A method and system for online life monitoring of a steam generating system of a photo-thermal power station

Abstract

The application provides a kind of photothermal power station steam generation system online life monitoring method and system, belong to solar photothermal power generation and industrial equipment digital twin and condition monitoring technical field, the monitoring method constructs system level zero-dimensional dynamic simulation model, by carrying out offline three-dimensional thermal coupling analysis to different heat exchanger, stress concentration parts are identified and extracted as local three-dimensional model.Online monitoring, use measured parameters and lumped parameter micro-element model to generate local boundary conditions to drive local three-dimensional model calculation.At the same time, according to the difference of running temperature life evaluation: for the equipment below threshold temperature, carry out fatigue life evaluation based on thermal coupling;For the equipment higher than or equal to threshold temperature, further carry out local creep analysis, realize high-precision life evaluation under the interaction of creep-fatigue by superposition processing.The application greatly reduces the amount of calculation, realizes the efficient, online real-time life monitoring of photothermal key equipment under high temperature complex working condition.

Description

Technical Field

[0001] This invention belongs to the field of solar thermal power generation and digital twin and condition monitoring technology of industrial equipment, specifically a method and system for online life monitoring of steam generation system in solar thermal power plants. Background Technology

[0002] Concentrated solar power (CSP) plants, as a form of renewable energy generation with advantages of large-scale, low-cost energy storage, have seen rapid development and widespread application globally in recent years. In a CSP plant, the Steam Generation System (SGS) is the core heat exchange hub for converting thermal energy into mechanical energy. It typically consists of multiple large heat exchanger devices, such as preheaters, evaporators, superheaters, and reheaters, connected in series or parallel. It is responsible for efficiently transferring heat from the high-temperature binary molten salt in the heat exchanger tower to the feedwater / steam, thereby driving the steam turbine generator set to generate electricity.

[0003] In the actual operation of concentrated solar power (CSP) plants, the units experience frequent start-ups and shutdowns and significant load variations due to uncontrollable meteorological factors such as the diurnal alternation of direct solar radiation (DNI) and cloud cover, as well as the grid's peak-shaving and frequency regulation requirements. This causes the heat exchangers in the steam generation system to endure severe fluid temperature fluctuations and alternating thermal loads over long periods. Even more critically, some core heat exchangers (such as superheaters and reheaters) operate at extremely high temperatures, typically exceeding 450°C or even reaching over 560°C. Under the combined effects of extreme high temperatures and alternating stress, the equipment is highly susceptible to fatigue microcracks. Simultaneously, significant creep occurs in the metallic materials at high temperatures. The interaction between creep and fatigue rapidly accelerates the degradation and failure of components such as tube bundles, tube sheets, and welds, seriously threatening the safe and stable operation of the power plant.

[0004] Currently, life assessment of heat exchangers largely relies on offline non-destructive testing after periodic unit shutdowns or theoretical fatigue calculations based on steady-state design parameters. This approach suffers from significant lag and cannot reflect the transient damage evolution process of equipment under real-time dynamic start-up, shutdown, and variable load conditions. Attempting to use 3D CFD or finite element analysis software (such as ANSYS, an engineering simulation software) to build a full-size solid model of the heat exchanger for online monitoring is insufficient due to the extremely complex structure of the heat exchanger and the massive number of meshes and nonlinear iterative calculations required, which cannot meet the real-time requirements of DCS control systems or monitoring platforms. While using simplified zero-dimensional lumped parameter models or one-dimensional thermodynamic system models offers fast calculation speeds, it only obtains macroscopic parameters at the equipment inlet and outlet, completely failing to capture the high-intensity localized stress concentrations and creep damage states of hidden internal structures (such as molten salt inlet and outlet tube sheets, steam inlet distributors, etc.).

[0005] Therefore, how to achieve high-precision solution of local stress in heat exchangers of steam generation systems under different temperature ranges and operating conditions without sacrificing real-time computation, and how to accurately carry out real-time online monitoring and evaluation including fatigue and creep, is an important technical challenge that urgently needs to be solved in the field of safe operation and maintenance of solar thermal power plants. Summary of the Invention

[0006] To overcome the problems of excessive computational load of full-size 3D models in the existing technologies, which prevent online real-time operation, and the inaccurate life assessment caused by the failure to fully consider the single fatigue or "creep-fatigue" interaction of equipment under different temperature zones, this invention proposes an online life monitoring method and system for the steam generation system of a solar thermal power plant.

[0007] Technical solution:

[0008] (I) This invention provides an online life monitoring method for a solar thermal power plant steam generation system, comprising the following steps:

[0009] Step 1: Construct a system-level zero-dimensional dynamic simulation model of the steam generation system of the solar thermal power plant; the system-level zero-dimensional dynamic simulation model is composed of multiple heat exchanger sub-models connected in series and / or in parallel; run the system-level zero-dimensional dynamic simulation model based on real-time collected operating status data to obtain the macroscopic parameters of the steam generation system of the solar thermal power plant;

[0010] Step 2, offline stage: Construct a global three-dimensional model of the steam generation system. Based on the macroscopic parameters obtained in Step 1, perform steady-state and transient thermo-mechanical coupling analysis to identify the stress concentration points of each heat exchanger in the steam generation system, and establish local three-dimensional models for the stress concentration points.

[0011] Step 3: During real-time online monitoring, the actual inlet detection parameters corresponding to the stress concentration location are collected through the system-level zero-dimensional dynamic simulation model, and then substituted into the lumped parameter micro-element model to calculate the micro-element outlet parameters of the stress concentration location; the actual inlet detection parameters and the micro-element outlet parameters are used as real-time boundary conditions and mapped into the local three-dimensional model.

[0012] Step 4: Based on the real-time boundary conditions obtained in Step 3, drive the local three-dimensional model to perform local thermo-mechanical coupling calculation (thermodynamic response calculation) to obtain the real-time temperature field and stress-strain field; and perform differentiated life assessment according to the actual operating temperature range of each heat exchanger.

[0013] Furthermore, in step 1, the system-level zero-dimensional dynamic simulation model is composed of multiple heat exchanger sub-models connected in series and / or in parallel, which are constructed based on the principles of heat transfer and fluid mechanics.

[0014] Furthermore, in step 1, the macroscopic parameters refer to the outlet parameters of each heat exchanger in the steam generation system of the solar thermal power plant, including the outlet temperature, pressure, and flow rate parameters.

[0015] When the system-level zero-dimensional dynamic simulation model is running, it calculates the macroscopic parameters of each heat exchanger under different operating conditions based on the real-time acquisition of the operating status data of the steam generation system of the solar thermal power plant, through the equations of mass conservation, energy conservation, and momentum conservation.

