Low-pressure Cylinder Research Articles

Recovering Low-Grade Heat from Flue Gas in a Coal-Fired Thermal Power Unit

To achieve the goals of carbon peaking and carbon neutrality, the retrofitting of existing coal-fired power plants is crucial to achieving energy-saving and emission reduction goals. A conventional recovery system of waste heat typically occurs downstream of the air preheater, where the energy quality in flue gas is low, resulting in limited coal-saving benefits. This study proposes a scheme involving a flue gas exchanger bypassing the air preheater and low-temperature economizers, which is used to transfer the waste heat from flue gas to primary and secondary air (System I). Additionally, a heat pump can be introduced to provide supplementary energy for primary and secondary air, as well as the condensate from the steam turbine (System II). The coal consumption rate and exergy efficiency are used to evaluate the two schemes. The results show that both waste heat recovery systems can increase the power output of the coal-fired unit by recovering waste heat. System II can boost power output by approximately 13.98 MW. The power increase in both waste heat recovery systems show a declining trend as the unit load decreases. This increased power is primarily attributed to the medium- and low-pressure cylinders, while the contributions from ultra-high-pressure and high-pressure cylinders are negligible. The increased power output for the medium-pressure cylinder ranges from approximately 3.49 to 3.58 MW, while the low-pressure cylinder has an increased power output of around 10.10 to 10.19 MW. The coal consumption rate is decreased from 250.3 g/(kW·h) to 247.5 g/(kW·h) under a full load condition for both systems, which can be augmented at lower load conditions. System II outperforms System I at 30% load condition, achieving a reduced coal consumption rate of 3.36 g/(kW·h). System I has an exergy efficiency of 40%, while System II shows a higher efficiency of 44%.

Evaluation and Improvement of the Flexibility of Biomass Blended Burning Units in a Virtual Power Plant

Aiming at the problems of small thermal power units and biomass mixed combustion units with small generation loads and insufficient primary frequency modulation capability, which cannot be connected to the virtual power plant, this paper adopts a variety of flexibility retrofit methods for the units and explores the peak load capability of the units. Then, multiple units are coupled, and the unit coupling scheme with better economy and environmental protection is screened using comprehensive evaluation indexes. While evaluating the peaking load space of multiple unit coupling, the units’ primary frequency regulation capability and new energy consumption capability are improved. According to the calculation results, the low-pressure cylinder zero-output retrofit has the largest peaking potential among different technical paths, in which unit #3 has 27.55 MW of peaking space. The compression heat pump decoupling retrofit has the best economy, in which the daily profit of unit #3 increases from 0.93 to 1.02 million CNY with an increase of 0.09 million CNY. After the unit has been retrofitted with steam extraction, the three units can be coupled to meet the national feed-in standards. The multiple unit coupling can accommodate up to 203.44 MW of other energy sources while meeting the standard.

Study of cracks in the last-stage rotor blade of a steam turbine and the corrosion fatigue properties of its materials

In this study, to clarify the failure mechanism of the last-stage rotor blade in the low-pressure cylinder of a steam turbine, the peculiarities of crack initiation and propagation on the inlet side of the last-stage rotor blade at a distance of 125–165 mm were analyzed, along with the corrosion fatigue properties of its materials. The results showed that crack initiation occurred at the tip of the pit due to a combination of factors: stress concentration at the tip of the pit, corrosion of the Cr-poor area near the prior austenite grain boundary, centrifugal tensile stress, and steam bending stress. The crack propagation could be divided into the initial intergranular and late transgranular propagation stages. The main reason for the initial intergranular propagation was stress corrosion, and the main reason for the later transgranular propagation was corrosion fatigue. High-frequency induction quenching technology can improve the microhardness of the blade's surface material and enhance the blade's resistance to water erosion, but it may also reduce the corrosion fatigue resistance of the blade material. The rotary bending corrosion fatigue test can effectively simulate the crack propagation process of the blade. These results are of great significance for the safe operation of the last-stage rotor blade in the low-pressure cylinder of a steam turbine.

