In this work, we study the thermochemical degradation and char conversion of wet wood particles. The work is split in two main parts: (1) the effect of the ash layer handling approach and (2) a parametric study over different relevant parameters. In the study of the ash layer handling, we investigate the effect of allowing the ash to remain on the surface of the particle when the char is converted (Model A), in contrast to removing the ash such that the reacting char layer is always exposed (Model B). It was found that the two modeling concepts yield significantly different mass losses and surface and center temperature predictions. Model B presents a faster thermal conversion, while the results predicted by Model A are in better agreement with what has been observed experimentally. A parametric study was also done, where the sensitivity to variations in thermal conductivity, specific surface area, and gas permeability was studied. It was found that thermal conductivity influences the time when drying and devolatilization are accomplished. This is because these conversion stages are heat-transfer-controlled. Char conversion is primarily affected by a shift to earlier times for the initialization of the final char conversion when higher thermal conductivities are used. It is found that the specific surface area smaller than a critical value can significantly affect the final char conversion time. Since char conversion is a key stage of wood combustion, the full conversion time is also affected. The gas permeability primarily affects mass diffusion into the particle. It was found that, up until a critical effective gas permeability, the modeling results are sensitive to assigned permeabilities.

中文翻译：

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模拟热木材颗粒转化：灰层建模和参数研究

在这项工作中，我们研究了湿木颗粒的热化学降解和炭转化。这项工作分为两个主要部分：（1）灰层处理方法的效果；（2）对不同相关参数的参数研究。在灰分层处理的研究中，我们研究了将焦炭转化（模型A）时允许灰分保留在颗粒表面的效果（与去除灰分相比，使反应的炭层始终暴露在外） （模型B）。发现这两个建模概念产生了明显不同的质量损失以及表面和中心温度预测。模型B表现出更快的热转化率，而模型A预测的结果与实验观察到的结果更好地吻合。还进行了参数研究 在此研究了对热导率，比表面积和气体渗透率变化的敏感性。已经发现，热导率影响完成干燥和脱挥发分的时间。这是因为这些转换阶段受热传递控制。当使用更高的热导率时，焦炭转化率主要受到最终焦炭转化率初始化的更早时间的影响。发现比表面积小于临界值可以显着影响最终的焦炭转化时间。由于焦炭转化是木材燃烧的关键阶段，因此完整转化时间也会受到影响。气体渗透率主要影响质量扩散到颗粒中。结果发现，直到达到临界有效气体渗透率，