Sorption Enhanced Steam Methane Reforming Research Articles

Numerical evaluation of steam methane reforming process with sorption enhanced in the circulating fluidized riser reactor

Sorption-enhanced steam methane reforming represents a highly auspicious technological breakthrough that delivers dual benefits of enabling the CO2 capture while also facilitating hydrogen production. The SE-SMR process in the riser is explored by MP-PIC model. After validating this model with experimental measurements, the solid thermal properties at particle scale and gas–solid hydrodynamics are evaluated, and the effect of solid flux and superficial velocity is discussed. Findings from the results suggest that: particles present axial and radial non-uniform distributions, featuring the dense-bottom and dilute-upper distribution, the core-annulus structure. In comparison to catalyst particles, sorbent particles demonstrate a larger heat transfer coefficient (HTC) in both axial and radial directions, and a smaller Reynolds number. The HTC of sorbent particles is approximately 1.36 times higher than that of catalyst particles. Large HTC is observed in the central region above solid inlet. The HTC of the particles in the center is three to five times that of the particles at the side walls.

Thermodynamic and Economic Analyses of a Novel Cooling, Heating and Power Tri-Generation System with Carbon Capture

The combined cooling, heating, and power (CCHP) system has attracted increasing attention due to its potential outstanding performance in thermodynamics, economics, and the environment. However, the conventional CCHP systems are carbon-intensive. To solve this issue, a low-carbon-emission CCHP system (LC-CCHP) is firstly proposed in this work by integrating a sorption-enhanced steam methane reforming (SE-SMR) process. In the LC-CCHP system, CO2 is continuously captured by the calcium loop so that low-carbon energy can be generated. Then, the LC-CCHP system thermodynamic model, mainly consisting of a dual fluidized bed reactor which includes the SE-SMR reactor and a CaCO3 calcination reactor, a hydrogen gas turbine, a CO2 reheater, and a lithium bromide absorption chiller, is built. To prove that the LC-CCHP model is reliable, the system major sub-unit model predictions are compared against data from the literature in terms of thermodynamics and economics. Finally, the effects of reforming temperature (Tref), the steam-to-carbon mole ratio (S/C), the calcium-to-carbon mole ratio (RCC), the equivalent ratio for gas turbine (RAE), and the hydrogen separation ratio (Sfg) on total energy efficiency (ηten), total exergy efficiency (ηtex), and carbon capture capability (Rcm) are detected. It is found that the minimum exergy efficiency of 64.5% exists at the calciner unit, while the maximum exergy efficiency of 78.7% appears at the gas turbine unit. The maximum energy efficiency and coefficient of performance of the absorption chiller are 0.52 and 1.33, respectively. When Tref=600 °C, S/C=4.0, RCC=7.62, RAE=1.20, and Sfg=0.27, the ηten, ηtex, and Rcm of the system can be ~61%, ~68%, and ~96%, and the average specific cost of the system is 0.024 USD/kWh, which is advanced compared with the parallel CCHP systems.

Optimizing hydrogen yield in sorption-enhanced steam methane reforming: A novel framework integrating chemical reaction model, ensemble learning method, and whale optimization algorithm

High hydrogen production is essential in sorption-enhanced steam methane reforming (SE-SMR). This study presents an innovative optimization framework to optimize the H2 yield of SE-SMR through a coupled reaction model, prediction surrogate model, and whale optimization algorithm. Firstly, a computational fluid dynamics chemical reaction model of SE-SMR is constructed. A database is established to consider the H2 yield of SE-SMR with temperature, pressure, velocity, and steam to carbon ratio. Then, a surrogate model is developed on the basis of eXtreme Gradient Boosting (XGBoost) to predict the H2 yield under various operating parameters. Finally, the surrogate model is exploited to calculate the fitness function of the whale optimization algorithm to construct an optimization framework for maximizing the H2 yield. The results show that the XGBoost ensemble surrogate model can predict the H2 yield of SE-SMR within 4 s with high accuracy. The optimization framework can optimize the maximum H2 yield and the corresponding operating parameters within 1 min. The optimization results are validated by applying the model and the percentage error of only 0.79 %. Moreover, under optimal operating conditions, methane is almost completely converted to hydrogen, and the dry hydrogen mole fraction could reach 95.96 %. The presented optimization framework can guide the prediction of H2 yield and the optimization of operating parameters in SE-SMR.

