Method for calculating influence of valve internal leakage flow on unit output

Abstract

The present application relates to the technical field of valve internal leakage and energy loss prediction, and specifically discloses a kind of calculation method of the influence of valve internal leakage flow on unit output.The method comprises: determining the saturated steam pressure, saturated steam entropy and critical mass flow of valve downstream according to the flow area of valve downstream pipeline and the pipe wall temperature of valve downstream, obtaining the leakage steam flow when saturated steam, and using the upstream fluid enthalpy value of valve, downstream fluid enthalpy value and downstream saturated steam enthalpy value to calculate and obtain the leakage flow before correction;Obtain the saturated water flow of leakage, obtain the flow correction factor according to the humidity of leakage fluid, and calculate and obtain the corrected leakage flow;Establish the model of valve with internal leakage, and change the leakage flow of valve to the corrected leakage flow, so as to calculate the output loss of unit.The present application can realize accurate estimation of valve internal leakage flow and influence on unit output by monitoring the pipe outer wall temperature downstream of valve.

Description

Technical Field

[0001] This invention belongs to the field of valve internal leakage and energy loss prediction technology, specifically relating to a method for calculating the impact of valve internal leakage flow on unit output. Background Technology

[0002] Valves are critical components of thermal systems in power plants such as thermal and nuclear power plants, serving as vital system isolation boundaries. Internal leaks not only cause energy loss, reducing unit power generation efficiency, but can also threaten the safety of equipment and personnel.

[0003] The location and flow rate of valve internal leakage are both random and uncertain. Extensive research has been conducted both domestically and internationally on valve internal leakage detection and location technologies, yielding fruitful results. However, existing valve internal leakage monitoring technologies can only detect whether internal leakage has occurred; they cannot accurately determine the extent of leakage or its impact on power plant unit output. Therefore, developing a technical method that can accurately predict valve internal leakage flow rate and its impact on unit output is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating the impact of valve internal leakage flow on unit output, which can predict valve internal leakage flow, thereby effectively assessing the degree of valve internal leakage and predicting the unit output loss caused by valve internal leakage.

[0005] The technical solution of the present invention is as follows: a method for calculating the impact of valve internal leakage flow on unit output, the method specifically including:

[0006] S1. Based on the flow area of ​​the downstream pipe and the pipe wall temperature downstream of the valve, determine the saturated steam pressure, saturated steam entropy and critical mass flow rate downstream of the valve, obtain the leakage steam flow rate when saturated steam is obtained, and use the enthalpy of the upstream fluid, the enthalpy of the downstream fluid and the enthalpy of the downstream saturated steam to calculate the leakage flow rate before correction.

[0007] S2. Obtain the saturated water flow rate of the leak, obtain the flow correction factor based on the humidity of the leaking fluid, and calculate the corrected leak flow rate.

[0008] S3. Establish a valve model for internal leakage, and calculate the unit's output loss by changing the valve's leakage flow rate to the corrected leakage flow rate.

[0009] The specific steps for obtaining the leaked flow before correction in S1 are as follows:

[0010] S1.1 Calculate the flow area of ​​the downstream pipe of the valve using the inner diameter of the pipe downstream of the valve;

[0011] S1.2 Measure the pipe wall temperature downstream of the valve, determine the saturated steam pressure, saturated steam enthalpy, and critical mass flow rate downstream of the valve, and obtain the leakage steam flow rate when the leakage fluid of the valve is saturated steam;

[0012] S1.3 Obtain the enthalpy of the fluid upstream of the valve and the enthalpy of the saturated water downstream of the valve, and calculate the leakage flow rate before correction.

[0013] The specific steps for obtaining the corrected leakage flow rate in S2 are as follows:

[0014] S2.1 Obtain the saturated water flow rate of the leak using the original leakage flow rate and the leakage steam flow rate when the valve leakage fluid is saturated steam;

[0015] S2.2 Calculate the humidity of the leaking fluid downstream of the valve and determine the flow correction factor;

[0016] S2.3 obtains the corrected leakage flow rate;

[0017] The corrected leakage flow rate is obtained based on the flow correction factor and the original leakage flow rate.

