State Reactor Research Articles

Effect of bioaugmentation on gas production and microbial community during anaerobic digestion in a low-temperature fixed-bed reactor.

Low temperature is one of the limiting factors for anaerobic digestion in cold regions. To improve the efficiency of anaerobic digestion for methane production in stationary reactors under low-temperature conditions, and to improve the structure of the microbial community for anaerobic digestion at low temperatures. We investigated the effects of different concentrations of exogenous Methanomicrobium (10, 20, 30%) and different volumes of carbon fiber carriers (0, 10, 20%) on gas production and microbial communities to improve the performance of low-temperature anaerobic digestion systems. The results show that the addition of 30% exogenous microorganisms and a 10% volume of carbon fiber carrier led to the highest daily (128.15 mL/g VS) and cumulative (576.62 mL/g VS) methane production. This treatment effectively reduced the concentrations of COD and organic acid, in addition to stabilizing the pH of the system. High-throughput sequencing analysis revealed that the dominant bacteria under these conditions were Acidobacteria and Firmicutes and the dominant archaea were Candidatus_Udaeobacter and Methanobacterium. While the abundance of microorganisms that metabolize organic acids was reduced, the functional abundance of hydrogenophilic methanogenic microorganisms was increased. Therefore, the synergistic effect of Methanomicrobium bioaugmentation with carbon fiber carriers can significantly improve the performance and efficiency of low-temperature anaerobic fermentation systems.

Numerical model for simulating the hydraulic parameters of the aeration system ensuring equal oxygenation of the compost heap

The aim of the work was to develop a mathematical model using equations of fluid mechanics that describe the dynamics of air flow in a part of the compost aerating system integrated with a stationary reactor. The results of the simulation show that adjusting the flow resistance along the entire length of the compost aerating duct, depending on the distance from the connection of the duct with the fan's pressure conduit pipe through gradually increasing the air outflow area by increasing the number of repeatable gaps, yields a uniform pressure distribution above the grate. The process parameters used for computation were relevant to composting a subscreen fraction separated from mixed municipal waste using 80 mm mesh screen (Fr<80 mm) under real conditions. Microsoft EXCEL 2010 software and STATISTICA version 13.3 by StatSoft were used for numerical and statistical analysis of the test results. The research results are presented in four tables and five figures and discussed in the text of the article. During tests performed in real conditions, various variants were tested for reactor filling level and air outflow active surfaces in subsequent grate parts (Fc (i)). It was found that the target waste layer thickness i.e. 3.0 m and Fc (i) changes, in accordance with the values of the developed model, result in a stable pressure distribution pd, amounting to 1506 Pa and 1495 Pa at the grate front and end part.

High-fidelity neutronics simulation of channel-type molten salt reactors

As one of the generation IV reactors, molten salt reactors (MSRs) have attracted much attention in recent years. Generally, molten salt acting as both fuel and coolant circulates through graphite channels and external primary loop in a liquid-fueled MSR with a channel-type core. To accurately simulate the neutronics of channel-type MSRs, a GPU paralleled high-fidelity neutron transport code ThorMOC has been improved by implementing a 3D rasterized coarse mesh finite difference (RCMFD) method and a quasi-2D delayed neutron precursor (DNP) drift model. A Molten Salt Reactor Experiment (MSRE) model and a small Thorium-based MSR (sTMSR) model with stationary and flowing fuel are used for the verification of the improved ThorMOC. The reference results of the two stationary reactor models are obtained from Monte Carlo code OpenMC, which indicates that ThorMOC performs a high accuracy for stationary MSR simulations. The reactivity loss caused by fuel flowing in the steady state MSRE is calculated by ThorMOC and agrees well with the measured value from the MSRE. Moreover, the influences of geometry simplifications of fuel channels and downcomer on the reactivity loss are evaluated by comparing their results with those of the high-fidelity model. The reactivity loss in the sTMSR core is computed, and the effects of fuel velocity in core channels and residence time outside the core on the reactivity loss are also analyzed. The whole-core transport calculations of the 3D MSRE and sTMSR core models with 8 energy groups cost several hundred seconds.

