Showing papers in "Thermal Engineering in 2015"

The influence of heat transfer conditions on the parameters characterizing the ignition of coal-water fuel particles

Abstract: The future of thermal power engineering both in Russia and abroad will depend in many respects on the use of coal as main fuel for generating heat and electricity. In this connection, matters concerned with development and introduction of new environmentally friendly and energy efficient coal firing technologies are becoming of much importance. Firing coal in the form of coal-water fuel is one of the most promising solutions. However, despite a rather long history of its development (more than 40 years), this technology has not found wide use as yet, which in all likelihood is due to lack of full mathematical and physicochemical models describing the processes that take place when a coal-water fuel particle undergoes thermal treatment and ignition. The article presents the results obtained from numerical solution of the coal-water fuel particle ignition problem taking into account simultaneously occurring main thermal treatment processes (thermal conductivity, water evaporation, filtration heat and mass transfer, thermal decomposition of the fuel organic part, and thermochemical interaction between water vapor and coke carbon). The ignition problem is solved using the finite difference method. For calculating the evaporation process taking into account nonequilibrium nature of the parameters at the interface boundary of the initial “coal-water fuel—dry coal” system, the method of capturing the phase transition front at the difference mesh node was used. The results obtained from numerical modeling were used for determining the conditions and parameters characterizing the ignition of coal-water fuel particles under the conditions typically existing in the furnace space of boiler units. The extent to which radiant heat transfer influences the ignition delay time is determined. It is shown that radiant heat transfer plays a determining role in the thermal preparation of fuel for ignition.

Unsteady heat transfer during subcooled film boiling

Abstract: Cooling of high-temperature bodies in subcooled liquid is of importance for quenching technologies and also for understanding the processes initiating vapor explosion. An analysis of the available experimental information shows that the mechanisms governing heat transfer in these processes are interpreted ambiguously; a more clear-cut definition of the Leidenfrost temperature notion is required. The results of experimental observations (Hewitt, Kenning, and previous investigations performed by the authors of this article) allow us to draw a conclusion that there exists a special mode of intense heat transfer during film boil- ing of highly subcooled liquid. For revealing regularities and mechanisms governing intense transfer of energy in this process, specialists of Moscow Power Engineering Institute’s (MPEI) Department of Engineering Thermal Physics conduct systematic works aimed at investigating the cooling of high-temperature balls made of different metals in water with a temperature ranging from 20 to 100°C. It has been determined that the field of temperatures that takes place in balls with a diameter of more than 30 mm in intense cooling modes loses its spherical symmetry. An approximate procedure for solving the inverse thermal conductivity problem for calculating the heat flux density on the ball surface is developed. During film boiling, in which the ball surface temperature is well above the critical level for water, and in which liquid cannot come in direct contact with the wall, the calculated heat fluxes reach 3–7 MW/m2.

Experimental study on free convection of sodium in a long cylinder

Abstract: The operation experience of sodium fast reactor shows that during design-basis validation of pipelines and equipment it is necessary to take into account the sodium free convection in the enclosures. The paper presents the results of experimental study of free convection of liquid sodium in a long thermo-insulated cylinder with the end heat supply and removal. The sodium-filled cylinder diameter is 168 mm, length is 850 mm. Three experiments for horizontal, inclined (at 45° to a vertical line) and vertical position of the cylinder were compared in detail. The Rayleigh number (based on cylinder diameter) is approximately same for three experiments and is equal to 5 × 106. The structure of large-scale and small-scale flows was analyzed. Nusselt number estimations being the intensity measure of heat transfer in case of free convection were obtained. A relationship between the flow structure and the Nusselt number is revealed.

