Packed Bed Tubular Reactor Research Articles

Modeling & experimental studies on enhancement of H2S conversion using catalytic membrane reactor for hydrogen production

Abstract Acidic gases such as H2S and CO2 are generated in the refineries during coal gasification. These pollutant gases need to be treated before releasing to the atmosphere. Conventionally, H2S gas is treated by Claus process in which H2S is converted to elemental S and H2O, in presence of O2 at ∼1,200 K. In the present energy scenarios, hydrogen has got importance as a source of clean fuel for industrial application. The H2S generated in the refineries can be a potential precursor of hydrogen. If this hydrogen can be obtained by thermal decomposition of H2S, that can increase the overall economic value of the H2S containing streams and the produced hydrogen can be used for hydrocracking and hydro-treating in refineries, as well as to synthesize value-added products for chemical industries. However, H2S thermal decomposition is an endothermic and equilibrium limited reaction (equilibrium conversion is only ∼15 % at 1,000 K), requiring a very high temperature (∼1,500 K) to achieve even a conversion of greater than 40 %. Packed Bed Catalytic Membrane Reactor (PBCMR) for thermal decomposition of H2S can be a potential technology augmentation and process intensification to increase this equilibrium conversion. In this work, modeling and experimental studies of H2S thermal decomposition using in-house designed & developed PBCMR have been carried out. The modeling studies were validated with experimental data. Clay-alumina ceramic tubular membrane (L: 250 mm; OD: 12 mm; thickness: 2 mm) was fabricated using extrusion process having an average membrane pore size of ∼1 μm and with a porosity of ∼20 %. Pt (2 %) coated alumina extrudes were used as catalyst to accelerate the reaction kinetics. Experimental studies showed that H2S to hydrogen conversion of ∼90 % is achieved using PBCMR at ∼1,523 K, compared to only ∼40 % conversion in a conventional packed bed tubular reactor (without membrane). Modelling studies were carried out to study the influence of operating parameters such as, reactor wall temperature, feed temperature, pressure and feed velocity. Studies showed that reactor wall temperature is having the most dominant effect on H2S conversion, which is confirmed by experimental findings. The studies offer useful insights into the application of PBCMR technology for management of waste gas stream containing H2S and recovery of hydrogen.

Enhanced CO2 Methanation over Nickel‐Based Unsupported Catalyst Synthesized by Chemical Precipitation Method

AbstractThis study investigated the catalytic CO2 methanation using nickel oxide (NiO) nanoparticles and nickel oxalate (NiC2O4) as catalysts. The NiC2O4 precursor was synthesized through a chemical precipitation reaction between nickel (II) nitrate hexahydrate (Ni(NO3)2.6H2O) and oxalic acid (H2C2O4.2H2O). Nickel oxide (NiO) nanoparticles were synthesized through thermal decomposition of NiC2O4 precursor at 450 °C in air. The samples were characterized by XRD, FTIR, BET, SEM, and EDX. The XRD and FTIR analyses revealed that the NiO nanoparticles were well‐crystallized having size 17.30 nm. The BET analysis of the NiO sample revealed mesoporous NiO nanoparticles with a specific surface area (SBET) of 29.08 m2/g and a narrow distribution of pore sizes. The catalytic performance of NiO and NiC2O4 catalysts studied for the CO2 methanation in tubular packed bed reactor at 150–550 °C and 1 atm. The reduced NiO nanoparticles exhibited more catalytic activity than the decomposed NiC2O4 catalyst. At 380 °C, 1 atm, and gas hourly space velocity (GHSV) of 9000 mL g−1 h−1, the reduced NiO nanoparticle catalyst showed high catalytic activity, with a maximum CO2 conversion of 85.54 %, 99 % CH4 selectivity, and 84.69 % CH4 yield. Furthermore, the NiO nanoparticle catalyst demonstrated excellent stability after 12 h of streaming at 380 °C.

