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Interaction between ash forming elements in woody biomass and two high alumina refractories part 2: transformation of crystalline compounds
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Höganäs Bjuf AB.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Two high alumina refractories, one brick and one pre fired castable was exposed to pure K2CO3, K2CO3 + CaCO3, and K2CO3 + CaCO3 + SiO2 at 1050°C and a CO2 atmosphere. A stratified investigation of crystalline phases was made with polycrystalline x-ray diffraction, and thermodynamic equilibrium calculations were performed to explore possible formation paths. A monoclinic polymorph of KAlSiO4 was formed to a large extent in both materials exposed to pure K2CO3. Throughout the affected part of the castable and a small layer close to the surface of the brick, a solid solution between KAlO2 and KAlSiO4 formed, K1-xAl1-xSixO2, x = 0.19. The affected area of the castable had 30-50 %wt new phases and made a sharp transition to unaffected material. The concentration of new phases in the brick was decreasing at an even rate from about 40 to 15%wt throughout the whole material thickness of 14 mm. Exposure to K2CO3 and CaCO3 showed the same phases and behavior, but no Ca-bearing phases could be detected. The mixture containing K2CO3, CaCO3 and SiO2 did not penetrate far into the material but formed the same phases in the affected areas. Wollastonite (CaSiO3) formed in the slag on top of these materials. The major mechanism for formation of new phases is suggested to be the formation of an initial melt composed of K2O and SiO2. This liquid is then dissolving refractory components and forms a liquid in equilibrium with KAlSiO4 and K1-xAl1-xSixO2.

Keywords [en]
Refractory corrosion, slag, biomass, gasification, phase transformation
National Category
Ceramics
Research subject
Materials Science
Identifiers
URN: urn:nbn:se:umu:diva-152661OAI: oai:DiVA.org:umu-152661DiVA, id: diva2:1256546
Funder
Bio4EnergyAvailable from: 2018-10-17 Created: 2018-10-17 Last updated: 2018-10-18
In thesis
1. Refractory corrosion in biomass gasification
Open this publication in new window or tab >>Refractory corrosion in biomass gasification
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Korrosion av eldfasta material i biomassaförgasning
Abstract [en]

To stop the net emission of CO2 to the atmosphere, we need to reduce our dependency of fossil fuels. Although a switch to a bio-based feedstock hardly can replace the total amount of fossils used today, utilization of biomass does still have a role in a future in combination with other techniques. Valuable chemicals today derived from fossils can also be produced from biomass with similar or new technology. One such technique is the entrained flow gasification where biomass is converted into synthesis gas. This gas can then be used as a building stone to produce a wide range of chemicals.

Slagging and corrosion problems are challenges presented by the ash forming elements in biomass during thermochemical energy conversion. The high temperature in the entrained flow process together with ash forming elements is creating a harsh environment for construction materials in the reactor. Severe corrosion and high wear rates of the lining material is a hurdle that has to be overcome to make the process more efficient.

The objective of this work is to investigate the nature of the destructive interaction between ash forming elements and refractory materials to provide new knowledge necessary for optimal refractory choice in entrained flow gasification of woody biomass. This has been done by studying materials exposed to slags in both controlled laboratory environments and pilot scale trials. Morphology, elemental composition and distribution of refractories and slag were investigated with scanning electron microscopy and energy dispersive X-ray spectroscopy. Crystalline phases were investigated with X-ray diffraction, and thermodynamic equilibrium calculations were done in efforts to explain and make predictions of the interaction between slag and refractory.

Observations of slag infiltration and formation of new phases in porous materials indicate severe deterioration. The presence of Si in the materials is limiting intrusion by increasing the viscosity of infiltrated slag. This is however only a temporary delay of severe wear considering the large amount of slag that is expected to pass the refractory surface. Zircon (or zirconium) (element or mineral?) based material show promising properties when modeled with thermodynamic equilibrium, but disassembling of sintered material and dissociation of individual grains was seen after exposure to a Si- and Ca-rich slag. Fused cast materials have a minimal slag contact where the only interaction is on the immediate hot face. Dissolution was however observed when exposed to a silicate-based slag, as was the formation of NaAlO2 after contact with black liquor.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2018. p. 62
Keywords
Refractory corrosion, slag, biomass, gasification
National Category
Energy Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:umu:diva-152664 (URN)978-91-7601-944-3 (ISBN)
Public defence
2018-11-09, Hörsal N360, Naturvetarhuet, Johan Bures väg 16, Umeå, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2018-10-19 Created: 2018-10-17 Last updated: 2018-10-18Bibliographically approved

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