[0016] Further, step 2 specifically involves: establishing a corresponding global three-dimensional model for each heat exchanger in the steam generation system using three-dimensional modeling software; under simulated unit startup, variable load, and steady-state operation conditions, using the macroscopic parameters obtained in step 1 as boundary conditions, performing steady-state and transient thermo-mechanical coupling analysis on the global three-dimensional model using finite element analysis software to identify stress concentration points in each heat exchanger, and establishing corresponding local three-dimensional models for the stress concentration points.

[0017] Furthermore, in step 2, the stress concentration areas include the molten salt inlet, molten salt outlet, steam inlet, and tube sheet weld area of ​​the heat exchanger.

[0018] Furthermore, in step 3, the actual inlet detection parameters include the inlet fluid temperature T of the micro-element at the stress concentration point during actual operation of the heat exchanger. f,in With the micro-element import pressure P in The micro-element outlet parameters include the micro-element outlet fluid temperature and micro-element outlet pressure at the stress concentration location.

[0019] Furthermore, in step 3, the formula for calculating the exit parameters of the infinitesimal element using the lumped parameter infinitesimal element model is as follows:

[0020] (1) Calculate the outlet fluid temperature T of the infinitesimal element f,out The formula is as follows:

[0021] ρ f ·c f ·ΔV·(dT f,out / dt) = q m,f ·c f ·(T f,in - T f,out ) - h local ·A micro ·(T f -T wall );

[0022] Where, ρ f c f q m,f Let T represent fluid density, specific heat capacity, and mass flow rate, respectively; ΔV be the volume of the infinitesimal element; and T be the volume of the infinitesimal element. f,inT represents the temperature of the inlet fluid of the micro-element. f,out h represents the outlet fluid temperature of the micro-element. local A is the local convective heat transfer coefficient. micro T represents the heat transfer area of ​​the micro-element wall. f With T wall Here, represents the average fluid temperature and the wall temperature, respectively, and t represents time.

[0023] (2) Calculate the outlet pressure P of the infinitesimal element out The formula is as follows:

[0024] P out = P in - ξ local ·(ρ f ·v² / 2);

[0025] Among them, P in To alleviate the pressure of micro-element imports, ξ local is the local drag coefficient, and v is the fluid velocity.

[0026] Furthermore, in step 4, the differentiated life assessment method is as follows:

[0027] Based on the actual physical characteristics of the steam generation system, a first temperature threshold is set. If the operating temperature of the heat exchanger is lower than the first set temperature threshold, a fatigue life assessment based on thermo-mechanical coupling is performed. If it is higher than or equal to the first set temperature threshold, a local creep analysis is further performed. Through superposition processing, a high-precision life assessment under the interaction of creep and fatigue is achieved.

[0028] Furthermore, in step 4, the multiple series-parallel heat exchangers in the steam generation system include a preheater, an evaporator, a superheater, and a reheater; the first set temperature threshold is set to 450°C, the operating temperature of the preheater and evaporator is below 450°C, and the operating temperature of the superheater and reheater is above or equal to 450°C.

[0029] Furthermore, in step 4, the specific method of the superposition process is as follows: calculate the pure fatigue damage degree based on the stress-strain field (alternating stress) obtained from the local three-dimensional model, combine it with the creep damage degree of the micro-element region under high temperature environment, calculate the total damage degree based on the linear cumulative damage theory or the nonlinear creep-fatigue interactive damage theory, and then infer the remaining online life of the heat exchanger.

[0030] Furthermore, in step 4, if the operating temperature of the heat exchanger is lower than the first set temperature threshold, a fatigue life assessment based on thermo-mechanical coupling is performed. The specific algorithm is as follows: (1) Fatigue damage calculation:

[0031] Based on the thermo-mechanical coupling calculation results of the local 3D model, the stress history is extracted, the cyclic load spectrum is extracted using the rainflow counting method, and the number of cycles n is obtained by combining the material's SN fatigue curve. i ; Calculation of pure fatigue damage D based on Miner's linear cumulative rule f .

[0032] D f =Σ(n i / N i );

[0033] Where, n i N represents the actual number of iterations. i This represents the fatigue life under corresponding stress.

[0034] (2) Based on the current cumulative fatigue damage degree D f By reverse calculation of the remaining online lifespan of key components:

[0035] Remaining number of loops = (1 - D) f ) × N dom N dom The dominant stress;

[0036] Remaining number of executions = (1 - D) f ) / D f , 工况 D f , 工况 For each working condition, the degree of damage per instance is specified.

[0037] Remaining running time = t run × (1 - D f ) / D f , t run This represents the cumulative operating time of the component since it was put into operation.

[0038] Furthermore, in step 4, if the operating temperature of the heat exchanger is higher than or equal to the first set temperature threshold, local creep analysis is performed. High-precision life assessment under creep-fatigue interaction is achieved through superposition processing. The specific algorithm is as follows: (1) Fatigue damage calculation: Based on the thermo-mechanical coupling calculation results of the local 3D model, the stress history is extracted, the cyclic load spectrum is extracted using the rainflow counting method, and the number of cycles n is obtained by combining the material's SN fatigue curve. i ; Calculation of pure fatigue damage D based on Miner's linear cumulative rule f .

[0039] D f =Σ(n i / N i );

[0040] Where, n i N represents the actual number of iterations. i This represents the fatigue life under corresponding stress.

[0041] (2) The steady creep rate was calculated based on Norton's formula, and the creep fracture time was calculated using the Larso-Miller parameter method; the creep damage D was calculated by integrating using Robindson's rule. c .

[0042] D c = Σ(t j / t r,j );

[0043] Among them, t j Under stress σ j Temperature T j Actual holding time under the conditions, t r,j For stress σ j Temperature T j Creep fracture time under certain conditions.

[0044] (3) Calculate the total damage using the linear cumulative method, or based on the nonlinear cumulative model, or according to the ASME bilinear rule;

[0045] When using the linear cumulative rule, the total damage degree D = D f + D c = Σ(n i / N i ) + Σ(t j / t r,j );

[0046] When using a nonlinear cumulative model or the ASME bilinear rule, the calculated (D) f D c Substitute the coordinate points into the ASME bilinear or nonlinear interactive damage envelope map of the material, and calculate the relative distance from the point to the failure boundary as the actual equivalent total damage.

