Reactor Configuration Research Articles

Development of a Novel Hydrodynamic Sequencing Batch Reactor for Landfill Leachate Treatment by Shortcut Biological Nitrogen Removal

This study introduced an alternative shortcut biological nitrogen removal (SBNR) process for landfill leachate treatment by developing a novel hydrodynamic sequencing batch reactor (H-SBR). The reactor could enhance the oxygen transfer rate (OTR) and nitrite accumulation ratio (NAR) by modifying internal hydrodynamic turbulence intensity. The average chemical oxygen demand (COD) and total nitrogen (TN) concentrations introduced into the reactor were 660 and 250 mg L−1, respectively, and the average removal efficiencies were 93% (COD) and 96% (TN). The effect of geometric parameters on oxygen transfer was estimated by performing a hydrodynamic model and a nonlinear least square analysis. After correcting the constants (α and β) of mass transfer coefficients (KLa) to values of 0.7361 and 1.2639, the model data fit the experiment well with an R-squared value of 0.99. The OTR improved by up to 30%, and hence, increased the NAR by up to 20% with a reduction of about 0.5 kg N kW−1 for power efficiency. The H-SBR development is innovative because the oxygen transfer efficiency was improved by the hydrodynamic modification of internal turbulence intensity, although not by mechanical equipment or chemical supplements. For the SBNR process, the modification of the reactor configuration for OTR enhancement could significantly improve nitrogen removal efficiency with successful nitrite accumulation. In addition to landfill leachate treatment, the H-SBR process can be employed in the treatment of low C/N ratio wastewaters.

Kinetics of acid hydrolysis of k-Carrageenan by in situ rheological follow-up

Water based solutions of κ-Carrageenan (1.5% weight concentration), a high molecular weight polysaccharide, were subjected to acid-catalyzed hydrolysis under controlled pH (≈3) and temperature (from 40 to 70 °C). The hydrolysis process involves selective attack of the Carrageenan glycosidic bonds α(1–3) and β(1–4), determining changes in the weight average molecular weight of the macromolecule and, as a consequence, on the gelling behavior. In this study we used transient rheological tests to monitor the hydrolysis reaction and its consequences on both the sol-gel transition and the final gel properties. Hydrolysis reaction has been modelled using a bi-exponential kinetics. To this end, a rotational rheometer was equipped with a batch reactor configuration, consisting of a cylindrical vessel and a double helix mixing tool. Both viscous and viscoelastic properties of the samples were measured quantitatively and related to the biopolymer molecular weight, replacing more complex molecular weight determinations by an easier methodology. By using the above experimental approach, kinetic constants and activation energies for the κ-Carrageenan hydrolysis were obtained as a function of the hydrolysis temperature. The latter, along with the hydrolysis reaction time, was also shown to be a relevant parameter in determining the possibility of gel formation and of the gel mechanical strength (in the range 10–600 Pa).

Non-uniform dissolved oxygen distribution and high sludge concentration enhance simultaneous nitrification and denitrification in a novel air-lifting reactor for municipal wastewater treatment: A pilot-scale study

Achieving simultaneous carbon and nitrogen removal with sludge-liquid separation in a single reactor offers a solution to land shortages and improves treatment efficiency in municipal wastewater treatment plants of megacities. This study proposes a novel air-lifting continuous-flow reactor configuration with an alternative-aeration strategy that creates multi-functional zones for anoxic, oxic, and settlement processes. The optimal operating conditions for the reactor include a long anoxic hydraulic retention time, low dissolved oxygen (DO) in the oxic zone, and no specific reflux for external nitrifying liquid, which exhibit a high nitrogen removal efficiency of over 90% in treating real sewage with C/N < 4 in the pilot-scale study. Results show that a high sludge concentration and a low DO concentration facilitate simultaneous nitrification and denitrification, and a well mixing of sludge and substrate in different reaction zones promotes mass transfer and microbial activity. The long-term operation enriches functional microbes for carbon storage and nutrient removal.

