Effect of hydrodynamics on Faradaic current efficiency in a fluorine electrolyser

Espinasse, G.; Peyrard, Michel; Nicolas, François; Caire, Jean-Pierre

doi:10.1007/s10800-006-9216-x

Cited by 7 publications

(14 citation statements)

References 7 publications

(10 reference statements)

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“…In industrial reactors, large gas release may however strongly influence the electrolyser performance due to hydrodynamic modifications [8] and decreases electrolyte conductivity. These phenomena are examined here, where the process sensitivity to either operating conditions or unknown parameters, such as H 2 bubble size and departure angle, is investigated.…”

Section: Overview Of Electrolyser Modelling Approachesmentioning

confidence: 99%

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Hydrogen production by the Westinghouse cycle: modelling and optimization of the two-phase electrolysis cell

Charton¹,

Rivalier²,

Ode³

et al. 2009

WIT Transactions on Engineering Sciences

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Hydrogen is currently viewed as a promising energy carrier for transportation applications. In this context, mass production of hydrogen is a major issue for the coming decades. Among the viable production processes, the hybrid sulphur cycle, or Westinghouse cycle, is studied by the Nuclear Energy Division of the French CEA. In this work, the influence of H 2 bubbles on the current distribution within the electrolyser is studied. Turbulent two-phase flow simulations are performed with Ansys-Fluent CFD code in the 3D calculation domain using an Euler-Euler model. The electrokinetic problem is solved in the same domain by a finite element code, Flux-Expert, which is able to compute the secondary current distribution by means of specific interfacial elements. Parameters including the cell orientation (vertical or horizontal electrode), flow regime and bubble size are investigated, and the current model development status and needs are discussed.

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Section: Overview Of Electrolyser Modelling Approachesmentioning

confidence: 99%

“…A k- turbulence model is also used in [3] and [8]. A less CPU-consuming model based on mixture-lengths is used in [4].…”

Section: Governing Equationsmentioning

confidence: 99%

Hydrogen production by the Westinghouse cycle: modelling and optimization of the two-phase electrolysis cell

Charton¹,

Rivalier²,

Ode³

et al. 2009

WIT Transactions on Engineering Sciences

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“…H. Roustan [1] has shown that to some extent the large gliding fluorine bubbles drag the electrolyte up along the anode. A numerical model was gradually developed in France to account for all the strongly linked phenomena involved in fluorine electrolysis [2][3][4][5][6]. The final numerical model combined two commercial codes, Flux-Expert (FE) and Estet-Astrid (EA), both distributed by Astek [7,8].…”

mentioning

confidence: 99%

“…The Estet-Astrid code took into account the forces acting on individual bubbles, namely buoyancy, drag force, lift force and added mass. Thanks to EA, Espinasse et al estimated the fraction of the hydrogen plume that recombines with fluorine and thereby decreases Faraday current efficiency in an industrial fluorine electrolyser [6]. Since the plume of hydrogen bubbles is so important in a fluorine electrolyser, experimental work was carried out to validate the accuracy of plume prediction by EA.…”

mentioning

confidence: 99%

“…The hydrogen bubbles evolving at the cathode are driven by the molten salt and in the absence of a separator between the anode and cathode compartments (no diaphragm is resistant enough for use in a fluorine electrolyser) they can come in contact with fluorine and recombine spontaneously into hydrofluoric acid. Espinasse et al [6] showed that when the intensity of the cell increases, Faraday efficiency decreases because of this recombination.…”

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confidence: 99%

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A hydraulic model to simulate the hydrodynamics of a fluorine electrolyser