OXIDATION OF n-OCTANE IN THE PRESENCE OF MANGANESE-POLYMER CATALYST AND SELECTION OF THE APPROPRIATE KINETIC MODEL

Oxidation of n-octane was carried out in a stationary reactor using immobilized manganese nanoparticles in various mass percentages (5 and 10 wt.%) on poly(4-vinylpyridine). It was found that manganese-containing catalysts immobilized in polymer are more active in the oxidation of n-octane than similar homogeneous catalysts. A kinetic model and an equation for calculating the oxidation of n-octane in the presence of a manganese-polymer catalyst were chosen for the calculation. Taking into account the kinetic model, the velocity constant of the specified process is calculated. A high conversion in the oxidation reaction of n-octane with molecular oxygen was obtained

Comparative Analysis of Lithium First Wall Concepts for Tokamak with Reactor Technologies

When developing the stationary fusion reactor, an unresolved issue is the design of its intra-chamber plasma-facing elements. It has now become obvious that among the materials conventionally used for intra-chamber elements, there are no solid structural materials that would meet the requirements for the long-term operation under the effect of the flux of fusion neutrons (14 MeV) with a density of ~1014 cm–2 s–1 and the heat flux with a power density of 10–20 MW/m2. An alternative solution to this problem is the use of liquid metals as a plasma-facing materials, and, first of all, the use of lithium, which has a low atomic number (low charge number Z). Other easily-melting metals are also considered, which have higher Z number, but lower saturation vapor pressure than lithium. This will make it possible to create the long-lived, heavy-to-damage and self-renewing surface of the intra-chamber elements, which will not contaminate the plasma. The main ideas of the alternative concept of the intra-chamber elements can be formulated based on the comprehensive analysis of the problems and requirements arising during the development of intra-chamber elements of the stationary reactor, for example, the DEMO-type reactor. The article presents the analysis of the possible design of the lithium-coated intra-chamber elements and discusses the main ideas of the lithium first wall concept for the tokamak with reactor technologies.

Effects of Halide Anions on Water Desalination based on Crystallization Methods: Freezing and Tetrahydrofuran Hydrate formation

In this study, the water desalination was performed using the freezing method and Tetrahydrofuran hydrate formation in a stationary reactor. The experimental setup includes two coaxial cylinders, which ice crystals deposit outside the cool inner cylinder; thus the salt concentration increases in the residual brine. In order to evaluate the performance of these methods, the removal percentage of salt was measured by the electrical conductivity instrument. The results show that the removal efficiency decreases with an increasing salt concentration in the freezing method while the different trend is observed in the hydrate formation method. As an important result, the salt removal efficiency of the hydrate formation method was higher than the freezing process. Also, to investigate the effect of the anionic size on the salt removal efficiency, the experiments were performed with NaCl, NaBr, NaF, and NaI, which have the same cations. The results show that the performance of desalination improves by increasing anionic radius. So the dissolved mineral components are removed in the following order. The removal of salts with a higher size is further by the hydrate-based and freezing desalination.

CATALYTIC CONVERSION OF BIOGAS INTO SYNTHESIS GAS ON Ni, Co AND Ni-Co CATALYSTS

The world's oil reserves are shrinking every day due to continuous production and processing using the most modern technologies. Scientists around the world are looking for different types of raw materials and ways to use the vast resources of natural gas as a substitute for oil. In this regard, considerable attention is paid to natural and associated gas as an alternative source of raw materials for the petrochemical industry. In this paper, Ni, Co and Ni-Co catalysts carried to θ-Al2O3 prepared by the traditional method of air impregnation for moisture capacity are studied. The developed compositions of monometallic and bimetallic compositions of catalysts were studied by the XRD method. The efficiency of the dry methane reforming reaction was investigated in a stationary reactor under the optimal process conditions found experimentally: T = 700 and 900oC, GHSV = 6000 h-1 and CH4:CO2: Ar = 1: 1: 1.

