共查询到20条相似文献,搜索用时 15 毫秒
1.
Kantilal Chouhan Shishir Sinha Shashi Kumar Surendra Kumar 《International Journal of Hydrogen Energy》2021,46(53):26809-26824
The paper aims to investigate the steam reforming of biogas in an industrial-scale reformer for hydrogen production. A non-isothermal one dimensional reactor model has been constituted by using mass, momentum and energy balances. The model equations have been solved using MATLAB software. The developed model has been validated with the available modeling studies on industrial steam reforming of methane as well as with the those on lab-scale steam reforming of biogas. It demonstrates excellent agreement with them. Effect of change in biogas compositions on the performance of industrial steam reformer has been investigated in terms of methane conversion, yields of hydrogen and carbon monoxide, product gas compositions, reactor temperature and total pressure. For this, compositions of biogas (CH4/CO2 = 40/60 to 80/20), S/C ratio, reformer feed temperature and heat flux have been varied. Preferable feed conditions to the reformer are total molar feed rate of 21 kmol/h, steam to methane ratio of 4.0, temperature of 973 K and pressure of 25 bar. Under these conditions, industrial reformer fed with biogas, provides methane conversion (93.08–85.65%) and hydrogen yield (1.02–2.28), that are close to thermodynamic equilibrium condition. 相似文献
2.
《International Journal of Hydrogen Energy》2019,44(21):10415-10426
The main goal of this research is the modeling and optimization of an industrial hydrogen unit in a domestic oil refinery at steady state condition. The considered process consists of steam methane reforming furnace, low and high temperature shift converters, CO2 absorption column and methanation reactor. In the first step, the reactors are heterogeneously modeled based on the mass and energy balance equations considering heat and mass transfer resistances in the gas and catalyst phases. The CO2 absorption column is simulated based on the equilibrium non-ideal approach. In the second step, a single objective optimization problem is formulated to maximize hydrogen production in the plant considering operating and economic constraints. The feed temperature, firebox temperature, and steam flow rate in the reformer, feed temperature in shift converters, lean amine flow rate in the absorption column, and feed temperature in the methanator are selected as decision variables. The calculated effectiveness factors and mass transfer coefficients prove that the methane reforming is inertia-particle mass transfer control, while shift and methanation reactions are surface reaction control. The simulation results show that applying the optimal condition on the system increases hydrogen production capacity from 85.93 to 105.5 mol s−1. 相似文献
3.
Celso Eduardo Tuna José Luz Silveira Márcio Evaristo da Silva Ronney Mancebo Boloy Lúcia Bolini Braga Nestor Proenza Pérez 《International Journal of Hydrogen Energy》2018,43(4):2108-2120
This work aims to investigate a biogas steam reforming prototype performance for hydrogen production by mass spectrometry and gas chromatography analyses of catalysts and products of the reform. It was found that 7.4% Ni/NiAl2O4/γ-Al2O3 with aluminate layer and 3.1% Ru/γ-Al2O3 were effective as catalysts, given that they showed high CH4 conversion, CO and H2 selectivity, resistance to carbon deposition, and low activity loss. The effect of CH4:CO2 ratio revealed that both catalysts have the same behavior. An increase in CO2 concentration resulted in a decrease in H2/CO ratio from 2.9 to 2.4 for the Ni catalyst at 850 °C, and from 3 to 2.4 for the Ru catalyst at 700 °C. In conclusion, optimal performance has been achieved in a CH4:CO2 ratio of 1.5:1. H2 yield was 60% for both catalysts at their respective operating temperature. Prototype dimensions and catalysts preparation and characterization are also presented. 相似文献
4.
