Reactor Design Research Articles

Numerical study of the particle-scale heat transfer in the HTR-PM pebble bed based on GPU-DEM

An essential aspect of the design of a pebble bed high-temperature gas-cooled reactor (HTGR) is the consideration of heat transfer. A particle-scale heat transfer model was developed based on the previous GPU-DEM numerical model. This model includes the heat conduction of the particles in contact, the radiative heat transfer among particles, and unidirectional convection heat transfer in the flow field. The comparison of the predicted results with the results of the TF-PBEC experiment demonstrates the accuracy of the conduction and radiation modules within the current model. Based on the current model and the porous media model, a numerical study of the natural convection heat transfer in the High-Temperature gas-cooled Reactor-Pebble-bed Module (HTR-PM) after reactor shutdown is performed. This paper systematically introduces the model design, pebble bed generation, flow field calculation, and heat transfer simulation. The results indicate that natural convection contributes to removing residual heat in the reactor core, and a higher pressure leads to better convection heat transfer. At extremely low Reynolds numbers (Re < 10), convection heat transfer is comparable to conduction and radiation, while for pressurized pebble beds (Re = 50–500), convection heat transfer dominates. Furthermore, the influence of different models used to calculate the Nusselt number of the results is compared and analyzed. For most cases, the differences in the temperature distribution of the pebble bed obtained from the different correlations are minor. However, the impact of porosity on the local Nusselt number cannot be ignored in the extremely low Reynolds numbers flows. Overall, the particle-scale heat transfer model can provide more effective reference information for the design and construction of an HTGR.

Analysis of the tri-hybrid Maxwell nanofluid flow with temperature-dependent thermophysical characteristics on static and dynamic surfaces employing Levenberg-Marquardt artificial neural networks

Using the Levenberg-Marquardt Artificial Neural Network (LM-ANN) model, this study applies computational neuroscience to the analysis of flow, heat, and mass transport characteristics. The novel characteristics of MHD Maxwell tri-hybrid nanofluid passing through static and moving wedge with temperature-dependent thermophysical properties (thermal conductivity, viscosity, diffusivity, and electrical field) in permeable, radiative, and mixed convection processes are investigated in this paper. Nonlinear PDEs are transformed into nonlinear ODEs using similarity variables. A dataset for the LM-ANN is generated across various scenarios by varying parameters such as the temperature-dependent viscosity parameter ( 0.07 − 0.1 ) , variable diffusivity parameter ( 0.4 − 2.5 ) , thermal buoyancy parameter ( 0.1 − 0.5 ) , nonlinear thermal buoyancy parameter ( 0.2 − 0.5 ) , thermal radiation ( 1 − 1.5 ) , buoyancy ratio parameter ( 0.2 − 0.5 ) , chemical reaction parameter ( 1 − 3 ) , and Schmidt number ( 1 − 3 ) using the Bvp5c numerical algorithm. The testing, training, and validation procedure of LM-ANN is utilized to examine the estimated solutions of specific situations, and the proposed algorithm is then validated. After that, the proposed LM-ANN is validated using regression analysis, MSE, and histogram analysis. The prescribed approach impeccably mirrors the recommended and cited findings, evincing a precision level within the realm of 10−9. Results indicate that increasing the permeability parameter from 1 to 1.2 and the temperature-dependent thermal conductivity parameter from 0.4 to 2.5 enhances the Nusselt number. Additionally, increasing the chemical reaction parameter from 1 to 3 leads to an increase in the Sherwood number. The significance of this study lies in its potential applications in industries such as aerospace, chemical processing, and energy systems, where efficient heat and mass transfer processes are crucial. For instance, the findings can be applied to enhance cooling techniques in high-performance aerospace components, optimize reactor designs in chemical plants, and improve thermal management in power generation systems.