Torrefaction of Sorghum Straw Pellets in a Stationary Reactor with a Feeding Screw

The effects of temperature and rotating speed of a feeding screw on the key performance parameters (mass yield, energy yield, and energy densification index) of torrefaction in a stationary reactor...

Evaluation of Discharged Fuel in Preproposed Breed-and-Burn Reactors from Proliferation, Decay Heat, and Radiotoxicity Aspects

The purpose of this technical note is to evaluate the discharged fuel of breed-and-burn (B&B) reactors. The discharged burnup in a B&B core can be high, and there is a concern that as decay heat increases, handling after a shutdown might be difficult. Because discharged fuels contain a number of plutonium nuclides, the potential for proliferation is also a concern. Moreover, radiotoxicity levels are an issue for geological disposal. As reference cores, two stationary wave reactor (SWR) cores proposed in our previous studies were used. The SWR is a special type of B&B reactor. Discharged fuels of the two SWR cores were evaluated by comparing them to a pressurized water reactor (PWR) and a fast breeder reactor. The discharged fuels of both SWR cores were not significantly worse than the reference PWR, even though the burnup was about 2.6 to 7.0 times higher.

A series of neutron time of flight method applications on the China Advanced Research Reactor

The advantages of time of flight method enable it to be widely used on stationary reactors. In this study, we reported several typical applications of time of flight method on the China Advanced Research Reactor (CARR). First, a new solution is designed to measure the beam characteristics including wavelengths, wavelength resolution rates and intensities of HOPG(002) monochromator for the unfiltered and filtered cases. Second, the changes in neutron wavelength spectra on the cross section of curved neutron guide CNGB end were examined and studied. It can be concluded that evident shape changes between neutron wavelength spectra along horizontal direction are mainly caused by the horizontal curving of curved neutron guide and dips at other wavelengths apart from 4 Å are mainly caused by small radius of curvature of curved neutron guide. Third, based on neutron velocity selector of small angle neutron scattering instrument at CARR, a calibration instrument is designed, and calibration experiments are conducted and simulated. The results indicate that the discrepancy between the experimental wavelength resolution rate and the theoretical one is caused by beam divergence linked with the critical reflection angle of neutron guide coating and the difference between experimental wavelength and the theoretical one is caused by the shape change of source neutron wavelength spectrum. These findings are reported here for the first time.

Major non-volatile intermediate products of photo-catalytic decomposition of ethylene

A complex kinetics of the photocatalytic decomposition of gaseous ethylene on nanoparticulate Fe(III) doped anatase TiO2 was analyzed in a continuous-flow fixed-bed reactor. The analysis evidenced the production of non-volatile intermediate reaction products, which cover the photocatalyst surface and delay the time of attaining the stationary reactor performance. As a result, the reaction yield slowly increases during the long-lasted (∼3 h) intermediate stage. Based on Raman, FTIR and thermal post-treatment analyses, we assigned the major non-volatile reaction product to polymeric oxidized hydrocarbons: furan and furfural oligomers. A theoretical model is proposed explaining the observed kinetics.

Synthesis, Characterization and Photocatalytic Efficiency of ZnO/MWCNT Nanocomposites Prepared Under Different Solvent Conditions.

Here we report the application of zinc oxide (ZnO) coated multi-walled carbon nanotube (MWCNT) composites in the photocatalytic decomposition of acetaldehyde (AA). Zinc oxide nanoparticles were successfully coated on the multi-walled carbon nanotube via impregnation process using zinc acetate (Zn(CH₃COO)₂×2H₂O) as precursor and sodium dodecyl sulfate (SDS) treated multiwalled carbon nanotube as raw material under different solvent conditions. The applied solvents during preparation were ethanol (EtOH) and water (H₂O). As-prepared materials were characterized by thermal analysis (TG), X-ray diffraction (XRD), specific surface area measurement (BET) and transmission electron microscopy (TEM) techniques. Photocatalytic efficiencies of as-prepared composites were investigated in a stationary reactor equipped with UV lamp. Decomposition of acetaldehyde was followed by using gas chromatography (GC). Observations revealed that using impregnation method and different solvents the preparation of ZnO/MWCNT nanocomposites can be controlled easily. The highest degradation rate was achieved with the nanocomposite was synthetized using ethanol as solvent. The photocatalytic experiments revealed that the composite has higher photocatalytic activity than that of both the zinc oxide nanoparticles and the mechanical mixture of multi-walled carbon nanotube and zinc oxide.