Adapting R4 simplifications of Anaerobic Digestion Model No. 1 (ADM1-R4) for pump-mixed biogas production

Modification of the production chain in biogas generation is a common tactic used in this industry. However, the selection of appropriate reactor configuration and operational parameters is a crucial task. In such cases, mathematical modeling provides great support. Herein, we adapted a simplified version of the Anaerobic Digestion Model No. 1 to a system in which the mechanical stirrer was replaced with an external pump that recirculated the reactor content. Despite having conceptual similarities with continuous stirred-tank reactors, this system exhibited considerable differences in the vertical distribution inside the tank. The model was optimized by using a “genetic algorithm” and “fmincon” function to test both approaches. The new model showed very high accuracy with a mean error of 5.9–9.8%, depending on the mixing intensity, whereas the previous reference models reached 19.7% error. Therefore, compared to the previous models, the simplification of the ordinary differential equation in our new model did not significantly decrease accuracy; in fact, the precision was even higher than before in some cases. Finally, the new model was practically applied to demonstrate its implementation in realistic scenarios.

Bioconversion of CO2 and potential of gas fermentation for mainstream applications: Critical advances and engineering challenges

AbstractThe undesirable consequences of climate change are attributed to the ever‐increasing emissions of greenhouse gases, especially carbon dioxide. For the sustainable development of human society, there is an urgent need to develop novel techniques for efficient conversion and utilization of carbon dioxide. Hence, carbon capture and storage, artificial bioconversion of carbon dioxide are topics of great interest for current researchers across the globe. Here, we elucidate the different techniques of carbon fixation, which fall under the broad categories of natural fixation pathways, thermo‐catalytic conversion techniques, and synthetic carbon fixation pathways. Based on a comparative analysis, gas fermentation is a promising method for the microbial conversion of CO2‐containing gases into fuels and chemicals. However, for mainstream applications, in‐depth reviews of different reactor configurations and the various engineering aspects related to process development are still lacking. We have analyzed the published literature relating to artificial bioconversion of carbon dioxide and focused on the factors like equipment selection and reactor design that can assist in scale‐up of gas fermentation technology. The review provides an in‐depth understanding of engineering aspects related to stirred tank and bubble column reactors, focusing on the technical design parameters and discussing the conditions for optimal operation and performance during commercial gas fermentation processes.

Development and assessment of algorithms for DEM-LES simulations of fluidized bed

The use of high-fidelity Discrete Element Method (DEM) coupled with Computational Fluid Dynamics (CFD) for particle-scale simulations demands extensive simulation times and restricts application to small particulate systems. DEM-CFD simulations require good performance and satisfactory scalability on high-performance computing platforms. A reliable parallel computing strategy must be developed to calculate the collision forces, since collisions can occur between particles that are not on the same processor, or even across processors whose domains are disjoint. The present paper describes a parallelization technique and a numerical verification study based on a number of tests that allow for the assessment of the numerical performance of DEM used in conjunction with Large-Eddy Simulation (LES) to model dense flows in fluidized beds. The fluid phase is computed through solving the volume-averaged four-way coupling Navier-Stokes equations, in which the Smagorinsky sub-grid scale tensor model is used. Furthermore, the performance of Sub-Grid Scale (SGS) turbulence models applied to Fluidized Bed Reactor (FBR) configurations has been assessed and compared. The developed numerical solver represents an interesting combination of techniques that work well for the present purpose of studying particle formation in fluidized beds.

Comparison of Raspberry Ketone Production via Submerged Fermentation in Different Bioreactors

Raspberry ketone (RK) has high commercial value in the food and healthcare industries. A biological route to this flavour compound is an attractive prospect, considering the need to meet consumer demands and sustainable goals; however, it is yet to become an industrial reality. In this work, fungal production of raspberry ketone (RK) and raspberry compounds (RC) via submerged fermentation of Nidula niveo-tomentosa was characterized in flask, stirred-tank reactor (STR), panel bioreactor (PBR), and fluidized bed reactor (FBR) configurations. The results indicate that the panel bioreactor resulted in larger, floccose pellets accompanied by maximum titres of 20.6 mg/L RK and 50.9 mg/L RC. The stirred-tank bioreactor with impeller mixing yielded compact elliptical pellets, induced the highest volumetric productivity of 2.0 mg L−1 day−1, and showed RK selectivity of 0.45. While differing mixing strategies had clear effects on pellet morphology, RK production presented a more direct positive relationship with cultivation conditions, and showed appropriate mixing and aeration favour RK to raspberry alcohol (RA). Overall, this paper highlights the importance of bioreactor design to fungal fermentation, and gives insight into green and industrial bioproduction of value-added natural compounds.

