Particle formation during pressurized entrained flow gasification of wood powder : effects of process conditions on chemical composition, nanostructure, and reactivity
Particle formation during pressurized entrained flow gasification of wood powder : effects of process conditions on chemical composition, nanostructure, and reactivity
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DOI：
10.1016/j.combustflame.2017.10.025
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发表时间：
2018-03
影响因子：
4.4
通讯作者：
H. Wiinikka;P. Toth;K. Jansson;R. Molinder;M. Broström;L. Sandström;J. Lighty;F. Weiland
中科院分区：
文献类型：
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作者：
H. Wiinikka;P. Toth;K. Jansson;R. Molinder;M. Broström;L. Sandström;J. Lighty;F. Weiland
以灰分为0.4 wt%的木粉为原料，研究了加压吹氧气化过程中操作条件对颗粒形成的影响。调查是在一个中试规模的气化炉在7巴(a)下进行的。测试了400和600 kW两个负载，氧当量比（λ）在0.25 ~ 0.50之间变化。利用低压级联冲击器分析颗粒浓度和质量尺寸分布，并利用扫描电镜、高分辨率透射电镜、能量色散光谱和热重分析对收集到的颗粒进行形貌、元素组成、纳米结构和反应性表征。为了量化颗粒的纳米结构和识别普遍的亚结构，采用了一种新的图像分析框架。结果表明，工艺温度和气化炉负荷对颗粒形成过程有显著影响。在低温（1060℃）下，形成的烟尘颗粒似乎具有抗氧化性；然而，当氧化过程在1119°C开始时，活性更强的颗粒核心开始内部燃烧。温度进一步升高（ > 1313°C）会导致反应性较差的粒子壳的氧化。当外壳因严重氧化而最终坍塌时，原有的烟尘颗粒形状和纳米结构也随之消失，产生的颗粒不再被认为是烟尘。相反，在最高温度（ > 1430°C）下的颗粒形状和纳米结构是无机含量和单个颗粒组成的无机元素的函数。这些影响共同导致煤烟颗粒在真实气化炉环境中，随着温度的升高，其纳米结构的有序度越来越低，反应活性越来越高；也就是说，他们遵循了与实验室规模研究中观察到的相反的趋势，这些研究中使用的燃料不含任何形成灰烬的元素，并且温度不受λ控制。
The influence of operating condition on particle formation during pressurized, oxygen blown gasification of wood powder with an ash content of 0.4 wt% was investigated. The investigation was performed with a pilot scale gasifier operated at 7 bar(a). Two loads, 400 and 600 kW were tested, with the oxygen equivalence ratio (λ) varied between 0.25 and 0.50. Particle concentration and mass size distribution was analyzed with a low pressure cascade impactor and the collected particles were characterized for morphology, elemental composition, nanostructure, and reactivity using scanning electron microscopy/high resolution transmission electron microscopy/energy dispersive spectroscopy, and thermogravimetric analysis. In order to quantify the nanostructure of the particles and identify prevalent sub-structures, a novel image analysis framework was used. It was found that the process temperature, affected both byλand the load of the gasifier, had a significant influence on the particle formation processes. At low temperature (1060 °C), the formed soot particles seemed to be resistant to the oxidation process; however, when the oxidation process started at 1119 °C, the internal burning of the more reactive particle core began. A further increase in temperature ( > 1313 °C) lead to the oxidation of the less reactive particle shell. When the shell finally collapsed due to severe oxidation, the original soot particle shape and nanostructure also disappeared and the resulting particle could not be considered as a soot anymore. Instead, the particle shape and nanostructure at the highest temperatures ( > 1430 °C) were a function of the inorganic content and of the inorganic elements the individual particle consisted of. All of these effects together lead to the soot particles in the real gasifier environment having less and less ordered nanostructure and higher and higher reactivity as the temperature increased; i.e., they followed the opposite trend of what is observed during laboratory-scale studies with fuels not containing any ash-forming elements and where the temperature was not controlled byλ.