276994 Validation of a Process Model of CO2 Capture in an Aqueous Solvent, Using an Implicit Molecular Based Treatment of the Reactions

Wednesday, October 31, 2012: 9:45 AM
408 (Convention Center )
Claire S. Adjiman, Charles V. Brand, Javier Rodriguez-Perez, Amparo Galindo and George Jackson, Centre for Process Systems Engineering, Dept of Chemical Engineering, Imperial College London, London, United Kingdom

Validation of a process model of CO2 capture in an aqueous solvent, using an implicit treatment of the reactions

C. V. Brand, J. Rodriguez-Perez, A. Galindo, G. Jackson, C .S. Adjiman

Departement of Chemical Engineering, Centre for Process Systems Engineering,

Imperial College London, London SW7 2AZ, United Kingdom

Carbon dioxide (CO2) emissions are considered by the majority of the scientific community to play a major role in climate change and particularly in global warming. In this context, the development of carbon capture systems is a necessity that must be addressed in the short term. The most promising early stage technology, both in terms of performance and applicability, is currently thought to be post-combustion CO2 absorption using amine solvents. There are, however, a number of concerns with the large scale deployment of this technology, including energy requirements, solvent degradation and the environmental and health impact resulting from loss of solvent and solvent degradation products. Modelling studies can play a useful role in addressing some of these issues and identifying the choice of solvent and operating conditions that yield the best performance. A key challenge is to develop models that can predict accurately the behaviour of the process, in the presence of limited experimental data.

We address this challenge by developing a complete CO2 absorber-desorber model that incorporates state-of-the-art thermodynamics integrated into a rate-based process model. A characteristic of the model is that all reactions are treated within the thermodynamic model, based on the assumption that the reaction kinetics are not rate-limiting. This greatly reduces the amount of experimental data required to model the interactions between the solvent and CO2 and therefore makes the approach ideally suited to study new solvents. Furthermore, no enhancement factor is used in our process model. Due to the transferability of the thermodynamic description, the same model is used for the absorber and the desorber. This approach is applied to CO2 capture using an aqueous monoethanolamine (MEA) solution. The extent to which pilot plant data can be modelled is examined in detail, allowing the validity of the assumptions to be verified

The thermodynamic model used to determine the vapour-liquid equilibrium and the chemical equilibrium is based on the statistical fluid association theory for potential of variable range (SAFT-VR) [1]. In the SAFT-VR thermodynamic description, the reactions are treated implicitly within a physical perspective, with the products of the chemical reaction treated as associated aggregates of the reactant molecules, so that there is no need to incorporate explicit rates of reaction, temperature-dependent equilibrium constants, or mass balances on the reaction products. This greatly simplifies the model. It has been shown that this approach yields a good representation of the vapour-liquid and chemical equilibria of mixtures of CO2, water and MEA under a wide range of conditions [2]. Different correlations for the rate-based equations governing the heat and mass transfer in the absorber are considered [3, 4].

The absorber-desorber process model is implemented in the gPROMS software and is validated using published pilot plant experimental data. The predictive capabilities of the mass transfer correlations used in this model are assessed through a sensitivity analysis and a scaling of the liquid-phase mass transfer coefficient is proposed. This scaling of the mass transfer is transferable to different operating conditions for both the absorber and the desorber and good predictions are obtained for the temperature and composition profiles in the gas and liquid phases.

[1] A. Gil-Villegas, A. Galindo, P. J. Whitehead, S. J. Mills, G. Jackson, and A. N. Burgess. J. Chem. Phys., 106(10):41684186, 1997.

[2] N. Mac Dowell, F. Llovell, C. S. Adjiman, G. Jackson, and A. Galindo. Ind. Eng. Chem. Res., 49, 1883-1899, 2003.

[3] K. Onda, E. Sada, and H. Takeuchi. J. Chem. Eng. Japan, 1(1):62-66, 1968.

[4] J. A. Rocha, J. L. Bravo and J. R Fair. Ind. Eng. Chem. Res., 32(4):641-651, 1993.

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