Release of potassium in association with structural evolution during biomass combustion
Release of potassium in association with structural evolution during biomass combustion
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DOI：
10.1016/j.fuel.2020.119524
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发表时间：
2020-11
期刊：
影响因子：
7.4
通讯作者：
Wen Cao;Jun Li;Leteng Lin;Xiaolei Zhang
中科院分区：
文献类型：
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作者：
Wen Cao;Jun Li;Leteng Lin;Xiaolei Zhang
了解钾释放的机理对于减轻生物质燃烧过程中钾引起的灰分问题至关重要。本文研究了操作条件对麦秸燃烧过程中钾离子释放和转化的影响，阐明了与生物质颗粒结构变化相关的钾离子释放电位。燃烧试验是在一个实验室规模的反应堆中进行的，工作温度和加热速率范围很广。研究发现，在高达1000℃的温度下，生物质样品的燃烧导致其初始钾含量的60%以上的释放。将升温速率从8°C/min提高到25°C/min，可以使钾的额外释放量达到初始量的20%。本研究得出了钾离子的三阶段释放机制：第一步释放阶段（400℃以下）、保持阶段（400 ~ 700℃）和第二阶段释放阶段（700℃以上）。进行了元素（即K、S、O、Si）分布的综合形貌分析；结果进一步证实，钾可能存在于生物质颗粒的茎状通道内，主要以无机盐的形式存在。在升温过程中，生物质颗粒结构的破坏和崩塌会使体内钾元素暴露出来，从而加速钾元素的释放和钾元素存在形态的转变。最后，提出了一种详细的温度依赖性钾释放机制，该机制可作为通过优化燃烧过程来减少有害钾化合物释放的指导。
A mechanistic understanding of potassium release is essential to mitigate the potassium-induced ash problems during biomass combustion. This work studies the effects of operational condition on the potassium release and transition during the combustion of wheat straw, and elucidate the release potential of potassium associated with the structural change of biomass particles. The combustion tests were carried out in a laboratory-scale reactor, working in a wide range of temperatures and heating rates. It was found that the combustion of biomass sample at a temperature up to 1000 °C results in a release of over 60% of its initial potassium content. Raising the heating rate from 8 °C/min to 25 °C/min could lead to an additional release of up to 20% of the initial amount of potassium. A three-stage potassium release mechanism has been concluded from this work: the initial-step release stage (below 400 °C), the holding stage (400–700 °C) and the second-step release stage (above 700 °C). Comprehensive morphology analysis with elemental (i.e. K, S, O, Si) distribution was carried out; the results further confirmed that potassium is likely to exist inside the stem-like tunnel of biomass particles, mainly in forms of inorganic salts. During the heating-up process, the breakdown and collapse of biomass particle structure could expose the internally located potassium and thus accelerate the release of potassium and the transform of its existing forms. Lastly, a detailed temperature-dependent release mechanism of potassium was proposed, which could be used as the guidance to mitigate the release of detrimental potassium compounds by optimising the combustion process.