Experimental study of liquid spreading in structured packings

Optimization of industrial gas-liquid columns dedicated to CO2 capture requires prediction of liquid distribution within packed beds. In this context, liquid hold-up as well as liquid spreading from a source point have been investigated for Mellapak 250.X structured packing. Local liquid hold-up measurements have been achieved in a 400 mm diameter column by means of gamma-ray tomography with operation in the counter-current mode at different positions downstream the source point injection. Liquid hold-up and retention map measurements have been performed for two fluid systems: Air / Water and Air / MEA 30wt.%. A correlation that relates global liquid hold-up and liquid load taking into account liquid viscosity is proposed. This correlation has been further used to determine spread factors using a simple dispersion model for all investigated operational conditions. Liquid dispersion model is found to well reproduce experimental data in the range of operational conditions that were tested which enables to determine spread factors for various operating conditions. The spread factor is observed not to vary with liquid load, gas capacity factor in the range of 20% to 80% of flooding nor liquid viscosity. This led us to stipulate that liquid dispersion is controlled by packing geometry only. Nevertheless, the effect of surface tension on liquid hold-up and dispersion is discussed since its effect is not fully understood and calls for further experiments if one wants to apply those results for hydrocarbons

Comparison of modern packings : assessing proper choice for post-combustion carbon capture absorption columns

CO2 capture from industrial flue gases is expected by IEA [1] to contribute to up to 19% of carbon mitigation by 2050. Absorption of CO2 into chemical solvents used in post-combustion capture processes is widely recognized as a reference path due to its high selectivity and CO2 recovery rate [2]. However, absorption and solvent regeneration columns required for that purpose are of huge sizes and further induce high investments impacting avoided CO2 cost. This impact is important enough so that it cannot be neglected when compared with operating unit costs [3]. We are presenting in this paper what is required in terms of packing characteristics, that is pressure drop, mass transfer performances and also liquid dispersion properties. This latter property, even if little discussed in the literature, is of great importance, since it will be used for determining the maximum height for packed beds as well as for column redistribution internals design. All these properties are presented for both random and structured packings and a discussion about packing choice is proposed, especially based mass transfer performances and on original dispersion results obtained for Mellapak and IMTP packing

Mass transfer and liquid hold-up determination in structured packing by CFD

Mass transfer and liquid hold-up in structured packing geometry are investigated using the volume of fluid method. Numerical simulations of two-dimensional co-current gas–liquid flow on structured packing with interfacial mass transfer are performed. The volume of fluid method is used to capture the gas–liquid interface motion. The mass transfer is computed by solving the concentration equation with an adapted modeling of the solubility (Haroun et al., 2010b). The liquid hold-up and the mass transfer are studied as function of liquid flow rate and structured packing geometry. Results show how the liquid flow rate and the complex geometry affect the liquid film flow topology and the interfacial mass transfer. For a specified packing geometry, it is demonstrated that for low liquid flow rate, the liquid film remains uniform and follow closely the profile of the structured wall. For uniform liquid film flow along packing wall, it is found that the liquid hold-up is in good agreement with the model proposed by Billet and Schultes (1999) and Raynal and Royon-Lebeaud (2007). When increasing the liquid flow rate, the liquid film does not follow the shape of the structured wall anymore, a static hold- up (recirculation zone) form in the cavities and grows as the Reynolds number increases until covering most of the packing cavities. The present work gives the liquid hold-up evolution for each liquid film flow regime according to the Reynolds number and the dimensionless amplitude of the corrugation. Concerning the liquid side mass transfer, it is found that the liquid side mass transfer is well predicted by the Higbie (1935) theory provided that adequate velocity and length scales are considered for exposure time determination. The exposure time of fluid element at the interface corresponds to the ratio between the curvilinear distance between two periodic corrugation contact point and the interface velocity. An exposure time model is proposed taking into the account physical and geometric parameters

