Andrii Kostikov

The object of the study is the energy processes in a heat-generating steam turbine operating with a deteriorated condenser vacuum for hot water supply (HWS). The problem of increasing the efficiency of a heating plant was solved, in which in the warm season HWS is provided by one turbine and a peak water boiler (PWB). Results obtained: a method for determining the optimal average operating modes of the object of the study was developed, tested on the PT-20-2.9/1.0 (PT-20) turbine (Ukraine) with a capacity of 20 MW of Kharkiv CHP-3. The proposed method is based on mathematical modeling of the thermal scheme of the turbine installation and optimization of its operating parameters. The maximum electricity generation was chosen as the optimality criterion while observing the design and operating limitations of the turbine. Optimization parameters: steam flow rate into the turbine head, network water temperature after its feed, and steam pressure in the condenser. The peculiarity of the obtained calculation results is connected with the absence of regenerative heaters in PT-20 and with the necessity to solve three optimization problems by the number of characteristic periods of operation of the heating plant. When operating on HWS, the temperature and average flow rate of the return network water change significantly during the day: night +65°С, ~3000 t/h, morning and evening peak times +51°С, ~4500 t/h, day +51°С, ~3600 t/h. The best performance indicators of the Kharkiv CHP-3 were obtained in the peak mode with three-stage (condenser, network heater and PWB) heating of network water, in other modes – two-stage (PWB turned off). The worst – in the night mode. The presented results on the optimization of the PT-20 operating modes on HWS are used at the Kharkiv CHP-3. After further development, the developed method can become the basis for determining the optimal seasonal operating modes of a heating plant with several steam turbines

The problem of rapid risk assessment for nuclear power plant operation under extreme conditions, which may significantly affect nuclear and radiation safety, is considered. Based on a probabilistic safety analysis approach, a methodology has been developed to evaluate accident risk. Its application enables plant personnel to quickly make decisions on the need to reduce the reactor power or shut down the power unit in the event of circumstances that could seriously compromise operational safety. A formula for calculating the maximum permissible reactor power at which the plant can continue to operate in extreme conditions is obtained. It is shown that in cases of events posing substantial risk and potentially leading to accidents, shutting down the unit is advisable, as safety limits may otherwise be exceeded.

To utilize the heat emitted into the atmosphere by a steam turbine generator, a sufficiently effective means of energy saving is the integration into the turbine thermal scheme of an absorption lithium bromide heat pump (AHP) with steam heating. The purpose of the study is to determine the efficiency of energy saving with an integrated AHP with a capacity of 17.3 MW, which is heated by steam from the turbine production selection with different pressures, using the example of a mathematical model of the PT-60/70-130/13 thermal scheme. The power of AHP was determined during previous studies. The state of the problem of recycling the circulating water of the steam turbine condenser cooling by using heat pumps is analyzed. The influence of the steam pressure in the production selection on the performance of the integrated turbine unit in the heating season is studied. The pressure in the production selection of the steam turbine varied from 1.66 MPa to 0.693 MPa. As an energy saving measure, it is proposed to install a steam screw machine with a nominal power of 1 MW to expand the steam to the parameters required for heating the steam turbine. The calculations were performed taking into account the average monthly outdoor temperatures in Ukraine in the heating season. The thermal load of the PT-60/70-130/13 with the integrated steam turbine was provided by setting fixed steam consumption to the consumer of 15 t/h, and network water for heat supply of 1600 t/h. Depending on the steam pressure from the production selection, the power of the recycling steam screw machine varied in the range of 0.651–1 MW. Integration of AHP 17.3 MW into PT-60/70-130/13, depending on the selected steam pressure in the production selection during operation in the heating period, leads to an increase in efficiency by 3.4–3.7 %, tangible savings in conventional fuel (5.8–6.4 %), improves the environment, saves 105–107 thousand tons of technical water, reduces harmful emissions into the atmosphere: greenhouse gases by 5.9–6.4 %, and 65.9–67.1 GW of heat from circulating water in the cooling tower. The consequence of this integration, which can be considered negative, is a decrease in total “useful” electricity generation (by 2.3–3.2 %). According to preliminary estimates, the integration of AHP 17.3 MW into PT-60/70-130/13 is a promising energy saving technology for implementation. At fuel prices (natural gas) of 300 USD/t с.f., and electricity of 150 USD/MW×h it has a simple payback period of ~ 2.9 years (investments are estimated at 3150 thousand USD), if AHP 17.3 MW is heated by steam, the pressure of which is in the range of 1.0–1.2 MPa. It is in this range of pressure of steam that heats the heat pump that we recommend operation. Bibl. 27, Fig. 2, Tab. 4.

A mathematical model for constructing an optimal loading schedule of a power unit with a small modular nuclear reactor is presented. The main conditions of operation of small modular nuclear reactors with constructive solutions similar to the development of NuScale are determined, and the architecture of the mathematical model for the search of optimal schedules of their operation is presented. The main attributes of the operating modes of small modular nuclear reactors and a mathematical model for simulating the control functions of the reactor operation schedules have been determined. The main components for displaying the results of purchase-lease/sale of electricity by the power-generating company have been determined. The objective function of maximizing the benefit from the operation of a small modular nuclear reactor and limiting the profitability of its operation is given. The basics of the methodology of using the model for building the optimal daily schedule of the functioning of a small modular nuclear reactor in the tasks of assessing the effect of the construction and operation of such reactors at a nuclear power plant have been formulated. Ref. 15, fig. 4, table.

