Extending the lifetime of boiler tubes under severe conditions with advanced coatings in waste and coal fired power plants

摘要

The thinning of boiler tubes due to the severe operational conditions can lead to premature tube rupture and unplanned outages. With increasing demands to burn higher ash content fuels (or mixed fuels) and also improve the boiler tube reliability, thermal sprayed coatings are continuing to prove a reliable and cost effective solution. New coating chemistries have proven themselves in long term boiler tube trials against erosion and also against corrosion. At a 5,053 MW lignite-fired power station where erosion wear was prevalent trials with various thermal spray coating over a period of 7 years identified a clear winner. In the severe corrosion conditions found whilst burning waste or biomass, a new type of "densified" thermal sprayed coatings has demonstrated its technical and commercial worth. The coating process can be performed in specialist workshops on new tubes and tube panels, with a variety of diameters and geometries, and it can also be performed in-situ in the boiler to refurbish and protect existing boiler tubes, even if they are already worn. The range of coatings not only offer more erosion resistant that the base metal tube but also superior corrosion resistance at the same time which can become an issue when burning certain types of fuel or when changing combustion parameters. The theoretic and practical aspects of the coatings and how they are applied will be discussed in detail along with case studies.