Early warning method and system for heat transfer deterioration of steam-water two-phase flow in water-cooled wall tube

Abstract

The present application relates to the technical field of boiler heating surface operation monitoring, and discloses a method and system for early warning of heat transfer deterioration of water-cooled wall pipe internal steam-water two-phase flow, which collects water-cooled wall pipe operation parameters and constructs a working condition characteristic vector, screens historical stable heat exchange samples to match similar working conditions, and obtains wall temperature and temperature rise rate upper envelope; based on the operation parameters, the equivalent temperature of the fluid in the pipe is calculated, the equivalent heat transfer response coefficient is solved in combination with the measured wall temperature, and the heat transfer capacity decay coefficient is obtained; the steam content trend quantity is calculated synchronously to determine the dry-out precursor correction quantity; the risk consistency of the risk enhancement of the water-cooled wall along the way and the risk aggregation of the adjacent pipe is verified. The heat transfer deterioration early warning index is constructed by comprehensively considering the wall temperature upper envelope, the temperature rise rate upper envelope, the heat transfer capacity decay coefficient, the dry-out precursor correction quantity and the risk consistency verification result, and the graded warning is output by comparing with the preset threshold value. The present application realizes early prediction of heat transfer deterioration and improves the pre-control ability of water-cooled wall pipe burst failure.

Description

Technical Field

[0001] This invention relates to the field of boiler heating surface operation monitoring technology, specifically to an early warning method and system for heat transfer deterioration in the steam-water two-phase flow within water-cooled wall tubes. Background Technology

[0002] The water-cooled wall of a power plant boiler is a core heat exchange component in the furnace, primarily responsible for absorbing radiant heat and converting the working fluid through evaporation. After being heated, the working fluid inside the tubes undergoes a transformation from underheated water to a two-phase flow of steam and water. During actual operation, various factors, such as uneven furnace heat load distribution, fluctuations in the mass flow rate inside the tubes, changes in the working fluid inlet enthalpy, operating pressure deviations, and frequent changes in unit load, can lead to problems such as increased steam content, thinning of the liquid film on the tube wall, localized drying of the working fluid, and a decrease in the heat transfer coefficient in some water-cooled wall sections. Once heat transfer deteriorates, even if the local heat absorption does not increase significantly, the tube wall temperature will rise rapidly, greatly increasing the probability of water-cooled wall overheating, material performance degradation, and tube rupture, directly affecting the safe and stable operation of the boiler unit.

[0003] Currently, water-cooled wall operation monitoring and early warning mainly rely on measured wall temperature, hydrodynamic simulation calculations, and fixed over-temperature threshold determination. This involves comparing the measured wall temperature with preset limits, or combining hydrodynamic and heat transfer calculations to determine abnormal flow, pressure, and wall temperature conditions, and then outputting early warning signals. However, the deterioration of heat transfer in the steam-water two-phase flow within water-cooled wall tubes is a gradual process. Before the wall temperature reaches the traditional over-temperature limit, early warning signs such as increased wall temperature response amplitude, accelerated temperature rise rate, intensified wall temperature fluctuations, prolonged recovery period after operating disturbances, and decreased equivalent heat transfer capacity already exist. Traditional fixed threshold early warning modes cannot distinguish between abnormal wall temperature changes caused by normal unit load changes and those caused by heat transfer capacity decline, and generally suffer from problems such as delayed early warnings and false alarms, making it difficult to capture early heat transfer degradation characteristics.

[0004] Existing patent CN101476715A discloses a method for early warning of water-cooled wall failure in power plant boilers. This method divides the water-cooled wall circuit, combines boiler structure and operation data to carry out hydrodynamic and wall temperature calculations, and completes stress, fatigue life and creep life analysis based on circuit flow, pressure and wall temperature parameters. It realizes online assessment of the risk of water-cooled wall hydrodynamic instability, wall temperature overheating and material failure, and can complete the judgment of operating status based on a small number of measuring points and heat transfer flow calculations.

[0005] However, this technical solution still has significant shortcomings. Its early warning system focuses on the overall failure and lifespan damage of the water-cooled wall, assessing operational risks solely through hydrodynamics, wall temperature calculations, and lifespan consumption. While it mentions that thermal and flow deviations can lead to heat transfer deterioration, it fails to construct a dynamic response envelope for the wall temperature under similar stable operating conditions based on real-time load, local heat absorption, working fluid flow rate, pressure, and inlet underenthalpy. Therefore, it cannot identify precursors to heat transfer deterioration by assessing the degree to which the actual wall temperature deviates from the stable heat transfer boundary. Furthermore, the solution lacks a mechanism for comparing real-time and baseline equivalent heat transfer response coefficients, making it unable to quantify the degree of heat transfer capacity degradation before the wall temperature exceeds limits. It also fails to consider cumulative heat absorption, inlet underenthalpy, and latent heat of vaporization to assess changes in vapor content and liquid film stability risks, and cannot verify precursors to localized drying through the characteristics of increasing risks along the pipe and the accumulation of risks in adjacent pipes. Under complex operating conditions such as deep peak shaving, rapid load change, combustion skew, and uneven flow distribution, existing technologies are unable to accurately identify early heat transfer deterioration caused by liquid film instability and localized drying, and cannot meet the operational requirements for early warning of water-cooled wall failures. Summary of the Invention

[0006] In order to overcome the defects of the prior art, the purpose of this invention is to provide an early warning method and system for the deterioration of heat transfer in the steam-water two-phase flow inside the water-cooled wall tube, so as to solve the technical problem that the prior art cannot accurately identify the early signs of heat transfer deterioration in the steam-water flow of the water-cooled wall and the warning is delayed.

