Reactor Unit Research Articles

Liquid–liquid equilibria of the ternary system (cyclopentanol + water + cyclopentyl formate) at (298.2–338.2) K: Measurements and correlation

Cyclopentanol is an important intermediate in a production of many chemical specialties. This paper relates to a development of a new technology of indirect cyclopentene hydration in the presence of formic acid and presents the data of liquid-liquid equilibrium (LLE) for the ternary system of (cyclopentanol + water + cyclopentyl formate) under atmospheric pressure and within a temperature range from 298.2 K to 338.2 K. The experiments were conducted in a temperature-controlled glass cell and the received data were correlated with nonrandom two-liquid (NRTL) and universal quasichemical (UNIQUAC) equations in order to obtain binary coefficients describing LLE of the given system. A consistency of the experimental tie-lines data was validated by the Bachman and Othmer-Tobias equations and the data fitting accuracy was evaluated by the use of the calculated average absolute deviation and the root-mean-square-error values. According to our best knowledge, the LLE of this system have not yet been published elsewhere and the values of binary interaction parameters should be used for the design of the reactor and separation units in the process of indirect cyclopentene hydration.

Continuous Multistage Synthesis and Functionalization of Sub-100 nm Silica Nanoparticles in 3D-Printed Continuous Stirred-Tank Reactor Cascades.

The controlled and continuous production of nanoparticles (NPs) with functionalized surfaces remains a technological challenge. We present a multistage synthetic platform, consisting of 3D-printed miniature continuous stirred-tank reactor (CSTR)cascades, for the continuous synthesis and functionalization of SiO2 NPs. The use of the CSTR platform provides ideal and rapid mixing of precursor solutions, precise injection of additional reagents for multistep reactions, and facile operation when using viscous solutions and handling of syntheses with longer reaction times. To exemplify the use of such custom-designed CSTR cascades, amine- and carbohydrate-functionalized SiO2 NPs are chosen as model reaction systems. In particular, the intensified flow reactor units allowed for the reproducible formation of SiO2 NPs with diameters less than 100 nm and narrow size distributions (3-8%). Most importantly, by assembling various 3D-printed CSTR cascades, we synthesized gluconolactone-capped polyethylenimine-modified silica NPs in a fully continuous manner. The inherent control over NP surface charge, reactor scalability, and the significant shortening of processing times (less than 10 min) compared to batch methodologies (several days) strongly indicate the ability of the reactor technology to accelerate continuous nanomanufacturing. In general, it provides a simple route for the reproducible preparation of functionalized NPs, thus expanding the gamut of flow reactors for material synthesis.

Hydrogen Production from the LOHC Perhydro-Dibenzyl-Toluene and Purification Using a 5 µm PdAg-Membrane in a Coupled Microstructured System.

Hydrogen bound in organic liquid hydrogen carriers (LOHC) such as dibenzyl-toluene enables simple and safe handling as well as long-term storage. This idea is particularly interesting in the context of the energy transition, where hydrogen is considered a key energy carrier. The LOHC technology serves as a storage between volatile energy and locally and timely independent consumption. Depending on the type of application, decisive specifications are placed on the hydrogen purity. In the product gas from dehydrogenation, however, concentrations of 100 to a few 1000 ppm can be found from low boiling substances, which partly originate from the production of the LOHC material, but also from the decomposition and evaporation of the LOHC molecules in the course of the enormous volume expansion due to hydrogen release. For the removal of undesired traces in the LOHC material, a pre-treatment and storage under protective gas is necessary. For purification, the use of Pd-based membranes might be useful, which makes these steps less important or even redundant. Heat supply and phase contacting of the liquid LOHC and catalyst is also crucial for the process. Within the contribution, the first results from a coupled microstructured system—consisting of a radial flow reactor unit and membrane separation unit—are shown. In a first step, the 5 µm thick PdAg-membrane was characterized and a high Sieverts exponent of 0.9 was determined, indicating adsorption/desorption driven permeation. It can be demonstrated that hydrogen is first released with high catalyst-related productivity in the reactor system and afterwards separated and purified. Within the framework of limited analytics, we found that by using a Pd-based membrane, a quality of 5.0 (99.999% purity) or higher can be achieved. Furthermore, it was found that after only 8 hours, the membrane can lose up to 30% of its performance when exposed to the slightly contaminated product gas from the dehydrogenation process. However, the separation efficiency can almost completely be restored by the treatment with pure hydrogen.

