Numerical simulation of fuel staged swirl combustion in the invert furnace of boiler on advanced ultra-supercritical steam parameters

The paper considers the schemes of Kuznetsky lean coal combustion for the M-shaped boiler. With such a boiler profile, it is possible to significantly reduce the length of main steamlines, which is especially important for the advanced ultra-supercritical parameters of the superheated steam. The furnace in this boiler unit is performed downward (invert). In this work, the aerodynamics of 6 combustion schemes was simulated by means of computational fluid dynamics. All considered schemes were designed on the basis of direct-flow burners and nozzles. For the most aerodynamically reasonable scheme the thermal processes in the boiler furnace firing Kuznetsky lean coal have been simulated by means of computational hydrodynamics. The simulation results showed a high efficiency of fuel burnout: loss due to unburned combustible equaled 0.1%, carbon-in-ash loss equaled 0.8%. Carbon monoxide concentration at the furnace outlet in conversion to excess air equal α = 1.4 amounted 226 mg/m3, the nitrogen oxides concentration in the flue gases (in conversion to normal conditions) equaled 424 mg/m3. It is appropriate to use the results obtained in this research in the development of new solid fuels combustion schemes.

CRITICAL FLOW PREDICTION MODELS FOR THE COOLANT AT SUPERCRITICAL PARAMETERS

An interest of the problems of various thermophysical and hydrodynamic phenomena in the nuclear industry, determined by the real application in the field of analysis of the accident scenarios related to the loss of coolant accident. For the generic super critical water reactor the meaning of the problem at the initial stage of the critical flow process, is the existing of the uncertainty in the accepting boundary conditions to predict the flow characteristics. The article provides an analytical review of existing approaches for describing the critical flow phenomenon of the medium and to focus on the current predictive models. A description of the physical nature of such a phenomenon is provided. The scope of consideration includes information from the literature for single and two-phase flow, taking into account their physical basis and the assumptions made. The task of the work was to analyze the information found and to evaluate and update the data on the application of the models to obtain the critical characteristic. It was supposed to highlight the physical aspects and peculiarities of this phenomenon, as applied to the coolant at supercritical parameters. To formulate important requirements to the representative critical flow model for the possibility of its use in the system codes for evaluation of the nuclear safety problems of promising fourth generation nuclear reactors.

Turbo-Expander Units on Low Boiling Working Fluids

The article examines the possibility of increasing the efficiency of the turbo-expander cycles on low-boiling working fluids using those methods that are used for steam turbines, viz. increasing the parameters of the working fluid before the turbo-expander and using secondary overheating. Thus, four schemes of the turbo-expander cycle are considered: the one without overheating of the low-boiling working fluid, the one with single overheating of low-boiling fluid, the one with double overheating and the one with double overheating at supercritical parameters. All the studied cycles were considered with a heat exchanger at the outlet of the turbo expander, designed to heat the condensate of a low-boiling working fluid formed in the condenser of the turbo expander unit. Cycles in P–h coordinates were built for the studied schemes. The method of thermodynamic analysis of the studied cycles based on the exergetic efficiency has been developed. The results of the research are presented in the form of Grassman-Shargut diagrams, which show exergy losses in the elements of the studied cycles on a scale, and also show the positive effect of the operation of the turbo-expander cycle in the form of electrical power. The analysis of the obtained results showed that the main losses that have a significant impact on the exergy efficiency are the losses of exergy in the recovery boiler. The increase of parameters of low-boiling working body, and the use of intermediate superheating reduce losses in the waste heat boiler and, consequently, increases exergetic efficiency of turbo-expander cycle. The turbo-expander cycle with double overheating at supercritical parameters of the low-boiling fluid is of the largest exergetic efficiency out of the schemes that have been examined.