[0018] The specific steps for obtaining the pipe wall temperature downstream of the valve, determining the saturated steam pressure, saturated steam enthalpy, and critical mass flow rate downstream of the valve in step S1.2, and obtaining the leakage steam flow rate value when the leakage fluid of the valve is saturated steam, are as follows:

[0019] S1.2.1 Measure the pipe wall temperature downstream of the valve;

[0020] Select a suitable temperature measuring point at the valve outlet and use an infrared thermometer or contact thermometer to measure the pipe wall temperature downstream of the valve to obtain the pipe wall temperature T downstream of the valve. d ;

[0021] S1.2.2 Determine the saturated steam pressure value downstream of the valve;

[0022] The pipe wall temperature T downstream of the valve was obtained from the measurement. d The corresponding saturated vapor pressure is obtained as P. d ;

[0023] S1.2.3 Determine the saturated vapor enthalpy downstream of the valve;

[0024] According to the downstream saturated steam pressure P of the valve d The corresponding downstream saturated vapor enthalpy of the valve is obtained as h. g ;

[0025] S1.2.4 Determine the critical mass flow rate;

[0026] According to the downstream saturated steam pressure P of the valve dand vapor enthalpy h g Obtain the corresponding critical mass flow rate Q p ;

[0027] S1.2.5 The leakage steam flow rate when saturated steam is obtained by using the flow area of ​​the downstream pipeline of the valve, the saturated steam pressure, and the critical mass flow rate technology.

[0028] The leakage steam flow rate Q when the leakage fluid of the valve is saturated steam can be obtained using the following formula. g for

[0029] Q g =Q p *A*P d

[0030] Among them, Q g Q represents the leakage steam flow rate when the leaking fluid from the valve is saturated steam; p P represents the critical mass flow rate downstream of the valve; A represents the flow area of ​​the pipe downstream of the valve; d This indicates the saturated steam pressure corresponding to the measured downstream pipe wall temperature of the valve.

[0031] The specific steps in step S1.3 to obtain the enthalpy of the fluid upstream of the valve and the enthalpy of the saturated water downstream of the valve, and to calculate the leakage flow rate before correction, are as follows:

[0032] S1.3.1 Obtain the enthalpy value of the fluid upstream of the valve;

[0033] Based on the existing valve upstream temperature T t and pressure P t Obtain the enthalpy h of the fluid upstream of the valve. t ;

[0034] S1.3.2 Obtain the enthalpy value of saturated water downstream of the valve;

[0035] Utilizing the downstream saturation pressure P of the valve d Obtain the enthalpy value h of the saturated water downstream of the valve. f ;

[0036] S1.3.3 Obtain the original leakage flow rate value using the downstream saturated vapor enthalpy, downstream saturated water enthalpy, upstream fluid enthalpy, and leakage vapor flow rate;

[0037] Calculate the leakage flow rate Q before correction. T for:

[0038]

[0039] Among them, Q T Indicates the leakage flow rate before correction; Q g This indicates the leakage steam flow rate when the leaking fluid from the valve is saturated steam; hg Indicates the saturated vapor enthalpy downstream of the valve; h t Indicates the enthalpy of the fluid upstream of the valve; h f This indicates the saturated enthalpy downstream of the valve.

[0040] The specific steps for obtaining the leaked saturated water flow rate in step S2, obtaining the flow rate correction factor based on the humidity of the leaking fluid, and calculating the corrected leak flow rate are as follows:

[0041] S2.1 Obtain the saturated water flow rate of the leak using the original leakage flow rate and the leakage steam flow rate when the valve leakage fluid is saturated steam;

[0042] Calculate the saturated water flow rate Q of the leak. f for:

[0043] Q f =Q T -Q g

[0044] Among them, Q f Q represents the saturated flow rate of the leaked water; T Indicates the leakage flow rate before correction; Q g This indicates the leakage steam flow rate when the leaking fluid from the valve is saturated steam.