Isentropic and exergy analyses of marine steam turbine segments at several loads

This research presents isentropic and exergy analyses of marine steam turbine segments at three loads. Turbine segment is a part of any cylinder which is placed between the steam entrance to the cylinder and first steam extraction, between steam extractions and finally between last steam extraction and steam exit from the cylinder. Division of each cylinder to the segments allows insight into the various cylinder parts operation and an observation is the cylinder properly balanced. The analyzed marine steam turbine is composed of two cylinders – High Pressure Cylinder (HPC) and Low Pressure Cylinder (LPC), while each cylinder has two segments. The dominant part of real mechanical power produced in HPC is actually produced in the first HPC part (segment 1), while in LPC, the dominant part of real mechanical power is produced in the last LPC part (segment 4). Segments 1 and 3 have the highest improvement potential (inlet segments of both HPC and LPC) due to the highest isentropic losses and exergy destructions. HPC is much better balanced cylinder because along with isentropic, also exergy efficiencies between its segments (segment 1 and segment 2) at all loads differ lower than 7%, while the same cannot be stated for the LPC which exergy efficiencies between segments (segment 3 and segment 4) at all loads differ more than 20%. Very low isentropic and exergy efficiencies of the segment 3, at all observed loads, indicate that this turbine segment is highly problematic and at least some of the turbine stages mounted in this segment have difficulties in operation or potential malfunction. In addition, segment 3 is also the highest influenced by the ambient temperature change in comparison to other segments. The ambient temperature increase from 5 °C up to 45 °C can decrease segment exergy efficiency between 1.31% and 3.17%, if all the segments and all loads of the analyzed marine steam turbine are observed.

Fracture Analysis and Repair of Last Stage Blade Reinforcement Boss for Low Pressure Cylinder Rotor of 330 MW Unit

The lace convex table of the final stage blade of a 330 MW turbine fractured. The reason was analyzed by fracture analysis, chemical composition analysis and metallographic analysis. It showed that the overload was the main reason for the fracture. Deformation of guide ring caused by fracture of guide ring bolt was the main reason of the overload. The analysis of the guide ring bolt showed that the brittleness of the guide ring bolt was the main reason for its fracture. It was suggested to strengthen the supervision of the manufacturing process of the guide ring bolt. The lace convex table was repaired by surfacing welding. A reasonable welding process was developed and the repair was successful.
 Abstract, Final stage blade, Lace convex table, Surfacing welding, Welding repair

Study of high power steam turbine forced oscilla-tions near operating frequency

Problem. Forced oscillations of the turbine unit-foundation-base system near the operating frequency are considered. Goal. The purpose of the work is to study forced vibrations of the turbine unit-foundation-base system near the operating frequency range to assess the vibration state of the system and determine the causes of increased vibrations. The object of the study is the turbine unit-foundation-base system. The system consists of a single reinforced concrete foundation on which a steam turbine and generator are installed. The subject of the study is the amplitude-frequency dependences of forced oscillations of the turbine unit-foundation-base system. Methodology. The study was carried out using vibration methods and the finite element method. Also worth noting is the use of original methods developed directly by the author for constructing models of complex mechanical engineering systems. Results. As a result of the research, three-dimensional finite element models of low-pressure cylinder housings, the foundation and the entire turbine unit-foundation-base system were built. The conducted research allows us to draw a conclusion regarding the reasons for the increased level of vibration near the operating frequency and directions for their prevention. Originality. Regarding the methods for constructing a model of the turbine unit-foundation-base system, it should be noted that they are unique. The features of the applied modeling method make it possible to take into account the variable interaction between the low-pressure cylinder bodies and the foundation. Fixpoints are also taken into account. Previous studies of the turbine unit-foundation-base system did not allow us to determine the causes of increased vibrations of the shaft line supports. Practical significance. The results of the work relate to direct practical application. As a result of the work, conclusions were drawn about the ways to increase the vibration reliability of the turbine unit-foundation-base system and further directions for research.