Temperature control strategy for safer and heat-efficient operations in a catalytic flow reactor

A new temperature control strategy for a packed-bed tubular reactor was proposed. Case studies of a highly exothermic 1st-order reaction and an actual 2nd-order reaction were conducted using the computational fluid dynamics software COMSOL Multiphysics® 4.4. Through the simulation, the important factors for reactor temperature control were confirmed, which were the parameters related to heat transfer. Based on the ratio of the heat generation rate to the heat transfer rate, a new dimensionless number was proposed for controlling the temperature increase within an acceptable range in a reactor. Through case studies, the validity of the proposed dimensionless number was confirmed, and an important value of a proportionality constant was derived from the results. Using the proposed dimensionless number, a reactor size can be maximized within an acceptable temperature increase. The results obtained in this study are expected to provide important guidelines for temperature control and maximization of production using flow reactors.

A numerical study of internally heating, counter-flow tubular packed bed reactor for methanol steam reforming

This study numerically investigates methanol steam reformer design using the COMSOL software. The reformer is heated with internal heating tubes (HTs). The effects of the reformer shape, the heating tube arrangement and heating rate are studied. Results show that a divergent reformer shape has the highest methanol conversion (68%) due to slower average flow rate of the reactants, longer residence time, and more heat absorption. For fixed heating rate, increasing the number of HTs increases the methanol conversion rate by up to 14.8% due to better heat transfer. Furthermore, methanol conversion can also be enhanced with increasing heating rate and placing HTs towards reactor center. The optimal design of a divergent tube with a divergent angle of 5° and 8 HTs has a maximum conversion rate of 94.5%. The results of this study are helpful for engineers working on designing an MSR with high-methanol conversion rate.

Gas-phase degradation of VOCs using supported bacteria biofilms.

Herein we report the use of Pseudomonas putida F1 biofilms grown on carbonized cellulosic fibers to achieve biodegradation of airborne volatile organic compounds (VOCs) in the absence of any bulk aqueous-phase media. It is believed that direct exposure of gaseous VOC substrates to biomass may eliminate aqueous-phase mass transfer resistance and facilitate VOC capture and degradation. When tested with toluene vapor as a model VOC, the supported biofilm could grow optimally at 300 p.p.m. toluene and 80% relative humidity, with a specific growth rate of 0.425 day-1 . During long-term VOC biodegradation tests in a tubular packed bed reactor, biofilms achieved a toluene degradation rate of 2.5 mg gDCW -1 h-1 during the initial growth phase. Interestingly, the P. putida F1 film kept biodegrading activity even at the stationary nongrowth phase. The supported biofilms with a biomass loading of 20% (wt) could degrade toluene at a rate of 1.9 mg gDCW -1 h-1 during the stationary phase, releasing CO2 at a rate of 6.4 mg gDCW -1 h-1 at the same time (indicating 100% conversion of substrate carbon to CO2 ). All of these observations promised a new type of "dry" biofilm reactors for efficient degradation of toxic VOCs without involving a large amount of water.

Combustion synthesis of lanthanum oxide supported Cu, Ni, and CuNi nanoparticles for CO2 conversion reaction

The reverse water gas shift (RWGS) process is considered a feasible method for lowering greenhouse gas emissions by utilizing CO2 and converting it to CO. Herein, we evaluated the catalytic conversion of CO2 through the RWGS reaction over transition metal nanoparticles supported on lanthanum. Catalysts of selected active metals (Cu, Ni, and CuNi) on lanthanum oxide support were investigated in a packed bed tubular reactor within a temperature range of 100–600 °C to assess their catalytic activity and selectivity towards CO. The results of the catalyst's activity and stability experiments showed maximum CO2 conversions of 57%, 68% and 74% for Cu–La2O3, Ni–La2O3, and CuNi–La2O3, respectively, at 600 °C and excellent stability over a 1440-min time on stream (TOS) with a carbon deposition rate of less than 3 wt%. However, among all investigated catalysts, only the 1 wt% Cu–La2O3 catalyst displayed a CO selectivity of 100% at all the studied temperatures, whereas the nickel-containing catalysts showed selectivity for methane along with carbon monoxide. Furthermore, the morphological properties of the support and catalysts, as well as the effect of the reaction conditions on the catalysts surface, were studied using a variety of techniques, including XRD, TEM, SEM-EDX and TPR. The results showed promising potential for the application of transition metal catalysts on lanthanum oxide support for RWGS that could be extended to other hydrogenation reactions.

