Steam-gas Mixture Research Articles

Carbonate Molten-salt Absorber/Reformer: Heating and Steam Reforming Performance of Reactor Tubes

Steam reforming of methane is a candidate process for converting concentrated high-temperature solar heat to chemical fuels because it is a high-temperature, highly endothermic process. We developed a tubular reformer system using novel double-walled reactor tubes with molten-salt thermal storage for solar reforming to produce hydrogen or synthetic gas (CO + H2) from a gas mixture of methane and steam using concentrated solar radiation as an energy source. The high heat capacity and large latent heat (heat of solidification) of the molten salt circumvents rapid temperature changes in the reactor tubes at high temperatures under fluctuating insolation. In this paper, we focused on under intermittent heating–cooling mode, the steam reforming performance of double-walled reactor tubes with Na2CO3/MgO composite thermal storage in comparison to pure Na2CO3 thermal storage. A heating mode using an electric furnace simulates reactor startup in the morning and reheating of the reactor by concentrated solar radiation after brief periods of cloud passage. The intermittent heating–cooling mode simulates fluctuating incident solar radiation during cyclic short-term cloud passage. The temperature variations of the catalyst and storage material, methane conversion, and higher heating value power of the reformed gas were examined for the double-walled reactor tubes and a single- wall reactor tube without thermal storage.

Modeling steam condensation from steam-air mixture in the inclined tubes of an air-cooled condenser

Specific features pertinent to the flow of steam-gas mixture are discussed as applied to the inclined tubes of air-cooled condensers used in steam turbine units, and the condensate film annular flow and “streamlet” models are analyzed. The calculated results are compared with the data obtained by other researchers. It is shown that with relatively small flow rates of steam-gas mixture typical for air-cooled condensers, the restoration of pressure along the channel may exceed the losses connected with hydraulic resistance. Data on the influence of cooling air temperature on the condensation process are also presented.

Thermodynamic substantiation of power generation using a steam-gas mixture with a variable composition of components

In incomplete conditions of initial information for the calculation of thermodynamic parameters of the steam-gas cycle, the ideal gas approximation is accepted. In order to increase the efficiency of using the energy of the steam-gas flow, the possibility of using a binary thermal power cycle is considered.

The generalized correlation for the evaluation of the influence of the Stefan flow on the heat transfer coefficient

The analytical equations for the steady-state heat-and-mass transfer in the steam evaporation/condensation processes from the steam-gas mixtures on the planar and spherical surfaces are derived. The vapor flow through the motionless dry gas is considered according to the method proposed by Maxwell for the solution of the diffusion problems.The relationships for the calculation of the coefficients taking into account an increase in the mass output and an increase or a decrease in the heat emission (depending on the directions of the heat-and-mass flows) as a result of the influence of the Stefan flow are presented.The derived relationships can be used to calculate the apparatuses in which the steam evaporation or condensation from the steam-gas mixture occurs (the coolers of the vapor from deaerators, the apparatuses for the deep utilization of the heat of the combustion products, the condensation boilers, etc.).

OVERVIEW OF CONTAINMENT FILTERED VENT UNDER SEVERE ACCIDENT CONDITIONS AT WOLSONG NPP UNIT 1

Containment Filtered Vent Systems (CFVSs) have been mainly equipped in nuclear power plants in Europe and Canada for the controlled depressurization of the containment atmosphere under severe accident conditions. This is to keep the containment integrity against overpressure during the course of a severe accident, in which the radioactive gas-steam mixture from the containment is discharged into a system designed to remove the radionuclides. In Korea, a CFVS was first introduced in the Wolsong unit-1 nuclear power plant as a mitigation measure to deal with the threat of over pressurization, following post-Fukushima action items. In this paper, the overall features of a CFVS installation such as risk assessments, an evaluation of the performance requirements, and a determination of the optimal operating strategies are analyzed for the Wolsong unit 1 nuclear power plant using a severe accident analysis computer code, ISAAC.

Measurement of non-condensable gas in a PWR small-break LOCA simulation test with LSTF for OECD/NEA ROSA Project and RELAP5 post-test analysis

An OECD/NEA ROSA Project experiment with the large scale test facility was conducted simulating a PWR 0.5% cold leg small-break loss-of-coolant accident with steam generator (SG) secondary-side depressurization as an accident management measure to clarify such complex phenomena as non-uniform flow among the SG U-tubes under natural circulation (NC) with non-condensable gas. Non-condensable gas inflow to the primary system from accumulator tanks was simulated with air. The gas concentration was measured at the SG outlet plenum by using a gas measurement device to measure oxygen concentration in steam–gas mixture that is developed employing a Zirconia sensor. Non-uniform flow behaviors were observed in the SG U-tubes with non-condensable gas ingress depending probably on gas accumulation rate as well as asymmetric NC between two loops. Air concentration in steam–gas mixture was estimated to be about 40-50% at the SG outlet plena after the U-tube downflow side became empty of liquid, which was a bit larger than the estimated value based on the gas phase temperature. Post-test analysis by JAEA-modified RELAP5/MOD3.2.1.2 code revealed that the code underpredicts the primary pressure a bit after the gas inflow with some discrepancies in the SG U-tube liquid level and the NC mass flow rate.