[0045] S2.2 Calculate the humidity of the leaking fluid downstream of the valve and determine the flow correction factor;

[0046] The humidity M of the leaking fluid downstream of the valve is calculated as follows:

[0047]

[0048] Where M represents the humidity of the leaking fluid downstream of the valve; Q f Q represents the saturated flow rate of the leaked water; T Indicates the leakage flow rate before correction;

[0049] Based on the humidity M of the leaking fluid, obtain the corresponding flow correction factor f;

[0050] S2.3 obtains the corrected leakage flow rate;

[0051] Calculate the corrected leakage flow rate Q c for:

[0052] Q C =Q T *f

[0053] Among them, Q C Indicates the corrected leakage flow rate; Q T represents the leakage flow rate before correction; f represents the flow correction factor.

[0054] The specific steps for establishing the valve model experiencing internal leakage in step S3 are as follows:

[0055] Based on the heat balance diagram of the power plant's thermal system, and the design parameters of the condenser, feedwater heater, steam-water separator-reheater, various pumps, and turbine, a thermal system model is established. The leakage flow rate of the valves is then adjusted to the corrected leakage flow rate Q. c Then, the output loss of the power plant unit was calculated using a thermal system model.

[0056] In step S1.2.1, the specific steps for selecting a suitable location at the valve outlet in measuring the pipe wall temperature downstream of the valve are as follows:

[0057] The temperature measurement point downstream of the valve should be at least ten times the pipe diameter away from the valve, and the location of the temperature measurement point should be far away from heat sources, cold sources, and the inlet and outlet of bypasses.

[0058] The significant advantage of this invention is that the method for calculating the impact of valve internal leakage flow on unit output does not require the installation of a flow detection device inside the downstream pipeline of the valve or modification of the thermal system. It can accurately predict the valve internal leakage flow and its impact on unit output by monitoring the temperature of the outer wall of the downstream pipeline, thus providing support for the inspection and maintenance of internal leakage valves and the improvement of unit output. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the calculation method for the impact of valve internal leakage flow on unit output according to the present invention. Detailed Implementation

[0060] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0061] like Figure 1 As shown, a method for calculating the impact of valve leakage flow on unit output is described. This method specifically includes:

[0062] S1. Based on the flow area of ​​the downstream pipe and the pipe wall temperature downstream of the valve, determine the saturated steam pressure, saturated steam entropy and critical mass flow rate downstream of the valve, obtain the leakage steam flow rate when saturated steam is obtained, and use the enthalpy of the upstream fluid, the enthalpy of the downstream fluid and the enthalpy of the downstream saturated steam to calculate the leakage flow rate before correction.

[0063] S1.1 Calculate the flow area of ​​the downstream pipe using the inner diameter of the valve; calculate the flow area A of the downstream pipe using the inner diameter D of the valve:

[0064]

[0065] S1.2 Measure the pipe wall temperature downstream of the valve, determine the saturated steam pressure, saturated steam enthalpy, and critical mass flow rate downstream of the valve, and obtain the leakage steam flow rate when the leakage fluid of the valve is saturated steam;

[0066] S1.2.1 Measure the pipe wall temperature downstream of the valve;

[0067] Select a suitable temperature measuring point at the valve outlet and use an infrared thermometer or contact thermometer to measure the pipe wall temperature downstream of the valve to obtain the pipe wall temperature T downstream of the valve. d ;

[0068] To avoid or reduce the impact of temperature conduction near valves or pipelines, the temperature measurement point downstream of the valve should be at least ten times the pipe diameter away from the valve, and the location of the temperature measurement point should be far away from heat sources, cold sources, and the inlet and outlet of bypasses.

