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Separation of carbon dioxide from flue gas (post-combustion capture) via gas hydrate crystallization Linga, Praveen

Abstract

This thesis examines the prospect of employing hydrate crystallization in a gas/liquid stirred vessel for separation of carbon dioxide (CO₂) from a flue gas mixture. A treated flue gas mixture contains CO₂, O₂ and N₂. Because O₂ and N₂ form hydrate at approximately same pressure-temperature conditions a model gas mixture to work with consists of 17 mol % CO₂ and 83 mol % N₂. Gas hydrates were formed in a 323 cm³ vessel at 273.7 K and constant pressures. The data enabled us to propose a process based on three hydrate stages coupled with a membrane separation stage. Two metrics, CO₂ recovery and separation factor were introduced to evaluate the efficiency of the process. The operating pressures were found to be 10, 5 and 2.5 MPa for the three stages. The high operating pressure required for the first stage necessitated the use of an additive to lower the pressure. Tetrahydrofuran (THF) was chosen and relevant thermodynamic and kinetic data were obtained and reported. The efficiency of the separation was also determined. It was concluded that a stream containing 96% CO₂ can be obtained from of a medium-pressure process consisting of three hydrate stages. The three stages operate at 2.5 MPa and 273.75 K without compromising the separation efficiency obtained without the addition of THF. A new apparatus was designed and built to demonstrate the hydrate process at a larger scale. The results showed an improvement in the kinetics and the separation efficiency. Finally, the kinetics of the hydrate crystallization were also studied using a fixed bed of silica sand particles and the results were compared with those obtained in the gas/liquid systems. The gas uptake was found to be significantly higher for the systems involving water dispersed in silica sand.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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