焦炭特性、灰分分布（灰膜、灰分稀释和灰分蒸发）和焦炭燃烧性能。还进行了三个结构参数对炭烧毁的相对重要性。高加热速率炭的内表面积对燃烧产生积极影响，燃烧温度较高，燃尽时间较短，而膨胀率和孔隙率则产生复杂的影响。由于内表面积的形成和破坏的综合影响，燃烧率最初增加然后随着炭转化率下降。物理结构参数对炭燃烧的重要性遵循以下顺序：内表面积>膨胀率>孔隙率。这些结果提供了对焦炭燃烧过程中物理结构影响的深入了解，并表明更高的加热速率有利于工业锅炉应用。