Математическое моделирование гидроочистки дизельного топлива

The principles of mathematical modeling of Hydrotreating diesel fuel in the representation of raw materials in the form of a set of narrow fractions in which the total content of various organosulphuric components is considered as a pseudocomponent are considered. As a result of the analysis of schemes of reactor blocks of Hydrotreating plants the most perspective two-reactor systems characterized by separate desulfurization of streams are revealed. It is shown that the preliminary fractionation of Hydrotreating raw materials into light and heavy fractions with the choice of the optimal boundary of fraction division can minimize the loading of the catalyst into the reactor unit. An algorithm for solving this problem, including experimental and computational fragments, is presented.

Synthesis, characterisation and preliminary corrosion behaviour assessment of simulant Fukushima nuclear accident fuel debris

ABSTRACTNuclear fuel debris generated at the Fukushima Daiichi nuclear power plant during the loss of coolant accident in 2011, still resides within the reactor units, constantly cooled by water. Until it is retrieved, the fuel debris will corrode, releasing radioactive elements into the coolant water and the ground surrounding the reactors. To predict the corrosion behaviour of these materials, and to establish parameters for experiments with U-containing and real fuel debris, the corrosion of two surrogate fuel debris materials, with a composition of Ce(1-x)ZrxO2 (x = 0.2 and 0.4), was investigated. Materials were synthesised by a wet chemistry route and pellets were sintered at 1700°C in air atmosphere. Due to the slow corrosion kinetics, aggressive conditions were applied, and corrosion experiments were performed in 9 mol.L-1 HNO3 under static conditions. The incorporation of Zr into the structure of Ce reduced the normalised dissolution rate; from (3.75 ± 0.15) × 10-6 g.m-2.d-1 to (4.96 ± 0.28) × 10-6 g.m-2.d-1 for RL(Ce) of Ce0.8Zr0.2O2 and Ce0.6Zr0.4O2, respectively.

Научные и проектные аспекты остекловывания жидких радиоактивных отходов АЭС с ВВЭР-1200

The article presents a comparison of technologies for liquid radioactive waste bottom sediment processing from NPPs with WWER-1200 reactor units. Vitrifi cation and cementing methods were compared based on the state of art in the development of the Unifi ed State System for Radioactive Waste Management, as well as engineering and design study of various processing methods. The research demonstrates that industrial use of the vitrifi cation method can be seen as a promising one when it comes to the processing of liquid radioactive waste from NPPs and radiochemical plants.

Using modeling to select catalyst dilution methods for mass transfer intensification in lab gas–liquid fixed-bed reactors

Heterogeneous catalyst testing methodology at the lab scale must provide intrinsic kinetics data for reactor design purposes as well as the intrinsic activity ranking during catalyst screening in the field of refining and petrochemistry. The significant downscaling of the past century coupled with the increasingly active catalytic formulations may introduce considerable momentum, mass and heat effects in experiments at small scale. Catalyst dilution has emerged as one versatile and robust way to reduce the impact of momentum and heat effects on heterogeneous catalyst testing. This paper presents a methodology based on global phenomena and catalyst dilution modeling to assess and optimize reactor loading techniques for specific problems. More particularly, the aim is to provide catalysts developers and kinetics experts with concrete guidelines for intensifying gas-liquid mass transfer in lab gas–liquid fixed-bed reactors through catalyst dilution. The methodology is applied to the kinetics determination of the oil residue Hydrodemetallation (HDM) and to the screening of catalysts for benzene hydrogenation. Layered dilution, consisting on the split of the catalyst in two beds separated by an intermediate bed containing an inert material of the same size as the catalyst, poorly improves gas–liquid mass transfer. Uniform dilution, based on the direct mixture of catalyst and inert material of the same size, significantly enhances gas–liquid mass transfer as the reactant local consumption per reactor unit volume is strongly reduced. Combinations of both abovementioned dilution techniques can be used with fast and/or high stoichiometric factor chemical systems operated at conversions higher than 70%. A new criterion is proposed to calculate the minimum dilution factor to guarantee negligible gas–liquid mass transfer limitations as a function of conversion, external mass transfer and global pseudo second-order kinetics.

