Modeling of fluidized bed membrane reactors for hydrogen production from steam methane reforming with Aspen Plus

Hydrogen production via steam methane reforming with in situ hydrogen separation in fluidized bed membrane reactors was simulated with Aspen Plus. The fluidized bed membrane reactor was divided into several successive steam methane sub-reformers and membrane sub-separators. The Gibbs minimum free energy sub-model in Aspen Plus was employed to simulate the steam methane reforming process in the sub-reformers. A FORTRAN sub-routine was integrated into Aspen Plus to simulate hydrogen permeation through membranes in the sub-separator based on Sieverts' law. Model predictions show satisfactory agreement with experimental data in the literature. The influences of reactor pressure, temperature, steam-to-carbon ratio, and permeate side hydrogen partial pressure on reactor performances were investigated with the model. Extracting hydrogen in situ is shown to shift the equilibrium of steam methane reactions forward, removing the thermodynamic bottleneck, and improving hydrogen yield while neutralizing, or even reversing, the adverse effect of pressure.     

Simulation and optimization of hydrogen production by steam reforming of natural gas for refining and petrochemical demands in Lebanon

Steam reforming of natural gas produces the majority of the world's hydrogen (H₂) and it is considered as a cost-effective method from a product yield and energy consumption point of view. In this work, we present a simulation and an optimization study of an industrial natural gas steam reforming process by using Aspen HYSYS and MATLAB software. All the parameters were optimized to successfully run a complete process including the hydrogen production zone units (reformer reactor, high temperature gas shift reactor HTS and low temperature gas shift reactor LTS) and the purification zone units (absorber and methanator). Optimum production of hydrogen (87,404 MT/year) was obtained by fixing the temperatures in the reformer and the gas shift reactors (HTS & LTS) at 900 °C, 500 °C and 200 °C respectively while maintaining a pressure of 7 atm, and a steam to carbon ratio (S/C) of 4. Moreover, ~99% of the undesired CO₂ and CO gases were removed in the purification zone and a reduction of energy consumption of 77.5% was reached in the heating and cooling units of the process.     

Thermodynamic analysis of hydrogen generation via oxidative steam reforming of glycerol

A thermodynamic analysis of the oxidative steam reforming of glycerol (OSRG) for hydrogen production has been carried out with Aspen plus ^TM. The reaction was investigated at ambient pressure within the carbon-to-oxygen (C/O) ratio of 0.5–3.0, steam-to-carbon (S/C) ratio of 0.5–8.0 and temperature of 400–850 °C. Higher C/O and S/C ratios favor the production of hydrogen from glycerol. The highest hydrogen selectivity is obtained at 600–700 °C. To predict the potential technical obstacles in the glycerol reforming process, the OSRG process was compared with oxidative steam reforming of ethanol (OSRE) in terms of hydrogen production, autothermal condition and carbon deposition. The selectivity to hydrogen via OSRG is lower than that via OSRE under identical conditions. To achieve autothermal reforming, higher S/C and C/O ratios are required for reforming of glycerol than for ethanol due to the higher oxygen content in a glycerol molecule. From the viewpoint of thermodynamics, the glycerol reforming is more resistant to the carbon deposition. On the basis of the thermodynamic analysis and the preliminary experimental study, suggestions were proposed to guide the development of the glycerol reforming technique.     

Hydrogen production by aqueous phase catalytic reforming of glycerine

Hydrogen is believed to be the one of the main energy carriers in the near future. In this research glycerine, which is produced in large quantities as a by-product of biodiesel process, was converted to hydrogen aiming to contribute to clean energy initiative. Conversion of glycerol to hydrogen was achieved via aqueous-phase reforming (APR) with Pt/Al₂O₃ catalyst. The experiments were carried out in an autoclave reactor and a continuous fixed-bed reactor. The effects of reaction temperature (160-280 °C), feed flow rate (0.05-0.5 mL/dak) and feed concentration (5-85 wt-% glycerine) on product distribution were investigated. Optimum temperature for hydrogen production with APR was determined as 230 °C. Maximum gas production rate was found at the feed flow rates around 0.1 mL/min. It was also found that hydrogen concentration in the gas product increased with decreasing glycerol concentration in the feed.     

