Computational fluid dynamics simulations of oxy-coal combustion for carbon capture at atmospheric and elevated pressures
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
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| Format: | Thesis |
| Language: | eng |
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Massachusetts Institute of Technology
2013
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| Online Access: | http://hdl.handle.net/1721.1/81694 |
| _version_ | 1811082482777325568 |
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| author | Chen, Lei, Ph. D. Massachusetts Institute of Technology |
| author2 | Ahmed F. Ghoniem. |
| author_facet | Ahmed F. Ghoniem. Chen, Lei, Ph. D. Massachusetts Institute of Technology |
| author_sort | Chen, Lei, Ph. D. Massachusetts Institute of Technology |
| collection | MIT |
| description | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013. |
| first_indexed | 2024-09-23T12:04:07Z |
| format | Thesis |
| id | mit-1721.1/81694 |
| institution | Massachusetts Institute of Technology |
| language | eng |
| last_indexed | 2024-09-23T12:04:07Z |
| publishDate | 2013 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| spelling | mit-1721.1/816942019-04-10T09:03:46Z Computational fluid dynamics simulations of oxy-coal combustion for carbon capture at atmospheric and elevated pressures Chen, Lei, Ph. D. Massachusetts Institute of Technology Ahmed F. Ghoniem. Massachusetts Institute of Technology. Department of Mechanical Engineering. Massachusetts Institute of Technology. Department of Mechanical Engineering. Mechanical Engineering. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013. Cataloged from PDF version of thesis. Includes bibliographical references (p. 229-239). Oxy-fuel combustion of solid fuels, often performed in a mixture of oxygen and wet or dry recycled carbon dioxide, has gained significant interest in the last two decades as one of the leading carbon capture technologies in power generation. The new combustion characteristics in a high-O₂ environment raise challenges for furnace design and operation, and should be modeled appropriately in CFD simulation. Based on a comprehensive literature review of the state-of-the-art research on the fundamentals of oxy-coal combustion, sub-models for the critical physical processes, such as radiation and char combustion, have been properly modified for the O₂-rich environment, and the overall performance of CFD simulation on oxy-coal combustion has been validated using Large-Eddy Simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) approaches. The predicted distributions on velocity, species, and temperature were compared with experimental results from the literature in order to validate the CFD simulation. Results show that although agreeing reasonably with the measured mean axial and tangential velocity, all the RANS turbulence models used in this study underestimate the internal recirculation zone size and the turbulence mixing intensity in the char combustion zone, while LES improves the predictions of internal recirculation zone size, the entrainment of oxygen from the staging stream, and the overall flame length than the RANS approaches. Special attention was given to the CO₂'s chemical effects on CO formation in oxy-fuel combustion, and its modeling approaches in CFD simulations. Detailed reaction mechanism (GRI-Mech 3.0) identifies that the reaction H+CO₂ -->/<-- OH+CO enhances the CO formation in the fuel-rich side of the diffusion flame due to the high CO₂ concentration, leading to a significantly higher CO concentration. Reasonable CO predictions can only be obtained using finite-rate mechanisms combining with reaction mechanisms considering the above-mentioned reaction in CFD simulations. The validated CFD approach was used to investigate the pressure's effects in a pressurized oxy-coal combustion system. The results show that, given a fixed reactor geometry and burner velocity, the particle residence time does not change with operating pressure due to its small Stokes number; on the other hand, the coal conversion time decreases significantly because of the enhanced reaction rates at elevated pressures. Therefore, the burner can be operated at a higher burner velocity at elevated operating pressure, which results in a much higher coal throughput using the same reactor size. For instance, the thermal load can be increased from 3 MWth to 60 MWth using a pressurized oxy-coal reactor, when the operating pressure increases from 4 bar to 40 bar. In order to investigate the slag behaviors in the pressurized oxy-coal combustor, a first-of-its-kind three-dimensional slag model has been developed, which can be applied in slagging coal combustion/gasification with any geometry. The method couples Volume of Fluid (VOF) model and Discrete Phase Model (DPM), and fully resolves the slag's behaviors such as the slag layer buildup, multiphase flow, as well as heat transfer. The results are in good agreement with experimental observations, and can be taken as a design tool for coal furnace/gasifier development. by Lei Chen. Ph.D. 2013-10-24T17:44:56Z 2013-10-24T17:44:56Z 2013 2013 Thesis http://hdl.handle.net/1721.1/81694 860900579 eng M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 239 p. application/pdf Massachusetts Institute of Technology |
| spellingShingle | Mechanical Engineering. Chen, Lei, Ph. D. Massachusetts Institute of Technology Computational fluid dynamics simulations of oxy-coal combustion for carbon capture at atmospheric and elevated pressures |
| title | Computational fluid dynamics simulations of oxy-coal combustion for carbon capture at atmospheric and elevated pressures |
| title_full | Computational fluid dynamics simulations of oxy-coal combustion for carbon capture at atmospheric and elevated pressures |
| title_fullStr | Computational fluid dynamics simulations of oxy-coal combustion for carbon capture at atmospheric and elevated pressures |
| title_full_unstemmed | Computational fluid dynamics simulations of oxy-coal combustion for carbon capture at atmospheric and elevated pressures |
| title_short | Computational fluid dynamics simulations of oxy-coal combustion for carbon capture at atmospheric and elevated pressures |
| title_sort | computational fluid dynamics simulations of oxy coal combustion for carbon capture at atmospheric and elevated pressures |
| topic | Mechanical Engineering. |
| url | http://hdl.handle.net/1721.1/81694 |
| work_keys_str_mv | AT chenleiphdmassachusettsinstituteoftechnology computationalfluiddynamicssimulationsofoxycoalcombustionforcarboncaptureatatmosphericandelevatedpressures |