Aspects Of Reactor Design Research Articles

Development and application in multiscale and multiphysics methodologies in Spain: Present and future trends

In the field of reactor physics analysis, the coupling of multiple physics phenomena plays a crucial role in enhancing the accuracy of predictions and understanding complex systems. Multiphysics refers to the study and analysis of physical phenomena that involve multiple interconnected physical processes occurring simultaneously in a nuclear system to ensure essential aspects of reactor design, safety analysis, and optimization, among others. Multiphysics encompasses various domains of physics, such as Thermal-Hydraulics, Neutronics, Structural Mechanics, Radiation Transport, Chemistry, and Materials Science. On the other hand, the Multiscale approach involves combining high-fidelity models with lower-fidelity ones to accurately capture the relevant physical phenomena in a Nuclear Power Plant (NPP). Multiscale involves three main scales: system level, core level, and detailed analysis scale. This paper presents an overview of the main research performed by Spanish groups in the field of multiphysics and multiscale calculations, particularly on thermal–hydraulic analysis. This revision is focused mainly on two key aspects: thermal–hydraulic multiscale coupling and thermal–hydraulic / neutronic coupling. The paper also includes the expected future trends in this field.

Advanced two-objective optimization of thickness and large-area homogeneity of ZnO ultrathin films deposited by atomic layer deposition

Semiconductor thin films and coatings have become one of the most relevant research fields due to their significant applications in priority energy-related technologies such as solar cells, photocatalysts, and smart windows. Since all these fields are conceived as tools to fight against the effects of climate change, a real impact requires the successful deposition of semiconductor films on large-area substrates such as windows, panels, pipes, and containers, to give rise to photoactive components suitable for buildings, industries, cars, and parks. However, scalability remains one of the major issues in almost all methodologies known for the deposition of semiconductor films, irrespective of the phase approach used, i.e., either from vapor- or liquid-phase. Here, a mathematical metamodel was applied to simulate the atomic layer deposition (ALD) of zinc oxide (ZnO) ultrathin films (a versatile photoactive material in energy-related research) and optimized their thickness and homogeneity over the whole area of 8 in.-diameter Si wafers. Knowing all ALD parameters that define the quality and properties of the deposited films, we delimitated a set of four metamodel-inputs (zinc precursor dose, purge, and the inner and outer carrier gas flows) based on literature review, expertise, costs, and reactor design aspects specific to the deposition of ZnO. The average thickness and homogeneity of the films were established as the two outputs of the metamodel, which were the object of optimization. Using advanced iterative procedures, we carried out three rounds of experiments that lead us to a set of ALD parameters to deposit a ZnO ultrathin film with an average thickness of 11.38 nm that leads to a deposition rate of 1.9 Å/cycle, which represents 90% of the highest reported value for ZnO by ALD (2.1 Å/cycle). The homogeneity over the whole 8 in.-diameter wafer reached 2.61 nm, which represents the smoothest distribution of thickness values in the entire deposited area. Given the origin of the limits constraining this optimization procedure, our results hold promise in supporting the transition from the laboratory-level synthesis of thin-film-based optoelectronic devices to their large-scale production. This could ultimately help to circumvent the difficulties faced in scaling the ALD technology and enable alternative deposition methodologies such as thermal ALD, otherwise inaccessible to the production chain.

Room-temperature chemical looping hydrogen production mediated by electrochemically induced heterogeneous Cu(I)/Cu(II) redox