[0069] S1.2.2 Determine the saturated steam pressure value downstream of the valve;

[0070] The pipe wall temperature T downstream of the valve was obtained from the measurement. d By consulting the table of water and water vapor properties, the corresponding saturated vapor pressure P is obtained. d ;

[0071] S1.2.3 Determine the saturated vapor enthalpy downstream of the valve;

[0072] According to the downstream saturated steam pressure P of the valve d By consulting the thermodynamic property tables of water and steam, the corresponding downstream saturated steam enthalpy of the valve, h, can be obtained. g ;

[0073] S1.2.4 Determine the critical mass flow rate;

[0074] According to the downstream saturated steam pressure P of the valve d and vapor enthalpy h g From the critical mass table under equilibrium isentropic conditions, obtain the corresponding critical mass flow rate Q. p ;

[0075] S1.2.5 The leakage steam flow rate when saturated steam is obtained by using the flow area of ​​the downstream pipeline of the valve, the saturated steam pressure, and the critical mass flow rate technology.

[0076] The leakage steam flow rate Q when the leakage fluid of the valve is saturated steam can be obtained using the following formula. g for

[0077] Q g =Q p *A*P d

[0078] Among them, Q g This indicates the leakage steam flow rate when the leaking fluid from the valve is saturated steam, expressed in lbm / hr; Q p The value of A represents the critical mass flow rate downstream of the valve, in lbm / hr; A represents the flow area of ​​the pipe downstream of the valve, in inches. 2 ;P d This indicates the saturated vapor pressure corresponding to the measured downstream pipe wall temperature of the valve, expressed in psia.

[0079] S1.3 Obtain the enthalpy of the fluid upstream of the valve and the enthalpy of the saturated water downstream of the valve, and calculate the leakage flow rate before correction;

[0080] S1.3.1 Obtain the enthalpy value of the fluid upstream of the valve;

[0081] Based on the existing valve upstream temperature T t and pressure P t The enthalpy h of the fluid upstream of the valve can be obtained by consulting the thermodynamic property table of water and water vapor. t ;

[0082] The power plant's PI system or field measuring instruments are used to obtain measurement data of upstream temperature and pressure of the valve.

[0083] S1.3.2 Obtain the enthalpy value of saturated water downstream of the valve;

[0084] Utilizing the downstream saturation pressure P of the valve d By consulting the table of thermodynamic properties of water and water vapor, the enthalpy value h of saturated water downstream of the valve can be obtained. f ;

[0085] S1.3.3 Obtain the original leakage flow rate value using the downstream saturated vapor enthalpy, downstream saturated water enthalpy, upstream fluid enthalpy, and leakage vapor flow rate;

[0086] Calculate the leakage flow rate Q before correction. T for:

[0087]

[0088] Among them, Q T This indicates the leakage flow rate before correction, in lbm / hr; Q g This indicates the leakage steam flow rate when the leaking fluid from the valve is saturated steam, expressed in lbm / hr; h g This indicates the saturated vapor enthalpy downstream of the valve, in units of btu / lbm; h t This indicates the enthalpy of the fluid upstream of the valve, in units of btu / lbm; h f This indicates the saturated enthalpy of water downstream of the valve, in units of btu / lbm.

[0089] S2. Obtain the saturated water flow rate of the leak, obtain the flow correction factor based on the humidity of the leaking fluid, and calculate the corrected leak flow rate.

[0090] S2.1 Obtain the saturated water flow rate of the leak using the original leakage flow rate and the leakage steam flow rate when the valve leakage fluid is saturated steam;

[0091] Calculate the saturated water flow rate Q of the leak. f for:

[0092] Q f =Q T -Q g

[0093] Among them, Q f Q represents the saturated water flow rate of the leak, expressed in lbm / hr. T This indicates the leakage flow rate before correction, in lbm / hr; Q g This indicates the leakage steam flow rate when the leaking fluid from the valve is saturated steam, expressed in lbm / hr.

[0094] S2.2 Calculate the humidity of the leaking fluid downstream of the valve and determine the flow correction factor;

[0095] The humidity M of the leaking fluid downstream of the valve is calculated as follows:

[0096]

[0097] Where M represents the humidity of the leaking fluid downstream of the valve, %rh; Q f Q represents the saturated water flow rate of the leak, expressed in lbm / hr. T This indicates the leakage flow rate before correction, in lbm / hr.

