Thermal Engineering最新文献

A concept has been proposed for the creation of regional liquefied natural gas (LNG) fuel complexes on the basis of thermal power plants, ensuring the expansion and reliable functioning of the gas fuel market. The concept provides for the transfer of fuel reserve systems for electric power facilities to LNG, which is produced directly at power plants, as well as the supply of LNG from power plants to regional consumers. A description of a foreign installation for extinguishing gas consumption peaks is given: the closest analogue of a power plant with an LNG fuel backup system. A comparative technical and economic analysis of projects for the construction of a fuel oil facility and an LNG backup fuel system for CHPP-22 of PAO Mosenergo showed that, with comparable capital costs, backup using LNG can provide an economic effect of up to 654 million rubles per year at 2023 prices. If there are large volumes of LNG storage, peak fuel shipments to consumers can be ensured, and the standard reserve will be restored using a liquefaction unit. Data are provided for calculating the costs and investments required to create complexes that guarantee the maintenance of standard emergency fuel reserves in the form of LNG for the CCGT-220 power unit (1778 million rubles excluding VAT). A methodology has been proposed for allocating the costs of a complex of emergency fuels, attributable to the cost of electric power and LNG sold to third-party consumers. It is shown that the relative increase in capital costs for the construction of CCGT-220 with emergency fuel in the form of LNG in relation to similar costs for a power unit with emergency diesel fuel is 1%. The cost of in-house LNG production has been assessed. Savings during the initial formation of standard emergency reserves for the power unit amounted to 72.45 million rubles. The advantage of creating a network of LNG complexes is formulated: reserve and emergency fuel reserves at thermal power plants provide a reliable fuel supply to regional markets.

Monitoring of thermal efficiency is of utmost importance for securing efficient NPP operation. To this end, the measurement instruments should have accuracy sufficient for the possibility of determining the actual values of thermal cycle circuit parameters, thermal efficiency, and deviations of the turbine set characteristics from their standardized indicators. The error with which the reactor thermal power is determined using the reactor core thermal-physical parameters and the steam generator parameters is estimated. It is shown that the best accuracy of determining the reactor thermal power can only be achieved through improving the accuracy of determining the steam generator thermal power. An analysis has shown that the error of determining the reactor thermal power is by more than 95% due to the error of determining the feed water flowrate. If we succeed in achieving more accurate determination of the reactor thermal power, it will be possible to obtain more accurate data on the electricity generation during operation at the nominal parameters in the mode with a specified neutron power due to maintaining of the reactor plant’s actual thermal power closest to its design value; in addition, it will be possible to extend the range of power outputs available for operation during operation in the mode of maintaining the specified electric power output by increasing its maximal value. Given the specified period of NPP operation, the maximum of its energy production serves as one of the criteria for economically efficient NPP operation. By using the developed mathematical model of the turbine set used in the NPP constructed according to the AES-2006 conceptual design (with a VVER-1200 reactor), the authors have revealed the effect of the error of determining the thermal cycle circuit parameters on the power unit electric power output and the parameters that have the highest influence on the error of estimating the electric power output. The influence of the error of determining the turbine thermal parameters, moisture separation and steam reheating, high- and low-pressure regeneration, and the turbine set low-grade heat part was analyzed, and the total error of determining the electric power output has been obtained based on the analysis results. These data make it possible to formulate the requirements for the accuracy of flowrate, temperature, and pressure measurements depending on the allowable error of determining the electric power output. An analysis of the operational data of the Leningrad-2 NPP, Novovoronezh-2 NPP, and Belarussian NPP power units has shown that the potential of increasing the electric power output due to improved accuracy of determining the thermal cycle circuit parameters makes 10–15 MW.

If severe accidents occur at nuclear power plants with light water coolant, large quantities of hydrogen may be released as a result of the zirconium-steam reaction. In order to avoid explosive consequences, hydrogen passive autocatalytic recombiners (PAR) are installed in the containment to remove hydrogen flamelessly. To substantiate the hydrogen explosion safety of nuclear power plants using computer modeling, calculations of the state of the vapor-gas atmosphere inside the containment are performed, taking into account the presence of PAR. Experimental data are needed to validate computational models of recombiners. The article presents the results of a comparison of experimental and calculated data on the characteristics of the RVK-500 hydrogen recombiner. A brief description of the BM-P experimental stand is given, on which, for the first time in Russia, it was possible to study the operation of an industrial recombiner in abnormal operating modes (start modes and modes with leakage flow). To simulate abnormal operating modes of the recombiner, a CFD model is used, which describes the flow inside the recombiner in a simplified formulation (based on volumetric energy sources and the concentration of components of the vapor-gas medium). A description of the CFD model used to solve the problem of simulating the operation of the BM-P stand with the RVK-500 recombiner installed (inside the measuring chamber) is presented. For the experimental mode with leakage flow, a detailed comparison was carried out with the results of calculations performed for sensor placement points (temperature and concentration of components of the vapor-gas medium). In total, calculated and experimental data on the performance of the recombiner were compared for seven experimental modes, including the normal operation mode of the recombiner under conditions of a quiescent environment.