[0047] (4) Based on the total damage level, estimate the remaining online life of key components:

[0048] a. Remaining lifetime under the linear cumulative method:

[0049] Remaining lifetime factor = 1 - D = 1 - (D) f + D c );

[0050] Number of remaining executable cycles N cycle,remain = (1 - D) / (ΔDf + ΔD c ), where ΔD f The fatigue damage increment ΔD for each future operating cycle f ΔD c The creep damage increment ΔD for each future operating cycle c ;

[0051] Remaining equivalent start-up times: Establish a dual-damage database for high-temperature operating conditions, with each operating condition corresponding to (D) f , 工况 D c , 工况 If the number of startups is 1 - D, then the remaining startup count = (1 - D) / (D) f , 启动 + D c , 启动 ), D f , 工况 D represents the single-cycle pure fatigue damage degree corresponding to each working condition. c , 启动 For each working condition, the corresponding single creep damage;

[0052] Remaining running time: If the cumulative running time t is known run For the corresponding total damage level D, the remaining running time = t run × (1 - D) / D;

[0053] b. When using the ASME bilinear rule:

[0054] Remaining number of cycles = λ;

[0055] Remaining equivalent number of starts = (1 - D) eff ) / (D f , 单次 + D c , 单次 ), where D f , 单次 D represents the increase in fatigue damage per single operating cycle. c , 单次 D represents the increment of creep damage generated in a single operating cycle. eff The current equivalent total damage (calculated based on the ASME interaction criterion);

[0056] Remaining running time: If the cumulative running time t is known ops Corresponding total damage degree D eff Then the remaining cumulative running time = t ops × (1 - D eff ) / D effOr, based on the creep damage rate, the remaining runtime = (1 - D) c ) / (dD c / dt), dD c / dt represents the current creep damage rate.

[0057] c. Remaining lifetime under the nonlinear interaction method, current damage state point (D) f,current D c,current Let the future damage growth direction be (ΔD). f , ΔD c Solve for the magnification factor λ required to reach the failure boundary. cyl , so that (D f,current + λ·ΔD f D c,current + λ·ΔD c If the value is located on the failure boundary, then:

[0058] Remaining number of cycles = λ;

[0059] Remaining equivalent start counts = λ (when the damage per cycle is constant), or more precisely, remaining equivalent start counts = (1 - D) eff,current ) / ΔD eff,cycle , ΔD eff,cycle This represents the equivalent damage increment for a single cycle under the nonlinear interaction criterion.

[0060] Remaining running time = λ × t cycle , t cycle The duration of high temperature during a single operating cycle;

[0061] The solution for λ requires a material-specific nonlinear damage envelope (such as the ASME bilinear or exponential envelope). This method assumes that future operating conditions (temperature, stress, cycle type) will be consistent with historical conditions. If the operating conditions change, the damage growth direction (ΔD) needs to be recalculated. f , ΔD c ).

[0062] (i) This invention provides an online life monitoring system for a solar thermal power plant steam generation system, including a data acquisition and zero-dimensional simulation module, an offline stress concentration location and dimensionality reduction module, a local boundary real-time generation module, and a differentiated life assessment module;

[0063] The data acquisition and zero-dimensional simulation module is used to acquire on-site unit operating status data and run a system-level zero-dimensional dynamic simulation model to obtain the macroscopic parameters of each heat exchanger.

[0064] The offline stress concentration localization and dimensionality reduction module is used to perform global thermo-mechanical coupling analysis on the heat exchanger, locate and extract the local three-dimensional model of the stress concentration area;

[0065] The local boundary real-time generation module is used to receive actual inlet detection parameters on site, quickly calculate micro-element outlet parameters through the lumped micro-element parameter model, and merge them into real-time inlet and outlet boundary conditions of the local three-dimensional model.

[0066] The differentiated life assessment module has a built-in switching logic with a threshold of 450℃, which is used to perform simple fatigue life accumulation calculation or total life accumulation calculation under the interaction of thermo-coupling and creep, and output real-time life warning to the monitoring terminal.

[0067] Beneficial effects:

[0068] 1. It achieves dimensionality reduction mapping from macroscopic scale to microscopic local scale.

[0069] This invention performs an offline phase to traverse and analyze a full-size global 3D model, accurately locating stress concentration areas such as molten salt inlets and extracting lightweight "local 3D models".

[0070] During online monitoring, the actual inlet detection parameters corresponding to stress concentration points are collected using a system-level zero-dimensional dynamic simulation model. The local micro-element outlet parameters are quickly calculated using a lumped parameter micro-element model and used as boundary conditions. This perfectly bridges the gap between system-level dynamic data and microstructure response, compressing the three-dimensional thermo-mechanical coupling process that originally required several days of calculation to the millisecond level. This completely breaks through the computing power bottleneck of three-dimensional physical field simulation in industrial online DCS systems.

[0071] 2. A differentiated damage assessment based on temperature range thresholds is proposed, which significantly improves prediction accuracy.

[0072] This invention deeply integrates the actual physical characteristics of molten salt steam generation systems, creatively classifying and monitoring equipment using 450℃ as a threshold. For preheaters / evaporators with temperatures below 450℃, the focus is on alternating thermodynamic fatigue analysis; while for superheaters / reheaters with temperatures ≥450℃, a local three-dimensional creep analysis is specifically introduced, and creep damage and thermodynamic fatigue damage are deeply interacted and superimposed. This mechanism fills the technical gap in online monitoring of heat exchangers in solar thermal power plants, which has long neglected the "creep-fatigue interaction effect," greatly improving the fidelity and accuracy of remaining life prediction under high-temperature and harsh operating conditions.

[0073] 3. It combines virtual and real dynamic mapping, making it highly adaptable to all working conditions.

[0074] This invention abandons traditional static design parameter assumptions and utilizes a system-level zero-dimensional dynamic model fused with measured data to accurately reproduce the thermodynamic shock characteristics of solar thermal power units during severe transient transitions such as early morning startup and sudden load reductions due to cloud cover. The method of deriving local outlet parameters from measured inlet parameters using a lumped parameter infinitesimal model ensures that the boundary conditions of the local three-dimensional model remain synchronized with the real industrial environment, giving the digital twin model high robustness and field adaptability. Attached Figure Description

[0075] Figure 1 This is an overall flowchart of an online life monitoring method for a solar thermal power plant steam generation system provided by an embodiment of the present invention;

[0076] Figure 2 This is a schematic diagram illustrating the mechanism for mapping and extracting macroscopic parameters from zero-dimensional dynamic simulation to boundary conditions of a local three-dimensional model in an embodiment of the present invention.

[0077] Figure 3 This is a working logic diagram for differentiated fatigue / creep damage assessment of equipment in different temperature ranges in an embodiment of the present invention.

[0078] Figure 4 This is a module architecture diagram of an online life monitoring system provided in an embodiment of the present invention. Detailed Implementation

[0079] The technical solution of the present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0080] Example 1

[0081] This invention provides an online life monitoring method for a steam generation system in a concentrated solar power (CSP) plant, aiming to perform real-time life tracking of a series-parallel SGS system (Steam Generation System) consisting of a preheater, evaporator, superheater, and reheater within a CSP plant. The flowchart of the online life monitoring method is shown below. Figure 1 As shown, the specific execution steps are as follows:

[0082] Phase 1: Model building and offline dimensionality reduction.

[0083] (1) Constructing a system-level zero-dimensional dynamic simulation model: In view of the frequent load change operation characteristics of the entire steam generation system (SGS), a system-level zero-dimensional dynamic simulation model is first established based on the principles of heat transfer and fluid mechanics. This model covers the series and parallel coupling of multiple heat exchanger model sub-models such as preheater, evaporator, superheater, and reheater. It can calculate the overall macroscopic outlet temperature, pressure and flow rate of each heat exchanger under various operating conditions such as unit temperature rise and start-up, constant pressure operation and sliding pressure load change.