《International Journal of Hydrogen Energy》2020,45(51):26637-26654
The potential of methanol reforming systems to greatly improve productivity in chemical reactors has been limited, due in part, to the effect of mass transfer limitations on the production of hydrogen. There is a need to determine whether or not a microchannel reforming reactor system is operated in a mass transfer-controlled regime, and provide the necessary criteria so that mass transfer limitations can be effectively eliminated in the reactor. Three-dimensional numerical simulations were carried out using computational fluid dynamics to investigate the essential characteristics of mass transport processes in a microchannel reforming reactor and to develop criteria for determining mass transfer limitations. The reactor was designed for thermochemically producing hydrogen from methanol by steam reforming. The mass transfer effects involved in the reforming process were evaluated, and the role of various design parameters was determined for the thermally integrated reactor. In order to simplify the mathematics of mass transport phenomena, use was made of dimensionless numbers or ratios of parameters that numerically describe the physical properties in the reactor without units. The results indicated that the performance of the reactor can be greatly improved by means of proper design of catalyst layer thickness and through adjusting feed composition to minimize or reduce mass transfer limitations in the reactor. There is not an effective method to reduce channel dimensions if the flow rate remains constant, or to reduce fluid velocities if the residence time is kept constant. The rate of the reforming reaction is limited by mass transfer near the entrance of the reactor and by kinetics further downstream, when the heat transfer in the autothermal system is efficient. Finally, the criteria that can be used to distinguish between different mass transport and kinetics regimes in the reactor with a first-order reforming reaction were presented. 相似文献
5.
Seyyed Mohammad Jokar Payam Parvasi Angelo Basile 《International Journal of Hydrogen Energy》2018,43(32):15321-15329
In this work, the performance of an industrial dense PdAg membrane reformer for hydrogen production with methane mixed reforming reaction was evaluated. The rate parameters of mixed reforming reaction on a Ni based catalyst optimized by using the experimental results. One-dimensional models have been considered to model the steam reforming industrial membrane reformer (SRIMR) and mixed reforming industrial membrane reformer (MRIMR). The models are validated by experimental data.The proficiency of MRIMR and SRIMR at similar conditions used as a basis of comparison in terms of temperature, methane conversion, hydrogen yield, syngas production rate and CO2 flow rate. Results revealed that the methane conversion, hydrogen yield and syngas production rate in MRIMR is considerably higher than SRIMR. Furthermore, the operation temperature of MRIMR could be 195 °C lower than that for SRIMR. This would contribute to a major decrease in process costs as well as a reduction in catalyst sintering. On the other hand, although MRIMR consumes CO2, the exited CO2 flow rate at the SRIMR is three times more than that of at the MRIMR, which is a main advantage of MRIMR from the environmental issues point of view. 相似文献
6.
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. 相似文献
7.
Junjie Chen Xuhui Gao Longfei Yan Deguang Xu 《International Journal of Hydrogen Energy》2018,43(29):12948-12969
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. 相似文献
8.
《International Journal of Hydrogen Energy》2022,47(37):16375-16397
Many attempts have been made to improve mass transfer by reducing the size of reactors. However, such reduction will fairly quickly reach practical limitations and numerous difficulties still remain. Catalytic washcoat shape and properties may be critical design factors, but the mechanisms for their effects on mass transfer characteristics are still not fully understood. To effectively eliminate problems associated with mass transport phenomena in microstructured steam-methanol reformers, the effects of washcoat shape and properties were investigated in various situations by performing computational fluid dynamics simulations. The dependence of the solution on mass transfer characteristics was reduced to a small number of dimensionless parameters. A dimensionless mass transfer analysis was carried out in terms of the Sherwood, Schmidt, and pore Reynolds numbers. The results indicated that the rate of mass transfer is predominantly controlled by washcoat properties, and porosity and effective thermal conductivity are fundamentally important. The rate of the reforming reaction is typically controlled by kinetics at a temperature of 480 K and limited by mass transfer at a temperature of 580 K. The shape of washcoats affects the overall mass transfer characteristics, depending on the structural and thermal properties of washcoats. The shape effect is limited by heat transfer. A three-fold increase in effectiveness factor can be achieved by increasing the effective thermal conductivity of the washcoat. Design recommendations were finally made to improve transport characteristics for the systems. 相似文献
9.
