H2 Mole Fraction Research Articles

Numerical analysis on the combustion characteristics of NH3/H2/air flames with elevated initial pressure and temperature

In response to the global warming crisis, NH3/H2 blended fuel has aroused great interest as a promising energy carrier. Consequently, this study aims to construct a laminar burning velocity (LBV) correlation and perform a comprehensive analysis of combustion characteristics for NH3/H2/air flames with elevated initial pressure and temperature. For a = 0–0.4 (H2 mole fraction), the model (SL=exp[∑i=12(ai⋅ΔHi∑i=12(ai⋅ΔHi)⋅lnSL,i)]) based on the energy fraction mixing rule has sufficient accuracy in predicting the LBVs of NH3/H2/air flames at various work conditions. For a = 0.4–1, the model SL=exp[∑i=12(ai⋅lnSL,i)] has a better performance. For NH3/H2/air flames, branching reactions (R1: H + O2 <=> O + OH and R68: NH2 + NH <=> N2H2 + H) are the main reactions that promote LBVs, while the recombination reactions (R9: H + O2(+M) <=> HO2(+M) and R67: NH2 + NH = N2H3) are the main reactions that suppress LBVs. Raising the initial pressure and temperature can accelerate the reaction rates of NH3/H2/air flames. Furthermore, it is discovered that the decrease in LBVs of NH3/H2/air flames with elevated initial pressure is mainly due to the thermal diffusivity greatly decrease. The increase in LBVs of NH3/H2/air flames with elevated initial temperature is the result of the increase both in reaction rate and thermal diffusivity. The overall reaction orders of NH3/H2/air flames decrease with rising initial pressure and H2 mole fraction. Finally, it is discovered that the hydrodynamic instabilities of NH3/H2/air flames obviously increase with elevated initial pressure, and decrease with elevated initial temperature. The diffusional-thermal instability slightly increases with elevated initial temperature, and the initial pressure has little influence on it.

An experimental and modeling study on polyoxymethylene dimethyl ether 3 (PODE3) oxidation in a jet stirred reactor

Polyoxymethylene dimethyl ether (PODEn, n ≥ 1) is a class of oxygenated fuels containing unique carbon-oxygen chain structure and a promising alternative fuel for diesel engines. In this study, low-temperature oxidation characteristics of PODE3 were studied experimentally and numerically. Experiments were performed in a jet-stirred reactor (JSR) at equivalence ratios of 0.5, 1.0 and 2.0, in the temperature range of 500 to 950 K, and at atmospheric pressure. Mole fractions of PODE3, O2, H2, CO, CO2, CH3OH and C1-C2 hydrocarbons were measured by gas chromatograph (GC). Experimental measurements were compared with the simulation results based on two literature low-temperature oxidation models, denoted as the He model and the Cai model, respectively. Good agreement was obtained between the measured and simulated fuel consumption profiles, while a deviation was observed between the experimental and simulation results on the mole fractions of O2 and intermediate products at medium temperatures. Reaction pathway analyses based on the two models were performed, revealing that the second O2-addition reaction pathway is more significant in the prediction by the Cai model than that by the He model. Sensitivity analyses pointed out that the most important reactions affecting fuel consumption are the H-abstraction reactions of PODE3, and the decomposition of H2O2 and the consumption of CH2O become more sensitive at medium temperatures.

Kinetics of thermal conversion of gaseous products of polypropylene pyrolysis using several detailed kinetic mechanisms

Thermal conversion (TC) of polypropylene pyrolysis gaseous products was studied numerically using three detailed kinetic mechanisms (DKMs) for the initial temperatures T0 ranging from 700 K to 1300 K and the initial pressure of 1 atm. Numerical simulations showed that all DKMs predicted similar qualitative behavior of the reacting mixture, however, they gave significantly different rates of the increase of the mole fractions of CH4 and H2 along with simultaneous decrease in C2+ hydrocarbons. The temperature increase in course of TC process was also found to be predicted differently by the three DKMs. Its characteristics depended on the initial temperature, some calculations showed smooth increase while in others explosionlike regimes were observed. The conversion products, along with methane and hydrogen, contained aromatic compounds C6+. Various DKMs gave significantly different TC characteristic times.