[0084] Real-time data on the operating status of the solar thermal power plant's steam generation system (inlet and outlet temperatures, pressures, flow rates, and time) is collected, and this data is used to run a system-level zero-dimensional dynamic simulation model to obtain the macroscopic parameters of the solar thermal power plant's steam generation system.

[0085] The macroscopic parameters of each heat exchanger are calculated based on the laws of conservation of mass, momentum, and energy. The specific calculation formula is as follows:

[0086] The mass conservation equation is: V·(dρ / dt) = q m,in - q m,out Where V is the effective volume of the heat exchanger, ρ is the fluid density, and q m,in and q m,out t represents the inlet and outlet mass flow rates, respectively; t represents time.

[0087] The energy conservation equation is: M·c p ·(dT out / dt) = q m,in ·h in - q m,out ·h out + K·A·Δt m Where M is the equivalent mass of the pipe wall and the medium, and c p For specific heat capacity, h in h out Here, K is the inlet and outlet enthalpy, K is the heat transfer coefficient, A is the heat transfer area, and Δt is the heat transfer area. m The macroscopic outlet temperature T is calculated from the logarithmic mean temperature difference. out ;

[0088] The momentum conservation (pressure drop) equation is: P out = P in - (f·L / D + Σξ)·(ρv² / 2) - ρgΔz, to calculate the macroeconomic export pressure P. out Among them, P in Let f be the inlet pressure, f be the Darcy friction factor, L be the pipe length, D be the pipe inner diameter, ∑ξ be the sum of all local resistance coefficients, and Δz be the height difference between the outlet and the inlet. ρ be the fluid density, v be the flow velocity, and g be the gravitational constant.

[0089] (2) Offline stage: Construct a global three-dimensional model of the steam generation system. Based on the macroscopic parameters obtained in step 1, perform steady-state and transient thermo-mechanical coupling analysis, identify the stress concentration points of each heat exchanger, and establish local three-dimensional models for the stress concentration points.

[0090] Specifically, SolidWorks 3D modeling software is used to create global 3D models for various heat exchangers in the steam generation system. Under simulated unit startup, variable load, and steady-state operation conditions, based on the macroscopic parameters obtained in step 1 as boundary conditions, finite element analysis software is used to perform steady-state and transient thermo-mechanical coupling analysis on the global 3D model to identify stress concentration areas of each heat exchanger, and to extract the stress concentration areas to create corresponding local 3D models.

[0091] By performing offline three-dimensional thermo-mechanical coupling analysis on different heat exchangers, the stress concentration areas were identified as the molten salt outlet, steam inlet, and tube sheet weld area.

[0092] In this embodiment, the parameter sequence calculated under extreme transient conditions (such as a sudden drop in molten salt temperature caused by rapid cloud cover) is used as boundary conditions. When imported into ANSYS Mechanical software for steady-state and transient thermo-mechanical coupling analysis, the simulated cloud map identifies the region with the worst internal stress distribution. Analysis reveals that the "molten salt inlet" region of the evaporator has an extremely high thermal stress gradient, making it a typical stress concentration area. Based on this, the mesh of non-critical parts in the global 3D model system is trimmed, and the structure of the "molten salt inlet" and its adjacent tube bundle and tube sheet regions is saved separately to establish a lightweight, high-mesh-density local 3D model, thereby achieving a dramatic reduction in computational load.

[0093] Phase 2: Online Real-Time Calculation and Dual-Source Boundary Mapping: During real-time online monitoring, the actual inlet detection parameters corresponding to the stress concentration points are collected through the system-level zero-dimensional dynamic simulation model, and the micro-element exit parameters of the stress concentration points are calculated by combining the lumped parameter micro-element model; the actual inlet detection parameters and micro-element exit parameters are used as real-time boundary conditions and mapped into the local three-dimensional model.

[0094] Figure 2 This is a schematic diagram illustrating the mechanism for mapping and extracting macroscopic parameters from zero-dimensional dynamic simulation to boundary conditions of a local three-dimensional model in an embodiment of the present invention. Specifically, during actual grid-connected operation of the power plant, the stress concentration location (such as the molten salt inlet of the evaporator) is collected in real time using field instruments and sensors. Figure 2 The actual inlet parameters (including real-time molten salt temperature and pressure) of the medium-temperature fluid inlet were obtained on-site. Subsequently, a lumped parameter micro-element model based on local energy conservation was introduced, and these inlet measured data were substituted into the calculation to quickly obtain the heat exchange and pressure drop of the micro-element structural section of the molten salt inlet, and then the outlet parameters of the micro-element section were deduced.

[0095] The specific derivation formula for calculating the exit parameters of the infinitesimal element using the lumped parameter infinitesimal element model is as follows:

[0096] For the extracted infinitesimal structural segment ΔV, the equation for calculation using local lumped energy balance is: ρf ·c f ·ΔV·(dT f,out / dt) = q m,f ·c f ·(T f,in - T f,out ) - h local ·A micro ·(T f - T wall ); where ρ f c f q m,f Let T represent fluid density, specific heat capacity, and mass flow rate, respectively; ΔV be the volume of the infinitesimal element; and T be the volume of the infinitesimal element. f,in T represents the temperature of the inlet fluid of the micro-element. f,out h represents the outlet fluid temperature of the micro-element. local A is the local convective heat transfer coefficient. micro T represents the heat transfer area of ​​the micro-element wall. f With T wall Here, t represents the average fluid temperature and the wall temperature, respectively, and t represents time.

[0097] The measured T obtained by using a system-level zero-dimensional dynamic simulation model f,in Substituting high-fidelity data such as pressure into the differential equation: ρ f ·c f ·ΔV·(dT f,out / dt) = q m,f ·c f ·(T f,in - T f,out ) - h local ·A micro ·(T f -T wall In this context, and in conjunction with the local infinitesimal element pressure drop formula P out = P in - ξ local ·(ρ f By performing explicit or implicit differential solutions (e.g., v² / 2), the outlet fluid temperature T of the micro-element can be derived in real time. f,out With pressure P out In the formula for local infinitesimal element pressure drop, P out For the export pressure of micro-element, P in For micro-element import pressure; ξ local is the local drag coefficient; v is the fluid velocity.

[0098] During this process, the measured high-fidelity import data and the export data calculated by the lumped parameter micro-element model are combined to form a complete "real-time boundary condition", which is instantly projected and loaded onto the mesh surface of the "local three-dimensional model" preset in the first stage, driving the local finite element solver to perform millisecond-level fast convergence calculation.

[0099] Phase 3: Differentiated interactive lifetime assessment based on temperature thresholds: Based on the real-time boundary conditions obtained in step 3, the local three-dimensional model is driven to perform local thermodynamic response calculations to obtain the real-time temperature field and stress-strain field; and differentiated lifetime assessments are performed according to the actual operating temperature range of each heat exchanger.

