This article shows incidents associated with the use of gas as an energy carrier. It presents selected incidents which have occurred in Poland and around the world in recent decades. Based on this, consequences of gas and air mixture explosions were analysed as well. The article presents the main causes of gas incidents which have taken place, as per instances which are similar worldwide. Incidents associated with the use of gas are not frequent, but at the same time very tragic as they often lead to illness or even death. In Poland, in the last twenty years, construction area disasters caused by gas explosions account for only 5% of all which have occurred, but the number of fatalities resulting from these cases is approximately 14%. The number of individuals injured reached 39% of all construction disaster victims. Considering all these facts, it is necessary to undertake wide preventive measures in order to increase safety in the use of gaseous fuels.

The results of experimental investigations on landfill gas separation on hollow fibres membranes made of poly (4 methylpentene-1) are presented. The effect of operating parameters on the performance and effectiveness of separation process has been described. Permeation process has been carried out in countercurrent flow for medium methane landfill gases. Obtained results have been analyzed in aspect to optimization process conditions.

Shale gas mining is mainly viewed as an industrial and economic issue. But we can also look at it from the scientific perspective. Why should we?

Aspiration dust probes of some isokinctic samplers have such a construction that enables them to measure the gas velocity at the point they arc placed in a duct, the measurement being required for maintaining isokinctic conditions and in determining the dust mass flow rate in the duct. The gas velocity is correlated with a probe specific pressure difference, a quantity measured directly when the train is in operation. This relationship is a mclrological characteristic of a given probe, being established in a calibration procedure. Two types of the above-mentioned probes, namely a pressure balance-type and an in-stack filtration probes (in two versions) combined with a type S velocity sensor, have been tested. The behaviour of the characteristics of the probes was studied in the flows of different turbulence at a laboratory stand. The achieved results, presented in the paper, show that the turbulence state of gas flow is the factor that shapes the mctrological characteristics. Facing the fact that the turbulence of gas flow in industrial installations is not identified during the dust concentration gravimetric measurements, this parameter constitutes a source of uncertainty of the gas velocity measurement. For the probes under test, the values of this uncertainty, varying with the gas velocity, were determined. The test and calculation procedures were described.

Paper presents the concept of energy storage system based on power-to-gas-to-power (P2G2P) technology. The system consists of a gas turbine co-firing hydrogen, which is supplied from a distributed electrolysis installations, powered by the wind farms located a short distance from the potential construction site of the gas turbine. In the paper the location of this type of investment was selected. As part of the analyses, the area of wind farms covered by the storage system and the share of the electricity production which is subjected storage has been changed. The dependence of the changed quantities on the potential of the hydrogen production and the operating time of the gas turbine was analyzed. Additionally, preliminary economic analyses of the proposed energy storage system were carried out.

Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards (110). The effects of substrate temperature and the Sb/Ga flux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

There are many IT tools available on the market that carry out various types of forecasts in the gas industry. Programming evolves with the availability and capability of computers. IT tools support the user in engineering calculations, but also present the obtained results in an interesting visualization, e.g. in the form of interactive charts. The software can support making business decisions, which, in turn, can be used as business intelligence. In the era of digitization, huge metadata of measurements are created, so conducting data analyzes in the energy sector is very common. Moreover, rapidly evolving artificial intelligence creates new opportunities. The article presents a sample analysis of calculations using RStudio, an integrated development environment for the R language, a programming language for statistical calculations and graphics. The aim of the article is to present the possibility of using R language software to make a forecast and to determine the quality of forecasts. The article aims to present the possibility of making forecasts based on mathematical models available in R packages and the possibilities offered by the forecasting platform to readers. The article presents the U.S. market and has a particular focus on Natural Gas Residential Consumption in Pennsylvania (publicly available data from the U.S. Energy Information Administration). This dataset represents the monthly consumption of natural gas between 2015 and 2020. Forecasts were presented over a span of 12 months.

HTAC (High Temperature Air Combustion) technology is one of the most important achievements in combustion engineering of recent years. The main idea of the technology is to organize combustion in such a way that reaction takes place in almost whole volume of combustion chamber with very uniform gas and temperature field. It can be done by preheating air above the ignition temperature of fuel, separation of air and fuel nozzles and by high recirculation inside the combustion chamber. Uniform and moderated temperatures result in very low thermal NO emission, and on the other hand, long enough rcsiclcncc time in the chamber results in low CO and incomplete products emission. In this paper authors present simple mathematical model which allows for estimation of influence of air temperature and flue gas recirculation rate on final emission on NO and CO.

