Vol 65, No 11 (2018)

The role of combined heat and power (CHP) plants in the electric power industry of Russia is shown. The operational efficiency analysis of public service CHP plants and the fuel, power, and age structure of the existing CHP plants are carried out. Their main problems, such as underuse of generating equipment, excessive production in the condensing mode, high degree of equipment wear, and technological heterogeneity, are identified. The necessity of technological renovation of the CHP plants is shown. The energy efficiency of the combined production of electric and thermal energy by the existing CHP plants is compared to modern technologies for their separate gas and coal production. It is shown that the thermal capacity of the CHP plants in Russia exceeds the required capacity by almost two times. Estimates of the CHP plant thermal capacity necessary to cover the current heat loads are obtained for Russian regions. Main directions of the CHP plants' renewal based on the use of competitive domestic equipment and operation according to the heat load schedule are determined. Systemic impacts achieved by technological renewal are determined for gas-fired CHP plants with allowance for the climatic and load features of the Russian regions. It is shown that the technological renewal of gas-fired CHP plants will allow saving up to 16% of today’s fuel consumption, reducing the total CHP thermal capacity by 47.5% with the same volume and heat supply mode. The operation of a CHP plant according to the heat load schedule leads to a reduction in the electric capacity of the CHP plant by 20% with an increase in electricity generation by 11%. As a result, the consumption of the installed electric and thermal capacity of the CHP plant increases dramatically as does the fuel efficiency and the annual loading balance of external gas-fired condensing power plants. The needs for GTPs and CCGTs required for the technological renovation of the CHP plants is assessed. The necessity for developing competitive domestic medium and high power GTPs is considered.

A new original basic process circuit of a fuel-free trigeneration plant simultaneously producing electricity, heat, and cold is considered. The plant can be used at technological transported gas pressure reduction stations instead of throttle devices conventionally used for this purpose. The plant process circuit involving, as its key components, an expander–generator unit and a vapor compression thermotransformer (VPTT) configured for simultaneously producing heat and cold, along with its operating principle, is described. The flow of transported gas (without combusting it) serves as the primary energy carrier supporting the plant operation. The gas flow energy is converted in mechanical work (as its pressure is decreased in the expander from the initial level at which gas arrives to the technological gas pressure reducing station to the level necessary according to the requirements of the gas utilization technology at the consumer end), and the generator connected to the expander converts this work into electricity. Part of the produced electricity is supplied to an external consumer, and its other part is used for driving the VPTT. The gas flow downstream of the expander supplied to the consumer and the flow of the VPTT working fluid, which takes heat from the cold carrier in the VPTT evaporator as it is transferred from a liquid to a gaseous state serve as the sources of cold in the plant. The working fluid downstream of the VPTT compressor serves as the source of heat; part of this is supplied to the consumer and its other part is used for heating gas upstream of the expander. The article presents the results from studying the effect the temperature to which gas upstream of the VPTT expander is heated by the heat of the VPTT working fluid has on the plant thermodynamic efficiency. The exergetic efficiency is taken as the thermodynamic efficiency criterion. The processes occurring in the plant when changing the gas heating temperature are subjected to a qualitative analysis. The results of calculations carried out using the plant mathematical model described in the article are presented. The obtained calculation results made it possible to determine the effect that the gas heating temperature upstream of the VPTT expander has on the specific (per unit flowrate of transported gas) electric, heating, and refrigeration capacities of the plant; on the specific exergy values of the same flows; and on the exergetic efficiency subject to the conditions adopted in the calculations.

In this paper, we analyzed advanced ground-based power gas turbine units with low-emission combustion chambers used for consecutive two-stage fuel combustion. Such low-emission combustion chambers have a wide range of stable performance modes with reduced emission of harmful substances. The two-stage combustion chambers used in gas turbine units of various capacities—small (for example, M7A-03 with a capacity of approximately 8–10 MW), medium (L20A and L30A with a capacity of 18–30 MW) and large (9HA and GT36 with a capacity of over 300 MW)—showed their universality, efficiency, and good possibilities for scaling. The designs of low-emission combustion chambers for gas turbine units of different capacities are fundamentally similar. They consist of two sequentially located combustion volumes (stages), and each of them has its own burner unit. The first burner unit is typical for low-emission combustion chambers with the combustion of the premixed air-fuel mixture and consists of swirlers, mixing zone, fuel injectors, and igniters. The second burner unit is located downstream, and air-fuel mixtures of a different composition are supplied into it through special holes. The combustion of the mixtures occurs at a lower oxygen content and higher temperature. The ignition, work until idling, and loading before switching to the low-emission mode and switching to it are performed by the operation regulation of the first burner unit. Fuel in the second burner unit is supplied when a certain temperature of the gases arriving from the first combustion stage is achieved, which ensures its self-ignition. The further load is regulated by the fuel supply to the second burner unit. The design implementation of the sequential two-stage combustion scheme and approaches to regulating fuel and air distribution over the stages that ensures stable nonpulsating combustion are different and so they are of great scientific and practical interest.

