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Effect of coal particle size distribution on packed bed pressure drop and gas flow distribution

机译：煤的粒径分布对填充床压降和气流分布的影响

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This paper focuses on the role of coal particle size distribution on pressure drop and gas flow distribution through packed coal beds. This fundamental knowledge is helpful in better understanding the operational behaviour of fixed bed dry bottom gasifiers. The Sasol synfuels plants in South Africa use 80 such gasifiers to convert more than 26 million tons of coal per annum to synthesis gas, and ensuring stable operation is of primary importance to ensure high synthesis gas production rates and gasifier availability. Pressure drop measurements on laboratory scale equipment were conducted to investigate the effect of particle size distribution on packed bed pressure drop. The well-known Ergun equation for pressure drop does not accommodate the effect of size distribution on pressure drop. A novel approach was followed to model pressure drop through simulated coal bed structures using Computational Fluid Dynamics (CFD). The coal bed structures were simulated by assuming that the coal particles are represented by randomised convex polyhedra in three-dimensional space. The computational space was divided into polyhedra using statistical Voronoi tessellation technique, which have been shown to be versatile in modelling problems in many fields, e.g. nitration, molecular physics, metallurgy, geology, forestry and astrophysics. This approach of flow modelling through packed coal beds is able to accommodate size distribution effects on pressure drop and gas flow distribution. The modelling work shows large deviations from plug flow with broad size distributions. The lowest bed pressure drop with the closest approximation to plug flow is obtained with the narrowest particle size distribution. Low gas flow rates are also beneficial for reducing excessive channel flow. Combustion profiles for different particle size distributions were studied using a pilot scale combustor. The combustion profiles provide confirmation of the CFD modelling results, namely that narrow particle size distributions and low gas flow rates reduce channel burning. Excessive channel burning was observed for broad particle size distributions, and is enhanced by high gas flow rates. The experimental and modelling work which was conducted, clearly indicate that narrow coal particle size distributions are desirable for optimum gas flow distribution and lowest packed bed pressure drop.
机译：本文着重研究煤颗粒尺寸分布对压降和填充煤床气流分布的作用。这些基础知识有助于更好地了解固定床干底气化炉的运行性能。南非的萨索尔（Sasol）合成燃料工厂使用80台这样的气化炉，每年将超过2600万吨的煤转化为合成气，确保稳定的运行对于确保高的合成气生产率和气化炉的可用性至关重要。在实验室规模的设备上进行了压降测量，以研究粒度分布对填充床压降的影响。众所周知的压降Ergun方程无法适应尺寸分布对压降的影响。遵循一种新颖的方法，使用计算流体动力学（CFD）对模拟煤层结构中的压降进行建模。通过假设煤颗粒由三维空间中的随机凸多面体表示来模拟煤层结构。使用统计Voronoi细分技术将计算空间划分为多面体，这已被证明可用于许多领域的建模问题。硝化，分子物理学，冶金，地质，林业和天体物理学。通过填充煤层进行流建模的这种方法能够适应尺寸分布对压降和气流分布的影响。建模工作表明，与柱塞流的偏差较大，尺寸分布较广。在最窄粒度分布的情况下，可获得与活塞流最接近的最低床压降。低气体流速也有利于减少过多的通道流量。使用中试燃烧室研究了不同粒径分布的燃烧曲线。燃烧曲线提供了CFD建模结果的确认，即狭窄的粒径分布和低气体流速减少了通道燃烧。对于较宽的粒度分布，观察到通道燃烧过度，并且由于高气体流速而加剧了燃烧。进行的实验和建模工作清楚地表明，窄煤颗粒尺寸分布对于最佳气流分布和最低填充床压降是理想的。

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