Development of a model of entrained flow coal gasification and study of aerodynamic mechanisms of action on gasifier operation

Abstract: Problems requiring solution in development of modern highly efficient gasification reactor of a promising high power integrated gasification combined-cycle plant are formulated. The task of creating and testing a numerical model of an entrained-flow reactor for thermochemical conversion of pulverized coal is solved. The basic method of investigation is computational fluid dynamics. The submodel of thermochemical processes, including a single-stage scheme of volatile substances outlet and three heterogeneous reactions of carbon residue conversion (complete carbon oxidation, Boudouard reaction and hydrogasification), is given. The mass loss rate is determined according to the basic assumptions of the diffusion–kinetic theory. The equations applied for calculation of the process of outlet of volatile substances and three stages of fuel gasifi-cation (diffusion of reagent gas toward the surface of the coal particle, heterogeneous reactions of gas with carbon on its surface, and homogeneous reactions beyond the particle surface) are presented. The universal combined submodel Eddy Dissipation/Finite Rate Chemistry with standard (built-in) constants is used for numerical estimates. Aerodynamic mechanisms of action on thermochemical processes of solid fuel gasification are studied, as exemplified by the design upgrade of a cyclone reactor of preliminary thermal fuel preparation. Volume concentrations of combustible gases and products of complete combustion in the syngas before and after primary air and pulverized coal flows' redistribution are given. Volume concentrations of CO in syngas at different positions of tangential secondary air inlet nozzle are compared.

Studying the characteristics of a 5 kW power installation on solid-oxide fuel cells with steam reforming of natural gas

Abstract: The results from tests of a 5 kW power plant on solid-oxide fuel cells (SOFCs), in which natural gas is used as fuel, are presented. The installation’s process circuit, the test procedure, and the analysis of the obtained results are described. The characteristics of the power plant developed by the Ural Industrial Company are investigated in four steady-state modes of its operation: with the SOFC nominal power capacity utilized by 40% (2 kW), 60% (3 kW), 90% (4.5 kW) and 110% (5.4 kW) (the peaking mode). The electrical and thermodynamic efficiencies are calculated for all operating modes, and the most efficient mode, in which the electrical efficiency reached almost 70%, is determined. The air excess coefficient and heat loss with flue gases q2 are determined, and it is revealed that the heat loss q5 decreases from 40 to 25% with increasing the load. Thermal balances are drawn up for the following components of the system the reformer, the SOFC battery, the catalytic burner for afterburning anode gases, the heat exchanger for heating the cathode air and the mixture of natural gas and steam, and the actual fuel utilization rates in the electrochemical generator are calculated. An equation for the resulting natural gas steam reforming reaction was obtained based on the results from calculating the equilibrium composition of reforming products for the achieved temperatures at the reformer outlet t3.

Experience of using municipal solid waste in the energy industry (An Overview)

Abstract: The status of municipal solid waste (MSW) utilization for energy purposes in Europe, the United States, and China is revealed, showing that MSW has long been among alternative fuels abroad and is widely used as a renewable energy source. Energy utilities often deal with the construction and operation of thermal waste-to-energy facilities. Currently, thanks to the use of the best available technologies (BAT), among which are incineration in mechanical grate stokers and in vertex fluidized-bed furnaces, and multistage gas treatment, the problems of environmentally safe operation of facilities for MSW-to-energy utilization have been fully resolved. The main research is aimed at improving the energy efficiency of these facilities, primarily, by increasing steam parameters and organizing its intermediate superheating. It is shown that a high efficiency of converting the MSW energy potential into electricity can also be reached by integrating MSW incinerators into the heat flow scheme of thermal power plants, whose main fuel is coal or gas. Examples are given of active foreign MSW-to-energy facilities improved to increase electricity efficiency to 30% and more.

