Influence of the main operating parameters on the DRPSA process design based on the equilibrium theory
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Influence of the main operating parameters on the DRPSA process design based on the equilibrium theory Ester Rossi1 · Giuseppe Storti1 · Renato Rota1 Received: 6 July 2020 / Revised: 17 September 2020 / Accepted: 24 September 2020 © The Author(s) 2020
Abstract Among the adsorption-based separation processes for gaseous mixtures, those exploiting pressure variations, so-called Pressure Swing Adsorption (PSA) processes, are the most popular. In this work, we focus on the specific PSA configuration known as Dual Reflux-Pressure Swing Adsorption (DR-PSA) given its ability to achieve sharp separations. In the case of binary mixtures, an analytical approach based on Equilibrium Theory has been proposed to identify the operating conditions for complete separation under the assumption of linear isotherms. This same approach is not available when the separation is not complete. Accordingly, in this work we study the features of non-complete separations by solving numerically a general DR-PSA model with parameter values suitable to approach equilibrium conditions (no mass transport resistances, no axial mixing, isothermal conditions and no pressure drop), thus reproducing the analytical solution when complete separations are examined. Even for non-complete separations, triangularly shaped regions at constant purity can be identified on a plane whose axes correspond to suitable design parameters. Moreover, we found a general indication on how to select the lateral feed injection position to limit the loss in product purities when complete separation is not established, whatever is the composition of the feeding mixture. Finally, a sensitivity analysis with respect to pressure ratio, light reflux ratio and heavy product flowrate is proposed in order to assess how to recover product purities according to the specific degrees of freedom of a DR-PSA apparatus. Keywords Dual-reflux · PSA design · Gas separation · Cyclic adsorption process · Detailed numerical modelling · Noncomplete separations Abbreviations A Heavy component B Light component BD Blowdown step C Capacity ratio, C =
𝛽A tFE ṅ LR RT PL Vbed 𝜀T
Dbed Diameter of the adsorption bed, m dp Diameter of the solid particles, m FE Feed step ṅ G Reflux ratio, G = ṅ LR feed
Hi Linear isotherm constant for component i , kgmolPa
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10450-020-00274-9) contains supplementary material, which is available to authorized users. * Renato Rota [email protected] 1
Chemistry, Materials and Chemical Engineering Department “Giulio Natta”, Politecnico di Milano, Via Mancinelli 7, 20131 Milan, Italy
kLDF Linear driving force constant, s−1 Lbed Bed length, m nHP,T Theorical heavy product number of moles produced in one cycle, mol nLP Light product number of moles produced in one cycle, mol nfeed Number of moles fed in one cycle, mol ṅ Molar flowrate, mol s ṅ feed Lateral feed flowrate, mol s ṅ HP Heavy product flowrate, mol s ṅ HP,T Theorical heavy product fl
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