Abstract Staged coal combustion is a promising solution to the alkali-induced slagging issue. It innovatively separates coal pyrolysis and char combustion into different reactors. This study investigated migration and transformation of sodium during staged coal combustion of two Zhundong coals in a fixed-bed apparatus. Behavior of sodium during coal pyrolysis and char combustion are integrated. Carbon coating on sodium species was experimentally confirmed for the first time by low-temperature oxygen-plasma ashing and ultrafine grinding. Up to 62 wt% of initial water-soluble Na in ZJ coal and 51 wt% in WCW coal were coated with the carbon matrix during coal pyrolysis. Coated water-soluble Na appeared from 500 °C and its amount reached a peak value at around 700 °C, followed by decrease over 700–1000 °C. Thermoplastic behavior of coal during pyrolysis is expected to play an important role in the formation of coating which hinders pretreatment of sodium. During char combustion, all coated water-soluble sodium species were exposed and participated in the subsequent release. Part of them can also react with minerals to generate insoluble and HCl-soluble sodium species. Char combustion is the main period of the sodium release while coal pyrolysis is the principal period of the generation of HCl-soluble Na.

中文翻译：

---

准东煤分级燃烧过程中钠的迁移转化及碳包覆的影响

摘要 煤分级燃烧是解决碱引起的结渣问题的一种很有前景的方法。它创新地将煤热解和焦炭燃烧分离到不同的反应器中。本研究调查了两种准东煤在固定床装置中分级燃烧过程中钠的迁移和转化。煤热解和焦炭燃烧过程中钠的行为是综合的。通过低温氧等离子灰化和超细研磨，首次实验证实了钠物种上的碳涂层。ZJ 煤中高达 62 wt% 的初始水溶性 Na 和 WCW 煤中高达 51 wt% 的初始水溶性 Na 在煤热解过程中被碳基质包覆。包覆的水溶性 Na 从 500°C 开始出现，其量在 700°C 左右达到峰值，然后在 700-1000°C 时减少。预计煤在热解过程中的热塑性行为在阻碍钠预处理的涂层形成中起重要作用。在炭燃烧过程中，所有包覆的水溶性钠物质都暴露出来并参与了随后的释放。它们中的一部分还可以与矿物质反应生成不溶性和 HCl 可溶性钠物质。焦炭燃烧是释放钠的主要时期，而煤热解是生成可溶于盐酸的钠的主要时期。