燃烧福建无烟煤的循环流化床锅炉飞灰及其未燃炭分析

Characterization of fly ash and unburned carbon from CFB boiler with burning Fujian anthracite

以三个燃烧福建无烟煤的商业CFB锅炉电厂飞灰为研究对象,分析飞灰的粒径和含碳量分布;观察并区分了飞灰中煤炭、烟怠、半焦和灰渣等颗粒的表面形貌;测定了飞灰炭的反应活性并与入炉煤作比较;并研究了飞灰炭的来源。结果表明,采用单级分离装置的CFB锅炉,粒径在0.038 5 mm^0.050 0 mm的飞灰质量最多,未燃炭份额也最高;而采用双级分离装置的CFB锅炉,飞灰质量分布和飞灰炭份额的峰值则出现在粒径为0.050 0 mm^0.075 0 mm处。飞灰主要由三种形貌的颗粒组成,颗粒状的未燃炭、絮团状的灰渣、和介于两者之间的半焦。与入炉煤相比,飞灰炭的反应活性较高,主要来源于入炉煤中的细粉和燃烧早期因破碎和磨蚀而产生的、来不及在炉膛中燃尽的细小含炭颗粒。入炉煤中易破碎、反应性较高的亮煤是构成电厂CFB锅炉飞灰炭的主要成分。

Fly ashes, obtained from three commercial CFB boilers with burning Fujian anthracites, were studied in this paper. By using standard dry-sieving techniques and LOI method, the size distributions of fly ashes and the carbon contents of different size fractions were measured. With the help of SEM and EDX technique, the particle superficial property of fly ash was examined and divided into carbon （soot, or graphite）, char, and slag. The residual carbon was enriched from fly ash by the floating-separation technique, and its reactivity was then measured via a non-isothermal TGA experiment. The results was compared with that of its corresponding parent coal. Furthermore, in a laboratory pilot scale fluidized bed furnace, the source of the unburned carbon in the fly ash was explored. It is shown that for CFB boilers using a single cyclone separator, the largest amount of fly ash particles lies in the particle size range from 0.038 5 mm to 0.050 0 mm, and so does the unburned carbon fraction; and for CFB boiler equipped with two separators, the largest amount of fly ash particles and unburned carbon fraction lies in a particle size range of 0. 050 0 mm - 0.075 0 mm. There are three kinds of particles existing in fly ashes, which are granular unburned carbon, flocculent slag and char. The reactivity of the unburned carbon in fly ashes is relatively higher than that of its parent feeding coal. It can be induced from this study that the unburned carbon in fly ashes comes primarily from the fines existed in the fed coal and produced by the attrition and fragmentation of coal particles, which cannot be totally burned in the earlier stage of combustion. The clarain, which is of high reactivity and frangible, may be the main originations of unburned carbon in fly ash.