CFD simulation with detailed chemistry of steam reforming of methane for hydrogen production in an integrated micro-reactor

micro-reactor has drawn more and more attention in recent years due to the process intensification on basic transport phenomena in micro-channels, which would often lead to the improved reactor performance. Steam reforming of methane (SRM) in micro-reactor has great potential to realize a low-cost, compact process for hydrogen production via an evident shortening of reaction time from seconds to milliseconds. This work focuses on the detailed modeling and simulation of a micro-reactor design for SRM reaction with the integration of a micro-channel for Rh-catalyzed endothermic reaction, a micro-channel for Pt-catalyzed exothermic reaction and a wall in between with Rh or Pt-catalyst coated layer. The elementary reaction kinetics for SRM process is adopted in the CFD model, while the combustion channel is described by global reaction kinetics. The model predictions were quantitatively validated by the experimental data in the literature. For the extremely fast reactions in both channels, the simulations indicated the significance of the heat conduction ability of the reactor wall as well as the interplay between the exothermic and endothermic reactions (e.g., the flow rate ratio of fuel gas to reforming gas). The characteristic width of 0.5 mm is considered to be a suitable channel size to balance the trade-off between the heat transfer behavior in micro-channels and the easy fabrication of micro-channels.     

Real time optimization of steam reforming of methane in an industrial hydrogen plant

The main goal of this research is modeling and real time optimization of an industrial steam methane reformer considering catalyst deactivation. In the first step, the reformer is heterogeneously modeled based on the mass and energy balance equations considering a detailed kinetic model. To prove the accuracy of developed model, the simulation results are compared with the available plant data at steady state condition. In the second step, based on the mechanism of catalyst deactivation, a first order decay model is proposed and the parameters of the model are calculated to minimize the absolute difference between calculated methane conversion and plant data. In the third step, an optimal control problem is formulated to maintain hydrogen production capacity at the desired level. Based on the formulated optimization problem, optimal dynamic trajectories of feed temperature and steam to methane ratio are calculated considering two strategies. Then, the performance of developed optimization procedure is proved considering furnace temperature and feed concentration as disturbance. The simulation results show that operating at the proposed optimal condition increases hydrogen production about 11.6%. In addition, the process emission performance defined as hydrogen to carbon dioxide ratio in the product is 6.72 and 7.03 at the conventional and optimized conditions, respectively.     

Bio-oil steam reforming,partial oxidation or oxidative steam reforming coupled with bio-oil dry reforming to eliminate CO2 emission

Biomass is carbon-neutral and utilization of biomass as hydrogen resource shows no impact on atmospheric CO₂ level. Nevertheless, a significant amount of CO₂ is always produced in biomass gasification processes. If the CO₂ produced can further react with biomass, then the biomass gasification coupled with CO₂ reforming of biomass will result in a net decrease of CO₂ level in atmosphere and produce the chemical raw material, syngas. To achieve this concept, a “Y” type reactor is developed and applied in bio-oil steam reforming, partial oxidation, or oxidative steam reforming coupled with CO₂ reforming of bio-oil to eliminate the emission of CO₂. The experimental results show that the reaction systems can efficiently suppress the emission of CO₂ from various reforming processes. The different coupled reaction systems generate the syngas with different molar ratio of CO/H₂. In addition, coke deposition is encountered in the different reforming processes. Both catalysts and experimental parameters significantly affect the coke deposition. Ni/La₂O₃ catalyst shows much higher resistivity toward coke deposition than Ni/Al₂O₃ catalyst, while employing high reaction temperature is vital for elimination of coke deposition. Although the different coupled reaction systems show different characteristic in terms of product distribution and coke deposition, which all can serve as methods for storage of the carbon from fossil fuels or air.     