New model of the simulation of the airbag inflation process, taking into account the influence of the airbag environment on the folding process, have been proposed. Equations describing a new model and the used numerical schemes were presented. The differences of the airbag fabric skin motion during the folding process, obtained by the use of different process models (existing and proposed), have been presented on the simple geometry examples. From the analysis of obtained results one acknowledged that the proposed model should be used in all calculations of the airbag operation in non-typical situations, out-of position occupants, side airbags, particularly in the case of small distances between the closed airbag and the elements of the body of the protected person.

The Bulletin of the Polish Academy of Sciences: Technical Sciences (Bull.Pol. Ac.: Tech.) is published bimonthly by the Division IV Engineering Sciences of the Polish Academy of Sciences, since the beginning of the existence of the PAS in 1952. The journal is peer‐reviewed and is published both in printed and electronic form. It is established for the publication of original high quality papers from multidisciplinary Engineering sciences with the following topics preferred: Artificial and Computational Intelligence, Biomedical Engineering and Biotechnology, Civil Engineering, Control, Informatics and Robotics, Electronics, Telecommunication and Optoelectronics, Mechanical and Aeronautical Engineering, Thermodynamics, Material Science and Nanotechnology, Power Systems and Power Electronics.

Journal Metrics: JCR Impact Factor 2018: 1.361, 5 Year Impact Factor: 1.323, SCImago Journal Rank (SJR) 2017: 0.319, Source Normalized Impact per Paper (SNIP) 2017: 1.005, CiteScore 2017: 1.27, The Polish Ministry of Science and Higher Education 2017: 25 points.

Abbreviations/Acronym: Journal citation: Bull. Pol. Ac.: Tech., ISO: Bull. Pol. Acad. Sci.-Tech. Sci., JCR Abbrev: B POL ACAD SCI-TECH Acronym in the Editorial System: BPASTS.

In this study, the effect of gas pressure on the shape and size of the AZ91 alloy powder produced by using the gas atomization method was investigated experimentally. Experiments were carried out at 820°C constant temperature in 2-mm nozzle diameter and by applying 4 different gas pressures (0.5, 1.5, 2.5 and 3.5 MPa). Argon gas was used to atomize the melt. Scanning electron microscope (SEM) to determine the shape of produced AZ91 powders, XRD, XRF and SEM-EDX analysis to determine the phases forming in the internal structures of the produced powders and the percentages of these phases and a laser measuring device for powder size analysis were used. Hardness tests were carried out to determine the mechanical properties of the produced powders. The general appearances of AZ91 alloy powders produced had general appearances of ligament, acicular, droplet, flake and spherical shape, but depending on the increase in gas pressure, the shape of the powders is seen to change mostly towards flake and spherical. It is determined that the finest powder was obtained at 820°C with 2 mm nozzle diameter at 3.5 MPa gas pressure and the powders had complex shapes in general.

Energy from different sources is fundamental to the economy of each country. Bearing in mind the limited reserves of non-renewable energy sources and the fact that their production from new deposits is becoming less economically viable, attention is paid to alternative energy sources, particularly those that are readily available or require no substantial financial investment. One possible solution may be to generate hydrogen, which will then be used for heat (energy) production using other methods. At the same time, these processes will be characterized by low emission levels compared to conventional energy sources. In recent years, more and more emphasis has been placed on the use of clean energy from renewable sources. New, more technically and economically efficient technologies are being developed. The energy use worldwide comes mostly from fossil fuel processing. It can be observed that the share of RES in global production is growing every year. At the end of the 1990s, the share of renewable energy sources was at 6–7%. Global trends indicate the increasing demand for renewable energy due to its form. Global hydrogen resources are practically inexhaustible, but the problem is its availability in molecular form. The article analyzed the use of hydrogen as a fuel. The basic problem is the inexpensive and easy extraction of hydrogen from its compounds; attention has been paid to water, which can easily be electrolytically decomposed to produce oxygen and hydrogen. Hydrogen generated by electrolysis can be stored, but due to its physicochemical properties, it is a costly process; therefore, a decision was made that it is better to store it with natural gas or use it for further reaction. In addition, hydrogen can be used as a substrate for binding and converting the increasingly problematic carbon dioxide, thus reducing its content in the atmosphere.

In recent years, changes have been made in the structure of primary energy use in the European

Union In addition, a reduction in the use of primary energy has also been observed. According to

the forecasts of the International Energy Agency, the European energy market will be subject to

further changes in the perspective of 2040. These may include the reduction of the energy consumption

and the change in the structure of the energy balance as a result pro-ecological activities.

Natural gas will be the only fossil energy carrier whose role in covering the energy demand will not

change. Along with the changes taking place in the European energy market, global changes can

also be observed. The EU Member States will continue to strive to diversify natural gas supplies.

