Abstract
Highly efficient electric power generation from biomass/waste fuels becomes an important worldwide issue to prevent global warming. In these plants, severe high-temperature corrosion and erosion-corrosion damage occur in boiler tubes influenced by HCl, SOx gases, and chlorides as contaminants in fuels. Coating technologies become important as a countermeasure for such damage, because of the easy maintenance, cost performance, and ease of application on various materials. In severe corrosive conditions of boilers, formation of dense, homogenous, and tough coating layers, as well as protective oxide layers of corrosion-resistant materials, are important. In the last 30 years, materials and coating processes applied in shop and on site have progressed based on many field observations and the consideration of deterioration mechanisms in order to maintain long lifetimes in the plants. Furthermore, new innovative coatings are now being developed by using advanced precise control, nanotechnologies, etc. This paper introduces recent trends of advanced coating developments and applications, such as weld-overlay, cladding, thermal spray coating, and slurry coating for biomass/waste boilers. Furthermore, the evaluation results of deterioration mechanisms and lifetime of coatings, and the future issue for innovative coatings, are presented.
Highlights
Promotion of high-level recycling and reduction of environmental load, such as NOx, SOx, and heavy metals, are the worldwide requirements against the burning of biomass and waste.The biomass/waste-to-energy plants are positioned in the center of stable renewable energy sources in many countries
This paper describes (a) the severe corrosive environment in biomass/WTE boilers to understand the cause of damage; (b) application trends and field observations of various coatings such as metals, cermet and ceramics that have good durability in waterwall tubes (WWTs) and SHTs compared with conventional materials; and (c) erosion corrosion damages and deterioration mechanisms of materials and coatings, especially in the case of thermal spraying
(b) Cr carbide–stainless steel and WC/Cr carbide–NiFe cermet coatings sprayed via the high velocity arc continuous spray (HVAC) or the high velocity air fuel (HVAF) process show good durability in circulated fluidized bed combustor (CFBC) sludge boilers [28]
Summary
Promotion of high-level recycling and reduction of environmental load, such as NOx , SOx , and heavy metals, are the worldwide requirements against the burning of biomass and waste. In order to realize the high performance biomass/WTE plants, an application of highly corrosion-resistant materials and coating processes have become an important issue, which are essential for realizing a high thermal efficiency and a total economy of plant operation. In order to improve the boiler efficiency and durability of boiler materials, it is considered necessary to apply optimum boiler design that prevents high-temperature corrosion and erosion corrosion in superheater tubes (SHTs) and waterwall tubes (WWTs). This paper describes (a) the severe corrosive environment in biomass/WTE boilers to understand the cause of damage; (b) application trends and field observations of various coatings such as metals, cermet and ceramics that have good durability in WWTs and SHTs compared with conventional materials; and (c) erosion corrosion damages and deterioration mechanisms of materials and coatings, especially in the case of thermal spraying
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