Numerical investigation of combustion characteristics in an oxygen transport reactor

The paper presents a numerical investigation of thermal characteristics of oxyfuel combustion in an oxygen transport reactor (OTR). The reactor is made of a combustion chamber of tubular shape and surrounded by an annular air flow compartment. The walls of the combustion chamber are made of dense, nonporous, mixed‐conducting ceramic membranes that only allow oxygen permeation from the annular air compartment into the combustion chamber. A mixture of CO₂ and CH₄ (sweep gas) enters the reactor from one side and mixes with the oxygen permeating through the ion transport membrane. The resulting combustion products (composed of H₂O and CO₂) are discharged from the other side of the reactor. The modeling of the flow process is based on a numerical solution of the conservation equations of mass, momentum, energy and species in the axi‐symmetric flow domain. The membrane is modeled as a selective layer in which the oxygen permeation depends on the prevailing temperatures as well as the oxygen partial pressure at both sides of the membrane. The comparison between reactive and separation‐only OTR units showed that combining reaction and separation increases significantly O₂ permeation rate to about 2.5 times under the assumptions given herein. Uniform axial temperature of about 1250 K is achieved in most of the reactor length with high CH₄ conversion of 75% to 35% for CH₄/CO₂ mass ratio ranging from 0.5/0.5 to 1.0/0. Since the thermal resistance of these membranes is low, the heat of reaction is mostly transferred to the air side with a portion used to heat the O₂ permeating flux. Copyright © 2013 John Wiley & Sons, Ltd.     

A comparative study of two H2‐redistribution strategies along the FT reactor using H2‐permselective membrane

In this study, a comparative study of two different hydrogen redistribution strategies along the Fischer‐Tropsch synthesis reactor using a Pd‐Ag membrane has been carried out. In the first strategy, fresh synthesis gas is flowing in the tube side in co‐current mode with reacting material in shell side so that the first segments of reactor use more hydrogen. In the second strategy, fresh synthesis gas is flowing in the tube side in counter‐current mode with reacting material in shell side so that last segments of reactor use more hydrogen. A one‐dimensional heterogeneous model was developed to compare two strategies from different standpoints. The model was checked using operating data of Fischer‐Tropsch synthesis reactor in pilot plant of Research Institute of Petroleum Industry in Iran. Simulation results show an enhancement in the yield of gasoline production, a decrease in undesired products formation (CO₃ and CH₄) and also a favorable temperature profile along both the configurations of membrane Fischer‐Tropsch reactor in comparison with conventional reactor. The comparison between co‐current and counter‐current configurations in terms of temperature, gasoline (C) and CO₂ yields, H₂ and CO conversions, and selectivity of components shows the reactor in the co‐current configuration operates with lower reactants' conversions and also lower permeation rate of hydrogen. On the contrary, our results demonstrated counter‐current‐mode decrease CO₂ and CH₄ as undesired products, better than other kinds of mentioned systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Study on different zero CO2 emission IGCC systems with CO2 capture by integrating OTM

In this paper, different zero CO₂ emission integrated gasification combined cycle (IGCC) systems based on the oxy‐fuel combustion method by integrating with oxygen ion transfer membrane (OTM) with and without sweep gas are proposed in order to reduce the energy consumption of CO₂ capture. By utilizing the Aspen Plus software, the overall system models are established. The performances of the proposed systems are compared with the traditional IGCC system without CO₂ capture and the zero CO₂ emission IGCC system based on the oxy‐fuel combustion method using the cryogenic air separation unit. In addition, the effects of OTM key parameters on the proposed system performance, such as the feed side pressure, permeate side pressure, and operating temperature, are investigated and analyzed. The results show that the efficiency of the zero CO₂ emission IGCC system based on the oxy‐fuel combustion method integrated with OTM without sweep gas is 6.67% lower than that of the traditional IGCC system without CO₂ capture, but 1.88% higher than that of the zero CO₂ emission IGCC system using the cryogenic air separation unit, and 0.64% lower than that of the proposed system with sweep gas. The research achievements will provide valuable references for further study on CO₂ capture based on IGCC with lower energy penalty. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparison study on different ITM‐integrated MCFC hybrid systems with CO2 recovery using sweep gas

