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Optimal Design, Modeling and Simulation of an Ethanol Steam Reforming Reactor
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The optimum design, modeling and simulation of a fixed bed multi-tube reformer for the renewable hydrogen production are carried out in the present paper. The analogies between plug flow model and a fixed bed reactor are used as design patterns. The steam reformer is designed to produce enough hydrogen to feed a 200kW fuel cell system (>2.19molH/s) and considering 85% of fuel utilization in the cell electrodes. The reactor prototype is optimized and then analyzed using a multiphysics and axisymmetric model, implemented on FEMLABM(R) where the differential mass balance by convection-diffusion and the energy balance for convection-conduction are solved. The temperature profile is controlled to maximize hydrogen production. The catalyst bed internal profiles and the effect of temperature on ethanol conversion and carbon monoxide production are discussed as well.
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... The optimum design, modelling and simulation of a fixed bed multi-tube reformer were described by Arteaga et al. [17]. The fuel processor size was suitable to feed a 200 kW FC system (>2.19 ...
A power unit constituted by a reformer section, a H2 purification section and a fuel cell stack is being tested c/o the Dept. of Physical Chemistry and Electrochemistry of Università degli Studi di Milano, on the basis of a collaboration with HELBIO S.A. Hydrogen and Energy Production Systems, Patras (Greece), supplier of the unit, and some sponsors (Linea Energia S.p.A., Parco Tecnologico Padano and Provincia di Lodi, Italy). The system size allows to co-generate 5 kWe (220 V, 50 Hz a.c.) + 5 kWt (hot water at 65 °C) as peak output. Bioethanol, obtainable by different non-food-competitive biomass, is transformed into syngas by a pre-reforming and reforming reactors couple and the reformate is purified from CO to a concentration below 20 ppmv, suitable to feed a proton exchange membrane fuel cell (PEMFC) stack that will be integrated in the fuel processor in a second step of the experimentation. This result is achieved by feeding the reformate to two water gas shift reactors, connected in series and operating at high and low temperature, respectively. CO concentration in the outcoming gas is ca. 0.4 vol% and the final CO removal to meet the specifications is accomplished by two methanation reactors in series. The second methanation step acts merely as a guard, since ca. 15 ppmv of CO are obtained already after the first reactor.The goals of the present project are to test the integrated fuel processor, to check the effectiveness of the proposed technology and to suggest possible adequate improvements.
... In the meanwhile, the modeling of the chemical system is still an open research subject. The work presented in Ref. [6] derives a complex simulation-oriented model of the ESR while [4] shows how to obtain a model oriented for control purposes. Both works share the fact that the catalytic packed bed reactor can be modeled using the same dynamic equations as those used for modeling a plug-flow reactor, found in [7]. ...
This paper focuses on the control of a low temperature ethanol steam reformer for in-situ hydrogen production. For this purpose, three optimization-based control configurations are proposed, namely, a linear model-based predictive controller, a linear quadratic regulator with output error integral action and a cascade control combining the two previous configurations. In all cases, control objectives aim at obtaining the desired flow of hydrogen while keeping the carbon monoxide at its nominal working point under input and output operational constraints. Output tracking and robustness of each configuration are compared using two key performance indicators that evaluate the output errors and the smoothness of the control signals. Simulation results allow to compare the charac-teristics of each control configuration when applied to the non-linear model of the ethanol steam reformer.
This chapter provides an overview of the application of computational fluid dynamics (CFD) to the analysis and design of hydrogen technologies. After presenting the CFD fundamentals the use of this tool to investigate relevant hydrogen production technologies is considered. These technologies are categorized into reactors for the reforming of gaseous fuels (fixed- and fluidized-bed reactors and catalytic wall microreactors) and reactors for the gasification and fast pyrolysis of biomass. Subsequently, the application of CFD for studying fuel cells (polymer electrolyte membrane and solid oxide fuel cells) and hydrogen-fueled internal combustion engines is discussed. It is shown that CFD is a very useful tool for advancing in the development and optimization of these technologies. The interest of CFD for assisting in the understanding of the behavior of hydrogen technologies is also important. Nevertheless there are also limitations regarding the description of chemical transformations and the physics of some complex phenomena such as in multiphasic systems. An effort is required in the coming years to expand the range of applications of CFD in the hydrogen energy field and also for improving the existing models and commercial codes.
Development work for a compact hydrogen supply system with a thermal output of 65 kW applying ethanol as fuel was started by IMM in collaboration with Rosetti Marino, an Italian plant engineering company. The system concept is comprised of an ethanol steam reformer operated at 10 bar, water−gas shift for the reduction of carbon monoxide in the reformate, a pressure swing adsorption for separating the hydrogen out of the reformate, and numerous heat exchangers and coupled evaporators/catalytic burners as balance-of-plant. The work included all aspects of the fuel processor, namely, development of a Rh/Co catalyst for ethanol steam reforming, the verification of its long-term durability in a 1000 h test, static and dynamic simulation work applying ASPEN plus and ASPEN Dynamics, setup of a control strategy, and finally the sizing and design of the reactors and the development of a full 3D-CAD model of the fuel processor.
In this work, we performed a kinetic modeling of the production of hydrogen by the catalytic reforming of crude ethanol over a 15%-Ni/Al 2 O 3 catalyst prepared by the co-precipitation technique. The kinetics experiments were carried out at atmospheric pressure in a packed bed tubular reactor (8 mm inside diameter, 150 mm heated length, 53.0 mm bed height), at temperature in the range of 593–793 K. Eley Rideal assumptions where the surface reaction involved an adsorbed species and a free gaseous species were used to develop the reaction mechanism and four models were proposed based on this mechanism, from which a new kinetic model based on the dissociation of adsorbed crude ethanol as the rate-determining step was developed for this novel catalytic process. This model was of the form: −r A = (2.08 × 10 3 e −4430/RT N A)/[1 + 3.83 × 10 7 N A ] 2 . The absolute average deviation between experimental rates and those predicted using this model was 6%.
