Gas-air Mixture Research Articles

Экспериментальное исследование и моделирование процесса формирования взрывоопасных концентраций

Excess pressure is the main indicator characterizing the magnitude of explosive loads during emergency gas explosions. The value of this parameter and the entire accident scenario as a whole directly depend on the concentration of gas entering the room. Any typical room is characterized by the presence of two processes: laminar and turbulent diffusion. The laminar diffusion coefficient depends on the main characteristics of the gas (pressure, temperature). The laminar diffusion coefficient depends on the main characteristics of the gas (pressure, temperature). The coefficient of turbulent diffusion is determined only by the turbulent structure of the considered medium. It is established that the incomplete vortex mixing of gas with air is sufficient for flame propagation. This indicates the importance of studying the process of turbulent diffusion from the point of view of the formation of explosive gas-air mixtures. The purpose of the study is the experimental and computational determination of the coefficient of methane turbulent diffusion. This characteristic is required to assess the state of the gas-air environment in the room. It can be used in the development of explosion prevention measures, for example, in the design of a ventilation system. The study of the process of formation of explosive concentrations was carried out on the basis of an experiment and subsequent comparison of its results with a calculation model. In the course of the studies, it was established that the coefficient of turbulent diffusion, due to which explosive mixtures are formed, exceeds the coefficient of molecular diffusion by two orders of magnitude or more and is at least 4∙10–3 m2/s. The applied mathematical model and calculation scheme adequately describe the course of the experiments. Determination of the turbulent diffusion coefficient will allow assessing the state of the gas-air environment in the room and determining the required measures to prevent a possible emergency explosion.

Assessment of potential risk during gas outflow at above-ground sections of the gas pipeline taking into account abnormal weather conditions of the North

The article presents a model for assessing the potential risk of gas leakage from aboveground sections of the gas pipeline at low temperatures.The influence of abnormal weather conditions on the magnitude of the excess pressure of the shock wave is substantiated. The safe distances during the explosion of a methane gas-air mixture cloud under conditions of temperature inversion are estimated. Based on the data obtained, a model for assessing potential risk has been developed.

Modeling of Coalmine Methane Flows to Estimate the Spacing of Primary Roof Breaks

The global challenge for the mining sector is the problem of “decarbonization” of coal mining. The modeling of emission flows of coalmine methane is stipulated by the need to prove the environmental effect of the implemented technological changes. For longwall geotechnology, the dynamics of methane concentration in the gas–air mixture extracted by the degassing system reflects the complex relationship between emission and geomechanical processes in the rock mass. In this regard, the aim of the work was to improve the methods for assessing the steps of caving the main roof when mining gas-coal seams. The method of work consisted of processing experimental data (smoothing—Loess, three-dimensional interpolation, regression—the method of least squares) to obtain reliable response functions in three-dimensional space. When developing algorithms in the Python language, the Vi Improved text editor was used. Graphical representation of the results was carried out in “Gnuplot”. As a result of modeling, it was found that the increase in the span of the main roof from 83 to 220 m (S = 1340–1120 m) in the distance range of 120 m in front of the stoping face line and up to 50 m behind it (L = −120–50 m) leads to an alternating cyclicity of local extrema of the dynamics of methane release, according to a polynomial dependence. This fact is a consequence of the implementation of deformation-wave processes in geo-environments, which produce cyclic nonlinearities in the nature of the aero-gas regime of mine methane emissions into anthropogenically disturbed rock masses. In addition, the influence of the situational geomechanical conditions of the excavation area in the goaf was clarified. This makes it possible to reliably identify the caving steps of the main roof.

STUDY OF SELECTED BURNER PARAMETERS ON THE GAS-AIR MIXTURE COMBUSTION

The study of the combustion of a gas-air mixture using burners opens possibilities for further research, in which it is possible to modify the parameters of existing burners (geometry, method combustion air distribution, ...). Flame length can be influenced by changing some of the burner parameters to achieve the best possible conditions in the combustion chamber. The topic of the article is to study the effect of changing burner parameters on the length and nature of the flame in the combustion chamber. For this, an existing burner simulation model was modified. The properties of the proposed changes were investigated using the ANSYS simulation software. Simulation confirmed the suitability of the proposed system for reducing the flame length and intensifying the mixing of gaseous media. Also, the results show that the effect of changing the angle of combustion air supply along the longitudinal axis of the burner significantly affects the mixing of the fuel and, consequently, the nature of the flame with the combustion products.

