Vol 65, No 10 (2018)

Increasing the efficiency of fuel use in the production of electricity and heat can be achieved by carrying out activities aimed at modernizing existing power plants. Such highly effective measures include equipping boilers with a condensing heat utilizer (CHU) that allows the use of low-potential heat of outgoing flue gases. When the flue gases are cooled in CHU below the dew point temperature of the water vapor contained therein, up to 12–15% of the heat recovery can be obtained, which can be used to heat the return-network water in the heat network. It is most effective to use CHU in boilers burning natural gas and biofuel whose combustion products contain a large amount of water vapor. The temperature of the return-network water has a great influence on the efficiency of the CHU use. Three characteristic ranges of utilization efficiency of low-potential heat, which depends on the temperature of the reverse network water, are selected. Various solutions are given that allow ensuring a high degree of utilization in CHU of the heat released during condensation of water vapor contained in the combustion products at the temperature of the reverse-network water close to the dew-point temperature. Examples of the successful application of CHU of various brands at power plants in the Nordic countries, namely Sweden, Denmark, Latvia, and Estonia, that have similar climatic conditions with Russia and similar district heating systems are considered. CHU with preheating and humidification of air supplied to the boiler for combustion, which will not only effectively utilize low-potential heat but also significantly reduce emissions of nitrogen oxides into the atmosphere, are also considered.

The outlet header of the high-pressure superheater is among the critical components affecting the service life of heat recovery steam generators (HRSG) of combined-cycle power plants (CCPP). Headers, heat-transfer tubes, and steam pipelines are protected against corrosion by running proper water chemistry to form thin protective films on the surfaces. These films formed on the inside surface of heat-transfer tubes protect against corrosion and also reduce thermal stresses in the tube walls during transients. They are formed on the inside of tube systems of HRSGs in CCPPs at temperatures above 230°С and with good deaeration. Results are presented of a numerical analysis of the influence of thin protective films on the state of thermal stresses in headers and steam pipelines of HRSGs used in CCPPs during various transients induced, for example, by startups from different initial thermal state or thermal shocks. Predictions were obtained for different film thicknesses assuming that the film thermal conductivity was less than thermal conductivity of the pipeline metal. The numerical results enabled the determination of the heating-up modes for headers and steam pipelines under which the effect of protective films is the greatest. It is demonstrated that the protective films have a considerable effect on stresses and damage accumulation in the pipeline wall induced basically by large temperature disturbances, such as thermal shocks. The effect of protective films on the thermally stressed state of unheated pipes was assessed by reducing the resourse consumption and accumulation of equivalent operating hours during transients. It is demonstrated that a 50 μm thick protective film alone can increase the service life of an HP steam superheater’s outlet header with a standard size of 426 × 34 mm by 6%.

Increasing the objectivity of comparison and ranking of working efficiency of steam-turbine installations of thermal power-stations' power-generating units under conditions when the accuracy of technical and economic indices (TEI) to be calculated by energy characteristics leaves much to be desired; in other words, the results of TEI analysis are far from objective, and the improvement of analysis techniques of TEI is not only actual but also necessary. Traditionally, the analysis consists of comparison of actual and normal values of TIEs. The discrepancies of these values define the reserve of thermal economy and recommendations ensuring the enhancement of working efficiency of thermal power stations (TPS). Systematic improvement of recommendations' reliability is ensured by experimental clarification of energy characteristics 4 years on average after the major repair of a power-generating unit (PGU). In time, wear leads to increasing the calculation error of rated values of techno-economic indices and amendments taking into account aging. Finally, there comes a point when a manual clarification of rated TEIs becomes economically unsuitable. In accordance with the Rules for Technical Operation, the analysis results of TEIs are needed to ensure the most economical operation of powergenerating units, the development of schedules of repair and adjustment and alignment of power-generating units, the estimation of quality of operational personnel work, and drawing up of accounts on the thermal efficiency. Personnel should solve all these problems, as well as many others, depending on the difference of the actual average monthly and approximate rated values of dozens of TEI. It is proposed, along with the methods of analysis, to apply the methods of synthesis of TEI. The methods of synthesis require overcoming the influence of difference in dimensions, the influence of interrelation of TEI, and the operating conditions of powergenerating units. The possibility for synthesis of TEI manually is practically excluded, since their bulkiness and multiplicity cause a high risk of erroneous decisions. An automated analysis and synthesis system of TEI of thermal power stations' power-generating units was developed. It provides, along with the information support of personnel, methodological support in the form of recommendations for enhancement of working effectiveness of both individual power-generating units and thermal power stations as a whole. The objectivity of these recommendations is undoubted within the framework of initial data.

