高碱煤钠赋存形态及其燃烧过程中迁移转化的研究进展

随着新疆超大煤田的相继发现，新疆煤凭借储量大、碱金属含量高、在热利用过程中易造成锅炉沾污、结垢等问题而得到普遍关注。对高碱煤在燃烧过程中钠挥发特性及其影响因素进行更全面的探究，可为高碱煤的高效清洁利用提供重要参考。本文统计、分析了已发表论文中高碱煤燃烧钠挥发特性的相关数据，研究得到，绝大多数高碱煤中的钠以水溶性钠为主，部分煤（神华宽沟煤和后峡煤）则以不溶性钠为主；不溶性钠含量较高的煤，盐酸可溶性钠和醋酸可溶性钠含量也较高。本文对比研究了四个主要影响钠迁移转化的因素（钠形态和含量、Cl的含量、灰组分和燃烧温度）得出，温度对钠挥发量的影响最大，温度的升高可显著增加钠挥发量，900℃后又可加快挥发速率；当钠含量分布在2000-4000 μg/g时，挥发量与总量之间具有良好的正相关，与可溶性钠含量无关；当燃料中Na和Cl物质的量比低于3.5时，Cl对钠的挥发有明显的促进作用，大于10以后，钠的挥发量较低；钠挥发量与Na和（Si+Al）-（Ca+Mg）]物质的量比有明显的负相关。本文根据现有的研究成果，考虑钠的赋存形态及影响挥发的因素后，将钠在燃煤过程中的迁移转化行为归纳为三个阶段（内部转化、外部挥发和转化、凝结）和四条路径。

Occurrence of sodium in high alkali coal and its transformation during combustion

With the discovery of super-huge coalfields located in Xinjiang province, the features of large coal reserves, sodium-rich in coal and the problems of boiler fouling during coal thermal utilization are paid more and more widespread attention. Also, more comprehensive investigation on the characteristics of sodium volatilization and its influencing factors in the combustion can provide an important reference for the efficient and clean utilization of high alkali coal. Therefore, a review was made to collect and analyze the relevant data about sodium volatilization characteristics during high alkali coal combustion from published materials. It is found that the sodium species in most of high alkali coal is dominated by water-soluble sodium (WS-Na), excepting few coals with insoluble sodium (HIS-Na) as main sodium species, e.g. Shenhua Kuanggou coal and Houxia coal. The coal ontaining higher HIS-Na has higher hydrochloride-soluble sodium (AS-Na) and ammonium acetate-soluble sodium (HS-Na) contents. Four influence factors including chlorine content, ash composition and combustion temperature, sodium form and content, which affects the sodium migration and transformation, were compared. It is concluded that the temperature has the greatest influence on sodium volatilization. The volatilization of sodium can be significantly increased with the increase of temperature, and the evaporation rate of sodium will be accelerated after 900 ℃. For the sodium content in 2000-4000 μg/g, there is a well positive correlation between the volatilization amount and the total amount of sodium, but it is irrelevant to the soluble sodium content. Chlorine can promote the volatilization of sodium as the molar ratio of Na to Cl is less than 3.5, while it has an inhibition as the molar ratio of Na to Cl exceeds 10. Moreover, a significant negative correlation is observed between the amount of sodium volatilization and the molar ratio of Na to(Si+Al)-(Ca+Mg)]. According to the existing research results, the migration and transformation behavior of sodium in coal combustion process is summarized into 3 stages consisting of internal conversion, external volatilization and conversion, as well as condensation, and 4 paths.