Calculate a batch adsorber with a fixed bed of sorbent

There is considered a method to define parameters for the adsorber with the fixed bed of sorbent. The paper reviews constructional features to clean gas-air mixtures and liquids from toxic contaminants.

Calibrating and Graduating of Multi-Sensor Gas Analyzer

Introduction. The article is devoted to the calibration and graduation of the multi-sensor gas analyzer developed at the V.M. Glushkov Institute of Cybernetics of National Academy of Sciences of Ukraine. The modern trend in the development of medical equipment, in particular, containing built-in measuring devices, consists in its miniaturization, intellectualization, the use of information technologies, and the introduction of wireless and network means of data transmission. The purpose of the article is to design, create electronics and software for recording the concentration of three gases (oxygen, carbon dioxide and carbon monoxide), test and calibrate the device. Results. Three prototypes of sensor modules for oxygen, carbon dioxide and carbon monoxide have been created. The structure, scheme of connection of sensor modules, and the principle of operation of the gas analyzer was described. Testing and optimization of these prototypes were performed. Auxiliary pneumatic equipment for checking the performance of devices, their calibration and graduation was manufactured. Measurement technique was developed and test measurements of the specified gases were performed. The calibration technique was developed and the device was calibrated using two test gas samples such as ethanol vapor and air-gas mixture of carbon dioxide. In addition, a special software has been developed, which allow observe a registered input signal from sensor modules and store it to the file. Conclusions. As a result of the work, prototype of the device was created, its testing, calibration and graduation were carried out at the State Enterprise "Ukrmetrteststandart", 4 certificates of metrological attestation were obtained. The gas analyzer can be used for screening of healthy persons based on study of exhalation to predict the risk of diseases. Keywords: multi-sensor gas analyzer, oxygen, carbon dioxide, carbon monoxide, calibration, graduation.

RESPIRATORY ORGANS PROTECTION FROM THE AMMONIA ACTION

The article deals with the issues of protection of the respiratory organs from the toxic effects of ammonia, based on the research of employees of the Physical-chemical institute for environment and human protection of MES OF Ukraine and NAS of Ukraine. The physicochemical properties of ammonia and its toxicological characteristics are discussed in detail. Emergency hygienic regulations and reference levels of its concentration in the air are given, depending on the severity of possible effects. Activated carbon, the most widely used for equipping gas-absorbing cartridges of respirators and industrial gas masks, does not have the ability to selectively absorb ammonia without treatment with chemically active compounds. To enhance selectivity, activated carbon is infiltrated with d-metal salts and organic polybasic acids. An alternative to granular charcoal sorbents are ion-exchange fibrous materials or impregnated fibrous chemisorbents (IFCS), which have a significantly lower weight and breathing resistance. Impregnation was carried out with solutions of citric acid, and glycerol, sodium chloride, and ethanol were used as modifiers to achieve a uniform distribution of citric acid on the surface of the fibers and increase adhesion to them. The study of the sorption characteristics of IFCS as part of the gas-absorbing cartridge of the «Klen-K1» respirator was carried out with dry and moistened samples under dynamic conditions close to the actual operation of respiratory protection equipment: NH3 concentration in the gas-air mixture 700 mg/m3 (35 TVL), relative humidity φ = 0 ÷ 72%, linear flow rate – 5,1 sm/s. It is shown that the humidity of the gas-air mixture plays a decisive role in the efficiency of ammonia sorption, it activates the protective properties of IFCS. It has been established that gas-absorbing cartridges equipped with the developed samples of IFCS impregnated with a 40.0% solution of citric acid with the addition of 3.3% glycerol and 1.0% sodium chloride provide the normalized requirements for class K1 gas filters (ammonia) with humidity of the inhaled air ≥ 30%. The presence of «free» water provides a more complete «activation» of the specified chemisorbent for this toxicant.