Computational particle fluid dynamics simulation of biomass gasification in an entrained flow gasifier

Entrained flow gasification is an established technology for coal and petroleum coke particles. The technology is being investigated extensively for biomass gasification to meet the requirement of the green energy targets. A three-dimensional computational particle fluid dynamics (CPFD) model is developed to simulate an Entrained Flow (EF) gasification reactor. The model is validated against experimental gas composition and process temperature reported from an experiment published in the literature. The interdependence between reactor hydrodynamics, thermal and reaction chemistry is demonstrated and described for an EF reactor. Simulations show zones of high and low temperatures suggesting different reaction zones, such as a partial combustion zone near the fuel injector followed by a gasification zone. Particles in the central region show high carbon conversion compared to the particles in the other zones. Char- O₂ and char-H₂O are significant in the gasifier entrance region, whereas the char-CO₂ reaction is prevalent throughout the reactor elevation. The optimal gasification performance (higher mole fraction of CO and H₂) is in the range of equivalence ratio 0.3 to 0.44.

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.

Catalytic Reforming of the Aqueous Phase Derived from Diluted Hydrogen Peroxide Oxidation of Waste Polyethylene for Hydrogen Production.

The thermal degradation and conversion of waste polyethylene (PE) using a two-step process including hydrothermal oxidation (HO) and aqueous phase reforming (APR) were investigated. The objective of this study was to achieve efficient disposal of waste PE and generate H2 in a mild and green way. The effects of various HO conditions on both HO and APR processes were studied. A high H2 O2 concentration caused overoxidation of PE resulting in more CO2 . Decreasing the H2 O2 concentration weakened the overoxidation. The process using diluted H2 O2 exhibited the highest selectivity for acetic acid among the produced carboxylic acids. When the HO temperature exceeded 200 °C, there was an increase in the CO2 yield during the HO process and a decrease in the H2 yield during the APR process. In addition, the effects of various monometallic and bimetallic catalysts on the reforming of the aqueous phase from the HO of PE were discussed. The highest H2 mole fraction (51.52 %) in gaseous products from the APR process was obtained with Ru/mesoporous carbon. Nevertheless, Ru-Ni exhibited a higher stability than the monometallic Ru catalyst.

CFD analysis of biomass steam gasification in fluidized bed gasifier: A parametric study by the assessment of drying stage

ABSTRACT In this study, CFD analysis was performed based on a comprehensive pyrolysis chemical reaction model to simulate the gasification process of biomass in a fluidized bed gasifier using almond shells as the biomass feedstock. A novel multi-phase CFD model consisting of 33 chemical reactions that cover all of the drying stages, detailed primary and secondary pyrolysis stages, as well as gasification stage, was adopted for the first time. Gasification temperature and steam-to-biomass ratio were selected as the main parameters and their effects on produced gas composition, lower heating value, char yield, tar content, and tar components were evaluated. The obtained results of the base case agreed to a reasonable extent with the results of the previous experimental works. According to the results, an increase in gasification temperature enhanced the mole fractions of H2 and CO. Therefore, it was recommended to use higher temperatures and steam-to-biomass ratio for production purposes of H2 and CO. The lower heating value decreased by a factor of 14.7% and 1.86% for increased values of gasification temperature and steam-to-biomass ratio, respectively. It was also observed that CH4 mole fraction has a strong effect on the lower heating value of the produced gas. Furthermore, char yield was found to have a declined trend with increasing gasification temperature; however, the reverse was valid with increasing steam-to-biomass ratio.

Syngas production by methane-rich combustion in a divergent burner of porous media

The superadiabatic combustion in porous media contributes to the efficient conversion of methane to syngas. In this paper, a divergent packed bed burner of two-layer was proposed to obtain the characteristics of methane partial oxidation. The divergent angle, interface location and pellet diameter were used to study the temperature and species distributions. Results indicate that the upper limit of velocity gradually decreased as the equivalence ratio increased and the limit of the divergent burner is obviously higher than that of the cylindrical one. The increasing of the divergent angle within a certain range enhances the methane conversion and the 15° shows the best among the selected five angles. The mole fractions of H2 and CO gradually decrease when the interface locations move from the cylindrical region to the divergent one. As the equivalence ratio increased from 1.3 to 3.5, the yields of H2 and CO and the energy conversion efficiency of syngas increase first and then decrease, and the maximum efficiency of 45.9% appears at the equivalence ratio of 2.0. The divergent region weakens the influence of inlet velocities and contributes to the stability of reforming reactions.