Golden Age of Gas and Its Impact on the World Energy, the Global Carbon Cycle and Climate

Abstract: Global and regional resource and environmental problems of production and use of unconventional gas (UG) are studied. Estimations for world and national reserves of various kinds of UG are presented. The dynamics of the gas share in total energy consumption and thermal power generation around the world is analyzed. Projections of the world production of conventional gas and UG are proposed. Variations in carbon dioxide concentration in the atmosphere and the corresponding changes in average global air temperature are calculated for various scenarios suggesting unconventional gas substitution of different energy sources. The possible consequences of expected climate changes for Russia’s power industry are analyzed. It is shown that, despite the uncertainty in the estimates of the economic and environmental consequences of shale gas (SG) production, its use, according to the available resource estimates, can make it possible to solve global and regional problems associated with energy (import substitution) and environment protection (replacing the less clean coal fuel). However, the development of the huge global resources of this type of fuel can have a significant effect on the chemical and thermal radiative balance of the Earth’s atmosphere, and it must be noted that the climatic effect of carbon dioxide emissions from the UG combustion greatly exceeds the consequences of methane leakage during its production. In order to sustain the stability of the global climate system, the development of the world’s large UG resources must be accompanied by an equivalent reduction in the use of coal. This is the only way for UG to become a safe energy bridge to the future, able to keep the climate system at the threshold of critical values. Direct effects of possible climatic changes on the territory of Russia for the domestic energy complex are estimated as more positive than adverse, mainly due to lower energy costs for space heating.

Modeling and full-scale tests of vortex plasma-fuel systems for igniting high-ash power plant coal

Abstract: The processes of supplying pulverized-coal fuel into a boiler equipped with plasma-fuel systems and its combustion in the furnace of this boiler are investigated. The results obtained from 3D modeling of conventional coal combustion processes and its firing with plasma-assisted activation of combustion in the furnace space are presented. The plasma-fuel system with air mixture supplied through a scroll is numerically investigated. The dependence of the swirled air mixture flow trajectory in the vortex plasma-fuel system on the scroll rotation angle is revealed, and the optimal rotation angle at which stable plasma-assisted ignition of pulverized coal flame is achieved is determined.

Increasing reliability of gas–air systems of piston and combined internal combustion engines by improving thermal and mechanic flow characteristics

Abstract: Results of experimental study of thermal and mechanical characteristics of gas exchange flow in piston and combined engines are presented. Ways for improving intake and exhaust processes to increase reliability of gas–air engine systems are proposed.

Hydrodynamics and heat transfer for pulsating laminar flow in channels

Abstract: The problem about laminar pulsating flow and heat transfer with high pulsation amplitudes of average cross-section velocity in a round tube and in a flat channel is solved using the finite element method. The difference scheme’s optimal parameters are determined. Data on the pulsation amplitude and phase are obtained for the hydraulic friction coefficient, tangential stress on the wall, liquid temperature, heat flux on the wall qw (at ϑw = const), and wall temperature ϑw (at qw = const) are obtained. Two characteristic modes, namely, quasi steady-state and high-frequency ones are separated based on the value of dimensionless pulsation frequency. During operation in the quasi steady-state mode, the values of all hydrodynamic and thermal quantities correspond to the values of time-average velocity at the given time instant. For operation in the high-frequency mode, it is shown that the dependences of the pulsating components of hydrodynamic and thermal quantities on the dimensionless pulsation frequency have the same pattern for rectilinear channels having different shapes of their cross section. It is found that certain nodal points exist on the distribution of thermal characteristics along the tube (liquid temperature, heat flux density on the wall at ϑw = const, and wall temperature at qw = const) in which the values of these quantities remain unchanged. The distances between the nodal points decrease with increasing the pulsation frequency. The pulsations of thermal quantities decay over the tube length.

Combined heat and power (cogeneration) plant based on renewable energy sources and electrochemical hydrogen systems

Abstract: The layout of a combined heat and power (cogeneration) plant based on renewable energy sources (RESs) and hydrogen electrochemical systems for the accumulation of energy via the direct and inverse conversion of the electrical energy from RESs into the chemical energy of hydrogen with the storage of the latter is described. Some efficient technical solutions on the use of electrochemical hydrogen systems in power engineering for the storage of energy with a cyclic energy conversion efficiency of more than 40% are proposed. It is shown that the storage of energy in the form of hydrogen is environmentally safe and considerably surpasses traditional accumulator batteries by its capacitance characteristics, being especially topical in the prolonged absence of energy supply from RESs, e.g., under the conditions of polar night and breathless weather. To provide the required heat consumption of an object during the peak period, it is proposed to burn some hydrogen in a boiler house.

