Better biomass boilers: Cracking the code of biomass corrosion

Louise Smyth

Biomass energy is a hot topic in our current climate. While some operators build new biomass-fired boilers, others retrofit old coal-fired boilers to burn biomass. Alcali- and sulphide-induced corrosion, however, has become a problem for many boilers. To tackle this problem, one expert in this sector has developed and field-tested a novel HVTS metal alloy cladding to cope with corrosion in biomass boilers. Among the adopters of this new technology is E.ON in Sweden, which is now benefiting from lower operational expenses.

The European operational team from Integrated Global Services (IGS) performed a high velocity thermal spray (HVTS) application at E.ON Värme Sverige Åbyverket, Örebro, Sweden, on a steam boiler in 2017. ÅP5 is a 170MW biomass-fired CFB boiler built in 1988 by Götaverken-Generator. The steam conditions are 150 bar/540°C.

Åbyverket wanted to upgrade the previously installed erosion protection in preparation for the fuel change during the boiler revamp. As part of this project 20m height of waterwalls were being changed on all four walls.

What is Biomass Fuel Made From?

Biomass fuel can be derived from various sources, including virgin wood, plants or animal residues, as well as recycled materials, such as demolition wood. Depending on the type of biomass, the combustion can generate more or less corrosion and erosion. The type of boiler is also an important factor: fluidised bed boilers will optimise combustion but will also generate erosion. Various factors influence the choice of erosion/corrosion protection.

Boiler Corrosion Control

Cyril Narjoz from IGS comments: “Some boiler operators believe that weld overlay is the only solution to protect boiler walls from biomass-induced corrosion safely. It was true many years ago, but now HVTS has proven its performance in several independent tests and practical applications. With its on-site application being much faster and easier than weld overlay, HVTS has become a favourable alternative for corrosion protection” HVTS Application for E.ON

For E.ON Värme Sverige, IGS applied 993.5m2 of HVTS during a three-week period, working 24/7 with eight spray units. Director of IGS European Operations, Petr Sovadina, states: “Our team is well-trained and experienced, however, this was our first large project in Scandinavia. We found E.ON engineers to be extremely sharp and skilled, this helped us avoid many obstacles during the project execution. We understand that operators need to squeeze critical path of boiler operations, and that is the reason why we mobilised an eight-gun team to spray 995m2 of waterwalls in just 21 days. We are proud of our quality and provide a warranty for our work.” A boiler engineer with 20 years of experience, Sovadina spent the past six years spraying metal alloy cladding to protect boiler surfaces.

Annual Inspection Produced Positive Results

In August 2018, IGS conducted its first annual inspection of the cladding, and the result was as expected: no deviation on the HVTS cladding thickness. A thickness mapping was performed and shared with the customer. E.ON’s site manager commented: “Our work is extremely important, that is why we choose the best service for our boilers. We closely monitor jobs performed in our boilers, and IGS has an experienced and quality-oriented team that listens to the customer needs and deliver on their promises.”

Inspection the following year was conducted and the report stated: “No black areas were detected (bleed through), the cladding turned out to be completely intact and without material loss. Measurements taken showed results similar to those from the year of application.”

IGS chief technology officer, Iain Hall, comments: “Developed and tested in 2016, our bespoke metal alloy cladding for boiler waterwalls has shown unprecedented corrosion resistance at high temperatures found in Biomass boilers combined with its ease of on-site application.”

IGS Delivers Specialised Services Worldwide

Having operational centres in strategic locations in North America, Europe, Asia and Africa, IGS delivers its services worldwide, but each market is special. Sören Stutin, general manager IGS Scandinavia, commented: “Scandinavia is a highly educated market. Our boiler engineers have a deep understanding of metal wastage problems in boilers and multi-year experience of using thermal spray solutions. But what is the most important – Scandinavian engineers are open to innovation and absorb the best available technology to improve their operations. Swedish engineers are well-educated, curious and savvy. That makes our boiler industry so advanced.”

As the European energy market is experimenting with different biomass fuels, boiler engineers will face more arduous corrosion situations. IGS can provide an effective barrier on the existing pressure parts, which will prevent further need of panel replacement.

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