Effect of ash on the performance of iron-based oxygen carrier in the chemical looping gasification of municipal sludge

As sludge ash is rich in alkali metals, the oxygen carrier (OC) performance in the multi-cycle chemical looping gasification (CLG) of dried sludge is affected by simultaneously cycling and accompanying ash. Fe-based OC was used in a lab-scale fluidized-bed reactor to investigate the multi-cycle CLG of dried sludge and to study the effect of accompanied ash on OC particle. The synthesis gas, carbon conversion rate, and reaction rate were monitored over several cycles. Physicochemical characterization of the OC was accomplished to determine its effective components and the alkali metal deposition from ash. The results showed that as the number of cycles increased, the mole fractions of H2 and CO2 in synthesis gas decreased and increased, respectively, both eventually stabilizing. The carbon conversion rate reached its peak in fifth cycle. The gasification rate of sludge reached its maximum value in the 14th cycle, slowing down and then stabilizing thereafter. The OC was loaded with more alkali metal during the cycle, whose activity was enhanced at the beginning. However, once the cycle number became higher than 25, ash spheroidization and sintering occurred on its surface. Accordingly, the OCs particle size and mass became a little larger for the accumulation of unreacted lattice oxygen.

Comparison and reduction of the chemical kinetic mechanisms proposed for thermal partial oxidation of methane (TPOX) in porous media

The effectiveness and reducibility of the methane combustion kinetic mechanisms were examined for the TPOX process in a porous medium. To this end, TPOX was successfully simulated using ANSYS CHEMKIN-Pro through a reactor network model composed of perfectly stirred and honeycomb-monolith reactors. The efficacy of six chemical kinetic mechanisms was compared for the equivalence ratios (ERs) ranging from 2.4 to 2.6 with a constant thermal load of 1540 kW/m2. This comparison revealed that Konnov was the most successful mechanism in the prediction of the H2 and CO mole fractions. This mechanism along with the GRI-3.0 and USC-Mech 2.0 mechanisms were then reduced by the direct relation graph with error propagation (DRGEPSA) followed by the full species sensitivity analysis (FSSA). This approach reduced the number of species from 119 to 29 for the Konnov mechanism, from 53 to 23 for the GRI 3.0 mechanism, and from 111 to 34 for the USC-Mech 2.0 mechanism.

Plasma Enhancement Gases separation via ceramic porous membranes for plasma exhaust processing system of DEMO

Plasma Enhancement Gases (PEGs), i.e. N2 and noble gases, are used to mitigate the heat load over plasma facing components. Therefore, in DEMO, the tokamak exhaust stream will contain a certain amount of these PEGs which require a dedicated purification and separation unit. In the last years, PEG separation using microporous ceramic membranes has been studied at ENEA Frascati laboratories in the framework of the EUROfusion programme. The experiments conducted with a binary gas mixture have revealed the poor separation capability of the multi-channel membranes as a consequence of their high permeance.In this activity, the behaviour of a commercial microporous single-channel membrane made of alpha alumina has been theoretically studied to evaluate its efficacy in separating H2 from PEGs. The analysis has considered a total feed flow rate of 20 L min−1 (at STP) having an equimolar composition of H2 with one of the following species: PEG (Ar or N2), D2 or He. The separation capability has been evaluated by assuming the upstream pressure in the range 200−1000 kPa and keeping the downstream pressure at 100 kPa. Considering the values of the permeances assessed in our previous work for single gas tests, the membrane length needed to achieve a given target of separation has been evaluated as a function of the H2 mole fraction in the retentate stream.

Different chemical effect of hydrogen addition on soot formation in laminar coflow methane and ethylene diffusion flames