Microstructural evolution in two alkali multicomponent silicate glasses as a result of long-term exposure to solid oxide fuel cell environments

The microstructural evolution in two potential solid oxide fuel cell (SOFC) sealing glass materials exposed to air and a gas mixture of steam + H2 + N2 at 800 °C up to 10000 h was determined. The glass exposures were performed on common SOFC substrates like alumina and zirconia. Characterization of the crystalline phases and pore size distribution was performed for the specimens with various exposure conditions. Comparison of the microstructural and chemical stability of the two glasses was performed based on known trends related to glass chemistry. It was observed that multicomponent glasses followed few rules for chemical and microstructural stability reported in the literature for glasses with fewer components. The two glasses examined in this study displayed adequate resistance to devitrification but marginal resistance to porosity changes in the SOFC environment exposure. The implications of the results for the design and long-term performance of SOFC seals are discussed.

Numerical modelling of convective vapour condensation with non‐condensable gases between two coaxial vertical cylinders

AbstractA problem of laminar film condensation from steam–gas mixtures between two coaxial cylinders is numerically analysed. A set of complete boundary layer equations is used to model simultaneous momentum, heat and mass transfer in the liquid film and the vapour–gas mixture. In order to locate accurately the liquid–mixture interface, a relevant change of coordinates is performed. Equations are solved using an implicit finite difference scheme. The liquid film thickness is determined from an iterative procedure based on the secant method. An analytical solution of the momentum equations of both phases at the end of condensation is also developed. Results presented include evolutions of field profiles and flow parameters from the inlet until the end of condensation. We also analyse the effects of the wall properties, the inlet conditions, the type of non‐condensable gas, the size of the annular space and the convective cooling coefficient.

Specific features pertinent to calculation of a condenser with inclined tubes

Matters concerned with calculation of heat and mass transfer during steam condensation from steam-gas mixtures in a condenser with inclined tubes used in production of sulfate-cellulose for recovering heat and chemical agents are discussed.

Coke Formation in Steam Reforming of Natural Gas over Rhodium/Alumina Catalysts: An Atomic Force Microscopy Study using the Oscillating Friction Mode

Abstract The initial stage of coke formation in steam reforming of natural gas over rhodium/alumina catalysts was studied microscopically. A well-defined model catalyst prepared by an aerosol technique was placed in a flow reactor to very mildly coke the catalyst sample. Therefore, a natural gas–steam mixture at steam-to-carbon ratios of unity was fed to the reactor operated for thirty minutes at atmospheric pressure and moderate temperatures of 650 ºC. Fresh and used catalyst samples were characterized by SEM-EDX and a recently developed AFM technique, the Oscillating Friction Microscopy (OFM), to analyze the friction characteristics of the sample. OFM combined with SEM-EDX allowed to distinguish between coke depositions, alumina support (Al2O3), and Rh particles and to locate the initial carbon deposition in the process. It was found that coke formation starts on the catalyst particle. The carbonaceous overlayer can be removed from the catalyst and the closely surrounding support by multiples scans with the AFM tip.

Simulating film condensation of steam from steam-gas mixtures with different compositions on the outer surface of vertical tubes used in a heat exchanger

A mathematical model of heat-and mass transfer processes in surface-type heat exchangers that use mixtures of steam with various noncondensable gases as heat carriers is presented. The results of numerical calculations are compared with experimental data reported in the literature. It is shown that the thermal-physical properties of the noncondensable component in a steam-gas mixture have an essential effect on the distribution of concentrations and temperatures over the heat exchanger length and on the heat flux transferred in it.

