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Interaction between ash forming elements in woody biomass and two high alumina refractories part 1: effects on morphology and elemental distribution
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]

To gain more knowledge about possibly destructive effects of ash-forming elements in woody biomass on refractory materials in entrained flow gasification, an exposure study was performed on two high alumina refractories. The materials, a pre-fired castable consisting of about 63 weight-% Al2O3, and a phosphate bonded brick with 83 weight-% Al2O3 was exposed to synthetic ash mixtures at 1050°C and 1 atm CO2 for 7 days. This paper presents distribution of ash-forming elements and morphology of the samples microstructure, while identification and distribution of crystalline compounds is presented in a separate paper. In the samples, potassium (K) had infiltrated the materials and reacted with different components, while calcium (Ca) did not seem to have any direct effect during these conditions. The matrix of the castable absorbed much K, became clogged and produced a distinct border between reacted and unaffected matrix. The coarser matrix of the phosphate bonded brick retained much of its porosity and had ash transported further into the material without a clear distinction between reacted and unaffected matrix. Grains with >30 atomic-% Si, formed a layer enriched in K, with a thickness up to 40 µm and cracks propagating through it. Grains mainly consisting of Al2O3 seemed unaffected by the exposure. When the ash was rich in SiO2, a melt was produced that restricted the attack on the refractories to the surface and coarser pores.

Keywords [en]
Refractory corrosion, slag, biomass, gasification
National Category
Ceramics
Research subject
Materials Science
Identifiers
URN: urn:nbn:se:umu:diva-152660OAI: oai:DiVA.org:umu-152660DiVA, id: diva2:1256536
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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Carlborg, MarkusBoström, DanBackman, Rainer

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