Proposal of a novel solar-driven thermochemical reactor for green hydrogen production using helical flow channels

The reactor is the core component of the hydrogen production system. Although hydrogen production using solar energy as the heat source can effectively reduce carbon emissions, the reactor faces the problem of uneven heating caused by the collector, and the uneven temperature distribution will significantly affect the hydrogen production process. A key characteristic of the heat collection in dish solar collectors is that the energy flux density is highest at the center and gradually decreases radially, resulting in an uneven heat distribution on the reactor surface. Therefore, the paper focuses on addressing the problem of the uneven distribution of solar concentrating temperature affecting the working efficiency of the reactor. In this study, the reactor’s flow channel is designed in a helical configuration to enable the reaction gas to enter at the edge, gradually flow inward along the helical channel, and exit at the central position. Through simulation studies of the reactor under various working conditions, it was found that the helical structure can effectively facilitate the continuous temperature rise of the reaction gas, with a methane conversion rate of 94.76 %, a hydrogen yield of 1.54 mol/mol, and a total energy conversion efficiency of 32.52 %. Thus, the design of the helical flow channels can effectively utilize the uneven solar heat distribution, allowing the reactor to operate efficiently. Previous studies have focused on enhancing the heat transfer performance of endothermic materials to achieve temperature uniformity; however, this paper adopts a novel approach by innovating the flow channel structure. This paper offers a new concept for the design of solar thermochemical reactors.

Conceptual design and optimization of heat rejection system for nuclear reactor coupled with supercritical carbon dioxide Brayton cycle used on Mars

During the conceptual design of the Mars surface nuclear reactor coupled with supercritical carbon dioxide Brayton cycle, the heat rejection system occupies most of the weight, and reducing the weight of heat rejection system can effectively cut down the transportation cost from Earth to Mars. This paper explored the feasibility of adopting a combination of heat pipe cooling device and convective heat exchanger to design the heat rejection system for the Mars surface nuclear power station, established flow and heat transfer model and weight model, developed a thermal-hydraulic design program for the heat rejection system, and verified its accuracy; then, the NSGA-II multi-objective optimization method is used to optimize the weight of heat rejection system. Pareto front shows that with higher heat rejection proportion of convective heat exchanger, corresponding inlet velocity of Mars' atmosphere should also be increased. As the optimization result of heat rejection system, the ratio of weight to heat rejection is between 0.94 kg/kW and 2.92 kg/kW, and the maximum power consumption of convective heat exchanger accounts for 3.29% of the total power generation.

Design update of DEMO BOP for HCPB BB concept with an energy storage system

An option for the Intermediate Coupling Design (ICD) of the European Demonstration Fusion Reactor (DEMO) Balance of Plant (BOP) configuration for Helium-Cooled Pebble Bed (HCPB) Breeding Blanket (BB) concept consists of the Primary Heat Transport System (PHTS), the Intermediate Heat Transfer System (IHTS), using HITEC salt as coolant, equipped with a thermal Energy Storage System (ESS), and the Power Conversion System (PCS). The aforementioned BOP configuration is capable of producing electricity continuously during the pulse time (2 h) and dwell time (10 min) of DEMO plant operation.The present study reports on the current (2023) thermal system design of DEMO HCPB ICD BOP for 12 operational states defined by the DEMO Design Central Team (DCT) in 2021. It was shown that the PCS is able to accommodate all of the 12 operational points defined based on the uncertainties of the energy map, provided that an additional bypass line at the outlet of the Divertor Cassettes (DIV-CAS) Heat Exchanger (HX) towards the low-pressure part of the feedwater line (to the condenser in this investigation) is installed in the system. This line is activated only in the cases, where the feedwater flow to the low temperature DEMO heat sources HXs is needed to be higher than that necessary to remove BB power at the Steam Generators (SGs). In all the other cases, the bypass line remains unused. Additionally, perspective improvements of DEMO HCPB BOP regarding thermal ESS, as well as PCS are discussed.

