Steam Turbine Model Research Articles

Experimental and Numerical Investigations of Steam Expansion Rate in Low Pressure Steam Turbine

Abstract This study focused on the expansion rate of steam; the effect on efficiency was investigated experimentally and numerically by varying the expansion rate of steam in the stage, where condensation occurs by varying the flowrate and inlet temperature using a five-stage model steam turbine. The steam expansion rate of the stator blades in each stage was evaluated from the measured wall pressure and total pressure. In addition, the turbine efficiency was evaluated from the measured torque and mass flowrate, and the effect of flowrate and condensing stage can be taken into account for losses caused by condensation. In addition, numerical calculations to account for the effects of nonequilibrium condensation were performed using ANSYS CFX. The numerical calculations were able to show the details of the nucleation situation and the resulting changes in flow patterns. Numerical evaluation of the subcooling loss showed that there was no difference in subcooling loss between different mass flow rates. The steam expansion rate was evaluated from the measurement results, and it was found that there was no difference in the steam expansion rate due to differences in mass flowrate. This corresponds to the numerical result that the subcooling loss does not vary with flowrate.

Система непрерывного мониторинга технического состояния и оперативной диагностики паровой турбины

Power equipment deterioration occurs during operation, it causes loss in reliability and efficiency, unscheduled shutdowns, and accidents. Now predictive analytics is one of the promising directions in the field of power engineering which allows to control and analyze the technical condition of power equipment. The problems of localization of deviation of technological parameters and detection of anomaly in the operation of power equipment are consistently solved in the framework of predictive analytics. The problems of deviations localization and anomalies detection are solved by the methods of statistical modeling and the classification algorithms respectively. However, for steam turbines the localization of deviation and the detection of anomalies having slow-flowing character are a difficult problem. Therefore, the issue of development of a method for continuous monitoring of technical condition and maintenance diagnostics based on a mathematical model of the steam turbine section flow characteristics is worth noticing. The method allows us to consider the effect of changes in the open flow area of the individual sections of a steam turbine on the pressure distribution over the steam flow path. The model of a steam turbine has been developed within the matrix formalization methodology. The solution of the system of linear and nonlinear equations is carried out by methods of computational mathematics. The solution of the optimization problems of the steam flow path diagnostics is carried out by methods of mathematical programming. A mathematical model of the cogeneration steam turbine Т-250/305-23.5-DB and a method for continuous condition monitoring and maintenance diagnostics of steam turbine have been developed. It allows us to localize deviation and detect anomaly by recovery of the open flow area of the individual sections of a steam turbine based on the pressure distribution over the steam flow path. The results of the statistical analysis prove that a mathematical model of the cogeneration steam turbine Т-250/305-23.5-DB has been recognized adequate. The method for continuous condition monitoring and maintenance diagnostics of steam turbine has demonstrated consistency of the obtained results and ability to solve diagnostic problems in practice. The developed model and method can be used as a module in the development of a software package for predictive analytics of power equipment.

A Study on the Performance Analysis of the High Pressure - Intermediate Pressure Steam Turbine Model for Co-generation Plants using Commercial Programs

A Study on the Performance Analysis of the High Pressure - Intermediate Pressure Steam Turbine Model for Co-generation Plants using Commercial Programs

Method of object-oriented modeling of steam turbine plants taking into account variations in turbine efficiency under variable operating modes

The article proposes an object-oriented method for modeling steam turbine plants. The novelty of the method is in the application of a steam turbine model that takes into account variations in internal efficiency under variable operating modes.The article presents the results of theoretical substantiation of nonlinear dependence of the power of the turbine compartments on the steam flow passing through them, based on the change in the internal efficiency of the stages under variable modes described by the Stodola-Flugel equation. An empirical dependence of the efficiency of the stage operation on the relative steam consumption is proposed. Recommendations on the use of empirical form in the development of models of steam turbine compartments are given. The empirical dependences of the relative internal efficiency of turbine compartments obtained from the results of thermal tests of an operating turbine unit are presented.As a factor of practical significance of the research, a model of PT-60-130/13 type steam turbine plant has been developed involving the use of an object-oriented programming language. Recommendations on the description of classes of objects within the steam turbine plant. The developed STP model enables to simulate any operating modes depending on electrical and thermal loads, as well as to take into account the influence of deviations of external factors from nominal values when developing a system of corrections or estimating an increase in fuel consumption associated with these deviations.

