Mixture Of Steam Research Articles

Simulation of basic gas mixing tests with condensation in the PANDA facility using the GOTHIC code

The paper reports the results of the assessment of the GOTHIC code using the data of four basic tests with condensation performed in the PANDA large-scale facility. Three of these experiments featured vertical injection, and in one the transient response due to a high-momentum horizontal injection (jet) was investigated. The injected fluid was either saturated steam or a superheated mixture of steam and helium, and the fluid initially present in the vessels was pure air. The simulations were carried out using a detailed three-dimensional representation of the vessels. In general, the results of the simulations, which used a relatively coarse mesh, were in good agreement with the data. Limitations in modelling local phenomena controlled by complex flow patterns (e.g. heat transfer in the region of an impinging jet) and the need for refined meshes to reproduce certain aspects of the transients (e.g. erosion of the interface between layers of different gas composition) were also identified. Finally, the analyses indicated that in two tests the role played by re-vaporisation of the condensate film was unexpectedly large, and this effect should be more carefully considered in the containment analyses and future model developments.

Simulation of containment jet flows including condensation

The validation of a CFD code for light-water reactor containment applications requires among others the presence of steam in the different flow types like jets or buoyant plumes and leads to the need to simulate condensation phenomena. In this context the paper addresses the simulation of two “HYJET” experiments from the former Battelle Model Containment by the CFD code CFX. These experiments involve jet releases into the multi-compartment geometry of the test facility accompanied by condensation of steam at walls and in the bulk gas. In both experiments mixtures of helium and steam are injected. Helium is used to simulate hydrogen. One experiment represents a fast jet whereas in the second test a slow release of helium and steam is investigated. CFX was earlier extended by bulk and wall condensation models and is able to model all relevant phenomena observed during the experiments. The paper focuses on the simulation of the two experiments employing an identical model set-up. This provides together with other validation exercises the information on how well a wider range of flowing conditions in a full containment simulation can be covered with a single set of models (e.g. turbulence and condensation model). Some aspects related to numerical and modelling uncertainties of CFD calculations are included in the paper by investigating different turbulence models together with the modelling errors of the differencing schemes applied.

Modeling Molten Fuel-Moderator Interactions for the CANDU Flow Blockage Accident

CANDU reactors are pressurized heavy water–moderated and heavy water–cooled reactor designs. During commissioning of nuclear power plants, a range of possible accidents must be considered to assure a plant’s robust design. Consider a complete channel blockage in the CANDU reactor. Such an extreme flow blockage event would result in fuel overheating, pressure tube failure, partial melting of fuel rods, and possible molten fuel–moderator interactions (MFMIs). The MFMI phenomenon would occur immediately after the pressure tube rupture and would involve a mixture of steam, hydrogen, and molten fuel being ejected into the surrounding moderator water in the form of a high-pressure vapor bubble mixture. This bubble mixture would accelerate the surrounding denser water, causing interfacial mixing due to hydrodynamic instabilities at the interface. As a result of these interfacial instabilities, water is entrained into the growing two-phase bubble mixture with attendant mass and heat transfer, e.g., water vaporization and fuel oxidation. A comprehensive model has been developed to investigate these complex phenomena resulting from a postulated complete flow blockage and complete pressure tube failure. This dynamic model serves as a baseline to characterize the pressure response due to a pressure tube rupture and the associated MFMI phenomena. Theoretical modeling of these interrelated complex phenomena is not known a priori, and therefore, a semiempirical approach is adopted.

Numerical analysis of hydrogen risk mitigation measures for support of ITER licensing

In the ITER wet bypass scenario, water leakage, air ingress and hot dust (Be, W, and C) in the vacuum vessel could generate combustible hydrogen–air–steam mixture. Hydrogen combustion may threaten the integrity of the ITER VV and lead to radioactivity release. To prevent hydrogen energetic combustion, nitrogen injection system in VV and hydrogen recombination system in the pressure suppression tank (ST) were proposed. The main objectives of this analysis are to study the distribution of hydrogen–air–steam mixtures in the ITER sub-volumes, to investigate the feasibility of the nitrogen injection system to fully inert the atmosphere in the VV and to evaluate the capability and efficiency of the hydrogen recombination system to remove hydrogen in the ST. 3D computational fluid dynamics (CFD) code GASFLOW was used to calculate the evolution of the mixtures and to evaluate the hydrogen combustion risks in the ITER sub-volumes. The results indicate that the proposed hydrogen risk mitigation systems will generally prevent the risks of hydrogen detonation and fast deflagration. However, the atmosphere in ITER sub-volumes cannot be completely inerted at the early stage of the scenario. Slow deflagrations could still generate quasi-static pressures above 1 bar in the VV. The structural impact of the thermal and pressure loads generated by hydrogen combustions will be investigated in future studies.

