High Pressure Steam Turbine Research Articles

Numerical investigations of transient thermal loading of steam turbines for SMR plants

One of the well-known technologies that fit well into the goal of reduction of greenhouse gas emissions is nuclear energy. In particular, the change in approach to the design and construction of nuclear power plants led to the development of small modular reactors (SMRs), which are characterized by a broader range of possible applications than large nuclear reactors and the ability to flexibly operate as per load demand. This paper presents an analysis of the thermal loads of a steam turbine rotor operating in a power plant with SMR. Steam-water cycle and turbine train of a 300 MW unit are presented. High-pressure steam turbine rotor and its thermal loading due to varying steam conditions are investigated for a cold startup designed with consideration of the thermal characteristics of nuclear reactors. It was shown by numerical simulations that steam condensation on rotor surfaces plays a crucial role in determining its thermal behaviour. Comparison with conventional rotors has shown that the thermal loading of nuclear turbine rotors is lower and more stable than that of conventional turbines.

Continuum damage mechanics of cyclic viscoplasticity using asymptotic numerical method

Conscious efforts on reduction of greenhouse gas emissions have led to an energy transition to renewable energy, however uncertainties of renewable energy production have resulted in higher thermal cycling demands from conventional power plants. Thermal load cycling at high temperature regions of steam turbine components leads to enhanced creep-fatigue damage accumulation. It is well established that such damage mechanism is numerically best predicted by unified constitutive modeling including damage as a variable as per the formalism of continuum damage mechanics at an expense of considerable computational efforts using finite element analysis. In this paper, the non-iterative Asymptotic Numerical Method (ANM), currently limited to partial cycle analysis with linear hardening plasticity model, is proposed for the first time to address cyclic viscoplasticity problems including damage capable of handling multiple cycles and most generalized loading conditions. Regularization techniques additionally necessary to implement loading-unloading-reloading criteria and advanced constitutive models etc. are presented. The constitutive model chosen for the formulation includes the non-linear multiple back stress variable modified Chaboche model to include damage combined with modified Chaboche-Rousselier isotropic hardening model to include damage, power law for viscoplasticity, Lemaitre’s damage potential and Kachanov-Rabotnov’s creep damage law. The method is verified with defined error measures and then applied to two high pressure steam turbine rotors, one with and another without thermal stress relief groove (TSRG) at the inlet under service type loading conditions to study the beneficial effect of the TSRG on creep-fatigue damage evolution. The accumulated errors of the proposed ANM and computational time are compared to a conventional Newton-Raphson solution.

The influence of stator-rotor interspace overlap of meridional contours on the efficiency of high-pressure steam turbine stages

The influence of stator-rotor interspace overlap of meridional contours on the efficiency of high-pressure steam turbine stages

Validation of the impedance spectroscopy method (MSID2/3) for NDT and SHM research in the power industry

The article presents a method for diagnosing steel blades of a high pressure steam turbine by analyzing the frequency of the electrical and magnetic parameters of the material during its operation. The methodology is historically derived from the analysis of normalized impedance components for defect detection and material selection. It was developed by and his research team. The extended possibilities of diagnostic tests of Multipoint Impedance Spectroscopy (SID2/3) are described, including material degradation processes and not only con tinuity defects. The test results were compared with structural studies, scanning electron microscopy (SEM) and energy dispersive X ray spectrometry (EDS) and wavelength dispersive (WDS). Impedance spectroscopy takes a significant place in diagnostic tests (NDT and SHM) in domestic literature and, thanks to the author, also in foreign literature. The topic was also presented at the World NDT Congress in Munich in 2018 [23]. Articles on this topic can be found on the NDT.net website [24]. Impedance spectroscopy is the subjec t of two doctoral theses and the promotion of Doctors of Technical Sciences [27, 28]. The thematic area covered by this article is mainly aimed at comparing the results with several selected methods.

Failure Analysis of High-Pressure Turbine Blades in Steam Power Plants

This paper describes the failure of high-pressure steam turbine blades. During the Serious Inspection, it was discovered that the ninth-stage high-pressure turbine blade had failed. The causes of blade failure are examined via visual inspection and destructive testing. The failure mechanism of the blades was determined by conducting mechanical properties testing, metallographic inspection, and energy spectrum analysis. The mechanical properties of the leaf and root blade specimens were within the range of blade steel for steam turbines according to the Chinese National Standard (GB/T 8732-2004), but the chemical composition was not identical. This is consistent with the root blade fracture pattern where the hardness value plotted from the test results is the lowest at the root blade location, which is the primary cause of fissure propagation.