Influence of flow conditions on the distribution of thermal stresses in the waterwall tubes connected by fins

In this study are presented results of numerical analysis of the thermal conditions of smooth waterwall tubes connected by fins and heated with equal heat flux. Inside tubes flows the water at supercritical parameters. The thermodynamic parameters at the inlet to each tube are similar but the mass flow of the fluid differs in each tube. Numerical model used for analysis allows to determine the temperature distribution, in online mode, in every control element of the analysed tubes and in the finite elements of the working fluid depending on the current thermodynamic parameters of the fluid and tubes. After calculation of the temperature distribution field, it can be used to determine the thermal stresses distribution in tubes and fins and determine the parts of elements, where the maximum values of the thermal stresses occur. The presented analysis was carried out for comparison of the thermal stresses distribution in small fragment of the combustion chamber wall in case of changing the fluid mass flows in neighbouring waterwall tubes.

Problems of abnormal dynamics of thermal hydraulic processes in prospective reactors with supercritical parameters of light water coolant

A complex of scientific and technical problems directly related to the priority of ensuring the operational safety and reliability of the cores of promising power nuclear reactors with supercritical thermodynamic parameters of a light-water coolant is systematized. The problems of implementation of effective heat removal from the surface of fuel elements and ensuring reliable calculation of thermal and hydrodynamic processes in turbulent flows of a supercritical coolant are considered. The main attention in the consideration of thermohydraulic processes in the near-critical region is paid to the conditionality of the physical nature of these processes by the regularities of transformation of the thermophysical properties of the coolant with changes in its temperature. It is noted that these phenomena have not been sufficiently studied and that modern designers of nuclear reactors with supercritical parameters practically do not have physically substantiated adequate ideas about the physical nature of an emergency mode of deteriorated heat transfer, which can arise unpredictably on the surface of a fuel element even if it is continuously cooled by a coolant with supercritical parameters. It is only known that the main physical sign of the occurrence of this emergency mode is a significant deterioration in heat transfer, which becomes abnormally low, but the physical reasons for such a dangerous anomaly are currently unknown. Based on the analysis of the molecular kinetics data of the near-wall coolant layer, it was proposed to consider such facts of an emergency decrease in the heat transfer intensity due to the appearance of an unknown pseudo-film boiling regime on the fuel element surface. In this context, it is shown that under the conditions under study, macromolecular assemblies in the form of pseudo-vapor formations can appear on the heat exchange surface, as a result of which the heat transfer on the fuel element surface is disturbed. Using experimental data, it is shown that there is a rather deep physical analogy between heat transfer in a supercritical thermodynamic system and the subcooled boiling process at subcritical parameters of the coolant. The dynamics of changes in the characteristics of the experimental spectra of acoustic emission of pseudo-boiling with a sequential increase in the thermal load is analyzed and it is shown that these phenomena can, in principle, be used in promising systems for diagnostic monitoring of reactors with supercritical parameters for early detection of the initial phases of pseudo-boiling and prompt prevention of the occurrence of emergency modes of deteriorated heat transfer

Subcritical Thermodynamic Cycles with Organic Medium and Isothermal Expansion

The efficiencies of the Organic Rankine Cycle (ORC) are not very high and only very seldom do they exceed 20%. The increase and optimization of initial parameters and certain modifications of the thermodynamic cycle make it possible to overcome these drawbacks. A new modified cycle has been described and analyzed in detail in the paper. Similarly to the Ericsson cycle for gas turbines, isothermal expansion in the turbine is suggested for the power plant with organic media. The new cycle and the typical ORC power plants have the same block diagram. The only difference is that expansion in the proposed cycle occurs not adiabatically but as an isothermal process. The thermodynamic calculations have been carried out for 11 various fluids and 4 different cycles. The obtained results have clearly shown that cycles with isothermal expansion (isothermal turbines) are characterized by remarkably higher efficiency than typical power plants with adiabatic turbines. The increase in efficiency varies from 6 to 12 percent points for cycles with saturated live vapor and from 4 to 7 percent points for cycles with superheated live vapor. The performed analyses have shown that it is possible to achieve a very high efficiency (over 45%) of organic cycle, which is a very competitive value. In such cases the proposed power plants can achieve an efficiency which is higher than that of modern steam turbine plants with supercritical parameters.

