Abstract:

Slagging and fouling are common problems in high-alkali coal-fired boilers. Meanwhile, a large amount of solid waste coal gangue from coal mining and coal washing needs to be reduced and utilized for economical and ecological considerations. Given this, cofiring high-alkali coal (HAC) with coal gangues (CG) was performed to verify the possibility of inhibiting ash-related problems of HAC meanwhile achieving resource utilization of CG. Besides, the evolution behaviors of pollution gases (SO₂ and NO) were examined. The results show that cofiring reaction follows a three dimensional diffusion model, and at proper ratios the activation energy of cofiring can be lower than that of mono-combustion. NO can be efficiently reduced during cofiring with the enhanced catalytic components in the blended fuels, while the reduction of SO₂ is largely determined by the blending ratio and ash compositions. Alkali metals are effectively retained in ashes thus lowering the fouling and slagging propensity, while alkaline metals participate the competitive reaction with silica and alumina components and that of SO₂ fixation reactions. The ash fusion temperatures can be adjusted through cofiring with CG with various inherent minerals, thus providing the opportunity to alleviate the ash-related problems for burning HAC in commercial boilers.

Key words: slagging and fouling, high-alkali coal, coal gangues, SO₂ and NO reduction, ash fusion temperatures

摘要：

结渣和沾污是高碱煤燃烧锅炉中普遍存在的难题。同时，源于采煤和洗煤的大量固废煤矸石出于经济和生态考虑亦须实现减量化处理和资源化利用。基于此，通过掺烧高碱煤与煤矸石抑制煤灰沾污和结渣发生以及实现煤矸石的资源化利用，同时考察掺烧过程中污染气体(SO₂和NO)的释放及减排行为。结果表明，高碱煤与煤矸石静态的掺烧反应服从三维扩散模型，在一定比例下掺烧反应活化能低于单一燃料燃烧的活化能。掺烧过程中焦炭和CO可还原NO，同时灰分中过渡金属组分可促进NO原位减排，而SO₂的减排效果很大程度上取决于两燃料的掺烧比例及其灰分组成。掺烧过程中碱金属有效固留于灰渣中，从而降低煤灰沾污和结渣倾向，而碱土金属(Ca，Mg等)可同时与灰分组成中的硅铝及气相中SO₂发生竞争反应。此外，通过改变掺烧煤矸石矿物组成可调节灰渣组成及熔融温度。本研究结果可为通过掺烧高碱煤与煤矸石来缓解锅炉沾污和结渣难题提供科学参考。

关键词: 结渣和沾污, 高碱煤, 煤矸石, SO₂和NO减排, 灰熔融温度