Abstract: This paper expounds the meaning and type of valve management of steam turbine governing system, explains and analyzes the application of valve management during the start-up process of steam turbine, and through the valve management in DEH regulating system of steam turbine, fully demonstrates that in DEH regulation system The importance of valve management, in order to achieve valve control in the control mechanism used by the special way.
Key words: valve management switching overlap degree CLC number: TM621 Document code: A Article ID: 1003-9082 (2017) 02-0304-01
First, the basic content of the valve management and main features introduced In the steam turbine DEH, the valve flow characteristic curve is an important function, the adjustment characteristic curve if the actual characteristics of the valve match, DEH control effect will reveal its advantages. When the DEH system is shipped from the factory, the set valve management curve is usually calculated based on the design of the steam turbine. In actual operation, it is often subject to the valve installation process, the layout of the pipeline and other environmental factors and human factors. Valve management in this issue, due to the existence of various plant problems to varying degrees, such as load changes occur in the unit variable load, slow regulation, resulting in control of the unit is difficult, this situation in a FM process, also showed a serious impact on The safety of the unit and the ability to change the load.
Valve Management For high-pressure regulating valves, each valve has a separate servo-control circuit. Valve management program is a high-pressure valve control in a single valve control (full arc into the steam approach) that is, the throttle control and sequence valve control (part of the arc into the steam approach) that is, nozzle adjustment between the procedures used to control and Determine the valve opening sequence. In the single-valve operating mode, the four adjustable doors open simultaneously to adjust the intake air volume. The total number of open adjustable doors increases with the increase of load, which can adapt to large changes of unit load. Valve operation due to the movement of each door, throttling loss, the unit's economic disadvantage. When the unit is under constant pressure with partial load, the sequential valve control can reduce the throttling loss of the adjusting door, so the unit obtains higher thermal efficiency. However, this method has the problems of uneven heating of the metal, thermal stress and impact of the blade to generate vibration. Therefore, the load capacity of the unit is limited. In order to eliminate the impact of main steam pressure changes and high load on the characteristics of the transfer door, before the flow - valve position conversion, the dynamic flow of the main steam pressure and load signals were dynamically corrected.
Valve management is the main role of the load control loop output flow request signal into a valve position request signal, and in the manual intervention, according to unit safety, economic operation and variable load requirements to achieve online single valve / non-interference switch valve , And can linearize the flow of the valve and convert the flow rate request value in the single valve or sequential valve control mode into the corresponding valve opening degree signal.
The main functions of valve management are as follows:
(1) to achieve online single valve / non-interference switch valve.
(2) During the valve control mode transition, if the load set point is unchanged, then DEH can keep the load basically unchanged.
(3) to achieve linear valve flow characteristics, and single-valve or sequential control of the flow rate of the request value is converted into the corresponding valve opening signal.
(4) Ensure that the DEH system can be switched from manual mode to automatic mode in a balanced manner.
(5) provide the best valve position.
By the valve control and single valve control thermal efficiency difference curve, indicating that the unit with a partial load, the sequential valve control can improve the thermal efficiency. Steam through the control valve when the door is always throttling loss, operation of the turbine requires minimizing throttling losses adjust the valve to improve the unit efficiency. In general, the throttling loss of the valve is minimized when the valve is close to full close or close to the maximum flow rate, ie the best valve position.
The system according to claim DEH unit load, the steam flow is calculated corresponding to the parameter, the value of this request inputted to the valve management program in order to control the valve gate opening degree.
The input flow rate is based on the rated main steam pressure. When the main steam pressure is not equal to the rated value, the same control valve opening steam flow obtained can not meet the control requirements, the load does not meet the required value. In this case, we can correct it through the load control loop. If the conversion into the door before the opening, the control output of the current output of the main steam pressure correction, and then press the corrected flow into the corresponding opening, press the opening to adjust the valve load can reach the required value, This is feedforward correction.