Thermodynamic and economic analysis of a revised Graz cycle using pure oxygen and hydrogen fuel

In order to improve the energy efficiency of hydrogen storage for power generation, in this work, an improved Graz cycle (R-Graz cycle) was proposed, which can realize more efficient hydrogen to electricity conversion. The modeling and optimization program of the cycle was developed based on MATLAB, and the thermodynamic properties of the working fluid were obtained by REFPROP. The results show that the R-Graz cycle can reach a net efficiency of 70.98% at the design point, which is about 0.5% higher than that of the Graz cycle with the same input parameters, and much higher than that of the modern gas-steam combined cycle. With the same amount of hydrogen input, the R-Graz cycle can produce 0.34% more electricity than the Graz cycle. At the design point, the levelized cost of electricity (LCOE) of the R-Graz cycle is 156.23 $/MWh, which is 0.22% lower than that of the Graz cycle, and the net present value is also higher. Analysis on the influence of key parameters shows that increasing the inlet temperature and pressure of the high-temperature gas turbine and the inlet temperature of the high-pressure steam turbine as well as reducing the condenser pressure are conducive to improving the R-Graz cycle efficiency, among which the influence of the inlet pressure of the high-temperature gas turbine and condenser pressure is particularly significant. This study also presents the impact of these key parameters on the LCOE. This research can effectively increase the conversion efficiency of electricity-hydrogen-electricity mode, and provides a new path for hydrogen utilization.

Optimum operation of an ejector-assisted combined flash-binary geothermal cycle using R245fa-isopentane mixture-based secondary working fluids

Combined flash binary geothermal cycle (CFBGC) is a traditional geothermal energy conversion technology. However, in a CFBGC, substantial exergy destruction occurs during the steam flashing. To address this issue, in the present study, the steam flashing device of the conventional CFBGC is replaced by an ejector. The ejector enhances steam cycle power output by ensuring a higher steam flow rate through the high-pressure steam turbine stage. The modified cycle is designated as the ejector assisted combined flash binary geothermal cycle (EACFBGC). To take advantage of temperature glide, various compositions of R245fa-isopentane mixture are considered as secondary working fluid. Optimum operating parameters corresponding to the maximum second law efficiencies of the proposed and conventional cycles are explored by applying an iterative method. Both considered cycles yield the highest second law efficiencies with the 0.7 mol fraction of isopentane in the working fluid mixture. For geo-fluid available at 170 °C, the second law efficiency of the optimized EACFBGC is about 8.08% higher than that of the optimized conventional CFBGC. The corresponding levelized cost of electricity (LCOE) is also 5.7% lower. In a word, the proposed EACFBGC can be considered as the upgraded CFBGC with higher energy conversion efficiency and a lower LCOE.

Artificial Intelligence Modeling-Based Optimization of an Industrial-Scale Steam Turbine for Moving toward Net-Zero in the Energy Sector.

Augmentation of energy efficiency in the power generation systems can aid in decarbonizing the energy sector, which is also recognized by the International Energy Agency (IEA) as a solution to attain net-zero from the energy sector. With this reference, this article presents a framework incorporating artificial intelligence (AI) for improving the isentropic efficiency of a high-pressure (HP) steam turbine installed at a supercritical power plant. The data of the operating parameters taken from a supercritical 660 MW coal-fired power plant is well-distributed in the input and output spaces of the operating parameters. Based on hyperparameter tuning, two advanced AI modeling algorithms, i.e., artificial neural network (ANN) and support vector machine (SVM), are trained and, subsequently, validated. ANN, as turned out to be a better-performing model, is utilized to conduct the Monte Carlo technique-based sensitivity analysis toward the high-pressure (HP) turbine efficiency. Subsequently, the ANN model is deployed for evaluating the impact of individual or combination of operating parameters on the HP turbine efficiency under three real-power generation capacities of the power plant. The parametric study and nonlinear programming-based optimization techniques are applied to optimize the HP turbine efficiency. It is estimated that the HP turbine efficiency can be improved by 1.43, 5.09, and 3.40% as compared to that of the average values of input parameters for half-load, mid-load, and full-load power generation modes, respectively. The annual reduction in CO2 measuring 58.3, 123.5, and 70.8 kilo ton/year (kt/y) corresponds to half-load, mid-load, and full load, respectively, and noticeable mitigation of SO2, CH4, N2O, and Hg emissions is estimated for the three power generation modes of the power plant. The AI-based modeling and optimization analysis is conducted to enhance the operation excellence of the industrial-scale steam turbine that promotes higher-energy efficiency and contributes to the net-zero target from the energy sector.