Phase transition Ni-Co-Ca-O bifunctional catalysts for high and stable hydrogen production from sorption enhanced steam methane reforming

Sorption enhanced steam methane reforming (SESMR) is an effective method to improve the efficiency of hydrogen production from methane reforming while fixing CO2 to reduce carbon emissions. However, the deactivation of adsorbents during high temperature recycling limits the utilization of SESMR. In this paper, by combining the phase transition process of Ca-Co-O species and Ni-Co alloy, we prepared a series of Ni-Co-Ca-O bifunctional catalysts for SESMR hydrogen production. The 1Ni4.5Co4.5CaO catalyst exhibited high catalytic activity in the SESMR reaction with hydrogen concentration exceeding 99.6 % and complete methane conversion. The catalyst also showed high stability in 50 cycle experiments with no significant reduction in hydrogen production and CO2 uptake performance. The Ni-Co-Ca-O bifunctional catalysts consisted of NiO and Co-Ca-O species, by analyzing the fresh and reacted catalysts, the mechanism of the catalyst with high catalytic activity and stability was revealed. Firstly, the catalyst formed Ni-Co alloy and CaO adsorbent by a reduction reaction, and then the SESMR hydrogen production reaction was carried out. After the complete conversion of CaO to CaCO3, the catalyst was re-formed into NiO and Co-Ca-O species by introducing O2 in the regeneration reaction to carry out a new cycle of reduction → hydrogen production. The synergistic interaction between the Ni-Co alloy enhanced the methane reforming and water gas shift reaction, leading to an increase in hydrogen production and methane conversion. The phase transition of Co from Co-Ca-O species to Ni-Co alloy and back to Co-Ca-O species inhibited the sintering of CaO, which significantly enhanced the cyclic stability of the catalyst. The results of this study are expected to provide a new pathway for the design of SESMR bifunctional catalysts.

Exergy analysis in intensification of sorption-enhanced steam methane reforming for clean hydrogen production: Comparative study and efficiency optimisation

Hydrogen has a key role to play in decarbonising industry and other sectors of society. It is important to develop low-carbon hydrogen production technologies that are cost-effective and energy-efficient. Sorption-enhanced steam methane reforming (SE-SMR) is a developing low-carbon (blue) hydrogen production process, which enables combined hydrogen production and carbon capture. Despite a number of key benefits, the process is yet to be fully realised in terms of efficiency. In this work, a sorption-enhanced steam methane reforming process has been intensified via exergy analysis. Assessing the exergy efficiency of these processes is key to ensuring the effective deployment of low-carbon hydrogen production technologies. An exergy analysis was performed on an SE-SMR process and was then subsequently used to incorporate process improvements, developing a process that has, theoretically, an extremely high CO2 capture rate of nearly 100 %, whilst simultaneously demonstrating a high exergy efficiency (77.58 %), showcasing the potential of blue hydrogen as an effective tool to ensure decarbonisation, in an energy-efficient manner.

Evaluation of the Effect of CaO on Hydrogen Production by Sorption-Enhanced Steam Methane Reforming.

The effect of heat released during CaO adsorption on sorption-enhanced steam methane reforming for hydrogen production is insufficiently understood. On this basis, Aspen Plus is used to study the effect of steam methane reforming on hydrogen production without/with CaO. At 700 °C and an O2 inflow of 7 mol/h, the molar flow and molar percentages of H2 are 20.62 and 67.35%. After adding CaO, at 700 °C with 4.5 mol/h of CaO, the heat release of CaO adsorption is 1.32 MJ/h, and the O2 inflow reduces to 4.3 mol/h. The molar flow and molar percentage of H2 are 22.80 mol/h and 85.94%. When 1.2 mol/h CH4 is combusted for CaCO3 decomposition in the calciner, regenerated CaO is transferred to the reforming reactor for calcium cycling, which consumes 2.4 mol/h of O2. For the entire cycle, 6.7 mol/h of O2.