[0100] Based on the actual physical characteristics of the molten salt steam generation system, the equipment is classified and monitored using 450℃ as the first set temperature threshold. The heat exchangers in the steam generation system include a preheater, an evaporator, a superheater, and a reheater; wherein the operating temperature of the preheater and evaporator is below 450℃, and the operating temperature of the superheater and reheater is above or equal to 450℃.

[0101] If the operating temperature of the heat exchanger is lower than the first set temperature threshold, the heat exchanger is monitored and evaluated in real time based on the results of the local thermo-mechanical coupling analysis and the fatigue life assessment algorithm. If the operating temperature of the heat exchanger is higher than or equal to the first set temperature threshold, the local three-dimensional model is used to further perform local creep analysis based on the local thermo-mechanical coupling analysis. The results of the thermo-mechanical coupling analysis and the results of the local creep analysis are superimposed to evaluate the interaction between thermo-mechanical coupling and creep, and a real-time online life assessment is performed.

[0102] After the local 3D model outputs high-precision strain and stress tensors, the system enters the differentiation discrimination branch, such as... Figure 3 As shown, the specific method is as follows:

[0103] The first step is to obtain the temperature-time history data of the three-dimensional thermo-coupled nodes output by the local three-dimensional model, and extract the current highest operating temperature T of the component node;

[0104] The second step is to determine whether the current highest operating temperature T is greater than or equal to 450℃.

[0105] (I) When the highest operating temperature T of the heat exchanger is < 450℃, it is determined that there is no significant creep phenomenon, and the pure fatigue life assessment algorithm (low-frequency pure fatigue life assessment subroutine) is executed: pure fatigue damage assessment is performed based on thermo-mechanical coupling, and the cumulative pure fatigue damage assessment results of the nodes are output. Specifically:

[0106] (1) Stress history extraction: Based on the thermo-mechanical coupling calculation results of the local three-dimensional model, the stress-time history data σ(t) of key nodes in the stress concentration area are extracted, including principal stresses. Von Mises equivalent stress The six components of the stress tensor This refers to the maximum principal stress. Intermediate principal stress, Minimum principal stress.

[0107] (2) Cyclic load spectrum identification: Cyclic load spectrum is extracted by rainflow counting method; The Rainflow Counting Method was used to identify the stress history cycles and extract the characteristic parameters of each stress cycle: stress amplitude Δσ. i = σ max,i - σ min,i Mean stress σ m,i = (σ max,i + σ min,i ) / 2, Number of iterations n i , σ max,i This refers to the maximum stress in the i-th cycle, σ. min,i It refers to the minimum stress in the i-th cycle.

[0108] (3) Fatigue life query, combined with the material SN fatigue curve to obtain the number of cycles; Based on the material's SN fatigue curve (stress-life curve), query or calculate the allowable number of cycles Nᵢ corresponding to each stress amplitude.

[0109] The general form of the SN curve is: N i = A·(Δσ i ) -m Where A is a material constant, m is the fatigue index, and Δσ i Stress amplitude, N i This represents the fatigue life (allowable number of cycles) at this stress amplitude. For different materials, the SN curve parameters should be obtained by consulting the relevant material handbook or standard (such as ASME Boiler and Pressure Vessel Code Section III).

[0110] (4) Mean stress correction; When non-zero mean stress exists, the Goodman correction formula or Gerber correction formula is used for correction: Goodman correction: Δσ eq,i = Δσ i / (1 - σ m,i / σ u ), where σ u This refers to the tensile strength of the material.

[0111] (5) Calculation of cumulative fatigue damage; for Based on Miner's linear cumulative damage rule, the pure fatigue damage degree D is calculated. f :

[0112] D f = Σ(n i / N i );

[0113] Where, n i For stress level σ i The actual number of iterations already performed, N i For stress level σ i The fatigue life of the material (determined by the SN curve), when D f When the value is 1, the component is considered to have reached fatigue failure.

[0114] (6) Remaining life estimation: Based on the current cumulative fatigue damage degree D f By reverse calculation of the remaining online lifespan of key components: a. Remaining lifetime factor = 1 - D f ; b. Remaining number of cycles (at the dominant stress level σ) dom (Next): n remain = (1 - D f ) × N dom ;

[0115] c. Remaining equivalent number of starts / variable load cycles: Establish a damage database for typical operating conditions (cold start, hot start, standard variable load, etc.), with the single-cycle damage degree D corresponding to each operating condition. f , 工况 ,but:

[0116] Remaining number of executions = (1 - D) f ) / D f , 工况 ; d. Remaining runtime (applicable to scenarios with relatively stable damage rates): If the cumulative runtime t is known... run (Hour) Corresponding damage level D f ,but:

[0117] Remaining running time = t run × (1 - D f ) / D f ;

[0118] Time-based remaining lifetime estimation is applicable to scenarios with stable damage rates.

[0119] (7) Multi-level early warning mechanism: Based on cumulative fatigue damage Df Set warning threshold: D f < 0.3 indicates normal operation (green); 0.3 ≤ D f <0.7 indicates a yellow warning and maintenance is recommended; 0.7 ≤ D f < 0.9 indicates an orange-level restriction for high-damage conditions, D f A value ≥ 0.9 indicates a red-level forced shutdown for maintenance.

[0120] The pure fatigue damage calculation method is applicable to preheaters and evaporators operating at temperatures below 450℃: creep in this temperature range is extremely weak and can be ignored. Based directly on alternating thermal and mechanical stresses calculated through local thermo-mechanical coupling, the cyclic load spectrum is extracted using the rainflow counting method. Combined with the material's SN fatigue curve and Miner's cumulative damage theory, the fatigue damage caused by each fluctuation in operating conditions is calculated, achieving pure fatigue-driven life assessment and early warning.

[0121] (ii) If the current highest operating temperature T ≥ 450℃, it is judged as a reverse creep phenomenon, and the creep-fatigue interactive damage assessment algorithm (high temperature creep-fatigue coupled life assessment subroutine) is executed: creep-fatigue interactive damage assessment is performed by superimposing local creep analysis, specifically:

[0122] (1) Fatigue damage D f Calculation (same as above for pure fatigue damage D) f ).

[0123] (2) Creep strain rate calculation: Based on the creep analysis results of the local three-dimensional model, the steady creep rate is calculated using the Norton-Bailey creep constitutive equation: ε̇ c = A·σ n ·exp(-Q / RT) Among them, ε̇ c Let σ be the creep strain rate, A be the material constant, σ be the equivalent stress, n be the stress exponent, Q be the creep activation energy, R be the gas constant (8.314 J / (mol·K)), and T be the absolute temperature (K).

