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The 610 MW subcritical power plant was originally designed to operate at a constant base load with fixed boiler steam pressure. However, due to grid oversupply conditions, the plant frequently operates at partial loads, resulting in increased inefficiencies caused by throttle losses, particularly during minimum load operations, which significantly reduce high-pressure (HP) turbine efficiency. This study investigates the impact of sliding pressure operation, which involves varying boiler steam pressure with load, on overall plant efficiency compared to constant pressure operation. A virtual plant simulation was employed to model the heat and mass balance of the power plant and simulate operational scenarios under varying steam pressures. The optimal simulation results were validated through direct testing on the plant, followed by performance analysis. The results reveal that sliding pressure operation improves HP turbine efficiency by 5-7%, reduces the net plant heat rate (NPHR) by 57 kcal/kWh, and enhances overall thermal efficiency by 0.35% at 57% load (350 MW). [ABSTRACT FROM AUTHOR]

Abstract—The article considers the efficiency and possibility of introducing into operation of VVER-1000 power units with the lifetime extended owing to the sliding pressure of the second circuit. The history of research by Russian nuclear engineers on VVER lifetime extension is reviewed. It is shown that reduction of fresh steam pressure within the allowed limits will make it possible to release additional reactivity through release of the temperature effect and to generate additional energy during the period of unit operation on the power effect. A mathematical model of changes in the main parameters of the reactor unit, including reactivity balance equations, Stodola–Flugel equation for the turbine, and heat balance and heat transfer equations in the steam generator, is compiled. The expected increase in power generation for modern fuel loadings of VVER-1000 reactors is calculated. The degree of compliance of the proposed mode with the current technological limitations of the large-series VVER-1000 power units is analyzed. The results of the analysis are confirmed by the numerical experiment on the multifunctional analyzer of the VVER-1000 unit modes developed by the National Research Nuclear University MEPhI built on the basis of the ENICAD environment and the certified diffusion neutronic code PROSTOR. Conclusions are drawn about the possibility of introducing the proposed mode into the operational practice of modern VVER-1000 power units. [ABSTRACT FROM AUTHOR]

The problem of performing deep unloading of power units is of great importance for power systems operated by PJSC Mosénergo and other companies, especially when taking into account the significant difference in electricity prices during the day and at night. As a rule, power units equipped with T-250-240 UTZ thermal steam turbines are arranged as boiler-turbine monoblocks, whose thermal start-up scheme is single-bypass. Here, fresh high-pressure steam is discharged directly into the condenser through the HP bypass, while steam removal following intermediate overheating is carried out directly in front of the intermediate pressure stop valve (IPSV) through a pipeline with shut-off valves. Since a combined sliding steam pressure is used when these power units operate under load, the unloading of the power unit comprises two stages: initial unloading to 80 – 85% nominal capacity at the nominal pressure of fresh steam and subsequent unloading of the unit to the technological minimum load at the sliding pressure of fresh steam with partially-open regulating control valves of the steam turbine HP (determined by the angle of rotation of the cam shaft at the level of 75 – 80°). With a turbine power of 120 MW and a sliding steam pressure of HP, the steam pressure in the selection will be about 1.2 – 1.4 MPa, which allows the use of a block steam collector to power the turbo drive of the feed pump at a lower steam temperature in the collector (250 – 280°C). At low loads, unloading of the unit can be carried out without switching to boiler power from a feeding electric pump. The safety of the equipment is ensured due to the presence of a regulating diaphragm that prevents the acceleration of the turbine rotor in the closed state. The turbo drive is powered by steam from the third selection of the turbine at high block loads of 100 – 120 MW; that is, when the power unit is unloaded, the feed water pump power supply scheme does not change. The hydraulic properties of the furnace walls have an unambiguous characteristic in the working area, which confirms their aperiodic stability, in particular, by tests carried out on the walls of the lower (LRS-I, LRS-II), intermediate (IRS) and upper (URS) radiant sections of the boiler in the load range up to 45% of nominal boiler capacity. Thermohydraulic maldistribution in the boiler heating surfaces does not exceed standard values to ensure reliable circulation during unloading of the power unit up to 40% of the rated capacity. Temperature fluctuations and irregularities in the distribution of the steam-water mixture in the panel of the middle radiation part have the maximum permissible values. Analysis of the temperature regime of the metal pipes of the lower and upper radiation part of the boiler showed that the temperature of the outer surface of the expanded pipe made of 12X1MF steel does not exceed 476°C, which provides a reliable temperature regime at the maximum permissible temperature of 570°C from the condition of sufficient margin for mechanical strength. [ABSTRACT FROM AUTHOR]