[0007] This invention is achieved through the following technical solution: In a first aspect, the present invention improves an early warning method for heat transfer degradation in a water-cooled wall tube, comprising: Collect operating parameters of water-cooled wall tubes; Construct a corresponding operating condition feature vector based on the operating parameters of the water-cooled wall tubes; Filter historical stable heat exchange condition samples, combine the current condition feature vector with similar samples, and generate the wall temperature upper envelope and temperature rise rate upper envelope corresponding to the current condition feature vector. The equivalent temperature of the fluid inside the water-cooled wall tube is calculated based on the operating parameters of the water-cooled wall tube, and the equivalent heat transfer response coefficient is solved by combining the measured wall temperature, thereby determining the heat transfer capacity degradation coefficient. The steam content trend is calculated based on the operating parameters of the water-cooled wall tubes, and the drying precursor correction is determined based on the steam content trend. Determine the risk enhancement status along the water-cooled wall tubes and the risk aggregation status of adjacent tubes, and complete the risk consistency verification; By integrating the upper envelope of wall temperature, upper envelope of temperature rise rate, heat transfer capacity degradation coefficient, drying precursor correction amount, and risk consistency verification results, the early warning index of heat transfer deterioration is calculated, and the corresponding warning result is output according to the preset threshold.

[0008] Preferably, the operating condition feature vector includes equivalent heat absorption per unit length, mass flow rate, pressure, inlet enthalpy deficit, unit load, unit load change rate, equivalent heat absorption per unit length change rate, and mass flow rate change rate.

[0009] The preferred method for selecting historically stable heat exchange condition samples is as follows: From historical operating data, data segments were selected where the unit load change rate, pressure fluctuation rate, feedwater flow fluctuation rate, equivalent heat absorption per unit length change rate, and wall temperature fluctuation amplitude were all below the corresponding stable thresholds, and no hydrodynamic anomalies, severe combustion deviations, or water-cooled wall leakage faults occurred, to construct a stable heat exchange sample library.

[0010] Preferably, the specific steps for generating the upper envelope of wall temperature and the upper envelope of temperature rise rate corresponding to the feature vector of the current operating condition are as follows: Calculate the comprehensive operating condition distance between the current operating condition feature vector and each historical sample in the stable heat exchange sample library, and select samples whose comprehensive operating condition distance is less than the similarity distance threshold to form a similar operating condition sample set; Based on the high quantile boundaries of wall temperature and temperature rise rate within the sample set of similar working conditions, the upper envelope of wall temperature and the upper envelope of temperature rise rate are respectively fitted.

[0011] Preferably, the calculation method for the equivalent temperature and equivalent heat transfer response coefficient of the fluid inside the pipe is as follows: The equivalent enthalpy of the fluid inside the water-cooled wall tube is calculated based on the inlet enthalpy and the cumulative heat absorbed along the tube. The equivalent temperature of the fluid inside the tube is then determined by combining the operating pressure. The equivalent heat transfer response coefficient is the ratio of the local equivalent heat absorption to the effective temperature difference between the wall temperature and the equivalent temperature of the fluid inside the pipe.

[0012] Preferably, after obtaining the heat transfer capacity decay coefficient, the wall temperature sensitivity coefficient is calculated based on the wall temperature change and the equivalent heat absorption per unit length within the sliding time window. The wall temperature sensitivity amplification coefficient is determined based on the degree of increase of the current wall temperature sensitivity coefficient relative to the reference wall temperature sensitivity coefficient under similar stable operating conditions.

[0013] The preferred method for calculating the correction amount for signs of drought is as follows: The vapor content trend is calculated by combining the difference between the product of the cumulative heat absorbed along the process and the mass flow rate and the inlet underenthalpy, and the product of the mass flow rate and the latent heat of vaporization. The liquid film stability margin is calculated based on the mass flow rate, pressure, inlet enthalpy deficit, local equivalent heat absorption, and vapor content trend after limiting. Finally, the correction amount for drying precursors is determined based on the liquid film stability margin.

[0014] The preferred method for risk consistency verification is: Based on the changes in the early warning index of heat transfer deterioration at adjacent height positions of the same water-cooled wall tube, the enhanced risk status along the tube is determined. The risk clustering status of adjacent pipes is determined by the proportion of pipe sections whose warning index exceeds the warning threshold among adjacent water-cooled wall pipes at the same height.

[0015] The preferred method for calculating the early warning index of heat transfer deterioration is as follows: The wall temperature envelope breakthrough degree, temperature rise rate envelope breakthrough degree, wall temperature fluctuation amplification degree, wall temperature recovery lag degree, heat transfer capacity decay coefficient, sensitivity amplification coefficient, and drying precursor correction amount are normalized and limited respectively. Combined with the normalization results of each index and the duration of the anomaly, the early warning index of heat transfer deterioration is calculated. The specific warning results output based on the preset threshold include: If the warning index exceeds the warning threshold, the heat transfer capacity degradation coefficient exceeds the degradation threshold, and any of the following conditions are met: the drought precursor correction exceeds the drought precursor threshold, the risk along the pipeline increases, or the risk of adjacent pipes accumulates, a regular warning level signal will be output. If the warning index exceeds the severe warning threshold, the wall temperature recovery lag exceeds the recovery lag threshold, and the actual wall temperature exceeds the upper envelope of the wall temperature, a severe warning level signal will be output.

[0016] Secondly, the present invention also provides an early warning method for heat transfer degradation in the steam-water two-phase flow within water-cooled wall tubes, comprising: The operation data access unit is used to collect the operating parameters of the water-cooled wall tubes; The operating condition normalization processing unit is used to construct a corresponding operating condition feature vector based on the operating parameters of the water-cooled wall tube. The stable heat transfer response envelope generation unit is used to screen historical stable heat transfer condition samples, combine the current condition feature vector with similar samples, and generate the wall temperature upper envelope and temperature rise rate upper envelope corresponding to the current condition feature vector. The heat transfer capacity degradation identification unit is used to calculate the equivalent temperature of the fluid inside the water-cooled wall tube based on the operating parameters of the water-cooled wall tube, and solve the equivalent heat transfer response coefficient by combining the measured wall temperature, thereby determining the heat transfer capacity degradation coefficient. The pre-drying correction unit is used to calculate the steam content trend based on the operating parameters of the water-cooled wall tubes, and to determine the pre-drying correction amount based on the steam content trend. The risk consistency judgment unit along the pipe and adjacent pipe is used to determine the enhanced risk state of water-cooled wall pipes and the risk aggregation state of adjacent pipes, and to complete the risk consistency verification. The early warning output unit integrates the upper envelope of wall temperature, upper envelope of temperature rise rate, heat transfer capacity degradation coefficient, drying precursor correction amount and risk consistency verification results to calculate the early warning index of heat transfer deterioration and output the corresponding early warning result according to the preset threshold.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention provides an early warning method for heat transfer deterioration in water-cooled wall tubes in a steam-water two-phase flow. By constructing upper envelopes of wall temperature and temperature rise rate matching the current operating conditions from historical stable heat transfer data based on current heat absorption, mass flow rate, pressure, inlet enthalpy deficit, and load changes, this method eliminates the influence of different loads and operational disturbances on wall temperature judgment, avoiding misjudging wall temperature rise during normal load changes as heat transfer deterioration. Simultaneously, by comparing the current equivalent heat transfer response coefficient with the benchmark equivalent heat transfer response coefficient under similar stable operating conditions, and combining this with steam content trends, liquid film stability margin, increased risk along the pipe, and risk accumulation in adjacent pipes, the method comprehensively identifies signs of heat transfer capacity decline and localized drying precursors in water-cooled wall tubes. This eliminates the reliance on wall temperature reaching fixed over-temperature limits for early warning, enabling risk assessment results to be output when heat transfer deterioration is still in its early stages. This improves the timeliness, accuracy, and false alarm resistance of identifying heat transfer deterioration in steam-water two-phase flow, providing a basis for water-cooled wall operation adjustments and over-temperature tube rupture risk prevention. Attached Figure Description