THE METHODOLOGY OF THE EXPERIMENTS ON TRITIUM GENERATION AND RELEASE FROM THE Li15.7Pb LEAD LITHIUM EUTECTIC UNDER REACTOR IRRADIATION

In this paper, the methodology of the experiments on tritium generation and release from the Li15.7Pb lead-lithium eutectic under neutron irradiation is presented. Using the MCNP software, the neutron-physical calculations were performed. As a result of calculations, the power of energy release from the sample and from the design elements of ampoule device at the level of 1 MW thermal power are determined. Using the ANSYS software packages, thermophysical calculations for different temperature modes of eutectic at 1–6 MW stationary reactor power levels has been carried out. Based on the calculations a special irradiation ampoule device (AD) was developed. The cleaning and filling of the lead-lithium eutectic into AD were conducted. The methodical experiments to determine the irradiation parameters of eutectics and to determine the mass-spectrometric registration modes of tritium in ampoule device was performed. The preliminary results of the methodical experiments were presented.

ChemInform Abstract: Capturing and Using CO2 as Feedstock with Chemical Looping and Hydrothermal Technologies

AbstractReview: 185 refs.

Analysis of the Correlation Function of the Neutron Field in a Critical Reactor Taking Account of the Neutron Intensity Regulation System

The influence of the parameters of the neutron intensity regulation system on the uncertainty of the neutron field in a critical stationary reactor is investigated. The spectral expansion method is used to obtain by means perturbation theory a relation for the neutron flux density distribution. On the basis of the relations obtained an expression for the correlation function of the neutron field is obtained and analyzed. Numerical modeling is used to determine the spatial distribution of the dispersion of the neutron field for different arrangements of the neutron detectors and control organs.

Calculation of the Covariation Matrix of the Neutron Flux Density in the Multigroup Diffusion Model of a Subcritical Reactor

The reconstruction of fields and adjustment of the parameters of reactor models are increasingly prioritized for reactor physics because the efficiency and safety of the control of a nuclear plant depend on solving them. The results of reconstruction and parameter adjustments are largely determined by the probability distributions of the computed and measured data. The probability distribution of the computed data in turn depends on the properties of the neutron-physical model and probabilistic characteristics of the parameters of this model. The present work is devoted to the search for and investigations of efficient algorithms for calculating the covariation functions of the neutron flux density. A model of a stationary subcritical reactor with an internal neutron source is studied. Linear perturbation theory, the theorem on the spectral decomposition of operators, and the theory of stochastic processes are the tools used for performing the analysis. The uncertainty of the nuclear data, the technological parameters of the core, and the inaccuracies in the model approximations give rise to a significant error in neutron-physical calculations. For this reason, reactor models must be verified and adjusted on the basis of measurements in order to make the control and design of reactor setups more reliable and efficient. The measurements and calculations can be compared with one another correctly only if their errors are taken into account. The problem of quantitative assessment of the computational uncertainty in the model parameters is solved by means of the theory of sensitivity and uncertainty analysis [1‐3]. Methods for evaluating the uncertainty of linear and nonlinear functions of the neutron field are now adequately developed [4, 5]. Less attention is given to the evaluation of the uncertainty of distributed characteristics: the neutron and temperature fields, distribution of the nuclear concentration, energy release fields, and so on. The probabilistic characteristics of the distributed parameters are used in the algorithms for reconstruction, adjustment, and optimal filtration of computational models [6‐9]. Of special value for these algorithms are the second moments of the function of state of a model ‐ the covariation matrices, to whose study the work is devoted. The aim of the present work is to study the structure of and search for efficient algorithms for calculating the covariation matrices of the neutron field on the basis of the multigroup diffusion approximation. The analysis is performed for a stationary subcritical reactor with a distributed internal neutron source.