Structural and thermal analysis on high-pressure steam turbine blade to determine the optimum material for its manufacturing

Blades of turbines are key elements of steam turbines. They are the main energy driven components at every stage of steam turbine where steam is pressurized to generate power. In view of designing, the material used and dimensions of blade govern the efficiency, consistency and durability of a steam turbine. In this paper the design of aerofoil profile of HP steam turbine blade is modelled by using computer-aided three-dimensional interactive application (CATIA). Various analytical data viz.., static structural analysis, transient structural analysis and transient thermal analysis are performed on different materials (ATI 720, Waspaloy, Molybdenum TZM, Incoloy alloy, Inconel alloy 725). Based on the analysis, Waspaloy material blade outperformed among all blades materials in terms of creep resistance and heat flux.

Numerical Study of Heat Transfer Characteristics in High Pressure Steam Turbine During Stop Unit Process with Sliding Pressure

During maintenance of the turbine and its auxiliary equipment, which requires a stop of the turbine oil system equipment and an open turbine casing, the first stage metal temperature requirement must be below 150°C. The normal stop unit method with natural cooling takes about 14 to 17 days. In order to speed up the cooling time to 5 days, a forced cooling turbine is needed using the stop unit method with sliding pressure. The heat transfer that occurs in the high-pressure turbine during the stop unit process with sliding pressure was investigated using the numerical method of CFD simulation. The 2D geometry design was made from high-pressure turbine cutouts images. Then meshing was made. The solver stage and the post-processing stage were set. The simulation was running in a steady state and followed by transients. The validation method was to compare the first stage metal temperature parameter between the actual process and the results of the CFD simulation at a load of 350 MW, then re-simulate it at 500 MW and 645 MW. The stop unit process with sliding pressure starting at 645MW resulted in the best final cooling compared to the stop unit at 500 MW and 350MW loads. By increasing the main steam flow, the resulting cooling increases. By increasing the value of the fluid flow velocity, the Reynolds number increases, so the convection heat coefficient also increases.

The Influence of Shutdown of Steam Turbine High-pressure Heater on Boiler and Auxiliary Equipment

The Influence of Shutdown of Steam Turbine High-pressure Heater on Boiler and Auxiliary Equipment

Specific Features of the Replacement of the Available Flow Path by the Optimal Flow Path when Upgrading the Steam Turbine High-Pressure Cylinder

This scientific paper gives the main research data obtained during the solution of the search problem to define optimal parameter values for the thermal circuit of the К-540-23.5 turbine unit that would provide the most efficient operation both for the optimal version of the high pressure cylinder (HPC) as part of the turbine unit and the turbine unit on the whole. The effect of the distribution of heat differences in the stages of the optimal flow part of the high pressure cylinder used by the К-540-23.5 turbine on the integral quality factors of the turbine unit has been assessed. The calculation studies of the thermal circuit of the turbine unit with the optimal flow section of the high-pressure cylinder showed that the temperature of the underheated feed water in the high pressure heater (HPH) arranged near the steam generator has the most critical effect on the power and economical efficiency of the high pressure cylinder and entire turbine unit. The two-criterion Pareto problem for the upgrading of the turbine unit was formulated and solved to define optimal underheating temperature values. Consideration was given to the two variants of the solution of the optimization problem for the feed water underheating temperature in the high pressure heater. Comparison and analysis of the two variants of solution for the two-criterion optimization problem showed the identity of the obtained data and it confirms the correctness of the problem formulation and the algorithms used for its solution.

Investigation of the Thermal Strength of Steam Turbine Diaphragms with Reduction of Axial Dimensions