Sulphuric acid decomposition using Cr–Fe2O3 catalyst in a tubular Packed Bed Reactor (PBR): Modeling and experimental studies

Catalytic decomposition of sulphur trioxide (SO3), is the rate-controlling and high temperature-endothermic reaction step in three-step decomposition of sulphuric acid. In this work, formulation of one dimensional (1-D) model, detailed transport modeling and experimental studies have been carried out for a non-isothermal, non-adiabatic, tubular-Packed Bed Reactor (PBR). This is to study the effect of heat and mass transfer resistances, in the catalyst bed and also within the catalyst particle, for the decomposition of SO3. 1-D model consists of set of coupled Differential Algebraic Equations (DAEs), which are numerically solved for axial profiles (Temperature, Flow, Pressure) with plug flow reactor assumption. Further, a double-porosity modeling of the reactor has been carried out for the detailed transport study using COMSOL MULTIPHYSICS® simulation software. Here transport equations with the rate law are solved for two different porosities (domains); micro pores inside the catalyst particle (ε) and macro pores (void fraction-φ) in the packing. Models are validated with experimental studies and the molar conversion of SO3 obtained using the models are compared with conversion of an isothermal PBR. Chromium doped iron oxide (Cr–Fe2O3) catalyst; a ‘pellet’ type catalyst is used in this experimental study. Experiments are carried out at different flow (liquid) rates (160–315 ml h−1), wall temperature (973–1243 K) and with two different catalyst bed lengths (catalyst loading of 555 g and 288 g). Double-porosity (COMSOL) model predictions are better close to the experimental data. A multi-scale analysis of the system has been carried out using the double-porosity model, in order to get an insight of concentration drops in the particle (pore diffusion resistance) and fluid film (film resistance) at various locations inside the reactor. Film resistance is found to be negligible when compared with the pore diffusion resistance, in the studied experimental conditions. Modeling of transport (heat and mass transfer) resistances together with kinetics of SO3-decomposition, in two different porous-domains in a PBR, is the novelty of present work. The developed models are useful for maximizing the conversion of SO3 (by tuning the model parameters) in a PBR by minimizing the heat and mass transfer resistances.

Combustion synthesis of copper ceria solid solution for CO2 conversion to CO via reverse water gas shift reaction

The reverse water–gas shift chemical (RWGS) reaction is a promising technique of converting CO2 to CO at low operating temperatures, with high CO selectivity and negligible side products. In this study, we investigate the synthesis of Cu/CeO2 catalyst using Solution Combustion Synthesis (SCS) technique and its performance for the RWGS reaction using a tubular packed bed reactor. Results indicate that the catalytic activity and stability of CeO2 at low and moderate temperatures can be effectively improved by the addition of a small quantity of copper (1 wt%). The conversion of CO2 improves with an increase in temperature, with a maximum value of 70% at 600 °C, showing a steady time on stream (TOS) performance for 1200 min with negligible carbon deposition of <0.05 wt%. The high catalyst activity is due to the synergistic interaction between the active Cu0 species and Ce3+-oxygen vacancy. The Cu/CeO2 catalyst was also found to have 100% selectivity for CO, and no CH4 was detected in the outlet stream. Moreover, the morphological characteristics of the support and catalysts (fresh and post-reaction samples), as well as the impact of reaction on the catalysts surface were investigated using various methods such as x-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy with energy dispersive x-ray spectra (SEM/EDX). The results demonstrate that Cu/CeO2 offers a good potential for being a robust RWGS catalyst with exclusive selectivity for CO without the undesired methanation side-reaction.