Thermodynamic analysis of methanol steam reforming to produce hydrogen for HT-PEMFC: An optimization study

A statistical modeling and optimization study on the thermodynamic equilibrium of methanol steam reforming (MSR) process was performed by using Aspen Plus and the response surface methodology (RSM). The impacts of operation parameters; temperature, pressure and steam-to-methanol ratio (H₂O/MeOH) on the product distribution were investigated. Equilibrium compositions of the H₂-rich stream and the favorable conditions within the operating range of interest (temperature: 25–600 °C, pressure: 1–3.0 atm, H₂O/MeOH: 0–7.0) were analyzed. Furthermore, ideal conditions were determined to maximize the methanol conversion, hydrogen production with high yield and to minimize the undesirable products such as CO, methane, and carbon. The optimum corresponding MSR thermodynamic process parameters which are temperature, pressure and H₂O/MeOH ratio for the production of HT-PEMFC grade hydrogen were identified to be 246 °C, 1 atm and 5.6, respectively.     

Optimization of hydrogen production from three reforming approaches of glycerol via using supercritical water with in situ CO2 separation

A pathway for hydrogen production from supercritical water reforming of glycerol integrated with in situ CO₂ removal was proposed and analyzed. The thermodynamic analysis carried out by the minimizing Gibbs free energy method of three glycerol reforming processes for hydrogen production was investigated in terms of equilibrium compositions and energy consumption using AspenPlus™ simulator. The effect of operating condition, i.e., temperature, pressure, steam to glycerol (S/G) ratio, calcium oxide to glycerol (CaO/G) ratio, air to glycerol (A/G) ratio, and nickel oxide to glycerol (NiO/G) ratio on the hydrogen production was investigated. The optimum operating conditions under maximum H₂ production were predicted at 450 °C (only steam reforming), 400 °C (for autothermal reforming and chemical looping reforming), 240 atm, S/G ratio of 40, CaO/G ratio of 2.5, A/G ratio of 1 (for autothermal reforming), and NiO/G ratio of 1 (for chemical looping reforming). Compared to three reforming processes, the steam reforming obtained the highest hydrogen purity and yield. Moreover, it was found that only autothermal reforming and chemical looping reforming were possible to operate under the thermal self-sufficient condition, which the hydrogen purity of chemical looping reforming (92.14%) was higher than that of autothermal reforming (52.98%). Under both the maximum H₂ production and thermal self-sufficient conditions, the amount of CO was found below 50 ppm for all reforming processes.     

Hydrogen production from glycerol steam reforming over Ni/La/Co/Al2O3 catalyst

Hydrogen production by steam reforming reaction of glycerol over Co/La/Ni-Al₂O₃ was studied in tubular fixed-bed reactor. The influences of operating parameters such as temperature, steam/carbon ratio, and weight hourly space velocity (WHSV) on hydrogen yield and carbon conversion were examined under atmospheric pressure. The results showed that carbon conversion increased with the increase of temperature and steam-to-carbon mole ratio (S/C). At 700°C, S/C=3:1, and WHSV=2.5h^?1, hydrogen yield and potential hydrogen yield were up to 77.64% and 89.64%, respectively; meanwhile, the carbon conversion reached 96.36%.     

Steam reforming of methanol,ethanol and glycerol over nickel-based catalysts-A review

Depletion of non-renewable energy sources such as coal and natural gas is paving the way to generate alternative energy sources. Hydrogen, a very promising alternative energy has the highest energy density (143 MJ/kg) compared to any known fuel and it has zero air pollution due to the formation of water as the only by-product after combustion. Currently, 95% of hydrogen is produced from non-renewable sources. Hydrogen production from renewable sources is considered a promising route for development of sustainable energy production. Steam reforming of renewable sources such as methanol, ethanol and glycerol is a promising route to hydrogen production. This review covers steam reforming of these three alcohols using Ni-based catalysts with different supports. Chemistry of the steam reforming reactions is discussed. Hydrogen yield depends on operating conditions, the nature of active metal and the catalyst support. Supports play an important role in terms of hydrogen selectivity and catalyst stability because of their basic characteristics and redox properties. Synthesis of suitable catalysts that can suppress coke formation during reforming is suggested.     

Conversion of biodiesel synthesis waste to hydrogen in membrane reactor: Theoretical study of glycerol steam reforming

Hydrogen production from waste glycerol, mainly producible as a by-product of biodiesel synthesis, is investigated as an attractive opportunity for exploiting renewable energy sources for further applications. Glycerol steam reforming using membrane technology was modeled by taking into accounts the maim transport phenomena, thermodynamic criteria and chemical process kinetics. A sensitivity analysis of operating conditions was made for key performance metrics such as glycerol conversion, hydrogen yield and hydrogen recovery. Glycerol conversion intensifies with enhancement of operating pressure and temperature, whereas high feed molar ratio and sweep ratio have limiting effect. Hydrogen permeation and subsequently, hydrogen recovery facilitates with increasing sweep gas ratio and sweep gas temperature. Hydrogen recovery enhances from 70% to 99% with increasing temperature from 350 to 500 °C at feed molar ratio of 3. Also, hydrogen recovery improves from 50% to 71% with increasing sweep ratio from 0 to 20 at 350 °C and 1 bar.     

