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1 Center for Energy Resources Engineering, Center, Technical University of Denmark 2 Department of Chemical and Biochemical Engineering, Technical University of Denmark 3 CERE – Center for Energy Ressources Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark 4 CAPEC-PROCESS, Department of Chemical and Biochemical Engineering, Technical University of Denmark
A thermodynamic model based on the Cubic-Plus-Association equation of state and the van der Waals-Platteeuw hydrate model is applied to perform a thermodynamic evaluation of gas hydrate forming systems relevant for post-combustion carbon dioxide capture.A modelling study of both fluid phase behaviour and hydrate phase behaviour is presented. Cycloalkanes ranging from cyclopropane to cyclohexane, represents a challenge for CPA, both in the description of the pure component densities and for liquid-liquid equilibrium (LLE) in the binary systems with water. It is concluded that an insufficient amount of reliable LLE data exist for the binary system of water and cyclopentane. Additional water-in-oil data in particular are desired for this system.An unpromoted hydrate-based capture process, operating isothermally at a temperature of 280. K is simulated. The minimum pressure requirement of the first stage is estimated to be 24.9. MPa. Applying three consecutive hydrate formation/dissociation stages (three-stage capture process), a carbon dioxide-rich product (97. mol%) may be delivered at a temperature of 280. K and a pressure of 3.65. MPa.A second capture process, where cyclopentane is incorporated as a thermodynamic hydrate promoter is simulated. At the presence of cyclopentane the minimum pressure requirement of the first stage (operating at 285. K) is lowered to 1.04. MPa. This process needs four consecutive hydrate formation/dissociation stages to produce a 95. mol% carbon dioxide-rich product stream. The vapour phases in the cyclopentane promoted process contains several mole percent cyclopentane at hydrate equilibrium conditions. At temperatures below 284. K, the entire cyclopentane bulk phase evaporates completely at hydrate forming conditions (pressures below 0.55. MPa).The present study suggests the hydrate-based separation technology to be unsuitable for the specific case of post-combustion carbon dioxide capture from power station flue gases, where operating pressures should preferably remain close to atmospheric. Even though the hydrate structure becomes available at low pressure conditions (by use of thermodynamic promoters), carbon dioxide may not necessarily enter the solid phase in significant amounts. © 2014 Elsevier B.V.
Fluid Phase Equilibria, 2014, Vol 375, p. 89-103
Carbon dioxide; Cyclopentane; Gas hydrates; Modelling; Promoter; Binary mixtures; Carbon capture; Carbon dioxide process; Combustion; Equations of state of gases; Hydration; Models; Phase equilibria; Systems (metallurgical); Temperature; Van der Waals forces; Cubic plus associations; Hydrate forming conditions; Liquid liquid equilibrium; Low-pressure conditions; Thermodynamic evaluation; Thermodynamic promoters
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