Том 65, № 3 (2018)

Various types of shroud, diaphragm, and end seals preventing idle leak of working steam are installed in the flow paths of steam turbine cylinders for improving their efficiency. Widely known labyrinth seals are most extensively used in the Russian turbine construction industry. The category of labyrinth seals also includes seals with honeycomb inserts. The developers of seals with honeycomb inserts state that the use of such seals makes it possible to achieve certain gain due to smaller leaks of working fluid and more reliable operation of the system under the conditions in which the rotor rotating parts may rub against the stator elements. However, a positive effect can only be achieved if the optimal design parameters of the honeycomb structure are fulfilled with due regard to the specific features of its manufacturing technology and provided that this structure is applied in a goal-seeking manner in the seals of steam and gas turbines and compressors without degrading their vibration stability. Calculated and preliminary assessments made by experts testify that the replacement of conventional labyrinth seals by seals with honeycomb inserts alone, due to which the radial gaps in the shroud seal can be decreased from 1.5 to 0.5 mm, allows the turbine cylinder efficiency to be increased at the initial stage by approximately 1% with the corresponding gain in the turbine set power output. The use of rectangular-cellular seals may result, according to estimates made by their developers, in a further improvement of turbine efficiency by 0.5–1.0%. The labor input required to fabricate such seals is six to eight times smaller than that to fabricate labyrinth seals with honeycomb inserts. Recent years have seen the turbine construction companies of the United States and Germany advertising the use of abradable (sealing) coatings (borrowed from the gas turbine construction technology) in the turbine designs instead of labyrinth seals. The most efficient performance of such seals in the turbine flow path is achieved with the sealing material-to-blade linear wear ratio equal to 10 : 1. According to estimates of the developers, application of abradable (sealing) coatings to all problem surfaces (resulting in the power output increased by 0.5–1.0%) is economically profitable even if this procedure is carried out under field conditions at a thermal power plant.

As experimental studies show, the rubbing of the rotor against the structure usually excites harmonics of different frequencies. In high-frequency regions, the power of the vibration signal appears to be considerable. The rotor—supports—stator system is in an unstable equilibrium state during the contact interaction between the rotor and the stator. The forces exerted on the rotor facilitate the excitation of the asynchronous rolling and its damping. The forces have been determined that facilitate the excitation of the progressive and retrograde rotor precession. The consideration of these forces in the algorithm for modeling the rotor-over-stator rolling development allows investigation of the impact of the components of the above forces on the behavior of the rotor system. The initial excitation—disturbance of the normal operation—of the rotor and subsequent unsteady oscillations of it result from sudden imbalance in the second span. The results of numerical modeling of the rubbing in the second span and the rotor-over-stator rolling upon change in the damping components of secondary (gyroscopic) components b_ij (i ≠ j) of the damping matrix are presented for the rotor on three bearing-supports considering the synergetic effect of the forces of various types exerted on the rotor. It is shown that change in one of the parameters of the excitation forces leads to ambiguity of the pattern (manifestation form) of the asynchronous rotor-over-stator rolling and proves the existence of more than one states towards which the rotor—supports—stator system tends. In addition to the rolling with a constant rotor—stator contact, oscillations of the rotor develop in the direction perpendicular to the common trajectory of the precession motion of the rotor’s center with transition to the vibro-impact motion mode. The oscillations of the rotor tend towards the symmetry center of the system (the stator bore center). The reason is the components of the stiffness and damping forces that act in the direction transverse to the rotor’s motion trajectory. Recommendations are given for eliminating dangerous consequences of the development of the asynchronous rolling fraught with great financial losses.

