Release characteristics of AAEMs and physicochemical structural evolution of char during rapid coal pyrolysis
-
摘要: 本研究基于高频炉反应器开展准东煤的快速热解实验,探究碱及碱土金属(AAEMs)的释放特性及其与煤焦理化性质演变的关联。热解停留时间、气氛是影响AAEMs迁移特性及煤焦理化性质演变的重要过程参数。研究表明,AAEMs的释放率随热解停留时间的延长而增大,Na、Mg和Ca的最大释放率分别为61.05%、64.47%、44.01%。CO2气氛能显著提高煤热解过程中AAEMs的释放率,CO2对Na释放的促进作用主要发生在快速热解初期,而对Mg和Ca释放的促进作用主要表现在快速热解中后期。CO2气氛促进挥发分释放,加快含氧官能团及脂肪族官能团分解,促进煤焦表面裂纹形成,从而促进煤快速热解过程煤中AAEMs的释放。Abstract: Rapid pyrolysis experiment of Zhundong coal was conducted in a high-frequency furnace to investigate release characteristics of alkali and alkaline earth metals (AAEMs) and its correlation with changes of physical and chemical properties of char. Residence time and atmosphere during pyrolysis were important process parameters that affected the migration characteristics of AAEMs and physicochemical structural evolution of char. Experimental results show that the release of AAEMs in coal char increases over time. The maximum release rate of Na, Mg and Ca is 61.05%, 64.47%, and 44.01%, respectively. Promoting effect of CO2 on release of Na mainly occurs in the initial stage of rapid pyrolysis, nevertheless the promoting effect on release of Mg and Ca mainly is in the middle and late stage. CO2 accelerates release of AAEMs by promoting release of volatiles, facilitating decomposition of oxygen-containing functional groups and aliphatic functional groups, and promoting formation of cracks on surface of coal char.
-
表 1 煤样的工业分析及元素分析
Table 1 Proximate analysis and ultimate analysis of coal sample
Sample Proximate analysis wad/% Ultimate analysis wad/% V FC A M N H C S O* ZD 27.54 59.76 5.49 7.21 0.66 3.27 69.05 0.63 13.69 ad: air dried basis; *: calculation by subtraction 表 2 灰分分析
Table 2 Ash analysis of coal sample
Sample Ash composition/% SiO2 Al2O3 K2O Na2O CaO Fe2O3 MgO others ZD 10.86 8.41 0.11 8.31 21.59 9.28 13.55 27.89 others: other grey components in grey samples such as SO3, P2O5, TiO2 etc 表 3 900 ℃下煤颗粒在不同长度加热管内的停留时间
Table 3 Residence time of coal particles in heating tubes of different lengths at 900 ℃
Atmosphere Residence time of different isothermal zone t/ms 40 mm 80 mm 120 mm 150 mm N2 164 328 492 615 CO2 159 317 475 594 -
[1] 吴学成, 王勤辉, 骆仲泱, 方梦祥, 岑可法. 不同常压流化床煤气化方案的模型预测Ⅰ. 模型建立及验证[J]. 燃料化学学报,2004,32(3):287−291. doi: 10.3969/j.issn.0253-2409.2004.03.007WU Xue-cheng, WANG Qin-hui, LUO Zhong-yang, FANG Meng-xiang, CEN Ke-fa. Kinetic model prediction for various coal gasification schemes in a fluidized bed Ⅰ. Model establishment and validation[J]. J Fuel Chem Technol,2004,32(3):287−291. doi: 10.3969/j.issn.0253-2409.2004.03.007 [2] 刘家利, 何红光. 新疆准东煤特性研究及其锅炉选型[J]. 热力发电,2010,39(8):38−40. doi: 10.3969/j.issn.1002-3364.2010.08.038LIU Jia-li, HE Hong-guang. Study on properties of Zhundong coal in Xinjiang region and type-selection for boilers burning this coal sort[J]. Therm Power Gener,2010,39(8):38−40. doi: 10.3969/j.issn.1002-3364.2010.08.038 [3] 齐晓宾, 宋国良, 宋维健, 吕清刚. 准东高碱煤气化解过程中碱金属迁移与结渣特性实验研究[J]. 燃料化学学报,2015,43(8):906−913. doi: 10.3969/j.issn.0253-2409.2015.08.002QI Xiao-bin, SONG Guo-liang, SONG Wei-jian, LV Qing-gang. Alkali metal migration and slagging characteristic during Zhundong high-alkali coal gasification[J]. J Fuel Chem Technol,2015,43(8):906−913. doi: 10.3969/j.issn.0253-2409.2015.08.002 [4] 刘大海, 张守玉, 陈川, 涂圣康, 金涛, 郑红俊, 吴巧美, 邓文祥, 唐文蛟, 施大钟, 吕俊复. 新疆高钠煤脱钠提质过程中钠存在形式[J]. 煤炭学报,2014,39(12):2519−2524.LIU Da-hai, ZHANG Shou-yu, CHEN Chuan, TU Sheng-kang, JIN Tao, ZHENG Hong-jun, WU Qiao-mei, DENG Wen-xiang, TANG Wen-jiao, SHI Da-zhong, LV Jun-fu. Existence form of sodium in the high sodium coals from Xinjiang during its sodium removal process[J]. J China Coal Soc,2014,39(12):2519−2524. [5] 周永刚, 范建 勇, 李培, 王炳辉, 赵虹. 