Recent Advances in the Photoreforming of Plastic Waste: Principles, Challenges, and Perspectives

Photoreforming (PR) technology is a green and sustainable approach to tackling the environmental pollution problems generated by plastic waste. In this review, recent advances in the PR of plastic waste are summarized that include the design of photocatalysts, regulations on the products, and innovations on the PR devices and compared to traditional methods. The scientific principles of PR reactions in thermodynamics and kinetics are discussed, and approaches to improve the efficiency of PR reactions are proposed, that involve enhancement in light absorption ability, charge carrier migration/separation efficiency, and surface reaction rate. Particularly, the enhancement for H2 production in the PR reaction is highlighted, and the applications using large-scale reactors are discussed, with advantages and disadvantages of recent reactor configurations. In conclusion, the perspectives on the applications of PR in plastic degradation and hydrogen evolution are given. This review thus comprehensively summarizes scientific principles, challenges, and perspectives of PR reactions on plastic waste to improve the overall efficiency and potential to be applied in the industry.

Effect of pressure and CO2 dilution on soot formation in laminar inverse coflow flame at conditions close to autothermal reforming

Autothermal reforming (ATR) is an important technology for hydrogen production from natural gas, where soot formation deserves particular attention as it may cause catalyst poisoning. The typical configuration of ATR reactors is that of an inverse diffusion flame (IDF). In this study, soot formation near ATR conditions is investigated experimentally and numerically, focusing on the effects of pressure and CO2 dilution in IDFs with pressure reaching 5 bar. The fuel stream consists of methane diluted with CO2 or N2. The mole fraction of O2 in the oxidant stream is 70%. Polycyclic aromatic hydrocarbons (PAHs) and soot volume fraction are measured by the planar laser-induced fluorescence (PLIF) and planar laser-induced incandesce (PLII) methods. High-fidelity simulations with a detailed soot aerosol model are also performed, and an empirical reactive soot inception model is proposed. A comparison of the results shows that the soot behavior is well predicted by the empirical reactive inception model but not fully captured by the physical inception model based on irreversible dimerization, demonstrating the importance of radical involvement in the soot inception process. Both measurements and predictions show a linear relationship between peak soot volume fraction and pressure, which can be explained by the linear increase of PAH molar concentration with pressure. Simulation analysis indicates that the dimer adsorption and HACA mechanism have a similar quantitative contribution to the soot growth. The CO2 shows stronger suppression effects in soot formation at the investigated pressures compared to N2. The contributions of chemical and thermal effects to soot suppression are numerically analyzed and the results indicate that the chemical effect of CO2 is mainly due to the removal of H radicals through the reaction CO2 + H→CO + OH, providing a soot suppression contribution of two times larger compared to the thermal one.

Biohydrogen production from lignocellulosic feedstock: Abiotic and biotic methods

Bioenergy is known as green energy produced from organic biomass, such as food leftovers, non-edible agri-residues, and municipal wastes through biotic and abiotic methods. Globally, generation of the most common renewable fuels including biohydrogen (bioH2), biogas, bioethanol, biofertilizers and bio plastics as fossil fuel substitutes by means of circular bioeconomy is gaining tremendous focus in support of environmental concerns. Carbon free bioH2 is considered as deemed fuel due to its multifaceted applications and potent ecological features. As the present commercial energy manufacturing methods tap on non-renewable fuels and associated high cost, there is an immediate need for full scale sustainable bioH2 production systems in accordance with regional demand through domestic innovations. Though, research on hydrogen production is not less common via conventional thermo chemical methods, it is essential to understand much regarding biological methods to achieve feasible transition from depleting fossil fuels to eco-friendly renewable energy. Thus, this review primarily focuses on different sustainable approaches for lignocellulosic biomass valorization towards bioH2 production along with potential thermo chemical approaches. In particular, bioH2 production from lignocellulosic biomass in the presence and absence of light by photo fermentation and dark fermentation, respectively, reactor configuration, importance of biocatalyst pretreatment and potential methods, and natural and mutant microalgal bioH2 evolution have been discussed in detail to address their industrial level applicability.