Применение расчетного кода TRACT для оценок радионуклидных составов и радиационных характеристик ОЯТ и РАО класса 1

The article presents the results of computational studies addressing radionuclide compositions and radiation characteristics of spent nuclear fuel from WWER-440 and BN-600 reactor units performed using new computer code TRACT. These studies are performed to acquire basic information enabling further forecasts of RW Class 1 characteristics generated from the reprocessing of these fuel types. The calculations allowed to identify the characteristics of WWER-440 and BN-600 SNF considering various irradiation and storage conditions, including different burnup levels and pre-reprocessing cooling times. Such data will enable further evaluation of possible ranges describing the characteristics of RW Class 1.

Применение удельного показателя для оценки объемов образования РАО при нормальной эксплуатации АЭС России

Generation of radioactive wastes (RW) is viewed a most urgent problem of radiation safety under normal operation of nuclear power plants (NPP). The paper demonstrates the application of a specifi c indicator (rate) of RW generation per unit of generated power (m3/GW·h) for a retrospective assessment and forecasting of RW generation volumes at Russian NPPs. Mean and median values of annual specifi c RW generation rates were calculated for each NPP based on published environmental reports of JSC Rosenergoatom Concern for the period of 2008—2018. Advantage of applying median values in retrospective and forecast assessments was shown. Medians for solid very low-level, low-level, intermediate-level and high-level radioactive waste amounted to 1.5·10−2 m3/GW·h, 3.3·10−2 m3/GW·h, 3.3·10−3 m3/GW·h and 2.8·10−4 m3/GW·h, respectively; for liquid low-level and intermediate-level waste these values accounted for 1.4·10−3 m3/GW·h, 2.5·10−3 m3/GW·h, respectively. NPPs with RBMK reactor units are characterized by the highest mean and median values of specifi c RW generation rates for all RW categories. Given various types of reactor facilities and their characteristic specifi c rates, retrospective estimates for the total volume of liquid RW was increased by 8 % and for solid RW — by 12 %. The forecast estimates based on specifi c rate medians, as well as on increased power generation planned for Russian NPPs indicates probable increase in RW generation volumes by 0.8—7.1 % (depending on waste category) from 2020 to 2027.

Continuous Flow Synthesis of Isoxazoles via Vinyl Azides from Friedel–Crafts Acylation of Alkynes: A Modulated Troubleshooting Optimization Approach

The synthesis of isoxazoles has been achieved in a continuous flow system composed of two reaction units: the Friedel-Crafts acylation of alkynes and the azide conjugate addition to the resulting β-chlorovinyl ketones followed by a photochemical-thermal reaction sequence. The salient feature of the current flow system includes the safe handling of potentially explosive organic azide species as well as the rapid conversion of batch reactions into flow conditions with the integration of multiple reactor units.

Model‐based equipment design for the biphasic production of 5‐hydroxymethylfurfural in a tubular reactor

AbstractHerein, a novel concept for the acid catalyzed dehydration of fructose (FRC) to 5‐hydroxymethylfurfural (5‐HMF) in a biphasic tubular reactor is presented. Reaction kinetic models were developed based on experiments performed in a newly developed lab‐scale autoclave that enables a decoupled investigation of single‐phase reaction and 5‐HMF mass transfer. Our reaction kinetic models allow an accurate description of the biphasic reaction. Subsequently, we integrate the reaction kinetic models in the model‐based design of a tailored reactor unit. This reactor unit employs the concept of in‐situ extraction in a countercurrent flow of a monodisperse droplet swarm within a continuous aqueous phase. From reactor calculations, we obtain a maximum 5‐HMF yield of 76% at full FRC conversion. Countercurrent in‐situ extraction enables over 99% 5‐HMF recovery in the organic phase.

