Abstract:

Arsenic volatilization characteristics of SJS bituminous coal were carried out on the high-temperature tube furnace from 600℃ to 1400℃ at different oxy-fuel atmospheres. Combined with FTIR analysis and thermodynamic analysis, and taking air condition into consideration, the effects of O₂, CO₂ and temperature on arsenic volatilization were studied. Results showed that the releasing proportion of arsenic increased with increasing temperature both in oxy-fuel and air combustion. Two arsenic mass loss peaks were observed at ＜900℃ and > 900℃ stages, separately. At temperature lower than 900℃ oxygen content was the major fact. The more O₂ ratio, the larger volatile proportion of arsenic. But at the same O₂ ratio condition, the higher CO₂ concentration brought down the emission of arsenic and thus the volatile proportion was decreased. At temperature higher than 900℃ the content of carbon dioxide was the major fact, The higher CO₂ concentration in oxy-fuel atmosphere hindered heat transfer, and thus higher temperature was needed for the decomposition of arsenates under the same conditions, which led to the delay of the intensive emission of arsenic compared to air condition. Besides, high CO₂ content in oxy-fuel condition resulted in the reductive atmosphere around coal particles, which caused arsenic compounds with high chemical valence being reduced to compounds with lower chemical valence, while the arsenic compounds with lower chemical valence were unstable and their fast decomposition led to the higher mass loss rate of arsenic in oxy-fuel condition than to the air condition.

Key words: oxy-fuel combustion, arsenic volatilization, temperature, O₂ concentration, CO₂ concentration

摘要：

选取SJS烟煤,利用高温管式炉模拟富氧燃烧,在600~1400℃温度范围内研究了O₂浓度、CO₂浓度及温度对砷挥发的影响,并进行了空气燃烧模式下的对比实验。对不同工况下的灰样进行FTIR表征并结合化学热力学软件模拟进行分析,结果表明:富氧气氛和空气气氛下煤中砷的挥发比例均随温度升高不断增大,并在低温区间(<900℃)和高温区间(>900℃)分别出现了砷的剧烈失重,但O₂浓度和CO₂浓度影响了不同气氛下砷的具体挥发行为。低温下(<900℃)O₂浓度是影响砷挥发的主要因素,O₂浓度越高,砷的挥发比例越大;相同O₂浓度下,CO₂浓度越高,砷的挥发比例越低,CO₂的存在抑制了煤中砷的挥发。高温下(>900℃)CO₂浓度是影响砷挥发的主要因素,富氧气氛下高CO₂浓度对热量的阻碍导致相同条件下砷酸盐发生分解需要更高的温度,因此富氧气氛下砷的挥发较空气模式滞后;此外CO₂在煤颗粒表面形成还原性气氛,高价态砷化合物向不稳定的低价态砷化合物转变,低价态砷化合物的快速分解导致高温下富氧气氛中砷的挥发速率较常规空气模式快。

关键词: 富氧燃烧, 砷挥发, 温度, O₂浓度, CO₂浓度