Improvement of water treatment at thermal power plants

Abstract: Prospective and existing technologies for water treatment at thermal power plants, including pretreatment, ion exchange, and membrane method are considered. The results obtained from laboratory investigations and industrial tests of the proposed technologies carried out at different thermal power plants are presented. The possibilities of improving the process and environmental indicators of water treatment plants are shown.

The influence of void fraction on the submerged perforated sheet hydraulic friction factor

Abstract: The results from an experimental investigation of two-phase flow motion through a submerged perforated sheet (SPS) obtained at the Elektrogorsk Research Center test facility are presented. The test facility, the test section of which is a transverse “cutout” from the full-scale PGV-1000 steam generator with the models of vessel internals, is described in detail. The procedure for carrying out trial startups is outlined, and the system of instrument and control devices is described. The SPS used in all experimental modes of operation had the perforation ratio (the hole area to the sheet area ratio) equal to 5.7%. The pressure in the system was around 7 MPa, and the flow rate of supplied steam was varied from 4.23 to 7.94 t/h, which corresponded to the steam velocity at the evaporation surface equal to 0.15–0.29 m/s. Distributions of pressure difference across the SPS and void fractions under the SPS and above it are obtained. The SPS hydraulic friction factor for a two-phase flow is determined as a result of processing the experimental data. A correction for two-phase nature of the flow for the SPS operating conditions is determined by comparing the obtained SPS hydraulic friction factor for a two-phase flow with the SPS hydraulic friction factor to single-phase flow of steam. It is shown that this correction can be either greater than unity (at low void fractions) or less than unity (at high void fractions).

Modeling of pulverized coal combustion processes in a vortex furnace of improved design. Part 1: Flow aerodynamics in a vortex furnace

Abstract: Some results of the complex experimental and numerical study of aerodynamics and transfer processes in a vortex furnace, whose design was improved via the distributed tangential injection of fuel-air flows through the upper and lower burners, were presented. The experimental study of the aerodynamic characteristics of a spatial turbulent flow was performed on the isothermal laboratory model (at a scale of 1 : 20) of an improved vortex furnace using a laser Doppler measurement system. The comparison of experimental data with the results of the numerical modeling of an isothermal flow for the same laboratory furnace model demonstrated their agreement to be acceptable for engineering practice.

A high-temperature gas-and-steam turbine plant operating on combined fuel

Abstract: A high-temperature gas–steam turbine plant (GSTP) for ultrasupercritical steam conditions is proposed based on an analysis of prospects for the development of power engineering around the world and in Russia up to 2040. The performance indicators of a GSTP using steam from a coal-fired boiler with a temperature of 560–620°C with its superheating to 1000–1500°C by firing natural gas with oxygen in a mixingtype steam superheater are analyzed. The thermal process circuit and design of a GSTP for a capacity of 25 MW with the high- and intermediate-pressure high-temperature parts with the total efficiency equal to 51.7% and the natural gas utilization efficiency equal to 64–68% are developed. The principles of designing and the design arrangement of a 300 MW GSTP are developed. The effect of economic parameters (the level and ratio of prices for solid fuel and gas, and capital investments) on the net cost of electric energy is determined. The net cost of electric energy produced by the GSTP is lower than that produced by modern combined-cycle power plants in a wide variation range of these parameters. The components of a high-temperature GSTP the development of which determines the main features of such installations are pointed out: a chamber for combusting natural gas and oxygen in a mixture with steam, a vacuum device for condensing steam with a high content of nondensables, and a control system. The possibility of using domestically available gas turbine technologies for developing the GSTP’s intermediate-pressure high-temperature part is pointed out. In regard of its environmental characteristics, the GSTP is more advantageous as compared with modern condensing power plants: it allows a flow of concentrated carbon dioxide to be obtained at its outlet, which can be reclaimed; in addition, this plant requires half as much consumption of fresh water.