Technology for the integrated development of low-temperature geothermal resources using the thermal and water potentials for various purposes is proposed. The heat of the thermal waters is utilized in a low-temperature district heating system and for heating the water in a hot water supply system. The water cooled in heat exchangers enters a chemical treatment system where it is conditioned into potable water quality and then forwarded to the household and potable water supply system. Efficient technologies for removal of arsenic and organic contaminants from the water have been developed. For the uninterrupted supply of the consumers with power, the technologies that use two and more types of renewable energy sources (RESs) have the best prospects. Technology for processing organic waste using the geothermal energy has been proposed. According to this technology, the geothermal water is divided into two flows, one of which is delivered to a biomass conversion system and the other is directed to a geothermal steam-gas power plant (GSGP). The wastewater arrives at the pump station from which it is pumped back into the bed. Upon drying, the biogas from the conversion system is delivered into the combustion chamber of a gas-turbine plant (GTP). The heat of the turbine exhaust gases is used in the GSGP to evaporate and reheat the low-boiling working medium. The working medium is heated in the GSGP to the evaporation temperature using the heat of the thermal water. High-temperature geothermal brines are the most promising for the comprehensive processing. According to the proposed technology, the heat energy of the brines is utilized to generate the electric power at a binary geothermal power station; the electric power is then used to extract the dissolved chemical components from the rest of the brine. The comprehensive utilization of high-temperature brines of the East-Precaucasian Artesian Basin will allow to completely satisfy the demand of Russia for lithium carbonate and sodium chloride.

A model is presented of the interphasic heat and mass transfer in the presence of noncondensable gases for the KORSAR/GP design code. This code was developed by FGUP NITI and the special design bureau OKB Gidropress. It was certified by Rostekhnadzor in 2009 for numerical substantiation of the safety of reactor installations with VVER reactors. The model is based on the assumption that there are three types of interphasic heat and mass transfer of the vapor component: vapor condensation or evaporation on the interphase under any thermodynamic conditions of the phases, pool boiling of the liquid superheated above the saturation temperature at the total pressure, and spontaneous condensation in the volume of gas phase supercooled below the saturation temperature at the vapor partial pressure. Condensation and evaporation on the interphase continuously occur in a two-phase flow and control the time response of the interphase heat and mass transfer. Boiling and spontaneous condensation take place only at the metastable condition of the phases and run at a quite high speed. The procedure used for calculating condensation and evaporation on the interphase accounts for the combined diffusion and thermal resistance of mass transfer in all regimes of the two-phase flow. The proposed approach accounts for, in a natural manner, a decrease in the rate of steam condensation (or generation) in the presence of noncondensing components in the gas phase due to a decrease (or increase) in the interphase temperature relative to the saturation temperature at the vapor partial pressure. The model of the interphase heat transfer also accounts for the processes of dissolution or release of noncondensing components in or from the liquid. The gas concentration at the interphase and on the saturation curve is calculated by the Henry law. The mass transfer coefficient in gas dissolution is based on the heat and mass transfer analogy. Results are presented of the verification of the interphase heat and mass transfer used in the KORSAR/GP code based on the data on film condensation of steam-air flows in vertical pipes. The proposed model was also tested by solving a problem of nitrogen release from a supersaturated water solution.

In recent years, combined-cycle units with heat-recovery steam generators have been constructed and commissioned extensively in the European part of Russia. By the example of the Kazan Cogeneration Power Station no. 3 (TETs-3), an affiliate of JSC TGK-16, the specific problems for most power stations with combined-cycle power units that stem from an elevated content of organic impurities in the feedwater of the heat-recovery steam generator (HRSG) are examined. The HRSG is fed with highly demineralized water in which the content of organic carbon is also standardized. It is assumed that the demineralized water coming from the chemical water treatment department of TETs-3 will be used. Natural water from the Volga River is treated to produce demineralized water. The results of a preliminary analysis of the feedwater demonstrate that certain quality indices, principally, the total organic carbon, are above the standard values. Hence, a comprehensive investigation of the feedwater for organic impurities was performed, which included determination of their structure using IR and UV spectroscopy techniques, potentiometric measurements, and element analysis; determination of physical and chemical properties of organic impurities; and prediction of their behavior in the HRSG. The estimation of the total organic carbon revealed that it exceeded the standard values in all sources of water comprising the feedwater for the HRSG. The extracted impurities were humic substances, namely, a mixture of humic and fulvic acids in a 20 : 80 ratio, respectively. In addition, an analysis was performed of water samples taken at all intermediate stages of water treatment to study the behavior of organic substances in different water treatment processes. An analysis of removal of the humus substances in sections of the water treatment plant yielded the concentration of organic substances on the HRSG condensate. This was from 100 to 150 μg/dm³. Organic impurities in boiler water can induce internal corrosion and deposits containing products of their degradation.