EFFECT OF CERTAIN CATALYTIC POISONS ON THE ACTIVITY OF CUPRUM-PALADIUM COMPLEXES APPLIED ON CARBON MATERIAL IN THE REACTION IN THE REACTION OF CARBON MONOXIDE OXIDATION BY AIR OXYGEN

Oxide and metal complex catalysts for low temperature gas-phase oxidation of carbon monoxide by air oxygen lose their activity under the action of chemical poisons such as SO2, H2S, PH3, H2O. We have developed a highly efficient Wacker-type catalyst in which the carrier is a carbon fiber material (CFM), the precursor of which was cellulose hydrate. For such a catalyst, there are no studies on the effect of catalytic poisons, namely SO2 and H2O, on its activity in the reaction of low-temperature oxidation of CO with oxygen. The morphology, elemental composition and adsorption properties of carbon fiber material and carbon monoxide oxidation catalyst are investigated. Pd(II)-Cu(II)/CFM relative to water vapor and sulfur dioxide, as well as their effect on the protective properties of the catalyst. SEM studies (scanning electron microscope) confirmed the morphology typical of CFM and found very small agglomerates in the case of the catalyst, which are formed by paratacamite Cu2(OH)3Cl crystallites caused by oxidation of the carbon surface by palladium (II). When applying the catalyst components, the fibers do not lose their shape, but the surface of the fibers is unevenly covered with impurities. Palladium (II) is reduced by a carbon surface by about 10%, agglomerates [Pdo]n are not observed, while fiber erosion increases and very small agglomerates are formed on the surface, which are formed by Cu2(OH)3Cl phase crystallites. Carbon material is generally characterized by a high content of carbon and oxygen, but their distribution is heterogeneous. In the analysis of adsorption isotherms, which are classified as type IV, it was found that CFM and the catalyst based on it belong to the microporous samples. It is proved that only at the relative humidity of the gas-air mixture, which is equal to 30% C < MPCSO2 (20 mg/m3). Catalyst poisoning does not disrupt the catalytic process, but with increasing amount of absorbed sulfur dioxide (QSO2 ) the degree of conversion of carbon monoxide decreases and especially sharply at the absorption of 10.3⋅10–4 mol SO2. Thus, the results obtained on the effect of relative humidity and the amount of adsorbed by the catalyst SO2 on the activity of Pd(II)-Cu(II)/CFM catalyst, indicate a significant reduction in the degree of conversion of carbon monoxide. Therefore, in the case of applying of such a catalyst, for example in respiratory protection against CO, a preliminary stage of absorption of moisture and sulfur dioxide should be provided.

The ignition characteristics of dual-fuel spray at different ambient methane concentrations under engine-like conditions

In the present study, dual-fuel ignition process of pilot diesel spray injection into a natural gas-air mixture under engine-like conditions is numerically investigated via large-eddy simulation (LES). Methane and n-dodecane are considered as surrogates for natural gas and diesel fuels, respectively. This study aims to provide understandings of kinetic interactions for dual-fuel spray during the ignition process. The effects of ambient methane concentration on the ignition delay times (IDTs), product distributions, and heat release rates (HRRs) during dual-fuel ignition process are emphasized. The results show that methane prolongs the IDT of n-dodecane, especially for the first-stage IDT. Kinetic analyses reveal that the competition for OH between the dehydrogenation reactions of methane (CH4 + OH <=> CH3 + H2O) and n-dodecane (RH + OH <=> R + H2O) results in the increasing first-stage IDT of pilot spray. Moreover, it is found that the retarding effect positively correlates with the methane concentration. For product distributions, it is observed that the transition of CH2O from fuel-lean to fuel-rich regions is inhibited in the first-stage ignition. In the second-stage ignition, the concentration of CO is decreased as the methane concentration increases and the area with high CO concentration is gradually shifted to the downstream of the spray. In addition, HRRs of low-temperature exothermic reactions appear at the radial periphery as well as the head of the spray front; HRRs of high-temperature exothermic reactions are gradually shifted from the head to the center of the spray with the increase of ambient methane concentration. The HRRs of low- and high-temperature reactions are decreased with increasing ambient methane concentration, and the major reactions for heat release at various ambient methane concentrations are different.