Recent advances in understanding ruthenium behaviour under air-ingress conditions during a PWR severe accident

In a hypothetical severe accident in a Pressurised Water Reactor (PWR), Fission Products (FPs) can be released from the overheated nuclear fuel and partially transported by gases, composed of a mixture of superheated steam and hydrogen, to the reactor containment. Subsequent air ingress into a damaged reactor core may lead to enhanced fuel oxidation, affecting some FP release, especially that of ruthenium. Ruthenium is of particular interest because of its high radiotoxicity and its ability to form very volatile oxides. In the reactor containment, such volatile forms are very hazardous as they are much less efficiently trapped than particulate forms by emergency filtered venting. In the four and a half years of SARNET, collaborative research dedicated to the “ruthenium story” has been performed by several partners. This paper presents the main achievements over the whole project period. Starting from experimental observations showing that fuel could be extensively oxidised by air to, and that a significant fraction of ruthenium inventory can be released, rather satisfactory models have been developed. In addition, the effect of the air interaction with Zircaloy cladding, as well as with UO 2 itself, has been studied. Experiments on the complex transformations of ruthenium oxides upon cooling through the reactor circuit have been performed. An unexpectedly large effect of temperature on the decomposition rate of gaseous ruthenium compounds has been found, as well as effects of the nature of circuit internal surfaces and other FP deposits. So it has been highlighted that various forms of ruthenium can reach the containment, but the most probable gaseous species under these conditions is ruthenium tetroxide. Preliminary analysis of ruthenium transport supports these conclusions. Experiments and analysis have also been launched on the radio-chemical reactions undergone by these ruthenium oxides in the reactor containment. Competing effects of gaseous decomposition to solid particles and re-volatilization from these ruthenium deposits have been demonstrated and modelled. The paper concludes by identifying the remaining work needed to achieve full resolution of the ruthenium source term issue. Recommendations are made for future research activities in the follow-up programme SARNET2.

Humidification tower for humid air gas turbine cycles: Experimental analysis

Abstract In the HAT (humid air turbine) cycle, the humidification of compressed air can be provided by a pressurised saturator (i.e. humidification tower or saturation tower), this solution being known to offer several attractive features. This work is focused on an experimental study of a pressurised humidification tower, with structured packing. After a description of the test rig employed to carry out the measuring campaign, the results relating to the thermodynamic process are presented and discussed. The experimental campaign was carried out over 162 working points, covering a relatively wide range of possible operating conditions. It is shown that the saturator behaviour, in terms of air outlet humidity and temperature, is primarily driven by, in decreasing order of relevance, the inlet water temperature, the inlet water over inlet dry air mass flow ratio and the inlet air temperature. The exit relative humidity is consistently over 100%, which may be explained partially by measurement accuracy and droplet entrainment, and partially by the non-ideal behaviour of air–steam mixtures close to saturation. Experimental results have been successfully correlated using a set of new non-dimensional groups: such a correlation is able to capture the air outlet temperature with a standard deviation σ = 2.8 K.

Adiabatic fixed-bed gasification of coal, dairy biomass, and feedlot biomass using an air–steam mixture as an oxidizing agent

Concentrated animal feeding operations, such as cattle feedlots and dairies, produce a large amount of manure, cattle biomass (CB), which can be included as renewable feedstock for locally based gasification for syngas (CO and H 2) production and subsequent use in power generation. Experimental results on effects of bed temperature and gas composition on the higher heating value (HHV) and energy recovery are presented for dairy biomass (DB) gasification using air and air–steam as oxidizers. Some experimental data are compared with adiabatic gasification modeling which includes atom balance conservation for assumed product species and chemical equilibrium analysis. Wyoming sub-bituminous coal (WYC) and Texas Lignite coal (TXL) are used as standard fuels for comparison purposes in modeling studies. Two main parameters are investigated in this study. One is the modified equivalence ratio (ER M) defined as the ratio of stochiometric oxygen to total oxygen supplied in the oxidizing mixture of air and steam. The second is a measure of how much steam is in the oxidizer and is called the air steam ratio (ASTR), which is defined as the ratio of oxygen supplied in the air to the total oxygen supplied in the oxidizer. The results suggested that gasification of CB and coals under higher ER M yield elevated concentrations of CO and CH 4, and low percentages of H 2 and CO 2, while higher ASTRs (less steam) produced mixtures poor in H 2, CO 2, and CH 4 and rich in CO with lower HHV. It was also found that FB and DB produced higher amounts of H 2 than WYC and TXL under the same ER M and ASTR.

