Thermal Engineering最新文献

The temperature of condensed phase particles formed during flame combustion of peat from Kirov oblast in a BKZ-210-140F boiler was studied using a pyrometric method. The authors elaborated an experimental-and-calculation procedure for pyrometry of the furnace enabling determination of the temperature of condensed phase particles (of coke and ash) in the gas phase transparency band. The measurements were taken using Raynger R3I 2MSC and Kelvin 2300 PLTs pyrometers having radiation receivers operating at a wavelength of 1.6 µm and in a spectral range from 1.0 to 1.6 µm, respectively. Dependences are obtained of the temperatures measured at different heights from the boiler furnace bottom to the measurement point (hereinafter referred to the boiler furnace height) (H = 9, 14, and 16 m), on the emissivity set on the pyrometers in the range from 0.1 to 1.0. Spectral and integral radiative energy flux densities sensed by the pyrometers were calculated. Brightness temperatures observed during peat combustion were determined. The software package developed by the authors was used for computational studies of the condensed phase emissivity as a function of the specified temperature considering the fuel burnout along the furnace height by solving the radiative transfer equation for a multicomponent radiating, absorbing, and scattering medium. The intersection of the experimental and predicted functions gave the emissivity and true temperatures of the condensed phase particles. According the measurements taken by the Raynger pyrometer, the particle temperature in the flame root part (H = 9 m) is equal to 1453 K; it is 1226 K in the flame middle part (H = 14 m) and 1334 K in the flame tail part (H = 16 m). For the Kelvin pyrometer, these temperatures were 1471, 1265, and 1343 K, respectively. The obtained particle temperatures enabled us to assess the risk of melting of the mineral part of the fuel and slagging of the furnace.

The article presents a review of the embodiments, in terms of construction material used (or shortly material embodiments), of the main heat transfer devices, namely, a vapor generator, condenser, and regenerative heat exchanger in the case of their optimal—in the authors’ opinion—use in the design of a thermal oil ORC unit. A shell-and-tube type device was considered for implementing both the thermal oil heated vapor generator and the water cooled condenser. A semi-welded plate device was also considered as an alternative to the latter. For an air cooled condenser, the material embodiment versions of devices with finned tube and microchannel heat transfer surface, and for the regenerative heat exchanger, versions with a plate-and-finned surface were studied. The choice of the most rational heat transfer, thermal insulation, and structural materials is substantiated with due regard to the specific features of the working media used. The currently-in-force regulatory documents stipulating the material embodiment of heat exchangers with suitable process operating conditions are analyzed, and an attempt is made to put the information in a systematic order using the experience of manufacturers as a basis. It has been found that the published catalogs of industrial equipment do not contain sufficient data on the materials used, technologies for connecting heat transfer elements (tubes with the tube sheet, plates, and heat exchanger components), and working media. As regards the proposals on the choice of material embodiment, they are limited to just one or two solutions. On the contrary, the regulatory documents present more various versions of materials. In the scientific-technical literature, materials that have not been yet put in operation and have not been included in standards are considered; however, they form promising ways for the development of this area. The performed analysis of all of the above-mentioned information sources enabled us to draw up recommendations on the optimal material embodiments for each of the devices considered, which ensure compliance with the unit’s operating conditions, including the temperature ones.

An analysis of greenhouse gas emissions from Russian energy sector was carried out in accordance with the Energy Strategy until 2050, and they were compared with the target indicators of the Low-Carbon Development Strategy of Russia until 2050. It was shown that fundamental trends in the development of global energy—the energy transition associated with the decarbonization of the global economy—were not taken into account when developing the Energy Strategy. The actual refusal to develop renewable energy sources and the failure to use carbon dioxide capture and storage technologies make it impossible to achieve the goal of carbon neutrality for the national economy by 2060, even taking into account the new increased estimates of carbon absorption by Russian forests. Ignoring the global trend towards abandoning coal fuel, recorded by authoritative national and foreign energy agencies (the Institute for Energy Research of the Russian Academy of Sciences, the International Energy Agency), has led to inflated estimates of Russian exports of this type of fuel, the world trade of which will decrease several times by 2050. Refined estimates of methane leaks during oil and gas production in Russia correspond in specific values to the indicators of other major producers of oil and gas resources (the United States and Canada), but are approximately two times lower than those obtained from the Earth’s remote sensing data. The main provisions of the two strategic documents on Russia’s development until the middle of the century contradict each other to a certain extent and, therefore, cannot be implemented simultaneously. The result of these contradictions could be Russia’s refusal to fulfill its pledges to decarbonize the economy and its withdrawal from the Paris Agreement, which will undoubtedly exacerbate the confrontation with growing global trends.