The article presents the results from numerical investigations into the hydrodynamics and temperature field in the KLT-40S reactor’s fuel assembly (FA) in the case of using microspherical fuel elements as nuclear fuel. The simulated FA has the same overall dimensions as the existing FA containing fuel rods, due to which it can be accommodated in the reactor core without the need of modifying the reactor design. The specific feature of an FA with micro fuel elements (MF FA) is the need to set up radial flow of coolant through the bed of micro fuel elements, which is achieved by using distribution and collection headers. The numerical simulation was carried out using the ANSYS Fluent computer code. The mathematical model implemented in the code has been refined and verified against the experimental data obtained by the authors on a model experimental setup whose design is similar to that of the considered FA containing micro fuel elements. Radial flow of coolant through the pebble bed is arranged in the model installation. The numerical and experimental data on pressure loss and temperature distribution in the bed estimated at different values of coolant mass velocity mass are compared with each other. The design of an FA containing micro fuel elements for the KLT-40S reactor is proposed. It has been found that almost purely radial flow of coolant can be set up with the perforation parameters (cross-section coefficients) higher than those mentioned in the literature. The serviceability of such a fuel assembly is demonstrated. The distributions of temperature, excess pressure, and coolant velocity and current lines are obtained. The perforation parameters of jackets confining the bed of micro fuel elements are presented.

The article presents and analyzes the results from topical thermophysical investigations aimed at substantiating the characteristics and assessing the safety of liquid metal cooled fast reactors: an advanced largecapacity fast sodium-cooled reactor and a fast lead-cooled reactor. We also outline the results from experimental investigations into hydrodynamics and heat transfer for stratified flow of coolant, into thermal hydraulics of a large-modular “sodium–water” steam generator in different modes of reactor operation, and into the fuel assembly degradation process in the course of a severe accident involving loss of sodium flowrate in a fast reactor. The basic mechanisms governing degradation of dummy fuel rod claddings are identified; the distribution of marker materials over the fuel assembly height in its ultimate state is estimated, and the phenomena of blocking the fuel assembly flow pass section and the marker materials being thrown to beyond the assembly boundaries are studied. The article demonstrates the advisability of using a combined sodium purification system built into the reactor vessel that contains cold traps as a mandatory element along with hot traps, which serve to perform accelerated removal of oxygen during the NPP operation at its nominal parameters. The results from thermal–hydraulic tests of the lead-cooled reactor core carried out on the 6B experimental setup and of the steam generator carried out on the SPRUT experimental setup installed at the SSC RF–IPPE are presented.1 It has been found from the experiments on the thermal–hydraulic model of the lead-cooled reactor’s steam generator that the steam temperatures at the outlets from both headers are identical with each other and so are the lead temperatures at the downcomer section outlet and in the main lead path. The experiments did not show pulsations of feedwater flowrate or pressure in the loops, which points to the stable nature of operation at partial load. The state of the technology of heavy metal coolants and the prospects for its future development are considered. It is shown that there is a possibility in principle to realize the required parameters of a high-temperature sodium-cooled fast reactor for producing large quantities of hydrogen, e.g., based on one of the thermochemical cycles or high-temperature electrolysis with a high electricity thermal utilization factor. The problems that must be solved during the further thermophysical investigations are analyzed.

Problems encountered in operation of saturated steam geothermal turbine units that stem from the specific features of a geothermal heat carrier are considered. A two-phase state, increased content of salts, and corrosiveness of geothermal working medium have a negative influence on the efficiency and reliability of the turbine’s first and last stages. Owing to high concentrations of impurities in the liquid phase, the first stages suffer from intense generation of deposits. The resulting decrease in the power output is due to both fouling of the flow path and significantly growing roughness of the turbine cascade blades. The flow of wet steam in the geothermal turbine flow path is accompanied by droplet impingement erosion of the last-stage blades and corrosion fatigue of the metal of rotor elements. In addition, the losses due to steam wetness in the flow path cause an essential decrease of the geothermal turbine efficiency. The article gives examples of erosioninduced damage inflicted to the last-stage rotor blades, corrosion fatigue of the metal of integrally-machined shroud elements, and deposits in the nozzle vane cascades of geothermal turbine stages. The article also presents the results from numerical investigations of the effect that the initial steam wetness has on the silicic acid concentration in the wet steam flow liquid phase in a 4.0 MW geothermal turbine’s stages. A method for achieving more efficient and reliable operation of the geothermal turbine low-pressure section by applying a secondary flash steam superheating system with the use of a hydrogen steam generator is proposed. The article presents a process arrangement for preparing secondary flash steam supplied to the geothermal turbine low-pressure section in which the flash steam is evaporated and superheated through the use of a hydrogen steam generator. The technical characteristics of the system for preparing secondary flash steam to be used in the intermediate inlet to the turbine were preliminarily assessed (taking the upgrading of the Mutnovsk geothermal power plant as an example), and it has been shown from this assessment that the wetness degree in the low-pressure section can be decreased down to its final value equal to 2.0%.

Summarized data on the number and types of solar collectors and solar plants in use in various countries of the world, as well as on the market development dynamics and specific thermal capacity of operating solar plants per 1000 people, are given. State demand stimulation activities for solar plants are presented for some countries. It is noted that the modern trend in the improvement of solar collectors is the price reduction for materials with the substitution of copper for aluminum in the absorber manufacturing and the reduction of the energy-output ratio using soldering, crimping, and adhesive joints instead of welding. The minimal cost of the generated heat energy is provided by centralized solar heat supply systems. The values of the area of solar plants in Russia (2017), their structure, the features of solar collectors, including Russian-made, are presented. It is indicated that constructions of solar collectors with the optimal cost-effectiveness ratio are in demand on the Russian market. The information on the state of development and use of solar heat plants in Russia is summarized. The main design decisions and operating features of large solar plants in Narimanov, Astrakhan oblast (4400 m²), and in Ust-Labinsk, Krasnodar krai (600 m²), have been considered. It is established that the prospects of the Russian market are determined by the solar radiation in regions as well as the costs of solar collectors and replaceable conventional energy carriers. With allowance for the existing trends and peculiarities of regional development, the prospective Russian solar power market is estimated at 1400000–1500000 m² (1100–1200 MW).