Characterization of deactivated and regenerated zeolite ZSM-5-based catalyst extrudates used in catalytic pyrolysis of biomass

A major issue in the catalytic fast pyrolysis (CFP) of biomass is the rapid deactivation of the typically employed zeolite-based catalysts. Detailed understanding of the deactivation pathways and the type and location of coke deposits are essential for the further development of improved or new catalyst materials, including appropriate regeneration protocols. Such deactivation and regeneration studies focus almost invariably on small-scale CFP reactor units employing catalyst materials in powder form. In this study, we report the in-depth characterization of deactivated and regenerated ZrO2-promoted zeolite ZSM-5 catalyst extrudates after ex-situ CFP tests carried out in a bench scale reactor. The findings support that coking is the main reason for catalyst deactivation, i.e. for the observed decreased activity in cracking and deoxygenation. Post-mortem characterization by confocal fluorescence microscopy reveals an egg-shell spatial distribution of the coke deposits within the catalyst extrudates. These deposits are heavily poly-aromatic in nature. The majority of the coke build-up occurs in the first 20 min of the reaction and is formed on the strong Brønsted acid sites, which promote deep deoxygenation and cracking. With increasing time-on-stream, the coke deposition slows down, occurring now mainly on the external surface of the zeolite to generate a softer, i.e. more hydrogen-rich, coke on the ZrO2 domains. The catalyst is readily regenerated via thermal oxidation in air, with optimal regeneration at 500 °C. This temperature removes all coke deposits, with no detrimental effect on the catalyst’s structural, textural and acid (type and strength) properties.

Highly Selective pH-Dependent Ozonation of Cyclohexane over Mn/γ-Al2O3 Catalysts at Ambient Reaction Conditions

The selective oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone (KA oil) is one of the imperative reactions in industrial processes. In this study, the catalytic performance of manganese-supported gamma alumina (Mn/γ-Al2O3) catalysts is investigated in the selective oxidation of cyclohexane at ambient conditions using ozone. The catalysts were prepared by the wet impregnation method, and their physio-chemical properties were studied by Fourier Transform Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDX), Transmission Electron Microscopy (TEM), Inductively Coupled Plasma (ICP) spectroscopy, and Brunauer Emmett and Teller (BET). The reaction conditions were optimised considering various parameters such as reaction time, pH, and various percentages of the manganese supported in gamma alumina. The oxidation of cyclohexane was conducted in an impinger reactor unit at pH 3, 7, and 11 for 1 h of ozonation time. The aliquots were collected after 30 min and 1 h of ozonation time and analysed with GC-MS and FT-IR spectroscopy. The 2.5% Mn/γ-Al2O3 catalyst exhibited a significantly enhanced catalytic performance at pH 3 and 7 with a percentage conversion of 9% and 15% at pH 3 and 7, respectively, after 30 min of ozonation time. However, after 1 h of ozonation time, the percentage conversions were increased to 23% and 29% at pH 3 and 7, respectively. At pH 11, 5% Mn/γ-Al2O3 exhibit high catalytic performance with a percentage conversion of 19% and 31% after 30 minutes and 1 h of ozonation time, respectively. The percentage selectivity obtained is 100% toward KA oil and/or cyclohexanone depending on pH and reaction time.

Multicriteria Optimization of the Catalytic Reforming Reactor Unit Using the Genetic Algorithm

The study is devoted to multicriteria optimization of the operation of the reactor unit intended for reforming of oil fractions. The optimization is based on the earlier developed mathematical model, which can take into account changes in the temperature and molar consumption of the reaction mixture during chemical transformations, the composition of the feedstock being processed, and the circulation quality and ratio of the hydrogen-containing gas. The following criteria are used in such optimization: octane number, yield of the target product (reformate), content of the sum of aromatic hydrocarbons, and content of benzene. The optimization was implemented using Pareto approximation with the genetic algorithm. Temperatures at the reactor inlets served as the control parameters. As a result of optimization, the sum content of aromatic hydrocarbons decreases from 56 to 45 wt.%, and the octane number measured by the research method (RON) decreases from 92.7 to 90.7 points. The three-criteria optimization is also considered; it provides a decrease in the benzene content from 4 to 3.08 wt.% with a decrease in RON from 92.7 to 91.8 points. In both cases, the decrease in the octane number is admissible, taking into account the fulfilled requirements to the limiting content of benzene and aromatic hydrocarbons in the reformate.