[0124] (3) Creep fracture time calculation: The creep fracture time t was calculated using the Larson-Miller parameter method. r :

[0125] LMP = T(C + log 10 t r );

[0126] Where LMP is the Larson-Miller parameter (found in the material handbook), T is the absolute temperature (K), C is the material constant (usually taken as 20), and t is the absolute temperature (K).r Creep fracture time (hours);

[0127] Conversely, creep rupture time: t r = 10 ((LMP / T) - C) .

[0128] (4) Cumulative creep damage calculation: Based on Robinson's fractional time rule, the creep damage degree D is calculated. c : D c = Σ(t j / t r,j ); Among them, t j For stress σ j Temperature T j Actual holding time under the conditions, t r,j For stress σ j Temperature T j Creep fracture time under certain conditions, when D c When the value is 1, the component is considered to have undergone creep fracture.

[0129] (5) Creep-fatigue interactive damage assessment: Based on material properties and working conditions, select an appropriate interactive damage model: use the linear accumulation method, or the nonlinear accumulation model, or the ASME bilinear rule to calculate the total damage.

[0130] a. Linear accumulation method:

[0131] This applies to situations where creep and fatigue develop independently. Total damage degree D = D f + D c Failure criterion: D ≥ 1, remaining lifetime factor = 1 - D.

[0132] b. ASME Bilinear Interaction Method:

[0133] Applicable to situations with significant interaction effects, based on the ASME Boiler and Pressure Vessel Code Section III. The calculated (D) f D c Substituting the coordinates into the ASME bilinear envelope: when D f When ≤ 0.3: D f + D c ≤ 1; when D f > 0.3: D f / 0.3 + D c / 1 ≤ 1. Or, in a more general form: D f / D f,limit +Dc / D c,limit ≤ 1, where D f,limit D represents the critical damage under pure fatigue conditions of the material. c,limit This refers to the critical damage under pure creep conditions of the material.

[0134] c. Nonlinear interactive damage envelope method:

[0135] For ferritic steels (such as P91, P92) or austenitic steels (such as Incoloy 800H), a material-specific nonlinear interactive damage envelope is used. The equivalent damage degree is defined as follows: (Euclidean distance method) or D eff = [(D f / D f,limit ) α + (D c / D c,limit ) β ] γ (Power law method), where α, β, and γ are material-related interaction exponents; Failure criterion: D eff ≥ 1.

[0136] When using a nonlinear cumulative model or the ASME bilinear rule, the calculated (D) f D c Substitute the coordinates into the ASME bilinear or nonlinear interactive damage envelope diagram of the material, and calculate the relative distance from the point to the failure boundary as the actual equivalent total damage.

[0137] (6) Remaining life calculation: a. Remaining lifetime under the linear cumulative method:

[0138] Remaining lifetime factor = 1 - D = 1 - (D) f + D c );

[0139] Number of remaining executable cycles N cycle,remain = (1 - D) / (ΔD f + ΔD c ), where ΔD f The fatigue damage increment ΔD for each future operating cycle f ΔD c The creep damage increment ΔD for each future operating cycle c ;

[0140] Remaining equivalent start-up times: Establish a dual-damage database for high-temperature operating conditions, with each operating condition corresponding to (D) f , 工况 D c ,工况 If the number of startups is 1 - D, then the remaining startup count = (1 - D) / (D) f , 启动 + D c , 启动 ), D f , 工况 D represents the single-cycle pure fatigue damage degree corresponding to each working condition. c , 启动 For each working condition, the corresponding single creep damage;

[0141] Remaining running time: If the cumulative running time t is known run For the corresponding total damage level D, the remaining running time = t run × (1 - D) / D.

[0142] b. Remaining lifetime under the ASME bilinear interaction method:

[0143] Remaining number of cycles = λ;

[0144] Remaining equivalent number of starts = (1 - D) eff ) / (D f , 单次 + D c , 单次 ), where D f , 单次 D represents the increase in fatigue damage per single operating cycle. c , 单次 D represents the increment of creep damage generated in a single operating cycle. eff The current equivalent total damage (calculated based on the ASME interaction criterion);

[0145] Remaining running time: If the cumulative running time t is known ops Corresponding total damage degree D eff Then the remaining cumulative running time = t ops × (1 - D eff ) / D eff Or, based on the creep damage rate, the remaining runtime = (1 - D) c ) / (dD c / dt), dD c / dt represents the current creep damage rate.

[0146] c. Remaining lifetime under the nonlinear interaction method, current damage state point (D) f,current D c,current Let the future damage growth direction be (ΔD). f , ΔD cSolve for the magnification factor λ required to reach the failure boundary, such that (D f,current + λ·ΔD f D c,current + λ·ΔD c If the value is located on the failure boundary, then:

[0147] Remaining number of cycles = λ;

[0148] Remaining equivalent start counts = λ (when the damage per cycle is constant), or more precisely, remaining equivalent start counts = (1 - D) eff,current ) / ΔD eff,cycle , ΔD eff,cycle This represents the equivalent damage increment for a single cycle under the nonlinear interaction criterion.

[0149] Remaining running time = λ × t cycle , t cycle The duration of high temperature during a single operating cycle.

[0150] Note: When using the nonlinear cumulative model or the ASME bilinear rule, the solution for λ must be based on the material-specific nonlinear damage envelope (such as the ASME bilinear or exponential envelope); this method assumes that future operating conditions (temperature, stress, cycle type) are consistent with historical operating conditions; if the operating conditions change, the damage growth direction (ΔD) needs to be recalculated. f , ΔD c ).

[0151] (7) Creep-dominant type identification and optimization suggestions: If D c >> D f (e.g. D) c / D f > 3) indicates that creep damage is dominant, and the following should be done: limit the high-temperature load time, optimize the operating temperature curve (appropriately reduce the temperature), and consider replacing the creep-resistant material.

[0152] (8) Multi-level early warning mechanism (for high-temperature components): Warning thresholds are set based on the total damage level D: Green indicates normal operation, Yellow indicates that high-damage conditions should be reduced, Orange indicates that shutdown and maintenance should be arranged, and Red indicates that startup is prohibited and mandatory maintenance should be carried out.

[0153] (9) Real-time monitoring output, outputting the following information in real time: current fatigue damage degree D f Its proportion, current creep damage degree Dc and its proportion, total damage degree D (or equivalent damage degree D) eff), Remaining lifetime factor (1-D), Remaining equivalent start-up count, Remaining operating hours, Distance to failure boundary, Health status level (red / orange / yellow / green).