Calcium-based pellets for continuous hydrogen production by sorption-enhanced steam methane reforming

Sorption-enhanced steam methane reforming (SESMR) can produce high-purity H2 in one step, while removing CO2 to reduce carbon emissions. The sorbents, catalysts or bifunctional composite used in this system typically exist in powder form, which is difficult to use in industrialized fluidized bed reactors. Granulation can effectively avoid reactor clogging, increase practicality and operability of the system. In this work, Al-modified CaO-based sorbents were granulated using the graphite-casting method and test its sorption-enhanced hydrogen production effects during methane steam reforming. The effects of granulation on the microstructure, carbonation reactivity and mechanical properties were characterized. The reaction conditions (temperature and water-gas ratio) and the combination method of catalyst and sorbent (powder mixing, pellets mixing, layered placement and bifunctional materials mixed evenly at the molecular level) on hydrogen yield were investigated. Results showed that CaO-based pellets after granulation had a fluffy and porous structure, exhibited excellent adsorption performance under low CO2 partial pressure. The average crushing load of 75Ca25Al and 15Ni70Ca15Al pellets exceeded 6 N, showing good mechanical strength. The optimal reaction temperature range was found to be 550–600 °C. Increasing the water-gas ratio and reducing the flow rate were effective ways of improving CH4 conversion and H2 purity. The bifunctional 15Ni70Ca15Al powder prepared by sol-gel method had no catalytic effect on CH4–H2O reforming at 600 °C. After granulation, the catalytic performance was improved and the purity of H2 reached 95%, but it declined rapidly during multiple SESMR cycles. In the case of mixed of two pellets (catalyst and sorbent), the outlet H2 reached almost 100% with no decay observed over 15 cycles. When the switching time of feed gas was set to 60 min, high-purity (>96%) hydrogen can be produced continuously for 600 min on the parallel two fixed-bed reactors.

Probing into the interactions among operating variables in blue hydrogen production: A new approach via design of experiments (DoE)

Anthropogenic CO2 emission is a key driver in global warming and climate change. Worldwide, H2 production accounts for 2.5% of this CO2 emission. A shift to clean methods of hydrogen production is required to reduce CO2 emissions, and to mitigate the effects of climate change. Developing optimised process models of H2 production processes is required in order to investigate the effects of operational variables of the process and their impacts on key performance indicators (KPIs). Within this study, a detailed rate-based model was implemented to simulate the reformer in Sorption Enhanced Steam Methane Reforming (SE-SMR), as well as Sorption-Enhanced Auto-Thermal Reforming (SE-ATR) processes. The results indicate that the SE-ATR/ATR corresponds to a significantly improved performance over the SMR with the optimal operating conditions for achieving the desired KPIs, including hydrogen purity (86%), hydrogen yield (36%), methane conversion (99%), and carbon capture rate (50%) at a temperature of 720 °C, a pressure of 20 bara, and an S/C ratio of 6. Whereas with SMR, the temperature, pressure, and S/C ratio should be adjusted to 975 °C, 20 bara, and 6, respectively, to achieve a hydrogen purity of 84%, a hydrogen yield of 42%, a methane conversion of 96%, and a carbon capture rate of 48%. The study provides insights into the optimal operating conditions to achieve maximum efficiency in the reformer, and demonstrates the effectiveness of incorporating DoE within process modelling as a tool for optimisation.

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.

Prediction of Combined Sorbent and Catalyst Materials for SE-SMR, Using QSPR and Multitask Learning.

The process of sorption enhanced steam methane reforming (SE-SMR) is an emerging technology for the production of low carbon hydrogen. The development of a suitable catalytic material, as well as a CO2 adsorbent with high capture capacity, has slowed the upscaling of this process to date. In this study, to aid the development of a combined sorbent catalyst material (CSCM) for SE-SMR, a novel approach involving quantitative structure–property relationship analysis (QSPR) has been proposed. Through data-mining, two databases have been developed for the prediction of the last cycle capacity (gCO2/gsorbent) and methane conversion (%). Multitask learning (MTL) was applied for the prediction of CSCM properties. Patterns in the data of this study have also yielded further insights; colored scatter plots were able to show certain patterns in the input data, as well as suggestions on how to develop an optimal material. With the results from the actual vs predicted plots collated, raw materials and synthesis conditions were proposed that could lead to the development of a CSCM that has good performance with respect to both the last cycle capacity and the methane conversion.