Studying the possibility of separate and joint combustion of Estonian shales and oil shale retort gas at thermal power plants

Abstract: Results from investigations of joint and separate combustion of shale with a low heating value and oil shale retort gas (OSRG) are presented. The question about the possibility of further using shale as basic fuel is presently placed on the agenda. This matter is connected with the fact that the environmental regulations are imposing increasingly more stringent limits on emissions of harmful substances and that a decrease in the shale heating value is predicted. An adequate mathematical model of one of the TP-101 boilers installed at the Estonian power plant was developed and verified for carrying out investigations. Criteria for determining the reliability, efficiency, and environmental safety of equipment operation were formulated based on the operating chart, regulatory documents, and environmental requirements. Assessment of the possibility of boiler operation and the boiler unit as a whole in firing shale with a low calorific value has shown that despite fulfilling the required superheated steam parameters, quite a number of limitations relating to reliable operation of the boiler are not complied with. In addition, normal operation of forced-draft equipment and mills is possible only at low loads. For operation with joint combustion of shale and OSRG, the fractions of degraded-quality shale and OSRG (by heat) at which reliable and efficient operation of the boiler and boiler unit is ensured in the entire working range of loads with fulfilling the environmental standards are determined. Proposals on modifying the equipment for joint combustion of shale and OSRG are formulated. Boiler operation with firing OSRG as main fuel was modeled for three versions of furnace waterwall thermal efficiency with a view to estimate possible changes of boiler operation in carrying out waterwall cleaning operations. Calculation results have shown that operation of the boiler and boiler unit meeting the elaborated criteria is possible in the entire working range of loads with essentially increased the air excess factor at the furnace outlet in low load modes.

Nuclear power propulsion system for spacecraft

Abstract: The proposed designs of high-power space tugs that utilize solar or nuclear energy to power an electric jet engine are reviewed. The conceptual design of a nuclear power propulsion system (NPPS) is described; its structural diagram, gas circuit, and electric diagram are discussed. The NPPS incorporates a nuclear reactor, a thermal-to-electric energy conversion system, a system for the conversion and distribution of electric energy, and an electric propulsion system. Two criterion parameters were chosen in the considered NPPS design: the temperature of gaseous working medium at the nuclear reactor outlet and the rotor speed of turboalternators. The maintenance of these parameters at a given level guarantees that the needed electric voltage is generated and allows for power mode control. The processes of startup/shutdown and increasing/reducing the power, the principles of distribution of electric energy over loads, and the probable emergencies for the proposed NPPS design are discussed.

Assessment of combustion of oil shale refinery by-products in a TP-101 boiler

Abstract: The most cost-efficient method for utilization of the oil shale refinery by-products, viz., the retort gas and the shale gasoline, for power generation is combustion of these products in power-generating oil shale-fired boilers. Calculation studies carried out at the Estonian electric power plant in Narva, an enterprise of EESTI ENERGIA, have shown that recycling of the flue gases in the furnace of a TP-101 boiler enables an increase in the portion of the oil shale refinery by-products burned in the boiler from the current 7% to 40%. Recycling of the flue gases is aimed at maintaining the temperatures in the furnace at a level characteristic of combustion of oil shale and reducing the nitric oxide concentration in the retort gas burners’ flame. The degree of the flue gas recycling depends on the percentage of the burnt oil shale refinery by-products in the total heat generation and increases with the increasing percentage. For the threshold value of 40% under the rated conditions, the flue gas recycling accounts for 10%. A complete changeover of the boiler to combustion of only the retort gas in place of the oil shale does not seem to be possible, since this will necessitate major modification to the TP-101 boiler heating surfaces. Considering the obtained results, as a pilot project, one boiler furnace was modified by installing six retort gas burners and a flue gas recycling system.

