Sorption-enhanced Steam Methane Reforming Process Research Articles

Computational particle fluid dynamics 3D simulation of the sorption-enhanced steam methane reforming process in a dual fluidized bed of bifunctional sorbent-catalyst particles

Sorption enhanced steam methane reforming (SE-SMR) is an efficient hydrogen production technology that combines steam methane reforming with CO2 capture. Reactions are shifted over their thermodynamic limits and hydrogen yield is enhanced, in more favorable thermodynamic conditions. Bifunctional sorbent-catalyst particles have been developed to assure stability over multiple cycles and to make the endothermic methane reforming and the exothermic CO2 capture completely integrated. Moreover, handling one granular material simplifies system management, reduces bed inventory and avoids the problem of segregation in case of two separated materials. The continuous and simultaneous operation of the process in a dual fluidized bed reactor (DFB), which combines a reformer and a calciner, for sorbent regeneration through high temperature calcination, increases productivity and allows a greater optimization.Aim of this work is the 3D simulation of the SE-SMR process in a DFB reactor, by the Computational Particle Fluid Dynamics (CPFD) method of the Barracuda VR® software. The simulation results in terms of solid flow, pressure balance and particles segregation are reported. A post-processing routine has been written to characterize bubbles in the two fluidized beds. The effects of bed inventory, superficial velocity and steam to methane ratio on hydrogen purity and methane conversion are discussed in the paper.

Sorption enhanced steam methane reforming in a bubbling fluidized bed reactor: Simulation and analysis by the CPFD method

This work reports the modelling and simulation results of a bubbling fluidized bed reactor using the Computational Particle Fluid Dynamics (CPFD) method of the Barracuda® software. The reactor under investigation is the carbonator installed in the ENEA ZECOMIX research infrastructure, where Steam Methane Reforming (SMR) happens simultaneous with CO2 capture via solid sorbents. In this intensified process, namely Sorption Enhanced Steam Methane Reforming (SE-SMR), steam methane reforming is coupled with high temperature CO2 sorption and calcium looping (CaL) process, in order to increase the H2 yield, beyond thermodynamic limits. Currently, the reactor is operated in batch mode and is used also for sorbent regeneration, by switching the fluidizing gas flow from steam/methane to oxy-burner combustion products. With the aim of studying the process when it is operated as a closed loop, in this paper the reactor is continuously fed by a fresh sorbent flow and a riser/calciner reactor for sorbent regeneration, to be connected with the carbonator, has been sized. The continuous circulation of solid material between the two reactors ensures the maintenance of different operating temperatures and therefore greater operational optimization.The numerical analysis presented in this paper will serve as a valid support for the experimental activities. For this purpose, a sensitivity study on the SE-SMR process has been conducted, by varying the main operating conditions (e.g. sorbent conversion, sorbent/catalyst ratio, fluidizing gas flow), to evaluate the hydrogen purity yield. Two different kinetic mechanisms have been compared for the gas phase reactions. A post-processing routine has been written, in order to analyze bubbles sizes and velocities inside the fluidized environment. The effect of sorbent and catalyst particles segregation has been also investigated. The same modelling approach has been used for the sizing of the fast riser calciner reactor.

Modelling and design of a novel calcination reactor integrated with a CO2 capture process for intensified hydrogen production

Sorption enhanced steam methane reforming (SE-SMR) is an advantageous process for the production of H2 and simultaneous CO2 capture with solid sorbents. Aiming at implementing a continuous SE-SMR process, it is necessary to foresee a regeneration step of the sorbent via its calcination, to make it available for further CO2 capture in the reforming reactor. This work focused on the design of a calcination reactor for the regeneration of a dolomite sorbent to couple with a methane reformer/carbonation reactor. Calcium carbonate (CaCO3) calcination in CO2 atmosphere was studied via thermo-gravimetric analysis (TGA) using naturally occurring dolomite, and kinetic parameters were extrapolated (pre-exponential factor Aapp = 6.28 E+25 s−1 and activation energy Eapp = 6.41 E+5 J/mol). A preliminary design of the calciner was defined and its performance was investigated with Computational Particle-Fluid Dynamics (CPFD) simulations. A first preliminary Geometry 1 showed some limitations in the CaCO3 conversion, due to insufficient particle residence time. An optimized Geometry 2 was developed with an internal tube (jacket tube) acting as obstacle for increasing the average residence time of the particles. A further simulation of this new geometry showed higher residence time and increased conversion rate of approximately 95% after 220 s of simulation.

