基于FES技术的O_(2)/CO_(2)燃烧气氛下准东煤中不同类型碱金属盐的释放特性

Release characteristics of different alkali metal salts in Zhundong coal under O_(2)/CO_(2) combustion atmosphere based on FES technology

O_(2)/CO_(2)燃烧技术被认为是一种清洁的燃煤发电技术,然而高碱准东煤燃烧过程中释放的大量碱金属通常是引起锅炉受热面积灰、结渣以及腐蚀的重要物质,严重危害了设备的安全稳定运行。因此,探讨O_(2)/CO_(2)燃烧气氛下准东煤中不同类型碱金属盐的释放特性对于煤炭的清洁高效利用具有重要意义。基于火焰发射光谱技术(FES),在金属丝网反应器上研究了煤粉燃烧过程中不同类型碱金属盐在O_(2)/N_(2)和O_(2)/CO_(2)两种气氛下的释放特性。结果表明:在O_(2)/N_(2)气氛下,挥发分燃烧会产生明亮的火焰;与O_(2)/N_(2)气氛相比,O_(2)/CO_(2)气氛下煤粉燃烧强度降低,火焰温度下降,着火时间延迟,挥发分和焦炭的燃烧时间延长,使得煤粉中气相Na的释放过程受到抑制。对于NaAc、Na_(2)CO_(3)和Na_(2)SO_(4)来讲,O_(2)/CO_(2)气氛延迟了其释放过程中质量浓度降低的时间,使煤粉中气相Na从开始释放就进入稳定释放阶段,气相Na质量浓度变化率波动不大;但NaCl会在释放的4 s左右质量浓度变化率变为负值,导致释放的气相Na质量浓度一直降低。同时CO_(2)气氛还会使得NaAc、NaCl等类型盐转化形成更难释放的Na_(2)CO_(3),进一步抑制气相Na的释放过程。而Na_(2)CO_(3)的质量释放率在O_(2)/CO_(2)气氛下也降低的主要原因则是CO_(2)抑制了Na_(2)CO_(3)向Na_(2)O的分解过程。Na_(2)SO_(4)则由于其本身释放就比较困难,因此其质量释放率降低的主要原因是燃料燃烧温度和强度降低导致的。

The O_(2)/CO_(2) combustion technology is a clean coal-fired power generation technology.However,a large amount of alkali metals released during the combustion of high-alkali coal is usually an important substance that causes ash deposition,slagging and corrosion on the heating surface of boiler,which seriously affect the safe and stable operation of equipment.It is of great significance to study the release characteristics of alkali metal salts with different occurrences in the Zhundong coal under the O_(2)/CO_(2) combustion atmosphere for the clean and efficient utilization of coal.Based on flame emission spectroscopy(FES),the release characteristics of different alkali metal salts in the O_(2)/N_(2) and O_(2)/CO_(2) atmo-spheres during pulverized coal combustion were studied in a metal wire mesh reactor.The results show that the combus-tion of volatile compounds produces a bright flame under the O_(2)/N_(2) atmosphere.The combustion intensity and flame tem-perature of the pulverized coal in the O_(2)/CO_(2) atmosphere decrease compared with that in the O_(2)/N_(2) atmosphere,the igni-tion time is delayed,the combustion time of volatiles and coke is prolonged,and the release of Na(g)is inhibited.For NaAc,Na_(2)CO_(3) and Na_(2)SO_(4),the O_(2)/CO_(2) atmosphere delays the decreasing time of mass concentration,so that the Na(g)in the pulverized coal enters a stable release stage from the beginning,and the mass concentration variation rate of Na(g)does not fluctuate much.However,the mass concentration variation rate of NaCl will turn negative about 4 seconds after release,resulting in a consistent decrease in the mass concentration of Na(g).At the same time,the CO_(2) atmosphere also causes the conversion of NaAc,NaCl and other types of salts to form Na_(2)CO_(3),which is more difficult to release,and fur-ther inhibits the release process of Na(g).The main reason that the mass release rate of Na_(2)CO_(3) also decreases under the O_(2)/CO_(2) atmosphere is that CO_(2) inhibits the decomposition process of Na_(2)CO_(3) to Na_(2)O.The Na_(2)SO_(4) is more difficult to re-lease itself,so the main reason for the reduction of its mass release rate is due to the reduction of fuel combustion temper-ature and intensity.