Modeling Fixed Bed Membrane Reactors for Hydrogen Production through Steam Reforming Reactions: A Critical Analysis

Hydrogen Recovery from Coke Oven Gas. Comparative Analysis of Technical Alternatives

The recovery of energy and valuable compounds from exhaust gases in the iron and steel industry deserves special attention due to the large power consumption and CO₂ emissions of the sector. In this sense, the hydrogen content of coke oven gas (COG) has positioned it as a promising source toward a hydrogen-based economy which could lead to economic and environmental benefits in the iron and steel industry. COG is presently used for heating purposes in coke batteries or furnaces, while in high production rate periods, surplus COG is burnt in flares and discharged into the atmosphere. Thus, the recovery of the valuable compounds of surplus COG, with a special focus on hydrogen, will increase the efficiency in the iron and steel industry compared to the conventional thermal use of COG. Different routes have been explored for the recovery of hydrogen from COG so far: i) separation/purification processes with pressure swing adsorption or membrane technology, ii) conversion routes that provide additional hydrogen from the chemical transformation of the methane contained in COG, and iii) direct use of COG as fuel for internal combustion engines or gas turbines with the aim of power generation. In this study, the strengths and bottlenecks of the main hydrogen recovery routes from COG are reviewed and discussed.

Study of Static and Dynamic Behavior of a Membrane Reactor for Hydrogen Production

The paper investigates the stability and bifurcation phenomena that can occur in membrane reactors for the production of hydrogen by ammonia decomposition. A simplified mixed model of the membrane reactor is studied and two expressions of hydrogen permeation are investigated. The effect of the model design and operating parameters on the existence of steady state multiplicity is discussed. In this regard, it is shown that the adsorption-inhibition effect caused by the competitive adsorption of ammonia can lead to the occurrence of multiple steady states in the model. The steady state multiplicity exists for a wide range of feed ammonia concentration and reactor residence time. The effect of the adsorption constant, the membrane surface area and its permeability on the steady state multiplicity is delineated. The analysis also shows that no Hopf bifurcation can occur in the studied model.

Effect of Asymmetric Membrane Structure on Hydrogen Transport Resistance and Performance of a Catalytic Membrane Reactor for Ethanol Steam Reforming

The performance of catalytic membrane reactors (CMRs) depends on the specific details of interactions at different levels between catalytic and separation parts. A clear understanding of decisive factors affecting their operational parameters can be provided via mathematical simulations. In the present paper, main results of numerical studies of ethanol steam reforming, followed by downstream hydrogen permeation through an asymmetric supported membrane, are reported. The membrane module consists of a thin selective layer supported on a substrate with graded porous structure. One-dimensional isothermal reaction–transport model for the CMR has been developed, and its validation has been carried out by using performance data from a lab-scale reactor with a disk-shaped membrane. Simulations demonstrate the model’s capabilities to analyze local concentrations gradients, as required to provide accurate estimates of the relationship between structure–property–performance. It was shown that transport properties of multilayer asymmetric membranes are highly related to the structural properties of each single layer.

Thermochemical Performance Analysis of the Steam Reforming of Methane in a Fixed Bed Membrane Reformer: A Modelling and Simulation Study