Optimization of hydrogen production via catalytic autothermal reforming of crude glycerol using response surface methodology and artificial neural network

In this work, the central composite design of the response surface methodology (RSM) and artificial neural network (ANN) were deployed to investigate process variables and optimize hydrogen gas production via autothermal reforming of crude glycerol using 5%Ni/CeZrCa catalyst in a packed bed tubular reactor. The input variables studied are reaction temperature, feed flow rate, steam to carbon ratio (S/C), oxygen to carbon ratio (O/C), and catalyst weight. The neural network analysis of these input variables measured their individual significance and contribution in the autothermal reforming process prior to the development of a quadratic polynomial model with RSM for predicting hydrogen yield as well as optimization. Statistical analyses showed that the mathematical model developed excellently represents the data with high model adequacy and no significant lack of fit. The results of the neural network input variable significance ranking approach showed that the reaction temperature contributed more than any other independent variable at a ranking weight of 53% while the O/C ratio showed the least impact at 3%. The results of the optimization gave the optimum parameters for hydrogen gas yield as follows; Temperature: 650°C, crude glycerol flow rate: 3.3 mmol C/min, S/C: 2.34, O/C: 0.052, and catalyst weight of 0.15 g with a maximum feed conversion of approximately 92% and 97% H2 yield. ANN provided a better regression with excellent statistical test values as follows R2: 0.999, MSE: 10−8, AAD: 0.34%, and RMSE: 3.5 × 10−4%. It is clear from the results of the model adequacy and error calculations that ANN is superior and has shown a better model fit than the RSM.

Two-step thermochemical cycles using fibrous ceria pellets for H2 production and CO2 reduction in packed-bed solar reactors

The thermochemical redox activity and performance of commercial-grade fibrous ceria pellets were determined including fuel production rates and yields from H2O and CO2 dissociation. Two solar reactors integrating the ceria pellets undergoing two-step thermochemical cycling (with temperature-swing between alternating redox steps) were experimentally tested. They consisted of packed-bed tubular and cavity-type solar reactors with direct or indirect heating of the reacting materials. The obtained fuel production rates compared favorably with the performance of other previously considered microstructured ceria materials such as templated foams, sintered felts, bioinspired or ordered macroporous morphologies. H2 production rates reached 2.3 mL.g−1.min−1 (with H2/O2 ratios approaching 2) in the indirectly-heated tubular reactor after reduction at 1400 °C and oxidation upon free cooling below 950 °C in steam atmosphere (57% molar content). The highest fuel production rate (~9.5 mL.g−1.min−1) and peak solar-to-fuel energy efficiency (~9.4%) were reached in the directly-irradiated cavity-type reactor (with a reduction step at 1400 °C under reduced pressure, and an oxidation step in pure CO2 below 950 °C). The reduction extent was favored at low pO2 (δ up to 0.056) and the fuel yields were thus improved notably (up to 315 μmol/g) by decreasing the total pressure below 0.1 bar during the reduction step. The fuel production rate increased when the oxidation temperature decreased (because the reaction was thermodynamically more favorable). An increase in CO2 partial pressure further promoted the oxidation kinetics (and decreased the pCO/pCO2 ratio, thus shifting the thermodynamic equilibrium toward CO product). The fibrous ceria structures exhibited stable morphologies with high fuel production performance similar to less scalable porous structures, thus offering the potential for versatile applications in packed-bed solar reactors.