Load on the steam flow request correction: In the low load conditions, the door opening is small, before and after the pressure drop, adjust the door to the internal critical flow, this time, flow and adjust the door opening into a one-to-one correspondence. However, as the load increases, the back door pressure increases, the differential pressure decreases before and after the door into a subcritical flow, the flow is not only related to the opening, but also with the back pressure. The differential pressure flow coefficient under the formula are as follows:
Steam flow rate, steam correction coefficient, overheating temperature, differential pressure before and after the valve, pressure before the valve, and pressure after the valve to achieve speed control and power control of the steam turbine by changing the opening of the regulating valve. In the single-valve control mode, high-pressure regulating valve opening is basically the same, the calculation is relatively simple. In the valve control mode, you need to determine the valve opening sequence, separate calculation of the opening of each valve. This is also the basis for economic analysis of steam turbine regulation.
Second, the valve flow characteristics optimization Because the actual flow characteristics of the valve objectively difficult to change, so the valve flow characteristics of the optimization program, we measured the actual flow characteristics of the valve curve, optimize the appropriate valve management curve. We based on the valve obtained by the actual flow curve of the inverse function of the valve management curve, you can achieve single-valve management curve optimization. For the optimization of the valve management curve needs to be based on the single, the valve management curve between the corresponding optimization. Currently, there are two modes: 1. Single, the use of the ratio between the valve, the bias correction mode; 2. Single, along the valve using a different valve management curve.
Third, the valve switching Valve management is essentially through the nozzle throttle with the gas (single valve control) and nozzle with steam (sequence valve control) of the interference-free switch to solve the process of variable load uniform heating and part load economy contradictions. This presents the concept of single-valve and sequential valves. Single-valve mode, the regulation level into the whole week into the steam, the blade evenly heated, fast load change rate, larger throttle loss, low thermal efficiency. In the sequential valve mode, the throttling loss is reduced and the thermal economy of the unit is improved, but the blades are heated unevenly and the load changing rate is slow. Therefore, the cold start or low parameter under the load when the general single-valve approach. In the process of variable load, it is desirable to improve the soaking process with throttling regulation. When the soaking process is completed, it is also desirable to use nozzle adjusting to improve the unit efficiency. In this condition, the operating mode is required to be switched by single valve / sequence valve Two kinds of adjustment of the interference-free switch.
For the constant pressure operation with the basic load conditions and sliding pressure operation of the peak load conditions, due to the regulation valve close to fully open state, the throttle adjustment and nozzle adjustment is very small, the valve switch is of little significance; part The load corresponds to partial pressure. For variable load operation under constant pressure, it is desirable to improve the soaking process with throttling during variable load. After completion, Achieve single valve / non-interference switch valve.
Fourth, the valve overlap degree of impact analysis In general, the degree of overlap, then adjust the door of the throttle loss, poor economy; overlap is small, it will adjust the total flow characteristics of the linearity of the poor, affecting the stability of the regulatory system. When using the nozzle adjustment, a plurality of adjustable doors turn on in turn, before the previous valve is not fully open, the next valve is opened in advance. When the current valve is fully open, the next valve to open in advance is called the valve overlap. Divided into the trip overlap and pressure overlap two types.
In accordance with the optimization program to achieve a single valve sequence valve switch, but also the unit in the single valve and sequence valve two ways with load stability test, high pressure cylinder efficiency test, the test shows that the unit load is low, the single valve mode Under the high-profile valve opening smaller, larger throttle loss, compared with the sequential valve, high-pressure cylinder efficiency is lower, less economical.
In the process of adjusting the door open, when the pressure is small, the inside of the adjusting door is the critical flow, at this moment, the flow of the regulating valve is linearly proportional to adjusting the lift of the valve. If the valve continues to open large, although the valve flow area is still increasing, but before and after the valve to reduce the pressure drop, flow increases with the increase of the trend of slowing. Subsequently, even if the valve lift continues to increase, but by the valve throat size constraints, the traffic increase is small. It is generally believed that: the pressure ratio before and after the valve is 0.95 ~ 0.98, that the valve is fully open. Adjustable valve effective relative lift of about 25%.
At present, large-scale thermal power generating units are equipped with valve management functions, so that the unit under different conditions, single-valve and multi-valve regulation switching function. The valve test speeding test, maintenance personnel can make the system to observe the turbine control performance, timely detection of problems to ensure the safe and stable operation of the unit.
References [1] Lin Feng. Turbine DEH system high-profile door control failure and its analysis [J]. Technology and Business .2013,3.