The chemical looping process is a promising technology for high-purity hydrogen production. However, this process is operated at high temperature (e.g., >600°C), leading to rigorous requirements in the aspects of reactor design and oxygen carriers. Here, we develop a room-temperature electrocatalytic chemical looping hydrogen production system using Cu(OH) 2 as the oxygen carrier and ascorbate as the fuel. The electrolyzer is assembled by coupling cathodic hydrogen evolution and anodic Cu 2 O electro-oxidation. Ascorbate acts as the reducible fuel to reduce the resultant Cu(OH) 2 into Cu 2 O and completes the redox loop. The assembled electrolyzer achieves a current density of 100 mA cm −2 at 0.94 V. The required electricity input per cubic hydrogen produced is 2.57 kWh Nm −3 H 2 , almost half of that for conventional water electrolysis (4.83 kWh Nm −3 H 2 ). This work not only provides a new approach for hydrogen production but also facilitates the development of an innovative catalytic process. • A room-temperature electrocatalytic chemical looping H 2 production system was reported • Operando methods revealed that RTECL works on the basis of Cu(OH) 2 /Cu 2 O redox • The electricity input for hydrogen produced is merely 2.57 kWh Nm 3 H 2 for RTECL As an ideal hydrogen production method, water electrolysis is limited by its high energy consumption because of oxygen evolution reaction with sluggish kinetics. A room-temperature electrocatalytic chemical looping (RETCL) hydrogen production system using Cu(OH) 2 as the oxygen carrier was reported. A two-step indirect process was demonstrated, including an electrocatalytic-driven catalyst oxidation reaction from Cu 2 O to Cu(OH) 2 and spontaneous redox reaction between Cu(OH) 2 and ascorbate to form Cu 2 O and dehydroascorbic acid. The assembled RETCL hydrogen production system needs only 0.94 V to drive 100 mA cm −2 and realizes electricity consumption as low as 2.23 kWh Nm −3 H 2 (half of that of sole water electrolysis). Ultra-low electricity consumption for hydrogen production was achieved based on a room-temperature electrocatalytic chemical looping (RETCL) hydrogen production system. A two-step, Cu(OH) 2 -mediated indirect process was proved for the RETCL system that the pivotal specie Cu(OH) 2 is generated by the electrically driven oxidation of Cu 2 O and spontaneously undergoes redox reaction with ascorbate to reform Cu 2 O, achieving electricity consumption of 2.23 kWh Nm −3 H 2 .

Kinetics and Reactor Design Aspects of Selective Methanation of CO over a Ru/γ-Al2O3 Catalyst in CO2/H2 Rich Gases

Polymer electrolyte membrane fuel cells (PEMFCs) for household applications utilize H2 produced from natural gas via steam reforming followed by a water gas shift (WGS) unit. The H2-rich gas contains CO2 and small amounts of CO, which is a poison for PEMFCs. Today, CO is mostly converted by addition of O2 and preferential oxidation, but H2 is then also partly oxidized. An alternative is selective CO methanation, studied in this work. CO2 methanation is then a highly unwanted reaction, consuming additional H2. The kinetics of CO methanation in CO2/H2 rich gases were studied with a home-made Ru catalyst in a fixed bed reactor at 1 bar and 160–240 °C. Both CO and CO2 methanation can be well described by a Langmuir Hinshelwood approach. The rate of CO2 methanation is slow compared to CO. CO2 is directly converted to methane, i.e., the indirect route via reverse water gas shift (WGS) and subsequent CO methanation could be excluded by the experimental data and in combination with kinetic considerations. Pore diffusion may affect the CO conversion (>200 °C). The kinetic equations were applied to model an adiabatic fixed bed methanation reactor of a fuel cell appliance.

A Review on Gas‐Liquid Reactions in Light Oil Sweetening: Kinetics and Reactor Design Aspects

AbstractThiols in liquefied petroleum gas are undesirable due to their foul odor and corrosive nature. The process of removing these thiols is termed as sweetening. Metal phthalocyanines are reported to be the most effective sweetening catalyst. However, the solubility of metal phthalocyanine is low in aqueous medium. Thus, in an effort to further improve upon the existing catalysts, a novel cobalt phthalocyanine sulfonamide catalyst was developed. Laboratory and commercial evaluation of this catalyst showed enhanced activity as compared to a commercial catalyst with comparable stability. With proven higher activity, comparable stability, design of grass root oxidizer using this catalyst is the next step. Design of oxidizers for an extractive sweetening process based on this catalyst in grass root refineries requires a rigorous kinetic model. The paper reviews the literature on sweetening kinetics and focuses on the concepts of design of laboratory reactors for reaction kinetics studies for such gas‐liquid reactions. Laboratory reactor systems can be useful for accurate estimation of kinetic parameters which can then be used to design industrial reactors and predict their performance.

Scale-Up Study of a Multiphase Photocatalytic Reactor—Degradation of Cyanide in Water over TiO2

This paper provides an integrated view on various aspects of reactor design for photocatalytic reactions and presents a scale-up study of photocatalytic reactors. This study focuses on degrading organic pollutants in the effluent of an integrated gasification coal combustion plant over TiO2, with the target of degrading cyanide to below its allowable emission threshold set by European legislation. Here, we show the interplay of different efficiencies that affect the overall apparent photonic efficiency and the reactor volume required to achieve a certain objective in conversion. The chosen reactor configuration is rectangular slurry-bubble-columns-in-series to ensure a good mass transfer rate per photoreactor while approaching plug-flow behavior as a sum, and a high reactor surface-area-to-volume ratio for a good capture of incident photons. We consider a simple 1D photonic description of a photoreactor, in the direction of incident solar light, and implement a bidirectional scattering model for photocatalytic particles and bubbles to calculate the local rate of photon absorption and the photon absorption efficiency in the photoreactor. We show that, implementing the principles of process intensification, the large scale degradation of cyanide to below European emission limits is achievable.