Previous study shows the ITM (oxygen ion transfer membrane)‐integrated MCFC (molten carbonate fuel cell) hybrid system with CO₂ recovery can maintain high efficiency; however, the oxygen partial pressure on the ITM permeate side is usually 1 atm, which requires a very high pressure ratio of the ITM air compressor in order to separate the oxygen; using the sweep gas can solve this problem. In this paper the ITM‐integrated MCFC hybrid systems with CO₂ recovery using different sweep gases are studied. With the Aspen plus software, two systems with different sweep gases are established, and their performances are compared with the benchmark system without sweep gas; the effects of key parameters on the optimum system performance are also investigated. Results show that compared with the benchmark system, the efficiencies of the systems with sweep gases are increased and the pressure ratios of the air compressors are decreased; the system using pure CO₂ as sweep gas can improve the system efficiency by 1.25%, which is superior to the system using the mixture gas of CO₂ and H₂O as sweep gas. Achievements from this paper will provide a valuable reference for CO₂ recovery from the MCFC hybrid power system with lower energy consumption. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of oxygen permeation through disc‐shaped BSCF ion transport membrane under reactive conditions

The present work investigates the performance of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ ion transport membrane for separation of oxygen and its simultaneous reaction with gaseous fuels. A 2‐D axisymmetric model is considered to investigate the flow and combustion characteristics of methane in a button cell experimental model. A model that includes surface kinetics on the permeate and feed sides together with the bulk diffusion for BSCF membrane is developed and validated well against the experimental results. The effects of reaction on oxygen permeation and combustion characteristics are presented. Firstly, the nonreactive cases are investigated for oxygen permeation only. Later, the effects of increasing CH₄% on the reactivity are explored. Finally, the effect of an increase in the operating temperatures on permeation of oxygen and reactivity are presented and quantified. It is found that the permeation of oxygen increases as the CH₄% is increased in the sweep side because of an increase in the volume flow rates. The reactivity increased with an increase in the CH₄%, however, beyond CH₄ = 2% in the sweep side the amount of unburned CH₄ also increased. It is also indicated that raising the operating temperatures results in shortened flame zones with more concentration in the vicinity of the ITM. Copyright © 2016 John Wiley & Sons, Ltd.     

A CFD study on H2-permeable membrane reactor for methane CO2 reforming: Effect of catalyst bed volume

A 2D axisymmetric model is developed for a H₂-permeable membrane reactor for methane CO₂ reforming. The effect of catalyst bed volume on CH₄ conversion and H₂ permeation rate is investigated. The simulation results indicate that catalyst bed volume with a shell radius of 9 mm is optimal for a tubular Vycor glass membrane with a diameter of 10 mm and H₂ permeance of 2x10⁻⁶ mol/m²/Pa/s. The concentration polarization at the retentate side and the accumulation of H₂ at permeate side make it hard to extract the H₂ production at the zone far from the membrane surface. Though increasing pressure at the retentate side enhances H₂ permeation, CH₄ conversion is even decreased due to unfavorable thermodynamics. And increasing sweep gas flow rate at permeate side benefits to both CH₄ conversion and H₂ permeation. This work highlights the importance of determining the optimal catalyst bed volume to match the membrane in the design of membrane reactors.     

