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.

以矿物煤为燃料的火力发电厂中，由于燃煤燃烧残渣（即灰分）中的硬颗粒冲击所引发的多种损伤机制作用，热交换器（heat exchanger）会出现严重磨损。针对处于强冲蚀工况下的关键部件，采用涂层防护是可行解决方案之一，因此涂层的选用值得重点考量。然而，涂层材料的选择需综合考量多项因素，其中侵蚀性灰分的特性尤为关键。本研究旨在表征某巴西燃煤发电厂产生的灰分，以及通过电弧喷涂（electric arc spraying）工艺制备的FeCrNbNi基金属涂层（FeCrNbNi-based metallic coating）。检测发现飞灰（fly ash）中未检出硫含量，且可明确，磨损主要源于硬颗粒的冲击与动能，这也是燃煤锅炉设备发生劣化的主要诱因。经评估，所制备的涂层经喷涂后，其孔隙与裂纹占比为(5±2)%（体积分数），氧化物含量为1.6%，硬度较灰分颗粒高出35%。现场运行的初步结果表明，相较于原始基体，该涂层的磨损率相对较低，在控制该工况下的材料劣化方面展现出优异的应用前景。