高碱金属准东煤结渣特性试验[J]. 浙江大学学报,2014,48(11):2061−2065.ZHOU Yong-gang, FAN Jian-yong, LI Pei, WANG Bing-hui, ZHAO Hong. Slagging characteristics of high alkalis Zhundong coal[J]. J Zhejiang Univ,2014,48(11):2061−2065. [6] 程可扬, 方云鹏, 吴亮, 祝宇涵, 朱荣锦, 胡义卿, 张生富. 碱金属碳酸盐对焦炭气化反应的催化动力学研究[C]//第十二届中国钢铁年会论文集: 北京: 冶金工业出版社, 2019.CHENG Ke-yang, FANG Yun-peng, WU Liang, ZHU Yu-han, ZHU Rong-jin, HU Yi-qing, ZHANG Sheng-fu. Kinetics of Coke Gasification Reaction under Catalysis of Alkali Carbonates[C]//Proceedings of the 12th CSM Steel Congress: Beijing: Metallurgical Industry Press, 2019. [7] 樊文克, 崔童敏, 李宏俊, 常清华, 郭庆华, 于广锁, 王辅臣. 碱金属碱土金属对神府煤焦气化活性的影响[J]. 燃料化学学报,2016,44(8):897−903. doi: 10.3969/j.issn.0253-2409.2016.08.001FAN Wen-ke, CUI Tong-ming, LI Hong-jun, CHANG Qing-hua, GUO Qing-hua, YU Guang-suo, WANG Fu-chen. Effect of AAEM on gasification reactivity of Shenfu char[J]. J Fuel Chem Technol,2016,44(8):897−903. doi: 10.3969/j.issn.0253-2409.2016.08.001 [8] 俞书才. 碱金属条件下焦炭与水蒸汽气化反应的研究[D]. 安徽: 安徽工业大学, 2017.YU Shu-cai. Research on gasification of coke with H2O under alkali condition[D]. Anhui: Anhui University of Technology, 2017. [9] MURRAY J B. Changes in state of combination of inorganic constituents during carbonization of Victorian brown coal[J]. Fuel,1973,52(2):105−111. doi: 10.1016/0016-2361(73)90030-6 [10] WEI X F, HUANG J J, LIU T F, FANG Y T, WANG Y. Transformation of alkali metals during gasification and gasification of a lignite[J]. Energy Fuels,2008,22(3):1840−1844. doi: 10.1021/ef7007858 [11] LI R B, CHEN Q, ZHANG X Z. Detailed investigation on sodium (Na) species release and transformation mechanism during gasification and char gasification of high-Na Zhundong coal[J]. Energy Fuels,2017,31:5902−5912. doi: 10.1021/acs.energyfuels.7b00410 [12] LI W Q, WANG L Y, QIAO Y, LIN J Y, WANG M J, CHANG L P. Effect of atmosphere on the release behavior of alkali and alkaline earth metals during coal oxy-fuel combustion[J]. Fuel,2015,139:164−170. doi: 10.1016/j.fuel.2014.08.056 [13] SONG G L, YANG S B, SONG W J, QI X B. Release and transformation behaviors of sodium during combustion of high alkali residual carbon[J]. Appl Therm Eng,2017,122:285−296. doi: 10.1016/j.applthermaleng.2017.04.139 [14] BAI Y H, ZHU S H, LUO K, GAO M Q, YAN L J, LI F. Coal char gasification in H2O/CO2: Release of alkali and alkaline earth metallic species and their effects on reactivity[J]. Appl Therm Eng,2017,112:156−163. doi: 10.1016/j.applthermaleng.2016.10.044 [15] YANG X H, LV P, ZHU S H, YAN L J, BAI Y H, LI F. Release of Ca during coal gasification and char gasification in H2O, CO2 and their mixtures[J]. J Anal Appl Pyrolysis,2018,132:217−224. doi: 10.1016/j.jaap.2018.02.008 [16] 常清华. 煤基碳黑的生成和氧化过程的实验及模拟研究[D]. 上海: 华东理工大学, 2020.CHANG Qing-hua. The experimental and simulation study of generation and oxidation of coal-derived soot[D]. Shanghai: East China University of Science and Technology. [17] ZHU H L, YU G S, GUO Q H, WANG X J. In situ raman spectroscopy study on catalytic gasification of a bituminous coal[J]. Energy Fuels,2017,31:5817−5827. doi: 10.1021/acs.energyfuels.6b03042 [18] SADEZKY A, MUCKENHUBER H, GRPTHE H, NIESSNER R, PÖSCHL U. Raman microspectroscopy of soot and related carbonaceous materials: Spectral analysis and structural information[J]. Carbon,2005,43(8):1731−1742. doi: 10.1016/j.carbon.2005.02.018 [19] ZHANG S, HAYASHI J, LI C Z. Volatilisation and catalytic effects of alkali and alkaline earth metallic species during the gasification and gasification of Victorian brown coal. Part IX. Effects of volatile-char interactions on char-H2O and char-O2 reactivities[J]. Fuel,2011,90(4):1655−1661. doi: 10.1016/j.fuel.2010.11.008