[0018] Figure 1 This is a flowchart of an early warning method for heat transfer deterioration in the steam-water two-phase flow inside the water-cooled wall tube in an embodiment of the present invention. Figure 2 This is a schematic diagram of the stable heat transfer response envelope generation process in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the breakthrough of the stable heat transfer response envelope in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the enhanced risk along the pipeline and the clustering of risks from adjacent pipelines in an embodiment of the present invention; Figure 5 This is a schematic diagram of an early warning system for heat deterioration in the steam-water two-phase flow inside the water-cooled wall tube in an embodiment of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0020] The purpose of this invention is to provide an early warning method and system for the deterioration of heat transfer in the steam-water two-phase flow inside water-cooled wall tubes, so as to solve the technical problem that the existing technology cannot accurately identify the early signs of heat transfer deterioration in the steam-water flow of water-cooled walls and the warning is delayed.

[0021] The present invention will now be described in further detail with reference to the accompanying drawings: Example 1 See Figure 1 In one embodiment of the present invention, an early warning method for heat transfer degradation in the steam-water two-phase flow within a water-cooled wall tube is provided, comprising: Step 1: Collect operating parameters of the water-cooled wall tubes; Specifically, it accesses distributed wall temperature data of the water-cooled wall, furnace heat load data, feedwater flow data, pressure data, unit load data, combustion side parameters, and water-cooled wall tube panel structural parameters.

[0022] The distributed wall temperature data includes data from multiple wall temperature measuring points arranged along the height of the water-cooled wall tubes, with each measuring point corresponding to a specific tube number and height position.

[0023] The first Water-cooled wall pipe At a height position The wall temperature at any given time is recorded as , will the Water-cooled wall pipe The equivalent heat absorption per unit length of a pipe section at a given height is denoted as... The length of the pipe section at this height is denoted as Then the local equivalent heat absorption of this height pipe section is .

[0024] The first The mass flow rate inside the root water-cooled wall tube is denoted as The cross-sectional area of ​​the flow within the pipe is denoted as , will the The mass flow rate inside the root water-cooled wall tube is denoted as It satisfies:

[0025] The inlet pressure of the water-cooled wall or the steam drum pressure is denoted as... , will the The enthalpy of the fluid at the inlet of the water-cooled wall tube is denoted as Let the enthalpy of saturated water under the current pressure be denoted as Let the saturated vapor enthalpy under the current pressure be denoted as Record the entrance enthalpy deficiency as It satisfies:

[0026] when When this occurs, it indicates that the inlet fluid has reached a superheated or high enthalpy state, and the system will... To avoid errors in judging the direction of vapor content trend due to a negative inlet enthalpy caused by a zero participation in the subsequent inlet heat margin calculation.

[0027] The unit load is denoted as .

[0028] Step 2: Construct the corresponding operating condition feature vector based on the operating parameters of the water-cooled wall tube; Specifically, a characteristic vector of operating conditions is constructed based on the heat input intensity, the heat-carrying capacity of the flow inside the pipe, and the load disturbance state, so that the wall temperature response under different loads, pressures, and flow rates can be compared under a unified benchmark.

[0029] No. Water-cooled wall pipe The feature vectors of the working conditions at each height position are:

[0030] in, Indicates the rate of change of unit load. This represents the rate of change of equivalent heat absorption per unit length in a localized area. This indicates the rate of change of mass flow rate within the pipe.

[0031] Further calculation of normalized heat load response This is used to characterize the relative thermal shock intensity experienced by the corresponding pipe section under conditions of unit flow heat carrying capacity and inlet thermal margin:

[0032] in, It is a very small positive number.

[0033] For once-through boilers or supercritical boilers Determined by the inlet flow distribution results of the water-cooled wall; For natural circulation or controlled circulation boilers It is estimated from the circulation ratio, water supply flow rate and pipe screen flow distribution coefficient.

[0034] Step 3: Filter historical stable heat exchange condition samples, combine the current condition feature vector with similar samples, and generate the wall temperature upper envelope and temperature rise rate upper envelope corresponding to the current condition feature vector. Specifically, a stable heat exchange sample library is first established. The stable heat exchange sample library does not directly use all historical operating data, but selects data segments from historical operating data that meet the stable heat exchange conditions.

[0035] The stable heat exchange conditions include: the unit load change rate is less than the load stability threshold, the pressure fluctuation rate is less than the pressure stability threshold, the feedwater flow fluctuation rate is less than the flow stability threshold, the change rate of equivalent heat absorption per unit length in the local area is less than the heat load stability threshold, the water-cooled wall temperature has not reached the over-temperature alarm value, the wall temperature sliding standard deviation is less than the wall temperature stability fluctuation threshold, and no hydrodynamic abnormality, severe combustion deviation alarm, or water-cooled wall leakage alarm is recorded within this time segment.

[0036] Historical data segments that meet the above conditions are marked as stable heat exchange samples and stored in the stable heat exchange sample library according to pipe number, height position, and operating condition feature vector.