Mechanism insights into sorption enhanced methane steam reforming using Ni-doped CaO for H2 production by DFT study

Sorption Enhanced Steam Methane Reforming (SESMR) provides a promising method to produce high purity hydrogen by in-situ CO2 capture. Ni-doped CaO (Ni-CaO) with catalytic and adsorption active sites can effectively improve the hydrogen production in the SESMR process. It is difficult to determine the enhancement mechanism of Ni-CaO in the SESMR simply by the research experiment. In this study, the reaction mechanisms of SESMR promoted by Ni in the presence of CaO were investigated by the density functional theory (DFT) calculations. The reaction pathway was determined by analyzing the activation barriers along the possible reaction pathways in the SESMR reaction. The SESMR reaction promoted by CaO was also studied as a comparison to clarify the catalysis of Ni. The reaction mechanism of SESMR on Ni and Ni-CaO surfaces was also compared. The results show that the SESMR reaction is more prone to follow path CH4 → CH3 → CH2 → CH → CHO → HCOO → CO2. The OH-assisted dissociation assists in the breaking of first C–H bond in CH4. Process CH3 → CH2 → CH is accomplished by direct dissociation in two steps. Next, CHO is spontaneously formed from CH and O. CHO is oxidized to generate HCOO. Finally, the CO2 is formed by the HCOO dehydrogenation path. The presence of Ni atoms causes a change in the reaction rate limiting step of the SESMR reaction from CH dissociation (on CaO surface) to CH3 dissociation (on Ni-CaO surface). Compared with the reaction energy barrier of CH dissociation (3.215 eV), the SESMR reaction of the Ni-CaO surface is easier to occur with lower reaction energy barrier of 2.030 eV. Besides, Ni reduces the adsorption energy of CH4 (-0.106 eV) and H2O (-1.32 eV) as well as increases the adsorption energy of H2 (-0.047 eV). The SMR reaction is easier to occur on the Ni surface than Ni-CaO surface. The DFT calculations determine the possible mechanism of Ni-CaO in SESMR for H2 production.

Sustainable hydrogen manufacturing via renewable-integrated intensified process for refueling stations

The widescale consumer adoption of hydrogen fuel cell electric vehicles (HFCEVs) is currently hindered by the high cost of small-scale hydrogen generation and the lack of extensive hydrogen refueling infrastructure. Natural gas-based hydrogen is cheaper when produced in large volumes but is also associated with high CO2 emissions. To counter these challenges, we propose a hybrid approach where both natural gas and renewables are integrated in a synergistic manner using a dynamic process intensification technology that can be deployed on-site for meeting local demands of refueling stations. The technology is based on sorption enhanced steam methane reforming (SE-SMR) that utilizes a combination of reaction with in-situCO2 adsorption for enhancing process modularity, productivity and efficiency thereby outperforming conventional SMR at small scale. We develop a mixed integer linear programming (MILP)-based optimization framework for simultaneous design and scheduling of the SE-SMR process. The simultaneous optimization provides a synergistic combination whereby the renewables allow sustainable hydrogen manufacturing and the dynamic SE-SMR allows optimal use of the intermittency of the renewables. The U.S. nationwide analysis indicates that for futuristic renewable prices and a hydrogen production capacity of 2 ton/day, hydrogen can be produced at 50% less cost compared to the current cost of small-scale hydrogen generation. The city-wise analysis with varying hydrogen demand shows that even with just 5% HFCEV market penetration level, hydrogen production cost less than $3/kg can be obtained at small scales across the United States with even cheaper hydrogen for large cities.

