Gas Mixture Stream Research Articles

Investigation of gas-bubbles separation from a liquid–gas mixture stream around a vertical 180° bend applied to gravity-driven separation using computing vision and computational fluid dynamics (CFD)

Separators are essential to many gas–liquid systems, especially to purge bubbles before the fluids enter specific equipment such as pumps or heat exchangers. Gravity, drag, buoyancy, and other forces exerted by the liquid over the bubbles are responsible for the separation process. A detailed analysis of the behavior of bubbles inside a separator is necessary to understand and improve the separation performance. This study combines high-speed video recording, object detection algorithm, and Computational Fluid Dynamic (CFD) simulation to understand the separation mechanism in a 180° bend separator. Bubble location and velocity have been acquired. Separated and unseparated bubbles have been identified to calculate the overall separation efficiency. The results have been utilized to validate a CFD model, which has been used to describe the flow further. Separation efficiency concerning bubble size and positions is also presented.

Innovative Method for the Mass Preparation of α″-Fe16N2 Powders via Gas Atomization

The iron nitride materials, especially α″-Fe16N2, are considered one of the most promising candidates for future rare-earth-free magnets. However, the mass production of α″-Fe16N2 powders as a raw material for permanent magnets is still challenging. In this work, starting from iron lumps as a raw material, we have managed to prepare the α″-Fe16N2 powders via the gas atomization method, followed by subsequent nitriding in an ammonia–hydrogen gas mixture stream. The particle size was controlled by changing the gas atomization preparation conditions. X-ray diffractograms (XRD) analyses show that the prepared powders are composed of α″-Fe16N2 and α-Fe phases. The α″-Fe16N2 volume ratio increases with decreasing powder size and increasing nitriding time, reaching a maximum of 57% α″-Fe16N2 phase in powders with size below 32 ± 3 μm after 96 h nitridation. The saturation magnetization reaches the value of 237 emu/g and a reasonable coercivity value of 884 Oe. Compared to the saturation magnetization values of α-Fe powders, the α″-Fe16N2 powders prepared through our proposed approach show an increase of up to 10% in saturation and demonstrate the possibility of mass production of α″-Fe16N2 powders as precursors of permanent magnets without rare earths.

How to select the flow rate of propane-butane for the effective burning of natural gas with low methane content using a flare

The paper discusses the problems related to the burning of gas mixtures containing flammable and non-flammable gases using a flare. Before being burned, such a gas mixture must be “enriched” with other flammable gases before it can be directed to the flare. In the case of some Polish gas reservoirs such as Cychry or Sulęcin, the composition of the gas mixture doesn’t make it possible to burn it using the flare because the content of inflammable components is too high and the gas mixture is inflammable. The gas from the reservoirs mentioned above contains above 90 percent of nitrogen and small percentages of flammable components. Sometimes, besides nitrogen, the gas mixture contains other inflammable gases like carbon dioxide, helium, and oxygen. Usually, the propane/butane is used for that purpose. The possibility of burning the gas mixture using the flare is particularly important if the toxic gases are present in the mixture – hydrogen sulfide in particular. The propane/butane gases are added to the stream of gas mixture meant for burning using a special appliance. The typical arrangement of a gas-burning installation (i.e. the flare) is shown and the destination of its components is discussed. The empirical formula is provided which allows us to recognize if the gas mixture is flammable or not. The composition of the gas mixture must be known to calculate the propane/butane flow rate, including percentages of flammable and inflammable components. The algorithm constructed for calculating the propane/butane flow rate is presented, which must be maintained to assure the flammability of the gas mixture destined for burning using the flare. The results of the calculations for four gas mixtures from the Polish gas reservoirs are provided. The presented method of determining the flammability of gas mixtures (or its inability to be burned) and the flow rate of the propane/butane mixture required for complete combustion is based on empirical relationships, which are provided in the paper and may be helpful in planning the assisted combustion of low methane gases (not suitable for further use) using a flare.