Purpose. To develop a maneuverable power plant (MPP) based on the NuScale small modular reactor (SMR) by selecting a thermal scheme structure for a steam turbine installation using minimal additional equipment and ensuring its operation in both nominal and peak modes with maximum efficiency. This also includes ensuring its maneuverability through the use of hydrogen technologies for generating, storing, and returning energy to the steam turbine cycle. Methodology. The study employed the method of mathematical modeling of thermodynamic cycles of thermal schemes of steam turbine installations (STI) with concentrated parameters, which makes it possible to describe the dynamics of systems consisting of discrete elements that are thermodynamic systems. Findings. Various structural options for the thermal scheme of the MPP based on the NuScale SMR for nominal operation were developed and mathematically modeled, followed by a comparative analysis of their energy efficiency. As a result, a scheme and operational parameters were selected with the highest electrical efficiency (net), which allows increasing the net efficiency of the NuScale SMR-based power plant from the developers’ announced 28 to 32.8 %. A thermal scheme for the MPP based on the SMR with an energy storage system was proposed. Applying this scheme allows increasing the net efficiency of a power plant based on NuScale SMR in peak mode to 34.8 %. Originality. A concept for creation and schematic solution for a prospective MPP based on an SMR capable of accumulating electrical energy was proposed. The main innovative solution regarding the structure of the technological scheme of the MPP based on the SMR is the organization of its operation in nominal and peak modes, which fundamentally differ in the thermodynamic cycle. In the nominal mode, the steam turbine installation operates on a thermodynamic cycle with steam separation, and in the peak mode without it, by increasing the temperature of fresh steam as a result of burning hydrogen and oxygen. Hydrogen and oxygen are produced in an electrolyzer during the power plant’s operation in the nominal mode by using the generated electricity “excess”. Practical value. Small modular reactors are currently mainly in the development stage. Additionally, the non-nuclear part of the SMR-based power plant, namely the STI, has not received sufficient attention, as evidenced by the literature. However, it plays a crucial role in the overall efficiency of the installation. The study focuses on the highly relevant issue of improving the efficiency of an SMR-based power plant by developing the structure of the STI thermal scheme involving hydrogen technologies. This will help reduce dependence on fossil hydrocarbons in the total volume of primary fuel and enable sustainable functioning of the Ukrainian energy system, as well as contribute to the preservation and improvement of the environmental state.

The article addresses the problem of determining the thermophysical characteristics (TPC) of soil based on results from a thermal-physics experiment involving temperature measurements for the rational design of heat pump (HP) systems. The approach relies on achieving a stable solution to the coefficient inverse problems of heat conduction (IPHC) using Tikhonov regularization principles with an effective algorithm for determining the regularization parameter. The functional minimization is carried out iteratively, where at each step, the minimum of a quadratic functional is sought. This functional is constructed through linearization of the functional dependence of computed temperature on the sought characteristic, represented as two additional terms of the Taylor series. The proposed approach has proven effective for both individual thermal-physical characteristics of the medium and for solving combined IPHC while simultaneously identifying soil TPC. The article emphasizes the independence of the convergence of the iterative parameter mathematical model search process from their initial approximation. At the same time, it should be noted that the accuracy of recovering the TPC of soil depends on the number of temperature measurement points: reducing their number decreases the precision of identification. Another factor affecting the accuracy of identification is the measurement error of temperatures at the thermometry points, which is modeled in the study as a random variable with zero mean and unit variance. Thus, numerical experiments have shown that the accuracy of identification decreases as the thermometry error increases.

The use of renewable fuel and energy resources as fuel makes it possible to reduce the cost of a unit of electrical and thermal energy, reduce the load on the main energy system of the state, and improve the overall environmental impact on the environment. When using a pyrolysis pre-furnace, it is possible to use as a primary fuel: waste wood, pellets, sunflower husks, buckwheat, etc., and the use of an air turbine avoids contamination of its working surface. The aim of the work is to increase the efficiency and economy of a cogeneration power plant with an air turbine, which includes the following main elements: a fuel bunker, a pyrolysis pre-furnace, a combustion chamber-mixer, an air heater, a compressor, an air turbine, electric generator, water heater, smoke exhauster and chimney. To achieve this aim, three options for the scheme of a cogeneration plant with an air turbine with an electric power of 300 kW and with and without different connection variants of a water heater are considered and analyzed in terms of energy and economic indicators. A thermodynamic analysis of the circuit solutions of a cogeneration plant and their comparison in terms of capital costs for the creation of the plant showed that with almost the same cost for the main elements, compared with the circuit where the water is heated by air after the turbine and with the circuit where there is no water heater, the circuit of a cogeneration plant with water heating by flue gas has the highest overall efficiency. This scheme was chosen as rational. As a result of replacing the source fuel with the heat of the air turbine exhaust, the overall efficiency of the cogeneration plant according to this scheme is 73.9 %, and the electrical efficiency is 36.2 %, which corresponds to the level of a gas turbine plant according to the Brayton cycle with regeneration of the working fluid heat, at a moderate value of the degree of air compression in the compressor πk=3. The latter causes the low specific capital cost of the main equipment of the cogeneration plant – 134.6 USD/kW (excluding inflation). Keywords: pyrolysis pre-furnace, air turbine, thermodynamic analysis, capital costs, overall efficiency, electrical efficiency.