Rational Mode Parameters of Power Units Operating in Modern Energy Market Conditions

The paper analyzes the operation of condensing and heating turbines in modern energy market conditions with an assessment of the impact of operating parameters of live and secondary steam on economic indicators. It has been shown that when operating at variable loads, the most effective in terms of high-pressure turbines is a rational reduction in the initial pressure ps (sliding pressure), which leads to an increase in thermal efficiency by 1-1.5%. The experimental results of a study of the vacuum effect in the condenser on fuel consumption are presented in the paper as well. Using a specific example of the K-320-26.5 turbine unit, the need for a rational choice of cooling water flow in winter season to ensure optimal vacuum is shown. The issue of choosing a rational steam reheat temperature tr is examined in more detail. It has been established that one of the main reasons for the decrease in the efficiency of turbine units when operating in variable modes is the irrational use of the reheat temperature and the heat of phase transition in the flow part of the low pressure cylinder. The physical explanation of these processes in the turbine as tr decreases is given in detail. It has been shown that, as a result of analyzing the operation of turbine units of various capacities, a rational choice of reheat temperature (reducing tr by 10-20 °C) increases thermal efficiency by 1-2 %, and turbine efficiency - by 0.4-1.0 %. It is recommended to consider the pressure of the hot steam of the high pressure cylinder (рs), the pressure in the condenser (рc=f(tcirc.water)), as well as the reheating temperature tr, which altogether leads to a reduction in heat consumption by 2.5-3.5 % as rational parameters of steam when operating in variable modes. In order to increase the economic efficiency of the operation of turbine units of TPPs and CPPs at reduced loads, it is recommended to revise the regulatory documentation on the current amendments for changes in the reheat temperature. It is stated that with strict adherence to the recommendations discussed above, fuel savings at TTPs and CHPs in Ukraine can amount to 250–300 thousand tons of coal per year.

Study on the characteristics of molten salt heat storage in the fast peak regulation of coal-fired power unit

The load variation rate of the coal-fired power unit in China is generally around 2%, and the new technology is needed to further improve the load variation rate and to increase the peak regulation benefits. In this paper, the molten salt is utilized to constructed the ?Carnot battery? based on the coal-fired power unit, in order to increase the load variation rate of the coal-fire power units, and the regulatory characteristics of the molten salt system during load variation processes and the coupling characteristics with the boiler and turbine are investigated. The results indicate that, the load variation rate in the 20-100% load can be improved to 6% Pe per minute for a 300 MW coal-fired power unit when molten salt system with power of 301 MW and thermal storage duration of 83.6 MWh is coupled, in which the maximum molten salt temperature is, and the steam produced by molten salt is added into the low pressure cylinder of turbine. The average power generation efficiency of the ?Carnot battery? constructed by the boiler and molten salt during the variable load regulation process is 38.72%, and the average power generation efficiency of the molten salt system is 24.57%. This study indicates that the small-scale molten salt systems can be used to improve the load variation rate of the coal-fired power units.

Thermal economy simulation study for a carbon capture power plant with combined heat and power based on absorption heat pump technology

The Combined Heat and Power (CHP) system represents an energy-efficient and environmentally-friendly approach to energy utilization. However, in the context of the “carbon peaking and carbon neutrality” strategy, ensuring low-carbon operation of CHP systems becomes imperative. In this study, based on absorption heat pump (AHP), an extraction condensing carbon capture (EC&CC) CHP coupled system and a low-pressure cylinder zero-output carbon capture (LCZ&CC) CHP coupled system are proposed, respectively. Furthermore, under the 100 % turbine heat acceptance (THA) operating condition, a variable operating condition study of heating load and carbon capture capacity is conducted. The results demonstrate that under identical heating load, the EC&CC CHP coupled system has superior thermal economy, with an average reduction of 1011.03 kJ/kWh in heat consumption of power generation and 34.54 g/kWh in coal consumption of power generation compared with the LCZ&CC CHP coupled system; For equivalent carbon capture capacity, the LCZ&CC CHP coupled system has superior thermal economy, with an average reduction of 771.28 kJ/kWh in heat consumption and 26.35 g/kWh in coal consumption of power generation compared with the EC&CC CHP coupled system. The EC&CC CHP coupled system has lower CO2 capture heat consumption, resulting in an average reduction of 135.67 t/h in carbon capture extraction compared with the LCZ&CC CHP coupled system. This study can provide guidance for optimizing the design of carbon capture CHP coupled systems.