A solar thermal sorption-enhanced steam methane reforming (SE-SMR) approach and its performance assessment

This paper proposes an integration of concentrating solar power (CSP) with a sorption-enhanced steam methane reforming (SE-SMR) process and assesses its overall solar-to-fuel conversion performance. A thermodynamic treatment of the SE-SMR process for H2 production is presented and evaluated in an innovative two reactors system configuration using CSP as a heat input. Four metal carbonate/metal oxide pairs are considered, and the equilibrium thermodynamics reveals that CaCO3/CaO pair is the most suitable candidate for this process. Additionally, a reactor-scale thermodynamic model is developed to determine the optimum operating conditions for the process. For the carbonation step, temperatures between 700 and 900 K and steam-to-methane ratio ≥4 are found to be the most favorable. Furthermore, an advanced process model, which utilizes operating conditions determined from the reactor-scale model, is developed to evaluate the process efficiency. The model predicts that the proposed process can achieve a solar-to-fuel efficiency ∼41% for calcination temperature of 1500 K and carbonation temperature of 800 K, without considering any solid heat recovery. An additional 2.5% increase in the process efficiency is feasible with the consideration of the solid heat recovery. This study shows the thermodynamic feasibility of integrating the SE-SMR process with CSP technologies.

Sensitivity analysis and artificial neural network-based optimization for low-carbon H2 production via a sorption-enhanced steam methane reforming (SESMR) process integrated with separation process

In this study, a sensitivity analysis was performed for an integrated SESMR process, and an optimization approach was formulated by developing an artificial neural network-based optimization (ANN-based optimization). The process comprised a cyclic fluidized bed (CFB), pressure swing adsorption (PSA), compressor, dehydrator, and other units. The PSA variables considerably affected product quality, while the CFB variables mainly contributed to other performance parameters. From the data analysis and domain knowledge, three main objectives and five main variables were selected for the process optimization. Thereafter, the ANN models were integrated with the economic model to formulate a SESMR-driven model for optimization. At the optimum conditions, the cost (1.7 $/kg) of the H2 (+99.99% purity) with 90.3% CO2 capture from the integrated SESMR process was 15% reduction compared to that of the SMR process, which agreed well with the US Department of Energy prediction (15–20%). These results suggest that the integrated SESMR process is valuable for the production of blue H2, and the ANN-based optimization is very effective for a complex integrated process.

Performance of Na2CO3-CaO sorbent in sorption-enhanced steam methane reforming

The addition of alkali molten salts has been reported as a strategy to overcome the sintering problem presented by calcium oxide in CO2 capture systems. In this work, the influence of sodium doping in a CaO sorbent was investigated in the sorption enhanced steam methane reforming process (SE-SMR). The goal was to increase the stability of the sorbent and, consequently, the efficiency of the process. For that, a Na-containing sorbent was prepared using the precipitation technique and a pure calcium oxide was obtained by calcination of CaCO3. The sorbents were physically mixed with 10 % Ni/Al2O3 catalyst and tested in 10 cycles of SE-SMR at 600 °C and CH4:H2O equals to 4. In general, both materials showed 100 % of CH4 conversion and H2 molar fraction of 93.5 vol.%. However, regarding the stability over the SE-SMR cycles, it was evidenced that the addition of sodium decreased the duration of pre-breakthrough comparing with the non-doped material. The XRD, SEM, and TGA results allowed us to observe an inverse relationship of particle diameter and CO2 capture performance. Na2CO3-CaO presented a larger average crystallite size compared to the pure CaO which led to a higher probability of the CaCO3 layers to inactivate the calcium oxide and, consequently, caused a strong sintering effect. Besides the presence of sodium, the precipitation method and the synthesis conditions could have favored the low initial CO2 uptake and poor stability of the Na2CO3-CaO sorbent.

