Remerciez-le!

Remerciez @Admin pour avoir partagé cet document gratuitement, de la manière la plus simple, en partageant sur les réseaux sociaux.

D o s s i e r Methodology for Process Development at IFP Energies nouvelles Mét

D o s s i e r Methodology for Process Development at IFP Energies nouvelles Méthodologies pour le développement de procédés à IFP Energies nouvelles Use of Computational Fluid Dynamics for Absorption Packed Column Design Yacine Haroun* and Ludovic Raynal IFP Energies nouvelles, Rond-point de l’échangeur de Solaize, BP 3, 69360 Solaize - France e-mail: yacine.haroun@ifpen.fr - ludovic.raynal@ifpen.fr * Corresponding author Abstract — Computational Fluid Dynamics (CFD) is today commonly used in a wide variety of process industries and disciplines for the development of innovative technologies. The present article aims to show how CFD can be used as an effective analysis and design tool for the development and design of packed gas/liquid absorption columns. It is ﬁrst shown how CFD can be used for the characterisation of packings. The different hydrodynamic and mass transfer design parameters are investigated and adapted CFD methods are suggested. Secondly, column distribution internal development is discussed to show how CFD simulations should be performed to improve the design of gas and liquid distributors. An example of the development of new distribution technologies for ﬂoating installation of a reactive absorption column is also presented. Résumé — Utilisation de la dynamique des ﬂuides numérique pour le design des colonnes d’absorption à garnissages — La dynamique des ﬂuides numérique (Computational Fluid Dynamics, CFD) est aujourd’hui couramment utilisée pour le développement de technologies innovantes dans de nombreux domaines et procédés industriels. Cet article a pour objectif de montrer comment la CFD peut être utilisée comme outil d’analyse et de dimensionnement pour le développement des colonnes d’absorption gaz-liquide à garnissages. En premier, il est présenté comment la CFD peut être utilisée pour caractériser les différents paramètres de dimensionnement d’un garnissage (hydrodynamique et transfert). Les méthodes CFD appropriées sont suggérées et discutées. En second, l’utilisation de la CFD pour le développement et l’optimisation des internes de distribution gaz-liquide est exposée. Un exemple de développement par CFD d’une nouvelle technologie de distribution pour une colonne d’absorption réactive sur une installation ﬂottante offshore est présenté. Oil & Gas Science and Technology – Rev. IFP Energies nouvelles Y. Haroun and L. Raynal, published by IFP Energies nouvelles, 2015 DOI: 10.2516/ogst/2015027 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. INTRODUCTION Gas/liquid absorption operation constitutes an important aspect in several industrial applications using packed col- umns such as distillation, reactive distillation, acid gas removal and solvent-based post-combustion CO2 capture. Reactive absorption packed columns consist of packing elements (structured or random packing) contacted by cocur- rent or counter-current gas-liquid ﬂow. Liquid mostly trick- les over the packing’s wall as ﬁlm ﬂow, with the gas being a continuous phase ﬂowing within the core of the packing ele- ments. The absorption of gases in the liquid solution is often accompanied by chemical reactions. The distribution of the liquid and gas phases in packing is ensured by the use of gas-liquid tray distributors situated at the top of each packed bed and the bottom gas distributor at the bottom of the col- umn (Billet, 1995; Kister, 1990; Olujic et al., 2004; Stemich and Spiegel, 2011). To meet the requirements of size optimisation of the col- umn (in terms of height and diameter) and pressure drop lim- itation, efﬁcient and high-capacity packings and appropriate design of the gas and liquid distributor are needed (Billet, 1995). The selection of the column internals requires a deep understanding of the purpose of the reactive absorption application and precise knowledge of the characteristics of the gas and liquid solvent ﬂows throughout the packed bed in terms of hydrodynamics (pressure drop, ﬂooding), mass transfer (gas-side and liquid-side mass transfer coefﬁcients) and indirectly, kinetics and thermodynamics (reaction regime, reaction acceleration factor). These parameters are used in process simulations to achieve optimum design. For example, in the particular case of post-combustion CO2 capture, Raynal et al. (2013) showed that the interfacial area is the key parameter for the absorber design. This leads to promoting structured packings for such a reactive absorp- tion application that offer higher geometric area per unit vol- ume, from at least 250 m2/m3 and preferentially more than 350 m2/m3, and a large void fraction (porosity), around 90%, which induce high mass transfer efﬁciency and low pressure drop, respectively (Lassauce et al., 2014). For high-pressure acid gas treatment, H2S removal efﬁciency