АЭС малой мощности с аккумулятором теплоты фазового перехода

Nuclear power plants (NPP) are characterized by low maneuverability. This fact exacerbates the problem of the balance of generated and consumed power when nuclear power plants are used as an energy source. This problem is especially relevant for isolated power systems. One of the ways to increase the maneuverability of nuclear power plants is to use heat accumulators directly in the NPP circuit. The study is carried out for two most attractive options of including a heat accumulator in the NPP circuit: 1) parallel to a high-pressure heater to heat feed water; 2) to generate additional steam for a low-pressure cylinder. The efficiency of each of the options is determined based on the calculation of thermal schemes of nuclear power plants with a heat accumulator. The authors have calculated the power of the turbine unit and electricity generation when a heat accumulator is included in the nuclear power plant circuit. The analysis of the data obtained shows that when using a heat accumulator in the NPP circuit in parallel with high pressure heater to heat feed water, the power of the turbine unit is increased by 7,2 % in the accumulator discharge mode, and additional electricity generation due to accumulated heat is 0,63 MJ for each kilogram of waste steam. When using a heat accumulator to generate additional steam for a low-pressure cylinder, the power of the turbine unit is increased by 6,6 % in the accumulator discharge mode, and the additional power generation due to the accumulated heat is 0,40 MJ per kilogram of waste steam. Application of heat accumulators in the NPP circuits will allow using the accumulated heat to generate additional electricity during high demand hours. Thus, the use of heat accumulators in NPP circuits is a way to increase the maneuverability of nuclear power plants, to reduce the negative impact of maneuverable modes on NPP equipment, and to reduce the number of liquid radioactive waste. The most effective and simple way to use the heat accumulator in the NPP circuit is to install it in parallel to the high-pressure heaters. In future, it is planned to determine the design of the heat accumulator, to model heat exchange processes in the heat accumulator

THERMAL STATE OF THE LOW-PRESSURE CYLINDER WORKING BLADES OF THE COGENERATION TURBINE T-250/300-240

The important problem of researching the temperature state of the low-pressure cylinder of a powerful cogeneration turbine, which works, unlike condensing turbines, in conditions of significant changes in electrical and thermal load, is considered. This is since the low-pressure cylinder of the cogeneration turbines in the heating season operates at the low-flow rate modes due to the large selection of steam for heating. Such operating conditions are accompanied by the nucleation of vortex structures in the flow path, which leads to a significant increase in mechanical energy losses and, consequently, to an increase in the temperature of the elements of the flow path. The aim of the study is to determine the thermal state of the steam in a wide range of changes in the operation modes of the cogeneration turbine. The analysis of the results of experimental studies obtained on full-scale low-pressure cylinders of a powerful T-250/300-240 steam turbine by various authors in conditions of wide changes in operating parameters (the pressure in the condenser, the steam consumption in the flow path, the temperature of the lower heating selection) was performed. This made it possible to determine the temperature distribution along the height of the working blade of the last stage, which is of the greatest interest in the conditions of operation at the low-flow rate modes. The location of the minimum temperature is established, and a dependence is proposed for its determination at the exit from the working wheel of the stage, considering that the main generator of heat during steam heating is a rotating vortex in the rim clearance. It is shown that the limiting value of steam consumption through the last stage, which corresponds to the transition of the flow from the area of wet steam to the area of superheated steam, at a given temperature level in the lower heating selection, depends on the pressure in the condenser and can be determined as a function of these parameters. At the same time, with a decrease in the temperature in the lower heating selection and the pressure in the condenser, it will lead to the fact that the transition from the west steam to the superheated steam is observed at lower consumption. The increase of process moisture at the outlet of the working wheel occurs when the steam flow is greater than its limiting value.