Modeling of sorption enhanced steam methane reforming in an adiabatic packed bed reactor using various CO2 sorbents

A 1-D heterogeneous model of sorption-enhanced steam methane reforming (SE-SMR) process in a packed bed reactor consisting of nickel catalyst well mixed with CO2 sorbent particles is investigated for three types of common sorbents. The performance of SE-SMR process is studied under low medium pressure conditions (3 – 11 bar) to find the optimum operating conditions. Optimal CaO sorption corresponding to 82% CH4 conversion and 85% H2 purity is found at 900 K, 3 bar, 3.5 kgm−2s−1 and S/C of 3.0. In contrast, lithium zirconate (LZC) and hydrotalcite (HTC) sorbents exhibited best sorptions under the operating conditions of 773 K, 5 bar and S/C of 3 with CH4 conversion of 91.3% and 55.2%, and H2 purity of 94.1% and 77.8% respectively. In these conditions, the CH4 conversion increased by 114%, 111% and 67% compared to the conventional SMR for the processes enhanced by HTC, LZC and CaO sorption respectively.

Dynamic model and performance of an integrated sorption-enhanced steam methane reforming process with separators for the simultaneous blue H2 production and CO2 capture

An integrated sorption-enhanced steam methane reforming (SESMR) process for simultaneous blue H2 production and CO2 capture is developed on the semi-central scale of ~ 48 ton H2/day. The developed SESMR process consists of a cyclic fluidized-bed (CFB) system, heating and pretreatment systems, CO2 capture system, a H2 pressure swing adsorption (PSA) system, compressors, and a combustor. To analyze the CFB system consisting of a bubbling fluidized-bed (BFB) reactor and fast fluidized-bed (FFB) regenerator, a dynamic model is formulated using the conservation equations combined with the Lagrange and Eulerian approaches and gas-velocity prediction. After a validation with reference, the developed CFB model is integrated with the dynamic model of the PSA and the algebraic equations for the other units to analyze the dynamic behavior and performance of the integrated SESMR process. The energy efficiency (82.2%) and H2 production cost of the SESMR process (12% reduction from that of the SMR process) are close to the prediction by the United States Department of Energy, let alone CO2 capture. According to the sensitivity analysis, the temperature of the BFB reactor is the most important factor because it considerably affects the production rate, product quality, CO2 capture, H2 cost, and energy efficiency. Since the CFB model has been shown to accurately predict the performance and reasonably explain the dynamic behaviors, it can be applied not only to the SESMR process but also to other CFB-related processes. The SESMR process contributes to the design, optimization, control, and decision-making processes relating to centralized or semi-central blue H2 production.

Prediction of sorption enhanced steam methane reforming products from machine learning based soft-sensor models

Carbon dioxide-abated hydrogen can be synthesised via various processes, one of which is sorption enhanced steam methane reforming (SE-SMR), which produces separated streams of high purity H2 and CO2. Properties of hydrogen and the sorbent material hinder the ability to rapidly upscale SE-SMR, therefore the use of artificial intelligence models is useful in order to assist scale up. Advantages of a data driven soft-sensor model over thermodynamic simulations, is the ability to obtain real time information dependent on actual process conditions. In this study, two soft sensor models have been developed and used to predict and estimate variables that would otherwise be difficult direct measured. Both artificial neural networks and the random forest models were developed as soft sensor prediction models. They were shown to provide good predictions for gas concentrations in the reformer and regenerator reactors of the SE-SMR process using temperature, pressure, steam to carbon ratio and sorbent to carbon ratio as input process features. Both models were very accurate with high R2 values, all above 98%. However, the random forest model was more precise in the predictions, with consistently higher R2 values and lower mean absolute error (0.002-0.014) compared to the neural network model (0.005-0.024).

