An Integrated Gas-Liquid Flow Analyser and Its Applications to Performance Predictions in Water Electrolysis Systems (original) (raw)
Related papers
CFD Modeling of Gas-Liquid Flow and Heat Transfer in a High Pressure Water Electrolysis System
Volume 1: Symposia, Parts A and B, 2006
A high-pressure water electrolysis system has been investigated numerically and experimentally. The advanced CFD model of two-phase flow, which calculated the 3D distributions of pressure, gas and liquid velocities and gas and liquid volume fractions, has been developed to account for all the major components in the system, and appropriate constitutive equations for two-phase flow parameters were selected for various parts of the system, such as the cell stack, riser, separator and downcomer. Heat transfer between the two phases, and between the gas-liquid mixture and cooling coils located in the gas-liquid separator was also accounted for. The model was validated using comparisons of predicted liquid flow rate with the liquid flow rate measured in the downcomer, where a single-phase liquid flow existed. The effects of pressure, current density, number of cells, and bubble size were investigated with the numerical model. The numerical predictions matched the general trends obtained from the experimental results with regard to the effects of pressure and current density on the liquid flow rate. The validated CFD model is being used as a cell design tool at Hydrogenics Corporation.
CFD Modeling of Gas-Liquid Flows in Water Electrolysis Units
This paper presents the results of computational fluid dynamics (CFD) modeling of gasliquid flows in water electrolysis systems. CFD is used as a cost-effective design tool at Stuart Energy Systems Corporation (SESC) to optimize the performance of different water electrolysis units produced by SESC. General-purpose CFD software is used as a framework for analyzing the gas -liquid flow characteristics (pressure, gas and liquid velocities, gas and liquid volume fractions). The analysis is based on solving the coupled two-fluid conservation equations under typical and alternative operating conditions with appropriate boundary conditions, turbulence models and constitutive inter-phase correlations. Numerical results have been validated based on the experimental data available for a low-pressure cell.
Two-phase electrolysis process modelling: from the bubble to the electrochemical cell scale
Simulation of Electrochemical Processes II, 2007
During two-phase electrolysis for hydrogen, aluminium or fluor production, there are bubbles which are created at electrodes which imply a great hydrodynamic acceleration but also quite important electrical properties and electrochemical processes disturbance. There are few works concerning the local modelling of electrochemical processes during a two-phase electrolysis process. Nevertheless, effects like the anode effect, particularly expensive on the point of the process efficiency, should need a better understanding. The goal of the present work is to present the modelling and the numerical simulation of the gas production, from the single bubble scale to the macroscopic electrochemical cell, during the two-phase electrolysis process. Bubbles are motion sources for the electrolysis cell flow, and then hydrodynamic properties are strongly coupled with species transport and electrical performances. The presence of bubbles modifies these global and local properties: the electrolysis cell and the current density distribution are modified. The present work shows theoretical modelling on both scales and also performance changes during the two-phase electrolysis processes.
3D CFD model of a multi-cell high-temperature electrolysis stack
International Journal of Hydrogen Energy, 2009
electrolysis Hydrogen production a b s t r a c t A three-dimensional (3D) computational fluid dynamics (CFDs) electrochemical model has been created to model high-temperature electrolysis stack performance and steam electrolysis in the Idaho National Laboratory (INL) Integrated Lab Scale (ILS) experiment. The model is made of 60 planar cells stacked on top of each other operated as solid oxide electrolysis cells (SOECs). Details of the model geometry are specific to a stack that was fabricated by Ceramatec, Inc. [References herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government, any agency thereof, or any company affiliated with the Idaho National Laboratory]. and tested at INL. Inlet and outlet plenum flow and distribution are considered. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. [References herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government, any agency thereof, or any company affiliated with the Idaho National Laboratory]. A solid oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell.
Heat Transfer, Part B, 2005
A one-dimensional model has been developed to predict the thermal and electrochemical behavior of a high-temperature steam electrolysis stack. This electrolyzer model allows for the determination of the average Nernst potential, cell operating voltage, gas outlet temperatures, and electrolyzer efficiency for any specified inlet gas flow rates, current density, cell active area, and external heat loss or gain. The model includes a temperature-dependent area-specific resistance (ASR) that accounts for the significant increase in electrolyte ionic conductivity that occurs with increasing temperature. Model predictions are shown to compare favorably with results obtained from a fully 3-D computational fluid dynamics model. The one-dimensional model was also employed to demonstrate the expected trends in electrolyzer performance over a range of operating conditions including isothermal, adiabatic, constant steam utilization, constant flow rate, and the effects of operating temperature.
Two-phase electrolysis process: From the bubble to the electrochemical cell properties
Chemical Engineering and Processing: Process Intensification, 2008
During two-phase electrolysis for aluminium, fluorine or hydrogen production there are bubbles which are created at the electrode which imply a great hydrodynamic acceleration but also a quite important electrical field and electrochemical processes disturbance. This disturbance can lead to the modification of the local current density and to anode effects for example. There are also few local experimental measurements in term of chemical composition, temperature or current density because considered media are often very aggressive (high temperature, very strong reactivity). Then, the modelling and numerical simulation appears to be one important tool to understand and optimize associated processes, though the rigorous validation of numerical calculations is difficult. The goal of the present work is the modelling and the numerical simulation of the local gas production at an industrial scale vertical electrode. Because bubbles modify species, heat and electricity transport and are motion sources, there is a strong coupling between all these phenomena and between the bubble scale and the macroscopic one. Because bubbles are at the origin of all macroscopic disturbances, it appears necessary to investigate phenomenological laws at the bubble scale. The finite volume of the Fluidyn ® and Fluent ® software has been used.