[0037] Each historical sample in the stable heat exchange sample library includes a historical operating condition feature vector, historical wall temperature, historical wall temperature change rate, historical equivalent heat absorption per unit length, historical mass flow rate, historical pressure, historical inlet underenthalpy, and the historical equivalent heat transfer response coefficient of the corresponding pipe section.

[0038] When establishing a stable heat exchange sample library, the system removes abnormally fluctuating data.

[0039] When the wall temperature change at a certain sampling point exceeds a set multiple of the median of the changes at adjacent sampling points, and the change does not correspond to changes in equivalent heat absorption per unit length, water flow rate, or pressure, the sampling point is marked as a measurement anomaly and will not participate in the generation of the steady-state heat transfer response envelope.

[0040] Based on the current operating condition feature vector A set of similar operating condition samples was formed from the stable heat exchange sample library. .

[0041] The system first calculates historical samples Overall operating condition distance from current operating conditions :

[0042] in, , , , , , , , These represent the normalized differences in corresponding parameters between historical samples and current operating conditions, respectively. to This is the distance adjustment coefficient.

[0043] The normalized difference is obtained by dividing the difference of the corresponding parameter by the standard deviation or allowable range of variation of the parameter in the stable heat exchange sample library, so that parameters of different dimensions can participate in the same distance calculation.

[0044] when Less than the similarity distance threshold At that time, historical samples Included in a sample set of similar working conditions .

[0045] If satisfied The number of historical samples is less than the minimum number of samples. Then according to Continue adding historical samples, starting from small and gradually increasing, until the number of samples in the similar working condition sample set reaches a certain threshold. .

[0046] If the number of samples in the similar working condition sample set exceeds the maximum number of samples. Then retain the one with the smallest combined working condition distance. A historical sample.

[0047] Through this process, the system can employ strict similarity screening when there are sufficient similar samples, and can still form a calculable stable heat transfer response envelope when there are insufficient similar samples.

[0048] Similar working condition sample set Each historical sample It has corresponding similarity weights The similarity weights are determined according to the following formula:

[0049] in, The smaller the value, the closer the historical sample is to the current operating conditions, and the greater its contribution to the stable heat transfer response envelope.

[0050] The reference wall temperature under the current operating condition is calculated based on a set of similar operating condition samples. Wall temperature envelope Reference temperature rise rate and the envelope of the temperature rise rate .

[0051] The reference wall temperature is determined according to the following formula:

[0052] Wall temperature envelope Determined based on the high quantile boundary of the wall temperature response under steady heat transfer conditions in a set of similar operating condition samples:

[0053] in, express Quantiles Value greater than And less than 1.

[0054] Combination Figure 3 The wall temperature envelope is not the safe protection temperature of the water-cooled wall, but the wall temperature response boundary that can be achieved under the current operating conditions and stable heat exchange state.

[0055] When the actual wall temperature has not exceeded the over-temperature alarm limit but has already exceeded the stable heat transfer response envelope, the system determines that there is a deviation in the heat transfer state at that location.

[0056] Reference temperature rise rate Determined by the weighted average of the wall temperature change rates under similar steady-state conditions:

[0057] Upper envelope of temperature rise rate Determined by the high quantile boundary of the wall temperature change rate under similar steady-state conditions:

[0058] Through the above processing, the system transforms the judgment of "whether the wall temperature is too high" into the judgment of "whether the wall temperature response has exceeded the explainable range of the steady heat transfer state under the current equivalent heat absorption per unit length, mass flow rate, pressure and load disturbance conditions".

[0059] Step 4: Calculate the equivalent temperature of the fluid inside the water-cooled wall tube based on the operating parameters of the water-cooled wall tube, and solve the equivalent heat transfer response coefficient by combining the measured wall temperature, and then determine the heat transfer capacity degradation coefficient. Specifically, determine whether the equivalent heat transfer capacity inside the water-cooled wall tubes has decreased.

[0060] First calculate the first Water-cooled wall pipe Equivalent temperature of fluid inside the pipe at each height position .

[0061] The equivalent temperature of the fluid inside the pipe is not a directly measured value, but is calculated from the inlet enthalpy, pressure, and cumulative heat absorption along the pipe.

[0062] No. Fluid equivalent enthalpy at a height position Determined according to the following formula:

[0063] Equivalent temperature of fluid inside the pipe According to pressure Equivalent enthalpy of fluid Sure:

[0064] Where T(·) represents the conversion function of thermophysical properties of water and water vapor.

[0065] The thermal property conversion function is implemented through water and water vapor property tables, a pre-set thermal property database, or a thermal property calculation program.

[0066] when When it is between the enthalpy of saturated water and the enthalpy of saturated vapor, Take the saturation temperature under the current pressure; when When below the enthalpy of saturated water or above the enthalpy of saturated vapor, The temperature of the underheated water or the temperature of the superheated steam are calculated based on the corresponding pressure and enthalpy.

[0067] The equivalent heat transfer response coefficient is calculated based on the relationship between local heat absorption and wall temperature response. .

[0068] To avoid the wall temperature and fluid temperature difference approaching zero or becoming negative due to low load, measurement errors, or overestimation of the fluid's equivalent temperature, a minimum effective temperature difference is set for the system. The equivalent heat transfer response coefficient is calculated according to the following formula:

[0069] in, It is used to characterize the equivalent heat transfer capacity per unit wall temperature difference at the current moment.

[0070] Furthermore, the benchmark equivalent heat transfer response coefficient is calculated based on a sample set of similar steady-state operating conditions. :

[0071] Heat transfer capacity degradation coefficient Determined according to the following formula:

[0072] when Furthermore, when the value continues to increase, it indicates that the equivalent heat transfer capacity of the current pipe section decreases relative to similar stable operating conditions.

[0073] This indicator is used to directly link abnormal wall temperatures with the deterioration mechanism of heat transfer in the two-phase flow of steam and water in water-cooled wall tubes, avoiding generalized anomaly identification based solely on temperature deviations.

[0074] The wall temperature sensitivity coefficient under heat load disturbance is also calculated. This is used to identify early signs of excessive wall temperature response caused by slight changes in the equivalent heat absorption per unit length.

[0075] in, This represents the change in wall temperature within the sliding time window. This represents the change in equivalent heat absorption per unit length within the same time window. The system calculates the reference wall temperature sensitivity coefficient based on similar steady-state conditions. And obtain the sensitivity amplification factor. :

[0076] when When the temperature rises, it indicates that the wall temperature response is amplified under the same heat absorption disturbance, reflecting the transformation of the local heat transfer state from stable heat transfer to deteriorating heat transfer.