[2] Dong Qingping, Liu Hongfei. DEH valve flow characteristics of the coordinated control of the unit [J] Technology and Industry .2013,2.
Key words: valve management switching overlap degree CLC number: TM621 Document code: A Article ID: 1003-9082 (2017) 02-0304-01
First, the basic content of the valve management and main features introduced In the steam turbine DEH, the valve flow characteristic curve is an important function, the adjustment characteristic curve if the actual characteristics of the valve match, DEH control effect will reveal its advantages. When the DEH system is shipped from the factory, the set valve management curve is usually calculated based on the design of the steam turbine. In actual operation, it is often subject to the valve installation process, the layout of the pipeline and other environmental factors and human factors. Valve management in this issue, due to the existence of various plant problems to varying degrees, such as load changes occur in the unit variable load, slow regulation, resulting in control of the unit is difficult, this situation in a FM process, also showed a serious impact on The safety of the unit and the ability to change the load.
Valve Management For high-pressure regulating valves, each valve has a separate servo-control circuit. Valve management program is a high-pressure valve control in a single valve control (full arc into the steam approach) that is, the throttle control and sequence valve control (part of the arc into the steam approach) that is, nozzle adjustment between the procedures used to control and Determine the valve opening sequence. In the single-valve operating mode, the four adjustable doors open simultaneously to adjust the intake air volume. The total number of open adjustable doors increases with the increase of load, which can adapt to large changes of unit load. Valve operation due to the movement of each door, throttling loss, the unit's economic disadvantage. When the unit is under constant pressure with partial load, the sequential valve control can reduce the throttling loss of the adjusting door, so the unit obtains higher thermal efficiency. However, this method has the problems of uneven heating of the metal, thermal stress and impact of the blade to generate vibration. Therefore, the load capacity of the unit is limited. In order to eliminate the impact of main steam pressure changes and high load on the characteristics of the transfer door, before the flow - valve position conversion, the dynamic flow of the main steam pressure and load signals were dynamically corrected.
Valve management is the main role of the load control loop output flow request signal into a valve position request signal, and in the manual intervention, according to unit safety, economic operation and variable load requirements to achieve online single valve / non-interference switch valve , And can linearize the flow of the valve and convert the flow rate request value in the single valve or sequential valve control mode into the corresponding valve opening degree signal.
The main functions of valve management are as follows:
(1) to achieve online single valve / non-interference switch valve.
(2) During the valve control mode transition, if the load set point is unchanged, then DEH can keep the load basically unchanged.
(3) to achieve linear valve flow characteristics, and single-valve or sequential control of the flow rate of the request value is converted into the corresponding valve opening signal.
(4) Ensure that the DEH system can be switched from manual mode to automatic mode in a balanced manner.
(5) provide the best valve position.
By the valve control and single valve control thermal efficiency difference curve, indicating that the unit with a partial load, the sequential valve control can improve the thermal efficiency. Steam through the control valve when the door is always throttling loss, operation of the turbine requires minimizing throttling losses adjust the valve to improve the unit efficiency. In general, the throttling loss of the valve is minimized when the valve is close to full close or close to the maximum flow rate, ie the best valve position.
The system according to claim DEH unit load, the steam flow is calculated corresponding to the parameter, the value of this request inputted to the valve management program in order to control the valve gate opening degree.
The input flow rate is based on the rated main steam pressure. When the main steam pressure is not equal to the rated value, the same control valve opening steam flow obtained can not meet the control requirements, the load does not meet the required value. In this case, we can correct it through the load control loop. If the conversion into the door before the opening, the control output of the current output of the main steam pressure correction, and then press the corrected flow into the corresponding opening, press the opening to adjust the valve load can reach the required value, This is feedforward correction.
Load on the steam flow request correction: In the low load conditions, the door opening is small, before and after the pressure drop, adjust the door to the internal critical flow, this time, flow and adjust the door opening into a one-to-one correspondence. However, as the load increases, the back door pressure increases, the differential pressure decreases before and after the door into a subcritical flow, the flow is not only related to the opening, but also with the back pressure. The differential pressure flow coefficient under the formula are as follows:
Steam flow rate, steam correction coefficient, overheating temperature, differential pressure before and after the valve, pressure before the valve, and pressure after the valve to achieve speed control and power control of the steam turbine by changing the opening of the regulating valve. In the single-valve control mode, high-pressure regulating valve opening is basically the same, the calculation is relatively simple. In the valve control mode, you need to determine the valve opening sequence, separate calculation of the opening of each valve. This is also the basis for economic analysis of steam turbine regulation.