One of the main elements of diversification of natural gas supplies is the use of LNG regasification

terminals. The reasons for that include the increasing production of natural gas, particularly in the

case of unconventional deposits, the ongoing development of liquefaction terminals, and, as a consequence,

an increase in the LNG supply in the global market. The article presents the utilization of

regasification terminals in the EU Member States and plans for the development of LNG terminals.

Europe has the opportunity to import natural gas through LNG terminals. However, until now,

these have been used to a limited extent. This may indicate that in addition to diversification tasks,

terminals can act as a safeguard against interruptions in gas supplies.

The authors presented problems related to utilization of exhaust gases of the gas turbine unit for production of electricity in an Organic Rankine Cycle (ORC) power plant. The study shows that the thermal coupling of ORC cycle with a gas turbine unit improves the efficiency of the system. The undertaken analysis concerned four the so called "dry" organic fluids: benzene, cyclohexane, decane and toluene. The paper also presents the way how to improve thermal efficiency of Clausius-Rankine cycle in ORC power plant. This method depends on applying heat regeneration in ORC cycle, which involves pre-heating the organic fluid via vapour leaving the ORC turbine. As calculations showed this solution allows to considerably raise the thermal efficiency of Clausius-Rankine cycle.

The present paper describes a cycle, which may be applied in sewage treatment plants as a system to convert biological waste into process heat and electricity. In sludge stabilization processes anaerobic fermentation acts as the source of methane, which can be used then to generate heat and electric current in gas turbines. Products of high-temperature oxidation can be utilized in organic Rankine cycles to generate electric power. Waste heat is used for heating the fermenting biomass. Energy balance equations mentioned in the thesis: organic Rankine cycle, regenerative gas turbine engine, anaerobic sludge stabilization system.

The article discusses the operation of solid oxide electrochemical cells (SOC) developed in the Institute of Power Engineering as prospective key components of power-to-gas systems. The fundamentals of the solid oxide cells operated as fuel cells (SOFC – solid oxide fuel cells) and electrolysers (SOEC – solid oxide fuel cells) are given. The experimental technique used for electrochemical characterization of cells is presented. The results obtained for planar cell with anodic support are given and discussed. Based on the results, the applicability of the cells in power-to-gas systems (P2G) is evaluated.

Natural gas combustion was carried out in air enriched with oxygen in the amount of 25 and 29% with addition of CO2 in place of part of nitrogen. The research was carried out at different flow rates of gas and oxygen excess ratios. The concentration of CO and NOx was analyzed. It has not been proved that the increased oxygen concentration influences significantly the CO concentration. However, the addition of CO2 caused a substantial variability of CO concentration in the exhaust gas, in contrast to the concentration of NOx which decreased monotonically. Model calculations, performed with use of FactSage, indicate an increase in the concentration of CO not only for the air enriched with oxygen, but after adding CO2 too, as well

Comparative calculations with a mathematical model designed by the authors, which takes into consideration energy transfer from gas flowing through a given channel to gas which penetrates this channel from an adjacent channel, as well as a model which omits this phenomenon, respectively, were made for the process of separating gas mixtures carried out with an inert sweep gas in the fourend capillary membrane module. Calculations were made for the process of biogas separation using a PMSP polymer membrane, relative to helium as the sweep gas. It was demonstrated that omitting the energy transfer in the mathematical model might lead to obtaining results which indicate that the capacity of the process expressed by the value of feed flux subjected to separation is by several percent higher than in reality.

The purpose of the work was initial modification of the construction of a commercially produced heat exchanger – recuperator with CFD (computational fluid dynamics) methods, based on designs and process parameters which were provided. Uniformity of gas distribution in the space between the tubes of the apparatus as well as the pressure drop in it were taken as modification criteria. Uniformity of the gas velocity field between the tubes of the heat exchanger should cause equalization of the local individual heat transfer coefficient values and temperature value. Changes of the apparatus construction which do not worsen work conditions of the equipment, but cause savings of constructional materials (elimination or shortening some parts of the apparatus) were taken into consideration.

This paper presents studies carried out in a pilot-scale plant for recovery of waste heat from a flue gas which has been built in a lignite-fired power plant. The purpose of the studies was to check the operation of the heat recovery system in a pilot scale, while the purpose of the plant was recovery of waste heat from the flue gas in the form of hot water with a temperature of approx. 90 °C. The main part of the test rig was a condensing heat exchanger designed and built on the basis of laboratory tests conducted by the authors of this paper. Tests conducted on the pilot-scale plant concerned the thermal and flow parameters of the condensing heat exchanger as well as the impact of the volumetric flow rate of the flue gas and the cooling water on the heat flux recovered. Results show that the system with a condensing heat exchanger for recovery of low-temperature waste heat from the flue gas enables the recovery of much higher heat flux as compared with conventional systems without a condensing heat exchanger.