Post‐oxidizing effects on surface characteristics of salt bath nitrocarburized AISI 02 tool steel type

AbstractThe effect of post‐oxidizing treatment on the characteristics of modified surface layers produced by salt bath nitrocarburizing on the industrial American Iron and Steel Institute (AISI) 02 tool steel types is investigated. Nitrocarburizing treatment is performed for 6 h and 8 h at 570 °C and post‐oxidizing treatment for 30, 60 and 90 min at 520 °C, using argon–steam mixture. Formed layers are characterized by their basic properties such as thickness layer, depth, surface hardness and wear resistance. Detailed estimation of the modified metal surface quality, in terms of chemical composition, formed phases, microstructures and diffusion mechanisms are performed by metallographic techniques, EDX, X‐ray diffraction, scanning electron microscopy (SEM) and glow discharge optical electron spectroscopy (GDOES). The corrosion resistance was investigated in 0.4 M H2SO4 solutions, using steady‐state electrochemical polarization methods. The obtained results revealed the existence of a superficial oxide layer which consists of magnetite (Fe3O4) and hematite (Fe2O3) and the presence of an ε‐phase associated with a small amount of γ′‐phase. Important improvements in wear, microhardness and corrosion resistance occur after these treatments and it is specifically concluded that the sole application of a nitrocarburizing treatment does not significantly ameliorate the corrosion resistance of the as‐received steel. In fact, post‐oxidation treatment contributes to increase corrosion resistance by forming a dense magnetite layer and at the same time, it partially covers the compound layer pores. Copyright © 2009 John Wiley & Sons, Ltd.

Carbon Capture by Sorption-Enhanced Water−Gas Shift Reaction Process using Hydrotalcite-Based Material

A novel route for precombustion decarbonization is the sorption-enhanced water−gas shift (SEWGS) process. In this process carbon dioxide is removed from a synthesis gas at elevated temperature by adsorption. Simultaneously, carbon monoxide is converted to carbon dioxide by the water−gas shift reaction. The periodic adsorption and desorption of carbon dioxide is induced by a pressure swing cycle, and the cyclic capacity can be amplified by purging with steam. From previous studies is it known that for SEWGS applications, hydrotalcite-based materials are particularly attractive as sorbent, and commercial high-temperature shift catalysts can be used for the conversion of carbon monoxide. Tablets of a potassium promoted hydrotalcite-based material are characterized in both breakthrough and cyclic experiments in a 2 m tall fixed-bed reactor. When exposed to a mixture of carbon dioxide, steam, and nitrogen at 400 °C, the material shows a breakthrough capacity of 1.4 mmol/g. The sharp adsorption front is accompa...

Noble Metal Core−Ceria Shell Catalysts For Water−Gas Shift Reaction

The metal−support interface is known to play a key role in many catalysis reactions. Using the microemulsion technique we report the preparation of a nanosized noble metal particle with an intimate contact with cerium oxide. The materials display better catalytic performance in the water−gas shift (WGS) reaction over the hydrogen-rich reformate−steam mixture without methane (side product) formation as compared with catalysts prepared by traditional methods. It is evident that the catalysts prepared by the microemulsion method show an unusual morphology and unique catalytic properties with the noble metal nanoparticle being embedded in a thin layer of cerium oxide, giving a maximum metal−support interface of three-dimensional interactions. In light of results obtained from material characterization as well as reaction rate orders and switching experiment studies over the catalysts, a discussion on possible reaction mechanism(s) taking place at the interface of this new type of catalyst is included in this paper.

Influence of Pyrolysis Environment on Liquid Product and Sulfur of Oil Shale

Oil shale samples from Ellajun Area were pyrolysed in different pyrolysing environments. Nitrogen, steam, mixture of steam and nitrogen, and mixture of hydrogen and steam were used as sweeping mediums. The experimental conditions were 500 g of sample weight, one atmospheric operating pressure, and 410°C to 550°C temperature range. Total weight loss of samples were recorded as a function of temperature. Condensed liquid products were distilled in a simple distillation. Un-condensable gases vented without analysis. The total weight loss of the sample increased with increasing retorting temperature, and the oil yield passed through a maximum value with total weight loss and increasing temperature. The distillation results showed a clear impact of the reaction environment on the percent volume distilled and the sulfur content of the liquid fraction.