Capturing and using CO2as feedstock with chemical looping and hydrothermal technologies

Summary Chemical looping technology for capturing and hydrothermal processes for conversion of carbon are discussed with focused and critical assessments. The fluidized and stationary reactor systems using solid, including biomass, and gaseous fuels are considered in chemical looping combustion, gasification, and reforming processes. Sustainability is emphasized generally in energy technology and in two chemical looping simulation case studies using coal and natural gas. Conversion of captured carbon to formic acid, methanol, and other chemicals is also discussed in circulating and stationary reactors in hydrothermal processes. This review provides analyses of the major chemical looping technologies for CO2 capture and hydrothermal processes for carbon conversion so that the appropriate clean energy technology can be selected for a particular process. Combined chemical looping and hydrothermal processes may be feasible and sustainable in carbon capture and conversion and may lead to clean energy technologies using coal, natural gas, and biomass. Copyright © 2014 John Wiley & Sons, Ltd.

Prospects for development of an innovative water-cooled nuclear reactor for supercritical parameters of coolant

The state of nuclear power engineering as of February 1, 2014 and the accomplished elaborations of a supercritical-pressure water-cooled reactor are briefly reviewed, and the prospects of this new project are discussed based on this review. The new project rests on the experience gained from the development and operation of stationary water-cooled reactor plants, including VVERs, PWRs, BWRs, and RBMKs (their combined service life totals more than 15 000 reactor-years), and long-term experience gained around the world with operation of thermal power plants the turbines of which are driven by steam with supercritical and ultrasupercritical parameters. The advantages of such reactor are pointed out together with the scientific-technical problems that need to be solved during further development of such installations. The knowledge gained for the last decade makes it possible to refine the concept and to commence the work on designing an experimental small-capacity reactor.

Study of startup conditions of a pulsed annular reactor

A new concept of reactor, which combines features of pulsed and stationary reactors, was proposed to produce intense neutronic fluxes. Such a reactor, known as Very Intense Continuous High Flux Pulsed Reactor (VICHFPR), consists of a subcritical core with an annular geometry and pulsed by a rotating reflector that acts as a reactivity modulator as it produces a short pulse (approximately equal to 1ms) of high intensity, leading the region near the pulser to prompt supercritical state.This work tends to analyze the startup conditions of a pulsed annular reactor. The neutron pulse evolution is analyzed since the reactivity modulator is brought upwards according to a helicoidal path from its initial position (distant from the core – where the multiplication factor has a subcritical value) up to the final position (near the core), in which a prompt supercritical state is reached. Part of the analysis is based on the variation of neutron reflection, which is a uniform function of the exit and reflection angles between the core and the modulator.As the initial and final parameters are known, a programming code is worked out to provide the multiplication factor and the flux intensity evolution. According to the obtained results, the conditions under which the modulator must be lifted up during the startup are established. Basically, these conditions are related to the analysis of the raising and the rotating velocities, the reflector saving and the initial distance between the reactor and the modulator.The pulsed annular reactor startup was divided into three stages. Because of its negative reactivity in the first two stages, the neutron multiplication is not large, while the last one, having a positive reactivity, shows an intense multiplication as is usually expected when handling pulsed systems. This last stage is quite sensitive to some reactor parameters such as the modulator rotation velocity and the final reactivity, but has little sensibility to the other reactor parameters.

Fast Pyrolysis of Biomass in Bubbling Fluidized Bed: A Model Study

This study proposes a model for the fast pyrolysis of biomass. A reaction scheme of a set of three parallel reactions followed by a set of two parallel reactions has been used to describe the primary and secondary reactions of biomass pyrolysis in a stationary bed reactor. A simple first-order kinetic approach has been applied to predict the product yields. The bed hydrodynamics, the mass transfer between phases and the reaction kinetics have been mathematically formulated. The effects of the operating parameters on the biomass pyrolysis product yield were simulated; the results show that the reaction temperature and nitrogen flow rate plays an important role in the yield of bio-oil. Good agreement between the predicted and measured results was obtained.