Liquid dispersion in packed columns: experiments and numerical modeling

In order to optimize the design of gas-liquid packed columns used in distillation or in absorption processes, it is of high importance to be able to predict liquid dispersion. Indeed, dispersion phenomena will impact the choice and design of liquid distributing devices and the height of the packed beds. For this, one mainly relies on industrial feedback and on some experimental results obtained at laboratory scale which cannot be directly extrapolated since their geometric characteristics are at least one order of magnitude less than industrial columns in terms of columns diameter and height. To fill this gap CFD simulation tools should be more used since they can apply to any scale. However the latter option requires adequate modeling in particular for dispersion forces which are little studied due to the lack of data for validation. The present paper aims at developing, from original dispersion experimental measurements, closure laws that can be implemented in CFD codes. Liquid spreading from a source point has been investigated for Mellapak 250.X packing via gamma-ray tomography measurements. Closure laws are discussed from a simple 1D model which enables to go further within the Eulerian two-fluid framework with original user-defined functions and associated models that take into account liquid dispersion in the packed bed. The latter is modeled as a porous medium with appropriate closure laws. The comparison between experiments and CFD results shows that the present approach is adequate and should be further developed in order to be more precise and adapted to more packings

From conceptual design to process design optimization: a review on flowsheet synthesis

International audienceThis paper presents the authors’ perspectives on some of the open questions and opportunities in Process Systems Engineering (PSE) focusing on process synthesis. A general overview of process synthesis is given, and the difference between Conceptual Design (CD) and Process Design (PD) is presented using an original ternary diagram. Then, a bibliometric analysis is performed to place major research team activities in the latter. An analysis of ongoing work is conducted and some perspectives are provided based on the analysis. This analysis includes symbolic knowledge representation concepts and inference techniques, i.e., ontology, that is believed to become useful in the future. Future research challenges that process synthesis will have to face, such as biomass transformation, shale production, response to spaceflight demand, modular plant design, and intermittent production of energy, are also discussed

Mass transfer and hydrodynamic characteristics of new carbon carbon packing: Application to CO2 post-combustion capture

A novel structured packing, the 4D packing, has been characterized in terms of hydrodynamics, effective area and gas side mass transfer coefficient. The increase of the 4D opening fraction allows to reduce pressure drop and to get a better capacity than Mellapak 500Y and 750Y, for which the geometric areas are similar. The 50% open 4D packing, 4D-50%, leads to effective areas which are higher than Mellapak 500Y ones, and doubled compared with Mellapak Plus 252Y ones. Effective areas for the 4D do not decrease when the opening fraction increases from 30 to 50%, this indicates that a non-negligible amount of droplets is generated at 50%. Gas side mass transfer coefficient had been measured with an original experimental method: water evaporation. Corresponding results seem to be in agreement with the literature, and with the fact that a large amount of droplets is generated. Correlations are proposed for both effective area and gas side mass transfer coefficient for the 4D-50%.The 4D-50% packing could be very interesting for post-combustion CO2 capture since it generates low pressure drop and a very high interfacial area. This will be further confirmed by an economic study for which the absorber plant will be designed with a rate based model

Corrosion in post-combustion CO 2 capture plants -comparisons between MEA 30% and new processes

International audienceCO 2 capture and storage (CCS) is one of the main option for CO 2 mitigation. Post-combustion capture processes using alkanolamines are considered as one of the preferred options for CCS, since their industrial viability was already demonstrated. Absorption-desorption by 30% monoethanolamine (MEA) represents the reference technology for post-combustion CO 2 capture. However, the cost of CO 2 removal with this MEA 30% process remains very large, and needs to be reduced. In CCS field, a lot of research program aim at developing new solvents, with a particular focus on the energy consumption needed at regeneration step. Minimizing solvent degradation is also often considered as the second immediate priority. Solvent degradation is usually caused by chemical reaction with oxygen, which is always present in post-combustion fumes. Other impurities, such as NO 2 or SO 2 , may also react with the solvent and form undesirable by-products. This paper is divided in two sections. In the first part, we propose a review of CO 2 capture with monoethanolamine, which represents the reference situation. Focus is given to corrosion aspects, including laboratory results and pilot plant studies. In the second part of the paper, we present two ways of improving CO 2 capture processes that are currently studied at IFPEN. The first one is an evolution of the reference 30% MEA process, using a higher MEA concentration in order to reduce the energy consumption. The second one uses a newly developed solvent, with improved performances. For both cases, specific corrosions tests will be presented, both in laboratory conditions and in pilot plant operations