F114 SOFC直接内部改質を想定したメタンの水蒸気改質実験(OS5 水素・燃料電池)

In this paper, the reaction rate of methane steam reforming over anode material was estimated to obtain the fundamental data for the analysis and the design of a solid oxide fuel cell (SOFC) with direct internal reforming. The cermet of Ni and yttria-stabilized zirconia (YSZ) was applied for the anode of SOFC. In the experiment, Ni/YSZ was used as a catalyst for methane steam reforming. The volume ratio of Ni to YSZ is 60% to 40% and the particle size was below 300 μm. A small tubular reactor, which was put inside an electric furnace, was employed, and the Ni/YSZ powder was put inside the reactor. Methane and steam mixture was supplied into the reactor. The composition of the dry gas after reforming was measured with a gas chromatograph equipment. Based on the experimental data, the turnover rate of methane was estimated. In addition, the pre-exponential factor, the activation energy and the reaction order were calculated, and therefore the reaction rate equation was obtained.

COUPLED FIELD ANALYSIS OF PRESSURE VESSEL FURNACE TUBE REDUCER USING FINITE ELEMENT METHOD

The reducer is a device used in boilers to distribute or collect steam water mixture from connected pipes used in the boilers are hollow cylindrical in shape, the connected reducers are more to suit the connected pipes with different diameters. The reducers in a boiler are subjected to the following loads: Internal steam pressure, Axial tensile load due to dead weight of connecting tubes, wind box, casing, buck stay and refractories, Furnace pressure load, Seismic load and Thermal stress due to uneven temperature distribution across the thickness of the reducer. Of these loads the effect of the internal pressure and axial tensile load due to dead load and thermal load on the reducer are considered in this analysis. Between two tubes of different diameters coactivity is ensured by reducer. The dimensions of the reducer are decided based on manufacturing facilities available and constraints. The reducer is checked to comply with the calculations and other requirements of relevant clause of statutory code, Indian Boiler Regulation (IBR). The aim of the analysis is to estimate exact stress and temperature distribution in reducer under actual working condition using Finite Element Method (FEM).

Supercapacitors based on hybrid carbon nanofibers containing multiwalled carbon nanotubes

Hybrid carbon nanofibers containing multiwalled carbon nanotubes (CNTs) were produced by electrospinning CNTs suspended in a solution of polyacrylonitrile in N,N-dimethylformamide, followed by carbonization and activation using a hydroperoxide–water steam mixture at 650 °C. Transmission electron microscopy and scanning electron microscopy were used to observe the morphology of the CNT-embedded carbon nanofibers. The specific surface area of the nanofibers was measured using the Brunauer–Emmett–Teller method. The electrochemical properties of the nanofibers were characterized by cyclic voltammetry and galvanotactic charge/discharge in 1 M H2SO4 electrolyte. The specific capacitance of electric double-layer capacitors containing CNT-embedded carbon nanofibers as electrodes reached 310 F g−1, which is almost double that obtained for capacitors containing virgin carbon nanofibers as electrodes. The CNTs embedded in the carbonized electrospun nanofibers provide improved conductive pathways for charge transfer in the electrodes and therefore lead to a significantly enhanced specific capacitance.

Nonlinear fluid–structure interaction calculation of the leakage behaviour of cracked concrete walls

In the case of severe accidents in nuclear power plants, containments are the last barrier to prevent the release of environmentally hazardous substances. Therefore, the leaktightness of the containment is of decisive importance for the safety and protection of the environment in case of an accident. A numerical model based on the Finite Element Method has been developed to calculate the leakage behaviour of reinforced concrete walls. Leakage flow and structural response are solved iteratively. For the calculation of the leakage flow a fluid model has been used which takes into account the condensation of the steam part within the air–steam mixture. Both, the release of the latent heat in the case of condensation and the following two-phase flow of air and water have been considered, too. Tests with the SIMIBE Experimental facility [Caroli, C., Coulon, N., Renson, C., 1995. Steam leakage through concrete cracks: parametric study with SIMIBE experiment and interpretation of the results. Tech. Rep. Commissariat A L’Energie Atomique (CEA)] are used for verification of the condensation and two-phase flow models.

