Electric Power Technology and Environmental Protection

【目的】燃煤排放的有毒痕量元素对环境和人体产生巨大的危害，明确燃煤过程中的痕量元素迁移转化特性对其有效脱 除及实现燃煤烟气的清洁排放具有重要的意义。【方法】本文以一台660 MW燃煤电厂的煤样为研究对象，采用管式炉燃烧实 验和化学热力学模拟系统考察了温度和气氛对燃煤过程中有毒痕量元素砷（As）、硒（Se）、铬（Cr）迁移转化特性的影响。【结果】 研究结果表明，不同燃烧工况下，As和Se主要分布在飞灰中，Cr主要分布在底渣中。空气气氛下温度的升高有利于As从底渣 向飞灰迁移，富氧气氛有利于As向烟气中迁移。700 ℃和900 ℃下，富氧气氛下O2 浓度的增加有利于底渣中As向飞灰中As的 转化，煤灰中的As主要为AlAsO4 （s）和Ca3 （AsO4 ）2 （s）。空气气氛下，随着温度的升高，Se发生了飞灰向底渣、以及从底渣和烟 气向飞灰的迁移。700 ℃和900 ℃下，富氧气氛中随着O2 浓度的增加，Se在飞灰中所占比例由54.3%上升至84.4%。飞灰和烟 气中的Se主要分别为CaSeO4 （s）和SeO2 （g）。空气气氛下温度升高促使Cr从底渣向飞灰迁移。60%O2 /40%CO2 气氛下Cr在各 组分中的分布与21%O2 /79%CO2 气氛具有相似性，且在烟气中分布比例达到24.9%。底渣和飞灰中Cr主要为Cr2 （SO4 ）3 、 CaCr2 O4 、CrO2 、Cr2 O3 。 【结论】燃煤过程中As、Se具有高挥发性，多分布于飞灰中；Cr具有难挥发性，多分布于底渣中，温度和O2 含量对As、Se、Cr迁移转化具有重要的影响。飞灰和烟气中As、Se的脱除和底渣中Cr的环境浸出应尤为关注。

[Objective] The toxic trace elements emitted from coal combustion have posed huge threats to the environment and human health. Clarifying the migration and transformation characteristics of trace elements during coal combustion is of great significance for their effective removal and clean emissions of coal-fired flue gas. [Methods] This work takes a coal sample from a 660 MW coal-fired power plant as the object, and uses tube furnace combustion experiments and chemical thermodynamic simulation to investigate the effects of temperature and atmosphere on the migration and transformation of toxic trace elements arsenic (As), selenium (Se), and chromium (Cr) during the coal combustion process.[Results] Under different combustion conditions, As and Se are primarily distributed in fly ash, while Cr is predominantly in bottom ash. An increase in temperature under an air atmosphere facilitates the migration of As from bottom ash to fly ash, while an oxygen-enriched atmosphere promotes the migration of As into the flue gas. At 700 ℃ or 900 ℃, an increase in O2 concentration in an oxygen-enriched atmosphere promotes the conversion of As in bottom ash to As in fly ash. The As present in coal ash is primarily in the form of AlAsO4 (s) and Ca3 (AsO4 )2 (s). In an air atmosphere, as the temperature rises, Se undergoes migration from fly ash to bottom ash, and from bottom ash and flue gas to fly ash. At 700 ℃ or 900 ℃, an increase in O2 concentration in an oxygen-enriched atmosphere enhances the distribution of Se in fly ash. The Se present in fly ash and flue gas is primarily in the forms of CaSeO4 (s) and SeO2 (g), respectively. An increase in temperature under an air atmosphere promotes the migration of Cr from bottom ash to fly ash. The distribution of Cr among the distributions in a 60% O2 /40% CO2 atmosphere is similar to that in a 21% O2 /79% CO2 atmosphere, with a higher proportion distributed in the flue gas. The Cr present in bottom ash and fly ash is primarily in the forms of Cr2 (SO4 )3 , CaCr2 O4 , CrO2 , and Cr2 O3 . [Conclusion] During the coal combustion process, As and Se have high volatility and are mostly distributed in fly ash, while Cr has low volatility with mostly distributed in bottom ash. Temperature and O2 concentration have important effects on the migration and transformation of As, Se, and Cr. Special attention should be paid to the removal of As and Se from fly ash and flue gas, as well as the environment leaching of Cr from bottom ash.