Methane steam reforming in a Pd-Ag membrane reformer: An experimental study on reaction pressure influence at middle temperature

In this experimental work, methane steam reforming (MSR) reaction is performed in a dense Pd-Ag membrane reactor and the influence of pressure on methane conversion, CO_x-free hydrogen recovery and CO_x-free hydrogen production is investigated. The reaction is conducted at 450 °C by supplying nitrogen as a sweep gas in co-current flow configuration with respect to the reactants. Three experimental campaigns are realized in the MR packed with Ni-ZrO catalyst, which showed better performances than Ni-Al₂O₃ used in a previous paper dealing with the same MR system. The first one is directed to keep constant the total pressure in both retentate and permeate sides of the membrane reactor. In the second case study, the total retentate pressure is kept constant at 9.0 bar, while the total permeate pressure is varied between 5.0 and 9.0 bar. As the best result of this work, at 450 °C and 4.0 bar of total pressure difference between retentate and permeate sides, around 65% methane conversion and 1.2 l/h of CO_x-free hydrogen are reached, further recovering 80% CO_x-free hydrogen over the total hydrogen produced during the reaction. Moreover, a study on the influence of hydrogen-rich gas mixtures on the hydrogen permeation through the Pd-Ag membrane is also performed and discussed.     

Experimental and numerical analysis of oxy‐fuel combustion in a porous plate reactor

The present work focuses on studying experimentally and numerically the oxy‐fuel combustion characteristics inside a porous plate reactor towards the application of oxy‐combustion carbon capture technology. Initially, non‐reactive flow experiments are performed to analyze the permeation rate of oxygen in order to obtain the desired stoichiometric ratios. A numerical model is developed for non‐reactive and reactive flow cases. The model is validated against the presently recorded experimental data for the non‐reacting flow cases, and it is validated against the available literature data for oxy‐fuel combustion for the reacting flow cases. A modified two‐step oxy‐combustion reaction kinetics model for methane is implemented in the present model. Simulations are performed over wide range of operating oxidizer ratios (O₂/CO₂ ratio), from OR = 0.2 to OR = 0.4, and over wide range of equivalence ratios, from φ = 0.7 to φ = 1.0. The flame length was decreased as a result of the increase of the oxidizer ratio. Effects of CO₂ recirculation amount on the oxy‐combustion flame stability are examined. A reduction in combustion temperature and increase in flame fluctuations are encountered while increasing CO₂ concentration inside the reactor. At high equivalence ratio, the combustion temperature and flame stability are improved. At low equivalence ratio, the flame length is increased, and the flame was moved towards the reactor center line. Copyright © 2015 John Wiley & Sons, Ltd.     

A comparison of hydrogen and methanol production in a thermally coupled membrane reactor for co‐current and counter‐current flows

This work considers three concentric tube reactors to prepare pure hydrogen, especially applicable in fuel cell technologies, with zero CO₂ emission. Hydrogen and methanol production rates are compared in a thermally coupled exothermic and endothermic reactor for co‐current and counter‐current modes. Synthesis of methanol is coupled with dehydrogenation of cyclohexane as a high content hydrogen carrier (7.1 wt%). The efficient coupling of exothermic and endothermic reactions increases the profitability of operation of the reactor, reduces the size of reactor and decreases the operational and capital costs. By inserting a hydrogen‐perm selective membrane into the reactor configuration, hydrogen can permeate selectively into the membrane, and hence, the third tube receives hydrogen. The simulation results are compared with the corresponded results for an industrial methanol fixed‐bed reactor, which operates under the same feed conditions. The influence of some operating variables is investigated on methanol and hydrogen yields during the performance of reactor. The results show higher methanol conversion, as the same as conventional reactor, and hydrogen for co‐current flow. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of sweep gas on hydrogen permeation of supported Pd membranes: Experimental and modeling