The use of OCM reactors for ignition enhancement of natural gas combustion for practical applications: Reactor design aspects

The major goal of the study is the improvement of the ignition characteristics of lean, premixed natural gas (NG) combustion under engine-like conditions. A new process is investigated involving the oxidative coupling of methane reaction (OCM) for the in situ production of C 2 hydrocarbons to be used as ignition enhancers during lean combustion of methane in internal combustion (IC) engines. Addition of the OCM product mixture enhances the ignition characteristics of lean methane/air mixtures, the beneficial effect resulting from the C 2H 4/C 2H 6 components. OCM in both conventional plug flow and packed-bed membrane reactors is modelled and optimised with respect to reactor conditions and ignition characteristics. An additional ignition technique that includes flowing a jet of a fuel/air stream against a hot inert surface has been implemented for quantifying the effect of the proposed ignition enhancers.

Kinetics and reactor design aspects of the synthesis of ionic liquids—Experimental and theoretical studies for ethylmethylimidazole ethylsulfate

Ionic liquids (ILs) are promising new solvents, e.g. for catalysis and separation processes. Currently, ILs are produced in batch reactors at comparatively high prices. So improved and continuous reactors are probably provitable. Reaction engineering aspects of the exothermic IL-synthesis are exemplarily discussed for ethylmethylimidazole ethylsulfate ([EMIM][EtSO 4]), formed by liquid phase alkylation of methylimidazole with diethylsulfate. Simulations based on the experimentally determined kinetic data show that an adiabatic loop reactor with an external heat exchange is the best choice, e.g. compared to expensive multi-tubular reactors, which are cooled intensively to avoid a runaway. The unfavourable dilution of the reactants in the loop reactor is outbalanced by the higher inlet temperature, which leads to a higher mean reaction rate (compared to multi-tubular reactors) and a much smaller reactor without exceeding the maximum temperature of 100 ∘ C (coloration of IL; long-term thermal stability). In addition, the design and operation of a loop reactor is straightforward and less complex. Compared to batch reactors, the hold-up is by a factor of 1000 lower, which is particularly advantageous for toxic reactants (here diethylsulfate). The results are beyond synthesis of [EMIM][EtSO 4] instructive for other ILs, and probably also for other exothermic reactions with a temperature limit.

Heterogeneous catalytic reactor design with optimum temperature profile I: application of catalyst dilution and side-stream distribution

A generic method for the design of reactors with optimal temperature profiles has been developed. This paper focuses on the use of side-streams and inert pellets to control the temperature profiles in addition to external cooling. These two aspects of reactor design have so far been developed separately and mainly applied to laboratory-scale reaction systems. In this work, a reactor design procedure is developed that considers the combination of these two aspects simultaneously. Nitrobenzene hydrogenation and ethylene oxidation in non-isothermal and non-adiabatic reactors are used as case studies. The results show that higher reactor performance, characterised by conversion, yield or selectivity, can be achieved with optimal temperature profiles manipulated by side-streams and inert pellets. Temperature can be effectively controlled to be below a certain maximum point that causes hot spots, or thermal run-away behaviour. Various reactor designs such as Packed-Bed Membrane Reactor (PBMR), Multi-Bed Multi-Tubular Reactor (MBMTR) with side-stream injection are considered and compared with typical fixed-bed reactors. Pseudo-homogeneous (1D) and heterogeneous (1D) reactor models are used for the modelling of the reactor with SQP (Successive Quadratic Programming) and stochastic methods applied for the optimisation.

A review of imperative technologies for wastewater treatment I: oxidation technologies at ambient conditions

Nowadays, due to the increasing presence of molecules, refractory to the microorganisms in the wastewater streams, the conventional biological methods cannot be used for complete treatment of the effluent and hence, introduction of newer technologies to degrade these refractory molecules into smaller molecules, which can be further oxidized by biological methods, has become imperative. The present work aims at highlighting five different oxidation processes operating at ambient conditions viz. cavitation, photocatalytic oxidation, Fenton's chemistry (belonging to the class of advanced oxidation processes) and ozonation, use of hydrogen peroxide (belonging to the class of chemical oxidation technologies). The work highlights the basics of these individual processes including the optimum operating parameters and the reactor design aspects with a complete overview of the various applications to wastewater treatment in the recent years. In the next article of this two article series on imperative technologies, hybrid methods (basically combination of the oxidation processes) will be discussed and the current work forms a useful foundation for the work focusing on hybrid technologies.

