| 1. |
- Corcoran, Angelica, 1988, et al.
(författare)
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Ash Properties of Ilmenite Used as Bed Material for Combustion of Biomass in a Circulating Fluidized Bed Boiler
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:12, s. 7672-7679
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Tidskriftsartikel (refereegranskat)abstract
- Both agglomeration of bed material and corrosion of heat transfer equipment are issues related to combustion of biomass in a fluidized bed boiler. The biomass-ash component potassium is considered a major contributor for both phenomena. In this study, the conventionally used bed material, silica sand, was replaced with up to 40 wt % by the natural ore ilmenite in Chalmers 12 MWth circulating fluidized bed (CFB) boiler. In this study the purpose was to evaluate the physical and chemical changes ilmenite undergoes during this process. Close observations revealed that ilmenite underwent segregation of iron to the surfaces and an enrichment of titanium in the particle core. The ash formed a calcium-rich double layer on the particle, surrounding the iron layer. A diffusion of potassium into the particle core was also seen which led to the formation of KTi8O16. In addition to evaluating how ash components interact with the material, the ilmenite was leached and investigated as a possible potassium capturer. Leaching experiments on the used ilmenite showed that calcium and potassium were leachable to a very limited degree, namely, to less than 0.2 and 1 wt %, respectively, of the total content. The diffusion of potassium into the core of the particle could reduce both agglomeration and corrosion issues and could thereby be of great value for the improvement of the resistance of the bed material agglomeration in the fluidized bed boiler.
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| 2. |
- Corcoran, Angelica, 1988, et al.
(författare)
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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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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 171, s. 39-44
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Tidskriftsartikel (refereegranskat)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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| 3. |
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| 4. |
- Corcoran, Angelica, 1988, et al.
(författare)
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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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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:8, s. 8845-8856
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Lind, Fredrik, 1978, et al.
(författare)
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12,000 Hours of Operation with Oxygen-Carriers in Industrially Relevant Scale (75,000 kWth).
- 2017
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Ingår i: VGB PowerTech.
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carrier aided combustion (OCAC) is a novel combustion method and a spin-off from chemical-looping combustion (CLC). The core of the technique lies in the utilization of an oxygen carrier (OC) as bed material, and the purpose to enhance the distribution of oxygen in fluidized bed (FB) boilers. The concept combines the robustness of the well-established technology FB boilers with the novel features of oxygen active properties introduced by the OC. Due to several similarities, the OCAC concept can also contribute with knowledge in a transitional path for the scale-up of other chemical-looping techniques, such as CLC, from lab to industrial scale. In this work, the first experiences are presented where a 75,000 kWth CFB-boiler has been operated with ilmenite (FeTiO3) as bed material during 12,000 hours with municipal solid waste as fuel. The investigation shows that ilmenite can replace the commonly used bed material silica-sand without any retrofitting of boiler equipment, and that ilmenite enhances the mass transfer of oxygen inside the furnace. The results show that ilmenite can drastically reduce the amount of carbon monoxide in the flue gas, even when the furnace is operated with an oxygen concentration that is lower compared to ordinary silica-sand operation. Even though still being in the early stages, this concept can contribute to overcome the threshold of understanding the mass transfer and mixing conditions in industrial conditions to enable scale-up of CLC.
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| 6. |
- Lind, Fredrik, 1978, et al.
(författare)
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Validation of the oxygen buffering ability of bed materials used for OCAC in a large scale CFB boiler
- 2017
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 316, s. 462-468
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carrier aided combustion (OCAC) is a novel concept where the inert bed material is fully or partly replaced by an oxygen carrying metal oxide to increase the oxygen distribution in fluidized bed combustors. In this work, the basic claim that metal oxides provide oxygen buffering and oxygen transporting properties is investigated further. The study includes initial experiments where an oxygen carrier has been used exclusively in large scale for combustion purposes. In the experiments, conducted in Chalmers 12 MWth CFB-boiler, distinct fuel pulses were introduced to the combustor as the boiler was operated at the same conditions, first with 100% silica sand and later during operation with 100% iron-titanium based metal oxide. The results from the experimental progression were explored further by creating a dynamic pulse response, in which the experimental data was used to derive the empirical coefficients. The results from the experiments and the subsequent evaluation of the dynamic response provide proof of the claim that the oxygen carrying bed material enhances the utilization of the oxygen provided to a boiler by distributing it in space and time.
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| 7. |
- Rydén, Magnus, 1975, et al.
(författare)
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Oxygen Carrier Aided Combustion (OCAC) of Wood Chips in a Semi-Commercial Circulating Fluidized Bed Boiler Using Manganese Ore as Bed Material
- 2016
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 6:11, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen Carrier Aided Combustion (OCAC) is realized by using an active oxygen-carrying bed material in fluidized bed boilers. The active material is reduced in fuel rich parts of the boiler and oxidized in air rich parts. Advantages could be achieved such as new mechanisms for oxygen transport in space and time. Here calcined manganese ore has been used as active bed material in a 12 MWth circulating fluidized bed boiler. The fuel was wood chips and the campaign lasted more than two weeks. From an operational point of view, manganese ore worked excellently. From the temperature profile of the boiler it can be concluded that fuel conversion was facilitated, especially in the dense bottom bed. The effect did not always translate to reduced emissions, which suggests that final combustion in the cyclone outlet was also influenced. Substituting 10% of the sand bed with manganese ore made it possible to reduce the air to fuel ratio without generating large amounts of CO. The use of 100% manganese ore resulted in higher emissions of CO than the sand reference, but, when combined sulphur feeding, dramatic reductions in CO emissions, up to 90% compared to sand reference, was achieved.
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