Second, the valve flow characteristics optimization Because the actual flow characteristics of the valve objectively difficult to change, so the valve flow characteristics of the optimization program, we measured the actual flow characteristics of the valve curve, optimize the appropriate valve management curve. We based on the valve obtained by the actual flow curve of the inverse function of the valve management curve, you can achieve single-valve management curve optimization. For the optimization of the valve management curve needs to be based on the single, the valve management curve between the corresponding optimization. Currently, there are two modes: 1. Single, the use of the ratio between the valve, the bias correction mode; 2. Single, along the valve using a different valve management curve.
Third, the valve switching Valve management is essentially through the nozzle throttle with the gas (single valve control) and nozzle with steam (sequence valve control) of the interference-free switch to solve the process of variable load uniform heating and part load economy contradictions. This presents the concept of single-valve and sequential valves. Single-valve mode, the regulation level into the whole week into the steam, the blade evenly heated, fast load change rate, larger throttle loss, low thermal efficiency. In the sequential valve mode, the throttling loss is reduced and the thermal economy of the unit is improved, but the blades are heated unevenly and the load changing rate is slow. Therefore, the cold start or low parameter under the load when the general single-valve approach. In the process of variable load, it is desirable to improve the soaking process with throttling regulation. When the soaking process is completed, it is also desirable to use nozzle adjusting to improve the unit efficiency. In this condition, the operating mode is required to be switched by single valve / sequence valve Two kinds of adjustment of the interference-free switch.
For the constant pressure operation with the basic load conditions and sliding pressure operation of the peak load conditions, due to the regulation valve close to fully open state, the throttle adjustment and nozzle adjustment is very small, the valve switch is of little significance; part The load corresponds to partial pressure. For variable load operation under constant pressure, it is desirable to improve the soaking process with throttling during variable load. After completion, Achieve single valve / non-interference switch valve.
Fourth, the valve overlap degree of impact analysis In general, the degree of overlap, then adjust the door of the throttle loss, poor economy; overlap is small, it will adjust the total flow characteristics of the linearity of the poor, affecting the stability of the regulatory system. When using the nozzle adjustment, a plurality of adjustable doors turn on in turn, before the previous valve is not fully open, the next valve is opened in advance. When the current valve is fully open, the next valve to open in advance is called the valve overlap. Divided into the trip overlap and pressure overlap two types.
In accordance with the optimization program to achieve a single valve sequence valve switch, but also the unit in the single valve and sequence valve two ways with load stability test, high pressure cylinder efficiency test, the test shows that the unit load is low, the single valve mode Under the high-profile valve opening smaller, larger throttle loss, compared with the sequential valve, high-pressure cylinder efficiency is lower, less economical.
In the process of adjusting the door open, when the pressure is small, the inside of the adjusting door is the critical flow, at this moment, the flow of the regulating valve is linearly proportional to adjusting the lift of the valve. If the valve continues to open large, although the valve flow area is still increasing, but before and after the valve to reduce the pressure drop, flow increases with the increase of the trend of slowing. Subsequently, even if the valve lift continues to increase, but by the valve throat size constraints, the traffic increase is small. It is generally believed that: the pressure ratio before and after the valve is 0.95 ~ 0.98, that the valve is fully open. Adjustable valve effective relative lift of about 25%.
At present, large-scale thermal power generating units are equipped with valve management functions, so that the unit under different conditions, single-valve and multi-valve regulation switching function. The valve test speeding test, maintenance personnel can make the system to observe the turbine control performance, timely detection of problems to ensure the safe and stable operation of the unit.
References [1] Lin Feng. Turbine DEH system high-profile door control failure and its analysis [J]. Technology and Business .2013,3.
[2] Dong Qingping, Liu Hongfei. DEH valve flow characteristics of the coordinated control of the unit [J] Technology and Industry .2013,2.
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