Membrane reactor processes are being increasingly proposed as an attractive solution for pure hydrogen production due to the possibility to integrate production and separation inside a single reactor vessel. High hydrogen purity can be obtained through dense metallic membranes, especially palladium and its alloys, which are highly selective to hydrogen. The use of thin membranes seems to be a good industrial solution in order to increase the hydrogen flux while reducing the cost of materials. Typically, the diffusion through the membrane layer is the rate-limiting step and the hydrogen permeation through the membrane can be described by the Sieverts’ law but, when the membrane becomes thinner, the diffusion through the membrane bulk becomes less determinant and other mass transfer limitations might limit the permeation rate. Another way to increase the hydrogen flux at a given feed pressure, is to increase the driving force of the process by feeding a sweep gas in the permeate side. This effect can however be significantly reduced if mass transfer limitations in the permeate side exist. The aim of this work is to study the mass transfer limitation that occurs in the permeate side in presence of sweep gas. A complete model for the hydrogen permeation through PdAg membranes has been developed, adding the effects of concentration polarization in retentate and permeate side and the presence of the porous support using the dusty gas model equation, which combines Knudsen diffusion, viscous flow and binary diffusion. By studying the influence of the sweep gas it has been observed that the reduction of the driving force is due to the stagnant sweep gas in the support pores while the concentration polarization in the permeate is negligible.     

Experimental and numerical study of oxy‐methane flames in a porous‐plate reactor mimicking membrane reactor operation

The work investigates the reacting flow field, oxy‐methane flame characteristics and location, and the species distributions in a porous‐plate reactor mimicking the operation of oxygen transport membrane reactors (OTMRs). The study was performed experimentally and numerically considering ranges of operating equivalence ratio, from 0.5 to 1.0, and CO₂ concentrations in the total oxidizer flow (O₂ and CO₂), from 0% to 55% (by Vol). Oxygen was supplied through a slightly pressurized top and bottom chambers to cross the two porous plates to the central chamber, where a premixed mixture of CH₄ and CO₂ is introduced. ANSYS Fluent 17.1 software was used to solve for conservation and radiative transfer equations in the full three‐dimensional (3‐D) domain. The modified Westbrook‐Dryer (Oxy‐WD) two‐step reduced mechanism for oxy‐methane combustion was adapted for the calculations of chemical kinetics. The captured flame shapes using a high‐speed camera were compared with the calculated ones, and the results showed good agreements. At fixed equivalence ratio, elongated flames were obtained at higher CO₂ concentrations due to the increase in the mainstream Reynolds number and reduction in reaction rates, which delays the completeness of combustion. At fixed CO₂ concentration, the increase in equivalence ratio resulted in more compact and intense flames. The effective mixing and flame stability resulted in complete fuel conversion under stoichiometric condition. Stable flames were located between the two porous plates at reasonable distance. This perfect flame location prevents the thermal fracture of the membranes and improves their oxygen permeation flux, resulting in better combustion characteristics when the results are projected on the case of OTMRs. This implies efficient and safe applicability of the OTMRs by the condition that membranes can provide sufficient oxygen flux for complete combustion. A warm outer recirculation zone (ORZ) was created beside each porous plate, which helps anchoring the flame at the leading edge of the porous plate. The range of temperature within the ORZ was 800 to 1600 K, which lies in the operability limits of membranes for the case of OTMRs. The effective complete mixing and flame stability resulted in complete fuel conversion under stoichiometric condition. The temperature and species distributions within the reactor are presented in detail over wide ranges of operating conditions. The results recommended the reactor operation under stoichiometric combustion condition based on performance and economic points of views. The results are promising when projected on the application of the OTMRs under oxy‐combustion conditions for clean and efficient energy production.     