[0098] Based on the humidity M of the leaking fluid, look up the table of the impact of humidity on steam passing through various obstacles to obtain the corresponding flow correction factor f;

[0099] S2.3 obtains the corrected leakage flow rate;

[0100] Calculate the corrected leakage flow rate Q c for:

[0101] Q c =Q T *f where Q C This indicates the corrected leakage flow rate, in lbm / hr; Q T The value represents the original leakage flow rate, expressed in lbm / hr; f represents the flow rate correction factor.

[0102] S3. Using existing thermal system simulation software, establish a valve model that has internal leakage, and calculate the unit's output loss by changing the leakage flow rate of the valve to the corrected leakage flow rate.

[0103] Based on the heat balance diagram of the power plant's thermal system, and the design parameters of the condenser, feedwater heater, steam-water separator-reheater, various pumps, and turbine, a thermal system model is established. The leakage flow rate of the valves is then adjusted to the corrected leakage flow rate Q. c Then, the output loss of the power plant unit was calculated using a thermal system model.

Claims

1. A method for calculating the impact of valve internal leakage flow on unit output, characterized in that, The method specifically includes: S1. Based on the flow area of ​​the downstream pipeline and the pipe wall temperature downstream of the valve, determine the saturated steam pressure, saturated steam entropy, and critical mass flow rate downstream of the valve to obtain the leakage steam flow rate at saturated steam. Then, using the enthalpy of the fluid upstream of the valve, the enthalpy of the fluid downstream of the valve, and the enthalpy of the saturated steam downstream, calculate the leakage flow rate before correction. Specifically, this includes: S1.1 Calculate the flow area of ​​the downstream pipe of the valve using the inner diameter of the pipe. S1.2 Measure the pipe wall temperature downstream of the valve, determine the saturated steam pressure, saturated steam enthalpy, and critical mass flow rate downstream of the valve, and obtain the leakage steam flow rate when the leakage fluid of the valve is saturated steam; S1.3 Obtain the enthalpy of the fluid upstream of the valve and the enthalpy of the saturated water downstream of the valve, and calculate the leakage flow rate before correction; S2. Obtain the saturated water flow rate of the leak, obtain the flow correction factor based on the humidity of the leaking fluid, and calculate the corrected leak flow rate. S3. Establish a valve model for internal leakage, and calculate the unit's output loss by changing the valve's leakage flow rate to the corrected leakage flow rate.

2. The method for calculating the impact of valve internal leakage flow on unit output according to claim 1, characterized in that, The specific steps for obtaining the corrected leakage flow rate in S2 are as follows: S2.1 Obtain the saturated water flow rate of the leak using the original leakage flow rate and the leakage steam flow rate when the valve leakage fluid is saturated steam; S2.2 Calculate the humidity of the leaking fluid downstream of the valve and determine the flow correction factor; S2.3 Obtain the corrected leakage flow rate; The corrected leakage flow rate is obtained based on the flow correction factor and the original leakage flow rate.

3. The method for calculating the impact of valve internal leakage flow on unit output according to claim 1, characterized in that, The specific steps for obtaining the pipe wall temperature downstream of the valve, determining the saturated steam pressure, saturated steam enthalpy, and critical mass flow rate downstream of the valve in step S1.2, and obtaining the leakage steam flow rate value when the leakage fluid of the valve is saturated steam, are as follows: S1.2.1 Measure the pipe wall temperature downstream of the valve; Select temperature measuring point at appropriate position at valve outlet, and measure temperature of pipe wall downstream of valve by using infrared temperature measuring instrument or contact thermometer to obtain pipe wall temperature T downstream of valve d ; wherein, the position of temperature measuring point downstream of valve should be at least ten times of pipe diameter away from valve, and the position of temperature measuring point should be far away from heat source or cold source and near to inlet and outlet of bypass S1.2.2 Determine the saturated steam pressure downstream of the valve; According to the measurement, the temperature T of the pipe wall downstream of the valve is obtained d , and the corresponding saturated vapor pressure P is obtained d ; S1.2.3 Determine the saturated vapor enthalpy downstream of the valve; According to the saturated steam pressure P downstream of the valve d , the corresponding saturated steam enthalpy h downstream of the valve is obtained g ; S1.2.4 Determine the critical mass flow rate; According to the saturated vapor pressure P downstream of the valve d and the vapor enthalpy h g , the corresponding critical mass flow Q p is obtained; S1.2.5 The leakage steam flow rate when saturated steam is obtained by using the flow area of ​​the downstream pipeline of the valve, the saturated steam pressure, and the critical mass flow rate technology. The leakage steam flow rate Q is obtained using the following equation when the valve leakage fluid is saturated steam g is where Q g represents the leakage steam flow rate when the valve is leaking a saturated vapor; Q p represents the critical flow rate downstream of the valve; A represents the flow area of the pipe downstream of the valve; P d represents the saturated vapor pressure corresponding to the measured pipe wall temperature downstream of the valve.