Traditional fluid mechanics edifies the indifference between liquid and gas flows as long as certain similarity parameters – most prominently the Reynolds number – are matched. This may or may not be the case for flows in nano- or microdevices. The customary continuum, Navier-Stokes modelling is ordinarily applicable for both air and water flowing in macrodevices. Even for common fluids such as air or water, such modelling bound to fail at sufficiently small scales, but the onset for such failure is different for the two forms of matter. Moreover, when the no-slip, quasi-equilibrium Navier – Stokes system is no longer applicable, the alternative modelling schemes are different for gases and liquids. For dilute gases, statistical methods are applied and the Boltzmann equation is the cornerstone of such approaches. For liquid flows, the dense nature of the matter precludes the use of the kinetic theory of gases, and numerically intensive molecular dynamics simulations are the only alternative rooted in first principles. The present article discusses the above issues, emphasizing the differences between liquid and gas transport at the microscale and the physical phenomena unique to liquid flows in minute devices.

As is well known, gas consumption and its prices depends on many factors including local factors, geopolitics, the development of the gas transport infrastructure (including liquefied natural gas), distribution and extraction costs – for example unconventional deposits (e.g. shale gas). The global gas market depends primarily on the economic relations between large gas producers and importers e.g. US-China, Middle East/US – Russia etc. (Olayele 2015). In individual countries, the price is also dependent on concluded contracts and delivery directions. Also it should be mentioned that the gas consumption depends on weather conditions, type of day of the year (holiday, business day, month) and economic situation (Kosowski et. al 2010). What impact has the appearance of the COVID-19 epidemic had on the European natural gas market?

The analyzed research problem concerned, in particular, two areas: gas consumption and its prices, in selected European countries in the aspect of the spread of the COVID-19 epidemic with reference to historical data from 2016–2019. Seven European countries belonging to the European Network of Transmission System Operators for Gas (ENTSOG) were selected, for which the highest inland consumption of natural gas by country was observed in the last year. The countries are presented in order or consumption: Germany, the United Kingdom, Italy, France, the Netherlands, Spain, Poland. The data has been downloaded from transmission system operators (TSOs) for each of these countries.

Furthermore the article showed information about the dates of governments restrictions (lockdown), LNG contract volumes, injection/withdrawal volumes (storage).

Describing the gas boiler fuel consumption as a time series gives the opportunity to use tools appropriate for the processing of such data to analyze this phenomenon. One of them are ARIMA models. The article proposes this type of model to be used for predicting monthly gas consumption in a boiler room working for heating and hot water preparation. The boiler supplies heat to a group of residential buildings. Based on the collected data, three specific models were selected for which the forecast accuracy was assessed. Calculations and analyses were carried out in the R environment using “forecast” and “ggplot2” packages. A good quality of the obtained forecasts has been demonstrated, confirming the usefulness of the proposed analytical tools. The article summary also indicates for what purposes the forecasts obtained in this way can be used. They can be useful for diagnosing the correct operation of a heat source. Registering fuel consumption at a level significantly deviating from the forecast should be a signal to immediately diagnose the boiler room and the heat supply system and to explain the reason for this difference. In this way, it is possible to detect irregularities in the operation of the heat supply system before they are detected by traditional methods. The gas consumption forecast is also useful for optimizing the financial management of the property manager responsible for the operation of the boiler room. On this basis, operating fees or financial operations with the use of periodic surplus capital may be planned.

The paper analyzed the natural gas sector in Ukraine for the period 2000 to 2018. This sector was affected by external factors, such as the crisis which began in late 2008/2009, as well as internal factors, including the situation in Ukraine after 2013 (the Annexation of Crimea). A comparative analysis was also conducted of the natural gas sector in European Union countries and Ukraine – compared the specificity of natural gas consumption in 2018. The analysis (I) examined the demand for natural gas in Ukraine between 2000 and 2018; (II) described changes in sources to cover Ukraine’s gas needs with a particular emphasis on its own production; (III) pointed to the fundamental changes that have occurred in the natural gas supply routes to the Ukrainian sector in recent years; (IV) stressed the growing role of own production in balancing Ukraine’s gas needs; (V) described the role of Ukraine as a transit country for Russian gas to be delivered to EU countries (in recent years, the volume of natural gas transmitted via the Ukrainian transmission system has been around 90 bcm annually); and (VI) looked at the structure of natural gas consumption in the Ukrainian gas sector and how it has changed in recent years. Unlike EU countries, the growing role of own production in balancing Ukraine’s natural gas needs was emphasized, which is consistent with the strategy of the Ukrainian government. Also, attention was drawn to the threats that may significantly reduce the role of Ukraine as an important transit country. The paper also puts forward the most important parameters concerning the underground natural gas storage facilities in Ukraine which is one of the largest in Europe.