The problem of deep purification of industrial gases of various impurities is urgent. The purification is usually performed using adsorption and absorption technologies, which are implemented using two-phase turbomachines with bulk condensation of the impurity in the flow path. The study is devoted to numerical simulation of the process of bulk condensation in the flow path of a radial-type refrigeration turbomachine, which is controlled by changing the flow-expansion ratio in the turbine. It is a direct continuation of the work wherein control of the process by changing the initial flow temperature was investigated. The working fluid was a mixture of air as an incondensable gas carrier and carbon dioxide as an impurity. It has been demonstrated that the process of bulk condensation proper and its depth can be controlled by changing the flow-expansion ratio. The conditions have been determined at which the process is localized predominantly in the impeller channels thereby reducing the risk of erosive wear and subsequent damage to the stage elements. For the first time, the reduction in the isentropic efficiency caused by condensation controlled by changing the flow-expansion ratio was numerically estimated for refrigeration turbomachines. The obtained data are close to the values for wet steam turbines presented in the literature. A procedure for calculating the characteristic and analyzing the results has been developed. It yields the optimal regimes using a multicriteria search with the requirements for the region where the phase transition should occur, and for the mean radius of the particles. It is shown that changing the expansion ratio may be insufficient to meet the specified requirements for the degree of condensation and isentropic efficiency offering deep purification of gases of impurities. Therefore, assessment is required as to whether the process rate can be controlled by changing the expansion ratio, the initial flow temperature, and the impeller speed.

Considered are NHFR or net heat flux reduction data in order to illustrate and quantify turbulent thermal convection phenomena within a unique and intricate cooled film environment along the extremity end of a transonic turbine airfoil with a rim in the form of a squealer. Of particular focus are the consequences of modifying the magnitude of GAP (tip gap magnitude) which is adjacent to the outer end of the airfoil. Data are given for a variety of cooled film ratio of blowing conditions, as the coolant film is provided by two separate plenums that are connected to a row of holes which are located along the top segment of the concave surface of the blade, as well as to two dusting cooled film holes located on the end extremity of the blade. Line-averaged NHFR data show different dependence upon RoB_u and RoB_d ratios of blowing, depending upon the magnitude of GAP. Especially for the trailing edge portion of the squealer tip surface of the airfoil, NHFR data vary significantly with aft ratio of blowing RoB_d for the 1.2 mm or smaller GAP arrangement, whereas very little variation with RoB_d is present for the 2.0 mm or larger GAP environment. Here, GAP is the thickness of the flow gap at the blade tip. In addition, line-averaged NHFR data associated with the smaller GAP are often higher than values associated with the larger GAP, when compared for the same squealer surface airfoil tip locations, and at the same approximate RoB_u and RoB_d ratios of blowing. The flow and local static pressure variations within tip gap regions, which vary as the magnitude of GAP is changed, are less influential in regard to the data associated with the top portion of the concave surface of the two-dimensional airfoil. The impact of the present arrangements and configuration is new and unique NHFR results for different GAP values for complex boundary layer and separation flow environments, which are different from all other data which are available within the archival literature.

The article presents the results of an analysis of applied and fundamental research carried out by leading global universities and companies on burner devices designed for burning liquid hydrocarbon fuels in the presence of superheated water vapor used in thermal power engineering, including those developed taking into account patent information. Directions for increasing the efficiency of burner devices and their main developers and manufacturers have been identified. On the market of liquid fuel burners used in thermal power engineering, there are universal burners designed for burning different fuels, including substandard ones. Such burners are difficult to maintain, and their operation is accompanied by loud noise and emissions of harmful substances into the atmosphere. Despite the significant shortcomings of liquid fuel burners offered on the market, steam burners are not being introduced into industry, remaining at the stage of pilot industrial samples. Improvement of burner devices is aimed at solving such problems as energy saving, reduction of emissions of harmful substances, simplicity of devices, and their versatility in the type and quality of fuel burned. Companies in the United States, Japan, China, the Republic of Korea, and Russia are conducting research and actively filing patents for burner devices, with the Kutateladze Institute of Thermophysics (Siberian Branch, Russian Academy of Sciences (IT SB RAS)) being among the top ten patent holders. Steam burners are patented for use in 25 areas of technology, primarily in the field of “thermal processes and apparatuses.” Moreover, patent-holding companies hardly sell patents for burner devices and their elements and do not provide licenses for their use but use them in their own production. The work carried out by the authors allows us to determine the level of third-party technologies in comparison with the technologies of the Kutateladze Institute of Thermophysics (Siberian Branch, Russian Academy of Sciences) and to develop recommendations for further research based on patent, scientific, and other published information.