Dynamic modelling and optimal control strategies for chemical-looping combustion in an industrial-scale packed bed reactor

The transient operation of a Chemical-looping Combustion (CLC) process in a large-scale packed bed reactor (PBR) unit is presented in this study. This work adapts 1-D heterogeneous dynamic model that considers mass and heat transport resistances in the oxygen carrier particle and the bulk fluid phase. The proposed industrial-scale model was compared using data available in the open literature and was used to study optimal control strategies that can increase power production and reduce fuel slip during the oxidation and reduction stages of this process, respectively. Moreover, promising (optimistic) and pessimistic (worst-case) scenarios were considered for this process and used to demonstrate the operational flexibility of the packed bed reactor under different process operating conditions. Results from these scenarios show an extensive recovery heat process and a near full methane conversion into CO2 and H2O during the oxidation and reduction stages, respectively. Similarly, the purge stages were performed relatively fast using low amounts of purge gas. Therefore, the present study bolsters the importance of the CLC PBR process as an attractive carbon capture and sequestration (CCS) technology that can potentially reduce the energy penalty often entailed in CO2 capture and sequestration.

Effect of operating conditions on HDS of CGO blended middle distillate

Abstract The utilization of heavier stream of petroleum hydrocarbon such as coker gas oil (CGO) via diluting with straight run gas oil (SRGO) (blended feed: SRGO and CGO; 30/70) in order to enhance the middle distillate pool of fuel (heating oil, diesel fuel, jet fuel, and kerosene). Usually, CGO fraction has a propensity to retain refractory sulfur, nitrogen and aromatics compounds. The former two elements are mainly associated with the aromatic sulfur and nitrogen compounds (i.e., refractory). Hence, a systematic study was conducted with the variation of hydrotreating operating conditions to convert sulfur, nitrogen, and aromatic compounds. The performance was carried out in a fixed bed bench-scale reactor unit, using a commercial CoMo/Al2O3 (catalyst X) catalyst after sulfidation. The CGO has a significantly higher amount of nitrogen, aromatic, and refractory sulfur compounds than that of SRGO, which makes this blend more challenging. Hence, the operating conditions have been investigated to remove sulfur and nitrogen compounds and improve the cetane index during the hydroprocessing. The variation in operating conditions is to achieve 450 ppmS in the hydrotreated product using CGO and SRGO blend as a feedstock. The conversion of sulfur and nitrogen compounds indicated that hydrodesulfurization (HDS) is selectively higher than hydrodenitrogenation (HDN) where hydrogenation played a crucial role in their selectivities at high conversion. The hydrogenation function also relates to the cetane index that decreases with increasing aromatic content. The degree of inhibition (HDS and cetane index) depends on the feed composition (nitrogen and aromatics) that consumes a large amount of hydrogen. Conclusively, beyond 90% of HDS conversion, most of the sulfur compounds are refractory, which requires a stronger hydrogenation function to remove steric-hindrance from the refractory molecule.

Designing for Situation Awareness in the Main Control Room of a Small Modular Reactor

The nuclear industry is entering into a generation in which Small Modular Reactors (SMRs) could provide solutions to the worlds future energy needs. New technology and operations will be associated with new Human Factors (HF) design challenges. Operators may be faced with a higher cognitive workloads while monitoring several reactor units at once from a central main control room (MCR), or when monitoring units remotely. Automated processes may be implemented to mitigate human error, however may also result in a reduced sense of operator awareness in situations where operators fail to develop an accurate mental model of plant status. The present article highlights design recommendations that should be considered during the early stages of SMR MCR design to optimize human performance. Also discussed is the potential applications of eye tracking, and virtual reality (VR) to inform designers on best practices in display design and control room environments, respectively.