Selecting the process arrangement for preparing the gas turbine working fluid for an integrated gasification combined-cycle power plant

Abstract: Introduction of a combined-cycle technology based on fuel gasification integrated in the process cycle (commonly known as integrated gasification combined cycle technology) is among avenues of development activities aimed at achieving more efficient operation of coal-fired power units at thermal power plants. The introduction of this technology is presently facing the following difficulties: IGCC installations are characterized by high capital intensity, low energy efficiency, and insufficient reliability and availability indicators. It was revealed from an analysis of literature sources that these drawbacks are typical for the gas turbine working fluid preparation system, the main component of which is a gasification plant. Different methods for improving the gasification plant chemical efficiency were compared, including blast air high-temperature heating, use of industrial oxygen, and a combination of these two methods implying limited use of oxygen and moderate heating of blast air. Calculated investigations aimed at estimating the influence of methods for achieving more efficient air gasification are carried out taking as an example the gasifier produced by the Mitsubishi Heavy Industries (MHI) with a thermal capacity of 500 MW. The investigation procedure was verified against the known experimental data. Modes have been determined in which the use of high-temperature heating of blast air for gasification and cycle air upstream of the gas turbine combustion chamber makes it possible to increase the working fluid preparation system efficiency to a level exceeding the efficiency of the oxygen process performed according to the Shell technology. For the gasification plant’s configuration and the GTU working fluid preparation system be selected on a well-grounded basis, this work should be supplemented with technical-economic calculations.

Advanced tendencies in development of photovoltaic cells for power engineering

Abstract: Development of solar power engineering must be based on original innovative Russian and world technologies. It is necessary to develop promising Russian technologies of manufacturing of photovoltaic cells and semiconductor materials: chlorine-free technology for obtaining solar silicon; matrix solar cell technology with an efficiency of 25–30% upon the conversion of concentrated solar, thermal, and laser radiation; encapsulation technology for high-voltage silicon solar modules with a voltage up to 1000 V and a service life up to 50 years; new methods of concentration of solar radiation with the balancing illumination of photovoltaic cells at 50–100-fold concentration; and solar power systems with round-the-clock production of electrical energy that do not require energy storage devices and reserve sources of energy. The advanced tendency in silicon power engineering is the use of high-temperature reactions in heterogeneous modular silicate solutions for long-term (over one year) production of heat and electricity in the autonomous mode.

Optimum load distribution between heat sources based on the Cournot model

Abstract: One of the widespread models of the heat supply of consumers, which is represented in the “Single buyer” format, is considered. The methodological base proposed for its description and investigation presents the use of principles of the theory of games, basic propositions of microeconomics, and models and methods of the theory of hydraulic circuits. The original mathematical model of the heat supply system operating under conditions of the “Single buyer” organizational structure provides the derivation of a solution satisfying the market Nash equilibrium. The distinctive feature of the developed mathematical model is that, along with problems solved traditionally within the bounds of bilateral relations of heat energy sources-heat consumer, it considers a network component with its inherent physicotechnical properties of the heat network and business factors connected with costs of the production and transportation of heat energy. This approach gives the possibility to determine optimum levels of load of heat energy sources. These levels provide the given heat energy demand of consumers subject to the maximum profit earning of heat energy sources and the fulfillment of conditions for formation of minimum heat network costs for a specified time. The practical realization of the search of market equilibrium is considered by the example of a heat supply system with two heat energy sources operating on integrated heat networks. The mathematical approach to the solution search is represented in the graphical form and illustrates computations based on the stepwise iteration procedure for optimization of levels of loading of heat energy sources (groping procedure by Cournot) with the corresponding computation of the heat energy price for consumers.

