Investigation on Flow Characteristics and Stability of Control Valves for Steam Turbines

2008 ◽  
Author(s):  
Guanwei Liu ◽  
Shunsen Wang ◽  
Hui Guo ◽  
Jingru Mao ◽  
Zhenping Feng ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Pressure Ratio ◽  
Control Valve ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Outlet Section ◽  
Steam Turbines ◽  
Control Valves ◽  
Structure Of Flow ◽  
Valve Disc

Through-flow capability and flow stability of some steam turbine control valves were studied by experimental investigation and numerical simulation. Based on the analysis of thermodynamic process in control valve, the relationship of flow coefficient, area ratio of valve outlet section to seat diameter section, pressure ratio and total pressure loss coefficient was deduced, and the expression of polytropic exponent was obtained. The relative deviations between formula results and experimental results are within 3%. Both expressions can be used for design and optimization to determine control valve parameters quantitatively. The results of 3D numerical simulation indicate that the topological structure of flow fields in all control valves is similar. The results of valve stability show that the airflow force acted on the valve disc depends on the vortex strength of flow around valve stem bush and valve disc, the asymmetric transonic impinging jet under the valve disc and the diffusing action. The valve operates steadily when the inlet and outlet Mach number are less than 0.15. As the unload degree is about 85%, stem vibrates at the operating conditions when pressure ratio is less than 0.8 and opening ratio is from 10% to 18%. A multihole annular orifice can make flow steady at all operating conditions.

Flow-induced vibration and noise in control valve

2015 ◽  
Vol 229 (18) ◽  
pp. 3368-3377 ◽  
Author(s):  
Li-fei Zeng ◽  
Guan-wei Liu ◽  
Jing-ru Mao ◽  
Shun-sen Wang ◽  
Qi Yuan ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Flow Pattern ◽  
Annular Flow ◽  
Pressure Ratio ◽  
Pressure Fluctuations ◽  
Control Valve ◽  
Steam Turbines ◽  
Core Flow ◽  
Control Valves ◽  
The Core

Control valves are used as flow regulators for steam turbines, which operate under wide ranges of valve openings and pressure ratios. The inherent throttling action and complex 3D flow in control valves result in vibration and intolerable noise at small and medium valve openings. The vibration and noise clearly are firmly with the flow pattern. Experiments and numerical simulation are the primary means of determining the mechanisms. In this paper, a phenomenon of sound mutation in control valve was experimentally observed by continuously changing the pressure ratio. This phenomenon is explained for the first time. Different noise and pressure fluctuations can appear even under the same condition, depending on the process of changing the pressure ratio. A method of continuously changing the pressure ratio was used in the unsteady numerical simulation to reveal the mechanism. The results show that sound mutation occurs due to the change of annular flow and core flow. The annular flow has a lower noise and a more stable flow pattern than the core flow. Sound mutation can be used as a simple way of determining the ranges of the core flow and the annular flow.

scholarly journals Some aspects of numerical simulation of control valves for steam turbines

2012 ◽  
Vol 25 ◽  
pp. 01052 ◽  
Author(s):  
Martin Hajšman ◽  
Dana Kovandová ◽  
Richard Matas
Keyword(s):  
Numerical Simulation ◽  
Steam Turbines ◽  
Control Valves

Reliability and Availability Prediction of Main Stop Valve and Control Valve Systems of Steam Turbines

2011 ◽  
Author(s):  
Jinyuan Shi ◽  
Yong Wang ◽  
Xiaoping Zhong ◽  
Zhicheng Deng
Keyword(s):  
Prediction Method ◽  
Control Valve ◽  
Design Stage ◽  
Steam Turbines ◽  
Stop Valve ◽  
Control Valves ◽  
Reliability Block Diagrams ◽  
And Control ◽  
The Mathematical Model ◽  
Reliability And Availability

A method for the reliability and the availability prediction of main stop valve and control valve systems of steam turbines is presented. The calculation models for the reliability and the availability of series, parallel and series-parallel systems of main stop valves and control valves are introduced. The reliability block diagrams, the availability block diagrams, formulas for the reliability prediction and the availability prediction of systems with 2 main stop valves and 2 control valves, 2 main stop valves and 4 control valves, 2 main stop valves and 6 control valves, 4 main stop valves and 4 control valves are given together with some examples. The mathematical model for the reliability and the availability prediction method of main stop valve and control valve systems of steam turbine is simple and the physical meaning is definite. The reliability and availability of main stop valve and control valve systems can be quantitatively already calculated and improved during the design stage. A basis is thus provided for the reliability and the availability design of main stop valve and control valve systems of steam turbines.