A numerical study on the active reaction thickness of nickel catalyst layers used in a low-pressure steam methane reforming process

With the advancement of fuel cell technologies and growing interest in the hydrogen economy, the small-scale, distributed production of hydrogen has recently been receiving considerable research attention. The steam methane reforming (SMR) process, an established industrial process for large-scale hydrogen production, can also be successfully deployed for small-scale, low-pressure hydrogen production systems, including compact reformers, microchannel reformers, plate reformers, and monolithic reformers. In this study, the active reaction thickness of nickel catalyst layers was numerically determined by solving one-dimensional reaction/diffusion problems with finite volume method. The small-scale SMR conditions were considered, such as the reforming pressure of 1–3 bar, reforming temperature of 600–800 °C, and steam-to-carbon ratio of 2–4. The results showed the active thickness for the steam reforming and reverse methanation reactions hardly exceeded 0.15 mm for 600 °C, 0.07 mm for 700 °C, and 0.05 mm for 800 °C, at the reforming pressure of 1 bar. Besides, the effects of the volume-specific nickel surface area and diffusion properties were also investigated.     

Optimization of bio-oil steam reforming process by thermodynamic analysis

A straightforward thermodynamic analysis of bio-oil steam reforming was carried out in the context of hydrogen and syngas production, employing Gibbs energy minimization method to determine equilibrium composition and global reaction heat. The bio-oil model compound was a mixture of acetic acid, phenol, and acetone. The effects of process variables, such as temperature and inlet S/C molar ratio, were investigated over a wide range of conditions. Thermodynamic analysis was performed using the software Aspen Plus v.11. It was identified the best operational conditions that could maximize syngas and further hydrogen production considering energy efficiency. The optimum production of hydrogen is 2.28 mol per carbon mole at S/C = 10 and 850 K, and syngas is 2.37 mol per carbon mole at S/C = 10 and 900 K. It has been demonstrated that the equilibrium calculations can be used to simulate these steam reforming reactions, given the catalyst's behavior.     

Renewable hydrogen generation by steam reforming of glycerol over zirconia promoted ceria supported catalyst

The study focuses on hydrogen production from steam reforming of glycerol over nickel based catalyst promoted by zirconia and supported over ceria. Catalyst was prepared by the wet-impregnation method and characterized by BET surface area analysis, X-ray diffraction technique and scanning electron microscopy (SEM) analysis. The performance of the catalyst was evaluated in terms of hydrogen yield, selectivity and glycerol conversion at 700 °C in a tubular fixed bed reactor. The effect of glycerol concentration in feed, space time (W/F_AO), temperature and time on stream (TOS) was analyzed for the catalyst Ni–ZrO₂/CeO₂ which showed the complete conversion of glycerol and high H₂ yield that corresponds to 3.95 mol of H₂ out of 7 mol. Thermodynamic analysis was also carried out using Aspen HYSYS for system having glycerol concentration 10 wt% and 20 wt% and experimental results were compared with thermodynamics. Kinetic study was carried out for the steam reforming of glycerol over Ni–ZrO₂/CeO₂ catalyst using the power law model. The values of activation energy and order of reaction were found to be 43.4 kJ/mol and 0.3 respectively.     

Combustion characteristics of anode off-gas on the steam reforming performance

The combination of steam reforming and HT-PEMFC has been considered as a proper set up for the efficient hydrogen production. Recycling anode off-gas is energy-saving strategy, which leads to enhance the overall efficiency of the HT-PEMFC. Thus, the recycling effect of anode off-gas on steam-reforming performance needs to be further studied. This paper, therefore, investigated that the combustion of anode off-gas recycled impacts on the steam reformer, which consists of premixed-flame burner, steam reforming and water-gas shift reactors. The temperature rising of internal catalyst was affected by lower heating value of fuels when the distance between catalyst and burner is relatively short, while by the flow rate of fuels and the steam to carbon ratio when its distance is long. The concentration of carbon monoxide was the lowest at 180 °C of LTS temperature, while NG and AOG modes showed the highest thermal efficiency at LTS temperature of 220–300 °C and 270–350 °C, respectively. The optimum condition of thermal efficiency to maximize hydrogen production was determined by steam reforming rather than water gas shift reaction. It was confirmed that the condition to obtain the highest thermal efficiency is about 650 °C of steam reforming temperature, regardless of combustion fuel and carbon monoxide reduction. The difference of hydrogen yield between upper and lower values is up to 1.5 kW as electric energy with a variation of thermal efficiency. Hydrogen yield showed the linear proportion to the thermal efficiency of steam reformer, which needs to be further increased through proper thermal management.     