The scientific and technical literature presents a large number of works dedicated to the experimental study of the critical out flow of saturated and subcooled liquid through cylindrical channels. Despite this, the available sources do not provide an assessment of the extent to which certain geometric parameters and operating conditions of experiments affect the critical outflow. This article is aimed at the analysis of experimental data using statistical methods and machine learning on critical outflow obtained at Elektrogorsk Research and Development Center (EREC, Russia). The purpose of the work is to identify statistical relationships between operating and geometric parameters, as well as to quantify the influence of these parameters on the critical mass flow rate and pressure. The analysis of experimental data for channels with a filleted inlet edge showed a strong influence of the inlet edge shape both on the value of the critical mass velocity and on the final pressure in the outlet section of the channel, which is established at the critical outflow mode. A comparison of the experimental data for channels with different shapes of the inlet section with the same operating and other geometric parameters showed that for channels with a rounded inlet edge, the critical mass velocity is approximately 25% higher than for channels with a sharp inlet edge. As the nozzle throat length increases, this difference decreases asymptotically. Among the regime parameters, the main contribution to the dispersion of the critical mass velocity is made by the undersaturation (subcooling) of the medium at the inlet which comprised 51% of the total influence of the regime and geometric parameters. An increase in the undersaturation and a decrease in the length of the channel throat lead to decrease in the back pressure necessary to establish the critical outflow mode. In extreme cases, the critical pressure ratio (outlet/inlet) can be 0.1, which is significantly lower than the generally accepted value of 0.5 in engineering practice. The results obtained can be used in the future for design of experiments aimed at expanding the range of operating parameters or optimization elements whose operation is based on the phenomenon of critical outflow.

Increasing the energy efficiency of thermal power plants operating according to the Rankine cycle is one of the priority tasks of the Russian energy sector. Despite a significant amount of scientific research, the efficiency of installations of this type still remains low. As a technological solution to increase their efficiency, the authors consider a modernized Rankine cycle in which an aqueous solution of lithium bromide is used as a working fluid, the condensation process of exhaust steam after the turbine is replaced by the process of its absorption, and the second working fluid is an absorbent. The features of the functioning of such a cycle are outlined, and the methodology for its calculation is presented. Studies have shown that the use of lithium bromide solution can reduce the steam pressure after the turbine and increase the useful heat drop as well as the degree of cycle filling. In addition, when the heat of the solution returned from the boiler is regenerated, the average temperature of the heat supply to the cycle increases, which also increases its thermal efficiency compared to the traditional circuit. The energy efficiency of the modernized cycle was analyzed and compared with the traditional Rankine cycle on water vapor. Calculations have shown that the use of a modernized cycle allows increasing thermal efficiency by an average of 1–2% compared to the traditional solution. The indicators characteristic of both steam power and absorption cycles were studied, and graphical dependences of efficiency on the main parameters were derived. The economic effect of using the modernized scheme is to reduce fuel consumption and emissions of harmful substances into the atmosphere in proportion to the reduction in fuel consumption.

The task of energy-efficient heat supply and removal in thermal control, heating and cooling systems is very relevant for many branches of technology. The paper presents the results of the development and study of a 21 m long loop heat pipe (LHP) that is a passive heat-transfer device operating on a closed evaporation-condensation cycle and using capillary pressure to pump a working fluid. These devices can be used in systems where the heat source and the heat sink are removed from each other by a distance measured in meters and even tens of meters, without the use of additional energy sources. The device has a 24 mm diameter evaporator with a 188 mm long heating zone, a vapor line and a liquid line (external/internal diameters of 8/6 mm and 6/4 mm). A 310 mm long pipe-in-pipe heat exchanger equipped with a cooling jacket was used as a condenser. The tests were conducted with the LHP in a horizontal position. Heat was removed from the condenser by forced convection of a water-ethylene glycol mixture with temperatures of 20 and –20°C and a flow rate of 6 dm³/min. The heat load supplied to the evaporator from the electric heater increased from 200 to 1700 W in the first case and to 1300 W in the second. The vapor temperature at the outlet of the evaporator varied from 25 to 62°C and from 24 to 30°C, respectively. Its maximum temperature difference along the length of the vapor line did not exceed 4°C. Such devices can be used in energy-efficient systems for utilizing low-potential heat, heating or cooling remote objects, and for uniformly distributing heat over a large surface area of heat sinks.