Oxy‐fuel combustion technology: current status,applications, and trends

The increased level of emissions of carbon dioxide into the atmosphere due to burning of fossil fuels represents one of the main barriers toward the reduction of greenhouse gases and the control of global warming. In the last decades, the use of renewable and clean sources of energies such as solar and wind energies has been increased extensively. However, due to the tremendously increasing world energy demand, fossil fuels would continue in use for decades which necessitates the integration of carbon capture technologies (CCTs) in power plants. These technologies include oxycombustion, pre‐combustion, and post‐combustion carbon capture. Oxycombustion technology is one of the most promising carbon capture technologies as it can be applied with slight modifications to existing power plants or to new power plants. In this technology, fuel is burned using an oxidizer mixture of pure oxygen plus recycled exhaust gases (consists mainly of CO₂). The oxycombustion process results in highly CO₂‐concentrated exhaust gases, which facilitates the capture process of CO₂ after H₂O condensation. The captured CO₂ can be used for industrial applications or can be sequestrated. The current work reviews the current status of oxycombustion technology and its applications in existing conventional combustion systems (including gas turbines and boilers) and novel oxygen transport reactors (OTRs). The review starts with an introduction to the available CCTs with emphasis on their different applications and limitations of use, followed by a review on oxycombustion applications in different combustion systems utilizing gaseous, liquid, and coal fuels. The current status and technology readiness level of oxycombustion technology is discussed. The novel application of oxycombustion technology in OTRs is analyzed in some details. The analyses of OTRs include oxygen permeation technique, fabrication of oxygen transport membranes (OTMs), calculation of oxygen permeation flux, and coupling between oxygen separation and oxycombustion of fuel within the same unit called OTR. The oxycombustion process inside OTR is analyzed considering coal and gaseous fuels. The future trends of oxycombustion technology are itemized and discussed in details in the present study including: (i) ITMs for syngas production; (ii) combustion utilizing liquid fuels in OTRs; (iii) oxy‐combustion integrated power plants and (iv) third generation technologies for CO₂ capture. Techno‐economic analysis of oxycombustion integrated systems is also discussed trying to assess the future prospects of this technology. Copyright © 2017 John Wiley & Sons, Ltd.     

Production of hydrogen from purge gases of ammonia plants in a catalytic hydrogen-permselective membrane reactor

The present study investigates hydrogen production in a hydrogen-permselective membrane reactor from purge gases of an ammonia plant. Hydrogen which initially exists in the purge gases and hydrogen that is produced from decomposition of ammonia on nickel–Alumina catalyst bed simultaneously permeate from reaction side to shell side through a thin layer of palladium–silver membrane. A sweep gas can be used in the shell side for increasing driving force. The amount of hydrogen that can be gained annually and effect of pressure, temperature, thickness of Pd–Ag layer, configuration of flow in the membrane reactor and sweep gas flow ratio have been studied. This study shows that the countercurrent mode is better than co-current mode of operation. The rate of hydrogen permeation increases with increasing of temperature, pressure and sweep gas flow rate. This approach produces and separates large amounts of hydrogen and decreases environmental impacts owing to ammonia emission.     

Pure hydrogen production by steam reforming of methane mixtures with various propane contents in a membrane reactor with the industrial nickel catalyst and a Pd–Ru alloy foil

Steam reforming of СН₄ mixtures containing 5, 10, and 15% С₃Н₈ was studied in a membrane reactor with the industrial nickel catalyst and a membrane as a foil 30 μm thick of a Pd–Ru alloy. The reaction was studied at temperatures of 773 and 823 K and the mixture gas hourly space velocities equal to 1800 and 3600 h⁻¹. Experiments were carried out under atmospheric pressure, and both sweep gas (N₂) and vacuum conditions in the permeate side were used for Н₂ recovery from the reaction mixture. The complete conversion of С₃Н₈ was observed under all conditions. It is shown for the first time that the main factor determining the influence of propane on the reaction parameters is the rate of Н₂ recovery from the reaction mixture. A negative influence of С₃Н₈ on methane reforming was observed only in experiments using the sweep gas. This fact was proposed to be related to the insufficient СО conversion in the water-gas shift reaction. For vacuum conditions in the permeate side of the membrane reactor, the rate of Н₂ recovery from the reaction mixture increases, which increases the CO conversion in the water-gas shift reaction. In this case, the negative effect of С₃Н₈ on methane reforming is minimum and is almost absent at 823 K. The conversion of methane is 93–97%, depending on the flow rate of the raw materials, and 75–80% Н₂ are recovered from the reaction mixture.     

