Characterization of Fly Ash and a Protective Coating for Brazilian Thermal Power Plant Boilers

Thermoelectric power plants that use mineral coal show high wear in heat exchanger due to the action of several damage mechanisms associated with the impact of hard particles from the residue of burnt coal, the ashes. The employment of coatings should be given into consideration particularly for critical components, which are subject to severe erosive conditions is one of the solutions. However, the choice of material will depend on several factors, including the properties of aggressive ashes. This paper aims to characterize ashes generated by a Brazilian coal-based power plant and a FeCrNbNi-based metallic coating obtained by the electric arc spraying process. No trace of sulfur content was found in fly ashes and it was defined that wear is mainly related to the impact and energy of hard particles are the leading causes of degradation in coal-fired boiler equipment. According to the assessment, applied coating showed (5 ± 2)% by volume of pores and cracks, with 1.6% of oxides after the spraying process and hardness 35% greater than ash particles. Preliminary results in field operation suggest that the material showed relatively low wear compared to the original substrate and showed great applicability in controlling material deterioration for this purpose.

以矿物煤为燃料的热电厂，其换热器（heat exchanger）会因燃煤残余物（灰渣）中的硬质颗粒冲击所关联的多种损伤机制作用，出现严重磨损。针对承受严重冲蚀工况的关键部件采用涂层防护是解决方案之一，对此应予以重点考量。然而，涂层材料的选择需综合多项因素，包括侵蚀性灰渣的特性。本研究旨在对某巴西燃煤热电厂产生的灰渣，以及通过电弧喷涂工艺（electric arc spraying process）制备的FeCrNbNi基金属涂层（FeCrNbNi-based metallic coating）进行表征。经检测，飞灰（fly ash）中未检出硫含量；且明确硬质颗粒的冲击与动能是导致燃煤锅炉设备劣化的主要磨损诱因。评估结果显示，该涂层的孔隙与裂纹体积占比为(5±2)%，喷涂后氧化物含量为1.6%，其硬度较灰渣颗粒高出35%。现场试运行的初步结果表明，相较于原始基材，该涂层的磨损程度相对较低，在该工况下的材料劣化控制方面展现出极佳的应用潜力。