Effect of nickel on combustion synthesized copper/ fumed‐SiO 2 catalyst for selective reduction of CO 2 to CO

In this study, we explore the effect of nickel incorporation in Cu/fumed‐SiO2 catalyst for CO2 reduction reaction. Two catalysts, Cu and CuNi supported on fumed silica were synthesized using a novel surface restricted combustion synthesis technique, where the combustion reaction takes place on the surface of the inert fumed‐SiO2 support. An active solution consisting of a known amount of metal nitrate precursors and urea (fuel) was impregnated on fumed silica. The catalyst loading was limited to 1 wt% to ensure localized combustions on the surface of fumed‐SiO2 by restricting the combustion energy density. The synthesized catalysts were tested for CO2 hydrogenation reaction using a tubular packed bed reactor between temperature 50°C and 650°C, where Cu/SiO2 showed high CO2 conversion to carbon monoxide, and the addition of Ni further improved the catalytic performance and showed some tendency for methane formation along with CO. Moreover, both the catalysts were highly stable under the reaction conditions and did not show any sign of deactivation for ~42 hours time on stream (TOS). The catalysts were characterized using X‐ray diffractometer (XRD), scanning electron microscope/energy dispersive X‐ray spectrometer (SEM/EDX), transmission electron microscope (TEM), and the Brunauer‐Emmet‐Teller (BET) surface area measurement technique to understand their structural properties and to assess the effect of CO2 conversion reaction. In situ DRIFTS was also used to investigate the reaction pathway followed on the surface of the catalysts.

Process intensification of dry reforming of methane by structured catalytic wall-plate microreactor

Dry reforming of methane (DRM) for syngas production has gained much attention because of its significant potential in greenhouse gas reduction and economic efficiency over steam reforming. The practical application of DRM has been hindered by problems of coking in cold spots, coking-induced blockage and pressure loss in the catalyst packed beds. The previous works developed a packed bed type microreactor with a blow-through channel, namely a catalytic wall-plate microreactor (CWPMR) to solve those problems. However, it did not outperform the conventional tubular packed bed reactor. Objective of this study is to process-intensify DRM by structuring CWPMR. A void space and micro-baffle were formed in the packed layer and in the blow-through channel, respectively. This study proposed the micro-structure to enhance convective heat and mass transfer, and resultant reaction efficiency. Particle-resolved CFD simulations verified the favorable effects of the micro-structure on flow distribution in CWPMR. Reaction experiments showed that the micro-structured CWPMR significantly outperformed the conventional reactor and reduced carbon deposition with the identical catalyst loading.

Analysis and Simulation of Catalytic Steam Prereforming of Hydrocarbons in Adiabatic Tubular Reactors

This work presents a dynamic model describing the catalytic steam prereforming of hydrocarbons (natural gas and naphtha) in adiabatic packed-bed tubular reactors. Pre-reforming is an additional ste...

Parametric Sensitivity Analysis for the Industrial Case of O-Xylene Oxidation to Phthalic Anhydride in a Packed Bed Catalytic Reactor

The operation of packed bed tubular reactors, for exothermic catalytic reactions, presents special challenges provoked by hotspot development. Their potential safety risk can be assessed using different mathematical methodologies, among them, the so-called parametric sensitivity analysis (PSA). This study deals with the identification of safe operational conditions (e.g., feed temperature conditions) for the catalytic oxidation of o-xylene. Three different reaction networks, with different degrees of complexity, were analyzed. Thus, the critical values of the operating parameters, allowing us to define run-away and stable operation conditions, were provided for different reactive configurations. The obtained results were compared with the data reported by various authors who used similar reaction rate laws. The purpose of the present study is to illustrate the peculiarities of the PSA and its application for the design, analysis, and operation of o-xylene multitubular catalytic reactor.