[0077] Step 5: Calculate the steam content trend based on the operating parameters of the water-cooled wall tubes, and determine the drying-up precursor correction based on the steam content trend. Specifically, the steam-water two-phase flow state inside the water-cooled wall tubes will be incorporated into the early warning judgment.

[0078] The system estimates the first step based on pressure, inlet enthalpy deficit, mass flow rate, and cumulative heat absorption along the path. Water-cooled wall pipe Equivalent vapor content trend at each altitude position :

[0079] in, It is used to characterize the degree of evaporation along the pipe and the trend of local steam content increase, and is not required to be equivalent to the actual instantaneous steam content inside the pipe.

[0080] This formula indicates that the cumulative heat absorbed along the process is first used to compensate for the inlet underenthalpy, and the portion exceeding the heat required for the inlet underenthalpy is used to characterize the vaporization trend.

[0081] To prevent abnormal data from distorting the correction for pre-drying conditions, the equivalent vapor content trend is limited to obtain the limited vapor content trend. :

[0082] in, This represents the upper limit of the trend in vapor content.

[0083] when When the value is less than 0, it indicates that the location has not yet reached a significant evaporation trend, and the zero participation is used to correct for signs of drying out. when > At that time, according to Involved in calculations to avoid excessive amplification of the risk index due to abnormal local heat load or flow rate estimation.

[0084] Fluid equivalent temperature and steam content trend Both are derived from the heat balance relationship along the path, but their functions are different.

[0085] Fluid equivalent temperature Used to construct the equivalent heat transfer response coefficient, reflecting the heat transfer temperature difference between the wall temperature and the fluid inside the pipe; Trend of vapor content Used to construct a pre-drying correction amount, reflecting the degree of evaporation along the pipe section and the risk of liquid film stability.

[0086] Further calculation of liquid film stability margin This is used to reflect the proximity of a local pipe section to areas where the liquid film is unstable or prone to drying out.

[0087] in, to This is the margin coefficient.

[0088] As mass flow rate, pressure, and inlet thermal margin increase, the liquid film stability margin also increases. When the local heat absorption and vapor content increase, the liquid film stability margin decreases.

[0089] Calculate the pre-drying correction amount based on the liquid film stability margin. :

[0090] in, This is the sensitivity coefficient.

[0091] when When it decreases, An increase indicates that the pipe section is closer to a state of thinning liquid film or a precursor to localized drying.

[0092] The drying precursor correction is not used as an alarm result alone, but is used to correct the early warning index of heat transfer deterioration, so that the same wall temperature anomaly has a higher risk weight under conditions of high vapor content, high heat absorption and low mass flow rate.

[0093] The wall temperature envelope breakthrough index is calculated based on the steady-state heat transfer response envelope. :

[0094] when When this occurs, it indicates that the actual wall temperature has exceeded the normal response boundary that can be explained under similar stable operating conditions.

[0095] Temperature rise rate envelope breakthrough indicator Calculate according to the following formula:

[0096] when When this occurs, it indicates that the actual wall temperature rise rate has exceeded the temperature rise rate boundary under similar steady-state heat transfer conditions.

[0097] Volatility Amplification Indicator The results were obtained by comparing the actual wall temperature fluctuation amplitude within the sliding time window with the baseline fluctuation amplitude in the stable heat transfer sample.

[0098] in, The length of the sliding time window. This represents the standard fluctuation amplitude of wall temperature in a set of samples with similar operating conditions.

[0099] Before being included in the early warning index, the volatility amplification indicator undergoes stability boundary normalization and is not directly weighted using its original multiple.

[0100] Recovery Lagging Indicators Used to determine whether the wall temperature remains abnormally high after a decrease in heat absorption or an increase in mass flow rate:

[0101] in, _{i,j}(t) represents the time required for the actual wall temperature to fall back to within the steady-state heat transfer response envelope. This is the baseline recovery time under similar stable operating conditions.

[0102] To ensure that different indicators can be included in the same early warning index, each indicator is normalized and its amplitude is limited.

[0103] For any index to be merged Its normalization result Determined according to the following formula:

[0104] in, It represents any one of the following indicators: wall temperature envelope breakthrough index, temperature rise rate envelope breakthrough index, fluctuation amplification index, recovery hysteresis index, heat transfer capacity decay coefficient, sensitivity amplification coefficient, or drying precursor correction amount. This represents the normal upper bound of the indicator in stable samples. This represents the high-risk boundary corresponding to this indicator.

[0105] After the above processing, each indicator is mapped to between 0 and 1, avoiding the unreasonable domination of the early warning index by a single indicator due to different dimensions and abnormal extreme values.

[0106] Abnormal duration factor Determined based on the duration of simultaneous occurrence of wall temperature envelope breakthrough, temperature rise rate envelope breakthrough, and heat transfer capacity decay:

[0107] in, To meet , or The number of consecutive sampling points that meet at least two of the conditions. This serves as a duration benchmark.

[0108] After normalizing the abnormal duration factor, we get .

[0109] The normalized wall temperature envelope breakthrough index, temperature rise rate envelope breakthrough index, fluctuation amplification index, recovery lag index, heat transfer capacity degradation coefficient, sensitivity amplification coefficient, and drying precursor correction are integrated, and the reliability is enhanced by using an anomaly duration factor to obtain an early warning index for heat transfer deterioration. :

[0110] in, , , , , , , , These are the normalized results for the corresponding indicators. , , , , , , , These are the weighting coefficients.

[0111] By using the anomaly duration factor as a multiplicative correction term, the system treats persistent anomalies as a risk confidence enhancement factor, rather than simply equating them with a single heat transfer anomaly type.

[0112] The weighting coefficients and thresholds are determined from the stable heat exchange sample library and known abnormal samples.

[0113] For water-cooled wall operation data with historical records of heat transfer deterioration, local drying, or manually confirmed abnormalities, the system treats them as abnormal samples and calculates the distinguishing power of each indicator between stable and abnormal samples.