Techno-economic analysis of low-carbon hydrogen production by sorption enhanced steam methane reforming (SE-SMR) processes

Hydrogen is an attractive energy carrier that will play a key role in future global energy transitions. This work investigates the techno-economic performance of six different sorption enhanced steam methane reforming (SE-SMR) configurations integrated with an indirect natural gas or biomass-fired calciner, oxy-fuel combustion and chemical-looping combustion for large-scale blue and carbon-negative hydrogen production. The techno-economic performance of the proposed cases was evaluated by their net efficiency, CO2 capture efficiency, levelised cost of hydrogen (LCOH), and costs of CO2 avoided and removal. A sensitivity analysis was also conducted to evaluate the key parameters and explore existing uncertainties that can affect the economic performance of the proposed SE-SMR processes. The results revealed that the proposed systems were comparable with conventional steam methane reforming (SMR) with carbon capture and storage (CCS). The LCOH of the proposed SE-SMR plants ranged from £1.90–2.80/kg, and the costs of CO2 avoided and removal ranged from £33-69/tonne and £58-107/tonne, respectively. By applying a carbon price (£16/tonne CO2), the costs of CO2 avoided and removal for the proposed SE-SMR processes could be significantly reduced. The results of cumulative discounted cash flow of SE-SMR plants at a hydrogen selling price of £3.00/kg indicated that all the investment of the proposed cases could be paid back after eight years, even if the carbon tax is zero.

Synthetic CaO-based sorbent for high-temperature CO2 capture in sorption-enhanced hydrogen production

Calcium precursor and surfactant addition on properties of synthetic alumina-containing CaO-based for CO2 capture and for sorption-enhanced steam methane reforming process (SE-SMR) were investigated. Results showed that the sorbent derived from calcium d-gluconic acid (CG-AN) offered CO2 sorption capacity of 0.38 g CO2/g sorbent, which is greater than 0.17 g CO2/g sorbent of the sorbent derived from calcium nitrate (CN-AN). Addition of CTAB surfactant during synthesis was found to enhance CO2 sorption capacity for CG-AN but not for CN-AN sorbents. Stability tests of the modified sorbents for 10 cycles showed that CG-AN-CTAB provided higher CO2 sorption capacity than CN-AN-CTAB for each corresponding cycle. Incorporation of CG-AN with Ni catalyst (Ni-CG-AN) using wet-mixing technique offered the longest pre-breakthrough period of 60 min for average maximum H2 purity of 88% at 600 °C and a steam/methane molar ratio of 3.

Optimal synthesis of periodic sorption enhanced reaction processes with application to hydrogen production

A systematic design and synthesis framework for multi-step, multi-mode and periodic sorption-enhanced reaction processes (SERP) is presented. The formulated nonlinear algebraic and partial differential equation (NAPDE)-based model simultaneously identifies optimal SERP cycle configurations, design specifications and operating conditions. Key modeling contributions include a generalized boundary-condition formulation and a representation that enables the selection of discrete operation modes and flow directions using continuous pressure variables. A simulation-based constrained grey-box optimization strategy is employed to obtain optimal cycles and design parameters. The framework has been used for designing two SERP systems, namely sorption-enhanced steam methane reforming (SE-SMR) and sorption-enhanced water gas shift reaction (SE-WGSR), for maximizing hydrogen productivity and minimizing hydrogen-production cost. Specifically, a cyclic SE-SMR process is designed that obtains 95% pure hydrogen from natural gas with 35% higher productivity and 10.86% lower cost compared to existing small-scale, distributed systems. The developed synthesis framework can also be applied for other applications.

Sol-gel-derived, CaZrO3-stabilized Ni/CaO-CaZrO3 bifunctional catalyst for sorption-enhanced steam methane reforming

Sorption-enhanced steam methane reforming (SESMR) that combines steam reforming of methane with in situ CO2 removal is a promising technology for H2 production, and bifunctional catalysts that integrate catalytic and absorptive sites into one body are believed to have reduced mass transfer resistances. However, it is still a challenge to prepare bifunctional catalysts with high stability. Here, we used a sol-gel technique based on the formation of citrate complexes to prepare a series of Ni/CaO-CaZrO3 bifunctional catalysts in which Ni, CaO and CaZrO3 acted as catalyst, sorbent and stabilizer, respectively. The stabilizer, Ni loading and CaO content had a direct effect on the structure and morphology of the catalyst, which in turn influenced its CO2 uptake and SESMR performance. Compared to Ni/CaO, the CaZrO3-stabilized Ni/CaO-CaZrO3 had smaller and fluffier grains, showing not only higher CO2 uptake and better stability in 50 carbonation-calcination cycles, but also higher stability during cyclic SESMR process. In particular, the catalyst with a Ni loading of 15wt%, CaO content of around 60wt% and CaZrO3 content of 25wt% presented the best SESMR performance by taking into account the catalytic activity and stability as well as the duration of the prebreakthrough period. However, the best catalyst was still subject to slow deactivation during a long-term stability test (up to 90 SESMR cycles), which was mostly due to the smooth and compact shell formed on the catalyst surface. The partially deactivated catalyst can be effectively reactivated by an additional carbonation step during the cyclic SESMR operation.

