Xinjiang lignite ash slagging and flow under the weak reducing environment at 1300 °C – Release of sodium out of slag and its modelling from the mass transfer perspective
Xinjiang lignite ash slagging and flow under the weak reducing environment at 1300 °C – Release of sodium out of slag and its modelling from the mass transfer perspective
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DOI：
10.1016/j.fuproc.2017.10.016
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发表时间：
2018-02
影响因子：
7.5
通讯作者：
Hengsong Ji;Xiaojiang Wu;Baiqian Dai;Lian Zhang
中科院分区：
文献类型：
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作者：
Hengsong Ji;Xiaojiang Wu;Baiqian Dai;Lian Zhang
在模拟旋流燃烧条件下，研究了新疆5种典型褐煤灰及其与粘土按不同比例混合后的结渣过程中Na的损失。将灰分样品装载在25°倾斜板上，并在1000-1300 °C下暴露于1%CO（氮平衡）中，在每个温度下最多2小时。除了实验方法外，还尝试了基于传质机理的建模。结果表明，所获得的Na损失率低于已报道的相同煤在煤粉燃烧厂中燃烧的Na损失率，在整个Na的40%至70%之间变化，这在很大程度上取决于灰或灰-粘土混合物的碱度。这里检查的反应温度施加的钠损失的边际影响。粘土的加入量和用量是影响粉煤灰质量的关键因素.在1300 °C的温和燃烧温度下，以灰质量为基础向碱性褐煤灰中添加8-10wt%的粘土是最佳的，同时加速炉渣流动速率和炉渣基质中的Na保留。粘土的加入减轻了钠蒸气对耐火材料的渗透和侵蚀，从而延长了耐火材料的使用寿命。Na损失速率受渣膜内Na蒸气的内部传质速率的支配，特别是在从1300 °C升高的温度下，当灰部分/大部分熔融时，以及当粘土被添加到原始新疆灰中时。对于在1200 °C之前很少熔化的原始灰，气-固反应占优势，导致Na蒸气被含Al和Fe的固体物质甚至耐火的绝热板捕获。相反，在1300 °C时，渣膜的形成使Na蒸汽传质系数急剧下降。在加入粘土后，由于形成更多的熔融物质和更致密的渣膜，阻力进一步增大。灰分中的原始Na含量已被证明在质量扩散控制制度中是微不足道的。
This study examined the Na loss upon the slagging of five typical Xinjiang lignite ashes and their blends with clay at different ratios, under the simulated cyclone combustion conditions. The ash samples were laden on a 25° – inclined plate and exposed in 1% CO (nitrogen balanced) at 1000–1300 °C for maximum 2 h at each temperature. Apart from experimental approach, modelling based on the mass transfer mechanism was also attempted. The results show that, the Na loss ratios achieved are lower than that has been reported for the combustion of the same coals in the pulverised – coal fired plants, varying from 40 to 70% of the entire Na that largely depends on the basicity of ash or ash – clay blend. The reaction temperatures examined here exert a marginal influence on the Na loss. The addition of clay to raw coal ash and its dosage amount are crucial. At a mild combustion temperature of 1300 °C, the addition of 8–10wt% clay, on the ash mass basis to a basic lignite ash is the optimum, simultaneously accelerating both slag flow rate and Na retention in slag matrix. Additionally, the addition of clay alleviated the penetration and corrosion of Na vapour into the refractory corundum, thus extended its lifespan. The Na loss rate is dominated by the internal mass transfer rate of Na vapour inside slag film, in particular at the elevated temperatures from 1300 °C when ash is partially/mostly molten, as well as when the clay is added into the original Xinjiang ash. For the original ash which is rarely molten before 1200 °C, the gas-solid reaction prevailed, leading to the capture of Na vapour by Al and Fe – bearing solid species and even the refractory corundum plate. In contrast, at 1300 °C, the formation of slag film decreased the Na vapour mass transfer coefficient drastically. The resistance was further enlarged by the formation of more molten species and a denser slag film upon the addition of clay. The original Na content in ash has proven insignificant in the mass diffusion control regime.