[0114] The greater the difference between the mean of a certain indicator in abnormal samples and the mean in stable samples, and the smaller the dispersion within the stable samples, the higher the weight of that indicator. Discrimination Determined according to the following formula:

[0115] in, For the first The mean of the class indicator in the abnormal samples, For the first The mean of the class indicator in a stable sample. The standard deviation is the value of the outlier samples. To stabilize the standard deviation in the sample. Weight of class indicators Determined according to the following formula:

[0116] in, Corresponding to the early warning index , , , , , or .

[0117] When there are no known abnormal samples, the system first normalizes each indicator to the same value range and sets the initial weights according to the mechanism correlation. The initial weights of the wall temperature envelope breakthrough indicator, the heat transfer capacity decay coefficient and the drying precursor correction amount are higher than those of the simple fluctuation amplification indicator. After obtaining manually confirmed abnormal samples, the weights are updated according to the discrimination score.

[0118] Each warning threshold is determined by the distribution of indicators in the stable heat exchange sample.

[0119] Early warning index threshold Take a stable heat exchange sample High percentile value, severe warning index threshold Take the higher quantile value:

[0120]

[0121] in, This represents the set of samples with stable heat transfer. Greater than , Greater than .

[0122] Heat transfer capacity degradation threshold Drying precursor correction threshold Recovery Lag Threshold Consistency threshold along the route and neighboring pipe aggregation threshold All values ​​were determined based on the high quantile of the corresponding index in the stable heat exchange sample.

[0123] By using this threshold determination method, the system can form an adaptive early warning boundary for different boilers, different water-cooled wall areas, and different historical fluctuation characteristics of measuring points.

[0124] Step 6: Determine the risk enhancement status along the water-cooled wall tube and the risk aggregation status of adjacent tubes, and complete the risk consistency verification; Specifically, determine whether the anomaly conforms to the enhanced evaporation law of the steam-water two-phase flow along the pipe in the water-cooled wall tube and the risk accumulation characteristics of the adjacent pipe area.

[0125] For the same water-cooled wall tube, as the fluid absorbs heat along the height direction, the vapor content trend usually increases along the flow direction. If the risk of heat transfer deterioration is real, the risk indicator will often show a gradual increase in the high heat absorption area or the high vapor content trend area.

[0126] Risk enhancement indicators along the route Calculate according to the following formula:

[0127] Simultaneously calculate the consistency index of vapor content trend. :

[0128] when >0 and When the value is greater than 0, it indicates that the direction of the enhancement of the early warning index is consistent with the direction of the enhancement of evaporation along the flow path of the two-phase flow of steam and water.

[0129] If the abnormal wall temperature only occurs at an isolated measuring point and does not meet the consistency requirement along the process, the system will lower its warning level or mark it as an anomaly to be confirmed.

[0130] Furthermore, the risk clustering index of adjacent pipes is calculated based on the risk status of adjacent water-cooled wall pipes at the same height. .

[0131] The first The set of adjacent tubes of a water-cooled wall tube is denoted as ,but:

[0132] in, Indicates the number of adjacent tubes. This is an indicator function.

[0133] The value is 1 if the condition inside the parentheses is true, and 0 otherwise.

[0134] when > At that time, the system determined that there was a risk clustering among adjacent pipes at the same height.

[0135] If the risk clustering index of adjacent pipes increases and the corresponding area has an equivalent heat absorption per unit length, If the temperature is high, the system identifies the region as a precursor to regional heat transfer deterioration caused by a combination of local combustion heat deviation and a decrease in the heat transfer capacity of the two phases within the tube.

[0136] Step 7: Integrate the upper envelope of wall temperature, upper envelope of temperature rise rate, heat transfer capacity degradation coefficient, drying precursor correction amount and risk consistency verification results, calculate the early warning index of heat transfer deterioration, and output the corresponding warning result according to the preset threshold.

[0137] Specifically, early warning results are output based on the early warning index, heat transfer capacity decay coefficient, drying precursor correction, risk consistency along the pipeline, and risk aggregation status of adjacent pipelines.

[0138] The warning results include attention level, warning level, and severe warning level.

[0139] The "Attention Level" indicates that the actual wall temperature has not yet exceeded the over-temperature alarm limit, but has already exceeded the response envelope of similar stable operating conditions or has shown a slight decline in heat transfer capacity. The warning level indicates that the wall temperature response is abnormal and the heat transfer capacity decline is continuously enhanced, and at least one of the following characteristics is met: a precursor to drying or a feature that extends along the path. A severe warning level indicates that the early warning index remains above the severe threshold and is accompanied by a significant recovery lag or a persistent breach of the wall temperature envelope.

[0140] When the following formula is satisfied, a warning level signal is output:

[0141] in, This serves as the threshold for early warning indicators. This is the threshold for heat transfer capacity degradation. Adjusting thresholds to indicate precursors to drought. As a consistency threshold along the process, This serves as a threshold for risk clustering in neighboring areas.

[0142] This judgment uses the decline in heat transfer capacity as the core condition, and uses signs of drying out, consistency along the pipe, or accumulation in adjacent pipes as supporting conditions, to avoid requiring all supporting conditions to be met at the same time and thus missing the early risks of heat transfer deterioration.

[0143] A severe warning level signal is output when the following formula is met:

[0144] in, The threshold for a severe early warning index. To restore the lag threshold.

[0145] The severe warning level does not require the wall temperature to have reached the traditional over-temperature alarm value. As long as the actual wall temperature remains outside the stable heat exchange response envelope, and there is a recovery lag and an increase in the comprehensive risk index, a severe warning can be issued in advance.

[0146] When outputting the early warning results, the primary source of risk should also be output.

[0147] like and The dominant risk is identified as an abnormal wall temperature response. like and The dominant risk is a system characterized by a decline in heat transfer capacity. like and Dominant, the system is marked as an enhanced risk of drought precursors; like or Dominant, the system marks it as an extended risk along the pipeline or adjacent pipe.

[0148] By identifying the primary sources of risk, operators can determine that risks are more likely to originate from combustion heat deviation, insufficient water supply flow, abnormal flow distribution in local pipe sections, or excessively rapid load changes.