The problem of a fully developed turbulent flow and developed heat transfer was solved numerically at a Reynolds number ranging from 5 × 10⁴ to 2 × 10⁵ for a spatially periodic model of a one-sided ribbed channel as a prototype of the flow path of an internal convective cooling system for a gas turbine blade. The flow and heat transfer were investigated at the Prandtl number of 0.7. The channel has a rectangular cross-section with an aspect ratio of 1.5. Square ribs with a 10% rib-to-channel height ratio are installed on one of the wide channel walls at an angle of 45° to the longitudinal axis of the channel. To quantify the effect of ribs on the flow and heat transfer, the integral parameters, such as hydraulic resistance factor and Nusselt number determined from the grid-converged solutions, are compared with the integral parameters for a fully developed flow and heat transfer in a smooth channel predicted by the same numerical method. The results of numerical simulation for the ribbed channel are also compared with published experimental data obtained under partly similar conditions. The predicted hydraulic resistance factor agrees well with the experiment. The predicted heat transfer agrees with the experiment within 11%, but the trends in heat transfer with increasing Reynolds number obtained using numerical and physical simulation are different. This difference may be caused by the fact that fully developed heat transfer could not be attained in the short experimental channel. Analytical power-law dependences on the Reynolds number are obtained for the hydraulic resistance factor and the Nusselt number pertaining to all channel walls and only to the ribbed wall. It is pointed out that the hydraulic resistance factor depends weakly on the Reynolds number, which is typical for local resistances, and the dependences for Nusselt numbers corrected for the specifics of the problem are close to the dependences for near-wall layers and flows in smooth channels.

The article addresses the problem of securing reliable and economically efficient operation of cogeneration combined cycle power plants (CCPPs) taking the PGU-450 unit as an example during its operation at partial loads and performing control of the electrical loads in the condensing mode and heat and electrical loads in the cogeneration mode. The main constraints hindering wide-scale involvement of CCPPs to control of electrical and heat loads are noted. The need to switch the gas turbines, which feature limited capacities of bearing variable loads, into a mild operation mode with shifting the main load on the steam turbine is pointed out. A technology of PGU-450 operation at partial loads is suggested: CCPP unloading in accordance with the operation manual to the gas turbine permissible base load, e.g., according to the environmental constraint during its operation in the condensing mode, and further decrease of the power unit electric output at a constant base power output of the gas turbines and heat recovery steam generators through decreasing the steam turbine output by applying bypass steam admission or shifting a part of the high-pressure cylinder (HPC) or the entire HPS, or the steam turbine as a whole to operate in the generator-driven mode. The article presents the results of applying various bypass steam admission configurations during the CCPP operation in the condensing mode, including when shifting part of the HPC or the entire HPC, and the steam turbine as a whole is shifted to operate in the generator-driven mode when the CCPP is shut down in a standby mode in passing off-peak load hours. It has been shown that the use of bypass steam admission during the CCPP operation in the cogeneration mode is more economically efficient than it is in the condensing mode. The article also shows the advantage, in terms of reliability and economic efficiency, of shifting the steam turbine to operate in the generator-driven mode instead of its shutdown during the PGU-450 unit’s operation in the gas turbine unit‒combined heat and power plant (GTU‒CHPP) mode and passing the electric load curve off-peak hours.

Modern requirements for the production of hydrogen with a minimum carbon footprint, the possibility of using polygenerating systems for production of electricity, heat, or useful products, and chemical-looping technologies for producing hydrogen combined with capture of carbon dioxide are considered. A new system has been developed that integrates the use of biomass as a fuel, chemical looping, and syngas production in a polygenerating system of interconnected reactors, which is very promising in maximizing the effectiveness of hydrogen production without a carbon footprint (or with a negative carbon footprint). A procedure and results of calculations of the composition and consumption of generator gas, material balance of a chemical looping system, heat values of chemical reactions in a system of interconnected reactors, heat balance and temperatures in individual reactors, and heat and material balances in exhaust gas heat recovery units are presented. The effect of the main operating conditions of a chemical looping system on temperatures in the reactors was determined on the basis of the calculated and material balances. The calculated efficiency in terms of hydrogen production (75.93%) is given. This value fits well into the broad outline of the results obtained in simulation of similar systems for chemical looping hydrogen production from metal oxides and can be considered as a guideline when developing engineering solutions within the scope of the proposed process flow diagram. Potential directions of further studies are set.

When using lead as a primary circuit coolant, certain difficulties arise not only from the side of the reactor plant (structural materials, fuel, etc.) but also from the side of the steam turbine cycle. A feature of the second circuit of a lead-cooled NPP is noted, such as the need to maintain a high temperature of the feedwater in front of the steam generator, caused by its melting/freezing temperature. For the pilot demonstration power unit with the BREST-OD-300 reactor plant, it was decided to use a mixing feedwater heater, which entailed the appearance of a second rise in the feed pump circuit. Due to the lack of electric drive pumps for such high parameters, it was proposed to use a hydraulic turbine driven pump as a feed pump behind the mixing feedwater heater. These pumps have a significant impact on efficiency due to the multistage energy conversion, and there is no recommendation for selecting resistance on the control valve of these pumps. A computational study was carried out to determine the optimal pressure drop on the control valve of the hydraulic turbine drive of the feed pump of the power unit with the BREST-OD-300 reactor plant. Optimal is understood as the ultimate minimum differential at which the valve is able to carry out regulation with specified quality criteria and ensure the lowest energy consumption for its own needs. Recommendations are given for choosing the optimal pressure drop on the control valve of the hydraulic turbine drive of the feed pump of a turbine unit with the BREST-OD-300 reactor. A methodology has been developed for solving problems of optimizing pressure drop in units of complex hydraulic systems.