The transition to oxy-fuel combustion power cycles is a prospective way to decrease carbon dioxide emissions into the atmosphere from the energy sector. To identify which technology has the highest efficiency and the lowest emission level, a thermodynamic analysis of the semiclosed oxy-fuel combustion combined cycle (SCOC-CC), the E-MATIANT cycle, and the Allam cycle was carried out. The modeling methodology has been described in detail, including the approaches to defining the working fluid properties, the mathematical models of the air separation unit, and the cooled gas turbine cycles’ calculation algorithms. The gas turbine inlet parameters were optimized using the developed modeling methodology for the three oxy-fuel combustion power cycles with CO₂ recirculation in the inlet temperature at a range of 1000 to 1700 °C. The effect of the coolant flow precooling was evaluated. It was found that a decrease in the coolant temperature could lead to an increase of the net efficiency up to 3.2% for the SCOC-CC cycle and up to 0.8% for the E-MATIANT cycle. The final comparison showed that the Allam cycle’s net efficiency is 5.6% higher compared to the SCOC-CC cycle, and 11.5% higher compared with the E-MATIANT cycle.

Nowadays, one of the most important areas in refining the energy sector in the developed countries is the transition to environmentally friendly technologies, and hydrogen energy production is the most promising of them. In this rapidly advancing area, significant progress in creating new technologies for hydrogen fuel generation, transportation, storage, and consumption has been recently observed, while a fast-growing number of research papers and implemented commercial projects related to hydrogen makes it necessary to give their general review. In particular, the combination of the latest achievements in this area is of particular interest with a view to analyzing the possibility of creating hydrogen fuel supply chains. This paper presents an analytical review of existing methods of hydrogen production, storage, and transportation, including their key economic and energy-related characteristics, and proposes an approach to the creation, analysis, and optimization of hydrogen supply chains. A mathematical model has been developed to determine the cost of hydrogen, taking into account the supply chain, including production, transport and storage. Based on the results of modeling in the given scenario conditions for 2030, 2040 and 2050, promising hydrogen supply chains have been established. Under the various scenario conditions, hydrogen production by 2050 is most preferable by the method of steam conversion of methane with a cost of 8.85 USD/kg H₂. However, due to the environmental effect, electrolysis also remains a promising technology with a cost of hydrogen produced of 17.84 USD/kg.

The world community is worried about the effects of global warming. A few agreements on the reduction of CO₂ emissions have been signed recently. A large part of these emissions is produced by the power production industry. Soon, the requirements for thermal power plant ecology and efficiency performance may become significantly higher. Thus, the contemporary problem is the development of highly efficient power production facilities with low toxic and greenhouse gas emission. An efficient way to reduce CO₂ emissions into the atmosphere, which implies maintaining economic growth, is the creation of closed thermodynamic cycles with oxy-fuel combustion. The Allam cycle is one of the most promising among oxy-fuel power plants. A 50 MW pilot Allam cycle plant was built in Texas. The design for a commercial system with an electrical output of 300 MW is under development. This work is devoted to the improvement of the efficiency and environmental safety of oxy-fuel combustion power cycles via the utilization of compressed working fluid heat. The results of computer simulation obtained using AspenONE software demonstrated that an additional circuit in the multi-flow regenerator might increase net efficiency by 3.5%. Besides this, the incorporation of a supercritical carbon dioxide (S–CO₂) Brayton cycle with recompression increased the efficiency by 0.2%. Therefore, the maximum net efficiency of the prospective power unit was 51.4%.

Today, with the increases in organic fuel prices and growing legislative restrictions aimed at increasing environmental safety and reducing our carbon footprint, the task of increasing thermal power plant efficiency is becoming more and more topical. Transforming combusting fuel thermal energy into electric power more efficiently will allow the reduction of the fuel cost fraction in the cost structure and decrease harmful emissions, especially greenhouse gases, as less fuel will be consumed. There are traditional ways of improving thermal power plant energy efficiency: increasing turbine inlet temperature and utilizing exhaust heat. An alternative way to improve energy efficiency is the use of supercritical CO₂ power cycles, which have a number of advantages over traditional ones due to carbon dioxide’s thermophysical properties. In particular, the use of carbon dioxide allows increasing efficiency by reducing compression and friction losses in the wheel spaces of the turbines; in addition, it is known that CO₂ turbomachinery has smaller dimensions compared to traditional steam and gas turbines of similar capacity. Furthermore, semi-closed oxy–fuel combustion power cycles can reduce greenhouse gases emissions by many times; at the same time, they have characteristics of efficiency and specific capital costs comparable with traditional cycles. Given the high volatility of fuel prices, as well as the rising prices of carbon dioxide emission allowances, changes in efficiency, capital costs and specific greenhouse gas emissions can lead to a change in the cost of electricity generation. In this paper, key closed and semi-closed supercritical CO₂ combustion power cycles and their promising modifications are considered from the point of view of energy, economic and environmental efficiency; the cycles that are optimal in terms of technical and economic characteristics are identified among those considered.

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