Study on a zero CO2 emission SOFC hybrid power system integrated with OTM using CO2 as sweep gas

A new zero CO₂ emission solid oxide fuel cell (SOFC) hybrid power system integrated with the oxygen ion transport membrane using CO₂ as sweep gas is proposed in this paper. The pure oxygen is picked up from the cathode outlet gas by the oxygen ion transport membrane with CO₂ as sweep gas; the oxy‐fuel combustion mode in the afterburner of SOFC is employed. Because the combustion product gas only consists of CO₂ and steam, CO₂ is easily captured with lower energy consumption by the condensation of steam. With the aspen plus soft, this paper builds the simulation model of the overall SOFC hybrids system with CO₂ capture. The exergy loss distributions of the overall system are analyzed, and the effects of the key operation parameters on the overall system performance are also investigated. The research results show that the new system still has a high efficiency after CO₂ recovery. The efficiency of the new system is around 65.03%, only 1.25 percentage points lower than that of the traditional SOFC hybrid power system(66.28%)without CO₂ capture. The research achievements from this paper will provide the valuable reference for further study on zero CO₂ emission SOFC hybrid power system with higher efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

A mechanistic investigation of a calcium-based oxygen carrier for chemical looping combustion

Chemical looping combustion (CLC) has been suggested as an energy-efficient method for the capture of carbon dioxide from combustion. It is indirect combustion by the use of an oxygen carrier, which can be used for CO₂ capture in power-generating processes. The possibility of CLC using a calcium-based oxygen carrier is investigated in this paper. In the air reactor air is supplied to oxidize CaS to CaSO₄, where oxygen is transferred from air to the oxygen carrier; the reduction of CaSO₄ to CaS takes place in the fuel reactor. The exit gas from the fuel reactor is CO₂ and H₂O. After condensation of water, almost pure CO₂ could be obtained. The thermodynamic and kinetic problem of the reduction reactions of CaSO₄ with CO and H₂ and the oxidization reactions of CaS with O₂ is discussed in the paper to investigate the technique possibility. To prevent SO₂ release from the process of chemical looping combustion using a calcium-based oxygen carrier, thermochemical CaSO₄ reduction and CaS oxidation are discussed. Thermal simulation experiments are carried out using a thermogravimetric analyzer (TGA). The properties of the products are characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray diffractometry (XRD), and the optimal reaction parameters are evaluated. The effects of reaction temperature, reductive gas mixture, and oxygen partial pressure on the composition of flue gas are discussed. The suitable temperature of the air reactor is between 1050 and 1150 °C and the optimal temperature of the fuel reactor between 900 and 950 °C.     

Optimization of hydrogen enrichment via palladium membrane in vacuum environments using Taguchi method and normalized regression analysis

In this study, the separation of hydrogen from gas mixtures using a palladium membrane coupled with a vacuum environment on the permeate side was studied experimentally. The gas mixtures composed of H₂, N₂, and CO₂ were used as the feed. Hydrogen permeation fluxes were measured with membrane operating temperature in the range of 320–380 °C, pressures on the retentate side in the range of 2–5 atm, and vacuum pressures on the permeate side in the range of 15–51 kPa. The Taguchi method was used to design the operating conditions for the experiments based on an orthogonal array. Using the measured H₂ permeation fluxes from the Taguchi approach, the stepwise regression analysis was also employed for establishing the prediction models of H₂ permeation flux, followed by the analysis of variance (ANOVA) to identify the significance and suitability of operating conditions. Based on both the Taguchi approach and ANOVA, the H₂ permeation flux was mostly affected by the gas mixture composition, followed by the retentate side pressure, the vacuum degree, and the membrane temperature. The predicted optimal operating conditions were the gas mixture with 75% H₂ and 25% N₂, the membrane temperature of 320 °C, the retentate side pressure of 5 atm, and the vacuum degree of 51 kPa. Under these conditions, the H₂ permeation flux was 0.185 mol s^?1 m^?2. A second-order normalized regression model with a relative error of less than 7% was obtained based on the measured H₂ permeation flux.     