Comparison study of thermochemical waste-heat recuperation by steam reforming of liquid biofuels

The concept of thermochemical exhaust heat recuperation by steam reforming of biofuels is considered. Thermochemical recuperation can be considered as an on-board hydrogen production technology. A schematic diagram of a fuel-consuming equipment with thermochemical heat recuperation is described. The thermodynamic analysis of the thermochemical recuperation systems was performed to determine the efficiency of using various fuels, in particular, methanol, ethanol, n-butanol, and glycerol. The thermodynamic analysis was performed by Gibbs free energy minimization method and implemented using the Aspen Hysys program. The thermodynamic analysis was performed for a wide temperature range from 400 to 900 K, for steam-to-fuel of 1, and pressures of 1 bar. The maximum fuel conversion reaches for the following temperatures: methanol - 600 K, ethanol - 730 K, n-butanol - 860 K, glycerol - 890 K. The dependence of the reforming enthalpy on temperature is determined. It was shown that the reaction enthalpy determines the heat transformation coefficient, which shows the ratio of the low heat value of synthetic fuel and the low heat value of the initial fuel. For all studied fuels, the maximum value of the transformation coefficient is observed for steam reforming of ethanol and the maximum heat transformation coefficient is 1.187. The temperature range is determined at which the maximum efficiency of the use of thermochemical recuperation occurs due to the reforming of biofuels. For methanol, the effective temperature is about 600 K, for ethanol is about 700 K, for n-butanol is 850 K, for glycerol is more than 900 K. The results obtained make it possible to efficiently select the type of fuel for thermochemical recuperation due to steam reforming.     

Comparative exergy analysis of sorption enhanced and conventional methane steam reforming

Exergy efficiency analysis tool is used to evaluate sorption enhanced steam reforming in comparison with the industrial hydrogen production route, steam reforming. The study focuses on hydrogen production for use in high pressure processes. Thermodynamic sensitivity analysis (effect of reforming temperature on hydrogen yield and reforming enthalpy) was performed to indicate the optimum temperature (650 °C) for the sorption enhanced reforming. The pressure was selected to be, for both cases, 25 bar, a typical pressure used in the industrial (conventional) process. Atmospheric pressure, 1000 °C and CO₂ as inert gas were specified as the optimum operating parameters for the regeneration of the sorbent after performing exergy efficiency analysis of three realistic case scenarios. Aspen Plus simulation process schemes were built for conventional and sorption enhanced steam reforming processes to attain the mass and energy balances required to assess comparatively exergy analysis. Simulation results showed that sorption enhanced reforming can lead to a hydrogen purity increase by 17.3%, along with the recovery of pure and sequestration-ready carbon dioxide. The exergy benefit of sorption enhanced reforming was calculated equal to 3.2%. Analysis was extended by adding a CO₂ separation stage in conventional reforming to reach the hydrogen purity of sorption enhanced reforming and enable a more effective exergy efficiency comparison. Following that analysis, sorption enhanced reforming gained 10.8% in exergy efficiency.     

Refuse derived fuel hydrogasification coupled with methane steam reforming

The hydrogasification of Refuse Derived Fuel (RDF) consisting of non-recyclable plastic polymers was combined with methane steam reforming in a “hydrogen self-sustained” loop configuration. The hydrogasification unit fed by 1000 kg/h of RDF was initially modeled by Aspen plus to define best operating conditions, namely temperature, pressure and hydrogen feed flow rate. After the simulations, the temperature of the hydrogasification process has been fixed at 300 °C, the pressure at 10 bar and the hydrogen feed flow rate at 140 kg/h. The steam reforming unit operates at 850 °C while the water-gas shift is conducted at 350 °C. When all the methane produced by hydrogasification is used to feed the steam reformer, which yields H₂ that is recycled back to the hydrogasifier, the net hydrogen production is 222 kg/h with an amount of CO₂ released of 2265 kg/h. For the different process configurations adopted, the energy efficiency of the process ranges 84–89%.     