A novel dual feedwater circuit for a parabolic trough solar power plant

The validated dynamic model of a parabolic trough power plant (PTPP) is improved by the combination of a new feedwater circuit (feedwater/HTF circuit) and a reference feedwater circuit (feedwater/steam circuit) as well as the development of the steam turbine model. Such design represents the first effort of research to utilize a dual feedwater circuit inside the PTPP to increase the power output in the daylight from 50 to 68 MWel and raise night operating hours at a lower cost. The purpose of increasing the operating night hours at a power (48 MWel) as in the reference PTPP is to get rid of the fossil fuel backup system and rely only on the absorbed solar energy and the stored energy in the molten salt. During daylight hours, the feedwater circuit is operated using Feedwater/HTF. In the transient period, the feedwater/HTF circuit will gradually be closed due to a decrease in solar radiation. Furthermore, the rest of the nominal feedwater mass flow rate (49 kg/s) is gradually replenished from the feedwater/steam circuit. After sunset, the entirety of the feedwater is heated based on the steam extracted from the turbine. The purpose of this improvement is to raise the number of nightly operational hours by reducing the nominal load from 61.93 to 48 MWel as a result of low energy demand during the evening hours. Therefore, a comparison study between the reference model and this optimization (optimization 2) is conducted for clear days (26th–27th/June and 13th–14th/July 2010) in order to understand the influence of dual feedwater circuit. The comparison indicates that the operational hours of the power block (PB) will be obviously increased. Moreover, this improvement reduces based on the fossil fuel system at night. As the last step, an economic analysis was performed on the costs of the referenced and the optimized PTPP as a function of the levelized energy cost (LEC). The results illustrate that the specific energy cost of a PTPP with 7.5 h of storage capacity is lowered by about 14.5% by increasing the output of the PTPP from 50 to 68 MWel.

Research on deep utilization technology of flue gas residual heat for large-capacity coal-fired units

The utilization of flue gas waste heat is an important measure to improve the power efficiency of coal-fired units. Traditional method is to arrange the heating surface after the air preheater, which can just recover the low-grade heat, low efficiency. For the engineering practice of a 1000MW double-reheat unit, three feasible schemes are proposed, namely scheme 1 “two-stage gas cooler plus cold air heater”, scheme 2 “air preheater bypass + two-stage flue gas cooler plus cold air heating” and scheme 3 “air preheater bypass + hot primary air temperature adjustment plus two-stage flue gas cooler plus cold air heater”. For the sake of evaluating the actual effects of different schemes objectively, the thermal characteristic calculation model of the four-part rotary air preheater was established by finite difference method, and then the effect of the inlet air temperature and the share of bypass flue gas on the thermal efficiency of the boiler were studied. The equivalent enthalpy drop method was used to establish the thermal characteristic model of steam turbine, and the influence of different heat distribution modes on the heat consumption rate of steam turbine was studied.. Considering the technical economy, the optimal bypass flue gas share of this scheme is 12%, which corresponds to the reduction of coal consumption for power supply of the unit by about 3.23g/kWh. Taking into account comprehensively, scheme 3 is recommended.

A new assessment mechanism of primary frequency regulation capability for a supercritical thermal power plant in deep peaking

AbstractWith the rapid development of renewable energy, the primary frequency control (PFC) is becoming more critical and significant to ensure the stability of the electrical power system. As the main role of PFC, the thermal power unit tends to in a wide operation interval, and the changes in PFC characteristics along with working conditions are inevitable. By decomposing and quantifying the dynamic energy conversion process, this paper proposes a novel mechanism to evaluate the PFC capability for the supercritical thermal power plants that covered 30%–100% of the rated load. In the mechanism, a refined steam turbine model is established to reflect the short‐term dynamic response of PFC by combining it with the coupling characteristics of the main steam valve and main steam pressure in the later phase. Meanwhile, as a new prior assessment index, the equivalent electricity has been put forward to quantify the PFC capability for the power plant. In a case study of a 600 MW supercritical power plant, the capacities of PFC under 30%–50% of the rated load are quantified for the first time. Comparison results between theoretical calculation and real PFC test show that the proposed PFC capability assessment mechanism has acceptable accuracy of 96.1%, which could be effective to assess the frequency response reserve and stability margin in the grid.