Particle size influence on the aluminum combustion dynamics in 1-m&lt;sup&gt;3&lt;/sup&gt; chamber

Introduction. The results of a standard study of the explosibility of aluminum air suspensions (AAS) can contribute to the development of AAS combustion physics. In particular, a complex of information about the polydispersity and of the AAS low explosion limit values in a 1-m3 chamber made it possible to determine the maximum particle size of the explosive fraction of a polydisperse sample d*m,t ≈ 40–50 µm (Poletaev, 2014). In the present work, a relationship is established between the AAS combustion dynamics in a 1-m3 chamber and persion. The dispersity of sample particles is described by the mass-average particle size of its explosive fraction (d*50), in contrast to the works of other researchers who use the mass-average size of all particles (d50).Initial data. Known information about the dispersity and explosion parameters of 15 aluminum samples studied in a 1-m3 chamber was used. The continuous particle size distribution functions necessary for calculating d*50 were represented by the Rosin – Rammler distributions filling the gaps between the discrete data of the sieve analysis of the samples.Combustion dynamics. The dynamics of AAS turbulent combustion in a 1-m3 chamber is represented by the maximum air suspension burn-up rate Ub. Ub was calculated using the formula (Kumar, 1992) intended for gas-air mixtures by substituting the AAS explosion parameters into this formula.Results and its discussion. A plot of the d*50 Ub complex versus d*50 is shown. The average value of the complex (≈ 33 µm·m/s) is constant in the range 10 ≤ d*50 ≤ 35 µm. The latter is typical for the product of the particle size and the normal velocity of the laminar flame in AAS (Ben Moussa, 2017) and indicates the similarity of the effect of particle dispersion on the dynamics of turbulent and laminar combustion of AAS.Conclusions. The dispersion of an explosive polydisperse aluminum sample is determined by the average particle size of the explosive fraction of the sample d*50. The similarity of the combustion patterns indicates a relationship between the mechanisms of laminar and turbulent flame propagation in AAS.

Characteristics of hollow bluff body-stabilized natural gas-air premixed flames with heat recirculation

The combined effects of flow recirculation and preheating on the premixed flame stability limits were employed via two flow configurations. In the first configuration, the natural gas-air mixture was set to flow around a bluff body whose orientation, number of vertices and vertex angle were varied. In the second configuration, an innovative design was developed where the fuel–air mixture was set to flow inside the bluff body as two opposing jets whose resultant flow is redirected to pass around the bluff body. The peak turbulent kinetic energy (T. K. E.) decreased from 7.24 to 4.94 m2/s2 with the star shape of 4 vertices as its orientation changed from 45 to 0° and such decrease was limited to 5.27 m2/s2 upon having a smaller vertex angle. A smaller drop from 7.24 to 6.0 m2/s2 was experienced when the 4 vertices were replaced by 5 vertices at 0° angle of orientation, while the drop continued to 4.3 m2/s2 upon having 6 vertices due to the reduction in the space available for eddies. A smaller peak T. K. E. of 2.33 m2/s2 was found with the star shape of 3 vertices because the sites for turbulence development were limited. With the star cross-section of 4 vertices at 45° angle of orientation, a maximum blow-off velocity as high as 51.5 m/s and a minimum lean limit as low as 0.40 were obtained. A further extension in the flame stability limits was provided via the second flow configuration due to the favorable effects of impingement and prolonged path of preheating. As the distance between the bluff body and the combustor separating wall decreased to 1.7 times the jet diameter, the blow-off velocity increased to 79.1 m/s; while the lean limit decreased to 0.31 with the star shape of 4 vertices at 45° angle of orientation.

Growth and B-Phycoerythrin Production of Red Microalga Porphyridium purpureum (Porphyridiales, Rhodophyta) under Different Carbon Supply.

