灰特性对燃煤炉内灰沉积行为的影响

Influence of Ash Characteristics on Ash Deposition in Coal Fired Boiler

为了解灰特性对燃煤炉内灰沉积行为的影响,以黄陵、神木和新汶3种具有不同灰特性的燃煤为研究对象,通过自制灰污热流探针和SiC结渣棒,分别模拟了正常情况及存在烟气冲墙贴壁情况下的锅炉受热面灰沉积行为,比较了灰渣外形、化学成分、熔融温度和热流变化率等特性参数,并通过对灰渣样品的X-射线衍射、扫描电镜及能谱分析,获得了3种燃煤灰沉积物的元素组成、矿物相及微观结构和形貌特征.结果表明,由于Ca、Fe的协同作用,黄陵煤的灰沉积特性强于神木和新汶煤,Ca、Fe是引起这类煤灰沉积的主要矿物元素,硬石膏、钙长石和赤铁矿是灰沉积物中的主要矿物相;当存在烟气冲墙贴壁时,灰沉积物中Fe含量很高,使熔融温度大大降低,从而加剧受热面的灰沉积过程,在工程实际中应采取相应措施,避免出现这种情况.

In order to find out the influence of ash characteristics on ash deposition, coals from Huangling, Shenmu and Xinwen, with different ash characteristics, were selected as subjects and burned in a trial furnace respectively. Two tests simulating ash deposition were done simultaneously, of which one simulated normal condition with a heat flux probe, and the other simulated ash deposition when combustion fumes rushed toward or onto the furnace wall by a self-made SiC rod. Some characteristic parameters of ash deposits from the three types of coals were compared, such as ash shape, chemical composition, fusion temperature and heat flux variance ratio. Elemental composition, mineral phase and microscopic structure of the ash deposit samples from the three types of coal were acquired by analysing X-ray diffraction, scanning electron microscope and energy spectrum. The results indicate that ash deposition tendency and characteristics of Huangling coal are stronger than those of Shenmu and Xinwen coals, owing to the synergetic effects of calcium and iron. The principal mineral elements giving rise to ash deposition are calcium and iron in Huangling coal, due to the fact that anhydrite, anorthite and hematite are essential mineral phases in ash deposits. In addition, contents of iron in ash deposits are exceedingly high on condition that combustion fumes rush onto furnace wall or tube, which lowers melting temperature of ash deposits considerably. Accordingly, the forming process of ash deposits in heat transfer surface is accelerated. This condition should be avoided in a pulverized coal boiler by adopting some corresponding measures.