Design of oscillatory helical baffled reactor and dual functional mesoporous catalyst for oxidative desulfurization of real diesel fuel

Enhancing real diesel fuel properties by expelling pollutants using a new design has received considerable interest in the present day. This work investigates the conversion of sulfur compounds via oxidation reaction with peracetic acid as an oxidant. For this purpose, a dual functional mesoporous catalyst was synthesized via loading active metal (iron oxide) nanoparticles over mesopore γ-alumina-anatase titanium oxide prepared via the impregnation procedure (IWI) and precipitation methods, respectively. The novel design of the mesoporous catalyst represents the dual functional catalyst in the oxidative desulfurization process (ODS). The mesoporous catalyst that was formulated underwent a comprehensive analysis using various characterization techniques such as physical adsorption-desorption under N2, X-ray diffraction-XRD, Fourier transforms infrared spectroscopy-FTIR, Field Emission Scanning Electron Microscopy-FESEM, Energy dispersive X-ray analyzer-EDX, and thermogravimetric analysis-TGA. A newly designed laboratory pilot plant for an oscillatory helical baffled reactor (OHBR) was developed and utilized for the ODS process to evaluate the performance of the synthesized mesopore catalyst. The investigated rapid conversion for sulfur removal was found to be 98.42 % under ambient operating conditions such as oscillation of frequency 2 Hz, oscillation of amplitude 8 mm, temperature of oxidation 80°C, and residence time of 9 min. It is clearly observed that the new design of OHBR and mesoporous catalyst highly affected sulfur removal, resulting in a clean diesel.

Experimental investigation of hydrodynamics and suspension characteristics in a boiling stirred tank reactor with helical coils

The boiling stirred tank reactor (BSTR) is widely used in the chemical industry, while the relevant basic data of hydrodynamics and suspension characteristics for reactor design are quite limited. In this work, the hydrodynamics and suspension characteristics in a BSTR with helical coils (BSTR@HC) were studied using three types of impellers. Particle image velocimetry and visualization experiments reveal different flow fields and nucleation processes of three impellers. Suspension experiments show that superficial vapor velocity, solid loading, and particle size play an important role for just-suspension impeller speed Njsv and power consumption Pjsv, while cloud height is mainly determined by superficial vapor velocity. Among the three impellers, radial impeller shows the best suspension performance in BSTR@HC. Correlations of Njsv and Pjsv were developed with relative mean deviations of 2.7% and 4.6%, respectively. Furthermore, a model for the estimation of energy efficiency was developed by evaluate specific power consumption εjsv.

Performance Analysis of Water Heat Pipe for Application of the Passive Cooling System in Nuclear Power Plants

Incorporating heat pipes into passive cooling systems in nuclear reactors offers the benefits of passive operation without external power, a simple design, and high thermal capacity. Accurate thermal performance prediction of the heat pipe is crucial for ensuring safe reactor design and operation. Prior studies on nuclear reactor systems utilizing heat pipes have focused on thermosyphons, which operate by gravity. However, to expand the range of heat pipe applications in reactor systems, experimental investigations of large-scale heat pipes driven by capillary pumping force are required. In this study, a water heat pipe with a 25.4-mm diameter and 4-m length was manufactured to provide thermal experimental results under extreme conditions, such as system rollover or loss-of-cooling accidents. A three-dimensional (3D) printing technique was used to fabricate the high-performance lattice capillary wick structure by combining cubic and diamond lattice structures. The 3D printed wick structure showed 21 to 165 times higher capillarity and enhanced surface properties compared to the screen mesh wick structure. Compared to wickless thermosyphons, the 3D printed wick heat pipe exhibited higher thermal conductivity, stable operation in both vertical and horizontal orientations, and faster startup under extreme conditions.