will be more sensitive to gas-side mass transfer, since H2S reacts instantaneously with amine-based solvent, and, due to high-pressure operation, the column design will consider diameter optimisation as more important than height and resulting pressure drop optimisation; the corresponding choice of packing would thus differ from ambient pressure CO2 post-combustion absorption. Much work and many experimental tests have been conducted in order to measure the packing characteristics and to develop adapted models (liquid holdup, effective area, gas-side and liquid-side mass transfer, pressure drop) for commercial packings (Billet, 1995; Bravo et al., 1985; Fair and Bravo, 1990) and design rules for distribution tech- nologies (Kister, 1990). However, developing understanding is still needed, especially for the development of new reac- tive absorption packings and internals, which involves vari- ous physical and geometrical parameters that cannot be easily investigated experimentally and are still not well understood. Besides, the corresponding experimental work is quite time-consuming and parametric optimisation is almost impossible. In this context, Computational Fluid Dynamics (CFD) is seen as a powerful tool in complement to experimental work to investigate performance characteristics and the develop- ment of original reactive absorption columns (Charpentier, 2009). In the last decade, CFD has been used more and more to calculate ﬂow characteristics in packed beds (Petre et al., 2003; Raynal and Royon-Lebeaud, 2007; Mohamed Ali et al., 2003). Indeed, the use of numerical simulation can provide a signiﬁcant gain in time and could limit the number of experiments. Another reason to use CFD is the possibility of accessing information on a local scale which is not mea- surable with experimental methods. The present article aims to show how CFD is used for the development of reactive absorption packed columns. Differ- ent CFD approaches and simulations are presented, address- ing hydrodynamic and mass transfer characterisation of packings as well as distributing tray evaluation and develop- ment. In the following ﬁrst section, the use of CFD for the char- acterisation of packing is presented. The second section focuses on the development of gas and liquid distribution internals by using CFD. 1 STRUCTURED PACKING CHARACTERISATION BY USING CFD As discussed in Raynal et al. (2013), the choice of the most adequate packing is linked to its performances in terms of pressure drop and mass transfer efﬁciency. There is no best packing which would offer high capacity, homogeneous dis- tribution and good mass transfer efﬁciency, since from one case to another the expectations and sensitivity of the pro- cess differ. The capacity of the packing, giving the maximum gas and liquid mass ﬂow rates, is used to determine the diam- eter of the column. This characteristic is often given by the pressure drop, and more exactly it corresponds to the ﬂood- ing limit over which operation is no longer possible. The mass transfer efﬁciency is used to determine the height of the column. This latter characteristic is much more difﬁcult to determine since, for reactive absorption application stud- ied in the framework of the two-ﬁlm theory, the mass trans- fer ﬂux is linked to ﬁve parameters (Danckwerts, 1970). Three of these parameters are directly linked to the packing 2 Oil & Gas Science and Technology – Rev. IFP Energies nouvelles contactor geometry and the gas/liquid operating conditions. These parameters are the following: the liquid-side mass transfer coefﬁcient, kL (m/s), the gas-side mass transfer coef- ﬁcient, kG (m/s), and the interfacial effective area, ae (m1). The two remaining parameters correspond to the thermody- namic and kinetic performances of the solvent given, respec- tively, by the Henry coefﬁcient, He (Pa.m3.mol1), and the acceleration factor coefﬁcient, E (-), both varying with pres- sure and temperature conditions and with solvent loading. All these parameters are linked in the following relationship giving the ﬂux for the chemical component j from the gas to the liquid: Uj mol = m3= s ¼ 1 1=kGae þ He=EkLae Pj HeCj;bulk where: Pj (Pa): the partial pressure of the component j in the gas phase Cj,bulk (mol/m3): the concentration of the compo- nent j in the liquid bulk. The characterisation of packing contactors consists of determining and modeling all parameters dealing with hydrodynamics and mass transfer. In recent years, several works can be found in the literature which deal with the CFD investigation of hydrodynamic (pressure drop, liquid hold-up, wetting, liquid distribution) and mass transfer design parameters (liquid- and gas-side mass transfer, accel- eration factor, effective area mass transfer). Petre et al. (2003) were among the ﬁrst authors to use CFD in order to calculate dry pressure drop in structured packings. They proposed an original approach by considering the uploads/Ingenierie_Lourd/ cfd-absorption-packed-colum-design.pdf