The effect of coagulation on the processes of growth and changes in the numerical concentration of carbon dioxide crystals

The process of phase transition to the solid state of carbon dioxide vapors contained in an expanding gas mixture stream consists of the formation of crystallization centers and subsequent growth of the crystals formed, due to an increase in the degree of supercooling of the stream. Crystals nucleate in certain sections of the flow part of the expanders and grow as they move in the flow. Therefore, crystals of carbon dioxide of various sizes can be found in each of certain sections. As a result of their interaction, coagulation, expressed as the adhesion of smaller crystals to larger ones, can occur. The influence of the coagulation process on the change in the number of smaller crystals and on the growth of larger ones is considered. Equations are given on the basis of which the calculations of the studied processes are made.

Analysis of methane production intensity during its displacement from a gas hydrate formation by carbon dioxide

The theoretical model is considered in the one-dimensional approximations and numerical solutions are obtained for the process of replacing methane with carbon dioxide from a hydrate in a formation saturated with methane and its hydrate when carbon dioxide is injected into the formation. The process is considered under thermobaric conditions corresponding to the stability region of methane gas and carbon dioxide and the region of existence of CO2 in the form of a gaseous phase. The case is considered when the rate of carbon dioxide hydrate formation is limited by diffusion of carbon dioxide through the formed hydrate layer between the gas mixture stream and methane hydrate. It is accepted that the hydration substitution process occurs without the release of water from the hydrate. To describe the mathematical model, the main equations are the mass conservation equations for methane, carbon dioxide and their hydrates, Darcy’s law for filtration, Fick’s law for diffusive mixing of the gas mixture, state equations for the gas phase, Dalton’s law, energy equation, diffusion equation for transport CO2 through the hydration layer at the pore microchannel scale. The dynamics of the mass flow rates of the outgoing carbon dioxide and methane recovered has been investigated. The influence of the diffusion coefficient, the absolute permeability and the length of the formation on the intensity of the methane produced as a result of the gas substitution process is analyzed. Three main stages of the process were identified: displacement of free methane from the reservoir; extraction of free methane obtained as a result of the beginning of hydrate substitution in the formation; complete conversion of methane hydrate to carbon dioxide hydrate and complete extraction of methane from the formation. It is determined how the two main factors relate to each other in terms of the degree of influence on the replacement rate: heat and mass transfer in the reservoir and the kinetics of the replacement process.

Kinetics of Reduction of CaO-FeO x -MgO-PbO-SiO2 Slags by CO-CO2 Gas Mixtures

Kinetics of the reaction of lead slags (PbO-CaO-SiO2-FeO x -MgO) with CO-CO2 gas mixtures was studied by monitoring the changes in the slag composition when a stream of CO-CO2 gas mixture was blown on the surface of thin layers of slags (3 to 10 mm) at temperatures in the range of 1453 K to 1593 K (1180 °C to 1320 °C). These measurements were carried out under conditions where mass transfer in the gas phase was not the rate-limiting step and the reduction rates were insensitive to factors affecting mass transfer in the slag phase. The results show simultaneous reduction of PbO and Fe2O3 in the slag. The measured specific rate of oxygen removal from the melts varied from about 1 × 10−6 to 4 × 10−5 mol O cm−2 s−1 and was strongly dependent on the slag chemistry and its oxidation state, partial pressure of CO in the reaction gas mixture, and temperature. The deduced apparent first-order rate constant increased with increasing iron oxide content, oxidation state of the slag, and temperature. The results indicate that under the employed experimental conditions, the rate of formation of CO2 at the gas-slag interface is likely to be the rate-limiting step.

The consideration of the turbulence influence on the gas explosion expansion in non-closed areas

In the gas explosions simulation practice in non-closed areas there is a common opinion of burning rate increase at turbulization of initial gas mixture stream. The article shows that in conditions of turbulization there is no increase of the burn rate, but of the flame front area. A wording change of pressure rise reason does not lead to a change of the calculation results, but gives the opportunity to look at the problem differently and interpret a physical process correctly. In order to prove it there are results of the vibrational combustion modeling in terms of gas explosion in the cylinder with an opening on the side. The results show that along with the pressure fluctuation there is burning area size fluctuation that occur synchronous and with the same amplitude. The modeling basis is the system of differential equations, that describe the adopted in gas dynamics fundamental conservation laws, the equation of state, written in the so-called Euler’s form. The system is supplemented with flame spread conditions. The system solution is based on the Russian method of the numerical approximation of this system-the large-particle method.

