Liu Yanquan, Cheng Leming, Ji Jieqiang, Wang Qinhui, Fang Mengxiang
State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University Hangzhou 310027 P. R. China
RSC Adv. 2018 Oct 2;8(59):33817-33827. doi: 10.1039/c8ra05997g. eCollection 2018 Sep 28.
High alkali and alkali earth metals (AAEMs) content in coal causes severe slagging and fouling during combustion in a boiler. In this study, the ash deposition behavior of a high-alkali coal at different bed temperatures and the effect of kaolin were investigated in a 30 kW circulating fluidized bed (CFB) test system using an ash slagging probe and deposition probe. The results show that the ash deposition tendency increases with the bed temperature. The condensation of NaSO is an important inducement for slag formation in the furnace. The melting or partial melting of slags is attributed to Na-Fe-Ca eutectics. At 920 °C, NaSO will react with CaSO to form the low-melting compound of NaSO-CaSO. The deposited ash on the convection-heating surface consists of granular particles. On the windward side, the layered-structure ash deposits, the inner and outer layers, are formed at the bed temperature of 920 °C but are absent at lower temperatures (820 °C and 870 °C). The formation of the inner layer consists of fine particles (<2 μm) and is closely related to NaSO. The size of the deposited ash in the outer layer is larger than 10 μm, while that on the leeward side is less than 10 μm. By adding kaolin in the coal, the slags are replaced by loose particles due to the absorption reactions between kaolin and alkali metals. The ash deposition tendency is improved and the optimal result is achieved when kaolin is added at an addition ratio of 3%.
煤中高碱金属和碱土金属（AAEMs）含量会导致锅炉燃烧过程中严重的结渣和积灰。本研究在30kW循环流化床（CFB）试验系统中，使用灰渣探针和沉积探针，研究了高碱煤在不同床温下的灰沉积行为以及高岭土的影响。结果表明，灰沉积倾向随床温升高而增加。NaSO的凝结是炉内结渣的重要诱因。炉渣的熔化或部分熔化归因于Na-Fe-Ca共晶。在920℃时，NaSO会与CaSO反应形成低熔点化合物NaSO-CaSO。对流受热面上的沉积灰由颗粒状颗粒组成。在迎风面，在920℃的床温下会形成分层结构的灰沉积物，即内层和外层，但在较低温度（820℃和870℃）下不存在。内层的形成由细颗粒（<2μm）组成，且与NaSO密切相关。外层沉积灰的尺寸大于10μm，而背风面的沉积灰尺寸小于10μm。通过在煤中添加高岭土，由于高岭土与碱金属之间的吸收反应，炉渣被松散颗粒取代。灰沉积倾向得到改善，当高岭土添加比例为3%时可达到最佳效果。