[0154] The creep-fatigue interactive damage assessment based on superimposed local creep analysis is suitable for superheaters and reheaters with operating temperatures ≥ 450℃. This temperature range is within the high-temperature creep-sensitive zone, especially since frequent load changes cause the structure to be subjected to alternating cycles of high-temperature load and alternating stress for extended periods. Therefore, in addition to obtaining the results of local thermo-mechanical coupling analysis, the local creep analysis module (using the Norton-Bailey creep constitutive equation) is further activated to calculate the creep strain and creep damage degree under high-temperature load. Subsequently, the fatigue damage and creep damage are physically superimposed using either the linear accumulation rule or the nonlinear creep-fatigue interactive damage map method. By back-calculating the total damage degree under the interaction at high frequency, the remaining equipment life that truly reflects the harsh physical nature of high-temperature photothermal conditions is output. The choice between linear or nonlinear methods here mainly depends on the high-temperature deformation mechanism of the material and whether strong microscopic coupling occurs between creep and fatigue damage. If the stress amplitude of the component is low and the high temperature holding time is short, and the microcracks and creep pores develop independently, then the linear accumulation rule (such as the Robinson-Miner rule) is selected; if there is significant viscoplastic deformation and creep and fatigue have strong microscopic interaction that accelerates failure, then the nonlinear creep-fatigue interaction damage map method (such as the ductile exhaustion method or strain range division method) is selected.

[0155] Example 2

[0156] Based on the monitoring method described in Example 1, this example provides an online life monitoring system for the steam generation system of a solar thermal power plant, deployed inside the power plant's DCS control center. Figure 4 As shown, its core includes:

[0157] (1) Data acquisition and zero-dimensional simulation module:

[0158] It is responsible for monitoring the high-frequency DNI prediction data sent from the bus and the current actual operating conditions, as well as the on-site unit operating status data; running a zero-dimensional dynamic simulation model containing the series and parallel relationships of multiple heat exchangers, performing macroscopic forward calculations on the thermodynamic state of the entire SGS system, and obtaining the macroscopic parameters (outlet dynamic parameters) of each heat exchanger.

[0159] (2) Offline stress concentration location and dimensionality reduction module:

[0160] Used to perform global thermo-mechanical coupling analysis on heat exchangers, locate and extract local 3D models of stress concentration areas.

[0161] As a static asset library, it stores high-risk and vulnerable local three-dimensional micro-element models (such as the inlet nozzles and outlet tube sheet areas of each heat exchanger) pre-calculated by ANSYS.

[0162] (3) Local boundary real-time generation module:

[0163] It is used to receive actual import detection parameters on site, quickly calculate the micro-element export parameters through the lumped parameter model, and merge them into real-time import and export boundary conditions of the local three-dimensional model.

[0164] The local boundary real-time generation module receives high-frequency measured inlet temperature and pressure from field sensors and quickly closes the local boundary condition network using lumped parameter formulas.

[0165] (4) Differentiated life assessment module:

[0166] It has built-in switching logic with a threshold of 450℃, which is used to perform pure fatigue damage assessment for cumulative life calculation, or to perform creep-fatigue interactive damage assessment with superimposed local creep analysis for total cumulative life calculation (total cumulative life calculation under thermo-coupling and creep interaction), and output real-time life warning to the monitoring terminal.

[0167] The differentiated life assessment module, serving as the final decision-making and early warning mechanism, incorporates a built-in 450℃ switching logic gateway. It separately schedules the corresponding "low-frequency pure fatigue life assessment subroutine" and "high-temperature creep-fatigue coupled life assessment subroutine," continuously updating the remaining usage cycles and hours. The real-time health status of each heat exchanger in the SGS system is then visually displayed on the monitoring interface using a red, yellow, and green three-color topology cloud map.

[0168] Example 3

[0169] To verify the effectiveness of the life monitoring method described in this invention, on-site measurements and monitoring were conducted using a high-temperature superheater of a 50MW tower solar thermal power plant as the object. The superheater's normal operating temperature is 530℃, and the tube bundle material is Incoloy 800H.

[0170] During a typical scenario where widespread cloud cover caused a rapid load reduction in the steam turbine, the power plant's DCS system recorded the transient process of the superheater inlet molten salt temperature dropping from 565℃ to 510℃ within 5 minutes, using a data sampling rate of 1 second. At this time, the measured main steam pressure inside the pipes decreased from 13.2 MPa to 10.5 MPa, and the flow rate decreased from 160 t / h to 110 t / h.

[0171] Using the zero-dimensional dynamic simulation module of this invention, it was calculated that the macroscopic outlet temperature of the superheater decreased from 530°C to 485°C within 5 minutes. Subsequently, the local boundary real-time generation module substituted the measured instantaneous drop curve from 565°C to 510°C at the inlet and related parameters into the lumped parameter micro-element model to calculate the convective heat transfer coefficient and local medium temperature gradient at the molten salt inlet tube micro-element. This was then used as a dynamic thermal boundary and applied to the pre-extracted high-temperature superheater inlet tube sheet local three-dimensional finite element model.

[0172] Through local thermo-mechanical coupling and creep interaction solutions, the peak equivalent stress in the central hole bridge region of the tube sheet was captured to reach 245 MPa, exceeding the yield limit of the material at that temperature. By extracting the stress-strain hysteresis loop during the cloud-induced load reduction process, the fatigue damage degree D caused by this transient condition was calculated. f Approximately 1.2 × 10 -4 Meanwhile, because the tube sheet was subjected to continuous operation at a high temperature of 530℃ for an extended period, the monitoring system extracted nearly a month's worth of continuous operating data to calculate its creep damage degree D. c 3.5×10 -4 Considering the significant nonlinear interaction effect exhibited by Incoloy 800H at this temperature, the differentiated life assessment module used the ASME standard creep-fatigue nonlinear damage envelope (bilinear interaction spectrum) for determination, and calculated the total equivalent damage to be approximately 6.0 × 10⁻⁶. -4 .

[0173] The assessment results show that the thermal shock caused by the cloud cover significantly accelerated equipment wear. The monitoring system subsequently triggered a yellow alert on the DCS terminal, indicating to maintenance personnel that the remaining lifespan of the equipment was approximately 160,000 hours (or approximately 1,600 equivalent start-ups / load changes), verifying the high sensitivity and accuracy of this invention in capturing high-frequency transient severe operating conditions and high-temperature interactive damage.

[0174] This invention significantly reduces the computational load and enables efficient, online, real-time lifespan monitoring of key photothermal equipment under high-temperature and complex operating conditions.

[0175] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention.

Claims

1. A method for online life monitoring of a steam generation system in a concentrated solar power plant, characterized in that, Includes the following steps: Step 1: Construct a system-level zero-dimensional dynamic simulation model of the steam generation system of the solar thermal power plant; the system-level zero-dimensional dynamic simulation model is composed of multiple heat exchanger sub-models connected in series and / or in parallel; run the system-level zero-dimensional dynamic simulation model based on real-time collected operating status data to obtain the macroscopic parameters of the steam generation system of the solar thermal power plant; Step 2, offline stage: Construct a global three-dimensional model of the steam generation system. Based on the macroscopic parameters obtained in Step 1, perform steady-state and transient thermo-mechanical coupling analysis to identify the stress concentration points of each heat exchanger in the steam generation system, and establish local three-dimensional models for the stress concentration points. Step 3: During real-time online monitoring, the actual inlet detection parameters corresponding to the stress concentration points are collected through the system-level zero-dimensional dynamic simulation model, and then substituted into the lumped parameter micro-element model to calculate the micro-element outlet parameters of the stress concentration points. The actual inlet detection parameters and the micro-element outlet parameters are used as real-time boundary conditions and mapped into the local three-dimensional model. Step 4: Based on the real-time boundary conditions obtained in Step 3, drive the local three-dimensional model to perform local thermo-mechanical coupling calculations to obtain the real-time temperature field and stress-strain field; and perform differentiated life assessments according to the actual operating temperature range of each heat exchanger.