Fuzzy reliability algorithm for the shutdown system of research reactor

Abstract Probabilistic safety assessment (PSA) has been applied to evaluate the safety of nuclear reactor systems. The results of PSA are used by designers, utilities and regulatory body to confirm the reactor design, to change operation procedures, to enhance the reliability of safety systems, or to modify regulation. Fault tree analysis (FTA) has been used as a deductive means for PSA. System components are assumed to always have defined failure probabilities; however, in reality this assumption is questionable and sometimes there is insufficient data about the failure probability of some components. To solve this problem, fuzzy approaches have been proposed and implemented. The aim of this study is to apply a fuzzy reliability algorithm to estimate basic events failure probabilities for the shutdown system of a research reactor. The reactor is a 22 MW light water open pool type material test reactor and the shutdown system is responsible for the fast shutdown of the reactor whenever safety limits are exceeded. Then, to illustrate the ability of the algorithm, the results are compared with real basic event failure probabilities. The results verify the competence of the algorithm and confirm that it can be applied as an alternative method when quantitative data are not available. Also, a risk importance measure is done on the fault tree of the shutdown system to illustrate which components need to be focused for improvements to achieve the safe operation of shutdown system.

Evaluating a green liquid phase plasma discharge process and working mechanism for remediating cobalt contamination in water

Cobalt is a toxic heavy metal contaminant in water and wastewater causing health concerns and on the other hand, a valuable element to recycle. In this study, performance of a novel and green continuous liquid phase plasma discharge (CLPD) process was investigated for removal and recovery of cobalt from aqueous solution without use of any catalysts or chemicals. The CLPD reactor design features two conductive channels and stable electric discharge at the orifice of two dielectric plates sandwiched among the electrodes. The effects of operating factors of the CLPD process were evaluated with liquid flow rate (25–100 mg/L) and applied power (200–300 W), and the highest removal efficiency of cobalt (93 %) was obtained within 25 min at a 50 ml/min liquid flow rate and 300 W applied power. The CLPD energy efficiency for cobalt removal under this condition was 27.44 g kW-1h−1. Reaction kinetics with scavenger tests revealed that oxidative reactive species, i.e., hydroxyl radical and superoxide radicals, produced at the discharge zone were responsible for cobalt removal from water by producing cobalt oxide particles and the reaction pathways were proposed. The CLPD process not only allowed for the efficient removal of cobalt (II) from water but also synthesized cobalt oxides particles with averaged size of 2.75 µm, which can be applied as catalyst. The overall results indicated that the novel CLPD is a robust and highly effective process to remove and recover cobalt from water.

Implementation of a Drift Flux Model into SAM with Development of a Verification and Validation Test Suite for Modeling of Noncondensable Gas Mixtures

The advanced thermal-hydraulic system code, System Analysis Module (SAM), was originally developed for the modeling of single-phase flow in advanced reactors. It has since been expanded to include a four-equation drift flux model for the modeling of two-phase flows containing a noncondensable gas. The model was expanded to support the modeling of molten salt reactor (MSR) designs in which the fuel is directly dissolved in the circulating coolant. These designs have shown that circulating gas bubbles can play an important role in the management of fission products and the operational behavior of the reactor. A drift flux model was implemented to more accurately capture the localized behavior of the void in the core and its impact on the mass transfer of fission products. A thorough assessment of the new model was performed by developing a verification and validation test suite. Verification problems were designed to test all major terms in the new governing equations. The new model converged to the correct solution at the expected order of accuracy for all verification cases. The validation cases included a wide range of flow and void conditions in different pipe geometries. Although higher void experiments show a slight underprediction of void by the drift flux model, experiments that aim to reproduce Molten Salt Reactor Experiment (MSRE) experimental conditions show good agreement with the model. The gas transport model was activated for a SAM model of the MSRE to demonstrate that it can be used in a more complex model. This gas transport model will be used along with an interfacial area transport equation being implemented in SAM for the prediction of mass transport behavior in MSR conditions.