scholarly journals Assessment of Residual Service Life of Cast Bodies of Control Valves of 220 MW Power Units

2020 ◽  
Vol 23 (4) ◽  
pp. 22-28
Author(s):  
Olha Yu. Chernousenko ◽  
◽  
Dmytro V. Ryndiuk ◽  
Vitalii A. Peshko ◽  
◽  
...  
Keyword(s):  
Service Life ◽  
Control Valve ◽  
Steam Turbines ◽  
Operating Life ◽  
Control Valves ◽  
Intermediate Pressure ◽  
Operating Modes ◽  
Residual Operating Life ◽  
Start Ups ◽  
Total Damage

In the regulatory documents of the Ministry of Energy and Coal Industry of Ukraine, the beyond-design operating life of the high-energy equipment of 220 MW power units is limited to the operating life of 220 thousand hours and 800 start-ups. To date, the high-temperature cast bodies of the control valves for the high- and intermediate-pressure cylinders of the K-200-130 200 MW steam turbines of DTEK Lugansk TPP have operated about 305–330 thousand hours with the total number of start-ups from 1438 to 1704, which exceeded the beyond-design service life characteristics. Therefore, it is necessary to assess the residual operating life of the control valve bodies of the high- and intermediate-pressure cylinders of K-200-130 steam turbines in order to determine the possibility of their further operation. These calculations were carried out on the basis of our earlier studies of the thermal and stress-strain states of cast turbine equipment. This paper establishes the values of stress intensity amplitudes, the values having been reduced to a symmetric loading cycle for the most typical variable operating modes. Using the experimental low-cycle fatigue curves for the 15Kh1M1FL steel, we established the values of the permissible number of start-ups and the cyclic damage accumulated in the base metal. We also determined the value of the static damage accumulated in the course of stationary operating modes according to our previously obtained experimental data on the long-term strength of the 15Kh1M1FL steel. The calculations showed that the total damage to the control valve bodies of the K-200-130 steam turbine of power unit 15 of DTEK Lugansk TPP is 97 and 98%. The residual operating life of the metal of the control valves of high-pressure cylinders is practically exhausted, being equal to 10 thousand hours. The residual life of the control valves of intermediate- pressure cylinders is 7 thousand hours, i.e. it is also practically exhausted, with safety factors for the number of cycles and strains at the level of 5 and 1.5, as well as the permissible 370,000 operating hours of the metal. With an increase in the permissible operating life of the metal to 470 thousand hours, according to experimental studies of Igor Sikorsky KPI, the total damage to the metal of cast valve bodies is reduced to 80%, and the residual metal life increases to 79,000 h and 75,000 h for the control valves of the high- and intermediate-pressure cylinders, respectively.

The Characteristics of Rotating Instabilities in Low Pressure Steam Turbines at Low Volume Flow Operation

2015 ◽  
Author(s):  
Roland Sigg ◽  
Timothy Rice
Keyword(s):  
Renewable Energy Sources ◽  
Low Pressure ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Low Flow ◽  
Small Scale ◽  
Steam Turbines ◽  
Original Design ◽  
Low Load

For flexible operation steam turbines may operate occasionally at low load. Operation away from the original design regime looks set to be an increasing trend mainly due to the presence of intermittently available renewable energy sources in the grid. This paper sets out an approach for considering low flow effects on turbine designs. At low load operating conditions rotating instabilities (RIS) can occur in the rear stages of LP steam turbines. The instabilities are comparable in many ways to rotating stall in compressors. Ideally the turbine blade natural frequencies should be designed to avoid the frequencies generated by the RIS system. The characteristics of RIS systems were experimentally investigated to understand the dependency with both flow coefficient and exhaust configuration. Correlations have been developed to characterize the dynamic pressure amplitudes and the fractional speed of the RIS moving around the wheel. The presented correlation based method is shown calibrated for a specific blade design. Two different test rigs provide the basis for the work presented. A low pressure model steam turbine provided detailed information for key blade/exhaust combinations. A simplified small scale air turbine was used to provide additional input for the behavior with alternative exhaust back wall position. Observations of the characteristic RIS behavior from model turbine tests are set in context with observed changes in the flow field.