Modelling and experimental investigation of compact packed bed design of methanol steam reformer

A comprehensive mathematical model was developed to analyse methanol steam reforming in catalytic packed-bed tubular reactor. All the important aspects of reaction kinetics of main reactions and thermodynamic terms of heat and mass transfer were studied for commercially available CuO/ZnO/Al2O3 catalysts from Süd-Chemie. This numerical model was simulated using Engineering Equation Solver (EES). Through the set of organized simulation studies, the basic operational boundary conditions of operating temperature (573 K) with respect to complete conversion of methanol and optimum hydrogen generation, optimum S/C ratio (1.4) of methanol water mixture feed and operating capacity of one tubular reactor array were discovered. At temperatures near 573 K it was found that the reformate gas does not require any purification/filtration to be supplied to a HT-PEMFC as the CO concentration in reformate gas was low (below 30000 ppm). The simulation work for understanding the effect of different operating condition(s) on the reformer performance generated design of experiment for investigation of the efforts carried out to evaluate, build and demonstrate a 0.25 kWe equivalent methanol reformer for HT-PEM fuel cell system.The paper discusses few of the important aspects on the experimental investigation of effect of operating conditions on methanol steam reformer design with packed bed configuration for hydrogen production. The basic investigation included the analysis of effect of design and operating parameters on the methanol conversion and quality of reformate gas generation (amount of CO). The investigation also covers the analysis of heat and mass transfer along with chemical reaction and generation of species to achieve optimum process parameters and system efficiency. These investigations led to finalise, the operating parameters and basic design philosophy of the packed bed tubular methanol steam reformer for 5 kWe HT-PEMFC system application.

Influence of Porosity in a Packed-Bed Tubular Reactor on Biodiesel Production from Soybean Oil and Supercritical Ethanol: An Experimental and Phenomenological Investigation

In the present study, the transesterification of soybean oil with ethanol under supercritical conditions was investigated using a packed-bed tubular reactor. The experiments were performed with an oil/alcohol molar ratio of 1:40, a pressure of 15 MPa, and different conditions of temperature (573–673 K), flow rate (0.5–1.0 mL/min), and bed porosity (0.32–1.0). A phenomenological model was developed to describe and analyze the results. The highest ester yield (98.99%) was obtained for the lower bed porosity (0.32), under 673 K and 0.5 mL/min with a residence time of 5.44 min. The kinetic and dispersion coefficients were estimated using the particle swarm optimization algorithm, and the model fitted the experimental data with an R2 coefficient of 0.97. The proposed kinetic model followed the behavior of the Arrhenius equations. Low values of dispersion were observed under conditions of lower flow rate and porosity. An analysis of the model allowed us to verify that the increase of the ester yield produced oc...

Effect of CeO2 loading of the Ce-Al mixed oxide on ultrahigh temperature water-gas shift performance over Ce-Al mixed oxide supported Ni catalysts

The purpose of this study is to investigate and to evaluate the effect of CeO2 loading in the Ce-Al mixed oxide (CeO2-Al2O3) on physicochemical properties as well as the ultrahigh temperature water-gas shift (UHT-WGS) catalytic performance of Ni/x wt.%CeO2-Al2O3 (xCe-Al; x = 1, 3, 5, 7, and 10) catalysts. The Al2O3 (Al) and the xCe-Al supports were synthesized via the sol-gel method. The Ni/Al and Ni/xCe-Al catalysts were prepared by the incipient wetness impregnation method. The catalysts were characterized using XRD, the N2 adsorption-desorption isotherms, H2-TPD, H2-TPR, TEM and TGA/DTA. The UHT-WGS catalytic performance of these catalysts were carried out in a packed-bed tubular reactor. The results reveal that adding CeO2 to the Al2O3 support for the Ni supported catalyst increased the surface area resulting in the enhancement of nickel dispersion and reducibility of the Ni/xCe-Al catalysts. However, under certain circumstances, bulk CeO2 can separate from the support to the catalyst surface and partially cover the Ni metal in the case of high CeO2 loading. Compared to other catalysts, the Ni/5Ce-Al catalyst illustrates the highest UHT-WGS catalytic activity (CO conversion >75%) with the maintainability. This proposed composition provides the appropriate Ni-Ce-Al interaction that also suppresses the graphitic/filamentous carbon.