How to choose endothermic process for thermochemical waste-heat recuperation?

The thermochemical waste-heat recuperation (TCR) systems by steam reforming of various hydrocarbon fuels are considered. A method for determining the TCR systems efficiency is proposed. The methodology is based on the determination of the heat recuperation rate and heat transformation coefficient. TCR due to steam reforming of methanol, ethanol, glycerol, propane, and methane was analyzed. To obtain the initial data for energy analysis of TCR systems, the thermodynamic analysis was performed. With the help of Aspen HYSYS was determined the synthesis gas composition and reaction enthalpy for all investigated variants. The investigation was performed for a wide temperature range from 400 to 1200 K, for the steam-to-fuel ratio of 1, and pressures of 1 bar. It was established that TCR due to the steam reforming of ethanol, glycerol, and propane in the temperature range above 800 K, it is possible to achieve complete recuperation of the exhaust after the furnace. As a results of investigation, the practical recommendations were given for choosing endothermic reaction for the thermochemical waste-heat recuperation systems: in the temperature range up to 600 K for TCR it is necessary to choose a methanol steam reforming reaction; in the temperature range from 600 to 1000 K - the reaction of steam reforming of ethanol and glycerol; in the temperature range above 1000 K - the reaction of steam reforming propane and methane.     

Thermodynamic analysis of high‐temperature helium heated fuel reforming for hydrogen production

In order to take full advantage of the heat from high temperature gas cooled reactor, thermodynamic analysis of high‐temperature helium heated methane, ethanol and methanol steam reforming for hydrogen production based on the Gibbs principle of minimum free energy has been carried out using the software of Aspen Plus. Effects of the reaction temperature, pressure and water/carbon molar ratio on the process are evaluated. Results show that the effect of the pressure on methane reforming is small when the reaction temperature is over 900 °C. Methane/CO conversion and hydrogen production rate increase with the water/carbon molar ratio. However the thermal efficiency increases first to the maximum value of 61% and then decreases gradually. As to ethanol and methanol steam reforming, thermal efficiency is higher at lower reaction pressures. With an increase in water–carbon molar ratio, hydrogen production rate increases, but thermal efficiency decreases. Both of them increase with the reaction temperature first to the highest values and then decrease slowly. At optimum operation conditions, the conversion of both ethanol and methanol approaches 100%. For the ethanol and methanol reforming, their highest hydrogen production rate reaches, respectively, 88.69% and 99.39%, and their highest thermal efficiency approaches, respectively, 58.58% and 89.17%. With the gradient utilization of the high temperature helium heat, the overall heat efficiency of the system can reach 70.85% which is the highest in all existing system designs. Copyright © 2014 John Wiley & Sons, Ltd.     

System optimization for effective hydrogen production via anaerobic digestion and biogas steam reforming

To construct a system for the effective hydrogen production from food waste, the conditions of anaerobic digestion and biogas reforming have been investigated and optimized. The type of agitator and reactor shape affect the performance of anaerobic digestion reactors. Reactors with a cubical shape and hydrofoil agitator exhibit high performance due to the enhanced axial flow and turbulence as confirmed by simulation of computational fluid dynamics. The stability of an optimized anaerobic digestion reactor has been tested for 60 days. As a result, 84 L of biogas is produced from 1 kg of food waste. Reaction conditions, such as reaction temperature and steam/methane ratio, affect the biogas steam reforming reaction. The reactant conversions, product yields, and hydrogen production are influenced by reaction conditions. The optimized reaction conditions include a reaction temperature of 700 °C and H₂O/CH₄ ratio of 1.0. Under these conditions, hydrogen can be produced via steam reforming of biogas generated from a two-stage anaerobic digestion reactor for 25 h without significant deactivation and fluctuation.     

Thermochemical waste-heat recuperation as on-board hydrogen production technology

Thermochemical waste-heat recuperation (TCR) as an on-board hydrogen production technology is considered. To determine the effectiveness of using TCR systems as an on-board hydrogen production technology and to assess the possibility of hydrogen production in TCR systems, a thermodynamic analysis of various hydrocarbon reforming reactions was carried out. The thermodynamic analysis has been realized via Aspen HYSYS software. Three steam reforming reactions with methane, methanol, and ethanol were investigated. It was established that the composition of the initial reaction mixture and the process temperature has a significant effect on the efficiency of the thermochemical heat recuperation system. The maximum efficiency of thermochemical heat recuperation systems due to steam reforming is achieved at 600 K for methanol; 700 K for ethanol and 900 K for methane.