《International Journal of Hydrogen Energy》2020,45(4):2527-2545
Three-dimensional numerical simulations were performed to address the thermal management issues associated with the design of a methanol reforming microchannel reactor for the portable production of hydrogen. The design of the reactor was fundamentally related to the direct coupling of reforming and combustion reactions by performing them on opposite sides of dividing walls in a parallel flow configuration. Effective autothermal operation was achieved through a combination of microchannel reactor technology with heat exchange in a direction perpendicular to the reacting fluid flow. Computational fluid dynamics simulations and thermodynamic analysis were carried out to investigate the effect of various design parameters on the characteristics of the generation, consumption, and exchange of thermal energy within the system. The results indicated that the ability to control temperature and temperature uniformity is of great importance to the performance of the system. The degree of temperature uniformity favorably affects the autothermal operation of the reactor. Temperature uniformity of the reactor can be improved by controlling the rate of heat transfer through a variety of factors such as wall thermal conductivity, fluid velocities, and dimensions. High wall thermal conductivity would be greatly beneficial to the performance of the system and the temperature uniformity of the reactor. 相似文献
10.
Junjie Chen Longfei Yan Wenya Song Deguang Xu 《International Journal of Hydrogen Energy》2018,43(31):14710-14728
This paper addresses the issues related to the design and operation of steam reforming combined with catalytic combustion in thermally integrated microchannel reactors for hydrogen production. Comparisons were made between methanol and methane steam reforming, representing a low and a high temperature process respectively, under the same operating conditions to determine whether methanol-based thermally integrated systems can be more energy-efficient than methane-based ones. Computational fluid dynamics simulations were performed to gain insight into the reactor performance and thermal behavior. The effect of various design parameters was investigated to identify suitable ranges of operating conditions, and an analysis of heat and mass transfer was performed to design a highly efficient system. It was shown that steam reforming of both fuels is feasible in millisecond reactors under a variety of conditions, but very careful design is necessary. Methanol reforming can be more efficient, offering a better solution not only to simplify design but also to improve power and efficiency. The wall thermal conductivity is essential to the design and optimization of these systems, as it can significantly affect the overall energy balance. There is no significant difference in reactor performance between different channel heights at the same flow rate. The ratio of the flow rates on opposite sides of the reactor is an important design parameter and must be carefully adjusted to improve efficiency and eliminate hot spots. Finally, a simple operating strategy was proposed to achieve variable power output, and design recommendations were made. 相似文献
11.
《International Journal of Hydrogen Energy》2014,39(35):20266-20275
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 (Ncc) 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 Ncc increases with rising reformer temperature. 相似文献
12.
《International Journal of Hydrogen Energy》2019,44(23):11546-11563
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. 相似文献
13.
《International Journal of Hydrogen Energy》2020,45(20):11438-11448
This work presents the characteristics of catalytic dimethyl ether (DME)/steam reforming based on a Cu–Zn/γ-Al2O3 catalyst for hydrogen production. A kinetic model for a reformer that operates at low temperature (200 °C–500 °C) is simulated using COMSOL 5.2 software. Experimental verification is performed to examine the critical parameters for the reforming process. During the experiment, superior Cu–Zn/γ-Al2O3catalysts are manufactured using the sol-gel method, and ceramic honeycombs coated with this catalyst (1.77 g on each honeycomb, five honeycombs in the reactor) are utilized as catalyst bed in the reformer to enhance performance. The steam, DME mass ratio is stabilized at 3:1 using a mass flow controller (MFC) and a generator. The hydrogen production rate can be significantly affected depending on the reactant's mass flow rate and temperature. And the maximum hydrogen yield can reach 90% at 400 °C. Maximum 8% error for the hydrogen yield is achieved between modeling and experimental results. These experiments can be further explored for directly feeding hydrogen to proton exchange membrane fuel cell (PEMFC) under the load variations. 相似文献
14.