Intensified dimethyl ether production from synthesis gas with CO2

Catalytic conversion of syngas to dimethyl ether (DME) is modeled in a microchannel reactor comprised of horizontal groups of rectangular shaped cooling and catalyst washcoated reaction channels involving counter–current flows of air and syngas, respectively. The steady–state model, deviating from the literature–based experimental data in the range of 3–14%, involves two–dimensional conservation of momentum, heat and species mass together with inter–channel heat exchange and reactive transport within porous catalyst layer composed of equivalent mass of uniformly mixed Cu–ZnO/Al2O3 and γ–Al2O3 catalysts. For the first time in the literature, the benefits of functional and volumetric intensification on the precise regulation of the interplay between exothermic equilibrium synthesis and dehydration reactions are demonstrated. Feeding syngas to the air–cooled microchannel reactor at 508 K, 50 bar, H2/CO = 2.5 and H2/CO2 = 10 elevates the inlet temperature by only 9 K which is significantly below ∼40 K of identically operated packed–bed tubular reactors. Increasing syngas feed temperature from 493 to 508 K elevates CO conversion from 33 to 45%, which eventually shifts DME yield from 2 to 3.6%, respectively. Similar qualitative trends are observed upon pressurizing syngas as well as feeding it at higher flow rates under CO–rich and CO2–lean conditions, all of which fundamentally promote CO hydrogenation, the primary contributor of the exothermic temperature rise that subsequently improves reactor performance under the control of intensified cooling. Even though they promote better regulation of hot–spot formation, the impacts of using thicker walls between the channels and thermally conductive reactor materials remain negligible.

Simulations of Hydrogen Production by Methanol Steam Reforming

Methanol is regarded as an important feedstock for hydrogen production due to its high energy density and superior transportability. A tubular packed-bed reactor performing the methanol steam reforming (MSR) process was modeled by adopting computational fluid dynamics (CFD) software to analyze its performance. Kinetic parameters of the reactions were adjusted according to the literatures and our previous experimental results. The methanol conversion, the hydrogen production rate, and the CO concentration in the produced mixture were evaluated by considering different levels of the length and temperature of the catalyst bed, the steam-to-carbon ratio and the space velocity of the feedstocks. Moreover, the correlation between the dimensionless parameter, Damköhler number, and the methanol conversion was also investigated.

Design of a methanation reactor for producing high-temperature supercritical carbon dioxide in solar thermochemical energy storage

Methane reforming with CO2 has been intensively investigated for solar thermochemical energy storage, including endothermic reactor design, reaction kinetics study and endothermic reactor performance analysis. A considerable body of research has been amassed concerning the charging loop, i.e., solar CO2 reforming of methane. However, little research has been conducted on the discharging loop, i.e., the subsequent heat recovery in a methanation reactor at temperatures high enough for electricity generation. This paper explores the preliminary design of a methanation reactor for producing sCO2 at 700 °C in solar thermochemical energy storage. A two-dimensional, steady-state, pseudo-homogeneous model is proposed to simulate heating secondary working fluid, e.g., sCO2, with methanation reaction in a tubular packed bed reactor. The model is validated by comparing temperature profiles and methane conversions generated in this study with the established data from other publications. Parametric studies are performed to investigate the effects of reactor diameters and mass flow rates on the reactor capital cost and energy efficiency. The results show that the estimated catalyst cost is comparable to the reactor wall material cost although the unit price of the catalyst is much higher. Basically, enhancing heat transfer by decreasing reactor diameters can reduce the capital cost. But the energy efficiency decreases with reactor diameters decreasing due to a larger pumping power required. Similarly, enhancing heat transfer by increasing the mass flow rates, i.e., the gas mass flow rate and the sCO2 mass flow rate, also reduces the cost. Different from the effect of decreasing reactor diameters, increasing the sCO2 mass flow rate cannot only reduce the cost but improve the energy efficiency, while increasing the syngas mass flow rate leads to a lower energy efficiency.