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.     

Exergoenvironmental analysis of a steam methane reforming process for hydrogen production

Steam methane reforming (SMR) is one of the most promising processes for hydrogen production. Several studies have demonstrated its advantages from the economic viewpoint. Nowadays process development is based on technical and economical aspects; however, in the near future, the environmental impact will play a significant role in the design of such processes. In this paper, an SMR process is studied from the viewpoint of overall environmental impact, using an exergoenvironmental analysis. This analysis presents the combination of exergy analysis and life cycle assessment. Components where chemical reactions occur are the most important plant components from the exergoenvironmental point of view, because, in general, there is a high environmental impact associated with these components. This is mainly caused by the exergy destruction within the components, and this in turn is mainly due to the chemical reactions. The obtained results show that the largest potential for reducing the overall environmental impact is associated with the combustion reactor, the steam reformer, the hydrogen separation unit and the major heat exchangers. The environmental impact in these components can mainly be reduced by improving their exergetic efficiency. A sensitivity analysis for some important exergoenvironmental variables is also presented in the paper.     

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.     

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.     

A framework for assessing economics of blue hydrogen production from steam methane reforming using carbon capture storage & utilisation

Hydrogen (H₂) generation using Steam Methane Reforming (SMR) is at present the most economical and preferred pathway for commercial H₂ generation. This process, however, emits a considerable amount of CO₂, ultimately negating the benefit of using H₂ as a clean industrial feedstock and energy carrier. That has prompted growing interest in enabling CO₂ capture from SMR for either storage or utilisation and producing zero-emission “blue H₂”. In this paper, we propose a spatial techno-economic framework for assessing blue hydrogen production SMR hubs with carbon capture, utilisation and storage (CCUS), using Australia as a case study. Australia offers a unique opportunity for developing such ‘blue H₂’ hubs given its extensive natural gas resources, availability of known carbon storage reservoirs and an ambitious government target to produce clean/zero-emission H₂ at the cost of <A$2 kg^?1 by 2030. Our results highlight that the H₂ production costs are unsurprisingly dominated by natural gas, with the additional capital requirement of carbon capture and storage (CCS) also playing a critical role. These outcomes are especially pertinent for eastern Australian states, as they are experiencing high natural gas costs and would generally require extensive CO₂ transport and storage infrastructure to tap potential storage reservoirs, ultimately resulting in a higher cost of producing H₂ (>A$2.7 kg_H2^?1). On the other hand, Western Australia offers lower gas pricing and relatively lesser storage costs, which would lead to more economically favourable hydrogen production (<A$2.2 kg_H2^?1). We further explore the possibility of utilising the emissions captured at blue SMR hubs by converting them into formic acid through CO₂ electroreduction, yielding revenue that will decrease the cost of blue H₂ and reduce the reliance on CO₂ storage. Our analysis reveals that formic acid production utilising a 10 MW CO₂ electrolyser can potentially reduce H₂ production costs by between 4 and 9%. Further cost reduction is possible by scaling the CO₂ electrolyser capacity to convert a larger portion of the emissions captured, albeit at the cost of higher capital investment, electricity consumption and saturating the market for formic acid. Thus, carbon utilisation for a range of products with high market demand represents a more promising approach to replacing the need for costly carbon storage. Overall, our modelling framework can be adapted for global application, particularly for regions interested in generating blue H₂ and extended to include other CO₂ utilisation opportunities and evaluate other hydrogen production technologies.     

Synthesis and characterization of supportless Ni-Pd-CNT nanocatalyst for hydrogen production via steam reforming of methane

Supportless Ni-Pd-0.1CNT foamy nanocatalyst with specific surface area of 611.3 m²/g was produced by electroless deposition of nickel, palladium and multiwall carbon nanotube (MWCNT) on interim polyurethane substrate. Application of temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) data into Kissinger (Redhead) kinetic model showed lessening of their activation energies due to Pd and CNT addition. Presence of foamy Ni/SiC caused 8% higher steam reforming of methane; while Ni-Pd-0.1CNT presence resulted in 22% higher methane conversion. The catalytic behavior of the samples was described by morphological and compositional studies which were carried out by transmission electron microscope (TEM), field emission scanning electron microscope (FESEM) equipped with energy dispersive spectroscopy (EDS) and atomic absorption spectrometer (AAS) pondered with Brunauer–Emmett–Teller (BET), TPR, TPO and X-ray diffraction (XRD).     