Catalytic performance of Ni/CaO-Ca5Al6O14 bifunctional catalyst extrudate in sorption-enhanced steam methane reforming

In this work, mm-sized shaped Ni/CaO-Ca5Al6O14 bifunctional catalyst extrudates were prepared by extruding sol–gel-derived Ni/CaO-Ca5Al6O14 powder, and applied to the sorption-enhanced steam methane reforming (SESMR) process. The Ca5Al6O14-stabilized bifunctional catalysts exhibited higher stability and CaO utilization efficiency than that of Ni/CaO when subjected to 50 carbonation–calcination cycles for CO2 capture, indicating the positive effect of Ca5Al6O14 incorporation. The Ni/CaO-Ca5Al6O14 extrudates possessed good activity and stability over 10 SESMR cycles, and showed advantages over the use of catalyst and sorbent mixture, including an extended prebreakthrough time and a higher catalytic activity. In particular, the Ni/CaO-Ca5Al6O14 extrudate consisting of 15wt% (mass fraction) Ni, 61.7wt% CaO and 23.3wt% Ca5Al6O14 provided high activity and stability for the SESMR process, even at a low H2O/CH4 molar ratio of 2 over 20 SESMR cycles. These results clearly demonstrate that the Ni/CaO-Ca5Al6O14 extrudate is an interesting candidate for the SESMR process.

Simulation of Hydrogen Production with In Situ CO2 Removal Using Aspen Plus

In this work, the sorption-enhanced steam methane reforming (SE-SMR) in which the integration of steam reforming reaction and carbon dioxide removal can be carried out in a single step was investigated in the thermodynamics aspects by using AspenPlusTM. Thermodynamics analysis was performed on both conventional steam methane reforming (SMR) and sorption-enhanced steam methane reformingprocesses based on minimization of Gibbs free energy method to determine the favorable operating conditions of each process. The effects of operating conditions (i.e., pressure, temperature and steam to carbon ratio) on hydrogen production were examined. The simulation results show that the optimal steam to carbon ratio is 6 and 5 for SMR and SE-SMR process, respectively. For SMR process, the maximum hydrogen purity of 78 % (dry basis) can be obtained at 950 K. While, the SE-SMR process offers two advantages over SMR process: (1) higher purity of hydrogen product can be achieved to 99 % (dry basis) and (2) required operating temperature is lower in the range of 700-850 K which is 100-150 K lower than SMR process, indicating that the SE-SMR process is less requirement of energy consumption.

Development of Al-stabilized CaO–nickel hybrid sorbent–catalyst for sorption-enhanced steam methane reforming