A heterogeneous dynamic model for the simulation and optimisation of the steam methane reforming reactor

In the current paper the dynamic behaviour of an industrial heterogeneous catalytic packed-bed reactor for the steam reforming of methane is examined. The model consists of a set of partial differential equations describing the physico-chemical processes that take place both in solid and gas phases accounting for diffusional limitations within the catalyst particles. The model was validated against literature data, while the heat provided to the reactor wall was optimised in terms of the optimal H₂ yield using a quadratic wall temperature profile. The values of the physico-chemical properties were adjusted to the severe operating conditions (high pressures and temperatures) of the reactor accounting for multicomponent gas mixture properties. It is shown that the 2-phase reactor concept along with the optimised wall temperature profile capture very well the dynamic conversion, the temperature and the partial pressure profiles both at bed and at particle level.     

A multi-scale dynamic two-dimensional heterogeneous model for catalytic steam methane reforming reactors

A multi-scale, dynamic, two-dimensional, heterogeneous model for catalytic steam methane reforming (SMR) is developed. The model, derived from first principles, accounts for diffusional limitations for both mass and energy within large industrial-scale catalyst particles. The diffusional limitations have been incorporated, not by the conventional method of computing the effectiveness factor, but by accounting for the transfer of species as a function of the concentration and temperature gradients existing between the gas phase and catalyst surface along the reactor length. The model has been validated with available industrial steady-state data from literature. The model was then used to study the dynamic behaviour of key variables and the effects of feed disturbances on catalyst core and tube wall temperatures.     

Exergy analysis of hydrogen production via steam methane reforming

The performance of hydrogen production via steam methane reforming (SMR) is evaluated using exergy analysis, with emphasis on exergy flows, destruction, waste, and efficiencies. A steam methane reformer model was developed using a chemical equilibrium model with detailed heat integration. A base-case system was evaluated using operating parameters from published literature. Reformer operating parameters were varied to illustrate their influence on system performance. The calculated thermal and exergy efficiencies of the base-case system are lower than those reported in literature. The majority of the exergy destruction occurs due to the high irreversibility of chemical reactions and heat transfer. A significant amount of exergy is wasted in the exhaust stream. The variation of reformer operating parameters illustrated an inverse relationship between hydrogen yield and the amount of methane required by the system. The results of this investigation demonstrate the utility of exergy analysis and provide guidance for where research and development in hydrogen production via SMR should be focused.     

Combined methane reforming by carbon dioxide and steam in proton conducting solid oxide fuel cells for syngas/power co-generation

Methane and carbon dioxide mixture can be used as the fuel in a proton conducting solid oxide fuel cell (SOFC) for power/syngas co-generation and greenhouse gas reduction. However, carbon deposition and low conversion ratio are potential problems for this technology. Apart from using functional catalytic layer in the SOFC to enhance CH₄ dry reforming, adding H₂O into the fuel stream could facilitate the CH₄ conversion and enhance the co-generation performance of the SOFC. In this work, the effects of adding H₂O to the CO₂CH₄ fuel on the performance of a tubular proton conducting SOFC are studied numerically. Results show that the CH₄ conversion is improved from 0.830 to 0.898 after adding 20% H₂O to the anode. Meanwhile, the current density is increased from 2832 A m⁻² to 3064 A m⁻² at 0.7 V. Sensitivity studies indicate that the H₂:CO ratio can be effectively controlled by the amount of H₂O addition and the H₂ starvation can be alleviated, especially at high current density conditions.     

Integrated solar combined cycle system with steam methane reforming: Thermodynamic analysis

The present paper considers an integrated solar combined cycle system (ISCCS) with an utilization of solar energy for steam methane reforming. The overall efficiency was compared with the efficiency of an integrated solar combined cycle system with the utilization of solar energy for steam generation for a steam turbine cycle. Utilization of solar energy for steam methane reforming gives the increase in an overall efficiency up to 3.5%. If water that used for steam methane reforming will be condensed from the exhaust gases, the overall efficiency of ISCCS with steam methane reforming will increase up to 6.2% and 8.9% for β = 1.0 and β = 2.0, respectively, in comparison with ISCCS where solar energy is utilized for generation of steam in steam turbine cycle. The Sankey diagrams were compiled based on the energy balance. Utilization of solar energy for steam methane reforming increases the share of power of a gas turbine cycle: two-thirds are in a gas turbine cycle, and one-third is in a steam turbine cycle. In parallel, if solar energy is used for steam generation for a steam turbine cycle, than the shares of power from a gas and steam turbine are almost equal.     