Recent advances in sub-stoichiometric TiO2 as reactive electrochemical membranes (REM) for bio-refractory pollutants removal: A critical review

Water stress must be addressed by developing cost-effective wastewater treatment technologies. Reactive electrochemical membranes (REM) have gained popularity in this scenario due to the benefits of both electrochemical advanced oxidation processes (EAOP) and membrane filtration processes (MFP) in reducing mass transport limitations and fouling issues. In this context, this review aims to consolidate recent advances in REM, focusing on sub-stoichiometric titanium oxide-based REM (TiSO-REM), mainly Ti4O7, the most promising ceramic material due to its high conductivity and ability to generate •OH. The primary fabrication methods for TiSO porous anodes are discussed, resulting in a significant reminder of their electrocatalytic, porosimetric and physicochemical intrinsic properties. In addition to the real advantages of using this material in flow-through configurations, which allow convection-enhanced mass transport and provide a high electrochemical surface area. The latest progresses in TiSO-REM are presented, with specific emphasis on understanding the main operating parameters in performance efficiency: the determinative key role among pollutant nature, matrix effect and anode in removal mechanisms, and where the anode is in relation to the cathode in the reactor design. These points are intended to identify process limitations and challenges to be overcome when implementing various reactor configurations until the scaling-up. All these aspects are reviewed critically in order to provide future research directions for the industrial advancement of this technique, which has proven to be more energy-efficient and therefore economically feasible than alternative EAOP.

Integrated CO2 capture and utilisation: A promising step contributing to carbon neutrality

The release of CO2 into the atmosphere is problematic; however, it is an abundant, renewable, and inexpensive carbon resource. In the past, the environmental problems caused by excessive CO2 emissions, such as global warming and ocean acidification, have become increasingly severe. Carbon capture and utilisation (CCU) has drawn intensive interest due to its capacity to sequester CO2 and utilise it as a carbon source to produce high-value chemicals and fuels. However, state-of-the-art CCU exhibits poor economics and technological complexity due to extensive energy input, a multiple reactor configuration, and sorbent transfer between reactors for sorbent regeneration. Integrated CO2 capture and utilisation (ICCU) directly utilises CO2-containing exhaust gas and in situ upgrades them into valuable products in a highly intensified process, representing a more direct and promising path for CO2 emission control. A series of high-performance dual functional materials (DFMs) composed of catalytic and adsorbent sites have succeeded in various ICCU applications. In this account, we first briefly introduced the research background of ICCU technology and the motivation for developing various ICCU applications. Furthermore, we conducted a detailed description of ICCU technology from three aspects: ICCU-methanation, ICCU-dry reforming methane (DRM) and ICCU-reverse water gas shift reaction (RWGS). In particular, we have investigated the optimal adsorption and catalytic sites for specific reaction characteristics and have solved the problem of temperature matching between the adsorption and catalytic sites. In addition, The mechanism underlying ICCU technology has been explored, and the effect of interfering components on catalytic performance in real plant flue gases for future applications has also been analysed. Significantly, the catalyst stability was effectively improved by investigating the causes of catalyst deactivation. Finally, although the technology of in situ CO2 capture and conversion is still in its preliminary stages, we can see that current research results already indicate promising prospects. In-situ capture and conversion of CO2 into high-value-added chemical feedstock will be a very attractive application for reducing greenhouse gases in the atmosphere and recycling carbon resources. We are also committed to promoting the industrialisation and large-scale production of ICCU technology.