2008
A three-dimensional computational fluid dynamics (CFD) electrochemical model has been created for detailed analysis of a high-temperature electrolysis stack (solid oxide fuel cells operated as electrolyzers). Inlet and outlet plenum flow distributions are discussed. Maldistribution of plena flow show deviations in per-cell operating conditions due to nonuniformity of species concentrations. Models have also been created to simulate experimental conditions and for code validation. Comparisons between model predictions and experimental results are discussed. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A solid-oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the electrolysis mode. Model results provide detailed pro...
Engineering Process Model For High- Temperature Electrolysis System Performance Evaluation
2005
In order to evaluate the potential hydrogen production performance of large-scale High-Temperature Electrolysis (HTE) operations, the INL has developed an engineering process model using the commercial systems-analysis code HYSYS. Using this code, a detailed process flowsheet has been defined that includes all the components that would be present in an actual plant such as pumps, compressors, heat exchangers, turbines, and the electrolyzer. Since the electrolyzer is not a standard HYSYS component, a custom onedimensional electrolyzer model was developed for incorporation into the overall HYSYS process flowsheet. This electrolyzer model allows for determination of operating voltage, gas outlet temperatures, and electrolyzer efficiency for any specified inlet gas flow rates, current density, cell active area, and external heat loss or gain. The one-dimensional electrolyzer model was validated by comparison with results obtained from a fully 3-D computational fluid dynamics model developed using FLUENT. This report provides details on the onedimensional electrolyzer model, the HYSYS process model for a 300 MW HTE plant, and some representative results of parametric studies performed using the HYSYS process model.
Pressure Analysis Investigation of PEM Electrolyzer Cell Used for Green Hydrogen Production , 2022
Increasing environmental concerns with climate change have led many people around the world to demand urgent action, forcing national governments to seek alternatives to carbon-based fuels. In the light of all this, it is of critical importance for our civilization that carbon-based energy sources are rapidly replaced by renewable and sustainable sources without carbon emissions. For this reason, the use of these clean energy sources and the efficiency of the processes in their production is a very important issue. In this study, 3-dimensional, two-phase (hydrogen and water) computational fluid dynamics (CFD) analysis was performed in a polymer electrolysis membrane cell (PEM). Analysis took place for 30 seconds. The water flow rate was kept constant at 260 ml/min. As a result of the analysis, pressure, gas volume fraction and velocity data in the manifolds and in the electrolysis channels where the electrolysis process takes place were interpreted. While the pressure change in the cell was quite high in the range of 0-1.8 seconds from the beginning of the flow, it was observed that a balance was formed in the pressure distribution after 1.8 seconds. It is understood that the number of channels in the model is a factor for the pressure inside the manifold and the cell. However, it was observed that the unit gas production amount in the cell also changed along the channels.
2019
Climate change and the accelerating depletion of fossil fuels have driven a tremendous surge in the development of clean and sustainable energy sources, e.g. wind, solar and hydro power. With an increasing market penetration of intermittent renewable energy generation, the need for energy storage is more apparent. Hydrogen has been identified as a suitable energy carrier and water electrolysis is the most promising way to produce it in a sustainable and environmentally friendly mode. PEM electrolysis is a rapidly evolving commercial technology which uses a solid polymer membrane as electrolyte in the device to split pure water into hydrogen and oxygen. A layered zero-dimension model has been developed for this manner to simulate the performance of a PEMEC stack in Aspen Custom Modeler. In addition to the electrochemical equations that represent the water dissociation reaction, the model includes water, hydrogen and oxygen mass transport phenomena, electro-osmotic drag, diffusion and permeabilities through the membrane. A further feature of the model is that it considers a time-dependent lumped energy balance equation to analyze the dynamic inertia of the system when the electrical input fluctuates. Suitable values and assumptions were made to identify the model’s parameters after an extended literature review. To calibrate and validate the model, a set of experimental data was used which comes from experimental work performed by researchers of Politecnico di Milano. The experimental data were analyzed and evaluated in terms of the daily profiles when the electrical power input varies, using Matlab as software for the analysis, and these values were then used for the calibration of the model. The model was calibrated and validated taking into consideration the most important parameters that affect the performance of the stack when it operates in steady state conditions. A sensitivity analysis was performed for each model’s parameter and suitable ranges were identified to fit the experimental data. In particular, the parameters under investigation were the exchange currents and the transfer coefficients for both anode and cathode, the membrane thickness and the resistivities of the electrodes both at anode and at cathode. The results of the calibration were evaluated in term of mean absolute relative terms (MARD) and the best solution was obtained with MARD equals to 0.105%. The model was validated against different datasets, both with the stack operated at peak load for a day-long time horizon and for a variable input power. The results of the model validation showed an appropriate fitting, MARD equals 0.3%, with the stack behavior. A preliminary dynamic system model was then implemented in Aspen Plus Dynamic to investigate the performance of the calibrated stack when the electrical input varies, considering the basic components that are present in an electrolyzer system: a heat exchanger, a water/oxygen and a water/hydrogen separator, a pump and two mixers. The data concerning the input-output flow rates, the variation of temperature and pressure of each component of the system were not available, so the assessment of the dynamic performance focused on the stack and the heat exchanger of the system that regulate the inlet anode temperature of the stack. The thermal capacity of the stack was obtained from the geometrical dimensions, with reasonable assumption on the materials of the stack. In this case, a calibration was not possible due to absence of suitable data. A comparison was performed in terms of current density and temperature between experimental and simulated results. The simulation predicted with good approximation both current density and temperature (4% and 3%) into two different sample profiles of the experimental data. Lastly, a comparison was made between experimental and simulated hydrogen production. The simulated hydrogen production was overestimated and also appear to have fluctuating profile, whereas the experimental hydrogen production was more stable. This difference was mainly due to the hydrogen purification columns which were not included in this preliminary dynamic model of the system.