CO2 methanation combined with NH3 decomposition by in situ H2 separation using a Pd membrane reactor

Combination of the reactions by means of membrane separation techniques are of interest. The CO₂ methanation was combined with NH₃ decomposition by in situ H₂ separation through a Pd membrane. The CO₂ methanation reaction in the permeate side was found to significantly enhance the H₂ removal rate of Pd membrane compared to the use of sweep gas. The reaction rate of CO₂ methanation was not influenced by H₂ supply through the Pd membrane in contrast to NH₃ decomposition in the retentate side. However, the CH₄ selectivity could be improved by using a membrane separation technique. This would be caused by the active dissociated H species which might immediately react with adsorbed CO species on the catalysts to CH₄ before those CO species desorbed. From the reactor configuration tests, the countercurrent mode showed higher H₂ removal rate in the combined reaction at 673 K compared to the cocurrent mode but the reaction rate in CO₂ methanation should be improved to maximize the perfomance of membrane reactor.     

Modeling and analysis of ceramic-carbonate dual-phase membrane reactor for carbon dioxide reforming with methane

A new high temperature tube-shell membrane reactor (MR) design for separation and utilization of CO₂ from the flue gas and for simultaneous production of syngas through carbon dioxide reforming of methane (CRM) is reported. The MR is based on a dual-phase CO₂ permeation membrane consisting of mixed-conducting oxide and molten carbonate phases. High temperature CO₂-containing flue gas and CH₄ are respectively fed into the shell and tube sides of the reactor packed with a reforming catalyst. Under performance conditions, CO₂ permeates selectively through the membrane from the shell side to the tube side and reacts with CH₄ to produce syngas. Additionally, the heat from the flue gas can transfer directly through the membrane to provide energy for the endothermic CRM reaction. An isothermal steady-state model was developed to simulate and analyze CRM in the MR in this work. The effect of the design and operational parameters, such as inlet CH₄ flow rate, shell side CO₂ partial pressure and the flue gas composition, i.e., containing O₂ or not, as well as the membrane thickness on the reactor performance with respect to the CH₄ conversion and the CO₂ permeation flux were investigated and discussed. The results show that the MR has a high efficiency in separating and utilizing CO₂ from the flue gas. For a CH₄ space velocity of 3265.31 h⁻¹, with a membrane thickness of 0.075 mm and the shell side CO₂ partial pressure of 1 atm, a CH₄ conversion of 48.06% and an average CO₂ permeation flux of 1.52 mL(STP) cm⁻² min⁻¹ through the membrane tube at 800 °C are obtained. Further improvement of the MR performance can be achieved by involving O₂ in the permeation process.     

Optimization of hydrogen production via coupling of the Fischer–Tropsch synthesis reaction and dehydrogenation of cyclohexane in GTL technology

In this study, a thermally-coupled reactor containing the Fischer–Tropsch synthesis reaction in the exothermic side and dehydrogenation of cyclohexane in the endothermic side has been modified using a hydrogen perm-selective membrane as the shell of the reactor to separate the produced hydrogen from the dehydrogenation process. Permeated hydrogen enters another section called permeation side to be collected by Argon, known as the sweep gas. This three-sided reactor has been optimized using differential evolution (DE) method to predict the conditions at which the reactants’ conversion and also the hydrogen recovery yield would be maximized. Minimizing the CO₂ and CH₄ yield in the reactor’s outlet as undesired products is also considered in the optimization process. To reach this goal, optimal initial molar flow rate and inlet temperature of three sides as well as pressure of the exothermic side have been calculated. The obtained results have been compared with the conventional reactor data of the Research Institute of Petroleum Industry (RIPI), the membrane dual – type reactor suggested for Fischer–Tropsch synthesis, and the membrane coupled reactor presented for methanol synthesis. The comparison shows acceptable enhancement in the reactor’s performance and that the production of hydrogen as a valuable byproduct should also be considered.