Previous studies showed that adding hydrogen (H2) can have an opposite chemical effect on soot formation: its chemical effect enhances and suppresses soot formation in methane (CH4) and ethylene (C2H4) diffusion flames, respectively. Such opposite chemical effect of H2 (CE-H2) remains unresolved. The different CE-H2 is studied numerically in the two laminar coflow diffusion flames. A detailed chemical mechanism with the addition of a chemically inert virtual species FH2 is used to model the gas-phase combustion chemistry in this study. Particularly, a reaction pathway analysis was performed based on the numerical results to gain insights into how H2 addition to fuel affects the pathways leading to the formation of benzene (A1) in CH4 and C2H4 flames. The numerical results show that the CE-H2 in CH4 diffusion flame to prompt soot formation is ascribed that the higher mole fraction of H atom promotes the formation of A1 and Acetylene (C2H2) and leads to higher nucleation rate and eventually higher soot surface growth rate. In contrast, adding H2 to C2H4 diffusion flames decreases soot nucleation and surface growth rate. The lower soot nucleation rate is due to the lower mole fractions of pyrene (A4), while the lower soot surface growth rate is due to the lower mole fractions of H atom and C2H2, higher mole fraction of H2 and lower soot nucleation rate. Furthermore, the CE-H2 in C2H4 diffusion flames promotes the formation of A1, but suppresses the formation of A4.

Effect of added struts and intake velocity on flame stabilization in supersonic combustors

In the present computational study, the impact of strut positions and the effect of inlet Mach numbers on the combustion efficiency are investigated in a strut-based supersonic combustor. An experimentally investigated model combustor developed at the German Aerospace Center (DLR) is simulated and validated. Then, a model combustor with three struts placed at different positions is investigated. Two-dimensional, compressible, reacting-flow governing equations are solved along with single-step chemistry reaction and k-ω SST turbulence model using a commercial CFD code FLUENT. The oblique shock from the struts has a profound influence on the mixing and combustion process. The H2O mole fraction, H2 mole fraction contours, and combustion efficiency of various configurations are compared for finding better mixing and flame stabilization. The combustion efficiency reduces when the two struts are located in farther downstream or placed at the same downstream location. At higher Mach numbers, the combustion is delayed, and the mixing of fuel with the supersonic mainstream is incomplete.

Syngas Characteristics From Catalytic Gasification of Polystyrene and Pinewood in CO2 Atmosphere

Abstract Syngas production from catalytic gasification of polystyrene and pinewood in CO2 atmosphere was investigated over Ni-Mg/Al2O3 catalyst in a fixed-bed reactor at 900 °C. A quasi in situ method was adopted for catalytic gasification wherein the catalyst placed downstream of the feedstock in the same reactor was used for enhanced syngas production. The effect of catalyst on evolutionary behavior, cumulative syngas yield, syngas composition, and cold gas efficiency was systematically analyzed. The results showed that addition of catalyst for polystyrene gasification resulted in enhanced yields of 63% H2, 20% CO, 119% CH4, and 85% C2-C3 yields. Enhanced H2 and light hydrocarbon yields were mainly from enhanced cracking of pyrolytic vapors from polystyrene degradation, while the CO yield was attributed to CO2-assisted reforming of benzene derivatives from primary cracking and polycyclic aromatic hydrocarbons (PAHs) from secondary gas phase condensations. The yields of H2, CO, CH4, and C2-C3 from pinewood gasification in the presence of catalyst was also enhanced by 150%, 14%, 39%, and 16%, respectively, indicating that Ni-Mg/Al2O3 catalyst can efficiently enhance syngas production in CO2-assisted gasification. A comparison of syngas composition between non-catalytic and catalytic conditions revealed improved syngas quality in catalytic gasification with increased H2 mole fraction but decreased CO mole fraction. Furthermore, cold gas efficiency enhanced from 44% to 57% in catalytic polystyrene gasification, and from 75% to 94% in catalytic pinewood gasification. The results suggest that catalytic CO2 gasification offers a promising pathway for efficient energy production from wastes plastics and biomass while simultaneously using CO2.

Continuous monitoring of hydrogen and carbon dioxide at Stromboli volcano (Aeolian Islands, Italy)