Intensifying single-stage denitrogen by a dissolved oxygen-differentiated airlift internal circulation reactor under organic matter stress: Nitrogen removal pathways and microbial interactions

Current research focuses on efficient single-stage nitrogen removal from organic matter wastewater using the partial nitritation-anammox (PNA) process. In this study, we constructed a single-stage partial nitritation-anammox and denitrification (SPNAD) system using a dissolved oxygen-differentiated airlift internal circulation reactor. The system was operated continuously for 364 days at 250 mg/L NH4+–N. During the operation, the COD/NH4+–N ratio (C/N) was increased from 0.5 to 4 (0.5, 1, 2, 3, and 4), and the aeration rate (AR) gradually increased. The results showed that the SPNAD system maintained efficient and stable operation at C/N = 1–2 and AR = 1.4–1.6 L/min, with an average total nitrogen removal efficiency of 87.2%. The removal pathways of pollutants in the system and the interactions between microbes were revealed by analyzing the changes in sludge characteristics and microbial community structure at different phases. As the influent C/N increased, the relative abundance of Nitrosomonas and Candidatus Brocadia decreased, and that of denitrifying bacteria, such as Denitratisoma, increased to 44%. The nitrogen removal pathway of the system gradually changed from autotrophic nitrogen removal to nitrification-denitrification. At the optimum C/N, the SPNAD system synergistically removed nitrogen through PNA and nitrification-denitrification. Overall, the unique reactor configuration facilitated the formation of dissolved oxygen compartments, providing a suitable environment for different microbes. An appropriate organic matter concentration maintained the dynamic stability of microbial growth and interactions. These enhance microbial synergy and enable efficient single-stage nitrogen removal.

Exploring the feasibility of next-generation CO2-based adsorption cooling systems using different adsorbent reactor configurations

The present investigation expounds on the effects of the reactor geometry, cycle time and heating/cooling fluid temperatures on the performance of a 4-bed CO2 adsorption cooling system. Cylindrical adsorbent reactors of varying aspect ratios (AR) with an optimum number of internal longitudinal fins and non-finned reactors are compared. The study confirms the substantial effect of reactor configuration on the system COP, specific cooling effect (SCE) and power, energy interactions during various processes and the total cycle time (TCT), which the equilibrium or lumped system analysis fails to predict. An increment of 98 % and 189 % in system COP and SCE is attained by varying the aspect ratio of the reactor with fins under subcritical operations. In continuation, a reduction of 41 % in TCT is observed. The study confirms the optimum adsorption/desorption time for which the COP and SCE are maximum, especially for higher AR reactors. It is noteworthy that proper selection of reactor aspect ratio results in a better system COP, even at lower heating fluid temperatures. During the transcritical operations, an increment of 23 % in COP and 6 % in SCE is achieved for a gas cooler exit temperature of 35 °C. Moreover, the reactor configuration also affects the optimum gas cooler pressure for the transcritical cycle, like the gas cooler exit temperature. One of the crucial observations is that, for a given combination of reactor configuration, heating/cooling fluid temperatures, and operating pressures, there exists a minimum cycle time below which a cyclic steady-state condition is impossible to achieve. During the subcritical and transcritical operations, a maximum COP of 0.1 and 0.052 is achieved for the proposed adsorption chiller configuration, respectively.

Process simulation and techno-economic analysis of olive oil mill wastewater steam reforming

Olive oil production contributes to environmental deterioration, mainly due to the land spreading of the pollutant effluents. One solution to treat these liquid effluents (olive mill wastewater - OMWW) is the steam reforming (OMWWSR) reaction.In this work, the effects of the main parameters that affect the OMWWSR process were studied: composition of the effluent, total pressure, and temperature of the reformer; furthermore, several reactor configurations were simulated: traditional reactor (TR), autothermal reactor (ATR), sorption-enhanced reactor (SER), and sorption-enhanced autothermal reactor (SEATR). All reactor configurations treated an effluent flow rate of approximately 12 tons/h, which equals the quantity of OMWW produced by a big Portuguese olive oil producer company. In addition, energy integration and techno-economic analyses were elaborated to reveal which reactor configuration(s) presented the most attractive results. It was verified that the ATR and SER presented higher performances in terms of H2 production per kmol of OMWW fed and energy consumption per kmol of H2 produced. Finally, it was observed that the ATR achieved a net present value (NPV) that ranged from 7.2 to 9.2 M€ and payback times (PB) which ranged from 3 to 2 years. Regarding the SER configuration, the NPV and PB ranged from 4.7 to 12.2 M€ and 5-2 years, respectively.