Determining heat loss into the environment based on comprehensive investigation of boiler performance characteristics

Abstract: A refined procedure for determining heat loss into the environment from heat-generating installations is presented that takes into account the state of their lining and heat insulation quality. The fraction of radiative component in the total amount of heat loss through the outer surfaces is determined. The results from experimental investigations of the thermal engineering and environmental performance characteristics of a foreign hot-water boiler in firing wood pellets are presented. A conclusion is drawn about the possibility of using such hot-water boilers for supplying heat to low-rise buildings, especially for the conditions of the North-Arctic region. The results from a thermal engineering investigation of wood pellets and furnace residue carried out on installations of a thermal analysis laboratory are presented together with the grain-size composition of fuel and indicators characterizing the mechanical strength of wood pellets. The velocity fields, flue gas flow rates, and soot particle concentrations are determined using the external filtration methods, and the composition of combustion products is investigated using a gas analyzer. The graphs of variation with time of boiler external surface temperature from the moment of achieving the nominal mode of operation and heat loss into the environment for stationary boilers are presented.

Solid fuel gasification in the global energy sector (a review)

Abstract: In the review of the Conference on Gasification of Solid Fuels, which was held on October 2013 by the United States, the commercial use of the most advanced coal gasification systems in the chemical and power industry is considered. Data on the projects of integrated solid fuel gasification combined-cycle plants, either being developed or exploited in the United States, as well as the nature and results performed in specialized organizations to improve the existing gasification equipment and systems, are presented.

Network information attacks on the control systems of power facilities belonging to the critical infrastructure

Abstract: The most large-scale accidents occurred as a consequence of network information attacks on the control systems of power facilities belonging to the United States’ critical infrastructure are analyzed in the context of possibilities available in modern decision support systems. Trends in the development of technologies for inflicting damage to smart grids are formulated. A volume matrix of parameters characterizing attacks on facilities is constructed. A model describing the performance of a critical infrastructure’s control system after an attack is developed. The recently adopted measures and legislation acts aimed at achieving more efficient protection of critical infrastructure are considered. Approaches to cognitive modeling and networked expertise of intricate situations for supporting the decision-making process, and to setting up a system of indicators for anticipatory monitoring of critical infrastructure are proposed.

Modeling of pulverized coal combustion processes in a vortex furnace of improved design. Part 2: Combustion of brown coal from the Kansk-Achinsk Basin in a vortex furnace

Abstract: This paper continues with the description of study results for an improved-design steam boiler vortex furnace, for the full-scale configuration of which the numerical modeling of a three-dimensional turbulent two-phase reacting flow has been performed with allowance for all the principal heat and mass transfer processes in the torch combustion of pulverized Berezovsk brown coal from the Kansk-Achinsk Basin. The detailed distributions of velocity, temperature, concentration, and heat flux fields in different cross sections of the improved vortex furnace have been obtained. The principal thermoengineering and environmental characteristics of this furnace are given.

Numerical simulation of heat and mass transfer processes in the nozzle and expansion unit of the separator-steam-generator system in waste-heat utilization complex

Abstract: Homogeneous equilibrium and nonequilibrium (relaxation) models are used to simulate flash boiling flows in nozzles. The simulation were performed using the author’s CFD-code ANES. Existing experimental data are used to test the realized mathematical model and the modified algorithms of ANES CFD-code. The results of test calculations are presented, together with data obtained for the nozzle and expansion unit of the steam generator and separator in the waste-heat system at ZAO NPVP Turbokon. The SIMPLE algorithm may be used for the transonic and supersonic flashing liquid flow. The relaxation model yields better agreement with experimental data regarding the distribution of void fraction along the nozzle axis. For the given class of flow, the difference between one- and two-dimensional models is slight.

Nuclear energy with inherent safety: Change of outdated paradigm, criteria

Abstract: Modern nuclear power technology still has significant sources of risk, and, weak links, such as, a threat of severe accidents with catastrophic unpredictable consequences and damage to the population, proliferation of nuclear weapon-usable materials, risks of long-term storage of toxic radioactive waste, risks of loss of major investments in nuclear facilities and their construction, lack of fuel resources for the ambitious role of nuclear power in the competitive balance of energy. Each of these risks is important and almost independent, though the elimination of some of them does not significantly alter the overall assessment of nuclear power.