Life cycle assessment of hydrogen production by methane decomposition using carbonaceous catalysts

Methane decomposition to yield hydrogen and carbon (CH₄ ? 2H₂ + C) is one of the cleanest alternatives, free of CO₂ emissions, for producing hydrogen from fossil fuels. This reaction can be catalyzed by metals, although they suffer a fast deactivation process, or by carbonaceous materials, which present the advantage of producing the catalyst from the carbon obtained in the reaction. In this work, the environmental performance of methane decomposition catalyzed by carbonaceous catalysts has been evaluated through Life Cycle Assessment tools, comparing it to other decomposition processes and steam methane reforming coupled to carbon capture systems. The results obtained showed that the decomposition using the autogenerated carbonaceous as catalyst is the best option when reaction conversions higher than 65% are attained. These were confirmed by 2015 and 2030 forecastings. Moreover, its environmental performance is highly increased when the produced carbon is used in other commercial applications. Thus, for a methane conversion of 70%, the application of 50% of the produced carbon would lead to a virtually zero-emissions process.     

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.     

Preparation of Ni-based egg-shell-type catalyst on cylinder-shaped alumina pellets and its application for hydrogen production via steam methane reforming

Nickel-based ‘egg-shell-type’ catalysts were prepared using cylinder-shaped alumina pellets as supports. In the egg-shell-type catalysts, nickel was selectively located in the outer region of the alumina pellets. Ethylene glycol or 1-octanol were used as hydrophobic solvents to retard internal penetration of the alumina pellets by the nickel nitrate solution. Without hydrophobic solvent, a ‘homo-type’ catalyst with even nickel distribution inside the alumina pellets was achieved. Cross-sectional images and SEM-EDS analysis of the cylinder-shaped alumina pellets showed that nickel concentration in the egg-shell-type catalyst was higher in the outer region and decreased towards the inner region of the alumina pellets. The egg-shell-type nickel distribution was maintained after subsequent magnesium impregnation and calcination processes. X-ray diffraction patterns and temperature programmed reduction profiles showed that the only difference between homo-type and egg-shell type catalysts, when their nickel loading was the same, was the nickel distribution inside pellets; and this was shown to cause significant difference in their catalytic activity in the steam methane reforming (SMR) reaction. For the homo-type catalyst, nickel loading of 3.5 wt% was insufficient for the SMR reaction, as metallic nickel particles were evenly distributed through the entire alumina pellet. However, nickel loading of 3.5 wt% was sufficient for the egg-shell-type catalyst, because active sites with metallic nickel particles were concentrated in the outer region of the pellets. These experimental results confirmed that the egg-shell-type nickel distribution is a favorable design for an SMR reaction catalyst.     

Sustainability assessment of hydrogen production by steam reforming

A specific methodology was applied to investigate the expected impact on sustainability of processes for hydrogen production by steam reforming of natural gas. Reference process schemes based on the current industrial state-of-the-art and on innovative steam reforming technologies were defined and assessed. The methodology allowed the calculation of a sustainability “fingerprint” of the reference schemes, based on sustainability key performance indicators. The results obtained evidenced the potential advantages of innovative processes, based on integrated conversion and internal membrane separation reactors. However, the valorization of the by-product streams is an essential requirement to reduce the impact on sustainability of these processes. Besides the improvement of the reaction section, the optimization of the overall separation efficiency and of energy requirement emerged as the key elements that control the overall sustainability performance of these processes.     

Integrating safety and economics in designing a steam methane reforming process

The recent explosion at a steam reforming facility producing hydrogen in California, U.S., suggests the need to revisit the design of the traditional steam methane reforming (SMR) process from a safety perspective to further enable the growth of the hydrogen economy. Specifically, it is important to analyze the interaction between process, economic and safety variables within the SMR process through an integrated model approach to maintain positive economics of hydrogen production while making the process safer. The integrated model described within this study consists of process synthesis, quantitative risk assessment and economic analysis sub-models facilitating a holistic design for the SMR process. The usefulness of the integrated model is demonstrated by evaluating alternatives based on the inherently safer design philosophy. For the considered base design, it was found that decreasing the pressure of purge gas exiting the purge gas compressor leads to a reduction in the jet-fire axial risk distance of purge gas with minor economic benefits. Also, increasing the temperature of syngas entering the condensation unit leads to a reduction in the jet-fire axial risk distance for both purge gas and syngas with slight decrease in process economics.     

Controllability study of an ethanol steam reforming process for hydrogen production

A system for ethanol steam reforming and purification of carbon monoxide (CO) designed to feed a PEM fuel cell has been modelled. From the model, we study the sensitivity and controllability emphasizing the study of the influence of the temperature on the output variables of interest. The results of the study of controllability are used for the identification of the best control structures.     