The problem of reducing the axial dimensions of steam turbine diaphragms is associated with the problem of steam turbine modernization performed by increasing the number of reactive blading stages and using existing foundations. Evaluation of the suitability of diaphragm design versions with established steam flow characteristics was carried out with constraints on short- and long-term strength conditions, as well as the accumulation of axial deflections due to creep. For computational research, there was introduced a methodology using the finite element method and Yu. M. Rabotnov’s theory of strain aging. The calculation of creep was reduced to solving an elastic-plastic problem with a deformation curve, which was represented by an isochronous creep curve for the time chosen. A software was used providing for the automated construction of the original computer diaphragm model with the help of guide-vane profile drawings and axial cross-sections of the diaphragm rim and body, as well as several geometric parameters. The calculated model of a welded diaphragm reproduces the main essential features of the structure, the material properties of its elements, as well as steam load. The exploratory studies of diaphragms with reduced axial dimensions were performed on the example of the second- and third-stage diaphragms of the high-pressure cylinder of the K-325-23.5 steam turbine. The original second- and third-stage diaphragm designs were considered to be basic, in relation to which, according to strength and rigidity parameters, the alternative ones were compared. Calculated data for the basic diaphragm design versions for 100 thousand operating hours were obtained. According to the calculations, maximum deflections are achieved at diaphragm edges, and the stresses, that are maximum at the points where the guide vanes are attached to the diaphragm rim and body, undergo a significant redistribution due to creep. Two approaches to the reduction of the axial dimensions of the second-stage diaphragm design of the steam turbine high pressure cylinder were involved. In the first approach, the reduction of the dimensions was achieved by proportionally reducing the guide-vane profile with a corresponding increase in the number of the guide vanes. In the second approach, the profile remained unchanged, but the axial dimensions of the diaphragm rim and body were reduced. The parameters of strength both in the elastic state at the beginning of operation and in the conditions of creep, as well as the accumulation of axial deflections were investigated. Based on the comparisons with the basic design, it was established that the second approach is more effective. Additional recommendations for the use of more heat-resistant steels for outlet guide vanes and the conditions of diaphragm attachment in the turbine casing are given.

Impact of the Generation System Parameters on the Frequency Response of the Power System: A UK Grid Case Study

The operation and the development of power system networks introduce new types of stability problems. The effect of the power generation and consumption on the frequency of the power system can be described as a demand/generation imbalance resulting from a sudden increase/decrease in the demand and/or generation. This paper investigates the impact of a loss of generation on the transient behaviour of the power grid frequency. A simplified power system model is proposed to examine the impact of change of the main generation system parameters (system inertia, governor droop setting, load damping constant, and the high-pressure steam turbine power fraction), on the primary frequency response in responding to the disturbance of a 1.32 GW generation loss on the UK power grid. Various rates of primary frequency responses are simulated via adjusting system parameters of the synchronous generators to enable the controlled generators providing a fast-reliable primary frequency response within 10 s after a loss of generation. It is concluded that a generation system inertia and a governor droop setting are the most dominant parameters that effect the system frequency response after a loss of generation. Therefore, for different levels of generation loss, the recovery rate will be dependent on the changes of the governor droop setting values. The proposed model offers a fundamental basis for a further investigation to be carried on how a power system will react during a secondary frequency response.

Optimal scheduling of flexible thermal power plants with lifetime enhancement under uncertainty

• The proposed method can limit equipment damage in different scenarios. • Damage can be reduced 40% with a revenue loss of less than 1%. • Different damage mechanisms in the equipment can be included in the method. • Variable uncertainty in power demand and price can be included. • Adequate selection of material design temperature reduces deterioration. Renewable energy sources have been the focal point to decarbonise the power sector. The large deployment of these intermittent power generation units requires mechanisms to balance the grid. Thermal power plants can provide this service by increasing the number of start-ups, shut-downs, and intraday ramps at the expense of higher deterioration in critical equipment, including high-pressure steam drums, turbine rotors and blades, and high-temperature heat exchangers and pipes. This work proposes a method to formulate the power generation scheduling of thermal power plants as a stochastic optimisation problem with limitations on the maximum damage in critical components. This method models the uncertainty associated with intermittent power generation from renewable sources with a scenario-tree whilst computing the deterioration of the equipment in each scenario to limit the maximum damage. Scheduling of a flexible natural gas combined cycle demonstrated how this methodology can reduce the deterioration of the superheating heat exchanger of the power plant with minimum detriment in power generation and revenue. Furthermore, the effect of the design temperature of the material on the total damage was analysed for a broad range of temperatures and operating profiles, showing how adequate selection of design temperature can reduce the deterioration of the equipment and enhance its lifetime.

Repair of Cracked 150 MW High-Pressure Steam Turbine Rotor Coupling

A 150 MW high-pressure steam turbine rotor in Philippine experienced cracking in coupling area. The root cause of crack failure was investigated, and it was revealed that alignment setup design from original equipment manufacturer (OEM) contributed to the failure. The cracked coupling was restored by weld build up back to original dimension and new alignment target was recalculated and the result was counterchecked by finite element analysis (FEA) method to verify the stress level reduction.