2. The monitoring method according to claim 1, characterized in that, In step 1, the system-level zero-dimensional dynamic simulation model is composed of multiple heat exchanger sub-models connected in series and / or in parallel, which are built based on the principles of heat transfer and fluid mechanics.

3. The monitoring method according to claim 1, characterized in that, In step 1, macroscopic parameters refer to the outlet parameters of each heat exchanger in the steam generation system of the solar thermal power plant, including outlet temperature, pressure, and flow rate parameters.

4. The monitoring method according to claim 1, characterized in that, In step 2, the stress concentration areas include the molten salt inlet, molten salt outlet, steam inlet, and tube sheet weld area of ​​the heat exchanger.

5. The monitoring method according to claim 1, characterized in that, In step 3, the micro-element outlet parameters include the micro-element outlet fluid temperature and micro-element outlet pressure at the stress concentration location, and the calculation formula is as follows: (1) Calculate the outlet fluid temperature T of the infinitesimal element f,out The formula is as follows: ρ f ·c f ·ΔV·(dT f,out / dt) = q m,f ·c f ·(T f,in - T f,out ) - h local ·A micro ·(T f -T wall ); Where, ρ f c f q m,f Let T represent fluid density, specific heat capacity, and mass flow rate, respectively; ΔV be the volume of the infinitesimal element; and T be the volume of the infinitesimal element. f,in T represents the temperature of the inlet fluid of the micro-element. f,out h represents the outlet fluid temperature of the micro-element. local A is the local convective heat transfer coefficient. micro T represents the heat transfer area of ​​the micro-element wall. f With T wall Here, represents the average fluid temperature and the wall temperature, respectively, and t represents time. (2) Calculate the outlet pressure P of the infinitesimal element out The formula is as follows: P out =P in - ξ local ·(r f ·v² / 2); Among them, P in To alleviate the pressure of micro-element imports, ξ local is the local drag coefficient, and v is the fluid velocity.

6. The monitoring method according to claim 1, characterized in that, In step 4, the differentiated life assessment method is as follows: Based on the actual physical characteristics of the steam generation system, a first temperature threshold is set. If the operating temperature of the heat exchanger is lower than the first set temperature threshold, a fatigue life assessment based on thermo-mechanical coupling is performed. If it is higher than or equal to the first set temperature threshold, a local creep analysis is further performed. The life assessment under the interaction of creep and fatigue is achieved through superposition processing.

7. The monitoring method according to claim 6, characterized in that, In step 4, the heat exchangers in the steam generation system include a preheater, an evaporator, a superheater, and a reheater; the first set temperature threshold is set to 450°C, the operating temperature of the preheater and evaporator is below 450°C, and the operating temperature of the superheater and reheater is above or equal to 450°C.

8. The monitoring method according to claim 6, characterized in that, In step 4, if the operating temperature of the heat exchanger is lower than the first set temperature threshold, a fatigue life assessment based on thermo-mechanical coupling is performed. The specific algorithm is as follows: (1) Fatigue damage calculation: Based on the thermo-mechanical coupling calculation results of the local 3D model, the stress history is extracted, the cyclic load spectrum is extracted using the rainflow counting method, and the number of cycles n is obtained by combining the material's SN fatigue curve. i ; Calculation of pure fatigue damage D based on Miner's linear cumulative rule f : D f =Σ(n i / N i ); Where, n i N represents the actual number of iterations. i This refers to the fatigue life under corresponding stress. (2) Based on the current cumulative fatigue damage f This allows us to estimate the remaining online lifespan of key components.

9. The monitoring method according to claim 6, characterized in that, In step 4, if the operating temperature of the heat exchanger is higher than or equal to the first set temperature threshold, further local creep analysis is performed. Life assessment under creep-fatigue interaction is achieved through superposition processing. The specific algorithm is as follows: (1) Fatigue damage calculation: Based on the thermo-mechanical coupling calculation results of the local 3D model, the stress history is extracted, the cyclic load spectrum is extracted using the rainflow counting method, and the number of cycles n is obtained by combining the material's SN fatigue curve. i ; Calculation of pure fatigue damage D based on Miner's linear cumulative rule f : D f =Σ(n i / N i ); Where, n i N represents the actual number of iterations. i This refers to the fatigue life under corresponding stress. (2) The steady creep rate was calculated based on Norton's formula, and the creep fracture time was calculated using the Larso-Miller parameter method; the creep damage D was calculated by integrating using Robindson's rule. c : D c = Σ(t j / t r,j ); Among them, t j Under stress σ j Temperature T j Actual holding time under the conditions, t r,j For stress σ j Temperature T j Creep fracture time under certain conditions; (3) The total damage degree is calculated by using the linear cumulative method, or based on the nonlinear cumulative model, or based on the ASME bilinear rule; When using the linear cumulative rule, the total damage degree D = D f + D c = Σ(n i / N i ) + Σ(t j / t r,j ); When using the nonlinear cumulative model or the ASME bilinear rule, the calculated (Df, Dc) coordinate points are substituted into the ASME bilinear or nonlinear interactive damage envelope map of the material, and the relative distance from the calculated point to the failure boundary is used as the actual equivalent total damage. (4) Based on the total damage, estimate the remaining online life of the key components.

10. A monitoring system based on the monitoring method according to any one of claims 1-9, characterized in that, It includes a data acquisition and zero-dimensional simulation module, an offline stress concentration location and dimensionality reduction module, a local boundary real-time generation module, and a differentiated life assessment module; The data acquisition and zero-dimensional simulation module is used to acquire on-site unit operating status data and run a system-level zero-dimensional dynamic simulation model to obtain the macroscopic parameters of each heat exchanger. The offline stress concentration localization and dimensionality reduction module is used to perform global thermo-mechanical coupling analysis on the heat exchanger, locate and extract the local three-dimensional model of the stress concentration area; The local boundary real-time generation module is used to receive actual inlet detection parameters on site, quickly calculate micro-element outlet parameters through the lumped micro-element parameter model, and merge them into real-time inlet and outlet boundary conditions of the local three-dimensional model. The differentiated life assessment module has a built-in switching logic with a threshold of 450℃, which is used to perform simple fatigue life accumulation calculation or total life accumulation calculation under the interaction of thermo-coupling and creep, and output real-time life warning to the monitoring terminal.

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