- France
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The optimal design of cryogenic systems for the separation of species that compose the air, mainly N2, O2 and Ar, has become a focus of attention in the development of low-CO2 emissions systems for the production of electrical energy... more
The optimal design of cryogenic systems for the separation of species that compose the air, mainly N2, O2 and Ar, has become a focus of attention in the development of low-CO2 emissions systems for the production of electrical energy and/or energy vectors, such as hydrogen. The pivotal action to optimize these processes and to reduce uncertainties related to the competitiveness with other separation technologies is the application of models that accurately reproduce thermodynamic and transport properties of mixtures of N2, Ar and O2. The purpose of this work is to analyse the available thermodynamic models considered as the most suitable for these systems. This paper compares the accuracy of two multi-parameter models (GERG-2008 and Bender) and of the Peng-Robinson equation-of-state, assessing their capability in calculating phase-equilibrium properties, density, enthalpic and volumetric properties change due to mixing. Moreover, it is shown the impact of inaccurate density calculat...
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Abstract The present paper aims to enhance the awareness of users of thermodynamic models on the impact that their accuracy may have in designing and operating units for the purification and compression of CO2-streams produced from... more
Abstract The present paper aims to enhance the awareness of users of thermodynamic models on the impact that their accuracy may have in designing and operating units for the purification and compression of CO2-streams produced from capture technologies. After providing a review on the composition of streams produced by coal- or gas-fired plants with post-/pre-/oxy-combustion CO2 capture, coupled with different purification technologies, the paper quantifies the influence of equations of state accuracy in designing and operating CO2 purification and compression units. A comparison is made between the results obtained from the cubic Peng-Robinson model combined with either classical vdW1f (van der Waals one fluid) mixing rules (i.e. the standard Peng-Robinson equation of state) or with recently optimized advanced mixing rules incorporating residual-excess-Helmholtz-energy ( a res E, γ ) models ( EoS / a res E, γ mixing rules). In detail, EoS / a res E, γ mixing rules combine the residual contribution of the Wilson a E , γ model and the formulation proposed by Lorentz, for the mixture co-volume term. It is shown that the improved accuracy of “PR + EoS / a res E, γ mixing rules” in the representation of vapour-liquid equilibrium properties of CCS mixtures, with respect to the standard PR EoS, may lead to the design of a halved-height stripping column for the reduction of the oxygen content in the captured CO2 stream. Moreover, the paper shows the effect of the applied thermodynamic model on the definition of the pressurization level of the captured fluid and on the computed power required for its compression.
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Abstract Mainly due to the complex thermodynamic modelling of high-pressure CO2-based mixtures containing supercritical components, none of the thermodynamic models present in the literature shows a sufficient accuracy level in describing... more
Abstract Mainly due to the complex thermodynamic modelling of high-pressure CO2-based mixtures containing supercritical components, none of the thermodynamic models present in the literature shows a sufficient accuracy level in describing both their low and high-pressure saturation properties. One of the most challenging thermodynamic tasks is, in fact, the representation of the critical region of high-pressure binary systems at the basis of the optimization of thermodynamic models for multicomponent systems treated by CO2 Capture and Storage (CCS) applications and Enhanced Oil Recovery (EOR) processes. The limited number of experimental data, on the one side, and the absence of a sufficiently accurate equation of state, on the other, pose doubts on the reliability and predictive capability of models especially when applied to complex multicomponent systems. The uncertainty about such capability drives engineers towards the oversizing of equipment and, thus, of the related costs. With the aim of filling some of the mentioned thermodynamic gaps, this work presents new experimental vapor-liquid equilibrium data for the systems CO2-N2, CO2-Ar and CO2-O2 and modelling results obtained from the successful application of the Peng-Robinson equation of state with an advanced class of mixing rules, that highly improve the representation of the critical region of these fluids.