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- Corcoran, Angelica, 1988, et al.
(author)
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Comparing the structural development of sand and rock ilmenite during long-term exposure in a biomass fired 12 MWth CFB-boiler
- 2018
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In: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 171, s. 39-44
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Journal article (peer-reviewed)abstract
- Oxygen Carrier Aided Combustion (OCAC) is a novel combustion concept with the purpose to increase the overall efficiency in conventional circulating fluidized bed (CFB) boilers. By replacing the commonly used bed material with an oxygen carrier (OC), the conceptual idea is to utilize the fluid dynamics in a CFB and the inherent oxygen transport supported by the OC to increase the oxygen distribution within the furnace in time and space. The OCAC concept has been successfully validated and further reached long-term demonstration in full scale operation (75-MW th ). This work presents a first evaluation of how ilmenite particles are affected in regard to mechanical resistance during long-term exposure to OCAC conditions in Chalmers 12-MW th CFB-boiler. A sand and a rock ilmenite are evaluated with regard to their mechanical stability. For evaluation, samples of the fresh materials and samples collected during operation in the Chalmers boiler are investigated. The study shows that the two materials differ in how the mechanical degradation occurs with exposure time. The sand ilmenite form cavities which are held together by an ash layer before they are shattered into numerous pieces, whereas the rock ilmenite develops distinct cracks that cause splitting of the particles.
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| 2. |
- Corcoran, Angelica, 1988, et al.
(author)
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Mechanism for Migration and Layer Growth of Biomass Ash on Ilmenite Used for Oxygen Carrier Aided Combustion
- 2018
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In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:8, s. 8845-8856
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Journal article (peer-reviewed)abstract
- Biomass is recognized as a CO2-neutral energy resource. However, biomass is a challenging fuel to combust because of its heterogeneity with regard to the content of inorganic constituents, volatiles, and moisture. Oxygen carrier aided combustion (OCAC) is a process advancement that provides enhanced combustion in existing circulating fluidized bed (CFB) units. The oxygen carrier has a central role in the OCAC concept through the oxygen transport it provides. The natural mineral ilmenite (FeTiO3) has been identified as a promising potential oxygen carrier. In order to ensure the feasibility even for long-term operation in industrial-scale processes, it is imperative to understand the evolution of the material during an OCAC process. In the present study, ilmenite was used as the bed material in the Chalmers 12 MWth CFB boiler during OCAC with woody biomass as fuel. Bed material samples were extracted from the bed inventory at different time intervals ranging from 5 to over 300 h. This paper proposes a mechanism for migration and layer growth of biomass ash on the ilmenite used as the oxygen carrier in a CFB combustor. It was found that with increased time of exposure, potassium migrated into the particle core. Longer process times led to the formation of a calcium layer around the particle, and simultaneously, migration of calcium inward on the particle was observed. Thermodynamic calculations were used along with analysis techniques in order to build a hypothesis for the possible mechanism of ash-bed material interaction.
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