Efficient selenate removal from impaired waters with TiO2-assisted electrocatalysis

Aquatic selenium (Se) oxyanions have profound ecosystem and human health impacts, necessitating their conversion and immobilization into elemental Se(0) to mitigate the aquatic Se pollution. While thermodynamically favorable, this transformation encounters kinetic limitations, especially for selenate (SeO42−) or Se(VI). To lower the activation barrier, we investigated the electrocatalytic Se(VI) transformation using five affordable catalysts on graphite cathodes, including TiO2, underpotentially deposited Cu (UPD Cu), underpotentially deposited Cd (UPD Cd), Co, and CuFe. Among these five catalysts, we identified characteristic Se(VI) reduction peaks for TiO2 through cyclic voltammetry. Other catalysts removed less than 5% of 1-mM Se(VI) in 24-h chronoamperometry tests while leaching ppm-level metal cations in the treated water. In contrast, TiO2 as the electrocatalyst could remove more than 80% of 1-mM Se(VI) with negligible catalyst dissolution. Mechanistic investigations revealed a six-electron Se(VI)/Se(0) reduction pathway at -0.30 V (vs. Ag/AgCl), resulting in red Se(0) deposits on the TiO2-coated graphite cathode. Further potential decrease to more negative than -0.45 V led to Se(-II) formation, triggering cathodic Se(0) dissolution and surface regeneration. Electrochemical impedance spectroscopy indicated that Se(VI) reduction was optimal with a moderate TiO2 loading of 0.55 mg cm−2 and acidic environments (pH=1.0∼2.5), achieving an optimized removal of 88.7 ± 2.3% under -0.70 V and an energy input of 3.6 kWh kg−1 Se. These findings lay the foundation for efficient selenate removal from impaired waters. Future efforts should evaluate catalyst performance over time and refine electrode and reactor designs to improve efficiency.

Neutronics–Thermal-Hydraulics–Coupled Transient Analysis for Reactor Power Change in an Inclined Offshore Floating Boiling Water Reactor

An application of the boiling water reactor (BWR) to an offshore floating nuclear power plant (OFNP) in Japan is discussed. The BWR-type OFNP has some challenges for practical use, although it has high economic efficiency because of downsizing and simplification. One challenge is understanding reactor kinetics under conditions specific to the marine environment. This study quantitatively clarifies the total and spatial changes in power when the BWR is inclined during regular operation. Therefore, the TRACE (TRAC/RELAP Advanced Computational Engine) and PARCS (Purdue Advanced Reactor Core Simulator) codes were used to perform a three-dimensional neutronics–thermal-hydraulics–coupled transient analysis. The calculation model is based on Peach Bottom II. This study clarifies the changing trend in total and local BWR power by inclination with simplified modeling and conditions. The reasons for such changes are discussed based on changes in several thermal-hydraulic parameters. The difference in BWR power against the inclinations is small. Thus, it is implied that the BWR-type OFNP is expected to have a stable power supply capability during natural disasters. However, to confirm the power stability of the BWR reactor under a full range of offshore external conditions, further research is required. A description of additional research needs that would further support the safety case for this reactor design are discussed.

Exploring the Feasibility of Quantum-Based Secure Communications for Nuclear Applications

Recent advancements in reactor designs could offer new revolutionary capabilities, including remote monitoring, increased flexibility, and reduced operation and maintenance costs. Embracing new digital technologies would allow for operational concepts such as semiautonomous or near-autonomous control, and two-way communications for real-time integration with the upcoming smart electric grid. However, such continuous data transmission from and toward a reactor site could potentially introduce new challenges and vulnerabilities, necessitating the prioritization of cybersecurity. Conventional information technology–based encryption schemes, which rely mostly on computational complexity, have been shown to be vulnerable to cyberattacks. With the advent of quantum computing, practically any asymmetric encryption could be potentially compromised. For example, it has been shown that a RSA-2048 bit key could be broken in 8 h. To address this challenge, we explore the feasibility of quantum key distribution (QKD) to secure communications. QKD is a physical layer security scheme relying on the laws of quantum mechanics instead of mathematical complexity. QKD promises not only unconditional security but also detection of potential intrusion, as it allows the communication parties to become aware of eavesdropping. To test the proposed hypothesis, a novel simulation tool (NuQKD) was developed to allow for real-time simulation of the BB84 QKD protocol between two remote terminals. A reference scenario is proposed, generic enough to cover various internal and external communication links to a reactor site. Using NuQKD, the internal and external data links were modeled, and receiver operating characteristic curves were calculated for various QKD configurations. A performance analysis was conducted, demonstrating that QKD can provide adequate secret key rates with low false alarms and has the potential of addressing the nuclear industry’s high standards of confidentiality for distance lengths up to 75 km of fiberoptics. Using a conservative estimation, QKD can provide up to 21.5 kbps of secret key rate for a distance of 1 km and 14.4 kbps at 10 km. The target secret key rates for the corresponding links were estimated at 16 kbps and 80 bps, respectively, based on the analysis of real data from a PUR-1 fully digital reactor. Consequently, QKD is shown to be compatible with existing and future point-to-point reactor communication architectures. These results motivate further study of quantum communications for nuclear reactors.

