Many new innovative products have been developed that help maintenance departments extend the life of critical power plant components. Dr Gary R Heath reports.
For many years energy demand has been strongly growing and will continue. The installation of new plant capacity can take years so there is an enormous pressure on power plants to improve operational output, efficiency and availability. Further, there is the constant requirement to reduce operating costs and the environmental impact of achieving these targets. The maintenance department can play a critical role by selecting longer-lasting key components to extend outage intervals and also reduce unplanned down-time and inventory.
Component repair rather than replacement produces immediate costs savings and also reduces the use of materials, energy and transport in producing these new components.
If the lifetime of the repaired part can be increased over that of a new part, plant performance and availability can also be improved, leading to significant energy savings and carbon generation.
After years of research, field tests and involvement of power plant engineers, many innovative products have been developed to support the maintenance departments extend the life of critical power plant components (by as much as five times).
Wear resistant plate solutions
For the wear protection of large surface areas such as chutes, coal mill cones, separator discs, blades or slag protections the ideal solution is the weld overlay wearplate. Castolin Eutectic have the widest global wearplate range sold under the name CastoDur Diamond Plates (CDP). CDP plates consist of an easy-to-weld steel plate over-laid with abrasion and erosion resistant alloys. Innovations have included the patented lightweight, smooth powder fused plate, superhard tungsten carbide plate and the first impact resistant plates.
A new stainless steel base metal allows these plates to provide optimal wear resistance in aggressive corrosion environments such include fans, cyclones, chutes, liners, etc.
Another recent development was to translate this technology into producing internal weld overlay of seamless tubes. The production technology allows wear protection coating of 3m long tubes of any internal diameter down to 82mm The major wear areas outside the boiler are usually on pneumatic transport piping and elbow of coal/fuel and ash removal. Here, original elbow lifetime increased by a factor of 3 by using a new design and the CastoTube solution.[Page Break]
The world's first NanoAlloy formulation was developed to provide outstanding abrasion and erosion resistance using an innovative nano structural engineering approach to alloy development based on a low cost ferrous base. This science was translated into a welding wire which could be used with normal welding equipment in the power plant but producing a protective overlay with a bulk hardness over 71HRC! Applications have been proven in the power industry in coal, ash and alternative fuel transport and grinding systems. Use in coal grinding systems have shown a five times improvement in wear life in key components.
Boiler tube protection
Castolin Eutectic was amongst one of the first companies to develop dense, thermally sprayed coatings to protect boiler tubes in power plants against wear and corrosion in the 1980s and have developed a considerable reputation and experience of these coatings. Essentially two systems have evolved one against erosion wear in coal fired boilers and one for corrosion resistance in waste incineration boilers.
In coal fired boilers, boiler tube wear occurs from erosion by hard particles (quartz) in the gas stream. The solution is to coat the tubes with a thin (0.7mm) but very hard (750-1000 HV) metal coating. Coating is by arc wire thermal spraying either on site in the boiler or in specialist coating workshops.
Where corrosion is a serious issue, such as in municipal waste incineration boilers, the high chlorine levels and high temperatures combine to give extreme corrosion of boiler tubes and premature outages. The solution requires a dense, highly corrosion resistant coating to be applied to the tubes, which has been achieved using a combination of patented, high molybdenum, nickel, silicon alloy in conjunction with a special coating deposition process (Spray and Fuse).[Page Break]
In the 1970s, Vertical Roller Mills (VRMs) became increasingly dominant for grinding raw materials mainly in the power industry due to their high energy efficiency and excellent drying capacity. The VRM components are subjected to severe wear and this wear can increase dramatically when high silica content is found in the raw materials. Consequently such wear problems can influence significantly the profitability of a plant. During the last decades, together with our partners we have proved that preventive maintenance on VRM can extend the critical component lifetime by as much as 100 per cent. This is done with automated weld overlay of the rollers and the tables, plus use of CDP wearplates on house and rotation parts. Such maintenance operations have been performed on over 60 units, with 80 per cent being on-site repairs but also many repairs in our workshops. More than 30 different VRM models have been weld overlaid for more than 20 companies throughout the world. From small VRM (roller: 1.65m Ø and table: 2.75m Ø) to massive ones (roller: 3.2m Ø and table: 5.5m Ø), we have been successful working on equipment from Polysius, Loesche or FLS and Raymond.
Together with the R&D department, the VRM team has developed special anti-wear products providing unbeatable resistance to abrasion, impact and erosion. The new TeroMatec wire EO 8338 (open arc wire) which provides an extra smooth surface but an extremely resistant coatings. In one recent application in the Middle East this new EO 8338 wire was able to reduce wear on the rollers from 9 grams per ton crushed to 3 grams when build up 40 mm thickness on a four roller system.
Castolin Eutectic's thermal power plant repair service package includes: products to solve wear problems; on-site and in-workshop refurbishment; increased service life over conventional welding alloys; environmental ethic values; fast and effective return to service; alloy development and in-house manufacturing.
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Dr Gary R Heath is Chief Technology Officer, Castolin Eutectic, Lausanne Switzerland. www.castolin.com