The geochemistry of volcanic gases has been fruitfully applied to identify important changes in the volcanic activity. This study reviews the dataset of the volcanic gas survey performed during 2009 and 2010 at Stromboli (Aeolian Islands – Italy). Dry gas collection occurred discontinuously at the crater fumaroles for subsequent chemical and isotopic (δ13C-CO2) analyses in the laboratory.A tailor-made device enabled continuous survey of H2 molar fraction and CO2 flux on the same site. Evaluation of the raw data was performed in accordance with air temperature, atmospheric pressure, wind speed and wind direction dataset. Both MLR (Multiple Linear Regression) and FFT (Fast Fourier Transform) analyses allowed filtering the dataset from the environmental effects. The MLR analysis indicated that wind speed and air temperature affected the CO2 flux. Changes in the atmospheric pressure promoted pumping effect of the fumarole gas and caused changes in the H2 molar fraction. The power spectral analysis revealed daily cycles in both gases. A digital signal filtering procedure enabled minimizing the environmental effects.This study confirmed that gas emissions from the crater fumaroles have both chemical ad isotopic composition similar to the magmatic gas phase. The results of the continuous survey showed that changes of both H2 and CO2 correlated with changes of the volcanic activity. Therefore, H2 and CO2 resulted effective tracers of the dynamics involving the plumbing system of Stromboli. Identification of changes in the gas emissions at open conduit volcanoes offers a great advance over the ground gas survey. The results of the continuous survey at Stromboli showed that H2 could apply as an auxiliary parameter of the CO2 flux in the surveillance programs of active volcanoes.

Effect of concentration inhomogeneity on the pulsating instability of hydrogen–oxygen detonations

One-dimensional, unsteady gaseous detonation propagation in a non-homogeneous medium is investigated numerically using the reactive, compressible Navier–Stokes equations with detailed chemistry. The effect of concentration inhomogeneity on the pulsating mode is modeled by a sinusoidal distribution of H2 mole fraction in a H2–O2 mixture. The mixture inhomogeneity, varied by changing the disturbance frequency and amplitude, has significant effects on the pulsating behavior of the detonation due to the interaction of the leading shock with the local gradient. Initially exhibiting a four-period pulsation, the detonation wave entering a non-homogeneous medium can adapt and re-establish into a new propagation mode. For a fixed, large-amplitude sinusoidal disturbance, the period-doubling limit cycle is prone to be destroyed, resulting in a chaotic mode for the propagating detonation front in the non-homogeneous mixture; lowering the disturbance frequency also favors a transition from a periodic pulsation to a chaotic one. When the disturbance amplitude decreases, the propagating detonation can transit quickly to a new pulsating behavior, which tends to be more regular. For a very small amplitude of inhomogeneous variation, it is found that the frequency corresponding to the wavelength close to that of the intrinsic pulsation in the uniform mixture makes the original four-period mode become a double-period mode; for a frequency less than this value, the double-period mode is prone to become more unstable. Consequently, this demonstrates that inhomogeneity could have a positive effect on stabilizing a pulsating detonation.

A priori DNS study of applicability of flamelet concept to predicting mean concentrations of species in turbulent premixed flames at various Karlovitz numbers

Complex-chemistry direct numerical simulation (DNS) data obtained earlier from lean hydrogen-air flames associated with corrugated flame (case A), thin reaction zone (case B), and broken reaction zone (case C) regimes of turbulent burning are analysed to directly assess capabilities of the flamelet approach to predict mean concentrations of species in a premixed turbulent flame. The approach consists in averaging dependencies of mole fractions, reaction rates, temperature, and density on a single combustion progress variable c, which are all obtained from the unperturbed laminar flame. For this purpose, four alternative definitions of c are probed and two probability density functions (PDFs) are adopted, i.e. either an actual PDF extracted directly from the DNS data or a presumed β-function PDF obtained using the DNS data on the first two moments of the c(x, t)-field. Results show that the mean density and mean mole fractions of H2, O2, and H2O are well predicted using both PDFs for each c, although the predictive capabilities are little worse in case C. In cases A and B, the use of the actual PDF and the fuel-based c also offers an opportunity to well predict mean mole fractions of O and H, whereas the mean mole fraction of OH is slightly underestimated. In the highly turbulent case C, the same approach performs worse, but still appears to be acceptable for evaluating the mean radical concentrations. The use of the β-function PDFs or another combustion progress variable yields substantially worse results for these radicals. When compared to the mean mole fractions, the mean rate of product creation, i.e. the source term in the transport equation for the mean combustion progress variable, is worse predicted even for a quantity (species concentration or temperature) adopted to define c and using the actual PDF. Consequently, turbulent burning velocity is not predicted either.