Application of Electrochemical Oxidation for Water and Wastewater Treatment: An Overview.

In recent years, the discharge of various emerging pollutants, chemicals, and dyes in water and wastewater has represented one of the prominent human problems. Since water pollution is directly related to human health, highly resistant and emerging compounds in aquatic environments will pose many potential risks to the health of all living beings. Therefore, water pollution is a very acute problem that has constantly increased in recent years with the expansion of various industries. Consequently, choosing efficient and innovative wastewater treatment methods to remove contaminants is crucial. Among advanced oxidation processes, electrochemical oxidation (EO) is the most common and effective method for removing persistent pollutants from municipal and industrial wastewater. However, despite the great progress in using EO to treat real wastewater, there are still many gaps. This is due to the lack of comprehensive information on the operating parameters which affect the process and its operating costs. In this paper, among various scientific articles, the impact of operational parameters on the EO performances, a comparison between different electrochemical reactor configurations, and a report on general mechanisms of electrochemical oxidation of organic pollutants have been reported. Moreover, an evaluation of cost analysis and energy consumption requirements have also been discussed. Finally, the combination process between EO and photocatalysis (PC), called photoelectrocatalysis (PEC), has been discussed and reviewed briefly. This article shows that there is a direct relationship between important operating parameters with the amount of costs and the final removal efficiency of emerging pollutants. Optimal operating conditions can be achieved by paying special attention to reactor design, which can lead to higher efficiency and more efficient treatment. The rapid development of EO for removing emerging pollutants from impacted water and its combination with other green methods can result in more efficient approaches to face the pressing water pollution challenge. PEC proved to be a promising pollutants degradation technology, in which renewable energy sources can be adopted as a primer to perform an environmentally friendly water treatment.

A syphon-downflow hanging sponge (DHS) reactor for improving the denitrification efficiency of sewage water treatment

The study focused on developing a low-cost down-flow hanging sponge (DHS) to enhance denitrification. The DHS reactor was modified by connecting with a syphon tube to maintain aerobic and anaerobic conditions. This method can simultaneously achieve nitrification and denitrification, requiring no extra energy for pumping. The study had two phases to evaluate the denitrification efficiency of the syphoned reactor at different reactor configurations. In the first phase, the syphon height was equal to the reactor height, and a water column was developed inside the DHS to create an anaerobic zone. The sCOD removal rates of syphon–DHS and conventional-DHS (control) were 75 ± 20% and 73 ± 19%, respectively, and the removal rates were almost similar in both reactors. However, the total nitrogen (TN) removal rate of syphon–DHS was 19 ± 3%, six folds greater than that of the conventional-reactor. In phase II, the syphon height of the developed DHS was changed to 3/5 of the DHS height. The sCOD and NH4+-N removal of syphon–DHS in the second phase were 62 ± 33% and 62 ± 31%, respectively, and approximately similar to the convectional DHSs’ performance. The anaerobic zone of the reactor facilitated enhancing the TN removal two folds than the conventional-reactor and was measured as 18 ± 16%. Nitrifiers, denitrifiers and anammox bacteria were present in the sludge samples of syphon–DHS as nitrogen-removing bacteria. The developed anaerobic conditions in the syphon–DHS enhanced denitrification without using extra energy for operation.

Insights into structure-performance relationship in radial flow fixed bed reactor for CO2 methanation

The extraction of petroleum and natural gas is often accompanied by a large number of associated gases, especially the high CO2 content reservoirs facing the emission of a large amount of CO2. CO2 methanation is recognized as one of the suitable candidates for CO2 utilization to reduce the emission of CO2. Because of the highly exothermic nature of the reaction, however, it is very important to enhance the heat transfer process inside the reactor and inhibit the formation of hot spots. In the fixed bed reactor, the heat transfer in the radial direction is greatly limited compared with that in the axial direction. Thus, this work adopted the radial flow reactor to evaluate the CO2 methanation process by the means of a numerical model based on OpenFOAM. Four types of radial flow reactor configurations, namely centrifugal Z-type, centrifugal Π-type, centripetal Z-type, and centripetal Π-type, were compared. The fluid flow, heat transfer, and reaction performances for these reactors were discussed under consistent operating conditions. Results show that the centrifugal Π-type structure has the most uniform flow field. In terms of heat transfer and reaction performance, the centripetal Z-type structure is the best among the four radial flow reactor configurations. These findings provide a theoretical basis and technical guidance for designing and developing radial flow reactors.