Natural Language Processing for aviation safety reports: from classification to interactive analysis

International audienceIn this paper we describe the different NLP techniques designed and used in collaboration between the CLLE-ERSS research laboratory and the CFH / Safety Data company to manage and analyse aviation incident reports. These reports are written every time anything abnormal occurs during a civil air flight. Although most of them relate routine problems, they are a valuable source of information about possible sources of greater danger. These texts are written in plain language, show a wide range of linguistic variation (telegraphic style overcrowded by acronyms or standard prose) and exist in different languages, even for a single company/country (although our main focus is on English and French). In addition to their variety, their sheer quantity (e.g. 600/month for a large airline company) clearly requires the use of advanced NLP and text mining techniques in order to extract useful information from them. Although this context and objectives seem to indicate that standard NLP techniques can be applied in a straightforward manner, innovative techniques are required to handle the specifics of aviation report text and the complex classification systems. We present several tools that aim at a better access to this data (classification and information retrieval), and help aviation safety experts in their analyses (data/text mining and interactive analysis). Some of these tools are currently in test or in use both at the national and international levels, by airline companies as well as by regulation authorities (DGAC, EASA , ICAO)

Numerical simulations of fish-friendly angled trashracks at model and real scale

Several amphihaline species, such as silver eels, suffer high mortality rates during their downstream migration, due to their passage through turbines. The combination of adapted trashracks (inclined or angled screen, lower bar spacing, …) with bypasses can efficiently prevent these mortalities. A numerical study has been carried out with such angled trashracks. Numerical results with model scale racks were validated against previous experimental results on model trashracks, resulting from head loss and velocity distribution measurements (Raynal et al., 2013). Real scale racks were then computed in order to evaluate the influence of both the bar spacing and the channel width on velocity distributions in real dimensions. The mesh generation and the numerical simulations were performed by the open source CFD software suite OpenFOAM. The trashrack solid comprised basic elements, individually created using CAD software and directly inserted in OpenFOAM’s mesh generation utility. For small scale configurations, grid refinement was applied at the flume walls, at trashrack bars and downstream of the trashrack, whereas only bars were refined for real scale racks. The resulting number of cells ranged between 100,000 and 1,500,000. Steady state results were obtained by solving the Reynolds-averaged Navier-Stokes (RANS) equations for an incompressible and monophasic flow. The k-ε, k-ε-based RNG, k-ω, k-ω-based shear stress transport (SST) and Spalart-Allmaras models were examined to select the most appropriate one in terms of computation time and result accuracy. Results show that the k-ε-RNG is the model best agreeing with experimental results. Two-dimensional calculations seem to provide quite satisfactory results although both the head losses and the size of the recirculation zone downstream of the trashrack are slightly under-estimated. Real scale results confirm experimental ones and show that the bar spacing slightly effects upstream velocity profiles. Downstream of the rack, simulations with different flume width demonstrated that the size of the recirculation zone is proportional to the channel width

Study on fish-friendly inclined and angled trashracks

This paper presents the results on trashrack head losses obtained by Raynal et al. [2013 a,b], [2014] for several configurations. More especially, it compares the head loss formulae proposed in these studies with various equations from the literature to improve energy losses prediction in fish-friendly configurations. These new predictive laws of head losses are applied to the renovation of a hydropower plant and show that inclined trashracks or angled trashracks with streamwise bars are reliable solutions when the bar spacing is reduced