Integrated Studies of Electrophysical Processes in Steam Turbines

The paper deals with comprehensive research in the field of electrization of wet steam flow in a turbine. The experience of the conducted studies on laboratory stands and full-scale objects (CHP and TPP) in Ukraine and the USA is introduced and generalized. It was shown that in the process of steam electrization, the charge density in the flow can reach very high values (an order of magnitude appears to be higher than in a thundercloud), and this phenomenon mainly has a negative effect on the turbine operation. Statistical data on the charge formation of the steam flow in the low-pressure cylinder of the turbine are presented. Results of the research to establish the main electrophysical factors of influence on the surface strength of the blade, such as electric fields, charge density and their polarity, are presented. The research results showed that such factors as the presence of a positively charged steam flow, constant and variable electric fields, which were most often recorded at operating turbines of CHPs and TPPs, significantly (by two or more times) intensify erosion-corrosion processes on the metal surfaces of the blades, thus reducing their working resource. Thermodynamic processes are studied both under conditions of natural electrification of a high-speed flow, which reduce the efficiency by about 0.3–0.35%, and under the influence of artificially created electric charges, which make it possible to increase the efficiency of the steam expansion process in the turbine by 2 or more percent. Various options of local input of electrical energy for steam ionization in the turbine are considered. At the same time, it is noted that for the practical implementation of these approaches, further careful design improvements and tests on model and full-scale installations are required. Water chemistry regimes are also considered in the context of their influence on the flow charge formation process, as well as on reliability and efficiency indicators of the turbine. Experimentally at an 800 MW turbine plant in the USA, it was shown that a change in the pH of the medium affects the intensity and polarity of the charge formation of the steam flow. The paper introduces the physical features of this phenomenon and notes the importance of these processes influence on the strength characteristics of the blades. Information on new methods and technologies that could lead to an increase in the operational efficiency and reliability of wet steam turbines, such as methods for input and removal of electrical energy into the flow; rational choice of water chemistry regimes; space charge neutralization, etc., is provided. These comprehensive electrophysical studies, considered in conjunction with thermal processes, can be characterized as a new scientific direction in the theory of steam turbines – thermal electrophysics.

Failure study of steam turbine Last-Stage rotor blades under a High-Speed wet steam environment

The failure mechanism of the last-stage rotor blade of the low-pressure cylinder of a steam turbine when exposed to high-speed wet steam was elucidated. The results indicated that the combined effects of water erosion, stress corrosion, and corrosion fatigue resulted in the failure of the shroud-lacing wire section (which was made of martensitic stainless steel through the high-frequency induction hardening method) on the steam inlet side. Furthermore, the combined action of the water hammer pressure of the secondary water droplets and the pressure of the cavitation jet caused water erosion and the formation of pits. Additionally, the combined action of the stress concentration at the ends of the pits, the stress concentration at the inlet side structure, and the alternating stress-induced crack initiation at the inlet-side shroud-lacing wire section. Finally, the crack propagation was accelerated by the combined action of stress corrosion and corrosion fatigue. This study provides theoretical guidance for inhibiting the growth of pits and prolonging the fatigue life of blades.

Cooling and dehumidification performance study of a new air conditioning system with double evaporation temperature

In order to improve the cooling and dehumidification performance of household air conditioners, a new air conditioning system with double evaporation temperature is proposed. The simulation model of the new system is established, the variation of system performance with compressor high/low pressure cylinder volume ratio, inlet air temperature, relative humidity, air speed, etc. are simulated and experimentally studied. The research results show that when the volume ratio of high and low pressure cylinders of compressor is 0.5∼1.2 and air speed 2.2 m/s, cooling COP of double evaporation temperature air conditioning system could obtain the maximum value. Compared with single evaporation temperature system, cooling COP of double evaporation temperature system can be increased 3%∼4.2%; the dehumidification capacity is 0.06∼0.61kg/h, about 1.69%∼5.83% higher.

Use of Synthetic Data in Maritime Applications for the Problem of Steam Turbine Exergy Analysis