4. The method for calculating the impact of valve internal leakage flow on unit output according to claim 1, characterized in that, The specific steps in step S1.3 to obtain the enthalpy of the fluid upstream of the valve and the enthalpy of the saturated water downstream of the valve, and to calculate the leakage flow rate before correction, are as follows: S1.3.1 Obtain the enthalpy value of the fluid upstream of the valve; Based on the existing valve upstream temperature T t and pressure P t Obtain the enthalpy h of the fluid upstream of the valve. t ; S1.3.2 Obtain the enthalpy value of saturated water downstream of the valve; Utilizing the downstream saturation pressure P of the valve d Obtain the enthalpy value h of the saturated water downstream of the valve. f ; S1.3.3 Obtain the original leakage flow rate value using the downstream saturated vapor enthalpy, downstream saturated water enthalpy, upstream fluid enthalpy, and leakage vapor flow rate; Calculate the uncorrected leakage flow rate Q T for: Among them, Q T Indicates the leakage flow rate before correction; Q g This indicates the leakage steam flow rate when the leaking fluid from the valve is saturated steam; h g Indicates the saturated vapor enthalpy downstream of the valve; h t Indicates the enthalpy of the fluid upstream of the valve; h f This indicates the saturated enthalpy downstream of the valve.

5. The method for calculating the impact of valve internal leakage flow on unit output according to claim 2, characterized in that, The specific steps for obtaining the leaked saturated water flow rate in step S2, obtaining the flow rate correction factor based on the humidity of the leaking fluid, and calculating the corrected leak flow rate are as follows: S2.1 Obtain the saturated water flow rate of the leak using the original leakage flow rate and the leakage steam flow rate when the valve leakage fluid is saturated steam; Calculate the saturated water flow rate Q of the leak. f for: Among them, Q f Q represents the saturated flow rate of the leaked water; T Indicates the leakage flow rate before correction; Q g This indicates the leakage steam flow rate when the leaking fluid from the valve is saturated steam. S2.2 Calculate the humidity of the leaking fluid downstream of the valve and determine the flow correction factor; The humidity M of the leaking fluid downstream of the valve is calculated as follows: Where M represents the humidity of the leaking fluid downstream of the valve; Q f Q represents the saturated flow rate of the leaked water; T Indicates the leakage flow rate before correction; Based on the humidity M of the leaking fluid, obtain the corresponding flow correction factor f; S2.3 Obtain the corrected leakage flow rate; Calculate the corrected leakage flow rate Q c for: Among them, Q C Indicates the corrected leakage flow rate; Q T represents the leakage flow rate before correction; f represents the flow correction factor.

6. The method for calculating the impact of valve internal leakage flow on unit output according to claim 1, characterized in that, The specific steps for establishing the valve model experiencing internal leakage in step S3 are as follows: Based on the heat balance diagram of the power plant's thermal system, and the design parameters of the condenser, feedwater heater, steam-water separator-reheater, various pumps, and turbine, a thermal system model is established. The leakage flow rate of the valves is then adjusted to the corrected leakage flow rate Q. c Then, the output loss of the power plant unit was calculated using a thermal system model.

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