High Temperature Corrosion Behavior in Biomass- and Waste-Fired Boilers - Insights into catastrophic corrosion and corrosion mitigation techniques
Doktorsavhandling, 2020

Carbon dioxide is contributing to the greenhouse effect and a significant part comes from the use of fossil fuels. Utilizing more renewable fuels is therefore a solution to decrease the net release of CO2 emissions to the atmosphere. This can be achieved by substituting fossil fuels, such as coal and oil, with renewable fuels, such as biomass and waste. However, the combustion of these renewable fuels releases corrosive species creating corrosion challenges for critical parts of the plants, resulting in lower electrical efficiency and higher maintenance costs. It is therefore necessary to understand and investigate the corrosion attack that occurs in this type of environment, in order to find sustainable solutions.

High-temperature corrosion research can be divided into two steps: laboratory investigations focus on determining the role or influence of different parameters such as water vapor content or specific corrosive species, while field investigations are more oriented towards in-situ studies to test ideas developed within laboratory studies for mitigation of the corrosion attack.

Both approaches are included within the scope of this thesis to broaden the knowledge about the accelerated corrosion of steels, as well as investigate different techniques of mitigation of high-temperature corrosion occurring in biomass- and waste-fired boilers.

The laboratory investigations in this thesis focused on KCl-induced corrosion of steels at elevated temperatures (600 °C). A setup allowing a continuous supply of a corrosive species (KCl) during the whole exposure was developed. This generated a corrosive environment mimicking a boiler environment and a corrosion attack better resembling the attack observed in commercial boilers compared to previous methods.

Within this setup, four commercial/steels/alloys were investigated and selected in such a way that they represent a broad range of material classes, but also to contain an increasing amount of nickel (from 0 wt.% to 62 wt.%). The results showed that the corrosion attack could be divided into two corrosion morphologies: general corrosion and steel grain boundary attack. Increasing the nickel content resulted in a decrease of the thickness of the general oxide scales. The corrosion attack of the steel grain boundary exhibited a different trend. The attack became more severe when nickel is part of the alloy’s composition.

In order to improve the understanding of the corrosion attack in this type of environment, an in-depth study of intergranular corrosion (steel grain boundary attack) in a stainless steel (304L) using the state-of-the-art combination of 3D tomography and TEM was performed. The grain boundary corrosion attack was characterized in detail and revealed new insights of how this complex attack progresses. Very small amounts of Cl were observed in the corrosion front together with very large depletion zones.

The design of a new material exhibiting outstanding corrosion resistance properties, excellent mechanical strength, and reasonable costs for application in biomass- and waste-fired boilers is both difficult and time-demanding. Another approach is to separate these properties using a base material (with good mechanical properties) with a corrosion resistant coating. In this work, a set of nickel-based coatings (NiCr, NiAl and NiCrAlY) were investigated in a KCl-rich environment for up to 168 hours. The results showed that the NiAl and NiCrAlY coatings performed well. However, it is necessary to perform a more advanced investigation, i.e. longer durations of exposure, to ascertain their reliability.

Another way to mitigate the high-temperature corrosion experienced in boilers would be to alter the environment. Two studies of this alternative solution were investigated in this thesis. A potential new position for superheaters predicted via CFD (Computational Fluid Dynamics) calculations was studied and showed that it is possible to decrease the amount of corrosive species (chlorides) in the deposits.

Within the similar scope of making the environment milder for the materials, another technical solution was investigated, the Sulfur Recirculation technique. In this setup, the corrosion history caused by a variation in fuel (corrosion memory effect) was studied and the results showed that the corrosion memory effect can influence positively (when exposed first in a mild environment) and negatively (when exposed first in a corrosive environment) the future corrosion behavior of a material.