Results of experimental investigations performed on 210–1200 MWel. power units at thermal and nuclear power stations yielded a statistical correlation of the corrosion rate for cooled copper conductors in water-cooling systems of the stator winding in a hydrogen-water cooled generator vs. cooling water quality characteristics, such as electrical conductivity, pH, and dissolved oxygen content. The content of dissolved oxygen in the cooling water is found to have a pronounced effect on the efficiency of corrosion protection of system elements. An engineering solution is proposed. It calls for installation of a small cavitation deaerator operating on superheated water in the cooling water return pipeline from the turbogenerator stator winding to a vacuum tank from which steam is removed by the main ejector of the turbine unit condenser or the deaerator’s own ejector. Special experimental investigations allowed the determination of the water deaeration efficiency in deaerators of the considered type. It is described by a dependence of a relative decrease in the content by weight of oxygen dissolved in the deaerated water on the water overheating at the deaerator inlet with reference to saturation temperature corresponding to the pressure in the steam suction pipeline. It was established by calculations that the proposed engineering solution decreased the corrosion rate of copper conductors in water-cooling systems of the stator winding, on average, by a factor of 2.1. Results of this investigation can be used in designing new power facilities or retrofitting process systems of operating hydrogen-water cooled turbogenerators.

The article deals with the issues of energy saving and increasing the efficiency of thermal energy. Energy saving issues are inextricably linked to the cost of heat for consumers. The costs of thermal energy transfer depend directly on thermal and hydraulic regimes of the heat supply system. A mathematical model and a method for calculating differential heat energy prices for all nodes and consumers of a heat supply system are discussed considering various heat production costs, the actual heat flow distribution, the location of the consumers in the network (the distance from the source), the structure and parameters of the network, and numerous internal and external disturbances of both a systematic and an accidental character. The above factors are taken into account by means of a thermo-hydraulic model for calculating the regimes of the heat supply system with intermediate temporal control nodes that serve as a basis for determination of the heat amount in every node at every time point. The proposed approach to the calculation of nodal prices can be interpreted as a method for solving the problem of distribution of the “price field” over the network for a given distribution of heat flows. The approach is based on three main principles, viz., the nodal balance of the heat cost, the equality of prices for the flows from the common node, and a differentiated increment of prices due to the variable component for the transfer of thermal energy for each of the sections of the calculation scheme. The proposed method for calculating the nodal prices of thermal energy can be used for multicriteria optimization of thermal and hydraulic regimes. The maximum utilization of the cheapest energy in the system or the minimum price of thermal energy for consumers can be the optimization criteria. The proposed approach makes it possible to differentiate prices within the regulatory period currently adopted in accordance with the process conditions of the heat supply system, namely, summer, autumn–spring, and winter conditions, including using peak-load sources. The operating modes have significant differences in the parameters of the heat-transfer medium, such as the flow rate and temperature of the network water.

Procedures of reducing waste water discharges into water bodies to safe levels are described. A technique of evaluating the minimum required water flow rate for the dilution of waste waters containing several harmful substances before their discharge into a water reservoir, as well as evaluating maximum allowable discharges (MADs) of wastewaters, is given. This technique makes it possible to take into account classes of hazard and the summation of effects of substances with the same limiting harmful indices. Expressions for determining the minimum required water flowrate for wastewater dilution were obtained from the condition of admissibility of the effect of several harmful substances on reservoir waters as well as from equations of substance balance in a mixer and the mathematical description of the process of eddy diffusion of substances in the flowing water reservoir. The conditions of admissibility of the effect are presented in the form of logical products of inequalities in which the sums of relative concentrations should not exceed the value of 1. An analytical expression of the dependence of relative substance concentration in the most contaminated jet of the control point of the river on the water flow rate for dilution has been obtained. It is shown that the minimum required water flow rate for wastewater predilution can be calculated only on the basis of a numerical method. An example of numerical calculation of the water flow rate for the predilution of technical facility waste waters containing two substances, polysulfide oil and nitrites, is given for illustrating and testing the technique. In addition to these two harmful substances, the reservoir upstream the point of wastewater discharge contained chrome and fluorine. For nitrites, chrome, and fluorine, the summation of their harmful effects was taken into account. For the example under consideration, it is shown that nitrites can be safely discharged without predilution if the unidirectionality of effects is not taken into account. If the summation of effects of harmful substances is taken into account, it is necessary to predilute waste waters at a dilution multiplicity of 6.4 and a decrease in oil and nitrite concentration by 6.8 and 7.3 times to ensure environmental safety.