The Effect of Nitrogen Cross-Over on Water Balance Measurements in Proton Exchange Membrane Fuel Cell Using Constant Temperature Anemometry

R&D on Proton exchange membrane fuel cells (PEMFC’s) technology has been accelerated in the last few years to reduce the dependency on fossil fuel. PEMFC’s operate by internally combining oxygen from air with hydrogen to form water and generate electricity and waste heat. The most common hurdle for enhanced PEMFC durability and performance is still the water management: the proton exchange membrane in the center of these fuel cells has to be hydrated in order to keep its ability to conduct protons from anode to cathode side while on the other hand excessive liquid water can lead to cell flooding and increased degradation rates of the cell. Thus, a detailed understanding of all aspects of water management in PEMFC is important. This includes the fuel cell water balance, i.e. the question which fraction of the product water leaves the fuel cell via the anode channels versus the cathode channel. Our research group is currently developing a state of art technology to obtain an ad-hoc and real time electrical signal of the fuel cell water balance by employing a constant temperature hot wire anemometry [1]. The hot wire sensor is placed in the anode outlet of PEMFC, and the voltage signal received gives valuable insight into heat and mass transfer phenomena which can be interpreted directly to real time PEMFC water balance. So far, ex-situ experiments have been conducted to measure the voltage signal of the hot wire anemometer for a known gas stream that contains a binary mixture of hydrogen and water vapour as would ideally leave the fuel cell anode. However, in an operating fuel cell there are two main uncertainties in this method: (i) there is some internal hydrogen crossover that does not load to an external current, thus the exact amount of hydrogen leaving the fuel cell anode is not known, and (ii) that there is nitrogen crossing over from the cathode side to the anode side, and this nitrogen does slighty falsify the voltage signal that the hot wire yields. The effects of nitrogen-cross over on the hot wire voltage signal at the anode outlet and consequently on the measured water balance (rd ) is studied in this work. In our previous work it was shown that the only unknown in the determination of the hot wire voltage signal is the equation that determines the heat transfer around the hot wire, and we have shown that it is necessary to employ a power-law equation as suggested by Hilpert: Nu = C Pr0.33 Rem where Re is the Reynolds number and Pr is the Prandtl number are calculated at film temperature. The constants C and m usually depend on the Re, and they will be determined out of the experimental data for the gas mixture, by plotting the measured (Nu/ Pr0.333 ) versus the Re number of the gas mixture stream. The missing C and m from Hilpert equation can then be easily obtained from a power-fit of the general form Y = CXm . Also, it was shown somewhere else that in fact only the exponent to the Reynolds number, of the gas mixture stream is important when determining the fuel cell water balance out of the hot wire signal [1]. The nitrogen-cross over is experimentally demonstrated by introducing 1% of nitrogen to the dry hydrogen molar flow. The 99%H2 +1%N2 of the dry mixture is humidified with water vapor by controlling the relative humidity (RH) of the dry mixture with in the range of (0-100)%RH, simulating the PEMFC anode outlet. The hot wire voltage is measured with and without nitrogen and it was slightly lower with the presence of 1 % nitrogen in the flow. The effect of the voltage reduction on the measured water balance can be neglected. This because the effect of 1% nitrogen on power law constant’s m which is used in determining the water balance as explained somewhere else is extremely low. It might be concluded that, the hot wire technique for measuring the water balance is still accurate and can be used for ad-hoc and real time water balance measurements and the nitrogen cross-over affect can be neglected, knowing that the 1% N2 is one order of magnitude higher than the actual concertation of 0.02 m2 active area cell used for lab testing. [1] Berning, T., & Al Shakhshir, S., Applying hot wire anemometry to directly measure the water balance in a proton exchange membrane fuel cell–Part 1: Theory. International Journal of Hydrogen Energy, 40(36) (2015), 12400-12412.

