Thermal Engineering最新文献

Abstract

The development of compact, safe, and efficient methods for storing hydrogen is one of the key problems of hydrogen energy. Currently used technologies for storing hydrogen in the form of compressed gas or cryogenic liquid require significant capital investments and maintenance costs for compressor and cryogenic equipment, are characterized by high energy costs, and their implementation requires special safety measures as well as the use of hydrogen-neutral structural materials. A promising way to solve these problems for medium-scale storage systems is the use of metal hydrides, which provide the simplest, most compact, and safe hydrogen storage compared to traditional methods. However, the high cost of hydride-forming materials hinders the implementation of this approach. The use of alloys based on the TiFe intermetallic compound would reduce the costs of metal hydride hydrogen storage by more than five times. This circumstance is the reason for the growing interest of specialists in the field of hydrogen energy technologies in hydrogen-storage materials based on titanium-iron alloys. Although hydrogen systems with the TiFe intermetallic compound and its derivatives have been studied for more than 50 years, the search for ways to increase the resistance of their hydrogen sorption characteristics to poisoning by oxygen-containing impurities in the gas and solid phases has become particularly relevant in recent years. This article provides an overview of research and development aimed at obtaining, studying the properties, and using titanium-iron alloys with improved hydrogen sorption characteristics. An analysis of the data presented in the scientific literature is presented, and approaches to the development of highly efficient hydride-forming materials based on the TiFe intermetallic compound and hydrogen-storage systems based on them are formulated.

Abstract

The industrial production of carbon sorbents from coal is a promising and relevant direction. The starting material is mainly brown coal, which is characterized by a high yield of volatile substances and low ash content. Of particular interest to the coal industry is the development of technology for producing sorbents from low-grade coals with a large specific surface area, high adsorption activity, and low cost. Existing methods for producing sorbents from coals that meet such criteria should be based on various thermophysical principles of influence on the source material. The work investigated one-stage and two-stage methods for producing sorbents from coal grades D and DG mined in Kuzbass. The one-stage technique consisted of steam gasification of the starting material in a fluidized bed. The two-stage technique was based on preliminary decarbonization in a muffle furnace followed by activation with superheated water vapor in a fluidized bed. As a result of experimental studies, samples of carbon sorbents were obtained from coals of low metamorphism. Analysis of textural characteristics showed that the specific surface area of the sorbents is up to 250 m²/g and adsorption activity up to 100 mg/g. It has been established that the composition of the mineral mass of the original coals significantly affects the adsorption activity of the resulting sorbents. Estimates show that the higher the ash basicity index, the higher the adsorption activity of the resulting carbon sorbent. With a one-stage method for producing sorbents from coal grades D and DG in a fluidized bed, a fairly high specific surface area is achieved with a relatively low adsorption activity in comparison with a two-stage method.

An Erratum to this paper has been published: https://doi.org/10.1134/S004060152403011X

Abstract

Given the growing share of nuclear power plants in the energy systems of the European part of Russia and the shortage of flexible generating capacities, there is a need to attract nuclear power plants to participate in covering the variable part of the electrical load schedule. The use of storage units, such as latent heat thermal energy storages (LHTES), capable of storing thermal energy received from nuclear power plant reactor units during off-peak hours in the power system and using it during peak load hours to generate electricity will improve the system efficiency of nuclear power plants. Based on the analysis, promising phase change materials (PCM) were identified for operation in thermal storage systems at temperatures from 200 to 300°C, which is determined by the characteristics of the steam turbine plant of a nuclear power plant, including the parameters of feed water and main steam. For the adopted process circuit of an installation with an LHTES with an increase in the temperature of the feed water after the high-pressure heaters of an indirest steam cycle nuclear power plant, the methodological basis for choosing design solutions for the storage system with lithium nitrate as a phase change material has been developed. Using the finite element method in a computer software package, modeling of unsteady heat transfer between this material and water for finned and unfinned pipes was carried out in relation to the LHTES elementary section. Based on the calculation results, graphs of the dependence of the thermal power of the section on the LHTES discharge duration were constructed. Methods are proposed for calculating the duration of LHTES discharge and the mass of the required phase change material when reducing thermal power. For a process circuit with an additional steam turbine unit with a capacity of 12 MW (for NPP power units with VVER-1200), the main characteristics of the latent heat thermal energy storage and the effectiveness of the proposed solution for different LHTES discharge durations are determined.