A software system for estimating the performance of a steam turbine condenser has been developed on the basis of its mathematical model, which takes into account the condenser interaction with the main ejector. The software system performs a number of key functions for diagnostics of condensing installations; in particular, it ranks the factors causing a growth of pressure in the condenser in comparison with its standard value in their significance and determines the decrease of electric power output resulting from deviation of each of the factors from their standard values. A distinctive feature of the developed software system is that it takes into account the interaction between the condensers and main ejectors in a wide range of steam loads and air in-leakages in the vacuum system, and the effect of this interaction on the turbine unit technical and economic indicators. It has been determined that, according to the results of the accomplished comparison between the predicted and standard data (i.e., verification), the accuracy of computation according to the mathematical models is more than sufficient for settling matters concerned with operational diagnostics of the condensing installation considered. By using the software system, one can analyze the steam turbine unit condenser performance, reveal the main factors causing degradation of its performance indicators, and make provisions for the measures on removing the revealed drawbacks and adjusting the most efficient condenser operation modes. By using the software system, it is also possible to construct the condenser standard and actual characteristics in the entire really permissible range of influencing parameters, diagnose the condenser heat transfer surface condition for any steam turbine units at combined heat and power plants (CHPPs) when specifying the necessary and sufficient input data on the design parameters of condensers and ejectors, and after carrying out the verification.

Units implementing the organic Rankine cycle (ORC) can utilize dozens of low-boiling substances, also called freons or refrigerants, as the working fluid. However, the classic solution for this cycle is the application of pentane and, therefore, this technology is sometimes called pentanoic. One of the main elements of the ORC unit circuit is the condenser, which is often a shell-and-tube heat exchanger cooled with circulating water. In spite of wide application of such apparatuses in steam turbine units, the elaboration of their design on the basis of the pentane technology is a challenging problem. For a prototype of this apparatuses, the KTR shell-and-tube condenser, which was previously often employed in refrigeration units with R12 refrigerant, is adopted in this work. Since chlorofluorocarbons and hydrochlorofluorocarbons have been phased out, equipment items intended for their application are also no longer manufactured by industry, which resulted in a shortage of information on their design and peculiarities of their design process. Hence, the authors carried out a search for and analysis of information about such apparatuses and developed and verified a procedure of design calculation of this equipment. In addition, models for calculating the heat-transfer coefficient during pentane condensation on tube bundles with rolled fins were reviewed, and these models were verified against experimental data on the condensation of propane, one of the closest homologues of pentane. The model proposed by A. Briggs and J.W. Rose has been found to yield the highest accuracy in engineering calculations of pentane condensers. Other models are also examined, which describe the effects of vapor shear and inundation of the lower tubes in the bundle on the heat-transfer coefficient during pentane condensation. It has been demonstrated that considering these effects during condensation of pentane and its homologues in the examined apparatus is impractical. The results of the design calculation of shell-and-tube condensers of pentane with a capacity of 173- and 2280-kW are presented. Recommendations for further optimization calculations are formulated.

A kinetic model is presented describing the formation of lead oxide vapor in the volume of a vapor bubble in the lead melt with its subsequent dissolution in the lead melt and crystallization in the bubble. The model is implemented in the approximation of homogeneous distribution of reagents and oxidation reaction products in the bubble volume. It is shown that vapor bubbles in the lead melt volume may be considered as chemical “microreactors” producing lead oxide vapor and nanoparticles in the bubble volume. The paper presents the results of calculation by a homogeneous model of the lead oxide vapor concentration in the bubble volume as a function of time and of the conditions for the possible formation of a soluble oxide shell on the bubble surface. The model includes mechanisms controlling lead evaporation and oxidation of lead vapor as it interacts with water vapor in the bubble volume and crystallization of lead vapor on the bubble inside surface with formation of a solid phase shell. Partial transformation of vapor bubbles into gas–vapor bubbles with an oxide shell could potentially affect their further behavior in the lead coolant. However, subsequent transport of the bubbles in the coolant circuit will lead to the dissolution of the oxide shell in the sections with the coolant at a higher temperature that will neutralize this negative effect. Moreover, formation of an oxide shell around the vapor bubbles can cause temporary trapping of hydrogen in the bubble volume.

Due to the continuous growth of municipal solid waste (MSW) volumes, their disposal with minimal negative impact on the environment is becoming a very urgent task. Thermal recycling of MSW is one of the most effective methods of their disposal because it allows not only to significantly reduce the volume of waste but also to obtain thermal and electrical energy. However, this process is accompanied by the formation of nitrogen oxides (NO_x), which contribute to the formation of smog and acid rain and negatively affect the environmental situation and public health. Therefore, the reduction of NO_x emissions is an important task for enterprises burning MSW with the release of electricity and heat to consumers. The article discusses selective noncatalytic reduction (SNCR) technologies used to reduce NO_x emissions at factories in Moscow oblast. The rationale for key technical decisions is presented, including the choice of reducing agent (urea), transport agent (air), and the reagent-injection system through nozzles arranged in three tiers. The results of calculations of the trajectories of the urea–air mixture jets in the cross-flow of flue gases are presented, confirming the effectiveness of the proposed configuration of the reducing agent supply system. It is shown that the use of air as a transporting agent in combination with the adopted nozzle placement scheme ensures uniform distribution of the reagent in the high-temperature zone, which increases the efficiency of NO_x reduction. The obtained results of the calculation studies can be used for further optimization of the SNCR system operation as well as for conducting operational tests at facilities engaged in MSW utilization.