Comparative evaluation of CO2 capture from flue gas by [Emim][Ac] ionic liquid, aqueous potassium carbonate (without activator) and MEA solutions in a packed column

The objective of the present work is to study and compare CO2 capacity absorption into 1-Ethyl-3-methylimidazolium acetate ionic liquid, [Emim][Ac], the aqueous 15w% MEA and 28w% K2CO3 (without activator) solutions, in a packed column. The CO2 absorption experiments were conducted in an absorbing column packed with randomly placed Rraschig rings. The gas mixture stream has a typical composition of post-combustion processes consisting of CO2 (7% v/v) diluted in N2 was used to test CO2 absorption in all experiment under 4bar at T=(343.15, 348.15, 353.15)K. In this work the effect of temperature, gas and liquid flow direction on CO2 absorption at constant pressure and inlet CO2 concentration were examined. The comparison of the used IL with both the aqueous MEA and K2CO3 solutions was done for the same absorption conditions. The results show that the aqueous MEA has the highest KOverall followed by the aqueous K2CO3 (without activator) and the [Emim][Ac] has shown the least KOverall. Experimental evidence suggests that for the same amount CO2 absorption from the gas mixture, the [Emim][Ac] needs much longer times than both the absorbents under investigation. The [Emim][Ac] shows enhancement by chemical absorption, being obtained the value of enhanced factor, EA, higher than 44. Consequently at higher temperatures the [Emim][Ac] behaves more efficiently. In case of the [Emim][Ac], the overall mass transfer increased significantly, from 2.812 to 4.187×10−6ms−1 as the temperature rises. Nevertheless in cases of using the aqueous MEA and K2CO3 solutions this remains constant for the temperature interval 343.15–353.15K. The behavior of the [Emim][Ac] was correlated with the mass transfer enhanced by the chemical reaction. The results show that liquid side mass transfer coefficient using packed bed contactor with the studied ionic liquid is lower than with both the absorbents. This can be attributed to significant impact of the viscosity of the ionic liquid as an important factor in the mass transfer and therefore in the separation in comparing with both the absorbent. At 343.15K and 4bar, on mass basis (kg CO2/kg absorbent), the studied IL showed 7% more CO2 absorption capacity than the aqueous MEA and 26% more than the aqueous K2CO3 (without activator) solutions.

Heating rate effect on the thermal behavior of some clays and their blends with oil shale ash additives

The heating rate effect on the thermal behavior of clays from Arumetsa and Kunda deposits (Estonia) and an illitic clay from Fuzerradvany (Hungary) was studied. Experiments were carried out under dynamic heating condition up to 1050 °C at the heating rates of 1.25, 2.5, 5 and 10 °C min−1 in a stream of gas mixture containing 79 % of Ar and 21 % of O2 with Setaram Labsys 1600 analyzer. Two different ashes were used as additives: the electrostatic precipitator ash from the first field and the cyclone ash formed, respectively, at circulating fluidized bed combustion (temperatures 750–830 °C) and pulverized firing (temperatures 1200–1400 °C) of Estonian oil shale at Estonian Power Plant. For calculation of kinetic parameters, the TG data were processed by the differential isoconversional Friedman method. The results of thermal analysis and the variation of the value of activation energy E along the reaction progress α indicated the complex character of decomposition of clays and their blends with Estonian oil shale ashes, and the certain differences in thermal behavior of different clays depending on their origin.

Study on the improvement of the capacity of amine-impregnated commercial activated carbon beds for CO2 adsorbing

Amine-based chemicals were impregnated onto activated carbon particles to improve its natural adsorption ability and selectivity to adsorb CO2 from gas mixture stream. Characterization results achieved by measuring the surface area with ASAP 2020 showed that the amine-based chemicals blocked the mostly micropore pores of the activated carbon particles. The amine-based chemicals used in this study were, monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP). The impregnation process and the subsequent blockage reduced the surface area of the activated carbon particles significantly but on the other hand enhanced the adsorption capacity and selectivity of the activated carbon for CO2 adsorption. Elemental analysis results using energy-dispersive X-ray spectroscopy showed that the impregnation process managed to attach the reactive N2 molecules onto the surface and inside the pores of the activated carbon particles. Images from field emission scanning electron microscope showed that due to impregnation process most of the pores of the activated carbon particles had been blocked by the MEA and AMP molecules. Sweeping exhausted non-impregnated activated carbon beds with 60ml/min pure nitrogen for 4h was enough for these beds to regain their original adsorption capacity but in contrast it was not enough to regenerate exhausted AMP, MEA-impregnated activated carbon beds to regain their original adsorption capability.