Evaluation of the Basic Neutronics and Thermal-Hydraulics for the Safety Evaluation of the Advanced Micro Reactor (AMR)

South Africa requires safe affordable distributed base load energy, one way to achieve this is to use nuclear power integrated with renewable energy sources on a decentralized basis. This suggests the development of its own micro modular nuclear reactor, to supply energy to towns, small communities, mines and processing plants. Large Light Water Reactors (LWRs) are expensive and require a large infrastructure development. A High Temperature Reactor (HTR) called the Advanced Micro Reactor (AMR) is in the process of being developed and the design philosophy is to design for inherent safety, maximally using technology that has been developed and validated in previous HTR programs albeit in a completely different and unique configuration. The concept is based on existing knowhow and experience/expertise in South Africa during the time of the Pebble Bed Modular reactor (PBMR) project. These AMR reactors are to be factory built to obtain good quality control and rolled out to various sites. Once the reactor has reached its end of life, it would be returned to a licensed organisation for refuelling. The AMR produces 10MW of thermal power. The reactor configuration uses hexagonal graphite blocks for structural and moderator material, which are arranged to form a cylindrical core layout. The fuel assemblies are silicon carbide tubes that house coated particle fuel, immersed in a lead-bismuth eutectic alloy (LBE). Each fuel assembly is contained in a boring within the graphite moderator that allows an annulus for cooling. There are 420 fuel assemblies in the core. Low enriched fuel in the form of UO₂ or UCO is used. Helium gas is used as coolant. The coolant enters the core at 450°C and exits at 750°C. The mechanical, neutronic and thermal-hydraulic design of the AMR, is being evaluated with assistance from STL Nuclear (Pty) Ltd., the University of Pretoria (UP), the North-West University and the South African Nuclear Energy Corporation (NECSA). The OSCAR-5 code package, together with the Serpent neutronic code were used to perform the basic neutronic studies while the Flownex package was used to determine the thermal-hydraulic and safety evaluation for the Design Base Accident (DBA) specifically the Depressurized Loss of Forced Cooling (DLOFC) event.

Coupling cellular substrates and radial flow reactors for enhanced exhaust abatement in automotive DeNOx-SCR

Cellular materials, such as open-cell foams and POCS, are envisioned as alternative structured substrates to the standard honeycomb monoliths for improving automotive DeNOx-SCR abatement efficiency thanks to their superior gas-to-solid mass transfer properties. The innovative substrates are numerically assessed through Computational Fluid Dynamics simulations to parametrically investigate their performances in terms of pressure drop and abatement efficiency in full-scale geometries as a function of cell size and operating conditions. Cellular substrates (open-cell foams and 3D printed POCS) are tested first as a direct replacement of the monolith preserving the catalyst loading and the standard device geometry. An increment in NO conversion is observed due to the enhanced gas–solid transfer. However, a concomitant unacceptable increase in the pressure drop across the device is apparent in all the conditions for both commercial foams and POCS. To avoid this issue, a radial flow configuration of the reactor is hereby proposed for the first time for mobile ATS systems to reduce the pressure drop. Such a configuration is only possible for cellular substrates, since they are characterized by isotropic permeability. The simulations revealed that the new reactor loaded with cellular materials is a compelling solution granting comparable or lower pressure drops than honeycomb monoliths with a concomitant improvement of the abatement efficiency. The best reactor configuration offered up to a 5% conversion increase and up to a 5-fold pressure drops reduction compared to the state-of-the-art. Even so, better performances than the honeycomb were found for other reactor configurations, allowing for a flexible choice of the final design.