Supercritical-pressure, Once-through Cycle Light Water Cooled Reactor Concept

The purpose of the study is to develop new reactor concepts for the innovation of light water reactors (LWR) and fast reactors. Concept of the once-through coolant cycle, supercritical-pressure light water cooled reactor was developed. Major aspects of reactor design and safety were analysed by the computer codes which were developed by ourselves. It includes core design of thermal and fast reactors, plant system, safety criteria, accident and transient analysis, LOCA, PSA, plant control, start up and stability. High enthalpy rise as supercritical boiler was achieved by evaluating the cladding temperature directly during transients. Fundamental safety principle of the reactor is monitoring coolant flow rate instead of water level of LWR. The reactor system is compact and simple because of high specific enthalpy of supercritical water and the once-through cycle. The major components are similar to those of LWR and supercritical thermal plant. Their temperature are within the experiences in spite of the high outlet coolant temperature. The reactor is compatible with tight fuel lattice fast reactor because of the high head pumps and low coolant flow rate. The power rating of the fast reactor is higher than the that of thermal reactor because of the high power density.

Supercritical-pressure, Once-through Cycle Light Water Cooled Reactor Concept.

The purpose of the study is to develop new reactor concepts for the innovation of light water reactors (LWR) and fast reactors. Concept of the once-through coolant cycle, supercritical-pressure light water cooled reactor was developed. Major aspects of reactor design and safety were analysed by the computer codes which were developed by ourselves. It includes core design of thermal and fast reactors, plant system, safety criteria, accident and transient analysis, LOCA, PSA, plant control, start up and stability. High enthalpy rise as supercritical boiler was achieved by evaluating the cladding temperature directly during transients. Fundamental safety principle of the reactor is monitoring coolant flow rate instead of water level of LWR. The reactor system is compact and simple because of high specific enthalpy of supercritical water and the once-through cycle. The major components are similar to those of LWR and supercritical thermal plant. Their temperature are within the experiences in spite of the high outlet coolant temperature. The reactor is compatible with tight fuel lattice fast reactor because of the high head pumps and low coolant flow rate. The power rating of the fast reactor is higher than the that of thermal reactor because of the high power density.

Fischer–Tropsch-synthesis with nitrogen-rich syngas: Fundamentals and reactor design aspects

An option in bringing remote natural gas reserves to the market is its conversion by Fischer–Tropsch (F–T)-synthesis into diesel oil and wax. The use of nitrogen-rich syngas (50 vol.%) could be an alternative to classical processes with nitrogen-free syngas because the investment costs are probably lower: syngas is produced by partial oxidation with air, which eliminates the need for an air separation plant, and a process with nitrogen-rich syngas does not utilize a recycle loop and a recycle compressor. For the development of such a process, the kinetics of F–T-synthesis was studied on an Fe-catalyst, indicating that nitrogen only dilutes syngas, and therefore, has no influence on the kinetics if the partial pressures of carbon monoxide and hydrogen are kept constant. Subsequently, the F–T-synthesis with nitrogen-rich syngas was investigated in wall-cooled single tube reactors. Based on the experimental data, a mathematical model for industrial multitubular F–T-reactors was developed. Model calculations indicate that nitrogen plays an important role in the operation of multitubular reactors by helping to remove the heat generated by the F–T-reaction. This leads to an optimum diameter of the tubes of 70 mm for nitrogen-rich syngas with respect to a stable and safe operation of the reactor, whereas for nitrogen-free syngas, the diameter is limited to about 45 mm. The production rate of diesel oil and wax per tube is, in case of nitrogen-rich syngas, about three times higher, which will decrease the number of tubes and the investment costs of industrial multitubular reactors. Detailed economic studies are still necessary to validate or disprove whether and under which circumstances the proposed process with nitrogen-rich syngas is an attractive alternative to classical processes with nitrogen-free syngas, especially in areas with remote natural gas resources.