Theory and practice of flame torcreting a 160-ton oxygen converter lining

A new concept is presented for the design of the dust duct and lance, based on a two-speed approach. Results are provided for studying the effect of powder concentration on the distribution of some parameters throughout the whole line, i.e. from the powder feeder to the lance nozzle. Results are obtained with use of a model of a two-speed gas mixture stream.

Nanocrystalline soft magnetic ribbon with α″-Fe 16N 2 nanocrystallites embedded in amorphous matrix

A nanostructure with α″-Fe 16N 2 nanocrystallites embedded in an amorphous matrix was prepared by annealing Fe 92B 8 amorphous alloy in a NH 3+H 2 gas mixture stream with subsequent quenching and annealing. The average grain size and the volume fraction of the α″-Fe 16N 2 phase are found to be 18 nm and 54%, respectively. The prepared sample exhibits a saturation magnetization of 2.35 T, a coercive force of 11.4 A/m, an initial permeability of 9.1×10 4 and a relaxation frequency of 4.1×10 4 Hz.

HELIO code prediction of hydrogen accumulation in non-vented steam pipelines

The thermal-hydraulic and physico-chemical code HELIO is developed for numerical simulations and analyses of radiolytic gases (hydrogen and oxygen) accumulation in non-vented steam pipelines of nuclear power plant systems. The HELIO code simulates all relevant process, such as the steam–radiolytic gases mixture convection, the condensate drainage, the buoyancy forces induced by concentration and related gas mixture density differences, the gas mixture and condensate film interfacial shear, the steam condensation in the presence of non-condensables, the non-condensables diffusion, and the radiolytic gases absorption and degassing on the liquid film surface. This paper presents HELIO code models, numerical solving procedure and three cases of results of three-dimensional radiolytic gases accumulation: (a) in a non-vented steam pipeline of the Residual Heat Removal System in the Hamaoka Nuclear Power Plant, (b) in a non-vented horizontal pipe connected with an elbow and a vertical pipe, and (c) in a slightly inclined, nearly horizontal pipe. The radiolytic gases accumulation in the mixture with steam is a very slow and long duration transient that is induced by the steam condensation due to heat losses to the atmosphere. The condensate is drained, while the concentration of remaining non-condensable radiolytic gases increases; the process that could lead to the formation of a critical hydrogen and oxygen concentration and subsequent explosion, as in case of the Hamaoka plant incident. In case of the Hamaoka steam pipeline geometry, presented results show an accumulation of the radiolytic gases from the closed top end of the pipeline, a formation of the concentration front and its propagation towards the open end. In the second analyzed case, the gas mixture circulates in the elbow and horizontal pipe due to buoyancy forces induced by concentration and related density differences. The circulation flow prevents the formation of radiolytic gases concentration front and an accumulated radiolytic gases concentration is low. The third case shows that under lower heat loss rates or higher pipe diameters the hydrogen–oxygen accumulation does not occur due to the buoyancy driven circulation of gas mixture; the circulation expels the gas mixture stream with a higher radiolytic gases concentration out of the pipe. Obtained results clarify mechanisms of the radiolytic gases accumulation and they are a support to the prescription of safety measures that should be applied in order to prevent an accumulation and eventual explosion.

Catalytic Linear Grooving of Graphite Surface Layers by Pt, Ru, and PtRu Nanoparticles

Abstract Platinum, Ru, and Pt0.5Ru0.5 nanoparticles prepared from respective metal complexes have been found to form grooves, i.e., nanochannels, on cleavage planes of HOPG at 900 °C under a gas mixture stream of hydrogen and nitrogen. The mutual orientation of these grooves observed by HRSEM and AFM was 30 or 60 degrees.