Red microalga Porphyridium purpureum (Bory) Drew is a well-known object of biotechnology due to its unique ability to synthesize a wide range of biologically active compounds. Enough minerals in an accessible form in a medium are a prerequisite for maintaining a high growth rate of P. purpureum. Carbon is the main element of microalgal biomass and is a component of all organic compounds. The work aimed to study the morphological features of cells and the accumulation and production of B-phycoerythrin and total protein in P. purpureum biomass in different ways of supplying CO2 into the culture. In Variant 1, CO2 was directly injected into a gas-air mixture (2-3 percent v/v) used for culture bubbling via capillary. In Variant 2, the air was supplied to the culture through the aquarium sparger. Variant 3 was like the first one but without the additional introduction of carbon dioxide. The application of the method for sparging atmospheric air led to a significant increase in both the productivity of the P. purpureum and the rate of protein and B-phycoerythrin synthesis in comparison with growing it using the air without spraying (two-and-a-half times, five times, and more than eight times, respectively). Moreover, there were significant changes in the morphological structure of P. purpureum cells, which were visualized both by microscopy and by changes in the color of the culture. Based on the experimental data obtained, the variants for the carbon supply experiment were ranked as follows: Variant 1 is better than Variant 2 and Variant 3. The use of atomization as a technological method made it possible to speed up the transfer of carbon dioxide from the air to the medium, which helped to keep the growth rate of P. purpureum biomass and B-phycoerythrin accumulation high.

Short-time cold atmospheric pressure plasma exposure can kill all life stages of the poultry red mite, Dermanyssus gallinae, under laboratory conditions

In the present study, the acaricidal effects of cold atmospheric pressure plasma treatment on poultry red mites of different developmental stages have been investigated under laboratory conditions using a dielectric barrier discharge system. A total of 1890 poultry red mites and 90 mite eggs, respectively, were exposed to the plasma under various parameter settings with a single plasma pulse generated using the gas mixture of the ambient air at atmospheric pressure. The results showed that all developmental stages of the poultry red mite could be killed by cold atmospheric pressure plasma treatment. Plasma exposure to mite eggs resulted in a complete 100% hatch inhibition regardless of the parameter settings. Post-exposure mortality rates of larvae, nymphs and adults showed significant differences after utilization of plasma at 10 W for 1.0 s. In addition, the mortality rate increased with progressing time after plasma exposure. An average mortality rate of 99.7% was observed after 12 h in all mites exposed to plasma, regardless of the selected plasma parameter, developmental stage, and nutritional status of the mites. Cold atmospheric pressure plasma has an acaricidal effect on all developmental stages of Dermanyssus gallinae, suggesting that it could be developed to an effective method for the control of poultry red mites in laying hen husbandry.

Adsorption of Xenon and Krypton onto Microporous Carbon Adsorbents from a Depleted Gas–Air Mixture

Adsorption of Xenon and Krypton onto Microporous Carbon Adsorbents from a Depleted Gas–Air Mixture

Разработка модели для определения оптимального состава RDF-топлива в Республике Беларусь

The article presents and substantiates a model for determining the blend composition of RDF fuel from municipal waste. The main goal of developing the model presented in the article was to prove the impossibility and inadmissibility of burning plastics of unknown composition as fuel in cement kilns as potential sources of formation of large volumes of persistent organic pollutants. This is the best justification for the environmental safety of the use of RDF fuel in the Republic of Belarus. With the introduction of a large number of plastics, it is necessary to equip additional emission treatment systems. The article describes the developed methodology for choosing the optimal composition of RDF fuel components, as well as calculating the volume of the gas-air mixture. The mathematical model was developed using the MS Excel program. Its main functions are: entering data into the database, calculating the optimal combinations of the RDF fuel composition, determining the calorific value, moisture content and ash content of the required mixture variant. In addition, the mathematical model analyzes the chemical composition of the required combination and derives indicators of the content of contaminants in the RDF fuel. Such characteristics of RDF fuel as calorific value, humidity, ash content are selected and analyzed. The assessment was made without taking into account emissions of heavy metals such as antimony, arsenic, lead, chromium, cobalt, copper, manganese, nickel, vanadium, cadmium, thallium. Due to the hazardous content of elements in the RDF fuel components, it must strictly not exceed the following values: S - 0.5%, Cl - 0.5%, F - 0.002%, Hg - 0.001%. 210 variants of the component composition of the RDF fuel were analyzed. Using calculations to determine the limits on the content of sulfur oxide, mercury and halogens in emissions, the optimal options for the composition of RDF fuel were determined, of which 12 were found to be satisfactory. The analysis of the content in RDF fuel of elements leading to the formation of certain pollutants (S, Cl, F, Hg), which are persistent organic pollutants, was carried out and their permissible concentrations in emissions during the combustion of RDF fuel were determined. Thus, options for optimal RDF fuel compositions that meet consumer and environmental requirements have been determined.