Problem issues of cores thermal-hydraulic calculation for prospective water-cooled reactors with supercritical parameters

The fundamental thermophysical features of the heat exchange process between the heated wall of a vertical channel and the light-water coolant of supercritical parameters concerning the conditions of heat-generating assemblies channels and cores of perspective energy nuclear reactors are considered. The available methods and recommendations for determining the limits of thermal load are analyzed. It is a guarantee the absence of the characteristic dangerous mode possibility of deteriorated heat exchange in these conditions and corresponding sharp rise in the channels wall temperature, which threatens their destruction. The physical nature of the occurrence of degraded heat transfer regimes remains unclear, and the existing approaches to the implementation of thermohydraulic calculation in such conditions are not sufficiently justified. The complex nature of intercellular heat and mass transfer in the fuel assembly and the presence of individual thermohydraulic cells with reduced levels of heat transfer intensity indicate that the existing method of determining the area of degraded heat transfer in the reactor core channels with supercritical parameters of the coolant is significantly simplified. Insufficient data and research results have been revealed to create adequate methods of heat-hydraulic calculation, suitable for taking into account the peculiarities of the heat transfer process complex flow under conditions of supercritical parameters of the coolant. The application of such methods should be the basis for ensuring the safe operation of prospective reactors and minimizing potential losses of a different nature from accidents caused by the destruction of cores through unacceptable heat transfer modes. To this end, the main direction of further research is identified.

Main Directions of Russian Developments of Prospective Structures of Water-Cooled Supercritical Pressure Reactors

An analytical review of the evolution of attempts to create, schematic and constructive solutions for energycooled nuclear reactors with nuclear steam overheating and supercritical parameters of the working fluid in the conditions of the former USSR and the Russian Federation was made. A comparison of a number of major technical and economic characteristics of main developments of tube and tank reactors is made, the available information on the results of experimental and industrial operation of AMB reactors structures is considered, their advantages and disadvantages are evaluated in terms of technical perfection, reliability, technical and economic performance as well as environmental safety. The expected reduction in capital costs of 40% during the transition of nuclear power units with a capacity of 1,000 MW to single-circuit promising SCWR reactors is achievable only if the steam temperature rises to 625 °C, which has not yet been mastered even in traditional power engineering. The specific energy intensity of reactor’s active zones promising Russian developments under the SCWR program is in most cases extremely high, which will have a negative impact on the characteristics of nuclear safety. The conclusion is made concerning the high probability of a significant increase in the accident rate of the SCWR reactor cores, due to the insufficient study of the heat transfer process characteristics on the heat transfer surface of the TVEL under the conditions of supercritical parameters of the coolant, in particular, such phenomena as pseudo film boiling and thermoacoustic vibrations. In general, insufficient level of completeness of the latest Russian developments and lack of final conceptual projects were noted, which does not provide sufficient grounds for choosing promising schematic and constructive decisions necessary for making reasonable forecasts about the possibility of using supercritical parameters of the coolant in the modern nuclear power industry in the near future.

Development and investigation of means of transportation, storage, gasification and refueling of cryogen liquids of space systems

The paper describes the development of hydrogen, oxygen, LNG (tank cars, container cars) stationary devices based on the existing constructions. The investigation results of liquid hydrogen losses on experimental cryogenic storage and transport tanks with different thermal insulation (multilayer-vacuum, powder-vacuum, screen-vacuum (with a nitrogen screen of different designs)) are presented. The paper presents the results of research on obtaining and maintaining pressure in the tank of a gasification plant with hydrogen supercritical parameters for long-term product delivery to the customer at variable or constant flowrate, both using an external source of hydrogen and a part of the hydrogen supplied to the consumer as a heat carrier. The paper presents a method and equipment of refueling the Orbiter fuel tanks with high-purity hydrogen for variable hydrogen mass and different number of tanks.