Apparent char kinetic rates are commonly used to predict pulverized coal char burning rates. These kinetic rates quantify the char burning rate based on the temperature of the particle and the oxygen concentration at the external particle surface, inherently neglecting the impact of variations in the internal diffusion rate and penetration of oxygen. To investigate the impact of bulk gas diffusivity on these phenomena during Zone II burning conditions, experimental measurements were performed of char particle combustion temperature and burnout for a subbituminous coal burning in an optical entrained flow reactor with helium and nitrogen diluents. The combination of much higher thermal conductivity and mass diffusivity in the helium environments resulted in cooler char combustion temperatures than in equivalent N₂ environments. Measured char burnout was similar in the two environments for a given bulk oxygen concentration but was approximately 60% higher in helium environments for a given char combustion temperature. To augment the experimental measurements, detailed particle simulations of the experimental conditions were conducted with the SKIPPY code. These simulations also showed a 60% higher burning rate in the helium environments for a given char particle combustion temperature. To differentiate the effect of enhanced diffusion through the external boundary layer from the effect of enhanced diffusion through the particle, additional SKIPPY simulations were conducted under selected conditions in N₂ and He environments for which the temperature and concentrations of reactants (oxygen and steam) were identical on the external char surface. Under these conditions, which yield matching apparent char burning rates, the computed char burning rate for He was 50% larger, demonstrating the potential for significant errors with the apparent kinetics approach. However, for specific application to oxy-fuel combustion in CO₂ environments, these results suggest the error to be as low as 3% when applying apparent char burning rates from nitrogen environments.

表观炭动力学速率通常用于预测煤焦粉的燃烧速率。这些动力学速率基于颗粒的温度和外部颗粒表面的氧气浓度来量化炭燃烧速率，从而固有地忽略了内部扩散速率和氧气渗透率变化的影响。为了研究在II区燃烧条件下散装气体扩散率对这些现象的影响，对焦炭颗粒燃烧温度和在含氦和氮稀释剂的光学夹带流反应器中燃烧次烟煤的燃尽进行了实验测量。氦气环境中更高的热导率和质量扩散率共同导致了比同等N ₂更低的焦炭燃烧温度环境。对于给定的整体氧气浓度，在两种环境下测得的焦炭燃尽情况相似，但对于给定的焦炭燃烧温度，在氦气环境中测得的燃尽程度大约高60％。为了增加实验测量值，使用SKIPPY代码对实验条件进行了详细的粒子模拟。这些模拟还表明，在给定的炭颗粒燃烧温度下，氦气环境中的燃烧速率提高了60％。为了区分通过外边界层的扩散增强效果和通过颗粒的扩散扩散效果，在选定的条件下，在N ₂中进行了附加的SKIPPY模拟在氦气环境中，外部焦炭表面上的反应物（氧气和蒸汽）的温度和浓度相同。在这些条件下，其产生的表观焦炭燃烧速率相匹配，计算出的He的焦炭燃烧速率要大50％，这表明表观动力学方法存在潜在的重大误差。但是，对于特定的CO ₂环境中的含氧燃料燃烧应用，这些结果表明，当应用氮环境中的表观焦炭燃烧速率时，该误差可低至3％。