Efficient operation of autothermal microchannel reactors for the production of hydrogen by steam methane reforming

Efficient conversion of methane to hydrogen has emerged as a significant challenge to realizing fuel cell-based energy systems. Autothermal microchannel reactors, coupling of exothermic and endothermic reactions in parallel channels, have become one of the most promising technologies in the field of hydrogen production. Such reactors were utilized as an intensified design for conducting the endothermic steam methane reforming reaction. The energy required by the endothermic process is supplied directly through the separating plates of the reactor structure from the exothermic process occurring on the opposing side. Optimal design problems associated with transport phenomena in such an autothermal system were analyzed. Various methods for designing and operating autothermal reactors employed in steam methane reforming were discussed. Computational fluid dynamics simulations were performed to identify the underlying principles of process intensification, and to delineate several design and operational features of the intensified reforming process. The results indicated that the autothermal reactor is preferable to be thermally conductive to ensure its structural integrity and maximum operating regime. However, the thermal properties of the reactor structure are not essential due to efficient heat transfer existing between endothermic and exothermic process streams. A reactor design which minimizes the mass transfer resistance is highly required, and the channel dimension is of critical importance. Furthermore, the challenges presented by the efficient operation of the autothermal system were identified, along with demonstrating the implementation of transport management in order to improve overall reactor performance and to mitigate extreme temperature excursions.     

Application of aspen plus to renewable hydrogen production from glycerol by steam reforming

Steam reforming is the most favored method for the production of hydrogen. Hydrogen is mostly manufactured by using steam reforming of natural gas. Due to the negative environmental impact and energy politics, alternative hydrogen production methods are being explored. Glycerol is one of the bio-based alternative feedstock for hydrogen production. This study is aimed to simulate hydrogen production from glycerol by using Aspen Plus. First of all, the convenient reactor type was determined. RPlug reactor exhibited the highest performance for the hydrogen production. A thermodynamic model was determined according to the formation of byproduct. The reaction temperature, water/glycerol molar feed ratio as reaction parameters and reactor pressure were investigated on the conversion of glycerol and yield of hydrogen. Optimum reaction parameters are determined as 500 °C of reaction temperature, 9:1 of water to glycerol ratio and 1 atm of pressure. Reactor design was also examined. Optimum reactor diameter and reactor length values were determined as 5 m and 50 m, respectively. Hydrogen purification was studied and 99.9% purity of H₂was obtained at 25 bar and 40 °C. The obtained results were shown that Aspen Plus has been successfully applied to investigate the effects of reaction parameters and reactor sizing for hydrogen production from glycerol steam reforming.     

Hydrogen production by steam reforming of methane over nickel based structured catalysts supported on calcium aluminate modified SiC

Steam reforming of methane (SRM) is an immensely important process for the production of hydrogen and syngas (H₂, CO). Ni-based alumina supported catalysts are conventionally used in the SRM process, but the coke formation and sintering are still challenging problems to develop an economical process. It was reported that the Lewis basicity of the support obviously plays a crucial role to prevent the coke formation, and basic supports such as calcium aluminate (CA_x) has shown superior resistance for carbon deposition, but in case of CA_x the major drawback is low thermal conductivity.In this work, in order to improve the catalytic performance of SRM, the Nickel based structured catalysts supported on the modified calcium aluminate (CA_x) with silicon carbide (SiC) were prepared. All synthesized catalysts were characterized by various techniques including N₂-physisorption, XRD, H₂-TPR, XPS, CO₂-TPR, TGA, TPH, and thermal conductivity analysis. It was found that the CA_x play an important role obtaining higher hydrogen yield and improved resistance to the carbon deposition. Even though, the methane conversion and H₂ yield efficiency for Ni supported on SiC modified CA_x/Al₂O₃ (NASC) catalyst was slightly lower than NAS and NAC catalysts, which caused by the weak interaction of active metal, but the NASC catalyst showed superior resistance to the coke formation compared to other catalysts. It was concluded that NASC catalysts is a promising candidates for the production of hydrogen by the steam reforming of methane.     