[0149] The system operates as follows: First, obtain data on water-cooled wall temperature, equivalent heat absorption per unit length, mass flow rate, mass flow rate, pressure, and inlet enthalpy deficit. Then, the operating condition characteristic vector and the normalized heat load response are generated; Then, based on the stable sample selection rules and the similar sample set formation rules, the stable heat transfer response envelope under the current operating conditions is constructed. Then, the equivalent temperature of the fluid inside the pipe, the equivalent heat transfer response coefficient, the heat transfer capacity decay coefficient, and the wall temperature sensitivity amplification coefficient were calculated. Then calculate the vapor content trend, liquid film stability margin, and drying precursor correction after the limit is applied; Finally, the indicators are normalized and limited for fusion, and the early warning level of heat transfer deterioration for the corresponding pipe section is output.

[0150] For example, during the load increase phase after a certain depth of peak shaving, the first Measured wall temperature at height j of the root water-cooled wall tube Although the temperature is still below the traditional over-temperature alarm limit, the system detected that the wall temperature at this location has exceeded the upper envelope of the wall temperature under similar stable operating conditions. At the same time, the rate of temperature rise exceeds .

[0151] Further calculations revealed that the equivalent heat transfer response coefficient Relative to the reference equivalent heat transfer response coefficient Decrease, heat transfer capacity degradation coefficient Continue to increase; The trend of vapor content after the limit is applied within the same time period. Rise, liquid film stabilization margin Decline, Precursor to Dryness Correction Increase.

[0152] Further confirmation indicates that the anomaly intensifies along the fluid flow direction, or that there is a risk accumulation in adjacent pipes at the same height.

[0153] At this point, the system determines that there is an early risk of heat deterioration in the steam-water two-phase flow of the pipe section and outputs a warning signal.

[0154] For example, under certain combustion deflection conditions, the equivalent heat absorption per unit length of a local area of ​​the water-cooled wall increases, but the traditional wall temperature alarm has not yet been triggered.

[0155] The system determined that the wall temperature rise in this area had exceeded the normal response range under the current heat absorption and mass flow conditions by using the response envelope of similar stable operating conditions. At the same time, it was found that the heat transfer capacity degradation coefficient of multiple adjacent water-cooled wall tubes at the same height had increased.

[0156] Based on this, the system determines that the risk is not a single-point sensor malfunction, but a precursor to regional heat transfer deterioration caused by a combination of high local heat load and reduced heat transfer capacity of the two-phase flow inside the pipe. The system then outputs the corresponding pipe screen area, risk level, and dominant risk source.

[0157] Example 2 This embodiment also provides an early warning method for the deterioration of heat transfer in the steam-water two-phase flow within water-cooled wall tubes, including: The operation data access unit is used to collect the operating parameters of the water-cooled wall tubes; The operating condition normalization processing unit is used to construct a corresponding operating condition feature vector based on the operating parameters of the water-cooled wall tube. The stable heat transfer response envelope generation unit is used to screen historical stable heat transfer condition samples, combine the current condition feature vector with similar samples, and generate the wall temperature upper envelope and temperature rise rate upper envelope corresponding to the current condition feature vector. The heat transfer capacity degradation identification unit is used to calculate the equivalent temperature of the fluid inside the water-cooled wall tube based on the operating parameters of the water-cooled wall tube, and solve the equivalent heat transfer response coefficient by combining the measured wall temperature, thereby determining the heat transfer capacity degradation coefficient. The pre-drying correction unit is used to calculate the steam content trend based on the operating parameters of the water-cooled wall tubes, and to determine the pre-drying correction amount based on the steam content trend. The risk consistency judgment unit along the pipe and adjacent pipe is used to determine the enhanced risk state of water-cooled wall pipes and the risk aggregation state of adjacent pipes, and to complete the risk consistency verification. The early warning output unit integrates the upper envelope of wall temperature, upper envelope of temperature rise rate, heat transfer capacity degradation coefficient, drying precursor correction amount and risk consistency verification results to calculate the early warning index of heat transfer deterioration and output the corresponding early warning result according to the preset threshold.

[0158] In summary, this invention provides an early warning method and system for heat transfer deterioration in the steam-water two-phase flow within water-cooled wall tubes. It acquires operational data such as water-cooled wall tube temperature, equivalent heat absorption per unit length, mass flow rate, pressure, inlet enthalpy, and unit load. Based on the current operating conditions, it selects similar samples from historical stable heat transfer samples to construct upper envelopes for wall temperature and temperature rise rate. Furthermore, it calculates the equivalent temperature of the fluid inside the tube, equivalent heat transfer response coefficient, heat transfer capacity degradation coefficient, vapor content trend, and drying-out precursor correction. Combining wall temperature envelope breakthrough, abnormal temperature rise rate, recovery lag, increased risk along the pipe, and risk accumulation in adjacent tubes, it determines an early warning index for heat transfer deterioration and outputs graded warning results. This invention can identify the risks of localized drying, liquid film instability, and heat transfer capacity degradation before the wall temperature reaches the traditional over-temperature alarm limit, improving the timeliness and accuracy of water-cooled wall safety operation monitoring.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for early warning of heat deterioration in the steam-water two-phase flow within a water-cooled wall tube, characterized in that, include: Collect operating parameters of water-cooled wall tubes; Construct a corresponding operating condition feature vector based on the operating parameters of the water-cooled wall tubes; Filter historical stable heat exchange condition samples, combine the current condition feature vector with similar samples, and generate the wall temperature upper envelope and temperature rise rate upper envelope corresponding to the current condition feature vector. The equivalent temperature of the fluid inside the water-cooled wall tube is calculated based on the operating parameters of the water-cooled wall tube, and the equivalent heat transfer response coefficient is solved by combining the measured wall temperature, thereby determining the heat transfer capacity degradation coefficient. The steam content trend is calculated based on the operating parameters of the water-cooled wall tubes, and the drying precursor correction is determined based on the steam content trend. Determine the risk enhancement status along the water-cooled wall tubes and the risk aggregation status of adjacent tubes, and complete the risk consistency verification; By integrating the upper envelope of wall temperature, upper envelope of temperature rise rate, heat transfer capacity degradation coefficient, drying precursor correction amount, and risk consistency verification results, the early warning index of heat transfer deterioration is calculated, and the corresponding warning result is output according to the preset threshold.