《International Journal of Hydrogen Energy》2019,44(3):1973-1987
The three-dimensional computational fluid dynamics (CFD) model was used in a sleeve-type steam methane reforming (SMR) reactor for H2 production of 2.5 Nm3/h from natural gas. The feed and combustion gases acted as a counter-current heat exchange owing to a narrow sleeve equipped between the combustor and catalyst-bed. The CFD results were validated against the experimental data of the SMR reactor with a sleeve gap size of 3 mm. The effect of the sleeve gap size and the flame shape on process performances such as H2 production rate, thermal efficiency, and uniformity of catalyst-bed temperature was investigated using the CFD model. The sleeve gap size influenced the gas velocity inside the sleeve gap and the convective heat transfer. The SMR reactor with a sleeve gap size of 7 mm showed the highest H2 production rate and thermal efficiency when comparing six sleeve gap sizes ranging from 2 to 10 mm. A new flame shape for the SMR reactor with the sleeve gap size of 7 mm was proposed to improve the process performances. 相似文献
15.
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. 相似文献
16.
The heat and mass transfer characteristics in a steam reformer are investigated via experimental and numerical approaches and a new configuration of packed catalysts is proposed for effective hydrogen production. Prior to the numerical investigation, parametric studies are carried for the furnace temperature, steam-to-carbon (S:C) ratio, and gas flow rate. After validation of the developed code, numerical work is undertaken to determine the relationship of the operating parameters. Based on the experimental and numerical results, and with the goal of obtaining optimum heat transfer characteristics and an efficient catalyst array, a new configuration for the packed bed is proposed and numerically investigated taking into account the endothermicity of the steam reforming reaction. A bed packed repeatedly with inert and active catalysts is found to be an efficient means to obtain the same, or better, hydrogen production with small amounts of the active catalysts compared with a typical steam reformer. 相似文献
17.
Abdelhakim Settar Rachid Nebbali Brahim Madani Saïd Abboudi 《International Journal of Hydrogen Energy》2017,42(2):1490-1498
This paper deals with a numerical study on the steam methane reforming reaction performances into a wall-coated steam methane reformer (WC-SMR), intended to produce hydrogen. In this work a new catalytic pattern, purporting to enhance the WC-SMR efficiency, is proposed. A comparison study is made between the new inter-catalytic layers pattern and a conventional one with a continuous catalytic layer pattern. Both WC-SMR models operate at similar conditions and at the same design parameters, except the catalytic zone length which is monitored by taking into account the inter-catalytic layers spacing or not. Our results show that, by adopting a catalytic surface with an inter-catalytic spacing, the methane conversion could be enhanced and thus the hydrogen production is intensified. 相似文献
18.
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. 相似文献
19.
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. 相似文献
20.
《International Journal of Hydrogen Energy》2020,45(58):32884-32898
Shanghai is one of the fastest growing regions of hydrogen energy in China. This paper researched feasible hydrogen sources in both internal and external Shanghai. This study comes up 9 hydrogen production methods and 6 transportation routes, ultimately forms 12 hydrogen supply solutions according to local conditions. The total cost in each solution is estimated including processes of hydrogen production, treatments, storage and transportation based on different transport distance. The results indicate that hydrogen supply cost is above 50 CNY/kgH2 for external hydrogen sources after long-distance transportation to Shanghai, such as hydrogen production from coal in Inner Mongolia and from renewables in Hebei. The total cost of on-site hydrogen production from natural gas can be controlled under 40 CNY/kgH2. When the price of wind power reduces to 0.5 CNY/kWh, hydrogen production from offshore wind power cooperating with hydrogen pipeline network has the greatest development potential for Shanghai hydrogen supply. 相似文献