Multiobjective optimization of a temperature mode in a reactor unit of gasoline catalytic reforming based on a kinetic model

Based on the previously developed kinetic model of gasoline catalytic reforming, the temperature regimes of gasoline catalytic reforming are optimized. Several target optimization functions are considered — yield of the main product required octane number with a restriction to benzene content (high-octane component, <2% by volume), etc. The proposed two-objective optimization problem for catalytic reforming of gasoline was solved with the Non-dominated Sorting Genetic Algorithm II (NSGA-II) in Matlab software environment The optimal inlet temperatures of the reaction mixture are determined for each reactor.

Linking heterogeneous distribution of radiocaesium in soils and pond sediments in the Fukushima Daiichi exclusion zone to mobility and potential bioavailability

During the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011 significant amounts of radiocaesium were released into the atmosphere from the reactor units 1, 2 and 3. This caused a non-uniform deposition, in composition and direction, of 134Cs and 137Cs in the near field (<30 km) from the reactors. In this work, we elucidate the influence of speciation, including radioactive particles, on mobility and potential bioavailability of radiocaesium in soils and sediments from sites located in different directions and distances from the FDNPP. Samples collected in September 2016 were characterized and subjected to sequential chemical extractions and simulated gastrointestinal fluid leaching, and the 137Cs and 134Cs activities were determined in bulk, grain-size and extracted fractions. The results show that radiocaesium was mainly irreversibly bound and in an inert form. Combined, the two forms contained >90% of the activity present in soils and ~84% in sediments. Digital autoradiography revealed that the inert fraction was predominantly associated with heterogeneities, an indication of radioactive particles. The frequency of heterogeneities was correlated with 137Cs activity concentrations, and both were in agreement with the ambient equivalent air doses measured in situ during sampling. Moreover, in situ gamma spectrometry measurements were used in the InSiCal software tool to derive 134Cs and 137Cs surface contamination. Soil activity concentrations and contamination density estimations, decay-corrected to the day of the FDNPP accident, resulted in 134Cs/137Cs ratios that match the reported release and deposition plumes from the reactor units. Overall, these results demonstrate the persistence of the particle contamination in the Fukushima near field and highlight the importance of including radioactive particles in environmental impact assessments.

Three-Dimensional Simulation of a VVER-1000 Reactor’s Pressure Chamber in the Modes with Asymmetrical Loop Operation Using a KORSAR/CFD Computation Code

The KORSAR/CFD code results from the development of the KORSAR/GP system code certified in 2009 by the Rostekhnadzor (Federal Service for Ecological, Technological, and Nuclear Supervision) as applied to the calculated justification of the safety for VVER reactors. One of the important aspects of development consists in the introduction of the CFD-module code into functional content for the simulation of spatial turbulent flows in the mixing chambers of reactors using a nested boundary method in the RANS-approximation. The CFD module is combined with a one-dimensional model according to a semi-implicit scheme as a standard code element. Calculation results using the KORSAR/CFD code are presented for the following three modes with the asymmetrical operation of a VVER-1000 reactor’s flow-circuit loops. They consist in breaking the steam pipeline in the steam generator, in connecting the main circulation pump while initially operating three pumps at the reactor power of 71% with respect to the nominal one, and in connecting a pump while initially operating two opposite pumps at the reactor power of 52% with respect to the nominal one. The calculations have been carried out based on the input data file for the NPP power unit with a VVER-1000 developed by the specialists in VVER design at OKB Gidropress, the Chief Designer in the field of VVER reactor units. A three-dimensional simulation of coupled neutron-physical and thermohydraulic processes in the reactor core has been performed. A thermohydraulic model of the reactor core has been used in a channel-by-channel approximation and a program block for the calculation of three-dimensional neutron kinetics. In the problems under consideration, the three-dimensional simulation domain for the CFD module includes four inlet manifolds and a part of the reactor pressure chamber before entering the holes in the elliptical bottom of the shaft. The holes in the elliptical bottom and the area beyond the shaft up to the outlet manifolds have been represented by the elements of a one-dimensional model. Based on the results of the calculations, the heat-carrier flow pattern in the reactor pressure chamber has been analyzed. A flow pattern effect exerted on the dynamics of the liquid temperature distribution at the entry into the fuel assemblies of the core and on the energy release power of the fuel assemblies in the simulated modes has been demonstrated.