Optimal Design of a Dual-Pressure Steam Turbine for Rankine Cycle Based on Constructal Theory

A one-dimensional dual-pressure steam turbine (ST) model for the marine Rankine cycle is built in this paper. Based on constructal theory, the optimal design of the dual-pressure ST is performed with a fixed total volume of the high- and low-pressure STs. The total power output (PO) of the dual-pressure ST is maximized. Seventeen parameters, including the dimensionless average diameters (DADs) of the stages, steam inlet angles (SIAs) of the stages, average reaction degrees (ARDs) of the stages, and volume ratio of the high-pressure ST are taken as optimization variables. The optimal structure parameters of the stages are gained. It reveals that the total PO of the dual-pressure ST is increased by 2.59% by optimizing the average diameter of the Curtis stage, and the change in the total PO is not obvious by optimizing the average diameter of the third stage of the low-pressure ST. Both the total PO and the corresponding efficiency of the dual-pressure ST are increased by 10.8% after simultaneously optimizing 17 variables with the help of the Matlab optimization toolbox. The novelty of this paper is introducing constructal theory into turbine performance optimization by varying seventeen structure, thermal and flow parameters, and the result shows that the constructal optimization effect is remarkable. Optimal designs of practical STs can be guided by the optimization results gained in this paper.

Test and simulation of primary frequency regulation of 600MW sub-critical thermal power units with wide load operation

To reveal the performance of primary frequency regulation of the 600MW sub-critical thermal power units in a wide load range and accurately simulate the process, the primary frequency regulation performance of a 600MW sub-critical thermal power unit was studied with a wide load ranging from 20% to 90% under rated conditions. The model of steam turbine in BPA was modified in consideration of steam pressure and the valve throttling effect. The primary frequency regulation performance of the unit was simulated with the modified model. The research results show that the primary frequency regulation performance of the thermal power unit is poor at low load and the results of simulation with the modified model are highly consistent with the tested data due to consideration of steam pressure and valve throttling effect, meaning that the model can be used to simulate the primary frequency regulation of the thermal power unit with wide load operation accurately.

Simulation test and parameter optimization of fast cut back of large thermal power plant in the condition of synchronization of large-scale wind power

Fast cut back (FCB) is an important condition in power control of steam turbine generator unit, which is closely related to the flexibility, safety and stability of thermal power unit. In this paper, the traditional single reheat steam turbine model were optimized and improved by adding the key links such as medium pressure control valve and bypass, and further adding the once through boiler, bypass control system, FCB action signal, excitation system and other models. A thermal power unit model suitable for FCB large disturbance condition simulation was established. The simulation results verify the effectiveness of the model, and meet the requirements of power system electromechanical transient simulation and FCB simulation. And then, this paper improved the PSO (Particle Swarm Optimization) algorithm, and combined the advantages of each algorithm in the aspects of calculation difficulty, convergence speed, accuracy, ability to jump out of local optimum, etc., puts forward and verifies the GA-PSO (Genetic Algorithm-PSO) optimization method. Finally, considering the stability and regulation performance of the system, the GA-PSO optimization algorithm was used to obtain the optimal values of the system component parameters. The simulation results indicated that the characteristics of optimized system damping was improved, which enhanced the regulation performance and stability of the system.

Optimization design of thermal system for industrial waste heat power generation

In order to improve the utilization rate of industrial waste heat and improve the fine design level of waste heat power station, this paper constructs the mathematical model of waste heat boiler and steam turbine, and puts forward the optimization design method of thermal system of waste heat power generation project. By using typical cases, it is proved that there is the optimal design pressure of HRSG, which makes the power generation of the system maximum, and provides a method to improve the power generation of HRSG.

Analysis of heat flow diagram of small-scale power generation system: Innovative approaches for improving techno-economic and ecological indices

In this paper, the heat flow diagram of steam turbine model K-6-35 has been analyzed for innovative approaches towards improving the techno-economic and ecological indices of the small-scale power generation system. The numerical analysis is performed using IPSEpro process simulation software based on heat balance method under four different cases. It was found that the study of Solar Assisted Power Generation (SAPG) system has important practical significance in power generation with minimum pollutants and maximum efficiency. Both fuel-saving (FS) and power-boosting (PB) operation modes of the SAPG system are considered. Various types of stand-alone solar thermal power plants exhibited very low overall efficiency with many ecological advantages compared to the conventional thermal power plant based on fossil fuels. Besides, SAPG system with FS mode presented higher techno-economic indices and operation performance. An important reduction in fuel consumption and pollutant emissions could be obtained with SAPG system. Considering the hourly, daily, monthly, and yearly amount of saved fuel and reduced pollutants in the whole power plant, the SAPG system with FS mode can largely contribute to high ecological indices power generation. A thermal efficiency increased by 1.31% with specific equivalent fuel consumption decreased by 22.54 g/kWh was obtained with SAPG system. The coal consumption was reduced by 4.75% when SAPG system operates in FS mode.