Design of dual-channel Swiss-roll reactor for high-performance hydrogen production from ethanol steam reforming through waste heat valorization

Steam reforming is one of the most economical and efficient methods for hydrogen production. However, one of its glaring issues is the heat supply, which is used to maintain the reactions. Among reactors for hydrogen production, Swiss-roll reactors have exhibited exceptional performance in sustaining the heat required for reactions. Furthermore, heat supply via waste heat recovery has been an attractive industrial prospect for improving the sustainability of hydrogen production. This study proposes a design of a novel Swiss-roll reactor with dual channels to harvest waste heat from the flue gas to sustain the steam reforming reactions. Ethanol is used as a feedstock due to its environmentally benign properties. Numerical simulations are conducted to establish the reactor's catalytic reactions and heat transfer phenomena under the variations of gas hourly space velocity (GHSV), steam-to-ethanol (S/E) ratio, and inlet flue gas temperature. Heat recovery improves at higher GHSVs and lower S/E ratios at the cost of less efficient hydrogen production, while high inlet flue gas temperature improves heat recovery and hydrogen production. The novel reactor design can fulfill complete ethanol conversion maintained by heat recovered from waste flue gas, achieving 86.6 % hydrogen production efficiency and 72.7 % heat recovery under optimal operating conditions.

Innovative Photocatalytic Reactor for Sustainable Industrial Water Decontamination: Utilizing 3D-Printed Components and Silica-Titania Trilayer Coatings

Industrial activities generate enormous quantities of polluted effluents, necessitating advanced methods of wastewater treatment to prevent potential environmental threats. Thus, the design of a novel photocatalytic reactor for industrial water decontamination, purification, and reuse is proposed as an efficient advanced oxidation technology. In this work, the development of the active reactor components is described, utilizing a two-step sol–gel technique to prepare a silica-titania trilayer coating on 3D-printed polymeric filters. The initial dip-coated SiO2 insulator further protects and enhances the stability of the polymer matrix, and the subsequent TiO2 layers endow the composite architecture with photocatalytic functionality. The structural and morphological characteristics of the modified photocatalytic filters are extensively investigated, and their performance is assessed by studying the photocatalytic degradation of the Triton X-100, a common and standard chemical surfactant, presented in the contaminated wastewater of the steel metal industry. The promising outcomes of the innovative versatile reactor pave the way for developing scalable, cost-effective reactors for efficient water treatment technologies.

Optimization of H2O2 Production in Biological Systems for Design of Bio-Fenton Reactors.