Simulating the thermal operating conditions in the thermal wells of ground-source heat-pump heat supply systems. Part I: Porous moisture freezing processes in soil

Abstract: The mathematical models laid down in the new blocks of the INSOLAR.GSHP.12 software system simulating unsteady operating conditions of ground-source heat-pump (GSHP) heat supply systems are presented. The new model blocks take into account the effect the freezing of porous moisture in soil has on the GSHP system performance efficiency. Illustration is given to the need of taking into account the porous moisture freezing/thawing processes in soil, and the results from investigations devoted to the opening possibilities of constructing adaptive GSHP systems with controlled intensity of heat transfer in the soil-thermal well system are presented. The development of software simulating the porous moisture phase state variation processes in soil was preceded by development of mathematical equations representing the thermal conditions of soil body involving porous moisture freezing/thawing processes. A description of these equations is also given in the article. In constructing the mathematical model, the notion “effective thermal conductivity” of soil was introduced for taking into account the latent heat of phase transition that releases during the freezing of moisture. The above-mentioned effective thermal conductivity of soil involves two components: the soil thermal conductivity coefficient itself and an additional term modifying the thermal conductivity value for taking into account the influence of phase transition. For quantitatively evaluating the soil effective thermal conductivity component that takes into account the influence of phase transition, the soil freezing zone radius around the thermal well was determined. The obtained analytic solutions have been implemented in the form of computer program blocks, after which a “numerical experiment” was carried out for estimating the effect the porous moisture freezing/thawing processes have on the soil thermal conditions. It was demonstrated during that experiment that the soil thermal conductivities determined without taking the porous moisture freezing/thawing phase transitions can differ from those determined with taking these transitions into account by a factor of 2 or more. A conclusion has been drawn from these findings about the importance of taking the phase transition phenomena into account in modeling the parameters of thermal wells and of the GSHP system as a whole.

Investigation of the effect of using tube inserts for the intensification of heat transfer

Abstract: In this work, heat transfer in channels containing inserts of different shapes was investigated using computational fluid dynamics (CFD) modeling techniques taking a gaslight water heater as an example. Three types of devices inserted in the water heater tube (flow swirlers) were investigated: star-shaped, coiled wire, and classic ones in the form of twisted tapes. In the present study, the RNG k-ɛ turbulence model is used to model the turbulent flow regime. This numerical simulation has been performed over a Reynolds number range of 5800–18500. In the studied range of Reynolds number the maximum thermal performance factor was obtained by the starry inserts with A star/A inlet = 0.50. The results have exposed that also the use of all tube inserts leads to a considerable increase in heat transfer and pressure drop over the smooth tube. In addition, the results revealed that both heat transfer rate and friction factor in the tube equipped with starry insert were significantly higher than those in the tube fitted with the coiled wire inserts and classic twisted tape.

Conversion of KVGM-100–150 boilers to cyclone-swirl burning of gas

Abstract: Heating sources of Vladivostok with boilers reconstructed in 2011 to gas burning is presented. The historical reference of the experience of boiler conversion to cyclone-swirl technology of burning of fuel oil and gas is given. Stages of the primary furnace and boiler upgrading are shown. Taking BKZ 75-16 and BKZ-120-100 boilers as examples, the principal differences of the swirl type of fuel burning from the burner type are demonstrated. Data of the KVGM-100–150 MTs boiler with cyclone-swirl burning of gas and fuel oil is represented. The mathematical model developed for the primary furnace with the 65 MW capacity gives detailed explanations to the features of mixing in the combustion chamber of the primary furnace, which substantiate conditions and places of the fuel injection. The practical result is supported by test data obtained on the operating equipment. To enhance the effectiveness of fuel consumption on six converted KVGM-100-150 MTs boilers, the convective section was restructured and the water circulation circuit was optimized. Comparative analysis of estimated and operating characteristics showed the efficiency increment. The application of cyclone-swirl technology made it possible to increase the effectiveness of the KVGM-100-150 boiler and improve its environmental indicators.