Abstract

Anion-deficient structures based on ({text{S}}{{{text{r}}}_{{0.5}}}{text{B}}{{{text{a}}}_{{0.5}}}{text{C}}{{{text{o}}}_{{1 - x}}}{text{F}}{{{text{e}}}_{x}}{{{text{O}}}_{{3 - delta }}}) synthesized from a melt in a stream of concentrated solar radiation with a density of 100–200 W/cm² created in a large solar furnace (LSF) were studied. Briquettes in the form of tablets made on the basis of a stoichiometric mixture of carbonates and metal oxides (({text{SrC}}{{{text{O}}}_{3}}) + ({text{BaC}}{{{text{O}}}_{3}}) + ({text{C}}{{{text{o}}}_{2}}{{{text{O}}}_{3}}) + ({text{F}}{{{text{e}}}_{2}}{{{text{O}}}_{3}})) were melted in a water-cooled melting unit in the LSF focal zone. Drops of the melt flowed into the water in a container located 40 cm below the melting unit. Such conditions contributed to the cooling of the melt at a rate of 10³ K/s. The castings were ground to a grinding fineness of 63 microns, dried at 673 K, and samples were molded from the resulting powder using semidry pressing (at a pressure of 100 MPa) in the form of tablets with a diameter of 20 mm and a height of 10 mm. The tablets were sintered in air at a temperature of 1050–1250°C. The structure, water absorption, and electrical properties of the finished samples were studied. The crystal lattice of the material had a perovskite structure with a unit cell parameter A = 4.04 × ({{10}^{{ - 10}}}) m of space group Рm3m. The area of homogeneity of compositions ({text{S}}{{{text{r}}}_{{0.5}}}{text{B}}{{{text{a}}}_{{0.5}}}{text{C}}{{{text{o}}}_{{1 - x}}}{text{F}}{{{text{e}}}_{x}}{{{text{O}}}_{{3 - delta }}}) corresponded to the interval x = [0; 0.7], where x is the amount of element introduced instead of the main one. The most optimal composition in terms of stability of structure and properties was ({text{S}}{{{text{r}}}_{{0.5}}}{text{B}}{{{text{a}}}_{{0.5}}}{text{C}}{{{text{o}}}_{{0.8}}}{text{F}}{{{text{e}}}_{{0.2}}}{{{text{O}}}_{{2.78}}}). The average crystallite size of the obtained materials is 30–40 μm. The grains are predominantly in the form of spherulites and curved cylinders. Samples of the material showed high resistance to water vapor. The values of structural parameters indicate that the material made from ({text{S}}{{{text{r}}}_{{0.5}}}{text{B}}{{{text{a}}}_{{0.5}}}{text{C}}{{{text{o}}}_{{0.8}}}{text{F}}{{{text{e}}}_{{0.2}}}{{{text{O}}}_{{2.78}}}) can be used as a catalyst in the generation of hydrogen and synthesis gas through reforming and oxidation of methane.

Abstract

Two design options for a heat-recovery turbine unit (HRTU), which generates electricity for self-contained power supply of gas mains’ compressor stations (GMCSs) using the heat of exhaust gases from gas-turbine engines (GTEs) driving gas-pumping units (GPUs), are examined. The working fluid of the recovery circuit is octafluorocyclobutane (c-C₄F₈, engineering name is RC318) in one of the two HRTUs and the exhaust gases of GPU GTE in the other HRTU. The HRTU operating on RC318 has a three-circuit cycle, including three turbines, three recuperative heat exchangers, three RC318 heaters, and one common condenser. An alternative design of HRTU is a vacuum-type GTU consisting of an overexpansion gas turbine, whose inlet is connected with the exhaust of GPU GTE, exhaust gas coolers, a cooled gas compressor, and an induced-draft fan. The excess power of this HRTU above the current power demand at the GMCS is used to create a vacuum at the exhaust of the gas turbine of the GPU GTE. The results are presented of the comparative balance calculations of parameters and characteristics of both HRTUs as applied to a 16-MW Ural GPU GTE. They were performed using the updated initial data and the software library RefProp (in the CoolProp high-level interface) for the calculation of thermodynamic parameters of working fluids. It has been demonstrated that a more compact and easier to implement gas-type HRTU (with an overexpansion gas turbine), although having a lower power than the RC318-type HRTU, can still fully cover the demand of the GMCS for high-quality power and also to solve the problem of substituting imported gas piston and diesel generators at the GMCS within the shortest possible time and with the lowest capital and operating expenditures.