Optimization of CO2 Supply for the Intensive Cultivation of Chlorella sorokiniana IPPAS C-1 in the Laboratory and Pilot-Scale Flat-Panel Photobioreactors.

Microalgae are increasingly being used for capturing carbon dioxide and converting it into valuable metabolites and biologically active compounds on an industrial scale. The efficient production of microalgae biomass requires the optimization of resources, including CO2. Here, we estimated the productivity of Chlorella sorokiniana IPPAS C-1 depending on CO2 concentrations and the ventilation coefficient of the gas-air mixture (GAM) in flat-panel photobioreactors (FP-PBRs) at laboratory (5 L) and pilot (18 L) scales. For the laboratory scale, the PBRs operated at 900 µmol quanta m−2 s−1 and 35.5 ± 0.5 °C; the optimal CO2 flow rate was estimated at 3 mL CO2 per 1 L of suspension per minute, which corresponds to 1.5% CO2 in the GAM and an aeration rate of 0.2 vvm. These parameters, being scaled up within the pilot PBRs, resulted in a high specific growth rate (µ ≈ 0.1 h−1) and high specific productivity (Psp ≈ 1 g dw L−1 d−1). The principles of increasing the efficiency of the intensive cultivation of C. sorokiniana IPPAS C-1 are discussed. These principles are relevant for the development of technological regimes for the industrial production of Chlorella in flat-panel PBRs of various sizes.

ENVIRONMENTAL SAFETY OF POWER PLANTS: DUAL-FUEL AND GAS ENGINES

The subject of this study is internal combustion engines capable of using gaseous fuels-gas and dual-fuel engines. The main technologies of using natural gas in piston engines from the standpoint of ensuring the highest energy efficiency and environmental safety are considered in the paper. It is noted that the use of natural gas as a fuel, regardless of the technology, reduces carbon dioxide emissions from combustion products by 28 % compared to liquid fuels. All known designs of gas and dual-fuel engines fundamentally implement two technologies, namely, the use of homogeneous or heterogeneous gas-air mixtures. The most common is the technology of homogeneous mixtures, which provides high fuel efficiency and the highest environmental safety indicators. This technology provides for the supply of low-pressure gas to the intake ducts of the engine through automatic gas valves. There are practically no sulfur oxides, solid particles in the exhaust gases of the engine, and the emission of nitrogen oxides can be provided at the level of the requirements of the Tier III standard. At the same time, the main disadvantage of the homogeneous mixture technology is the potential penetration of natural gas with a high level of greenhouse effect (which is up to 28 times higher than the effect of carbon-acid gas) into the exhaust tract of the engine - “methane slippage”. This negative aspect can be largely minimized through the use of heterogeneous technology, when fuel gas is fed directly into the cylinder of a dual-fuel engine under high pressure, up to 50 bar, at the end of the compression process. This technology is becoming widespread in the structures of two-stroke engines due to the specifics of their gas exchange process. However, the high dynamics of the heat release process in the implementation of heterogeneous technology of gas-air mixtures is associated with a high emission of nitrogen oxides, commensurate with the emission of NOx by a diesel engine. Based on the analysis of the parameters and characteristics of the products of leading manufacturers implementing various technologies for using natural gas as fuel, conclusions about the potential advantages and prospects of using gas and dual-fuel engines are made.

