Measurement of atomic sodium release during pyrolysis and combustion of sodium-enriched Zhundong coal pellet
Measurement of atomic sodium release during pyrolysis and combustion of sodium-enriched Zhundong coal pellet
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DOI：
10.1016/j.combustflame.2016.10.020
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发表时间：
2017-02
影响因子：
4.4
通讯作者：
Zhihua Wang;Yingzu Liu;R. Whiddon;Kaidi Wan;Yong He;J. Xia;K. Cen
中科院分区：
文献类型：
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作者：
Zhihua Wang;Yingzu Liu;R. Whiddon;Kaidi Wan;Yong He;J. Xia;K. Cen
针对高钠煤（准东）颗粒的燃烧，提出了表面温度、颗粒直径和近端钠浓度场的时间分辨测量。使用非共振平面激光诱导荧光 (PLIF) 对煤球周围的原子钠分布进行成像。原子钠的释放曲线显示了燃烧的三个阶段：(I) 脱挥发分阶段、(II) 炭烧尽阶段和 (III) 灰分反应阶段。钠浓度最高峰值出现在烧焦阶段，而灰化阶段持续时间最长。分析了燃烧不同阶段的径向和轴向钠浓度衰减。在烧焦和灰化阶段，原子钠的最大浓度在颗粒附近。在脱挥发分阶段，挥发性气体的燃烧在远离煤球表面的地方产生高温区域，从而促进了该区域中钠化合物的分解。原子钠浓度的轴向衰减受所有燃烧阶段的化学反应控制。原子钠通量（Na*flux）的计算表明，较小的颗粒在脱挥发分和烧焦阶段比较大的颗粒更强烈地释放原子钠。钠释放的机理是从Na*通量的时间导数、颗粒表面温度(T)和颗粒直径(d)推断出来的。在脱挥发分阶段，只有Na*通量和T表现出变化，表明原子钠的释放是由于煤球团的热解造成的。在烧焦阶段，三个参数的时间导数服从共同趋势，表明钠的释放与颗粒中有机成分的燃烧有关。在灰分反应阶段，Tandd 保持恒定，表明原子钠的释放可能归因于灰分中的缓慢过程，可能是钠从结晶固体中蒸发。本研究开发了两步钠释放动力学，模拟结果与煤球团三个燃烧阶段的测量结果非常吻合。
Temporally resolved measurements of surface temperature, pellet diameter and proximal sodium concentration field are presented for the combustion of a high sodium coal (Zhundong) pellet. Non-resonant Planar laser-induced fluorescence (PLIF) was used to image the atomic sodium distribution around the coal pellet. The release profile of atomic sodium demonstrates three phases of combustion: (I) the devolatilization stage, (II) the char burnout stage, and (III) the ash reaction stage. Highest peak sodium concentration occurred in the char burnout stage, while the ash stage had the longest duration. The radial and axial sodium concentration decay during different phases of combustion was analyzed. During char burnout and ash stages, the maximum concentration of atomic sodium was near the pellet. In the devolatilization stage, burning of volatile-gases creates a high temperature region away from the surface of the coal pellet, which enhances the decomposition of sodium compounds in this region. Axial decay of atomic sodium concentration was governed by chemical reactions during all combustion stages. Calculation of atomic sodium flux (Na*flux) indicate that the smaller pellet releases atomic sodium more strongly in the devolatilization and char burnout stages than larger pellet. The mechanism of sodium release was inferred from the time derivatives of Na*flux, pellet-surface temperature (T) and pellet diameter (d). During the devolatilization stage, only Na*fluxandTshow variations, indicating that atomic sodium release is due to pyrolysis of the coal pellet. In the char burnout stage, time derivatives of the three parameters obey a common trend, indicating that the sodium release is associated with the burning of organic components in the pellet. In the ash reaction stage,Tanddremain constant, indicating that the release of atomic sodium may be attributed to slow processes in the ash, likely vaporization of sodium from crystalline solids. A two-steps sodium release kinetics has been developed in this study and the simulation results agree well with measurements at three burning stages of coal pellet.