Formation of secondary inorganic aerosols by power plant emissions exhausted through cooling towers in Saxony

The fraction of ambient PM10 that is due to the formation of secondary inorganic particulate sulfate and nitrate from the emissions of two large, brown-coal-fired power stations in Saxony (East Germany) is examined. The power stations are equipped with natural-draft cooling towers. The flue gases are directly piped into the cooling towers, thereby receiving an additionally intensified uplift. The exhausted gas-steam mixture contains the gases CO, CO2, NO, NO2, and SO2, the directly emitted primary particles, and additionally, an excess of 'free' sulfate ions in water solution, which, after the desulfurization steps, remain non-neutralized by cations. The precursor gases NO2 and SO2 are capable of forming nitric and sulfuric acid by several pathways. The acids can be neutralized by ammonia and generate secondary particulate matter by heterogeneous condensation on preexisting particles. The simulations are performed by a nested and multi-scale application of the online-coupled model system LM-MUSCAT. The Local Model (LM; recently renamed as COSMO) of the German Weather Service performs the meteorological processes, while the Multi-scale Atmospheric Transport Model (MUSCAT) includes the transport, the gas phase chemistry, as well as the aerosol chemistry (thermodynamic ammonium-sulfate-nitrate-water system). The highest horizontal resolution in the inner region of Saxony is 0.7 km. One summer and one winter episode, each realizing 5 weeks of the year 2002, are simulated twice, with the cooling tower emissions switched on and off, respectively. This procedure serves to identify the direct and indirect influences of the single plumes on the formation and distribution of the secondary inorganic aerosols. Surface traces of the individual tower plumes can be located and distinguished, especially in the well-mixed boundary layer in daytime. At night, the plumes are decoupled from the surface. In no case does the resulting contribution of the cooling tower emissions to PM10 significantly exceed 15 microg m(-3) at the surface. These extreme values are obtained in narrow plumes on intensive summer conditions, whereas different situations with lower turbulence (night, winter) remain below this value. About 90% of the PM10 concentrations in the plumes are secondarily formed sulfate, mainly ammonium sulfate, and about 10% originate from the primarily emitted particles. Under the assumptions made, ammonium nitrate plays a rather marginal role. The analyzed results depend on the specific emission data of power plants with flue gas emissions piped through the cooling towers. The emitted fraction of 'free' sulfate ions remaining in excess after the desulfurization steps plays an important role at the formation of secondary aerosols and therefore has to be measured carefully.

Possibility of obtaining hydrogen from coal/waste–tyre mixture

Technically applicable gas with a high hydrogen content (ca 78%) was obtained through a two-stage pyrolysis of the mixture of Lazy bituminous coal with 15% waste tyre-rubber. The experiments were carried out in a laboratory pyrolysis unit with a 100 g charge. The incorporation of a thermal-degradation module in the stream of steam–gas mixture at the output of the pyrolysis reactor induced the decomposition of volatile products and significantly increased the yield of hydrogen. The influence of temperature of the cracking module (in the range between 900 and 1200 °C) on the amount of hydrogen in the pyrolysis gas was monitored. The solid by-product (carbonaceous residue) may be used as smokeless fuel or a sorbent precursor.

Development and adoption of measures for increasing the safety of power-generating units of nuclear power plants with RBMK reactors in 1986–2005

The basic stages and directions of upgrading and reconstruction of the power-generating units of nuclear power plants with RBMK reactors over a period of 20 yr since the Chernobyl accident are reflected in this paper. The greatest amount of work was done in 1986–1990 on all units with RBMK-1000 and-1500 reactors which were operating at that time in the USSR. The purpose of the upgrade was to improve the neutron-physical characteristics of the reactor cores, increase the response speed of the safety and control system and decrease the positive effect of water outflow from the cooling loop of this system, increase the flow capacity of the systems performing emergency discharge of the steam-gas mixture from the reactor, and improve the basic operating documentation.

Gasification of biomass chars in steam–nitrogen mixture

Abstract Some agricultural and waste biomass samples such as sunflower shell, pinecone, rapeseed, cotton refuse and olive refuse were first pyrolyzed in nitrogen, and then, their chars were gasified in a gas mixture of steam and nitrogen. Experiments were performed using the thermogravimetric analysis technique. Pyrolysis of the biomass samples was performed at a heating rate of 20 K/min from ambient to 1273 K in a dynamic nitrogen atmosphere of 40 cm 3 min −1 . The obtained chars were cooled to ambient temperature and then gasified up to 1273 K in a dynamic atmosphere of 40 cm 3 min −1 of a mixture of steam and nitrogen. Derivative thermogravimetric analysis profiles from gasification of the chars were derived, and the mass losses from the chars were interpreted in terms of temperature. It was concluded that gasification characteristics of biomass chars were fairly dependent on the biomass properties such as ash and fixed carbon contents and the constituents present in the ash. Different mechanisms in the three temperature intervals, namely water desorption at lower temperatures, decomposition of hydroxide minerals to oxide minerals and formation of carbon monoxide at medium temperatures and production of hydrogen at high temperatures govern the behavior of the char during the gasification process. The chars from pinecone and sunflower shell could be easily gasified under the mentioned conditions. In order to further raise the conversion yields, long hold times should be applied at high temperatures. However, the chars from rapeseed and olive refuse were not gasified satisfactorily. Low ash content and high fixed carbon content biomass materials are recommended for use in gasification processes when char from pyrolysis at elevated temperatures is used as a feedstock.