Hydrogen from ethanol: Theoretical optimization of a PEMFC system integrated with a steam reforming processor

In this paper the energetic optimization of a proton exchange membrane fuel cell integrated with a steam reforming system using ethanol as fuel is analysed. In order to obtain high hydrogen production, a thermodynamic analysis of the steam reforming process has been carried out and the optimal operating conditions has been defined. Moreover, the overall efficiency of the PEMFC-SR system has been investigated as a function of the fuel utilization factor and the effects of the anodic off-gas recirculation have been evaluated.     

Experimental evaluation and empirical modelling of palm oil mill effluent steam reforming

The current work describes a novel application of steam reforming process to treat palm oil mill effluent (POME), whilst co-generating H₂-rich syngas from the treatment itself. The effects of reaction temperature, partial pressure of POME and gas-hourly-space-velocity (GHSV) were determined. High crystallinity 20 wt%Ni/80 wt%Al₂O₃ catalyst with smooth surface was prepared via impregnation method. Baseline runs revealed that the prepared catalyst was highly effective in destructing organic compounds, with a two-fold enhancement observed in the presence of 20 wt% Ni/80 wt%Al₂O₃ catalyst, despite its low specific surface area (2.09 m² g^?1). In addition, both the temperature and partial pressure of POME abet the COD reduction. Consequently, the highest COD reduction of 99.7% was achieved, with a final COD level of 73 ± 5 ppm from 27,500 ppm, at GHSV of 40,000 mL/h.g_cat and partial pressure of POME equivalent to 95 kPa at 1173 K. In terms of gaseous products, H₂ was found to be the major component, with selectivity ranged 51.0%–70.9%, followed by CO₂ (17.7%–34.1%), CO (7.7%–18.4%) and some CH₄ (0.6%–3.3%). Furthermore, quadratic models with high R²-values were developed.     

Two-dimensional thermal analysis of radial heat transfer of monoliths in small-scale steam methane reforming

Monolithic catalysts have received increasing attention for application in the small-scale steam methane reforming process. The radial heat transfer behaviors of monolith reformers were analyzed by two-dimensional computational fluid dynamic (CFD) modeling. A parameter study was conducted by a large number of simulations focusing on the thermal conductivity of the monolith substrate, washcoat layer, wall gap, radiation heat transfer and the geometric parameters (cell density, porosity and diameter of monolith). The effective radial thermal conductivity of the monolith structure, k_r,eff, showed good agreement with predictions made by the pseudo-continuous symmetric model. This influence of the radiation heat transfer is low for highly conductive monoliths. A simplified model has been developed to evaluate the importance of radiation for monolithic reformers under different conditions. A wall gap as thin as 0.05 mm significantly decreased k_r,eff, while the radiation heat transfer showed limited improvement. A pseudo-homogenous two-dimensional model combined with the symmetric model has been developed for a quick evaluation of geometric parameters for a monolith reformers. Monolithic reformers based on highly conductive substrates e.g., Ni and SiC showed great potential for small-scale hydrogen production.     

Toward autonomous control of microreactor system for steam reforming of methanol

Since the introduction of microchemical systems (MCS) in the last decade, it has been recognized that one of the most crucial challenges is the implementation of an appropriate control strategy. A novel study in realizing a controllable miniature chemical plant for a small-scale hydrogen source for fuel cells is presented. Catalytic steam reforming (SR) reaction of a methanol–water mixture was the model reaction studied. A microscaled reactor, sensors and actuators, were successfully prepared and integrated by using microelectromechanical systems (MEMS) technology. Microfabricated system components were then interconnected with a comprehensive control algorithm which could form the basis for an eventual autonomous, self-contained system.     

