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High temperature interactions between K-rich biomass ash and MgO-based refractories
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.ORCID-id: 0000-0003-1170-2203
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish Mineral Processing Research Association - MinFo, C/O Cementa, Stockholm, Sweden.ORCID-id: 0000-0002-8230-8847
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.ORCID-id: 0000-0002-0555-5924
Visa övriga samt affilieringar
2023 (Engelska)Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 43, nr 8, s. 3770-3777Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

MgO-based refractories are used in lime kilns to withstand the high temperature and chemical environment. Efforts to reduce CO2 emissions have led to an increased interest to use bio-based fuels as alternatives to traditional fossil sources. The potential for refractory corrosion from a potassium-rich biomass ash was investigated by studying the infiltration of olive pomace ash into magnesia/spinel refractories. Refractory samples were exposed to the ash at up to 1400 °C for 15–60 min in a CO2–rich atmosphere. Molten ash infiltrated the refractories through pores and grain boundaries to a depth of up to 9.6 mm, which was quantified with a new systematic procedure. The phase KAlO2 was identified inside the refractories after exposure, indicating an attack of spinel components by potassium. Phases found in the ash residues also indicated the migration of refractory constituents. Thermochemical equilibrium calculations were also used to investigate the ash/refractory chemistry.

Ort, förlag, år, upplaga, sidor
Elsevier, 2023. Vol. 43, nr 8, s. 3770-3777
Nyckelord [en]
Biomass ash; Lime kiln; Magnesia; Olive pomace; Potassium; Refractory corrosion; Slag infiltration
Nationell ämneskategori
Kemiteknik
Identifikatorer
URN: urn:nbn:se:umu:diva-205465DOI: 10.1016/j.jeurceramsoc.2023.01.058ISI: 000955011500001Scopus ID: 2-s2.0-85148748148OAI: oai:DiVA.org:umu-205465DiVA, id: diva2:1741935
Forskningsfinansiär
Bio4EnergyEnergimyndigheten, 34721-3Energimyndigheten, 47198-1Tillgänglig från: 2023-03-07 Skapad: 2023-03-07 Senast uppdaterad: 2023-11-15Bibliografiskt granskad
Ingår i avhandling
1. Assessment of bio-based fuel ash effects on magnesia refractory materials in quicklime production kilns
Öppna denna publikation i ny flik eller fönster >>Assessment of bio-based fuel ash effects on magnesia refractory materials in quicklime production kilns
2023 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Utvärdering av biobaserade bränsleaskors effekter på magnesiumoxidbaserade refraktorer i brännugnar för kalkproduktion
Abstract [en]

Limestone is calcined into quicklime in lime kilns at temperatures above 1000°C. Heat is supplied through combustion inside the kilns, which are insulated with a lining of refractory bricks to mitigate heat loss and to protect the kiln from the hot, chemically aggressive, and mechanically abrasive environment. While magnesia bricks have proven to be effective lining materials, they are still susceptible to extensive wear in lime kilns, especially in the burn zone. Refractory corrosion, in particular, can occur when melted fuel ash infiltrates the refractory materials through pores and small cracks. This resultant wear can lead to high maintenance and operational costs, often due to unplanned kiln shutdowns.

To reduce the release of fossil-based carbon dioxide into the atmosphere from lime production kilns, there is a growing interest in introducing bio-based fuels with only relatively minor modifications to the process. Biomass fuels can be sourced from bio-based waste streams from industries or be specifically cultivated for combustion. However, the ash content and properties of bio-based fuels tend to be problematic from an ash chemistry perspective. Therefore, before introducing a new fuel source, it is essential to investigate its potential effects on the kiln lining material. 

In this thesis work, the interactions between melted olive pomace ash and coal ash with commercially available magnesia refractory materials, primarily composed of periclase (MgO) with minor amounts of spinel (MgAl2O4), were studied. A procedure for quantifying the intrusion depths was described. Refractory samples were exposed to the fuel ashes under a simulated lime kiln atmosphere with high CO2 levels at 1200 and 1400°C for 15 and 60 minutes. Cold crushing strength tests were conducted on refractory samples exposed to coal and olive pomace ash, along with CaO powder, at 1400°C for 96 hours. Additionally, postmortem analyses of spent MgO-based refractory bricks were carried out to investigate their chemical characterization and resistance to slag attack after serving as part of the lining in a quick lime rotary kiln for six months.

The morphology and elemental compositions of the exposed samples were examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Crystalline phases were investigated with powder X-ray diffraction. Thermodynamic equilibrium calculations were performed to further investigate the ash’s melting behavior in contact with the refractories.

The results indicated that the potassium-rich olive pomace ash exhibited a greater tendency to infiltrate compared to the silicon-rich coal ash, while the latter formed a glassy melt layer on top of the refractory samples. The ash slags primarily infiltrated through the porous matrix and grain boundaries of the refractory materials. Also, refractory phases were observed in both types of ashes, indicating migration of refractory constituents. K2MgSiO4 phase was found in the olive pomace ash residues on top of the samples, both for the 1200°C and 1400°C exposures. Similarly, Al6Si2O13 phase was dominant in the residual coal ash, in both the 1200°C and 1400°C exposed samples. None of these phases were present in the original ashes.

The results of the postmortem analysis revealed that there was no potassium (K) from the fuel ash present on the hot side of the refractory bricks. However, some K was detected in the middle and back parts of the bricks. On the other hand, some phases, possibly connected to degradation, could be found on the hot side of the bricks, where most of the wear was observed.

The crushing strengths increased after exposure for all samples, except for those exposed exclusively to coal ash. One possible explanation for this is that the refractory materials exhibited a sintered structure, as a result of their interaction with the ashes and CaO. However, in the samples exposed to coal ash, forsterite (Mg2SiO4) was identified, which can be considered a corrosion product.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå University, 2023. s. 57
Nyckelord
Refractory corrosion, ash slag intrusion, lime kiln, MgO refractory, coal ash, olive pomace ash, biomass fuel, crushing strength, potassium (K), silicon (Si).
Nationell ämneskategori
Keramteknik Korrosionsteknik Energiteknik
Forskningsämne
materialvetenskap
Identifikatorer
urn:nbn:se:umu:diva-216749 (URN)978-91-8070-230-0 (ISBN)978-91-8070-231-7 (ISBN)
Disputation
2023-12-14, Hörsal NAT.D.480, Naturvetarhuset, Umeå universitet, Umeå, 13:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2023-11-23 Skapad: 2023-11-15 Senast uppdaterad: 2023-12-11Bibliografiskt granskad

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Kumar Wagri, NareshCarlborg, MarkusEriksson, MatiasMa, CharlieBroström, MarkusAndersson, Britt M.

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Kumar Wagri, NareshCarlborg, MarkusEriksson, MatiasMa, CharlieBroström, MarkusAndersson, Britt M.
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Institutionen för tillämpad fysik och elektronik
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