The HG-2100/25.4-YM16 boiler, manufactured by Harbin Boiler Co., operates as part of the 660‑MW power unit at the Troitsk district power plant (DPP). An analysis of the boiler design showed that many technical solutions adopted in the boiler differed from those commonly used by Russian manufactures. The aim of the study is to simulate and optimize the boiler startup technology without using the circulation pump (CP) but with ensuring reliable operation of the boiler components. For achieving this aim, the following main tasks must be solved: to substantiate reliable operation criteria of boiler components during the startup, to develop adapted static and adapted dynamic boiler analysis models (SM and DM, respectively), and to study the possibility of boiler starting without using the CP. The main criteria for reliable operation of the boiler's lower and upper radiant parts (LRP and URP, respectively) are the absence of a scale formation process (the design temperature of the metal outer surface must be below its permissible value) and stable motion of medium. However, the results of predicting the steam superheating surface metal temperature in a dynamic mode are not sufficiently accurate. Therefore, the reliability criterion adopted for these surfaces was the steam flowrate downstream of the separator, the values of which in the boiler starting modes with and without the pump should be close to each other. The reliable operation criterion of the low-pressure steam superheater outlet stage (LPSS2) is the gas temperature at the furnace outlet, which shall not be higher in starting without the CP. The numerical analyses were carried out using the Boiler Designer software package. The boiler adapted static model was developed taking into account the authors' previous works and with comparing them with the results of manufacturer's calculations. After that, the boiler adapted dynamic model was developed on the basis of its static model. To this end, the trends of real startup modes with participation of the circulation pump provided by Troitsk DPP specialists were used. Based on these data, taken together with the experience gained from the authors' previous numerical analyses and expert estimates, the dynamic model tuning was performed. Three boiler starting modes from its cold state were studied in detail: one with the pump (at the feed water temperature tf.w = 104°С) and two modes without the pump (at tf.w = 104 and 150°С). In all cases, the following startup stages were considered: hot flushing, turbine kicking, kicking mode end, and reaching the boiler once-through operation mode. The last stage corresponded to 30% of the boiler maximum continuous rating (BMCR). An analysis of the obtained results has shown that the adopted reliability criteria are fulfilled for all boiler operation modes and stages. [ABSTRACT FROM AUTHOR]

The operation of a steam boiler in a sliding pressure mode is characterized by certain advantages in comparison with the usual mode of equipment operation: it becomes possible to reduce the power unit's minimum allowable load, reduce the electric energy expenditures for driving the feed pump, and reduce the specific reference fuel consumption. Increasing the equipment energy efficiency is a priority task for all power plants. Shifting a power unit for operation in a sliding pressure mode is a universal way to solve this problem irrespectively of the boiler type (drum or once-through) and the kind of combusted fuel (coal, natural gas, or fuel oil). Up to date, practical implementation of boiler operation in a sliding pressure mode has not received wide application in Russia. The existing examples of a power unit's operation at sliding pressure are mainly associated with the transient conditions of equipment operation and are only related to once-through boilers. In drum boilers, practical studies of their operation at sliding pressure were not carried out in view of certain difficulties connected with the change of heat transfer conditions in the waterwall heating surfaces. The article presents the results of activities aimed at shifting the Cherepet state-owned district power plant (SDPP) 225-MW power units equipped with Ep-630-13.8-565/570KT (the TPE-223 model) drum boilers for operation at sliding pressure. These boilers use grade D coal from the Kuznetsk field as the main fuel. The operation of the power units was modeled using the Boiler Designer computer program, and a procedure for estimating the economic feasibility of shifting the power units to operate at sliding pressure was elaborated. Based on the results of preliminary studies, operational and adjustment tests of the power units were carried out, which confirmed the possibility and economic feasibility of shifting them to operation in the sliding pressure mode. The study results are presented, and the possibility of extending such practices to a significant part of the operating boiler and turbine equipment at the power plants of Russia is evaluated. [ABSTRACT FROM AUTHOR]