Film Condensations on Horizontal and Slightly Inclined upward and downward Facing Plates

Condensation experiments were carried out at atmospheric pressure using water-cooled horizontal and slightly inclined flat plates, varying the air concentrations and the orientations (upward or downward facing). The plate was suspended in a cylindrical test section and exposed to a very slow flow of pure steam or mixtures of steam and air from underneath. For the slightly inclined cases, the test results showed good agreement with the existing studies and reproduced the typical inclined plate phenomena. For the horizontal cases, the downward facing plate showed twice as high heat transfer rates as the upward facing one. The air contained in the steam showed negligible effects for the upward facing plate but a systematic decrease in heat transfer for the downward facing one. The condensation heat transfer beneath the downward facing horizontal plate is influenced by the surface wetting characteristics.

Effects of changes in reservoir thermodynamic conditions on 222Rn composition of discharged fluids: study for two wells at Los Azufres geothermal field (Mexico)

Abstract 222Rn anomalies that occurred at the time of the 19 September 1985 M8.1 Michoacan, Mexico, earthquake in fluids from two wells of Los Azufres, geothermal field were studied considering (i) the changes in well‐bottom thermodynamic conditions (pressure, enthalpy and steam/water ratio) and (ii) the discharged mass flow rates. In the studied steam well the anomalously high 222Rn concentration (as compared with background data) was observed on 11 September and was due to an important compressive process, which formed two‐phase fluids at reservoir, where usually single steam occurred. This caused the increase in 222Rn, as it remained in the steam. The compressive process was partially induced by changes in the production conditions at wellhead (because a well test was being developed) when sampling, but it was also seismic‐induced, as similar 222Rn anomalies were observed in other steam wells for which stable conditions at sampling were maintained. Another case is given for a two‐phase well where anomalously low 222Rn values (compared to background data) were recorded in September–October 1985. As stable conditions were maintained during sampling (1983–1986), 222Rn data were correlated to ?twb> the total mass flow rates produced by the well. Results suggested that the well produced two types of liquid–steam mixtures with a common end‐member regarding the liquid, but implying two ‘end‐member’ fluids with different 222Rn contents. The most 222Rn enriched end‐member was regarded as the original reservoir steam while that with relatively lower 222Rn concentration was stated as likely constituted by a mixture of reservoir and reinjection fluids. From the linear correlations, 222Rn contents for both end‐members were estimated while the 222Rn composition of the reservoir liquid feeding the studied well was estimated to be negligible compared to steam from the intersection of both curves. As one anomalously low 222Rn value was measured for a sample collected on the 12 September 1985, it seemed that a seismic‐induced process increased the reservoir permeability just before the earthquake allowing the liquid to reach the production zones of some two‐phase wells. This interpretation was supported by the behaviour of gas species (CO2 and N2) and δD in the two‐phase well studied and injection mass flow rates in one probably‐related reinjection well.

Modelling of methanol-to-hydrogen steam reforming with a heat flux distributed along a microchannel

The flow of reacting mixture of methanol and steam in a 2D microslot was studied numerically at activation of the reactions on the channel wall. This modelling was carried out in the framework of Navier — Stokes equations for a laminar flow of multicomponent compressible gas. Correlations between thermal, diffusion, and physical-chemical processes were studied under the conditions of intense endothermic reaction and external heat supply distributed along the channel. It is shown that not only the amount of heat supplied to the reaction zone is essential, but also the mode of heat supply along the channel length is important, which allows optimization of the compact reactor for hydrogen production.

A remining technology of underground coal gasification at Zhongliangshan Coal Mine

The field trail used a mixture of steam and air with various levels of oxygen enrichment. Steady conditions were achieved in the field trail which produced high quality hydrogen-enriched syngas. To understand and optimize the UCG process, a simplified heat and mass transfer model was presented, providing a predictive tool for temperature and the major constituents of the syngas production. The model is compared with the field trail measurements for air and two levels of oxygen enrichment, showing reasonable agreement for the channel temperature and product syngas concentration profile.

Deterministic safety analysis of the reference accidental sequence for the European HCPB TBM system

In order to investigate the accidental behavior of the helium cooled test blanket module and its auxiliary systems, a particular sequence has been selected for the deterministic analyses in the frame of the EFDA licensing task for ITER. This sequence starts from an ex-vessel loss of coolant with simultaneous assumed failure of the plasma shutdown system. This paper presents the study of this sequence with the use of various assumptions and code-dependent modeling (RELAP5, MELCOR and ANSYS). Two different variants of the sequence are analyzed depending on the assumption of the failure of water-cooled component of ITER. The resulting transients show the effect of the exposure of the Be pebble beds on air and on a mixture of air and steam.