A bioethanol processing system to feed a 200 kW solid oxide fuel cell (SOFC) is simulated and evaluated in the present paper. The general scheme of the process is composed of vaporization, heating, bioethanol steam reforming (ESR) and SOFC stages. The performance pseudo-homogeneous model of the reactor, consisting of the catalytic ESR using a Ni/Al2O3 catalyst, has been developed based on the principles of classical kinetics and thermodynamics through a complex reaction scheme and a Lagmuir-Hishelwood kinetic pattern. The resulting model is employed to evaluate the effect of several design and operation parameters on the process (tube diameter between 3.81 and 7.62 cm, catalyst pellets diameter 0.1–0.5 cm, temperature 673–873 K, space time (θ) 1–10 (g min/cm3) and water/ethanol molar ratio (RAE), 1–6). It can be concluded that higher water/ethanol ratio (RAE = 5:1) and temperatures (above 773 K) favors hydrogen yield (YH = 4.1) and selectivity (SH = 91%), while the heat consumed in vaporization and heating stages is strongly increased at the same conditions. At temperatures above 773 K and RAE > 6, the reforming efficiencies exhibit a plateau because of the thermodynamics constraints of the process. The SOFC stack is arranged in parallel and needs 83 cells of 0.4 A/cm2 and 1 m2.
Oxidative steam reforming of ethanol for hydrogen production in order to feed a solid polymer fuel cell (SPFC) has been studied over several catalysts at on board conditions (a molar ratio of H2O/EtOH and of O2/EtOH equal to 1.6 and 0.68 respectively) and a reforming temperature between 923 and 1073 K. Two Ni (11 and 20 wt.%)/Al2O3 catalysts and five bimetallic catalysts, all of them supported on Al2O3, were tested. The bimetallic catalysts were Ni (approximately 20 wt.%) based catalysts doped with Cr (0.65 wt.%), Fe (0.6 wt.%), Zn (0.7 wt.%) or Cu (0.6 and 3.1 wt.%). The results in terms of H2 production and CO2/COx ratio obtained over Ni-based catalysts supported on Al2O3 are compared with those obtained over Ni–Cu/SiO2 and Rh/Al2O3 catalysts reported in our previous works. Tendencies of the product selectivities are analyzed in the light of the reaction network proposed.
The thermodynamic feasibility of the steam reforming of ethanol has been re-examined under conditions conducive to carbon formation using a modified approach. The findings are compared with the previously published results of Garcia and Laborde. In addition, the computations are extended to high water-to-ethanol ratios (and higher temperatures) as applicable to dilute stream produced during the fermentation of molasses. Equilibrium hydrogen yields as high as 5.5 mole per mole of ethanol in the feed are obtainable as against the stoichiometric value of 6.0.
In this work, the ethanol steam reforming on Ni/γAl2O3 catalyst at temperatures between 573 and 773 K was studied and an overall reaction scheme as a function of temperature was proposed. It can be concluded that higher water/ethanol ratio (6:1) and higher temperature (773 K) promote hydrogen production (91% selectivity). Over Ni-based catalyst there would not be evidences that water gas shift reaction occurs. The presence of oxygen in the feed produces a favorable effect on carbon deposition; nevertheless the carbon monoxide production is not reduced.
Bio-ethanol is a prosperous renewable energy carrier mainly produced from biomass fermentation. Reforming of bio-ethanol provides a promising method for hydrogen production from renewable resources. Besides operating conditions, the use of catalysts plays a crucial role in hydrogen production through ethanol reforming. Rh and Ni are so far the best and the most commonly used catalysts for ethanol steam reforming towards hydrogen production. The selection of proper support for catalyst and the methods of catalyst preparation significantly affect the activity of catalysts. In terms of hydrogen production and long-term stability, MgO, ZnO, CeO2, and La2O3 are suitable supports for Rh and Ni due to their basic characteristics, which favor ethanol dehydrogenation but inhibit dehydration. As Rh and Ni are inactive for water gas shift reaction (WGSR), the development of bimetallic catalysts, alloy catalysts, and double-bed reactors is promising to enhance hydrogen production and long-term catalyst stability. Autothermal reforming of bio-ethanol has the advantages of lesser external heat input and long-term stability. Its overall efficiency needs to be further enhanced, as part of the ethanol feedstock is used to provide low-grade thermal energy. Development of millisecond-contact time reactor provides a low-cost and effective way to reform bio-ethanol and hydrocarbons for fuel upgrading. Despite its early R&D stage, bio-ethanol reforming for hydrogen production shows promises for its future fuel cell applications.
A rigorous numerical model was developed to simulate the production of hydrogen from the reforming of crude ethanol in a packed bed tubular reactor (PBTR). The model was based on the coupling of mass and energy balance equations as well as a new kinetic model developed for the process. The simulation results for crude ethanol conversion were found to be in accordance with the experimental data obtained at various operating conditions. This confirms the validity of the numerical model. A further validation of the model was obtained by using the model to simulate a well-documented reaction process. In addition, the predicted variations of the concentration and temperature profiles for our process in the radial direction indicate that the assumption of plug flow and isothermal behavior is justified within certain kinetics operating conditions. However, even within these operating conditions, our results have proven that the axial dispersion terms in both the mass and the energy balance equations cannot be neglected.