Abstract
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.
Highlights
In Brazil, electricity generation is mainly from hydroelectric power plants, representing 61% of total production
The presence of iron can be associated with a probable oxidation of pyrite and/or related to the segregation of minerals containing this element during a probable pre-treatment of coal
The ashes particles generated by Brazilian mineral coal used in boilers of thermoelectric plants presented a predominantly spherical morphological aspect with a higher frequency of particles (56 wt.%) for granulometric range between 75 and 90 μm, being essentially a combination of alumina, silica and iron oxide, of an alkaline character in terms of pH
Summary
In Brazil, electricity generation is mainly from hydroelectric power plants, representing 61% of total production. The main deterioration mechanisms in power plant boilers are creep damage, microstructural degradation, erosion by fly-ash and high-temperature fatigue, embrittlement, carburization, hydrogen damage, graphitization, thermal shock, liquid metal embrittlement, and high-temperature corrosion of various types[3,4,5]. These mechanisms are associated with long-term exposure to high-temperatures, strain generated by particles impact, and corrosive action of combustion products, which can be intensified due to high temperatures[5,6]. One of the proposed solutions for the erosion problem is the use of materials more resistant than the aggressor agent with
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