The treatment of antibiotic wastewater, which is known for its micro-toxicity, inhibition, and poor biochemistry, poses significant challenges, including complex processes, high energy demands, and secondary pollution. Bio-Fenton, a novel Fenton technology, enables the in situ production of H2O2 at near-neutral pH, having low energy requirements and sustainable properties, and reduces the hazards of H2O2 transportation and storage. We preliminary self-designed a heterogeneous Bio-Fenton reactor. An aerobic SBBR system with pure algae, pure bacteria, and bacteria-algae symbiosis was first constructed to investigate the optimal process conditions through the effects of carbon source concentration, light duration, bamboo charcoal filling rate, and dissolved oxygen (DO) content on the H2O2 production and COD removal. Second, the reactor was constructed by adding iron-carrying catalysts to remove ROX and SDZ wastewater. The results demonstrated that the optimal operating parameters of aerobic SBBR were an influent carbon source concentration of 500 mg/L, a water temperature of 20 ± 2 °C, pH = 7.5, a dissolved oxygen content of 5 mg/L, a light-dark ratio of 12 h:12 h, a light intensity of 2500 Lux, an HRT of 10 h, and a bamboo charcoal filling rate of 33%. Given these conditions, the bacterial-algal system was comprehensively found to be the most suitable biosystem for this experiment. Ultimately, the dynamically coupled Bio-Fenton process succeeded in the preliminary removal of 41.32% and 42.22% of the ROX and SDZ from wastewater, respectively.

Design and stabilization of direct autothermal methane steam reformation reactor for producing hydrogen via optimizing oxygen distributed feeding

Direct autothermal methane reforming is an energy-efficient way of hydrogen production. However, significant hot spot is always encountered near the reactor inlet, causing catalyst sinter and even reactor damage. Hence, bed temperature regulation by oxygen distributed feeding was numerically investigated using a one-dimensional heterogeneous model. Simulation results show oxygen feeding along full length of reactor leads to low methane and oxygen conversion despite avoiding hot spot. Elevating feeding temperature solves this problem, but requires extra heat. Shortening feeding length to 1/10 of reactor reduces maximum bed temperature by 100 K; Half oxygen fed into reactor inlet and the other along the length further reduces maximum bed temperature and avoids the transient runaway. Optimization results show that oxygen parabolically and totally fed along the front part of the reactor length shows better performance than that feeding half along reactor length and the other into reactor inlet.

The tubular baffled reactor and its potential for the biological methanation of carbon dioxide

The biological Power to Methane process (PtM) is gaining ground as an answer to the long-term renewable energy storage problem. Methane is an efficient hydrogen carrier, has an established worldwide transport infrastructure and can serve as a link between renewable power generation and a circular carbon economy. One of the defining factors regarding the scalability of the PtM process is the design of the reactor as it can determine the production rate/energy expenditure ratio. The tubular baffled reactor, a popular reactor design within the chemical industry has been assessed in the present study as a biomethanation reactor for the first time. The experiments were conducted with mixed cultures and the results point to high gas-liquid mass transfer capabilities as indicated by the methanation rates achieved (>90 % CH4 at 270 L/L/d mixed gas input rate). The gas/liquid flow ratio appears to have a stronger effect on methanation than the gas residence time. The working length of the reactor determines the pressure drop experienced by the culture, with higher pressure drops showing a negative correlation to methanogenesis.

One‐dimensional kinetic model with novel bubble size equation in molten‐metal bubble column reactors for CH4 pyrolysis

AbstractNon‐oxidative methane pyrolysis produces hydrogen and solid carbon without CO2 in molten‐metal bubble column reactors (MMBCRs). One‐dimensional MMBCR models, which involve bubble hydrodynamics, reactions, heat transfer, and axial dispersion, have been developed for reactor design; however, empirical equations of the mean bubble size derived from bench‐scale experiments have also been used for industrial‐scale MMBCRs. In this study, a novel bubble size equation based on dimensionless numbers was proposed for the bubbling, transient, and slugging flow regimes, which is applicable to both bench‐ and industrial‐scale reactors. Using the MMBCR model coupled with the new bubble size, reaction kinetic parameters were identified for four bench‐scale MMBCRs with Te‐based alloys in the bubbling flow regime. In four industrial‐scale MMBCRs at 980°C, belonging to the transient flow regime for an H2 production of 10,000 Nm3/h, the bubble size and methane conversion were approximately 40 mm and under 35%, respectively.