High Temperature Corrosion of FeCrAl Alloys in Biomass- and Waste-fired Boilers - The Influence of Alloying Elements in Prediction and Mitigation of Corrosion in Harsh Environments
Doktorsavhandling, 2020

Combustion of biomass and waste for heat and power production is an alternative to fossil fuels and can be an important step towards a more sustainable future. The electrical efficiency of the fuel-to-energy conversion process is largely dependent on the steam parameters (temperature and pressure) of the combined heat and power (CHP) plants. Meanwhile, the boiler environment when utilizing these fuels is complex and can be characterized by high levels of corrosive species, such as water vapor and alkali chlorides. These species contribute to highly corrosive conditions that results in rapid material degradation of boiler components and limits the operating temperature.

Stainless steels are commonly used to reduce material degradation in these types of corrosive environments because of their high temperature corrosion resistance. This is attributed to their ability to form a protective chromium-rich oxide scale. However, in the highly corrosive environment of biomass- and waste-fired boilers these scales have been found to rapidly break down and result in the formation of less protective iron-rich oxide scales. The present thesis elucidates the potential of improving the corrosion resistance by introducing alumina-forming alloys (FeCrAl alloys) and/or improving the properties of the fast-growing oxide scales formed after breakaway oxidation.

The results show that the oxidation process can be divided into a primary and a secondary corrosion regime, i.e. the corrosion behavior before and after breakaway oxidation. This concept was utilized when investigating the influence of alloying elements on the corrosion resistance of FeCr(Al) model and coatings in a broad range of corrosive environments. Cr, Al and Si was found to significantly influence the corrosion behavior of FeCr(Al) alloys in both the primary and secondary corrosion regime. However, the criteria for a high corrosion resistance differed for the two corrosion regimes. HVAF-sprayed and overlay-welded coatings demonstrated the potential of providing high corrosion resistance within the primary and secondary corrosion regime, respectively. The applicability of the findings was shown to extend from simplified laboratory environments to the complex conditions of a waste-fired boiler.

The novel insights, presented in this work, contribute to new perspectives on high temperature corrosion resistance, which are valuable in material development and corrosion prediction in harsh environments.

FeCrAl alloys

High Temperature Corrosion

Coatings

Silicon

Overlay Welding

Waste

HVAF

Breakaway Oxidation

Biomass

HA1
Opponent: Prof. Marcel Somers, Denmarks Technical University, Denmark

Författare

Johan Eklund

Chalmers, Kemi och kemiteknik, Energi och material, Oorganisk miljökemi

J. Eklund, A. Persdotter, I. Hanif, S. Bigdeli, T. Jonsson - Secondary corrosion protection of FeCr(Al) model alloys at 600 ° C– The influence of Cr and Al after breakaway corrosion

The influence of silicon on the corrosion properties of FeCrAl model alloys in oxidizing environments at 600 °C

Corrosion Science,; Vol. 144(2018)p. 266-276

Artikel i vetenskaplig tidskrift

J. Eklund, I. Hanif, T. Jonsson - High temperature corrosion behaviour of FeCrAlSi alloys in the presence of water vapour and KCl at 600 °C – The influence of Cr content

High-Temperature Corrosion of HVAF-Sprayed Ni-Based Coatings for Boiler Applications

Oxidation of Metals,; (2019)

Artikel i vetenskaplig tidskrift

Field exposure of FeCrAl model alloys in a waste-fired boiler at 600°C: The influence of Cr and Si on the corrosion behaviour

Materials and Corrosion,; Vol. 70(2019)p. 1476-1485

Artikel i vetenskaplig tidskrift

The increasing emissions of greenhouse gases since the middle of the 20th century has had great impact on global warming. A significant part of these emissions originates from the utilization of fossil fuels, and with the growing demand of electricity the contribution of fossil fuels has increased. Substituting fossil fuels for more CO2-neutral fuels is therefore of the utmost importance.  Biomass and waste are potential alternatives for the combined heat and electricity production in boilers. However, high levels of corrosive species are released upon the combustion of these alternatives and results in rapid material degradation of boiler components and high maintenance costs. This limits the operating parameters of the boiler, and consequently the electrical efficiency of the boiler process is reduced.

Utilizing corrosion resistant materials and coatings are potential approaches to mitigate high temperature corrosion in biomass- and waste-fired boilers. Understanding the underlying mechanisms of the corrosion attack is crucial for developing materials with high corrosion resistance in the intended application. The corrosion resistance of steels generally depends on their ability to form and retain slow-growing oxide scales. FeCr(Al) alloys are known for their excellent corrosion resistance at elevated temperatures due to their ability to form chromia and/or alumina scales. However, the harsh environments of biomass- and waste-fired boilers has been shown to have a high tendency to break down these oxide scales, which results in the formation of a faster-growing iron-rich oxide scale. This phenomenon is generally referred to as breakaway oxidation. In the present work, the corrosion behavior before and after breakaway oxidation was defined as the primary and secondary corrosion regime.

This work has focused on investigating the influence of alloying elements on the corrosion behavior of FeCr(Al) alloys in the primary and secondary corrosion regimes. The criteria for optimizing the corrosion resistance in the two corrosion regimes was found to differ significantly. The applicability of the findings was shown to extend from simplified laboratory environments to the complex environments of biomass- and waste-fired boilers. These insights provide new perspectives in the development of materials and coatings for various harsh environments.

Ämneskategorier

Oorganisk kemi

Materialkemi

Korrosionsteknik

Drivkrafter

Hållbar utveckling

Styrkeområden

Energi

Materialvetenskap

Infrastruktur

Chalmers materialanalyslaboratorium

ISBN

978-91-7905-394-9

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4861

Utgivare

Chalmers tekniska högskola

HA1

Opponent: Prof. Marcel Somers, Denmarks Technical University, Denmark

Mer information

Senast uppdaterat

2021-01-14