A reformer performance model for fuel cell applications

A performance model for a reformer, consisting of the catalytic partial oxidation (CPO), high- and low-temperature water-gas shift (HTWGS and LTWGS), and preferential oxidation (PROX) reactors, has been formulated. The model predicts the composition and temperature of the hydrogen-rich reformed fuel-gas mixture needed for the fuel cell applications. The mathematical model equations, based on the principles of classical thermodynamics and chemical kinetics, were implemented into a computer program. The resulting software was employed to calculate the chemical species molar flow rates and the gas mixture stream temperature for the steady-state operation of the reformer. Typical computed results, such as the gas mixture temperature at the CPO reactor exit and the profiles of the fractional conversion of carbon monoxide, temperature, and mole fractions of the chemical species as a function of the catalyst weight in the HTWGS, LTWGS, and PROX reactors, are here presented at the carbon-to-oxygen atom ratio (C/O) of 1 for the feed mixture of n-decane (fuel) and dry air (oxidant).

Diffusion Coefficient Determination of Sodium Iodide Vapor in Rare Gases with Use of Ionization Sensor

The diffusion coefficients of sodium iodide vapor in the rare gases, argon, krypton and xenon, are determined by a method combining the analysis of measured diffusing mass with continuous monitoring of the sodium iodide vapor concentration in a flowing stream of sodium iodide-rare gas mixture. The flowing sodium iodide vapor is ionized upon its passage over a heated filament, and the generated ions are collected by a negatively-charged arched plate saddling the filament. The resulting ion current, measured by digital current meter, is integrated in time to obtain cumulative values from outset of run. The curve of the integrated values plotted against time approaches linearity with progress of run. The asymptote of the curve intersects the time axis at a point whose position serves to determine the diffusion coefficient, by applying an equation derived from the formula given by Carslaw and Jaeger. The coefficients thus determined for the three rare gases in runs at temperatures between 660°C and 710°C have proved to agree well with the values estimated using the semi-empirical correlation presented by Wilke and Lee.

Diffusion Coefficient Determination of Sodium Iodide Vapor in Rare Gases with Use of Ionization Sensor.

The diffusion coefficients of sodium iodide vapor in the rare gases, argon, krypton and xenon, are determined by a method combining the analysis of measured diffusing mass with continuous monitoring of the sodium iodide vapor concentration in a flowing stream of sodium iodide-rare gas mixture. The flowing sodium iodide vapor is ionized upon its passage over a heated filament, and the generated ions are collected by a negatively-charged arched plate saddling the filament. The resulting ion current, measured by digital current meter, is integrated in time to obtain cumulative values from outset of run. The curve of the integrated values plotted against time approaches linearity with progress of run. The asymptote of the curve intersects the time axis at a point whose position serves to determine the diffusion coefficient, by applying an equation derived from the formula given by Carslaw and Jaeger. The coefficients thus determined for the three rare gases in runs at temperatures between 660°C and 710°C have proved to agree well with the values estimated using the semi-empirical correlation presented by Wilke and Lee.

Gas blending and control process

This paper describes a useful and relatively inexpensive method of controlling the concentration of gaseous components in a blended gas mixture when a secondary gaseous component is available at a higher pressure than a primary gas (or gas mixture) stream. For illustrative purposes, a specific case involving a reactive gas blending process is described within this report in order to exemplify the process but there are many other potential applications for the process and/or the apparatus described within this paper.

Ozone-enhanced molecular beam deposition of nickel oxide (NiO) for sensor applications

For the deposition of nickel oxide (NiO) a molecular beam deposition process in an ozone atmosphere was developed. Pure gaseous ozone is received from a cooling system, which stores only O 3 at −78°C from a O 2/O 3 gas mixture stream, created with an ozone generator. The ozone is released by heating up the system to room temperature. For the deposition process nickel is evaporated while a constant ozone partial pressure is adjusted in the growth chamber. The reactive species of ozone reacts on the substrate surface with the impinging metal atoms to form the compound. This process was carried out in an ultra high vacuum (UHV) chamber to create pure nickel oxide films at room temperature and to study the fundamental layer properties for sensor applications. These films were characterized with respect to their stoichiometric and optical properties by Auger Electron spectroscopy and ellipsometry. The gas sensitivity of the films (as deposited and annealed) on various gases (H 2, NH 3, NO 2, SO 2, CO) was investigated by work function measurements.