Caire

Espinasse²,

Dupoizat³

et al. 2009

Simulation of Electrochemical Processes III

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Fluorine electrolysis is characterized by very large overpotentials and bubble effects that are not yet fully understood. The two-phase free flows appearing in the fluorine reactor are complex and attributable mainly to hydrogen bubbles evolving at the cathode. However, large fluorine bubbles gliding along the anode help to drag the electrolyte up along the anode and in doing so also take part to the two-phase movement. The fluorine electrolyser has been modelled in the past but there has been no means of comparing hydraulic computations with measurements in such an aggressive environment. A hydraulic model is presented here to test the ability of the Estet-Astrid finite volume code to model the fluorine reactor. The two-phase free flow was modelled using an Euler-Euler scheme assuming bubbles of uniform diameter. Laser Particle Image Velocimetry was used to measure both gas and liquid velocities. This paper presents the experimental study and the model made to obtain the plume shape. Numerical and experimental results are compared and some discrepancies are explained. Improvements are suggested for future modelling

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Hydrogen filter press electrolyser modelled by coupling Fluent ® and Flux Expert ® codes

Jomard¹,

Feraud²,

Morandini³

et al. 2007

J Appl Electrochem

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Mass production of hydrogen is a major issue for the coming decades particularly to decrease greenhouse gas production. The development of fourth-generation high-temperature nuclear reactors has led to renewed interest for hydrogen production. In France, the CEA is investigating new processes using nuclear reactors, such as the Westinghouse hybrid cycle. A recent study was devoted to electrical modeling of the hydrogen electrolyzer, which is the key unit of this process. In this electrochemical reactor, hydrogen is reduced at the cathode and SO 2 is oxidized at the anode with the advantage of a very low voltage cell. This paper describes an improved model coupling the electrical and thermal phenomena with hydrodynamics in the electrolyzer, designed for a priori computational optimization of our future pilot cell. The hydrogen electrolyzer chosen here is a filter press design comprising a stack of identical cathode and anode compartments separated by a membrane. In a complex reactor of this type the main coupled physical phenomena involved are forced convection of the electrolyte flows, the plume of evolving hydrogen bubbles that modifies the local electrolyte conductivity, and all the irreversible processes that contribute to local overheating (Joule effect, overpotentials, etc.). The secondary current distribution was modeled with a commercial FEM code, Flux Expert 1 , which was customized with specific finite interfacial elements capable of describing the potential discontinuity associated with the electrochemical overpotential. Since the finite element method is not capable of properly describing the complex two-phase flows in the cathode compartment, the Fluent 1 CFD code was used for thermohydraulic computations. In this way each physical phenomenon was modeled using the best numerical method. The coupling implements an iterative process in which each code computes the physical data it has to transmit to the other one: the two-phase thermohydraulic problem is solved by Fluent 1 using the Flux-Expert 1 current density and heat sources; the secondary distribution and heat losses are solved by FluxExpert 1 using the Fluent 1 temperature field and flow velocities. A set of dedicated library routines was developed for process initiation, message passing, and synchronization of the two codes. The first results obtained with the two coupled commercial codes give realistic distributions for the electrical current density, gas fraction, and velocity in the electrolyzer. This approach allows us to optimize the design of a future experimental device. Notation CpHeat capacity (J kg -1 K -1 ) gGravitational acceleration (m s -2 ) J Current density (A m -2 ) Current density normal to the interface (A m -2 ) kThermal conductivity (W m -1 K -1 ) ñNormal vector NBN Number of integration points Q S Surface heat sources (W m -2 )Nanometric discontinuity thickness of potential (m) d S Dirac surface distribution e g Gas fraction qDensity (kg m -3 ) gOverpotential (V) rViscous stress tensor (Pa) rElectrical conductivity (X -1 m -...

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Effect of hydrodynamics on Faradaic current efficiency in a fluorine electrolyser

Cited by 7 publications

References 7 publications

Hydrogen production by the Westinghouse cycle: modelling and optimization of the two-phase electrolysis cell

Hydrogen production by the Westinghouse cycle: modelling and optimization of the two-phase electrolysis cell

A hydraulic model to simulate the hydrodynamics of a fluorine electrolyser

Hydrogen filter press electrolyser modelled by coupling Fluent ® and Flux Expert ® codes

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