In this work, Al-stabilized CaO–Ni hybrid sorbent–catalysts integrated in a single particle with various nickel loadings (12, 18 and 25 wt% NiO) were developed and tested in cyclic hydrogen production by sorption-enhanced steam methane reforming (SESMR) process. A simple wet-mixing technique based on limestone acidification and two-step calcination was employed to produce hybrid materials with different nickel loadings. All developed materials were characterized by BET, XRD, SEM and TEM and studied during 25 CO 2 sorption/regeneration cycles as well as for 10 SESMR cycles. Based on both CO 2 sorption and SESMR results, it was concluded that the proposed hybrid sorbent–catalyst with NiO loading of 25 wt% led to the best performances: (i) CaO molar conversion is 41.2% at the end of the 25th sorption cycle and (ii) average CH 4 conversion and H 2 production efficiency during 10 SESMR cycles are remarkable (99.1% and 96.1%, respectively). For the most efficient hybrid sorbent–catalyst (25 wt% NiO), the influence of CH 4 flow rate and steam to carbon ratio (S/C) was also investigated, as well as its behavior during long-term cyclic operation of SESMR (30 cycles), where the H 2 production time was just limited to pre-breakthrough period. The very efficient performance (average of H 2 yield 97.3%) of the proposed hybrid sorbent–catalyst material in long-term operation confirmed its high potential for use in SESMR process. • Al–stabilized CaO–nickel hybrid sorbent–catalyst prepared by limestone acidification. • The hybrid sorbent–catalyst with 25 wt% NiO provided the best results. • CH 4 conversion of 99.1% in cyclic SESMR operation (10 cycles). • H 2 production efficiency of 96.1% (10 cycles) and 97.3% (30 cycles).

The modeling of circulating fluidized bed reactors for SE-SMR process and sorbent regeneration

A circulating fluidized bed reactor operated in a continuous mode was simulated within two sets of 3D cylindrical coordinates for the downer and riser. The computation of the two reactor units was coupled through the common time step and solid flux. The simulation system was used to study the sorption enhanced steam methane reforming (SE-SMR) and sorbent regeneration simultaneously as carried out in the downer and riser of a circulating fluidized bed reactor. The hydrodynamic behaviors of the downer and the riser were illustrated. The chemical process behavior analysis was compared with that from the simulations operated with the solids in batch mode for the two processes. The similarities and differences of continuous mode and batch mode reactor operations were discussed. It was concluded that high sorbent capacity favors the batch mode operation for the CO2 sorption in the SE-SMR process. In the continuous operation of the SE-SMR and regeneration units, only a small part of sorbent capacity was utilized.

Simulations of Steam Methane Reforming/Sorption-Enhanced Steam Methane Reforming Bubbling Fluidized Bed Reactors by a Dynamic One-Dimensional Two-Fluid Model: Implementation Issues and Model Validation

Multiphase flows and in particular dispersed flows are frequently encountered in a variety of important process facilities in the chemical industry; herein, the fluidized bed reactors. Whereas the internal and external solid fluxes in the fluidized bed reactors are generally determined by empirical correlations or prescribed in the Kunii–Levenspiel type of models, the two-fluid models serve as highly relevant in the progress of commercial reactors for processes such as the novel sorption-enhanced steam methane reforming (SE-SMR) technology because the solid flux incorporated in the two-fluid model allows for dynamic modeling of interconnected fluidized bed reactors. Nevertheless, the two- and three-dimensional two-fluid models are yet too computationally demanding for chemical process evaluation studies due to the complexity of the gas–solid flow in the bed. Hence, these models are not efficient for studies of the processes such as the SE-SMR technology where the solid particles are transported between reactor units for utilization and recovery of the characteristic solid property, i.e. CO2-capture and CO2-release. Thus, the aim of the present study is to derive a model that allows for a more complex description of the fluidized bed reactors relative to the frequently used Kunii–Levenspiel type of models. On the other hand, the model should not predict details in the flow, as the two- and three-dimensional two-fluid models, in order to ensure reasonable simulation costs. Hence, in this study, the classical SIMPLE algorithm is extended to compressible two-phase reactive flows. The governing equations are cross-sectional averaged to smooth out the details in the flow. The suggested dynamic one-dimensional Eulerian–Eulerian two-fluid model is applied to investigate the reactive gas–solid flows of the SMR and SE-SMR processes; and moreover, the simulation results are compared with the results of the more complex two-dimensional model with a solid stress closure based on kinetic theory of granular flow. The one-dimensional model predictions of the chemical process performance are in good agreement with the corresponding profiles predicted with the two-dimensional model. The deviations are larger comparing the internal flow details but these do not owe significant impact on the chemical process which to a large extent is determined by the imposed temperature in the reactor.