Economic analysis of hydrogen production from steam reforming process: A literature review

The interest in steam reforming process as an efficient method for hydrogen production has been greatly increasing, due to its efficiency during hydrogen production and low environmental problems compared to other techniques. The main objective of this review was to present a comprehensive study of environmental, economic aspects of hydrogen production from steam reforming of raw materials such as biomass, bio-gas, ethanol, and natural gas. From literature review, it was found that among methods for hydrogen production, steam reforming of natural gas has lower installed capital due to the precence of high amounts of unconverted hydrocarbons in the produced gas (so-called tar) during other methods such as steam reforming of bio-gas.     

Methanol steam reforming integrated with oxidation in a conical annulus micro-reactor

A micro-channel reactor with circular cross section was numerically studied. Inside the inner cylinder and the annulus section, steam reforming and oxidation reactions were occurred, respectively. With the variation in diameter of the annulus section along the reactor length, the effect of diameter changing was also studied. In this case, outer section is an incomplete cone. The results showed that conical annulus (right inlet) micro-reactor (when the diameter of the cone decreased along the reactor length) represents higher temperatures and conversions. Then, influences of some parameters were considered in this micro-reactor. With increasing some parameters such as inlet temperature and the steam to carbon ratio of inlet flow, methanol conversion increases, and increasing some other parameters such as flow rate, solid thickness and porosity of bed leads to the methanol conversion decreases as well. Effect of various diameters in this micro-reactor was considered. Also when oxidation reaction happened inside outer cone, the better results was represented.     

Techno-economic assessment of solar steam reforming of methane in a membrane reactor using molten salts as heat transfer fluid

This paper reports the results obtained in a techno-economic analysis of the Steam Methane Reforming (SMR) technology aided with solar heat, developed and demonstrated in the European FCH JU project CoMETHy: a compact membrane reformer heated with molten salt up to 550 °C allowed to simultaneously carry out methane steam reforming, water-gas-shift reaction and hydrogen separation. This reactor can be integrated with new generation Concentrating Solar Thermal (CST) systems to supply the process heat. Experimental validation of the technology has been successfully achieved in a pilot scale plant and the results recently published. In this paper, we introduce a fully-integrated scheme and operation strategies of a plant on the 1500 Nm³/h hydrogen production scale. Then, techno-economic analysis of this new solar-driven process is presented to evaluate its competitiveness. Considering a plant capacity of 1500 Nm³/h (pure hydrogen production) and today's costs for the methane feed and the CST technology, obtained Hydrogen Production Cost (HPC) are in the range of 2.8–3.3 €/kg for a “solar-hybrid” system with high capacity factor (8000 h/year operation) and 4.7 €/kg for a “solar-only” case, while HPC≅1.7 €/kg can be obtained with the conventional route under equivalent assumptions. However, a sensitivity analysis shows that the expected drop of the cost of the CST technology will bring the HPC around 2.4 €/kg for the “solar-hybrid” case and close to 3.4 €/kg for the “solar-only” case, thus making the cost of solar reforming closer to conventional SMR with CO₂ capture and with wind/solar electrolysis in the future. In the “solar-hybrid” case total CO₂ production can be reduced by 13–29% with 58–70% of produced CO₂ recovered as pure stream (at 1.3 bar); in the “solar-only” case total CO₂ production can be reduced by 52% and 100% of produced CO₂ recovered as pure stream (at 1.3 bar). However, compared to the conventional route, CO₂ avoidance costs are still relatively high (≥137 €/ton_CO2) and process optimization measures required. Therefore, optimization measures have been outlined to increase the overall process efficiency and further reduce the HPC.     