Dynamic Simulation as a Tool for Optimizing Pressure Control Valve Performance

2002 ◽  
Author(s):  
Jack W. Broyles ◽  
Roger W. Shirt
Keyword(s):  
Simulation Model ◽  
Dynamic Simulation ◽  
Control Valve ◽  
Pressure Control ◽  
Simulation Software ◽  
Operating Conditions ◽  
Process Data ◽  
Control Valves ◽  
Tuning Parameters ◽  
Pump Station

Control valves installed for pump station pressure control are typically tuned and commissioned at the low end of the flow range and well below the safe operating limits in order to avoid pressure excursions and line shutdowns during commissioning. Tuning parameters selected for best performance at low flowrates often produce poor performance at high flowrates requiring dampened tuning parameters and slower valve actuator speeds. This results in sluggish responses to pressure changes. Enbridge has undertaken a case study to examine three control valves which exhibited poor control characteristics. The goal of this study was to produce an optimal tuning strategy that could be implemented with a high degree of confidence over the entire range of operating conditions. To accomplish this, the IDEAS (AMEC Technologies, Inc.) dynamic simulation software package was utilized. The pipeline was modeled from the pump station upstream of the station of interest to the downstream pump station. The model consists of pipeline sections, pumps, control valves and other process elements that are hydraulically linked. Station discharge and suction pressures are controlled via PI controllers with adjustable set points, ramp rates and tuning constants. Valve full stroke actuator speed can also be varied. Information required to develop the simulation model included station elevations, pipeline lengths, pump curves and control valve Cv curves. The three simulation models developed for this study have been calibrated against process data by adjusting piping resistances. The inherent nonlinearities present in the control valve system were quantified through use of the simulation model. Various strategies to alleviate the adverse effects of these nonlinearities have been studied. Use of a simulation tool also resulted in increasing the awareness of trade-offs present in design and tuning of control valve systems.

Effect of Inlet Steam Temperature on the HP Section Efficiency of a Steam Turbine

2015 ◽  
Author(s):  
Yiping Fu ◽  
Thomas Winterberger
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Pressure Ratio ◽  
Control Valve ◽  
Combined Cycle ◽  
Steam Turbines ◽  
Steam Temperature ◽  
Load Range ◽  
Lp Turbine ◽  
The Relationship

Steam turbines for modern fossil and combined cycle power plants typically utilize a reheat cycle with High Pressure (HP), Intermediate Pressure (IP), and Low Pressure (LP) turbine sections. For an HP turbine section operating entirely in the superheat region, section efficiency can be calculated based on pressure and temperature measurements at the inlet and exhaust. For this case HP section efficiency is normally assumed to be a constant value over a load range if inlet control valve position and section pressure ratio remain constant. It has been observed that changes in inlet steam temperature impact HP section efficiency. K.C. Cotton stated that ‘the effect of throttle temperature on HP turbine efficiency is significant’ in his book ‘Evaluating and Improving Steam Turbine Performance’ (2nd Edition, 1998). The information and conclusions provided by K.C. Cotton are based on test results for large fossil units calculated with 1967 ASME steam tables. Since the time of Mr. Cotton’s observations, turbine configurations have evolved, more accurate 1997 ASME steam tables have been released, and our ability to quickly analyze large quantities of data has greatly increased. This paper studies the relationship between inlet steam temperature and HP section efficiency based on both 1967 and 1997 ASME steam tables and recent test data, which is analyzed computationally to reveal patterns and trends. With the efficiencies of various inlet pressure class HP section turbines being calculated with both 1967 and 1997 ASME steam tables, a comparison reveals different characteristics in the relationship between inlet steam temperature and HP section efficiency. Recommendations are made on how the results may be used to improve accuracy when testing and trending HP section performance.

Flow Accelerated Corrosion in Steam Condensate Piping and Valves: Problems Faced and Actions Taken

2011 ◽  
Author(s):  
K. C. Upreti ◽  
Sai Vamsidhar Bontha
Keyword(s):  
Control Valve ◽  
Operating Conditions ◽  
Accelerated Corrosion ◽  
Control Valves ◽  
Steam Condensate ◽  
Root Cause ◽  
Erosion Corrosion ◽  
On Line ◽  
Condensate System ◽  
Flow Accelerated Corrosion

