The performance of biomass pyrolysis reactors depends on the interplay between chemical reactions, heat and mass transfer, and multiphase flow. These processes occur over a wide range of scales ranging from molecular to reactor level. Accurate predictions of the reactor behavior necessitate integrating adequate kinetic and particle-scale biomass devolatilization models with reactor-level CFD simulations. Global kinetic schemes and homogeneous particle models neglecting spatial variations are commonly used in CFD simulations. Recent CFD investigations have focused on using a spatially resolved particle description modeled by the mass, species, and energy conservation equations. However, the impact of these particle-scale models on the CFD predictions is unclear. This work investigates the role of particle-scale models of biomass devolatilization in CFD–DEM simulations of biomass pyrolysis in fluidized beds. To this end, spatially resolved and homogeneous particle models using a multistep kinetic scheme (with 24 reactions, 19 solid species, and 20 gas species) are integrated with a CFD–DEM framework. The impact of particle-scale models on three-dimensional CFD–DEM simulations is assessed for low (Bi = 0.26) and high (Bi = 1.6) Biot numbers. The relevant time scales are computed to analyze the coupling among various processes. We show that the particle-scale models primarily affect the transient behavior of species composition and bed hydrodynamics within the fluidized bed and have negligible impact on the product composition and yield at the reactor outlet. The cost of CFD–DEM simulations remained unchanged while using the homogeneous model. In contrast, it increased by 20% using the spatially resolved intraparticle model. This increase in cost is attributed to solving the governing equations of the intraparticle model and storing data for a spatially resolved biomass particle.

中文翻译：

---

颗粒尺度模型对生物质热解 CFD-DEM 模拟的影响


生物质热解反应器的性能取决于化学反应、传热传质以及多相流之间的相互作用。这些过程发生在从分子水平到反应器水平的广泛范围内。反应器行为的准确预测需要将足够的动力学和颗粒尺度生物质脱挥发分模型与反应器级 CFD 模拟相结合。 CFD 模拟中通常使用忽略空间变化的全局动力学方案和均质粒子模型。最近的 CFD 研究重点是使用由质量、物种和能量守恒方程建模的空间解析粒子描述。然而，这些粒子尺度模型对 CFD 预测的影响尚不清楚。这项工作研究了生物质脱挥发分的颗粒尺度模型在流化床生物质热解的 CFD-DEM 模拟中的作用。为此，使用多步动力学方案（具有 24 个反应、19 种固体物质和 20 种气体物质）的空间分辨均匀粒子模型与 CFD-DEM 框架集成。颗粒尺度模型对三维 CFD-DEM 模拟的影响通过低 (Bi = 0.26) 和高 (Bi = 1.6) 毕奥数进行评估。计算相关的时间尺度来分析各个过程之间的耦合。我们表明，颗粒尺度模型主要影响流化床内物质组成和床层流体动力学的瞬态行为，并且对反应器出口处的产物组成和产率的影响可以忽略不计。使用均质模型时，CFD-DEM 模拟的成本保持不变。相比之下，使用空间分辨粒子内模型则增加了 20%。 成本的增加归因于求解颗粒内模型的控制方程以及存储空间分辨生物质颗粒的数据。