Methodology to evaluate contribution of thermal power plant flexibility to power system stability when increasing share of renewable energies: Classification and additional fuel cost of flexible operation

A methodology to evaluate the contribution of thermal power plant operational flexibility to the stable supply of electricity when increasing the share of intermittent renewable energy sources is developed. The operational flexibility required for load frequency control (LFC) unit of a secondary control reserve is classified with respect to the available output range (AOR), the minimum load (Pmin) versus AOR ratio (Lmin, =Pmin/AOR), and the maximum full activation time (Max. FAT). By applying the classification of the operational flexibility to a frequency analysis using the Automatic Generation Control 30 (AGC30) model, defined by the Institute of Electrical Engineering of Japan (IEEJ), we validated the effect of the classification on the stability of electricity supply. To estimate the contribution of the operational flexibility of coal-fired power plants to the demand–supply balance of a power system, the base and advanced operational flexibility performances of coal-fired power plants are assumed to operate as an LFC unit of the secondary control reserve. Since a coal mill needs a long time to change the flow rate of pulverized coal, the throttling valve control of the high-pressure steam turbine during partial load operation is needed to ensure a rapid response of load change of coal-fired power plants. The energy loss of coal-fired power plants during the high-pressure steam turbine throttling valve control is evaluated and the contribution of the LFC operation of coal-fired power plants to the demand–supply balance is estimated by unit commitment analysis. Throttling valve control at a low load is responsible for the increase in the equivalent forced outage factor (EFOF) of the coal-fired power plants; thus, the additional fuel cost of replacing the LFC unit with liquefied natural gas-fired steam cycle and gas turbine combined cycle power plants is estimated, which is required for the secure supply of electricity.

Comparative analysis of power distribution, exergy losses and exergy efficiencies of the 200 MW steam turbine for three operating modes with and without turbine steam extraction

The paper calculates the power, exergy losses and exergy efficiencies of the high, medium and low pressure steam turbine, as well as the total exergy losses and exergy efficiency of the 200 MW steam turbine. The calculation was performed for three modes of operation of the steam turbine with a load of 100%, 90% and 80%. For all three operating modes, the calculation of the analyzed parameters includes the operation of the steam turbine with and without turbine steam extraction. Based on the obtained results, a comparative analysis of steam turbine parameters was performed for all three operating modes and for operation with and without turbine steam extraction. Comparative analysis of the obtained results will show the influence of different operating modes of steam turbine with and without turbine steam removal on power, exergy losses and exergy efficiency of each module individually, but also on the total values of analyzed steam turbine parameters. The comparative analysis will also include the influence of mass steam flows from all turbine subtractions on the total steam turbine power losses for the three operating modes.

Performance improvement of low-pressure cylinder in high back pressure steam turbine for direct heating

It is the general retrofit to remove the last stages in the low-pressure cylinder of steam turbine for high back pressure direct heating, which can avoid the exergy loss caused by the traditional extracting steam heating mode of combined heat and power. However, the flow field of low-pressure cylinder will change. In this study, the last stage flow field of low pressure cylinder of such high back pressure turbine, as well as the temperature distribution, is analyzed and optimized by setting the diversion ring. Low-pressure cylinder of the 300 MW steam turbine is selected as the research object. The optimal scheme is obtained after analyzing vortex distribution, static pressure recover coefficient and total pressure loss coefficient in flow field under different heating conditions. The results show that adding appropriate diversion ring bringing about vortex effectively reduced, leading to a sharp increase of 7.84% in efficiency of low-pressure cylinder and 0.63in statistic pressure recover efficient. It is also contributing to an apparently decrease of 0.95 in total pressure loss efficient. All results indicate that the aerodynamic performance of low-pressure cylinder has obvious promotion. Under high back pressure heating condition, the structure of low-pressure cylinder of steam turbine changed.

Steam turbine bottoming cycle deterioration under different load conditions

This paper investigates the performance diagnostics and the deterioration analysis of the steam cycle, which is the bottoming cycle of a combined cycle power plant. A proposed model has been created to simulate the steam turbine (ST) performance at various loads and working conditions in order to estimate the deterioration percentages of the steam cycle components. Performance modeling and degradation analysis have been performed on 2650 reading points over five operational years (2013–2017). The deterioration percentage was studied for different load conditions including full load (100%) and part loads (75% and 50%). The degradation of the steam cycle components has been investigated namely: the high-pressure steam turbine, the low-pressure steam turbine, and the condensate extraction pump. Besides, the effects of the degradation of the components on the ST generated power, and the overall steam cycle thermal efficiency have been studied. This analysis has been performed according to the actual logged data obtained from the power plant; this gives a realistic value to this study. The results indicate that the deterioration percentage increase with time and operational load, whereas the degradation rate decreased with time. Moreover, ambient air conditions affected the low-pressure steam turbine (LPST) performance and degradation by increasing the air-cooled condenser backpressure. Furthermore, the maximum degradation of the steam turbine components reached −2.1% in the LPST and the maximum overall deterioration of the steam turbine reached −2.97% at the full operational load.