Numerical and experimental simulation of accident processes using KMS large-scale test facility under the program of training university students for nuclear power industry

The KMS large-scale test facility is being constructed at NITI site and designed to model accident processes in VVER reactor plants and provide experimental data for safety analysis of both existing and future NPPs. The KMS phase I is at the completion stage. This is a containment model of 2000 m3 volume intended for experimentally simulating heat and mass transfers of steam-gas mixtures and aerosols inside containment. The KMS phase II will incorporate a reactor model (1:27 scale) and be used for analysing a number of events including primary and secondary LOCA. The KMS program for background training of university students in the nuclear field will include preparation and conduction of experiments, analysis of experiment data. The KMS program for background training of university students in nuclear will include: participation in the development and application of experiment procedures, preparation and carrying out experiments; carrying out pretest and post-test calculations with different computer codes; on-the-job training as operators of experiment scenarios; training of specialists in measurement and information acquisition technologies.

Sorption of cesium iodide radioactive aerosols on metal felt during oxidative hydrolysis in steam gas-system

The behavior of 137Cs 131I radioactive aerosols at sorption in a column packed with Bekipor WB metal felt from argon, air, and steam-gas flow was studied to assess the possibility of formation of CsI ⋅ CsOH and CsI3 in the course of CsI oxidative hydrolysis. The layer distribution of radionuclides in the column was analyzed as influenced by temperature (405–560 K), carrier gas humidity (up to 60 vol %), flow velocity (2–6 cm s1), and amount of cesium iodide sorbed on the felt (0.7–65.0 mg). It was found that the oxidative hydrolysis under certain conditions yields CsI ⋅ CsOH and CsI3 aerosols. Although under the experimental conditions studied the sorption of radionuclides on the metal felt is nearly quantitative (97–99%), escape of the radionuclides from the column upon prolonged passing of steam-gas mixtures cannot be excluded.

Plasma-chemical preparation of nanostructured catalysts for low-temperature steam conversion of carbon monoxide: catalytic activity

The “warm walls” (WW) plasma-chemical reactors (PCR) synthesized catalyst samples (types LTC-1–3) give up by activity compared to their industrial analogues; and these synthesized in PCR with “cold walls” (CW) (types LTC-7–9) have a commensurable activity compared to those of the industrial catalysts used by the Bulgarian company CHIMCO-Vratza. Their activities were defined by using a model gas simulating the industrial one for temperatures and a volume rate of the steam–gas mixture similar to those used in the industrial process of low-temperature steam conversion of CO. The enhanced catalytic activity of the plasma-chemically synthesized samples is owing to: the faulty crystal lattice structure of the catalytically active phases; the nanodispersed sample composition (the crystal sizes of the catalytically active phases ranges from 10 to 40 nm); the presence of Cu 2O in the fresh samples, apart form the presence of CuO; the content of cuprous oxides—30–38 mass%; the even distribution of the ultradispersed components, the high porosity, specific surface and dispersity of the phases. Due to the bonding of a portion of the elemental Cu in the CuAl 2O 4 spinel crystal lattice, the plasma-chemically synthesized samples type LTC have a high thermal resistance which exceeds that of their conventional industrial analogues. The high specific surface of the plasma-chemically synthesized samples for low-temperature steam conversion of CO, their homogenous chemical composition, high formation rate of their active surface by reduction, high activity and thermal resistance, represent a precondition to extend the investigation on developing a plasma-chemical technology for their industrial synthesis in the catalyst workshops.

Optimization of Synthesis of 2,4-Dinitrophenylhydrazones under Carbon Dioxide Pressure

Catalytic synthesis of 2,4-dinitrophenylhydrazones formed in the aqueous reaction mixture of aliphatic and aromatic carbonyl derivatives with 2,4-dinitrophenylhydrazine in the presence of carbonic acid protons under pressure of the CO2-H2O a steam-gas mixture was studied for the example of synthesis of p-quinone-mono-2,4-dinitrophenylhydrazone.

Condensation Heat Transfer in Wide Range of Non-condensing Gas Fraction

For condensation from a steam-gas mixture flowing normal to horizontal rows of tubes, an approximate equation was obtained with an analogy relation between heat and mass transfer taking account of the mass absorption effect on the wall in the previous study. These correlations gave good predictions when the non-condensing gas fraction was more than 75%. At the fraction less than 75%, some modification is necessary on the mass transfer correlation because it was obtained from the heat transfer correlation without the condensation. Condensation heat transfer on horizontal stainless steel tubes was investigated experimentally for the modification of mass transfer correlation. The experiment was conducted in a wide range of non-condensing gas fraction and the modification was proposed.