Co–solvent effects on hydrothermal co–gasification of coal/biomass mixtures for hydrogen production

The use of low–rank coals for hydrogen production by gasification can create advantageous options to overcome a potential energy crisis. In this study, the effects of 8 different solvents on gasification and hydrogen yield in coal/biomass co–solvent hydrothermal gasification were investigated. The most effective co–solvent on product conversion and high hydrogen yield was found N–methyl pyrrolidone (NMP) and tetrahydrofuran (THF). Total gas volumes and hydrogen yields obtained from the co–solvent gasification of coal/sorghum blends were higher than the arithmetical sum of the average values of the yields from individual solvent and coal/sorghum blend gasifications. The increase in the hydrogen yield was 11 mol H2/kg feed with the co–solvent THF due to the synergistic effects of THF on hydrogen production. Solvent concentration was effective on both total gas volumes and hydrogen yields. In the catalytic (K2CO3/CaO) runs with a concentration of 20 % (v/v) NMP co–solvent 98.8 ± 0.1 mol H2/kg feed was achieved with a dramatic decrease of CO content in the produced gas mixture. The comparison of the results obtained from subcritical and supercritical water conditions showed that in catalytic processes co–solvent was more effective towards feedstock conversion and almost the same hydrogen yields obtained at lower pressures under the subcritical water conditions.

MODELING OF THE PROCESS OF PRIMARY AIR SUCTION IN A HOUSEHOLD GAS BURNER ON BIOGAS FUEL

Statement of the problem. The process of suction of primary air into the housing of a gas burner device for domestic use during the combustion of gas fuel with different methane content in the composition is considered. It is necessary to develop a computer model of the movement of the gas-air mixture for a gas with a methane content of 50 to 90 % vol., with varying the height of the primary air regulator H from 0 to 19.25 mm and determine the concentration of O2 in the gas-air mixture at the outlet of the openings of the gas burner device, based on the results obtained, determine the rational dimensions of the primary air supply regulator. Results. The results of computer simulation of primary air suction by a flow of combustible gas inside the gas burner housing when using combustible gas with different methane content in the composition using the Ansys Fluent software package are presented. 3D modeling of the design of a gas burner equipped with a primary air supply regulator has been performed. The process under study was carried out by varying the methane content in the composition of the gas used and the height of the primary air regulator. The dependences of the oxygen content in the composition of the formed gas-air mixture on the composition of the combustible gas were determined, which made it possible to obtain the required dimensions of the primary air regulator.Conclusions. As a result of computer modeling, it was found that with a decrease in the methane content in the composition of the combustible gas, it is necessary to use a primary air regulator with a higher height H, which will ensure the suction of a smaller amount of primary air to ensure complete combustion of the combustible gas of the adopted composition.

Arc decomposition behavior of C 4 F 7 N/Air gas mixture and biosafety evaluation of its by‐products

At present, reports on the arc interruption and decomposition behaviour of a C4F7N/air gas mixture especially the biosafety of its by-products are limited. Herein, a 57% C4F7N/43% air gas mixture was employed as an arc-quenching medium to conduct 200 breaking tests on a load switch (630 A/24 kV). The arc interruption and decomposition behaviour of the gas mixture were evaluated, and the biosafety of the decomposition products was assessed based on an acute inhalation toxicity test. It was found that the average arcing time of the 200 breakings was about 10.1 ms and that breakings were basically completed at the zero-crossing of the second or third current half-cycle. The gas mixture after breaking decomposed dramatically (the C4F7N content decreased by 75.6%), generating a large number of gaseous by-products (CO, CF4, C2F6, C3F8, CF3CN, C4F8, CO2, C4F10N2, C3F6, C2N2, etc.) as well as solid by-products (carbon particles). The lethal concentration (LC50) of 50% (LC50, 4 h) of C4F7N/air after 200 breakings was 31 ppm (male mice) and 34 ppm (female mice), respectively, and the toxicity was classified as Grade 1. In general, C4F7N has an arc interruption capability, albeit weaker than that of SF6 under the same conditions. After breaking, the C4F7N gas mixture has a relatively high acute inhalation toxicity, and relevant safety protection measures for research or operation personnel are strictly needed.