Load Frequency Control of Pumped Storage Power Station Based on LADRC

The pumped storage power station has the characteristics of frequency-phase modulation, energy saving, and economy, and has great development prospects and application value. In order to cope with the large-scale integration and intermittency of renewable energy and improve the ability of pumped storage units to participate in power grid frequency modulation, this paper proposed a load frequency control (LFC) strategy for pumped storage units based on linear active disturbance rejection technology. Firstly, based on the operating characteristics of the pumped storage power station, the LFC model of the two-area reheat steam turbine under nonlinear conditions such as governor dead zone and generation rate constrains was established. Secondly, a second-order linear active disturbance rejection control (LADRC) was designed. The feasibility and control performance of the proposed LFC system were quantitatively analyzed through simulation. The results show that the LADRC has better control effect and stronger robustness than fractional-order proportion integration differentiation (FOPID) and traditional proportion integration differentiation (PID) controller. Finally, the pumped storage power station was added, and it was found that it has better correction performance under both generating and pumping operations, which greatly improved the dynamic response of secondary frequency modulation.

Detailed and verified NPP model for safe interconnection with electrical grid

A precise understanding for nuclear power plant (NPP) response to grid disturbances is required to ensure safe and reliable operation for both NPP and power grid. NPP performance is studied by dynamic modeling and simulation, since it is not practical to study it by experiments. In this work, a mathematical model for complete pressurized water reactor NPP is represented based on MATLAB/Simulink. First, the main parts of the model (reactor, steam generator, pressurizer, and steam turbine) are studied and verified individually. Then, those parts are connected together in a highly controlled system to test the overall plant behavior under load changes. The results of simulation indicate that the plant is capable to regulate its output according to electrical grid demand and reach the steady-state conditions. Thus, a high degree of safe interface between the electric grid and NPP is achieved.

RATIONALIZATION OF THE APPROACHES OF NUMERICAL SIMULATION OF THE GEOMETRICALLY COMPLEX ROTATING EQUIPMENT OF ELECTRICAL STATIONS

The basic equipment of the most domestic power units is operated at thermal and nuclear power plants and has exhausted its design resource. Given the lack of funding for the energy sector, it is difficult to re-equip old equipment with new equipment in the near term. It is advisable to ensure a high residual experience of current equipment, based on the study of individual resource performance of specific equipment. The task of estimating the residual resource of power equipment is solved using the methods of computer simulation of separate operating modes. It is clear that taking into account all the features of a full-scale geometric model in mathematical analysis will lead to a significant increase in the human effort and resources of computer and computer engineering. Therefore, the purpose of this research is to rationalize the mathematical model of the rotor cylinder medium pressure steam turbine K-200-130. Two variants of replacement of working blades and bandage fasteners are proposed and investigated. The models are verified on the basis of a comparison of the calculated critical and natural frequencies of the rotors with the data provided by the manufacturers of the given thermal power equipment. The proposed model of rotor with replacement of the working blades with toroidal rings of equivalent length and mass has been successfully verified, and the error of calculation does not exceed 5.5%. Therefore, the rationalization method proposed in this paper can be used to reduce wasted resources in computer modeling of complex rotating equipment.

Analysis of the stage group efficiency of steam turbine based on the unified model for coal-fired power unit

During actual operation of the unit, the group efficiency inevitably deviates from the design value and influences the unit heat consumption rate. This paper conduct a series of turbine stage efficiency analysis of the influence of unit energy consumption based on the basic equations for economic analysis, combined with the variable condition of steam turbine model. 1000 MW unit produced by DFSTW as the research object, this paper calculates the load of several groups of different stage group efficiency, and the amount of change of the unit coal consumption. Summarizing, this paper analyses the stage group efficiency influence on the power supply coal consumption rate of the unit, and the variation of stage group efficiency influence on the unit energy consumption with the load change. The results can provide great reference for the operation optimization of thermal power unit.