Sorption enhanced steam reforming of methane over waste-derived CaO promoted MgNiAl hydrotalcite catalyst for sustainable H2 production

The waste-derived CaO promoted Mg-Ni-Al (MNA) based hydrotalcite hybrid catalysts were synthesized by co-precipitation and wet impregnation method and tested for sorption enhanced steam methane reforming (SESMR) for hydrogen (H2) production. The catalysts were characterized using X-ray diffractometer (XRD), Field emission scanning electron miscroscopy (FESEM), Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, Brauner Emmett teller (BET), laser particle size analyzer, Temperature programmed reduction (TPR), Thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). Various CaO loadings varying from 0% to 15% into the MNA-based hydrotalcite catalysts (MNA HTc) were assessed for SESMR in a fixed bed reactor. The results revealed that 10% CaO@MNA exhibited the best performance in terms of a longer pre-breakthrough period with respect to other compositions. The CH4 fraction, H2 purity, and CO2 production in the absence of CaO were marked at 60%, 55%, and 14% respectively. However, the CH4 fraction and H2 purity increased to 77% and 80%, while CO2 decreased to 3% in the pre-breakthrough period for 10% CaO @ MNA at 650 °C, WHSV 2000 mL CH4 g−1h−1 and S/C of 2.0. The nanocomposite 10%CaO@MNA was tested over three consecutive SESMR cycles at 650 °C to analyze its regeneration capacity. The hybrid catalyst was also tested at various temperatures from 650° to 850°C to investigate the effect of CaO sorbent. It was found that elevated temperatures > 750 °C likely reduced the carbonation reaction and shifted the technique to SMR. The spent catalyst exhibited negligible carbon formation on the catalyst surface. The catalytic performance of the reported catalyst-sorbent system is encouraging for further regeneration studies for SMR and other reforming techniques.

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.

Sorption-enhanced steam methane reforming over Ni/Al2O3/KNaTiO3 bifunctional material

The performance of a new lab-made bifunctional material Ni/Al2O3/KNaTiO3 for producing high purity H2 via sorption-enhanced steam methane reforming (SESMR) was investigated. A series of bifunctional materials with 10 wt% Ni loading but different wt% ratios of KNaTiO3 and Al2O3 was prepared by wetness impregnation method. All the materials were calcined at 700 °C for 3 hours and screened for their catalytic activity in a continuous flow fixed-bed reactor. The material containing 50 wt% each of KNaTiO3 and Al2O3 (designated as HM) was found to be the best choice. The optimum process parameters for the production of high purity H2 were determined: temperature = 700 °C, steam to carbon (S/C) molar ratio = 6 and gas-hourly space velocity (GHSV) = 2000 cm3 g-1 h-1. The values of CH4 conversion, H2 yield and H2 purity were 87, 87 and 90%, respectively, at the optimum reaction conditions. The adsorption capacity of HM was found to be 14.7 wt%. With a breakthrough time of 10 min, the material was stable for 8 adsorption-desorption cycles. The regeneration of HM was achieved with N2 gas at the same reaction temperature. Overall, the activity of this material for SESMR was very promising.

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.

A natural gas-based eco-friendly polygeneration system including gas turbine, sorption-enhanced steam methane reforming, absorption chiller and flue gas CO2 capture unit