Deposits

Waste

Ni-based alloys

Sulfur Recirculation

TEM

High-temperature corrosion

Stainless steel

Biomass

KCl-induced corrosion

Coatings

3D tomography

Pater Noster (2034, Forskarhus 1)
Opponent: Flemming Jappe Frandsen, Associate professor, DTU Chemical Engineering, Department of Chemical and Biochemical Engineering

Författare

Julien Phother Simon

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

Continuous KCl addition in high temperature exposures of 304 L – A way to mimic a boiler environment

Corrosion Science,; Vol. 167(2020)

Artikel i vetenskaplig tidskrift

Phother-Simon, J. Hanif, I. Liske, J. Jonsson, T. High-temperature corrosion of P91/T91, 304L, Sanicro 28 and Inconel 625 exposed at 600 °C under continuous KCl deposition

Phother-Simon, J. Hanif, I. Liske, J. Jonsson, T. The influence of a KCl-rich environment on the corrosion attack of 304L: 3D FIB/SEM and TEM investigation

KCl-induced corrosion of Ni-based alloys containing 35–45 wt% Cr

Materials and Corrosion,; Vol. 70(2019)p. 1486-1506

Artikel i vetenskaplig tidskrift

Effect of water vapor on the oxidation behavior of HVAF-sprayed NiCr and NiCrAlY coatings

Materials and Corrosion - Werkstoffe und Korrosion,; Vol. 69(2018)p. 1431-1440

Artikel i vetenskaplig tidskrift

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

Oxidation of Metals,; (2019)

Artikel i vetenskaplig tidskrift

Dolores Paz, M. Phother-Simon, J. Mikkelsen, L. Jonsson, T. Increased steam temperature with Steamboost superheater: The effect of the combustion in deposits and high temperature corrosion

Dolorez Paz, M. Phother-Simon, J. Andersson, S. Jonsson, T. High-temperature corrosion memory in a waste-fired boiler: Influence of sulfur

“Global warming” and “greenhouse effect” are terms that became well-known to the general public. The greenhouse effect is a phenomenon where greenhouse gases (GHGs) confines some of heat from the Sun on Earth’s surface. If GHGs is increased in the atmosphere, more heat can be confined. One of the main GHGs contributing to the greenhouse effect is carbon dioxide (CO2). Since the industrial revolution, humans have increased the concentration of carbon dioxide in the atmosphere more than a third. This results in global warming and changes in the climate, such as e.g. more intense storms, drier droughts, and changes of the habitats. It is, therefore, necessary to decrease the amount of GHGs released to the atmosphere in order to minimize climate changes.

A significant contribution to the release of carbon dioxide to the atmosphere comes from the use of fossil fuels. As an example, the majorities of the world’s powerplants uses fossil fuels such as coal and oil to produce electricity and district heating. Unfortunately, the combustion of these fossil fuels lead to the formation of carbon dioxide, originating from non-renewable resources. Utilizing renewable fuels instead is a solution to decrease the net release of CO2 emissions to the atmosphere. However, the combustion of renewable fuels, such as biomass (e.g. wood chips, forest residue or straw) and waste (e.g. municipal or industrial waste), results in the formation of ashes and gases which are corrosive towards e.g. superheaters in the powerplants. This results in a lower electrical efficiency and higher maintenance costs.

For this reason, many universities, research institutes and companies are investigating these corrosion phenomena and aiming at reducing the material degradation, in order to make the heat and power production via biomass- and waste-fired powerplants more competitive than fossil fuel-fired powerplants. As an example, my work was focused on the corrosion experienced by stainless steels. Experiments were conducted at Chalmers in order to improve the understanding of the corrosion phenomena while other experiments were carried out directly in powerplants to investigate ways to mitigate the corrosion.

Ämneskategorier

Materialteknik

ISBN

978-91-7905-353-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4820

Utgivare

Chalmers tekniska högskola

Pater Noster (2034, Forskarhus 1)

Opponent: Flemming Jappe Frandsen, Associate professor, DTU Chemical Engineering, Department of Chemical and Biochemical Engineering

Mer information

Senast uppdaterat

2020-09-10