Performance analysis of syngas production in a water thermal plasma reactor

Water thermal plasma gasification is a promising gasification technology aiming at providing sustainable disposal for various wastes. In this study, thermochemical modeling and optimization of a water thermal plasma reactor is carried out in order to enhance H2 and CO production from propane gasification. The novelty of present study is that the plasma reactor is considered as two connected partially stirred reactors for steam dissociation and propane gasification. Various detailed chemical mechanisms are evaluated against previously published experimental data and thermodynamic results. Influences of important parameters on syngas production, such as argon temperature and flow rate as well as steam and propane flow rates have been studied. It is found that the temperature and flow rate of argon have major impacts on hydrogen production due to changing the concentration of H radicals in the steam dissociation part. In particular, reducing argon temperature by 30% can result in 14% increase in H2 mole fraction. Also, 20% reduction in argon flow rate would increase H2 concentration by 9.5%. The present modeling approach will be useful in further investigations to improve the construction of a plasma reactor and defining best operational conditions for syngas production.

Effects of H2 Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame.

Flame extinction is one of the most essential critical flame features in combustion because of its relevance to combustion safety, efficiency, and pollutant emissions. In this paper, detailed simulations were conducted to investigate the effect of H2 addition on dimethyl ether spherical diffusion flame in microgravitational condition, in terms of flame structure, flammability, and extinction mechanism. The mole fraction of H2 in the fuel mixture was varied from 0 to 15% by 5% in increment. The chemical explosive mode analysis (CEMA) method was employed to reveal the controlling physicochemical processes in extinction. The results show that the cool flame in microgravitational diffusive geometry had the “double-reaction-zone” structure which consisted of rich and lean reaction segments, while the hot flame featured the “single-reaction-zone” structure. We found that the existence of “double-reaction-zone” was responsible for the stable self-sustained cool flame because the lean zone merged with the rich zone when the cool flame was close to extinction. Additionally, the effect of H2 addition on the cool flame was distinctively different from that of the hot flame. Both hot- and cool-flame flammability limits were significantly extended because of H2 addition but for different reasons. Besides, for each H2 addition case, the chemical explosive mode eigenvalues with the complex number appeared in the near-extinction zone, which implies the oscillation nature of flame in this zone which may induce extinction before the steady-state extinction turning point on the S-curve. Furthermore, as revealed by CEMA analysis, contributions of the most dominated species for extinction changed significantly with varying H2 additions, while contributions of the key reactions for extinction at varying H2 additions were basically identical.

The effect of non-uniform temperature on the sorption-enhanced steam methane reforming in a tubular fixed-bed reactor

The effect of non-uniform temperature on the sorption-enhanced steam methane reforming (SE-SMR) in a tubular fixed-bed reactor with a constant wall temperature of 600 °C is investigated numerically by an experimentally verified unsteady two-dimensional model. The reactor uses Ni/Al2O3 as the reforming catalyst and CaO as the sorbent. The reaction of SMR is enhanced by removing the CO2 through the reaction of CaO + CO2 → CaCO3 based on the Le Chatelier's principle. A non-uniform temperature distribution instead of a uniform temperature in the reactor appears due to the rapid endothermic reaction of SMR followed by an exothermic reaction of CO2 sorption. For a small weight hourly space velocity (WHSV) of 0.67 h−1 before the CO2 breakthrough, both a low and a high temperature regions exist simultaneously in the catalyst/sorbent bed, and their sizes are enlarged and the temperature distribution is more non-uniform for a larger tube diameter (D). Both the CH4 conversion and the H2 molar fraction are slightly increased with the increase of D. Based on the parameters adopted in this work, the CH4 conversion, the H2 and CO molar fractions at D = 60 mm are 84.6%, 94.4%, and 0.63%, respectively. After CO2 breakthrough, the reaction of SMR dominates, and the reactor performance is remarkably reduced due to low reactor temperature.For a higher value of WHSV (4.03 h−1) before CO2 breakthrough, both the reaction times for SMR and CO2 sorption become much shorter. The size of low temperature region becomes larger, and the high temperature region inside the catalyst/sorbent bed doesn't exist for D ≥ 30 mm. The maximum temperature difference inside the catalyst/sorbent bed is greater than 67 °C. Both the CH4 conversion and H2 molar fraction are slightly decreased with the increase of D. However, this phenomenon is qualitatively opposite to that for small WHSV of 0.67 h−1. The CH4 conversion and H2 molar fraction at D = 60 mm are 52.6% and 78.7%, respectively, which are much lower than those for WHSV = 0.67 h−1.