Flow accelerated corrosion (FAC) is a combined form of erosion, corrosion and Cavitation. This is prominent in steam condensate lines which results in fast reduction of thickness in piping, piping components and valves. It is estimated that this problem is faced by majority of plants. There has been an increased emphasis on correcting these problems due to fatal accidents that occurred in 1986, 1995, 1996 and 2004 at various locations around the world. [3] After commissioning of the plant, Steam condensate system erosion/corrosion problem started appearing within one year of operation. To ensure uninterrupted plant running on line sealing was done and monitoring was done by proper thickness checking. These on line sealing points were replaced during available opportunity. In some cases plant shutdown was taken to replace leaking piping components & these incidents resulted into revenue loss to company. Aggressive inspection programs were taken up for thickness measurement on condensate lines and as a proactive measure, elbows were encapsulated with higher size elbows, reducers by on line welding/furmaniting with special clamps. Similarly gate and globe valves in condensate service also started failing as a result of erosion of body seat rings. Globe valves installed on bypass lines of control valves were found passing. Once these valves were operated for maintenance of control valves they could not be closed. In some cases valve body developed leak due to high velocity erosion. Various studies conducted for replacing these components by higher schedule fittings & pipes but it did not improve the situation except for slight increase in life of these components. Velocities were calculated at various locations and higher velocity, condensate impingement/cavitation was found as root cause of problems. This problem was solved by various methods like using higher metallurgy P11, P22 material, line size increase with increase in control valve sizing, lay out changes etc. This helped in improving reliability of condensate system and reducing risk associated with failure of piping. This paper presents a variety of cases where single-phase and two-phase steam flows, caused erosion-corrosion damage mainly at turn points of elbows and valves. It was observed that the presence, even of a small amount of the vapor phase can significantly increase the velocity of the condensate. This paper describes the mechanism of failures by study of the failed components, operating conditions & piping lay out. In this study velocity of steam /condensate at reducing section was found to be very high. Other various contributing factors like control valve / piping sizing, metallurgical requirements, effectiveness of steam traps, flow velocity and valve design (globe & gate) were also studied. The main causes of the failures are discussed and recommendations are provided to rectify the root cause of the problems & avoid similar problems in the future.

Effect of Impeller Blade Trimming on the Performance of a 5.5:1 Pressure Ratio Centrifugal Compressor

2012 ◽  
Author(s):  
Daniel Swain ◽  
Abraham Engeda
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Compressor Blade ◽  
Operating Conditions ◽  
Performance Characteristics ◽  
Flow Coefficient ◽  
Impeller Blade ◽  
Compressor Design

Centrifugal compressor blade trimming can be used for the purpose of changing the performance characteristics of an impeller or allowing a single impeller design to be used for a range of operating conditions. There are a number of methods of impeller blade trimming that may be employed to change the impeller flowrate, the pressure ratio, or both; however, the limitations of blade trimming and the effect on the flow field are not well understood. In this study, CFD is used to model the effects of three different methods of blade trimming on a single centrifugal compressor design. Impeller performance characteristics and analysis of the flow field are presented for a series of trims for each of the three trimming methods. Each method of trimming was found to be limited at some point by choke. Shifting the original shroud profile both axially and radially in proportion to the desired flow coefficient allowed the pressure ratio and efficiency of the original impeller to be maintained while changing the flow coefficient. Trimming the blades along the meridional length in proportion to the desired new flow coefficient without regard to the original shroud profile produced similar results, but allowed the impeller to be trimmed further than was practical using the radial-axial shroud offset method. Trimming the blades axially so that the original shroud profile is maintained produced a change in pressure ratio while maintaining the original impeller flow coefficient.

scholarly journals Aeroacoustics Analysis of Globe Control Valves

2018 ◽  
Vol 15 (3) ◽  
pp. 5547-5561
Author(s):  
A. S. Prakash ◽  
K. S. Ram ◽  
V. R. Kishore
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Control Valve ◽  
Control Device ◽  
Pressure Level ◽  
Flow Coefficient ◽  
Process Industries ◽  
Fluid Medium ◽  
Control Valves ◽  
Globe Control Valve

Flow-induced noise in control valves is one of the greatest challenges faced by several industries and commonly used flow control device in process industries is globe control valves (GCV). In the present work numerical analysis was performed to study aeroacoustics of globe control valve. Axisymmetric globe control valve (2.54 cm) was analysed numerically using 2D large eddy simulation (LES) turbulence model for different valve openings. The Ffowcs-Williams and Hawkings (FWH) model was used to model the aero-acoustic. The fluid medium in the valve is air. It was observed that the sound pressure level (SPL) decreases with increase in the opening of the valve. The modification in the design of the control valve was considered to reduce SPL without affecting the inherent characteristic, flow coefficient (Cv). The design modifications in the control valve considered were chamfering the seat and filleting the plug of the valve. Out of these modifications, the 20° chamfer to the inlet side of seat gave the least sound pressure level for the various openings of the globe control valve.

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