Large power units have to run under deep variable load operations to reduce the regulation peak of power systems. The sliding pressure operation is now recognized as one of the most effective ways to improve economy and safety at variable load operations. In this paper, we examine the effects of back pressure and steam extraction on the optimum sliding pressure operation curve and analyze the limitations of the traditional sliding pressure operation curve design methods. Consequently, we propose a new optimization method for the sliding pressure operation that uses the main steam flow rate as an independent variable. Our results show that the sliding pressure operation curve obtained via the proposed method can overcome the effect of the heating steam extraction capacity and back pressure on the unit. The proposed method also satisfies the economic operation in different working conditions, and can easily be implemented in the Distributed Control System (DCS) transformation. Optimization transformation of the variable load running economy by application of the method in an air-cooled unit resulted in significant improvement. It significantly enhances the safety and efficiency of thermal power generating units, which are dominant in China. [ABSTRACT FROM AUTHOR]

Global concerns regarding greenhouse gas emissions and global warming have necessitated the speed up in using renewable energies and more efficient use of fossil fuels in the oil and gas industry. Harvesting gas turbine heat by organic Rankine bottoming cycles has raised as a potential solution to cut carbon dioxide emissions in offshore oil and gas installations. Offshore power cycles are expected to operate most of their operational life at part-loads where they suffer from poor efficiency. The purpose of this article is to boost the part-load efficiency of offshore organic Rankine cycles and keep it as close as possible to the design value. Here an operational strategy based on cooling water flow control is developed and added to a sliding pressure control logic and a variable area nozzle turbine control strategy. An in-house tool is developed for the design of organic Rankine cycles and the simulation of off-design control strategies. A design methodology is presented to optimize the cycle power output while minimizing the cycle footprint offshore. The proposed control strategy was successful in keeping the part-load efficiency close to design value and achieving a 5% reduction of annual carbon dioxide emissions. [ABSTRACT FROM AUTHOR]

Technical solutions for the hydraulic layout of the water-steam circuit and a new type of starting separator for the P-50R boiler of the No. 3 power unit at the Kashirskaya SRPP, as well as and results of their in-service confirmation are presented. [ABSTRACT FROM AUTHOR]

This paper presents an analytical study of the stationary response of a liquid loaded on its free surface by an ideal pressure step moving in a constant direction at a constant velocity. The acoustic pressure in the liquid is found, in four different examples, by means of the Fourier Transform. Two loading regimes are considered; subsonic and supersonic. Two configurations of liquid domains are also studied, the first one is a half infinite space while the second one is bounded by a rigid bottom at a finite depth. For the two supersonic cases, a simple reasoning based on the existence of a front of discontinuity in the liquid and on the property of reflection of waves confirms the result of the mathematical investigations. The results obtained for the steady state case are of intererest, even when the loading is not exactly stationary, such as the presure produced by an explosion occurring in the vicinity of the surface of a liquid. Two numerically resolved examples are presented, which confirm this assumption. [ABSTRACT FROM AUTHOR]

Results of testing a novel process of startup of 800-MW supercritical-pressure units at sliding pressure in the entire conduit of the once-through boiler with the temperature of extraneous steam in the station-service header supplying the turbine-feeding pump reduced to ∼250°C and intermediate transfer of its feed to its own steam through the available station-service starting-shedding device are given. It is shown that the use of this process makes it possible to fully pass to steam supply of the unit from the colder second extraction of the turbine. A variant of updating the steam feeding circuit is suggested. [ABSTRACT FROM AUTHOR]