Combustibility of dried sewage sludge and its mineral transformation at different oxygen content in drop tube furnace
Combustibility of dried sewage sludge and its mineral transformation at different oxygen content in drop tube furnace
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DOI：
10.1016/j.fuproc.2003.10.021
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发表时间：
2004-07
影响因子：
7.5
通讯作者：
Lian Zhang;Masahide Ito;A. Sato;Y. Ninomiya;T. Sakano;Chikao Kanaoka;M. Masui
中科院分区：
文献类型：
--
作者：
Lian Zhang;Masahide Ito;A. Sato;Y. Ninomiya;T. Sakano;Chikao Kanaoka;M. Masui
在实验室沉降炉中对两种污泥进行了燃烧试验，以了解其燃烧特性和矿物质的变化规律。实验条件选择为：反应温度为1200 °C;氧含量为10%、30%和50%;停留时间为0.6 ~ 2.4 s。实验结果表明，增加污泥中的氧含量可以显著提高污泥的燃烧性能。具有高挥发性物质的污泥，例如，污泥B中的70.8%在50%O2下不能完全燃烧，这是由于形成的灰包围着燃烧的炭，阻碍了氧向未燃碳的扩散，约2-6%的未燃碳保留在灰中，粒径约1.5 μm。此外，在低氧条件下，污泥中的主要矿物化合物，包括氧化钙、氧化磷和铝硅酸盐，主要在焦炭中聚结形成大的熔融团聚体。氧含量的增加导致污泥快速分解，因此，形成许多液滴并浓缩成细颗粒。最后，建立了钠和锌的蒸发模型，考虑了这两种元素与焦炭的内扩散和它们与磷酸盐的反应。仿真结果与实验结果有较好的一致性。钠主要在灰层内受其内部传质扩散控制而释放。相反，锌释放的控制下，内部传质扩散和它与熔融磷酸盐的反应。氧含量的提高降低了灰层中的扩散阻力，从而使更多的钠和锌蒸发。
Combustion of two kinds of sludge was studied in a laboratory-scaled drop tube furnace to understand their combustibility and evolution of mineral matters in the process. Experimental conditions were selected as: reaction temperature was 1200 °C; oxygen content was 10%, 30% and 50%, and the residence time varied from 0.6 to 2.4 s. The experimental results show that increasing the oxygen content significantly improved the combustibility of sludge. Sludge with high volatile matter, e.g., 70.8% in sludge B, could not combust completely even at 50% O2, which is due to the fact that the formed ash surrounded the combusting char, it acted as a resistance for the diffusion of oxygen to unburnt carbon, about 2–6% unburnt carbon, having particle size of about 1.5 μm, was kept in the ash. In addition, at low oxygen content, the major mineral compounds in sludge, including calcium oxide, phosphorus oxide and aluminosilicate, mainly underwent coalescence within char to form the large molten agglomerates. Increasing oxygen content resulted in the rapid decomposition of sludge, and accordingly, many droplets were formed and condensed into fine particles. Finally, the vaporization model for both sodium and zinc was built considering the internal diffusion of both two elements with char and their reaction with phosphates. The simulation results had a fairly good consistence with experiments. Sodium was mainly released under the controlling of its internal mass-transfer diffusion within ash layer. Conversely, zinc was released under the controlling of both internal mass-transfer diffusion and its reaction with molten phosphate salts. Improving oxygen content mitigated the diffusion resistance in ash layer, and hence, more the sodium and zinc were vaporized.