Vol 44, No 4 (2025)

Biochars from the seaweed Saccharina japonica were obtained by stepwise pyrolysis at temperatures of 300, 400, 500, 700, 900 °C. Its characteristics and properties were studied: elemental composition, specific surface area and total pore volume, particle size distribution, as well as characteristic functional groups were determined using IR-Fourier spectroscopy. With an increase in the pyrolysis temperature from 300 °C to 900 °C, the biochar yield decreases from 50.4% to 22.7%. The biochar obtained at 500 °C has the largest specific surface area – 38.6 m²/g. As the pyrolysis temperature increases, the elemental composition of the biochar changes: the content of carbon, hydrogen, nitrogen decreases, and the content of sulfur and oxygen increases.

A thermodynamic assessment of the modes of non-catalytic conversion of acid gases and methane to produce syngas was carried out. The air and steam-air conversion modes of a mixture of hydrogen sulfide, carbon dioxide and methane were studied. Model compositions of gases with different contents of hydrogen sulfide (10, 20 and 30 vol.%) and methane (depending on the stoichiometric fuel excess coefficient) were considered. It has been shown that high temperature leads up the conversion of reagents and the syngas formation. With an increase in the amount of methane, the yield of hydrogen increased over the entire temperature range under consideration (1273–1873 K), but conversion rate of hydrogen sulfide decreased significantly. Increasing the amount of hydrogen sulfide in the initial mixture reduces the yield of synthesis gas. Adding water vapor in amounts up to 5 vol.% leads to an increase in the syngas yield and the [H₂]/[CO] ratio. The maximum ratio H₂/CO = 2.1 was achieved during air conversion of a mixture with 10 vol.% hydrogen sulfide with the same amount of CO₂ with a stoichiometric fuel excess ratio of 10 and T = 1873 K.

A two-dimensional model of combustion of a premixed methane-air mixture inside a plane-parallel channel of a slit burner consisting of a set of parallel metal plates made of heat-resistant material is proposed. The task is described by a system of equations representing the laws of conservation of energy in the gas and solid phase, mass and elemental composition of the gas phase, taking into account the course of a complex chemical reaction, heat exchange between the gas and the surface of the plates, radiation from heated plates, thermal conductivity in the plates, molecular and convective heat and mass transfer in the gas. Calculations using the proposed model provide a completely adequate idea of the combustion process in the channel of a slot burner. Quantitative agreement with the experiment was obtained for the maximum value of the specific combustion power, which can exceed 500 W/cm². In calculations using the proposed model, it is shown that the specific combustion power in the burner device under consideration may exceed 500 W/cm². As the gas flow velocity (specific combustion power) increases, the chemical reaction zone moves along the channel axis towards the exit. In this case, the flame front with a peak on the axis of symmetry of the channel stretches more strongly along the plate. In a stoichiometric mixture, the flame front shifts closer to the channel entrance, and the concentration of carbon monoxide in the combustion products at the channel exit is significantly higher than in a lean mixture. As the velocity of the gas mixture at the channel entrance increases, the concentration of CO at the channel outlet of the channel grows, although it remains small. The obtained results qualitatively correspond to the experimental results of the study of slit combustion.

A numerical and analytical solution has been carried out for the hydrodynamic problem of the collapse of a cylindrical cavity in a freely spreading layer of solid explosive upon impact. Based on the results of calculations of the conditions for the initiation of HMX-type explosive charges, the critical impact parameters, geometric and physical-mechanical characteristics of the layer and the properties of the gas cavity were determined. The dual role of gas in the cavity was established, in some cases facilitating or preventing the process of explosion occurrence.

The paper discusses the issues of gas-dynamic similarity in the problem of high-pressure hydrogen release into air and the possibility of laboratory modeling of the process by reducing the initial pressure at a fixed ratio of hydrogen and air pressures. The fundamental factor in the considered problem is the probability of hydrogen spontaneous ignition, which significantly limits the applicability of gas-dynamic similarity in modeling the considered process. It is shown, however, that for large values of the hydrogen and air pressure ratio (from 200 to 700 and higher) in view of the small values of the hydrogen ignition delay time, one can speak about the gas-dynamic similarity in a wide range of initial pressures. This should allow laboratory modeling the process of high-pressure hydrogen release with subsequent spontaneous ignition in atmospheric air at reduced pressure.

The influence of the choice of a detailed kinetic mechanism (DKM) on the structure of a laminar flame for lean hydrogen-air mixtures has been studied by means of numerical simulation using a CHEMKIN-Pro software module. It is shown that the choice of three detailed kinetic mechanisms (DKMs), differing in the rate constants of elementary reactions, the number of reaction pathways, and the presence of additional components, has virtually no effect on flame propagation velocity and flame structure. It is found that small differences in the local sensitivity of heat release to elementary reactions can provide reliable information on possible ways of influencing flame propagation.

An analytical review of investigations dedicated to a behavior of tanks with compressed and liquefied hydrogen in a fire is presented. It was mentioned that the compressed hydrogen is stored as a rule in vessels made of composite materials, and the liquefied hydrogen is stored in double-wall isothermal tanks. The vessel with a compressed hydrogen is destructed after 5-15 min of an action of a fire, if no fire proofing is made for these vessels. A destruction of the vessel made of the composite materials takes place at gas pressures exceeding an initial pressure not more than on 10%. A rupture occurs due to a loss of polymer compound. A fire resistance limit of a such vessel is inversely proportional to an intensity of a thermal action of the fire. But the fire resistance limit of the liquefied hydrogen tank can reach several tens minutes depending on parameters of a thermal isolation. Shock waves, fireballs and fragments of the tanks are the main hazardous factors of the accidents with a rupture of the hydrogen tanks. Sizes of hazardous zones can reach several tens meters depending on the parameters of the tanks. The largest sizes were observed in the case of the fireballs.

A numerical analysis of microparticle heating in clouds, formed by microparticles, that were observed in a neon glow discharge plasma at cryogenic temperature has been carried out. The relationship between the temperature of the microparticle surface and the parameters of the cloud is demonstrated. It has been revealed that the collective effect of the cloud on the plasma results in a reduction in the heating of microparticles within the cloud, when compared to the heating of a test microparticle in a discharge with an identical value of discharge current and gas pressure. The temperature of a microparticle is observed to be contingent upon its position within the cloud. The evidence indicates that the temperature of the microparticles at the cloud periphery can exceed that at the cloud center. It was found that in denser clouds, the temperature profile of microparticles is levelled out.