Effect of CO2 gasification reaction on char particle combustion in oxy-fuel conditions
Effect of CO2 gasification reaction on char particle combustion in oxy-fuel conditions
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DOI：
10.1016/j.fuel.2013.12.004
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发表时间：
2014-03
期刊：
影响因子：
7.4
通讯作者：
D. Kim;Sangmin Choi;C. Shaddix;M. Geier
中科院分区：
文献类型：
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作者：
D. Kim;Sangmin Choi;C. Shaddix;M. Geier
煤焦CO2气化在烟气再循环的富氧燃烧环境中可能发挥重要作用，但其对总反应速率的影响尚未得到明确的认识。为了明确CO2气化对煤粉焦富氧燃烧的可能影响，采用表观焦反应性和单膜模型（包括Stefan流对质量和能量传递的影响）对煤粉焦颗粒进行了燃尽模拟。三个氧气浓度（21%，30%，和5%O2），代表空气，氧燃料，和缺氧燃烧环境进行了模拟。采用一种新的实验方法直接测定了亚烟煤半焦在高温常压下的CO2气化速率。测得的气化率略高于以前的测量。模拟结果表明，吸热气化反应降低了焦炭颗粒的温度，从而降低了氧化速率。但由于直接气化反应对碳耗的贡献，焦炭燃尽时间和碳耗均有所改善。气化反应对贫氧环境中的焦炭燃尽时间和相对碳消耗以及富氧环境中的颗粒温度下降（对于给定的气体温度）具有较大的影响。此外，气化反应对焦炭燃烧的影响随着气体温度的升高和颗粒尺寸的增大而增大。此外，据观察，气化反应的影响取决于假定的动力学速率，这突出了在模拟中使用可靠的动力学参数的重要性。基于目前的研究结果，重要的是要包括气化反应CO2模拟焦炭燃烧在富氧燃烧环境中。
CO2gasification of coal char may play an important role in oxy-combustion environments with flue gas recirculation (FGR), but its effect on the overall reaction rate has not been clearly understood. To give clarity to the likely impact of CO2gasification on the oxy-combustion of pulverized coal chars, burnout simulations of coal char particles were carried out, adopting apparent char reactivity and a single-film model that includes the Stefan flow effect on mass and energy transfer. Three oxygen concentrations (21%, 30%, and 5% O2), representing air, oxy-fuel, and oxygen-deficient combustion environments were simulated. A new experimental approach was used to directly measure the CO2gasification rate of a subbituminous coal char at high temperatures and atmospheric pressure. The measured gasification rate is somewhat higher than previous measurements. The simulation results show that the endothermic gasification reaction reduces the char particle temperature and thereby reduces the oxidation rates. However, due to the contribution of the direct gasification reaction on carbon consumption, the char burnout time and the carbon consumption were improved. The gasification reaction has a greater influence on the char burnout time and the relative carbon consumption in an oxygen-deficient environment and on the drop of particle temperature in an oxygen-enriched environment (for a given gas temperature). In addition, the influence of the gasification reaction on char combustion increases as the gas temperature increases and as the particle size increases. Further, it was observed that the impact of the gasification reaction is dependent on the presumed kinetic rate, which highlights the importance of using reliable kinetic parameters in simulations. Based on the present results, it is important to include the gasification reaction by CO2when simulating char combustion in oxy-fuel combustion environments.