Pore-Resolving Simulations of Biomass Char Particle Combustion
Pore-Resolving Simulations of Biomass Char Particle Combustion
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DOI：
10.1016/j.proci.2022.07.098
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发表时间：
2022-09
影响因子：
3.4
通讯作者：
Dongyu Liang;Simcha Singer
中科院分区：
文献类型：
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作者：
Dongyu Liang;Simcha Singer
在II区条件下，生物质焦形态影响颗粒尺度的燃烧行为，在该区域中，非均相反应和颗粒内扩散共同控制着总的燃烧速率。此外，颗粒尺度的过程影响反应堆尺度的输出，而反应堆尺度的模拟对颗粒尺度模型很敏感。然而，大多数焦炭颗粒燃烧模型采用粗粒、有效的连续体方法，这种方法在亚网格尺度上处理所有孔隙率。当存在接近颗粒大小的大而不规则的气孔时，有效连续体方法是不有效或不准确的。因此，利用X射线微CT(Micro-CT)获得的实际生物质焦颗粒几何形状的三维孔洞分辨CFD模拟方法首次用于研究生物质焦颗粒(∼100µm)的形态对II区燃烧的影响。与更大的毫米到厘米大小的颗粒相比，亚毫米、高纵横比的生物质炭颗粒表现出局部的反应物渗透到颗粒最里面的区域，这是由于连接到外表面的大孔的存在。氧摩尔分数分布受大孔形态控制，随距离表面的增加呈非单调分布，在大孔周围的厚微孔炭区达到极小值。孔分辨模拟和等效的、空间分辨的有效连续介质模拟的比较表明，即使在微孔焦中，有效连续介质模型也低估了反应物的渗透。然后，在30个孔隙分辨颗粒模拟和几个采用颗粒特定参数的有效性因子模型之间进行了仔细的比较。通常使用的均匀圆柱体模型严重低估了这些真实松炭颗粒的有效性因子，而可访问的空心圆柱体模型在对所有30个颗粒平均时，相对误差不到10%。
Biomass char morphology affects combustion behavior at the particle scale for zone II conditions, in which both heterogeneous reaction and intra-particle diffusion govern the overall rate. Furthermore, particle-scale processes affect reactor-scale outputs, and reactor-scale simulations are sensitive to particle-scale models. However, most char particle combustion models employ coarse-grained, effective-continuum approaches, which treat all porosity at the subgrid-scale. Effective-continuum approaches are not valid or accurate in the presence of large, irregular pores which can approach the size of the particle. A 3-D, pore-resolving CFD simulation approach using real biomass char particle geometries obtained from X-ray micro-computed tomography (micro-CT) is therefore used to examine the impact of morphology on zone II combustion for pulverized (∼100 µm) biomass char particles for the first time. In contrast to larger, millimeter to centimeter sized particles, the sub-millimeter, high aspect ratio biomass char particles exhibited localized reactant penetration into the innermost regions of the particles, facilitated by the presence of large pores connected to the external surface. The oxygen mole fraction distributions were governed by the large pore morphology, were non-monotonic with distance from the surface, and achieved minima in thick microporous char regions surrounding the large pores. A comparison between the pore-resolving simulation and an equivalent, spatially resolved, effective-continuum simulation revealed that even in the microporous char, the effective-continuum model underpredicted reactant penetration. A careful comparison was then performed between 30 pore-resolving particle simulations and several effectiveness factor models that employed particle-specific parameters. Commonly used uniform cylinder models significantly underpredicted effectiveness factors for these real pulverized pine char particles, while accessible hollow cylinder models achieved less than 10% relative error when averaged over all 30 particles.