Modelling of one-dimensional heterogeneous catalytic steam methane reforming over various catalysts in an adiabatic packed bed reactor

Kinetic data relevant to steam methane reforming (SMR) are often applied to catalysts and conditions for which they have not been derived. In this work, kinetic rates for the two SMR and water gas shift reactions were derived for 12 commonly used reforming catalysts based on conversion data obtained from the literature. Subsequently, these rates were tested in dynamic operation, steady-state, and equilibrium using a 1-D reactor model developed in-house with gPROMS model builder. Modelling outputs were further validated independently at equilibrium using the software chemical equilibrium with applications (CEA), and the literature. The effect of variables such as temperature, pressure, steam to carbon ratio (S/C), and gas mass flux (G_s) on the performance of the SMR process was then studied in terms of fuel and steam conversion (%), H₂ purity (%), H₂ yield (wt. % of CH₄) and selectivity of the carbon-based products. A comparative study was then performed for the 12 catalysts. Some catalysts showed better activity owing to their fast kinetics when they are tested in mild industrial conditions, while others performed better in more severe industrial conditions, substantiating that the choice of a catalyst ought to depend on the operating conditions.     

Production of synthesis gas by partial oxidation and steam reforming of biomass pyrolysis oils

As the lowest cost biomass-derived liquids, pyrolysis oils (also called bio-oils) represent a promising vector for biomass to fuels conversion. However, bio-oils require upgrading to interface with existing infrastructure. A potential pathway for producing fuels from pyrolysis oils proceeds through gasification, the conversion to synthesis gas. In this work, the conversion of bio-oils to syngas via catalytic partial oxidation over Rh–Ce is evaluated using two reactor configurations. In one instance, pyrolysis oils are oxidized in excess steam in a freeboard and passed over the catalyst in a second zone. In the second instance, bio-oils are introduced directly to the catalyst. Coke formation is avoided in both configurations due to rapid oxidation. H₂ and CO can be produced autothermally over Rh–Ce catalysts with millisecond contact times. Co-processing of bio-oil with methane or methanol improved the reactor operation stability.     

Assessment of CO2 capture options from various points in steam methane reforming for hydrogen production

Steam methane reforming (SMR) is currently the main hydrogen production process in industry, but it has high emissions of CO₂, at almost 7 kg CO₂/kg H₂ on average, and is responsible for about 3% of global industrial sector CO₂ emissions. Here, the results are reported of an investigation of the effect of steam-to-carbon ratio (S/C) on CO₂ capture criteria from various locations in the process, i.e. synthesis gas stream (location 1), pressure swing adsorber (PSA) tail gas (location 2), and furnace flue gases (location 3). The CO₂ capture criteria considered in this study are CO₂ partial pressure, CO₂ concentration, and CO₂ mass ratio compared to the final exhaust stream, which is furnace flue gases. The CO₂ capture number (N_cc) is proposed as measure of capture favourability, defined as the product of the three above capture criteria. A weighting of unity is used for each criterion. The best S/C ratio, in terms of providing better capture option, is determined. CO₂ removal from synthesis gas after the shift unit is found to be the best location for CO₂ capture due to its high partial pressure of CO₂. However, furnace flue gases, containing almost 50% of the CO₂ in produced in the process, are of great significance environmentally. Consequently, the effects of oxygen enrichment of the furnace feed are investigated, and it is found that this measure improves the CO₂ capture conditions for lower S/C ratios. Consequently, for an S/C ratio of 2.5, CO₂ capture from a flue gas stream is competitive with two other locations provided higher weighting factors are considered for the full presence of CO₂ in the flue gases stream. Considering carbon removal from flue gases, the ratio of hydrogen production rate and N_cc increases with rising reformer temperature.     

Effect of palladium addition on catalytic activity in steam methane reforming over Ni-YSZ porous membrane

This study investigated the additive effects of palladium, and the deposition method of palladium on Ni-YSZ porous membrane in steam methane reforming. Pd–Ni-YSZ porous membrane prepared by the wet impregnation method showed superior catalytic activity, where the methane conversion reached 94.6% at 650 °C, with H₂ yield above 3.9. The palladium particles were well dispersed, and the Pd–Ni-YSZ porous membrane exhibited high adsorption capacity for water. The addition of palladium and the deposition method of palladium are very important for the steam methane reforming reaction.