Pd-based membrane reformers have been substantially studied in the past as a promising reformer to produce high-purity H₂ from thermochemical conversion of methane (CH₄). A variety of research approaches have been taken in the experimental and theoretical fields. The main objective of this work is a theoretical modelling to describe the process variables of the Steam Reforming of Methane (SRM) method on the Pd-based membrane reformer. These process variables describe the specific aims of each equation of the mathematical model characterizing the performance from reformer. The simulated results of the mole fractions of components (MFCs) at the outlet of the Fixed Bed Reformer (FBR) and Packed-Bed Membrane Reformer (PBMR) have been validated. When the H₂O/CH₄ ratio decreases in PBMR, the Endothermic Reaction Temperature (ERT) is notably increased (998.32 K) at the outlet of the PBMR’s reaction zone. On the other hand, when the H₂O/CH₄ ratio increases in PBMR, the ERT is remarkably decreased (827.83 K) at the outlet of the PBMR’s reaction zone. An increase of the spatial velocity (S_sp) indicates a reduction in the residence time of reactant molecules inside PBMR and, thus, a decrease of the ERT and conversion of CH₄. In contrast, a reduction of the S_sp shows an increase of the residence time of reactant molecules within PBMR and, therefore, a rise of the ERT and conversion of CH₄. An increase of the H₂O/CH₄ ratio raises the conversion rate (CR) of CH₄ due to the reduction of the coke content on the catalyst particles. Conversely, a reduction of the H₂O/CH₄ ratio decreases the CR of CH₄ owing to the increase of the coke content on the catalyst particles. Contrary to the CR of CH₄, the consumption-based yield (CBY) of H₂ sharply decreases with the increase of the H₂O/CH₄ ratio. An increase of the ERT raises the thermochemical energy storage efficiency (η_tese) from 68.96% (ERT = 1023 K), 63.21% (ERT = 973 K), and 48.12% (ERT = 723 K). The chemical energy, sensible heat, and heat loss reached values of 384.96 W, 151.68 W, and 249.73 W at 973 K. The selectivity of H₂ presents higher amounts in the gaseous mixture that varies from 60.98 to 73.18 while CH₄ showed lower values ranging from 1.41 to 2.06. Our work is limited to the SRM method. In terms of future uses of this method, new works can be undertaken using novel materials (open-cell foams) and the physical-mathematical model (two-dimensional and three-dimensional) to evaluate the concentration polarization inside membrane reactors.

Preliminary Equipment Design for On-Board Hydrogen Production by Steam Reforming in Palladium Membrane Reactors

Hydrogen, as an energy carrier, can take the main role in the transition to a new energy model based on renewable sources. However, its application in the transport sector is limited by its difficult storage and the lack of infrastructure for its distribution. On-board H2 production is proposed as a possible solution to these problems, especially in the case of considering renewable feedstocks such as bio-ethanol or bio-methane. This work addresses a first approach for analyzing the viability of these alternatives by using Pd-membrane reactors in polymer electrolyte membrane fuel cell (PEM-FC) vehicles. It has been demonstrated that the use of Pd-based membrane reactors enhances hydrogen productivity and provides enough pure hydrogen to feed the PEM-FC requirements in one single step. Both alternatives seem to be feasible, although the methane-based on-board hydrogen production offers some additional advantages. For this case, it is possible to generate 1.82 kmol h−1 of pure H2 to feed the PEM-FC while minimizing the CO2 emissions to 71 g CO2/100 km. This value would be under the future emissions limits proposed by the European Union (EU) for year 2020. In this case, the operating conditions of the on-board reformer are T = 650 °C, Pret = 10 bar and H2O/CH4 = 2.25, requiring 1 kg of catalyst load and a membrane area of 1.76 m2.

Progress in Modeling of Silica-Based Membranes and Membrane Reactors for Hydrogen Production and Purification

Hydrogen is seen as the new energy carrier for sustainable energy systems of the future. Meanwhile, proton exchange membrane fuel cell (PEMFC) stacks are considered the most promising alternative to the internal combustion engines for a number of transportation applications. Nevertheless, PEMFCs need high-grade hydrogen, which is difficultly stored and transported. To solve these issues, generating hydrogen using membrane reactor (MR) systems has gained great attention. In recent years, the role of silica membranes and MRs for hydrogen production and separation attracted particular interest, and a consistent literature is addressed in this field. Although most of the scientific publications focus on silica MRs from an experimental point of view, this review describes the progress done in the last two decades in terms of the theoretical approach to simulate silica MR performances in the field of hydrogen generation. Furthermore, future trends and current challenges about silica membrane and MR applications are also discussed.