Zhang Hong, Wu Suozhen, Yang Yunfei, Cheng Jianlin, Lun Fei, Wang Qingsong
State Key Laboratory of Coal Processing and Efficient Utilization, Ministry of Education, China University of Mining & Technology, Xuzhou, Jiangsu 221116, China.
School of Chemical Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116, China.
ACS Omega. 2020 Feb 25;5(9):4386-4394. doi: 10.1021/acsomega.9b02928. eCollection 2020 Mar 10.
This study aims to explore the mechanism under which ash deposition propensity is improved by coal blending in a real modern boiler situation. In this paper, Zhundong coal (ZD), from northwestern China, known to have a heavy ash deposition problem in boilers, was blended with Jincheng anthracite (JC), which has a high ash fusion temperature (AFT). The density composition of the coal blend, which reflects the mineral distribution in pulverized coals, was found to change during the intergrinding process. The higher rank coal JC was found to be more concentrated in its lower and highest density fractions. The variances in the chemical composition among density fractions in the pulverized coal blend were found greatly narrowed as compared with the parent coals. AFT results indicate that the ash melting behavior in the coal blend (ZD/JC = 50:50) varies with density, which is confirmed by corresponding slag contents calculated with FactSage 7.1. Particle size distributions of the density fractions in ZD, JC, and the coal blend were determined with a laser particle analyzer. The size distribution of ash particles in each density fraction was estimated according to the char morphology, which is deduced from the ash content and coal particle size distribution. Minerals in the lowest density fractions will form ash with a particle size of around 2 μm. Included minerals in the medium density fractions will form ash particles with size related to its ash content, and excluded minerals will undergo slight fragmentation and have a ash particle size similar to the corresponding coal particles. A comprehensive comparison between ash volume, ash particle size, and softening temperature indicates that ash deposition propensity of the coal blend is improved not only because of an apparent increase in AFT but also because of an apparent decrease in the total volume of ash particles possibly arriving on the deposition surface.
本研究旨在探索在实际现代锅炉工况下通过配煤改善积灰倾向的机制。在本文中，来自中国西北部的准东煤（ZD），已知在锅炉中存在严重的积灰问题，与具有高灰熔点（AFT）的晋城无烟煤（JC）进行了混合。发现反映煤粉中矿物质分布的混煤密度组成在混合研磨过程中发生了变化。发现变质程度较高的煤JC在其较低和最高密度级分中更为集中。与原煤相比，发现煤粉混煤中密度级分之间的化学成分差异大大缩小。AFT结果表明，混煤（ZD/JC = 50:50）中的灰熔融行为随密度而变化，这通过使用FactSage 7.1计算的相应炉渣含量得到了证实。用激光粒度分析仪测定了ZD、JC和混煤中密度级分的粒度分布。根据由灰分含量和煤粒度分布推导得出的焦炭形态，估算了每个密度级分中灰颗粒的尺寸分布。最低密度级分中的矿物质将形成粒径约为2μm的灰。中等密度级分中包含的矿物质将形成与其灰分含量相关的粒径的灰颗粒，而排除的矿物质将经历轻微破碎并具有与相应煤颗粒相似的灰颗粒尺寸。灰体积、灰颗粒尺寸和软化温度之间的综合比较表明，混煤的积灰倾向得到改善，不仅是因为AFT明显升高，还因为可能到达沉积表面的灰颗粒总体积明显减少。