Poly-generation systems have attracted a lot of attention due to the increment of efficiency as well as reducing energy penalties, costs and pollutants. Extensive research has been done on these systems in recent years. The current work is done with the aim of simulating an environmentally friendly poly-generation system in the power plant of Shahrood city in Iran. In this way, a poly-generation system is simulated in Aspen Plus software which consists of: I) a gas turbine (GT) for power generation with natural gas fuel of Shahroud power plant, that its flue gas is utilized to supply heat for other cycles and streams, II) a sorption-enhanced chemical looping reforming (SECLR) which simultaneously generates H2 by steam methane reforming (SMR) and uptakes produced CO2 by calcium adsorbent during the carbonation/calcination reactions. In this section, there is also a chemical looping combustion (CLC) based on redox reactions of Ni/NiO to provide heat of the reactors, III) a NH3/H2O absorption refrigeration system to yield the cooling demand, IV) a high-pressure steam generation unit and V) a MEA-based post-combustion CO2 capture unit (PCC) for flue gas. In this system, an attempt has been made to prevent heat loss by internal streams, especially gas turbine exhaust gas, so that energy loss is minimized. Moreover, environmental issues are also prioritized to reduce the CO2 emissions as much as possible. The proposed process is capable of producing 133.3 MW power, 9.875 MW cooling, 50 kg/s high-pressure steam and 0.384 kg/s hydrogen. The mass flow rates of CO2 captured in the SECLR and PCC sections are 2.6 kg/s and 15.35 kg/s, respectively. Moreover, the total energy efficiency of the integrated system is 68.74%. Ultimately, a sensitivity analysis was performed to identify the key parameters and their influence on the process performance.

The operation types and operation window for high-purity hydrogen production for the sorption enhanced steam methane reforming in a fixed-bed reactor

The operation types and operation window for high-purity H2 production for the sorption enhanced steam methane reforming (SE-SMR) with Ni/Al2O3 catalyst and CaO sorbent in a fixed-bed reactor are investigated by an experimentally verified 2D numerical method. Four chemical reactions including steam reforming, water gas shift, global steam reforming, and CO2 sorption are considered. The operation window is defined as the H2 and CO molar fractions at outlet satisfying both yH2,out ≥ 90% and yCO,out ≤ yCO,allow (= 1%, 2% or 3%) in dry base. Under the conditions of yH2,out and yCO,allow, there are six operation types, of which 2 types are within the operation window and 4 types are not within the operation window as the temperature, weight hourly space velocity (WHSV) and steam to methane (S/C) molar ratio vary. For a common case of S/C = 3, the operation windows for yCO,allow = 3% at WHSV = 8.5 h−1 and 42.5 h−1 are located at 570–670 °C and 640–690 °C respectively, based on the parameters in this work. The operation window of temperature is wider with decreasing WHSV, and it becomes wider remarkably as the S/C ratio increases. The lowest temperature inside the operation window is 550 °C. The effects of the temperature, WHSV and S/C ratio on the operating types, yH2,out and yCO,out are also presented and discussed in details.

Transient reaction phenomena of sorption-enhanced steam methane reforming in a fixed-bed reactor

The transient chemical reaction phenomena of the sorption-enhanced steam methane reforming (SE-SMR) by using Ni/Al2O3 catalyst and CaO sorbent in a tubular fixed-bed reactor were numerically investigated by an experimentally verified unsteady 2D model. Four chemical reactions are involved in SE-SMR including steam reforming (SR), water gas shift (WGS), global steam reforming (GSR), and CO2 sorption. The reaction process in time is divided into period 1, transient period, and period 2. The high-purity H2 is produced in period 1 which is defined as the outlet molar fractions of H2 ≥ 90% and CO ≤ 1% (dry basis) in this work. In the first half of period 1, the endothermic reaction rates of SR and GSR are dominant in the entrance region of catalyst/sorbent bed. The WGS and CO2 sorption reactions are triggered by SR and GSR reactions. The heat transfer from the wall plays an important role. Higher CaO conversion, temperature, and reaction rates appear first near the wall region, then they gradually expand to the central region.In the second half of period 1, a sharp wave-shaped curve of strong CO2 sorption reaction occurred in downstream becomes dominant and it moves to downstream almost at a constant speed, as time progresses. The peak value of the CO2 sorption reaction is more than twice larger than that of SR or WGS. The SR and WGS reaction rates are significantly enhanced by CO2 sorption reaction. The great sorption, WGS, and SR reactions result in a high-purity H2 production with the outlet molar fractions of 95.8% H2, 0.998% CO, and 0.73% CO2 at the end of period 1, based on the parameters used in this work such as reactor temperature of 600 °C. The maximum CaO conversion is about 76% in end of period 1 and the average CaO conversion in the reactor is 51%. The 2D distributions of CaO conversion, temperature, and reaction rates are also presented and discussed.