Technology for gasifying pulverised bio-fuels including agricultural residues

This paper presents both the fundamental and technological aspects of gasification of pulverisable agro-residues, more particularly rice husk. The fundamental aspects are related to the times required for flaming and char conversion processes. The technological aspects described here are related to the gasification process using a cyclone reactor. The aspects of reactor design, cooling and cleaning systems are addressed. Limiting the tar fraction in the gas needs good mixing between the gas and the red hot char arranged in a circulating fluid bed for the ash handling system. Cleaning the gas (of particulates and some tar) is achieved by a centrifugal separation process aided by the injection of a water jet. The experience gained from the developmental programme on the gasifier operation leading to power generation via the dual-fuel mode on an existing diesel engine is also described. The gasifier operates on an air-to-fuel ratio of 0.95 to 1.0 and the consumption rate of husk when the gas is fed to an internal combustion engine in dual-fuel mode with 80% diesel replacement is 1.5–1.55 kg/kWh of electrical energy, confirmed from several long duration tests. This is lower than the value of to 2 to 2.2 kg/kWh reported for Chinese gasifiers. The conversion-fixed carbon in the rice husk char achieved in the reactor is about 50%, the cold gas efficiency being about 70%. The fuel is pulverised to a mean size of 0.75 mm with about 35% by weight less than 0.4 mm. The reduction in the size of the agricultural residues is to enable the same gasifier to be used for all the pulverisable fuels; accordingly, the same gasifier is able to successfully gasify sawdust and sugarcane trash. Some issues related to handling sugarcane trash are also discussed. The treatment of the ash/residue is in the dry mode and therefore, the requirement of water is comparable to that in wood gasifiers and is much less than in Chinese fixed bed gasifiers. Another important aspect of the study is the measurement of the NO x in the engine exhaust which has shown that the NO x level for the dual-fuel mode is one-eighth of that in diesel-alone mode over the entire power range up to full load.

Reactor Design of the Advanced Neutron Source

The ongoing preconceptual and conceptual reactor design of the Advanced Neutron Source (ANS) is explored. The ANS is being designed for materials sciences, isotope production, and fundamental physics research. A reactor design based on previously developed technology can meet the performance requirements set by the user community for a new ANS to serve all fields of neutron science. These requirements include the capability of producing a peak thermal neutron flux over five times higher than that in use at any currently operating steady-state facility. Achievement of these ultrahigh flux levels involves many interesting aspects of reactor design. The reactor characteristics of the current preconceptual reference design are presented. The attainment of this design was reached by following a design strategy that best met the safety and user requirements. The design has evolved over the last 5 yr from two concepts proposed in 1985. The trade-offs and selection of many reactor parameters are described to illustrate how and why the current design was achieved. Further reactor design is planned, leading to an ANS operating by 1999 for use by scientists of many disciplines.

Aerosol Behavior and Light Water Reactor Source Terms

The major developments in nuclear aerosol modeling following the accident to pressurized water reactor Unit 2 at Three Mile Island are briefly reviewed and the state of the art summarized. The importance and implications of these developments for severe accident source terms for light water reactors are then discussed in general terms. The treatment is not aimed at identifying specific source term values but is intended rather to illustrate trends, to assess the adequacy of the understanding of major aspects of aerosol behavior for source term prediction, and demonstrate in qualitative terms the effect of various aspects of reactor design. Areas where improved understanding of aerosol behavior might lead to further reductions in current source terms predictions are also considered.

Plasma Synthesis of Ceramic Powders

Condensation from plasmas has been shown to yield very fine, high purity powders from even the most refractory materials. Elementary particles in these powders are often single crystals, as fine as 50 nm diameter. These particles vary widely in agglomeration state; in some systems they are essentially independent, while in others hard agglomerates as large as several microns are observed. In this article the geometric aspects of reactor design which are thought to influence these powder structures are reviewed, along with three case studies in powder microstructure. Finally, the structure of the “typical” plasma powder is compared with expectations from alternative preparation routes.The development of new, energy-efficient processing strategies for ceramic fabrication has become a rapid growth field over the last ten years. Most of these strategies rely on minimizing diffusion requirements during densification by improving both the chemical homogeneity and the initial density of the powder compact to be consolidated; both requirements dictate unusual care in the synthesis of the starting powders. In the oxide systems most extensively studied to date, the required powders can often be produced by precipitation from aqueous solutions and/or emulsions. In the carbide and nitride systems widely envisaged for the next generation of structural applications, these techniques are difficult and gas-phase synthesis routes appear more attractive. In fact, even the leading practitioners of the precipitation arts write enthusiastically of aerosol synthesis methods for the oxides.

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Aspects of Reactor Design for the Anionic Copolymerization of Styrene and Butadiene to a Random Copolymer

Aspects of Reactor Design for the Anionic Copolymerization of Styrene and Butadiene to a Random Copolymer

The physics of the core of the Polytechnical University’s Training Reactor

A brief description is given of the measurements and calculations of the ZR-5 project which worked out the nuclear design of the Polytechnical University’s Training Reactor. The system of programs — the reactor physical model — used in the calculations is described together with some of the experimental techniques, that have confirmed high precision and great potential value. It is emphasized that most nuclear aspects of reactor design and operation can be effectively studied with such a calculation model.