Continuous high-purity hydrogen production by sorption enhanced steam reforming of ethanol over modified lithium silicate

Sorption-enhanced steam reforming of ethanol (SE-SRE) with in-situ CO₂ removal is an environmentally friendly and sustainable approach for hydrogen production. Researches on continuous production of high-purity H₂ by SE-SRE over the modified Li₄SiO₄ sorbent were conducted using two parallel reactor in this work. The low cost Li₄SiO₄ derived from rice husk ash (RHA) is a promising high-temperature CO₂ sorbent. However, the poor adsorption kinetics of RHA-Li₄SiO₄ sorbent at low CO₂ concentration is the major challenge. The metallic elements (K, Ca, Al, Mg) were employed to modify the RHA-Li₄SiO₄ for efficient CO₂ capture. The developed sorbents were characterized and tested to study the role of dopants on the crystal, textural, microstructure and CO₂ adsorption kinetics and cyclic stability. Results indicated that K doping effectively inhibited the growth of crystal aggregation and resulted in a fluffy morphology with abundant pores and higher specific surface area, while the addition of Ca, Al and Mg formed a nubby structure with larger particle size. K-doped RHA-Li₄SiO₄ exhibited the best CO₂ uptake properties and the optimal K doping molar content was 0.02 with the maximum capture capacity of 34.16 wt%, which is higher than 27.1 wt% of pure RHA-Li₄SiO₄. Then, the effect of operating conditions on the enhancement behaviors was considered in the SE-SRE system. High-purity H₂ (above 96%) was achieved by coupling K(0.02)/RHA-Li₄SiO₄ sorbent with Ni-based catalyst under the optimum condition (T: 525 °C, liquid hourly space velocity: 0.9 mL/(g·h), sorbent/catalyst: 4 and steam/carbon: 8.0). The adsorption activity of K(0.02)/RHA-Li₄SiO₄ maintained at a high level in ten SE-SRE/regeneration cycles. Finally, a scheme including two parallel fixed-bed reactors was designed and operated periodically for continuous production of high-purity H₂. The reaction switching time was shown to depend strongly on the pre-breakthrough time and operating conditions. As the reaction switching time was 40 min, the products were always only H₂ and CH₄ (no CO and CO₂ appear) and the H₂ purity remained above 90% during 400 min, confirming high purity hydrogen stream can be obtained continuously.     

Underwater vehicle hydrogen production from methanol steam reforming using hydrogen peroxide

Methanol steam reforming (MSR) can supply hydrogen (H₂) to underwater vehicles equipped with a fuel cell. Low reaction temperatures ensure the composition of the reformed gas suitable for the H₂ purification unit and increase the design freedom of a reforming plant. However, such temperatures decrease the catalyst activity and thereby the methanol (MeOH) conversion and H₂ production. Herein, hydrogen peroxide (H₂O₂) was supplied with MeOH and water (H₂O) to ensure sufficient MeOH conversion and H₂ production at low temperatures. A tube reactor loaded with a commercial Cu/Zn catalyst was installed in an electric furnace maintained at 200–250 °C, and MeOH and 0 wt%, 11.88 wt%, 22.51 wt%, and 32.07 wt% H₂O₂ were supplied. When the furnace temperature was 200 °C, the MeOH conversion was 49.3% at 0 wt% H₂O₂ but 93.5% at 32.07 wt% H₂O₂. The effect of adding H₂O₂ was greater under the temperature conditions where the MeOH conversion was 100% or less. To analyze the effect of H₂O₂ addition on catalyst durability, the furnace was maintained at 200 °C, and the reactor was continuously operated for 110 h with 0 wt% and 32.07 wt% H₂O₂. The addition of H₂O₂ did not significantly decrease the Cu/Zn catalyst durability.     

Millisecond methane steam reforming for hydrogen production: A computational fluid dynamics study

The potential of methane steam reforming to produce hydrogen in thermally integrated micro-chemical systems at short contact times was theoretically explored. Methane steam reforming coupled with methane catalytic combustion in microchannel reactors for hydrogen production was studied numerically. A two-dimensional computational fluid dynamics model with detailed chemistry and transport was developed. To provide guidelines for optimal design, reactor behavior was studied, and the effect of design parameters such as catalyst loading, channel height, and flow arrangement was evaluated. To understand how steam reforming can happen at millisecond contact times, the relevant process time scales were analyzed, and a heat and mass transfer analysis was performed. The importance of energy management was also discussed in order to obtain a better understanding of the mechanism responsible for efficient heat exchange between highly exothermic and endothermic reactions. The results demonstrated the feasibility of the design of millisecond reforming systems, but only under certain conditions. To achieve this goal, process intensification through miniaturization and the improvement in catalyst performance is very important, but not sufficient; very careful design and implementation of the system is also necessary to enable high thermal integration. The channel height plays an important role in determining the efficiency of heat exchange. A proper balance of the flow rates of the combustible and reforming streams is an important design criterion. Reactor performance is significantly affected by flow arrangement, and co-current operation is recommended to achieve a good energy balance within the system. The catalyst loading must be carefully designed to avoid insufficient reactant conversion or hot spots. Finally, operating windows were identified, and engineering maps for designing devices with desired power were constructed.