Optimization study on a modern regeneration boiler cold end operation and its feedwater system integration into energy system of a paper mill

The potential of modern regeneration boiler cold end and feedwater system integration with energy system of a paper mill is studied and measures for its better exploitation are proposed and assessed. Mathematical model has been developed, comprising material and heat balances, heat transfer equations, and steam turbine model. Its accuracy has been tested on the design and actual operation of a real system firing 70 t/h of dry solids. The simulation coped with design and measured data very well and also followed the operation changes performed in field tests excellently. Nine proposals aimed at real system efficiency improvement were assessed on the yearly benefit and simple payback period base, with yearly benefit resulting either from marginal fuel savings (scenario 1) or from condensing power production increase (scenario 2). Immediately applicable measures included deaeration at full steam pressure and heat load minimization in the first stage of the boiler feedwater regenerative heating—this novel finding contradicts the boiler design where full load regenerative heating is applied. Further measures increase the internal and external (available in paper mill) heat utilization. Their combination yielded either up to a 7 t/h internal steam consumption decrease (2.25% of nominal boiler steam output, scenario 1) or up to a 1.4 MW electricity production increase (2% of nominal steam turbine power output). Several of the proposed measures merit attention of boiler vendors and paper mills energy managers as viable tools towards low energy intensity pulp and paper mill industrial sector.

Influence of the Tip Clearance on the Aeroelastic Characteristics of a Last Stage Steam Turbine

In this paper, the tip clearance effects on the aeroelastic stability of a last-stage steam turbine model are investigated. Most of the unsteady aerodynamic work contributing to flutter of the long blades of the last-stage of a steam turbine is done near the tip of the blade. The flow in this region is transonic and sensitive to geometric parameters such as the tip clearance height. The KTH Steam Turbine Flutter Test Case was chosen as the test case, which is an open geometry with similar parameters to modern free-standing last-stage steam turbines. The energy method based on 3D URANS simulation was applied to investigate the flutter characteristics of the rotor blade with five tip gap height varying from 0–5% of the chord length. The numerical results show that the global aerodynamic damping for the least stable inter-blade phase angle (IBPA) increases with the tip gap height. Three physical mechanisms are found to cause this phenomenon. The primary cause of the variation in total aerodynamic damping is the interaction between tip clearance vortex and the trailing edge shock from the adjacent blade. Another mechanism is the acceleration of the flow near the aft side of the suction surface in the tip region due to the well-developed tip leakage vortex when the tip clearance height is greater than 2.5% of chord. This causes a stabilizing effect at the least stable IBPA. The third mechanism is the oscillation of the tip leakage vortex due to the blade vibration. This has a negative influence on the aeroelastic stability.

Research on the Mathematical Model of Combined Cycle Power Plant for Power System Simulation for PSD-BPA

Based on the analysis of the combined cycle unit dynamic characteristics and the demand of power system simulation, basic principles of combined cycle unit modeling are presented. Through mathematical derivation and reasonable simplification, mathematical model of gas turbine and steam turbine is integrated into the general structure of power system simulation software. The problem that the power system simulation software has no special combined cycle model is solved, the accuracy of the model is verified by comparing the simulation results with the field test data, and research results are helpful to improve the accuracy of power system simulation.

Operational optimization of industrial steam systems under uncertainty using data‐Driven adaptive robust optimization

This article addresses the operational optimization of industrial steam systems under device efficiency uncertainty using a data‐driven adaptive robust optimization approach. A semiempirical model of steam turbine is first developed based on process mechanism and operational data. Uncertain parameters of the proposed steam turbine model are further derived from the historical process data. A robust kernel density estimation method is then used to construct the uncertainty sets for modeling these uncertain parameters. The data‐driven uncertainty sets are incorporated into a two‐stage adaptive robust mixed‐integer linear programming (MILP) framework for operational optimization of steam systems to minimize the total operating cost. Integer variables are introduced to model the on/off decisions of the steam turbines and electrical motors, which are the major energy consumers of the steam system. By applying the affine decision rule, the proposed multilevel optimization model is transformed into its robust counterpart, which is a single‐level MILP problem. The proposed framework is applied to the steam system of a real‐world ethylene plant to demonstrate its applicability. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16500 2019