Machine learning applications have demonstrated the potential to generate precise models in a wide variety of fields, including marine applications. Still, the main issue with ML-based methods is the need for large amounts of data, which may be impractical to come by. To assure the quality of the models and their robustness to different inputs, synthetic data may be generated using other ML-based methods, such as Triplet Encoded Variable Autoencoder (TVAE), copulas, or a Conditional Tabular Generative Adversarial Network (CTGAN). With this approach, a dataset can be trained using ML methods such as Multilayer Perceptron (MLP) or Extreme Gradient Boosting (XGB) to improve the general performance. The methods are applied to the dataset containing mass flow, temperature, and pressure measurements in seven points of a marine steam turbine as inputs, along with the exergy efficiency (η) and destruction (Ex) of the whole turbine (WT), low-pressure cylinder (LPC) and high-pressure cylinder (HPC) as outputs. The achieved results show that models trained on synthetic data achieve slightly worse results than the models trained on original data in previous research, but allow for the use of as little as two-thirds of the dataset to achieve these results. Using R2 as the main evaluation metric, the best results achieved are 0.99 for ηWT using 100 data points and MLP, 0.93 for ηLPC using 100 data points and an MLP-based model, 0.91 for ηHPC with the same method, and 0.97 for ExWT, 0.96 for ExLPC, and 0.98 for ExHPC using a the XGB trained model with 100 data points.

Analysis of the Design of Henry Muncaster’s Two-Cylinder Compound Vertical Steam Engine with Speed Control

This article offers an analysis, from the mechanical engineering viewpoint, of an invention by Henry Muncaster from 1912: the two-cylinder compound vertical steam engine with speed control. This is an invention with a large number of components (106) that was used as an engine in boats and railways. The ultimate objective of this investigation was to determine the operating conditions (maximum pressures of water vapor in the admission of high- and low-pressure cylinders) according to the criteria of resistance of materials since there is no information about this. Therefore, two critical operating conditions were simulated that resemble the start-up of the machine (flywheel locked as the most unfavorable situation) in order to determine those operating conditions that ensure both its safety and optimal operation. For this, a static linear analysis based on the finite element method (FEM) of the 3D CAD model was carried out under real operating conditions, according to the criteria of resistance of materials, using the Autodesk Inventor Nastran 2023 software. The results of the static linear analysis (von Mises stress, displacement and safety factor) confirmed the maximum values of the vapor pressure in the admission of the cylinders: 0.3 MPa on the high-pressure piston plunger and 0.15 MPa on the low-pressure piston plunger.

Comparative study on flexibility enhancement of combined heat and power for wind power accommodation

Flexibility enhancement of coal-fired combined heat and power units is an essential approach for improving the wind power accommodation and a significant low-carbon way to achieve clean urban heating. To consume excess wind power, this paper proposed a novel combined heat and power system integrated with the various flexible technologies. The EBSILON software was applied for modeling the proposed thermal systems and analyzing the thermal performance under different operating conditions. On this basis, the mechanism of their heating compensation and wind power consumption was revealed and the indicator, the heating compensation capacity, was presented considering from both peak shaving and coal-savings perspectives. Compared with the conventional system, the wind power accommodation rate of the novel system had a maximum increment of 31.7% and the standard coal consumption had a maximum reduction of 14.3%. Meanwhile, by adding dynamic payback period and internal rate of return, the techno-economic performances were more reasonable and precise. The results showed that the heating compensation capacities of absorption heat pumps, low-pressure cylinder of turbine removal and thermal energy storage with extracted steam from turbine are 0.29 t/MWh, 0.26 t/MWh, and 0.25 t/MWh, respectively, which are better than that of other technologies. The net annual revenue of thermal energy storage system could reach 3.87 M$, 0.57 and 0.37 M$ higher than that of low-pressure cylinder of turbine removal and absorption heat pumps, respectively. It can be concluded that thermal energy storage can be the best to balance the peak shaving demand and techno-economic performance. In all, the proposed systems provided a promising method for the flexibilization of coal-fired combined heat and power units alongside new renewable systems.