A radiant cooling heat exchanger is one of key components in a closed-cycle power installation and is the bulkiest structural part of a spacecraft. The most well-elaborated version of a cooler, known as a panel-type radiator (PR), is made according to the process arrangement of radiating panels. Selecting the optimal coolant is one of important issues in designing a PR. A liquid metal coolant in the form of molten Na–K mixture is presently regarded to be the most preferred one for these purposes. It features thermal stability, resistance to radiation, and a very high thermal conductivity. The main negative feature of Na–K melt is its explosion hazard when exposed to air, a circumstance due to which difficulties are encountered in experimentally perfecting the PR design under on-land conditions. We consider high-temperature organic coolants as an alternative to a liquid metal coolant. The aim of this study was to compare the effectiveness of using different coolants for the class of PR systems whose properties and geometrical characteristics are close to the prototypes developed at the State Scientific Center (SSC) Keldysh Research Center from composite materials on the basis of carbon fibers with high thermal conductivity. To this end, a mathematical model and relevant calculation procedure have been developed. The results from the performed calculations testify that, in view of a low specific heat of liquid metal coolant, its mass flow-rate should be a factor of 2–2.5 higher than the flowrate of high-temperature organic coolant, which entails essential loss of energy for pumping. Thus, the use of high-temperature organic coolants is more preferable for a certain class of PRs with parameters close to the considered ones. Turbulent flow of coolant is an important condition, due to which significant requirements are posed to its viscous characteristics. A diphenyl mixture can be regarded as the most efficient high-temperature coolant for the considered class of PRs.

Upon analyzing the methods for processing epidemiologically hazardous medical waste (MW), it has been shown that the problem of safe disposal of MW with respect to the formation of polychlorinated dibenzo-para-dioxins and dibenzofurans (dioxins and furans) is acute and requires scientifically sound solutions. The typical morphological and elemental composition of the MW classes B and C and their thermal properties were determined, and the modern literature on the processes of thermal detoxification of dangerous MW was analyzed. It has been found that the process of pyrolysis is the most adaptive to various types of solid waste. Currently, pyrolysis attracts special attention due to its flexibility in treating various combinations of wastes only by changing the operating parameters of the process, such as temperature and heating rate. Pyrolysis is particularly important in connection with the growing amount of polymers in the waste of medical institutions, including those containing chlorine. In this case, the pyrolysis method presents the possibility of using a number of circuit solutions to prevent the formation of dioxins and furans. It has been shown that the use of the pyrolysis method ensures, along with full satisfaction of the requirements of sanitary and hygienic standards, the environmental safety of the MW detoxification process as compared to other high temperature methods (combustion and gasification). Next, possible directions of utilization of secondary resources received in the process under consideration were analyzed. In the proposed scheme of the installation for safe disposal of medical waste on the basis of the pyrolysis process, its products (excess gas, heat of the products of combustion, etc.) are expected to be used to generate electrical and thermal energy; semicoke as a solid residue of the process will be converted to activated carbon.

Technology of zinc metering into the coolant has already been used for more than 20 years at foreign nuclear power stations (NPS) with PWR reactors for reducing radiation fields on the equipment and suppressing corrosion cracking of nickel-rich alloys. The most likely forms in which zinc compounds can exist in the primary coolant circuit of water-cooled power reactors (such as VVER, PWR, or BWR) were assessed, and the data on their solubility were analyzed. It is demonstrated that zinc oxides and silicates feature the minimum solubility under the primary coolant circuit conditions. The conditions for crystallization of compounds on the surface of fuel rod cladding in the core in case of local boiling (i.e., subcooled liquid boiling) were analyzed. A review is presented of foreign publications with the assessment of the risk that zinc compounds are contained in zinc deposits on the surface of fuel rods when zinc is metered into the coolant of PWR power units with a thermally stressed core. The predictions are presented of the limit thickness of the deposits at which zinc oxides and silicates can precipitate into them in case of local subcooled boiling on the fuel rod surface. The predictions are presented for the effect of the concentration of boric acid, silica, and zinc in the coolant on the limit thickness of depositions at which zinc compounds can crystalize. It is demonstrated that, in the presence of boric acid, zinc can interact with borates with the formation of borate complexes, which reduce the risk of deposition of zinc silicates in the layer of deposits on the fuel rod surface. The calculated results confirm that increasing the thickness of oxide film on fuel rods increases the risk of crystallization of zinc compounds in the core.