2. The method for early warning of heat deterioration in steam-water two-phase flow within a water-cooled wall tube according to claim 1, characterized in that, The operating condition characteristic vector includes equivalent heat absorption per unit length, mass flow rate, pressure, inlet enthalpy deficit, unit load, unit load change rate, equivalent heat absorption per unit length change rate, and mass flow rate change rate.

3. The method for early warning of heat deterioration in the steam-water two-phase flow within a water-cooled wall tube according to claim 1, characterized in that, The selection method for the historical stable heat exchange condition samples is as follows: From historical operating data, data segments were selected where the unit load change rate, pressure fluctuation rate, feedwater flow fluctuation rate, equivalent heat absorption per unit length change rate, and wall temperature fluctuation amplitude were all below the corresponding stable thresholds, and no hydrodynamic anomalies, severe combustion deviations, or water-cooled wall leakage faults occurred, to construct a stable heat exchange sample library.

4. The method for early warning of heat deterioration in steam-water two-phase flow within a water-cooled wall tube according to claim 1, characterized in that, The specific steps for generating the upper envelope of wall temperature and upper envelope of temperature rise rate corresponding to the feature vector of the current operating condition are as follows: Calculate the comprehensive operating condition distance between the current operating condition feature vector and each historical sample in the stable heat exchange sample library, and select samples whose comprehensive operating condition distance is less than the similarity distance threshold to form a similar operating condition sample set; Based on the high quantile boundaries of wall temperature and temperature rise rate within the sample set of similar working conditions, the upper envelope of wall temperature and the upper envelope of temperature rise rate are respectively fitted.

5. The method for early warning of heat deterioration in steam-water two-phase flow within a water-cooled wall tube according to claim 1, characterized in that, The calculation method for the equivalent temperature and equivalent heat transfer response coefficient of the fluid inside the pipe is as follows: The equivalent enthalpy of the fluid inside the water-cooled wall tube is calculated based on the inlet enthalpy and the cumulative heat absorbed along the tube. The equivalent temperature of the fluid inside the tube is then determined by combining the operating pressure. The equivalent heat transfer response coefficient is the ratio of the local equivalent heat absorption to the effective temperature difference between the wall temperature and the equivalent temperature of the fluid inside the pipe.

6. The method for early warning of heat deterioration in the steam-water two-phase flow within a water-cooled wall tube according to claim 1, characterized in that, After obtaining the heat transfer capacity degradation coefficient, the wall temperature sensitivity coefficient is calculated based on the wall temperature change and the equivalent heat absorption per unit length within the sliding time window. The wall temperature sensitivity amplification coefficient is determined based on the degree of increase of the current wall temperature sensitivity coefficient relative to the reference wall temperature sensitivity coefficient under similar stable operating conditions.

7. The method for early warning of heat deterioration in the steam-water two-phase flow within a water-cooled wall tube according to claim 1, characterized in that, The calculation method for the pre-drying correction is as follows: The vapor content trend is calculated by combining the difference between the product of the cumulative heat absorbed along the process and the mass flow rate and the inlet underenthalpy, and the product of the mass flow rate and the latent heat of vaporization. The liquid film stability margin is calculated based on the mass flow rate, pressure, inlet enthalpy deficit, local equivalent heat absorption, and vapor content trend after limiting. Finally, the correction amount for drying precursors is determined based on the liquid film stability margin.

8. The method for early warning of heat deterioration in steam-water two-phase flow within a water-cooled wall tube according to claim 1, characterized in that, The risk consistency verification method is as follows: Based on the changes in the early warning index of heat transfer deterioration at adjacent height positions of the same water-cooled wall tube, the enhanced risk status along the tube is determined. The risk clustering status of adjacent pipes is determined by the proportion of pipe sections whose warning index exceeds the warning threshold among adjacent water-cooled wall pipes at the same height.

9. The method for early warning of heat deterioration in steam-water two-phase flow within a water-cooled wall tube according to claim 1, characterized in that, The calculation method for the early warning index of heat transfer deterioration is as follows: The wall temperature envelope breakthrough degree, temperature rise rate envelope breakthrough degree, wall temperature fluctuation amplification degree, wall temperature recovery lag degree, heat transfer capacity decay coefficient, sensitivity amplification coefficient, and drying precursor correction amount are normalized and limited respectively. Combined with the normalization results of each index and the duration of the anomaly, the early warning index of heat transfer deterioration is calculated. The specific warning results output based on the preset threshold include: If the warning index exceeds the warning threshold, the heat transfer capacity degradation coefficient exceeds the degradation threshold, and any of the following conditions are met: the drought precursor correction exceeds the drought precursor threshold, the risk along the pipeline increases, or the risk of adjacent pipes accumulates, a regular warning level signal will be output. If the warning index exceeds the severe warning threshold, the wall temperature recovery lag exceeds the recovery lag threshold, and the actual wall temperature exceeds the upper envelope of the wall temperature, a severe warning level signal will be output.

10. A method for early warning of heat deterioration in the steam-water two-phase flow within a water-cooled wall tube, characterized in that, include: The operation data access unit is used to collect the operating parameters of the water-cooled wall tubes; The operating condition normalization processing unit is used to construct a corresponding operating condition feature vector based on the operating parameters of the water-cooled wall tube. The stable heat transfer response envelope generation unit is used to screen historical stable heat transfer condition samples, combine the current condition feature vector with similar samples, and generate the wall temperature upper envelope and temperature rise rate upper envelope corresponding to the current condition feature vector. The heat transfer capacity degradation identification unit is used to calculate the equivalent temperature of the fluid inside the water-cooled wall tube based on the operating parameters of the water-cooled wall tube, and solve the equivalent heat transfer response coefficient by combining the measured wall temperature, thereby determining the heat transfer capacity degradation coefficient. The pre-drying correction unit is used to calculate the steam content trend based on the operating parameters of the water-cooled wall tubes, and to determine the pre-drying correction amount based on the steam content trend. The risk consistency judgment unit along the pipe and adjacent pipe is used to determine the enhanced risk state of water-cooled wall pipes and the risk aggregation state of adjacent pipes, and to complete the risk consistency verification. The early warning output unit integrates the upper envelope of wall temperature, upper envelope of temperature rise rate, heat transfer capacity degradation coefficient, drying precursor correction amount and risk consistency verification results to calculate the early warning index of heat transfer deterioration and output the corresponding early warning result according to the preset threshold.

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