POWER EXPENSES TO DRIVE A TURBINE STAGE UNDER LOW-FLOW MODES

The task of determining the power consumption during the operation of the turbine stage in the low-cost mode is considered. To solve it, a theoreticalexperimental approach was used, based on the one-dimensional theory of the movement of a incompressible working medium and the results of an experimental study of a number of models of large fanning degrees, in which the working medium is air. When operating heating turbines, the lowpressure cylinders work in the area of low-cost modes up to 85 % of the time, both with a partially and completely closed rotary diaphragm of the regulating stage. When the volumetric flow rate of steam in the flow part of the low-pressure cylinder at low-flow modes is reduced, a sleeve separation of the flow develops and a vortex is formed in the inter-crown gap of the stage. The mode in which the power supplied to the impeller is spent on maintaining these currents corresponds to the "pure" ventilation mode. In contrast to the existing methods for determining the ventilation power losses in the stages of large fanning, the paper proposes a dependence based on the geometric configuration of the stages of the low-pressure cylinder of the heating turbines and their operating conditions. Taking into account the processes in the stage and the data obtained on the experimental stand, formulas were determined account the components of power losses - the function of the influence of the flow exit angles from the guide apparatus of the stage; influence of fanning l/Dmid; influence of the relative width of the working blade B/Dmid and the angle of inclination of the peripheral meridional circuit γm. The obtained dependences, which allow determining the coefficients of power consumption for the stage in the ventilation mode and the operation mode before idling, make it possible to calculate power consumption in the entire range of changes in low-flow modes. On the example of the last stage of the T-250/300-240 turbine, a comparison of the results of calculation studies according to the proposed dependence with the results obtained in real conditions of full-scale experiments was performed, which showed that their difference does not exceed 5 %.

Termodinamička analiza i usporedba dviju propulzijskih parnih turbina

This paper presents thermodynamic (energy and exergy) analysis and comparison of two different marine propulsion steam turbines based on their operating parameters from exploitation. The first turbine did not possess steam reheating and had only two cylinders (high-pressure and low-pressure cylinders), while the second turbine possesses steam reheating and has one additional cylinder (intermediate-pressure cylinder). In the literature at the moment, there cannot be found a direct and exact comparison of these two marine steam turbines and their cylinders based on real exploitation conditions. Along with energy and exergy analyses, the research it is investigated the sensitivity of exergy parameters to the ambient temperature change for both turbines and each cylinder. It is also presented the influence of the steam reheating process on the energy and exergy efficiency of the entire power plant. For both observed turbines and their cylinders it is valid that relative losses and efficiencies (both energy and exergy) are reverse proportional. The operation of an intermediate pressure cylinder from a steam turbine with reheating is the closest to optimal. Due to the different origins of losses considered in energy and exergy analyses, each analysis detects different turbine cylinders as the most problematic ones. The steam reheating process decreases losses and increases efficiencies (both energy of each turbine cylinder and the whole turbine. The whole turbine with reheating has an energy efficiency equal to 81.46% and an exergy efficiency equal to 86.48%, while the whole turbine without reheating has energy and exergy efficiencies equal to 76.47% and 80.94%, respectively. Exergy parameters of a steam turbine without reheating as well as its cylinders are much more influenced by the ambient temperature change in comparison to the steam turbine with reheating and its cylinders. The steam reheating process will increase the efficiency of the whole power plant in real exploitation conditions between 10% and 12%.

Study on flow characteristics of leakage in the last stage inner blade tip clearance of steam turbine

Internal steam leakage in steam turbines from the high-pressure side to the low-pressure side through clearances causes loss, resulting in reduced efficiency and potentially compromising the safe operation of the turbine. Therefore, a comprehensive understanding of the flow characteristics of leakage through blade tip clearances is crucial to improve the efficiency of steam turbines. In this paper, the last stage blades of the low-pressure cylinder of a certain 600 MW ultra-supercritical steam turbine unit were studied. A wet steam flow model and a turbulence model were established, and the flow characteristics of the last stage under different inlet parameters, outlet parameters, and tip clearance sizes were analyzed. The results showed that an increase in the clearance size affects the inlet and outlet steam angles of the rotor blades, with significant changes occurring near the blade tip. The main flow velocity inside the rotor blade channel fluctuates violently starting from the 70% axial position. The high entropy region is located near the exit flow region of the rotor blade, with its range expanding as the clearance size increases. The entropy change is significant at 60% blade height and above, with more intense changes occurring in the blade tip area. The relative leakage amount and efficiency change uniformly with clearance variation. Generally, for every 0.1% increase in clearance height, the relative leakage amount increases by ∼0.31%–0.42%, and the stage efficiency decreases by 0.34%–0.44%. The results of this study can provide a theoretical basis and guidance for improving the flow efficiency of steam turbines.